bluuebunny/crossref_metadata_2025 huggingface dataset:
Deep earthquake rupture histories determined by global stacking of broadband P waveforms
Authors: Persh Steven E. , Houston Heidi
Published: April 2004

We conduct a systematic investigation of time histories of moment release in deep earthquakes, whose physical mechanism remains unknown. We have constructed source time functions (STFs) of 111 large deep earthquakes (depth ≥100 km and Mw ≥ 6.4) by stacking P waveforms from broadband seismograms recorded by the Global Seismographic Network. Aligning and stacking waveforms cancels noise and allows us to identify the rupture initiation and termination times accurately. Each STF is scaled to a reference moment of 1019 N m, using the duration‐moment relation τ ∝ M01/3. In order to investigate depth dependence of the STFs, we bin them into three depth ranges, 100–350 km, 350–550 km, and deeper than 550 km, based on physical properties of the mantle and the distribution of the data. We infer a change in character near 550 km. Earthquakes deeper than about 550 km are shorter, have simpler time functions, and are more uniform in their characteristics. Further, we find longer than expected scaled durations and greater complexity in the 350–550 km depth range. The scaled durations of the 350–550 km earthquakes do not decrease with depth as 1/VS, instead possessing a slightly longer average scaled duration than those 100–350 km deep. We further categorize the earthquakes by subduction zone and find a similar depth dependence within individual zones. Finally, the events that have achieved highest moment rate in the first 1–2 s after initiation tend to be deeper and/or larger events, the latter suggesting that dynamic rupture propagation affects the final size of the earthquake. The depth dependence of duration and complexity suggests more complicated rupture histories between 350 and 550 km and a possible change in the physical mechanism of rupture at about 550 km.
Three‐dimensional numerical simulation of M2 internal tides in the East China Sea
Authors: Niwa Yoshihiro , Hibiya Toshiyuki
Published: April 2004

The East China Sea and adjacent seas are one of the most significant generation regions of the M2 internal tide in the world's oceans. In the present study, we investigate the distribution and energetics of the M2 internal tide around the continental shelf edge in the East China Sea using a three‐dimensional numerical model. The numerical experiment shows that M2 internal tides are effectively generated over prominent topographic features such as the subsurface ridges in the Bashi/Luzon and Tokara Straits, the ridges along the Ryukyu Island chain, and the continental shelf slope in the East China Sea, the former particularly so. All of these topographic features are characterized by steep slopes at the depth of the thermocline onto which the M2 barotropic tide is almost normally incident. The M2 internal tides propagating away from these multiple source regions interfere with each other to create a complicated wave pattern. It is found that the calculated pattern of the M2 internal tide agrees well with TOPEX/Poseidon altimeter observations. The conversion rate from M2 barotropic to baroclinic energy over the whole analyzed model domain is estimated to be 35 GW. Roughly 10% of the energy in the M2 surface tide incident on the prominent topographic features is converted to the M2 internal tide, although about half of the M2 internal tidal energy is subject to local dissipation in close proximity to the generation sites.
A methodology for snow data assimilation in a land surface model
Authors: Sun Chaojiao , Walker Jeffrey P. , Houser Paul R.
Published: April 2004

Snow cover has a large influence on heat fluxes between the land and atmosphere because of its high albedo and insulating thermal properties. Hence accurate snow representation in coupled land‐ocean‐atmosphere global climate models has the potential to greatly increase prediction accuracy. To this end, a one‐dimensional extended Kalman filter analysis scheme has been developed to assimilate observed snow water equivalent into the NASA Seasonal‐to‐Interannual Prediction Project (NSIPP) catchment‐based land surface model. This study presents the results from a set of data assimilation “twin” experiments using an uncoupled version of the land surface model. First, “true” snow states are generated by spinning‐up the land surface model for 1987 using an observation‐constrained version of the European Centre for Medium‐Range Weather Forecasts (ECMWF) 15‐year Re‐Analysis (ERA‐15) data set for atmospheric forcing. A degraded 1987 simulation was then made by initializing the model with no snow on 1 January 1987. A third simulation assimilated the synthetically generated snow water equivalent “observations” from the true simulation into the degraded simulation once a day. This study illustrates that by assimilating snow water equivalent observations, which are readily available from remote sensing satellites, other state variables (i.e., snow depth and temperature) can be retrieved and effects of poor initial conditions removed. Runoff and atmospheric flux predictions are also improved.
Sunlight transmission through desert dust and marine aerosols: Diffuse light corrections to Sun photometry and pyrheliometry
Authors: Russell P. B. , Livingston J. M. , Dubovik O. , Ramirez S. A. , Wang J. , Redemann J. , Schmid B. , Box M. , Holben B. N.
Published: April 2004

Desert dust and marine aerosols are receiving increased scientific attention because of their prevalence on intercontinental scales and their potentially large effects on Earth radiation, climate, other aerosols, clouds, and precipitation. The relatively large size of dust and marine aerosol particles produces scattering phase functions that are strongly forward peaked. Hence Sun photometry and pyrheliometry of these aerosols are more subject to diffuse light errors than is the case for smaller aerosols. We quantify these diffuse light effects for common Sun photometer and pyrheliometer fields of view (FOV), using data on dust and marine aerosols from (1) Aerosol Robotic Network (AERONET) measurements of sky radiance and solar beam transmission and (2) in situ measurements of aerosol layer size distribution and chemical composition. Accounting for particle nonsphericity is important when deriving dust size distribution from both AERONET and in situ aerodynamic measurements. We obtain correction factors that can be applied to Sun photometer or pyrheliometer results for aerosol optical depth (AOD) or direct beam transmission. The corrections are negligible (less than ∼1% of AOD) for Sun photometers with narrow FOV (half‐angle η < ∼1°), but they can be as large as 10% of AOD at 354 nm wavelength for Sun photometers with η = 1.85°. For pyrheliometers (which can have η up to ∼2.8°), corrections can be as large as 16% at 354 nm. AOD correction factors are well correlated with AOD wavelength dependence (hence Ångström exponent). We provide best fit equations for determining correction factors from Ångström exponents of uncorrected AOD spectra, and we demonstrate their application to vertical profiles of multiwavelength AOD.
Iron oxides and light absorption by pure desert dust: An experimental study
Authors: Alfaro S. C. , Lafon S. , Rajot J. L. , Formenti P. , Gaudichet A. , Maillé M.
Published: April 2004

