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Experimental Information (experimental + information)
Selected AbstractsThe impacts of rising CO2 concentrations on Australian terrestrial species and ecosystemsAUSTRAL ECOLOGY, Issue 6 2010MARK J. HOVENDEN Abstract The increasing atmospheric concentration of carbon dioxide ([CO2]) contributes to global warming and the accompanying shifts in climate. However, [CO2] itself has the potential to impact on Australia's terrestrial biodiversity, due to its importance in the photosynthetic process, which underlies all terrestrial food webs. Here, we review our knowledge regarding the impacts of elevated [CO2] on native terrestrial species and ecosystems, and suggest key areas in which we have little information on this topic. Experimental information exists for 70 (or less than 0.05%) of Australia's native terrestrial plant and animal species. Of these, 68 are vascular plants. The growth of Australian woody species is more reliably increased by elevated [CO2] than it is in grasses. At the species level, the most overwhelming responses to increased [CO2] are a reduction in plant nitrogen concentration and an increase in the production of secondary metabolites. This is of particular concern for Australia's unique herbivorous and granivorous marsupials, for which no information is available. While many plant species also displayed increased growth rates at higher [CO2], this was far from universal, indicating that changes in community structure and function are likely, leading to alterations of habitat quality. Future research should be directed to key knowledge gaps including the relationship between [CO2], fire frequency and fire tolerance and the impacts of increasing [CO2] for Australia's iconic browsing mammals. We also know virtually nothing of the impacts of the increasing [CO2] on Australia's unique shrublands and semi-arid/arid rangelands. In conclusion, there is sufficient information available to be certain that the increasing [CO2] will affect Australia's native biodiversity. However, the information required to formulate predictions concerning the long-term future of almost all organisms is far in excess of that currently available. [source] Hypertrophic Scars and Keloids,A Review of Their Pathophysiology, Risk Factors, and Therapeutic ManagementDERMATOLOGIC SURGERY, Issue 2 2009DOLORES WOLFRAM MD BACKGROUND Hypertrophic scars and keloids result from an abnormal fibrous wound healing process in which tissue repair and regeneration-regulating mechanism control is lost. These abnormal fibrous growths present a major therapeutic dilemma and challenge to the plastic surgeon because they are disfiguring and frequently recur. OBJECTIVE To provide updated clinical and experimental information on hypertrophic scars and keloids so that physicians can better understand and properly treat such lesions. METHODS A Medline literature search was performed for relevant publications and for diverse strategies for management of hypertrophic scars and keloids. CONCLUSION The growing understanding of the molecular processes of normal and abnormal wound healing is promising for discovery of novel approaches for the management of hypertrophic scars and keloids. Although optimal treatment of these lesions remains undefined, successful healing can be achieved only with combined multidisciplinary therapeutic regimens. [source] Atomic-Level Studies of Molecular Self-Assembly on Metallic SurfacesADVANCED MATERIALS, Issue 10-11 2009Giulia Tomba Abstract Shrinking devices to the nanoscale, while still maintaining accurate control on their structure and functionality is one of the major technological challenges of our era. The use of purposely directed self-assembly processes provides a smart alternative to the troublesome manipulation and positioning of nanometer-sized objects piece by piece. Here, we report on a series of recent works where the in-depth study of appropriately chosen model systems addresses the two key-points in self-assembly: building blocks selection and control of bonding. We focus in particular on hydrogen bonding because of the stability, precision and yet flexibility of nanostructures based on this interaction. Complementing experimental information with advanced atomistic modeling techniques based on quantum formalisms is a key feature of most investigations. We thus highlight the role of theoretical modeling while we follow the progression in the use of more and more complex molecular building blocks, or "tectons". In particular, we will see that the use of three-dimensional, flexible tectons promises to be a powerful way to achieve highly sophisticated functional nanostructures. However, the increasing complexity of the assembly units used makes it generally more difficult to control the supramolecular organization and predict the assembling mechanisms. This creates a case for developing novel analysis methods and ever more advanced modeling techniques. [source] Inter-relations between experimental and computational aspects of slope stability analysisINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2003R. Baker Abstract Most conventional