Neutron diffraction, magnetization and ESR studies of pseudocubic Nd(0.75)Ba(0.25)MnO3 and its unusual critical behavior above Tc

Results of structural neutron diffraction study, magnetization and ESR measure-ments are presented for insulating Nd0.75Ba0.25MnO3, Tc = 129 K. The crystal structure is refined in the range 4.2-300 K. The compound is found to exhibit the Jahn-Teller (JT) transition at 250 K. The field cooled (FC) magnetization data are in a reasonable agreement with the predictions for a 3D isotropic ferromagnet above Tc. However, these measurements reveal a difference between the FC and zero FC data in the paramagnetic region. ESR results are also in a correspondence with behavior of a cubic ferromagnet above T* = 143 K. It is shown that an anisotropic exchange coupling of the Mn and Nd magnetic moments can give a substantial contribution in ESR linewidth masking its critical enhan-cement. The different temperature treatments of the sample reveal a temperature hysteresis of the ESR spectra below T* indicating an anomalous response in the paramagnetic region. The study of phase transition in this manganite suggests change in its character from the second to first order at T*. The conventional free energy including the magnetization and magnetic field is not found to describe the first order transition. This suggests that the charge, orbital and JT phonon degrees of freedom, in addition to magnetization, may be the critical variables, the unusual character of the transition being determined by their coupling. Unconventional critical behavior is attributed to orbital liquid metallic phase that coexists with the initial orbital ordered phase below T*.Comment: 18 pages, 5 figures, submitted to Phys. Rev.

Three-Point Functions of Quarter BPS Operators in N=4 SYM

In a recent paper hep-th/0109064, quarter-BPS chiral primaries were constructed in the fully interacting four dimensional N=4 Super-Yang-Mills theory with gauge group SU(N). These operators are annihilated by four supercharges, and at order g^2 have protected scaling dimension and normalization. Here, we compute three-point functions involving these quarter-BPS operators along with half-BPS operators. The combinatorics of the problem is rather involved, and we consider the following special cases: (1) correlators of two half-BPS primaries with an arbitrary chiral primary; (2) certain classes of and < quarter quarter quarter > three-point functions; (3) three-point functions involving the Delta correlators with the special quarter-BPS operator made of single and double trace operators only. The analysis in cases (1)-(3) is valid for general N, while (4) is a large N approximation. Order g^2 corrections to all three-point functions considered in this paper are found to vanish. In the AdS/CFT correspondence, quarter-BPS chiral primaries are dual to threshold bound states of elementary supergravity excitations. We present a supergravity discussion of two- and three-point correlators involving these bound states.Comment: 44 pages, Latex, eps figures, uses epsfig.sty; references adde

Alternative fast quantum logic gates using nonadiabatic Landau-Zener-St\"{u}ckelberg-Majorana transitions

A conventional realization of quantum logic gates and control is based on resonant Rabi oscillations of the occupation probability of the system. This approach has certain limitations and complications, like counter-rotating terms. We study an alternative paradigm for implementing quantum logic gates based on Landau-Zener-St\"{u}ckelberg-Majorana (LZSM) interferometry with non-resonant driving and the alternation of adiabatic evolution and non-adiabatic transitions. Compared to Rabi oscillations, the main differences are a non-resonant driving frequency and a small number of periods in the external driving. We explore the dynamics of a multilevel quantum system under LZSM drives and optimize the parameters for increasing single- and two-qubit gates speed. We define the parameters of the external driving required for implementing some specific gates using the adiabatic-impulse model. The LZSM approach can be applied to a large variety of multi-level quantum systems and external driving, providing a method for implementing quantum logic gates on them.Comment: 15 pages, 12 figure

ДОСВІД ВПРОВАДЖЕННЯ ОНЛАЙН-ТЕХНОЛОГІЙ У СИСТЕМУ ПІДГОТОВКИ ФАХІВЦІВ ГАЛУЗІ ЗНАНЬ 22 “ОХОРОНА ЗДОРОВ’Я”

The aim of the work – to analyze the introduction into the educational process of Medical (Pharmaceutical) Institutions of Higher Education of elective courses in the form of distance learning based on the online course technology, implemented on the edX platform located on the Azure cloud virtual server.The main body. The article presents the experience of introducing modern online technologies into the system of training of specialists in the field of knowledge 22 “PUBLIC HEALTH”. The authors show the sequence of organizational steps to be taken, to implement the full cycle of e-learning technologies: from elaborating an online course to organizing the process of students’ self-study with online services. We found the main difficulties of implementing the innovative forms of education into the conservative system in which educational process is organized at medical universities: organization of free choice of disciplines in the training of specialists; ensuring quality organization of students’ self-study; introduction of new methods of training for the KROK licensed exam, and ways to resolve them were suggested.Conclusion. Implementation of e-learning technologies in the system of graduate education at a medical university in the format of elective courses makes it possible to provide students with real choice of courses as well as to reflect the most advanced scientific and practical achievements in the content of these courses, brings elements of interactivity into the learning process, and also creates conditions for remote monitoring of students’ academic activity by teachers.Мета роботи – проаналізувати впровадження в навчальний процес ВМ(Ф)НЗ курсів за вибором за формою дистанційного навчання за технологією онлайн-курсів, які реалізовані на платформі edX, що розташована на віртуальному сервері хмари Azure.Основна частина. У статті представлено досвід впровадження сучасних технологій у форматі on line в систему підготовки фахівців галузі знань 22 “Охорона здоров’я”. Автори розкривають послідовність організаційних кроків до вирішення завдання реалізації повного циклу технологій e-learning: від розробки онлайн-курсу до організації процесу самостійної роботи студентів з онлайн-сервісами. Розкриті основні складнощі імплементації інноваційних форм навчання до консервативної системи організації навчального процесу медичного університету, а саме: організація вільного вибору дисциплін при підготовці фахівців, забезпечення якісної організації самостійної роботи студента, запровадження нових методів підготовки до ліцензійного іспиту “Крок”, та запропоновані шляхи їх вирішення.Висновок.Імплементація технологій e-learning у систему додипломної освіти медичного університету курсів у форматі курсів за вибором дозволяє надати студентам реальний вибір курсів, а також відображати в контенті цих курсів найсучасніші досягнення науково-практичного напрямку, привносить елементи інтерактивності до процесу навчання, а також створює умови для дистанційного моніторингу навчальної активності студентів викладачами.

