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[en] Thermogravitational convection (Rayleigh–Bénard convection, RBC) is developed in a layer of normal He I heated on the top at temperatures below the maximum point of liquid 4He density T ≤ Tm = 2.178 K. It is determined experimentally that the emergence of RBC in the layer bulk is accompanied by the excitation of a vortex flow on the free He I surface. At the same time, in a cylindrical vessel small vortices form two large-scale vortices (vortex dipole) with time with the sizes limited by the cylindrical vessel diameter. As the liquid temperature increases above Tm, the convective motion in the bulk of a non-uniformly heated layer decays rapidly, and vortex motion on the He I surface also persists. The results of the study of vortex system evolution with time in the absence of RBC (in the absence of energy pumping) have shown that during long-term observation (more than 1300 s) the non-linear interaction between weakly decaying large-scale vortices leads to small vortices emerging on the He I surface. (author)
[en] Full text: The transition between laminar and turbulent flows around a quartz tuning fork oscillating in superfluid 4He and concentrated solutions (5 and 15 % 3He in 4He) with frequency ω in the temperature range 0.3–2.3 K was studied. The temperature dependences of the transition critical velocity vcr amplitude were obtained and it was shown that the ratio vcr ~ √ ηω/ρ with one fitting parameter can be used for describing these dependences in concentrated solutions of 3He in 4He with viscosity η and density ρ, but this ratio does not fulfill for the temperature dependence of vcr of pure 4He in whole studied temperature range. It was also shown that in concentrated solutions 3He–4He, in a contrary to pure 4He, the temperature almost does not affect the value of the flow resistance coefficient in both laminar and turbulent modes. There are constructed the concentration dependences of the flow resistance coefficient in the laminar mode normalized to the effective cross section area of the oscillating body in the 0.5–1 K temperature range. The calculated dependences showed that in the region of low solution concentrations, with x3 < 1 % of 3He, the normalized coefficient weakly depends on the concentration of 3He and can be qualitatively described by the ratio λ/S ~ √ ρηω. In the concentration range with x3 > 1 % of 3He, the coefficient rises sharply and the reason for this increase is currently not understood. In general, the results of the study show that an increase in the concentration of 3He in a solution leads to an increase in its stability with respect to the occurrence of turbulence with an increase in the excitation force of a quartz tuning fork. (author)
[en] This article is devoted to the further development of mathematical models of the process of exhaustion of extracted mineral resources. A new mathematical model is proposed, which allows combining the advantages and getting rid of the disadvantages of previous models. The model uses the transition of the growth rate of fossil resource extraction to a stationary value. The initial known parameters of the model are: the explored residual volume of the fossil resource, the initial volume of the extraction of the resource, the initial growth rate of the extraction of the resource, the rate of decline in the growth rate of production. An example of the application of the proposed model for forecasting production and exhaustion for natural uranium is given.
[ru]Данная статья посвящена развитию математических моделей процесса исчерпания добываемых ископаемых ресурсов. Предложена новая математическая модель, позволившая объединить преимущества и избавиться от недостатков предыдущих моделей. В этой модели используется переход темпа роста добычи ископаемого ресурса к стационарному значению. Исходными известными параметрами являются: разведанный остаточный объем ископаемого ресурса, начальный объем добычи ресурса, начальный темп роста добычи ресурса, показатель спада темпа роста добычи. Приведен пример применения предложенной модели прогнозирования добычи и исчерпания для природного урана.
[en] An analytical model is proposed for studying the effect of surface recombination on the characteristics of a solar cell based on a nanowire with a radial p-n junction formed between its ‘core’ and ‘shell’ of different types of conductivity. When varying over a wide range of shell widths, the effect of surface recombination on such important parameters of a solar cell as short circuit current, open circuit voltage, and the efficiency of solar energy conversation into electrical energy is considered. It is shown that the relatively low open circuit voltage, often observed experimentally in such solar cells, can be caused by significant surface recombination on the sidewall of the nanowire, the role of which increases with decreasing nanowire diameter and increasing surface to volume ratio
[en] The spectrum of spinless modes in the model with SU(2)L × U(1)R symmetric four-quark interactions proposed by Miransky, Tanabashi, and Yamawaki is studied. For simplicity, only the four-fermion interactions of the top and bottom quarks are considered. Spinless modes result from spontaneous symmetry breaking of electroweak interactions and are bound quark–antiquark states associated with two SU(2) doublets of Higgs fields. Their dynamics is described by the effective Lagrangian obtained by the Schwinger–De Witt method. The spectrum is represented by five types of excitations, the masses of which are expressed in terms of the model parameters. It is shown that the model leads to phenomenologically acceptable values both for the quark masses mt = 173 GeV, mb = 4.18 GeV, and for the mass of the standard Higgs state mχ1 = 125 GeV. The masses of particles composing the second Higgs doublet were calculated: mh± = 275 GeV, mχ2 = 346 GeV, mφ0 = 125 GeV. The Nambu sum rule and the conditions for its fulfillment in theories with broken U(1)A symmetry are discussed.
