bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical study on propagation mechanism and bio‐medicine applications of plasma jet
Authors: Cheng He , Liu Xin , Lu Xinpei , Liu Dawei
Published: June 2016

In this study, the propagation mechanism of plasma jet and some bio‐medical applications are investigated by two‐dimensional numerical model. The key equations of plasma physics and chemistry related with plasma jet are firstly introduced. The simulation results suggest that the sheath forms near the dielectric tube inner surface, which results in the plasma channel to shrink in the radial direction inside the dielectric tube. The photoionisation of air species plays a crucial role in the transition from the localised discharge to streamer. The Penning ionisation increases the electric conductivity of the plasma channel and facilitates the formation of ring‐shaped plasma bullet. For the plasma jet in the open air, electron‐impact dissociation of H2O, electron neutralisation of H2O+, as well as dissociation of H2O by O(1D) are found to be the main reactions to produce OH. For micro plasma jet, the higher ignition voltage as the tube diameter decreased is attributed to the deceasing pre‐avalanche electron density inside the tube. The simulation of plasma treatment of bacteria biofilm indicates that the mean free path of charged species in µm scale permitted the plasma penetrate into the cavity of the biofilm, and the structure of the biofilm results in the non‐uniform distribution of ROS and RNS. The simulation of plasma treatment of cells immersed in liquid suggests that the HO2 generated by plasma aqueous species is the only way for superoxide to penetrate cell membrane and damage cytosolic fumarase B.
Optimal generation scheduling of interconnected wind‐coal intensive power systems
Authors: Wang Songyan , Yu Daren , Yu Jilai , Zhang Wei , Foley Aoife , Li Kang
Published: June 2016

Large scale wind power generation complicated with restrictions on the tie line plans may lead to significant wind power curtailment and deep cycling of coal units during the valley load periods. This study proposes a dispatch strategy for interconnected wind‐coal intensive power systems (WCISs). Wind power curtailment and cycling of coal units are included in the economic dispatch analysis of regional systems. Based on the day‐ahead dispatch results, a tie line power plan adjustment strategy is implemented in the event of wind power curtailment or deep cycling occurring in the economic dispatch model, with the objective of reducing such effects. The dispatch strategy is designed based on the distinctive operation characteristics of interconnected WCISs, and dispatch results for regional systems in China show that the proposed strategy is feasible and can improve the overall system operation performance.
Post‐retirement utilisation of synchronous generators to enhance security performances in a wind dominated power system
Authors: Masood Nahid‐Al , Yan Ruifeng , Saha Tapan Kumar , Bartlett Simon
Published: June 2016

Power system security concerns due to significant wind generation could be twofold: first, the frequency response and second, the short‐circuit performance. Continuous development of wind energy may cause economic replacement and retirement of existing synchronous generators. Modern wind turbine generators do not inherently offer inertia and governor response after a disturbance, which may result in declining frequency response behaviour. Besides, they have limited fault current contribution, which may cause unacceptable short‐circuit ratio at the grid connection point of those wind power plants. Traditionally, frequency response and short‐circuit performance are individually improved. However, both of them are concurrently affected by high wind penetration. Hence, a common approach to simultaneously enhance both indices is essential. Therefore, this study introduces an idea of operating some of the retired synchronous generators in the synchronous condenser mode, which is termed as ‘post‐retirement scheme (PRS)’. Such a second use of the retired synchronous generators can jointly upgrade frequency response and short‐circuit strength during high wind generation. This study also proposes a methodology to evaluate when and how much PRS should be deployed for ensuring an adequate security performance in a wind dominated power system.
Wide‐band modelling and transient analysis of the multi‐conductor transmission lines system considering the frequency‐dependent parameters based on the fractional calculus theory
Authors: Liu Xin , Ti Chenyang , Liang Guishu
Published: June 2016

The transient analysis of multi‐conductor transmission lines should consider the frequency‐dependent characteristics due to the skin effect. Fully considering the inherent fractional order characteristics of the frequency‐dependent effect, a general wide‐band modelling method is proposed. The fractional order vector fitting method is adopted to approximate the frequency‐dependent parameters and the corresponding fractional differential equations can be obtained by the inverse Laplace transformation. The backward difference is a practical method to solve the fractional differential equations; however, a linear convolution must be calculated, which will lead to a heavy computation complexity. To address this issue, a new recursive convolution method for the fractional differential equations is proposed and an efficient solution is achieved. Furthermore, considering the indispensability of the passivity verification of a system for the transient simulation, the passivity verification by extending the Hamiltonian matrix for the fractional order systems is studied and a practical criterion is proposed. Three examples are considered to validate the proposed method: (i) a single underground cable, (ii) three‐phase underground cable, and (iii) an experimental transformer under very fast transient voltage. The simulation results are compared with the results obtained by power systems computer‐aided design or measurements and good agreements are achieved.
Analysis of the frequency‐based control of a master/slave micro‐grid
Authors: Buticchi Giampaolo , De Carne Giovanni , Barater Davide , Zou Zhixiang , Liserre Marco
Published: June 2016

