bluuebunny/crossref_metadata_2025 huggingface dataset:
Ball-grid array architecture for microfabricated ion traps
Authors: Guise Nicholas D. , Fallek Spencer D. , Stevens Kelly E. , Brown K. R. , Volin Curtis , Harter Alexa W. , Amini Jason M. , Higashi Robert E. , Lu Son Thai , Chanhvongsak Helen M. , Nguyen Thi A. , Marcus Matthew S. , Ohnstein Thomas R. , Youngner Daniel W.
Published: May 2015

State-of-the-art microfabricated ion traps for quantum information research are approaching nearly one hundred control electrodes. We report here on the development and testing of a new architecture for microfabricated ion traps, built around ball-grid array (BGA) connections, that is suitable for increasingly complex trap designs. In the BGA trap, through-substrate vias bring electrical signals from the back side of the trap die to the surface trap structure on the top side. Gold-ball bump bonds connect the back side of the trap die to an interposer for signal routing from the carrier. Trench capacitors fabricated into the trap die replace area-intensive surface or edge capacitors. Wirebonds in the BGA architecture are moved to the interposer. These last two features allow the trap die to be reduced to only the area required to produce trapping fields. The smaller trap dimensions allow tight focusing of an addressing laser beam for fast single-qubit rotations. Performance of the BGA trap as characterized with 40Ca+ ions is comparable to previous surface-electrode traps in terms of ion heating rate, mode frequency stability, and storage lifetime. We demonstrate two-qubit entanglement operations with 171Yb+ ions in a second BGA trap.
Two-band luminescence from an intrinsic defect in spherical and terraced MgO nanoparticles
Authors: Pikhitsa Peter V. , Kim Changhyuk , Chae Sukbyung , Shin Seungha , Jung Sekwon , Kitaura Mamoru , Kimura Shin-ichi , Fukui Kazutoshi , Choi Mansoo
Published: May 2015

Luminescent defect centers in wide bandgap materials such as MgO are of great interest for science and technology. Magnesium oxide nanocubes obtained by the self-combustion of Mg metal have long exhibited only a broad 2.9 eV cathodoluminescence band owing to oxygen vacancies (F centers). However, in this work, a room-temperature ultraviolet 4.8 eV cathodoluminescence band has been observed coincident with a 2.5 eV band of the same intensity from an unexplored intrinsic defect in MgO terraced nanocubes and nanospheres produced from Mg metal combustion in an H2/O2 flame. Synchrotron radiation excitation spectra reveal that the excitation energy at the onset of both bands is just above the bandgap energy of 7.7 eV, where electrons and holes are generated. We determine that a defect, responsible for both emission bands, creates proximal anion-cation vacancy pairs named P centers that may appear instead of F centers because of changes in the MgO nanoparticle growth conditions.
On the evolution of the steady state in gold-silica nanocomposites under sustained irradiation
Authors: Vu T. H. Y. , Ramjauny Y. , Hayoun M. , Rizza G. , Perruchas S.
Published: May 2015

We investigate the kinetic evolution of a nanocomposite submitted to sustained irradiation. The study focuses on gold nanoparticles embedded within a silica host matrix. Irradiations with 4 MeV Au ++ ions are performed in the temperature range from 300 K to 1100 K and for fluences up to 8 × 1016 cm−2. The experimental results are combined with kinetic Monte Carlo simulations to fully characterize the kinetic evolution of the nanoparticles under irradiation. In particular, the change of the steady state with the temperature is investigated in details. First, we demonstrate the existence of a direct-coarsening regime at high temperature, e.g., above 900 K, and of a coarsening-resistant regime at low temperature, e.g., below 700 K. Second, we show that the transition between these two regimes takes place in a temperature region, where the nucleation of new nanoparticles is hindered, and the mass is redistributed among the existing nanoparticles. We also use our experimental results to critically analyze the existing theoretical models. As it has recently been pointed out that the physical principles underlying precipitation under irradiation are similar to those that govern the behavior of driven alloys, this work can be considered as an attempt to bridge the gap between two fields of experimental and theoretical studies, viz., those on driven alloys and those on metal-glass nanocomposites submitted to a sustained irradiation.
Time lagged ordinal partition networks for capturing dynamics of continuous dynamical systems
Authors: McCullough Michael , Small Michael , Stemler Thomas , Iu Herbert Ho-Ching
Published: May 2015

We investigate a generalised version of the recently proposed ordinal partition time series to network transformation algorithm. First, we introduce a fixed time lag for the elements of each partition that is selected using techniques from traditional time delay embedding. The resulting partitions define regions in the embedding phase space that are mapped to nodes in the network space. Edges are allocated between nodes based on temporal succession thus creating a Markov chain representation of the time series. We then apply this new transformation algorithm to time series generated by the Rössler system and find that periodic dynamics translate to ring structures whereas chaotic time series translate to band or tube-like structures—thereby indicating that our algorithm generates networks whose structure is sensitive to system dynamics. Furthermore, we demonstrate that simple network measures including the mean out degree and variance of out degrees can track changes in the dynamical behaviour in a manner comparable to the largest Lyapunov exponent. We also apply the same analysis to experimental time series generated by a diode resonator circuit and show that the network size, mean shortest path length, and network diameter are highly sensitive to the interior crisis captured in this particular data set.
Reactivable passive radio-frequency identification temperature indicator
Authors: Windl Roman , Bruckner Florian , Abert Claas , Suess Dieter , Huber Thomas , Vogler Christoph , Satz Armin
Published: May 2015

