bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Terrain Mask on RAIM Availability
Authors: Radišić Tomislav , Novak Doris , Bucak Tino
Published: December 2009

Receiver Autonomous Integrity Monitoring (RAIM) is a method, used by an aircraft's receiver, for detecting and isolating faulty satellites of the Global Navigation Satellite System (GNSS). In order for a receiver to be able to detect and isolate a faulty satellite using a RAIM algorithm, a couple of conditions must be met: a minimum number of satellites, and an adequate satellite geometry. Due to the highly predictable orbits of the GPS satellites, a RAIM availability prediction can be done easily. A number of RAIM methods exist; however, none of them takes into account the precise terrain masking of the satellites for the specific location. They consider a uniform fixed mask angle over the whole horizon. This paper will introduce the variable mask RAIM algorithm in order to show to what extent the terrain can affect the RAIM availability and how much it differs from the conventional algorithms.
Seismic wave generation by a nonisotropic explosion source
Authors: Stevens Jeffry L. , Baker G. Eli
Published: December 2009

We develop a general solution for seismic wave generation by an explosion source in a spherical cavity, and then a specific solution for a point explosion source offset from the cavity center. We find that the offset causes a dipole component to the source which generates S waves and causes angular variation in P wave amplitude and shape. The S waves vanish at zero frequency but may be a sizable fraction of the P waves at frequencies of interest. We also perform a nonlinear axisymmetric calculation of an offset explosion in a spherical cavity, which causes a complex source due to cavity reverberations and generates S waves comparable to those found from the analytic solution. The solution has application to shear wave generation by decoupled explosions, and explains at least part of the shear waves observed from such explosions. Data from a pair of explosions centered and offset from the center of a spherical cavity show the expected enhancement of shear waves from the offset source.
Oceanic response to interactive momentum flux over Southern Hemisphere sea ice
Authors: Cheon Woo Geun , Stössel Achim
Published: December 2009

The Southern Ocean (SO) winds affect the global ocean circulation via their direct atmosphere‐to‐ocean wind‐stirring effects remotely driving the North Atlantic (NA) overturning. In this study, an indirect atmosphere–sea ice–ocean buoyancy‐driven effects under the SO winds are investigated in the framework of a coupled sea ice–ocean general circulation model. Over the SO sea ice, an interactive momentum flux (IMF) forcing is introduced to investigate the effect of the strength of the sea ice–atmosphere coupling on the long‐term ocean circulation. To estimate the robustness of the oceanic response to the IMF parameterization, it is applied to three fundamentally different reference experiments. By allowing the strength of the momentum flux between atmosphere and sea ice to vary in response to the simulated sea ice conditions, the IMF enhances wind‐driven sea ice divergence to increase the fraction of leads and polynyas, which intensifies convection. The ensuing increase in dense water formation along Antarctica increases the amount of Antarctic Bottom Water being formed, which intensifies the Southern Hemisphere (SH) overturning and indirectly weakens the NA overturning. As a result of these hemispheric changes, the meridional density gradient across the Antarctic Circumpolar Current (ACC) increases, leading to an increase in the ACC. This study shows that the SH atmosphere–sea ice–ocean system can play an active, primary role in the global ocean circulation and provides insights on the possible linkage between the SH winds, the SH overturning, and the NA overturning via buoyancy‐driven effects associated with SO sea ice.
Hindcasting of decadal‐timescale estuarine bathymetric change with a tidal‐timescale model
Authors: Ganju Neil K. , Schoellhamer David H. , Jaffe Bruce E.
Published: December 2009

Hindcasting decadal‐timescale bathymetric change in estuaries is prone to error due to limited data for initial conditions, boundary forcing, and calibration; computational limitations further hinder efforts. We developed and calibrated a tidal‐timescale model to bathymetric change in Suisun Bay, California, over the 1867–1887 period. A general, multiple‐timescale calibration ensured robustness over all timescales; two input reduction methods, the morphological hydrograph and the morphological acceleration factor, were applied at the decadal timescale. The model was calibrated to net bathymetric change in the entire basin; average error for bathymetric change over individual depth ranges was 37%. On a model cell‐by‐cell basis, performance for spatial amplitude correlation was poor over the majority of the domain, though spatial phase correlation was better, with 61% of the domain correctly indicated as erosional or depositional. Poor agreement was likely caused by the specification of initial bed composition, which was unknown during the 1867–1887 period. Cross‐sectional bathymetric change between channels and flats, driven primarily by wind wave resuspension, was modeled with higher skill than longitudinal change, which is driven in part by gravitational circulation. The accelerated response of depth may have prevented gravitational circulation from being represented properly. As performance criteria became more stringent in a spatial sense, the error of the model increased. While these methods are useful for estimating basin‐scale sedimentation changes, they may not be suitable for predicting specific locations of erosion or deposition. They do, however, provide a foundation for realistic estuarine geomorphic modeling applications.
Coherent composition of glacial dust on opposite sides of the East Antarctic Plateau inferred from the deep EPICA ice cores
Authors: Marino F. , Castellano E. , Nava S. , Chiari M. , Ruth U. , Wegner A. , Lucarelli F. , Udisti R. , Delmonte B. , Maggi V.
Published: December 2009