Renewable energy penetration in the low‐voltage grid faces several limitations due to the current grid topology. Master/slave micro‐grids could help solving these issues, by offering additional services to the grid such as the power management of the distributed power energy sources. In some cases, the power produced by the distributed energy sources exceeds the local consumption of the low‐voltage grid. The consequent reverse power flow can be either dangerous (for the medium voltage) or impossible (for a micro‐grid with limited storage). The droop characteristic of commercial inverter can be exploited to avoid this behaviour. However, stability problems can arise due to a low phase‐locked‐loop (PLL) bandwidth. This study investigates the stability of this solution depending on the bandwidth of the PLL of the distributed power generation sources.
Synchronisation of bistatic radar using chaotic AM and chaos‐based FM waveforms
Authors: Pappu Chandra Sekhar , Flores Benjamin C. , Debroux Patrick S. , Verdin Berenice , Boehm James
Published: June 2016

The authors developed a technique to synchronise a bistatic radar that uses a chaotic system to generate and process either wideband amplitude modulated (AM) or frequency modulated (FM) waveforms thereby extracting high‐resolution information from the targets. For chaotic AM bistatic radar, a generalised projective synchronisation approach that includes a driving oscillator at the transmitter and a response oscillator at the receiver is considered. The receiver accepts a scaled version of the transmitted waveform where the scaling factor α accounts for space propagation losses that may not be known a priori. However, AM synchronisation is highly susceptible to noise. Alternatively, FM bistatic radar is implemented with a chaos‐based FM waveform. Demodulation of this waveform using a phase lock loop is required to recover the instantaneous frequency which represents a chaotic state variable. The recovered and transmitter instantaneous frequencies are synchronised by using either generalised projective synchronisation or complete replacement synchronisation. The synchronised output is then used to reconstruct the FM waveform. They show that the short‐time cross‐correlation of the transmitted and reconstructed waveforms is high and its self‐noise is negligible. Through entropy analysis of the cross‐correlogram, they found that the bistatic FM radar performs better than the bistatic AM radar.
IDEPAR: a multichannel digital video broadcasting‐terrestrial passive radar technological demonstrator in terrestrial radar scenarios
Authors: Jarabo‐Amores Maria‐Pilar , Bárcena‐Humanes Jose‐Luis , Gómez‐del‐Hoyo Pedro , Rey‐Maestre Nerea , Juara‐Casero Diego , Gaitán‐Cabañas Fco‐Javier , Mata‐Moya David
Published: June 2016

Passive bistatic radars (PBRs) sensors are emerging technologies that have sparked interest due to the advantages derived from the use of opportunity illuminators instead of dedicated transmitters. An important research effort is being carried out, mainly focused on the analysis of the illuminators waveforms and the development of system demonstrators, being the detection and tracking of low flying aircrafts the most extended validation scenario. IDEPAR is a digital video broadcasting‐terrestrial (DVB‐T)‐based multichannel PBR technological demonstrator, developed in the University of Alcalá. The main contributions of this study are the radar scenario, detection of terrestrial vehicles in semi‐urban environments, and the development of a general and complete design methodology, that will allow the definition of system design requirements for any system and application. To validate system performance, real data were processed and detection and tracking results were evaluated using global positioning system data from cooperative targets. Reference signal processing algorithms were used. Results showed the feasibility of DVB‐T‐based PBRs for detecting and tracking low speed terrestrial vehicles in semi‐urban scenarios.
Optimal single relay position of a 3‐coil wireless power transfer system
Authors: Niu Wangqiang , Wang Jianhua , Chu Jianxin , Gu Wei
Published: June 2016

It seems a good idea to place the relay coil in the middle to maximise the load voltage in a 3‐coil wireless power transfer system; however, no literature points out clearly the reason and the necessary conditions that it holds. In this study, the complex relationship between coupling coefficients and distances is approximated by a simple polynomial, and then a rigorous analysis is carried out to show clearly that the optimal relay coil position of a 3‐coil wireless power transfer system is just the middle of the drive loop and the load loop under the symmetrical condition that coil quality factors of the drive loop and the load loop are equal, and furthermore the middle is not the optimal position if the symmetrical condition is destroyed. Finally, the theoretical results are confirmed by the physical experiments.
Performance analysis of single‐electron transistor at room‐temperature for periodic symmetric functions operation
Authors: Miralaie Mostafa , Mir Ali
Published: June 2016

For the first time, the authors have investigated the analysis of the room‐temperature operation of single‐electron transistor (SET) for periodic symmetric functions (PSFs). They demonstrate that in SETs due to the Pauli exclusion principle the distance between current peaks against bias voltage in coulomb oscillations will be asymmetric. Also, because the separated energy levels have unequal tunnel‐barrier resistance, different tunnelling current rates are obtained for each level. So, the unequal peak‐to‐valley current ratio (PVCR) will be observed in the coulomb oscillations, and therefore the operation of room‐temperature of silicon SET‐based PSFs is impossible.
Pore‐scale contact angle measurements of CO2–brine–glass beads system using micro‐focused X‐ray computed tomography
Authors: Lv Pengfei , Liu Yu , Jiang Lanlan , Song Yongchen , Huang Qingxun
Published: June 2016