A low cost, passive radio-frequency identification (RFID) temperature indicator with (re-) activation at any point of time is presented. The capability to detect a temperature excursion is realized by magnets and a solution with a melting point at the critical temperature. As the critical temperature is exceeded, a magnetic indicator switches to non-reversible and this can be monitored via a giant magnetoresistance sensor connected to a RFID tag. Depending on the solutions or metal alloys, detection of critical temperatures in a wide range from below 0 °C and up to more than 100 °C is possible. The information if a threshold temperature was exceeded (indicator state) as well as the identification number, current temperature, and user defined data can be obtained via RFID.
Correlation of magnetostriction variation on magnetic loss and noise for power transformer
Authors: Cheng Shan-Jen , Liu Jui-Jung , Chang Yeong-Hwa , Fu Chao-Ming , Hsu Chang-Hung , Lee Chun-Yao , Chang Chia-Wen
Published: May 2015

Magnetostriction (MS)-caused strain in single-phase three-legged cores with different core cutting forms, which suffer from induced magnetic loss and noise, was studied. It is found that adopting each different core form types induces magnetostriction ε variation in a transformer core operating with a high-frequency AC signal. The results are compared with finite element analysis simulations. It is also indicated that magnetostriction ε variations are significant in the rolling direction and along limbs and yokes. In this paper, it is proposed that core corner sides and T-joint parts without cutting structure, the core exhibits lower core loss and lower heat dissipation due to the fact that the magnetic flux that passes through corner sides shows lower magnetostriction variation. The magnetic properties resulting from magnetostriction variation in core loss and heat dissipation phenomena are significantly different from other core forms because of stronger contributions from magnetostatic forces. The main contribution for reducing core loss and noise, making them much less in corner numbers and cutting-fabricated forms, can be expected to come from lower magnetic flux and magnetostriction variation.
Extended law of corresponding states for protein solutions
Authors: Platten Florian , Valadez-Pérez Néstor E. , Castañeda-Priego Ramón , Egelhaaf Stefan U.
Published: May 2015

The so-called extended law of corresponding states, as proposed by Noro and Frenkel [J. Chem. Phys. 113, 2941 (2000)], involves a mapping of the phase behaviors of systems with short-range attractive interactions. While it has already extensively been applied to various model potentials, here we test its applicability to protein solutions with their complex interactions. We successfully map their experimentally determined metastable gas–liquid binodals, as available in the literature, to the binodals of short-range square-well fluids, as determined by previous as well as new Monte Carlo simulations. This is achieved by representing the binodals as a function of the temperature scaled with the critical temperature (or as a function of the reduced second virial coefficient) and the concentration scaled by the cube of an effective particle diameter, where the scalings take into account the attractive and repulsive contributions to the interaction potential, respectively. The scaled binodals of the protein solutions coincide with simulation data of the adhesive hard-sphere fluid. Furthermore, once the repulsive contributions are taken into account by the effective particle diameter, the temperature dependence of the reduced second virial coefficients follows a master curve that corresponds to a linear temperature dependence of the depth of the square-well potential. We moreover demonstrate that, based on this approach and cloud-point measurements only, second virial coefficients can be estimated, which we show to agree with values determined by light scattering or by Derjaguin-Landau-Verwey-Overbeek (DLVO)-based calculations.
Underlying theory of a model for the Renner–Teller effect in tetra-atomic molecules: X2Πu electronic state of C2H2+
Authors: Perić M. , Jerosimić S. , Mitić M. , Milovanović M. , Ranković R.
Published: May 2015

In the present study, we prove the plausibility of a simple model for the Renner–Teller effect in tetra-atomic molecules with linear equilibrium geometry by ab initio calculations of the electronic energy surfaces and non-adiabatic matrix elements for the X2Πu state of C2H2+. This phenomenon is considered as a combination of the usual Renner–Teller effect, appearing in triatomic species, and a kind of the Jahn–Teller effect, similar to the original one arising in highly symmetric molecules. Only four parameters (plus the spin–orbit constant, if the spin effects are taken into account), which can be extracted from ab initio calculations carried out at five appropriate (planar) molecular geometries, are sufficient for building up the Hamiltonian matrix whose diagonalization results in the complete low-energy (bending) vibronic spectrum. The main result of the present study is the proof that the diabatization scheme, hidden beneath the apparent simplicity of the model, can safely be carried out, at small-amplitude bending vibrations, without cumbersome computation of non-adiabatic matrix elements at large number of molecular geometries.
A direct numerical simulation investigation of the synthetic jet frequency effects on separation control of low-Re flow past an airfoil
Authors: Zhang Wei , Samtaney Ravi
Published: May 2015

