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5 Temperature dependence of lower critical field of YBCO Superconductor
Get PDFWe report the detailed study of the temperature dependence of the lower critical field (H-c1) of the YBa2Cu3O7 superconductor by magnetization measurements. The curve shows the multiband gap behavior of the sample. It is found that the sample is not a single BCS type superconductor. H-c1 is measured as the point at which the curve deviates from a Meissner-like linear M(H) curve to a nonlinear path. The H-c1 for YBCO at different temperatures from 10K to 85K has been determined by magnetization measurements M(H) with applied field parallel to the c-axis. The sample phase purity has been confirmed by Rietveld fitted X-ray diffraction data. The amplitude (1-17Oe) dependent AC susceptibility confirms the granular nature of superconducting compound. Using Bean model we calculated the temperature dependency of inter-grain critical current density and J(c)(0) is found as 699.14kAcm(-2)
Probing the Mechanism for Bipolar Resistive Switching in Annealed Graphene Oxide Thin Films
No full textThe bipolar resistive switching (BRS) between a metallic low resistance state (LRS) and an insulating high resistance state (HRS) is demonstrated for annealed graphene oxide (GO) thin film-based device structures with aluminum (Al) as one of the contact electrodes. An optimal switching of similar to 10(4) order is recorded for Al/GO (200 degrees C)/indium tin oxide (ITO) among the device structures in metal (M-2)/GO (T)/metal (M-1) configurations (M-1 = Al, Au, or ITO and M-2 = Au or Al), fabricated using GO (T)/metal (M-1), annealed at different temperatures, T = 100, 200, 300, and 400 degrees C. The initial Ohmic conduction for electronic transport and the presence of metal contents through GO thin films in the X-ray photoelectron spectroscopy support the physical evidence of Al filament formation between the two electrodes as imaged by the high-resolution transmission electron microscopy. The speculated mechanism for BRS in repeated voltage sweep cycles is attributed to the current triggered breaking of metal filaments because of the combined effect of Joules heating and Peltier heat generation at LRS -> HRS transition, and electric field induced migration of metal atoms, leading to the formation of metal filaments through the GO film at the HRS up arrow LRS transition. The higher switching ratio exhibited in the current study could be translated to engineer simple and low-cost resistive memory devices
Impedance Spectroscopy of Aqueous Solution Samples of Different Glucose Concentrations for the Exploration of Non-Invasive-Continuous-Blood-Glucose-Monitoring
No full textContinuous blood-glucose-monitoring provides maximal information about the fluctuations of blood-glucose levels throughout the day and thus plays a vital role in controlling the blood-glucose level in diabetes. The conventional methods of testing blood-glucose level are invasive, painful and are unsuitable for continuous monitoring. Thus, the battle for developing bloodless and painless blood-glucose monitors has begun from past three decades. Electrical bio-impedance spectroscopy has been suggested as one of the potential technique for the development of such monitors. The present work is aimed at impedance spectroscopy to demonstrate the variation in electrical bio-impedance properties of blood with the change in glucose concentration. Glucose-dependent electrical impedance parameters of aqueous solution samples, of increasing glucose concentration have been determined to accomplish the same. The glucose-dependent capacitance and conductance illustrates the direct variations in impedance parameters with respect to change in glucose concentration. Measurement automation program is developed to ease the measurement procedure, to support continuous measurement, and to compute short-term repeatability of measurement results. The experimental results of the present work will be used to implement electrical bio-impedance spectroscopy technique in the development of non-invasive-continuous-blood-glucose monitoring system
Highly Luminescent Dual Mode Polymeric Nanofiber-Based Flexible Mat for White Security Paper and Encrypted Nanotaggant Applications
