bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of large dynamic range, low‐power, high‐precision ROIC for quantum dot infrared photo‐detector
Authors: Gupta H.S. , Kumar A.S.K. , Chakrabarti S. , Paul S. , Parmar R.M. , Samudraiah D.R.M. , Baghini M.S. , Sharma D.K.
Published: July 2013

Hybrid infrared (IR) focal plane arrays consist of an array of IR photo‐detectors, bump‐bonded to a silicon CMOS readout integrated circuit (ROIC) chip. Design and optimisation of ROIC for quantum dot IR detectors is a multidimensional problem. The major design challenge is to select appropriate readout circuit topology to meet the large dynamic range requirement of quantum dot IR photo‐detectors within the area dictated by the matched pixel size. Proposed is an efficient design optimisation for ROIC. The optimisation is based on a proposed decision matrix, which leads to a decision merit for ROIC design. Four main specifications, i.e. charge handling capacity, noise, power dissipation and detector bias voltage variations, have been considered. Various architectures have been compared using circuit design, simulation and implementation. The targeted ROIC specifications for a test chip containing a 4 × 4 array are: 5 Mē charge handling capacity, 30 × 30 µm maximum pixel size, snapshot mode of operation, variable integration time, 5 megapixels/s (Mpps) readout rate and readout noise of 600ē at ambient temperature. Also presented is a design with 5 Mē charge handling capacity, which has not been reported for 180 nm CMOS process earlier.
Design of ultra‐wideband bandstop filter using defected ground structure
Authors: Chen Fu‐Chang , Zhang Ning‐Yu , Zhang Pei‐Sheng , Chu Qing‐Xin
Published: July 2013

A simple wideband bandstop filter which yields equal ripples in the stopband is described. The filter comprises only two resonators and a connecting transmission line. Ultra‐wide stopband characteristic is achieved by realising three transmission zeros near the passband edges. Stopband rejection depth and bandwidth can be controlled by impedances of the configuration. The defected ground structure is chosen to realise the high impedance line. To validate the proposed topology, a compact microstrip bandstop filter centred at 1.5 GHz with a measured 20 dB rejection bandwidth of about 139% is fabricated.
Low‐profile circularly polarised loop antenna assisted with an effective PMC bandwidth
Authors: Li H. , Xu K.W. , Wang X.B. , Kanan R. , Ran L.X.
Published: July 2013

Proposed is an ultra‐low‐profile loop antenna backed by an electromagnetic bandgap (EBG) surface reflector, where the EBG surface can effectively exhibit the property of a perfect magnetic conductor (PMC) inside a deliberately designed bandwidth. It is shown that, assisted by the effective PMC bandwidth, while the proposed antenna is with a 0.07‐λ spacing between the loops and the EBG reflector, its axial ratio (AR) and voltage standing wave ratio (VSWR) performances are significantly improved. Experimental measurements show that the prototype antenna has a 3 dB AR bandwidth of 17% with an input VSWR less than 1.6. The proposed approach can find a wide range of low‐profile circularly polarised (CP) antenna applications.
Laser‐controlled superconducting switch for low‐field NMR applications
Authors: Lechéa N. , Filloy‐Corbrion C. , Holé S.
Published: July 2013

In the case of a low‐field nuclear magnetic resonance (NMR) system, the sensible magnetic sensor can be screened or even damaged by the large magnetic field produced during the polarisation phase. A switch is then necessary to preserve this sophisticated sensor. A simple and efficient switch is described here. It is made of a twisted and wound wire heated by a laser beam, in which the alignment is simple by construction. The switch can be used without any additional contact in sensing coils, has a low inductance and flips within milliseconds. It is shown that the switch resistance in open conditions is sufficient for low‐field NMR applications and that a memory behaviour can be exhibited.
Single‐stage battery charger for light electric vehicles based on DC‐SRC with current‐boosting circuit
Authors: Yoon Y.‐D. , Kwon S.‐M. , Lee J.‐Y.
Published: July 2013

A single‐stage battery charger for light electric vehicles to improve lifetime by removing high‐voltage electrolytic capacitors is suggested. The proposed charger is based on a diode‐clamped series resonant converter equipped with a current‐boosting circuit, which increases the power factor by removing dead zones in the line current. The feasibility of the proposed charger has been verified with a 1.7 kW prototype.
Avalanche current read‐out circuit for low‐jitter parallel photon timing
Authors: Crotti M. , Rech I. , Gulinatti A. , Ghioni M.
Published: July 2013

A circuit for single‐photon avalanche diode (SPAD) current read‐out, for photon timing applications, is proposed. The circuit consists of a single‐transistor transimpedance amplifier with a gigahertz bandwidth: the feedback loop fixes the SPAD anode voltage and allows obtaining a high time resolution with a very high equivalent current threshold (almost 700 µA). The transimpedance stage is followed by a lowpass filter that reduces the crosstalk of other on‐chip detectors and makes the designed structure suitable for multi‐detector systems. The presented discrete components prototype achieves a state‐of‐the‐art resolution of 34.4 ps full width at half maximum, has negligible crosstalk between the different pixels and opens the way for the development of an integrated structure with a large number of channels.
Improved optical orthogonal frequency‐division multiplexing performance using non‐linear signal compression in intensity modulation and direct detection transmission systems incorporating parameter‐relaxed digital‐to‐analogue converters/analogue‐to‐digital converters
Authors: Zheng Xing , Tang Jianming
Published: August 2013

