bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrahigh-temperature metamorphism and decompression history of sapphirine granulites from Rajapalaiyam, southern India: implications for the formation of hot orogens during Gondwana assembly
Authors: TSUNOGAE T. , SANTOSH M.
Published: July 2009

Sapphirine-bearing Mg–Al granulites from Rajapalaiyam in the southern part of the Madurai Block provide critical evidence for Late Neoproterozoic–Cambrian ultrahigh-temperature (UHT) metamorphism in southern India. Poikiloblastic garnet in quartzo-feldspathic and pelitic granulites contain inclusions of fine-grained subidioblastic to xenoblastic sapphirine associated with quartz, suggesting that the rocks underwentT> 1000°C peak metamorphism. Quartz inclusions in spinel within garnet are also regarded as clear evidence for a UHT condition. Inclusions of orthopyroxene within porphyroblastic garnet in the sapphirine-bearing rocks show the highest Al2O3content of up to 10.3 wt%, suggestingT= 1050–1070°C andP= 8.5–9.5 kbar. Temperatures estimated from ternary feldspar and other geothermometers (T= 950–1000°C) further support extreme thermal metamorphism in this region. Xenoblastic spinel inclusions in sapphirine coexisting with quartz suggest that the spinel + quartz assemblage pre-dates the sapphirine + quartz assemblage, probably implying a cooling fromT~ 1050°C or an anticlockwiseP–Tpath. The FMAS reaction sapphirine + quartz + garnet → orthopyroxene + sillimanite indicates a cooling from the sapphirine + quartz stability field after the peak metamorphism. Corona textures of orthopyroxene + cordierite (± sapphirine), orthopyroxene + sapphirine + cordierite, and cordierite + spinel around garnet suggest subsequent near-isothermal decompression followed by decompressional cooling towardT= 650–750°C andP= 4.5–5.5 kbar. The sapphirine–quartz association and related textures described in this study have an important bearing on the UHT metamorphism and exhumation history of the Madurai Block, as well as on the tectonic evolution of the continental deep crust in southern India. Our study provides a typical example for extreme metamorphism associated with collisional tectonics during the Late Neoproterozoic–Cambrian assembly of the Gondwana supercontinent.
Support for Free Trade: Self-Interest, Sociotropic Politics, and Out-Group Anxiety
Authors: Mansfield Edward D. , Mutz Diana C.
Published: July 2009

Although it is widely acknowledged that an understanding of mass attitudes about trade is crucial to the political economy of foreign commerce, only a handful of studies have addressed this topic. These studies have focused largely on testing two models, both of which emphasize that trade preferences are shaped by how trade affects an individual's income. The factor endowments or Heckscher-Ohlin model posits that these preferences are affected primarily by a person's skills. The specific factors or Ricardo-Viner model posits that trade preferences depend on the industry in which a person works. We find little support for either of these models using two representative national surveys of Americans. The only potential exception involves the effects of education. Initial tests indicate that educational attainment and support for open trade are directly related, which is often interpreted as support for the Heckscher-Ohlin model. However, further analysis reveals that education's effects are less representative of skill than of individuals' anxieties about involvement with out-groups in their own country and beyond. Furthermore, we find strong evidence that trade attitudes are guided less by material self-interest than by perceptions of how the U.S. economy as a whole is affected by trade.
What Governments Maximize and Why: The View from Trade
Authors: Gawande Kishore , Krishna Pravin , Olarreaga Marcelo
Published: July 2009

Policymaking power enables governments to redistribute income to powerful interests in society. However, some governments exhibit greater concern for aggregate welfare than others. This government behavior may itself be endogenously determined by a number of economic, political, and institutional factors. Trade policy, being fundamentally redistributive, provides a valuable context in which the welfare-mindedness of governments may be empirically evaluated. This article investigates quantitatively the welfare-mindedness of governments and attempts to understand these political and institutional determinants of the differences in government behavior across countries.
Determining Trade Policy: Do Voters Hold Politicians Accountable?
Authors: Guisinger Alexandra
Published: July 2009

Models of trade policy often depend on the efficient aggregation of individual preferences. While much of the recent empirical work on trade focuses on whether domestic coalitions form along class or sectoral lines, the process of preference aggregation itself remains understudied. In democratic countries, voting is typically assumed to be an unproblematic mechanism for aggregating preferences, but such an assumption may be misleading when the salience of trade policy is low or heterogeneous throughout the electorate. Using data from a survey of 36,501 potential voters in the 2006 U.S. midterm congressional elections, this article explores the salience of trade policy for voters as a whole and for populations predicted to be most affected by changing trade patterns. The article offers an estimation of trade policy salience based on the degree to which voters held Senate incumbents accountable for their 2005 vote on the Central American Free Trade Agreement, relative to roll call votes on other issues of the day. The article finds trade policy salience to be relatively low in terms of stated importance, in voters' knowledge of their representatives' policy positions, and in its effect on voters' propensity to vote for the incumbent. The low salience of trade policy, particularly among highly affected groups, calls into question voter-driven models of trade policy.
Lone Mothers, Ethnicity and Welfare Dynamics
Authors: MOKHTAR CHRISTINA , PLATT LUCINDA
Published: July 2009