slope stability calculations are based on the linear Mohr,Coulomb failure criterion. However, a substantial amount of experimental evidence suggests that failure criteria of many soils are not linear particularly in the range of small normal stresses. This departure from linearity is significant for slope stability calculations since for a wide range of practical stability problems, critical slip surfaces are shallow and normal stresses acting on such surfaces are small. There exists a technical difficulty in performing strength measurements in the range of small normal stresses relevant to such slope stability problems. As a result, in many practical situations strength measurements are performed at much larger normal stresses then those relevant for the stability problem under consideration. When this is the case, use of the Mohr,Coulomb criterion amounts to a linear extrapolation of experimental information (obtained at large normal stresses), into the range of small normal stresses, which is relevant to the problem. This extrapolation results with very significant overestimation of calculated safety factors in cases when there is large mismatch between experimental and relevant ranges of normal stresses. The present work delineates the extent of this problem and suggests a practical way to overcome it. Copyright © 2003 John Wiley & Sons, Ltd. [source] The search for low energy conformational families of small peptides: Searching for active conformations of small peptides in the absence of a known receptor,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2007Katrina W. Lexa Abstract Breast cancer is the most common cancer among women. Tamoxifen is the preferred drug for estrogen receptor-positive breast cancer treatment, yet many of these cancers are intrinsically resistant to tamoxifen or acquire resistance during treatment. Therefore, scientists are searching for breast cancer drugs that have different molecular targets. Previous work revealed that 8-mer and cyclic 9-mer peptides inhibit breast cancer in mouse and rat model systems, interacting with an unknown receptor, while peptides smaller than eight amino acids did not inhibit breast cancer. We have shown that the use of replica exchange molecular dynamics predicts structure and dynamics of active peptides, leading to the discovery of smaller peptides with full biological activity. These simulations identified smaller peptide analogs with a conserved turn, a ,-turn formed in the larger peptides. These analogs inhibit estrogen-dependent cell growth in a mouse uterine growth assay, a test showing reliable correlation with human breast cancer inhibition. We outline the computational methods that were tried and used with the experimental information that led to the successful completion of this research. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Robust identification/invalidation in an LPV frameworkINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 3 2010Fernando D. Bianchi Abstract A robust linear parameter varying (LPV) identification/invalidation method is presented. Starting from a given initial model, the proposed method modifies it and produces an LPV model consistent with the assumed uncertainty/noise bounds and the experimental information. This procedure may complement existing nominal LPV identification algorithms, by adding the uncertainty and noise bounds which produces a set of models consistent with the experimental evidence. Unlike standard invalidation results, the proposed method allows the computation of the necessary changes to the initial model in order to place it within the consistency set. Similar to previous LPV identification procedures, the initial parameter dependency is fixed in advance, but here a methodology to modify this dependency is presented. In addition, all calculations are made on state-space matrices which simplifies further controller design computations. The application of the proposed method to the identification of nonlinear systems is also discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source] CAD,ICAD complex structure derived from saturation transfer experiment and simulated annealing without using pairwise NOE informationJOURNAL OF MOLECULAR RECOGNITION, Issue 1 2004Tomoki Matsuda Abstract Saturation transfer experiments were performed for the 2H- and 15N-labeled mouse CAD domain of the caspase-activated deoxyribonuclease and the CAD domain of its inhibitor to reveal the protein,protein complexed conformation. Based on the physical model for the spin diffusion, a novel method was developed to reconstruct the complexed structure using the simulated annealing calculation. The complementarity in the molecular surface shape and the electrostatic potential distribution provide a good measure for the assessment of the putative complexed conformation, despite much less experimental information than the conventional distance geometry calculation. Copyright © 2004 John Wiley & Sons, Ltd. [source] Chain Connectivity and Conformational Variability of Polymers: Clues to an Adequate Thermodynamic Description of Their Solutions, 1MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2003Maria