bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison between Dc′‐values obtained from a dynamic rupture model and waveform inversion
Authors: Yasuda Takumi , Yagi Yuji , Mikumo Takeshi , Miyatake Takashi
Published: July 2005

We investigate the validity of a method for estimating the critical slip‐weakening distance (Dc), which was proposed by Mikumo and Yagi [2003], for a dynamic rupture model of a recent earthquake. Assuming a uniform distribution of Dc on the fault, we simulated spontaneous dynamic rupture process and generated the synthetic waveforms that would be observed at actual recording stations. Then, we carried out kinematic inversion of the synthetic waveforms and obtained the slip‐rate time functions on each subfault. We estimate Dc from these functions and discuss whether the assumed Dc could be recovered correctly. We also investigated the rupture propagation effect over each subfault with a finite dimension and the effects from the waveform inversion and band‐pass filtering processes on the estimate of Dc. We found that the propagation effect could cause an apparent correlation between the recovered Dc′‐values and the final slip.
Measurement of phase fluctuations for transmitted waves in random media
Authors: Zheng Yingcai , Wu Ru‐Shan
Published: July 2005

Transmission fluctuations of log‐amplitude and phase can be used to construct coherence functions to infer the statistical characteristics of crustal and mantle small‐scale heterogeneities. Recent numerical simulations of wave propagation in random media have revealed an apparent discrepancy between simulations and theory for phase coherence functions. In this paper, we show that the reported discrepancy is a result of the inappropriate phase estimates adopted in some literature. Using unwrapped phase fluctuations, instead of estimates of the fluctuations obtained by picking first arrivals by the threshold method, we find that the theory and the results derived from finite difference simulations are consistent. The method of first arrival picking does not yield adequate estimates of phase fluctuation due to the scattering dispersion of waves in the random medium. Phase unwrapping is viable and allows correct inference of medium properties.
Multidimensional quasi‐linear diffusion of radiation belt electrons
Authors: Albert J. M. , Young S. L.
Published: July 2005

We consider diffusion of outer zone radiation belt electrons by chorus waves. Quasi‐linear diffusion coefficients valid outside the plasmasphere have only been calculated recently, and indicate that the energy and cross diffusion rates can be comparable to that for pitch angle diffusion. Proper solution of the diffusion equation for phase space density must therefore be based on the full diffusion tensor, but this has been plagued by numerical problems associated with the large and rapidly varying cross terms. To circumvent this, techniques are developed for transforming to variables in which the cross diffusion term vanishes. A model calculation shows significant diffusion of phase space density at L = 4.5 from 0.2 MeV up to a few MeV in less than a day.
A systematic study of effects of solar wind density on auroral electrojets
Authors: Shue J.‐H. , Kamide Y. , Newell P. T.
Published: July 2005

The subject of effects of solar wind density (Np) on auroral electrojets has recently received increasing attention. For “unbiased” events in which only Np varied significantly but other solar wind parameters were relatively constant, we calculated rates of change of the auroral electrojets per unit change of Np (dAU/dNp and dAL/dNp). Here we report that the distribution of dAU/dNp and dAL/dNp binned by the Z component of interplanetary magnetic field (IMF) shows a butterfly pattern. The rates are found to be small for northward IMF. As the southward IMF becomes larger, the distribution bifurcates–one branch extending to positive rates and the other to negative rates. Although it has been commonly believed that the enhanced Np increases the auroral electrojets, the enhanced Np can also decrease the auroral electrojets with a 49% probability.
Tides on the Ross Ice Shelf observed with ICESat
Authors: Padman Laurie , Fricker Helen Amanda
Published: July 2005

The Ice, Cloud and land Elevation Satellite (ICESat) provides the first opportunity for measurement of surface elevation hi over the portions of the Antarctic ice shelves that are south of the European Remote Sensing (ERS) satellite maximum latitude (81.5°S). The dominant source of short‐period variability in hi is ocean tides. We use crossover elevation difference (Δhi) data from the Ross Ice Shelf (RIS) to demonstrate ICESat's ability to detect the tidal signal, and to compare the accuracy of several tide models. The root‐mean‐square (rms) value of all RIS measurements of Δhi is ≈0.74 m; after removing the tide using the most accurate model, the rms of the residual signal in regions of optimal model performance is ≈0.16 ± 0.03 m. This value corresponds to an uncertainty in hi of 0.11 ± 0.02 m. We postulate that the primary sources of the residual signal are tide model errors and the inverse barometer effect.
Variations of the mean winds and diurnal tides in the mesosphere and lower thermosphere observed by WINDII from 1992 to 1996
Authors: Zhang Shengpan P. , Shepherd G. G.
Published: July 2005

Wind measurements of the satellite‐based Wind Imaging Interferometer (WINDII) for Februaries of 1992–1996 are used to investigate the variations of the dynamics in the mesosphere and lower thermosphere (90–120 km) between 40°S and 40°N and any possible connection with the solar cycle. The period of 1992–1996 is in the descending phase of solar cycle 22, in that the solar F10.7 flux (2800 MHz) decreases from about 300 to 70 in units of 10−22 Wm−2 Hz−1. The salient features are as follows. (1) Mean zonal winds in the tropical region and upward propagating diurnal tides in the subtropical regions are stronger in 1992, 1993 and 1995 than in 1994 and 1996. (2) The mean eastward winds below 100 km at mid‐latitudes in February 1992 are larger in the winter hemisphere and smaller in the summer hemisphere compared to those in the other four years. (3) There is significant enhancement of the upward propagating diurnal tide above 100 km in February 1992, particularly in the winter hemisphere; and the diurnal amplitude in 1996 is the smallest among the five Februaries. (4) The upward propagating diurnal tide has a higher altitude range in 1992 than in 1996 by 2–4 km. (5) The in situ thermospheric diurnal tide at mid‐latitudes above 100 km in the summer hemisphere has amplitudes at 50 ms−1 in February 1992 compared to that in February 1996 at 8 ms−1.
Disappearance of Pacific Water in the northwestern Fram Strait
Authors: Falck Eva , Kattner Gerhard , Budéus Gereon
Published: July 2005

