In this work, a simulation of the CZTSSe (Cu2ZnSn(S,Se)4) solar cell with Al/ZnO:Al/ZnO(i)/CdS/CZTSSe/Mo structure have been studied using the SCAPS-ID (Solar Cell Capacitance Simulator in one Dimension). The simulation results have been validated with real experimental results. Next, a novel structure is proposed in which a back surface field (BSF) layer is inserted in order to boost the solar cell performance, a CZTSSe layer has been used as (BSF) layer. The efficiency of CZTSSe solar cell increases from 12,3 to 15,3 % by inserting a BSF layer. Finally, an optimization of different physical parameters (Thickness and doping concentration) of BSF layer has been done, and the optimum values are determined. In this research work, the proposed structure of CZTSSe solar cells with optimum parameters showed higher functional properties. The maximum value of efficiency achieved was 16,98 % with <$EJ sub sc ~=~36,31> mA/cm<^>2, <$EV sub ac ~=~0,69> V, and FF = 69,60 % under 1,5G AM illumination.

Magnetization, ac initial magnetic susceptibility, resistance, magnetoresistance, thermal expansion and magnetostriction measurements were performed for R_{1 - x}Sr_xMnO₃ (R = Sm, x = 0,33, 0,40, 0,45; R = Nd, x = 0,33, 0,45) compounds. For all compounds in the T_C region we have observed a large volume contraction DELTA V / V approx 0,1 % and unusual behavior of the volume magnetostriction w, namely, a peak of anomalous magnitude of negative volume magnetostriction on the w(T) curve. We have obtained a giant negative volume magnetostriction ~ 5 ^. 10^-4 at a relatively low magnetic field B = 0,9T and ~ 10^-3 at a high magnetic field B = 13T for Sm samples. The magnetostriction of Nd compounds is one order of magnitude less. For all compounds the giant magnetostriction is accompanied by colossal negative magnetoresistance equal to 78, 72, and 44 % at B = 0,9T for Sm compounds with x = 0,33, 0,40, and 0,45, respectively. All of the observed properties are explained in the framework of an electronic phase separation model.

Выяснен вопрос касательно повышения надежности вспомогательных машин электропоездов переменного тока при эксплуатации в реальных условиях. Предложен инженерный метод определения влияния несимметрии питающего напряжения и отклонения его от номинального значения на нагревание изоляции вспомогательных машин. Установлено, что в случае, когда вспомогательные машины электропоездов переменного тока работают при коэффициенте несимметрии напряжений 10 % и более и отклонении питающего напряжения от номинального порядка 0,6 в относительных единицах, то возможен перегрев их изоляции, даже если она будет иметь класс Н. Впервые освещен вопрос о суммарном нагревании изоляции при таких сочетаниях граничных параметров качества энергии, когда каждый из них способствует увеличению нагревания изоляции по сравнению с номинальным режимом системы "вращающийся фазорасщепитель - вспомогательные машины". Проведенные исследования позволяют установить граничные значения параметров качества питающей электроэнергии (коэффициента несимметрии, отклонения питающего напряжения от номинального значения), при которых дополнительный перегрев изоляции данного класса под влиянием указанных факторов не будет превышать установленного значения.

