Controlling chaos in spatially extended beam-plasma system by the continuous delayed feedback

In present paper we discuss the control of complex spatio-temporal dynamics in a {spatially extended} non-linear system (fluid model of Pierce diode) based on the concepts of controlling chaos in the systems with few degrees of freedom. A presented method is connected with stabilization of unstable homogeneous equilibrium state and the unstable spatio-temporal periodical states analogous to unstable periodic orbits of chaotic dynamics of the systems with few degrees of freedom. We show that this method is effective and allows to achieve desired regular dynamics chosen from a number of possible in the considered system.Comment: 12 pages, 12 figure

Design of optical components for terahertz/sub-terahertz imaging systems

Abstract. The possibility of using the lenses with an aspherical surface for terahertz/ sub-terahertz (THz/sub-THz) imaging systems has been considered. Diffraction-limited optical system of four identical plano-convex aspheric lenses has been obtained. Tests of the lenses have been performed on the specially made stand. These calculated and experimental data have similar values, which confirms the use of such lenses in the THz/ sub-THz imaging systems

DANSSino: a pilot version of the DANSS neutrino detector

DANSSino is a reduced pilot version of a solid-state detector of reactor antineutrinos (to be created within the DANSS project and installed under the industrial 3 GW(th) reactor of the Kalinin Nuclear Power Plant -- KNPP). Numerous tests performed at a distance of 11 m from the reactor core demonstrate operability of the chosen design and reveal the main sources of the background. In spite of its small size (20x20x100 ccm), the pilot detector turned out to be quite sensitive to reactor antineutrinos, detecting about 70 IBD events per day with the signal-to-background ratio about unity.Comment: 16 pages, 11 figures, 3 tables. arXiv admin note: substantial text overlap with arXiv:1304.369

Использование новейших технологий для создания асферических линз ТГц/суб-ТГц диапазона

В багатьох областях науки і техніки існує потреба в формуванні зображень терагерцового/субтерагерцового (ТГц/суб-ТГц) діапазонів спектру. Такі системи активно використовуються в навігації, біології, медицини, безпеки, а також для виявлення наркотичних та вибухових речовин. Одними з важливих компонентів ТГц/суб-ТГц техніки є оптичні елементи. На сьогодні запропоновано багато системи з використанням позаосьових дзеркал та лінз. Основною задачею залишається вибір матеріалу та технології виготовлення, з урахуванням оптимального співвідношення ціна-якість. Робота присвячена розрахункам, виготовленню та тестуванню асферичних лінз для ТГц/суб-ТГц діапазонів спектру зі застосуванням новітніх технологій їх виготовлення. Проведені дослідження якості розрахованих та виготовлених асферичних лінз із АВС пластику, за допомогою 3D друку, показали чітке відтворення форми сигналу та відповідність розмірів розрахункам функції розсіяння точки; зниження ціни виробу в декілька разів. Суттєвим недоліком таких лінз є зменшення сигналу випромінювання, що є головним при використанні приймачів з невеликою чутливістю. Для таких випадків запропоновано використання додаткових заходів по підвищенню коефіцієнта пропускання лінз. Отримані результати показали можливість використання менш затратної 3-D технології друку для створення оптики ТГц/суб-ТГц діапазонів.A lot of areas of science and technology needs in the imaging terahertz / subterahertz (THz / sub-THz) range of the spectrum. Such systems are widely used in navigation, biology, medicine, security, as well as to detect drugs and explosives. The optical elements are very important for this technique. A lot of systems with off-axis mirrors and lenses used today. The choice of material and manufacturing technology remains a major challenge, given the optimal price-performance ratio. The paper is devoted to calculations and fabrication of aspheric lenses for THz / sub-THz spectral ranges with the latest technology. ABC plastic lenses were designed manufactured using 3D printing. Studies have shown a clear reproduction of the calculated waveform matching sizes and the point spread function; reduction in price of the product several times. A significant disadvantage of lenses is made of the radiation attenuation of the signal due to transmission loss. For such cases, it was suggested the use of additional measures to improve the surface finish, through the use of 3D printers with a ball filled with plastic 20-50 microns, or additional surface polishing. The results showed the possibility of using less expensive 3-D printing technology to create THz/sub-THz optics range. Obtained lenses can be used in problems THz imaging/sub-THz range, provided the increase of transmittance.В многих областях науки и техники существует потребность в формировании изображений терагерцового/субтерагерцового (ТГц/суб-ТГц) диапазонов спектра. Такие системы активно используются в навигации, биологии, медицине, безопасности, а также для выявления наркотических и взрывчатых веществ. Одними из важных компонентов ТГц/суб-ТГц техники являются оптические элементы. В настоящее время предложено много систем с использованием внеосевых зеркал и линз. Основной задачей остается выбор материала и технологии изготовления, с учетом оптимального соотношения цена-качество. Работа посвящена расчетам и изготовлению асферических линз для ТГц/суб-ТГц диапазонов спектра с применением новейших технологий их изготовления. Проведенные исследования качества рассчитанных и изготовленных асферических линз из АВС пластика, с помощью 3D печати, показали четкое воспроизведение формы сигнала и соответствие размеров расчетам функции рассеяния точки; снижение цены изделия в несколько раз. Существенным недостатком изготовленных линз является уменьшение сигнала излучения, за счет потери на пропускание. Для таких случаев предложено использование дополнительных мер по повышению чистоты поверхности, путем использования 3D принтеров с шаровым наполнением пластиком 20-50 мкм, или дополнительной полировкой поверхности. Полученные результаты показали возможность использования менее затратной 3-D технологии печати для создания оптики ТГц/суб-ТГц диапазонов

