bluuebunny/crossref_metadata_2025 huggingface dataset:
The NStED Exoplanet Transit Survey Service
Authors: von Braun K. , Abajian M. , Ali B. , Baker R. , Berriman G. B. , Chiu N-M. , Ciardi D. R. , Good J. , Kane S. R. , Laity A. C. , McElroy D. L. , Monkewitz S. , Payne A. N. , Ramirez S. , Schmitz M. , Stauffer J. R. , Wyatt P. L. , Zhang A.
Published: February 2009

The NASA Star and Exoplanet Database (NStED) is a general purpose stellar archive with the aim of providing support for NASA's planet finding and characterization goals, stellar astrophysics, and the planning of NASA and other space missions. There are two principal components of NStED: a database of (currently) 140,000 nearby stars and exoplanet-hosting stars, and an archive dedicated to high-precision photometric surveys for transiting exoplanets. We present a summary of the latter component: the NStED Exoplanet Transit Survey Service (NStED-ETSS), along with its content, functionality, tools, and user interface. NStED-ETSS currently serves data from the TrES Survey of the Kepler Field as well as dedicated photometric surveys of four stellar clusters. NStED-ETSS aims to serve both the surveys and the broader astronomical community by archiving these data and making them available in a homogeneous format. Examples of usability of ETSS include investigation of any time-variable phenomena in data sets not studied by the original survey team, application of different techniques or algorithms for planet transit detections, combination of data from different surveys for given objects, statistical studies, etc. NStED-ETSS can be accessed at http://nsted.ipac.caltech.edu.
Identifying Non-transiting Terrestrial Planets with Transit Timing Data
Authors: Veras Dimitri , Ford Eric B.
Published: February 2009

Both ground and space-based transit observatories are poised to significantly increase the number of known transiting planets and the number of precisely measured transit times. A planet's transit times represent a clock that can be used to infer the presence of additional planets. Although modeling the transit time variations (TTVs) of a known system is simple, interpreting those variations in terms of the mass and orbital elements of a perturbing planet is much more challenging. Because mutual planetary perturbations are often the dominant source of TTVs, the observable signal can be extremely complex. In these proceedings, we present early results based on a simplistic analysis of the root-mean-square TTV deviation amplitude. We are preparing a more thorough analysis based on a computationally efficient surrogate Bayesian model, which may be combined with analytic approximations and n-body integrations in order to establish the sensitivity of TTV observations to terrestrial-like planets as a function of the system architecture. Besides aiding the interpretation of future transit timing observations, we hope our results can help maximize the productivity of transit timing follow-up campaigns by guiding survey design decisions such as the choice of targets, required precision, and desired number/time span of TTV observations.
Observability of the General Relativistic Precession of Periastra in Exoplanets
Authors: Jordán Andrés , Bakos Gáspár Á.
Published: February 2009

The general relativistic precession rate of periastra in close-in exoplanets can be orders of magnitude larger than the magnitude of the same effect for Mercury. The realization that some of the close-in exoplanets have significant eccentricities raises the possibility that this precession might be detectable. We explore here the observability of the periastra precession using radial velocity and transit light curve observations. Our analysis is independent of the source of precession, which can also have significant contributions due to additional planets and tidal deformations. We find that precession of the periastra of the magnitude expected from general relativity can be detectable in timescales of ≲10 years with current observational capabilities by measuring the change in the primary transit duration or in the time difference between primary and secondary transits. Radial velocity curves alone would be able to detect this precession for super-massive, close-in exoplanets orbiting inactive stars if they have ~100 datapoints at each of two epochs separated by ~20 years. The contribution to the precession by tidal deformations may dominate the total precession in cases where the relativistic precession is detectable. Studies of transit durations withKeplermight need to take into account effects arising from the general relativistic and tidal induced precession of periastra for systems containing close-in, eccentric exoplanets. Such studies may be able to detect additional planets with masses comparable to that of Earth by detecting secular variations in the transit duration induced by the changing longitude of periastron.
The impact of stellar jitter on the confirmation of transiting exoplanet candidates around Solar-like stars
Authors: Tingley Brandon , Grundahl Frank , Kjeldsen Hans
Published: February 2009

The radial velocity technique is commonly used to classify transiting exoplanet candidates. However, stars are intrinsically noisy in radial velocity. No good description of this noise has yet been proffered, although activity in general has been suggested as the source, making it impossible to evaluate its effect on signal detection. In this poster, we propose an activity-based model that incorporates both light and dark stellar spots, capable of producing both photometric and radial velocity time series. We demonstrate its consistency with both SOHO/VIRGO photometry and SOHO/GOLF radial velocities. We then use this model to establish lower and upper limits on the effects of intrinsic stellar noise on the metal lines used to follow up transit candidates, making use of Monte Carlo simulations. Based on these results, we can suggest an optimal observational sampling rate.
Ground-based detections of sodium in HD 209458b's atmosphere in two data sets
Authors: Albrecht S. , Snellen I. , de Mooij E. , Le Poole R.
Published: February 2009

