Synchronization transitions and sensitivity to asymmetry in the bimodal Kuramoto systems with Cauchy noise.

We analyze the synchronization dynamics of the thermodynamically large systems of globally coupled phase oscillators under Cauchy noise forcings with a bimodal distribution of frequencies and asymmetry between two distribution components. The systems with the Cauchy noise admit the application of the Ott-Antonsen ansatz, which has allowed us to study analytically synchronization transitions both in the symmetric and asymmetric cases. The dynamics and the transitions between various synchronous and asynchronous regimes are shown to be very sensitive to the asymmetry degree, whereas the scenario of the symmetry breaking is universal and does not depend on the particular way to introduce asymmetry, be it the unequal populations of modes in a bimodal distribution, the phase delay of the Kuramoto-Sakaguchi model, the different values of the coupling constants, or the unequal noise levels in two modes. In particular, we found that even small asymmetry may stabilize the stationary partially synchronized state, and this may happen even for an arbitrarily large frequency difference between two distribution modes (oscillator subgroups). This effect also results in the new type of bistability between two stationary partially synchronized states: one with a large level of global synchronization and synchronization parity between two subgroups and another with lower synchronization where the one subgroup is dominant, having a higher internal (subgroup) synchronization level and enforcing its oscillation frequency on the second subgroup. For the four asymmetry types, the critical values of asymmetry parameters were found analytically above which the bistability between incoherent and partially synchronized states is no longer possible.

Generation of Few- and Subcycle Radiation in Midinfrared-to-Deep-Ultraviolet Range During Plasma Production by Multicolor Femtosecond Pulses.

Our closed-form analytical formulas and numerical calculations show that the plasma production by a two-color (or, more generally, multicolor) femtosecond pulse leads to generation of strong few- and subcycle radiation. The spectral composition of the radiation is defined by the numerous combination frequencies of the ionizing pulse. The radiation duration is equal to the ionization duration, which is much shorter than the multicolor pump. The phenomenon opens a new direct (without additional compression) way to create tunable sources of extremely short pulses with smooth envelopes and spectra in a broad range stretching from the midinfrared to the deep ultraviolet.

Ionization-Induced Multiwave Mixing: Terahertz Generation with Two-Color Laser Pulses of Various Frequency Ratios.

Ultrafast strong-field ionization is shown to be accompanied by atypical multiwave mixing with the number of mixed waves defined by the dependence of the ionization rate on the field strength. For two-color laser pulses of various frequency ratios, this results in the excitation of a free-electron current at laser combination frequencies and possibly in the excitation of the zero-frequency (residual) current responsible for terahertz (THz) generation in a formed plasma. The high-order nature of ionization-induced wave mixing may cause THz generation with uncommon laser frequency ratios (such as 2:3 and 3:4) to be virtually as effective as that with the commonly used frequency ratio of 1:2.

Transient and periodic spatiotemporal structures in a reaction-diffusion-mechanics system.

We study transient spatiotemporal structures induced by a weak space-time localized stimulus in an excitable contractile fiber within a two-component globally coupled reaction-diffusion model. The model which we develop allows us to analyze various regimes of excitation spreading and determine origin of the induced structures for various contraction types (defined by the fiber fixation) and global coupling strengths. One of the most notable effects we observed is the after-excitation effect. It leads to emergence of multiple excitation pulses excited by a single external stimulus and can result in long-lasting transient activity and appearance of new oscillatory attractor regimes, including the ones with multiple phase clusters.

Two-color laser-plasma generation of terahertz radiation using a frequency-tunable half harmonic of a femtosecond pulse.

We investigate for the first time, both experimentally and theoretically, low-frequency terahertz (THz) emission from the ambient air ionized by a two-color femtosecond laser pulse containing, besides the fundamental-frequency main field, a weak additional field tunable near the frequency of the half harmonic. By controlling the mutual polarization and the powers of the main and additional fields, we determine the dependences of the THz power and polarization on the parameters of the two-color pulse. We also discover the resonantlike dependence of the THz yield on the frequency detuning of the additional field. The analytical formulas obtained using the model of the free-electron residual current density give an excellent agreement with the experimental results.

Ionization-induced conversion of ultrashort Bessel beam to terahertz pulse.

We examine the conical terahertz emission from the superluminous ionization front created in air by an axicon-focused femtosecond laser pulse. We develop the theoretical model that explains the experimental results and predicts new possibilities to control terahertz pulse parameters.

[Method of using local hypothermia of the spinal cord in spinalized patients during the postoperative period]. / K metodike primeneniia lokal'noi gipotermii spinnogo mozga u spinal'nykh bol'nykh v posleoperatsionnom periode.

From analysis of observations over 61 spinal patients with acute and neglected injuries to the spinal cord the authors conclude that the use of local hypothermia of the spinal cord in the postoperative period has a favorable effect: reduces the muscle tonus, prevents edema, pain formation, and hemorrhage occurring after surgical intervention on the spinal cord, and produces an analgesic effect. Further mastering of the techniques of hypothermia is necessary.