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Various Possibilities (various + possibility)
Selected AbstractsPhotosensitive Nanocomposites: Highly Non-Linear Quantum Dot Doped Nanocomposites for Functional Three-Dimensional Structures Generated by Two-Photon Polymerization (Adv. Mater.ADVANCED MATERIALS, Issue 22 201022/2010) Baohua Jia, Min Gu, and co-workers report on p.,2463 on novel quantum dot functionalized photosensitive nanocomposites showing ultrahigh third-order nonlinearity. The cover image shows functional three-dimensional micronano photonic structures, for example, photonic crystals can be fabricated in such active nanocomposites using the versatile two-photon poly-merisation method, opening various possibilities in active micro/nano devices, such as ultrafast switching, signal regeneration, and high speed demultiplexing systems. [source] An assessment of endocrine disruption in mollusks and the potential for developing internationally standardized mollusk life cycle test guidelines,INTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT, Issue 3 2008Peter Matthiessen Abstract This paper summarizes what is known about the endocrine systems of mollusks and how they can be disrupted by exogenous substances. It then examines the various possibilities for using mollusk-based toxicity tests to detect and assess the environmental risks of endocrine-disrupting chemicals (EDCs). It is concluded that there are no internationally standardized tests with mollusks available at present that are suitable for assessing the risks of long-term exposure to EDCs but that several published methods show potential. At the present state of knowledge, the most promising mollusk species for use in partial life cycle testing is probably the fresh- and brackish-water mesogastropod, Potamopyrgus antipodarum, which is known to be responsive to both direct and indirect androgens and to estrogens (and their mimics). Less experience of full life cycle testing exists with mollusks, but the freshwater pulmonate gastropod Lymnaea stagnalis at present offers the best possibility for a practical procedure. In both cases, there is a need for substantial test optimization and validation before these procedures could form the basis of international guidelines. [source] Numerical simulation of granular materials by an improved discrete element methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2005J. Fortin Abstract In this paper, we present an improved discrete element method based on the non-smooth contact dynamics and the bi-potential concept. The energy dissipated during the collisions is taken into account by means of restitution coefficients. The interaction between particles is modelled by Coulomb unilateral contact law with dry friction which is typically non-associated: during the contact, the sliding vector is not normal to the friction cone. The main feature of our algorithm is to overcome this difficulty by means of the bi-potential theory. It leads to an easy implement predictor,corrector scheme involving just an orthogonal projection onto the friction cone. Moreover the convergence test is based on an error estimator in constitutive law using the corner stone inequality of the bipotential. Then we present numerical simulations which show the robustness of our algorithm and the various possibilities of the software ,MULTICOR' developed with this approach. Copyright © 2004 John Wiley & Sons, Ltd. [source] Four Motives for Community InvolvementJOURNAL OF SOCIAL ISSUES, Issue 3 2002C. Daniel Batson A conceptual analysis is offered that differentiates four types of motivation for community involvement: egoism, altruism, collectivism, and principlism. Differentiation is based on identification of a unique ultimate goal for each motive. For egoism, the ultimate goal is to increase one's own welfare; for altruism, it is to increase the welfare of another individual or individuals; for collectivism, to increase the welfare of a group; and for principlism, to uphold one or more moral principles. As sources of community involvement, each of these four forms of motivation has its strengths; each also has its weaknesses. More effective efforts to stimulate community involvement may come from strategies that orchestrate motives so that the strengths of one motive can overcome weaknesses of another. Among the various possibilities, strategies that combine appeals to either altruism or collectivism with appeals to principle may be especially promising. [source] The mass assembly of fossil groups of galaxies in the Millennium simulationMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007Ali Dariush ABSTRACT The evolution of present-day fossil galaxy groups is studied in the Millennium simulation. Using the corresponding Millennium gas simulation and semi-analytic galaxy catalogues, we select fossil groups at redshift zero according to the conventional observational criteria, and trace the haloes corresponding to these groups backwards in time, extracting the associated dark matter, gas and galaxy properties. The space density of the fossils from this study is remarkably close to the observed estimates and various possibilities for the remaining discrepancy are discussed. The fraction of X-ray bright systems which are fossils appears to be in reasonable agreement with observations, and the simulations predict that fossil systems will be found in significant numbers (3,4 per cent of the population) even in quite rich clusters. We find that fossils assemble a higher fraction of their mass at high redshifts, compared to non-fossil groups, with the ratio of the currently assembled halo mass to final mass, at any epoch, being about 10,20 per cent higher for fossils. This supports the paradigm whereby fossils represent undisturbed, early-forming systems in which large galaxies have merged to form a single dominant elliptical. [source] Cosmic reionization constraints on the nature of cosmological perturbationsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006Pedro