Complete gate control of supercurrent in graphene p-n junctions

In a conventional Josephson junction of graphene, the supercurrent is not turned off even at the charge neutrality point, impeding further development of superconducting quantum information devices based on graphene. Here we fabricate bipolar Josephson junctions of graphene, in which a p-n potential barrier is formed in graphene with two closely spaced superconducting contacts, and realize supercurrent ON/OFF states using electrostatic gating only. The bipolar Josephson junctions of graphene also show fully gate-driven macroscopic quantum tunnelling behaviour of Josephson phase particles in a potential well, where the confinement energy is gate tuneable. We suggest that the supercurrent OFF state is mainly caused by a supercurrent dephasing mechanism due to a random pseudomagnetic field generated by ripples in graphene, in sharp contrast to other nanohybrid Josephson junctions. Our study may pave the way for the development of new gate-tuneable superconducting quantum information devices.open114344sciescopu

Postoperative irradiation after implant placement: A pilot study for prosthetic reconstruction

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Modulation doping in ZnO nanorods for electrical nanodevice applications

We introduce a modulation-doping method to control electrical characteristics of ZnO nanorods. Compared with a conventional homogeneous doping method, the modulation-doping method generates localized doping layers along the circumference in ZnO nanorods, useful for many device applications. Here, we investigated electrical, structural, and optical characteristics of Ga-doped ZnO nanorods with the dopant modulation layers. Electrical conductivity of ZnO nanorods was controlled by changing either dopant mole fraction or the number of modulation-doped layers. Furthermore, the modulation-doped nanorod field effect transistors exhibited precisely controlled conductance in the order of magnitude without degradation of electron mobility. The effects of the doping on structural and optical characteristics of the nanorods are also discussed.open112126sciescopu

Wetting state on hydrophilic and hydrophobic micro-textured surfaces: Thermodynamic analysis and X-ray visualization

In this study, the wetting state on hydrophobic and hydrophilic micro-textured surfaces was investigated. High spatial resolution synchrotron X-ray radiography was used to overcome the limitations in visualization in previous research and clearly visualize the wetting state for each droplet under quantified surface conditions. Based on thermodynamic characteristics, a theoretical model for wetting state depending on the chemical composition (intrinsic contact angle) and geometrical morphology (roughness ratio) of the surfaces was developed. (C) 2015 AIP Publishing LLC.open1143sciescopu

A survey of knowledge, attitudes and practice of emergency contraception among university students in Cameroon

<p>Abstract</p> <p>Background</p> <p>Unsafe abortion is a major public health problem in low-and-middle income countries. Young and unmarried women constitute a high risk group for unsafe abortions. It has been estimated that widespread use of emergency contraception may significantly reduce the number of abortion-related morbidity and mortality. The purpose of this study was to evaluate the knowledge, attitudes and experiences on emergency contraceptive pills by the university students in Cameroon in order to develop and refine a national health programme for reducing unwanted pregnancies and their associated morbidity and mortality.</p> <p>Methods</p> <p>A convenient sample of 700 students of the University of Buea (Cameroon) was selected for the study. Data was collected by a self-administered, anonymous and pre-tested questionnaire.</p> <p>Results</p> <p>The response rate was 94.9% (664/700). General level of awareness of emergency contraceptive pills was 63.0% (418/664). However, knowledge of the general features of emergency contraceptive pills was low and misinformation was high among these students. Knowledge differed according to the source of information: informal source was associated with misinformation, while medical and informational sources were associated with better knowledge. Although the students generally had positive attitudes regarding emergency contraceptive pills, up to 65.0% (465/664) believed that emergency contraceptive pills were unsafe. Those with adequate knowledge generally showed favourable attitudes with regards to emergency contraceptive pills (Mann-Whitney U = 2592.5, p = 0.000). Forty-nine students (7.4%) had used emergency contraceptive pills themselves or had a partner who had used them.</p> <p>Conclusion</p> <p>Awareness of emergency contraception pills by Cameroonian students is low and the method is still underused. Strategies to promote use of emergency contraception should be focused on spreading accurate information through medical and informational sources, which have been found to be reliable and associated with good knowledge on emergency contraceptive pills.</p

