Closed Abrikosov Vortices in a Superconducting Cylinder

The new type of solutions of the London equation for type-II superconductors is obtained to describe the ring-shaped (toroidal) Abrikosov vortices. The specific feature of these solutions is the self-consistent localization of both the supercurrent and the magnetic field, enabling one to construct compact magnetic structures inside a superconductor. The torus vortex contraction caused by the vortex instability leads to the destruction of the Cooper pairing and the formation of a normal electron stream in the vicinity of the torus axis. The thermodynamic condition for the excitation of a small closed vortex by a bunch of charged particles contains the fine-structure constant as a determining parameter.Comment: LaTex using revtex, 12 pages. 5 Figures available upon request from [email protected] Accepted for publication in Physica

The monoid of queue actions

We investigate the monoid of transformations that are induced by sequences of writing to and reading from a queue storage. We describe this monoid by means of a confluent and terminating semi-Thue system and study some of its basic algebraic properties, e.g., conjugacy. Moreover, we show that while several properties concerning its rational subsets are undecidable, their uniform membership problem is NL-complete. Furthermore, we present an algebraic characterization of this monoid's recognizable subsets. Finally, we prove that it is not Thurston-automatic

AC conductivity of a niobium thin film in a swept magnetic field

We report the results of the measurement the ac conductivity of a Nb superconducting thin film in a swept dc magnetic field. In the mixed state the swept dc field creates vortices at the film surface which pass through the film and form the observed ac conductivity. Vortex rate generation does not depend on the value of the dc field and there is a large plateau-like region of dc magnetic fields where the dissipation is approximately constant. A proposed phenomenological model describes quite well the main features of the ac response in these fields including its dependency on the sweep rate, ac amplitude, frequency, and value of the second and third harmonics.Comment: 7 pages and 10 figures; Journal of Physics: Condensed Matter, 201

Is Vtb=1 ?

The strongest constraint on Vtb presently comes from the 3 x 3 unitarity of the CKM matrix, which fixes Vtb to be very close to one. If the unitarity is relaxed, current information from top production at Tevatron still leaves open the possibility that Vtb is sizably smaller than one. In minimal extensions of the standard model with extra heavy quarks, the unitarity constraints are much weaker and the EW precision parameters entail the strongest bounds on Vtb. We discuss the experimental perspectives of discovering and identifying such new physics models at the Tevatron and the LHC, through a precise measurement of Vtb from the single top cross sections and by the study of processes where the extra heavy quarks are produced.Comment: 19 pages, 8 figure

Baryogenesis via lepton number violating scalar interactions

We study baryogenesis through lepton number violation in left-right symmetric models. In these models the lepton number and CP violating interactions of the triplet higgs scalars can give rise to lepton number asymmetry through non-equilibrium decays of the $SU(2)_L$ triplet higgs and the right handed neutrinos. This in turn generates baryon asymmetry during the electroweak anomalous processes.Comment: 14 pages, UTPT-93-1

Sortilin regulates sorting and secretion of Sonic hedgehog

Sonic Hedgehog (Shh) is a secreted morphogen that is an essential regulator of patterning and growth. The Shh full-length protein undergoes autocleavage in the ER to generate the biologically active amino-terminal ShhN fragment, which is destined for secretion. Few receptors have been identified that control the trafficking of this morphogen through the secretory pathway. We identified Sortilin (Sort1), a member of the VPS10P domain receptor family, as a novel Shh trafficking receptor. We demonstrate that Sort/Shh interact using co-IP and proximity ligation in transfected cells and that they co-localize to the Golgi. Sort1 overexpression causes re-distribution of ShhN, and to a lesser extent ShhFL, to the Golgi and reduces Shh secretion. We show loss of Sort1 can partially rescue Hedgehog-associated patterning defects in a mouse model of deficient Shh processing and that Sort1 levels negatively regulate anterograde Shh transport in axons in vitro and Hh-dependent axon-glial interactions in vivo Taken together, we conclude that Shh and Sort1 can interact at the level of the Golgi and that Sort1 directs Shh away from the pathways that promote its secretion

Three point SUSY Ward identities without Ghosts

We utilise a non-local gauge transform which renders the entire action of SUSY QED invariant and respects the SUSY algebra modulo the gauge-fixing condition, to derive two- and three-point ghost-free SUSY Ward identities in SUSY QED. We use the cluster decomposition principle to find the Green's function Ward identities and then takes linear combinations of the latter to derive identities for the proper functions.Comment: 20 pages, no figures, typos correcte

Magnetic Phase Diagram of GdNi2B2C: Two-ion Magnetoelasticity and Anisotropic Exchange Couplings

Extensive magnetization and magnetostriction measurements were carried out on a single crystal of GdNi2B2C along the main tetragonal axes. Within the paramagnetic phase, the magnetic and strain susceptibilities revealed a weak anisotropy in the exchange couplings and two-ion tetragonal-preserving alpha-strain modes. Within the ordered phase, magnetization and magnetostriction revealed a relatively strong orthorhombic distortion mode and rich field-temperature phase diagrams. For H//(100) phase diagram, three field-induced transformations were observed, namely, at: Hd(T), related to the domain alignment; Hr(T), associated with reorientation of the moment towards the c-axis; and Hs(T), defining the saturation process wherein the exchange field is completely counterbalanced. On the other hand, For H//(001) phase diagram, only two field-induced transformations were observed, namely at: Hr(T) and Hs(T). For both phase diagrams, Hs(T) follows the relation Hs[1-(T/Tn)^2]^(1/2)kOe with Hs(T-->0)=128.5(5) kOe and Tn(H=0)=19.5 K. In contrast, the thermal evolution of Hr(T) along the c-axis (much simpler than along the a-axis) follows the relation Hr[1-T/Tr]^(1/3) kOe where Hr(T-->0)=33.5(5) kOe and Tr(H=0)=13.5 K. It is emphasized that the magnetoelastic interaction and the anisotropic exchange coupling are important perturbations and therefore should be explicitly considered if a complete analysis of the magnetic properties of the borocarbides is desired

Multiple Singular Emission in Gauge Theories

I derive a class of functions unifying all singular limits for the emission of a given number of soft or collinear gluons in tree-level gauge-theory amplitudes. Each function is a generalization of the single-emission antenna function of ref. [1]. The helicity-summed squares of these functions are thus also generalizations to multiple singular emission of the Catani--Seymour dipole factorization function.Comment: Corrections for final journal version (sign in eqn. (6.11), equation references, typos in indices) & removal of comment about FD

Fundamental constants and tests of general relativity - Theoretical and cosmological considerations

The tests of the constancy of the fundamental constants are tests of the local position invariance and thus of the equivalence principle. We summarize the various constraints that have been obtained and then describe the connection between varying constants and extensions of general relativity. To finish, we discuss the link with cosmology, and more particularly with the acceleration of the Universe. We take the opportunity to summarize various possibilities to test general relativity (but also the Copernican principle) on cosmological scales.Comment: Proceedings of the workshop ``The nature of gravity, confronting theory and experiment in space'', ISSI, Bern, october 200