bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of four‐state inverter using quantum dot gate‐quantum dot channel field effect transistor
Authors: Karmakar S.
Published: August 2013

Quaternary logic can be implemented using quantum dot gate‐quantum dot channel field effect transistors (QDG‐QDCFETs) which produce four states in their transfer characteristics. A circuit model is used to simulate a four‐state state inverter which is the basic building block of any multi‐valued logic (MVL) circuit design. A basic problem of MVL implementation is the noise margin. The stable nature of the transfer characteristics of the QDG‐QDCFET can make them a promising circuit element in future MVL circuit design. Comparison of fabricated device characteristics and the model data is shown.
Combined one‐dimensional lowpass and highpass filters for subband transformer
Authors: Rajovic V. , Savic G. , Ceperkovic V. , Prokin M.
Published: August 2013

Subband transformation coefficients are typically computed by first filtering and downsampling of an input uncompressed signal and then subsequently filtering and downsampling the result intermediate signals with a set of lowpass and highpass filters. State‐of‐the‐art subband transformers are complex, which increases consumed power. A novel method for significantly decreasing the complexity of subband transformers to a minimum is presented. This solution was implemented in a field programmable gate array, together with various methods for compression and decompression.
Method to compensate dispersion effect applied to time domain reflectometry
Authors: Sommervogel L. , El Sahmarany L. , Incarbone L.
Published: August 2013

A new post‐processing approach which aims at reducing the dispersion effect of the wave travelling inside a waveguide is presented. The main objective is to improve the time domain reflectometry measurements performed over long‐distance cables, relative to the wavelength λ. A real‐case scenario is presented so that the gain of this method can be appreciated.
High‐performance wide‐VDDH‐range level converter for mixed‐signal systems
Authors: Kim Jungmoon , Kim Chulwoo
Published: August 2013

A high‐performance wide‐VDDH‐range level converter (LC) is presented for mixed‐signal systems. The proposed LC achieves a low power‐delay product over a wide range of VDDH with VDDL in the near‐threshold region. The proposed LC uses a feed‐forward signal to pull down the output voltage at low VDDH, without increasing the size of the nMOS diode for the pseudo‐VDDL. A comparison with conventional LCs shows that the proposed LC not only supports high VDDH but is also robust at low VDDH while exhibiting high performance.
Ambiguity analysis of HD FM waveforms for use in passive radar
Authors: Smith G.E. , Garry J.L. , Ewing R.L. , Baker C.J.
Published: August 2013

Analogue VHF waveforms have been used extensively as signals of opportunity in passive radar concepts. They have time‐varying ambiguity properties determined by the instantaneous nature of the broadcast content and correspondingly this results in a time‐varying radar performance. In this reported work, the ambiguity properties of high definition (HD) FM signals are examined. It is shown that the digital modulation imposed on these transmissions results in more stable ambiguity properties better suited to reliable and consistent passive radar performance.
Measurement of normalised radar cross‐section of polystyrene foam at 60 GHz
Authors: Kaneko K. , Seki K. , Ihara T.
Published: August 2013

The backscattering measurement of a rectangular solid volume of polystyrene foam (width: 0.92 m; height: 0.9 m; depth: 1.82 m) carried out at frequencies ranging from 59 to 60 GHz is described with horizontal polarisation for both transmission and reception antennas. The volume fraction of polystyrene in the measured material is about 0.01. The normalised radar cross‐section of the measured polystyrene foam sample is estimated as 2.9 × 10−3(±3 × 10−4) m2/m3 by using the range‐resolved data of the backscattered power arising from inside of the polystyrene foam volume. When using polystyrene foam as a support for radar targets in radar measurements, this result is considered useful for quantitatively estimating the intensity of the unwanted backscattered waves due to the foam.
Low‐noise and high‐gain wideband LNA with gm‐boosting technique
Authors: Li Zhiqun , Chen Liang , Wang Zengqi , Wu Chenjian , Cao Jia , Zhang Meng , Wang Chong , Liu Yang , Wang Zhigong
Published: August 2013

A broadband low‐noise amplifier (LNA) is proposed. The active gm‐boosting technique is utilised to reduce the common‐gate (CG) LNA noise figure and improve gain. An implemented prototype using 0.13 μm CMOS technology is evaluated using on‐wafer probing. S11 and S22 are below − 10 dB across 0.1–5 GHz. Measurements show a power gain of 18.3 dB with a − 3 dB bandwidth from 100 MHz to 2.1 GHz and an IIP3 of − 7 dBm at 2 GHz. The measured noise figure is better than 2.5 dB below 2.1 GHz, better than 4.5 dB below 5 GHz and at 500 MHz it obtains its minimum value 1.8 dB. The LNA consumes 14 mW from 1.5 V supply and occupies an area of 0.04 mm2.
High‐resolution technique for simultaneous measurement of phase noise of multi‐wavelength optical systems
Authors: Anthur A.P. , Venkitesh D.
Published: August 2013

A technique is proposed and demonstrated to simultaneously measure the phase noise of four‐wave mixing components, using a combination of heterodyning and delayed self‐heterodyning techniques.
Combination of step sizes for affine projection algorithm with variable mixing parameter
Authors: Choi Jong Hyun , Cho Hyeonwoo , Jeong Jae Jin , Kim Sang Woo
Published: August 2013

