bluuebunny/crossref_metadata_2025 huggingface dataset:
Deutschsprachige Version des Fragebogens für Rechenangst (FRA) für 6- bis 9-jährige Kinder
Authors: Krinzinger Helga , Kaufmann Liane , Dowker Ann , Thomas Gemma , Graf Martina , Nuerk Hans-Christoph , Willmes Klaus
Published: September 2007

Zusammenfassung: Einleitung: Rechenangst ist ein häufiges Phänomen und oft mit Dyskalkulie assoziiert. Dementsprechend wichtig ist ein standardisiertes Instrument zur Früherkennung von Rechenangst, welches nun in der deutschsprachigen Version des Fragebogens für Rechenangst (FRA) für 6- bis 9-jährige Kinder (Originalversion: Thomas & Dowker, 2000) vorliegt. Fragestellung: Handelt es sich beim FRA um ein reliables und valides Messinstrument? Gibt es Geschlechtsunterschiede bezüglich Rechenangst? Gibt es diesbezügliche Veränderungen im Verlauf der ersten Schuljahre? Methode: Der Selbstbeurteilungsfragebogen FRA wurde gemeinsam mit dem Dyskalkulietest TEDI-MATH (Kaufmann et al., in Vorbereitung) insgesamt 450 Kindern der ersten bis dritten Grundschulstufe vorgelegt (je mindestens 40 Jungen und 40 Mädchen pro Halbjahr). Ergebnis: Die interne Konsistenz des Fragebogens (Cronbach’s Alpha) liegt zwischen 0.83 und 0.91. Korrelationen zwischen Rechenleistung, Selbsteinschätzung und Einstellung zum Rechnen sowie Rechenangst waren großteils signifikant. Den signifikanten Geschlechtsunterschieden (Mädchen erzielten relativ zu Jungen negativere Werte) wurde mit geschlechtskorrigierten Normwerten Rechnung getragen. Systematische Veränderungen mit dem Alter wurden nicht beobachtet. Schlussfolgerungen: Erstmals liegt mit dem FRA ein für die klinische Praxis (Dyskalkuliediagnostik und -intervention) wichtiges und kindgerechtes deutschsprachiges Instrument zur Erfassung der Rechenangst bei Grundschulkindern vor. Es zeichnet sich durch hohe Reliabilität, geschlechtsspezifische Normierung sowie ökonomische Durchführbarkeit aus.
Intercomparison of tropical tropospheric humidity in GCMs with AMSU‐B water vapor data
Authors: Brogniez Hélène , Pierrehumbert Raymond T.
Published: September 2007

We make use of microwave measurements of the tropical free tropospheric relative humidity (FTH) to evaluate the extent to which the water vapor distribution in four general circulation models is faithful to reality. The comparison is performed in the tropics by sorting the FTH in dynamical regimes defined upon the 500 hPa vertical velocity. Because microwave radiation penetrates non‐rainy and warm clouds, we are able to estimate the FTH over most of the dynamical regimes that characterize the tropics. The comparisons reveal that two models simulate a free troposphere drier than observed (<10%), while the others agree with the observations. Despite some differences, the level of agreement is good enough to lend confidence in the representation of atmospheric moistening processes. A climate change scenario, tested on two models, shows a tendency to maintain the FTH to an almost fixed value be it an ascending or a subsiding regime.
Effects of mesoscopic‐scale fault structure on dynamic earthquake ruptures: Dynamic formation of geometrical complexity of earthquake faults
Authors: Ando Ryosuke , Yamashita Teruo
Published: September 2007

We develop a new hierarchical earthquake rupture model that takes into account mesoscopic‐scale fault structure; shear branches nucleated on the main fault are specifically assumed as an example of mesoscopic‐scale fault structure. We numerically investigate dynamic formation of fault geometry and its effects on dynamic earthquake rupture process based on this rupture model. As long as the length of the main fault is below a certain threshold Lm, the growth of these branches is shown to be arrested spontaneously soon after their nucleation. The spatial distribution of arrested branches is shown to form a self‐similar geometrical structure. This suggests the existence of a simple scaling relationship between small and large events as long as the length of the main fault is below the threshold Lm. However, once the length of the main fault exceeds Lm, a limited number of branches begin unstable growth, and their sizes soon become comparable to that of the main fault. In other words, mesoscopic‐scale branches are spontaneously transformed into macroscopic‐scale ones. This finding indicates the critical importance of the consideration of mesoscopic‐scale fault structure in understanding rupture dynamics: Once macroscopic‐scale branches are formed, they change the fault geometry, which will considerably affect the rupture dynamics. The emergence of macroscopic branches suggests that the above mentioned simple scaling relation is never valid above a critical length Lm. Our study thus indicates that relationship between small and large earthquakes is complicated by the spontaneous transformation of a mesoscopic‐scale fault structure into a macroscopic‐scale one.
Transport of radon‐222 and methyl iodide by deep convection in the GFDL Global Atmospheric Model AM2
Authors: Donner Leo J. , Horowitz Larry W. , Fiore Arlene M. , Seman Charles J. , Blake Donald R. , Blake Nicola J.
Published: September 2007

