Computational and experimental study of air-core HTS transformer electrothermal behaviour at current limiting mode

The paper provides the results of the experimental and computational study of the processes occurring in high temperature superconducting transformer windings while secondary winding is short-circuited. The obtained mathematical simulation matches closely with the experimental results. The temperature variation curves for superconducting windings were analysed, and conclusions were made on the necessity of changes in HTS transformer design, namely the necessity of windings heat-insulation from each other and adding a high-resistance coating material for HTS wire in HTS transformer primary winding

Spin-polarized electric currents in diluted magnetic semiconductor heterostructures induced by terahertz and microwave radiation

We report on the study of spin-polarized electric currents in diluted magnetic semiconductor (DMS) quantum wells subjected to an in-plane external magnetic field and illuminated by microwave or terahertz radiation. The effect is studied in (Cd,Mn)Te/(Cd,Mg)Te quantum wells (QWs) and (In,Ga)As/InAlAs:Mn QWs belonging to the well known II-VI and III-V DMS material systems, as well as, in heterovalent AlSb/InAs/(Zn,Mn)Te QWs which represent a promising combination of II-VI and III-V semiconductors. Experimental data and developed theory demonstrate that the photocurrent originates from a spin-dependent scattering of free carriers by static defects or phonons in the Drude absorption of radiation and subsequent relaxation of carriers. We show that in DMS structures the efficiency of the current generation is drastically enhanced compared to non-magnetic semiconductors. The enhancement is caused by the exchange interaction of carrier spins with localized spins of magnetic ions resulting, on the one hand, in the giant Zeeman spin-splitting, and, on the other hand, in the spin-dependent carrier scattering by localized Mn2+ ions polarized by an external magnetic field.Comment: 14 pages, 13 figure

The sine-Gordon model with integrable defects revisited

Application of our algebraic approach to Liouville integrable defects is proposed for the sine-Gordon model. Integrability of the model is ensured by the underlying classical r-matrix algebra. The first local integrals of motion are identified together with the corresponding Lax pairs. Continuity conditions imposed on the time components of the entailed Lax pairs give rise to the sewing conditions on the defect point consistent with Liouville integrability.Comment: 24 pages Latex. Minor modifications, added comment

Classical Poisson structures and r-matrices from constrained flows

We construct the classical Poisson structure and $r$-matrix for some finite dimensional integrable Hamiltonian systems obtained by constraining the flows of soliton equations in a certain way. This approach allows one to produce new kinds of classical, dynamical Yang-Baxter structures. To illustrate the method we present the $r$-matrices associated with the constrained flows of the Kaup-Newell, KdV, AKNS, WKI and TG hierarchies, all generated by a 2-dimensional eigenvalue problem. Some of the obtained $r$-matrices depend only on the spectral parameters, but others depend also on the dynamical variables. For consistency they have to obey a classical Yang-Baxter-type equation, possibly with dynamical extra terms.Comment: 16 pages in LaTe

Infrared problem for the Nelson model on static space-times

We consider the Nelson model with variable coefficients and investigate the problem of existence of a ground state and the removal of the ultraviolet cutoff. Nelson models with variable coefficients arise when one replaces in the usual Nelson model the flat Minkowski metric by a static metric, allowing also the boson mass to depend on position. A physical example is obtained by quantizing the Klein-Gordon equation on a static space-time coupled with a non-relativistic particle. We investigate the existence of a ground state of the Hamiltonian in the presence of the infrared problem, i.e. assuming that the boson mass tends to 0 at infinity

Dissipationless Disk Accretion

We consider disk accretion resulting purely from the loss of angular momentum due to the outflow of plasma from a magnetized disk. In this limiting case, the dissipation due to the viscosity and finite electrical conductivity of the plasma can be neglected. We have obtained self-consistent, self-similar solutions for dissipationless disk accretion. Such accretion may result in the formation of objects whose bolometric luminosities are lower than the flux of kinetic energy in the ejected material.Comment: 17 pages, 6 figures, published in Astronomy Reports, Vol.49, No.1, 2005, p.57 (submitted September 13, 2003). Unfortunately, we did not upload the paper to astro-ph before, but since the topic is now of interest we feel that the paper would benefit the communit