The dust provenance identification through isotopic and geochemical tracers focused mostly on ice cores drilled in the Pacific‐Indian sector of Antarctica, where a common provenance of dust from Southern South America during glacial ages was demonstrated. Conversely, in other areas of the East Antarctic Plateau as Dronning Maud Land provenance was deduced indirectly from back trajectory analyses and soluble chemistry records. In this work, we present the first comparison of major elemental composition of dust archived in two ice cores from opposite sides of Antarctica, in the framework of the EPICA Project. Mineral particles extracted from the EDC and EDML cores date back to glacial MIS 2, 4 and 6, over the last 200 kyr. Results reveal a coherent geochemical dust composition at both locations, providing experimental evidence of a common provenance over the wide area of East Antarctica during glacials, and key analytical constrains for atmospheric general circulation models.
Sulfur dioxide inhibits calcium carbonate precipitation: Implications for early Mars and Earth
Authors: Halevy I. , Schrag D. P.
Published: December 2009

Recent studies have suggested a role for sulfur dioxide (SO2) in maintaining relatively warm surface temperatures on early Mars. Here we show experimentally, that SO2 concentrations orders of magnitude lower than those required for it to have been of climatic importance strongly affect the aqueous chemistry and the precipitated mineral assemblage. At near‐neutral pH, part‐per‐billion concentrations of SO2 prevent the formation of calcium carbonate in favor of hannebachite, a hydrated calcium sulfite. In the presence of iron, possible precursors to phyllosilicate minerals and iron carbonate co‐precipitate with hannebachite. This provides an explanation for the existence of early Noachian phyllosilicates in the apparent dearth of outcrop‐scale calcium carbonates. Oxidation of this precipitated assemblage produces sulfates, iron oxides and acidity, consistent with evidence for late Noachian–early Hesperian acid‐sulfate dominated environments. For early Earth, the results allow placing an upper limit on atmospheric SO2 concentrations for any period in which carbonates exist in the geologic record.
Strong bottom currents and cyclogenesis in Drake Passage
Authors: Chereskin T. K. , Donohue K. A. , Watts D. R. , Tracey K. L. , Firing Y. L. , Cutting A. L.
Published: December 2009

Observations from 38 bottom‐moored Current and Pressure Recording Inverted Echo Sounders (CPIES) deployed in Drake Passage during the 2007–2008 International Polar Year provide unprecedented coverage of near‐bottom currents and pressures spanning the entire Antarctic Circumpolar Current. Year‐long‐mean currents exceed 10 cm s−1 north of the Polar Front, and mean directions are not, in general, aligned with the surface fronts. Topographic steering is most evident at the continental margins. Deep eddy kinetic energy (EKE) is maximum at about 200 cm2 s−2 between the Subantarctic and Polar Fronts, coinciding with the location but about one quarter of the value of a maximum in surface EKE. Multiple high‐speed current events, with peak speeds of 60–70 cm s−1 and lasting 30 to 70 days, are coherent across sites separated by 45 km. The observed spinup of eddies coinciding with meanders in the surface fronts is consistent with deep cyclogenesis.
Seasonal salt budget in the northeast Pacific Ocean
Authors: Ren Li , Riser Stephen C.
Published: December 2009

The mixed layer salinity budget in the northeastern subarctic Pacific is evaluated using 5 years (2003–2007) of Argo profiling float data, precipitation and evaporation, geostrophic velocity data, and wind stress observations. In this region the mixed layer salinity has a strong seasonal cycle, driven by seasonality in precipitation, evaporation, Ekman advection, and entrainment. Geostrophic advection effects show relatively little seasonal variability. Precipitation and Ekman effects in this area generally result in net decreases in salinity, while the evaporation, geostrophic advection, and entrainment terms yield increases. Within an annual cycle, the salinity tendency is positive during winter and fall, balanced by surface fluxes (evaporation and precipitation), entrainment, and geostrophic advection. The salinity tendency is negative during spring and summer. During these two seasons, it appears that salinity is controlled by precipitation, evaporation, and geostrophic advection. Overall, the precipitation term makes the largest contribution to the seasonal salinity budget, and the entrainment is especially important in autumn and winter.
Validation of the Harvard Lyman‐α in situ water vapor instrument: Implications for the mechanisms that control stratospheric water vapor
Authors: Weinstock E. M. , Smith J. B. , Sayres D. S. , Pittman J. V. , Spackman J. R. , Hintsa E. J. , Hanisco T. F. , Moyer E. J. , St. Clair J. M. , Sargent M. R. , Anderson J. G.
Published: December 2009

