bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple method to reduce congestion in bufferless network‐on‐chip
Authors: Oxman G. , Weiss S.
Published: April 2014

A simple method that reduces congestion in the bufferless network‐on‐chip (NoC) is proposed. The method uses the time average of link utilisation as its congestion measure, and is applicable to deflection routing algorithms. A cycle‐based NoC simulator is used to evaluate a bufferless NoC with and without the congestion reduction, and the performance and energy consumption are found to improve under heavy load.
Design of power divider with bandpass response and notched band
Authors: Xiao Long , Peng Hao , Yang Tao
Published: April 2014

A novel multilayer in‐phase slotline power divider with bandpass response and one tunable notched band is proposed. The presented power divider employs the structure of microstrip‐to‐slotline transition to split the input signals over the frequency range 3.5–10 GHz. A wide upper stopband is obtained by using an interdigital configuration and introducing a defected ground structure. A quarter‐wavelength short‐circuited stub is utilised to obtain the tunable notched band in the passband. The experimental results indicate that the proposed power divider has good phase balance, high isolation between output ports, good return losses at all ports and flat group delay over a wide frequency range.
Ultra‐energy‐efficient CMOS/magnetic non‐volatile flip‐flop based on spin‐orbit torque device
Authors: Jabeur K. , Di Pendina G. , Prenat G.
Published: April 2014

The spin‐orbit‐torque magnetic tunnel junction (SOT‐MTJ) is a promising device for data storage. Most of the issues encountered with scalable spin transfer‐torque (STT) devices are visibly moved. Thanks to a three‐terminal architecture, the reliability is increased by separating the read and the write paths. Furthermore, SOT‐induced magnetisation switching can be very fast, thanks to a low‐resistive writing path. The writing operation is symmetrical. Thus, it requires the same current density to switch between the parallel and antiparallel states. All these advantages make the SOT‐MTJ device an ultimate candidate for introducing non‐volatility in ultra‐fast and power‐efficient integrated circuits. A mixed CMOS/magnetic non‐volatile flip‐flop (NVFF) is described. The proposed architecture offers the possibility to use the usual CMOS flip‐flop functionality with possible magnetic data store and restore operations while keeping non‐volatility when the circuit is powered off. With a 135 nm dimension, the SOT‐MTJ‐based NVFF demonstrated a very high switching with a 5× decrease in terms of writing energy/bit when compared with an STT device.
Miniature filtering power divider with increased isolation bandwidth
Authors: Chao Shih‐Fong , Li You‐Ruei
Published: April 2014

A novel filtering power divider (PD) with an extended isolation bandwidth is proposed. Adopting a frequency‐dependent resistor–inductor–capacitor isolation network enabled designing and improving isolation performance. An embedded 90° filtering line was realised by employing two coupled quarter‐wavelength resonators to achieve a bandpass response and a compact circuit size. The filtering PD was designed and implemented at a centre frequency of 1 GHz, and the isolation bandwidth (> 20 dB) was extended from DC to 2.2f0.
Theoretical and experimental broadband tissue‐equivalent phantoms at microwave and millimetre‐wave frequencies
Authors: Aminzadeh R. , Saviz M. , Shishegar A.A.
Published: April 2014

Several phantoms have been fabricated for reflection measurements from human tissues in the range of 26.5–40 GHz. For the first time, a novel composition is introduced for fabrication of low‐cost simple tissue‐equivalent phantoms. The effective medium theory is applied to estimate the dielectric properties of phantoms consisting of polyethylene (PE) powder and the results are verified by dielectric properties measurement on the proposed phantoms. It is shown that mixing theory can estimate the dielectric properties of the PE‐based phantoms with minimum error. Therefore, the amount of the ingredients can be estimated theoretically.
Adaptive mode configuration in two‐tier macro‐femtocell networks
Authors: Khan Furqan Hameed , Choi Young‐June
Published: April 2014

Femtocells equipped with cognitive capabilities are able to efficiently utilise the empty spaces of macrocell spectrum. This makes it possible to enhance the spectral efficiency of the available spectrum for end users. In a two‐tier macro–femtocell network, ‘extra’ macrocell resources need to be carefully and efficiently utilised by the femto‐tier network, without having any negative impact on the performance of an existing macrocell network. Hence to attain self‐configurable features in femtocell networks, this research proposes adaptive approaches through which femtocells can manage their coverage by controlling the transmission power to improve the network performance while alleviating the cross‐tier interference. Since the interference problem is a very serious issue in the deployment of closed access mode compared with open access mode, the authors propose a mode selection mechanism that enables femtocells to automatically configure their modes to resolve interference issues while meeting the minimum quality‐of‐service requirements for their registered users. Simulation results confirm that the proposed mechanisms improve the overall capacity and spectral efficiency while reducing the outage probability.
Sliding window Dixon's tests for malicious users’ suppression in a cooperative spectrum sensing system
Authors: Shrivastava Shivanshu , Rajesh Alentattil , Bora Prabin Kumar
Published: April 2014