This article investigates the ethnic patterning of exit from means-tested benefits in a UK town. Lone parents in the UK face high risks of poverty and high rates of receipt of means-tested, out-of-work benefits. There has been extensive policy concern with lone parents' poverty and with potential ‘welfare dependency’. Investigation of welfare dynamics has unpacked the notion of welfare dependency, and has stimulated policy to better understand the factors associated with longer rather than shorter durations. However, within this analysis, there has been little attention paid to ethnicity. This is despite the fact that the extensive literature on the UK's minority ethnic groups has emphasised diversity in both rates of lone parenthood and risks of poverty. To date we have little understanding of ethnic variation in lone parents' welfare dynamics. Using a data set drawn from administrative records, this article analyses the chances of leaving means-tested benefit for a set of lone mothers in a single town, exploring whether there is variation by ethnic group. We find that, controlling for basic demographic characteristics, there is little evidence to suggest that ethnicity affects the chances of benefit exit, even between groups where rates of lone parenthood are very different.
Medicine and Management in English Primary Care: A Shifting Balance of Power?
Authors: SHEAFF ROD
Published: July 2009

The English NHS has been repeatedly restructured since 1991. Drawing on multiple case studies in English primary health care from 1998 to 2005 and on (other) published studies, this article uses Therborn's theory of power to make a framework analysis of how these reforms redistributed power between medicine and management in NHS primary care. Legal changes ended the GP monopoly of primary medical care provision and, with greater managerial discretion in NHS spending, allowed more diverse organisational forms of primary care provision to appear, although general practice remained predominant. Changes in managerial and professional ideologies relaxed the restrictions on managerial decisions about general practice. Re-negotiations between the medical profession and the state mostly tended to increase managerial power. Evidence-based medicine has tended to weaken the impersonal sources of medical power. On balance, these events have tended to increase managerial power over medical practice. They also suggest adjustments to Therborn's conceptualisation of power.
Concise formulae for the atmospheric correction of hemispherical thermal radiation measured near the ground surface
Authors: Kotani Ayumi , Sugita Michiaki
Published: July 2009

This paper presents the analysis of the atmospheric effects on the measurement of the thermal radiation near the ground surface. The difference of the thermal radiation L at surface and L at some height z was evaluated for various atmospheric conditions and for different sensor heights with the LOWTRAN 7 radiation transfer code. It was found that in many cases the effects of transmission of radiation primarily due to the presence of water vapor and secondarily to other minor gases and aerosols are not negligible for the upward component of thermal radiation, whereas they can be neglected for downward component. Based on the results of LOWTRAN 7 calculations, a simple regression equation of atmospheric path transmissivity τa in terms of the total water vapor w within the air layer between the surface and the sensor height and that of emittance from the air layer between the ground and the sensor height La in terms of w and temperature were obtained; these will then allow the practical estimation of τa and La from measurements of air temperature and humidity near the ground for the atmospheric correction of the upward thermal radiation measured at a certain height. This procedure can be applied to derive net radiation at the ground surface from a four‐component radiometer measurement above the ground and also to derive surface radiative temperature from pyrgeometer measurements of the upward long‐wave radiation.
Seismic modeling of multidimensional heterogeneity scales of Mallik gas hydrate reservoirs, Northwest Territories of Canada
Authors: Huang Jun‐Wei , Bellefleur Gilles , Milkereit Bernd
Published: July 2009

In hydrate‐bearing sediments, the velocity and attenuation of compressional and shear waves depend primarily on the spatial distribution of hydrates in the pore space of the subsurface lithologies. Recent characterizations of gas hydrate accumulations based on seismic velocity and attenuation generally assume homogeneous sedimentary layers and neglect effects from large‐ and small‐scale heterogeneities of hydrate‐bearing sediments. We present an algorithm, based on stochastic medium theory, to construct heterogeneous multivariable models that mimic heterogeneities of hydrate‐bearing sediments at the level of detail provided by borehole logging data. Using this algorithm, we model some key petrophysical properties of gas hydrates within heterogeneous sediments near the Mallik well site, Northwest Territories, Canada. The modeled density, and P and S wave velocities used in combination with a modified Biot‐Gassmann theory provide a first‐order estimate of the in situ volume of gas hydrate near the Mallik 5L‐38 borehole. Our results suggest a range of 528 to 768 × 106 m3/km2 of natural gas trapped within hydrates, nearly an order of magnitude lower than earlier estimates which did not include effects of small‐scale heterogeneities. Further, the petrophysical models are combined with a 3‐D finite difference modeling algorithm to study seismic attenuation due to scattering and leaky mode propagation. Simulations of a near‐offset vertical seismic profile and cross‐borehole numerical surveys demonstrate that attenuation of seismic energy may not be directly related to the intrinsic attenuation of hydrate‐bearing sediments but, instead, may be largely attributed to scattering from small‐scale heterogeneities and highly attenuate leaky mode propagation of seismic waves through larger‐scale heterogeneities in sediments.
Gas hydrate saturations estimated from fractured reservoir at Site NGHP‐01‐10, Krishna‐Godavari Basin, India
Authors: Lee M. W. , Collett T. S.
Published: July 2009

