bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of spatial structure of plasma potential and density fluctuations by multichannel heavy ion beam probe on large helical device
Authors: Ohshima Shinsuke , Ido Takeshi , Shimizu Akihiro , Nishiura Masaki , Nakano Haruhisa
Published: November 2008

Heavy ion beam probe (HIBP) on large helical device is currently equipped with three channel detectors, which can observe three spatial points simultaneously inside the plasma with resolution of ∼10 mm. The beam trajectories and observation point location are calculated numerically and optimized allowing for the identification of the mode structure in multichannel (up to 9) HIBP measurements. The calculations show that the radial and poloidal wavenumbers can be identified by proper changing and choosing of the beam energy and trajectory.
OZSPEC-2: An improved broadband high-resolution elliptical crystal x-ray spectrometer for high-energy density physics experiments (invited)
Authors: Heeter R. F. , Anderson S. G. , Booth R. , Brown G. V. , Emig J. , Fulkerson S. , McCarville T. , Norman D. , Schneider M. B. , Young B. K. F.
Published: November 2008

A novel time, space, and energy-resolved x-ray spectrometer has been developed which produces, in a single snapshot, a broadband and relatively calibrated spectrum of the x-ray emission from a high-energy density laboratory plasma. The opacity zipper spectrometer (OZSPEC-1) records a nearly continuous spectrum for x-ray energies from 240to5800eV in a single shot. The second-generation OZSPEC-2, detailed in this work, records fully continuous spectra on a single shot from any two of these three bands: 270–650, 660–1580, and 1960–4720eV. These instruments thus record thermal and line radiation from a wide range of plasmas. These instruments’ single-shot bandwidth is unmatched in a time-gated spectrometer; conversely, other broadband instruments are either time-integrated (using crystals or gratings), lack spectral resolution (diode arrays), or cover a lower energy band (gratings). The OZSPECs are based on the zipper detector, a large-format (100×35mm) gated microchannel plate detector, with spectra dispersed along the 100mm dimension. OZSPEC-1 and -2 both use elliptically bent crystals of OHM, RAP, and/or PET. Individual spectra are gated in 100ps. OZSPEC-2 provides one-dimensional spatial imaging with 30–50μm resolution over a 1500μm field of view at the source. The elliptical crystal design yields broad spectral coverage with resolution E∕ΔE>500, strong rejection of hard x-ray backgrounds, and negligible source broadening for extended sources. Near-term applications include plasma opacity measurements, detailed spectra of inertial fusion Hohlraums, and laboratory astrophysics experiments.
Scaling laws for energetic ions from the commissioning of the new Los Alamos National Laboratory 200 TW Trident laser
Authors: Flippo K. A. , Workman J. , Gautier D. C. , Letzring S. , Johnson R. P. , Shimada T.
Published: November 2008

The recent Los Alamos National Laboratory Trident laser enhanced from 30 to 200 TW in power allows more than 100 J to be delivered on target in 500 fs with a spot size smaller than 12 μm at full width at half maximum. 15 μm flat-foil targets have been observed to produce proton beams in excess of 50 MeV at an intensity of only ∼4×1019 W/cm2 with efficiencies approaching 5%. The Trident laser beam characteristics are presented along with the data compared to published scaling laws for proton acceleration.
One-dimensional neutron imager for the Sandia Z facility
Authors: Fittinghoff David N. , Bower Dan E. , Hollaway James R. , Jacoby Barry A. , Weiss Paul B. , Buckles Robert A. , Sammons Timothy J. , McPherson Leroy A. , Ruiz Carlos L. , Chandler Gordon A. , Torres José A. , Leeper Ramon J. , Cooper Gary W. , Nelson Alan J.
Published: November 2008

A multiinstitution collaboration is developing a neutron imaging system for the Sandia Z facility. The initial system design is for slit aperture imaging system capable of obtaining a one-dimensional image of a 2.45 MeV source producing 5×1012 neutrons with a resolution of 320 μm along the axial dimension of the plasma, but the design being developed can be modified for two-dimensional imaging and imaging of DT neutrons with other resolutions. This system will allow us to understand the spatial production of neutrons in the plasmas produced at the Z facility.
Blast wave energy diagnostic
Authors: Tierney Thomas E. , Tierney Heidi E. , Idzorek George C. , Watt Robert G. , Peterson Robert R. , Peterson Darrell L. , Fryer Christopher L. , Lopez Mike R. , Jones Michael C. , Sinars Daniel , Rochau Gregory A. , Bailey James E.
Published: November 2008

The distance radiation waves that supersonically propagate in optically thick, diffusive media are energy sensitive. A blast wave can form in a material when the initially diffusive, supersonic radiation wave becomes transonic. Under specific conditions, the blast wave is visible with radiography as a density perturbation. [Peterson et al., Phys. Plasmas 13, 056901 (2006)] showed that the time-integrated drive energy can be measured using blast wave positions with uncertainties less than 10% at the Z Facility. In some cases, direct measurements of energy loss through diagnostic holes are not possible with bolometric and x-ray radiometric diagnostics. Thus, radiography of high compression blast waves can serve as a complementary technique that provides time-integrated energy loss through apertures. In this paper, we use blast waves to characterize the energy emerging through a 2.4 mm aperture and show experimental results in comparison to simulations.
Air-voids embedded high efficiency InGaN-light emitting diode
Authors: Park Eun-Hyun , Jang Jin , Gupta Shalini , Ferguson Ian , Kim Cheol-Hoi , Jeon Soo-Kun , Park Joong-Seo
Published: November 2008