The Dixon's outlier detection scheme has recently been applied to suppress a malicious secondary user (SU) in a centralised fusion‐based cognitive radio cooperative spectrum sensing system. This study proposes to apply the Dixon's test on the smaller overlapping groups of SUs’ energy data, thereby increasing the detection performance particularly for multiple malicious users (MUs). The test is applied for each sample of the energy data. Simulation results demonstrate that the proposed methods are efficient in suppressing single and multiple MUs.
Aggregate interference modelling and static resource allocation in closed and open access femtocells
Authors: Hosseinzadeh‐Salati Azam S. , Nasiri‐Kenari Masoumeh
Published: April 2014

Femtocell has appeared as a solution to increase both the coverage and the capacity of cellular networks. However, interference problem between the macrocell and the femtocell must be solved before any deployment. Since femtocells are deployed by home users in random locations, decentralised interference management schemes remain worth of investigation. In this study, the author deal with the problem of aggregate interference modelling and static resource allocation in orthogonal frequency division multiple access (OFDMA)‐based two‐tier femtocell networks for both closed and open access femtocells. It is assumed that for macrocell users (MUs), spectrum allocation is accomplished through fractional frequency reuse. The author's objective is to maximise the femtocell user's throughput while maintaining as low as its possible impact on the MUs’ performance. Their proposed algorithm is decentralised, and based on some measurements, needs to be performed only when femtocell access point is plugged in. Simulation results show the accuracy of their model and the effectiveness of the proposed scheme compared to the previous methods.
Tunable differential‐mode bandpass filters with wide tuning range and high common‐mode suppression
Authors: Mao Jinrong , Che Wenquan , Ma Yalin , Chen Jianxin
Published: April 2014

Tunable differential‐mode filters with wide tuning range and high common‐mode suppression are proposed. Step‐impedance resonators terminated with varactors are proposed and used to construct the tunable filter. Symmetrical parallel coupled lines terminated with varactors are used as a negative coupling bisection, which results in convenient tuning of coupling coefficient and bandwidth control. Capacitors are placed at the four ports to adjust the external quality factor. With these techniques and the choice of a high capacitance ratio varactor, a wide tuning range up to 75% has been achieved. Tunable differential‐mode filters with constant absolute bandwidth (ABW) and constant fractional bandwidth (FBW) are realised, respectively. The constant ABW filter has a −3 dB bandwidth of 95 ± 10 MHz and an insertion loss of 5.7 − 2.5 dB. The constant FBW filter has a −3 dB bandwidth of 9.8 ± 1.2% and an insertion loss of 6.0 − 1.7 dB. In addition, a capacitor is loaded on the symmetry plane to misalign common‐mode resonant frequencies, resulting in high common‐mode noise rejection in the whole frequency range.
Non‐linear intermittent instabilities and their control in an interleaved DC/DC converter
Authors: Deivasundari Parvathyshankar , Uma Govindarajan , Vincent Christy , Murali Krishnamurthy
Published: April 2014

The undesirable intermittent instabilities in periodically driven parallel power converter are caused due to periodic interferences in input voltage. This is a more common problem in power electronic circuit design and such operations are usually avoided by controlling the circuit parameters. In this study, the mechanism and conditions for the emergence of intermittent instabilities and remerging chaotic band attractors (or Feigenbaum sequences) in a master–slave controlled parallel buck converter are investigated. It is found that sinusoidal‐type interference in input voltage at frequencies near the switching frequency or its rational multiples of this circuit results typically in period‐bubbling, chaos and intermittency. It is also shown that an optimal, phase‐shifted sinusoidal interference added to the reference voltage controls the period‐bubbling behaviour and significantly extends the parameter range of desirable period‐1 operation. The dynamics of this converter has been first investigated with suitable numerical simulations. The ordered and the chaotic dynamics of this system have been further mathematically described and analysed with a simple discrete map and experimental means. Experimental observations are found to be in good agreement with the analytical and simulation results.
Cascaded multilevel converter for medium‐voltage motor drive capable of regenerating with part of cells
Authors: Zha Xiaoming , Xiong Lan , Gong Jinwu , Liu Fei
Published: April 2014

A new regenerative cascaded multilevel converter and its control strategy based on V/f control has been presented. The converter employs insulated gate bipolar transistor‐based rectifiers as active front end (AFE) only in part of cells and diode‐based rectifiers in the rest cells. Those cells with AFE enable the converter to deliver the power generated by the motor to the grid. In the course of the motor's deceleration, the converter controls the output phase difference of the two types of cells to feed the motor generated electrical energy back to the grid through the cells with AFE and keep other cells’ DC‐link voltages stable. Simulation results of a 6‐kV six‐cell cascaded converter with one regenerative cell per phase and an experiment conducted on a laboratory cascaded converter verify that the control strategy is feasible and the drive system's speed regulation performance is improved. Compared with the converter with AFE in each cell, this converter has lower complexity and lower cost.
Low‐cost wind resource assessment for small‐scale turbine installations using site pre‐screening and short‐term wind measurements
Authors: Weekes Shemaiah Matthias , Tomlin Alison S.
Published: April 2014

