Superconductivity in doped FeTe1-xSx (x= 0.00 to 0.25) single crystals

We report self flux growth and characterization of FeTe1-xSx (x= 0.00 to 0.25) single crystal series. Surface X-ray diffraction (XRD) exhibited crystalline nature with growth in (00l) plane. Micro-structural (electron microscopy) images of representative crystals showed the slab-like morphology and near stoichiometric composition. Powder XRD analysis (Rietveld) of single crystals exhibited tetragonal structure with P4/nmm space group and decreasing a and c lattice parameters with increase in x. Electrical resistivity measurements (R-T) showed superconductivity with Tconset at 9.5K and 8.5K for x =0.10 and x =0.25 respectively. The un-doped crystal exhibited known step like anomaly at around 70K. Upper critical field Hc2(0), as calculated from magneto transport for x =0.25 crystal is around 60Tesla and 45Tesla in H//ab and H//c directions. Thermal activation energy [U0(H)] calculated for x =0.10 and 0.25 crystals followed weak power law, indicating single vortex pinning at low fields. Mossbauer spectra for FeTe1-xSx crystals at 300K and 5K are compared with non superconducting FeTe. Both quadrupole splitting (QS) and isomer shift (IS) for S doped crystals were found to decrease. Also at 5K the hyperfine field for x =0.10 superconducting crystal is decreased substantially from 10.6Tesla (FeTe) to 7.2Tesla. For x =0.25 crystal, though small quantity of un-reacted Fe is visible at room temperature, but unlike x =0.10, the low temperature (5K) ordered FeTe hyperfine field is nearly zero.Comment: 20 Pages Text + Figs: Accepted Mat. Res. Exp, Mat. Rex. Exp. (2018

Electronic structure and Fermi surface topology of binary and ternary compounds

To explore the material properties, electronic structure calculations are very much useful and can be obtained from the well known density functional theory(DFT) calculations. In the present thesis, we have focussed on the Fermi surface calculations and try to link the same with other physical properties. In addition, we have also explored the pressure effect on properties of the system. For the present study, we have selected different types of compounds which are Ni-based Heusler compounds, Nb-based A-15 compounds, Sn-based binary compounds and few magnetic compounds(one Zr-based Heusler compound and other Mn-based compounds). Electronic structure, mechanical, vibrational properties of Ni-based Heusler compounds, Ni2XAl (X=Ti, Zr, Hf, V, Nb, and Ta), Ni2NbGa and Ni2NbSn, are presented both at ambient and under compression. Among the mentioned compounds, Ni2NbAl, Ni2NbGa and Ni2NbSn are experimentally reported as superconductors at ambient and our calculated superconducting transition temperature (Tc) and electron-phonon coupling constant (λep) values are in good agreement with the experiments. In addition, we have predicted superconducting nature in Ni2VAl with electron-phonon coupling constant (λep) around 0.68, which leads to superconducting transition temperature (Tc) around ∼4 K (by using coulomb pseudopotential μ∗ = 0.13), which is a relatively high transition temperature for Ni based Heusler alloys and are compared with other Ni2NbY (Y = Al, Ga and Sn) compounds. From the calculated Fermi surfaces, flat Fermi sheets are observed along X

Alkaline Protease Bioprocess Optimization through Response Surface Methodology for Alkaliphilic Bacillus subtilis SHmIIIa Mutant Strain from Warangal-Telangana

The present investigations were carried out to enhance the alkaline protease production by a mutant strain Bacillus subtilis SH2 isolated from slaughter house soils of Warangal and improved through two-tier mutagenesis first by UV and then HNO2. Initially three efficient mutants with over production of alkaline protease were identified and among them only one stable mutant SHmIIIa was selected for further improvement through popular Response Surface Methodology of the FFCCD. Only X2 agitation, X6 KH2PO4 and interactive effects of X3*X3 inoculum, X4*X5 glucose and peptone have shown a significant improvement. The maximum alkaline protease production was achieved with the medium containing of X1 pH 9.8; X2 agitation 237.5 rpm; X3, inoculum size 4%; X4, glucose 6 g/L; X5, peptone 4g/L and X6, KH2PO4 2 g/L; under batch fermentative conditions with 33.33 fold increase

