bluuebunny/crossref_metadata_2025 huggingface dataset:
Training Needs Of New Mexico Agricultural Education Teachers Related To Inclusion Of Students With Special Needs
Authors: Andreasen Randall J. , Seevers Brenda S. , Dormody Thomas J. , VanLeeuwen Dawn M.
Published: April 2010

The purpose of this study was to describe New Mexico secondary agricultural education teachers' perceptions of the importance and their level of competence on state special needs inclusion competencies and skills for teaching students with special needs.Additionally, this study sought to determine pre-service and in-service training needs for working with students with special needs.A census of New Mexico agricultural education teachers received a mail questionnaire during spring and summer 2003.The inclusion competencies most in need of strengthening among the teachers were: understanding special education regulations, understanding different levels of special education services, understanding different levels of disabilities, and understanding the social needs of special education students.The special education teaching skills most in need of strengthening were: dealing with uncooperative special education students, working with more than one type of disability, keeping special education students on task, and adapting facilities for special education students.
Carbon Fibers
Authors: Minus Marilyn L. , Kumar Satish
Published: April 2010

Carbon fibers have been studied extensively since the 1960s due to their high strength (3–7 GPa), high modulus (200–500 GPa), compressive strength (1–3 GPa), shear modulus (10–15 GPa), and low density (1.75–2.00 g/cm3). Carbon fibers are derived from several precursors, including isotropic pitch, mesophase pitch, and polyacrylonitrile (PAN) being the predominant precursor used today. Carbon fibers made from pitch can have modulus, thermal, and electrical conductivities as high as 900 GPa, 1000 W/mK, and 106S/m, respectively. The properties of carbon fibers make them useful for reinforcements in composite applications. Carbon fibers have become a dominant material in the aerospace industry, and their usage in automotive, sporting good, and other industries continue to grow as their cost continues to come down.
Chiral Separations
Authors: Gübitz Gerald , Schmid Martin G.
Published: April 2010

The development of chiral separation methods became very important in recent years since it is known that the biological or pharmacological activities of compounds of biological or pharmaceutical interest is mostly restricted to one of the enantiomers. Starting in the late 1960s with classical column liquid chromatography and the first direct gc separation, subsequently methods for HPLC and TLC were developed. More recently, electromigration techniques such as capillary zone electrophoresis, capillary electrokinetic chromatography and capillary electrochromatography found application for chiral separation. A broad spectrum of chiral separation principles have been developed in the 1970s, 1980s and first half of the 1990s, in which mainly applications of these basic separation principles were published. Several thousand publications appeared in this field. Miniaturized systems such as micro‐chip capillary electrophoresis attracted increasing attention in recent years. On the other hand, preparative HPLC found access into industrial production of enantiopure drugs. This article gives an overview of the diversity of chiral separation principles and their mechanisms. Due to the nature of stereoselectivity, there will never exist a universal chiral separation method, the choice of the method always has to be adapted to the problem. However, a few predictions are possible. This article does list applications, beacuse of space constrainds.
Noble Gases
Authors: Hwang Shuen‐Cheng , Lein Robert D. , Morgan Daniel A.
Published: April 2010

The noble gases are characterized by completely filled valence electron shells. Helium, argon, and neon are commercially available, but krypton, xenon, and radon are quite rare. Principal uses of commercial helium include those as a lifting gas, as an inert carrier gas, and as a cryogenic refrigerant. Helium‐3 and helium‐4, which are both stable isotopes used in cryogenics, differ significantly in their liquid properties because of quantum mechanical effects. Argon finds use principally as an inert gas in industries ranging from electronic ones to steelmaking. Neon is employed as a filling gas in detection chambers and in light sources from commercial signs to lasers. Sources and properties of these gases are discussed. Production of helium from natural gas, and of argon and neon from air separation plants, is presented.
Pigments, Inorganic
Authors: Swiler Daniel R.
Published: April 2010

Inorganic pigments, black, white, or colored, are an integral part of many decorative and protective coatings. These materials are produced and marketed as fine powders that are then dispersed in the desired media. Inorganic pigments are used for the mass coloration of plastics, fibers, paper, rubber, glass, cement, glazes, and porcelain enamels, as well as for colorants in printing inks, cosmetics, and markers, such as crayons. Pigment properties including particle size, tinting power, and hiding strength are discussed.

