bluuebunny/crossref_metadata_2025 huggingface dataset:
Helminths parasitizing larval fish from Pantanal, Brazil
Authors: Lacerda A.C.F. , Santin M. , Takemoto R.M. , Pavanelli G.C. , Bialetzki A. , Tavernari F.C.
Published: October 2008

Fish larvae of ‘corvinas’ (Pachyurus bonariensis and Plagioscion ternetzi) from Sinhá Mariana Lagoon, Mato Grosso State, were collected from March 2000 to March 2004, in order to determine the parasitic fauna of fishes. Larvae from the two species were parasitized by the same endoparasites: Contracaecum sp. Type 2 (larvae) (Nematoda: Anisakidae) in the mesentery and Neoechinorhynchus (Neoechinorhynchus) paraguayensis (Acanthocephala: Neoechinorhynchidae) in the stomach and the terminal portion of the intestine. Statistical analysis showed that there was a significant positive correlation between the standard length of hosts and the abundance of acanthocephalans and nematodes, and that the prevalence of nematodes presented a significant positive correlation with the standard length of the two species of hosts, indicating the presence of a cumulative process of infection. The present study constitutes the first record of nematodes and acanthocephalans parasitizing larval fish, as well as the first record of endoparasites in fish larvae in Brazil. In addition, it lists a new locality and two species of hosts for Contracaecum sp. Type 2 (larva) and N. (N.) paraguayensis.
Dimensions of compact invariant sets of some expanding maps
Authors: YAYAMA YUKI
Published: October 2008

We study the Hausdorff dimension and measures of full Hausdorff dimension for a compact invariant set of an expanding non-conformal map on the torus given by an integer-valued diagonal matrix. The Hausdorff dimension of a ‘general Sierpiński carpet’ was found by McMullen and Bedford and the uniqueness of the measure of full Hausdorff dimension in some cases was proved by Kenyon and Peres. We extend these results by using compensation functions to study a general Sierpiński carpet represented by a shift of finite type. We give some conditions under which a general Sierpiński carpet has a unique measure of full Hausdorff dimension and study the properties of the unique measure.
Building language towers with Ziggurat
Authors: FISHER DAVID , SHIVERS OLIN
Published: October 2008

Ziggurat is a meta-language system that permits programmers to develop Scheme-like macros for languages with nontrivial static semantics, such as C or Java (suitably encoded in an S-expression concrete syntax). Ziggurat permits language designers to construct ‘towers’ of language levels with macros; each level in the tower may have its own static semantics, such as type systems or flow analyses. Crucially, the static semantics of the languages at two adjacent levels in the tower can be connected, allowing improved reasoning power at a higher level to be reflected down to the static semantics of the language level below. We demonstrate the utility of the Ziggurat framework by implementing higher level language facilities as macros on top of an assembly language, utilizing static semantics such as termination analysis, a polymorphic type system and higher order flow analysis.
(Non)Behavioral Economics
Authors: Güth Werner
Published: October 2008

Economic theory has evolved without paying proper attention to behavioral approaches, especially to social, economic, and cognitive psychology. This has recently been addressed by including behavioral economics courses in many doctoral study programs. Although this new development is most welcome, the typical topics of the behavioral economics courses like aversion theories and simple adaptive (learning or evolutionary) dynamics are not truly behavioral. More specifically, we question whether neoclassical repairs or game-fitting exercises as well as more or less mechanical adaptation processes qualify as behavioral approaches. To avoid criticizing without offering alternatives, we suggest some truly behavioral concepts, especially the satisficing approach.
Stratigraphy and structure of interior layered deposits in west Candor Chasma, Mars, from High Resolution Stereo Camera (HRSC) stereo imagery and derived elevations
Authors: Fueten F. , Stesky R. , MacKinnon P. , Hauber E. , Zegers T. , Gwinner K. , Scholten F. , Neukum G.
Published: October 2008

Interior layered deposits (ILDs) within western Candor Chasma were studied by mapping lithologies, measuring layer attitudes and comparing the stratigraphy of two adjacent mounds. Layering tends to dip in the same direction as the local topographic slope, although at different angles. Regionally consistent attitudes do exist, suggesting postdepositional block rotations. The stratigraphy of two adjacent mounds correlates, but the thicknesses of the units differ. Most layered material appears to have been deposited conformably, with one late major unconformity. Several fault populations are identified and correlate well with regional faults associated with the formation of Valles Marineris. The data suggest that here the ILDs predate the faulting and may be early basin fill. According to our model for ILD formation, ILDs are deposited syntectonically during early basin collapse. Subsequent subsidence of surrounding areas, accompanied by little or no sedimentation, left the early deposits as individual mounds, remnants of the former subbasins. Stratigraphic differences between mounds resulted from different subsidence rates of subbasins. A significant change in depositional environment, from depositional to a near cessation of deposition and the onset of a major erosion event, possibly coincided with the opening of the main Valles Marineris troughs. We further suggest that groundwater played an important role in the formation of sulfates. The youngest unit identified, not including surficial deposits, is likely the result of a posttectonic, regionally limited volcanic event. If basin collapse continued following the cessation of deposition, this model can also account for mounds within closed basins, such as Hebes.
Analyzing spatial data: An assessment of assumptions, new methods, and uncertainty using soil hydraulic data
Authors: Zimmermann B. , Zehe E. , Hartmann N. K. , Elsenbeer H.
Published: October 2008