An algorithm that introduces a novel scheme for the combination of the two adaptation terms of the affine projection algorithm with different step sizes is proposed. The mixing parameter of the proposed algorithm is determined by minimising the mean‐square deviation. The simulation results show that the proposed algorithm has a faster convergence rate and a smaller steady‐state error than other existing combination algorithms.
Efficient foreground detection for real‐time surveillance applications
Authors: Gruenwedel S. , Petrović N.I. , Jovanov L. , Niño‐Casta‐ñeda J.O. , Pižurica A. , Philips W.
Published: August 2013

The problem of foreground detection in real‐time video surveillance applications is addressed. Proposes is a framework, which is computationally cheap and has low memory requirements. It combines two simple processing blocks, both of which are essentially background subtraction algorithms. The main novelty of the approach is a combination of an autoregressive moving average filter with two background models having different adaptation speeds. The first model, having a lower adaptation speed, models long‐term background and detects foreground objects by finding areas in the current frame which significantly differ from the proposed background model. The second model, with a higher adaptation speed, models the short‐term background and is responsible for finding regions in the scene with a high foreground object activity. The final foreground detection is built by combining the outputs from these building blocks. The foreground obtained by the long‐term modelling block is verified by the output of the short‐term modelling block, i.e. only the objects exhibiting significant motion are detected as real foreground objects. The proposed method results in a very good foreground detection performance at a low computational cost.
Miniaturised two‐layer slit‐patch structure for decoupling printed antennas
Authors: Li Q. , Feresidis A.P.
Published: August 2013

A miniaturised double‐layer slit‐patch structure is introduced for decoupling two closely spaced co‐planar waveguide‐fed printed monopoles with a common ground. The double‐layer structure consists of a slit etched on the common ground between the antennas and a conducting dipole element printed on a very thin dielectric film separating the two layers. Simulated results of the antennas’ performance as well as measurements of fabricated prototypes are presented.
Design of rectifier with extended operating input power range
Authors: Sun H.C. , Zhong Z. , Guo Y.X.
Published: August 2013

A novel rectifier with a considerably extended operating input power range is presented for wireless power transmission applications. The rectifier utilises a depletion‐mode to enhance the diode's breakdown voltage while its built‐in voltage is preserved. As a result, in comparison with traditional rectifiers, this proposed rectifier can achieve a high RF‐to‐DC conversion efficiency in a much wider input power range. Measurement results show that a conversion efficiency of more than 50% can be obtained over the input power range from − 13.5 to 16.7 dBm, proving that this rectifier is suitable for the wireless power transmission applications with varying input power levels.
Generation of UWB pulses using direct modulation of semiconductor laser and optical filtering
Authors: Le Q.T. , Briggmann D. , Kueppers F.
Published: August 2013

A new method to generate ultra‐wideband (UWB) pulses based on direct modulation of laser and optical filtering is demonstrated. The intensity modulation and the frequency modulation of the directly modulated laser are combined by the optical filter, which performs a photonic electro‐optical derivative operation. Gaussian driving pulses are used in order to generate monocycles for ultra‐wideband systems. In association with laser power oscillation, doublet waveforms could also be obtained. Monocycle and doublet pulses are experimentally generated with fractional bandwidths of 139 and 105%, respectively.
Unified split‐step precise integration time‐domain method for dispersive media
Authors: Liu Qi , Ma Xikui , Chen Feng
Published: August 2013

Based on the use of auxiliary differential equations, a unified split‐step precise integration time‐domain (SS‐PITD) method is proposed for modelling wave propagation in linear dispersive media. The unification of this method is achieved by using a general expression to represent the Debye, Lorentz and Drude dielectric medium models. Moreover, due to the introduction of the SS scheme, the original two‐dimensional (2D) or 3D electromagnetic problem reduces to a set of 1D sub‐problems which can be efficiently solved by using the conventional PITD algorithm. It leads to a great reduction in the requirement of computation time and storage space. The proposed method is verified with a numerical example and compared with the finite‐difference time‐domain method.
Tuning power spectrum of semiconductor and intracavity‐etalon based modelocked laser via detuning
Authors: Seo D.S. , Leaird D.E. , Weiner A.M.
Published: August 2013

A report is presented on the tuning of the frequency envelope of a broadband comb source generated from a semiconductor‐based modelocked ring laser with an intracavity high finesse Fabry‐Pérot etalon (FPE). By deliberately adjusting the matching condition between FPE transmission peaks and lasing optical comb frequencies, ∼ 7 nm tuning of more than 200 optical frequency comb lines spaced by 10 GHz is achieved.
SAR image despeckling using adaptive multiscale products thresholding in directionlet domain
Authors: Sethunadh R. , Thomas T.
Published: August 2013

A directionlet transform (DT)‐based multiscale products thresholding is presented which uses a generalised cross‐validation (GCV) technique for synthetic aperture radar image despeckling. DT has gained popularity over the past few years as an anisotropic, critically sampled and perfect reconstruction transform with directional vanishing moments along any two directions. In this reported work, the multiscale correlation of DT is exploited by multiplying the adjacent scale coefficients to enhance edge structures while weakening noise. An optimal subband adaptive threshold based on GCV is then computed using this multiscale product. The despeckled image is finally synthesised by using the threshold applied DT coefficients. The employment of DT results in the significant features in images evolving with high magnitudes across scales, while the noise decays rapidly. The proposed scheme outperforms many of the traditional despeckling schemes in terms of speckle reduction and edge preservation.
3D printing technique for fabrication of frequency selective structures for built environment
Authors: Sanz‐Izquierdo B. , Parker E.A.
Published: August 2013