We present results of direct numerical simulations of a synthetic jet (SJ) based separation control of flow past a NACA-0018 (National Advisory Committee for Aeronautics) airfoil, at 10° angle of attack and Reynolds number 104 based on the airfoil chord length C and uniform inflow velocity U0. The actuator of the SJ is modeled as a spanwise slot on the airfoil leeward surface and is placed just upstream of the leading edge separation position of the uncontrolled flow. The momentum coefficient of the SJ is chosen at a small value 2.13 × 10−4 normalized by that of the inflow. Three forcing frequencies are chosen for the present investigation: the low frequency (LF) F+ = feC/U0 = 0.5, the medium frequency (MF) F+ = 1.0, and the high frequency (HF) F+ = 4.0. We quantify the effects of forcing frequency for each case on the separation control and related vortex dynamics patterns. The simulations are performed using an energy conservative fourth-order parallel code. Numerical results reveal that the geometric variation introduced by the actuator has negligible effects on the mean flow field and the leading edge separation pattern; thus, the separation control effects are attributed to the SJ. The aerodynamic performances of the airfoil, characterized by lift and lift-to-drag ratio, are improved for all controlled cases, with the F+ = 1.0 case being the optimal one. The flow in the shear layer close to the actuator is locked to the jet, while in the wake this lock-in is maintained for the MF case but suppressed by the increasing turbulent fluctuations in the LF and HF cases. The vortex evolution downstream of the actuator presents two modes depending on the frequency: the vortex fragmentation and merging mode in the LF case where the vortex formed due to the SJ breaks up into several vortices and the latter merge as convecting downstream; the discrete vortices mode in the HF case where discrete vortices form and convect downstream without any fragmentation and merging. In the MF case, the vortex dynamics is at a transition state between the two modes. The low frequency actuation has the highest momentum rate during the blowing phase and substantially affects the flow upstream of the actuator and triggers early transition to turbulence. In the LF case, the transverse velocity has a 1%U0 pulsation at the position 18%C upstream of the actuator.
Formation of size-controlled and luminescent Si nanocrystals from SiOxNy/Si3N4 hetero-superlattices
Authors: Zelenina A. , Sarikov A. , Gutsch S. , Zakharov N. , Werner P. , Reichert A. , Weiss C. , Zacharias M.
Published: May 2015

Silicon nanocrystals formed in the annealed SiNx/Si3N4 superlattices are attractive for research due to the smaller band offsets of Si3N4 matrix to Si in comparison with commonly used SiOx/SiO2 superlattices. However, the annealed SiNx/Si3N4 structures contain an increased number of nanocrystal interface defects, which completely suppress nanocrystal emission spectrum. In this work, we study a novel SiOxNy/Si3N4 hetero multilayer combination, which compromises the major issues of SiOx/SiO2 and SiNx/Si3N4 superlattices. The annealed SiOxNy/Si3N4 superlattices are investigated by TEM, demonstrating a precise sublayer thicknesses control. The PL spectra of the annealed SiOxNy/Si3N4 superlattices are centered at 845–950 nm with an expected PL peak shift for silicon nanocrystals of different sizes albeit the PL intensity is drastically reduced as compared to SiO2 separation barriers. The comparison of PL spectra of annealed SiOxNy/Si3N4 superlattice with those of SiOxNy/SiO2 superlattice enables the analysis of the interface quality of silicon nanocrystals. Using the literature data, the number of the interface defects and their distribution on the nanocrystal facets are estimated. Finally, it is shown that the increase of the Si3N4 barrier thickness leads to the increased energy transfer from the Si nanocrystals into the Si3N4 matrix, which explains an additional drop of the nanocrystal PL intensity.
Spin-reorientation and weak ferromagnetism in antiferromagnetic TbMn0.5Fe0.5O3
Authors: Nhalil Hariharan , Nair Harikrishnan S. , R. Sanathkumar , Strydom André M. , Elizabeth Suja
Published: May 2015

Orthorhombic single crystals of TbMn0.5Fe0.5O3 are found to exhibit spin-reorientation, magnetization reversal, and weak ferromagnetism. Strong anisotropy effects are evident in the temperature dependent magnetization measurements along the three crystallographic axes a, b, and c. A broad magnetic transition is visible at TNFe/Mn=286 K due to paramagnetic to AxGyCz ordering. A sharp transition is observed at TSRFe/Mn=28 K, which is pronounced along c axis in the form of a sharp jump in magnetization where the spins reorient to GxAyFz configuration. The negative magnetization observed below TSRFe/Mn along c axis is explained in terms of domain wall pinning. A component of weak ferromagnetism is observed in field-scans along c-axis but below 28 K. Field-induced steps-like transitions are observed in hysteresis measurement along b axis below 28 K. It is noted that no sign of Tb-order is discernible down to 2 K. TbMn0.5Fe0.5O3 could be highlighted as a potential candidate to evaluate its magneto-dielectric effects across the magnetic transitions.
Communication: Nucleation of water on ice nanograins: Size, charge, and quantum effects
Authors: Marciante Mathieu , Calvo Florent
Published: May 2015

The sticking cross sections of water molecules on cold size-selected water clusters have been simulated using classical and quantum (path-integral) molecular dynamics trajectories under realistic conditions. The integrated cross sections for charged clusters show significant size effects with comparable trends as in experiments, as well as essentially no sign effect. Vibrational delocalization, although it contributes to enlarging the geometric cross sections, leads to a counter-intuitive decrease in the dynamical cross section obtained from the trajectories. These results are interpreted based on the apparent reduction in the effective interaction between the projectile and the target owing to zero-point effects.
New approach to folding with the Coulomb wave function
Authors: Blokhintsev L. D. , Kadyrov A. S. , Mukhamedzhanov A. M. , Savin D. A.
Published: May 2015

Due to the long-range character of the Coulomb interaction theoretical description of low-energy nuclear reactions with charged particles still remains a formidable task. One way of dealing with the problem in an integral-equation approach is to employ a screened Coulomb potential. A general approach without screening requires folding of kernels of the integral equations with the Coulomb wave. A new method of folding a function with the Coulomb partial waves is presented. The partial-wave Coulomb function both in the configuration and momentum representations is written in the form of separable series. Each term of the series is represented as a product of a factor depending only on the Coulomb parameter and a function depending on the spatial variable in the configuration space and the momentum variable if the momentum representation is used. Using a trial function, the method is demonstrated to be efficient and reliable.
Ion conduction and relaxation in PEO-LiTFSI-Al2O3 polymer nanocomposite electrolytes
Authors: Das S. , Ghosh A.
Published: May 2015