To improve the light extraction efficiency of InGaN-light emitting diode (LED), inverted hexagonal cone shaped air voids with {10–11} GaN crystal planes were formed between a patterned sapphire substrate and GaN epitaxial layer using a H3PO4-based hot chemical etching method. The air-voids embedded LED showed 12% and 210% higher optical power than a patterned substrate LED and a flat substrate LED, respectively. A ray tracing simulation revealed that the light extraction through the top face of the air-voids embedded LED was dramatically increased due to a strong light reflection and redirection by the air voids.
A novel experimental method for the measurement of the caloric curves of clusters
Authors: Chirot Fabien , Feiden Pierre , Zamith Sébastien , Labastie Pierre , L’Hermite Jean-Marc
Published: November 2008

A novel experimental scheme has been developed in order to measure the heat capacity of mass selected clusters. It is based on controlled sticking of atoms on clusters. This allows one to construct the caloric curve, thus determining the melting temperature and the latent heat of fusion in the case of first-order phase transitions. This method is model-free. It is transferable to many systems since the energy is brought to clusters through sticking collisions. As an example, it has been applied to Na90+ and Na140+. Our results are in good agreement with previous measurements.
The Hall–Petch breakdown at high strain rates: Optimizing nanocrystalline grain size for impact applications
Authors: Trelewicz Jason R. , Schuh Christopher A.
Published: November 2008

The breakdown of Hall–Petch strength scaling is investigated in nanocrystalline Ni–W alloys at high strain rates, using dynamic hardness testing at grain sizes ranging from 3to150nm. Whereas quasistatic tests show a strength plateau below about 15nm, high-rate tests (indentation strain rate of ∼103s−1) exhibit a pronounced strength peak and a regime of “inverse Hall–Petch” weakening. This effect is shown to be the result of a grain size-dependent rate sensitivity that exhibits a maximum at a grain size near 10–20nm. High strain rates are also shown to promote shear banding at nanocrystalline grain sizes.
Effects of background noise on generating coherent packets of hairpin vortices
Authors: Kim Kyoungyoun , Sung Hyung Jin , Adrian Ronald J.
Published: November 2008

We examine the autogeneration process by which new hairpin vortices are created from a sufficiently strong hairpin vortex, leading to the formation of a hairpin packet. Emphasis is placed on the effects of background noise on packet formation. The initial conditions are given by conditionally averaged flow fields associated with the second quadrant (Q2) event in the fully turbulent channel flow direct numerical simulation (DNS) database at Reτ=395. The nonlinear evolution of the initial vortical structure is tracked by performing a spectral simulation. Background noise is introduced by adding small amplitude perturbations to the initial field or by imposing momentum forcing. The background noise gives rise to chaotic development of a hairpin packet. The hairpins become asymmetric, leading to much more complicated packet structures than are observed in the symmetric hairpin vortex train of the flow with a clean background. However, the chaotic packets show the same properties as the clean packet in terms of the rate of growth of vertical and spanwise dimensions and the distance between successive vortices, suggesting that the autogeneration mechanism is robust. The background noise leads to a decrease in the minimum value of the Q2 strength required to trigger autogeneration, indicating that background noise enhances autogeneration, especially in the buffer layer. The autogeneration process is more enhanced by the background noise with wavenumbers kx<kz. Conditionally averaged flow fields around the tall attached vortices in the hairpin packet show that they are associated with elongated low-momentum structures in the streamwise direction. Finally, the autogeneration process was tested in a real turbulent environment taken from an instantaneous field of a turbulent channel flow DNS. The generation of secondary hairpin vortices is clearly observed upstream of the primary hairpin.
On the use of kriging for enhanced data reconstruction in a separated transitional flat-plate boundary layer
Authors: Gunes Hasan , Rist Ulrich
Published: November 2008

Kriging method for data reconstruction and spatial enhancement of stereo-particle image velocimetry (S-PIV) data for a transitional boundary layer with a laminar separation bubble is investigated. Particularly, the effect of various variogram models and their parameters are studied in detail. In addition, we show that missing data clusters, or black zones, which often occur in PIV measurements, can be estimated using kriging provided the data are well correlated. An important issue in PIV measurements is that built-in PIV data processing software might have problems to detect or to correct spurious erroneous vectors called “outliers.” It is shown that these outliers can be eliminated or greatly alleviated using kriging. λ2 isosurface and stream traces show that noisy vortical structures are eliminated but the main coherent structures are well preserved and smoothed, thus procedures for the detection and tracking of vortex core lines can be effectively applied on kriged data. Analytical test data for a more quantitative evaluation of the performance of kriging are given in the Appendices.
Optical levitation and transport of microdroplets: Proof of concept
Authors: Nagy Peter T. , Neitzel G. Paul
Published: November 2008

