bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasminogen-dependent and -independent Proteolytic Activity of Murine Endothelioma Cells with Targeted Inactivation of Fibrinolytic Genes
Authors: Lijnen H R , Wagner E F , Collen D
Published: July 2018

Plasminogen-dependent and -independent proteolytic activity of murine endothelioma (End) cells that were derived from mice with targeted inactivation of the tissue-type plasminogen activator (t-PA -/-), urokinase-type plasminogen activator (u-PA-/-) or plasminogen activator inhibitor-1 (PAI-1 -/- genes was studied with the use of fibrin and extracellular matrix degradation assays. In a buffer milieu, the activation rate of plasminogen (final concentration 0.25 µM) with wild-type and t-PA-/- End cells (3 X 104 to 4 X 106 cells/ml) was comparable, but it was about 4-fold reduced with u-PA -/- End cells and 3-fold enhanced with PAI-1End cells. Plasminogen activation was markedly reduced by addition of amiloride or of anti-murine u-PA antibodies but not by addition of anti-murine t-PA antibodies, and it was not stimulated by addition of fibrin. Lysis of125I-fibrin labeled matrix in the presence of plasminogen was comparable with wild-type, t-PA-/- and PAI-1-/- End cells (50% lysis in 3 h with 0.7 to 1.5 X 106 cells/ml), but was significantly reduced with u-PA-/- End cells (50% lysis in 20 h with 0.87 X 106 cells/ml). Lysis of3H-proline labeled extracellular matrix in the presence of plasminogen with wild-type, t-PA-/- and PAI-1-/- End cells (20% lysis in 48 h with 3 to 5 X 106 cells/ml) was comparable, but it was virtually abolished with u-PA-/- End cells. In the absence of plasminogen, lysis of both the fibrin and the extracellular matrix by all four cell types was drastically reduced and was virtually abolished by addition of phenylmethylsulfonylfluoride or 1,10 phenanthroline.

These data indicate that the proteolytic activity of the transformed murine endothelioma cells, measured in plasminogen activation or matrix degradation assays, is essentially u-PA-related and largely plasminogen-dependent.
Antithrombin III-Independent Effect of Depolymerized Holothurian Glycosaminoglycan (DHG) on Acute Thromboembolism in Mice
Authors: Nagase Hideki , Kitazato Keiko T , Sasaki Eiji , Hattori Masahiko , Kitazato Kenji , Saito Hidehiko
Published: July 2018

A previous study in this laboratory showed that depolymerized holothurian glycosaminoglycan (DHG) has two different antithrombin III (ATIII)-independent inhibitory effects on the in vitro blood coagulation system: heparin cofactor II (HCII)-dependent inhibition of thrombin, and ATIII- and HCII-independent inhibition of factor X activation by factor IXa-factor Villa complex (Nagase et al. Blood 85, 1527-1534, 1995). In the present study, we compared the antithrombotic effects of DHG in normal and in ATIII-deficient mice with those of unfractionated heparin (UFH) and low molecular weight heparin (LMWH). DHG, unlike UFH and LMWH, exerted an in vivo antithrombotic effect even in mice with decreased plasma ATIII activity (about 30% of normal). We then compared the anticoagulant and antithrombotic effects of DHG in mice with those of high molecular weight (HMW)-DHG, low molecular weight (LMW)-DHG, and dermatan sulfate (DS). In terms of in vitro anticoagulant activity assessed by use of purified human components, DHGs (DHG, HMW-DHG, and LMW-DHG) had different anti-thrombin activity in the presence of HCII and anti-factor Xase activities, which differences were dependent on the molecular weight. With respect to in vivo antithrombotic activity, DHG, HMW-DHG, and LMW-DHG showed almost the same inhibitory effect on acute thromboembolism in mice (minimum effective dose [MED]: >0.3 mg/kg). Since the antithrombotic activities of DHGs were not correlated with the anticoagulant-specific activities, the contribution of the two anticoagulant activities to the in vivo antithrombotic effect of DHGs remains unknown. However, DHG was more effective against acute thromboembolism in mice than DS (MED >1 or >3 mg/kg), which showed no inhibitory activity toward factor Xase. Therefore, it seems that factor Xase inhibition contributes greatly to the antithrombotic effect of DHG and that DHG exerts this effect in mice mainly by inhibiting factor Xase.
Value of Preoperative MRI and Examination under Anesthesia for Differentiating Complete from Partial Anterior Cruciate Ligament Tears
Authors: Cavinatto Leonardo , Gupta Sunny , Morgan Craig , Bartolozzi Arthur R.
Published: July 2018

Partial tears of the anterior cruciate ligament (ACL) recently regained attention due to a better understanding of the two distinct bundles of the ligament and the possibility of single-bundle reconstruction procedures. An accurate diagnosis is important as it influences treatment options and patient prognosis. The aim of this study was to evaluate the value of examination under anesthesia (EUA) and magnetic resonance imaging (MRI) for differentiating partial from complete ACL tears. For this purpose, this prospective case series included 95 consecutive patients undergoing primary ACL reconstruction surgeries. MRI, EUA, and MRI combined with EUA were performed preoperatively, and results were compared with arthroscopy. Our data showed that ACL lesions were diagnosed as partial tears in 42.1% (n = 40) of EUA, 23.2% (n = 22) of MRI, and 11.6% (n = 11) of arthroscopies. EUA and MRI demonstrated sensitivity of 100 and 90.1%, and specificity of 65.5 and 85.6%, respectively. Combined EUA and MRI demonstrated sensitivity of 100% and specificity of 83.1%. Our study revealed that preoperatively MRI and EUA may help surgeons early identify partial ACL tears and influence treatment decisions.
Logarithmic conformal field theories of type B
n, ℓ = 4 and symplectic fermions
Authors: Flandoli Ilaria , Lentner Simon
Published: July 2018

