bluuebunny/crossref_metadata_2025 huggingface dataset:
Pseudomonas syringae naturally lacking the canonical type III secretion system are ubiquitous in nonagricultural habitats, are phylogenetically diverse and can be pathogenic
Authors: Diallo Moudjahidou Demba , Monteil Caroline L , Vinatzer Boris A , Clarke Christopher R , Glaux Catherine , Guilbaud Caroline , Desbiez Cécile , Morris Cindy E
Published: January 2012

The type III secretion system (T3SS) is an important virulence factor of pathogenic bacteria, but the natural occurrence of variants of bacterial plant pathogens with deficiencies in their T3SS raises questions about the significance of the T3SS for fitness. Previous work on T3SS-deficient plant pathogenic bacteria has focused on strains from plants or plant debris. Here we have characterized T3SS-deficient strains of Pseudomonas syringae from plant and nonplant substrates in pristine nonagricultural contexts, many of which represent recently described clades not yet found associated with crop plants. Strains incapable of inducing a hypersensitive reaction (HR−) in tobacco were detected in 65% of 126 samples from headwaters of rivers (mountain creeks and lakes), snowpack, epilithic biofilms, wild plants and leaf litter and constituted 2 to 100% of the P. syringae population associated with each sample. All HR− strains lacked at least one gene in the canonical hrp/hrc locus or the associated conserved effector locus, but most lacked all six of the genes tested (hrcC, hrpL, hrpK1, avrE1 and hrpW1) and represented several disparate phylogenetic clades. Although most HR− strains were incapable of causing symptoms on cantaloupe seedlings as expected, strains in the recently described TA-002 clade caused severe symptoms in spite of the absence of any of the six conserved genes of the canonical T3SS according to PCR and Southern blot assays. The phylogenetic context of the T3SS variants we observed provides insight into the evolutionary history of P. syringae as a pathogen and as an environmental saprophyte.
Proteus mirabilis interkingdom swarming signals attract blow flies
Authors: Ma Qun , Fonseca Alicia , Liu Wenqi , Fields Andrew T , Pimsler Meaghan L , Spindola Aline F , Tarone Aaron M , Crippen Tawni L , Tomberlin Jeffery K , Wood Thomas K
Published: January 2012

Flies transport specific bacteria with their larvae that provide a wider range of nutrients for those bacteria. Our hypothesis was that this symbiotic interaction may depend on interkingdom signaling. We obtained Proteus mirabilis from the salivary glands of the blow fly Lucilia sericata; this strain swarmed significantly and produced a strong odor that attracts blow flies. To identify the putative interkingdom signals for the bacterium and flies, we reasoned that as swarming is used by this bacterium to cover the food resource and requires bacterial signaling, the same bacterial signals used for swarming may be used to communicate with blow flies. Using transposon mutagenesis, we identified six novel genes for swarming (ureR, fis, hybG, zapB, fadE and PROSTU_03490), then, confirming our hypothesis, we discovered that fly attractants, lactic acid, phenol, NaOH, KOH and ammonia, restore swarming for cells with the swarming mutations. Hence, compounds produced by the bacterium that attract flies also are utilized for swarming. In addition, bacteria with the swarming mutation rfaL attracted fewer blow flies and reduced the number of eggs laid by the flies. Therefore, we have identified several interkingdom signals between P. mirabilis and blow flies.
Usual Energy Intake Mediates the Relationship Between Food Reinforcement and BMI
Authors: Epstein Leonard H. , Carr Katelyn A. , Lin Henry , Fletcher Kelly D. , Roemmich James N.
Published: January 2012

The relative reinforcing value of food (RRVfood) is positively associated with energy consumed and overweight status. One hypothesis relating these variables is that food reinforcement is related to BMI through usual energy intake. Using a sample of two hundred fifty‐two adults of varying weight and BMI levels, results showed that usual energy intake mediated the relationship between RRVfoodand BMI (estimated indirect effect = 0.0027, bootstrapped 95% confidence intervals (CIs) 0.0002–0.0068, effect ratio = 0.34), controlling for age, sex, minority status, education, and reinforcing value of reading (RRVreading). Laboratory and usual energy intake were correlated (r= 0.24,P< 0.001), indicating that laboratory energy intake could provide an index of eating behavior in the natural environment. The mediational relationship observed suggests that increasing or decreasing food reinforcement could influence body weight by altering food consumption. Research is needed to develop methods of modifying RRVfoodto determine experimentally whether manipulating food reinforcement would result in changes in body weight.
Distinct roles in folding, CD81 receptor binding and viral entry for conserved histidine residues of hepatitis C virus glycoprotein E1 and E2
Authors: Boo Irene , teWierik Kevin , Douam Florian , Lavillette Dimitri , Poumbourios Pantelis , Drummer Heidi E.
Published: January 2012

