English chemist John Frederick Daniell developed a voltaic cell in 1836 which used zinc and copper and solutions of their ions.
Das Lied der Deutschen
Das Lied der Deutschen ("The Song of the German people"), also known as Deutschlandlied, ("The Song of Germany"), is a song written by Joseph Haydn and Hoffmann von Fallersleben. Part of this song is the national anthem of Germany (German National Anthem).
A line from this song, "Einigkeit und Recht und Freiheit" ("Unity and justice and freedom") is the motto of Germany.
The music was written by Haydn in 1797 as the anthem of Austria. It was called "Gott erhalte Franz den Kaiser" ("God protect our Emperor Franz"). The words which are used today were written by the poet August Heinrich Hoffman von Fallersleben in 1841.
Today, the first line "Germany, Germany above all" sounds too strong for some people, and is often misunderstood. Fallersleben wanted a united Germany when he wrote it. At that time, Germany was not one country, but many small countries. So "Germany above all" meant that the most important thing to do was to have a unified Germany. Also, the poet was in Heligoland, where people spoke German but were ruled by the British.
Fallersleben's music was very popular in Germany during the second part of the 19th century. This song was not a national anthem then, but a patriotic song supporting a united German state. In 1918, it replaced the anthem of the German Empire "Heil Dir im Siegerkranz" ("Praise to the war-winner"), when the Emperor Wilhelm II lost power at the end of the First World War. In 1921, a "fourth stanza", a new part or verse, was written by poet Albert Matthai with words about the difficult life in Germany at that time. This verse was rarely used.
During the time of Hitler, only the first part of the song was used. This was often followed by a Nazi party song. This offended the international audience as the first stanza supports Germany holding colonial powers in non-consenting nations.
After the Second World War, Germany was divided into two countries. In 1949, the new Western Germany tried to get a new song for the national anthem. Another song was chosen, written by poet Rudolf Alexander Schröder. It was not very popular. Finally, the third part of the Fallersleben song was made into the national anthem.
In the other part of Germany, the Eastern Germany, the words of poet Johannes R. Becher ("Auferstanden aus Ruinen" - "Re-built from the Ruins") were used with a song written by Hanns Eisler. It was not very popular, and from the 1970s the words were not sung, because of the line "Germany, [our] unified fatherland".
After East and West Germany united again in 1990, the Fallersleben song again became the national anthem of Germany but only the third part is used. Today, the first part of the song is popular with nationalist extremists.
Cavity
A cavity is a hole.
It can also mean:
Evidence
Evidence is something that is used to support an argument. It gives examples of why something is true.
For example, if someone come across a cup of spilled milk, that person could look for evidence as to how the milk was spilled. If hairs of a cat and paw prints were found on the ground, they could be evidence that a cat was the cause of the spilled milk. If a witness saw the cat spilling the milk, her testimony would also be evidence.
Dyadic
A dyadic is a math function that needs two things in order to give something out. Addition and multiplication are dyadic. Powers are also dyadic. There are many more functions that are dyadic.
Dyadic may specifically refer to:
Hill
A hill is a landform that is higher than the surrounding terrain and that is smaller than a mountain. Hill is a highland of much lower elevation than a mountain. Normally it is not as steep as a mountain. The surface of a hill is much more stable than that of a dune. Hill have long been used for hill forts.
Enzyme
An enzyme is a protein molecule in cells which works as a biological catalyst. Enzymes speed up chemical reactions in the body, but do not get used up in the process, therefore can be used over and over again.
Almost all biochemical reactions in living things need enzymes. With an enzyme, chemical reactions go much faster than they would without the enzyme. Other biocatalysts are catalytic RNA molecules, called ribozymes.
The substances at the start of a reaction are called substrates. The substances at the end of a reaction are the products. Enzymes work on the substrates, and turn them into products. The study of enzymes is called enzymology.
The first enzyme was found in 1833 by Anselme Payen.
There are thousands of different enzymes and each one is specific to the reaction which it catalyses. Enzymes have names which show what they do. Enzyme names usually end in –ase to show that they are enzymes. Examples of this include ATP synthase. It makes a chemical called ATP. Another example is DNA polymerase. It reads an intact DNA strand and uses it as a template to make a new strand.
One example of an enzyme is amylase, found in saliva. It breaks down starch molecules into smaller glucose and maltose molecules. Another kind of enzyme is lipase. It breaks down fats into smaller molecules, fatty acids and glycerol.d
The proteases are a whole class of enzymes. They break down other enzymes and proteins back into amino acids. Nucleases are enzymes that cut DNA or RNA, often in specific place in the molecule.
Enzymes are not only for breaking large chemicals into smaller chemicals. Other enzymes take smaller chemicals and build them up into bigger chemicals, and do many other chemical tasks. The classification below lists the main types.
Biochemists often draw a picture of an enzyme to use as a visual aid or map of the enzyme. This is hard to do because there may be hundreds or thousands of atoms in an enzyme. Biochemists can not draw all this detail. Instead, they use ribbon models as pictures of enzymes. Ribbon models can show the shape of an enzyme without having to draw every atom.
Most enzymes will not work unless the temperature and pH are just right. In mammals the right temperature is usually about 37C degrees (body temperature). The correct pH can vary greatly. Pepsin is an example of an enzyme that works best when pH is about 1.5.
Heating an enzyme above a certain temperature will destroy the enzyme permanently. It will be broken down by protease and the chemicals will be used again.
Some chemicals can help an enzyme do its job even better. These are called "activators". Sometimes, a chemical can slow down an enzyme or even make the enzyme not work at all. These are called "inhibitors". Most drugs are chemicals that either speed up or slow down some enzyme in the human body.
Enzymes are very specific. In 1894 Emil Fischer suggested that both the enzyme and the substrate have "specific complementary geometric shapes" that fit exactly into one another. This is often referred to as "the lock and key" model. However, this model fails to explain what happens next.
In 1958, Daniel Koshland suggested a modification to the lock and key model. Since enzymes are rather flexible structures, the active site is reshaped by interactions with the substrate. As a result, the substrate does not simply bind to a rigid active site. The amino acid side-chains of the active site are bent into positions so the enzyme does its catalytic work. In some cases, such as glycosidases, the substrate molecule also changes shape slightly as it enters the active site.
The general equation for an enzyme reaction is:
Enzymes lower the activation energy of a reaction by forming an intermediary complex with the substrate. This complex is called an enzyme-substrate complex.