We present two separate ground-based detections of sodium in the transmission spectrum of HD 209458b. First we reanalyzed an archival data set from the HDS spectrograph on Subaru, which shows sodium at a >5σ level. Secondly, our preliminary results of a UVES/VLT data set indicate sodium absorption at a similar level, although the data cover the eclipse only partially. Both results are fully consistent with the HST results of Charbonneau et al. (2002). The Na D absorption feature seems to be resolved in the narrowest passband.
Atmospheric composition and structure of HD209458b
Authors: Désert J.-M. , Vidal-Madjar A. , des Etangs A. Lecavelier , Sing D. , Ehrenreich D. , Hébrard G. , Ferlet R.
Published: February 2009

Transiting planets like HD209458b offer a unique opportunity to scrutinize their atmospheric composition and structure. Transit spectroscopy probes the transition region between the day and night sides, called the limb. We present a re-analysis of existing HST/STIS transmission spectra of HD209458b's atmosphere. From these observations we identify H2 Rayleigh scattering, derive the absolute Sodium abundance and quantify its depletion in the upper atmosphere, extract a stratospheric T-P profile and find a temperature inversion and explain broad band absorptions with the presence of TiO and VO molecules.
Dynamical Simulations of HD 69830
Authors: Payne Matthew J. , Ford Eric B. , Wyatt Mark C. , Booth Mark
Published: February 2009

Previous studies have developed models for the growth and migration of three planets orbiting HD 69830. We perform n-body simulations using MERCURY (Chambers 1999) to explore the implications of these models for: 1) the excitation of planetary orbits via planet-planet interactions, 2) the accretion and clearing of a putative planetesimal disk, 3) the distribution of planetesimal orbits following migration, and 4) the implications for the origin of the observed infrared emission from the HD 69830 system. We report preliminary results that suggest new constraints on the formation of HD 69830.
Why have no transiting planets been found in star clusters?
Authors: Janes Kenneth , Kim Ji-Hyun
Published: February 2009

Since the suggestion by Janes 1996 that star clusters might be attractive targets to search for transiting planets, there have been more than 20 searches in both open and globular clusters. To date, no confirmed hot Jupiter transiting planets have been found in clusters. We review the statistics for finding short-period planets and we summarize the open cluster work to date, including our own (so far negative) search in NGC 7789. While individually, the negative results are not surprising, the consistent failure to find planets in clusters may suggest differences in the formation or evolution of planetary systems in clusters.
Phase-differential NIR integral field spectroscopy of transiting Hot Jupiters
Authors: Angerhausen Daniel , Krabbe Alfred , Iserlohe Christof
Published: February 2009

Transiting exoplanets provide a unique opportunity for follow up exploration through phase-differential observation of their emission and transmission spectra. From such spectra immediate clues about the atmospheric composition and the planets chemistry can be drawn. Such information is of imminent importance for the theory of the formation of planets in general as well as for their particular evolution. Ground-based spectroscopy of exoplanet transits is a needful extension of results already obtained through space-based observations. We present results of an exploratory study to use near-infrared integral field spectroscopy to observe extrasolar planets. We demonstrate how adaptive optics-assisted integral field spectroscopy compares with other spectroscopic techniques currently applied. An advanced reduction method using elements of a spectral-differential decorrelation method is also discussed. We have tested our concept with a K-Band time series observations of HD209458b and HD189733b obtained with SINFONI at the VLT and OSIRIS at Keck during secondary transits at a spectral resolution of R=3000.
The Impact of Transiting Planet Science on the Next Generation of Direct-Imaging Planet Searches
Authors: Carson Joseph C.
Published: February 2009

Within the next five years, a number of direct-imaging planet search instruments, like the VLT SPHERE instrument, will be coming online. To successfully carry out their programs, these instruments will rely heavily on a-priori information on planet composition, atmosphere, and evolution. Transiting planet surveys, while covering a different semi-major axis regime, have the potential to provide critical foundations for these next-generation surveys. For example, improved information on planetary evolutionary tracks may significantly impact the insights that can be drawn from direct-imaging statistical data. Other high-impact results from transiting planet science include information on mass-to-radius relationships as well as atmospheric absorption bands. The marriage of transiting planet and direct-imaging results may eventually give us the first complete picture of planet migration, multiplicity, and general evolution.
Getting More For Your Money: Identifying and Confirming Long-Period Planets with Kepler
Authors: Yee Jennifer C. , Gaudi B. Scott
Published: February 2009

Kepler will monitor enough stars that it is likely to detect single transits of planets with periods longer than the mission lifetime. We show that by combining the Kepler photometry of such transits with precise radial velocity (RV) observations taken over ~3 months, and assuming circular orbits, it is possible to estimate the periods of these transiting planets to better than 20% (for planets with radii greater than that of Neptune) and the masses to within a factor of 2 (for planet masses mp ≥ MJup). We also explore the effects of eccentricity on these quantities.
The PLATO space mission: studying planetary transits and stellar oscillations simultaneously
Authors: Fridlund Malcolm
Published: February 2009

