111 research outputs found
Ionization of hydrogen and hydrogenic ions by antiprotons
Presented here is a description of the ionization of hydrogen and hydrogenic
ions by antiproton-impact, based on very large scale numerical solutions of the
time-dependent Schr\"odinger equation in three spatial dimensions and on
analysis of the topology of the electronic eigenenergy surfaces in the plane of
complex internuclear distance. Comparison is made with other theories and very
recent measurements.Comment: RevTex document, 11 pages, 4 Postscript figures are available from
the authors, in press Phys. Rev. Let
Magneto-intersubband oscillations in two-dimensional systems with an energy spectrum split due to spin-orbit interaction
In the present paper we study magneto-intersubband oscillations (MISO) in HgTe/Hg1-xCdxTe single quantum well with "inverted" and "normal" spectra and in In1-xGaxAs/In1-yAlyAs quantum wells with normal band ordering. For all the cases when two branches of the spectrum arise due to spin-orbit splitting, the mutual arrangement of the antinodes of the Shubnikov-de Haas oscillations and the maxima of MISO occurs opposite to that observed in double quantum wells and in wide quantum wells with two subbands occupied and does not agree with the theoretical predictions. A "toy" model is proposed that explains qualitatively this unusual result. © 2020 American Physical Society.We are grateful to A. A. Bykov, I. V. Gornyi, D. G. Polyakov, O. E. Raichev, M. A. Zudov, and V. Ya. Aleshkin for useful discussions. The work has been supported in part by the Russian Foundation for Basic Research (Grant No. 18-02-00050), by Act 211 Government of the Russian Federation (Agreement No. 02.A03.21.0006), by the Ministry of Science and Higher Education of the Russian Federation (Project No. FEUZ-2020-0054), and by the FASO of Russia (theme “Electron” No. 01201463326)
Electronic Configuration of Yb Compounds
The total energy differences between divalent and trivalent configurations of Yb ions in a number of Yb compounds are studied. Two different band theoretical methods, which differ in the treatment of the localized f electrons, are used. The results show that in all Yb compounds the valence energy differences are equal to the energy needed to localize an f electron. These valence energy differences correlate with the number of f electrons hybridizing with the conduction bands in the trivalent configuration. For divalent YbS, the pressure induced f-electron delocalization implies an intermediate valency, as also indicated by experiment
2.4 Micrometer Cutoff Wavelength AlGaAsSb/InGaAsSb Phototransistors
We report the first AlGaAsSb/InGaAsSb phototransistors with a cutoff wavelength (50% of peak responsivity) of 2.4 micrometers operating in a broad range of temperatures. These devices are also the first AlGaAsSb/InGaAsSb heterojunction phototransistors (HPT) grown by molecular beam epitaxy (MBE). This work is a continuation of a preceding study, which was carried out using LPE (liquid phase epitaxy)-grown AlGaAsSb/InGaAsSb/GaSb heterostructures. Although the LPE-related work resulted in the fabrication of an HPT with excellent parameters [1-4], the room temperature cutoff wavelength of these devices (approximately 2.15 micrometers) was determined by fundamental limitations implied by the close-to-equilibrium growth from Al-In-Ga-As-Sb melts. As the MBE technique is free from the above limitations, AlGaAsSb/InGaAsSb/GaSb heterostructures for HPT with a narrower bandgap of the InGaAsSb base and collector - and hence sensitivity at longer wavelengths (lambda) - were grown in this work. Moreover, MBE - compared to LPE - provides better control over doping levels, composition and width of the AlGaAsSb and InGaAsSb layers, compositional and doping profiles, especially with regard to abrupt heterojunctions. The new MBE-grown HPT exhibited both high responsivity R (up to 2334 A/W for lambda=2.05 micrometers at -20 deg C.) and specific detectivity D* (up to 2.1 x 10(exp 11) cmHz(exp 1/2)/W for lambda=2.05 micrometers at -20 deg C)
Elastic scattering of hadrons
Colliding high energy hadrons either produce new particles or scatter
elastically with their quantum numbers conserved and no other particles
produced. We consider the latter case here. Although inelastic processes
dominate at high energies, elastic scattering contributes considerably (18-25%)
to the total cross section. Its share first decreases and then increases at
higher energies. Small-angle scattering prevails at all energies. Some
characteristic features are seen that provide informationon the geometrical
structure of the colliding particles and the relevant dynamical mechanisms. The
steep Gaussian peak at small angles is followed by the exponential (Orear)
regime with some shoulders and dips, and then by a power-law drop.
