bluuebunny/crossref_metadata_2025 huggingface dataset:
The IceCube neutrino observatory: latest results on the search for point sources and status of IceCube construction
Authors: Castermans Thierry P.A. , Karle Albrecht
Published: December 2007

The AMANDA neutrino telescope, prototype instrument of the IceCube neutrino observatory at South Pole, has collected data since 2000 in its final configuration. A period of 1001 days of livetime between 2000 and 2004 has been analysed in order to find evidence of a neutrino signal coming from point-like sources such as microquasars, active galactic nuclei, supernovae remnants or gamma ray bursts. A sensitivity to fluxes of νμ + νμ + ντ + ντ of dΦ/dE =1.0 · 10−10 (E/TeV)−2 · TeV−1 cm−2 s−1 was reached in the energy range between 1.6 TeV and 1.6 PeV. No significant excess over the background has been found so far. Flux upper limits infered from this study can constrain certain neutrino emission models of X-ray binaries. IceCube will have a substantially higher sensitivity. Currently at 10% of its final extension, it will comprise 4800 optical sensors deployed along 80 strings by early 2011, instrumenting one cubic kilometre volume of ice and 1 km2 at the surface.
Single Star Scidar first light from Dôme C
Authors: Vernin Jean , Chadid Merieme , Aristidi Eric , Azouit Max , Sadibekova Tatiana , Trinquet Hervé
Published: December 2007

In the recent years, a lot of instruments have been put into operation during the polar summer at DômeC., Then, during the first polar night when the Astro-Concordia sation was open for the first time during winter, about 40 balloons (Azouit & Vernin) instrumented to measure optical turbulence profiles and 2 Differencial Image Motion Monitors (DIMM) were setup. The main results from this first important campaign are found in Agabi et al. (2006). It appears from this first night time observations that almost all the optical turbulence was concentrated in the first 30 m above the ice. At an elevation of 8.5 m above the ice the seeing is about 1″.4, while above an elevation of 30 m the seeing drops down to 0″.36. This last figure is coherent with the estimation from Lawrence et al. (2004) if one takes into account that they were not sensitive to the first 30 m., which corresponds to the turbulent surface layer.
Atmospheric scintillation at Dome C, Antarctica
Authors: Kenyon Suzanne L. , Lawrence Jon S. , Ashley Michael C. B. , Storey John W. V. , Tokovinin Andrei , Fossat Eric
Published: December 2007

Dome C, Antarctica is one of the most promising astronomical sites in the world (Fossat & Candidi 2003, and references therein). Dome C boasts low wind speeds, very cold temperatures and little precipitation. The atmospheric turbulence is very weak compared to temperate sites, leading to sub-arcsecond seeing conditions (Lawrence et al. 2004; Agabi et al. 2006).
CAMISTIC: THz/submm astronomy at Dome C in Antarctica
Authors: Minier Vincent , Durand Gilles , Lagage Pierre-Olivier , Talvard M.
Published: December 2007

Submillimetre (submm) astronomy is the prime technique to unveil the birth and early evolution of a broad range of astrophysical objects. It is a relatively new branch of observational astrophysics which focuses on studies of the cold Universe, i.e., objects radiating a significant – if not dominant – fraction of their energy at wavelengths ranging from ∼ 100 μm to ∼ 1 mm. Submm continuum observations are particularly powerful to measure the luminosities, temperatures and masses of cold dust emitting objects. Examples of such objects include star-forming clouds in our Galaxy, prestellar cores and deeply embedded protostars, protoplanetary disks around young stars, as well as nearby starburst galaxies and dust-enshrouded high-redshift galaxies in the early Universe.
Impairing and Monitoring Glucose Catabolite Repression in l‐Carnitine Biosynthesis
Authors: Sevilla A. , Cánovas M. , Keller D. , Reimers S. , Iborra J. L.
Published: December 2007

Signal transduction pathways are usually avoided when optimizing a biotransformation process because they require complex mathematical formulations. The aim of this work was to use a Systems Biology approach to optimize and monitor the biotransformation of l‐carnitine using signal transduction pathways. To this end, a dynamic model was constructed, integrating the metabolic pathways of l‐carnitine biosynthesis as well as the expression of this metabolism by means of its regulation by transcription factors such as cAMP‐CRP and CaiF. The model was validated using different C‐sources as well as different reactor feeding approaches. A linear relationship between the external cellular cAMP and the l‐carnitine production levels was predicted before being experimentally confirmed in several scenarios. Moreover, results of the model simulations and subsequent experimental findings demonstrated that the addition of exogenous cAMP was able to restore the l‐carnitine production when glucose was used as C‐source. Additionally, a way to monitor the l‐carnitine biosynthesis by using the level of cAMP as a marker of the biotransformation state was in silico and experimentally demonstrated.
Cooling of the Atlantic by Saharan dust
Authors: Lau K. M. , Kim K. M.
Published: December 2007

Using aerosol optical depth, sea surface temperature, top‐of‐the‐atmosphere solar radiation flux, and oceanic mixed‐layer depth from diverse data sources that include NASA satellites, NCEP reanalysis, in situ observations, as well as long‐term dust records from Barbados, we examine the possible relationships between Saharan dust and Atlantic sea surface temperature. Results show that the estimated anomalous cooling pattern of the Atlantic during June 2006 relative to June 2005 due to attenuation of surface solar radiation by Saharan dust remarkably resemble observations, accounting for approximately 30–40% of the observed change in sea surface temperature. Historical data analysis show that there is a robust negative correlation between atmospheric dust loading and Atlantic SST consistent with the notion that increased (decreased) Saharan dust is associated with cooling (warming) of the Atlantic during the early hurricane season (July–August–September).
Decadal change in the relationship between the oceanic entrainment temperature and thermocline depth in the far western tropical Pacific
Authors: Zhang Rong‐Hua , Busalacchi Antonio J. , Xue Yan
Published: December 2007