Bercea Abstract This is the first of two parts investigating the Flory-Huggins interaction parameter, ,, as a function of composition and chain length. Part 1 encompasses experimental and theoretical work. The former comprises the synthesis of poly(dimethylsiloxane)s with different molar mass and the measurements of their second osmotic virial coefficients, A2, in solvents of diverse quality as a function of M via light scattering and osmotic pressures. The theoretical analysis is performed by subdividing the dilution process into two clearly separable steps. It yields the following expression for ,o, the , value in range of pair interaction: ,o,=,,,,,,,,. The parameter , measures the effect of contact formation between solvent molecules and polymer segments at fixed chain conformation, whereas the parameter , quantifies the contributions of the conformational changes taking place in response to dilution; , becomes zero for theta conditions. The influences of M are exclusively contained in the parameter , The new relation is capable of describing hitherto incomprehensible experimental findings, like a diminution of ,o with rising M. The evaluation of experimental information for different systems according to the established equation displays the existence of a linear interrelation between , and ,. Part 2 of this investigation presents the generalization of the present approach to solutions of arbitrary composition and discusses the physical meaning of the parameters in more detail. Conformational response, ,, as a function of ,, the interaction parameter for fixed conformation. [source] Polymer Chain Collapse in Supercritical Fluids.MACROMOLECULAR SYMPOSIA, Issue 1 2009Abstract The phase behavior of a polymer in a supercritical solvent at the LCST equilibrium limits is described in this work, in the proximity of , point, proposing the use of a conformational parameter, ,. The results obtained by molecular simulation in an NVT ensemble have been correlated by extensive, varied experimental information. The relationship between polymer/solvent solubility parameters has shown that the behavior of these systems is a function of the energetic structure-interaction relationship between the polymer chain and the solvent. , results in a generalized parameter indicative of the phase stability of the solution. At greater magnitudes, the solution becomes unstable, requiring elevated pressure to stabilize. However, stable solutions are found at lower pressures when , approaches 1. The experimental evidence, together with the determination of the solubility parameter with the Sanchez-Lacombe equation (also obtained from the literature) strengthens this observation. The analysis of the polar contribution on the Hansen Parameter (HSP) enables their effect to be studied in systems where high polar interactions between the polymer and solvent (as in the case of biopolymers) are expected. [source] Theoretical Modeling in Hemodynamics of MicrocirculationMICROCIRCULATION, Issue 8 2008JACK LEE ABSTRACT Over the past decades, theoretical modeling has become an indispensable component of research into the hemodynamics of microcirculation. Numerous studies rely on modeling to provide quantitative insights into the interacting biophysical mechanisms that govern microcirculatory flow. The mechanical deformation of hematocytes has been addressed by continuum and molecular-informed computational models based on a growing body of experimental information. Theoretical analyses of single-vessel flow and blood rheology have led to a range of modeling approaches. Until recently, computational constraints limited direct simulations of multi-particle flows involving deformation and/or aggregation, but recent studies have begun to address this challenge. Network-level analyses have provided insights into the biophysical principles underlying the design of the microcirculation. This approach has been used to complement available experimental data and to derive empirical models of microvascular blood rheology. Continued increases in computational performance applied to current modeling techniques will enable larger scale simulations. In order to exploit this opportunity, integration of diverse theoretical approaches within a multi-scale framework is needed. [source] Predicting solid compounds via global exploration of the energy landscape of solids on the ab initio level without recourse to experimental informationPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2010J. Christian Schön Abstract Predicting which crystalline modifications can exist in a chemical system requires the global exploration of its energy landscape. Due to the large computational effort involved, in the past this search for sufficiently stable minima has been performed employing a variety of empirical potentials and cost functions followed by a local optimization on the ab initio level. However, this might introduce some bias favoring certain types of chemical bonding and entails the risk of overlooking important modifications that are not modeled accurately using empirical potentials. In order to overcome this critical limitation, it