bluuebunny/crossref_metadata_2025 huggingface dataset:
Reversible Inhibition of the Pollen Germination and the Stigma Penetration in Crocus vernus ssp. vernus (Iridaceae) Following Fumigations with NO2, CO, and O3 Gases
Authors: Chichiriccò G. , Picozzi P.
Published: November 2007

Abstract: We assessed the pollen hydration, the pollen germination, and the stigma papilla penetration of Crocus vernus subsp. vernus (Iridaceae) after 2 h fumigations with O3, NO2, and CO gases within humidified (90 ‐ 100 % RH) box experiments. When the pollen and the pistil were separately fumigated, the pollen retained the capacity to emit a tube which penetrated papilla, and the stigma papillae retained the receptivity; when the pistils were first pollinated and then fumigated, the capacity of pollen to hydrate was not affected, but the germination was significantly reduced. The vulnerability to gases became evident at 0.3 ppm O3, 0.2 ppm NO2, and 0.5 ppm CO. The inhibition curves as a function of the gas concentrations were of an exponential type, and they saturated at 2 ppm NO2, 25 ppm CO, and 0.5 ppm O3, with germination percentages of 17 %, 27 %, and 60 %, respectively. Both the pollen germination and the papilla penetration were fully restored by prolonging for 60 ‐ 90 min the incubation at 90 ‐ 100 % RH, after the cessation of fumigations. The vulnerability of the pollen‐papilla system is discussed.
Truncated Hemoglobins in Actinorhizal Nodules of Datisca glomerata
Authors: Pawlowski K. , Jacobsen K. R. , Alloisio N. , Ford Denison R. , Klein M. , Tjepkema J. D. , Winzer T. , Sirrenberg A. , Guan C. , Berry A. M.
Published: November 2007

Abstract: Three types of hemoglobins exist in higher plants, symbiotic, non‐symbiotic, and truncated hemoglobins. Symbiotic (class II) hemoglobins play a role in oxygen supply to intracellular nitrogen‐fixing symbionts in legume root nodules, and in one case (Parasponia sp.), a non‐symbiotic (class I) hemoglobin has been recruited for this function. Here we report the induction of a host gene, dgtrHb1, encoding a truncated hemoglobin in Frankia‐induced nodules of the actinorhizal plant Datisca glomerata. Induction takes place specifically in cells infected by the microsymbiont, prior to the onset of bacterial nitrogen fixation. A bacterial gene (Frankia trHbO) encoding a truncated hemoglobin with O2‐binding kinetics suitable for the facilitation of O2 diffusion (Tjepkema et al., 2002) is also expressed in symbiosis. Nodule oximetry confirms the presence of a molecule that binds oxygen reversibly in D. glomerata nodules, but indicates a low overall hemoglobin concentration suggesting a local function. Frankia TrHbO is likely to be responsible for this activity. The function of the D. glomerata truncated hemoglobin is unknown; a possible role in nitric oxide detoxification is suggested.
Honeybees Enhance Reproduction without Affecting the Outcrossing Rate in Endemic Pedicularis densispica (Orobanchaceae)
Authors: Xia J. , Sun S. G. , Guo Y. H.
Published: November 2007

Abstract: There has been substantial debate in recent years surrounding the impact of introduced honeybees on native biota. This study reports on an investigation of Pedicularis densispica, a subalpine annual herb endemic to Southwest China, in an attempt to determine the impact of introduced domestic honeybees on pollen dispersal and thus on their reproductive success and mating system. Honeybees were introduced into the study site in 2004, and a sudden seasonal pollinator shift from bumblebees to honeybees was observed. Intra‐ and inter‐plant visits by different pollinators were recorded in the field in 2003 and 2004. Fruit and seed sets prior to and after the pollinator shift were measured. Experimental pollinations were performed to characterize the breeding system. Outcrossing rates at the seed stage were estimated for both years using RAPD markers. Our results indicated that honeybees foraged between plants more frequently than bumblebees did. Our results also revealed that the introduction of honeybees significantly enhanced reproductive success. However, no significant difference was detected between the outcrossing rates due to bumblebee and honeybee pollination. P. densispica was almost completely outcrossing (tm= 0.956 and 0.967, respectively in 2003 and 2004) but partially self‐compatible. This study presents the first report of the outcrossing rate in the genus Pedicularis and reveals a limited influence of pollination on the mating system in P. densispica. The pollinator shift did not reduce reproductive success of the plants and honeybees may be used to augment pollinator services for nectariferous P. densispica.
Specialized Mycorrhizal Colonization Pattern in AchlorophyllousEpirixanthesspp. (Polygalaceae)
Authors: Imhof S.
Published: November 2007

