66 research outputs found
Polarizable molecular interactions in condensed phase and their equivalent nonpolarizable models
Earlier, using phenomenological approach, we showed that in some cases
polarizable models of condensed phase systems can be reduced to nonpolarizable
equivalent models with scaled charges. Examples of such systems include ionic
liquids, TIPnP-type models of water, protein force fields, and others, where
interactions and dynamics of inherently polarizable species can be accurately
described by nonpolarizable models. To describe electrostatic interactions, the
effective charges of simple ionic liquids are obtained by scaling the actual
charges of ions by a factor of 1/sqrt(eps_el), which is due to electronic
polarization screening effect; the scaling factor of neutral species is more
complicated. Here, using several theoretical models, we examine how exactly the
scaling factors appear in theory, and how, and under what conditions,
polarizable Hamiltonians are reduced to nonpolarizable ones. These models allow
one to trace the origin of the scaling factors, determine their values, and
obtain important insights on the nature of polarizable interactions in
condensed matter systems.Comment: 43 pages, 3 figure
Restoring the full velocity field in the gaseous disk ofthe spiral galaxy NGC 157
We analyse the line-of-sight velocity field of ionized gas in the spiral
galaxy NGC 157 which has been obtained in the H\alpha emission at the 6m
telescope of SAO RAS. The existence of systematic deviations of the observed
gas velocities from pure circular motion is shown. A detailed investigation of
these deviations is undertaken by applying a Fourier analysis of the azimuthal
distributions of the line-of-sight velocities at different distances from the
galactic center. As a result of the analysis, all the main parameters of the
wave spiral pattern are determined: the corotation radius, the amplitudes and
phases of the gas velocity perturbations at different radii, and the velocity
of circular rotation of the disk corrected for the velocity perturbations due
to spiral arms. At a high confidence level, the presence of the two giant
anticyclones in the reference frame rotating with the spiral pattern is shown;
their sizes and the localization of their centers are consistent with the
results of the analytic theory and of numerical simulations. Besides the
anticyclones, the existence of cyclones in residual velocity fields of spiral
galaxies is predicted. In the reference frame rotating with the spiral pattern
these cyclones have to reveal themselves in galaxies where a radial gradient of
azimuthal residual velocity is steeper than that of the rotation velocity
(abridged).Comment: 23 pages including 25 eps-figures. Accepted for publication in A&
The impact of chronic stress on human health
Most people associate stress with negative feelings. This is the physical and psychological response of the body that helps us better cope with a critical situation. The body releases hormones that speed up the heart rate and bring the muscles into full combat readiness. But chronic stress can have severe consequences. Stress can be caused by everyday worries, problems at work, or an accidental quarrel with relatives. More serious life circumstances, such as a doctor's disappointing diagnosis, war, or the death of a loved one, lead to chronic stress. Stress affects a person's emotions, mood, and behavior. No less important, and often more serious, is its effect on the human body
Giant Cyclones in Gaseous Discs of Spiral Galaxies
We report detection of giant cyclonic vortices in the gaseous disc of the
spiral galaxy NGC 3631 in the reference frame rotating with the spiral pattern.
A presence of such structures was predicted by the authors for galaxies, where
the radial gradient of the perturbed velocity exceeds that of the rotational
velocity. This situation really takes place in NGC 3631.Comment: 13 pages, 4 EPS and 3 PS figure
The Locality Problem in Quantum Measurements
The locality problem of quantum measurements is considered in the framework
of the algebraic approach. It is shown that contrary to the currently
widespread opinion one can reconcile the mathematical formalism of the quantum
theory with the assumption of the existence of a local physical reality
determining the results of local measurements. The key quantum experiments:
double-slit experiment on electron scattering, Wheeler's delayed-choice
experiment, the Einstein-Podolsky-Rosen paradox, and quantum teleportation are
discussed from the locality-problem point of view. A clear physical
interpretation for these experiments, which does not contradict the classical
ideas, is given.Comment: Latex, 40 pages, 7 figure
New Angles on Standard Force Fields: Toward a General Approach for Treating Atomic-Level Anisotropy
Nearly all standard force fields
employ the “sum-of-spheres”
approximation, which models intermolecular interactions purely in
terms of interatomic distances. Nonetheless, atoms in molecules can
have significantly nonspherical shapes, leading to interatomic interaction
energies with strong orientation dependencies. Neglecting this “atomic-level
anisotropy” can lead to significant errors in predicting interaction
energies. Herein, we propose a simple, transferable, and computationally
efficient model (MASTIFF) whereby atomic-level orientation dependence
can be incorporated into ab initio intermolecular force fields. MASTIFF
includes anisotropic exchange-repulsion, charge penetration, and dispersion
effects, in conjunction with a standard treatment of anisotropic long-range
(multipolar) electrostatics. To validate our approach, we benchmark
MASTIFF against various sum-of-spheres models over a large library
of intermolecular interactions between small organic molecules. MASTIFF
achieves quantitative accuracy, with respect to both high-level electronic
structure theory and experiment, thus showing promise as a basis for
“next-generation” force field development
Bose-Einstein condensate as a diagnostic tool for an optical lattice formed by 1064 nm laser light
Recently, the thulium atom has been cooled down to the temperature of
Bose-Einstein condensation. While the condensate of the thulium atom has a lot
of applications in quantum simulations and other areas of physics, it can also
serve as a unique diagnostic tool for many atomic experiments. In the present
study, the Bose-Einstein condensate of the thulium atom was successfully
utilized to diagnose an optical lattice and detect unwanted reflections in the
experiments with the 1064 nm optical lattice, which will further be used in a
quantum gas microscope experiment
New Structures in Galactic Disks: Predictions and Discoveries
Original paper can be found at http://www.astrosociety.org/pubs/cs/222-252.html--Copyright Astronomical Society of the Pacific --Our main goal is to review: 1) some physical mechanisms which form the observed structures in galactic disks; 2) the discovery of new galactic structures predicted earlier. Specifically in the first part of the paper we discuss some questions associated with spiral structure. The second part is devoted to the prediction and discovery of giant vortices in gaseous disks of the grand design spiral galaxies using method of reconstruction of the full three-component velocity field from the observed line-of-sight velocity field. In the third part, we give some arguments in favour of existence of the slow bars in the grand design spiral galaxies
Current and emerging opportunities for molecular simulations in structure-based drug design
An overview of the current capabilities and limitations of molecular simulation of biomolecular complexes in the context of computer-aided drug design is provided. Steady improvements in computer hardware coupled with more refined representations of energetics are leading to a new appreciation of the driving forces of molecular recognition. Molecular simulations are poised to more frequently guide the interpretation of biophysical measurements of biomolecular complexes. Ligand design strategies emerge from detailed analyses of computed structural ensembles. The feasibility of routine applications to ligand optimization problems hinges upon successful extensive large scale validation studies and the development of protocols to intelligently automate computations
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