Theoretical computations based on Mie theory indicate that absorption of light by desert dust aerosols should be highly sensitive to their content in iron oxides (hematite, goethite, etc.). A selective extraction method that has been developed recently now allows quantification of these minerals in aerosol samples less than 500 μg in mass. Thus it is now possible to assess experimentally the part played by iron oxide minerals on dust absorption properties. In this paper we present an adaptation of Bond et al.'s [1999] method for measuring mineral dust mass absorption efficiencies and deriving single scattering albedo values at two wavelengths (325 and 660 nm). It consists in measuring simultaneously the aerosol mass concentration with a TEOM microbalance, its scattering properties in the visible spectrum with a 3 wavelength nephelometer, and attenuation at the 2 aforementioned λ with a dual‐wavelength aethalometer. At first the method is applied to nonabsorbing (iron oxide‐free) aerosols in order to check the magnitude of the “apparent absorption” due to scattering artifacts. In good agreement with Bond et al.'s results for visible wavelengths, it is found that 2% of scattering is misinterpreted as absorption. This proportion is also found to be practically insensitive to the aerosol size distribution. After these preliminary measurements the method is applied to aerosols generated by shaking three natural soil samples collected in one of the main Chinese dust source (Gobi desert), in northern Sahara (Tunisia), and in the Sahel (Niger). For these aerosols, mass absorption efficiencies are found to range between 10−2 and 2 10−2 m2 per gram of aerosol at 660 nm and to increase linearly with the iron oxide content at the rate of 0.56 m2 per gram of iron oxide. Owing to the larger absorbing potential of iron oxides at short wavelengths, mass absorption efficiencies at 325 nm are about 6 times larger than at 660 nm. At this last wavelength the single scattering albedo (SSA) is found to decrease from 0.97 for Chinese and Tunisian aerosols to 0.95 for the Niger one that also happens to have the largest iron oxide content (6.5% in mass). At 325 nm the SSA is much lower for the three aerosols (∼0.80) than at 660 nm. These values are similar to recent results obtained close to major mineral dust sources by inversion of Sun photometer or satellite data. Finally, simple computations performed for conditions that prevail at regional scale in the vicinity of important dust sources show that, even when mineral dust is mixed with strongly absorbent particles such as black carbon (BC), the effect of iron oxides on light absorption is in the same order of magnitude as the one of BC.
Challenges Facing the U.S. Space Weather Public‐Private Sector Partnership
Authors: Fisher Genene
Published: April 2004

America's reliance on technological systems that are vulnerable to space weather is growing at a rapid pace. Because such vital everyday technology as electric power grids, satellites, and navigation and communication systems are affected by space weather, it is essential to have the best possible space weather services. Although both the federal government and the private sector provide the bulk of currently available space weather products and services, a partnership between the two has been slow to develop and currently faces several challenges.
TOMS‐derived erythemal irradiance versus measurements at the stations of the Argentine UV Monitoring Network
Authors: Cede Alexander , Luccini Eduardo , Nuñez Liliana , Piacentini Rubén D. , Blumthaler Mario , Herman Jay R.
Published: April 2004

The major factors causing differences between satellite‐derived and ground‐based ultraviolet (UV) erythemal irradiances and doses are discussed. Measurements totaling more than 4700 days during 1997–1999 were obtained at 8 stations (22°S–64°S) of the Argentine UV Monitoring Network. The satellite retrieval uses radiative transfer calculations for cloud‐ and aerosol‐free conditions multiplied by correction factors for clouds and aerosols. Key parameters are total ozone, cloud optical depth, and surface albedo derived from Total Ozone Mapping Spectrometer (TOMS). When no aerosol correction is applied, systematic differences of satellite‐derived erythemal irradiance relative to ground‐based measurements amount to +1% at a tropical high‐altitude Andean location, +10% at stations in the central Pampas, +5% at southern Patagonian sites, and −7% at the southernmost continental and Antarctic stations with varying snow cover. When an aerosol correction is applied by estimating “minimum” and “maximum” aerosol loading, the systematic differences are within ±10% for all “snow‐free” stations. To reduce the differences at places with varying snow conditions, an “average surface‐albedo climatology” must be used instead the TOMS climatology of minimum albedo. Although the statistical uncertainty of the differences increases with TOMS reflectivity, the systematic difference is independent of TOMS reflectivity for most of the stations, so on average the comparison for cloudy situations is as good as for clear‐sky conditions. The comparison for daily erythemal doses gives similar results with smaller statistical uncertainty. Measured uncertainties are in agreement with a theoretical analysis. For most locations, well‐characterized ground‐based instruments should agree with TOMS satellite estimations within 10% if aerosol corrections are known.
A receptor-like kinase from Arabidopsis thaliana is a calmodulin-binding protein
Authors: CHARPENTEAU Martine , JAWORSKI Krzysztof , RAMIREZ Bertha C. , TRETYN Andrzej , RANJEVA Raoul , RANTY Benoît
Published: April 2004

