450 research outputs found
Spiders (Aranei) in the vegetation layer of agrocenoses in Leningrad Region, Russia
The research was carried out in 2012–2018 on fields of the Menkovsky Branch of the Agrophysical Research Institute, located in the Gatchina District of Leningrad Region. The study included cenoses of winter rye, winter wheat, spring wheat, spring barley, spring rapeseed, potatoes, narrow-leaved lupine, as well as perennial grasses – a mixture of meadow timothy and red clover. Collection of material on Aranei was timed to the phenological phases of a development of cultivated plants. The species composition, abundance, habitat distribution and population dynamics of spiders were studied in the vegetation layer of agrocenoses. The species composition includes at least 85 species; the abundance is from 0.23 to 1.03 specimens/10 swings of the net, depending on the characteristics of the agrocenosis. The spider complex in the herbage layer consists of representatives of the families Thomisidae, Araneidae, Philodromidae, Tetragnatidae and Lycosidae. The total number of spiders varies noticeably from year to year, increasing significantly in years with heavy rainfalls in June. The highest indices of abundance of spiders were typical for the fields with perennial grasses, and the least of all individuals were caught in the herbage of spring rapeseeds and potatoes. The maximum densities of spiders in the vegetation layer of agrocenoses is observed during the second and third decades of May, species diversity – in the period from the third decade of June to the second decade of Jul
Electron transport through interacting quantum dots
We present a detailed theoretical investigation of the effect of Coulomb
interactions on electron transport through quantum dots and double barrier
structures connected to a voltage source via an arbitrary linear impedance.
Combining real time path integral techniques with the scattering matrix
approach we derive the effective action and evaluate the current-voltage
characteristics of quantum dots at sufficiently large conductances. Our
analysis reveals a reach variety of different regimes which we specify in
details for the case of chaotic quantum dots. At sufficiently low energies the
interaction correction to the current depends logarithmically on temperature
and voltage. We identify two different logarithmic regimes with the crossover
between them occurring at energies of order of the inverse dwell time of
electrons in the dot. We also analyze the frequency-dependent shot noise in
chaotic quantum dots and elucidate its direct relation to interaction effects
in mesoscopic electron transport.Comment: 21 pages, 4 figures. References added, discussion slightly extende
Progress report of investigations on gyrotron ECR ion source SMIS 37
A review of experimental investigations on ion production in plasma developed on SMIS 37 source at the Institute of Applied Physics of RAS (Nizhny Novgorod) is reported. Pulsed power gyrotron with emission frequency 37.5 GHz was used for plasma creation and heating in the simple magnetic mirror trap. Magnetic field with value up to 3.5 T was created by pulsed coils. Experiments were carried out in nitrogen as operating gas. Formation of multicharged ions in dense plasma in different regimes of plasma confinement was investigated. In this report we describe some investigations of instabilities of the plasma in the trap. Low frequency instabilities are analyzed basing on the results of plasma high-speed image registration. Also, whistler cyclotron instability was observed. Short pulses of accelerated electrons with energy about 10 keV are measured. Detected short pulses of microwave emission of the plasma characterize cyclotron instability too. Dense plasma of singly charged ions obtained in the trap with the plug magnetic field much less than resonant value. Flux of the plasma exceeds 0,1 A/cm2, electron temperature is about 20 eV. Such plasma seems to be interesting for surface modification
Energy calibration of the NaI(Tl) calorimeter of the SND detector using cosmic muons
The general purpose spherical nonmagnetic detector (SND) is now taking data
at VEPP-2M collider in BINP (Novosibirsk) in the centre of mass energy
range of GeV. The energy calibration of the NaI(Tl) calorimeter
of the SND detector with cosmic muons is described. Using this method, the
energy resolution of for 500 MeV photons was achieved.Comment: 15 pages, Latex, 11 figures (.EPS
Search for direct production of a2(1320) and f2(1270) mesons in e+e- annihilation
A search for direct production of C-even resonances a2(1320) and f2(1270) in
e+e- annihilation was performed with SND detector at VEPP-2M e+e- collider. The
upper limits of electronic widths of these mesons were obtained at 90%
confidence level:
Gamma(a2(1320) \to e+e-) < 0.56 eV,
Gamma(f2(1270) \to e+e-) < 0.11 eV.Comment: 6 pages, 5 figures, 1 table. Submitted to Phys. Lett.
