bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards the characterization of the hot Neptune/super-Earth population around nearby bright stars
Authors: Lovis C. , Mayor M. , Bouchy F. , Pepe F. , Queloz D. , Udry S. , Benz W. , Mordasini C.
Published: February 2009

The HARPS search for low-mass extrasolar planets has been ongoing for more than 4 years, targeting originally about 400 bright FGK dwarfs in the solar neighbourhood. The published low-mass planetary systems coming from this survey are fully confirmed by subsequent observations, which demonstrate the sub-m/s long-term stability reached by HARPS. The complex RV curves of these systems have led us to focus on a smaller sample of stars, accumulating more data points per star. We perform a global search in our data to assess the existence of the large population of ice giants and super-Earths predicted by numerical simulations of planet formation. We indeed detect about 45 candidates having minimum masses below 30 M⊕ and orbital periods below 50 days. These numbers are preliminary since the existence of these objects has to be confirmed by subsequent observations. However, they indicate that about 30% of solar-type stars may have such close-in, low-mass planets. Some emerging properties of this low-mass population are presented. We finally discuss the prospects for finding transiting objects among these candidates, which may possibly yield the first nearby, transiting super-Earth.
Misaligned spin-orbit in the XO-3 planetary system?
Authors: Hébrard G. , Bouchy F. , Pont F. , Loeillet B. , Rabus M. , Bonfils X. , Moutou C. , Boisse I. , Delfosse X. , Desort M. , Eggenberger A. , Ehrenreich D. , Forveille T. , Lagrange A.-M. , Lovis C. , Mayor M. , Pepe F. , Perrier C. , Santos N. C. , Queloz D. , Ségransan D. , Udry S. , Vidal-Madjar A.
Published: February 2009

The SOPHIE Consortium started a large program of exoplanets search and characterization in the Northern hemisphere with the new spectrograph SOPHIE at the 1.93-m telescope of Haute-Provence Observatory, France. The objectives of this program are to characterize the zoo of exoplanets and to bring strong constraints on their processes of formation and evolution using the radial velocity technique. We present here new SOPHIE measurements of the transiting planet host star XO-3. This allowed us to observe the Rossiter-McLaughlin effect and to refine the parameters of the planet. The unusual shape of the radial velocity anomaly during the transit provides a hint for a nearly transverse Rossiter-McLaughlin effect. The sky-projected angle between the planetary orbital axis and the stellar rotation axis should be λ = 70° ± 15° to be compatible with our observations. This suggests that some close-in planets might result from gravitational interaction between planets and/or stars rather than migration. This result requires confirmation by additional observations.
Kinematics of the SWEEPS transiting planet candidates
Authors: Clarkson Will , Sahu Kailash , Anderson Jay , Smith T. Ed , Brown Thomas M. , Casertano Stefano , Rich R Michael , Bond Howard E. , Livio Mario , Minniti Dante , Panagia Nino , Renzini Alvio , Valenti Jeff , Zoccali Manuela
Published: February 2009

In 2004 a deep sequence of HST images of the Bulge was used to identify sixteen transiting extrasolar planet candidates (the SWEEPS candidates; Sahu et al. 2006), of which at least seven are likely to be true planets. Of these, SWEEPS-4 is almost certainly in the disk, and was shown through radial velocity followup to contain a planetary companion; the identification of the remaining fifteen candidates was left undetermined.

We have used a repeat visit in 2006 to attach proper motions to some 180,000 objects, including all sixteen SWEEPS candidates. This has allowed us to build a sample of bulge stars to unprecedented purity. A population of more than 13,000 bulge objects is kinematically isolated, with fewer than thirty disk contaminants. We use the mean bulge and disk populations to test the balance of kinematic associations for the sixteen SWEEPS candidates. Assuming both the detectability and the astrophysical false-positive fraction to be similar for disk and bulge, we find the fraction of stars with planets in the bulge to be consistent with that in the disk.
A time-dependent radiative model for the atmosphere of the eccentric transiting planets
Authors: Iro Nicolas , Deming Drake
Published: February 2009

We present a time-dependent radiative model for the atmosphere of the transiting planets that takes into account the eccentricity of their orbit. We investigate the temporal temperature and flux variations due to the planet-star distance variability. We will also discuss observational aspects with Spitzer measurements.
The hydrogen exosphere of exoplanet HD 209458b detected with HST/ACS
Authors: Ehrenreich D. , des Etangs A. Lecavelier , Hébrard G. , Désert J.-M. , Vidal-Madjar A. , McConnell J. C. , Parkinson C. D. , Ballester G. E. , Ferlet R.
Published: February 2009

Exospheric atomic hydrogen escaping from the planet HD 209458b provides the largest observational signature ever detected for an extrasolar planet atmosphere. We present observations of this transiting planet's extended exosphere with the Advanced Camera for Surveys on board the Hubble Space Telescope. From the two transit light curves obtained at Lyman α, we find an in-transit absorption of (8.0±5.7)%, in good agreement with previous studies. These new constraints on the size of the exosphere strengthens the evaporation scenario. Full details are provided in Ehrenreich et al. (2008).
Absorption Spectra of the Prototype Hot-Jupiters: determination of atmospheric constituents and structure
Authors: Sing David K. , Lecavelier A. , Désert J.-M. , Vidal-Madjar A. , Ballester G.
Published: February 2009