The interaction between the thermocline and mixed layer is a key process important to the El Niño‐Southern Oscillation (ENSO) in the tropical Pacific climate system. Decadal changes in the relationships between the depth of 20°C isotherm (D20C) and the temperature of subsurface water entrained into the mixed layer (Te) are analyzed using observed temperature data during the periods 1955‐2003 in association with the 1976–77 climate shift. The thermocline in the western tropical Pacific is anomalously deep before the shift, but shallow after the shift. It is found that the relationship has undergone decadal change in the far western tropical Pacific (west of 160°E). The effects of the decadal changes in the D20C‐Te relationships on ENSO properties are further examined using an intermediate coupled model (ICM). It is demonstrated that ENSO properties are sensitive to the decadal changes in the D20C‐Te relationship in the far western tropical Pacific.
Validation of Ozone Monitoring Instrument total ozone column measurements using Brewer and Dobson spectrophotometer ground‐based observations
Authors: Balis D. , Kroon M. , Koukouli M. E. , Brinksma E. J. , Labow G. , Veefkind J. P. , McPeters R. D.
Published: December 2007

In this paper we present validation results of the total ozone column data products of the Ozone Monitoring Instrument (OMI) on board the NASA EOS‐AURA satellite through comparisons with ground‐based observations by Dobson and Brewer spectrophotometer instruments. Quality‐controlled and archived total ozone column data from these ground‐based instruments located at stations worldwide have been used to validate more than 2 a of total ozone column observations from OMI. There are two operationally available satellite total ozone column data products, based on the OMI‐TOMS and the OMI‐DOAS retrieval algorithms, respectively. Validation with ground‐based data focused on global comparisons and seasonal dependence and the possible dependence on latitude and solar zenith angle. Our results show a globally averaged agreement of better than 1% for OMI‐TOMS data and better than 2% for OMI‐DOAS data with the ground‐based observations. The OMI‐TOMS data product is shown to be of high overall quality with no significant dependence on solar zenith angle or latitude. The OMI‐DOAS data product shows no significant dependence on latitude except for the high latitudes of the Southern Hemisphere where it systematically overestimates the total ozone value. In addition a significant dependence on solar zenith angle is found between OMI‐DOAS and ground‐based data. Comparisons of satellite and ground‐based data tend to show a marginal seasonal dependence even though it remains unclear whether this dependence originates from the ground‐based or spaceborne observations.
Nonlinear scaling schemes for Lennard-Jones interactions in free energy calculations
Authors: Steinbrecher Thomas , Mobley David L. , Case David A.
Published: December 2007

Alchemical free energy calculations provide a means for the accurate determination of free energies from atomistic simulations and are increasingly used as a tool for computational studies of protein-ligand interactions. Much attention has been placed on efficient ways to deal with the “endpoint singularity” effect that can cause simulation instabilities when changing the number of atoms. In this study we compare the performance of linear and several nonlinear transformation methods, among them separation shifted “soft core” scaling, for a popular test system, the hydration free energy of an amino acid side chain. All the nonlinear methods yield similar results if extensive sampling is performed, but soft core scaling provides smooth λ curves that are best suited for commonly used numerical integration schemes. Additionally, results from a more flexible solute, hexane, will also be discussed.
Structure of SiAu16: Can a silicon atom be stabilized in a gold cage?
Authors: Sun Qiang , Wang Qian , Chen Gang , Jena Puru
Published: December 2007

Nanostructures of Au and Si as well as Au–Si hybrid structures are topics of great current interest from both scientific and technological points of view. Recent discovery of Au clusters having fullerenelike geometries and the possibility of endohedral complexes with Si atoms inside the Au cage opens new possibilities for designing Au–Si nanostructures. Using ab initio simulated annealing method we have examined the stability of Si–Au16 endohedral complex. Contrary to what we believed, we find that the endohedral configuration is metastable and the structure where Si atom binds to the exterior surface of the Au16 cage is the lowest energy structure. The bonding of Si to Au cluster mimics its behavior of that in bulk and liquid phase of Au. In addition, doping of Si in high concentration would cause fracture and embrittlement in gold nanostructures just as it does in the bulk phase. Covalent bonding between Au–Au and Au–Si is found to be a dominant feature in the stability of the Au–Si nanostructures. Our study provides insight that may be useful in fabricating hybrid Au–Si nanostructures for applications microelectronics, catalysis, biomedine, and jewelry industry.
On the growth of carbon nanofibers on glass with a Cr layer by inductively coupled plasma chemical vapor deposition: The effect of Ni film thickness
Authors: Wei H. W. , Tung C. H. , Sung M. S. , Leou K. C. , Tsai C. H.
Published: December 2007