The protonation of histidine in acidic environments underpins its role in regulating the function of pH-sensitive proteins. For pH-sensitive viral fusion proteins, histidine protonation in the endosome leads to the activation of their membrane fusion function. The HCV (hepatitis C virus) glycoprotein E1–E2 heterodimer mediates membrane fusion within the endosome, but the roles of conserved histidine residues in the formation of a functional heterodimer and in sensing pH changes is unknown. We examined the functional roles of conserved histidine residues located within E1 and E2. The E1 mutations, H222A/R, H298R and H352A, disrupted E1–E2 heterodimerization and reduced virus entry. A total of five out of six histidine residues located within the E2 RBD (receptor-binding domain) were important for the E2 fold, and their substitution with arginine or alanine caused aberrant heterodimerization and/or CD81 binding. Distinct roles in E1–E2 heterodimerization and in virus entry were identified for His691 and His693 respectively within the membrane-proximal stem region. Viral entry and cell–cell fusion at neutral and low pH values were enhanced with H445R, indicating that the protonation state of His445 is a key regulator of HCV fusion. However, H445R did not overcome the block to virus entry induced by bafilomycin A1, indicating a requirement for an endosomal activation trigger in addition to acidic pH.
Caveolae optimize tissue factor–Factor VIIa inhibitory activity of cell-surface-associated tissue factor pathway inhibitor
Authors: Maroney Susan A. , Ellery Paul E. , Wood Jeremy P. , Ferrel Josephine P. , Bonesho Catherine E. , Mast Alan E.
Published: January 2012

TFPI (tissue factor pathway inhibitor) is an anticoagulant protein that prevents intravascular coagulation through inhibition of fXa (Factor Xa) and the TF (tissue factor)–fVIIa (Factor VIIa) complex. Localization of TFPI within caveolae enhances its anticoagulant activity. To define further how caveolae contribute to TFPI anticoagulant activity, CHO (Chinese-hamster ovary) cells were co-transfected with TF and membrane-associated TFPI targeted to either caveolae [TFPI–GPI (TFPI–glycosylphosphatidylinositol anchor chimaera)] or to bulk plasma membrane [TFPI–TM (TFPI–transmembrane anchor chimaera)]. Stable clones had equal expression of surface TF and TFPI. TX-114 cellular lysis confirmed localization of TFPI–GPI to detergent-insoluble membrane fractions, whereas TFPI–TM localized to the aqueous phase. TFPI–GPI and TFPI–TM were equally effective direct inhibitors of fXa in amidolytic assays. However, TFPI–GPI was a significantly better inhibitor of TF–fVIIa than TFPI–TM, as measured in both amidolytic and plasma-clotting assays. Disrupting caveolae by removing membrane cholesterol from EA.hy926 cells, which make TFPIα, CHO cells transfected with TFPIβ and HUVECs (human umbilical vein endothelial cells) did not affect their fXa inhibition, but significantly decreased their inhibition of TF–fVIIa. These studies confirm and quantify the enhanced anticoagulant activity of TFPI localized within caveolae, demonstrate that caveolae enhance the inhibitory activity of both TFPI isoforms and define the effect of caveolae as specifically enhancing the anti-TF activity of TFPI.
Organic photovoltaic cells based on unconventional electron donor fullerene and electron acceptor copper hexadecafluorophthalocyanine
Authors: Yang J. L. , Sullivan P. , Schumann S. , Hancox I. , Jones T. S.
Published: January 2012

We demonstrate organic discrete heterojunction photovoltaic cells based on fullerene (C60) and copper hexadecafluorophthalocyanine (F16CuPc), in which the C60 and F16CuPc act as the electron donor and the electron acceptor, respectively. The C60/F16CuPc cells fabricated with conventional and inverted architectures both exhibit comparable power conversion efficiencies. Furthermore, we show that the photocurrent in both cells is generated by a conventional exciton dissociation mechanism rather than the exciton recombination mechanism recently proposed for a similar C60/F16ZnPc system [Song et al., J. Am. Chem. Soc. 132, 4554 (2010)]. These results demonstrate that new unconventional material systems are a potential way to fabricate organic photovoltaic cells with inverted as well as conventional architectures.
Interpretation of the I-Regime and transport associated with relevant heavy particle modes
Authors: Coppi B. , Zhou T.
Published: January 2012

The excitation of a novel kind of heavy particle [B. Coppi et al., Phys. Rev. Lett. 17, 377 (1966); B. Coppi and T. Zhou, MIT(LNS) Report HEP 09/04, 2009, Cambridge, MA [Phys. Lett. A 375, 2916 (2011)]] mode at the edge of the plasma column is considered as the signature of the I-confinement Regime [R. McDermott et al., Bull. Am. Phys. Soc. 53, 112 (2008); R. McDermott et al., Phys. Plasmas 16, 056103 (2009); E. Marmar et al., Bull. Am. Phys. Soc. 54, 97 (2009); D. Whyte et al., Nucl. Fusion 50, 105005 (2010); A. Hubbard et al., Phys. Plasmas 18, 056115 (2011)]. The outward transport of impurities produced by this mode is in fact consistent with the observed expulsion of them from the main body of the plasma column (a high degree of plasma purity is a necessary feature for fusion burning plasmas capable of approaching ignition). Moreover, the theoretically predicted mode phase velocity, in the direction of the electron diamagnetic velocity, has been confirmed by relevant experimental analyses [I. Cziegler, private communication (2010)] of the excited fluctuations (around 200 kHz). The plasma “spontaneous rotation” in the direction of the ion diamagnetic velocity is also consistent, according to the accretion theory [B. Coppi, Nucl. Fusion 42, 1 (2002)] of this phenomenon, with the direction of the mode phase velocity. Another feature of the mode that predicted by the theory is that the I-Regime exhibits a knee of the ion temperature at the edge of the plasma column, but not one of the particle density as the mode excitation factor is the relative main ion temperature gradient exceeding the local relative density gradient. The net plasma current density appearing in the saturation stage of the relevant instability, where the induced particle and energy fluxes are drastically reduced, is associated with the significant amplitudes of the poloidal magnetic field fluctuations [D. Whyte et al., Nucl. Fusion 50, 105005 (2010); A. Hubbard et al., Phys. Plasmas 18, 056115 (2011)] observed to accompany the density fluctuations. The theoretical implications of the significant electron temperature fluctuations [A. White, private communication (2011)] observed are discussed.
Modelling of the internal dynamics and density in a tens of joules plasma focus device
Authors: Márquez Ariel , González José , Tarifeño-Saldivia Ariel , Pavez Cristian , Soto Leopoldo , Clausse Alejandro
Published: January 2012