PLATO (PLAnetary Transits and Oscilliations of stars) is a proposed mission of the European Space Agency's Science programme Cosmic Vision 2015–2025, currently under industrial study, and with a planned launch by the end of 2017. Its task is to better understand the properties of exoplanetary systems. As such it will detect and characterise exoplanets using their transit signature in front of a large sample of bright stars and simultaneously measuring the seismic oscillations of the parent star of these exoplanets. The mission will be orbiting the Sun-Earth L2 point, which provides a stable thermal environment and maximum uninterrupted observing efficiency. The payload consists of a number (> 28) of individual catadioptric telescopes, covering > 550 sq. degrees. Since the goal is to search for terrestrial exoplanets within the habitable zone of their host stars, and carry out asteroseismological observations of the host stars, very high photometric precision, high time resolution, and high duty-cycle visible photometry is required. Ground-based observations are needed to complement the observations made by PLATO to allow for further exoplanetary characterization. This paper consists of a summary of the preliminary results achieved by the ESA internal pre-assessment study.
Flow separation and resuspension beneath shoaling nonlinear internal waves
Authors: Boegman Leon , Ivey Gregory N.
Published: February 2009

Laboratory observations are presented showing the structure and dynamics of the turbulent bottom boundary layer beneath nonlinear internal waves (NLIWs) of depression shoaling upon sloping topography. The adverse pressure gradient beneath the shoaling waves causes the rear face to steepen, flow separation to occur, and wave‐induced near‐bottom vortices to suspend bed material. The resuspension is directly attributed to the near‐bed viscous stress and to near‐bed patches of elevated positive Reynolds stress generated by the vortical structures. These results are consistent with published field observations of resuspension events beneath shoaling NLIWs. Elevated near‐bed viscous stresses are found throughout the domain at locations that are not correlated to the resuspension events. Near‐bed viscous stress is thus required for incipient sediment motion but is not necessarily a precursor for resuspension. Resuspension is dependent on the vertical velocity field associated with positive Reynolds stress and is also found to occur where the mean (wave‐averaged) vertical velocity is directed away from the bed. The results are interpreted by analogy to the eddy‐stress and turbulent bursting resuspension models developed for turbulent channel flows.
Drying of a partially saturated rock matrix by fracture ventilation: Experiments and modeling in a single fracture‐matrix system
Authors: Sakaki Toshihiro , Rajaram Harihar
Published: February 2009

We present an efficient approach for modeling drying resulting from airflow through fractures embedded within a rock matrix by coupling a nonlinear diffusion equation for moisture transport in the matrix with a depth‐averaged quasi steady state advection‐dispersion equation for the vapor transport in the fracture. Coupling between the moisture transport equation in the fracture and matrix is achieved by applying Kelvin's equation at the fracture‐matrix interface. The proposed modeling approach was then validated based on a single fracture‐matrix drying experiment involving airflow through a fracture sandwiched between two matrix blocks. The moisture diffusivity for the rock matrix was first estimated in a one‐dimensional matrix drying experiment using a mass balance method. Numerical simulations based on our coupled modeling approach captured the important characteristics of the drying behavior in the single fracture‐matrix experiment. Additional numerical simulations are presented to clarify the factors controlling drying behavior. The important features of drying in a single fracture‐matrix system are as follows: (1) The total evaporation rate exhibits an initial constant value at early time, followed by a 1/t decrease with time. (2) At early time a “drying toe” forms near the fracture entrance and propagates along the fracture length as the fracture‐matrix interface becomes progressively drier. During this period, the moisture content distributions in the rock matrix are two‐dimensional, with gradients both parallel and perpendicular to the fracture. (3) At late time, after the drying toe reaches the end of the fracture, a “drying front” forms and propagates away from the fracture‐matrix interface, leading to a largely one‐dimensional (perpendicular to the fracture) variation of moisture content in the rock matrix. The experimental measurements could not fully resolve the early time two‐dimensional moisture content variations due to the coarse resolution, precluding a rigorous comparison with simulated behavior. However, the later‐time one‐dimensional moisture content variation observed in the experimental data was reasonably reproduced in the numerical simulations.
Anisotropic structure beneath central Java from local earthquake tomography
Authors: Koulakov Ivan , Jakovlev Andrey , Luehr Birger G.
Published: February 2009

In this study we present the new tomographic code ANITA which provides 3‐D anisotropic P and isotropic S velocity distribution based on P and S traveltimes from local seismicity. For the P anisotropic model, we determine four parameters for each parameterization cell. This represents an orthorhombic anisotropy with one predefined direction oriented vertically. Three of the parameters describe slowness variations along three horizontal orientations with azimuths of 0°, 60°, and 120°, and one is a perturbation along the vertical axis. The nonlinear iterative inversion procedure is similar to that used in the LOTOS code. We have implemented this algorithm for the updated data set of central Java, part of which was previously used for the isotropic inversion. It was obtained that the crustal and uppermost mantle velocity structure beneath central Java is strongly anisotropic with 7–10% of maximal difference between slow and fast velocity in different directions. In the forearc (area between southern coast and volcanoes), the structure of both isotropic and anisotropic structure is strongly heterogeneous. Variety of anisotropy orientations and highly contrasted velocity patterns can be explained by a complex block structure of the crust. Beneath volcanoes we observe faster velocities in vertical direction, which is probably an indicator for vertically oriented structures (channels, dykes). In the crust beneath the middle part of central Java, north to Merapi and Lawu volcanoes, we observe a large and very intense anomaly with a velocity decrease of up to 30% and 35% for P and S models, respectively. Inside this anomaly E‐W orientation of fast velocity takes place, probably caused by regional extension stress regime. In a vertical section we observe faster horizontal velocities inside this anomaly that might be explained by layering of sediments and/or penetration of quasi‐horizontal lenses with molten magma. In the mantle, trench parallel anisotropy is observed throughout the study area. Such anisotropy in the slab entrained corner flow may be due to presence of B‐type olivine having predominant axis parallel to the shear direction, which appears in conditions of high water or/and melting content.
Magnitude‐frequency distributions of boundary shear stress along a rapidly eroding bedrock river
Authors: Barbour J. R. , Stark C. P. , Lin C.‐W. , Chen H. , Horng M.‐J. , Ko C.‐P. , Yi T.‐C. , Tsai T.‐T. , Chang W.‐S. , Lee S.‐P. , Huang C.
Published: February 2009

