bluuebunny/crossref_metadata_2025 huggingface dataset:
Multi‐functional distributed generation unit for power quality enhancement
Authors: Zeng Zheng , Yang Huan , Guerrero Josep M. , Zhao Rongxiang
Published: February 2015

A multi‐functional distributed generation unit (MFDGU) and its control strategy are proposed in this study for the purpose of enhancing power quality in low‐voltage networks. By using the 3H‐bridge converter structure, an MFDGU can be applied in 3‐phase 4‐wire low‐voltage distribution networks to compensate harmonic, reactive and unbalanced currents. A reduced‐order model of the MFDGU is derived through a weighted‐average‐current‐feedback approach, showing the robustness and stability of the proposed approach. The Fryze–Buchholz–Dpenbrock power theory is employed to generate the current reference of the MFDGU, which can be easily implemented in three‐phase networks. A 15 kVA prototype consisting of three full bridge converters has been built and tested. Experimental results show the feasibility of the proposed topology and control strategy.
Effect of friction stir welding tool on temperature, applied forces and weld quality
Authors: Papahn Hossein , Bahemmat Pouya , Haghpanahi Mohammad , Pour Aminaie Iman
Published: February 2015

In friction stir welding (FSW), a proper selection of the FSW tool is an important factor which, as an appropriate tool, cannot only improve the quality of the weld but also diminish the destructive effects including applied forces and high temperature induced during the welding process. This research is aimed to scrutinise the effect of the tool geometries on the axial and translational forces, temperature and mechanical properties for AA7075‐T6 are investigated. The threaded tapered, non‐threaded triangular and non‐threaded cylindrical pins were employed. It was observed that the tool shoulder diameter was directly correlated with the generated temperature, axial and translational forces and weld characteristics. Moreover, the lowest amounts of measured forces were recorded in the case of threaded tapered pin whereas the generated temperature, UTS, elongation and grain size were higher for this pin as compared with the other pins. Nevertheless, in the tapered pin, hardness is lower than that of the other pins. It was also shown that the created fluctuations during the FSW process and stabilising time were lower for the threated tapered pin compared with the other two pins.
Citrate ions and chloride ions involved in the synthesis of anisotropic silver nanostructures
Authors: Tang Junqi , Zhao Qianrun , Zhang Ning , Man Shi‐Qing
Published: February 2015

Anisotropic metal nanoparticles are of considerable interest to researchers because of their unique optical, electronic and catalytic properties compared with spherical nanoparticles. This Letter describes how chloride ions and citrate ions can be added to silver (Ag) nitrate solution to synthesise anisotropic silver nanostructures especially to form the Ag nanowires (AgNWs) without high hydrothermal or solvothermal operating temperatures. The AgCl colloidal precipitates were produced in the initial stage promoting the reduction of free silver ions and helping control silver ions at low concentration for the growth of AgNWs. The synthesis of AgNWs was also temperature and hydroxide radical dependent since the citrate ions could direct the growth of AgNWs at proper temperatures (over 130°C) in the absence of chloride ions. Transmission electron microscopy and UV–vis absorption spectra have been used to investigate the obtained products. The experimental results suggested that the chloride ions played a crucial role in directing the growth of anisotropic Ag nanostructures.
Synthesis of platinum nanoparticles with higher stability in ionic liquid–Nafion film and their electrocatalytic application
Authors: Zhang Qing , Pan Dawei , Zhang HaiYun , Han HaiTao
Published: February 2015

4‐(3‐methyl‐1‐imidazolio)‐1‐butanesulphonic acid triflate (BSMIMOTF)–Nafion film is introduced as a novel catalyst support. Nafion is used as the conductive membrane for BSMIMOTF immobilisation. A uniform distribution of spherical platinum nanoparticles (PtNPs) 10–30 nm in diameter can be electrochemically deposited on the membranous BSMIMOTF–Nafion matrix. Compared with the PtNPs on a bare and Nafion‐modified electrode, the proposed sulphonyl‐terminated ionic liquid (IL)–Nafion stabilised PtNPs exhibit higher electrocatalytic activity and better stability towards the electro‐oxidation of methanol. The IL–Nafion film as a new catalyst support has great potential application in direct‐methanol fuel cells.
What Can Money do? Feminist Theory in Austere Times
Authors: Adkins Lisa
Published: February 2015

What can money do? Can it be put to work to address deepening forms of social and economic inequality associated with the financial crisis, ongoing recession and still unfolding politics of austerity? Can we have faith in money as an injustice-remedying substance in a crisis-ridden and (still thoroughly) financialised reality? While the latter scenario is implied in recent feminist calls to redistribute resources to redress widening socio-economic inequalities under austerity, in this article I suggest that such a redistributive logic fails to account for the shifting capacities of resources, including the capacities of money. To track these shifting capacities, I revisit the demands of the 1970s women's liberation movement and especially the assumptions at play in these demands that money both measure and distribute justice. While these assumptions were arguably politically efficacious in that moment, in the contemporary present, pervasive financialisation has involved a material transformation to the capacities of money, a transformation that, I will suggest, leaves its justice-distributing potential in doubt. This article therefore not only calls for careful exploration of the capacities of resources in analyses of crisis, recession and austerity, but also for feminist theory to rethink redistributive justice in the light of such transformations. Central to these considerations is money in the wages form.
Transcending the Impact of the Financial Crisis in the United Kingdom: Towards Plan F—a Feminist Economic Strategy
Authors: Pearson Ruth , Elson Diane
Published: February 2015