Abstract:Roots of the achlorophyllousEpirixanthes papunanaandE. elongatawere sectioned in complete series in order to reconstruct the three‐dimensional mycorrhizal colonization pattern within their tissues. Hyphal morphology, vesicles, as well as the exclusively intracellular mode of colonization indicate aParis‐type of arbuscular mycorrhiza showing a hitherto unknown colonization pattern: (1) the outer cortex is colonized by persistent straight‐growing hyphae which branch in a cascading manner, (2) a specific layer (called layer 2) is inhabited by persistent hyphal coils, (3) in the cells of the anatomically distinct inner cortex parenchyma layer (called layer 1) the hyphae immediately degenerate, and (4) the layer outside to layer 2 (called layer 3) is either transitional layer 2 when penetrated from the outer cortex or the fungal material degenerates when colonized from the layer 2. This complex colonization pattern is a reasonable adaptation to the particular demands ofEpirixanthesas a myco‐heterotrophic plant. It not only allows a sustained benefit from the fungal symbiont but also provides a two‐level distribution system of hyphae within the roots. The outer cortex hyphae function as a permanent intraradical resource of living fungi providing connection to the external mycelium as well as a coarse distribution of hyphae within the root. Layer 2 represents the fine scale distribution of hyphae, having access to all potentially digesting cells of the layers 1 and 3. Common structural features of mycorrhizae in myco‐heterotrophic plants are pointed out in order to find putative prerequisites for their heterotrophic mode of life.
Thermodynamics and kinetics of competing aggregation processes in a simple model system
Authors: Nag Ambarish , Berry R. Stephen
Published: November 2007

A simple model system has been used to develop thermodynamics and kinetics for bulk and surface aggregation processes capable of competing with each other. The processes are the stepwise aggregation of monomers in a fluid medium and on an inpenetrable solid surface bounding the fluid medium, besides the adsorption and desorption of the same species at the solid-fluid interface. Emphasis is on aggregation processes in the high friction limit. The theoretical model is used to compare the kinetics and thermodynamics of the processes and to infer the conditions in which one process dominates another, in the high friction limit, such as in a liquid. The motivation of this study is obtaining insight into competition between aggregation in solution and on an adjoining surface, such as a cell membrane.
Mobile trap algorithm for zinc detection using protein sensors
Authors: Inamdar Munish V. , Lastoskie Christian M. , Fierke Carol A. , Sastry Ann Marie
Published: November 2007

We present a mobile trap algorithm to sense zinc ions using protein-based sensors such as carbonic anhydrase (CA). Zinc is an essential biometal required for mammalian cellular functions although its intracellular concentration is reported to be very low. Protein-based sensors like CA molecules are employed to sense rare species like zinc ions. In this study, the zinc ions are mobile targets, which are sought by the mobile traps in the form of sensors. Particle motions are modeled using random walk along with the first passage technique for efficient simulations. The association reaction between sensors and ions is incorporated using a probability (p1) upon an ion-sensor collision. The dissociation reaction of an ion-bound CA molecule is modeled using a second, independent probability (p2). The results of the algorithm are verified against the traditional simulation techniques (e.g., Gillespie’s algorithm). This study demonstrates that individual sensor molecules can be characterized using the probability pair (p1,p2), which, in turn, is linked to the system level chemical kinetic constants, kon and koff. Further investigations of CA-Zn reaction using the mobile trap algorithm show that when the diffusivity of zinc ions approaches that of sensor molecules, the reaction data obtained using the static trap assumption differ from the reaction data obtained using the mobile trap formulation. This study also reveals similar behavior when the sensor molecule has higher dissociation constant. In both the cases, the reaction data obtained using the static trap formulation reach equilibrium at a higher number of complex molecules (ion-bound sensor molecules) compared to the reaction data from the mobile trap formulation. With practical limitations on the number sensors that can be inserted/expressed in a cell and stochastic nature of the intracellular ionic concentrations, fluorescence from the number of complex sensor molecules at equilibrium will be the measure of the intracellular ion concentration. For reliable detection of zinc ions, it is desirable that the sensors must not bind all the zinc ions tightly, but should rather bind and unbind. Thus for a given fluorescence and with association-dissociation reactions between ions and sensors, the static trap approach will underestimate the number of zinc ions present in the system.
On the calculation of velocity-dependent properties in molecular dynamics simulations using the leapfrog integration algorithm
Authors: Cuendet Michel A. , van Gunsteren Wilfred F.
Published: November 2007

Widely used programs for molecular dynamics simulation of (bio)molecular systems are the Verlet and leapfrog algorithms. In these algorithms, the particle velocities are less accurately propagated than the positions. Important quantities for the simulation such as the temperature and the pressure involve the squared velocities at full time steps. Here, we derive an expression for the squared particle velocity at full time step in the leapfrog scheme, which is more accurate than the standardly used one. In particular, this allows us to show that the full time step kinetic energy of a particle is more accurately computed as the average of the kinetic energies at previous and following half steps than as the square of the average velocity as implemented in various molecular dynamics codes. Use of the square of the average velocity introduces a systematic bias in the calculation of the instantaneous temperature and pressure of a molecular dynamics system. We show the consequences when the system is coupled to a thermostat and a barostat.
Statistical mechanics of time independent nondissipative nonequilibrium states
Authors: Williams Stephen R. , Evans Denis J.
Published: November 2007

We examine the question of whether the formal expressions of equilibrium statistical mechanics can be applied to time independent nondissipative systems that are not in true thermodynamic equilibrium and are nonergodic. By assuming that the phase space may be divided into time independent, locally ergodic domains, we argue that within such domains the relative probabilities of microstates are given by the standard Boltzmann weights. In contrast to previous energy landscape treatments that have been developed specifically for the glass transition, we do not impose an a priori knowledge of the interdomain population distribution. Assuming that these domains are robust with respect to small changes in thermodynamic state variables we derive a variety of fluctuation formulas for these systems. We verify our theoretical results using molecular dynamics simulations on a model glass forming system. Nonequilibrium transient fluctuation relations are derived for the fluctuations resulting from a sudden finite change to the system’s temperature or pressure and these are shown to be consistent with the simulation results. The necessary and sufficient conditions for these relations to be valid are that the domains are internally populated by Boltzmann statistics and that the domains are robust. The transient fluctuation relations thus provide an independent quantitative justification for the assumptions used in our statistical mechanical treatment of these systems.
Analysis of integral expressions for effective Born radii
Authors: Mongan John , Svrcek-Seiler W. Andreas , Onufriev Alexey
Published: November 2007