Adaptively modulated optical orthogonal frequency‐division multiplexing (AMOOFDM) using non‐linear signal compression (NSC) (AMOOFDM‐NSC) is proposed and numerically explored, for the first time, in intensity modulation and direct detection (IMDD) single‐mode fibre transmission systems for cost‐sensitive optical access networks. AMOOFDM‐NSC utilises a simple cosine operation to compress digital electrical OFDM signals prior to performing digital‐to‐analogue conversion and optical intensity modulation in the transmitter. Compared with conventional AMOOFDM, AMOOFDM‐NSC can not only significantly lower requirements on minimum quantisation bits and sampling rates of digital‐to‐analogue/analogue‐to‐digital convertors, but also simultaneously doubles the signal transmission capacity for quantisation bits of < 4. In addition, AMOOFDM‐NSC also shows excellent system flexibility and has good performance robustness to variations in system characteristics. AMOOFDM‐NSC may have great potential for providing a cost‐effective technical solution for practical implementations in cost‐sensitive access networks.
Controllable stretched pulse and dissipative soliton emission using non‐linear polarisation rotation and cavity loss tuning mechanism
Authors: Tan Sin Jin , Harun Sulaiman Wadi , Ahmad Harith
Published: August 2013

The authors demonstrate a controllable generation of a stretched pulse and dissipative soliton in a normal dispersion erbium‐doped fibre laser (EDFL) based on non‐linear polarisation rotation technique. It is found that the mode‐locking could self‐start in the EDFL even without inserting a polariser in the cavity because of the large residual polarisation‐dependent loss of a cavity component. By slightly adjusting a polarisation controller, a stretched pulse can be switchable to the dissipative soliton, while maintaining the repetition rate of 2.5 MHz. The stretched pulse has a pulse width of 0.35 ps with energy of 127.6 pJ, whereas the dissipative soliton has a pulse width of 0.60 ps with energy of 208.4 pJ.
Takagi–Sugeno–Kang type probabilistic fuzzy neural network control for grid‐connected LiFePO4 battery storage system
Authors: Lin Faa‐Jeng , Huang Ming‐Shi , Hung Ying‐Chih , Kuan Chi‐Hsuan , Wang Sheng‐Long , Lee Yih‐Der
Published: August 2013

A Takagi–Sugeno–Kang type probabilistic fuzzy neural network (TSKPFNN) control is proposed to control a grid‐connected LiFePO4 battery storage system in this study. First, the modelling of the battery and bidirectional AC–DC converter are described in detail. Then, the active and reactive power controls using phase‐lock loop are briefly introduced. Moreover, to improve the control performance of the grid‐connected LiFePO4 battery storage system, the TSKPFNN control, which combines the advantages of Takagi–Sugeno–Kang type fuzzy logic system and three‐dimensional membership function, is developed. The network structure, online learning algorithm using delta adaptation law and convergence analysis of the TSKPFNN are described in detail. Furthermore, a 32‐bit fixed‐point digital signal processor, TMS320F28035, is adopted for the implementation of the proposed intelligent controlled battery storage system. Finally, some experimental results are illustrated to show the validity of the proposed TSKPFNN control for the grid‐connected LiFePO4 battery storage system.
Analytical optimisation of solid‐round‐wire windings conducting dc and ac non‐sinusoidal periodic currents
Authors: Wojda Rafal P. , Kazimierczuk Marian K.
Published: August 2013

In this study, an analytical optimisation of solid‐round‐wire windings conducting both the dc and ac non‐sinusoidal periodic currents is performed. A closed‐form analytical equation is derived for the normalised solid‐round‐wire diameter to achieve the minimum power loss for inductors conducting ac non‐sinusoidal periodic currents superimposed on the dc component. The low‐ and medium‐frequency normalised winding ac resistance for the nth harmonic frequency is derived and used to obtain the normalised total‐power‐valley diameter at the local minimum of the winding dc and ac power losses. Additionally, an equation for the local minimum of the winding dc and ac power losses is derived. A high‐frequency approximation of Dowell's equation at the nth harmonic frequency is used to derive the normalised total‐power‐critical wire diameter at which the total winding power loss (dc and ac) is equal to the total winding power loss at the local minimum. A design procedure of the inductor with an optimised winding diameter operating in pulsewidth‐modulated dc–dc buck converter in discontinuous conduction mode is presented. Experimental verification of the presented theory and comparison of the total winding power loss of the inductors with different solid‐round‐wire gauge are performed.
A soft‐switching post‐regulator for multi‐outputs dual forward DC/DC converter with tight output voltage regulation
Authors: Su Bin , Wen Huiqing , Zhang Junming , Lu Zhengyu
Published: August 2013

An improved soft‐switching post‐regulator topology for multi‐outputs dual forward DC/DC converter is presented. A delay‐trailing modulation method is proposed. ZVSZCS on/zero‐current‐switching off conditions can be realised on both the primary MOSFETs and the secondary rectifying diodes. Excellent decoupling among different outputs and tight output voltage regulation are achieved. The efficiency is improved due to single power‐conversion stage and share in the primary components. The operating principle and main feature of this improved topology are analysed. Key design issue including zero‐voltage‐switching operation, maximum duty ratio of the primary side MOSFETs and parameter determination for the primary magnetising inductor and the secondary additional redistribution capacitor are discussed. Finally, an experimental prototype with two outputs (300–400 V input, 48 V, 6.5 A and 24 V, 11 A outputs) is built to verify the theoretical analysis. The measured efficiency at normal operation input voltage (400 V) is improved by about 0.5–2%, and the measured efficiency under light loads is improved by more than 2%.
100 mV–1.2 V fully‐integrated DC–DC converters for thermal energy harvesting
Authors: Bassi Giovanni , Colalongo Luigi , Richelli Anna , Kovacs‐Vajna Zsolt Miklós
Published: August 2013