We have studied the effect of the thickness of catalytic Ni film for the growth of vertically aligned carbon nanofibers (VA-CNFs) on glass substrates coated with a conductive underlayer of Cr. Both the pretreatment process through which the catalytic Ni nanoparticles were formed and the growth of well-aligned CNFs were carried out in an inductively coupled plasma chemical vapor deposition (ICP-CVD) system. The VA-CNFs were characterized by scanning electron microscopy, Raman spectroscopy, as well as field emission measurements. The results of VA-CNF growth shows that as the Ni film thicknesses decrease, not only the length but also the density of the CNFs drop, although the density of catalytic Ni nanoparticles increases. The variation of CNF density with Ni film thicknesses is believed to be a result of the detachment of the CNFs from the substrate, caused by the electrostatic force produced by the plasma sheath electric field, as well as an ion-enhanced chemical etching effect due to atomic/ionic hydrogen, during the ICP-CVD growth. A field emission measurement apparatus based on a metallic probe of spherical anode structure was also constructed in this study. An electrostatic image model was employed to determine the electric field distribution on the cathode surface. Along with the standard F−N field emission model, the dependence of field emission current density on the cathode surface electric field, as well as an effective field enhancement factor, were extracted from the current-voltage measurement results. The threshold electric field (Ethreshold, for a current density of 1 mA/cm2) increases from 9.2 V/μm to 13.1 V/μm, and then drops to 11.5 V/μm for the CNFs with Ni film thicknesses of 20 nm, 30 nm, and 40 nm, respectively. The electrostatic model results also indicate that the 20 nm case has the greatest space-charge effect on the emission current, consistent with the growth results that the 20 nm case has the lowest CNF density. On the other hand, the CNF length of the 40 nm case is longer than that of the 30 nm one, while the densities are nearly the same; as a result, Ethreshold for the 30 nm case is higher.
Effect of Al doping on the magnetic and electrical properties of Zn(Cu)O based diluted magnetic semiconductors
Authors: Chakraborti D. , Trichy G. , Narayan J. , Prater J. T. , Kumar D.
Published: December 2007

The effect of Al doping on the magnetic properties of Zn(Cu)O based dilute magnetic semiconducting thin films has been systematically investigated. Epitaxial thin films have been deposited onto sapphire c-plane single crystals using pulsed laser deposition technique. X-ray diffraction and high resolution transmission electron microscopy studies show that the Zn(Cu,Al)O films are epitaxially grown onto (0001) sapphire substrates with a 30°/90° rotation in the basal plane. The large lattice misfit of the order of 16% is accommodated by matching integral multiples of lattice and substrate planes. In these large mismatch systems, the resulting films are fully relaxed following deposition of the first complete monolayer of ZnO (consistent with a critical thickness that is less than one monolayer). Magnetic hysteresis measurements indicate that the pure Zn(Cu)O thin films are ferromagnetic at room temperature. Doping with up to 5% Al (n type) does not significantly affect the ferromagnetism even though it results in an increase in carrier densities of more than 3 orders of magnitude, rising from 1×1017 to 1.5×1020 cm−3. However, for Al additions above 5%, a drop in net magnetization is observed. Annealing the films in an oxygen atmosphere at 600 °C also resulted in a dramatic drop in magnetic moment of the samples. These results strongly suggest that carrier induced exchange is not directly responsible for the magnetic properties of these materials. Rather, a defect mediated exchange mechanism needs to be invoked for this system.
Left-handed metamaterial design for Čerenkov radiation
Authors: Wu Bae-Ian , Lu Jie , Kong Jin Au , Chen Min
Published: December 2007

The design of a new type of left-handed material (LHM), having two dimensions of negative permittivities and one dimension of negative permeability, is presented in this paper for the observation and demonstration of the LH properties of Čerenkov radiation, which is a transverse magnetic (TM) electromagnetic wave. For a unit cell’s dimension of 5 mm, a LH band is observed between 6 and 7 GHz upon a TM incidence. We also use an antenna array to model a traveling current source, representing a single frequency component of a moving charged particle, demonstrating the feasibility and basis of observing backward Čerenkov radiation experimentally with LHM.
Bifurcation and hysteresis phenomena in two-dimensional sail-sail-flow interactions
Authors: Sugimoto Takeshi
Published: December 2007

This is the first report of complex bifurcation and manyfold hysteresis phenomena in the physics behind a pair of sails set in a flow of two dimensions. The formalism is based on inviscid vorticity theory, and the basic equations consist of a pair of integro-differential equations subject to a pair of nonlinear integral constraints. The method of solution is built up with the boundary element method for the integro-differential equations as well as the Newton–Raphson method for parameter search by use of the nonlinear integral constraints. Three types of configurations are considered as case studies on effects due to overlapping of the jib sail upon the main sail. Numerical analyses predict three sets of solutions: The convex-convex sail shapes, the concave-convex sail shapes, and the concave-concave sail shapes as well as two- or threefold hysteresis in aerodynamic and structural characteristics. Experimental observations confirm the existence of all the three solution sets, and moreover another set, the convex-concave sail shapes, is found by the experiment. The three case studies show that too much overlap of sails fails to obtain high lift.
Hydrogen concentration and bonding configuration in polycrystalline diamond films: From micro-to nanometric grain size
Authors: Michaelson Sh. , Ternyak O. , Akhvlediani R. , Hoffman A. , Lafosse A. , Azria R. , Williams O. A. , Gruen D. M.
Published: December 2007

