1,800 research outputs found
Wigner-Crystal Formulation of Strong-Coupling Theory for Counter-ions Near Planar Charged Interfaces
We present a new analytical approach to the strong electrostatic coupling
regime (SC), that can be achieved equivalently at low temperatures, high
charges, low dielectric permittivity etc. Two geometries are analyzed in
detail: one charged wall first, and then, two parallel walls at small
distances, that can be likely or oppositely charged. In all cases, one type of
mobile counter-ions only is present, and ensures electroneutrality (salt free
case). The method is based on a systematic expansion around the ground state
formed by the two-dimensional Wigner crystal(s) of counter-ions at the
plate(s). The leading SC order stems from a single-particle theory, and
coincides with the virial SC approach that has been much studied in the last 10
years. The first correction has the functional form of the virial SC
prediction, but the prefactor is different. The present theory is free of
divergences and the obtained results, both for symmetrically and asymmetrically
charged plates, are in excellent agreement with available data of Monte-Carlo
simulations under strong and intermediate Coulombic couplings. All results
obtained represent relevant improvements over the virial SC estimates. The
present SC theory starting from the Wigner crystal and therefore coined Wigner
SC, sheds light on anomalous phenomena like the counter-ion mediated
like-charge attraction, and the opposite-charge repulsion
Performance of the Colorado wind-profiling network, part 1.5A
The Wave Propagation Laboratory (WPL) has operated a network of radar wind Profilers in Colorado for about 1 year. The network consists of four VHF (50-MHz) radars and a UHF (915-MHz) radar. The Platteville VHF radar was developed by the Aeronomy Laboratory (AL) and has been operated jointly by WPL and AL for several years. The other radars were installed between February and May 1983. Experiences with these radars and some general aspects of tropospheric wind measurements with Doppler radar are discussed
Vortex Solutions in Two-Higgs-Doublet Systems
We analyze the existence of string-like defects in a two-Higgs-doublet system
having as gauge group. We are
able to show that, when certain relations among the parameters hold, these
configurations satisfy a set of first order differential equations (Bogomol'nyi
equations) and their energy is proportional to their topological charge.}Comment: 9 page
Photon Channelling in Foams
Experiments by Gittings, Bandyopadhyay, and Durian [Europhys. Lett.\
\textbf{65}, 414 (2004)] demonstrate that light possesses a higher probability
to propagate in the liquid phase of a foam due to total reflection. The authors
term this observation photon channelling which we investigate in this article
theoretically. We first derive a central relation in the work of Gitting {\em
et al.} without any free parameters. It links the photon's path-length fraction
in the liquid phase to the liquid fraction . We then construct
two-dimensional Voronoi foams, replace the cell edges by channels to represent
the liquid films and simulate photon paths according to the laws of ray optics
using transmission and reflection coefficients from Fresnel's formulas. In an
exact honeycomb foam, the photons show superdiffusive behavior. It becomes
diffusive as soon as disorder is introduced into the foams. The dependence of
the diffusion constant on channel width and refractive index is explained by a
one-dimensional random-walk model. It contains a photon channelling state that
is crucial for the understanding of the numerical results. At the end, we
shortly comment on the observation that photon channelling only occurs in a
finite range of .Comment: 9 pages, minor change
Developing theory in motivational interviewing: academic and practitioner perspectives from MICBT integration
Motivational Interviewing (MI) and Cognitive Behaviour Therapy (CBT) are both
evidence based psychosocial interventions. Motivational interviewing has not
sought to develop its own comprehensive theory (Miller & Rollnick, 2012)
although it has developed hypotheses on why MI works. This project has looks
at what an integration of these two approaches can tell us about motivational
interviewing’s theory, hypothesised mechanisms of action and efficacy. It has set
out to examine and explore existing theory through qualitative research. This
included Semi structured interviews with researchers and practitioners who are
experts in the integration of MI and CBT (MICBT). Their views and existing
literature were used develop understanding about MI efficacy. A critical realist
philosophical framework and Theoretical Thematic analysis was used to explore
and test MI theory. A number of themes around hypothesised mechanisms and
MI theory emerged from both sets of participants. These included psychological
safety, alliance, responding to resistance, acceptance, compassion and positive
emotion. A relational rather than a technical practice was emphasised and the
theory relating to that observed. Theory around Power, its negative and positive
operation in people’s lives arose frequently; as did hypothesised mechanisms
relating to power differentials and MI as a ‘power yielding’ approach. Building on
insights from evolutionary theory, links were made to a more detailed
consideration of the effects of social context on research, practice and the ability
of individuals to make change. This project challenges a narrow-individualised
approach to research and intervention, emphasising the need to take into account
the effects of social inequality and individual social circumstances.