A two‐stage approach to low‐cost wind resource assessment for small‐scale wind installations has been investigated in terms of its ability to screen for non‐viable sites and to provide accurate wind power predictions at promising locations. The approach was implemented as a case study at ten UK locations where domestic‐scale turbines were previously installed. In stage one, sites were pre‐screened using a boundary‐layer scaling model to predict the mean wind power density, including estimated uncertainties, and these predictions were compared to a minimum viability criterion. Using this procedure, five of the seven non‐viable sites were correctly identified without direct onsite wind measurements and none of the viable sites were excluded. In stage two, more detailed analysis was carried out using 3 months onsite wind measurements combined with measure–correlate–predict (MCP) approaches. Using this process, the remaining two non‐viable sites were identified and the available wind power density at the three viable sites was accurately predicted. The effect of seasonal variability on the MCP‐predicted wind resource was considered and the implications for financial projections were highlighted. The study provides a framework for low‐cost wind resource assessment in cases where long‐term onsite measurements may be too costly or impractical.
Investigation of a slip joint connection between the monopile and the tower of an offshore wind turbine
Authors: Segeren Maxim L.A. , Lourens Eliz‐Mari , Tsouvalas Apostolos , van der Zee Tjeerd J.J.
Published: April 2014

To circumvent the current industry problems related to the settling of grouted connections, a steel‐to‐steel or slip joint connection is proposed for fitting a transition piece onto an installed monopile foundation. In the first part of this contribution, a simplified dynamic analysis of the installation of such a joint is considered. Slip‐stick equations of motion are derived for a discrete mass model of the joint. The slip distances under self‐weight, with an initial velocity and under a harmonic loading are calculated numerically. The results show that the desired settlement under a harmonic loading can be achieved for various combinations of amplitudes and frequencies. In the second part of this contribution, the static capacities and the dynamic response of the slip joint under extreme loads are determined by means of a finite element (FE) model in which the two parts of the joint are initially in full contact. In these analyses, small cone angles and large overlaps are identified as most conducive for a successful transferral of the loads in the slip joint. The dynamic assessment of the FE model shows that the slip joint continues to stick and the stresses remain well below the plastic limit throughout the duration of an extreme operating gust.
Side‐band algorithm for automatic wind turbine gearbox fault detection and diagnosis
Authors: Zappalá Donatella , Tavner Peter J. , Crabtree Christopher J. , Sheng Shuangwen
Published: April 2014

Improving the availability of wind turbines is critical for minimising the cost of wind energy, especially offshore. The development of reliable and cost‐effective gearbox condition monitoring systems (CMSs) is of concern to the wind industry, because the gearbox downtime has a significant effect on the wind turbine availabilities. Timely detection and diagnosis of developing gear defects is essential for minimising an unplanned downtime. One of the main limitations of most current CMSs is the time consuming and costly manual handling of large amounts of monitoring data, therefore automated algorithms would be welcome. This study presents a fault detection algorithm for incorporation into a commercial CMS for automatic gear fault detection and diagnosis. Based on the experimental evidence from the Durham Condition Monitoring Test Rig, a gear condition indicator was proposed to evaluate the gear damage during non‐stationary load and speed operating conditions. The performance of the proposed technique was then successfully tested on signals from a full‐size wind turbine gearbox that had sustained gear damage, and had been studied in a National Renewable Energy Laboratory's (NREL) programme. The results show that the proposed technique proves efficient and reliable for detecting gear damage. Once implemented into the wind turbine CMSs, this algorithm can automate the data interpretation, thus reducing the quantity of the information that the wind turbine operators must handle.
Improving windfarm operation practice through numerical modelling and Supervisory Control and Data Acquisition data analysis
Authors: Castellani Francesco , Garinei Alberto , Terzi Ludovico , Astolfi Davide , Gaudiosi Mario
Published: April 2014

Usually, wind energy assessment on a new windfarm is conducted with maximum effort prior to the installation of the turbines by using both numerical and experimental investigations. Yet, often the windfarm performances during operation are not as good as expected. This issue can be investigated with a deep analysis of the operational conditions of the windfarm. The large amount of data collected by the SCADA (Supervisory Control and Data Acquisition) systems installed on the turbines can be very helpful. In the present study, the performances of a windfarm were analysed through the elaboration of the SCADA data from a windfarm in southern Italy; in this site, Sorgenia Green installed nine aerogenerators with a rated power of 2 MW each, on a hilly area with gentle slopes. A systematic approach is proposed to isolate the downtime because of malfunctioning and a manifold investigation is applied to the operational phase: several methods (polar efficiency plot, multidimensional graphical analysis, sectorial power curve and misalignment index, respectively) are suggested and applied for unveiling the sectors where the production output is most affected by the wake interactions. Numerical windflow modelling is performed in the wind rose sectors where underproduction is highlighted by a SCADA data analysis: finally, a SCADA database is employed for testing the goodness of the simulations.
Statistical characterisation of single‐stranded DNA motion near glass surface beyond diffusion coefficient
Authors: Uehara Satoshi , Hanasaki Itsuo , Arai Yoshiyuki , Nagai Takeharu , Kawano Satoyuki
Published: April 2014

