bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in Optic Nerve Sheath Diameter in Response to Various Levels of End-Tidal Carbon Dioxide in Healthy Patients under General Anesthesia
Authors: Kapoor Indu , Khandelwal Ankur , Mahajan Charu , Prabhakar Hemanshu , Bithal Parmod Kumar
Published: May 2018

Background Intracranial pressure (ICP) monitoring is an essential component in management of traumatic brain-injured (TBI) patients. While invasive techniques are associated with many complications, noninvasive nature of ultrasonographic measurement of optic nerve sheath diameter (ONSD) is now becoming popular. Carbon dioxide (CO2) alters the ICP by changing the size of cerebral vasculature. We aimed to assess the effect of (hypercarbia and hypocarbia) different levels of end-tidal carbon dioxide (EtCO2) on ONSD.

Methods Thirty adult patients aged between 18 and 65 years, undergoing brachial plexus injury surgery under general anesthesia, were enrolled. Following standard anesthetic protocol, ONSD was measured at different time points of EtCO2. ONSD was measured at EtCO2 of 40 and then 30 mm Hg to assess change in ONSD due to hypocarbia (Thypocarbia). Similarly, ONSD was measured at EtCO2 of 50 mm Hg to assess change in ONSD due to hypercarbia (Thypercarbia). The mean of three ONSD values at each time point was taken as the final value. The generalized estimating equation (GEE) was used to analyze correlation between different levels of EtCO2 and ONSD.

Results The calculated 95% confidence interval (CI) for the difference of two measures (Thypocarbia, EtCO2 40 and 30 mm Hg) on ONSD was −0.056 to −0.036, and the calculated CI for the difference of other two measures (Thypercarbia, EtCO2 40 and 50 mm Hg) on ONSD was 0.044 to 0.077, and thus were observed to be significant.

Conclusions ONSD changes significantly in response to different EtCO2 levels in healthy non-neurosurgical patients under general anesthesia.
Fabrication of tunable diffraction grating by imprint lithography with photoresist mold
Authors: Yamada Itsunari , Ikeda Yusuke , Higuchi Tetsuya
Published: May 2018

We fabricated a deformable transmission silicone [poly(dimethylsiloxane)] grating using a two-beam interference method and imprint lithography and evaluated its optical characteristics during a compression process. The grating pattern with 0.43 μm depth and 1.0 μm pitch was created on a silicone surface by an imprinting process with a photoresist mold to realize a simple, low-cost fabrication process. The first-order diffraction transmittance of this grating reached 10.3% at 632.8 nm wavelength. We also measured the relationship between the grating period and compressive stress to the fabricated elements. The grating period changed from 1.0 μm to 0.84 μm by 16.6% compression of the fabricated element in one direction, perpendicular to the grooves, and the first-order diffraction transmittance was 8.6%.
A new experimental apparatus for emissivity measurements of steel and the application of multi-wavelength thermometry to continuous casting billets
Authors: Wang Peng , Hu Zhenwei , Xie Zhi , Yan Ming
Published: May 2018

An experimental apparatus has been designed for measuring the emissivity of a steel surface in both vacuum and oxidation atmosphere. The sample is heated with the method of electromagnetic induction in order to ensure the temperature uniformity. The radiance emitted from a sample is measured using a fiber-optic Fourier transform infrared spectrometer. Using this unique apparatus, we investigated the spectral (2-6 μm) and directional (0°-86°) emissivity of stainless steel 304 with different degrees of surface oxidation at temperatures ranging from 800 to 1100 °C. The experimental results show that the emissivity increases slightly with increasing temperature, which accords with the Hagen-Rubens relation. The emissivity increases rapidly at the initial stage of oxidation, but gradually reaches to a constant value after 20 min. In addition, the directional emissivity has a maximum value at the measuring angle of about 75°. The maximum uncertainty of emissivity is only 3.0% over all the measuring ranges, indicating that this experimental apparatus has a high reliability. In order to measure the surface temperature of casting billets based on multi-wavelength thermometry, the bivariate emissivity function with the two variables, wavelength and temperature, is determined. Temperature measurement results based on our technique are compared with those from common dual-wavelength radiation thermometry. Our approach reduces the measured temperature fluctuation from ±20.7 °C to ±2.8 °C and reflects the temperature variation with the changes of production parameters in real time.
Inverse problem of central configurations in the collinear 5-body problem
Authors: Davis Candice , Geyer Scott , Johnson William , Xie Zhifu
Published: May 2018

In this paper, we study the inverse problem of collinear central configurations of a 5-body problem: given a collinear configuration q = (−s − 1, −1, r, 1, t + 1) of 5 bodies, does there exist positive masses to make the configuration central? Here we proved the following results: If r = 0 and s = t > 0, there always exist positive masses to make the configuration central and the masses are symmetrical such that m1 = m5, m2 = m4, and m3 is an arbitrary parameter. Specially if r = 0 and s=t=s¯, the configuration q=(−s¯−1,−1,0,1,s¯+1) is always a central configuration for any positive masses 0 < m2 = m4 < ∞ when m1 = m5 are fixed at particular values, which only depend on s¯ and m3. s¯ is the unique real root of a fifth order polynomial and numerically s¯≈1.396 812 289. If r = 0 and s ≠ t > 0, there also always exist positive masses to make the configuration central. For any r ∈ (0, 1) [or r ∈ (−1, 0)], there exist a set E14 (or E25) in the first quadrant of st-plane where every configuration is a central configuration for some positive masses. However, no configuration in the complement of E14 (or E25) is a central configuration for any positive masses.
Protein gradients in single cells induced by their coupling to “morphogen”-like diffusion
Authors: Nandi Saroj Kumar , Safran Sam A.
Published: May 2018