Inorganic pigments of largest commercial interest are the white titanium dioxide; the colorful natural and synthetic iron oxides; various zinc compounds; and carbon black. Many transition‐metal and some rare‐earth compounds are used as chromophores in host oxides such as spinel to produce stable and affordable pigments. Environmentally benign, colorfast replacements are being sought for the historically popular, highly colored lead and cadmium compounds which have proven toxic.
Quinolines and Isoquinolines
Authors: Finley K. Thomas
Published: April 2010

The fusion of a pyridine and a benzene ring produces two heterocyclic aromatic systems usually referred to by their common names, quinoline and isoquinoline. In addition to the chemistry to be expected, this combination opens a wide range of additional possibilities. It is therefore not surprising that both quinoline and isoquinoline have been the subject of extensive studies ranging from the theoretical to the most applied. The dye and photographic industries, the metallurgical, analytical, and polymer sciences all provide extensive examples. However, it continues to be the medical field and the pharmaceutical industry that provides the major driving force for an impressive array of studies of the synthesis and properties of molecules containing these structures. The toxicity of these compounds is sufficient to warrant care in their handling. The literature has been reviewed through March, 2005.
Quinones
Authors: Thomas Finley K.
Published: April 2010

Quinones, possessing two α,β‐unsaturated carbonyl groups usually in a six carbon atom ring, represent a unique structural unit. Their centrality in the synthesis of such important commercial substances as dyes and pharmaceuticals has resulted in extensive study of a variety of synthons. In living matter, they are ubiquitous and vital to human metabolism. Quinones are of special interest to biochemists and to both synthetic and theoretical organic chemists. The types of reactions most often reported are nucleophilic addition, photochemistry, cycloaddition, electrophilic addition, radical alkylation, electrochemical, oxidation, and nucleophilic substitution. The synthesis of quinones is usually accomplished through oxidation of phenols or anilines. A wide variety of oxidants has been used, but quinones of higher oxidation potential are often the reagent of choice. Quinones of low molecular weight should be treated with care in their storage and handling.
Release Agents
Authors: Owen Michael J.
Published: April 2010

Release agents are used in a wide variety of industries to control or eliminate the adhesion between surfaces. Key product requirements and trends are reviewed and a classification based on chemical type is presented. The mechanisms of release are reviewed, emphasizing the importance of minimizing both the strength of the interaction across the interface and the degree of contact. The dominant role of materials such as those based on aliphatic hydrocarbon and fluorocarbon entities or particulate solids is thus explained. Simple thermodynamic arguments are presented stressing the need for release surfaces to have lower surface energies than the substrates they are designed to function with. Industrial applications are succinctly summarized, focusing on the specific needs of each particular application and the types of release agents currently used therein. The categories considered are metal, glass, rubber, plastics, textiles, adhesive transfer processes, furniture, and food. Economic aspects and health and safety factors are also briefly considered.
Reverse Osmosis
Authors: Meyer D. E. , Williams M. , Bhattacharyya D.
Published: April 2010

Reverse osmosis is a highly effective separation technology used industrially in several areas, including desalination of seawater and brackish water and wastewater treatment. Membrane materials and types of modules used in reverse osmosis, as well as theoretical bases and operational aspects, are presented. A discussion of flux limiting conditions caused by concentration polarization and membrane fouling is included, as is that of the pretreatments required for process feed streams. The application of reverse osmosis for the separation of hazardous organic compounds from aqueous systems, for wastewater treatment, desalination, ultrapure water production, and food processing are reviewed in terms of membrane performance. The emerging applications involving solvent resistant membranes, and functionalized membranes are also included. The concept of nanofiltration and its applications are also discussed. General design considerations and economics are reviewed.
Sonochemistry
Authors: Ashokkumar Muthupandian , Mason Timothy J.
Published: April 2010

Sonochemistry is a relatively new term that arrived on the scene in the late 1970s and was then simply defined as the uses of ultrasound in chemistry and processing. Ultrasound is part of the overall sound spectrum, but is generally classified as sound beyond the frequency that can be detected by the human ear. Sometimes called “silent sound” it ranges from 20 kHz to 10 MHz within which it can be roughly subdivided into three main regions: low frequency, high power ultrasound (20–100 kHz); intermediate frequency, medium power ultrasound (100 kHz–1 MHz); and high frequency, low power ultrasound (1–10 MHz). The range from 20 kHz to 1 MHz is generally used in sonochemistry, whereas frequencies > 1 MHz are more commonly used in nondestructive testing and medicine. The driving force for sonochemistry is acoustic cavitation, which is the formation of small cavities in a fluid produced by ultrasound that undergo highly energetic collapse. A number of text books have been published that explore different aspects of sonochemistry.

This article aims to provide the readers with a fundamental understanding of acoustic cavitation and its associated physical and chemical effects. Detailed information on the events that are involved in acoustic cavitation is discussed in the first section. Among the major effects generated by acoustic cavitation is Sonoluminescence and Sonochemistry, but only brief information is provided on the former since it is not the primary focus of this article. The majority of the discussion is focused upon Sonochemistry within which reactions have been subdivided into different categories, as suggested in the literature. Although sonochemistry is useful for a variety of applications, two areas that are particularly prominent are materials synthesis and the degradation of organic pollutants.
Water Desalination
Authors: Wilf Mark
Published: April 2010

