Nanoscale Electrostatic Control of Oxide Interfaces

We develop a robust and versatile platform to define nanostructures at oxide interfaces via patterned top gates. Using LaAlO$_3$/SrTiO$_3$ as a model system, we demonstrate controllable electrostatic confinement of electrons to nanoscale regions in the conducting interface. The excellent gate response, ultra-low leakage currents, and long term stability of these gates allow us to perform a variety of studies in different device geometries from room temperature down to 50 mK. Using a split-gate device we demonstrate the formation of a narrow conducting channel whose width can be controllably reduced via the application of appropriate gate voltages. We also show that a single narrow gate can be used to induce locally a superconducting to insulating transition. Furthermore, in the superconducting regime we see indications of a gate-voltage controlled Josephson effect.Comment: Version after peer review; includes additional data on superconductivit

The Role of Visual Features in Text-Based CAPTCHAs: An fNIRS Study for Usable Security

To mitigate dictionary attacks or similar undesirable automated attacks to information systems, developers mostly prefer using CAPTCHA challenges as Human Interactive Proofs (HIPs) to distinguish between human users and scripts. Appropriate use of CAPTCHA requires a setup that balances between robustness and usability during the design of a challenge. The previous research reveals that most usability studies have used accuracy and response time as measurement criteria for quantitative analysis. The present study aims at applying optical neuroimaging techniques for the analysis of CAPTCHA design. The functional Near-Infrared Spectroscopy technique was used to explore the hemodynamic responses in the prefrontal cortex elicited by CAPTCHA stimulus of varying types. )e findings suggest that regions in the left and right dorsolateral and right dorsomedial prefrontal cortex respond to the degrees of line occlusion, rotation, and wave distortions present in a CAPTCHA. The systematic addition of the visual effects introduced nonlinear effects on the behavioral and prefrontal oxygenation measures, indicative of the emergence of Gestalt effects that might have influenced the perception of the overall CAPTCHA figure.Comment: 24 pages, 32 figures, Computational Intelligence and Neuroscienc

Superconducting quantum point contact with split gates in the two dimensional LaAlO3/SrTiO3 superfluid

One of the hallmark experiments of quantum transport is the observation of the quantized resistance in a point contact formed with split gates in GaAs/AlGaAs heterostructures. Being carried out on a single material, they represent in an ideal manner equilibrium reservoirs which are connected only through a few electron mode channel with certain transmission coefficients. It has been a long standing goal to achieve similar experimental conditions also in superconductors, only reached in atomic scale mechanically tunable break junctions of conventional superconducting metals, but here the Fermi wavelength is so short that it leads to a mixing of quantum transport with atomic orbital physics. Here we demonstrate for the first time the formation of a superconducting quantum point contact (SQPC) with split gate technology in a superconductor, utilizing the unique gate tunability of the two dimensional superfluid at the LaAlO3/SrTiO3 (LAO/STO) interface. When the constriction is tuned through the action of metallic split gates we identify three regimes of transport: (i) SQPC for which the supercurrent is carried only by a few quantum transport channels. (ii) Superconducting island strongly coupled to the equilibrium reservoirs. (iii) Charge island with a discrete spectrum weakly coupled to the reservoirs. Our experiments demonstrate the feasibility of a new generation of mesoscopic all-superconductor quantum transport devices.Comment: 18 page

Abdominal Splenosis Mimicking Peritoneal Metastasis in Prostate-Specific Membrane Antigen PET/CT, Confirmed With Selective Spleen SPECT/CT

Ga-68-prostate-specific membrane antigen (PSMA) PET/CT is a rapidly evolving diagnostic technique to image prostate cancer. In contrast to the name PSMA, various tissues show Ga-68-PSMA uptake in PET/CT imaging. We present a case of a 68-year-old man with prostate cancer who underwent Ga-PSMA PET/CT. Along with metastatic lymph nodes, multiple nodular lesions within the peritoneal spaces of all 4 quadrants of the abdomen showed high PSMA expression. Because of a history of splenic rupture, a Tc-99m-labeled heat-denatured erythrocyte scintigraphy and SPECT were performed. Peritoneal lesions showed high uptake, confirming widespread peritoneal splenosis

Enhanced localized surface plasmon resonance obtained in two step etched silicon nanowires decorated with silver nanoparticles

We report on localized surface plasmon resonance (LSPR) of silicon nanowires decorated with silver nanoparticles. Hydrogen peroxide in metal-assisted-etching method degenerates the surface of nanowires and creates oxygen-related defect sites. These defect sites enhance the infrared absorption at higher frequencies and emit visible light by band-to-band radiative recombination. Moreover, an almost 50-fold enhanced LSPR was obtained for 24 nm thick silver deposited 5 mu m long silicon nanowires. This enhancement was attributed to the change in the dielectric constant of effective medium created by defect states. LSPR wavelength could be tuned by changing the silver particle size and nanowire length. (C) 2013 AIP Publishing LLC