Screening a cDNA expression library with a radiolabelled calmodulin (CaM) probe led to the isolation of AtCaMRLK, a receptor-like kinase (RLK) of Arabidopsis thaliana. AtCaMRLK polypeptide sequence shows a modular organization consisting of the four distinctive domains characteristic of receptor kinases: an amino terminal signal sequence, a domain containing seven leucine-rich repeats, a single putative membrane-spanning segment and a protein kinase domain. Using truncated versions of the protein and a synthetic peptide, we demonstrated that a region of 23 amino acids, located near the kinase domain of AtCaMRLK, binds CaM in a calcium-dependent manner. Real-time binding experiments showed that AtCaMRLK interacted in vitro with AtCaM1, a canonical CaM, but not with AtCaM8, a divergent isoform of the Ca2+ sensor. The bacterially expressed kinase domain of the protein was able to autophosphorylate and to phosphorylate the myelin basic protein, using Mn2+ preferentially to Mg2+ as an ion activator. Site-directed mutagenesis of the conserved lysine residue (Lys423) to alanine, in the kinase subdomain II, resulted in a complete loss of kinase activity. CaM had no influence on the autophosphorylation activity of AtCaMRLK. AtCaMRLK was expressed in reproductive and vegetative tissues of A. thaliana, except in leaves. Disruption in the AtCaMRLK coding sequence by insertion of a DsG transposable element in an Arabidopsis mutant did not generate a discernible phenotype. The CaM-binding motif of AtCaMRLK was found to be conserved in several other members of the plant RLK family, suggesting a role for Ca2+/CaM in the regulation of RLK-mediated pathways.
A combination of both arginine- and lysine-specific gingipain activity of Porphyromonas gingivalis is necessary for the generation of the mu-oxo bishaem-containing pigment from haemoglobin
Authors: SMALLEY John W. , THOMAS Michael F. , BIRSS Andrew J. , WITHNALL Robert , SILVER Jack
Published: April 2004

The black pigment of Porphyromonas gingivalis is composed of the µ-oxo bishaem complex of Fe(III) protoporphyrin IX (µ-oxo oligomer, dimeric haem), namely [Fe(III)PPIX]2O. P. gingivalis W50 and Rgp (Arg-gingipain)- and Kgp (Lys-gingipain)-deficient mutants K1A, D7, E8 and W501 [Aduse-Opoku, Davies, Gallagher, Hashim, Evans, Rangarajan, Slaney and Curtis (2000) Microbiology 146, 1933–1940] were grown on horse blood/agar for 14 days and examined for the production of µ-oxo bishaem. µ-oxo Bishaem was detected by UV–visible, Mössbauer and Raman spectroscopies in wild-type W50 and in the black-pigmented RgpA- and RgpB-deficient mutants (W501 and D7 respectively), whereas no haem species were detected in the straw-coloured colonies of Kgp-deficient strain K1A. The dark brown pigment of the double RgpA/RgpB knockout mutant (E8) was not composed of µ-oxo bishaem, but of a high-spin monomeric Fe(III) protoporphyrin IX species (possibly a haem–albumin complex). In vitro incubation of oxyhaemoglobin with cells of the W50 strain and the RgpA- and RgpB-deficient mutants (W501 and D7) resulted in the formation of µ-oxo bishaem via methaemoglobin as an intermediate. Although the Kgp-deficient strain K1A converted oxyhaemoglobin into methaemoglobin, this was not further degraded into µ-oxo bishaem. The double RgpA/RgpB knockout was also not capable of producing µ-oxo bishaem from oxyhaemoglobin, but instead generated a haemoglobin haemichrome. Inhibition of Arg-X protease activity of W50, W501, D7 and K1A with leupeptin, under conditions where Lys-X protease activity was unaffected, prevented the production of µ-oxo bishaem from oxyhaemoglobin, but resulted in the formation of a haemoglobin haemichrome. These results show that one or both of RgpA and RgpB gingipains, in addition to the lysine-specific gingipain, is necessary for the production of µ-oxo bishaem from haemoglobin by whole cells of P. gingivalis.
Mutation of cysteine 214 in Gi1 alpha subunit abolishes its endogenous GTPase activity
Authors: WANG Yuren , TAWA Gregory , SMITH Deborah , KRISHNAMURTHY Girija , YOUNG Kathleen H.
Published: April 2004

The functional consequences of the mutation of a conserved Cys-214 in Gαi1 have been investigated. We reported herein that substitutions of Cys-214 of Gαi1 to either alanine or tryptophan abolished the intrinsic GTPase activity. Free phosphate release from [32P]GTP-bound Gαi1 C214A or [32P]GTP-bound Gαi1 C214W was at least 30-fold lower than that of the wild-type Gαi1 in single-turnover GTPase assays. Consistently, tryptic proteolysis of C214A and C214W proteins showed that they were partially protected by GTP, further confirming that the GTPase activity in both mutant proteins was impaired. Expression of C214A or C214W mutants in Chinese hamster ovary K1 cells caused significant inhibition of forskolin-stimulated adenylate cyclase activity. However, the mutations did not significantly affect the GTP[S] (guanosine 5´-[γ-[35S]thio]triphosphate)-binding activity. Both C214A and C214W mutants serve as good substrates for pertussis toxin-catalysed ADP ribosylation, indicating that they interact well with βγ subunits. Moreover, RGS4 protein, a GTPase-activating protein for Gαi1, cannot interact with Cys-214 mutants even in the presence of AlF4−, which induces the transition state of Gα. In summary, our findings suggest that C214A or C214W are GTPase-deficient mutants and can functionally serve as constitutively active forms of Gαi1 in cells.
Two novel non-cationic defensin-like antimicrobial peptides from haemolymph of the female tick, Amblyomma hebraeum
Authors: LAI Ren , LOMAS Lee O. , JONCZY Jan , TURNER Philip C. , REES Huw H.
Published: April 2004

