bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantity‐activity relationship of denitrifying bacteria and environmental scaling in streams of a forested watershed
Authors: O'Connor Ben L. , Hondzo Miki , Dobraca Dina , LaPara Timothy M. , Finlay Jacques C. , Brezonik Patrick L.
Published: November 2006

The spatial variability of subreach denitrification rates in streams was evaluated with respect to controlling environmental conditions, molecular examination of denitrifying bacteria, and dimensional analysis. Denitrification activities ranged from 0 and 800 ng‐N gsed−1d−1with large variations observed within short distances (<50 m) along stream reaches. A log‐normal probability distribution described the range in denitrification activities and was used to define low (16% of the probability distribution), medium (68%), and high (16%) denitrification potential groups. Denitrifying bacteria were quantified using a competitive polymerase chain reaction (cPCR) technique that amplified thenirKgene that encodes for nitrite reductase. Results showed a range ofnirKquantities from 103to 107gene‐copy‐number gsed−1. A nonparametric statistical test showed no significant difference innirKquantities among stream reaches, but revealed that samples with a high denitrification potential had significantly highernirKquantities. Denitrification activity was positively correlated withnirKquantities with scatter in the data that can be attributed to varying environmental conditions along stream reaches. Dimensional analysis was used to evaluate denitrification activities according to environmental variables that describe fluid‐flow properties, nitrate and organic material quantities, and dissolved oxygen flux. Buckingham's pi theorem was used to generate dimensionless groupings and field data were used to determine scaling parameters. The resulting expressions between dimensionless NO3−flux and dimensionless groupings of environmental variables showed consistent scaling, which indicates that the subreach variability in denitrification rates can be predicted by the controlling physical, chemical, and microbiological conditions.
Interactions between environmental change and shallow water carbonate buildup along the northern Tethyan margin and their impact on the Early Cretaceous carbon isotope record
Authors: Föllmi Karl B. , Godet Alexis , Bodin Stephane , Linder Pascal
Published: November 2006

The evolution of the Early Cretaceous, northern Tethyan carbonate platform was not only influenced by changes in sea level, detrital influx, and surface water temperature but also by changes in trophic levels. We distinguish between phases of carbonate production dominated by oligotrophic photozoan communities and by mesotrophic and eventually colder‐water heterozoan communities. Superimposed on this bimodal trend in platform evolution were phases of platform demise for which we provide improved age control based on ammonite biostratigraphy. The initial phase of these episodes of platform demise corresponds in time to episodes of oceanic anoxic events and environmental change in general. On the basis of a comparison between the temporal changes in an Early Cretaceous, ammonite‐calibratedδ13C record from southeastern France and coeval changes in the platform record, we suggest that the history of carbon fractionation along the northern Tethyan margin was not only influenced by changes in the oceanic carbon cycle such as in the rate of production and preservation of organic and carbonate carbon and in the size of the oceanic dissolved inorganic carbon reservoir, but it was also influenced by the above‐mentioned changes in the ecology and geometry of the adjacent carbonate platform. Phases of photozoan carbonate production induced positive trends in the hemipelagic carbonateδ13C record. Phases of heterozoan carbonate production pushed theδ13C system toward more negative values. Platform drowning episodes implied an initial increase inδ13C values, followed by a longer‐term decrease inδ13C values.
Computer simulation of enhanced backscattering from randomly distributed spherical scatterers at 30 GHz and comparison with measurement
Authors: Oguchi Tomohiro , Ihara Toshio
Published: November 2006

This paper presents a computer simulation of backscattering enhancement from randomly distributed spherical water scatterers at 30 GHz, corresponding to laboratory measurements. Because of the finiteness in the scattering volume size, we adopt a very simple direct simulation method, together with a sampling of the scattering paths for triple scattering and higher to minimize computer time. The spherical wavefront and the directivity functions of transmitting and receiving antennas are taken into account. The simulation results agree favorably with measurements. Some of the knowledge on the detailed characteristics of enhanced backscattering is also obtained.
Enhancement of wind erosion by fire‐induced water repellency
Authors: Ravi Sujith , D'Odorico Paolo , Herbert Bruce , Zobeck Ted , Over Thomas M.
Published: November 2006

The occurrence of fire and the subsequent increase in wind erosion are known to affect vegetation dynamics in dryland landscapes. Fires act as a disturbance on shrubs and trees and expose the soil surface to the erosive action of wind, thereby affecting the loss and redistribution of soil nutrients. Despite the relevance of wind erosion and fires to the dynamics of arid ecosystems, the interactions between these two processes remain poorly understood. We have investigated how a representative water repellent organic compound released by burning biomass and absorbed in the soil may enhance soil erodibility. To this end, we carried out a series of wind tunnel experiments, laboratory tests, and theoretical analyses to assess the effect of fire‐induced water repellency on the soil susceptibility to wind erosion. The experiments were carried out using clean, well‐sorted sand which was artificially coated with palmitic acid, a common water repellency inducing fatty acid found in most plants. The results indicate that fire‐induced water repellency enhances soil erodibility, causing a drop in wind erosion threshold velocity. The results are explained by the effect of water repellent compounds on soil‐water contact angle and on the strength of interparticle wet‐bonding forces.
PharmGKB: Capturing knowledge to catalyze pharmacogenomics research
Authors: Altman Russ
Published: November 2006

