Detailed Understanding (detailed + understanding)

Distribution by Scientific Domains
Distribution within Life Sciences

Selected Abstracts

Fluid dynamics of nodal flow and left,right patterning in development

Julyan H.E. Cartwright
Abstract The manner in which the nodal flow determines the breaking of left,right symmetry during development is a beautiful example of the application of fluid dynamics to developmental biology. Detailed understanding of this crucial developmental process has greatly advanced by the transfer of ideas between these two disciplines. In this article, we review our and others' work on applying fluid dynamics and dynamical systems to the problem of left,right symmetry breaking in vertebrates. Developmental Dynamics 237:3477,3490, 2008. © 2008 Wiley-Liss, Inc. [source]

Gender, light and water effects in carbon isotope discrimination, and growth rates in the dioecious tree Ilex aquifolium

R. Retuerto
Abstract 1.,Detailed understanding of the specific physiology of sexes in dioecious species is required to explain patterns in gender dimorphism. Under controlled-environment conditions we tested the hypothesis that sexes of the dioecious tree holly Ilex aquifolium L. (Aquifoliaceae) differed in growth and long-term potential water-use efficiency, as measured by carbon isotope discrimination (,13C), and that these differences were dependent on the environmental context. 2.,Patterns of response in ,13C to the various combinations of light and water were gender-specific. Under more xeric conditions, females maintained significantly higher ,13C than males. 3.,Female plants exhibited significantly greater relative diameter growth rates than male plants. 4.,As expected, ,13C significantly increased with decreasing irradiance, and decreased with increasing limitation in water supply. Light and water effects were not independent, with a more pronounced drought effect in decreasing leaf ,13C under unshaded than under shaded conditions. 5.,Our results suggest that between-sex differences in physiology are context-dependent. Future studies attempting to assess gender dimorphism should take more account of gender-specific interactions with the environment. Gender-specific efficiency in water use could play a decisive role in explaining gender differences in growth and ecological interactions. [source]

Correlating Raman peak shifts with phase transformation and defect densities: a comprehensive TEM and Raman study on silicon

Thomas Wermelinger
Abstract Silicon is the most often used material in micro electromechanical systems (MEMS). Detailed understanding of its mechanical properties as well as the microstructure is crucial for the reliability of MEMS devices. In this paper, we investigate the microstructure changes upon indentation of single crystalline (100) oriented silicon by transmission electron microscopy (TEM) and Raman microscopy. TEM cross sections were prepared by focused ion beam (FIB) at the location of the indent. Raman microscopy and TEM revealed the occurrence of phase transformations and residual stresses upon deformation. Raman microscopy was also used directly on the cross-sectional TEM lamella and thus microstructural details could be correlated to peak shape and peak position. The results show, however, that due to the implanted Ga+ ions in the lamella the silicon Raman peak is shifted significantly to lower wavenumbers. This hinders a quantitative analysis of residual stresses in the lamella. Furthermore, Raman microscopy also possesses the ability to map deformation structures with a lateral resolution in the submicron range. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Progress in the design of low molecular weight thrombin inhibitors

Stuti Srivastava
Abstract Intravascular thrombosis and its complication, embolism, is a leading cause of morbidity and mortality throughout the world. Past few decades have seen a great deal of progress in the development of antithrombotic agents, though the current treatment options are limited to heparin, LMW heparins, and warfarin. Detailed understanding of the biochemical and biophysical mechanisms of activation and regulation of blood coagulation have helped in developing specific inhibitors of enzymes, especially thrombin, within the coagulation cascade. Thrombin plays a central role in the coagulation cascade and so has become the primary target for the development of antithrombotic drugs. The review covers the main pharmacological aspects of haemostasis and thrombosis and provides an update on low molecular weight thrombin inhibitors along with the limitations of the prevalent antithrombotic agents. Recent developments in small molecule inhibitors of Protease Activated Receptor-1 (PAR-1) which can be helpful for the treatment of thrombotic and vascular proliferative disorders, have also been discussed. © 2004 Wiley Periodicals, Inc. [source]

Detailed understanding of enhanced specific antibody productivity in NS0 myeloma cells

Soo Hean Gary Khoo
Abstract The understanding of how cellular productivity is modulated in cell lines is of significant importance in the biopharmaceutical industry. Often, single molecular mechanisms fail to fully explain how specific antibody productivity is enhanced during proliferation arrest. Previously, we reported that certain physiological changes occur when proliferation is arrested by p21CIP1 over expression. In this work, we correlate physiological and molecular factors to enhance antibody productivity. Using biomass, cell volume and total cellular protein content as a basis for determining specific productivity, it was found that total cellular protein correlated best with cellular productivity. This meant that there was no preferential increase in antibody production relative to cellular proteins in arrested cultures. However, molecular analysis of mRNA transcription and stability indicated that both processes were altered in arrested cultures resulting in up to threefold increased heavy chain mRNA levels. While flow cytometric analysis revealed that arrested cells had elevated translational capacity for both heavy and light chains, the heavy to light chain polypeptide ratio was 10,50% higher than in the control. This resulted in a lower extracellular accumulation of light chains and a better utilization of cellular resources for the formation of complete antibodies. Active transcriptional regulation of heavy and light chain mRNA and the modulation of translational activities play a vital role in the modulation of overall antibody productivity of these cells. The combined effect of heavy chain mRNA enhancement and the increased cellular assembly capacity was determined to effectively increase specific productivity. Biotechnol. Bioeng. 2009;102: 188,199. © 2008 Wiley Periodicals, Inc. [source]

