bluuebunny/crossref_metadata_2025 huggingface dataset:
Profile measurements in the plasma edge of mega amp spherical tokamak using a ball pen probe
Authors: Walkden N. R. , Adamek J. , Allan S. , Dudson B. D. , Elmore S. , Fishpool G. , Harrison J. , Kirk A. , Komm M.
Published: February 2015

The ball pen probe (BPP) technique is used successfully to make profile measurements of plasma potential, electron temperature, and radial electric field on the Mega Amp Spherical Tokamak. The potential profile measured by the BPP is shown to significantly differ from the floating potential both in polarity and profile shape. By combining the BPP potential and the floating potential, the electron temperature can be measured, which is compared with the Thomson scattering (TS) diagnostic. Excellent agreement between the two diagnostics is obtained when secondary electron emission is accounted for in the floating potential. From the BPP profile, an estimate of the radial electric field is extracted which is shown to be of the order ∼1 kV/m and increases with plasma current. Corrections to the BPP measurement, constrained by the TS comparison, introduce uncertainty into the ER measurements. The uncertainty is most significant in the electric field well inside the separatrix. The electric field is used to estimate toroidal and poloidal rotation velocities from E × B motion. This paper further demonstrates the ability of the ball pen probe to make valuable and important measurements in the boundary plasma of a tokamak.
On the minimal set of conservation laws and the Hamiltonian structure of the Whitham equations
Authors: Maltsev A. Ya.
Published: February 2015

We consider the questions connected with the Hamiltonian properties of the Whitham equations in case of several spatial dimensions. An essential point of our approach here is a connection of the Hamiltonian structure of the Whitham system with the finite-dimensional Poisson bracket defined on the space of periodic or quasi-periodic solutions. From our point of view, this approach gives a possibility to construct the Hamiltonian structure of the Whitham equations under minimal requirements on the properties of the initial system. The Poisson bracket for the Whitham system can be considered here as a deformation of the finite-dimensional bracket with the aid of the Dubrovin–Novikov procedure of bracket averaging. At the end, we consider the examples where the constructions of the paper play an essential role for the construction of the Poisson bracket for the Whitham system.
Thermal collapse and hierarchy of polymorphs in a faujasite-type zeolite and its analogous melt-quenched glass
Authors: Palenta Theresia , Fuhrmann Sindy , Greaves G. Neville , Schwieger Wilhelm , Wondraczek Lothar
Published: February 2015

We examine the route of structural collapse and re-crystallization of faujasite-type (Na,K)-LSX zeolite. As the first step, a rather stable amorphous high density phase HDAcollapse is generated through an order-disorder transition from the original zeolite via a low density phase LDAcollapse, at around 790 °C. We find that the overall amorphization is driven by an increase in the bond angle distribution within T-O-T and a change in ring statistics to 6-membered TO4 (T = Si4+, Al3+) rings at the expense of 4-membered rings. The HDAamorph transforms into crystalline nepheline, though, through an intermediate metastable carnegieite phase. In comparison, the melt-derived glass of similar composition, HDAMQ, crystallizes directly into the nepheline phase without the occurrence of intermediate carnegieite. This is attributed to the higher structural order of the faujasite-derived HDAcollapse which prefers the re-crystallization into the highly symmetric carnegieite phase before transformation into nepheline with lower symmetry.
Ni80Fe20 nanodisks by nanosphere lithography for biomedical applications
Authors: Tiberto P. , Barrera G. , Celegato F. , Conta G. , Coïsson M. , Vinai F. , Albertini F.
Published: February 2015

A novel nanofabrication technique based on self-assembling of polystyrene nanospheres and aimed to obtain magnetic nanodisks suspended in ethanol is here presented. Free-standing Ni80Fe20 disks having lateral dimension around 650 nm and thickness 30 nm were obtained by using nanosphere lithography on a sputtered continuous thin film. The multi-step nanofabrication process will be explained, in detail. The process end-product can be used as suitable magnetic carriers having nearly monodispersed size and simultaneously displaying high saturation magnetization and low-coercivity. Magnetisation reversal has been studied by room-temperature hysteresis loop measurements in either dot arrays attached on a substrate or in liquid-dispersed free-standing nanodisks. In both samples, the reversal is marked by magnetic vortex nucleation/annihilation. Such a behavior is confirmed for Ni80Fe20 dot arrays by measuring magnetic domain configuration, while numerical simulation is used for confirming magnetization reversal process in nanodisks.
Magneto-transport anisotropy in epitaxially grown hybrid MnAs/GaAs multilayer
Authors: Song J. H. , Cui Y. , Lee J. J. , Ketterson J. B.
Published: February 2015

Using molecular-beam epitaxy, we grew a MnAs/GaAs multilayer on a GaAs(100) substrate and compared its magneto-transport characteristics to those of a single-layer MnAs thin film. The crystal orientation of the MnAs layers in both samples was type-B. M–H measurements revealed two-fold symmetric magnetic anisotropy on the surface with the easy and hard direction of magnetization. When the current flowed along the hard direction, the MnAs/GaAs multilayer exhibited negative magnetoresistance below Curie temperature; when the current flowed along the easy direction, it turned positive. We suggest that this peculiar anisotropic magneto-transport behavior in the multilayer originated from two-dimensional carrier confinement and spin-orbit coupling.
Temperature-controlled metal/ligand stoichiometric ratio in Ag-TCNE coordination networks
Authors: Rodríguez-Fernández Jonathan , Lauwaet Koen , Herranz Maria Ángeles , Martín Nazario , Gallego José María , Miranda Rodolfo , Otero Roberto
Published: February 2015

