bluuebunny/crossref_metadata_2025 huggingface dataset:
The supercritical accretion disk in SS 433 and ultraluminous X-ray sources
Authors: Fabrika S. N. , Abolmasov P. K. , Karpov S.
Published: May 2007

SS 433 is the only known persistent supercritical accretor, it may be very important for understanding ultraluminous X-ray sources (ULXs) located in external galaxies. We describe main properties of the SS 433 supercritical accretion disk and jets. Basing on observational data of SS 433 and published 2D simulations of supercritical accretion disks we estimate parameters of the funnel in the disk/wind of SS 433. We argue that the UV radiation of the SS 433 disk (∼ 50000 K, ∼ 1040erg/s) is roughly isotropic, but X-ray radiation (∼ 107K, ∼ 1040erg/s) of the funnel is mildly anisotropic. A face-on SS 433 object has to be ultraluminous in X-rays (1040–41erg/s). Typical time-scales of the funnel flux variability are estimated. Shallow and very broad (0.1-0.3c) and blue-shifted absorption lines are expected in the funnel X-ray spectrum.
Imaging compact supermassive binary black holes with Very Long Baseline Interferometry
Authors: Taylor G. B. , Rodriguez C. , Zavala R. T. , Peck A. B. , Pollack L. K. , Romani R. W.
Published: May 2007

We report on the discovery of a supermassive binary black-hole (SBBH) system in the radio galaxy 0402+379, with a projected separation between the two black holes of just 7.3 pc. This is the most compact SBBH pair yet imaged by more than two orders of magnitude. These results are based upon multi-frequency imaging using the Very Long Baseline Array (VLBA) which reveal two compact, variable, flat-spectrum, active nuclei within the elliptical host galaxy of 0402+379. Multi-epoch observations from the VLBA also provide constraints on the total mass and dynamics of the system. The two nuclei appear stationary while the jets emanating from the weaker of the two nuclei appear to move out and terminate in bright hot spots. The discovery of this system has implications for the number of compact binary black holes that might be sources of gravitational radiation. The VLBI Imaging and Polarimetry Survey (VIPS) currently underway should discover several more SBBHs.
The central 80×200 pc of M83: how many black holes and how massive are they?
Authors: Dottori H. , Díaz R. , Rodrigues I. , Agüero M. P. , Mast D.
Published: May 2007

The central ≈ 80×200 pc of the barred spiral galaxy M83 (NGC 5236) has been observed with the GEMINI-S+CIRPASS configuration which produced 490 spectra with a spectral resolving power of 3200, centered at 1.3 microns, oriented NW-SE. We determine the kinematics of this region with 0.36″ sampling and sub-arcsec resolution. Disk-like motions have been detected in Paβ at parsec scales around: a) the optical nucleus, b) the center of the external K-band isophotes coincident with that of the CO velocity map both also tracing the center of the bulge, and c) a hidden condensation located at (R,θ)=(158pc, 301o). The present resolution allows to detect other minor whirls, not discussed here. The disk around (a) has a radius of ∼8 pc and the two around (b) and (c) can be traced approximately up to 50–60 pc from their kinematical centers.

The rotation curves have been fitted by Satoh like spheroids+disk indicating masses of ≈4× 106M⊙, 60– 70× 106M⊙ and 30– 40× 106M⊙ respectively. Limit to the masses of central BHs can be set by supposing that the central unresolved line broadening inside each condensations is dominated by the BH as far as allowed by the central error bars. The BH +Satoh models were smoothed with a 9 pc Gaussian. The upper mass limit derived for the BH is for (a) ∼ 106 / sin(i)M⊙, and for (b) and (c) 0.2–1.0× 106 / sin(i)M⊙. Many questions arise from this interesting nucleus: are we witnessing a unique phenomenon or simply a barred galaxy with ongoing strong SF in our backyard? Does each one of the condensations host a BH indeed? or is there only one at the bulge center? Which is the fate of this complex scenario?
Relationship between X-shaped radio sources and double-double radio galaxies
Authors: Chen Xian , Liu Fukun
Published: May 2007

Both the X-shaped radio galaxies and double-double radio galaxies (DDRGs) are suggested in the literature to be due to the binary-accretion disk interaction or to the coalescence of SMBBHs. These models suggest some relationship between the two types of radio sources. In this paper, we collected data from literatures for two samples of X-shaped and double-double radio galaxies together with a control sample of FRII radio galaxies and statistically investigate their properties.

