6,010 research outputs found
Ions in glass forming glycerol: Close correlation of alpha and fast beta relaxation
We provide broadband dielectric loss spectra of glass-forming glycerol with
varying additions of LiCl. The measurements covering frequencies up to 10 THz
extend well into the region of the fast beta process, commonly ascribed to
caged molecule dynamics. Aside of the known variation of the structural alpha
relaxation time and a modification of the excess wing with ion content, we also
find a clear influence on the shallow loss minimum arising from the fast beta
relaxation. Within the framework of mode-coupling theory, the detected
significant broadening of this minimum is in reasonable accord with the found
variation of the alpha-relaxation dynamics. A correlation between
alpha-relaxation rate and minimum position holds for all ion concentrations and
temperatures, even below the critical temperature defined by mode-coupling
theory.Comment: 5 pages, 5 figure
Present state of power electronics circuitry and perspectives of its development
This paper is devoted mainly to the circuitry, because element base is a big independent issue. Let us say a few words about terminology. A modern converter can be rarely represented as a simple device like “rectifier”, “inverter” etc. It usually consists of the combination of several units, performing elementary functions. For such multistage units it makes sense to use a definition of converter “technology”, keeping in mind some actions with electric current for a certain purpose. It is similar to the step activities in chemistry: to take a substance, to heat it etc. After the formulation of a goal and a number of necessary actions it is possible to present a corresponding structure circuit. According to described above we tried to mention basic technologies used in modern power electronics. The perspectives of the electronics in the nearest future are connected with the further improvement of basic technologies, because their combination allows for developing new technologies. In our opinion, there are four such technologies.Стаття присвячена проблемам схемотехніки у сучасній енергетиці. Розглянуто декілька напрямків розробок електроприводів, відмічено їхні переваги та недоліки. Описано сучасні схемотехнічні можливості та перспективні напрямки їхнього подальшого розвитку в Україні
Pressure dependence of the upper critical field of MgB2 and of YNi2B2C
We present measurements of H under pressure in MgB and in
YNiBC. The changes in the shape of H are interpreted within
current models and show the evolution of the main Fermi surface velocities
and electron-phonon coupling parameters with pressure. In
MgB the electron-phonon coupling strength of the nearly two dimensional
band, responsible for the high critical temperature, is more affected
by pressure than the band coupling, and the hole doping of the
band decreases. In YNiBC, the peculiar positive curvature of
H is weakened by pressure.Comment: 5 pages, 5 figure
High-Pressure Amorphous Nitrogen
The phase diagram and stability limits of diatomic solid nitrogen have been
explored in a wide pressure--temperature range by several optical spectroscopic
techniques. A newly characterized narrow-gap semiconducting phase has
been found to exist in a range of 80--270 GPa and 10--510 K. The vibrational
and optical properties of the phase produced under these conditions
indicate that it is largely amorphous and back transforms to a new molecular
phase. The band gap of the phase is found to decrease with pressure
indicating possible metallization by band overlap above 280 GPa.Comment: 5 pages, 4 figure
Inelastic scattering of protons from He and Li in a folding model approach
The proton-inelastic scattering from He and Li nuclei are
studied in a folding model approach. A finite-range, momentum, density and
isospin dependent nucleon-nucleon interaction (SBM) is folded with realistic
density distributions of the above nuclei. The renormalization factors N
and N on the real and volume imaginary part of the folded potentials are
obtained by analyzing the respective elastic scattering data and kept unaltered
for the inelastic analysis at the same energy. The form factors are generated
by taking derivatives of the folded potentials and therefore required
renormalizations. The values are extracted by fitting the p +
He,Li inelastic angular distributions. The present analysis of
p + He inelastic scattering to the 3.57 MeV excited state, including
unpublished forward angle data (RIKEN) confirms L = 2 transition. Similar
analysis of the p + He inelastic scattering angular distribution leading to
the 1.8 MeV (L = 2) excited state fails to satisfactorily reproduce the data.Comment: one LaTeX file, five PostScript figure
Temperature Inversion Symmetry in Gauge-Higgs Unification Models
The temperature inversion symmetry is studied for the
finite temperature effective potential of the N=1, , supersymmetric
model, on the orbifold . For the
value of the Wilson line parameter ( breaks to a
), it is found that the effective potential contains a symmetric part
and an anti-symmetric part under , with, . When
(for which, remains unbroken) it is found that the only
contribution to the effective potential that spoils the temperature inversion
symmetry comes from the fermions in the fundamental representation of the gauge
group, with or , parities. This is interesting since it
implies that the bulk effective potential corresponding to models with orbifold
fixed point localized fundamental fermions (and with no bulk fundamental
fermions) has the temperature inversion symmetry.Comment: 21 pages, version accepted for publication in Theoretical and
Mathematical Physic
First-Principles Calculation of the Superconducting Transition in MgB2 within the Anisotropic Eliashberg Formalism
We present a study of the superconducting transition in MgB2 using the
ab-initio pseudopotential density functional method and the fully anisotropic
Eliashberg equation. Our study shows that the anisotropic Eliashberg equation,
constructed with ab-initio calculated momentum-dependent electron-phonon
interaction and anharmonic phonon frequencies, yields an average
electron-phonon coupling constant lambda = 0.61, a transition temperature Tc =
39 K, and a boron isotope-effect exponent alphaB = 0.31 with a reasonable
assumption of mu* = 0.12. The calculated values for Tc, lambda, and alphaB are
in excellent agreement with transport, specific heat, and isotope effect
measurements respectively. The individual values of the electron-phonon
coupling lambda(k,k') on the various pieces of the Fermi surface however vary
from 0.1 to 2.5. The observed Tc is a result of both the raising effect of
anisotropy in the electron-phonon couplings and the lowering effect of
anharmonicity in the relevant phonon modes.Comment: 4 pages, 3 figures, 1 tabl
Pellet charge exchange helium measurement using neutral particle analyzer in large helical device
It is very important to investigate the confinement of alpha particles, which will be produced by nuclear reactions in ITER and fusion reactors. The pellet charge exchange (PCX) measurement is one of the most powerful methods because it can directly provide the profile of the alpha particle energy spectra in a plasma. In the large helical device, PCX using tracer encapsulated solid pellet (TESPEL) has been tried in many hydrogen and helium plasmas, including helium accelerated by using the cyclotron resonance heating. In the PCX, we use the compact neutral particle analyzer without simultaneous mass separation ability. The helium particle measurement can be achieved by the application of voltage in the condenser plate. The scattering of hydrogen particle is carefully considered during the estimation of the helium amount. The radial helium profiles can also be obtained by comparing four TESPEL injection shots with/without higher harmonic fast wave heating and at applied plate voltages for He or H, respectively
The influence of direct -meson production to the determination on the nucleon strangeness asymmetry via dimuon events in neutrino experiments
Experimentally, the production of oppositely charged dimuon events by
neutrino and anti-neutrino deep inelastic scattering (DIS) is used to determine
the strangeness asymmetry inside a nucleon. Here we point out that the direct
production of -meson in DIS may make substantial influence to the
measurement of nucleon strange distributions. The direct -meson production
is via the heavy quark recombination (HQR) and via the light quark
fragmentation from perturbative QCD (LQF-P). To see the influence precisely, we
compute the direct -meson productions via HQR and LQF-P quantitatively and
estimate their corrections to the analysis of the strangeness asymmetry. The
results show that HQR has stronger effect than LQF-P does, and the former may
influence the experimental determination of the nucleon strangeness asymmetry.Comment: 9 latex pages, 7 figure
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