bluuebunny/crossref_metadata_2025 huggingface dataset:
Ectomycorrhizal fungi contribute to soil organic matter cycling in sub-boreal forests
Authors: Phillips Lori A , Ward Valerie , Jones Melanie D
Published: October 2013

Soils of northern temperate and boreal forests represent a large terrestrial carbon (C) sink. The fate of this C under elevated atmospheric CO2 and climate change is still uncertain. A fundamental knowledge gap is the extent to which ectomycorrhizal fungi (EMF) and saprotrophic fungi contribute to C cycling in the systems by soil organic matter (SOM) decomposition. In this study, we used a novel approach to generate and compare enzymatically active EMF hyphae-dominated and saprotrophic hyphae-enriched communities under field conditions. Fermentation-humus (FH)-filled mesh bags, surrounded by a sand barrier, effectively trapped EMF hyphae with a community structure comparable to that found in the surrounding FH layer, at both trophic and taxonomic levels. In contrast, over half the sequences from mesh bags with no sand barrier were identified as belonging to saprotrophic fungi. The EMF hyphae-dominated systems exhibited levels of hydrolytic and oxidative enzyme activities that were comparable to or higher than saprotroph-enriched systems. The enzymes assayed included those associated with both labile and recalcitrant SOM degradation. Our study shows that EMF hyphae are likely important contributors to current SOM turnover in sub-boreal systems. Our results also suggest that any increased EMF biomass that might result from higher below-ground C allocation by trees would not suppress C fluxes from sub-boreal soils.
History of the 3Rs in Toxicity Testing: From Russell and Burch to 21st Century Toxicology
Authors: Stephens Martin L. , Mak Nina S.
Published: October 2013

Toxicity testing is a key part of the process of assessing the hazards, safety, or risk that chemicals and other substances pose to humans, animals, or the environment. Standardized methods for such testing, typically involving animals, began to emerge during the first half of the 20th century. In 1959, British scientists William Russell and Rex Burch proposed a framework for reducing, refining, or replacing animal use in toxicology and other forms of biomedical experimentation. This “3Rs” or “alternatives” approach emerged at a time of growing sensitivity to the use of animals in experimentation, and progress in its implementation has been spurred by a growing appreciation of the power of emerging science and technology and the limitations of animal-based approaches. The 3Rs approach, although slow to be embraced, increasingly become a framework for change in toxicity testing during the last quarter of the 20th century. These years saw measurable growth in research activity related to the 3Rs, along with the establishment of 3Rs-based organizations and centers, journals, websites, funding sources, and conferences. As the field matured, the principles for validating new and revised alternative tests were formulated and pioneered. The 3Rs framework reached a tipping point in 2007 with the emergence of a U.S. National Research Council report proposing a radically different, largely animal-free approach to toxicity testing, encapsulated in the phrase “21st Century Toxicology.” This chapter reviews these developments, examines 3Rs trends in the toxicological literature, presents measures of the impact of 3Rs activity, and concludes with a summary of some of the remaining challenges to the development, validation, regulatory acceptance, and implementation of 3Rs methods.
Carcinogenicity Testing
Authors: Zeiger Errol
Published: October 2013

In vitro and short-term in vivo test systems for identifying chemicals with carcinogenic potential are described. Unlike other toxicity endpoints typically measured, cancer is the cumulative effect of a series of molecular, cellular, and tissue changes proceeding sequentially. Therefore, no single endpoint test system would be expected to accurately identify carcinogens and discriminate them from noncarcinogens, so that the only definitive test for carcinogenesis is a chronic animal test. The in vitro test systems currently used do not measure the induction of cancer, but mutation or genetic damage which is an initial step in the development of a cancer. However, a significant proportion of chemical carcinogens are not mutagenic and therefore not detected by the current genetic toxicity tests. For this reason, genetic toxicity tests are considered to be predictive for the effect because they do not measure cancer, per se, or all the events leading to the tumor. These genetic toxicity tests are not predictive of noncarcinogenicity because of the high proportion of carcinogens that are negative. Because of the central role carcinogenicity testing plays in the regulation of chemicals, efforts are underway to develop tests, or test combinations, that will be more predictive of both carcinogenicity and noncarcinogenicity.
Bis-dithiano perylene diimide: synthesis and characterization of a novel ring system
Authors: Cormier Russell A. , Gregg Brian A.
Published: October 2013

The first bis-dithiano perylene diimide is synthesized and its optoelectronic properties characterized.
Robust fault detection for discrete‐time stochastic systems with non‐homogeneous jump processes
Authors: Yin Yanyan , Shi Peng , Liu Fei , Teo Kok Lay
Published: October 2013

The problem of robust fault detection (RFD) is studied for a class of discrete‐time stochastic systems with non‐homogeneous jump processes. First, a filter‐based residual signal generator is constructed. To guarantee the sensitivity to faults and robustness against unknown inputs, both H∞ performance and a new performance index are considered. Then an FD filter, which minimises the influences of the disturbances, modelling uncertainties and increases the sensitivity to faults, is designed. A sufficient condition for ensuring the existence of RFD filter in terms of linear‐matrix inequalities is established. A simulation is carried out, illustrating that the proposed RFD filter can detect the faults after their occurrences in a timely manner.
Discrete inventory control in systems with perishable goods – a time‐delay system perspective
Authors: Ignaciuk Przemysław
Published: October 2013