We find that the wings of X-shaped radio galaxies and the outer and inner lobes of DDRGs tend to be perpendicular to the major axis of the host galaxy (or dust structures), while the active lobes orient randomly. Both X-shaped and double-double radio galaxies are low luminous FRII or FRI/FRII transitional radio sources with the similar dimensionless accretion rate ṁ ∼ 0.01, which is about the transitional accretion rate given in the literature.

All the statistic results can be reconciled if there is an evolutionary relationship between X-shaped and double-double radio galaxies, in the sense that X-shaped radio galaxies may be due to the interaction of active SMBBHs and accretion disk and DDRGs due to the removal of inner disk region and the coalescence of SMBBHs.
Formation history of supermassive black holes in a viable cosmological window
Authors: Coimbra-Araújo Carlos H. , Friaça Amâncio C. S.
Published: May 2007

We show, performing a viable cosmological window, that only the magneto hydrodynamic (MHD) disk model is capable to explain how an intermediate mass black hole (IMBH) (with masses ∼ 103M⊙) grows unto a supermassive black hole (SMBH) (with masses ∼ 107M⊙). We still calculate the supermassive stars sequence of stability. Those stars, with synthetized helium or oxygen cores, collapse to form IMBHs. In our calculation we show that the primordial stars must have rapid rotation if they are in the stable part of the sequence.
Polarization from an orbiting spot
Authors: Dovčiak Michal , Karas Vladimír , Matt Giorgio
Published: May 2007

The polarization from a spot orbiting around Schwarzschild and extreme Kerr black holes is studied. The time dependence of the degree and angle of polarization during the spot revolution is examined as a function of the observer's inclination angle and black hole angular momentum. The gravitational and Doppler shifts, lensing effect as well as time delays are taken into account.
Activity type of galaxies in HyperLeda
Authors: Gavrilović N. , Mickaelian A. , Petit C. , Popović L. Č. , Prugniel P.
Published: May 2007

The HyperLeda database (!http://leda.univ-lyon1.fr) is a tool to study the physics of galaxies. It is based on compilations of heterogeneous data (from large surveys and literature) which are cross-identified and homogenized to produce a uniform representation of the galaxies. We have added in the database a characterization of the nuclear and starburst activity from the Véron and Véron catalogue.

It is now possible to retrieve an activity type for the HyperLeda galaxies having this attribute, and to select list of objects from constraints on activity type. For example, one may select all Sy2 galaxies within some magnitude limits and/or redshift.
Physical properties of emitting plasma near massive black holes: the Broad Line Region
Authors: Ilić D. , Mura G. La , Popović L. Č , Shapovalova A. I. , Ciroi S. , Chavushyan V. H. , Rafanelli P. , Burenkov A. N. , Marcado A.
Published: May 2007

We apply the Boltzmann-Plot (BP) method to the Balmer lines to estimate the physical propertiesin the Broad Line Region of Active Galactic Nuclei. We study the Balmer lines of a sample of 90 AGN from Sloan Digital Sky Survey database, as well as the time variability of the BP parameter A of NGC 5548.
Optical variability of X-ray selected blazars
Authors: Kurtanidze Omar M. , Nikolashvili Maria G. , Kimeridze Givi N. , Sigua Lorand A. , Kapanadze Bidzina Z.
Published: May 2007

We present optical R band photometry of nine X-ray selected BL Lac objects: 1ES 0229+200, 1ES 0323+022, 1ES 502+675, 1ES 0647+250, 1ES 0806+524, 1ES0927+500, 1ES 1028+511, 1ES 1959+650, 1ES2344+514.