The two prototype hot-Jupiter exoplanets HD209458b and HD189733b are currently offering an unprecedented view of their atmospheres. As discussed here, primary transit transmission spectra provide the opportunity to identify specific atomic and molecular species, determine their abundances, and recover temperature-pressure-altitude information. We present a reanalysis of existing HST/STIS data on HD209458b, providing a complete optical transmission spectrum. Analysis of this spectrum have revealed: (1) the planetary abundance of sodium which is ~2X solar (2) a depletion of sodium at high altitudes due to condensation or ionization (3) Rayleigh scattering by H2 (3) a high temperature at pressures of 10's mbar consistent with the dayside inversion (4) a separate high-altitude hot temperature from the planet's thermosphere and (5) likely absorption by TiO/VO. While HD209458b and HD189733b are currently the best candidates for these studies, another ~10 exoplanets are good targets with today's instruments for future transmission-based atmospheric detections.
Detection of Planetary Emission from TrES-2 using Spitzer/IRAC
Authors: O'Donovan Francis T. , Charbonneau David , Harrington Joseph , Seager Sara , Deming Drake , Knutson Heather A.
Published: February 2009

We present here results from observations of TrES-2 made using the Infrared Array Camera on the Spitzer Space Telescope. We monitored this transiting system during two secondary eclipses, when the planetary emission is blocked by the star. The resulting decrease in flux is 0.135 ± 0.036%, 0.245 ± 0.027%, 0.162 ± 0.064%, and 0.295 ± 0.066%, at 3.6-μm, 4.5-μm, 5.8-μm, and 8.0-μm, respectively. We find evidence for a temperature inversion in the atmosphere of TrES-2, which is predicted by Fortney and collaborators based on the proposed importance of TiO and VO opacities for this highly irradiated gas giant. We also find the time of the center of the eclipse to be consistent with predictions from transit timing observations of TrES-2. This implies that TrES-2 most likely has a circular orbit, and thus does not obtain additional thermal energy from tidal dissipation of a non-zero orbital eccentricity, a proposed explanation of the large planetary radius.
Inverting Phase Curves to Map Exoplanets
Authors: Cowan Nicolas B. , Agol Eric
Published: February 2009

One of the most exciting results of the Spitzer era has been the ability to construct longitudinal brightness maps from the infrared phase variations of hot Jupiters. We presented the first such map in Knutsonet al. (2007), described the mapping theory and some important consequences in Cowan & Agol (2008) and presented the first multi waveband map in Knutsonet al. (2008). In these proceedings, we begin by putting these maps in historical context, then briefly describe the mapping formalism. We then summarize the differences between the complementary N-Slice and Sinusoidal models and end with some of the more important and surprising lessons to be learned from a careful analytic study of the mapping problem.
A behavioral template beach profile model for predicting seasonal to interannual shoreline evolution
Authors: Davidson M. A. , Turner I. L.
Published: February 2009

This contribution presents a simple behavioral template model for beach profile evolution which is calibrated and tested against a 6‐year time series of shoreline position, derived from a coastal imaging system at the Gold Coast, Australia. From a coastal management perspective, the position of the shoreline is arguably one of the most important morphodynamic parameters to be monitored and predicted and therefore forms the focus of this paper. The template model attempts to encapsulate some of the current understanding of coastal dynamics deduced from both scientific investigations and observations. The model framework is based on a simple relaxation model, whereby the profile approaches a template exponentially with time under conditions of constant forcing. The template evolves dynamically in response to incident wave forcing such that when a threshold value of the dimensionless fall velocity (Ω = Hs/wTp, where Hs = offshore significant wave height, Tp = peak wave period, and w = sediment fall velocity) is exceeded, the beach face erodes and flattens, and the shoreline retreats landward, forming an erosional scarp and a breakpoint bar. Conversely, when the Ω falls below threshold, progradation and steepening of the shoreface ensues, accompanied by the evolution of a swash bar and breakpoint step. The Gold Coast data are used to calibrate the threshold value of Ω (≈4.0) which is close to the time series mean (3.8). Testing the calibrated model on unseen data shows that it is able to reproduce the dominant seasonal/interannual shoreline succession observed at this site and up to 77% of the detrended shoreline variability.
Dry snow slab quasi‐brittle fracture initiation and verification from field tests
Authors: McClung D. M.
Published: February 2009