The magnitude‐frequency distribution of boundary shear stress frames erosion rates in bedrock rivers, but empirical constraints are rare, particularly for extreme floods. Here we present measurements of mean stress τb and its frequency distribution along a fast‐eroding river in Taiwan. We construct rating functions of discharge and hydraulic geometry using high‐resolution satellite images of flood patterns, river stage time‐series, topographic profiles, and post‐flood field surveys. The method allows us to assess the spatiotemporal variation in τb along the channel. The boundary shear stress PDF p(τb) has a steep power‐law tail, and includes semiannual floods generating τb ≈ 100–200 Pa and 50‐year, 3000 m3 s−1 events driving τb ≥ 300 Pa. All such floods contribute to modification of the coarse alluvial cover and erosion of the bedrock bed. Given the steep tail decay in p(τb), the rapid channel incision probably owes more to the exceptional frequency of moderate shear stresses than to the magnitude of the extremes.
Cassini RADAR images at Hotei Arcus and western Xanadu, Titan: Evidence for geologically recent cryovolcanic activity
Authors: Wall S. D. , Lopes R. M. , Stofan E. R. , Wood C. A. , Radebaugh J. L. , Hörst S. M. , Stiles B. W. , Nelson R. M. , Kamp L. W. , Janssen M. A. , Lorenz R. D. , Lunine J. I. , Farr T. G. , Mitri G. , Paillou P. , Paganelli F. , Mitchell K. L.
Published: February 2009

Images obtained by the Cassini Titan Radar Mapper (RADAR) reveal lobate, flowlike features in the Hotei Arcus region that embay and cover surrounding terrains and channels. We conclude that they are cryovolcanic lava flows younger than surrounding terrain, although we cannot reject the sedimentary alternative. Their appearance is grossly similar to another region in western Xanadu and unlike most of the other volcanic regions on Titan. Both regions correspond to those identified by Cassini's Visual and Infrared Mapping Spectrometer (VIMS) as having variable infrared brightness, strengthening the case that these are recent cryovolcanoes.
Intra‐annual relationships between polar ozone and the SAM
Authors: Fogt Ryan L. , Perlwitz Judith , Pawson Steven , Olsen Mark A.
Published: February 2009

Observed co‐variations between polar total column ozone and the Southern Hemisphere Annular Mode (SAM) during 1962–2004 are presented and evaluated in a chemistry‐climate model (CCM). Results show that austral spring total column ozone variability at South Pole is significantly related to the SAM, perhaps up to four months later; this relationship is only seen in simulations that include ozone depletion. The austral spring SAM also is linked to following late spring – early summer total column ozone over the polar cap, since both respond to the wave‐driving of the stratosphere. Overall, the CCM captures many of the observed ozone‐SAM links, but over‐predicts the relationship between spring ozone and austral summer SAM, as a consequence of the delayed breakdown of the polar vortex in the CCM.
Westward propagation of barrier layer formation in the 2006–07 Rossby wave event over the tropical southwest Indian Ocean
Authors: Chowdary J. S. , Gnanaseelan C. , Xie S. P.
Published: February 2009

A suite of satellite and in‐situ observations are used to study ocean‐atmospheric conditions over the tropical Southwest Indian Ocean (SWIO) during 2006–2007 when El Nino and an Indian Ocean dipole took place simultaneously. Argo profiles reveal a pronounced up‐westward propagation of subsurface warming in the southern tropical Indian Ocean associated with Rossby waves traveling on the sloping thermocline. With the thermocline deepening by 60 m, a thick barrier layer forms and propagates with the Rossby wave, potentially contributing to the mixed layer warming.
Characterization of ULF pulsations by THEMIS
Authors: Sarris T. E. , Liu W. , Kabin K. , Li X. , Elkington S. R. , Ergun R. , Rankin R. , Angelopoulos V. , Bonnell J. , Glassmeier K. H. , Auster U.
Published: February 2009

The THEMIS five‐probe constellation was launched in 17 February 2007 to study substorms; however its instrumentation and the alignment at distances <1RE among some of the THEMIS probes, particularly in the first period of its mission, provides unique opportunities to study ULF pulsations in the magnetosphere. In the case study presented, electric and magnetic field fluctuations are identified as field line resonances and their modes of oscillation are discussed. Phase‐difference calculations between probes allow estimates of the mode number of the fluctuations. These observations give an excellent source for the verification of model estimates of frequency and polarization of the various modes of field line resonances.
What causes southeast Australia's worst droughts?
Authors: Ummenhofer Caroline C. , England Matthew H. , McIntosh Peter C. , Meyers Gary A. , Pook Michael J. , Risbey James S. , Gupta Alexander Sen , Taschetto Andréa S.
Published: February 2009