Environmental scientists today enjoy an ever‐increasing array of geostatistical methods to analyze spatial data. Our objective was to evaluate several of these recent developments in terms of their applicability to real‐world data sets of the soil field‐saturated hydraulic conductivity (Ks). The intended synthesis comprises exploratory data analyses to check for Gaussian data distribution and stationarity; evaluation of robust variogram estimation requirements; estimation of the covariance parameters by least‐squares procedures and (restricted) maximum likelihood; use of the Matérn correlation function. We furthermore discuss the spatial prediction uncertainty resulting from the different methods. The log‐transformed data showed Gaussian uni‐ and bivariate distributions, and pronounced trends. Robust estimation techniques were not required, and anisotropic variation was not evident. Restricted maximum likelihood estimation versus the method‐of‐moments variogram of the residuals accounted for considerable differences in covariance parameters, whereas the Matérn and standard models gave very similar results. In the framework of spatial prediction, the parameter differences were mainly reflected in the spatial connectivity of theKsfield. Ignoring the trend component and an arbitrary use of robust estimators would have the most severe consequences in this respect. Our results highlight the superior importance of a thorough exploratory data analysis and proper variogram modeling, and prompt us to encourage restricted maximum likelihood estimation, which is accurate in estimating fixed and random effects.
Stacked gabbro units and intervening mantle: A detailed look at a section of IODP Leg 305, Hole U1309D
Authors: Suhr Guenter , Hellebrand Eric , Johnson Kevin , Brunelli Daniele
Published: October 2008

Hole U1309D (Integrated Ocean Drilling Program (IODP) Legs 304/305) penetrated 1415 m into the seafloor of the Atlantis Massif, an oceanic core complex at 30°N, Mid‐Atlantic Ridge. More than 96% of all recovered rocks are gabbroic. On the basis of a mineral chemical overview, we suggest that between ≤800 and 1100 m below sea floor (mbsf), a magmatic unit occurs, ranging from olivine gabbro and troctolite in the lower part to gabbronorite and oxide gabbro in the upper part. Below 1235 mbsf, massive gabbronorites/oxide gabbros were drilled and they may represent the roof of an underlying magmatic unit. The focus here is on the zone where both units interact and screens, totaling 50 m, of a microstructurally distinct, olivine‐rich troctolite occur. We argue that the olivine‐rich troctolite is a former mantle rock which was converted to a crust‐mantle transition zone dunite at the base of the upper magmatic unit. Later, as melts derived from the lower magmatic unit percolated through it, it was equilibrated to a more evolved chemistry and transformed to a fine‐grained, olivine‐rich troctolite. Our main arguments against a possible cumulate nature of the olivine‐rich troctolite are the lack of a systematic downhole trend in compatible elements within the olivine‐rich troctolite, its distinctly fine‐grained microstructure, the high Cr content of cpx, and its Ni‐rich olivine composition. The high NiO for a given Mg/(Mg + Fe) in the olivine‐rich troctolite can be modeled by simple equilibration of relict mantle olivine with a mildly evolved melt. Evidence for the percolation of evolved melts through the olivine‐rich troctolites are Ti‐rich, interstitial pyroxenes and, as inclusions in Cr‐spinel, highly evolved amphiboles and orthopyroxenes plus the occurrence of millimeter‐scale noritic veins. The percolation by evolved melts would also be the major difference to otherwise conceptually similar rocks from the ophiolitic crust‐mantle transition zone.
A model for the production of sulfur floc and “snowblower” events at mid‐ocean ridges
Authors: Crowell Brendan W. , Lowell Robert P. , Von Damm Karen L.
Published: October 2008

At mid‐ocean ridges following magmatic eruptions, biogenic floc emerges from the seafloor and blankets regions of the seafloor in what have been called “snowblower” events. The floc often consists of filaments of elemental sulfur, and similar byproducts have been produced by hydrogen sulfide oxidizing bacteria in the laboratory. In this paper we estimate the rate of sulfur floc production in two ways. First, we compare the flux of H2S from high temperature vents and adjacent diffuse flow near 9°50′N on the East Pacific Rise to estimate the rate at which subsurface microbes use H2S to produce elemental sulfur in the shallow crust since the 1991 eruption. Second, we use the data from laboratory experiments to provide an upper estimate of sulfur floc production during a volcanic eruption. The results suggest that that the floc observed during “snowblower” events is most likely a combination of a bloom event and floc that has been stored in the crust between eruption cycles. The calculations also suggest that a ∼1% reduction in crustal porosity would result from the microbial production and storage of sulfur floc during the 1991 to 2000 time interval.
Hydroacoustic methodology for detection, localization, and quantification of gas bubbles rising from the seafloor at gas seeps from the eastern Black Sea
Authors: Nikolovska Aneta , Sahling Heiko , Bohrmann Gerhard
Published: October 2008

