bluuebunny/crossref_metadata_2025 huggingface dataset:
Monetary Darwinism: The Political Economy of Monetary Relations
Authors: GALLAROTTI GIULIO M.
Published: October 2007

According to theories of evolution, species evolve according to survival imperatives generated by their physical environments. Traits are selected and rejected based on their adaptability to the structures of the physical world in which these species live. Biological differences mirror differences in climate; the acutely developed senses of many species have adapted either for capturing prey or eluding predators, and so forth. So too in economic systems do we observe changes in human behaviour modes and policies that suggest adaptation. With respect to money, scholars continue to look for the most important adaptation mechanisms to explain the evolution of international monetary relations. What was once the preserve of strictly economic analysis has now become open ground for a wider array of social scientific analyses. In only a few short decades the study of monetary relations has developed into a more fully multi- and interdisciplinary enterprise. The four books reviewed here represent some of the latest attempts at constructing a broader social scientific explanation of monetary history. These valuable works complement one another in filling gaps in the literature on a complex and more diverse adaptation of monetary relations. Above all they stand as impressive political economies of monetary relations. Moure and Kettell concentrate on specific cases of monetary policy transformation in the interwar period, while Flandreau et al. and Obstfeld and Taylor cover a broader evolutionary timeline. The value of the contributions lies in several factors.
Delusions of Grandeur: New Perspectives on the History of the European Community
Authors: GILBERT MARK
Published: October 2007

All four of these books are interesting additions to the corpus of historical research into European integration. Parr and Poggiolini's books are precise, document-based accounts of the trials and tribulations surrounding Britain's accession to the European Economic Community (EEC); Ludlow's book, which is based on an imposing quantity of archive research in six countries, is the most important work in English to date on the evolution of the European Community (EC) in the period that elapsed between Charles de Gaulle's veto of British entry and the Hague summit of December 1969, when the member states’ leaders ‘brought to an end a seven year struggle over its purpose, mode of operation and membership’ (p. 198). Gillingham's book reads like a 300-page op-ed in the Wall Street Journal, and is largely concerned with current events rather than history, but that does not mean that it has nothing of relevance for historians, as I hope to show at the end of this review.
On the variation of interplanetary magnetic cloud type through solar cycle 23: Wind events
Authors: Lepping R. P. , Wu C.‐C.
Published: October 2007

This statistical study examines the change in interplanetary magnetic cloud (MC) type, based on Wind observations of 100 MCs, taken during solar cycle 23 and split into three intervals: the minimum and rising phase of the cycle (over the years 1995–1998), the maximum phase (1999–2001), and the declining phase (2002 to early 2006). MC type refers to the profile of the latitude (orBZ, in geocentric solar ecliptic (GSE) coordinates) of the magnetic field within the MC, such as N‐to‐S (i.e., north‐to‐south from start to end), S‐to‐N, all S, almost all S, and so forth, with 10 categories in all. One of the main findings is that the strictly S‐to‐N events were very prevalent early in the cycle (i.e., 33% for the first phase) and tended to decrease in number as the cycle proceeded and that the strictly N‐to‐S cases had very low frequency of occurrence early in the cycle (i.e., 8% for the first phase) but tended to increase in number (22%) toward the end of the cycle, equal to the number of S‐to‐N events in that phase. When all S‐to‐N and N‐to‐S types for the full cycle are considered, the former clearly dominated over the latter by 1.4‐to‐1.
Comparison of measured and modeled ozone above McMurdo Station, Antarctica, 1989–2003, during austral winter/spring
Authors: Mercer J. L. , Kröger C. , Nardi B. , Johnson B. J. , Chipperfield M. P. , Wood S. W. , Nichol S. E. , Santee M. L. , Deshler T.
Published: October 2007

Fifteen years of ozonesonde measurements at McMurdo Station, Antarctica (78°S), are used to test the ability of the SLIMCAT off‐line 3‐D chemical transport model to reproduce Antarctic stratospheric ozone in the period of August–October over many annual cycles. Two versions of SLIMCAT, both previously used in Arctic studies, are used in a detailed quantitative comparison for total column ozone and ozone mixing ratios (O3MR) at the vertical resolution of SLIMCAT. The newer model run, EC, forced by ERA‐40 ECMWF meteorological (re)analyses, uses a general circulation model (GCM) radiation scheme to derive vertical transport and has improved chemistry and denitrification. The older run, UK, uses UKMO analyses and the MIDRAD scheme. Run EC shows good agreement with measured total column ozone (within ±10%). Run UK has similar agreement except during the annual ozone depletion period when run UK overestimates total column ozone by ∼20% in many years. Linear regression of O3MR shows run EC is in excellent agreement with measurements, R2 = 0.89. Run UK does not agree as well at higher altitudes in late winter. Overall, the newer version of SLIMCAT, with improved vertical velocity due to the use of the GCM radiation scheme and improved vertical and temporal resolution due to the use of ERA‐40 ECMWF (re) analyses, does well in reproducing variations in Antarctic ozone concentrations over many annual cycles, indicating SLIMCAT can make useful contributions to chemistry climate models (CCM).
Sorbing tracer experiments in a crystalline rock fracture at Äspö (Sweden): 1. Experimental setup and microscale characterization of retention properties
Authors: Widestrand H. , Byegård J. , Cvetkovic V. , Tullborg E.‐L. , Winberg A. , Andersson P. , Siitari‐Kauppi M.
Published: October 2007