There are important conjectures about logarithmic conformal field theories (LCFT’s), which are constructed as a kernel of screening operators acting on the vertex algebra of the rescaled root lattice of a finite-dimensional semisimple complex Lie algebra. In particular, their representation theory should be equivalent to the representation theory of an associated small quantum group. This article solves the case of the rescaled root lattice Bn/2 as a first working example beyond A1/p. We discuss the kernel of short screening operators, its representations, and graded characters. Our main result is that this vertex algebra is isomorphic to a well-known example: The even part of n pairs of symplectic fermions. In the screening operator approach, this vertex algebra appears as an extension of the vertex algebra associated with A1n/2, which are n copies of the even part of one pair of symplectic fermions. The new long screenings give the new global Cn-symmetry. The extension is due to a degeneracy in this particular case: Rescaled long roots still have an even integer norm. For the associated quantum group of divided powers, the first author has previously encountered matching degeneracies: It contains the small quantum group of type A1n and the Lie algebra Cn. Recent results by Farsad, Gainutdinov, and Runkel on symplectic fermions suggest finally the conjectured category equivalence to this quantum group. We also study the other degenerate cases of a quantum group, giving extensions of LCFT’s of type Dn, D4, A2 with larger global symmetry Bn, F4, G2.
Theoretical efficiency of hybrid solar thermoelectric-photovoltaic generators
Authors: Lorenzi Bruno , Chen Gang
Published: July 2018

This work analyses the potential of hybrid solar thermoelectric photovoltaic generators (HSTEPVGs) through evaluating their efficiency in converting solar power into electricity for a system consisting of a PV cell placed directly on top of a thermoelectric generator. A theoretical model for terrestrial application which includes the possibility of thermal and optical concentrations is reported. As in the case of pure solar thermoelectric generators, an optimal operation temperature also exists for HSTEPVGs determined by the temperature dependences of both the solar cells and the thermoelectric generators. The study reports an efficiency gain of 4%–5% with respect to the sole PV case, especially in the case of optical concentrations which mitigate the solar cell temperature sensitivity. In addition to these interesting results, the work also reveals the major constrains expected for this approach, along with technological challenges especially regarding the optical properties of the device encapsulation and the solar cell degradation.
In-operando photoelectron spectroscopy for batteries: Set-up using pristine thin film cathode and first results on NaxCoO2
Authors: Guhl Conrad , Kehne Philipp , Ma Qianli , Tietz Frank , Alff Lambert , Komissinskiy Philipp , Jaegermann Wolfram , Hausbrand René
Published: July 2018

A model all-solid-state battery cell with a thin film NaxCoO2 cathode was assembled under ultra-high vacuum conditions and cycled inside the vacuum chamber, using a dedicated sample holder. We present in-operando x-ray photoelectron spectroscopy measurements of a NaxCoO2 cathode at different charging states. During battery operation, the change in sodium content, the change in cobalt oxidation state, and the evolution of the O1s and VB emissions could be monitored. Comparison with a conventional post-mortem analysis technique showed that the new measurement technique produces comparable results regarding the oxidation state of the transition metal, but sodium and oxygen results show differences due to cathode/electrolyte interfacial reactions for conventional analysis. By using surface layer-free samples in the presented techniques, we could circumvent such reactions and obtain reliable spectra for the pure bulk-like active cathode material.
Using reduced density matrix techniques to capture static and dynamic correlation in the energy landscape for the decomposition of the CH2CH2ONO radical and support a non-IRC pathway
Authors: Smart Scott E. , Scrape Preston G. , Butler Laurie J. , Mazziotti David A.
Published: July 2018

The unexpected abundance of HNO in the photodecomposition of the radical 2-nitrosooxy ethyl (CH2CH2ONO) is investigated through calculations of the potential energy surface by the anti-Hermitian contracted Schrödinger equation (ACSE) method, which directly generates the 2-electron reduced density matrix. The ACSE, which is able to balance single-reference (dynamic) and multi-reference (static) correlation effects, reveals some subtle correlation effects along the intrinsic reaction coordinate (IRC) en route to NO + oxirane, an IRC which offers a potential bifurcation to the HNO + vinoxy product channel. These effects were not fully captured by either single-reference techniques, such as coupled cluster, or multi-reference techniques, such as second-order multi-reference perturbation theory. These correlation effects reveal small to moderate energy changes in key transition states, which have implications for the reaction mechanism as related to the production of HNO.
Detection of local vibrational modes induced by intrinsic defects in undoped BaSi2 light absorber layers using Raman spectroscopy
Authors: Sato Takuma , Hoshida Hirofumi , Takabe Ryota , Toko Kaoru , Terai Yoshikazu , Suemasu Takashi
Published: July 2018