Two fully‐integrated DC/DC converters for energy harvesting applications are presented. The startup‐voltages of the converters are, respectively, 140 and 100 mV, the output voltage exceeds 1.2 V, with a power efficiency of about 20%. The architectures for boosting such extremely low voltages are based on an ultra‐low‐voltage oscillator cross connected to a capacitive converter. The overall circuits do not require any external components and can be fully integrated in a standard complementary metal oxide semiconductor low‐voltage technology. The converters have been designed in United Microelectronics Corporation 180 nm process.
Real and reactive power control of hybrid excited wind‐driven grid‐connected doubly fed induction generators
Authors: Vijayakumar Krishnasamy , Kumaresan Natarajan , Ammasai Gounden Nanjappa Gounder , Tennakoon Sarath B.
Published: August 2013

This study proposes a simple topology which consists of a single sinusoidal pulse width modulation (SPWM) inverter and battery banks with wind‐driven doubly fed induction generators (DFIGs) to dispatch a controllable power to the grid. The excitation of the rotor is established using an SPWM inverter supplied through a set of batteries with the stator connected to the grid. The proposed system supplies the desired real and reactive power to the grid by appropriately charging/discharging the batteries depending on excess/deficit power from the wind. A closed‐loop controller has been developed for this purpose which involves varying the rotor voltage magnitude and frequency. The entire control strategy proposed in this study has been implemented using TMS320LF2407A DSP controller and detailed procedure for such implementation is presented. The steady‐state analysis and phasor diagram representation of the system have been developed and presented. Experimental results obtained on a three‐phase, four‐pole, 50 Hz, 5 kVA DFIG together with the closed‐loop controller under steady‐state and dynamic operating conditions, confirm the usefulness of the proposed system. The experimental results have been compared with predicted values and a very close agreement between the two is observed.
Assessing detector performance, with application to Pareto coherent multilook radar detection
Authors: Weinberg Graham Victor
Published: August 2013

A necessary and sufficient condition is established, which can be used to compare the performance of two radar detection schemes. This means that the performance of detectors can be measured relative to a benchmark detector. In the context of coherent multilook detection in a Pareto clutter environment, the whitening matched filter (WMF) detector, which is optimal for Gaussian clutter, has been observed to perform very well as a suboptimal detector. Based upon this, variations of the WMF are constructed and analysed.
Spaceborne/airborne bistatic synthetic aperture radar focusing on an analytical bistatic point target reference spectrum
Authors: Xu Haisheng , Song Hongjun , Deng Yunkai , Wang Robert , Shan Xiuming , Yuan Jian , Wang Chunle
Published: August 2013

An analytical bistatic point target reference spectrum (BPTRS) is proposed. The BPTRS is derived from the one‐to‐one relationship between slow time and Doppler frequency with no Taylor series expansions. Based on the BPTRS, a two‐dimensional frequency‐domain focusing algorithm for spaceborne/airborne bistatic synthetic aperture radar is developed. The algorithm exploits a range‐dependent sub‐blocks processing method to perform range cell migration correction and quadratic Doppler term compensation, and then a scaled inverse Fourier transformation and a sinc interpolation are used to correct the geometric distortions in azimuth and range, respectively. Some simulation experiments are also presented to verify their performance.
Focusing highly squinted data with motion errors based on modified non‐linear chirp scaling
Authors: Gaogao Liu , Li Peng , Tang ShiYang , Zhang Linrang
Published: August 2013

The motion compensation (MOCO) plays a significant role to accommodate the motion errors caused by atmosphere turbulence and/or aircraft maneuvers in airborne synthetic aperture radar configurations. In broadside or small squint cases, the well‐focused image can be obtained by the typical two‐step MOCO to have the quadratic motion errors compensated. However, with the increasing of squint angle, not only the high‐order motion errors, but also the azimuth‐variant errors must be taken into account. In this study, a modified non‐linear chirp scaling (MNLCS) algorithm is proposed to handle this problem in highly‐squinted case. The key is to use the method of series reversion to cover the high‐order motion errors, the MNLCS to precondition the data to process the azimuth‐variant components and a series expansion to obtain an accurate form of the signal spectrum. The skewed spectrum in highly‐squinted case is reduced through the use of a linear range cell migration correction. The simulated results have shown the MNLCS algorithm can handle data with more complicated geometries than the previous algorithm.
Performance assessment of aided Global Navigation Satellite System for land navigation
Authors: Angrisano Antonio , Gaglione Salvatore , Gioia Ciro
Published: August 2013

