bluuebunny/crossref_metadata_2025 huggingface dataset:
Luminescence and Raman scattering of nonpolymerized and photopolymerized fullerene films at 297 and 5K
Authors: Karachevtsev V. A. , Glamazda A. Yu. , Pashinskaya V. A. , Peschanskiĭ A. V. , Plokhotnichenko A. M. , Fomin V. I.
Published: August 2007

Luminescence and Raman scattering spectroscopy are used to study nonpolymerized and photopolymerized (with 45% and 85% polymerization) fullerene films (0.5μm thick on a Si substrate) at 5 and 297K. The films were polymerized while they were being deposited and irradiated with UV light. The wide-band emission observed at room temperature from a nonpolymerized fullerene film becomes structured at 5K. A short-wavelength band peaking at 695nm appears in the emission. The intensity of this band decreases with polymerization. Analysis of the low-temperature luminescence spectra of fullerene shows that polymerization is accompanied by a shift of the luminescence bands into the red region. Low-temperature investigations revealed lines in the Raman scattering spectrum of an 85% polymerized film which peak at the frequencies 1466 and 1461cm−1. These lines are due to the vibrations of fullerene dimers and a polymerized chain, respectively. Dimers predominate in a film with 45% polymerization in the polymerized phase, while the fraction of dimers in an 85% polymerized film decreases and chain formations predominate.
Transition strengths and first-order properties of excited states from local coupled cluster CC2 response theory with density fitting
Authors: Kats Danylo , Korona Tatiana , Schütz Martin
Published: August 2007

A new ab initio method for calculating transition strengths and orbital-unrelaxed first-order properties of singlet ground and excited states of extended molecular systems is presented. It is based on coupled cluster response theory at the level of the CC2 model with local approximations introduced to the doubles-excitation part of the wave function. Density fitting is employed for the calculation of the electron repulsion integrals, so that—with the exception of doubles amplitudes—only three-indexed objects do occur in the formalism. The new method was tested by performing calculations for a set of various molecules and excited states and by comparing the results with corresponding canonical (nonlocal) calculations. It turned out that for calculating transition strengths and properties of excited states the ordinary Boughton-Pulay domains are insufficient in numerous cases. To circumvent this problem a new scheme for extending domains is proposed, which is based on the solution of the coupled perturbed localization and Hartree-Fock equations. When such extended domains are used, a satisfactory agreement between canonical and local results is achieved.
Central limit theorem for a class of relativistic diffusions
Authors: Angst Jürgen , Franchi Jacques
Published: August 2007

Two similar Minkowskian diffusions have been considered, on one hand by Debbasch and co-workers [J. Math. Phys. 40, 2891 (2001); Eur. Phys. J. 19, 37 (2001); 23, 487 (2001); J. Stat. Phys. 88, 945 (1997); 90, 1179 (1998)], and on the other hand by Dunkel and Hänggi [Phys. Rev. E 71, 016124 (2005); 72, 036106 (2005)]. We address here two questions, asked by Debbasch and Rivet [J. Stat. Phys. 90, 1179 (1998)] and by Dunkel and Hänggi [Phys. Rev. E 71, 016124 (2005); 72, 036106 (2005)], respectively, about the asymptotic behavior of such diffusions. More generally, we establish a central limit theorem for a class of Minkowskian diffusions, to which the two above ones belong. As a consequence, we correct a partially wrong guess by Dunkel and Hänggi [Phys. Rev. E 71, 016124 (2005)].
Short pulse laser train for laser plasma interaction experiments
Authors: Kline J. L. , Shimada T. , Johnson R. P. , Montgomery D. S. , Hegelich B. M. , Esquibel D. M. , Flippo K. A. , Gonzales R. P. , Hurry T. R. , Reid S. L.
Published: August 2007

A multiframe, high-time resolution pump-probe diagnostic consisting of a consecutive train of ultrashort laser pulses (∼ps) has been developed for use with a chirped pulse amplification (CPA) system. A system of high quality windows is used to create a series of 1054nm picosecond-laser pulses which are injected into the CPA system before the pulse stretcher and amplifiers. By adding or removing windows in the pulse train forming optics, the number of pulses can be varied. By varying the distance and thickness of the respective optical elements, the time in between the pulses, i.e., the time in between frames, can be set. In our example application, the CPA pulse train is converted to 527nm using a KDP crystal and focused into a preformed plasma and the reflected laser light due to stimulated Raman scattering is measured. Each pulse samples different plasma conditions as the plasma evolves in time, producing more data on each laser shot than with a single short pulse probe. This novel technique could potentially be implemented to obtain multiple high-time resolution measurements of the dynamics of physical processes over hundreds of picoseconds or even nanoseconds with picosecond resolution on a single shot.
Morphology of Fe/MgO(001) ultrathin films
Authors: Reitinger Rüdiger , Sepiol Bogdan , Vogl Gero , Pfau Bastian , Stadler Lorenz-Mathias , Stankov Svetoslav , Zontone Federico , Spiridis Nika , Korecki Józef
Published: August 2007