This is a powerpoint presentation made initially at the Cold Spring Harbor meeting on Pharmacogenomics, November 2006. It discusses the PharmGKB (http://www.pharmgkb.org/) and how we are building a pipeline for annotation of knowledge. In particular, we are focusing on pathway knowledge, "Very important Pharmacogene" annotations, and curation of the pharmacogenomics literature. We are building an ontology-based system to capture and aggregate knowledge, for use by our curators.
Detection of the Ischemic Penumbra Using pH-Weighted MRI
Authors: Sun Phillip Zhe , Zhou Jinyuan , Sun Weiyun , Huang Judy , van Zijl Peter CM
Published: November 2006

The classic definition of the ischemic penumbra is a hypoperfused region in which metabolism is impaired, but still sufficient to maintain cellular polarization. Perfusion- and diffusion-weighted MRI (PWI, DWI) can identify regions of reduced perfusion and cellular depolarization, respectively, but it often remains unclear whether a PWI—DWI mismatch corresponds to benign oligemia or a true penumbra. We hypothesized that pH-weighted MRI (pHWI) can subdivide the PWI—DWI mismatch into these regions. Twenty-one rats underwent permanent middle cerebral artery occlusion and ischemic evolution over the first 3.5 h post-occlusion was studied using multiparametric MRI. End point was the stroke area defined by T2-hyperintensity at 24 h. In the acute phase, areas of reduced pH were always larger than or equal to DWI deficits and smaller than or equal to PWI deficits. Group analysis showed that pHWI deficits during this phase coincided with the resulting infarct area at endpoint. Final infarcts were smaller than PWI deficits (range 65% to 90%, depending on the severity of the occlusion) and much larger than acute DWI deficits. These data suggest that the outer boundary of the hypoperfused area showing a decrease in pH without DWI abnormality may correspond to the outer boundary of the ischemic penumbra, while the hypoperfused region at normal pH may correspond to benign oligemia. These first results show that pHWI can provide information complementary to PWI and DWI in the delineation of ischemic tissue.
The Pierce-diode approximation to the single-emitter plasma diode
Authors: Ender A. Ya. , Kuhn S. , Kuznetsov V. I.
Published: November 2006

The possibility of modeling fast processes in the collisionless single-emitter plasma diode (Knudsen diode with surface ionization, KDSI) by means of the Pierce-diode is studied. The KDSI is of practical importance in that it is an almost exact model of thermionic energy converters (TICs) in the collisionless regime and can also be used to model low-density Q-machines. At high temperatures, the Knudsen TIC comes close to the efficiency of the Carnot cycle and hence is the most promising converter of thermal to electric energy. TICs can be applied as component parts in high-temperature electronics. It is shown that normalizations must be chosen appropriately in order to compare the plasma characteristics of the two models: the KDSI and the Pierce-diode. A linear eigenmode theory of the KDSI is developed. For both nonlinear time-independent states and linear eigenmodes without electron reflection, excellent agreement is found between the analytical potential distributions for the Pierce-diode and the corresponding numerical ones for the KDSI. For the states with electron reflection, the agreement is satisfactory in a qualitative sense. A full classification of states of both diodes for the regimes with and without electron reflection is presented. The effect of the thermal spread in electron velocities on the potential distributions and the (ε,η) diagrams is analyzed. Generally speaking, the methodology developed is usefully applicable to a variety of systems in which the electrons have beam-like distributions.
Observers, observables, spinors, and the confusion of tongues
Authors: Miralles David , Pozo José M.
Published: November 2006

Choquet-Bruhat was the first to give a proper physical definition of covariant spinors, taking into account the reference system and treating them as equivalence classes defined from the transformation laws of the representatives when the reference system is changed. Recently, Rodriguez et al.[ Int. J. Theor. Phys. 35, 1849 (1996)] have adapted this procedure from covariant spinors to the case of algebraic and operator spinors. These approaches are restrained in the sense that the type of spinor is chosen from the beginning, and it does not admit a general formulation. In this paper, we present a unified definition that is valid for any type of the space of representation, being independent of its particular properties. In our formulation the three types of spinors appear as particular cases of the general definition. Moreover, we stick out the importance of the bilinear covariants in the definition of spinors. From this, we recognize a completely different kind of spinor, characterized by the different nature of their bilinears. The unnoticed difference between this last one, which we have called right-operator spinors, and the previous (left-)operator spinors has been motive of a long time discussion.
The interface effect of carbon nanotube suspension on the thermal performance of a two-phase closed thermosyphon
Authors: Xue H. S. , Fan J. R. , Hu Y. C. , Hong R. H. , Cen K. F.
Published: November 2006

An aqueous solution of carbon nanotubes, treated by a concentrated nitric/sulfuric acid mixture to disentangle the nanotubes, was utilized as the working medium in a two-phase closed thermosyphon to investigate its performance. In comparison with the thermosyphon filled with a distilled water medium, the one filled with carbon nanotube suspension has a high evaporation section wall temperature, incipience temperature, and excursion, as well as thermal resistance. The carbon nantotubes’ nanofluid deteriorates the performance of the gravity-assisted heat pipe. Measurements employing the maximum bubble pressure method demonstrate that suspending carbon nanotubes in bulk water gives rise to increased surface tension. In addition, the contact angle of suspension obtained with the sessile drop method on a copper plate is much smaller than that of water. Alterations of solid-liquid-vapor interfacial properties, arising from the addition of carbon nanotubes, change the boiling mechanism and thus deteriorate the boiling heat transfer.
Ionization and double ionization of small water clusters
Authors: Müller Imke B. , Cederbaum Lorenz S.
Published: November 2006

