bluuebunny/crossref_metadata_2025 huggingface dataset:
Transverse structure of wind‐driven flow at the entrance to an estuary: Nansemond River
Authors: Narváez Diego A. , Valle‐Levinson Arnoldo
Published: September 2008

Observations of current velocity profiles were combined with an analytical solution to study the transverse partition of the wind‐driven flow in an estuary, the Nansemond River, which is a tributary of the James River in the Chesapeake Bay. Observations spanned two periods of nearly 3 months in autumn‐winter of 2003–2004 and spring‐summer 2004. The wind‐driven circulation consisted of downwind flow over the shoal and upwind flow in the channel at the entrance to the estuary. This pattern developed mainly with landward winds and provided observational evidence that sustains analytical and numerical model results. The transverse structure of the flow showed synoptic temporal variability (3–7 days), which corresponded to the variability of winds and sea level. Synoptic variability seemed to be more influential in autumn‐winter than in spring‐summer. However, variability of 1–2 days was persistent in both periods of observation. Also, the transverse structure of the wind‐driven flows was linked to a counterclockwise recirculation pattern previously observed with survey data. Part of the flow going into the tributary over the shoal might recirculate and form or enhance the outflow in the channel. As suggested by the temporal scale of the wind, the recirculation might weaken or even reverse direction every 3–7 days at the entrance to the estuary. Further detailed studies are needed to better define the extent of this recirculation.
A novel ecological role of the Firmicutes identified in thermophilic microbial fuel cells
Authors: Wrighton Kelly C , Agbo Peter , Warnecke Falk , Weber Karrie A , Brodie Eoin L , DeSantis Todd Z , Hugenholtz Philip , Andersen Gary L , Coates John D
Published: September 2008

Significant effort is currently focused on microbial fuel cells (MFCs) as a source of renewable energy. Most studies concentrate on operation at mesophilic temperatures. However, anaerobic digestion studies have reported on the superiority of thermophilic operation and demonstrated a net energy gain in terms of methane yield. As such, our studies focused on MFC operation and microbiology at 55 °C. Over a 100-day operation, these MFCs were stable and achieved a power density of 37 mW m−2 with a coulombic efficiency of 89%. To infer activity and taxonomic identity of dominant members of the electricity-producing community, we performed phylogenetic microarray and clone library analysis with small subunit ribosomal RNA (16S rRNA) and ribosomal RNA gene (16S rDNA). The results illustrated the dominance (80% of clone library sequences) of the Firmicutes in electricity production. Similarly, rRNA sequences from Firmicutes accounted for 50% of those taxa that increased in relative abundance from current-producing MFCs, implying their functional role in current production. We complemented these analyses by isolating the first organisms from a thermophilic MFC. One of the isolates, a Firmicutes Thermincola sp. strain JR, not only produced more current than known organisms (0.42 mA) in an H-cell system but also represented the first demonstration of direct anode reduction by a member of this phylum. Our research illustrates the importance of using a variety of molecular and culture-based methods to reliably characterize bacterial communities. Consequently, we revealed a previously unidentified functional role for Gram-positive bacteria in MFC current generation.
Phenotypic and genetic diversification of Pseudanabaena spp. (cyanobacteria)
Authors: Acinas Silvia G , Haverkamp Thomas H A , Huisman Jef , Stal Lucas J
Published: September 2008

Pseudanabaena species are poorly known filamentous bloom-forming cyanobacteria closely related to Limnothrix. We isolated 28 Pseudanabaena strains from the Baltic Sea (BS) and the Albufera de Valencia (AV; Spain). By combining phenotypic and genotypic approaches, the phylogeny, diversity and evolutionary diversification of these isolates were explored. Analysis of the in vivo absorption spectra of the Pseudanabaena strains revealed two coexisting pigmentation phenotypes: (i) phycocyanin-rich (PC-rich) strains and (ii) strains containing both PC and phycoerythrin (PE). Strains of the latter phenotype were all capable of complementary chromatic adaptation (CCA). About 65 kb of the Pseudanabaena genomes were sequenced through a multilocus sequencing approach including the sequencing of the16 and 23S rRNA genes, the ribosomal intergenic spacer (IGS), internal transcribed spacer 1 (ITS-1), the cpcBA operon encoding PC and the IGS between cpcA and cpcB. In addition, the presence of nifH, one of the structural genes of nitrogenase, was investigated. Sequence analysis of ITS and cpcBA-IGS allowed the differentiation between Pseudanabaena isolates exhibiting high levels of microdiversity. This multilocus sequencing approach revealed specific clusters for the BS, the AV and a mixed cluster with strains from both ecosystems. The latter comprised exclusively CCA phenotypes. The phylogenies of the 16 and 23S rRNA genes are consistent, but analysis of other loci indicated the loss of substructure, suggesting that the recombination between these loci has occurred. Our preliminary results on population genetic analyses of the PC genes suggest an evolutionary diversification of Pseudanabaena through purifying selection.
Pulmonary Diffusing Capacity for Nitric Oxide During Exercise in Morbid Obesity
Authors: Zavorsky Gerald S. , Kim Do J. , McGregor Elspeth R. , Starling Jennifer M. , Gavard Jeffrey A.
Published: September 2008