,-Herpesviruses and cellular signaling in AIDS-associated malignancies

CANCER SCIENCE, Issue 9 2007
Kohji Noguchi
,-Herpesviruses, Epstein,Barr virus (EBV/HHV-4) and Kaposi's sarcoma-associated herpesvirus (KSHV/HHV-8), are involved in human carcinogenesis, particularly in immunocompromised patients. Virus-associated malignancies are becoming of significant concern for the mortality of long-lived immunocompromised patients, and therefore, research of advanced strategies for AIDS-related malignancies is an important field in cancer chemotherapy. Detailed understanding of the EBV and KSHV lifecycle and related cancers at the molecular level is required for novel strategies of molecular-targeted cancer chemotherapy. The present review gives a simple outline of the functional interactions between KSHV- and EBV-viral gene products and host cell deregulated signaling pathways as possible targets of chemotherapy against AIDS-related malignancies. (Cancer Sci 2007; 98: 1288,1296) [source]

Wavelet Packet-Autocorrelation Function Method for Traffic Flow Pattern Analysis

Xiaomo Jiang
A detailed understanding of the properties of traffic flow is essential for building a reliable forecasting model. The discrete wavelet packet transform (DWPT) provides more coefficients than the conventional discrete wavelet transform (DWT), representing additional subtle details of a signal. In wavelet multiresolution analysis, an important decision is the selection of the decomposition level. In this research, the statistical autocorrelation function (ACF) is proposed for the selection of the decomposition level in wavelet multiresolution analysis of traffic flow time series. A hybrid wavelet packet-ACF method is proposed for analysis of traffic flow time series and determining its self-similar, singular, and fractal properties. A DWPT-based approach combined with a wavelet coefficients penalization scheme and soft thresholding is presented for denoising the traffic flow. The proposed methodology provides a powerful tool in removing the noise and identifying singularities in the traffic flow. The methods created in this research are of value in developing accurate traffic-forecasting models. [source]

Application of High Current and Current Zero Simulations of High-Voltage Circuit Breakers

C. M. Franck
Abstract This paper reports on the use of computational fluid dynamic (CFD) simulations to predict the interruption behaviour of high-voltage circuit breakers (HV-CB) using the self-blast principle. Two different levels of accuracy of the arc model are proven to be sufficiently accurate for simulating the high-current phase and the period around current zero (CZ). For the high-current phase, a simplified equivalent model of the arc is implemented to predict the pressure build-up, and even more important to accurately trace the hot gas from the arcing zone into the exhausts and the heating volume. A detailed analysis of the gas mixing in the heating volume for different arcing times and current amplitudes showed the optimum geometrical design of the heating volume. For the CZ phase, a more detailed arc model is needed including the effects of ohmic heating, radiative energy transfer, and turbulent cooling fully resolved in space and time. The validation with experiments was done and shows good agreement which justifies the use of the implemented model. With it, scaling laws varying only one parameter at a time (pressure and applied current slope) were derived and confirm previously found empirical laws. This is of particular interest, as it is very difficult to derive such scaling laws from experiments where the scatter is always very large and where it is impossible to vary only one parameter at a time. The influence of the most important geometrical parameters of the nozzle on the interruption performance is shown. In addition to previous experimental indications of this, the simulation reveals that turbulent cooling on the arc edge is the main reason for the difference in interruption performance. Moreover, the exact spatio-temporal build-up of arc resistance and with it the detailed understanding of the arc interruption process is possible and shown here for the first time. These simulations enable us to predict HV-CB performance and to minimise the number of development tests and are routinely used in new development projects. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Processing and presentation of (pro)-insulin in the MHC class II pathway: the generation of antigen-based immunomodulators in the context of type 1 diabetes mellitus

Timo Burster
Abstract Both CD4+ and CD8+ T lymphocytes play a crucial role in the autoimmune process leading to T1D. Dendritic cells take up foreign antigens and autoantigens; within their endocytic compartments, proteases degrade exogenous antigens for subsequent presentation to CD4+ T cells via MHC class II molecules. A detailed understanding of autoantigen processing and the identification of autoantigenic T cell epitopes are crucial for the development of antigen-based specific immunomodulators. APL are peptide analogues of auto-immunodominant T cell epitopes that bind to MHC class II molecules and can mediate T cell activation. However, APL can be rapidly degraded by proteases occurring in the extracellular space and inside cells, substantially weakening their efficiency. By contrast, protease-resistant APL function as specific immunomodulators and can be used at low doses to examine the functional plasticity of T cells and to potentially interfere with autoimmune responses. Here, we review the latest achievements in (pro)-insulin processing in the MHC class II pathway and the generation of APL to mitigate autoreactive T cells and to activate Treg cells. Copyright © 2010 John Wiley & Sons, Ltd. [source]