Since 1995, a large region of Australia has been gripped by the most severe drought in living memory, the so‐called “Big Dry”. The ramifications for affected regions are dire, with acute water shortages for rural and metropolitan areas, record agricultural losses, the drying‐out of two of Australia's major river systems and far‐reaching ecosystem damage. Yet the drought's origins have remained elusive. For Southeast Australia, we show here that the “Big Dry” and other iconic 20th Century droughts, including the Federation Drought (1895–1902) and World War II drought (1937–1945), are driven by Indian Ocean variability, not Pacific Ocean conditions as traditionally assumed. Specifically, a conspicuous absence of Indian Ocean temperature conditions conducive to enhanced tropical moisture transport has deprived southeastern Australia of its normal rainfall quota. In the case of the “Big Dry”, its unprecedented intensity is also related to recent higher temperatures.
Impact of the solar wind dynamic pressure on the Region 2 field‐aligned currents
Authors: Nakano S. , Ueno G. , Ohtani S. , Higuchi T.
Published: February 2009

The relationship between the Region 2 field‐aligned currents and the solar wind dynamic pressure is investigated using magnetic field data from Defense Meteorological Satellite Program‐F13 (DMSP‐F13). The generation of the Region 2 currents is associated with the direction of the magnetic pressure gradient in the magnetosphere, in relation to that of the thermal pressure gradient. Past spacecraft observations have suggested that the spatial distribution of the magnetic pressure in the magnetosphere varies with the solar wind dynamic pressure. Therefore, we can expect that the Region 2 currents would depend on the solar wind dynamic pressure. We compared the Region 2 field‐aligned current intensity at the altitude of the ionosphere, as derived using magnetic field data from DMSP‐F13, with the solar wind dynamic pressure derived from OMNI2 hourly data. It was confirmed that the Region 2 current intensity depends on the solar wind dynamic pressure during magnetic storms. During nonstorm times, however, the correlation between the Region 2 currents and the solar wind dynamic pressure is weak. The weak correlation during nonstorm times suggests that the plasma pressure in the ring current region is also essential for the effect of the solar wind dynamic pressure on the Region 2 currents.
Magnetic study of the UHP eclogites from the Chinese Continental Scientific Drilling (CCSD) Project
Authors: Liu Qingsheng , Liu Qingsong , Yang Tao , Zeng Qingli , Zheng Jianping , Luo Yinhe , Qiu Ning , Xu Haijun , Jin Zhenmin
Published: February 2009

To establish the relationships between rock magnetism of eclogites and the corresponding retrograded metamorphic processes, this study integrated both rock magnetism and metamorphic petrology of 171 eclogite samples with different degree of retrograded metamorphism at the depth range of 100–2050 m of the main hole of the Chinese Continental Scientific Drilling (CCSD) Project, located in the Sulu ultrahigh pressure (UHP) metamorphic belt, eastern China. Results show that the average density is a suitable indicator for the degree of the retrograded metamorphism. Opaque minerals in variable eclogites are mainly magnetite, ilmenite, pyrite, and hematite. With increasing the metamorphic retrogression, the concentration of opaque minerals generally increases; however, magnetic properties of eclogites first increase from well‐preserved eclogite to partially retrogressed eclogites because of the neoformation of coarse grained magnetite particles, and then decrease for the completely retrogressed eclogites because of the consumption of the magnetite particles and the formation of weakly magnetic minerals (e.g., hematite). These processes can be summarized as garnet + omphacite + rutile + SiO2 + H2O → amphibole + plagioclase + magnetite + ilmenite → amphibole + epidote + hematite + ilmenite. The retrograded metamorphic eclogites with elevated magnetic properties take up 25% of all rocks and thus are one of major magnetic rocks in the CCSD main hole located in the Sulu UHP area. Therefore the significant volumes of retrograded eclogites may account for the magnetic anomalies flanking the northeastern part of the Sulu UHP metamorphic belt.
Internal solitary waves induced by flow over a ridge: With applications to the northern South China Sea
Authors: Shaw Ping‐Tung , Ko Dong Shan , Chao Shenn‐Yu
Published: February 2009

The generation of internal solitary waves by barotropic tides over a ridge is studied in a nonhydrostatic numerical model under idealized oceanographic settings. The experiments examine the effects of ridge width, barotropic tidal strength, and stratification on wave generation. The barotropic tidal flow produces internal wave beams emitting from the ridge top if the slope of the ridge exceeds a critical value equal to the slope of the wave beam. Reflection and refraction of a wave beam in an upper ocean waveguide associated with a strong shallow thermocline produce horizontally propagating internal tides. When the local Froude number over a ridge is not small, lee waves generated on the ridge convert enough energy from the barotropic tides to the internal tides to form tidal bores and solitary waves. Increasing stratification at ridge depths enhances the generation of internal waves, particularly at the diurnal periods. In the Luzon Strait, the slope of the wave beam decreases in spring and summer as stratification at the ridge depths increases, favoring the generation of internal tides. Without the presence of a strong shallow thermocline, internal solitary waves are not observed east of the Luzon Strait. In the northern South China Sea, internal solitary waves are likely observed from April to July when a strong shallow thermocline is present. A deep mixed layer in winter suppresses the production of internal solitary waves.
Ozone correlation lengths and measurement uncertainties from analysis of historical ozonesonde data in North America and Europe
Authors: Liu Guiping , Tarasick David W. , Fioletov Vitali E. , Sioris Christopher E. , Rochon Yves J.
Published: February 2009