One of the many ways cells transmit information within their volume is through steady spatial gradients of different proteins. However, the mechanism through which proteins without any sources or sinks form such single-cell gradients is not yet fully understood. One of the models for such gradient formation, based on differential diffusion, is limited to proteins with large ratios of their diffusion constants or to specific protein-large molecule interactions. We introduce a novel mechanism for gradient formation via the coupling of the proteins within a single cell with a molecule, that we call a “pronogen,” whose action is similar to that of morphogens in multi-cell assemblies; the pronogen is produced with a fixed flux at one side of the cell. This coupling results in an effectively non-linear diffusion degradation model for the pronogen dynamics within the cell, which leads to a steady-state gradient of the protein concentration. We use stability analysis to show that these gradients are linearly stable with respect to perturbations.
Mechanical properties of silicon in subsurface damage layer from nano-grinding studied by atomistic simulation
Authors: Zhang Zhiwei , Chen Pei , Qin Fei , An Tong , Yu Huiping
Published: May 2018

Ultra-thin silicon wafer is highly demanded by semi-conductor industry. During wafer thinning process, the grinding technology will inevitably induce damage to the surface and subsurface of silicon wafer. To understand the mechanism of subsurface damage (SSD) layer formation and mechanical properties of SSD layer, atomistic simulation is the effective tool to perform the study, since the SSD layer is in the scale of nanometer and hardly to be separated from underneath undamaged silicon. This paper is devoted to understand the formation of SSD layer, and the difference between mechanical properties of damaged silicon in SSD layer and ideal silicon. With the atomistic model, the nano-grinding process could be performed between a silicon workpiece and diamond tool under different grinding speed. To reach a thinnest SSD layer, nano-grinding speed will be optimized in the range of 50-400 m/s. Mechanical properties of six damaged silicon workpieces with different depths of cut will be studied. The SSD layer from each workpiece will be isolated, and a quasi-static tensile test is simulated to perform on the isolated SSD layer. The obtained stress-strain curve is an illustration of overall mechanical properties of SSD layer. By comparing the stress-strain curves of damaged silicon and ideal silicon, a degradation of Young’s modulus, ultimate tensile strength (UTS), and strain at fracture is observed.
Magnetic rings
Authors: Dolbeault Jean , Esteban Maria J. , Laptev Ari , Loss Michael
Published: May 2018

We study functional and spectral properties of perturbations of the operator −(∂s+i a)2 in L2(S1). This operator appears when considering the restriction to the unit circle of a two-dimensional Schrödinger operator with the Bohm-Aharonov vector potential. We prove a Hardy-type inequality on R2 and, on S1, a sharp interpolation inequality and a sharp Keller-Lieb-Thirring inequality.
Effect of inductively coupled plasma and plasma parameters on magnetron sputtered Al-Doped ZnO highly conductive thin films at low-temperature
Authors: Sahu Bibhuti Bhusan , Jin Su Bong , Xiang Piao Jin , Kim Jay Bum , Han Jeon Geon
Published: May 2018

This work reports a detailed study on the low-temperature synthesis of highly conductive transparent Al-doped ZnO films using magnetron sputtering with the support of an inductively coupled plasma (ICP) source. It is seen that the ICP source is quite useful to provide significant ionization and excitation reactions conducive to the film growth in the magnetron plasmas. The effect of different plasma parameters on the film properties is investigated in detail. Data reveal that tailoring of vacancies of oxygen and extrinsic dopants (Al0 and Al3+) and plasma chemistry in high electron density discharges could provide simultaneous enrichment in the carriers' mobility and concentration. A plausible mechanism involving the correlation between the carrier mobility and the electron-hole interaction is realized for degenerately doped wide bandgap semiconductors.
Heat conduction tuning by hyperbranched nanophononic metamaterials
Authors: Li Bing , Tan K. T. , Christensen Johan
Published: May 2018

Phonon dispersion and thermal conduction properties of hyperbranched nanostructures with unique topological complexity are theoretically and numerically investigated in this research. We present analytical cantilever-in-mass models to analyze and control the inherent resonance hybridization in hyperbranched nanomembranes containing different configurations and cross sections. We show that these local resonances hosted by hyperbranched nanopillars can generate numerous flat bands in the phonon dispersion relation and dramatically lower the group velocities, consequently resulting in a significant reduction of the thermal conductivity. The applicability of the proposed analytical models in thermal conductivity tuning is demonstrated, and a superior performance in reducing the heat flux in nano-structured membranes is exhibited, which can potentially lead to improved thermoelectric energy conversion devices.
CdCl2 passivation of polycrystalline CdMgTe and CdZnTe absorbers for tandem photovoltaic cells
Authors: Swanson Drew E. , Reich Carey , Abbas Ali , Shimpi Tushar , Liu Hanxiao , Ponce Fernando A. , Walls John M. , Zhang Yong-Hang , Metzger Wyatt K. , Sampath W. S. , Holman Zachary C.
Published: May 2018