The structural and magnetic properties of iron clusters resulting from the evaporation of five monolayers of iron on a polished MgO(001) substrate are examined by grazing-incidence small-angle x-ray scattering, and conversion electron Mössbauer spectroscopy. Volmer-Weber-growth is observed for room-temperature deposition, giving rise to spherical, superparamagnetic islands. Subsequent annealing causes coarsening and the particles become hemispherical. In the early stages of annealing cluster diffusion takes place, whereas later, Ostwald ripening is the dominant coarsening mechanism. The diffusion coefficient is independent from the crystallographic directions in the MgO(001) surface as it is proven by the isotropic island distribution and shape. The superparamagnetic state of the particles is conserved during the whole annealing process. For ultrathin iron layers we show that, in contrast to bulk iron, the Curie temperature lies well below room temperature.
Probing molecular symmetry effects in the ionization of N2 and O2 by intense laser fields
Authors: Okunishi M. , Shimada K. , Prümper G. , Mathur D. , Ueda K.
Published: August 2007

High-resolution electron spectroscopy is used to explore the role played by molecular symmetry in determining the morphology of the energy spectra of electrons ejected when N2 and O2 are irradiated by intense laser fields. In O2, the low-energy part of the electron spectrum is curtailed due to the destructive interference brought about by the antibonding nature of the O2 valence orbital. The high-energy tail of the spectrum is also suppressed by virtue of electron rescattering being of little consequence in O2. In contrast, in N2, which has a bonding valence orbital, the electron dynamics follow the pattern that has been established for atomic ionization in strong optical fields.
In situ microfluidic flow rate measurement based on near-field heterodyne grating method
Authors: Katayama Kenji , Uchimura Hisato , Sakakibara Hitomi , Kikutani Yoshikuni , Kitamori Takehiko
Published: August 2007

The near-field heterodyne grating (NF-HDG) method was applied to flow rate measurements in a microtube. The NF-HDG method is a newly developed optical technique based on photothermal effects. In this technique, pump light is shone on a transmission grating in front of a fluid channel and the inside liquid is heated with a pattern of the grating due to the Talbot effect. Another probe light is similarly shone on the same place as the pump light, and the diffraction by the transmission grating (reference) and the diffraction by the temporally generated thermal grating inside the fluid channel (signal) are mixed and detected (heterodyne detection). Theoretical analysis reveals that the dependence of the heterodyne signal intensity on the flow rate originates from the change in the heterodyne phase difference between the signal and reference, and the experimentally obtained calibration curves can be fitted with the theoretically predicted function. Furthermore, the optical setup was optimized based on the theoretical analysis of the Talbot effect. Flow rates of the order of nl/min were quantitatively measured, and the detection limit of the flow rate was 17nl∕min.
Design and construction of microclimate monitoring system
Authors: Kamunda Caspah , Carelse Xavier Francis , Mathuthu Manny , Makarau Amos
Published: August 2007

A portable and user-friendly weather monitoring system based on the PIC16F876 microcontroller is described. This instrument measures three parameters: temperature in the range from −10to+70°C within ±1°C using an LM335 temperature sensor, wind speed from 0to10m∕s within ±0.1m∕s using a heated bead thermistor, and solar radiation from 0to1000W∕m2 within ±10W∕m2 using a solar cell. These variables are displayed digitally, one at a time, with a 5s separation. The values are stored on EEPROM at 2min intervals. The instrument is intended for use in agriculture and for educational purposes.
Vortex ratchet effect in a niobium film with spacing-graded density of pinning sites
Authors: Wu T. C. , Horng Lance , Wu J. C. , Cao R. , Koláček Jan , Yang T. J.
Published: August 2007

The vortex propagation exhibits rectification effect in Nb superconductors with spacing-graded density of holes. A rectified dc voltage is obtained when the vortex lattice is driven by ac current. The asymmetric geometry of the pinning array produces a significant influence on the vortex motion. The rectified voltage depends considerably on the amplitude of the applied ac current and the magnetic field. The experimental results reveal a drastic change of the vortex rectification for magnetic field above∕below the first matching field. The reason may be that the interstitial vortices are formed in the film above the first matching field. A reversible vortex motion is induced by the interstitial vortices for the field above the first matching field.
Rotational microrheology of multilayered finite elastic media
Authors: Tracqui Philippe , Ohayon Jacques
Published: August 2007

This paper presents derivations of the torque-rotation angle relationship for a rigid spherical bead embedded in a composite medium made of n isotropic and linear elastic layers. Analytical solutions are provided for both compressible and incompressible solids, assuming no-slip conditions between the rigid spherical inclusion and its adjacent medium as well as between elastic layers. Thanks to these general formulas, we investigated the effect of finite size media on the torque-bead rotation response and derived the exact relationship linking apparent and intrinsic elastic moduli of the medium. Thus, this result can be applied to characterize precisely the mechanical heterogeneity and architecture of soft biomaterials, including cells, from real magnetocytometry experiments. This point is exemplified in the case of a bilayer medium which, interestingly, allows distinguishing cellular cortex from deep cytoskeleton. We found that rotational microrheology experiments are well suited to characterize locally the elastic properties of the layer in contact with the probe as soon as the layer thickness is larger than two-bead diameters.
Number of different binary functions generated by NK-Kauffman networks and the emergence of genetic robustness
Authors: Romero David , Zertuche Federico
Published: August 2007