The valence ionization and double ionization spectra of the water molecule, of the water dimer, and the cyclic water clusters (H2O)3 and (H2O)4 are calculated by ab initio Green’s function methods and discussed in some detail. Particular attention is paid to the analysis of the development of the spectra with increasing cluster size. Electronic decay following inner valence ionization is addressed and a crude estimate for the kinetic energy spectrum of the secondary electrons is given for the clusters.
Intramolecular energy transfer in heteroleptic red phosphorescent dopants
Authors: Lee Jun Yeob
Published: November 2006

Intramolecular energy transfer in heteroleptic red phosphorescent dopant materials with mixed ligand units in one molecule was studied. 1-phenylisoquinoline (piq) and phenylpyridine (ppy) moieties were introduced as ligands for Ir based phosphorescent dopants and light emission mechanism was investigated. Intramolecular energy transfer from ppy ligand to piq ligand resulted in pure red emission without any green emission from ppy. Current efficiency of red devices was improved from 4to4.8cd∕A by using mixed ligand structures.
Monochromator beamline for FLASH
Authors: Martins M. , Wellhöfer M. , Hoeft J. T. , Wurth W. , Feldhaus J. , Follath R.
Published: November 2006

The design of a high resolution monochromator for the vacuum ultraviolet free electron laser at Hamburg (FLASH), DESY, is described. The monochromator is constructed as a plane grating monochromator using collimated light. Modifications have been made to take into account the free electron laser (FEL) beam characteristics, in particular, the extremely high peak power density of the radiation. Ray tracing simulations yield a resolving power in the range of 10 000–70 000 depending on the photon energy and the grating in use. Our monochromator is equipped with a 200line∕mm grating for the energy range of 20–200eV—the operation regime of FLASH—and a high resolution 1200line∕mm grating for the energy range of 100–600eV, covering the higher harmonic radiation of the FEL.
Spectroscopy of GaAs∕AlGaAs quantum-cascade lasers using hydrostatic pressure
Authors: Jin S. R. , Ahmad C. N. , Sweeney S. J. , Adams A. R. , Murdin B. N. , Page H. , Marcadet X. , Sirtori C. , Tomić S.
Published: November 2006

The authors have measured the output spectrum and the threshold current in 9.2μm wavelength GaAs∕Al0.45Ga0.55As quantum-cascade lasers at 115K as a function of hydrostatic pressure up to 7.3kbars. By extrapolation back to ambient pressure, thermally activated escape of electrons from the upper lasing state up to delocalized states of the Γ valley is shown to be an important contribution to the threshold current. On the other hand leakage into the X valley, although it has a very high density of states and is nearly degenerate with the Γ band edge in the barrier, is insignificant at ambient pressure.
Magnetostatic waves in layered materials and devices
Authors: Khalili Amiri Pedram , Rejaei Behzad
Published: November 2006

Magnetostatic wave propagation in multilayers of ferro-/ferrimagnetic and nonmagnetic, dielectric slabs is investigated using an effective medium theory and the transfer matrix method. The propagation in multilayers with antiparallel directions of magnetization is analyzed, in particular. Antiparallel multilayers support (overall) bulk waves at frequencies much higher than single layers or parallel-magnetization structures. As possible applications of these multilayers, waveguides and resonators are proposed and discussed.
Microstructure of epitaxial lateral overgrown AlN on trench-patterned AlN template by high-temperature metal-organic vapor phase epitaxy
Authors: Imura M. , Nakano K. , Kitano T. , Fujimoto N. , Narita G. , Okada N. , Balakrishnan K. , Iwaya M. , Kamiyama S. , Amano H. , Akasaki I. , Shimono K. , Noro T. , Takagi T. , Bandoh A.
Published: November 2006

A high-quality thick AlN layer without cracks was grown on sapphire by the combination of the high-temperature metal-organic vapor phase epitaxial growth and epitaxial lateral overgrowth methods. The dislocation behavior and growth mode of AlN are investigated in detail. The dislocation density of the AlN layer thus grown was less than 107cm−2.
Starlike dendrimers in solutions: Structural properties and internal dynamics
Authors: Rathgeber Silke , Monkenbusch Michael , Hedrick James L. , Trollsås Mikael , Gast Alice P.
Published: November 2006

We measured the shape and the internal dynamics of starlike dendrimers under good solvent conditions with small-angle neutron scattering and neutron spin-echo (NSE) spectroscopy, respectively. Architectural parameters such as the spacer length and generation were varied in a systematic manner. Structural changes occurring in the dendrimers as a function of these parameters are discussed, i.e., in terms of the fractal dimension and deviations of the radius of gyration from the Gaussian value. A first cumulant evaluation of the NSE spectra for each scattering vector q separately yields the length scale dependent relaxation rates. We observe a local minimum in the normalized relaxation rates Ω(q)∕q3 on length scales corresponding to the overall dendrimer dimension. The dynamics is discussed within a Rouse-Zimm approach generalized to the case of starlike dendrimers of arbitrary geometry. The model allows an identification of the modes contributing to the relaxation of the dendrimer in the q and time range of the NSE experiment. The local minimum is due to collective breathing motions of (parts of) the dendrons relative to each other. Shape fluctuations are not observed.
Direct observation of the evolution of occupied and unoccupied energy levels of two silole derivatives at their interfaces with magnesium
Authors: Watkins N. J. , Mäkinen A. J. , Gao Y. , Uchida M. , Kafafi Z. H.
Published: November 2006

