A cusp electron gun for millimeter wave gyrodevices

The experimental results of a thermionic cusp electron gun, to drive millimeter and submillimeter wave harmonic gyrodevices, are reported in this paper. Using a "smooth" magnetic field reversal formed by two coils this gun generated an annular-shaped, axis-encircling electron beam with 1.5 A current, and an adjustable velocity ratio alpha of up to 1.56 at a beam voltage of 40 kV. The beam cross-sectional shape and transported beam current were measured by a witness plate technique and Faraday cup, respectively. These measured results were found to be in excellent agreement with the simulated results using the three-dimensional code MAGIC

The black hole dynamical horizon and generalized second law of thermodynamics

The generalized second law of thermodynamics for a system containing a black hole dynamical horizon is proposed in a covariant way. Its validity is also tested in case of adiabatically collapsing thick light shells.Comment: JHEP style, 8 pages, 2 figures, version to appear in JHEP with typos correcte

Geometric Mean Neutrino Mass Relation

Present experimental data from neutrino oscillations have provided much information about the neutrino mixing angles. Since neutrino oscillations only determine the mass squared differences $\Delta m^2_{ij} = m^2_i - m^2_j$, the absolute values for neutrino masses $m_i$ can not be determined using data just from oscillations. In this work we study implications on neutrino masses from a geometric mean mass relation $m_2=\sqrt{m_1 m_3}$ which enables one to determined the absolute masses of the neutrinos. We find that the central values of the three neutrino masses and their $2\sigma$ errors to be $m_1 = (1.58\pm 0.18){meV}$, $m_2 = (9.04\pm 0.42){meV}$, and $m_3 = (51.8\pm 3.5){meV}$. Implications for cosmological observation, beta decay and neutrinoless double beta decays are discussed.Comment: 7 pages. Talk given at COSPA06. A reference adde

A covariant entropy conjecture on cosmological dynamical horizon

We here propose a covariant entropy conjecture on cosmological dynamical horizon. After the formulation of our conjecture, we test its validity in adiabatically expanding universes with open, flat and closed spatial geometry, where our conjecture can also be viewed as a cosmological version of the generalized second law of thermodynamics in some sense.Comment: JHEP style, 9 pages, 1 figure, typos corrected, accepted for publication in JHE

Dorsoventral patterning of the Xenopus eye involves differential temporal changes in the response of optic stalk and retinal progenitors to Hh signalling

Background: Hedgehog (Hh) signals are instrumental to the dorsoventral patterning of the vertebrate eye, promoting optic stalk and ventral retinal fates and repressing dorsal retinal identity. There has been limited analysis, however, of the critical window during which Hh molecules control eye polarity and of the temporal changes in the responsiveness of eye cells to these signals. Results: In this study, we used pharmacological and molecular tools to perform stage-specific manipulations of Hh signalling in the developing Xenopus eye. In gain-of-function experiments, most of the eye was sensitive to ventralization when the Hh pathway was activated starting from gastrula/neurula stages. During optic vesicle stages, the dorsal eye became resistant to Hh-dependent ventralization, but this pathway could partially upregulate optic stalk markers within the retina. In loss-of-function assays, inhibition of Hh signalling starting from neurula stages caused expansion of the dorsal retina at the expense of the ventral retina and the optic stalk, while the effects of Hh inhibition during optic vesicle stages were limited to the reduction of optic stalk size. Conclusions: Our results suggest the existence of two competence windows during which the Hh pathway differentially controls patterning of the eye region. In the first window, between the neural plate and the optic vesicle stages, Hh signalling exerts a global influence on eye dorsoventral polarity, contributing to the specification of optic stalk, ventral retina and dorsal retinal domains. In the second window, between optic vesicle and optic cup stages, this pathway plays a more limited role in the maintenance of the optic stalk domain. We speculate that this temporal regulation is important to coordinate dorsoventral patterning with morphogenesis and differentiation processes during eye development