Morbidly obese individuals may have altered pulmonary diffusion during exercise. The purpose of this study was to examine pulmonary diffusing capacity for nitric oxide (DLNO) and carbon monoxide (DLCO) during exercise in these subjects. Ten morbidly obese subjects (age = 38 ± 9 years, BMI = 47 ± 7 kg/m2, peak oxygen consumption or O2peak = 2.4 ± 0.4 l/min) and nine nonobese controls (age = 41 ± 9 years, BMI = 23 ± 2 kg/m2, O2peak = 2.6 ± 0.9 l/min) participated in two sessions: the first measured resting O2 and O2peak for determination of wattage equating to 40, 75, and 90% oxygen uptake reserve (O2R). The second session measured pulmonary diffusion from single‐breath maneuvers of 5 s each, as well as heart rate (HR) and O2 over three workloads. DLNO, DLCO, and pulmonary capillary blood volume were larger in obese compared to nonobese groups (P ≤ 0.06) only when expressed relative to alveolar volume (VA). The slope between O2 and all measures of pulmonary diffusion, whether or not expressed to VA, were not different between groups (P > 0.10). The morbidly obese have increased pulmonary diffusion per unit increase in VA compared with nonobese controls which may be due to a lower rise in VA per unit increase in O2 in the obese during exercise.
The catalytic role of INCENP in Aurora B activation and the kinetic mechanism of Aurora B/INCENP
Authors: Yang Jingsong , Zappacosta Francesca , Annan Roland S. , Nurse Kelvin , Tummino Peter J. , Copeland Robert A. , Lai Zhihong
Published: September 2008

Aurora kinases are a family of serine/threonine protein kinases that play essential roles in mitosis and cytokinesis. AurB (Aurora B kinase) has shown a clear link to cancer and is being pursued as an attractive cancer target. Multiple small molecules targeting AurB have entered the clinic for the treatment of cancer. A protein cofactor, INCENP (inner centromere protein), regulates the cellular localization and activation of AurB. In the present study, we examined the effect of INCENP on the activation kinetics of AurB and also elucidated the kinetic mechanism of AurB-catalysed substrate phosphorylation. We have concluded that: (i) substoichoimetric concentrations of INCENP are sufficient for AurB autophosphorylation at the activation loop residue Thr232, and hence INCENP plays a catalytic role in AurB autophosphorylation; (ii) AurB/INCENP-catalysed phosphorylation of a peptide substrate proceeds through a rapid equilibrium random Bi Bi kinetic mechanism; and (iii) INCENP has relatively minor effects on the specific activity of AurB using a peptide substrate when compared with its role in AurB autoactivation. These results indicate that the effects of INCENP, and probably accessory proteins in general, may differ when enzymes are acting on different downstream targets.
Atomic Transition Probabilities of Silicon. A Critical Compilation
Authors: Kelleher D. E. , Podobedova L. I.
Published: September 2008

This compilation is the third in a series of updates to a critical compilation published in 1969 by Wiese et al. [Atomic Transition Probabilities, Vol. II: Sodium through Calcium, NSRDS-NBS Vol. 22 (U.S. GPO, Washington, D.C., 1969)]. Atomic transition probabilities have been critically evaluated and compiled for about 5800 spectral lines of silicon (nuclear charge Z=14). The cited values and their estimated uncertainties are based on our consideration of all available theoretical and experimental literature sources. All ionization stages (except for hydrogenic) are covered, and the data are presented in separate tables for each atom and ion. Separate listings are given for “allowed” (electric dipole) and “forbidden” (magnetic dipole plus electric and magnetic quadrupole) transitions. In each spectrum, lines are grouped into multiplets which are arranged in order of ascending lower and upper level energies, respectively. For each line, the emission transition probability Aki, the line strength S, and (for allowed lines) the absorption oscillator strength fik are given, together with the spectroscopic designation, the wavelength, the statistical weights, and the energy levels of the lower and upper states. The estimated relative uncertainties of the line strength are also indicated, as are the source citations. We include only those lines whose transition rates are deemed sufficiently accurate to qualify as reference values. Short introductions precede the tables for each ion.
CODATA recommended values of the fundamental physical constants: 2006
Authors: Mohr Peter J. , Taylor Barry N. , Newell David B.
Published: September 2008

This paper gives the 2006 self-consistent set of values of the basic constants and conversion factors of physics and chemistry recommended by the Committee on Data for Science and Technology (CODATA) for international use. Further, it describes in detail the adjustment of the values of the constants, including the selection of the final set of input data based on the results of least-squares analyses. The 2006 adjustment takes into account the data considered in the 2002 adjustment as well as the data that became available between 31 December 2002, the closing date of that adjustment, and 31 December 2006, the closing date of the new adjustment. The new data have led to a significant reduction in the uncertainties of many recommended values. The 2006 set replaces the previously recommended 2002 CODATA set and may also be found on the World Wide Web at physics.nist.gov/constants.
Viscosity of concentrated sucrose and trehalose aqueous solutions including the supercooled regime
Authors: Longinotti M. Paula , Corti Horacio R.
Published: September 2008

