Far infrared reflectance of a mixed phase Y-Ba-Cu-O superconductor

The response of polycrystalline Tl–Ba–Ca–Cu–O superconducting thin films on short laser pulses has been investigated for radiation between 10 mgrm and 500 mgrm wavelength. Fast signals with time constants less than 1 ns were observed for wavelengths longer than about 100 mgrm whereas for shorter wavelengths only a bolometric signal could be detected

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.

Immune Boosting Explains Regime-Shifts in Prevaccine-Era Pertussis Dynamics

Understanding the biological mechanisms underlying episodic outbreaks of infectious diseases is one of mathematical epidemiology’s major goals. Historic records are an invaluable source of information in this enterprise. Pertussis (whooping cough) is a re-emerging infection whose intermittent bouts of large multiannual epidemics interspersed between periods of smaller-amplitude cycles remain an enigma. It has been suggested that recent increases in pertussis incidence and shifts in the age-distribution of cases may be due to diminished natural immune boosting. Here we show that a model that incorporates this mechanism can account for a unique set of pre-vaccine-era data from Copenhagen. Under this model, immune boosting induces transient bursts of large amplitude outbreaks. In the face of mass vaccination, the boosting model predicts larger and more frequent outbreaks than do models with permanent or passively-waning immunity. Our results emphasize the importance of understanding the mechanisms responsible for maintaining immune memory fo

Experimental evidence of low frequency defect vibrations in the fcc metal lead observed by superconducting tunneling

Superconducting tenneling measurements of Al-AlxOy-Pb junctions taken after low temperature irradiation with 10 MeV oxygen ions are reported. The normalized differential conductance ?norm = (dI/dU)s/ (dI/dU)n shows additional low frequency structures to an enhancement of the Eliashberg function ?2F(?) in the range from 1.5 to 3.2 meV. The position in energy and the annealing behaviour corroborate that vibrational modes or irradiation induced self-interstitials are observed

Inelastic-electron-tunneling spectroscopy of derivates of benzoic acid and effects due to irradiation with 3 MeV protons at 4.2 K

Inelastic-Electron-Tunneling-Spectroscopy was used to investigate in-situ the irradiation damage of benzoic acid and the derivates p-cyanobenzoic acid and p-aminobenzoic acid at 4.2 K with 3 MeV protons. Benzoic acid is one order of magnitude less sensitive to irradiation than the derivates on account of its delocalized ?-electron system. Substituents located at the carbon ring tend to change the distribution of the electrons at the C6-ring leading to an enhanced sensitivity to irradiation. After irradiation, the samples were annealed at 293 K in order to get information about the stability of possibly formed molecular fragments at room temperature

Langmuir - Blodgett films of trivalent rare earth arachidates −- preparation and characterization

Ultrathin films of rare earth arachidates were prepared by the standard Langmuir-Blodgett technique and analyzed by various surface-sensitive experimental methods. In-situ investigations on the subphase provided information about the dependence of the film stability of the counter ion used. In general the stability increases with its atomic number. Heavy ion induced desorption mass spectrometry and photoelectron spectroscopy confirm the formation of trivalent rare earth arachidate salts. The surface morphology was examined by atomic force microscopy which demonstrates that these films have good transfer properties on gold/silicon substrates

The influence of structural inhomogeneities on superconductivity and transport properties in amorphous (Mo0.6Ru0.4)85B15 films

Cluster films of amorphous (Mo0.6Ru0.4)85B15, where the degree of structural inhomogeneity can be controlled by the size of the clusters, were prepared by dc-sputtering in argon atmosphere. The cluster size was adjusted by the argon pressure during preparation. With increasing size of the clusters the resistance increases from 170 microohmscm for a homogeneous film to about 4000 microohmscm at a cluster radius of about 100 Å, whereas the superconducting transition temperature decreases from 6.7 K to 2.5 K. This will be explained by a reduced coupling between the clusters with increasing size and therefore a reduced diffusivity of the conduction electrons. Irradiation with 20 MeV sulphur ions results in an increase of Tc to over 6 K and a decrease of by over a factor of 10 at a fluence of 2 × 1016 cm?2, which can be explained by the destruction of the granular structure and the formation of a dense, homogeneous film

Electronic structure of electron-doped superconducting curpates studied by photoelectron spectroscopy

Photoemission data of n-type superconducting $RE_{2−x}Ce_xCuO_{4−δ}$ (RE = Pr, Nd and Sm) and $Nd_2CuO_{4−y}F_y$ are presented. An XPJ and an XPS resonant photoemission study reveals that the RE elements are trivalent with decreasing 4f-O 2p-hybridization from RE = Pr to Sm, whereas Ce has a valence of 3.6. The partial Cu$_3$d emission shows valence band satellites indicating the existence of strong electron-electron correlation. These results can be well reproduced by cluster calculations. An decrease of the on-site Coulomb repulsion energy U from RE = Pr to Sm is found in $RE_{2−x}Ce_xCuO_{4−δ}$