Low field magnetocaloric effect and heat capacity of A-site ordered NdBaMn2O6 manganite

The magnetocaloric effect (MCE) in the A-site ordered manganite NdBaMn2O6 is studied. The MCE in this compound has an anomalous behavior. In low magnetic fields, the abrupt transitions between direct and inverse magnetocaloric effect are observed. In a relatively strong magnetic field H=11 kOe the direct and inverse effects are observed only at cooling, while the heating mode reveals only an inverse MCE. The value of the MCE (-{\Delta}S=0.7 J/kg K and {\Delta}S= 1.02 J/kg K for {\Delta}H=11 kOe) does not reach high values, but the proximity of the effects occurring at room temperatures expects the use of both effects in the magnetic cooling technology.Comment: 10 pages, 6 figure

Direct and Inverse Magnetocaloric effects in A-site ordered PrBaMn2O6 manganite in low magnetic fields

The magnetocaloric effect (MCE) of A-site ordered PrBaMn2O6 manganite has been studied by direct methods and by the specific heat measurements. Direct measurements of the MCE in low magnetic fields were performed using recently proposed modulation technique and by classic direct method in high fields. Direct and inverse MCE are observed at Curie and Neel points correspondingly. A value of the inverse MCE in the heating run is less than in the cooling regime. This effect can be attributing to competition between ferromagnetic and antiferromagnetic interactions. Indirectly estimated and direct MCE values considerably differ in around first order AF transition.Comment: 8 pages, 5 figure

Gravitational fields with a non Abelian bidimensional Lie algebra of symmetries

Vacuum gravitational fields invariant for a bidimensional non Abelian Lie algebra of Killing fields, are explicitly described. They are parameterized either by solutions of a transcendental equation (the tortoise equation) or by solutions of a linear second order differential equation on the plane. Gravitational fields determined via the tortoise equation, are invariant for a 3-dimensional Lie algebra of Killing fields with bidimensional leaves. Global gravitational fields out of local ones are also constructed.Comment: 8 pagese, latex, no figure

THEORETIC AND METHODOLOGICAL ASPECTS OF STATE SYSTEM FUNCTIONING FOR INDUSTRIAL PRODUCTION EXPORT SUPPORT

Abstract. The article deals with the theoretical and methodological aspects of state system functioning for industrial product export support. In the work the authors justify that international trade is the most important form of international economic relations. They clarified the reasons and the expediency of trade relations establishment between different countries. As was shown in the article, the structure of world trade has changed significantly in recent years. These changes are greatly influenced by NTP, which in its turn causes the deepening of the international division of labor and the strengthening of international trade. In the context of growing globalization and taking into account the fact that Russia is the part of the WTO, the study of the national economy competitiveness state and the development ofthe ways to enhance Russia international competitiveness on this basis is especially important. Nowadays, exportimport operations are a key element of the country long-term strategy, which is aimed at industrial production task modernization solution and economy restructuring. Drawing on international experience, Russia should develop a system of measures of state support for exports, taking into account national characteristics. The results of the research allow us to place the emphasis in the evaluation of international trade and the support from state structure further expansion.Keywords: international trade, integration, modernization, diversification, export, competitiveness, worldeconomy

IR-spectroscopy and AFM-microscopy of the surface of gamma-irradiated GaS and GaS:Yb layered single crystals

For the first time, information on the surface relief of the layered GaS and doped GaS:Yb single crystals subjected to gamma-irradiation was obtained using atomic force microscopy (AFM) and Fourier-transform infrared spectroscopy (FTIR). It was found that GaS is characterized by a non-uniform distribution of irregularities with different heights and periodicities, and when doping crystals with Yb atoms, the distribution of irregularities becomes more orderly, the height and periodicity of irregularities decreases. In the FTIR spectra, changes in the reflection coefficients of the surface of GaS and GaS:Yb single crystals are observed as a function of the gammairradiation dose (Фγ = 30…200 krad), and on the basis of spectroscopic and microscopic changes, it was found that doped single crystals are the most radiation-resistant.Вперше методами атомно-силової мікроскопії (АСМ) і ІК-фур'є-спектроскопії отримано інформацію про рельєф поверхні нелегованих GaS і легованих монокристалів GaS:Yb, підданих гамма-опроміненню. Встановлено, що для монокристалів GaS характерний нерівномірний розподіл нерівностей з різною висотою і періодичністю, а при легуванні кристалів атомами Yb розподіл нерівностей упорядкується, їх висота і періодичність зменшаться. В ІК-фур’є-спектрах спостерігаються зміни коефіцієнтів відбиття поверхні монокристалів GaS і GaS:Yb в залежності від дози гамма-опромінення (Фγ = 30...200 крад), і на основі цих змін встановлено, що леговані монокристали є більш радіаційно стійкими.Впервые методами атомно-силовой микроскопии (АСМ) и ИК-фурье-спектроскопии получена информация о рельефе поверхности нелегированных GaS и легированных монокристаллов GaS:Yb, подвергнутых гамма-облучению. Установлено, что для монокристаллов GaS характерно неравномерное распределение неровностей с различной высотой и периодичностью, а при легировании кристаллов атомами Yb распределение неровностей упорядочится, их высота и периодичность уменьшатся. В ИК-фурьеспектрах наблюдаются изменения коэффициентов отражения поверхности монокристаллов GaS и GaS:Yb в зависимости от дозы гамма-облучения (Фγ = 30…200 крад), и на основе этих изменений установлено, что легированные монокристаллы являются более радиационно стойкими