Conventional methods for measuring contact angle are usually applied on smooth surfaces. Methods concerning contact angle determinations performed directly on pore surfaces of porous media have rarely been reported. This work approaches the pore‐scale measurement of local contact angle in a CO2–brine–glass beads system, using micro‐focused X‐ray computed tomography (micro‐CT). Both drainage and imbibition experiments with 0.1 ml/min injection rate were conducted at 40°C and 8 MPa. The effectiveness of this pore‐scale approach is confirmed by comparing the results with the results gathered from traditional sessile drop methodology. Observations indicate that the contact angle hysteresis phenomenon was not so obvious for intermediate‐wet glass beads in the employed experimental setting. In real reservoir circumstances, the roughness and capillary variation caused significant deviations in contact angle distribution for both drainage and imbibition, even in rock cores consisting of a single‐phase material.
Lebenslaufforschung in der Epidemiologie und den Sozialwissenschaften. Gemeinsam einsam?
Authors: Richter M. , Günther S. , Herke M.
Published: June 2016

Der Lebenslauf wird zunehmend als Schlüssel zu einem besseren Verständnis der Entwicklung von Gesundheit und gesundheitlicher Ungleichheiten angesehen. Ziel des Aufsatzes ist es, das Potenzial einer umfassenden, interdisziplinären Perspektive auf den Lebenslauf und die Gesundheit zu untersuchen, die soziologische und psychologische Theorien und Modelle integriert und so einen stärkeren Dialog zwischen der Epidemiologie und den Sozialwissenschaften ermöglicht. Dabei werden zentrale Prinzipien und Konzepte aus den verschiedenen Forschungsdisziplinen diskutiert, die sich mit der Bedeutung des Lebenslaufs auseinandersetzen. Es wird ein theoriegestützter Forschungsrahmen abgeleitet, der den interdisziplinären Austausch fördert und illustriert, wie eine bio-psycho-soziale Perspektive auf den Lebenslauf stärker in den Bereich der Epidemiologie übertragen werden kann. Die paradigmatischen Prinzipien der interdisziplinären Lebenslaufforschung (human agency, timing, linked lives und historical context) bieten einen wichtigen theoretischen Rahmen für eine holistische, theoriebasierte Sicht auf den Lebenslauf und seine ineinander verflochtenen Verläufe. Der Stressprozess repräsentiert in diesem Kontext einen wichtigen ätiologischen Mechanismus zwischen den Lebenslaufprinzipien und Gesundheit. Um die Entwicklung von Gesundheit und gesundheitlicher Ungleichheiten besser als bislang zu verstehen, bedarf es eines interdisziplinären Ansatzes. Die hier vorgeschlagenen theoretischen Beiträge zur Lebenslaufepidemiologie ergänzen den wertvollen methodischen Fokus des Forschungsfeldes und können den interdisziplinären Dialog stärken.
Production of high density molecular beams with wide velocity scanning
Authors: Sheffield L. S. , Woo S. O. , Rathnayaka K. D. D. , Lyuksyutov I. F. , Herschbach D. R.
Published: June 2016

We describe modifications of a pulsed rotating supersonic beam source that improve performance, particularly increasing the beam density and sharpening the pulse profiles. As well as providing the familiar virtues of a supersonic molecular beam (high intensity, narrowed velocity distribution, and drastic cooling of rotation and vibration), the rotating source enables scanning the translational velocity over a wide range. Thereby, beams of any atom or molecule available as a gas can be slowed or speeded. Using Xe beams in the slowing mode, we have obtained lab speeds down to about 40 ± 5 m/s with density near 1011 cm−3 and in the speeding mode lab speeds up to about 660 m/s and density near 1014 cm−3. We discuss some congenial applications. Providing low lab speeds can markedly enhance experiments using electric or magnetic fields to deflect, steer, or further slow polar or paramagnetic molecules. The capability to scan molecular speeds facilitates merging velocities with a codirectional partner beam, enabling study of collisions at very low relative kinetic energies, without requiring either beam to be slow.
X-ray imaging and 3D reconstruction of in-flight exploding foil initiator flyers
Authors: Willey T. M. , Champley K. , Hodgin R. , Lauderbach L. , Bagge-Hansen M. , May C. , Sanchez N. , Jensen B. J. , Iverson A. , van Buuren T.
Published: June 2016

Exploding foil initiators (EFIs), also known as slapper initiators or detonators, offer clear safety and timing advantages over other means of initiating detonation in high explosives. This work outlines a new capability for imaging and reconstructing three-dimensional images of operating EFIs. Flyer size and intended velocity were chosen based on parameters of the imaging system. The EFI metal plasma and plastic flyer traveling at 2.5 km/s were imaged with short ∼80 ps pulses spaced 153.4 ns apart. A four-camera system acquired 4 images from successive x-ray pulses from each shot. The first frame was prior to bridge burst, the 2nd images the flyer about 0.16 mm above the surface but edges of the foil and/or flyer are still attached to the substrate. The 3rd frame captures the flyer in flight, while the 4th shows a completely detached flyer in a position that is typically beyond where slappers strike initiating explosives. Multiple acquisitions at different incident angles and advanced computed tomography reconstruction algorithms were used to produce a 3-dimensional image of the flyer at 0.16 and 0.53 mm above the surface. Both the x-ray images and the 3D reconstruction show a strong anisotropy in the shape of the flyer and underlying foil parallel vs. perpendicular to the initiating current and electrical contacts. These results provide detailed flyer morphology during the operation of the EFI.
Converse magneto-electric coefficient of concentric multiferroic composite ring
Authors: Chavez Andres C. , Lopez Mario , Youssef George
Published: June 2016