We fabricate BaSi2 epitaxial films on Si(111) substrates by molecular beam epitaxy and investigate point defects inside the films using Raman spectroscopy with the help of first-principles calculation. Point defects such as Ba substituted for Si antisites, Si vacancies, and Si interstitials are considered as candidates for native point defects in BaSi2. Vibration analysis based on first-principles calculation suggests that local vibrational modes caused by these point defects appear at around 430, 480, and 560 cm−1, respectively, and are in good agreement with Raman peak positions. Comparing calculations with Raman spectra of the films formed with different Ba to Si deposition rate ratios RBa/RSi from 1.0 to 5.1, we conclude that the density of point defects reaches a minimum at RBa/RSi = 2.2. Furthermore, the position of Raman peaks at approximately 490 cm−1 shifts to a lower wavenumber, depending on RBa/RSi and thereby the density of point defects.
Dynamics of Janus motors with microscopically reversible kinetics
Authors: Huang Mu-Jie , Schofield Jeremy , Gaspard Pierre , Kapral Raymond
Published: July 2018

Janus motors with chemically active and inactive hemispheres can operate only under nonequilibrium conditions where detailed balance is broken by fluxes of chemical species that establish a nonequilibrium state. A microscopic model for reversible reactive collisions on a Janus motor surface is constructed and shown to satisfy detailed balance. The model is used to study Janus particle reactive dynamics in systems at equilibrium where generalized chemical rate laws that include time-dependent rate coefficients with power-law behavior are shown to describe reaction rates. While maintaining reversible reactions on the Janus catalytic hemisphere, the system is then driven into a nonequilibrium steady state by fluxes of chemical species that control the chemical affinity. The statistical properties of the self-propelled Janus motor in this nonequilibrium steady state are investigated and compared with the predictions of a fluctuating thermodynamics theory. The model has utility beyond the examples presented here, since it allows one to explore various aspects of nonequilibrium fluctuations in systems with self-diffusiophoretic motors from a microscopic perspective.
Single molecule electrophoresis of star polymers through nanopores: Simulations
Authors: Katkar H. H. , Muthukumar M.
Published: July 2018

We study the translocation of charged star polymers through a solid-state nanopore using coarse-grained Langevin dynamics simulations, in the context of using nanopores as high-throughput devices to characterize polymers based on their architecture. The translocation is driven by an externally applied electric field. Our key observation is that translocation kinetics is highly sensitive to the functionality (number of arms) of the star polymer. The mean translocation time is found to vary non-monotonically with polymer functionality, exhibiting a critical value for which translocation is the fastest. The origin of this effect lies in the competition between the higher driving force inside the nanopore and inter-arm electrostatic repulsion in entering the pore, as the functionality is increased. Our simulations also show that the value of the critical functionality can be tuned by varying nanopore dimensions. Moreover, for narrow nanopores, star polymers above a threshold functionality do not translocate at all. These observations suggest the use of nanopores as a high-throughput low-cost analytical tool to characterize and separate star polymers.
Polyelectrolyte association and solvation
Authors: Chremos Alexandros , Douglas Jack F.
Published: July 2018

There has been significant interest in the tendency of highly charged particles having the same charge to form dynamic clusters in solution, but an accepted theoretical framework that can account for this ubiquitous phenomenon has been slow to develop. The theoretical difficulties are especially great for flexible polyelectrolytes due to the additional complex coupling between the polyelectrolyte chain configurations and the spatial distribution of the ionic species in solution. For highly charged polyelectrolytes, this leads to the formation of a diffuse “polarizable” cloud of counter-ions around these polymers, an effect having significant implications for the function of proteins and other natural occurring polyelectrolytes, as emphasized long ago by Kirkwood and co-workers. To investigate this phenomenon, we perform molecular dynamics simulations of a minimal model of polyelectrolyte solutions that includes an explicit solvent and counter-ions, where the relative affinity of the counter-ions and the polymer for the solvent is tunable through the variation of the relative strength of the dispersion interactions of the polymer and ions. In particular, we find that these dispersion interactions can greatly influence the nature of the association between the polyelectrolyte chains under salt-free conditions. We calculate static and dynamic correlation functions to quantify the equilibrium structure and dynamics of these complex liquids. Based on our coarse-grained model of polyelectrolyte solutions, we identify conditions in which three distinct types of polyelectrolyte association arise. We rationalize these types of polyelectrolyte association based on the impact of the selective solvent affinity on the charge distribution and polymer solvation in these solutions. Our findings demonstrate the essential role of the solvent in the description of the polyelectrolyte solutions, as well as providing a guideline for the development of a more predictive theory of the properties of the thermodynamic and transport properties of these complex fluids.
Interchange destabilization of collisionless tearing modes by temperature gradient
Authors: Nasr S. , Smolyakov A. I. , Migliano P. , Zarzoso D. , Garbet X. , Benkadda S.
Published: July 2018

Using a fluid theory, the stability of collisionless tearing modes in plasmas is analyzed in the presence of an inhomogeneous magnetic field, electron temperature and density gradients. It is shown that small scale modes, characterized by a negative stability parameter (Δ′<0), can be driven unstable due to a combination of the magnetic field and electron temperature gradients. The destabilization mechanism is identified as of the interchange type similar to that for toroidal electron temperature gradient modes.
Observations of the magneto-Rayleigh-Taylor instability and shock dynamics in gas-puff Z-pinch experiments
Authors: de Grouchy P. W. L. , Kusse B. R. , Banasek J. , Engelbrecht J. , Hammer D. A. , Qi N. , Rocco S. , Bland S. N.
Published: July 2018

