Laxman Singh

Limits on light weakly interacting massive particles from the CDEX-1 experiment with ap-type point-contact germanium detector at the China Jinping Underground Laboratory

We report results of a search for light Dark Matter WIMPs with CDEX-1 experiment at the China Jinping Underground Laboratory, based on 53.9 kg-days of data from a p-type point-contact germanium detector enclosed by a NaI(Tl) crystal scintillator as anti-Compton detector. The event rate and spectrum above the analysis threshold of 475 eVee are consistent with the understood background model. Part of the allowed regions for WIMP-nucleus coherent elastic scattering at WIMP mass of 6-20 GeV are probed and excluded. Independent of interaction channels, this result contradicts the interpretation that the anomalous excesses of the CoGeNT experiment are induced by Dark Matter, since identical detector techniques are used in both experiments.

Measurement of Nu(e)-bar -Electron Scattering Cross-Section with a CsI(Tl) Scintillating Crystal Array at the Kuo-Sheng Nuclear Power Reactor

The {nu}{sub e}-e{sup -} elastic scattering cross section was measured with a CsI(Tl) scintillating crystal array having a total mass of 187 kg. The detector was exposed to an average reactor {nu}{sub e} flux of 6.4x10{sup 12} cm{sup -2} s{sup -1} at the Kuo-Sheng Nuclear Power Station. The experimental design, conceptual merits, detector hardware, data analysis, and background understanding of the experiment are presented. Using 29882/7369 kg-days of Reactor ON/OFF data, the standard model (SM) electroweak interaction was probed at the squared 4-momentum transfer range of Q{sup 2{approx}}3x10{sup -6} GeV{sup 2}. The ratio of experimental to SM cross sections of {xi}=[1.08{+-}0.21(stat){+-}0.16(sys)] was measured. Constraints on the electroweak parameters (g{sub V},g{sub A}) were placed, corresponding to a weak mixing angle measurement of sin{sup 2{theta}}{sub W}=0.251{+-}0.031(stat){+-}0.024(sys). Destructive interference in the SM {nu}{sub e}-e process was verified. Bounds on anomalous neutrino electromagnetic properties were placed: neutrino magnetic moment at {mu}{sub {nu}{sub e}} <3.3x10{sup -32} cm{sup 2}, both at 90% confidence level.

Dielectric studies of a nano-crystalline CaCu2.90Zn0.10Ti4O12 electro-ceramic by one pot glycine assisted synthesis from inexpensive TiO2 for energy storage capacitors

A facile way for the synthesis of nano-crystalline CaCu2.90Zn0.10Ti4O12 (CCZTO) using a solution combustion technique based on the glycine–nitrate process with inexpensive solid TiO2 powder as the raw material is introduced in this manuscript, for the first time. The precursor powder was calcined between 200 °C and 850 °C for 3 h in air. Phase formation, crystalline nature, morphology and chemical purity of the fabricated CCZTO were investigated with TG/DTA, FT-IR, FT-Raman, XRD, SAED patterns, SEM, TEM, EDX and XPS analyses, respectively. The XRD results indicated that all sintered samples had a major CaCu3Ti4O12 structure with some amount of CaTiO3 and CuO. The bright-field TEM micrographs revealed that the particle size was in the range of 15–50 nm, which was in good agreement with the average crystallite size obtained from XRD. SEM micrographs of the sintered CCZTO ceramics showed the average grain sizes were in the range of 800 nm–7 μm. EDX and XPS studies confirmed the stoichiometry and purity of the ceramics. The nature of the relaxation behavior of the ceramics was rationalized using impedance and modulus spectroscopy. The activation energies calculated from the grain-boundary relaxation time constant were found to be in the range of 0.79–0.52 eV, which confirmed the Maxwell–Wagner type of relaxation present in the ceramic. Our inexpensive novel solution chemistry based method for CCZTO_16h gives a high dielectric constant (799) and low dielectric loss (0.091) at 100 Hz at room temperature, which has potential significance for cost-effective technological applications in microelectronic devices.

Tribological studies of stearic acid-modified CaCu2.9Zn0.1Ti4O12 nanoparticles as effective zero SAPS antiwear lubricant additives in paraffin oil

