bluuebunny/crossref_metadata_2025 huggingface dataset:
Geophysical and hydrogeological experiments from a shallow hydrothermal system at Solfatara Volcano, Campi Flegrei, Italy: Response to caldera unrest
Authors: Bruno Pier Paolo G. , Ricciardi Giovanni P. , Petrillo Zaccaria , Di Fiore Vincenzo , Troiano Antonio , Chiodini Giovanni
Published: June 2007

Integration of high‐resolution geophysical and hydrogeological investigations at Solfatara Volcano, Campi Flegrei, Italy, allowed us to (1) image the shallow and intermediate subsurface to the crater, (2) elucidate patterns in the shallow subsurface degassing, and (3) refine and upgrade volcano‐monitoring strategies for this dynamic area. Our results show that the subsurface to the crater can be divided roughly into two zones: a dry, outcropping layer overlying a horizon saturated by hydrothermal fluids. Within this saturated zone, intersections of dominant NW‐ and ENE‐striking structural lineaments act as preferential escape conduits for the fluids which generate high microseismic noise amplitudes in the southeastern part of the crater. Hydrogeological data suggest an uprising of the isotherms below Solfatara crater, and a marked increment of fluid degassing, over the last 40 years. Sudden variations of both seismic noise level and noise cycling are positively correlated with early stages of ground inflation during the AD 2000 uplift. We believe therefore that monitoring of seismic noise can be used for upgrading early warning strategies in this sector of the Campi Flegrei volcanic system.
Ozone source attribution and its modulation by the Arctic oscillation during the spring months
Authors: Hess Peter G. , Lamarque Jean‐Francois
Published: June 2007

We use the Model of Ozone and Related Tracers (MOZART‐2) driven by National Center for Environmental Prediction (NCEP) meteorology between 1980 and 2001 to examine the signature of the Arctic oscillation (AO) on tropospheric ozone during February and March. Regionally, the AO can modulate ozone by up to 5 parts per billion by volume (ppbv). We examine the modulation of ozone produced from Asian, American, and European emissions separately, the modulation of ozone produced from all tropospheric emissions, and the modulation of ozone transported from the stratosphere. During the positive phase of the AO, the simulations show a statistically significant decrease in zonally averaged ozone throughout the depth of the troposphere north of approximately 50°N. This decrease is attributed to a decrease in the stratospheric component of ozone. The longitudinal response of ozone to the AO in the upper troposphere is dictated by the changes in tropopause height associated with the AO, such that lower (higher) heights imply increased (decreased) ozone. Locally, the modulation of stratospheric ozone dominates the ozone signal throughout the depth of the troposphere over Northern Canada and the Arctic, where the AO is correlated with ozone decreases. In other locations, the local response to the AO is governed by changes in the transport of ozone produced in the troposphere. These locations include the lower troposphere over the Atlantic basin, where ozone is negatively correlated with the AO, and the lower troposphere over Europe and Eastern Siberia, where ozone is positively correlated with the AO.
An improved measure of ozone depletion in the Antarctic stratosphere
Authors: Huck P. E. , Tilmes S. , Bodeker G. E. , Randel W. J. , McDonald A. J. , Nakajima H.
Published: June 2007

Ozone mass deficit is a commonly used index to quantify Antarctic ozone depletion. However, as currently defined, this measure is not robust with respect to reflecting chemical ozone loss within the Antarctic vortex. Therefore, in this study, a new definition of ozone mass deficit (OMD) is developed. The 220 Dobson Unit based value currently used as the threshold for ozone depletion has been replaced with a new ozone background representative of pre‐ozone‐hole conditions. Second, the new OMD measure is based on ozone measurements within the dynamical vortex. A simpler method is also proposed whereby calculation of the vortex edge is avoided by using the average latitude of the vortex edge (62°S) as the spatial limiting contour. An indication of the errors in OMD introduced when using this simpler approach is provided. By comparing vortex average total ozone loss (defined using the new background and limiting contour) with partial column accumulated chemical ozone loss calculated with the tracer‐tracer correlation method for 1992–2004 and in more detail for 1996 and 2003, it is shown that the new OMD measure is representative of chemical ozone loss within the vortex. In addition the new criteria have been applied to the calculation of ozone hole area. The sensitivity of the new measures to uncertainties in the background have been quantified. The new ozone loss measures underestimate chemical ozone loss in highly dynamically disturbed years (2002 and 2004), and criteria for identifying these years are presented. The new measures should aid chemistry‐climate model intercomparisons since ozone biases in the models are avoided.
Simulated ducting of high‐frequency atmospheric gravity waves in the presence of background winds
Authors: Yu Yonghui , Hickey Michael P.
Published: June 2007

A new nonlinear and time‐dependent model is used to derive the total perturbation energy flux of two gravity wave packets propagating from the troposphere to the lower thermosphere. They are excited by a heat source and respectively propagate in an eastward and westward direction in the presence of a zonal wind. Analysis of the refractive index, the power spectra and the total perturbation energy flux allows us to correctly interpret the ducting characteristics of these two wave packets. In our study the wind acts as a directional filter to the wave propagations and causes noticeable spectral variations at higher altitudes. We are the first that time‐resolve the total perturbation energy flux influenced by the winds and the simulations have immediate impacts to the airglow observations on certain wave spectra.
Using drill cutting separates to estimate the strength of narrow shear zones at SAFOD
Authors: Morrow C. , Solum J. , Tembe S. , Lockner D. , Wong T.‐F.
Published: June 2007