During the Indian National Gas Hydrate Program Expedition 01 (NGHP‐01), one of the richest marine gas hydrate accumulations was discovered at Site NGHP‐01‐10 in the Krishna‐Godavari Basin. The occurrence of concentrated gas hydrate at this site is primarily controlled by the presence of fractures. Assuming the resistivity of gas hydrate–bearing sediments is isotropic, the conventional Archie analysis using the logging while drilling resistivity log yields gas hydrate saturations greater than 50% (as high as ∼80%) of the pore space for the depth interval between ∼25 and ∼160 m below seafloor. On the other hand, gas hydrate saturations estimated from pressure cores from nearby wells were less than ∼26% of the pore space. Although intrasite variability may contribute to the difference, the primary cause of the saturation difference is attributed to the anisotropic nature of the reservoir due to gas hydrate in high‐angle fractures. Archie's law can be used to estimate gas hydrate saturations in anisotropic reservoir, with additional information such as elastic velocities to constrain Archie cementation parameters m and the saturation exponent n. Theory indicates that m and n depend on the direction of the measurement relative to fracture orientation, as well as depending on gas hydrate saturation. By using higher values of m and n in the resistivity analysis for fractured reservoirs, the difference between saturation estimates is significantly reduced, although a sizable difference remains. To better understand the nature of fractured reservoirs, wireline P and S wave velocities were also incorporated into the analysis.
Seismic structure, gravity anomalies, and flexure of the Amazon continental margin, NE Brazil
Authors: Watts A. B. , Rodger M. , Peirce C. , Greenroyd C. J. , Hobbs R. W.
Published: July 2009

Seismic and gravity data have been used to determine the structure of the sediments, crust, and upper mantle that underlie the Amazon continental margin, offshore NE Brazil. Seismic reflection profile data reveal a major unconformity at ∼7 s two‐way travel time (TWTT) which we interpret as marking the onset of the transcontinental Amazon River and the formation of the Amazon deep‐sea fan system in the late Miocene. Seismic refraction data show mean sediment velocities that decrease by >1.5 km s−1 in a seaward direction. We attribute this decrease to facies changes associated with sediment progradation and the development of topset, foreset, and bottomset beds. Seismic refraction data show that the sediments are underlain by oceanic crust that has a similar velocity structure compared to elsewhere in the Atlantic Ocean but is unusually thin (∼4.2 km). We attribute the thin crust to either slow seafloor spreading or a limited magma supply during the initial rifting of South America and Africa in the Early Cretaceous. The seismic data have been used to construct a new sediment thickness grid that together with gravity anomaly data, suggests the Amazon fan loaded lithosphere with an unusually high flexural strength. While a high‐strength lithosphere explains the overall depth of the seismic Moho, there are discrepancies (of up to 2 km) beneath the upper fan, where the modeled flexed Moho is shallower than the seismic Moho, and beneath the middle fan, where it is deeper. Gravity and seismic modeling suggest these discrepancies are caused by lateral changes in subcrustal density such that the mantle underlying the upper fan is denser than it is beneath the middle fan. We attribute these lateral density differences to proximity to the Ceara Rise, which is believed to have formed during the Late Cretaceous in a mid‐ocean ridge setting. Fan loading of a relatively strong, dense, and, hence, cold lithosphere predicts stress orientations that are consistent with borehole breakout data and the location and height of the Gurupé Arch onshore. Despite its proximity to “leaky” transform faults, the margin that underlies the Amazon fan appears to be of nonvolcanic origin. The main differences with other nonvolcanic margins, such as West Iberia and Newfoundland, are a greater sediment accumulation, a narrower zone of transitional crust, and a lack of any evidence for extreme extension and mantle serpentinization.
Development of a physically based dust emission module within the Weather Research and Forecasting (WRF) model: Assessment of dust emission parameterizations and input parameters for source regions in Central and East Asia
Authors: Darmenova Kremena , Sokolik Irina N. , Shao Yaping , Marticorena Beatrice , Bergametti Gilles
Published: July 2009

Significant problems with modeling dust emission are highlighted. Not only do dust emission schemes rely on various assumptions, but also their implementation within a regional or global model presents challenges. This paper provides an in‐depth comparative analysis of two different physically based schemes that were originally developed by Marticorena and Bergametti (1995) and Shao et al. (1996) with some recent improvements. Both schemes were implemented in a dust module (DuMo) and coupled with the Weather Research and Forecasting (WRF) model. Here we examine the physical parameterizations employed by these schemes, identify the key input parameters, and establish linkages between them by developing a new data set for dust sources in Central and East Asia. The relative importance of the input parameters is assessed through partial derivatives. The major issues involved in implementing the physically based schemes within a regional model are also discussed. Consistent implementation of two state‐of‐the‐art dust schemes within the same regional model enables us to bracket inherent uncertainties in simulated dust emission. The results of a case study based on WRF–DuMo simulations are presented to demonstrate associated biases in the magnitude and spatial patterns of emitted dust vertical fluxes. Also, recommendations on the selection of input parameters, including land and meteorological variables, to achieve an improved modeling of dust emission in Central and East Asia are provided.
A model for the long‐profile shape of submarine canyons
Authors: Gerber Thomas P. , Amblas David , Wolinsky Matthew A. , Pratson Lincoln F. , Canals Miquel
Published: July 2009