Generalized Born (GB) models provide a computationally efficient means of representing the electrostatic effects of solvent and are widely used, especially in molecular dynamics (MD). Accurate and facile computation of the effective Born radii is a key for the performance of GB models. Here, we examine a simple integral prescription, R6, based on the exact solution of the Poisson-Boltzmann (PB) equation for a perfect sphere. Numerical tests on 22molecules representing a variety of structural classes show that R6 may be more accurate than the more complex integral-based approaches such as GBMV2. At the same time, R6 is computationally less demanding. Fundamental limitations of current integration-based methods for calculating effective radii, including R6, are explored and the deviations from the numerical PB results are correlated with specific topological and geometrical features of the molecular surface. A small systematic bias observed in the R6-based radii can be removed with a single, transferable constant offset; when the resulting effective radii are used in the “classical” (Still et al.’s) GB formula to compute the electrostatic solvation free energy, the average deviation from the PB reference is no greater than when the “perfect” (PB-based) effective radii are used. This deviation is also appreciably smaller than the uncertainty of the PB reference itself, as estimated by comparison to explicit solvent.
Model analysis of a double-stage Hall effect thruster with double-peaked magnetic field and intermediate electrode
Authors: Perez-Luna J. , Hagelaar G. J. M. , Garrigues L. , Boeuf J. P.
Published: November 2007

A hybrid fluid-particle model has been used to study the properties of a double-stage Hall effect thruster where the channel is divided into two regions of large magnetic field separated by a low-field region containing an intermediate, electron-emitting electrode. These two features are aimed at effectively separating the ionization region from the acceleration region in order to extend the thruster operating range. Simulation results are compared with experimental results obtained elsewhere. The simulations reproduce some of the measurements when the anomalous transport coefficients are adequately chosen. However, they raise the question of a complete separation of the ionization and acceleration regions and the necessity of an electron-emissive intermediate electrode. The calculation method for the electric potential in the hybrid model has been improved with respect to our previous work and is capable of a complete two-dimensional description of the magnetic configurations of double-stage Hall effect thrusters.
Unique role of hydrophilic ionic liquid in modifying properties of aqueous Triton X-100
Authors: Behera Kamalakanta , Pandey Mrituanjay D. , Porel Mintu , Pandey Siddharth
Published: November 2007

Modification of important physicochemical properties of aqueous surfactant solutions can be achieved by addition of environmentally benign room temperature ionic liquids (ILs). While low aqueous solubility of “hydrophobic” ILs limits the amount of IL that may be added to achieve desired changes in the physicochemical properties, hydrophilic ILs do not have such restrictions associated to them. Alterations in the key physicochemical properties of aqueous solutions of a common nonionic surfactant Triton X-100 (TX100) on addition of up to 30wt% hydrophilic IL 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) are reported. The presence of micellar aggregates in as high as 30wt% [bmim][BF4]-added aqueous TX100 solutions is established by dynamic light scattering and fluorescence probe behavior. Increasing the concentration of [bmim][BF4] results in decrease in average micellar size and aggregation number and increase in critical micelle concentration, indicating an overall unfavorable aggregation process. Increase in the dipolarity and the microfluidity of the probe cybotactic region within the palisade layer of the micellar phase upon [bmim][BF4] addition implies increased water penetration and the possibility of TX100-[bmim][BF4] interactions. While the changes in some of the physicochemical properties indicate the role of [bmim][BF4] to be similar to a cosurfactant, the IL acts like a cosolvent as far as changes in other properties are concerned. Effectiveness of IL [bmim][BF4] in modifying physicochemical properties of aqueous TX100 is demonstrated.
Theory of damped quantum rotation in nuclear magnetic resonance spectra. II. Numerical simulations for the benzene rotor
Authors: Ratajczyk T. , Szymański S.
Published: November 2007

In Part I of this series of papers, the damped quantum rotation (DQR) theory, formulated originally for hindered threefold molecular rotors in solids, was generalized to the N-fold case. The stochastic dynamics of such objects, evidenced in NMR line shapes, was shown to be more complicated than in the standard model of classical jumps between the wells of the N-fold torsional potential. Actually, it comprises certain quantum rate (i.e., coherence-damping) processes subject to the requirements of the Pauli principle. The jump picture is recovered only when the quantum rates fit specific patterns. In this work, one of the ways of approaching such a classical limit is identified for the benzene rotor. This is inferred from a quantum mechanical model whose validity was earlier confirmed for a methyl group. Based on that model, theoretical calculations for the benzene ring dynamics in a clathrate crystal, 1-(9-anthryloxy)anthraquinone/benzene-d6, confronted with the pertinent literature data, point to possible deviations from the classical limit. However, the predicted DQR effects are too small to be observed in solid echo H2 NMR spectra of the C6D6 isotopomer. The chances of detecting the effects are improved when Carr-Purcell echo H1 spectra of a single crystal of the isotopomer including C6H6 as a guest are considered. The substantial differences in the sensitivity to the DQR effects of the spectra of protonated and deuterated benzene are concerned with different magnitudes of the intramolecular dipolar spin couplings. The dynamic isotope effect (C6D6 vs C6H6), which is small in this case, is only of secondary importance. Legitimacy of the use of the jump model in H2 NMR line shape studies of benzene-d6 is fully confirmed by the present considerations. However, the physical significance of the dynamic parameters extracted from such studies is shown from a new perspective.
Dynamics of excitation of backward waves in long inhomogeneous systems
Authors: Savilov A. V. , Bespalov P. A. , Ronald K. , Phelps A. D. R.
Published: November 2007