P. Avelino ABSTRACT We study the reionization history of the Universe in cosmological models with non-Gaussian density fluctuations, taking them to have a renormalized ,2 probability distribution function parametrized by the number of degrees of freedom, ,. We compute the ionization history using a simple semi-analytical model, considering various possibilities for the astrophysics of reionization. In all our models we require that reionization is completed prior to z= 6, as required by the measurement of the Gunn,Peterson optical depth from the spectra of high-redshift quasars. We confirm previous results demonstrating that such a non-Gaussian distribution leads to a slower reionization as compared to the Gaussian case. We further show that the recent WMAP three-year measurement of the optical depth due to electron scattering, ,= 0.09 ± 0.03, weakly constrains the allowed deviations from Gaussianity on the small scales relevant to reionization if a constant spectral index is assumed. We also confirm the need for a significant suppression of star formation in minihaloes, which increases dramatically as we decrease ,. [source] An extensive study of dynamical friction in dwarf galaxies: the role of stars, dark matter, halo profiles and MONDMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006F. J. Sánchez-Salcedo ABSTRACT We investigate the in-spiralling time-scales of globular clusters (GCs) in dwarf spheroidal (dSph) and dwarf elliptical (dE) galaxies, due to dynamical friction (DF). We address the problem of these time-scales having been variously estimated in the literature as much shorter than a Hubble time. Using self-consistent two-component (dark matter and stars) models, we explore mechanisms which may yield extended DF time-scales in such systems in order to explain why dwarf galaxies often show GC systems. As a general rule, dark matter and stars both give a comparable contribution to the dynamical drag. By exploring various possibilities for their gravitational make-up, it is shown that these studies help to constrain the parameters of the dark matter haloes in these galaxies, as well as to test alternatives to dark matter. Under the assumption of a dark halo having a central density core with a typical King core radius somewhat larger than the observed stellar core radius, DF time-scales are naturally extended upwards of a Hubble time. Cuspy dark haloes yield time-scales ,4.5 Gyr, for any dark halo parameters in accordance with observations of stellar line-of-sight velocity dispersion in dSph galaxies. We confirm, after a detailed formulation of the DF problem under the alternative hypothesis of modified Newtonian dynamics (MOND) and in the lack of any dark matter, that due to the enhanced dynamical drag of the stars, the DF time-scales in MOND would be extremely short. Taking the well-measured structural parameters of the Fornax dSph and its GC system as a case study, we conclude that requiring DF time-scales comparable to the Hubble time strongly favours dark haloes with a central core. [source] Mode crystallography of distorted structuresACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2010J. M. Perez-Mato The description of displacive distorted structures in terms of symmetry-adapted modes is reviewed. A specific parameterization of the symmetry-mode decomposition of these pseudosymmetric structures defined on the setting of the experimental space group is proposed. This approach closely follows crystallographic conventions and permits a straightforward transformation between symmetry-mode and conventional descriptions of the structures. Multiple examples are presented showing the insight provided by the symmetry-mode approach. The methodology is shown at work, illustrating its various possibilities for improving the characterization of distorted structures, for example: detection of hidden structural correlations, identification of fundamental and marginal degrees of freedom, reduction of the effective number of atomic positional parameters, quantitative comparison of structures with the same or different space group, detection of false refinement minima, systematic characterization of thermal behavior, rationalization of phase diagrams and various symmetries in families of compounds etc. The close relation of the symmetry-mode description with the superspace formalism applied to commensurate superstructures is also discussed. Finally, the application of this methodology in the field of ab initio or first-principles calculations is outlined. At present, there are several freely available user-friendly computer tools for performing automatic symmetry-mode analyses. The use of these programs does not require a deep knowledge of group theory and can be applied either a posteriori to analyze a given distorted structure or a priori to parameterize the structure to be determined. It is hoped that this article will encourage the use of these tools. All the examples presented here have been worked out using the program AMPLIMODES [Orobengoa et al. (2009). J. Appl. Cryst.42, 820,833]. [source] Integration of Microreaction Technology into the CurriculumCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 3 2005R. Gorges Abstract As a pioneer in Germany, the Institute of Technical Chemistry and Environmental Chemistry at the Friedrich Schiller University in Jena has integrated microreaction technology into its curriculum of industrial chemistry. This essay describes how traditional lab classes in industrial chemistry are replaced or supplemented by microreaction components. It is shown how lab classes on heat transfer, heterogeneous catalysis, mixing and stirring, and photochemistry were modified to meet this objective. In addition to the practical training in different lab classes, microreaction technology was also implemented in lectures, and thus the knowledge about the various possibilities and advantages of this new technology is instilled in future generations of chemists at an early stage of their education. [source] | |||||||||||||