This article addresses water availability and use with special emphasis on the role and current level of technology of water desalination. The major desalination processes, using membranes or distillation, are described. These are multistage flash evaporation (MSF), multi‐effect distillation (ME), vapor compression distillation (VC), freeze–desalination, reverse osmosis (RO), and electrodialysis (ED). Within the membrane processes category important features of major applications: nanofiltration, brackish RO, wastewater reclamation and seawater desalination are discussed. Description of desalination hybrid systems and key references are provided. The use of renewable energy for water desalination by solar stills, ocean–thermal energy conversion plants, wind, and photovoltaic cells is presented. Two of the key technical problems in desalination, scale deposition and prevention, and corrosion and the proper choice of materials to be used for construction of desalination system, are discussed. Basic equations are provided for the evaluation and preliminary design of MSF and RO, which are currently the leading water desalination processes. The leading professional and governmental organizations involved with desalination, and their activities, are described.
Wine
Authors: Butzke Christian E. , Singleton Vernon L.
Published: April 2010

The unmodified wordWinesignifies the juice of grapes fermented by wine yeast and appropriately finished into an alcoholic beverage. Wine's complex composition, abundant types and styles, and elusive definition of quality represent a product that combines chemical technology and human culture like no other. The history of wine growing and making is intertwined with the development of western civilization while today the global wine industry makes a substantial contribution to modern value‐added agriculture that has far‐reaching impact on the economies of all winegrape‐producing countries. Sensory evaluation and wine appreciation in addition to analytical quality control are key aspects of crafting and marketing this unique commodity. A wine's value depends much on its typicity, particular regional character, varietal diversity and vintage‐to‐vintage variation rather than on a standardization that is often sought in other food products. Internationally, wine production techniques, including grape processing, fermentation, maturation and aging, blending and stabilization, have become rather similar leaving the location, weather and climate of the vineyards to be the crucial factor for the quality of the bottled product. The wine industry and its viticultural and enological practices are tightly regulated and controlled in most countries, while moderate consumption of wine continues to play a vital role in human nutrition, health, well‐being and social interaction.
Xylenes and Ethylbenzene
Authors: Cannella William J.
Published: April 2010

This article reviews the properties, commercial manufacturing aspects, and uses of the three xylene isomers, ie,o‐xylene,m‐xylene, andp‐xylene, and the ethylbenzene present in mixed xylene streams. Chemical reactions discussed are migration of the alkyl groups, including 1,2 intramolecular shifts and transalkylation; reactions of the alkyl groups, including oxidation, polycondensation, and ammoxidation; reactions of the aromatic ring; and complex formation. Aspects of commercial manufacture that are covered include initial production of mixed xylenes; separation processes used to produce high purityp‐xylene,o‐xylene, andm‐xylene; and xylene isomerization processes. Catalytic reforming and toluene disproportionation/transalkylation are the primary mixed xylene production routes discussed. The xylene isomer separation processes of crystallization, adsorption, and complex formation are described. The commercially important xylene isomerization processes are reviewed. Analytical techniques economic data, and important health and safety factors are also summarized.
Hemodialysis
Authors: Ofsthun Norma J.
Published: April 2010

Hemodialysis is the most commonly‐employed process for cleaning the blood of a patient with kidney failure. In hemodialysis, blood flows on one side of a semipermeable membrane and dialysate solution flows on the other side of the membrane. Today, the typical artificial kidney, or dialyzer, consists of approximately ten thousand cylindrical polymer membranes (“hollow fibers”) through which blood flows. The hollow fibers contain pores which are large enough to let toxins pass, but small enough to retain plasma proteins. Dialysate, a solution containing physiological concentrations of several key solutes, flows around the hollow fibers in a counter‐current direction. Hemodialysis cleans the blood by a combination of diffusion, in which toxins move across the hollow fiber wall from high concentration (blood side) to low concentration (dialysate side), and convection, in which solutes are swept along with the fluid that moves through the membrane pores (from blood to dialysate) as a result of a pressure gradient. Small molecular weight waste products (<500 kDa) normally excreted in urine are transferred across the membrane primarily by diffusion, and flow down the drain with the dialysate. Excess water that accumulates between treatments is also removed, leading to convective removal of molecules in the so‐called “middle molecule” range of 500 to ∼15,000 Da. A typical hemodialysis regimen calls for three treatments per week, with each treatment lasting 3.5–4.0 hours. Approximately one million patients worldwide receive chronic hemodialysis today.

