bluuebunny/crossref_metadata_2025 huggingface dataset:
Heterogeneous coupling of the Sumatran megathrust constrained by geodetic and paleogeodetic measurements
Authors: Chlieh M. , Avouac J. P. , Sieh K. , Natawidjaja D. H. , Galetzka John
Published: May 2008

Geodetic and paleogeodetic measurements of interseismic strain above the Sumatran portion of the Sunda subduction zone reveal a heterogeneous pattern of coupling. Annual banding in corals provides vertical rates of deformation spanning the last half of the 20th century, and repeated GPS surveys between 1991 and 2001 and continuous measurements at GPS stations operated since 2002 provide horizontal velocities. Near the equator, the megathrust is locked over a narrow width of only a few tens of kilometers. In contrast, the locked fault zone is up to about 175 km wide in areas where great interplate earthquakes have occurred in the past. Formal inversion of the data reveals that these strongly coupled patches are roughly coincident with asperities that ruptured during these events. The correlation is most spectacular for rupture of the Mw 8.7 Nias‐Simeulue earthquake of 2005, which released half of the moment deficit that had accumulated since its previous rupture in 1861, suggesting that this earthquake was overdue. Beneath the Mentawai islands, strong coupling is observed within the overlapping rupture areas of the great earthquakes of 1797 and 1833. The accumulated slip deficit since these events is slowly reaching the amount of slip that occurred during the 1833 earthquake but already exceeds the slip that occurred during the 1797 earthquake. Thus, rerupture of part of the Mentawai patch in September 2007 was not a surprise. In contrast, coupling is low below the Batu islands near the equator and around Enggano island at about 5°S, where only moderate earthquakes (Mw < 8.0) have occurred in the past two centuries. The correlation of large seismic asperities with patches that are locked during the interseismic period suggests that they are persistent features. This interpretation is reinforced by the fact that the large locked patches and great ruptures occur beneath persistent geomorphologic features, the largest outer arc islands. Depth‐ and convergence‐rate‐dependent temperature might influence the pattern of coupling, through its effect on the rheology of the plate interface, but other influences are required to account for the observed along‐strike heterogeneity of coupling. In particular, subduction of the Investigator Fracture Zone could be the cause for the low coupling near the equator.
Mixed layer analysis of a mesoscale eddy in the Antarctic Polar Front Zone
Authors: Cisewski Boris , Strass Volker H. , Losch Martin , Prandke Hartmut
Published: May 2008

Microstructure, acoustic Doppler current profiler, and conductivity‐temperature‐depth (CTD) profiles were taken in a mesoscale eddy in the Antarctic Polar Front Zone at about 2°15′E, 49°15′S during the R/V Polarstern cruise ANT XXI/3 within the scope of the European Iron Fertilization Experiment in January–March 2004. The mixed layer depth (MLD), calculated from the composite of CTD‐ and microstructure sonde (MSS)‐derived data, was 97.6 ± 20.6 m. No significant correlation between the wind work (E10) and the MLD (r = 0.02 to 0.22) was found. However, the analysis revealed a negative correlation between the surface buoyancy flux (B) and the MLD 1/2 d later. Two approaches were used to estimate the actively mixing layer depth (AMLD). First, the actively mixing layer was determined subjectively by analyzing the MSS‐derived density, energy dissipation, and Thorpe scale profiles, and second, the mixed layer model embedded in a general circulation model was used. The overall mean of the determined depths of the actively mixing layer (AMLDMSS = 66.4 ± 28.8 m) agreed with the model‐predicted boundary layer depths (BLD) (BLDKPP = 69.1 ± 29.5 m), but the individual values sometimes were differing considerably. We deduced estimates of the vertical diffusivity (Kz) from the MSS‐derived energy dissipation rates and Thorpe scales. Both methods showed that Kz decreased with depth from order of magnitude 10−1 m2 s−1 in the actively mixed layer to order of 10−4 m2 s−1 in the pycnocline.
Soil respiration in perennial grass and shrub ecosystems: Linking environmental controls with plant and microbial sources on seasonal and diel timescales
Authors: Carbone Mariah S. , Winston Gregory C. , Trumbore Susan E.
Published: May 2008

A mechanistic understanding of soil respiration is a major impediment to predicting terrestrial C fluxes spatially and temporally. Automated measurements of soil respiration offer the high‐resolution information necessary to observe temporal variation in soil respiration, but spatially these measurements are under‐represented in water‐limited and non‐forested ecosystems. We measured soil respiration with automated chambers over the growing season, at two sites with the same semi‐arid climate, but with different dominant vegetation, perennial grasses and shrubs in the Owens Valley, CA, USA. An isotope mass balance technique was used to partition soil respiration into autotrophic and heterotrophic components at two time points, early and late growing season. Results showed large differences in the magnitude of growing season soil respiration between the two sites (910 versus 126 g C m−2 for grasses and shrubs respectively over 5 months). We attribute this to site differences in soil water availability and belowground allocation and productivity. Diel patterns of soil respiration between the two sites were similar. Temperature explained most of the diel variability in the early growing season, when soil moisture was greatest. As soil moisture declined over the growing season, diel patterns became increasingly decoupled temporally from temperature due to increased water‐limitation on surface heterotrophic sources and hypothesized strong photosynthetic control over soil respiration rates. Partitioning of soil respiration into autotrophic and heterotrophic sources showed the dominance of autotrophic sources across seasons and ecosystems. However, heterotrophic respiration was more dynamic from early to late growing season, declining in the grass ecosystem; and a surprising increase in the shrub ecosystem, attributed to warming of the soil profile enhancing microbial decomposition at depth.
Effects of diffuse radiation on canopy gas exchange processes in a forest ecosystem
Authors: Knohl Alexander , Baldocchi Dennis D.
Published: May 2008

