An arbitrary order time-stepping algorithm for tracking particles in inhomogeneous magnetic fields

The Lorentz equations describe the motion of electrically charged particles in electric and magnetic fields and are used widely in plasma physics. The most popular numerical algorithm for solving them is the Boris method, a variant of the Störmer-Verlet algorithm. Boris method is phase space volume conserving and simulated particles typically remain near the correct trajectory. However, it is only second order accurate. Therefore, in scenarios where it is not enough to know that a particle stays on the right trajectory but one needs to know where on the trajectory the particle is at a given time, Boris method requires very small time steps to deliver accurate phase information, making it computationally expensive. We derive an improved version of the high-order Boris spectral deferred correction algorithm (Boris-SDC) by adopting a convergence acceleration strategy for second order problems based on the Generalised Minimum Residual (GMRES) method. Our new algorithm is easy to implement as it still relies on the standard Boris method. Like Boris-SDC it can deliver arbitrary order of accuracy through simple changes of runtime parameter but possesses better long-term energy stability. We demonstrate for two examples, a magnetic mirror trap and the Solev'ev equilibrium, that the new method can deliver better accuracy at lower computational cost compared to the standard Boris method. While our examples are motivated by tracking ions in the magnetic field of a nuclear fusion reactor, the introduced algorithm can potentially deliver similar improvements in efficiency for other applications

PROBLEMS OF UNAUTHORIZED INTERFERENCE TO THE WORK OF UAV AND METHODS OF ITS SOLVING

This article is sanctified to the actual subject -research of unmanned aerial vehicles(UAV). The flow diagram of UAV is shown in this scientific work, the information about advantages, prospects and methods of UAV application in the different spheres of life is brought up. The basic methods of unauthorized access to management and software are analysed. The examples of unauthorized interference to the work of UAV control system are shown and the possible solutions of  UAV defence are offered. Anapparatus, which gives an opportunity to find out the place of UAV stay on certain territory and report about it, is analysed.The list of developing safe methods of counteraction to the UAV is given to consideration. The questions of  home soldiery unmanned aerial vehicles, that become more important with every day, are considered. The types of possible attacks are analyzed. It is educed that basic defense is still the cryptosystem of UAV control system defense.  This article allows you to delve into the issues and benefits caused by new unmanned aerial techniques, understand the seriousness of the problems and prospects, the ability to research and development in this direction.Данная статья посвящена достаточно актуальной тематике - исследованию беспилотных летательных аппаратов (БПЛА). В данной научной работе показано структурную схему БПЛА, приведена информация о преимуществах, перспективах и способах применения БПЛА в различных сферах жизни. Проанализированы основные способы несанкционированного доступа к программному обеспечению и управлению. Продемонстрировано примеры несанкционированного вмешательства в работу системы управления БПЛА и предложены возможные решения защиты БПЛА. Проанализировано аппаратуру, что дает возможность выявлять пребывания БПЛА на определенной территории и сообщать об этом. Подается к рассмотрению перечень разрабатываемых безопасных способов противодействия беспилотным летательным аппаратам. Рассмотрены вопросы отечественных военных беспилотных летательных аппаратов, которые становятся более важными с каждым днем. Проанализированы типы возможных атак и выявлено, что основной защитой остается криптографическая система защиты канала управления БПЛА. Данная статья позволяет углубиться в проблемы и преимущества вызваны новой беспилотной летательной техникой, понять серьезность проблем и перспектив, возможность развития и исследований в этом направлении.Дана стаття присвячена досить актуальній тематиці - дослідженню безпілотних літальних апаратів (БПЛА). В даній науковій праці показано структурну схему БПЛА, наведена інформація про переваги, перспективи та способи застосування БПЛА в різних сферах життя. Проаналізовано основні способи несанкціонованого доступу до програмного забезпечення і керування. Продемонстровано приклади несанкціонованого втручання у роботу системи керування БПЛА і запропоновано можливі рішення захисту БПЛА. Проаналізовано апаратуру, що дає можливість виявляти перебування БПЛА на певній території і повідомляти про це. Подається до розгляду перелік розроблюваних безпечних способів протидії безпілотним літальним апаратам. Розглянуто питання вітчизняних військових безпілотних літальних апаратів, які стають  важливішими з кожним днем. Проаналізовано типи можливих атак і виявлено, що основним захистом залишається криптографічна система захисту каналу керування БПЛА. Дана стаття дозволяє заглибитися в проблеми і переваги викликані новою безпілотною літальною технікою, зрозуміти серйозність проблем і перспектив, можливість розвитку і досліджень в цьому напрямку

