1,067 research outputs found
Luttinger-liquid-like transport in long InSb nanowires
Long nanowires of degenerate semiconductor InSb in asbestos matrix (wire
diameter is around 50 \AA, length 0.1 - 1 mm) were prepared. Electrical
conduction of these nanowires is studied over a temperature range 1.5 - 350 K.
It is found that a zero-field electrical conduction is a power function of the
temperature with the typical exponent .
Current-voltage characteristics of such nanowires are found to be nonlinear and
at sufficiently low temperatures follows the power law . It
is shown that the electrical conduction of these nanowires cannot be accounted
for in terms of ordinary single-electron theories and exhibits features
expected for impure Luttinger liquid. For a simple approximation of impure LL
as a pure one broken into drops by weak links, the estimated weak-link density
is around per cm.Comment: 5 pages, 2 figure
Properties of quasi-periodic pulsations in solar flares from a single active region
We investigate the properties of a set of solar flares originating from a
single active region (AR) that exhibit QPPs, and look for signs of the QPP
periods relating to AR properties. The AR studied, best known as NOAA 12192,
was unusually long-lived and produced 181 flares. Data from the GOES, EVE,
Fermi, Vernov and NoRH observatories were used to determine if QPPs were
present in the flares. For the soft X-ray GOES and EVE data, the time
derivative of the signal was used. Power spectra of the time series data
(without any form of detrending) were inspected, and flares with a peak above
the 95% confidence level in the spectrum were labelled as having candidate
QPPs. The confidence levels were determined taking account of uncertainties and
the possible presence of red noise. AR properties were determined using HMI
line of sight magnetograms. A total of 37 flares (20% of the sample) show good
evidence of having QPPs, and some of the pulsations can be seen in data from
multiple instruments and in different wavebands. The QPP periods show a weak
correlation with the flare amplitude and duration, but this may be due to an
observational bias. A stronger correlation was found between the QPP period and
duration of the QPP signal, which can be partially but not entirely explained
by observational constraints. No correlations were found with the AR area,
bipole separation, or average magnetic field strength. The fact that a
substantial fraction of the flare sample showed evidence of QPPs using a strict
detection method with minimal processing of the data demonstrates that these
QPPs are a real phenomenon, which cannot be explained by the presence of red
noise or the superposition of multiple unrelated flares. The lack of
correlation between the QPP periods and AR properties implies that the
small-scale structure of the AR is important, and/or that different QPP
mechanisms act in different cases.Comment: 23 pages, 57 figures. Accepted for publication by Astronomy &
Astrophysic
Diffusion and Transport Coefficients in Synthetic Opals
Opals are structures composed of the closed packing of spheres in the size
range of nano-to-micro meter. They are sintered to create small necks at the
points of contact. We have solved the diffusion problem in such structures. The
relation between the diffusion coefficient and the termal and electrical
conductivity makes possible to estimate the transport coefficients of opal
structures. We estimate this changes as function of the neck size and the
mean-free path of the carriers. The theory presented is also applicable to the
diffusion problem in other periodic structures.Comment: Submitted to PR
Numerical model of Electron Cyclotron Resonance Ion Source
Important features of Electron Cyclotron Resonance Ion Source (ECRIS)
operation are accurately reproduced with a numerical code. The code uses the
particle-in-cell technique to model a dynamics of ions in ECRIS plasma. It is
shown that gas dynamical ion confinement mechanism is sufficient to provide the
ion production rates in ECRIS close to the experimentally observed values.
Extracted ion currents are calculated and compared to the experiment for few
sources. Changes in the extracted ion currents are obtained with varying the
gas flow into the source chamber and the microwave power. Empirical scaling
laws for ECRIS design are studied and the underlying physical effects are
discussed.Comment: 24 pages, 41 figure
Numerical simulations of gas mixing effect in Electron Cyclotron Resonance Ion Sources
The particle-in-cell MCC code NAM-ECRIS is used to simulate the ECRIS plasma
sustained in a mixture of Kr with O2, N2, Ar, Ne and He. The model assumes that
ions are electrostatically confined in ECR zone by a dip in the plasma
potential. Gain in the extracted krypton ion currents is seen for the highest
charge states; the gain is maximized when oxygen is used as the mixing gas. A
special feature of oxygen is that most of singly charged oxygen ions are
produced after dissociative ionization of oxygen molecules with the large
kinetic energy release of around 5 eV per ion. Increased loss rate of energetic
lowly charged ions of the mixing element requires building up of the retarding
potential barrier close to ECR surface to equilibrate electron and ion losses
out of the plasma. In the mixed plasmas, the barrier value is large (~1 V)
compared to the pure Kr plasma (~0.01 V), with the longer confinement times of
krypton ions and with the much higher ion temperatures
On Optical Properties Of Ion Beams Extracted From Electron Cyclotron Resonance Ion Source
Ion extraction from DECRIS-PM source is simulated by using initial
distributions of ions at the extraction aperture obtained with NAM-ECRIS code.
Three-dimensional calculations of plasma emissive surface are done and ions are
traced in the extraction region. The ion beam profiles show strong aberrations
due to shape of plasma meniscus; hollow beam features are reproduced, as well
as changes in profiles for different focusing conditions
Optical properties of small polarons from dynamical mean-field theory
The optical properties of polarons are studied in the framework of the
Holstein model by applying the dynamical mean-field theory. This approach
allows to enlighten important quantitative and qualitative deviations from the
limiting treatments of small polaron theory, that should be considered when
interpreting experimental data. In the antiadiabatic regime, accounting on the
same footing for a finite phonon frequency and a finite electron bandwidth
allows to address the evolution of the optical absorption away from the
well-understood molecular limit. It is shown that the width of the multiphonon
peaks in the optical spectra depends on the temperature and on the frequency in
a way that contradicts the commonly accepted results, most notably in the
strong coupling case. In the adiabatic regime, on the other hand, the present
method allows to identify a wide range of parameters of experimental interest,
where the electron bandwidth is comparable or larger than the broadening of the
Franck-Condon line, leading to a strong modification of both the position and
the shape of the polaronic absorption. An analytical expression is derived in
the limit of vanishing broadening, which improves over the existing formulas
and whose validity extends to any finite-dimensional lattice. In the same
adiabatic regime, at intermediate values of the interaction strength, the
optical absorption exhibits a characteristic reentrant behavior, with the
emergence of sharp features upon increasing the temperature -- polaron
interband transitions -- which are peculiar of the polaron crossover, and for
which analytical expressions are provided.Comment: 16 pages, 6 figure
Determination of technological parameters for continiuous casting of a hollow pipe billet
This article presents a method for calculating the speed of a hollow steel billet continuous casting for the seamless hot-rolled pipes production. As the initial data, used the values of the technological parameters of a round pipe billet production at the Pavlodar branch of LLP âKSP Steelâ and physical modeling data of a hollow aluminum billet continuous casting at the laboratory facility of Toraighyrov University. The recalculation of the modeling results into the actual volumes of industrial production was carried out according to the condition of the similarity criterion of Fourier numbers. The casting speed of a steel hollow billet are determined, the increase of which, compared with a solid billet, amounted to 16 %
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