The frequency selectivity of an array of triple cross elements fabricated using an additive manufacturing technique is assessed, to demonstrate the feasibility of using three‐dimensional (3D) printing techniques in frequency selective structure production. The process is a candidate for the fabrication of frequency sensitive components in buildings, in situations where the electromagnetic architecture is an important consideration. As a simple symmetrical 3D element, the triple cross is part of a class of elements suitable for crystal‐like configurations. The basic performance of the array is summarised through simulations and experimental results.
Error rate analysis of M‐PSK with magnitude modulation envelope control
Authors: Gomes M. , Dinis R. , Silva V. , Cercas F. , Tomlinson M.
Published: August 2013

Magnitude modulation (MM) envelope control is an efficient way of reducing the peak‐to‐average power ratio (PAPR) of single‐carrier (SC) signals and improves an SC system's overall power efficiency. However, MM techniques reduce the PAPR at the cost of introducing distortion, highlighting a need to characterise the symbol error rate (SER) performance loss due to MM. This reported work focuses on the M‐PSK case. An exact probability density function (PDF) based on the generalised extreme value distribution is proposed to model the statistical distribution of MM factors generated by MM techniques applied to SC constant amplitude constellations. By considering MM distortion as a form of fading, it is shown that this PDF may be used to derive an accurate union bound of the SER of M‐PSK transmission on the additive white Gaussian channel channel when using MM envelope control.
Location optimisation for antennas by asynchronous particle swarm optimisation
Authors: Liao Shu‐Han , Chiu Chien‐Ching , Ho Min‐Hui
Published: August 2013

A novel optimisation procedure for the location of the transmitter in 3 × 3 multiple input multiple output wireless local area network wireless communication systems is presented. The optimal antenna location for maximising the channel capacity is searched by particle swarm optimiser (PSO) and asynchronous particle swarm optimisation (APSO). There are two different receiver locations considered in the simulation. These two cases are: (i) the transmitter is mobile in the whole indoor environment and the receivers are located on the tables spaced in intervals uniformly distributed (ii) the transmitter is mobile and the receivers are space in uniformly distributed intervals in the whole indoor environment. Numerical results have shown that the proposed PSO and APSO methods are transmit antenna location is optimised to increase channel capacity. The APSO has better optimisation results compared with the PSO and numerical results also show that the APSO outperforms the PSO in convergence speed.
Development of adaptive perturb and observe‐fuzzy control maximum power point tracking for photovoltaic boost dc–dc converter
Authors: Zainuri Muhammad Ammirrul Atiqi Mohd , Radzi Mohd Amran Mohd , Che Soh Azura , Rahim Nasrudin Abd
Published: August 2013

This study presents an adaptive perturb and observe (P&O)‐fuzzy control maximum power point tracking (MPPT) for photovoltaic (PV) boost dc–dc converter. P&O is known as a very simple MPPT algorithm and used widely. Fuzzy logic is also simple to be developed and provides fast response. The proposed technique combines both of their advantages. It should improve MPPT performance especially with existing of noise. For evaluation and comparison analysis, conventional P&O and fuzzy logic control algorithms have been developed too. All the algorithms were simulated in MATLAB‐Simulink, respectively, together with PV module of Kyocera KD210GH‐2PU connected to PV boost dc–dc converter. For hardware implementation, the proposed adaptive P&O‐fuzzy control MPPT was programmed in TMS320F28335 digital signal processing board. The other two conventional MPPT methods were also programmed for comparison purpose. Performance assessment covers overshoot, time response, maximum power ratio, oscillation and stability as described further in this study. From the results and analysis, the adaptive P&O‐fuzzy control MPPT shows the best performance with fast time response, less overshoot and more stable operation. It has high maximum power ratio as compared to the other two conventional MPPT algorithms especially with existing of noise in the system at low irradiance.
Light‐weight framework for security‐sensitive wireless sensor networks applications
Authors: Jokhio Sana H. , Jokhio Imran Ali , Kemp Andrew H.
Published: August 2013

For certain security‐sensitive wireless sensor network (WSN) applications, physical location information of the sensor nodes must not be disclosed to any unauthorised entity. During the localisation phase for such applications the physical locations of sensor nodes are kept secret. Globally, a number of secure location estimation schemes have been proposed from various perspectives, but some important constraints of sensor nodes are often ignored. The considered limitations during design of those schemes vary with respect to varying research perspective. In this study, we propose a novel security framework for secure location estimation of sensor nodes suitable for security‐sensitive WSN applications. The proposed framework aims to provide security, scalability, adaptability and optimise power consumption during the secure location estimation phase of a wireless sensor network. The designed framework consists of a two‐way authentication scheme, a light‐weight encryption mechanism and a novel secure key generation algorithm. The study discusses strengths of the components if used for secure localisation individually, as well as when used together as interactive parts of a security framework for WSN applications.
High gain single GaAs nanowire photodetector
Authors: Wang Hao
Published: August 2013