Land navigation includes the methods to determine the time varying position and velocity of a moving object on Earth surface using suitable measurements; it is typically performed in signal‐degraded environments where GPS signals are blocked or degraded; hence GPS‐only cannot guarantee an accurate and continuous positioning. The multi‐constellation approach is a possible way to fill this gap. In this work GPS/GLONASS systems are combined and single point algorithm performance is assessed for different configurations in urban scenario. GLONASS is nearly fully operational and its inclusion guarantees satellite availability improvement, but the GPS/GLONASS multi‐constellation use involves the addition, as further unknown, of the intersystem time‐scale offset. The considered estimation techniques are Least Squares and Kalman filter. The first method uses only the measurement model, with the drawback of solution unavailability during GNSS outages. The last uses, in addition to a measurement model, a process model allowing the estimation of the unknowns in case of GNSS outage. To improve both methods performances aiding are considered on height and intersystem time scale offset. The main purposes of this work are the performance assessment of a multi‐constellation system relative to GPS‐only, adopting the aforesaid estimators, and the benefit evaluation of the aiding.
Tropospheric effects on L‐band geosynchronous circular SAR imaging
Authors: Kou Leilei , Xiang Maosheng , Wang Xiaoqing , Zhu Minhui
Published: August 2013

Circular synthetic aperture radar (SAR) imaging on the geosynchronous orbit has significant potential advantages, such as high resolution three‐dimensional imaging, large coverage, but it also has challenges to overcome. One major problem limiting the high‐resolution geosynchronous circular SAR (GEOCSAR) performances is the atmospheric effects including the tropospheric and ionospheric effects. In this study, the authors mainly consider the tropospheric effects on L‐band GEOCSAR imaging. Since the integration time of GEOCSAR may be as long as 24 h, and the coverage can reach 1/3 of the Earth's surface, the effects of the spatial and temporal variation of the tropospheric refractive index cannot be ignored if well focused images are to be obtained. The analysis shows that the temporal variation of the tropospheric refractive index may cause severe degradation of the SAR images; the spatial variation of the refractive index and the tropospheric turbulence are not the important factor limiting the GEOCSAR imaging performance.
Airborne behaviour monitoring using Gaussian processes with map information
Authors: Oh Hyondong , Shin Hyo‐Sang , Kim Seungkeun , Tsourdos Antonios , White Brian A.
Published: August 2013

This study proposes an airborne behaviour monitoring methodology of ground vehicles based on a statistical learning approach with domain knowledge given by road map information. To monitor and track the moving ground target using unmanned aerial vehicle aboard a moving target indicator, an interactive multiple model (IMM) filter is firstly applied. The IMM filter consists of an on‐road moving mode using a road‐constrained filter and an off‐road moving mode using a conventional filter. Mode probability is also calculated from the IMM filter, and it provides deviation of the vehicle from the road. Then, a novel hybrid algorithm for anomalous behaviour recognition is developed using a Gaussian process regression on velocity profile along the one‐dimensionalised position of the vehicle, as well as the deviation of the vehicle. To verify the feasibility and benefits of the proposed approach, a numerical simulation is performed using realistic car trajectory data in a city traffic.
Using omega‐K algorithm for bistatic synthetic aperture radar image formation based on modified extended Loffeld's bistatic formula
Authors: Zamani Mohammad , Modarres‐Hashemi Mahmood
Published: August 2013

Bistatic synthetic aperture radar (BSAR) as a way of Earth remote sensing has been developed considerably in recent years, both theoretically and practically due to its unsubstitutable services. BSAR frequency‐domain processing algorithms are efficient ways of image formation in comparison to ideal two‐dimensional matched filtering and to relatively accurate and time‐consuming time‐domain algorithms. Among these frequency‐domain algorithms, omega‐K is the most precise. The starting and key step of frequency‐domain algorithms is the derivation of bistatic spectrum. Recently, a new bistatic spectrum is reported, which is probably the latest and the most modified version of Loffeld's bistaic formula (LBF), maintaining its accuracy even in azimuth‐variant configurations with high squint angles. So far, this spectrum has only been used within range‐Doppler algorithm to process BSAR data. The authors investigate the possibility and results of applying this modified version of LBF as a basis for omega‐K algorithm. Two approaches, based on Stolt interpolation and inverse scaled Fourier transform, are examined and their effectiveness in general azimuth‐variant geometry is validated through several simulations. The proposed implementations show higher performance in terms of image quality measurements as compared to extended LBF‐based implementations.
Hollow gold nanorectangles: The roles of polarization and substrate
Authors: Near Rachel D. , El-Sayed Mostafa A.
Published: July 2013

Dimers of hollow gold nanorectangles ((197 ± 4) × (134 ± 6) nm outside and (109 ± 5) × (53 ± 3) nm inside) were fabricated via electron beam lithography with interparticle separations ranging from 27 ± 2 nm to 596 ± 8 nm. Spectroscopic investigation of these arrays showed multiple peaks under illumination polarized both parallel and perpendicular to the interparticle axis. Discrete dipole approximation theoretical calculations were used to investigate the nature of these multiple peaks. These calculations demonstrate that the multiple peaks arise due to a combination of multiple plasmon modes and interactions with the substrate. The substrate effects are more pronounced for the parallel polarization because parallel polarization (along the long axis) of the nanorectangles results in a much stronger dipole mode than for the perpendicular polarization (along the short axis). Next, we show how these peaks change, as the hollow nanorectangles are brought within coupling range of one another. In this endeavor, we make use of our previously reported method to directly convert scanning electron microscope images of the nanoparticles into the shape files for the theoretical calculations.
Strain hardening and jump-like deformation of ultrafine polycrystalline Al-Li solid solutions at 0.5 K
Authors: Isaev N. V. , Shumilin S. E. , Zabrodin P. A. , Geidarov V. G. , Grigorova T. V. , Fomenko V. S. , Braude I. S. , Pustovalov V. V.
Published: August 2013

