1,488 research outputs found
A numerical study of a binary Yukawa model in regimes characteristic of globular proteins in solutions
The main goal of this paper is to assess the limits of validity, in the
regime of low concentration and strong Coulomb coupling (high molecular
charges), for a simple perturbative approximation to the radial distribution
functions (RDF), based upon a low-density expansion of the potential of mean
force and proposed to describe protein-protein interactions in a recent
Small-Angle-Scattering (SAS) experimental study. A highly simplified Yukawa
(screened Coulomb) model of monomers and dimers of a charged globular protein
(-lactoglobulin) in solution is considered. We test the accuracy of the
RDF approximation, as a necessary complementary part of the previous
experimental investigation, by comparison with the fluid structure predicted by
approximate integral equations and exact Monte Carlo (MC) simulations. In the
MC calculations, an Ewald construction for Yukawa potentials has been used to
take into account the long-range part of the interactions in the weakly
screened cases. Our results confirm that the perturbative first-order
approximation is valid for this system even at strong Coulomb coupling,
provided that the screening is not too weak (i.e., for Debye length smaller
than monomer radius). A comparison of the MC results with integral equation
calculations shows that both the hypernetted-chain (HNC) and the Percus-Yevick
(PY) closures have a satisfactory behavior under these regimes, with the HNC
being superior throughout. The relevance of our findings for interpreting SAS
results is also discussed.Comment: Physical Review E, in press (2005
Using Spectral Method as an Approximation for Solving Hyperbolic PDEs
We demonstrate an application of the spectral method as a numerical
approximation for solving Hyperbolic PDEs. In this method a finite basis is
used for approximating the solutions. In particular, we demonstrate a set of
such solutions for cases which would be otherwise almost impossible to solve by
the more routine methods such as the Finite Difference Method. Eigenvalue
problems are included in the class of PDEs that are solvable by this method.
Although any complete orthonormal basis can be used, we discuss two
particularly interesting bases: the Fourier basis and the quantum oscillator
eigenfunction basis. We compare and discuss the relative advantages of each of
these two bases.Comment: 19 pages, 14 figures. to appear in Computer Physics Communicatio
Blending using ODE swept surfaces with shape control and C1 continuity
Surface blending with tangential continuity is most widely applied in computer aided design, manufacturing systems, and geometric modeling. In this paper, we propose a new blending method to effectively control the shape of blending surfaces, which can also satisfy the blending constraints of tangent continuity exactly. This new blending method is based on the concept of swept surfaces controlled by a vector-valued fourth order ordinary differential equation (ODE). It creates blending surfaces by sweeping a generator along two trimlines and making the generator exactly satisfy the tangential constraints at the trimlines. The shape of blending surfaces is controlled by manipulating the generator with the solution to a vector-valued fourth order ODE. This new blending methods have the following advantages: 1). exact satisfaction of 1C continuous blending boundary constraints, 2). effective shape control of blending surfaces, 3). high computing efficiency due to explicit mathematical representation of blending surfaces, and 4). ability to blend multiple (more than two) primary surfaces
A novel screen-printed multi-component nanocomposite ink with a pressure sensitive electrical resistance functionality
Here, a novel functional ink is described that is composed of multiple nanoscale components and exhibits pronounced touch pressure sensitive electrical properties ideal for applications in switching, sensing and touch sensitive surfaces. The ink can be screen-printed and the as-printed ink displays a large and reproducible touch pressure sensitive electrical resistance and, in contrast to some other composite materials, the resistance changes occur down to the smallest applied pressures. Detailed scanning electron microscopy shows the complex nanoscale structure of the composite that is critical for the electrical behavior. Current-voltage measurements, under static compressive loading, show monotonic non-linear behavior at low compression and ohmic behavior at higher loadings
Sex differences in metabolic and adipose tissue responses to juvenile-onset obesity in sheep