Using MHD theory, coupled differential equations were generated using a lumped parameter model to describe the internal behaviour of the pinch compression phase in plasma focus discharges. In order to provide these equations with appropriate initial conditions, the modelling of previous phases was included by describing the plasma sheath as planar shockwaves. The equations were solved numerically, and the results were contrasted against experimental measurements performed on the device PF-50J. The model is able to predict satisfactorily the timing and the radial electron density profile at the maximum compression.
A spin-adapted size-extensive state-specific multi-reference perturbation theory with various partitioning schemes. II. Molecular applications
Authors: Mao Shuneng , Cheng Lan , Liu Wenjian , Mukherjee Debashis
Published: January 2012

Following the theoretical development of a spin-adapted state-specific multi-reference second-order perturbation theory (SA-SSMRPT2) as expounded in the preceding publication, we discuss here its implementation and the results of its applications to potential energy curves (PECs) of various electronic states of small molecules. In particular, we illustrate its efficacy in states of various spin multiplicities and varying multi-reference character. Both Møller–Plesset (MP) and Epstein–Nesbet (EN) type of partitions have been explored. Also, a straightforward Rayleigh–Schrödinger (RS) and Brillouin–Wigner (BW) version of the SA-SSMRPT2 have been studied. Ground state PECs were computed for singlet states of HF, BH, and H2O molecules as well as the doublet state of NH2 and BeH radicals and compared to corresponding full configuration interaction numbers, which serve as benchmark results. As an extensive application on a production level, the ground state PECs of N2, a classic example of multiple-bond breaking, were calculated using cc-pVXZ (X = 3,4,5) basis and then extrapolated to obtain estimates of the complete basis set limit. Vibrational energy levels were extracted from these N2 PECs, which compare favorably to the experimental values. In addition, extensive studies were also carried out on PECs of the seven low-lying excited states of the N2 molecule. Finally, it is shown that the flexibility to relax configuration coefficients in SA-SSMRPT2 helps to provide good descriptions for the avoided crossing between the two lowest 1Σ states of the LiF molecule. Our results indicate (1) that more studies are needed to draw firm conclusions about the relative efficacies of the MP and EN results and (2) that the RS version works so well as compared to the BW version that the extra computational expenses needed in the later formalism is not warranted.
Simulation of the sea of electrons in metals using three-dimensional cell-by-cell automation
Authors: Quesnel David J. , Zhang Yingrui
Published: January 2012

A 3D cellular automation discretely moves electrons in a metal according to combined thermal and electrical driving forces by including all of the metal cations and all of the loosely bound electrons comprising the sea of electrons to compute the local electric fields. This cell-by-cell automation is asynchronous, acting on individual species sequentially with immediate neighborhood updates, thereby capturing the outcomes of temporally sparse thermally activated events. Calculations are carried out in a personal computer using the graphics processing unit to efficiently update the electric fields. A population of electron and missing-electron pairs is created to allow the metal to generate a dynamic equilibrium distribution of moving charge at each electron site that is then responsible for creating appropriate fields and potentials while simultaneously maintaining local charge neutrality. Examples are given to show that the simulation produces the expected zero fields inside conductors, the expected localization of excess charge of either sign on the surface of a conductor, and the expected equipotential inside a metal. Exterior fields caused by excess charge are consistent with Gauss’s law and excess charge accumulates at sharp corners. Surface relaxation of the lattice of cation and electron sites thought to occur at free surfaces appears to be required to enable a zero equipotential in a zero net charge system. The possibility that these relaxations create an electric double layer within the metal that is needed to terminate the effect of the periodic array of cations is under consideration. The approach is useful to examine interactions between electrons in metals and ions in solution expected during interfacial electrochemistry, but may have deeper implications on the origin of the equations governing electrostatics by linking them to localized 1/r2 Coulomb interactions.
Electrical modeling of Cu(In,Ga)Se2 cells with ALD-Zn1−xMgxO buffer layers
Authors: Pettersson J. , Edoff M. , Platzer-Björkman C.
Published: January 2012

Electrical modeling of Cu(In,Ga)Se2 solar cells with Zn1−xMgxO buffer layers is performed. A number of different device models are implemented and tested by comparing simulation results and measurement data. Room temperature light-soaking and dark-light cross-over behavior as well as low-temperature characteristics of these cells are studied. The light-soaking improvements in the solar cell parameters are attributed to an increase in buffer donor density, due to persistent photo conductivity, that counteracts charged acceptors in the absorber-buffer region. Dark-light JV-curve cross-over is explained by deep acceptor defects with small electron capture cross-section, in the buffer. Best correspondence to measurements on ZnO and Zn0.83Mg0.17O cells is obtained with models including absorber-buffer interface acceptor states. No wideband-gap surface defect layer is needed to reproduce measurement data.
Time dynamics of self-pumped reflection gratings in a photorefractive polymer
Authors: Banerjee P. P. , Buller S. H. , Liebig C. M. , Basun S. A. , Cook G. , Evans D. R. , Blanche P.-A. , Thomas J. , Christenson C. W. , Peyghambarian N.
Published: January 2012