The deposition of tetracyanoethylene (TCNE) on Ag(111), both at Room Temperature (RT, 300 K) and low temperatures (150 K), leads to the formation of coordination networks involving silver adatoms, as revealed by Variable-Temperature Scanning Tunneling Microscopy. Our results indicate that TCNE molecules etch away material from the step edges and possibly also from the terraces, which facilitates the formation of the observed coordination networks. Moreover, such process is temperature dependent, which allows for different stoichiometric ratios between Ag and TCNE just by adjusting the deposition temperature. X-ray Photoelectron Spectroscopy and Density Functional Theory calculations reveal that charge-transfer from the surface to the molecule and the concomitant geometrical distortions at both sides of the organic/inorganic interface might facilitate the extraction of silver atoms from the step-edges and, thus, its incorporation into the observed TCNE coordination networks.
Angular distribution of energetic argon ions emitted by a 90 kJ Filippov-type plasma focus
Authors: Pestehe S. J. , Mohammadnejad M.
Published: February 2015

Characteristics of the energetic argon ions emitted by a 90 kJ Filippov-type plasma focus are studied by employing an array of Faraday cups. The Faraday cups are designed to minimize the secondary electron emission effects on their response. Angular distribution of the ions is measured, and the results indicate a highly anisotropic emission with a dip at the device axis and a local maximum at the angle of 7° with respect to the axis. It has been argued that this kind of anisotropic emission may be related to the surfatron acceleration mechanism and shown that this behavior is independent of the working gas pressure. It has been also demonstrated that this mechanism is responsible for the generation of MeV ions. Measuring the total ion number at different working gas pressures gives an optimum pressure of 0.3 Torr. In addition, the energy spectrum of ions is measured by taking into account of the ambient gas effects on the energy and charge of the ions. The current neutralization effect of electrons trapped in the ion beam as well as the effect of conducting boundaries surrounding the beam, on the detected signals are investigated.
Magnetic property and possible half-metal behavior in Co-doped graphene
Authors: Li Zhongyao , Xie Wenze , Liu Xingen , Wu Yong
Published: February 2015

The magnetic property and band structures of Co-monolayer doped graphene were examined on the basis of density-functional theory. The magnetic moment of the system is closely related to the interfacial spacing. Magnetic-nonmagnetic transition would be produced by decreasing the layer distance. Although the magnetic moment can also be reduced by increasing the lattice constant, the ground states are magnetic states under tension. Besides, the increase of lattice constant greatly enlarges the direct and indirect gaps of spin-down bands near the Fermi level. With a little increase of the Fermi level or the electron density, half-metal behavior would be expectable in the Co-doped graphene under tension.
The competing oxide and sub-oxide formation in metal-oxide molecular beam epitaxy
Authors: Vogt Patrick , Bierwagen Oliver
Published: February 2015

The hetero-epitaxial growth of the n-type semiconducting oxides β-Ga2O3, In2O3, and SnO2 on c- and r-plane sapphire was performed by plasma-assisted molecular beam epitaxy. The growth-rate and desorbing flux from the substrate were measured in-situ under various oxygen to metal ratios by laser reflectometry and quadrupole mass spectrometry, respectively. These measurements clarified the role of volatile sub-oxide formation (Ga2O, In2O, and SnO) during growth, the sub-oxide stoichiometry, and the efficiency of oxide formation for the three oxides. As a result, the formation of the sub-oxides decreased the growth-rate under metal-rich growth conditions and resulted in etching of the oxide film by supplying only metal flux. The flux ratio for the exclusive formation of the sub-oxide (e.g., the p-type semiconductor SnO) was determined, and the efficiency of oxide formation was found to be the highest for SnO2, somewhat lower for In2O3, and the lowest for Ga2O3. Our findings can be generalized to further oxides that possess related sub-oxides.
The impact of surface damage region and edge recombination on the effective lifetime of silicon wafers at low illumination conditions
Authors: Hameiri Ziv , Ma Fa-Jun
Published: February 2015

The effective minority carrier lifetime of p-type silicon wafers passivated by silicon nitride and of n-type silicon wafers passivated by aluminium oxide often decreases significantly as the excess carrier concentration decreases. Several theories have been postulated to explain this effect. The main ones are asymmetric carrier lifetimes, high recombination within a surface damage region, and edge recombination. As in some cases, the effective lifetime measurements can be fitted quite well by all these effects, it is challenging to determine the main cause for the suppressed performance at low illumination. This is partly due to the fact that no study has yet included a sufficiently large set of wafers and advanced modelling to examine all these theories. The aim of this study is to determine the most likely theory based on a set of undiffused p- and n-type wafers of different sizes, passivated with both silicon nitride and aluminium oxide. Quasi-steady-state photoluminescence measurements were used in order to investigate effective lifetime at very low carrier densities, without artifact effects that commonly limit photoconductance-based measurements. Advanced modelling using Sentaurus was used to investigate the impact of different parameters—such as the fixed charge within the dielectric—on the recombination at the edge and within the surface damage region. These models were then used to simulate the measurement results. It is shown that asymmetrical surface lifetime cannot explain the observed reduction when the dielectric is highly charged (either positively or negatively). It is also shown that although edge recombination influences the effective lifetime at low excess carrier concentration, it alone cannot explain the effective lifetime reduction. It is therefore concluded that the presence of a surface damage region is the more likely explanation for the effective lifetime decrease of the studied wafers.
Two-dimensional mesoscale simulations of shock response of dry sand
Authors: Dwivedi S. K. , Pei L. , Teeter R.
Published: February 2015