We determine the average number ϑ(N,K) of NK-Kauffman networks that give rise to the same binary function. We show that for N⪢1, there exists a connectivity critical value Kc such that ϑ(N,K)≈eφN (φ>0) for KKc. We find that Kc is not a constant but scales very slowly with N as Kc≈log2log2(2N∕ln2). The problem of genetic robustness emerges as a statistical property of the ensemble of NK-Kauffman networks and impose tight constraints in the average number of epistatic interactions that the genotype-phenotype map can have.
Charge order suppression and weak ferromagnetism in La1∕3Sr2∕3FeO3 nanoparticles
Authors: Gao F. , Li P. L. , Weng Y. Y. , Dong S. , Wang L. F. , Lv L. Y. , Wang K. F. , Liu J.-M. , Ren Z. F.
Published: August 2007

Perovskite-type polycrystalline La1∕3Sr2∕3FeO3 particles with different sizes (80–2000nm) were prepared using a simple sol-gel technique. In samples of nanoparticles with a diameter of less than 300nm, weak ferromagnetism was observed at room temperature, which was attributed to the lattice distortion. The magnetic and specific heat measurements suggest that the charge ordering state was largely suppressed due to the lowering of the particle size, but the charge ordering temperature remained unaffected.
Anchoring phthalocyanine molecules on the 6H-SiC(0001)3×3 surface
Authors: Baffou G. , Mayne A. J. , Comtet G. , Dujardin G. , Sonnet Ph. , Stauffer L.
Published: August 2007

The adsorption of individual metal-free phthalocyanine molecules on the 6H-SiC(0001)3×3 surface was studied using the scanning tunneling microscope supported by density functional theory calculations. Phthalocyanine molecules were found to be chemisorbed through a reaction of two conjugated imide groups with two silicon adatoms. This type of anchoring opens numerous perspectives for the organic functionalization of a biocompatible wide band gap semiconductor.
Phason mode of electromagnons in terbium manganite with sinusoidal antiferromagnetic structure
Authors: Chupis I. E.
Published: August 2007

The interaction of light with electromagnons in a sinusoidally modulated antiferromagnetic phase of TbMnO3 is examined. It is predicted that the frequency dependence of the dielectric tensor εzz changes substantially at the transition from a sinusoidal into a spiral magnetic phase with spontaneous electric polarization. The phason mode of such a transition is an electromagnon mode in which the magnetoelectric phase is due to modulation of the magnetic structure.
Influence of crystallographic steps on properties of ferroelectric ultrathin films: An ab initio study
Authors: Prosandeev S. , Bellaiche L.
Published: August 2007

A first-principles-based approach is used to investigate the effect of a crystallographic step on the existence and morphology of the recently discovered periodic nanostripe domains [S. K. Streiffer et al., Phys. Rev. Lett. 89, 067601 (2002)] in Pb(Zr1−xTix)O3 ultrathin films. It is found that these domain structures do not vanish in the presence of such defect but rather evolve to form original stripe configurations to accommodate this step. The morphology and energetics of these original configurations are provided. Their dependencies on the film’s thickness and the step’s height is also discussed.
Quantum well intrasubband photodetector for far infared and terahertz radiation detection
Authors: Ting David Z.-Y. , Chang Yia-Chung , Bandara Sumith V. , Gunapala Sarath D.
Published: August 2007

The authors present a theoretical analysis on the possibility of using the dopant-assisted intrasubband absorption mechanism in quantum wells for normal-incidence far infrared/terahertz radiation detection. The authors describe the proposed concept of the quantum well intrasubband photodetector (QWISP), which is a compact semiconductor heterostructure device compatible with existing GaAs focal-plane array technology, and present theoretical results demonstrating strong normal-incidence absorption and responsivity in the QWISP.
Low threshold 1260nm (GaIn) (NAs) semiconductor disk laser
Authors: Diehl W. , Brick P. , Kunert B. , Reinhard S. , Volz K. , Stolz W.
Published: August 2007

Low threshold cw laser emission from a semiconductor disk laser emitting at 1260nm was demonstrated. Using high quality metal-organic vapor phase epitaxy (GaIn) (NAs) material, nonradiative processes could be minimized. As a consequence, threshold pump power densities have been reduced down to 5kW∕cm2. The capture efficiency of carriers into the quantum wells was found to be uncritical.
Edge emitting quantum cascade microlasers on InP with deeply etched one-dimensional photonic crystals
Authors: Semmel J. , Nähle L. , Höfling S. , Forchel A.
Published: August 2007

Edge emitting quantum cascade microlasers based on InP have been fabricated and investigated. Deeply etched Bragg mirrors have been manufactured at the end of the resonators, to reduce the mirror losses of short cavity devices. In order to achieve the required high aspect ratio, an optimized plasma dry etching process has been developed, which allows monolithic device fabrication in a single dry etching step. The short resonator length results in a large Fabry-Pérot mode spacing, which leads to a single mode operation. A side mode suppression ratio of about 20dB at 80K has been observed.
Nonvolatile memory devices with Cu2S and Cu-Pc bilayered films
Authors: Chen Liang , Xia Yidong , Liang Xuefei , Yin Kuibo , Yin Jiang , Liu Zhiguo , Chen Yong
Published: August 2007