The spatio-temporal dynamics of excitation of a long backward-wave oscillator with a profiled resonant parameter is studied in detail. It is shown that the transition to multifrequency regimes of the rf generation occurs due to splitting the long oscillator into several shorter single-frequency oscillators with different eigenfrequencies. This fact can be useful, in particular, for an explanation of the dynamics of the intense cyclotron radiation, which is detected escaping from Earth in the kilometric wavelength range.
Fast thermal desorption spectroscopy study of H∕D isotopic exchange reaction in polycrystalline ice near its melting point
Authors: Lu Haiping , McCartney Stephanie A. , Sadtchenko Vlad
Published: November 2007

Using fast thermal desorption spectroscopy, a novel technique developed in our laboratory, we investigated the kinetics of H∕D isotopic exchange in 3μm thick polycrystalline H2O ice films containing D2O layers at thicknesses ranging from 10to300nm at a temperature of −2.0±1.5°C. According to our results over the duration of a typical fast thermal desorption experiment (3–4ms), the isotopic exchange is confined to a 50±10nm wide reaction zone located at the boundary between polycrystalline H2O and D2O ice. Combining these data with a theoretical analysis of the diffusion in polycrystalline medium, we establish the range of possible values for water self-diffusion coefficients and the grain boundary widths characteristic of our ice samples. Our analysis shows that for the grain boundary width on the order of a few nanometers, the diffusivity of D2O along the grain boundaries must be at least two orders of magnitude lower than that in bulk water at the same temperature. Based on these results, we argue that, in the limit of low concentrations of impurities, polycrystalline ice does not undergo grain boundary premelting at temperatures up to −2°C.
Ions in a binary asymmetric dipolar mixture: Mole fraction dependent Born energy of solvation and partial solvent polarization structure
Authors: Kashyap Hemant K. , Biswas Ranjit
Published: November 2007

Mean spherical approximation (MSA) for electrolyte solution has been extended to investigate the role of partial solvent polarization densities around an ion in a completely asymmetric binary dipolar mixture. The differences in solvent diameters, dipole moments, and ionic size are incorporated systematically within the MSA framework in the present theory for the first time. In addition to the contributions due to difference in dipole moments, the solvent-solvent and ion-solvent size ratios are found to significantly affect the nonideality in binary dipolar mixtures. Subsequently, the theory is used to investigate the role of ion-solvent and solvent-solvent size ratios in determining the nonideality in Born free energy of solvation of a unipositive rigid ion in alcohol-water and dimethyl sulfoxide–acetonitrile mixtures, where the solvent components are represented only by their molecular diameters and dipole moments. Nonideality in Born free energy of solvation in such simplified mixtures is found to be stronger for smaller ions. The slope of the nonideality for smaller alkali metal ions in methanol-water mixture is found to be opposite to that for larger ion, such as quaternary tertiary butyl ammonium ion. For ethanol-water mixtures, the slopes are in the same direction for all the ions studied here. These results are in qualitative agreement with experiments, which is surprising as the present MSA approach does not include the hydrogen bonding and hydrophobic interactions present in the real mixtures. The calculated partial polarization densities around a unipositive ion also show the characteristic deviation from ideality and reveal the microscopic origin of the ion and solvent size dependent preferential solvation. Also, the excess free energy of mixing (in the absence of any ion) for these binary mixtures has been calculated and a good agreement between theory and experiment has been found.
Evolution of wake structure and wake-induced loads along the path of freely rising axisymmetric bodies
Authors: Ern Patricia , Fernandes Pedro C. , Risso Frédéric , Magnaudet Jacques
Published: November 2007

This paper reports on the zigzagging motion of disks of various thicknesses rising freely under the effect of buoyancy in a liquid otherwise at rest. Time sequences of the velocity fields around the moving body were obtained using particle image velocimetry and are presented for two bodies with contrasted diameter-to-thickness ratios. The differences observed between the two cases are discussed in relation with the evolution of the loads acting on the body and of the displacement and rotation of the body during a period of the zigzag. The crucial influence of the phase difference between the vortical force and torque on the path is underlined.
Exponential spatial decay of spin-spin correlations in translation invariant quasifree states
Authors: Aschbacher Walter H. , Barbaroux Jean-Marie
Published: November 2007