Forest ecosystems across the globe show an increase in ecosystem carbon uptake efficiency under conditions with high fraction of diffuse radiation. Here, we combine eddy covariance flux measurements at a deciduous temperate forest in central Germany with canopy‐scale modeling using the biophysical multilayer model CANVEG to investigate the impact of diffuse radiation on various canopy gas exchange processes and to elucidate the underlying mechanisms. Increasing diffuse radiation enhances canopy photosynthesis by redistributing the solar radiation load from light saturated sunlit leaves to nonsaturated shade leaves. Interactions with atmospheric vapor pressure deficit and reduced leaf respiration are only of minor importance to canopy photosynthesis. The response strength of carbon uptake to diffuse radiation depends on canopy characteristics such as leaf area index and leaf optical properties. Our model computations shows that both canopy photosynthesis and transpiration increase initially with diffuse fraction, but decrease after an optimum at a diffuse fraction of 0.45 due to reduction in global radiation. The initial increase in canopy photosynthesis exceeds the increase in transpiration, leading to a rise in water‐use‐efficiency. Our model predicts an increase in carbon isotope discrimination with water‐use‐efficiency resulting from differences in the leaf‐to‐air vapor pressure gradient and atmospheric vapor pressure deficit. This finding is in contrast to those predicted with simple big‐leaf models that do not explicitly calculate leaf energy balance. At an annual scale, we estimate a decrease in annual carbon uptake for a potential increase in diffuse fraction, since diffuse fraction was beyond the optimum for 61% of the data.
Reappraisal of the fossil methane budget and related emission from geologic sources
Authors: Etiope Giuseppe , Lassey Keith R. , Klusman Ronald W. , Boschi Enzo
Published: May 2008

Converging evidence from new top‐down and bottom‐up estimates of fossil “radiocarbon‐free” methane emissions indicates that natural geologic sources account for a substantial component of the atmospheric methane budget. Comparing emission estimates based on atmospheric 14CH4 (“radiomethane”) with geologic emissions from seepage, including terrestrial macroseeps, microseepage, marine seeps, and geothermal/volcanic emissions from the Earth's crust, shows that such “geo‐CH4” sources can be conservatively estimated at 53 ± 11 Tg yr−1 globally. This makes geo‐CH4 second in importance to wetlands as a natural methane source. Such a new appraisal can easily be accommodated within the uncertainty of the global methane budget as recently compiled, and recognizes the importance of geophysical out‐gassing of methane generated within the lithosphere. We propose a new coherent contemporary budget in which 30 ± 5% (based on atmospheric radiomethane measurements) of the global source of 582 ± 87 Tg yr−1 has fossil origin, both natural and anthropogenic.
Attribution of cyclogenesis region sea surface temperature change to anthropogenic influence
Authors: Gillett N. P. , Stott P. A. , Santer B. D.
Published: May 2008

Previous research has identified links between tropical cyclone activity and sea surface temperatures in the tropical cyclogenesis regions of the North Atlantic and Western North Pacific. Other work has demonstrated that warming in these regions is inconsistent with simulated internal variability. After evaluating the variability of a suite of climate models on a range of timescales, we use detection and attribution methods and a suite of 20th century simulations including anthropogenic and natural forcing to identify a significant response to external forcing in both regions during the June–November hurricane season over the 20th century. We then use separate simulations of the response to natural and anthropogenic forcing to identify anthropogenic influence independently of natural influence in both the Atlantic and Pacific Cyclogenesis Regions.
Chronic ethanol intake modulates vascular levels of endothelin‐1 receptor and enhances the pressor response to endothelin‐1 in anaesthetized rats
Authors: Tirapelli C R , Legros E , Brochu I , Honoré J‐C , Lanchote V L , Uyemura S A , De Oliveira A M , D'Orléans‐Juste P
Published: May 2008

Background and purpose:

The contribution of endothelin‐1 (ET‐1) to vascular hyper‐reactivity associated with chronic ethanol intake, a major risk factor in several cardiovascular diseases, remains to be investigated.

Experimental approach:

The biphasic haemodynamic responses to ET‐1 (0.01–0.1 nmol kg−1, i.v.) or to the selective ETB agonist, IRL1620 (0.001–1.0 nmol kg−1, i.v.), with or without ETA or ETB antagonists (BQ123 (c(DTrp‐Dasp‐Pro‐Dval‐Leu)) at 1 and 2.5 mg kg−1 and BQ788 (N‐cis‐2,6‐dimethyl‐piperidinocarbonyl‐L‐γ‐methylleucyl1‐D‐1methoxycarbonyltryptophanyl‐D‐norleucine) at 0.25 mg kg−1, respectively) were tested in anaesthetized rats, after 2 weeks' chronic ethanol treatment. Hepatic parameters and ET receptor protein levels were also determined.

Key results:

The initial hypotensive responses to ET‐1 or IRL1620 were unaffected by chronic ethanol intake, whereas the subsequent pressor effects induced by ET‐1, but not by IRL1620, were potentiated. BQ123 at 2.5 but not 1 mg kg−1 reduced the pressor responses to ET‐1 in ethanol‐treated rats. Conversely, BQ788 (0.25 mg kg−1) potentiated ET‐1‐induced increases in mean arterial blood pressure in control as well as in ethanol‐treated rats. Interestingly, in the latter group, increases in heart rate, induced by ET‐1 at a dose of 0.025 mg kg−1 were enhanced following ETB receptor blockade. Finally, we observed higher levels of ETA receptor in the heart and mesenteric artery and a reduction of ETB receptor protein levels in the aorta and kidney from rats chronically treated with ethanol.

Conclusions and implications:

Increased vascular reactivity to ET‐1 and altered protein levels of ETA and ETB receptors could play a role in the pathogenesis of cardiovascular complications associated with chronic ethanol consumption.