An organic bistable device with a structure Cu∕Cu2S/copperphthalocyanine (Cu-Pc)∕Pt was fabricated. Compared to the single layer organic device composed of Cu∕Cu-Pc∕Pt, the bilayer devices were observed to show distinct bistability with the resistance ratio of the off/on states up to 107 and low switch voltage (0.75–0.85V). At least 105 switching cycles were achieved in the “write-read-erase-read” cycle voltage. The filament mechanism for the device is supported by the “metallic” behavior in their temperature dependence of the resistance in the on state. Such a memory device provides a promising structure for the nonvolatile memory.
Compact and polarization controlled 1.55μm vertical-cavity surface-emitting laser using single-layer photonic crystal mirror
Authors: Boutami Salim , Benbakir Badhise , Leclercq Jean-Louis , Viktorovitch Pierre
Published: August 2007

Vertical-cavity surface-emitting lasers (VCSELs) consist of a gain medium in which feedback is generally accomplished by two distributed Bragg reflectors (DBRs), for which sufficient reflectivity has to be achieved in order to obtain laser emission. As a consequence, DBRs generally consist of very thick layer stacks. In this letter, the authors report the realization of a VCSEL, of which the top mirror consists of a single-layer one-dimensional photonic crystal mirror (PCM). This PCM enables significantly improved device compactness and total polarization control, while providing a directive and single lateral mode emission.
Thickness dependence of the trap states in organic thin film of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine
Authors: Chu Ta-Ya , Song Ok-Keun
Published: August 2007

The authors have investigated the relationship between the trap states (exponential trap distribution in energy and density) and the thickness of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine (NPB). The thickness dependent hole mobility of NPB can be attributed to the trap states. The origin of deep trap states at thinner film can be attributed to both surface dipole of buckminsterfullerene and the interaction between NPB and indium tin oxide at the interface. The influence of interfacial trap states on charge drift mobility is getting weaker as the thickness increases and is negligible when the thickness of NPB is thicker than 300nm.
ErpA, an iron–sulfur (Fe–S) protein of the A-type essential for respiratory metabolism in
Escherichia coli
Authors: Loiseau Laurent , Gerez Catherine , Bekker Martijn , Ollagnier-de Choudens Sandrine , Py Béatrice , Sanakis Yannis , Teixeira de Mattos Joost , Fontecave Marc , Barras Frédéric
Published: August 2007

Understanding the biogenesis of iron–sulfur (Fe–S) proteins is relevant to many fields, including bioenergetics, gene regulation, and cancer research. Several multiprotein complexes assisting Fe–S assembly have been identified in both prokaryotes and eukaryotes. Here, we identify in
Escherichia coli
an A-type Fe–S protein that we named ErpA. Remarkably,
erpA
was found essential for growth of
E. coli
in the presence of oxygen or alternative electron acceptors. It was concluded that isoprenoid biosynthesis was impaired by the
erpA
mutation. First, the eukaryotic mevalonate-dependent pathway for biosynthesis of isopentenyl diphosphate restored the respiratory defects of an
erpA
mutant. Second, the
erpA
mutant contained a greatly reduced amount of ubiquinone and menaquinone. Third, ErpA bound Fe–S clusters and transferred them to apo-IspG, a protein catalyzing isopentenyl diphosphate biosynthesis in
E. coli
. Surprisingly, the
erpA
gene maps at a distance from any other Fe–S biogenesis-related gene. ErpA is an A-type Fe–S protein that is characterized by an essential role in cellular metabolism.
Feedback regulation of p38 activity via ATF2 is essential for survival of embryonic liver cells
Authors: Breitwieser Wolfgang , Lyons Steve , Flenniken Ann Marie , Ashton Garry , Bruder Gail , Willington Mark , Lacaud Georges , Kouskoff Valerie , Jones Nic
Published: August 2007

The ATF2 transcription factor is phosphorylated by the stress-activated mitogen-activated protein kinases (MAPKs) JNK and p38. We show that this phosphorylation is essential for ATF2 function in vivo, since a mouse carrying mutations in the critical phosphorylation sites has a strong phenotype identical to that seen upon deletion of the DNA-binding domain. In addition, combining this mutant with a knockout of the ATF2 homolog, ATF7, results in embryonic lethality with severe abnormalities in the developing liver and heart. The mutant fetal liver is characterized by high levels of apoptosis in developing hepatocytes and haematopoietic cells. Furthermore, we observe a significant increase in active p38 due to loss of a negative feedback loop involving the ATF2-dependent transcriptional activation of MAPK phosphatases. In embryonic liver cells, this increase drives apoptosis, since it can be suppressed by chemical inhibition of p38. Our findings demonstrate the importance of finely regulating the activities of MAPKs during development.
Cotranscriptional recruitment of the dosage compensation complex to X-linked target genes
Authors: Kind Jop , Akhtar Asifa
Published: August 2007