Two non-cationic defensin-like antimicrobial peptides, named Amblyomma defensin peptide 1 and Amblyomma defensin peptide 2, were identified from the hard tick, Amblyomma hebraeum, by a combination of suppression subtractive hybridization for differentially expressed genes and proteomics. cDNA clones encoding each of these two defensin-like antimicrobial peptides were isolated from the differentially expressed cDNA library of the tick synganglia (central nervous system). The preproproteins deduced from the cDNA sequences each have 92 amino acid residues. Amblyomma defensin peptide 2 was purified from the haemolymph of fed female ticks. The purified peptide displayed antibacterial activity against Gram-negative and Gram-positive bacteria. Amblyomma defensin peptide 1 was further identified by protein chip capture combined with SELDI-TOF (surface-enhanced laser desorption/ionization–time-of-flight) MS. By screening for differentially expressed proteins, it was found that the expression of Amblyomma defensin peptide 1 was upregulated during 4 days post-feeding. Our findings firstly provide two defensin-like antimicrobial peptides that are particularly novel in being anionic, together with corresponding cDNA sequences, in hard ticks, and prove that the combination of suppression subtractive hybridization and protein profiling is a powerful method to study differentially expressed proteins, especially for organisms without available genome sequence information.
Structural and functional dissection of the adhesive domains of Plasmodium falciparum thrombospondin-related anonymous protein (TRAP)
Authors: AKHOURI Reetesh Raj , BHATTACHARYYA Arindam , PATTNAIK Priyabrata , MALHOTRA Pawan , SHARMA Amit
Published: April 2004

TRAP (thrombospondin-related anonymous protein) is a sporozoite surface protein that plays a central role in hepatocyte invasion. We have developed procedures for recombinant production of the entire ECD (extracellular domain) and A domain of TRAP using bacterial- and baculovirus-expression systems respectively. The ECD and A domain were purified to homogeneity and migrated on gel-filtration columns as non-aggregated, monomeric proteins. These adhesive modules bound to HepG2 cells in a dose-dependent and bivalent cation-independent manner. The binding of ECD and the A domain to HepG2 cells was inhibited poorly by an excess of sulphatide analogues, suggesting the presence of as yet unidentified receptors for the A domain on hepatocytes. Using surface-plasmon-resonance-based sensor technology (Biacore), we demonstrate that TRAP ECD has higher affinity for heparin (KD=40 nM) compared with the A domain (KD=79 nM). We also present a three-dimensional structure of the A domain based on the crystal structure of the homologous von Willebrand factor A1 domain. The TRAP A domain shows two spatially distinct ligand-binding surfaces. One surface on the A domain contains the MIDAS (metal-ion-dependent adhesion site) motif, where point mutations of Thr131 and Asp162 correlate with impairment of cell infectivity by sporozoites. The other surface contains a putative heparin-binding site and consists of a basic residue cluster. Our studies suggest that TRAP interacts with multiple receptors during the hepatocyte invasion process. Our results also pave the way for inclusion of these high-quality recombinant TRAP domains in subunit-based vaccines against malaria.
Complementation of the yeast deletion mutant DeltaNCE103 by members of the beta class of carbonic anhydrases is dependent on carbonic anhydrase activity rather than on antioxidant activity
Authors: CLARK Daniel , ROWLETT Roger S. , COLEMAN John R. , KLESSIG Daniel F.
Published: April 2004

In recent years, members of the β class of CAs (carbonic anhydrases) have been shown to complement ΔNCE103, a yeast strain unable to grow under aerobic conditions. The activity required for complementation of ΔNCE103 by tobacco chloroplast CA was studied by site-directed mutagenesis. E196A (Glu196→Ala), a mutated tobacco CA with low levels of CA activity, complemented ΔNCE103. To determine whether restoration of ΔNCE103 was due to residual levels of CA activity or whether it was related to previously proposed antioxidant activity of CAs [Götz, Gnann and Zimmermann (1999) Yeast 15, 855–864], additional complementation analysis was performed using human CAII, an α CA structurally unrelated to the β class of CAs to which the tobacco protein belongs. Human CAII complemented ΔNCE103, strongly arguing that CA activity is responsible for the complementation of ΔNCE103. Consistent with this conclusion, recombinant NCE103 synthesized in Escherichia coli shows CA activity, and ΔNCE103 expressing the tobacco chloroplast CA exhibits the same sensitivity to H2O2 as the wild-type strain.
Elucidation of eukaryotic elongation factor-2 contact sites within the catalytic domain of Pseudomonas aeruginosa exotoxin A
Authors: YATES Susan P. , MERRILL Allan R.
Published: April 2004