Water of Pacific origin, entering the Arctic Ocean through the Bering Strait, exits the Arctic Ocean through the Canadian Archipelago and the Fram Strait. The amount and timing of Pacific Water export through these gates depend on the upper circulation of the Arctic Ocean and react accordingly on changes. Nutrient and hydrographic data from four cruises to the area north of the Fram Strait in 1984, 1990, 1997, and 2004 show that substantial changes have occurred lately in the amount of Pacific Waters delivered to the Fram Strait and hence further to the Atlantic Ocean. While the data from 1984, 1990, and 1997 all showed considerable amounts of Pacific Water above the shelf and slope northeast of Greenland, this strong signal had completely vanished in 2004. The arrival of a previously not observed cold halocline layer at the area can be recognized in 1997.
Modulation of station rainfall over the western Pacific by the Madden‐Julian oscillation
Authors: Matthews Adrian J. , Li Hoi Yee Yvonne
Published: July 2005

Rainfall data from 140 stations in the PACRAIN network in the tropical western Pacific are analysed to assess the signal due to the Madden‐Julian oscillation (MJO). During northern winter, the station rainfall difference between the wet and dry phases of the MJO is up to 6 mm day−1, compared to the climatological mean value of 12 mm day−1. The anomalies have a strong spatial coherence, with over 80% of the individual point station anomalies having the same sign as the large‐scale rainfall anomaly, as determined by the mainly satellite‐derived CMAP rainfall product.
Relationship between frontal dust storms and transient eddy activity in the northern hemisphere of Mars as observed by Mars Global Surveyor
Authors: Wang Huiqun , Zurek Richard W. , Richardson Mark I.
Published: July 2005

We have compiled a catalog of frontal dust storms in the northern hemisphere using Mars Orbiter Camera daily global maps spanning ∼2.3 Martian years of Mars Global Surveyor (MGS) observations (from 1999 to 2003). The most vigorous frontal storms that flush dust to the low latitudes occur in early‐mid fall and mid‐late winter, away from the northern winter solstice. While many streaks are observed in the polar hood during the winter solstice period, no frontal dust storms are observed in the vicinity of the north polar region. We have also analyzed simultaneous MGS Thermal Emission Spectrometer (TES) temperature data and found statistically significant negative temperature anomalies associated with frontal storms. In the lowest scale height of the atmosphere, the geographical and seasonal distributions of temperature standard deviations associated with transient variations agree well with the distributions of frontal storms. The correlation deteriorates with increasing altitude, suggesting that lower‐level temperature waves are associated with the frontal dust storms. Specifically, eastward traveling m = 3 waves with periods of 2–3 sols appear to be closely related to the development of flushing frontal storms.
Genetic and pharmacological inactivation of the adenosine A2A receptor attenuates 3‐nitropropionic acid‐induced striatal damage
Authors: Fink J. Stephen , Kalda Anti , Ryu Hoon , Stack Edward C. , Schwarzschild Michael A. , Chen Jiang‐Fan , Ferrante Robert J.
Published: July 2005

Adenosine A2A receptor (A2AR) antagonism attenuates 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐induced dopaminergic neurodegeneration and quinolinic acid‐induced excitotoxicity in the neostriatum. As A2ARs are enriched in striatum, we investigated the effect of genetic and pharmacological A2A inactivation on striatal damage produced by the mitochondrial complex II inhibitor 3‐nitropriopionic acid (3‐NP). 3‐NP was administered to A2AR knockout (KO) and wild‐type (WT) littermate mice over 5 days. Bilateral striatal lesions were analyzed from serial brain tissue sections. Whereas all of the 3‐NP‐treated WT mice (C57BL/6 genetic background) had bilateral striatal lesions, only one of eight of the 3‐NP‐treated A2AR KO mice had detectable striatal lesions. Similar attenuation of 3‐NP‐induced striatal damage was observed in A2AR KO mice in a 129‐Steel background. In addition, the effect of pharmacological antagonism on 3‐NP‐induced striatal neurotoxicity was tested by pre‐treatment of C57Bl/6 mice with the A2AR antagonist 8‐(3‐chlorostyryl) caffeine (CSC). Although bilateral striatal lesions were observed in all mice treated either with 3‐NP alone or 3‐NP plus vehicle, there were no demonstrable striatal lesions in mice treated with CSC (5 mg/kg) plus 3‐NP and in five of six mice treated with CSC (20 mg/kg) plus 3‐NP. We conclude that both genetic and pharmacological inactivation of the A2AR attenuates striatal neurotoxicity produced by 3‐NP. Since the clinical and neuropathological features of 3‐NP‐induced striatal damage resemble those observed in Huntington's disease, the results suggest that A2AR antagonism may be a potential therapeutic strategy in Huntington's disease patients.
Lipopolysaccharide‐induced increase in signalling in hippocampus is abrogated by IL‐10 – a role for IL‐1β?
Authors: Lynch Aileen M. , Walsh Christine , Delaney Ada , Nolan Yvonne , Campbell Veronica A. , Lynch Marina A.
Published: July 2005