Dosage compensation is a process required to balance the expression of X-linked genes between males and females. In Drosophila this is achieved by targeting the dosage compensation complex or the male-specific lethal (MSL) complex to the male X chromosome. In order to study the mechanism of targeting, we have studied two X-chromosomal genes, mof and CG3016, using chromatin immunoprecipitation as well as immuno-FISH analysis on transgenic flies. We show that MSL complex recruitment requires the genes to be in a transcriptionally active state. MSL complex recruitment is reversible because blocking transcription severely reduces MSL binding to its target genes. Furthermore, targeting cues are found toward the 3′ end of the gene and depend on the passage of the transcription machinery through the gene, whereby the type of promoter and the direction of transcription are dispensable. We propose a model of dynamic MSL complex binding to active genes based on exposed DNA target elements.
Angiomotin regulates endothelial cell migration during embryonic angiogenesis
Authors: Aase Karin , Ernkvist Mira , Ebarasi Lwaki , Jakobsson Lars , Majumdar Arindam , Yi Chunling , Birot Olivier , Ming Yue , Kvanta Anders , Edholm Dan , Aspenström Pontus , Kissil Joseph , Claesson-Welsh Lena , Shimono Akihiko , Holmgren Lars
Published: August 2007

The development of the embryonic vascular system into a highly ordered network requires precise control over the migration and branching of endothelial cells (ECs). We have previously identified angiomotin (Amot) as a receptor for the angiogenesis inhibitor angiostatin. Furthermore, DNA vaccination targeting Amot inhibits angiogenesis and tumor growth. However, little is known regarding the role of Amot in physiological angiogenesis. We therefore investigated the role of Amot in embryonic neovascularization during zebrafish and mouse embryogenesis. Here we report that knockdown of Amot in zebrafish reduced the number of filopodia of endothelial tip cells and severely impaired the migration of intersegmental vessels. We further show that 75% of Amot knockout mice die between embryonic day 11 (E11) and E11.5 and exhibit severe vascular insufficiency in the intersomitic region as well as dilated vessels in the brain. Furthermore, using ECs differentiated from embryonic stem (ES) cells, we demonstrate that Amot-deficient cells have intact response to vascular endothelial growth factor (VEGF) in regard to differentiation and proliferation. However, the chemotactic response to VEGF was abolished in Amot-deficient cells. We provide evidence that Amot is important for endothelial polarization during migration and that Amot controls Rac1 activity in endothelial and epithelial cells. Our data demonstrate a critical role for Amot during vascular patterning and endothelial polarization.
Polimeric Electrolyte Membrane Fuel Cells: Characterization Test Under Variable Temperature and Relative Humidity Conditions
Authors: Rinaldi Fabio , Marchesi Renzo
Published: August 2007

The aim of this work is the performance study of a polimeric electrolyte membrane stack. Extreme conditions of temperature and relative humidity, such as those that may be found in practical situations (i.e., automotive), have been considered. The research has been developed by Department of Energetics of Politecnico di Milano in collaboration with Nuvera Fuel Cells Europe, under confidential agreement. In order to select the proper electrolyte that can be used to build a stack suitable for automotive applications, three different types of material have been tested in single fuel cells, under different conditions of temperature and relative humidity by mean of a climatic chamber. Both traditional (Nafion®) and new materials have been tested in single cells of 16cm2 of active area. The three electrolyte materials have been tested also by measuring the protonic conductance, in different conditions of relative humidity. After these tests, an electrolyte has been chosen that was made with a coated catalyst membrane having a thickness of 35μm, which has been used to build a six-cell stack with an active area of 500cm2. The performances of the stack have been evaluated, in continuous operation, with air temperatures ranging from 50°C to −40°C. A series of start-up tests has been carried out with an air temperature ranging between 0°C and −25°C.
Load Leveling of Fuel Cell System by Oxygen Concentration Control of Cathode Gas
Authors: Obara Shin’ya
Published: August 2007

The capacity reduction of a solid-polymer-membrane-type fuel cell (PEFC) with a reformer by load leveling and by improving the efficiency of part-load operation of the reformer is considered. The power generation efficiency of a fuel cell improves by supplying gas with a high oxygen concentration to the cathode. During periods of low electricity demand, the fuel cell is operated using reformed gas and air, and water electrolysis operation is also performed. When the electric power load is large, gases stored in cylinders are supplied to the fuel cell for operation. Using the proposed method, high efficiency operation and a reduction in the fuel cell capacity are possible.
Flow Characterization of a Polymer Electronic Membrane Fuel Cell Manifold and Individual Cells Using Particle Image Velocimetry
Authors: Grega Lisa , McGarry Matthew , Begum Mahfuja , Abruzzo Ben
Published: August 2007

Detailed measurements of flow through a model of a fuel cell stack were made using particle image velocimetry (PIV). The objective was to obtain high caliber sets of velocity fields in both the inlet manifold and within the cells over a range of Reynolds numbers in order to provide a benchmark for computational fluid dynamics (CFD) data and to demonstrate relationships between flow distributions in the manifold and those along the cells of the stack. A scaled up model was built and placed in a wind tunnel under uniform inlet flow conditions. Using the PIV technique, instantaneous flowfields were captured which were then averaged to obtain mean and fluctuating velocity statistics. Based on analysis of the data, relationships were found between manifold and cell flow distributions. Within the inlet manifold, magnitudes of normalized streamwise velocities were found to increase towards the aft of the manifold with Reynolds number. This was believed to be associated with the more severe cell flow maldistributions which were found to exist with increasing Reynolds numbers. Examination of instantaneous velocity distributions in the manifold demonstrated the existence of discrete vortical structures and complex fluid motions towards the aft, resulting in increased velocity fluctuations in this region. Velocity fluctuations within the cells were also found to increase towards the aft of the stack, leading to higher flow unsteadiness in these cells.
Hyperstoichiometric La1.9Sr0.1NiO4+δ Mixed Conductor as Novel Cathode for Intermediate Temperature Solid Oxide Fuel Cells
Authors: Aguadero A. , Escudero M. J. , Pérez M. , Alonso J. A. , Daza L.
Published: August 2007