We describe a series of experiments performed to study the shock structure generated during the implosion of a gas-puff Z-pinch. The Z-pinch is produced by a double-annular gas-puff with a center jet driven by Cornell University's COBRA generator operating with a 1 MA, 200 ns current pulse. Using 532 nm laser interferometry and 100 MHz multi-frame cameras, a shock structure is observed to form early in the implosion. The shock appears to be created by a current layer at the outer radius of the imploding plasma which acts as a piston moving inward at several hundred km s−1. The dynamics of the shock and its radial position ahead of the piston agree well with a simple uniform density model outlined in the study by Potter [Nucl. Fusion 18(6), 813 (1978)]. The outer surface of the current layer is observed to be Magneto-Rayleigh-Taylor unstable. The growth rate of this instability is found to depend on the radial density profile of the material within the layer of high-density fluid between the shock and the piston, as predicted by recent theoretical work [see, e.g., D. Livescu, Phys. Fluids 16(1), 118 (2004)]. Growth rates measured in krypton implosions, where the post-shock material is found to decay quasi-exponentially away from the piston, were more than ten times smaller than those recorded in otherwise identical implosions in argon plasmas, where the material between the shock and the piston was observed to maintain a uniform density.
Development of a laser amplification system for the multi-pass Thomson scattering system for GAMMA 10/PDX
Authors: Yoshikawa M. , Kohagura J. , Chikatsu M. , Shima Y. , Sakamoto M. , Nakashima Y. , Ezumi N. , Minami R. , Yasuhara R. , Yamada I. , Funaba H. , Minami T. , Kenmochi N.
Published: July 2018

The multi-pass Thomson scattering (MPTS) system is a useful technique for increasing the Thomson scattering (TS) signal intensities and improving the TS diagnostic time resolution. The MPTS system developed in GAMMA 10/PDX has a polarization-based configuration with an image relaying system. The MPTS system has been constructed for enhancing the Thomson scattered signals for the improvement of measurement accuracy and the megahertz sampling time resolution. However, in the normal MPTS system, the MPTS signal intensities decrease with the pass number because of the damping due to the optical components. Subsequently, we have developed a new MPTS system with the laser amplification system. The laser amplification system can improve the degraded laser power after six passes in the multi-pass system to the initial laser power. For the first time worldwide, we successfully obtained the continued multi-pass signals after the laser amplification system in the gas scattering experiments.
Mid-wavelength high operating temperature barrier infrared detector and focal plane array
Authors: Ting David Z. , Soibel Alexander , Khoshakhlagh Arezou , Rafol Sir B. , Keo Sam A. , Höglund Linda , Fisher Anita M. , Luong Edward M. , Gunapala Sarath D.
Published: July 2018

We analyze and compare different aspects of InAs/InAsSb and InAs/GaSb type-II superlattices for infrared detector applications and argue that the former is the most effective when implemented for mid-wavelength infrared detectors. We then report results on an InAs/InAsSb superlattice based mid-wavelength high operating temperature barrier infrared detector. At 150 K, the 50% cutoff wavelength is 5.37 μm, the quantum efficiency at 4.5 μm is ∼52% without anti-reflection coating, the dark current density under −0.2 V bias is 4.5 × 10−5 A/cm2, and the dark-current-limited and the f/2 black-body (300 K background in 3–5 μm band) specific detectivities are 4.6 × 1011 and 3.0 × 1011 cm-Hz1/2/W, respectively. A focal plane array made from the same material exhibits a mean noise equivalent differential temperature of 18.7 mK at 160 K operating temperature with an f/2 optics and a 300 K background, demonstrating significantly higher operating temperature than InSb.
Investigation of the retention performance of an ultra-thin HfO2 resistance switching layer in an integrated memory device
Authors: Kim Gil Seop , Park Tae Hyung , Kim Hae Jin , Ha Tae Jung , Park Woo Young , Kim Soo Gil , Hwang Cheol Seong
Published: July 2018

The retention behavior of a HfO2 resistive switching memory device with a diameter of 28 nm and an ultra-thin (1 nm) HfO2 layer as the switching layer was examined. Ta and TiN served as the oxygen vacancy (VO) supplying the top and inert bottom electrodes, respectively. Unlike the retention failure phenomenon reported in other thicker oxide-based resistance switching memory devices, the current of both the low and high resistance states suddenly increased at a certain time, causing retention failure. Through the retention tests of the devices in different resistance states, it was concluded that the involvement of the reset step induced the retention failure. The pristine device contained a high portion of VO-rich region and the location of the border between the VO-rich and VO-free regions played the critical role in governing the retention performance. During the reset step, this borderline moves towards the Ta electrode, but moves back to the original location during the retention period, which eventually induces the reconnection of the disconnected conducting filament (in a high resistance state) or strengthens the connected weak portion (low resistance state). The activation energy for the retention failure mechanism was 0.15 eV, which is related to the ionization of neutral VO to ionized VO.
Effect of ∇B drift on the H-mode power threshold in upper single null plasmas with ITER-like tungsten divertor on EAST
Authors: Chen L. , Xu G. S. , Yan N. , Nielsen A. H. , Liu J. B. , Gao W. , Chen R. , Qu H. , Ding F. , Mao H. M. , Sun Z. , Zhang L. , Li M. H. , Zhang W. , Hu G. H. , Shao L. M. , Wu X. Q. , Du H. F. , Xu J. C. , Li Y. L. , Zhao N. , Lan H. , Ye Y. , Zhang H. , Wang H. Q. , Ding S. Y. , Wang L. , Wan B. N. ,   EAST Team
Published: July 2018