Mineralogical and retardation properties of rock materials responsible for water‐rock interaction in in situ migration experiments with sorbing radioactive tracers were studied in laboratory experiments. The porosity was studied by water saturation measurements and the PMMA method was used for detailed porosity characterization of heterogeneity distributions and porosity profiles toward the fracture surface. Mylonite and altered diorite sampled in the rim zone of the fracture and representative bulk rock types were investigated by batch sorption measurements with crushed materials and through‐diffusion and in‐diffusion experiments in intact rock pieces. Autoradiography was used for visualization of in‐diffusion profiles of sorbing tracers. The use of detailed porosity information and quantitative data on heterogeneity in porosity is shown to significantly improve the interpretation and evaluation of laboratory‐scale diffusion experiments. We show through the combined approach of detailed porosity characterization and laboratory sorption and diffusion investigations that we can distinguish retention properties of bulk rock and altered rock and provide qualitative and quantitative data of heterogeneous rock properties that expand the possibility for including relevant processes in the interpretation of the results of in situ tracer tests.
Effects of macro‐scale bed roughness geometry on flow resistance
Authors: Canovaro F. , Paris E. , Solari L.
Published: October 2007

Flow field over macro‐roughness elements, as, for example, in flow conditions such as of steep mountain streams, is investigated by means of a theoretical model and a laboratory study with the main aim of understanding the influence of concentration and planimetric disposition of grain roughness on flow resistance. A theoretical model for the average velocity distribution profile over a bed with macro‐roughness elements is developed herein. The model is based on a two‐layer approach which takes into account the displacement of the main flow due to the drag around the roughness. The laboratory study is composed of an extensive set of flume experiments in the case of steep slopes and large relative roughness conditions. For a given flow discharge and bed slope, various experiments have been carried out with different pattern and spacing of the roughness elements constituted by river pebbles. Application of the theoretical model to the experimental results enables the determination of how flow resistance is affected by the macro‐roughness; in particular, it appears that when the concentration of the roughness is within an optimal range, flow resistance is maximum.
Source‐ and substrate‐specific export of dissolved organic matter from permafrost‐dominated forested watershed in central Siberia
Authors: Prokushkin A. S. , Gleixner G. , McDowell W. H. , Ruehlow S. , Schulze E.‐D.
Published: October 2007

Terrestrial and aquatic dissolved organic matter (DOM) was characterized to trace the likely processes of DOM formation and stream export in a permafrost‐dominated watershed in central Siberia. Stream samples were collected in spring (May–June 2003) and summer (July–August 2003) at both low flow and stormflow. Dissolved organic matter was analyzed by pyrolysis/gas chromatography/mass spectrometry, and identified pyrolysis products were simultaneously analyzed for compound‐specific isotope ratios by isotope ratio mass spectrometry. Pyrograms of terrestrial and stream DOM contained a similar series of pyrolysis products, suggesting a terrestrial origin for DOM in the small stream draining our study catchment. However, despite the overall similarity of chemical composition of stream DOM at different seasons, we also observed distinct differences in isotopic fingerprint between seasons and hydrologic phases (stormflow versus low flow). This variation appears to be due to the changing origin of stream DOM from different soil layers and the catchment sources following permafrost thawing during the frost‐free period. In general, chemical and isotopic composition of stream DOM was similar to DOM produced in soils of colder north facing slopes (P < 0.01) with a shallow active layer. South facing slopes with deeper active layers produce little DOM that enters the stream, suggesting that DOM produced in the active layer is retained and stabilized in underlying, unfrozen mineral soils. Climate change that results in additional seasonal thawing of permafrost‐dominated landscapes will decrease the amount of DOM exported to riverine systems and change its chemical composition.
A chemical kinetic approach to estimate dynamic shear stress during the 1999 Taiwan Chi‐Chi earthquake
Authors: Hirono Tetsuro , Yokoyama Tadashi , Hamada Yohei , Tanikawa Wataru , Mishima Toshiaki , Ikehara Minoru , Famin Vincent , Tanimizu Masaharu , Lin Weiren , Soh Wonn , Song Sheng‐Rong
Published: October 2007

Estimation of the dynamic shear stress on a fault during an earthquake is important for understanding the earthquake itself. Using a chemical kinetic approach, we examined the thermal decomposition of carbonate minerals to estimate the shear stress on the Taiwan Chelungpu fault, which slipped during the 1999 Chi‐Chi earthquake. The reaction rate of the decomposition was related to temperature by using the Arrhenius equation, and the chemical kinetics, taking into account the temperature change over time caused by frictional heating and heat conduction, was solved by the finite difference method. The dynamic shear stress during the Chi‐Chi earthquake was deduced to be 1.31 MPa, and the frictional coefficient to be 0.04–0.05. This estimated value agrees with the hypothesis that friction along the Chelungpu fault was low.
Using reversed magnetic flux spots to determine a planet's inner core size
Authors: Stanley S. , Zuber M. T. , Bloxham J.
Published: October 2007

