59 research outputs found
Interaction of phonons at superfluid helium-solid interfaces
A new method of obtaining the interaction Hamiltonian of phonons at
superfluid helium-solid interface is proposed in the work. Equations of
hydrodynamic variables are obtained in terms of second quantization if helium
occupies a half-space. The contributions of all processes to the heat flux from
solid to superfluid helium are calculated based on the obtained Hamiltonian.
The angular distribution of phonons emitted by a solid is found in different
processes. It is shown that all the exit angles of superfuild helium phonons
are allowed. The obtained results are compared with experimental data and with
previous theoretical works.Comment: 9 pages, 3 figure
On the low-temperature lattice thermal transport in nanowires
We propose a theory of low temperature thermal transport in nano-wires in the
regime where a competition between phonon and flexural modes governs the
relaxation processes. Starting with the standard kinetic equations for two
different types of quasiparticles we derive a general expression for the
coefficient of thermal conductivity. The underlying physics of thermal
conductance is completely determined by the corresponding relaxation times,
which can be calculated directly for any dispersion of quasiparticles depending
on the size of a system. We show that if the considered relaxation mechanism is
dominant, then at small wire diameters the temperature dependence of thermal
conductivity experiences a crossover from to -dependence.
Quantitative analysis shows reasonable agreement with resent experimental
results.Comment: 12 pages, 3 eps figure
Pressure of thermal excitations in superfluid helium
We find the pressure, due to the thermal excitations of superfluid helium, at
the interface with a solid. The separate contributions of phonons, rotons
and rotons are derived. The pressure due to rotons is shown to be
negative and partially compensates the positive contribution of rotons,
so the total roton pressure is positive but several times less than the
separate and roton contributions. The pressure of the quasiparticle
gas is shown to account for the fountain effect in . An experiment is
proposed to observe the negative pressure due to rotons.Comment: 14 pages, 4 figure
ТЕОРЕТИЧНІ ОСНОВИ ЗБЕРЕЖЕННЯ ЕКОЛОГІЧНОЇ РІВНОВАГИ
Much of the territory of Ukraine is in poor condition due to saturation of the environment by various toxic compounds. Human impacts that affect the level of environmental safety have been increasing constantly. The accumulation of waste has become one of the most important factors of environmental pollution, negative influence on all of its components. The generalized mathematical model of the process of ensuring ecological balance at the macro level – the state level has been devised. Objective function and resource constraints problem of minimizing the deviation from the ecological balance at a fixed time interval has been formulated.Значна частина території України перебуває у екологічно незадовільному стані через перенасичення навколишнього середовища різними токсичними сполуками. Постійно зростає техногенне навантаження, що впливає на рівень екологічної безпеки. Головним завданням на ближчий час має стати мінімізація підвищення рівня антропогенного впливу на довкілля Розроблена узагальнена математична модель процесу забезпечення екологічної рівноваги на макрорівні – рівні держави. Сформульована цільова функція та ресурсні обмеження задачі мінімізації відхилення від екологічної рівноваги на фіксованому часовому інтервалі
Evolution of a pulse of noninteracting quasiparticles with dispersion and initial angular width
The evolution of a pulse of noninteracting quasiparticles, caused by their different velocities
and angular distribution of momenta, is studied theoretically. Equations are found that describe
the shape of the pulse surface at any time. The time of the beginning, end and duration of the density
of the quasiparticle energy flux is determined at a general spatial point. The quasiparticle energy
density is considered at all times and positions, and it is shown that the region of high energy
density, in the middle of the pulse, is equal to the initial energy density under certain conditions.
