bluuebunny/crossref_metadata_2025 huggingface dataset:
Inflation detected at Mount Veniaminof, Alaska, with campaign GPS
Authors: Fournier Thomas , Freymueller Jeff
Published: October 2008

In 2005 a repeat GPS campaign was conducted at 12 sites on Mt.Veniaminof Volcano and the surrounding region. A previous survey in 2002 provided initial locations for the sites. The deformation that occurred in the three years between the two surveys consist of ∼2–4 cm of displacement caused by the northwest convergence of the Pacific and North America Plates and ∼0.5–1 cm displacements caused by a deep intrusion that may be associated with eruptive activity in 2003–2005. The site velocities are corrected for compression using a pre‐existing model for a locked subduction zone and the residuals modeled with volcanic sources in homogeneous and layered material. Although the data are fit equally well by several source models, we nevertheless gain important information about the deformation source. The best fitting models have depths that range from 3 to 17 km.
Crustal structure of the southern margin of the African continent: Results from geophysical experiments
Authors: Stankiewicz J. , Parsiegla N. , Ryberg T. , Gohl K. , Weckmann U. , Trumbull R. , Weber M.
Published: October 2008

A number of geophysical onshore and offshore experiments were carried out along a profile across the southern margin of the African Plate in the framework of the Inkaba yeAfrica project. Refraction seismic experiments show that Moho depth decreases rapidly from over 40 km inland to around 30 km at the present coast before gently thinning out toward the Agulhas‐Falkland Fracture Zone, which marks the transition zone between the continental and oceanic crust. In the region of the abruptly decreasing Moho depth, in the vicinity of the boundary between the Namaqua‐Natal Mobile Belt and the Cape Fold Belt, lower crustal P‐wave velocities up to 7.4 km/s are observed. This is interpreted as metabasic lithologies of Precambrian age in the Namaqua‐Natal Mobile Belt, or mafic intrusions added to the base of the crust by younger magmatism. The velocity model for the upper crust has excellent resolution and is consistent with the known geological record. A joint interpretation of the velocity model with an electrical conductivity model, obtained from magnetotelluric studies, makes it possible to correlate a high‐velocity anomaly north of the center of the Beattie magnetic anomaly with a highly resistive body.
A comparison study of data assimilation algorithms for ozone forecasts
Authors: Wu Lin , Mallet V. , Bocquet M. , Sportisse B.
Published: October 2008

The objective of this paper is to evaluate the performances of different data assimilation schemes with the aim of designing suitable assimilation algorithms for short‐range ozone forecasts in realistic applications. The underlying atmospheric chemistry‐transport models are stiff but stable systems with high uncertainties (e.g., over 20% for ozone daily peaks (Hanna et al., 1998; Mallet and Sportisse, 2006b), and much more for other pollutants like aerosols). Therefore the main difficulty of the ozone data assimilation problem is how to account for the strong model uncertainties. In this paper, the model uncertainties are either parameterized with homogeneous error correlations of the model state or estimated by perturbing some sources of the uncertainties, for example, the model uncertain parameters. Four assimilation methods have been considered, namely, optimal interpolation, reduced‐rank square root Kalman filter, ensemble Kalman filter, and four‐dimensional variational assimilation. These assimilation algorithms are compared under the same experimental settings. It is found that the assimilations significantly improve the 1‐day ozone forecasts. The comparison results reveal the limitations and the potentials of each assimilation algorithm. In our four‐dimensional variational method, the low dependency of model simulations on initial conditions leads to moderate performances. In our sequential methods, the optimal interpolation algorithm has the best performance during assimilation periods. Our ensemble Kalman filter algorithm perturbs the uncertain parameters to approximate model uncertainties and has better forecasts than the optimal interpolation algorithm during prediction periods. This could partially be explained by the low dependency on the uncertainties in initial conditions. The sensitivity analysis on the algorithmic parameters is also conducted for the design of suitable assimilation algorithms for ozone forecasts.
On the value of soil moisture measurements in vadose zone hydrology: A review
Authors: Vereecken H. , Huisman J. A. , Bogena H. , Vanderborght J. , Vrugt J. A. , Hopmans J. W.
Published: October 2008

We explore and review the value of soil moisture measurements in vadose zone hydrology with a focus on the field and catchment scales. This review is motivated by the increasing ability to measure soil moisture with unprecedented spatial and temporal resolution across scales. We highlight and review the state of the art in using soil moisture measurements for (1) estimation of soil hydraulic properties, (2) quantification of water and energy fluxes, and (3) retrieval of spatial and temporal dynamics of soil moisture profiles. We argue for the urgent need to have access to field monitoring sites and databases that include detailed information about variability of hydrological fluxes and parameters, including their upscaled values. In addition, improved data assimilation methods are needed that fully exploit the information contained in soil moisture data. The development of novel upscaling methods for predicting effective moisture fluxes and disaggregation schemes toward integrating large‐scale soil moisture measurements in hydrological models will increase the value of soil moisture measurements. Finally, we recognize a need to develop strategies that combine hydrogeophysical measurement techniques with remote sensing methods.
Dihydrotestosterone Stimulates Cerebrovascular Inflammation through NFκB, Modulating Contractile Function
Authors: Gonzales Rayna J , Duckles Sue P , Krause Diana N
Published: October 2008