The study of planetary magnetic fields can provide important information on a planet's interior structure and composition. Here we use numerical dynamo models to demonstrate that it is possible to determine information on a fundamental core property: inner core size, from observations of intense, small‐scale radial magnetic flux patches. The inner core size is discernable from the boundary between different types of intense magnetic flux patches inside and outside the inner core tangent cylinder. This type of study could help in determining the solid inner core size in Mercury, Ganymede, Jupiter and Saturn. For Mercury and Ganymede, the inner core size would then provide useful constraints on thermal evolution models for these bodies.
Effect of electromagnetic ion cyclotron wave normal angle distribution on relativistic electron scattering in outer radiation belt
Authors: Khazanov G. V. , Gamayunov K. V.
Published: October 2007

We present the equatorial and bounce‐averaged pitch angle diffusion coefficients for the scattering relativistic electrons by He+‐mode electromagnetic ion cyclotron waves. Both the model (prescribed) and self‐consistent distributions over the wave normal angle are considered. The main results of our calculation can be summarized as follows: First, in comparison with field‐aligned waves, intermediate and highly oblique waves decrease the bounce‐averaged scattering rate near the edge of the loss cone by up to orders of magnitude if the electron energy does not exceed a threshold (∼2–5 MeV) depending on specified plasma and/or wave parameters. Second, for greater electron energies, oblique waves operating the ∣n∣ > 1 resonances are more effective and provide the same bounce‐averaged diffusion rate near the edge of the loss cone as field‐aligned waves do.
Observations of structured optical emissions and particle precipitation equatorward of the traditional auroral oval
Authors: Pedersen T. , Mishin E. , Oksavik K.
Published: October 2007

High‐sensitivity all‐sky images from south‐central Alaska show the common occurrence of slow‐moving, faint optical emissions at 557.7 and 427.8 nm well equatorward of the discrete aurora. These emissions appear over a continuum of forms ranging from homogenous longitudinal bands to bands with irregular structure on their poleward edge to widely distributed arrays of vortex‐like curls and widely spaced spots on the order of 10 km in diameter. These forms appear to correspond to various stages in the temporal evolution of nearly corotating precipitation regions populated by particles injected from more distant areas of the magnetosphere and may exhibit morphological control by an instability operating on cold plasma near the plasmapause. Although these phenomena are most common in the evening hours and typically persist for hours at a time, one case demonstrates that the features can remain throughout the night on occasion. These faint optical features appear to be colocated with regions of enhanced background counts in DMSP particle measurements and to be associated with the ring current/outer radiation belt region equatorward of subauroral polarization streams (SAPS). The features can occur in conjunction with HF and MF radio frequency absorption, at levels which are often too low to show up on routine absorption instruments such as the riometer. This has practical implications on the operation and interpretation of ionospheric interaction experiments carried out in the subauroral region.
Solar wind time history contribution to the day‐of‐year variation in geomagnetic activity
Authors: Weigel R. S.
Published: October 2007

The day‐of‐year (DOY) variation in the average value of a solar wind driver of geomagnetic activity has been shown to explain only a minority of the observed amplitude of DOY variation in geomagnetic activity. The proxies for solar wind driving used to show this are averages of a solar wind measurement in the same hour or 3‐hour interval as the geomagnetic activity measurement. This model of solar wind driving of geomagnetic activity does not account for the observation that the solar wind state in a given time interval can have an effect on activity that lasts many hours. In this work we show a model that includes the solar wind time history predicts a much higher DOY variation in both auroral zone and midlatitude geomagnetic activity. This model is used to estimate the solar wind contribution in two geomagnetic activity measures that exhibit a semiannual DOY variation: the am index and postmidnight ground magnetic field measurements in the auroral zone. The estimated solar wind driver contribution to the DOY variation in the am index is 75%, which is approximately twice the amount of previous estimates. Solar wind driving is estimated to explain 40–60% of the DOY variation in the magnetic field measured by auroral zone ground magnetometers in the postmidnight sector, where previous estimates were near zero.
Seasonal distribution and flux of radium isotopes on the southeastern U.S. continental shelf
Authors: Moore Willard S.
Published: October 2007

Enrichments of radium isotopes in coastal waters have served as indicators of submarine groundwater discharge (SGD). Because coastal waters exchange with the open ocean on a timescale of weeks to months, seasonal patterns of radium isotope distributions may be used to indicate changes in SGD through the year. Here I report the seasonal distributions of four naturally occurring radium isotopes measured throughout the water column of the southeastern U.S. continental shelf, commonly known as the South Atlantic Bight (SAB). The study area extended from Onslow Bay, North Carolina, to Crescent Beach, Florida. Activities of the long‐lived isotopes were highest off the coast of Georgia. In the summer, high activities extended throughout the study area, but during spring and winter, they decreased markedly off the coast of SC. The primary source of excess 226Ra and 228Ra (that is activities in excess of open ocean values) is shown to be SGD. Because the activities of these isotopes in SGD differ little with season, the lower excess activities off South Carolina imply lower rates of SGD during the spring and winter. The excess inventories and fluxes of 226Ra and 228Ra provide an estimate of the residence time of water on the shelf. These residence times range from 30 to 60 days with a mean of about 40 days.
Sequential variation of atmospheric mercury in Tokai‐mura, seaside area of eastern central Japan
Authors: Osawa Takahito , Ueno Takashi , Fu FengFu
Published: October 2007

