Collapse of the charge ordering gap of Nd_{0.5}Sr_{0.5}MnO_{3} in an applied magnetic field

We report results of tunneling studies on the charge ordering compound Nd_{0.5}Sr_{0.5}MnO_{3} in a magnetic field up to 6T and for temperature down to 25K.We show that a gap (2\Delta_{CO} \approx 0.5eV opens up in the density of state (DOS) at the Fermilevel (E_F) on charge ordering (T_{CO}=150K) which collapses in an applied magnetic field when the charge ordered state melts. There is a clear correspondence between the behavior of the resistivity and the gap formation and its collapse in an applied magnetic field. We conclude that a gap in the DOS at E_F is necessary for the stability of the charge ordered state.Comment: 4 pages REVTeX, 5 postscript figures included, submitted to Phys. Rev. Let

Carbon materials as electrocatalysts for oxygen reduction in phosphoric acid medium

The behaviour of acstylene black (Indian grade) as catalyst support material is reported. The acetylene black is heat treated (activated) at variour temperatures in nitrogen atmosphere. The surface area of the various heat treated samples is obtained. Platinum is deporited into the carbon bye reported technique. The of platinum agglomeration on the carbon in identified through scanning electron microscope. The above catalyst is applied to glassy carbon disc. The electrochemical surface area of the catalyst ie determined by the hydrogen absorption and oxidation in alkaline medium. Similar electrodes (disc, dia 6 mm) are used in H3PO4 medium. Cyclic vottammograms are obtained in the oxygen evolution region and oxygen reduction region. The exchange current density of the catalyst for oxygen evolution and reduction ir reported for different catalyst loadings

EVALUATION OF STANDARDS OF SOME SELECTED COSMETIC PREPARATIONS

The aim of the present work is to analyze the standards of marketed cosmetic products which are largely consumed in day to day life of the people. The cosmeceutical should be tested for efficacy to ensure a proven skin benefit and also to substantiate marketing claims. The work was done by keeping the ideas of Bureau of Indian Standards to analyze the cosmetic products. The evaluation for the following cosmetics such as tooth pastes (Colgate, Closeup, Pepsodent, Vicco and Anchor) and face powders (Ponds, Eva, Fa, Cuticura and Spinz) are performed for their quality. All the marketed tooth pastes and face powders which had been evaluated complied with the standards specified by Bureau of Indian Standards. Hence all the selected marketed tooth pastes and selected face powders were found to be of good quality

Cooling rate dependence of the antiferromagnetic domain structure of a single crystalline charge ordered manganite

The low temperature phase of single crystals of Nd$_{0.5}$Ca$_{0.5}$MnO$_3$ and Gd$_{0.5}$Ca$_{0.5}$MnO$_3$ manganites is investigated by squid magnetometry. Nd$_{0.5}$Ca$_{0.5}$MnO$_3$ undergoes a charge-ordering transition at $T_{CO}$=245K, and a long range CE-type antiferromagnetic state is established at $T_N$=145K. The dc-magnetization shows a cooling rate dependence below $T_N$, associated with a weak spontaneous moment. The associated excess magnetization is related to uncompensated spins in the CE-type antiferromagnetic structure, and to the presence in this state of fully orbital ordered regions separated by orbital domain walls. The observed cooling rate dependence is interpreted to be a consequence of the rearrangement of the orbital domain state induced by the large structural changes occurring upon cooling.Comment: REVTeX4; 7 pages, 4 figures. Revised 2001/12/0

A novelty approach to solve an economic dispatch problem for a renewable integrated micro-grid using optimization techniques

Introduction. The renewable integrated microgrid has considered several distributed energy sources namely photovoltaic power plant, thermal generators, wind power plant and combined heat and power source. Economic dispatch problem is a complex operation due to large dimension of power systems. The objective function becomes non linear due to the inclusion of many constraints. Hourly demand of a commercial area is taken into consideration for performing economic dispatch and five combinations are considered to find the best optimal solution to meet the demand. The novelty of the proposed work consists of a Sparrow Search Algorithm is used to solve economic load dispatch problem to get the better convergence and accuracy in power generation with minimum cost. Purpose. Economic dispatch is performed for the renewable integrated microgrid, in order to determine the optimal output of all the distributed energy sources present in the microgrid to meet the load demand at minimum possible cost. Methods. Sparrow Search Algorithm is compared with other algorithms like Particle Swarm Optimization, Genetic Algorithm and has been proved to be more efficient than Particle Swarm Optimization, Genetic Algorithm and Conventional Lagrange method. Results. The five combinations are generation without solar power supply system and Combined Heat and Power source, generation without solar and wind power supply systems, generation including all the distributed energy sources, generation without wind power supply system and Combined Heat and Power source, generation without thermal generators. Practical value. The proposed optimization algorithm has been very supportive to determine the optimal power generation with minimal fuel to meet the large demand in commercial area

