4.5Specificity of Enzymes and the Reaction Mechanism
All metabolic reactions within a cell occur through the catalytic actions of enzymes. A “catalyst” is any substance that increases the reaction rate without itself being converted before or after the reaction. However, it cannot accelerate the reaction without being completely involved in the reaction. In fact, the catalyst binds to the reactants (called the substrate), accelerates the reaction, and then repeatedly separates from the reaction products; thus, it continuously accelerates a specific reaction. Therefore, enzymes can only promote a specific biochemical reaction involving specific substances to which they can bind.
At the beginning of the 20th century, enzymes were recognized as important substances that held a key to the miracle of life. To better understand enzymes and their types, considerable efforts have been made to repeatedly purify and obtain enzymes in their highly active forms. Because enzymes are highly active even in trace amounts, almost nothing is left by the time they have been sufficiently purified. Highly sensitive techniques are currently available for analyzing enzymes, but at the beginning of the 20th century, purification of enzymes was extremely difficult. In 1926, urease was crystallized and found to be composed of proteins (see Column the bottom). However, at that time, proteins were neither clearly defined nor was their structure clearly understood. Research over the past few centuries has found that enzymes are macromolecular substances generally comprising proteins. Proteins are complexes of amino acids bound together by peptide bonds. Proteins will be described in greater detail after Chapter 6. An enzyme may sometimes contain components that are not proteins, and these are grouped under the term “prosthetic groups.” Representative prosthetic groups include heme, present in hemoglobin, cytochrome, and coenzymes such as NAD. Some enzymes can bind to metal ions such as iron or magnesium. These enzymes are mainly related to substrate-binding and redox reactions. Because many coenzymes cannot be synthesized in the body, they must be ingested as vitamins.
Crystallization of Enzymes
Column Fig. 4-1 Microscopic Photograph of a Protein Crystal
Crystal of the cytochrome b6f complex obtained from thermophilic cyanobacteria. It is a major protein complex that acts as an electron transfer component in the delivery of an electron from photosystem II to photosystem I. Its crystal structure was identified by the current Osaka University professor Genji Kurisu. Refer to Chapter 16 for details on photosynthesis.
Currently, it is well known that enzymes are proteins, but at the beginning of the 20th century, they were often not believed to be proteins. In 1926, James Sumner showed that enzymes are proteins. He first crystallized urease, which hydrolyzes urea to produce ammonia and carbon dioxide, from Canavalia beans to clarify its properties as a substance. Thereafter, many different enzymes have been crystallized. Furthermore, X-ray crystallography helped in establishing the arrangement of atoms in crystals. In 1958–1959, John Kendrew and Max Perutz described the crystal structures of myoglobin and hemoglobin. Proteins have a high molecular weight, and determination of their crystal structures required collection of data from many diffraction points and a powerful computer for processing these data. Another critical problem was the fact that X-rays damage proteins. Recently, data can be collected from multiple diffraction points using short-exposure X-ray irradiation and electron density distribution can be calculated. Using these methods, efforts are being made to explain the crystal structures of many proteins discovered by genome analysis.
Specificity of Enzymes and the Reaction Mechanism
Enzymes act on specific substances and catalyze specific reactions. This indicates that an enzyme has two types of specificity—a substrate specificity and a reaction specificity. An enzyme displays its catalytic activity by identifying and binding to its specific substrate. The catalytic reaction is also predetermined. For example, the enzyme called amylase acts on starch (glucose polymer) and produces maltose (a disaccharide consisting two glucose molecules), but it cannot isolate the glucose molecules. When considering acids (hydrogen ions) as examples of inorganic catalysts, glucose polymers of varied length are produced by severing the saccharide chains of starch at random. In other words, the reaction specificity of acids is low. Moreover, acids can act on substances other than starch such as proteins or macromolecular substances, and thus, they do not have high substrate specificity.
Fig. 4-5 Triple Catalysts composing the Active Center of Chymotrypsin
The hydrogen atom nucleus (proton) of the hydroxyl group (OH group) of serine residue 195 is strongly attracted to the lone electron of N of histidine residue 57. Hence, O of the serine residue has a negative charge and attacks the carbonyl carbon (slight positive charge) of the substrate’s peptide bond. This is the initial stage of peptide bond hydrolysis. The red arrows indicate electron transfer.
The high specificity of enzymes has been found to be supported by their steric structures. The active center of enzymes is shaped such that they bind particularly well with specific substrates, and the amino acid side chains are arranged such that binding with a specific functional group of the substrate can occur. Proteinaceous enzymes act effectively as catalysts because of special amino acid residues at the active centers, which impart a special reactivity as a result of their interactions with other amino acid residues. For example, the catalytic triad of chymotrypsin (Fig. 4-5). The figure indicates that of the amino acids comprising the enzyme, serine containing a hydroxyl group attacks the peptide bond as the active center. Hydrogen ions are extracted by aspartic acid and histidine, which are sterically associated amino acids. Thus, the serine side chain achieves an ionized state such as -CH2-O−. To maintain these characteristics and this steric structure, enzymes generally have a pH that is most suitable for their activity. Although the reaction rate increases with temperature, the steric structure is destroyed at high temperatures by denaturation. Thus, enzymes can function appropriately only at an optimal reaction temperature. A more detailed explanation of the steric structures of enzymes will be provided in Chapter 6.
The mechanism of enzymatic reactions has been studied since a long time by analyzing the protein composition of enzymes and their steric structures. At the beginning of the 20th century, the German scientists Leonor Michaelis and Maud Menten, who were studying an enzyme called invertase, later proposed a method for describing enzyme kinetics based on the following experimental facts.
In an enzymatic reaction, the initial reaction rate V is increased by increasing the concentration [S] of the substrate S. However, in cases where the amount of enzyme added to the reaction system is fixed, no matter how much you increase [S], V cannot increase over a certain limit (Fig. 4-6). This extrapolated value is called Vmax. In other words, V is saturated with regard to [S]. The phenomenon of saturation is characteristic of catalytic reactions and is explained as the binding of a catalyst and substrate. The phenomenon of saturation is observed because even if there is an abundance of substrate molecules, the number of substrate binding sites available for the catalyst is limited.
This is shown by a mathematical formula, and study of the rate of an enzymatic reaction is called kinetics. A simple enzymatic reaction is considered below. Invertase is an enzyme that hydrolyzes sucrose to produce glucose and fructose. Although a large quantity of water is involved in this reaction, it does not have an effect on the reaction rate, and hence, only sucrose (represented by [S]) is considered to be the substrate. The enzyme molecule is represented by E. Although there are two types of products formed, they are both represented by P. The concentration of the reaction products is considered in a range that does not affect the reaction rate. Important assumptions made here include the assumption that the enzyme and substrate bind reversibly and that a portion of the bonded substrate and enzyme will yield products through the primary reaction.
E + S ↔ ES → E + P
At this point, the following general equations are established.
These are called the Michaelis–Menten equations. Here Vmax refers to the maximum initial reaction rate, and Km refers to the Michaelis constant. Km represents [S] that gives an initial reaction rate of ½ Vmax. This equation is essentially a hyperbolic function demonstrating the phenomenon of saturation. The equation is derived on the basis of certain assumptions (Refer to Column on Page 55 for the derivation) that in reality do not always hold true for all enzymatic reactions. However, in practice, the equation holds true for many enzymatic reactions, and Km is used as an index showing affinity between the enzyme and substrate (smaller the Km, greater the affinity).
One application of this formula is the classification of inhibitors of enzymatic reactions. Although inhibitors are classified according to their effect on Km and Vmax, among those, only competitive inhibitors will be discussed here. When a substance with a structure similar to that of a substrate binds to the substrate binding site of the enzyme but does not participate in an enzymatic reaction, it interferes with the original substrate reaction and is called a competitive inhibitor. For example, succinate dehydrogenase, an enzyme in the citric acid cycle (see Fig. 4-3 and Fig. 16-3 of Chapter 16), is inhibited by malonic acid (HOOC-CH2-COOH), a substance analogous to succinic acid (HOO-CH2-CH2-COOH). Thus, the observed Km increases, but Vmax does not change, in the presence of the inhibitor.
In addition, allosteric regulation is another factor that exerts an effect on enzymatic activity. Allosteric regulation is commonly observed in enzymes composed of multimers. During this regulation, the steric structure of the constituent components change cooperatively when a regulator molecule binds to a site (the allosteric site) other than the active center. This causes the multimer to alternately switch between the high and low activity states depending on the large changes in the conformational state of the enzyme due to the allosteric regulator.
Derivation of the Michaelis−Menten Equation
In 1925, George Briggs and John Haldane derived the currently used Michaelis–Menten equation. In the simple enzymatic reaction mentioned in this textbook, dependence of the initial reaction rate on the concentration of the substrate is considered. If the total concentration of the enzyme is set as E0, then
E0 = [E] + [ES] ---------- (1)
At stable conditions assumed, no change is observed in the concentration of the intermediate ES,
which can be rewritten as follows:
[S][E] − Km[ES] = 0 ----------- (2)
>> [ES], the concentration of the separated substrate is considered the overall concentration of the substrate.
If [E] is removed from (1) and (2), then
By substituting (3) in the equation for the initial reaction rate V, the result obtained is as follows:
This gives Vmax = k2E0. Note that the enzyme E and the substrate S are in rapid equilibrium, and if k1,
k−1 >> k2, then km can give a dissociation constant for the enzyme and substrate of