We study the spatial decay of the transversal spin-spin correlations in translation invariant quasifree states on the canonical anticommutation relation algebra on the discrete line. We establish a simple criterion on the spectrum of the density of the quasifree state which ensures the decay to be exponential. Moreover, we illustrate exponential and slower decay with the example of the XY spin chain out of equilibrium, in thermal equilibrium at positive temperature, in the ground state, and in the chaotic state.
Formation and reduction of pyramidal hillocks on m-plane {11¯00} GaN
Authors: Hirai A. , Jia Z. , Schmidt M. C. , Farrell R. M. , DenBaars S. P. , Nakamura S. , Speck J. S. , Fujito K.
Published: November 2007

Surface morphology and hillock reduction were studied on m-plane {11¯00} n-type GaN films and light emitting diode structures grown by metal organic chemical vapor deposition on low defect-density m-plane GaN substrates. For nominally on-axis m-plane films, predominantly pyramidal hillocks were observed, which were composed of two faces symmetrically inclined by 0.1°–0.25° to the ±[112¯0] a direction and two faces inclined by 0.5°–0.95° to the [0001¯] c− and the [0001] c+ directions, respectively. All faces of the pyramidal hillocks for the nominally on-axis GaN films had clearly defined step-terrace structures. Gradual changes in nominal miscut angles from 0° to 10° along the a and the c− directions succeeded in a continuous hillock reduction yielding atomically flat surfaces.
Integrable lattices and their sublattices. II. From the B-quadrilateral lattice to the self-adjoint schemes on the triangular and the honeycomb lattices
Authors: Doliwa A. , Nieszporski M. , Santini P. M.
Published: November 2007

An integrable self-adjoint 7-point scheme on the triangular lattice and an integrable self-adjoint scheme on the honeycomb lattice are studied using the sublattice approach. The star-triangle relation between these systems is introduced, and the Darboux transformations for both linear problems from the Moutard transformation of the B-(Moutard) quadrilateral lattice are obtained. A geometric interpretation of the Laplace transformations of the self-adjoint 7-point scheme is given and the corresponding novel integrable discrete three-dimensional system is constructed.
Nonlinear properties of relativistically intense laser in plasmas
Authors: Qiao Bin , Lai C. H. , Zhou C. T. , He X. T. , Wang X. G. , Yu M. Y.
Published: November 2007

Nonlinear characteristics including spatial chaos and patterns associated with relativistically intense laser-plasma interaction are studied theoretically and numerically using a model relativistic nonlinear Schrödinger equation. It is shown that in the phase space irregular homoclinic orbit crossings exist. The latter are verified and investigated numerically. The spatial chaos and complex patterns of the laser wave field can be attributed to the relativistic electron mass variation as well as the ponderomotive-force driven electron-density modulation. The formation of complex patterns results from stochastic partition of energy in the Fourier modes.
Experimental study of small-amplitude lateral vibrations of an axisymmetric liquid bridge
Authors: Ferrera C. , Montanero J. M.
Published: November 2007

Optical imaging is used to measure the interface deformation due to small-amplitude lateral vibrations of an axisymmetric liquid bridge with a precision of the order of micrometers. Crucial aspects of the experimental procedure are identified. Comparison with the predictions of the Navier–Stokes equations for zero capillary number shows good agreement, even for oscillation amplitudes much smaller than the pixel size. A possible application of the experimental procedure is to measure the surface tension for zero Bond number.
Helicon wave modes, their damping and absorption in lossy plasma loaded conducting waveguide
Authors: Ganguli A. , Sahu B. B. , Tarey R. D.
Published: November 2007

Exact results are presented for the first time for the helicon (H) wave and associated Trivelpiece-Gould (TG) wave modes of a cold, uniform, lossy plasma column inside a conducting waveguide. Both Landau and collisional damping are considered. Contrary to expectation, it is found that even in cases of severe damping, the axial propagation constant is modified only marginally, and damping shows up mainly in the radial propagation constant of only one of the two waves (TG or H). A consequence of such damping is that the damped wave does not form a standing wave in the radial direction; it remains a traveling wave, decaying as it propagates inwards from the plasma surface. These traveling waves can be absorbed efficiently near the plasma surface if their radial wavelengths are short, as usually happens with the TG waves. Unlike previous work, however, where only damping of the TG waves has been reported, the present work also reports damping of H waves. An attempt has been made to understand the damping behavior of the different modes in terms of certain “reduced” dispersion relations obtained from a modified Appleton-Hartree equation derived for the present work.
Fluid theory of radial angular momentum flux of plasmas in an axisymmetric magnetic field
Authors: Wong S. K. , Chan V. S.
Published: November 2007

The fluid equations of Mikhailovskii and Tsypin have been applied to the problem of radial transport of angular momentum of plasmas in an axisymmetric magnetic field with flux surfaces of arbitrary shape [P. J. Catto and A. N. Simakov, Phys. Plasmas 12, 012501 (2005)]. In this paper, compact expressions for the radial angular momentum flux for both up down symmetric and asymmetric flux surfaces are obtained by utilizing the ratio of poloidal to toroidal magnetic fields as an additional small parameter. A systematic expansion of the fluid equations in the ratio of gyroradius over plasma and magnetic field scale length is performed, followed by a subsidiary expansion in the ratio of collisional mean free path to the scale length. A derivation of the equations of Mikhailovskii and Tsypin is also presented in a form that facilitates application to the transport problem.
Some results on the Zeeman topology
Authors: Dossena Giacomo
Published: November 2007