As single-junction silicon solar cells approach their theoretical limits, tandems provide the primary path to higher efficiencies. CdTe alloys can be tuned with magnesium (CdMgTe) or zinc (CdZnTe) for ideal tandem pairing with silicon. A II-VI/Si tandem holds the greatest promise for inexpensive, high-efficiency top cells that can be quickly deployed in the market using existing polycrystalline CdTe manufacturing lines combined with mature silicon production lines. Currently, all high efficiency polycrystalline CdTe cells require a chloride-based passivation process to passivate grain boundaries and bulk defects. This research examines the rich chemistry and physics that has historically limited performance when extending Cl treatments to polycrystalline 1.7-eV CdMgTe and CdZnTe absorbers. A combination of transmittance, quantum efficiency, photoluminescence, transmission electron microscopy, and energy-dispersive X-ray spectroscopy clearly reveals that during passivation, Mg segregates and out-diffuses, initially at the grain boundaries but eventually throughout the bulk. CdZnTe exhibits similar Zn segregation behavior; however, the onset and progression is localized to the back of the device. After passivation, CdMgTe and CdZnTe can render a layer that is reduced to predominantly CdTe electro-optical behavior. Contact instabilities caused by inter-diffusion between the layers create additional complications. The results outline critical issues and paths for these materials to be successfully implemented in Si-based tandems and other applications.
Realization of metamagnetic martensitic transformation with multifunctional properties in Co50V34Ga16 Heusler alloy
Authors: Liu Changqin , Li Zhe , Zhang Yuanlei , Huang Yinsheng , Ye Miaofu , Sun Xiaodong , Zhang Guojie , Cao Yiming , Xu Kun , Jing Chao
Published: May 2018

In this work, we have developed a ferromagnetic shape memory alloy Co50V34Ga16 with a metamagnetic martensitic transformation (MT) from the high-magnetization austenitic phase to the low-magnetization martensitic phase. As a consequence of a strong coupling between structure and magnetic degrees of freedom, the metamagnetic MT of this alloy is relatively sensitive to the external magnetic field, thus giving rise to a field-induced reverse MT. Associated with such a unique behavior, both considerable inverse magnetocaloric effect (9.6 J/kg K) and magnetostrain (0.07%) have also been obtained under the magnetic field change of 3 T. Our experimental results indicate that this kind of Co-V based alloy probably becomes an alternatively promising candidate for applications in magnetic sensors and magnetic refrigeration.
Thin film superconducting quantum interferometer with ultralow inductance
Authors: Bondarenko S. I. , Krevsun A. V. , Ilichev E. V. , Hubner U. , Koverya V. P. , Link S. I.
Published: May 2018

A simple method has been developed for manufacturing a thin film superconducting quantum interferometer (SQI) with ultralow inductance (∼10−13 H). Current-voltage and voltage-field characteristics of the SQI are presented. The basic design equations are obtained and confirmed experimentally. The SQI has been used for the first time to determine the penetration depth of a magnetic field into a film of 50% In-50% Sn alloy.
Pinning and critical currents of heterogeneous superconductors in different structural states
Authors: Sokolenko V. I. , Karas V. I.
Published: May 2018

The critical currents of a composite Nb3Sn-based superconductor are found to increase as a result of low intensity ultrasonic interactions. In terms of a mechanism for interactions of vortices with grain boundaries based on electron scattering at the boundaries, a reduction in the compressive forces in an Nb3Sn layer during ultrasonic interactions leads to an increase in the elementary pinning force because of a reduction in the coherence length and increases in the superconducting transition temperature and the electron specific heat. It is shown that for single-crystal niobium with a high density of uniformly distributed dislocations in fields close to Hc2, the field dependence of the volume pinning force corresponds to a system of effective point centers that satisfy a rarefaction criterion. The first order interaction of a vortex with these kinds of pinning centers greatly exceeds the characteristic for interactions of the vortex with single helical and edge dislocations.
Spatial characterization of the edge barrier in wide superconducting films
Authors: Sivakov A. G. , Turutanov O. G. , Kolinko A. E. , Pokhila A. S.
Published: May 2018

The current-induced destruction of superconductivity is discussed in wide superconducting thin films, whose width is greater than the magnetic field penetration depth, in weak magnetic fields. Particular attention is paid to the role of the boundary potential barrier (the Bin-Livingston barrier) in critical state formation and detection of the edge responsible for this critical state with different mutual orientations of external perpendicular magnetic field and transport current. Critical and resistive states of the film were visualized using the space-resolving low-temperature laser scanning microscopy (LTLSM) method, which enables detection of critical current-determining areas on the film edges. Based on these observations, a simple technique was developed for investigation of the critical state separately at each film edge, and for the estimation of residual magnetic fields in cryostats. The proposed method only requires recording of the current-voltage characteristics of the film in a weak magnetic field, thus circumventing the need for complex LTLSM techniques. Information thus obtained is particularly important for interpretation of studies of superconducting film single-photon light emission detectors.
Dissipation effects in superconducting heterostructures with tungsten nanorods as weak links
Authors: Shaternik V. E. , Shapovalov A. P. , Suvorov O. Yu. , Zhitlukhina E. S. , Belogolovskii M. A. , Febvre P. , Kordyuk A. A.
Published: May 2018

