Hydrodynamics of liquids of arbitrarily curved flux-lines and vortex loops

We derive a hydrodynamic model for a liquid of arbitrarily curved flux-lines and vortex loops using the mapping of the vortex liquid onto a liquid of relativistic charged quantum bosons in 2+1 dimensions recently suggested by Tesanovic and by Sudbo and collaborators. The loops in the flux-line system correspond to particle-antiparticle fluctuations in the bosons. We explicitly incorporate the externally applied magnetic field which in the boson model corresponds to a chemical potential associated with the conserved charge density of the bosons. We propose this model as a convenient and physically appealing starting point for studying the properties of the vortex liquid

Instabilities in the Flux Line Lattice of Anisotropic Superconductors

The stability of the flux line lattice has been investigated within anisotropic London theory. This is the first full-scale investigation of instabilities in the `chain' state. It has been found that the lattice is stable at large fields, but that instabilities occur as the field is reduced. The field at which these instabilities first arise, $b^*(\epsilon,\theta)$, depends on the anisotropy $\epsilon$ and the angle $\theta$ at which the lattice is tilted away from the $c$-axis. These instabilities initially occur at wavevector $k^*(\epsilon,\theta)$, and the component of $k^*$ along the average direction of the flux lines, $k_z$, is always finite. As the instability occurs at finite $k_z$ the dependence of the cutoff on $k_z$ is important, and we have used a cutoff suggested by Sudb\ospace and Brandt. The instabilities only occur for values of the anisotropy $\epsilon$ appropriate to a material like BSCCO, and not for anisotropies more appropriate to YBCO. The lower critical field $H_{c_1}(\phi)$ is calculated as a function of the angle $\phi$ at which the applied field is tilted away from the crystal axis. The presence of kinks in $H_{c_1}(\phi)$ is seen to be related to instabilities in the equilibrium flux line structure.Comment: Extensively revised paper, with modified analysis of elastic instabilities. Calculation of the lower critical field is included, and the presence of kinks in $H_{c_1}$ is seen to be related to the elastic instabilities. 29 pages including 16 figures, LaTeX with epsf styl

Sequence and phylogenetic analyses of the twin-arginine targeting (Tat) protein export system

Twin-arginine targeting (Tat) protein secretion systems consist of two protein types, members of the TatA and TatC families. Homologues of these proteins are found in many archaea, bacteria, chloroplasts and mitochondria. Every prokaryotic organism with a fully sequenced genome exhibits either neither family member, or between one and three paralogues of these two family members. The Arabidopsis thaliana genome encodes three of each. Although many mitochondrially encoded TatC homologues have been identified, corresponding TatA homologues have not been found in this organelle. Phylogenetic analyses reveal that most prokaryotic Tat systems consist of one TatC homologue and two sequence-divergent TatA homologues (TatA and TatB). When only one TatA homologue is present, TatB is missing, and when three TatA homologues are present, the third one arose by duplication of TatA, not TatB. Further, homologues most resembling TatB are more sequence-divergent than those more closely resembling TatA. In contrast to the TatA family, the TatC family shows phylogenetic clustering in strict accordance with organismal type. These results are discussed in terms of their probable structural, functional and evolutionary significance

Vortex-line liquid phases: Longitudinal superconductivity in the lattice London model

We study the vortex-line lattice and liquid phases of a clean type-II superconductor by means of Monte Carlo simulations of the lattice London model. Motivated by a recent controversy regarding the presence, within this model, of a vortex-liquid regime with longitudinal superconducting coherence over long length scales, we directly compare two different ways to calculate the longitudinal coherence. For an isotropic superconductor, we interpret our results in terms of a temperature regime within the liquid phase in which longitudinal superconducting coherence extends over length scales larger than the system thickness studied. We note that this regime disappears in the moderately anisotropic case due to a proliferation, close to the flux-line lattice melting temperature, of vortex loops between the layers.Comment: 8 pages, Revtex, with eps figures. To appear in Phys. Rev.