The project has illustrated some of the reality of translating theory into real-world
practice and suggests expanding MI theory so that it is more contextualised. The
centrality of understanding power and power structures may be a useful addition
to an understanding of why MI works. An increased awareness of social context
and its impacts raise questions about how individual and societal level
interventions could work together to improve health behaviour change. Finally, a
number of suggestions for future research are made, including that individualised
interventions need to be evaluated in real-world services, with direct consultation
of and involvement of service users
ChromatoShiny: an interactive R/Shiny App for plotting chromatography profiles [version 2; peer review: 2 approved]
BackgroundUnicorn™ software on Äkta liquid chromatography instruments outputs chromatography profiles of purified biological macromolecules. While the plots generated by the instrument software are very helpful to inspect basic chromatogram properties, they lack a range of useful annotation, customization and export options.MethodsWe use the R Shiny framework to build an interactive app that facilitates the interpretation of chromatograms and the generation of figures for publications.ResultsThe app allows users to fit a baseline, to highlight selected fractions and elution volumes inside or under the plot (e.g. those used for downstream biochemical/biophysical/structural analysis) and to zoom into the plot. The app is freely available at https://ChromatoShiny.bio.ed.ac.uk.ConclusionsIt requires no programming experience, so we anticipate that it will enable chromatography users to create informative, annotated chromatogram plots quickly and simply.FPLC instruments used to purify macromolecules output the UV intensity values over the elution volume. However, the software used with these instruments is not usually used to generate the figures for publication. To facilitate the analysis of chromatograms and generation of publication figures, we developed a web app which is possible to use without programming skills. The app is working on Äkta .txt files and is able to fit a baseline, to highlight fractions on and under the plot and to zoom into the plot. The app is designed for Äkta instruments, but the data from other softwares can be entered in the provided template and plotted accordingly. The app is well suited for plotting many similar plots. The plots can be downloaded in various formats. The app is equipped with instructions and has a user friendly interface. We hope that the app will become a helpful tool for displaying chromatograms from various FPLC softwares
Open/Closed String Topology and Moduli Space Actions via Open/Closed Hochschild Actions
In this paper we extend our correlation functions to the open/closed case.
This gives rise to actions of an open/closed version of the Sullivan PROP as
well as an action of the relevant moduli space. There are several unexpected
structures and conditions that arise in this extension which are forced upon us
by considering the open sector. For string topology type operations, one cannot
just consider graphs, but has to take punctures into account and one has to
restrict the underlying Frobenius algebras. In the moduli space, one first has
to pass to a smaller moduli space which is closed under open/closed duality and
then consider covers in order to account for the punctures
Anomalous temperature dependence of surface tension and capillary waves at liquid gallium
The temperature dependence of surface tension \gamma(T) at liquid gallium is
studied theoretically and experimentally using light scattering from capillary
waves. The theoretical model based on the Gibbs thermodynamics relates the
temperature derivative of \gamma to the surface excess entropy -\Delta S.
Although capillary waves contribute to the surface entropy with a positive sign
the effect of dipole layer on \Delta S is negative. Experimental data collected
at a free Ga surface in the temperature range from 30 to 160 C show that the
temperature derivative of the tension changes sign near 100 C.Comment: 11 pages, 1 Postscript figure, submitted to J. Phys.
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