Thin-film hybrid heterostructures formed by superconducting molybdenum-rhenium-alloy films with a critical temperature of about 9 K and nanoscale silicon-based semiconducting interlayers with metallic tungsten nanorods have been fabricated and studied. Current-voltage characteristics of the junctions were measured at 4.2 K and under influence of 11 GHz microwave irradiation. The evidence of a quasi-one-dimensional transport through the tungsten weak links disrupted by phase-slip centers was revealed in MoRe/doped Si/MoRe trilayers under irradiation by a high-frequency field. Also, measured current-voltage characteristics of five-layer MoRe/doped Si/MoRe/doped Si/MoRe devices exhibit a strong influence of a dissipation state in the MoRe interlayer. Namely, the switching from a superconducting state with low dissipation to a finite-conductance regime can be initiated by the emergence of an extra phase-slip center in the MoRe interlayer. Possible physical mechanisms of the two findings are discussed.
Through-hole energy-density threshold of silicon induced by combined millisecond and nanosecond pulsed laser
Authors: Lv Xueming , Pan Yunxiang , Jia Zhichao , Li Zewen , Ni Xiaowu
Published: May 2018

We report herein the experimental investigation of the through-hole energy-density threshold of silicon irradiated by a double-pulse laser. The double pulse consists of a 1 ms pulse and a time-delayed 5 ns pulse and is referred to as a combined-pulse laser (CPL). A modified level-set method is used to calculate the process of millisecond laser drilling, and we study how the time delay affects the CPL. The results show that the through-hole energy-density threshold decreases with increasing delay time between the CPL pulses. In addition, the energy density of the nanosecond pulse strongly affects the through-hole energy-density threshold. We also consider the thickness and the doping concentration of the silicon wafers. Compared with the results for single-ms-pulse irradiation, the CPL produces a better through-hole energy-density threshold because the surface ablation caused by the nanosecond pulse increases the energy absorbed by the silicon wafer from the millisecond pulse.
Monte Carlo sampling in diffusive dynamical systems
Authors: Tapias Diego , Sanders David P. , Altmann Eduardo G.
Published: May 2018

We introduce a Monte Carlo algorithm to efficiently compute transport properties of chaotic dynamical systems. Our method exploits the importance sampling technique that favors trajectories in the tail of the distribution of displacements, where deviations from a diffusive process are most prominent. We search for initial conditions using a proposal that correlates states in the Markov chain constructed via a Metropolis-Hastings algorithm. We show that our method outperforms the direct sampling method and also Metropolis-Hastings methods with alternative proposals. We test our general method through numerical simulations in 1D (box-map) and 2D (Lorentz gas) systems.
In-situ co-doping of sputter-deposited TiO2:WN films for the development of photoanodes intended for visible-light electro-photocatalytic degradation of emerging pollutants
Authors: Delegan N. , Pandiyan R. , Komtchou S. , Dirany A. , Drogui P. , El Khakani M. A.
Published: May 2018

We report on the magnetron sputtering deposition of in-situ codoped TiO2:WN films intended for electro-photocatalytic (EPC) applications under solar irradiation. By varying the RF-magnetron sputtering deposition parameters, we were able to tune the in-situ incorporation of both N and W dopants in the TiO2 films over a wide concentration range (i.e., 0–9 at. % for N and 0–3 at. % for W). X-ray photoelectron spectroscopy analysis revealed that both dopants are mostly of a substitutional nature. The analysis of the UV-Vis transmission spectra of the films confirmed that the optical bandgap of both TiO2:N and TiO2:WN films can be significantly narrowed (from 3.2 eV for undoped-TiO2 down to ∼2.3 eV for the doped ones) by tuning their dopant concentrations. We were thus able to pinpoint an optimal window for both dopants (N and W) where the TiO2:WN films exhibit the narrowest bandgap. Moreover, the optimal codoping conditions greatly reduce the recombination defect state density compared to the monodoped TiO2:N films. These electronically passivated TiO2:WN films are shown to be highly effective for the EPC degradation of atrazine (pesticide pollutant) under sunlight irradiation (93% atrazine degraded after only 30 min of EPC treatment). Indeed, the optimally codoped TiO2:WN photoanodes were found to be more efficient than both the undoped-TiO2 and equally photosensitized TiO2:N photoanodes (by ∼70% and ∼25%, respectively) under AM1.5 irradiation.
On the relationship between field cycling and imprint in ferroelectric Hf0.5Zr0.5O2
Authors: Fengler F. P. G. , Hoffmann M. , Slesazeck S. , Mikolajick T. , Schroeder U.
Published: May 2018

Manifold research has been done to understand the detailed mechanisms behind the performance instabilities of ferroelectric capacitors based on hafnia. The wake-up together with the imprint might be the most controversially discussed phenomena so far. Among crystallographic phase change contributions and oxygen vacancy diffusion, electron trapping as the origin has been discussed recently. In this publication, we provide evidence that the imprint is indeed caused by electron trapping into deep states at oxygen vacancies. This impedes the ferroelectric switching and causes a shift of the hysteresis. Moreover, we show that the wake-up mechanism can be caused by a local imprint of the domains in the pristine state by the very same root cause. The various domain orientations together with an electron trapping can cause a constriction of the hysteresis and an internal bias field in the pristine state. Additionally, we show that this local imprint can even cause almost anti-ferroelectric like behavior in ferroelectric films.
Note: Space qualified solid state photon counting detector with reduced detection delay temperature drift
Authors: Prochazka Ivan , Blazej Josef , Kodet Jan
Published: May 2018