In this paper, we will experimentally investigate the power threshold (PL-H) in upper single null plasmas with an ITER-like tungsten divertor under different ∇B drift directions on EAST [F. Ding et al., Commissioning and PSI Behavior of the ITER-Like W/Cu Divertor in EAST 22nd PSI, Rome (2016)]. The power threshold for the low (L) to high (H) confinement mode has a clear and positive toroidal magnetic field, BT, dependence when the ∇B drift points toward the primary X-point (B×∇B↑). A factor of 2–3 increase in PL-H is observed for the ∇B drift away from the primary X-point (B×∇B↓). The edge and core impurities quantified by spectroscopy measurements show comparable levels for the transitions for both drift directions. On the other hand, it is found that the divertor Dα emission just prior to the L-H transition is lower for B×∇B↑, compared with that for B×∇B↓. The upper in-out divertor asymmetry, as manifested by particle fluxes measured by the divertor triple Langmuir probe, is most marked for B×∇B↓, and with significantly more particle flux to the outer divertor. The reversing field increases the particle flux into the upper inner and lower outer divertor, reducing the in-out asymmetry. One important distinction between the two field directions has been observed, with respect to the amplitude of the scrape-off layer (SOL) parallel flow. A dedicated experiment under similar target plasma conditions shows a lower SOL density and thus a steeper density gradient slightly inside the separatrix, where a lower PL-H is found for the B×∇B↑, compared to that for B×∇B↓. We, therefore, conclude that the field-dependent SOL plasma conditions play an important role in the transition physics.
Measurement of incandescent microparticle acceleration using stereoscopic imaging
Authors: Chu Pinghan , Wolfe Bradley T. , Wang Zhehui
Published: July 2018

Microparticles ranging from sub-microns to millimeter in size are a common form of matter in magnetic fusion environment, and they are highly mobile due to their small mass. Different forces in addition to gravity can affect their motion both inside and outside the plasmas. Several recent advances open up new diagnostic possibilities to characterize the particles’ motion and their forces: high-speed imaging camera technology, microparticle injection techniques developed for fusion, and image processing software. Extending our earlier work on high-temperature 4D microparticle tracking using exploding wires [Z. Wang et al. Rev. Sci. Instrum. 87, 11D601 (2016)], we report here the latest results on time-resolved microparticle acceleration measurement. New particle tracking algorithm is found to be effective in particle tracking even when there are a large number of particles close to each other. Epipolar constraint is used for track-pairing from two-camera views. The error field based on an epi-geometry model is characterized on the basis of a large set of 2D track data and 3D track reconstructions. Accelerations based on individual reconstructed 3D tracks are obtained. Force sensitivity in the order of ten gravitational acceleration has been achieved. High-speed imaging is a useful diagnostic tool for microparticle physics, computer model validation, and mass injection technology development for magnetic fusion.
Resonance fluorescence from an atomic-quantum-memory compatible single photon source based on GaAs droplet quantum dots
Authors: Tripathi Laxmi Narayan , He Yu-Ming , Dusanowski Łukasz , Wroński Piotr Andrzej , Lu Chao-Yang , Schneider Christian , Höfling Sven
Published: July 2018

Single photon sources, which are compatible with quantum memories, are important components of quantum networks. In this article, we show optical investigations on isolated GaAs/Al0.25Ga0.75As quantum dots grown via droplet epitaxy, which emit single photons on resonance with the Rb-87-D2 line (780 nm). Under continuous wave resonant excitation conditions, we observe bright, clean, and narrowband resonance fluorescence emission from such a droplet quantum dot. Furthermore, the second-order correlation measurement clearly demonstrates the single photon emission from this resonantly driven transition. Spectrally resolved resonance fluorescence of a similar quantum dot yields a linewidth as narrow as 660 MHz (2.7 μeV), which corresponds to a coherence time of 0.482 ns. The observed linewidth is the smallest reported so far for strain free GaAs quantum dots grown via the droplet method. We believe that this single photon source can be a prime candidate for applications in optical quantum networks.
Measurements of DIII-D poloidal field by fiber-optic pulsed polarimetry
Authors: Kimura W. D. , Dhillon D. S. , Munaretto S. , Strait E. J. , Du D. , Loranger S. , Boisvert J.-S. , Kashyap R.
Published: July 2018

A new technique for measuring the spatial and temporal structure of the poloidal field is presented, whereby the magnetic field causes the polarization of light traveling through an optical fiber to rotate via the Faraday effect by an amount proportional to the strength of the field oriented along the fiber. In fiber optic pulsed polarimetry, changes in the polarization of the backscatter light from the fiber are detected, thereby permitting measurement of the field as a function of position along the fiber. In this proof-of-principle experiment, specially prepared single-mode fibers with weak fiber Bragg gratings were installed in the poloidal direction on the outside of the thermal blanket on DIII-D. Light at 532 nm from a mode-locked Nd:YAG laser was injected into the optical fibers. The laser repetition rate was 895 kHz with a pulse length of <10 ps, resulting in ∼1 μs temporal resolution. A photodetector system measured the Stokes polarization components necessary to determine the amount of polarization rotation. For this experiment, bandwidth limitations of the detectors resulted in a spatial resolution of ≈2 cm. The measured temporal and spatial distributions of the poloidal field are consistent with inductive probe measurements and Elastodynamic Finite Integration Technique reconstructions of the spatial distribution. This demonstrates the ability of this technique to provide real-time detection of the temporal and spatial variations of the poloidal field. Besides revealing more detailed information about the plasma, this new diagnostic capability can also help in detecting instabilities in real time, thereby enabling enhanced machine protection.
High voltage, high current GaN-on-GaN p-n diodes with partially compensated edge termination
Authors: Wang Jingshan , Cao Lina , Xie Jinqiao , Beam Edward , McCarthy Robert , Youtsey Chris , Fay Patrick
Published: July 2018

