805 research outputs found
Adiabatic hyperspherical study of triatomic helium systems
The 4He3 system is studied using the adiabatic hyperspherical representation.
We adopt the current state-of-the-art helium interaction potential including
retardation and the nonadditive three-body term, to calculate all low-energy
properties of the triatomic 4He system. The bound state energies of the 4He
trimer are computed as well as the 4He+4He2 elastic scattering cross sections,
the three-body recombination and collision induced dissociation rates at finite
temperatures. We also treat the system that consists of two 4He and one 3He
atoms, and compute the spectrum of the isotopic trimer 4He2 3He, the 3He+4He2
elastic scattering cross sections, the rates for three-body recombination and
the collision induced dissociation rate at finite temperatures. The effects of
retardation and the nonadditive three-body term are investigated. Retardation
is found to be significant in some cases, while the three-body term plays only
a minor role for these systems.Comment: 24 pages 6 figures Submitted to Physical Review
An order parameter equation for the dynamic yield stress in dense colloidal suspensions
We study the dynamic yield stress in dense colloidal suspensions by analyzing
the time evolution of the pair distribution function for colloidal particles
interacting through a Lennard-Jones potential. We find that the equilibrium
pair distribution function is unstable with respect to a certain anisotropic
perturbation in the regime of low temperature and high density. By applying a
bifurcation analysis to a system near the critical state at which the stability
changes, we derive an amplitude equation for the critical mode. This equation
is analogous to order parameter equations used to describe phase transitions.
It is found that this amplitude equation describes the appearance of the
dynamic yield stress, and it gives a value of 2/3 for the shear thinning
exponent. This value is related to the mean field value of the critical
exponent in the Ising model.Comment: 8 pages, 2 figure
Cold three-body collisions in hydrogen-hydrogen-alkali atomic system
We have studied hydrogen-hydrogen-alkali three-body systems in the adiabatic
hyperspherical representation. For the spin-stretched case, there exists a
single H molecular state when is one of the bosonic alkali atoms:
Li, Na, K, Rb and Cs. As a result, the {\em
only} recombination process is the one that leads to formation of H
molecules, H+H+H+H, and such molecules will be stable
against vibrational relaxation. We have calculated the collision rates for
recombination and collision induced dissociation as well as the elastic
cross-sections for H+H collisions up to a temperature of 0.5 K, including
the partial wave contributions from = to . We have also found
that there is just one three-body bound state for such systems for
= and no bound states for higher angular momenta.Comment: 10 pages, 5 figures, 4 table
Highly accurate calculations of the rotationally excited bound states in three-body systems
An effective optimization strategy has been developed to construct highly
accurate bound state wave functions in various three-body systems. Our
procedure appears to be very effective for computations of weakly bound states
and various excited states, including rotationally excited states, i.e. states
with . The efficiency of our procedure is illustrated by computations
of the excited states in the and muonic
molecular ions, states in the non-symmetric and
ions and and states in He atom(s)
Diffusive transport in networks built of containers and tubes
We developed analytical and numerical methods to study a transport of
non-interacting particles in large networks consisting of M d-dimensional
containers C_1,...,C_M with radii R_i linked together by tubes of length l_{ij}
and radii a_{ij} where i,j=1,2,...,M. Tubes may join directly with each other
forming junctions. It is possible that some links are absent. Instead of
solving the diffusion equation for the full problem we formulated an approach
that is computationally more efficient. We derived a set of rate equations that
govern the time dependence of the number of particles in each container
N_1(t),N_2(t),...,N_M(t). In such a way the complicated transport problem is
reduced to a set of M first order integro-differential equations in time, which
can be solved efficiently by the algorithm presented here. The workings of the
method have been demonstrated on a couple of examples: networks involving
three, four and seven containers, and one network with a three-point junction.
Already simple networks with relatively few containers exhibit interesting
transport behavior. For example, we showed that it is possible to adjust the
geometry of the networks so that the particle concentration varies in time in a
wave-like manner. Such behavior deviates from simple exponential growth and
decay occurring in the two container system.Comment: 21 pages, 18 figures, REVTEX4; new figure added, reduced emphasis on
graph theory, additional discussion added (computational cost, one
dimensional tubes
Tomographic imaging and scanning thermal microscopy: thermal impedance tomography
The application of tomographic imaging techniques developed for medical applications to the data provided by the scanning thermal microscope will give access to true three-dimensional information on the thermal properties of materials on a mm length scale. In principle, the technique involves calculating and inverting a sensitivity matrix for a uniform isotropic material, collecting ordered data at several modulation frequencies, and multiplying the inverse of the matrix with the data vector. In practice, inversion of the matrix in impractical, and a novel iterative technique is used. Examples from both simulated and real data are given
Individual risk factors associated with exertional heat illness: A systematic review
This is the final version. Available on open access from Wiley via the DOI in this record. Despite the widespread knowledge of exertional heat illness (EHI) and clear guidance for its
prevention, the incidence of EHI remains high. We carried out a systematic review of available
literature evaluating the scientific evidence underpinning the risk factors associated with EHI.
