bluuebunny/crossref_metadata_2025 huggingface dataset:
An acanthocephalan parasite boosts the escape performance of its intermediate host facing non-host predators
Authors: MEDOC V. , BEISEL J.-N.
Published: May 2008

Among the potential effects of parasitism on host condition, the ‘increased host abilities’ hypothesis is a counterintuitive pattern which might be predicted in complex-life-cycle parasites. In the case of trophic transmission, a parasite increasing its intermediate host's performance facing non-host predators improves its probability of transmission to an adequate, definitive host. In the present study, we investigated the cost of infection with the acanthocephalanPolymorphus minutuson the locomotor/escape performance of its intermediate host, the crustaceanGammarus roeseli. This parasite alters the behaviour of its intermediate host making it more vulnerable to predation by avian definitive hosts. We assessed the swimming speeds of gammarids using a stressful treatment and their escape abilities under predation pressure. Despite the encystment ofP. minutusin the abdomen of its intermediate host, infected amphipods had significantly higher swimming speeds than uninfected ones (increases of up to 35%). Furthermore, when interacting with the non-host crustacean predatorDikerogammarus villosus, the highest escape speeds and greatest distances covered by invertebrates were observed for parasitized animals. The altered behaviour observed among the manipulated invertebrates supported the ‘increased host abilities’ hypothesis, which has until now remained untested experimentally. The tactic of increasing the ability of infected intermediate hosts to evade potential predation attempts by non-host species is discussed.
Evolutionary conservation of actin-binding proteins inTrypanosoma cruziand unusual subcellular localization of the actin homologue
Authors: MELO L. D. B. DE , SANT'ANNA C. , REIS S. A. , LOURENÇO D. , SOUZA W. DE , LOPES U. G. , CUNHA-E-SILVA N. L.
Published: May 2008

The actin cytoskeleton controls pivotal cellular processes such as motility and cytokinesis, as well as cell-cell and cell-substrate interactions. Assembly and spatial organization of actin filaments are dynamic events regulated by a large repertoire of actin-binding proteins. This report presents the first detailed characterization of theTrypanosoma cruziactin (TcActin). Protein sequence analysis and homology modelling revealed that the overall structure ofT. cruziactin is conserved and that the majority of amino-acid changes are concentrated on the monomer surface. Immunofluorescence assays using specific polyclonal antibody against TcActin revealed numerous rounded and punctated structures spread all over the parasitic body. No pattern differences could be found between epimastigotes and trypomastigotes or amastigotes. Moreover, in detergent extracts, TcActin was localized only in the soluble fraction, indicating its presence in the G-actin form or in short filaments dissociated from the microtubule cytoskeleton. The trypanosomatid genome was prospected to identify actin-binding and actin-related conserved proteins. The main proteins responsible for actin nucleation and treadmilling in higher eukaryotes are conserved inT. cruzi.
Imaginative scrub-jays, causal rooks, and a liberal application of Occam's aftershave
Authors: Emery Nathan J. , Clayton Nicola S.
Published: May 2008

We address the claim that nonhuman animals do not represent unobservable states, based on studies of physical cognition by rooks and social cognition by scrub-jays. In both cases, the most parsimonious explanation for the results is counter to the reinterpretation hypothesis. We suggest that imagination and prospection can be investigated in animals and included in models of cognitive architecture.
Analogical apes and paleological monkeys revisited
Authors: Thompson Roger K. R. , Flemming Timothy M.
Published: May 2008

We argue that formal analogical reasoning is not a uniquely human trait but is found in chimpanzees, if not in monkeys. We also contest the claim that the relational matching-to-sample task is not exemplary of analogical behavior, and we provide evidence that symbolic-like treatment of relational information can be found in nonhuman species, a point in contention with the relational reinterpretation hypothesis.
Visuomotor delay in interceptive actions
Authors: Benguigui Nicolas , Baurès Robin , Runigo Cyrille Le
Published: May 2008

Neural delays, which are generally defined as visuomotor delays in interceptive actions, must be compensated to enable accurate timing in movement. Visuomotor delays can depend on the kind of task, the use of information, and the skill of the performer. The compensation for such delays does not necessarily require prediction or representation but can be made by an attunement of some parameters in what is called a law of control.
Prediction and postdiction: Two frameworks with the goal of delay compensation
Authors: Eagleman David M.
Published: May 2008

Although prediction is one of the key tasks of intelligent brains, it often proves impossible in an unpredictably changing world. Hence, brains often decide what happened retrospectively. This framework of postdiction, the opposite of prediction, stands as an alternative or complimentary framework to prediction. I further show how motor-sensory recalibration demonstrates delay compensation at the perceptual level.
Perception of direction is not compensated for neural latency
Authors: Krekelberg Bart
Published: May 2008

Neural activity in the middle temporal area (MT) is strongly correlated with motion perception. I analyzed the temporal relationship between the representation of direction in MT and the actual direction of a stimulus that continuously changed direction. The representation in MT lagged the stimulus by 45 msec. Hence, as far as the perception of direction is concerned, the hypothesis of lag compensation can be rejected.
Moving backward through perceptual compensation
Authors: Öğmen Haluk , Patel Saumil S. , Purushothaman Gopathy , Bedell Harold E.
Published: May 2008