Langmuir wave linear evolution in inhomogeneous nonstationary anisotropic plasma

Equations describing the linear evolution of a non-dissipative Langmuir wave in inhomogeneous nonstationary anisotropic plasma without magnetic field are derived in the geometrical optics approximation. A continuity equation is obtained for the wave action density, and the conditions for the action conservation are formulated. In homogeneous plasma, the wave field E universally scales with the electron density N as E ~ N^{3/4}, whereas the wavevector evolution varies depending on the wave geometry

Search for sterile neutrinos at the DANSS experiment

DANSS is a highly segmented 1~m${}^3$ plastic scintillator detector. Its 2500 one meter long scintillator strips have a Gd-loaded reflective cover. The DANSS detector is placed under an industrial 3.1~$\mathrm{GW_{th}}$ reactor of the Kalinin Nuclear Power Plant 350~km NW from Moscow. The distance to the core is varied on-line from 10.7~m to 12.7~m. The reactor building provides about 50~m water-equivalent shielding against the cosmic background. DANSS detects almost 5000 $\widetilde\nu_e$ per day at the closest position with the cosmic background less than 3$\%$. The inverse beta decay process is used to detect $\widetilde\nu_e$. Sterile neutrinos are searched for assuming the $4\nu$ model (3 active and 1 sterile $\nu$). The exclusion area in the $\Delta m_{14}^2,\sin^22\theta_{14}$ plane is obtained using a ratio of positron energy spectra collected at different distances. Therefore results do not depend on the shape and normalization of the reactor $\widetilde\nu_e$ spectrum, as well as on the detector efficiency. Results are based on 966 thousand antineutrino events collected at 3 distances from the reactor core. The excluded area covers a wide range of the sterile neutrino parameters up to $\sin^22\theta_{14}<0.01$ in the most sensitive region.Comment: 10 pages, 13 figures, version accepted for publicatio

Experimental and Theoretical Investigation into the Effect of the Electron Velocity Distribution on Chaotic Oscillations in an Electron Beam under Virtual Cathode Formation Conditions

The effect of the electron transverse and longitudinal velocity spread at the entrance to the interaction space on wide-band chaotic oscillations in intense multiple-velocity beams is studied theoretically and numerically under the conditions of formation of a virtual cathode. It is found that an increase in the electron velocity spread causes chaotization of virtual cathode oscillations. An insight into physical processes taking place in a virtual cathode multiple velocity beam is gained by numerical simulation. The chaotization of the oscillations is shown to be associated with additional electron structures, which were separated out by constructing charged particle distribution functions.Comment: 9 pages, 8 figure

Detection of IR and sub/THz radiation using MCT thin layer structures: design of the chip, optical elements and antenna pattern

Two-color un-cooled narrow-gap MCT (mercury-cadmium-telluride) semiconductor thin layers, grown by liquid phase epitaxy or molecular beam epitaxy methods on high resistivity CdZnTe or GaAs substrates, with bow-type antennas were considered both as sub-terahertz direct detection bolometers and 3...10-micrometer infrared photoconductors. Optical system with aspheric THz lenses were designed and manufactured. An antenna pattern of structures on the thick substrate was discussed, and sensitivity of detector in both IR and sub-THz regions was measured

Structural and Functional Insights into the Pilotin-Secretin Complex of the Type II Secretion System

Gram-negative bacteria secrete virulence factors and assemble fibre structures on their cell surface using specialized secretion systems. Three of these, T2SS, T3SS and T4PS, are characterized by large outer membrane channels formed by proteins called secretins. Usually, a cognate lipoprotein pilot is essential for the assembly of the secretin in the outer membrane. The structures of the pilotins of the T3SS and T4PS have been described. However in the T2SS, the molecular mechanism of this process is poorly understood and its structural basis is unknown. Here we report the crystal structure of the pilotin of the T2SS that comprises an arrangement of four α-helices profoundly different from previously solved pilotins from the T3SS and T4P and known four α-helix bundles. The architecture can be described as the insertion of one α-helical hairpin into a second open α-helical hairpin with bent final helix. NMR, CD and fluorescence spectroscopy show that the pilotin binds tightly to 18 residues close to the C-terminus of the secretin. These residues, unstructured before binding to the pilotin, become helical on binding. Data collected from crystals of the complex suggests how the secretin peptide binds to the pilotin and further experiments confirm the importance of these C-terminal residues in vivo