Concentrations of gaseous elemental mercury (GEM) were continuously measured from October 2005 to August 2006 in Tokai‐mura (36.27°N, 140.36°E), a small city on the Pacific side of central Japan. The concentration of atmospheric mercury in summer and autumn is higher than in winter and spring, and an 11‐month average of 1‐hour measurements is 3.78 ± 1.62 ng/m3 (n = 7551). Our results showed that changes in the GEM level in Tokai‐mura are largely determined by temperature and relative humidity, but are independent of wind speed and direction. Two contrary patterns were observed in the daily cycle of GEM concentrations: the most frequent pattern of lower concentrations at noon and a pattern of higher concentrations at noon, which was only observed in November. Our results showed that two nearby potential anthropogenic sources of mercury, a coal‐fired power plant and incineration facility, have only little effect on the gaseous elemental mercury (GEM) in Tokai‐mura based on only GEM measurements.
Estimated optical constants of gypsum in the regions of weak absorptions: Application of scattering theories and comparisons to independent measurements
Authors: Roush Ted L. , Esposito Francesca , Rossman George R. , Colangeli Luigi
Published: October 2007

Diffuse reflectance spectra of multiple grain size fractions are used to estimate the optical constants of gypsum over the 0.4–15 μm wavelength region. Two independent scattering theories are used to iteratively determine the imaginary index of refraction from the measured reflectance. We compare the results of these two with each other and with imaginary indices of gypsum reported in the literature. We find that the scattering theory results are more sensitive in the infrared to weak spectral features that are clearly distinguished in the diffuse reflectance spectra. However, we find the scattering results provide a poor determination of the optical constants in the regions of relatively strong absorptions. At visible and near‐infrared wavelengths we provide a comparison to the results obtained from analysis of the diffuse reflectance to results obtained from direct transmission measurements of several gypsum crystals having different sample thicknesses. We find the simplest models of the transmission reproduce the observed spectra. The different sample thicknesses for the transmission measurements and different grain sizes in the scattering theories allow evaluation of the imaginary index of refraction over a wide range of values. We find the imaginary index of refraction determined from scattering theories is in remarkable agreement with those obtained from transmission spectra. Different models of the reflectance and transmittance have associated strengths and weaknesses, and we conclude that combining these models provides a more accurate determination of the optical constants of a material when compared to using each separately. We combine the resulting real and imaginary indices of refraction with those reported at infrared wavelengths to provide values covering visual, near‐infrared, and infrared wavelengths (0.4–333 μm, 25000–30 cm−1).
Wildfire thermochronology and the fate and transport of apatite in hillslope and fluvial environments
Authors: Reiners P. W. , Thomson S. N. , McPhillips D. , Donelick R. A. , Roering J. J.
Published: October 2007

Wildfire heating of the outer few centimeters of exposed rock or soil generates short‐duration, high‐temperature thermal events that produce characteristic thermochronologic signatures in minerals. Contrasting activation energies of fission track annealing and He diffusion in apatite lead to a kinetic crossover whereby wildfire heating resets fission track (FT) ages much faster than (U‐Th)/He ages, resulting in “inverted” FT‐He ages in single grains. This can be used to trace wildfire‐affected detritus at the Earth's surface. We show that in exposed bedrock, inverted apatite FT‐He ages vary systematically with depth to ∼3 cm, and detrital clasts on hillslopes also show strong but heterogeneous wildfire‐resetting signatures. In soils, colluvium, and low‐order channel sediments, strongly wildfire‐reset apatite grains are abundant, and in some cases dominate the population of detrital apatite, to depths at least as great as 10 cm. Wildfire‐reset apatite is rare, however, in fluvial sediments sampled from larger basins, indicating a strong fractionation of apatite populations from hillslopes to rivers. Characteristic dissolution features in hillslope apatite and slower relative dissolution rates of other common minerals suggest that wildfire‐reset apatite grains are rare or absent in rivers because they dissolve relatively rapidly in soil profiles. Apatite that does contribute to fluvial sediments is likely to be dominantly derived from bedrock landslides in steep regions or from large clasts containing grains protected from both wildfire heating and dissolution. This means that apatite in fluvial sediment is spatially fractionated with respect to its sources in the catchment, even if catchment erosion rates are spatially uniform.
Localization of ‘Candidatus Endobugula sertula’ and the bryostatins throughout the life cycle of the bryozoan Bugula neritina
Authors: Sharp Koty H , Davidson Seana K , Haygood Margo G
Published: October 2007