Dry snow slab avalanches initiate from shear fracture in a thin weak layer underneath a planar slab of cohesive snow. In this paper, field data from more than 400 snow shear fracture tests are analysed and applied to the problem of snow slab release and snow pack instability evaluation. The paper contains a new, but simple, analytical model to estimate the critical length for fracture. The model contains the assumption of a finite fracture process zone which may be a significant fraction of the slab depth D or the critical length L for weak layer shear fracture. The results suggest that the ratio L/D is of order 1 for both the data and the model as previously predicted for the snow slab. Using a combination of experimental results from laboratory tests, two sets of field data and the new model, suggests that previous theoretical arguments about snow slab release over almost 30 years are congruent with the field data. Simple extension to explain viscoelastic temperature effects and slope normal weak layer deformation on snow slab instability evaluation is included in the analysis. Since the experimental field data contain viscoelastic effects and slope normal effects, it is imperative to account for these in the model and for snow slab instability evaluation.
Estimating carbon release caused by land use changes over Canada's north during 1985–1990 and 1990–2000 using satellite Earth observation
Authors: Chen Wenjun , Blain Dominique , Li Junhua , Fraser Robert , Zhang Yu , Leblanc Sylvain , Koehler Klause , Olthof Ian , Wang Jixin , McGovern Mark
Published: February 2009

This study estimates the greenhouse gas removal/emission due to land use changes (LUC) over Canada's arctic and subarctic landmass to meet Canada's reporting obligation to the United Nations Framework Convention on Climate Change (UNFCCC). Using Landsat scenes circa 1985, 1990, and 2000, as well as GIS information, we estimated the rate of LUC over Canada's north being 548 ha a−1 during 1985–1990 and 725 ha a−1 during 1990–2000. We then developed circa 2000 baseline aboveground biomass maps for the areas affected by these LUC by applying the relationships between measured aboveground biomass and a combination of Landsat and JERS‐1 data. From these aboveground biomass maps and LUC estimates, we calculated that the LUC activities over Canada's north released 29,000 ± 4400 t CO2 a−1 during 1985–1990 and 41,000 ± 6200 t CO2 a−1 during 1990–2000. Only aboveground biomass was considered. Monte Carlo simulation method was used to quantify the overall error caused by uncertainties in estimates of LUC area and CO2 emission. Because soil carbon stock over Canada's arctic and subarctic ecosystems can be 10–100 time larger than that of aboveground biomass, accurately quantifying soil carbon stock change caused by LUC should be a priority in future studies.
Uncertainty assessment via Bayesian revision of ensemble streamflow predictions in the operational river Rhine forecasting system
Authors: Reggiani P. , Renner M. , Weerts A. H. , van Gelder P. A. H. J. M.
Published: February 2009

Ensemble streamflow forecasts obtained by using hydrological models with ensemble weather products are becoming more frequent in operational flow forecasting. The uncertainty of the ensemble forecast needs to be assessed for these products to become useful in forecasting operations. A comprehensive framework for Bayesian revision has been recently developed and applied to operational flood forecasting with deterministic weather forecasts. The Bayesian revision yields a posterior density, conditional on all information available to the forecaster at the onset of a forecast run. This conditional density objectively quantifies the uncertainty. Here the Bayesian approach is generalized for use with ensemble weather predictions. An end‐to‐end application of a Bayesian postprocessor for ensemble streamflow forecasts in the river Rhine forecasting system is presented. A verification of the postprocessor shows good performance when compared in terms of the ranked probability skill score to non‐Bayesian uncertainty assessment, such as ranking threshold exceedance probabilities for members of a streamflow ensemble prediction. In this context it is also addressed how the proposed Bayesian processor can serve in supporting rational decision making for flood warning under conditions of uncertainty.
Latitudinal signature of Earth's magnetic field variation over the last 5 million years
Authors: Harrison Christopher G. A.
Published: February 2009

In order to investigate the latitudinal effect of the geomagnetic field variation, a new data set consisting of virtual geomagnetic poles (VGPs) from all latitudes has been produced. Since the updated data set was limited to data with VGPs within 45° of the geographic poles, data from lava flows with low‐latitude VGPs were added. More rigorous criteria were used to winnow the data. The data were divided into groups from different observation latitudes. In each group it was shown that the distribution of VGP latitudes could be described by a predominance of poles (average 82%) following a Fisher distribution with the rest following a distribution that would produce a uniform number of poles as a function of latitude. A distribution composed of two Fisher distributions also fit the data very well. For the case using a Fisher distribution plus a uniform distribution, the Fisher distribution changed such that the angular standard deviation (ASD) of VGPs from a set of observations taken at the equator is about 10° and the ASD at 60° observation latitude is about 19°. These results are similar to some results seeking to determine the ASD of VGPs as a function of observation latitude using other methods, which have been recently published, but there are also discrepancies. The results allow us to model inclination distributions as a function of observation latitude for comparison with data in which only the inclination is known, such as data from drill holes. It is shown that in order not to have doubt about the polarity of the inclination data, a drill hole has to be located at an absolute latitude greater than 27° for there to be less than a 5% error. This has major importance for the location of the “Mission to the MOHO” of the Integrated Ocean Drilling Program. The results also confirm that the sources of the nondipole field located in the outer core have to be more than twice as strong at high latitudes than at low latitudes so as to produce the observed increase in VGP scatter with observation latitude. The model of the secular variation proposed here is in no way a theory about how the secular variation happens, but it does allow those who wish to develop such a theory to have a model distribution with which to check their predictions.
Display of ice crystal flutter in atmospheric light pillars
Authors: Borovoi Anatoli , Kustova Natalia
Published: February 2009