Progressive disappearance of the c-axis tunneling barrier in Bi2Sr2CaCu2O8+x single crystals near T-c

We observed an enhancement of the differential conductance dI/dV around the zero bias in junctions of Au/Bi2Sr2CaCu2O8+x(Bi2212) single crystals near the superconducting transition temperature of Bi2212 crystals with the tunneling current along the c axis. We attribute such an enhancement to an Andreev reflection (AR) between the surface Cu-O bilayer, which is in the normal state, and the next superconducting bilayer below the crystal surface. The continuous evolution from a gap-like depression to the AR peak structure of the dI/dV curves around the zero bias indicates weakening of the barrier strength of the non-superconducting layers between adjacent Cu-O bilayers as the temperature is raised up to T-c. We suggest that the fact can be conveniently used to investigate the possible existence of preformed pairs in the pseudogap state above T-c.X111sciescopuskciothe

Mechanism of the c-axis dissipation in Bi2Sr2CaCu2O8-x single crystals

We have measured resistivities both in the ab-plane and dong the c-axis on Bi2Sr2CaCu2O8-x single crystals in magnetic fields oriented parallel to the c-axis. Both the ab-plane and the c-axis magnetoresistivities at low temperatures are described by the thermally activated flux creep model with the same value of the thermal activation energy, which scales with H-0.3+/-0.1. We also found a narrow temperature region where the ratio of the c-axis to the ab-plane conductivity in the mixed state exhibits a negative slope with temperature, as predicted by the Koshelev model. In this temperature regime, the c-axis dissipation is presumably due to the phase slips between the Cu-O bilayers caused by the diffusive motion of the pancake vortices in different layers.X116sciescopu

The c-axis dissipation and vortex phases in Bi2Sr2CaCu2O8+x crystals

We report on measurements of the resistivities of Bi2Sr2CaCu2O8+x crystals along the c axis (rho(c)) as well as in the ab plane (rho(ab)) in magnetic fields applied parallel to the c-axis (H parallel to c) from 10 Oe to 60 kOe. From the temperature dependence of the resistivity ratio rho(ab)/rho(c) in relatively low magnetic field below 1 kOe, we identified the vortex-solid, pancake-vortex and possible line-vortex phases. This suggests that a vortex solid in highly anisotropic high-T-c superconductors like Bi2Sr2CaCu2O8+x crystals, at least in this nonequilibrium situation, exhibits a two-stage transition into a vortex gas via a vortex liquid. (C) 1997 Elsevier Science Ltd.X112sciescopu

Observation of a truly superconducting phase in the c-axis conduction of Bi2Sr2CaCu2O8+x single crystal in zero magnetic field

We report results on isothermal current-voltage (IV) measurements of a Bi2Sr2CaCu2O8+x single crystal taken both in the ab-plane and along the c-axis in zero magnetic field. Decreasing the temperature, a bulk zero-resistance state develops in sequence characterized by three temperatures, T-c(c), T-g, and T-c(ab). In the temperature range of T > T-c(ab), the in-plane IV curves are all ohmic. The out-of-plane IV curves show very diverse behaviors; ohmic in the high-temperature region above T-c(c), highly nonlinear with an ohmic tail consistent with the effect of thermal fluctuations on Josephson coupling between Cu-O layers for T-g < T < T-c(c), and a down-turn behavior in logarithmic scale showing a true superconducting state with zero linear resistance for T < T-g. This down-turn of the c-axis IV curves is reminiscent of the vortex-glass behavior seen in the in-plane resistivities in an external magnetic field and cannot be explained by the conventional interlayer Josephson coupling model with thermal fluctuation effects.X112sciescopu

Resistance enhancement of the intrinsic surface junction of Bi2Sr2CaCu2O8+x single crystal under radio-frequency irradiation

It is found that radio-frequency irradiation significantly enhances the c-axis resistance near the superconducting transition of the CuO2 bi-layer located on the surface of a Bi2Sr2CaCu2O8+x single crystal. The features of this resistance anomaly are similar to those observed recently in the mesoscopic aluminum wires and structures with normal-metal/supeconductor interfaces, where the resistance anomaly is caused by the nonequilibrium charge-imbalance effect.X113sciescopu