An undoped single GaAs nanowire (NW) photodetector based on a metal–semiconductor–metal Schottky diode structure is fabricated by a focused ion beam method. The photoconductive gain of the device reaches 20 000 at low laser excitation. Bias-dependence of gain proves that the surface contributes more to the gain at higher bias because of an increased surface charge region. The spectral response demonstrates not only the band-edge absorption profile of the single GaAs NW, but also the existence of leaky-mode resonance.
New forcing scheme to sustain particle-laden homogeneous and isotropic turbulence
Authors: Mallouppas G. , George W. K. , van Wachem B. G. M.
Published: August 2013

This paper evaluates the effect of forcing to sustain turbulence on the transfer function of the fluid with particles suspended in a homogeneous and isotropic flow. As mentioned by Lucci et al. [“Modulation of isotropic turbulence by particles of Taylor length-scale size,” J. Fluid Mech.650, 5–55 (2010)10.1017/S0022112009994022], there are three limitations of forcing particle-laden homogeneous and isotropic turbulence: (a) large fluctuations on the temporal evolution of the kinetic energy are created when forcing is active at low wavenumbers, (b) the redistribution of energy is affected when forcing is performed over all wavenumbers, and (c) the nonlinear transfer function of the fluid due to the triadic interactions is affected when forcing is active over a wavenumber range. These limitations make the interpretation of the effects of particles on the energy spectrum of the fluid difficult. A new forcing scheme in physical space has been designed which avoids these limitations in wavenumber space, so the spectral effects of particles can be evaluated. The performance of this forcing scheme is tested using Direct Numerical Simulations. It is shown that the nonlinear transfer function of the fluid with the current forcing scheme is only affected at the wavenumbers it is acting, consistent with the theory. Even so, the spatial coherence and phase spectra between the two-way coupling and the fluid computed from the simulations show that the new forcing scheme is only moderately correlated even for the forced wavenumbers, with correlation coefficient typically about 10%.
Coupled-plasmon-controlled transmission in distributed Bragg structures
Authors: Rohde Charles , Deutsch Miriam
Published: August 2013

Using the finite element method, we investigate plasmon-mediated transmission in a periodically modulated metal-insulator-metal grating. We compute the eigenmodes of a silver-silica-silver conformal coating atop an array of close-packed silica rods, and correlate them with extinction and transmission characteristics of the structure. We observe efficient coupling of impinging plane-waves to gap plasmon modes, allowing control of both bandwidth and intensity of the transmitted radiation.
Active microrheology: Fixed-velocity versus fixed-force
Authors: Swan James W. , Zia Roseanna N.
Published: August 2013

In active microrheology, a probe particle is driven by an external force through a complex medium and its motion studied in order to infer properties of the embedding material. It is conducted in two limiting forms: either the probe is propelled by a fixed force, as with magnetic tweezers, or it is driven at a fixed velocity, as with optical tweezers. Recent work has shown that the mean probe motion can be interpreted as an effective material viscosity, but that this viscosity depends on whether the fixed-force or fixed-velocity mode is employed. We compute the effective viscosity probed by fixed-velocity active microrheology of a dilute colloidal dispersion. A comparison is made between this new result and the effective viscosity probed in the fixed-force mode. In the absence of hydrodynamic interactions, the particle-phase contributions to the effective viscosity for the two modes differ by exactly a factor of two. A simple scaling argument has been previously advanced to rationalize this difference: in the fixed-force mode, the probe is free to diffuse, and thus the relaxation time scale is set by the relative diffusivity between probe and bath. However, in the fixed-velocity mode, thermal motion of the probe particle is “frozen out” because the probe cannot diffuse; the relaxation rate is thus halved. The ratio of the two rates is independent of how quickly the probe particle is driven through the suspension—the extent and shape of microstructural deformation is the same for the two cases. In contrast, when the suspended particles interact hydrodynamically, the distortions to the suspension microstructure in the fixed-velocity versus fixed-force modes differ. We show that, depending on the strength of the hydrodynamic interactions, the ratio of the fixed-velocity to the fixed-force microstructural contributions to the effective viscosity may be as small as 1.3, and only approaches 2.0 when hydrodynamic interactions among the particles are negligibly weak. While this ratio varies both as a function of the strength of the deformation imposed and of the strength of hydrodynamic interactions, the fixed-velocity effective viscosity agrees qualitatively with that already measured for the fixed-force mode: the colloidal dispersion thins in the limit of weak hydrodynamic interactions; and it first thins and then thickens in the limit of strong hydrodynamic interactions, as the strength of deformation increases, recovering characteristics of shear-(force-) thinning and thickening well known in colloidal dispersions. The agreement between the two, and with traditional macrorheological approaches, shows that both fixed-force and fixed-velocity provide a useful tool for the interrogation of complex fluids.
A time digitizer for space instrumentation using a field programmable gate array
Authors: Rogacki S. , Zurbuchen T. H.
Published: August 2013