This is a study of the effect of microstructure created by severe plastic deformation (SPD) and annealing on strain hardening and jump-like deformation in Al-Li alloys. It is shown that under tension at 0.5 K, SPD processed polycrystals retain a significant strain hardening rate and have high strength and ductility. SPD also simulates unstable (jump-like) flow of the polycrystals owing to dislocation dynamics that shows up as stress jumps in the tension curve. The average amplitude of the jumps increases with strain, while the dislocation amplitude distribution corresponds to collective motion of dislocation avalanches with a distinctive scale. Jump-like deformation is partially suppressed by high-temperature annealing, while the distribution of the jump amplitudes is described by a power law. The relationship established between the coefficient of strain hardening and the average stress jump amplitude suggests a common dislocation dynamic for strain hardening and jump-like deformation at low temperatures. The observed features of low-temperature plastic deformation are treated as a consequence of changes in the grain sizes and density of dislocations owing to SPD and annealing.
Thermoelectric effect in single layer epitaxial graphene formed on semiconductor substrate. Simple analytical model
Authors: Alisultanov Z. Z.
Published: August 2013

In this paper we have investigated thermoelectric effect in the epitaxial graphene on a semiconductor substrate using a simple model. We have obtained the expressions for static conductance and thermopower of the epitaxial graphene. The thermopower of the epitaxial graphene can be abnormally large near the edges of the semiconductor band gap.
Chirality dependence of quantum thermal transport in carbon nanotubes at low temperatures: A first-principles study
Authors: Hata Tomoyuki , Kawai Hiroki , Ohto Tatsuhiko , Yamashita Koichi
Published: July 2013

We study the transport properties of single-walled carbon nanotubes (SWCNTs) using the nonequilibrium Green's function method based on first-principles calculations. We compared three SWCNTs with different chiralities (3, 3), (5, 0), and (4, 2), and found that the thermal conductance varies significantly with the chirality, especially at low temperatures. Such differences are attributed to the dependence on the chirality of the frequency of the lowest optical mode and phonon-phonon interaction with the semi-infinite leads. To obtain accurate low-vibrational frequencies, a force constant correction based on the Lagrange undetermined multiplier method was employed. The phonon-phonon interaction was analyzed in terms of the projection of the phonon coupling with the semi-infinite leads onto the normal modes of the center region. Our result indicates that high optical mode frequency and weak phonon coupling on the armchair (3, 3) SWCNT are the origin of the long quantized plateau found in the experimental thermal conductance.
Linear and nonlinear density response functions for a simple atomic fluid
Authors: Dalton Benjamin A. , Glavatskiy Kirill S. , Daivis Peter J. , Todd B. D. , Snook Ian K.
Published: August 2013

We use molecular dynamics simulations to investigate the linear and nonlinear density response functions for simple fluids under the influence of spatially periodic external fields. Using a direct Fourier space decomposition of the instantaneous microscopic density for the perturbed fluid we can clearly identify the distinct order of response. Using a single component sinusoidal longitudinal force for a set of wavelengths and amplitudes we show that in the linear response regime the proportionality between the external field amplitude and the density perturbation can be used to determine the linear density response function, and hence the pair correlation function, static liquid structure factor, and lowest order direct correlation function. We show also that for large external field amplitudes a single component external field can be used to determine the form for lowest order and second lowest order nonlinear response functions for restricted regions of the total response function spaces.
Confinement dynamics of a semiflexible chain inside nano-spheres
Authors: Fathizadeh A. , Heidari Maziar , Eslami-Mossallam B. , Ejtehadi M. R.
Published: August 2013

We study the conformations of a semiflexible chain, confined in nano-scaled spherical cavities, under two distinct processes of confinement. Radial contraction and packaging are employed as two confining procedures. The former method is performed by gradually decreasing the diameter of a spherical shell which envelopes a confined chain. The latter procedure is carried out by injecting the chain inside a spherical shell through a hole on the shell surface. The chain is modeled with a rigid body molecular dynamics simulation and its parameters are adjusted to DNA base-pair elasticity. Directional order parameter is employed to analyze and compare the confined chain and the conformations of the chain for two different sizes of the spheres are studied in both procedures. It is shown that for the confined chains in the sphere sizes of our study, they appear in spiral or tennis-ball structures, and the tennis-ball structure is more likely to be observed in more compact confinements. Our results also show that the dynamical procedure of confinement and the rate of the confinement are influential parameters of the structure of the chain inside spherical cavities.
Proton dynamics in ice VII at high pressures
Authors: Finkelstein Y. , Moreh R.
Published: August 2013

We calculated the proton kinetic energies Ke(H) of ice under high pressures up to 63 GPa by assuming the harmonic approximation. The input measured optical frequencies of vibration, libration, and translation of ice VII versus pressure as well as the H2O geometry and the distances ROH necessary for calculating Ke(H) (at 298 K) were taken from the literature. The resulting Ke(H) values were found to decrease gradually with increasing pressure, approaching the region where the H-atom is symmetrically hydrogen bonded between two oxygens in the OH-O system. Interestingly, the Ke(H) results were found to be consistent with those of other materials such as Rb3H(PO4)2 and KH2PO4 having similar ROH and ROO distances in the OH-O system. Similar calculations were also carried out for D2O.
Jet spectroscopy of buckybowl: Electronic and vibrational structures in the S and S1 states of triphenylene and sumanene
Authors: Kunishige Sachi , Kawabata Megumi , Baba Masaaki , Yamanaka Takaya , Morita Yuki , Higashibayashi Shuhei , Sakurai Hidehiro
Published: August 2013