A spatial and temporal correlation analysis is performed on the WOUDC (World Ozone and Ultraviolet Radiation Data Centre) ozonesonde data from 13 midlatitude stations in North America and Europe. The data records span more than 40 years at some stations, and a total of more than 27,000 ozonesonde profiles are utilized. The spatial correlation coefficients between pairs of stations decrease with increasing station separation distance, following a power exponential correlation function. The horizontal distance for the correlation coefficient to decrease by a factor of e is about 1000–2000 km in the stratosphere with a peak at around 22‐km altitude, and is about 500–1000 km in the troposphere. The autocorrelation coefficient decreases rapidly with time lag, and the timescale of the autocorrelation varies between about 1.5 and 3.5 days in the troposphere but is generally longer in the stratosphere at 2–6 days. The extrapolation of the correlation functions to zero station distance or zero time lag yields estimates of the intrinsic uncertainty of ozonesonde measurements. The uncertainty is found to be less than 7% for 20–30‐km altitudes in the stratosphere, about 15% in the troposphere, and to have larger values near the tropopause and at the surface. The results are broadly consistent with those from the recent JOSIE and BESOS experiments, and other intercomparisons, with the additional measurement uncertainty probably reflecting changes in ozonesonde type, model, manufacture, and preparation procedure during the period of the record.
Sand dune dynamics and climate change: A modeling approach
Authors: Yizhaq H. , Ashkenazy Y. , Tsoar H.
Published: February 2009

We provide several examples for the coexistence of active and fixed sand dunes under similar climatic conditions, namely, with respect to wind power and precipitation rate. A model is developed for dune vegetation cover that includes wind power, precipitation rate, and anthropogenic effects, such as grazing and wood gathering. The model reproduces the observed dune's bistability and shows that under intense human pressure and prolonged droughts the fixed dunes may turn active. Moreover, the model shows that the dune reactivation process is almost irreversible, as a fixed dune will become active only under the action of very strong winds and can then return to the fixed state only when wind power decreases far below the levels under which the initial dune maintained its stability. Similar hysteretic behavior of dune mobility is predicted by the model with respect to changing precipitation and human pressure parameters.
Physical fractionation of soil organic matter: Destabilization of deep soil carbon following harvesting of a temperate coniferous forest
Authors: Diochon A. C. , Kellman L.
Published: February 2009

Developing a better understanding of the processes involved in controlling soil carbon (C) storage and turnover in native forest soils is critical if we are to fully understand the role land management activities play in the global C cycle. Separating soil organic matter (SOM) into discrete fractions has been successfully used to isolate changes in the structure and function of the SOM pool in response to land management activities but investigations in native forest systems are rare. Using a density fractionation procedure, we isolated and characterized three distinct SOM fractions (free, intra‐aggregate, and organo‐mineral) across a postharvest forest age sequence. We describe age related variations in each of these fractions with respect to their contribution to soil mass, C storage, C concentrations, C‐to‐N ratios, and δ13C ratios. In conceptual models of SOM pool structure, the organo‐mineral fraction is assumed to be largely stable. We show that harvesting may increase the potential for loss of soil C (i.e., destabilize the soil C pool) and that a significant portion of the soil C pool may be cycling on decadal timescales. Isotopic evidence is consistent with a period of C loss attributable to increased rates of decomposition, with losses below 20 cm driving the trend. We encourage investigators studying the effects of forest harvesting on SOM storage to consider the deeper mineral soil (20+ cm) and how we may increase SOM turnover time and stabilization capacity in a native forest system.
Estimating porosity with ground‐penetrating radar reflection tomography: A controlled 3‐D experiment at the Boise Hydrogeophysical Research Site
Authors: Bradford John H. , Clement William P. , Barrash Warren
Published: February 2009

To evaluate the uncertainty of water‐saturated sediment velocity and porosity estimates derived from surface‐based, ground‐penetrating radar reflection tomography, we conducted a controlled field experiment at the Boise Hydrogeophysical Research Site (BHRS). The BHRS is an experimental well field located near Boise, Idaho. The experimental data set consisted of 3‐D multioffset radar acquired on an orthogonal 20 × 30 m surface grid that encompassed a set of 13 boreholes. Experimental control included (1) 1‐D vertical velocity functions determined from traveltime inversion of vertical radar profiles (VRP) and (2) neutron porosity logs. We estimated the porosity distribution in the saturated zone using both the Topp and Complex Refractive Index Method (CRIM) equations and found the CRIM estimates in better agreement with the neutron logs. We found that when averaged over the length of the borehole, surface‐derived velocity measurements were within 5% of the VRP velocities and that the porosity differed from the neutron log by less than 0.05. The uncertainty, however, is scale dependent. We found that the standard deviation of differences between ground‐penetrating‐radar‐derived and neutron‐log‐derived porosity values was as high as 0.06 at an averaging length of 0.25 m but decreased to less than 0.02 at length scale of 11 m. Additionally, we used the 3‐D porosity distribution to identify a relatively high‐porosity anomaly (i.e., local sedimentary body) within a lower‐porosity unit and verified the presence of the anomaly using the neutron porosity logs. Since the reflection tomography approach requires only surface data, it can provide rapid assessment of bulk hydrologic properties, identify meter‐scale anomalies of hydrologic significance, and may provide input for other higher‐resolution measurement methods.
Variable‐density groundwater flow and solute transport in fractured rock: Applicability of the Tang et al. [1981] analytical solution
Authors: Graf T. , Simmons C. T.
Published: February 2009

