Profiles of electrostatic potential across the water-vapor, ice-vapor and ice-water interfaces

Ice-water, water-vapor interfaces and ice surface are studied by molecular dynamics simulations with the SPC/E model of water molecules having the purpose to estimate the profiles of electrostatic potential across the interfaces. We have proposed a methodology for calculating the profiles of electrostatic potential based on a trial particle, which showed good agreement for the case of electrostatic potential profile of the water-vapor interface of TIP4P model calculated in another way. The measured profile of electrostatic potential for the pure ice-water interface decreases towards the liquid bulk region, which is in agreement with simulations of preferential direction of motion of Li$^{+}$ and F$^{-}$ solute ions at the liquid side of the ice-water interface. These results are discussed in connection with the Workman-Reynolds effect.Comment: 7 pages, 5 figure

Pressure-driven flow of oligomeric fluid in nano-channel with complex structure. A dissipative particle dynamics study

We develop a simulational methodology allowing for simulation of the pressure-driven flow in the pore with flat and polymer-modified walls. Our approach is based on dissipative particle dynamics and we combine earlier ideas of fluid-like walls and reverse flow. As a test case we consider the oligomer flow through the pore with flat walls and demonstrate good thermostatting qualities of the proposed method. We found the inhomogeneities in both oligomer shape and alignment across the pore leading to a non-parabolic velocity profiles. The method is subsequently applied to a nano-channel decorated with a polymer brush stripes arranged perpendicularly to the flow direction. At certain threshold value of a flow force we find a pillar-to-lamellar morphological transition, which leads to the brush enveloping the pore wall by a relatively smooth layer. At higher flow rates, the flow of oligomer has similar properties as in the case of flat walls, but for the narrower effective pore size. We observe stretching and aligning of the polymer molecules along the flow near the pore walls.Comment: 14 pages, 12 figure

Direct calculation of interfacial tensions from computer simulation: Results for freely jointed tangent hard sphere chains

We develop a methodology for the calculation of surface free energies based on the probability distribution of a wandering interface. Using a simple extension of the NpT sampling, we allow the interface area to randomly probe the available space and evaluate the surface free energy from histogram analysis and the corresponding average. The method is suitable for studying systems with either continuous or discontinuous potentials, as it does not require explicit evaluation of the virial. The proposed algorithm is compared with known results for the surface tension of Lennard--Jones and Square Well fluid, as well as for the interface tension of a bead--spring polymer model and good agreement is found. We also calculate interfacial tensions of freely jointed tangent hard sphere chains on athermal walls for a wide range of chain lengths and densities. The results are compared with three different theoretical approaches, Scaled Particle Theory, the Yu and Wu density functional theory and an analytical approximation based on the latter approach. Whereas SPT only yields qualitative results, the last two approaches are found to yield very good agreement with simulations.Comment: 20 pages, 6 figures, Phys. Rev. E in press

Density functional approach for inhomogeneous star polymers

We propose microscopic density functional theory for inhomogeneous star polymers. Our approach is based on fundamental measure theory for hard spheres, and on Wertheim's first- and second-order perturbation theory for the interparticle connectivity. For simplicity we consider a model in which all the arms are of the same length, but our approach can be easily extended to the case of stars with arms of arbitrary lengths.Comment: 4 pages, 3 figures, submitte

Scientific Standards and the Regulation of Genetically Modified Insects

Experimental releases of genetically modified (GM) insects are reportedly being evaluated in various countries, including Brazil, the Cayman Islands (United Kingdom), France, Guatemala, India, Malaysia, Mexico, Panama, Philippines, Singapore, Thailand, the United States of America, and Vietnam. GM mosquitoes (Aedes aegypti) have already been released for field trials into inhabited areas in the Cayman Islands (2009–?), Malaysia (2010–2011), and Brazil (2011–2012). Here, we assess the regulatory process in the first three countries permitting releases (Malaysia, US, and the Cayman Islands) in terms of pre-release transparency and scientific quality. We find that, despite 14 US government–funded field trials over the last 9 years (on a moth pest of cotton), there has been no scientific publication of experimental data, and in only two instances have permit applications been published. The world's first environmental impact statement (EIS) on GM insects, produced by US authorities in 2008, is found to be scientifically deficient on the basis that (1) most consideration of environmental risk is too generic to be scientifically meaningful; (2) it relies on unpublished data to establish central scientific points; and (3) of the approximately 170 scientific publications cited, the endorsement of the majority of novel transgenic approaches is based on just two laboratory studies in only one of the four species covered by the document. We find that it is not possible to determine from documents publically available prior to the start of releases if obvious hazards of the particular GM mosquitoes released in Malaysia, the Cayman Islands, and Brazil received expert examination. Simple regulatory measures are proposed that would build public confidence and stimulate the independent experimental studies that environmental risk assessments require. Finally, a checklist is provided to assist the general public, journalists, and lawmakers in determining, from documents issued by regulators prior to the start of releases, whether permit approval is likely to have a scientifically high quality basi

A new procedure for microarray experiments to account for experimental noise and the uncertainty of probe response