The diffusion of single‐stranded DNA (ssDNA) molecules near a glass surface by total internal reflection fluorescence microscopy has been observed. Substantially smaller diffusion coefficients compared to the bulk are caused by phenomenologically different types of surface effect that is not necessarily adsorptive. In particular, preliminary treatments of the glass substrate by low and high concentrations of KOH lead to highly and much less adsorptive effects on the ssDNA molecules, respectively. These characteristics beyond diffusion coefficients are elucidated by the difference of two ensemble‐averaging methods of mean square displacement for diffusion coefficients due to the non‐uniformity of the molecular motion, which is further confirmed by the distribution of displacements and tracked duration.
Directional acoustic response of a silicon disc‐based microelectromechanical systems structure
Authors: Mackie David James , Jackson Joseph Curt , Brown James Gordon , Uttamchandani Deepak , Windmill James Frederick Charles
Published: April 2014

A microelectromechanical systems (MEMS)‐based structure capable of operating mechanically as a directional acoustical sensor is presented. The structure, fabricated through the commercially available SOIMUMPS foundry process, consists of two circular discs attached to a central suspension beam, fixed at both ends. The design of the structure resembles other directional MEMS microphones that mimic the directional hearing organ of the parasitoid fly, Ormia ochracea. Modal analysis and mechanical acoustic directionality analysis using both laser Doppler vibrometry and finite element modelling have been implemented. It is demonstrated that this coupled MEMS structure exhibits an acoustic directional response, with a one‐to‐one relationship between the relative vibration amplitudes of the two coupled discs and the angle of sound, from −75° to +60°.
Quaternary Cu2CdSnS4 nanoparticles synthesised by microwave irradiation method
Authors: Guan Hao , Shi YuFen , Hou Haijun , Wang Xu , Yu Fangli
Published: April 2014

Quaternary Cu2CdSnS4 (CCTS) nanoparticles were synthesised via a microwave irradiation method. The as‐synthesised CCTS nanoparticles were characterised by X‐ray diffraction, energy dispersive spectroscopy, scanning electron microscopy, transmission electron microscopy and UV–vis–NIR absorbance spectroscopy measurements. It is shown that the CCTS nanoparticles exhibit a sphere‐like shape and a suitable bandgap (Eg = 1.26 eV), indicating they are a potential candidate for application as the absorber layer in thin film solar cells.
Carbon dioxide resistive sensor based on titanium oxide nanowires doped with potassium
Authors: Lee Inhee
Published: April 2014

Potassium‐doped titanium oxide (TiO2) nanowires are fabricated by the moisture‐assisted, direct oxidation of a thin film of titanium at 650°C. The influence of the fabrication conditions on the structure and morphology of the nanowires was investigated. It was shown that the presence of potassium (K) is necessary for the formation of the nanowires. The density of growth of the nanowires was high, and the lengths of the nanowires were tens of micrometres. The K‐doped TiO2 nanowires showed the possibility of use as a sensing material because of their significant and consistent response to responding to carbon dioxide (CO2) gas. In addition, H2 plasma treatment improved the sensitivity of the CO2 gas sensor made of K‐doped TiO2 nanowires. Although the sensing mechanism is not clear, this development suggests opportunities for the fabrication of simple and inexpensive CO2 microsensors with low power consumption.
Synthesis of Fe3O4@SiO2@Ce0.5Mn0.5O2 core–shell–shell magnetic submicrospheres as photocatalyst for methyl orange degradation
Authors: Zhang Linfeng , Wu Yuanxin
Published: April 2014

Core–shell–shell composite (Fe3O4@SiO2@Ce0.5Mn0.5O2) submicrospheres were successfully synthesised by homogeneous precipitation of Ce and Mn on Fe3O4@SiO2 spheres, which were prepared by a modified sol–gel method with the presence of Fe3O4 particles. The synthesised multilayer‐structured nanocomposites were characterised by X‐ray diffraction, Fourier transform infrared spectroscopy, a transmission electron microscope and a vibrating sample magnetometer. The results show that the magnetic Fe3O4 cores were well wrapped by the coating layer of SiO2 with a thickness of 20 nm in the amorphous phase, and the Ce0.5Mn0.5O2 nanoparticles with a diameter of about 20 nm were attached on the SiO2 shell. The magnetic measurements indicated that the Fe3O4@SiO2@Ce0.5Mn0.5O2 submicrospheres had a superparamagnetism property with the saturation magnetisation of 32.5 eum g−1. At the same time, the composites demonstrated a high photocatalytic activity for methyl orange (MO) degradation with efficiency up to 94.5% under UV irradiation within 1 h. Moreover, the submicrospheres were found to be stable under repeated applications of up to five successive cycles with a nearly constant photocatalytic activity. It is expected that the catalyst could be used for trace pollutants (MO) removal from water and recycled because of its superparamagnetism properties and high photocatalytic activity.
Morphology, structure, optical property and photoelectrochemical property of TiO2 nanoflower films synthesised via liquid phase deposition technique
Authors: Rahman M.Y.A. , Umar A.A. , Roza L. , Salleh M.M.
Published: April 2014