Profiles of emission lines generated by rings orbiting braneworld Kerr black holes

In the framework of the braneworld models, rotating black holes can be described by the Kerr metric with a tidal charge representing the influence of the non-local gravitational (tidal) effects of the bulk space Weyl tensor onto the black hole spacetime. We study the influence of the tidal charge onto profiled spectral lines generated by radiating tori orbiting in vicinity of a rotating black hole. We show that with lowering the negative tidal charge of the black hole, the profiled line becomes to be flatter and wider keeping their standard character with flux stronger at the blue edge of the profiled line. The extension of the line grows with radius falling and inclination angle growing. With growing inclination angle a small hump appears in the profiled lines due to the strong lensing effect of photons coming from regions behind the black hole. For positive tidal charge ($b>0$) and high inclination angles two small humps appear in the profiled lines close to the red and blue edge of the lines due to the strong lensing effect. We can conclude that for all values of $b$, the strongest effect on the profiled lines shape (extension) is caused by the changes of the inclination angle.Comment: Accepted by General Relativity and Gravitatio

Orbital resonances in discs around braneworld Kerr black holes

Rotating black holes in the brany universe of the Randall-Sundrum type are described by the Kerr geometry with a tidal charge b representing the interaction of the brany black hole and the bulk spacetime. For b<0 rotating black holes with dimensionless spin a>1 are allowed. We investigate the role of the tidal charge b in the orbital resonance model of QPOs in black hole systems. The orbital Keplerian, the radial and vertical epicyclic frequencies of the equatorial, quasicircular geodetical motion are given and their radial profiles are discussed. The resonant conditions are given in three astrophysically relevant situations: for direct (parametric) resonances, for the relativistic precession model, and for some trapped oscillations of the warped discs, with resonant combinational frequencies. It is shown, how b could influence matching of the observational data indicating the 3:2 frequency ratio observed in GRS 1915+105 microquasar with prediction of the orbital resonance model; limits on allowed range of the black hole parameters a and b are established. The "magic" dimensionless black hole spin enabling presence of strong resonant phenomena at the radius where \nu_K:\nu_{\theta}:\nu_r=3:2:1 is determined in dependence on b. Such strong resonances could be relevant even in sources with highly scattered resonant frequencies, as those expected in Sgr A*. The specific values of a and b are given also for existence of specific radius where \nu_K:\nu_{\theta}:\nu_r=s:t:u with 5>=s>t>u being small natural numbers. It is shown that for some ratios such situation is impossible in the field of black holes. We can conclude that analysing the microquasars high-frequency QPOs in the framework of orbital resonance models, we can put relevant limits on the tidal charge of brany Kerr black holes.Comment: 31 pages, 19 figures, to appear in General Relativity and Gravitatio

Ricci flat rotating black branes with a conformally invariant Maxwell source

We consider Einstein gravity coupled to an $U(1)$ gauge field for which the density is given by a power of the Maxwell Lagrangian. In $d$-dimensions the action of Maxwell field is shown to enjoy the conformal invariance if the power is chosen as $d/4$. We present a class of charge rotating solutions in Einstein-conformally invariant Maxwell gravity in the presence of a cosmological constant. These solutions may be interpreted as black brane solutions with inner and outer event horizons or an extreme black brane depending on the value of the mass parameter. Since we are considering power of the Maxwell density, the black brane solutions exist only for dimensions which are multiples of four. We compute conserved and thermodynamics quantities of the black brane solutions and show that the expression of the electric field does not depend on the dimension. Also, we obtain a Smarr-type formula and show that these conserved and thermodynamic quantities of black branes satisfy the first law of thermodynamics. Finally, we study the phase behavior of the rotating black branes and show that there is no Hawking--Page phase transition in spite of conformally invariant Maxwell field.Comment: 13 pages, one figur

Modification of the ground state in Sm-Sr manganites by oxygen isotope substitution

The effect of $^{16}$O $\to$ $^{18}$O isotope substitution on electrical resistivity and magnetic susceptibility of Sm$_{1-x}$Sr$_x$MnO$_3$ manganites is analyzed. It is shown that the oxygen isotope substitution drastically affects the phase diagram at the crossover region between the ferromagnetic metal state and that of antiferromagnetic insulator (0.4 $< x <$ 0.6), and induces the metal-insulator transition at for $x$ = 0.475 and 0.5. The nature of antiferromagnetic insulator phase is discussed.Comment: 4 pages, 3 eps figures, RevTeX, submitted to Phys. Rev. Let

Structure and magnetocaloric properties of La1-xKxMnO3 manganites

A technology of obtaining the single-phase ceramic samples of La1-xKxMnO3 manganites and the dependence of their structural parameters on the content of potassium has been described. Magnetocaloric effect (MCE) in the obtained samples has been measured by two independent methods: by classical direct methodic and by a method of magnetic field modulation. The values of MCE obtained by both methods have been substantially differed. The explanation of the observed divergences is given. The correlation between the level of doping and MCE value has been defined. The value of TC determined by the MCE maximum has been conformed to the literature data received by other methods.Comment: 14 pages, 6 figures, 3 table