In the target article Nijhawan speculates that visual perceptual mechanisms compensate for neural delays so that moving objects may be perceived closer to their physical locations. However, the vast majority of published psychophysical data are inconsistent with this speculation.
Single mechanism, divergent effects; multiple mechanisms, convergent effect
Authors: Sheth Bhavin R. , Wu Daw-An
Published: May 2008

It is commonplace for a single physiological mechanism to seed multiple phenomena, and for multiple mechanisms to contribute to a single phenomenon. We propose that the flash-lag effect should not be considered a phenomenon with a single cause. Instead, its various aspects arise from the convergence of a number of different mechanisms proposed in the literature. We further give an example of how a neuron's generic spatio-temporal response profile can form a physiological basis not only of “prediction,” but also of many of the other proposed flash-lag mechanisms, thus recapitulating a spectrum of flash-lag phenomena. Finally, in agreeing that such basic predictive mechanisms are present throughout the brain, we argue that motor prediction contributes more to biological fitness than visual prediction.
The mechanisms responsible for the flash-lag effect cannot provide the motor prediction that we need in daily life
Authors: Smeets Jeroen B. J. , Brenner Eli
Published: May 2008

The visual prediction that Nijhawan proposes cannot explain why the flash-lag effect depends on what happens after the flash. Moreover, using a visual prediction based on retinal image motion to compensate for neuronal time delays will seldom be of any use for motor control, because one normally pursues objects with which one intends to interact with ones eyes.
NONPARAMETRIC ESTIMATION OF THE DIFFUSION COEFFICIENT OF STOCHASTIC VOLATILITY MODELS
Authors: Renò Roberto
Published: May 2008

In this paper, new fully nonparametric estimators of the diffusion coefficient of continuous time models are introduced. The estimators are based on Fourier analysis of the state variable trajectory observed and on the estimation of quadratic variation between observations by means of realized volatility. The estimators proposed are shown to be consistent and asymptotically normally distributed. Moreover, the Fourier estimator can be iterated to get a fully nonparametric estimate of the diffusion coefficient in a bivariate model in which one state variable is the volatility of the other. The estimators are shown to be unbiased in small samples using Monte Carlo simulations and are used to estimate univariate and bivariate models for interest rates.
Neither Sheep nor Peacocks: T. O. Elias and Post-colonial International Law
Authors: LIM C. L.
Published: May 2008

This article takes as its starting point the characterization of T. O. Elias as a representative of a ‘weak’ form of anti-colonial scholarship. Elias had sought to show that the ancient African kingdoms had participated in international legality with European states on an equal footing. The view has arisen in contemporary scholarship that this mode of argumentation is typical of the weak strain, evincing only a continued tendency to underestimate the imperial nature of international law itself. A related criticism is that many Third World scholars like Elias view international law's claim to universality and its ability to be inclusive as relatively unproblematic concepts. This article presents two interlocking claims. First, that while Elias was persuaded by the idea of a universal legal order derived from European thought, he never accepted the European view of universality. Vitoria and Grotius had paved the way for the idea of a universal legal order, but, as Elias was consistently aware, the extension of the European law of nations to Africa and Asia in the name of universality was unaccompanied by theoretical recognition in European legal thought that such universality cannot be unilaterally achieved on specific cultural terms. Second, that Elias did not view universality as an unproblematic concept. While he considered the legal order inherited from the European law of nations never to have been universal in its application, the post-colonial legal order could in principle approximate more closely to an ideal of democratic universality. We focus on Elias's attempt to substitute the doctrinal requirement of individual, sovereign consent with majoritarian lawmaking based on democratic theory, and his faith in the machinery of the United Nations as a ‘technology’ which post-colonial states would employ to put democratic majoritarianism into practice.
A Critical Appraisal of the International Legal Tradition of Taslim Olawale Elias
Authors: GATHII JAMES THUO
Published: May 2008

This essay critically examines T. O. Elias's international legal scholarship, especially in so far as he sought to reclaim, or claim, a place in international legal history for Africa. Having found that Africa contributed to the formation of international law, Elias argued in favour of reforming its rules so that they could serve the interests of the newly independent African states. In this respect he influenced many contemporary international lawyers in Africa and elsewhere. In particular, his singling out of sovereignty as a barrier to reforming international law is shared by generations of international legal scholars who have criticized states for placing too high a premium on their sovereignty, thereby placing insuperable barriers to their acceptance of egalitarian goals, expressed by, for example, the international bill of human rights. The essay also contrasts Elias to scholars of international law who took the colonial legacy of international law as a barrier to reforming it so that it was consistent with the interests of so-called post-colonial African states.
When British Justice (in African Colonies) Points Two Ways: On Dualism, Hybridity, and the Genealogy of Juridical Negritude in Taslim Olawale Elias
Authors: TOUFAYAN MARK
Published: May 2008