Transport of radon‐222 and methyl iodide by deep convection is analyzed in the Geophysical Fluid Dynamics Laboratory (GFDL) Atmospheric Model 2 (AM2) using two parameterizations for deep convection. One of these parameterizations represents deep convection as an ensemble of entraining plumes; the other represents deep convection as an ensemble of entraining plumes with associated mesoscale updrafts and downdrafts. Although precipitation patterns are generally similar in AM2 with both parameterizations, the deep convective mass fluxes are more than three times larger in the middle‐ to upper troposphere for the parameterization consisting only of entraining plumes, but do not extend across the tropopause, unlike the parameterization including mesoscale circulations. The differences in mass fluxes result mainly from a different partitioning between convective and stratiform precipitation; the parameterization including mesoscale circulations detrains considerably more water vapor in the middle troposphere and is associated with more stratiform rain. The distributions of both radon‐222 and methyl iodide reflect the different mass fluxes. Relative to observations (limited by infrequent spatial and temporal sampling), AM2 tends to simulate lower concentrations of radon‐222 and methyl iodide in the planetary boundary layer, producing a negative model bias through much of the troposphere, with both cumulus parameterizations. The shapes of the observed profiles suggest that the larger deep convective mass fluxes and associated transport in the parameterization lacking a mesoscale component are less realistic.
A case study of boundary layer ventilation by convection and coastal processes
Authors: Dacre H. F. , Gray S. L. , Belcher S. E.
Published: September 2007

It is often assumed that ventilation of the atmospheric boundary layer is weak in the absence of fronts, but is this always true? In this paper we investigate the processes responsible for ventilation of the atmospheric boundary layer during a nonfrontal day that occurred on 9 May 2005 using the UK Met Office Unified Model. Pollution sources are represented by the constant emission of a passive tracer everywhere over land. The ventilation processes observed include shallow convection, turbulent mixing followed by large‐scale ascent, a sea breeze circulation and coastal outflow. Vertical distributions of tracer are validated qualitatively with AMPEP (Aircraft Measurement of chemical Processing Export fluxes of Pollutants over the UK) CO aircraft measurements and are shown to agree impressively well. Budget calculations of tracers are performed in order to determine the relative importance of these ventilation processes. Coastal outflow and the sea breeze circulation were found to ventilate 26% of the boundary layer tracer by sunset of which 2% was above 2 km. A combination of coastal outflow, the sea breeze circulation, turbulent mixing and large‐scale ascent ventilated 46% of the boundary layer tracer, of which 10% was above 2 km. Finally, coastal outflow, the sea breeze circulation, turbulent mixing, large‐scale ascent and shallow convection together ventilated 52% of the tracer into the free troposphere, of which 26% was above 2 km. Hence this study shows that significant ventilation of the boundary layer can occur in the absence of fronts (and thus during high‐pressure events). Turbulent mixing and convection processes can double the amount of pollution ventilated from the boundary layer.
High‐latitude remote sensing of mesospheric wind speeds and carbon monoxide
Authors: Burrows S. M. , Martin C. L. , Roberts E. A.
Published: September 2007

We present high‐resolution ground‐based measurements of mesospheric carbon monoxide (CO) taken in the years 2002–5 from the AST/RO sub‐millimeter telescope, located at Amundsen‐Scott South Pole Station. These include the first winter measurements of CO directly from one of the geographic poles, which agree well with expected high concentrations within the polar vortex. We also use CO as a tracer to estimate mesospheric neutral wind speeds, by measuring small Doppler shifts in the rotational emission spectrum. We highlight the potential of high‐resolution radiometric measurements mesospheric winds to fill a significant experimental data gap.
Climate sensitivity of tropical and subtropical marine low cloud amount to ENSO and global warming due to doubled CO2
Authors: Zhu Ping , Hack James J. , Kiehl Jeffrey T. , Bretherton Christopher S.
Published: September 2007

In this study, we systematically analyzed the sensitivity of tropical and subtropical marine low cloud amount to the short‐term climate anomaly associated with the 1997–1998 El Niño and the long‐term climate change caused by doubled CO2 using the International Satellite Cloud Climatology Project (ISCCP) cloud measurements, European Centre for Medium‐Range Weather Forecasting (ECMWF) reanalyses, and the sea surface temperature (SST) forced and coupled simulations performed by the latest version of the National Center for Atmospheric Research (NCAR) and Geophysical Fluid Dynamics Laboratory (GFDL) climate models. It is found that the changes in low cloud amount associated with the 1997–1998 El Niño and the doubled CO2 induced climate change have different characteristics and are controlled by different physical processes. Most reduction in low cloud amount related to the 1997–1998 El Niño occurs in the eastern tropical Pacific associated with an upward large‐scale motion and a weak atmospheric stability measured by the 500 hPa vertical velocity and the potential temperature difference between 700 hPa and the surface, and is negatively correlated to the local SST anomaly. In addition to the other mechanisms suggested by the previous studies, our analyses based on the ISCCP observations indicate that the change in atmospheric convective activities in these regions is one of the reasons responsible for the change in low cloud amount. In contrast, most increase in low cloud amount due to doubled CO2 simulated by the NCAR and GFDL models occurs in the subtropical subsidence regimes associated with a strong atmospheric stability, and is closely related to the spatial change pattern of SST consistent with previous studies. The increase in low cloud amount appears to favor the location where SST is less increased. After removing the background mean SST increase due to doubled CO2, the results show a clear negative correlation between the change in low cloud and the SST change. An analysis based on the simple atmospheric mixed layer model demonstrates a thermodynamic reason for such a change. The increase in the above‐inversion atmospheric stratification due to doubled CO2 tends to reduce the mixed layer depth in the areas with a small temperature increase, which helps to trap the moisture within the mixed layer, thus, favors low cloud formation.
Evaluation of the GOME Water Vapor Climatology 1995–2002
Authors: Lang R. , Casadio S. , Maurellis A. N. , Lawrence M. G.
Published: September 2007