This study considers the problem of providing efficient control of periodic‐review production–inventory systems with perishable goods. The stock storage and replenishment is modelled as a first‐order process with delay subject to external perturbations. The study investigates formally the classical delay compensation mechanisms used in inventory control and shows deficiencies of inventory position and Smith predictor‐based concepts in the context of systems with deteriorating stock. Then, a new dead‐time compensation mechanism is developed and non‐linear control law synthesised. The proposed control scheme is proved robust with respect to arbitrary demand and delay variations.
Optimum utilisation of self‐excited induction generator
Authors: Chauhan Yogesh K. , Yadav Vinod K. , Singh Bhim
Published: October 2013

The voltage and frequency of three‐phase self‐excited induction generator (SEIG) depend upon various factors such as prime mover speed, capacitance value, load etc. The poor voltage and frequency regulation are the main constraints for poor performance of SEIG. The improved performance can be achieved through short shunt SEIG configuration. In this study, the utilisation of SEIG is transformed into a number of novel functions. The combination of speed, series and shunt capacitances as design parameters are selected for short shunt SEIG in order to provide optimum values for voltage regulation (VR), frequency regulation (FR), loadability, voltage/frequency regulation and to provide optimum performance, defined as a weighted combination of VR, FR and loadability. The effect of weights, speed and power factor on designed parameters is also assessed for a generic application on SEIG. Correspondingly, an optimisation is proposed using particle swarm optimisation, a heuristic approach considering various equality and inequality constraints related to SEIG. This study is carried out for resistive and inductive loads. The simulated results are validated with test results.
Geometric modelling of the wavelet coefficients for image watermarking using optimum detector
Authors: Hamghalam Mohammad , Mirzakuchaki Sattar , Akhaee Mohammad Ali
Published: October 2013

In this study, a robust image watermarking method based on geometric modelling is presented. Eight samples of wavelet approximation coefficients on each image block are utilised to construct two line segments in the two‐dimensional space. The authors change the angle formed between these line segments for data embedding. Geometrical tools are used to solve the tradeoff between the transparency and robustness of the watermark data. They analytically determine the probability density function of the embedding angle for Gaussian samples. Maximum‐likelihood decoder is implemented in the receiver side. Owing to embedding in the angle between two line segments, the proposed scheme has high robustness against the gain attacks. In addition, using the low frequency components of the image blocks for data embedding, high robustness against noise and compression attacks has been achieved. Experimental results confirm the validity of the theoretical analyses given in this study and show the superiority of the proposed method against common attacks, such as Gaussian filtering, median filtering and scaling attacks.
Tall microstrip transmission lines for dielectric resonator antenna applications
Authors: Rashidian Atabak , Shafai Lotfollah , Klymyshyn David M.
Published: October 2013

Dielectric resonator antennas (DRAs) excited by tall microstrip transmission lines (TMLs) are investigated. Two different TML–DRA structures are proposed and the impact of TML parameters on the antenna performance is studied when low‐loss and lossy substrates are used. To validate the effectiveness of this approach, a set of prototype antennas was fabricated, measured and compared with simulation results. A good agreement is obtained. It is found that by adjusting TML parameters, excellent impedance matching and coupling to low‐permittivity DRAs are achieved even on high‐permittivity substrates. The impedance bandwidth of a single‐mode simple‐shape rectangular DRA with ɛrd = 9 can be as high as 25%. The radiation efficiency of the antenna on extremely lossy substrates is significantly improved and based on the measured results over 80% efficiency with a gain ranging from 4.2 to 5.5 dBi along the impedance bandwidth can be expected. Since TML is a low‐loss transmission line, the DRA is a low‐loss radiator and low‐permittivity DRAs can be well matched by TML, the TML–DRA forms an excellent wideband antenna system with high radiation efficiency.
Modelling and control of a DC–DC quadratic boost converter with R2P2
Authors: Morales‐Saldaña Jorge Alberto , Loera‐Palomo Rodrigo , Palacios‐Hernández Elvia , González‐Martínez Jorge Luis
Published: October 2013

In the past years, the development of topologies with step‐up capacities has been important to satisfy the new requirement of renewable source energy. This study presents a quadratic boost converter based on the reduced redundant power processing (R2P2) principle, well as the controller design methodology using current‐programmed control to satisfy the specifications of output voltage regulation. Non‐linear and linear models are developed; the latter exhibits fourth‐order characteristic dynamics with complex right‐half plane zeros. In the proposed control scheme, the current of the switch is used for feedback purposes. When the current loop is implemented, the fourth‐order dynamics are changed to a dominant first order, which simplifies the controller design of outer loop. For this loop, a conventional controller is designed. At the end, experimental results are given for a 23 W quadratic boost converter, where open‐loop and closed‐loop responses are compared.
SPICE model of thyristors with amplifying gate and emitter‐shorts
Authors: Zekry Abdelhalim A. , Sayah Gihan Taha , Soliman Fouad A.
Published: October 2013

