bluuebunny/crossref_metadata_2025 huggingface dataset:
Lightweight and low‐cost thin film photovoltaics for large area extra‐terrestrial applications
Authors: Lamb Daniel Ash , Irvine Stuart J.C. , Clayton Andrew James , Barrioz Vincent , Kartopu Giray , Baker Mark A. , Underwood C.I. , Grilli Rossana , Kimber Rick , Hall James
Published: April 2015

This work describes progress towards achieving a flexible, high specific power and low‐cost photovoltaic (PV) for emerging large area space applications. The study reports the highest conversion efficiency of 15.3% AM1.5G for a CdTe device on ultra‐thin cerium‐doped cover glass, the standard protective material for extra‐terrestrial PVs. The deposition technique used for all of the semiconductor layers comprising the device structure was atmospheric pressure metal organic chemical vapour deposition. Improvements to the device structure over those previously reported led to a Voc of 788 mV and a relatively low series resistance of 3.3 Ω·cm2. These were largely achieved by the introduction of a post‐growth air anneal and a refinement of the front contact bus bars, respectively. The aluminium‐doped zinc oxide transparent conductive oxide, being the first layer applied to the cover glass, was subject to thermal shock cycling +80 to (−) 196°C to test the adhesion under the extreme conditions likely to be encountered for space application. Scotch Tape testing and sheet resistance measurements before and after the thermal shock testing demonstrated that the aluminium‐doped zinc oxide remained well adhered to the cover glass and its electrical performance unchanged.
Modified Covariance Matrix Adaptation – Evolution Strategy algorithm for constrained optimization under uncertainty, application to rocket design
Authors: Chocat Rudy , Brevault Loïc , Balesdent Mathieu , Defoort Sébastien
Published: April 2015

The design of complex systems often induces a constrained optimization problem under uncertainty. An adaptation of CMA-ES(λ, μ) optimization algorithm is proposed in order to efficiently handle the constraints in the presence of noise. The update mechanisms of the parametrized distribution used to generate the candidate solutions are modified. The constraint handling method allows to reduce the semi-principal axes of the probable research ellipsoid in the directions violating the constraints. The proposed approach is compared to existing approaches on three analytic optimization problems to highlight the efficiency and the robustness of the algorithm. The proposed method is used to design a two stage solid propulsion launch vehicle.
Impact of Preoperative Hematocrit Level on Length of Stay after Surgery on the Lumbar Spine
Authors: Guan Jian , Karsy Michael , Schmidt Meic H. , Bisson Erica F.
Published: April 2015

Study Design

Retrospective case series.

Objective

Recent studies suggest that baseline hematocrit (Hct) levels may affect the surgical outcomes after orthopedic procedures. The authors examined whether preoperative Hct values had a significant effect on the hospital length of stay (LoS) after lumbar spinal procedures.

Methods

We retrospectively reviewed patients who underwent routine lumbar spine procedures from November 2012 through September 2013. Patients were included if they had both a baseline Hct and hospital LoS recorded. Patients were divided into two groups: those with an Hct ≥ 40% (nonanemic) and those with an Hct < 40% (anemic). LoS after surgery was evaluated for each group.

Results

One hundred seventeen patients underwent lumbar spine procedures for lumbar stenosis ( n = 34), symptomatic lumbar disk herniation ( n = 39), lumbar spondylolisthesis ( n = 26), lumbar adjacent segment disease ( n = 8), or symptomatic recurrent lumbar disk herniation ( n = 10). Mean LoS was 3.3 and 2.4 days in anemic (27 patients) and nonanemic groups (90 patients), respectively ( p = 0.02). The linear regression analysis demonstrated that a decrease in Hct was associated with a longer stay. A decrease from preoperative to postoperative day 1 Hct of 3.5 points resulted in an increased LoS of 1 day ( R2 = 0.145; p = 0.002). The correlation of Hct decrease with longer LoS remained (β = 0.167, p = 0.006) after adjusting for other variables with multivariate regression analysis.

Conclusions

Lower preoperative Hct or a substantial decrease in Hct may contribute to longer hospitalization after lumbar spine surgery. These findings should prompt an investigation into the strategies for optimizing Hct levels in patients with preoperative anemia prior to lumbar spine procedures.
Traumatic Spondylolisthesis of the Axis Vertebra in Adults
Authors: Schleicher Philipp , Scholz Matti , Pingel Andreas , Kandziora Frank
Published: April 2015

Study Design

Narrative review.

Objective

To elucidate the current concepts in diagnosis and treatment of traumatic spondylolisthesis of the axis.

Methods

Literature review using PubMed, Google Scholar, and Cochrane databases.