British Journal of Pharmacology (2008) 154, 971–981; doi:10.1038/bjp.2008.157; published online 12 May 2008
Increased susceptibility of annexin‐A1 null mice to nociceptive pain is indicative of a spinal antinociceptive action of annexin‐A1
Authors: Ayoub S S , Yazid S , Flower R J
Published: May 2008

Background and purpose:

Annexin‐A1 (ANXA1), a glucocorticoid‐regulated protein, mediates several of the anti‐inflammatory actions of the glucocorticoids. Previous studies demonstrated that ANXA1 is involved in pain modulation. The current study, using ANXA1 knockout mice (ANXA1−/−), is aimed at addressing the site and mechanism of the modulatory action of ANXA1 as well as possible involvement of ANXA1 in mediating the analgesic action of glucocorticoids.

Experimental approach:

The acetic acid‐induced writhing response was performed in ANXA1−/−and wild‐type (ANXA1+/+) mice with spinal and brain levels of prostaglandin E2(PGE2) examined in both genotypes. The effect of the ANXA1 peptomimetic Ac2‐26 as well as methylprednisolone on the writhing response and on spinal cord PGE2of ANXA1+/+and ANXA1−/−was compared. The expression of proteins involved in PGE2synthesis, cytosolic phospholipase A2(cPLA2) and cyclooxygenases (COXs), in the spinal cord of ANXA1+/+and ANXA1−/−was also compared.

Key results:

ANXA1−/−mice exhibited a significantly greater writhing response and increased spinal cord levels of PGE2compared with ANXA1+/+mice. Ac2‐26 produced analgesia and reduced spinal PGE2levels in ANXA1+/+and ANXA1−/−mice, whereas methylprednisolone reduced the writhing response and spinal PGE2levels in ANXA1+/+, but not in ANXA1−/−mice. The expression of cPLA2, COX‐1, COX‐2 and COX‐3 in spinal cord tissues was upregulated in ANXA1−/−compared with ANXA1+/+.

Conclusions and implications:

We conclude that ANXA1 protein modulates nociceptive processing at the spinal level, by reducing synthesis of PGE2by modulating cPLA2and/or COX activity. The analgesic activity of methylprednisolone is mediated by spinal ANXA1.

British Journal of Pharmacology(2008)154, 1135–1142; doi:10.1038/bjp.2008.166; published online 12 May 2008
The μ‐opioid receptor agonist morphine, but not agonists at δ‐ or κ‐opioid receptors, induces peripheral antinociception mediated by cannabinoid receptors
Authors: Da Fonseca Pacheco D , Klein A , De Castro Perez A , Da Fonseca Pacheco C M , De Francischi J N , Duarte I D G
Published: May 2008

Background and purpose:

Although participation of opioids in antinociception induced by cannabinoids has been documented, there is little information regarding the participation of cannabinoids in the antinociceptive mechanisms of opioids. The aim of the present study was to determine whether endocannabinoids could be involved in peripheral antinociception induced by activation of μ‐, δ‐ and κ‐opioid receptors.

Experimental approach:

Nociceptive thresholds to mechanical stimulation of rat paws treated with intraplantar prostaglandin E2(PGE2, 2 μg) to induce hyperalgesia were measured 3 h after injection using an algesimetric apparatus. Opioid agonists morphine (200 μg), (+)‐4‐[(alphaR)‐alpha‐((2S,5R)‐4‐Allyl‐2,5‐dimethyl‐1‐piperazinyl)‐3‐ methoxybenzyl]‐N,N‐diethylbenzamide (SNC80) (80 μg), bremazocine (50 μg); cannabinoid receptor antagonistsN‐(piperidin‐1‐yl)‐5‐(4‐ iodophenyl)‐1‐(2,4‐dichlorophenyl)‐4‐methyl‐1H‐pyrazole‐3‐carboxamide (AM251) (20–80 μg), 6‐iodo‐2‐methyl‐1‐[2‐(4‐morpholinyl) ethyl]‐1H‐indol‐3‐yl(4‐methoxyphenyl) methanone (AM630) (12.5–100 μg); and an inhibitor of methyl arachidonyl fluorophosphonate (MAFP) (1–4 μg) were also injected in the paw.

Key results:

The CB1‐selective cannabinoid receptor antagonist AM251 completely reversed the peripheral antinociception induced by morphine in a dose‐dependent manner. In contrast, the CB2‐selective cannabinoid receptor antagonist AM630 elicited partial antagonism of this effect. In addition, the administration of the fatty acid amide hydrolase inhibitor, MAFP, enhanced the antinociception induced by morphine. The cannabinoid receptor antagonists AM251 and AM630 did not modify the antinociceptive effect of SNC80 or bremazocine. The antagonists alone did not cause any hyperalgesic or antinociceptive effect.

Conclusions and implications:

Our results provide evidence for the involvement of endocannabinoids, in the peripheral antinociception induced by the μ‐opioid receptor agonist morphine. The release of cannabinoids appears not to be involved in the peripheral antinociceptive effect induced by κ‐ and δ‐opioid receptor agonists.

British Journal of Pharmacology(2008)154, 1143–1149; doi:10.1038/bjp.2008.175; published online 12 May 2008
Cannabidiol, extracted fromCannabis sativa, selectively inhibits inflammatory hypermotility in mice
Authors: Capasso R , Borrelli F , Aviello G , Romano B , Scalisi C , Capasso F , Izzo A A
Published: May 2008

Background and purpose:

Cannabidiol is aCannabis‐derived non‐psychotropic compound that exerts a plethora of pharmacological actions, including anti‐inflammatory, neuroprotective and antitumour effects, with potential therapeutic interest. However, the actions of cannabidiol in the digestive tract are largely unexplored. In the present study, we investigated the effect of cannabidiol on intestinal motility in normal (control) mice and in mice with intestinal inflammation.