Submarine canyons are shaped by turbidity currents flowing down the continental slope. But canyon morphology also depends on the patterns of sediment deposition that drive long‐term outbuilding of continental margins. Relating the importance of each to the shape of canyon long profiles provides a tool for inferring process from observed (modern and buried) canyon morphologies. Here we present a morphodynamic model that predicts the equilibrium long‐profile curvature of a canyon affected by turbidity currents and background sedimentation, with the latter defined by the average sigmoidal shape of many clastic margin clinoforms. The model includes the effects of margin progradation (i.e., seaward advance through time) and the down canyon evolution of turbidity currents. We contrast predictions for equilibrium long‐profile shape under three sets of conditions. In the absence of background sedimentation and progradation, the graded canyon long profile is concave and described by a simple power law slope‐distance relationship that arises from down canyon increases in discharge due to flow evolution. Similar slope‐distance predictions exist for rivers where discharge instead increases from tributary input. Adding background sedimentation can generate graded convex long‐profile segments in a manner analogous to rivers experiencing uplift. The curvature of an equilibrium long profile that progrades basinward with constant form depends on the relative importance of turbidity‐current deposition and background sedimentation. To illustrate and quantify model predictions in the field, we present examples of canyons from modern continental margins thought to reasonably approximate each of the three cases.
Nutrient and salinity decadal variations in the central and eastern North Pacific
Authors: Di Lorenzo E. , Fiechter J. , Schneider N. , Bracco A. , Miller A. J. , Franks P. J. S. , Bograd S. J. , Moore A. M. , Thomas A. C. , Crawford W. , Peña A. , Hermann A. J.
Published: July 2009

Long‐term timeseries of upper ocean salinity and nutrients collected in the Alaskan Gyre along Line P exhibit significant decadal variations that are shown to be in phase with variations recorded in the Southern California Current System by the California Cooperative Oceanic Fisheries Investigation (CalCOFI). We present evidence that these variations are linked to the North Pacific Gyre Oscillation (NPGO)—a climate mode of variability that tracks changes in strength of the central and eastern branches of the North Pacific gyres and of the Kuroshio‐Oyashio Extension (KOE). The NPGO emerges as the leading mode of low‐frequency variability for salinity and nutrients. We reconstruct the spatial expressions of the salinity and nutrient modes over the northeast Pacific using a regional ocean model hindcast from 1963‐2004. These modes exhibit a large‐scale coherent pattern that predicts the in‐phase relationship between the Alaskan Gyre and California Current timeseries. The fact that large‐amplitude, low‐frequency fluctuations in salinity and nutrients are spatially phase‐locked and correlated with a measurable climate index (the NPGO) open new avenues for exploring and predicting the effects of long‐term climate change on marine ecosystem dynamics.
Arctic air temperature change amplification and the Atlantic Multidecadal Oscillation
Authors: Chylek Petr , Folland Chris K. , Lesins Glen , Dubey Manvendra K. , Wang Muyin
Published: July 2009

Understanding Arctic temperature variability is essential for assessing possible future melting of the Greenland ice sheet, Arctic sea ice and Arctic permafrost. Temperature trend reversals in 1940 and 1970 separate two Arctic warming periods (1910–1940 and 1970–2008) by a significant 1940–1970 cooling period. Analyzing temperature records of the Arctic meteorological stations we find that (a) the Arctic amplification (ratio of the Arctic to global temperature trends) is not a constant but varies in time on a multi‐decadal time scale, (b) the Arctic warming from 1910–1940 proceeded at a significantly faster rate than the current 1970–2008 warming, and (c) the Arctic temperature changes are highly correlated with the Atlantic Multi‐decadal Oscillation (AMO) suggesting the Atlantic Ocean thermohaline circulation is linked to the Arctic temperature variability on a multi‐decadal time scale.
Latitudinal dependence of the ionospheric response to solar eclipses
Authors: Le Huijun , Liu Libo , Yue Xinan , Wan Weixing , Ning Baiqi
Published: July 2009

In this study, we statistically analyze the latitudinal dependence of F2‐layer peak electron densities (NmF2) and total electron content (TEC) responses to solar eclipses by using the ionosonde observations during 15 eclipse events from 1973 to 2006 and the GPS TEC observations during six solar eclipse events from 1999 to 2006. We carried out a model study on the latitudinal dependence of eclipse effects on the ionosphere by running a theoretical ionospheric model with the total eclipse occurring at 13 latitudes from 0°N to 60°N at intervals of 5°. Both the observations and simulations show that the NmF2 and TEC responses have the same latitudinal dependence: the eclipse effects on NmF2 and TEC are smaller at low latitudes than at middle latitudes; at the middle latitudes (>40°), the eclipse effect decreases with increasing latitude. The simulations show that the smaller NmF2 responses at low latitudes are mainly because of much higher heights of hmF2 at low latitudes and electron density response decreasing rapidly with increasing height. For the eclipse effects at the middle latitudes (>40°), the simulations show that the smaller NmF2 or TEC response at higher latitude is mainly ascribed to the larger downward diffusion flux induced by the larger dip angle at this region, which can partly make up for the plasma loss and alleviate the depression of electron density in the F region. The simulated results show that there is an overall decrease in electron temperature throughout the entire height range at the middle latitude, but for the low latitudes the eclipse effect on electron temperature is much smaller at high heights, which is mainly because of the much smaller reduction of photoelectron production rate at its conjugate low heights where only a partial eclipse with small eclipse magnitude occurs.
Direct Visualization of Mouse Brain Oxygen Distribution by Electron Paramagnetic Resonance Imaging: Application to Focal Cerebral Ischemia
Authors: Shen Jiangang , Sood Rohit , Weaver John , Timmins Graham S , Schnell Aaron , Miyake Minoru , Kao Joseph PY , Rosen Gerald M , Liu Ke Jian
Published: July 2009