The electronic structures of 2,5-bis(6′-(2′,2″-bipyridyl))-1,1-dimethyl-3,4-diphenyl silacyclopentadiene (PyPySPyPy) and 2,5-di-(3-biphenyl)-1,1-dimethyl-3,4-diphenyl silacyclopentadiene (PPSPP) at their interfaces with Mg were investigated using ultraviolet, inverse, and x-ray photoemission spectroscopies. PyPySPyPy and PPSPP have been used as both electron injection/transport layers and emitters in high-efficiency organic light-emitting diodes (OLEDs). Deposition of either PyPySPyPy or PPSPP onto Mg results in the appearance of two energy levels within the energy gap of the organic. Upon deposition of Mg onto PyPySPyPy there is a shift of the occupied energy level structure to higher binding energy, away from the Fermi level, and appearance of two energy levels within the energy gap of PyPySPyPy. The lowest unoccupied molecular orbital is also shifted to higher binding energy. Upon deposition of Mg onto PPSPP there is also a rigid shift of the occupied energy level structure to higher binding energy, away from the Fermi level, but there are no apparent energy levels created within the energy gap of PPSPP. The different chemical reactivity of the two silole derivatives with magnesium is shown to have pronounced effects on the formation of cathode contacts in OLED structures.
Electro-optical modulation for a boron nitride nanotube probed by first-principles calculations
Authors: Chen Chun-Wei , Lee Ming-Hsien , Lin Yu-Ting
Published: November 2006

The electro-optical modulation effect of a (10,0) boron nitride nanotube is investigated by first-principles, density functional theory calculations. The optical properties of boron nitride nanotubes can be tuned through perturbation by a transverse electric field. Large optical anisotropy in variations of the absorption spectra and refractive indices in response to external electric field is found. In addition, a method called the band-resolved absorption density analysis technique is developed to investigate the detailed optical absorption transition processes. The result is consistent with the recent experimental observation [M. Ishigami et al., Phys. Rev. Lett. 94, 56804 (2005)] and suggests that the boron nitride nanotubes can be a promising material for electro-optical modulation device applications.
Characterization of multipoint diffraction strain and tilt sensor based on moiré interferometer and multichannel imaging position-sensitive detector
Authors: Iqbal Salman , Asundi Anand
Published: November 2006

A multipoint diffraction strain and tilt sensor using a multichannel imaging position-sensitive detector has been developed and characterized, with the novel feature of simultaneous measurement of strain and tilt at a large array of points. Unlike conventional interferometry based systems, this new whole-field measurement system uses principles of diffraction to directly measure strain at the desired points. The system utilizes a moiré interferometer for the generation of two coherent and symmetric beams, which illuminate a high-frequency diffraction grating, bonded on the surface of the sample under test. The core of the system is a charge coupled device camera fitted with an array of microlenses, which samples the diffracted beam into an array of beamlets. The camera with lens array, which is being used as array-type multichannel position-sensitive detectors, senses the shift of the individual microspots. The deviation is then processed and the normal and shear strains are calculated at that spot along with rigid-body tilt. The combined results are graphically shown to the user as two-dimensional strain and tilt maps. Simultaneous strain measurement at more than 1300 points has been successfully obtained with the spatial resolution of better than 150μm. This novel technique has many useful features compared to other whole-field optical strain measurement techniques and is expected to be very valuable in experimental mechanics of microsystems and devices.
A novel method for measuring the bending rigidity of model lipid membranes by simulating tethers
Authors: Harmandaris Vagelis A. , Deserno Markus
Published: November 2006

The tensile force along a cylindrical lipid bilayer tube is proportional to the membrane’s bending modulus and inversely proportional to the tube radius. We show that this relation, which is experimentally exploited to measure bending rigidities, can be applied with even greater ease in computer simulations. Using a coarse-grained bilayer model we efficiently obtain bending rigidities that compare very well with complementary measurements based on an analysis of thermal undulation modes. We furthermore illustrate that no deviations from simple quadratic continuum theory occur up to a radius of curvature comparable to the bilayer thickness.
Thermosensitive core-shell particles as model systems for studying the flow behavior of concentrated colloidal dispersions
Authors: Crassous J. J. , Siebenbürger M. , Ballauff M. , Drechsler M. , Henrich O. , Fuchs M.
Published: November 2006