The solid state photon counting detector is one of the key components of a measurement chain for laser time transfer ground to space. The photon counting approach significantly reduces systematic errors of the time transfer. The requirements put on the detection precision and the stability of laser time transfer are increasing and reaching sub-picosecond levels now. The temperature variations in the space environment limit the long term detection delay stability of detectors. Therefore, we have modified the existing space qualified solid state photon counter control circuit which compensates to a high degree the temperature variations of detection delay. We have optimized the detection delay change with operating temperature and reached the lowest temperature coefficient as low as 20 fs/K in a temperature range of +22 to +46 °C. The timing resolution and photon detection probability remained unchanged at the values of 40 ps FWHM and 30%, respectively. Thanks to the low temperature drift of the detector, the limiting precision of the laser time transfer chain characterized by time deviation is lower than 40 fs for 2000 s averaging time. These detection delay stability parameters are, to our knowledge, the best ever reported for any photon counting detector. This modification of the detector control circuit did not affect the space qualification of the device, which is expected to be used in future laser time transfer space missions.
Prospects for laser-driven ion acceleration through controlled displacement of electrons by standing waves
Authors: Magnusson J. , Mackenroth F. , Marklund M. , Gonoskov A.
Published: May 2018

During the interaction of intense femtosecond laser pulses with various targets, the natural mechanisms of laser energy transformation inherently lack temporal control and thus commonly do not provide opportunities for a controlled generation of a well-collimated, high-charge beam of ions with a given energy of particular interest. In an effort to alleviate this problem, it was recently proposed that the ions can be dragged by an electron bunch trapped in a controllably moving potential well formed by laser radiation. Such standing-wave acceleration (SWA) can be achieved through reflection of a chirped laser pulse from a mirror, which has been formulated as the concept of chirped-standing-wave acceleration (CSWA). Here, we analyse general feasibility aspects of the SWA approach and demonstrate its reasonable robustness against field structure imperfections, such as those caused by misalignment, ellipticity, and limited contrast. Using this, we also identify prospects and limitations of the CSWA concept.
Helium atom line-intensity ratios as an integrated diagnostic tool for low-pressure and low-density plasmas
Authors: Ueda Akira , Shikama Taiichi , Teramoto Tatsuya , Higashi Takanori , Iida Yohei , Hasuo Masahiro
Published: May 2018

The intensity ratios between specific pairs of helium atom (HeI) emission lines are functions of the electron temperature (Te) and density (ne), and these functions have been used for the analysis of Te and ne in various types of discharge plasma. We applied this method to a low-density (ne < 1018 m−3) plasma, where the procedure of the analysis is markedly different from that of higher-density plasmas. The 21S and 23S metastable atom densities are affected by transport, making it practically necessary to set Te, ne, the metastable atom densities, and the optical escape factors, which represent the effect of photoexcitation, as unknown variables and determine them simultaneously. Conversely, the transport of metastable atoms can be evaluated from the analysis.
Temperature-induced collapse of a disordered peptide observed by three sampling methods in molecular dynamics simulations
Authors: Hicks Alan , Zhou Huan-Xiang
Published: May 2018

The conformational ensembles of a disordered peptide, polyglutamine Q15, over a wide temperature range were sampled using multiple replicates of conventional molecular dynamics (cMD) simulations as well as two enhanced sampling methods, temperature replica exchange (TREMD) and replica exchange with solute tempering (REST). The radius of gyration, asphericity, secondary structure, and hydrogen bonding patterns were used for the comparison of the sampling methods. Overall, the three sampling methods generated similar conformational ensembles, with progressive collapse at higher temperatures. Although accumulating the longest simulation time (90 μs), cMD at room temperature missed a small subspace that was sampled by both TREMD and REST. This subspace was high in α-helical content and separated from the main conformational space by an energy barrier. REST used less simulation time than TREMD (36 μs versus 42 μs), and this gap is expected to widen significantly for larger disordered proteins. We conclude that REST is the method of choice for conformational sampling of intrinsically disordered proteins.
Multiscale enhanced sampling of glucokinase: Regulation of the enzymatic reaction via a large scale domain motion
Authors: Moritsugu Kei , Terada Tohru , Kokubo Hironori , Endo Satoshi , Tanaka Toshimasa , Kidera Akinori
Published: May 2018