Our previous studies show that long-term testosterone treatment augments vascular tone under physiological conditions and exacerbates endotoxin-induced inflammation in the cerebral circulation. However, testosterone can be metabolized by aromatase to estrogen, evoking a balance between androgenic and estrogenic effects. Therefore, we investigated the effect of the nonaromatizable androgen receptor agonist, dihydrotestosterone (DHT), on the inflammatory nuclear factor-κB (NFκB) pathway in cerebral blood vessels. Cerebral arteries were isolated from orchiectomized male rats treated chronically with DHT in vivo. Alternatively, pial arteries were isolated from orchiectomized males and were exposed ex vivo to DHT or vehicle in culture medium. DHT treatment, in vivo or ex vivo, increased nuclear NFκB activation in cerebral arteries and increased levels of the proinflammatory products of NFκB activation, cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS). Effects of DHT on COX-2 and iNOS were attenuated by flutamide. In isolated pressurized middle cerebral arteries from DHT-treated rats, constrictions to the selective COX-2 inhibitor NS398 or the selective iNOS inhibitor L-nil, [L-N6-(Iminoethyl)lysine], were increased, confirming a functional consequence of DHT exposure. In conclusion, activation of the NFκB-mediated COX-2/iNOS pathway by the selective androgen receptor agonist, DHT, results in a state of vascular inflammation. This effect may contribute to sex-related differences in cerebrovascular pathophysiology.
Ubiquitin binding modulates IAP antagonist-stimulated proteasomal degradation of c-IAP1 and c-IAP2
Authors: Blankenship John W. , Varfolomeev Eugene , Goncharov Tatiana , Fedorova Anna V. , Kirkpatrick Donald S. , Izrael-Tomasevic Anita , Phu Lilian , Arnott David , Aghajan Mariam , Zobel Kerry , Bazan J. Fernando , Fairbrother Wayne J. , Deshayes Kurt , Vucic Domagoj
Published: October 2008

A family of anti-apoptotic regulators known as IAP (inhibitor of apoptosis) proteins interact with multiple cellular partners and inhibit apoptosis induced by a variety of stimuli. c-IAP (cellular IAP) 1 and 2 are recruited to TNFR1 (tumour necrosis factor receptor 1)-associated signalling complexes, where they mediate receptor-induced NF-κB (nuclear factor κB) activation. Additionally, through their E3 ubiquitin ligase activities, c-IAP1 and c-IAP2 promote proteasomal degradation of NIK (NF-κB-inducing kinase) and regulate the non-canonical NF-κB pathway. In the present paper, we describe a novel ubiquitin-binding domain of IAPs. The UBA (ubiquitin-associated) domain of IAPs is located between the BIR (baculovirus IAP repeat) domains and the CARD (caspase activation and recruitment domain) or the RING (really interesting new gene) domain of c-IAP1 and c-IAP2 or XIAP (X-linked IAP) respectively. The c-IAP1 UBA domain binds mono-ubiquitin and Lys48- and Lys63-linked polyubiquitin chains with low-micromolar affinities as determined by surface plasmon resonance or isothermal titration calorimetry. NMR analysis of the c-IAP1 UBA domain–ubiquitin interaction reveals that this UBA domain binds the classical hydrophobic patch surrounding Ile44 of ubiquitin. Mutations of critical amino acid residues in the highly conserved MGF (Met-Gly-Phe) binding loop of the UBA domain completely abrogate ubiquitin binding. These mutations in the UBA domain do not overtly affect the ubiquitin ligase activity of c-IAP1 or the participation of c-IAP1 and c-IAP2 in the TNFR1 signalling complex. Treatment of cells with IAP antagonists leads to proteasomal degradation of c-IAP1 and c-IAP2. Deletion or mutation of the UBA domain decreases this degradation, probably by diminishing the interaction of the c-IAPs with the proteasome. These results suggest that ubiquitin binding may be an important mechanism for rapid turnover of auto-ubiquitinated c-IAP1 and c-IAP2.
The ongoing legitimacy project: corporate philanthropy as protective strategy
Authors: Miller Justin
Published: October 2008

Combining insights from institutional theory and resource dependence theory, this paper suggests that legitimacy is a scarce intangible resource that is always contested. Legitimacy, as a socially defined resource, represents relational power within a community. The various members of an organizational field, therefore, seek to gain, maintain, defend, and deny to others, access to the legitimacy resource. The author looks to the issue of healthcare‐related employment benefits, and notes that organizations deny such benefits in communities containing strong labor movements, substituting less expensive corporate philanthropic practices in order to demonstrate commitment to the social contract and norms of legitimacy while simultaneously denying the legitimacy of organized labor's agenda. In communities without strong labor movements, however, corporations are less encumbered in providing healthcare benefits because in such communities they do not need to work to deny the legitimacy of organized labor.
O
17
and N93b NMR investigation of magnetoelectric effect in Pb(Fe1/2Nb1/2)O3
Authors: Blinc Robert , Laguta Valentin V. , Zalar Boštjan , Zupančič Blaž , Itoh Mitsuru
Published: October 2008