Для обеспечения надежности, безопасности, а самое главное - непрерывности перевозочного процесса, необходимо разрабатывать, внедрять, а затем и усовершенствовать автоматизированные методы диагностики аппаратов, устройств и систем железнодорожного транспорта. Только лишь системы, которые работают в режиме реального времени и передают данные о мгновенном состоянии объектов контроля, могут своевременно обнаружить какие-либо неисправности и таким образом обеспечить дополнительное временя на их устранение работниками железнодорожного транспорта. Стрелочные переводы являются одним из важнейших и ответственных узлов, а поэтому требуют разработки и внедрения подобной системы диагностики. Достижение цели наблюдения и контроля за объектами железнодорожной автоматики в режиме реального времени возможно только с применением автоматизированного процесса диагностирования состояния объектов. Для этого необходимо знать диагностические признаки объекта контроля, по которым определять его состояние в каждый момент времени. Наиболее рациональным способом дистанционной диагностики является анализ формы и спектра тока, протекающего в силовых цепях объектов железнодорожной автоматики. Стрелочные переводы содержат электродвигатели, которые получают питание по электрическим цепям, а форма токовой кривой зависит как от состояния самого электродвигателя, так и от условий технического содержания стрелки. Для исследования и анализа работы стрелочного электродвигателя переменного тока разработана его математическая модель. Проведен расчет параметров и взаимозависимостей между основными показателями, влияющими на работу асинхронной машины. Получены результаты работы модели в виде временных зависимостей формы сигналов токовых кривых от нагрузки на валу двигателя. В процессе моделирования построена модель стрелочного электродвигателя переменного тока, которая удовлетворяет условиям адекватности. На основании построенной модели можно изучать работу электродвигателя в различных режимах работы, записывать и анализировать кривую тока, как реакцию на различные изменения нагрузки на валу.

We have studied the instability of the current flow in a superconducting tape of the second generation and the transition of the tape into the resistive state. Contrary to usually studied quasisteady regimes of the instability development, we consider here the adiabatic case of fast sample heating. Two kinds of measurements of the current-voltage characteristics (CVC) have been performed, specifically, using the tape excitation by a single sine-shaped current pulse <$E I(t)~=~I sub 0> sin (<$E omega t>) with different amplitudes I0 and by a continuous ac current flow. The main results were obtained for the current amplitudes I0 exceeding the critical current value Ic. We have found that the dynamic CVC are practically reversible for low amplitudes, whereas they become irreversible and assume the N-shaped form for higher current amplitudes. The dynamic CVC are found to change radically if the dissipated energy attains some threshold value Wth which is equal to about 5 mJ/cm for our tapes. Once achieving this energy, the tape transits to the resistive state due to a normal domain formation. The development of instability for a continuous ac current flow was studied for a relatively small amplitude when the energy dissipated per one half-cycle is much lower than Wth. Even in this case, the tape transition to the resistive state occurs owing to an effect of energy accumulation (heat pumping). Due to this pumping, the transition takes place after a definite number of ac current periods when the total accumulated energy reaches the same threshold value Wth. The specific features of dynamic CVC

are qualitatively interpreted within an approach where the appearance of the resistive domain is taken into account. Estimations performed on the basis of the CVC agree well with our experimental data. The results obtained can be useful for the design of superconducting fault current limiters.

Індекс рубрикатора НБУВ: В368.31

Рубрики:

Надпровідність. Надпровідники

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 
Повний текст  Наукова періодика України 

We investigated the properties of a system where the itinerant electrons coexist and interact with the preformed local pairs. Using the nonperturbative continuous unitary transformation technique we show that Andreev-type scattering between these charge carriers gives rise to the enhanced diamagnetic response and is accompanied by appearance of the Drude peak inside the pseudogap regime ω ≤ 2Δ_pg. Both effects are caused by the short-range superconducting correlations above the transition temperature T_c. In fact, the residual diamagnetism has been detected by the torque magnetometry in the lanthanum and bismuth cuprate superconductors at temperatures up to ~ 1,5T_c. In this work we show how the superconducting correlations can be observed in the ac and dc conductivity.

The static and dynamic aspects of magnetic behavior of the complex of iron with 1-nitroso-2-naphthol Na[FeO6(C10H6N)3] as a function of temperature, frequency and magnetic field have been analysed. The ac susceptibility (<$E chi sub ac>) and dc magnetization (<$E M sub dc>) were measured over a temperature range of 1,5 - 200 K in external magnetic field up to 90 kOe and over a frequency range of 95 - 2000 Hz. The experimental data indicate the absence of magnetic long range order in this complex. The magnetization does not reach a saturation in field of 90 kOe at 1,5 K. At low temperatures, the following characteristic peculiarities of magnetic behavior of complex studied have been found, namely : cusp-like anomalies in the ac susceptibility and zero field coold (ZFC) magnetization at <$E T sub roman cusp~=~17> K; frequency dependence of the reusp temperature; remanence and time-dependent relaxation of ZFC magnetization. Attempts were made to compare the <$E chi sub ac> and <$E M sub dc> anomalies in complex studied with those of other magnetic systems. Comparison of characteristic peculiarities of magnetic behavior of the spin-glasses and superparamagnets was also performed. Although superparamagnetic behavior should not be completely ruled out as an explanation of the freezing phenomena in sample studied, the analysis of experimental results strongly suggests that the spin-glass-like behavior is a more consistent explanation.