АТОМНО-АБСОРБЦИОННЫЙ СПЕКТРОМЕТР «КОЛИБРИ-ААС» ДЛЯ ОДНОВРЕМЕННОГО МНОГОЭЛЕМЕНТНОГО АНАЛИЗА

A desktop continuum source electrothermal atomic absorption spectrometer for the simultaneous multielement determination was developed based on a “Kolibri-2” polychromator and a MAES multichannel spectrum analyzer with a photodetector linear array. The device provided rapid monitoring of absorption spectra in the wavelength range of 190–360 nm with a single exposure time of 5 ms and atomization pulses of 1–2 seconds. The high luminosity of the spectrometer made it possible to use a low-power deuterium lamp as a continuum source. The heat treatment and the atomization of the samples was carried out in a longitudinally heated tube furnace with programmable heating. The processing of the spectral data, including the recording of the absorption, subtraction of the spectral background, linearization of the dependence of absorption on the concentration of atomic vapor, and the construction of the calibration graphs was performed automatically using a modified “Atom” software algorithm. The analysis of the series of multielement solutions had shown that, despite the relatively low spectral resolution, the device allowed for the direct simultaneous determination of elements by resonance lines in a concentration range of up to 4 orders of magnitude. Furthermore, the detection limits of the elements were comparable to or lower than those for the sequential flame atomic absorption spectrometry or the inductively coupled plasma atomic emission analysis. The comparison of the results of direct determination of micro and macro components in water from the rivers of Gorny Altai and the Laboratory of Isotope-Geochemical Methods of Analysis of the Institute of Geology and Mineralogy (IGM), SB RAS confirmed the correctness of the analysis. At this stage of the development, “Kolibri-AAS” spectrometers could replace flame AAS instruments for the sequential determination of elements in solutions in analytical laboratories. In the future, as the atomization technique and software are improved, the spectrometer could be used to analyze solid and liquid organic and inorganic substances.Keywords: atomic absorption spectrometry, spectrometer, electrothermal atomizer, simultaneous multi-element analysis, continuum sourceDOI: http://dx.doi.org/10.15826/analitika.2018.22.4.002(Russian)S.S. Boldova1,2, *V.A. Labusov1,2,3, D.A. Katskov4, D.O. Selyunin1,2, M.S. Saushkin1,2, I.A. Zarubin1,2,3 and Z.V. Semenov1,21Institute of Automation and Electrometry, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga, 1, Novosibirsk,  630090, Russian Federation2VMK-Optoelektronika, pr. Akademika Koptyuga, 1, Novosibirsk, 630090, Russian Federation3Novosibirsk State Technical University, pr. K. Marksa, 20, Novosibirsk, 630073, Russian Federation4 Tshwane University of Technology, Pretoria, 0001, South AfricaНастольный атомно-абсорбционный спектрометр с источником непрерывного спектра и электротермическим атомизатором для одновременного определения элементов сконструирован на базе полихроматора «Колибри-2» и многоканального анализатора спектров МАЭС с линейкой фотодетекторов. Прибор осуществляет быстрый мониторинг спектра поглощения в диапазоне длин волн 190-360 нм с временем однократной экспозиции 5 мс при 1-2 секундных импульсах атомизации пробы. Высокая светосила спектрометра позволяет использовать в качестве источника излучения непрерывного спектра дейтериевую лампу малой мощности. Термообработка и атомизация пробы проводятся в продольно нагреваемой трубчатой печи с программируемым нагревом. Обработка спектральных данных, включающая регистрацию абсорбции, учет спектрального фона, линеаризацию зависимости абсорбции от концентрации атомного пара и построение градуировочных графиков, производится автоматически с помощью модифицированной программы «Атом». На примере анализа серии многоэлементных растворов показано, что, несмотря на сравнительно низкое спектральное разрешение, прибор позволяет осуществлять прямое одновременное определение элементов по резонансным линиям в диапазоне концентраций до 4 порядков. При этом пределы обнаружения элементов оказываются сравнимыми или ниже аналогичных показателей для последовательного атомно-абсорбционного анализа с пламенной атомизацией или атомно-эмиссионного анализа с индуктивно связанной плазмой. Сопоставление результатов прямого определения микро- и макрокомпонентов в водах рек Горного Алтая с данными лаборатории изотопно-геохимических методов анализа Института геологии и минералогии СО РАН подтвердило правильность анализа. На данном этапе разработки спектрометр «Колибри-ААС» может заменить в аналитических лабораториях пламенные ААС приборы для последовательного определения элементов в растворах. В перспективе, по мере усовершенствования технологии атомизации и программного обеспечения, предполагается использовать спектрометр для анализа твердых и жидких органических и неорганических веществ.Ключевые слова: атомно-абсорбционная спектрометрия, спектрометр, электротермический атомизатор, одновременный многоэлементный анализ, источник непрерывного спектраDOI: http://dx.doi.org/10.15826/analitika.2018.22.4.00