[ru]Изучается спектр бесспиновых мод в модели с SU(2)L × U(1)R симметричными четырехкварковыми взаимодействиями, предложенной Миранским, Танабаши и Ямаваки. Для простоты рассматриваются только четырехфермионные взаимодействия топ- и боттом-кварков. Бесспиновые моды возникают в результате спонтанного нарушения симметрии электрослабых взаимодействий и являются связанными кварк-антикварковыми состояниями, ассоциируемыми с двумя SU(2) -дублетами хиггсовских полей. Их динамика описывается эффективным лагранжианом, полученным методом Швингера–Де Витта. Спектр представлен пятью типами возбуждений, массы которых выражаются через параметры модели. Показано, что модель ведет к феноменологически приемлемым значениям как для масс кварков mt = 173 ГэВ, mb = 4,18 ГэВ, так и для массы стандартного хиггсовского состояния mχ1 = 125 ГэВ. Вычислены массы частиц, составляющих второй хиггсовский дублет: mh± = 275 ГэВ, mχ2 = 346 ГэВ, mφ0 = 125 ГэВ. Обсуждается правило сумм Намбу и условия его выполнения в теориях с нарушенной U(1)A-симметрией.
[en] The total electron state densities are calculated and analyzed for graphene nanoribbon boundaries of various chirality, as well as the local density of states for individual atoms, pertained to such nanoribbons. The presence of sharp resonances near Fermi level in total densities of electron states is demonstrated for the graphene nanostrips with zig-zag boundaries. Noticeably, these resonances emerge only at local densities of atoms pertained to the sublattice directly outward the nearest boundary, i.e., with dangling bonds on the constituent atoms. The semiconducting gaps appear in the spectra of graphene nanobands, which contain the boundaries of armchair chirality with a number of constituent atomic lines either multiple of three or yielding residual one when divided by three. Gap-width depends on the band width only and is the same for all the atoms in the band. Electron spectra of nanostrips with the boundaries of armchair chirality evidence a metallic behavior, if the residual of the number of atomic lines, divided by three, is equal two, though semiconducting gaps on local densities are still manifested for a number of the atoms. (author)
[en] The article describes the experiments carried out from 2018 to 2019 at the DC-60 accelerator complex of Astana branch of the INP (Almaty, Kazakhstan) to develop methods for production of intense beams of multicharged ions of nickel, chrome, silicium, and cobalt with the use of volatile organometallic compounds MIVOC (Metal Ions from Volatile Compounds). As a result, for the first time at the DC-60 cyclotron beams of nickel, chrome, silicium, and cobalt ions were obtained. Acceleration modes of 58Ni11+, 52Cr10+, 28Si5+, and 59Co12+ ions to the energy of 1.75 MeV/nucleon are optimized.
[ru]Дано описание экспериментальных работ по получению высокоинтенсивных пучков ионов металлов из ЭЦР-источника циклотрона ДЦ-60 (Институт ядерной физики, Алма-Ата, Казахстан) с использованием метода испарения металлоорганических соединений MIVOC (Metal Ions from Volatile Compounds). В результате проведенных работ получены пучки ионов никеля, хрома, кремния и кобальта. Проведена оптимизация режимов ускорения полученных пучков ионов до энергии 1,75 МэВ/нуклон.
[en] The observation of a nonstationary thermoelectric effect — a spontaneous electric polarization of a cell with liquid He II under thermal excitation of standing waves of a second sound in it — was confirmed (Fiz. Nizk. Temp. 30, 1321 (2004)). In the temperature range 1.4 K < T < 2 K, the connection of this effect with the thermal and hydrodynamic properties of He II is studied in detail. It has been established that the dependence of the amplitude of the electric potential oscillations on the excitation intensity changes significantly during the transition from the laminar to the turbulent regime of thermal oscillations. The threshold value of the excitation power w = w0(T) was registered: in the region w < w0, the potential oscillations are regular and their amplitude increases in proportion to the power; when w > w0, the electrical response acquires a random character with an increase in fluctuations and an amplitude decreasing to zero, a kind of electromagnetic “noise” is observed. The results of the experiments are compared with the conclusions of the theory of flexoelectric polarization of liquid helium. The polarization of liquid helium upon the excitation of the first sound waves and the shock waves of pressure and temperature is also discussed. (author)
[en] The physical properties of different types of HTSC are analyzed in the two-fluid model of superconducting (SC) state formation depending on the different location of SC slots ∆ and Δ1 in the energy spectra. In this model, when doping with oxygen in CuO2 planes the charge density waves (CDW) formed in the oxygen anion system are transformed into local electron pairs (LEP) by Cu ion oscillations at T * . At Tc < T* LEP create an SC state and a gap Δ1. Besides, there is a restructuring of the p and d bands. The band gap ∆E decreases. At ∆E ∼ Δ1 decaying LEP are transferred from the occupied States of the p band of oxygen anions to the free d subband of Cu ions because of the thermal excitation. The SC state and the d-type gap Δ in the d subband can be connected to the antiferromagnetic (AF) fluctuations. In tunnel experiments without oxygen anions and oscillating Cu ions, the LEP experience strong Coulomb repulsion of electrons. Therefore, the LEP and Δ1 respectively will be strongly distorted in contrast to the slight change in the Cooper pairs of conventional superconductors in such experiments. It seems that the LEP are transitioning into another state, which can be called a state of CDW type with pseudo-gap Σ. It is also necessary to take into account minor changes in the electron pairs and the second gap Δ created by the antiferromagnetic fluctuations. (author)
[en] The temperature dependences of the longitudinal and transverse conductivity of YBa2Cu3O7–δ single crystals irradiated with high-energy electrons were measured. It was found that, in contrast to unirradiated YBa2Cu3O7–δ single crystals, the absolute value of the anisotropy of the normal electrical resistance ρc/ρab significantly decreases with an increase in the number of structural defects in the volume of the experimental sample. In this case, the dependence ρc/ρab(T) is well described both by means of the universal “law 1/2” and the usual exponential expression for thermally activated conductivity. (author)