Enhanced sampling yields a comprehensive structural ensemble or a free energy landscape, which is beyond the capability of a conventional molecular dynamics simulation. Our recently developed multiscale enhanced sampling (MSES) method employs a coarse-grained model coupled with the target physical system for the efficient acceleration of the dynamics. MSES has demonstrated applicability to large protein systems in solution, such as intrinsically disordered proteins and protein-protein and protein-ligand interactions. Here, we applied the MSES simulation to an important drug discovery target, glucokinase (GCK), to elucidate the structural basis of the positive cooperativity of the enzymatic reaction at an atomistic resolution. MSES enabled us to compare two sets of the free energy landscapes of GCK, for the glucose-bound and glucose-unbound forms, and thus demonstrated the drastic change of the free energy surface depending on the glucose concentration. In the glucose-bound form, we found two distinct basins separated by a high energy barrier originating from the domain motion and the folding/unfolding of the α13 helix. By contrast, in the glucose-unbound form, a single flat basin extended to the open and super-open states. These features illustrated the two distinct phases achieving the cooperativity, the fast reaction cycle staying in the closed state at a high glucose concentration and the slow cycle primarily in the open/super-open state at a low concentration. The weighted ensemble simulations revealed the kinetics of the structural changes in GCK with the synergetic use of the MSES results; the rate constant of the transition between the closed state and the open/super-open states, kC/O = 1.1 ms−1, is on the same order as the experimental catalytic rate, kcat = 0.22 ms−1. Finally, we discuss the pharmacological activities of GCK activators (small molecular drugs modulating the GCK activity) in terms of the slight changes in the domain motion, depending on their chemical structures as regulators. The present study demonstrated the capability of the enhanced sampling and the associated kinetic calculations for understanding the atomistic structural dynamics of protein systems in physiological environments.
Simple method for the characterization of intense Laguerre-Gauss vector vortex beams
Authors: Allahyari E. , JJ Nivas J. , Cardano F. , Bruzzese R. , Fittipaldi R. , Marrucci L. , Paparo D. , Rubano A. , Vecchione A. , Amoruso S.
Published: May 2018

We report on a method for the characterization of intense, structured optical fields through the analysis of the size and surface structures formed inside the annular ablation crater created on the target surface. In particular, we apply the technique to laser ablation of crystalline silicon induced by femtosecond vector vortex beams. We show that a rapid direct estimate of the beam waist parameter is obtained through a measure of the crater radii. The variation of the internal and external radii of the annular crater as a function of the laser pulse energy, at fixed number of pulses, provides another way to evaluate the beam spot size through numerical fitting of the obtained experimental data points. A reliable estimate of the spot size is of paramount importance to investigate pulsed laser-induced effects on the target material. Our experimental findings offer a facile way to characterize focused, high intensity complex optical vector beams which are more and more applied in laser-matter interaction experiments.
Bernstein modes in a non-neutral plasma column
Authors: Walsh Daniel , Dubin Daniel H. E.
Published: May 2018

This paper presents theory and numerical calculations of electrostatic Bernstein modes in an inhomogeneous cylindrical plasma column. These modes rely on finite Larmor radius effects to propagate radially across the column until they are reflected when their frequency matches the upper hybrid frequency. This reflection sets up an internal normal mode on the column and also mode-couples to the electrostatic surface cyclotron wave (which allows the normal mode to be excited and observed using external electrodes). Numerical results predicting the mode spectra, using a novel linear Vlasov code on a cylindrical grid, are presented and compared to an analytical Wentzel Kramers Brillouin (WKB) theory. A previous version of the theory [D. H. E. Dubin, Phys. Plasmas 20(4), 042120 (2013)] expanded the plasma response in powers of 1/B, approximating the local upper hybrid frequency, and consequently, its frequency predictions are spuriously shifted with respect to the numerical results presented here. A new version of the WKB theory avoids this approximation using the exact cold fluid plasma response and does a better job of reproducing the numerical frequency spectrum. The effect of multiple ion species on the mode spectrum is also considered, to make contact with experiments that observe cyclotron modes in a multi-species pure ion plasma [M. Affolter et al., Phys. Plasmas 22(5), 055701 (2015)].
Coupled-cluster treatment of molecular strong-field ionization
Authors: Jagau Thomas-C.
Published: May 2018

Ionization rates and Stark shifts of H2, CO, O2, H2O, and CH4 in static electric fields have been computed with coupled-cluster methods in a basis set of atom-centered Gaussian functions with a complex-scaled exponent. Consideration of electron correlation is found to be of great importance even for a qualitatively correct description of the dependence of ionization rates and Stark shifts on the strength and orientation of the external field. The analysis of the second moments of the molecular charge distribution suggests a simple criterion for distinguishing tunnel and barrier suppression ionization in polyatomic molecules.
Dynamical analysis of surface-insulated planar wire array Z-pinches
Authors: Li Yang , Sheng Liang , Hei Dongwei , Li Xingwen , Zhang Jinhai , Li Mo , Qiu Aici
Published: May 2018

The ablation and implosion dynamics of planar wire array Z-pinches with and without surface insulation are compared and discussed in this paper. This paper first presents a phenomenological model named the ablation and cascade snowplow implosion (ACSI) model, which accounts for the ablation and implosion phases of a planar wire array Z-pinch in a single simulation. The comparison between experimental data and simulation results shows that the ACSI model could give a fairly good description about the dynamical characteristics of planar wire array Z-pinches. Surface insulation introduces notable differences in the ablation phase of planar wire array Z-pinches. The ablation phase is divided into two stages: insulation layer ablation and tungsten wire ablation. The two-stage ablation process of insulated wires is simulated in the ACSI model by updating the formulas describing the ablation process.
Airborne ultrasound surface motion camera: Application to seismocardiography
Authors: Shirkovskiy P. , Laurin A. , Jeger-Madiot N. , Chapelle D. , Fink M. , Ing R. K.
Published: May 2018