СТРАТЕГІЯ ВПРОВАДЖЕННЯ КУРСІВ ЗА ВИБОРОМ НА БАЗІ ТЕХНОЛОГІЇ ОНЛАЙН-КУРСІВ НА ПЛАТФОРМІ edX

A sequential strategy of implementation elective online courses at medical university on the basis of distance learning technology is revealed in the article. It is shown that successful implementation of online courses is possible in the presence of such components as academic staff readiness to develop new learning technologies and the acceptance of the fact of their changing role in the educational process; students’ readiness to use distance learning technologies; availability of infrastructure at university that provides distance learning services; presence of a quality assurance system for courses content. Particular attention is paid to the need to change the structural organization of the educational process and the role of instructors in the implementation process. The authors substantiated their choice of the Open edX platform for online courses development based on some criteria.У статті розкрита послідовна стратегія впровадження в медичному університеті курсів за вибором на базі технології дистанційного навчання у вигляді онлайн-курсів. Показано, що успішне впровадження онлайн-курсів можливо при наявності таких складових, як: готовність викладацького складу до опанування нових технологій навчання та зміни своєї ролі в навчальному процесі; готовність студентів до використання дистанційних технологій навчання; наявність інфраструктури в університеті, яка забезпечує сервіси дистанційного навчання; наявність системи перевірки якості контенту онлайн-курсів, які розробляються. Особлива увага звертається на необхідність зміни структури навчального процесу та ролі викладачів при впровадженні онлайн-курсів. Авторами обґрунтовано вибір платформи для розробки онлайн-курсів Open edX за критеріями

Conservation laws for multidimensional systems and related linear algebra problems

We consider multidimensional systems of PDEs of generalized evolution form with t-derivatives of arbitrary order on the left-hand side and with the right-hand side dependent on lower order t-derivatives and arbitrary space derivatives. For such systems we find an explicit necessary condition for existence of higher conservation laws in terms of the system's symbol. For systems that violate this condition we give an effective upper bound on the order of conservation laws. Using this result, we completely describe conservation laws for viscous transonic equations, for the Brusselator model, and the Belousov-Zhabotinskii system. To achieve this, we solve over an arbitrary field the matrix equations SA=A^tS and SA=-A^tS for a quadratic matrix A and its transpose A^t, which may be of independent interest.Comment: 12 pages; proof of Theorem 1 clarified; misprints correcte

A Fermi Surface Model for Large Supersymmetric AdS_5 Black Holes

We identify a large family of 1/16 BPS operators in N=4 SYM that qualitatively reproduce the relations between charge, angular momentum and entropy in regular supersymmetric AdS_5 black holes when the main contribution to their masses is given by their angular momentum.Comment: 32 pages, 6 figures, LaTeX uses JHEP3 class; ver 2- added acknowledgment, minor change

The Faraday effect and phase transition in the CH 3 NH 3 PbI 3 halide perovskite single crystal

The spin degree of freedom of charge carriers in halide-perovskite semiconductors can be highly useful for information photonics applications. The Faraday effect is known to be the best indicator of paramagnetism of the material and of the spin-light interaction. In this work, the Faraday effect is demonstrated, for the first time, in a hybrid organic-inorganic halide perovskite MAPbI3 (MA+=CH3NH+3). The Faraday rotation and birefringence were measured across the tetragonal-cubic phase transition at 327 K. The Faraday rotation is strongly suppressed below the phase transition temperature due to anisotropy (linear birefringence) of the tetragonal crystal phase. The situation changes drastically above the phase transition temperature, when the crystal becomes optically isotropic. The emerging Faraday rotation obeys the Curie law, demonstrating its population-related paramagnetic nature. This observation opens new prospects for application of these systems and for their investigations using methods of the polarization noise spectroscopy applicable to optically anisotropic materials.Comment: 12 pages, 5 figure

Spin noise of a halide perovskite

We report on first observation of spin noise in a strongly birefringent semiconductor -- halide perovskite single crystal MAPbI$_3$. The observed spin noise resonance is ascribed to free holes with a record spin dephasing time of 4 ns. The spin dynamics is found to be affected by the residual light absorption of the crystal providing renormalization of the Larmor frequency. Extended spin noise spectroscopy with rotating magnetic field allowed us not only to evaluate the $g$-factor anisotropy, but also to distinguish two different spin subsystems tentatively associated to twinning of the crystal.Comment: 14 pages, 11 figure