The O17 and N93b quadrupole perturbed nuclear magnetic resonance spectra of multiferroic Pb(Fe1/2Nb1/2)O3 have been measured. The results show that the ordering at TN=143 K is antiferromagnetic with spin canting and that there is another magnetic transition around 20 K. The system consists of dielectric nanodomains and superparamagnetic clusters that order at TN, producing the magnetoelectric effect.
Serrated deformation of metals and alloys at low temperatures (Review)
Authors: Pustovalov V. V.
Published: October 2008

Plastic deformation at constant rate and low temperatures starting with 20–30K, as a rule, occurs in the form of oscillations of the deforming stress (serrated deformation). Low-temperature serrated deformation (LTSD) appears under special conditions where deformation occurs as a result of the specific conditions of dislocation dynamics and, possibly, as result of special physical conditions of deformation (low thermal conductivity and specific heat of the sample, heat exchange with the cooling medium). A large number of experimental and theoretical works have been performed since the discovery of LTSD in the 1950s but not even one review has appeared. Further advances in understanding the mechanism of LTSD and the development of a theory of this phenomenon require that the experimental data be systematized. As a rule, individual experimental facts have been used when theories of LTSD have been compared with experiment. The present review attempts to collect as much accessible experimental data as possible, systematize these data, determine the main characteristics of LTSD, examine theoretical hypotheses, compare theory with experiment, and suggest possible mechanisms for low-temperature serrated deformation.
Magnetic proximity effect in La0.7Ca0.3MnO3∕La0.9Ca0.1MnO3 multilayer films with diffusive interfaces
Authors: Prokhorov V. G. , Kaminsky G. G. , Lee Y. P. , Park S. Y. , Hyun Y. H. , Park J. S. , Svetchnikov V. L.
Published: October 2008

The structural, magnetic, and transport properties of La0.7Ca0.3MnO3∕La0.9Ca0.1MnO3 multilayer films prepared by rf-magnetron sputtering are investigated. High-resolution electron-microscopy studies reveal the formation of different crystal structures in the constituent sublayers, but without sharp and well-defined interfaces. At the same time, small regions of double-period modulated phase exist in the La0.9Ca0.1MnO3 sublayers at room temperature, manifesting the formation of a charge-ordered antiferromagnetic state. The magnetic measurements reveal a significant enhancement of the ferromagnetic ordering in the La0.9Ca0.1MnO3 layers due to a strong magnetic coupling between the constituent sublayers. The multilayer films show anisotropic saturation magnetization at low temperature and an alternating shape of the temperature-dependent anisotropic magnetoresistance near the metal-insulator transition.
Molecular solvent model of cylindrical electric double layers: A systematic study by Monte Carlo simulations and density functional theory
Authors: Goel Teena , Patra Chandra N. , Ghosh Swapan K. , Mukherjee Tulsi
Published: October 2008

We present the Monte Carlo simulation and density functional study of structure of cylindrical double layers considering solvent as the third component. We have chosen molecular solvent model, where ions and solvent molecules are considered as charged and neutral hard spheres, respectively, having equal diameter. The polyionic cylinder is modeled as an infinite, rigid, and impenetrable charged hard cylinder surrounded by the electrolyte and the solvent spheres. The theory is partially perturbative where the hard-sphere interactions are treated within the weighted density approach, the corresponding ionic interactions have been evaluated through second-order functional Taylor expansion with respect to the bulk electrolyte. The Monte Carlo simulations have been performed in canonical ensemble. The system is studied at varying concentrations of electrolyte ions and the solvent molecules, at different valences of the electrolyte, at different sizes of hard spheres, and at varying surface charge density. The theory and the simulation results are found to be in good agreement at different parametric conditions. The hard-sphere exclusion effects due to molecular nature of the solvent are shown to have special implications in characterizing diffuse layer phenomena such as layering and charge inversion.
An efficient and exact stochastic simulation method to analyze rare events in biochemical systems
Authors: Kuwahara Hiroyuki , Mura Ivan
Published: October 2008

In robust biological systems, wide deviations from highly controlled normal behavior may be rare, yet they may result in catastrophic complications. While in silico analysis has gained an appreciation as a tool to offer insights into system-level properties of biological systems, analysis of such rare events provides a particularly challenging computational problem. This paper proposes an efficient stochastic simulation method to analyze rare events in biochemical systems. Our new approach can substantially increase the frequency of the rare events of interest by appropriately manipulating the underlying probability measure of the system, allowing high-precision results to be obtained with substantially fewer simulation runs than the conventional direct Monte Carlo simulation. Here, we show the algorithm of our new approach, and we apply it to the analysis of rare deviant transitions of two systems, resulting in several orders of magnitude speedup in generating high-precision estimates compared with the conventional Monte Carlo simulation.
The structure of mixed H2O–OH monolayer films on Ru(0001)
Authors: Tatarkhanov M. , Fomin E. , Salmeron M. , Andersson K. , Ogasawara H. , Pettersson L. G. M. , Nilsson A. , Cerdá J. I.
Published: October 2008