Pseudomonas aeruginosa produces the virulence factor, ETA (exotoxin A), which catalyses an ADP-ribosyltransferase reaction of its target protein, eEF2 (eukaryotic elongation factor-2). Currently, this protein–protein interaction is poorly characterized and this study was aimed at identifying the contact sites between eEF2 and the catalytic domain of ETA (PE24H, an ETA from P. aeruginosa, a 24 kDa C-terminal fragment containing a His6 tag). Single-cysteine residues were introduced into the toxin at 21 defined surface-exposed sites and labelled with the fluorophore, IAEDANS [5-(2-iodoacetylaminoethylamino)-1-napthalenesulphonic acid]. Fluorescence quenching studies using acrylamide, and fluorescence lifetime and wavelength emission maxima analyses were conducted in the presence and absence of eEF2. Large changes in the microenvironment of the AEDANS [5-(2-aminoethylamino)-1-naphthalenesulphonic acid] probe after eEF2 binding were not observed as dictated by both fluorescence lifetime and wavelength emission maxima values. This supported the proposed minimal contact model, which suggests that only small, discrete contacts occur between these proteins. As dictated by the bimolecular quenching constant (kq) for acrylamide, binding of eEF2 with toxin caused the greatest change in acrylamide accessibility (>50%) when the fluorescence label was near the active site or was located within a known catalytic loop. All mutant proteins showed a decrease in accessibility to acrylamide once eEF2 bound, although the relative change varied for each labelled protein. From these data, a low-resolution model of the toxin–eEF2 complex was constructed based on the minimal contact model with the intention of enhancing our knowledge on the mode of inactivation of the ribosome translocase by the Pseudomonas toxin.
Interactions of histatin 5 and histatin 5-derived peptides with liposome membranes: surface effects, translocation and permeabilization
Authors: den HERTOG Alice L. , SANG Harro W. WONG FONG , KRAAYENHOF Ruud , BOLSCHER Jan G. M. , HOF Wim VAN'T , VEERMAN Enno C. I. , AMERONGEN Arie V. NIEUW
Published: April 2004

A number of cationic antimicrobial peptides, among which are histatin 5 and the derived peptides dhvar4 and dhvar5, enter their target cells and interact with internal organelles. There still are questions about the mechanisms by which antimicrobial peptides translocate across the membrane. We used a liposome model to study membrane binding, translocation and membrane-perturbing capacities of histatin 5, dhvar4 and dhvar5. Despite the differences in amphipathic characters of these peptides, they bound equally well to liposomes, whereas their membrane activities differed remarkably: dhvar4 translocated at the fastest rate, followed by dhvar5, whereas the histatin 5 translocation rate was much lower. The same pattern was seen for the extent of calcein release: highest with dhvar4, less with dhvar5 and almost none with histatin 5. The translocation and disruptive actions of dhvar5 did not seem to be coupled, because translocation occurred on a much longer timescale than calcein release, which ended within a few minutes. We conclude that peptide translocation can occur through peptide–phospholipid interactions, and that this is a possible mechanism by which antimicrobial peptides enter cells. However, the translocation rate was much lower in this model membrane system than that seen in yeast cells. Thus it is likely that, at least for some peptides, additional features promoting the translocation across biological membranes are involved as well.
The RGS (regulator of G-protein signalling) and GoLoco domains of RGS14 co-operate to regulate Gi-mediated signalling
Authors: TRAVER Sabine , SPLINGARD Anne , GAUDRIAULT Georges , de GUNZBURG Jean
Published: April 2004

RGS (regulator of G-protein signalling) proteins stimulate the intrinsic GTPase activity of the α subunits of heterotrimeric G-proteins, and thereby negatively regulate G-protein-coupled receptor signalling. RGS14 has been shown previously to stimulate the GTPase activities of Gαo and Gαi subunits through its N-terminal RGS domain, and to down-modulate signalling from receptors coupled to Gi. It also contains a central domain that binds active Rap proteins, as well as a C-terminal GoLoco/G-protein regulatory motif that has been shown to act in vitro as a GDP-dissociation inhibitor for Gαi. In order to elucidate the respective contributions of the three functional domains of RGS14 to its ability to regulate Gi signalling, we generated RGS14 mutants invalidated in each of its domains, as well as truncated molecules, and assessed their effects on Gi signalling via the βγ pathway in a stable cell line ectopically expressing the Gi-coupled M2 muscarinic acetylcholine receptor (HEK-m2). We show that the RGS and GoLoco domains of RGS14 are independently able to inhibit signalling downstream of Gi. Targeting of the isolated GoLoco domain to membranes, by myristoylation/palmitoylation or Rap binding, enhances its inhibitory activity on Gi signalling. Finally, in the context of the full RGS14 molecule, the RGS and GoLoco domains co-operate to confer maximal activity on RGS14. We therefore propose that RGS14 combines the inhibition of Gi activation or coupling to receptors via its GoLoco domain with stimulation of the GTPase activity of Gαi–GTP via its RGS domain to negatively regulate signalling downstream of Gi.
Effect of hypervolaemic haemodilution on cerebral glutamate, glycerol, lactate and free radicals in heatstroke rats
Authors: CHANG Chen-Kuei , CHIU Wen-Ta , CHANG Ching-Ping , LIN Mao-Tsun
Published: April 2004