Building on previously published details of the laboratory calibrations of the Harvard Lyman‐α photofragment fluorescence hygrometer (HWV) on the NASA ER‐2 and WB‐57 aircraft, we describe here the validation process for HWV, which includes laboratory calibrations and intercomparisons with other Harvard water vapor instruments at water vapor mixing ratios from 0 to 10 ppmv, followed by in‐flight intercomparisons with the same Harvard hygrometers. The observed agreement exhibited in the laboratory and during intercomparisons helps corroborate the accuracy of HWV. In light of the validated accuracy of HWV, we present and evaluate a series of intercomparisons with satellite and balloon borne water vapor instruments made from the upper troposphere to the lower stratosphere in the tropics and midlatitudes. Whether on the NASA ER‐2 or WB‐57 aircraft, HWV has consistently measured about 1–1.5 ppmv higher than the balloon‐borne NOAA/ESRL/GMD frost point hygrometer (CMDL), the NOAA Cryogenic Frost point Hygrometer (CFH), and the Microwave Limb Sounder (MLS) on the Aura satellite in regions of the atmosphere where water vapor is <10 ppmv. Comparisons in the tropics with the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite show large variable differences near the tropopause that converge to ∼10% above 460 K, with HWV higher. Results we show from the Aqua Validation and Intercomparison Experiment (AquaVIT) at the AIDA chamber in Karlsruhe do not reflect the observed in‐flight differences. We illustrate that the interpretation of the results of comparisons between modeled and measured representations of the seasonal cycle of water entering the lower tropical stratosphere is dictated by which data set is used.
Compact Reconnaissance Imaging Spectrometer for Mars observations of northern Martian latitudes in summer
Authors: Calvin W. M. , Roach L. H. , Seelos F. P. , Seelos K. D. , Green R. O. , Murchie S. L. , Mustard J. F.
Published: December 2009

This paper brings together initial results obtained of the high northern latitudes in Mars years 28 and 29, between October 2006 and October 2008. These measurements confirm many previous models and shed new light on the nature of polar surface materials, particularly in intermediate‐albedo units of the polar layered deposits, many of which are found to be ice‐rich. We identify hydrated non ice materials present in many low‐albedo troughs, as well as in the circumpolar erg that was previously associated with gypsum. We identify icy outlier deposits that may be related to subsurface thermophysical properties and permafrost. New observations of the gypsum‐rich dune material constrain models for its formation and distribution. Intrinsic properties of ice content and grain size are found to be independent of the albedo of fine layered units and may provide a novel method for stratigraphic identification and correlation.
Speak to me, melody
Authors: Rinaldi Andrea
Published: December 2009

Is the ability to create and appreciate music special, or is it just a different form of communication? Andrea Rinaldi takes a look at the latest research into the origin and function of music.
The public option
Authors: Kuzma Jennifer , Meghani Zahra
Published: December 2009

US President Barack Obama has called for more public participation in regulatory decisions. Jennifer Kuzma and Zahra Meghani explore the possible consequences for the regulation and approval of genetically modified crops in the USA.
A potential role for RAG‐1 in NK cell development revealed by analysis of NK cells during ontogeny
Authors: Andrews Daniel M , Smyth Mark J
Published: December 2009

Little is known regarding natural killer (NK) cell development in hematopoietic and visceral organs during ontogeny. We sought to determine NK cell accumulation during ontogeny and whether organ‐specific niches altered development. Neonatal NK cells in the bone marrow, spleen and lung exist as immature CD27+/CD11Blo cells. The first appearance of mature CD27lo/CD11B+ cells occurs at 3 weeks of age whereas maturation is complete by 8 weeks. In contrast, maturation of liver NK cells is essentially finished at 2 weeks. A role for RAG‐1 (recombination‐activating gene‐1 product) in NK cell development was suggested as RAG‐1‐deficient mice accumulated NK cells differently. Surprisingly, bone marrow and spleen NK cells are absent in neonatal RAG‐1−/− mice and an overrepresentation of a precursor NK cell subset, found normally in the liver, was observed in the bone marrow of RAG‐1−/− mice. As mice lacking specific adaptive immune elements, including T and/or B cells, have normal NK cell repertoires, a more direct role for RAG during NK cell development cannot be excluded. Liver NK cells may represent an independent pool of cells from those developing out of the bone marrow, and RAG‐1 itself may have a significant role in NK cell development.
Evidence of STAT5‐dependent and ‐independent routes to CD8 memory formation and a preferential role for IL‐7 over IL‐15 in STAT5 activation
Authors: Kemp Roslyn A , Pearson Claire F , Cornish Georgina H , Seddon Benedict P
Published: December 2009

Interleukin (IL)‐7 and IL‐15 have non‐redundant roles in promoting development of memory CD8+ T cells. STAT5 is activated by receptors of both cytokines and has also been implicated as a requirement for generation of memory. To determine whether STAT5 activity was required for IL‐7 and IL‐15‐mediated generation of memory, we expressed either wild type (WT) or constitutively active (CA) forms of STAT5a in normal effector cells and then observed their ability to form memory in cytokine replete or deficient hosts. Receptor‐independent CA‐STAT5a significantly enhanced memory formation in the absence of either cytokine but did not mediate complete rescue. Interestingly, WT‐STAT5a expression enhanced memory formation in a strictly IL‐7‐dependent manner, suggesting that IL‐7 is a more potent activator of STAT5 than IL‐15 in vivo. These data suggest that the non‐redundant requirement for IL‐7 and IL‐15 is mediated through differential activation of both STAT5‐dependent and STAT5‐independent pathways.
Effects of biological drug adalimumab on tumour necrosis factor‐α‐converting enzyme activation
Authors: Lisi Sabrina , Sisto Margherita
Published: December 2009