Scanning tunneling microscopy (STM) and x-ray absorption spectroscopy (XAS) have been used to study the structures produced by water on Ru(0001) at temperatures above 140 K. It was found that while undissociated water layers are metastable below 140 K, heating above this temperature produces drastic transformations, whereby a fraction of the water molecules partially dissociate and form mixed H2O–OH structures. X-ray photoelectron spectroscopy and XAS revealed the presence of hydroxyl groups with their O–H bond essentially parallel to the surface. STM images show that the mixed H2O–OH structures consist of long narrow stripes aligned with the three crystallographic directions perpendicular to the close-packed atomic rows of the Ru(0001) substrate. The internal structure of the stripes is a honeycomb network of H-bonded water and hydroxyl species. We found that the metastable low temperature molecular phase can also be converted to a mixed H2O–OH phase through excitation by the tunneling electrons when their energy is 0.5 eV or higher above the Fermi level. Structural models based on the STM images were used for density functional theory optimizations of the stripe geometry. The optimized geometry was then utilized to calculate STM images for comparison with the experiment.
Phase separation under ultraslow cooling: Onset of nucleation
Authors: Vollmer J.
Published: October 2008

We discuss the interplay between a slow continuous drift of temperature, which induces continuous phase separation, and the nonlinear diffusion term in the ϕ4-model for phase separation of a binary mixture. This leads to a bound for the stability of diffusive demixing. It is demonstrated that the same findings apply in other models, except for slight modifications of the bound. In practice stable diffusive demixing can only be achieved when special precautions are taken in experiments on real mixtures. Therefore, the recent observations on complex dynamical behavior in such systems should be considered as a new challenge for understanding generic features of phase-separating systems.
Evidence for molecular-assisted recombination of He+ from particle balance measurements in helium-hydrogen mixture plasmas in PISCES-A
Authors: Cai Laizhong , Tynan George R. , Hollmann Eric M.
Published: October 2008

Particle balance measurements of He+ ions in He∕H mixture plasma are performed by using wall probes, plunging probes, and spectroscopy. The measurements indicate that radial loss to the chamber wall is the dominant ion sink; nevertheless, a missing ion sink is observed as the plasma hydrogen fraction is increased. This sink term is attributed to hydrogen-mediated recombination of He+ ions, so-called molecular-assisted recombination (MAR). Independent evidence for MAR (acting on hydrogen ions, however) is seen in anomalously large Hα∕Hγ ratios at the cold plasma edge.
Conformational response of supercoiled DNA to confinement in a nanochannel
Authors: Lim Wilber , Ng Siow Yee , Lee Chinchai , Feng Yuan Ping , van der Maarel Johan R. C.
Published: October 2008

Monte Carlo simulations were done to study the conformation of supercoiled DNA confined in a nanochannel. The molecule has a superhelical density of around −0.05 and is bathed in a monovalent salt solution with an ionic strength of 2, 10, or 150 mM. The cross-sectional diameter of the circular shaped nanochannel was varied in the range of 10 to 80 nm. The conformational properties were characterized by the writhing number and the distribution in the distance between the two opposing strands of the superhelix. With increasing confinement, as set by a smaller tube diameter and/or decreased screening of the Coulomb interaction, the supercoil becomes more tightly interwound and long-range structural features such as branching and the formation of hairpins are progressively suppressed. Analysis of the energetics shows a concurrent increase in electrostatic energy and energy of interaction of the supercoil with the wall, but the elastic twisting energy decreases. Confinement in a nanochannel or otherwise hence results in a decrease in the absolute value of the twist exerted on the duplex. The bending energy remains approximately constant, which means that there are no significant deflections from the wall. The simulation results are interpreted with theory based on the wormlike chain model, including the effects of the wall, charge, elasticity, and configurational entropy. It was found that the theory is reasonably successful in predicting the structural response to the confinement at the local level of the diameter and pitch of the supercoil.
Ab initio potential energy surfaces for both the ground (X̃ A1′) and excited (Ã A1″) electronic states of HGeCl and the absorption and emission spectra of HGeCl/DGeCl
Authors: Lin Sen , Xie Daiqian , Guo Hua
Published: October 2008

Potential energy surfaces for the ground (X̃ A1′) and excited (Ã A1″) electronic states of HGeCl and the transition dipole moment surface were obtained using an internally contracted multireference configuration interaction method with the Davidson correction and an augmented correlation-consistent polarized valence quadruple zeta basis set. Calculated vibrational energy levels of HGeCl and DGeCl on both the ground and excited electronic states are in excellent agreement with available experimental data. In addition, the absorption and emission spectra of both HGeCl and DGeCl were obtained using an efficient single Lanczos propagation method and the agreement with experimental spectra is also excellent.
Phenomenological theory of magnetization reversal in nanosystems with competing anisotropies
Authors: Leonov A. A. , Rößler U. K. , Bogdanov A. N.
Published: October 2008

The interplay between intrinsic and surface/interface-induced magnetic anisotropies strongly influences magnetization processes in nanomagnetic systems. We develop a micromagnetic theory to describe the field-driven reorientation in nanomagnets with cubic and uniaxial anisotropies. Spin configurations in competing phases and parameters of accompanying multidomain states are calculated as functions of the applied field and the magnetic anisotropies. The constructed magnetic phase diagrams allow to classify different types of the magnetization reversal and to provide detailed analysis of the switching processes in magnetic nanostructures. The calculated magnetization profiles of isolated domain walls show that the equilibrium parameters of such walls are extremely sensitive to applied magnetic field and values of the competing anisotropies and can vary in a broad range. For nanolayers with perpendicular anisotropy the geometrical parameters of stripe domains have been calculated as functions of a bias field. The results are applied to analyze the magnetization processes as observed in various nanosystems with competing anisotropies, mainly, in diluted magnetic semiconductor films (Ga,Mn)As.
Convection in deep vertically shaken particle beds. III. Convection mechanisms
Authors: Klongboonjit Sakon , Campbell Charles S.
Published: October 2008