The recent achievements in the accelerometer-based seismocardiography field indicate a strong potential for this technique to address a wide variety of clinical needs. Recordings from different locations on the chest can give a more comprehensive observation and interpretation of wave propagation phenomena than a single-point recording, can validate existing modeling assumptions (such as the representation of the sternum as a single solid body), and provide better identifiability for models using richer recordings. Ultimately, the goal is to advance our physiological understanding of the processes to provide useful data to promote cardiovascular health. Accelerometer-based multichannel system is a contact method and laborious for use in practice, and also even ultralight accelerometers can cause non-negligible loading effects. We propose a contactless ultrasound imaging method to measure thoracic and abdominal surface motions, demonstrating that it is adequate for typical seismocardiogram (SCG) use. The developed method extends non-contact surface-vibrometry to fast 2D mapping by originally combining multi-element airborne ultrasound arrays, a synthetic aperture implementation, and pulsed-waves. Experimental results show the ability of the developed method to obtain 2D seismocardiographic maps of the body surface 30 × 40 cm2 in dimension, with a temporal sampling rate of several hundred Hz, using ultrasound waves with the central frequency of 40 kHz. Our implementation was validated in-vivo on eight healthy human participants. The shape and position of the zone of maximal absolute acceleration and velocity during the cardiac cycle were also observed. This technology could potentially be used to obtain more complete cardio-vascular information than single-source SCG in and out of clinical environments, due to enhanced identifiability provided by the distributed measurements, and observation of propagation phenomena.
The paradox of characteristics of silicon detectors operated at temperature close to liquid helium
Authors: Eremin V. , Shepelev A. , Verbitskaya E. , Zamantzas C. , Galkin A.
Published: May 2018

The aim of this study is to give characterization of silicon p+/n/n+ detectors for the monitoring systems of the Large Hadron Collider machine at CERN with the focus on justifying the choice of silicon resistivity for the detector operation at the temperature of 1.9–10 K. The detectors from n-type silicon with the resistivity of 10, 4.5, and 0.5 kΩ cm were investigated at the temperature from 293 up to 7 K by the Transient Current Technique with a 660 nm pulse laser and alpha-particles. The shapes of the detector current pulse response allowed revealing a paradox in the properties of shallow donors of phosphorus, i.e., native dopants in the n-type Si. There was no carrier freeze-out on the phosphorus energy levels in the space charge region (SCR), and they remained positively charged irrespective of temperature, thus limiting the depleted region depth. As for the base region of a partially depleted detector, the levels became neutral at T < 28 K, which transformed silicon to an insulator. The reduction of the activation energy for carrier emission in the detector SCR estimated in the scope of the Poole-Frenkel effect failed to account for the impact of the electric field on the properties of phosphorus levels. The absence of carrier freeze-out in the SCR justifies the choice of high resistivity silicon as the only proper material for detector operation in a fully depleted mode at extremely low temperature.
First-principles calculations of phonons and Raman and infrared spectra in Cd-IV-N2 compounds
Authors: Lyu Sai , Lambrecht Walter R. L.
Published: May 2018

A first-principles study of the phonons at the zone center in Cd-IV-N2 compounds is presented with IV = Si, Ge, Sn. The calculations are performed for the most likely Pbn21 crystal structure, after showing that it is indeed lower in total energy compared to the closely related Pmc21 structure. The normal mode frequencies are calculated using density functional perturbation theory and symmetry labeled. The longitudinal optical-transverse optical splittings are determined using the Born effective charges which are also reported. These are used to simulate polarized Raman spectra for different scattering configurations as well as the infrared absorption and reflection spectra. The mode frequencies are found to decrease from Si to Ge to Sn as group-IV cation. The spectra show a wide variety of number of prominent peaks and relative intensities in spite of the great similarities of these three materials. Phonon densities of states and their analysis in atom by atom contributions are also reported.
Silicon-on-insulator with hybrid orientations for heterogeneous integration of GaN on Si (100) substrate
Authors: Zhang Runchun , Zhao Beiji , Huang Kai , You Tiangui , Jia Qi , Lin Jiajie , Zhang Shibin , Yan Youquan , Yi Ailun , Zhou Min , Ou Xin
Published: May 2018

Heterogeneous integration of materials pave a new way for the development of the microsystem with miniaturization and complex functionalities. Two types of hybrid silicon on insulator (SOI) structures, i.e., Si (100)-on-Si (111) and Si (111)-on-Si (100), were prepared by the smart-cut technique, which is consist of ion-slicing and wafer bonding. The precise calculation of the lattice strain of the transferred films without the epitaxial matching relationship to the substrate was demonstrated based on X-ray diffraction (XRD) measurements. The XRD and Raman measurement results suggest that the transferred films possess single crystalline quality. With a chemical mechanical polishing (CMP) process, the surface roughness of the transferred thin films can be reduced from 5.57 nm to 0.30 nm. The 4-inch GaN thin film epitaxially grown on the as-prepared hybrid SOI of Si (111)-on-Si (100) by metalorganic chemical vapor deposition (MOCVD) is of improved quality with a full width at half maximum (FWHM) of 672.54 arcsec extracted from the XRD rocking curve and small surface roughness of 0.40 nm. The wafer-scale GaN on Si (111)-on-Si (100) can serve as a potential platform for the one chip integration of GaN-based high electron mobility transistors (HEMT) or photonics with the Si (100)-based complementary metal oxide semiconductor (CMOS).
Effect of post-implantation annealing on Al–N isoelectronic trap formation in silicon: Al–N pair formation and defect recovery mechanisms
Authors: Mori Takahiro , Morita Yukinori , Matsukawa Takashi
Published: May 2018