Experimental approach:

Motilityin vivowas measured by evaluating the distribution of an orally administered fluorescent marker along the small intestine; intestinal inflammation was induced by the irritant croton oil; contractilityin vitrowas evaluated by stimulating the isolated ileum, in an organ bath, with ACh.

Key results:

In vivo, cannabidiol did not affect motility in control mice, but normalized croton oil‐induced hypermotility. The inhibitory effect of cannabidiol was counteracted by the cannabinoid CB1receptor antagonist rimonabant, but not by the cannabinoid CB2receptor antagonist SR144528 (N‐[‐1S‐endo‐1,3,3‐trimethyl bicyclo [2.2.1] heptan‐2‐yl]‐5‐(4‐chloro‐3‐methylphenyl)‐1‐(4‐methylbenzyl)‐pyrazole‐3‐carboxamide), by the opioid receptor antagonist naloxone or by the α2‐adrenergic antagonist yohimbine. Cannabidiol did not reduce motility in animals treated with the fatty acid amide hydrolase (FAAH) inhibitorN‐arachidonoyl‐5‐hydroxytryptamine, whereas loperamide was still effective.In vitro, cannabidiol inhibited ACh‐induced contractions in the isolated ileum from both control and croton oil‐treated mice.

Conclusions and implications:

Cannabidiol selectively reduces croton oil‐induced hypermotility in micein vivoand this effect involves cannabinoid CB1receptors and FAAH. In view of its low toxicity in humans, cannabidiol may represent a good candidate to normalize motility in patients with inflammatory bowel disease.

British Journal of Pharmacology(2008)154, 1001–1008; doi:10.1038/bjp.2008.177; published online 12 May 2008
Automated overexpression and isotopic labelling of biologically active oncoproteins in the cyanobacterium Anabaena sp. PCC 7120
Authors: Desplancq Dominique , Rinaldi Anne‐Sophie , Hörzer Helen , Ho Yu , Nierengarten Hélène , Atkinson R. Andrew , Kieffer Bruno , Weiss Etienne
Published: May 2008

We have previously shown the cyanobacterium Anabaena sp. PCC 7120 to be a suitable host for the production of isotopically labelled recombinant proteins using the nitrate‐inducible nir expression system. However, the expression of toxic proteins such as oncoproteins proved to be difficult, as expression levels decreased shortly after induction, while growth continued. To overcome this limitation, we have developed a method of auto‐induction of the nir promoter in which cells are grown to high cell density in a bioreactor in the presence of ammonium and nitrate. Since ammonium is the preferred nitrogen source and acts as a repressor of the nir promoter, induction occurs only when the ammonium had been depleted. Using this novel auto‐induction method, both oncoproteins E6 and gankyrin were expressed at high levels in a folded conformation and were shown to be biologically active after purification. Furthermore, under similar conditions of growth in auto‐inducing medium, the use of 15N‐ and 13C‐labelled mineral salts yielded isotopic enrichment of these proteins at levels above 95%, making them suitable for NMR‐based structural analysis in a cost‐effective manner.
Mutation of Trp29 of human equilibrative nucleoside transporter 1 alters affinity for coronary vasodilator drugs and nucleoside selectivity
Authors: Paproski Robert J. , Visser Frank , Zhang Jing , Tackaberry Tracey , Damaraju Vijaya , Baldwin Stephen A. , Young James D. , Cass Carol E.
Published: May 2008

hENT1 (human equilibrative nucleoside transporter 1) is inhibited by nanomolar concentrations of various structurally distinct coronary vasodilator drugs, including dipyridamole, dilazep, draflazine, soluflazine and NBMPR (nitrobenzylmercaptopurine ribonucleoside). When a library of randomly mutated hENT1 cDNAs was screened using a yeast-based functional complementation assay for resistance to dilazep, a clone containing the W29G mutation was identified. Multiple sequence alignments revealed that this residue was highly conserved. Mutations at Trp29 were generated and tested for adenosine transport activity and inhibitor sensitivity. Trp29 mutations significantly reduced the apparent Vmax and/or increased the apparent Km values for adenosine transport. Trp29 mutations increased the IC50 values for hENT1 inhibition by dipyridamole, dilazep, NBMPR, soluflazine and draflazine. NBMPR and soluflazine displayed remarkably similar trends, with large aromatic substitutions at residue 29 resulting in the lowest IC50 values, suggesting that both drugs could interact via ring-stacking interactions with Trp29. The W29T mutant displayed a selective loss of pyrimidine nucleoside transport activity, which contrasts with the previously identified L442I mutant that displayed a selective loss of purine nucleoside transport. W29T, L442I and the double mutant W29T/L442I were characterized kinetically for nucleoside transport activity. A helical wheel projection of TM (transmembrane segment) 1 suggests that Trp29 is positioned close to Met33, implicated previously in nucleoside and inhibitor recognition, and that both residues line the permeant translocation pathway. The data also suggest that Trp29 forms part of, or lies close to, the binding sites for dipyridamole, dilazep, NBMPR, soluflazine and draflazine.
The presence of an ER exit signal determines the protein sorting upon ER exit in yeast
Authors: Watanabe Reika , Castillon Guillaume A. , Meury Anja , Riezman Howard
Published: May 2008

