Magnetic vortex-antivortex crystals generated by spin-polarized current

We study vortex pattern formation in thin ferromagnetic films under the action of strong spin-polarized currents. Considering the currents which are polarized along the normal of the film plane, we determine the critical current above which the film goes to a saturated state with all magnetic moments being perpendicular to the film plane. We show that stable square vortex-antivortex superlattices (\emph{vortex crystals}) appears slightly below the critical current. The melting of the vortex crystal occurs with current further decreasing. A mechanism of current-induced periodic vortex-antivortex lattice formation is proposed. Micromagnetic simulations confirm our analytical results with a high accuracy.Comment: 12 pages, 11 figure

ІНФОРМАЦІЙНІ ЗАСОБИ СПРИЯННЯ ЗЕЛЕНОМУ ТУРИЗМУ

It has been determined that rural green tourism in Ukraine has a significant share in the tourism market. However, it is not the state institutions that promote it, but the efforts of NGOs and green tourism market actors. At the same time, the development of green tourism can solve a complex problem in depressed rural areas. Green tourism in Ukraine could be used as a tool for promoting modern advertising, marketing, researching tourists' needs, and stimulating them to improve the quality of services. The purpose of the work was to develop a new approach to creating information tools for the organization, marketing, advertisings of green tourism, improving the quality of services of this type of activity of rural population and developing a software product that implements this approach. In order to achieve this goal and solve the problems of the article, it is proposed to use a counter rating system and modern cloud technologies, on the basis of which a pilot sample of the software product was developed. The assessment of the subjects of green tourism and the package of typical tourist needs will be formed in the analysis of consumer requests. The review of the scientific literature was also conducted, analyzing both the identified consumer requirements for green tourism providers and the possible range of undetermined requirements, the main groups of criteria for evaluating the activities of the subjects of green tourism market, and other indicators by which the databases were formed. The scientific novelty of the obtained results lies in the formation of an original approach to the creation of a universal software complex for green tourism, the introduction of digital technologies in the field of marketing, the advertising of which has hitherto been carried out by amateur methods. The developed pilot sample of the software complex proves that it is the most adapted for use, updating of databases, and also provides the opportunity to reduce the cost of both computer hardware, software and its maintenance. It is created as a universal tool, including, for marketing and advertising, stimulating to improve the quality of green tourism services.Визначено, що сільський зелений туризм в Україні впевнено займає вагому частку на туристичному ринку. Але його поширенню скоріше сприяють не державні інституції, а зусилля громадських організацій і суб’єктів ринку зеленого туризму. Водночас розвиток зеленого туризму може розв’язати комплекс проблем у депресивних сільських районах. Інструментом поширення зеленого туризму в Україні могли б стати сучасні програмні засоби реклами, маркетингу, вивчення потреб туристів, стимулювання до підвищення якості послуг. Мета нашого дослідження — розроблення нового підходу до створення інформаційних інструментів організації, маркетингу, реклами зеленого туризму, підвищення якості послуг цього виду діяльності сільського населення та розробка програмного продукту, який реалізує цей підхід. Для досягнення мети і вирішення завдань запропоновано використання зустрічної рейтингової системи і сучасних хмарних технологій, на базі яких розроблено пілотний зразок програмного продукту. Оцінка суб’єктів зеленого туризму і пакет типових потреб туристів будуть формуватися при аналізі запитів споживачів. Також проведено огляд наукової літератури і проаналізовано, як виявлені вимоги споживачів до надавачів послуг зеленого туризму, так і можливий спектр невиявлених вимог, основні групи критеріїв оцінки діяльності суб’єктів ринку зеленого туризму та інші показники, за атрибутами яких сформовано бази даних. Наукова новизна одержаних результатів полягає у формуванні оригінального підходу до створення універсального програмного комплексу для зеленого туризму, впровадження цифрових технологій у галузь, маркетинг, реклама якої досі провадилися аматорськими методами. Розроблений пілотний зразок програмного комплексу довів, що він є максимально адаптованим для користування, оновлення та поповнення баз даних, а також надає можливість зменшення витрат як на комп’ютерне обладнання, програмне забезпечення, так і на його супроводження. Його створено як універсальний інструмент, у тому числі для маркетингу і реклами, стимулювання до підвищення якості послуг зеленого туризму

Magnetic Vortex Core Reversal by Excitation of Spin Waves

Micron-sized magnetic platelets in the flux closed vortex state are characterized by an in-plane curling magnetization and a nanometer-sized perpendicularly magnetized vortex core. Having the simplest non-trivial configuration, these objects are of general interest to micromagnetics and may offer new routes for spintronics applications. Essential progress in the understanding of nonlinear vortex dynamics was achieved when low-field core toggling by excitation of the gyrotropic eigenmode at sub-GHz frequencies was established. At frequencies more than an order of magnitude higher vortex state structures possess spin wave eigenmodes arising from the magneto-static interaction. Here we demonstrate experimentally that the unidirectional vortex core reversal process also occurs when such azimuthal modes are excited. These results are confirmed by micromagnetic simulations which clearly show the selection rules for this novel reversal mechanism. Our analysis reveals that for spin wave excitation the concept of a critical velocity as the switching condition has to be modified.Comment: Minor corrections and polishing of previous versio