Electron paramagnetic resonance imaging (EPRI) is a new modality for visualizing O2 distribution in tissues, such as the brain after stroke or after administration of drugs of abuse. We have recently shown that 3-acetoxymethoxycarbonyl-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl [1] is a pro-imaging agent that can cross the blood–brain barrier. After hydrolysis by esterases, the anion of 3-carboxy-2,2,5,5-tetramethyl-1-tetramethyl-1-pyrrolidinyloxyl [2] is trapped in brain tissue. In this study, we investigated the feasibility of using this to map the changes of O2 concentration in mouse brain after focal ischemia. The decrease in tissue O2 concentration in the ischemic region of mouse brain was clearly visualized by EPRI. The hypoxic zone mapped by EPRI was spatially well correlated with the infarction area in the brain imaged by diffusion-weighted magnetic resonance imaging (MRI). Finally, we observed a decrease in the size of the hypoxic region when the mouse breathed higher levels of O2. This finding suggests that EPRI with specifically designed nitroxides is a promising imaging modality for visualizing O2 distribution in brain tissue, especially in an ischemic brain. We believe that this imaging method can be used for monitoring the effects of therapeutic intervention aimed at enhancing brain O2 supply, which is crucial in minimizing brain injury after stroke.
Homocysteine and stroke: another brick in the wall
Authors: Sacco Simona , Carolei Antonio
Published: July 2009

After a long debate, due to conflicting data from clinical studies, homocysteine is now largely accepted as a risk factor for cardiovascular diseases including stroke. To date, the role of elevated homocysteine levels in stroke recurrences has not been evaluated. In the present issue of Clinical Science, Zhang and co-workers prove that Chinese patients with high homocysteine levels have an increased risk of stroke recurrence and of all-cause mortality with respect to patients with lower levels. Remarkably, in their study, high homocysteine levels were associated with an increased risk of stroke recurrence for atherothrombotic stroke and intracerebral haemorrhage, but not lacunar stroke. The study by Zhang and co-workers provides important information for clinical practice and represents the basis for further investigations, as it raises questions referring to the puzzling relationship between homocysteine and cardiovascular disease. Moreover, the results support the hypothesis that, for undisclosed reasons, the relationship between homocysteine and cardiovascular disease may not be homogeneous for all the conditions encompassed in the category of cardiovascular disease, being peculiar for stroke patients. The finding of an association between high homocysteine levels and a risk of recurrent stroke or all-cause mortality in patients with intracerebral haemorrhage should be taken with caution until this same result is confirmed in other case series with different ethnicity.
Interpretation of the field enhancement factor for electron emission from carbon nanotubes
Authors: Smith R. C. , Silva S. R. P.
Published: July 2009

The local electric fields in the vicinity of the tips of metallic nanotubes are calculated. The variation in the field enhancement factor as a function of internanotube separation, anode-substrate separation, and height and radius of the nanotube is reported. Calculations show that the field induced electron emission current, based on the Fowler–Nordheim theory, is reduced when the intertube separation is less than twice the height of the nanotube. The location of the anode plane is shown to be important when the anode-substrate separation is less than three times the height of the nanotube. The results also predict that the macroscopic threshold field for electron emission should decrease as the anode-substrate separation D decreases. For separations greater than three times the height of the nanotube, the threshold field becomes constant and independent of anode-cathode geometry. Conversely, the manner in which applied electric field is defined is crucial if the results are be understood better. Experimental field emission measurements made on an isolated carbon nanotube confirms the need for a new interpretation of the electric field around stand alone point emitters.
On the possibility of entropy wind in superfluid helium
Authors: Pushkina N. I.
Published: July 2009

The possibility of quasistationary normal-component flow arising in superfluid helium in the presence of sufficiently intense first- and second-sound waves propagating in the helium is examined. The equations describing the flow are derived. The contributions of the energy dissipation at the shock front and the viscosity of the medium to the appearance of flows are analyzed for the case of second-sound waves. The possibility of observing the phenomenon experimentally is assessed.
Dynamic dislocation effects in low-temperature creep stimulated in β-tin single crystals by a superconducting transition
Authors: Natsik V. D. , Soldatov V. P. , Kirichenko G. I. , Ivanchenko L. G.
Published: July 2009