X-ray diffraction and magnetic using dc and ac methods measurements of the polycrystalline and nanosize REMnO3 (RE = Pr, Nd) powdered samples have been performed. The nanosize manganites were synthesized with a sol-gel method at different (800, 850 and <$E900~symbol Р roman C>) temperatures. The average size of synthesized nanoparticles (from 56 to 89 nm) and polycrystalline powders (above 200 nm) was estimated using the x-ray diffraction data. All the compounds studied crystallize in the orthorhombic crystal structure (space group Pnma) at room temperature with smaller values of the lattice parameters in the nanosamples. The temperature-dependent ac magnetic susceptibilities show a sharp high-temperature peak connected with Mn magnetic moments ordering. The low-temperature maximum of magnetic susceptibility is proposed to be due to the polarization of the rareearth sublattice by an effective exchange field of the Mn ordered sublattice. The antiferromagnetic ordering of Mn sublattice and paramagnetic Curie temperatures as well as the magnetic moment values for the nanosize samples were found to be smaller than those for polycrystalline sample.

Індекс рубрикатора НБУВ: В371.236 + В377.3

Рубрики:

Магнітні властивості твердих тіл. Магнетики

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 
Повний текст  Наукова періодика України 

We have studied the temperature dependence of the ac magnetic susceptibility <$Echi (T)~=~chi prime (T)~+~chi symbol Т (T)> of YBCO tapes in a parallel magnetic field in both the Meissner and vortex states. For the vortex state, we have observed two maximums in the <$Echi symbol Т (T)> dependence. The position and the magnitude of one of these maxima are described well by the nonlocal critical state model. The second maximum and corresponding kink in the function <$Echi prime (T)> observed close to the temperature Tc of the superconducting transition are unexpected. The origin of this maximum cannot be explained within the usual notions of the high-temperature superconductivity. We suppose that it is related to some magnetic restructuring in the superconducting layer just above Tc. Our results put a question on the correctness of the interpretation of some previous microwave experiments.

A magnetic nanoparticle in a vortex state is a promising candidate for the information storage. One bit of information corresponds to the upward or downward magnetization of the vortex core (vortex polarity). Generic properties of the vortex polarity switching are insensitive of the way how the vortex dynamics was excited: by an ac magnetic field, or by an electrical current. We study theoretically the switching process and describe in detail its mechanism, which involves the creation and annihilation of an intermediate vortex-antivortex pair.

Measurements of the electrical response of granular Sn-Ge thin films below the superconducting transition temperature are reported. Addition of an external noise to the magnetic field applied to the sample is found to increase the sample voltage response to a small externally applied ac signal. The gain coefficient for this signal as well as the signal-to-noise ratio displays clear maxima at particular noise levels. We interpret these observations as a stochastic resonance in the percolative Josephson media that occurs close to the percolation threshold.

Nanoelectromagnetomechanical systems (NEMMS) open up a new path for the development of high speed autonomous nanoresonators and signal generators that could be used as actuators, for information processing, as elements of quantum computers etc. Those NEMMS that include ferromagnetic layers could be controlled by the electric current due to effects related with spin transfer. In the present paper we discuss another situation when the current-controlled behavior of nanorod that includes an antiferro- (instead of one of ferro-) magnetic layer. We argue that in this case ac spin-polarized current can also induce resonant coupled magnetomechanical oscillations and produce an oscillating magnetization of antiferromagnetic (AFM) layer. These effects are caused by i) spin-transfer torque exerted to AFM at the interface with nonmagnetic spacer and by ii) the effective magnetic field produced by the spin-polarized free electrons due to sd-exchange. The described nanorod with an AFM layer can find an application in magnetometry and as a current-controlled high-frequency mechanical oscillator.