This reported study was concerned with the synthesis of TiO2 nanoflowers as a photovoltaic material of the photoelectrochemical cell (PEC) via the phase liquid deposition technique. It highlighted the effect of the growth time on the morphology of TiO2 samples. Three growth times were chosen, namely 2, 4 and 6 h. The morphology was examined by scanning electron microscopy (SEM). The nanoflowers' morphology of the TiO2 sample grown for 4 h was then chosen to be characterised by cross‐sectional SEM, X‐ray diffraction, ultraviolet–visible and photoelectrochemical measurement. The sample was crystalline with anatase phase. The sample showed the strongest absorption at 330 nm. The TiO2 nanoflowers PEC demonstrated the Jsc and Voc of 0.046 mAcm−2 and 0.26 V, respectively.
Growth process and magnetic anisotropy of amorphous Lax Zny Oz nanowire arrays
Authors: Wang Fang‐Kuo , Yuan Xiao‐You
Published: April 2014

Amorphous Lax Zny Oz nanowire arrays with average diameters of 90 nm have been fabricated by chemical co‐precipitation under subatmospheric pressure suction filtration in porous anodic aluminium oxide template. The growth process of Lax Zny Oz nanowire arrays was investigated through scanning electron microscopy, and the morphology, structure and components of the nanowire arrays were characterised by transmission electron microscopy, X‐ray diffraction and energy dispersive X‐ray spectroscopy. The room temperature hysteresis loops of Lax Zny Oz nanowire arrays shows that the ratio of coercive force Hc (//)/Hc (⊥) achieved is about 13, and saturation magnetisation Ms (//)/Ms (⊥) is 1.3. The nanowire arrays possess obvious magnetic anisotropy arising from the shape anisotropy, and the easily magnetised direction is parallel to the axis of the nanowire arrays, which may determine potential applications on ultra‐high‐density magnetic memory material.
IUPAC-NIST Solubility Data Series. 102. Solubility of Nonsteroidal Anti-inflammatory Drugs (NSAIDs) in Neat Organic Solvents and Organic Solvent Mixtures
Authors: Acree William E.
Published: April 2014

Solubility data are compiled and reviewed for 33 nonsteroidal anti-inflammatory drugs dissolved in neat organic solvents and in well-defined binary and ternary organic solvents. The compiled solubility data were retrieved primarily from the chemical and pharmaceutical literature covering the period from 1980 to the beginning of 2014.
A model for the latent heat of melting in free standing metal nanoparticles
Authors: Shin Jeong-Heon , Deinert Mark R.
Published: April 2014

Nanoparticles of many metals are known to exhibit scale dependent latent heats of melting. Analytical models for this phenomenon have so far failed to completely capture the observed phenomena. Here we present a thermodynamic analysis for the melting of metal nanoparticles in terms of their internal energy and a scale dependent surface tension proposed by Tolman. The resulting model predicts the scale dependence of the latent heat of melting and is confirmed using published data for tin and aluminum.
Geometric moment extraction equipment for image processing applications
Authors: Kumar Ahlad , Paramesran Raveendran
Published: April 2014

An equipment for calculating 2nd, 3rd, and higher order geometric moments by using accumulators, adders, subtractors, and multiplier blocks has been presented. The performance analysis of the proposed equipment with the existing systems in terms of speed and power dissipation has been carried out and has been shown that the computational time to calculate the geometric moments is reduced to half and the power dissipation is reduced by a factor of about 3 at a clock frequency of 10 MHz. The hardware has been implemented in BSIM4.3.0 50 nm technology operating at 1 V and its functionality has been verified using P-Spice simulator.
Equivalence of donor and acceptor fits of temperature dependent Hall carrier density and Hall mobility data: Case of ZnO
Authors: Brochen Stéphane , Feuillet Guy , Pernot Julien
Published: April 2014

In this work, statistical formulations of the temperature dependence of ionized and neutral impurity concentrations in a semiconductor, needed in the charge balance equation and for carrier scattering calculations, have been developed. These formulations have been used in order to elucidate a confusing situation, appearing when compensating acceptor (donor) levels are located sufficiently close to the conduction (valence) band to be thermally ionized and thereby to emit (capture) an electron to (from) the conduction (valence) band. In this work, the temperature dependent Hall carrier density and Hall mobility data adjustments are performed in an attempt to distinguish the presence of a deep acceptor or a deep donor level, coexisting with a shallower donor level and located near the conduction band. Unfortunately, the present statistical developments, applied to an n-type hydrothermal ZnO sample, lead in both cases to consistent descriptions of experimental Hall carrier density and mobility data and thus do not allow to determine the nature, donor or acceptor, of the deep level. This demonstration shows that the emission of an electron in the conduction band, generally assigned to a (0/+1) donor transition from a donor level cannot be applied systematically and could also be attributed to a (−1/0) donor transition from an acceptor level. More generally, this result can be extended for any semiconductor and also for deep donor levels located close to the valence band (acceptor transition).
Complex statistics and diffusion in nonlinear disordered particle chains
Authors: Antonopoulos Ch. G. , Bountis T. , Skokos Ch. , Drossos L.
Published: April 2014