In this work, a new SPICE model is developed for power thyristors, which contains amplifying gate and emitter‐shorts. This model is based on the two‐dimensional two‐transistor circuit model of a thyristor. The authors use Gummel–Poon circuit model that takes into consideration the high injection effects and the conductivity modulation of the low n‐doped region. The model parameters are defined and extracted according to a new methodology. The simulation results are compared with experimental measurements. It has been found that the developed model satisfactorily describes the performance of the thyristor under practical operating conditions.
Neural network controlled grid interfaced solar photovoltaic power generation
Authors: Singh Bhim , Shahani Dilip Tekchand , Verma Arun Kumar
Published: October 2013

This study deals with a NN (neural‐network)‐based control algorithm of a grid interfaced SPV (solar photovoltaic) generating system. The proposed grid interfaced SPV generating system utilises a NN control algorithm‐based on the LMS (least mean‐square), known as Adaline (adaptive linear element) to estimate reference grid currents. A DC–DC boost converter is used for achieving the maximum power point tracking between SPV and DC bus of four‐leg VSC (voltage source converter) interfaced to a three‐phase, four‐wire distribution system. The four‐leg VSC of SPV generating system is also used for the compensation of the reactive power for zero voltage regulation or for power factor correction along with load balancing, elimination of load harmonics currents and mitigation of neutral current at PCC (point of common coupling) in three‐phase four‐wire distribution system. The DC bus of VSC is supported by a capacitor which is fed by SPV energy through a DC–DC boost converter. A laboratory prototype of proposed grid interfaced SPV generating system is developed to validate its developed model and the NN‐based control algorithm.
Stability issues and modelling of ripple‐based constant on‐time control schemes operating in discontinuous conduction mode
Authors: Wei I‐Chieh , Lin Yu‐Cheng , Chen Ching‐Jan , Chen Dan
Published: October 2013

Ripple‐based constant on‐time (RBCOT) control schemes have recently received much attention for the DC converters used in many applications, mainly because of the relatively high efficiency under light‐load condition while preserving other features such as fast step‐load response and small component count. Since the converter is usually operated under discontinuous conduction mode (DCM) under light‐load condition, an effort to investigate the RBCOT schemes under DCM is practically important. Rigorous mathematical analyses are used to investigate the feedback stability issues of the buck converters using RBCOT control schemes operating in DCM. Two RBCOT control schemes are considered: the basic RBCOT scheme and the basic RBCOT with virtual‐inductor‐current signal (VICRBCOT). It is proved that it is always stable for the basic RBCOT converter operating in DCM, but that is not the case for the VICRBCOT converters. A proper design procedure to maintain stability for both the continuous conduction mode and the DCM operations in VICRBCOT converters is proposed and verified.
Fabrication of copper nanowires using overpotential electrodeposition and anodic aluminium oxide template
Authors: Chung C.‐K. , Yang C.Y. , Liao M.W. , Li S.L.
Published: October 2013

Overpotential is widely used in electrodeposition of copper nanowires (Cu NWs). However, the value of >2 is harmful for nanowires formation. In this reported study, pulse technology is used to solve the problem. The authors have investigated the effects of potential and voltage mode on the formation of Cu NWs via a porous anodic aluminium oxide template using the electrochemical deposition method. Cu NWs were synthesised by electrochemical deposition in 0.2 M CuSO4‐based solution under different potential modes of direct current (DC) and pulse. Scanning electron microscopy and grazing incidence X‐ray diffraction were used to examine the nanostructure, morphology and phase of Cu NWs. The Cu NWs deposited by pulse mode exhibited a high aspect ratio despite a high potential of 2–3 V, whereas that at higher DC potential was rather short because of hydrogen generation in reduction reaction. The hydrogen byproduct during Cu NWs synthesis can be effectively released at the off period of pulse deposition for good nanowires formation.
The role of Rydberg and continuum levels in computing high harmonic generation spectra of the hydrogen atom using time-dependent configuration interaction
Authors: Luppi Eleonora , Head-Gordon Martin
Published: October 2013

We study the role of Rydberg bound-states and continuum levels in the field-induced electronic dynamics associated with the High-Harmonic Generation (HHG) spectroscopy of the hydrogen atom. Time-dependent configuration-interaction (TD-CI) is used with very large atomic orbital (AO) expansions (up to L = 4 with sextuple augmentation and off-center functions) to describe the bound Rydberg levels, and some continuum levels. To address the lack of ionization losses in TD-CI with finite AO basis sets, we employed a heuristic lifetime for energy levels above the ionization potential. The heuristic lifetime model is compared against the conventional atomic orbital treatment (infinite lifetimes), and a third approximation which is TD-CI using only the bound levels (continuum lifetimes go to zero). The results suggest that spectra calculated using conventional TD-CI do not converge with increasing AO basis set size, while the zero lifetime and heuristic lifetime models converge to qualitatively similar spectra, with implications for how best to apply bound state electronic structure methods to simulate HHG. The origin of HHG spectral features including the cutoff and extent of interference between peaks is uncovered by separating field-induced coupling between different types of levels (ground state, bound Rydberg levels, and continuum) in the simulated electronic dynamics. Thus the origin of deviations between the predictions of the semi-classical three step model and the full simulation can be associated with particular physical contributions, which helps to explain both the successes and the limitations of the three step model.
Broad-band magnetic induction probe calibration using a frequency-corrected reference probe
Authors: Hill Carrie
Published: October 2013