This paper sets out a framework for understanding the impacts of the financial crisis and its aftermath that is based on the idea of three interacting spheres: finance, production and reproduction. All of these spheres are gendered and globalised. The gendered impact of the current crisis is discussed in terms of the impact on unemployment, employment protection and security, public sector services, social security benefits, pensions, and the real value of wages and living standards. Drawing on the analysis of the UK Women's Budget Group, the paper demonstrates that the biggest falls in disposable income as the result of austerity policies by the Conservative-led government since 2010 have been borne by the most vulnerable women—lone mothers, single women pensioners and single women without children. Working-age couples without children have been least affected. The paper then goes on to discuss what an alternative economic strategy, based on feminist political economy, might look like. It utilises the notion of the ‘reproductive bargain’, first developed to understand the transition in Cuba in the 1990s. It sets out a possible feminist economic strategy that insists on the incorporation of reproductive and care work into the analysis of alternative economic policies and links employment, wages and social security payments to public provisioning of trans-generational reproductive services. It suggests feasible strategies to finance the proposed Plan F—a feminist economic strategy.
Crisis, Austerity and Gendered Governance: A Feminist Perspective
Authors: Griffin Penny
Published: February 2015

Feminist scholars have been highly attentive to the ways that crises have become an everyday technique of global governance. They are particularly sensitive to the mechanisms through which ‘crisis management’ entrenches the power of particular economic orders and constrains the possibilities, and space, for contestation and critique. This paper seeks to contribute to but also to extend existing feminist research on financial crisis by arguing that, over the course of what has commonly been labelled the ‘global financial crisis’, the emergence of ‘crisis governance feminism’ has enabled existing structures and mechanisms of gendered privilege, such as the global financial industry, to suppress calls for their overhaul and to re-entrench their power in the global political economy. Adopting a discursive approach to gender and governance that situates gender centrally in understanding governance discourses and their reproduction of common sense (about what people do, how they labour, where they invest and so on), this paper argues that the governance of crisis in the contemporary era, in particular the various actors, institutions, policies and ideas that have sought to describe and ‘contain’ the global financial crisis, are gendered. Gender has become, in the contemporary global political economy, a technique of governance, and with deleterious effects. Despite inciting more discussion of ‘gender’ in economic systems than ever before (particularly in terms of discussions of ‘economic competitiveness’), this paper argues that the ‘global financial crisis’ has precipitated and continues to reproduce techniques of governance that trivialise feminist concerns while further embedding a masculinised, white and elitist culture of global financial privilege.
Facilitating guest transport in clathrate hydrates by tuning guest-host interactions
Authors: Moudrakovski Igor L. , Udachin Konstantin A. , Alavi Saman , Ratcliffe Christopher I. , Ripmeester John A.
Published: February 2015

The understanding and eventual control of guest molecule transport in gas hydrates is of central importance for the efficient synthesis and processing of these materials for applications in the storage, separation, and sequestration of gases and natural gas production. Previously, some links have been established between dynamics of the host water molecules and guest-host hydrogen bonding interactions, but direct observation of transport in the form of cage-to-cage guest diffusion is still lacking. Recent calculations have suggested that pairs of different guest molecules in neighboring cages can affect guest-host hydrogen bonding and, therefore, defect injection and water lattice motions. We have chosen two sets of hydrate guest pairs, tetrahydrofuran (THF)-CO2 and isobutane-CO2, that are predicted to enhance or to diminish guest–host hydrogen bonding interactions as compared to those in pure CO2 hydrate and we have studied guest dynamics in each using 13C nuclear magnetic resonance (NMR) methods. In addition, we have obtained the crystal structure of the THF-CO2 sII hydrate using the combined single crystal X-ray diffraction and 13C NMR powder pattern data and have performed molecular dynamics-simulation of the CO2 dynamics. The NMR powder line shape studies confirm the enhanced and delayed dynamics for the THF and isobutane containing hydrates, respectively, as compared to those in the CO2 hydrate. In addition, from line shape studies and 2D exchange spectroscopy NMR, we observe cage-to-cage exchange of CO2 molecules in the THF-CO2 hydrate, but not in the other hydrates studied. We conclude that the relatively rapid intercage guest dynamics are the result of synergistic guest A–host water–guest B interactions, thus allowing tuning of the guest transport properties in the hydrates by choice of the appropriate guest molecules. Our experimental value for inter-cage hopping is slower by a factor of 106 than a published calculated value.
A localized momentum constraint for non-equilibrium molecular dynamics simulations
Authors: Smith E. R. , Heyes D. M. , Dini D. , Zaki T. A.
Published: February 2015