A new technique for microfluidic transport of liquid droplets in “lab-on-a-chip” (LOC) applications is described in which droplets are levitated above or between solid planar surfaces through the use of thermocapillarity, the variation in a liquid’s surface tension with temperature. Levitated liquid droplets are not in contact with solid surfaces and so may be transported from point-to-point along arbitrary paths with little friction. In addition, the lack of liquid-solid contact virtually eliminates the potential for sample-to-sample contamination. The new technique therefore addresses three issues associated with existing LOC devices employing microchannels: droplet pathway constraints, transport speed, and sample-to-sample contamination.
Diblock copolymer based self-assembled nanomagnetoelectric
Authors: Ren Shenqiang , Briber Robert M. , Wuttig Manfred
Published: November 2008

A magnetoelectric (ME) composite with controlled nanostructures is synthesized using coassembly of two inorganic precursors with a block copolymer. This solution processed material consists of hexagonally arranged ferromagnetic cobalt ferrite [CoFe2O4 (CFO)] nano cylinders within a matrix of ferroelectric lead zirconium titanate [Pb1.1(Zr0.53Ti0.47)O3 (PZT)] when thin films were prepared by spin coating. The initial magnetic permeability of the self-assembled CFO/PZT nanocomposite changes by a factor of 5 through the application of 2.5V. This work also demonstrates that a block copolymer can be used to simultaneously template two compound inorganic phases to form a nanoscale composite.
The sound from mixing layers simulated with different ranges of turbulence scales
Authors: Kleinman Randall R. , Freund Jonathan B.
Published: November 2008

The role of turbulence scales in generating far-field sound in free shear flows is studied via direct numerical simulations of temporally developing, Mach 0.9 mixing layers. Four flows were simulated, starting from the same initial conditions but with Reynolds numbers that varied by a factor of 12. Above momentum thickness Reynolds number Reδm≈300, all the mixing layers radiate over 85% of the acoustic energy of the apparently asymptotically high-Reynolds-number value that we are able to compute. Turbulence energy and pressure wavenumber spectra show the expected Reynolds number dependence; the two highest Reynolds number simulations show evidence of an inertial range and Kolmogorov scaling at the highest wavenumbers. Far-field pressure spectra all decay much more rapidly with wavenumber than the corresponding near-field spectra and show significantly less sensitivity to Reynolds number. Low wavenumbers account for nearly all of the radiated acoustic energy. Far-field streamwise wavenumber pressure spectra scale well with the layer momentum thickness, consistent with the insensitivity to Reynolds number of the largest turbulence structures. At higher wavenumbers the streamwise spectra scale best with the Taylor microscale. Interestingly, none of the spanwise far-field pressure spectra scale well with momentum thickness despite doing so in the near-field turbulence. Instead they scale well at all wavenumbers with the turbulence microscale. Implications of these results for large-eddy simulation of jet noise are discussed.
Local isotropy of the velocity and vorticity fields in a boundary layer at high Reynolds numbers
Authors: Wallace James M. , Ong Lawrence
Published: November 2008

Measurements of the velocity and vorticity field with a 12-sensor hot-wire probe were carried out in the boundary layer of the test section ceiling of the NASA Ames 80×120 ft2 wind tunnel at a turbulence Reynolds number of Rλ≈875. Tests of local isotropy were applied to the data obtained at y/δ=0.1. In the inertial subrange, which extended over a decade of wave numbers for this experiment, both the velocity and vorticity component one-dimensional kx spectra agree well with the isotropic spectra of Kim and Antonia [J. Fluid Mech. 251, 219 (1993)]. This agreement extends into the dissipation range up to wave numbers at which the accuracy of the measurements is limited because of spatial resolution and other sources of error. Additional tests of local isotropy, from the characteristics of the Reynolds shear stress correlation coefficient cospectrum and from the isotropic relationships between the kx spectra of the streamwise velocity and vorticity components with the kx spectra of the respective cross-stream components, also show evidence of local isotropy at these higher wave numbers.
Thermal transport by lattice excitations in hexagonal rare-earth manganites
Authors: Jiang L. , Zhang M. , Jiang Q.
Published: November 2008

Thermal transport mechanism in a ferroelectricity-magnetism-coexisting system, hexagonal YMnO3 is investigated. In addition to the acoustic phonon contribution, heat transport induced by optical phonon is taken into account to explain the excess thermal conductivity above TN. Magnetoelectric coupling effect on both acoustic and optical phonons is embodied by change in Debye and Einstein temperatures, respectively. Magnon-phonon resonant interaction is considered as one of the scattering mechanisms that correct relaxation time of acoustic phonon thermal conductivity. Our theoretical fitting is in good agreement with the experimental data.
Asymptotic flow profiles for incompressible flows with a periodic pressure gradient
Authors: Kapoor Atam , Choi Phillip Y. K.
Published: November 2008