Finite impedances of magnetic induction probes attenuate and shift the field fluctuations measured by the probe so that they differ from the measured signal at the digitizer. These effects vary with frequency. Traditionally, impedance effects have been accounted for in the calibration process by sweeping the frequency of the magnetic field source through a range of frequencies. Situations arise where the conventional calibration method is not feasible due to probe geometry or hardware constraints. A new calibration technique is presented in this paper which calibrates the probe in situ at a single frequency and uses impedance measurements of the probe assembly across the desired frequency range to account for broad-band effects. The in situ calibration technique requires a reference probe with a known proportionality constant NA and known impedances. Impedance effects are corrected in the probe signal using broad-band impedance measurements included in a transfer function in frequency space. The in situ calibration technique is shown to be complicated by capacitive coupling between the probes and the high voltage source coil. Circuit modeling demonstrates that this coupling introduces negligible attenuation and a small phase-delay so that the relative phase-delay between the reference and target probe signals can be corrected by shifting the signals in time. In summary, this calibration method extends traditional single-frequency calibration techniques to broad-band applications, accounting for important non-ideal effects to improve the accuracy of the magnetic field measurement.
A transparent Pyrex μ-reactor for combined in situ optical characterization and photocatalytic reactivity measurements
Authors: Dionigi F. , Nielsen M. G. , Pedersen T. , Hansen O. , Chorkendorff I. , Vesborg P. C. K.
Published: October 2013

A new Pyrex-based μ-reactor for photocatalytic and optical characterization experiments is presented. The reactor chamber and gas channels are microfabricated in a thin poly-silicon coated Pyrex chip that is sealed with a Pyrex lid by anodic bonding. The device is transparent to light in the UV-vis-near infrared range of wavelengths (photon energies between ∼0.4 and ∼4.1 eV). The absorbance of a photocatalytic film obtained with a light transmission measurement during a photocatalytic reaction is presented as a proof of concept of a photocatalytic reactivity measurement combined with in situ optical characterization. Diffuse reflectance measurements of highly scattering photocatalytic nanopowders in a sealed Pyrex μ-reactor are also possible using an integrating sphere as shown in this work. These experiments prove that a photocatalyst can be characterized with optical techniques after a photocatalytic reaction without removing the material from the reactor. The catalyst deposited in the cylindrical reactor chamber can be illuminated from both top and bottom sides and an example of application of top and bottom illumination is presented.
Anomalous magnetic behavior below 10 K in YCrO3 nanoparticles obtained under droplet confinement
Authors: Singh Inderjeet , Nigam A. K. , Landfester Katharina , Muñoz-Espí Rafael , Chandra Amreesh
Published: October 2013

Nanoparticles of multiferroic YCrO3 synthesized using the droplet confinement of miniemulsions show unusual features in the magnetic properties at low temperatures, which have not been reported before. Below 10 K, there is a sudden increase in the magnetization, and the nature of M–H hysteresis loops changes appreciably. The hysteresis loop shows two contributions, one similar to ferromagnetic and another similar to that expected from antiferromagnetic systems. This behavior can be understood by the formation of elongated grains or mesocrystals. It is remarkable that YCrO3 behaves quite differently from other multiferroic chromates such as ACrO3 (A = In, Sc, Sm).
Structural and optical properties of ZnO and ZnO:Fe nanoparticles under dense electronic excitations
Authors: Kumar Shiv , Asokan K. , Singh Ranjan Kr. , Chatterjee S. , Kanjilal D. , Ghosh Anup K.
Published: October 2013

We report on the changes in structural, morphological, and optical properties of sol-gel derived ZnO and ZnO:Fe nanoparticles due to dense electronic excitations produced by heavy ion irradiations using 200 MeV Ag+15 ion beams. X-ray diffraction studies with Rietveld refinement show that the samples are single phase and tensile strain has been developed in the ion-irradiated samples. The Raman spectroscopy measurements show that ion-irradiation results in microscopic structural disorders and breaking of translational symmetry giving rise to local distortions in the lattice. Atomic force microscopy studies show that roughness of the pellets increases strongly for pure ZnO as compared with Fe-doped ZnO due to ion-irradiation. Fourier transform infrared analysis confirms tetrahedral coordination of O ions surrounding the Zn-ions and surface modification of the nanoparticles. The UV-Vis spectroscopy measurements show that the band gap increases on Fe doping which may be due to 4s–3d and 2p–3d interactions and the Burstein-Moss band filling effect. The band gap decreases after irradiation which can be interpreted on the basis of creation of some new localized energy states above the valence band. Photoluminescence (PL) intensity is enhanced and two new emission bands viz. a blue band at ∼480 nm (related to surface defects) and a green band at ∼525 nm (related to O vacancies) are observed in ion-irradiated nanoparticles. The enhancement of PL-intensity in irradiated samples is attributed to the increase of different defect states and Zn−O bonds on the surfaces of the irradiated nanoparticles arising from surface modification.
The escape of a charged dendrimer from an oppositely charged planar surface
Authors: Welch P. M.
Published: October 2013