An accurate knowledge of the 3‐D water vapor (WV) field is still limited, because of the limited capabilities of sensors in the past to cover the whole Earth’s surface and the lower part of the troposphere, as well as to measure over reasonably long time series. We show here water vapor total column retrieved from seven years of Global Ozone Monitoring Experiment (GOME) measurements collected from August 1995 until August 2002. Our aim is two‐fold: (1) to evaluate the accuracy and the limitations of the GOME water vapor total column and (2) to demonstrate its potential for climate studies. The column retrieval makes use of two innovative techniques operating in tandem, namely the University of Graz empirical air mass factor ratioing technique (IGAM) and the Spectral Structure Parameterization (SSP) retrieval method. The GOME instrument and its follow‐up instruments (SCIAMACHY and GOME‐2), using these algorithms, have the capability to cover nearly the whole globe in cloud‐free situations and collect robust WV total column information over more than 3 decades. In this work we evaluate the results for the first 7 years against independent in situ measurements from the operational WMO radiosonde network, against high spatial resolution water vapor columns from MERIS (the Medium Resolution Imaging Spectrometer on EnviSat) and also compare with ERA40 model results. The GOME water vapor total column exhibits a bias of less than 2.5% with an uncertainty of around 5 mm for collocated measurements against radiosonde and MERIS measurements. Spatial patterns and trends in the global distribution of WV total column fields from GOME against re‐analysis model results are well correlated with temperature in the tropics, and exhibit a lesser degree of correlation in the extra tropics. Cloud‐free total columns from GOME can be systematically lower by up to 5 mm in the sub‐tropics with respect to the all‐sky case. In contrast, the impact of the diurnal cycle on the monthly mean values is found to be very small.
Comparing different methods for assessing ground truth of rover data analysis for the 2005 season of the Life in the Atacama Project
Authors: Thomas G. W. , Peate I. Ukstins , Nakamoto J. , Pudenz E. , Glasgow J. , Bretthauer J. , Cabrol N. , Wettergreen D. , Grin E. , Coppin P. , Dohm J. M. , Piatek J. L. , Warren‐Rhodes K. , Hock A. N. , Weinstein S. , Fisher G. , Diaz G. Chong , Cockell C. , Marinangeli L. , Minkley N. , Moersch J. , Ori G. G. , Smith T. , Stubb K. , Wagner M. , Waggoner A. S.
Published: September 2007

The scientific success of a remote exploration rover mission depends on the right combination of technology, teamwork and scientific insight. In order to quantitatively evaluate the success of a rover field trial, it is necessary to assess the accuracy of scientific interpretations made during the field test. This work compares three structured approaches to assessing the ground truth of scientific findings from a science team conducting a remote investigation of a locale using an autonomous rover. For the first approach, independent assessment, the daily science summaries were analyzed and reduced to a series of 1082 factual statements, which were treated as hypotheses. An independent scientist traveled to the field area to assess these hypotheses. For the second approach, guided self‐study, the mission scientists themselves traveled to the field area and evaluated their own scientific interpretations. The third approach, discrepancy investigation, searched for the root causes of differences between the scientific interpretations made in the control room and those made in the field. The independent investigation provided sensitive, quantitative data, but suffered from the lack of context and continuity developed in the mission control room. The guided evaluation benefited from the context of the mission, but lacked clarity and consistency. The discrepancy investigation provided insight into the root causes behind the discrepancies, but was expensive and time consuming. The independent investigation method yielded particularly compelling results, but each method offers advantages and a comprehensive rover field trial assessment should include a combination of all three.
Impact of coating development on the hydraulic and transport properties in argillaceous limestone fracture
Authors: Noiriel Catherine , Madé Benoît , Gouze Philippe
Published: September 2007

Results are reported for an acidic water flow‐through experiment conducted in a fractured argillaceous limestone sample (73% carbonates). The change in fracture geometry and related parameters is reported for six data sets obtained from synchrotron X‐ray microtomography experiments. High‐resolution three‐dimensional images of the sample allowed quantification of the changes in fracture morphology at a spatial resolution of 6 μm. Mineral mass loss and permeability changes in the sample were also determined. Several physico‐chemical phenomena were identified during the experiment. Initial smooth fracture surfaces evolved rapidly toward rough surfaces with uneven clay coverage due to the preferential dissolution of carbonate minerals compared to clay minerals whose dissolution rate is about 106 slower. A microporous clay coating progressively developed at the fluid‐rock interface during heterogeneous dissolution of the fracture, while the global dissolution rate of the fracture walls exponentially decreased. The increase in surface roughness and the presumed reorganization of clays caused a progressive reduction in permeability. During the last flow‐through stage, a large decrease in sample permeability was attributed to the large removal of clay particles; this process was responsible for a dramatic collapse of the fracture walls near the sample inlet and led to the development of preferential flow pathways. The development of the clay coating also acted as a barrier to flow and mass transfer between calcite grains and bulk solution and affected transport processes within the fracture.
Color of brown carbon: A model for ultraviolet and visible light absorption by organic carbon aerosol
Authors: Sun Haolin , Biedermann Laura , Bond Tami C.
Published: September 2007