A method which controls momentum evolution in a sub-region within a molecular dynamics simulation is derived from Gauss’s principle of least constraint. The technique for localization is founded on the equations by Irving and Kirkwood [J. Chem. Phys. 18, 817 (1950)] expressed in a weak form according to the control volume (CV) procedure derived by Smith et al. [Phys. Rev. E. 85, 056705 (2012)]. A term for the advection of molecules appears in the derived constraint and is shown to be essential in order to exactly control the time evolution of momentum in the subvolume. The numerical procedure converges the total momentum in the CV to the target value to within machine precision in an iterative manner. The localized momentum constraint can prescribe essentially arbitrary flow fields in non-equilibrium molecular dynamics simulations. The methodology also forms a rigorous mathematical framework for introducing coupling constraints at the boundary between continuum and discrete systems. This functionality is demonstrated with a boundary-driven flow test case.
Electronic structure at transition metal phthalocyanine-transition metal oxide interfaces: Cobalt phthalocyanine on epitaxial MnO films
Authors: Glaser Mathias , Peisert Heiko , Adler Hilmar , Aygül Umut , Ivanovic Milutin , Nagel Peter , Merz Michael , Schuppler Stefan , Chassé Thomas
Published: February 2015

The electronic structure of the interface between cobalt phthalocyanine (CoPc) and epitaxially grown manganese oxide (MnO) thin films is studied by means of photoemission (PES) and X-ray absorption spectroscopy (XAS). Our results reveal a flat-lying adsorption geometry of the molecules on the oxide surface which allows a maximal interaction between the π-system and the substrate. A charge transfer from MnO, in particular, to the central metal atom of CoPc is observed by both PES and XAS. The change of the shape of N-K XAS spectra at the interface points, however, to the involvement of the Pc macrocycle in the charge transfer process. As a consequence of the charge transfer, energetic shifts of MnO related core levels were observed, which are discussed in terms of a Fermi level shift in the semiconducting MnO films due to interface charge redistribution.
Comb-locked cavity ring-down spectrometer
Authors: Gatti Davide , Sala Tommaso , Gotti Riccardo , Cocola Lorenzo , Poletto Luca , Prevedelli Marco , Laporta Paolo , Marangoni Marco
Published: February 2015

Extreme frequency accuracy and high sensitivity are obtained with a novel comb-locked cavity-ring-down spectrometer operating in the near-infrared from 1.5 to 1.63 μm. A key feature of our approach is the tight frequency locking of the probe laser to the comb, ensuring very high reproducibility and accuracy to the frequency axis upon scanning the comb repetition rate, as well as an efficient light injection into a length-swept high-finesse passive cavity containing the gas sample. Spectroscopic tests on the (30012) ← (00001) P14e line of CO2 at ∼1.57 μm demonstrate an accuracy of ∼17 kHz on the line center frequency in a Doppler broadening regime over the time scale of about 5 min, corresponding to four consecutive spectral scans of the absorption line. Over a single scan, which consists of 1500 spectral points over 75 s, the limit of detection is as low as 5.7 × 10−11 cm−1.
Defect chemistry and chalcogen diffusion in thin-film Cu2ZnSnSe4 materials
Authors: Harvey Steven P. , Repins Ingrid , Teeter Glenn
Published: February 2015

Selenium diffusion in polycrystalline thin-film Cu2ZnSn(S,Se)4 (CZTSe) on molybdenum-coated soda-lime glass substrates was investigated by in situ monitoring of the molybdenum back-contact resistance during high-temperature selenization treatments. In these measurements, selenium diffusion through the CZTSe layer results in conversion of the molybdenum layer to MoSe2, increasing the sheet resistance of the film stack. By monitoring the rate of MoSe2 formation as a function of annealing temperature, an activation energy of 0.5 ± 0.1 eV has been measured for selenium diffusion in CZTSe. The partial pressure dependence of chalcogen diffusion suggests that chalcogen vacancies are not the defect controlling chalcogen diffusion in thin-film CZTSe.
Hydroxyapatite: Vibrational spectra and monoclinic to hexagonal phase transition
Authors: Slepko Alexander , Demkov Alexander A.
Published: February 2015

Fundamental studies of biomaterials are necessary to deepen our understanding of their degradation and to develop cure for related illnesses. Biomineral hydroxyapatite Ca10(PO4)6(OH)2 is the main mineral constituent of mammal bone, and its synthetic analogues are used in biomedical applications. The mineral can be found in either hexagonal or monoclinic form. The transformation between these two phases is poorly understood, but knowing its mechanism may be critical to reversing processes in bone related to aging. Using density functional theory, we investigate the mechanisms of the phase transformation and estimate the transition temperature to be 680 K in fair agreement with the experimental temperature of 470 K. We also report the heat capacity of hydroxyapatite and a peculiarity in its phonon dispersion that might allow for non-destructive measurements of the crystal composition with applications in preventive medical screening for bone mineral loss.
Theoretical study of a screened Hartree–Fock exchange potential using position-dependent atomic dielectric constants
Authors: Shimazaki Tomomi , Nakajima Takahito
Published: February 2015