For certain orientations of Josephson junctions between two <$E p sub x>-wave or two <$E d>-wave superconductors, the subgap Andreev bound states produce a <$E 4 pi>-periodic relation between the Josephson current <$E I> and the phase difference <$E phi :~I~inf~sin ( phi "/" 2)>. Consequently, the ac Josephson current has the fractional frequency <$E eV "/" h bar> where <$E V> is the dc voltage. In the tunneling limit, the Josephson current is proportional to the first power (not square) of the electron tunneling amplitude. Thus, the Josephson current between unconventional superconductors is carried by single electrons, rather than by Cooper pairs. The fractional ac Josephson effect can be observed experimentally by measuring frequency spectrum of microwave radiation from the junction.

The single crystal needle shape samples of diamagnetically diluted cobalt ludwigite CoMgGaO2BO3 have been grown by the flux method. The results of x-ray diffraction and both dc and ac magnetic measurements are presented. The unit cell volume undergoes a noticable growth under dilution from 328,31 <$E roman A back 35 up 35 symbol Р sup 3> for the parent compound Co3O2BO3 to 345,46 <$E roman A back 35 up 35 symbol Р sup 3> for CoMgGaO2BO3. The temperature of magnetic transition is considerably lower for the latter compound (25 К against 43 К for Co3O2BO3). The dc magnetization temperature dependencies undergo the splitting of field cooled and zero-field cooled regimes and the ac magnetic susceptibility temperature dependencies are frequency dependent pointing out a possible spin-glass freezing in the magnetic system.

We present the Condon domain phase diagram for a silver single crystal measured in magnetic fields up to 28 T and temperatures down to 1,3 K. A standard ac method with a pickup coil system is used at low frequency for the measurements of the de Haas - van Alphen effect (dHvA). The transition point from the state of homogeneous magnetization to the inhomogeneous Condon domain state (CDS) is found as the point where a small irreversibility in the dHvA magnetization arises, as manifested by an extremely nonlinear response in the pickup voltage showing threshold character. The third harmonic content in the ac response is used to determine with high precision the CDS phase boundary. The experimentally determined Condon domain phase diagram is in good agreement with the theoretical prediction calculated by the standard Lifshitz - Kosevich formula.

Floquet spectrum of electrons in graphene superlattice subjected to the ac electric field was investigated. The ac-field vector was assumed to oscillate perpendicularly to the superlattice axis. In the vicinity of extra Dirac points of superlattice band structure the gap was shown to be dynamically induced by the acfield. Such effects are due to the nonadditivity of the electron spectrum of graphene superlattice.

The effect of acute nitroxoline inhalation on experimental animals was studied. The test was performed on 4 groups of white rats, containing 8 animals, by intranasal administration of 0,2 ml of nitroxoline solution. Animals of the control group were injected with 0,2 ml of 0,9 % NaCl solution. The experimental groups were formed according to the concentration of the single inhalation effect of a substance that corresponded to the suprathreshold, threshold and subthreshold concentrations of the compound in the working zone air concerning the calculated threshold of a single inhalation action. It was determined that acute nitroxoline inhalation effect in the following concentrations - 706,8, 235,6 and 78,5 mg/m<^>3 - did not cause changes in the blood hemogram, biochemical parameters and circulating immune complexes on the first day of the experiment. The noticeable tendency towards the decreased erythrocyte count and the increased bilirubin level was observed on the second day after a single inhalation effect of the compound in animals of the experimental groups, although the indicators were not statistically significant (p >> 0,05). The concentration of nitroxoline 706,8 mg/m<^>3 prolonged the duration of thiopental sleep by 1,9 times on the first day (p << 0,001) and by 1,3 times on the second day (p << 0,01) of the experiment. The obtained results proved the failure of the physiological detoxifying capacities of the body to conjugate and remove nitroxoline from the body completely during 24 hours. Conclusions: the threshold of nitroxoline acute action (Lim ac) due to the duration of thiopental sleep for white rats in case of inhalation was 706,8 mg/m<^>3. The chemical structure of the nitroxoline molecule did not reveal the properties of a valuable antigen capable of triggering toxic and allergic reactions in case of the single inhalation effect on the body.