Taslim Elias's scholarship on the impact of English common law on the growth of African customary law illustrates the intersectionality negotiated between ‘centre’ and ‘periphery’, universal and subaltern laws. His intellectual portrait is also useful as a heuristic device to excise the doctrines, strategies, imageries, and narratives of progress elaborated about ‘Africa’ and ‘law’. Elias decried the contempt and ignorance exhibited by colonial masters towards native customs and laws; he also vilified judicially crafted ‘repugnancy’ and ‘public policy’ doctrines as instruments of colonial policy to prevent British justice from looking both ways, by ensuring that British standards were the ‘objective’ criteria of abrogation and change. Yet he nonetheless saw these doctrines and English law as a unifying force in the emergence of a unified Nigerian legal system. This article argues that this paradox in Elias's work and his struggle against the asserted dualism between English law and African customary law must be situated in the context of the rise of an African legal consciousness or juridical Negritude, home to various political projects of nation-building, African cultural liberation, and development which strategically intersected in their unstable relationship to law and Western culture. This signals a turn to ‘hybridity’ in legal discourse and Elias's professional trajectory seeking to develop a uniform common law for Nigeria as a way to explicate the workings of this relationship, and how African law is inscribed in the interplay of cultural forces constantly (re)negotiating the boundaries of their engagement with one another. This, in turn, reveals a complex picture of mediating between the simultaneous participation of Third World intellectuals in various struggles and personal or ideological projects within African humanism, which an analysis structured around the stability of centres/peripheries conventionally distorts.
Testing Co-operation: The International Criminal Court and National Authorities
Authors: RASTAN ROD
Published: May 2008

The ICC Statute sets up a system for enforcement whereby the Court's decisions are to be effected by domestic authorities. The article explores the implications of this institutional design in terms of the legal tools at the Court's disposal and the extent to which the ICC can adjudicate issues related to state co-operation. At the same time, it examines the responsibilities assumed by all states parties under the Statute to secure compliance, including in situations where the requested national authorities are unwilling or unable to co-operate. It suggests that to be sucessful, the co-operation regime under the ICC Statute will require a dynamic set of interactions between the individual state and the collective.
A Special Tribunal for Lebanon: The UN Security Council and the Emancipation of International Criminal Justice
Authors: MÉGRET FRÉDÉRIC
Published: May 2008

Discussions on the creation of the Special Tribunal for Lebanon have focused on its impact on Lebanese sovereignty and, specifically, the fact that a Chapter VII resolution seems to bypass Lebanese democracy. Simply relying on the idea of a ‘breach of international peace and security’ to overcome these arguments is not helpful. It is more useful to locate the creation of the Tribunal within evolving international criminal justice practices. These practices are increasingly constraining the Security Council's own work rather than the contrary, as international criminal justice gradually emancipates itself from the confines of ‘international peace and security’ and becomes a logic unto itself.
The role of dietary niacin intake and the adenosine-5′-diphosphate-ribosyl cyclase enzyme CD38 in spatial learning ability: is cyclic adenosine diphosphate ribose the link between diet and behaviour?
Authors: Young Genevieve S. , Kirkland James B.
Published: May 2008

The pyridine nucleotide NAD+is derived from dietary niacin and serves as the substrate for the synthesis of cyclic ADP-ribose (cADPR), an intracellular Ca signalling molecule that plays an important role in synaptic plasticity in the hippocampus, a region of the brain involved in spatial learning. cADPR is formed in part via the activity of the ADP-ribosyl cyclase enzyme CD38, which is widespread throughout the brain. In the present review, current evidence of the relationship between dietary niacin and behaviour is presented following investigations of the effect of niacin deficiency, pharmacological nicotinamide supplementation and CD38 gene deletion on brain nucleotides and spatial learning ability in mice and rats. In young male rats, both niacin deficiency and nicotinamide supplementation significantly altered brain NAD+and cADPR, both of which were inversely correlated with spatial learning ability. These results were consistent across three different models of niacin deficiency (pair feeding, partially restricted feeding and niacin recovery). Similar changes in spatial learning ability were observed inCd38− / − mice, which also showed decreases in brain cADPR. These findings suggest an inverse relationship between spatial learning ability, dietary niacin intake and cADPR, although a direct link between cADPR and spatial learning ability is still missing. Dietary niacin may therefore play a role in the molecular events regulating learning performance, and further investigations of niacin intake, CD38 and cADPR may help identify potential molecular targets for clinical intervention to enhance learning and prevent or reverse cognitive decline.
Benthic foraminifer Mg/Ca anomalies in South Atlantic core top sediments and their implications for paleothermometry
Authors: Raitzsch Markus , Kuhnert Henning , Groeneveld Jeroen , Bickert Torsten
Published: May 2008