In the present study, we attempted to assess the mechanisms underlying the neuroprotective effect of hypervolaemic haemodilution in rat heatstroke. In anaesthetized rats treated with normal saline (NS) immediately after the onset of heatstroke induced by Ta (ambient temperature) of 42 °C for 88 min, followed by Ta of 24 °C for 12 min, the values for MAP (mean arterial pressure), ICP (intracranial pressure), CPP (cerebral perfusion pressure), CBF (cerebral blood blow), brain PO2 (partial pressure of O2) and striatal glutamate, glycerol, lactate/pyruvate ratio, hydroxyl radicals and neuronal damage score were 42±3 mmHg, 33±3 mmHg, 9±3 mmHg, 109±20 BPU (blood perfusion units), 6±1 mmHg, 51±7 µmol/l, 24±3 µmol/l, 124±32, 694±22% of baseline and 2.25±0.05 respectively. In animals treated with 10% albumin immediately after the onset of heatstroke (Ta of 42 °C for 88 min), the values for MAP, ICP, CPP, CBF, brain PO2 and striatal glutamate, glycerol, lactate/pyruvate ratio, hydroxyl radicals and neuronal damage score were 64±6 mmHg, 10±2 mmHg, 54±5 mmHg, 452±75 BPU, 15±2 mmHg, 3±2 µmol/l, 4±2 µmol/l, 7±3, 119±7% of baseline and 0.38±0.05 respectively. Apparently, the heatstroke-induced arterial hypotension, intracranial hypertension, cerebral hypoperfusion, cerebral ischaemia, brain hypoxia, increased levels of striatal glutamate, glycerol, lactate/pyruvate ratio and hydroxyl radicals, and increased striatal neuronal damage score values were all attenuated significantly by the induction of hypervolaemic haemodilution in rats immediately at the onset of heatstroke. These results demonstrate that the neuroprotective effect of hypervolaemic haemodilution is associated with a decrease in the elevation of glutamate, glycerol, lactate and free radicals in brain exposed to experimental heatstroke-induced cerebral ischaemia/hypoxia injury.
Effects of a Mediterranean-inspired diet on blood lipids, vascular function and oxidative stress in healthy subjects
Authors: AMBRING Anneli , FRIBERG Peter , AXELSEN Mette , LAFFRENZEN Magdalena , TASKINEN Marja-Riitta , BASU Samar , JOHANSSON Mats
Published: April 2004

Mediterranean-inspired diets have been shown to decrease cholesterol levels in patients with hypercholesterolaemia, who frequently exhibit endothelial dysfunction. The aims of the present study are to improve endothelial function by dietary intervention in healthy subjects with lipid levels representative of a Western population. Twenty-two healthy subjects (mean total cholesterol, 5.6 mmol/l) were given a Mediterranean-inspired diet rich in ω-3 fatty acids and sterol esters, but low in saturated fat, or an ordinary Swedish diet, for 4 weeks in a randomized cross-over study. The composition of the diets were: in the Swedish diet, 2090 kcal (where 1 kcal=4.184 kJ; 48% of energy from carbohydrate, 15% from protein and 36% from fat) and 19 g of fibre; in the Mediterranean-inspired diet, 1869 kcal (48% of energy from carbohydrate, 16% from protein, 34% from fat) and 40 g of fibre. After each dietary period, fasting blood lipids, insulin and glucose levels, as well as apo B (apolipoprotein B) and LDL (low-density lipoprotein) particle size, were analysed. Endothelial-dependent and -independent vasodilation was measured invasively by venous occlusion plethysmography, and arterial distensibility was assessed by echocardiography tracking. Fibrinolytic capacity across the forearm, as well as oxidative stress measured through urinary F2-isoprostane, were evaluated. Total, LDL- and apo B-cholesterol and triacylglycerol (triglyceride) concentrations were decreased by 17%, 22%, 16% and 17% respectively, after the Mediterranean-inspired diet compared with the Swedish diet (P<0.05 for all). However, no differences in plasma concentrations of insulin and glucose and LDL particle size, endothelial function, arterial distensibility, fibrinolytic capacity or oxidative stress were detected. Treatment for 4 weeks with a Mediterranean-inspired diet decreased blood lipids in healthy individuals with a low-risk profile for cardiovascular disease. This beneficial effect was not mirrored in vascular function or oxidative stress evaluation.
Effect of hyperglycaemia on glucose concentration of human nasal secretions
Authors: WOOD David M. , BRENNAN Amanda L. , PHILIPS Barbara J. , BAKER Emma H.
Published: April 2004

Glucose is not detectable in airways secretions of normoglycaemic volunteers, but is present at 1–9 mmol·l-1 in airways secretions from people with hyperglycaemia. These observations suggest the existence of a blood glucose threshold at which glucose appears in airways secretions, similar to that seen in renal and salivary epithelia. In the present study we determined the blood glucose threshold at which glucose appears in nasal secretions. Blood glucose concentrations were raised in healthy human volunteers by 20% dextrose intravenous infusion or 75 g oral glucose load. Nasal glucose concentrations were measured using modified glucose oxidase sticks as blood glucose concentrations were raised. Glucose appeared rapidly in nasal secretions once blood glucose was clamped at approx. 12 mmol·l-1 (n=6). On removal of the clamp, nasal glucose fell to baseline levels in parallel with blood glucose concentrations. An airway glucose threshold of 6.7–9.7 mmol·l-1 was identified (n=12). In six subjects with normal glucose tolerance, blood glucose concentrations rose above the airways threshold and nasal glucose became detectable following an oral glucose load. The presence of an airway glucose threshold suggests that active glucose transport by airway epithelial cells normally maintains low glucose concentrations in airways secretions. Blood glucose exceeds the airway threshold after a glucose load even in people with normal glucose tolerance, so it is likely that people with diabetes or hyperglycaemia spend a significant proportion of each day with glucose in their airways secretions.
Reversal of diuretic-induced hepatic encephalopathy with infusion of albumin but not colloid
Authors: JALAN Rajiv , KAPOOR Dharmesh
Published: April 2004