Parenterally administered lipopolysaccharide (LPS) increases the concentration of the pro‐inflammatory cytokine interleukin‐1β (IL‐1β) in the rat hippocampus and evidence suggests that this effect plays a significant role in inhibiting long‐term potentiation (LTP). The anti‐inflammatory cytokine IL‐10, antagonizes certain effects of IL‐1β, so if the effects of LPS are mediated through an increase in IL‐1β, it might be predicted that IL‐10 would also abrogate the effect of LPS. Here, we report that IL‐10 reversed the inhibitory effect of LPS on LTP and the data couple this with an inhibitory effect on the LPS‐induced increase in IL‐1β. LPS treatment increased hippocampal expression of IL‐1 receptor Type I protein. Consistent with the LPS‐induced increases in IL‐1β concentration and receptor expression, were downstream changes which included enhanced phosphorylation of IRAK and the stress‐activated kinases, JNK and p38; these LPS‐induced changes were reversed by IL‐10, which concurs with the idea that these events are triggered by increased activation of IL‐1RI by IL‐1β. We provide evidence which indicates that LPS treatment leads to evidence of cell death and this was reversed in hippocampus prepared from LPS‐treated rats which received IL‐10. The evidence is therefore consistent with the idea that IL‐10 acts to protect neuronal tissue from the detrimental effects induced by LPS.
The role of neutral sphingomyelinase produced ceramide in lipopolysaccharide‐mediated expression of inducible nitric oxide synthase
Authors: Won Je‐Seong , Im Yeong‐Bin , Khan Mushfiquddin , Singh Avtar K. , Singh Inderjit
Published: July 2005

Lipopolysaccharide (LPS) and interferon‐γ (IFN) treatment of C6 rat glioma cells increased the intracellular ceramide level and the expression of the inducible nitric oxide synthase (iNOS) gene. To delineate the possible role of ceramide in the induction of iNOS, we examined the source of intracellular ceramide and associated signal transduction pathway(s) with the use of inhibitors of intracellular ceramide generation. The inhibitor of neutral sphingomyelinase (3‐O‐methylsphingomyelin, MSM) inhibited the induction of iNOS, whereas inhibitor of acidic sphingomyelinase (SR33557) or that of ceramide de novo synthesis (fumonisin B1) had no effect on the induction of iNOS. MSM‐mediated inhibition of iNOS induction was reversed by the supplementation of exogenous C8‐ceramide, suggesting that ceramide production by neutral sphingomyelinase (nSMase) is a key mediator in the induction of iNOS. The MSM‐mediated inhibition of iNOS gene expression correlated with the decrease in the activity of ras. Inhibition of co‐transfected iNOS promoter activity by dominant negative ras supported the role of ras in the nSMase‐dependent regulation of iNOS gene. NF‐κB DNA binding activity and its transactivity were also reduced by MSM pretreatment, and were completely reversed by the supplementation of C8‐ceramide. As the dominant negative ras also reduced NF‐κB transactivity, NF‐κB activation may be downstream of ras. Our results suggest that ceramide generated by nSMase may be a critical mediator in the regulation of iNOS gene expression via ras‐mediated NF‐κB activation under inflammatory conditions.
Phospholipase D2 modulates agonist‐induced µ‐opioid receptor desensitization and resensitization
Authors: Koch Thomas , Brandenburg Lars‐Ove , Liang Yingjian , Schulz Stefan , Beyer Andrea , Schröder Helmut , Höllt Volker
Published: July 2005

Receptor phosphorylation, arrestin binding, uncoupling from G protein and subsequent endocytosis have been implicated in G protein‐coupled receptor desensitization after chronic agonist exposure. In search of proteins regulating the µ‐opioid receptor endocytosis, we have recently established that activation of phospholipase D (PLD)2 is required for agonist‐induced µ‐opioid receptor endocytosis. In this study, we determined the effect of PLD2 activity on the desensitization and resensitization rate of the µ‐opioid receptor. We clearly demonstrated that inhibition of PLD2‐mediated phosphatidic acid formation by alcohol (1‐butanol or ethanol) or overexpression of a dominant negative mutant of PLD2 prevented agonist‐mediated endocytosis and resulted in a faster desensitization rate of the µ‐opioid receptor after chronic (d‐Ala2, Me Phe4, Glyol5)enkephalin treatment in human embryonic kidney 293 cells. Moreover, inhibition of PLD2 activity led to an impairment of the resensitization rate of the µ‐opioid receptor. In summary, our data strongly suggest that PLD2 is a modulator of agonist‐induced endocytosis, desensitization and resensitization of the µ‐opioid receptor.
Amyloid‐β‐induced toxicity of primary neurons is dependent upon differentiation‐associated increases in tau and cyclin‐dependent kinase 5 expression
Authors: Liu Tianbing , Perry George , Chan Hsien W. , Verdile Giuseppe , Martins Ralph N. , Smith Mark A. , Atwood Craig S.
Published: July 2005