The promise and the potential consequences of the global transport of mycorrhizal fungal inoculum

Mark W. Schwartz
Abstract Advances in ecology during the past decade have led to a much more detailed understanding of the potential negative consequences of species' introductions. Moreover, recent studies of mycorrhizal symbionts have led to an increased knowledge of the potential utility of fungal inoculations in agricultural, horticultural and ecological management. The intentional movement of mycorrhizal fungal species is growing, but the concomitant potential for negative ecological consequences of invasions by mycorrhizal fungi is poorly understood. We assess the degree to which introductions of mycorrhizal fungi may lead to unintended negative, and potentially costly, consequences. Our purpose is to make recommendations regarding appropriate management guidelines and highlight top priority research needs. Given the difficulty in discerning invasive species problems associated with mycorrhizal inoculations, we recommend the following. First, careful assessment documenting the need for inoculation, and the likelihood of success, should be conducted prior to inoculation because inoculations are not universally beneficial. Second, invasive species problems are costly and often impossible to control by the time they are recognized. We recommend using local inoculum sources whenever possible. Third, non-sterile cultures of inoculum can result in the movement of saprobes and pathogens as well as mutualists. We recommend using material that has been produced through sterile culture when local inoculum is not available. Finally, life-history characteristics of inoculated fungi may provide general guidelines relative to the likelihood of establishment and spread. We recommend that, when using non-local fungi, managers choose fungal taxa that carry life-history traits that may minimize the likelihood of deleterious invasive species problems. Additional research is needed on the potential of mycorrhizal fungi to spread to non-target areas and cause ecological damage. [source]

Policy options for alcohol price regulation: the importance of modelling population heterogeneity

ADDICTION, Issue 3 2010
Petra Sylvia Meier
ABSTRACT Context and aims Internationally, the repertoire of alcohol pricing policies has expanded to include targeted taxation, inflation-linked taxation, taxation based on alcohol-by-volume (ABV), minimum pricing policies (general or targeted), bans of below-cost selling and restricting price-based promotions. Policy makers clearly need to consider how options compare in reducing harms at the population level, but are also required to demonstrate proportionality of their actions, which necessitates a detailed understanding of policy effects on different population subgroups. This paper presents selected findings from a policy appraisal for the UK government and discusses the importance of accounting for population heterogeneity in such analyses. Method We have built a causal, deterministic, epidemiological model which takes account of differential preferences by population subgroups defined by age, gender and level of drinking (moderate, hazardous, harmful). We consider purchasing preferences in terms of the types and volumes of alcoholic beverages, prices paid and the balance between bars, clubs and restaurants as opposed to supermarkets and off-licenses. Results Age, sex and level of drinking fundamentally affect beverage preferences, drinking location, prices paid, price sensitivity and tendency to substitute for other beverage types. Pricing policies vary in their impact on different product types, price points and venues, thus having distinctly different effects on subgroups. Because population subgroups also have substantially different risk profiles for harms, policies are differentially effective in reducing health, crime, work-place absence and unemployment harms. Conclusion Policy appraisals must account for population heterogeneity and complexity if resulting interventions are to be well considered, proportionate, effective and cost-effective. [source]

Individualized assessment and treatment program for alcohol dependence: results of an initial study to train coping skills

ADDICTION, Issue 11 2009
Mark D. Litt
ABSTRACT Aims Cognitive,behavioral treatments (CBT) are among the most popular interventions offered for alcohol and other substance use disorders, but it is not clear how they achieve their effects. CBT is purported to exert its beneficial effects by altering coping skills, but data supporting coping changes as the mechanism of action are mixed. The purpose of this pilot study was to test a treatment in which coping skills were trained in a highly individualized way, allowing us to determine if such training would result in an effective treatment. Design Participants were assigned randomly to a comprehensive packaged CBT program (PCBT), or to an individualized assessment and treatment program (IATP). The IATP program employed experience sampling via cellphone to assess coping skills prior to treatment, and provided therapists with a detailed understanding of patients' coping strengths and deficits. Setting Out-patient treatment. Participants A total of 110 alcohol-dependent men and women. Measurements Participants in both conditions completed experience sampling of situations, drinking and coping efforts prior to, and following, 12 weeks of treatment. Time-line follow-back procedures were also used to record drinking at baseline and post-treatment. Findings IATP yielded higher proportion of days abstinent (PDA) at post-treatment (P < 0.05) than did PCBT, and equivalent heavy drinking days. IATP also elicited more momentary coping responses and less drinking in high-risk situations, as recorded by experience sampling at post-treatment. Post-treatment coping response rates were associated with decreases in drinking. Conclusions The IATP approach was more successful than PCBT at training adaptive coping responses for use in situations presenting a high risk for drinking. The highly individualized IATP approach may prove to be an effective treatment strategy for alcohol-dependent patients. [source]