In patients with cirrhosis, dehydration induced by diuretics is a common precipitant of hepatic encephalopathy (HE), which may respond to volume expansion. The mechanism of HE in this situation is not fully understood. The present study evaluates the effect of plasma volume expansion on the severity of HE, plasma and urinary ammonia in patients with diuretic-induced HE. Fifteen patients with alcoholic cirrhosis and diuretic-induced HE of Grade 2 or more were enrolled. In eight patients, 4.5% human albumin solution (HAS) was used for volume expansion and in seven patients colloid (Gelofusine®) was used. Significant improvement of HE Grade was observed at 24 h and was sustained at 72 h (P<0.05) only in the group treated with HAS. There were similar and statistically significant reductions in plasma ammonia concentration, plasma renin activity and angiotensin II and an increase in mean arterial pressure, renal plasma flow and urinary ammonia excretion in both groups. Plasma malondialdehyde was elevated in both groups, but was reduced significantly only in the group treated with HAS. The findings of the present study show that plasma volume expansion results in significant reduction in plasma ammonia concentration, possibly through an increase in urinary ammonia excretion. This reduction in ammonia concentration translates into an improvement in mental state only in those patients treated with HAS in whom concomitant reduction in oxidative stress was observed. These data support the notion that other factors, such as oxidative stress, act as adjuncts to ammonia in the pathogenesis of diuretic-induced HE and suggest a possible role for albumin infusion in its treatment.
Serum levels of endostatin, vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) in patients with acute myocardial infarction undergoing early reperfusion therapy
Authors: SEKO Yoshinori , FUKUDA Shuichi , NAGAI Ryozo
Published: April 2004

Angiogenesis is controlled by anti-angiogenic factors as well as by angiogenic factors, such as VEGF (vascular endothelial growth factor) and HGF (hepatocyte growth factor). Endostatin, a potent endogenous angiogenesis inhibitor, is known to inhibit endothelial proliferation and suppress tumour growth. However, to date, little is known about the pathophysiology of endostatin in ischaemia/reperfusion. To investigate the mechanisms of angiogenesis induced by myocardial ischaemia/reperfusion in more detail, we studied the circulating levels of endostatin, VEGF and HGF in 17 patients with acute myocardial infarction, who underwent early reperfusion therapy. In all patients, serum endostatin, VEGF and HGF levels before reperfusion were increased significantly compared with those in 17 control subjects (endostatin, 49.2±11.7 ng/ml, but not detectable in controls; VEGF, 685.6±150.3 pg/ml compared with 173.7±33.6 pg/ml; HGF, 3638±1285 pg/ml compared with 59±13 pg/ml; values are means±S.E.M.). After reperfusion, the serum endostatin and VEGF levels decreased significantly, but still remained higher than those in control subjects (endostatin, 19.6±7.0 ng/ml; VEGF, 284.2±90.2 pg/ml). In contrast, serum HGF levels increased significantly (15 146±2230 pg/ml) after reperfusion. These data indicated that serum levels of endostatin changed in parallel with those of VEGF in response to myocardial ischaemia/reperfusion, and the marked increase in serum HGF levels after reperfusion seemed to be, at least in part, due to heparin administration. Our data offer a possible anti-endostatin therapy in patients with acute myocardial infarction to facilitate collateral vessel formation.
Inflammation and endothelial dysfunction: intimate companions in the pathogenesis of vascular disease?
Authors: SATTAR Naveed
Published: April 2004

There is increasing evidence to implicate inflammation as an important precursor of endothelial dysfunction. This mechanistic link is apparent across the entire spectrum of inflammatory status, i.e. endothelial function is apparent following acute infection, and in subjects with chronic high-grade inflammation and, perhaps most importantly, persistent low-grade inflammation. The recognition of this relationship has present therapeutic ramifications, but also requires that future longitudinal studies determining the predictive ability of endothelial function measures for vascular events should incorporate markers of inflammation as potential confounders. In this issue of Clinical Science, Fichtlscherer and co-workers describe a link between endothelial function and sPLA2 (secretory non-pancreatic type II phospholipase A2) serum activity.
Growth and properties of molecular beam epitaxially grown ferromagnetic Fe-doped TiO2 rutile films on TiO2(110)
Authors: Kim Y. J. , Thevuthasan S. , Droubay T. , Lea A. S. , Wang C. M. , Shutthanandan V. , Chambers S. A. , Sears R. P. , Taylor B. , Sinkovic B.
Published: April 2004

We have grown epitaxial Fe-doped TiO2 rutile films on rutile TiO2(110) substrates, and have explored the resulting compositional, structural, morphological and magnetic properties. Clusters of mixed TiO2 rutile and Fe3O4 form on the surface of a continuous rutile epitaxial film during growth. Room-temperature ferromagnetism is observed, and is associated with the formation of secondary phase Fe3O4 rather than a true diluted magnetic oxide semiconductor.
Optical characterization of n- and p-doped 4H–SiC by electroreflectance spectroscopy
Authors: Demir Gazi , Renfro Timothy E. , Glosser R. , Saddow S. E.
Published: April 2004

We have studied the electroreflectance (ER) spectra of n- and p-type 4H–SiC polytype samples from 3 to 6.5 eV. The fundamental band gap and higher lying critical points are measured at room temperature. For this polytype, we observe band-gap narrowing in one of the structures with higher doping concentration.
Room-temperature operation of an electrically driven terahertz modulator
Authors: Kleine-Ostmann T. , Dawson P. , Pierz K. , Hein G. , Koch M.
Published: April 2004

In this letter, we report the room-temperature operation of an electrically controlled THz modulator. The modulation is achieved by reducing the electron density in a gated two-dimensional electron gas structure, which leads to an increase in the transmitted intensity of an incident beam of THz radiation. By depleting an electron gas of density 1012 cm−2, we achieved a maximum modulation depth of 3% for a pulse of terahertz radiation covering the range of frequencies from 0.1 to 2 THz.
Toward ultrahigh-flux photovoltaic concentration
Authors: Gordon Jeffrey M. , Katz Eugene A. , Feuermann Daniel , Huleihil Mahmoud
Published: April 2004