Stearic acid modified ceramic nanoparticles SCCZTO-6 h, SCCZTO-8 h and SCCZTO-12 h of average sizes 60, 80 and 90 nm were prepared from CCZTO-6 h, CCZTO-8 h and CCZTO-12 h respectively (where CCZTO represents CaCu2.9Zn0.1Ti4O12; 6 h, 8 h and 12 h are the sintering times). The SCCZTO nanoparticles have been characterized by Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM). Tribological behavior of these nanoparticles in liquid paraffin oil has been evaluated using a four-ball lubricant tester and compared with conventional high SAPS containing zinc dialkyldithiophosphates (ZDDP). All antiwear tests have been performed using an optimized concentration of the SCCZTO nanoparticles (1% w/v) by varying the load for a 30 min test duration and by varying the test durations at 392 N load. Various tribological parameters such as mean wear scar diameter (MWD), friction coefficient (μ), mean wear volume (MWV), running-in, steady-state and overall wear rates show that all the SCCZTO nanoparticles act as efficient antiwear additives and possess a high load carrying capacity. The best tribological behavior is shown by SCCZTO-6 h, followed by SCCZTO-8 h and then SCCZTO-12 h. The surface morphology and roughness of the wear scar have been studied by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) respectively. AFM and SEM micrographs of the wear scar in the presence of SCCZTO-6 h and SCCZTO-8 h at 392 N applied load for a 90 min test duration show a drastic decrease in surface roughness. Energy-Dispersive X-ray (EDX) analysis of the worn surface under similar experimental conditions in the presence of SCCZTO-6 h nanoparticles exhibits the presence of calcium, copper, zinc, titanium and oxygen on the worn steel surface indicating tribosinterization and/or adsorption of the additive on the rubbing surface resulting in the formation of a strong tribofilm. X-ray Photoelectron Spectroscopy (XPS) of the tribofilm shows the presence of CaO, CuO, Cu2O, TiO2, Fe2O3 and adsorbed carbon in the form of –C–C– and –C(O)O– moieties.

A Search of Low-Mass WIMPs with p-type Point Contact Germanium Detector in the CDEX-1 Experiment

The CDEX-1 experiment conducted a search of low-mass (< 10 GeV/c2) Weakly Interacting Massive Particles (WIMPs) dark matter at the China Jinping Underground Laboratory using a p-type point-contact germanium detector with a fiducial mass of 915 g at a physics analysis threshold of 475 eVee. We report the hardware set-up, detector characterization, data acquisition and analysis procedures of this experiment. No excess of unidentified events are observed after subtraction of known background. Using 335.6 kg-days of data, exclusion constraints on the WIMP-nucleon spin-independent and spin-dependent couplings are derived.

Influence of Zn doping on microstructures and dielectric properties in CaCu3Ti4O12 ceramic synthesised by semiwet route

Abstract A single phase of calcium copper titanate [CaCu3Ti4O12 (CCTO)] was produced at lower temperature and shorter calcination time via a novel semiwet route. Undoped CCTO and zinc doped CaCu3−xZnxTi4O12 samples with x = 0·10, 0·20 and 0·30 were prepared by this method for the first time using solid TiO2 powder in metal nitrate solutions. The CaCu3−xZnxTi4O12 ceramics were characterised by thermogravimetric/differential thermal analysis, X-ray diffraction, SEM and EDX techniques. The SEM images of the sintered CaCu3−xZnxTi4O12 ceramics showed average grain size in the ranges of 2–6, 8–13, 12–16 and 14–20 μm for x = 0·00, 0·10, 0·20 and 0·30 respectively. Energy dispersive X-ray spectroscopy studies confirm the purity of parent and Zn doped CCTO ceramics. At room temperature, the dielectric constants of Zn doped CCTO are always higher than pure CCTO. CaCu3−xZnxTi4O12 (x = 0·20) ceramic has the maximum value of ϵr≈4347 along with the minimum value of tan δ≈0·14 at 1 kHz.

Sintering effects on dielectric properties of Zn-doped CaCu3Ti4O12 ceramic synthesized by modified sol-gel route

CaCu2.90Zn0.10Ti4O12 ceramic was synthesized by a novel semi-wet route and calcined at 800°C in air for 8 h. The obtained powder was divided into three parts and sintered in air at 950°C for 6 h, 8 h, and 12 h, separately. XRD results confirmed the single phase formation of all the sintered samples with similar cubic structure of CaCu3Ti4O12 (CCTO). Scanning electron micrographs of the CaCu2.9Zn0.1Ti4O12 ceramic sintered for 6 h shows bimodal grain size distribution. Increasing the sintering time significantly promotes the grain growth and microstructural densification. The sintering duration was found to have tremendous influence on microstructure and dielectric properties of CaCu2.90Zn0.10Ti4O12 ceramic. The CaCu2.9Zn0.1Ti4O12 ceramic sintered for 12 h exhibited high dielectric constant εr ∼ 5971 at 1 kHz and room temperature. It is found that εr is independent at high frequency and weakly dependent on temperature.

DIELECTRIC PROPERTIES OF ULTRAFINE Zn-DOPED CaCu3Ti4O12 CERAMIC

Ultrafine powder of CaCu2.80Zn0.20Ti4O12 ceramic was prepared using a novel semi-wet method. DTA/TG analysis of dry powder gives pre-information about formation of final product around 800°C. The formation of single phase was confirmed by X-ray diffraction analysis. The average particle size of sintered powder of the ceramic obtained from XRD and Transmission electron microscopy was found 59 nm and 102 nm, respectively. Energy Dispersive X-ray studies confirm the stoichiometry of the synthesized ceramic. Dielectric constant of the ceramic was found to be 2617 at room temperature at 1 kHz.

Dielectric properties of CaCu2·9Co0·1Ti4O12 and CaCu3Ti3·9Co0·1O12 ceramics synthesized by semi-wet route

The effect of Co + 2 doping on Cu + 2 and Ti + 4 sites in calcium copper titanate, CaCu3Ti4O12, has been examined. The doped compositions, CaCu

Preparation and Characterization of Nanostructured CaCu2.90Zn0.10Ti4O12 Ceramic

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