Regulation of whole bacterial pathogen transcription within infected hosts

My-Van La
Abstract DNA microarrays are a powerful and promising approach to gain a detailed understanding of the bacterial response and the molecular cross-talk that can occur as a consequence of host,pathogen interactions. However, published studies mainly describe the host response to infection. Analysis of bacterial gene regulation in the course of infection has confronted many challenges. This review summarizes the different strategies used over the last few years to investigate, at the genomic scale, and using microarrays, the alterations in the bacterial transcriptome in response to interactions with host cells. Thirty-seven studies involving 19 different bacterial pathogens were compiled and analyzed. Our in silico comparison of the transcription profiles of bacteria grown in broth or in contact with eukaryotic cells revealed some features commonly observed when bacteria interact with host cells, including stringent response and cell surface remodeling. [source]

Genetic influences on behavioral inhibition and anxiety in juvenile rhesus macaques

J. Rogers
In humans and other animals, behavioral responses to threatening stimuli are an important component of temperament. Among children, extreme behavioral inhibition elicited by novel situations or strangers predicts the subsequent development of anxiety disorders and depression. Genetic differences among children are known to affect risk of developing behavioral inhibition and anxiety, but a more detailed understanding of genetic influences on susceptibility is needed. Nonhuman primates provide valuable models for studying the mechanisms underlying human behavior. Individual differences in threat-induced behavioral inhibition (freezing behavior) in young rhesus monkeys are stable over time and reflect individual levels of anxiety. This study used the well-established human intruder paradigm to elicit threat-induced freezing behavior and other behavioral responses in 285 young pedigreed rhesus monkeys. We examined the overall influence of quantitative genetic variation and tested the specific effect of the serotonin transporter promoter repeat polymorphism. Quantitative genetic analyses indicated that the residual heritability of freezing duration (behavioral inhibition) is h2 = 0.384 (P = 0.012) and of ,orienting to the intruder' (vigilance) is h2 = 0.908 (P = 0.00001). Duration of locomotion and hostility and frequency of cooing were not significantly heritable. The serotonin transporter polymorphism showed no significant effect on either freezing or orienting to the intruder. Our results suggest that this species could be used for detailed studies of genetic mechanisms influencing extreme behavioral inhibition, including the identification of specific genes that are involved in predisposing individuals to such behavior. [source]

Geochemical Factors Controlling Radium Activity in a Sandstone Aquifer

GROUND WATER, Issue 4 2006
Tim Grundl
Geochemical processes behind the occurrence of radium activities in excess of the U.S. EPA's drinking water limit of 5 pCi/L combined radium were investigated in a regional sandstone aquifer located in southeastern Wisconsin. Geochemical speciation modeling (PHREEQC 2.7) combined with a detailed understanding of the regional flow system provided by recent flow modeling efforts was used to determine that radium coprecipitation into barite controls radium activity in the unconfined portion of the aquifer. As the aquifer transitions from unconfined to confined conditions, radium levels rise and the water becomes more sulfate rich yet the aquifer remains at saturation with barite throughout. Calculations based on published distribution coefficients and the observed Ra:Ba atomic ratios indicate that barite contains ,12 ,g/kg coprecipitated radium. Confined portions of the aquifer have high concentrations of sulfate, and barium concentrations become too low to be an effective control on radium activity. Additional, as yet undefined, controls on radium are operative in the downgradient, confined portion of the aquifer. [source]

Nucleation-Governed Reversible Self-Assembly of an Organic Semiconductor at Surfaces: Long-Range Mass Transport Forming Giant Functional Fibers,

G. De, Luca
Abstract The use of solvent-vapor annealing (SVA) to form millimeter-long crystalline fibers, having a sub-micrometer cross section, on various solid substrates is described. Thin films of a perylene-bis(dicarboximide) (PDI) derivative, with branched alkyl chains, prepared from solution exhibit hundreds of nanometer-sized PDI needles. Upon exposure to the vapors of a chosen solvent, tetrahydrofuran (THF), the needles re-organize into long fibers that have a remarkably high aspect ratio, exceeding 103. Time- and space-resolved mapping with optical microscopy allows the self-assembly mechanism to be unravelled; the mechanism is found to be a nucleation-governed growth, which complies with an Avrami-type of mechanism. SVA is found to lead to self-assembly featuring i),long-range order (up to the millimeter scale), ii),reversible characteristics, as demonstrated through a series of assembly and disassembly steps, obtained by cycling between THF and CHCl3 as solvents, iii),remarkably high mass transport because the PDI molecular motion is found to occur at least over hundreds of micrometers. Such a detailed understanding of the growth process is fundamental to control the formation of self-assembled architectures with pre-programmed structures and physical properties. The versatility of the SVA approach is proved by its successful application using different substrates and solvents. Kelvin probe force microscopy reveals that the highly regular and thermodynamically stable fibers of PDI obtained by SVA exhibit a greater electron-accepting character than the smaller needles of the drop-cast films. The giant fibers can be grown in,situ in the gap between microscopic electrodes supported on SiOx, paving the way towards the application of SVA in micro- and nanoelectronics. [source]