Specular patterns in the atmosphere caused by ice crystals with preferably horizontal orientation are quantitatively described by use of a bidirectional phase function for a fluttering plate. The main qualitative features of the sun pillars and overground light pillars are explained. Possibilities to retrieve the probability density for orientation of the preferably oriented crystals from the specular patterns are discussed.
Low‐frequency seismic signals recorded by OBS at Stromboli volcano (Southern Tyrrhenian Sea)
Authors: Sgroi Tiziana , Montuori Caterina , Agrusta Roberto , Favali Paolo
Published: February 2009

Five three‐component broadband ocean bottom seismometers (OBSs) were deployed on the seafloor around the Aeolian Islands (Southern Tyrrhenian Sea). By comparing OBSs digital seismograms, we found a low‐frequency seismicity recorded only at OBS05, the nearest seafloor station to Stromboli volcano. This seismicity appears in the form of a continuous seismic signal (tremor‐like‐signal) as well as a considerable number of shock‐like events. We focused on recordings from OBS05 to verify their correlation with Stromboli volcanic activity. From the spectral analysis, we observed low‐frequency events (LP events), superposed upon the continuous background noise (tremor). LP events and tremor, showing similar energy fluctuations and frequency content, appear to be produced by the same dynamic processes. We interpret this low‐frequency seismicity as probably originating from a continuous uprising of gas bubbles from the deeper part of the Stromboli magmatic column. This could highlight the existence of a deeper source for low‐frequency seismicity.
Observation and modeling of the injection observed by THEMIS and LANL satellites during the 23 March 2007 substorm event
Authors: Liu W. L. , Li X. , Sarris T. , Cully C. , Ergun R. , Angelopoulos V. , Larson D. , Keiling A. , Glassmeier K. H. , Auster H. U.
Published: February 2009

During the encounter of a substorm on 23 March 2007, the THEMIS constellation observed energetic particle injections and dipolarizations in the premidnight sector. Clear injection and dipolarization signatures were observed during the main intensification by three probes (A, B, and D) in the region around 11 RE and 2100 local time (LT). THEMIS C, which was leading in the constellation at 8.3 RE, also observed a clear injection signature, but the dipolarization was not so clear. From the timing based on these observations, a fast westward expanding ion injection and dipolarization front was identified. In combination with the energetic particle observations from Los Alamos National Laboratory (LANL) geosynchronous satellites, the particle injection seemed to initiate between 2100 and 0100 LT. This event provides an excellent opportunity to examine the dipolarization and particle injection processes beyond geosynchronous orbit and over a wide LT range. We model this injection event by means of test particle simulation, setting up an initial particle distribution and sending an earthward dipolarization‐like pulse from the tail that also expands azimuthally, then recording the ions and electrons at the various satellite locations. Most features of the injected particles are reproduced by the test particle simulation. These include not only the earthward injections but also the fast westward expansion of the injection, as well as the timing of the injections as observed among different satellites that made the observations. On the basis of the observations and the simulation results, we suggest that this substorm injection was initiated around 2300 LT, farther down the tail, and propagated radially inward and expanded azimuthally.
Energetic plasma sheet electrons and their relationship with the solar wind: A Cluster and Geotail study
Authors: Burin des Roziers E. , Li X. , Baker D. N. , Fritz T. A. , Friedel R. , Onsager T. G. , Dandouras I.
Published: February 2009

The statistical relationship between tens of kiloelectron volts plasma sheet electrons and the solar wind, as well as >2 MeV geosynchronous electrons, is investigated using plasma sheet measurements from Cluster (2001–2005) and Geotail (1998–2005) and concurrent solar wind measurements from ACE. Plasma sheet selection criteria from previous studies are compared, and this study selects a new combination of criteria that are valid for both polar‐orbiting and equatorial‐orbiting satellites. Plasma sheet measurements are mapped to the point of minimum ∣B∣, using the Tsyganenko T96 magnetic field model, to remove measurements taken on open field lines, which reduces the scatter in the results. Statistically, plasma sheet electron flux variations are compared to solar wind velocity, density, dynamic pressure, interplanetary magnetic field (IMF) Bz, and solar wind energetic electrons, as well as >2 MeV electrons at geosynchronous orbit. Several new results are revealed: (1) There is a strong positive correlation between energetic plasma sheet electrons and solar wind velocity, (2) this correlation is valid throughout the plasma sheet and extends to distances of XGSM = −30 RE,, (3) there is evidence of a weak negative correlation between energetic plasma sheet electrons and solar wind density, (4) energetic plasma sheet electrons are enhanced during times of southward interplanetary magnetic field (IMF), (5) there is no clear correlation between energetic plasma sheet electrons and solar wind electrons of comparable energies, and (6) there is a strong correlation between energetic electrons (>38 keV) in the plasma sheet and >2 MeV electrons at geosynchronous orbit measured 2 days later.
First RHESSI terrestrial gamma ray flash catalog
Authors: Grefenstette B. W. , Smith D. M. , Hazelton B. J. , Lopez L. I.
Published: February 2009