Tumour necrosis factor‐α (TNF‐α)‐converting enzyme (TACE) is a membrane‐bound metalloprotease and disintegrin. It is produced by a number of host cells and is known to shed and release cell‐bound cytokines, particularly members of the TNF family. No investigations into the regulation of this enzyme by autoantibodies have been reported. In this study, we tested the hypothesis that anti‐Ro/SSA autoantibodies, purified from IgG fractions of patients with primary Sjögren's syndrome, are capable to regulate TACE expression and activation in human salivary gland epithelial cells (SGEC). We also evaluated the potential physiological and therapeutic consequences of TNF‐α blocking by the biological agent adalimumab, the first fully human (100% human peptide sequences) therapeutic anti‐TNF‐α antibody, on post‐translational regulation of TACE. Taken together, our results show a dose‐dependent increase in TACE expression in anti‐Ro/SSA Abs‐treated SGEC, followed by internalization, pro‐domain shedding and activation of TACE protein. Adalimumab treatment brought TACE expression to levels than those observed in untreated SGEC. These findings, showing the presence of autoantibodies‐dependent mechanisms by which TACE levels are regulated in human SGECs, may have implications in the context of current investigations on the pathological role of autoantibodies.
Transforming the Axiomisation of Ontologies: The Ontology Pre-Processor Language
Authors: Egaña Aranguren Mikel , Stevens Robert , Antezana Erick
Published: December 2009

As ontologies are developed there is a common need to transform them, especially from those that are axiomatically lean to those that are axiomatically rich. Such transformations often require large numbers of axioms to be generated that affect many different parts of the ontology. This paper describes the Ontology Pre-Processor Language (OPPL), a domain-specific macro language, based in the Manchester OWL Syntax, for manipulating ontologies written in OWL. OPPL instructions can add/remove entities, and add/remove axioms (semantics or annotations) to/from entities in an OWL ontology. OPPL is suitable for applying the same change to different ontologies or at different development stages, and for keeping track of the changes made (e.g. in pipelines). It is also suitable for defining independent modelling macros (e.g. Ontology Design Patterns) that can be applied at will and systematically across an ontology. The presented OPPL Instruction Manager is a Java library that processes OPPL instructions making the changes to an OWL ontology. A reference implementation that uses the OPPL Instruction Manager is also presented. The use of OPPL has been demonstrated in the Cell Cycle Ontology
Familial Aggregation of Age-Related Hearing Loss in an Epidemiological Study of Older Adults
Authors: Raynor Laura A. , Pankow James S. , Miller Michael B. , Huang Guan-Hua , Dalton Dayna , Klein Ronald , Klein Barbara E. K. , Cruickshanks Karen J.
Published: December 2009

Purpose

To estimate the genetic contributions to presbycusis.

Method

Presbycusis was assessed by audiometric measurements at 3 waves of the population-based Epidemiology of Hearing Loss Study (EHLS). Measurements from the most recent hearing examination were used, at which time the subjects (3,510 participants from the EHLS study) were between 48 and 100 years of age. Heritability of presbycusis was estimated using maximum likelihood methods in 973 biological relative pairs from 376 families. Familial aggregation was also evaluated by tetrachoric correlations, odds ratios, and lambda statistics in 594 sibling pairs from 373 sibships.

Results

The prevalence of presbycusis conformed to previous research, increasing with age and male sex. Heritability estimates for presbycusis adjusted for age, sex, education level, and exposure to work noise exceeded 50%, and siblings of an affected relative were at 30% higher risk. When stratified by sex, estimates of familial aggregation were higher in women than men.

Conclusions

There is evidence that genetic factors contribute to age-related hearing loss in this population-based sample. The familial aggregation is stronger in women than in men.
The Development of Distinct Speaking Styles in Preschool Children
Authors: Redford Melissa A. , Gildersleeve-Neumann Christina E.
Published: December 2009

Purpose

To examine when and how socially conditioned distinct speaking styles emerge in typically developing preschool children’s speech.

Method

Thirty preschool children, ages 3, 4, and 5 years old, produced target monosyllabic words with monophthongal vowels in different social–functional contexts designed to elicit clear and casual speaking styles. Thirty adult listeners were used to assess whether and at what age style differences were perceptible. Children’s speech was acoustically analyzed to evaluate how style-dependent differences were produced.

Results

The ratings indicated that listeners could not discern style differences in 3-year-olds' speech but could hear distinct styles in 4-year-olds' and especially in 5-year-olds' speech. The acoustic measurements were consistent with these results: Style-dependent differences in 4- and 5-year-olds' words included shorter vowel durations and lower fundamental frequency in clear compared with casual speech words. Five-year-olds' clear speech words also had more final stop releases and initial sibilants with higher spectral energy than did their casual speech words. Formant frequency measures showed no style-dependent differences in vowel production at any age nor any differences in initial stop voice onset times.

Conclusion

Overall, the findings suggest that distinct styles develop slowly and that early style-dependent differences in children’s speech are unlike those observed in adult clear and casual speech. Children may not develop adultlike styles until they have acquired expert articulatory control and the ability to highlight the internal structure of an articulatory plan for a listener.
Spoken Word Recognition in Toddlers Who Use Cochlear Implants
Authors: Grieco-Calub Tina M. , Saffran Jenny R. , Litovsky Ruth Y.
Published: December 2009

Purpose

The purpose of this study was to assess the time course of spoken word recognition in 2-year-old children who use cochlear implants (CIs) in quiet and in the presence of speech competitors.