Liquid crystal anchoring transitions on aligning substrates processed by plasma beam

We observe a sequence of the anchoring transitions in nematic liquid crystals (NLC) sandwiched between the hydrophobic polyimide substrates treated with the plasma beam. There is a pronounced continuous transition from homeotropic to low tilted (nearly planar) alignment with the easy axis parallel to the incidence plane of the plasma beam (the zenithal transition) that takes place as the exposure dose increases. In NLC with positive dielectric anisotropy, a further increase in the exposure dose results in in-plane reorientation of the easy axis by 90 degrees (the azimuthal transition). This transition occurs through the two-fold degenerated alignment characteristic for the second order anchoring transitions. In contrast to critical behavior of anchoring, the contact angle of NLC and water on the treated substrates monotonically declines with the exposure dose. It follows that the surface concentration of hydrophobic chains decreases continuously. The anchoring transitions under consideration are qualitatively interpreted by using a simple phenomenological model of competing easy axes which is studied by analyzing anchoring diagrams of the generalized polar and non-polar anchoring models.Comment: revtex4, 18 pages, 10 figure

Effective anisotropy of thin nanomagnets: beyond the surface anisotropy approach

We study the effective anisotropy induced in thin nanomagnets by the nonlocal demagnetization field (dipole-dipole interaction). Assuming a magnetization independent of the thickness coordinate, we reduce the energy to an inhomogeneneous onsite anisotropy. Vortex solutions exist and are ground states for this model. We illustrate our approach for a disk and a square geometry. In particular, we obtain good agreement between spin-lattice simulations with this effective anisotropy and micromagnetic simulations.Comment: ReVTeX, 14 pages, 6 figure

PEN: a low energy test of lepton universality

Allowed charged $\pi$ meson decays are characterized by simple dynamics, few available decay channels, mainly into leptons, and extremely well controlled radiative and loop corrections. In that sense, pion decays represent a veritable triumph of the standard model (SM) of elementary particles and interactions. This relative theoretical simplicity makes charged pion decays a sensitive means for testing the underlying symmetries and the universality of weak fermion couplings, as well as for studying pion structure and chiral dynamics. Even after considerable recent improvements, experimental precision is lagging far behind that of the theoretical description for pion decays. We review the current state of experimental study of the pion electronic decay $\pi^+ \to e^+\nu_e(\gamma)$, or $\pi_{e2(\gamma)}$, where the $(\gamma)$ indicates inclusion and explicit treatment of radiative decay events. We briefly review the limits on non-SM processes arising from the present level of experimental precision in $\pi_{e2(\gamma)}$ decays. Focusing on the PEN experiment at the Paul Scherrer Institute (PSI), Switzerland, we examine the prospects for further improvement in the near term.Comment: 11 pages, 5 figures; paper presented at the XIII International Conference on Heavy Quarks and Leptons, 22-27 May 2016, Blacksburg, Virginia, US

Search for astro-gravity correlations

A new approach in the gravitational wave experiment is considered. In addition to the old method of searching for coincident reactions of two separated gravitational antennae it was proposed to seek perturbations of the gravitational detector noise background correlated with astrophysical events such as neutrino and gamma ray bursts which can be relaibly registered by correspondent sensors. A general algorithm for this approach is developed. Its efficiency is demonstrated in reanalysis of the old data concerning the phenomenon of neutrino-gravity correlation registered during of SN1987A explosion.Comment: 29 pages (LaTeX), 4 figures (EPS

Design, Commissioning and Performance of the PIBETA Detector at PSI

We describe the design, construction and performance of the PIBETA detector built for the precise measurement of the branching ratio of pion beta decay, pi+ -> pi0 e+ nu, at the Paul Scherrer Institute. The central part of the detector is a 240-module spherical pure CsI calorimeter covering 3*pi sr solid angle. The calorimeter is supplemented with an active collimator/beam degrader system, an active segmented plastic target, a pair of low-mass cylindrical wire chambers and a 20-element cylindrical plastic scintillator hodoscope. The whole detector system is housed inside a temperature-controlled lead brick enclosure which in turn is lined with cosmic muon plastic veto counters. Commissioning and calibration data were taken during two three-month beam periods in 1999/2000 with pi+ stopping rates between 1.3*E3 pi+/s and 1.3*E6 pi+/s. We examine the timing, energy and angular detector resolution for photons, positrons and protons in the energy range of 5-150 MeV, as well as the response of the detector to cosmic muons. We illustrate the detector signatures for the assorted rare pion and muon decays and their associated backgrounds.Comment: 117 pages, 48 Postscript figures, 5 tables, Elsevier LaTeX, submitted to Nucl. Instrum. Meth.