Temperature enhanced persistent currents and "ϕ0/2\phi_0/2 periodicity"

We predict a non-monotonous temperature dependence of the persistent currents in a ballistic ring coupled strongly to a stub in the grand canonical as well as in the canonical case. We also show that such a non-monotonous temperature dependence can naturally lead to a $\phi_0/2$ periodicity of the persistent currents, where $\phi_0$=h/e. There is a crossover temperature $T^*$, below which persistent currents increase in amplitude with temperature while they decrease above this temperature. This is in contrast to persistent currents in rings being monotonously affected by temperature. $T^*$ is parameter-dependent but of the order of $\Delta_u/\pi^2k_B$, where $\Delta_u$ is the level spacing of the isolated ring. For the grand-canonical case $T^*$ is half of that for the canonical case.Comment: some typos correcte

Paramagnetic Meissner effect in superconductors from self-consistent solutions of Ginzburg-Landau equations

The paramagnetic Meissner effect (PME) is observed in small superconducting samples, and a number of controversial explanations of this effect are proposed, but there is as yet no clear understanding of its nature. In the present paper PME is considered on the base of the Ginzburg-Landau theory (GL). The one-dimensional solutions are obtained in a model case of a long superconducting cylinder for different cylinder radii R, the GL-parameters \kappa and vorticities m. Acording to GL-theory, PME is caused by the presence of vortices inside the sample. The superconducting current flows around the vortex to screeen the vortex own field from the bulk of the sample. Another current flows at the boundary to screen the external field H from entering the sample. These screening currents flow in opposite directions and contribute with opposite signs to the total magnetic moment (or magnetization) of the sample. Depending on H, the total magnetization M may be either negative (diamagnetism), or positive (paramagnetism). A very complicated saw-like dependence M(H) (and other characteristics), which are obtained on the base of self-consistent solutions of the GL-equations, are discussed.Comment: 6 pages, 5 figures, RevTex, submitted to Phys. Rev.

Role of \u3cem\u3ePanicum turgidum\u3c/em\u3e Dominated Rangelands in Conservation of \u3cem\u3eCaralluma edulis\u3c/em\u3e in Thar Desert, India

Rangelands are colonized vast natural landscapes in the form of grasslands. These are mostly dominated by native grass species. Once a patch is colonized by a pioneer species, complex interactions may develop among plants of different species. The frequency of positive interactions has been shown to be high in harsh environments, particular in arid environments, where it has been identified as a driving mechanism of vegetation dynamics (Bruno et al., 2003). These processes commonly involve nurse plants (Niering et al., 1963) that facilitate the establishment of other plants species beneath their canopies (Franco and Nobel, 1988). Based on this principle we hypothesized that Panicum turgidum, Forssk., may act as a potential nurse plant for a number of other plant species in the Thar Desert. In this region, this plant is one of the main component of vegetation patches surrounded by a bare soil matrix, in association with a restricted number of other species. Our objective was to characterize the positive associations of P. turgidum with Caralluma edulis in the Thar Desert. The Thar Desert is characterized by high velocity wind, huge shifting and rolling sand dunes; high diurnal variation of temperature; scarce rainfall; intense solar radiation and high rate of evaporation. Thar Desert receives between 100 to 500 mm of rainfall every year, 90% of which is received between July and September. The sandy soils of the desert have a rapid infiltration rate of water, poor fertility, low humus content due to rapid oxidation and high salinity. Though, all conditions are very hostile for the existence of life, some grasses like Lasiurus sindicus, Panicum turgidum, Dichanthium annulatum, Ochthochloa compressa (syn. Eleusine compressa), Cenchrus ciliaris and Cenchrus setigerus perform well in desert. Among these grasses Panicum turgidum is major component of vegetation on sand dunes. Worldwide, the distribution of P. turgidum extends in the Sahara from Mauritania across North Africa with extensions into the Sahel, and through the Arabian Peninsula to Pakistan and India (Poilecot, 1999). It is a perennial Saharan species of family Poaceae, growing as dense tussocks up to 1.5m in height, and creating dense hillocks up to 0.4m high. P. turgidum is highly resistant to water stress, and is a major component of the vegetation of the inter-mountain zones of the Thar (Poilecot, 1996). The seeds serve as a grain substitute in the diet of the Tuareg inhabitants and the straw as fodder for livestock and as roofing material. P. turgidum is also a component of the diet of wild animals of high conservation value such as Addax nasomaculatus, Blainville, Oryx dammah, Cretzschmar and Struthio camelus, L. (Poilecot, 1999). P. turgidum has the merit of being resistant to drought and also an effective sand-binding xerophyte. Wind-borne sand usually accumulates around the bushes of P. turgidum forming isolated mounds that gradually enlarge and eventually coalesce and form sandy patches

Heat Capacity of Mesoscopic Superconducting Disks

We study the heat capacity of isolated giant vortex states, which are good angular momentum ($L$) states, in a mesoscopic superconducting disk using the Ginzburg-Landau (GL) theory. At small magnetic fields the $L$=0 state qualitatively behaves like the bulk sample characterized by a discontinuity in heat capacity at $T_c$. As the field is increased the discontinuity slowly turns into a continuous change which is a finite size effect. The higher $L$ states show a continuous change in heat capacity at $T_c$ at all fields. We also show that for these higher $L$ states, the behavior of the peak position with change in field is related to the paramagnetic Meissner effect (irreversible) and can lead to an unambiguous observation of positive magnetization in mesoscopic superconductors.Comment: Final versio