Ion conduction and relaxation in PEO-LiTFSI-Al2O3 polymer nanocomposite electrolytes have been studied for different concentrations of Al2O3 nanoparticles. X-ray diffraction and differential scanning calorimetric studies show that the maximum amorphous phase of PEO is observed for PEO-LiTFSI embedded with 5 wt. % Al2O3. The maximum ionic conductivity ∼3.3 × 10−4 S cm−1 has been obtained for this composition. The transmission electron microscopic image shows a distribution of Al2O3 nanoparticles in all compositions with size of <50 nm. The temperature dependence of the ionic conductivity follows Vogel-Tamman-Fulcher nature, indicating a strong coupling between ionic and polymer chain segmental motions. The scaling of the ac conductivity implies that relaxation dynamics follows a common mechanism for different temperatures and Al2O3 concentrations. The imaginary modulus spectra are asymmetric and skewed toward the high frequency sides of the maxima and analyzed using Havriliak-Negami formalism. The temperature dependence of the relaxation time obtained from modulus spectra also exhibits Vogel-Tamman-Fulcher nature. The values of the stretched exponent obtained from Kohlrausch-Williams-Watts fit to the modulus data are fairly low, suggesting highly non-exponential relaxation for all concentrations of Al2O3 in these electrolytes.
Modeling interface-controlled phase transformation kinetics in thin films
Authors: Pang E. L. , Vo N. Q. , Philippe T. , Voorhees P. W.
Published: May 2015

The Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation is widely used to describe phase transformation kinetics. This description, however, is not valid in finite size domains, in particular, thin films. A new computational model incorporating the level-set method is employed to study phase evolution in thin film systems. For both homogeneous (bulk) and heterogeneous (surface) nucleation, nucleation density and film thickness were systematically adjusted to study finite-thickness effects on the Avrami exponent during the transformation process. Only site-saturated nucleation with isotropic interface-kinetics controlled growth is considered in this paper. We show that the observed Avrami exponent is not constant throughout the phase transformation process in thin films with a value that is not consistent with the dimensionality of the transformation. Finite-thickness effects are shown to result in reduced time-dependent Avrami exponents when bulk nucleation is present, but not necessarily when surface nucleation is present.
Temperature evolution of carrier dynamics in GaNxPyAs1−y−xalloys
Authors: Baranowski M. , Kudrawiec R. , Luce A. V. , Latkowska M. , Yu K. M. , Kuang Y. J. , Misiewicz J. , Tu C. W. , Walukiewicz W.
Published: May 2015

The temperature dependence of carrier dynamics in GaNxAs1−yPy alloys has been investigated by time resolved photoluminescence. This investigation has shown that the decay time constant does not change significantly up to 100 K, and then starts to decrease rapidly above this temperature. Additionally, the decay times at the high-energy side of the spectrum decrease faster than those at the low-energy side. The effects have been explained by the interplay between carrier capture by radiative and nonradiative recombination centers. Detailed simulations show that the effect of carrier localization in the investigated materials is better described by double-scale potential fluctuations that are related to (i) distribution of localized states energy and (ii) bandgap fluctuations. In addition, it was observed that the increase in nitrogen concentration leads to a shorter decay time at room temperature, which is attributed to a larger concentration of non-radiative recombination centers. Furthermore, a post-growth annealing step leads to a longer decay time at room temperature, which is attributed to a reduction in non-radiative recombination centers. At low temperatures, the role of non-radiative centers is suppressed, and therefore the decay time does not differ significantly for samples with either different nitrogen concentrations or in both the as-grown and annealed samples.
Broadband high-efficiency transmission asymmetry by a chiral bilayer bar metastructure
Authors: Wang Ying-Hua , Shao Jian , Li Jie , Liu Zongbang , Li Jiaqi , Dong Zheng-Gao , Zhai Ya
Published: May 2015

A chiral metallic metastructure composed of bilayer twisted bars is proposed to realize a broadband asymmetric transmission for linearly and circularly polarized incident light, aimed at sustaining high efficiency of unidirectional polarization conversion over the whole operation band. Such a one-way propagation results from the chiral structural arrangement that destroys the rotational and translational symmetries in all directions. Moreover, its ultra-broad bandwidth, mainly depending on the bar length, originates from the subwavelength plasmon coupling between long- and short-bar dipole-like responses. The efficient broadband one-way characteristic exhibits a structure with promising prospects for metadevices capable of unidirectional polarization conversion manipulation.
Hybrid metamaterial device with wideband absorption and multiband transmission based on spoof surface plasmon polaritons and perfect absorber
Authors: Li Si-Jia , Gao Jun , Cao Xiang-Yu , Zhang Zhao , Liu Tao , Zheng Yue-Jun , Zhang Chen , Zheng Gui
Published: May 2015