In yeast, there are at least two vesicle populations upon ER (endoplasmic reticulum) exit, one containing Gap1p (general aminoacid permease) and a glycosylated α-factor, gpαF (glycosylated proα-factor), and the other containing GPI (glycosylphosphatidylinositol)-anchored proteins, Gas1p (glycophospholipid-anchored surface protein) and Yps1p. We attempted to identify sorting determinants for this protein sorting event in the ER. We found that mutant Gas1 proteins that lack a GPI anchor and/or S/T region (serine- and threonine-rich region), two common characteristic features conserved among yeast GPI-anchored proteins, were still sorted away from Gap1p-containing vesicles. Furthermore, a mutant glycosylated α-factor, gpαGPI, which contains both the GPI anchor and S/T region from Gas1p, still entered Gap1p-containing vesicles, demonstrating that these conserved characteristics do not prevent proteins from entering Gap1p-containing vesicles. gpαF showed severely reduced budding efficiency in the absence of its ER exit receptor Erv29p, and this residual budding product no longer entered Gap1p-containing vesicles. These results suggest that the interaction of gpαF with Erv29p is essential for sorting into Gap1p-containing vesicles. We compared the detergent solubility of Gas1p and the gpαGPI in the ER with that in ER-derived vesicles. Both GPI-anchored proteins similarly partitioned into the DRM (detergent-resistant membrane) in the ER. Based on the fact that they entered different ER-derived vesicles, we conclude that DRM partitioning of GPI-anchored proteins is not the dominant determinant of protein sorting upon ER exit. Interestingly, upon incorporation into the ER-derived vesicles, gpαGPI was no longer detergent-insoluble, in contrast with the persistent detergent insolubility of Gas1p in the ER-derived vesicles. We present different explanations for the different behaviours of GPI-anchored proteins in distinct ER-derived vesicle populations.
Benchmark calculations for reduced density-matrix functional theory
Authors: Lathiotakis N. N. , Marques Miguel A. L.
Published: May 2008

Reduced density-matrix functional theory (RDMFT) is a promising alternative approach to the problem of electron correlation. Like standard density functional theory, it contains an unknown exchange-correlation functional, for which several approximations have been proposed in the last years. In this article, we benchmark some of these functionals in an extended set of molecules with respect to total and atomization energies. Our results show that the most recent RDMFT functionals give very satisfactory results compared to standard quantum chemistry and density functional approaches.
High channel mobility 4H-SiC metal-oxide-semiconductor field-effect transistor with low temperature metal-organic chemical-vapor deposition grown Al2O3 gate insulator
Authors: Hino S. , Hatayama T. , Kato J. , Tokumitsu E. , Miura N. , Oomori T.
Published: May 2008

Ultrahigh channel mobility is demonstrated for 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) with Al2O3 gate insulators fabricated at low temperatures by metal-organic chemical-vapor deposition. Relatively high field effect channel mobility of 64cm2∕Vs is obtained when the Al2O3 gate insulator is deposited at 190°C. Furthermore, extremely high field effect mobility of 284cm2∕Vs was obtained for a MOSFET fabricated with an ultrathin thermally grown SiOx layer inserted between the Al2O3 and SiC.
Effectively doubling the magnetic field in spin-12–spin-1, HSQC, HDQC, coupled HSQC, and coupled HDQC in solution NMR
Authors: Chandra Shekar S. , Backer Jonathan M. , Girvin Mark E.
Published: May 2008

Pulse sequences for spin-12–spin-1 pair heteronuclear single quantum correlation (HSQC), heteronuclear double quantum correlation (HDQC), and coupled-HSQC, and coupled-HDQC NMR spectroscopies are outlined, and experimental realization for a C13–H2 pair is demonstrated in solution state. In both the coupled versions, conditions for generation of in-phase and antiphase multiplets in either dimension are arrived at. The patterns and the intensity ratios are explained. The double quantum (2Q) experiments confirm doubling of both the shift frequency and the splitting due to coupling (to spin 12) of the 2Q coherence emanating from spin 1. The frequency doubling is equivalent to the corresponding single quantum (1Q) coherence at double the magnetic field strength. The coupling doubling, however, is independent of the magnetic field strength and a signature feature of the 2Q coherence. The ramification of the relative relaxation rates of 1Q and 2Q coherences is discussed.
The relationship between local order, long range order, and sub-band-gap defects in hafnium oxide and hafnium silicate films
Authors: Hill D. H. , Bartynski R. A. , Nguyen N. V. , Davydov Albert C. , Chandler-Horowitz Deane , Frank Martin M.
Published: May 2008

We have measured x-ray absorption spectra (XAS) at the oxygen K edge for hafnium oxide (HfO2) films grown by chemical vapor deposition (CVD) and atomic layer deposition (ALD), as well as for hafnium silicate (HfSiO) films grown by CVD. The XAS results are compared to x-ray diffraction (XRD) and spectroscopic ellipsometry (SE) data from the same films. Features characteristic of crystalline HfO2 are observed in the XAS spectra from all CVD-grown HfO2 films, even for a thickness of 5 nm where XRD is not sensitive. XAS and XRD spectra from the ALD-grown HfO2 films exhibit the signature of crystallinity only for films that are 20 nm or thicker. These characteristic XAS features are absent in all HfSiO films measured, which is consistent with their being amorphous. The appearance of these peaks in XAS and XRD is correlated with sub-band-gap absorption in the SE spectra, which appears to be intrinsic to crystalline HfO2 in the monoclinic phase.
Negative Poisson’s ratios in siliceous zeolite MFI-silicalite
Authors: Sanchez-Valle Carmen , Lethbridge Zoe A. D. , Sinogeikin Stanislav V. , Williams Jennifer J. , Walton Richard I. , Evans Kenneth E. , Bass Jay D.
Published: May 2008

Brillouin scattering measurements of the single-crystal elastic properties of the as-made zeolite silicalite ∣(C3H7)4NF∣4[Si96O192]-MFI provides the first experimental evidence for on-axis negative Poisson’s ratios (auxeticity) in a synthetic zeolite structure. MFI laterally contracts when compressed and laterally expands when stretched along x1 and x2 directions in the (001) plane (ν12=−0.061, ν21=−0.051). The aggregate Poisson’s ratio of MFI, although positive, has an anomalously low value ν=0.175(3) compared to other silicate materials. These results suggest that the template-free MFI-silicalite [Si96O192] might have potential applications as tunable sieve where molecular discriminating characteristics are adjusted by application of stress along specific axes.
Vibrational overtone initiated unimolecular dissociation of HOCH2OOH and HOCD2OOH: Evidence for mode selective behavior
Authors: Matthews Jamie , Fry Juliane L. , Roehl Coleen M. , Wennberg Paul O. , Sinha Amitabha
Published: May 2008