Chiral Bismuth-Rhodium Paddlewheel Complexes Empowered by London Dispersion: The C-H Functionalization Nexus

Heterobimetallic [BiRh] tetracarboxylate catalysts endowed with 1,3-disilylated phenylglycine paddlewheels benefit from interligand London dispersion. They were originally designed for asymmetric cyclopropanation but are now shown to perform very well in asymmetric C−H functionalization reactions too. Because of the confined ligand sphere about the derived donor/acceptor carbenes, insertions into unhindered methyl groups are kinetically favored, although methylene units also react with excellent levels of asymmetric induction; even gaseous ethane is a suitable substrate. Moreover, many functional groups in both partners are tolerated. The resulting products are synthetically equivalent to the outcome of traditional asymmetric ester alkylation, allylation, benzylation, propargylation and aldol reactions and therefore constitute a valuable nexus to more conventional chemical logic

Renormalization group study of the conductances of interacting quantum wire systems with different geometries

We examine the effect of interactions between the electrons on the conductances of some systems of quantum wires with different geometries. The systems include a wire with a stub in the middle, a wire containing a ring which can enclose a magnetic flux, and a system of four wires which are connected in the middle through a fifth wire. Each of the wires is taken to be a weakly interacting Tomonaga-Luttinger liquid, and scattering matrices are introduced at all the junctions. Using a renormalization group method developed recently for studying the flow of scattering matrices for interacting systems in one dimension, we compute the conductances of these systems as functions of the temperature and the wire lengths. We present results for all three regimes of interest, namely, high, intermediate and low temperature. These correspond respectively to the thermal coherence length being smaller than, comparable to and larger than the smallest wire length in the different systems, i.e., the length of the stub or each arm of the ring or the fifth wire. The renormalization group procedure and the formulae used to compute the conductances are different in the three regimes. We present a phenomenologically motivated formalism for studying the conductances in the intermediate regime where there is only partial coherence. At low temperatures, we study the line shapes of the conductances versus the electron energy near some of the resonances; the widths of the resonances go to zero with decreasing temperature. Our results show that the conductances of various systems of experimental interest depend on the temperature and lengths in a non-trivial way when interactions are taken into account.Comment: Revtex, 17 pages including 15 figure

Persistent Currents in the Presence of a Transport Current

We have considered a system of a metallic ring coupled to two electron reservoirs. We show that in the presence of a transport current, the persistent current can flow in a ring, even in the absence of magnetic field. This is purely a quantum effect and is related to the current magnification in the loop. These persistent currents can be observed if one tunes the Fermi energy near the antiresonances of the total transmission coefficient or the two port conductance.Comment: To appear in Phys. Rev. B. Three figures available on reques

A dual point description of mesoscopic superconductors

We present an analysis of the magnetic response of a mesoscopic superconductor, i.e. a system of sizes comparable to the coherence length and to the London penetration depth. Our approach is based on special properties of the two dimensional Ginzburg-Landau equations, satisfied at the dual point $(\kappa = \frac{1}{\sqrt{2}}).$ Closed expressions for the free energy and the magnetization of the superconductor are derived. A perturbative analysis in the vicinity of the dual point allows us to take into account vortex interactions, using a new scaling result for the free energy. In order to characterize the vortex/current interactions, we study vortex configurations that are out of thermodynamical equilibrium. Our predictions agree with the results of recent experiments performed on mesoscopic aluminium disks.Comment: revtex, 20 pages, 9 figure

To study the pattern of suspected adverse drug reactions in patients coming to the department of dermatology in Gauhati Medical College and Hospital, Guwahati, Assam, India

Background: Cutaneous adverse drug reactions (ADRs) are the commonest ADRs (30-45%) and are responsible for about 2% of hospital admissions. This study was conducted to study the pattern of ADRs coming to the department of dermatology in a Tertiary Health Care Hospital. The objectives of the study were to assess the causality, severity, preventability, age distribution, sex distribution and the reactions occurring.Methods: Cross-sectional study. The suspected adverse drug reactions (ADRs) reported from the department of dermatology in the Spontaneous ADR reporting form was analysed in this study over a period of one year.Results: A total of 513 cases of reported ADRs were analysed. The highest number of ADRs was reported in the Age group 21-40 years with female preponderance. Erythematous maculopapular lesions were the most common ADR and maximum cases of ADRs were observed with steroids. Most cases were found to be probable (causality assessment), of mild severity and were probably preventable.Conclusions: The study showed that a number of drugs cause dermatological ADRs. These ADRs vary in their appearance, duration, causality, severity, and preventability

NMR implementation of Quantum Delayed-Choice Experiment

We report the first experimental demonstration of quantum delayed-choice experiment via nuclear magnetic resonance techniques. An ensemble of molecules each with two spin-1/2 nuclei are used as target and the ancilla qubits to perform the quantum circuit corresponding the delayed-choice setup. As expected in theory, our experiments clearly demonstrate the continuous morphing of the target qubit between particle-like and wave-like behaviors. The experimental visibility of the interference patterns shows good agreement with the theory.Comment: Revised text, more figures adde