Single and molecular ion irradiation-induced effects in GaN : experiment and cumulative MD simulations

An investigation of mechanisms of enhancement of irradiation-induced damage formation in GaN under molecular in comparison to monatomic ion bombardment is presented. Ion-implantation-induced effects in wurtzite GaN bombarded with 0.6 keV amu(-1) F, P, PF2, PF4, and Ag ions at room temperature are studied experimentally and by cumulative MD simulation in the correct irradiation conditions. In the low dose regime, damage formation is correlated with a reduction in photoluminescence decay time, whereas in the high dose regime, it is associated with the thickness of the amorphous/disordered layer formed at the sample surface. In all the cases studied, a shift to molecular ion irradiation from bombardment by its monatomic constituents enhances the damage accumulation rate. Implantation of a heavy Ag ion, having approximately the same mass as the PF4 molecule, is less effective in surface damage formation, but leads to noticeably higher damage accumulation in the bulk. The cumulative MD simulations do not reveal any significant difference in the total amount of both point defects and small defect clusters produced by light monatomic and molecular ions. On the other hand, increased production of large defect clusters by molecular PF4 ions is clearly seen in the vicinity of the surface. Ag ions produce almost the same number of small, but more large defect clusters compared to the others. These findings show that the higher probability of formation of large defect clusters is important mechanism of the enhancement of stable damage formation in GaN under molecular, as well as under heavy monatomic ion irradiation.Peer reviewe

Морфология и экологические особенности Sparganium × longifolium (Typhaceae) в центре Европейской части России

The increasing impact of anthropogenic factors and climate change affect the growth of a number of taxa of hybrid nature. These taxa are widespread among various taxonomic groups of aquatic and semi-aquatic plants. The genus Sparganium L. В is not an exception. In that regard, the aim of this study is to conduct biomorphological investigation of Sparganium × longifolium Turcz. ex Ledeb., evaluate qualitative and quantitative criteria for the hybrid similarities and differences with its parental species, as well as to analyze data on its habitat characteristics. Samples were collected in 2014–2016 from waterbodies in European Russia (Tver and Yaroslavl oblasts). In the study on biomorphology of S. × longifolium we used live and fixed materials, as well as herbarium funds of IBIW, MXA and MW. To establish and specify taxonomic features of the hybrid under study, indicating to its similarity with a certain ancestral species, our data on the morphology and ecology of S. emersum Rehm. and S. gramineum Georgi. are used. During field studies, the type of water object where the hybrid was detected, ecological characteristics of its habitat (type of soil, depth, water temperature and pH) are determined; the list of taxa which enter into the cenosis composition is compiled. The biomorphological investigation of S. × longifolium shows that by life form this hybrid, as well as its parental species, is a vegetative-mobile evidently-polycentric annual or biennial plant of vegetative origin with a racemose root system. The following should be attributed to the characteristic features justifying the hybrid origin of S. × longifolium: 1) a wider, slightly carinated lamina (as in S. emersum); 2) a branched inflorescence (as in S. gramineum); 3) the lower covering leaf of inflorescence, often exceeding the total length of the latter; 4) fruits with a straight (as in S. emersum) as well as bent (as in S. gramineum) style. Interestingly, some populations of S. × longifolium are rich in terate forms that can be explained by back crossing with one of the parental species or pleiotropic mutation(s). It is established that S. × longifolium is not widespread in European Russia, is a typically freshwater species, occurring in the littoral zone of mesotrophic and dystrophic waterbodies (usually in lakes of glacier origin). At present, its appearance in lake ecosystems is due to accelerated eutrophication caused by increasing human activities. Perhaps earlier this hybrid formation occurred in peripheral zones of the range of S. gramineum under cyclic climate changes. Observations suggest that S. × longifolium exceeds S. gramineum in ecological potential. At the same time, habitat features of the latter have an effect on the hybrid’s distribution potential (limitation of habitat spectrum), which is hardly exceeds S. emersum in its ecological and coenotic characteristics. 154   На основе современных подходов к анализу жизненных форм рассмотрена морфология вегетативной и генеративной сферы Sparangium × longifolium Turcz. ex Ledeb. (S. emersum Rehm. × S. gramineum Georgi). По жизненной форме S. × longifolium, как и его родительские виды, представляет собой вегетативно-подвижный явнополицентрический малолетник вегетативного происхождения с кистевидной корневой системой. В работе установлен промежуточный характер конкретных признаков гибрида, либо смещение того или иного признака в сторону одного из родительских видов. К характерным особенностям, подтверждающим гибридное происхождение S. × longifolium, следует отнести: 1) наличие более широкой, слегка килеватой листовой пластинки (как у S. emersum); 2) наличие разветвленного соцветия (как у S. gramineum); 3) нижний кроющий лист соцветия, часто превышающий общую длину последнего; 4) наличие плодов как с прямым (как у S. emersum), так и с загнутым (как у S. gramineum) столбиком. Отдельные популяции S. × longifolium изобилуют тератными формами, которые могут быть объяснены наличием возвратного скрещивания, либо мутации(й) с плейотропным проявлением. Анализ пыльцы гибрида на жизнеспособность показал преобладание стерильной пыльцы над фертильной. Установлено, что S. × longifolium – малораспространенный на территории Европейской части России – типично пресноводный вид, встречающийся в прибрежной зоне мезотрофных и дистрофных водных объектов (обычно в озерах ледникового происхождения). Появление популяций гибрида в озерах обусловлено их стремительной эвтрофикацией в результате антропогенной деятельности. Ранее образование этого гибрида, вероятно, происходило в периферийных частях ареала S. gramineum при циклических изменениях климата. Вместе с тем, особенности местообитания последнего накладывают «отпечаток» на потенциал распространения гибрида (ограниченность спектра местообитаний), который вряд ли может превзойти по своим эколого-ценотическим характеристикам S. emersum.&nbsp