The materials La2−xSrxNiO4+δ(x=0,0.1) with K2NiF4 structure have been studied in order to explore their potential use as cathodes for intermediate temperature solid oxide fuel cells. The introduction of Sr in the La2NiO4+δ lattice produces an enhancement of the electric conductivity but is accompanied by a decrease of ionic transport species. Neutron powder diffraction data show a transition from orthorhombic to tetragonal symmetry with the incorporation of Sr in the LaO sublattice. Excess oxygen determined by iodometric titration shows that strontium insertion generates a decrease of the interstitial oxygen. In order to avoid the concomitant decrease of the ionic conductivity, the system underwent heat treatments under high oxygen pressure (200bar, 650°C). As a result, the O2− treated La1.9Sr0.1NiO4+δ exhibited an increase of the amount of interstitial oxygens (δ=0.17) but with improved electronic properties. The polarization resistances measured for these materials vary between 8Ωcm2 and 0.1Ωcm2 in air at the temperature range of 700–975°C. This remarkable behavior enables us to propose this material as an alternative cathode for IT-SOFC.
Thermal-Fluid-Dynamic Simulation of a Proton Exchange Membrane Fuel Cell Using a Hierarchical 3D-1D Approach
Authors: Cordiner Stefano , Mulone Vincenzo , Romanelli Fabio
Published: August 2007

The use of proton exchange membrane fuel cells (PEFC) based power trains and stationary systems has been technically demonstrated but is still far from commercial application. Technical development is still required to reach cost and durability targets, and to this aim, modeling and simulation are useful tools to obtain both better understanding of the fundamental occurring processes and to shorten design-associated costs and time. In this paper, a hierarchical 3D-1D approach is proposed, to overcome the deficiencies of a full 1D approach and the characteristic computational costs of a full 3D approach. The polymeric membrane and catalyst layers are represented by a local 1D model, while channels, gas diffusion layers, and solid electrodes are modeled by a full 3D approach. The model capabilities are first investigated with respect to experimental data by means of a full fuel cell simulation; the main chemical, fluid dynamic, and thermal fields are then analyzed in a straight channel configuration. The proposed 3D/1D model is able to accurately represent PEFC specific phenomena and their physical coupling. It could be then successfully applied to both design and development.
Effects of Splitter Blades on Deep Well Pump Performance
Authors: Gölcü M. , Usta N. , Pancar Y.
Published: August 2007

Impellers with splitter blades have been used in turbomachinery design for both pumps and compressors. Increasing the number of blades increases the head of the pump, however, it causes a decrease in efficiency due to the blockage effect of the blade thickness and friction. The impellers with splitter blades between two long blades can be used to alleviate the serious clogging at the inlet of the impeller caused by more blades. In this study, impellers having a different number of blades (z=3, 4, 5, 6, and 7) with and without splitter blades (25, 35, 50, 60, and 80% of the main blade length) were tested in a deep well pump. The effects of the main blade number and lengths of splitter blades on the pump performance have been investigated. While the number of main blades and the lengths of the splitter blades of a principal impeller were changed, the other parameters such as pump casing, blade inlet and outlet angles, blade thickness, impeller inlet and outlet diameters, were kept the same.
New API RP2A Tubular Joint Strength Design Provisions
Authors: Pecknold David , Marshall Peter , Bucknell Justin
Published: August 2007

The development of the new API RP2A (22nd edition) parametric static strength prediction equations for planar circular hollow section tubular joints is described. Prediction equations are presented for brace axial, brace in-plane bending, and brace out-of-plane bending loads. The prediction equations are based on screened test databases, augmented, and extended by an extensive new series of validated nonlinear finite element simulations for nonoverlapping K joints, double tee (DT/X) joints, and T joints. The increased reliability (reduced scatter) provided by the new static strength formulation was used to justify a reduction of the load factor of safety to 1.6 from the previous value of 1.7.
On Simplified Models for the Rate- and Time-Dependent Performance of Stratified Thermal Storage
Authors: Ji Ying , Homan K. O.
Published: August 2007

In direct sensible thermal storage systems, both the energy discharging and charging processes are inherently time-dependent as well as rate-dependent. Simplified models which depict the characteristics of this transient process are therefore crucial to the sizing and rating of the storage devices. In this paper, existing models which represent three distinct classes of models for thermal storage behavior are recast into a common formulation and used to predict the variations of discharge volume fraction, thermal mixing factor, and entropy generation. For each of the models considered, the parametric dependence of key performance measures is shown to be expressible in terms of a Peclet number and a Froude number or temperature difference ratio. The thermal mixing factor for each of the models is reasonably well described by a power law fit with Fr2Pe for the convection-dominated portion of the operating range. For the uniform and nonuniform diffusivity models examined, there is shown to be a Peclet number which maximizes the discharge volume fraction. In addition, the cumulative entropy generation from the simplified models is compared with the ideally-stratified and the fully-mixed limits. Of the models considered, only the nonuniform diffusivity model exhibits an optimal Peclet number at which the cumulative entropy generation is minimized. For each of the other models examined, the cumulative entropy generation varies monotonically with Peclet number.
The Performance of the Kalina Cycle System 11(KCS-11) With Low-Temperature Heat Sources
Authors: Madhawa Hettiarachchi H. D. , Golubovic Mihajlo , Worek William M. , Ikegami Yasuyuki
Published: August 2007