We recommend ultraviolet and visible absorption spectra to represent particular types of atmospheric organic particles. Spectra of liquids and particles can be compared using the absorption coefficient of bulk material divided by material density. Reported absorption by absorbing organic aerosol from combustion is greater than that of organic material isolated by humic acid extraction. We examine ultraviolet and visible spectra of 200 organic compounds, concluding that visible absorption may be attributable to n → π* electronic transitions in a small fraction of oxygenated compounds. Absorption spectra can be communicated using the band‐gap and Urbach relationships instead of the absorption Angstrom exponent. Water‐soluble atmospheric aerosol has a band‐gap of about 2.5 eV; insoluble aerosol may have a lower band‐gap and higher absorption. Although different types of organic carbon may exhibit a continuum in absorption, there is a sharp distinction between the most‐absorbing organic carbon and black carbon.
Microbial nanowires: Is the subsurface “hardwired”?
Authors: Ntarlagiannis Dimitrios , Atekwana Estella A. , Hill Eric A. , Gorby Yuri
Published: September 2007

The Earth's shallow subsurface results from integrated biological, geochemical, and physical processes. Methods are sought to remotely assess these interactive processes, especially those catalysed by micro‐organisms. Using saturated sand columns and the metal reducing bacterium Shewanella oneidensis MR‐1, we show that electrically conductive appendages called bacterial nanowires are directly associated with electrical potentials. No significant electrical potentials were detectable in columns inoculated with mutant strains that produced non‐conductive appendages. Scanning electron microscopy imaging revealed a network of nanowires linking cells‐cells and cells to mineral surfaces, “hardwiring” the entire length of the column. We hypothesize that the nanowires serve as conduits for transfer of electrons from bacteria in the anaerobic part of the column to bacteria at the surface that have access to oxygen, akin to a biogeobattery. These results advance understanding of the mechanisms of electron transport in subsurface environments and of how microorganisms cycle geologic material and share energy.
Quantifying scaling in the velocity field of the anisotropic turbulent solar wind
Authors: Chapman S. C. , Hnat B.
Published: September 2007

Solar wind turbulence is dominated by Alfvénic fluctuations with power spectral exponents that somewhat surprisingly evolve toward the Kolmogorov value of −5/3, that of hydrodynamic turbulence. We analyze in situ satellite observations at 1AU and show that the turbulence decomposes linearly into two coexistent components perpendicular and parallel to the local average magnetic field and determine their distinct intermittency independent scaling exponents. The first of these is consistent with recent predictions for anisotropic MHD turbulence and the second is closer to Kolmogorov‐like scaling.
Dust provenance in Antarctic ice during glacial periods: From where in southern South America?
Authors: Gaiero Diego M.
Published: September 2007

The origin of dust deposited in East Antarctica is not fully understood yet. This study demonstrates that, contrary to Nd, Sr isotopes are strongly fractionated in the finest‐sized material representing potential dust sources in South America. Analysis of Nd isotopes suggests that Argentine loess, Southern Ocean sediments and Antarctic dust, may all have a related origin or can represent comparable mechanisms of eolian sediment transport and deposition. This analysis also concludes that the Patagonian signature can explain a high proportion of the isotopic composition of dust trapped in Antarctic ice during glacial periods. The Puna‐Altiplano plateau emerges as the second possible important sediment contributor explaining the crustal‐like signature found in East Antarctic dust and should be considered as a potential source area when Quaternary paleoclimate is reconstructed from Argentine loess, Antarctic dust and South Atlantic sediment records.
Recovery of temperature records from slow‐growing corals by fine scale sampling of skeletons
Authors: Cohen Anne L. , Thorrold Simon R.
Published: September 2007

We used laser ablation inductively coupled plasma mass spectrometry (LA ICP‐MS) to analyze Sr/Ca ratios in 5 colonies of the Atlantic corals, Diploria labyrinthiformis and Montastrea franski, each growing less than 5 mm yr−1. By targeting the centers of septa we avoided thickening deposits to achieve an analytical sampling resolution of 5‐10 days. The sensitivity of Sr/Ca to temperature (−0.096 mmol/mol/°C) is ∼3 times higher than previously reported for these species and equivalent to that exhibited by fast‐growing Porites corals from the Indo‐Pacific. The Sr/Ca‐sea surface temperature (SST) calibrations derived from these corals were not statistically different and were independent of colony growth rate over the period studied. Data from 4 D. labyrinthiformis colonies were pooled to produce a single Sr/Ca‐SST calibration with a calculated standard error on the predicted ocean temperature of ±0.51°C. Applying our calibration to Sr/Ca analyses of D. labyrinthiformis skeleton deposited in the late 18th century indicated that average annual sea surface temperatures around Bermuda were ∼1°C cooler than today.
Effect of solid flow above a subducting slab on water distribution and melting at convergent plate boundaries
Authors: Cagnioncle Amandine‐Marie , Parmentier E. M. , Elkins‐Tanton Linda T.
Published: September 2007