High frequency magnetic oscillations of the organic metal θ\theta-(ET)4_4ZnBr4_4(C6_6H4_4Cl2_2) in pulsed magnetic field of up to 81 T

De Haas-van Alphen oscillations of the organic metal $\theta$-(ET)$_4$ZnBr$_4$(C$_6$H$_4$Cl$_2$) are studied in pulsed magnetic fields up to 81 T. The long decay time of the pulse allows determining reliable field-dependent amplitudes of Fourier components with frequencies up to several kiloteslas. The Fourier spectrum is in agreement with the model of a linear chain of coupled orbits. In this model, all the observed frequencies are linear combinations of the frequency linked to the basic orbit $\alpha$ and to the magnetic-breakdown orbit $\beta$.Comment: 6 pages, 4 figure

Luminescence in anion-deficient hafnia nanotubes

Hafnia-based nanostructures and other high-k dielectrics are promising wide-gap materials for developing new opto- and nanoelectronics devices. They possess a unique combination of physical and chemical properties such as insensitivity to electrical and optical degradation, radiation damage stability, a high specific surface area, and an increased concentration of the appropriate active electron-hole centers. The present paper aims to investigate the structural, optical, and luminescent properties of anodized non-stoichiometric $HfO_2$ nanotubes. As-grown amorphous hafnia nanotubes and nanotubes annealed at 700{\deg}C with a monoclinic crystal lattice served as samples. It has been shown that the bandgap $E_g$ for direct allowed transitions amounts to $5.65\pm0.05$ eV for amorphous and $5.51\pm0.05$ eV for monoclinic nanotubes. For the first time, we have studied the features of the intrinsic cathodoluminescence and photoluminescence of the obtained nanotubular $HfO_2$ structures with an atomic deficiency in the anion sublattice at temperatures of 10 and 300 K. A broad emission band with a maximum of 2.3-2.4 eV has been revealed. We have also conducted an analysis of the kinetic dependencies of the observed photoluminescence for synthesized $HfO_2$ samples in the millisecond range at room temperature. It showed that there are several types of optically active capture and emission centers based on vacancy states in the $O_{3f}$ and $O_{4f}$ positions with different coordination numbers and a varied number of localized charge carriers ($V^0$, $V^-$, and $V^{2-}$). The uncovered regularities can be used to optimize the functional characteristics of developed-surface luminescent media based on nanotubular and nanoporous modifications of hafnia.Comment: 15 pages, 6 figures, 3 tables, 50 reference

ПРОБЛЕМЫ, СВЯЗАННЫЕ С ОПРЕДЕЛЕНИЕМ НЕОБХОДИМОГО КОЛИЧЕСТВА ТОПЛИВА ПРИ ПЛАНИРОВАНИИ ПОЛЕТОВ ПО СТАНДАРТНЫМ ТРАЕКТОРИЯМ ПРИБЫТИЯ (STAR), КОТОРЫЕ ИМЕЮТ УЧАСТКИ ДЛЯ ЗАДЕРЖКИ ВОЗДУШНЫХ СУДОВ