The viscosity of aqueous solutions of sucrose and trehalose is analyzed over a wide range of concentrations and temperatures covering the normal liquid and supercooled liquid regions, close to the glass transition temperature. These sugar solutions are fragile systems whose viscosity exhibits temperature dependence with a large departure from Arrhenius behavior. A description of the temperature and concentration dependences of the solution viscosity is given in terms of a scaled Arrhenius representation, which adopts the reduced temperature Tg∕T as the state variable. A comparison with results obtained from other theoretical or semiempirical equations is also presented.
IUPAC-NIST Solubility Data Series. 86. Ethers and Ketones with Water. Part 4. C4 and C5 Ketones with Water
Authors: Góral Marian , Wiśniewska-Gocłowska Barbara
Published: September 2008

The mutual solubilities and related liquid-liquid equilibria of six binary systems of C4 and C5 ketones with water are exhaustively and critically reviewed. Acetone, the only C3 ketone, is soluble with water in all proportions; C6 and higher ketones will be treated in subsequent parts of this volume. Reports of experimental determination of solubility that appeared in the primary literature prior to the middle of 2007 are compiled. For all six systems, sufficient data are available to allow critical evaluation. All data are expressed as mass percent and mole fraction as well as the originally reported units. In addition to the standard evaluation criteria used throughout the Solubility Data Series, a method based on the evaluation of all experimental data for a given series of ketones was used.
Characterization of nanofibers formed by self-assembly of β-peptide oligomers using small angle x-ray scattering
Authors: Pizzey Claire L. , Pomerantz William C. , Sung Bong-June , Yuwono Virany M. , Gellman Samuel H. , Hartgerink Jeffery D. , Yethiraj Arun , Abbott Nicholas L.
Published: September 2008

Helical oligomers of β-peptides represent a particularly promising type of building block for directed assembly of organic nanostructures because the helical secondary structure can be designed to be very stable and because control of the β-amino acid sequence can lead to precise patterning of chemical functional groups over the helix surfaces. In this paper, we report the use of small angle x-ray scattering measurements (SAXS) to characterize nanostructures formed by the directed assembly of β-peptide A with sequence H2N-β3hTyr-β3hLys-β3hPhe-ACHC-β3hPhe-ACHC-β3hPhe-β3hLys-ACHC-ACHC-β3hPhe-β3hLys-CONH2. Whereas prior cryo-TEM studies have revealed the presence of nanofibers in aqueous solutions of β-peptide A, SAXS measurements from the nanofibers were not well-fit by a form factor model describing solid nanofibers. An improved fit to the scattering data at high q was obtained by using a form factor model describing a cylinder with a hollow center and radial polydispersity. When combined with a structure factor calculated from the polymer reference interaction site model (PRISM) theory, the scattered intensity of x-rays measured over the entire q range was well described by the model. Analysis of our SAXS data suggests a model in which individual β-peptides assemble to form long cylindrical nanofibers with a hollow core radius of 15Å (polydispersity of 21%) and a shell thickness of 20Å. This model is supported by negative stain transmission electron microscopy.
Simulation and laser vibrometry characterization of piezoelectric AlN thin films
Authors: Hernando J. , Sánchez-Rojas J. L. , González-Castilla S. , Iborra E. , Ababneh A. , Schmid U.
Published: September 2008

In this paper, the electric field induced deformations of sputter-deposited piezoelectric aluminum nitride thin films sandwiched between electrodes on top of a silicon substrate are studied by numerical calculations and scanning laser interferometric measurements. In our calculations based on the finite element method, the results show the displacement of the top and bottom surfaces of both the thin film and the substrate, for either a free or a perfectly clamped structure. The confirmation that the bottom surface of the film is deformed reveals the limitations of techniques that only access the top surface, as well as the double-beam interferometric configuration, under specific conditions. In addition, the simulations demonstrate the dependence of the displacements on the size of the upper electrode and the contribution of the transverse piezoelectric coefficient d31 to the features of the displacement profiles. A laser scanning vibrometry technique was used to measure deformations on the top surface with subpicometer vertical resolution. By comparing the calculated and the experimental displacement profiles, an advanced approach is discussed to obtain accurate quantitative information of both coefficients d31 and d33.
Subthreshold slope and transconductance degradation model in cycled hot electron injection programed/hot hole erased silicon-oxide-nitride-oxide-silicon memories
Authors: Daniel Ramiz , Ruzin Arie , Roizin Yakov , Shaham-Diamand Yossi
Published: September 2008

A physical model is presented for the subthreshold slope and transconductance degradation after program/erase cycling of silicon-oxide-nitride-oxide-silicon memory cells with thick bottom oxide, programed by hot electrons and erased by hot holes. Using a charge-pumping technique, it is shown that the generation of interface states is one of the mechanisms responsible for the degradation of the subthreshold slope and transconductance. In this article, we show the correlation between the increase in the charge pumping current and the decrease in the subthreshold slope and transconductance. Practical solutions are proposed to reduce the influence of the subthreshold slope and transconductance degradation on the overall device performance.
Current transport in semiconductor nanowires with built-in barriers based on a 1D transfer matrix calculation
Authors: Zervos M. , Pelekanos N. T.
Published: September 2008