We reported on the design, realization, and numerical characterization of a hybrid metamaterial (HM) with the absorption and transmission at different frequencies based on the spoof surface plasmon polaritons and perfect absorber. A unit cell is composed of a three-layer metamaterial with double orthogonal split ring resonators and a ground plate loaded with two-sided metallic grooves. It is shown that the hybrid metamaterial primarily exhibits a broadband polarization-sensitive absorption from 6.57 to 28.16 GHz with a full-width at half-maximum in one direction and a multiband transmission in the opposite one. When the incidence is parallel to HM, the ground plate loaded with two-sided metallic grooves can support a structural vibration of spoof surface plasmon polaritons. To demonstrate design, a HM device easily implemented using common printed circuit board fabrication method is fabricated and measured and the experimental results agree well with the simulated results.
Optimization of Brownian ratchets for the manipulation of charged components within supported lipid bilayers
Authors: Roth J. S. , Zhang Y. , Bao P. , Cheetham M. R. , Han X. , Evans S. D.
Published: May 2015

In probability theory, there is a counter-intuitive result that it is possible to construct a winning strategy from two individually losing (or at most breaking-even) “games” by alternating between them. The work presented here demonstrates the application of this principle to supported lipid bilayers (SLBs) in order to create directed motion of charged lipid components in the membrane, which was achieved through the use of “Brownian ratchets” in patterned SLBs. Both a finite element analysis model and an experimental setup have been used to investigate the role of key parameters for the operation of these ratchets: (1) the asymmetry of the ratchet teeth and (2) the relation of the ratchet height to the period of the applied electric field. Importantly, we find that the efficiency of the ratchet for a given charged species is dependent on the diffusion coefficient. This opens the possibility for separation of membrane species according to their size or viscous drag coefficient within the membrane.
Two-dimensional and three-dimensional dynamic imaging of live biofilms in a microchannel by time-of-flight secondary ion mass spectrometry
Authors: Hua Xin , Marshall Matthew J. , Xiong Yijia , Ma Xiang , Zhou Yufan , Tucker Abigail E. , Zhu Zihua , Liu Songqin , Yu Xiao-Ying
Published: May 2015

A vacuum compatible microfluidic reactor, SALVI (System for Analysis at the Liquid Vacuum Interface), was employed for in situ chemical imaging of live biofilms using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Depth profiling by sputtering materials in sequential layers resulted in live biofilm spatial chemical mapping. Two-dimensional (2D) images were reconstructed to report the first three-dimensional images of hydrated biofilm elucidating spatial and chemical heterogeneity. 2D image principal component analysis was conducted among biofilms at different locations in the microchannel. Our approach directly visualized spatial and chemical heterogeneity within the living biofilm by dynamic liquid ToF-SIMS.
Design, fabrication, and performance analysis of GaN vertical electron transistors with a buried p/n junction
Authors: Yeluri Ramya , Lu Jing , Hurni Christophe A. , Browne David A. , Chowdhury Srabanti , Keller Stacia , Speck James S. , Mishra Umesh K.
Published: May 2015

The Current Aperture Vertical Electron Transistor (CAVET) combines the high conductivity of the two dimensional electron gas channel at the AlGaN/GaN heterojunction with better field distribution offered by a vertical design. In this work, CAVETs with buried, conductive p-GaN layers as the current blocking layer are reported. The p-GaN layer was regrown by metalorganic chemical vapor deposition and the subsequent channel regrowth was done by ammonia molecular beam epitaxy to maintain the p-GaN conductivity. Transistors with high ON current (10.9 kA/cm2) and low ON-resistance (0.4 mΩ cm2) are demonstrated. Non-planar selective area regrowth is identified as the limiting factor to transistor breakdown, using planar and non-planar n/p/n structures. Planar n/p/n structures recorded an estimated electric field of 3.1 MV/cm, while non-planar structures showed a much lower breakdown voltage. Lowering the p-GaN regrowth temperature improved breakdown in the non-planar n/p/n structure. Combining high breakdown voltage with high current will enable GaN vertical transistors with high power densities.
Tip-induced domain growth on the non-polar cuts of lithium niobate single-crystals
Authors: Alikin D. O. , Ievlev A. V. , Turygin A. P. , Lobov A. I. , Kalinin S. V. , Shur V. Ya.
Published: May 2015

Currently, ferroelectric materials with designed domain structures are considered as a perspective material for new generation of photonic, data storage, and data processing devices. Application of external electric field is the most convenient way of the domain structure formation. Lots of papers are devoted to the investigation of domain kinetics on polar surface of crystals while the forward growth remains one of the most mysterious stages due to lack of experimental methods allowing to study it. Here, we performed tip-induced polarization reversal on X- and Y-non-polar cuts in single-crystal of congruent lithium niobate which allows us to study the forward growth with high spatial resolution. The revealed difference in the shape and length of domains induced on X- and Y-cuts is beyond previously developed theoretical approaches used for the theoretical consideration of the domains growth at non-polar ferroelectric surfaces. To explain experimental results, we used kinetic approach with anisotropy of screening efficiency along different crystallographic directions.
Strain-tunable topological quantum phase transition in buckled honeycomb lattices
Authors: Yan Jia-An , Cruz Mack A. Dela , Barraza-Lopez Salvador , Yang Li
Published: May 2015