Method

Children who use CIs and age-matched peers with normal acoustic hearing listened to familiar auditory labels, in quiet or in the presence of speech competitors, while their eye movements to target objects were digitally recorded. Word recognition performance was quantified by measuring each child’s
reaction time
(i.e., the latency between the spoken auditory label and the first look at the target object) and
accuracy
(i.e., the amount of time that children looked at target objects within 367 ms to 2,000 ms after the label onset).

Results

Children with CIs were less accurate and took longer to fixate target objects than did age-matched children without hearing loss. Both groups of children showed reduced performance in the presence of the speech competitors, although many children continued to recognize labels at above-chance levels.

Conclusion

The results suggest that the unique auditory experience of young CI users slows the time course of spoken word recognition abilities. In addition, real-world listening environments may slow language processing in young language learners, regardless of their hearing status.
Effects of Vascular Dementia on Cognition and Linguistic Communication: A Case Study
Authors: Mahendra Nidhi , Engineer Nisha
Published: December 2009

Purpose: Vascular dementia is the second most common cause of dementia after Alzheimer's's disease. The purpose of this case report is to describe the evolution and progression of vascular dementia over two years and detail its effects on multiple measures of cognition and linguistic communication.

Methods: Data from multiple sources (e.g., medical records, direct testing, staff reports, and client observations) has been integrated to provide a detailed report of the effects of vascular dementia on global cognitive status and on specific domains of attention, episodic and semantic memory, executive function, visuospatial ability, linguistic comprehension, and linguistic expression.

Results and Conclusions: Vascular dementia affects multiple cognitive domains including language and communicative function. Clinical implications are presented for choice of tests and language tasks for evaluating the effects of vascular dementia on linguistic communication.
Fermiology via the electron momentum distribution (Review Article)
Authors: Kontrym-Sznajd G.
Published: December 2009

Investigations of the Fermi surface via the electron momentum distribution reconstructed from either angular correlation of annihilation radiation or Compton scattering experimental spectra are presented. The basis of these experiments and mathematical methods applied in reconstructing three-dimensional electron momentum densities from line or plane projections measured in these experiments are described. Finally, papers where such techniques have been applied to study the Fermi surface of metallic materials are reviewed.
Development of macroturbulent instability in a YBCO single crystal
Authors: Voloshin I. F. , Kalinov A. V. , Fisher L. M. , Yampol’skii V. A. , Bobyl A. , Johansen T. H.
Published: December 2009

An experimental study of macroturbulence in a superconducting YBCO single crystal is carried out. This macroturbulent instability arises upon a change of sign of the external magnetic field, resulting in the formation of a magnetization-reversal front, which divides the sample into regions occupied by vortices with opposite orientation (vortices and antivortices). The measurements are made by magnetooptical methods at a temperature of 40K. It is found that the development time of the macroturbulence depends substantially on the value of the external magnetic field H. With increasing H the macroturbulent process, which is accompanied by annihilation of vortices and antivortices, is accelerated on account of enhancement of the magnetic flux creep.
On the theoretical description of low-temperature effects in metals and doped semiconductors on the basis of the quantum theory of an electron liquid
Authors: Okulov V. I. , Pamyatnykh E. A. , Silin V. P.
Published: December 2009

A formulation of the initial principles of the quantum theory of an electron liquid as a basis for a theoretical description of the contribution of weakly excited single-particle states of an electronic system to the low-temperature properties of solids is presented. The present quantum-mechanical formulation, which leaves the real single-particle basis initially unspecified, makes it possible to study the role of the interelectronic interaction in the presence of orbital quantization and in circumstances where other quantum phenomena play a large role. A brief description is given of the derivation of the basic thermodynamic relations and expressions are given for the specific heat, elastic moduli, and magnetic susceptibility, all obtained on the basis of the Fermi-liquid approach without the conventionally used model assumptions. The application of the theory presented here to the description of the role of the interelectronic interaction in thermodynamic phenomena in systems with hybridized electronic states, formed by impurity donor resonance levels in the conduction band of a crystal, is examined. A formulation of an equation for the spontaneous localized spin magnetic moment in hybridized states is also presented.
A mesoscale model of DNA interaction with functionalized nanopore
Authors: Liu Yaling , Iqbal Samir M.
Published: December 2009

Functionalized nanopores have been used recently for the detection of specific DNA. The interactions between the DNA and the nanopore are not well understood due to the small size of DNA/nanopore and dynamic translocation process. Various chemical modifications have also been applied on nanopore surfaces for improved signal yield and selective detection. This paper develops an understanding of the interactions between translocating DNA and chemically modified nanopore surfaces. An energy-based mesoscale computational model is used to elucidate critical interrelationships between physical properties of the nanopore, electric field strength, and translocation kinetics. We report a nonlinear increase in DNA translocation speed with increasing electric field strength. The model predicts a transition in translocation from hybridization-driven to electric field-driven, in agreement with experimental data. This work advances the molecule-level understanding of the DNA-nanopore interface, and can help in designing optimized lab-on-chip devices for molecule based diagnosis.
Pressure effects on the stability of magnetic structure of Mn3Zn1−xGexN (x=,0.1)
Authors: Kong X. B. , Sun Y. , Yang L. X. , Yu Y. , Jin C. Q. , Wang C. , Yu R. C.
Published: December 2009