The converse magnetoelectric (CME) coefficient of an artificial, multiferroic composite cylinder was determined for two interface boundary conditions; specifically epoxy-bonded and shrink-fit. The composite consists of two concentrically bonded rings with the inner and outer rings made from Terfenol-D and lead zirconate titanate, respectively. The diameter of the inner annulus was 25 mm, and the outer ring diameter was 30 mm. Electric fields ranging from 20 kV/m to 80 kV/m with AC components cycling at frequencies from 4 kHz to 50 kHz were applied for actuation of the composite. A magnetic bias field from 0 Oe to 2300 Oe was applied for enhancement of the CME coefficient. It has been found that the maximum CME for epoxy-bonded rings occurs at lower bias magnetic field than shrink-fitted rings. Resonance for the epoxy-bonded composite was found to be 36 kHz whereas the resonant frequency for the shrink-fit structure was 34 kHz. The maximum CME coefficients were approximately 535 mG/V at 100 Vpp and 330 mG/V at 400 Vpp for the epoxy-bonded and shrink-fit configurations, respectively.
Microphysics of mass-transport in coupled droplet-pairs at low Reynolds number and the role of convective dynamics
Authors: Dong Qingming , Sau Amalendu
Published: June 2016

Interfacial mass-transport and redistribution in the micro-scale liquid droplets are important in diverse fields of research interest. The role of the “inflow” and the “outflow” type convective eddy-pairs in the entrainment of outer solute and internal relocation are examined for different homogeneous and heterogeneous water droplet pairs appearing in a tandem arrangement. Two micro-droplets of pure (rain) water interact with an oncoming outer air stream (Re ≤ 100) contaminated by uniformly distributed SO2. By virtue of separation/attachment induced non-uniform interfacial shear-stress gradient, the well-defined inflow/outflow type pairs of recirculating eddy-based convective motion quickly develops, and the eddies effectively attract/repel the accumulated outer solute and control the physical process of mass-transport in the droplet-pair. The non-uniformly shear-driven flow interaction and bifurcation of the circulatory internal flow lead to growth of important micro-scale “secondary” eddies which suitably regroup with the adjacent “primary” one to create the sustained inflow/outflow type convective dynamics. The presently derived flow characteristics and in-depth analysis help to significantly improve our understanding of the micro-droplet based transport phenomena in a wider context. By tuning “Re” (defined in terms of the droplet diameter and the average oncoming velocity of the outer air) and gap-ratio “α,” the internal convective forcing and the solute entrainment efficiency could be considerably enhanced. The quantitative estimates for mass entrainment, convective strength, and saturation characteristics for different coupled micro-droplet pairs are extensively examined here for 0.2 ≤ α ≤ 2.0 and 30 ≤ Re ≤ 100. Interestingly, for the compound droplets, with suitably tuned radius-ratio “B” (of upstream droplet with respect to downstream one) the generated “inflow” type coherent convective dynamics helped to significantly augment the centre-line mass flow, which in turn facilitate faster saturation of the upstream droplet. However, for heterogeneous droplet-pairs containing solid nucleus, while increased solid-fraction “S” (the ratio between the radius of the solid nucleus and that of the droplet) through 0.25 ≤ S ≤ 0.45 caused gradual reductions of convective strength and mass absorption rate (RSO2) for the upstream droplet, beyond a critical value S ≥ 0.45 the RSO2 therein continued to rise again owing to the reduced film thickness.
Emitter/absorber interface of CdTe solar cells
Authors: Song Tao , Kanevce Ana , Sites James R.
Published: June 2016

The performance of CdTe solar cells can be very sensitive to the emitter/absorber interface, especially for high-efficiency cells with high bulk lifetime. Performance losses from acceptor-type interface defects can be significant when interface defect states are located near mid-gap energies. Numerical simulations show that the emitter/absorber band alignment, the emitter doping and thickness, and the defect properties of the interface (i.e., defect density, defect type, and defect energy) can all play significant roles in the interface recombination. In particular, a type I heterojunction with small conduction-band offset (0.1 eV ≤ ΔEC ≤ 0.3 eV) can help maintain good cell efficiency in spite of high interface defect density, much like with Cu(In,Ga)Se2 (CIGS) cells. The basic principle is that positive ΔEC, often referred to as a “spike,” creates an absorber inversion and hence a large hole barrier adjacent to the interface. As a result, the electron-hole recombination is suppressed due to an insufficient hole supply at the interface. A large spike (ΔEC ≥ 0.4 eV), however, can impede electron transport and lead to a reduction of photocurrent and fill-factor. In contrast to the spike, a “cliff” (ΔEC < 0 eV) allows high hole concentration in the vicinity of the interface, which will assist interface recombination and result in a reduced open-circuit voltage. Another way to mitigate performance losses due to interface defects is to use a thin and highly doped emitter, which can invert the absorber and form a large hole barrier at the interface. CdS is the most common emitter material used in CdTe solar cells, but the CdS/CdTe interface is in the cliff category and is not favorable from the band-offset perspective. The ΔEC of other n-type emitter choices, such as (Mg,Zn)O, Cd(S,O), or (Cd,Mg)Te, can be tuned by varying the elemental ratio for an optimal positive value of ΔEC. These materials are predicted to yield higher voltages and would therefore be better candidates for the CdTe-cell emitter.
Optical properties of group-3 metal hexaboride nanoparticles by first-principles calculations
Authors: Yoshio Satoshi , Maki Koichiro , Adachi Kenji
Published: June 2016