The electromagnetic response of the superconducting ferromagnets RuSr2Gd1,5Ce0,5Cu2O10 (Ru - 1222 Gd) in an ac magnetic field of finite amplitude is investigated. Taking into account weak links between granules and magnetization of the magnetic sublattice, it is shown that the response of a sample in a superconducting state with the fundamental frequency and frequency of the 3rd harmonic can be described by the nonlinear equation for the macroscopic field. Generation of the harmonic at temperatures above superconducting transition corresponds to Rayleigh's mechanism. Using various regimes of a sample cooling, the internal magnetic field determined by the magnetic sublattice was measured. This is direct evidence of the coexistence of ferromagnetic and superconductive order parameters in high-<$E T sub c> ruthenocuprates.

We synthesized (CuO, CaO2, and BaO)y/<$Eroman {Cu sub 0,5 Tl sub 0,5 Ba sub 2 Ca sub 2 Cu sub 3 O} sub {10- delta }> (y = 0,5 %, 10 %, 15 %) composites by solid-state reaction and characterized by x-ray diffraction, scanning electron microscopy, dc-resistivity, and Fourier transform infrared spectroscopy. Frequency and temperature dependent dielectric properties such as real and imaginary part of dielectric constant, dielectric loss, and ac-conductivity of these composites are studied by capacitance and conductance measurement as a function of frequency (10 kHz to 10 MHz) and temperature (78 to 300 K). The x-ray diffraction analysis reveals that the characteristic behavior of <$Eroman {Cu sub 0,5 Tl sub 0,5 Ba sub 2 Ca sub 2 Cu sub 3 O} sub {10- delta }> superconductor phase and its structure is nearly undisturbed by doping of nanoparticles. The scanning electron microscopy images show the improvement in the intergranular links among the superconducting grains with increasing nanoparticles concentration. Microcracks are healed up with the inclusion of these nanoparticles and superconducting volume fraction is also increased. The dielectric properties of these composites strongly depend upon the frequency and temperature. The zero resistivity critical temperature and dielectric properties show opposite trend with the addition of nanoparticles in <$Eroman {Cu sub 0,5 Tl sub 0,5 Ba sub 2 Ca sub 2 Cu sub 3 O} sub {10- delta }> superconductor matrix.

Ferromagnetic nickel (Ni) nanoparticles were added in <$E roman {(Cu sub 0,5 Tl sub 0,5 )Ba sub 2 Ca sub 2 Cu sub 3 O sub {10- delta}}> (CuTl-1223) superconducting matrix to get Nix/CuTl-1223; x = 0 - 1,00 wt % nanoparticles-superconductor composites. Temperature- and frequency-dependent dielectric properties of CuTl-1223 superconducting phase with different contents of Ni nanoparticles were studied. Different dielectric parameters such as dielectric constant (<$E {epsilon prime} sub r>, <$E {epsilon symbol Т} sub r>), dielectric tangent loss (tan <$E delta>) and ac conductivity (<$E sigma sub ac>) were determined from experimentally measured capacitance and conductance at different frequencies from 10 kHz to 10 MHz and at different operating temperatures from 78 to 290 K. The values of <$E {epsilon prime} sub r> and <$E {epsilon symbol Т} sub r> were found maximal at smaller frequencies and started to decrease at higher frequencies. The value of <$E sigma sub ac> is high at high frequency unlike to <$E {epsilon prime} sub r> and <$E {epsilon symbol Т} sub r>, which is due to release of space charges at high frequencies. Peaks in tan <$E delta> graphs represent the resonance phenomenon at certain frequencies in these samples. Non-monotonic behavior in variation of dielectric parameters with temperature of Nix/CuTl-1223 samples was observed particularly at high temperatures which was due to thermal instability of the system at high temperatures.