The Forgotten Legacy of George H.W. Bush
The Forgotten Legacy of George H.W. Bush by By Johnny Liberty The Free Thought Project
On Friday November 30th, former President George H.W. Bush passed away at the age of ninety four, according to a statement released by his friends and family.
Statement by the 43rd President of the United States, George W. Bush, on the passing of his father this evening at the age 94. pic.twitter.com/oTiDq1cE7h
— Jim McGrath (@jgm41) December 1, 2018
While the establishment celebrates the life of the former president and Americans line up to mourn their fallen leader, the facts that are being reported in the mainstream media are far different than the legacy he is leaving behind.
The Early Years
George Herbert Walker Bush was born on June 12, 1924 in Massachusetts to Prescott Sheldon Bush and Dorothy (Walker) Bush. Shortly after his birth, the family moved to Connecticut where he began his formal education at Greenwich Country Day School. At the age of eighteen, Bush joined the U.S. Navy.
During his tenure in the Navy, Bush was stationed with Torpedo Squadron 51 aboard the USS San Jacinto. On August 1, 1944 his unit launched an operation against the Japanese in the Bonin Islands. On September 2, 1944, Bush’s aircraft was downed leading to the death of eight Navy airmen, leaving Bush as the lone survivor. The episode later became known as the Chichijima incident and led to the future president being hailed as a war hero.
Upon graduating from Yale, Bush began his career in politics and was elected chairman of the Harris County, Texas Republican Party in 1963. Three years later, Bush was elected to the US House of Representatives, marking the beginning of a meteoric rise which resulted in him being named director of the Central Intelligence Agency in 1976.
Before he was named head of the CIA, Bush was already heavily involved in covert operations according a book released in 2010, by author Russ Baker. In his book, Family of Secrets: The Bush Dynasty, America’s Invisible Government, and the Hidden History of the Last Fifty Years Baker revealed the relationship between Bush and former President Richard Nixon. A relationship, the author asserts, that eventually led to the Watergate scandal and Nixon’s resignation.


Blog written by: Mirjam Gommers, Communications Advisor G4AW
Posted on: March 8, 2020 International Women's Day
There is a gender gap in agriculture in low-income countries. A gap between the resources and the rights available to men who work the land and those available to women who do the same while studies conducted for project Drawdown have demonstrated that countries with higher levels of gender equality have higher average yields and put less pressure on the environment.
According to the Food and Agriculture Organization of the United Nations (FAO), if all women smallholders receive equal access to productive resources, their farm yields will rise by 20 to 30 percent, total agricultural output in low-income countries will increase by 2.5 to 4% and the number of undernourished people in the world will drop by 12 to 17%. That means about 100 to 150 million people will no longer be hungry.
The Drawdown research demonstrated that if women have access to the same resources as men their outputs exceed men’s by 7-23%. And when agricultural plots produce well there is less pressure to deforest for additional ground. And where regenerative practices replace chemical-intensive ones, the soil becomes a carbon storehouse. An effective weapon to fight climate change. And last but not least the same research shows us that if women smallholders get equal rights to land and resources, they will grow more food, feed their families better throughout the year and gain more household income. When women earn more, they reinvest 90% of the money they make into education, health and nutrition for their families and communities, compared to 30 to 40% for men. A stronger business case for gender equality is nearly impossible.
G4AW for gender equality
The 2016-2030 Sustainable Development Goals, have gender equality and women’s empowerment at their core (SDG 5), stating that it is not only a fundamental human right but also a foundation for a peaceful, prosperous and sustainable world. The UN has defined 9 targets and 14 indicators for SDG 5 including female land rights and ownership, one of the biggest challenges facing women in agriculture today. In order to ensure women are equally included in their projects the G4AW Programme issued a publication in 2017: ‘Including women smallholder farmers: a business case for success’. The report includes best practices and an approach to include men and woman on an equal footing in G4AW projects. Several G4AW projects have indicated that they see opportunities to include more women in the coming years and some of them have included women right from the start. Like the MUIIS project in Uganda, where 75% of the women and 62% of the men are active in the agricultural sector.
These opportunities need to be supported by a gender analysis that helps to unravel how G4AW services, products and outreach could be developed in a way that addresses the needs of both women and men. With the global population growing to reach an expected 9.7 billion by 2050 and climate change negatively affecting crop production we will need to not only eradicate gender inequality in order to fight hunger but also look at innovate ways to implement agricultural practices in a sustainable way. For those interested to include women smallholder farmers in G4AW countries there is a list of organizations on our website, that have experience on including gender in projects in their countries and are helping the next generation of women rise up to their potential. Over the next few months we will be publishing updates on how we support gender equality across our projects and share best practices.


The Little Brown Bat is a nocturnal animal and part of species of mammal that can actually fly called bats. Allot of the little brown bat life style is still shrouded in mystery, but we do know is that little brown bats sleep under overpasses, bridges, homes, and caves. They sleep upside down hanging from the ceiling. There homes are usually close to there food. They eat is bugs mostly moths, crickets, mosquitoes and other fly insects. They have this ability called echo location which they use sound waves to pick up on objects like trees and insects. They are mainly preyed on by owls and other nocturnal predators. To identify a little brown bat is spotting there flying. There wings move much faster than birds wings except the hummingbird and the little brown bat only appears after sunset, while birds only hide in trees or buildings and make allot of noises.


Temple Beth Jacob’s Holocaust Torah Scroll
Temple Beth Jacob’s Sefer Torah is number 894. It came from the towns of Kolin-Nymburk. It was written in the year 1800. Temple Beth Jacob received the scroll in January of 1993.
About Kolin-Nymburk: Prior to World War I, Czechoslovakia had approximately 93,000 Jews, and of them, 19,000 lived in Prague. By the beginning of World War II, the population had grown to approximately 117,550. Kolin had about 3,500 Jews – Nymburk was a smaller town on the outskirts of Kolin. There was one synagogue and a Jewish bakery in Kolin. In 1939, the rabbi of the communities gathered the Jews, collected millions of Czech kroner and petitioned the French, Spanish, Belgian and Dutch governments to allow Jews to settle in their “dark colonies,” without any expenses to the colonial powers. These Jews were mostly middle class merchants, with some cattle traders and some farmers. They started to learn trades under the rabbi’s guidance, which they hoped they would use in the colonies. The rabbi had extensive correspondence with these governments and their representatives. He presented them with gifts and gave financial guarantees that the Jews would be of no burden to the colonial powers. Negotiations dragged on, until it was too late. Rabbi Richard Feder returned from concentration camp and wrote a book in 1947 entitled Zidovska Tragie (Jewish Tragedy), the first book on Holocaust. He listed all the Kolin and Nymburk Jews who belonged to the Jewish community who perished in concentration camps. Nymburk had a Jewish population of 2,068 before the War. They were all deported to Terezin on three transports from Kolin. Only 134 survived.
About Scroll 894: The scroll is not kosher – meaning it is not fit for regular use. It appears to have fire and water damage beyond repair. Still, Temple Beth Jacob honors and uses the scroll in a few settings. First, our confirmands read from this scroll each year at Confirmation to honor those who lives were lost and did not live to become Jewish adults. Second, we include the scroll in our annual community-wide Holocaust remembrance service. Third, upon special request and for compelling reasons, a bar or bat mitzvah student who wishes to read from the Holocaust scroll may do so when being called to the Torah as a bar or bat mitzvah.
The Nazis and the Czech Jews: The Demise of the Jewish Communities
Jews had lived in Bohemia and Moravia for more than a thousand years. Over that time a rich Jewish culture developed, centered on Prague and spread across a large number of communities throughout the country. When the Munich Agreement was signed on 29 September 1938, Britain and France agreed to Hitler’s demand to be given the German speaking border regions of Czechoslovakia, and the Germans marched in. The Jews from about sixty congregations in the prosperous industrial and commercial towns in the Sudetenland had two or three days to flee to the interior, which was still a free and sovereign country. They left behind their synagogues, which were in German hands in time for the destruction of the Pogrom of November 1938, when synagogues across the expanded Germany, which now included the Sudetenland, were burned or vandalized and looted. In almost every case the ritual treasures of these Sudetenland synagogues were destroyed or lost.
In the remainder of Czechoslovakia, the synagogues and their swollen congregations were safe for the time being, and there was no program of destruction, even when the Germans invaded the rest of the country in March 1939. In 1940, the congregations were closed down, but the Jewish community administration was used by the Germans to execute their stream of decrees and instructions. In 1941 the first deportations started and the mass deportations of the Jews took place throughout 1942 and into January 1943. The Nazis decided to liquidate the communal and private Jewish property in the towns, including the contents of the synagogues. In 1942, Dr. Stein of the Juedische Kultusgemeinde in Prague wrote to all Jewish communities, instructing them to send the contents of their synagogues to the Jewish Museum in Prague. Thus the Torah Scrolls, gold and silver and ritual textiles were sent, along with thousands of books. The remaining Jews were deported in 1943 and 1944, but quite a number survived.
The Saving of the Judaica – The inventory of the Prague Jewish Museum expanded by fourteen times as a result, and a large number of Jews were put to work by the Germans to sort, catalog and put into storage all the items that had come from over one hundred congregations in Bohemia and Moravia. It needed over forty warehouses; many of them deserted Prague synagogues, to store all these treasures. When the task was eventually completed, the Jews who had been put to this work were themselves deported to the Terezin concentration camp and death. There were few survivors.
It was once accepted that the accumulation of this vast hoard of Judaica was intended by the Nazis to become their museum to the extinct Jewish race. There is, however, no evidence that any such museum was ever planned. The Prague Jewish Museum had been in existence since 1906, and was not created in order to house the Judaica collected in 1942. In 2012, the Prague Jewish Museum published “Ark of Memory” by Magda Veselska, a history of the museum that includes a clear explanation of how it was the Jews of Prague that worked before, during and after the war to protect a legacy that was threatened with destruction. After the defeat of Germany, a free and independent Czechoslovakia emerged, but it was a country largely without Jews. Most of the surviving Jews in Prague and the rest of Bohemia and Moravia were from Slovakia and further east from Subcarpathian Ruthenia. Prague, which had had a Jewish population of 54,000 in 1940, was reduced to under 8,000 by 1947, and many of these were to leave.
Czechoslovakia and the Communists –On 27 February 1948, after less than three years of post war freedom, the Communists staged a coup and took over the government of Czechoslovakia. The Prague Jewish Museum came under government control, and was staffed mainly by non-Jewish curators. In 1958, the 18th century Michle Synagogue became the warehouse which housed hundreds of Torah Scrolls from the large Prague Jewish community and what was left from the smaller communities of Bohemia and Moravia. The collection did not include scrolls from Slovakia, which the Germans had put under a separate administration. The Scrolls were left totally neglected.
The Communists Sale of the Scrolls – Eric Estorick, an American living in London, was an art dealer who paid many visits to Prague in the early 1960’s. He got to know many Prague artists, whose work he exhibited at his Grosvenor Gallery. Being a frequent visitor to Prague, he came to the attention of the authorities. He was approached by officials from Artia, the state corporation that had responsibility for trade in works of art, and was asked if he would be interested in buying some Torah Scrolls. Unknown to him, the Israelis had been approached previously with a similar offer, but the negotiations had come to nothing. Estorick was taken to the Michle Synagogue where he was faced with wooden racks holding anything up to 2000 Scrolls. He was asked if he wanted to make an offer, and replied that he knew certain parties in London who might be interested.
London: The Memorial Scrolls Trust
1564 Scrolls Came to London – On his return to London, he contacted Ralph Yablon, a well-known philanthropist with a great interest in Jewish art, history, and culture. Yablon became the benefactor who put up the money to buy the Scrolls. First, Chimen Abramsky, who was to become Professor of Hebrew Studies at the University of London, was asked to go to Prague for twelve days in November 1963 to examine the Scrolls and to report on their authenticity and condition. On his return to London, it was decided that Estorick should go to Prague and negotiate a deal, which he did. Two lorries laden with 1564 Scrolls arrived at the Westminster Synagogue on 7 February 1964. After months of sorting, examining and cataloging each Scroll, the task of distributing them began, with the aim of getting the Scrolls back into the life of Jewish congregations across the world. The Memorial Scrolls Trust was established to carry out this task.
The Memorial Scrolls Trust and The Silent Messengers – It is the duty of the Memorial Scrolls Trust to care for these scrolls and to ensure that they are given a prominent role in the spiritual and educational life of the institutions to which they have been entrusted. The Trust endeavors to help these organizations to build a bond with the community symbolized by their Memorial Scroll, and to maintain a continuous awareness of the special significance of these scrolls.
Each Memorial Scroll is a messenger from a community that was lost, but does not deserve to be forgotten.
For more information on the Czech Torah Scrolls, visit their website at https://www.memorialscrollstrust.org/scroll-holders/