We report on a comprehensive investigation of the flow behavior of colloidal thermosensitive core-shell particles at high densities. The particles consist of a solid core of poly(styrene) onto which a network of cross-linked poly(N-isopropylacrylamide) is affixed. Immersed in water the shell of these particles will swell if the temperature is low. Raising the temperature above 32°C leads to a volume transition within this shell which leads to a marked shrinking of the shell. The particles have well-defined core-shell structure and a narrow size distribution. The remaining electrostatic interactions due to a small number of charges affixed to the core particles can be screened by adding 0.05M KCl to the suspensions. Below the lower critical solution temperature at 32°C the particles are purely repulsive. Above this transition, a thermoreversible coagulation takes place. Lowering the temperature again leads to full dissociation of the aggregates formed by this process. The particles crystallize for effective volume fractions between 0.48 and 0.55. The crystallites can be molten by shear in order to reach a fluid sample again. The reduced shear stress measured in this metastable disordered state was found to be a unique function of the shear rate and the effective volume fraction. These reduced flow curves thus obtained can be described quantitatively by the theory of Fuchs and Cates [Phys. Rev. Lett. 89, 248304 (2002)] which is based on the mode-coupling theory of the glass transition.
Domain patterning thin crystalline ferroelectric film with focused ion beam for nonlinear photonic integrated circuits
Authors: Li Xijun , Terabe Kazuya , Hatano Hideki , Zeng Huarong , Kitamura Kenji
Published: November 2006

Domain patterning thin ferroelectric films creates nonlinear optical devices. Unfortunately, pinholes cause conventional electrical domain-poling methods to short circuit when used on thin film. We have applied a focused ion beam (FIB) to pattern the ferroelectric domains of LiNbO3 single crystalline films with thicknesses of 800nm–2μm. FIB can fabricate domains 100 times faster than a scanning probe microscope and can be applied to irregular surface structures. Furthermore, FIB is compatible with semiconductor device processing techniques, which paves the way for monolithic nonlinear photonic integrated circuits in ferroelectrics.
On the structure of (2+1)-dimensional commutative and noncommutative integrable equations
Authors: Wang Jing Ping
Published: November 2006

We develop the symbolic representation method to derive the hierarchies of (2+1)-dimensional integrable equations from the scalar Lax operators and to study their properties globally. The method applies to both commutative and noncommutative cases in the sense that the dependent variable takes its values in C or a noncommutative associative algebra. We prove that these hierarchies are indeed quasi-local in the commutative case as conjectured by Mikhailov and Yamilov [J. Phys. A 31, 6707 (1998)]. We propose a ring extension in the noncommutative case based on the symbolic representation. As examples, we give noncommutative versions of Kadomtsev-Petviashvili (KP), modified Kadomtsev-Petviashvili (mKP), and Boussinesq equations.
Perturbative analysis of the tearing mode saturation
Authors: Militello F. , Hastie R. J. , Porcelli F.
Published: November 2006

The saturation of the tearing mode in a plasma column is investigated in the framework of the resistive magnetohydrodynamics approximation. In particular, a perturbative procedure is adopted to evaluate the structure of the magnetic island in three relevant physical conditions, depending on the model for the evolution of the resistivity, which may be affected by the growth of the mode. In cylindrical geometry, which is well suited to describe a large-aspect-ratio, low-beta tokamak plasma, the magnetic island is asymmetric with respect to the magnetic surface where reconnection occurs. New relations for the saturated island width ws as a function of the relevant features of the equilibrium current density profile, i.e., its gradient and curvature at the reconnecting surface, are obtained. Finally, equivalent relations are also derived in the slab limit.
Helix formation in linear achiral dendronized polymers: A computer simulation study
Authors: Christopoulos D. K. , Terzis A. F. , Vanakaras A. G. , Photinos D. J.
Published: November 2006

We present a molecular simulation study of the structure of linear dendronized polymers. We use excluded volume interactions in the context of a generic coarse grained molecular model whose geometrical parameters are tuned to represent a poly(paraphenylene) backbone with benzyl ether, Fréchet-type dendrons. We apply Monte Carlo sampling in order to investigate the formation of packing-induced chiral structures along the polymer backbone of these chemically achiral systems. We find that helical structures can be formed, usually with defects consisting of domains with reversed helical handedness. Clear signs of helical arrangements of the dendrons begin to appear for dendritic generation g=4, while for g=5 these arrangements dominate and perfect helices can be observed as equilibrium structures obtained from certain types of starting configurations.
Transport of a heated granular gas in a washboard potential
Authors: Costantini Giulio , Cecconi Fabio , Marini-Bettolo-Marconi Umberto
Published: November 2006

We study numerically the motion of a one dimensional array of Brownian particles in a washboard potential, driven by an external stochastic force and interacting via short range repulsive forces. In particular, we investigate the role of instantaneous elastic and inelastic collisions on the system dynamics and transport. The system displays a locked regime, where particles may move only via activated processes and a running regime where particles drift along the direction of the applied field. By tuning the value of the friction parameter controlling the Brownian motion we explore both the overdamped dynamics and the underdamped dynamics. In the two regimes we considered the mobility and the diffusivity of the system as functions of the tilt and other relevant control parameters such as coefficient of restitution, particle size, and total number of particles. We find that while in the overdamped regime the results for the interacting systems present similarities with the known noninteracting case, in the underdamped regime the inelastic collisions determine a rich variety of behaviors among which is an unexpected enhancement of the inelastic diffusion.
Piezoelectric properties in perovskite 0.948(K0.5Na0.5)NbO3–0.052LiSbO3 lead-free ceramics
Authors: Zhang Shujun , Xia Ru , Shrout Thomas R. , Zang Guozhong , Wang Jinfeng
Published: November 2006