Number--conserving model for boson pairing

An independent pair ansatz is developed for the many body wavefunction of dilute Bose systems. The pair correlation is optimized by minimizing the expectation value of the full hamiltonian (rather than the truncated Bogoliubov one) providing a rigorous energy upper bound. In contrast with the Jastrow model, hypernetted chain theory provides closed-form exactly solvable equations for the optimized pair correlation. The model involves both condensate and coherent pairing with number conservation and kinetic energy sum rules satisfied exactly and the compressibility sum rule obeyed at low density. We compute, for bulk boson matter at a given density and zero temperature, (i) the two--body distribution function, (ii) the energy per particle, (iii) the sound velocity, (iv) the chemical potential, (v) the momentum distribution and its condensate fraction and (vi) the pairing function, which quantifies the ODLRO resulting from the structural properties of the two--particle density matrix. The connections with the low--density expansion and Bogoliubov theory are analyzed at different density values, including the density and scattering length regime of interest of trapped-atoms Bose--Einstein condensates. Comparison with the available Diffusion Monte Carlo results is also made.Comment: 21 pages, 12 figure

Analytical results on quantum interference and magnetoconductance for strongly localized electrons in a magnetic field: Exact summation of forward-scattering paths

We study quantum interference effects on the transition strength for strongly localized electrons hopping on 2D square and 3D cubic lattices in the presence of a magnetic field B. These effects arise from the interference between phase factors associated with different electron paths connecting two distinct sites. For electrons confined on a square lattice, with and without disorder, we obtain closed-form expressions for the tunneling probability, which determines the conductivity, between two arbitrary sites by exactly summing the corresponding phase factors of all forward-scattering paths connecting them. An analytic field-dependent expression, valid in any dimension, for the magnetoconductance (MC) is derived. A positive MC is clearly observed when turning on the magnetic field. In 2D, when the strength of B reaches a certain value, which is inversely proportional to twice the hopping length, the MC is increased by a factor of two compared to that at zero field. We also investigate transport on the much less-studied and experimentally important 3D cubic lattice case, where it is shown how the interference patterns and the small-field behavior of the MC vary according to the orientation of B. The effect on the low-flux MC due to the randomness of the angles between the hopping direction and the orientation of B is also examined analytically.Comment: 24 pages, RevTeX, 8 figures include

Sustainable nitrogen fixation from synergistic effect of photo-electrochemical water splitting and atmospheric pressure N2 plasma

In this study, nitrogen fixation in the electrolyte was achieved by atmospheric pressure non-thermal plasma generated by a sinusoidal power supply (with an applied voltage of 10 kV and frequency of 33 kHz). Ammonia measurements on plasma exposed electrolyte at several working gas and purging gas conditions revealed that nitrogen plasma in the same gas environment is more favourable for plasma-assisted ammonia synthesis. In addition, photo-electrochemical water splitting was performed by irradiating UV light on a titanium dioxide semiconductor photo-anode to generate hydrogen donor in nitrogen reduction reaction. The amount of ammonia synthesized by this synergistic process of photo-electrochemical water splitting and nitrogen plasma is six times higher than that obtained by nitrogen plasma alone. An increase in the co-synthesized NOX concentrations and background contamination at reaction site reduces the ammonia synthesis rate and Faraday efficiency. However, the ammonia production efficiency was increased up to 72% by using a proton-exchange membrane which prevents the diffusion of oxygen evolved from water splitting into the plasma, and by reducing the axial distance between the plasma electrode and reaction site. The sustainable nitrogen fixation process reported herein can be performed at atmospheric pressure conditions without a direct input of hydrogen gas or any catalyst

Coherent Phonons in Carbon Nanotubes and Graphene

We review recent studies of coherent phonons (CPs) corresponding to the radial breathing mode (RBM) and G-mode in single-wall carbon nanotubes (SWCNTs) and graphene. Because of the bandgap-diameter relationship, RBM-CPs cause bandgap oscillations in SWCNTs, modulating interband transitions at terahertz frequencies. Interband resonances enhance CP signals, allowing for chirality determination. Using pulse shaping, one can selectively excite speci!c-chirality SWCNTs within an ensemble. G-mode CPs exhibit temperature-dependent dephasing via interaction with RBM phonons. Our microscopic theory derives a driven oscillator equation with a density-dependent driving term, which correctly predicts CP trends within and between (2n+m) families. We also find that the diameter can initially increase or decrease. Finally, we theoretically study the radial breathing like mode in graphene nanoribbons. For excitation near the absorption edge, the driving term is much larger for zigzag nanoribbons. We also explain how the armchair nanoribbon width changes in response to laser excitation.Comment: 48 pages, 41 figure

What Can We Learn about Smoking from 150 Years of Italian Data?

This paper estimates dynamic demand models for tobacco consumption in Italy from 1871 to 2010. The empirical analysis is based on an entirely new dataset. Because the tobacco sector was mostly managed by the state, rich and detailed historical documentation is available. Price elasticities are estimated both for aggregate tobacco consumption and its four major components (cigars, cigarettes, cut to- 25 bacco, and snuff) for three separate sub-periods: 1871–1913, 1919–1939, and 1946–2010. Elasticities consistently belong to a narrow set. We discuss the public policy implications of a seemingly iso-elastic tobacco demand function