We used modern epibenthic foraminifer tests of Cibicidoides mundulus and Planulina wuellerstorfi from South Atlantic core top sediments in order to establish Mg/Ca‐temperature relationships for the temperature range from 0 to 15°C. We obtained the following calibrations: Mg/Ca (mmol/mol) = 0.830*exp(0.145*BWT (°C)) for P. wuellerstorfi, and Mg/Ca (mmol/mol) = 0.627*exp(0.143*BWT (°C)) for C. mundulus. However, a number of tests, especially those bathed in North Atlantic Deep Water, revealed higher Mg/Ca ratios than predicted from the calibration. Our data suggest that Δ[CO32−] of bottom water exerts a significant control on ΔMg/Ca (temperature‐corrected) of C. mundulus (ΔMg/Ca = 0.017*Δ[CO32−] − 0.14), while ΔMg/Ca of P. wuellerstorfi is more likely to be governed by TCO2 (ΔMg/Ca = −0.007*TCO2 + 15). Since both Δ[CO32−] and TCO2 are closely linked to [CO32−], it is inferred that carbonate ion acts as secondary control, after temperature, on benthic shell Mg/Ca below ∼4°C. A drop in [CO32−] by 25 μmol/kg at 4 km water depth, as suggested for the Last Glacial Maximum, would decrease Mg/Ca by up to 0.4 mmol/mol, which leads to an underestimation of bottom water temperature by ∼3.5°C. Therefore our results indicate that the Mg/Ca thermometer should be used cautiously for benthic foraminifers where changes in the carbonate chemistry are present in the paleoceanographic record.
The 26 May 2006 magnitude 6.4 Yogyakarta earthquake south of Mt. Merapi volcano: Did lahar deposits amplify ground shaking and thus lead to the disaster?
Authors: Walter T. R. , Wang R. , Luehr B.‐G. , Wassermann J. , Behr Y. , Parolai S. , Anggraini A. , Günther E. , Sobiesiak M. , Grosser H. , Wetzel H.‐U. , Milkereit C. , Sri Brotopuspito P. J. K. , Harjadi P. , Zschau J.
Published: May 2008

Indonesia is repeatedly unsettled by severe volcano‐ and earthquake‐related disasters, which are geologically coupled to the 5–7 cm/a tectonic convergence of the Australian plate beneath the Sunda Plate. On Saturday, 26 May 2006, the southern coast of central Java was struck by an earthquake at 2254 UTC in the Sultanate Yogyakarta. Although the magnitude reached only Mw = 6.4, it left more than 6,000 fatalities and up to 1,000,000 homeless. The main disaster area was south of Mt. Merapi Volcano, located within a narrow topographic and structural depression along the Opak River. The earthquake disaster area within the depression is underlain by thick volcaniclastic deposits commonly derived in the form of lahars from Mt. Merapi Volcano, which had a major influence leading to the disaster. In order to more precisely understand this earthquake and its consequences, a 3‐month aftershock measurement campaign was performed from May to August 2006. We here present the first location results, which suggest that the Yogyakarta earthquake occurred at 10–20 km distance east of the disaster area, outside of the topographic depression. Using simple model calculations taking material heterogeneity into account we illustrate how soft volcaniclastic deposits may locally amplify ground shaking at distance. As the high degree of observed damage may have been augmented by the seismic response of the volcaniclastic Mt. Merapi deposits, this work implies that the volcano had an indirect effect on the level of earthquake destruction.
Tropical cyclone variations in Louisiana, U.S.A., since the late eighteenth century
Authors: Mock Cary J.
Published: May 2008

Plentiful documentary and pre‐twentieth century instrumental data from Louisiana, U.S.A., provide a record of continuous tropical cyclones, with daily resolution dating back to the late eighteenth century. The reconstruction provided new specific information for 83 storms prior to 1872. Parts of the early and mid‐nineteenth century exhibit greater tropical cyclone and hurricane activity than at any time within the last few hundred years. A major hurricane that impacted southeast Louisiana in August 1812 is very likely the closest landfalling hurricane known to impact New Orleans. The longer temporal perspective provides insight on historical hurricane impacts and information on assessing future hurricane mitigation strategies concerning potential worst‐case scenarios.
Surface heat flow and the mantle contribution on the margins of Australia
Authors: Goutorbe Bruno , Lucazeau Francis , Bonneville Alain
Published: May 2008

We present thermal data from 473 oil exploration wells in Australia and New Zealand. Approximately 2300 bottom‐hole temperatures are corrected to form a homogeneous set along with 86 temperatures from reservoir tests. Thermal conductivity profiles are estimated from a set of geophysical well logs using a recently developed neural network approach. Retaining wells in which temperature and thermal conductivity data overlap over an interval greater than 1000 m, we estimate 10 heat flow values in the Taranaki basin of New Zealand and 270 values in the northwestern, western, and southern margins and in the intracontinental Canning basin of Australia. The values are in the range 30–80 mW m−2. As a result of several differences in the data and methods, our heat flow values are 10–20 mW m−2 lower compared to previously published estimates for the same wells in New Zealand. For Australia, our values are consistent with previously measured values and trends in the continental and marine regions. On the northwestern and southeastern margins, we interpret the variations as reflecting changes in the nature of the underlying basement. Consistent with onshore data, it is inferred that the Archean crust is depleted in radiogenic elements compared to Proterozoic regions and that recent volcanism affects the eastern Paleozoic area. After removing from surface heat flow the sediment contributions, including a permanent radiogenic heat component and a transient sedimentation effect, a simple crustal model suggests that mantle heat flow on the continental margin bordering the Pilbara craton is higher than below the craton itself. Moreover, heat flow corrected for the sediment contributions is markedly lower in the Petrel intracontinental basin than in the adjacent margin, although the crust is thinner below this latter region. As both are underlaid by the same basement, this observation may indicate that the mantle contribution is also higher below that margin. Such a higher mantle heat flow on old continental margins is consistent with experiments of fluid convection below an insulating lid and suggests that the thermal regime of the continental lithosphere never returns to its prerift state, as usually assumed by several thermomechanical models of evolution of continental margins.
Bromine counts from XRF scanning as an estimate of the marine organic carbon content of sediment cores
Authors: Ziegler Martin , Jilbert Tom , de Lange Gert J. , Lourens Lucas J. , Reichart Gert‐Jan
Published: May 2008