Results

The traumatic spondylolisthesis of the axis accounts to 5% of all cervical spine injuries and is defined by a bilateral separation of the C2 vertebral body from the neural arch. The precise location of the fracture line may vary widely. For understanding the pathobiomechanics, the involvement of the C2–C3 disk is essential. Although its synonym “hangman's fracture” suggests an extension moment as primary injury mechanism, flexion moments are also proven to cause such fracture morphology. The axial force vector (distraction versus compression) is thought to have a significant effect on the neurologic involvement. The most widely accepted classifications, according to Effendi and modified by Levine, regard the displacement of the C2 vertebral body and possible locking of the facet joints. For decisions on conservative versus surgical therapy, a definitive statement about the stability is essential. The stability is determined by involvement of the C2–C3 disk and longitudinal ligaments, which frequently cannot be assessed by X-ray or computed tomography alone. The assessment of this soft tissue injury therefore requires additional imaging either by magnetic resonance imaging to display the disk and longitudinal ligaments or dynamic fluoroscopy to assess functional behavior of the C2–C3 motion segment. If stability is proven, an immobilization of the cervical spine in a semirigid cervical collar is sufficient. Unstable lesions require surgical stabilization. The standard procedure is an anterior C2–C3 diskectomy and fusion, because of the lower morbidity of the anterior approach and the motion preservation between C1 and C2. In rare cases (irreducible locked facet joints, the necessity of decompression of the vertebral artery, contraindication for anterior approach), a posterior approach is sometimes necessary. Isolated direct screw osteosynthesis is of little value, because it only makes sense in cases with an intact C2–C3 disk, which is usually regarded as stable and therefore might be treated conservatively.

Conclusions

Overall, the clinical evidence regarding traumatic spondylolisthesis of the axis is very low and mainly based on small case series, expert opinion, laboratory findings, and theoretical considerations.
From chemical systems to systems chemistry: Patterns in space and time
Authors: Showalter Kenneth , Epstein Irving R.
Published: April 2015

We present a brief, idiosyncratic overview of the past quarter century of progress in nonlinear chemical dynamics and discuss what we view as the most exciting recent developments and some challenges and likely areas of progress in the next 25 years.
Response analysis of a laminar premixed M-flame to flow perturbations using a linearized compressible Navier-Stokes solver
Authors: Blanchard M. , Schuller T. , Sipp D. , Schmid P. J.
Published: April 2015

The response of a laminar premixed methane-air flame subjected to flow perturbations around a steady state is examined experimentally and using a linearized compressible Navier-Stokes solver with a one-step chemistry mechanism to describe combustion. The unperturbed flame takes an M-shape stabilized both by a central bluff body and by the external rim of a cylindrical nozzle. This base flow is computed by a nonlinear direct simulation of the steady reacting flow, and the flame topology is shown to qualitatively correspond to experiments conducted under comparable conditions. The flame is then subjected to acoustic disturbances produced at different locations in the numerical domain, and its response is examined using the linearized solver. This linear numerical model then allows the componentwise investigation of the effects of flow disturbances on unsteady combustion and the feedback from the flame on the unsteady flow field. It is shown that a wrinkled reaction layer produces hydrodynamic disturbances in the fresh reactant flow field that superimpose on the acoustic field. This phenomenon, observed in several experiments, is fully interpreted here. The additional perturbations convected by the mean flow stem from the feedback of the perturbed flame sheet dynamics onto the flow field by a mechanism similar to that of a perturbed vortex sheet. The different regimes where this mechanism prevails are investigated by examining the phase and group velocities of flow disturbances along an axis oriented along the main direction of the flow in the fresh reactant flow field. It is shown that this mechanism dominates the low-frequency response of the wrinkled shape taken by the flame and, in particular, that it fully determines the dynamics of the flame tip from where the bulk of noise is radiated.
Instabilities in a capacitively coupled oxygen plasma
Authors: Küllig C. , Wegner Th. , Meichsner J.
Published: April 2015

Periodic fluctuations in the frequency range from 0.3 to 3 kHz were experimentally investigated in capacitively coupled radio frequency (13.56 MHz) oxygen plasma. The Gaussian beam microwave interferometry directly provides the line integrated electron density fluctuations. A system of two Langmuir probes measured the floating potential spatially (axial, radial) and temporally resolved. Hence, the floating potential fluctuation development is mapped within the discharge volume and provides a kind of discharge breathing and no wave propagation. Finally, it was measured the optical emission pattern of atomic oxygen during the fluctuation as well as the RF phase resolved optical emission intensity at selected phase position of the fluctuation by an intensified charge-coupled device camera. The deduced excitation rate pattern reveals the RF sheath dynamics and electron heating mechanisms, which is changing between low and high electronegativity during a fluctuation cycle. A perturbation calculation was taken into account using a global model with 15 elementary collision processes in the balance equations for the charged plasma species (O2+, e, O−, O2−) and a harmonic perturbation. The calculated frequencies agree with the experimentally observed frequencies. Whereby, the electron attachment/detachment processes are important for the generation of this instability.
Hyperfine structure and magnetic properties of Zn doped Co2Z hexaferrite investigated by high-field Mössbauer spectroscopy
Authors: Lim Jung Tae , Kim Chul Sung
Published: April 2015