It has previously been reported that amyloid‐β (Aβ) peptide is neurotrophic to undifferentiated but neurotoxic to differentiated primary neurons. The underlying reasons for this differential effect is not understood. Recently, the toxicity of Aβ to neurons was shown to be dependent upon the activation of cyclin‐dependent kinase 5 (Cdk5), thought to promote tau phosphorylation that leads to cytoskeletal disruption, morphological degeneration and apoptosis. Here we report that Cdk5, tau, and phosphorylated‐tau (P‐tau) are expressed at very low levels in undifferentiated primary neurons, but that the expression of Cdk5 and tau and the phosphorylation of tau increase markedly between 4 and 8 days of differentiation in vitro. Tau expression decreased after this time, as did the level of P‐tau, to low levels by 17 days. Aβ induced tau phosphorylation of neurons only after ≥ 4 days of differentiation, a time that coincides with the onset of Aβ toxicity. Blocking tau expression (and therefore tau phosphorylation) with an antisense oligonucleotide completely blocked Aβ toxicity of differentiated primary neurons, thereby confirming that tau was essential for mediating Aβ toxicity. Our results demonstrate that differentiation‐associated changes in tau and Cdk‐5 modulate the toxicity of Aβ and explain the opposite responses of differentiated and undifferentiated neurons to Aβ. Our results predict that only cells containing appreciable levels of tau are susceptible to Aβ‐induced toxicity and may explain why Aβ is more toxic to neurons compared with other cell types.
Homodimerization of adenosine A2A receptors: qualitative and quantitative assessment by fluorescence and bioluminescence energy transfer
Authors: Canals Meritxell , Burgueño Javier , Marcellino Daniel , Cabello Núria , Canela Enric I. , Mallol Josefa , Agnati Luigi , Ferré Sergi , Bouvier Michel , Fuxe Kjell , Ciruela Francisco , Lluis Carmen , Franco Rafael
Published: July 2005

The results presented in this paper show that adenosine A2A receptor (A2AR) form homodimers and that homodimers but not monomers are the functional species at the cell surface. Fluorescence resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET) techniques have been used to demonstrate in transfected HEK293 cells homodimerization of A2AR, which are heptaspanning membrane receptors with enriched expression in striatum. The existence of homodimers at the cell surface was demonstrated by time‐resolved FRET. Although agonist activation of the receptor leads to the formation of receptor clusters, it did not affect the degree of A2AR–A2AR dimerization. Both monomers and dimers were detected by immunoblotting in cell extracts. However, cell surface biotinylation of proteins has made evident that more than 90% of the cell surface receptor is in its dimeric form. Thus, it seems that homodimers are the functional form of the receptor present on the plasma membrane. A deletion mutant version of the A2A receptor, lacking its C‐terminal domain, was also able to form both monomeric and dimeric species when cell extracts from transfected cells were analyzed by immunoblotting. This suggests that the C‐terminal tail does not participate in the dimerization. This is relevant as the C‐terminal tail of A2AR is involved in heteromers formed by A2AR and dopamine D2 receptors. BRET ratios corresponding to A2AR–A2AR homodimers were higher than those encountered for heterodimers formed by A2AR and dopamine D2 receptors. As A2AR and dopamine D2 receptors do indeed interact, these results indicate that A2AR homodimers are the functional species at the cell surface and that they coexist with A2AR/D2 receptor heterodimers.
Toll‐like receptor 2 (TLR2) mediates astrocyte activation in response to the Gram‐positive bacterium Staphylococcus aureus
Authors: Esen Nilufer , Tanga Flobert Y. , DeLeo Joyce A. , Kielian Tammy
Published: July 2005

Astrocytes play an important role in initiating and regulating CNS immune responses through the release of proinflammatory cytokines and chemokines. Here we demonstrate that primary astrocytes are capable of recognizing the Gram‐positive bacterium Staphylococcus aureus and its cell wall product peptidoglycan (PGN) and respond by producing numerous proinflammatory mediators including interleukin‐1β (IL‐1β), tumor necrosis factor‐α (TNF‐α), macrophage inflammatory protein‐1β (MIP‐1β), MIP‐2, and monocyte chemoattractant protein (MCP‐1). Astrocytes have recently been shown to express Toll‐like receptor 2 (TLR2), a pattern recognition receptor important for recognizing structural components of various Gram‐positive bacteria, fungi, and protozoa. However, the functional significance of TLR2 in mediating astrocyte activation remains unknown. Primary astrocytes from TLR2 knockout mice were used to evaluate the role of TLR2 in astrocyte responses to S. aureus and PGN. The results demonstrate that TLR2 is essential for maximal proinflammatory cytokine and chemokine production, but not phagocytosis, in primary astrocytes following S. aureus and PGN exposure. In addition, both stimuli led to a significant increase in TLR2 mRNA expression in wild‐type astrocytes as assessed by real‐time quantitative RT–PCR. These findings suggest that astrocytes may play a key role in the initial antibacterial immune response in the CNS through engagement of TLR2.
Photochemical abiotic synthesis of amino-acid precursors from simulated planetary atmospheres by vacuum ultraviolet light
Authors: Takahashi Jun-ichi , Masuda Hitomi , Kaneko Takeo , Kobayashi Kensei , Saito Takeshi , Hosokawa Teruo
Published: July 2005