In a 1967 paper [E. C. Zeeman, “The topology of Minkowski space,” Topology 6, 161–170 (1967)], Zeeman proposed a new topology for Minkowski space-time, physically motivated but much more complicated than the standard one. Here a detailed study is given of some properties of the Zeeman topology which had not been considered at the time. The general setting refers to Minkowski space-time of any dimension k+1. In the special case k=1, a full characterization is obtained for the compact subsets of space-time; moreover, the first homotopy group is shown to be nontrivial.
Dirac oscillator with minimal lengths and free particle on AdS2 and S2
Authors: Sadeghi J.
Published: November 2007

We use two different types of laddering equations which are realized by the associated Gegenbauer functions. We show that the Dirac oscillator equation with minimal lengths can be written to form associated Gegenbauer functions. This leads us to write the Dirac oscillator equation in terms of first order equations. By changing some variable in two types of equations, we have some u(1,1) and u(2) algebras. These algebras correspond to AdS2 and S2. Finally, we conclude that all quantum states from the Dirac oscillator (presence of minimal lengths) correspond to the quantum states of free particle on AdS2 and S2.
Pseudodifferential operator with a nonanalytic symbol on a half-line
Authors: Kaikina Elena
Published: November 2007

We study the initial-boundary value problem for the nonlinear pseudodifferential equations with nonanalytic symbol. We study traditionally important problems of a theory of nonlinear partial differential equations, such as global in time existence of solutions to the initial-boundary value problem and the asymptotic behavior of solutions for large time.
High-resolution imaging of local oxidation in polyfluorene thin films by nonlinear near-field microscopy
Authors: Biagioni P. , Celebrano M. , Zavelani-Rossi M. , Polli D. , Labardi M. , Lanzani G. , Cerullo G. , Finazzi M. , Duò L.
Published: November 2007

The authors demonstrate nonlinear near-field two-photon photoluminescence imaging of organic semiconductors by coupling femtosecond light pulses to a scanning near-field optical microscope (SNOM) based on hollow-pyramid cantilevered probes. Two-photon excitation of the blue-emitting poly(9,9-dioctylfluorene) (PFO) is found to selectively address keto-defect units, which are responsible for a shifted green-orange emission. This effect is exploited to map oxidized sites in PFO thin films with high contrast and spatial resolution, introducing nonlinear SNOM as an effective technique to characterize oxygen-induced degradation in electroluminescent materials.
Tunneling spectroscopy of the Heusler compound Co2Cr0.6Fe0.1Al
Authors: Jourdan M. , Conca A. , Herbort C. , Kallmayer M. , Elmers H. J. , Adrian H.
Published: November 2007

The bias voltage and magnetization direction dependent differential conductivity dI∕dV(Vbias) of tunneling junctions with the Heusler compound Co2Cr0.6Fe0.4Al (CCFA) was investigated. The junctions contain AlOx tunneling barriers and Co counter electrodes. A pronounced shoulder in the differential conductivity with parallel electrode magnetization and a sign change of the tunneling magnetoresistance at a bias voltage of ≃±500 mV were the most prominent features observed. The measurements are discussed in the framework of band structure related effects and inelastic excitations. X-ray absorption spectroscopy (XAS-TEY) investigations show that the CCFA/Al interface has an increased Fe content compared to the sputter target composition, presumably due to Fe buffer layer interdiffusion.
Electromigration behavior of 60 nm dual damascene Cu interconnects
Authors: Pyun Jung Woo , Baek Won-Chong , Zhang Lijuan , Im Jay , Ho Paul S. , Smith Larry , Smith Gregory
Published: November 2007

Electromigration (EM) reliability was investigated for Cu fine lines fabricated using a SiON trench filling process down to 60 nm in linewidth. EM was observed to be dominated by intrinsic failures due to void formation in the line trench. The lifetimes of 60 nm lines were longer than those of 125 nm lines with the standard damascene structure which can be attributed to a distinct via/metal-1 configuration with less process-induced defects at the via interface. The line scaling effect on EM reliability was investigated using three linewidths: 60, 110, and 185 nm. EM lifetimes were found to be similar for different linewidths, consistent with intrinsic failures caused by void formation in the line trench driven by interfacial mass transport. Statistical, multilinked EM test structures demonstrated a monomodal failure distribution for the fine lines, indicating suppression of processing-induced extrinsic defects although processing control on line dimension and geometry remained an issue. The activation energies were found to be around 0.80 eV for both fine lines and standard lines, indicating that interface diffusion dominates mass transport in Cu lines.
Numerical modeling study of the unipolar accumulation transistor
Authors: Fonash Stephen J. , Iqbal Md Mash-hud , Udrea Florin , Migliorato Piero
Published: November 2007

A unipolar accumulation transistor configuration has recently been proposed and experimentally demonstrated. This transistor has a simple structure with Ohmic contacts and only one doping type. The device, termed the accumulation metal oxide semiconductor field effect transistor (AMOSFET), relies on having a nanoscale depth dimension, which forces the current through an accumulated (on state) or depleted (off state) region. Detailed numerical modeling presented here elucidates the previously proposed and experimentally observed AMOSFET features. These include linear and saturation currents which depend on doping rather than gate capacitance, good subthreshold swing behavior, and low threshold voltages. This modeling predicts on-off ratios exceeding 109.
Vacancy-arsenic clusters in germanium
Authors: Chroneos A. , Grimes R. W. , Uberuaga B. P. , Brotzmann S. , Bracht H.
Published: November 2007