XRF sediment core scanning technology is increasingly used to quantify sediment composition. The overall good correlation between biophilic halogen bromine (Br) and sedimentary total organic carbon (TOC) potentially allows the fast estimation of down core TOC profiles by XRF scanning. In order to test this approach we present data from the Arabian Sea and a Mediterranean brine basin, comparing XRF core scanning Br data with discrete sample TOC analyses. Overall, Br counts and TOC show a clear correlation, except when stable carbon isotope and C/N data indicate intervals characterized by enhanced input of terrestrial organic matter. Hence, solid phase Br is exclusively associated with marine organic matter (MOC) and can be used as a direct estimate of this parameter after a calibration is established. High pore water Br in the brine core steepens the Br/TOC correlation but after salt correction shows a nearly identical gradient to that of the Arabian Sea core.
The evolution of the core‐surface flow over the last seven thousands years
Authors: Wardinski I. , Korte M.
Published: May 2008

We analyze the core‐surface flow over the last seven thousands years derived from CALS7k.2, a continuous model of the geomagnetic field and its secular variation for the period 5000 BC to 1950 AD. This model relies on indirect observations of the geomagnetic field through the sampling of natural archives (lake sediments, lavas) and archaeological artifacts. An extensive comparison between gufm1, a historical field model spanning the interval 1590 to 1990, and CALS7k.2 is carried out. While both are similar in their descriptions of the large scale core field, their agreement compares poorly in terms of secular variation. The differences are primarily caused by the different data quality used to build these models. Such a comparison is essential for assessing the reliability of the results of flow inversion. We seek instantaneous core flow solutions that are purely toroidal and tangentially geostrophic for which we can reasonably neglect the effect of magnetic diffusion. Our flow solutions suggest that the core‐surface flow undergoes different regimes of zonal flow direction, with epochs of mainly westward flow alternating with epochs of mainly eastward flow. The episodes of eastward and westward flow are robust as they are obtained for purely toroidal and tangentially geostrophic flow. The changes in the large scale zonal flow direction seem to recur with a typical period of between 540 and 1050 years. Variations in thermal and magnetic winds occurring on timescales comparable with the convective overturn of the liquid outer core could account for the observed zonal flow variations.
Doppler spreading of internal gravity waves by an inertia‐wave packet
Authors: Vanderhoff J. C. , Nomura K. K. , Rottman J. W. , Macaskill C.
Published: May 2008

Present Doppler‐spreading models for the high wave number end of atmospheric and oceanic internal wave spectra either neglect the time dependence of the background long‐wave shear entirely, or ignore time‐dependent effects in their parameterization of dissipation. Through ray tracing and numerical simulations the Doppler spreading of an idealized interaction between a short internal‐wave packet by an inertia‐wave packet is examined. The results are sufficient to show that time dependence in the long‐wave shear can make a significant difference to short‐wave behavior, and will need to be taken into account in future modeling efforts.
Objective analysis of marine winds with the benefit of the Radarsat‐1 synthetic aperture radar: A nonlinear regression framework
Authors: Danielson Richard E. , Dowd Michael , Ritchie Harold
Published: May 2008

Surface wind analyses are constructed from spaceborne synthetic aperture radar (SAR) measurements along coastal regions of eastern and western North America and collocated operational marine wind forecasts. Each analysis minimizes the error sum of squares of the wind forecast, the SAR backscatter, and wind direction that is inferred from the SAR backscatter gradient. The relative importance of the SAR wind information is defined by its expected error covariances. Parameters that define these covariances are postulated for half the analyses by comparison with an independent set of buoy observations. The remaining analyses are found to compare better with buoy observations than conventional analysis approaches. It is suggested that SAR wind information generally be weighted strongly in an analysis and that an error covariance length scale of O[10 km] is appropriate.
Horizontal lightning propagation, preliminary breakdown, and electric potential in New Mexico thunderstorms
Authors: Coleman L. M. , Stolzenburg M. , Marshall T. C. , Stanley M.
Published: May 2008

