Acoustics of tachyon Fermi gas

We consider a Fermi gas of free tachyons as a continuous medium and find whether it satisfies the causality condition. There is no stable tachyon matter with the particle density below critical value $n_T$ and the Fermi momentum $k_F<\sqrt{\frac 32}m$ that depends on the tachyon mass $m$. The pressure $P$ and energy density $E$ cannot be arbitrary small, but the situation $P>E$ is not forbidden. Existence of shock waves in tachyon gas is also discussed. At low density $n_T<n<3.45n_T$ the tachyon matter remains stable but no shock wave do survive.Comment: 14 pages, 2 figures (color

Shock waves in superconducting cosmic strings: growth of current

Intrinsic equations of motion of superconducting cosmic string may admit solutions in the shock-wave form that implies discontinuity of the current term \chi. The hypersurface of discontinuity propagates at finite velocity determined by finite increment \Delta \chi =\chi_+ -\chi_-. The current increases \chi_+>\chi_- in stable shocks but transition between spacelike (\chi >0) and timelike (\chi<0) currents is impossible.Comment: 13 pages, 3 figure

Parametric frequency mixing in the magneto-elastically driven FMR-oscillator

We demonstrate the nonlinear frequency conversion of ferromagnetic resonance (FMR) frequency by optically excited elastic waves in a thin metallic film on dielectric substrates. Time-resolved probing of the magnetization directly witnesses magneto-elastically driven second harmonic generation, sum- and difference frequency mixing from two distinct frequencies, as well as parametric downconversion of each individual drive frequency. Starting from the Landau-Lifshitz-Gilbert equations, we derive an analytical equation of an elastically driven nonlinear parametric oscillator and show that frequency mixing is dominated by the parametric modulation of FMR frequency

Double bracket dissipation in kinetic theory for particles with anisotropic interactions

We derive equations of motion for the dynamics of anisotropic particles directly from the dissipative Vlasov kinetic equations, with the dissipation given by the double bracket approach (Double Bracket Vlasov, or DBV). The moments of the DBV equation lead to a nonlocal form of Darcy's law for the mass density. Next, kinetic equations for particles with anisotropic interaction are considered and also cast into the DBV form. The moment dynamics for these double bracket kinetic equations is expressed as Lie-Darcy continuum equations for densities of mass and orientation. We also show how to obtain a Smoluchowski model from a cold plasma-like moment closure of DBV. Thus, the double bracket kinetic framework serves as a unifying method for deriving different types of dynamics, from density--orientation to Smoluchowski equations. Extensions for more general physical systems are also discussed.Comment: 19 pages; no figures. Submitted to Proc. Roy. Soc.

Collapsing dynamics of attractive Bose-Einstein condensates

The self-similar collapse of 3D and quasi-2D atom condensates with negative scattering length is examined. 3D condensates are shown to blow up following the scenario of {\it weak collapse}: The inner core of the condensate diverges with an almost zero particle number, while its tail distribution spreads out to large distances with a constant density profile. For this case, the 3-body recombination arrests the collapse, but it weakly dissipates the atoms. The confining trap then reforms the condensate at later times. In contrast, 2D condensates undergo a {\it strong collapse}: The atoms stay mainly located at center and recombination sequentially absorbs a significant amount of particles.Comment: 4 pages, submitted for publicatio

Hydrodynamic Instability of the Flux-antiflux Interface in Type-II Superconductors

The macroturbulence instability observed in fluxline systems during remagnetization of superconductors is explained. It is shown that when a region with flux is invaded by antiflux the interface can become unstable if there is a relative tangential flux motion. This condition occurs at the interface when the viscosity is anisotropic, e.g., due to flux guiding by twin boundaries in crystals. The phenomenon is similar to the instability of the tangential discontinuity in classical hydrodynamics. The obtained results are supported by magneto-optical observations of flux distribution on the surface of a YBCO single crystal with twins.Comment: 12 pages, 3 figures, submitted to Physical Review Letter