Sex is a major factor determining adipose tissue distribution and the subsequent adverse effects of obesity-related disease including type 2 diabetes. The role of gender on juvenile obesity and the accompanying metabolic and inflammatory responses is not well established. Using an ovine model of juvenile onset obesity induced by reduced physical activity, we examined the effect of gender on metabolic, circulatory, and related inflammatory and energy-sensing profiles of the major adipose tissue depots. Despite a similar increase in fat mass with obesity between genders, males demonstrated a higher storage capacity of lipids within perirenal-abdominal adipocytes and exhibited raised insulin. In contrast, obese females became hypercortisolemic, a response that was positively correlated with central fat mass. Analysis of gene expression in perirenal-abdominal adipose tissue demonstrated the stimulation of inflammatory markers in males, but not females, with obesity. Obese females displayed increased expression of genes involved in the glucocorticoid axis and energy sensing in perirenal-abdominal, but not omental, adipose tissue, indicating a depot-specific mechanism that may be protective from the adverse effects of metabolic dysfunction and inflammation. In conclusion, young males are at a greater risk than females to the onset of comorbidities associated with juvenile-onset obesity. These sex-specific differences in cortisol and adipose tissue could explain the earlier onset of the metabolic-related diseases in males compared with females after obesity
Social Effects in Science: Modelling Agents for a Better Scientific Practice
Science is a fundamental human activity and we trust its results because it
has several error-correcting mechanisms. Its is subject to experimental tests
that are replicated by independent parts. Given the huge amount of information
available, scientists have to rely on the reports of others. This makes it
possible for social effects to influence the scientific community. Here, an
Opinion Dynamics agent model is proposed to describe this situation. The
influence of Nature through experiments is described as an external field that
acts on the experimental agents. We will see that the retirement of old
scientists can be fundamental in the acceptance of a new theory. We will also
investigate the interplay between social influence and observations. This will
allow us to gain insight in the problem of when social effects can have
negligible effects in the conclusions of a scientific community and when we
should worry about them.Comment: 14 pages, 5 figure
What young people want from health-related online resources: a focus group study
The growth of the Internet as an information source about health, particularly amongst young people, is well established. The aim of this study was to explore young people's perceptions and experiences of engaging with health-related online content, particularly through social media websites. Between February and July 2011 nine focus groups were facilitated across Scotland with young people aged between 14 and 18 years. Health-related user-generated content seems to be appreciated by young people as a useful, if not always trustworthy, source of accounts of other people's experiences. The reliability and quality of both user-generated content and official factual content about health appear to be concerns for young people, and they employ specialised strategies for negotiating both areas of the online environment. Young people's engagement with health online is a dynamic area for research. Their perceptions and experiences of health-related content seem based on their wider familiarity with the online environment and, as the online environment develops, so too do young people's strategies and conventions for accessing it
Recommended from our members
Coronary Artery Reperfusion
The effects of coronary artery reperfusion 3 hr after coronary occlusion on contractile function and the development of myocardial damage at 24 hr was studied experimentally. In 14 control and 6 reperfused dogs, relationships between epicardial ST segment elevation 15 min after coronary occlusion and myocardial creatine phosphokinase activity (CPK) and histologic appearance 24 hr later were examined. The electrocardiograms were recorded from 10 to 15 sites on the left ventricular epicardium and transmural samples for CPK and histology were obtained from the same sites where epicardial electrocardiograms had been recorded. An inverse relation existed between ST segment elevation (mv) 15 min after occlusion and log CPK activity (IU/ mg of protein) 24 hr later, log CPK = - 0.06ST + 1.26. In dogs subjected to coronary artery reperfusion, there was significantly less CPK depression (log CPK = - 0.01ST + 1.31, [P < 0.01]) than that expected from the control group. In the control group 97% of specimens showing ST segment elevations over 2 mv at 15 min showed abnormal histology 24 hr later. In contrast, in the reperfused group 43% of sites exhibiting elevated ST segment at 15 min showed abnormal histology 24 hr later. In six additional dogs it was shown that the paradoxical movement of the left ventricular wall could be reversed within 1 hr of perfusion. Therefore, by enzymatic and histologic criteria, as well as by functional assessment, coronary artery reperfusion 3 hr after occlusion resulted in salvage of myocardial tissue
- …