An approach to realizing high-voltage, high-current vertical GaN-on-GaN power diodes is reported. We show that by combining a partially compensated ion-implanted edge termination (ET) with sputtered SiNx passivation and optimized ohmic contacts, devices approaching the fundamental material limits of GaN can be achieved. Devices with breakdown voltages (Vbr) of 1.68 kV and differential specific on resistances (Ron) of 0.15 mΩ cm2, corresponding to a Baliga figure of merit of 18.8 GW/cm2, are demonstrated experimentally. The ion-implantation-based ET has been analyzed through numerical simulation and validated by experiment. The use of a partially compensated ET layer, with approximately 40 nm of the p-type anode layer remaining uncompensated by the implant, is found to be optimal for maximizing Vbr. The implant-based ET enhances the breakdown voltage without compromising the forward characteristics. Devices exhibit near-ideal scaling with area, enabling currents as high as 12 A for a 1 mm diameter device.
Numerical study of the discharge properties of atmospheric dielectric barrier discharge by using 200 kHz/13.56 MHz excitations
Authors: Kong F. R. , Zhang Z. L. , Jiang B. H.
Published: July 2018

In this work involving an atmospheric dielectric barrier discharge system, the feasibility of independence control of key plasma parameters through strategic modulation of applied dual-frequency excitation sources is demonstrated. In this paper, a one-dimensional fluid model with semi-kinetic method has been used to investigate the discharge properties of atmospheric dielectric barrier discharge by using 200 kHz/13.56 MHz excitations. Bearing good consistency and coherence with experimental results, the electrical characteristics and typical electron dynamics are studied numerically. It is revealed that the application of the high frequency excitation can restrain the increment of the low frequency current component and is effective in preventing the discharge from transitioning to a filamentary mode. This method then suggests and enables possible approaches to obtain discharges with good stability in described DBD systems.
Engineering magnetic heterostructures to obtain large spin Hall efficiency for spin-orbit torque devices
Authors: Huang Lisen , He Shikun , Yap Qi Jia , Lim Sze Ter
Published: July 2018

By sandwiching a CoFeB ferromagnetic layer between Ta and Pt heavy metals with an opposite spin Hall angle, spin currents of the same polarity are transmitted from both interfaces of the Ta/CoFeB/Pt trilayer to the CoFeB layer simultaneously. Here, we investigated the spin-orbit torque, magnetization dynamics, and interface spin transmission efficiency of the trilayer heterostructure by spin-torque ferromagnetic resonance. A large effective spin Hall angle, substantially larger than both Ta and Pt, was obtained in the Ta/CoFeB/Pt stack. The thickness-dependence study showed that with the reducing of CoFeB thickness, Gilbert damping enhances by spin pumping and spin Hall angle increases by the spin Hall effect and the Rashba effect. Furthermore, the spin transparency derived from effective spin mixing conductance was 0.63 ± 0.07 and 0.48 ± 0.02 at the CoFeB/Pt and Ta/CoFeB interfaces, respectively. Hence, the spin Hall angle could be further enhanced by improving the spin transmission efficiency at the interface. Our method of increasing spin-orbit torque through stack engineering would have potential applications in domain wall racetrack memory, logic gates, and magnetic tunnel junctions.
Direct observation of ferroelectricity in Ca3Mn2O7 and its prominent light absorption
Authors: Liu Meifeng , Zhang Yang , Lin Ling-Fang , Lin Lin , Yang Shengwei , Li Xiang , Wang Yu , Li Shaozhen , Yan Zhibo , Wang Xiuzhang , Li Xiao-Guang , Dong Shuai , Liu Jun-Ming
Published: July 2018

Layered perovskites A3M2O7 are known to exhibit the so-called hybrid improper ferroelectricity. Despite experimentally confirmed cases (e.g., nonmagnetic M = Ti and Sn), the ferroelectricity in magnetic Ca3Mn2O7 remains a puzzle. Here, the structural, ferroelectric, magnetoelectric, and optical properties of Ca3Mn2O7 are systematically investigated. Switchable polarization is directly measured, demonstrating its ferroelectricity. In addition, magnetoelectric response is also evidenced, implying the coupling between magnetism and ferroelectricity. Furthermore, strong visible light absorption is observed, which can be understood from its electronic structure. Its direct and appropriate bandgap, as well as wide conducting bands, makes Ca3Mn2O7 a potential candidate for ferroelectric photoelectric applications.
Optical and electrical investigation of DC micro-hollow cathode discharge in He/O2 and He/H2 mixture
Authors: Cho Deog Gyun , Moon Se Youn
Published: July 2018