These theoretical results are discussed in relation to experimental data on the evolution of a pulse
of noninteracting phonons in superfluid helium
Аналіз методів контролю та оцінки радіаційної стійкості на прикладі модельних (Zn-O)-GaP світлодіодів
Introduction and problem statement. Research relevance of most important parameters of LEDs — resistance to ionizing radiation — for their use in civilian hardware, aerospace, nuclear and radioelectronics onboard equipment is shown. Samples and experimental technique. Samples obtaining method for studying of neutron irradiation influence on the LEDs is indicated. The neutron irradiation influence on the basic characteristics (light intensity) given current and voltage is investigated. Experimental results interpretation shows that for this model current radiative component associated with electrons injection in the optically active p-region. Radiative excitons recombination occurs at the (Zn-O)-complexes, the concentration of which is a linear function. An experimental study light intensity dependences of fluens and damage constant finding. Theoretically and experimentally investigated the light intensity dependence of neutron irradiation fluens at given current. The (IV0/IV) dependencies from fluens neutrons with energy >= 0,1 MeV and fixed voltage of 1,65 V is presented. It shown that light intensity reduction while irradiation at the fixed current is much faster than at the fixed voltage. The calculation formula and (IV0/IV) dependence from neutrons fluens for set of 25 LEDs at nominal current 10 mA are received. Conclusions. The neutron irradiation influence with energy above 0,1 and 2,65 MeV on the light intensity red glow (Zn-O)-LEDs is indicated. It shown that damage constant is proportional to the neutrons momentum. The calculated light intensity dependence from fluens at given current is received.В работе исследовано влияние нейтронного облучения с энергией свыше 0,1 и 2,65 МэВ на силу света (Zn-O)-светодиодов с красным цветом свечения. Показа-но, что излучательная компонента тока, связана с инжекцией электронов в оптиче-ски активную р-область с линейным распределением активаторов люминесценции, при заданном напряжении была линейной функцией безызлучательного времени жизни и, следовательно, флуенса нейтронного облучения. На основании изучения вольт-амперных характеристик предложена модель, согласно которой безызлучательная рекомбинация преобладает в высокоомном компенсированном слое, который разделя-ет р-и n-области, где имеет место режим высокого уровня инжекции. Сделан вывод, что константа повреждаемости светодиодов пропорциональна импульсу нейтронов.В роботі досліджено вплив нейтронного опромінення з енергією понад 0,1 і 2,65 МеВ на силу світла (Zn-O)-світлодів з червоним кольором світіння. Показано, що випромінювальна компонента струму, пов'язана з інжекцією електронів в оптично активну р-область з лінійним розподілом активаторів люмінесценції, при заданій напрузі була лінійною функцією безвипромінювального часу життя і, отже, флюенса нейтронного опромінення. На підставі вивчення вольт-амперних характеристик запропонована модель, згідно з якою безвипромінювальна рекомбінація переважає в високоомному компенсованому шарі, що розділяє р-і-n-області, в якій має місце режим високого рівня інжекції. Зроблено висновок, що константа пошкоджуваності світлоділодів пропорційна імпульсу нейтронів
Short-Wave Excitations in Non-Local Gross-Pitaevskii Model
It is shown, that a non-local form of the Gross-Pitaevskii equation allows to
describe not only the long-wave excitations, but also the short-wave ones in
the systems with Bose-condensate. At given parameter values, the excitation
spectrum mimics the Landau spectrum of quasi-particle excitations in superfluid
Helium with roton minimum. The excitation wavelength, at which the roton
minimum exists, is close to the inter-particle interaction range. It is shown,
that the existence domain of the spectrum with a roton minimum is reduced, if
one accounts for an inter-particle attraction.Comment: 5 pages, 5 figures, UJP style; presented at Bogolyubov Kyiv
Conference "Modern Problems of Theoretical and Mathematical Physics",
September 15-18, 200
Epidemiological analysis of the lyme borreliosis incidence in Rostov region
Purpose: to conduct an epidemiological analysis of the Lyme borreliosis incidence in Rostov region to determine the modern nosoareal and to identify the characteristics of the epidemic process in clinical practice.Materials and methods: the analysis of incidence was performed according to the data provided by the Center for Hygiene and Epidemiology in Rostov Region with the use of the traditional methods of retrospective and operational analysis. For data processing we used generally accepted methods of variational statistics.Results: the level and the long-term dynamics of incidence of Lyme borreliosis (LB) in Rostov region during the period from 2012 to 2018 have been analyzed. It was determinated that human infection occurs in natural, mixed and anthropurgic foci, with an obvious seasonal character - increasing in May-July. The most affected is working-age population from urban areas. The illness is flowing in erythemal form of moderate severity. We have determined that the modern nosoareal consists of 22 administrative territories of the region.Conclusion: The obtained data indicate relevance and necessity for proper clinical and epidemiological researches in the study of Lyme borreliosis in Rostov region
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