2,171 research outputs found
Radical re-appraisal of water structure in hydrophilic confinement
The structure of water confined in MCM41 silica cylindrical pores is studied
to determine if confined water really is simply a version of the bulk liquid
which can be substantially supercooled without crystallisation. A combination
of total neutron scattering from the porous silica, both wet and dry,and
computer simulation using a realistic model of the scattering substrate isused.
The water in the pore is divided into three regions: core, interfacial and
overlap. The average local densities of water in these simulations are found to
be about 20% lower than bulk water density, while the density in the core
region is below, but closer to, the bulk density. There is a decrease in both
local and core densities when the temperature is lowered from 298K to 210K. The
radical proposal is made here that water in hydrophilic confinement is under
significant tension, around -100MPa, inside the pore
Comment on "Oxygen as a Site Specific Probe of the Structure of Water and Oxide Materials", PRL 107, 144501 (2011)
A recent paper by Zeidler et al. (PRL 107, 144501 (2011)) describes a neutron
scattering experiment on water in which oxygen isotope substitution is
successfully achieved for the first time. Differences between scattering
patterns with different oxygen isotopes give a combination of the O-O and O-H
(or O-D) structure factors, and the method elegantly minimizes some of the
problematic inelasticity effects associated with neutron scattering from
hydrogen. Particular conclusions of the new work are that the OH bond length in
the light water molecule is about 0.005A longer than the same bond in heavy
water, and that the hydrogen bond peaks in both liquids are at about the same
position. Notwithstanding the substantial progress demonstrated by the new
work, the comparison with our own results (PRL, 101, 065502 (2008)) by Zeidler
et al. is in our opinion misleading.Comment: 2 pages, 1 figure
Parton distribution function for quarks in an s-channel approach
We use an s-channel picture of hard hadronic collisions to investigate the
parton distribution function for quarks at small momentum fraction x, which
corresponds to very high energy scattering. We study the renormalized quark
distribution at one loop in this approach.
In the high-energy picture, the quark distribution function is expressed in
terms of a Wilson-line correlator that represents the cross section for a color
dipole to scatter from the proton. We model this Wilson-line correlator in a
saturation model. We relate this representation of the quark distribution
function to the corresponding representation of the structure function
F_T(x,Q^2) for deeply inelastic scattering
Techniques for QCD calculations by numerical integration
Calculations of observables in quantum chromodynamics are typically performed
using a method that combines numerical integrations over the momenta of final
state particles with analytical integrations over the momenta of virtual
particles. I describe the most important steps of a method for performing all
of the integrations numerically.Comment: 36 pages with 16 postscript figure
Recommended from our members
A republic of consumers: Jo Littler in discussion with Clive Barnett and Kate Soper
Clive Barnett is a human geographer at the Open University and is part of a team working on a project entitled ‘Governing the Subjects and Spaces of Ethical Consumption’. Kate Soper, a professor of philosophy and a cultural theorist based at London Metropolitan University, is working with Lyn Thomas on their ‘Alternative Hedonism and the Theory and Politics of Consumer Culture’ project.1 Jo Littler interviewed them both about the cultural and political implications of the expansion of green, ethical and anti-consumerism
If nonhuman animals can suicide, why don’t they?
An evolutionary analysis suggests that selection is unlikely to have tolerated the capacity for intentional self-killing in nonhuman animals. The potential to escape pain by suicide would have presented a recurrent and severe adaptive problem for an animal with a reproductive future to protect. If the potential for suicide arose in the evolutionary past, anti-suicide mechanisms may have co-evolved, as we believe they have in adult humans. Peña-Guzmán’s (2017) argument that some nonhuman animals can suicide is incomplete without an account of the defences that result in the vast majority opting not to
Orientational correlations in liquid acetone and dimethyl sulfoxide: A comparative study
The structure of acetone and dimethyl sulfoxide in the liquid state is investigated using a combination of neutron diffractionmeasurements and empirical potential structure refinement (EPSR) modeling. By extracting the orientational correlations from the EPSR model, the alignment of dipoles in both fluids is identified. At short distances the dipoles or neighboring molecules are found to be in antiparallel configurations, but further out the molecules tend to be aligned predominately as head to tail in the manner of dipolar ordering. The distribution of these orientations in space around a central molecule is strongly influenced by the underlying symmetry of the central molecule. In both liquids there is evidence for weak methyl hydrogen to oxygen intermolecular contacts, though these probably do not constitute hydrogen bonds as such
Investigations on the structure of dimethyl sulfoxide and acetone in aqueous solution
Aqueous solutions of dimethyl sulfoxide (DMSO) and acetone have been investigated using neutron diffraction augmented with isotopic substitution and empirical potential structure refinement computer simulations. Each solute has been measured at two concentrations—1:20 and 1:2 solute:water mole ratios. At both concentrations for each solute, the tetrahedral hydrogen bonding network of water is largely unperturbed, though the total water molecule coordination number is reduced in the higher 1:2 concentrations. With higher concentrations of acetone, water tends to segregate into clusters, while in higher concentrations of DMSO the present study reconfirms that the structure of the liquid is dominated by DMSO-water interactions. This result may have implications for the highly nonideal behavior observed in the thermodynamic functions for 1:2 DMSO-water solutions
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