No full textIncreasing counterfeiting of important data, currency, stamp papers, branded products etc., has become a major security threat which could lead to serious damage to the global economy. Consequences of such damage are compelling for researchers to develop new high-end security features to address full-proof solutions. Herein, we report a dual mode flexible highly luminescent white security paper and nanotaggants composed of nanophosphors incorporated in polymer matrix to form a nanofiber-based mat for anti-counterfeiting applications. The dual mode nanofibers are fabricated by electrospinning technique by admixing the composite of NaYF4:Eu3+@NaYF4:Yb3+, Er3+ nanophosphors in the polyvinyl alcohol solution. This flexible polymer mat derived from nanofibers appears white in daylight, while emitting strong red (NaYF4:Eu3+) and green (NaYF4:Yb3+, Er3+) colors at excitation wavelengths of 254 nm and 980 nm, respectively. These luminescent nanofibers can also be encrypted as a new class of nanotaggants to protect confidential documents. These obtained results suggest that highly luminescent dual mode polymeric nanofiber-based flexible white security paper and nanotaggants could offer next-generation high-end unique security features against counterfeiting
Assessment of satellite-retrieved surface UVA and UVB radiation by comparison with ground-measurements and trends over Mega-city Delhi
No full textSolar UV radiation reaching the Earths surface is known to have various effects on human health and on the ecosystem. Ground-based measurements of surface UV radiation are spatially sparse and in many cases do not provide long time series. Higher spatial coverage can be provided by measurements from satellite based instruments, but these measurements need to be compared to ground-based measurements of sufficient quality before they can be used in health and ecosystem applications. Here, we compare the measurements of surface solar UV radiation in UVA (315-400 nm) and UVB (280-315 nm) bands with the satellite retrievals (CERES) and validate the latter at an urban location, Delhi, India. We have also used MODIS-retrieved aerosol optical depth (AOD) and cloud optical depth (COD) data to see the effect of atmospheric opacity on UV radiation. Ground based measurements of UVA and UVB were performed from 01 October, 2012 to 30 September, 2015: Correlations between daily surface measurements and CERES-derived surface UV fluxes showed very good agreement (r similar to 0.92-0.93) over Delhi. We found a negative correlation between UV fluxes and AOD over Delhi during all seasons. A unit increase in AOD leads to a decrease of similar to 4-5 Wm(-2) in UVA and similar to 0.09-0.14 Wm(-2) in UVB over Delhi. The trend analysis from monthly mean CERES-derived UV fluxes for 17 years data reveals that UVA and UVB are decreasing similar to 0.07 Wm(-2) yr(-1) and 0.003 Wm(-2) yr(-1), respectively with AOD increase (similar to 0.005 yr(-1)) over Delhi. The simultaneous increase in aerosol loading with decrease in UV fluxes at the surface may be explained as a masking effect of ever increasing pollution on surface UV radiation over Delhi. Our results show similar to 10% and similar to 20% decrease (with respect to mean) in UVA and UVB surface fluxes, respectively during last 17 years
Green synthesis, characterization and antimicrobial activity of zinc oxide quantum dots using &ITEclipta alba&IT
No full textThe present study focused on the green and sustainable synthesis of zinc oxide (ZnO) quantum dots (QDs) using zinc acetate (precursor) and Eclipta alba leaf extract as a reducing agent. The synthesis of ZnO QDs was monitored by ultraviolet-visible absorption spectroscopy at wavelength (lambda(max)) 324 nm. The optimal synthesis of ZnO QDs was recorded at temperature 40 degrees C, pH 7, 5 mL zinc acetate (5 mM), 7 mL leaf extract and reaction time of 75 min. The transmission electron microscopy (TEM) depicted homogeneous distribution of spherical ZnO QDs with mean particle size of 6 nm that comparable to biomolecules. The selected area electron diffraction (SAED) analysis revealed crystalline nature of ZnO QDs having a hexagonal wurtzite phase with lattice constants a = b = 0.32 nm and c = 0.52 nm. Furthermore, the physical interactions between ZnO QDs and E. coli cells were studied by TEM and agar well diffusion methods that showed enhanced antimicrobial activity. Overall, these unique size and quite stable QDs open up possibilities of applications in a number of commercial consumers, clinical products and fluorescence labeling including the antimicrobial agent
Facile fabrication of p- and n-type half-Heusler alloys with enhanced thermoelectric performance and low specific contact resistance employing spark plasma sintering