Space instruments such as time-of-flight (TOF) mass spectrometers and altimeters rely on time-to-digital converters (TDCs) to measure accurately times in the picosecond to microsecond range. Time-to-digital conversion is often implemented with analog circuitry or more recently with custom ASIC (Application Specific Integrated Circuit) devices. The analog approach may be costly in terms of circuit board area and parts count, while ASIC development is risky and costly when system requirements may change. Here, we present a highly flexible, accurate, and low-cost field-programmable gate array (FPGA) implementation of such TDC functionality. Compared with other technologies, this method reduces the parts count in TOF-supporting circuits and provides design flexibility in TOF instrumentation, especially for use in space or for applications with a number of sensors too small to warrant the development of a dedicated ASIC. Our technique can accommodate one or more STOP pulse measurements for each START pulse as signal reference, effectively providing measurements of multiple times-of-flight with the same start trigger. Alternatively, all pulse event edges can receive an absolute time stamp, enabling a broad set of new sensor applications. This novel design is based on the construction of a delay-line internal to the FPGA. Propagation variations due to temperature and supply voltage, which typically limit FPGA-based timing designs, are automatically compensated, allowing active signal processing 100% of the time. A methodology for the characterization of internal delay-line timing and nonlinearity has also been developed and is not specific to a particular FPGA architecture. We describe the design of this FPGA-based TDC and also describe detailed tests with a Xilinx XC2V1000. For single non-repetitive events, this design achieves 60 ps accuracy (standard deviation of error); a simplified implementation is suitable for non-reprogrammable FPGAs.
A comparative study of methods to compute the free energy of an ordered assembly by molecular simulation
Authors: Moustafa Sabry G. , Schultz Andrew J. , Kofke David A.
Published: August 2013

We present a comparative study of methods to compute the absolute free energy of a crystalline assembly of hard particles by molecular simulation. We consider all combinations of three choices defining the methodology: (1) the reference system: Einstein crystal (EC), interacting harmonic (IH), or r−12 soft spheres (SS); (2) the integration path: Frenkel-Ladd (FL) or penetrable ramp (PR); and (3) the free-energy method: overlap-sampling free-energy perturbation (OS) or thermodynamic integration (TI). We apply the methods to FCC hard spheres at the melting state. The study shows that, in the best cases, OS and TI are roughly equivalent in efficiency, with a slight advantage to TI. We also examine the multistate Bennett acceptance ratio method, and find that it offers no advantage for this particular application. The PR path shows advantage in general over FL, providing results of the same precision with 2–9 times less computation, depending on the choice of a common reference. The best combination for the FL path is TI+EC, which is how the FL method is usually implemented. For the PR path, the SS system (with either TI or OS) proves to be most effective; it gives equivalent precision to TI+FL+EC with about 6 times less computation (or 12 times less, if discounting the computational effort required to establish the SS reference free energy). Both the SS and IH references show great advantage in capturing finite-size effects, providing a variation in free-energy difference with system size that is about 10 times less than EC. This result further confirms previous work for soft-particle crystals, and suggests that free-energy calculations for a structured assembly be performed using a hybrid method, in which the finite-system free-energy difference is added to the extrapolated (1/N→0) absolute free energy of the reference system, to obtain a result that is nearly independent of system size.
Exploring covalently bonded diamondoid particles with valence photoelectron spectroscopy
Authors: Zimmermann Tobias , Richter Robert , Knecht Andre , Fokin Andrey A. , Koso Tetyana V. , Chernish Lesya V. , Gunchenko Pavel A. , Schreiner Peter R. , Möller Thomas , Rander Torbjörn
Published: August 2013

We investigated the valence electronic structure of diamondoid particles in the gas phase, utilizing valence photoelectron spectroscopy. The samples were singly or doubly covalently bonded dimers or trimers of the lower diamondoids. Both the bond type and the combination of bonding partners are shown to affect the overall electronic structure. For singly bonded particles, we observe a small impact of the bond on the electronic structure, whereas for doubly bonded particles, the connecting bond determines the electronic structure of the highest occupied orbitals. In the singly bonded particles a superposition of the bonding partner orbitals determines the overall electronic structure. The experimental findings are supported by density functional theory computations at the M06-2X/cc-pVDZ level of theory.
O-atom transport catalysis by neutral manganese oxide clusters in the gas phase: Reactions with CO, C2H4, NO2, and O2
Authors: Yin Shi , Wang Zhechen , Bernstein Elliot R.
Published: August 2013

Reactions of CO, C2H4, NO2, and O2 with neutral MnmOn clusters in a fast flow reactor are investigated both experimentally and theoretically. Single photon ionization at 118 nm is used to detect neutral cluster distributions through time of flight mass spectrometry. MnmOn clusters are generated through laser ablation of a manganese target in the presence of 5% O2/He carrier gas. A strong size dependent reactivity of MnmOn clusters is characterized. Reactions Mn2O5/Mn3O7 + CO → Mn2O4/Mn3O6 + CO2 are found for CO oxidation by MnmOn clusters, while only association products Mn2O3-5C2H4 and Mn3O5-7C2H4 are observed for reactions of C2H4 with small MnmOn clusters. Reactions of MnmOn clusters with NO2 and O2 are also investigated, and the small Mn2On clusters are easily oxidized by NO2. This activation suggests that a catalytic cycle can be generated for the Mn2O5 cluster: Mn2O5 + CO + NO2 → Mn2O4 + CO2 + NO2 → Mn2O5 + CO2 + NO. Density functional theory (DFT) calculations are performed to explore the potential energy surfaces for the reactions Mn2O4,5/Mn3O7 + CO → Mn2O3,4/Mn3O6 + CO2, Mn2O5 + C2H4 → Mn2O4 + CH3CHO, and Mn2O4 + NO2 → Mn2O5 + NO. Barrierless and thermodynamically favorable pathways are obtained for Mn2O5/Mn3O7 + CO and Mn2O4 + NO2 reactions. A catalytic cycle for CO oxidation by NO2 over a manganese oxide surface is proposed based on our experimental and theoretical investigations. The various atom related reaction mechanisms explored by DFT are in good agreement with the experimental results. Condensed phase manganese oxide is suggested to be a good catalyst for low temperature CO oxidation by NO2, especially for an oxygen rich sample.
Primary and secondary pyroelectric coefficients of rhombohedral and tetragonal single-domain relaxor-PbTiO3 single crystals
Authors: Tang Yanxue , Zhang Shujun , Shen Zongyang , Jiang Wenhua , Luo Jun , Sahul Raffi , Shrout Thomas R.
Published: August 2013