Characteristics of lightning flashes in three storms are compared to simultaneous electric field (E) measurements at various altitudes to examine three hypotheses. The first is the idea that horizontal lightning branches propagate at altitudes near potential extrema (or wells). The analyses show that horizontal lightning activity and potential extrema are coincident in time and altitude, and so are consistent with the idea that lightning moves charges into potential wells as a means of using a storm's electrostatic energy to drive a lightning flash's dielectric breakdown processes. Second, these data are used to verify the usual interpretation of breakdown polarity of lightning radiation sources detected by the Lightning Mapping Array. The third hypothesis investigated is that normal cloud‐to‐ground flashes have a period of preliminary breakdown if and only if a potential well for negative charge exists between the altitudes of flash initiation and ground. The analyses show that in 14 flashes when a low‐level well was indicated, the period of preliminary breakdown before the first return stroke lasted an average of 117 ms, considerably longer than the average lifetime of a stepped leader. In 15 flashes in which no low‐level well was indicated, the time between initiation and first return stroke averaged 15 ms.
Inferring microphysical processes occurring in mesoscale convective systems from radar measurements and isotopic analysis
Authors: Narayana Rao T. , Radhakrishna B. , Srivastava Rohit , Mohan Satyanarayana T. , Narayana Rao D. , Ramesh R.
Published: May 2008

An attempt has been made, for the first time, to effectively utilize the synergy of various approaches providing microphysical information of precipitation to study short term variations in a Mesoscale Convective System (MCS). A campaign has been conducted wherein rain samples are collected during the passage of MCSs over Gadanki, India, and simultaneously a powerful VHF radar and disdrometer have been operated to infer the characteristics of the vertical structure and rain drop size distribution (DSD) of precipitation. Besides the convection and transition rain, two distinctly different phases of the stratiform rain are identified. Evaporation of rain drops seems to be significant in both convection and stratiform portions of MCS. Observed changes in the temporal variation of the stable oxygen isotope ratios (δ18O) of precipitation are interpreted in terms of microphysical processes leading to isotopic fractionation. The pattern of variability in isotopic abundance is found to be different from convection to transition and to stratiform rain. The present analysis clearly shows that the height (or temperature) and the rain regime of condensation are of paramount importance in determining δ18O. Correlations of δ18O with rainfall integral parameters stress the need for caution in interpreting the depleted isotopic ratios are due to high rainfall and/or bigger drops.
Northward propagation of the subseasonal variability over the eastern Pacific warm pool
Authors: Jiang Xianan , Waliser Duane E.
Published: May 2008

Previous studies suggest that easterly vertical shear of summer mean flow could be a key factor in the northward propagation of the subseasonal variability (SSV) over the Asian monsoon region (e.g., Jiang et al., 2004). Analysis indicates that this same mechanism may also be dictating propagation features over the eastern Pacific (EPAC). Consistent with the presence of local easterly vertical wind shear, northward propagation of the SSV is also evident over the EPAC with a phase speed of about 0.6 deg day−1. Moreover, similar to its counterpart in the Indian Ocean, the northward propagating SSV over this region is also characterized by positive anomalies of equivalent barotropic vorticity and lower‐tropospheric specific humidity, and planetary boundary layer (PBL) convergence, to the north of the convection center. Thus, the present study provides another independent example of the essential role that easterly vertical wind shear may be playing in regulating the meridional migration of the SSV.
Transport of conservative solutes in simulated fracture networks: 2. Ensemble solute transport and the correspondence to operator‐stable limit distributions
Authors: Reeves Donald M. , Benson David A. , Meerschaert Mark M. , Scheffler Hans‐Peter
Published: May 2008

In networks where individual fracture lengths follow a fractal distribution, ensemble transport of conservative solute particles at the leading plume edge exhibit characteristics of operator‐stable densities. These densities have, as their governing equations of transport, either fractional‐order or integer‐order advection‐dispersion equations. Model selection depends on the identification of either multi‐Gaussian or operator‐stable transport regimes, which in turn depends on the power law exponent of the fracture length distribution. Low to moderately fractured networks with power law fracture length exponents less than or equal to 1.9 produce solute plumes that exhibit power law leading‐edge concentration profiles and super‐Fickian plume growth rates. For these network types, a multiscaling fractional advection‐dispersion equation (MFADE) provides a model of multidimensional solute transport where different rates of power law particle motion are defined along multiple directions. The MFADE model is parameterized by a scaling matrix to describe the super‐Fickian growth process, in which the eigenvectors correspond to primary fracture group orientations and the eigenvalues code fracture length and transmissivity. The approximation of particle clouds by a multi‐Gaussian (a subset of the operator stable) for densely fractured networks with finite variance fracture length distributions can be ascribed to the classical ADE where Fickian scaling rates pertain along orthogonal plume growth directions. Fracture networks show long‐term particle retention in low‐velocity fractures so that coupling of the equations of motion with retention models such as continuous time random walk or multirate mobile/immobile will increase accuracy near the source. Particle arrival times at exit boundaries for multi‐Gaussian plumes vary with spatial density. Generally, arrival times are faster in sparsely fractured domains where transport is governed by a few very long fractures.
Neural Stem/Progenitor Cells Promote Endothelial Cell Morphogenesis and Protect Endothelial Cells against Ischemia via HIF-1α-Regulated VEGF Signaling
Authors: Roitbak Tamara , Li Lu , Cunningham Lee Anna
Published: May 2008