A technique is presented for estimating frictional strength of narrow shear zones based on hand selection of drillhole cuttings separates. Tests were conducted on cuttings from the SAFOD scientific drillhole near Parkfield, California. Since cuttings are mixed with adjacent material as they travel up the drillhole, these fault‐derived separates give a better representation of the frictional properties of narrow features than measurements from the bulk material alone. Cuttings from two shear zones (one an active trace of the San Andreas fault) contain a significant weight percent of clay‐rich grains that exhibit deformation‐induced slickensides. In addition, cuttings from the active SAF trace contain around 1% serpentine. Coefficients of friction for clay‐rich and serpentine grains were 0.3–0.5 and 0.4–0.45, respectively. These values are around 0.12 lower than the friction coefficient of the corresponding bulk cuttings, providing an improved estimate of the frictional strength of the San Andreas fault.
Prediction of sea surface temperatures in the western Mediterranean Sea by neural networks using satellite observations
Authors: Garcia‐Gorriz Elisa , Garcia‐Sanchez Joan
Published: June 2007

We use artificial neural networks (ANNs) to predict sea surface temperatures (SSTs) in the western Mediterranean Sea. The ANNs are trained with meteorological variables as input and concurrent satellite‐derived SSTs as target. The trained ANNs predict well both the seasonal and the interannual variability of SST in that region. We also reproduce the impact of the heat wave that occurred during the summer of 2003 on the SSTs of the western Mediterranean Sea. The ANN technique allows us to predict SST maps in the western Alboran Sea for time coordinates before SST satellite availability. The presence and later partial collapse of the western Alboran gyre throughout 1980 is detected with good agreement by both the ANN predictions and the concurrent results from a 3‐D circulation model. The same methodology is used to reconstruct incomplete SST satellite images.
Mechanism of weakening of west Luzon eddy during La Niña years
Authors: Zheng Zhe‐Wen , Ho Chung‐Ru , Kuo Nan‐Jung
Published: June 2007

Multi‐satellite sea level anomalies from January 1993 to December 2004 are used to investigate the variability of sea surface features in the South China Sea (SCS). Applying empirical orthogonal function (EOF) analysis, the dominant spatial features and corresponding temporal variability are revealed. The most remarkable characteristic of variability on an interannual time scale is the abnormal weakening of meso‐scale eddy off west Luzon (west Luzon eddy, WLE) during 1998–2001. The possible mechanism inducing the weakening is found to be associated with a large‐scale forcing over the Pacific intruding into the northern SCS along the northern coast of Luzon. Moreover, the tight correlation between the Niño3.4 sea surface temperature index and the interannual variability of large‐scale forcing indicates that La Niña events may modulate the west Pacific water entering the northern SCS which contributes to the weakening of the WLE eventually.
A fractal approach to the recession of spring hydrographs
Authors: Hergarten S. , Birk S.
Published: June 2007

We present an analytical theory for the recession of spring hydrographs after precipitation events, focusing on short time scales. While other approaches mostly predict an exponential decay over long times, we obtain a power‐law decrease of discharge at short times. Similar to established well functions, the power‐law exponent is related to the spatial dimension. In extension to these models, our approach relates the exponent to the dimension of a highly permeable conduit system. This dimension may take non‐integer values, and we provide a geometric realization for fracture systems with fractal dimensions between two and three.
Double pharmacological challenge on repolarization opens new avenues for drug safety research
Authors: Thomsen M B
Published: June 2007

The pharmaceutical industry is testing new potential drugs for their propensity to prolong human cardiac repolarization, and regards this as a sign of proarrhythmic risk. Many studies have dethroned the common perception that prolonged repolarization is a reliable surrogate marker for torsades de pointes (TdP) arrhythmia. Both the pharmaceutical industry and the regulatory bodies are neglecting the available proarrhythmia models. In vitro studies have suggested that combined pharmacological hits on repolarization will produce a superior substrate for in vivo proarrhythmia, compared to the single‐drug assessment. By using consecutive pharmacological challenges, a simple model is proposed, in which combinatorial pharmacology is employed to provoke TdP in the conscious dog. The pharmaceutical industry interested in evaluating the proarrhythmic potential of their present and future drugs now has a simple means of doing so.

British Journal of Pharmacology (2007) 151, 909–911; doi:10.1038/sj.bjp.0707299
Species‐specificin vitropharmacological effects of the cannabinoid receptor 2 (CB2) selective ligand AM1241 and its resolved enantiomers
Authors: Bingham B , Jones P G , Uveges A J , Kotnis S , Lu P , Smith V A , Sun S‐C , Resnick L , Chlenov M , He Y , Strassle B W , Cummons T A , Piesla M J , Harrison J E , Whiteside G T , Kennedy J D
Published: June 2007

Background and purpose:

Racemic (R,S) AM1241 is a cannabinoid receptor 2 (CB2)‐selective aminoalkylindole with antinociceptive efficacy in animal pain models. The purpose of our studies was to provide a characterization of R,S‐AM1241 and its resolved enantiomersin vitroandin vivo.

