Exciton-Polariton scattering for defect detection in cold atom Optical Lattices

We study the effect of defects in the Mott insulator phase of ultracold atoms in an optical lattice on the dynamics of resonant excitations. Defects, which can either be empty sites in a Mott insulator state with one atom per site or a singly occupied site for a filling factor two, change the dynamics of Frenkel excitons and cavity polaritons. While the vacancies in first case behave like hard sphere scatters for excitons, singly occupied sites in the latter case can lead to attractive or repulsive scattering potentials. We suggest cavity polaritons as observation tool of such defects, and show how the scattering can be controlled in changing the exciton-photon detuning. In the case of asymmetric optical lattice sites we present how the scattering effective potential can be detuned by the cavity photon polarization direction, with the possibility of a crossover from a repulsive into an attractive potential.Comment: 9 pages, 10 figure

Tunable exciton interactions in optical lattices with polar molecules

Rotational excitation of polar molecules trapped in an optical lattice gives rise to rotational excitons. Here we show that non-linear interactions of such excitons can be controlled by an electric field. The exciton--exciton interactions can be tuned to induce exciton pairing, leading to the formation of biexcitons. Tunable non-linear interactions between excitons can be used for many applications ranging from the controlled preparation of entangled quasiparticles to the study of polaron interactions and the effects of non-linear interactions on quantum energy transport in molecular aggregates.Comment: Some typos have been corrected in this versio

COMPARISON OF EFFECTS OF ENALAPRIL AND UNCONTROLLED ANTIHYPERTENSIVE THERAPY ON INSULIN RESISTANCE, ENDOTHELIUM FUNCTION, MARKERS OF INFLAMMATION AND PLATELET ACTIVITY IN PATIENTS WITH METABOLIC SYNDROME

Aim. To assess influence of enalapril and uncontrolled antihypertensive therapy on insulin resistance, endothelium function, markers of inflammation, and platelet activity in patients with metabolic syndrome (MS). Material and methods. 41 patients with MS (21 women and 20 men, aged 58±2 years) were included into open parallel controlled study. MS was defined according to III report of USA Educational Program on cholesterol (2001). Patients were divided into 2 groups. Patients of the 1st group received enalapril (Enam, Dr. Reddy’s) 10 mg daily with further dose titration to 20 mg daily. Patients of the  2nd group continued receiving the same antihypertensive therapy as before (15% - inhibitors of angiotensin converting enzymes, 15% - в-blockers, 15% - diuretics, and 20% of patients - combined therapy). Study duration was 12 weeks. Results. Therapy with enalapril during 3 months resulted into significant decrease in systolic and diastolic blood pressure (BP) by 13 and 9% respectively. BP level decreased insignificantly (by 4,5 and 2% respectively) in controlled group. Ratio of plasma concentration of glucose to insulin in the 1st group increased by 14% before glucose load, and by 25% (p<0,05) 2 hours after peroral glucose load, while in the 2nd group decrease in these figures was noted by 12 and 5% respectively. This shows that treatment with enalapril, unlike uncontrolled antihypertensive therapy, lead to decrease in insulin resistance. Cuff test revealed significant increase in growth of brachial artery diameter in the group of patients, who received enalapril (12% before treatment, and 17% after treatment). Regular antihypertensive therapy didn’t change this parameter significantly (13 and 13,8% respectively). C-reactive protein level decreased by 48% (p<0,05) in the 1st group. Insignificant increase of this marker’s level was observed in the 2nd group. Platelet functional activity in both groups didn’t change significantly. Conclusion.  Together with strong antihypertensive effect, enalapril monotherapy is more efficient than regular antihypertensive therapy in reducing insulin resistance and chronic subclinical inflammation, as well as it has priority in improving endothelium depending vasodilatation