Understanding stress variations in pulsating flows due to periodic pressure gradients is fundamentally significant for the design and optimization of various medical apparatuses and for understanding biological phenomena. Oscillating flows have been dealt analytically and experimentally in great detail in the past. In this paper, a three-dimensional lattice boltzmann model is used to simulate the pulsating flows in a rectangular duct due to low, moderate, and high periodic pressure gradients. Asymptotic forms for velocity (valid for high frequencies) valid in different regions of the channel have been matched with the analytical results. The evolution of annular effects in the flow along with the Stokesian layer characteristics have been followed. Stress analysis at different points of the wall of the duct has been carried out to show regions of high stress and stress rates.
Superconducting properties of Nb thin films deposited on porous silicon templates
Authors: Trezza M. , Prischepa S. L. , Cirillo C. , Fittipaldi R. , Sarno M. , Sannino D. , Ciambelli P. , Hesselberth M. B. S. , Lazarouk S. K. , Dolbik A. V. , Borisenko V. E. , Attanasio C.
Published: November 2008

Porous silicon, obtained by electrochemical etching, has been used as a substrate for the growth of nanoperforated Nb thin films. The films, deposited by UHV magnetron sputtering on the porous Si substrates, inherited their structure made of holes of 5 or 10 nm diameter and of 10–40 nm spacing, which provide an artificial pinning structure. The superconducting properties were investigated by transport measurements performed in the presence of magnetic field for different film thickness and substrates with different interpore spacing. Perpendicular upper critical fields measurements present peculiar features such as a change in the Hc2⊥(T) curvature and oscillations in the field dependence of the superconducting resistive transition width at H≈1 T. This field value is much higher than typical matching fields in perforated superconductors, as a consequence of the small interpore distance.
Attosecond nonlinear Fourier transformation spectroscopy of CO2 in extreme ultraviolet wavelength region
Authors: Okino Tomoya , Yamanouchi Kaoru , Shimizu Toshihiko , Ma Ri , Nabekawa Yasuo , Midorikawa Katsumi
Published: November 2008

The interferometric autocorrelation functions of attosecond pulse trains in the time domain were measured by detecting CO22+ as well as the atomic and molecular fragment ions generated via two-photon absorption of intense vacuum ultraviolet-extreme ultraviolet light by CO2. It was demonstrated that the Fourier transformation of the interferometric autocorrelation functions of the respective fragment ions appearing in a time-of-flight mass spectrum exhibit spectroscopic information in the frequency domain corresponding to the two-photon photofragment excitation spectra of CO2 and the double ionization excitation spectrum to form CO22+.
Creating cellular and molecular patterns via gravitational force with liquid droplets
Authors: Cheng Chao-Min , LeDuc Philip R.
Published: November 2008

We modified polydimethylsiloxane to have an elastic modulus of single kilopascals, and then used the gravitational force of falling liquid droplets to pattern molecules on a surface. This allowed us to construct uniform patterns over a large area with control over both molecular patterning and surface topography. The straightforward nature of this technique makes it potentially amenable to low-cost production and rapid prototyping of cellular and molecular patterns.
Electrical impedance tomography with an optimized calculable square sensor
Authors: Cao Zhang , Wang Huaxiang , Xu Lijun
Published: November 2008

Electrical impedance tomography is a technique that reconstructs the medium distribution in a region of interest through electrical measurements on its boundary. In this paper, an optimized square sensor was designed for electrical impedance tomography in order to obtain maximum information over the cross section of interest, e.g., circulating fluidized beds, in the sense of Shannon information entropy. An analytical model of the sensor was obtained using the conformal transformation. The model indicates that the square sensor possesses calculable property, which allows the calculation of standard values of the sensor directly from a single dimensional measurement that can be made traceable to the SI unit of length. Based on the model, the sensitivity maps and electrical field lines can be calculated in less than a second. Two model based algorithms for image reconstruction, i.e., back projection algorithm based on electrical field lines and iterative Lavrentiev regularization algorithm based on the sensitivity map, were introduced. Simulated results and experimental results validate the feasibility of the algorithms.
Time-of-flight mobility measurements in organic field-effect transistors
Authors: Dost R. , Das A. , Grell M.
Published: November 2008

We implement the “time-of-flight” (TOF) method for charge carrier mobility (μ) measurements in organic field-effect transistors (OFETs) by applying voltage steps, VS, to OFETs. We use the electric scheme for OFET-TOF introduced by Dunn et al. [Appl. Phys. Lett. 88, 063507 (2006)]. Our investigation of a series of low-threshold poly(triaryl amine) OFETs with different channel lengths, L, suggests that in the OFET-TOF setup, the effective voltage driving carriers across the channel, VTOF, is reduced from VS by a constant voltage that coincides with the OFET’s threshold voltage, VT: VTOF=VS−VT. Under this assumption, TOFs scale as expected from theory with both VS and channel length, L, and the extracted dynamically acquired μ agrees excellently between different samples, and experimental protocols (variation of VS / variation of L). However, “dynamic” μ is higher than the “static” μ conventionally extracted from saturated transfer characteristics, which is also less consistent between samples. Also, we observe that the TOF in OFETs switching from OFF→ON is longer than the TOF in the same OFET switching ON→OFF under the same VS. We rationalize this difference by trap filling in the populated OFET channel.
Coulomb interaction among transporting charge carriers confined in two dimensions
Authors: Buh G. H. , Park Ji-Yong , Kuk Young
Published: November 2008