The effect of post-implantation annealing (PIA) on Al–N isoelectronic trap (IET) formation in silicon has been experimentally investigated to discuss the Al–N IET formation and implantation-induced defect recovery mechanisms. We performed a photoluminescence study, which indicated that self-interstitial clusters and accompanying vacancies are generated in the ion implantation process. It is supposed that Al and N atoms move to the vacancy sites and form stable Al–N pairs in the PIA process. Furthermore, the PIA process recovers self-interstitial clusters while transforming their atomic configuration. The critical temperature for the formation/dissociation of Al–N pairs was found to be 450 °C, with which we describe the process integration for devices utilizing Al–N IET technology.
High-mobility field-effect transistor based on crystalline ZnSnO3 thin films
Authors: Minato Hiroya , Fujiwara Kohei , Tsukazaki Atsushi
Published: May 2018

We propose crystalline ZnSnO3 as a new channel material for field-effect transistors. By molecular-beam epitaxy on LiNbO3(0001) substrates, we synthesized films of ZnSnO3, which crystallizes in the LiNbO3-type polar structure. Field-effect transistors on ZnSnO3 exhibit n-type operation with field-effect mobility of as high as 45 cm2V−1s−1 at room temperature. Systematic examination of the transistor operation for channels with different Zn/Sn compositional ratios revealed that the observed high-mobility reflects the nature of stoichiometric ZnSnO3 phase. Moreover, we found an indication of coupling of transistor characteristics with intrinsic spontaneous polarization in ZnSnO3, potentially leading to a distinct type of polarization-induced conduction.
Age of a charcoal band in fluvial sediments, Keiyasi, Sigatoka Valley, Fiji: possible indicator of a severe drought throughout the Southwest Pacific 4500-5000 years ago
Authors: Nunn P. D. , Thaman R. R. , Duffy L. , Finikaso S. , Ram N. , Swamy M.
Published: May 2018

A 14C date for a charcoal band near the base of the High (10 m) Terrace in the middle Sigatoka Valley (western Viti Levu Island, Fiji) shows that this terrace accumulated mostly within the past 4-5000 years showing it to be a Holocene rather than a Pleistocene (Last Interglacial) landform as previously thought. The charcoal band also indicates that there was extensive, perhaps catastrophic, burning of forests and perhaps an associated local extirpation/extinction of forest taxa. The notion that humans may have been responsible for the forest burning represented by this charcoal band is rejected on account of its age predating known human arrival by at least one thousand years. Attention is drawn to the contemporaneity of this charcoal band and those found in Bonatoa Bog (southeast Viti Levu Island) and in New Caledonia, some 1300 km southwest of Fiji, suggesting that catastrophic forest burning during this period may have been widespread and a regionwide response to a period of prolonged aridity 4500-5000 years ago, possibly associated with a unusually severe El Niño event.
β-Damascenone-yielding precursor(s) from Cabernet Sauvignon grapes
Authors: Naiker Mani
Published: May 2018

β-Damascenone, a potent aroma component of in a variety of grapes and wines, has a sensory threshold of approximately 2ng/L in water. This C13 norisoprenoid ketone is principally generated from hydrolyzable precursors, which was glycosidically bound. Isolation of β-damascenone-yielding precursors from Cabernet Sauvignon grape skins using C18 reversed phase chromatography followed by droplet countercurrent chromatography yielded multiple chromatographically distinguishable precursor fractions. The existence of multiple precursors was further evident from the varying ratios of 3-hydroxy- β-damascone (the by-product): β-damascenone generated upon acid hydrolysis of the chromatographically distinguishable precursor fractions.
Heavy metal contamination of the Lami coastal environment, Fiji
Authors: Gangaiya Philomena , Tabudravu Jioji , South Robin , Sotheeswaran Subramanium
Published: May 2018

Contamination of the coastal environment of small island countries is of concern because people's livelihoods in these countries are intimately linked to the resources of the coastal zone. The Lami estuary in Fiji is located downstream of an industrial area and is used extensively for fishing and other recreational activities. Sediment samples from twenty-nine sites within the area were analysed for copper, lead and zinc to determine whether the area is contaminated with heavy metals. Within the estuary, significant enrichment is evident, with heavy metal concentrations exceeding some of those from other known contaminated sites in the country. Although copper contamination appears to be restricted to a few sites within the estuary, contamination with lead and zinc seems to be spreading to areas further away from the shore. Metal distribution patterns clearly indicate adjacent factories to be the main source of contamination. The results show that contrary to popular belief, highly contaminated sites do exist in the relatively pristine coastal environments of island countries like Fiji.
Notes on the Natural History of Cycas seemannii (Cycadaceae)
Authors: Keppel Gunnar
Published: May 2018

Cycas seemannii occurs in several habitats in Vanuatu, New Caledonia, Fiji and Tonga, but is mostly coastal. Growth rates are about 5-15cm.yr-1 and sex ratios observed were almost neutral. Mechanisms to survive in adverse environments are discussed. Female plants were found to produce, on average, longer leaves with more leaflets than male plants. Larvae of an unidentified moth, which are parasitised by at least two species of wasps, mine the leaflets of C. seemannii. Reproduction occurs mainly by seeds and bulbils. Wind appears to be the major pollination agent. Seed dispersal, other than oceanic, appears to be inefficient.