The time dynamics of self-pumped reflection gratings in a commonly used photorefractive polymer PDCST:PVK:ECZ-BBP:C60 with no additional electron sources or traps is investigated. While holes are normally the mobile charges and responsible for grating formation, our experimental observations, analyzed using multi-exponential fitting curves, show evidence of electrons in addition to holes as charge carriers, particularly above an applied field of 40 V/μm. The dependence of effective carrier mobilities on the applied electric field, deduced from experimental results, show stronger field dependence of electron mobility at high electric fields. At an applied field of 70 V/μm, electron and hole mobilities become approximately equal, and the contribution of electrons on grating formation becomes significant.
A lattice model of the translational dynamics of nonrotating rigid rods
Authors: Tse Ying-Lung Steve , Andersen Hans C.
Published: January 2012

We present a lattice model of oriented, nonrotating, rigid rods in three dimensions with random walk dynamics, computer simulation results for the model, and a theory for the translational diffusion constant of the rods in the perpendicular direction, D⊥, in the semidilute regime. The theory is based on the “tube model” of Doi-Edwards (DE) theory for the rotational diffusion constant of rods that can both translate and rotate in continuous space. The theory predicts that D⊥ is proportional to (νL3)−2, where ν is the concentration of rods and L is the length of the rods, which is analogous to the Doi-Edwards scaling law for rotational diffusion. The simulations find that, as νL3 is increased, the approach to the limit of DE scaling is slow, and the −2 power in the DE scaling law is never quite achieved even at the highest concentration (νL3 = 200) simulated. We formulate a quantitative theory for the prefactor in the scaling relationship using only DE ideas, but it predicts a proportionality constant that is much too small. To explain this discrepancy, we modify the DE approach to obtain a more accurate estimate of the average tube radius and take into account effects of perpendicular motion of rods that are not included in the original DE theory. With these changes, the theory predicts values of D⊥ that are in much better agreement with the simulations. We propose a new scaling relationship that fits the data very well. This relationship suggests that the DE scaling law is the correct description of the scaling for infinitely thin rods only in the limit of infinite concentration, and that corrections to the DE scaling law because of finite concentration are significant even at concentrations that are well inside the semidilute regime. The implications of these results for the DE theory of rotating rods are discussed.
A flexible Bloch mode method for computing complex band structures and impedances of two-dimensional photonic crystals
Authors: Lawrence Felix J. , Botten Lindsay C. , Dossou Kokou B. , McPhedran R. C. , Martijn de Sterke C.
Published: January 2012

We present a flexible method that can calculate Bloch modes, complex band structures, and impedances of two-dimensional photonic crystals from scattering data produced by widely available numerical tools. The method generalizes previous work which relied on specialized multipole and finite element method (FEM) techniques underpinning transfer matrix methods. We describe the numerical technique for mode extraction, and apply it to calculate a complex band structure and to design two photonic crystal antireflection coatings. We do this for frequencies at which other methods fail, but which nevertheless are of significant practical interest.
Particle-size effects on the suppression of charge ordering in Nd0.8Na0.2MnO3
Authors: Samantaray B. , Srivastava S. K. , Ravi S.
Published: January 2012

In this work, we have studied the suppression of the charge-ordered (CO) state in Nd0.8Na0.2MnO3 compound by varying the particle size and the applied magnetic field. The bulk samples with a particle size of D ≥ 140 nm exhibit different magnetic ground states, such as paramagnetic (PM), charge-ordering, ferromagnetic-cluster-glass (FM-CG), and reentrant-spin-glass-like (RSG) behavior. The complete suppression of charge ordering could be observed by reducing the particle size down to 50 nm. The field variation of magnetization curves at different temperatures show field-induced reversible transition from the antiferromagnetic (AFM) CO state to the FM state beyond a threshold field (HC). The M–H loops recorded at 5 K, show a distinct field-induced transition from a spin-frozen state to a FM state, especially on bulk samples with particle sizes of D ≥ 140 nm. T–H phase diagrams were constructed for samples with different particle sizes. The phase boundary between CO-AFM and FM states was found to shift toward higher temperature and lower magnetic fields with a decrease in particle size. Moreover, the phase-separation region was also found to narrow down with a decrease in particle size. The boundary of the spin-frozen state is found to shift toward lower temperature and magnetic field with decrease in particle size. The observed result could be explained based on the core-shell model.
The effect of dust size distribution and dust charge fluctuation on dust acoustic solitary waves in a magnetized dusty plasma
Authors: Maitra Sarit
Published: January 2012

Dust acoustic solitary waves in a magnetized dusty plasma are studied taking into account the effect of dust size and dust charge variations. Using the analytical and numerical results the influence of different plasma parameters on dust acoustic solitary waves are examined. It is observed that the dust size distribution and dust charge variation have significant contributions on the characteristics of dust acoustic solitary waves.
Evolution of nanoscale roughness in Cu/SiO2 and Cu/Ta interfaces
Authors: Warren Andrew P. , Sun Tik , Yao Bo , Barmak Katayun , Toney Michael F. , Coffey Kevin R.
Published: January 2012