Detailed acoustic investigation of bubble streams rising from the seafloor were conducted during R/V Meteor cruise M72/3a at a deep submarine hydrocarbon seep environment. The area is located offshore Georgia (eastern part of the Black Sea) at a water depth between 840 m and 870 m. The sediment echosounder Parasound DS‐3/P70 was used for detecting bubbles in the water column that causes strong backscatter in the echographs (“flares”). Employing the swath echsounder Kongsberg EM710 flares in the water column were mapped along the entire swath width of approximately 1000 m at high spatial resolution. The exact location of the flares could be extracted manually. Subsequently, the horizontally looking sonar Kongsberg digital telemetry MS1000 mounted on a remotely operated vehicle (ROV) was utilized to quantify the flux of bubbles. A model was developed that is based on the principle of finding the “acoustic mass” in order to quantify the bubble flux at various seeps. The acoustic approach from the backscatter data of the ROV sonar resulted in bubble fluxes in the range of 0.01 to 5.5 L/min (corresponding to 0.037 to 20.5 mol CH4/min) at in situ conditions (∼850 m water depth, ∼9°C). Independent flux estimations using a funnel‐shaped device showed that the acoustic model consistently produced lower values but the offset is less than 12%. Furthermore, the deviation decreased with increasing flux rates. A field of bubble streams was scanned three times from different directions in order to reveal the reproducibility of the method. Flux estimations yielded consistent fluxes of about 2 l/min (7.4 mol CH4/min) with variations of less than 10%. Although gas emissions have been found at many sites at the seafloor in a range of geological settings, the amount of escaping gas is still largely unknown. With this study presenting a novel method of quantifying bubble fluxes employing a horizontally looking sonar system, it is intended to contribute to the global effort of better constraining bubble fluxes at deep‐sea settings.
Velocity structure of upper ocean crust at Ocean Drilling Program Site 1256
Authors: Swift Stephen , Reichow Marc , Tikku Anahita , Tominaga Masako , Gilbert Lisa
Published: October 2008

We examine shipboard physical property measurements, wireline logs, and vertical seismic profiles (VSP) from Ocean Drilling Program/Integrated Ocean Drilling Program Hole 1256D in 15 Ma ocean crust formed at superfast spreading rates to investigate lateral and vertical variations in compressional velocity. In general, velocities from all methods agree. Porosity is inversely related to velocity in both the logging and laboratory data. We infer that microfracturing during drilling is minor in the upper 1 km of basement, probably due to connected pores and, thus, low effective stress. The closure of porosity to very low values coincides with the depth below which laboratory velocities diverge from logging velocities. We infer that porosity controls velocity in layer 2, lithostatic pressure controls the thickness of seismic layer 2, and the distribution of flow types determines seismic velocity in the upper 200 m of basement. In the sheeted dikes, changes in physical properties, mineralogy, and chemistry define clusters of dikes.
GRACE observes small‐scale mass loss in Greenland
Authors: Wouters B. , Chambers D. , Schrama E. J. O.
Published: October 2008

Using satellite gravity data between February 2003 and January 2008, we examine changes in Greenland's mass distribution on a regional scale. During this period, Greenland lost mass at a mean rate of 179 ± 25 Gt/yr, equivalent to a global mean sea level change of 0.5 ± 0.1 mm/yr. Rates increase over time, suggesting an acceleration of the mass loss, driven by mass loss during summer. The largest mass losses occurred along the southeastern and northwestern coast in the summers of 2005 and 2007, when the ice sheet lost 279 Gt and 328 Gt of ice respectively within 2 months. In 2007, a strong mass loss is observed during summer at elevations above 2000 m, for the first time since the start of the observations.
Whistler waves associated with magnetic reconnection
Authors: Fujimoto Keizo , Sydora Richard D.
Published: October 2008

A two‐dimensional particle‐in‐cell simulation in a large system demonstrates that whistler waves are generated and associated with magnetic reconnection. The whistlers are driven by the electron temperature anisotropy formed in the downstream region of the electron outflow, where the magnetic field is intensified due to the pileup of the field lines. The anisotropic electrons are mainly produced by the adiabatic heating in the perpendicular direction. The present results indicate no evidence that the whistler waves control the dissipation processes in the electron diffusion region, while they scatter the electrons in the pitch‐angle distribution and somewhat contribute to the electron momentum transport along the field lines. The wave properties in the present simulation are well consistent with recent Cluster observations.
A “sufficient” condition combination for rapid intensifications of tropical cyclones
Authors: Yang Ruixin , Sun Donglian , Tang Jiang
Published: October 2008

Rapid Intensifications (RI) of tropical cyclones (TCs) provide major error sources in the challenging task of TC intensity forecasting. There are many factors that affect the RI processes of TCs, and identifying the combination of conditions most favorable to RI development is very time consuming when using traditional statistical data analysis methods. Data mining techniques are implemented to the data for SHIPS (Statistical Hurricane Intensity Prediction Scheme), an operational hurricane intensity forecasting model, to identify the “optimal” RI condition combinations when the number of affecting factors is given. One such combination (high latitude, low longitude, the TC being in an intensification phase, an initial intensity far away from the maximum potential intensity, high steering layer value, and low relative eddy flux convergence) gives such a high RI probability that the combination can be considered as a sufficient condition for RI, which almost guarantees that an RI will take place.
Intermittent MHD structures and classical discontinuities
Authors: Greco A. , Chuychai P. , Matthaeus W. H. , Servidio S. , Dmitruk P.
Published: October 2008