Many of the envisioned applications of dendrimers revolve around placing these molecules at and removing them from charged interfaces. Herein, we provide a prescription for the conditions needed to release a charged dendrimer from an oppositely charged flat substrate. Identifying an effective segment step length that reflects the intramolecular repulsions due to excluded volume and electrostatics, as well as the dendrimer's branching, provides the essential concept leading to an analytical prediction for the boundary between captured and free molecules. We find that this effective step length obeys trends similar to those predicted for linear chains, but is modified by the dendrimer's connectivity. Moreover, the boundary predicted for the capture of linear chains holds for dendrimers once this effective step length is employed. Monte Carlo computer simulations of coarse-grained model dendrimers escaping from charged surfaces validate these findings. The simulations consider generations 2 through 6 with a range of lengths between the branch points, as well as a range of solution ionic strengths and surface charge densities.
Discrete particle simulations and experiments on the collapse of wet granular columns
Authors: Gabrieli Fabio , Artoni Riccardo , Santomaso Andrea , Cola Simonetta
Published: October 2013

Small quantities of liquid in a granular material control the flow dynamics as well as the triggering and jamming phases. In order to study this problem, some experimental collapse tests conducted in a rectangular box were reproduced with a 1:1 scale numerical model using the Discrete Element Method. In simulations the effect of the capillary bridges has been investigated implementing a mid-range attractive force between particles based on the minimum energy approach. Also a bonding-debonding mechanism was incorporated in the algorithm and the volume of each sessile drop on the particle surface was considered during its motion. The influence of some variables was investigated with respect to the final slope profiles and the runout lengths: the initial liquid content, the particle size, the solid density, the liquid surface tension, and the liquid-solid contact angle. Also the crucial effect of the confinement walls on the collapse phenomenon was investigated: wet particles adhere to the lateral walls providing a higher flow resistance in comparison to the same material in dry conditions. It was observed that particles with largest path-lengths are localized near the movable wall at a middle-height of the initial column sample. Other particles at the surface moves in a rigid way especially if they were wet and with a low solid density. The “fidelity” of each particle with respect to the nearest neighbours was evaluated allowing to recognize the emergence of clusters of particles and rigid parts, to extract the failure surface and to localize where debonding mechanisms concentrate in the wet case.
Engineering the plasmonic optical properties of cubic silver nanostructures based on Fano resonance
Authors: Yang Zhi , Wang Minqiang , Song Xiaohui , Deng Jianping , Yao Xi
Published: October 2013

The plasmonic optical properties of nanostructures including a dimer, a linear chain, a T-shaped nanostructure, and a 2D array consisting of Ag nanocubes have been investigated using the discrete dipole approximation method. The simulation results indicate that both the interparticle gap and polarization have an important impact on far-field and near-field characteristics. With decreasing interparticle distance for four nanostructures, the plasmon resonance peak is monotonically red-shifted and the electric intensity enhancement factor increases rapidly due to increased interparticle coupling interaction. Moreover, we also find that a T-shaped nanostructure has the largest electric intensity enhancement factor compared with other three nanostructures due to the coupling interaction at the intersection. This coupling is caused by the radiative interference between subradiant and superradiant resulting in Fano resonance. These results show how nanostructure arrangement design, gap adjustment, and polarization control can be used to achieve high field enhancements.
Local vibrational properties of GaAs studied by extended X-ray absorption fine structure
Authors: Ahmed S. I. , Aquilanti G. , Novello N. , Olivi L. , Grisenti R. , Fornasini P.
Published: October 2013

Extended X-ray absorption fine structure (EXAFS) has been measured at both the K edges of gallium and arsenic in GaAs, from 14 to 300 K, to investigate the local vibrational and thermodynamic behaviour in terms of bond expansion, parallel, and perpendicular mean square relative displacements and third cumulant. The separate analysis of the two edges allows a self-consistent check of the results and suggests that a residual influence of Ga EXAFS at the As edge cannot be excluded. The relation between bond expansion, lattice expansion, and expansion due to anharmonicity of the effective potential is quantitatively clarified. The comparison with previous EXAFS results on other crystals with the diamond or zincblende structure shows that the values of a number of parameters determined from EXAFS are clearly correlated with the fractional ionicity and with the strength and temperature interval of the lattice negative expansion.
Single molecule counting statistics for systems with periodic driving
Authors: Zheng Yujun , Brown Frank L. H.
Published: October 2013

We extend the generating function approach for calculation of event statistics observed in single molecule spectroscopy to cases where the single molecule evolves under explicitly time-dependent and periodic perturbation. Floquet theory is used to recast the generating function equations for the periodically driven system into effective equations devoid of explicit time-dependence. Two examples are considered, one employing simple stochastic dynamics and the other quantum dynamics, to demonstrate the versatility and numerical accuracy of the methodology.
Complex of heavy magnetic ions and luminescent silicon nanoparticles
Authors: Hoang T. , Stupca M. , Mantey K. , Maximenko Y. , Elhalawany N. , Carr C. , Yu H. , Nayfeh M. H. , Morgan H.
Published: October 2013