Medline, PsycINFO, SportDiscus and Embase were searched from inception to January 2019 with
no date limitation, with supplementary searches also being performed. Search terms included
permutations of risk and heat illness, with only studies in English included. Study selection,
data extraction and quality assessment, using the QUALSYST tool, were performed by two
independent reviewers. Of 8898 articles identified by the searches, 42 were included in the
systematic review as primary evidence demonstrating a link between a risk factor and EHI. The
quality scores ranged from 57.50 to 100%, and studies were generally considered to be of strong
quality. The majority of risks attributable to EHI were categorized as those associated with lifestyle factors. The findings from the systematic review suggest complex manifestation of EHI through multiple risk factors rather than any one factor in isolation. Further research is needed
to explore the accumulation of risk factors to help in development of effective preventative measures
Recognition of Membrane Sterols by Polyene Antifungals Amphotericin B and Natamycin, A 13C MAS NMR Study
The molecular action of polyene macrolides with antifungal activity, amphotericin B
and natamycin, involves recognition of sterols in membranes. Physicochemical and
functional studies have contributed details to understanding the interactions between
amphotericin B and ergosterol and, to a lesser extent, with cholesterol. Fewer molecular
details are available on interactions between natamycin with sterols. We use solid state
13C MAS NMR to characterize the impact of amphotericin B and natamycin on mixed
lipid membranes of DOPC/cholesterol or DOPC/ergosterol. In cholesterol-containing
membranes, amphotericin B addition resulted in marked increase in both DOPC and
cholesterol 13C MAS NMR linewidth, reflecting membrane insertion and cooperative
perturbation of the bilayer. By contrast, natamycin affects little either DOPC or cholesterol
linewidth but attenuates cholesterol resonance intensity preferentially for sterol core with
lesser impact on the chain. Ergosterol resonances, attenuated by amphotericin B, reveal
specific interactions in the sterol core and chain base. Natamycin addition selectively
augmented ergosterol resonances from sterol core ring one and, at the same time, from
the end of the chain. This puts forward an interaction model similar to the head-to-tail
model for amphotericin B/ergosterol pairing but with docking on opposite sterol faces.
Low toxicity of natamycin is attributed to selective, non-cooperative sterol engagement
compared to cooperative membrane perturbation by amphotericin B
Noise-induced perturbations of dispersion-managed solitons
We study noise-induced perturbations of dispersion-managed solitons by
developing soliton perturbation theory for the dispersion-managed nonlinear
Schroedinger (DMNLS) equation, which governs the long-term behavior of optical
fiber transmission systems and certain kinds of femtosecond lasers. We show
that the eigenmodes and generalized eigenmodes of the linearized DMNLS equation
around traveling-wave solutions can be generated from the invariances of the
DMNLS equations, we quantify the perturbation-induced parameter changes of the
solution in terms of the eigenmodes and the adjoint eigenmodes, and we obtain
evolution equations for the solution parameters. We then apply these results to
guide importance-sampled Monte-Carlo simulations and reconstruct the
probability density functions of the solution parameters under the effect of
noise.Comment: 12 pages, 6 figure
Approximate action-angle variables for the figure-eight and other periodic three-body orbits
We use the maximally permutation symmetric set of three-body coordinates,
that consist of the "hyper-radius" , the
"rescaled area of the triangle" ) and the (braiding) hyper-angle , to analyze the "figure-eight"
choreographic three-body motion discovered by Moore \cite{Moore1993} in the
Newtonian three-body problem. Here are the two
Jacobi relative coordinate vectors. We show that the periodicity of this motion
is closely related to the braiding hyper-angle . We construct an
approximate integral of motion that together with the hyper-angle
forms the action-angle pair of variables for this problem and show that
it is the underlying cause of figure-eight motion's stability. We construct
figure-eight orbits in two other attractive permutation-symmetric three-body
potentials. We compare the figure-eight orbits in these three potentials and
discuss their generic features, as well as their differences. We apply these
variables to two new periodic, but non-choreographic orbits: One has a
continuously rising in time , just like the figure-eight motion, but
with a different, more complex periodicity, whereas the other one has an
oscillating temporal behavior.Comment: 11 pages, 19 figure
- …