Simulations were done to gain insight whether the shock response of dry sand at low stresses would vary with porosity and whether the effects of friction between grains under confinement could be extracted from the planar plate impact experimental data. The sand sample was modeled as grains separated by voids representing porosity. The simulation procedure coupled grain deformations with frictional sliding at grain boundaries. The shock response of dry sand varied considerably with porosity. The sample compacted through pore closure followed by inelastic pore collapse mechanisms affecting the inhomogeneous response and shock rise time. The sample attained final compaction in the shock state long after attaining peak longitudinal velocity/stress. The calculated shock Hugoniot for a sample of high (40%) porosity was in agreement with experimental data. The Us-Up slopes for sand of 10% and 20% porosity were found to be negative. The calculated σH-ρH Hugoniot suggested that the two slopes would become positive at higher stresses in order to approach the solid Z-cut quartz Hugoniot at full compaction. High porosity sand may never exhibit negative slopes. It is concluded that the effects of friction between grains can be successfully extracted from a coupled experimental-computational approach. This requires measuring the velocity profile in the back buffer, elastic buffer material, and code capable of simulating frictional sliding between grains. The dispersion effect increased the slope of the velocity profile with propagation distance but did not result in a wave speed reduction or shock attenuation. This may be due to the small grain size and sample thickness as well as the absence of grain fragmentation in the present simulations.
Experimental multiplexing of quantum key distribution with classical optical communication
Authors: Wang Liu-Jun , Chen Luo-Kan , Ju Lei , Xu Mu-Lan , Zhao Yong , Chen Kai , Chen Zeng-Bing , Chen Teng-Yun , Pan Jian-Wei
Published: February 2015

We demonstrate the realization of quantum key distribution (QKD) when combined with classical optical communication, and synchronous signals within a single optical fiber. In the experiment, the classical communication sources use Fabry-Pérot (FP) lasers, which are implemented extensively in optical access networks. To perform QKD, multistage band-stop filtering techniques are developed, and a wavelength-division multiplexing scheme is designed for the multi-longitudinal-mode FP lasers. We have managed to maintain sufficient isolation among the quantum channel, the synchronous channel and the classical channels to guarantee good QKD performance. Finally, the quantum bit error rate remains below a level of 2% across the entire practical application range. The proposed multiplexing scheme can ensure low classical light loss, and enables QKD over fiber lengths of up to 45 km simultaneously when the fibers are populated with bidirectional FP laser communications. Our demonstration paves the way for application of QKD to current optical access networks, where FP lasers are widely used by the end users.
Increasing ferromagnetic resonance frequency using lamination and shape
Authors: El-Ghazaly A. , White R. M. , Wang S. X.
Published: February 2015

The magnetic permeability frequency spectrum is one of the most critical properties for the operation of high frequency magnetic devices in the gigahertz regime. Permeability is fairly constant up to the ferromagnetic resonance (FMR) frequency, at which point the relative permeability drops to unity. Extending FMR to higher frequencies is thus imperative for developing GHz-range magnetic devices. The simulation and experimental investigations presented in this paper demonstrate how stacking layers to form a laminated film increases the FMR frequency by allowing flux closure between layers along the induced easy-axis direction. This flux closure reduces the demagnetization factor along the easy-axis direction by two orders of magnitude. This effect, however, is only observable in patterned films where the shape anisotropy is enough to result in variation of the FMR frequency. Experiments using patterned magnetic cores were performed to illustrate this effect. Through detailed investigation of the permeability spectra of both single layer and laminated CoTaZr magnetic films patterned into 500 μm × L films (where L ranged from 200 μm to 1000 μm), the FMR frequency was extracted and proven to increase as a result of lamination. The degree to which the frequency is boosted by lamination increases exponentially as the length of the film is decreased. Through a combination of lamination and shape demagnetization, the effective anisotropy, which directly relates to FMR frequency, was shown to increase by about 100%.
Hot-wire anemometry for superfluid turbulent coflows
Authors: Durì Davide , Baudet Christophe , Moro Jean-Paul , Roche Philippe-Emmanuel , Diribarne Pantxo
Published: February 2015

We report the first evidence of an enhancement of the heat transfer from a heated wire to an external turbulent coflow of superfluid helium. We used a standard Pt-Rh hot-wire anemometer and overheat it up to 21 K in a pressurized liquid helium turbulent round jet at temperatures between 1.9 K and 2.12 K. The null-velocity response of the sensor can be satisfactorily modeled by the counterflow mechanism, while the extra cooling produced by the forced convection is found to scale similarly as the corresponding extra cooling in classical fluids. We propose a preliminary analysis of the response of the sensor and show that—contrary to a common assumption—such sensor can be used to probe local velocity in turbulent superfluid helium.
Charge transport through exciton shelves in cadmium chalcogenide quantum dot-DNA nano-bioelectronic thin films
Authors: Goodman Samuel M. , Noh Hyunwoo , Singh Vivek , Cha Jennifer N. , Nagpal Prashant
Published: February 2015

