30,254 research outputs found
On the contact values of the density profiles in an electric double layer using density functional theory
A recently proposed local second contact value theorem [Henderson D., Boda
D., J. Electroanal. Chem., 2005, 582, 16] for the charge profile of an electric
double layer is used in conjunction with the existing Monte Carlo data from the
literature to assess the contact behavior of the electrode-ion distributions
predicted by the density functional theory. The results for the contact values
of the co- and counterion distributions and their product are obtained for the
symmetric valency, restricted primitive model planar double layer for a range
of electrolyte concentrations and temperatures. Overall, the theoretical
results satisfy the second contact value theorem reasonably well, the agreement
with the simulations being semi-quantitative or better. The product of the co-
and counterion contact values as a function of the electrode surface charge
density is qualitative with the simulations with increasing deviations at
higher concentrations.Comment: 10 pages, 8 figure
Struggling to a monumental triumph : Re-assessing the final stages of the smallpox eradication program in India, 1960-1980
The global smallpox program is generally presented as the brainchild of a handful of actors from the WHO headquarters in Geneva and at the agency's regional offices. This article attempts to present a more complex description of the drive to eradicate smallpox. Based on the example of India, a major focus of the campaign, it is argued that historians and public health officials should recognize the varying roles played by a much wider range of participants. Highlighting the significance of both Indian and international field officials, the author shows how bureaucrats and politicians at different levels of administration and society managed to strengthen—yet sometimes weaken—important program components. Centrally dictated strategies developed at WHO offices in Geneva and New Delhi, often in association with Indian federal authorities, were reinterpreted by many actors and sometimes changed beyond recognition
Influence of anisotropic ion shape, asymmetric valency, and electrolyte concentration on structural and thermodynamic properties of an electric double layer
Grand canonical Monte Carlo simulation results are reported for an electric
double layer modelled by a planar charged hard wall, anisotropic shape cations,
and spherical anions at different electrolyte concentrations and asymmetric
valencies. The cations consist of two tangentially tethered hard spheres of the
same diameter, . One sphere is charged while the other is neutral. Spherical
anions are charged hard spheres of diameter . The ion valency asymmetry 1:2
and 2:1 is considered, with the ions being immersed in a solvent mimicked by a
continuum dielectric medium at standard temperature. The simulations are
carried out for the following electrolyte concentrations: 0.1, 1.0 and 2.0 M.
Profiles of the electrode-ion, electrode-neutral sphere singlet distributions,
the average orientation of dimers, and the mean electrostatic potential are
calculated for a given electrode surface charge, , while the contact
electrode potential and the differential capacitance are presented for varying
electrode charge. With an increasing electrolyte concentration, the shape of
differential capacitance curve changes from that with a minimum surrounded by
maxima into that of a distorted single maximum. For a 2:1 electrolyte, the
maximum is located at a small negative value while for 1:2, at a small
positive value.Comment: 10 pages, 6 figure
Double layer for hard spheres with an off-center charge
Simulations for the density and potential profiles of the ions in the planar
electrical double layer of a model electrolyte or an ionic liquid are reported.