This paper reports that the pressure effects on the electronic transport properties of Mn3ZnN and Mn3Zn0.9Ge0.1N were measured under pressures up to 2.4 GPa. Cooling and warming cycles of the temperature-dependent magnetization curves of Mn3ZnN show a hysteresis phenomenon near the transition, implying a first order transition. The cracks which appear in the vicinity of magnetic transition at ambient pressure for Mn3ZnN and at applied pressures not more than 0.3 GPa for Mn3Zn0.9Ge0.1N are restrained under higher pressures. The paramagnetic-antiferromagnetic transition temperature TN decreases almost linearly at the rate of 1.9 and 51 K/GPa for Mn3ZnN and Mn3Zn0.9Ge0.1N respectively, which is explained by the model of TN discussed by Fruchart and the Labbé–Jardin tight-binding approximation model.
Application of a simple asynchronous mechanical light chopper to multielectron coincidence spectroscopy
Authors: Ito Kenji , Penent Francis , Hikosaka Yasumasa , Shigemasa Eiji , Suzuki Isao H. , Eland John H. D. , Lablanquie Pascal
Published: December 2009

A simple asynchronous mechanical light chopper, based on modification of a turbo-molecular pump, has been developed to extend the interval between light pulses in single bunch operation at the Photon Factory storage ring. A pulse repetition rate of 80 kHz was achieved using a cylinder rotating at 48000 rpm, with 100 slits of 80 μm width. This allows absolute timing of particles up to 12.48 μs instead of the single-bunch period of 624 ns. We have applied the chopper together with a light pulse monitor to measure multielectron coincidence spectra using a magnetic bottle time-of-flight electron spectrometer. With such a system, the electron energies are determined without any ambiguity, the folding of coincidence spectra disappears and the effect of false coincidences is drastically reduced.
Translation-rotation correction factor in the theory of homogeneous nucleation
Authors: Vosel S. V. , Onischuk A. A. , Purtov P. A.
Published: December 2009

An analytical formula for the correction factor which is to multiply the classical expression for the nucleation rate to account the translation and rotation of the critical nucleus is proposed. The formula is based on the Reiss approach considering the contribution from the clusters translational degrees of freedom, Frenkel's kinetic theory of liquids, and Kusaka's theory. Using this formula we determined the correction factor for argon vapor-to-liquid phase nucleation for the temperature range 80–110 K. These evaluations are in a good agreement with the correction factor calculated numerically by Kusaka (2006). Basing on the Gibbs theory of capillarity it is also shown that for the case of ideal gas-to-liquid nucleation the exponent in the classical formula for the rate of nucleation is strictly equal to the reversible work of drop formation.
Simple model analysis on the negative-ion extraction from a plasma
Authors: Lishev St. , Shivarova A. , Tarnev Kh.
Published: December 2009

Extraction of negative hydrogen ions from a plasma is analyzed with a view to the description of the extraction region of the negative hydrogen ion-beam sources developed for additional heating of fusion plasmas. The numerical procedure introduced in the study is a modification of the indirect Poisson–Vlasov method. It uses a condition for the plasma meniscus and employs analogy with the particle-in-cell model simulation. The analysis of the results shows that the charged particle velocity distribution at the entrance of the extraction region influences the properties of the extracted beams and its effect should be considered when conditions for well converged beams are looked for through variation in the plasma density and in the potentials of the electrodes of the extraction system.
Self-assembled Au nanoparticles in SiO2 by ion implantation and wet oxidation
Authors: Charnvanichborikarn S. , Wong-Leung J. , Williams J. S.
Published: December 2009

Implantation, annealing, and oxidation processes have been used to form Au nanoparticles with a narrow size and depth distribution in a SiO2 layer. Different approaches have been attempted: in particular, the gettering of Au to fill preformed nanocavities (obtained by H-implantation and annealing) and thus overcome the broad particle size distribution that is normally associated with nanoparticles formed by implantation and annealing. The results suggest that nanocavities cannot be directly formed in SiO2 by H-implantation and a subsequent annealing due partly to the high mobility of H atoms in SiO2. However, cavities formed in Si are useful in obtaining a narrow size and depth distribution of Au precipitates: the Si substrate can then be oxidized to form Au nanoparticles in SiO2. Sequential wet oxidations of Si samples containing Au nanoparticles have revealed several interesting phenomena, namely, segregation of Au particles at a growing oxide interface, Au-enhanced oxidation, dissolution and reprecipitation of Au precipitates during oxidation, and preferential wetting of Au on the oxide layer. In particular, the Au dissolution and reprecipitation processes are Si interstitial mediated. By completely oxidizing the top Si layer, an array of Au precipitates can be confined at a precise depth within a SiO2 layer corresponding to the front interface of a buried oxide layer. The size distribution of the resulting Au precipitates in SiO2 is smallest when Au is first gettered to cavities and vacancies are subsequently introduced into the Si layer prior to oxidation.
Pyroelectric surface charge in hydroxyapatite ceramics
Authors: Tofail S. A. M. , Baldisserri C. , Haverty D. , McMonagle J. B. , Erhart J.
Published: December 2009