Excitement is growing in India about a rotavirus vaccine that could be available by next year. If approved, it will be the first low-priced rotavirus vaccine developed in India.
“This is an important scientific breakthrough against rotavirus infections, the most severe and lethal cause of childhood diarrhea, responsible for approximately 100,000 deaths of small children in India each year,” says Dr. K. VijayRaghavan, secretary of India’s Department of Biotechnology, which partnered with pharmaceuticals firm Bharat Biotech to develop and test the vaccine. “The clinical results indicate that the vaccine, if licensed, could save the lives of thousands of children each year in India.”
In May, Bharat Biotech and India’s biotechnology department released results of clinical trials showing that their vaccine reduced severe rotavirus-caused diarrhea by 56 percent in a child’s first year of life, with protection continuing into the second year. At the equivalent of $1 per dose, the vaccine will be 40 times cheaper than rotavirus vaccines made by Britain-based GlaxoSmithKline and U.S.-based Merck.
The World Health Organization estimates that rotavirus causes 527,000 deaths each year, most of them among young children in Africa and Asia.
STUDY: UNIVERSAL EDUCATION POSSIBLE IN RESOURCE-RICH COUNTRIES
Developing countries with abundant natural resources can make dramatic advances toward universal education by managing their resources better, says a new United Nations study. The study argues that if their governments properly managed revenues from natural resources, the 17 countries studied could raise an extra $5 billion for education each year.
Revenue from the natural resources, if transparently handled by governments and used for education, could enable these countries to reach more than 11 million out-of-school children, the study says. “Many countries have mismanaged the income from their natural resources, have poorly negotiated with extractive companies or have made misguided spending choices,” says Pauline Rose, Director of the Global Monitoring Report. “In some cases, the funds have been channeled into armed conflicts instead of towards education.”
Most low- and middle-income countries that are rich in natural resources have struggled to channel their riches toward sustained development, the study says. Many of these countries have been unprepared to deal with the sudden discovery of an oil field or ore deposits. If countries with recently discovered resources, such as Uganda and Ghana, set aside a significant chunk of revenue for education, they could offer universal schooling, the study found.
PERU’S POVERTY RATE FALLS AGAIN
Continuing a hopeful trend, Peru’s poverty rate fell 2 percentage points last year to 25.8 percent, reported the South American country’s national statistics agency, INEI. Just three years ago, 30.8 percent of Peru’s population lived below the poverty line, according to INEI.
Still, about 7.8 million people live below the poverty line in Peru, including 1.8 million in extreme poverty — defined as living on less than $1.25 per day per person. And it’s worse in rural areas than in cities: 16.6 percent of the urban population lives in poverty, compared with 53 percent in rural areas. And yet, those numbers also have been dropping in recent years.
The statistics agency, which bases its figures on annual household surveys, credits continued economic growth with the decline in Peru’s poverty rate.
The Peruvian economy has grown by an average of 6.4 percent each year since 2002, according to the World Factbook.
CHILDREN NEED HOPE TO THRIVE
The importance of hope among children is catching the interest of researchers, readers and reporters. A new book about the topic has become a best-seller, and a Gallup poll revealing that hope helps students succeed is making headlines.
How Children Succeed: Grit, Curiosity, and the Hidden Power of Character by Paul Tough notes that children’s abilities to overcome setbacks are pivotal in developing traits such as optimism, perseverance, grit and curiosity — characteristics that Tough calls “noncognitive skills.” Tough writes that children living in poverty face a significant disadvantage compared with children living in affluence, so developing skills such as optimism and perseverance is crucial for children in poverty.
Meanwhile, a Gallup poll of American high school seniors looked into the hope, engagement and well-being of U.S. students in grades 5 to 12. It found that hope — defined as the combination of ideas, energy and excitement for goals — more accurately predicted students’ success in college than their test scores.
“Helping students uncover their strengths, rather than their weaknesses, and develop their potential should be the paramount focus for education,” writes Eric Cooper, founder and president of the National Urban Alliance for Effective Education, in an article reflecting on the Gallup poll results.
Compassion has long realized the importance of hope, and our local partners nurture it within sponsored children. Sponsors can incubate hope by encouraging children to think the future will be better and to take specific steps to make it so. At Compassion’s child development centers, children learn that they are loved and that God has a plan for their futures. Many complete “My Plan for Tomorrow,” a guide to help them set goals for success in school and beyond.


Fibromyalgia is a chronic pain disorder generally caused by amplification of pain processing in the central nervous system, including the brain and spinal cord. Fibromyalgia is a dynamic condition, meaning that the pain intensity can change from day to day; people with fibromyalgia can have sudden, significant experiences of widespread pain known as fibromyalgia flare ups, or fibro flares.
Research has shed light on the underlying central nervous system mechanisms underlying the symptoms of fibromyalgia, including the presence of fibromyalgia flare ups. Besides chronic widespread pain, one of the primary diagnostic criteria for the condition, many people have additional symptoms that may make their overall picture of fibromyalgia much more severe. Those can include things like stress, cognitive difficulties (often known as “fibro fog”), or fatigue.
Where does fibromyalgia pain come from?
Before we dive in to fibromyalgia, let’s start with some definitions about different types of pain.
Acute Pain versus Chronic Pain
Acute pain is a type of pain that has a very specific onset, often caused by a specific event. Some examples of acute pain triggers could include an injury from a car accident, or pain while recovering from a surgery.
There are many different types of events that can cause acute pain. Typically, those types of pain experiences are initiated by the peripheral nervous system, or nerves outside of the brain and spinal cord.
However, sometimes acute pain can persist even when the onset event or injury has resolved; for example, a patient who has recently had surgery might still experience pain even after the surgery site has fully healed. This is known as chronic pain.
Central Sensitization: Bottom-Up versus Top-Down
Why does chronic pain occur? Unlike with acute pain, the peripheral nervous system may not be delivering pain signals to the central nervous system. Instead, over time, the central nervous system and how it processes pain has changed such that, even after there’s a resolution of that acute issue, the pain persists. We call this change central sensitization, which is known to underlie most chronic pain conditions.
The experience of chronic pain for someone with fibromyalgia may be different than someone who has gone through an infectious process such as COVID-19 or Epstein-Barr virus or Lyme disease. Not everyone with chronic pain acute pain that preceded their chronic pain; for example, someone who had significant stress on the body, either in childhood or adulthood, may experience chronic pain. These types of experiences can lead to the central nervous system becoming activated and hypersensitive without any type of peripheral problem, such as a surgery or an injury. We distinguish those two things as either bottom-up or top-down central sensitization.
What is similar between both forms of central sensitization is that the chronic pain is present, and generally speaking, these types of chronic pain have similar treatment approaches.
Why do fibromyalgia flare ups occur?
Because fibromyalgia symptoms can exist on a spectrum, people can have very significant experiences of widespread pain that vary from day to day, week to week, or even month to month. They can also have very distressing associated symptoms (e.g., fatigue, stress, and trouble thinking), but there may also be times where those symptoms aren’t as severe.
When you think about the central nervous system and how the brain functions, you can think of your brain as a volume control knob on a radio. At times, that knob may be turned way up, as if the volume is on max. This leads to an experience of more painful areas and higher pain severity as well as increased levels of fatigue, fibro fog, and trouble sleeping.
These amplifications, or changes in the “pain volume control,” are how you can think about a fibro flare: the volume level of pain that people with fibromyalgia experience on a daily basis is cranked way up, and often leads to more symptoms.
What triggers fibromyalgia flare ups?
Many different things can trigger a fibromyalgia flare up and increase the pain volume control, including:
- Difficulty sleeping
- Change in the level of stress
- Increase in anxiety
- Having illnesses can increase inflammation in the body
- Weather changes
- Dealing with emotionally difficult events (e.g., illness or death, divorce, etc)
Managing fibromyalgia flare ups
While fibro flare triggers can vary from person to person, people with fibromyalgia can learn how to recognize what their triggers are that lead to their flares, and what self-care practices or other treatment strategies can help them manage their symptoms. Knowing your unique #flare triggers is power, because you can be aware and mindful of when a flare might occur.
Practices like light movement or stretching, sleep and rest, Cognitive Behavioral Therapy (CBT), Acceptance and Commitment Therapy (ACT), breathing and mindfulness work, music or art therapy, and other techniques can contribute to self-care practices to help move through fibro flares.