The effect of fluid density variations on mixed convective (advective and density‐driven) transport in fractured rock is examined. Assuming a representative natural hydraulic gradient in a vertical fracture, breakthrough curves for variable‐density systems are shown to be significantly different from those with constant‐density conditions for even very small solute source concentrations (as low as approximately 2.3 g L−1 total dissolved solids, corresponding to 6.4% of seawater salinity). We compare analytical solutions with results of fully coupled numerical simulations of variable‐density groundwater flow and solute transport in fractured rock. Current analytical solutions for solute transport in fractured rock do not account for fluid density variations and therefore fail to predict variable‐density transport. Using a mixed convection ratio analysis, we determine the hydrogeologic conditions where variable‐density transport is important and hence when analytical solutions fail to predict variable‐density transport in fractured rock. We present a modified velocity term that includes a density‐driven flow component in a vertical fracture to account for fluid density variations. The modified velocity term is incorporated into the standard Tang et al. (1981) analytical solution. The original density‐invariant analytical solution is shown to be applicable near a solute source and at early time, while the velocity‐modified density‐variant solution gives very good results for long‐term and far‐field behavior. These results suggest that analytical solutions may still be useful for analyzing variable‐density transport in fractured rock. This study has implications for the analysis of dense plume transport in fractured rock where reliable long‐term predictions are important.
Information System for Tourism Activity Monitoring and Forecasting Indicators as an Experience for Portugal
Authors: Ramos Célia , Perna Fernando
Published: February 2009

In view of presenting the development of an information system (IS) associated with a real world case and an economic sector, namely tourism, the present article is the result of the methodological development of the scientific research study known as IMPACTUR - Tourism Activity Monitoring and Forecasting Indicators. The system that is the object of the current article is directed at tourism as an emerging sector of the economy geared towards excellence in some regions, thus requiring proper tools that allow decision-makers to acquire all possible slight advantages that are so essential to being the best. The IS formulated for IMPACTUR is one of these tools, innovative in Portugal and abroad, providing statistical information online related to tourism. It should be pointed out that it stores updated and timely information that is processed and made available in an electronic format via a website to all tourism professionals and researchers.
Four dimensional visualization of highly transient fuel sprays by microsecond quantitative x-ray tomography
Authors: Liu Xin , Im Kyoung-Su , Wang Yujie , Wang Jin , Tate Mark W. , Ercan Alper , Schuette Daniel R. , Gruner Sol M.
Published: February 2009

An ultrafast x-ray microtomography technique based on synchrotron x rays and a fast-framing x-ray detector was developed to reconstruct the highly transient sprays in four dimensions with microsecond-temporal resolution in the near-nozzle region. The time-resolved quantitative fuel distribution allowed a realistic numerical fluid dynamic simulation with initial conditions based on the measurement, which demonstrates that the fuel has completed the primary breakup upon exiting the nozzle. The secondary-breakup-based simulation agrees well with the experimental fuel-volume fraction distribution, which challenges most existing simulation assumptions and results.
Experimental results and model for the permeability of sprayed NiZn ferrite films
Authors: Acher O. , Ledieu M. , Abe M. , Tada M. , Nakagawa T.
Published: February 2009

The high-frequency permeabilities of several NiZn ferrite films prepared by spray plating were investigated up to 6GHz. An adaptation of the Bouchaud–Zérah effective medium model provided an analytical expression for the microwave permeability, with a simple dependence on the magnetization distribution. An excellent agreement with the experimental results was obtained, in the demagnetized state as well as in the remnant state.
Synthesis, crystal structure, and magnetic properties of ε-GaIII FxeIII O2−x3 nanorods
Authors: Namai Asuka , Sakurai Shunsuke , Ohkoshi Shin-ichi
Published: February 2009

A series of ε-GaxFe2−xO3 nanorods, which have orthorhombic structures of Pna21, was prepared by combining the reverse-micelle and the sol-gel methods. The coercive fields at 300 K changed over a wide range between 15.5 kOe (x=0.09) and 0.9 kOe (x=0.83). The measured saturation magnetization (Ms) in the sample for x=0.43 was 46.0 emu g−1 at 4 K but 25.6 emu g−1 at 300 K, which is 1.7 times larger than the Ms of the original ε-Fe2O3. This enhanced value is due to the different occupancies of Ga3+ ions in the four types of Fe sites.
Multiterminal semiconductor/ferromagnet probes for spin-filter scanning tunneling microscopy
Authors: Vera Marún I. J. , Jansen R.
Published: February 2009