Convection in a deep vertically vibrated two-dimensional cell of granular material occurs in the form of counter-rotating cells that move material from the walls to the center of the channel and back again. At least for deep beds, where for much of the cycle, particles are in long duration contact with their neighbors, convection only appears for a short potion of every third vibrational period. That period is delimited by the interaction of three types of internal waves, a compression wave, and two types of expansion waves. Four mechanisms are identified that drive the four basic motions of convection: (1) particles move upward at the center as the result of compression wave, (2) downward at the wall as a combined effect of frictional holdback by the walls and the downward pull of gravity, (3) from the center to the walls along the free surface due to the heaping of the bed generated by the compression wave, and (4) toward the center in the interior of the box to form the bottom of convection rolls due to the relaxation of compressive stresses caused by an expansion wave. Convection only occurs when the conditions are right for all four mechanisms to be active simultaneously.
Theoretical and experimental investigations of a polyalkylated-thieno[3,2-b]thiophene semiconductor
Authors: Northrup J. E. , Chabinyc M. L. , Hamilton R. , McCulloch I. , Heeney M.
Published: October 2008

Theoretical and experimental investigations were performed for the organic semiconductor poly(3,6-dialkylthieno[3,2-b]thiophene-co-thieno[3,2-b]thiophene) (PATT). The properties of PATT were investigated with density functional calculations, x-ray diffraction, and differential scanning calorimetry. In PATT the backbone is constructed such that its alkyl side-chain separations are intermediate between those exhibited by poly(3-hexylthiophene) and poly(2,5-bis(3- alkylthiophen-2-yl)thieno[3,2-b]thiophene). An objective is to test whether such an intermediate side-chain separation leads to increased bonding strength between layers and perhaps promotes improved crystalline order and hole mobility. Measurements of hole mobility in solution processed thin film transistors employing PATT as the semiconductor indicate a mobility of 0.024 cm2/V s. Density functional calculations predict that the planar conjugated backbone of PATT is tilted. The driving force for tilting, a structural feature exhibited by many organic semiconductors, is shown to be electrostatic energy reduction.
Macroscopic electrostatic potentials and interactions in self-assembled molecular bilayers: The case of Newton black films
Authors: Gamba Z.
Published: October 2008

We propose a very simple but “realistic” model of amphiphilic bilayers, simple enough to be able to include a large number of molecules in the sample but nevertheless detailed enough to include molecular charge distributions, flexible amphiphilic molecules, and a reliable model of water. All these parameters are essential in a nanoscopic scale study of intermolecular and long range electrostatic interactions. We also propose a novel, simple, and more accurate macroscopic electrostatic field for model bilayers. This model goes beyond the total dipole moment of the sample, which on a time average is zero for this type of symmetrical samples; i.e., it includes higher order moments of this macroscopic electric field. We show that by representing it with a superposition of Gaussians, it can be analytically integrated, and therefore its calculation is easily implemented in a molecular dynamics simulation (even in simulations of nonsymmetrical bi- or multilayers). In this paper we test our model by molecular dynamics simulations of Newton black films.
Molecular transistors based on BDT-type molecular bridges
Authors: Wheeler W. D. , Dahnovsky Yu.
Published: October 2008

In this work we study the effect of electron correlations in molecular transistors with molecular bridges based on 1,4-benzene-dithiol (BDT) and 2-nitro-1,4-benzene-dithiol (nitro-BDT) by using ab initio electron propagator calculations. We find that there is no gate field effect for the BDT based transistor in accordance with the experimental data. After verifying the computational method on the BDT molecule, we consider a transistor with a nitro-BDT molecular bridge. From the electron propagator calculations, we predict strong negative differential resistance at small positive and negative values of source-drain voltages. The explanation of the peak and the minimum in the current is given in terms of the molecular orbital picture and switch-on (-off) properties due to the voltage dependencies of the Dyson poles (ionization potentials). When the current is off, the electronic states on both electrodes are populated resulting in the vanishing tunneling probability due to the Pauli principle. Besides the minimum and the maximum in the I-V characteristics, we find a strong gate field effect in the conductance where the peak at Vsd=0.15eV and Eg=4×10−3a.u. switches to the minimum at Eg=−4×10−3a.u. A similar behavior is discovered at the negative Vsd. Such a feature can be used for fast current modulation by changing the polarity of a gate field.
Excitation mechanism in the photoisomerization of a surface-bound azobenzene derivative: Role of the metallic substrate
Authors: Hagen Sebastian , Kate Peter , Leyssner Felix , Nandi Dhananjay , Wolf Martin , Tegeder Petra
Published: October 2008