For the purpose of investigating the photon energy dependence of the photoinduced abiotic synthesis of organic molecules, gas mixtures that simulate typical planetary atmospheres, including a carbon source (CO or CH4), a nitrogen source (N2 or NH3), and H2O, were irradiated with synchrotron radiation through a vacuum-ultraviolet transmitting window. Three kinds of window material, fused silica, synthetic quartz, and MgF2, were used as a high-energy-cutting filter, whose absorption-edge energies are 6.4, 8.1, and 10.5eV, respectively. Three types of gas mixture, Titan-type (CH4–N2–H2O), comet-type (CO–NH3–H2O), and primitive-Earth-type (CO–N2–H2O), were irradiated with vacuum-ultraviolet photons in the three energy ranges. After the irradiation, amino-acid formation yields in the acid-hydrolyzed solution of the product were measured with a high-performance liquid chromatograph method. From the Titan- and comet-type mixtures, amino acids were detected by irradiation with photons lower than 8.1eV. For both mixtures, the averaged quantum yields of glycine generation in the photon energy region of 7–10.5eV were of the order of 10−5, which was larger by about one order than that in the region 5–8eV. On the other hand, from the primitive-Earth-type mixture, amino-acid formation was difficult to detect even with irradiation as high as 10.5eV, even though amino acids were generated in comparable yields from the Titan- and comet-type mixtures by irradiation with soft x rays or proton beam, whose energies are much higher. These results suggest that the vacuum ultraviolet light is a more effective energy source for the generation of the precursors of bioorganic compounds in extraterrestrial environments than in primitive-Earth atmosphere.
Fabrication of strained silicon on insulator by strain transfer process
Authors: Jin Bo , Wang Xi , Chen Jing , Cheng Xinli , Chen Zhijun
Published: July 2005

The fabrication of ultrathin strained silicon layer directly on insulator is demonstrated. 50nm strained silicon on insulator layers were fabricated by a method which includes four steps: Epitaxial growth of strained SiGe on ultrathin silicon on insulator (SOI) substrates, ion implantation, postannealing process, and etch-back process. Strain of the layer was observed by Raman spectroscopy. 0.72% tensile strain was maintained in the strained silicon layer even after removing the SiGe film. The strained layer was the result of strain equalization and transfer process between the SiGe film and top silicon layer.
Nonlinear effects and Joule heating in I-V curves in manganites
Authors: Mercone Silvana , Frésard Raymond , Caignaert Vincent , Martin Christine , Saurel Damien , Simon Charles , André Gilles , Monod Philippe , Fauth François
Published: July 2005

We study the influence of the Joule effect on the nonlinear behavior of the transport I-V curves in polycrystalline samples of the manganite Pr0.8Ca0.2MnO3 by using the crystalline unit-cell parameters as an internal thermometer in x-ray and neutron diffractions. We develop a simple analytical model to estimate the temperature profile in the samples. Under the actual experimental conditions we show that the internal temperature gradient or the difference between the temperature of the sample and that of the thermal bath is at the origin of the nonlinearity observed in the I-V curves. Consequences on other compounds with colossal magnetoresistance are also discussed.
Interaction of two unequal corotating vortices
Authors: Trieling R. R. , Fuentes O. U. Velasco , van Heijst G. J. F.
Published: July 2005

Previous high-resolution contour dynamics calculations [Dritschel and Waugh, Phys. Fluids A 4, 1737 (1992)] have shown that in two-dimensional inviscid flow the interaction of two unequal corotating vortices with uniform vorticity is not always associated with vortex growth and may lead to vortices smaller than the original vortices. In the present study, we investigate whether these results also hold for two-dimensional vortices with continuous vorticity distributions. Similar flow regimes are found as for uniform vorticity patches, but the variation of the flow regimes with the initial vortex radii and peak vorticities is more complicated and strongly dependent on the initial shape of the vorticity profile. It is found that the “halo” of low-value vorticity, which surrounds the cores of continuous vortices, significantly increases the critical distance at which the weaker vortex is destroyed. The halo also promotes the vortex cores to merge more efficiently, since it accounts for a substantial part of the loss of circulation into filaments. Simple transformation rules and merger criteria are derived for the inviscid interaction between two Gaussian vortices. The strong dependence of the flow regimes on the initial vorticity distribution partly explains why previous laboratory experiments in an electron plasma [Mitchell and Driscoll, Phys. Fluids 8, 1828 (1996)] show complete merger of two unequal vortices in a range of parameter space where contour dynamics simulations with uniform vorticity patches predict partial merger or partial straining-out of the smaller vortex. It is shown that the measured times for complete merger are in reasonable agreement with inviscid dynamics when the vortices are very similar. For more distinct vortices the weaker vortex is often observed to be destroyed on a time scale much smaller than expected from inviscid numerical simulations. An explanation for this discrepancy is given by the combined effects of vortex stripping and viscous diffusion, which leads to an enhanced erosion of the weaker vortex. These results are verified by laboratory experiments in a conventional (rotating) fluid.
Electron-hole asymmetry and two-state lasing in quantum dot lasers
Authors: Viktorov E. A. , Mandel Paul , Tanguy Yann , Houlihan John , Huyet Guillaume
Published: July 2005

We study the decrease of the ground-state output with increasing current in two-state quantum dot lasing. We show that the asymmetry in the thermal population redistribution breaks the symmetric dynamical evolution of the electron-hole pairs. This fully explains the transition from two-state to single-state lasing observed experimentally. The model also reproduces the temperature dependence of the two-state lasing.
Description of surfaces associated with Grassmannian sigma models on Minkowski space
Authors: Grundland A. M. , Šnobl L.
Published: July 2005

We construct and investigate smooth orientable surfaces in su(N) algebras. The structural equations of surfaces associated with Grassmannian sigma models on Minkowski space are studied using moving frames adapted to the surfaces. The first and second fundamental forms of these surfaces as well as the relations between them as expressed in the Gauss–Weingarten and Gauss–Codazzi–Ricci equations are found. The scalar curvature and the mean curvature vector expressed in terms of a solution of Grassmanian sigma model are obtained.
Observation of two-photon-induced photoluminescence in ZnO microtubes
Authors: Zhang C. F. , Dong Z. W. , You G. J. , Qian S. X. , Deng H. , Gao H. , Yang L. P. , Li Y.
Published: July 2005