Low-temperature creep of high-purity β-tin single crystals oriented for plastic slip in the system (100)⟨010⟩is studied. The experiments are performed in the temperature interval 0.5<T<Tc, where Tc≈3.7K is the critical superconducting transition temperature. The samples were loaded above the yield stress and nonstationary creep was induced in them by using a magnetic field to induce a transition from the normal (N) into the superconducting (S) state. It is established that the time dependence of the post-NS-transition increase of deformation consists of three stages: transition, exponential, and logarithmic. A theory of creep is developed in the Appendix for a physical interpretation of these stages; the theory is based on the ideas of thermally activated, quantum (tunneling), and dynamic motion of dislocations in a Peierls potential relief taking account of their electronic and radiation drag. The particularities associated with the manifestation of the dynamical properties of the dislocation strings at the individual stages of creep are analyzed in detail. The transition of the samples into a superconducting state sharply decreases the electronic stopping of the dislocations and increases the contribution of the dynamic component of the dislocation flux to the creep rate. Comparing the experimental and theoretical results made it possible to obtain empirical values of some phenomenological parameters of the dislocations of the creep model.
Density functional theory based first-principle calculation of Nb-doped anatase TiO2 and its interactions with oxygen vacancies and interstitial oxygen
Authors: Kamisaka Hideyuki , Hitosugi Taro , Suenaga Takahiro , Hasegawa Tetsuya , Yamashita Koichi
Published: July 2009

The structure and electronic properties of Nb-doped anatase (TNO) were studied from first principles using the density functional theory based band structure method. Four independent types of unit cells were studied; i.e., pure anatase, anatase with Nb dopant at Ti sites (NbTi), and cells with either interstitial oxygen (Oi) or oxygen vacancies (VO). In addition, a unit cell with a NbTi and Oi, and a cell with NbTi and VO were investigated to clarify the role of nonstoichiometry in TNO. From the calculated results, the importance of the adjacent NbTi–VO and NbTi–Oi structures was pointed out, and the experimental observation of the relationship between nonstoichiometry and electronic conductivity was rationalized. The shape of the impurity states found in these structures was used to comprehend the experimental observation of carrier concentration and the charge state of Nb dopant. The changes in lattice constants supported the existence of these structures as well. On the contrary, the cell with a simple NbTi did not show significant changes in structure and electronic properties, other than the emission of an electron in the conduction band. A stabilization of the impurity state was observed in the adjacent NbTi–VO structure compared to the VO. The possibility of an essential role of this state in electric conduction was discussed. The formation of the adjacent NbTi–Oi structure by O2 gas annealing was discussed using statistical mechanics. The Gibbs free energies were calculated for Oi atoms in TNO and compared to that of O2 molecules in the gas phase. The analysis was qualitatively consistent with experimental behavior under the assumption of the NbTi–VO structures.
Measurements of thermal effusivity of a fine wire and contact resistance of a junction using a T type probe
Authors: Wang Jianli , Gu Ming , Zhang Xing , Wu Gangping
Published: July 2009

The thermal effusivity of a fine wire and the thermal contact resistance of a junction have been measured by a modified T type probe using a periodic heating method. The modified T type probe is made of a short periodic heated platinum wire and a test wire with one end contacting to the midpoint of the hot wire. Dimensionless expressions for the temperature responses of the hot wire with respect to the thermal effusivity of the test wire and the thermal contact resistance of the junction between the test wire and the hot wire were presented. A measurement system based on a flexible resolution A/D board and a LABVIEW-based virtual lock-in was setup. The probe was further verified by measuring four kinds of commercially available metallic wires at room temperature. The obtained thermal contact resistances were repeatable, with the calculated thicknesses of about 1 to 2 μm. The present method can further be applied to measure the thermal effusivity of nonconductive wires, and to analyze the thermal contact resistance of nano/microscale junction.
Thermal stability and formation barrier of a high-energetic material N8 polymer nitrogen encapsulated in (5,5) carbon nanotube
Authors: Ji Wei , Timoshevskii V. , Guo H. , Abou-Rachid Hakima , Lussier Louis-Simon
Published: July 2009

We report the density functional theory total energy calculations of thermal stability and formation barrier of polymer nitrogen confined in carbon nanotubes (CNT). The analysis suggests that N8 polymer nitrogen encapsulated in (5,5) carbon nanotube [N8@CNT(5,5)] is thermally (meta)stable at a finite temperature up to energy scale of at least 5000 K, similar to nitrogen molecule gas phase confined in CNT [N2@CNT(5,5)]. The energetic difference between these two phases of N does not significantly change with temperature. A barrier of 1.07 eV was found for the formation of N8@CNT(5,5) from N2@CNT(5,5), while the dissociation barrier was found to be 0.2 eV. Snapshots of the reaction pathway show that the transition state is composed by a N2 and a N6 inside a CNT(5,5).
Evolution of the bounded magnetized jet and comparison with Helimak experiments
Authors: Dahlburg R. B. , Horton W. , Rowan W. L. , Correa C. , Perez J. C.
Published: July 2009