Significance of processes in the near-stream zone on stream water acidity in a small acidified forested catchment

Jens Fölster
Abstract The near-stream zone has received increasing attention owing to its influence on stream water chemistry in general and acidity in particular. Possible processes in this zone include cation exchange, leaching of organic matter and redox reactions of sulphur compounds. In this study the influences of processes in the near-stream zone on the acidity in runoff from a small, acidified catchment in central southern Sweden were investigated. The study included sampling of groundwater, soil water and stream water along with hydrological measurements. An input,output budget for the catchment was established based on data from the International Co-operative Programme on Integrated Monitoring at this site. The catchment was heavily acidified by deposition of anthropogenic sulphur, with pH in stream water between 4·4 and 4·6. There was also no relationship between stream flow and pH, which is indicative of chronic acidification. Indications of microbial reduction of sulphate were found in some places near the stream, but the near-stream zone did not have a general impact on the sulphate concentration in discharging groundwater. The near-stream zone was a source of dissolved organic carbon (DOC) in the stream, which had a median DOC of 6·8 mg L1. The influence on stream acidity from organic anions was overshadowed by the effect of sulphate, however, except during a spring flow episode, when additional organic matter was flushed out and the sulphate-rich ground water was mixed with more diluted event water. Ion exchange was not an important process in the near-stream zone of the Kindla catchment. Different functions of the near-stream zone relating to discharge acidity are reported in the literature. In this study there was even a variation within the site. There is therefore a need for more case studies to provide a more detailed understanding of the net effects that the near-stream zone can have on stream chemistry under different circumstances. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Introduction: Why Reflect Collectively on Capacities for Change?,

IDS BULLETIN, Issue 3 2010
Peter Clarke
,Capacity development' implies a promise of growing self-reliance, national ownership and sustainability, yet practice seems consistently to fall short of this emancipatory promise. This introduction argues for a reframing of capacity development for emancipatory social change. Articles in this IDS Bulletin show how understanding and practice must engage with complexity, appreciate the importance of specific culture and context, and continually address the role of power in shaping relationships, understandings and practices. Values and leadership are fundamental drivers of capacity development processes. This IDS Bulletin argues against a deficit approach based on linear causal logic and replicable ,best practice'. Instead, practitioners are encouraged to develop a detailed understanding of the culture and dynamics of specific contexts, to detect energies for positive change and work to connect and facilitate them. Learning is at the centre of the approach. Capacity development is understood as a collective process of learning in action for social change. Support for capacity development processes demands a critical development practice that implies mutual learning, with an emphasis on reflective and experiential approaches. However, this reframing implies enormous challenges for development practice, and therefore considerable personal and organisational commitment. [source]

Bioaccessibility studies of ferro-chromium alloy particles for a simulated inhalation scenario: A comparative study with the pure metals and stainless steel

Klara Midander
Abstract The European product safety legislation, REACH, requires that companies that manufacture, import, or use chemicals demonstrate safe use and high level of protection of their products placed on the market from a human health and environmental perspective. This process involves detailed assessment of potential hazards for various toxicity endpoints induced by the use of chemicals with a minimum use of animal testing. Such an assessment requires thorough understanding of relevant exposure scenarios including material characteristics and intrinsic properties and how, for instance, physical and chemical properties change from the manufacturing phase, throughout use, to final disposal. Temporary or permanent adverse health effects induced by particles depend either on their shape or physical characteristics, and/or on chemical interactions with the particle surface upon human exposure. Potential adverse effects caused by the exposure of metal particles through the gastrointestinal system, the pulmonary system, or the skin, and their subsequent potential for particle dissolution and metal release in contact with biological media, show significant gaps of knowledge. In vitro bioaccessibility testing at conditions of relevance for different exposure scenarios, combined with the generation of a detailed understanding of intrinsic material properties and surface characteristics, are in this context a useful approach to address aspects of relevance for accurate risk and hazard assessment of chemicals, including metals and alloys and to avoid the use of in vivo testing. Alloys are essential engineering materials in all kinds of applications in society, but their potential adverse effects on human health and the environment are very seldom assessed. Alloys are treated in REACH as mixtures of their constituent elements, an approach highly inappropriate because intrinsic properties of alloys generally are totally different compared with their pure metal components. A large research effort was therefore conducted to generate quantitative bioaccessibility data for particles of ferro-chromium alloys compared with particles of the pure metals and stainless steel exposed at in vitro conditions in synthetic biological media of relevance for particle inhalation and ingestion. All results are presented combining bioaccessibility data with aspects of particle characteristics, surface composition, and barrier properties of surface oxides. Iron and chromium were the main elements released from ferro-chromium alloys upon exposure in synthetic biological media. Both elements revealed time-dependent release processes. One week exposures resulted in very small released particle fractions being less than 0.3% of the particle mass at acidic conditions and less than 0.001% in near pH-neutral media. The extent of Fe released from ferro-chromium alloy particles was significantly lower compared with particles of pure Fe, whereas Cr was released to a very low and similar extent as from particles of pure Cr and stainless steel. Low release rates are a result of a surface oxide with passive properties predominantly composed of chromium(III)-rich oxides and silica and, to a lesser extent, of iron(II,III)oxides. Neither the relative bulk alloy composition nor the surface composition can be used to predict or assess the extent of metals released in different synthetic biological media. Ferro-chromium alloys cannot be assessed from the behavior of their pure metal constituents. Integr Environ Assess Manag 2010;6:441,455. © 2009 SETAC [source]