Graphene-based modulation-doped superlattice structures

The electronic transport properties of graphene-based superlattice structures are investigated. A graphene-based modulation-doped superlattice structure geometry is proposed and consist of periodically arranged alternate layers: InAs/graphene/GaAs/graphene/GaSb. Undoped graphene/GaAs/graphene structure displays relatively high conductance and enhanced mobilities at elevated temperatures unlike modulation-doped superlattice structure more steady and less sensitive to temperature and robust electrical tunable control on the screening length scale. Thermionic current density exhibits enhanced behaviour due to presence of metallic (graphene) mono-layers in superlattice structure. The proposed superlattice structure might become of great use for new types of wide-band energy gap quantum devices.Comment: 5 figure

Effects of inhomogeneous broadening on reflection spectra of Bragg multiple quantum well structures with a defect

The reflection spectrum of a multiple quantum well structure with an inserted defect well is considered. The defect is characterized by the exciton frequency different from that of the host's wells. It is shown that for relatively short structures, the defect produces significant modifications of the reflection spectrum, which can be useful for optoelectronic applications. Inhomogeneous broadening is shown to affect the spectrum in a non-trivial way, which cannot be described by the standard linear dispersion theory. A method of measuring parameters of both homogeneous and inhomogeneous broadenings of the defect well from a single CW reflection spectrum is suggested.Comment: 27 pages, 6 eps figures; RevTe

Разборная отражательная антенная решетка Ku-диапазона частот на основе микрополоскового элемента в виде мальтийского креста

Introduction. Reflectarrays have a number of design and functional advantages over their closest analogue - reflector antennas (RA). Although microstrip elements are the most preferred reflectarray elements, single-layer microstrip elements do not allow accurate phase control due to the limited phase adjustment range and a high phase slope. The use of multilayer elements significantly complicates the antenna design and increases its cost. The development of a single-layer element that allows more than 360° phase adjustment and a low phase curve slope is urgent.Aim. To develop a single-layer microstrip phase-correcting element with a phase adjustment range of more than 360° and to design a reflectarray on its basis for operation in satellite communication networks.Materials and methods. Numerical studies were carried out using finite element analysis and the finite-difference time-domain method. Radiation patterns were measured using the near-field scanning method in an anechoic chamber.Results. A phase-correcting element based on a single-layer Maltese cross-shaped microstrip element with close to linear dependence of element size on the phase of the reradiated wave and more than 360° phase adjustment range was developed. On the basis of the investigated element, a foldable reflectarray was designed. The reflector consists of four subarrays, which provide its compact folding for transportation. The results of experimental studies confirmed a high efficiency of the reflectarray, the gain of which is 1.5 dB lower than that of an identical overall dimensions RA in a 7 % operating frequency band. The operating frequency band of the reflectarray in 1 dB gain zone was 11 %.Conclusion. On the basis of a Maltese cross microstrip element, it is possible to implement a single-layer reflectarray with a more than 10 % frequency band. The developed prototype showed the possibility of creating highly efficient foldable reflectarrays for operation in satellite communication and television terminals.Введение. Отражательные антенные решетки (ОАР) обладают рядом конструктивных и функциональных преимуществ относительно ближайшего аналога – зеркальных антенн (ЗА). Наиболее предпочтительными элементами ОАР являются микрополосковые, однако однослойные микрополосковые элементы зачастую не позволяют точно скорректировать фазу в ОАР из-за ограниченного диапазона фазовой регулировки и высокой крутизны фазовой кривой. Использование многослойных элементов заметно усложняет и удорожает конструкцию антенны. В связи с этим актуален поиск однослойных элементов, обеспечивающих фазовую регулировку более 360° с малой крутизной фазовой кривой.Цель работы. Разработка однослойного микрополоскового фазокорректирующего элемента отражательного типа с диапазоном регулировки более 360° и создание на его основе ОАР для работы в сетях спутниковой связи.Материалы и методы. Численные исследования проведены методом конечных элементов и методом конечных разностей во временно́й области. Характеристики направленности измерялись сканированием ближнего поля в безэховой камере.Результаты. Разработан фазокорректирующий элемент на основе однослойного микрополоскового резонатора в виде мальтийского креста с близкой к линейной зависимостью фазы отраженной волны от размера элемента, обеспечивающий диапазон фазовой регулировки более 360°. На основе исследованного элемента разработана и изготовлена разборная конструкция ОАР, в которой рефлектор состоит из четырех подрешеток, что обеспечивает компактное свертывание ОАР для транспортировки. Результаты экспериментальных исследований показали высокую эффективность ОАР, коэффициент усиления (КУ) которой на 1.5 дБ ниже КУ ЗА идентичных габаритных размеров в относительной полосе рабочих частот (ОПРЧ) 7 %. ОПРЧ ОАР по уровню снижения КУ на 1 дБ составила 11 %.Заключение. На основе элемента в виде мальтийского креста возможна реализация однослойных ОАР с ОПРЧ более 10 %. Разработанный макет показал возможность создания высокоэффективных сворачиваемых ОАР для работы в составе терминалов спутниковой связи и телевидения