We examine statistics of rapid spatial variations of the magnetic field in simulations of magnetohydrodynamic (MHD) turbulence, by analyzing intermittency properties, and by using classical methods for identifying discontinuities. The methods identify similar structures, and give very similar event distribution functions. When the results are scaled to the correlation length, the average waiting times agree with typically reported waiting times between solar wind discontinuities. Thus discontinuities may be related to flux tube boundaries and intermittent structures that appear spontaneously in MHD turbulence.
Eddy‐induced meridional heat transport in the ocean
Authors: Volkov Denis L. , Lee Tong , Fu Lee‐Lueng
Published: October 2008

A global ocean data synthesis product at eddy‐permitting resolution from Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) project are used to estimate the oceanic eddy heat transport. We show that in a number of locations the time‐mean eddy heat transport constitutes a considerable portion of the total time‐mean heat transport, in particular, in the tropics, in the Southern Ocean and in the Kuroshio Current. This research demonstrates that the variability of the eddy heat transport is a significant contributor to the variability of the total heat transport and globally it explains about 1/3 of its variance. Eddies are also found to explain a significant portion of the seasonal‐interannual heat transport variance.
High‐spectral resolution simulation of polarization of skylight: Sensitivity to aerosol vertical profile
Authors: Zeng Jing , Han Qingyuan , Wang Jun
Published: October 2008

A vector radiative transfer model was used in conjunction with the line‐by‐line radiative transfer model and the database of high‐resolution transmission (HITRAN) molecular absorption to simulate the degree of linear polarization of skylight in cloud‐free conditions. Differences between simulated and measured polarization data in high‐spectral resolution are found to be within 1% after aerosol scattering and gas absorptions are carefully considered. Limiting experiments are conducted at wavelengths around 0.760–0.765 μm O2‐A absorption band for the same columnar aerosol optical thickness but different aerosol profiles. Results showed that the degree of linear polarization of skylight at surface varies strongly and is sensitive to the vertical change of tropospheric aerosol mass (or extinction) as the wavelengths approach to the edge of O2‐A absorption band. However, such sensitivity is minimal at all wavelengths when the aerosol composition or single scattering properties are vertically homogeneous. This study suggests that the polarization data can be used together with radiance data to constrain the simulation of vertical distribution of aerosol composition in chemistry transport models.
Earthquakes induced by water injection at ∼3 km depth within the Rongchang gas field, Chongqing, China
Authors: Lei Xinglin , Yu Guozheng , Ma Shengli , Wen Xueze , Wang Qiang
Published: October 2008

Unwanted water, amounting more than 1 million m3, has been injected intermittently at a pumping pressure of 2.1–2.9 MPa (over hydrostatic) at 2.6–2.9 km depth within the Rongchang gas field, western Chongqing, China, since July 1988. The injections have induced more than 32,000 surface‐recorded earthquakes, including 2 of ML ≥ 5, 14 of ML ≥ 4, and more than 100 of ML ≥ 3 up until the end of 2006. We examined the epidemic‐type aftershock sequence (ETAS) model and the temporal evolution of several statistics of the earthquake sequence. The random component in the ETAS model can be considered as an indicator of fluid‐driven activity, while the rate of Omori‐law‐type aftershocks indicates stress triggering of the preceding earthquakes. We observed three distinct seismic activity phases that were coincident with different injection periods. Phase I corresponds to initial injections with low injection rate (long time interval) and shows a vast majority of Omori‐type events and only 8% externally forced activity. Phase II corresponds to a period of high injection rates and shows intense earthquake activity characterized by a high percentage (45%) of fluid‐driven earthquakes. Phase III demonstrates decreasing seismicity as a result of a lowering in the injection rate; more than 70% of earthquakes occurred randomly over time, indicating the dominance of external triggering. The physical mechanism that induced the Rongchang earthquake sequence was a change in Coulomb's failure stress caused by pore pressure diffusion and transformed from seismic slip of preceding earthquakes. A pressure increase of 2.1–2.9 MPa at the injection well is more than sufficient to induce failure within the local formations.
Fast and accurate ray‐tracing algorithms for real‐time space geodetic applications using numerical weather models
Authors: Hobiger T. , Ichikawa R. , Koyama Y. , Kondo T.
Published: October 2008

The atmospheric excess path delay is a major contributor to the error budget of space geodetic positioning applications and should therefore be reduced to the maximum possible extent. Numerical weather models are undergoing improvements with regard to their spatial resolution, which enables the compensation of troposphere propagation errors by applying corrections obtained from ray‐tracing through three‐dimensional meteorologic fields. Since in the selection of the locations of the grid points priority is given to the requirements of meteorologists rather than the facilitation of efficient ray‐tracing algorithms, we propose a method that can resample and refine the large data cubes onto regular grids using a sophisticated and fast method developed at the National Institute of Information and Communications Technology (NICT). Once these data sets are generated, ray‐tracing algorithms can be applied in order to compute atmospheric excess path delays in real time for several users using off‐the‐shelf PCs. We present three different ray‐tracing strategies and discuss their advantages and bottlenecks with regard to accuracy and data throughput.
Atmospheric consequences of cosmic‐ray variability in the extragalactic shock model
Authors: Melott Adrian L. , Krejci Alex J. , Thomas Brian C. , Medvedev Mikhail V. , Wilson Graham W. , Murray Michael J.
Published: October 2008