On models of fractal networks

Walter Arrighetti
Abstract A couple of iterative models for the theoretical study of fractal networks whose topologies are generated via iterated function systems is presented: a lumped-parameter impedor-oriented one and a two-port-network-oriented one. With the former, the voltage and current patterns give a detailed understanding of the electromagnetic fields' self-similar distribution throughout the network; on the other hand, model complexity exponentially increases with the prefractal iteration order. The latter ,black-box' model only controls port-oriented global parameters that are the ones commonly used in the integration of different electronic systems, and its complexity is independent of prefractal order. Sierpinski gasket and carpet topologies are reported as examples. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Molecular Transport Junctions: Clearing Mists,

M. Lindsay
Abstract Recent progress in the measurement and modeling of transport in molecular junctions has been very significant. Tunnel transport in the Landauer,Imry regime is now broadly understood for several systems, although a detailed understanding of the role of contact geometry is still required. We overview some clear indications from recent research and note the quite reasonable agreement between measured and calculated conductance in metal,molecule,metal junctions. The next challenge lies in obtaining a microscopic understanding of charge transport that involves reduction or oxidation of molecules. [source]

Archaeological Reconnaissance of the 1865 American-Built Sub Marine Explorer at Isla San Telmo, Archipielago de las Perlas, Panama

James P. Delgado
A wrecked submarine lying in the inter-tidal zone of Isla San Telmo, off Panama's coast, has been identified as Sub Marine Explorer, a rare surviving example of a mid-19th-century submersible. One of the world's first successful lock-out dive-chambers, the craft had a fatal design aspect that ultimately harmed its crew and may have killed the builder through the effects of pressure. Documentation of the submarine provides a detailed understanding of this technologically advanced but flawed craft. © 2006 The Author [source]

Molecular relaxation and metalloenzyme active site modeling

James W. Whittaker
Abstract Metalloenzymes represent a broad class of important biomolecules containing an essential metal ion cofactor in their catalytic active sites, forming biologic metal complexes that perform a wide range of important functions: activation of small molecules (O2, N2, H2, CO), atom transfer chemistry, and the control of oxidation equivalents. The structures of many metalloenzyme active sites have been defined by X-ray crystallography, revealing transition metal ions in unique low-symmetry environments. These bioinorganic complexes present significant challenges for computational studies aimed at going beyond crystal structures to develop a detailed understanding of the catalytic mechanisms. Considerable progress has been made in the theoretical characterization of these sites in recent years, supported by the availability of efficient computational tools, in particular density functional methods. However, the ultimate success of a theoretical model depends on a number of factors independent of the specific computational method used, including the quality of the initial structural data, the identification of important environmental perturbations and constraints, and experimental validation of theoretical predictions. We explore these issues in detail and illustrate the effects of molecular relaxation in calculations of two metalloenzymes, manganese superoxide dismutase and galactose oxidase. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 [source]

Rhinoceros behaviour: implications for captive management and conservation

All species of rhinoceros are, to varying degrees, threatened with extinction because of poaching, habitat loss, human-rhinoceros conflict, hunting and civil unrest. Clearly the threats facing the five remaining species (Black rhinoceros Diceros bicornis, White rhinoceros Ceratotherium simum, Greater one-horned rhinoceros Rhinoceros unicornis, Javan rhinoceros Rhinoceros sondaicus and Sumatran rhinoceros Dicerorhinus sumatrensis) are anthropogenic. Although many disciplines are important for conservation, understanding the behaviour characteristics of a species should be considered a key component when developing wildlife-management and conservation strategies. A general overview of the behaviour of rhinoceros is presented, addressing ecology and social organization, activity and habitat use, feeding strategies, courtship and reproduction, and anti-predator behaviour. The implications of behavioural studies for successful management and husbandry of rhinoceros in captivity are discussed in sections on group size and composition, enclosure design and enrichment programmes, activity patterns, introductions, reproduction, hand-rearing, and health and stress. Finally, there is some discussion about the implications of this knowledge for in situ conservation in relation to designing protected areas, further aspects of animal health and stress, and reintroduction and translocation. A detailed understanding of rhinoceros behaviour is important for survival both in range-country protected areas and captivity, and such knowledge should be used to provide the most appropriate animal care and environments for these species. [source]