Magnetized jets are important features of many systems of physical interest. To date, most interest has focused on solar and space physics and astrophysical applications, and hence the unbounded magnetized jet, and its cousin, the unbounded magnetized wake, have received the most attention. This work presents calculations of a bounded, magnetized jet for a laboratory experiments in the Helimak device [K. W. Gentle and H. He, Plasma Sci. Technol. 10, 284 (2008)]. The Helimak device has a toroidal magnetic field with a controlled velocity flow that represents jets in bounded systems. Experimental and theoretical features include three spatial dimensions, the inclusion of resistivity and viscosity, and the presence of no-slip walls. The results of the linearized model are computed with a Chebyshev-τ algorithm. The bounding walls stabilize the ideal varicose mode found in unbounded magnetized jets. The ideal sinuous mode persists in the bounded system. A comparison theorem is proved showing that two-dimensional modes are more unstable than the corresponding three-dimensional modes for any given set of system parameters. This result is a generalization of the hydrodynamic Squires theorem. An energy-stress theorem indicates that the Maxwell stress is crucial for the growth of the instability. The results of the analysis are consistent with the observed plasma fluctuations with in the limits of using a simple model for the more complex measured jet velocity flow profile. The working gas is singly ionized argon and the jet velocity profile is accurately measured with Doppler shift spectroscopy.
Wavelength control with grating imprinted fiber Sagnac loop mirror by polarization and strain tuning
Authors: Lu Ping , Men Liqiu , Chen Qiying
Published: July 2009

Wavelength control by the use of fiber Bragg grating (FBG) imprinted polarization maintaining fiber (PMF) Sagnac loop mirror (SLM) is proposed and demonstrated through polarization and strain tuning. The Bragg wavelengths of the FBG in the PMF along slow or fast axis show redshifts with the increase in strain with sensitivities of 8.77×10−4 and 9.11×10−4 nm/με, respectively, whereas the interferometric peak wavelength of the SLM exhibits a blueshift with a sensitivity of 1.9437×10−2 nm/με for the peak with an order number of 420. The opposite strain sensitivities and the pronounced difference in the bandwidth of the FBG resonance peak and that of the SLM, together with the controllability on the wavelength spacing of the SLM neighboring transmission maxima, provide a variety of alternatives to realize wavelength tuning for many practical applications.
Slow dynamics of the α and α′ relaxation processes in poly(methyl methacrylate) through the glass transition studied by mechanical spectroscopy
Authors: Wu Xuebang , Zhou Xuemao , Liu Changsong , Zhu Zhengang
Published: July 2009

In this paper, low-frequency mechanical spectroscopy has been used to study poly(methyl methacrylate) (PMMA) melt around the glass transition temperature Tg for shedding light on its unique relaxation behaviors. The mechanical spectra show an asymmetrical broad structure with a maximum peak on the high-temperature side and a shoulder peak on the low-temperature side. The shoulder peak corresponds to the α relaxation due to the local segmental motion; while the maximum peak is assigned to the α′ relaxation due to the slow motion of longer chain segments or chains. The α relaxation mode has a stronger temperature dependence of relaxation time than the α′ mode, causing the α′ mode to merge with the α mode with decreasing temperature toward Tg. Time-temperature superposition (TTS) breaks down in the entire temperature range due to the different friction coefficients of the α and α′ relaxations. For only the α′ process, TTS is found to hold for PMMA melt, where the high-frequency decay of the mechanical loss decreases like a power law of the frequency with an exponent of −1/3. Moreover, compared with the dielectric results, the relaxation times of β and α relaxations from mechanical measurements are about one order of magnitude slower than those from dielectric experiments.
Analysis of photoluminescence background of Raman spectra of carbon nanotips grown by plasma-enhanced chemical vapor deposition
Authors: Wang B. B. , Ostrikov K. , Tsakadze Z. L. , Xu S.
Published: July 2009

Carbon nanotips with different structures were synthesized by plasma-enhanced hot filament chemical vapor deposition and plasma-enhanced chemical vapor deposition using different deposition conditions, and they were investigated by scanning electron microscopy and Raman spectroscopy. The results indicate that the photoluminescence background of the Raman spectra is different for different carbon nanotips. Additionally, the Raman spectra of the carbon nanotips synthesized using nitrogen-containing gas precursors show a peak located at about 2120 cm−1 besides the common D and G peaks. The observed difference in the photoluminescence background is related to the growth mechanisms, structural properties, and surface morphology of a-C:H and a-C:H:N nanotips, in particular, the sizes of the emissive tips.
Photothermal technique using individual cantilevers for quality monitoring in thin film devices
Authors: Gotoh Tamihiro
Published: July 2009

An innovative photothermal technique has been developed to obtain optical absorption spectra of thin film devices. This technique is based on the bending effect induced by thermal expansion of a cantilever. The thin and transparent cantilever contacts a sample and when the sample is heated by photoexcitation, heat flows into the cantilever. The thermal expansion on sample side of the cantilever causes bending of cantilever beam. Main advantage of this method is adaptable to measure any sample structure and this can be used for quality monitoring in thin film devices such as solar cells and optical disks.
Electric and magnetic properties of the four most stable CHNO isomers from ab initio CCSD(T) studies
Authors: Mladenović Mirjana , Elhiyani Mohamed , Lewerenz Marius
Published: July 2009

