bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient scrolling videotext detection with adaptive temporal differential approach
Authors: Hsia Shih‐Chang , Chang‐Jian Nan‐Tsai
Published: July 2014

This study presents an efficient algorithm for the detection of scrolling text on continuous frames. The proposed scheme adopts both spatial and temporal computation as well as pre‐processing to differentiate among noise, text and background information. Scrolling text is detected using temporal differentiation among inter‐frames and then the region in which the scrolling text appears is identified as a rectangle. Simulation results demonstrate that the proposed algorithm is capable of precisely differentiating scrolling text in any direction, along any of the frame boundaries without false detection or missed text. In a comparison using quantised measurements, the proposed method outperforms all competing algorithms.
Image processing system dedicated to a visual intra‐cortical stimulator
Authors: Ghannoum Anthony , Ghafar‐Zadeh Ebrahim , Sawan Mohamad
Published: July 2014

Microstimulation is a feasible method targeting visual impairment. In this paper, the authors focus on intra‐cortical stimulation to cover the broader spectrum of the issue with the aim of providing a better suited visual aid. They present an overall modular architecture and focus on creating re‐usable image processing tools that can be used for image simplification and recognition tasks. One of the main challenges in the image processing path is the real‐time restriction; hence they resort to field‐programmable gate array (FPGA) hardware acceleration. Herein they demonstrate and describe the architecture of an image feature extractor based on the difference of Gaussians that is at once accurate, generic and low on resources. This architecture also features a Huffman encoding engine that proves useful when resorting to software–hardware (SW–HW) hybrid implementations, and a technique of calibrating and calculating the phosphene map.
Design and implement of transceiver system for hybrid rocket with coplanar wraparound antenna at 433 MHz
Authors: Tsai Pang‐Chun , Lin Hsin‐Piao , Lin Ding‐Bing , Chang Ching‐Jen
Published: July 2014

This study aims to implement the telematics between hybrid rockets and the ground receiving station. In order to significantly reduce the rocket weight, fibre‐reinforced plastic is used for the hybrid rocket casing, on which coplanar wraparound antennas with an operating frequency of 433 MHz are designed. The antenna structure contains three coplanar printed patches, among which the middle printed patch is the primary radiator and the resonant length appears a wavelength for the metallic surface case. An RF module with high receiver sensitivity and a high‐power power amplifier are included to enhance the communication coverage of hybrid rockets and the ground receiving station so that the station can effectively track the hybrid rocket. Finally, the radio wave propagation model is used for calculating the link budget such that the communication coverage between rocket transmitters and the ground receiving station can be estimated, and on‐site measurement and verification are preceded.
Miniaturisation method for coupled‐line bandpass filters with identical and minimal number of reactive elements
Authors: Lim Taejun , Min Byung‐Wook , Lee Yongshik
Published: July 2014

This study presents an improved method of reactive loading for miniaturisation of coupled‐line filters. Compared to the previous method, the proposed method requires a reduced number of reactive elements. Moreover, miniaturisation is accomplished with equal reactance. Effectively, this further decreases the number of reactive elements. Therefore apart from improved loss performance because of the reduced number of low‐Q lumped elements, low‐cost fabrication and simpler design procedure are also achieved while maintaining a similar rate of miniaturisation. A complete set of design equations is provided for both shunt‐capacitive and series‐inductive loading. The ideal simulation results, which are in excellent agreement with those of conventional counterparts based on λ/4 lines, theoretically validate the method, whereas the experimental results that match the ideal results better than the previous method demonstrate the practicality of the proposed method.
Meta‐surfaces and antennas' radiation characteristics enhancement: planar microstrip and microstrip‐based quasi‐aperture antennas
Authors: Niroo‐Jazi Mahmoud , Denidni Tayeb A. , Chaharmir Mohammad Reza , Sebak Abdel R.
Published: July 2014

Meta‐surfaces as artificial magnetic conductors or high impedance surfaces to control the electromagnetic fields excited by a microstrip patch resonator are investigated for planar and non‐planar structures. In the planar structure, two types of meta‐surfaces are used as electromagnetic transducers to transform the captured non‐radiating waves to radiated space waves, leading to about 4 dBi gain enhancement. Alternatively, by applying these surfaces as E‐plane fences in two sides of a patch, a compact microstrip‐based quasi‐aperture antenna is proposed. The proposed antenna not only improves the gain up to 8 dBi, but also provides almost a symmetric radiation pattern by controlling the phase distribution of electric fields in the antenna aperture. Using near electric‐field pattern inspection and characterising the meta‐surfaces, the radiation mechanism of the proposed antennas are delineated. Two antenna prototypes are fabricated and tested and, confirming the simulated ones, the corresponding measured results are presented.
Increasing throughput in IEEE 802.11 by optimal selection of backoff parameters
Authors: Parker Ben M. , Schormans John Alexander , Gilmour Steven G.
Published: July 2014