Dielectric-dependent screened Hartree–Fock (HF) exchange potential and Slater-formula have been reported, where the ratio of the HF exchange term mixed into potentials is inversely proportional to the dielectric constant of the target semiconductor. This study introduces a position-dependent dielectric constant method in which the dielectric constant is partitioned between the atoms in a semiconductor. These partitioned values differ depending on the electrostatic environment surrounding the atoms and lead to position-dependent atomic dielectric constants. These atomic dielectric constants provide atomic orbital-based matrix elements for the screened exchange potentials. Energy band structures of several semiconductors and insulators are also presented to validate this approach.
Integral wall model for large eddy simulations of wall-bounded turbulent flows
Authors: Yang X. I. A. , Sadique J. , Mittal R. , Meneveau C.
Published: February 2015

A new approach for wall modeling in Large-Eddy-Simulations (LES) is proposed and tested in various applications. To properly include near-wall physics while preserving the basic economy of equilibrium-type wall models, we adopt the classical integral method of von Karman and Pohlhausen (VKP). A velocity profile with various parameters is proposed as an alternative to numerical integration of the boundary layer equations in the near-wall zone. The profile contains a viscous or roughness sublayer and a logarithmic layer with an additional linear term that can account for inertial and pressure gradient effects. Similar to the VKP method, the assumed velocity profile coefficients are determined from appropriate matching conditions and physical constraints. The proposed integral wall-modeled LES (iWMLES) method is tested in the context of a pseudo-spectral code for fully developed channel flow with a dynamic Lagrangian subgrid model as well as in a finite-difference LES code including the immersed boundary method and the dynamic Vreman eddy-viscosity model. Test cases include a fully developed half-channel at various Reynolds numbers, a fully developed channel flow with unresolved roughness, a standard developing turbulent boundary layer flows over smooth plates at various Reynolds numbers, over plates with unresolved roughness, and a case with resolved roughness elements consisting of an array of wall-mounted cubes. The comparisons with data show that the proposed iWMLES method provides accurate predictions of near-wall velocity profiles in LES while, similarly to equilibrium wall models, its cost remains independent of Reynolds number and is thus significantly lower compared to existing zonal or hybrid wall models. A sample application to flow over a surface with truncated cones (representing idealized barnacle-like roughness elements) is also presented, which illustrates effects of subgrid scale roughness when combined with resolved roughness elements.
A miniature microcontroller curve tracing circuit for space flight testing transistors
Authors: Prokop N. , Greer L. , Krasowski M. , Flatico J. , Spina D.
Published: February 2015

This paper describes a novel miniature microcontroller based curve tracing circuit, which was designed to monitor the environmental effects on Silicon Carbide Junction Field Effect Transistor (SiC JFET) device performance, while exposed to the low earth orbit environment onboard the International Space Station (ISS) as a resident experiment on the 7th Materials on the International Space Station Experiment (MISSE7). Specifically, the microcontroller circuit was designed to operate autonomously and was flown on the external structure of the ISS for over a year. This curve tracing circuit is capable of measuring current vs. voltage (I-V) characteristics of transistors and diodes. The circuit is current limited for low current devices and is specifically designed to test high temperature, high drain-to-source resistance SiC JFETs. The results of each I-V data set are transmitted serially to an external telemetered communication interface. This paper discusses the circuit architecture, its design, and presents example results.
A novel technique for investigation of complete and partial anisotropic wetting on structured surface by X-ray microtomography
Authors: Santini M. , Guilizzoni M. , Fest-Santini S. , Lorenzi M.
Published: February 2015

An experimental study about the anisotropic wetting behavior of a surface patterned with parallel grooves is presented as an application example of a novel technique for investigation of complete and partial anisotropic wetting on structured surface by X-ray microtomography. Shape of glycerin droplets on such surface is investigated by X-ray micro computed tomography (microCT) acting as a non-intrusive, full volume 3D microscope with micrometric spatial resolution. The reconstructed drop volumes enable to estimate the exact volumes of the drops, their base contours, and 3D static contact angles, based on true cross-sections of the drop-surface couple. Droplet base contours are compared to approximate geometrical contour shapes proposed in the literature. Contact angles along slices parallel and perpendicular to the grooves direction are compared with each other. The effect of the sessile drop volume on the wetting behavior is discussed. The proposed technique, which is applicable for any structured surface, enables the direct measure of Wenzel ratio based on the microCT scan in the wetted region usually inapproachable by any others. Comparisons with simplified models are presented and congruence of results with respect to the minimum resolution needed is evaluated and commented.
A validation of a simple model for the calculation of the ionization energies in X-ray laser-cluster interactions
Authors: White Jeff , Ackad Edward
Published: February 2015

The outer-ionization of an electron from a cluster is an unambiguous quantity, while the inner-ionization threshold is not, resulting in different microscopic quantum-classical hybrid models used in laser-cluster interactions. A simple local ionization threshold model for the change in the ionization energy is proposed and examined, for atoms and ions, at distances in between the initial configuration of the cluster to well into the cluster's disintegration. This model is compared with a full Hartree-Fock energy calculation which accounts for the electron correlation effects using the coupled cluster method with single and double excitations with perturbative triples (CCSD(T)). Good agreement is found between the two lending a strong theoretical support to works which rely on such models for the final and transient properties of the laser-cluster interaction.
Modification of particle-laden near-wall turbulence: Effect of Stokes number
Authors: Lee Junghoon , Lee Changhoon
Published: February 2015