Hydrous fluids derived by dehydration of the downgoing slab at convergent plate boundaries are thought to provoke wet melting in the wedge above the downgoing plate. We have investigated the distribution of hydrous fluid and subsequent melt in the wedge using two‐dimensional models that include solid mantle flow and associated temperature distributions along with buoyant fluid migration and melting. Solid mantle flow deflects hydrous fluid from their buoyant vertical migration through the wedge. Melting therefore does not occur directly above the region where hydrous fluids are released from the slab. A melting front develops where hydrous fluids first encounter mantle material hot enough to melt. Wet melting is influenced by solid flow through the advection of fertile mantle material into the wet melting region and the removal of depleted material. The region of maximum melting occurs where the maximum flux of water from slab mineral dehydration reaches the wet melting region. The extent of melting (F) and melt production rates increase with increasing convergence rate and grain size due to increased temperatures along the melting front and to increased fractions of water reaching the melting front, respectively. The position of isotherms above the wet solidus varies with increasing slab dip and thereby also influencesFand melt production rates. Applying the understanding of wet melting from this study to geochemical studies of the Aleutians may help elucidate the processes influencing fluid migration and melt production in that region. Estimates of the timescale of fluid migration, seismic velocity variation, and attenuation are also investigated.
Close temporal correspondence between geomagnetic anomalies and earthquakes during the 2002–2003 eruption of Etna volcano
Authors: Currenti G. , Del Negro C. , Johnston M. , Sasai Y.
Published: September 2007

The early stages of the 2002–2003 lateral eruption at Mount Etna were accompanied by slow changes (over some hours) and some rapid step offsets in the local magnetic field. At five monitoring locations, the total magnetic field intensity has been measured using continuously operating Overhauser magnetometers at a sampling rate of 10 s. The very unique aspect of these observations is the close temporal correspondence between magnetic field offsets and earthquakes that occurred in the upper northern flank of the volcano on 27 October 2002 prior to a primary eruption. Rapid coseismic changes of the magnetic field were clearly identified for three of the most energetic earthquakes, which were concentrated along the Northeast Rift at a depth of about 1 km below sea level. Coseismic magnetic signals, with amplitudes from 0.5 to 2.5 nT, have been detected for three of the largest seismic events located roughly midway between the magnetic stations. We quantitatively examine possible geophysical mechanisms, which could cause the magnetic anomalies. The comparison between magnetic data, seismicity and surface phenomena implies that piezomagnetic effects are the primary physical mechanism responsible for the observed magnetic anomalies although the detailed cause of the rapid high stress change required is not clear. The modeling of the observed coseismic magnetic changes in terms of piezomagnetic mechanism provides further evidence of the complex interaction between volcanic and tectonic processes during dike propagation along the Northeast Rift.
The degree of anisotropy for mid‐ocean currents from satellite observations and an eddy‐permitting model simulation
Authors: Huang Huei‐Ping , Kaplan Alexey , Curchitser Enrique N. , Maximenko Nikolai A.
Published: September 2007

The degree of anisotropy is calculated for the mid‐ocean currents estimated from satellite altimetry and simulated with a numerical model of the Pacific Ocean. A high resolution eddy‐permitting model is used for its ability to simulate mid‐ocean multiple zonal flows, crucial for the evaluation of the degree of anisotropy. Using a commonly defined parameter of anisotropy, α, that falls between −1 and 1 and equals 0, −1, and 1 for an isotropic, purely meridional, and purely zonal flow, respectively, it is found that α increases from nearly zero for weekly data to significantly positive values for seasonally and annually averaged data. This tendency of increasing zonal anisotropy with averaging time is true for the surface geostrophic velocity from satellite altimetry and for both surface and deep‐ocean velocities from the model simulation. The absolute value of α for the simulated surface currents agree with that derived from satellite observation, reaffirming the reliability of both data sets. In the model simulation, the behavior of α at the surface is very similar to that at 1000 m, indicating a deep structure of the zonally elongated features in the middle of the Pacific Ocean. The implications of these findings are discussed in the context of oceanic eddies, Rossby waves, and zonal jets.
Searching for resonances in the reaction Cl+CH4→HCl+CH3: Quantum versus quasiclassical dynamics and comparison with experiments
Authors: Martínez Rodrigo , González Miguel , Defazio Paolo , Petrongolo Carlo
Published: September 2007

A quantum-mechanical (QM) and quasiclassical trajectory (QCT) study was performed on the title reaction, using a pseudotriatomic ab initio based surface. Probabilities and integral cross sections present some clear peaks versus the collision energy Ecol, which we assign to Feshbach resonances of the transition state, where the light H atom oscillates between the heavy Cl and CH3 groups. For ground-state reactants, reactivity is essentially of quantum origin (QCT observables and oscillations are smaller, or much smaller, than QM ones), and the calculated integral cross section and product distributions are in reasonable agreement with the experiment. The reaction occurs through an abstraction mechanism, following both a direct and an indirect mechanism. The quasiclassical trajectory calculations show the participation of a short-lived collision complex in the microscopic reaction mechanism. Finally, QCT differential cross sections of Cl+CH4→HCl (ν′=0and1)+CH3 oscillate versus Ecol, whereas experimentally this only occurs for HCl (ν′=1). This theoretical result and other oscillating properties found here could, however, be related to the existence of a Feshbach resonance for the production of HCl (ν′=1), as suggested by experimentalists.
Connection between the virial equation of state and physical clusters in a low density vapor
Authors: Merikanto Joonas , Zapadinsky Evgeni , Lauri Antti , Napari Ismo , Vehkamäki Hanna
Published: September 2007

