340 research outputs found
Thermal Bogoliubov transformation in nuclear structure theory
Thermal Bogoliubov transformation is an essential ingredient of the thermo
field dynamics -- the real time formalism in quantum field and many-body
theories at finite temperatures developed by H. Umezawa and coworkers. The
approach to study properties of hot nuclei which is based on the extension of
the well-known Quasiparticle-Phonon Model to finite temperatures employing the
TFD formalism is presented. A distinctive feature of the QPM-TFD combination is
a possibility to go beyond the standard approximations like the thermal
Hartree-Fock or the thermal RPA ones.Comment: 8 pages, Proceedings of the International Bogolyubov Conference
"Problems of Theoretical and Mathematical Physics", August 23 -- 27, 2009,
Dubna, Russi
Nonlinear electron transport in normally pinched-off quantum wire
Nonlinear electron transport in normally pinched-off quantum wires was
studied. The wires were fabricated from AlGaAs/GaAs heterostructures with
high-mobility two-dimensional electron gas by electron beam lithography and
following wet etching. At certain critical source-drain voltage the samples
exhibited a step rise of the conductance. The differential conductance of the
open wires was noticeably lower than e^2/h as far as only part of the
source-drain voltage dropped between source contact and saddle-point of the
potential relief along the wire. The latter limited the electron flow injected
to the wire. At high enough source-drain voltages the decrease of the
differential conductance due to the real space transfer of electrons from the
wire in GaAs to the doped AlGaAs layer was found. In this regime the sign of
differential magnetoconductance was changed with reversing the direction of the
current in the wire or the magnetic field, whet the magnetic field lies in the
heterostructure plane and is directed perpendicular to the current. The
dependence of the differential conductance on the magnetic field and its
direction indicated that the real space transfer events were mainly mediated by
the interface scattering.Comment: LaTeX 2e (epl.cls) 6 pages, 3 figure
Microscopic Calculation of Total Ordinary Muon Capture Rates for Medium - Weight and Heavy Nuclei
Total Ordinary Muon Capture (OMC) rates are calculated on the basis of the
Quasiparticle Random Phase Approximation for several spherical nuclei from
90^Zr to 208^Pb. It is shown that total OMC rates calculated with the free
value of the axial-vector coupling constant g_A agree well with the
experimental data for medium-size nuclei and exceed considerably the
experimental rates for heavy nuclei. The sensitivity of theoretical OMC rates
to the nuclear residual interactions is discussed.Comment: 27 pages and 3 figure
A magnetically-induced Coulomb gap in graphene due to electron-electron interactions
Insights into the fundamental properties of graphene's Dirac-Weyl fermions
have emerged from studies of electron tunnelling transistors in which an
atomically thin layer of hexagonal boron nitride (hBN) is sandwiched between
two layers of high purity graphene. Here, we show that when a single defect is
present within the hBN tunnel barrier, it can inject electrons into the
graphene layers and its sharply defined energy level acts as a high resolution
spectroscopic probe of electron-electron interactions in graphene. We report a
magnetic field dependent suppression of the tunnel current flowing through a
single defect below temperatures of 2 K. This is attributed to the
formation of a magnetically-induced Coulomb gap in the spectral density of
electrons tunnelling into graphene due to electron-electron interactions
РАСЧЕТ ГИДРАВЛИЧЕСКИХ ПАРАМЕТРОВ МЕДНЫХ КРИСТАЛЛИЗАТОРОВ СО СЛОЖНЫМ СОЕДИНЕНИЕМ КАНАЛОВ
A mathematical model and algorithm of the hydraulic calculation of the crystallization wall with a complex connection of a periodically repeated system of horizontal and vertical channels are considered. A computer program allowing one to perform the hydraulic calculation of the crystallizer plate having an arbitrary number of channels of various forms and sizes is created based on the developed mathematical model. The possibilities of this software product when designing copper crystallizes to select their geometric parameters and rational regimes of hydraulic operation are shown.Рассмотрены математическая модель и алгоритм гидравлического расчета стенки кристаллизатора со сложным соединением периодически повторяющейся системы горизонтальных и вертикальных каналов. По разработанной математической модели создана компьютерная программа, позволяющая проводить гидравлический расчет стенки кристаллизатора, имеющей произвольное количество каналов различных форм и размеров. Показаны возможности этого программного продукта при конструировании медных кристаллизаторов для выбора их геометрических параметров и рациональных режимов гидравлической работы
Strong fragmentation of low-energy electromagnetic excitation strength in Sn
Results of nuclear resonance fluorescence experiments on Sn are
reported. More than 50 transitions with MeV were
detected indicating a strong fragmentation of the electromagnetic excitation
strength. For the first time microscopic calculations making use of a complete
configuration space for low-lying states are performed in heavy odd-mass
spherical nuclei. The theoretical predictions are in good agreement with the
data. It is concluded that although the E1 transitions are the strongest ones
also M1 and E2 decays contribute substantially to the observed spectra. In
contrast to the neighboring even Sn, in Sn the
component of the two-phonon quintuplet built on top of
the 1/2 ground state is proved to be strongly fragmented.Comment: 4 pages, 3 figure
Symmetry Breaking in Few Layer Graphene Films
Recently, it was demonstrated that the quasiparticle dynamics, the
layer-dependent charge and potential, and the c-axis screening coefficient
could be extracted from measurements of the spectral function of few layer
graphene films grown epitaxially on SiC using angle-resolved photoemission
spectroscopy (ARPES). In this article we review these findings, and present
detailed methodology for extracting such parameters from ARPES. We also present
detailed arguments against the possibility of an energy gap at the Dirac
crossing ED.Comment: 23 pages, 13 figures, Conference Proceedings of DPG Meeting Mar 2007
Regensburg Submitted to New Journal of Physic
Observation of Dispersion in the J=2+ Collective Modes of He-3-B by Nonlinear Acoustic Spectroscopy
Parametric excitation yields new results, which cannot be obtained by conventional linear spectroscopy, on the collective modes in superfluid He-3-B. In our ultrasonic experiments, performed in a chamber with four quartz crystals, we have excited the real squashing (J = 2+) modes by two simultaneous sound waves which are mutually either parallel, orthogonal, or antiparallel. Qualitatively these results are in agreement with the theoretical dispersion relation of the J = 2+ modes, and quantitatively we have been able to extract the collective-mode velocities from the line splittings in zero magnetic field
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