The IEEE 802.11 standard uses Carrier Sense Multiple Access with Collision Avoidance to avoid multiple devices simultaneous transmitting on a shared transmission medium. In this study, Bianchi's model for IEEE 802.11 is studied and the authors suggest some important improvements. Firstly, they expand the state space of the Markov chain to model the evolution of a network, instead of a single device. Secondly, they relax the assumption that the network must be saturated. Thirdly, they extend the model to allow for heterogeneous devices with different transmission profiles. They use this new model to perform Monte Carlo simulation to discover the impact of the minimum and maximum contention window times (CWmin and CWmax) in the standard on measures of throughput in a network. By exhaustive search over a parameter space, they find optimal values for these devices for any given network model, and show that the recommended parameters in the IEEE 802.11 standard are not optimal. They consider both average and minimum throughput, and show that increases in throughput of around 8% are possible for saturated networks, and that even greater improvements are possible for any case in which the traffic sources are not homogeneous, that is, any real scenario.
SDRP: secure and dynamic routing protocol for mobile ad‐hoc networks
Authors: Ghosh Uttam , Datta Raja
Published: July 2014

RSA‐based secure routing protocols are computationally expensive because of the use of large public keys and/or signatures that are disadvantageous for mobile ad‐hoc networks. In this study, the authors proposed a secure dynamic routing protocol, named SDRP, which uses identity‐based scheme with pairing on elliptic curve. It makes use of signature and ‘Message Authentication Code’ algorithms to provide end‐to‐end, hop‐to‐hop and whole‐route authentications. The proposed SDRP has several advantages over the existing RSA‐based secure routing solutions. Firstly, it requires fewer signature generations and verifications on a route. Secondly, the SDRP makes use of an identity‐based scheme which is certificate‐less, thus saving routing overhead (RO) and storage. Finally, it uses a hardware address to generate its small size of public key. Both the qualitative analysis and the simulation results show that the proposed SDRP provides secure routes and better packet delivery fraction and with significantly less RO and latency compared with previous RSA‐based secure routing protocols.
Shuffled frog leaping algorithm‐based static synchronous compensator for transient stability improvement of a grid‐connected wind farm
Authors: Hasanien Hany M.
Published: July 2014

The shuffled frog leaping algorithm (SFLA) is presented, to optimally design multiple proportional–integral (PI) controllers of the static synchronous compensator (STATCOM) system with the purpose of improving the transient stability of a grid‐connected wind farm. The control strategy of the STATCOM system depends on a sinusoidal pulse width modulation voltage source converter, which is controlled by the cascaded PI control scheme. The response surface methodology is used to establish a second‐order fitted model of the transient voltage responses at the point of common coupling in terms of PI controllers’ parameters. For realistic responses, a three‐mass drive train model is used for the wind turbine generator system because of its great influence on the dynamic analyses. The SFLA code is built using MATLAB software. The effectiveness of optimised PI‐controlled STATCOM by the SFLA is then compared to that optimised by genetic algorithms technique taking into consideration symmetrical and unsymmetrical fault conditions. The proposed control scheme is applied to a real grid‐connected wind farm system at Hokkaido Island, Japan. The validity of the proposed system is verified by the simulation results, which are performed using PSCAD/EMTDC software environment. With the proposed SFLA‐based STATCOM, the transient stability of a grid‐connected wind farm can be enhanced.
Unitary power control strategy for low‐power wind energy conversion system using active speed stall control for full‐load regime
Authors: Burlibasa (Scarlat) Adriana , Munteanu Iulian , Bratcu Antoneta Iuliana
Published: July 2014

This study deals with the control of a low‐power off‐grid wind energy conversion system. As rotor blades are not pitchable, control is ensured by variable‐speed operation in order to limit harvested power in high winds and to maximise it at low winds. Turbine power regulation is achieved through active speed stall control, which supposes operation at low rotational speed values. In this way, operation within admissible limits of rotational speed and torque is also ensured. A unique power controller is designed, with classical proportional–integral (PI) structure and switched parameters and references. An original solution for switching controller parameters so as to avoid local instability and preserve smooth transition between partial‐load and full‐load operating regimes is proposed. Switching is performed in an operating point where power controller output is sufficiently deep in saturation and the antiwindup structure is active. Guidelines for choosing this switching point are provided. This control structure does not require estimation of either wind speed or wind torque, or use of gain scheduling structures. The proposed approach is validated through experiments on a dedicated real‐time simulator.
Linear minimum mean squared estimation of measurement bias driven by structured unknown inputs
Authors: Zhou Lin , Liang Yan , Zhou Jie , Yang Feng , Pan Quan
Published: July 2014

In this study, a generalised systematic bias (SB) is presented, which is represented via a dynamic model driven by structured unknown inputs (UI). The online SB estimation is implemented in two steps. In the first step, the state‐free SB measurement and the UI‐free SB dynamic model are derived in the case that UI‐free condition holds. In the second step, the linear minimum mean squared filter is obtained via orthogonal principle, and the sufficient condition of filtering stability is presented. A simulation about target tracking is given to verify the proposed method.
Investigations of dielectric monitoring on an energised transformer oil–paper insulation system
Authors: Yang Xu , Nielsen Shawn , Ledwich Gerard
Published: July 2014