We carry out Monte Carlo simulations of physical Lennard-Jones and water clusters and show that the number of physical clusters in vapor is directly related to the virial equation of state. This relation holds at temperatures clearly below the critical temperatures, in other words, as long as the cluster-cluster interactions can be neglected—a typical assumption used in theories of nucleation. Above a certain threshold cluster size depending on temperature and interaction potential, the change in cluster work of formation can be calculated analytically with the recently proposed scaling law. The breakdown of the scaling law below the threshold sizes is accurately modeled with the low order virial coefficients. Our results indicate that high order virial coefficients can be analytically calculated from the lower order coefficients when the scaling law for cluster work of formation is valid. The scaling law also allows the calculation of the surface tension and equilibrium vapor density with computationally efficient simulations of physical clusters. Our calculated values are in good agreement with those obtained with other methods. We also present our results for the curvature dependent surface tension of water clusters.
Dynamic disorder in single-molecule Michaelis-Menten kinetics: The reaction-diffusion formalism in the Wilemski-Fixman approximation
Authors: Chaudhury Srabanti , Cherayil Binny J.
Published: September 2007

Single-molecule equations for the Michaelis-Menten [Biochem. Z. 49, 333 (1913)] mechanism of enzyme action are analyzed within the Wilemski-Fixman [J. Chem. Phys. 58, 4009 (1973); 60, 866 (1974)] approximation after the effects of dynamic disorder—modeled by the anomalous diffusion of a particle in a harmonic well—are incorporated into the catalytic step of the reaction. The solution of the Michaelis-Menten equations is used to calculate the distribution of waiting times between successive catalytic turnovers in the enzyme β-galactosidase. The calculated distribution is found to agree qualitatively with experimental results on this enzyme obtained at four different substrate concentrations. The calculations are also consistent with measurements of correlations in the fluctuations of the fluorescent light emitted during the course of catalysis, and with measurements of the concentration dependence of the randomness parameter.
Prostate specific antigen detection using AlGaN∕GaN high electron mobility transistors
Authors: Kang B. S. , Wang H. T. , Lele T. P. , Tseng Y. , Ren F. , Pearton S. J. , Johnson J. W. , Rajagopal P. , Roberts J. C. , Piner E. L. , Linthicum K. J.
Published: September 2007

Antibody-functionalized Au-gated AlGaN∕GaN high electron mobility transistors (HEMTs) were used to detect prostate specific antigen (PSA). The PSA antibody was anchored to the gate area through the formation of carboxylate succinimdyl ester bonds with immobilized thioglycolic acid. The AlGaN∕GaN HEMT drain-source current showed a rapid response of less than 5s when target PSA in a buffer at clinical concentrations was added to the antibody-immobilized surface. The authors could detect a wide range of concentrations from 10pg∕mlto1μg∕ml. The lowest detectable concentration was two orders of magnitude lower than the cutoff value of PSA measurements for clinical detection of prostate cancer. These results clearly demonstrate the promise of portable electronic biological sensors based on AlGaN∕GaN HEMTs for PSA screening.
On stratification control of the velocity fluctuations in sedimentation
Authors: Gómez Daniel Chehata , Bergougnoux Laurence , Hinch John , Guazzelli Élisabeth
Published: September 2007

We have tested whether stratification can govern local velocity fluctuations in suspensions of sedimenting spheres. Comparison of the proposed scaling for local control of fluctuations by stratification to experimental data demonstrates that this mechanism cannot account for the reduction of the observed velocity fluctuations.
Influence of chemical and magnetic interface properties of Co-Fe-B/MgO/Co-Fe-B tunnel junctions on the annealing temperature dependence of the magnetoresistance
Authors: Schmalhorst J. , Thomas A. , Reiss G. , Kou X. , Arenholz E.
Published: September 2007

The knowledge of chemical and magnetic conditions at the Co40Fe40B20∕MgO interface is important to interpret the strong annealing temperature dependence of tunnel magnetoresistance of Co-Fe-B/MgO/Co-Fe-B magnetic tunnel junctions, which increases with annealing temperature from 20% after annealing at 200 °C up to a maximum value of 112% after annealing at 350 °C. While the well defined nearest neighbor ordering indicating crystallinity of the MgO barrier does not change by the annealing, a small amount of interfacial Fe-O at the lower Co-Fe-B/MgO interface is found in the as grown samples, which is completely reduced after annealing at 275 °C. This is accompanied by a simultaneous increase of the Fe magnetic moment and the tunnel magnetoresistance. However, the tunneling magnetoresistance of the MgO based junctions increases further for higher annealing temperature which cannot be caused by Fe-O reduction. The occurrence of an x-ray absorption near-edge structure above the Fe and Co L edges after annealing at 350 °C indicates the recrystallization of the Co-Fe-B electrode. This is a prerequisite for coherent tunneling and has been suggested to be responsible for the further increase of the tunneling magnetoresistance above 275 °C. Simultaneously, the B concentration in the Co-Fe-B decreases with increasing annealing temperature, at least some of the B diffuses toward or into the MgO barrier and forms a B2O3 oxide.
Incorporation of oxygen into thermally evaporated germanium and optical characterization of the resulting films
Authors: Al-Kuhaili M. F. , Durrani S. M. A.
Published: September 2007

