Sensitivity of surface resistance measurement of HTS thin films by cavity resonator, dielectric resonator and microstrip line resonator

Microwave surface resistance (R _s) of silver-doped YBa₂Cu₃O_7-δ (YBCO) thin film, deposited by laser ablation technique on 10 mm × 10 mm LaAlO₃ substrate, has been measured by resonant techniques in the frequency range from 5 GHz to 20 GHz. The geometrical factor of the sample and the resonator has been determined theoretically by the knowledge of the electromagnetic field distribution in the resonators. The microwave surface resistance of the superconducting sample is then extracted from the measured Q value as a function of temperature. The sensitivity of the R _s measurement, that is, the relative change in the Q value with the change in the R _s value is determined for each resonator.     

RF sputtered thin films of highT cY-Ba-Cu-O

Y-Ba-Cu-O films are grown on strontium titanate substrates by RF sputtering from a single composite target. A barium-deficient annular ring with diameter equal to that of the target dimension is repeatedly observed. Films inside this ring are deposited exclusively at the close target-substrate distance. At larger distances the films grow more in exterior regions rather than in the interior region of the ring. Stoichiometry, structural morphology and superconducting transition temperatures are studied for various regions of the film. The films are superconducting when sintered in flowing oxygen at 950°C with onset at 100 K and a broad transition width.     

Instrumentation for PSD-based neutron diffractometers at Dhruva reactor

Linear position sensitive detectors (PSDs) are widely used to configure neutron diffractometers and other instruments. Necessary front-end electronics and a data acquisition system [1] is developed to cater to such instruments built around the Dhruva research reactor in BARC. These include three diffractometers with multiple PSDs and four with single PSD. The front-end electronics consists of high voltage units, preamplifiers [2],shaping amplifiers, ratio ADCs (RDC) [3]. The data acquisition system consists of an interface card and software. Commercially available hardware like temperature controller or stepper motor controller connected over GPIB or RS232 are also integrated in the data acquisition system. The data acquisition is automated so that it can continue unattended for control parameter like temperature, thus enabling optimum utilization of available beam time. The instrumentation is scalable and can be easily configured for various instrumental requirements. The front-end electronics and the data acquisition system are described here.     

Bridgehead Nitrogen Heterocycles: Facile Synthesis of Imidazo [2,1-b]-1,3,4-Thiadiazoles Using Hypervalent Iodine

2,6-Diarylimidazo [2,1-b]-1,3,4-thiadiazoles (3) were synthesized by reactions of either α-haloketones with 2-aminothiadiazoles (1) or directly with acetophenones in the presence of [hydroxy(p-tosyloxy)iodo]benzene. The latter method is convenient and versatile.     

New tetranuclear Cu(II) complexes: synthesis, structure, and magnetic properties

The synthesis, structure, and magnetic properties of two new tetranuclear Cu(II) complexes containing N,N,N',N'-tetraethylpyridine-2,6-dithiocarboxamide (S-dept) of formula [Cu(2)Cl(2)(mu-S-dept)(2)][Cu(2)Cl(4)(mu-Cl)(2)] (1) and [Cu(2)(mu-Cl)(2)(S-dept)(2)][CuCl(3)(EtOH)](2) (2) are reported. Their X-ray crystal structures reveal that the complexes are composed of anionic and cationic dimers, that in both cases contain the metal centers which interact via Coulombic and/or hydrogen bonding interactions. In both cases, the Cu centers in the anionic moieties adopt a slightly distorted tetrahedral geometry whereas for the cationic moieties they adopt a square-pyramidal type of geometry. Magnetic susceptibility data show that compounds 1 and 2 present an overall antiferromagnetic behavior arising from the contribution of both anionic and cationic moieties. For 1, the best fit obtained gave J(1) = -2.62 +/- 0.19 cm(-1), J(2) = -19.54 +/- 0.47 cm(-1), and g(2) = 2.164 +/- 0.004 cm(-1) (R = 8.28 x 10(-5)) whereas for 2 it gave J(1) = 4.48 +/- 2.73 cm(-1), g(1) = 2.20 +/- 0.03, J(2) = -11.26 +/- 2.01 cm(-1), and g(2) = 2.10 +/- 0.03 (R = 1.15 x 10(-4)). The nature of the superexchange pathways in 1 and 2 is discussed on the basis of structural, magnetic, and molecular orbital considerations. Theoretical calculations are performed at the extended Huckel level in order to obtain their molecular orbitals and energies using their crystallographic data.     

Isothermal and non-isothermal crystallization kinetics of PVA + ionic liquid [BDMIM][BF4]-based polymeric films

The effect of ionic liquid (IL), 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM][BF₄], on crystallization behavior of poly(vinyl alcohol) (PVA) has been studied by isothermal and non-isothermal differential scanning calorimetry techniques. The PVA + IL based polymer electrolyte films have been prepared using solution casting technique. To describe the isothermal and non-isothermal crystallization kinetics, several kinetic equations have been employed on PVA + IL based films. There is strong dependence of the peak crystallization temperature (T_c), relative degree of crystallity (X_t), half-time of crystallization (t_1/2), crystallization rate constants (Avrami K_t and Tobin A_T), and Avrami (n) and Tobin (n_T) exponents on the cooling rate and IL loading.     

On martingale characterizations for some generalized space fractional Poisson processes

We obtain martingale characterizations for the generalized space fractional Poisson process (GSFPP) and for counting processes with Bern?tein intertimes. These serve as extensions of the Watanabe's characterization for the classical homogenous Poisson process. The corresponding assertion for the space fractional Poisson process (SFPP) is obtained as a particular case of our results.     

Effective potentials and threshold anomaly

The strongE andL dependence of the effective elastic channel potentials is shown to be an implicit radial kinetic energy (ε) dependence. It is also shown that this effective potential satisfies the dispersion relation inε variable at the strong absorption radius. Further, the experimental data for both elastic and fusion channels are consistent with thisL-dependence of the corresponding effective potentials. The effective transfer channel potentials derived using CRC code FRESCO are shown to exhibit strong energy dependence as a result of couplings. The energy dependence of effective transfer strength for¹⁶O+²⁰⁸Pb and¹⁶O+²³²Th systems is determined using the experimental transfer angular distributions.