A hollow cathode discharge source was developed using a negatively biased micro-hole cathode to generate high density point-like plasma. Through electrical and optical investigations, the properties of gas discharge plasmas such as dissipated power, electronic excitation temperature, and rotational temperature were compared in glow and hollow cathode discharge conditions. In the hollow cathode discharge mode, the power consumption and excitation temperature were larger. It was also observed that the relatively higher intensity of vacuum ultraviolet (VUV) oxygen triple lines in He/O2 plasma and VUV hydrogen Lyman-α line in He/H2 plasma were realized in the hollow cathode discharge mode.
A non-collinear double MgO based perpendicular magnetic tunnel junction
Authors: Lourembam James , Chen Bingjin , Huang Aihong , Allauddin Salauddeen , Lim Sze Ter
Published: July 2018

Double MgO based magnetic free layers are state-of-the-art solutions for providing high performance perpendicular spin-transfer torque-magnetic random access memory devices. We provide device measurements showing reduction of switching current in perpendicular magnetic tunnel junctions (p-MTJs) using non-collinear ferromagnets on the double MgO template. This structure is engineered by introducing an in-plane ferromagnetic cap, which produces in-plane stray field effects on the free layer. The non-collinear structure delivers ∼53% reduction in critical current density in STT switching without weakening the thermal stability of the devices. The advantages in device performance using non-collinearity in magnetization is sustained down to ∼20 nm MTJs. Micromagnetic simulations suggest inherent differences in the magnetization reversal process between our proposed non-collinear p-MTJ and a well-known double MgO based p-MTJ.
Experiments on wake structures behind a microparticle in a magnetized plasma flow
Authors: Jung Hendrik , Greiner Franko , Piel Alexander , Miloch Wojciech J.
Published: July 2018

The wake behind a spherical microparticle in a magnetized ion flow is studied experimentally by analyzing the arrangement of a pair of particles. It is shown that there are two stable particle arrangements at intermediate magnetic inductions, whereas only oblique (horizontal) particle configurations are found at the highest magnetic field. Self-consistent collisional molecular dynamics simulations of the particle system show that the underlying mechanism of these arrangements is the weakening of attractive wake forces by the increasing magnetic field. Plasma instabilities provide a trigger for the onset of the transition between the two different arrangements. Furthermore, the course of the transition is qualitatively explained by the charge variation of the downstream particle in the wake of the upstream particle. In addition, a thorough analysis of the sheath by means of particle-in-cell simulations in combination with particle resonance measurements yields consistent values of the particle mass and charge, as well as the levitating electric field and ion flow velocity.
Superconducting nano Josephson junctions patterned with a focused helium ion beam
Authors: Cho Ethan Y. , Zhou Yuchao W. , Cho Jennifer Y. , Cybart Shane A.
Published: July 2018

We report the fabrication of nanoscale wires and Josephson junctions in 25 nm thick YBa2Cu3O7–δ thin films with wire widths as narrow as 50 nm. Our approach utilizes a finely focused gas field ion source from a helium ion microscope to directly modify the material on the nanometer scale to convert irradiated regions of the film into insulators. In this manner, the film remains intact and no material is milled or removed. Transport data show that the electrical properties, critical current and conductance, scale linearly with the lithographically defined width ensuring that the actual and lithographically defined dimensions are commensurate with each other. Unlike in typical ion damage proximity effect Josephson junctions, we observe a low temperature saturation of the critical current and near temperature interdependent resistance which we attribute to a narrower and more resistive barrier. Furthermore, we also demonstrate the ability to fabricate devices exhibiting high resistance and capacitance with hysteretic underdamped Josephson junction properties. This patterning technique allows for a broad range of electrical properties for Josephson devices that will expand potential applications.
Efficiency of the gyrotron with single and double confocal resonators
Authors: Nusinovich G. S.
Published: July 2018

Low-voltage gyrotrons operating at near-terahertz frequencies are of great interest for numerous applications. Development of such gyrotrons in conventional configurations faces significant difficulties, especially in the case of operation at cyclotron harmonics. Some of these problems can be mitigated by using confocal resonators formed either by one pair of mirrors (a single configuration) or two pairs of mirrors (a double configuration). This paper describes the study of the effect of transverse nonuniformity of the resonator field on the gyrotron efficiency in both configurations. The study includes the analysis of operation in soft and hard self-excitation regimes.
Compensated thermal conductivity of metallically conductive Ta-doped TiO2
Authors: Suh Joonki , Sarkar Tarapada , Choe Hwan Sung , Park Joonsuk , Venkatesan T. , Wu Junqiao
Published: July 2018

Electrical and thermal conductivities of epitaxial, high-quality Ta-doped TiO2 (Ta:TiO2) thin films were experimentally investigated in the temperature range of 35–375 K. Structurally identified as the anatase phase, degenerate Ta doping leads to high electrical conductivity in TiO2, reaching >105 (Ω-m)−1 at 5 at. % of Ta, making it a potential candidate for indium-free transparent conducting oxides. In stark contrast, Ta doping suppresses the thermal conductivity of TiO2 via strong phonon-impurity scattering imposed by the Ta dopant which has a high mass contrast with Ti that it substitutes. For instance, the near-peak value shows a >50% reduction, from 9.0 down to 4.4 W/m-K, at just 2 at. % doping at 100 K. Interestingly, further Ta doping beyond 2 at. % no longer reduces the measured total thermal conductivity, which is attributed to a high electronic contribution to thermal conduction that compensates the alloy-scattering loss, as well as possibly the renormalization of phonon dispersion relation in the heavy doping regime originating from doping-induced lattice stiffening. As a result, at high Ta doping, TiO2 exhibits high electrical conductivity without much degradation of thermal conductivity. For example, near room temperature, 5 at. % Ta doped TiO2 shows over 3 orders of magnitude enhancement in electrical conductivity from undoped TiO2, but with only less than 10% reduction in thermal conductivity. The metallic Ta:TiO2 maintaining reasonable good thermal conductivity might find application in energy devices where good conduction to both charge and heat is needed.
Enhanced irradiance sensitivity of 4H-SiC based ultraviolet sensor introducing laterally gated Al/SiO2/SiC tunnel diode structure with low gate bias
Authors: Chang P. K. , Hwu J. G.
Published: July 2018