LaB6 nanoparticles are widely used as solar control materials for strong near-infrared absorption and high visible transparency. In order to elucidate the origin of this unique optical property, first-principles calculations have been made for the energy-band structure and dielectric functions of RIIIB6 (RIII = Sc, Y, La, Ac). On account of the precise assessment of the energy eigenvalues of vacant states in conduction band by employing the screened exchange method, as well as to the incorporation of the Drude term, dielectric functions and various physical properties of LaB6 have been reproduced in excellent agreement with experimental values. Systematic examinations of dielectric functions and electronic structures of the trivalent metal hexaborides have clarified the origin of the visible transparency and the near-infrared plasmon absorption of RIIIB6 nanoparticles.
Kinetic energy and scalar spectra in high Rayleigh number axially homogeneous buoyancy driven turbulence
Authors: Pawar Shashikant S. , Arakeri Jaywant H.
Published: June 2016

Kinetic energy and scalar spectra from the measurements in high Rayleigh number axially homogeneous buoyancy driven turbulent flow are presented. Kinetic energy and concentration (scalar) spectra are obtained from the experiments wherein density difference is created using brine and fresh water and temperature spectra are obtained from the experiments in which heat is used. Scaling of the frequency spectra of lateral and longitudinal velocity near the tube axis is closer to the Kolmogorov-Obukhov scaling, while the scalar spectra show some evidence of dual scaling, Bolgiano-Obukhov scaling followed by Obukhov-Corrsin scaling. These scalings are also observed in the corresponding second order spatial structure functions of velocity and concentration fluctuations.
Two dimensional kinetic analysis of electrostatic harmonic plasma waves
Authors: Fonseca-Pongutá E. C. , Ziebell L. F. , Gaelzer R. , Yoon P. H.
Published: June 2016

Electrostatic harmonic Langmuir waves are virtual modes excited in weakly turbulent plasmas, first observed in early laboratory beam-plasma experiments as well as in rocket-borne active experiments in space. However, their unequivocal presence was confirmed through computer simulated experiments and subsequently theoretically explained. The peculiarity of harmonic Langmuir waves is that while their existence requires nonlinear response, their excitation mechanism and subsequent early time evolution are governed by essentially linear process. One of the unresolved theoretical issues regards the role of nonlinear wave-particle interaction process over longer evolution time period. Another outstanding issue is that existing theories for these modes are limited to one-dimensional space. The present paper carries out two dimensional theoretical analysis of fundamental and (first) harmonic Langmuir waves for the first time. The result shows that harmonic Langmuir wave is essentially governed by (quasi)linear process and that nonlinear wave-particle interaction plays no significant role in the time evolution of the wave spectrum. The numerical solutions of the two-dimensional wave spectra for fundamental and harmonic Langmuir waves are also found to be consistent with those obtained by direct particle-in-cell simulation method reported in the literature.
Three species one-dimensional kinetic model for weakly ionized plasmas
Authors: Gonzalez J. , Donoso J. M. , Tierno S. P.
Published: June 2016

A three species one-dimensional kinetic model is presented for a spatially homogeneous weakly ionized plasma subjected to the action of a time varying electric field. Planar geometry is assumed, which means that the plasma evolves in the privileged direction of the field. The energy transmitted to the electric charges is channelized to the neutrals thanks to collisions, a mechanism that influences the plasma dynamics. Charge-charge interactions have been designed as a one-dimensional collision term equivalent to the Landau operator used for fully ionized plasmas. Charge-neutral collisions are modelled by a conservative drift-diffusion operator in the Dougherty's form. The resulting set of coupled integro-differential equations is solved with the stable and robust propagator integral method. This semi–analytical method feasibility accounts for non–linear effects without appealing to linearisation or simplifications, providing conservative physically meaningful solutions even for initial or emerging sharp velocity distribution function profiles. It is found that charge-neutral collisions exert a significant effect since a quite different plasma evolution arises if compared to the collisionless limit. In addition, substantial differences in the system motion are found for constant and temperature dependent collision frequencies cases.
A liquid jet setup for x-ray scattering experiments on complex liquids at free-electron laser sources
Authors: Steinke I. , Walther M. , Lehmkühler F. , Wochner P. , Valerio J. , Mager R. , Schroer M. A. , Lee S. , Roseker W. , Jain A. , Sikorski M. , Song S. , Hartmann R. , Huth M. , Strüder L. , Sprung M. , Robert A. , Fuoss P. H. , Stephenson G. B. , Grübel G.
Published: June 2016

In this paper we describe a setup for x-ray scattering experiments on complex fluids using a liquid jet. The setup supports Small and Wide Angle X-ray Scattering (SAXS/WAXS) geometries. The jet is formed by a gas-dynamic virtual nozzle (GDVN) allowing for diameters ranging between 1 μm and 20 μm at a jet length of several hundred μm. To control jet properties such as jet length, diameter, or flow rate, the instrument is equipped with several diagnostic tools. Three microscopes are installed to quantify jet dimensions and stability in situ. The setup has been used at several beamlines performing both SAXS and WAXS experiments. As a typical example we show an experiment on a colloidal dispersion in a liquid jet at the X-ray Correlation Spectroscopy instrument at the Linac Coherent Light Source free-electron laser.
Donor and double-donor transitions of the carbon vacancy related EH6∕7 deep level in 4H-SiC
Authors: Booker I. D. , Janzén E. , Son N. T. , Hassan J. , Stenberg P. , Sveinbjörnsson E. Ö.
Published: June 2016