The primary and secondary pyroelectric coefficients were determined for binary (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN-PT) and ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PIN-PMN-PT) relaxor-PT single crystals. The secondary pyroelectric coefficients were calculated from the thermodynamic inter-relationship between the piezoelectric, elastic, and thermal expansion coefficients. Poling along [111] and [001] directions resulted in single-domain state of “1R” and “1T” and a macroscopic symmetry of 3m and 4mm for rhombohedral (x = 0.28) and tetragonal (x = 0.42) crystals, respectively, enabling relatively large values of pyroelectric coefficients p ≥ 5.7 × 10−4 C/m2 K. The calculated results show that the secondary pyroelectric coefficients are in the range of (−0.62 ∼ −1.06) × 10−4 C/m2 K for rhombohedral crystals and (0.70 ∼ 1.14) × 10−4 C/m2 K for tetragonal crystals, significantly lower than that of primary pyroelectric coefficients, which is important for thermal directional and imaging applications. In contrast, high d15 piezoelectric coefficients (>2000 pC/N), together with zero pyroelectric coefficients in thickness shear crystals, also makes them promising candidates for piezoelectric sensors where thermal noise is undesirable.
Nanoparticle characterization of Er-doped SnO2 pellets obtained with different pH of colloidal suspension
Authors: Ravaro Leandro P. , Scalvi Luis V. A. , Tabata Américo S. , Pontes Fenelon M. L. , Oliveira José B. B.
Published: August 2013

SnO2:2 at. %Er xerogel samples were obtained by sol-gel technique from colloidal suspensions with distinct pHs. The evaluation of critical regions inside the nanocrystallite is fundamental for the interpretation of the influence of pH on the emission data. In this way, the nanocrystal depletion layer thickness was obtained with the help of photoluminescence, Raman, X-ray diffraction, and field-emission gun scanning electron microscopy measurements. It was observed that acid suspensions (pH < 7) lead to high surface disorder in which a larger number of cross-linked bonds Sn-O-Sn among nanoparticles are present. For these samples, the nanoparticle depletion layer is larger as compared to samples obtained from other pH. Photoluminescence measurement in the near infrared region indicates that the emission intensity of the transition 4I13/2 → 4I15/2 is also influenced by the pH of the starting colloidal suspension, generating peaks more or less broadened, depending on location of Er3+ ions in the SnO2 lattice (high or low symmetry sites).
Dynamic deformation of strongly nonlinear toroidal rubber elements
Authors: Lee Chien-Wei , Nesterenko Vitali F.
Published: August 2013

Dynamic deformation of rubber toroidal elements (o-rings) was investigated under dynamic loading conditions at strain rates 102 s−1. The forces acting on o-rings were simultaneously monitored using an accelerometer and strain gauges, while global engineering strains were independently determined by a synchronized high speed camera. Dynamic non-linear stress-strain relation was compared with empirical relation obtained from static loading of o-rings. The paper presents first experimental results and analysis of dissipative properties of o-rings during dynamic compression and unloading. The strongly nonlinear force-strain and strain-rate dependent behavior was described using nonlinear viscoelastic relation with only one adjustable parameter.
Magnetism of CoFe2O4 ultrathin films on MgAl2O4 driven by epitaxial strain
Authors: Gatel C. , Warot-Fonrose B. , Matzen S. , Moussy J.-B.
Published: August 2013

We report on the correlations between magnetic anisotropy and strain state in CoFe2O4 ultrathin films grown on MgAl2O4(100) and MgAl2O4(111) substrates. By local strain analysis using the geometric phase method, a significant in-plane compressive strain is observed for the (001) orientation while a full relaxation is detected for the (111) orientation. The relaxation process in CoFe2O4(111) layers induces interface dislocations and a large amount of antiphase boundaries while a pseudomorphic growth is observed for the (001) direction, decreasing significantly the density of antiphase boundaries. By comparing the magnetoelastic energy terms, the correlation between strain state and resultant magnetization is discussed.
Single ferromagnetic layer magnetic random access memory
Authors: Xing M.-J. , Jalil M. B. A. , Ghee Tan Seng , Jiang Y.
Published: August 2013