We investigate dynamically and statistically diffusive motion in a Klein-Gordon particle chain in the presence of disorder. In particular, we examine a low energy (subdiffusive) and a higher energy (self-trapping) case and verify that subdiffusive spreading is always observed. We then carry out a statistical analysis of the motion, in both cases, in the sense of the Central Limit Theorem and present evidence of different chaos behaviors, for various groups of particles. Integrating the equations of motion for times as long as 109, our probability distribution functions always tend to Gaussians and show that the dynamics does not relax onto a quasi-periodic Kolmogorov-Arnold-Moser torus and that diffusion continues to spread chaotically for arbitrarily long times.
Variational formulation of oscillating fluid clusters and oscillator-like classification. II. Numerical study of pinned liquid clusters
Authors: Kurzeja Patrick S. , Steeb Holger
Published: April 2014

A numerical study of pinned, oscillating water clusters is presented. Two main models represent a liquid bridge between the walls of two particles and a water column enclosed in a slender pore channel, respectively. Variations include material properties (density, viscosity, surface tension, contact angle) and geometric properties (volume, slenderness, winding, interfacial areas). They are initially based on water clusters in 1 mm pore-space, which are weakly damped at eigenfrequencies around a few hundred Hz. Stiffness and damping are characterized by eigenfrequency and damping coefficient of an equivalent 1-dim. harmonic-oscillator model. Finally, frequency dependence of the dynamical properties is demonstrated. The comprehensive quantitative analysis extends and explains relationships between geometric and material properties and the response to harmonic stimulation. Furthermore, interpolation functions of characteristic dynamic properties are provided for use in multiphase theories. The frequency dependence of cluster stiffness and damping was proven and of limited influence on the stimulation of two typical, weakly damped liquid clusters.
Hydrodynamic radius approximation for spherical particles suspended in a viscous fluid: Influence of particle internal structure and boundary
Authors: Cichocki Bogdan , Ekiel-Jeżewska Maria L. , Wajnryb Eligiusz
Published: April 2014

Systems of spherical particles moving in Stokes flow are studied for different particle internal structures and boundaries, including the Navier-slip model. It is shown that their hydrodynamic interactions are well described by treating them as solid spheres of smaller hydrodynamic radii, which can be determined from measured single-particle diffusion or intrinsic viscosity coefficients. Effective dynamics of suspensions made of such particles is quite accurately described by mobility coefficients of the solid particles with the hydrodynamic radii, averaged with the unchanged direct interactions between the particles.
Perturbative quantum field theory in the framework of the fermionic projector
Authors: Finster Felix
Published: April 2014

We give a microscopic derivation of perturbative quantum field theory, taking causal fermion systems and the framework of the fermionic projector as the starting point. The resulting quantum field theory agrees with standard quantum field theory on the tree level and reproduces all bosonic loop diagrams. The fermion loops are described in a different formalism in which no ultraviolet divergences occur.
Streakline-based closed-loop control of a bluff body flow
Authors: Roca Pablo , Cammilleri Ada , Duriez Thomas , Mathelin Lionel , Artana Guillermo
Published: April 2014

A novel closed-loop control methodology is introduced to stabilize a cylinder wake flow based on images of streaklines. Passive scalar tracers are injected upstream the cylinder and their concentration is monitored downstream at certain image sectors of the wake. An AutoRegressive with eXogenous inputs mathematical model is built from these images and a Generalized Predictive Controller algorithm is used to compute the actuation required to stabilize the wake by adding momentum tangentially to the cylinder wall through plasma actuators. The methodology is new and has real-world applications. It is demonstrated on a numerical simulation and the provided results show that good performances are achieved.
Metrics for long wavelength asymmetries in inertial confinement fusion implosions on the National Ignition Facility
Authors: Kritcher A. L. , Town R. , Bradley D. , Clark D. , Spears B. , Jones O. , Haan S. , Springer P. T. , Lindl J. , Scott R. H. H. , Callahan D. , Edwards M. J. , Landen O. L.
Published: April 2014

We investigate yield degradation due to applied low mode P2 and P4 asymmetries in layered inertial confinement fusion implosions. This study has been performed with a large database of >600 2D simulations. We show that low mode radiation induced drive asymmetries can result in significant deviation between the core hot spot shape and the fuel ρR shape at peak compression. In addition, we show that significant residual kinetic energy at peak compression can be induced by these low mode asymmetries. We have developed a metric, which is a function of the hot spot shape, fuel ρR shape, and residual kinetic energy at peak compression, that is well correlated to yield degradation due to low mode shape perturbations. It is shown that the ρR shape and residual kinetic energy cannot, in general, be recovered by inducing counter asymmetries to make the hot core emission symmetric. In addition, we show that the yield degradation due to low mode asymmetries is well correlated to measurements of time dependent shape throughout the entire implosion, including early time shock symmetry and inflight fuel symmetry.
Thermal equation of state of solid naphthalene to 13 GPa and 773 K: In situ X-ray diffraction study and first principles calculations
Authors: Likhacheva Anna Y. , Rashchenko Sergey V. , Chanyshev Artem D. , Inerbaev Talgat M. , Litasov Konstantin D. , Kilin Dmitry S.
Published: April 2014

