22 research outputs found
An equilibrium thermostatistics of a nonextensive finite system: Canonical distribution and entropy
A simple model is presented to illustrate the equilibrium thermostatistics of a nonentensive finite system. Interaction between the finite system and the reservoir is taken into account as a nonextensive term λ H1H2 in the expression of total energy ( H1 and H2 are the energy of the finite system and the reservoir respectively, λ is nonadditivity parameter). In the present paper, a case with harmonic reservoir potential is considered. Energy probability distribution, average energy, heat capacity and entropy function for energy distribution are derived in different finite systems including those with constant density of state in energy, the ideal gas and the phonon gas. © 2012 Elsevier B.V. All rights reserved
Dynamic nuclear polarization and ESR hole burning in As doped silicon
We present an experimental study of the Dynamic Nuclear Polarization (DNP) of Si-29 nuclei in silicon crystals of natural abundance doped with As in the temperature range 0.1-1 K and in a strong magnetic field of 4.6 T. This ensures a very high degree of electron spin polarization, extremely slow nuclear relaxation and optimal conditions for realization of Overhauser and resolved solid effects. We found that the solid effect DNP leads to the appearance of a pattern of holes and peaks in the ESR line, separated by the super-hyperfine interaction between the donor electron and Si-29 nuclei closest to the donor. On the contrary, the Overhauser effect DNP mainly affects the remote Si-29 nuclei having the weakest interaction with the donor electron. This leads to the appearance of a very narrow (approximate to 3 mG wide) hole in the ESR line. We studied relaxation of the holes after burning, which is caused by the nuclear spin diffusion. Analyzing the dynamics of the hole in the spectrum with a simple one-dimensional diffusion model leads to a value of the diffusion coefficient D = 8(3) x 10(-9) G(2) s(-1). Our data indicate that the spin diffusion is not completely prevented even in the frozen core near the donors. The emergence of the narrow hole after the Overhauser DNP may be explained by a partial "softening" of the frozen core caused by decoupling of the donor electron and remote Si-29 nuclei
Efficient dynamic nuclear polarization of phosphorus in silicon in strong magnetic fields and at low temperatures
© 2014 American Physical Society. Efficient manipulation of nuclear spins is important for utilizing them as qubits for quantum computing. In this work we report record high polarizations of 31P and Si29 nuclear spins in P-doped silicon in a strong magnetic field (4.6 T) and at temperatures below 1 K. We reached 31P nuclear polarization values exceeding 98% after 20 min of pumping the high-field electron spin resonance (ESR) line with a very small microwave power of 0.4 μW. We evaluate that the ratio of the hyperfine-state populations increases by three orders of magnitude after 2 hours of pumping, and an extremely pure nuclear spin state can be created, with less than 0.01 ppb impurities. A negative dynamic nuclear polarization has been observed by pumping the low-field ESR line of 31P followed by the flip-flip cross relaxation, the transition which is fully forbidden for isolated donors. We estimate that while pumping the ESR transitions of 31P also the nuclei of Si29 get polarized, and polarization exceeding 60% has been obtained. We performed measurements of relaxation rates of flip-flop and flip-flip transitions which turned out to be nearly temperature independent. Temperature dependence of the 31P nuclear relaxation was studied down to 0.75 K, below which the relaxation time became too long to be measured. We found that the polarization evolution under pumping and during relaxation deviates substantially from a simple exponential function of time. We suggest that the nonexponential polarization dynamics of 31P donors is mediated by the orientation of Si29 nuclei, which affect the transition probabilities of the forbidden cross-relaxation processes
Search for directional associations between Baikal Gigaton Volume Detector neutrino-induced cascades and high-energy astrophysical sources
Baikal-GVD has recently published its first measurement of the diffuse
astrophysical neutrino flux, performed using high-energy cascade-like events.
We further explore the Baikal-GVD cascade dataset collected in 2018-2022, with
the aim to identify possible associations between the Baikal-GVD neutrinos and
known astrophysical sources. We leverage the relatively high angular resolution
of the Baikal-GVD neutrino telescope (2-3 deg.), made possible by the use of
liquid water as the detection medium, enabling the study of astrophysical point
sources even with cascade events. We estimate the telescope's sensitivity in
the cascade channel for high-energy astrophysical sources and refine our
analysis prescriptions using Monte-Carlo simulations. We primarily focus on
cascades with energies exceeding 100 TeV, which we employ to search for
correlation with radio-bright blazars. Although the currently limited neutrino
sample size provides no statistically significant effects, our analysis
suggests a number of possible associations with both extragalactic and Galactic
sources. Specifically, we present an analysis of an observed triplet of
neutrino candidate events in the Galactic plane, focusing on its potential
connection with certain Galactic sources, and discuss the coincidence of
cascades with several bright and flaring blazars.Comment: 10 pages, 3 figure
Studies of the ambient light of deep Baikal waters with Baikal-GVD
The Baikal-GVD neutrino detector is a deep-underwater neutrino telescope
under construction and recently after the winter 2023 deployment it consists of
3456 optical modules attached on 96 vertical strings. This 3-dimensional array
of photo-sensors allows to observe ambient light in the vicinity of the
Baikal-GVD telescope that is associated mostly with water luminescence. Results
on time and space variations of the luminescent activity are reviewed based on
data collected in 2018-2022
Monitoring of optical properties of deep waters of Lake Baikal in 2021-2022
We present the results of the two-year (2021-2022) monitoring of absorption
and scattering lengths of light with wavelength 400-620 nm within the effective
volume of the deep underwater neutrino telescope Baikal-GVD, which were
measured by a device Baikal-5D No.2. The Baikal-5D No.2. was installed during
the 2021 winter expedition at a depth of 1180 m. The absorption and scattering
lengths were measured every week in 9 spectral points. The device Baikal-5D
No.2 also has the ability to measure detailed scattering and absorption
spectra. The data obtained make it possible to estimate the range of changes in
the absorption and scattering lengths over a sufficiently long period of time
and to investigate the relationship between the processes of changes in
absorption and scattering. An analysis was made of changes in absorption and
scattering spectra for the period 2021-2022
Large neutrino telescope Baikal-GVD: recent status
The Baikal-GVD is a deep-underwater neutrino telescope being constructed in
Lake Baikal. After the winter 2023 deployment campaign the detector consists of
3456 optical modules installed on 96 vertical strings. The status of the
detector and progress in data analysis are discussed in present report. The
Baikal-GVD data collected in 2018-2022 indicate the presence of cosmic neutrino
flux in high-energy cascade events consistent with observations by the IceCube
neutrino telescope. Analysis of track-like events results in identification of
first high-energy muon neutrino candidates. These and other results from
2018-2022 data samples are reviewed in this report
An equilibrium thermostatistics of a nonextensive finite system: Canonical distribution and entropy
A simple model is presented to illustrate the equilibrium thermostatistics of a nonentensive finite system. Interaction between the finite system and the reservoir is taken into account as a nonextensive term λ H1H2 in the expression of total energy ( H1 and H2 are the energy of the finite system and the reservoir respectively, λ is nonadditivity parameter). In the present paper, a case with harmonic reservoir potential is considered. Energy probability distribution, average energy, heat capacity and entropy function for energy distribution are derived in different finite systems including those with constant density of state in energy, the ideal gas and the phonon gas. © 2012 Elsevier B.V. All rights reserved