The present work studies the incorporation of hydrogen and its bonding configuration in diamond films composed of diamond grains of varying size which were deposited by three different methods: hot filament (HF), microwave (MW), and direct current glow discharge (dc GD) chemical vapor deposition (CVD). The size of diamond grains which constitute the films varies in the following way: hundreds of nanometers in the case of HF CVD (“submicron size,” ∼300nm), tens of nanometers in the case of MW CVD (3–30nm), and a few nanometers in the case of dc GD CVD (“ultrananocrystalline diamond,” ∼5nm). Raman spectroscopy, secondary ion mass spectroscopy, and high resolution electron energy loss spectroscopy (HR-EELS) were applied to investigate the hydrogen trapping in the films. The hydrogen retention of the diamond films increases with decreasing grain size, indicating that most likely, hydrogen is bonded and trapped in grain boundaries as well as on the internal grain surfaces. Raman and HR-EELS analyses show that at least part of this hydrogen is bonded to sp2- and sp3-hybridized carbon, thus giving rise to typical CH vibration modes. Both vibrational spectroscopies show the increase of (sp2)-CH mode intensity in transition from submicron to ultrananocrystalline grain size. The impact of diamond grain size on the shape of the Raman and HR-EELS hydrogenated diamond spectra is reported and discussed.
Wavelet-based local region-of-interest reconstruction for synchrotron radiation x-ray microtomography
Authors: Li Lingqi , Toda Hiroyuki , Ohgaki Tomomi , Kobayashi Masakazu , Kobayashi Toshiro , Uesugi Kentaro , Suzuki Yoshio
Published: December 2007

Synchrotron radiation x-ray microtomography is becoming a uniquely powerful method to nondestructively access three-dimensional internal microstructure in biological and engineering materials, with a resolution of 1μm or less. The tiny field of view of the detector, however, requires that the sample has to be strictly small, which would limit the practical applications of the method such as in situ experiments. In this paper, a wavelet-based local tomography algorithm is proposed to recover a small region of interest inside a large object only using the local projections, which is motivated by the localization property of wavelet transform. Local tomography experiment for an Al–Cu alloy is carried out at SPring-8, the third-generation synchrotron radiation facility in Japan. The proposed method readily enables the high-resolution observation for a large specimen, by which the applicability of the current microtomography would be promoted to a large extent.
Compact soft x-ray spectrometer for plasma diagnostics at the Heidelberg Electron Beam Ion Trap
Authors: Lapierre A. , Crespo López-Urrutia J. R. , Baumann T. M. , Epp S. W. , Gonchar A. , González Martínez A. J. , Liang G. , Rohr A. , Soria Orts R. , Simon M. C. , Tawara H. , Versteegen R. , Ullrich J.
Published: December 2007

A compact flat-field soft x-ray grazing-incidence grating spectrometer equipped with a cryogenically cooled back-illuminated charge-coupled device camera was built and implemented at the Heidelberg Electron Beam Ion Trap. The instrument spans the spectral region from 1to37nm using two different gratings. In slitless operation mode, it directly images a radiation source, in this case ions confined in an electron beam ion trap, with high efficiency and reaching hereby a resolving power of λ∕Δλ≅130 at 2nm and of λ∕Δλ≅600 at 28nm. Capable of automatized operation, its low noise and excellent stability make it an ideal instrument not only for spectroscopic diagnostics requiring wide spectral coverage but also for precision wavelength measurements.
On the exponential decay of the n-point correlation functions and the analyticity of the pressure
Authors: Lo Assane
Published: December 2007

The goal of this paper is to provide estimates leading to a direct proof of the exponential decay of the n-point correlation functions for certain unbounded models of Kac type. The methods are based on estimating higher order derivatives of the solution of the Witten Laplacian equation on 1-forms associated with the Hamiltonian of the system. We also provide a formula for the Taylor coefficients of the pressure that is suitable for a direct proof of the analyticity.
Improved charge injection characteristics of Ge nanocrystals embedded in hafnium oxide for floating gate devices
Authors: Das S. , Das K. , Singha R. K. , Dhar A. , Ray S. K.
Published: December 2007

Metal-oxide-semiconductor capacitors with a trilayer structure consisting of Ge+HfO2 layers sandwiched between HfO2 tunnel and cap oxides were fabricated on p-Si substrates. Ge nanocrystals embedded in SiO2 were also studied for comparison. Cross-sectional transmission electron micrographs revealed the formation of spherical shaped Ge nanocrystals. The optical and charge storage characteristics of trilayer structures were studied through photoluminescence spectroscopy and capacitance-voltage measurements, respectively. An enhancement of the charge injection capability into nanocrystals was observed for the device with HfO2 as tunnel and cap oxide. The optical emission characteristics support the carrier confinement in Ge nanocrystals embedded in oxide matrices.
Influence of copper precipitation on the formation of denuded zone in Czochralski silicon
Authors: Xu Jin , Yang Deren , Moeller H. J.
Published: December 2007

The influence of copper precipitation on the formation of denuded zone (DZ) in Czochralski silicon was systematically investigated by means of scanning infrared microscopy (SIRM) and optical microscopy. It was found that, for conventional furnace high-low-high annealing, the DZ cannot be obtained only in the specimens contaminated by copper impurity at the very beginning of the heat treatment, indicating that the copper precipitates with high density generated in the region just below the surface during the first annealing step. Additionally, the width of the DZ changed according to the copper contamination sequence, indicating that the contamination temperature, that is, the corresponding equilibrium concentration of interstitial copper in the silicon, can influence significantly the thermodynamics and kinetic process of the formation of copper precipitates. For rapid thermal–low-high annealing, the tendency is nearly the same, while the contrast of the bulk microdefects revealed by SIRM is somewhat lower. On the basis of the experiments, it is suggested that the formation of DZ is strongly influenced by the copper precipitation mechanism, which is mainly controlled by the annealing temperature and point defects.
Conduction band offset at the InN∕GaN heterojunction
Authors: Wang Kejia (Albert) , Lian Chuanxin , Su Ning , Jena Debdeep , Timler John
Published: December 2007