A one dimensional (1D) transfer matrix calculation of current transport in semiconductor nanowires with built-in barriers is described within the effective mass approximation by taking into account (i) the quantum confinement in the radial direction and (ii) the Fermi level position with respect to the 1D sub-band(s), both of which can be determined analytically. We calculate the current-voltage (I-V) characteristic for an InAs nanowire, which has a radius of 200 Å and two 50 Å InP, built-in barriers, which define a 150 Å long InAs quantum disk and find that a peak in the current occurs at an applied voltage of 72 mV, corresponding to resonant tunneling of carriers through the double barriers. This is in good agreement with the I-V curve measured in a similar nanowire at a temperature of 4.2 K, where resonant tunneling occurs at 80 mV. It is deduced that the Fermi level is ≈26 meV above the conduction band edge at the surface of the specific InAs nanowire, which is ten times lower than the Fermi level pinning at inverted InAs thin film surfaces. We discuss the importance of the strain and surface depletion.
High-power AlInGaN-based violet laser diodes with InGaN optical confinement layers
Authors: Lee Sung-Nam , Son J. K. , Paek H. S. , Sung Y. J. , Kim K. S. , Kim H. K. , Kim H. , Sakong T. , Park Y. , Ha K. H. , Nam O. H.
Published: September 2008

InGaN optical confinement layers (OCLs) were introduced into blue-violet AlInGaN-based laser diodes (LDs), resulting in the drastic improvements of lasing performance. Comparing with conventional LD structure, the lowest threshold current density of 2.3kA∕cm2 has been achieved by adding 100-nm-thick InGaN OCLs which represented maximum optical confinement factor. Additionally, we observed the high quantum efficiency and the uniform emission intensity distribution of InGaN quantum wells grown on lower InGaN OCL than on typical GaN layer. Upper InGaN OCL can reduce Mg diffusion from p-type layers to InGaN active region by separating the distance between InGaN quantum wells and p-type layers.
Isolating the spectra of cluster ion isomers using Ar-“tag” -mediated IR-IR double resonance within the vibrational manifolds: Application to NO2−⋅H2O
Authors: Elliott Ben M. , Relph Rachael A. , Roscioli Joseph R. , Bopp Joseph C. , Gardenier George H. , Guasco Timothy L. , Johnson Mark A.
Published: September 2008

We demonstrate a method for isolating the vibrational predissociation spectra of different structural isomers of mass-selected cluster ions based on a population-labeling double resonance scheme. This involves a variation on the “ion dip” approach and is carried out with three stages of mass selection in order to separate the fragment ion signals arising from a fixed-frequency population-monitoring laser and those generated by a scanned laser that removes population of species resonant in the course of the scan. We demonstrate the method on the Ar-tagged NO2−⋅H2O cluster, where we identify the spectral patterns arising from two isomers. One of these structures features accommodation of the water molecule in a double H-bond arrangement, while in the other, H2O attaches in a single ionic H-bond motif where the nominally free OH group is oriented toward the N atom of NO2−. Transitions derived from both the NO2− and H2O constituents are observed for both isomers, allowing us to gauge the distortions suffered by both the ion and solvent molecules in the different hydration arrangements.
Generating properly weighted ensemble of conformations of proteins from sparse or indirect distance constraints
Authors: Lin Ming , Lu Hsiao-Mei , Chen Rong , Liang Jie
Published: September 2008

Inferring three-dimensional structural information of biomacromolecules such as proteins from limited experimental data is an important and challenging task. Nuclear Overhauser effect measurements based on nucleic magnetic resonance, disulfide linking, and electron paramagnetic resonance labeling studies can all provide useful partial distance constraint characteristic of the conformations of proteins. In this study, we describe a general approach for reconstructing conformations of biomolecules that are consistent with given distance constraints. Such constraints can be in the form of upper bounds and lower bounds of distances between residue pairs, contact maps based on specific contact distance cutoff values, or indirect distance constraints such as experimental ϕ-value measurement. Our approach is based on the framework of sequential Monte Carlo method, a chain growth-based method. We have developed a novel growth potential function to guide the generation of conformations that satisfy given distance constraints. This potential function incorporates not only the distance information of current residue during growth but also the distance information of future residues by introducing global distance upper bounds between residue pairs and the placement of reference points. To obtain protein conformations from indirect distance constraints in the form of experimental ϕ-values, we first generate properly weighted contact maps satisfying ϕ-value constraints, we then generate conformations from these contact maps. We show that our approach can faithfully generate conformations that satisfy the given constraints, which approach the native structures when distance constraints for all residue pairs are given.
Spectral and entropic characterizations of Wigner functions: Applications to model vibrational systems
Authors: Luzanov A. V.
Published: September 2008

The Wigner function for the pure quantum states is used as an integral kernel of the non-Hermitian operator K̂, to which the standard singular value decomposition (SVD) is applied. It provides a set of the squared singular values treated as probabilities of the individual phase-space processes, the latter being described by eigenfunctions of K̂K̂+ (for coordinate variables) and K̂+K̂ (for momentum variables). Such a SVD representation is employed to obviate the well-known difficulties in the definition of the phase-space entropy measures in terms of the Wigner function that usually allows negative values. In particular, the new measures of nonclassicality are constructed in the form that automatically satisfies additivity for systems composed of noninteracting parts. Furthermore, the emphasis is given on the geometrical interpretation of the full entropy measure as the effective phase-space volume in the Wigner picture of quantum mechanics. The approach is exemplified by considering some generic vibrational systems. Specifically, for eigenstates of the harmonic oscillator and a superposition of coherent states, the singular value spectrum is evaluated analytically. Numerical computations are given for the nonlinear problems (the Morse and double well oscillators, and the Henon–Heiles system). We also discuss the difficulties in implementation of a similar technique for electronic problems.
Phase transformations in poled PZN-4.5%PT single crystal revealed by combined property measurements and high-resolution diffraction technique
Authors: Chang W. S. , Lim L. C. , Yang P. , Tu C.-S. , Wang F.-T. , Tseng C.-T.
Published: September 2008