is necessary to employ ab initio energy functions during the global optimization phase of the structure prediction. In this paper, we review the current state of the field of structure prediction on the ab initio level. [source] Property-averaging applied to determination of volume contraction in binary-solid liquid-fluidized bedsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2008Renaud Escudié Abstract This communication examines experimental information from the literature on the volume contraction that can occur when two monocomponent particle species that have a diameter ratio and a buoyancy-corrected density ratio on opposite sides of unity are subjected to liquid fluidization as a binary mixture. Attempts are made to predict this volume contraction by applying monocomponent bed expansion equations using averaged properties of the binary solids. It was found that this method works better if the equations are anchored to experimental monocomponent voidages by the fractional bed volume change that they predict than if the equations are used directly. However, greater prediction accuracy can be achieved by correlation of the adjustable parameter G of the Westman, Am Ceramic Soc, 19, 127,129, (1936) equation, originally applied to binary packed beds. On examine dans cet article des données expérimentales de la littérature scientifique sur la contraction de volume qui peut survenir lorsque deux espèces de particules à composante unique d'un rapport de diamètre et d'un rapport de masse volumique corrigé par la flottabilité plus grands et plus petits que l'unité sont soumises à une fluidisation de liquide comme un mélange binaire. On tente de prédire cette contraction de volume en appliquant des équations d'expansion de lit dans le cas monocomposant et en utilisant les propriétés moyennées des solides binaires. On a trouvé que cette méthode fonctionnait mieux lorsque les équations sont étroitement liées aux degrés de vide monocomposants expérimentaux par le changement de volume de lit factionnaire qu'elles prédisent, que lorsque ces équations sont utilisées directement. Néanmoins, une meilleure précision dans la prédiction peut être obtenue par la corrélation de l'équation du paramètre G ajustable de Westman, Am Ceramic Soc, 19, 127,129, (1936), appliquée originellement aux lits garnis binaires. [source] The Fas system in the seminiferous epithelium and its possible extra-testicular roleANDROLOGIA, Issue 1 2003A. Riccioli Summary. The Fas system is involved in the control of immune system homeostasis and nonfunctional Fas system leads to autoimmune disease in mice and humans. The Fas system is a mechanism through which cells expressing Fas ligand (FasL) induce apoptosis of Fas expressing cells. In mouse and rat, the testis represents the main source of constitutive FasL in the body. The roles so far proposed for this molecule in the testis, such as maintenance of immunoprivilege and regulation of physiological germ cell apoptosis, need to be reconsidered as both hypotheses are based on an erroneous cellular location of FasL in the seminiferous epithelium. Recently, we demonstrated that in rodents FasL mRNA is present in germ cells and not in Sertoli cells, and that FasL protein is displayed on the surface of spermatozoa. Here we propose that, for the mouse spermatozoa, the FasL may represent a self-defence mechanism against lymphocytes present in the female genital tract. To verify this hypothesis, we performed crossings between males gld, with nonfunctional FasL, and syngenic or nonsyngenic females. We observed a significant decrease of litter size in outbred crossings with gld males compared with wild-type males, suggesting a possible role of FasL in immunoprotection of the sperm in the female genital tract. The possibility that in humans, by analogy with mouse, FasL plays a self-protective role for the spermatozoon cannot be excluded, and awaits experimental information on the expression of FasL on human sperm cells. [source] Particle Flow Modelling in Slurry-Fed Stirred VesselsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 3 2004F. Scargiali Abstract Despite its importance, experimental information on the Residence Time Distribution (RTD) of solid particles in continuous-flow stirred vessels is still scant. In this work, experimental data on particle RTD in a high-aspect-ratio vessel stirred by three equally-spaced Rushton turbines, obtained by means of Twin Systems Approach (TSA), are employed to assess the suitability of the well known Axial-Dispersion Model to describe particle behavior in the investigated system. The data analysis and model parameter assessment are preceded by a discussion on the utility of self-recirculated systems in carrying out experiments concerning continuous slurry-fed apparatuses. In particular, the suitability of single recirculated systems is discussed and a way to extract numerical RTD data from the relevant experiments is proposed. The advantages and disadvantages of employing instead a couple of twin systems, as it was actually done to obtain the experimental data employed in this work, is shortly discussed. [source] | |||||||||||||||||||