Disordered Type-II Superconductors: A Universal Phase Diagram for Low-Tc_c Systems

A universal phase diagram for weakly pinned low-T$_c$ type-II superconductors is revisited and extended with new proposals. The low-temperature ``Bragg glass'' phase is argued to transform first into a disordered, glassy phase upon heating. This glassy phase, a continuation of the high-field equilibrium vortex glass phase, then melts at higher temperatures into a liquid. This proposal provides an explanation for the anomalies observed in the peak effect regime of 2H-NbSe$_2$ and several other low-T$_c$ materials which is independent of the microscopic mechanisms of superconductivity in these systems.Comment: 23 pages, 9 figure

Engineering design of vertical test stand cryostat

Under Indian Institutions and Fermilab collaboration, Raja Ramanna Centre for Advanced Technology and Fermi National Accelerator Laboratory are jointly developing 2K Vertical Test Stand (VTS) cryostats for testing SCRF cavities at 2K. The VTS cryostat has been designed for a large testing aperture of 86.36 cm for testing of 325 MHz Spoke resonators, 650 MHz and 1.3 GHz multi-cell SCRF cavities for Fermilab's Project-X. Units will be installed at Fermilab and RRCAT and used to test cavities for Project-X. A VTS cryostat comprises of liquid helium (LHe) vessel with internal magnetic shield, top insert plate equipped with cavity support stand and radiation shield, liquid nitrogen (LN{sub 2}) shield and vacuum vessel with external magnetic shield. The engineering design and analysis of VTS cryostat has been carried out using ASME B&PV Code and Finite Element Analysis. Design of internal and external magnetic shields was performed to limit the magnetic field inside LHe vessel at the cavity surface <1 {micro}T. Thermal analysis for LN{sub 2} shield has been performed to check the effectiveness of LN{sub 2} cooling and for compliance with ASME piping code allowable stresses

Scenario of Accelerating Universe from the Phenomenological \Lambda- Models

Dark matter, the major component of the matter content of the Universe, played a significant role at early stages during structure formation. But at present the Universe is dark energy dominated as well as accelerating. Here, the presence of dark energy has been established by including a time-dependent $\Lambda$ term in the Einstein's field equations. This model is compatible with the idea of an accelerating Universe so far as the value of the deceleration parameter is concerned. Possibility of a change in sign of the deceleration parameter is also discussed. The impact of considering the speed of light as variable in the field equations has also been investigated by using a well known time-dependent $\Lambda$ model.Comment: Latex, 9 pages, Major change

Scalar Field Dark Matter

This work is a review of the last results of research on the Scalar Field Dark Matter model of the Universe at cosmological and at galactic level. We present the complete solution to the scalar field cosmological scenario in which the dark matter is modeled by a scalar field $\Phi$ with the scalar potential $V(\Phi)=V_{0}(cosh {(\lambda \sqrt{\kappa_{0}}\Phi)}-1)$ and the dark energy is modeled by a scalar field $\Psi$, endowed with the scalar potential $\tilde{V}(\Psi)= \tilde{V_{0}}(\sinh{(\alpha \sqrt{\kappa_{0}}\Psi)})^{\beta}$, which together compose the 95% of the total matter energy in the Universe. The model presents successfully deals with the up to date cosmological observations, and is a good candidate to treat the dark matter problem at the galactic level.Comment: 11 pagez, 5 figures, REVTeX. To appear in proceedings of the ``Mexican Meeting on Exact Solutions and Scalar Fields in Gravity '', in honour of Heinz Dehnen's 65th Birthday and Dietrich Kramer's 60th Birthday. Mexico D.F., Mexico, in press. More info at http://www.fis.cinvestav.mx/~siddh/PHI

ON THE POSSIBLE USE OF OPTICAL ROTATION MEASUREMENTS FOR DETECTING WEAKLY IR ACTIVE MODES

IR activity of normal modes of a crystal is usually investigated through reflection or transmission measurements. We propose here another way which should be useful for studying modes of weak IR activity. The method involves measuring the rotation angle θ, of the plane of polarization of a monochromatic beam of frequency ω, as the beam traverses a crystal of thickness d. By studying θ as a function of incident frequency ω one would observe a 'resonance' close to each IR active frequency ωj. The method would be feasible if there is appreciable transmission of the beam that is the oscillator strength of the mode is small. We suggest a system, namely, LIKSO4, where this idea could be applied. In particular we discuss how the symmetric stretching mode of SO4 which is IR inactive for a free ion but is weakly IR active in this crystal, could be investigated using different wavelengths of a CO2 laser. Potentiality of the proposed technique for investigating phase transitions, wherein certain Raman active modes acquire weak IR activity across the transition are mentioned

ANOMALOUS TEMPERATURE DEPENDENCE OF A LO MODE IN LiKSO4

Raman scattering measurements for LiKSO4 over the temperature range 200 K to 725 K are reported. The results corroborate the occurrence of a phase transition at 700 K and also exhibit two unusual lattice dynamical features viz an invested LO-TO splitting and an increase in the frequency of a normal mode with rise in temperature. A phenomenological explanation for these features is given

Plasticity in moving and pinned vortex matter

The role of plasticity generated by quenched disorder in soft vortex matter is observed in both the plastic flow of vortices at low velocities and in plastic deformation in the pinned state. Some special experimental consequences of plasticity and the attendant metastability are summarized