Variability on long time scales within one magnitude in R band was found for all of the observed objects, except 1ES 0229+200 and 1ES0927+500. Largest variation was detected for 1ES 0502+675 and equals to 1.07 mag. Only few objects show statistically significant variation on intra-day scale.
Detailed structure of the X-ray jet in 4C 19.44 (PKS1354+195)
Authors: Schwartz D. A. , Harris D. E. , Landt H. , Siemiginowska A. , Perlman E. S. , Cheung C. C. , Gelbord J. M. , Worrall D. M. , Birkinshaw M. , Jorstad S. G. , Marscher A. P. , Stawarz L.
Published: May 2007

We investigate the variations of the magnetic field, Doppler factor, and relativistic particle density along the jet of a quasar at z=0.72. We chose 4C 19.44 for this study because of its length and straight morphology. The 18 arcsec length of the jet provides many independent resolution elements in the Chandra X-ray image. The straightness suggests that geometry factors, although uncertain, are almost constant along the jet. We assume the X-ray emission is from inverse Compton scattering of the cosmic microwave background. With the aid of assumptions about jet alignment, equipartition between magnetic-field and relativistic-particle energy, and filling factors, we find that the jet is in bulk relativistic motion with a Doppler factor ≈ 6 at an angle no more than 10∘ to the line of sight over de-projected distances ≈ 150–600 kpc from the quasar, and with a magnetic field ≈10 μGauss.
Outburst of the unique X-ray transient CI Cam and its impact on the system
Authors: Šimon V. , Bartolini C. , Guarnieri A. , Piccioni A. , Hanžl D.
Published: May 2007

We argue that the outburst of CI Cam (XTE J0421+560), probably containing a black hole, was caused by the thermal instability of the accretion disk. Applying the model of King & Ritter (1998), we obtain a realistic disk mass and radius. The differences from soft X-ray transients belonging to the low-mass X-ray binaries can be explained if the disk in CI Cam heats up an extended envelope and/or a strong jet is formed. We resolve several spectral components in the optical colors in quiescence after the outburst; they vary in a complicated way during a possible 1350 d cycle.

We find indications that the variations of the source of the optical light can be related to those of the X-ray source in quiescence. The accretion disk seems to refill at present. Nowadays, only non-periodic intra-night optical (∼0.02 mag) fluctuations are present. As regards the absence of coherent changes in the optical band, we point out the similarities in the situation of CI Cam and the microquasar LS5039/RX J1826–1450.
Chilled disks in ultraluminous X-ray sources
Authors: Soria Roberto , Kuncic Zdenka , Gonçalves Anabela C.
Published: May 2007

If the standard disk-blackbody approximation is used to estimate black hole (BH) masses in ultraluminous X-ray sources (ULXs), the inferred masses are ∼ 1000 M⊙. However, we argue that such an approximation cannot be applied to ULXs, because their disks are only radiating a small fraction of the accretion power, and are therefore cooler than they would be in a thermal-dominant state, for a given BH mass. Instead, we suggest that a different phenomenological approximation should be used, based on three observable parameters: disk luminosity, peak temperature, and ratio between thermal and non-thermal emission. This method naturally predicts masses ∼ 50 M⊙, more consistent with other theoretical and observational constraints.
Humpy LNRF-velocity profiles in accretion discs orbiting rapidly rotating Kerr black holes: a possible relation to epicyclic oscillations
Authors: Stuchlík Zdeněk , Slaný Petr , Török Gabriel
Published: May 2007