The Fellowship of Messines Association was formed in May 2002, by a diverse range of individuals from Loyalist, Republican and Trade Union backgrounds united in their realisation of the necessity to confront sectarianism in our society as a necessary means to realistic peace building.
The Association has networks of co-operation and support across the region and is dedicated to creating opportunities for participants from across all divides to engage in joint study and training programmes and dialogues around the questions of “History, Identity and Politics. The Decade of Centenaries has been a primary focus of the work as the Messines Fellowship.
A key driver for their work on the Decade of Centenaries has been to address the lack of access to a shared and common history, particularly one that enables participants to comprehend the issues of conflict and poverty, of culture, identity and heritage. Crucially, it seeks to use these engagements and discussion on Centenaries events to find common ground and tangible opportunities for individuals of all ages and from diverse cultures and heritages to engage and work together as active citizens.
The Centenaries events have utilised a shared learning collaboration between community activists and academics, who are opinion formers and influencers, to produce a learning programme and research papers to enable individuals to be self-critical and analytical about their own, and others history, culture and identity.
What worked well and what, if anything, didn't?
The difference it has made is to bring diverse communities of interest together, particularly often those living in communities most affected by violence and conflict, to engage in discussion that ensures that the decade of centenaries is used not just as a reference of the past but also to consider how it might or might not predict the future.
There is still a need for this work as the Decade of Centenaries continues and to include other significant “historical” events, that have strongly influenced political identity and action for example the events of 1921 and 1922 in Ireland and their impact. There is a need for historical contemporary events such as the events in 1969, the Loyalist Strike and the Sunningdale Agreement to be addressed.
More recently a clear need has been identified among those community leaders and peace influencers to widen the accessibility of the programmes to specifically target young people and those from minority communities of interest who, for diverse reasons, are disengaged or excluded from a sense of their identity as valued citizens.
Finding resources and building sustainability to ensure that this work continues is an ongoing challenge.
Harry Donaghy, firstname.lastname@example.org


There has been comment about salaries in the US public sector being higher than those in the private sector. This is despite the better conditions and job security:
Federal employees’ average compensation has grown to more than double what private sector workers earn, a USA TODAY analysis finds.
Federal workers have been awarded bigger average pay and benefit increases than private employees for nine years in a row. The compensation gap between federal and private workers has doubled in the past decade.
For a comparison broken down by industry sector see Federal pay ahead of private industry
In response to this it has been claimed that if you control for qualifications then the public sector salaries are not greater than private. Essentially they are saying that the pubic sector jobs are higher skilled, so people earn more money. Qualifications are used as a surrogate measure for skills:
Many of the most common state and local government jobs require higher education: teachers, social workers, nurses and university professors. In Michigan, more than half of the state jobs require that applicants have at least a bachelor’s degree.
“Thus, the fact that public sector workers receive greater average compensation than private sector workers should be no more surprising than the fact that those with more skills and education earn more,” said the study.
This is misguided because it ignores the effects of:
- Credential creep in the public sector. The public sector tends to lack objective measures of performance such as profits or revenue when considering which people to hire or promote. Hence it relies more on paper qualifications. Over time this results in staff with more and higher paper qualifications than warranted or than the private sector.
- More generous study leave provisions and fewer working hours. This makes it is easier for employees to gain qualifications. Thus the better qualifications of the workforce partly reflect the cushier conditions rather than higher skilled work or employees.
- Incentives in bureaucracies to expand the number of employees and their apparent skill level. The number of people in a department and the number of people reporting to a manager can influence execuitive salaries. Excess staff can be put to use writing and reviewing briefs. This may appear to be more highly skilled work than many private sector jobs. But it is of little value to society as a whole, which on occasion would actually be better off if no one performed those tasks. As they say “Idle hands, mischief make”. This tends to be in the form of misguided government programs or onerous reporting requirements.
The combined effect of these influences on the qualifications of government workers is to invalidate their use as a proxy or surrogate for comparing skills in the public and private sectors. It is wrong to claim higher wages in the government sector are justified because their work is more complicated and requires higher skills than the private sector as demonstrated by the better qualifications of its workers.
There are a lot more to skills than qualifications. Hence new graduates tend to earn less than those who have been in the workforce for ten or twenty years. Knowledge gained through work experience is essential to many jobs and indicates more about skills than the academic qualifications held. The fact that the privates sector can be hesitant about hiring people who have spent too long in the government sector says much about their relative skills, including their work ethic.
Attempts to undermine concerns about government salaries exceeding private ones on the basis of qualifications are erroneous or deceitful.
It is notable that this conclusion can be reached without asking if salaries in the private sector better:
- Reflect value of output. Salaries in the private sector may be better connected to the value to society of the workers output than are government ones.
- Direct resources. Salaries in the private sector help direct people and resources to their best use through the effects of price signals in a free or semi-free market economy. This is not done by salaries and resources determined by government directive as demonstrated by resource misallocation in communist countries and government “stimulus” programs in the West
- Value of qualifications. It is not clear if many of the politically correct courses impart many useful skills to go along with their lefty conceptual framework.
There may well be differences in skill levels between the government and private sector. But this can not be measured by qualifications or wages. The average private sector worker may be more skilled in terms of creating value to society than their more credentialed government equivalent.