Although microarrays are routine analysis tools in biomedical research, theystill yield noisy output that often requires experimental confirmation. Manystudies have aimed at optimizing probe design and statistical analysis totackle this problem. However, less emphasis has been placed on controlling thenoise inherent to the experimental approach. To address this problem, weinvestigate here a procedure that controls for such experimental variance andcombine it with an assessment of probe performance. Two custom arrays were usedto evaluate the procedure: one based on 25mer probes from an Affymetrix designand the other based on 60mer probes from an Agilent design. To assessexperimental variance, all probes were replicated ten times. To assess probeperformance, the probes were calibrated using a dilution series of targetmolecules and the signal response was fitted to an absorption model. We foundthat significant variance of the signal could be controlled by averaging acrossprobes and removing probes that are nonresponsive. Thus, a more reliable signalcould be obtained using our procedure than conventional approaches. We suggestthat once an array is properly calibrated, absolute quantification of signalsbecomes straight forward, alleviating the need for normalization and referencehybridizations.<br

A Revised Design for Microarray Experiments to Account for Experimental Noise and Uncertainty of Probe Response

Background Although microarrays are analysis tools in biomedical research, they are known to yield noisy output that usually requires experimental confirmation. To tackle this problem, many studies have developed rules for optimizing probe design and devised complex statistical tools to analyze the output. However, less emphasis has been placed on systematically identifying the noise component as part of the experimental procedure. One source of noise is the variance in probe binding, which can be assessed by replicating array probes. The second source is poor probe performance, which can be assessed by calibrating the array based on a dilution series of target molecules. Using model experiments for copy number variation and gene expression measurements, we investigate here a revised design for microarray experiments that addresses both of these sources of variance. Results Two custom arrays were used to evaluate the revised design: one based on 25 mer probes from an Affymetrix design and the other based on 60 mer probes from an Agilent design. To assess experimental variance in probe binding, all probes were replicated ten times. To assess probe performance, the probes were calibrated using a dilution series of target molecules and the signal response was fitted to an adsorption model. We found that significant variance of the signal could be controlled by averaging across probes and removing probes that are nonresponsive or poorly responsive in the calibration experiment. Taking this into account, one can obtain a more reliable signal with the added option of obtaining absolute rather than relative measurements. Conclusion The assessment of technical variance within the experiments, combined with the calibration of probes allows to remove poorly responding probes and yields more reliable signals for the remaining ones. Once an array is properly calibrated, absolute quantification of signals becomes straight forward, alleviating the need for normalization and reference hybridizations

School violence, school differences and school discourses

This article highlights one strand of a study which investigated the concept of the violenceresilient school. In six inner-city secondary schools, data on violent incidents in school and violent crime in the neighbourhood were gathered, and compared with school practices to minimise violence, accessed through interviews. Some degree of association between the patterns of behaviour and school practices was found: schools with a wider range of wellconnected practices seemed to have less difficult behaviour. Interviews also showed that the different schools had different organisational discourses for construing school violence, its possible causes and the possible solutions. Differences in practices are best understood in connection with differences in these discourses. Some of the features of school discourses are outlined, including their range, their core metaphor and their silences. We suggest that organisational discourse is an important concept in explaining school effects and school differences, and that improvement attempts could have clearer regard to this concept

First Gale Western Butte Capping-Unit Compositions, and Relationships to Earlier Units Along Curiosity's Traverse

The Curiosity rover has been traversing through the clay-bearing unit (Glen Torridon; GT), approaching Greenheugh pediment, a large, fan-shaped surface surrounding the mouth of Gediz Vallis on the lower slope of Mt. Sharp. The pediment unconformably overlies the underlying bedrock, and is hence younger than units of the Mt. Sharp group. Orbital imaging of the pediment has shown it to have a slightly lower albedo and higher thermal inertia than neighboring units, to be relatively retentive of craters (e.g., erosion resistant), and to exhibit curved bedforms suggestive of lithified eolian bedforms. No diagnostic spectral signature has been observed from orbit. Recent rover positions allowed remote imaging of the contact between Greenheugh pediment and the eroded Murray formation strata below it, showing that the pediment capping material is cross-bedded and relatively thin (1-3 m), and suggesting that the pediment may have been much larger at one time. As Curiosity approached the edge of the pediment, the team investigated two buttes named Central and Western. The latter butte contains dark capping material that initially looked similar to the pediment cap, but close inspection revealed important physical differences. Here we report on compositions from ChemCam of two float rocks that appear to have rolled down from the capping unit, and on potential relation-ships to other targets along the traverse of the rover

Revisiting wetting, freezing, and evaporation mechanisms of water on copper

Wetting of metal surfaces plays an important role in fuel cells, corrosion science, and heat-transfer devices. It has been recently stipulated that Cu surface is hydrophobic. In order to address this issue we use high purity (1 1 1) Cu prepared without oxygen, and resistant to oxidation. Using the modern Fringe Projection Phase-Shifting method of surface roughness determination, together with a new cell allowing the vacuum and thermal desorption of samples, we define the relation between the copper surface roughness and water contact angle (WCA). Next by a simple extrapolation, we determine the WCA for the perfectly smooth copper surface (WCA = 34°). Additionally, the kinetics of airborne hydrocarbons adsorption on copper was measured. It is shown for the first time that the presence of surface hydrocarbons strongly affects not only WCA, but also water droplet evaporation and the temperature of water droplet freezing. The different behavior and features of the surfaces were observed once the atmosphere of the experiment was changed from argon to air. The evaporation results are well described by the theoretical framework proposed by Semenov, and the freezing process by the dynamic growth angle model