Two-photon photoemission spectroscopy is employed to elucidate the electronic structure and the excitation mechanism in the photoinduced isomerization of the molecular switch tetra-tert-butyl-azobenzene (TBA) adsorbed on Au(111). Our results demonstrate that the optical excitation and the mechanism of molecular switching at a metal surface is completely different compared to the corresponding process for the free molecule. In contrast to direct (intramolecular) excitation operative in the isomerization in the liquid phase, the conformational change in the surface-bound TBA is driven by a substrate-mediated charge transfer process. We find that photoexcitation above a threshold hν≈2.2 eV leads to hole formation in the Au d-band followed by a hole transfer to the highest occupied molecular orbital of TBA. This transiently formed positive ion resonance subsequently results in a conformational change. The photon energy dependent photoisomerization cross section exhibit an unusual shape for a photochemical reaction of an adsorbate on a metal surface. It shows a thresholdlike behavior below hν≈2.2 eV and above hν≈4.4 eV. These thresholds correspond to the minimum energy required to create single or multiple hot holes in the Au d-bands, respectively. This study provides important new insights into the use of light to control the structure and function of molecular switches in direct contact with metal electrodes.
Improving the B3LYP bond energies by using the X1 method
Authors: Wu Jianming , Xu Xin
Published: October 2008

Recently, we proposed the X1 method which combines density functional theory method (B3LYP) with a neural network correction for an accurate yet efficient prediction of heats of formation [J. M. Wu and X. Xu, J. Chem. Phys. 127, 214105 (2007)]. In the present work, we examine the X1 performance to calculate bond energies. We use 32 radicals and 115 molecules to set up 142 bond dissociation reactions. For the total of 147 heats of formations and 142 bond energies, B3LYP leads to mean absolute deviations of 4.54 and 6.26 kcal/mol, respectively, while X1 reduces the corresponding errors to 1.41 and 2.45 kcal/mol.
Area dependent efficiency of organic solar cells
Authors: Gupta Dhritiman , Bag Monojit , Narayan K. S.
Published: October 2008

Efficiency estimations of organic solar cells are observed to be dependent on the dimensions of electrode defining the active area. We address this issue and explore the manner in which efficiency scales in polymer solar cells by studying these devices as a function of electrode area and incident beam size. The increase in efficiency for smaller active areas can be explained by the reduced electrical resistive loss, the enhanced optical effects, and the finite additional fraction of photogenerated carriers in the vicinity of the perimeter defined by the metal electrode
Stable and unstable invariant manifolds in a partially chaotic magnetic configuration generated by nonlinear reconnection
Authors: Borgogno D. , Grasso D. , Pegoraro F. , Schep T. J.
Published: October 2008

A numerical contour dynamics code has been employed to calculate the stable and unstable manifolds related to two interacting magnetic island chains. The magnetic configuration is generated by a nonlinear reconnection process described in D. Borgogno et al. [Phys. Plasmas. 12, 032309 (2005)]. The appearance of the first homoclinic and heteroclinic intersections of the dominant manifolds are shown and one of the associated uniformly hyperbolic orbits is given. The stickiness of the field lines around the island and the eventual development of global stochasticity are discussed. The basic geometry of the magnetic configuration is periodic so that the structure of the manifolds may be compared with the one obtained with Poincaré plots.
High precision (14 bit), high density (octal) analog to digital converter for spectroscopy applications
Authors: Subramaniam E. T. , Jain Mamta , Bhowmik R. K. , Tripon Michel
Published: October 2008

Nuclear and particle physics experiments with large number of detectors require signal processing and data collection strategies that call for the ability to collect large amount of data while not sacrificing the precision and accuracy of the data being collected. This paper deals with the development of a high precision pulse peak detection, analog to digital converter (ADC) module with eight independent channels in plug-in daughter card motherboard model, best suited for spectroscopy experiments. This module provides multiple channels without cross-talk and of 14 bit resolution, while maintaining high density (each daughter card has an area of just 4.2″×0.51″) and exhibiting excellent integral nonlinearity (≤±2 mV or ±0.02% full scale reading) and differential nonlinearity (≤±1%). It was designed, developed and tested, in house, and gives added advantages of cost effectiveness and ease of maintenance.
Dopant-enhanced atmospheric pressure glow discharge ionization source for ion mobility spectrometry
Authors: Dong Can , Wang Lina , Wang Weiguo , Hou Keyou , Li Haiyang
Published: October 2008

A dopant-enhanced atmospheric pressure direct current glow discharge ionization source for ion mobility spectrometry (APDCGD-IMS) has been described. It is shown that the ion intensity can be greatly increased by addition of species with ionization energy lower than that of buffer gas when the direction of the electric field between the target electrode and the extraction electrode was opposite to that of the drift field. With N2 as the buffer gas, adding O2 (or air), acetone, and CH2Cl2 with certain concentration can enhanced the ion intensity more than one order of magnitude, and for O2, it was found that the enhancement depending on both the concentration of O2 and the flow rate of the carrier gas, and the largest enhancements of the signal intensity for electron in negative mode and reaction ion in positive mode reached at O2 concentration about 1.5%–2%. The main physicochemical processes were summarized and discussed, and a zero-dimensional reaction rate model was set up to simulate the corresponding results. It was proposed that the enhancement of signal intensity was ascribed to the various ionization processes and reactions in APDCGD.
Gadolinium calcium oxyborate piezoelectric single crystals for ultrahigh temperature (>1000 °C) applications
Authors: Zhang Shujun , Frantz Eric , Xia Ru , Everson William , Randi Joseph , Snyder David W. , Shrout Thomas R.
Published: October 2008