Synchrotron x-ray scattering was used to study the evolution of interface roughness with annealing for a series of Cu thin films. The films were encapsulated in SiO2 or Ta/SiO2 and prepared by sputter deposition. Specular x-ray reflectivity was used to determine the root mean square roughness for both the upper and the lower Cu/SiO2 (or Cu/Ta) interfaces. The lateral roughness was studied by diffuse x-ray reflectivity. Annealing the films at 600 °C resulted in a smoothing of only the upper interface for the Cu/SiO2 samples, while the lower Cu/SiO2 interfaces and both interfaces for the Ta encapsulated films did not evolve significantly. This difference in kinetics is consistent with the lower diffusivity expected of Cu in a Cu/Ta interface (compared to a Cu/SiO2 interface) and the mechanical rigidity of the lower Cu/SiO2 interface. As a function of roughness wavelength, the upper Cu/SiO2 interfaces exhibited a roughness decay with annealing that was only 12.5% of that expected for classical capillarity driven smoothening of a free surface.
Experimental evidence of a triadic resonance of plane inertial waves in a rotating fluid
Authors: Bordes Guilhem , Moisy Frédéric , Dauxois Thierry , Cortet Pierre-Philippe
Published: January 2012

Plane inertial waves are generated using a wavemaker, made of oscillating stacked plates, in a rotating water tank. Using particle image velocimetry, we observe that, after a transient, the primary plane wave is subject to a subharmonic instability and excites two secondary plane waves. The measured frequencies and wavevectors of these secondary waves are in quantitative agreement with the predictions of the triadic resonance mechanism. The secondary wavevectors are found systematically more normal to the rotation axis than the primary wavevector: this feature illustrates the basic mechanism at the origin of the energy transfers towards slow, quasi two-dimensional, motions in rotating turbulence.
Enhanced crystallization of GeTe from an Sb2Te3 template
Authors: Simpson R. E. , Fons P. , Kolobov A. V. , Krbal M. , Tominaga J.
Published: January 2012

Crystalline Sb2Te3 templates reduce the crystallization time of the phase change material GeTe by four orders of magnitude to 20 ns. Structural measurements and density functional theory molecular dynamics atomistic modeling show that this reduction is a direct consequence of textured crystal growth from a plane of octahedral crystal nucleation centers. The nucleation template serves to reduce the crystallization activation energy by 2.6 eV allowing crystallization to proceed at a temperature 95 °C lower than that of the untemplated GeTe film.
Spherical momentum distribution of the protons in hexagonal ice from modeling of inelastic neutron scattering data
Authors: Flammini D. , Pietropaolo A. , Senesi R. , Andreani C. , McBride F. , Hodgson A. , Adams M. A. , Lin L. , Car R.
Published: January 2012

The spherical momentum distribution of the protons in ice is extracted from a high resolution deep inelastic neutron scattering experiment. Following a recent path integral Car-Parrinello molecular dynamics study, data were successfully interpreted in terms of an anisotropic Gaussian model, with a statistical accuracy comparable to that of the model independent scheme used previously, but providing more detailed information on the three dimensional potential energy surface experienced by the proton. A recently proposed theoretical concept is also employed to directly calculate the mean force from the experimental neutron Compton profile, and to evaluate the accuracy required to unambiguously resolve and extract the effective proton potential from the experimental data.
Ion acoustic solitons in a plasma with two-temperature kappa-distributed electrons
Authors: Baluku T. K. , Hellberg M. A.
Published: January 2012

Existence domains and characteristics of ion acoustic solitons are studied in a two-temperature electron plasma with both electron components being kappa-distributed, as found in Saturn’s magnetosphere. As is the case for double-Boltzmann electrons, solitons of both polarities can exist over restricted ranges of fractional hot electron density ratio for this plasma model. Low κ values, which indicate increased suprathermal particles in the tail of the distribution, yield a smaller domain in the parameter space of hot density fraction and normalized soliton velocity (f, M), over which both soliton polarities are supported for a given plasma composition (the coexistence region). For some density ratios that support coexistence, solitons occur even at the lowest (critical) Mach number (i.e., at the acoustic speed), as found recently for a number of other plasma models. Like Maxwellians, low-κ distributions also support positive potential double layers over a narrow range of low fractional cool electron density (<10%).
Strong Langmuir turbulence in Kappa distributed plasmas
Authors: Liu San-Qiu , Chen Hui
Published: January 2012

Superthermal electrons are often observed in space and astrophysics and can be appropriate modeled by the family of Kappa distribution functions. Taking the nonlinear wave-wave, wave-particle interactions and the effect of superthermal electrons into account, the strong Langmuir turbulence is investigated in kinetic regime. The modified Zakharov equations are obtained for the case of no damping or driving terms. On the basis of these equations, dynamics of collapse have been studied by the means of the general virial theorem, and the collapse thresholds which are strong modified by superthermal index κe are given.
An analogy of Taylor’s instability criterion in Couette and rotating-magnetic-field-driven flows
Authors: Ungarish Marius
Published: January 2012