We study the optical properties of luminescent silicon nanoparticles in the presence of magnetic ions of iron or erbium under wet conditions and electric biasing. Upon the introduction of the ions under zero biasing, the brightness is enhanced with some spectral change. Under biasing including breakdown field conditions, the enhancement remains stable and is maintained after recovery of the particles into nanosolid films using electric spray. The ion-nanoparticle interaction is analyzed using first principle atomistic calculations employing unrestricted Hartree-Fock density functional theory. The calculations yield configurations, which show strong binding and stability. The complexes promise diverse applications in magnetic/optical imaging, spatially programmable deposition, spin-based memories and transistors, infrared communications, filtration, as well as interplanetary and interstellar observation and modeling.
Molecular dynamics study of nanobubbles in the equilibrium Lennard-Jones fluid
Authors: Zhukhovitskii D. I.
Published: October 2013

We employ a model, in which the density fluctuations in a bulk liquid are represented as presence of the clusters of molecules with the lowered number of nearest neighbors (number of bonds). The nanobubble size distribution is calculated on the basis of a close analogy between the surface part of the work of formation for a cluster and for a nanobubble. The pre-exponential factor for this distribution is related to the fluid compressibility. Estimates made for different liquids show that it can be noticeably different from that adopted in the classical nucleation theory (CNT). Molecular dynamics (MD) simulation is performed for a liquid inside a macroscopic droplet of molecules interacting via the Lennard-Jones potential plus a long-range tail. The nanobubbles are identified by clusters of bond-deficient particles with the optimum number of bonds that provide the maximum nanobubble number density and maximum resolvable nanobubble equimolar size. The results of MD simulation are in qualitatively better agreement with proposed theory than with CNT.
Direct numerical simulation of drag reduction in a turbulent channel flow using spanwise traveling wave-like wall deformation
Authors: Tomiyama Nobuhito , Fukagata Koji
Published: October 2013

Drag reduction effects by a spanwise traveling wave of wall deformation in a turbulent channel flow are investigated by means of direct numerical simulation. The flow rate is kept constant at the bulk Reynolds number of Reb = 5600. A parametric study is performed by varying three parameters of the wave (i.e., the amplitude, the wavenumber, and the phase speed). Within the range of parameters investigated, the maximum drag reduction rate and the maximum net energy saving rate are found to be 13.4% and 12.2%, respectively. The drag reduction rate is found to be reasonably scaled by a product of the magnitude of the induced velocity and the thickness of the Stokes layer. An analysis using the FIK identity [K. Fukagata, K. Iwamoto, and N. Kasagi, “Contribution of Reynolds stress distribution to the skin friction in wall-bounded flows,” Phys. Fluids 14, L73 (2002)] with a three-component decomposition reveals that the drag reduction is mainly attributed to a decrease in the random component of the Reynolds shear stress. The turbulence statistics are investigated in detail and the drag reduction mechanism is explained by the induced spanwise flow due to the traveling wave rather than the riblet-like geometric structure. Although the amount of drag reduction rate is comparable to that of the conventional riblets, the quasi-streamwise vortices are found to be suppressed even when the spanwise wavelength is larger than the typical diameter of quasi-streamwise vortices.
Stratified turbulence and small-scale internal waves above deep-ocean topography
Authors: van Haren Hans
Published: October 2013

When ocean's internal tidal waves “beach” at underwater topography, they transform from more or less linear into highly nonlinear waves that can break with generation of vigorous turbulent mixing. Although most mixing occurs in the half hour around a steep (bottom-)front leading the upslope moving internal tide phase, relatively large mixing also occurs some distance of several tens of meters off the bottom, just prior to the downslope moving internal tide phase and initiated by high-frequency “small-scale” internal waves. Details of this off-bottom small-scale mixing in a stratified natural environment and some of its variability per tidal period are presented here in two case studies using high-resolution temperature observations (61 sensors at 1 m intervals; <10−3 °C precision) at a 969 m deep site south of New Zealand. The observations shed some light on stratified turbulence that is generated in a relatively thick (∼30 m) weakly stratified layer and in the strongly stratified interfaces above and below. The interfacial internal waves generate turbulence with largest dissipation rate and temperature variance at the edge of the upper interface and the weakly stratified layer. When these waves steep nonlinearly, immediate moderate turbulence generation is observed below, throughout the weakly stratified layer. Largest turbulence is generated by 25 m high asymmetric Holmboe overturns.
Transient photoluminescence from silicon wafers: Finite element analysis
Authors: Wang Kai , McLean William , Kampwerth Henner
Published: October 2013

This paper presents an accurate and practical mathematical model of time-resolved photoluminescence (PL) response from silicon wafers generated by fast repetitive excitation pulses. The model is valid under low level injection condition and takes into account the depth dependence of carrier generation, diffusion, and surface recombination. Finite element analysis is employed for the carrier density and PL computations. By comparing computational results with results obtained from PC1D (a computer program solving fully coupled nonlinear equations for quasi-one-dimensional carrier transportation in crystalline semiconductor devices, especially focusing on photovoltaic devices), the validity of this method is confirmed. Early stage application and the limitations of this method have been studied, and future work has been proposed.
The effect of sulfur covalent bonding on the electronic shells of silver clusters
Authors: Pedicini Anthony F. , Reber Arthur C. , Khanna Shiv N.
Published: October 2013