Nonstationary generation of electromagnetic radiation in nonequilibrium mirror-confined plasma
We demonstrate the use of a laboratory setup based on a magnetic mirror trap with plasma sustained by a gyrotron radiation under the electron cyclotron resonance conditions aimed at identifying the role of the background plasma as a trigger of the electron cyclotron instability. New regime of instability has been revealed during the plasma decay after the gyrotron switch-off when the plasma density becomes low enough, so that the electron plasma frequency is much less than the electron gyrofrequency. At this stage, we observe the excitation of electromagnetic waves which propagate nearly perpendicular to the magnetic field and cause precipitation of energetic electrons to the trap ends. The instability is detected as series of quasi-periodic broadband pulses of electromagnetic radiation (25…27 GHz frequency, typical pulse duration of 1…10 microseconds) and related precipitation of energetic (>10 keV) electrons. These emissions of the fast electrons can be attributed to the development of the kinetic instability of the extraordinary wave propagating quasiperpendicular to the magnetic field near the fundamental cyclotron harmonic.Исследованы временные и частотные характеристики квазипериодических импульсов электромагнитного излучения в распадающейся плазме импульсного ЭЦР-разряда в прямой аксиально-симметричной магнитной ловушке. Зарегистрированы серии квазипериодических импульсов электромагнитного излучения на частоте 25...27 ГГц с типичной длительностью импульса 1...10 мкс и связанные с ними высыпания энергичных (> 10 кэВ) электронов. Наблюдаемое излучение интерпретировано как результат резонансного взаимодействия горячих электронов с быстрой необыкновенной волной, распространяющейся в разреженной плазме поперек внешнего магнитного поля.Досліджено часові та частотні характеристики квазіперіодичних імпульсів електромагнітного випромінювання в плазмі, що розпадається, імпульсного ЕЦР-розряду в прямій аксіально-симетричній магнітній пастці. Зареєстровані серії квазіперіодичних імпульсів електромагнітного випромінювання на частоті 25...27 ГГц з типовою тривалістю імпульсу 1...10 мкс та пов'язані з ними висипання енергійних (> 10 кеВ) електронів. Випромінювання, що спостерігається, інтерпретовано як результат резонансної взаємодії гарячих електронів з швидкою незвичайною хвилею, що розповсюджується в розрідженій плазмі поперек зовнішнього магнітного поля
New approach for a “point-like” neutron source creation based on sharp focusing of a high quality deuteron beam produced by high-current gasdynamic ECR ion source
Generation of wideband electromagnetic radiation on a decay stage of a mirror-confined plasma produced by ECR discharge
A specific nonlinear regime of electron cyclotron instability is discussed aimed at explanation of complex temporal patterns of stimulated electromagnetic radiation from a mirror trap with non-equilibrium plasma typical of ECR discharge. This regime is characterized by self-modulation of a plasma cyclotron maser due to coherent interference of two counter-propagating unstable waves with degenerate frequencies. The proposed simple theoretical model allows reproducing multi-scale behavior of quasi-periodic pulses of electromagnetic radiation and precipitation of energetic electrons detected at a laboratory setup based on a mirror trap with plasma sustained by mm-wave gyrotron radiation.Обсуждается новый нелинейный режим электронно-циклотронной неустойчивости, объясняющий сложную временную динамику импульсов электромагнитного излучения сильнонеравновесной плазмы ЭЦР-разряда в прямой магнитной ловушке. Режим реализуется при самомодуляции циклотронного мазера полем биений двух встречных неустойчивых волн с вырожденными частотами. Предложенная простая теоретическая модель позволяет воспроизвести многомасштабную структуру импульсов электромагнитного излучения и высыпания энергичных электронов, зарегистрированных в лабораторном эксперименте с использованием прямой ловушки с плазмой, поддерживаемой излучением гиротрона миллимeтрового диапазона.Обговорюється новий нелінійний режим електронно-циклотронної нестійкості, що пояснює складну часову динаміку імпульсів електромагнітного випромінювання сильнонеравномірної плазми ЕЦР-розряду в прямій магнітній пастці. Режим реалізується при самомодуляціі циклотронного мазера полем биття двох зустрічних нестійких хвиль з виродженими частотами. Запропонована проста теоретична модель дозволяє відтворити багатомасштабну структуру імпульсів електромагнітного випромінювання та висипання енергійних електронів, зареєстрованих у лабораторному експерименті з використанням прямої пастки з плазмою, що підтримується випромінюванням гіротрона миллиметрового діапазону
Radiative decays of light vector mesons
The new data on radiative decays into
from SND experiment at VEPP-2M
collider are presented.Comment: 5 pages, 2 figures, talk given at 8th International Conference on
Hadron Spectroscopy (HADRON 99), Beijing, China, 24-28 Aug 199
New experimental data for the decays and from SND detector
The processes and have been
studied with SND detector at VEPP-2M collider in the vicinity of
resonance. The branching ratios and were obtained.Comment: 5 pages, 4 figures, talk given at 8th International Conference on
Hadron Spectroscopy (HADRON 99), Beijing, China, 24-28 Aug 199
- …