In this article, the process of hemodialysis, design requirements for dialyzers, and properties of currently available hemodialysis membranes, introducing terminology peculiar to the dialysis industry that may be unfamiliar to scientists in other fields are reviewed.
Reliability
Authors: Murthy D. N. Prabhakar , Blischke Wallace R.
Published: April 2010

Reliability is important in chemical plants for economic and safety reasons. The reliability of a plant depends on the decisions made during the design and construction of the plant as well the maintenance actions performed during the operation of the plant. Reliability theory deals with various analytical aspects of reliability (science, engineering, modeling, optimization, etc). A proper understanding of reliability theory is important for the design and construction of reliable plants and to ensure high reliability during the operation of the plant. The article gives a brief introduction to some basic concepts from reliability theory and discusses areas of interest to chemical engineers. It concludes with an illustrative example from the chemical industry.
CNSStimulants
Authors: Nichols David E.
Published: April 2010

This chapter briefly describes the development, structure–activity relationships, and mechanism of action for the important psychostimulants such as amphetamines, methylphenidate, and cocaine. Derived from natural products known for centuries, at low doses these drugs lead to increased arousal, improved performance on tasks of vigilance and alertness, and a sense of self‐confidence and well being. High doses can produce feelings of elation or euphoria, and result in profound abuse liability. This chapter reviews the current and future use of psychostimulants, as well as other drugs that cause CNS arousal, albeit by different mechanisms.
Crystallization Kinetics
Authors: Hobbs Jamie K.
Published: April 2010

Crystallization kinetics is the area of polymer science that deals with the rate at which randomly ordered chains transform into highly ordered crystals, and includes every aspect of the resultant structure that is dependent on the route that was taken between those different states. It is a broad and mature area of scientific research, given and uncommon diversity when compared to the crystallization of small molecules because of the wide range of different chemistries and chain topologies that are available to macromolecules. These add layers of comlexity that can make it difficult to find generalizing principles. The article concentrates on principles and observations that have the widest applicability.

Crystallizable polymers form semicrystalline materials containing chains or fractions of chains that are trapped in nonequilibrium, amorphous states. Because of this semicrystalline nature, the crystal morphology, rather than the underlying crystal structure, often controls the final properties of a polymer article. Because polymers crystallize so far from equilibrium conditions, a simple examination of the phase diagram gives us little insight into the crystal morphology that is formed or the route that is taken to its formation. To understand, and ultimately control, such behavior, it is necessary to gain an understanding of the kinetics of crystallization, as it is the kinetics of the process that define the structure and properties of the material.
Forensic Analysis
Authors: Bartick Edward G. , Palenik Skip
Published: April 2010

This article is as an introduction to forensic applications of polymer analysis. The ubiquity of polymeric materials in our environment results in these items frequently being found at crime scenes and as the subject of civil cases and subsequently considered as evidentially important. This hybrid subject of forensic science, concerning both legal and scientific evaluation of polymeric materials, is introduced to combine both aspects. The article provides a brief introduction to how evidence is viewed from a legal perspective and an overview of analytical methods used in the forensic examination of evidence. Since microscopy and spectroscopy contribute the greatest amount of information in the least amount of time, they are emphasized in this work. Examples of casework are provided to illustrate the forensic process. Illustrations of fiber and paint analysis are provided to demonstrate the forensic approach of these two important categories of polymers that frequently serve as evidence in casework.
Surface Analysis
Authors: Briggs David
Published: April 2010

The surface properties of polymers are important in many applications and they are dependent on the structure and composition of the outermost molecular layers. The surface layer thickness involved is typically of the order of a few nanometers. Understanding surface structure–property relationships therefore requires analytical techniques which have this degree of surface sensitivity (or specificity). Two techniques stand out: X‐ray photoelectron spectroscopy (XPS), also known as ESCA (electron spectroscopy for chemical analysis), and secondary ion mass spectrometry (SIMS). The information provided by these methods is highly complementary and they are frequently used in combination. This article describes the physical bases and analytical capabilities of XPS and SIMS and illustrates their application in polymer surface characterization.
Photopolymerization, Cationic
Authors: Sipani Vishal , Scranton Alec B.
Published: April 2010

Photopolymerizations are chain reactions in which propagating active centers (free radicals or cations) are produced by a photochemical event. The use of light, rather than heat, to initiate the polymerization offers several advantages, including spatial and temporal control, energy efficiency, and high polymerization rates. In addition, cationic photopolymerizations offer advantages over their free‐radical counterparts since they are not inhibited by oxygen and may continue to react long after the illumination has ceased. This article provides an overview of the important aspects of cationic photopolymerizations, including initiators, monomers, and polymerization kinetics. Commonly used photoinitiator systems for ultraviolet or visible light have been described, and the reaction mechanisms have been explored. The photoinitiation step is especially important because it is the step that distinguishes these reactions from their thermally initiated counterparts. A description of traditional cationically polymerizable monomers as well as recently developed, highly reactive monomers is also provided. Finally, representative kinetic rate expressions have been presented to illustrate the link between the reaction mechanism and the polymerization rate, and to identify the important variables that affect the polymerization. This article provides a valuable resource for any scientist or engineer who is considering cationic photopolymerizations for a study or an application.
Bacterial Cell Wall
Authors: Young Kevin D
Published: April 2010

Most bacteria are encased in walls that protect the cells against lysis by osmotic forces from within and from chemical or biological assaults from outside. These walls are assembled in layers consisting of four principal components: inner membrane, peptidoglycan, outer membrane and S‐layer. The first two are the basic constituents of bacterial walls, the outer membrane is a hallmark of one branch of bacteria and S‐layers are optional in many different microorganisms. The two fundamental types of wall are Gram‐type positive, which have no outer membrane, and Gram‐type negative, which have an outer membrane. Bacteria also produce various secondary polymers, such as teichoic or mycolic acids, that associate with peptidoglycan and alter its chemical characteristics. Finally, and in addition to its protective role, the wall imparts to bacterial cells their specific shapes and is organised to facilitate the transport of vital chemicals into and out of the cell.