It has been suggested that galactic shock asymmetry induced by our galaxy's infall toward the Virgo Cluster may be a source of periodicity in cosmic‐ray exposure as the solar system oscillates normally to the galactic plane, thereby inducing an observed terrestrial periodicity in biodiversity. There are a number of plausible mechanisms by which cosmic rays might affect terrestrial biodiversity. Here we investigate one of these mechanisms, the consequent ionization and dissociation in the atmosphere, resulting in changes in atmospheric chemistry, which culminate in the depletion of ozone and a resulting increase in the dangerous solar UVB flux on the ground. We estimate the enhancement of cosmic‐ray intensity for a range of reasonable parameters of the galactic wind and galactic magnetic field, and use these to compute steady‐state atmospheric effects. At the lower end of this range, we find that the effects are far too small to be of serious consequence. At the upper end of this range, the level of ozone depletion approaches that currently experienced due to anthropogenic effects such as accumulated chlorofluorocarbons, i.e., ∼2.1% global average loss of ozone column density. We discuss some of the possible effects. While much smaller intensity than the atmospheric effects of a nearby galactic gamma‐ray burst, the duration of the effects would be about 106 times greater. Current ozone depletion is a documented stress on the biosphere; it is not clear whether its consequences would be severe if of extended duration. We conclude that, for estimates at the upper end of the reasonable range of the cosmic‐ray variability over geologic time, the mechanism of atmospheric ozone depletion may provide a small additional stress, enhancing the impact of other events. However, in order to account for large fluctuations in biodiversity correlated with cosmic‐ray flux, other mechanisms should be investigated.
Growth and collapse of a deeply eroded orogen: Insights from structural, geophysical, and geochronological constraints on the Pan‐African evolution of NE Mozambique
Authors: Viola G. , Henderson I. H. C. , Bingen B. , Thomas R. J. , Smethurst M. A. , de Azavedo S.
Published: October 2008

This paper presents results of a large multidiciplinary geological mapping project in NE Mozambique, with a focus on the structural evolution of this part of the East African Orogen (EAO). It integrates field structural studies with geophysical interpretations and presents new geochronological data. The tectonic architecture of NE Mozambique can be subdivided into five megatectonic units on the basis of lithology, structure and geochronology: unit 1, Paleoproterozoic Ponta Messuli Complex in the extreme NW corner of NE Mozambique, which represents the local NW foreland to the EAO; unit 2, a collage of Mesoproterozoic metamorphic complexes, which forms the basement to unit 3, a stack of Neoproterozoic, NW directed imbricate thrust nappes named here the “Cabo Delgado Nappe Complex” (CDNC); unit 4, restricted Neoproterozoic metasedimentary basins; and unit 5, two exotic Neoproterozoic granulite mélange complexes. The units were assembled during a long and complex history of NW directed shortening, which commenced with nappe stacking and emplacement of the CDNC over the Mesoproterozoic basement terranes toward the NW foreland. It is proposed that the CDNC and the Eastern Granulites farther north in Tanzania are remnants of Neoproterozoic volcanic arcs and microcontinents formed “outboard” of the Mesoproterozoic continent after 596 ± 11 Ma. Field and potential field geophysical data show that the nappes were folded by regional‐scale NE–SW trending folds that formed in response to a later stage of the same shortening episode and this episode gave rise to the Lurio Belt, a prominent structural feature of northern Mozambique and a key element (often as suture zone) in many Gondwana reconstructions. The Lurio Belt is here interpreted as a structure generated during folding of the CDNC during later stages of the progressive shortening event. It is, however, a repeatedly reactivated shear zone, probably at the site of an older (Mesoproterozoic?) discontinuity, with an intense pure shear deformation history. It is cored by strongly attenuated lenses of a granulitic tectonic mélange, the Ocua Complex (megatectonic unit 5) and is intruded by Late Pan‐African granitoids of the Malema Suite. The compressional phase of the orogen was postdated by NW–SE directed extension. New U‐Pb zircon and monazite dates show that extension was initiated at circa 540 Ma in the eastern Lurio Belt. It is argued that extension was the result of a major episode of orogenic collapse of the EAO, initiated by gravitational instabilities resulting from crustal thickening during the shortening phase.
DHEA-Neuroprotection and -Neurotoxicity after Transient Cerebral Ischemia in Rats
Authors: Li Zhen , Cui Shengzhong , Zhang Zhuo , Zhou Rong , Ge Yingbin , Sokabe Masahiro , Chen Ling
Published: October 2008