The polycrystalline samples of Ba3Co2−xZnxFe24O41 (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were synthesized by the standard solid-state-reaction method. Based on the XRD patterns analyzed by Rietveld refinement, the structure was determined to be single-phased hexagonal with space group of P63/mmc. With increasing Zn ion concentration, the unit cell volume (Vu) of samples was increased, as the sites of Fe3+ ions changed from tetrahedral to octahedral sites. We have obtained zero-field Mössbauer spectra of all samples at various temperatures ranging from 4.2 to 750 K. The measured spectra below TC were analyzed with six distinguishable sextets due to the superposition of ten-sextets for Fe sites, corresponding to the Z-type hexagonal ferrite. Also, the hyperfine field (Hhf) and electric quadrupole shift (EQ) have shown abrupt changes around spin transition temperature (TS). In addition, Mössbauer spectra of all samples at 4.2 K were taken with an applied field ranging from 0 to 50 kOe, which indicates the decrease in the canting angle between applied field and Hhf of samples with increasing Zn concentration.
Particle visualization in high-power impulse magnetron sputtering. I. 2D density mapping
Authors: Britun Nikolay , Palmucci Maria , Konstantinidis Stephanos , Snyders Rony
Published: April 2015

Time-resolved characterization of an Ar-Ti high-power impulse magnetron sputtering discharge has been performed. This paper deals with two-dimensional density mapping in the discharge volume obtained by laser-induced fluorescence imaging. The time-resolved density evolution of Ti neutrals, singly ionized Ti atoms (Ti+), and Ar metastable atoms (Armet) in the area above the sputtered cathode is mapped for the first time in this type of discharges. The energetic characteristics of the discharge species are additionally studied by Doppler-shift laser-induced fluorescence imaging. The questions related to the propagation of both the neutral and ionized discharge particles, as well as to their spatial density distributions, are discussed.
Sensitive fast electron spectrometer in adjustable triode configuration with pulsed tunable laser for research on photo-induced field emission cathodes
Authors: Mingels S. , Porshyn V. , Bornmann B. , Lützenkirchen-Hecht D. , Müller G.
Published: April 2015

We have completed an ultra-high vacuum system for sensitive fast electron spectroscopy from cold cathodes in triode configuration under high electric fields E (<100 MV/m) and pulsed tunable laser illumination (3.5 ns, 10 Hz, hν = 0.5-5.9 eV, and 0.3-17 mJ). The cathodes are prepared and inserted under clean room conditions and can be precisely 3D-positioned, cooled or heated (77-400 K). Commissioning results with the upgraded system are presented. Field emission measurements with a W tip yielded an energy resolution of 14 meV at 4 eV pass energy and a precise determination of the emitter work function, size, and temperature. Photoemission spectroscopy of short electron bunches from a virgin and laser-ablated S-GaP crystal and quantum efficiency measurements revealed surface states, energy relaxation, and band structure effects. In conclusion, this novel system is ready now for the development and characterization of photo-induced field emission cathodes.
Tunable delay time and Hartman effect in graphene magnetic barriers
Authors: Ban Yue , Wang Lin-Jun , Chen Xi
Published: April 2015

Tunable group delay and Hartman effect have been investigated for massless Dirac electrons in graphene magnetic barriers. In the presence of magnetic field, dwell time is found to be equal to net group delay plus the group delay contributing from the lateral shifts. The group delay times are discussed in both cases of normal and oblique incidence, to clarify the nature of Hartman effect. In addition, the group delay in transmission can be modulated from subluminality to superluminality by adjusting the magnetic field, which may also lead to potential applications in graphene-based microelectronics.
Non-equilibrium Green's functions study of discrete dopants variability on an ultra-scaled FinFET
Authors: Valin R. , Martinez A. , Barker J. R.
Published: April 2015

In this paper, we study the effect of random discrete dopants on the performance of a 6.6 nm channel length silicon FinFET. The discrete dopants have been distributed randomly in the source/drain region of the device. Due to the small dimensions of the FinFET, a quantum transport formalism based on the non-equilibrium Green's functions has been deployed. The transfer characteristics for several devices that differ in location and number of dopants have been calculated. Our results demonstrate that discrete dopants modify the effective channel length and the height of the source/drain barrier, consequently changing the channel control of the charge. This effect becomes more significant at high drain bias. As a consequence, there is a strong effect on the variability of the on-current, off-current, sub-threshold slope, and threshold voltage. Finally, we have also calculated the mean and standard deviation of these parameters to quantify their variability. The obtained results show that the variability at high drain bias is 1.75 larger than at low drain bias. However, the variability of the on-current, off-current, and sub-threshold slope remains independent of the drain bias. In addition, we have found that a large source to drain current by tunnelling current occurs at low gate bias.
Electrodeposited Co93.2P6.8 nanowire arrays with core-shell microstructure and perpendicular magnetic anisotropy
Authors: Nasirpouri F. , Peighambari S. M. , Samardak A. S. , Ognev A. V. , Sukovatitsina E. V. , Modin E. B. , Chebotkevich L. A. , Komogortsev S. V. , Bending S. J.
Published: April 2015

We demonstrate the formation of an unusual core-shell microstructure in Co93.2P6.8 nanowires electrodeposited by alternating current (ac) in an alumina template. By means of transmission electron microscopy, it is shown that the coaxial-like nanowires contain amorphous and crystalline phases. Analysis of the magnetization data for Co-P alloy nanowires indicates that a ferromagnetic core is surrounded by a weakly ferromagnetic or non-magnetic phase, depending on the phosphor content. The nanowire arrays exhibit an easy axis of magnetization parallel to the wire axis. For this peculiar composition and structure, the coercivity values are 2380 ± 50 and 1260 ± 35 Oe, parallel and perpendicular to the plane directions of magnetization, respectively. This effect is attributed to the core-shell structure making the properties and applications of these nanowires similar to pure cobalt nanowires with an improved perpendicular anisotropy.
Linear scaling density matrix real time TDDFT: Propagator unitarity and matrix truncation
Authors: O’Rourke Conn , Bowler David R.
Published: April 2015