Surface charge of pyroelectric nature is measured in poled hydroxyapatite ceramics. The average pyroelectric constant can range from 0.1 to 40 nC cm−2 K−1 at temperatures of 300–500 °C, while at 27–60 °C the value ranges from 15 to 64 nC cm−2 K−1. The higher temperature values are comparable to conventional pyroelectric ceramics such as LiTaO3 or PZT. The lower temperature values are four orders higher than those observed in bone and tendon.
Intense SrF radical beam for molecular cooling experiments
Authors: Tu Ming-Feng , Ho Jia-Jung , Hsieh Chih-Chiang , Chen Ying-Cheng
Published: December 2009

We have developed a continuous SrF radical beam for the loading of helium buffer gas cooling. The SrF molecules are efficiently generated by high-temperature chemical reaction of the solid precursor SrF2 with boron in a graphite oven. The beam properties are characterized with laser-induced fluorescence spectroscopic method. We obtain a molecular flux of up to 2.1×1015 sr−1 s−1 at the detection region for all rotational states. The dependence of the flux on oven temperature suggests that even higher flux is possible if a higher temperature in the oven is achieved.
Two-dimensional femtosecond stimulated Raman spectroscopy: Observation of cascading Raman signals in acetonitrile
Authors: Wilson Kristina C. , Lyons Brendon , Mehlenbacher Randy , Sabatini Randy , McCamant David W.
Published: December 2009

A new methodology for two-dimensional Raman spectroscopy—termed two-dimensional femtosecond stimulated Raman spectroscopy (2D-FSRS)—is presented and experimental results for acetonitrile are discussed. 2D-FSRS can potentially observe molecular anharmonicity by measuring the modulation of the frequency of a probed Raman mode, at frequency ωhi, by the coherent motion of an impulsively driven mode, at frequency ωlow. In acetonitrile, the signal is generated by driving the CCN bend (379 cm−1) and CC stretch (920 cm−1) into coherence via impulsive stimulated Raman scattering and subsequently probing the stimulated Raman spectrum of the CC stretch, the CN stretch (2250 cm−1) and the CH stretch (2942 cm−1). The resultant signal can be generated by two alternative mechanisms: a fifth-order Raman process that would directly probe anharmonic coupling between the two modes, or a third-order cascade in which a third-order coherent Raman process produces a field that goes on to participate in a third-order stimulated Raman transition. The third-order cascade is shown to dominate the 2D-FSRS spectrum as determined by comparison with the predicted magnitude of the two signals, the 2D spectrum of a mixed isotope experiment, and the concentration dependence of the signal. In acetonitrile, theoretical calculations of the vibrational anharmonicity indicate that the third-order cascade signal should be 104 times larger than the fifth-order Raman signal. 2D-FSRS signals are observed between acetonitrile’s CCN bend, of E symmetry, and several different A1 modes but are forbidden by symmetry in the fifth-order pathway. A 2D-FSRS spectrum of a 50:50 mixture of acetonitrile and d3-acetonitrile shows equivalent intensity for intramolecular coupling peaks and intermolecular coupling peaks, indicating that the observed signal cannot be probing molecular anharmonicity. Finally, the magnitudes of the 2D-FSRS peaks are observed to be proportional to the square of the number density, supporting the cascade mechanism.
High resolution x-ray investigation of periodically poled lithium tantalate crystals with short periodicity
Authors: Bazzan M. , Sada C. , Argiolas N. , Busacca A. C. , Oliveri R. L. , Stivala S. , Curcio L. , Sanseverino S. Riva
Published: December 2009

Domain engineering technology in lithium tantalate is a well studied approach for nonlinear optical applications. However, for several cases of interest, the realization of short period structures (<2 μm) is required, which make their characterization difficult with standard techniques. In this work, we show that high resolution x-ray diffraction is a convenient approach for the characterization of such structures, allowing us to obtain in a nondestructive fashion information such as the average domain period, the domain wall inclination, and the overall structure quality.
Photoluminescence of self-assembled InAs/GaAs quantum dots excited by ultraintensive femtosecond laser
Authors: Huang Shihua , Ling Yan
Published: December 2009

This paper presents the ultrahigh excitation intensity-dependent photoluminescence (UEIPL) spectra of self-assembled InAs/GaAs quantum dots (QDs) excited by femtosecond laser with power intensity up to 450 kW/cm2. Upon ultraintensive excitation, many emission features from QDs and underneath wetting layer (WL) have been observed. As a result of band filling, two emission features D1 and D3 due to the ground (n=1) and second excited state (n=3) transitions, and an emission band from GaAs barrier layer state transition have been distinguished at the experimental temperature of 77K. In addition, an emission feature DD has been identified as the superposition of n=2 (first excited state) in QD and defect state transitions. Moreover, both heavy-hole (HH) and light-hole (LH) states in WL, which are usually optically inactive in emission type of experiment, have been derived from the sample subjected to ultraintensive laser excitation. The ultraintensive excitation generates ultrahigh transient carrier density in QDs and WL. As a result of very strong carrier-carrier and carrier-phonon scattering, all emission peaks shift toward lower photon energy with the increasing excitation power due to lattice heating effect. Further investigations also show that WL could effectively assist in the thermally escape of carriers in QDs; it acts as a channel to facilitate the thermal redistribution of excitons in QDs as well. The UEIPL measurement seems to be a valid alternative to photoreflectance measurements for the investigation of QD and WL system.
Correlation between near infrared emission and bismuth radical species of Bi2O3-containing aluminoborate glass
Authors: Masai Hirokazu , Takahashi Yoshihiro , Fujiwara Takumi , Suzuki Takenobu , Ohishi Yasutake
Published: December 2009