Sumanene is a typical buckybowl molecule with C3v symmetry. We observed a fluorescence excitation spectrum and a dispersed fluorescence spectrum of sumanene in a supersonic jet. Bowl effects were clarified by comparing the spectra with those of triphenylene (D3h symmetry), which is a planar prototype of nonplanar sumanene. The S1 1A1 ← S0 1A1 transition is symmetry allowed. We found the \documentclass[12pt]{minimal}\begin{document}$0_0^0$\end{document}000 band in the fluorescence excitation spectrum at 357.78 nm; this band was missing in the forbidden \documentclass[12pt]{minimal}\begin{document}$S_1 \;^1A_1^{\prime }$\end{document}S1A1′1 ← \documentclass[12pt]{minimal}\begin{document}$S_0 \;^1A_1^{\prime }$\end{document}S0A1′1 transition of triphenylene. The transition moment was shown to be along the oblate symmetric top axis (out of plane) by the observed rotational contour. A large number of vibronic bands were observed, unlike in triphenylene. Some were considered to be out-of-plane vibrational modes, which lead to a bowl-to-bowl inversion reaction assisted by in-plane vibrations. We found that the vibronic bands were markedly weak in the high energy region of triphenylene-d12. This indicates that the fluorescence quantum yield is very low at the high vibrational levels in the S1 state due to the rapid radiationless transition. The main process is considered to be internal conversion to the S0 state. The nonplanar structural distortion may also enhance radiationless transitions. We could not, however, observe weakening of the vibronic bands in the fluorescence excitation spectrum of sumanene.
Comparison of volume and surface area nonpolar solvation free energy terms for implicit solvent simulations
Authors: Lee Michael S. , Olson Mark A.
Published: July 2013

Implicit solvent models for molecular dynamics simulations are often composed of polar and nonpolar terms. Typically, the nonpolar solvation free energy is approximated by the solvent-accessible-surface area times a constant factor. More sophisticated approaches incorporate an estimate of the attractive dispersion forces of the solvent and/or a solvent-accessible volume cavitation term. In this work, we confirm that a single volume-based nonpolar term most closely fits the dispersion and cavitation forces obtained from benchmark explicit solvent simulations of fixed protein conformations. Next, we incorporated the volume term into molecular dynamics simulations and find the term is not universally suitable for folding up small proteins. We surmise that while mean-field cavitation terms such as volume and SASA often tilt the energy landscape towards native-like folds, they also may sporadically introduce bottlenecks into the folding pathway that hinder the progression towards the native state.
Empirical determination of the energy band gap narrowing in highly doped n+ silicon
Authors: Yan Di , Cuevas Andres
Published: July 2013

Highly doped regions in silicon devices should be analyzed using Fermi-Dirac statistics, taking into account energy band gap narrowing (BGN). An empirical expression for the BGN as a function of dopant concentration is derived here by matching the modeled and measured thermal recombination current densities J0 of a broad range of n+ dopant concentration profiles prepared by phosphorus diffusion. The analysis is repeated with Boltzmann statistics in order to determine a second empirical expression for the apparent energy band gap narrowing, which is found to be in good agreement with previous work.
Analysis of a high power microwave radial line slot antenna
Authors: Peng Shengren , Yuan Chengwei , Shu Ting
Published: August 2013

A traditional radial line slot antenna (RLSA) is a high gain planar array. To improve the power handling capacity, we design a radial line slow wave structure which replaces a traditional dielectric sheet in the radial waveguide of the traditional RLSA. This high power microwave (HPM) RLSA is fed from a double-layered radial line waveguide to realize the directional radiation of the microwave. However, the track of the widen slot array on the upper waveguide could cause large reflection, which disturbs the normal antenna operation, accordingly a reflection canceling slot is added to the lower waveguide, the key technology employed in the design of the HPM RLSA and the antenna return-loss is effectively improved. This article mainly gives the design theory of this antenna, which is confirmed by the simulations and experiments. At 9.4 GHz, the calculated aperture efficiency reaches more than 40%, the reflectance is less than 0.1, the radiation efficiency is more than 99% and its measured power-handling capacity exceeds 700 MW.
Suspended polymer nanobridge on a quartz resonator
Authors: Yun Minhyuk , Lee Seongjae , Yim Changyong , Jung Namchul , Thundat Thomas , Jeon Sangmin
Published: July 2013

A chemical vapor sensor based on a free-standing polystyrene (PS) nanofilm suspended between the tines of a quartz tuning fork (QTF) is demonstrated. Exposure to ethanol vapor decreased the modulus of the PS membrane, which resulted in a decrease in the resonance frequency of the QTF as a function of ethanol concentration. The suspended PS membrane structure on the QTF allowed gas molecules to diffuse into the membrane from both the top and bottom allowing faster response. The QTF response time was found to be 6.5 times faster than the response time of a conventional PS film-coated resonator sensor.
Interfacial refractive index sensing using visible-excited intrinsic zinc oxide photoluminescence coupled to whispering gallery modes
Authors: Moirangthem Rakesh Singh , Erbe Andreas
Published: August 2013