Vascular cells provide a neural stem/progenitor cell (NSPC) niche that regulates expansion and differentiation of NSPCs within the germinal zones of the embryonic and adult brain under both physiologic and pathologic conditions. Here, we examined the NSPC—endothelial cell (NSPC/EC) interaction under conditions of ischemia, both in vitro and after intracerebral transplantation. In culture, embryonic mouse NSPCs supported capillary morphogenesis and protected ECs from cell death induced by serum starvation or by transient oxygen and glucose deprivation (OGD). Neural stem/progenitor cells constitutively expressed hypoxia-inducible factor 1α (HIF-1α) transcription factor and vascular endothelial growth factor (VEGF), both of which were increased approximately twofold after the exposure of NSPCs to OGD. The protective effects of NSPCs on ECs under conditions of serum starvation and hypoxia were blocked by pharmacological inhibitors of VEGF signaling, SU1498 and Flt-1-Fc. After intracerebral transplantation, NSPCs continued to express HIF-1α and VEGF, and promoted microvascular density after focal ischemia. These studies support a role for NSPCs in stabilization of vasculature during ischemia, mediated via HIF-1α-VEGF signaling pathways, and suggest therapeutic application of NSPCs to promote revascularization and repair after brain injury.
Opioid and chemokine receptor heterodimers: arranged marriages or dangerous liaisons?
Authors: Hébert Terence E.
Published: May 2008

Heterodimerization of GPCRs (G-protein-coupled receptors) has begun to be appreciated as a rich new vein for drug discovery. The possibility of developing modulators for different GPCRs which work at allosteric sites other than the ligand-binding site is not new, but the notion of using a dimeric receptor partner as the target for this intervention has not yet percolated into the broader industrial community. In the present article, I discuss this notion in the context of the heterodimeric δ-opioid receptor–CXCR2 chemokine receptor dimer identified by Parenty et al., in this issue of the Biochemical Journal.
MicroRNAs: role in cardiovascular biology and disease
Authors: Zhang Chunxiang
Published: May 2008

miRNAs (microRNAs) comprise a novel class of endogenous, small, non-coding RNAs that negatively regulate gene expression via degradation or translational inhibition of their target mRNAs. Recent studies have demonstrated that miRNAs are highly expressed in the cardiovascular system. Although we are currently in the initial stages of understanding how this novel class of gene regulators is involved in cardiovascular biological functions, a growing body of exciting evidence suggests that miRNAs are important regulators of cardiovascular cell differentiation, growth, proliferation and apoptosis. Moreover, miRNAs are key modulators of both cardiovascular development and angiogenesis. Consequently, dysregulation of miRNA function may lead to cardiovascular diseases. Indeed, several recent reports have demonstrated that miRNAs are aberrantly expressed in diseased hearts and vessels. Modulating these aberrantly expressed miRNAs has significant effects on cardiac hypertrophy, vascular neointimal lesion formation and cardiac arrhythmias. Identifying the roles of miRNAs and their target genes and signalling pathways in cardiovascular disease will be critical for future research. miRNAs may represent a new layer of regulators for cardiovascular biology and a novel class of therapeutic targets for cardiovascular diseases.
Advanced synthesis for advancing heterogeneous catalysis
Authors: Stair Peter C.
Published: May 2008

There are tremendous needs and opportunities for the understanding and application of heterogeneous catalysis in the solution of vexing technological problems. Nanoscale, catalytically active phases, particularly metal nanoparticles and metal oxide clusters, supported on high surface area oxides (supported catalysts) are one of the most important classes of heterogeneous catalysts. The problem of inhomogeneity and the limits it places on the understanding of catalytic chemistry has led to substantial efforts to produce more uniform catalyst systems via more synthetic control. This article highlights an approach adopted at Argonne National Laboratory for the synthesis of uniform supported metal and oxide particles.
A topos foundation for theories of physics: I. Formal languages for physics
Authors: Döring A. , Isham C. J.
Published: May 2008

This paper is the first in a series whose goal is to develop a fundamentally new way of constructing theories of physics. The motivation comes from a desire to address certain deep issues that arise when contemplating quantum theories of space and time. Our basic contention is that constructing a theory of physics is equivalent to finding a representation in a topos of a certain formal language that is attached to the system. Classical physics arises when the topos is the category of sets. Other types of theory employ a different topos. In this paper, we discuss two different types of language that can be attached to a system S. The first is a propositional language PL(S); the second is a higher-order, typed language L(S). Both languages provide deductive systems with an intuitionistic logic. The reason for introducing PL(S) is that, as shown in Paper II of the series, it is the easiest way of understanding, and expanding on, the earlier work on topos theory and quantum physics. However, the main thrust of our program utilizes the more powerful language L(S) and its representation in an appropriate topos.
Insights from first principles molecular dynamics studies toward infrared multiple-photon and single-photon action spectroscopy: Case study of the proton-bound dimethyl ether dimer
Authors: Li Xiaohu , Moore David T. , Iyengar Srinivasan S.
Published: May 2008