Quantum dot (QD), or semiconductor nanocrystal, thin films are being explored for making solution-processable devices due to their size- and shape-tunable bandgap and discrete higher energy electronic states. While DNA has been extensively used for the self-assembly of nanocrystals, it has not been investigated for the simultaneous conduction of multiple energy charges or excitons via exciton shelves (ES) formed in QD-DNA nano-bioelectronic thin films. Here, we present studies on charge conduction through exciton shelves, which are formed via chemically coupled QDs and DNA, between electronic states of the QDs and the HOMO-LUMO levels in the complementary DNA nucleobases. While several challenges need to be addressed in optimizing the formation of devices using QD-DNA thin films, a higher charge collection efficiency for hot-carriers and our detailed investigations of charge transport mechanism in these thin films highlight their potential for applications in nano-bioelectronic devices and biological transducers.
Two-color detector: Mercury-cadmium-telluride as a terahertz and infrared detector
Authors: Sizov F. , Zabudsky V. , Dvoretskii S. , Petryakov V. , Golenkov A. , Andreyeva K. , Tsybrii Z.
Published: February 2015

In this paper, issues associated with the development of infrared (IR) and terahertz (THz) radiation detectors based on HgCdTe are discussed. Two-color un-cooled and cooled to 78 K narrow-gap mercury-cadmium-telluride semiconductor thin layers with antennas were considered both as sub-THz (sub-THz) direct detection bolometers and 3–10 μm IR photoconductors. The noise equivalent power (NEP) for one of the detectors studied at ν ≈ 140 GHz reaches NEP300 K ≈ 4.5 × 10−10 W/Hz1/2 and NEP78 K ≈ 5 × 10−9 W/Hz1/2. The same detector used as an IR photoconductor showed the responsivity at temperatures T = 78 K and 300 K with signal-to-noise ratio S/N ≈ 750 and 50, respectively, under illumination by using IR monochromator and globar as a thermal source.
Roughness effects in uncompensated antiferromagnets
Authors: Charilaou M. , Hellman F.
Published: February 2015

Monte Carlo simulations show that roughness in uncompensated antiferromagnets decreases not just the surface magnetization but also the net magnetization and particularly strongly affects the temperature dependence. In films with step-type roughness, each step creates a new compensation front that decreases the global net magnetization. The saturation magnetization decreases non-monotonically with increasing roughness and does not scale with the surface area. Roughness in the form of surface vacancies changes the temperature-dependence of the magnetization; when only one surface has vacancies, the saturation magnetization will decrease linearly with surface occupancy, whereas when both surfaces have vacancies, the magnetization is negative and exhibits a compensation point at finite temperature, which can be tuned by controlling the occupancy. Roughness also affects the spin-texture of the surfaces due to long-range dipolar interactions and generates non-collinear spin configurations that could be used in devices to produce locally modified exchange bias. These results explain the strongly reduced magnetization found in magnetometry experiments and furthers our understanding of the temperature-dependence of exchange bias.
Impedance analysis of Al2O3/H-terminated diamond metal-oxide-semiconductor structures
Authors: Liao Meiyong , Liu Jiangwei , Sang Liwen , Coathup David , Li Jiangling , Imura Masataka , Koide Yasuo , Ye Haitao
Published: February 2015

Impedance spectroscopy (IS) analysis is carried out to investigate the electrical properties of the metal-oxide-semiconductor (MOS) structure fabricated on hydrogen-terminated single crystal diamond. The low-temperature atomic layer deposition Al2O3 is employed as the insulator in the MOS structure. By numerically analysing the impedance of the MOS structure at various biases, the equivalent circuit of the diamond MOS structure is derived, which is composed of two parallel capacitive and resistance pairs, in series connection with both resistance and inductance. The two capacitive components are resulted from the insulator, the hydrogenated-diamond surface, and their interface. The physical parameters such as the insulator capacitance are obtained, circumventing the series resistance and inductance effect. By comparing the IS and capacitance-voltage measurements, the frequency dispersion of the capacitance-voltage characteristic is discussed.
Size effects in the thermal conductivity of gallium oxide (β-Ga2O3) films grown via open-atmosphere annealing of gallium nitride
Authors: Szwejkowski Chester J. , Creange Nicole C. , Sun Kai , Giri Ashutosh , Donovan Brian F. , Constantin Costel , Hopkins Patrick E.
Published: February 2015

Gallium nitride (GaN) is a widely used semiconductor for high frequency and high power devices due to of its unique electrical properties: a wide band gap, high breakdown field, and high electron mobility. However, thermal management has become a limiting factor regarding efficiency, lifetime, and advancement of GaN devices and GaN-based applications. In this work, we study the thermal conductivity of beta-phase gallium oxide (β-Ga2O3) thin films, a component of typical gate oxides used in such devices. We use time domain thermoreflectance to measure the thermal conductivity of a variety of polycrystalline β-Ga2O3 films of different thicknesses grown via open atmosphere annealing of the surfaces of GaN films on sapphire substrates. We show that the measured effective thermal conductivity of these β-Ga2O3 films can span 1.5 orders of magnitude, increasing with an increased film thickness, which is indicative of the relatively large intrinsic thermal conductivity of the β-Ga2O3 grown via this technique (8.8 ± 3.4 W m−1 K−1) and large mean free paths compared to typical gate dielectrics commonly used in GaN device contacts. By conducting time domain thermoreflectance (TDTR) measurements with different metal transducers (Al, Au, and Au with a Ti wetting layer), we attribute this variation in effective thermal conductivity to a combination of size effects in the β-Ga2O3 film resulting from phonon scattering at the β-Ga2O3/GaN interface and thermal transport across the β-Ga2O3/GaN interface. The measured thermal properties of open atmosphere-grown β-Ga2O3 and its interface with GaN set the stage for thermal engineering of gate contacts in high frequency GaN-based devices.
Coaxial Ag/ZnO/Ag nanowire for highly sensitive hot-electron photodetection
Authors: Zhan Yaohui , Li Xiaofeng , Wu Kai , Wu Shaolong , Deng Jiajia
Published: February 2015