Real time, density matrix based, time dependent density functional theory (TDDFT) proceeds through the propagation of the density matrix, as opposed to the Kohn-Sham orbitals. It is possible to reduce the computational workload by imposing spatial cutoff radii on sparse matrices, and the propagation of the density matrix in this manner provides direct access to the optical response of very large systems, which would be otherwise impractical to obtain using the standard formulations of TDDFT. Following a brief summary of our implementation, along with several benchmark tests illustrating the validity of the method, we present an exploration of the factors affecting the accuracy of the approach. In particular, we investigate the effect of basis set size and matrix truncation, the key approximation used in achieving linear scaling, on the propagator unitarity and optical spectra. Finally, we illustrate that, with an appropriate density matrix truncation range applied, the computational load scales linearly with the system size and discuss the limitations of the approach.
Control of the spin to charge conversion using the inverse Rashba-Edelstein effect
Authors: Sangiao S. , De Teresa J. M. , Morellon L. , Lucas I. , Martinez-Velarte M. C. , Viret M.
Published: April 2015

We show here that using spin orbit coupling interactions at a metallic interface it is possible to control the sign of the spin to charge conversion in a spin pumping experiment. Using the intrinsic symmetry of the “Inverse Rashba Edelstein Effect” (IREE) in a Bi/Ag interface, the charge current changes sign when reversing the order of the Ag and Bi stacking. This confirms the IREE nature of the conversion of spin into charge in these interfaces and opens the way to tailoring the spin sensing voltage by an appropriate trilayer sequence.
Wetting state on hydrophilic and hydrophobic micro-textured surfaces: Thermodynamic analysis and X-ray visualization
Authors: Yu Dong In , Doh Seung Woo , Kwak Ho Jae , Kang Hie Chan , Ahn Ho Seon , Park Hyun Sun , Kiyofumi Moriyama , Kim Moo Hwan
Published: April 2015

In this study, the wetting state on hydrophobic and hydrophilic micro-textured surfaces was investigated. High spatial resolution synchrotron X-ray radiography was used to overcome the limitations in visualization in previous research and clearly visualize the wetting state for each droplet under quantified surface conditions. Based on thermodynamic characteristics, a theoretical model for wetting state depending on the chemical composition (intrinsic contact angle) and geometrical morphology (roughness ratio) of the surfaces was developed.
Nonlinear effects of electric fields in the Belousov-Zhabotinsky reaction dissolved in a microemulsion
Authors: Dähmlow Patricia , Müller Stefan C.
Published: April 2015

Labyrinth-like Turing patterns are investigated under the influence of an electric field. The patterns form in the ferroin-catalyzed Belousov-Zhabotinsky reaction embedded in the sodium-bis (2-ethylhexyl) sulfosuccinate (AOT) water-in-oil microemulsion. For two different values of the droplet fraction above and below the percolation transition of the system, the electric field induced drift of the patterns is different. Above the percolation transition, a linear increase of the drift velocity with increasing electric field strength is found. However, below the percolation transition, this increase shows an exponential behavior. The patterns are also observed to reorient under high electrical field strength, such that they are arranged perpendicular with respect to the field lines.
Adiabatic-connection fluctuation-dissipation DFT for the structural properties of solids—The renormalized ALDA and electron gas kernels
Authors: Patrick Christopher E. , Thygesen Kristian S.
Published: April 2015

We present calculations of the correlation energies of crystalline solids and isolated systems within the adiabatic-connection fluctuation-dissipation formulation of density-functional theory. We perform a quantitative comparison of a set of model exchange-correlation kernels originally derived for the homogeneous electron gas (HEG), including the recently introduced renormalized adiabatic local-density approximation (rALDA) and also kernels which (a) satisfy known exact limits of the HEG, (b) carry a frequency dependence, or (c) display a 1/k2 divergence for small wavevectors. After generalizing the kernels to inhomogeneous systems through a reciprocal-space averaging procedure, we calculate the lattice constants and bulk moduli of a test set of 10 solids consisting of tetrahedrally bonded semiconductors (C, Si, SiC), ionic compounds (MgO, LiCl, LiF), and metals (Al, Na, Cu, Pd). We also consider the atomization energy of the H2 molecule. We compare the results calculated with different kernels to those obtained from the random-phase approximation (RPA) and to experimental measurements. We demonstrate that the model kernels correct the RPA’s tendency to overestimate the magnitude of the correlation energy whilst maintaining a high-accuracy description of structural properties.
Anisotropy effects in magnetic hyperthermia: A comparison between spherical and cubic exchange-coupled FeO/Fe3O4 nanoparticles
Authors: Khurshid H. , Alonso J. , Nemati Z. , Phan M. H. , Mukherjee P. , Fdez-Gubieda M. L. , Barandiarán J. M. , Srikanth H.
Published: April 2015

