bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reliability
Authors: Murthy D. N. Prabhakar , Blischke Wallace R. 
Published: April 2010

Abstract
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

AbstractThis 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

AbstractCrystallization 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

AbstractThis 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

Abstract
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

AbstractPhotopolymerizations 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

Abstract

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

Abstract

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

AbstractNAD(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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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.