The conduction-band offset between GaN and InN is experimentally determined. InN∕n-type GaN isotype heterojunctions grown by molecular beam epitaxy are observed to exhibit Schottky-junction like behavior based on rectifying vertical current flow. From capacitance-voltage measurements on the heterojunction, the Schottky barrier height is found to be ∼0.94eV. The photocurrent spectroscopy measurement by backside illumination reveals an energy barrier height of 0.95eV across the heterojunction, consistent with the capacitance measurement. By combining electrical transport, capacitance-voltage, and photocurrent spectroscopy measurement results, the conduction band offset between InN and GaN is estimated to be ΔEC=1.68±0.1eV.
Photoelectron spectroscopy of individual nanowires of Si and Ge
Authors: Haight Richard , Sirinakis George , Reuter Mark
Published: December 2007

We describe an experiment designed to carry out photoelectron spectroscopy on individual nanowires of Si and Ge. Laser generated, 150fs pulses of 200nm light (6.2eV) were focused onto a single Si or Ge nanowire; the ensuing photoemitted electrons were measured with 20meV resolution. Fermi level locations within the individual Si and Ge nanowire band gaps and work functions of hydrogen terminated nanowires were measured. Polarization dependent electron emission was observed and compared with Mie theory.
Effect of dislocation density on efficiency droop in GaInN∕GaN light-emitting diodes
Authors: Schubert Martin F. , Chhajed Sameer , Kim Jong Kyu , Schubert E. Fred , Koleske Daniel D. , Crawford Mary H. , Lee Stephen R. , Fischer Arthur J. , Thaler Gerald , Banas Michael A.
Published: December 2007

Measurements of light-output power versus current are performed for GaInN∕GaN light-emitting diodes grown on GaN-on-sapphire templates with different threading dislocation densities. Low-defect-density devices exhibit a pronounced efficiency peak followed by droop as current increases, whereas high-defect-density devices show low peak efficiencies and little droop. The experimental data are analyzed with a rate equation model to explain this effect. Analysis reveals that dislocations do not strongly impact high-current performance; instead they contribute to increased nonradiative recombination at lower currents and a suppression of peak efficiency. The characteristics of the dominant recombination mechanism at high currents are consistent with processes involving carrier leakage.
Effect of current crowding on whisker growth at the anode in flip chip solder joints
Authors: Ouyang Fan-Yi , Chen Kai , Tu K. N. , Lai Yi-Shao
Published: December 2007

Owing to the line-to-bump configuration in flip chip solder joints, current crowding occurs when electrons enter into or exit from the solder bump. At the cathode contact, where electrons enter into the bump, current crowding induced pancake-type void formation has now been observed widely. At the anode contact, where electrons exit from the bump, we report here that whisker is formed. Results of both eutectic SnPb and SnAgCu solder joints are presented and compared. The cross-sectioned surface in SnPb showed dimple and bulge after electromigration, while that of SnAgCu remained flat. The difference is due to a larger back stress in the SnAgCu, consequently, electromigration in SnAgCu is slower than that in SnPb. Nanoindentation markers were used to measure the combined atomic fluxes of back stress and electromigration.
Geiger-mode avalanche photodiodes at 2μm wavelength
Authors: Duerr E. K. , Manfra M. J. , Diagne M. A. , Bailey R. J. , Donnelly J. P. , Connors M. K. , Turner G. W.
Published: December 2007

Geiger-mode avalanche photodiodes (APDs) with response at 2μm have been developed in the antimonide material system. At 77K, the APDs demonstrated a dark count rate of 210kHz and an injection probability–avalanche probability product of 35% at 4.5V of overbias.
Intrinsic lattice thermal conductivity of semiconductors from first principles
Authors: Broido D. A. , Malorny M. , Birner G. , Mingo Natalio , Stewart D. A.
Published: December 2007

We present an ab initio theoretical approach to accurately describe phonon thermal transport in semiconductors and insulators free of adjustable parameters. This technique combines a Boltzmann formalism with density functional calculations of harmonic and anharmonic interatomic force constants. Without any fitting parameters, we obtain excellent agreement (<5% difference at room temperature) between the calculated and measured intrinsic lattice thermal conductivities of silicon and germanium. As such, this method may provide predictive theoretical guidance to experimental thermal transport studies of bulk and nanomaterials as well as facilitating the design of new materials.
Radial evolution of dielectric barrier glowlike discharge in helium at atmospheric pressure
Authors: Luo Haiyun , Liang Zhuo , Lv Bo , Wang Xinxin , Guan Zhicheng , Wang Liming
Published: December 2007

The radial evolution of dielectric barrier discharge in helium at atmospheric pressure was studied by taking end-view photographs of the discharge during one current pulse using a fast-gated intensified charge coupled device. The photographs were transformed into three-dimensional images that make the radial evolution of the discharge more visualized. It was found that the discharge begins with a weak Townsend discharge covering the entire electrode surface, develops much more rapidly in the central part where the electric field is higher, and spreads radially outward.
Effects of rearrangement and allelic exclusion of
JJAZ1
/
SUZ12
on cell proliferation and survival
Authors: Li Hui , Ma XianYong , Wang Jinglan , Koontz Jason , Nucci Marisa , Sklar Jeffrey
Published: December 2007