Specific heat study of single crystalline Pr0.63_{0.63} Ca0.37_{0.37} MnO3_{3} in presence of a magnetic field

We present the results of a study of specific heat on a single crystal of Pr$_{0.63}$Ca$_{0.37}$MnO$_3$ performed over a temperature range 3K-300K in presence of 0 and 8T magnetic fields. An estimate of the entropy and latent heat in a magnetic field at the first order charge ordering (CO) transition is presented. The total entropy change at the CO transition which is $\approx$ 1.8 J/mol K at 0T, decreases to $\sim$ 1.5 J/mol K in presence of 8T magnetic field. Our measurements enable us to estimate the latent heat $L_{CO}$ $\approx$ 235 J/mol involved in the CO transition. Since the entropy of the ferromagnetic metallic (FMM) state is comparable to that of the charge-ordered insulating (COI) state, a subtle change in entropy stabilises either of these two states. Our low temperature specific heat measurements reveal that the linear term is absent in 0T and surprisingly not seen even in the metallic FMM state.Comment: 8 pages (in RevTEX format), 12 figures (in postscript format) Submitted to Phys. Rev.

Relations between structural distortions and transport properties in Nd0.5_{0.5}Ca0.5_{0.5}MnO3_3 strained thin films

Strained thin films of charge/orbital ordered (CO/OO) $Nd_{0.5}Ca_{0.5}MnO_3$ (NCMO) with various thickness have grown on (100)-SrTiO$_3$ and (100)-LaAlO$_3$ substrates, by using the Pulsed Laser Deposition (PLD) technique. The thickness of the films influences drastically the transport properties. As the thickness decreases, the CO transition increases while at the same time the insulator-to-metal transition temperature decreases under application of a 7T magnetic field. Clear relationships between the structural distortions and the transport properties are established. They are explained on the basis of the elongation and the compression of the Mn-O-Mn and Mn-O bond angles and distances of the \QTR{it}{Pnma} structure, which modify the bandwidth and the Jahn-Teller distortion in these materialsComment: 11 pages, 6 figures. to be published in Journal Physics: Condensed Matte

ANTI-DIABETIC EFFECT OF POLYHERBAL FORMULATION IN OGTT AND STREPTOZOTOCIN-INDUCED DIABETIC RAT MODEL

Objective: The present study investigates the efficacy of DiaKure, a poly herbal formulation composed of powder of different herbs on blood glucose level of normal and diabetic rats.Methods: The raw materials were collected made it into a powder formulation. Streptozotocin 60 mg/kg was administered as a single i. p. Injection for induction of type 1 diabetes. After one week of streptozotocin injection, animals showing glycosuria (fasting blood sugar level>200 mg/dL) were considered as diabetic. The hypoglycemic activity and glucose tolerance test were studied in normal and Streptozotocin-induced diabetic rats after administration of DiaKure at a dose of 300 mg/kg. Blood glucose was determined by a glucose monitor.Results: At a dose of 200 and 300 mg/kg p. o., DiaKure showed a hypoglycemic effect at a varying degree of significance (P<0.05-0.001) in normal rats in comparison with the respective control group. Maximum effect of DiaKure treatment in the glucose tolerance test occurred at 120thminute of glucose administration in normal rats.Conclusion: The results indicate significant hypoglycemic activity of DiaKure in male albino rats.Â

Multiferroic nature of charge-ordered rare earth manganites

Charge-ordered rare earth manganites Nd0.5Ca0.5MnO3, La0.25Nd0.25Ca0.5MnO3, Pr0.7Ca0.3MnO3 and Pr0.6Ca0.4MnO3 are found to exhibit dielectric constant anomalies around the charge-ordering or the magnetic transition temperatures. Magnetic fields have a marked effect on the dielectric properties, indicating the presence of coupling between the magnetic and electrical order parameters. The observation of magnetoferroelectricity in these manganites is in accord with the recent theoretical predictions of Khomskii and coworkers