Fabrication and characterization of copper oxide-silicon nanowire heterojunction photodiodes

WOS: 000331468100013In this study, copper oxide (CuO) thin film/silicon (Si) nanowire heterojunctions have been fabricated and their optoelectronic performances have been investigated. Vertically aligned n-type Si nanowires have been fabricated using metal-assisted etching (MAE) technique. CuO thin films were synthesized by the sol-gel method and deposited onto the nanowires through spin-coating. Fabricated nanowire heterojunction devices exhibited excellent diode behaviour compared to the planar heterojunction control device. The rectification ratios were found to be 105 and 101 for nanowire and planar heterojunctions, respectively. The improved electrical properties and photosensitivity of the nanowire heterojunction diode was observed, which was related to the three-dimensional nature of the interface between the Si nanowires and the CuO film. Results obtained in this work reveal the potential of Si nanowire-based heterojunctions for various optoelectronic devices.Scientific and Technical Research Council of Turkey (TUBITAK); Turkish Academy of Sciences (TUBA)GA and FAA would like to thank The Scientific and Technical Research Council of Turkey (TUBITAK) Post-Doctoral Fellowship for financial support. HEU acknowledges support from the Distinguished Young Scientists award of the Turkish Academy of Sciences (TUBA). Middle East Technical University (METU) Central Laboratory facilities are also greatly acknowledged

The Change in Luteal Blood Flow and Luteal Size after Beta Carotene and GnRH Injections in Early Pregnant Dairy Cows

FINDIK, Murat/0000-0003-1408-2548; Kucukaslan, Ibrahim/0000-0002-3458-4409;WOS: 000311195800022The aim of this study was to determine the effectiveness of intramuscular injections of beta-carotene (beta C) and GnRH on luteal size (LS), luteal blood flow (LBF) and serum beta C concentrations in early pregnant cows. Twenty-nine Holstein-Friesian cows with a mature corpus luteum (>19mm) were randomly assigned to two groups: pc not received (beta C-; n=15) or received (beta C-; n=14). All cows were treated with PGF(2)alpha and inseminated twice, 48 and 72h after the treatment. Last Al was considered to be day 0. All cows received GnRH on day inseminations, 7 and 17. Different from the beta C-, the beta C+ group received beta C intramuscularly on day 7 and 17. In both groups, measurement of LS and LBF were performed on days 7, 10, 17,27 and 37 by transrectal B-mode and colour Doppler ultrasonography. Blood samples were collected on each examination day. Only cows that became pregnant were included in the statistical evaluation. The concentration o beta C in the beta C+ group was higher than in the beta C- at all examination days except day 17 (P0.05). The LS and LBF of beta C+ group on day 7 (P<0.05) and 27 (P<0.01) was higher than in the beta C- group and values increased significantly until day 37 (LS: P<0.05, LBF: P<0.01). We conclude that beta C injections significantly increased serum beta C concentrations, as well as LS and LBF

The effect of beta-carotene and GnRH administration on luteal size and luteal blood flow after synchronization with prostaglandin F-2 alpha in cows

14th Annual Conference of the European-Societies-Domestic-Animals-Reproduction/22nd Annual Meeting of the EU-AI-Vets -- SEP 15-22, 2010 -- Eger, HUNGARYFINDIK, Murat/0000-0003-1408-2548; Kucukaslan, Ibrahim/0000-0002-3458-4409WOS: 000280355200115…European Soc Domest Anim Reproduc

Quantum interference in an interfacial superconductor

The two-dimensional superconductor formed at the interface between the complex oxides, lanthanum aluminate (LAO) and strontium titanate (STO) [1] has several intriguing properties [2–6] that set it apart from conventional superconductors. Most notably, an electric field can be used to tune its critical temperature (Tc) [7], revealing a dome-shaped phase diagram reminiscent of high Tc superconductors [8]. So far, experiments with oxide interfaces have measured quantities which probe only the magnitude of the superconducting order parameter and are not sensitive to its phase. Here, we perform phase-sensitive measurements by realizing the first superconducting quantum interference devices (SQUIDs) at the LAO/STO interface. Furthermore, we develop a new paradigm for the creation of superconducting circuit elements, where local gates enable insitu creation and control of Josephson junctions. These gate-defined SQUIDs are unique in that the entire device is made from a single superconductor with purely electrostatic interfaces between the superconducting reservoir and the weak link. We complement our experiments with numerical simulations and show that the low superfluid density of this interfacial superconductor results in a large, gate-controllable kinetic inductance of the SQUID. Our observation of robust quantum interference opens up a new pathway to understand the nature of superconductivity at oxide interfaces