Germanium powder was thermally evaporated under a vacuum onto unheated substrates as well as substrates heated to 200 °C. The striking feature was that the resulting films were transparent. Chemical analysis using x-ray photoelectron spectroscopy depth profiling indicated that oxygen was present throughout the thickness of the films, and therefore the films were composed of substoichiometric germanium oxide. The source of oxygen was investigated, and traced to the source material. Subsequently, the optical constants and the band gaps of the films were determined from spectrophotometric measurements. These properties were found to be intermediate between those of pure germanium and germanium dioxide, with values appropriate for optical applications in the visible range.
Cr-doping-induced phase separation and MR effect in the manganite Pr0.5Ca0.5Mn1−xCrxO3 system
Authors: Cao Shixun , Li Wenjuan , Zhang Jincang , Kang Baojuan , Gao Tian , Jing Chao
Published: September 2007

Systematic study on magnetic and electrical transport properties has been performed on the Cr-doped Pr0.5Ca0.5Mn1−xCrxO3 (x=0, 0.03, 0.05, 0.07, 0.10) system. The results show that Cr-doping leads to melting of the charge ordering and induces phase separation. For the sample x=0.10, reentrant spin glass behavior is observed and the slowing down model is applicable. The reentrant spin glass behavior and the phase coexistence of charge ordering (CO) and the ferromagnetic metal phase (FMM) are responsible for the changing magnetoresistance effect of the system. The phase separation or coexistence of the CO and FM phase induced by Cr-doping plays an important role in the low temperature properties for the system.
Nitrogen incorporation and optical studies of GaAsSbN∕GaAs single quantum well heterostructures
Authors: Nunna Kalyan , Iyer S. , Wu L. , Li J. , Bharatan S. , Wei X. , Senger R. T. , Bajaj K. K.
Published: September 2007

In this work, the effects of N incorporation on the optical properties of GaAsSbN∕GaAs single quantum wells (SQWs) have been investigated using temperature, excitation, and magnetic dependencies of photoluminescence (PL) characteristics. These layers were grown in an elemental solid source molecular beam epitaxy system with a rf plasma N source. The N concentrations in the range of 0.5%–2.5% were investigated in this study. The SQW with N∼0.5% exhibits a behavior similar to that in an intermediate regime where the contributions from the localized states in the band gap are dominant. The temperature and excitation dependencies of the PL characteristics indicate that for the N concentration of 0.9% and above, the alloy behavior is analogous to that of a regular alloy and the changes in optical properties are only marginal. The conduction band effective mass (meff) values computed from the magnetophotoluminescence spectra using a variational formalism and the band anticrossing model are in good agreement and indicate enhanced values of meff. However, there is no significant variation in meff values of QWs for N⩾0.9%. Small redshift of about 30–50meV for the temperature variations from 10to300K in conjunction with unusually small blueshift observed in the excitation dependence of PL for N⩾0.9% indicate that this system holds a great promise for laser applications at 1.55μm and beyond.
An adhesion model for elastic-plastic fractal surfaces
Authors: Peng Y. F. , Guo Y. B.
Published: September 2007

The strong adherence (stiction) of adjacent surfaces is a major design concern in microelectromechanical system. The present research concerns the elastic-plastic adhesion of a rough surface contacting with a rigid flat. Rough surface is characterized by fractal geometry using a two-variable Weierstrass-Mandelbrot function [The Fractal Geometry of Nature (Freeman, New York, 1982)]. The microcontact model of single asperity is established in terms of fractal parameters, and the plastic adhesion model is also developed with the Dugdale approximation to consider the adhesive interaction within and outside the contact area. Then according to the plastic flow criterion, the Maguis-Dugdale transition theory [Adhesion of Adhesion and Rapture of Elastic Solids (Springer-Verlag, New York, 2005)] and the plastic adhesion model are used to solve the elastic-plastic adhesive interaction for the two approaching surfaces by incorporating the fractal surface model. Simulations of the adherence force versus the approaching distance of surfaces are performed. The necessity of considering the plastic deformation in microsized interface adhesion is also validated by comparing the result of the presented model with that of the Morrow model [J. Tribol 127, 206 (2005)]. The influence of fractal parameters on adherence force shows that controlling the surface topography is a readily means to control the adherence force for the elastic-plastic adhesion of rough surfaces, which is due to the intermolecular adhesive interactions.
Effective density-of-states distribution of polycrystalline silicon thin-film transistors under hot-carrier degradation
Authors: Lee Ming-Hsien , Chang Kai-Hsiang , Lin Horng-Chih
Published: September 2007

In this work, quantitative information for nonuniform hot-carrier degradation, especially under mild stressing condition, is investigated. A test structure capable of revealing hot-carrier degradations of polycrystalline silicon (poly-Si) thin-film transistors in specific portions of the channel is employed. Effective density-of-states (DOS) distributions at the damaged sites can be extracted using field-effect conductance method, thus providing an effective tool to evaluate the impact of hot-carrier degradations. By measuring along individual sections of the channel, it becomes possible to extract the DOS for the device as a whole. The combination of the proposed test structure and DOS extraction technique also provides a powerful tool for modeling and simulating current-voltage characteristics of thin-film transistors under hot-carrier stressing.
Buckling analysis of abnormal multiwalled carbon nanotubes
Authors: Liew K. M. , Wang J. B. , He X. Q. , Zhang H. W.
Published: September 2007