Spherical and cubic exchange-coupled FeO/Fe3O4 nanoparticles, with different FeO:Fe3O4 ratios, have been prepared by a thermal decomposition method to probe anisotropy effects on their heating efficiency. X-ray diffraction and transmission electron microscopy reveal that the nanoparticles are composed of FeO and Fe3O4 phases, with an average size of ∼20 nm. Magnetometry and transverse susceptibility measurements show that the effective anisotropy field is 1.5 times larger for the cubes than for the spheres, while the saturation magnetization is 1.5 times larger for the spheres than for the cubes. Hyperthermia experiments evidence higher values of the specific absorption rate (SAR) for the cubes as compared to the spheres (200 vs. 135 W/g at 600 Oe and 310 kHz). These observations point to an important fact that the saturation magnetization is not a sole factor in determining the SAR and the heating efficiency of the magnetic nanoparticles can be improved by tuning their effective anisotropy.
Force-extension curves for broken-rod macromolecules: Dramatic effects of different probing methods for two and three rods
Authors: Alexeev A. V. , Maltseva D. V. , Ivanov V. A. , Klushin L. I. , Skvortsov A. M.
Published: April 2015

We study force-extension curves of a single semiflexible chain consisting of several rigid rods connected by flexible spacers. The atomic force microscopy and laser optical or magnetic tweezers apparatus stretching these rod-coil macromolecules are discussed. In addition, the stretching by external isotropic force is analyzed. The main attention is focused on computer simulation and analytical results. We demonstrate that the force-extension curves for rod-coil chains composed of two or three rods of equal length differ not only quantitatively but also qualitatively in different probe methods. These curves have an anomalous shape for a chain of two rods. End-to-end distributions of rod-coil chains are calculated by Monte Carlo method and compared with analytical equations. The influence of the spacer’s length on the force-extension curves in different probe methods is analyzed. The results can be useful for interpreting experiments on the stretching of rod-coil block-copolymers.
Magnetic properties of CuFe1−xCrxO2 nanoparticles surrounded by amorphous SiO2
Authors: Mori K. , Hachisu M. , Yamazaki T. , Ichiyanagi Y.
Published: April 2015

CuFe1−xCrxO2 (0 ≤ x ≤ 1.0) nanoparticles surrounded by amorphous SiO2 with an average diameter of 30–50 nm were synthesized using a wet chemical method. The annealing temperatures were controlled to yield various sizes of single-phase CuFe1−xCrxO2 nanoparticles. CuFeO2 bulk crystal is known to have a multiferroic delafossite structure with two Néel temperatures of 11 and 14 K; however, the transition temperature shifted higher as the Cr–ion doping level increased. In addition, the lattice constants decreased in accordance with increased Cr-ion doping, which was confirmed by X-ray diffraction measurements. The magnetization curves showed weak ferromagnetic behavior and no coercivity was observed. Hence, frustration in the triangular lattice of the delafossite structure can be released by Cr–ion doping and higher magnetization can be expected. A fine structure analysis through X-ray absorption fine structure measurements was also conducted. It was found that the structure of the Cu ion is similar to that of Cu2O, and the c axis of the CuFe1−xCrxO2 should be shortened by the Cr–ion doping.
Aero-optical measurements in a subsonic, turbulent boundary layer with non-adiabatic walls
Authors: Gordeyev Stanislav , Cress Jacob A. , Smith Adam , Jumper Eric J.
Published: April 2015

This paper presents experimental studies of aero-optical distortions due to a turbulent boundary layer over a range of subsonic speeds with the underlying wall both heated above and cooled below the adiabatic wall temperature. A statistical scaling model, based on extended strong Reynolds analogy is derived and shown to correctly predict experimentally observed results. The temperature mismatch between the flow and the wall was shown to have a profound effect on the level aero-optical aberrations, as the heated wall amplifies them and the cooled wall significantly reduces distortions. The importance of an inclusion of the pressure term in explaining the boundary-layer density fluctuations with the cooled wall is also discussed.
Performance of subgrid-scale models in coarse large eddy simulations of a laminar separation bubble
Authors: Cadieux Francois , Domaradzki Julian A.
Published: April 2015

The flow over many blades and airfoils at moderate angles of attack and Reynolds numbers ranging from 104 to 105 undergoes separation due to the adverse pressure gradient generated by surface curvature. In many cases, the separated shear layer then transitions to turbulence and reattaches, closing off a recirculation region—the laminar separation bubble. An equivalent problem is formulated by imposing suitable boundary conditions for flow over a flat plate to avoid numerical and mesh generation issues. Recent work demonstrated that accurate large eddy simulation (LES) of such a flow is possible using only O(1%) of the direct numerical simulation (DNS) resolution but the performance of different subgrid-scale models could not be properly assessed because of the effects of unquantified numerical dissipation. LES of a laminar separation bubble flow over a flat plate is performed using a pseudo-spectral Navier-Stokes solver at resolutions corresponding to 3% and 1% of the chosen DNS benchmark by Spalart and Strelets (2000). The negligible numerical dissipation of the pseudo-spectral code allows an unambiguous assessment of the performance of subgrid-scale models. Three explicit subgrid-scale models—dynamic Smagorinsky, σ, and truncated Navier-Stokes (TNS)—are compared to a no-model simulation (under-resolved DNS) and evaluated against benchmark DNS data focusing on two quantities of critical importance to airfoil and blade designers: time-averaged pressure (Cp) and skin friction (Cf) predictions used in lift and drag calculations. Results obtained with explicit subgrid-scale models confirm that accurate LES of laminar separation bubble flows is attainable with as low as 1% of DNS resolution, and the poor performance of the no-model simulation underscores the necessity of subgrid-scale modeling in coarse LES with low numerical dissipation.
Visualization of He II forced flow around a cylinder
Authors: Chagovets T. V. , Van Sciver S. W.
Published: April 2015