The phase transformation of annealed and poled 0.955Pb(Zn1/3Nb2/3)O3–0.045PbTiO3 (PZN-4.5%PT) single crystals has been studied by means of combined bulk property measurements (dielectric permittivity and thermal current density measurements) and microstructural characterization (polarized light microscope and high-resolution x-ray diffraction). Our results showed that upon heating under zero-field condition, poled PZN-4.5%PT undergoes a R-(R+RNT+T+TNT)-(T+TNT)-C transformation sequence, where (R+RNT) and (T+TNT) denote that the rhombohedral and tetragonal phases present consist of a mixture of microscopic (R,T) and nanotwin (RNT,TNT) domains and C denotes the cubic phase. The RNT and TNT nanotwin domains were detected only in the temperature vicinity of the R-T transformation, possibly as a means to alleviate the transformation stress in the material. These nanotwin diffractions can be easily mistaken as monoclinic diffractions.
Potential energy surface and unimolecular dynamics of stretched n-butane
Authors: Lourderaj Upakarasamy , McAfee Jason L. , Hase William L.
Published: September 2008

The potential energy surface (PES) and unimolecular reaction dynamics of stretched n-butane are investigated, as a model for a stretched “normal” alkane or straight chain polymer. The nature of the PES for stretched n-butane depends on the extent of stretching. If it is less than that required to reach the inflection points in the CC stretch potentials and the CC torsions are considered free rotors, there is only one potential energy minimum, with each bond elongated. However, for stretching past these inflection points, the PES has three minima and each has one bond longer than the other two, i.e., CCCC, CCCC, and CCCC. There are three transition states (TSs) connecting these minima. A linear alkane, consisting of n carbon atoms and stretched past its CC inflection points, has (n−1) minima and (n−1)(n−2)∕2 TSs connecting them. For stretching less than that required to reach the CC inflection points, the only unimolecular pathways are dissociations to form the C+CCC, CC+CC, and CCC+C products. However, with stretching past the CC inflection points, isomerizations between the three potential energy minima may also occur. The relative importance of isomerization versus dissociation depends on the relative size of their barriers. For slight stretching past the CC inflection points, the isomerization barriers are much lower than those for dissociation and relaxation between the minima is much faster than dissociation. Thus, the molecule samples these minima randomly during its dissociation, with a density of states that comprises the complete PES. With extensive stretching past the inflection points, isomerizations between the potential energy minima do not occur and only dissociation for the excited minima occurs, e.g., CCCC→C+CCC. For intermediate stretching past the CC inflection points, the rates for the isomerization and dissociation pathways are competitive and both must be considered in modeling the dissociation kinetics. Microcanonical chemical dynamics simulations are performed to study the unimolecular kinetics of n-butane in three stretched configurations: Stretched less than the CC inflection point; stretched slightly beyond the CC inflection point; and stretched significantly beyond the CC inflection point. The resulting unimolecular dynamics were found to be in excellent agreement with RRKM theory. Frequency ν factors, determined by fitting the trajectory unimolecular rate constants to the classical harmonic RRKM rate constant expression, depend upon the extent of stretching and vary from 1.0×1012–8.4×1016s−1. For a molecule with a large number of vibrational degrees of freedom and high excess energy, it is shown that the classical harmonic RRKM and classical harmonic transition state theory rate constants, k(E) and k(T), are equivalent.
V-shaped electro-optic response observed in a chiral ferroelectric smectic liquid crystal
Authors: Manjuladevi V. , Panarin Yu. P. , Song Jang-Kun , Vij J. K. , Sadashiva B. K.
Published: September 2008

We report on the observation of V-shaped switching in a ferroelectric liquid crystal cell over a wide range of temperatures. Results of the optical transmittance in the visible region give us the helical pitch for various temperatures of the ferroelectric liquid crystalline compound used. We show that the helical pitch, in addition to the spontaneous polarization (PS) and thickness of the alignment layer of the cell, is an important factor in giving V-shaped switching. A longer or helical compensated mixture gives a better V-shaped switching.
First-principles investigation on electronics characteristics of benzene derivatives with different side groups
Authors: Zhang Z. H. , Yang Z. , Yuan J. H. , Zhang H. , Ding X. Q. , Qiu M.
Published: September 2008

The electronics properties for benzene derivatives with different side groups connected to two gold electrodes with symmetric contacts are investigated by using first-principles methods based on the density functional theory. We have found that a bias can induce a transition from the electron-withdrawing behaviors to the electron-denoting behaviors for the OH side group in a phenoldithiol molecule. The degree of asymmetry of the I-V characteristics and the magnitudes in current depend remarkably on the type and number of attached side groups. The detailed analysis illustrates that the “doping” effect of the side groups and the asymmetry of potential profile in devices under different bias polarities are intrinsic origins leading to such observed phenomena. The results show that it is feasible to import some particular characteristics to a benzene-dithiol molecular device through an attachment of different side groups.
Role of oxygen atoms in CaF2 crystals doped with Eu atom
Authors: Nishimura Suzuka , Terashima Kazutaka , Nagayoshi Hiroshi
Published: September 2008