The possibility of exploiting low-temperature heat sources has been of great significance with ever increasing energy demand. Optimum and cost-effective design of the power cycles provide a means of utilization of low-temperature heat sources which might otherwise be discarded. In this analysis, the performance of the Kalina cycle system 11 (KCS11) is examined for low-temperature geothermal heat sources and is compared with an organic Rankine cycle. The effect of the ammonia fraction and turbine inlet pressure on the cycle performance is investigated in detail. Results show that for a given turbine inlet pressure, an optimum ammonia fraction can be found that yields the maximum cycle efficiency. Further, the maximum cycle efficiency does not necessarily yield the optimum operating conditions for the system. In addition, it is important to consider the utilization of the various circulating media (i.e., working fluid, cooling water, and heat resource) and heat exchanger area per unit power produced. For given conditions, an optimum range of operating pressure and ammonia fraction can be identified that result in optimum cycle performance. In general, the KCS11 has better overall performance at moderate pressures than that of the organic Rankine cycle.
Inquiry with Laser Printer Diffraction Gratings
Authors: Van Hook Stephen J.
Published: August 2007

The pages of The Physics Teacher have featured several clever designs for homemade diffraction gratings using a variety of materials—cloth,1 lithographic film,2 wire,3 compact discs,4 parts of aerosol spray cans,5 and pseudoliquids and pseudosolids.6 A different and inexpensive method I use to make low-resolution diffraction gratings takes advantage of specialty transparency film designed for use with laser printers. A standard laser printer can print black lines (separated by a white line) at 60 black lines/cm (about 150 lines/in), which is a small enough spacing to produce a crude diffraction grating [see Fig. 1(a)] that is sufficient for the physics inquiry activities described in this paper.
March of the Planets
Authors: Thompson Bruce
Published: August 2007

The motion of the planets in their orbits can be demonstrated to students by using planetarium software programs.1 These allow time to be sped up so that the relative motions are readily observed. However, it is also valuable to have the students understand the real speed of the planets in their orbits. This paper describes an exercise that gives students a good understanding of real-time motions and then allows other questions to be asked to encourage further understanding of planetary geometry and motion.
Thinking About Bernoulli
Authors: Kamela Martin
Published: August 2007

One of the most fun demonstrations in a freshman mechanics class is the levitation of a ball in a steady air stream even when the jet is directed at an angle. This and other demonstrations1 are often used to argue for the validity of Bernoulli's principle. As cautioned by some authors,2–4 however, it is important to avoid making sweeping statements such as “high speed implies lower pressure” with respect to interpreting the popular demonstrations. In this paper I present a demonstration that can be used in conjunction with the discussion of Bernoulli's principle to encourage students to consider assumptions carefully. Specifically, it shows that a correlation of high speed with lower fluid pressure is not true in general.
A NEURAL NETWORK MODEL OF METAPHOR UNDERSTANDING WITH DYNAMIC INTERACTION BASED ON A STATISTICAL LANGUAGE ANALYSIS: TARGETING A HUMAN-LIKE MODEL
Authors: TERAI ASUKA , NAKAGAWA MASANORI
Published: August 2007

The purpose of this paper is to construct a model that represents the human process of understanding metaphors, focusing specifically on similes of the form an "A like B". Generally speaking, human beings are able to generate and understand many sorts of metaphors. This study constructs the model based on a probabilistic knowledge structure for concepts which is computed from a statistical analysis of a large-scale corpus. Consequently, this model is able to cover the many kinds of metaphors that human beings can generate. Moreover, the model implements the dynamic process of metaphor understanding by using a neural network with dynamic interactions. Finally, the validity of the model is confirmed by comparing model simulations with the results from a psychological experiment.
NONNEGATIVE TENSOR FACTORIZATION FOR CONTINUOUS EEG CLASSIFICATION
Authors: LEE HYEKYOUNG , KIM YONG-DEOK , CICHOCKI ANDRZEJ , CHOI SEUNGJIN
Published: August 2007

In this paper we present a method for continuous EEG classification, where we employ nonnegative tensor factorization (NTF) to determine discriminative spectral features and use the Viterbi algorithm to continuously classify multiple mental tasks. This is an extension of our previous work on the use of nonnegative matrix factorization (NMF) for EEG classification. Numerical experiments with two data sets in BCI competition, confirm the useful behavior of the method for continuous EEG classification.
TOWARDS REASONING AND COORDINATING ACTION IN THE MENTAL SPACE
Authors: MOHAN VISHWANATHAN , MORASSO PIETRO
Published: August 2007