Blood group antigens and immune responses,detailed knowledge is necessary to prevent immunization and to follow up immunized individuals

A. Husebekk
Background The immune system is educated to detect and react with foreign antigens and to tolerate self-antigen. Transfusion of blood cells and plasma and pregnancies challenge the immune system by the introduction of foreign antigens. The antigens may cause an immune response, but in many instances this is not the case and the individual is not immunised after exposure of blood group antigens. Aims The aim of the presentation is to dissect some immune responses to blood group antigens in order to understand the mechanism of immunisation. Methods The results of immune responses to blood group antigens can be detected by the presence of antibodies to the antigens. If the antibodies are of IgG class, the activated B cells have received help from antigen specific T cells. Both antibodies, B cells and T cells can be isolated from immunised individuals and studied in the laboratory. Also B-cell receptors and T-cell receptors as well as MHC molecules on antigen presenting cells can be studied and models of the immune synapses can be created in vitro. Results The most classic immune responses in transfusion medicine and in incompatible pregnancies are immune responses to the RhD antigen on red cells, HLA class I molecules on white cells and platelets and human platelet antigens. The nature of these antigens are different; RhD antigens are part of a large complex, present on red cells from RhD positive individuals and completely lacking on red cells from RhD negative individuals. It is likely that many peptides derived from this antigen complex may stimulate T cells and B cells. HLA antigens are highly polymorphic and the antigens are known to induce strong alloimmune responses. The HPA antigens are created by one amino acid difference in allotypes based on a single nucleotide polymorphism at the genetic level. HPA 1a induce immune responses in 10% of HPA 1b homozygote pregnant women. The result of these immune responses is destruction of blood cells with clinical consequences connected to the effect of transfusions or the outcome of pregnancies. Summary/Conclusions Even though there is emerging knowledge about the immune responses to some of the blood group antigens, more information must be gained in order to understand the complete picture. The action of the innate immune response initiating the adaptive immune response to blood group antigens is not well understood. A detailed understanding of both the innate ad the adaptive part of the immune response is necessary to identify individuals at risk for immunisation and to prevent immunisation to blood group antigens. [source]

Computational studies of nonadiabatic effects in gas,surface encounters

Cécile Corriol
Model studies are presented, each of which employs a different approach to solving the problem of nonadiabatic dynamics occurring at a solid surface. The jumping wave packet-type approach involving dynamics on two potential energy surfaces punctuated by Franck,Condon transitions was applied to the dynamics of CO desorbed from Ru following energetic electron bombardment. Classical dynamics was also employed in this system to gain a more detailed understanding of the factors important to the final molecular state distribution. To study charge transfer from an alkali-halide surface to a scattering atom, we have used full multi-surface quantum dynamics. A simple, but effective, analysis method was used to make a more detailed connection between the potential energy surfaces and the dynamics. To study the fate of the transferred electron and to model how this depends on substrate and projectile species, we have used a four-dimensional wave packet implementation in which two of the dimensions explicitly account for the electron dynamics. Finally, we consider the famous electron,hole pair excitation problem, from a density functional theory perspective. Spin nonadiabaticity is found to be a new important feature in gas,metal surface interactions. [source]

Grassland-breeding waders: identifying key habitat requirements for management

Summary 1Habitat loss and degradation of wetland ecosystems, principally through large-scale drainage and conversion to arable farmland, have been implicated in the widespread, dramatic declines of breeding waders across Europe. Managing the remaining wetlands to reverse these declines will require a detailed understanding of their habitat requirements. 2In the UK, grazing marshes are key components of the remaining wetlands in both coastal and inland sites, and the structure of grazing marsh habitat can differ between these locations. Redshank Tringa totanus is a declining wader species that breeds in both marsh types. We quantified the habitat features that influence redshank selection of breeding and nest site locations, across coastal and inland marshes, in eastern England. 3On both marsh types, breeding location and breeding densities within fields were positively related to the lengths of pool edge and all wet features, respectively. Nest site location was principally influenced by vegetation characteristics, with soil penetrability also important on inland sites but proximity to wet features and vegetation type at the nest important on coastal sites. Hatching probability was higher when the surrounding soils were more penetrable. 4Synthesis and applications. The wet features of critical importance for breeding redshank are common on coastal marshes and can be deliberately established on inland sites. Coastal marshes are often rare and frequently threatened by dynamic coastal processes, whereas inland marshes are more abundant but largely unsuitable for breeding waders at present. These analyses highlight the scope for improving the management of inland marshes for breeding redshank. As habitat suitable for breeding redshank frequently supports a range of other wader species, this information can also direct management efforts to improve breeding wader populations in the wider countryside. [source]