Bulk and Interfacial Shear Thinning of Immiscible Polymers

Nonequilibrium molecular dynamics simulations are used to study the shear thinning behavior of immiscible symmetric polymer blends. The phase separated polymers are subjected to a simple shear flow imposed by moving a wall parallel to the fluid-fluid interface. The viscosity begins to shear thin at much lower rates in the bulk than at the interface. The entire shear rate dependence of the interfacial viscosity is consistent with a shorter effective chain length $s^*$ that also describes the width of the interface. This $s^*$ is independent of chain length $N$ and is a function only of the degree of immiscibility of the two polymers. Changes in polymer conformation are studied as a function of position and shear rate.Shear thinning correlates more closely with a decrease in the component of the radius of gyration along the velocity gradient than with elongation along the flow. At the interface, this contraction of chains is independent of $N$ and consistent with the bulk behavior for chains of length $s^*$. The distribution of conformational changes along chains is also studied. Central regions begin to stretch at a shear rate that decreases with increasing $N$, while shear induced changes at the ends of chains are independent of $N$.Comment: 8 pages, 8 figure

Statistical Theory for Incoherent Light Propagation in Nonlinear Media

A novel statistical approach based on the Wigner transform is proposed for the description of partially incoherent optical wave dynamics in nonlinear media. An evolution equation for the Wigner transform is derived from a nonlinear Schrodinger equation with arbitrary nonlinearity. It is shown that random phase fluctuations of an incoherent plane wave lead to a Landau-like damping effect, which can stabilize the modulational instability. In the limit of the geometrical optics approximation, incoherent, localized, and stationary wave-fields are shown to exist for a wide class of nonlinear media.Comment: 4 pages, REVTeX4. Submitted to Physical Review E. Revised manuscrip

Hopf algebras in dynamical systems theory

The theory of exact and of approximate solutions for non-autonomous linear differential equations forms a wide field with strong ties to physics and applied problems. This paper is meant as a stepping stone for an exploration of this long-established theme, through the tinted glasses of a (Hopf and Rota-Baxter) algebraic point of view. By reviewing, reformulating and strengthening known results, we give evidence for the claim that the use of Hopf algebra allows for a refined analysis of differential equations. We revisit the renowned Campbell-Baker-Hausdorff-Dynkin formula by the modern approach involving Lie idempotents. Approximate solutions to differential equations involve, on the one hand, series of iterated integrals solving the corresponding integral equations; on the other hand, exponential solutions. Equating those solutions yields identities among products of iterated Riemann integrals. Now, the Riemann integral satisfies the integration-by-parts rule with the Leibniz rule for derivations as its partner; and skewderivations generalize derivations. Thus we seek an algebraic theory of integration, with the Rota-Baxter relation replacing the classical rule. The methods to deal with noncommutativity are especially highlighted. We find new identities, allowing for an extensive embedding of Dyson-Chen series of time- or path-ordered products (of generalized integration operators); of the corresponding Magnus expansion; and of their relations, into the unified algebraic setting of Rota-Baxter maps and their inverse skewderivations. This picture clarifies the approximate solutions to generalized integral equations corresponding to non-autonomous linear (skew)differential equations.Comment: International Journal of Geometric Methods in Modern Physics, in pres