Superfluidity in a Three-flavor Fermi Gas with SU(3) Symmetry

We investigate the superfluidity and the associated Nambu-Goldstone modes in a three-flavor atomic Fermi gas with SU(3) global symmetry. The s-wave pairing occurs in flavor anti-triplet channel due to the Pauli principle, and the superfluid state contains both gapped and gapless fermionic excitations. Corresponding to the spontaneous breaking of the SU(3) symmetry to a SU(2) symmetry with five broken generators, there are only three Nambu-Goldstone modes, one is with linear dispersion law and two are with quadratic dispersion law. The other two expected Nambu-Goldstone modes become massive with a mass gap of the order of the fermion energy gap in a wide coupling range. The abnormal number of Nambu-Goldstone modes, the quadratic dispersion law and the mass gap have significant effect on the low temperature thermodynamics of the matter.Comment: 9 pages, 2 figures, published versio

Comparative Study of BCS-BEC Crossover Theories above TcT_c: the Nature of the Pseudogap in Ultra-Cold Atomic Fermi Gases

This paper presents a comparison of two finite-temperature BCS-Bose Einstein condensation (BEC) crossover theories above the transition temperature: Nozieres Schmitt-Rink (NSR) theory and finite $T$-extended BCS-Leggett theory. The comparison is cast in the form of numerical studies of the behavior of the fermionic spectral function both theoretically and as constrained by (primarily) radio frequency (RF) experiments. Both theories include pair fluctuations and exhibit pseudogap effects, although the nature of this pseudogap is very different. The pseudogap in finite $T$-extended BCS-Leggett theory is found to follow a BCS-like dispersion which, in turn, is associated with a broadened BCS-like self energy, rather more similar to what is observed in high temperature superconductors (albeit, for a d-wave case). The fermionic quasi-particle dispersion is different in NSR theory and the damping is considerably larger. We argue that the two theories are appropriate in different temperature regimes with the BCS-Leggett approach more suitable nearer to condensation. There should, in effect, be little difference at higher $T$ as the pseudogap becomes weaker and where the simplifying approximations used in the BCS-Leggett approach break down. On the basis of momentum-integrated radio frequency studies of unpolarized gases, it would be difficult to distinguish which theory is the better. A full comparison for polarized gases is not possible since there is claimed to be inconsistencies in the NSR approach (not found in the BCS-Leggett scheme). Future experiments along the lines of momentum resolved experiments look to be very promising in distinguishing the two theories.Comment: 16 pages, 11 figure

Bosonic Reduction of Susy Generalized Harry Dym Equation

In this paper we construct the two component supersymmetric generalized Harry Dym equation which is integrable and study various properties of this model in the bosonic limit. In particular, in the bosonic limit we obtain a new integrable system which, under a hodograph transformation, reduces to a coupled three component system. We show how the Hamiltonian structure transforms under a hodograph transformation and study the properties of the model under a further reduction to a two component system. We find a third Hamiltonian structure for this system (which has been shown earlier to be a bi-Hamiltonian system) making this a genuinely tri-Hamiltonian system. The connection of this system to the modified dispersive water wave equation is clarified. We also study various properties in the dispersionless limit of our model.Comment: 21 page

K+ -> pi+ nu nu(bar) and FCNC from non-universal Z' bosons

Motivated by the E787 and E949 result for K+ -> pi+ nu nu(bar) we examine the effects of a new non-universal right-handed Z' boson on flavor changing processes. We place bounds on the tree-level FCNC from K-K(bar) and B-B(bar) mixing as well as from the observed CP violation in kaon decay. We discuss the implications for K -> pi nu nu(bar), B -> X nu nu(bar) and B -> tau+ tau-. We find that existing bounds allow substantial enhancements in the K+ -> pi+ nu nu(bar) rate, particularly through a new one-loop Z' penguin operator.Comment: Typos corrected, references added, version to appear in PR