Tkachenko modes as sources of quasiperiodic pulsar spin variations

We study the long wavelength shear modes (Tkachenko waves) of triangular lattices of singly quantized vortices in neutron star interiors taking into account the mutual friction between the superfluid and the normal fluid and the shear viscosity of the normal fluid. The set of Tkachenko modes that propagate in the plane orthogonal to the spin vector are weakly damped if the coupling between the superfluid and normal fluid is small. In strong coupling, their oscillation frequencies are lower and are undamped for small and moderate shear viscosities. The periods of these modes are consistent with the observed ~100-1000 day variations in spin of PSR 1828-11.Comment: 7 pages, 3 figures, uses RevTex, v2: added discussion/references, matches published versio

Vortex lattice stability and phase coherence in three-dimensional rapidly rotating Bose condensates

We establish the general equations of motion for the modes of a vortex lattice in a rapidly rotating Bose-Einstein condensate in three dimensions, taking into account the elastic energy of the lattice and the vortex line bending energy. As in two dimensions, the vortex lattice supports Tkachenko and gapped sound modes. In contrast, in three dimensions the Tkachenko mode frequency at long wavelengths becomes linear in the wavevector for any propagation direction out of the transverse plane. We compute the correlation functions of the vortex displacements and the superfluid order parameter for a homogeneous Bose gas of bounded extent in the axial direction. At zero temperature the vortex displacement correlations are convergent at large separation, but at finite temperatures, they grow with separation. The growth of the vortex displacements should lead to observable melting of vortex lattices at higher temperatures and somewhat lower particle number and faster rotation than in current experiments. At zero temperature a system of large extent in the axial direction maintains long range order-parameter correlations for large separation, but at finite temperatures the correlations decay with separation.Comment: 10 pages, 2 figures, Changes include the addition of the particle density - vortex density coupling and the correct value of the shear modulu

Energy losses of fast heavy-ion projectiles in dense hydrogen plasmas

It has been recently shown that the Bethe-Larkin formula for the energy losses of fast heavy-ion projectiles in dense hydrogen plasmas is corrected by the electron-ion correlations [Phys. Rev. Lett. \textbf{101}, 075002 (2008)]. We report numerical estimates of this correction based on the values of $g_{ei}(0)$ obtained by numerical simulations in [Phys. Rev. E \textbf{61}, 3470 (2000)]. We also extend this result to the case of projectiles with dicluster charge distribution. We show that the experimental visibility of the electron-ion correlation correction is enhanced in the case of dicluster projectiles with randomly orientated charge centers. Although we consider here the hydrogen plasmas to make the effect physically more clear, the generalization to multispecies plasmas is straightforward.Comment: 5 pages, 1 figure. International Conference on Strongly Coupled Coulomb Systems 2008, Camerino (Italy). To appear in J. Phys.

Rapidly rotating Bose-Einstein condensates in anharmonic potentials

Rapidly rotating Bose-Einstein condensates confined in anharmonic traps can exhibit a rich variety of vortex phases, including a vortex lattice, a vortex lattice with a hole, and a giant vortex. Using an augmented Thomas-Fermi variational approach to determine the ground state of the condensate in the rotating frame -- valid for sufficiently strongly interacting condensates -- we determine the transitions between these three phases for a quadratic-plus-quartic confining potential. Combining the present results with previous numerical simulations of small rotating condensates in such anharmonic potentials, we delineate the general structure of the zero temperature phase diagram.Comment: 5 pages, 5 figure

Дворівнева інтелектуальна система контролю роботи сонячних панелей

Studied the degradation rate and characteristics of solar cells. Developed the algorithm forsolar cell characteristic analysis. Developed system for real time tracking and analysis of solar panelvolt-ampere characteristicsРассмотрен уровень деградации и основные характеристики солнечных элементов. Разработан алгоритм дляанализа характеристик солнечных элементов. Разработана система для мониторинга и анализа характеристикпанелей в реальном времениРозглянуто рівень деградації та основні характеристики сонячних елементів. Розроблено алгоритм для аналізу характеристик сонячних елементів. Розроблено систему для моніторингу та аналізу характеристик панелей вреальному час

Vortices in Spatially Inhomogeneous Superfluids

We study vortices in a radially inhomogeneous superfluid, as realized by a trapped degenerate Bose gas in a uniaxially symmetric potential. We show that, in contrast to a homogeneous superfluid, an off-axis vortex corresponds to an anisotropic superflow whose profile strongly depends on the distance to the trap axis. One consequence of this superflow anisotropy is vortex precession about the trap axis in the absence of an imposed rotation. In the complementary regime of a finite prescribed rotation, we compute the minimum-energy vortex density, showing that in the rapid-rotation limit it is extremely uniform, despite a strongly inhomogeneous (nearly) Thomas-Fermi condensate density $\rho_s(r)$. The weak radially-dependent contribution ($\propto \nabla^2\ln\rho_s(r)$) to the vortex distribution, that vanishes with the number of vortices $N_v$ as $\frac{1}{N_v}$, arises from the interplay between vortex quantum discretness (namely their inability to faithfully support the imposed rigid-body rotation) and the inhomogeneous superfluid density. This leads to an enhancement of the vortex density at the center of a typical concave trap, a prediction that is in quantitative agreement with recent experiments (cond-mat/0405240). One striking consequence of the inhomogeneous vortex distribution is an azimuthally-directed, radially-shearing superflow.Comment: 22 RevTeX pages, 20 figures, Submitted to PR