Single-nanowire photodetectors (SNPDs) are mostly propelled by p-n junctions, where the detection wavelength is constrained by the band-gap width. Here, we present a simple doping-free metal/semiconductor/metal SNPD, which shows strong detection tunability without such a material constraint. The proposed hot-electron SNPD exhibits superior optical and electrical advantages, i.e., optically the coaxial design leads to a strong asymmetrical photoabsorption and results in a high unidirectional photocurrent, as desired by the hot-electron collection; electrically the hot-electrons are generated in the region very close to the barrier, facilitating the electrical transport. Rigorous calculations predict an unbiased photoresponsivity of ∼200 nA/mW.
Current-driven non-linear magnetodynamics in exchange-biased spin valves
Authors: Seinige Heidi , Wang Cheng , Tsoi Maxim
Published: February 2015

This work investigates the excitation of parametric resonance in exchange-biased spin valves (EBSVs). Using a mechanical point contact, high density dc and microwave currents were injected into the EBSV sample. Observing the reflected microwave power and the small rectification voltage that develops across the contact allows detecting the current-driven magnetodynamics not only in the bulk sample but originating exclusively from the small contact region. In addition to ferromagnetic resonance (FMR), parametric resonance at twice the natural FMR frequency was observed. In contrast to FMR, this non-linear resonance was excited only in the vicinity of the point contact where current densities are high. Power-dependent measurements displayed a typical threshold-like behavior of parametric resonance and a broadening of the instability region with increasing power. Parametric resonance showed a linear shift as a function of applied dc bias which is consistent with the field-like spin-transfer torque induced by current on magnetic moments in EBSV.
Tunable negative thermal expansion related with the gradual evolution of antiferromagnetic ordering in antiperovskite manganese nitrides Ag1−xNMn3+x (0 ≤ x ≤ 0.6)
Authors: Lin J. C. , Tong P. , Tong W. , Lin S. , Wang B. S. , Song W. H. , Zou Y. M. , Sun Y. P.
Published: February 2015

The thermal expansion and magnetic properties of antiperovskite manganese nitrides Ag1−xNMn3+x were reported. The substitution of Mn for Ag effectively broadens the temperature range of negative thermal expansion and drives it to cryogenic temperatures. As x increases, the paramagnetic (PM) to antiferromagnetic (AFM) phase transition temperature decreases. At x ∼ 0.2, the PM-AFM transition overlaps with the AFM to glass-like state transition. Above x = 0.2, two new distinct magnetic transitions were observed: One occurs above room temperature from PM to ferromagnetic (FM), and the other one evolves at a lower temperature (T*) below which both AFM and FM orderings are involved. Further, electron spin resonance measurement suggests that the broadened volume change near T* is closely related with the evolution of Γ5g AFM ordering.
Raman scattering investigation of large positive magnetoresistance material WTe2
Authors: Kong W.-D. , Wu S.-F. , Richard P. , Lian C.-S. , Wang J.-T. , Yang C.-L. , Shi Y.-G. , Ding H.
Published: February 2015

We have performed polarized Raman scattering measurements on WTe2, for which an extremely large positive magnetoresistance has been reported recently. We observe 5 A1 phonon modes and 2 A2 phonon modes out of 33 Raman active modes, with frequencies in good accordance with first-principles calculations. The angular dependence of the intensity of the peaks observed is consistent with the Raman tensors of the C2v point group symmetry attributed to WTe2. Although the phonon spectra suggest neither strong electron-phonon nor spin-phonon coupling, the intensity of the A1 phonon mode at 160.6 cm−1 shows an unconventional decrease with temperature decreasing, for which the origin remains unclear.
Full-direct method for imaging pharmacokinetic parameters in dynamic fluorescence molecular tomography
Authors: Zhang Guanglei , Pu Huangsheng , He Wei , Liu Fei , Luo Jianwen , Bai Jing
Published: February 2015

Images of pharmacokinetic parameters (also known as parametric images) in dynamic fluorescence molecular tomography (FMT) can provide three-dimensional metabolic information for biological studies and drug development. However, the ill-posed nature of FMT and the high temporal variation of fluorophore concentration together make it difficult to obtain accurate parametric images in small animals in vivo. In this letter, we present a method to directly reconstruct the parametric images from the boundary measurements based on hybrid FMT/X-ray computed tomography (XCT) system. This method can not only utilize structural priors obtained from the XCT system to mitigate the ill-posedness of FMT but also make full use of the temporal correlations of boundary measurements to model the high temporal variation of fluorophore concentration. The results of numerical simulation and mouse experiment demonstrate that the proposed method leads to significant improvements in the reconstruction quality of parametric images.
Widely bandgap tunable amorphous Cd–Ga–O oxide semiconductors exhibiting electron mobilities ≥10 cm2 V−1 s−1
Authors: Yanagi Hiroshi , Sato Chiyuki , Kimura Yota , Suzuki Issei , Omata Takahisa , Kamiya Toshio , Hosono Hideo
Published: February 2015