Turbulent channel flows laden with particles are investigated using direct numerical simulation with a point-force approximation for small, heavy particles with a diameter smaller than the Kolmogorov length scale of the flow. The Stokes numbers based on the wall units considered in our study are St+ = 0.5, 5, 35, and 125. The main purpose of this study is to examine the effect of Stokes number on turbulence modification in a channel. We found that particles with St+ = 0.5 enhance turbulence by increasing the occurrence of quasistreamwise vortices, while larger-Stokes-number particles attenuate turbulence. Particles with St+ = 0.5 act as an energy source in the streamwise direction in the high-speed regions and low-speed streaks near the wall, which may increase the instability of the low-speed streaks responsible for the birth of new quasistreamwise vortices. However, particles that have been just swept into the low-speed streaks with a long memory due to turbophoresis act as an energy sink in the streamwise direction. This streamwise interaction is maximized for St+ = 35. On the other hand, maximum preferential concentration outside vortical regions occurs when St+ = 5, but their streamwise interaction with the fluid is weak, rather similarly to the case of St+ = 0.5. Thus, the turbulence is less suppressed than St+ = 35.
Obtaining strong ferromagnetism in diluted Gd-doped ZnO thin films through controlled Gd-defect complexes
Authors: Roqan I. S. , Venkatesh S. , Zhang Z. , Hussain S. , Bantounas I. , Franklin J. B. , Flemban T. H. , Zou B. , Lee J.-S. , Schwingenschlogl U. , Petrov P. K. , Ryan M. P. , Alford N. M.
Published: February 2015

We demonstrate the fabrication of reproducible long-range ferromagnetism (FM) in highly crystalline GdxZn1−xO thin films by controlling the defects. Films are grown on lattice-matched substrates by pulsed laser deposition at low oxygen pressures (≤25 mTorr) and low Gd concentrations (x ≤ 0.009). These films feature strong FM (10 μB per Gd atom) at room temperature. While films deposited at higher oxygen pressure do not exhibit FM, FM is recovered by post-annealing these films under vacuum. These findings reveal the contribution of oxygen deficiency defects to the long-range FM. We demonstrate the possible FM mechanisms, which are confirmed by density functional theory study, and show that Gd dopants are essential for establishing FM that is induced by intrinsic defects in these films.
Maximizing semi-active vibration isolation utilizing a magnetorheological damper with an inner bypass configuration
Authors: Bai Xian-Xu , Wereley Norman M. , Hu Wei
Published: February 2015

A single-degree-of-freedom (SDOF) semi-active vibration control system based on a magnetorheological (MR) damper with an inner bypass is investigated in this paper. The MR damper employing a pair of concentric tubes, between which the key structure, i.e., the inner bypass, is formed and MR fluids are energized, is designed to provide large dynamic range (i.e., ratio of field-on damping force to field-off damping force) and damping force range. The damping force performance of the MR damper is modeled using phenomenological model and verified by the experimental tests. In order to assess its feasibility and capability in vibration control systems, the mathematical model of a SDOF semi-active vibration control system based on the MR damper and skyhook control strategy is established. Using an MTS 244 hydraulic vibration exciter system and a dSPACE DS1103 real-time simulation system, experimental study for the SDOF semi-active vibration control system is also conducted. Simulation results are compared to experimental measurements.
On nonlinear evolution of low-frequency Alfvén waves in weakly-expanding solar wind plasmas
Authors: Nariyuki Y.
Published: February 2015

A multi-dimensional nonlinear evolution equation for Alfvén waves in weakly-expanding solar wind plasmas is derived by using the reductive perturbation method. The expansion of solar wind plasma parcels is modeled by an expanding box model, which includes the accelerating expansion. It is shown that the resultant equation agrees with the Wentzel-Kramers-Brillouin prediction of the low-frequency Alfvén waves in the linear limit. In the cold and one-dimensional limit, a modified derivative nonlinear Schrodinger equation is obtained. Direct numerical simulations are carried out to discuss the effect of the expansion on the modulational instability of monochromatic Alfvén waves and the propagation of Alfvén solitons. By using the instantaneous frequency, it is quantitatively shown that as far as the expansion rate is much smaller than wave frequencies, effects of the expansion are almost adiabatic. It is also confirmed that while shapes of Alfvén solitons temporally change due to the expansion, some of them can stably propagate after their collision in weakly-expanding plasmas.
Space charge induced beam instability in periodic focusing channel
Authors: Li Chao , Qin Qing
Published: February 2015