A laterally gated Al/SiO2/SiC structure composed of an inner circular tunnel diode (TD) and an outer annular TD is investigated in this work to demonstrate the improved ultraviolet (UV) response in comparison with a single metal–oxide–semiconductor (MOS) TD or a conventional photodiode scheme. The current of the inner TD (ID) can interrelate with the bias of the outer TD (VG) against the voltage of inner TD (VD). This coupling effect will increase if the outer TD is negatively biased, thereby augmenting the optical current ratio and the responsivity. The lateral flow of holes is determined by the variation of the intermediate hole barrier between the inner and outer TDs. Once the hole potential at the outer TD overtops that at the inner TD, photogenerated holes from the outer TD can flow to the inner TD. Moreover, the suggested coupled TD design exhibits distinct increments in photocurrent under various illumination levels because of the coupling effect. For VD = −1.5 V and VG = −2 V, the optical current ratio reaches 12 841 at 303 K, and the obtained responsivity attains 0.0052 at 383 K with a light irradiance of 50 mW/cm2. Hence, the laterally gated MOS device can operate at elevated temperatures and heightened optical intensities, making it a promising UV sensor with enhanced irradiance sensitivity.
A gallium-free alternative finds the middle ground for high operating temperature infrared arrays
Authors: Wolverton Mark
Published: July 2018

A gallium-free superlattice allows for effective mid-wavelength IR detectors that operate at higher temperatures than its gallium counterpart.
Tagging investigations with small estuarine-associated fish: tag evaluation, capture methodologies and assessment of capture stress and survival in yellow-eyed mullet Aldrichetta forsteri
Authors: Cook Denham G. , Jaksons Peter , Jerrett Alistair R.
Published: July 2018

Estuarine ecosystems present a dynamic and often biologically challenging marine environment. Resident and migratory fish occupying these environments must cope with a multitude of variations associated with physiochemical characteristics, interspecies interactions, environmental degradation and variable feed availability. Using the yellow-eyed mullet Aldrichetta forsteri as an exemplar of many other small-bodied, estuarine-inhabiting fish, we sought to assess the suitability of an array of different tag types in tank-based experiments. The survival consequences of wild capture, handling and tagging procedures were then investigated using condition and reflex impairment criteria and simulated release. It was determined that T-bar and passive integrated transponder tags were suitable tag types, but that tagging fish smaller than 50g (~170mm) was detrimental to survival. Using a ‘low-impact’ trap design improved post-capture tagging and survival compared with an alternative capture method. In combination, the possibility of using small-bodied fish for tag–recapture studies is demonstrated and the utilisation of comparable fish for investigations into estuarine population dynamics and ecosystem interactions is advocated.
Gradual progression from sensory to task-related processing in cerebral cortex
Authors: Brincat Scott L. , Siegel Markus , von Nicolai Constantin , Miller Earl K.
Published: July 2018

Significance

The earliest stages of processing in cerebral cortex reflect a relatively faithful copy of sensory inputs, but intelligent behavior requires abstracting behaviorally relevant concepts and categories. We examined how this transformation progresses through multiple levels of the cortical hierarchy by comparing neural representations in six cortical areas in monkeys categorizing across three visual domains. We found that categorical abstraction occurred in a gradual fashion across the cortical hierarchy and reached an apex in prefrontal cortex. Categorical coding did not respect classical models of large-scale cortical organization. The dimensionality of neural population activity was reduced in parallel with these representational changes. Our results shed light on how raw sensory inputs are transformed into behaviorally relevant abstractions.
Separation of circadian- and behavior-driven metabolite rhythms in humans provides a window on peripheral oscillators and metabolism
Authors: Skene Debra J. , Skornyakov Elena , Chowdhury Namrata R. , Gajula Rajendra P. , Middleton Benita , Satterfield Brieann C. , Porter Kenneth I. , Van Dongen Hans P. A. , Gaddameedhi Shobhan
Published: July 2018

Significance

Shift workers, whose schedules are misaligned relative to their suprachiasmatic nuclei (SCN) circadian pacemaker, are at elevated risk of metabolic disorders. In a study of simulated day- versus night-shift work followed by a constant routine, we separated plasma-circulating metabolites according to whether their 24-h rhythms aligned with the central SCN pacemaker or instead reflected externally imposed behavioral schedules. We found that rhythms in many metabolites implicated in food metabolism dissociated from the SCN pacemaker rhythm, with the vast majority aligning with the preceding sleep/wake and feeding/fasting cycles. Our metabolomics study yields insight into the link between prolonged exposure to shift work and the spectrum of associated metabolic disorders by providing a window into peripheral oscillators and the biobehavioral factors that orchestrate them.