98 research outputs found
Investigation of the proportional discharge mechanism in nonelectronegative gases
A shape of the signals in proportional chamber with preamplification gap and
electron component extraction from proportional discharge has been
investigated. It was shown for Penning mixtures that in proportional discharge
besides the primary avalanches there is also the tail of secondary avalanches
caused by metastable and nonmetastable Penning effects. For different mixtures
of gases the duration of the signals caused by secondary avalanches are equal
to ~ n*10 microseconds (n = 1 - 10), the total charge of secondary avalanches
is comparable or larger than in primary avalanches.Comment: 13 pages, 8 figure
Study of Characteristics of the Quasi-spherical Measurement Modules of the Cherenkov Water Calorimeter NEVOD
AbstractThe use of quasi-spherical modules with several PMTs with flat photocathodes in Cherenkov water detectors is discussed. Properties of the response of such modules are examined. The characteristics of the quasi-spherical module with six PMTs that is used in the Cherenkov water calorimeter NEVOD are considered. The results of studying the isotropy of the amplitude response of this module and the quality of reconstruction of light direction with a single module and with a group of modules are demonstrated
Photoinduced absorption from localized intra-gap states
A model is developed for photoinduced absorption from localized states
observed in femtosecond pump-probe experiments in high-Tc superconductors and
other materials. The dynamics of localized carriers are described in terms of
phenomenological approach similar to that originaly proposed by Rothwarf and
Taylor. Expanding the relaxation rate in powers of the order parameter we have
shown that density of localized carriers is sensitive to Tc. From the analysis
of the experimental data on YBa2Cu3O(7-x) and K0.3MoO3 we conclude that
significant intra-gap density of localized states exists in these materials.
Temperature dependence of the density of photoexcited localized carriers in
underdoped YBa2Cu3O(7-x) and in K0.3MoO3 is consistent with the observation of
the pseudogap above Tc.Comment: 4 pages, 2 figures, acepted for publication in Physica C, invited
poster presented at M2S, Feb. 20 - 25, 2000, Houston, US
Magnetooptics in Gold and Silver NanoSizes Low-Dimensional Objects
The spectra of optical absorption and of magnetic circular dichroism (MCD) have been measured in the 350–1150 nm wavelength range for a set of colloidal solutions containing Au and Ag nanoparticles. The average size of Au nanoparticles was 6 nm and having thiolate coatings with different degrees of chirality. (The average size of Ag nanoparticles was 14 nm and having citrate coatings) The form of absorption and MCD spectra suggests the dipole character of interband transitions involving the 5d–6(sp) for Au orbitals and 4d–5(sp) for Ag orbitals. The absence (within the experimental error) of the MCD spectra dependence on the coating type rules out the hypothesis on the orbital nature of the observed magnetism. We argue that the spin polarization plays the dominant role in the magnetism both for Au and Ag nanoparticles.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3534
Spin state crossover in Co3BO5
We have investigated the spin and oxidation states of Co in Co3BO5 using x-ray magnetic circular dichroism (XMCD) and dc magnetic susceptibility measurements. At low temperatures, XMCD experiments have been performed at the Co K-edge in Co3BO5 and Co2FeBO5 single crystals in the fully ferrimagnetically ordered phase. The Co (K-edge) XMCD signal is found to be related to the Co2+ magnetic sublattices in both compounds, providing strong experimental support for the low-spin (LS) Co3+ scenario. The paramagnetic susceptibility is highly anisotropic. An estimation of the effective magnetic moment in the temperature range 100-250 K correlates well with two Co2+ ions in the high-spin (HS) state and some orbital contribution, while Co3+ remains in the LS state. The crystal structure of the Co3BO5 single crystal has been solved in detail at the T range 296-703 K. The unit cell parameters and volume show anomalies at 500 and 700 K. The octahedral environment of the Co4 site strongly changes with heating. The generalized gradient approximation with Hubbard U correction calculations have revealed that, at low-temperatures, the system is insulating with a band gap of 1.4 eV, and the Co2+ ions are in the HS state, while Co3+ are in the LS state. At high temperatures (T > 700 K), the charge ordering disappears, and the system becomes metallic with all Co ions in 3d7 electronic configuration and HS state. © 2021 American Physical Society
Excitations of a Bose-Einstein condensate in a one-dimensional optical lattice
We investigate the low-lying excitations of a stack of weakly-coupled
two-dimensional Bose-Einstein condensates that is formed by a one-dimensional
optical lattice. In particular, we calculate the dispersion relations of the
monopole and quadrupole modes, both for the ground state as well as for the
case in which the system contains a vortex along the direction of the lasers
creating the optical lattice. Our variational approach enables us to determine
analytically the dispersion relations for an arbitrary number of atoms in every
two-dimensional condensate and for an arbitrary momentum. We also discuss the
feasibility of experimentally observing our results.Comment: 16 pages, 5 figures, minor changes,accepted for publication in Phys.
Rev.
Tunneling of quantum rotobreathers
We analyze the quantum properties of a system consisting of two nonlinearly
coupled pendula. This non-integrable system exhibits two different symmetries:
a permutational symmetry (permutation of the pendula) and another one related
to the reversal of the total momentum of the system. Each of these symmetries
is responsible for the existence of two kinds of quasi-degenerated states. At
sufficiently high energy, pairs of symmetry-related states glue together to
form quadruplets. We show that, starting from the anti-continuous limit,
particular quadruplets allow us to construct quantum states whose properties
are very similar to those of classical rotobreathers. By diagonalizing
numerically the quantum Hamiltonian, we investigate their properties and show
that such states are able to store the main part of the total energy on one of
the pendula. Contrary to the classical situation, the coupling between pendula
necessarily introduces a periodic exchange of energy between them with a
frequency which is proportional to the energy splitting between
quasi-degenerated states related to the permutation symmetry. This splitting
may remain very small as the coupling strength increases and is a decreasing
function of the pair energy. The energy may be therefore stored in one pendulum
during a time period very long as compared to the inverse of the internal
rotobreather frequency.Comment: 20 pages, 11 figures, REVTeX4 styl
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