An electro-optic modulator (EOM) (or electrooptic modulator) is a device which can be used for controlling the power (→ intensity modulators), phase (→ phase modulators) or polarization of light with an electrical control signal. It typically contains one or two Pockels cells, and possibly additional optical elements such as polarizers. Different types of Pockels cells are shown in Figure 1 and are described more in detail in the article on Pockels cells. The principle of operation is based on the linear electro-optic effect (also called the Pockels effect), i.e., the modification of the refractive index of a nonlinear crystal by an electric field in proportion to the field strength.
Most EOMs are operated with free-space laser beams, but there are also fiber-coupled modulators, where the Pockels cell is placed between two fiber collimators. Such devices typically have an insertion loss around 4 dB and can handle only limited power levels, e.g. 50 mW.
Frequently used nonlinear crystal materials for EOMs are potassium di-deuterium phosphate (KD*P = DKDP), potassium titanyl phosphate (KTP), beta-barium borate (BBO) (the latter for higher average powers and/or higher switching frequencies), also lithium niobate (LiNbO3), lithium tantalate (LiTaO3) and ammonium dihydrogen phosphate (NH4H2PO4, ADP). In addition to these inorganic electro-optic materials, there are also special polymers for modulators.
The voltage required for inducing a phase change of π is called the half-wave voltage (Vπ). For a Pockels cell, it is usually hundreds or even thousands of volts, so that a high-voltage amplifier is required. Suitable electronic circuits can switch such large voltages within a few nanoseconds, allowing the use of EOMs as fast optical switches. In other cases, a modulation with smaller voltages is sufficient, e.g. when only a small amplitude or phase modulation is required.
Types of Electro-optic Modulators
The simplest type of electro-optic modulator is a phase modulator containing only a Pockels cell, where an electric field (applied to the crystal via electrodes) changes the phase delay of a laser beam sent through the crystal. The polarization of the input beam often has to be aligned with one of the optical axes of the crystal, so that the polarization state is not changed.
Many applications require only a small (periodic or nonperiodic) phase modulation. For example, this is often the case when one uses an EOM for monitoring and stabilizing a resonance frequency of an optical resonator. Resonant modulators (see below) are often used when a periodic modulation is sufficient, and make possible a large modulation depth with a moderate drive voltage. The modulation depth can in some cases be so high that dozens of sidebands are generated in the optical spectrum (comb generators, frequency combs).
Note that an electro-optic modulator is not suitable for frequency modulation, or precisely speaking only for limited short-term frequency changes. For example, it could not be used to generate a constant change of optical frequency of an optical signal, since that would imply a linearly increasing phase delay (without any limit to the phase excursion).
Depending on the type and orientation of the nonlinear crystal, and on the direction of the applied electric field, the phase delay can depend on the polarization direction. A Pockels cell can thus be seen as a voltage-controlled waveplate, and it can be used for modulating the polarization state. For a linear input polarization (often oriented at 45° to the crystal axes), the output polarization will in general be elliptical, rather than simply a linear polarization state with a rotated direction.
Amplitude or Intensity Modulators
Combined with other optical elements, in particular with polarizers, Pockels cells can be used for other kinds of modulation. In particular, an amplitude modulator (Figure 2) is based on a Pockels cell for modifying the polarization state and a polarizer for subsequently converting this into a change in transmitted optical amplitude and power.
An alternative technical approach is to use an electro-optic phase modulator in one arm of a Mach–Zehnder interferometer in order to obtain amplitude modulation. This principle is often used in integrated optics (for photonic integrated circuits), where the required phase stability is much more easily achieved than with bulk optical elements.
Optical switches are modulators where the transmission is either switched on or off, rather than varied gradually. Such a switch can be used, e.g., as a pulse picker, selecting certain pulses from a train of ultrashort pulses, or in cavity-dumped lasers (with an EOM as cavity dumper) and regenerative amplifiers.
Temperature Drifts; Thermally Compensated Devices
In configurations where the induced relative phase change between two polarization directions is used, thermal influences can be disturbing. They result in a drift of the operation point, which may have to be compensated with an automatically adjusted bias voltage. Additional electronics may be used for such purposes, deriving the required bias voltage from some optical signals.
Some electro-optic modulators contain two matched Pockels cells in an athermal configuration where the temperature dependence of the relative phase shift is largely canceled. There are also configurations with four crystals of exactly the same length, canceling both birefringence effects and spatial walk-off. Various types of multi-crystal designs are used, depending on the material and the exact requirements.
Resonant Versus Broadband Devices
For some applications, a purely sinusoidal modulation with constant frequency is required. In that case, it is often beneficial to use an electrically (not mechanically) resonant electro-optic modulator, containing a resonant LC circuit. The input voltage of the device can then be substantially lower than the voltage across the electrodes of the Pockels cell. A high ratio of these voltages requires a high Q factor of the LC circuit and reduces the bandwidth in which strong resonant enhancement can be achieved. The disadvantage of using a resonant device is that one loses flexibility: changing the resonance frequency requires the exchange of at least one electric component.
Broadband modulators are optimized for operation in a wide frequency range, which typically starts at zero frequency. A high modulation bandwidth typically requires a Pockels cell with a small electric capacitance, and excludes the exploitation of a resonance.
For particularly high modulation bandwidths e.g. in the gigahertz region, integrated optical traveling-wave modulators are often used. Here, the electric drive signal generates an electromagnetic wave (microwave) propagating along the electrodes in the direction of the optical beam. Ideally, the phase velocities of both waves are matched so that efficient modulation is possible even for frequencies which are so high that the electrode length corresponds to several wavelengths of the microwave.
A number of properties should be considered before purchasing an electro-optic modulator:
- The device must have a sufficiently large open aperture, particularly in cases with high peak powers. A high crystal quality and appropriate electrode geometry are required for uniform switching or modulation across the full open aperture. The price can significantly rise for increasing aperture sizes.
- For switching ultrashort pulses, effects of Kerr nonlinearity and chromatic dispersion may be relevant, which depend on the crystal material and length and also on the beam radius. (Significant effects of this kind often cannot be avoided and thus have to be taken into account in the design of, e.g., a regenerative amplifier.)
- Depending on the device design, the polarization of the incoming beam may or may not be maintained in the output.
- A phase modulator may generate unwanted amplitude modulation, and vice versa. This depends strongly on the design.
- As electro-optic materials are also piezo-electric, the applied voltage can introduce mechanical vibrations, which themselves can affect the refractive index via the elasto-optic effect. Around certain mechanical resonance frequencies, the modulator response may be strongly modified. This can be a problem particularly for broadband modulators. In switching applications, unwanted ringing effects can occur. Such effects depend strongly on the crystal material, dimensions, orientation and mechanical design.
- Both high optical average powers and high switching frequencies can induce thermal problems. The thermal handling and thus the power and frequency capabilities depend on various construction details.
- The crystal(s) should have high-quality anti-reflection coatings, designed for the required range of operation wavelengths, and of course a good material transparency, in order to minimize the insertion loss.
- Rejected optical beams may be absorbed within the modulator device, or (particularly for high-power devices) leave the device at a more or less convenient location and direction.
- The switching speed (rise time, fall time) depends on properties of both the modulator (e.g. via its capacitance) and the electronic driver.
- Electro-optic modulators can be purchased in fiber-coupled form, with different types of connectors and fibers (e.g. single-mode or multimode).
Note that a proper mechanical mount is also required, often with means to align the modulator precisely in various directions.
It is important to use an electronic driver which is both well matched to the EOM and suitable for the particular application. For example, different kinds of EOMs require different drive voltages, and the driver should also be designed for the given electrical capacitance of the EOM. Some drivers are suitable for a purely sinusoidal modulation, whereas broadband devices work in a large range of modulation frequencies. Many problems can be avoided by purchasing an electro-optic modulator together with the electronic driver from the same supplier, because the responsibility for the overall performance is then at one place.
Some typical applications of electro-optic modulators are:
- modulating the power of a laser beam, e.g. for laser printing, high-speed digital data recording, or high-speed optical communications
- in laser frequency stabilization schemes, e.g. with the Pound–Drever–Hall method
- Q switching of solid-state lasers (where the EOM serves to block the laser resonator before the pulse is to be emitted)
- active mode locking (where the EOM modulates the resonator losses or the optical phase with the round-trip frequency or a multiple thereof)
- switching pulses in pulse pickers, regenerative amplifiers and cavity-dumped lasers
The RP Photonics Buyer's Guide contains 42 suppliers for electro-optic modulators. Among them:
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See also: electro-optic effect, electro-optics, Pockels effect, Pockels cells, Pockels cell drivers, pulse pickers, nonlinear crystal materials, optical modulators, intensity modulators, phase modulators, cavity dumping, regenerative amplifiers, active mode locking, electroabsorption modulators, acousto-optic modulators
and other articles in the categories nonlinear optics, photonic devices
This encyclopedia is authored by Dr. Rüdiger Paschotta, the founder and executive of RP Photonics Consulting GmbH. How about a tailored training course from this distinguished expert at your location? Contact RP Photonics to find out how his technical consulting services (e.g. product designs, problem solving, independent evaluations, training) and software could become very valuable for your business!


The divisional structure is considered as a viable structure for organizations and it is broken down into different areas. These areas are product, market and geographic structures.
Product Structure: The employees are grouped together in the product structure and this grouping is based upon the specific products that are produced by the company. For example a company produces three different products like product ‘a’, product ‘b’ and product ‘c’. Therefore, in this condition there would be three divisions for each product.
Market Structure: In the market structure the employees are based together and this division is related with the structure of the market. Like markets can be divided in the form of individual customers and business oriented customers (Gibson, 2008).
Advantages of divisional structure: In this structure the employees and the managers are attentive with respect to their products and customers. The divisional structure is quite flexible in nature and it is responsive to change. The coordination among the divisions is possible in this structure. The performance check is quite an easy task in this form and each and every strategic business unit is considered as a free standing unit and that is the reason why managers report directly to the CEO.
Disadvantages of divisional structure: One of the major disadvantages of divisional structure is the duplication of activities and certain resources. Sometimes extra costs are incurred and the marketing research department is maintained by every division on its own. The structure losses a great amount of efficiency and economies of scale and it might also result in lack of technical specialization and training. A sense of unwanted competition is developing in the organization and organizations believe that they are competition with each other.
Kindly order term papers, essays, research papers, dissertations, thesis, book reports from the order page.


