Energetic Properties (energetic + property)

Distribution by Scientific Domains


Selected Abstracts


Structure, reactivity and spectroscopic properties of minerals from lateritic soils: insights from ab initio calculations

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2007
E. Balan
Summary We review here some recent applications of ab initio calculations to the modelling of spectroscopic and energetic properties of minerals, which are key components of lateritic soils or govern their geochemical properties. Quantum mechanical ab initio calculations are based on density functional theory and density functional perturbation theory. Among the minerals investigated, zircon is a typical resistant primary mineral. Its resistance to weathering is at the origin of the peculiar geochemical behaviour of Zr, an element often used in mass balance calculations of continental weathering. Numerical modelling gives a unique picture of the origin of the chemical durability and radiation-induced amorphization of zircon. We also present several applications of ab initio calculations to the description of properties of secondary minerals, such as kaolinite-group minerals and gibbsite. Special attention is given to the calculation of infrared and Raman spectra. Surface properties and particle shape are major properties of finely-divided materials such as clay minerals. We show how theoretical modelling of infrared spectroscopic data provides information on natural samples at both the microscopic (atomic structure) and macroscopic (particle shape) length-scale. The systematic comparison of experimental and theoretical data significantly improves our understanding of mineral transformations during soil formation and evolution in lateritic environments. [source]


Why are species' body size distributions usually skewed to the right?

FUNCTIONAL ECOLOGY, Issue 4 2002
Jan Koz, owski
Summary 1.,Species' body size distributions are right-skewed, symmetric or left-skewed, but right-skewness strongly prevails. 2.,Skewness changes with taxonomic level, with a tendency to high right-skewness in classes and diverse skewness in orders within a class. Where the number of lower taxa allows for analysis, skewness coefficients have normal distributions, with the majority of taxa being right-skewed. 3.,Skewness changes with geographical scale. For a broad range, distributions in a class are usually right-skewed. For a narrower scale, distributions remain right-skewed or become symmetric or even close to uniform. 4.,The prevailing right-skewness of species' body size distributions is explained with macroevolutionary models, the fractal character of the environment, or body size optimization. 5.,Macroevolutionary models assume either size-biased speciation and extinction, or the existence of a constraint on small size. Macroevolutionary mechanisms seem insufficient to explain the pattern of species' body size distributions, but they may operate together with other mechanisms. 6.,Optimization models assume that directional and then stabilizing selection works after speciation events. There are two kinds of optimization approaches to study species' body size distributions. Under the first approach, it is assumed that a single energetic optimum exists for an entire taxon, and that species are distributed around this optimum. Under the second approach, each species has a separate optimum, and the species' body size distribution reflects the distribution of optimal values. 7.,Because not only energetic properties but also mortality are important in determining optimal sizes, only the second approach, that is, seeking the distribution of optimal values, seems appropriate in the context of life-history evolution. This approach predicts diverse shapes of body size distributions, with right-skewness prevailing. [source]


Development and Testing of Energetic Materials: The Concept of High Densities Based on the Trinitroethyl Functionality

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2009
Michael Göbel
Abstract The development of new energetic materials is an emerging area of materials chemistry facilitated by a worldwide need to replace materials used at present, due to environmental considerations and safety requirements, while at the same time securing high performance. The development of such materials is complex, owing to the fact that several different and apparently mutually exclusive material properties have to be met in order for a new material to become widely accepted. In turn, understanding the basic principles of structure property relationships is highly desirable, as such an understanding would allow for a more rational design process to yield the desired properties. This article covers the trinitroethyl functionality and its potential for the design of next generation energetic materials, and describes relevant aspects of energetic materials chemistry including theoretical calculations capable of reliably predicting material properties. The synthesis, characterization, energetic properties, and structure property relationships of several new promising compounds displaying excellent material properties are reported with respect to different kinds of applications and compared to standard explosives currently used. Based on a review of trinitroethyl-containing compounds available in the literature, as well as this new contribution, it is observed that high density can generally be obtained in a more targeted manner in energetic materials taking advantage of noncovalent bonding interactions, a prerequisite for the design of next generation energetic materials. [source]


Time-resolved two-photon photoemission at metal,dielectric interfaces

ISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2005
Wolfram Berthold
We review the influence of rare-gas layers on image-potential states at metal surfaces. Experiments on Xe, Kr, and Ar on Cu(100) and on Xe/Ru(0001) that use the technique of time-resolved two-photon photoemission are discussed. The energetic position of the electron affinity, the geometry of the adsorbate layer, and dielectric screening are the factors that influence the dynamical and energetic properties of the states. Theories on various levels are compared, including 1- and 3-dimensional models and the GW approximation of many-body theory. We also present new results on buried interface states that exist in the band gaps of both the Cu(100) substrate and a thick adsorbed Ar layer. [source]