Transport and magnetic anomalies due to A-site ionic size mismatch in La0.5_{0.5}Ca0.5−x_{0.5-x}Ba_{x}MnO3_3

We present results of electrical resistivity, magnetoresistance and ac and dc magnetic susceptibility on polycrystalline samples of the type La(0.5)Ca(0.5-x)Ba(x)MnO(3) synthesized under identical heat treatment conditions. The substitution of larger Ba ions for Ca results in a non- monotonic variation of the curie temperature as the system evolves from a charge ordered insulating state for x=0 to a ferromagnetic metallic state for x=0.5. An intermediate compositino, x=0.1, interestingly exhibits ferromagnetic. insulating behaviour with thermal hysteresis in ac chi around the curie tem- perature (120K). The x=0.2 and 0.3 compounds exhibit semiconducting like behavior as the temperature is lowered below 300K, with a broad peak in rho around 80-100K: These compositions exhibit a weak increase in rho as the temperature lowered below 30K, indicative of electron localization effects. These compositions also undergo ferromagnetic transitions below about 200 and 235K respectively, though these are non-hysteretic; above all, for these compositions, MR is large and conveniently measurable over the entire tempera- ture range of measurement below Tc. This experimental finding may be of interest from the application point of view. We infer that the A-site ionic-size mismatch plays a crucial role in the deciding these properties.Comment: 5 pages, 6 Figures, Resubmitted with extended abstract on 26 Nov, 199

The dynamics and control of large flexible space structures-IV

The effects of solar radiation pressure as the main environmental disturbance torque were incorporated into the model of the rigid orbiting shallow shell and computer simulation results indicate that within the linear range the rigid modal amplitudes are excited in proportion to the area to mass ratio. The effect of higher order terms in the gravity-gradient torque expressions previously neglected was evaluated and found to be negligible for the size structures under consideration. A graph theory approach was employed for calculating the eigenvalues of a large flexible system by reducing the system (stiffness) matrix to lower ordered submatrices. The related reachability matrix and term rank concepts are used to verify controllability and can be more effective than the alternate numerical rank tests. Control laws were developed for the shape and orientation control of the orbiting flexible shallow shell and numerical results presented

Heat capacity and Mosssbauer study of Self flux grown FeTe Single Crystal

We report mainly the heat capacity and Mossbauer study of self flux grown FeTe single crystal, which is ground state compound of the Fe chalcogenides superconducting series, i.e., FeTe1-x(Se/S)x. The as grown FeTe single crystal is large enough to the tune of few cm and the same crystallizes in tetragonal structure having space group of P4/nmm. FeTe shows the structural/magnetic phase transition at 70K in both magnetic and resistivity measurements. Heat capacity measurement also confirms the coupled structural/magnetic transition at the same temperature. The Debye model fitting of low temperature (below 70K) heat capacity exhibited Debye temperature to be 324K. M\"Ossbauer spectra are performed at 300K and 5K. The 300K spectra showed two paramagnetic doublets and the 5K spectra exhibited hyperfine magnetic sextet with an average hyperfine field of 10.6Tesla matching with the results of Yoshikazu Mizuguchi et al.Comment: Short MS-12 pages text + figs: Accepted Letter - J. Sup. Novel Ma

A Routing Delay Predication Based on Packet Loss and Explicit Delay Acknowledgement for Congestion Control in MANET

In Mobile Ad hoc Networks congestion control and prevention are demanding because of network node mobility and dynamic topology. Congestion occurs primarily due to the large traffic volume in the case of data flow because the rate of inflow of data traffic is higher than the rate of data packets on the node. This alteration in sending rate results in routing delays and low throughput. The Rate control is a significant concern in streaming applications, especially in wireless networks. The TCP friendly rate control method is extensively recognized as a rate control mechanism for wired networks, which is effective in minimizing packet loss (PL) in the event of congestion. In this paper, we propose a routing delay prediction based on PL and Explicit Delay Acknowledgement (EDA) mechanism for data rate and congestion control in MANET to control data rate to minimize the loss of packets and improve the throughput. The experiment is performed over a reactive routing protocol to reduce the packet loss, jitter, and improvisation of throughput