Dehydroepiandrosterone (DHEA) has been implicated not only to prevent N-methyl-d-aspartate (NMDA)-induced neurotoxicity but also to enhance Ca2+ influx through NMDA receptor (NMDAr). However, these DHEA effects, which would produce inconsistent outcomes about neuronal damages, are not well studied in ischemia-induced cerebral damages. Herein, we report that a single administration of DHEA (20 mg/kg) during 3 to 48 h after transient global cerebral ischemia in rats exerted neuroprotective effects such as reduction of ischemia-induced neuronal death in the hippocampal CA1 and improvement of ischemia-induced deficits in spatial learning. By contrast, at 1 h before or after ischemia, the administration of DHEA exacerbated the ischemia-induced neuronal death and learning impairment. This DHEA neurotoxicity appeared to be caused by DHEA itself, but not through its metabolite testosterone, and was inhibited by a pretreatment with the NMDAr blocker MK801 or the sigma-1 (σ1) receptor antagonist NE100. However, the DHEA neuroprotection was blocked by NE100. These results show that DHEA not only provides robust ischemic neuroprotection with a long therapeutic opportunity but also exerts neurotoxicity when administered during ischemia and early reperfusion, which points to the importance of administration timing of DHEA in the clinical treatment of brain damages by the transient brain ischemia including stroke.
The structure of degradable quantum channels
Authors: Cubitt Toby S. , Ruskai Mary Beth , Smith Graeme
Published: October 2008

Degradable quantum channels are among the only channels whose quantum and private classical capacities are known. As such, determining the structure of these channels is a pressing open question in quantum information theory. We give a comprehensive review of what is currently known about the structure of degradable quantum channels, including a number of new results as well as alternate proofs of some known results. In the case of qubits, we provide a complete characterization of all degradable channels with two dimensional output, give a new proof that a qubit channel with two Kraus operators is either degradable or anti-degradable, and present a complete description of anti-degradable unital qubit channels with a new proof. For higher output dimensions we explore the relationship between the output and environment dimensions (dB and dE, respectively) of degradable channels. For several broad classes of channels we show that they can be modeled with an environment that is “small” in the sense of ΦC. Such channels include all those with qubit or qutrit output, those that map some pure state to an output with full rank, and all those which can be represented using simultaneously diagonal Kraus operators, even in a non-orthogonal basis. Perhaps surprisingly, we also present examples of degradable channels with “large” environments, in the sense that the minimal dimension dE>dB. Indeed, one can have dE>14dB2. These examples can also be used to give a negative answer to the question of whether additivity of the coherent information is helpful for establishing additivity for the Holevo capacity of a pair of channels. In the case of channels with diagonal Kraus operators, we describe the subclasses that are complements of entanglement breaking channels. We also obtain a number of results for channels in the convex hull of conjugations with generalized Pauli matrices. However, a number of open questions remain about these channels and the more general case of random unitary channels.
Impact of quantum confinement and quantum confined Stark effect on biexciton binding energy in GaN∕AlGaN quantum wells
Authors: Stokker-Cheregi F. , Vinattieri A. , Feltin E. , Simeonov D. , Levrat J. , Carlin J.-F. , Butté R. , Grandjean N. , Gurioli M.
Published: October 2008

We report on time-resolved photoluminescence measurements carried out along the thickness gradient of two types of GaN∕AlGaN quantum wells with low Al content in the barriers (5% and 9%, respectively). A reduction of the biexciton binding energy with increasing well thickness is observed, as a result of the reduced quantum confinement and the increasing impact of the quantum confined Stark effect. In the sample with 5% Al content in the barriers, for thicknesses of the well region larger than ∼9 monolayers, the biexciton binding energy is found to be smaller than that measured for bulk GaN.
Annealing effect on the microstructure modification and tribological properties of amorphous carbon nitride films
Authors: Wang Zhou , Wang Chengbing , Wang Qi , Zhang Junyan
Published: October 2008

The influences of thermal annealing on the microstructural and tribological properties of amorphous carbon nitride films were investigated. X-ray photoelectron spectroscopy, Raman spectroscopy, and Fourier transform infrared spectrometer were utilized to characterize bond configuration and chemical state of the films. The results indicated that at low annealing temperatures (200 and 300 °C), the volatile species and surface contamination are easily dissociated without obvious bulk modification; while at high annealing temperatures (400 and 500 °C), the microstructure of carbon nitride films changed and favored a graphitization process, which indicated the growth of more graphitic film structures. The faint Raman signal of C≡N decreased with annealing temperature (TA) and completely disappeared at TA of 500 °C, indicating that nitrile bonds were thermal unstable under high temperature. Surprisingly, the tribological properties of the films showed a remarkably decreasing in friction coefficient as the TA increased; it is attributed to the graphitization of carbon nitride films during thermal annealing, which favored transfer film formation between the carbon nitride films and counterface materials. The transfer films benefit the decrease in coefficient of friction.
Electric field modulation nanospectroscopy for characterization of individual β-FeSi2 nanodots
Authors: Naruse Nobuyasu , Mera Yutaka , Nakamura Yoshiaki , Ichikawa Masakazu , Maeda Koji
Published: October 2008