Whispering gallery modes (WGMs) excited by the intrinsic photoluminescence (PL) in zinc oxide microspherical resonators are investigated in this work. The microspheres were synthesized via a one-pot hydrothermal technique. A polymer was applied after the synthesis to fill remaining pores in the oxide particle. Defect-related ZnO PL was excited in the visible, coupling to WGMs. The observed WGMs red-shift with increasing refractive index of the surrounding medium with a sensitivity of 90–100 nm/refractive index unit. The spherical microresonators may be used to investigate binding to and structure at the particle/solution interface.
Electrostatic method to estimate the mechanical properties of suspended membranes applied to nickel-coated graphene oxide
Authors: Sridi Nawres , Lebental Berengere , Azevedo Joel , Gabriel Jean Christophe P. , Ghis Anne
Published: August 2013

We propose a method to estimate the bending rigidity and Young's modulus of thin conducting suspended membranes based on measuring the deflection of the membranes submitted to an electrostatic force. Our electrostatic method appears easier to implement and more reliable than AFM-based localized force-displacement measurements to estimate the bending rigidity and Young's modulus of slightly inhomogeneous materials. We apply the method on suspended graphene oxide (GO) sheets coated with a 5 nm thick Ni layer, providing a demonstration of electrostatic actuation for GO sheets. For a 7.7 nm thick membrane, a Young modulus of 360 GPa is found.
In-situ metalorganic chemical vapor deposition and capacitance-voltage characterizations of Al2O3 on Ga-face GaN metal-oxide-semiconductor capacitors
Authors: Liu X. , Yeluri R. , Kim J. , Lal S. , Raman A. , Lund C. , Wienecke S. , Lu J. , Laurent M. , Keller S. , Mishra U. K.
Published: August 2013

The in-situ metalorganic chemical vapor deposition of Al2O3 on Ga-face GaN metal-oxide-semiconductor capacitors (MOSCAPs) is reported. Al2O3 is grown using trimethylaluminum and O2 in the same reactor as GaN without breaking the vacuum. The in-situ MOSCAPs are subjected to a series of capacitance-voltage measurements combined with stress and ultraviolet-assisted techniques, and the results are discussed based on the presence of near-interface states with relatively fast and slow electron emission characteristics. The in-situ MOSCAPs with Al2O3 grown at 900 and 1000 °C exhibit very small hystereses and charge trappings as well as average near-interface state densities on the order of 1012 cm−2eV−1.
Scientists dig deep in Tohoku fault to crack earthquake’s secrets
Authors: Feder Toni
Published: August 2013

Nine months of data from the world’s deepest observatory agree with lab measurements on a controversial quake parameter.
Preparation and Structures of Group 12 and 14 Element Halide–Carbene Complexes
Authors: Ibrahim Al-Rafia S. M. , Lummis Paul A. , Swarnakar Anindya K. , Deutsch Kelsey C. , Ferguson Michael J. , McDonald Robert , Rivard Eric
Published: August 2013

The synthesis of a series of N-heterocyclic carbene (NHC) complexes involving zinc, cadmium, and the heavy Group 14 elements germanium, tin, and lead is reported. The direct reaction between the bulky carbene IPr (IPr = (HCNDipp)2C:, Dipp = 2,6-iPr2C6H3) and the Group 14 halide reagents GeCl4 and SnCl4 afforded the 1 : 1 complexes IPr·ECl4 (E = Ge and Sn) in high yield; similarly, ZnI2 interacted with IPr in THF to give the THF-bound complex IPr·ZnI2·THF. CdCl2 underwent divergent chemistry with IPr and the major product isolated was the imidazolium salt [IPrH][IPr·CdCl3], which could be converted into IPr·CdCl2·THF upon treatment with Tl[OTf]. In addition, the stable PbII amide adduct, IPr·PbBr(NHDipp), was prepared. Each of the new carbene–element halide adducts was treated with the hydride sources Li[BH4] and Li[HBEt3] in order to potentially access new element hydride adducts and/or clusters. In most instances scission of the element–carbene bonds transpired, except in the case of IPr·ZnI2·THF, which reacted with two equivalents of Li[BH4] to yield the thermally stable bis(borohydride) zinc complex IPr·Zn(BH4)2.
Equine oviduct explant culture: a basic model to decipher embryo–maternal communication
Authors: Nelis Hilde , D'Herde Katharina , Goossens Karen , Vandenberghe Lynn , Leemans Bart , Forier Katrien , Smits Katrien , Braeckmans Kevin , Peelman Luc , Van Soom Ann
Published: August 2013