Eddy turbulence parameters inferred from radar observations at Jicamarca

Significant electron density striations, neutral temperatures 27 K above nominal, and intense wind shear were observed in the E-region ionosphere over the Jicamarca Radio Observatory during an unusual event on 26 July 2005 (Hysell et al., 2007). In this paper, these results are used to estimate eddy turbulence parameters and their effects. Models for the thermal balance in the mesosphere/lower thermosphere and the charged particle density in the E region are developed here. The thermal balance model includes eddy conduction and viscous dissipation of turbulent energy as well as cooling by infrared radiation. The production and recombination of ions and electrons in the E region, together with the production and transport of nitric oxide, are included in the plasma density model. Good agreement between the model results and the experimental data is obtained for an eddy diffusion coefficient of about 1&amp;times;10&lt;sup&gt;3&lt;/sup&gt; m&lt;sup&gt;2&lt;/sup&gt;/s at its peak, which occurs at an altitude of 107 km. This eddy turbulence results in a local maximum of the temperature in the upper mesosphere/lower thermosphere and could correspond either to an unusually high mesopause or to a double mesosphere. Although complicated by plasma dynamic effects and ongoing controversy, our interpretation of Farley-Buneman wave phase velocity (Hysell et al., 2007) is consistent with a low Brunt-Väisälä frequency in the region of interest. Nitric oxide transport due to eddy diffusion from the lower thermosphere to the mesosphere causes electron density changes in the E region whereas NO density modulation due to irregularities in the eddy diffusion coefficient creates variability in the electron density

Particularităţile hemodinamicii renale la pacienţii cu ciroze hepatice

Conferinţa naţională în medicina internă din Republica Moldova cu participare internaţională, 19-20 mai 2011, Chişinău, Republica MoldovaSummary. Perfoming color Doppler ultrasonography in patients with cirrhosis we investigated whether the RI and PI is useful in the detection of renal hemodynamic derangement and in the establishment of diagnosis in functional kidney failure.Actualitate. Pacienţii cu vasoconstricţie renală au o retenţie de sodiu mai pronunţată, activitate secretorie a vasopresinei mai crescută şi necesită doze mai mari de diuretice pentru prevenirea şi tratarea ascitei comparativ cu bolnavii cu perfuzie renală normală. În acest context este reactualizată aprecierea hemodinamicii renale la bolnavii cu ciroză cu ajutorul Dopplerografiei vaselor renale. Scopul lucrării: valorificarea indicilor hemodinamicii renale la pacienţii cu ciroze hepatice şi rolul lor în detectarea timpurie a complicaţiilor renale. Materiale şi metode. În studiu au fost incluşi 114 pacienţi cu ciroze hepatice, 64 bărbaţi (56,5%) şi 50 femei (43,5%), cărora li s-a efectuat ecografia Doppler Duplex a arterelor renale la nivelul trunchiurilor arterelor renale drepte şi stângi, la nivelul arterelor renale segmentare la ambii rinichi, cu determinarea indicelui pulsatil (IP) şi indicelui de rezistenţă (IR). Rezultate. Valorile IR pe ARD şi ARS crescute semnificativ la pacienţii cu ciroză hepatică clasa Child-Pugh B şi C, comparativ cu clasa Child –Pugh A (<0,001), IP la grupele respective a înregistrat o creştere nesimnificativă (>0,005). Viteza maximă sistolică a arterelor renale (ARSD) şi viteza minimă diastolică (ARSD) au avut diferenţe statistic semnificative între loturile cercetate (p<0,001), datele Dopplerografiei renale confirmând scăderea vascularizării renale odată cu progresia suferinţei hepatice, atât la nivel de trunchi, cât şi la nivel de artere segmentare renale. Concluzii. Se determină o scădere a vitezei sistolice maxime şi diastolice minime în arterele renale, ce denotă o circulaţie sangvină renală compromisă la pacienţii cu ciroză. Creşterea semnificativă a valorilor IR şi IP este prezentă la bolnavii cu ciroză hepatică clasa Child-Pugh B şi C, ceea ce confirmă prezenţa rezistenţei renale crescute în stadiile avansate ale cirozei şi riscul înalt al complicaţiilor renale