Experimental approach:

Competition binding assays were performed using membranes from cell lines expressing recombinant human, rat, and mouse CB2receptors. Inhibition of cAMP was assayed using intact CB2‐expressing cells. A mouse model of visceral pain (para‐phenylquinone, PPQ) and a rat model of acute inflammatory pain (carrageenan) were employed to characterize the compoundsin vivo.

Key results:

In cAMP inhibition assays, R,S‐AM1241 was found to be an agonist at human CB2, but an inverse agonist at rat and mouse CB2receptors. R‐AM1241 bound with more than 40‐fold higher affinity than S‐AM1241, to all three CB2receptors and displayed a functional profile similar to that of the racemate. In contrast, S‐AM1241 was an agonist at all three CB2receptors. In pain models, S‐AM1241 was more efficacious than either R‐AM1241 or the racemate. Antagonist blockade demonstrated that thein vivoeffects of S‐AM1241 were mediated by CB2receptors.

Conclusions and implications:

These findings constitute the firstin vitrofunctional assessment of R,S‐AM1241 at rodent CB2receptors and the first characterization of the AM1241 enantiomers in recombinant cell systems andin vivo. The greater antinociceptive efficacy of S‐AM1241, the functional CB2agonist enantiomer of AM1241, is consistent with previous observations that CB2agonists are effective in relief of pain.

British Journal of Pharmacology(2007)151, 1061–1070; doi:10.1038/sj.bjp.0707303
In silicopharmacology for drug discovery: applications to targets and beyond
Authors: Ekins S , Mestres J , Testa B
Published: June 2007

Computational (in silico) methods have been developed and widely applied to pharmacology hypothesis development and testing. Thesein silicomethods include databases, quantitative structure‐activity relationships, similarity searching, pharmacophores, homology models and other molecular modeling, machine learning, data mining, network analysis tools and data analysis tools that use a computer. Such methods have seen frequent use in the discovery and optimization of novel molecules with affinity to a target, the clarification of absorption, distribution, metabolism, excretion and toxicity properties as well as physicochemical characterization. The first part of this review discussed the methods that have been used for virtual ligand and target‐based screening and profiling to predict biological activity. The aim of this second part of the review is to illustrate some of the varied applications ofin silicomethods for pharmacology in terms of the targets addressed. We will also discuss some of the advantages and disadvantages ofin silicomethods with respect toin vitroandin vivomethods for pharmacology research. Our conclusion is that thein silicopharmacology paradigm is ongoing and presents a rich array of opportunities that will assist in expediating the discovery of new targets, and ultimately lead to compounds with predicted biological activity for these novel targets.

British Journal of Pharmacology(2007)152, 21–37; doi:10.1038/sj.bjp.0707306
Dimethyl sulphoxide relaxes rabbit detrusor muscle by decreasing the Ca2+ sensitivity of the contractile apparatus
Authors: Shiga K‐i , Hirano K , Nishimura J , Niiro N , Naito S , Kanaide H
Published: June 2007

Background and purpose:

The intravesical administration of dimethyl sulphoxide (DMSO) is used to alleviate the symptoms of interstitial cystitis. We investigated the relaxant effect of DMSO and its underlying mechanism in the detrusor muscle.

Experimental approach:

The effects of DMSO on contraction, on Ca2+ sensitivity of myofilaments, and on myosin light chain (MLC) phosphorylation were investigated in both intact and α‐toxin‐permeabilized strips of rabbit detrusor muscle.

Key results:

In fura‐PE3‐loaded strips, DMSO (>1%) induced a significant relaxation during sustained contractions induced by 60 mM K+‐depolarization or 10 μM carbachol, while having no effect on the [Ca2+]i level. DMSO decreased the level of MLC phosphorylation during the contractions induced by 60 mM K+ and 10 μM carbachol. DMSO also inhibited both the contraction and MLC phosphorylation induced by calyculin‐A in intact strips. In the α‐toxin‐permeabilized preparations, DMSO relaxed the Ca2+‐induced contraction and also inhibited the tension development induced by a stepwise increment of Ca2+ concentrations. Such a relaxant effect of DMSO was enhanced in the presence of phosphate.

Conclusions and implications:

DMSO relaxes rabbit detrusor muscle by decreasing the Ca2+ sensitivity of myofilaments. Inhibition of the kinase activities involved in myosin phosphorylation may play a major role in DMSO‐induced Ca2+ desensitization. Inhibition of the cross‐bridge cycling at the step of phosphate release may also contribute to the relaxant effect of DMSO. Such relaxant effects of DMSO could be linked to the therapeutic effect of DMSO in interstitial cystitis.

British Journal of Pharmacology (2007) 151, 1014–1024; doi:10.1038/sj.bjp.0707317
Preservation of mitochondrial function may contribute to cardioprotective effects of Na+/Ca2+exchanger inhibitors in ischaemic/reperfused rat hearts
Authors: Motegi K , Tanonaka K , Takenaga Y , Takagi N , Takeo S
Published: June 2007

Background and purpose:

Na+/Ca2+exchanger (NCX) inhibitors are known to attenuate myocardial reperfusion injury. However, the exact mechanisms for the cardioprotection remain unclear. The present study was undertaken to examine the mechanism underlying the cardioprotection by NCX inhibitors against ischaemia/reperfusion injury.

Experimental approach:

Isolated rat hearts were subjected to 35‐min ischaemia/60‐min reperfusion or 20‐min ischaemia/60‐min reperfusion. NCX inhibitors (3‐30 μM KB‐R7943 (KBR) or 0.3‐1 μM SEA0400 (SEA)) were given for 5 min prior to ischaemia (pre‐ischaemic treatment) or for 10 min after the onset of reperfusion (post‐ischaemic treatment).