Coherent exciton-vibrational dynamics and energy transfer in conjugated organics

Coherence, signifying concurrent electron-vibrational dynamics in complex natural and man-made systems, is currently a subject of intense study. Understanding this phenomenon is important when designing carrier transport in optoelectronic materials. Here, excited state dynamics simulations reveal a ubiquitous pattern in the evolution of photoexcitations for a broad range of molecular systems. Symmetries of the wavefunctions define a specific form of the non-adiabatic coupling that drives quantum transitions between excited states, leading to a collective asymmetric vibrational excitation coupled to the electronic system. This promotes periodic oscillatory evolution of the wavefunctions, preserving specific phase and amplitude relations across the ensemble of trajectories. The simple model proposed here explains the appearance of coherent exciton-vibrational dynamics due to non-adiabatic transitions, which is universal across multiple molecular systems. The observed relationships between electronic wavefunctions and the resulting functionalities allows us to understand, and potentially manipulate, excited state dynamics and energy transfer in molecular materials.Fil: Nelson, Tammie R.. Los Alamos National Laboratory; Estados UnidosFil: Ondarse Alvarez, Dianelys. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Oldani, Andres Nicolas. Universidad Nacional de Quilmes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rodríguez Hernández, Beatriz. Universidad Nacional de Quilmes; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Alfonso Hernandez, Laura. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Galindo, Johan F.. Universidad Nacional de Colombia; ColombiaFil: Kleiman, Valeria D.. University of Florida; Estados UnidosFil: Fernández Alberti, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Roitberg, Adrián. University of Florida; Estados UnidosFil: Tretiak, Sergei. Los Alamos National Laboratory; Estados Unido

Raman and nuclear magnetic resonance investigation of alkali metal vapor interaction with alkene-based anti-relaxation coating

The use of anti-relaxation coatings in alkali vapor cells yields substantial performance improvements by reducing the probability of spin relaxation in wall collisions by several orders of magnitude. Some of the most effective anti-relaxation coating materials are alpha-olefins, which (as in the case of more traditional paraffin coatings) must undergo a curing period after cell manufacturing in order to achieve the desired behavior. Until now, however, it has been unclear what physicochemical processes occur during cell curing, and how they may affect relevant cell properties. We present the results of nondestructive Raman-spectroscopy and magnetic-resonance investigations of the influence of alkali metal vapor (Cs or K) on an alpha-olefin, 1-nonadecene coating the inner surface of a glass cell. It was found that during the curing process, the alkali metal catalyzes migration of the carbon-carbon double bond, yielding a mixture of cis- and trans-2-nonadecene.Comment: 5 pages, 6 figure

Effect of Intra-molecular Disorder and Inter-molecular Electronic Interactions on the Electronic Structure of Poly-p-Phenylene Vinylene (PPV)

We investigate the role of intra-molecular conformational disorder and inter-molecular electronic interactions on the electronic structure of disorder clusters of poly-p-phenylene vinylene (PPV) oligomers. Classical molecular dynamics is used to determine probable molecular geometries, and first-principle density functional theory (DFT) calculations are used to determine electronic structure. Intra-molecular and inter-molecular effects are disentangled by contrasting results for densely packed oligomer clusters with those for ensembles of isolated oligomers with the same intra-molecular geometries. We find that electron trap states are induced primarily by intra-molecular configuration disorder, while the hole trap states are generated primarily from inter-molecular electronic interactions.Comment: 4 pages, 4 figures. Compile with pdflate

Morphology Effectively Controls Singlet-Triplet Exciton Relaxation and Charge Transport in Organic Semiconductors

We present a comparative study of ultrafast photo-conversion dynamics in tetracene (Tc) and pentacene (Pc) single crystals and Pc films using optical pump-probe spectroscopy. Photo-induced absorption in Tc and Pc crystals is activated and temperature-independent respectively, demonstrating dominant singlet-triplet exciton fission. In Pc films (as well as C$_{60}$-doped films) this decay channel is suppressed by electron trapping. These results demonstrate the central role of crystallinity and purity in photogeneration processes and will constrain the design of future photovoltaic devices.Comment:

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Contains research objectives and reports on one research projects.Lincoln Laboratory, Purchase Order DDL B-00368U. S. ArmyU. S. NavyU. S. Air Force under Air Force Contract AF19(604)-7400National Institutes of Health (Grant MH-04737-02

Molecular-orbital-free algorithm for excited states in time-dependent perturbation theory

A non-linear conjugate gradient optimization scheme is used to obtain excitation energies within the Random Phase Approximation (RPA). The solutions to the RPA eigenvalue equation are located through a variational characterization using a modified Thouless functional, which is based upon an asymmetric Rayleigh quotient, in an orthogonalized atomic orbital representation. In this way, the computational bottleneck of calculating molecular orbitals is avoided. The variational space is reduced to the physically-relevant transitions by projections. The feasibility of an RPA implementation scaling linearly with system size, N, is investigated by monitoring convergence behavior with respect to the quality of initial guess and sensitivity to noise under thresholding, both for well- and ill-conditioned problems. The molecular- orbital-free algorithm is found to be robust and computationally efficient providing a first step toward a large-scale, reduced complexity calculation of time-dependent optical properties and linear response. The algorithm is extensible to other forms of time-dependent perturbation theory including, but not limited to, time-dependent Density Functional theory.Comment: 9 pages, 7 figure