Coordinate-independent definition of the characteristic, so-called “humpy” frequency related to the positive gradient of the orbital velocity in locally non-rotating frames around nearly extreme Kerr black holes is given and compared with the epicyclic and orbital frequencies for both Keplerian thin discs and limiting marginally stable thick discs.
Magnetotelluric measurements across the Beattie magnetic anomaly and the Southern Cape Conductive Belt, South Africa
Authors: Weckmann U. , Ritter O. , Jung A. , Branch T. , de Wit M.
Published: May 2007

The Beattie Magnetic Anomaly (BMA) and the Southern Cape Conductive Belt (SCCB), two of Earth's largest continental geophysical anomalies, extend across the southern African continent in an east‐west direction. To resolve structural details of the SCCB, a high‐resolution magnetotelluric study was conducted in March 2004, along a 150‐km‐long N‐S profile across the Karoo Basin in South Africa. A two‐dimensional conductivity model at a scale of the entire crust exhibits three distinct zones of high conductivity: (1) Beneath the surface trace of the axis of the BMA we observe a high‐conductivity anomaly at 5 to 10 km depth; however, it remains enigmatic whether both geophysical anomalies have the same source. (2) A shallow, regionally continuous subhorizontal band of high conductivity can be linked to a 50‐ to 70‐m‐thick pyritic‐carbonaceous marker horizon intersected in deep boreholes. (3) Several highly conductive synformal features in the mid crust are newly imaged near the northern extremity of the profile. Our data generally support the existence of a deeper conductivity belt but allow for a much better definition of crustal conductivity in this region. Such laterally confined zones of crustal conductivity can only be resolved with a dense site spacing and broadband recordings.
A smoothed particle hydrodynamics model for reactive transport and mineral precipitation in porous and fractured porous media
Authors: Tartakovsky Alexandre M. , Meakin Paul , Scheibe Timothy D. , Wood Brian D.
Published: May 2007

A numerical model based on smoothed particle hydrodynamics (SPH) was used to simulate reactive transport and mineral precipitation in porous and fractured porous media. The stability and numerical accuracy of the SPH‐based model was verified by comparing its results with analytical results and finite element numerical solutions. The numerical stability of the model was also verified by performing simulations with different time steps and different number of particles (different resolutions). The model was used to study the effects of the Damkohler and Peclet numbers and pore‐scale heterogeneity on reactive transport and the character of mineral precipitation and to estimate effective reaction coefficients and mass transfer coefficients. Depending on the combination of Damkohler and Peclet numbers the precipitation may be uniform throughout the porous domain or concentrated mainly at the boundaries where the solute is injected and along preferential flow paths. The effective reaction rate coefficient and mass transfer coefficient exhibited hysteretic behavior during the precipitation process as a result of changing pore geometry and solute distribution. The changes in porosity and fluid fluxes resulting from mineral precipitation were also investigated. It was found that the reduction in the fluid flux increases with increasing Damkohler number for any particular reduction in the porosity. The simulation results show that the SPH, Lagrangian particle method is an effective tool for studying pore‐scale flow and transport. The particle nature of SPH models allows complex physical processes such as diffusion, reaction, and mineral precipitation to be modeled with relative ease.
Estimating Eliassen‐Palm flux using COSMIC radio occultation
Authors: Leroy S. S. , Anderson J. G.
Published: May 2007

We present a methodology for analyzing the Eliassen‐Palm (E‐P) flux in the troposphere and stratosphere using GPS radio occultation data from the COSMIC project. In this methodology, geopotential height and temperature are mapped on constant pressure surfaces using a Bayesian interpolation scheme with a spherical harmonic basis, and the components of the E‐P flux are evaluated using geostrophic winds. We perform a simulation‐analysis study using the NCEP/NCAR Reanalysis as truth. E‐P fluxes are evaluated daily, and it is found that patterns of E‐P flux are estimated faithfully, and extrema in the vertical and horizontal components are underestimated by 5–10% and by 30–40%, respectively. Monthly hemispheric averages of the vertical component of the E‐P flux at the tropopause can be estimated to <5%. The error is due to the geostrophic approximation and spatial coverage, mostly the latter: COSMIC GPS radio occultation only resolves atmospheric eddies with scales greater than 1000 km on a daily basis.
Airborne measurements indicate large methane emissions from the eastern Amazon basin
Authors: Miller John B. , Gatti Luciana V. , d'Amelio Monica T. S. , Crotwell Andrew M. , Dlugokencky Edward J. , Bakwin Peter , Artaxo Paulo , Tans Pieter P.
Published: May 2007