The classical stability solution of Taylor for the Couette flow between a rotating inner cylinder and a stationary outer cylinder is used to model the “critical magnetic Taylor number,” Tacr, in a flow of a liquid metal driven by a rotating magnetic field (RMF) in a cylindrical cavity characterized by the parameter H= height/radius. (The magnetic Taylor number is defined as Ta=σωBo2Ro4/(2ρν2), where σ,ν, and ρ are the electrical conductivity, kinematic viscosity, and density of the liquid; ω and Bo are the magnetic field frequency and induction; Ro is the radius of the cavity; the cr superscript means “critical”) In typical conditions, the RMF flow develops a solid-body-rotating core analogous to the inner rotating cylinder, embedded in a layer in which the swirl decays to zero at the outer wall. Using small-Ekman-number approximations for the core and gap flow, the analogy yields an insightful expression for Tacr. In particular, the model indicates that Tacr depends strongly on the parameter H. Comparisons of the present theoretical results with available realistic data show a good qualitative agreement and plausible quantitative agreement. The model was improved by an empirical adjustment of a coefficient and can be used as simple approximate prediction tool for Tacr in a quite wide range of cylindrical cavity configurations.
Transport coefficients and cross sections for electrons in water vapour: Comparison of cross section sets using an improved Boltzmann equation solution
Authors: Ness K. F. , Robson R. E. , Brunger M. J. , White R. D.
Published: January 2012

This paper revisits the issues surrounding computation of electron transport properties in water vapour as a function of E/n0 (the ratio of the applied electric field to the water vapour number density) up to 1200 Td. We solve the Boltzmann equation using an improved version of the code of Ness and Robson [Phys. Rev. A 38, 1446 (1988)], facilitating the calculation of transport coefficients to a considerably higher degree of accuracy. This allows a correspondingly more discriminating test of the various electron–water vapour cross section sets proposed by a number of authors, which has become an important issue as such sets are now being applied to study electron driven processes in atmospheric phenomena [P. Thorn, L. Campbell, and M. Brunger, PMC Physics B 2, 1 (2009)] and in modeling charged particle tracks in matter [A. Munoz, F. Blanco, G. Garcia, P. A. Thorn, M. J. Brunger, J. P. Sullivan, and S. J. Buckman, Int. J. Mass Spectrom. 277, 175 (2008)].
Linear differential equations and multiple zeta-values. III. Zeta(3)
Authors: Zakrzewski Michał , Żołądek Henryk
Published: January 2012

We consider the hypergeometric equation (1 − t)∂t∂t∂g + x3g = 0, whose unique analytic solution φ1(t; x) = 1 + O(t) near t = 0 for t = 1 becomes a generating function for multiple zeta values φ1(1; x) = f3(x) = 1 − ζ(3)x3 + ζ(3, 3)x6 − …. We apply the so-called WKB method to study solutions of the hypergeometric equation for large x and we calculate corresponding Stokes matrices. We prove that the function f3(x) near x = ∞ is also expressed via WKB type functions which subject to some Stokes phenomenon. This implies that f3(x) satisfies a sixth order linear differential equation with irregular singularity at infinity.
Effect of ionization distribution on the low frequency oscillations mode in Hall thrusters
Authors: Liqiu Wei , Chunsheng Wang , Ke Han , Daren Yu
Published: January 2012

It is found that the discharge parameters have notable effects on the mode of discharge current low frequency oscillation in Hall thrusters, but different discharge parameters might form the similar low frequency oscillation mode. In order to study the mechanism of oscillation mode formation, the ionization distribution in the discharge channel was measured experimentally, and one-dimensional quasi-neutrality hydrodynamic model was used to study the relationship between ionization distribution and the oscillation mode. Researches show that the low frequency oscillation with a narrow and condensed ionization distribution has the mode of lower amplitude and scattered frequency. The low frequency oscillation amplitude would become high and have dominative frequency component with the relative wide ionization distribution. Therefore, it can be concluded that the difference of ionization distribution characteristics is the main reason of the oscillation mode variation, and discharge parameters are only the external control parameters of ionization distribution characteristics.
Electrical test method using high density plasmas for high-end printed circuit boards
Authors: Oh Se-Jin , Kim Young-Cheol , Chung Chin-Wook
Published: January 2012

A novel electrical test method that uses high-density plasmas, such as inductively coupled discharges, is proposed to detect open/short failures of high-end printed circuit boards (PCBs). The PCB is inserted into the plasma chamber with the top side facing the plasma sheath, and the bottom of the PCB is connected to the probe pin for the dc voltage bias and current measurements. A failure, including a latent open, can be precisely detected by biasing the dc voltage near the plasma potential due to the specific characteristics of the sheath formed on the PCB surface.
Monte Carlo analysis of electron relaxation process and transport property of wurtzite InN
Authors: Wang S. L. , Liu H. X. , Gao B. , Fan J. B. , Ma F. , Kuang Q. W.
Published: January 2012

Both the electron relaxation process and the transport property of wurtzite InN have been investigated using an ensemble Monte Carlo method. The band structure of the classic three valleys model is adopted, and the anisotropy of the band structure by Herring-Volt transform is also taken into consideration. The peak velocity in the Γ-A direction (c-direction) is higher than that in the Γ-M direction (basal plane), and the onset of negative differential mobility (NDM) appears at relatively lower electric field. Both velocity transport and the energy relaxation process in three valleys have been investigated. It has been found that the electrons in the high valley also show obvious energy overshoot besides the total energy overshoot. Based on the correlation of the drift velocity and the average energy versus time in the lowest valley, it has been concluded that nonparabolicity of band structure impacts the velocity overshoot greatly. Further research shows that nonparabolicity also plays an important role in NDM at low electric field, whereas intervalley scattering becomes important to NDM at high electric field. The total average energy overshoot is mainly caused by the intervalley scattering. Finally, the velocity undershoot in wurtzite InN is observed by applying a pulse electric field on simulated electrons.
Electrical, dielectric and spectroscopic studies on MnO doped LiI–AgI–B2O3 glasses
Authors: Moguš-Milanković A. , Pavić L. , Srilatha K. , Srinivasa Rao Ch. , Srikumar T. , Gandhi Y. , Veeraiah N.
Published: January 2012