Using medium- and high-resolution multi-spectra fitting of deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS), optical O-DLTS and optical-electrical (OE)-MCTS measurements, we show that the EH6∕7 deep level in 4H-SiC is composed of two strongly overlapping, two electron emission processes with thermal activation energies of 1.49 eV and 1.58 eV for EH6 and 1.48 eV and 1.66 eV for EH7. The electron emission peaks of EH7 completely overlap while the emission peaks of EH6 occur offset at slightly different temperatures in the spectra. OE-MCTS measurements of the hole capture cross section σp0(T) in p-type samples reveal a trap-Auger process, whereby hole capture into the defect occupied by two electrons leads to a recombination event and the ejection of the second electron into the conduction band. Values of the hole and electron capture cross sections σn(T) and σp(T) differ strongly due to the donor like nature of the deep levels and while all σn(T) have a negative temperature dependence, the σp(T) appear to be temperature independent. Average values at the DLTS measurement temperature (∼600 K) are σn2+(T) ≈ 1 × 10−14 cm2, σn+(T) ≈ 1 × 10−14 cm2, and σp0(T) ≈ 9 × 10−18 cm2 for EH6 and σn2+(T) ≈ 2 × 10−14 cm2, σn+(T) ≈ 2 × 10−14 cm2, σp0(T) ≈ 1 × 10−20 cm2 for EH7. Since EH7 has already been identified as a donor transition of the carbon vacancy, we propose that the EH6∕7 center in total represents the overlapping first and second donor transitions of the carbon vacancy defects on both inequivalent lattice sites.
Increasing minority carrier lifetime in as-grown multicrystalline silicon by low temperature internal gettering
Authors: Al-Amin M. , Murphy J. D.
Published: June 2016

We report a systematic study into the effects of long low temperature (≤500 °C) annealing on the lifetime and interstitial iron distributions in as-grown multicrystalline silicon (mc-Si) from different ingot height positions. Samples are characterised in terms of dislocation density, and lifetime and interstitial iron concentration measurements are made at every stage using a temporary room temperature iodine-ethanol surface passivation scheme. Our measurement procedure allows these properties to be monitored during processing in a pseudo in situ way. Sufficient annealing at 300 °C and 400 °C increases lifetime in all cases studied, and annealing at 500 °C was only found to improve relatively poor wafers from the top and bottom of the block. We demonstrate that lifetime in poor as-grown wafers can be improved substantially by a low cost process in the absence of any bulk passivation which might result from a dielectric surface film. Substantial improvements are found in bottom wafers, for which annealing at 400 °C for 35 h increases lifetime from 5.5 μs to 38.7 μs. The lifetime of top wafers is improved from 12.1 μs to 23.8 μs under the same conditions. A correlation between interstitial iron concentration reduction and lifetime improvement is found in these cases. Surprisingly, although the interstitial iron concentration exceeds the expected solubility values, low temperature annealing seems to result in an initial increase in interstitial iron concentration, and any subsequent decay is a complex process driven not only by diffusion of interstitial iron.
Some strategies for improving caloric responses with ferroelectrics
Authors: Liu Yang , Scott James F. , Dkhil Brahim
Published: June 2016

Many important breakthroughs and significant engineering developments have been achieved during the past two decades in the field of caloric materials. In this review, we address ferroelectrics emerging as ideal materials which permit both giant elastocaloric and/or electrocaloric responses near room temperature. We summarize recent strategies for improving caloric responses using geometrical optimization, maximizing the number of coexisting phases, combining positive and negative caloric responses, introducing extra degree of freedom like mechanical stress/pressure, and multicaloric effect driven by either single stimulus or multiple stimuli. This review highlights the promising perspective of ferroelectrics for developing next-generation solid-state refrigeration.
Intra- and inter-atomic optical transitions of Fe, Co, and Ni ferrocyanides studied using first-principles many-electron calculations
Authors: Watanabe Shinta , Sawada Yuki , Nakaya Masato , Yoshino Masahito , Nagasaki Takanori , Kameyama Tatsuya , Torimoto Tsukasa , Inaba Yusuke , Takahashi Hideharu , Takeshita Kenji , Onoe Jun
Published: June 2016

We have investigated the electronic structures and optical properties of Fe, Co, and Ni ferrocyanide nanoparticles using first-principles relativistic many-electron calculations. The overall features of the theoretical absorption spectra for Fe, Ni, and Co ferrocyanides calculated using a first-principles many-electron method well reproduced the experimental one. The origins of the experimental absorption spectra were clarified by performing a configuration analysis based on the many-electron wave functions. For Fe ferrocyanide, the experimental absorption peaks originated from not only the charge-transfer transitions from Fe2+ to Fe3+ but also the 3d-3d intra-transitions of Fe3+ ions. In addition, the spin crossover transition of Fe3+ predicted by the many-electron calculations was about 0.24 eV. For Co ferrocyanide, the experimental absorption peaks were mainly attributed to the 3d-3d intra-transitions of Fe2+ ions. In contrast to the Fe and Co ferrocyanides, Ni ferrocyanide showed that the absorption peaks originated from the 3d-3d intra-transitions of Ni3+ ions in a low-energy region, while from both the 3d-3d intra-transitions of Fe2+ ions and the charge-transfer transitions from Fe2+ to Ni3+ in a high-energy region. These results were quite different from those of density-functional theory (DFT) calculations. The discrepancy between the results of DFT calculations and those of many-electron calculations suggested that the intra- and inter-atomic transitions of transition metal ions are significantly affected by the many-body effects of strongly correlated 3d electrons.
Enhanced magnetoelectric properties of BiFeO3 on formation of BiFeO3/SrFe12O19 nanocomposites
Authors: Das Anusree , Chatterjee Souvik , Bandyopadhyay Sudipta , Das Dipankar
Published: June 2016