The transverse evolution of the envelope of an intense, unbunched ion beam in a linear periodic transport channel can be modeled for the approximation of linear self-fields by the Kapchinskij-Vladimirskij envelope equation. The envelope mismatched modes, or the second order even mode [I. Hofmann, Phys. Rew. E 57, 4713 (1998)], are the lowest order of resonance leading to collective instability that the designer should avoid, which suggests that an accelerator system should be established in the parameter region where the zero beam current phase advance σ0 less than 90°. In this paper, we systemically studied the resonance mechanisms which result in confluent resonance in quadrupole Focusing-Defocusing (FD) channel and parametric resonance in solenoid channel. We propose that the mismatch modes cannot be exactly separated in FD channel; if one mode is excited, there is always some contribution of the other. To verify the influence of the confluent resonance and parametric resonance, the 2D Poissons solver in the self-consistent particle-in-cell simulation code TOPOPIC is adopted to study the beam evolution in both channels. Our simulations results show that the emittance show significant growth both in the confluent resonance stop band and parametric resonance stop band. The influences of the higher order of resonance are also discussed.
An integrated platform enabling optogenetic illumination of Caenorhabditis elegans neurons and muscular force measurement in microstructured environments
Authors: Qiu Zhichang , Tu Long , Huang Liang , Zhu Taoyuanmin , Nock Volker , Yu Enchao , Liu Xiao , Wang Wenhui
Published: February 2015

Optogenetics has been recently applied to manipulate the neural circuits of Caenorhabditis elegans (C. elegans) to investigate its mechanosensation and locomotive behavior, which is a fundamental topic in model biology. In most neuron-related research, free C. elegans moves on an open area such as agar surface. However, this simple environment is different from the soil, in which C. elegans naturally dwells. To bridge up the gap, this paper presents integration of optogenetic illumination of C. elegans neural circuits and muscular force measurement in a structured microfluidic chip mimicking the C. elegans soil habitat. The microfluidic chip is essentially a ∼1 × 1 cm2 elastomeric polydimethylsiloxane micro-pillar array, configured in either form of lattice (LC) or honeycomb (HC) to mimic the environment in which the worm dwells. The integrated system has four key modules for illumination pattern generation, pattern projection, automatic tracking of the worm, and force measurement. Specifically, two optical pathways co-exist in an inverted microscope, including built-in bright-field illumination for worm tracking and pattern generation, and added-in optogenetic illumination for pattern projection onto the worm body segment. The behavior of a freely moving worm in the chip under optogenetic manipulation can be recorded for off-line force measurements. Using wild-type N2 C. elegans, we demonstrated optical illumination of C. elegans neurons by projecting light onto its head/tail segment at 14 Hz refresh frequency. We also measured the force and observed three representative locomotion patterns of forward movement, reversal, and omega turn for LC and HC configurations. Being capable of stimulating or inhibiting worm neurons and simultaneously measuring the thrust force, this enabling platform would offer new insights into the correlation between neurons and locomotive behaviors of the nematode under a complex environment.
Passive removal of immiscible spacers from segmented flows in a microfluidic probe
Authors: van Kooten Xander F. , Autebert Julien , Kaigala Govind V.
Published: February 2015

Microfluidic probes (MFPs) are a class of non-contact, scanning microfluidic devices that hydrodynamically confine nanoliter volumes of a processing liquid on a surface immersed in another liquid. So far only chemical processes using a single processing liquid have been implemented using MFPs. In this letter, we present the design and implementation of a probe head that allows segmented two-phase flows to be used, which will enable different chemical species to be sequentially delivered to a surface in defined volumes and concentrations. Central to this probe head is a spacer-removal module comprising blocking pillars in the injection channel, a bypass and an orifice leading to the aspiration channel. We present a capillarity-based analytical model that provides insight into the functionality of the module based on geometrical parameters. In addition, we study the difference between two- and three-channel modules and predict a 30% reduction in fluctuation of the footprint of the confined liquid for the three-channel module. We show that such a module with a 15 μm pillar spacing, a 30 μm orifice width, and an oblique angle of 30° can remove immiscible spacers (Fluorinert FC-40) from an aqueous flow at a rate of up to 15 spacers per second while maintaining hydrodynamic confinement of processing liquid.
Sub-nanosecond delays of light emitted by streamer in atmospheric pressure air: Analysis of N2(C3Πu) and N2+(B2Σu+) emissions and fundamental streamer structure
Authors: Hoder T. , Bonaventura Z. , Bourdon A. , Šimek M.
Published: February 2015

Theoretical analysis of ultra-short phenomena occurring during the positive streamer propagation in atmospheric pressure air is presented. Motivated by experimental results obtained with tens-of-picoseconds and tens-of-microns precision, it is shown that when the streamer head passes a spatial coordinate, emission maxima from N2 and N2+ radiative states follow with different delays. These different delays are caused by differences in the dynamics of populating the radiative states, due to different excitation and quenching rates. Associating the position of the streamer head with the maximum value of the self-enhanced electric field, a delay of 160 ps was experimentally found for the peak emission of the first negative system of N2+. A delay dilatation was observed experimentally on early-stage streamers and the general mechanism of this phenomenon is clarified theoretically. In the case of the second positive system of N2, the delay can reach as much as 400 ps. In contrast to the highly nonlinear behavior of streamer events, it is shown theoretically that emission maximum delays linearly depend on the ratio of the streamer radius and its velocity. This is found to be one of the fundamental streamer features and its use in streamer head diagnostics is proposed. Moreover, radially resolved spectra are synthesized for selected subsequent picosecond moments in order to visualize spectrometric fingerprints of radial structures of N2(C3Πu) and N2+(B2Σu+) populations created by streamer-head electrons.
Hamiltonian and action principle formalisms for spin-1/2 magnetohydrodynamics
Authors: Lingam M.
Published: February 2015

