1,574 research outputs found
Ge-substitutional defects and the r3xr3 <--> 3x3 transition in alpha--SnGe(111)
The structure and energetics of Ge substitutional defects on the
alpha-Sn/Ge(111) surface are analyzed using Density Functional Theory (DFT)
molecular dynamics (MD) simulations. An isolated Ge defect induces a very local
distortion of the 3x3 reconstruction, confined to a significant downwards
displacement (-0.31 A) at the defect site and a modest upward displacement
(0.05 A) of the three Sn nearest neighbours with partially occupied dangling
bonds. Dynamical fluctuations between the two degenerate ground states yield
the six-fold symmetry observed around a defect in the experiments at room
temperature. Defect-defect interactions are controlled by the energetics of the
deformation of the 3x3 structure: They are negligible for defects on the
honeycomb lattice and quite large for a third defect on the hexagonal lattice,
explaining the low temperature defect ordering.Comment: 4 pages, Revtex, 7 Encapsulated Postscript figures, uses epsf.sty.
Submitted to Phys. Rev. Let
Dose, exposure time, and resolution in Serial X-ray Crystallography
The resolution of X-ray diffraction microscopy is limited by the maximum dose
that can be delivered prior to sample damage. In the proposed Serial
Crystallography method, the damage problem is addressed by distributing the
total dose over many identical hydrated macromolecules running continuously in
a single-file train across a continuous X-ray beam, and resolution is then
limited only by the available molecular and X-ray fluxes and molecular
alignment. Orientation of the diffracting molecules is achieved by laser
alignment. We evaluate the incident X-ray fluence (energy/area) required to
obtain a given resolution from (1) an analytical model, giving the count rate
at the maximum scattering angle for a model protein, (2) explicit simulation of
diffraction patterns for a GroEL-GroES protein complex, and (3) the frequency
cut off of the transfer function following iterative solution of the phase
problem, and reconstruction of an electron density map in the projection
approximation. These calculations include counting shot noise and multiple
starts of the phasing algorithm. The results indicate counting time and the
number of proteins needed within the beam at any instant for a given resolution
and X-ray flux. We confirm an inverse fourth power dependence of exposure time
on resolution, with important implications for all coherent X-ray imaging. We
find that multiple single-file protein beams will be needed for sub-nanometer
resolution on current third generation synchrotrons, but not on fourth
generation designs, where reconstruction of secondary protein structure at a
resolution of 0.7 nm should be possible with short exposures.Comment: 19 pages, 7 figures, 1 tabl
Linkage disequilibrium fine mapping of quantitative trait loci: A simulation study
Recently, the use of linkage disequilibrium (LD) to locate genes which
affect quantitative traits (QTL) has received an increasing
interest, but the plausibility of fine mapping using linkage
disequilibrium techniques for QTL has not been well studied. The main
objectives of this work were to (1) measure the extent and pattern of
LD between a putative QTL and nearby markers in finite populations and
(2) investigate the usefulness of LD in fine mapping QTL in simulated
populations using a dense map of multiallelic or biallelic marker
loci. The test of association between a marker and QTL and the power
of the test were calculated based on single-marker regression
analysis. The results show the presence of substantial linkage
disequilibrium with closely linked marker loci after 100 to 200
generations of random mating. Although the power to test the
association with a frequent QTL of large effect was satisfactory, the
power was low for the QTL with a small effect and/or low
frequency. More powerful, multi-locus methods may be required to map
low frequent QTL with small genetic effects, as well as combining both
linkage and linkage disequilibrium information. The results also
showed that multiallelic markers are more useful than biallelic
markers to detect linkage disequilibrium and association at an equal
distance
Effect of antiseptic gels in the microbiologic colonization of the suture threads after oral surgery
Three different bioadhesive gels were evaluated in a double-blind randomized clinical trial in which microbial growth in the suture thread was assessed following post-surgical application of the aforementioned gels. Also assessed in this trial were, the intensity of post-surgical pain as well as the degree of healing of the patients' surgical wounds. A total of 21 patients (with 42 wisdom teeth) participated in this trial. Chlorhexidine gel, chlorhexidine-chitosan gel, and hyaluronic acid gel were evaluated, with a neutral water-based gel serving as the control agent. The aerobic and facultative anaerobic bacterial recovery on blood agar was lower in the placebo group than in the experimental groups. The most significant difference (p = 0.04) was observed in the chlorhexidine-chitosan group. in which the growth of Blood Agar and Mitis Salivarius Agar was significantly higher than in the placebo group. The intensity of post-surgical pain was very similar among all the groups. Significantly better healing rates were observed in the patients treated with chlorhexidine-chitosan gel when compared with those who used the placebo gel (p = 0.03), and in particular when compared with those patients who used hyaluronic acid gel (p = 0.01). Through our microbiological analyses, we were able to conclude that none of the bioadhesive gels tested resulted in beneficial reductions in the bacterial/fungal populations. However, the healing rates of patients who were treated with chlorhexidine-chitosan were better than those of the patients who used either the placebo gel or the hyaluronic acid gel
The Problem of Non-Renewable Energy Resources in the Production of Physical Capital