The time evolution of trapped charge carriers in an oxide layer as in a charge-trap nonvolatile memory was studied experimentally with electrostatic force microscopy and Monte Carlo simulation based on Smoluchowski equation for a localized charge system. Experimental results show non-Fickian behavior as suggested by our calculation. In the charge carrier transport in an oxide, the ratio of the drift current driven by the self-induced electric field to the diffusion current was explicitly solved for Gaussian and Lorentzian charge distributions in two dimensions. The ratio is scaled by a quantity of the total charge divided by the characteristic width of the charge distribution. It was found that the drift current is comparable to the diffusion current when charge of 10−16 C is confined within a region of micrometer size.
Signal processing and frequency-dependent associative memory based on nanoswitches
Authors: Cervera Javier , Ramírez Patricio , Mafé Salvador
Published: November 2008

A signal processing concept based on nanoscale switches whose conductance can be tuned by an external stimulus between two (ON and OFF) states is proposed and analyzed theoretically. The building block of the system is formed by a metal nanoparticle linked to two electrodes by an organic ligand and a molecular switch. When we apply an alternating potential to the system of the same frequency as the periodic variation between the ON and OFF states induced on the switch, the net charge delivered by the system exhibits a sharp resonance. This resonance can be used to process an external signal by selectively extracting the weight of the different harmonics. In addition, a frequency-dependent associative memory that exploits the resonance property is also demonstrated. The general properties of the signal processing concept that are required for practical implementation are analyzed for different temperatures, times, conductance ratios, applied potentials, and noise conditions.
On the explanation of the barrier heights of InP Schottky contacts by metal-induced gap states
Authors: Mönch Winfried
Published: November 2008

The barrier heights of metal-semiconductor or Schottky contacts are explained by the continuum of metal-induced gap states (MIGSs). A verification of the theoretically predicted values requires experimental barrier heights of Schottky contacts, which are not only intimate, abrupt, and free of impurities but also laterally homogeneous. Such data may be obtained from current-voltage and capacitance-voltage characteristics. Results of corresponding studies with Ag, Au, Cr, Pd, and Ti contacts on InP were recently published. The barrier heights of the respective laterally homogeneous Schottky contacts evaluated from those experimental data quantitatively confirm the predictions of the MIGS theory.
In situ study of surface reactions of atomic layer deposited LaxAl2−xO3 films on atomically clean In0.2Ga0.8As
Authors: Aguirre-Tostado F. S. , Milojevic M. , Lee B. , Kim J. , Wallace R. M.
Published: November 2008

The surface reactions of LaxAl2−xO3 ultrathin films deposited on atomically clean In0.2Ga0.8As by atomic layer deposition are studied by in situ high resolution x-ray photoelectron spectroscopy. Using 1:2 alternating cycles of La2O3 and Al2O3 results in a La:Al concentration ratio of 1:10. We found that the LaxAl2−xO3∕InGaAs interface consisted of interfacial Ga-suboxides and As–As bonds but no As- or In-oxides were detected. This suggests an interface formed by Ga–O–Al and Ga–O–La bonds from the precursor reaction.
Capillary well microplate
Authors: Ng Tuck Wah , Yu Yang , Tan Han Yen , Neild Adrian
Published: November 2008

Microplates with deep hydrophobic coated wells are standard tools in analytical research and clinical diagnostic screening. High throughput screening demands the dispensation of small volumes of liquid; which, in turn, exacts precise positioning in instrumentation. This precision condition can be significantly relaxed in the approach described here where droplets are released at the entrance of the well and fill it by capillary forces alone; provided that a critical diameter to volume condition dependent on the liquid-solid hydophibicity is fulfilled. After filling, the liquid column typically remains stationary even if the bottom end of the well is open.
The response of semiconductor optical amplifiers containing lateral composition modulation in the quantum wells
Authors: Czaban J. A. , Thompson D. A.
Published: November 2008

Tensile strained quantum wells are used to change the polarization sensitivity of semiconductor optical amplifiers. However, lateral composition modulation (LCM), which is present in the quantum wells of the device, is shown to impact the device performance. A broadening of the spectral gain is seen as recombinations from the conduction band to the heavy hole band in the In-rich regions of the LCM. This additional component to the gain from the quantum well will reduce the device gain efficiency at a specific wavelength for a given current, or it may be used to broaden the gain spectrum of an individual quantum well.
Thermally excited tunneling from a metastable electronic state in a single-Cooper-pair transistor
Authors: Rees D. G. , Glasson P. , Simkins L. R. , Collin E. , Antonov V. , Frayne P. G. , Meeson P. J. , Lea M. J.
Published: November 2008

Metastable electron traps and two-level systems (TLSs) are common in solid-state devices and lead to background charge movement and charge noise in single-electron and single-Cooper-pair transistors. We present measurements of the real-time capture and escape of individual electrons in metastable trapped states at very low temperatures, leading to charge offsets close to 1e. The charge movement exhibits thermal excitation to a hysteretic tunneling transition. The temperature dependence and hysteresis can be explained by the coupling of a TLS to a quasiparticle trap.
Quench detection in YBa2Cu3O7−δ coated conductors using interferometric techniques
Authors: Angurel L. A. , Martínez E. , Lera F. , Recuero S. , Andrés N. , Arroyo M. P. , Xie Y. Y. , Selvamanickam V.
Published: November 2008