LiI–AgI–B2O3 glasses doped with different concentrations of MnO (ranging from 0 to 0.8 mol%) were prepared. Electrical and dielectric properties have been studied over a wide frequency range of 10−2 – 106 Hz and in the temperature range from 173 to 523 K. The valence states of manganese ions and their coordination in the glass network have been investigated using optical absorption, luminescence, and ESR spectroscopy. The analysis of the spectroscopic results has indicated that the manganese ions exist in both Mn2+ and Mn3+ states and occupy octahedral and tetrahedral positions. With increasing MnO concentration there is a gradual increase in the tetrahedral occupancy of Mn2+ ions at the expense of octahedral occupancy in the glass network. The results of dc conductivity have indicated that when T > θD/2, the small polaron hopping model is appropriate and the conduction is adiabatic in the nature. Further, the analysis of experimental data indicates that there is a mixed, ionic and electronic, conduction. It has been observed that the electrical conductivity decreases as the concentration of MnO increases suggesting the electronic conduction controlled by polaron hopping between manganese ions. In the low temperature region, up to 250 K, the ac conductivity is nearly temperature independent and varies linearly with frequency, which can be explained by the quantum mechanical tunneling (QMT) model. The dielectric properties have been analyzed in the framework of complex dielectric permittivity and complex electrical modulus formalisms. The evolution of the complex permittivity as a function of frequency and temperature has been investigated.
Different growth regimes on prepatterned surfaces: Consistent evidence from simulations and experiments
Authors: Lied Fabian , Mues Tanja , Wang Wenchong , Chi Lifeng , Heuer Andreas
Published: January 2012

Molecule deposition on a prepatterned substrate is a recently developed technique to generate desired structures of organic molecules on surfaces via self-organization. For the case of prepatterned stripes, the time-resolved process of structure formation is studied via lattice Monte Carlo simulations. By systematic variation of the interaction strength, three distinct growth regimes can be identified: localized growth, bulge formation, and cluster formation. All three growth regimes can be recovered in the experiment when choosing appropriate organic molecules. Some key microscopic observables, reflecting the properties of the structure formation, display a non-monotonous dependence on the interaction strength.
Probing origin of room temperature ferromagnetism in Ni ion implanted ZnO films with x-ray absorption spectroscopy
Authors: Srivastava P. , Ghosh S. , Joshi B. , Satyarthi P. , Kumar P. , Kanjilal D. , Buerger D. , Zhou S. , Schmidt H. , Rogalev A. , Wilhelm F.
Published: January 2012

We report x-ray absorption at Zn and Ni K-edges in 200 keV Ni2+ ion implanted ZnO/sapphire films. The implantation fluences are 6 × 1015 and 2 × 1016 ions/cm2, corresponding to 2% and 7% Ni in a ZnO matrix. The measurements reveal a marginal substitution of Ni in ZnO in both the films and also rule out the presence of ferromagnetic Ni metal clusters. The M-H and field cooled-zero field cooled measurements performed via SQUID magnetometry show that the films are ferromagnetic at room temperature, and the saturation magnetization of 2% Ni film is appreciably higher than that of 7% Ni film. The origin of ferromagnetism is understood on the basis of the oxygen vacancy mediated bound magnetic polaron model.
First principles analysis on interaction between vacancy near surface and dimer structure of silicon crystal
Authors: Kamiyama Eiji , Sueoka Koji
Published: January 2012

We investigated the interactions between the dimer structures in a reconstructed Si (100) surface and a vacancy to understand the behavior of the point defects near the surface using first principles calculations. The calculated results showed that even a vacancy set in the ninth layer from the surface affects the charges around the dimers. This effect intensifies if the vacancy moves to the surface. Similar to the vacancies in a bulk, Jahn-Teller distortion occurred at atoms around the vacancy. When the introduced vacancy approaches to the fourth layer from the bottom, this distortion increased, and thus decreases the total energy. The third layer, in which forming a vacancy requires the highest energy, becomes a singularity layer in a Si (100) surface with dimer structures. The model, in which a vacancy was introduced into the fifth layer from the surface, came to have a vacancy in the fourth layer as an optimized structure due to a Si atom moving from the fourth to the fifth layer. We can see a clear interaction between the vacancy-originated charges and the surface dimer-originated one in this movement. As a consequence, the nature of the interaction between a surface dimer and a vacancy is intermediated by their accompanying charges.
Charge separation in CdSe/CdTe hetero-nanowires measured by electrostatic force microscopy
Authors: Schäfer Sebastian , Reich Aina , Wang Zhe , Kipp Tobias , Mews Alf
Published: January 2012

The charge state of free standing axial type-II CdSe/CdTe hetero-nanowires is monitored via electrostatic force microscopy. The CdSe and the CdTe segment which are identified by Raman spectroscopy are found to be negatively and positively charged, respectively. The charge state is monitored without and with local illumination. We found that the magnitude of opposite charging in the respective nanowire segment is increasing with illumination power, which is attributed to a charge separation of the photogenerated electron-hole pairs across the CdSe/CdTe interface.
The effect of Fe2+ ions on dielectric and magnetic properties of Yb3Fe5O12 ceramics
Authors: Su Jie , Lu Xiaomei , Zhang Junting , Sun Hui , Zhang Chao , Jiang Zhenghao , Ju Changcheng , Wang Zhijun , Huang Fengzhen , Zhu Jinsong
Published: January 2012