“A nation is not conquered until the hearts of its women are on the ground. Then, it is done, no matter how brave its warriors nor how strong its weapons.”
On April 20, 1910, the Department of Indian Affairs invited tenders for the immediate construction of an industrial school at the St. Eugene Mission near Cranbrook. It would be one of the first in the province and would replace the existing school established two decades earlier. In early June, Fernie contractor J. J. Woods was awarded the task. Authorization arrived from Ottawa the following month and work began on July 26, 1911.
On the afternoon of Nov. 1 1911, Oblate Missionary Father Beck laid the cornerstone of the building in front of a large gathering comprised chiefly of members of the Kootenay (Ktunaxa) tribe. R.T. Galbraith, local Indian Agent of eighteen years, gave a short address followed by Father Beck. The keynote of Father Beck’s address dealt with the fact that “the true Christian made the best man and therefore the Canadian government took care to see that its Indian protégées should have every opportunity of becoming good Christians. In closing he impressed upon the Indian parents to realize their responsibility and see to it that their children enjoyed the privilege of the training given at the residential school.”
The cornerstone itself contained a written history of the establishment of the school, two Cranbrook and one Nelson newspapers, coins of the reign of Kings Edward and George and (perhaps somewhat oddly) medals fashioned from copper taken from Lord Nelson’s flagship “Victory.” What was not included was the fact that many residential schools soon to be constructed throughout Canada, would function in the most Draconian fashion imaginable, with children of all ages torn away from their homes for the duration of their “education” and held as little more than prisoners while being subjected to abuses and deprivations of the worst sort. That lay in the future, however. First came the building.
The construction of the St. Eugene school carried on through the spring of 1912. Various delays, including an extended wait for the granite steps of the main entrance and the boilers necessary for the heating system slowed things and thus it was not until Dec. 1912, that the school was more or less complete. It stood as one of the largest buildings in western Canada, a bleak, concrete behemoth hulking over the landscape, a constant reminder to parents that their children were now firmly in the hands of the Federal government and its appointed taskmasters.
Fifty-five feet high and composed of nearly 27,000 exterior concrete blocks with 350,000 locally manufactured bricks in the interior, it was proclaimed as one of the most up-to-date building for the purpose in the west.
Upon entering the main entrance one passed through a vestibule into a corridor to the left of which was the Sister Superior’s reception room and staff living room. To the right stood the Indian Agent’s office and a parlour, bedroom and bath for visiting officials. To the fore stood the staff and visitor’s dining rooms, the staff infirmary and convalescent wards and a bathing area. A corridor connected to the Mission-style chapel at the rear of the building. At the southern end stood the girls classrooms and to the north, that of the boys.
The upper floor held the dormitories, with the Sister’s in the center and the children’s at each end. Connected to both the Sister’s and the girl’s dormitory was a loggia, or outdoor sleeping balcony, connected to an infirmary with the same for the boys on the other end. The exposed sleeping areas were intended, so it was reported, “for the treatment of the children that may from time to time develop or exhibit signs of tubercular troubles or for the children who are fresh into the school from the reserve, where they live very largely in the open air and tents.” (It should be noted that a 2011 Canadian government inquiry into deaths of students at Indian residential schools failed to ascertain actual numbers although numerous other reports and research papers have made educated guesses. Overcrowding, poor sanitation and a lack of medical care led to a high rate of tuberculosis and whooping cough causing death rates in some schools estimated as high as 50 – 60 per cent. Compulsory government sterilization of students was also practiced in some provinces.)
Each end of the basement contained recreation, shower and toilet rooms for the children while the central portion was taken up by the large main dining room, kitchen, larder and cold storage rooms. The foremost section contained the heating plant adjoining a generator room (containing a 15 horsepower gasoline engine which produced all light at the Mission including the two hundred bulbs in the school) and a dispensary. The bakery, creamery and living quarters for the farm instructors and janitor sat beneath the chapel. Under the basement floor was the sewage drainage system leading to a large septic tank 350 ft. from the building. The attic was reserved as a recreational space during inclement weather and storage.
As to the schooling received, a 1910 school report issued by Father Beck indicates that education consisted largely of the tending of gardens, orchards and farm animals. Boys were given some manual training while girls studied the “domestic arts.” The school closed in 1970. It is now part of the St. Eugene Mission Resort.
Next week: The Black Robes of the White Man’s Burden.