Key results:

With 35‐min ischaemia/60‐min reperfusion, pre‐ or post‐ischaemic treatment with KBR or SEA neither enhanced post‐ischaemic contractile recovery nor attenuated ischaemia‐ or reperfusion‐induced Na+accumulation and damage to mitochondrial respiratory function. With the milder model (20‐min ischaemia/reperfusion), pre‐ or post‐ischaemic treatment with 10 μM KBR or 1 μM SEA significantly enhanced the post‐ischaemic contractile recovery, associated with reductions in reperfusion‐induced Ca2+accumulation, damage to mitochondrial function, and decrease in myocardial high‐energy phosphates. Furthermore, Na+influx to mitochondriain vitrowas enhanced by increased concentrations of NaCl. KBR (10 μM) and 1 μM SEA partially decreased the Na+influx.

Conclusions and implications:

The NCX inhibitors exerted cardioprotective effects during relatively mild ischaemia. The mechanism may be attributable to prevention of mitochondrial damage, possibly mediated by attenuation of Na+overload in cardiac mitochondria during ischaemia and/or Ca2+overload via the reverse mode of NCX during reperfusion.

British Journal of Pharmacology(2007)151, 963–978; doi:10.1038/sj.bjp.0707321
Universal bounds on the attractor of the Navier-Stokes equation in the energy, enstrophy plane
Authors: Dascaliuc R. , Foias C. , Jolly M. S.
Published: June 2007

We continue our examination of the projection of the global attractor of the two-dimensional Navier-Stokes equations in a normalized, dimensionless energy, enstrophy plane. In this plane the attractor must lie above the line of slope 1 through the origin (an immediate consequence of the Poincaré inequality). We showed in Dascaliuc et al. [J. Dyn. Differ. Equ. 17, 629–649 (2005)] that the attractor must also lie below a parabola (the square root curve). Here we optimize this parabola to obtain a sharper bound. These bounds are universal; they are independent of viscosity, domain size, and strength of the force. The effectiveness of the bounds is demonstrated on Galerkin approximations of modest size (up to 1372 modes).
Constructal microchannel networks of rarefied gas with minimal flow resistance
Authors: Gosselin Louis , da Silva Alexandre K.
Published: June 2007

In this article, we answer the question of how to optimally design a rarefied gas distribution network from a source point to a given number of equidistant users such that the diameters of the pipes used to carry the fluid fall in the microscale. A slip boundary condition is used to take into account the effects introduced by the smallness of the pipes. By specifying the overall pressure drop across the network, we maximize the total mass flow rate through the dendritic structure under global volume constraint using an evolutionary algorithm. Four complexity levels are considered, nbif=0, 1, 2, and 3, where nbif is the number of levels of bifurcation present in the structure. The results show that the version of Murray’s law originally proposed in order to determine the optimal diameters of the pipes is not valid when rarefaction is present, since the power-law exponent varies significantly with the number of outlet users N. Additionally, the results show that the bifurcation angles decrease in the presence of rarefaction as N increases. The article ends by exploring the robustness of nonoptimized complex gas distribution networks.
Fracture, water dissociation, and proton conduction in SiO2 nanochains
Authors: Cao Chao , He Yao , Torras Juan , Deumens Erik , Trickey S. B. , Cheng Hai-Ping
Published: June 2007

A basic issue in nanoscale systems is whether large-scale behavior occurs or not. At and above the mesoscale, the water-silica interaction is known to have large effects, e.g., the geological importance of hydrolytic weakening. Here, we show that water not only substantially weakens a silica nanochain that has been the focus of much recent research but also leads to novel proton conduction. The SiO2 chain consists of a string of orthogonal (planes alternating vertically and horizontally) two-membered rings. We treat two cases of adjacent water to understand both local and collective motion in the system. The first is two water molecules, the second is a water monolayer film that coats the entire chain. Structure, charge separation, stress dependent bond breaking and formation, and proton conduction are discussed based on results obtained at the room temperature. The simulations have been performed using both first-principles molecular dynamics and a novel multiscale quantum-classical software system.
Coriolis coupling effects in the calculation of state-to-state integral and differential cross sections for the H+D2 reaction
Authors: Chu Tian-Shu , Han Ke-Li , Hankel Marlies , Balint-Kurti Gabriel G.
Published: June 2007

The quantum wavepacket parallel computational code DIFFREALWAVE is used to calculate state-to-state integral and differential cross sections for the title reaction on the BKMP2 surface in the total energy range of 0.4–1.2eV with D2 initially in its ground vibrational-rotational state. The role of Coriolis couplings in the state-to-state quantum calculations is examined in detail. Comparison of the results from calculations including the full Coriolis coupling and those using the centrifugal sudden approximation demonstrates that both the energy dependence and the angular dependence of the calculated cross sections are extremely sensitive to the Coriolis coupling, thus emphasizing the importance of including it correctly in an accurate state-to-state calculation.
Recombination dynamics in ultraviolet light-emitting diodes with Si-doped AlxGa1−xN∕AlyGa1−yN multiple quantum well active regions
Authors: Chen K. X. , Xi Y. A. , Mont F. W. , Kim J. K. , Schubert E. F. , Liu W. , Li X. , Smart J. A.
Published: June 2007