The ions of a real electrolyte or an ionic liquid are usually not spheres; in
ionic liquids, the cations are molecular ions. In the past, this asymmetry has
been modelled by considering spheres that are asymmetric in size and/or valence
(viz., the primitive model) or by dimer cations that are formed by tangentially
touching spheres. In this paper we consider spherical ions that are asymmetric
in size and mimic the asymmetrical shape through an off-center charge that is
located away from the center of the cation spheres, while the anion charge is
at the center of anion spheres. The various singlet density and potential
profiles are compared to (i) the dimer situation, that is, the constituent
spheres of the dimer cation are tangentially tethered, and (ii) the standard
primitive model. The results reveal the double layer structure to be
substantially impacted especially when the cation is the counterion. As well as
being of intrinsic interest, this off-center charge model may be useful for
theories that consider spherical models and introduce the off-center charge as
a perturbation.Comment: 11 pages, 7 figure
An extended model of the quantum free-electron laser
Previous models of the quantum regime of operation of the Free Electron Laser
(QFEL) have performed an averaging and the application of periodic boundary
conditions to the coupled Maxwell - Schrodinger equations over short, resonant
wavelength intervals of the interaction. Here, an extended, one-dimensional
model of the QFEL interaction is presented in the absence of any such averaging
or application of periodic boundary conditions, the absence of the latter
allowing electron diffusion processes to be modeled throughout the pulse. The
model is used to investigate how both the steady-state (CW) and pulsed regimes
of QFEL operation are affected. In the steady-state regime it is found that the
electrons are confined to evolve as a 2-level system, similar to the previous
QFEL models. In the pulsed regime Coherent Spontaneous Emission (CSE) due to
the shape of the electron pulse current distribution is shown to be present in
the QFEL regime for the first time. However, unlike the classical case, CSE in
the QFEL is damped by the effects of quantum diffusion of the electron
wavefunction. Electron recoil from the QFEL interaction can also cause a
diffusive drift between the recoiled and non-recoiled parts of the electron
pulse wavefunction, effectively removing the recoiled part from the primary
electron-radiation interaction.Comment: Submitted to Optics Expres
Time and Difficulty with Tasks and Illness Characteristics Among Caregivers of Individuals Receiving Daily Home Hemodialysis
poster abstractEnd Stage Renal Disease (ESRD) affected approximately 594,374 people in 2010. Patients
receiving dialysis often need help with activities of daily living and tasks outside dialysis
treatments. The burden of providing assistance and support for such patients can be
overwhelming for caregivers, regardless of the modality. This study examined several factors
that may be associated with time and difficulty of tasks experienced by caregivers of individuals
receiving daily home hemodialysis (HHD). Examining relationships between caregivers age,
caregiver income, length of time on dialysis, and patient co-morbidities with perceived time and
difficulty with tasks may assist with focusing interventions within specific demographic groups.
The purpose of this study is to examine these relationships. This study used existing data from a
mixed-methods study. The original study examined needs, concerns, strategies, and advice of
daily home hemodialysis caregivers. Participants included 16 caregivers, recruited from a large
daily home hemodialysis program in a Mid-western city. There was no relationship between
length of time the patient was receiving HHD and time or difficulty with tasks. There was no
relationship between age of the caregiver and time or difficulty with tasks. There was no
relationship between income and time or difficulty with tasks. There was no relationship between
the number of patient comorbidities and time or difficulty with tasks. One important limitation of
this study, and possibly the reason that no significant results were discovered, is the small sample
size. This study was designed to look at possible factors that may increase perceived caregiver
burden. Although there were no relationships found between selected demographic or clinical
variables and perceived time expenditure and difficulty with tasks, future research should
examine other variables such as relationship of caregiver to patient, caregiver health and comorbidities,
and level of involvement of home dialysis staff
Bose-Einstein Condensate Driven by a Kicked Rotor in a Finite Box
We study the effect of different heating rates of a dilute Bose gas confined
in a quasi-1D finite, leaky box. An optical kicked-rotor is used to transfer
energy to the atoms while two repulsive optical beams are used to confine the
atoms. The average energy of the atoms is localized after a large number of
kicks and the system reaches a nonequilibrium steady state. A numerical
simulation of the experimental data suggests that the localization is due to
energetic atoms leaking over the barrier. Our data also indicates a correlation
between collisions and the destruction of the Bose-Einstein condensate
fraction.Comment: 7 pages, 8 figure
Foundations of Quantum Discord
This paper summarizes the basics of the notion of quantum discord and how it
relates to other types of correlations in quantum physics. We take the
fundamental information theoretic approach and illustrate our exposition with a
number of simple examples.Comment: 3 pages, special issue edited by Diogo de Oliveira Soares Pinto et a
- …