We present a summary of data from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) terrestrial gamma ray flash (TGF) catalog. We describe the RHESSI search algorithm and discuss its limitations due to its design emphasis on cleanliness rather than completeness. This search algorithm has identified 820 TGFs between March of 2002 and February of 2008. Radiation damage to the RHESSI detectors has resulted in a decreased sensitivity after early 2006 and a corresponding decrease in the number of identified TGFs in the years 2006–2008. Prior to this, the average rate of occurrence was one TGF every 2.35 days. RHESSI has seen multiple TGFs associated with a single storm system, either in the same orbit or in the subsequent orbit. The X‐ray flux in a 100 ms pedestal region surrounding all of the TGFs is (1.3 ± 1.9) × 10−3 times the average peak flux of a TGF. We show that RHESSI was counting at or near its maximum throughput during the peak 50 μs of many of the TGFs and that we do not yet know the maximum possible brightness of a TGF. On short time scales, some TGFs may be much brighter than could be observed by either RHESSI or BATSE. Finally, we show that there is no detectable change in the spectrum of TGFs when they are grouped by brightness, geographic latitude, geomagnetic latitude, or the local day or night.
Shape and volume change of pressurized ellipsoidal cavities from deformation and seismic data
Authors: Amoruso A. , Crescentini L.
Published: February 2009

We present exact expressions for the volume change of a pressurized ellipsoidal cavity in an infinite homogeneous elastic medium. The expressions can be used as approximate solutions also for a homogeneous half‐space. We show that previously published widely used expressions are correct for spheres but underestimate the ratio of the volume change to the product of pressure and volume in any other case. We discuss the capability to infer the shape of a single ellipsoidal cavity from far‐field deformation measurements. Our results indicate that source axis ratios may often be hard to estimate, whereas it may be easier to infer the volume change of the source. We also consider the case of a source region consisting of interconnected pressurized ellipsoidal cavities, neglecting mutually induced stress. If all the cavities share the same shape and orientation, the source is seen in the far field as a single ellipsoidal cavity and it is possible to compute the total volume change from surface displacements. The shape of the apparent single ellipsoid is the same as the shape of the constituting cavities and not of the source region. In any other case a single ellipsoidal cavity might even be unable to give the same surface displacements as the ensemble of cavities. Since sudden volume change of a cavity can generate seismic waves, we discuss the decomposition of the related moment tensor into isotropic, double‐couple, and compensated linear‐vector dipole force systems in case of magma exchange between two ellipsoidal cavities, giving relations for the moment tensor components.
Modeling the distribution of H2O and HDO in the upper atmosphere of Venus
Authors: Liang Mao‐Chang , Yung Yuk L.
Published: February 2009

The chemical and dynamical processes in the upper atmosphere of Venus are poorly known. Recently obtained vertical profiles of trace species from the Venus Express mission, such as HCl, H2O, and HDO, provide new information to constrain these processes. Here, we simulate these profiles, using the model we have developed and described in a related paper by Yung et al. (2008), with special emphasis on the modeling of H2O and HDO. A new mechanism, the photo‐induced isotopic fractionation effect (PHIFE) of H2O and HCl, is incorporated into our model. The observed enhancement of HDO could be attributed to (1) preferential destruction of H2O relative to HDO via PHIFE and (2) escape of hydrogen that enhances the abundance of D and hence its parent molecule HDO. Over a wide range of the sensitivity of the results to the changes of the two mechanisms, we find that the observed profiles of HDO and H2O profiles cannot be explained satisfactorily by current knowledge of chemical and dynamical processes in this region of the atmosphere. Several conjectures to tackle the problems are discussed.
Cone fields in SW Elysium Planitia: Hydrothermal venting on Mars?
Authors: Lanz Julia K. , Saric Matthias B.
Published: February 2009

We have studied a large cone field in SW Elysium Planitia that shows unique characteristics that have, as yet, not been described elsewhere on Mars. Pitted cones and cone fields are quite common on Mars and the Elysium Planitia region where they have been mainly interpreted as pseudocraters. The cones in the study area differ from cones elsewhere on Mars in morphology, geologic setting, and their assemblage with pitted ridges as well as their close association to Aeolis Planum–Medusae Fossae Formation (MFF) material. The cones appear almost exclusively along an extensive contact zone, several hundred kilometers long, where lava flows that emanated from the Cerberus Fossae flooded fine‐grained MFF material of the Aeolis Planum complex. Particularly striking is the observation that several cones in the study area have developed on top of mesas and terraces of Aeolis Planum material that were embayed but not overflowed by lava and can thus not be explained as pseudocraters. We propose that the striking assemblage of these structures was formed by a combination of pseudocrater formation and hydrothermal venting through mesas of Aeolis Planum‐MFF material by a process similar to hydrothermal vent complexes on Earth. The voluminous Cerberus Fossae lava flows that flooded the study area covered large parts of Aeolis Planum material, initiating the mobilization of volatiles and leading to hydrothermal activity along the lava‐MFF contact. Furthermore, our observations strongly support the hypothesis that the volatile content of the MFF is (or was) high, at least in that part of the MFF constituting the Aeolis Planum complex.
Solar‐wind control of the hot oxygen corona around Mars
Authors: Kaneda Kaori , Terada Naoki , Machida Shinobu
Published: February 2009