Electric and magnetic properties obtained from CCSD(T)/(aug-)cc-pCVXZ (X=T, Q, or 5) electronic structure calculations are reported for isocyanic acid, HNCO, cyanic acid, HOCN, fulminic acid, HCNO, and isofulminic acid, HONC, in their ground electronic states. Comparison of the theoretical results with the available experimentally derived values shows very satisfactory agreement. The new data should be helpful for the identification of these molecules due to characteristic hyperfine structure patterns in their microwave spectra. A brief discussion of the electronic structure properties, based on the electric field gradients, Mulliken population analysis of the total electron density, and molecular orbitals, is provided for the four CHNO isomers and the related HCN/HNC system.
The multiscale coarse-graining method. III. A test of pairwise additivity of the coarse-grained potential and of new basis functions for the variational calculation
Authors: Das Avisek , Andersen Hans C.
Published: July 2009

The multiscale coarse-graining (MS-CG) method, proposed by Izvekov and Voth [J. Phys. Chem. B 109, 2469 (2005); Izvekov and VothJ. Chem. Phys. 123, 134105 (2005)], is a method for determining the effective potential energy function for a coarse-grained model of a fluid using data obtained from molecular dynamics (MD) simulation of the corresponding atomically detailed model. The method has been given a rigorous statistical mechanical basis [Noid et al. J. Chem. Phys. 128, 244114 (2008); Noid et al.,J. Chem. Phys. 128, 244115 (2008)]. The coarse-grained (CG) potentials obtained using the MS-CG method are an approximate variational solution for the exact many-body potential of mean force for the coarse-grained sites. In this paper we apply this method to study the many-body potential of mean force among solutes in a simple model of a solution of Lennard-Jones particles. We use a new set of basis functions for the variational calculation that is useful when the coarse-grained potential is approximately equal to an arbitrarily complicated pairwise additive, central interaction among the sites of the coarse-grained model. For this model, pairwise additivity of the many-body potential of mean force is a very good approximation when the solute concentration is low, and it becomes less accurate for high concentrations, indicating the importance of many-body contributions to the coarse-grained potential. The best possible pairwise additive CG potential of the solute particles is found to be quite long ranged for all concentrations except those for which the mole fraction of solute is very close to unity. We discuss strategies for construction of short-ranged potentials for efficient but accurate CG MD simulation. We also discuss how the choice of basis functions for the variational calculation can be used to provide smoothing of the calculated CG potential function to overcome statistical sampling error in the atomistic simulation data used for the generation of the potential.
Quantification of turbulence properties in bubble plumes using vortex identification methods
Authors: Bryant D. B. , Seol D.-G. , Socolofsky S. A.
Published: July 2009

Turbulence characteristics within bubble plumes are quantified in the laboratory using particle image velocimetry (PIV) data and postprocessing techniques to identify continuous phase vortices and their properties. Experiments are conducted using a single, high-speed Phantom camera (frame rate 250 Hz); images are preprocessed to eliminate signatures from the bubbles, resulting in high temporal and spatial resolution PIV data for the continuous phase only. The local swirl strength is used to identify vortices in the flow field. By combining the velocity fields and identified vortex maps, the vortex size probability distribution and the relationship of the vortex size, circulation and enstrophy with respect to the position in the plume are quantified. Results demonstrate that these quantities are self-similar when nondimensionalized by the plume radius and center line velocity. A direct relationship is also identified between vortex size and the corresponding average circulation and enstrophy. Modulation of the turbulent energy spectrum compared to a single-phase plume is noted and is attributed to the presence of the bubbles in the flow. Vortex size and energy density are greatest in the shear layers at the edge of the round plume, indicating that shear instability, and not bubble wakes, is the dominant process of large-scale turbulent and coherent structure generation in bubble plumes.
rf amplification in a three-terminal magnetic tunnel junction with a magnetic vortex structure
Authors: Nozaki T. , Kubota H. , Yuasa S. , Shiraishi M. , Shinjo T. , Suzuki Y.
Published: July 2009

We fabricated a three-terminal MgO-based magnetic tunnel junction including a free layer for use as a vortex-type spin structure. The resonant motion of the magnetic vortex core, excited by the application of rf current to the free layer, was successfully detected through the tunneling magnetoresistance effect using a homodyne detection technique. By analyzing the detected dc signal, we were able to qualitatively estimate the efficiency of the spin-transfer induced excitation. From the parameters obtained in the experiment, we found that substantial voltage gain can be realized with this device.
Interface reconstruction in V-oxide heterostructures determined by x-ray absorption spectroscopy
Authors: Wadati H. , Hawthorn D. G. , Geck J. , Regier T. Z. , Blyth R. I. R. , Higuchi T. , Hotta Y. , Hikita Y. , Hwang H. Y. , Sawatzky G. A.
Published: July 2009

We present an x-ray absorption study of the dependence of the V oxidation state on the thickness of LaVO3 (LVO) and capping LaAlO3 (LAO) layers in the multilayer structure of LVO sandwiched between LAO. We found that the change of the valence of V as a function of LAO layer thickness can be qualitatively explained by a transition between electronically reconstructed interfaces and a chemical reconstruction. The change as a function of LVO layer thickness is complicated by the presence of a considerable amount of V4+ in the bulk of the thicker LVO layers.