Key Concepts:

The cell wall protects bacteria from lysis, chemical assault and attack by the immune system.

The bacterial cell wall consists of an inner (plasma) membrane, a rigid peptidoglycan exoskeleton and, in some cases, an outer membrane and/or an S‐layer.

Peptidoglycan is composed of a long chain of repeating disaccharides linked to one another by short peptide side chains, which creates a single macromolecule surrounding the bacterial cell.

The biological properties of many bacterial cell walls are strengthened or enhanced by the addition of secondary cell wall glycopolymers.

The bacterial world is divided into two main groups: those that have a single membrane (the plasma or inner membrane) and those that have two membranes (inner and outer membranes).

S‐layers are paracrystalline arrays of a single protein that completely cover the exterior of many bacteria.

Bacterial shape is determined by cytoskeleton proteins that direct the synthesis of the overall structure of peptidoglycan.
Protein Translocation across Membranes
Authors: Perry Andrew J
Published: April 2010

Cells are divided into compartments that serve to separate and coordinate metabolic processes. In eukaryotic cells, almost all enzymes, along with proteins involved in their maintenance, are encoded by genes in the nucleus. Proteins are translated in the cytoplasm, and must be targeted to the correct compartment within the cell in order to faithfully carry out their function. To achieve this, proteins are synthesized with signal sequences that guide them to receptor proteins that in turn transfer them to large transmembrane protein channels of organelles. The molecular machinery for protein translocation has evolved to capture and recognize proteins with the correct targeting signals encoded in their amino acid sequence. These diverse classes of translocases pass substrate proteins across, or into, membranes cotranslationally or posttranslationally. Protein substrates are moved by active pushing, pulling, electrophoretic and Brownian ratchet mechanisms. Most translocases operate on unfolded polypeptides, whereas some can transport partially or fully folded proteins.

Key Concepts:

Cells contain sophisticated molecular machines to recognize and translocate proteins across membranes and into their correct organelles.

Proteins are targeted to subcellular locations via targeting signals encoded in their amino acid sequence. These usually exist as linear sequences in the
N
‐ or
C
‐terminal region of the protein; however, some targeting signals occur within internal segments of the substrate polypeptide. Not all targeting signals are well defined.

Receptors associated with the translocase and in the cytosol specifically recognize targeting signals.

Translocases contain pores through which the substrate proteins can pass. Most translocase pores are only large enough to accommodate unfolded proteins, although some appear to be able to accommodate fully folded polypeptides.

Molecular chaperones maintain substrates in an unfolded state before translocation and assist their correct folding after translocation.

The force required to translocate proteins across membranes can come from several sources; the electrophoretic potential or pH gradient across the membrane, an ATP‐ or GTP‐driven pushing or pulling mechanism and an ATP‐driven Brownian ratchet mechanism.
NAD+andNADP+as Prosthetic Groups for Enzymes
Authors: Oppenheimer Norman J
Published: April 2010

NAD(P)+(nicotinamide–adenine dinucleotide (phosphate)) serves as a coenzyme forpyridine nucleotide‐dependent dehydrogenasecatalysed redox reactions. When the coenzyme behaves as a nondissociable prosthetic group it can function to promote aldehyde dismutation with nicotinoproteins as well as regularalcohol dehydrogenases. The tightly bound coenzyme can also be used to conduct reversible redox reactions to catalyse epimerization of sugar hydroxyls and to trigger elimination reactions; for example,nucleotidyl diphosphohexose‐4,6‐dehydratases,ornithine cyclodeaminaseandS‐adenosyl‐l‐homocysteine hydrolase. Finally inurocanasethe nicotinamide ring can participate directly as a Lewis acid to catalyse a complex rearrangement reaction. An important feature of these reactions is that because the coenzyme does not dissociate that they are independent of the NAD+/NADH (reduced form of nicotinamide–adenine dinucleotide) ratio of the cell.

Key Concepts:

In the standard spectrophotometric assay of dehydrogenases coenzyme release is rate limiting, but when the coenzyme cannot or does not dissociate then chemistry becomes limiting and reaction rates can be much faster when substrates are present for both forward and reverse reactions.