The global behavior and escape rate of hot oxygen atoms around Mars and their response to different solar wind dynamic pressure (PSW) conditions are investigated using a multidimensional time‐dependent magnetosheath‐ionosphere‐exosphere (Msh‐I‐E) coupling model. Recently we reported that an increase in PSW leads to a short‐term increase in the escape rate of nonthermal oxygen using a one‐dimensional (1‐D) Msh‐I‐E model. The model used in the present paper is a multidimensional version of our previous 1‐D model. For the exosphere model, we adopt a three‐dimensional Monte Carlo approach above a 250‐km altitude, while a time‐dependent two‐stream approach is employed below 250 km. The exosphere model is coupled with a two‐dimensional resistive magnetohydrodynamic model of the magnetosheath‐ionosphere interaction, assuming axial symmetry with respect to the Sun‐Mars line. The results of the present model are consistent with the results of the 1‐D model. The escape rate of hot oxygen for PSW = 0.36 nPa is roughly twice that for PSW = 1.43 nPa under steady state conditions. For nonstationary conditions, where PSW is suddenly increased from 0.36 to 1.43 nPa, the escape rate is temporarily enhanced by a factor of 2.3 to 4.5 compared with that of the steady state case. The hot oxygen density is found to be less dependent on PSW than is the escape rate.
Exploring glacier dynamics with subglacial water pressure pulses: Evidence for self‐organized criticality?
Authors: Kavanaugh J. L.
Published: February 2009

In order to determine whether brief excursions, or “pulses,” in subglacial water pressure inferred by Kavanaugh and Clarke (2000, 2001) occur, water pressures at the bed of Trapridge Glacier, Yukon, Canada, were recorded using an interface board that continuously monitored a pressure transducer. During the 231 day period between 16 July 2005 and 4 March 2006, more than 7000 pressure pulses were recorded, with magnitudes reaching nearly 3 times the flotation value. Comparison of the pressure pulse record with those from a number of other instruments installed in this soft‐bedded glacier indicates that these pulses are generated by stress transients that compress the water within the borehole; calculations suggest that these transients are as large as 75 times the nominal driving stress. Both the magnitudes and interevent times for these pulses are well fitted by power law distributions that are remarkably similar to those exhibited by earthquakes. These similarities suggest that the ice‐bed interface of a soft‐bedded glacier behaves much like an earthquake fault and raises the possibility that such glaciers self‐organize to a critical state. Further evidence for self‐organized criticality (SOC) of soft‐bedded glaciers is suggested by an examination of well‐known ice dynamical properties and the rheological properties of subglacial sediments, which suggests that SOC might be a natural consequence of the rate‐independent behavior of subglacial sediments.
In situ measures of methanotroph activity in upland soils: A reaction‐diffusion model and field observation of water stress
Authors: von Fischer Joseph C. , Butters Gregory , Duchateau Paul C. , Thelwell Roger J. , Siller Richard
Published: February 2009

Laboratory assays of methanotroph activity in upland (i.e., well‐drained, oxic) ecosystems alter soil physical structure and weaken inference about environmental controls of their natural behavior. To overcome these limitations, we developed a chamber‐based approach to quantify methanotroph activity in situ on the basis of measures of soil diffusivity (from additions of an inert tracer gas to the chamber headspace), methane concentration change, and analysis of results with a reaction‐diffusion model. The analytic solution to this model predicts that methane consumption rates are equally sensitive to changes in methanotroph activity and diffusivity, but that doubling either of these parameters leads to only a √2 increase in consumption. With a series of simulations, we generate guidelines for field deployments and show that the approach is robust to plausible departures from assumptions. We applied the approach on a dry grassland in north central Colorado. Our model closely fit measured changes in methane concentrations, indicating that we had accurately characterized the biophysical processes underlying methane uptake. Field patterns showed that, over a 7‐week period, soil moisture fell from 38% to 15% water‐filled pore spaces, and diffusivity doubled as the larger soil pores drained of water. However, methane uptake rates fell by ∼40%, following a 90% decrease in methanotroph activity, suggesting that the decline in methanotroph activity resulted from water stress to methanotrophs. We anticipate that future application of this approach over longer timescales and on more diverse field sites has potential to provide important insights into the ecology of methanotrophs in upland soils.
Hydrological trend analysis in the Yellow River basin using a distributed hydrological model
Authors: Cong Zhentao , Yang Dawen , Gao Bing , Yang Hanbo , Hu Heping
Published: February 2009