The micrometer-sized ZnO tubes were fabricated by a hydrothermal method and characterized by scanning electron microscopy, high resolution transmission microscopy and micro-Raman spectroscopy. Photoluminescence (PL) emission from ZnO microtubes excited by light in the ultraviolet range from xenon lamp was measured. By using nanosecond laser beam at 527nm to excite ZnO microtube, we observed two-photon induced PL emission with an intense peak at 3.15eV and a weak peak at 2.65eV, which was confirmed by the quadratic dependence of the emission intensity on the excitation power.
A model for the formation of “optimal” vortex rings taking into account viscosity
Authors: Kaplanski F. B. , Rudi Y. A.
Published: July 2005

The evolution of a viscous vortex ring from thin to thick-cored form is considered using an improved asymptotic solution, which is obtained after impressing a spatially uniform drift on the first-order solution of the Navier–Stokes equations. The obtained class of rings can be considered as the viscous analog solution to the Norbury vortices and classified in terms of the ratio of their initial outer radius to the core radius. The model agrees with the reported theoretical and experimental results referring to the post-formation and the formation stages. By using the matching procedure suggested earlier and the obtained properties of the viscous vortex ring, it is found that when the length-to-diameter aspect ratio L∕D reaches the limiting value 4.0 (“formation number”), the appropriate values of the normalized energy and circulation become around 0.3 and 2.0, respectively. An approach that enables to predict the “formation number” is proposed.
Incipient breaking of unsteady waves on sheared currents
Authors: Yao Aifeng , Wu Chin H.
Published: July 2005

Incipient breaking of unsteady waves on sheared currents is experimentally investigated. A new wave-generation technique, based on the iterative frequency-focusing concept with the consideration of effects of Doppler shift and current shear, is developed. The surface displacement, the wavelength, and the phase speed of waves at the breaking onset on shear currents are measured. It is found that the steepness of unsteady, incipient breaking waves is altered by the sign and magnitude of current shear (or vorticity). A current with a positive shear, as would be the case in a wind-driven current, reduces the steepness of an unsteady incipient breaking wave. A negatively sheared current, such as the jet-like ebb current at a tide inlet, leads to steeper incipient breaking waves. The magnitude of reduction/increase in wave steepness is proportional to the strength of a current shear. In particular, a negative shear can alter the wave steepness more significantly in comparison to a positive shear of the same magnitude. Interestingly, the trend of crest-trough asymmetry with respect to the change of a current shear is in contrast to the limiting wave steepness. A positively sheared current can dramatically increase crest-trough asymmetry for unsteady waves. Dimensionless amplitudes of unsteady waves at incipient breaking are well correlated with surface current drifts. Positive/negative surface drifts lead to the reduced/increased dimensionless wave amplitudes. However, the change in dimensionless wave amplitude of unsteady waves is much smaller than that of steady waves.
Ge diffusion in Ge metal oxide semiconductor with chemical vapor deposition HfO2 dielectric
Authors: Lu N. , Bai W. , Ramirez A. , Mouli C. , Ritenour A. , Lee M. L. , Antoniadis D. , Kwong D. L.
Published: July 2005

We report a study on Ge diffusion and its impact on the electrical properties of TaN∕HfO2∕Ge metal-oxide-semiconductor (MOS) device. It is found that Ge diffusion depends on the amount of GeO2 formed at the HfO2∕Ge interface and can be retarded by surface nitridation. It is speculated that Ge diffusion is in the form of GeO or Ge-riched HfGeO. Effective suppression of Ge diffusion by NH3 nitridation has resulted in improved electrical properties of TaN∕HfO2∕Ge MOS device, including equivalent oxide thickness (EOT), leakage current, hysteresis, and interface state density. The degradation of leakage current after high temperature post metallization anneal (PMA) is found to be due to Ge diffusion.
Sample-profile estimate for fast atomic force microscopy
Authors: Salapaka Srinivasa , De Tathagata , Sebastian Abu
Published: July 2005

In this letter, a design scheme that achieves an optimal tip-sample force regulation with an ideal topography image reconstruction is presented. It addresses the problem of obtaining accurate sample profiles when scanning at high bandwidth while maintaining a constant cantilever-tip sample force in atomic force microscopes. In this design scheme, the objective of maintaining a constant tip-sample force while scanning at high bandwidth does not impose limitations on the reconstruction of the sample topography. It is shown that the proposed scheme provides a faithful replica of the sample at all relevant scanning speeds limited only by the inaccuracy in the model for the atomic force microscope. This provides an improvement over existing designs where the sample profile reconstruction is typically bandwidth limited. Comparison with the existing methods of using the control signal as the image is provided. The experimental results corroborate the theoretical development.
Polarization of strained BaTiO3∕SrTiO3 artificial superlattice: First-principles study
Authors: Kim Leejun , Kim Juho , Jung Donggeun , Lee Jaichan , Waghmare Umesh V.
Published: July 2005

We performed first-principles calculation to investigate the effect of epitaxial strain on lattice instabilities and polarization behavior of BaTiO3∕SrTiO3 artificial lattice with very short stacking period, i.e., BaTiO31unitcell∕SrTiO31unitcell(BTO∕STO). The structural analysis of BTO∕STO artificial superlattice under in-plane compressive state showed enhanced stability of the tetragonal phase. On the other hand, the stability of monoclinic phase was enhanced when the BTO∕STO was in the in-plane tensile state. The phase transition from tetragonal to the monoclinic phase occurs at the misfit strain of −0.25%. As the misfit strain of BTO∕STO superlattice increases from −0.25%to−1.5% (in-plane compressive state), the tetragonal superlattice exhibits an increasing polarization along the [001] direction. In the monoclinic phase, the polarization of the superlattice rotates progressively toward [110] direction with increasing the misfit strain, and the magnitude of the polarization simultaneously increases with the rotation. The first-principles study shows that the phase stability and polarization vector is sensitively influenced by the lattice misfit strain.
Imaging and spectroscopy of individual CdSe nanocrystals on atomically resolved surfaces
Authors: Bernard R. , Comtet G. , Dujardin G. , Huc V. , Mayne A. J.
Published: July 2005