Lead-free piezoelectric ceramics, with the nominal composition of 0.948(K0.5Na0.5)NbO3–0.052LiSbO3 (KNN-LS5.2), were synthesized by conventional solid-state sintering, and the piezoelectric and electromechanical properties were characterized as a function of temperature. The Curie temperature of the KNN based perovskite material was found to be 368°C with an orthorhombic-tetragonal polymorphic phase transition (TO-T) temperature at approximately ∼35°C. The room temperature dielectric permittivity (ε33T∕ε0) and loss were found to be 1380 and 2%, respectively, with piezoelectric properties of k33∼62% and d33∼265pC∕N and k31∼30% and d31∼−116pC∕N. The temperature dependence of the properties mimicked the compositional variation seen in the proximity of a morphotropic phase boundary [e.g., lead zirconate titanate (PZT)], with a maxima in the dielectric and piezoelectric properties and a corresponding “softening” of the elastic properties. Unlike that found for PZT-type materials, the modified KNN material exhibited characteristics of both “soft” and “hard” piezoelectricities owing to the distinctly different domain states associated with orthorhombic and tetragonal phases.
Is it possible for steady-state convection to exist in the absence of volume force?
Authors: Kono Akihiro
Published: November 2006

In this communication, we discuss a fundamental question as to whether local heating and cooling of the gas in a closed volume can induce steady-state convection without the effect of any volume force. The answer to this question is important for understanding the basic properties of microplasmas, in which strong local heating of the gas by the plasma and cooling by the wall occurs in a very small volume. Theoretical and computational analyses of the problem under the assumption of low Mach number laminar flow indicate that, although there does exist a mechanism yielding the driving force for convection, the viscosity of a real gas is too large, or the thermal conductivity of a real gas is too small, for the steady-state convection to be maintained.
Phase transition and critical issues in structure-property correlations of vanadium oxide
Authors: Narayan J. , Bhosle V. M.
Published: November 2006

Vanadium oxide (VO2) exhibits a very interesting semiconductor to metal transition as the crystal structure changes from tetragonal or rutile to monoclinic upon cooling close to 68°C. The characteristics of this transition are very interesting scientifically and are of immense technological importance due to a variety of sensor- and memory-type applications. We have processed high-quality films of VO2 by pulsed laser deposition, which were grown epitaxially on (0001) sapphire substrate via domain matching epitaxy, involving matching of integral multiples of lattice planes between the film of monoclinic structure and the sapphire substrate. These films exhibit a sharp transition near 68°C, large amplitude, and very small hysteresis, similar to bulk single crystal of VO2. The sharpness and amplitude of the transition and the hysteresis upon heating and cooling are found to be a strong function of crystal structure and microstructure (grain size, characteristics of grain boundaries, and defect content). Here, we propose a model to establish microstructure-property correlations in crystalline and amorphous phases of VO2, which can be used to rationalize our experimental observations as well as those available in the literature. Based upon this model, we predict specific microstructures leading to properties needed for various sensor- and memory-type devices.
11
–
13
GHz
electron cyclotron resonance plasma source using cylindrically comb-shaped magnetic-field configuration for broad ion-beam processing
Authors: Asaji Toyohisa , Kato Yushi , Sato Fuminobu , Iida Toshiyuki , Saito Junji
Published: November 2006

An electron cyclotron resonance (ECR) plasma source for broad ion-beam processing has been upgraded by a cylindrically comb-shaped magnetic-field configuration and 11–13GHz frequency microwaves. A pair of comb-shaped magnets surrounds a large-bore discharge chamber. The magnetic field well confines plasmas with suppressing diffusion toward the axial direction of the cylindrical chamber. The magnetic field is constructed with a multipole and two quasiring permanent magnets. The plasma density clearly increases as compared with that in a simple multipole magnetic-field configuration. The frequency of microwaves output from the traveling-wave tube amplifier can be easily changed with an input signal source. The plasma density for 13GHz is higher than that for 11GHz. The maximum plasma density has reached approximately 1018m−3 at a microwave power of only 350W and a pressure of 1.0Pa. The enhancement of plasma generation by second-harmonic resonance and microwave modes has been investigated. The plasma density and the electron temperature are raised around the second-harmonic resonance zone. And then, the ion saturation current is periodically increased with varying the position of the plate tuner. The distance between the peaks is nearly equal to half of the free-space wavelength of microwave. The efficiency of ECR has been improved by using the comb-shaped magnetic field and raising microwave frequency, and then the high-density plasma source has been accomplished at low microwave power.
Intermolecular sequential energy transfer in thin films of a white emitting copolymer
Authors: Anni M. , Lattante S. , De Kok M. M. , Cingolani R. , Gigli G.
Published: November 2006

The authors investigated the energy transfer between the chromophors of a white emitting polyspirobifluorene copolymer containing a blue emitting backbone, a green, and a red emitting dye. They demonstrate that the green dye is mainly excited by blue→green Förster resonant energy transfer (FRET), with a Förster radius R0bg=35Å. The red dye is instead excited by direct blue→red FRET (R0br=21Å) and by sequential blue→green→red FRET (R0gr=31Å). Finally, the authors show that the FRET processes, fundamental to have white emission, are of intermolecular nature, while intramolecular energy migration and transfer are negligible.
Hole-injection isomerization of photochromic diarylethene for organic molecular memory
Authors: Tsujioka Tsuyoshi , Iefuji Natsuko , Jiapaer Aini , Irie Masahiro , Nakamura Shinichiro
Published: November 2006