In a wide range of P-T conditions, such fundamental characteristics as compressibility and thermoelastic properties remain unknown for most classes of organic compounds. Here we attempt to clarify this issue by the example of naphthalene as a model representative of polycyclic aromatic hydrocarbons (PAHs). The elastic behavior of solid naphthalene was studied by in situ synchrotron powder X-ray diffraction up to 13 GPa and 773 K and first principles computations to 20 GPa and 773 K. Fitting of the P-V experimental data to Vinet equation of state yielded T0 = 8.4(3) GPa and T′ = 7.2 (3) at V0 = 361 Å3, whereas the thermal expansion coefficient was found to be extremely low at P > 3 GPa (about 10−5 K−1), in agreement with theoretical estimation. Such a diminishing of thermal effects with the pressure increase clearly demonstrates a specific feature of the high-pressure behavior of molecular crystals like PAHs, associated with a low energy of intermolecular interactions.
Confinement induced binding of noble gas atoms
Authors: Khatua Munmun , Pan Sudip , Chattaraj Pratim K.
Published: April 2014

The stability of Ngn@B12N12 and Ngn@B16N16 systems is assessed through a density functional study and ab initio simulation. Although they are found to be thermodynamically unstable with respect to the dissociation of individual Ng atoms and parent cages, ab initio simulation reveals that except Ne2@B12N12 they are kinetically stable to retain their structures intact throughout the simulation time (500 fs) at 298 K. The Ne2@B12N12 cage dissociates and the Ne atoms get separated as the simulation proceeds at this temperature but at a lower temperature (77 K) it is also found to be kinetically stable. He-He unit undergoes translation, rotation and vibration inside the cavity of B12N12 and B16N16 cages. Electron density analysis shows that the He-He interaction in He2@B16N16 is of closed-shell type whereas for the same in He2@B12N12 there may have some degree of covalent character. In few cases, especially for the heavier Ng atoms, the Ng-N/B bonds are also found to have some degree of covalent character. But the Wiberg bond indices show zero bond order in He-He bond and very low bond order in cases of Ng-N/B bonds. The energy decomposition analysis further shows that the ΔEorb term contributes 40.9% and 37.3% towards the total attraction in the He2 dimers having the same distances as in He2@B12N12 and He2@B16N16, respectively. Therefore, confinement causes some type of orbital interaction between two He atoms, which akins to some degree of covalent character.
Generation of a quasi-monoenergetic high energy proton beam from a vacuum-sandwiched double layer target irradiated by an ultraintense laser pulse
Authors: Nam Kim Kyung , Lee Kitae , Hee Park Seong , Young Lee Ji , Uk Jeong Young , Vinokurov Nikolay , Gi Kim Yong
Published: April 2014

An acceleration mechanism to generate a high energy proton beam with a narrow energy spread in the laser-induced plasma acceleration of a proton beam is proposed; this mechanism employs two thin foils separated by a narrow vacuum gap. Instead of a thin sheath field at the plasma surfaces, it utilizes an electrostatic field formed in the bulk of the plasma. From a one-dimensional fluid analysis, it has been found that with an appropriate target thickness, protons on the front surface of the second layer can be fed into the plasma, in which the protons are accelerated by an electrostatic field built into the bulk of the plasma. This leads to a proton beam with higher energy and a narrower energy spread than those accelerated at the rear surface of the second layer. The acceleration mechanism is also verified by a two-dimensional particle-in-cell simulation. With a 27-fs long and 2×1019 W/cm2 intense laser pulse, a proton beam with an 18-MeV peak energy and a 35% energy spread is generated. The peak energy is higher than that from the rear surface of the second layer by a factor of 3.
Assessing the accuracy of the isotropic periodic sum method through Madelung energy computation
Authors: Ojeda-May Pedro , Pu Jingzhi
Published: April 2014

We tested the isotropic periodic sum (IPS) method for computing Madelung energies of ionic crystals. The performance of the method, both in its nonpolar (IPSn) and polar (IPSp) forms, was compared with that of the zero-charge and Wolf potentials [D. Wolf, P. Keblinski, S. R. Phillpot, and J. Eggebrecht, J. Chem. Phys. 110, 8254 (1999)]. The results show that the IPSn and IPSp methods converge the Madelung energy to its reference value with an average deviation of ∼10−4 and ∼10−7 energy units, respectively, for a cutoff range of 18–24a (a/2 being the nearest-neighbor ion separation). However, minor oscillations were detected for the IPS methods when deviations of the computed Madelung energies were plotted on a logarithmic scale as a function of the cutoff distance. To remove such oscillations, we introduced a modified IPSn potential in which both the local-region and long-range electrostatic terms are damped, in analogy to the Wolf potential. With the damped-IPSn potential, a smoother convergence was achieved. In addition, we observed a better agreement between the damped-IPSn and IPSp methods, which suggests that damping the IPSn potential is in effect similar to adding a screening potential in IPSp.
Photoisomerization action spectrum of retinal protonated Schiff base in the gas phase
Authors: Coughlan N. J. A. , Catani K. J. , Adamson B. D. , Wille U. , Bieske E. J.
Published: April 2014