Imaging and spectroscopy of individual CdSe nanocrystals have been performed with the scanning tunneling microscope (STM) on atomically resolved hydrogenated Si(100) surfaces. The CdSe nanocrystals have been deposited under vacuum onto the surface by using the pulse valve method. Two different types of CdSe nanocrystals, capped either with trioctylphosphine oxide ligands or with cadmium stearate ligands, have been studied to optimize their anchoring to the surface. The I(V) spectroscopy shows a characteristic resonant excitation spectrum through the unoccupied levels of the nanocrystals with no significant charging effect. This suggests that the nanocrystals are weakly coupled to the surface, thus requiring a stronger coupling with the STM tip to achieve a measurable tunnel current. These results demonstrate the importance of depositing nanocrystals on clean and atomically well-defined surfaces for reliable measurement of their properties.
Three-dimensional modeling of nanoscale Seebeck measurements by scanning thermoelectric microscopy
Authors: Bian Zhixi , Shakouri Ali , Shi Li , Lyeo Ho-Ki , Shih C. K.
Published: July 2005

A three-dimensional electrothermal model has been developed to investigate the spatial resolution of the scanning thermoelectric microscopy (SThEM). We found that if the electrical resistivity of the sample changes abruptly, the SThEM will measure a voltage close to the local thermoelectric voltage where electrical resistivity is relatively low, rather than a simple weighted average of the thermoelectric voltage distribution based on the temperature profile. This is due to the presence of internal currents in the sample. The spatial resolution of the Seebeck profiling is limited by the finite value of the phonon mean free path of the sample and the tip size of the microscopy. With a tip size around 1 nm, the scanning thermoelectric microscopy can achieve a spatial resolution of the physical limit defined by the statistical nature of the charge carrier and phonon behavior in a very small region.
Ontogeny and pathway of formation of 5α-androstane-3α,17β-diol in the testes of the immature brushtail possum Trichosurus vulpecula
Authors: Wilson Jean D. , Shaw Geoffrey , Renfree Marilyn B. , Auchus Richard J. , Leihy Michael W. , Eckery Douglas C.
Published: July 2005

The testicular androgen 5α-androstane-3α,17β-diol (androstanediol) mediates virilisation in pouch young of a marsupial, the tammar wallaby, and is the principal androgen formed in immature rodent testes. To chart the pattern of androstanediol formation in another marsupial species, the testes or fragments of testes from brushtail possums (Trichosurus vulpecula) that spanned the age range from early pouch young to mature adults were incubated with 3H-progesterone and the products were identified by high-performance liquid chromatography. The only 19-carbon steroids identified in pouch young and adult testes were the Δ4-3-keto-steroids testosterone and androstenedione. However, androstanediol and another 5α-reduced androgen (androsterone) were synthesised by testes from Day 87–200 males and these appeared to be formed from the 5α-reduction and 3-keto reduction of testosterone and androstenedione. In the prostate and glans penis of the immature male, 3H-androstanediol was converted to dihydrotestosterone. We conclude that the timing of androstanediol formation in the possum testis resembles the process in rodents rather than in the tammar wallaby and that any androstanediol in the circulation probably acts in target tissues via conversion to dihydrotestosterone.
Dopamine responsiveness is regulated by targeted sorting of D2 receptors
Authors: Bartlett Selena E. , Enquist Johan , Hopf Frederic W. , Lee Josephine H. , Gladher Fredrik , Kharazia Viktor , Waldhoer Maria , Mailliard William S. , Armstrong Randall , Bonci Antonello , Whistler Jennifer L.
Published: July 2005

Aberrant dopaminergic signaling is a critical determinant in multiple psychiatric disorders, and in many disease states, dopamine receptor number is altered. Here we identify a molecular mechanism that selectively targets D2 receptors for degradation after their activation by dopamine. The degradative fate of D2 receptors is determined by an interaction with G protein coupled receptor-associated sorting protein (GASP). As a consequence of this GASP interaction, D2 responses in rat brain fail to resensitize after agonist treatment. Disruption of the D2-GASP interaction facilitates recovery of D2 responses, suggesting that modulation of the D2-GASP interaction is important for the functional down-regulation of D2 receptors.
Helicobacter pylori Colonization in Infants in a Periurban Community in Karachi, Pakistan
Authors: Nizami Shaikh Qamaruddin , Bhutta Zulfiqar Ahmed , Weaver Lawrence , Preston Tom
Published: July 2005

Background:

The prevalence and incidence of Helicobacter pylori in children in Pakistan is not known.

Objectives:

To measure the prevalence and age of acquisition of Helicobacter pylori infection/colonization in infants in a peri‐urban community in Karachi, Pakistan.

Setting:

Field based epidemiologic study in a peri‐urban community in Karachi, Pakistan.

Methods:

Infants aged 1 to 3 months were recruited from a birth cohort from the community. 13C‐urea breath test (13C‐UBT) was performed on recruitment, and the test was repeated at 2, 3, 6, and 9 months of age.