The optical transparency in function of wavelength of CaF2 crystals doped with Eu (denoted by CaF2:Eu) has been measured. The optical absorption occurs below λ=400 nm depending on the amount of Eu atoms doped. The short wavelength below 400 nm has been shifted to around λ=425 nm. As a result, the 425 nm wavelength increased and the light below 400 nm was cut through CaF2:Eu crystals. This scintillating effect has been found much increased by adding oxygen atoms in crystals. This is due to the distortion of electrical and structural symmetry in crystals by adding oxygen atoms in the form of oxide materials.
High resolution flat crystal spectrometer for the Shanghai EBIT
Authors: Xiao J. , Gao Y. , Zhang X. , Lu D. , Hu W. , Gao M. , Chen W. , Zou Y.
Published: September 2008

We report on a high resolution flat crystal spectrometer designed for the Shanghai EBIT. Its energy range is from 0.5 to 10 keV. Three crystals can be installed in the vacuum chamber simultaneously, and its effective Bragg angle can be covered from 15° to 75°. A vacuum version charge-coupled device detector is used for detection of photons. An energy resolution under 1 eV was reached in measurements of the 4.5 keV Kα1 line by using an x-ray generator with a titanium anode. The spectrometer was also tested to operate well on the Shanghai EBIT by observing the lines of tungsten at around 3.2 keV.
Femtosecond midinfrared study of the photoinduced Wolff rearrangement of diazonaphthoquinone
Authors: Wolpert Daniel , Schade Marco , Brixner Tobias
Published: September 2008

Time-resolved vibrational femtosecond spectroscopy is employed to investigate the photoinduced Wolff rearrangement reaction of diazonaphthoquinone (DNQ) dissolved in different solvents (methanol and water). DNQ is an important compound in commercial Novolak photoresists. Upon photoexcitation the ketene intermediate appears within 300 fs, indicating that the ketene is formed in a very fast concerted process involving N2 loss and rearrangement. The strong shift of the vibrational band, assigned to the ketene by density functional theory calculations and experimental infrared spectra, toward higher wavenumbers is attributed to vibrational cooling. The relaxation time depends on the solvent (10 ps in methanol and 3 ps in water). However, the spectroscopic data show that the indirect ketene formation via a carbene intermediate might also be involved in the reaction process contributing to the ketene formation on the 10 ps time scale.
Molecular representation of molar domain (volume), evolution equations, and linear constitutive relations for volume transport
Authors: Eu Byung Chan
Published: September 2008

In the traditional theories of irreversible thermodynamics and fluid mechanics, the specific volume and molar volume have been interchangeably used for pure fluids, but in this work we show that they should be distinguished from each other and given distinctive statistical mechanical representations. In this paper, we present a general formula for the statistical mechanical representation of molecular domain (volume or space) by using the Voronoi volume and its mean value that may be regarded as molar domain (volume) and also the statistical mechanical representation of volume flux. By using their statistical mechanical formulas, the evolution equations of volume transport are derived from the generalized Boltzmann equation of fluids. Approximate solutions of the evolution equations of volume transport provides kinetic theory formulas for the molecular domain, the constitutive equations for molar domain (volume) and volume flux, and the dissipation of energy associated with volume transport. Together with the constitutive equation for the mean velocity of the fluid obtained in a previous paper, the evolution equations for volume transport not only shed a fresh light on, and insight into, irreversible phenomena in fluids but also can be applied to study fluid flow problems in a manner hitherto unavailable in fluid dynamics and irreversible thermodynamics. Their roles in the generalized hydrodynamics will be considered in the sequel.
Three-dimensional orientation determination of the emission dipoles of single molecules: The shot-noise limit
Authors: Hohlbein Johannes , Hübner Christian G.
Published: September 2008

The power of three-dimensional orientation detection of single emitting dipoles using a sophisticated scheme with three detectors in a confocal microscope is quantitatively explored by means of Monte Carlo simulations. We show that several hundreds of photons are sufficient for a reliable orientation determination. In typical single-molecule experiments, time resolutions in the submillisecond range for orientation trajectories become accessible. Experimental data on fluorescent latex beads and single perylene monoimide molecules show that a properly aligned setup can perfectly reproduce the simulated data. The simulations and experimental data highlight the potential of our method and give practical guidelines for its application.
Enhancement in middle-ultraviolet emission in a surface-plasmon-assisted coaxial nanocavity
Authors: Zhuang Qingrui , Feng Xia , Yang Zhilin , Kang Junyong , Yuan Xiaoli
Published: September 2008