The vibrational overtone induced unimolecular dissociation of HMHP (HOCH2OOH) and HMHP-d2 (HOCD2OOH) into OH and HOCH2O (HOCD2O) fragments is investigated in the region of the 4νOH and 5νOH bands. The unimolecular dissociation rates in the threshold region, corresponding to the 4νOH band, exhibit measurable differences associated with excitation of the OH stretch of the alcohol versus the peroxide functional group, with the higher energy alcohol OH stretching state exhibiting a slower dissociation rate compared to the lower energy peroxide OH stretch in both HMHP and HMHP-d2. Predictions using the Rice–Ramsperger–Kassel–Marcus theory give rates that are in reasonably good agreement with the measured dissociation rate for the alcohol OH stretch but considerably differ from the measured rates for the peroxide OH stretch in both isotopomers. The present results are interpreted as suggesting that the extent of intramolecular vibrational energy redistribution (IVR) is different for the two OH stretching states associated with the two functional groups in HMHP, with IVR being substantially less complete for the peroxide OH stretch. Analysis of the OH fragment product state distributions in conjunction with phase-space theory simulation gives a D0 value of 38±0.7kcal∕mole for breaking the peroxide bond in HMHP.
Time-dependent multiconfiguration theory for electronic dynamics of molecules in intense laser fields: A description in terms of numerical orbital functions
Authors: Kato Tsuyoshi , Kono Hirohiko
Published: May 2008

The equations of motion (EOMs) for spin orbitals in the coordinate representation are derived within the framework of the time-dependent multiconfiguration theory developed for electronic dynamics of molecules in intense laser fields. We then tailor the EOMs for diatomic (or linear) molecules to apply the theory to the electronic dynamics of a hydrogen molecule in an intense, near-infrared laser field. Numerical results are presented to demonstrate that the time-dependent numerical multiconfiguration wave function is able to describe the correlated electron motions as well as the ionization processes of a molecule in intense laser fields.
Nanogranular structures formed by combinatorial control processing of size-selected metal nanoparticles
Authors: Huh Seung Hun , Riu Doh Hyung , Kim Chang Yeoul , Naono Yasutomo , Nakamura Tsuneyuki , Sugiyama Akinori , Nakajima Atsushi
Published: May 2008

Nanogranular films and lines, which are composed of size-selected Au, Ni, and Pt nanoparticles (NPs) and which exhibit an intermediate structure between that of the individual NPs and that of polycrystalline ones, were produced by a fully physical process. By using a combination of techniques such as lithography, lift-off, size selection, and aerosol deposition, well-designed Au lines (linewidth W=80 nm) and thickness-controlled rectangular patterns could be produced, while Ni and Pt NPs did not form continuous lines if the linewidth was less than W=150 nm. This difference might be explained by the extent of collision-induced surface melting during NP deposition onto the substrate.
The potential and device physics of interdigitated thin-film solar cells
Authors: Metzger Wyatt K.
Published: May 2008

The device physics of thin-film solar cells with interdigitated p-n junctions is examined for a range of spatial sizes, band offsets, and material parameters. The results are illustrated by focusing on recent nanoscale concepts for Cu(In,Ga)Se2 solar cells. Ideally, nanoscale interdigitated junctions can improve solar cell performance relative to planar-junction devices, and make reasonably high solar cell efficiencies (>15%) attainable even with mediocre electro-optical materials.
Melting mechanism of monolayers adsorbed in cylindrical pores: The influence of the pore wall roughness
Authors: Kuchta B. , Firlej L. , Denoyel R. , Rols S. , Johnson M. R. , Coasne B.
Published: May 2008

We have analyzed the mechanism of melting of molecular layers adsorbed in porous materials with cylindrical pores and rough pore walls. The working example studied here is a monolayer of methane molecules adsorbed in MCM-41 pore of diameter 2R=4nm. Both experimental (neutron scattering) and simulation (Monte Carlo) results demonstrate the strong influence of the wall roughness on the melting mechanism. In particular, the transformation between solidlike and liquidlike monolayer phases adsorbed on a rough surface is observed over a broad temperature range, and solidlike properties persist even above the bulk methane melting temperature.
Anomalous temperature-dependent exchange bias in Fe films deposited on Si substrates with the native oxide layer
Authors: Wang Wenhong , Takano Fumiyoshi , Takenaka Masato , Akinaga Hiro , Ofuchi Hironori
Published: May 2008

The temperature dependence of the exchange bias has been investigated in Fe films deposited on the Si substrates with the native oxidize layer. A crossover from negative to positive exchange bias has been observed with increasing temperature at 30 K, accompanied with the maximum of the coercivity. This effect could be understood as a result of the exchange coupling between the ferromagnetic Fe film and the spin-glasslike Fe oxides particles formed spontaneously at the interface, where the direction of their end spins controls the sign of exchange bias.
Femtosecond pulsed laser ablation dynamics and ablation morphology of nickel based superalloy CMSX-4
Authors: McDonald Joel P. , Ma Shuwei , Pollock Tresa M. , Yalisove Steven M. , Nees John A.
Published: May 2008