‘Candidatus Endobugula sertula,’ the uncultivated γ-proteobacterial symbiont of the marine bryozoan Bugula neritina, synthesizes bryostatins, complex polyketides that render B. neritina larvae unpalatable to predators. Although the symbiosis is well described, little is known about the locations of ‘E. sertula’ or the bryostatins throughout larval settlement, metamorphosis and early development. In this study, we simultaneously localized ‘E. sertula’ and the bryostatins in multiple stages of the B. neritina life cycle, using a novel bryostatin detection method based on its known ability to bind mammalian protein kinase C. Our results suggest that the bryostatins are deposited onto the exterior of B. neritina larvae during embryonic development, persist on the larval surface throughout metamorphosis and are shed prior to cuticle formation. During metamorphosis, ‘E. sertula’ remains adhered to the larval pallial epithelium and is incorporated into the preancestrula cystid tissue layer, which ultimately develops into a bud and gives rise to the next zooid in the colony. Colocalization of bryostatin signal with aggregates of ‘E. sertula’ in buds of ancestrulae suggested new synthesis of bryostatins in ancestrulae. In adult B. neritina colonies, symbiont microcolonies were observed in the funicular cords of rhizoids, which likely result in asexual transmission of ‘E. sertula’ to regenerated colonies. Furthermore, bryostatin signal was detected on the surface of the rhizoids of adult B. neritina colonies. Through simultaneous localization of the bryostatins and the ‘E. sertula,’ we determined how ‘E. sertula’ is transmitted, and identified shifts in bryostatin localization throughout the life cycle of the host B. neritina.
Soil fungal abundance and diversity: another victim of the invasive plant Centaurea maculosa
Authors: Broz Amanda K , Manter Daniel K , Vivanco Jorge M
Published: October 2007

Interactions between plants and soil microbes are important determinants of both above- and belowground community composition, and ultimately ecosystem function. As exotic plants continue to invade and modify native plant communities, there has been increasing interest in determining the influence of exotic invasives on native soil microbial communities. Here, using highly sensitive molecular techniques, we examine fungal abundance and diversity in the soil surrounding a particularly aggressive invasive plant species in North America, Centaurea maculosa Lam. In mixed stands, we show that this invasive weed can alter the native fungal community composition within its own rhizosphere and that of neighboring native plants. At higher densities, the effect of C. maculosa on native soil fungal communities was even greater. Our results demonstrate that this invasive weed can have significant effects not only on visible aboveground biodiversity but also on the native soil microbial community that extends beyond its rhizosphere.
Ab initio calculation of temperature effects in the optical response of open-shell sodium clusters
Authors: Lopez del Puerto Marie , Tiago Murilo L. , Chelikowsky James R.
Published: October 2007

Many properties of atomic clusters have been found to be size dependent, e.g., the optical response. There are, however, factors other than size that can also play an important role in determining the properties of nanoscale systems. Temperature, in particular, has been shown to have a strong effect on the optical response of open-shell sodium clusters. We incorporate the temperature effect on the optical absorption spectra by combining pseudopotentials, Langevin molecular dynamics, and time-dependent density functional theory. We have done calculations for several open-shell sodium clusters, Na4+, Na7+, and Na11+, for which experimental data are available for comparison. We find that the positions of the lower energy peaks of the calculated spectra correspond very well to the peaks in the experimental spectra, although the local density approximation tends to overestimate the gap of the smaller clusters by up to 0.2eV and underestimate the gap of the largest cluster by 0.4eV. We fit the width of the peaks in the lower-temperature calculations to the corresponding experimental result to obtain the instrumental linewidth. We then use this same width for the high-temperature calculations and find very good agreement with experiment. Finally, we analyze the transitions that contribute to the observed peaks in the absorption spectra and we plot the effective valence charge density for specific transitions for each cluster. We find that for the two smaller clusters the absorption spectra are dominated by transitions from the occupied levels to a few (three for Na4+ and five for Na7+) empty levels, although the contribution from transitions to other empty levels can still be significant. In contrast, the absorption spectra for Na11+ come from a greater mixture of transitions as evidenced in the analysis as well as in the plot of the effective valence charge density.
Taylor bubbles in liquid filled annuli: Some new observations
Authors: Agarwal V. , Jana A. K. , Das G. , Das P. K.
Published: October 2007

Taylor bubbles rising through a vertical concentric annulus do not wrap around the inner tube completely. The two edges of the bubble are separated by a liquid bridge which increases with an increase of the inner radius. However, the change in the shape of the Taylor bubbles in annuli with extremely small inner diameter has not yet been reported. In the present investigation, several experiments have been performed in circular and noncircular annuli to understand the influence of the inner and outer wall on the bubble shape. The bubble has been observed to assume a completely different shape in both circular and square annuli with a very thin inner rod. Nevertheless, the rise velocity for such situations agree with the prediction of the model proposed by Das et al. [Chem. Eng. Sci. 53, 977 (1998)] when the outer pipe is circular but fails for a square outer pipe.
Application of Ewald summations to long-range dispersion forces
Authors: in ’t Veld Pieter J. , Ismail Ahmed E. , Grest Gary S.
Published: October 2007

Results illustrating the effects of using explicit summation terms for the r−6 dispersion term on the interfacial properties of a Lennard-Jones fluid and SPC/E water are presented. For the Lennard-Jones fluid, we find that the use of long-range summations, even with a short “crossover radius,” yields results that are consistent with simulations using large cutoff radii. Simulations of SPC/E water demonstrate that the long-range dispersion forces are of secondary importance to the Coulombic forces. In both cases, we find that the ratio of the box size L‖ to the crossover radius rck plays an important role in determining the magnitude of the long-range dispersion correction, although its effect is secondary when Coulombic interactions are also present.
The effect of acoustic radiation on the development of instabilities in convergent spherical liquid-gas systems
Authors: Chapyak E. J. , Godwin R. P. , Blewett P. J.
Published: October 2007