Low-buckled silicene is a prototypical quantum spin Hall insulator with the topological quantum phase transition controlled by an out-of-plane electric field. We show that this field-induced electronic transition can be further tuned by an in-plane biaxial strain ε, owing to the curvature-dependent spin-orbit coupling (SOC): There is a Z2 = 1 topological insulator phase for biaxial strain |ε| smaller than 0.07, and the band gap can be tuned from 0.7 meV for ε=+0.07 up to 3.0 meV for ε=−0.07. First-principles calculations also show that the critical field strength Ec can be tuned by more than 113%, with the absolute values nearly 10 times stronger than the theoretical predictions based on a tight-binding model. The buckling structure of the honeycomb lattice thus enhances the tunability of both the quantum phase transition and the SOC-induced band gap, which are crucial for the design of topological field-effect transistors based on two-dimensional materials.
Impact of repeated uniaxial mechanical strain on p-type flexible polycrystalline thin film transistors
Authors: Chen Bo-Wei , Chang Ting-Chang , Hung Yu-Ju , Hsieh Tien-Yu , Tsai Ming-Yen , Liao Po-Yung , Chen Bo-Yao , Tu Yi-Hsien , Lin Yuan-Yao , Tsai Wu-Wei , Yan Jing-Yi
Published: May 2015

This letter investigates the effect of repeated bending of flexible p-channel low-temperature polycrystalline–silicon thin-film transistors employing an ultra-low-temperature process (<673 K). Experimental results reveal that interface state density (Nit) and grain boundary trap density (Ntrap) after 10 000 width-axis tensile strain bending iterations are more pronounced than after equivalent width-axis compressive strain bending. Extracted interface and grain boundary traps both increase, which elevate trap assisted leakage. Furthermore, the bending distorts the Si–Si bonds in the polycrystalline silicon (Poly-Si) film, which causes more significant negative bias temperature instability (NBTI) degradation because strain-induced weak Si–Si bonds can react with dissociated H during NBTI stress.
Direct correlation and strong reduction of native point defects and microwave dielectric loss in air-annealed (Ba,Sr)TiO3
Authors: Zeng Z. Q. , Podpirka A. , Kirchoefer S. W. , Asel T. J. , Brillson L. J.
Published: May 2015

We report on the native defect and microwave properties of 1 μm thick Ba0.50Sr0.50TiO3 (BST) films grown on MgO (100) substrates by molecular beam epitaxy (MBE). Depth-resolved cathodoluminescence spectroscopy (DRCLS) showed high densities of native point defects in as-deposited BST films, causing strong subgap emission between 2.0 eV and 3.0 eV due to mixed cation VC and oxygen Vo vacancies. Post growth air anneals reduce these defects with 2.2, 2.65, and 3.0 eV VO and 2.4 eV VC intensities decreasing with increasing anneal temperature and by nearly two orders of magnitude after 950 °C annealing. These low-defect annealed BST films exhibited high quality microwave properties, including room temperature interdigitated capacitor tunability of 13% under an electric bias of 40 V and tan δ of 0.002 at 10 GHz and 40 V bias. The results provide a feasible route to grow high quality BST films by MBE through post-air annealing guided by DRCLS.
Fabrication of ten-fold photonic quasicrystalline structures
Authors: Sun XiaoHong , Wu YuLong , Liu Wen , Liu Wei , Han Juan , Jiang Lei
Published: May 2015

Compared to periodic crystals, quasicrystals have higher point group symmetry and are more favorable in achieving complete band-gaps. In this report, a top-cut prism interferometer is designed to fabricate ten-fold photonic quasicrystalline structures. By optimizing the exposing conditions and material characteristics, appropriate quasicrystals have been obtained in the SU8 photoresist films. Atomic Force Microscopy and laser diffraction are used to characterize the fabricated structures. The measurement results show the consistence between the theoretical design and experiments. This will provide guidance for the large-area and fast production of ten-fold quasicrystalline structures with high quality.
The flora of ultramafic soils in the Australia–Pacific Region: state of knowledge and research priorities
Authors: van der Ent Antony , Jaffré Tanguy , L'Huillier Laurent , Gibson Neil , Reeves Roger D.
Published: May 2015

In the Australia–Pacific Region ultramafic outcrops are both widespread and extensive, covering thousands of km2. Soils derived from ultramafic bedrock impose edaphic challenges and are widely known to host highly distinctive floras with high levels of endemism. In the Australia–Pacific Region, the ultramafics of the island of New Caledonia are famed for harbouring 2150 species of vascular plants of which 83% are endemic. Although the ultramafic outcrops in Western Australia are also extensive and harbour 1355 taxa, only 14 species are known to be endemic or have distributions centred on ultramafics. The ultramafic outcrops in New Zealand and Tasmania are small and relatively species-poor. The ultramafic outcrops in Queensland are much larger and host 553 species of which 18 (or possibly 21) species are endemic. Although New Caledonia has a high concentration of Ni hyperaccumulator species (65), only one species from Western Australia and two species from Queensland have so far been found. No Ni hyperaccumulator species are known from Tasmania and New Zealand. Habitat destruction due to forest clearing, uncontrolled fires and nickel mining in New Caledonia impacts on the plant species restricted to ultramafic soils there. In comparison with the nearby floras of New Guinea and South-east Asia, the flora of the Australia–Pacific Region is relatively well studied through the collection of a large number of herbarium specimens. However, there is a need for studies on the evolution of plant lineages on ultramafic soils especially regarding their distinctive morphological characteristics and in relation to hyperaccumulation.
Characterisation of the deleted in azoospermia like (Dazl)–green fluorescent protein mouse model generated by a two-step embryonic stem cell-based strategy to identify pluripotent and germ cells
Authors: Ramos-Ibeas Priscila , Pericuesta Eva , Fernández-González Raúl , Gutiérrez-Adán Alfonso , Ramírez Miguel Ángel
Published: May 2015