All transmission lines have some even and odd mode impedance
The list of terms used to describe transmission line impedance, including differential lines, is extensive. You have terms like even mode, odd mode, characteristic, differential, common mode...I’m having trouble thinking of another area that uses so many adjectives to describe a single term in one application area. Transmission line impedance, particularly even and odd mode impedance, becomes important in a real PCB as transmission lines cannot be considered in isolation.
As newer products start running at higher frequencies, and with digital devices running at lightning fast switching speeds, more designers need to consider how their traces will act like transmission lines. A proper determination of transmission line impedance is critical for correct impedance matching, especially when we look at newer high frequency analog circuits.
Getting Started: Characteristic Impedance
When most folks talk about transmission lines, they generally refer to the line’s characteristic impedance. If you use the lumped circuit model for a transmission line, you’ll find that the characteristic impedance of a transmission line is just the ratio of the per-length inductance to per-length capacitance:
Characteristic impedance of a lossy transmission line
Note that R and G account of the resistance of the conductor and parasitic conductance of the substrate, respectively, both on a per unit length basis. These values are both low and can be ignored at moderate frequencies (i.e., hundreds of MHz), which reduces to the well-known equation for characteristic impedance for a lossless transmission line:
Characteristic impedance of a lossless transmission line
There are some prominent folks in the signal integrity community that will tell you the above equations are wrong, but then they will present equations that derive the inductance of a transmission line circuit and its capacitance in terms of the geometry of the line and its return path (i.e., any nearby ground or power planes). Obviously, the models are equivalent conceptually. The important point here is this: the characteristic impedance only depends on the geometry of the line, and its return path, and the material properties of the substrate at high frequencies. This begs the question: what happens when there is another nearby transmission line?
Even and Odd Mode Impedance
Transmission lines on a PCB are rarely routed in isolation, and they may be routed in parallel with common or differential driving. If we bring a second line near the first line, there is some mutual capacitance and inductance between the two lines, which will affect the current produced in each line when the pair is driven. The way in which the pair is driven (common mode vs. differential driving) will also determine the impedance of each of the transmission lines.
Why should this occur? If only one of the lines was driven, why should the other line matter? The effect of driving arises because of the capacitance between the two lines. When there is a potential difference between the two lines, one line can cause a current to discharge into the neighboring line, just like a discharging. An astute engineer will recognize this as capacitive crosstalk. Eric Bogatin presents this wonderfully in an old presentation, but the explanation is relevant today.
With two transmission lines, the voltage and current in both lines can be written using matrices, as shown below. Note that the impedance due to coupling (sometimes called mutual impedance) depends on the spacing between the two lines, the mutual inductance, and mutual capacitance.
Impedance matrix for a pair of transmission lines
Ultimately, your goal is to design the two lines so that the odd, even, common, or differential mode impedance takes a specific value. Oftentimes, the specified design requirement for a differential pair is its differential impedance, while the specified design requirement for a single-ended transmission line is usually the characteristic impedance. However, as you will see, coupling between neighboring single-ended transmission lines causes the actual impedance seen by a signal on a single ended trace to be different from the characteristic value.
Proper impedance controlled routing requires determining the even or odd mode impedance of each transmission line, as this is the impedance that will be seen by a driver and receiver in an interconnect. This then determines how you will design your trace geometry to ensure impedance matching throughout your interconnects.
Even and Odd Mode Impedance
Under common mode driving (same magnitude, same polarity), the even mode impedance is the impedance of one transmission line in the pair. In other words, this is the impedance the signal actually experiences as it travels on an individual line. In terms of the characteristic impedance in line 1, mutual impedance, and current in line 1, the even mode impedance is:
Even mode impedance for commonly-driven transmission lines
In the case where you are routing differential pairs, then the potential between the two pairs will always be opposing (i.e., equal in magnitude but opposite in polarity). The odd mode impedance is the impedance of one transmission line when the pair is driven differentially. In terms of the characteristic impedance in line 1, mutual impedance, and current in line 1, the odd mode impedance is:
Odd mode impedance for differentially-driven transmission line.
To summarize, the common and differential impedances are:
Even and odd mode impedance vs. differential and common mode impedance
Is There Ever Perfect Impedance Matching?
Very simply, you will probably never have perfect impedance matching, both for even and odd mode impedance. There are a number of reasons for this, which include manufacturing imperfections, imperfect symmetry and spacing along the length of transmission lines, roughness at the copper/substrate interface, and tolerances on components in termination networks or drivers/receivers.
However, with consistent length matching and symmetry along a set of transmission lines, you can come close to perfect impedance matching. The issue of length matching is particularly important. From the perspective of skew in digital circuits, length matching ensures that digital signals are arriving within the same time window, and that the intended gates on the receiver are switching simultaneously.
From an impedance perspective, this ensures that the impedance of an individual line is actually the differential or common mode impedance, meaning the potential difference between the pairs is consistent along the entire length of the line. This prevents impedance mismatch within a single transmission line. Note that this is one reason that bends, turns, and vias in transmission lines need to be very carefully designed, as each of these elements can create an impedance discontinuity, leading to reflections.
At the driver side of a transmission line, another problem with trying to perfectly match impedance is that the output impedance of some ICs will be different in the ON and OFF states. MOSFET power amplifiers and components with MOSFET drivers are some good examples. The output impedance from a MOSFET driver is a quadratic function of the gate-source voltage and the switching threshold, and the switching threshold depends on temperature, the presence of any body effect, and slightly on the drain-source voltage itself when the gate is underdriven. These factors make it difficult to perfectly match the impedance of a single-ended line to the input impedance of a driver.
Whether you are routing transmission lines in a high speed digital system or other RF wireless application, you can determine the right impedance matching conditions throughout your board with the right PCB layout and design software. Allegro PCB Designer and Cadence’s full suite of analysis tools can help you examine the characteristic impedance matrix for a set of transmission lines, allowing you to determine the real even and odd mode impedance in your transmission lines and ensure your signals are not degraded.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.
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Choose your Saab Model
The Formation of SAAB
Saab Automobile was most recently known as a subsidiary of General Motors (GM). Much of its greater fame and history, however, are connected to Sweden and its efforts during World War II. The name Saab comes from the Saab Group, formerly known as Svenska Aeroplan Aktie Bologet (Swedish Aeroplane Corporation), which translates to "Swedish Airplane Incorporated" in English. However, SAAB's original name comes from Carl Bücker's 1921 start up in Sweden named Svenska Aero AB. Following the end of World War I and the signing of the Treaty of Versailles in 1919, Germany was forbidden to manufacture any sort of aircraft. The restriction was later limited to military aircraft. While civilian aircraft manufacturing was permitted, there were still plenty of restrictions. In order to get around these types of hindrances, Bücker licensed aircraft from Heinkel Flugzeugwerke and Caspar-Werke, both German manufacturers, to be built in Sweden. With the help of Ernst Heinkel, Svenska Aero manufactured planes both for the Heinkel company and the Swedish Armed Forces. Shortly after, Svenska Aero began to design and develop its own planes. However, Swedish Armed Forces were mainly interested in prototypes, and the lack of demand eventually forced Bücker to sell in 1932 to AB Svenska Järnvägsverkstädernas Aeroplanavdelning (ASJA).
SAAB was initially created in response to the growing fear of German advancement in the beginning of World War II. By 1937, many European countries were wary of Germany's intentions. A major problem Sweden had noticed with its own air force was the lack of updated and modern equipment. While their air force would have been largely effective in WWI, many of their planes had been rendered outdated by the 1930s. In 1937, it was decided by the Swedish government to reestablish SAAB as a crown-corporation to compete with ASJA in manufacturing planes for recon. As the war began, the two companies merged as SAAB, and became the official company for Swedish military aircraft manufacturing.
SAAB in WWII
The Junkers Ju 86 Bomber, which had been a German innovation by the Junkers aircraft manufacturer, was SAAB's first crack at the aeronautic industry. By the time production started, the Junkers Bomber was out of commission in Germany. Although they declared neutrality after the German invasion of Poland in September of 1939, it was still seen as a wise endeavor to be prepared for any possible attack. After all, Finland, Sweden's neighbor, had also declared neutrality, but by November of 1939 was fending off an invasion from the USSR.
With the success of the bomber, SAAB continued to license and manufacture modern aircraft. This included the Saab 17-which was a two-seater plane and was the first Swedish plane made entirely of metal. It could be used as a dive bomber, and was fit to land on ground and water as well. SAAB also built the Saab 18, which first flew in 1942. It featured twin engines and was equipped with ejection seats and air-to-surface missiles. It entered service two years later in 1944.
As the war was coming to an end, the company realized that sustaining their production was going to be next to impossible with the impending decline in demand. Production of commercial airlines would require downsizing, so, in order to keep up stable production, SAAB tinkered with the idea of creating an automotive division. After seeing similar companies, such as ANA, import car kits from Chrysler, SAAB decided they wanted their automotive division to be as Swedish as possible and to offer a car that was capable of traversing the snow-covered north and rainy and foggy south. In 1944, SAAB began to seriously consider manufacturing its own cars by assembling a team of several people lead by chief engineer Gunnar Ljungström and designer Sixten Sason.
The First Automobile
After less than 6 months of planning, the first prototype was built. Known as the Saab 92001 or the Ursaab, it was a front-wheel-drive car with a two-stroke German engine. The prototype was deemed successful outside of its appearance. The hand-built, overly-aerodynamic design, clearly evident of its airplane-designer influence, was considered too radical and tough to market, so the model would succeed it, the Saab 92, was designed with a rounder rear and carved wheel wells to exude a more modern look. Soon the Saab 92 was ready for production. Yet Europe after World War II was still hostile in certain parts, and in response to events like the 1948 Berlin Blockade, aircraft military production dominated civilian production. A scarcity of steel pushed back Saab 92 production back to December of 1949.
The delayed release of the 92 lead to a surplus in military paint, so, naturally, it was only available in one color: dark green. The styling was considered peculiar and aerodynamic, but the changes were justified as it was still a relatively popular car in Sweden, particularly because it was capable of navigating the perilous landscape. The 92 came with a two-stroke two-cylinder engine with 25 horsepower and was known for its tendency to smoke out of the exhaust. Eventually the need to build an improvement was tantamount to SAAB's future automotive success, so they began to develop a new model, known as the 93. Around this time, SAAB also changed its name from its acronym to the stylization of Saab.
The 93, 95, and 96
In 1955 the Saab 93 was revealed for the 1956 model year. The newer model included a trunk and larger rear window and ran on a two-stroke three-cylinder engine that could kick 33 horsepower. It also entered the world rally circuit to establish a reputation and expand its popularity. Yet a big setback to consumers was the vehicle's requirement for mixed oil and gas. Many cars in this era simply ran on gasoline, but the Saab 93 needed a mixture. There was even a tag on the gas cap that served as a reminder. Regardless, Saab still pushed its luck in the US market in 1956, making the 93 the first Saab vehicle for sale in the US. The car was targeted towards the more upscale buyer. With no establishment in the US, a lack of foreign parts meant it would be long and expensive to get a repair. Yet Saab's constant success in rally racing lead to cult-like following that attracted loyal buyers and fans. This helped Saab boost and retain a presence in the US.
The off-road setting of rally racing also showed how able the car was at navigating rough terrain. Rally racing provided an opportunity for automakers to show off, and Saab excelled at this. The 93 was a huge hit in the circuit, racking up several wins thanks to racers like Erik Carlsson. But apart from racing, Saab looked to offer a more family-orientated car for the masses. This lead to the creation of the Saab 95 in 1959, which was a two-door station wagon with a four-speed transmission. It could seat seven and expanded remarkably in size to offer more passenger and storage room. It was later upgraded with a V4 engine in 1967 and ran until 1978.
A year later, in 1960, the Saab 96 was revealed. As the 93's successor, it featured an 841cc 38 horsepower 3-cylinder engine, three-speed transmission, and an improved rear window and interior. The 96 was so successful that it boosted sales nearly 45 percent. This allowed Saab to increase its production to 30-40,000 cars a year. The 96 was also popular for its sport model. As a growing interest in sports cars developed, especially in the US, the Granturismo 750 (GT, also known as the Montecarlo 850 in the US) came out in 1962. It came with a 55 horsepower engine and significantly upgraded the performance. The Saab 96 itself also improved by offering a four-speed transmission. Also, after listening to many of its customers, Saab placed a four-stroke Ford V4 in the 1967 model. Advances like the four-stroke allowed Saab to develop cars like the 1967 Sonnet coupe, which was based off an early 1956 convertible prototype designed by Sason. Models like the GT and the 96 boosted sales so substantially that Saab had sold nearly 300,000 models to date in 1965. The four-stroke turned out to be a hit, and Saab teamed up with the British automaker Triumph to produce engines for future models. One of these was the Saab 99, which was the first new model since the 96 and was essentially an upgraded version of the 95. With a more fuel efficient engine, it was also known for its innovative heated seats and headlight wipers.
The Scania-Vabis Merger
In 1969, Saab merged with Scania-Vabis, a Swedish company that manufactured trucks and buses, to form Saab-Scania AB. A driving reason for the merger was to give Saab the means to build its own engines. By the early ‘70s the company comprised two divisions: one for passenger cars-the Saab Car Division, and one for trucks-the Scania Division. Saab's distinguished logo of the Griffin-like bird derived from Scania-Vabis, who modeled their logo after the Swedish Scania province coat of arms. The merger was successful, and halfway through the decade Saab went on to build its one millionth truck.
1978 proved to be a big year for the company. They formed a partnership with the Italian automaker Fiat where they developed the Type Four chassis. Saab also introduced its first turbo model with the 99. It was a smash hit, and as the decade turned Saab was credited as one of the early pioneers of the turbo-charged front-wheel-drive car. Unfortunately, Saab left the rally circuit in 1980, but it's fun to imagine that they might have been a dominant force.
The ‘80s brought many more advances, and the Saab 900 was the first Saab made with computerized robot technology. It was built on the 99 platform and came equipped with independent suspension and coil springs, but it was the turbocharged engines of the 900 that grabbed most hearts. It was seen as the successor to Saab's previous models after the 96 was discontinued in 1980 and the 99 ended in 1984. But apart from its great performance, it was also lauded as one of the safest cars in the world.
By the ‘90s Saab teamed up with General Motors. Half of the Saab Car Division was split to GM in 1990 for $600 million. As it was seen as a near luxury vehicle, the main issue was that its prices failed to match production. GM saw use for Saab since they were struggling to market their own Opel brand in Europe, and Saab saw the effort as an opportunity to boost its presence in the US.
The situation would not be so simple. A large portion of the company had been owned by the Wallenberg family. The Wallenbergs, known as one of Sweden's most prominent families and whose financial success stretches across several Swedish industries, had been involved in the reformation of SAAB since the beginning. Dr. Marcus Wallenberg had been on the board of Saab since its merger with ASJA in 1939, and eventually became chairman after the Saab-Scania merger. After his death in 1982, his son Marcus Wallenberg took over his position. So, through their holding company known as Investor AB, Wallenberg purchased the remaining shares, splitting the company into 50-50 ownership.
However, despite the ingenious and quirky innovations, Saab was still losing money. They were the first company to offer chlorofluorocarbon-free air conditioning, and also the first to create a car controlled by a joystick. In 1992 a prototype for the 9000, codenamed the Prometheus, dropped the steering wheel in favor of a central joystick. The steering, however, was far from ideal. The easily maneuverable electronic steering was far too sensitive to be considered a serious and viable alternative to the old -fashioned steering wheel, but the idea was far ahead of its time. The concept of steering electronically is something a few cars have adopted today, and has been recently researched by several automotive giants.
In dire need of a new direction, Saab abandoned the 9000 and 900 series in preparation for two new models: the 9-3 and 9-5 series. The early versions of these models are considered the last true Saabs since GM bought the remaining shares for a 100% ownership in Saab in 2000 for $125 million.
The 9-3 and 9-5: Saab's Last Attempt at the Auto Industry
The 9-5 was released for the 1998 model year in Europe, and the 1999 model year for the US. It came as a front-wheel drive four-door sedan with 2.3L four-cylinder turbo engine with 185 horsepower. In 2002 an optional V6 was added for higher trims, as well as a five-speed automatic. Later models came with a six-speed automatic or manual transmission.
Along with the 9-5 came the 9-3. It was the more flexible version of the two, offering coupe, convertible, or hatchback models. It came with a 2.0L four-cylinder turbo engine with 175 horsepower. Compared to the 9-5, it came with several more trim options as well, and followed the same kind of upgrades, such as an eventual six-speed automatic or manual transmission.
Unfortunately Saab was headed for extinction after 2009. In 2010, GM agreed to sell the company to the Dutch sports car maker Spyker Cars NV for $74 million. GM agreed to supply the engines and transmissions, but much of the production failed due to a lack of funds. In 2011, after failing to find sufficient investments, Spyker intended to sell Saab to the Chinese automobile company Youngman, but the deal was blocked by GM-who still had sufficient shares to steer the direction of the company-to prevent the sale of Saab to a competitor in China, where GM was fairly successful. The National Electric Vehicle Sweden AB (NEVS) bought Saab out of bankruptcy in 2012 to build an electric version of the Saab 9-3, but there have been no signs of profitable success. Saab is currently owned by NEVS, but its future is still unclear. Hopefully this isn't the end for Saab. The constant attempts at resurrection attest to the original and unique passion instilled in the vehicles that over the years its loyal enthusiasts have grown to love.