We extend previous analytical work on instability growth in spherically convergent fluid systems by characterizing linear perturbation dynamics on the collapse of a gas-filled spherical cavity surrounded by an incompressible fluid. We also investigate energy damping mechanisms related to fluid compressibility and provide estimates of the conditions under which dynamic compressibility significantly affects modal behavior. The number of modes affected by compressibility is a function of the maximum radial Mach number achieved during the cavity collapse. At a maximum Mach number (Mm) of about 0.04 only the radial mode (spherical harmonic n=0) is affected. At Mm about 0.4, modes with n≤4 are affected and at Mm greater than about 0.5 all modes are strongly influenced.
On the positive channel threshold voltage of metal gate electrodes on high-permittivity gate dielectrics
Authors: Schaeffer J. K. , Gilmer D. C. , Samavedam S. , Raymond M. , Haggag A. , Kalpat S. , Steimle B. , Capasso C. , White B. E.
Published: October 2007

Factors responsible for the undesirably high values of positive-channel (p-channel) threshold voltage (Vt) in high-κ metal oxide semiconductor transistors are investigated. In silicon/silicon dioxide/hafnium dioxide/metal gate transistors an anomalous nonlinear relationship between the equivalent oxide thickness (EOT) and Vt occurs when the silicon dioxide (SiO2) interface layer is sufficiently thin (<2.3 nm). The deviation from the expected EOT versus Vt behavior is shown to be related to processing temperature, metal work-function, substrate doping type, and thickness of the high-κ material. This result, coupled with charge trapping measurements on samples with different SiO2 interface layer thickness, suggests that the loss of negative fixed charge via the tunneling of trapped electrons to the substrate is a possible explanation for the elevated p-channel Vt.
Formation of a resonant microcavity in hydrogen ion-implanted silicon-on-insulator structures
Authors: Tyschenko I. E. , Talochkin A. B. , Bagaev E. M. , Cherkov A. G. , Popov V. P. , Misiuk A. , Yankov R. A.
Published: October 2007

Studies have been carried out on silicon-on-insulator (SOI) structures after the implantation of 24 keV, 3×1017 cm−2 hydrogen ions, and annealing at temperatures of 200−1000 °C in an argon ambient at either atmospheric pressure or under conditions of hydrostatic compression at 6 and 12 kbar. Photoluminescence (PL), Raman spectroscopy, secondary ion mass spectrometry, and high-resolution electron microscopy have been used to characterize the optical and structural properties of the resulting SOI structures. It has been found that annealing at a pressure above 6 kbar leads to a wavelength-selective increase (up to 37×) in the intensity of the PL from hydrogen implanted SOI samples. The appearance of fine structure in the PL spectrum correlates with the impeded outdiffusion of hydrogen from the implanted top Si layer as well as with the suppressed process of hydrogen microbubble formation in the near-surface region as a result of the annealing at a pressure P>6 kbar. These processes enable one to fabricate an optical resonant microcavity with mirrors formed by the air/silicon and the top Si layer/SiO2 interfaces, and the optically active layer resulting from the implantation of hydrogen and the subsequent annealing. Theoretical calculations of the PL spectra in the resonator help explain some of the specific spectral features. The mechanism of the observed photoluminescence has been discussed in terms of recombination processes occurring in nanometer-sized amorphous silicon regions saturated with hydrogen.
Emergence of singular structures in Oldroyd-B fluids
Authors: Thomases Becca , Shelley Michael
Published: October 2007

Numerical simulations reveal the formation of singular structures in the polymer stress field of a viscoelastic fluid modeled by the Oldroyd-B equations driven by a simple body force. These singularities emerge exponentially in time at hyperbolic stagnation points in the flow and their algebraic structure depends critically on the Weissenberg number. Beyond a first critical Weissenberg number the stress field approaches a cusp singularity, and beyond a second critical Weissenberg number the stress becomes unbounded exponentially in time. A local approximation to the solution at the hyperbolic point is derived from a simple ansatz, and there is excellent agreement between the local solution and the simulations. Although the stress field becomes unbounded for a sufficiently large Weissenberg number, the resultant forces of stress grow subexponentially. Enforcing finite polymer chain lengths via a FENE-P penalization appears to keep the stress bounded, but a cusp singularity is still approached exponentially in time.
Spin reorientation and magnetocaloric effect study in HoAl2 by a microscopic model Hamiltonian
Authors: de Oliveira Isaías G. , Garcia D. C. , von Ranke P. J.
Published: October 2007

The magnetocaloric properties in HoAl2 were fully investigated using a model Hamiltonian that takes into account the exchange magnetic interaction and the crystalline electrical field anisotropy. We have shown that spin reorientation has an influence on the magnetocaloric effect. An anomalous valley was predicted to exist in the magnetocaloric curves, and it was ascribed to the spin reorientation. All theoretical results were obtained using the proper model parameters found in the literature for this compound.
Study of Marangoni-natural convection in a two-layer liquid system with density inversion using a lattice Boltzmann model
Authors: Chang Qingming , Alexander J. Iwan D.
Published: October 2007