The nature of the bonding in AgnSm0/− clusters, n = 1–7; m = 1–4, has been analyzed to understand its effect on the electronic shell structure of silver clusters. First-principle investigations reveal that the sulfur atoms prefer 2 or 3-coordinate sites around a silver core, and that the addition of sulfur makes the planar structures compact. Molecular orbital analysis finds that the 3p orbitals of sulfur form a bonding orbital and two weakly bonding lone pairs with silver. We examine the electronic shell structures of Ag6Sm, which are two electrons deficient of a spherical closed electronic shell prior to the addition of sulfur, and Ag7Sm− clusters that contain closed electronic shells prior to the addition of sulfur. The Ag6S4 cluster has a distorted octahedral silver core and an open shell with a multiplicity of 3, while the Ag7Sn− clusters have compact geometries with enhanced stability, confirming that the clusters maintain their electronic shell structure after bonding with sulfur.
Effects of magnetic and nonmagnetic impurities on the spin susceptibility of a noncentrosymmetrical superconductor: Application to CePt3Si
Authors: Yavari H. , Mokhtari M. , Tamaddonpour M.
Published: October 2013

The combined effect of nonmagnetic and magnetic impurities on the spin susceptibility of a noncentrosymmetrical superconductor by considering a Cooper pairing model with a two-component order parameter composed of spin-singlet and spin-triplet pairing components is investigated. For clean superconductor CePt3Si, the low-temperature dependence (T→0) of spin susceptibility is linear which suggests that the gap function has line nodes, consistent with our gap model. We will show that in the presence of magnetic impurities the susceptibility does not vanish even in the absence of spin orbit coupling and in the region where the energy gap still is finite, and in the low concentration of magnetic impurities the spin susceptibility at zero temperature is proportional to impurity concentration.
Quantitative mapping of fast voltage pulses in tunnel junctions by plasmonic luminescence
Authors: Grosse Christoph , Etzkorn Markus , Kuhnke Klaus , Loth Sebastian , Kern Klaus
Published: October 2013

An optical read-out technique is demonstrated that enables mapping the time-dependent electrostatic potential in the tunnel junction of a scanning tunneling microscope with millivolt and nanosecond accuracy. We measure the time-dependent intensity of plasmonic light emitted from the tunnel junction upon excitation with a nanosecond voltage pulse. The light intensity is found to be a quantitative measure of the voltage between tip and sample. This permits non-invasive mapping of fast voltage transients directly at the tunnel junction. Knowledge of the pulse profile reaching the tunnel junction is applied to optimize the experiment's time response by actively shaping the incident pulses.
First-principles study of stability and properties on β-SiC/TiC(111) interface
Authors: Li Jian , Yang Yanqing , Feng Guanghai , Luo Xian , Sun Qing , Jin Na
Published: October 2013

The interfacial properties of β-SiC/TiC(111), such as work of adhesion, interface energy, fracture toughness, bonding nature, were investigated using first-principles calculations. Twenty four interface models with different terminations, carbon sublattice, and stacking sites were investigated. The thermodynamic stability of SiC/TiC(111) decreases as the order of C/C, Si/Ti, C/Ti, and Si/C terminations. The C/C-terminated top-site-stacked models (CCU3, CCT3) are most stable with the largest work of adhesion, smallest interface energy, and largest interfacial fracture toughness. The interfacial fracture toughness is predicted as 3.6 ∼ 4.3 MPa·m1/2. The valence electron density and partial density of states indicate that the interfacial bonding is mainly contributed from covalent C-C interactions caused by the hybridization of C-2p. The interfacial Si-C and Ti-C bonds are less covalent and much weaker than the interior ones, and the interfacial bonds are more inclined to decompose. The carbon layer is likely to form on the interface due to the decomposition. Our calculation results are compared and in line with previous investigations.
Surface effects and magnetic ordering in few-nanometer-sized ε-Fe2O3 particles
Authors: Balaev D. A. , Dubrovskiy A. A. , Shaykhutdinov K. A. , Bayukov O. A. , Yakushkin S. S. , Bukhtiyarova G. A. , Martyanov O. N.
Published: October 2013

The magnetic properties of ε-Fe2O3 nanoparticles with an average size of 3.4 nm in a silica gel matrix are investigated using Mössbauer technique, electron spin resonance, and magnetic measurements. Two magnetic subsystems reveal in magnetic measurements. Paramagnetic subsystem is formed by the Fe(III) ions in the smallest (<3.5 nm) particles' shell, while ferrimagnetic ordering in the “core” of the particles results in superparamagnetic behavior. The superparamagnetic behavior of the investigated samples is observed up to ∼800 K. The magnetic moment of the particles is formed by both the ferrimagnetic ordering characteristic of ε-Fe2O3 and the additional effect of uncompensated sublattices (planes).
Spin-orbit interaction induced spin selective transmission through a multi-terminal mesoscopic ring
Authors: Dey Moumita , Maiti Santanu K. , Sil Sreekantha , Karmakar S. N.
Published: October 2013