The hydrological cycle has been highly influenced by climate change and human activities, and it is significant for analyzing the hydrological trends that occurred in past decades in order to understand past changes and to predict future trends. The water crisis of the Yellow River basin has drawn much attention from around the world, especially the drying up of the main river along the lower reaches during the 1990s. By incorporating historical meteorological data and available geographic information related to the conditions of the landscape, a distributed hydrological model has been employed to simulate the natural runoff without consideration of artificial water intake. On the basis of the data observed and the results simulated by the model, the hydrological trends have been analyzed quantitatively for evaluating the impact from climate change and human activity. It is found that the simulated natural runoff follows a similar trend as the precipitation in the entire area being studied during the last half century, and this implies that changes in the natural runoff are mainly controlled by the climate change rather than land use change. Changes in actual evapotranspiration upstream of the Lanzhou gauge are controlled by changes in both precipitation and potential evaporation, while changes of actual evapotranspiration downstream of the Lanzhou gauge are controlled mainly by the changes in precipitation. The difference between the annual observed runoff and the simulated runoff indicates that there is little artificial water consumption upstream of the Lanzhou gauge, but the artificial water consumption becomes larger downstream of the Lanzhou gauge. The artificial water consumption shows a significant increasing trend during the past 50 years and is the main cause of the drying up of the Yellow River. However, in contrast to the common perception that the serious drying up downstream of the Yellow River during the 1990s is caused by the rapid increase of artificial water consumption during the same period, it has been found that the main cause of this aggravation is the drier climate that has existed since the 1990s. The main reason that the drying‐up situation became better in the 21st century is because of the enhanced water resources management since 2000.
An optimized routing model for flood forecasting
Authors: Price Roland K.
Published: February 2009

A conceptual flow routing model for flood forecasting is adopted for a reach of river given only historic upstream and downstream stage hydrographs and the associated in‐bank rating curves, local rainfall, and minimal additional information. The ungauged lateral inflows are generated by a unit hydrograph rainfall‐runoff model. The model is calibrated by optimizing the parameters of the functional form for the average cross section along the reach, the base lateral inflow and the peak of the unit hydrograph, and the rating curve extensions downstream and upstream. The model is confirmed by applying it to a synthetic river reach and then to the forecasting of floods in a reach of the River Wye, UK.
Spin motive force in magnetic nanostructures
Authors: Ohe Jun-ichiro , Maekawa Sadamichi
Published: February 2009

In a ferromagnetic metal, a nonconservative force acting on the spin degree of freedom of electrons gives rise to the spin motive force, which is in contrast to the electromotive force acting on the charge degree of electrons. The spin motive force induced by the motion of the magnetic vortex core in a magnetic disk is examined in the numerical simulation method. By introducing the motive force in the Landau–Lifshitz equation for magnetic dynamics, the electromotive force is obtained near the vortex core. The experimental setup for observing the electric field is proposed.
In/Er-codoped LiNbO3 crystals with enhanced 1.5 μm emission and suppressed upconversion emission
Authors: Sun Liang , Yang Chun-Hui , Li Ai-Hua , Xu Yu-Heng , Zhao Lian-Cheng
Published: February 2009

1.5   μ m emission and green upconversion emission properties in In/Er-codoped LiNbO3 crystals were investigated by using both steady-state and time-resolved emission spectra. The 1.5 mol % In2O3 codoping results in the lengthening of 1.5 μm emission lifetime by 13.9% and simultaneously the shortening of 550 nm green upconversion emission lifetime by 52.5%. The decay behavior of the green upconversion emission of the In/Er-codoped crystal shows obviously nonexponential. These spectroscopic characteristics are related with the lower concentration of the cluster sites of Er3+ ion and possible cross-relaxation energy transfer processes. The above emission results are further supported by the theoretical emission results based on Judd–Ofelt theory.
Physical origin of the incommensurate spin spiral structure in Mn3Si
Authors: Hortamani M. , Sandratskii L. , Zahn P. , Mertig I.
Published: February 2009

We report first-principles study of the magnetic structure of Mn3Si. The Mn atoms form two sublattices. One of them is (MnI) characterized by large atomic magnetic moments and the other one (MnII) possesses induced moments. It is shown that in agreement with experiment the magnetic ground state is a spin spiral. We found that the spiral magnetic structure is formed as a result of the competition between direct antiferromagnetic interaction of the MnI magnetic moments and indirect ferromagnetic interaction of the same moments through the magnetic moment of the MnII sublattice. We demonstrate that this competition is strongly volume dependent and leads to volume dependence of the wave vector of the spin spiral. These properties are related to the volume dependence of the induced moments of MnII atoms.
Magnetic phases in ultrathin helimagnetic holmium films
Authors: Cinti Fabio , Cuccoli Alessandro , Rettori Angelo
Published: February 2009

Detailed Monte Carlo simulations of Ho magnetic thin films are here presented. The system is described by a Heisenberg model with easy-plane single-ion anisotropy and seven coupling constants, as obtained by experimental neutron scattering measurements. The critical behavior landscape comes out extremely complex and fascinating. In fact, for the analyzed thicknesses of 8–16, it is seen that by increasing the temperature the films show, after the distorted helical configuration, a temperature range where disordered inner planes coexist with surface ones in a block ordered state. At low temperature, it is also found that the progressive reduction in the number of layers do not imply a sudden helical order suppression but rather, as a consequence of surface effects, a gradual passage to a fanlike order, accompanied by the helix distortion, is observed.
Constant permeability of (Fe0.75B0.20Si0.05)96Nb4 bulk metallic glass prepared by B2O3 flux melting and Cu-mold casting
Authors: Bitoh T. , Shibata D.
Published: February 2009