We report an experimental investigation of He II forced flow over a cylindrical obstacle by a flow visualization technique that uses micron scale solid hydrogen particles. It was found in the range of Reynolds numbers studied, 1500 < Red < 11 500, that the flow pattern has a tendency to form a wake with a dynamic separation point similar to that in classical fluids. Furthermore, we did not confirm the existence of large-scale turbulent structures both upstream and downstream of the cylinder as have been observed in He II thermal counterflow across the cylinder at the same range of Reynolds numbers.
On the thermodynamic efficiency of a nickel-based multiferroic thermomagnetic generator: From bulk to atomic scale
Authors: Sandoval Samuel M. , Sepulveda Abdon E. , Keller Scott M.
Published: April 2015

A model is developed to correlate the effects of size on the thermodynamic efficiency for a nickel-based multiferroic thermomagnetic generator device. Three existing models are combined in order to estimate this correlation, they are (1) thermodynamic efficiency relations, (2) a model of ferromagnetic transition behavior, and (3) the bond-order length strength correlation. At the smallest size considered, a monolayer of nickel atoms shows a reduction in Curie temperature from its bulk value of Tc,Bulk=630 K to Tc,ML=240 K. This difference is analytically shown to affect the thermodynamic efficiency values when compared to bulk. Various nickel nanofilms are considered as a working body, such that the combined model predicts relative efficiency values that are comparable to the bulk scale, but operating closer to room-temperature when compared to bulk form. This result is unexpected since the absolute efficiency is shown to increase as a function of decreasing size, this discrepancy is explained as a consequence of Curie point suppression. The combined model is also applied to a hypothetical composite made of separated layers of nickel with distinct thicknesses. This composite material is predicted to spread the ferromagnetic transition across a much larger temperature range as compared to bulk nickel, such that this material may be better suited for different applications; for example, as a sensor or thermal switch. Moreover, this combined model is also shown to give a lower-bound estimate for thermodynamic efficiency, since the actual performance depends on material characterizations that have yet to be determined.
Loading relativistic Maxwell distributions in particle simulations
Authors: Zenitani Seiji
Published: April 2015

Numerical algorithms to load relativistic Maxwell distributions in particle-in-cell (PIC) and Monte-Carlo simulations are presented. For stationary relativistic Maxwellian, the inverse transform method and the Sobol algorithm are reviewed. To boost particles to obtain relativistic shifted-Maxwellian, two rejection methods are proposed in a physically transparent manner. Their acceptance efficiencies are ≈50% for generic cases and 100% for symmetric distributions. They can be combined with arbitrary base algorithms.
Magnetic vortex gyration affected by Dzyaloshinskii–Moriya interaction
Authors: Luo Y. M. , Zhou C. , Won C. , Wu Y. Z.
Published: April 2015

The effect of the Dzyaloshinskii–Moriya interaction (DMI) on magnetic vortex gyration is investigated systematically through micromagnetic simulations. Our results show that the DMI can lift the degeneracy of vortex gyration eigenfrequencies for vortices with left- and right-handedness. For vortex gyration excited by an in-plane AC resonant field, the DMI can strongly influence the gyration amplitude and the critical field for core switching, depending on the sign of the DMI and the vortex handedness. The DMI-induced edge state has a strong effect on the vortex core gyration as the core approaches the disk edge.
Near-infrared light absorption by polycrystalline SiSn alloys grown on insulating layers
Authors: Kurosawa Masashi , Kato Motohiro , Yamaha Takashi , Taoka Noriyuki , Nakatsuka Osamu , Zaima Shigeaki
Published: April 2015

High-Sn-content SiSn alloys are strongly desired for the next-generation near-infrared optoelectronics. A polycrystalline growth study has been conducted on amorphous SiSn layers with a Sn-content of 2%–30% deposited on either a substrate of SiO2 or SiN. Incorporating 30% Sn into Si permits the crystallization of the amorphous layers at annealing temperatures below the melting point of Sn (231.9 °C). Composition analyses indicate that approximately 20% of the Sn atoms are substituted into the Si lattice after solid-phase crystallization at 150–220 °C for 5 h. Correspondingly, the optical absorption edge is red-shifted from 1.12 eV (Si) to 0.83 eV (Si1−xSnx (x ≈ 0.18 ± 0.04)), and the difference between the indirect and direct band gap is significantly reduced from 3.1 eV (Si) to 0.22 eV (Si1−xSnx (x ≈ 0.18 ± 0.04)). These results suggest that with higher substitutional Sn content the SiSn alloys could become a direct band-gap material, which would provide benefits for Si photonics.
Magnetism in graphene oxide induced by epoxy groups
Authors: Lee Dongwook , Seo Jiwon , Zhu Xi , Cole Jacqueline M. , Su Haibin
Published: April 2015