Recent results from laboratory, field and remote sensing measurements suggest the presence of large methane emissions from the Amazon basin. Here we present regionally integrative, direct trace gas observations from two sites that confirm the presence of large fluxes of methane in eastern Amazônia. Air samples collected on aircraft near Santarém (2.9°S, 55.0°W) and Manaus (2.6°S, 60.0°W) in eastern and central Amazônia show large enhancements of CH4 that are not seen at the NOAA/ESRL background sites in the tropical Atlantic Ocean. From the surface to about four km, enhancements averaging 34 ppb and up to 200 ppb occur throughout the year and we calculate emissions averaging 27 mg CH4/m2/day from upwind sources.
Plasma blobs and irregularities concurrently observed by ROCSAT‐1 and Equatorial Atmosphere Radar
Authors: Yokoyama Tatsuhiro , Su Shin‐Yi , Fukao Shoichiro
Published: May 2007

Plasma density enhancements, or plasma blobs, and radar backscatter plumes in the nighttime equatorial F region, both of which are intriguing phenomena associated with equatorial spread F (ESF), were concurrently observed for the first time on 8 March 2004 along a common magnetic flux tube. The observational results are strong evidence of a close relationship between plasma bubbles and blobs in the equatorial ionosphere. Plasma blobs were detected by Republic of China Scientific Satellite (ROCSAT)‐1 at a dip latitude of ∼9°N, while the 47‐MHz Equatorial Atmosphere Radar (EAR) in Sumatra, Indonesia, observed the backscatter plume associated with plasma density depletions, or plasma bubbles, at dip latitudes of as high as 13°S. The plumes grew upward with large Doppler velocity away from the radar late in the premidnight sector, in association with the appearance of the plasma blobs. The zonal structure and upward drift velocity of the blobs correspond to those of the plumes on the common magnetic flux tube. Localized eastward polarization electric fields probably play an important role in the generation of plasma blobs as well as the resurgence of the plumes.
Automated identification of lava flow structures using local Fourier spectrum of digital elevation data
Authors: Lescinsky David T. , Skoblenick Stephanie V. , Mansinha Lalu
Published: May 2007

The rheological parameters of a lava flow can be inferred by studying structural features on the solidified lava surface. We have developed a technique using the S‐transform (a localized Fourier transform) to analyze and interpret digital elevation data. We examined structural features of a silicic lava flow, the Medicine Lake dacite flow in California. The S‐transform accurately identified and located both repeating and single‐instance structures. Several classes of structures were identified in the data, including the following: localized short wavelength features (1.3–3.6 m in wavelength) identified as large blocks and repeating medium wavelength features (5–8, 10–16, 18–26, 30–36, and 56–67 m in wavelength) identified as multiple generations of crustal folding. Fold wavelengths determined by the S‐transform and a model of compressional folding associated with near surface viscosity gradients were used to evaluate the rheology of the Medicine Lake dacite flow. The similarity of the amount of strain during folding events and the wavelength ratio of successive generations of folding suggest that the flow rheology remained relatively constant during folding of the flow surface. Repeating long wavelength features (67–70‐ and 105–140‐m wavelengths) were identified as the spacing of crease structures. Crease structures were recognized by the absence of short wavelength features at the location of their smooth flanks and by a central spike corresponding to the central trough. The limitations and applicability of this approach lie in the accuracy and resolution of the digital elevation data used.
Intercomparison of SCIAMACHY nitrogen dioxide observations, in situ measurements and air quality modeling results over Western Europe
Authors: Blond N. , Boersma K. F. , Eskes H. J. , van der A R. J. , Van Roozendael M. , De Smedt I. , Bergametti G. , Vautard R.
Published: May 2007

The Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) satellite spectrometer provides detailed information on the nitrogen dioxide (NO2) content in the planetary boundary layer. NO2 tropospheric column retrievals of SCIAMACHY and its predecessor Global Ozone Monitoring Experiment are characterized by errors of the order of 40%. We present here a new SCIAMACHY tropospheric retrieval data set for the year 2003. The cloud free satellite observations are compared to surface measurements and simulations over western Europe performed with the regional air‐quality model CHIMERE. The model has a resolution of 50 km similar to the satellite observations. For these comparisons, averaging kernels are applied to the collocated model profiles to remove the dependency of the comparison on a priori NO2 profile information used in the retrieval. The consistency of both SCIAMACHY and CHIMERE outputs over sites where surface measurements are available allows us to be confident in evaluation of the model over large areas not covered by surface observations. CHIMERE underestimates surface NO2 concentrations for urban and suburban stations which we mainly attribute to the low representativeness of point observations. No such bias is found for rural locations. The yearly average SCIAMACHY and CHIMERE spatial NO2 distributions show a high degree of quantitative agreement over rural and urban sites: a bias of 5% (relative to the retrievals) and a correlation coefficient of 0.87 (n = 2003). On a seasonal basis, biases are smaller than 20% and correlation coefficients are larger than 0.75. Spatial correlations between both the model and satellite columns and the European Monitoring and Evaluation Program (EMEP) emission inventory are high in summer (r = 0.74, n = 1779) and low in winter (r = 0.48, n = 1078), related to seasonal changes in lifetime and transport. On the other hand, CHIMERE and SCIAMACHY columns are mutually consistent in summer (r = 0.82) and in winter (r = 0.79). This shows that CHIMERE simulates the transport and chemical processes with a reasonable accuracy. The NO2 columns show a high daily variability. The daily NO2 pollution plumes observed by SCIAMACHY are often well described by CHIMERE both in extent and in location. This result demonstrates the capabilities of a satellite instrument such as SCIAMACHY to monitor the NO2 concentrations over large areas on a daily basis. It provides evidence that present and future satellite missions, in combination with CTM and surface data, will contribute to improve quantitative air quality analyses at a continental scale.
Particle nucleation following the O3 and OH initiated oxidation of α‐pinene and β‐pinene between 278 and 320 K
Authors: Burkholder James B. , Baynard Tahllee , Ravishankara A. R. , Lovejoy Edward R.
Published: May 2007

Measurements of particle nucleation following the gas phase oxidation of α‐pinene and β‐pinene are reported. Particle nucleation following ozonolysis and O3 plus OH initiated monoterpene oxidation was measured in a 70‐L Teflon bag reactor over the temperature range 278 to 320 K. Particle concentration temporal profiles were measured for a range of initial monoterpene and ozone concentrations using ultrafine condensation particle counters. Profiles were interpreted using a coupled gas phase chemistry and kinetic multicomponent nucleation model to determine the molar yield of the nucleating species in the ozonolysis experiments to be 1 × 10−5 and 0.009, for α‐pinene and β‐pinene, respectively. OH initiated oxidation was found to increase the nucleator yield for α‐pinene, approximately a factor of three, but not for β‐pinene. The molar yield of condensable reaction products (vapor pressure < 20 ppt at 296 K) was determined to be 0.06 for both α‐pinene and β‐pinene and was independent of the oxidation source. Particle growth, which is determined by the condensable reaction products, was nearly temperature independent. Atmospheric box model calculations of nucleation and particle growth for α‐pinene and β‐pinene oxidation under typical tropospheric conditions are presented and showed that (1) nucleation can be significant under favorable conditions, (2) nucleation is dominated by OH initiated oxidation, and (3) the partitioning of the condensable monoterpene oxidation products made a significant contribution to the growth of atmospheric aerosol and was capable of explaining the observed particle growth rates commonly observed in remote forests.
An intercomparison of global oceanic precipitation climatologies
Authors: Quartly Graham D. , Kyte Elizabeth A. , Srokosz Meric A. , Tsimplis Michael N.
Published: May 2007