Polycomb group genes (PcGs) have been implicated in cancer based on altered levels of expression observed in certain tumors and the behavior of cultured cells containing inserted PcG transgenes. Endometrial stromal tumors provide evidence for a direct causal relationship because they contain several chromosomal translocations and resultant gene fusions involving PcGs, the most common of which joins portions of the
JAZF1
gene to the PcG
JJAZ1/SUZ12
. We show here that both benign and malignant forms of this tumor have the
JAZF1–JJAZ1
fusion but only the malignant form also exhibits exclusion of the unrearranged
JJAZ1
allele. To evaluate the effects of both the
JJAZ1/SUZ12
fusion and allelic exclusion on functions related to cell growth, we studied HEK293 cells that were modified with respect to
JJAZ1
expression. We found that the
JAZF1–JJAZ1
fusion restored levels of the polycomb protein EZH2 and histone 3 lysine 27 trimethylation, which were reduced by knockdown of endogenous JJAZ1. At the same time, the presence of
JAZF1–JJAZ1
markedly inhibited apoptosis and induced above normal proliferation rates, although the latter effect occurred only when normal
JJAZ1
was suppressed. Our findings suggest a genetic pathway for progression of a benign precursor to a sarcoma involving increased cell survival associated with acquisition of a PcG rearrangement, followed by accelerated cellular proliferation upon allelic exclusion of the unrearranged copy of that gene. Furthermore, these results indicate the likely functional importance of allelic exclusion of genes disrupted by chromosomal translocations, as seen in a variety of other cancers.
Co-evolving residues in membrane proteins
Authors: Fuchs Angelika , Martin-Galiano Antonio J. , Kalman Matan , Fleishman Sarel , Ben-Tal Nir , Frishman Dmitrij
Published: December 2007

Motivation: The analysis of co-evolving residues has been exhaustively evaluated for the prediction of intramolecular amino acid contacts in soluble proteins. Although a variety of different methods for the detection of these co-evolving residues have been developed, the fraction of correctly predicted contacts remained insufficient for their reliable application in the construction of structural models. Membrane proteins, which constitute between one-fourth and one-third of all proteins in an organism, were only considered in few individual case studies.

Results: We present the first general study of correlated mutations in α-helical membrane proteins. Using seven different prediction algorithms, we extracted co-evolving residues for 14 membrane proteins having a solved 3D structure. On average, distances between correlated pairs of residues lying on different transmembrane segments were found to be significantly smaller compared to a random prediction. Covariation of residues was frequently found in direct sequence neighborhood to helix–helix contacts. Based on the results obtained from individual prediction methods, we constructed a consensus prediction for every protein in the dataset that combines obtained correlations from different prediction algorithms and simultaneously removes likely false positives. Using this consensus prediction, 53% of all predicted residue pairs were found within one helix turn of an observed helix–helix contact. Based on the combination of co-evolving residues detected with the four best prediction algorithms, interacting helices could be predicted with a specificity of 83% and sensitivity of 42%.

Availability:  http://webclu.bio.wzw.tum.de/helixcorr/

Contact:  d.frishman@wzw.tum.de

Supplementary information: Supplementary data are available at Bioinformatics online.
Diabetes mellitus following gestational diabetes: role of subsequent pregnancy
Authors: Russell C , Dodds L , Armson BA , Kephart G , Joseph KS
Published: December 2007

Objective  This study was designed to determine the rate of diabetes up to 13 years after pregnancies complicated by gestational diabetes and to identify risk factors for developing diabetes. The role of a subsequent pregnancy, with and without gestational diabetes, was also examined.

Design  This was a retrospective cohort study of women with gestational diabetes.

Population and setting  Women who had gestational diabetes in their first pregnancy between 1989 and 2002 were identified through a population‐based perinatal database in Nova Scotia, Canada.

Methods  Subsequent diagnoses of diabetes, up to 13 years after the first pregnancy, were obtained from physician billing and hospital discharge databases. Cox proportional hazards regression models were used to estimate adjusted relative risks (RR) and 95% confidence intervals.

Main outcome measures  Diagnosis of diabetes after pregnancy.

Results  Of the 1401 nulliparous women with gestational diabetes, 251 women (17.9%) developed diabetes in the follow‐up period. The cumulative incidence at 1, 5, and 10 years was 5.9, 14.8, and 22.2%, respectively. Factors significantly associated with an increased risk of developing diabetes mellitus included a pre‐pregnancy weight of ≥86 kg (RR = 1.8, 95% CI 1.2–2.9), insulin therapy during the index pregnancy (RR = 4.1, 95% CI 2.1–7.9), neonatal hypoglycaemia (RR = 2.6, 95% CI 1.6–4.2), and a subsequent pregnancy with gestational diabetes (RR = 2.3, 95% CI 1.6–3.4).

Conclusion  Indicators of the severity of gestational diabetes, defined by insulin use, neonatal hypoglycaemia, and recurrent gestational diabetes in a subsequent pregnancy, are important in predicting a subsequent diagnosis of diabetes. Our findings do not support the theory that subsequent pregnancy, per se, increases the risk of developing diabetes.
Obstetric outcomes subsequent to intrauterine death in the first pregnancy
Authors: Black M , Shetty A , Bhattacharya S
Published: December 2007

Objective  To compare obstetric outcomes in the pregnancy subsequent to intrauterine death with that following live birth in first pregnancy.

Design  Retrospective cohort study.

Setting  Grampian region of Scotland, UK.

Population  All women who had their first and second deliveries in Grampian between 1976 and 2006.

Methods  All women delivering for the first time between 1976 and 2002 had follow up until 2006 to study their next pregnancy. Those women who had an intrauterine death in their first pregnancy formed the exposed cohort, while those who had a live birth formed the unexposed cohort.

Main outcome measures  Maternal and neonatal outcomes in the second pregnancy, including pre‐eclampsia, placental abruption, induction of labour, instrumental delivery, caesarean delivery, malpresentation, prematurity, low birthweight and stillbirth.