Frequency domain spectroscopy (FDS) is being used to assess the insulation condition of oil–paper power transformers. However, it has to date only been implemented on de‐energised transformers, which requires the transformers to be shut down for an extended period and may cause significant costs. To solve this issue, a newly improved monitoring method based on the FDS principle is proposed to implement the dielectric measurement on energised transformers. Moreover, a chirp waveform excitation and its novel processing method are introduced. Compared with the conventional FDS results, dielectric results from the energised insulation system have higher tanδ values because of the increased losses. To further understand the insulation ageing process, the effects of the geometric capacitance are removed from the measured imaginary admittance of the insulation system to enhance the ageing signature. The resulting imaginary admittance is then shown to correlate well with the central time constant in return voltage measurements results. The proposed methods address the issues on techniques used on energised transformers and provide a clue for on‐line FDS diagnostic application.
Gait motion simulator for kinematic tests of above knee prostheses
Authors: Yilmaz Atila , Orhanli Tuna
Published: July 2014

In this study, a basic gait motion simulator mechanism combining control units and electromechanic hardware has been proposed and implemented for the test stages of knee prostheses. The main goal to develop such simulator equipment is to regenerate predefined and controllable periodic movement, specifically hip vertical displacement and thigh angle motion applied to above‐knee prosthesis so that test studies will be less dependent to human trials in any development phase. Gait motion simulator performance tests were conducted with both an image‐based motion measurement system and a direct‐type motion measurement system. In the hip simulator performance evaluation phase, accelerometer and video signals were collected simultaneously from the experimental system for kinematic analysis. The overall system consists of a hip simulator, a microcontroller‐controlled prosthetic knee and a solid ankle cushion heel foot on a treadmill. Experimental results were evaluated for assessing the degree of approximation of the natural periodic hip movement by designed electromechanical simulator. The analysis showed that the test platform presented in this study is a useful yet low budget alternative to more expensive general‐purpose electromechanic test devices for development purposes.
Preparation and characterisation of carbon‐modified TiO2 composite
Authors: Deng Qin , Han Yue , Liu Yan , Deng Shihuai , Yang Gang , Shen Fei , Peng Hong , Wang Lilin , Zhang Yanzong
Published: July 2014

Carbon‐modified TiO2 composite was synthesised via the template method and multi‐step calcinations by using a tinfoil package. The carbon‐coated TiO2 (C–TiO2) composite was characterised via X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy and N2 sorption and thermogravimetry. TiO2 was wrapped up in a carbon layer with a thickness of less than 1 nm. The specific surface area and pore volume of C–TiO2 were 95.6 m2 g−1 and 0.247 cm3 g−1, respectively. The C–TiO2 composite exhibited mesopore structures, showed preferable adsorption capacity for methyl orange and had a higher photocatalytic activity than its unmodified counterpart.
A Rare Case of Multiregional Spinal Stenosis: Clinical Description, Surgical Complication, and Management Concept Review
Authors: Hong Choon Chiet , Liu Ka Po Gabriel
Published: July 2014

Study Design

Case report and literature review.

Objective

Multiregional spinal stenosis (MRSS) has not been described in the English literature, although a few studies report the concept of tandem spinal stenosis. Due to the concurrent spinal stenosis occurring in three separate regions of the spine, clinical presentation of MRSS may be less distinct, and its surgical treatment priorities and challenges differ from single-region spinal stenosis. The purpose of this article is to describe a new concept and a rare case of MRSS as separated segments of spinal stenosis in the cervical, thoracic, and lumbar spine.

Methods

A retrospective case description of MRSS and surgical strategies used in managing such extensive multiregional stenosis and its potential complications.

Results

A novel surgical strategy using a combination of laminectomies with fusion and laminoplasty without fusion to treat this patient with such extensive cervical to thoracic myelopathic cord compression is described. Initial good recovery after cervical cord decompression was followed by a delayed recurrence of symptoms from thoracic cord compression. The subsequent thoracic surgical decompression, its complications and management, and patient recovery are discussed with a literature review highlighting the possible mechanisms for postoperative loss of neurologic function after thoracic decompression.

Conclusion

MRSS is a rare cause of extensive compression of multiple regions of the spinal cord. To the best of the authors’ knowledge, this report is the first to use the term multiregional spinal stenosis to describe this new emergent clinical entity, surgical management strategies, and potential complications.
Migratory Intradural Disk Herniation and a Strategy for Intraoperative Localization
Authors: Daffner Scott D. , Sedney Cara L. , Rosen Charles L.
Published: July 2014

Study Design

Case report.

Objective

Describe a case of intradural disk herniation and a method for intraoperative localization.

Methods

Intradural disk herniations are uncommon but well described. The diagnosis of these lesions is often difficult, and sometimes they may be diagnosed only through an intradural exploration after an expected disk fragment cannot be located. We report the case of an intradural disk herniation with an additional diagnostic difficulty—a migrated intradural disk.

Results

We present the first intraoperative imaging evidence of disk migration and propose a strategy to locate intradural disk fragments prior to durotomy.

