1,357 research outputs found
Phonon-mediated electron spin phase diffusion in a quantum dot
An effective spin relaxation mechanism that leads to electron spin
decoherence in a quantum dot is proposed. In contrast to the common
calculations of spin-flip transitions between the Kramers doublets, we take
into account a process of phonon-mediated fluctuation in the electron spin
precession and subsequent spin phase diffusion. Specifically, we consider
modulations in the longitudinal g-factor and hyperfine interaction induced by
the phonon-assisted transitions between the lowest electronic states. Prominent
differences in the temperature and magnetic field dependence between the
proposed mechanisms and the spin-flip transitions are expected to facilitate
its experimental verification. Numerical estimation demonstrates highly
efficient spin relaxation in typical semiconductor quantum dots.Comment: 5 pages, 1 figur
Early Life Relict Feature in Peptide Mass Distribution
Molecular mass of a biomolecule is characterized in mass spectroscopy by the monoisitopic mass M~mono~ and the average isotopic mass M~av~. We found that peptide masses mapped on a plane made by two parameters derived from M~mono~ and M~av~ form a peculiar global feature in form of a band-gap 5-7 ppm wide stretching across the whole peptide galaxy, with a narrow (FWHM 0.2 ppm) line in the centre. The a priori probability of such a feature to emerge by chance is less than 1:100. Peptides contributing to the central line have elemental compositions following the rules S=0; Z = (2C - N - H)/2 =0, which nine out of 20 amino acid residues satisfy. The relative abundances of amino acids in the peptides contributing to the central line correlate with the consensus order of emergence of these amino acids, with ancient amino acids being overrepresented in on-line peptides. Thus the central line is a relic of ancient life, and likely a signature of its emergence in abiotic synthesis. The linear correlation between M~av~ and M~mono~ reduces the complexity of polypeptide molecules, which may have increased the rate of their abiotic production. This, in turn may have influenced the selection of these amino acid residues for terrestrial life. Assuming the line feature is not spurious, life has emerged from elements with isotopic abundances very close to terrestrial levels, which rules out most of the Galaxy
On the theory of transport phenomena in ferrofluids. Effect of chain-like aggregates
The paper deals with the theoretical study of the effect of chain-like aggregates on diffusion and magnetophoretic transport in ferrofluids. Analysis shows that the appearance of the chains leads to a strong anisotropy of the diffusion transport-the coefficient of diffusion in the direction of applied magnetic field is significantly more than that in the perpendicular direction. The presence of the chains in a ferrofluid strongly affects the coefficient of the particle magnetophoresis. © 2012 Elsevier B.V. All rights reserved
Shear thickening of dense suspensions due to energy dissipation in lubrication layers between particles
This paper deals with a theoretical study of the shear thickening effects in concentrated suspensions of non-Brownian particles. Our analysis shows that an increase of the shear rate of the suspension flow leads to a decrease of the mean thickness of the gaps between the nearest particles in dense suspensions. In turn, this leads to the growth of energy dissipation in these gaps, which means an increase of the suspension effective viscosity with the shear rate. © 2013 American Physical Society
Structurization of ferrofluids in the absence of an external magnetic field
Structural transformations in a model ferrofluid in the absence of an external magnetic field have been theoretically studied. The results agree with well-known laboratory experiments and computer simulations in showing that, if the concentration of particles and their magnetic interaction energy are below certain critical values, most particles form separate linear chains. If these parameters exceed the critical values, most particles concentrate so as to form branched network structures. The passage from chains to network has a continuous character rather than represents a discontinuous first-order phase transition. © Pleiades Publishing, Inc., 2013
Hydrodynamic Modes in a Trapped Strongly Interacting Fermi Gases of Atoms
The zero-temperature properties of a dilute two-component Fermi gas in the
BCS-BEC crossover are investigated. On the basis of a generalization of the
variational Schwinger method, we construct approximate semi-analytical formulae
for collective frequencies of the radial and the axial breathing modes of the
Fermi gas under harmonic confinement in the framework of the hydrodynamic
theory. It is shown that the method gives nearly exact solutions.Comment: 11 page
Heat exchange within the surrounding biological tissue during magnetic hyperthermia
The paper deals with mathematical modeling and theoretical study of the heat distribution within the surrounding biological tissue during the effect of the magnetic hyperthermia. The mathematical model is formulated and solved numerically by using the finite difference method. The intensity of heat production is used in the present model. The obtained results allow predicting the temperature change in tumor as well as in the surrounding tissue depending on intensity of the tumor heating. © 2020 International Information and Engineering Technology Association.Russian Foundation for Fundamental Investigations, RFFI: 18-08-00178, 19-52-45001Ministry of Science and Higher Education of the Russian FederationThis paper has been supported by RFFI, grants 18-08-00178, 19-52-45001 and the state program of the Ministry of Science and Higher Education of the Russian Federation (theme “Magnet” and Contract No. 02.A03.21.006)
The law of action and reaction for the effective force in a nonequilibrium colloidal system
We study a nonequilibrium Langevin many-body system containing two 'test'
particles and many 'background' particles. The test particles are spatially
confined by a harmonic potential, and the background particles are driven by an
external driving force. Employing numerical simulations of the model, we
formulate an effective description of the two test particles in a
nonequilibrium steady state. In particular, we investigate several different
definitions of the effective force acting between the test particles. We find
that the law of action and reaction does not hold for the total mechanical
force exerted by the background particles, but that it does hold for the
thermodynamic force defined operationally on the basis of an idea used to
extend the first law of thermodynamics to nonequilibrium steady states.Comment: 13 page
Activated Ion Electron Capture Dissociation (AI ECD) of proteins: synchronization of infrared and electron irradiation with ion magnetron motion.
Here, we show that to perform activated ion electron capture dissociation (AI-ECD) in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer equipped with a CO(2) laser, it is necessary to synchronize both infrared irradiation and electron capture dissociation with ion magnetron motion. This requirement is essential for instruments in which the infrared laser is angled off-axis, such as the Thermo Finnigan LTQ FT. Generally, the electron irradiation time required for proteins is much shorter (ms) than that required for peptides (tens of ms), and the modulation of ECD, AI ECD, and infrared multiphoton dissociation (IRMPD) with ion magnetron motion is more pronounced. We have optimized AI ECD for ubiquitin, cytochrome c, and myoglobin; however the results can be extended to other proteins. We demonstrate that pre-ECD and post-ECD activation are physically different and display different kinetics. We also demonstrate how, by use of appropriate AI ECD time sequences and normalization, the kinetics of protein gas-phase refolding can be deconvoluted from the diffusion of the ion cloud and measured on the time scale longer than the period of ion magnetron motion
Separable Structure of Many-Body Ground-State Wave Function
We have investigated a general structure of the ground-state wave function
for the Schr\"odinger equation for identical interacting particles (bosons
or fermions) confined in a harmonic anisotropic trap in the limit of large .
It is shown that the ground-state wave function can be written in a separable
form. As an example of its applications, this form is used to obtain the
ground-state wave function describing collective dynamics for trapped
bosons interacting via contact forces.Comment: J. Phys. B: At. Mol. Opt. Phys. 33 (2000) (accepted for publication
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