Surprising hidden order unites prime numbers and crystal-like materials
Kevin McElwee for the Office of the Dean for Research
Sept. 5, 2018 11:41 a.m.
The seemingly random digits known as prime numbers are not nearly as scattershot as previously thought. A new analysis by Princeton University researchers has uncovered patterns in primes that are similar to those found in the positions of atoms inside certain crystal-like materials.
The researchers found a surprising similarity between the sequence of primes over long stretches of the number line and the pattern that results from shining X-rays on a material to reveal the inner arrangement of its atoms. The analysis could lead to predicting primes with high accuracy, said the researchers. The study was published Sept. 5 in the Journal of Statistical Mechanics: Theory and Experiment.
“There is much more order in prime numbers than ever previously discovered,” said Salvatore Torquato, Princeton’s Lewis Bernard Professor of Natural Sciences, professor of chemistry and the Princeton Institute for the Science and Technology of Materials. “We showed that the primes behave almost like a crystal or, more precisely, similar to a crystal-like material called a ‘quasicrystal.’”
Primes are numbers that can only be divided by 1 and themselves. Very large primes are the building blocks of many cryptography systems. Primes appear to be sprinkled randomly along the number line, although mathematicians have discerned some order. The first few primes are 2, 3, 5, 7 and 11, becoming more sporadic higher in the number line.
Torquato and his colleagues have found that that, when considered over large swaths of the number line, prime numbers are more ordered than previously believed, falling within the class of patterns known as “hyperuniformity.”
Hyperuniform materials have special order at large distances and include crystals, quasicrystals and special disordered systems. Hyperuniformity is found in the arrangement of cone cells in bird eyes, in certain rare meteorites, and in the large-scale structure of the universe.
The team showed that the order they found in the prime numbers maps to the pattern that results when X-rays interact with certain forms of matter. As a chemist, Torquato is familiar with X-ray crystallography, shining X-rays through a crystal’s three-dimensional atomic lattice. With diamonds or other crystals, this will result in a predictable pattern of bright spots or peaks, known as Bragg peaks.
Compared to typical crystals, quasicrystals yield a distinct and more complex arrangement of Bragg peaks. The peaks in a typical crystal form at regular intervals with empty gaps between them. In quasicrystals, between any two selected Bragg peaks is another Bragg peak.
The pattern that Torquato and his colleagues discovered in the primes is similar to that of quasicrystals and another system called limit-periodic order, but it differs enough that the researchers call it “effectively limit-periodic” order. The prime numbers appear in “self-similar” groupings, meaning that between peaks of certain heights, there are groupings of smaller peaks, and so on.
The team discovered strong indications of such a pattern using computer simulations to see what would happen if prime numbers were treated like a string of atoms subjected to X-rays. In work published in the Journal of Physics A in February, the researchers reported finding a surprising pattern of Bragg-like peaks, indicating that the prime patterns were highly ordered.
The current study uses number theory to provide a theoretical foundation for those previous numerical experiments. The researchers realized that although primes appear random over short intervals, Torquato said, at sufficiently long stretches of the number line, sense can be made out of otherwise seemingly chaotic numbers.
“When you go to that distinguished limit, ‘Boom!’” he said, snapping his fingers. “The ordered structure pops out.”
Torquato co-authored the paper with Ge Zhang, who earned his doctorate in chemistry in 2017, and mathematics graduate student Matthew de Courcy-Ireland.
De Courcy-Ireland said that similar numerical patterns were described by the “circle method” developed nearly a century ago to find patterns in primes. “For me, what is interesting is taking these results that go back to 1922 and reformulating them in some way that gives you a new example, a system with a bunch of properties that is very interesting, and one that maybe could point the way to where you could look for more physical examples,” he said.
The discovery may aid research in both mathematics and materials science. “Prime numbers have beautiful structural properties, including unexpected order, hyperuniformity and effective limit-periodic behavior,” said Torquato. “The primes teach us about a completely new state of matter.”
“What’s fascinating about this paper is that it gives us a different perspective on the primes: instead of viewing them as numbers, we can view them as particles and try to map out their structure via X-ray diffraction,” said Henry Cohn, a principal researcher at Microsoft Research who was not involved with the study. “It turns out to give us the same sort of information as traditional number-theoretic methods, and to tie in beautifully with previous work. It’s a beautiful new perspective on this information, and it opens up new connections with materials science and scattering theory.”
The study, “Uncovering multiscale order in the prime numbers via scattering,” by Salvatore Torquato, Ge Zhang and Matthew de Courcy-Ireland, was published in the Journal of Statistical Mechanics: Theory and Experiment on Sept. 5 (DOI: 10.1088/1742-5468/aad6be). It was supported by the National Science Foundation (DMR-1714722) and the Natural Sciences and Engineering Research Council of Canada. A more detailed set of proofs is also posted online.
https://www.princeton.edu/news/2018/09/ ... -materials


June 12, 2009
Stress, DNA Damage Responsible For Grey Hair
Those stubborn grey hairs that come with age really are signs of stress, albeit of the cellular kind, according to a new Japanese study.
Genotoxic stress, which is anything that damages our DNA, sets off a chain reaction in which specialized cells known as melanocyte stem cells (MSCs) become damaged, ultimately resulting in a malfunction of the cells responsible for hair color.Scientists discovered that the type of genotoxic stress that damages DNA depletes the MSCs in hair follicles that make pigment-producing melanocytes. When exposed to the stress, these MSCs differentiate into mature melanocytes themselves, rather than dying off. Therefore, anything that can limit genotoxic stress might also stop the graying from taking place, the researchers said.
"The DNA in cells is under constant attack by exogenously- and endogenously-arising DNA-damaging agents such as mutagenic chemicals, ultraviolet light and ionizing radiation," said Emi Nishimura of Tokyo Medical and Dental University.
"It is estimated that a single cell in mammals can encounter approximately 100,000 DNA damaging events per day," she added.
However, cells have sophisticated ways to repair damaged DNA and prevent the damage being passed on to their daughter cells.
"Once stem cells are damaged irreversibly, the damaged stem cells need to be eliminated to maintain the quality of the stem cell pools," Nishimura explained.
"We found that excessive genotoxic stress triggers differentiation of melanocyte stem cells," she said, adding that differentiation might be a more sophisticated way to eliminate those cells instead of fostering their death.
Nishimura's team had previously traced the loss of hair color to the gradual dying off of the stem cells that maintain a continuous supply of new melanocytes, which give hair its youthful color. It turns out that those specialized stem cells are not only lost, they also differentiate into fully committed pigment cells, and in the wrong place.
The current study, which used mice, found that irreparable DNA damage, in this case that caused by ionizing radiation, is responsible.
Furthermore, the "caretaker gene" known as ATM (ataxia telangiectasia) serves as a stemness checkpoint that protects against MSCs differentiation, the researchers found. That's why people with Ataxia-telangiectasia, an aging syndrome caused by an ATM gene mutation, will gray prematurely.
The study supports to the idea that genome instability is a significant factor in aging. It also supports the "stem cell aging hypothesis", which says that DNA damage to long-lived stem cells can be a major driver for many of the conditions that come with age.
In addition to the aging-associated stem cell depletion typically seen in MSCs, quantitative and qualitative alterations to blood stem cells, cardiac muscle, and skeletal muscle have also been reported, the researchers said. Stresses on stem cell pools and genome maintenance failures are also thought responsible for the decline of tissue renewal capacity and the accelerated appearance of aging-related characteristics.
"In this study, we discovered that hair graying, the most obvious aging phenotype, can be caused by the genomic damage response through stem cell differentiation, which suggests that physiological hair graying can be triggered by the accumulation of unavoidable DNA damage and DNA-damage response associated with aging through MSC differentiation," the researchers wrote.
A separate study recently reported by European scientists found that going grey was caused by a build up of hydrogen peroxide due to normal wear and tear of the hair follicles. The hydrogen peroxide blocked the normal production of melanin, the scientists wrote in the report, which was published by the Federation of the American Societies for Experimental Biology.
The current study was published in the June 12 issue of the journal Cell.
On the Net:
- Tokyo Medical and Dental University
- Cell: Genotoxic Stress Abrogates Renewal of Melanocyte Stem Cells by Triggering Their Differentiation


Categories: Solar Flare Sun
Will Solar Flares Cause A 2012 Apocalypse?
Many apocalyptic predictions call for doomsday to occur in 2012. The most specific apocalypse is predicted for December 21, 2012 based on the Mayan calendar. Other 2012 doomsday predictions are derived from Biblical, astrological, or Nostradamus interpretations.
But should we be concerned about solar storms in 2012? Heliophysicist Alex Young from NASA Goddard Space Flight Center sorts out truth from fiction.
- Brevard County Public Schools