We have engineered magnetism in graphene oxide. Our approach transforms graphene into a magnetic insulator while maintaining graphene's structure. Fourier transform infrared spectroscopy spectra reveal that graphene oxide has various chemical groups (including epoxy, ketone, hydroxyl, and C-O groups) on its surface. Destroying the epoxy group with heat treatment or chemical treatment diminishes magnetism in the material. Local density approximation calculation results well reproduce the magnetic moments obtained from experiments, and these results indicate that the unpaired spin induced by the presence of epoxy groups is the origin of the magnetism. The calculation results also explain the magnetic properties, which are generated by the interaction between separated magnetic regions and domains. Our results demonstrate tunable magnetism in graphene oxide based on controlling the epoxy group with heat or chemical treatment.
Probing magnetic and electric optical responses of silicon nanoparticles
Authors: Permyakov Dmitry , Sinev Ivan , Markovich Dmitry , Ginzburg Pavel , Samusev Anton , Belov Pavel , Valuckas Vytautas , Kuznetsov Arseniy I. , Luk'yanchuk Boris S. , Miroshnichenko Andrey E. , Neshev Dragomir N. , Kivshar Yuri S.
Published: April 2015

We study experimentally both magnetic and electric optically induced resonances of silicon nanoparticles by combining polarization-resolved dark-field spectroscopy and near-field scanning optical microscopy measurements. We reveal that the scattering spectra exhibit strong sensitivity of electric dipole response to the probing beam polarization and attribute the characteristic asymmetry of measured near-field patterns to the excitation of a magnetic dipole mode. The proposed experimental approach can serve as a powerful tool for the study of photonic nanostructures possessing both electric and magnetic optical responses.
Detection of small single-cycle signals by stochastic resonance using a bistable superconducting quantum interference device
Authors: Sun Guozhu , Zhai Jiquan , Wen Xueda , Yu Yang , Kang Lin , Xu Weiwei , Chen Jian , Wu Peiheng , Han Siyuan
Published: April 2015

We propose and experimentally demonstrate detecting small single-cycle and few-cycle signals by using the symmetric double-well potential of a radio frequency superconducting quantum interference device (rf-SQUID). We show that the response of this bistable system to single- and few-cycle signals has a non-monotonic dependence on the noise strength. The response, measured by the probability of transition from initial potential well to the opposite one, becomes maximum when the noise-induced transition rate between the two stable states of the rf-SQUID is comparable to the signal frequency. Comparison to numerical simulations shows that the phenomenon is a manifestation of stochastic resonance.
Evidence for a defect level above the conduction band edge of InAs/InAsSb type-II superlattices for applications in efficient infrared photodetectors
Authors: Prins A. D. , Lewis M. K. , Bushell Z. L. , Sweeney S. J. , Liu S. , Zhang Y.-H.
Published: April 2015

We report pressure-dependent photoluminescence (PL) experiments under hydrostatic pressures up to 2.16 GPa on a mid-wave infrared InAs/InAs0.86Sb0.14 type-II superlattice (T2SL) structure at different pump laser excitation powers and sample temperatures. The pressure coefficient of the T2SL transition was found to be 93 ± 2 meV·GPa−1. The integrated PL intensity increases with pressure up to 1.9 GPa then quenches rapidly indicating a pressure induced level crossing with the conduction band states at ∼2 GPa. Analysis of the PL intensity as a function of excitation power at 0, 0.42, 1.87, and 2.16 GPa shows a clear change in the dominant photo-generated carrier recombination mechanism from radiative to defect related. From these data, evidence for a defect level situated at 0.18 ± 0.01 eV above the conduction band edge of InAs at ambient pressure is presented. This assumes a pressure-dependent energy shift of −11 meV·GPa−1 for the valence band edge and that the defect level is insensitive to pressure, both of which are supported by an Arrhenius activation energy analysis.
Rapid response of thermo-sensitive hydrogels with porous structures
Authors: Maeda Shingo , Kato Terukazu , Kogure Hikaru , Hosoya Naoki
Published: April 2015

Poly(N-isopropylacrylamide)(PNIPAAm) hydrogel is thermo-sensitive, and undergoes a volume phase transition from a swollen state to a shrunken state. Typically, after immersing poly(N-isopropylacrylamide) hydrogels into hot water above the critical temperature, they undergo a two-step shrinking process, which leads to very slow dynamics. However, potential applications, including soft actuators, drug delivery systems, and cell cultures, demand a quick response. Herein, we synthesize chemically crosslinked PNIPAAm porous hydrogels made of nanofiber mats. Our hydrogels rapidly shrink without the two-step shrinking. The response of this porous gel is over 100 times faster than that of the typical gel.
Effects of dopant concentration on structural and near-infrared luminescence of Nd3+-doped beta-Ga2O3 thin films
Authors: Wu Zhenping , Bai Gongxun , Hu Qingrong , Guo Daoyou , Sun Changlong , Ji Liyuan , Lei Ming , Li Linghong , Li Peigang , Hao Jianhua , Tang Weihua
Published: April 2015

