Iordanskii Force and the Gravitational Aharonov-Bohm effect for a Moving Vortex

I discuss the scattering of phonons by a vortex moving with respect to a superfluid condensate. This allows us to test the compatibility of the scattering-theory derivation of the Iordanskii force with the galilean invariance of the underlying fluid dynamics. In order to obtain the correct result we must retain $O(v_s^2)$ terms in the sound-wave equation, and this reinforces the interpretation, due to Volovik, of the Iordanskii force as an analogue of the gravitational Bohm-Aharonov effect.Comment: 20 pages, LaTe

Magnetoresistance and dephasing in a two-dimensional electron gas at intermediate conductances

We study, both theoretically and experimentally, the negative magnetoresistance (MR) of a two-dimensional (2D) electron gas in a weak transverse magnetic field $B$. The analysis is carried out in a wide range of zero-$B$ conductances $g$ (measured in units of $e^2/h$), including the range of intermediate conductances, $g\sim 1$. Interpretation of the experimental results obtained for a 2D electron gas in GaAs/In$_x$Ga$_{1-x}$As/GaAs single quantum well structures is based on the theory which takes into account terms of higher orders in $1/g$, stemming from both the interference contribution and the mutual effect of weak localization (WL) and Coulomb interaction. We demonstrate that at intermediate conductances the negative MR is described by the standard WL "digamma-functions" expression, but with a reduced prefactor $\alpha$. We also show that at not very high $g$ the second-loop corrections dominate over the contribution of the interaction in the Cooper channel, and therefore appear to be the main source of the lowering of the prefactor, $\alpha\simeq 1-2/\pi g$. We further analyze the regime of a "weak insulator", when the zero-$B$ conductance is low $g(B=0)<1$ due to the localization at low $T$, whereas the Drude conductance is high, $g_0>>1.$ In this regime, while the MR still can be fitted by the digamma-functions formula, the experimentally obtained value of the dephasing rate has nothing to do with the true one. The corresponding fitting parameter in the low-$T$ limit is determined by the localization length and may therefore saturate at $T\to 0$, even though the true dephasing rate vanishes.Comment: 36 pages, 16 figure

Inertial and fluctuational effects on the motion of a Bose superfluid vortex

We study the motion of a vortex under the influence of a harmonic force in an approximately two dimensional trapped Bose-condensed gas. The Hall-Vinen-Iordanskii equations, modified to include a fluctuational force and an inertial mass term, are solved for the vortex motion. The mass of the vortex has a strong influence on the time it takes the vortex to escape the trap. Since the vortex mass also depends on the trap size we have an additional dependence on the trap size in the escape time which we compare to the massless case.Comment: Submitted to J. Low. Temp. Phy

Polyhydroxyalkanoates Composites and Blends: Improved Properties and New Applications

Composites of Polyhydroxyalkanoates (PHAs) have been proven to have enhanced properties in comparison to the pure form of these polyesters. Depending on what polymer or material is added to PHAs, the enhancement of different properties is observed. Since PHAs are explored for usage in diverse fields, understanding what blends affect what properties would guide further investigations towards application. This article reviews works that have been carried out with composite variation for application in several fields. Some properties of PHAs are highlighted and composite variation for their modulations are explored