Amorphous oxide semiconductors exhibit large electron mobilities; however, their bandgaps are either too large for solar cells or too small for deep ultraviolet applications depending on the materials system. Herein, we demonstrate that amorphous Cd–Ga–O semiconductors display bandgaps covering the entire 2.5–4.3 eV region while maintaining large electron mobilities ≥10 cm2 V−1 s−1. The band alignment diagram obtained by ultraviolet photoemission spectroscopy and the bandgap values reveal that these semiconductors form type-II heterojunctions with p-type Cu2O, which is suitable for solar cells and solar-blind ultraviolet sensors.
Power-efficient production of photon pairs in a tapered chalcogenide microwire
Authors: Meyer-Scott Evan , Dot Audrey , Ahmad Raja , Li Lizhu , Rochette Martin , Jennewein Thomas
Published: February 2015

Using tapered fibers of As2Se3 chalcogenide glass, we produce photon pairs at telecommunication wavelengths with low pump powers. We found maximum coincidences-to-accidentals ratios of 2.13 ± 0.07 for degenerate pumping with 3.2 μW average power, and 1.33 ± 0.03 for non-degenerate pumping with 1.0 μW and 1.5 μW average power of the two pumps. Our results show that the ultrahigh nonlinearity in these microwires could allow single-photon pumping to produce photon pairs, enabling the production of large entangled states, heralding of single photons after lossy transmission, and photonic quantum information processing with nonlinear optics.
Development of vertically aligned ZnO-nanowires scintillators for high spatial resolution x-ray imaging
Authors: Kobayashi Masakazu , Komori Jun , Shimidzu Kaiji , Izaki Masanobu , Uesugi Kentaro , Takeuchi Akihisa , Suzuki Yoshio
Published: February 2015

Newly designed scintillator of (0001)-oriented ZnO vertical nanowires (vnws) for X-ray imaging was prepared on a Ga-doped ZnO/soda-lime glass by electrodeposition, and the light emission feature was estimated in a synchrotron radiation facility. The ZnO-vnws scintillator revealed a strong light emission and improved resolution on CMOS image compared with that for the ZnO-layer scintillator, although the light emission performance was deteriorated in comparison to the Lu3Al5O12:Ce3+. The light emission property closely related to the nanostructure and the resultant photoluminescence characteristic.
SWI/SNF chromatin remodeling regulates alcohol response behaviors in
Caenorhabditis elegans
and is associated with alcohol dependence in humans
Authors: Mathies Laura D. , Blackwell GinaMari G. , Austin Makeda K. , Edwards Alexis C. , Riley Brien P. , Davies Andrew G. , Bettinger Jill C.
Published: February 2015

Significance

Alcohol abuse is a significant social problem for which the molecular etiology is poorly understood. One recognized component of the progression to abuse disorders is the development of alcohol tolerance, and recently epigenetic modification of gene expression has been implicated in tolerance. Here, we use
Caenorhabditis elegans
to show that the conserved switching defective/sucrose nonfermenting (SWI/SNF) chromatin-remodeling complex, which modifies the transcriptional status of target genes, is required in adults and neurons for the development of acute alcohol tolerance. We predicted that allelic variation in genes that modify tolerance phenotypes may modify abuse liability in humans, and we identified a significant association between variation in one member of the SWI/SNF complex and a diagnosis of alcohol dependence in a human genomewide association study.
Detecting cancers through tumor-activatable minicircles that lead to a detectable blood biomarker
Authors: Ronald John A. , Chuang Hui-Yen , Dragulescu-Andrasi Anca , Hori Sharon S. , Gambhir Sanjiv S.
Published: February 2015

Significance

Blood-based cancer diagnosis is highly attractive, but current strategies suffer because they rely on the detection of endogenous molecules that often are secreted into the circulation by both malignant and nonmalignant cells. One solution to this problem is to avoid nonmalignant tissue expression by artificially engineering tumor cells to express a unique reporter not normally expressed by any tissue. This study shows that systemic administration of nonviral safe vectors we call “tumor-activatable minicircles” allows one to distinguish tumor-bearing from tumor-free subjects reliably and to assess tumor burden simply by measuring blood levels of such a reporter. Our system represents an alternative paradigm for improved cancer detection and could enable more timely interventions to combat this devastating disease.
An underlying mechanism for the increased mutagenesis of lagging-strand genes in
Bacillus subtilis
Authors: Million-Weaver Samuel , Samadpour Ariana N. , Moreno-Habel Daniela A. , Nugent Patrick , Brittnacher Mitchell J. , Weiss Eli , Hayden Hillary S. , Miller Samuel I. , Liachko Ivan , Merrikh Houra
Published: February 2015

Significance

Replication and transcription can occur concurrently and use the same DNA template. This can cause genomic instability such as common fragile site instability in eukaryotes, and accelerated evolution of lagging-strand genes in bacteria. Here, we report an underlying mechanism that increases mutation rates of lagging-strand genes in
Bacillus subtilis.
We find that this process is mediated through the transcription-dependent activity of the Y-family polymerase, PolY1, in transcription-coupled nucleotide excision repair. We find that PolY1, likely through this mechanism, reduces the potentially problematic impacts of specifically lagging-strand transcription on replisome progression and genomic instability. This work shows that gene orientation, together with transcription, can cause differential activities of repair mechanisms, specifically increasing mutagenesis in lagging-strand genes.
Tunable assembly of amyloid-forming peptides into nanosheets as a retrovirus carrier
Authors: Dai Bin , Li Dan , Xi Wenhui , Luo Fang , Zhang Xiang , Zou Man , Cao Mi , Hu Jun , Wang Wenyuan , Wei Guanghong , Zhang Yi , Liu Cong
Published: February 2015