Conclusion

Intradural disk herniations should be suspected when intraoperative findings are not congruent with imaging findings. An intraoperative myelogram may be helpful.
The CoLaPipe—The new Cottbus large pipe test facility at Brandenburg University of Technology Cottbus-Senftenberg
Authors: König Franziska , Zanoun El-Sayed , Öngüner Emir , Egbers Christoph
Published: July 2014

The CoLaPipe is a novel test facility at the Department of Aerodynamics and Fluid Mechanics, Brandenburg University of Technology Cottbus-Senftenberg (BTU Cottbus-Senftenberg), set up to investigate fully developed pipe flow at high Reynolds numbers (Rem ⩽ 1.5 × 106). The design of the CoLaPipe is closed-return with two available test sections providing a length-to-diameter ratio of L/D = 148 and L/D = 79. Within this work, we introduce the CoLaPipe and describe the various components in detail, i.e., the settling chamber, the inlet contraction, the blower, bends, and diffusers as well as the cooling system. A special feature is the numerically optimized contraction design. The applications of different measuring techniques such as hot-wire anemometry and static pressure measurements to quantitatively evaluate the mean flow characteristics and turbulence statistics are discussed as well. In addition, capabilities and limitations of available and new pipe flow facilities are presented and reconsidered based on their length-to-diameter ratio, the achieved Reynolds numbers, and the resulting spatial resolution. Here, the focus is on the facility design, the presentation of some basic characteristics, and its contribution to a reviewed list of specific questions still arising, e.g., scaling and structural behavior of turbulent pipe flow as well as the influence of the development length on turbulence investigations.
Soliton solutions and chaotic motion of the extended Zakharov-Kuznetsov equations in a magnetized two-ion-temperature dusty plasma
Authors: Zhen Hui-Ling , Tian Bo , Wang Yu-Feng , Sun Wen-Rong , Liu Li-Cai
Published: July 2014

The extended Zakharov-Kuznetsov (eZK) equation for the magnetized two-ion-temperature dusty plasma is studied in this paper. With the help of Hirota method, bilinear forms and N-soliton solutions are given, and soliton propagation is graphically analyzed. We find that the soliton amplitude is positively related to the nonlinear coefficient A, while inversely related to the dispersion coefficients B and C. We obtain that the soliton amplitude will increase with the mass of the jth dust grain and the average charge number residing on the dust grain decreased, but the soliton amplitude will increase with the equilibrium number density of the jth dust grain increased. Upon the introduction of the periodic external forcing term, both the weak and developed chaotic motions can occur. Difference between the two chaotic motions roots in the inequality between the nonlinear coefficient l2 and perturbed term h1. The developed chaos can be weakened with B or C decreased and A increased. Periodic motion of the perturbed eZK equation can be observed when there is a balance between l2 and h1.
Reciprocal relations in electroacoustics
Authors: Chassagne C. , Bedeaux D.
Published: July 2014

In a colloidal suspension, one can generate sound waves by the application of an alternating electric field (Electrokinetic Sonic Amplitude, i.e., ESA). Another phenomenon is electrophoresis (Electrophoretic Mobility, i.e., EM) where a colloidal particle moves relative to the solvent in an electric field. Vice versa one can generate electric fields or electric currents by sound waves (Colloid Vibration Potential/Current, i.e., CVP/CVI). In 1988 and 1990, O’Brien [J. Fluid Mech. 190, 71–86 (1988) and O’Brien, J. Fluid Mech. 212, 81–93 (1990)] derived a reciprocal relation between the proportionality coefficients of the EM and CVI phenomena. In this paper, we will generalize his proof by constructing the relevant entropy production from which the linear force-flux relations follow. General relations are derived for electrolyte solutions, of which colloidal suspensions are a particular case. The relations between CVI, CVP, EM, and ESA are discussed. O’Brien's reciprocal relation then follows as an Onsager relation. The relation is valid for any applied electric field frequency, particle surface charge and particle concentration (even in the presence of particle-particle interactions) provided the system is isotropic.
Manchester code telemetry system for well logging using quasi-parallel inductive-capacitive resonance
Authors: Xu Lijun , Chen Jianjun , Cao Zhang , Liu Xingbin , Hu Jinhai
Published: July 2014

In this paper, a quasi-parallel inductive-capacitive (LC) resonance method is proposed to improve the recovery of MIL-STD-1553 Manchester code with several frequency components from attenuated, distorted, and drifted signal for data telemetry in well logging, and corresponding telemetry system is developed. Required resonant frequency and quality factor are derived, and the quasi-parallel LC resonant circuit is established at the receiving end of the logging cable to suppress the low-pass filtering effect caused by the distributed capacitance of the cable and provide balanced pass for all the three frequency components of the Manchester code. The performance of the method for various encoding frequencies and cable lengths at different bit energy to noise density ratios (Eb/No) have been evaluated in the simulation. A 5 km single-core cable used in on-site well logging and various encoding frequencies were employed to verify the proposed telemetry system in the experiment. Results obtained demonstrate that the telemetry system is feasible and effective to improve the code recovery in terms of anti-attenuation, anti-distortion, and anti-drift performances, decrease the bit error rate, and increase the reachable transmission rate and distance greatly.
Measurement of spatial and temporal behavior of Hα emission from Aditya tokamak using a diagnostic based on a photomultiplier tube array
Authors: Chowdhuri M. B. , Ghosh J. , Manchanda R. , Kumar Ajay , Banerjee S. , Ramaiya N. , Virani Niral , Mali Aniruddh , Amardas A. , Kumar Pintu , Tanna R. L. , Gupta C. N. , Bhatt S. B. , Chattopadhyay P. K.
Published: July 2014