A Hamiltonian and Action Principle formulation of spin-1/2 magnetohydrodynamics is presented via a first-principles derivation of the underlying Lagrangian, and the associated Hamiltonian. The derivation invokes the notion of “frozen-in” constraints, symmetry breaking, and similarities with Ginzburg-Landau theory to arrive at the relevant terms in the Hamiltonian. The model thus obtained includes the effects of spin and other quantum corrections and is shown to be in full agreement with existent models in the literature. It is also indicated how two-fluid effects, gyroviscosity, and anisotropic pressure can be included in the model, in addition to incorporating higher-order (nonlinear) quantum spin corrections. An interesting analogy with the theory of liquid crystals is also highlighted.
Spectroscopic investigation of the spatiotemporal dynamics of an electric field in plasma of a beam-type high-voltage discharge in helium
Authors: Demkin V. P. , Mel'nichuk S. V.
Published: February 2015

In the present work, a method of determining the spatiotemporal characteristics of the electric field strength in an accelerating gap and a plasma flare of a beam-type high-voltage pulsed discharge in He at moderate pressure is presented. The method is based on spectroscopic data on the Stark splitting of π-components of He 2P–4Q transitions; Q = D(4921.93 Å), F(4920.35 Å) in the near-cathode region of the discharge and on the spatiotemporal characteristics of intensities of He(2s1S–3p1P0) spectral lines with λ = 5015 Å and He+(3d–4f) spectral lines with λ = 4685 Å measured experimentally and calculated from the data of statistical simulation of the electron kinetics by the Monte Carlo method. The shape and strength of the electric field of the space charge in the interelectrode gap and the drift region of the discharge are estimated. It is demonstrated that the electric field created by the current pulse of uncompensated space charge in the near-anode region changes the discharge regime and causes degradation of the electron beam in the plasma flare. It is established that the flux of secondary electrons from the drift region to the anode has significant effect on the radiation intensity distribution in this region of the discharge.
Epitaxial growth of (1 1 1)-oriented spinel CoCr2O4/Al2O3 heterostructures
Authors: Liu Xiaoran , Choudhury D. , Cao Yanwei , Middey S. , Kareev M. , Meyers D. , Kim J.-W. , Ryan P. , Chakhalian J.
Published: February 2015

High quality (1 1 1)-oriented CoCr2O4/Al2O3 heterostructures were synthesized on the sapphire (0 0 0 1) single crystal substrates by pulsed laser deposition. The structural properties are demonstrated by in-situ reflection high energy electron diffraction, atomic force microscopy, X-ray reflectivity, and X-ray diffraction. X-ray photoemission spectroscopy confirms that the films possess the proper chemical stoichiometry. This work offers a pathway to fabricating spinel type artificial quasi-two-dimensional frustrated lattices by means of geometrical engineering.
Nonthermal and geometric effects on the symmetric and anti-symmetric surface waves in a Lorentzian dusty plasma slab
Authors: Lee Myoung-Jae , Jung Young-Dae
Published: February 2015

The nonthermal and geometric effects on the propagation of the surface dust acoustic waves are investigated in a Lorentzian dusty plasma slab. The symmetric and anti-symmetric dispersion modes of the dust acoustic waves are obtained by the plasma dielectric function with the spectral reflection conditions the slab geometry. The variation of the nonthermal and geometric effects on the symmetric and the anti-symmetric modes of the surface plasma waves is also discussed.
Ion concentration polarization on paper-based microfluidic devices and its application to preconcentrate dilute sample solutions
Authors: Yang Ruey-Jen , Pu Hao-Hsuan , Wang Hsiang-Li
Published: February 2015

Microfluidic paper-based analytical devices (μPADs) are a promising solution for a wide range of point-of-care applications. The feasibility of inducing ion concentration polarization (ICP) on μPADs has thus far attracted little attention. Accordingly, this study commences by demonstrating the ICP phenomenon in a μPAD with a Nafion ion-selective membrane. We are the first to measure the current-voltage curve on a Nafion-coated μPAD in order to indicate that the ion depletion occurs and the ICP is triggered when the current reaches the limiting current. The ICP effect is then exploited to preconcentrate fluorescein on μPADs incorporating straight and convergent channels. By an optimal geometric design, it is shown that the convergent channel results in a greater preconcentration effect than the straight channel. Specifically, a 20-fold enhancement in the sample concentration is achieved after 130 s given an initial concentration of 10−5 M and an external potential of 50 V. By contrast, the straight channel yields only a 10-fold improvement in the concentration after 180 s. Further, the practical feasibility of the proposed convergent-channel μPAD is demonstrated using fluorescein isothiocyanate labeled bovine serum albumin. The experimental results show that a 15-fold enhancement of the initial sample concentration (10−5 M) is obtained after 120 s given an external potential of 50 V.
Optimizing direct magnetoelectric coupling in Pb(Zr,Ti)O3/Ni multiferroic film heterostructures
Authors: Feng Ming , Wang Jian-jun , Hu Jia-Mian , Wang Jing , Ma Jing , Li Hai-Bo , Shen Yang , Lin Yuan-Hua , Chen Long-Qing , Nan Ce-Wen
Published: February 2015