Significance

Many proteins enter the amyloid state, which is associated with human diseases and is also involved in many biological events. Amyloid formed by various proteins has a uniform “cross-β” structure with protein units stacking repetitively into fibrils. This unique structure brings amyloid favorable mechanical and chemical properties, and inspires the exploration of amyloid as a novel class of bionanomaterials. On the other hand, the uniform fibrillar structure limits the application of amyloid materials for a diverse function. This paper illustrates our discovery, structure characterization, design, and application of an amyloid-based structure, termed “amyloid-like nanosheet.” This nanosheet enriches the architectures of amyloid materials and will aid researchers in designing and investigating amyloid with new functions.
Anticancer drug nanomicelles formed by self-assembling amphiphilic dendrimer to combat cancer drug resistance
Authors: Wei Tuo , Chen Chao , Liu Juan , Liu Cheng , Posocco Paola , Liu Xiaoxuan , Cheng Qiang , Huo Shuaidong , Liang Zicai , Fermeglia Maurizio , Pricl Sabrina , Liang Xing-Jie , Rocchi Palma , Peng Ling
Published: February 2015

Significance

Nanotechnology-based drug delivery is expected to bring new hope for cancer treatment by enhancing anticancer drug efficacy, overcoming drug resistance, and reducing drug toxicity. In this respect, we developed an innovative drug delivery system based on a self-assembling amphiphilic dendrimer, which can generate supramolecular nanomicelles with large void space in their core to encapsulate anticancer drugs with high loading capacity. The resulting drug-encapsulated nanomicelles can effectively enhance drug potency and combat drug resistance by promoting cellular uptake and decreasing efflux of the anticancer drug. Moreover, this drug delivery system can significantly reduce the systemic toxicity of the free drug. The present study illustrates a successful example of how advances in dendrimer nanotechnology can be advantageously implemented to foster therapeutic perspectives.
Century-scale trends and seasonality in pH and temperature for shallow zones of the Bering Sea
Authors: Fietzke Jan , Ragazzola Federica , Halfar Jochen , Dietze Heiner , Foster Laura C. , Hansteen Thor Henrik , Eisenhauer Anton , Steneck Robert S.
Published: February 2015

Significance

Increasing atmospheric CO
2
concentrations are potentially affecting marine ecosystems twofold, by warming and acidification. The rising amount of CO
2
taken up by the ocean lowers the saturation state of calcium carbonate, complicating the formation of this key biomineral used by many marine organisms to build hard parts like skeletons or shells. Reliable time-series data of seawater pH are needed to evaluate the ongoing change and compare long-term trends and natural variability. For the high-latitude ocean, the region facing the strongest CO
2
uptake, such time-series data are so far entirely lacking. Our study provides, to our knowledge, the first reconstruction of seasonal cycle and long-term trend in pH for a high-latitude ocean obtained from 2D images of stable boron isotopes from a coralline alga.
On the principle of ion selectivity in Na
+
/H
+
-coupled membrane proteins: Experimental and theoretical studies of an ATP synthase rotor
Authors: Leone Vanessa , Pogoryelov Denys , Meier Thomas , Faraldo-Gómez José D.
Published: February 2015

Significance

The biological function of many membrane proteins requires a continuous energy supply. Differences in the electrochemical potential of Na
+
and H
+
across membranes, resulting from the metabolism of cellular nutrients or light harvesting, are the most prominent source of energy, aside from ATP. To harness this electrochemical energy, membrane proteins capture Na
+
or H
+
from their environment and couple their functional mechanisms to the translocation of these ions from one side of the membrane to the other. Here, we use experimental and computer simulation methods to investigate the structural and energetic factors that enable a crucial membrane enzyme, the ATP synthase, to selectively recognize Na
+
or H
+
. We envisage that these insights will apply to other classes of membrane proteins too.
Heritable symbiosis: The advantages and perils of an evolutionary rabbit hole
Authors: Bennett Gordon M. , Moran Nancy A.
Published: February 2015

Many eukaryotes have obligate associations with microorganisms that are transmitted directly between generations. A model for heritable symbiosis is the association of aphids, a clade of sap-feeding insects, and
Buchnera aphidicola
, a gammaproteobacterium that colonized an aphid ancestor 150 million years ago and persists in almost all 5,000 aphid species. Symbiont acquisition enables evolutionary and ecological expansion; aphids are one of many insect groups that would not exist without heritable symbiosis. Receiving less attention are potential negative ramifications of symbiotic alliances. In the short run, symbionts impose metabolic costs. Over evolutionary time, hosts evolve dependence beyond the original benefits of the symbiosis. Symbiotic partners enter into an evolutionary spiral that leads to irreversible codependence and associated risks. Host adaptations to symbiosis (e.g., immune-system modification) may impose vulnerabilities. Symbiont genomes also continuously accumulate deleterious mutations, limiting their beneficial contributions and environmental tolerance. Finally, the fitness interests of obligate heritable symbionts are distinct from those of their hosts, leading to selfish tendencies. Thus, genes underlying the host–symbiont interface are predicted to follow a coevolutionary arms race, as observed for genes governing host–pathogen interactions. On the macroevolutionary scale, the rapid evolution of interacting symbiont and host genes is predicted to accelerate host speciation rates by generating genetic incompatibilities. However, degeneration of symbiont genomes may ultimately limit the ecological range of host species, potentially increasing extinction risk. Recent results for the aphid–
Buchnera
symbiosis and related systems illustrate that, whereas heritable symbiosis can expand ecological range and spur diversification, it also presents potential perils.
Hadal biosphere: Insight into the microbial ecosystem in the deepest ocean on Earth
Authors: Nunoura Takuro , Takaki Yoshihiro , Hirai Miho , Shimamura Shigeru , Makabe Akiko , Koide Osamu , Kikuchi Tohru , Miyazaki Junichi , Koba Keisuke , Yoshida Naohiro , Sunamura Michinari , Takai Ken
Published: February 2015

