470 research outputs found
Spin waves in diluted magnetic quantum wells
We study collective spin excitations in two-dimensional diluted magnetic
semiconductors, placed into external magnetic field. Two coupled modes of the
spin waves (the electron and ion modes) are found to exist in the system along
with a number of the ion spin excitations decoupled from the electron system.
We calculate analytically the spectrum of the waves taking into account the
exchange interaction of itinerant electrons both with each other and with
electrons localized on the magnetic ions. The interplay of these interactions
leads to a number of intriguing phenomena including tunable anticrossing of the
modes and a field-induced change in a sign of the group velocity of the ion
mode
Use of superplastic deformation and diffusion welding to form a tee designed with a complex set of internal stiffening elements
A method is described for making a tee designed with a complex set of internal stiffening elements. The article describes the main stages of the modern process of pneumothermal forming in the superplastic regime with the use of diffusion welding. The production of a tee by superplastic pneumothermal forming after diffusion welding is modeled and the calculated results are presented. © 2013 Springer Science+Business Media New York
Condensation of a tetrahedra rigid-body libration mode in HoBaCo4O7 : the origin of phase transition at 355 K
Rietveld profiles, Moessbauer spectra and x-ray absorption fine structure
(XAFS) were analyzed through the structural phase transition at Ts = 355 K in
HoBaCo4O7. Excess of the oxygen content over O7 was avoided via annealing the
samples in argon flow at 600 degree C. Space groups (S.G.) Pbn21c and P63mc
were used to refine the structure parameters in the low- and high-temperature
phases, respectively. Additionally, the Cmc21 symmetry was considered as a
concurrent model of structure of the low-temperature phase. In the
high-temperature phase, severe anisotropy of thermal motion of the major part
of the oxygen atoms was observed. This anisotropic motion turns to be quenched
as the sample is cooled below Ts. The variation of quadrupole splitting near Ts
is not similar to a steplike anomaly frequently seen at the charge-ordering
transition. We observe instead a dip-like anomaly of the average quadrupole
splitting near Ts. Narrow distribution of the electric field gradient (EFG)
over different cobalt sites is observed and explained on the basis of
point-charge model. XAFS spectra show no evidence of significant difference
between YBaCo4O7 (T > Ts) and HoBaCo4O7 (T < Ts). The origin of the transition
at Ts is ascribed to the condensation of the libration phonon mode associated
with the rigid-body rotational movements of the starlike tetrahedral units, the
building blocks of kagome network. It is shown that the condensation of the
libration mode is not compatible with translation symmetry for the hexagonal
S.G., but compatible for the orthorhombic S.G. The orthorhombic lattice
parameters and EFG components (Vxx, Vyy, Vzz) vary smoothly with temperature at
approaching Ts and closely follow each other.Comment: 13 figure
Effect of the average velocity of the free part of the semifinished product on the process of pneumothermal forming in the superplastic regime
Results are presented from two experiments involving the pneumothermal forming of a cellular product of alloy OT4-1 in the superplastic regime. It was determined that the average velocity of the free part of the semifinished product must be taken into account when using a model in which the stresses depend directly on the deformation rate. © 2013 Springer Science+Business Media New York
The Monte Carlo Event Generator DPMJET-III
A new version of the Monte Carlo event generator DPMJET is presented. It is a
code system based on the Dual Parton Model and unifies all features of the
DTUNUC-2, DPMJET-II and PHOJET 1.12 event generators. DPMJET-III allows the
simulation of hadron-hadron, hadron-nucleus, nucleus-nucleus, photon-hadron,
photon-photon and photon-nucleus interactions from a few GeV up to the highest
cosmic ray energies.Comment: 6 pages, Talk given at the Conference ``Monte Carlo 2000'', Lisbon,
Portugal, 23-26 Oct. 200
Role of magnetic degrees of freedom in a scenario of phase transformations in steel
The diversity of mesostructures formed in steel at cooling from a
high-temperature austenite ("gamma") phase is determined by the interplay of
shear reconstructions of crystal lattice and diffusion of carbon. Combining
first-principles calculations with large-scale phase-field simulations we
demonstrate a decisive role of magnetic degrees of freedom in the formation of
energy relief along the Bain path of "gamma"-"alpha" transformation and, thus,
in this interplay. We show that there is the main factor, namely, the magnetic
state of iron and its evolution with temperature which controls the change in
character of the transformation. Based on the computational results we propose
a simple model which reproduces, in good agreement with experiment, the most
important curves of the phase transformation in Fe-C, namely, the lines
relevant to a start of ferrite, bainite, and martensite transformations.
Phase-field simulations within the model describe qualitatively typical
patterns at these transformations
Investigation of Anti-Relaxation Coatings for Alkali-Metal Vapor Cells Using Surface Science Techniques
Many technologies based on cells containing alkali-metal atomic vapor benefit
from the use of anti-relaxation surface coatings in order to preserve atomic
spin polarization. In particular, paraffin has been used for this purpose for
several decades and has been demonstrated to allow an atom to experience up to
10,000 collisions with the walls of its container without depolarizing, but the
details of its operation remain poorly understood. We apply modern surface and
bulk techniques to the study of paraffin coatings, in order to characterize the
properties that enable the effective preservation of alkali spin polarization.
These methods include Fourier transform infrared spectroscopy, differential
scanning calorimetry, atomic force microscopy, near-edge X-ray absorption fine
structure spectroscopy, and X-ray photoelectron spectroscopy. We also compare
the light-induced atomic desorption yields of several different paraffin
materials. Experimental results include the determination that crystallinity of
the coating material is unnecessary, and the detection of C=C double bonds
present within a particular class of effective paraffin coatings. Further study
should lead to the development of more robust paraffin anti-relaxation
coatings, as well as the design and synthesis of new classes of coating
materials.Comment: 12 pages, 12 figures. Copyright 2010 American Institute of Physics.
This article may be downloaded for personal use only. Any other use requires
prior permission of the author and the American Institute of Physics. The
following article appeared in the Journal of Chemical Physics and may be
found at http://link.aip.org/link/?JCP/133/14470
PLACE OF LOW-MOLECULAR-WEIGHT HEPARINS IN INTENSIVE THERAPY OF HEPATIC INSUFFICIENCY
The practical significance of heparin low-molecular fractions as inhibitors of inflammation and antithrombin III consumption reduction were studied. That is most critical in acute hepatic failure. The study was performed using the low-molecular-weight heparin (Nadroparin calcium) in low (prophylactic) doses of 2000 anti-factor Xa units daily per 1 meter squared in the form of continuous intravenous infusion. The cohort study proved the nadroparin positive effect on carbohydrate and protein metabolism in children with acute poisoning by hepatotoxic poisons, The significant decrease in the quantitative assessment of disseminated intravascular coagulation relative to the comparison group has been revealed, and the decrease in 28-day mortality from 42 to 13 % has been found in children receiving nadroparin. Conclusions are drawn on the feasibility of introducing low molecular weight heparins into the intensive care regimen of liver failure
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