Hole-injection recording of organic semiconductor memory with a photochromic diarylethene memory layer was investigated by using a device structure with an electron block layer (EBL). Devices with thicker EBL showed faster current decrease, that is, high isomerization efficiency. The high efficiency of isomerization originating from the long lifetime of a cationic state was achieved by hole injection with low voltage. Hole-isomerization recording has the potential for very low power consumption organic memory.
Installation of electric field electron beam blanker in high-resolution transmission electron microscopy
Authors: Hayashida Misa , Kimura Yoshihide , Taniguchi Yoshifumi , Otsuka Masayuki , Takai Yoshizo
Published: November 2006

We have newly installed an electric field electron beam blanker in a transmission electron microscopy, which chops an electron beam very quickly without the effect of hysteresis. The electric field, which is generated by the electron beam blanker, deflects the electron beam, and the electron beam is intercepted by an aperture. The response time of the beam blanker is 50μs. Therefore, a very short pulsed electron beam enables a charge-coupled device camera to directly expose an electron beam spot or diffraction pattern. Moreover, we measured the response of a deflector coil, which is usually used as an electron beam blanker, using our electron beam blanker. Our beam blanker will become a key component in a computer-assisted minimal dose system, which enables us to reduce the electron dose of the sample.
Comparison of near-interface traps in Al2O3∕4H-SiC and Al2O3∕SiO2∕4H-SiC structures
Authors: Avice Marc , Grossner Ulrike , Pintilie Ioana , Svensson Bengt G. , Nilsen Ola , Fjellvag Helmer
Published: November 2006

Aluminum oxide (Al2O3) has been grown by atomic layer deposition on n-type 4H-SiC with and without a thin silicon dioxide (SiO2) intermediate layer. By means of capacitance-voltage and thermal dielectric relaxation current measurements, the interface properties have been investigated. Whereas for the samples with an interfacial SiO2 layer the highest near-interface trap density is found at 0.3eV below the conduction band edge Ec, the samples with only the Al2O3 dielectric exhibit a nearly trap-free region close to Ec. For the Al2O3∕SiC interface, the highest trap density appears between 0.4 and 0.6eV below Ec. The results indicate the possibility for SiC-based metal-oxide-semiconductor field-effect transistors with Al2O3 as the gate dielectric layer in future high performance devices.
Real time x-ray observation of lattice pulling during growth of epitaxial Pb(Zr,Ti)O3 films
Authors: Wang R.-V. , Stephenson G. B. , Fong D. D. , Jiang F. , Fuoss P. H. , Eastman J. A. , Streiffer S. K. , Latifi K. , Thompson Carol
Published: November 2006

Using surface-sensitive grazing incidence synchrotron x-ray scattering and fluorescence, the authors have monitored the evolution of strain and Zr composition in situ during metal-organic chemical vapor deposition of Pb(Zr,Ti)O3 epitaxially grown on (001) SrTiO3. The Zr fraction of the growing surface increases dramatically as the film relaxes, resulting in compositional nonuniformity in the growth direction. The observed composition variation can be quantitatively explained by the lattice pulling model, which includes strain energy in the thermodynamic equilibria for growth.
High power ultraviolet light emitting diodes based on GaN∕AlGaN quantum wells produced by molecular beam epitaxy
Authors: Cabalu J. S. , Bhattacharyya A. , Thomidis C. , Friel I. , Moustakas T. D. , Collins C. J. , Komninou Ph.
Published: November 2006

In this paper, we report on the growth by molecular beam epitaxy and fabrication of high power nitride-based ultraviolet light emitting diodes emitting in the spectral range between 340 and 350nm. The devices were grown on (0001) sapphire substrates via plasma-assisted molecular beam epitaxy. The growth of the light emitting diode (LED) structures was preceded by detailed materials studies of the bottom n-AlGaN contact layer, as well as the GaN∕AlGaN multiple quantum well (MQW) active region. Specifically, kinetic conditions were identified for the growth of the thick n-AlGaN films to be both smooth and to have fewer defects at the surface. Transmission-electron microscopy studies on identical GaN∕AlGaN MQWs showed good quality and well-defined interfaces between wells and barriers. Large area mesa devices (800×800μm2) were fabricated and were designed for backside light extraction. The LEDs were flip-chip bonded onto a Si submount for better heat sinking. For devices emitting at 340nm, the measured differential on-series resistance is 3Ω with electroluminescence spectrum full width at half maximum of 18nm. The output power under dc bias saturates at 0.5mW, while under pulsed operation it saturates at approximately 700mA to a value of 3mW, suggesting that thermal heating limits the efficiency of these devices. The output power of the investigated devices was found to be equivalent with those produced by the metal-organic chemical vapor deposition and hydride vapor-phase epitaxy methods. The devices emitting at 350nm were investigated under dc operation and the output power saturates at 4.5mW under 200mA drive current.
Nanometal-oxide-semiconductor field-effect-transistor contact and gate silicide instability during gate dielectric breakdown
Authors: Tung Chih Hang , Pey Kin Leong , Ranjan Rakesh , Tang Lei Jun , Ang Diing Shenp
Published: November 2006