Significance

Although many microbial explorations for hadal sediments began in the 1950s, the hadal water is the least-explored microbial biosphere. In this study, unexpected microbial ecosystems associated with the hadal trench water were discovered down to a 10,257-m water depth in the Challenger Deep of the Mariana Trench, which is the deepest ocean on Earth. We found the enrichment of heterotrophic population in the hadal water (6,000 ∼10,257 m) microbial communities, whereas the chemolithotrophic populations were more abundant in the upper abyssal waters. This observation suggested that the hadal microbial biosphere was supported by the endogenous recycling of organic matter in the hadal waters associated with the trench geomorphology.
Morphogenesis checkpoint kinase Swe1 is the executor of lipolysis-dependent cell-cycle progression
Authors: Chauhan Neha , Visram Myriam , Cristobal-Sarramian Alvaro , Sarkleti Florian , Kohlwein Sepp D.
Published: February 2015

Significance

Little information is currently available on how a cell coordinates the expansion of its membranes with growth and cell-cycle progression. Synthesis (lipogenesis) and degradation (lipolysis) of the major storage lipid triacylglycerol (TG) are regulated in yeast by the cyclin-dependent kinase Cdc28. TG breakdown provides precursors for the synthesis of sphingolipids, which in turn regulate cell-cycle progression upon exit from G0 phase of the cell cycle via the regulatory circuit comprised of Cdc55 phosphatase, Swe1 morphogenesis checkpoint kinase, and Cdc28 cyclin-dependent kinase. This finding unveils an unexpected function of the Swe1 morphogenesis checkpoint kinase in regulating lipolysis-dependent cell-cycle entry from G0.
Dual role of tree florigen activation complex component
FD
in photoperiodic growth control and adaptive response pathways
Authors: Tylewicz Szymon , Tsuji Hiroyuki , Miskolczi Pál , Petterle Anna , Azeez Abdul , Jonsson Kristoffer , Shimamoto Ko , Bhalerao Rishikesh P.
Published: February 2015

Significance

Perennial plants display seasonal cycles of growth. For example, in the trees of boreal temperate forests, growth must cease prior to the advent of winter and cold hardiness must be acquired to survive extreme low temperature. Growth cessation and activation of transcriptional programs underlying adaptive responses associated with cold hardiness are photoperiodically controlled. We show that the evolutionarily conserved protein FD implicated in the control of flowering mediates photoperiodic control of seasonal growth in trees by forming a complex with FLOWERING LOCUS T (FT) protein.
FD
genes of hybrid aspen display neofunctionalization and, in contrast to
Arabidopsis
, have evolved functions that are independent of their interaction with FT, such as transcriptional control of the adaptive response and bud maturation pathways in trees.
Rapid selection against arbovirus-induced apoptosis during infection of a mosquito vector
Authors: O’Neill Katelyn , Olson Bradley J. S. C. , Huang Ning , Unis Dave , Clem Rollie J.
Published: February 2015

Significance

Understanding the factors that cause mosquitoes to resist arbovirus infection could lead to new strategies to control disease transmission. One antiviral response that may play a role in mosquito immunity is apoptosis, a type of cell suicide that is often induced by virus infection. However, apoptosis is rarely seen in arbovirus-infected mosquitoes. To understand why, we infected mosquitoes with an arbovirus that expresses a proapoptotic gene called
reaper
and found that the Reaper-expressing virus had replication defects in mosquitoes. We also observed strong selective pressure against retention of
reaper
in the virus genome. These results indicate that apoptosis is a strong antiviral response in mosquitoes and may explain why it is usually not observed in coevolved arbovirus–vector relationships.
Initial viral load determines the magnitude of the human CD8 T cell response to yellow fever vaccination
Authors: Akondy Rama S. , Johnson Philip L. F. , Nakaya Helder I. , Edupuganti Srilatha , Mulligan Mark J. , Lawson Benton , Miller Joseph D. , Pulendran Bali , Antia Rustom , Ahmed Rafi
Published: February 2015

Significance

Current vaccine development against persistent infections such as HIV and tuberculosis focuses on eliciting CD8 T cell immunity through the use of replication-incompetent or single-cycle vectors. Although inherently safe, these vectors deliver limited amounts of antigen. We investigate how antigen load affects the CD8 response by analyzing the viral load and the magnitude of the specific CD8 response after immunization with the live attenuated yellow fever vaccine (YFV-17D). Our results show that the magnitude of the CD8 response is proportional to the amount of antigen when virus load is below a threshold value and saturates above. This finding highlights the requirement that T cell-based vaccines deliver sufficient antigen to elicit a large CD8 response that may be needed for protection.