Moving to suburbia: ontogenetic and evolutionary consequences of life on predator-free islands

Daniel T. Blumstein
Aim Many species find themselves isolated from the predators with which they evolved. This situation commonly occurs with island biota, and is similar to moving from the dangerous inner-city to the suburbs. Economic thinking tells us that we should expect costly antipredator behaviour to be lost if it is no longer beneficial. The loss of antipredator behaviour has important consequences for those seeking to translocate or reintroduce individuals from predator-free islands back to the predator-rich mainland, but we have neither a detailed understanding of the mechanisms of loss nor information on the time course of relaxed selection. Some antipredator behaviours are experience-dependent: experience with predators is required for their proper performance. In these cases, antipredator behaviour is lost after only a single generation of isolation, but it should be able to be regained following exposure to predators. Other behaviours may be more `hard-wired'. The evolutionary loss of antipredator behaviour may occur over as few as several generations, but behaviours may also persist for many thousands of years of predator-free living. Location Australia and New Zealand. Methods I discuss the results of a series of studies designed to document the mechanisms and time course of relaxed selection for antipredator behaviour in macropodid marsupials. Controlled studies of visual, acoustic and olfactory predator recognition, as well as field studies of antipredator vigilance focused on several species of kangaroos and wallabies. Results Visual predator recognition may be retained following 9500 years of relaxed selection, but olfactory and acoustic predator recognition may have to be learned. Insular populations allow humans to approach closer before fleeing than mainland animals. Insular species may retain `group size effects' , the ability to seek safety in numbers , when they are exposed to any predators. Main conclusions I suggest that the presence of any predators may be an important factor in maintaining functional antipredator behaviour. Managers should pay particular attention as to the source and evolutionary history of their population when planning translocations or reintroductions. [source]

Targeted Deletion of the Sclerostin Gene in Mice Results in Increased Bone Formation and Bone Strength,,

Xiaodong Li
Abstract Introduction: Sclerosteosis is a rare high bone mass genetic disorder in humans caused by inactivating mutations in SOST, the gene encoding sclerostin. Based on these data, sclerostin has emerged as a key negative regulator of bone mass. We generated SOST knockout (KO) mice to gain a more detailed understanding of the effects of sclerostin deficiency on bone. Materials and Methods: Gene targeting was used to inactivate SOST and generate a line of SOST KO mice. Radiography, densitometry, ,CT, histomorphometry, and mechanical testing were used to characterize the impact of sclerostin deficiency on bone in male and female mice. Comparisons were made between same sex KO and wildtype (WT) mice. Results: The results for male and female SOST KO mice were similar, with differences only in the magnitude of some effects. SOST KO mice had increased radiodensity throughout the skeleton, with general skeletal morphology being normal in appearance. DXA analysis of lumbar vertebrae and whole leg showed that there was a significant increase in BMD (>50%) at both sites. ,CT analysis of femur showed that bone volume was significantly increased in both the trabecular and cortical compartments. Histomorphometry of trabecular bone revealed a significant increase in osteoblast surface and no significant change in osteoclast surface in SOST KO mice. The bone formation rate in SOST KO mice was significantly increased for trabecular bone (>9-fold) at the distal femur, as well as for the endocortical and periosteal surfaces of the femur midshaft. Mechanical testing of lumbar vertebrae and femur showed that bone strength was significantly increased at both sites in SOST KO mice. Conclusions:SOST KO mice have a high bone mass phenotype characterized by marked increases in BMD, bone volume, bone formation, and bone strength. These results show that sclerostin is a key negative regulator of a powerful, evolutionarily conserved bone formation pathway that acts on both trabecular and cortical bone. [source]

Performance of DFT in modeling electronic and structural properties of cobalamins

Jadwiga Kuta
Abstract Computational modeling of the enzymatic activity of B12 -dependent enzymes requires a detailed understanding of the factors that influence the strength of the CoC bond and the limits associated with a particular level of theory. To address this issue, a systematic analysis of the electronic and structural properties of coenzyme B12 models has been performed to establish the performance of three different functionals including B3LYP, BP86, and revPBE. In particular the cobalt,carbon bond dissociation energies, axial bond lengths, and selected stretching frequencies have been analyzed in detail. Current analysis shows that widely used B3LYP functional significantly underestimates the strength of the CoC bond while the nonhybrid BP86 functional produces very consistent results in comparison to experimental data. To explain such different performance of these functionals molecular orbital analysis associated with axial bonds has been performed to show differences in axial bonding provided by hybrid and nonhybrid functionals. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1429,1437, 2006 [source]