Spin dependent transport in a multi-terminal mesoscopic ring is investigated in presence of Rashba and Dresselhaus spin-orbit interactions. Within a tight-binding framework, we use a general spin density matrix formalism to evaluate all three components (Px, Py, and Pz) of the polarization vector associated with the charge current through the outgoing leads. It explores the dynamics of the spin polarization vector of current propagating through the system subjected to the Rashba and/or the Dresselhaus spin-orbit couplings. The sensitivity of the polarization components on the electrode-ring interface geometry is discussed in detail. Our present analysis provides an understanding of the coupled spin and electron transport in mesoscopic bridge systems.
Band offsets and carrier dynamics of type-II InAs/GaSb superlattice photodetectors studied by internal photoemission spectroscopy
Authors: Lao Yan-Feng , Pitigala P. K. D. D. P. , Unil Perera A. G. , Plis E. , Krishna S. S. , Wijewarnasuriya Priyalal S.
Published: October 2013

We use internal photoemission spectroscopy to determine the conduction band offset of a type-II InAs/GaSb superlattice (T2SL) pBp photodetector to be 0.004 (±0.004) eV at 78 K, confirming its unipolar operation. It is also found that phonon-assisted hole transport through the B-region disables its two-color detection mode around 140 K. In addition, photoemission yield shows a reduction at about an energy of longitudinal-optical phonon above the threshold, confirming carrier-phonon scattering degradation on the photoresponse. These results may indicate a pathway for optimizing T2SL detectors in addition to current efforts in material growth, processing, substrate preparation, and device passivation.
On the sonic composites without/with defects
Authors: Chiroiu Veturia , Brişan Cornel , Popescu Mihaela , Girip Iulian , Munteanu Ligia
Published: October 2013

The sound attenuation in a sonic composite without/with point defects is studied using a new method that combines the features of the cnoidal method and the genetic algorithm. Acoustic scatterers are composed by piezoceramic hollow spheres of functionally graded materials—the Reddy and cosine graded hollow spheres. This method enables to obtain the dispersion relation for defect modes, and the prediction of the evanescent nature of the modes inside the band-gaps.
Low polarization dependent beam deflector based on Bragg reflector waveguide for C-band wavelength demultiplexing
Authors: Gu Xiaodong , Matsutani Akihiro , Koyama Fumio
Published: October 2013

We report a miniature beam deflector with a large angular dispersion based on a Bragg reflector waveguide operating in a full-C band. The device is extremely small with an effective footprint of 20 × 100 μm2. Continuous beam deflection of over 40° was obtained with large angular dispersion of ∼1°/nm. Polarization dependence was largely alleviated by optimizing the optical core thickness. Further decrease in the polarization dependence below 0.1° can be expected after considering the material birefringence inside the waveguide. A possible channel number can exceed 300, which could be the highest in C-band demultiplexing technologies ever reported.
Molecular phylogeny of the superfamily Palaemonoidea (Crustacea : Decapoda : Caridea) based on mitochondrial and nuclear DNA reveals discrepancies with the current classification
Authors: Kou Qi , Li Xinzheng , Chan Tin-Yam , Chu Ka Hou , Gan Zhibin
Published: October 2013

Palaemonoidea is one of the most speciose superfamilies of Caridea. Since it was established, several classification schemes of Palaemonoidea have been proposed and modified. However, the current classification of Palaemonoidea is still in dispute. In this study, one mitochondrial gene (16S rRNA) and three nuclear genes (histone 3, 18S rRNA and 28S rRNA) were used to explore the phylogenetic relationships among the subgroups of the superfamily Palaemonoidea, including seven families with 25 affiliated genera. Based on the combined data with both maximum likelihood and Bayesian inference analyses, the results support the monophyly of Anchistioididae and Hymenoceridae. In contrast, Gnathophyllidae is suggested to be paraphyletic and Palaemonidae is shown to be a polyphyletic group. Our analyses reveal that the subfamily Palaemoninae could be approximately divided into three clades, and the branchiostegal groove is the probable morphological evidence of the environmental transition from sea to fresh water. Besides, for some of the Palaemonoidea families, their taxonomic status is obscure. A revision of Palaemonoidea and a re-evaluation of its constituent taxa appear to be necessary even though the systematic status of the subfamily Pontoniinae is still undetermined.
Hidden in the highlands: the description and phylogenetic position of a novel endemic freshwater crab species (Potamonautidae : Potamonautes) from Zimbabwe
Authors: Phiri Ethel E. , Daniels Savel R.
Published: October 2013

A recent sampling endeavour of freshwater crabs along the high-lying streams of the Nyanga mountain range in Mutare (Eastern Highlands, Zimbabwe) yielded a morphologically distinct, as yet undescribed species. The novel Zimbabwean species is compared to the 16 described species from southern Africa based on mtDNA sequence data derived from three partial gene sequences (12S rRNA, 16S rRNA and COI). The new Zimbabwean species was found to be a sister taxon to Potamonautes mulanjeensis. These two species are morphologically and genetically easily differentiated. The new species is described as Potamonautes mutareensis, sp. nov. and is compared morphologically to the known freshwater crab species of southern Africa. A dichotomous key to the four described freshwater crab species that occur in Zimbabwe is also provided. Our results suggest that species diversity and endemism of freshwater decapods and other habitat specialists is likely to be high in unsampled mountainous regions.