Results  The exposed cohort (n = 364) was at increased risk of pre‐eclampsia (OR 3.1, 95% CI 1.7–5.7); placental abruption (OR 9.4, 95% CI 4.5–19.7); induction of labour (OR 3.2, 95% CI 2.4–4.2); instrumental delivery (OR 2.0, 95% CI 1.4–3.0); elective (OR 3.1, 95% CI 2–4.8) and emergency caesarean deliveries (OR 2.1, 95% CI 1.5–3.0); and prematurity (OR 2.8, 95% CI 1.9–4.2), low birthweight (OR 2.8, 95% CI 1.7–4.5) and malpresentation (OR 2.8, 95% CI 2.0–3.9) of the infant as compared with the unexposed cohort (n = 33 715). The adjusted odds ratio for stillbirth was 1.2 and 95% CI 0.4–3.4.

Conclusion  While the majority of women with a previous stillbirth have a live birth in the subsequent pregnancy, they are a high‐risk group with an increased incidence of adverse maternal and neonatal outcomes.
Impact of the use of antenatal corticosteroids on mortality, cerebral lesions and 5‐year neurodevelopmental outcomes of very preterm infants: the EPIPAGE cohort study
Authors: Foix‐L’Hélias L , Marret S , Ancel P‐Y , Marchand L , Arnaud C , Fresson J , Picaud J‐C , Rozé J‐C , Theret B , Burguet A , Larroque B , Kaminski M ,   the EPIPAGE Study Group
Published: December 2007

Objective To assess the impact of antenatal corticosteroids (ACS) on neonatal mortality, cerebral lesions and 5‐year neurodevelopmental outcome of infants born at 24–27 and 28–32 weeks of gestational age (GA).

Design Observational population‐based study including all births at GAs between 22 and 32 weeks in 1997 in nine regions of France. Survivors were assessed at the age of 5 years.

Sample and methods The population enrolled in the follow up comprised 2323 infants; there were 23 deaths before age 5 years and outcome at 5 years was available for up to 1781 subjects. Two GA subgroups (24–27 and 28–32 weeks of GA) were analysed separately. Propensity scores were used to reduce bias in the estimation of the association between ACS treatment and outcomes.

Main outcome measures Neonatal death, neonatal white matter injury, cerebral palsy, mental processing composite (MPC) of the Kaufman Assessment Battery for Children test and behavioural difficulties at 5 years.

Results In the 28‐ to 32‐week GA subgroup, there was a significant association between ACS and a decreased risk of both neonatal death (OR = 0.61 [0.41–0.91]) and white matter injury (OR = 0.60 [0.46–0.79]) but only a nonsignificant trend for improved 5‐year outcome (cerebral palsy, MPC < 70). In the 24‐ to 27‐week GA subgroup, ACS was associated with a significant decrease risk of neonatal death (OR = 0.43 [0.27–0.68]) but there was only a trend for a lower risk of white matter injury and no beneficial impact on outcome at 5 years. Limiting the analysis to only those who received complete courses of ACS did not modify the results.

Conclusion The study shows that ACS therapy greatly increases the survival of very preterm infants, including the most immature, but there is little evidence that ACS affects long‐term neurodevelopmental and behavioural outcome in 28‐ to 32‐week survivors, and none in <28‐week survivors.
A 2‐year follow‐up study of anxiety and depression in women referred for colposcopy after an abnormal cervical smear
Authors: Hellsten C , Sjöström K , Lindqvist PG
Published: December 2007

Objectives  The aim of this study was to determine if there were any long‐lasting elevated anxiety levels in women attending colposcopy after an abnormal cervical smear.

Design  Prospective study.

Setting  Department of Obstetrics and Gynaecology, Malmö University Hospital, Sweden.

Population  One hundred consecutive women were invited to participate when referred for colposcopy.

Methods  Women in the study group completed the State–Trait Anxiety Inventory, the Montgomery–Åsberg Depression Rating Scale—self‐rate (MADRS‐S) and had a psychosocial interview prior to colposcopy at their two follow‐up visits.

Main outcome measures  State anxiety levels and depression scores at first visit, 6 months and 2 years.

Results  At follow up, levels of state anxiety and the depression scores of the women studied had decreased and were comparable to those of Swedish normative data. Two variables from the MADRS‐S, ‘ability to focus on different activities’ and ‘emotional involvement with others and in activities’ were the most prominent for women with moderate to severe depression. At the 2‐year visit, 30% of the women still had a fear of cancer.

Conclusions  Referral for colposcopy after an abnormal cervical smear does not seem to result in long‐lasting anxiety and depression. However, a subgroup of women, with the initially highest depression scores, still had at 2‐year state anxiety levels and depression scores significantly higher than normal. Almost one‐third of the women still had a fear of cancer in spite of lower 2‐year state anxiety levels.
Modulation of 5‐HT3 receptor desensitization by the light chain of microtubule‐associated protein 1B expressed in HEK 293 cells
Authors: Sun Hui , Hu Xiang‐Qun , Emerit Michel B. , Schoenebeck Jeffrey C. , Kimmel Cassin E. , Peoples Robert W. , Miko Angela , Zhang Li
Published: December 2007