Ultraviolet (UV) light-emitting diodes with AlxGa1−xN∕AlyGa1−yN multiple quantum well active regions, doped in the barriers with different Si doping levels, show a sharp near-band edge emission line (UV luminescence). Some samples have a broad subband gap emission band centered at about 500 nm (green luminescence) in addition to the near-band edge emission. The electroluminescence intensities of the UV and green emission line are studied as a function of the injection current. For the sample grown on the AlN substrate under optimized growth conditions, the UV luminescence intensity increases linearly with the injection current, following a power law with an exponent of 1.0, while the green luminescence intensity increases sublinearly with the injection current. On the contrary, the samples grown on the sapphire substrate show a superlinear (to the power of 2.0) and linear (to the power of 1.0) dependence on the injection current for the UV and green luminescence, respectively. A theoretical model is proposed to explain the relationship between the luminescence intensities and the injection current. The results obtained from the model are in excellent agreement with the experimental results. The model provides a method to evaluate the dominant recombination process by measuring the exponent of the power-law dependence.
Compositional dependence of the elastic constants of dilute GaAs1−xNx alloys
Authors: Beaudry J.-N. , Shtinkov N. , Masut R. A. , Desjardins P. , Jiménez Riobóo R. J.
Published: June 2007

High-resolution Brillouin spectroscopy experiments were carried out to determine the velocity of surface acoustic waves (SAW) as a function of composition in GaAs1−xNx/GaAs(100) epilayers (0<x<0.037) grown by organometallic vapor phase epitaxy. Experimental data were analyzed using simulations of surface acoustic wave velocities. For all compositions investigated, SAW velocity measurements in both the [100] and [110] crystallographic directions are in close agreement with values predicted assuming linearly interpolated elastic constants between those of GaAs and GaN.
Approximative “one particle” bridge function B(1)(r) for the theory of simple fluids
Authors: Bomont Jean-Marc , Bretonnet Jean-Louis
Published: June 2007

New properties for the one particle bridge function B(1)(r), which are necessary to the calculation of the excess chemical potential βμex, are derived for the hard sphere fluid. The method, which only requires the knowledge of the bridge function B(2)(r), is based on an investigation of the correlation function dependence on the Kirkwood charging parameter. In this framework, the unavoidable question of topological homotopy is addressed. As far as B(2)(r) is considered as exact, this work provides useful information on B(1)(r) in the well identified dynamical regimes of the hard sphere fluid. Signatures of the transitions between these regimes are identified on the trends of B(1)(r). This approach provides self-consistent results for βμex that agree very well with simulation data.
Cathodoluminescence spectroscopy of epitaxial-lateral-overgrown nonpolar (11-20) and semipolar (11-22) GaN in relation to microstructural characterization
Authors: Gühne T. , Bougrioua Z. , Vennéguès P. , Leroux M. , Albrecht M.
Published: June 2007

Low temperature spatially resolved cathodoluminescence was carried out on GaN films grown by the epitaxial-lateral-overgrowth (ELO) technique with the nonpolar (11-20) and the semipolar (11-22) orientations on R- and M-sapphires, respectively. Defect related optical transitions were identified and their localization was correlated to different regions of ELO. The sample microstructure was further investigated by plan-view and cross-section transmission electron microscopies. It is shown that the defect related emissions are mainly localized in the seed of the samples, but different defects occur as well in the wings, especially in the case of nonpolar GaN. The structural defect densities are lowest in the overgrown wings of semipolar GaN. In particular, the [0001] wing region of semipolar ELO-GaN is almost defect-free with a cathodoluminescence spectrum dominated by the GaN band-edge emission at 3.476eV.
Dresselhaus spin-orbit coupling effect on the shot noise in resonant double-barrier structures
Authors: Zhu Rui , Guo Yong
Published: June 2007

The authors have investigated the zero-frequency shot noise of current through resonant double-barrier structures. Taking into account the spin-orbit coupling (SOC) effect, general expressions for the shot noise in fully phase-coherent mesoscopic conductors are derived based on the scattering approach. It is found that the Dresselhaus SOC can greatly affect the average current I, shot noise S, and Fano factor of resonant diode structures. A large shot noise suppression with the Fano factor below 0.5 observed experimentally can be illustrated by the influence of the Dresselhaus SOC effect.
Epitaxial relationship between wurtzite GaN and β-Ga2O3
Authors: Víllora Encarnación G. , Shimamura Kiyoshi , Kitamura Kenji , Aoki Kazuo , Ujiie Takekazu
Published: June 2007

The epitaxial relationship between wurtzite GaN and monoclinic β-Ga2O3 is studied by transmission electron microscopy. GaN is grown on β-Ga2O3 by molecular beam epitaxy without any low-temperature buffer layer, obtaining c plane GaN on a plane β-Ga2O3. The effect of the surface nitridation, which is necessary for the epitaxial growth, is analyzed at the atomic level. The lattice mismatch has a minimum of 2.6% for the in-plane epitaxial relationship ⟨011⟩Ga2O3‖⟨101¯0⟩GaN.
Structural and electrical characteristics of atomic layer deposited high κ HfO2 on GaN
Authors: Chang Y. C. , Chiu H. C. , Lee Y. J. , Huang M. L. , Lee K. Y. , Hong M. , Chiu Y. N. , Kwo J. , Wang Y. H.
Published: June 2007