Nanocomposites (NCs) comprising (1−x) BiFeO3 (BFO) and x SrFe12O19 (SRF) (x = 0.1, 0.2, 0.3, and 0.4) have been prepared by a sol-gel route. Presence of pure phases of both BiFeO3 (BFO) and SrFe12O19 (SRF) in the NCs for x = 0.3 and 0.4 has been confirmed by Rietveld analysis of XRD data though a minor impurity phase is observed in the case of x = 0.1 and 0.2 NCs. Transmission electron micrographs of the NCs show that particles are mostly spherical with average size of 30 nm. M-H measurements at 300 and 10 K indicate predominantly ferrimagnetic behavior of all the NCs with an increasing trend of saturation magnetization values with increasing content of SRF. Dielectric constant (εr) of the NCs at room temperature shows a dispersive behavior with frequency and attains a constant value at higher frequency. εr − T measurements reveal an increasing trend of dielectric constant of the NCs with increasing temperature and show an anomaly around the antiferromagnetic transition temperature of BFO, which indicates magnetoelectric coupling in the NCs. The variation of capacitance in the presence of magnetic field confirms the enhancement of magnetoelectric effect in the NCs. 57Fe Mössbauer spectroscopy results indicate the presence of only Fe3+ ions in usual crystallographic sites of BFO and SRF.
Microfluidic rheology of active particle suspensions: Kinetic theory
Authors: Alonso-Matilla Roberto , Ezhilan Barath , Saintillan David
Published: June 2016

We analyze the effective rheology of a dilute suspension of self-propelled slender particles confined between two infinite parallel plates and subject to a pressure-driven flow. We use a continuum kinetic model to describe the configuration of the particles in the system, in which the disturbance flows induced by the swimmers are taken into account, and use it to calculate estimates of the suspension viscosity for a range of channel widths and flow strengths typical of microfluidic experiments. Our results are in agreement with previous bulk models, and in particular, demonstrate that the effect of activity is strongest at low flow rates, where pushers tend to decrease the suspension viscosity whereas pullers enhance it. In stronger flows, dissipative stresses overcome the effects of activity leading to increased viscosities followed by shear-thinning. The effects of confinement and number density are also analyzed, and our results confirm the apparent transition to superfluidity reported in recent experiments on pusher suspensions at intermediate densities. We also derive an approximate analytical expression for the effective viscosity in the limit of weak flows and wide channels, and demonstrate good agreement between theory and numerical calculations.
Insulator-based dielectrophoretic diagnostic tool for babesiosis
Authors: Adekanmbi Ezekiel O. , Ueti Massaro W. , Rinaldi Brady , Suarez Carlos E. , Srivastava Soumya K.
Published: June 2016

Babesia species are obligate intraerythrocytic tick-borne protozoan parasites that are the etiologic agents of babesiosis, a potentially life-threatening, malaria-like illness in humans and animals. Babesia-infected people have been known to suffer from complications including liver problems, severe hemolytic anemia, and kidney failure. As reported by the Food and Drug Administration, 38% of mortality cases observed in transfusion recipients were associated with transfusion transmitted diseases of which babesiosis is the chief culprit. As of now, no tests have been licensed yet for screening blood donors for babesiosis. Current diagnostic tools for babesiosis including enzyme-linked immunosorbent assay, fluorescence in situ hybridization, and polymerase chain reaction are expensive and burdened with multifarious shortcomings. In this research, a low-cost, high-specificity, quick, and easy-to-use insulator-based dielectrophoretic diagnostic tool is developed for characterizing and concentrating Babesia-infected cells in their homogenous mixture with healthy cell population. In this work, a mixture of Babesia-infected (varying parasitemia) and healthy red blood cells (RBCs or erythrocytes) was exposed to non-uniform electric fields in a fabricated microfluidic platform to manipulate and sort the Babesia-infected cells within a minute. At DC voltage configurations of 10 V and 0/6 V in the inlet and the two outlet channels, respectively, the diseased cells were seen to flow in a direction different from the healthy RBCs. Bright field and fluorescence microscopy were utilized to present qualitative differentiation of the healthy erythrocytes from the infected cells. The proposed micro device platform was able to enrich RBCs from 0.1% to ∼70% parasitemia. This device, when finally developed into a point-of-care diagnostic chip, would enhance the detection of Babesia-infected erythrocytes and as well serve as a precursor to babesiosis vaccine development.
Torsional mode ultrasonic helical waveguide sensor for re-configurable temperature measurement
Authors: Periyannan Suresh , Rajagopal Prabhu , Balasubramaniam Krishnan
Published: June 2016