Equine embryos remain for 6 days in the oviduct and thus there is a need for an in vitro model to study embryo–oviductal interactions in the horse, since this subtle way of communication is very difficult to analyse in vivo. Until now, no equine oviduct explant culture model has been characterised both morphologically and functionally. Therefore, we established a culture system for equine oviduct explants that maintained epithelial morphology during 6 days of culture, as revealed by light microscopy and transmission electron microscopy. We demonstrated the presence of highly differentiated, tall columnar, pseudostratified epithelium with basal nuclei, numerous nucleoli, secretory granules and apical cilia, which is very similar to the in vivo situation. Both epithelium and stromal cells originating from the lamina propria are represented in the explants. Moreover, at least 98% of the cells remained membrane intact and fewer than 2% of the cells were apoptotic after 6 days of culture. Although dark-cell degeneration, which is a hypoxia-related type of cell death, was observed in the centre of the explants, quantitative real-time PCR failed to detect upregulation of the hypoxia-related marker genes HIF1A, VEGFA, uPA, GLUT1 and PAI1. Since the explants remained morphologically and functionally intact and since the system is easy to set up, it appears to be an excellent tool for proteome, transcriptome and miRNome analysis in order to unravel embryo–maternal interactions in the horse.
From the physics of interacting polymers to optimizing routes on the London Underground
Authors: Yeung Chi Ho , Saad David , Wong K. Y. Michael
Published: July 2013

Optimizing paths on networks is crucial for many applications, ranging from subway traffic to Internet communication. Because global path optimization that takes account of all path choices simultaneously is computationally hard, most existing routing algorithms optimize paths individually, thus providing suboptimal solutions. We use the physics of interacting polymers and disordered systems to analyze macroscopic properties of generic path optimization problems and derive a simple, principled, generic, and distributed routing algorithm capable of considering all individual path choices simultaneously. We demonstrate the efficacy of the algorithm by applying it to: (
i
) random graphs resembling Internet overlay networks, (
ii
) travel on the London Underground network based on Oyster card data, and (
iii
) the global airport network. Analytically derived macroscopic properties give rise to insightful new routing phenomena, including phase transitions and scaling laws, that facilitate better understanding of the appropriate operational regimes and their limitations, which are difficult to obtain otherwise.
Structural and dynamic studies of the transcription factor ERG reveal DNA binding is allosterically autoinhibited
Authors: Regan Michael C. , Horanyi Peter S. , Pryor Edward E. , Sarver Jessica L. , Cafiso David S. , Bushweller John H.
Published: July 2013

The Ets-Related Gene (ERG) belongs to the Ets family of transcription factors and is critically important for maintenance of the hematopoietic stem cell population. A chromosomal translocation observed in the majority of human prostate cancers leads to the aberrant overexpression of ERG. We have identified regions flanking the ERG Ets domain responsible for autoinhibition of DNA binding and solved crystal structures of uninhibited, autoinhibited, and DNA-bound ERG. NMR-based measurements of backbone dynamics show that uninhibited ERG undergoes substantial dynamics on the millisecond-to-microsecond timescale but autoinhibited and DNA-bound ERG do not. We propose a mechanism whereby the allosteric basis of ERG autoinhibition is mediated predominantly by the regulation of Ets-domain dynamics with only modest structural changes.
MAIT cells are critical for optimal mucosal immune responses during in vivo pulmonary bacterial infection
Authors: Meierovics Anda , Yankelevich Wei-Jen Chua , Cowley Siobhán C.
Published: July 2013

Significance

Mucosa-associated invariant T (MAIT) cells are an innate T-cell subset uniquely activated by microbe-derived vitamin B metabolites. Thus far, little is known about MAIT cell contributions to defense against pathogens in vivo. Using murine respiratory tularemia as a model of mucosal infection, we show that MAIT cells are required for the prompt initiation of immune responses in the lungs. Surprisingly, MAIT cells also actively contributed to immunity throughout the later stages of infection. Thus, MAIT cells are a unique T-cell subset with wide-ranging activities that may be harnessed to improve future vaccines and adjuvants used at mucosal surfaces.
Mechanisms of actin disassembly
Authors: Brieher William
Published: July 2013

The actin cytoskeleton is constantly assembling and disassembling. Cells harness the energy of these turnover dynamics to drive cell motility and organize cytoplasm. Although much is known about how cells control actin polymerization, we do not understand how actin filaments depolymerize inside cells. I briefly describe how the combination of imaging actin filament dynamics in cells and using in vitro biochemistry progressively altered our views of actin depolymerization. I describe why I do not think that the prevailing model of actin filament turnover—cofilin-mediated actin filament severing—can account for actin filament disassembly detected in cells. Finally, I speculate that cells might be able to tune the mechanism of actin depolymerization to meet physiological demands and selectively control the stabilities of different actin arrays.
G protein–coupled receptor kinase 2 (GRK2) is localized to centrosomes and mediates epidermal growth factor–promoted centrosomal separation
Authors: So Christopher H. , Michal Allison , Komolov Konstantin E. , Luo Jiansong , Benovic Jeffrey L.
Published: August 2013

G protein–coupled receptor kinases (GRKs) play a central role in regulating receptor signaling, but recent studies suggest a broader role in modulating normal cellular functions. For example, GRK5 has been shown to localize to centrosomes and regulate microtubule nucleation and cell cycle progression. Here we demonstrate that GRK2 is also localized to centrosomes, although it has no role in centrosome duplication or microtubule nucleation. Of interest, knockdown of GRK2 inhibits epidermal growth factor receptor (EGFR)–mediated separation of duplicated centrosomes. This EGFR/GRK2-mediated process depends on the protein kinases mammalian STE20-like kinase 2 (Mst2) and Nek2A but does not involve polo-like kinase 1. In vitro analysis and dominant-negative approaches reveal that GRK2 directly phosphorylates and activates Mst2. Collectively these findings demonstrate that GRK2 is localized to centrosomes and plays a central role in mitogen-promoted centrosome separation most likely via its ability to phosphorylate Mst2.