Cathodoluminescence spectrum of a single Zn–Zn2SiO4 core-shell nanocable exhibits a strong emission at 293nm accompanied with a weaker splitting peak at its long wavelength side. Experiment and ab initio calculation results indicate that the UV emissions are associated with the Zn2SiO4 surface states. Finite-difference time-domain simulations show that a surface-plasmon-assisted nanocavity can selectively confine and enhance the electric field energy of the 293nm light due to the smallest mode volume and the highest finesse among surface plasmon resonance, whispering gallery, and waveguide modes. Further temperature dependence experiment and correlative theoretical derivation suggest that the splitting is associated with a strong coupling between the nanocavity and the emitter.
Nano-Ag on vanadium dioxide. II. Thermal tuning of surface plasmon resonance
Authors: Xu Gang , Huang Chun-Ming , Tazawa Masato , Jin Ping , Chen De-Ming
Published: September 2008

Thermal tuning of the localized surface plasmon resonance (LSPR) of Ag nanoparticles on a thermochromic thin film of VO2 was studied experimentally. The tuning is strongly temperature dependent and thermally reversible. The LSPR wavelength λSPR shifts to the blue with increasing temperature from 30 to 80 °C, and shifts back to the red as temperature decreases. A smart tuning is achievable on condition that the temperature is controlled in a stepwise manner. The tunable wavelength range depends on the particle size or the mass thickness of the metal nanoparticle film. Further, the tunability was found to be enhanced significantly when a layer of TiO2 was introduced to overcoat the Ag nanoparticles, yielding a marked sensitivity factor ΔλSPR/Δn, of as large as 480 nm per refractive index unit (n) at the semiconductor phase of VO2.
Kinetics and chemical analysis of photoinduced interdiffusion in nanolayered Se/As2S3 films
Authors: Adarsh K. V. , Naik Ramakanta , Sangunni K. S. , Kokenyesi S. , Jain H. , Miller Alfred C.
Published: September 2008

We have studied the kinetics of photoinduced effects in nanolayered Se/As2S3 film by in situ optical absorption measurements, which reveal that photodarkening in these films is followed by photoinduced diffusion. An increase in disorder during photodarkening and its subsequent decrease during photoinduced diffusion were also observed. The observation of photodarkening of Se at room temperature when confined between As2S3 layers suggests that the glass transition temperature of Se shifts to higher energy. The analysis shows that the atoms which take part in photodarkening play a vital role in photoinduced diffusion. The x-ray photoelectron spectroscopy measurements show the atomic movements during photoinduced diffusion. It also shows that some of the As–S bonds are converted into As–Se bonds. Since it is energetically difficult to break an As–S bond to form an As–Se bond, we assume that the new bond formations are taking place by the bond rearrangement mechanism.
Epitaxial silicon minority carrier diffusion length by photoluminescence
Authors: Baek D. H. , Kim S. B. , Schroder D. K.
Published: September 2008

Photoluminescence (PL) is a convenient contactless method to characterize semiconductors. Its use for room-temperature silicon characterization has only recently been implemented. We have developed the relevant theory and compared it with experimental data initially for bulk Si wafers and then extended it to moderately doped epitaxial layers on heavily doped substrates. Our theory predicts the PL behavior as a function of epilayer and substrate doping densities making it possible to provide epilayer properties such as doping densities, minority carrier diffusion length, and surface recombination velocity.
Electrical and structural properties of AlN/GaN and AlGaN/GaN heterojunctions
Authors: Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Markov A. V. , Yugova T. G. , Dabiran A. M. , Wowchak A. M. , Cui B. , Osinsky A. V. , Chow P. P. , Pearton S. J. , Scherbatchev K. D. , Bublik V. T.
Published: September 2008

The electrical and structural properties of AlN/GaN heterostructures grown by molecular beam epitaxy on sapphire are compared with those of AlGaN/GaN heterostructures. The structural characteristics as assessed by x-ray diffraction show little difference but the electron density in the two-dimensional electron gas is about twice higher for AlN/GaN structures with only slightly lower mobility than in AlGaN/GaN. By proper choice of the Fe doping in GaN(Fe) and the thickness of unintentionally doped GaN layers, the composite buffer of the structure can be made semi-insulating. The current through the AlN/GaN structures is determined by tunneling through the AlN barrier and is much higher than that for AlGaN/GaN films due to the lower thickness of AlN compared to AlGaN. Increasing the thickness of AlN from 3 to 4 nm decreases the leakage current by about an order of magnitude.
Advances in the mass spectrometric study of the laser vaporization of graphite
Authors: Pflieger R. , Sheindlin M. , Colle J.-Y.
Published: September 2008

Reliable experimental data on graphite vaporization and especially on carbon vapor composition exist only up to 2500–3000 K. Data measured at higher temperatures are questionable due to several experimental limitations, such as the difficult temperature determination and the not straightforward correlation of measured temperatures and intensities of signals in mass spectra. That is why a new method of high-temperature mass spectrometry with laser vaporization was developed, in order to extend the accessible temperature range while overcoming these limitations and to shed more light on the still poorly known behavior of carbon at high temperatures. Thus, carbon sublimation relative partial pressures of the species C1, C2, C3, C4, and C5 were measured up to 4100 K. Moreover, the values of the relative vaporization coefficients of C1, C2, C3, C4, and C5, estimated by comparison of the experimentally obtained partial pressures with the predicted equilibrium ones, are proposed.
Dependences of nitrogen incorporation behaviors on the crystallinity and phase distribution of atomic layer deposited Hf-silicate films with various Si concentrations
Authors: Park Tae Joo , Kim Jeong Hwan , Jang Jae Hyuck , Na Kwang Duk , Hwang Cheol Seong , Yoo Jeong Ho
Published: September 2008