Pump-probe shadowgraphic imaging of single pulse femtosecond laser ablation was performed to investigate the dynamics of material removal during femtosecond laser machining of the intermetallic superalloy CMSX-4. Time-resolved shadowgraphic images were collected, which showed the presence of an expanding shock wave in the air in front of the target, following the onset of laser ablation. The dimensions of the shock wave were measured as a function of time (0–10.3ns), following the onset of ablation. The energy release associated with the observed shock wave and the pressure at the shock wave front versus time as a function of incident laser fluence (1.27–62.8J∕cm2) were inferred from the shock dynamics. The measured shock wave dynamics and inferred shock energy release are discussed in light of the evolving ablation morphology and ablated crater depth as a function of incident laser fluence.
Silicon-germanium interdiffusion in high-germanium-content epitaxial heterostructures
Authors: Ozguven Nevran , McIntyre Paul C.
Published: May 2008

We report on multilayer x-ray reflectivity measurements of the Si–Ge interdiffusivity in epitaxial SixGe1−x∕SiyGe1−y superlattices that have an average Ge composition of 91at.%. The extracted activation enthalpy (3.20±0.2eV) is substantially smaller than that previously reported for Si-rich SiGe alloys and the interdiffusivity value at typical dopant anneal temperatures is, therefore, much larger for the Ge-rich heterostructures. The activation enthalpy for interdiffusion measured for the ⟨XGe⟩=0.91 superlattice is reasonably consistent with a linear interpolation between the recently reported value for an alloy with ⟨XGe⟩≈0.5 and that reported for self-diffusion in pure Ge.
Phasematching in semiconductor nonlinear optics by linear long-period gratings
Authors: Hayat Alex , Elor Yotam , Small Eran , Orenstein Meir
Published: May 2008

We experimentally demonstrate a phasematching technique for frequency conversion in nonlinear semiconductor structures by employing linear long-period gratings. We designed a specific semiconductor photonic device for second harmonic generation using coupled-mode equations with parameters extracted from beam propagation method simulations. Optical frequency converters were fabricated according to the design with the main feature; linear long-period weak gratings imprinted on semiconductor waveguides, providing the required photon momentum difference for matching the phases of the different-wavelength photons. The measured nonlinear conversion efficiency and its spectrum comply with our theoretical predictions.
Preparation of ortho-para ratio controlled D2 gas for muon-catalyzed fusion
Authors: Imao H. , Ishida K. , Kawamura N. , Matsuzaki T. , Matsuda Y. , Toyoda A. , Strasser P. , Iwasaki M. , Nagamine K.
Published: May 2008

A negative muon in hydrogen targets, e.g., D2 or D–T mixture, can catalyze nuclear fusions following a series of atomic processes involving muonic hydrogen molecular formation (muon-catalyzed fusion, μCF). The ortho-para state of D2 is a crucial parameter not only for enhancing the fusion rate but also to precisely investigate various muonic atom processes. We have developed a system for controlling and measuring the ortho-para ratio of D2 gas for μCF experiments. We successfully collected para-enriched D2 without using liquid-hydrogen coolant. Ortho-enriched D2 was also obtained by using a catalytic conversion method with a mixture of chromium oxide and alumina. The ortho-para ratio of D2 gas was measured with a compact Raman spectroscopy system. We produced large volume (5–30l at STP), high-purity (less than ppm high-Z contaminant) D2 targets with a wide range of ortho-para ratios (ortho 20%–99%). By using the ortho-para controlled D2 in μCF experiments, we observed the dependence of μCF phenomena on the ortho-para ratio.
A broadband Fourier transform microwave spectrometer based on chirped pulse excitation
Authors: Brown Gordon G. , Dian Brian C. , Douglass Kevin O. , Geyer Scott M. , Shipman Steven T. , Pate Brooks H.
Published: May 2008

Designs for a broadband chirped pulse Fourier transform microwave (CP-FTMW) spectrometer are presented. The spectrometer is capable of measuring the 7–18GHz region of a rotational spectrum in a single data acquisition. One design uses a 4.2Gsamples∕s arbitrary waveform generator (AWG) to produce a 1μs duration chirped pulse with a linear frequency sweep of 1.375GHz. This pulse is sent through a microwave circuit to multiply the bandwidth of the pulse by a factor of 8 and upconvert it to the 7.5–18.5GHz range. The chirped pulse is amplified by a traveling wave tube amplifier and broadcast inside the spectrometer by using a double ridge standard gain horn antenna. The broadband molecular free induction decay (FID) is received by a second horn antenna, downconverted, and digitized by a 40Gsamples∕s (12GHz hardware bandwidth) digital oscilloscope. The second design uses a simplified pulse generation and FID detection scheme, employing current state-of-the-art high-speed digital electronics. In this spectrometer, a chirped pulse with 12GHz of bandwidth is directly generated by using a 20Gsamples∕s AWG and upconverted in a single step with an ultrabroadband mixer. The amplified molecular emission is directly detected by using a 50Gsamples∕s digital oscilloscope with 18GHz bandwidth. In both designs, fast Fourier transform of the FID produces the frequency domain rotational spectrum in the 7–18GHz range. The performance of the CP-FTMW spectrometer is compared to a Balle–Flygare–type cavity-FTMW spectrometer. The CP-FTMW spectrometer produces an equal sensitivity spectrum with a factor of 40 reduction in measurement time and a reduction in sample consumption by a factor of 20. The CP-FTMW spectrometer also displays good intensity accuracy for both sample number density and rotational transition moment. Strategies to reduce the CP-FTMW measurement time by another factor of 90 while simultaneously reducing the sample consumption by a factor of 30 are demonstrated.
Structural and morphological properties of GaN buffer layers grown by ammonia molecular beam epitaxy on SiC substrates for AlGaN/GaN high electron mobility transistors
Authors: Corrion A. L. , Poblenz C. , Wu F. , Speck J. S.
Published: May 2008