The interplay between buoyancy-induced and surface tension-driven convection in a two-layer liquid system is investigated using a hybrid thermal multiphase lattice Boltzmann method. The upper layer and the lower density inversion layer are thermally and mechanically coupled. The global flow patterns are visualized and the local and average heat transfer rates along the wall estimated in terms of the Nusselt number are plotted. The dependence of fluid flow and heat transfer on the density inversion parameter, Marangoni number, and size aspect ratio, etc., is investigated. The present work shows that the flow pattern is qualitatively and quantitatively different from the double-layer case without density inversion.
Ultraweak azimuthal anchoring of a nematic liquid crystal on a planar orienting photopolymer
Authors: Nespoulous Mathieu , Blanc Christophe , Nobili Maurizio
Published: October 2007

The search of weak anchoring is an important issue for a whole class of liquid crystal displays. In this paper we present an orienting layer showing unreached weak planar azimuthal anchoring for 4-n-pentyl-4′-cyanobiphenyl nematic liquid crystal (5CB). Azimuthal extrapolation lengths as large as 80μm are easily obtained. Our layers are made with the commercial photocurable polymer Norland optical adhesive 60. The anisotropy of the film is induced by the adsorption of oriented liquid crystal molecules under a 2T magnetic field applied parallel to the surfaces. We use the width of surface π-walls and a high-field electro-optical method to measure, respectively, the azimuthal and the zenithal anchorings. The azimuthal anchoring is extremely sensitive to the ultraviolet (UV) dose and it also depends on the magnetic field application duration. On the opposite, the zenithal anchoring is only slightly sensitive to the preparation parameters. All these results are discussed in terms of the adsorption/desorption mechanisms of the liquid crystal molecules on the polymer layer and of the flexibility of the polymer network.
Light-intensity measurements in optical waveguides using prism couplers
Authors: Caballero-Calero O. , Carnicero J. , Alcazar A. , de la Paliza G. , García-Cabañes A. , Carrascosa M. , Cabrera J. M.
Published: October 2007

In view of its central role in many optical waveguide applications, the absolute measurement of the actual light intensity propagating within a planar waveguide has been critically revised. Using prism couplers and proton exchanged LiNbO3 waveguides, several approaches have been experimentally checked and compared. A method is proposed and demonstrated, which combines the measurements of the light power out coupled from the waveguide edge and from the output prism. Reliable power measurements are obtained within a 5% error. A simplified version consists in a previous calibration of the setup in order to measure only the power coming from output coupler. Although inaccuracy rises up to ∼15%, it can be useful in many practical applications because of its simplicity. To assess and compare both methods, they have been applied to the measurement of light-intensity dependences of photovoltaic currents and optical damage thresholds in proton exchanged LiNbO3 guides.
A hot-wire probe for thermal measurements of nanowires and nanotubes inside a transmission electron microscope
Authors: Dames C. , Chen S. , Harris C. T. , Huang J. Y. , Ren Z. F. , Dresselhaus M. S. , Chen G.
Published: October 2007

A hot wire probe has been developed for use inside a transmission electron microscope to measure the thermal resistance of individual nanowires, nanotubes, and their contacts. No microfabrication is involved. The probe is made from a platinum Wollaston wire and is pretensioned to minimize the effects of thermal expansion, intrinsic thermal vibrations, and Lorentz forces. An in situ nanomanipulator is used to select a particular nanowire or nanotube for measurement, and contacts are made with liquid metal droplets or by electron-beam induced deposition. Detailed thermal analysis shows that for best sensitivity, the thermal resistance of the hot-wire probe should be four times that of the sample, but a mismatch of more than two orders of magnitude may be acceptable. Data analysis using the ratio of two ac signals reduces the experimental uncertainty. The range of detectable sample thermal resistances spans from approximately 103to109K∕W. The probe can also be adapted for measurements of the electrical conductance and Seebeck coefficient of the same sample. The probe was used to study a multiwalled carbon nanotube with liquid Ga contacts. The measured thermal resistance of 3.3×107K∕W had a noise level of approximately ±3% and was repeatable to within ±10% upon breaking and re-making the contact.
Experimental study on electron mobility in ultrathin-body silicon-on-insulator metal-oxide-semiconductor field-effect transistors
Authors: Uchida Ken , Koga Junji , Takagi Shin-ichi
Published: October 2007

The electron mobility in ultrathin-body (UTB) silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors (MOSFETs) with SOI thicknesses from 2.3to60nm is measured in a wide temperature range from 25to300K. In UTB SOI MOSFETs with SOI thickness ranging from 5to20nm, a monotonic decrease of electron mobility with a decrease in SOI thickness is observed at room temperature. At extremely low temperature (25K), however, the electron mobility of UTB SOI MOSFETs with SOI thickness of 5.7nm is not degraded but is almost the same as that of thick-body SOI MOSFETs. On the other hand, in UTB SOI MOSFETs with SOI thickness ranging from 3.5to4.5nm, an increase of electron mobility with a decrease in SOI thickness is clearly demonstrated at the effective normal field of around 0.3MV∕cm at 300K. It is concluded that the decrease of electron mobility in SOI thickness ranging from 5to20nm is due to the increased phonon scattering in thinner SOI films. The observed enhancement of electron mobility with decreasing SOI thickness from 4.5to3.5nm is ascribed to the subband structure modulation induced by quantum confinement effects in nanoscale SOI films. The impact of SOI thickness fluctuations on electron mobility and the methods to evaluate the thickness of ultrathin SOI films are also discussed.
Deposition of single-crystal Ti2AlN thin films by reactive magnetron sputtering from a 2Ti:Al compound target
Authors: Joelsson T. , Flink A. , Birch J. , Hultman L.
Published: October 2007