We have used finite temperature ab initio molecular dynamics simulations in conjunction with computation of critical quantum nuclear effects to probe the differences between single-photon argon tagged action spectral results and infrared multiple-photon dissociation experiments for a proton bound molecular ion system. We find that the principal difference between the results in these experimental techniques is essentially that of cluster temperature. The multiple-photon dissociation experiments conducted using room temperature ions reflect a larger degree of conformational freedom compared to the colder single-photon argon tagged action spectral results. Our ab initio molecular dynamics simulation techniques accurately capture the effects of conformational sampling, adequately reproduce both spectra, and can be utilized to assign the dynamically averaged finite temperature spectra.
Effect of Mn doping on the electric and dielectric properties of ZnO epitaxial films
Authors: Oshio T. , Masuko K. , Ashida A. , Yoshimura T. , Fujimura N.
Published: May 2008

The Mn doping effects on the electric and dielectric properties of ZnO epitaxial films were studied. To optimize the stoichiometry of undoped ZnO film prepared by pulsed laser deposition, we evaluated the intensity ratio of the optical emission from excited oxygen atoms (O*) and excited zinc atoms (Zn*) generated by ablating a ZnO ceramic target in plume. The leakage current of undoped ZnO film decreased with an increase of the ratio I(O777*)∕I(Zn335*). Mn doping of ZnO was also effective in decreasing the leakage current. The ZnO:4at.% Mn had a very small leakage current, eight orders of magnitude less than that of undoped ZnO. With a Mn concentration above 4at.%, on the other hand, the leakage current was increased. The activation energy in ZnO:Mn obtained from the temperature dependence of the ac conductivity revealed that oxygen vacancy was responsible for the large current at the Mn concentration below 2at.%. For the sample with the Mn concentration of 2–3at.%, dominant conduction in ZnO:Mn epitaxial films originated from the interstitial Zn. When the Mn concentration was above 4at.%, the conduction was governed by the substitution of Zn atoms in the oxygen site. Impedance analysis revealed that the origin for large resistivity of ZnO:Mn films was not the ZnO/electrode interface but the bulky part of the films.
Improvement of n-channel metal-oxide-semiconductor transistors by tensile stress despite increase in both on and subthreshold off currents
Authors: Yang Peizhen , Lau W. S. , Ng Tiong Liang , Ho V. , Loh C. H. , Toh L. F. , Liu Y. , Siah S. Y. , Chan L.
Published: May 2008

We found that tensile stress actually increases both the on current and the subthreshold off current for n-channel metal-oxide-semiconductor transistors because of an increase in mobility. Our theory is that stress engineering works because the increase in the subthreshold off current can be easily offset by a slight increase in the saturation threshold voltage, while the increase in the on current can be offset only by a much larger increase in the saturation threshold voltage. In this paper, experimental variation in the saturation threshold voltage is achieved by the statistical variation in gate length and short-channel effect. Thus, the overall effect is an improvement.
Onset of shear layer instability in flow past a cylinder
Authors: Mittal Sanjay , Kottaram Jacob J. , Kumar Bhaskar
Published: May 2008

Global stability analysis of the flow past a cylinder is carried out to determine the critical Re for the onset of shear layer instability. To suppress the wake mode that leads to von Kármán vortex shedding, flow past one-half of the cylinder is studied. The linearized perturbation equations for an incompressible flow are written in a moving frame of reference that travels with the perturbation and solved using a stabilized finite element method. The critical Re for the onset of convective instability is found to be approximately 54. Excellent agreement is observed between the results from global stability analysis and direct time integration of linearized disturbance equations. The wake and shear layer modes for a full cylinder are compared. Results are also presented for stability analysis of the time-averaged flow.
Structures and electronic properties of small FeBn (n=1–10) clusters
Authors: Yang Zhi , Xiong Shi-Jie
Published: May 2008

The geometries, stabilities, electronic properties, and magnetism of FeBn clusters up to n=10 are systematically studied with density functional theory. We find that our optimized structures of FeB2, FeB3, FeB4, and FeB5 clusters are more stable than those proposed in previous literature. The results show that it is favorable for the Fe atom to locate at the surface, not at the center of the cluster, and that FeB4 and FeB9 clusters exhibit high stability. For all the FeBn clusters studied, we find the charge transfer from Fe to B site and the coexistence of ionic and covalent bonding characteristics. The computed total magnetic moments of the lowest-energy structures oscillate with the cluster size and are quenched at n=4, 6, 8, and 10.
Structure properties of BiFeO3 films studied by micro-Raman scattering
Authors: Yang Y. , Sun J. Y. , Zhu K. , Liu Y. L. , Wan L.
Published: May 2008

BiFeO 3 (BFO) films deposited on SrTiO3 (001) substrates and on LaNiO3-coated SrTiO3 (001) substrates with different annealing ambiences of oxygen and nitrogen were studied by using micro-Raman spectroscopy and x-ray diffraction (XRD). XRD showed that the films are in single-phase with rhombohedral structure. According to the analysis of the group theory, 13 Raman-active modes, which can be classified as 4A1 and 9E modes, have been observed in the BiFeO3 films. Raman spectra along the growth direction of the BFO films in the side-view scattering geometry were performed by the Raman mapping technique. The variations of Raman shift and Raman bandwidth in different depths of the films imply the existence of residual strain along the growth direction of the BFO films. These results are very useful for the understanding of the depth dependence of the physical properties including the interface and surface structure of the BFO films.