This paper introduces an ultrasonic torsional mode based technique, configured in the form of a helical “spring-like” waveguide, for multi-level temperature measurement. The multiple sensing levels can be repositioned by stretching or collapsing the spring to provide simultaneous measurements at different desired spacing in a given area/volume. The transduction is performed using piezo-electric crystals that generate and receive T(0,1) mode in a pulse echo mode. The gage lengths and positions of measurements are based on machining multiple reflector notches in the waveguide at required positions. The time of fight (TOF) measurements between the reflected signals from the notches provide local temperatures that compare well with co-located thermocouples.
Waveguiding and bending modes in a plasma photonic crystal bandgap device
Authors: Wang B. , Cappelli M. A.
Published: June 2016

Waveguiding and bending modes are investigated in a fully tunable plasma photonic crystal. The plasma device actively controls the propagation of free space electromagnetic waves in the S to X band of the microwave spectrum. An array of discharge plasma tubes form a square crystal lattice exhibiting a well-defined bandgap, with individual active switching of the plasma elements to allow for waveguiding and bending modes to be generated dynamically. We show, through simulations and experiments, the existence of transverse electric (TE) mode waveguiding and bending modes.
Production and health performance of Holstein, Brown Swiss and their crosses under subtropical environmental conditions
Authors: El-Tarabany Mahmoud S. , Roushdy Elshimaa M. , El-Tarabany Akram A.
Published: June 2016

The thermal environment is a major factor that can negatively affect milk production and health traits of dairy cows. The objective of this study was to assess the production and health traits of the pure Holstein (HO), Brown Swiss (BS), first generation crossbred (BH) and the backcross (BC) cows under subtropical Egyptian conditions, in addition to investigating the impact of temperature–humidity index (THI) on milk production traits. Pure HO, BH crossbred and BC backcross cows had significantly higher 305-milk yield (MY) (9145, 8914 and 9021 kg, respectively), and total-MY (10 694, 9845 and 10 118 kg, respectively), than pure BS. However, the BS and BH crossbred cows had significantly shorter days open (121 and 131 days, respectively), than pure HO and BC backcross cows (160 and 154 days, respectively). Furthermore, pure HO cows at greater THI had decreased daily-MY and peak-MY in a rate of 23.8% and 12.9%, respectively, compared with lesser THI conditions. In contrast, production traits of pure BS and BH cows were more adapted with conditions of heat stress, even though slight deterioration of peak-MY was recorded in BH cows, ultimately at the greater THI level. The BH crossbred had significantly lower incidence of feet problems, clinical mastitis and metritis (crude odds ratio = 0.45, 0.54 and 0.47; P = 0.027, 0.046 and 0.041, respectively), suggesting an overall amelioration in their reproductive and general health parameters in comparison with their pure HO contemporaries. Our results indicate that the first generation crossbred (BH) has a more stable production performance and adaptability than pure HO under subtropical conditions.
Estimating the economic value of soil organic carbon for grains cropping systems in Western Australia
Authors: Petersen E. H. , Hoyle F. C.
Published: June 2016

Soil organic carbon (SOC) has the potential to benefit soil function and fertility, and in agricultural production systems, it is considered integral to sustainable farming. We analyse the value of SOC in cropping systems of the south-west of Western Australia in terms of agronomic benefits from increasing productivity (through increased plant-available water-holding capacity) and reducing fertiliser use (due to increased mineralisation of nitrogen). We also present the potential value of SOC in terms of sequestration benefit if landholders were able to participate in a carbon-sequestration program. We estimate the marginal value of SOC (the value of a soil with more SOC, by 1 t C/ha, than a standard soil) to be AU$7.1–8.7/t C.ha.year, depending on rainfall zone and crop type. Approximately 75% of this value is the estimated sequestration value, 20% is the nitrogen-replacement value, and 5% is the estimated productivity improvement value. Over 50 years, this equates $130–160/t C.ha depending on the rainfall zone. These values are sensitive to variations in fertiliser and carbon prices. Our results imply this it is unlikely that the SOC benefits will drive practice change in the south-west of Western Australia.
Changes in the properties of Fijian Oxisols over 30 years of sugarcane cultivation
Authors: Morrison R. J. , Gawander J. S.
Published: June 2016

Sugarcane production plateaued in Fiji at ~4 million tonnes annually (average ~55 t/ha) during the latter part of the 1980s but, in recent years, despite the continuing release of high yielding varieties, the total production has decreased to under 3 million tonnes (average ~45 t/ha). This study was initiated to study the changes in the properties of Oxisols following sugarcane cultivation to ascertain whether yield declines were due to degradation of soil biophysical and chemical properties. The study lasted from 1978 (when the soils were first cleared for agriculture) to 2009. Soil (0–15, 30–40 and 70–80 cm) properties including pH, organic carbon, cation exchange capacity, water retention, bulk density, phosphate retention and exchangeable bases were monitored. The observed topsoil changes could generally be related to changes in organic matter and associated ion exchange properties. The major changes occurred in the first three years after clearing, but some changes continued for many years. Subsoil samples (30–40 cm) showed an increase in organic carbon after cane cultivation, probably due to soil mixing during land preparation, organic matter movement during cropping and decay of sugarcane roots. At 70–80 cm, small but significant increases in organic carbon were observed along with small decreases in pH. Overall, these changes indicate that careful management of topsoils is essential for maintaining soil fertility and hence sugarcane productivity on these highly weathered soils.