The photophysical behaviour of the isolated retinal protonated n-butylamine Schiff base (RPSB) is investigated in the gas phase using a combination of ion mobility spectrometry and laser spectroscopy. The RPSB cations are introduced by electrospray ionisation into an ion mobility mass spectrometer where they are exposed to tunable laser radiation in the region of the S1 ← S0 transition (420–680 nm range). Four peaks are observed in the arrival time distribution of the RPSB ions. On the basis of predicted collision cross sections with nitrogen gas, the dominant peak is assigned to the all-trans isomer, whereas the subsidiary peaks are assigned to various single, double and triple cis geometric isomers. RPSB ions that absorb laser radiation undergo photoisomerization, leading to a detectable change in their drift speed. By monitoring the photoisomer signal as a function of laser wavelength an action spectrum, extending from 480 to 660 nm with a clear peak at 615 ± 5 nm, is obtained. The photoisomerization action spectrum is related to the absorption spectrum of isolated retinal RPSB molecules and should help benchmark future electronic structure calculations.
The Raman spectrum of CaCO3 polymorphs calcite and aragonite: A combined experimental and computational study
Authors: De La Pierre Marco , Carteret Cédric , Maschio Lorenzo , André Erwan , Orlando Roberto , Dovesi Roberto
Published: April 2014

Powder and single crystal Raman spectra of the two most common phases of calcium carbonate are calculated with ab initio techniques (using a “hybrid” functional and a Gaussian-type basis set) and measured both at 80 K and room temperature. Frequencies of the Raman modes are in very good agreement between calculations and experiments: the mean absolute deviation at 80 K is 4 and 8 cm−1 for calcite and aragonite, respectively. As regards intensities, the agreement is in general good, although the computed values overestimate the measured ones in many cases. The combined analysis permits to identify almost all the fundamental experimental Raman peaks of the two compounds, with the exception of either modes with zero computed intensity or modes overlapping with more intense peaks. Additional peaks have been identified in both calcite and aragonite, which have been assigned to 18O satellite modes or overtones. The agreement between the computed and measured spectra is quite satisfactory; in particular, simulation permits to clearly distinguish between calcite and aragonite in the case of powder spectra, and among different polarization directions of each compound in the case of single crystal spectra.
Scattering matrix approach to the dissociative recombination of HCO+ and N2H+
Authors: Fonseca dos Santos S. , Douguet N. , Kokoouline V. , Orel A. E.
Published: April 2014

We present a theoretical study of the indirect dissociative recombination of linear polyatomic ions at low collisional energies. The approach is based on the computation of the scattering matrix just above the ionization threshold and enables the explicit determination of all diabatic electronic couplings responsible for dissociative recombination. In addition, we use the multi-channel quantum-defect theory to demonstrate the precision of the scattering matrix by reproducing accurately ab initio Rydberg state energies of the neutral molecule. We consider the molecular ions N2H+ and HCO+ as benchmark systems of astrophysical interest and improve former theoretical studies, which had repeatedly produced smaller cross sections than experimentally measured. Specifically, we demonstrate the crucial role of the previously overlooked stretching modes for linear polyatomic ions with large permanent dipole moment. The theoretical cross sections for both ions agree well with experimental data over a wide energy range. Finally, we consider the potential role of the HOC+ isomer in the experimental cross sections of HCO+ at energies below 10 meV.
Optical fiber Sagnac interferometer for sensing scalar directional refraction: Application to magnetochiral birefringence
Authors: Loas G. , Alouini M. , Vallet M.
Published: April 2014

We present a setup dedicated to the measurement of the small scalar directional anisotropies associated to the magnetochiral interaction. The apparatus, based on a polarization-independent fiber Sagnac interferometer, is optimized to be insensitive to circular anisotropies and to residual absorption. It can thus characterize samples of biological interests, for which the two enantiomers are not available and/or which present poor transmission. The signal-to-noise ratio is shown to be limited only by the source intensity noise, leading to a detection limit of Δϕ = 500 nrad Hz−1/2. It yields a limit on the magnetochiral index nMC < 4 × 10−13 T−1 at 1.55 μm for the organic molecules tested.
Oscillating motions of neutrally buoyant particle and red blood cell in Poiseuille flow in a narrow channel
Authors: Shi Lingling , Yu Yao , Pan Tsorng-Whay , Glowinski Roland
Published: April 2014

Two motions of oscillation and vacillating breathing (swing) of red blood cell with a stiffened membrane have been observed in bounded Poiseuille flows [L. Shi, T.-W. Pan, and R. Glowinski, “Deformation of a single blood cell in bounded Poiseuille flows,” Phys. Rev. E 85, 16307 (2012)]. To understand such motions, we have compared them with the oscillating motion of a neutrally buoyant particle of the same shape in Poiseuille flow in a narrow channel since a suspended cell is actually a neutrally buoyant entity. In a narrow channel, the particle can be held in the central region for a while with its mass center moving up and down if it is placed at the centerline initially. Its inclination angle oscillates at the beginning; but its range of oscillation keeps increasing and at the end the particle tumbles when the particle migrates away from the centerline due to the inertia effect. When the particle mass center is restricted to move only on the channel centerline, the inclination angle has been locked to a fixed angle without oscillation. Since the mass center of a deformable cell always migrates toward the channel central region in Poiseuille flow, its inclination angle behaves similar to the aforementioned oscillating motion of the particle as long as the cell keeps the long body shape and moves up and down. But when the up-and-down oscillation of the cell mass center damps out, the oscillating motion of the inclination angle also damps out and the cell inclination angle also approaches to a fixed angle.