Digital speckle pattern interferometry has been used to detect inhomogeneous heating in YBa2Cu3O7−δ coated conductors. The analysis was performed in a sample with a controlled defect, which causes a significant local reduction in the critical current value, Ic. The experiments, which were performed with the sample surrounded by nitrogen vapor, have shown that the location of the initial hot spot leading to the complete transition to the normal state of the conductor (quench) is strongly dependent on the sample cooling configuration. When the sample is mainly cooled by gas convection, the quench always starts in the low-Ic region, while for improved cooling configurations the initial hot spot does not always coincide with this region. The results have been compared with those obtained by direct electric field measurements along the sample in nitrogen vapor and liquid.
RNA-assisted catalysis in a protein enzyme: The 2′-hydroxyl of tRNA
Thr
A76 promotes aminoacylation by threonyl-tRNA synthetase
Authors: Minajigi Anand , Francklyn Christopher S.
Published: November 2008

Aminoacyl-tRNA synthetases (aaRSs) join amino acids to 1 of 2 terminal hydroxyl groups of their cognate tRNAs, thereby contributing to the overall fidelity of protein synthesis. In class II histidyl-tRNA synthetase (HisRS) the nonbridging
S
p
-oxygen of the adenylate is a potential general base for aminoacyl transfer. To test for conservation of this mechanism in other aaRSs and the role of terminal hydroxyls of tRNA in aminoacyl transfer, we investigated the class II
Escherichia coli
threonyl-tRNA synthetase (ThrRS). As with other class II aaRSs, the rate-determining step for ThrRS is amino acid activation. In ThrRS, however, the 2′-OH of A76 of tRNA
Thr
and a conserved active-site histidine (His-309) collaborate to catalyze aminoacyl transfer by a mechanism distinct from HisRS. Conserved residues in the ThrRS active site were replaced with alanine, and then the resulting mutant proteins were analyzed by steady-state and rapid kinetics. Nearly all mutants preferentially affected the amino acid activation step, with only a modest effect on aminoacyl transfer. By contrast, H309A ThrRS decreased transfer 242-fold and imposed a kinetic block to CCA accommodation. His-309 hydrogen bonds to the 2′-OH of A76, and substitution of the latter by hydrogen or fluorine decreased aminoacyl transfer by 763- and 94-fold, respectively. The proton relay mechanism suggested by these data to promote aminoacylation is reminiscent of the NAD
+
-dependent mechanisms of alcohol dehydrogenases and sirtuins and the RNA-mediated catalysis of the ribosomal peptidyl transferase center.
Two protonation switches control rhodopsin activation in membranes
Authors: Mahalingam Mohana , Martínez-Mayorga Karina , Brown Michael F. , Vogel Reiner
Published: November 2008

Activation of the G protein-coupled receptor (GPCR) rhodopsin is initiated by light-induced isomerization of the retinal ligand, which triggers 2 protonation switches in the conformational transition to the active receptor state Meta II. The first switch involves disruption of an interhelical salt bridge by internal proton transfer from the retinal protonated Schiff base (PSB) to its counterion, Glu-113, in the transmembrane domain. The second switch consists of uptake of a proton from the solvent by Glu-134 of the conserved E(D)RY motif at the cytoplasmic terminus of helix 3, leading to pH-dependent receptor activation. By using a combination of UV–visible and FTIR spectroscopy, we study the activation mechanism of rhodopsin in different membrane environments and show that these 2 protonation switches become partially uncoupled at physiological temperature. This partial uncoupling leads to ≈50% population of an entropy-stabilized Meta II state in which the interhelical PSB salt bridge is broken and activating helix movements have taken place but in which Glu-134 remains unprotonated. This partial activation is converted to full activation only by coupling to the pH-dependent protonation of Glu-134 from the solvent, which stabilizes the active receptor conformation by lowering its enthalpy. In a membrane environment, protonation of Glu-134 is therefore a thermodynamic rather than a structural prerequisite for activating helix movements. In light of the conservation of the E(D)RY motif in rhodopsin-like GPCRs, protonation of this carboxylate also may serve a similar function in signal transduction of other members of this receptor family.
The geometric and the atomic world views
Authors: Bohr Aage , Mottelson Ben R. , Ulfbeck Ole
Published: November 2008