A photo multiplier tube (PMT) array based spectroscopic diagnostic with fast time response of 10 μs and spatial resolution ∼3 cm has been developed and installed on Aditya tokamak to study the spatial and temporal behavior of Hα emissions from typical discharges. Collimated light has been collected from the plasma along 16 lines of sight passing through entire plasma poloidal cross section of Aditya and detected by two 8 channels PMT arrays after selecting Hα emission using interference filter. The studies are carried out during plasma formation phase of Aditya by changing vertical field and its delay with respect to loop voltage. It is observed that plasma initiated in the high field side in typical discharges of Aditya. The plasma formation position is matched with null field location estimated through simulation.
Electronic nonadiabatic effects in low temperature radical-radical reactions. I. C(3P) + OH(2Π)
Authors: Maergoiz A. I. , Nikitin E. E. , Troe J.
Published: July 2014

The formation of collision complexes, as a first step towards reaction, in collisions between two open-electronic shell radicals is treated within an adiabatic channel approach. Adiabatic channel potentials are constructed on the basis of asymptotic electrostatic, induction, dispersion, and exchange interactions, accounting for spin-orbit coupling within the multitude of electronic states arising from the separated reactants. Suitable coupling schemes (such as rotational + electronic) are designed to secure maximum adiabaticity of the channels. The reaction between C(3P) and OH(2Π) is treated as a representative example. The results show that the low temperature association rate coefficients in general cannot be represented by results obtained with a single (generally the lowest) potential energy surface of the adduct, asymptotically reaching the lowest fine-structure states of the reactants, and a factor accounting for the thermal population of the latter states. Instead, the influence of non-Born–Oppenheimer couplings within the multitude of electronic states arising during the encounter markedly increases the capture rates. This effect extends up to temperatures of several hundred K.
P-doping-free III-nitride high electron mobility light-emitting diodes and transistors
Authors: Li Baikui , Tang Xi , Wang Jiannong , Chen Kevin J.
Published: July 2014

We report that a simple metal-AlGaN/GaN Schottky diode is capable of producing GaN band-edge ultraviolet emission at 3.4 eV at a small forward bias larger than ∼2 V at room temperature. Based on the surface states distribution of AlGaN, a mature impact-ionization-induced Fermi-level de-pinning model is proposed to explain the underlying mechanism of the electroluminescence (EL) process. By experimenting with different Schottky metals, Ni/Au and Pt/Au, we demonstrated that this EL phenomenon is a “universal” property of metal-AlGaN/GaN Schottky diodes. Since this light-emitting Schottky diode shares the same active structure and fabrication processes as the AlGaN/GaN high electron mobility transistors, straight-forward and seamless integration of photonic and electronic functional devices has been demonstrated on doping-free III-nitride heterostructures. Using a semitransparent Schottky drain electrode, an AlGaN/GaN high electron mobility light-emitting transistor is demonstrated.
Design and initial characterization of a compact, ultra high vacuum compatible, low frequency, tilt accelerometer
Authors: O’Toole A. , Peña Arellano F. E. , Rodionov A. V. , Shaner M. , Sobacchi E. , Dergachev V. , DeSalvo R. , Asadoor M. , Bhawal A. , Gong P. , Kim C. , Lottarini A. , Minenkov Y. , Murphy C.
Published: July 2014

A compact tilt accelerometer with high sensitivity at low frequency was designed to provide low frequency corrections for the feedback signal of the Advanced Laser Interferometer Gravitational Wave Observatory active seismic attenuation system. It has been developed using a Tungsten Carbide ceramic knife-edge hinge designed to avoid the mechanical 1/f noise believed to be intrinsic in polycrystalline metallic flexures. Design and construction details are presented; prototype data acquisition and control limitations are discussed. The instrument's characterization reported here shows that the hinge is compatible with being metal-hysteresis-free, and therefore also free of the 1/f noise generated by the dislocation Self-Organized Criticality in the metal. A tiltmeter of this kind will be effective to separate the ground tilt component from the signal of horizontal low frequency seismometers, and to correct the ill effects of microseismic tilt in advanced seismic attenuation systems.
Quantum efficiency investigations of type-II InAs/GaSb midwave infrared superlattice photodetectors
Authors: Giard E. , Ribet-Mohamed I. , Jaeck J. , Viale T. , Haïdar R. , Taalat R. , Delmas M. , Rodriguez J.-B. , Steveler E. , Bardou N. , Boulard F. , Christol P.
Published: July 2014

We present in this paper a comparison between different type-II InAs/GaSb superlattice (T2SL) photodiodes and focal plane array (FPA) in the mid-wavelength infrared domain to understand which phenomenon drives the performances of the T2SL structure in terms of quantum efficiency (QE). Our measurements on test photodiodes suggest low minority carrier diffusion length in the “InAs-rich” design, which penalizes carriers' collection in this structure for low bias voltage and front side illumination. This analysis is completed by a comparison of the experimental data with a fully analytic model, which allows to infer a hole diffusion length shorter than 100 nm. In addition, measurements on a FPA with backside illumination are finally presented. Results show an average QE in the 3–4.7 μm window equal to 42% for Ubias = −0.1 V, 77 K operating temperature and no anti-reflection coating. These measurements, completed by modulation transfer function and noise measurements, reveal that the InAs-rich design, despite a low hole diffusion length, is promising for high performance infrared imaging applications.
Coherently driven, ultrafast electron-phonon dynamics in transport junctions
Authors: Szekely Joshua E. , Seideman Tamar
Published: July 2014