Abnormal multiwalled carbon nanotubes (MWNTs) with an interlayer distance of less than 0.34nm are proposed and optimized based on molecular dynamics simulation, in which the second-generation Tersoff-Brenner potential and Lennard-Jones (12-6) potential are used to characterize the intratube interatomic interaction and the intertube van der Waals (vdW) interaction, respectively. Then, a multishell continuum model that is combined with a refined vdW force model is used to carry out the buckling analysis of abnormal MWNTs (including two-, four-, and six-walled MWNTs) and to investigate the effect of the vdW interaction of abnormal MWNTs. The numerical results show that the effect of the vdW interaction is more significant for abnormal MWNTs than for normal MWNTs and that the vdW interaction of abnormal MWNTs cannot be neglected. The critical buckling strains of abnormal MWNTs are greatly enhanced compared with those of normal MWNTs, which suggests that abnormal MWNTs may be excellent candidates as enforced fibers of nanocomposites.
Transverse domain walls in nanoconstrictions
Authors: Backes D. , Schieback C. , Kläui M. , Junginger F. , Ehrke H. , Nielaba P. , Rüdiger U. , Heyderman L. J. , Chen C. S. , Kasama T. , Dunin-Borkowski R. E. , Vaz C. A. F. , Bland J. A. C.
Published: September 2007

The spin structure of domain walls in constrictions down to 30nm is investigated both experimentally with electron holography and with simulations using a Heisenberg model. Symmetric and asymmetric transverse domain walls for different constriction sizes are observed, consistent with simulations. The experimentally observed asymmetric transverse walls can be further divided into tilted and buckled walls, the latter being an intermediate state just before the vortex nucleation. As the constriction width decreases, the domain wall width decreases faster than linearly, which leads to very narrow domain walls for narrow constrictions.
Strain-relaxed structure in (001)∕(100)-oriented epitaxial PbTiO3 films grown on (100) SrTiO3 substrates by metal organic chemical vapor deposition
Authors: Nakaki Hiroshi , Kim Yong Kwan , Yokoyama Shintaro , Ikariyama Rikyu , Funakubo Hiroshi , Nishida Ken , Saito Keisuke
Published: September 2007

The authors grew (001)- and (001)∕(100)-oriented epitaxial PbTiO3 films with various thicknesses on (100)SrTiO3 substrates. They used x-ray diffraction to measure the angles between surface normal [001] of (001)-oriented domains and [100] of (100)-oriented domains. The angles were found to be approximately 3.6° when the film thickness exceeded 1100nm. This value is consistent with the value obtained by a geometric calculation for strain-free PbTiO3. This result suggests that thick epitaxial PbTiO3 films grown on (100)SrTiO3 substrates have a fully strain-relaxed structure.
Canonical and nonlinear vector coherent states of generalized models with spin-orbit interaction
Authors: Ben Geloun Joseph , Hounkonnou M. Norbert
Published: September 2007

Through canonical and f deformation quantizations, classes of nonlinear spin-orbit interaction models are considered. These generalized models are relevant in condensed matter physics and quantum optics in domains of nonlinear spin-Hall effect or of the multiphoton Jaynes-Cummings [Proc. IEEE 51, 89 (1963)] model, for instance. A spectral decomposition follows the exact diagonalization of the Hamiltonian and leads to the definition of ladder operators acting on the associated Hilbert space. Nonlinear vector coherent states are then constructed from a general lowering operator action. Explicit solutions of their related moment problems in ordinary and f-deformed theories are displayed, thus providing new classes of coherent states for such generalized spin-orbit models.
Thermodynamic formalism of minimum heat source temperature for driving advanced adsorption cooling device
Authors: Saha Bidyut Baran , Chakraborty Anutosh , Koyama Shigeru , Srinivasan Kandadai , Ng Kim Choon , Kashiwagi Takao , Dutta Pradip
Published: September 2007

This letter presents a thermodynamic formulation to calculate the minimum driving heat source temperature of an advanced solid sorption cooling device, and it is validated with experimental data. This formalism has been developed from the rigor of the Boltzmann distribution function and the condensation approximation of adsorptive molecules. An interesting and useful finding has been established from this formalism that it is possible to construct a solid sorption refrigeration device that operates in a cycle transferring heat from a low temperature source to a heat sink with a driving heat source at a temperature close to but above ambient.
Giant strain in lead-free piezoceramics Bi0.5Na0.5TiO3–BaTiO3–K0.5Na0.5NbO3 system
Authors: Zhang Shan-Tao , Kounga Alain Brice , Aulbach Emil , Ehrenberg Helmut , Rödel Jürgen
Published: September 2007

Piezoelectric actuators convert electrical into mechanical energy and are implemented for many large-scale applications such as piezoinjectors and ink jet printers. The performance of these devices is governed by the electric-field-induced strain. Here, the authors describe the development of a class of lead-free (0.94−x)Bi0.5Na0.5TiO3–0.06BaTiO3–xK0.5Na0.5NbO3 ceramics. These can deliver a giant strain (0.45%) under both unipolar and bipolar field loadings, which is even higher than the strain obtained with established ferroelectric Pb(Zr,Ti)O3 ceramics and is comparable to strains obtained in Pb-based antiferroelectrics.
Resonant Raman scattering in hydrogen and nitrogen doped ZnO
Authors: Friedrich F. , Nickel N. H.
Published: September 2007

Raman backscattering measurements were performed on single crystal ZnO for different excitation wavelengths before and after ion implantation with hydrogen and nitrogen. In addition to the formation of H- and N-related defects due to implantation, anomalous Raman modes were observed. Recently, the anomalous Raman modes have been attributed to the disorder-induced activation of silent modes. However, we will show that part of the observed modes are due to the resonantly enhanced longitudinal optical phonons.