The impact of growth conditions on the surface morphology and structural properties of ammonia molecular beam epitaxy GaN buffers layers on SiC substrates was investigated. The threading dislocation (TD) density was found to decrease with decreasing NH3:Ga flux ratio, which corresponded to an increase in surface roughness and reduction in residual compressive lattice mismatch stress. Furthermore, the dislocation density and compressive stress decreased for increasing buffer thickness. TD inclination was proposed to account for these observations. Optimized surface morphologies were realized at high NH3:Ga flux ratios and were characterized by monolayer-high steps, spiral hillocks, and pyramidal mounds, with rms roughness of ∼1.0 nm over 2×2 μm2 atomic force microscopy images. Smooth surface morphologies were realized over a large range of growth temperatures and fluxes, and growth rates of up to 1 μm/h were achieved. TD densities in the buffers as low as 3×109 cm−2 were demonstrated. These buffers were highly insulating and were used in recently reported AlGaN/GaN HEMTs with power densities of >11 W/mm at 4 and 10 GHz.
Magnetic behavior of Ni nanoparticles with high disordered atomic structure
Authors: Nunes W. C. , De Biasi E. , Meneses C. T. , Knobel M. , Winnischofer H. , Rocha T. C. R. , Zanchet D.
Published: May 2008

This report concerns the magnetic properties of colloidal Ni nanoparticles (NPs) obtained by chemical reduction of Ni(II) salt in an organic solvent. The NPs present a complex and disordered atomic structure, where small clusters of a few Ni atoms appear to coexist within each NP. These NPs exhibit interesting magnetic properties, with a low temperature ferromagnetic order followed by a transition from ferromagnetic to a “spin-glass-like” state as the temperature decreases. The results are discussed considering the role of the atomic ordering of the NPs on the corresponding magnetic behavior.
Mechanism of flexural resonance frequency shift of a piezoelectric microcantilever sensor during humidity detection
Authors: Zhu Qing , Shih Wan Y. , Shih Wei-Heng
Published: May 2008

We have examined the flexural resonance frequency shift of a piezoelectric microcantilever sensor (PEMS) during humidity detection and have shown that the flexural resonance frequency shift of the PEMS during detection was a result of Young’s modulus change of its piezoelectric layer. Because of the piezoelectric layer’s Young’s modulus change, the PEMS flexural resonance frequency shift was more than 300 times larger than could be accounted for by mass loading.
Inkjet printed polymer light-emitting devices fabricated by thermal embedding of semiconducting polymer nanospheres in an inert matrix
Authors: Fisslthaler Evelin , Sax Stefan , Scherf Ullrich , Mauthner Gernot , Moderegger Erik , Landfester Katharina , List Emil J. W.
Published: May 2008

An aqueous dispersion of semiconducting polymer nanospheres was used to fabricate polymer light-emitting devices by inkjet printing in an easy-to-apply process with a minimum feature size of 20μm. To form the devices, the electroluminescent material was printed on a nonemitting polystyrene matrix layer and embedded by thermal annealing. The process allows the printing of light-emitting thin-film devices without extensive optimization of film homogeneity and thickness of the active layer. Optical micrographs of printed device arrays, electroluminescence emission spectra, and I∕V characteristics of printed ITO/PEDOT:PSS/PS/SPN/Al devices are presented.
Bi
1.5
Zn
1.0
Nb
1.5
O
7
∕
Mn
-doped Ba0.6Sr0.4TiO3 heterolayered thin films with enhanced tunable performance
Authors: Fu Wangyang , Wang Hong , Cao Lingzhu , Zhou Yueliang
Published: May 2008

Bi 1.5 Zn 1.0 Nb 1.5 O 7 ∕ Mn -doped Ba0.6Sr0.4TiO3 heterolayered thin films were deliberately deposited on Pt∕Ti∕SiO2∕Si substrate by pulsed laser deposition and used as tunable materials. The hetero-layered films exhibit prominently enhanced tunable performance compared to previous reported dielectric/ferroelectric layered composite films, i.e., a repeatable large tunability of 55%–60% measured under dc bias field of 570kV∕cm, with temperature insensitive permittivity near room temperature, while the dielectric losses can be safely maintained below 0.5%. The results indicate that Bi1.5Zn1.0Nb1.5O7∕Mn-doped Ba0.6Sr0.4TiO3 heterolayered thin films are excellent candidates for electrically steerable applications.
A terahertz quantum cascade laser grown by low-pressure metalorganic vapor phase epitaxy
Authors: Sirigu Lorenzo , Rudra Alok , Kapon Eli , Amanti Maria I. , Scalari Giacomo , Faist Jérôme
Published: May 2008

Demonstration of a terahertz quantum cascade laser grown by a low-pressure metalorganic vapor phase epitaxy is reported. The structural analysis of the grown structure shows a very high degree of vertical uniformity and sharp interfaces. Lasing emission at λ=90μm up to 93K with a threshold current density Jth=330A∕cm2 at 7K was obtained in a structure incorporating a single plasmon waveguide.
Effects of heat dissipation on unipolar resistance switching in Pt∕NiO∕Pt capacitors
Authors: Chang S. H. , Chae S. C. , Lee S. B. , Liu C. , Noh T. W. , Lee J. S. , Kahng B. , Jang J. H. , Kim M. Y. , Kim D.-W. , Jung C. U.
Published: May 2008

We fabricated Pt∕NiO∕Pt capacitor structures with various bottom electrode thicknesses tBE and investigated their resistance switching behaviors. The capacitors with tBE⩾50nm exhibited typical unipolar resistance memory switching, while those with tBE⩽30nm showed threshold switching. This interesting phenomenon can be explained in terms of the temperature-dependent stability of conducting filaments. In particular, the thinner tBE makes dissipation of Joule heat less efficient, so the filaments will be at a higher temperature and become less stable. This study demonstrates the importance of heat dissipation in resistance random access memory.