Spontaneous segregation on a hybrid chiral surface

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2008
Szabelski
Abstract Segregation of enantiomers in two-dimensional adsorbed layers is a process that is usually controlled by anisotropic directional interactions between adsorbed molecules. In this contribution, we propose a simple theoretical model in which the chiral segregation occurs even though the lateral interactions are neglected. In particular, we consider a solid surface composed of two domains with different patterns of active sites being mirror images of each other. The domains of opposite handedness represent crystal facets of a composite chiral material which are adjoined to form a heterochiral adsorbing surface. To explore equilibrium properties of the system, we use Canonical Ensemble Monte Carlo method for a square lattice. The influence of factors such as energetic properties of the surface and density of the adsorbed layer on the extent of separation is examined. The obtained results indicate that effective two-dimensional separation on the hybrid chiral surface assumed in our model can be achieved only at sufficiently low adsorbate densities. The results also suggest that the segregation on the hybrid surface would be a promising method of enantiodiscrimination for those chiral molecules which do not exhibit strong lateral interactions. © 2008 Wiley Periodicals, Inc. J Comput Chem 2008 [source]


Molecular dynamics simulation of clustered DNA damage sites containing 8-oxoguanine and abasic site

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2005
Hirofumi Fujimoto
Abstract Clustered DNA damage sites induced by ionizing radiation have been suggested to have serious consequences to organisms, such as cancer, due to their reduced probability to be repaired by the enzymatic repair machinery of the cell. Although experimental results have revealed that clustered DNA damage sites effectively retard the efficient function of repair enzymes, it remains unclear as to what particular factors influence this retardation. In this study, approaches based on molecular dynamics (MD) simulation have been applied to examine conformational changes and energetic properties of DNA molecules containing clustered damage sites consisting of two lesioned sites, namely 7,8-dihydro-8-oxoguanine (8-oxoG) and apurinic/apyrimidinic (AP) site, located within a few base pairs of each other. After 1 ns of MD simulation, one of the six DNA molecules containing a clustered damage site develops specific characteristic features: sharp bending at the lesioned site and weakening or complete loss of electrostatic interaction energy between 8-oxoG and bases located on the complementary strand. From these results it is suggested that these changes would make it difficult for the repair enzyme to bind to the lesions within the clustered damage site and thereby result in a reduction of its repair capacity. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 788,798, 2005 [source]


Ultrahigh-resolution crystallography and related electron density and electrostatic properties in proteins

JOURNAL OF SYNCHROTRON RADIATION, Issue 3 2008
Claude Lecomte
With an increasing number of biological macromolecular crystal structures measured at ultrahigh resolution (1,Ĺ or better), it is necessary to extend to large systems the experimental valence electron density modelling that is applied to small molecules. A database of average multipole populations has been built, describing the electron density of chemical groups in all 20 amino acids found in proteins. It allows calculation of atomic aspherical scattering factors, which are the starting point for refinement of the protein electron density, using the MoPro software. It is shown that the use of non-spherical scattering factors has a major impact on crystallographic statistics and results in a more accurate crystal structure, notably in terms of thermal displacement parameters and bond distances involving H atoms. It is also possible to obtain a realistic valence electron density model, which is used in the calculation of the electrostatic potential and energetic properties of proteins. [source]


Fallback foods of temperate-living primates: A case study on snub-nosed monkeys

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2009
Cyril C. Grueter
Abstract Only a few primate species thrive in temperate regions characterized by relatively low temperature, low rainfall, low species diversity, high elevation, and especially an extended season of food scarcity during which they suffer from dietary stress. We present data of a case study of dietary strategies and fallback foods in snub-nosed monkeys (Rhinopithecus bieti) in the Samage Forest, Northwest Yunnan, PRC. The snub-nosed monkeys adjusted intake of plant food items corresponding with changes in the phenology of deciduous trees in the forest and specifically showed a strong preference for young leaves in spring. A non-plant food, lichens (Parmeliaceae), featured prominently in the diet throughout the year (annual representation in the diet was about 67%) and became the dominant food item in winter when palatable plant resources were scarce. Additional highly sought winter foods were frost-resistant fruits and winter buds of deciduous hardwoods. The snub-nosed monkeys' choice of lichens as a staple fallback food is likely because of their spatiotemporal consistency in occurrence, nutritional and energetic properties, and the ease with which they can be harvested. Using lichens is a way to mediate effects of seasonal dearth in palatable plant foods and ultimately a key survival strategy. The snub-nosed monkeys' fallback strategy affects various aspects of their biology, e.g., two- and three-dimensional range use and social organization. The higher abundance of lichens at higher altitudes explains the monkeys' tendency to occupy relatively high altitudes in winter despite the prevailing cold. As to social organization, the wide temporal and spatial availability of lichens strongly reduces the ecological costs of grouping, thus allowing for the formation of "super-groups." Usnea lichens, the snub-nosed monkeys' primary dietary component, are known to be highly susceptible to human-induced environmental changes such as air pollution, and a decline of this critical resource base could have devastating effects on the last remaining populations. Within the order Primates, lichenivory is a rare strategy and only found in a few species or populations inhabiting montane areas, i.e., Macaca sylvanus, Colobus angolensis, and Rhinopithecus roxellana. Other temperate-dwelling primates rely mainly on buds and bark as winter fallback foods. Am J Phys Anthropol 140:700,715, 2009. © 2009 Wiley-Liss, Inc. [source]