Defect Formation in Quench-Cooled Superfluid Phase Transition

We use neutron absorption in rotating 3He-B to heat locally a 10 micrometer-size volume into normal phase. When the heated region cools back in microseconds, vortex lines are formed. We record with NMR the number of lines as a function of superflow velocity and compare to the Kibble-Zurek theory of vortex-loop freeze-out from a random network of defects. The measurements confirm the calculated loop-size distribution and show that also the superfluid state itself forms as a patchwork of competing A and B phase blobs. This explains the A to B transition in supercooled neutron-irradiated 3He-A.Comment: RevTex file, 4 pages, 3 figures, resubmitted to Phys. Rev. Let

Event horizons and ergoregions in 3He

Event horizons for fermion quasiparticles naturally arise in moving textures in superconductors and Fermi superfluids. We discuss the example of a planar soliton moving in superfluid 3He-A, which is closely analogous to a charged rotating black hole. The moving soliton will radiate quasiparticles via the Hawking effect at a temperature of about 5 \mu K, and via vacuum polarization induced by the effective `electromagnetic field' and `ergoregion'. Superfluid 3He-A thus appears to be a useful system for experimental and theoretical simulations of quantum effects related to event horizons and ergoregions.Comment: RevTex, 8 pages, 3 figures, submitted to Phys. Rev. D, corrected after referee repor

Involutive orbits of non-Noether symmetry groups

We consider set of functions on Poisson manifold related by continues one-parameter group of transformations. Class of vector fields that produce involutive families of functions is investigated and relationship between these vector fields and non-Noether symmetries of Hamiltonian dynamical systems is outlined. Theory is illustrated with sample models: modified Boussinesq system and Broer-Kaup system.Comment: LaTeX 2e, 10 pages, no figure

Protostellar Feedback in Massive Star Forming Regions

We examine mechanical feedback mechanisms during the protostellar phase through jets and outflows. To do so, we make use of velocity-resolved CII observations at 158 $\mu$m taken with the SOFIA observatory. We identify CII emitting cavities at velocities ranging from 1-2 km s$^{-1}$ to 15 km s$^{-1}$ relative to the Veil shell ($v_\mathrm{LSR}$ = 13 km s$^{-1}$). The momentum and dynamical timescales of these cavities imply that the cavities in Orion were formed by fossil and active outflows from stars with luminosities ranging from 10$^3$ to 10$^5$ L$_\odot$. The momentum deposited during protostellar feedback is $\sim$1/6 of the momentum of the Veil shell deposited through winds from $\theta^1$ Ori C. By creating cavities, the fossil outflows may already have broken the Veil shell, and outflows from less massive stars may have made the Veil shell porous

Boojums in Rotating Two-Component Bose-Einstein Condensates

A boojum is a topological defect that can form only on the surface of an ordered medium such as superfluid $^3$He and liquid crystals. We study theoretically boojums appearing between two phases with different vortex structures in two-component BECs where the intracomponent interaction is repulsive in one phase and attractive in the other. The detailed structure of the boojums is revealed by investigating its density distribution, effective superflow vorticity and pseudospin texture.Comment: 4 pages, 4 figure

Efficiency retention at high current injection levels in m-plane InGaN light emitting diodes

We investigated the internal quantum efficiency (IQE) and the relative external quantum efficiency (EQE) of m-plane InGaN light emitting diodes(LEDs) grown on m-plane freestanding GaN emitting at ∼400 nm for current densities up to 2500 A/cm2. IQE values extracted from intensity and temperature dependent photoluminescencemeasurements were consistently higher, by some 30%, for the m-plane LEDs than for reference c-plane LEDs having the same structure, e.g., 80% versus 60% at an injected steady-state carrier concentration of 1.2×1018 cm−3. With increasing current injection up to 2500 A/cm2, the maximum EQE is nearly retained in m-plane LEDs, whereas c-plane LEDs exhibit approximately 25% droop. The negligible droop in m-plane LEDs is consistent with the reported enhanced hole carrier concentration and light holes in m-plane orientation, thereby enhanced hole transport throughout the active region, and lack of polarization induced field. A high quantum efficiency and in particular its retention at high injection levels bode well for m-plane LEDs as candidates for general lighting applications

Effect of quantum noise on Coulomb blockade in normal tunnel junctions at high voltages

We have investigated asymptotic behavior of normal tunnel junctions at voltages where even the best ohmic environments start to look like RC transmission lines. In the experiments, this is manifested by an exceedingly slow approach to the linear behavior above the Coulomb gap. As expected on the basis of the quantum theory taking into account interaction with the environmental modes, better fits are obtained using 1/sqrt{V}- than 1/V- dependence for the asymptote. These results agree with the horizon picture if the frequency-dependent phase velocity is employed instead of the speed of light in order to determine the extent of the surroundings seen by the junction.Comment: 9 pages, 4 figures, submitted to Phys. Rev.

Big bang simulation in superfluid 3He-B -- Vortex nucleation in neutron-irradiated superflow

We report the observation of vortex formation upon the absorption of a thermal neutron in a rotating container of superfluid $^3$He-B. The nuclear reaction n + $^3$He = p + $^3$H + 0.76MeV heats a cigar shaped region of the superfluid into the normal phase. The subsequent cooling of this region back through the superfluid transition results in the nucleation of quantized vortices. Depending on the superflow velocity, sufficiently large vortex rings grow under the influence of the Magnus force and escape into the container volume where they are detected individually with nuclear magnetic resonance. The larger the superflow velocity the smaller the rings which can expand. Thus it is possible to obtain information about the morphology of the initial defect network. We suggest that the nucleation of vortices during the rapid cool-down into the superfluid phase is similar to the formation of defects during cosmological phase transitions in the early universe.Comment: 4 pages, LaTeX file, 4 figures are available at ftp://boojum.hut.fi/pub/publications/lowtemp/LTL-95009.p

Dynamical modelling of the elliptical galaxy NGC 2974

In this paper we analyse the relations between a previously described oblate Jaffe model for an ellipsoidal galaxy and the observed quantities for NGC 2974, and obtain the length and velocity scales for a relevant elliptical galaxy model. We then derive the finite total mass of the model from these scales, and finally find a good fit of an isotropic oblate Jaffe model by using the Gauss-Hermite fit parameters and the observed ellipticity of the galaxy NGC 2974. The model is also used to predict the total luminous mass of NGC 2974, assuming that the influence of dark matter in this galaxy on the image, ellipticity and Gauss-Hermite fit parameters of this galaxy is negligible within the central region, of radius $0.5R_{\rm e}.$Comment: 7 figure