Results:

One hundred forty‐eight infants were recruited and had 13C‐UBT on 319 occasions over a period of 2 years. Two hundred thirty‐one = (72%) tests were positive: 80% (49/61) infants at 1 month of age, 79% (33/42) at 2 month of age, 76% (92/121) at 3 month of age, 58% (37/64) at 6 months of age, and 67% (20/30) at 9 months of age.

Conclusions:

The study reveals an early colonization/infection of infants and a high prevalence of Helicobacter pylori in a peri‐urban community in Karachi, Pakistan.
Whole Body Bone Mineral Content Is Similar at Discharge from the Hospital in Premature Infants Receiving Fortified Breast Milk or Preterm Formula
Authors: De Schepper Jean , Cools Filip , Vandenplas Yvan , Louis Olivia
Published: July 2005

Background:

Prematurely born infants, especially those with very low birth weight (<1500 g) are at risk for metabolic bone disease.

Objectives:

The influence of the type of oral feeding regimen and of other potential determinants of whole bone mineral content in prematurely born infants, when they approached full gestation, were evaluated. Previous studies have mainly examined effects at the level of regional bone.

Methods:

34 infants (21males and 13 females), all born between 25.4 and 33.7 weeks of gestation, were studied before discharge. Whole body bone mineral content measurements were made just before hospital discharge using a commercial densitometer (Hologic QDR 4500, Hologic Inc, Waltham, MA) at a median age of 40 days (range, 10 to 115 days) after birth.

Results:

Expressed as a percentage of whole body mass, bone mass ranged between 0.86% and 1.99%, was similar between girls and boys and correlated positively with birth weight SD (r = 0.42; P < 0.05) and body weight SD (r = 0.35; P < 0.05). No difference in bone mass percentage was found between the different types of oral feedings (fortified human milk and preterm formula) or medications studied (corticoids and diuretics).

Conclusions:

Whereas prenatal and postnatal weight gain determines the degree of bone mineralization of premature infants, it appears that the type of oral feeding does not affect differently the postnatal bone mineralization of premature infants, when assessed at the moment of discharge.
Hepatitis B Vaccination Rate of Homeless Children in Baltimore
Authors: Schwarz K , Garrett B , Lamoreux J , Bowser YD , Weinbaum C , Alter M J
Published: July 2005

Objective:

To investigate the hepatitis B vaccination rate in homeless children 2 to 18 years old living in Baltimore City.

Methods:

During a 21‐month period, 250 children from homeless shelters were enrolled.

Results:

The percent of children who had received 3 or more doses of hepatitis B vaccine was inversely related to age; 90% in 2‐ to 5‐year‐olds and 29% in 13‐ to 18‐year‐olds (P < 0.0001). Seventy percent of 2‐ to 5‐year‐olds had at least some of their vaccine history recorded in the Baltimore Immunization Registry Program but the history was complete in only half. Forty‐two percent of 13‐ to 18‐year‐olds had no hepatitis B vaccine doses recorded in any source; 49 per cent of 10‐ to 18‐year‐olds were either not immunized or had received only one hepatitis B vaccine dose.

Conclusions:

Hepatitis B vaccine coverage is high in homeless children up to 9 years of age, whereas the majority of homeless children 10 years of age and older are unprotected against hepatitis B virus infection. Tracking the vaccine records in homeless children is labor intensive. Better public health strategies to deliver hepatitis B vaccine to older homeless children are urgently needed.
Characterizing the viscoelastic properties of thin hydrogel-based constructs for tissue engineering applications
Authors: Ahearne Mark , Yang Ying , El Haj Alicia J , Then Kong Y , Liu Kuo-Kang
Published: July 2005

We present a novel indentation method for characterizing the viscoelastic properties of alginate and agarose hydrogel based constructs, which are often used as a model system of soft biological tissues. A sensitive long working distance microscope was used for measuring the time-dependent deformation of the thin circular hydrogel membranes under a constant load. The deformation of the constructs was measured laterally. The elastic modulus as a function of time can be determined by a large deformation theory based on Mooney–Rivlin elasticity. A viscoelastic theory, Zener model, was applied to correlate the time-dependent deformation of the constructs with various gel concentrations, and the creep parameters can therefore be quantitatively estimated. The value of Young's modulus was shown to increase in proportion with gel concentration. This finding is consistent with other publications. Our results also showed the great capability of using the technique to measure gels with incorporated corneal stromal cells. This study demonstrates a novel and convenient technique to measure mechanical properties of hydrogel in a non-destructive, online and real-time fashion. Thus this novel technique can become a valuable tool for soft tissue engineering.
A model problem concerning recoverable strains of shape-memory polycrystals
Authors: Bhattacharya K , Suquet P.M
Published: July 2005

This paper addresses a model problem of nonlinear homogenization motivated by the study of the shape-memory effect in polycrystalline media. Specifically, it numerically computes the set of recoverable strains in a polycrystal given the set of recoverable strains of a single crystal in the two-dimensional scalar (or antiplane shear) setting. This problem shares a direct analogy with crystal plasticity. The paper considers typical or random polycrystals where the grains are generated by a Voronoi tesselation of a set of random points and are randomly oriented. The numerical results show that for such microstructures, the Taylor bound appears to be the most accurate (though pessimistic) bound when the anisotropy is moderate, and that recent Kohn–Little–Goldsztein outer bounds overestimate the recoverable strains when the anisotropy is large. The results also show that the stress tends to localize on tortuous paths that traverse (poorly oriented) grains as the polycrystal reaches its limit of recoverable strain.