Although the vast majority of studies of transport via molecular-scale heterojunctions have been conducted in the (static) energy domain, experiments are currently beginning to apply time domain approaches to the nanoscale transport problem, combining spatial with temporal resolution. It is thus an opportune time for theory to develop models to explore both new phenomena in, and new potential applications of, time-domain, coherently driven molecular electronics. In this work, we study the interaction of a molecular phonon with an electronic wavepacket transmitted via a conductance junction within a time-domain model that treats the electron and phonon on equal footing and spans the weak to strong electron-phonon coupling strengths. We explore interference between two coherent energy pathways in the electronic subspace, thus complementing previous studies of coherent phenomena in conduction junctions, where the stationary framework was used to study interference between spatial pathways. Our model provides new insights into phase decoherence and population relaxation within the electronic subspace, which have been conventionally treated by density matrix approaches that often rely on phenomenological parameters. Although the specific case of a transport junction is explored, our results are general, applying also to other instances of coupled electron-phonon systems.
Investigation of the effect of a bumpy base on granular segregation and transport properties under vertical vibration
Authors: Liao C. C. , Hunt M. L. , Hsiau S. S. , Lu S. H.
Published: July 2014

This study experimentally investigates the effect of a bumpy base on the Brazil-nut phenomenon in a vertically vibrated granular bed. The rise dynamics of an intruder is determined by the particle tracking method. The results indicate that the rise time increases with an increase in the base roughness, and the variation of the rise time with different base factors is more pronounced with smaller vibration acceleration and higher vibration frequency. A theoretical model is employed to measure the penetration length of the intruder and the drag force between the intruder and the immersed beads. The penetration length is reduced and the drag force is enhanced with surface roughness of the base. Additionally, the transport properties of the vibrated glass beads are also measured and discussed. With greater base roughness, the strength of the diffusive and convective motion is reduced leading to a weaker Brazil-nut effect.
High angular momentum states of lithium atom, studied with symmetry-projected explicitly correlated Gaussian lobe functions
Authors: Strasburger Krzysztof
Published: July 2014

Method of construction of wave functions approximating eigenfunctions of the \documentclass[12pt]{minimal}\begin{document}$\hat{L}^2$\end{document}L̂2 operator is proposed for high angular momentum states of few-electron atoms. Basis functions are explicitly correlated Gaussian lobes, projected onto irreducible representations of finite point groups. Variational calculations have been carried out for the lowest states of lithium atom, with quantum number L in the range from 1 to 8. Nonrelativistic energies accurate to several dozens of nanohartree have been obtained. For 22P, 32D, and 42F states they agree well with the reference results. Transition frequencies have been computed and compared with available experimental data.
Frequency stabilization of a 1083 nm fiber laser to 4He transition lines with optical heterodyne saturation spectroscopies
Authors: Gong W. , Peng X. , Li W. , Guo H.
Published: July 2014

Two kinds of optical heterodyne saturation spectroscopies, namely, frequency modulation spectroscopy (FMS) and modulation transfer spectroscopy (MTS), are demonstrated for locking a fiber laser to the transition lines of metastable 4He atoms around 1083 nm. The servo-loop error signals of FMS and MTS for stabilizing laser frequency are optimized by studying the dependence of the peak-to-peak amplitude and slope on the optical power of pump and probe beams. A comparison of the stabilization performances of FMS/MTS and polarization spectroscopy (PS) is presented, which shows that MTS exhibits relatively superior performance with the least laser frequency fluctuation due to its flat-background dispersive signal, originated from the four-wave mixing process. The Allan deviation of the stabilized laser frequency is 5.4 × 10−12@100 s with MTS for data acquired in 1000 s, which is sufficiently applicable for fields like laser cooling, optical pumping, and optical magnetometry.
An in situ runaway electron diagnostic for DIII-D
Authors: Wurden G. A. , Oertel J. A. , Evans T. E.
Published: July 2014

We are designing a new diagnostic based on laser inverse Compton scattering to study the dynamics of runaway electron formation during killer-pellet triggered disruptions in DIII-D, and their subsequent loss. We can improve the expected S/N ratio by using a high-intensity short-pulse laser combined with gated x-ray imagers. With 80 ps sampling, time-of-flight spatial resolution within the laser chord can be obtained. We will measure the time-resolved spatial profile and energy distribution of the runaway electrons while they are in the core of the tokamak plasma.
Robust regression on noisy data for fusion scaling laws
Authors: Verdoolaege Geert
Published: July 2014

We introduce the method of geodesic least squares (GLS) regression for estimating fusion scaling laws. Based on straightforward principles, the method is easily implemented, yet it clearly outperforms established regression techniques, particularly in cases of significant uncertainty on both the response and predictor variables. We apply GLS for estimating the scaling of the L-H power threshold, resulting in estimates for ITER that are somewhat higher than predicted earlier.
Prospects for x-ray polarimetry measurements of magnetic fields in magnetized liner inertial fusion plasmas
Authors: Lynn Alan G. , Gilmore Mark
Published: July 2014