Polycrystalline Pt thin films of different thicknesses (0–75 nm) were introduced using magnetron sputtering in Pb(Zr0.52Ti0.48)O3 (PZT, 400 nm in thickness)/Pt/Ni multiferroic film heterostructures, aimed at optimizing the transfer efficiency of magnetostrictive strain from the bottom Ni foil to the top PZT film and thus the direct magnetoelectric (ME) coupling. The ME voltage coefficient αE31 was directly measured, while the strain transfer efficiency k was obtained by combined experimental and theoretical analysis. At the optimum Pt-thickness of 30 nm, the polycrystalline film heterostructure shows the largest αE31 of 772 mV cm−1 Oe−1 at a low dc magnetic bias field of 86 Oe, as well as the highest k of 83% that is comparable to that in epitaxial quasi-2-2 film heterostructures.
Impact of carbon-doping on time dependent dielectric breakdown of SiO2-based films
Authors: Zhao Larry , Barbarin Yohan , Croes Kristof , Baklanov Mikhail R. , Verdonck Patrick , Tőkei Zsolt , Claeys Cor
Published: February 2015

Impact of carbon-doping on time dependent dielectric breakdown (TDDB) of three SiO2-based films was investigated under two different breakdown mechanisms, one involving Cu ion injection and the other caused by intrinsic dielectric degradation without Cu injection. In the case of breakdown dominated by dielectric degradation, an undoped SiO2 film shows better TDDB performance than the two other carbon-doped SiO2 or organo-silicate glass films, suggesting that carbon-doping makes the films weaker for dielectric breakdown. In contrast, in the case of breakdown involving Cu ion injection, the two carbon-doped films show better TDDB performance than the undoped SiO2, suggesting that the presence of the carbon slows down Cu ion injection and therefore leads to less TDDB degradation.
Transcriptome profiling of muscle by RNA-Seq reveals significant differences in digital gene expression profiling between Angus and Luxi cattle
Authors: Liu G. F. , Cheng H. J. , You W. , Song E. L. , Liu X. M. , Wan F. C.
Published: February 2015

The development of massively parallel sequencing technologies enables the sequencing of total cDNA to identify unigene expression and to discover novel regions of transcription. Here, we report the first use of RNA sequencing (RNA-Seq) to find the digital gene expression profiles (DGEs) associated with the growth and development of muscle in Chinese Luxi and Angus beef cattle. More than 9 243 921 clean reads were found in samples of muscle tissue. We found 232 DGEs between Luxi cattle and Angus cattle (false discovery ratio ≤0.001 and |log2 ratio| ≥1). Among the DGEs, we determined that 147 genes were downregulated and 85 genes were upregulated. Gene Ontology and KEGG Pathway analyses were performed to analyse the biological role of the DGEs and determine their contribution to the differences seen in muscle growth and development between local Chinese Luxi cattle and the introduced Angus cattle. The results suggest that RNA-Seq is a useful tool for predicting differences in gene expression between Luxi and Angus beef cattle; moreover, our results provides unprecedented resolution of mRNAs that are expressed across the two breeds.
Genetic variation within and between subpopulations of the Australian Merino breed
Authors: Swan Andrew A. , Brown Daniel J. , van der Werf Julius H. J.
Published: February 2015

Genetic variation within and between Australian Merino subpopulations was estimated from a large breeding nucleus in which up to 8500 progeny from over 300 sires were recorded at eight sites across Australia. Subpopulations were defined as genetic groups using the Westell–Quaas model in which base animals with unknown pedigree were allocated to groups based on their flock of origin if there were sufficient ‘expressions’ for the flock, or to one of four broad sheep-type groups otherwise (Ultra/Superfine, Fine/Fine-medium, Medium/Strong, or unknown). Linear models including genetic groups and additive genetic breeding values as random effects were used to estimate variance components for 12 traits: yearling greasy and clean fleece weight (ygfw and ycfw), yearling mean and coefficient of variation of fibre diameter (yfd and ydcv), yearling staple length and staple strength (ysl and yss), yearling fibre curvature (ycuv), yearling body wrinkle (ybdwr), post-weaning weight (pwt), muscle (pemd) and fat depth (pfat), and post-weaning worm egg count (pwec). For the majority of traits, the genetic group variance ranged from approximately equal to two times larger than the additive genetic (within group) variance. The exceptions were pfat and ydcv where the genetic group to additive variance ratios were 0.58 and 0.22, respectively, and pwec and yss where there was no variation between genetic groups. Genetic group correlations between traits were generally the same sign as corresponding additive genetic correlations, but were stronger in magnitude (either more positive or more negative). These large differences between genetic groups have long been exploited by Merino ram breeders, to the extent that the animals in the present study represent a significantly admixed population of the founding groups. The relativities observed between genetic group and additive genetic variance components in this study can be used to refine the models used to estimate breeding values for the Australian Merino industry.