Results from various theoretical approaches are compared with experimental
data. Phenomenological models claiming to describe this process are reviewed.
The unitarity condition predicts an exponential fall for the differential cross
section with an additional substructure to occur exactly between the low
momentum transfer diffraction cone and a power-law, hard parton scattering
regime under high momentum transfer. Data on the interference of the Coulomb
and nuclear parts of amplitudes at extremely small angles provide the value of
the real part of the forward scattering nuclear amplitude.
The real part of the elastic scattering amplitude and the contribution of
inelastic processes to the imaginary part of this amplitude (the so-called
overlap function) at nonforward transferred momenta are also discussed.
Problems related to the scaling behavior of the differential cross section are
considered. The power-law regime at highest momentum transfer is briefly
described.Comment: 72 pages, 11 Figures; modified Physics-Uspekhi 56 (2013)
The Hyperspherical Four-Fermion Problem
The problem of a few interacting fermions in quantum physics has sparked
intense interest, particularly in recent years owing to connections with the
behavior of superconductors, fermionic superfluids, and finite nuclei. This
review addresses recent developments in the theoretical description of four
fermions having finite-range interactions, stressing insights that have emerged
from a hyperspherical coordinate perspective. The subject is complicated, so we
have included many detailed formulas that will hopefully make these methods
accessible to others interested in using them. The universality regime, where
the dominant length scale in the problem is the two-body scattering length, is
particularly stressed, including its implications for the famous BCS-BEC
crossover problem Derivations and relevant formulas are also included for the
calculation of challenging few-body processes such as recombination.Comment: 66 pages, 33 figure
Dirac's Observables for the Rest-Frame Instant Form of Tetrad Gravity in a Completely Fixed 3-Orthogonal Gauge
We define the {\it rest-frame instant form} of tetrad gravity restricted to
Christodoulou-Klainermann spacetimes. After a study of the Hamiltonian group of
gauge transformations generated by the 14 first class constraints of the
theory, we define and solve the multitemporal equations associated with the
rotation and space diffeomorphism constraints, finding how the cotriads and
their momenta depend on the corresponding gauge variables. This allows to find
quasi-Shanmugadhasan canonical transformation to the class of 3-orthogonal
gauges and to find the Dirac observables for superspace in these gauges.
The construction of the explicit form of the transformation and of the
solution of the rotation and supermomentum constraints is reduced to solve a
system of elliptic linear and quasi-linear partial differential equations. We
then show that the superhamiltonian constraint becomes the Lichnerowicz
equation for the conformal factor of the 3-metric and that the last gauge
variable is the momentum conjugated to the conformal factor. The gauge
transformations generated by the superhamiltonian constraint perform the
transitions among the allowed foliations of spacetime, so that the theory is
independent from its 3+1 splittings. In the special 3-orthogonal gauge defined
by the vanishing of the conformal factor momentum we determine the final Dirac
observables for the gravitational field even if we are not able to solve the
Lichnerowicz equation. The final Hamiltonian is the weak ADM energy restricted
to this completely fixed gauge.Comment: RevTeX file, 141 page
Narusheniya ritma serdtsa u patsientov s sakharnym diabetom 2 tipa
Цель исследования: оценить распространенность различных НРС у пациентов с СД 2 и определить структурно-функциональные нарушения миокарда, тяжесть и частоту наиболее часто встречаемого НРС при СД 2, а также взаимосвязь с изменениями углеводного обмена и ИР.
Материалы и методы. В исследование было включено 70 пациентов с различными НРС и СД 2 и 41 больной с НРС без СД 2. Определяли содержание общего холестерина и триглицеридов, уровень гликемии, С-пептида, ИР (НОМА2-IR index, норма 1,0) и функциональную способность -клетки поджелудочной железы (HOMA2-%В, нормальное значение 100%), уровень HbA1c (%). Проводили суточное мониторирование ЭКГ. Оценивали тяжесть приступов ФП.
Результаты. Наиболее встречаемым НРС в выборочной группе больных СД 2 была ФП со средней частотой рецидивов. Для пациентов с НРС и СД 2 в сравнении с группой больных НРС без СД 2 характерно более выраженное ремоделирование сердца с преобладанием КГМ ЛЖ. ГИ и ИР, обусловливая активацию симпатической нервной системы, способствуют формированию КГМ ЛЖ у больных с ФП и СД 2. ГИ и ИР, обусловливая активацию симпатической нервной системы, увеличивают частоту встречаемости ФП у пациентов с длительностью СД 2 менее 5 лет и способствуют увеличению тяжести рецидивов ФП при СД 2
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