The effect of B2O3 flux melting on the soft magnetic properties of (Fe0.75B0.20Si0.05)96Nb4 bulk metallic glass prepared by casting has been investigated. Ring-shaped bulk specimens that were prepared by B2O3 flux melting and Cu-mold casting (fluxed specimens) show a flat hysteresis curve, indicating a good linear relationship between the magnetic induction and the applied magnetic field. Although the permeability of the fluxed specimens is lower than that of the specimens prepared by conventional Cu-mold casting by one order of magnitude, their coercivities are almost same. These results show that it is possible to develop a new soft magnetic material that exhibits constant permeability with low core loss.
An equivalent stress for the influence of multiaxial stress on the magnetic behavior
Authors: Daniel Laurent , Hubert Olivier
Published: February 2009

A main limitation of most models describing the effect of stress on the magnetic behavior is that they are restricted to uniaxial—tensile or compressive—stress. An idea to overcome this strong limitation is to define a fictive uniaxial stress, the equivalent stress that would change the magnetic behavior in a similar manner than a multiaxial one. A new definition of such an equivalent stress is proposed based on an equivalence in terms of magnetoelastic energy. This equivalent stress is compared with former proposals and validated using experimental results carried out under biaxial mechanical loading.
Pinning synchronization of delayed dynamical networks via periodically intermittent control
Authors: Xia Weiguo , Cao Jinde
Published: February 2009

This paper investigates the synchronization problem for a class of complex delayed dynamical networks by pinning periodically intermittent control. Based on a general model of complex delayed dynamical networks, using the Lyapunov stability theory and periodically intermittent control method, some simple criteria are derived for the synchronization of such dynamical networks. Furthermore, a Barabási–Albert network consisting of coupled delayed Chua oscillators is finally given as an example to verify the effectiveness of the theoretical results.
Spin-filtering effect in the transport through a single-molecule magnet Mn12 bridged between metallic electrodes
Authors: Barraza-Lopez Salvador , Park Kyungwha , García-Suárez Víctor , Ferrer Jaime
Published: February 2009

Electronic transport through a single-molecule magnet Mn12 in a two-terminal setup is calculated using the nonequilibrium Green’s function method in conjunction with density-functional theory. A single-molecule magnet Mn12 is bridged between Au(111) electrodes via thiol group and alkane chains such that its magnetic easy axis is normal to the transport direction. A computed spin-polarized transmission coefficient in zero bias reveals that resonant tunneling near the Fermi level occurs through some molecular orbitals of majority spin only. Thus, for low bias voltages, a spin-filtering effect such as only one spin component contributing to the conductance is expected. This effect would persist even with inclusion of additional electron correlations.
A particle-based multiscale model for submicron fluid flows
Authors: Mukhopadhyay Saumyadip , Abraham John
Published: February 2009

A particle-based multiscale model for submicron fluid flow is proposed in this work. The model is based on a combination of a dissipative-particle dynamics (DPD) model for the mesoscales and molecular dynamics (MD) for the atomistic scales. The coarse-graining procedure involved in deriving DPD from MD is systematically exploited in this work to transition from the atomistic region to the mesoscale region. Coarse-graining results in filtering of smaller scales. The continuity of thermodynamic and transport properties across the interface is facilitated by appropriate selection of model parameters and the modeling of particle flux across layers. The model is applied to solve Poiseuille and Couette flows and flow over a rough wall. Results are compared with full-scale MD simulations. The model is also employed to solve microscale flows with slip at the wall. In the case of the Poiseuille and Couette flows, the results are found to differ from the analytical solutions by less than 10%. The differences with full-scale MD simulation results are within 5% for flow over an obstacle. The reduction in computational cost with increasing coarse graining is also evaluated.
Normalized kinetic energy as a hydrodynamical global quantity for inhomogeneous anisotropic turbulence
Authors: Cortet Pierre-Philippe , Diribarne Pantxo , Monchaux Romain , Chiffaudel Arnaud , Daviaud François , Dubrulle Bérengère
Published: February 2009

We introduce a hydrodynamical global quantity δ that characterizes turbulent fluctuations in inhomogeneous anisotropic flows. This time dependent quantity is constructed as the ratio of the instantaneous kinetic energy of the flow to the kinetic energy of the time-averaged flow. Such a normalization based on the dynamics of the flow makes this quantity comparable from one turbulent flow to any other. We show that δ(t) provides a useful quantitative characterization of any turbulent flow through generally only two parameters, its time average δ¯ and its variance δ2. These two quantities present topological and thermodynamical properties since they are connected, respectively, to the distance between the instantaneous and the time-averaged flow and to the number of degrees of freedom of the flow. Properties of δ¯ and δ2 are experimentally studied in the typical case of the von Kármán flow and used to characterize the scale by scale energy budget as a function of the forcing mode as well as the transition between two flow topologies.