High κ HfO2 was deposited on n-type GaN (0001) using atomic layer deposition with Hf(NCH3C2H5)4 and H2O as the precursors. Excellent electrical properties of TiN∕HfO2∕GaN metal-oxide-semiconductor diode with the oxide thickness of 8.8nm were obtained, in terms of low electrical leakage current density (∼10−6A∕cm2 at VFB+1V), well behaved capacitance-voltage (C-V) curves having a low interfacial density of states of 2×1011cm−2eV−1 at the midgap, and a high dielectric constant of 16.5. C-V curves with clear accumulation and depletion behaviors were shown, along with negligible frequency dispersion and hysteresis with sweeping biasing voltages. The structural properties studied by high-resolution transmission electron microscopy and x-ray reflectivity show an atomically smooth oxide/GaN interface, with an interfacial layer of GaON ∼1.8nm thick, as probed using x-ray photoelectron spectroscopy.
Correlation of spectral luminescence with threading dislocations in green-light-emitting InGaN quantum wells
Authors: Brooksby J. C. , Mei J. , Ponce F. A.
Published: June 2007

A direct correlation has been established between the spatial variation of spectral luminescence and the distribution of threading dislocations in a green-light-emitting InGaN quantum well structure grown on a sapphire substrate. Transmission electron microscopy and monochromatic cathodoluminescence images, taken from the same region, indicate that the nature of the quantum well emission is influenced by the microstructure of the underlying GaN. The microstructure is defined by threading dislocations that reflect a columnar structure with low-angle grain boundaries. A strong correlation is observed between this microstructure and the peak and low-energy portion of the quantum well luminescence, with threading dislocations as boundaries between bright and darker regions. The high-energy portion of the luminescence is localized and is generally complementary to the rest of the spectrum.
Self-phase modulation in photonic-crystal-slab line-defect waveguides
Authors: Oda Hisaya , Inoue Kuon , Tanaka Yu , Ikeda Naoki , Sugimoto Yoshimasa , Ishikawa Hiroshi , Asakawa Kiyoshi
Published: June 2007

The authors observed self-phase modulation in spectral domain at 1.50μm in AlxGa1−xAs-based photonic-crystal-slab line-defect waveguides. Adopting a sample with x=0.18 has enabled the authors to avoid two-photon absorption, causing undesirable free-carrier-induced refractive-index change. Variation of the observed spectrum with input pulse peak power is well reproduced by theoretical simulation. They find that a 1.6ps light pulse of 2.5pJ suffices for causing a phase shift of π in a 1mm long sample owing to tight light confinement and nonlinear refractive index n2 due to instantaneous optical Kerr effect is (3.8±1.2)×10−13cm2∕W. A possibility of developing ultrafast all-optical switch due to n2 is discussed
AlGaN based tunable hyperspectral detector
Authors: Tripathi N. , Grandusky J. R. , Jindal V. , Shahedipour-Sandvik F. , Bell L. D.
Published: June 2007

The application of III-nitrides to the development of a tunable hyperspectral detector is reported. The device consists of a triangular step barrier provided by a heterostructure of AlN∕AlxGa1−xN∕GaN. The structure is carefully designed to avoid relaxation of strained layers to prevent further introduction of defects and cracking due to the large tensile strain between different layers of the device. This structure is envisioned for tunable detection of ultraviolet through infrared wavelengths. The particular device structure reported here is expected to span detection energies from ∼1to2eV and from 3.4to5.4eV. The adjustable height of the triangular barrier with applied bias voltage provides tunability of the detected wavelength. The results from a first generation device are reported.
Study of the transport properties of annealed (Ga,Mn)As by x-ray absorption spectroscopy
Authors: Ji C. J. , Cao X. C. , Han Q. F. , Qiu K. , Zhong F. , Li X. H. , He H. T. , Wang J. N. , Wang Y. Q.
Published: June 2007

A systematic Mn L-edge x-ray absorption is carried out on carefully prepared Ga0.946Mn0.054As ferromagnetic semiconductors with varying As2∕Ga flux ratio. It is found that the L3 peak of the absorption spectroscopy is enhanced after low temperature (LT) annealing. Furthermore it is shown that a more localized electronic structure nearly like the d5 high-spin state is obtained. It can be attributed to breaking the MnS–MnI pairs during the annealing process. Furthermore the authors present a direct evidence for a slightly increase of the Mn substitutional concentration due to LT annealing.
Temperature dependent study of InAlAs–InP∕GaAsSb∕InP double heterojunction bipolar transistors
Authors: Wang Che-ming , Hsin Yue-Ming , Zhu Haijun , Kuo J. M. , Kao Y. C.
Published: June 2007

In Al As – In P ∕ Ga As Sb ∕ In P double heterojunction bipolar transistors (HBTs) with InAlAs–InP composite emitter have been grown, fabricated, and characterized at various temperatures from 77to400K. The InAlAs–InP composite emitter structure effectively reduces electron pileup in the InP∕GaAsSb base-emitter junction and hence increases current gain, especially in the low-base-current region. The turn-on voltage shows a slightly different temperature dependence (−1.66mV∕K) from conventional InGaAs based HBTs due to the composite emitter. The activation energy study for the base (0.74eV) and collector currents (0.98eV) indicates the high quality of the base layer and the effect of InAlAs–InP composite emitter.
Investigation of group delay, loss, and disorder in a photonic crystal waveguide by low-coherence reflectometry
Authors: Combrié Sylvain , Tran Nguyen-Vi-Quynh , Weidner Evelin , De Rossi Alfredo , Cassette Simone , Hamel Philippe , Jaouën Yves , Gabet Renaud , Talneau Anne
Published: June 2007