The atomic world view is based on the notion that matter is built of elementary constituents called atoms, and quantum mechanics was created in the pursuit of this view with probabilistic events caused by atomic particles. This conception involves unresolved ambiguities linked to the notion of an elementary quantum of action. The resolution of these problems in quantum mechanics requires a new, geometric, world view, which recognizes the occurrence of events, clicks in counters, coming without a cause, referred to as fortuitous. The possibility of a rational theory of probabilities for such events is based on the assignment to the individual click of a proper value of an element of (flat) space–time symmetry. Thereby, the distributions of uncaused clicks can be endowed with a geometric content in terms of the irreducible representations of space–time symmetry. Through fortuity, space–time invariance itself thus acquires a hitherto unrecognized role. Departing from the norms of physical theory, the uncaused click is not a measurement of something, and the reality mirrored in the distributions is the geometry of space time itself, and not a property of an imagined object. The geometric world view involves only the dimensions of space and time, and the absence of an irreducible dimension of mass is seen as the result of the discovery of new physical phenomena. Accordingly Planck's constant has no place in fundamental theory and is seen as a relic of dimensions that have become superfluous.
Discovery of phosphorylation motif mixtures in phosphoproteomics data
Authors: Ritz Anna , Shakhnarovich Gregory , Salomon Arthur R. , Raphael Benjamin J.
Published: November 2008

Motivation: Modification of proteins via phosphorylation is a primary mechanism for signal transduction in cells. Phosphorylation sites on proteins are determined in part through particular patterns, or motifs, present in the amino acid sequence.

Results: We describe an algorithm that simultaneously discovers multiple motifs in a set of peptides that were phosphorylated by several different kinases. Such sets of peptides are routinely produced in proteomics experiments.Our motif-finding algorithm uses the principle of minimum description length to determine a mixture of sequence motifs that distinguish a foreground set of phosphopeptides from a background set of unphosphorylated peptides. We show that our algorithm outperforms existing motif-finding algorithms on synthetic datasets consisting of mixtures of known phosphorylation sites. We also derive a motif specificity score that quantifies whether or not the phosphoproteins containing an instance of a motif have a significant number of known interactions. Application of our motif-finding algorithm to recently published human and mouse proteomic studies recovers several known phosphorylation motifs and reveals a number of novel motifs that are enriched for interactions with a particular kinase or phosphatase. Our tools provide a new approach for uncovering the sequence specificities of uncharacterized kinases or phosphatases.

Availability: Software is available at http:/cs.brown.edu/people/braphael/software.html.

Contact:  aritz@cs.brown.edu; braphael@cs.brown.edu

Supplementary information:  Supplementary data are available at Bioinformatics online.
Chromosomal instability mediated by non-B DNA: Cruciform conformation and not DNA sequence is responsible for recurrent translocation in humans
Authors: Inagaki Hidehito , Ohye Tamae , Kogo Hiroshi , Kato Takema , Bolor Hasbaira , Taniguchi Mariko , Shaikh Tamim H. , Emanuel Beverly S. , Kurahashi Hiroki
Published: November 2008

Chromosomal aberrations have been thought to be random events. However, recent findings introduce a new paradigm in which certain DNA segments have the potential to adopt unusual conformations that lead to genomic instability and nonrandom chromosomal rearrangement. One of the best-studied examples is the palindromic AT-rich repeat (PATRR), which induces recurrent constitutional translocations in humans. Here, we established a plasmid-based model that promotes frequent intermolecular rearrangements between two PATRRs in HEK293 cells. In this model system, the proportion of PATRR plasmid that extrudes a cruciform structure correlates to the levels of rearrangement. Our data suggest that PATRR-mediated translocations are attributable to unusual DNA conformations that confer a common pathway for chromosomal rearrangements in humans.
Creation and categorization of knowledge in automotive components SMEs in India
Authors: Pillania Rajesh K.
Published: November 2008

Purpose

New knowledge creation has gained currency in the global knowledge economy. It is important not only for big firms, but for small and medium size enterprises (SMEs) also. Indian automotive components sector is one of the fastest growing sectors of Indian economy and is dominated by SMEs. This research work aims to study the knowledge creation and categorization in SMEs in Indian automotive components sector.

Design/methodology/approach

This paper uses a survey method to collect primary data to study knowledge creation and categorization in automotive components manufacturers.

Findings

Among various kinds of knowledge, knowledge about customers is given most importance. Though new knowledge creation is gaining importance, research and development spending as percentage of turnover are very low. International automotive components manufacturers have a better perception about knowledge creation compared to the prevalent view in Indian firms. In terms of relevance, latest and timeliness, Indian and international automotive components manufacturers pay little credence to the knowledge available through government institutions and industry associations. Industry associations and governments need to have a re‐appraisal of their practices and make their working more useful, fast and updated.

Practical implications

This work has policy implications for government and industry associations. Corrective measures are suggested for industry associations and government bodies for contributing to knowledge creation and implementing knowledge management in organizations.

Originality/value

First of its kind study in SMEs, particularly automotive components sector in India. It studies the current state of knowledge creation and categorization and suggests guidelines for improving knowledge creation in SMEs.
National port competitiveness: implications for India
Authors: Jim Wu Yen‐Chun , Lin Chia‐Wen
Published: November 2008

Purpose

The purpose of this study is to perform an international comparison of logistics/port operations with a main focus on India.

Design/methodology/approach

Using data from the transportation and freight service industry during 2000‐2005, this study first conducts revealed comparative advantage (RCA) analysis to investigate India's logistics competitiveness and then uses data envelopment analysis (DEA) to analyze the efficiency of India's container port operations.