Electronic structure calculations are used to investigate the structures and relative energies of defect clusters formed between arsenic atoms and lattice vacancies in germanium and, for comparison, in silicon. It is energetically favorable to form clusters containing up to four arsenic atoms tetrahedrally coordinated around a vacancy. Using mass action analysis, the relative concentrations of arsenic atoms in different vacancy-arsenic clusters, unbound arsenic atoms, and unbound vacancies are predicted. At low temperatures the four arsenic-vacancy cluster is dominant over unbound vacancies while at higher temperatures unbound vacancies prevail. In terms of concentration, no intermediate size of cluster is ever of significance.
Damage-free electrodes fabrication for top emitting organic light emitting diodes by transfer fabrication
Authors: Seo Soon-Min , Jang Chang-Hyun
Published: November 2007

We report a simple procedure for the integration of the top emitting organic light emitting diode (TOLED), which permits minimum defects at the interface between a top metal electrode and an organic film. This method relies on the transfer of patterned metal electrodes to an organic substrate with a relatively high adhesive property. TOLED, integrated by the transfer fabrication, demonstrates better performance, a reduction of turn-on voltage and an increase of maximum current efficiency, in comparison with fabricated devices by conventional shadow mask method.
Self-separated freestanding GaN using a NH4Cl interlayer
Authors: Lee Hyun-Jae , Lee S. W. , Goto H. , Lee Sang-Hyun , Lee Hyo-Jong , Ha J. S. , Goto Takenari , Cho M. W. , Yao T. , Hong Soon-Ku
Published: November 2007

Thick GaN films were grown on void buffer layer by hydride vapor phase epitaxy. The void-buffer layers were consisted of NH4Cl, GaN dots, and low-temperature (LT) GaN buffer layer. Instead of GaN, NH4Cl was easily synthesized in NH3 and HCl atmospheres by simply lowering the growth temperature to 500°C, and LT GaN buffer growth was followed during increasing substrate temperature to 600°C. The LT GaN buffer acted as a protecting layer against evaporation of the NH4Cl and a seeding layer for the high temperature (HT) GaN. The NH4Cl layer between a sapphire substrate with GaN dots and the LT GaN buffer were fully evaporated during the HT GaN growth at 1040°C. Many voids were formed at interface caused by evaporation of the NH4Cl layer, which strongly assisted self-separation of thick HT GaN during cooldown after the growth resulting in a 200μm thick freestanding (FS) GaN. The FS GaN showed smooth surface morphology and absence of any crack. The a-axis and c-axis lattice constants of FS GaN were 3.189 and 5.185Å, respectively, which well agrees with those of strain-free bulk GaN. The observed donor-bound exciton emission peak at 3.4718eV agreed with the peak position of bulk GaN. All these features indicate that the obtained FS GaN through the self-separation process is nearly strain-free.
Nondestructive electrical characterization of integrated interconnect line-to-line spacing for advanced semiconductor chips
Authors: Chen Fen , McLaughlin Paul S. , Chanda Kaushik
Published: November 2007

Poor process controls may cause huge line spacing variation across a semiconductor wafer during back-end-of-the-line integration in advanced semiconductor integrated circuit fabrication. As a consequence, significant degradation in yield, performance, and reliability may be observed. Line spacing variation also imposes challenges for accurate time dependent dielectric breakdown reliability lifetime projection. In this paper, a nondestructive, fast electrical method for determining a line-to-line spacing of a semiconductor chip is proposed. The method includes experimentally determining a slope from capacitance measurement (kCA), experimentally determining a slope from current-voltage measurement (kSE), and finally determining a line-to-line spacing from the slope kCA and the slope kSE. The line-to-line spacing determined from this method shows an excellent agreement with constructional analysis data.
Rational synthesis and tunable optical properties of quasialigned Zn1−xMgxO nanorods
Authors: Lu J. G. , Zhang Y. Z. , Ye Z. Z. , Zeng Y. J. , Huang J. Y. , Wang L.
Published: November 2007

Quasialigned, single-crystal Zn1−xMgxO (x=0–0.32) nanorods were synthesized on Si substrates by thermal evaporation. Zn1−xMgxO nanorods grew along the [0001] crystal direction and had uniform hexagonal planes with diameters of 420–120nm. The predominant ultraviolet luminescence could be tuned from 379 (x=0) to 305nm (x=0.32) at room temperature. This blueshift indicated the band gap engineering in Zn1−xMgxO nanorods. Temperature-dependent photoluminescence was used to illustrate the free-exciton emission from Zn1−xMgxO nanorods. The exciton binding energy decreased from 59 (x=0) to 49meV (x=0.18) and then increased to 54meV (x=0.32).
Two-photon photocurrent spectroscopy of electron intersubband relaxation and dephasing in quantum wells
Authors: Schneider Harald , Maier Thomas , Walther Martin , Liu H. C.
Published: November 2007

Resonantly enhanced nonlinear absorption between conduction subbands in InGaAs∕AlGaAs quantum wells induces a two-photon photocurrent under femtosecond excitation, which is exploited to determine electron intersubband relaxation and dephasing times. The approach allows us to study systematically the dependence of these time constants on structural parameters, including carrier density and modulation/well doping, and to discriminate between different scattering processes.
Negative spin polarization in (La,Sr)CoO3 probed by a magnetic tunnel junction with (La,Sr)MnO3
Authors: Ishii Y. , Yamada H. , Sato H. , Akoh H. , Kawasaki M. , Tokura Y.
Published: November 2007