A strong correlation between bismuth radical species and emission in the near infrared (NIR) region of SnO-doped bismuth-containing aluminoborate glass, (CaO–B2O3–Bi2O3–Al2O3–TiO2) (CaBBAT), was observed. Since the activation energy of the NIR emission was similar to that of electron spin resonance signal, it is expected that bismuth radical species in the CaBBAT glass is an origin of the NIR emission. Compared to the observed emission spectra with energy diagram of previous data, we have confirmed that bismuth ion possessing low valence is the origin of broad emission in the NIR region.
Magnetic domain wall collision around the Walker breakdown in ferromagnetic nanowires
Authors: Djuhana Dede , Piao Hong-Guang , Yu Seong-Cho , Oh Suhk Kun , Kim Dong-Hyun
Published: December 2009

We have explored a fundamental phenomenon of magnetic domain wall collision in ferromagnetic nanowires using a micromagnetic simulation. With a systematic variation of an applied field strength, the domain wall collision phenomenon is observed around the Walker breakdown. Collision dynamics is found to mainly depend on domain wall inner structures. In the case of antiparallel transverse walls, it is found that the domain wall structure is preserved even after the collision, while parallel transverse walls experience multiple collisions with switching transverse components of colliding domain walls. After the Walker breakdown, collision of two domain walls comprises of creation and annihilation of a vortex and an antivortex. It is revealed that the collision dynamics of domain walls with an antivortex structure becomes strikingly distinctive depending on the relative direction of two colliding antivortex cores. Collision of vortex walls is observed to be associated with a complex interaction among vortex, antivortex, and even a tiny unreversed magnetic domain.
Carrier relaxation dynamics in SnxNy nanowires grown by chemical vapor deposition
Authors: Othonos Andreas , Zervos Matthew
Published: December 2009

Carrier relaxation dynamics in tin nitride (SnxNy) nanowires have been investigated using femtosecond transient absorption spectroscopy. The nanowires were grown directly on quartz using chemical vapor deposition and had diameters ≤200 nm and lengths up to 2 μm. Steady state optical transmission measurements suggest that the band gap is ∼2.9 eV while time resolved measurements reveal that free carrier absorption dominates the carrier dynamics and overcomes state filling within 0.5 ps of the incoming excitation pulse even when probing above the band edge. This is a unique and markedly different behavior compared to what we have observed in other semiconductor nanowires and it is attributed to fast scattering of the photogenerated carriers out of the excitation energy region and possible rise in the lattice temperature due to energy relaxation. Carrier relaxation occurs through two channels with a fast time constants of ≈200 ps and a slow time constant ranging between 5 and 8 ns while intensity measurements reveal negligible contribution from nonlinear effects such as Auger recombination.
Universal nonexponential relaxation: Complex dynamics in simple liquids
Authors: Turton David A. , Wynne Klaas
Published: December 2009

The dynamics of the noble-gas liquids underlies that of all liquids making them an important prototypical model system. Using optical Kerr-effect spectroscopy we show that for argon, krypton, and xenon, both the librational and diffusional contributions to the spectrum are surprisingly complex. The diffusional relaxation appears as a stretched-exponential, such as widely found in studies of structured (e.g., glass-forming) liquids and as predicted by mode-coupling theory. We show that this behavior is remarkably similar to that measured in water and suggest that it is a fundamental or universal property.
One dimensional model for water and aqueous solutions. Part V. Monte Carlo simulation of dilute solutions of hard rod in waterlike particles
Authors: Lyubartsev Alexander , Ben-Naim Arieh
Published: December 2009

We have carried out Monte Carlo simulation on the primitive one dimensional model for water described earlier [A. Ben-Naim, J. Chem. Phys. 128, 024506 (2008)]. We show that by taking into account second nearest neighbor interactions, one can obtain the characteristic anomalous solvation thermodynamic quantities of inert solutes in water. This model clearly demonstrates the molecular origin of the large negative entropy of solvation of an inert solute in water.
Diffusion of flexible, charged, nanoscopic molecules in solution: Size and pH dependence for PAMAM dendrimer
Authors: Maiti Prabal K. , Bagchi Biman
Published: December 2009

In order to understand self-diffusion (D) of a charged, flexible, and porous nanoscopic molecule in water, we carry out very long, fully atomistic molecular dynamics simulation of PAMAM dendrimer up to eight generations in explicit salt water under varying pH. We find that while the radius of gyration (Rg) varies as N1∕3, the self-diffusion constant (D) scales, surprisingly, as N−α, with α=0.39 at high pH and 0.5 at neutral pH, indicating a dramatic breakdown of Stokes–Einstein relation for diffusion of charged nanoscopic molecules. The variation in D as a function of radius of gyration demonstrates the importance of treating water and ions explicitly in the diffusion process of a flexible nanoscopic molecule. In agreement with recent experiments, the self-diffusion constant increases with pH, revealing the importance of dielectric friction in the diffusion process. The shape of a dendrimer is found to fluctuate on a nanosecond time scale. We argue that this flexibility (and also the porosity) of the dendrimer may play an important role in determining the mean square displacement of the dendrimer and the breakdown of the Stokes–Einstein relation between diffusion constant and the radius.