23 research outputs found
Dynamics of ring dark solitons in Bose-Einstein condensates and nonlinear optics
Quasiparticle approach to dynamics of dark solitons is applied to the case of
ring solitons. It is shown that the energy conservation law provides the
effective equations of motion of ring dark solitons for general form of the
nonlinear term in the generalized nonlinear Schroedinger or Gross-Pitaevskii
equation. Analytical theory is illustrated by examples of dynamics of ring
solitons in light beams propagating through a photorefractive medium and in
non-uniform condensates confined in axially symmetric traps. Analytical results
agree very well with the results of our numerical simulations.Comment: 10 pages, 4 figure
Condition for convective instability of dark solitons
Simple derivation of the condition for the transition point from absolute
instability of plane dark solitons to their convective instability is
suggested. It is shown that unstable wave packet expands with velocity equal to
the minimal group velocity of the disturbance waves propagating along a dark
soliton. The growth rate of the length of dark solitons generated by the flow
of Bose-Einstein condensate past an obstacle is estimated. Analytical theory is
confirmed by the results of numerical simulations
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Interference structure of above-threshold ionization versus above-threshold detachment
Laser-induced electron detachment or ionization of atoms and negative ions is considered. In the context of the saddle-point evaluation of the strong-field approximation (SFA), the velocity maps of the direct electrons (those that do not undergo rescattering) exhibit a characteristic structure due to the constructive and destructive interference of electrons liberated from their parent atoms/ions within certain windows of time. This structure is defined by the above-threshold ionization rings at fixed electron energy and by two sets of curves in momentum space on which destructive interference occurs. The spectra obtained with the SFA are compared with those obtained by numerical solution of the time-dependent Schrödinger equation. For detachment, the agreement is excellent. For ionization, the effect of the Coulomb field is most pronounced for electrons emitted in a direction close to laser polarization, while for nearperpendicular emission the qualitative appearance of the spectrum is unaffected
Surface activity distribution measurements and establishment of a dose rate map inside the destroyed Chernobyl reactor
Modulation control and spectral shaping of optical fiber supercontinuum generation in the picosecond regime
Numerical simulations are used to study how fiber supercontinuum generation
seeded by picosecond pulses can be actively controlled through the use of input
pulse modulation. By carrying out multiple simulations in the presence of
noise, we show how tailored supercontinuum Spectra with increased bandwidth and
improved stability can be generated using an input envelope modulation of
appropriate frequency and depth. The results are discussed in terms of the
non-linear propagation dynamics and pump depletion.Comment: Aspects of this work were presented in Paper ThJ2 at OECC/ACOFT 2008,
Sydney Australia 7-10 July (2008). Journal paper submitted for publication 30
July 200
Properties of 15Cr12WNiMoV steel after vacuum activated chromium plating of its surface
In this work, we studied the properties of samples from steel 15Cr12WNiMoV after vacuum activated chromium plating at temperatures of 1070 and 1100 °C for 4 and 10 h. It was found that after chemical-thermal treatment on the samples a diffusion layer with a thickness of 50 to 130 µm is formed, consisting of 56…82 wt.% of chromium, the rest is iron. Metallographic studies were carried out on the samples and tests for heat resistance were carried out at a temperature of T = 900 °C. It was found that chrome-plated samples significantly exceed the initial samples and nitrided ones in terms of heat resistance. Tests of samples for tensile strength after chromium plating showed a significant increase in strength indicators for ultimate strength and yield strength. The plasticity characteristics of these samples are reduced.Проведені дослідження властивостей зразків зі сталі 15Х12ВНМФ після вакуумного активованого хромування при температурах 1070 і 1100 °С протягом 4 і 10 год. Установлено, що після хіміко-термічної обробки на зразках формується дифузійний шар товщиною від 50 до 130 мкм, що складається з 56…82 ваг.% хрому, інше – залізо. На зразках були проведені металографічні дослідження й здійснені випробування на жаростійкість при Т = 900 °С. Установлено, що хромовані зразки по жаростійкості значно перевершують вихідні зразки й азотовані. Проведені випробування зразків на міцність на розрив після хромування показали істотне збільшення міцностних показників для межі міцності й межі текучості. Характеристики пластичності цих зразків зменшуються.Проведены исследования свойств образцов из стали 15Х12ВНМФ после вакуумного активированного хромирования при температурах 1070 и 1100 °С в течение 4 и 10 ч. Установлено, что после химикотермической обработки на образцах формируется диффузионный слой толщиной от 50 до 130 мкм, состоящий из 56…82 вес.% хрома, остальное – железо. На образцах были проведены металлографические исследования и осуществлены испытания на жаростойкость при Т = 900 °С. Установлено, что хромированные образцы по жаростойкости значительно превосходят исходные образцы и азотированные. Проведенные испытания образцов на прочность на разрыв после хромирования показали существенное увеличение прочностных показателей для предела прочности и предела текучести. Характеристики пластичности этих образцов уменьшаются
Peculiarities of neutron fields formation in the systems “neutron producing target – moderator” irradiated by high energy particles
The theoretical and experimental evidence of similarity of neutron spectra formed in sub-critical systems driven
by external proton and neutron beamsПредставлено теоретичнi та експериментальнi докази подiбності спектрiв нейтронiв, що утворюються в
пiдкритичних системах, керованих зовнiшнiми протонним та нейтронним пучками.Представлены теоретические и экспериментальные доказательства подобия спектров нейтронов, образу-
ющихся в подкритических системах, управляемых внешними протонным и нейтронным пучками