By using perovskite (La,Sr)MnO3 (LSMO)-based magnetic tunnel junctions with LaAlO3 barrier, we have experimentally revealed the spin state of (La,Sr)CoO3 (LSCO) that was employed as the counterelectrode of the junctions. Inverse tunnel magnetoresistance (TMR) up to −14% was observed at 10K in low-bias measurement. This indicates that t2g↓ electrons are the majority at the Fermi level in the LSCO band structure, taking into account the half-metallic character of LSMO. The temperature dependence of the interfacial spin polarization of LSCO as deduced from the TMR ratio indicates the reduction of the Curie temperature at the interface by 70K. The TMR ratio exhibits an asymmetric bias dependence in qualitative agreement with the calculated spin band structure of LSCO.
Huge magnetoresistive effects using space charge limited current in ZnO∕SiO2 system
Authors: Miyanishi Shintaro , Yagura Motoji , Teraguchi Nobuaki , Shirakawa Kazuhiko , Sakuno Keiichi , Murakami Yoshiteru , Kojima Kunio , Takahashi Akira , Ohta Kenji
Published: November 2007

Huge magnetoresistive effects were observed in a metal/insulator current-in-plane (CIP) diode feeding space charge limited (SCL) current. The insulator laterally toward opposite gold (Au) electrodes was fabricated on a SiO2 substrate by the standard photolithography method using dry etching. The insulator consisted of a SiO2∕ZnO∕SiO2∕ZnO multilayer sputtered on the substrate. Current-voltage curves showed Ohmic property and SCL current characteristics accompanied by Child-Langmuir and Mott-Gurney laws derived from first order differential calculus. Current-magnetic field curves indicated the huge magnetoresistive effects up to 1010% under the magnetic field of 0.3T at room temperature. The current-magnetic field curves have even symmetry for the applied magnetic field. The Au/insulator CIP diode is abruptly switched between a conducting state and an insulating state by the applied magnetic field.
Elastic properties of Fe–Mn random alloys studied by ab initio calculations
Authors: Music Denis , Takahashi Tetsuya , Vitos Levente , Asker Christian , Abrikosov Igor A. , Schneider Jochen M.
Published: November 2007

We have studied the influence of the Mn content on the elastic properties of Fe–Mn random alloys (space group of Fm3¯m) using ab initio calculations. The magnetic effects in Fe–Mn alloys have a strong influence on the elastic properties, even above the Néel temperature. As the Mn content is increased from 5to40at.%, the C44 elastic constant is unaffected, while C11 and C12 decrease. This behavior can be understood based on the magnetovolume effect which softens the lattice. Since the amplitude of local magnetic moments is less sensitive to volume conserving distortions, the softening is not present during shearing.
Growth of a-plane GaN on lattice-matched ZnO substrates using a room-temperature buffer layer
Authors: Kobayashi Atsushi , Kawano Satoshi , Ueno Kohei , Ohta Jitsuo , Fujioka Hiroshi , Amanai Hidetaka , Nagao Satoru , Horie Hideyoshi
Published: November 2007

Nonpolar a-plane GaN films were grown on nearly lattice-matched a-plane ZnO substrates by pulsed laser deposition. Growth of GaN on a-plane ZnO at conventional growth temperatures (around 700°C) resulted in the formation of polycrystalline materials, probably due to the interface reactions between GaN and ZnO. However, single crystalline a-plane GaN with an atomically flat surface can be grown on ZnO at room temperature in the layer-by-layer mode. X-ray diffraction and photoluminescence measurements revealed that high-quality a-plane GaN films can also be grown at elevated substrate temperatures (up to 700°C) by using a RT a-plane GaN film as a buffer layer.
Discontinuous temperature-dependent macroscopic strain due to ferroelastic domain switching and structural phase transitions in barium strontium titanate
Authors: Wang Can , Aguado Fernando , Redfern Simon A. T.
Published: November 2007

Remnant strain has been measured as a function of temperature in (Ba0.8Sr0.2)TiO3 (BST) ceramic by mechanical poling in three point bending configuration. BST ceramic exhibits recoverable macroscopic strain with shape memory effect and three jumps in the temperature-dependent strain during thermal cycling under applied force. The jumps are associated with the three structural phase transitions of BST, as confirmed by the simultaneous measurements of dynamic modulus and internal friction. In addition, the orthorhombic phase of BST exhibits a significantly higher strain comparing to that in the tetragonal and rhombohedral phases. X-ray diffraction confirms that the macroscopic strain is due to ferroelastic domain switching and particularly the dominant contribution to the higher macroscopic strain at orthorhombic phase is the higher probability of non-180° domain switching rather than the variation of domain switching strain at different phases.
Electrically tunable photonic crystals with nonlinear composite materials
Authors: Wang G. , Huang J. P. , Yu K. W.
Published: November 2007

Based on nonlinear composite materials, we exploit theoretically a class of electrically tunable one-dimensional double-layer photonic crystals (PCs), namely, composite-dielectric and composite-composite PCs. For such PCs, extensive and precise tunability of photonic band gaps can be readily achieved by choosing appropriate pump ac or dc electric fields.