Findings

The study's findings suggest that in terms of India's logistics competitiveness, its freight industry is relatively competitive while its transportation industry is not. Overall, while the study indicates that India's largest container port (Jawaharlal Nehru) is not very efficient; the RCA analysis shows that India still has a relative comparative advantage over its industrialized counterparts except for Japan and France in the transportation service industry. Interestingly, the DEA results also indicate that the efficiency value of the container port in India is second only to the US port of Los Angeles among the ports examined in industrialized countries.

Research limitations/implications

RCA indicators are only able to examine past and present industry conditions based on export results, and do not provide a detailed explanation of the reasons for changes in levels of competitiveness. As for DEA analysis, this study focused only on land and equipment as input variables primarily because of a lack of data on worker efficiency. It is suggested that there is an urgent need for an overhaul of port equipment if India wants to accommodate the growing volume of imports and exports in the future.

Originality/value

This paper provides a first step toward gaining insights into India's current logistics/port competitiveness position in comparison with other emerging markets and advanced economies. This paper also contributes to providing a better understanding of the competitiveness of emerging economies (BRICs & Next 11), which are viewed as rising stars and have not yet been fully investigated in the existing literature. Several recommendations are also provided.
Monte Carlo simulation and a value‐at‐risk of concessionary project
Authors: Du Xiaofeng , Li Amory N.
Published: November 2008

Purpose

The purpose of this paper is to propose a comprehensive approach to the valuation of an infrastructure concession right and quantitative risk management projects in the People's Republic of China.

Design/methodology/approach

The paper outlines a methodology, incorporating an economic model to appraise the dynamic value and risk of concession investment in the context of the design of concession contracts.

Findings

The framework of the study simulates the present value of net cash flow and identifies probability with different parameters in concession contracts as a way to establish a correlation between parameters and net present value distribution. Moreover, the paper uses the technique of value‐at‐risk to set up an economic model to appraise the dynamic value and risk of a concession investment and analyse the key issues in the concession contracts design phase.

Research limitations/implications

It is difficult to estimate precisely the distribution of parameters in the model. In particular, estimating shortfalls in the rate of return of the concession project, the appreciation rate of the future operating cash flow and the market rate of return all have significant impact on the results.

Practical implications

This study frames examines the concession rights mode in a traffic infrastructure construction project and provides potential developers and potential host governments with a reasoned approach to evaluating risk and capital investment in potential concession projects.

Originality/value

The paper offers insights into the risk management, financing and valuation of infrastructure concession rights concerning the Guangshen Freeway in China.
Exploring maintenance strategies in Chinese product manufacturing companies
Authors: Gebauer Heiko , Pützr Felix , Fischer Thomas , Wang Chunzhi , Lin Jie
Published: November 2008

Purpose

The purpose of this paper is to explore maintenance strategies for manufacturing equipment in Chinese firms.

Design/methodology/approach

Data were collected from Chinese companies using a questionnaire administered during face‐to‐face interviews and two established methodologies in strategic management research, exploratory factor analysis and cluster analysis, were used to analyze the data.

Findings

The results suggest that despite increasing competitive capabilities of Chinese firms, their maintenance strategies are often restricted to corrective maintenance. Only very few Chinese firms have already implemented predictive maintenance approach, total productive maintenance programs or the strategic outsourcing of maintenance activities.

Research limitations/implications

The research limitations stem from typical issues related to the use of exploratory factor analysis and cluster analysis (for example reliance on the subjective judgment of the researcher or the provision of clusters although no meaningful groups are embedded in the sample).

Practical implications

The findings highlight potential strategies for Chinese firms to improve their maintenance management.

Originality/value

This paper deals with a neglected area of operations management by exploring the maintenance approaches in fast growing Chinese manufacturing industries.
Human resource management practices and workers' job satisfaction
Authors: Ileana Petrescu Alina , Simmons Rob
Published: November 2008

Purpose

The purpose of this paper is to investigate the relationship between human resource management (HRM) practices and workers' overall job satisfaction and their satisfaction with pay.

Design/methodology/approach

The paper uses British data from two different cross‐sectional datasets. It estimates probit models with overall job satisfaction and satisfaction with pay as subjective dependent variables.

Findings

After controlling for personal, job and firm characteristics, it is found that several HRM practices raise workers' overall job satisfaction and their satisfaction with pay. However, these effects are only significant for non‐union members. Satisfaction with pay is higher where performance‐related pay and seniority‐based reward systems are in place. A pay structure that is perceived to be unequal is associated with a substantial reduction in both non‐union members' overall job satisfaction and their satisfaction with pay. Although HRM practices can raise workers' job satisfaction, if workplace pay inequality widens as a consequence then non‐union members may experience reduced job satisfaction.

Research limitations/implications

The data sets used in the analysis are cross‐sectional, presenting a snapshot of impacts of HRM practices on job satisfaction at a particular point in time. Dynamic effects are therefore not captured.

Originality/value

The paper adds to the empirical literature on effects of HRM practices, focussing on impacts on both overall job satisfaction and satisfaction with pay. A novel feature of the paper is the use of two separate data sets to develop complementary empirical results.