We propose a magnetic random access memory (MRAM) device in which both the writing and reading processes are realized within a single ferromagnetic (FM) layer. The FM layer is sandwiched between layers of heavy element and oxide to enhance the Rashba spin-orbit coupling (RSOC). When the in-plane FM moments are oriented at some intermediate angle to the current direction, the RSOC effect induces a spin accumulation in the FM layer, which in turn generates a Rashba spin torque field via the s-d exchange interaction. This field acts as the writing field of the memory device. The RSOC also induces a charge accumulation in the transverse direction via the inverse spin Hall effect (ISHE), which can be used to realize the memory read-out. The writing and read-out processes of the proposed memory are modeled numerically via the non-equilibrium Green's function technique. Besides the advantages of Rashba spin torque writing, i.e., no spin injection and symmetrical data-writing process, this single FM layer MRAM design does away with having a giant magnetoresistive or magnetic tunnel junction multilayer structure by utilizing the ISHE for the read-out process.
Entropy production in hot-phonon energy conversion to electric potential
Authors: Shin Seungha , Kaviany Massoud
Published: August 2013

We apply phonon and electron nonequilibrium-population statistical entropy analysis to the recently introduced phonon energy to electric potential conversion heterobarrier with its height optimized for optical phonon absorption under steady electric current. The entropy production rates for phonon and electron subsystems depend on their interaction kinetics and occupancy distributions, indicating the direction of the processes. Under upstream thermal equilibrium among electrons and acoustic and optical phonons, we predict an upper limit of 42% energy conversion for GaAs heterobarrier at 300 K, while the reported Monte Carlo prediction of 19% efficiency is below this limit. We show that for upstream electrons in thermal equilibrium with the acoustic phonons, while under supply of hot optical phonons, the conversion efficiency increases significantly, making integration of the barrier into optical phonon emitting circuits and devices very attractive.
Temperature characteristics of spontaneous emission and optical gain in blue InGaN/GaN quantum well structures
Authors: Park Seoung-Hwan , Moon Yong-Tae
Published: August 2013

Temperature characteristics of the light emission in blue InGaN/GaN quantum well (QW) structures were investigated using the multiband effective mass theory. The light emission intensity decreases gradually with increasing temperature because of the reduction in the optical matrix element due to the decrease in the potential well depth. On the other hand, the spillover is shown to be negligible in the investigated range of temperature and the T0 value of about 255 K is obtained. The radiative recombination coefficient Beff decreases from 0.3 × to 0.2×10−4 cm6/s at the sheet carrier density of 5×1012 cm−2 when changing from 300 to 400 K. As a result, the internal efficiency is reduced with increasing temperature because of the reduction in the radiative recombination rate.
First principles and experimental study of the electronic structure and phase stability of bulk thallium bromide
Authors: Smith Holland M. , Zhou Yuzhi , Ciampi Guido , Kim Hadong , Cirignano Leonard J. , Shah Kanai S. , Haller E. E. , Chrzan D. C.
Published: August 2013

We apply state-of-art first principle calculations to study the polymorphism and electronic structure of three previously reported phases of TlBr. The calculated band structures of NaCl-structure phase and orthorhombic-structure phase have different features than that of commonly observed CsCl-structure phase. We further interpret photoluminescence spectra based on our calculations. Several peaks close to calculated band gap values of the NaCl-structure phase and the orthorhombic-structure phase are found in unpolished TlBr samples.
Research on the effect of crystal structures on W-TiO2 nanotube array photoelectrodes by theoretical and experimental methods
Authors: Xin Yanjun , Wang Yicheng , Liu Huiling , Ma Dong , Cheng Wei
Published: August 2013

W-doped/undoped TiO2 nanotube array (TNAs) photoelectrodes with different nanostructures were successfully fabricated using the anodization method. Their morphology and characteristics were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and ultra violet/visible light diffuse reflectance spectra (UV/vis/DRS). Their electronic structure and optical properties were studied by means of first-principle. Photocatalytic (PC) performance of W-TNAs photoelectrodes with different crystal structures was evaluated using the decomposition rates of Rhodamine B (Rh.B) under xenon light illumination. The results demonstrated that W substituting Ti broadened the width of conduction band (CB) and valence band (VB) of anatase and rutile TiO2, reduced the band gap of rutile TiO2 and even caused its red-shift. W incorporated into TNAs photoelectrodes extended light absorption threshold and enhanced its utilization of solar light and PC activity, particularly, the PC performance of W-TNAs photoelectrodes with mixed crystal and rutile crystal structure.
Rectifying behaviors introduced by nitrogen-vacancy complex in spiral chirality single walled carbon nanotube device
Authors: Cheng Caiping , Hu Huifang , Wei Yan , Zhang Zhaojin , Wang Xiaowei , Zhao Juan , Peng Ping
Published: August 2013

By applying nonequilibrium Green's functions in combination with density-functional theory, the effects of nitrogen-vacancy complex on electronic transport properties are investigated in spiral chirality single walled carbon nanotube device. The results show that rectifying behaviors can be tuned by introducing the complex defects with vacancy and nitrogen atoms. Moreover, current-voltage characteristics and negative differential conductance behavior can also be observed in this model. The mechanisms for these interesting phenomena are suggested.
Ferroelectric film bulk acoustic wave resonators for liquid viscosity sensing
Authors: Vorobiev A. , Gevorgian S.
Published: August 2013