No full textHalf-Heusler (HH) materials have been actively explored for thermoelectric (TE) based power generation applications in the mid-temperature regime. In the current work, we demonstrate the defect engineering in non-stoichiometric HH alloys to realize a state-of-the-art ZT 1 at 873 K for both n-type Zr0.5Hf0.5Ni1-xSn and p-type Zr0.5Hf0.5Co1+xSb0.8Sn0.2 (x = 0.04) compositions. This enhanced ZT leads to high conversion efficiency of -9% with a high output power density similar to 9 Wcm(2) in both the synthesized n and p-type HH alloys, estimated using cumulative temperature dependence model. A time efficient fabrication route of HH device thermo-elements with Ti electrical contacts, employing spark plasma sintering process, is also demonstrated in the optimized defect engineered HH compositions. A low specific contact resistivity of <10 m Omega.cm(2) in both n-type and p-type HH/Ti thermo-elements was realized, which suggests exciting opportunities and possibilities for achieving highly efficient TE based power generation
Effect of Pressure on Bonding Environment and Carrier Transport of a-Si:H Thin Films Deposited Using 27.12 MHz Assisted PECVD Process
No full textInvestigation of carrier transport in hydrogenated amorphous silicon (a-Si:H) thin films deposited at various pressures (0.03 - 0.53 Torr) using 27.12 MHz assisted high frequency Plasma Enhanced Chemical vapor Deposition (PECVD) process is presented. From results of Steady State Photocarrier Grating (SSPG) the carrier diffusion length was found to vary from 0.098 - 0.189 mu m. Moreover a direct influence of ambipolar diffusion length was observed with the transport mechanism for deposition pressure in the range (0.13 - 0.53 Torr). There was a correlation observed for photosensitivity and microstructure parameter with mobility lifetime (mu tau) product and diffusion length of carriers. Diffusion length and mu tau product were observed to be maximum (0.189 mu m and 0.471 x 10(-8) cm(2) V-1) for the film having high photosensitivity (7.2x10(3)) deposited at a rate similar to 1.39 angstrom/s at 0.53 Torr deposition pressure. In addition to electrical transport properties, the effect of deposition pressure on structural and optical properties was also studied using various characterization tools such as Raman, UV-Vis and infrared spectroscopy
APMP.EM-S12 Comparison of Standards for the Calibration of Voltage, Current and Resistance Meters
No full textThe 14 Meeting of the APMP Technical Committee on Electricity and Magnetism, held on 5 December 2011 in Kobe, Japan, decided to hold a comparison of standards for the calibration of voltage, current and resistance meters at the lowest attainable level of uncertainty. This comparison
complements the APMP.EM-S8 comparison using a 6.5 digit multimeter and the following comparisons of primary standards that provide traceability for the calibration of voltage, current and resistance meters: APMP.EM-K2: DC high resistance at 10 MΩ, 1 GΩ(in progress); APMP.EM.BIPM-K11.3: DC voltage, 10 V and 1.018 V (completed); APMP.EM-K6.a: AC/DC transfer at 3 V (completed); APMP.EM-K9: AC/DC transfer at 500 V, 1000 V (completed). The National Measurement Institute, Australia (NMIA) has been appointed as the pilot laboratory
Study of enhancement in the dielectric and electrical properties of WO3-doped LiF nano-composite
No full textWe report the dielectric and electrical behavior of thermally evaporated lithium fluoride (LiF)-tungsten trioxide (WO3) (x wt% WO3-doped LiF; x = 0, 1, 3, 5, 7, 10) nano-composite thin films at room temperature over a wide range of frequencies from 0.1 Hz to 1 MHz. Among the various doping concentrations of WO3, the 5 wt% WO3-doped LiF nano-composite thin film reaches to the maximum dielectric constant similar to 25, compared with those of pure LiF similar to 9 thin film. The electrical studies of the films have been done by complex impedance spectroscopy and show the presence of grain and grain boundaries contribution in the films for all doping concentrations. The relaxation behavior in the nano-composite films has been observed in the dielectric curve at low frequencies which is superimposed by electrode polarization. The non-Debye type of relaxation in the films has been observed in the impedance and modulus curve. The peaks appearing at low frequencies for each doping concentration in loss tangent spectrum show the presence of relaxing dipoles in the films. An increment in the ac conductivity has been observed with doping concentration up to 5%. The ac conductivity curves obey the jump relaxation power law where an electrode polarization effect can be seen at low-frequency region