Двухдиапазонная отражательная антенная решетка Ka/Q-диапазонов частот

Introduction. Duplex satellite communication is commonly arranged using two spaced frequency bands, with one band receiving and the other band transmitting signals to a satellite. The main task of a communications satellite antenna system consists in providing an identical coverage area across all involved frequency bands, which is often a challenging task for conventional parabolic reflector antennas. Reflectarrays allow an independent control of the reradiated wave phase in spaced frequency bands, which can be used to create efficient multi-band antenna systems for modern communication satellites.Aim. To develop a Ka/Q-frequency range phase-correcting element and to create on its basis a dual-band reflectarray for operation with orthogonal circular polarizations and identical gains in a given sector of angles in significantly spaced frequency ranges.Materials and methods. Numerical studies were carried out using the finite element analysis method. Radiation patterns were measured using the near field scanning method.Results. A single-layer dual-band phase-correcting reflectarray element was developed for operation with orthogonal circular polarizations with low losses and a weak dependence of the relative position of the elements on the phase characteristic. On the basis of the proposed element, a reflectarray consisting of 24 465 two-frequency elements was synthesized and manufactured. The developed prototype of a single-layer dual-band reflectarray demonstrated good characteristics, with the efficiency reaching 56 and 36 % in the Ka- and Q-frequency ranges, respectively, and an almost identical minimum gain in the ±0.75° angle sector.Conclusion. The research results confirm the potential of the developed reflectarray to successfully replace conventional parabolic reflectors installed both on modern communication satellites and as part of ground-based satellite terminals in the millimeter wavelength range.Введение. Для организации дуплексной спутниковой связи, как правило, используются два разнесенных диапазона частот: один – для приема, второй – для передачи сигнала на спутник. Основной задачей антенной системы спутника связи является обеспечение идентичной зоны покрытия во всех задействованных диапазонах частот, что зачастую затруднительно с использованием традиционных параболических зеркальных антенн. Отражательные антенные решетки (ОАР) позволяют осуществлять независимое управление фазой переизлученной волны в разнесенных диапазонах частот, что может быть использовано для создания эффективных многодиапазонных антенных систем современной спутниковой связи.Цель работы. Разработка фазокорректирующего элемента Ka/Q-диапазонов частот и создание на его основе двухдиапазонной ОАР для работы с ортогональными круговыми поляризациями, обладающей идентичными коэффициентами усиления (КУ) в заданном секторе углов в значительно разнесенных диапазонах частот.Материалы и методы. Численные исследования проведены методом конечных элементов. Характеристики направленности измерялись методом сканирования в ближнем поле антенны.Результаты. Разработан однослойный двухдиапазонный фазокорректирующий элемент ОАР для работы с ортогональными круговыми поляризациями с малыми потерями и слабой зависимостью фазовой характеристики от взаимного расположения элементов. На основе предложенного элемента синтезирована и изготовлена ОАР, состоящая из 24 465 двухчастотных элементов. Разработанный макет однослойной двухдиапазонной ОАР продемонстрировал хорошую эффективность, коэффициент использования поверхности достигает 56 и 36 %, соответственно, в Ka- и Q-диапазонах частот при практически идентичном минимальном КУ в секторе углов ±0.75°.Заключение. Результаты исследований показывают возможность ОАР с успехом замещать традиционные параболические рефлекторы как на современных спутниках связи, так и в составе наземных спутниковых терминалов в миллиметровом диапазоне длин волн