Magnetized Liner Inertial Fusion (MagLIF) experiments, where a metal liner is imploded to compress a magnetized seed plasma may generate peak magnetic fields ∼104 T (100 Megagauss) over small volumes (∼10−10m3) at high plasma densities (∼1028m−3) on 100 ns time scales. Such conditions are extremely challenging to diagnose. We discuss the possibility of, and issues involved in, using polarimetry techniques at x-ray wavelengths to measure magnetic fields under these extreme conditions.
Unravelling the physical mechanisms that determine microstructural evolution of ultrathin Volmer-Weber films
Authors: Elofsson V. , Lü B. , Magnfält D. , Münger E. P. , Sarakinos K.
Published: July 2014

The initial formation stages (i.e., island nucleation, island growth, and island coalescence) set characteristic length scales during growth of thin films from the vapor phase. They are, thus, decisive for morphological and microstructural features of films and nanostructures. Each of the initial formation stages has previously been well-investigated separately for the case of Volmer-Weber growth, but knowledge on how and to what extent each stage individually and all together affect the microstructural evolution is still lacking. Here, we address this question using growth of Ag on SiO2 from pulsed vapor fluxes as a case study. By combining in situ growth monitoring, ex situ imaging and growth simulations we systematically study the growth evolution all the way from nucleation to formation of a continuous film and establish the effect of the vapor flux time domain on the scaling behaviour of characteristic growth transitions (elongation transition, percolation and continuous film formation). Our data reveal a pulsing frequency dependence for the characteristic film growth transitions, where the nominal transition thickness decreases with increasing pulsing frequency up to a certain value after which a steady-state behaviour is observed. The scaling behaviour is shown to result from differences in island sizes and densities, as dictated by the initial film formation stages. These differences are determined solely by the interplay between the characteristics of the vapor flux and time required for island coalescence to be completed. In particular, our data provide evidence that the steady-state scaling regime of the characteristic growth transitions is caused by island growth that hinders coalescence from being completed.
Method of determining kinetic boundary conditions in net evaporation/condensation
Authors: Kon Misaki , Kobayashi Kazumichi , Watanabe Masao
Published: July 2014

The aim of the present study is to develop the method of determining the kinetic boundary condition (KBC) at a vapor-liquid interface in net evaporation/condensation. We proposed a novel method for determining the KBC by combining the numerical simulations of the mean field kinetic theory and the molecular gas dynamics. The method was evaluated on steady vapor flow between two liquid slabs at different temperatures. A uniform net mass flux in the vapor phase induced by net evaporation and condensation is obtained from the numerical simulation of the mean field kinetic theory for both vapor and liquid phases. The KBC was specified by using the uniform net mass flux, and the numerical simulation of the molecular gas dynamics was conducted for the vapor phase. Comparing the macroscopic variables in the vapor phase obtained from both numerical simulations, we can validate the KBC whether the appropriate solutions are obtained. Moreover, the evaporation and condensation coefficients were estimated uniquely. The results showed that the condensation and evaporation coefficients were identical and constant in net evaporation. On the other hand, in net condensation, the condensation coefficient increased with the collision molecular mass flux. We also presented the applicable limit of the KBC which is assumed to be the isotropic Gaussian distribution at the liquid temperature. From these results, the KBCs in net evaporation and condensation, which enable the exact macroscopic variables to be determined, were proposed.
Carbon-rich icosahedral boron carbide designed from first principles
Authors: Jay Antoine , Vast Nathalie , Sjakste Jelena , Duparc Olivier Hardouin
Published: July 2014

The carbon-rich boron-carbide (B11C)C-C has been designed from first principles within the density functional theory. With respect to the most common boron carbide at 20% carbon concentration B4C, the structural modification consists in removing boron atoms from the chains linking (B11C) icosahedra. With C-C instead of C-B-C chains, the formation of vacancies is shown to be hindered, leading to enhanced mechanical strength with respect to B4C. The phonon frequencies and elastic constants turn out to prove the stability of the carbon-rich phase, and important fingerprints for its characterization have been identified.
Engineering of the band gap and optical properties of thin films of yttrium hydride
Authors: You Chang Chuan , Mongstad Trygve , Maehlen Jan Petter , Karazhanov Smagul
Published: July 2014

Thin films of oxygen-containing yttrium hydride show photochromic effect at room temperature. In this work, we have studied structural and optical properties of the films deposited at different deposition pressures, discovering the possibility of engineering the optical band gap by variation of the oxygen content. In sum, the transparency of the films and the wavelength range of photons triggering the photochromic effect can be controlled by variation of the deposition pressure.
Reduced ultraviolet light induced degradation and enhanced light harvesting using YVO4:Eu3+ down-shifting nano-phosphor layer in organometal halide perovskite solar cells
Authors: Chander Nikhil , Khan A. F. , Chandrasekhar P. S. , Thouti Eshwar , Swami Sanjay Kumar , Dutta Viresh , Komarala Vamsi K.
Published: July 2014