Single-crystal Ti2AlN (0001) thin films were grown on (111) oriented MgO substrates kept at 830°C by ultrahigh vacuum dc reactive magnetron sputtering from a compound 2Ti:Al target in a mixed Ar∕N2 discharge. The effects of variations in the nitrogen partial pressure on the phase composition of the films were studied. Results from transmission electron microscopy, x-ray diffraction, and elastic recoil detection analysis show a narrow region for growth of Ti2AlN MAX phase with respect to the nitrogen content in the discharge. Perovskite Ti3AlN and intermetallic Ti3Al and TiAl phases dominate at nitrogen depletion. For overstoichiometric deposition conditions with respect to Ti2AlN, a phase mixture with NaCl-structured TiN is obtained. Epitaxial growth is observed with a layer-by-layer mode on the 0001 basal planes for all phases. A superstructure in the TiN phase is also observed along [111] with the repetition distance of 7.34Å, most likely related to Al segregation. Nanoindentation shows that the film hardness increases from 11to27GPa with increasing nitrogen content and corresponding phase transformations from Ti–Al intermetallics to Ti3AlN, Ti2AlN, and TiN.
Exact canonical drift Hamiltonian formalism with pressure anisotropy and finite perturbed fields
Authors: Cooper G. A. , Jucker M. , Cooper W. A. , Graves J. P. , Isaev M. Yu.
Published: October 2007

A Hamiltonian formulation of the guiding center drift orbits is extended to pressure anisotropy and field perturbations in axisymmetric systems. The Boozer magnetic coordinates are shown to retain canonical properties in anisotropic pressure plasmas with finite electrostatic perturbations and electromagnetic perturbed fields that solely affect the parallel component of the magnetic vector potential. The equations of motion developed in the Boozer coordinate frame are satisfied by direct verification of the drift velocities. A numerical application illustrates the significance of retaining all second order terms.
Effect of point defects on copper-related deep levels in p-type Czochralski silicon
Authors: Wang Weiyan , Yang Deren , Yu Xuegong , Ma Xiangyang , Que Duanlin
Published: October 2007

The effect of point defects on the copper (Cu)-related deep levels in p-type Czochralski (Cz) silicon has been investigated. It was found that generally five deep levels Ev+0.14eV, Ev+0.17eV, Ev+0.32eV, Ev+0.35eV, and Ev+0.46eV were related to Cu in the p-type Cz silicon. Among them, the newly found levels Ev+0.35eV and Ev+0.32eV can be influenced by the point defects introduced during rapid thermal process. The intensity of level Ev+0.35eV increased with the introduced vacancies, while that of level Ev+0.32eV was dependent on the silicon interstitials. Moreover, the electronic states of those two levels were ascribed to be localized states. Based on the experimental facts, it is believed that the origins of levels Ev+0.35eV and Ev+0.32eV are the complex of Cu and vacancy and that of Cu and silicon interstitials, respectively.
Real-time x-ray studies of gallium nitride nanodot formation by droplet heteroepitaxy
Authors: Wang Yiyi , Özcan Ahmet S. , Sanborn Christopher , Ludwig Karl F. , Bhattacharyya Anirban , Chandrasekaran Ramya , Moustakas Theodore D. , Zhou Lin , Smith David J.
Published: October 2007

Self-organized gallium nitride nanodots have been fabricated using droplet heteroepitaxy on c-plane sapphire by plasma-assisted molecular beam epitaxy at different substrate temperatures and Ga fluxes. Nanoscale Ga droplets were initially formed on the sapphire substrate at high temperatures by Ga deposition from an effusion cell in an ultrahigh vacuum growth chamber. Subsequently, the droplets were converted into GaN nanodots using a nitrogen plasma source. The process was monitored and controlled using real-time grazing-incidence small-angle x-ray scattering. The samples were examined postgrowth by in situ grazing incidence x-ray diffraction and reflection high-energy electron diffraction, which confirmed the epitaxial relationship between the GaN nanodots and the sapphire surface. X-ray diffraction indicated that the wurtzite phase was dominant at higher substrate temperature (710°C), but a mixture of wurtzite and zinc blende phases was present at a substrate temperature of 620°C. Ex situ atomic force microscopy and transmission electron microscopy analyses showed that the dot size distribution was bimodal. A thin GaN continuous layer of ∼ three monolayers thick was observed by transmission electron microscopy on the sample grown at a substrate temperature of 620°C, but no such layer was observed for the substrate temperature of 710°C. This suggests that there is little mobility of Ga atoms in contact with the sapphire substrate at the lower temperature so that they cannot easily diffuse to nearby droplets and instead form a thin layer covering the surface.