The authors propose highly resolved optical low-coherence reflectometry for investigating low-loss photonic crystal slab waveguides. This technique allows a fast, reliable, and straightforward measurement of the group delay and propagation losses for both TE and TM polarizations. The agreement with theory is very good. These measurements reveal effects related to structural disorder. The versatility and deep physical insight of this measurement technique will play a key role in the study of slow-light devices such as photonic crystal waveguides.
Transient property of optically pumped organic film of different fluorescence lifetimes
Authors: Fukuda Takeshi , Okada Tomoko , Wei Bin , Ichikawa Musubu , Taniguchi Yoshio
Published: June 2007

The authors have investigated the direct relationship between the fluorescence lifetime (FL) and the transient photoluminescence (PL) response of organic materials to examine the applicability of organic light-emitting diodes as light sources for optical communications. Transient PL responses of organic materials with different FLs were measured as a frequency dependence of PL intensity pumped by a modulated violet laser diode. The authors have revealed that the cutoff frequency of PL intensity is significantly related to FL of an organic film. The −3dB cutoff frequency of 1,4-bis[2-[4-[N,N-di(p-tolyl)amino]phenyl]vinyl]benzene (DSB) has reached about 160MHz, which is much higher than that of other organic materials. This is because the FL of DSB is shortest among all the organic materials used in this study.
Enhancement of ultraviolet lasing from Ag-coated highly disordered ZnO films by surface-plasmon resonance
Authors: Abiyasa A. P. , Yu S. F. , Lau S. P. , Leong Eunice S. P. , Yang H. Y.
Published: June 2007

Large improvement in random lasing action at ultraviolet wavelength has been achieved from highly disordered ZnO films with Ag coating. The lasing threshold can be reduced by two times and slope efficiency can be increased by 5.5 times. The improvement is due to the presence of Ag coating, which enhances the surface coupling of lasing emission from the ZnO films by surface-plasmon resonance and reduces the scattering loss experienced by the random cavity modes. Furthermore, the enhancement of lasing efficiency is dependent on the Ag coating’s surface roughness, which can be controlled through the surface morphology of ZnO films.
Contact-dependent inhibition of EGFR signaling by Nf2/Merlin
Authors: Curto Marcello , Cole Banumathi K. , Lallemand Dominique , Liu Ching-Hui , McClatchey Andrea I.
Published: June 2007

The neurofibromatosis type 2 (NF2) tumor suppressor, Merlin, is a membrane/cytoskeleton-associated protein that mediates contact-dependent inhibition of proliferation. Here we show that upon cell–cell contact Merlin coordinates the processes of adherens junction stabilization and negative regulation of epidermal growth factor receptor (EGFR) signaling by restraining the EGFR into a membrane compartment from which it can neither signal nor be internalized. In confluent Nf2−/− cells, EGFR activation persists, driving continued proliferation that is halted by specific EGFR inhibitors. These studies define a new mechanism of tumor suppression, provide mechanistic insight into the poorly understood phenomenon of contact-dependent inhibition of proliferation, and suggest a therapeutic strategy for NF2-mutant tumors.
Seasonal variation in serum concentrations of reproductive hormones and urinary excretion of 6‐sulfatoxymelatonin in men living north and south of the Arctic Circle: a longitudinal study
Authors: Ruhayel Yasir , Malm Gunilla , Haugen Trine B. , Henrichsen Trine , Bjørsvik Cathrine , Grotmol Tom , Sæther Thomas , Malm Johan , Figenschau Yngve , Rylander Lars , Levine Richard J. , Giwercman Aleksander
Published: June 2007

Objective  Seasonal variation in photoperiod or temperature may influence human reproductive biology. The present study evaluated whether seasonal changes occurred in the levels of reproductive hormones and the major melatonin metabolite, 6‐sulfatoxymelatonin (aMT6s), in populations exposed to extreme variation in photoperiod and temperature.

Design  Two separate cohorts of Norwegian men were recruited from the general population in either of two locations: Tromsø (69·5°N, n = 92) or Oslo (60°N, n = 112), located north and south of the Arctic Circle (66·5°N), respectively.

Measurements  Four blood and 12‐h overnight urine samples were obtained on separate occasions over a 12‐month period, including during the photoperiod maximum and minimum. Serum concentrations of FSH, LH, testosterone (T), oestradiol (E2), SHBG and the urinary excretion of aMT6s were assessed.

Results  Statistical analysis using generalized estimating equations indicated that LH levels were lowest during early winter in both locations (both P = 0·01). In Tromsø, free T and E2 concentrations peaked during early winter (P = 0·02 and 0·003, respectively). In Oslo, free T levels were lowest during early winter (P = 0·06) whereas E2 levels were lowest during late summer (P < 0·001). Urinary aMT6s concentrations were lowest during early summer in Tromsø and Oslo. Concentrations peaked during early winter in Tromsø (P < 0·001) and during late winter in Oslo (P < 0·001).