Unlike a purely reactive system where the motor output is exclusively controlled by the actual sensory input, a cognitive system must be capable of running mental processes which virtually simulate action sequences aimed at achieving a goal. The mental process either attempts to find a feasible course of action compatible with a number of constraints (Internal, Environmental, Task Specific etc) or selects it from a repertoire of previously learned actions, according to the parameters of the task. If neither reasoning process succeeds, a typical backup strategy is to look for a tool that might allow the operator to match all the task constraints. This further necessitates having the capability to alter ones own goal structures to generate sub-goals which must be successfully accomplished in order to achieve the primary goal. In this paper, we introduce a forward/inverse motor control architecture (FMC/IMC) that relaxes an internal model of the overall kinematic chain to a virtual force field applied to the end effector, in the intended direction of movement. This is analogous to the mechanism of coordinating the motion of a wooden marionette by means of attached strings. The relaxation of the FMC/IMC pair provides a general solution for mentally simulating an action of reaching a target position taking into consideration a range of geometric constraints (range of motion in the joint space, internal and external constraints in the workspace) as well as effort-related constraints (range of torque of the actuators, etc.). In case, the forward simulation is successful, the movement is executed; otherwise the residual "error" or measure of inconsistency is taken as a starting point for breaking the action plan into a sequence of sub actions. This process is achieved using a recurrent neural network (RNN) which coordinates the overall reasoning process of framing and issuing goals to the forward inverse models, searching for alternatives tools in solution space and formation of sub-goals based on past context knowledge and present inputs. The RNN + FMC/IMC system is able to successfully reason and coordinate a diverse range of reaching and grasping sequences with/without tools. Using a simple robotic platform (5 DOF Scorbot arm + Stereo vision) we present results of reasoning and coordination of arm/tool movements (real and mental simulation) specifically directed towards solving the classical 2-stick paradigm from animal reasoning at a non linguistic level.
TOPOLOGICAL BLACK HOLES AND MOMENTUM FOUR-VECTOR
Authors: PIRINCCIOGLU NURETTIN , BINBAY FIGEN , ACIKGOZ IRFAN , AYDOGDU OKTAY
Published: August 2007

We consider the energy–momentum definition of the Møller in both general relativity and teleparallel gravity to evaluate the energy distribution (due to both matter and fields including gravitation) associated with the topological black holes with a conformally coupled scalar field. Our results show that the energy depends on the mass M and charge Q of the black holes and cosmological constant Λ. In some special limits, the expression of the energy reduces to the energy of the well-known spacetimes. The results also support the viewpoint of Lessner that the Møller energy–momentum formulation is a powerful concept of the energy–momentum. Furthermore, the energy obtained in teleparallel gravity is also independent of the teleparallel dimensionless coupling constants which means that it is valid not only in the teleparallel equivalent of the general relativity but also in any teleparallel model.
JOINT PROBABILITIES REPRODUCING THREE EPR EXPERIMENTS ON TWO QUBITS
Authors: ROY S. M. , ATKINSON D. , AUBERSON G. , MAHOUX G. , SINGH V.
Published: August 2007

An eight-parameter family of the most general non-negative quadruple probabilities is constructed for EPR–Bohm–Aharonov experiments when only three pairs of analyser settings are used. It is a simultaneous representation of three different Bohr-incompatible experimental configurations involving mutually noncommuting observables valid for arbitrary quantum states.
NONLINEAR SCHRÖDINGER EQUATIONS WITH UNBOUNDED AND DECAYING RADIAL POTENTIALS
Authors: SU JIABAO , WANG ZHI-QIANG , WILLEM MICHEL
Published: August 2007

We establish some embedding results of weighted Sobolev spaces of radially symmetric functions. The results are then used to obtain ground state solutions of nonlinear Schrödinger equations with unbounded and decaying radial potentials. Our work unifies and generalizes many existing partial results in the literature.
TRANSIENT DYNAMICS AND QUASISTATIONARY EQUILIBRIA OF CONTINUOUS-TIME LINEAR STOCHASTIC CELLULAR AUTOMATA VOTER MODELS WITH MULTISCALE NEIGHBORHOODS
Authors: HIEBELER DAVID E.
Published: August 2007

This paper studies asynchronously-updated linear voter cellular automata models, with local and global interactions. In the locally-interacting model, sites copy the states of randomly-chosen sites in the local neighborhood; in the globally-interacting model, sites copy the states of sites chosen at random from the entire lattice. A multiscale model is also considered, mixing the two types of interactions. Such models can be used to model simple genetic drift, or the spread of opinions or ideas. The pair approximation moment-closure method is used to develop systems of differential equations describing the dynamics of the models with k states per site; stochastic spatially explicit simulations are also used. In simulations on large lattices, state frequencies among sites remain relatively constant at their initial values, while autocorrelations between adjacent sites move toward quasiequilibrium distributions and then remain constant with minor stochastic fluctuations. Full analytical solutions for the transient dynamics of the local autocorrelation (clustering) among adjacent sites are obtained with k = 2 states, and compared with simulations. Both show that increasing global interactions decreases spatial autocorrelation, and that even in the absence of long-distance interaction, there will still be mixing among the states. That is, the lattice will not converge to a quasiequilibrium configuration where regions in different states are maximally isolated from each other (completely segregated), but instead sites will have a strictly positive probability of being adjacent to sites in different states.