A concept of accurate liquid viscosity sensing, using bulk acoustic wave (BAW) resonators, is proposed. The proposed BAW resonators use thin ferroelectric films with the dc field induced piezoelectric effect allowing for generation of pure longitudinal acoustic waves in the thickness excitation mode. This makes it possible to utilize exclusively shear liquid particle displacement at the resonator side walls and, therefore, accurate viscosity evaluation. The BAW resonators with the dc field induced piezoelectric effect in 0.67BiFeO3–0.33BaTiO3 ferroelectric films are fabricated and their liquid viscosity sensing properties are characterized. The resonator response is analyzed using simple model of a harmonic oscillator damped by a viscous force. It is shown that the resonator Q-factor is inversely proportional to the square root of the viscosity-density product. The viscosity measurement resolution is estimated to be as high as 0.005 mPa·s, which is 0.5% of the water viscosity.
Theoretical study of structural stabilities and magnetic properties of doped transition metals in MnTe vs ZnTe and CdTe: Reduced clustering trend and enhanced magnetic coupling
Authors: Wu Jian-Ming , Chen Xing-Yuan , Lin Shi-Yuan , Zhao Yu-Jun
Published: August 2013

Clustering and weak magnetic coupling of doped transition metals (TMs) have hampered the potential spintronic applications of many magnetic semiconductors. Here, the influence of the host crystal magnetic background on the magnetic coupling and clustering of TM impurities is studied theoretically, with a comparison of a series of TMs (V, Cr, Fe, Co, and Ni) in MnTe, ZnTe, and CdTe hosts. We found that the antiferromagnetic (AFM) background of MnTe degrades the clustering tendency of the studied TM impurities (except Ni). Meanwhile, the AFM background of MnTe significantly enhances the magnetic coupling of doped Fe, Co, and Ni pairs in general, either ferromagnetically (for Fe, Ni) or antiferromagnetically (for Co). The enhanced ferromagnetic coupling and weakened clustering of Fe impurities in MnTe imply that an AFM background of host semiconductors may aid the development of high TC magnetic semiconductors with intrinsic magnetism.
Temperature-dependent phonon shifts in monolayer MoS2
Authors: Lanzillo Nicholas A. , Glen Birdwell A. , Amani Matin , Crowne Frank J. , Shah Pankaj B. , Najmaei Sina , Liu Zheng , Ajayan Pulickel M. , Lou Jun , Dubey Madan , Nayak Saroj K. , O'Regan Terrance P.
Published: August 2013

We present a combined experimental and computational study of two-dimensional molybdenum disulfide and the effect of temperature on the frequency shifts of the Raman-active E2g and A1g modes in the monolayer. While both peaks show an expected red-shift with increasing temperature, the frequency shift is larger for the A1g mode than for the E2g mode. This is in contrast to previously reported bulk behavior, in which the E2g mode shows a larger frequency shift with temperature. The temperature dependence of these phonon shifts is attributed to the anharmonic contributions to the ionic interaction potential in the two-dimensional system.
Comparison of GaAsP solar cells on GaP and GaP/Si
Authors: Lang Jordan R. , Faucher Joseph , Tomasulo Stephanie , Nay Yaung Kevin , Larry Lee Minjoo
Published: August 2013

We demonstrate metamorphic ∼1.7 eV GaAsxP1−x (x = 0.71 − 0.73) solar cells on high-quality GaP/Si templates and compare them to cells co-grown on bulk GaP. Both n+-emitter/p-base and p+-emitter/n-base polarities are explored. Cells with n-type bases demonstrate current-voltage characteristics that are similar to p-type base cells, but with blue-shifted peak quantum efficiencies. Threading dislocation densities for cells on GaP/Si were 0.92 − 1.3 × 107 cm−2, significantly lower than previous reports but higher than cells grown on bulk GaP. An open-circuit voltage of 1.12 V was obtained for a 1.71 eV cell on Si, leading to a promising bandgap-voltage offset of 0.59 V.
Strained-Si/strained-Ge type-II staggered heterojunction gate-normal-tunneling field-effect transistor
Authors: Hsu William , Mantey Jason , Register Leonard F. , Banerjee Sanjay K.
Published: August 2013

A SiGe-based n-channel tunnel field-effect transistor design employing a strained-Si/strained-Ge staggered-gap heterojunction with a small effective band-gap (122 meV) at the interface is investigated via numerical simulations using a semi-classical quantum correction obtained from the density-gradient model. A gate-normal tunneling geometry is used to increase tunneling area and reduce subthreshold swing. The strain leads to degeneracy breaking among the silicon conduction band valleys, reducing the density of states and associated quantum capacitance with better gate-to-tunnel barrier coupling. Performance evaluation using a figure-of-merit “I60,” where the drain current corresponds to a subthreshold slope of 60 mV/decade, suggests that the device has the potential to be competitive with modern metal-oxide-semiconductor field-effect transistors.
Circadian rhythms in Neurospora crassa on a polydimethylsiloxane microfluidic device for real-time gas perturbations
Authors: Lee Kang Kug , Ahn Chong H. , Hong Christian I.
Published: August 2013

Racetubes, a conventional system employing hollow glass tubes, are typically used for monitoring circadian rhythms from the model filamentous fungus, Neurospora crassa. However, a major technical limitation in using a conventional system is that racetubes are not amenable for real-time gas perturbations. In this work, we demonstrate a simple microfluidic device combined with real-time gas perturbations for monitoring circadian rhythms in Neurospora crassa using bioluminescence assays. The developed platform is a useful toolbox for investigating molecular responses under various gas conditions for Neurospora and can also be applied to other microorganisms.