We have investigated structural and near-infrared (NIR) luminescence of Nd3+-doped β-Ga2O3 thin films (Nd:Ga2O3) with different Nd3+ doping concentrations. With an increase of Nd3+ content, the crystal lattice of the films expands, while the energy band gap shrinks. Moreover, NIR luminescence is investigated as a function of Nd3+ doping concentration. The measured results are related to the structural change and energy transfer of cross relaxation process ascribed to 4F3/2—4I9/2, 4F3/2—4I11/2, and 4F3/2—4I13/2 of the phosphor films. This work implies that the enhanced NIR luminescence and blue-shift observation are associated with the lattice distortion and the variation in the crystal field of Nd: Ga2O3.
Experimental characterization of a coaxial plasma accelerator for a colliding plasma experiment
Authors: Wiechula J. , Hock C. , Iberler M. , Manegold T. , Schönlein A. , Jacoby J.
Published: April 2015

We report experimental results of a single coaxial plasma accelerator in preparation for a colliding plasma experiment. The utilized device consisted of a coaxial pair of electrodes, accelerating the plasma due to J×B forces. A pulse forming network, composed of three capacitors connected in parallel, with a total capacitance of 27 μF was set up. A thyratron allowed to switch the maximum applied voltage of 9 kV. Under these conditions, the pulsed currents reached peak values of about 103 kA. The measurements were performed in a small vacuum chamber with a neutral-gas prefill at gas pressures between 10 Pa and 14 000 Pa. A gas mixture of ArH2 with 2.8% H2 served as the discharge medium. H2 was chosen in order to observe the broadening of the Hβ emission line and thus estimate the electron density. The electron density for a single plasma accelerator reached peak values on the order of 1016 cm−3. Electrical parameters, inter alia inductance and resistance, were determined for the LCR circuit during the plasma acceleration as well as in a short circuit case. Depending on the applied voltage, the inductance and resistance reached values ranging from 194 nH to 216 nH and 13 mΩ to 23 mΩ, respectively. Furthermore, the plasma velocity was measured using a fast CCD camera. Plasma velocities of 2 km/s up to 17 km/s were observed, the magnitude being highly correlated with gas pressure and applied voltage.
Radiation damage in a micron-sized protein crystal studied via reciprocal space mapping and Bragg coherent diffractive imaging
Authors: Coughlan H. D. , Darmanin C. , Phillips N. W. , Hofmann F. , Clark J. N. , Harder R. J. , Vine D. J. , Abbey B.
Published: April 2015

For laboratory and synchrotron based X-ray sources, radiation damage has posed a significant barrier to obtaining high-resolution structural data from biological macromolecules. The problem is particularly acute for micron-sized crystals where the weaker signal often necessitates the use of higher intensity beams to obtain the relevant data. Here, we employ a combination of techniques, including Bragg coherent diffractive imaging to characterise the radiation induced damage in a micron-sized protein crystal over time. The approach we adopt here could help screen for potential protein crystal candidates for measurement at X-ray free election laser sources.
Communication: Local structure-mobility relationships of confined fluids reverse upon supercooling
Authors: Bollinger Jonathan A. , Jain Avni , Carmer James , Truskett Thomas M.
Published: April 2015

We examine the structural and dynamic properties of confined binary hard-sphere mixtures designed to mimic realizable colloidal thin films. Using computer simulations, governed by either Newtonian or overdamped Langevin dynamics, together with other techniques including a Fokker-Planck equation-based method, we measure the position-dependent and average diffusivities of particles along structurally isotropic and inhomogeneous dimensions of the fluids. At moderate packing fractions, local single-particle diffusivities normal to the direction of confinement are higher in regions of high total packing fraction; however, these trends are reversed as the film is supercooled at denser average packings. Auxiliary short-time measurements of particle displacements mirror data obtained for experimental supercooled colloidal systems. We find that average dynamics can be approximately predicted based on the distribution of available space for particle insertion across orders of magnitude in diffusivity regardless of the governing microscopic dynamics.
Development and validation of protocols for product stewardship in transgenic white clover (Trifolium repens L.): detection of the AMV CP and npt2 transgenes in pollen, honey and honey bees
Authors: Panter S. , Mouradov A. , Smith K. F. , Spangenberg G.
Published: April 2015

There are no current commercial releases of genetically modified white clover, but several research groups are working on traits such as virus resistance, stress tolerance and bloat safety that are likely to provide large economic benefits for livestock farmers. However, white clover pollen is a common constituent of honey produced by bees foraging white clover flowers. Therefore, there is a need to develop tools to detect the presence of genetically modified pollen in white clover honey. The results presented in this paper describe the development and application of PCR-based techniques to detect the Alfalfa mosaic virus coat protein gene (AMV CP) and the neomycin phosphotransferase 2 selectable marker gene (npt2) in genetically modified white clover pollen, whether this pollen is collected fresh, from honey bees that have been foraging white clover, or from honey. Further research and development will be required to develop ‘field-ready’ tools for the detection and quantification of these transgenes in pollen and honey products. However, this paper demonstrates prospects and principles in pollen and honey from honeybees foraging transgenic white clover.