Large‐scale patterns of precipitation are important for the changes they may effect upon the circulation of the ocean. However, marine precipitation is very hard to quantify accurately. Four independent climatologies are examined to compare their estimates of the annual mean precipitation, and the seasonal and interannual variations. One data set, Global Precipitation Climatology Project (GPCP), is based upon satellite data, the other three on output of weather forecast reanalyses from the National Centers for Environmental Prediction (NCEP) and the European Centre for Medium‐Range Weather Forecasts (ECMWF). Although all data sets have their errors, there is general agreement on the geographical patterns of precipitation. All the models had higher rain rates in the tropics than shown by the satellite data, and also greater seasonal ranges. However, GPCP has 10–25% more precipitation than NCEP and ECMWF in most of the southern regions, because of their weak representation of convergence zones; NCEP2, a more recent version of the NCEP reanalysis, shows a marked improvement in this area. However, in most regions NCEP2 exhibits a larger seasonal range than shown by other data sets, particularly for the Tropical Pacific. Both NCEP and NCEP2 often show a seasonal cycle lagging 2 months or more behind GPCP. Of the three reanalysis climatologies, ECMWF appears best at realizing the position and migration of rain features. The interannual variations are correlated between all four data sets; however, the correlation coefficient is only large for regions that have a strong response to El Niño and La Niña events, or for comparisons of the two NCEP reanalyses. Of the data sets evaluated, GPCP has the most internal consistency, with no long‐term trend in its regional averages, and it alone shows the deficit in Mediterranean precipitation coincident with the Eastern Mediterranean Transient.
Tropopause height and zonal wind response to global warming in the IPCC scenario integrations
Authors: Lorenz David J. , DeWeaver Eric T.
Published: May 2007

The change in the extratropical circulation under global warming is studied using the climate models participating in the Intergovernmental Panel on Climate Change (IPCC) fourth assessment report. The IPCC models predict a strengthening and a poleward shift of the tropospheric zonal jets in response to global warming. The change in zonal jets is also accompanied by a strengthening and a poleward and upward shift of transient kinetic energy and momentum flux. Similar changes in circulation are simulated by a simple dry general circulation model (GCM) when the height of the tropopause is raised. The similarity between the simple GCM and the IPCC models suggests that the changes in midlatitude circulation are predominantly driven by a rise in the height of the tropopause, and that other factors such as increased moisture content and the change in the low‐level pole‐to‐equator temperature gradient, play a secondary role. In addition, the variability about the ensemble‐mean of the zonal wind response is significantly correlated with the variability of the tropopause height response over the polar cap, especially in the Southern Hemisphere.
Wind waves in shallow microtidal basins and the dynamic equilibrium of tidal flats
Authors: Fagherazzi S. , Palermo C. , Rulli M. C. , Carniello L. , Defina A.
Published: May 2007