Yb3Fe5O12 ceramics with garnet structure were prepared employing the solid-state reaction method. The results reveal that the emergence of Fe2+ ions greatly affects dielectric relaxation, magnetic relaxation, saturation magnetization, and magnetoelectric coupling, which was further confirmed by oxygen treatment. More interestingly, the magnetoelectric coefficient (α) reaches 28 ps m−1 at room temperature, which is among the largest values for present single-phase magnetoelectric materials.
High-pressure study of tetramethylsilane by Raman spectroscopy
Authors: Qin Zhen-Xing , Zhang Jian-Bo , Troyan Ivan , Palasyuk Taras , Eremets Mikhail , Chen Xiao-Jia
Published: January 2012

High-pressure behavior of tetramethylsilane, one of the Group IVa hydrides, was investigated by Raman scattering measurements at pressures up to 142 GPa and room temperature. Our results revealed the phase transitions at 0.6, 9, and 16 GPa from both the mode frequency shifts with pressure and the changes of the full width half maxima of these modes. These transitions were suggested to result from the changes in the inter- and intra-molecular bonding of this material. We also observed two other possible phase transitions at 49–69 GPa and 96 GPa. No indication of metallization in tetramethylsilane was found with stepwise compression to 142 GPa.
Role of atomic terraces and steps in the electron transport properties of epitaxial graphene grown on SiC
Authors: Kuramochi H. , Odaka S. , Morita K. , Tanaka S. , Miyazaki H. , Lee M. V. , Li S.-L. , Hiura H. , Tsukagoshi K.
Published: January 2012

Thermal decomposition of vicinal SiC substrates with self-organized periodic nanofacets is a promising method to produce large graphene sheets toward the commercial exploitation of graphene's superior electronic properties. The epitaxial graphene films grown on vicinal SiC comprise two distinct regions of terrace and step; and typically exhibit anisotropic electron transport behavior, although limited areas in the graphene film showed ballistic transport. To evaluate the role of terraces and steps in electron transport properties, we compared graphene samples with terrace and step regions grown on 4H-SiC(0001). Arrays of field effect transistors were fabricated on comparable graphene samples with their channels parallel or perpendicular to the nanofacets to identify the source of measured reduced mobility. Minimum conductivity and electron mobility increased with the larger proportional terrace region area; therefore, the terrace region has superior transport properties to step regions. The measured electron mobility in the terrace region, ∼1000 cm2/Vs, is 10 times larger than that in the step region, ∼100 cm2/Vs. We conclusively determine that parasitic effects originate in regions of graphene that grow over step edges in 4H-SiC(0001).
Transient spectral dependence of photoinduced magneto-optical Faraday effect in CdTe quantum dots
Authors: Ma Hong , Jin Zuanming , Zhang Zhengbing , Ma Guohong , Wang Lianhui
Published: January 2012

The time-resolved photo-induced magneto-optical response of water soluble cadmium telluride (CdTe) colloidal quantum dots (QDs) is studied in the spectral range across the first exciton (1S3/21Se) transition at room temperature without external magnetic field. Spectral dependence of the Faraday ellipticity reaches an extremum near the first exciton transition energy, while the Faraday rotation shows a sign reversal, which indicates that the spectral dependence of photo-induced Faraday effect evolves from a diamagnetic to a paramagnetic behavior during the exciton spin relaxation process in CdTe QDs.
Isoprenoid biosynthesis is required for miRNA function and affects membrane association of ARGONAUTE 1 in
Arabidopsis
Authors: Brodersen Peter , Sakvarelidze-Achard Lali , Schaller Hubert , Khafif Mehdi , Schott Grégory , Bendahmane Abdelhafid , Voinnet Olivier
Published: January 2012

Plant and metazoan microRNAs (miRNAs) guide ARGONAUTE (AGO) protein complexes to regulate expression of complementary RNAs via base pairing. In the plant
Arabidopsis thaliana
, the main miRNA effector is AGO1, but few other factors required for miRNA activity are known. Here, we isolate the genes defined by the previously described
miRNA action deficient
(
mad
) mutants,
mad3
and
mad4
. Both genes encode enzymes involved in isoprenoid biosynthesis.
MAD3
encodes 3-hydroxy-3-methylglutaryl CoA reductase (HMG1), which functions in the initial C
5
building block biogenesis that precedes isoprenoid metabolism. HMG1 is a key regulatory enzyme that controls the amounts of isoprenoid end products.
MAD4
encodes sterol C-8 isomerase (HYDRA1) that acts downstream in dedicated sterol biosynthesis. Using yeast complementation assays and
in planta
application of lovastatin, a competitive inhibitor of HMG1, we show that defects in HMG1 catalytic activity are sufficient to inhibit miRNA activity. Many isoprenoid derivatives are indispensable structural and signaling components, and especially sterols are essential membrane constituents. Accordingly, we provide evidence that AGO1 is a peripheral membrane protein. Moreover, specific hypomorphic mutant alleles of
AGO1
display compromised membrane association and AGO1-membrane interaction is reduced upon knockdown of HMG1/MAD3. These results suggest a possible basis for the requirement of isoprenoid biosynthesis for the activity of plant miRNAs, and unravel mechanistic features shared with their metazoan counterparts.