We report a simple method to mitigate ultra-violet (UV) degradation in TiO2 based perovskite solar cells (PSC) using a transparent luminescent down-shifting (DS) YVO4:Eu3+ nano-phosphor layer. The PSC coated with DS phosphor showed an improvement in stability under prolonged illumination retaining more than 50% of its initial efficiency, whereas PSC without the phosphor layer degraded to ∼35% of its initial value. The phosphor layer also provided ∼8.5% enhancement in photocurrent due to DS of incident UV photons into additional red photons. YVO4:Eu3+ layer thus served a bi-functional role in PSC by reducing photo-degradation as well as enhancing energy conversion efficiency.
Thermal conductivity of meso-porous germanium
Authors: Isaiev M. , Tutashkonko S. , Jean V. , Termentzidis K. , Nychyporuk T. , Andrusenko D. , Marty O. , Burbelo R. M. , Lacroix D. , Lysenko V.
Published: July 2014

Thermal conductivity value of sponge-like meso-porous germanium (meso-PGe) layers measured by means of photoacoustic technique is reported. The room temperature thermal conductivity value is found to be equal to 0.6 W/(m K). The experimental results are in excellent agreement with molecular dynamic and Monte Carlo simulations. Both experiments and simulations show an important thermal conductivity reduction of the meso-PGe layers compared to the bulk Ge. The obtained results reveal meso-PGe as an interesting candidate for both thermoelectric and photovoltaic applications in which thermal transport is a really crucial issue.
Carbon impurities on graphene synthesized by chemical vapor deposition on platinum
Authors: Ping Jinglei , Fuhrer Michael S.
Published: July 2014

We report nanocrystalline carbon impurities coexisting with graphene synthesized via chemical vapor deposition on platinum. For certain growth conditions, we observe micron-size island-like impurity layers which can be mistaken for second graphene layers in optical microscopy or scanning electron microscopy. The island orientation depends on the crystalline orientation of the Pt, as shown by electron backscatter diffraction, indicating growth of carbon at the platinum surface below graphene. Dark-field transmission electron microscopy indicates that in addition to uniform single-crystal graphene, our sample is decorated with nanocrystalline carbon impurities with a spatially inhomogeneous distribution. The impurity concentration can be reduced significantly by lowering the growth temperature. Raman spectra show a large D peak, however, electrical characterization shows high mobility (∼8000 cm2/Vs), indicating a limitation for Raman spectroscopy in characterizing the electronic quality of graphene.
Anharmonic effects in the thermoelectric properties of PbTe
Authors: Al-Otaibi Jawaher , Srivastava G. P.
Published: July 2014

In this work, we investigate the crystal anharmonic effects in the thermoelectric properties of n-type PbTe. The lattice thermal transport coefficient is computed by employing an isotropic continuum model for the dispersion relation for acoustic as well as optical phonon branches, an isotropic continuum model for crystal anharmonicity, and the single-mode relaxation time scheme. The electronic components of the transport coefficients in a wide temperature range are calculated using the isotropic-nearly-free-electron model, interaction of electrons with deformation potential of acoustic phonons, and the effect of the band non-parabolicity. It is found that the transverse optical branches play a major role in determining the phonon conductivity and the thermoelectric figure of merit of this material.
Evaluation of the two-photon absorption characteristics of GaSb/GaAs quantum rings
Authors: Wagener M. C. , Carrington P. J. , Botha J. R. , Krier A.
Published: July 2014

The optical parameters describing the sub-bandgap response of GaSb/GaAs quantum rings solar cells have been obtained from photocurrent measurements using a modulated pseudo-monochromatic light source in combination with a second, continuous photo-filling source. By controlling the charge state of the quantum rings, the photoemission cross-sections describing the two-photon sub-bandgap transitions could be determined independently. Temperature dependent photo-response measurements also revealed that the barrier for thermal hole emission from the quantum rings is significantly below the quantum ring localisation energy. The temperature dependence of the sub-bandgap photo-response of the solar cell is also described in terms of the photo- and thermal-emission characteristics of the quantum rings.
Scanning tunneling microscopy study of morphology and electronic properties in (K0.7Na0.3)Fe2−ySe2 single crystal
Authors: Trifonov A. S. , Ovchenkov Y. A. , Presnov D. E. , Belosludov R. , Boltalin A. I. , Liu M. , Morozov I. V. , Nejo H. , Vasiliev A. N.
Published: July 2014

We investigated the microstructure of the iron selenide superconductor (K0.7Na0.3)Fe2−ySe2 with a Tc = 32 K and a near 100% Meissner screening volume fraction. Topography and electron transport properties were studied using electron microscopy and ultra-high vacuum scanning tunneling microscopy (STM) techniques. Room temperature STM measurements reliably identify spatial variations of the local electronic properties of this material. The studied crystals consist of continuous regions with significantly different shapes of current-voltage curves reflecting different electronic transport properties of these regions. Fitting of the local current-voltage curves with the Simmons model for metal-dielectric-metal structure confirmed a phase separation in the sample to a metal and semiconducting phases. The observed regions have dimensions in the range of several tenths of a micrometer and indicate a phase separation in the sample.