Regulation of ligand‐gated ion channel (LGIC) function and trafficking by cytoskeleton proteins has been the topic of recent research. Here, we report that the light chain (LC1) of microtubule‐associated protein 1B (MAP1B) specifically interacted with the 5‐HT3A receptor, a predominant serotonin‐gated ion channel in the brain. LC1 and 5‐HT3A receptors were colocalized in central neurons and in HEK 293 cells expressing 5‐HT3A receptors. LC1 reduced the steady‐state density of 5‐HT3A receptors at the membrane surface of HEK 293 cells and significantly accelerated receptor desensitization time constants from 3.8 ± 0.3 s to 0.8 ± 0.1 s. However, LC1 did not significantly alter agonist binding affinity and single‐channel conductance of 5‐HT3A receptors. On the other hand, application of specific LC1 antisense oligonucleotides and nocodazole, a microtubule disruptor, significantly prolonged the desensitization time of the recombinant and native neuronal 5‐HT3 receptors by 3‐ to 6‐fold. This kinetic change induced by nocodazole was completely rescued by addition of LC1 but not GABAA receptor‐associated protein (GABARAP), suggesting that LC1 can specifically interact with 5‐HT3A receptors. These observations suggest that the LC1–5‐HT3A receptor interaction contributes to a mechanism that regulates receptor desensitization kinetics. Such dynamic regulation may play a role in reshaping the efficacy of 5‐HT3 receptor‐mediated synaptic transmission.
Accumulation of cytoplasmic calcium, but not apamin‐sensitive afterhyperpolarization current, during high frequency firing in rat subthalamic nucleus cells
Authors: Teagarden Mark , Atherton Jeremy F. , Bevan Mark D. , Wilson Charles J.
Published: December 2007

The autonomous firing pattern of neurons in the rat subthalamic nucleus (STN) is shaped by action potential afterhyperpolarization currents. One of these is an apamin‐sensitive calcium‐dependent potassium current (SK). The duration of SK current is usually considered to be limited by the clearance of calcium from the vicinity of the channel. When the cell is driven to fire faster, calcium is expected to accumulate, and this is expected to result in accumulation of calcium‐dependent AHP current. We measured the time course of calcium transients in the soma and proximal dendrites of STN neurons during spontaneous firing and their accumulation during driven firing. We compared these to the time course and accumulation of AHP currents using whole‐cell and perforated patch recordings. During spontaneous firing, a rise in free cytoplasmic calcium was seen after each action potential, and decayed with a time constant of about 200 ms in the soma, and 80 ms in the dendrites. At rates higher than 10 Hz, calcium transients accumulated as predicted. In addition, there was a slow calcium transient not predicted by summation of action potentials that became more pronounced at high firing frequency. Spike AHP currents were measured in voltage clamp as tail currents after 2 ms voltage pulses that triggered action currents. Apamin‐sensitive AHP (SK) current was measured by subtraction of tail currents obtained before and after treatment with apamin. SK current peaked between 10 and 15 ms after an action potential, had a decay time constant of about 30 ms, and showed no accumulation. At frequencies between 5 and 200 spikes s−1, the maximal SK current remained the same as that evoked by a single action potential. AHP current did not have time to decay between action potentials, so at frequencies above 50 spikes s−1 the apamin‐sensitive current was effectively constant. These results are inconsistent with the view that the decay of SK current is governed by calcium dynamics. They suggest that the calcium is present at the SK channel for a very short time after each action potential, and the current decays at a rate set by the deactivation kinetics of the SK channel. At high rates, repetitive firing was governed by a fast apamin‐insensitive AHP current that did not accumulate, but rather showed depression with increases in activation frequency. A slowly accumulating AHP current, also insensitive to apamin, was extremely small at low rates but became significant with higher firing rates.
Ageing diminishes endothelium‐dependent vasodilatation and tetrahydrobiopterin content in rat skeletal muscle arterioles
Authors: Delp Michael D. , Behnke Bradley J. , Spier Scott A. , Wu Guoyao , Muller‐Delp Judy M.
Published: December 2007

Ageing reduces endothelium‐dependent vasodilatation through an endothelial nitric oxide synthase (NOS) signalling pathway. The purpose of this study was to determine whether arginase activity diminishes endothelium‐dependent vasodilatation in skeletal muscle arterioles from old rats, and whether NOS substrate (l‐arginine) and cofactor (tetrahydrobiopterin; BH4) concentrations are reduced. First‐order arterioles were isolated from the soleus muscle of young (6 months old) and old (24 months old) male Fischer 344 rats. In vitro changes in luminal diameter in response to stepwise increases in flow were determined in the presence of the NOS inhibitor NG‐nitro‐l‐arginine methyl ester (l‐NAME, 10−5 mol l−1), the arginase inhibitor Nω‐hydroxy‐nor‐l‐arginine (NOHA, 5 × 10−4 mol l−1), exogenous l‐arginine (3 × 10−3 mol l−1) or the precursor for BH4 synthesis sepiapterin (1 μmol l−1). Arteriolar l‐arginine and BH4 content were determined via HPLC. Ageing decreased flow‐mediated vasodilatation by 52%, and this difference was abolished with NOS inhibition. Neither inhibition of arginase activity nor addition of exogenous l‐arginine had any effect on flow‐mediated vasodilatation; arteriolar l‐arginine content was also not different between age groups. BH4 content was lower in arterioles from old rats (94 ± 8 fmol (mg tissue)−1) relative to controls (234 ± 21 fmol (mg tissue)−1), and sepiapterin elevated flow‐mediated vasodilatation in arterioles from old rats. These results demonstrate that the impairment of endothelium‐dependent vasodilatation induced by old age is due to an altered nitric oxide signalling mechanism in skeletal muscle arterioles, but is not the result of increased arginase activity and limited l‐arginine substrate. Rather, the age‐related deficit in flow‐mediated vasodilatation appears to be the result, in part, of limited BH4 bioavailability.