Electronic structures of individual β-FeSi2 nanodots were investigated using electric field modulation spectroscopy combined with scanning tunneling microscopy (STM-EFMS) by optimizing experimental conditions to enhance the inherently small signal due to a small number of photocarriers generated in a single nanodot. The obtained STM-EFMS spectra in different schemes for electric field modulation exhibited common features around 0.73 eV, which agreed well with the indirect absorption edge of β-FeSi2 bulk crystal. Maps of the STM-EFMS signal prove that the 0.73 eV signal arises from individual nanodots with a spatial resolution of a few nanometers. Those results strongly suggest that the present β-FeSi2 nanodots are indirect semiconductors.
Improvement of light extraction from high-power flip-chip light-emitting diodes by femtosecond laser direct structuring of the sapphire backside surface
Authors: Kuna Ladislav , Haase Anja , Sommer Christian , Zinterl Ernst , Krenn Joachim R. , Wenzl Franz P. , Pachler Peter , Hartmann Paul , Tasch Stefan , Leising Günther
Published: October 2008

We report on the structuring of the backside surface of sapphire substrates in high-power flip-chip light-emitting diodes (LEDs) by femtosecond laser direct writing. Varying the laser powers has been found to affect the sizes of the inscribed patterns on a submicron scale which facilitates the control of the structure sizes with high precision. Accordingly, since on the one hand the light extraction efficiency reveals a strong dependence on pattern sizes, and on the other hand, femtosecond laser structuring provides a simple opportunity to inscribe diverse structures along the LED surfaces, LEDs with laterally controlled light extraction efficiencies can be fabricated.
Electron irradiation-induced phase transformation in α-FeSi2
Authors: Naito Muneyuki , Ishimaru Manabu , Valdez James A. , Sickafus Kurt E.
Published: October 2008

Structural changes of α-FeSi2 induced by electron beam irradiation have been investigated using transmission electron microscopy (TEM). Single crystals of Si(111) were implanted with 120 keV Fe ions at −150 °C to a fluence of 1.0×1017 /cm2, followed by thermally annealing at 350–550 °C. Cross-sectional and plan-view TEM observations revealed the formation of the metastable α-FeSi2 in the annealed samples. Under high-energy electron beam irradiation, the α-phase changed to a metastable crystalline phase whose structure is close to the CsCl structure. The phase transformation was caused mainly by displacement damage processes and suggests a low displacement energy for Fe atoms (<9 eV). To explain these observations, it was considered that vacancies in α-FeSi2 are responsible for the electron irradiation-induced phase transformation.
Correlation between the latent heats and cohesive energies of metal clusters
Authors: Starace Anne K. , Neal Colleen M. , Cao Baopeng , Jarrold Martin F. , Aguado Andrés , López José M.
Published: October 2008

Dissociation energies have been determined for Aln+ clusters (n=25–83) using a new experimental approach that takes into account the latent heat of melting. According to the arguments presented here, the cohesive energies of the solidlike clusters are made up of contributions from the dissociation energies of the liquidlike clusters and the latent heats for melting. The size-dependent variations in the measured dissociation energies of the liquidlike clusters are small and the variations in the cohesive energies of solidlike clusters result almost entirely from variations in the latent heats for melting. To compare with the measured cohesive energies, density-functional theory has been used to search for the global minimum energy structures. Four groups of low energy structures were found: Distorted decahedral fragments, fcc fragments, fcc fragments with stacking faults, and “disordered.” For most cluster sizes, the measured and calculated cohesive energies are strongly correlated. The calculations show that the variations in the cohesive energies (and the latent heats) result from a combination of geometric and electronic shell effects. For some clusters an electronic shell closing is responsible for the enhanced cohesive energy and latent heat (e.g., n=37), while for others (e.g., n=44) a structural shell closing is the cause.
Approximate treatment of higher excitations in coupled-cluster theory. II. Extension to general single-determinant reference functions and improved approaches for the canonical Hartree–Fock case
Authors: Kállay Mihály , Gauss Jürgen
Published: October 2008

The theory and implementation of approximate coupled-cluster (CC), in particular approximate CC singles, doubles, triples, and quadruples methods, are discussed for general single-determinant reference functions. While the extension of iterative approximate models to the non-Hartree–Fock case is straightforward, the generalization of perturbative approaches is not trivial. In contrast to the corresponding perturbative triples methods, there are additional terms required for non-Hartree–Fock reference functions, and there are several possibilities to derive approximations to these terms. As it turns out impossible to develop an approach that is consistent with the canonical Hartree–Fock-based theory, several new approximations have been implemented and their performance for total energies and heats of formation has been assessed. The numerical results show that the performance of the methods does not depend strongly on the approximations assumed. Furthermore, the new perturbative quadruples methods, when applied to canonical Hartree–Fock reference functions, outperform at least for absolute energies the existing ones without increasing the computational costs.
Community structures and role detection in music networks
Authors: Teitelbaum T. , Balenzuela P. , Cano P. , Buldú Javier M.
Published: October 2008

We analyze the existence of community structures in two different social networks using data obtained from similarity and collaborative features between musical artists. Our analysis reveals some characteristic organizational patterns and provides information about the driving forces behind the growth of the networks. In the similarity network, we find a strong correlation between clusters of artists and musical genres. On the other hand, the collaboration network shows two different kinds of communities: rather small structures related to music bands and geographic zones, and much bigger communities built upon collaborative clusters with a high number of participants related through the period the artists were active. Finally, we detect the leading artists inside their corresponding communities and analyze their roles in the network by looking at a few topological properties of the nodes.
Rotational spectrum and molecular properties of pyridine⋯xenon
Authors: Tang Shouyuan , Evangelisti Luca , Velino Biagio , Caminati Walther
Published: October 2008