We report experimental results with a miniature fiber-optic photovoltaic concentrator with (a) deliverable power density up to 104 suns (10 W/mm2), (b) solar cell efficiencies above 30%, (c) completely passive cooling, (d) uniform and individualized cell illumination, and (e) assembly from readily available components. Measurements include the sensitivity of the conversion efficiency of tandem III–V cells to (1) power input, (2) flux distribution, and (3) the modified spectrum from the fiber-optic concentrators. Our results augur favorably for the feasibility of such designs at concentration levels as high as thousands of suns.
One-dimensional ordered structure of α-sexithienyl on Cu(110)
Authors: Kiguchi Manabu , Entani Shiro , Saiki Koichiro , Yoshikawa Genki
Published: April 2004

We have studied atomic structures of α-sexithienyl (6T) films grown on Cu(110) by near-edge x-ray absorption fine structure (NEXAFS). A one-dimensional (1D) ordered structure of 6T with its molecular long axis parallel to the Cu[001] direction could be fabricated by deposition at 300 K and subsequent annealing at 360 K. Polarization- and azimuth-dependent NEXAFS revealed the formation process of the 1D structure and showed the molecular orientation in the in-plane direction directly. We propose a method to obtain the orientation distribution function of molecules using NEXAFS.
Piezoelectric response of engineered domains in ferroelectrics
Authors: Ahluwalia Rajeev , Lookman Turab , Saxena Avadh , Cao Wenwu
Published: April 2004

We study the formation of engineered ferroelectric domains in two dimensions based on a continuum approach that incorporates the long-range elastic and electrostatic interactions. The model is also used to simulate the piezoelectric properties of the engineered domain configurations and the response is compared with that of an analogous single domain state. The results show that the low field piezoelectric constants for the engineered configuration are very close to those obtained for the corresponding single domain state and the domain wall influence is not significant. For high fields, domain walls act as nucleation sites for an electric field induced structural transition.
Room-temperature deep-ultraviolet lasing at 241.5 nm of AlGaN multiple-quantum-well laser
Authors: Takano Takayoshi , Narita Yoshinobu , Horiuchi Akihiko , Kawanishi Hideo
Published: April 2004

Room-temperature deep-ultraviolet lasing of AlxGa1−xN multiple-quantum-well lasers with an Al composition x of 0.66 was achieved at 241.5 nm under pulsed optical pumping. The threshold pumping power was approximately 1200 kW/cm2 at room temperature. The shortest lasing wavelength was 231.8 nm at 20 K. The laser structure was grown on a high-quality AlN layer, which was grown on a 4H-SiC substrate by inserting an AlN/GaN multibuffer-layer structure between the substrate and the AlN layer. Temperature dependence of lasing wavelength was also estimated to be 0.01 and 0.03 nm/K in the temperature region from 20 to 150 K and from 160 K to room temperature, respectively. The laser cavity was made of a cleaved facet of AlGaN epitaxial layers and a SiC substrate. For this purpose, it was necessary to polish the wafer to a thickness of less than 100 μm. The optimal wafer thickness for cleaving in our experiments was 60–70 μm.
Screened-exchange determination of the optical properties of large gap insulators: CaF2
Authors: Kim Miyoung , Zhao Yu-Jun , Freeman A. J. , Mannstadt W.
Published: April 2004

Optical measurements have provided an extremely difficult challenge to existing electronic band structure calculations. Although CaF2, an important large gap insulator, has been intensively investigated, no parameter-free first-principles calculations have been done due to the well-known failure of the local density approximation (LDA) in treating excited states. Here, we present results of fully first-principles calculations of the electronic structure and optical properties of CaF2 with the self-consistent screened-exchange LDA method implemented in the highly precise full-potential linearized augmented plane wave approach. The calculated optical energy gap, 12.05 eV, is in excellent agreement with experiment (12.0±0.1 eV) and so greatly improves the LDA result (7.23 eV). The optical properties, including the imaginary part of the dielectric function and the reflectance determined ab initio with full matrix elements and no parameters, are found to be in good agreement with experiment.
Electronic structure of ZnO nanorods studied by angle-dependent x-ray absorption spectroscopy and scanning photoelectron microscopy
Authors: Chiou J. W. , Jan J. C. , Tsai H. M. , Bao C. W. , Pong W. F. , Tsai M.-H. , Hong I.-H. , Klauser R. , Lee J. F. , Wu J. J. , Liu S. C.
Published: April 2004

Angle-dependent x-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy measurements were performed to differentiate local electronic structures at the tips and sidewalls of highly aligned ZnO nanorods. The overall intensity of the O K-edge XANES spectra is greatly enhanced for small photon incident angles. In contrast, the overall intensity of the Zn K-edge XANES is much less sensitive to the photon incident angle. Both valence-band photoemission and O K-edge XANES spectra show substantial enhancement of O 2p derived states near the valence band maximum and conduction band minimum, respectively. The spatially resolved Zn 3d core level spectra from tip and sidewall regions show the lack of chemical shift. All the results consistently suggest that the tip surfaces of the highly aligned ZnO nanorods are terminated by O ions and the nanorods are oriented in the [0001̄] direction.
First principle study of core/shell structure quantum dots
Authors: Li Jingbo , Wang Lin-Wang
Published: April 2004

The electronic states of core/shell CdSe/CdS and CdSe/CdTe heterostructure quantum dots are studied by large-scale first-principles calculations. According to their natural band-offset alignments CdSe/CdS is a type-I heterostructure and CdSe/CdTe is a type-II heterostructure. We found that, the electron state changes very little, but the hole wave function in CdSe/CdS quantum dots has been localized within the core, while the hole wave function in CdSe/CdTe quantum dots is localized within the shell. The hole state in CdSe/CdTe quantum dots has drastically different characteristics as in CdSe and CdSe/CdS quantum dots. The band alignment, strain effect, and quantum confinement are all important to determine the electronic structures of these systems.