ReCa 4 O ( BO 3 ) 3 oxyborate crystals (ReCOB, where Re is a rare earth element such as Gd) were grown using the Czochralski pulling technique. The crystals belong to Cm space group and the relationships of the as-grown crystal morphology with crystallographic and physical coordinates were determined. The optimum length extensional and thickness shear vibrations of GdCOB were found for (ZYl)40° and (YXt)33° cuts, with electromechanical coupling factors k32 and k26, being on the order of 17.5% and 25% and piezoelectric coefficients d32 and d26 around −4.5 and 11.7 pC/N, respectively. Of particular significance is the nearly temperature independent behavior up to >1000 °C. Together with its high resistivity (∼5×106 Ω cm at 1000 °C) and high mechanical quality factor (∼4000 at 1000 °C) make GdCOB and/or ReCOB crystals promising candidates for the next generation sensing applications at ultrahigh temperature (>1000 °C).
Delta-doping optimization for high quality p-type GaN
Authors: Bayram C. , Pau J. L. , McClintock R. , Razeghi M.
Published: October 2008

Delta (δ−) doping is studied in order to achieve high quality p-type GaN. Atomic force microscopy, x-ray diffraction, photoluminescence, and Hall measurements are performed on the samples to optimize the δ-doping characteristics. The effect of annealing on the electrical, optical, and structural quality is also investigated for different δ-doping parameters. Optimized pulsing conditions result in layers with hole concentrations near 1018 cm−3 and superior crystal quality compared to conventional p-GaN. This material improvement is achieved thanks to the reduction in the Mg activation energy and self-compensation effects in δ-doped p-GaN.
Small molecule sensitizers for near-infrared absorption in polymer bulk heterojunction solar cells
Authors: Peet J. , Tamayo A. B. , Dang X.-D. , Seo J. H. , Nguyen T.-Q.
Published: October 2008

A low band gap small molecule chromophore has been incorporated into a polymer/fullerene bulk heterojunction (BHJ) solar cell yielding increased carrier generation in the near infrared and increased overall short circuit current. The use of a small concentration of a soluble oligothiophene with a diketopyrrolopyrrole core can extend the absorption and photocurrent of poly(3-hexyl thiophene):[6,6]-phenyl C71 butyric acid methyl ester solar cells to 800 nm. Photocurrent from the dye embedded within the polymer BHJ is demonstrated, and the use of soluble small molecule sensitizers as a path toward high efficiency solar cells is discussed.
Self-diffusion in germanium isotope multilayers at low temperatures
Authors: Hüger E. , Tietze U. , Lott D. , Bracht H. , Bougeard D. , Haller E. E. , Schmidt H.
Published: October 2008

Self-diffusion in intrinsic single crystalline germanium was investigated between 429 and 596 °C using G70e/Gnate isotope multilayer structures. The diffusivities were determined by neutron reflectometry from the decay of the first and third order Bragg peak. At high temperatures the diffusivities are in excellent agreement with literature data obtained by ion beam sputtering techniques, while considerably smaller diffusion lengths between 0.6 and 4.1 nm were measured. At lower temperatures the accessible range of diffusivities could be expanded to D≈1×10−25 m2 s−1, which is three orders of magnitude lower than the values measured by sputtering techniques. Taking into account available data on Ge self-diffusion, the temperature dependence is accurately described over nine orders of magnitude by a single Arrhenius equation. A diffusion activation enthalpy of 3.13±0.03 eV and a pre-exponential factor of 2.54×10−3 m2 s−1 for temperatures between 429 and 904 °C are obtained. Single vacancies are considered to prevail self-diffusion in Ge over the whole temperature range.
Resonances of individual lithographic gold nanowires in the infrared
Authors: Neubrech F. , Weber D. , Lovrincic R. , Pucci A. , Lopes M. , Toury T. , de La Chapelle M. Lamy
Published: October 2008

With infrared spectroscopic microscopy using synchrotron radiation, we systematically studied resonant light scattering from electron-beam lithographically produced gold nanowires (nanostripes) with diameters in the 100 nm range and with various lengths below 1 to about 2.5 μm. Similar to electrochemically grown cylindrical wires of high crystalline quality, clear antennalike plasmon resonances were observed for these stripelike and less-perfect wires. The resonance wavelength shifts with length as theoretically predicted for cylindrical gold antennas in the optical range. Surprisingly, also the extinction cross section of the nanostripes is equal to that measured for highly crystalline cylinders.
Solar cells on low-resistivity boron-doped Czochralski-grown silicon with stabilized efficiencies of 20%
Authors: Lim Bianca , Hermann Sonja , Bothe Karsten , Schmidt Jan , Brendel Rolf
Published: October 2008