Contact and gate silicide migration induced by gate dielectric breakdown transient has been observed in various silicide materials, including Ni, Co, and Ti silicides, used across several generations of metal-oxide-semiconductor field effect transistor (MOSFET) process technology nodes with different device geometries, gate dielectric materials, and stress conditions. This failure mechanism occurs during gate dielectric breakdown transient on both anode and cathode sides and on both n- and p-MOSFETs. The wear-out mechanisms are discussed and believed to be responsible for the instability and transformation observed.
H
∕
D
isotope effect on the dihydrogen bond of NH4+⋯BeH2 by ab initio path integral molecular dynamics simulation
Authors: Hayashi Aiko , Shiga Motoyuki , Tachikawa Masanori
Published: November 2006

In order to investigate the H∕D isotope effect on a dihydrogen bonded cation system, we have studied NH4+⋯BeH2 and its isotopomers by ab initio path integral molecular dynamics. It is found that the dihydrogen bond can be exchanged by NH4+ rotation. The deuterated isotopomer (ND4+⋯BeD2; DD) can exchange the dihydrogen bond more easily than other isotopomers such as (NH4+⋯BeH2; HH). This unusual isotope effect is ascribed to the “quantum localization” which occurs when the effective energy barrier for the rotational mode becomes higher by the zero point energy of other modes. We also found that the binding energy of dihydrogen bonds for DD species is the smallest among the isotopomers.
Energy transfer of highly vibrationally excited azulene. III. Collisions between azulene and argon
Authors: Liu Chen-Lin , Hsu Hsu Chen , Lyu Jia-Jia , Ni Chi-Kung
Published: November 2006

The energy transfer dynamics between highly vibrationally excited azulene molecules (37582cm−1 internal energy) and Ar atoms in a series of collision energies (200, 492, 747, and 983cm−1) was studied using a crossed-beam apparatus along with time-sliced velocity map ion imaging techniques. The angular resolved collisional energy-transfer probability distribution functions were measured directly from the scattering results of highly vibrationally excited azulene. Direct T-V∕R energy transfer was found to be quite efficient. In some instances, nearly all of the translational energy is transferred to vibrational/rotational energy. On the other hand, only a small fraction of vibrational energy is converted to translational energy (V-T). Significant amount of energy transfer from vibration to translation was observed at large collision energies in backward and sideway directions. The ratios of total cross sections between T-V∕R and V-T increases as collision energy increases. Formation of azulene-argon complexes during the collision was observed at low enough collision energies. The complexes make only minor contributions to the measured translational to vibrational/rotational (T-V∕R) energy transfer.
Electron emission from ferroelectric copolymer thin films of vinylidene fluoride and trifluoroethylene
Authors: Li Junjie , Neo Yoichiro , Mimura Hidenori , Omote Kenji , Yokoo Kuniyoshi
Published: November 2006

Electron emission from ferroelectric copolymer thin films consisting of vinylidene fluoride and trifluoroethylene (PVDF-TrFE) are reported. The ∼3μm thick copolymer thin films were deposited by spin coating and were then annealed to improve their crystallinity. The as-annealed films exhibited an electron emission capability, as anticipated; an emission charge within the range from 122to308pC∕cycle occurs at a positive excitation voltage with different excitation frequencies. It was found that the electron emission process of the PVDF-TrFE thin films differs from the conventional ferroelectric electron emission. A possible emission mechanism is proposed, which suggests that an amorphous phase in the polymer films plays an important role in trapping and emitting electrons.
Rings of triple-walled carbon nanotube bundles
Authors: Yu Hao , Zhang Qunfeng , Luo Guohua , Wei Fei
Published: November 2006

The formation of rings composed of uniformly sized triple-walled carbon nanotubes has been demonstrated and characterized by high resolution transmission electron microscopy. These rings are found in the products from acetylene decomposition on Fe∕MgO catalyst in a fluidized bed. This finding expands the libratory of building blocks based on nanotubes and demonstrates the existence of crystalline structures from complex multiwalled carbon nanotubes.
Identification of trapping defects in 4H-silicon carbide metal-insulator-semiconductor field-effect transistors by electrically detected magnetic resonance
Authors: Dautrich Morgen S. , Lenahan Patrick M. , Lelis Aivars J.
Published: November 2006

In conventional Si∕SiO2-based metal oxide semiconductor devices, performance-limiting semiconductor/dielectric interface traps are localized precisely at the Si∕SiO2 boundary. The authors show that in high-quality SiC∕SiO2-based devices, this is not necessarily the case. Magnetic resonance and electrical measurements indicate that in relatively high quality 4H-SiC metal-insulator-semiconductor field-effect transistors, there exist relatively high concentrations of intrinsic deep level defect centers extending below the SiC∕SiO2 interface into the SiC bulk. The primary defect observed is almost certainly an intrinsic defect of high symmetry, most likely a silicon vacancy center.
Uniformity of postprocessing of dense nanotube arrays by neutral and ion fluxes
Authors: Levchenko I. , Ostrikov K. , Tam E.
Published: November 2006

The advantages of using low-temperature plasma environments for postprocessing of dense nanotube arrays are shown by means of multiscale hybrid numerical simulations. By controlling plasma-extracted ion fluxes and varying the plasma and sheath parameters, one can selectively coat, dope, or functionalize different areas on nanotube surfaces. Conditions of uniform deposition of ion fluxes over the entire nanotube surfaces are obtained for different array densities. The plasma route enables a uniform processing of lateral nanotube surfaces in very dense (with a step-to-height ratio of 1:4) arrays, impossible via the neutral gas process wherein radical penetration into the internanotube gaps is poor.