This paper studies the possibilities of technical progress to deal with the growth limit problem imposed by the usage of non-renewable energy resources, when physical capital production is relatively more energy-intensive than consumption. In particular, this work presents the conditions under which energy-saving technologies can sustain long-run growth, although energy is produced by means of non-renewable energy resources. The mechanism behind that is energy efficiency
Analysis of platelets from a diet-induced obesity rat model: elucidating platelet dysfunction in obesity
Obesity is one of the main health problems in industrialized countries. The contribution of multiple factors developed in obesity can hardly be modeled in vitro. In this context, the development of animal models mimicking human obesity could be essential. The aim of the present study was to compare platelets from a diet-induced obesity (DIO) rat model with their lean control group in order to elucidate platelet dysfunction mechanisms in obesity and correlate the results with previous data from morbid obese patients. In parallel, we also established a blood collection and platelet isolation methodology to study the DIO rat model at biochemical and functional level. Optimal blood collection was obtained from vena cava and platelet isolation was based on a serial of centrifugations avoiding platelet activation. Our results show that the DIO rat model simulate obesity pathologically since weight gain, fasting glucose and platelet counts are increased in obese rats. Interestingly, platelet levels of the active form of Src (pTyr(419)) showed a tendency to increase in DIO rats pointing towards a potential dysfunction in Src family kinases-related signalling pathways in obesity. Moreover, platelets from DIO rats adhere more to collagen compared with the control group, pointing towards Glycoprotein VI (GPVI) as one of the dysregulated receptors in obesity, in agreement with our recent studies in humans. These results confirm that obesity, in line with human studies, present a platelet dysregulation, and highlight the relevance of considering novel antithrombotic drug targets in these patients, such as GPVI
Exosomes in head and neck cancer. Updating and revisiting
Exosomes have gone from being considered simple containers of intracellular waste substances to be considered important carriers of cellular signals. Its broad capacity to promote tumour growth, both in situ and metastatic, has greatly intensified scientific research on them. In the same way and depending on its content, its tumour suppressive properties have opened a window of light and hope in the fight against cancer. In the present review we try to gather in a simple and understandable way the most relevant knowledge to date on the role of exosomes in oral squamous cell carcinoma, helping to understand their process of formation, release and activity on the tumour microenvironment
Kesterite thin films of Cu2ZnSnS4 obtained by spray pyrolysis
Thin films of Cu2ZnSnS4 CZTS were deposited using the spray pyrolysis method as relatively fast and vacuum free method. Obtained samples were analyzed using the X Ray Fluorescence, grazing incidence X Ray Diffraction and Raman Spectroscopy techniques. Analysis showed close to stoichiometry composition of the films with kesterite type structure but poor crystalline quality and possible existence of secondary phases. To improve the quality of the films, the as prepared layers were annealed in the presence of elemental Sn and S. Comparison of the results before and after annealing showed a strong improvement of the crystalline quality and a significant reduction of concentration of secondary phases of the films without significant change of composition. The measured optical band gap is equal to 1.52 and 1.55 eV in the as prepared and annealed films, respectively. The optical absorption coefficient is found to be gt; 10 4 cm
Leukocyte Associated Immunoglobulin Like Receptor 1 Regulation and Function on Monocytes and Dendritic Cells During Inflammation
Inhibitory receptors are crucial immune regulators and are essential to prevent exacerbated responses, thus contributing to immune homeostasis. Leukocyte associated immunoglobulin like receptor 1 (LAIR-1) is an immune inhibitory receptor which has collagen and collagen domain containing proteins as ligands. LAIR-1 is broadly expressed on immune cells and has a large availability of ligands in both circulation and tissues, implicating a need for tight regulation of this interaction. In the current study, we sought to examine the regulation and function of LAIR-1 on monocyte, dendritic cell (DC) and macrophage subtypes, using different in vitro models. We found that LAIR-1 is highly expressed on intermediate monocytes as well as on plasmacytoid DCs. LAIR-1 is also expressed on skin immune cells, mainly on tissue CD14(+) cells, macrophages and CD1c(+) DCs. In vitro, monocyte and type-2 conventional DC stimulation leads to LAIR-1 upregulation, which may reflect the importance of LAIR-1 as negative regulator under inflammatory conditions. Indeed, we demonstrate that LAIR-1 ligation on monocytes inhibits toll like receptor (TLR)4 and Interferon (IFN)-alpha- induced signals. Furthermore, LAIR-1 is downregulated on GM-CSF and IFN-gamma monocyte-derived macrophages and monocyte-derived DCs. In addition, LAIR-1 triggering during monocyte derived-DC differentiation results in significant phenotypic changes, as well as a different response to TLR4 and IFN-alpha stimulation. This indicates a role for LAIR-1 in skewing DC function, which impacts the cytokine expression profile of these cells. In conclusion, we demonstrate that LAIR-1 is consistently upregulated on monocytes and DC during the inflammatory phase of the immune response and tends to restore its expression during the resolution phase. Under inflammatory conditions, LAIR-1 has an inhibitory function, pointing toward to a potential intervention opportunity targeting LAIR-1 in inflammatory conditions
- …