Shallow microtidal basins are characterized by extensive areas of tidal flats that lie within specific ranges of elevation. These landforms are inherently flat and their evolution strongly depends on the balance between sedimentary and erosive processes. Here we present a stochastic point model for tidal flat evolution to study the influence of tidal currents and wind waves on tidal flat equilibrium. The model accounts for sediment deposition and sediment resuspension by wind waves and is applied to the Venice lagoon, Italy. Model results show that the equilibrium elevation of tidal flats depends on the relationship between shear stress caused by wind waves and depth. It is found that wind wave shear stresses peak for a specific water depth which is a function of the local wave climate and fetch distance. Above this critical depth, tidal flats are unstable, since an increase in elevation reduces wave height and therefore erosion, preventing the system from recovering equilibrium conditions. The critical depth for equilibrium depends on fetch distance but not on substrate characteristics and, for the Venice lagoon, varies from −1.5 m for unlimited fetch (>3000 m) to −0.6 m for a fetch of 1000 m. The sediment characteristics determine instead the sediment input necessary to maintain the tidal flat in equilibrium at a specific elevation. Sediment inputs for tidal flats composed of fine sand need to be much higher than those required for tidal flats composed of cohesive material. Finally, we show that the spring‐neap modulation of the tide is critical for tidal flat equilibrium, with erosive events occurring mostly during spring conditions that equilibrate the sediment deposition during neap tide.
Nonmarket valuation of water quality in a rural transition economy in Turkey applying an a posteriori bid design
Authors: Bederli Tümay Aylin , Brouwer Roy
Published: May 2007

In this paper, we investigate the economic benefits associated with public investments in wastewater treatment in one of the special protected areas along Turkey's touristic Mediterranean coast, the Köyceğiz‐Dalyan watershed. The benefits, measured in terms of boatable, fishable, swimmable and drinkable water quality, are estimated using a public survey format following the contingent valuation (CV) method. The study presented here is the first of its kind in Turkey. The study's main objective is to assess public perception, understanding, and valuation of improved wastewater treatment facilities in the two largest population centers in the watershed, facing the same water pollution problems as a result of lack of appropriate wastewater treatment. We test the validity and reliability of the application of the CV methodology to this specific environmental problem in a rural transition economy and evaluate the transferability of the results within the watershed. In order to facilitate willingness to pay (WTP) value elicitation we apply a novel dichotomous choice procedure where bid design takes place a posteriori instead of a priori. The statistical efficiency of different bid vectors is evaluated in terms of the estimated welfare measures' mean square errors using Monte Carlo simulation. The robustness of bid function specification is analyzed through average WTP and standard deviation estimated using parametric and nonparametric methods.
Coupling between geochemical reactions and multicomponent gas and solute transport in unsaturated media: A reactive transport modeling study
Authors: Molins S. , Mayer K. U.
Published: May 2007

The two‐way coupling that exists between biogeochemical reactions and vadose zone transport processes, in particular gas phase transport, determines the composition of soil gas. To explore these feedback processes quantitatively, multicomponent gas diffusion and advection are implemented into an existing reactive transport model that includes a full suite of geochemical reactions. Multicomponent gas diffusion is described on the basis of the dusty gas model, which accounts for all relevant gas diffusion mechanisms. The simulation of gas attenuation in partially saturated landfill soil covers, methane production, and oxidation in aquifers contaminated by organic compounds (e.g., an oil spill site) and pyrite oxidation in mine tailings demonstrate that both diffusive and advective gas transport can be affected by geochemical reactions. Methane oxidation in landfill covers reduces the existing upward pressure gradient, thereby decreasing the contribution of advective methane emissions to the atmosphere and enhancing the net flux of atmospheric oxygen into the soil column. At an oil spill site, methane oxidation causes a reversal in the direction of gas advection, which results in advective transport toward the zone of oxidation both from the ground surface and the deeper zone of methane production. Both diffusion and advection contribute to supply atmospheric oxygen into the subsurface, and methane emissions to the atmosphere are averted. During pyrite oxidation in mine tailings, pressure reduction in the reaction zone drives advective gas flow into the sediment column, enhancing the oxidation process. In carbonate‐rich mine tailings, calcite dissolution releases carbon dioxide, which partly offsets the pressure reduction caused by O2 consumption.
Cooperation on Congo volcanic and environmental risks
Authors: Tedesco D. , Badiali L. , Boschi E. , Papale P. , Tassi F. , Vaselli O. , Kasereka C. , Durieux J. , DeNatale G. , Amato A. , Cattaneo M. , Ciraba H. , Chirico G. D. , Delladio A. , Demartin M. , