bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron Spin Resonance Spectroscopy
Authors: Chiesa Mario , Giamello Elio 
Published: September 2006

AbstractElectron spin resonance (ESR) or Electron paramagnetic resonance (EPR) spectroscopy is an experimental technique for detecting and characterizing chemical systems bearing one or more unpaired electrons. The application of the technique, the background of which is similar to the more diffused nuclear magnetic resonance (NMR) spectroscopy, therefore concerns (i) organic and inorganic free radicals, (ii) trapped radicals in various matrices, including irradiated solids (radiation chemistry), frozen inert matrices and solid surfaces, (iii) transition metal ion compounds in classical inorganic systems or in biological systems, (iv) excited paramagnetic states (triplets) and several other systems of relevant scientific interest. The aim of this article is to provide an overall survey on the basic principles and on the various applications of the technique. This is done by describing, first, the physical basis of the electron resonance phenomenon (microwave absorption when the system is in the line of force of a strong external magnetic field) and, subsequently, the main types of interactions that the unpaired electron undergoes in the chemical system to which it belongs and which determines the features of the experimental spectra. These are essentially (i) the magnetic interaction of the electron with nuclei of nonzero nuclear spin (hyperfine interaction) which determines the multiline structure of the spectrum (hyperfine structure) and (ii) the interaction of the electron spin with the electron orbital angular momentum, occurring through the so‐called spin–orbit coupling. This latter interaction causes the dependence of the resonance on the orientation of the radical in the external magnetic field. Particular emphasis will be given to the different types of spectra observed according to the physical state of the investigated sample (liquid solutions, single solid crystals or microcrystalline powdered solids). In the last case (powders), the essential methodology for understanding the often complex profiles of the experimental spectra is described. Advanced electron resonance techniques, essentially ENDOR (electron–nuclear double resonance) and time‐resolved EPR will also be briefly mentioned.The final part of the article is devoted to some analytical applications of the technique, including spin trapping (an essential tool for the detection and quantitative evaluation of reactive short‐lived radicals), radiation dosimetry (with applications to medical problems and irradiated foodstuff analysis) and dating of geologically relevant systems.
High‐Performance Liquid Chromatography Nuclear Magnetic Resonance
Authors: Dorn Harry C. 
Published: September 2006

AbstractThe direct coupling of high‐performance liquid chromatography (HPLC) to nuclear magnetic resonance (NMR) has evolved as a powerful new tool (HPLC/NMR) for the analysis of mixtures. The technique was originally reported in the late 1970s, but was generally limited by NMR detector sensitivity constraints and the availability of routine high magnetic field dispersion instruments (11.8–17.6 T, 500–750 MHz1H‐NMR). During the early 1980s, the HPLC/NMR technique was applied to problems involving the analysis of mixtures that were typically not sample limited, such as petroleum fuels. In the early 1990s, the advent of commercial HPLC/NMR equipment provided the impetus for a worldwide growth spurt of the HPLC/NMR technique. As outlined in this review, the HPLC/NMR technique has evolved as a powerful tool for applications involving polymers, pharmaceuticals, and biological mixtures.An inherent advantage of HPLC/NMR is the ability to monitor the NMR chemical shift dimension. This dimension is particularly relevant for those applications involving structural isomer identification and has distinct advantages in comparison with the more commonly employed HPLC/MS (mass spectrometry) technique. Although sensitivity limitations of NMR as a detector are still a concern, the development of more complex hyphenated combinations (such as HPLC/NMR/MS) will undoubtedly continue, especially in the areas of pharmaceutical and drug development. Other technical and phenomenological considerations of the HPLC/NMR technique are presented in this review. Finally, a number of related variant techniques including capillary electrophoresis nuclear magnetic resonance (CE/NMR), capillary zone electrophoresis (CZE), capillary electrochromatography (CEC), supercritical fluid chromatography (SFC), and dynamic nuclear polarization (DNP) are also discussed.
Two‐, Three‐ and Four‐ Dimensional Nuclear Magnetic Resonance of Biomolecules
Authors: Craik David J. , Scanlon Martin J. 
Published: September 2006

Abstract

Nuclear magnetic resonance (NMR) is associated with transitions, induced by radiofrequency (RF) irradiation, between energy levels of nuclei with nonzero spin quantum numbers in a magnetic field. Traditional “one‐dimensional” (1D) NMR spectra are presented as a plot of signal intensity versus applied frequency and provide information about the chemical environment of magnetically active nuclei. This is used to deduce information about the chemical structure and dynamics of molecules containing the magnetically active nuclei (most often protons). The frequencies of individual nuclei are referred to as their chemical shifts. Multidimensional NMR encompasses a range of related techniques, based on application of a variety of precisely timed RF pulses to the sample, which extends traditional 1D NMR into two, three, or four frequency dimensions. These additional frequency dimensions may be the same as the first frequency dimension, referred to as homonuclear multidimensional NMR, or different, referred to as heteronuclear NMR. In multidimensional NMR of biomolecules the most common frequencies correspond to
1
H in the directly detected dimension and one or more of
1
H,
13
C or
15
N in the additional dimensions. Peaks in such spectra are defined by their intensity and by their frequency coordinates in two, three, or four dimensions obtained by extrapolation back to the respective frequency axes, which are in turn determined by the nature of the applied RF pulse sequences. The intensity and chemical shifts of such peaks provide information about chemical environment, molecular connectivity, or spatial proximity of the participating nuclei. Multidimensional NMR has major advantages over 1D NMR: reduction of peak overlap and provision of information on connectivity (either through bonds or through space). Multidimensional NMR of biomolecules is usually done for samples in solution at millimolar concentration. Where experiments require the use of
13
C or
15
N frequencies, it is usually necessary to enrich isotopically the macromolecule with these nuclei to >90%. This is readily achieved with modern molecular biology techniques and does not present a major limitation. The biggest limitation relates to molecular size, with studies generally limited to macromolecules of less than approximately 35 kDa.
X‐Ray Photoelectron andAuger Electron Spectroscopy
Authors: Turner Noel H. 
Published: September 2006

AbstractThe use of X‐ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) to analyze the surface composition and chemical environment of solids has been well established since about the early 1970s. These approaches find many applications in both basic and applied scientific investigations. The basic principles, i.e. surface sensitivity, the experimental observations employing these procedures, and the working methods, are described. The instrumentation utilized with the commonly available equipment for these approaches is summarized also.
Portable Systems for Energy‐DispersiveX‐Ray Fluorescence
Authors: Cesareo Roberto , Gigante Giovanni E. , Castellano Alfredo , Iwanczyk Jan S. 
Published: September 2006

AbstractPortable energy‐dispersive X‐ray fluorescence (EDXRF) spectrometers are becoming very popular in many fields for the on‐site analysis of elements. This is mainly because EDXRF is a nondestructive, multielemental technique that is extremely well suited for the analysis of any material.An EDXRF spectrometer mainly consists of an X‐ or γ‐ray excitation source, an X‐ray detector with electronics, and a pulse height analyzer. Recent technological developments have resulted in small, low‐power, dedicated X‐ray tubes, thermoelectrically cooled semiconductor detectors, and small pulse height analyzers. Therefore, completely portable EDXRF spectrometers are available that can be assembled on‐site, having the size of a book and a weight ranging from as light as 500 g (using a radioactive source) to a few kilograms (using an X‐ray tube). These spectrometers can be employed for on‐site analysis in various fields, such as works of art, alloys, soil, environmental samples, forensic medicine, paper, waster materials, mineral ores and their products, or anywhere a portable apparatus would be required.This paper reviews the present status of the development and application of EDXRF portable systems. The various components of a portable system are described: the radiation source, i.e. small, low‐power, dedicated X‐ray tubes or alternatively radioactive sources that emit X‐rays or low‐energy γ‐rays; and X‐ray detectors, i.e. scintillators, proportional gas counters and semiconductor detectors, with special emphasis on the recent thermoelectrically cooled X‐ray detectors: Si‐PIN (silicon positive–intrinsic– negative), Si‐strip and CZT (cadmium–zinc–telluride).Commercial systems are considered, and finally the most common and significant applications are described.
K
arl
F
ischer Moisture Determination
Authors: Schöffski Katrin , Strohm Dieter 
Published: September 2006

Abstract
The Karl Fischer (KF) titration is a method of determining the water content of solid, liquid and gaseous samples. It is the technique preferred for use in industrial quality control. In principle it involves the oxidation of sulfur dioxide by iodine, in the presence of water, in a buffered solution. An alcohol is used as the preferred solvent. The water is converted stoichiometrically and therefore its quantity is determined indirectly. The end‐point (EP) is reached when there is an excess of iodine. It can be indicated visually, photometrically or electrochemically. According to state‐of‐the‐art technology a double platinum electrode determines a voltammetric indication. The KF titration can be carried out either volumetrically or by coulometry. For a volumetric titration the iodine is added by volume to the titration cell containing the sample. In a coulometric titration iodide is oxidized at a platinum electrode and the iodine formed reacts with the water. The amount of current necessary in the generation of the iodine is directly related to the quantity of iodine generated, according to Faraday's first law. In practice, special titrators for the KF titration are available. Preformulated reagents are similarly available ready for use. Water in an extensive number of materials can be determined by KF titration. Chemicals, pharmaceuticals, oils, plastics and foodstuffs are examples of typical sample types. The measurement range spans a few ppm to 100% water. The KF titration is described in ISO 760 and as part of many other international standard procedures. Other methods for the determination of water content include loss‐on‐drying, IR spectroscopy or azeotropic distillation.
Quantitative Spectroscopic Calibration
Authors: Mark Howard 
Published: September 2006

Abstract
Spectroscopic calibration is the process of using mathematical calculations to relate the measured spectroscopic properties of a set of samples to the chemical composition (and sometimes other properties) of those samples. Any of several algorithms are employed to perform these calculations. Regardless of the algorithms used, however, successful execution of this process depends on properly performing several tasks before and after the main calibration algorithm is applied: selecting a suitable set of calibration samples to “train” the system, using the correct algorithm to match the characteristics of the measured data, and properly evaluating and validating the calibration model developed. In this article, these various aspects of calibrating spectroscopic instruments to perform quantitative analysis are discussed. The article ends with an overview of the various algorithms that are available to perform the calibration process.
Acid Rain
Authors: Butler Thomas J. 
Published: September 2006

Abstract

Acid rain is a popular term that can include all forms of precipitation, as well as fog and cloudwater, that is more acidic than expected from natural causes. Natural background levels of precipitation acidity tend to be around pH of 5.1 to 5.2. This compares with present annual average values of pH 4.3 to 4.4 for parts of eastern North America, and pH values less than 4.5 for large areas of Europe, and eastern Asia. As pH decreases, H
+
concentration or acidity increases exponentially. Individual storms in affected areas, especially in the summer, can often produce pH values below 3.5, and cloudwater in some areas can be below pH 3.0. A more appropriate term than acid rain is ‘acidic deposition’, which includes both wet and dry deposition (gases and particles) of acidic compounds to the earth's surface from the atmosphere. Accurate measurements of dry deposition are unfortunately much more difficult to measure than wet deposition. However, dry deposition can account for 10%–70% of the total amount of acidic deposition.
Age–Growth Modeling
Authors: Nokoe K. Sagary 
Published: September 2006

Abstract
Growth of an individual or group of organisms is defined as the change in dimensions over time. Growth rates vary between and within plant and animal species. They are generally influenced by both genetic and phenotypic factors, and may be negative or positive. Positive growth relates to increases in dimensions (weight, height, and number of component parts) over time, while negative or decay growth refers to the decline over time. Human interference, either intentionally or accidentally, environmental influences and management practices can substantially influence the growth forms and patterns of individuals and population. Age/growth functions constitute important analytical tools in the management of natural resources. These models are explicit expressions of both theory and empirical knowledge, and are useful for growth and yield prediction, computation of sustainable crop yields, and evaluation of alternative management strategies, among others. The approach to age/growth modeling may be based on either primary (single) unit or stand (aggregate of units). Irrespective of modeling philosophy, the goal is identification of the most parsimonious and biologically‐reasonable model that best describes the relationship between the response variable (which is a measure of growth) and time (age). Biologically reasonable models involve parameters to which meaningful interpretation may be assigned.
Bayesian Graphical Models
Authors: Jensen Finn Verner 
Published: September 2006

AbstractMathematically, a Bayesian graphical model is a representation of the joint probability distribution for a set of variables. The most frequently used type of Bayesian graphical models are Bayesian networks, but other types exist and Bayesian networks can be seen as a special type of Chain Graphs. The structural part of a Bayesian graphical model is a graph consisting of nodes and edges. The nodes represent variables. The set of all variables, called the universe, is denotedU. A variable may be discrete or continuous. For the sake of simplicity this article focuses on models with only discrete variables, and refers to the variable values as states. An edge between two nodesAandBindicates a direct influence between the state ofAand the state ofB.
Binary Data
Authors: Piegorsch Walter W. 
Published: September 2006

Abstract

Environmental data often occur in discrete form, such as the number of individuals living near a waste site, or whether or not a subject develops cancer after exposure to an environmental agent. This latter example is one of the simplest forms of discrete data: a dichotomous indicator of whether or not an event has occurred, i.e. a ‘success’ or a ‘failure’. Such an outcome can be coded simply as either 1 or 0 – corresponding to success or failure – and we refer to this as a case of
binary data
. If the data on each subject or unit in the study are coded in this binary fashion, and if each subject contributes one and only one such binary observation to the experimental data, we call this a case of
ungrouped binary data
. Alternatively, when the subjects have some underlying or coordinating feature that relates them, it is common to group the like subjects and record the proportion of subjects responding; i.e. take the proportion Y/N, where Y is the number of observed successes out of the N observed subjects in the common group. This is
grouped binary data
.
Bioaccumulation
Authors: Voit Eberhard O. 
Published: September 2006

Abstract
The accumulation of contaminants in organisms is crucial to environmental risk assessments. It depends on the chemical and physical properties of the contaminant and the ecosystem, the type of exposure (e.g. acute or chronic), and the efficiency with which organisms assimilate, metabolize, and eliminate the compound. To judge the severity of exposure and the efficacy of remediation, one must understand the complex dynamics of chemicals as they affect ecosystems. The sheer number of chemical components and the multitude, nonlinearity, and temporal dependence of the governing biological, chemical, physical, and geological processes and cycles make this a daunting task. Most research has focused on specific scenarios, emphasizing aquatic (freshwater and marine) ecosystems and either heavy metals or large organics. While much has been learned, generalizations of the results often fail, and a true understanding of the dynamics of contaminant accumulation has not yet been achieved.
Biodiversity
Authors: Ver Hoef Jay M. 
Published: September 2006

Abstract
Biodiversity is closely related to diversity. However, biodiversity has come to be concerned with the conservation of variation of different levels of biological organization, from genes to populations, communities, ecosystems, and landscapes. Biodiversity ranges across spatial and temporal scales. For the elements of concern (genes to landscapes), biodiversity can be measured as the number of different types of elements, the relative frequencies of the different elements, or the number of different processes such as gene flow or nutrient flow. This article emphasizes methods for conserving biodiversity. Biodiversity is rarely used in a sentence without the word ‘conservation’. When discussing biodiversity, it is assumed that high biodiversity is desirable and should be preserved. The arguments for conserving biodiversity are many and varied, from aesthetic to the stability of our environment to future cures for cancer and other uses of nature's raw biological material that cannot yet be imagined.
Biogeography
Authors: Ver Hoef Jay M. 
Published: September 2006

Abstract
Biogeography, as defined by Brown and Lomolino, is ‘the science that attempts to document and understand spatial patterns of biodiversity. It is the study of distributions of organisms, both past and present, and of related patterns of variation over the earth in the numbers and kinds of living things.’ Biogeography can be split taxonomically, with phytogeographers studying plants, and zoogeographers studying animals. Biogeography can also be split by time, with paleoecology studying relationships between organisms and past environments, and ecological biogeography studying present distributions of organisms and how they relate to the physical and biotic environment. Biogeography is at the crossroads of multiple disciplines: sytematics, ecology, evolution, geology, and climatology, to name a few.
Cardiac Toxicology
Authors: Coull Brent A. , Wellenius Gregory A. 
Published: September 2006

Abstract
Cardiovascular disease is still the primary killer in the US, claiming 953 110 lives in 1997. Thus, a major goal in environmental health research is risk assessment of environmental agents having potentially detrimental effects on heart function. This article focuses on the role electrocardiography has played in the assessment of cardiac toxicity.
Change‐Point Methods
Authors: Jandhyala Venkata K. , Fotopoulos Stergios B. , El‐Shaarawi Abdel 
Published: September 2006

Abstract
This article reviews recent applications of change‐point methods for modeling non‐stationarities in environmental data. In particular, we emphasize maximum likelihood based methods for the detection and estimation of parameter changes at unknown times in environmental time series data.
Defoliation
Authors: Candy Steven G. , Zalucki Myron P. 
Published: September 2006

AbstractFrom ancient times, mankind has attempted either to harness or prevent defoliation of trees and plants. The positive and negative impact of defoliation by invertebrates (chiefly insects), vertebrates, plant diseases or abiotic factors such as air pollution is an integral part of agriculture, forestry, and natural resource management. Defoliation is ‘an unseasonable reduction in the foliage cover of a plant due to attacks by insects or fungal disease, or as a result of other factors such as drought, storms, or chemicals in the atmosphere’. Defoliation encompasses partial or complete loss of the plant's foliage and partial or complete loss of individual leaves. The most significant impacts of natural defoliation are crop losses in agriculture and production forestry and, for native plant communities, possible changes in structure and species composition and loss of amenity values. It is not possible to review in this article the huge amount of information available on defoliation. In terms of measurement, estimation, or prediction there are a number of commonalities across the range of activities in which quantification of defoliation is required.
Detection Limits
Authors: Van Der Voet Hilko 
Published: September 2006

Abstract

In analytical chemistry the
detection limit
(also called
limit of detection (LOD)
or
minimum detectable value
) is considered a fundamental performance characteristic of methods of analysis. Basically, it is the lowest level (concentration, amount) of an analyte that can be reliably detected when chemical analysis is executed according to a well‐defined operating procedure in a state of statistical control. Thus, if the analyte is present at a lower level it may well be detected on single occasions, but in replicated analyses it will fail to be detected in a sizeable percentage of attempts. However, if the analyte is present at the level of the detection limit (or a higher level) the probability of detecting the analyte is at least a specific high value (commonly 95% is used in operational definitions of the detection limit). Being a performance characteristic, the detection limit is used to determine whether the analytical method is fit for the intended purpose: it quantifies the capability of detection of the analytical method as described in the operating procedure. This can only be done if the operating procedure includes a decision rule to decide whether the analyte is declared detected or not.
Atmospheric Dispersion: Heavy Gases
Authors: Nielsen Morten 
Published: September 2006

AbstractManufacturers, distributing agents, and public authorities need to formulate safety policies for toxic and flammable gases. This involves a wide range of aspects: intrinsic process safety, equipment, alarm systems, handling procedures, personnel training, spatial planning, and the likelihood and consequences of possible accidents. Gas dispersion is an important task in the consequence analysis and in the context of industrial accidents the source buoyancy and momentum may alter the flow and turbulence fields significantly. This calls for special dispersion models.