Dismutation of aldehydes and reactions catalysed by nicotinoproteins can occur without any change in the concentration of exogenous NADH, that is, no spectrophotometric change hence they are difficult to observe and assay.

For enzymes with tightly bound coenzyme, their reactions are not directly influenced by changes in the ratio of NAD+/NADH in the cell.

With the exception of nicotinoproteins, enzymes with nondissociable NAD+can be inactivated by its reduction to NADH in the absence of the normal substrate, that is, there is no independent means of exchanging out the bound NADH or oxidizing it.

In spite of the chiral nature of their active sites epimerases catalyse an overall nonstereospecific reaction. Although the hydride transfer reaction retains its exquisite stereochemical fidelity the binding of the substrate has greatly decreased stringency allowing reactions with either epimer, hence eventually leading to the thermodynamically favoured mixture.

In addition to redox reactions the catalytic machinery of dehydrogenases can promote a wide range of other chemistry including dehydrations and rearrangements provided the substrate can be properly activated and bound in the appropriate juxtaposition to the coenzyme.

The pyridinium ring of NAD+can serve as a Lewis acid for reactions where protonation does not provide the correct pathway.
Tombusviridae
Authors: Sit Tim L , Lommel Steven A
Published: April 2010

The
Tombusviridae
is a relatively large and diverse family of soil‐borne viruses that have single‐stranded, positive‐sense, RNA (
ribonucleic acid
) genomes and that share morphological, structural, molecular and genetic features. Their high titres, compact genomes and extremely stable virions lend to their attractiveness as research subjects. Indeed, the
Tombusviridae
are a particularly well‐characterized family of viruses in the areas of virus structure, gene expression strategies, virus movement, the support of satellite viruses and defective‐interfering RNAs as well as RNA recombination. Although the
RNA‐dependent RNA polymerases
share a great deal of sequence identity, the capsid proteins can be separated by the presence (or absence) of a
C
‐terminal protruding domain which gives the virions a bumpy appearance in electron micrographs. Transmission of several members by fungal zoospores in a species‐specific manner has been reported. The virions of several members have been utilized for biotechnology purposes.

Key Concepts:

Virions are nonenveloped and extremely stable.

Tombusviridae
species replicate to high titres within their host cells.

RNA genomes are small with a limited number of gene products that serve multiple functions.

RNA–RNA interactions control gene expression in several genera.

Viral‐encoded suppressors of RNA silencing act at several different stages in the response cascade.

Several members transmitted through soil by specific fungal zoospores.
Lysogeny
Authors: Campbell Allan M
Published: April 2010

Lysogeny is the harbouring of a quiescent bacteriophage genome by a growing bacterial host. Coliphage lambda (the paradigmatic example) is treated in most detail and other phages are compared to it. The role of regulatory proteins in determining the fate of the infected cell is indicated as well as variations seen in other phages. Insertion of lambda
deoxyribonucleic acid
(DNA) into the host chromosome by circularisation and site‐specific recombination is described and compared to transposon‐like insertion by phage Mu, plasmid formation by phage P1 and single‐strand insertion by the filamentous cholera phage CTXϕ. The mechanism of shifting from lysogenic to lytic growth due to repressor degradation mediated by
RecA
protein activated by single‐stranded DNA (ssDNA) is outlined. Hypotheses on the role of lysogeny in nature are discussed.

Key Concepts:

Latent viruses, whose genomes persist in the host over long periods in absence of ongoing infection, are common throughout the living world and are implicated in human maladies such as shingles.

Site‐specific recombination, which entails breakage and joining of DNA at specific sequences, is used by viruses and plasmids and facilitates separation of daughter chromosomes in bacterial cell division.

DNA looping occurs when protein molecules which bind to noncontiguous DNA sites also bind to each other, bringing together DNA sites that are normally some distance apart.

In transposition, some DNA elements, including viral genomes, move from one site to another by action of transposases encoded by the element.

Some latent viruses can perpetuate their genomes without integration into the chromosome by plasmid formation, where viral genomes replicate autonomously to keep pace with cell division.

Prophage induction is the activation of a prophage to produce active viruses by treating lysogenic cells with various agents.
Specific Neural Connection Formation in the Developing Nervous System
Authors: Lett Robyn LM , O'Connor Timothy P
Published: April 2010

To construct a properly functioning nervous system, neurons must form precise and specific connections during embryonic development. Many theories have been proposed to explain how connectivity might be established, including the concept of ‘chemoaffinity’, ‘labelled lines’ and ‘segmental pathfinding’. Evidence now shows that each of these theories is best explained by guidance cue and receptor interactions at the growing tip of the neuron, the growth cone. The behaviour of growth cones resulting in the establishment of functional connections is governed by receptor signalling in the growth cone in response to the presence of extracellular guidance cues. The main families of guidance cues include netrins, ephrins, slits and semaphorins, although morphogens also have guidance cue roles. It is the complex arrangement of these cues then that directs axon extension through a series of intermediate targets before growth cones finally recognise their final target and form a synapse.