Conclusions  LH levels exhibited similar changes in both locations, whereas the patterns of changes of the sex steroid concentrations differed, possibly indicating different underlying mechanisms. Excretion of aMT6s was lowest during early summer in both locations, indicating that the long natural photoperiod was sufficient to cause suppression of melatonin secretion. Whether these changes have any biological significance remains uncertain.
Genetic polymorphism of CYP2D6 influences susceptibility to papillary thyroid cancer
Authors: Lemos Manuel C. , Carrilho Francisco , Rodrigues Fernando , Coutinho Eduarda , Gomes Leonor , Carvalheiro Manuela , Regateiro Fernando J.
Published: June 2007

Objective  Xenobiotic‐metabolizing enzymes are widely polymorphic and confer interindividual variation in the ability to detoxify carcinogens or to activate pro‐carcinogens. A common polymorphism of cytochrome P450 2D6 (CYP2D6) results in lack of enzyme activity and has been associated with an altered susceptibility to several cancers. The aim of this study was to investigate the association between the CYP2D6 poor metaboliser genotype and the risk of papillary thyroid cancer (PTC).

Design  Retrospective case‐control study.

Patients  One hundred and eighty‐seven patients with PTC and 256 controls.

Measurements  Genotyping was performed by PCR and restriction enzyme analysis to detect the presence of the common CYP2D6*4 poor metaboliser allele.

Results  The frequency of individuals with the homozygous poor metaboliser genotype was lower in the patient group [1·6 vs. 5·5%, P = 0·037, OR = 0·28 (95% CI 0·09–0·93)]. The CYP2D6*4 allele frequency was also lower in the patient group [13·4 vs. 21·7%, P = 0·002, OR = 0·56 (95% CI 0·39–0·80)].

Conclusions  The results suggest that the poor metaboliser genotype is associated with a protective effect against PTC. This could be explained by a possible role of CYP2D6 on the metabolic activation of putative environmental chemical thyroid carcinogens or by linkage to another cancer‐causing gene. Further research may allow the identification of metabolic risk factors and contribute towards understanding the molecular mechanisms involved in thyroid carcinogenesis.
A novel compound heterozygous mutation of the aromatase gene in an adult man: reinforced evidence on the relationship between congenital oestrogen deficiency, adiposity and the metabolic syndrome
Authors: Maffei Laura , Rochira Vincenzo , Zirilli Lucia , Antunez Paula , Aranda Claudio , Fabre Bibiana , Simone Maria L. , Pignatti Elisa , Simpson Evan R. , Houssami Souheir , Clyne Colin D. , Carani Cesare
Published: June 2007

Background  Descriptions of new cases of human aromatase deficiency are useful for a better understanding of male oestrogen pathophysiology, as some aspects remain controversial.

Objective  To present a new case of an adult man affected by aromatase deficiency, along with a description of clinical phenotype, and hormonal and genetic analysis.

Design  Case report study.

Patient  A 25‐year‐old man with continuing linear growth, eunuchoid body habitus and diffuse bone pain.

Measurements  Amplification and sequencing of all coding exons with their flanking intronic sequences of the CYP19A1 gene. Aromatase expression of the mutant human cDNAs was compared with wild type. Serum LH, FSH, testosterone, oestradiol, insulin, glucose, glycosylated haemoglobin (HbA1c), serum lipids and liver enzymes were measured. Histological analysis of liver and testis biopsies was performed.

Results  Two novel heterozygous compound inactivating mutations of the CYP19A1 gene were disclosed. The first mutation is at bp380 (T→G) in exon IV and the second one at bp 1124 (G→A) in exon IX. LH and testosterone were normal, FSH was slightly elevated, and serum oestradiol undetectable. The subject showed a metabolic syndrome characterized by abdominal obesity, hyperinsulinaemia, acanthosis nigricans and nonalcoholic fatty liver disease.

Conclusions  These novel mutations improve our knowledge on genetics of the CYP19A1 gene. This new case of aromatase deficiency sheds new light on the heterogeneity of mutations in the CYP19A1 gene causing loss of function of the aromatase enzyme. The evidence of metabolic syndrome and of obesity associated with congenital oestrogen deprivation emphasizes the role of oestrogens in fat accumulation and distribution in men, a role that has long been partially overlooked in these patients.
Role of the innate immune system in host defence against bacterial infections: focus on the Toll‐like receptors
Authors: Albiger B. , Dahlberg S. , Henriques‐Normark B. , Normark S.
Published: June 2007

The innate immunity plays a critical role in host protection against pathogens and it relies amongst others on pattern recognition receptors such as the Toll‐like receptors (TLRs) and the nucleotide‐binding oligomerization domains proteins (NOD‐like receptors, NLRs) to alert the immune system of the presence of invading bacteria. Since their recent discovery less than a decade ago, both TLRs and NLRs have been shown to be crucial in host protection against microbial infections but also in homeostasis of the colonizing microflora. They recognize specific microbial ligands and with the use of distinct adaptor molecules, they activate different signalling pathways that in turns trigger subsequent inflammatory and immune responses that allows a immediate response towards bacterial infections and the initiation of the long‐lasting adaptive immunity. In this review, we will focus on the role of the TLRs against bacterial infections in humans in contrast to mice that have been used extensively in experimental models of infections and discuss their role in controlling normal flora or nonpathogenic bacteria. We also highlight how bacteria can evade recognition by TLRs.