The deleted in azoospermia like (Dazl) gene is preferentially expressed in germ cells; however, recent studies indicate that it may have pluripotency-related functions. We generated Dazl–green fluorescent protein (GFP) transgenic mice and assayed the ability of Dazl-driven GFP to mark preimplantation embryo development, fetal, neonatal and adult tissues, and in vitro differentiation from embryonic stem cells (ESCs) to embryoid bodies (EBs) and to primordial germ cell (PGC)-like cells. The Dazl-GFP mice were generated by a two-step ESC-based strategy, which enabled primary and secondary screening of stably transfected clones before embryo injection. During preimplantation embryo stages, GFP was detected from the zygote to blastocyst stage. At Embryonic Day (E) 12.5, GFP was expressed in gonadal ridges and in neonatal gonads of both sexes. In adult mice, GFP expression was found during spermatogenesis from spermatogonia to elongating spermatids and in the cytoplasm of oocytes. However, GFP mRNA was also detected in other tissues harbouring multipotent cells, such as the intestine and bone marrow. Fluorescence was maintained along in vitro Dazl-GFP ESC differentiation to EBs, and in PGC-like cells. In addition to its largely known function in germ cell development, Dazl could have an additional role in pluripotency, supporting these transgenic mice as a valuable tool for the prospective identification of stem cells from several tissues.
Multiple roles of hypoxia in ovarian function: roles of hypoxia-inducible factor-related and -unrelated signals during the luteal phase
Authors: Nishimura Ryo , Okuda Kiyoshi
Published: May 2015

There is increasing interest in the role of oxygen conditions in the microenvironment of organs because of the discovery of a hypoxia-specific transcription factor, namely hypoxia-inducible factor (HIF) 1. Ovarian function has several phases that change day by day, including ovulation, follicular growth and corpus luteum formation and regression. These phases are regulated by many factors, including pituitary hormones and local hormones, such as steroids, peptides and cytokines, as well as oxygen conditions. Hypoxia strongly induces angiogenesis because transcription of the potent angiogenic factor vascular endothelial growth factor (VEGF) is regulated by HIF1. Follicular development and luteal formation are accompanied by a marked increase in angiogenesis assisted by HIF1–VEGF signalling. Hypoxia is also one of the factors that induces luteolysis by suppressing progesterone synthesis and by promoting apoptosis of luteal cells. The present review focuses on recent studies of hypoxic conditions, as well as HIF1-regulated genes and proteins, in the regulation of ovarian function.
Cytoplasmic dynein regulates its attachment to microtubules via nucleotide state-switched mechanosensing at multiple AAA domains
Authors: Nicholas Matthew P. , Berger Florian , Rao Lu , Brenner Sibylle , Cho Carol , Gennerich Arne
Published: May 2015

Significance

Cytoplasmic dynein is the primary minus-end–directed microtubule (MT) motor. It is unclear how dynein coordinates ATP hydrolysis and MT attachment within and between its two motor domains, each containing four AAA+ ATPases (AAA: ATPase associated with various cellular activities), AAA1–4. We characterize how mechanical tension and nucleotide states of AAA1 and AAA3 regulate dynein–MT binding. Dynein binds MTs tighter when subjected to tension opposite its normal motility. ADP binding to AAA3 unexpectedly weakens MT-binding strength and reduces the bond strength anisotropy. Finally, AAA3 “gates” the activity of AAA1: ATP binding to AAA1 induces MT release only if AAA3 contains nucleotide. This work expands understanding of the role of force in dynein mechanochemistry and identifies regulatory functions of AAA3.
Oncogenic and RASopathy-associated K-RAS mutations relieve membrane-dependent occlusion of the effector-binding site
Authors: Mazhab-Jafari Mohammad T. , Marshall Christopher B. , Smith Matthew J. , Gasmi-Seabrook Geneviève M. C. , Stathopulos Peter B. , Inagaki Fuyuhiko , Kay Lewis E. , Neel Benjamin G. , Ikura Mitsuhiko
Published: May 2015

Significance

KRAS
(Kirsten rat sarcoma viral oncogene homolog) is frequently mutated in pancreatic, colon, and lung tumors, which predicts poor clinical outcome, whereas germ-line mutations are associated with developmental disorders, including Noonan syndrome. Although K-RAS is an attractive anticancer target, no clinically successful inhibitors are available. Most disease-associated mutations elevate the activated GTP-bound form of KRAS; however, some remain unexplained. KRAS signals from cellular membranes; however, our studies revealed that its association with the membrane surface sequesters its binding site for effector proteins, hampering signaling. Some disease-associated
KRAS
mutations disrupt this autoinhibition, identifying a new gain-of-function mechanism and explaining how certain Noonan syndrome mutations activate K-RAS signaling. Importantly, these findings open new avenues for therapeutic strategies to target oncogenic K-RAS through stabilizing autoinhibitory interactions with the membrane.
Organization and dynamics of the nonhomologous end-joining machinery during DNA double-strand break repair
Authors: Reid Dylan A. , Keegan Sarah , Leo-Macias Alejandra , Watanabe Go , Strande Natasha T. , Chang Howard H. , Oksuz Betul Akgol , Fenyo David , Lieber Michael R. , Ramsden Dale A. , Rothenberg Eli
Published: May 2015