Key concepts:

Historical theories of connectivity can be explained by the expression and action of guidance cues and their receptors upon growth cone behaviour.

Growth cones are the sensory apparatus of an axon required for proper target identification and formation of functional connections.

Disruption of connectivity due to alterations in guidance cue expression during development can result in severe disorders.

Guidance through inhibition is the predominant form of growth cone directional control.

Molecules traditionally known for their roles in tissue morphogenesis are also found to have important roles as axonal guidance cues.
Inflammation: Acute
Authors: Cain Derek W , Kelsoe Garnett
Published: April 2010

Inflammation represents the response of vascularised tissue to damage resulting from infection or injury. An acute inflammatory response comprises four phases: detection of harmful stimuli, recruitment of effector molecules and cells, elimination of pathogens and cellular debris and restoration of tissue homeostasis. Several receptor families, including Toll‐like receptors, Nod‐like receptors and C‐type lectins, recognise molecules associated with microbial pathogens and cellular damage. Signals mediated by these receptors stimulate the release of inflammatory molecules that alter vascular permeability at sites of tissue damage. Changes in vascular endothelium promote the exudation of plasma and the recruitment of leucocytes for the clearance of microorganisms and necrotic tissue. Inflammatory mediators also exert systemic effects that contribute to immune defence in a process called the acute‐phase response. Successful clearance of injurious agents and tissue damage abates inflammatory signals and is followed by the formation of granulation tissue and the initiation of tissue remodelling.

Key Concepts:

Tissues are continuously surveyed for infection and cellular damage by cells and molecules that recognise pathogen‐ and damage‐associated molecular patterns.

Recognition of infection or cellular damage activates inflammation locally and systemically to eliminate microbial pathogens and damaged tissue.

Inflammatory signals recruit neutrophils and macrophages into inflamed tissues where they release toxic factors and phagocytose pathogens and cellular debris.

The resolution of inflammation is followed by tissue repair and remodelling.
Antigen–Antibody Binding
Authors: Kumagai Izumi , Tsumoto Kouhei
Published: April 2010

Antibodies are a family of glycoproteins that bind specifically to foreign molecules (antigens). The antibody‐binding sites are formed by six segments of variable structure (CDRs) supported by a scaffolding of essentially invariant architecture (framework regions). Shape complementarity of binding surfaces (in the case of protein antigens) or close contact with small antigens (hapten, peptide or others), with some complementation of water molecules, is important. The binding of an antigen to an antibody takes place by the formation of multiple noncovalent bonds between the antigen and the amino acids of the binding site. The increase in van der Waals contancts and buried surfaces on complexation correlates well with the affinity, and hydrogen‐bond formation is in principle critical for high specificity and affinity of an antibody for the target. Antibodies have at least two antigen‐binding sites, which increase the apparent affinity, called avidity, of antibodies for the targets.

Key Concepts:

The binding between antibodies and antigens has high specificity and affinity resulting from various structural and energetic aspects. Multivalency of antibodies is important to understand the interaction of an antibody with its antigen.
Lymphocyte Development
Authors: Zhang Yu
Published: April 2010

Like haematopoietic cells of other lineages, both B and T lymphocytes arise from haematopoietic stem cells. Although B‐cell development takes place in the bone marrow, T cells are generated in the thymus. With the support of specialised micro‐environmental milieus, the progenitors unfold intrinsic genetic programs and progress through multiple intermediate stages to develop into antigen‐responsive lymphocytes. A constant theme during this process is lineage diversification. The role of several critical factors has been revealed in recent years, including that of transcription factor
Pax5
(paired box 5) and
Notch1
signal in B‐ and T‐lineage specification and commitment. In addition, lymphoid development is characterised by somatic recombination of the genes encoding antigen receptors. Such a process ensures the generation of an extremely diversified repertoire of antigen receptors. This newly generated repertoire is then subjected to strict selection before being added to the peripheral pool of mature lymphocytes.

Key Concepts:

The differentiation from haematopoietic stem cells to antigen‐responsive mature lymphocytes is accompanied by sequential changes in gene expression and orderly rearrangements of the genes encoding antigen receptors.

Division of the lymphoid developmental pathways into multiple stages provides a useful framework to dissect the cellular and molecular mechanisms of cell differentiation. But it should be recognised that the transition from one stage to the next is not necessarily as sharp as implied in the diagram.

Lineage specification and commitment is a protracted process, during which cells destined for one lineage does not lose potentials for alternative lineages until relatively late. It is always important to distinguish potential from predominant cell fate.

Cells at different developmental stages are associated with specialised micro‐environmental niches, and migration in and out of these niches is essential for the orderly progression of differentiation.

The micro‐environmental milieus either determine the fate to be adopted by a progenitor or provide signals to allow cell‐intrinsic developmental programs to progress.