We describe the fabrication of multiterminal semiconductor/ferromagnet probes for a new technique to study magnetic nanostructures: spin-filter scanning tunneling microscopy. We describe the principle of the technique, which is based on spin-polarized tunneling and subsequent analysis of the spin polarization using spin-dependent transmission in the probe tip. We report the fabrication of the probes having a submicron semiconductor/ferromagnet heterostructure at the end of the tip.
Tunneling magnetoresistance in (Ga,Mn)As/Al–O/CoFeB hybrid structures
Authors: Du G. X. , Babu M. Ramesh , Han X. F. , Deng J. J. , Wang W. Z. , Zhao J. H. , Wang W. D. , Tang Jinke
Published: February 2009

Tunneling magnetoresistance (TMR) in Ga0.92Mn0.08As/Al–O/Co40Fe40B20 trilayer hybrid structure as a function of temperature from 10 to 50 K with magnetic field |H|≤2000 Oe has been studied. TMR ratio of 1.6% at low fields at 10 K was achieved with the applied current of 1 μA. The behavior of junction resistance was well explained by the tunneling resistance across the barrier. Strong bias dependences of magnetoresistance and junction resistance were presented.
Current driven magnetization reversal in microstructured spin valve with current-in-plane configuration
Authors: Kuo C. Y. , Chao C. T. , Ou J. Y. , Horng Lance , Wu J. C. , Wu Te-Ho , Tsunoda M. , Takahashi M.
Published: February 2009

The current induced magnetization reversals on the free layer of patterned spin valve ellipse have been investigated using differential magnetoresistance (MR) measurements, in which various direct currents were superimposed to 14 μA alternating current for the MR measurements. Conventional field scanned MR minor loops and subminor loops were measured under different scan ranges of magnetic field to verify the existing metastable states. The magnetization transitions between metastable states were realized in the dc scanned MR loop, in which the resistance levels were identified in accordance with the field scanned MR loop. This phenomenon is believed to be associated with the domain wall motion pushed by the direct current.
Planar Hall effect of Permalloy films on Si(111), Si(100), and glass substrates
Authors: Jen S. U. , Wang P. J. , Tseng Y. C. , Chiang H. P.
Published: February 2009

Different thicknesses, tf=7.5–100 nm, of Permalloy (Py) films were deposited on Si(111), Si(100), and glass substrates, respectively, at Ts=270 °C. The sensitivities (SH) of the planar Hall effect (PHE) and temperature coefficient of resistance (TCR) of the film samples were measured from room temperature to T=250 °C. When 10 nm≤tf≤100 nm, SH increases as tf decreases, in agreement with theory. However, when tf<10 nm, SH decreases instead due to the coalescence condition, as indicated by an abnormal increase in the sheet resistance R◻ of the film sample. Moreover, we have studied the nonlinear deviation of the PHE signal at field |H|=6 Oe, defined as ξ, and the temperature stability of PHE sensitivity as [△SH/△T]. In summary, we find (A) the Py(10 nm)/Si(111) sample has the highest SH(RT)=340 Ω/T because its surface is the smoothest with the lowest anisotropy field Hk; (B) the other properties, such as ξ, [△SH/△T], and TCR, of the Py(10 nm)/Si(111) sample are inferior to those of the Py(10 nm)/glass sample; (C) ξ remains almost the same, as RT≤T≤100 °C; (D) negative TCR values of the Py/Si(111) and Py/Si(100) samples are related to the substrate contributions, e.g., TCR, thermal expansion coefficient α, and thermoelectric power β of Si.
Cr
3
+
electron paramagnetic resonance study of Sn1−xCrxO2 (0.00≤x≤0.10)
Authors: Misra Sushil K. , Andronenko S. I. , Rao S. , Bhat Subray V. , Van Komen Chadd , Punnoose A.
Published: February 2009

This paper reports on the liquid-helium-temperature (5 K) electron paramagnetic resonance (EPR) spectra of Cr3+ ions in the nanoparticles of SnO2 synthesized at 600 °C with concentrations of 0%, 0.1%, 0.5%, 1%, 1.5%, 2.0%, 2.5%, 3.0%, 5.0%, and 10%. Each spectrum may be simulated as overlap of spectra due to four magnetically inequivalent Cr3+ centers characterized by different values of the spin-Hamiltonian parameters. Three of these centers belong to Cr3+ ions in orthorhombic sites, situated near oxygen vacancies, characterized by very large zero-field splitting parameters D and E, presumably due to the presence of nanoparticles in the samples. The fourth EPR spectrum belongs to the Cr3+ ions situated at sites with tetragonal symmetry, substituting for the Sn4+ ion, characterized by a very small value of D. In addition, there appears a ferromagnetic resonance line due to oxygen defects for samples with Cr3+ concentrations of ≤2.5%. Further, in samples with Cr3+ concentrations of ≥2.5%, there appears an intense and wide EPR line due to the interactions among the Cr3+ ions in the clusters formed due to rather excessive doping; the intensity and width of this line increase with increasing concentration. The Cr3+ EPR spectra observed in these nanopowders are very different from those in bulk SnO2 crystals.