The rotational spectra of six isotopologues of pyridine-xenon, two isotopes of the nitrogen atom (N14 and N15) in pyridine with three isotopes of the rare gas atom (X129e, X131e, and X132e) have been measured by pulsed jet Fourier transform microwave spectroscopy. The complex has a structure with the xenon atom located in the plane of symmetry perpendicular to the aromatic ring plane. Its distance from the center of mass of pyridine is 3.81 Å, and it is tilted—with respect to the c principal axis of pyridine—by 7° toward the N atom. The N14 and X131e nuclear quadrupole coupling constants have been determined for the isotopologues containing these nuclei. Information on the dynamics of the Xe van der Waals motions was obtained from the centrifugal distortion and from the changes in the planar moments of inertia in going from pyridine to pyridine⋯Xe.
Inertial effects in the nonlinear transient relaxation of rigid rodlike molecules in a strong dc electric field
Authors: Titov Serguey V. , Kalmykov Yuri P. , Coffey William T.
Published: October 2008

A method of calculation of nonlinear transient responses of an assembly of noninteracting polar linear molecules due to sudden changes in a strong external dc electric field is presented. The infinite hierarchy of differential-recurrence relations for the decay functions describing the relaxation of the system is derived by averaging the underlying inertial Langevin equation. The solution of this hierarchy is obtained in terms of matrix continued fractions. The integral relaxation time and the spectrum of the electric polarization for various nonlinear transient responses (step-on, step-off, and rapidly rotating field) are calculated for typical values of the model parameters. The nonlinear transient responses exhibit pronounced nonlinear effects due to the strong dc field. Analytical equations for the quantities of interest are presented in the overdamped limit. Furthermore, the linear response relaxation function and linear dynamic susceptibility are obtained as a particular case of a general nonlinear theory.
The organization of intrinsic computation: Complexity-entropy diagrams and the diversity of natural information processing
Authors: Feldman David P. , McTague Carl S. , Crutchfield James P.
Published: October 2008

Intrinsic computation refers to how dynamical systems store, structure, and transform historical and spatial information. By graphing a measure of structural complexity against a measure of randomness, complexity-entropy diagrams display the different kinds of intrinsic computation across an entire class of systems. Here, we use complexity-entropy diagrams to analyze intrinsic computation in a broad array of deterministic nonlinear and linear stochastic processes, including maps of the interval, cellular automata, and Ising spin systems in one and two dimensions, Markov chains, and probabilistic minimal finite-state machines. Since complexity-entropy diagrams are a function only of observed configurations, they can be used to compare systems without reference to system coordinates or parameters. It has been known for some time that in special cases complexity-entropy diagrams reveal that high degrees of information processing are associated with phase transitions in the underlying process space, the so-called “edge of chaos.” Generally, though, complexity-entropy diagrams differ substantially in character, demonstrating a genuine diversity of distinct kinds of intrinsic computation.
A new procedure for the quantitative analysis of extended x-ray absorption fine structure data in total reflection geometry
Authors: Benzi F. , Davoli I. , Rovezzi M. , d’Acapito F.
Published: October 2008

A novel code for the analysis of extended x-ray absorption fine structure (EXAFS) data collected in total reflection mode (reflEXAFS) is presented. The procedure calculates the theoretical fine structure signals appearing in the reflectivity spectrum starting from the ab initio EXAFS calculations. These signals are then used in complex structural refinement (i.e., also including multiple scattering paths) with usual fitting programs of EXAFS data. A test case consisting in the analysis of a gold film collected at different incidence angles is presented in detail.
Tunneling nanotube radio
Authors: Dragoman D. , Dragoman M.
Published: October 2008

The tunneling nanotube radio is a miniaturized radio based on a single nanotube. The tunneling nanotube radio is electrically tunable in the entire FM or AM band and is biased with batteries. These features of the tunneling nanotube radio are in contrast with previous nanoradio based on field emission, which is biased at a few hundred volts and not tunable in the entire frequency band allocated for radio stations.
The role of anisotropy in the response of the titanium alloy Ti–6Al–4V to shock loading
Authors: Millett J. C. F. , Whiteman G. , Bourne N. K. , Gray G. T.
Published: October 2008

Manganin stress gauges in lateral orientation have been used to monitor the shock response of Ti–6Al–4V when loaded either parallel to or radial to the long axis of the original bar stock studied in this investigation. Materials characterization has shown that the c-axis of the hexagonal unit cell is preferentially orientated radially to the axis of the bar. Shear strengths measured along the long axis of the bar were found to be in agreement with previous data in the literature, while strength in the radial direction was found to be significantly lower. It was also noted that the lateral stress, when measured in the radial direction, displayed a pronounced drop in the lateral stress after reaching the peak shock stress unlike the longitudinal orientation. This decrease is indicative of an increase in shear strength behind the shock front. In both instances, it is postulated that extensive deformation twinning during the early stages of deformation in the shock and thereafter c+a slip and dislocation tangling builds up over a longer time period, resulting in the higher degree of hardening noted.