Lymphocyte development is an expensive process for the host as the majority of the developing cells die by apoptosis as the result of selection against cells with nonproductively rearranged antigen receptor genes, cells incapable of recognising self‐MHC, or cells reactive to self‐antigens.

The quantitative differences in signal strength have a remarkable impact on fate choice by developing lymphocytes, such as positive‐versus‐negative selection, αβ‐versus‐γδ‐lineage diversification, CD4‐versus‐CD8‐lineage decision and Treg cell development.
Proteins: Fundamental Chemical Properties
Authors: Cozzone Alain J
Published: April 2010

Proteins are the most abundant class of biological macromolecules as they represent over 50% of the dry weight of cells. They are involved in virtually all chemical reactions and processes occurring in life forms as well as in the mechanical support and filamentous architecture within and between cells. Irrespective of their functional or structural role, they all are formed from the same 20 building blocks, called amino acids, which are joined end‐to‐end through covalent linkages termed peptide bonds.

The size, ionisation properties and hydrophobicity/hydrophilicity of the constituent amino acids influence the solubility, stability and structural organisation of proteins that exist essentially in either aqueous or membrane environments.

The amino acid sequences (primary structures) determine the higher structural levels (secondary and tertiary) of proteins and specify their biological properties.

Key Concepts:

Proteins occupy a prominent position in all biological systems, both quantitatively and qualitatively.

Irrespective of their structural or functional role, all proteins are built from the same fundamental blocks, the amino acids.

The physico‐chemical properties of the constituent amino acids determine the structure and biological function of proteins.
Plant Organ Primordia
Authors: Kidner Catherine A
Published: April 2010

Plants are made up of the shoot axis, the root axis and the organs produced by each including leaves, petals, some tendrils, some thorns and lateral roots. These organs are produced throughout the lifespan of the plant, their production involves changes in cell fate, delineating boundaries, patterning the new organ and controlling its outgrowth. Shoot organs are formed in a regular pattern on the flanks of the shoot apical meristem. They lose the indeterminacy of meristem cells. Signals from the meristem pattern the organ, establishing an upper (adaxial) and a lower (abaxial) side. Organs of the root are produced from nonmeristematic cells the peri‐cycle cells which surround the vasculature. If these cells receive the correct signal they start to divide and produce a new indeterminate meristem. This meristem activates as it breaks through the primary root tissues.

Key Concepts:

Plant organs form throughout the lifespan of the plant.

Shoot organs include leaves, floral organs and some tendrils or thorns.

Shoot organs form on the flanks of the shoot apical meristem.

Root organs include lateral roots and nodules.

Root organs form by the dedifferentiation of pericycle cells and activation of new meristems.

Auxin plays a key role in the origin of new organs.

Patterning of organs occurs early in their development.
Lateral/Secondary Roots
Authors: Guyomarc'h Soazig , Lucas Mikaël , Laplaze Laurent
Published: April 2010

The plant root system is made of an elongating primary root of embryonic origin as well as multiple lateral or secondary roots initiated post‐embryonically. Initiation, organisation and emergence/elongation of lateral roots are tightly regulated by local and global, as well as endogenous and environmental factors, resulting in the adaptation of the whole root system to its functions. The plant hormone
auxin
is a key player in lateral root initiation, development and elongation. Yet, complex interactions with other hormones such as cytokinins, ethylene, brassinosteroids or abscisic acid (ABA) are also involved. Transcription factors and other proteins of unknown function have been identified in the signalling cascades regulating lateral root formation in response to endogenous or environmental cues. Progresses in understanding the multiple regulations of lateral root formation open new possibilities to use these strategies for plant adaptation to abiotic stresses such as drought or nutrient deprivation.

Key Concepts:

The regulation of lateral root formation influences the overall architecture of the root system and its adaptation to various constraints.

The commitment of pericycle cells to become lateral root founder cells is the first step of formation of secondary roots and determines their positioning.
Positional Information in Plant Development
Authors: Pallakies Helge , Simon Rüdiger
Published: April 2010

Tissue patterning during organogenesis in plants is based on precise cell fate determination of undifferentiated cells, which are derived from stem cells that reside in meristems. Cell fate determination has been shown to be largely dependent on the position of the differentiating cell in the plant body, and not on the lineage. A number of mechanisms were identified that provide positional information to cells or cell populations. Plant hormones like
auxin
establish gradients or local concentration maxima; cell–cell signalling enables communication between adjacent cell layers via secreted ligands and membrane‐associated receptors; transcription factors can act noncellautonomously and integrate cell behaviour, and long range signals can be transported between cells through plasmodesmata. In addition, the cell wall itself may trigger position‐dependent differentiation. In most developmental processes, a variety of information from different sources acts on the same cell to control cell fate decisions.

Key Concepts:

Cell fate determination depends on the position of a cell within the plant, not on its clonal origin.

A cell gains positional information from a combination of sources in a constant process until differentiation.