The article deals with the fuel planning problems for flights planned via standard arrival routes (STAR), with delay legs. Implementation of new standard arrival routes based on area navigation principles leads to increasing airspace capacity and reducing workload for both flight crews and air traffic controllers. More and more air navigation service providers implement modern STARs which include delay legs as their components. Delay legs are being used as modern alternative to delay actions performed with short time holding patterns or radar vectoring procedures. But, new STAR types’ implementation without changing fuel planning procedures has led to fuel consumption increase. The nature of problem is shown in the article with reference to recently designed, published and implemented Pulkovo airport new standard arrival routes with delay legs. The calculations made with the use of automated flight planning systems and shown extra fuel consumption are given. Contributing negative factors are described. Suggested methods of solving the problems allow avoiding extra fuel consumption and reducing pollution. The procedure for using the new approach to planning and performing flight via STARs with delay legs is described. Implementation of the new approach in arrival trajectory design, flight planning and flight performance via standard arrival routes with delay legs is actual for the existing arrival routes and the routes being projected.В статье дано описание проблем, связанных с определением необходимого количества топлива при планировании полетов по стандартным траекториям прибытия (STAR), имеющим участки для задержки воздушных судов. Новые маршруты прибытия, основанные на применении зональной навигации, позволили увеличить пропускную способность воздушного пространства, снизить загруженность диспетчеров УВД и экипажей воздушных судов. Все большее количество провайдеров аэронавигационного обслуживания внедряет современные траектории прибытия, составной частью которых являются участки для задержки воздушных судов. Участки для задержки воздушных судов используются как современная альтернатива краткосрочным зонам ожидания и векторению с целью задержки воздушного судна. Однако внедрение новых видов стандартных траекторий прибытия, без изменения подходов к планированию полетов по ним, привело к росту расхода авиационного топлива. В статье раскрывается суть проблемы планирования полета по новым видам траекторий прибытия на примере недавно спроектированных, опубликованных и введенных в эксплуатацию стандартных траекторий прибытия аэропорта Пулково, включающих участки для задержки воздушных судов. Приводятся расчеты с применением автоматизированных систем планирования полета, показывающие объем дополнительного расхода топлива. Описываются сопутствующие негативные факторы. Предлагаются методы решения проблем, позволяющие избежать роста расхода топлива и неблагоприятных выбросов в атмосферу. Описывается порядок использования нового подхода к планированию и выполнению полета по стандартным траекториям прибытия, имеющим участки для задержки воздушных судов. Внедрение нового подхода к проектированию, планированию и выполнению полетов по стандартным траекториям прибытия, имеющим участки для задержки воздушных судов, актуально для существующих и проектируемых траекторий прибытия

Segre Types of Symmetric Two-tensors in n-Dimensional Spacetimes

Three propositions about Jordan matrices are proved and applied to algebraically classify the Ricci tensor in n-dimensional Kaluza-Klein-type spacetimes. We show that the possible Segre types are [1,1...1], [21...1], [31\ldots 1], [z\bar{z}1...1] and degeneracies thereof. A set of canonical forms for the Segre types is obtained in terms of semi-null bases of vectors.Comment: 14 pages, LaTeX, replaced due to a LaTex erro

Quantum oscillations in the linear chain of coupled orbits: the organic metal with two cation layers theta-(ET)(4)CoBr(4)(C(6)H(4)Cl(2))

Analytical formulae for de Haas-van Alphen (dHvA) oscillations in linear chain of coupled two-dimensional (2D) orbits (Pippard's model) are derived systematically taking into account the chemical potential oscillations in magnetic field. Although corrective terms are observed, basic (alpha) and magnetic breakdown-induced (beta and 2beta - alpha) orbits can be accounted for by the Lifshits-Kosevich (LK) and Falicov-Stachowiak semiclassical models in the explored field and temperature ranges. In contrast, the 'forbidden orbit' beta - alpha amplitude is described by a non-LK equation involving a product of two classical orbit amplitudes. Furthermore, strongly non-monotonic field and temperature dependence may be observed for the second harmonics of basic frequencies such as 2alpha and the magnetic breakdown orbit beta + alpha, depending on the value of the spin damping factors. These features are in agreement with the dHvA oscillation spectra of the strongly 2D organic metal theta- theta-(ET)(4)CoBr(4)(C(6)H(4)Cl(2)).Comment: to be published in Europhysics Letters (2012

Diffuse-Charge Dynamics in Electrochemical Systems

The response of a model micro-electrochemical system to a time-dependent applied voltage is analyzed. The article begins with a fresh historical review including electrochemistry, colloidal science, and microfluidics. The model problem consists of a symmetric binary electrolyte between parallel-plate, blocking electrodes which suddenly apply a voltage. Compact Stern layers on the electrodes are also taken into account. The Nernst-Planck-Poisson equations are first linearized and solved by Laplace transforms for small voltages, and numerical solutions are obtained for large voltages. The ``weakly nonlinear'' limit of thin double layers is then analyzed by matched asymptotic expansions in the small parameter $\epsilon = \lambda_D/L$, where $\lambda_D$ is the screening length and $L$ the electrode separation. At leading order, the system initially behaves like an RC circuit with a response time of $\lambda_D L / D$ (not $\lambda_D^2/D$), where $D$ is the ionic diffusivity, but nonlinearity violates this common picture and introduce multiple time scales. The charging process slows down, and neutral-salt adsorption by the diffuse part of the double layer couples to bulk diffusion at the time scale, $L^2/D$. In the ``strongly nonlinear'' regime (controlled by a dimensionless parameter resembling the Dukhin number), this effect produces bulk concentration gradients, and, at very large voltages, transient space charge. The article concludes with an overview of more general situations involving surface conduction, multi-component electrolytes, and Faradaic processes.Comment: 10 figs, 26 pages (double-column), 141 reference