This study examined the nitrogen incorporation behavior of atomic layer deposited HfO2 and Hf-silicate films with various Si concentrations during thermal annealing under a NH3 atmosphere. The level of crystallization and the phase distribution of the films (crystalline HfO2 and amorphous Hf-silicate and SiO2) had a significant effect on extent of nitrogen incorporation. There was virtually no nitrogen incorporation in the crystallized HfO2. Under the condition that the Hf-silicate films were not phase-separated and crystallized during thermal nitridation, the excess HfO2 and SiO2 phases that did not contribute to the amorphous HfSiO4 phase were easily nitrided. On the other hand, the amorphous HfSiO4 phase was barely nitrided. Therefore, it was concluded that the level of nitrogen concentration in the Hf-silicate films decreased with increasing Si concentration in the films. The changes in the capacitance equivalent thickness, gate leakage current density, and flatband voltage shift of the various films after thermal nitridation were consistent with the nitrogen concentration in the films.
Electric self-inductance of quasi-two-dimensional magnetic-dipolar-mode ferrite disks
Authors: Sigalov M. , Kamenetskii E. O. , Shavit R.
Published: September 2008

An electric current flowing around a loop produces a magnetic field and hence a magnetic flux through the loop. The ratio of the magnetic flux to the electric current is called the (magnetic) self-inductance. Can there be a dual situation with a magnetic current flowing around a loop and producing an electric field and hence an electric flux through the loop? Following the classical electrodynamics laws an answer to this question should be negative. Nevertheless, special spectral properties of magnetic-dipolar modes in a quasi-two-dimensional ferrite disk show that there are the double-valued-function loop magnetic currents which may produce eigenelectric fields and hence eigenelectric fluxes through the loop. In this case one can definitely introduce a notion of an electric self-inductance as the ratio of the electric flux to the magnetic current. In this paper we show experimentally that in the magnetic-dipolar-mode ferrite disks there exist eigenelectric fluxes. These fluxes are very sensitive to the permittivity parameters of materials abutting to a ferrite disk. Dielectric samples above a ferrite disk with a higher permittivity than air confine the electric field closely outside the ferrite, thereby changing the loop magnetic currents and thus transforming the magnetic-dipolar-mode oscillating spectrum.
Charged particle transport through a periodic electrostatic potential having a small spatial period
Authors: Ordonez C. A.
Published: September 2008

A classical trajectory Monte Carlo study is reported regarding charged particle transport through an electrostatic potential, which is periodic with a spatial period that is smaller than the radius of cylindrical electrodes that produce the potential. The electrodes are identically shaped and have alternating applied voltages. A Fourier series procedure is developed for obtaining computationally fast solutions for the electrostatic potential, and various quantities are determined by simulating the motion of particles that pass through the axis of symmetry. It is found that for the configuration studied, axial transport is possible for a large range of values of both the angle of divergence with respect to the axis of symmetry (angles reaching at least 100 mrad) and the particle kinetic energy (kinetic energies that span more than four orders of magnitude). The results are not dependent on the particle mass or sign of charge.
Nanoparticle-induced light scattering for improved performance of quantum-well solar cells
Authors: Derkacs D. , Chen W. V. , Matheu P. M. , Lim S. H. , Yu P. K. L. , Yu E. T.
Published: September 2008

We report on the improved performance of InP∕InGaAsP quantum-well waveguide solar cells via light scattering from deposited dielectric or metal nanoparticles. The integration of metal or dielectric nanoparticles above the quantum-well solar cell device is shown to couple normally incident light into lateral optical propagation paths, with optical confinement provided by the refractive index contrast between the quantum-well layers and surrounding material. With minimal optimization, short-circuit current density increases of 12.9% and 7.3% and power conversion efficiency increases of 17% and 1% are observed for silica and Au nanoparticles, respectively.
A sharp boundary model for the vertical and kink stability of large aspect-ratio vertically elongated tokamak plasmas
Authors: Fitzpatrick R.
Published: September 2008

A relatively straightforward version of the well-known sharp boundary model is developed in order to investigate the ideal n=0 and n=1 stability of large aspect-ratio, high-β, tokamak plasmas with vertically elongated poloidal cross sections which are surrounded by either ideal, resistive, or partial conducting walls. All calculations made using the model reduce to comparatively simple matrix eigenvalue problems. Various example calculations are described.
Monitoring the Bragg peak location of 73MeV∕u carbon ions by means of prompt γ-ray measurements
Authors: Testa E. , Bajard M. , Chevallier M. , Dauvergne D. , Le Foulher F. , Freud N. , Létang J.-M. , Poizat J.-C. , Ray C. , Testa M.
Published: September 2008

By means of a time-of-flight technique, we measured the longitudinal profile of prompt γ-rays emitted by 73MeV∕u C13 ions irradiating a polymethyl methacrylate target. This technique allowed us to minimize the shielding against neutrons and scattered γ-rays, and to correlate prompt gamma emission to the ion path. This correlation, together with a high counting rate, paves the way toward real-time monitoring of the longitudinal dose profile during ion therapy treatments. Moreover, the time correlation between the prompt gamma detection and the transverse position of the incident ions measured by a beam monitor can provide real-time three dimensional control of the irradiation.