Significance

Nonhomologous end-joining (NHEJ) is the main pathway for repair of DNA double-strand breaks (DSBs), the most cytotoxic form of DNA damage resulting from ionizing radiation, chemotherapeutics, and normal cellular processes. The mechanisms that control NHEJ play key roles in development, in immunity, and in response to cancer therapy; however, the current state of knowledge regarding the physical nature of the NHEJ repair process is limited. Here we used super-resolution microscopy to define the organization of NHEJ complexes in cells, showing that long filaments form at either side of the break. Single-molecule FRET revealed dynamic behavior in which breaks can pair in an adjacent, non–end-to-end configuration.
Evaluating a groundwater supply contamination incident attributed to Marcellus Shale gas development
Authors: Llewellyn Garth T. , Dorman Frank , Westland J. L. , Yoxtheimer D. , Grieve Paul , Sowers Todd , Humston-Fulmer E. , Brantley Susan L.
Published: May 2015

Significance

New techniques of high-volume hydraulic fracturing (HVHF) are now used to unlock oil and gas from rocks with very low permeability. Some members of the public protest against HVHF due to fears that associated compounds could migrate into aquifers. We report a case where natural gas and other contaminants migrated laterally through kilometers of rock at shallow to intermediate depths, impacting an aquifer used as a potable water source. The incident was attributed to Marcellus Shale gas development. The organic contaminants—likely derived from drilling or HVHF fluids—were detected using instrumentation not available in most commercial laboratories. More such incidents must be analyzed and data released publicly so that similar problems can be avoided through use of better management practices.
Multisite interaction with Sufu regulates Ci/Gli activity through distinct mechanisms in Hh signal transduction
Authors: Han Yuhong , Shi Qing , Jiang Jin
Published: May 2015

Significance

Hedgehog (Hh) signaling controls embryonic development and adult tissue homeostasis by regulating the Cubitus interruptus (Ci)/Glioma-associated oncogene homolog (Gli) family of transcription factors. Abnormal Hh pathway activity causes congenital disease and cancer. As a conserved negative regulator of the Hh signaling pathway, the tumor suppressor protein Suppressor of fused (Sufu) binds and inhibits Ci/Gli, but how Sufu contacts Ci/Gli and how Sufu–Ci/Gli interaction inhibits Hh signaling activity remain poorly understood. Here we identified a conserved Sufu-binding site in the C-terminal region of Ci/Gli. Further characterization of this Sufu-binding site provided insight into how Sufu blocks Ci/Gli activation in the nucleus. Understanding the mechanism by which Sufu regulates Ci/Gli activity is important for developing therapeutic treatment of cancers caused by abnormal Hh pathway activation.
Bats adjust their mouth gape to zoom their biosonar field of view
Authors: Kounitsky Pavel , Rydell Jens , Amichai Eran , Boonman Arjan , Eitan Ofri , Weiss Anthony J. , Yovel Yossi
Published: May 2015

Significance

This study shows how an animal actively and functionally controls its sensory field of view by means of changing its emitter aperture. This would be similar to a human ability to zoom in on a visual scene. The study was performed in a natural situation with wild bats. To perform the study, we developed tools to record and analyze bats’ beams and faces simultaneously. We show that bats rapidly and dramatically alter their biosonar field of view to functionally adjust sensory acquisition. They do so by changing their mouth gape. Hence, we show that bats change the shape of their emitter for active sensing.
Antigenic cooperation among intrahost HCV variants organized into a complex network of cross-immunoreactivity
Authors: Skums Pavel , Bunimovich Leonid , Khudyakov Yury
Published: May 2015

Significance

Immune escape by continuous genetic diversification is commonly described using a metaphor of “arms race” between virus and host. Here we show, however, that hepatitis C virus (HCV) genetic heterogeneity facilitates a stable state of immune adaptation rather than perpetuates an arms race. We developed a mathematical model that considers variation in breadth of immunoreactivity among antibodies and antigens and the contribution of immune memory to humoral response against HCV. The model applied to a complex network of cross-immunoreactivity suggests antigenic cooperation among variants as a mechanism of mitigating the immune pressure on certain HCV variants. Cooperative action of antigens results from their differential capability to bind or elicit highly polyspecific antibodies. Antigenic cooperation is a new target for therapeutic- and vaccine-development strategies.
Apolipoprotein CIII links islet insulin resistance to β-cell failure in diabetes
Authors: Åvall Karin , Ali Yusuf , Leibiger Ingo B. , Leibiger Barbara , Moede Tilo , Paschen Meike , Dicker Andrea , Daré Elisabetta , Köhler Martin , Ilegems Erwin , Abdulreda Midhat H. , Graham Mark , Crooke Rosanne M. , Tay Vanessa S. Y. , Refai Essam , Nilsson Stefan K. , Jacob Stefan , Selander Lars , Berggren Per-Olof , Juntti-Berggren Lisa
Published: May 2015

Significance

Insulin resistance and β-cell failure are the major defects in type 2 diabetes. We now demonstrate that local insulin resistance-induced increase in apolipoprotein CIII (apoCIII) within pancreatic islets causes promotion of an intraislet inflammatory milieu, increased mitochondrial metabolism, deranged regulation of β-cell cytoplasmic free Ca
2+
concentration ([Ca
2+
]
i
), and apoptosis. Decreasing apoCIII in vivo in animals with insulin resistance improves glucose tolerance, and apoCIII knockout islets transplanted into diabetic mice, with high systemic levels of apoCIII, demonstrate a normal [Ca
2+
]
i
response pattern and no hallmarks of inflammation. Hence, under conditions of islet insulin resistance, locally produced apoCIII is an important diabetogenic factor involved in impairment of β-cell function and may thus constitute a novel target for the treatment of type 2 diabetes.