Recently, it was shown that the boron-oxygen complex responsible for the light-induced lifetime degradation in oxygen-rich boron-doped silicon can be permanently deactivated by illumination at elevated temperatures. Since the degradation is particularly harmful in low-resistivity Czochralski silicon (Cz-Si), we apply the deactivation procedure to a high-efficiency rear interdigitated single evaporation emitter wrap-through solar cell made on 1.4Ωcm B-doped Cz-Si. The energy conversion efficiency is thereby increased by more than 1% absolute compared to the degraded state to 20.3% on a designated area of 92cm2 and is furthermore shown to be stable under illumination at room temperature.
Simple theoretical model for the temperature stability of InAs/GaAs self-assembled quantum dot lasers with different p-type modulation doping levels
Authors: Jin C. Y. , Liu H. Y. , Jiang Q. , Hopkinson M. , Wada O.
Published: October 2008

We have developed a simple theoretical model to account for the effects of different p-doping levels on the temperature-dependent performance of InAs/GaAs self-assembled quantum dot (QD) lasers. An assumption of equal occupation probabilities among QDs has been applied for operating conditions near the lasing threshold. Theoretical results indicate that there is an optimum p-doping region, which can provide the lowest temperature dependence of lasing threshold at room temperature.
Immobilization of DNA-Au nanoparticles on aminosilane-functionalized aluminum nitride epitaxial films for surface acoustic wave sensing
Authors: Chiu Chi-Shun , Lee Hong-Mao , Kuo Cheng-Tai , Gwo Shangjr
Published: October 2008

A generic method for immobilization of gold nanoparticle bioconjugates onto aluminum nitride (AlN) surfaces using aminosilane molecules as cross-linkers is demonstrated for surface acoustic wave (SAW) sensor applications. Electrostatic interaction between positively charged surface amine groups and negatively charged DNA-Au nanoparticle conjugates allows the self-assembly of a probe nanoparticle monolayer onto functionalized AlN surfaces under physiological conditions. Both 10 and 20 nm Au nanoparticles bound with thiolated oligonucleotides were employed in the detection scheme. We show that Au nanoparticles can play multiple roles in SAW sensing for probe immobilization, signal amplification, and labeling.
Fabrication of triangular nanochannels using the collapse of hydrogen silsesquioxane resists
Authors: Choi Sookyung , Yan Minjun , Adesida Ilesanmi
Published: October 2008

We report a simple method to fabricate nanometer-scale channels using hydrogen silsesquioxane (HSQ) resists. The collapse of high-aspect-ratio structures during the rinse and drying steps results in self-formed enclosed triangular-shaped channels. Using electron-beam lithography, dense arrays of HSQ triangular nanochannels were fabricated with high precision. This approach provides significant flexibility in design and simplicity in processing. We also show that the properties of HSQ resists are well suited for the fabrication of buried nanochannel structures.
Expression of follicle-stimulating hormone and luteinising hormone binding sites in the bitch ovary during the follicular phase
Authors: Saint-Dizier Marie , Jaffré Nina , Reynaud Karine , Remy Benoît , Thoumire Sandra , Chastant-Maillard Sylvie
Published: October 2008

In the female dog, in contrast with most mammals, the growing follicle starts to luteinise several days before ovulation. Little is known about the physiological control of the final follicular growth in this species. In order to better understand the pituitary regulation of follicular growth, specific binding sites for FSH and LH were localised and quantified by autoradiography using [125I]-porcine (p) gonadotrophins on ovarian sections (7 μm) from adult Beagle bitches during the follicular phase. Follicles were analysed either before the LH surge (n = 4 bitches; n = 117 follicles) or after the LH surge and before ovulation (n = 5 bitches; n = 110 follicles). FSH binding sites were specifically and homogeneously expressed at high levels on granulosa cells of all healthy follicles from the preantral stage onwards. In contrast, LH binding sites were detected homogeneously and at high levels only on granulosa cells of follicles larger than 1 mm in diameter, including luteinised follicles. Theca binding of LH (but not FSH) was also observed, but only when using high concentrations of [125I]-pLH. The overall incidence of atresia was 45.8% and was dependent upon follicular diameter. Quantitative analysis of labelling showed that atretic follicles had reduced levels of both FSH and LH binding sites compared with healthy follicles. In healthy follicles, levels of both FSH and LH binding sites changed with follicle diameter. Compared with other mammals, the acquisition of LH binding on canine granulosa cells occurs in smaller sized follicles relative to the size of ovulation.
Simulation model for contraceptive management of the Assateague Island feral horse population using individual-based data
Authors: Ballou Jonathan D. , Traylor-Holzer Kathy , Turner Allison , Malo Aurelio F. , Powell David , Maldonado Jesus , Eggert Lori
Published: October 2008

The National Park Service (NPS) manages a culturally significant population of feral horses (Equus caballus) inhabiting the Maryland portion of Assateague Island, a barrier island in the eastern United States. Rapid growth of this population over the past few decades from 28 to 166 horses negatively impacts native species and ecological processes on the island. Since 1994, contraception via porcine zona pellucida vaccine has been used to control horse numbers, although herd reduction has been slower than initially expected, leading NPS to consider other management options. An individual-based stochastic simulation model was developed using the Vortex software program to examine the effects of different management strategies on the population. Data from the managed population were used to populate the model parameters. Model projections over the next 50 years using current management practices show an average rate of population decline of 13% per year, suggesting that the population will reach the management target of 80–100 horses in 5–8 years. The effectiveness of contraception to reduce the herd and maintain it at various target sizes of 20–100 horses was also assessed. The accumulation of inbreeding at each target population size was also modelled.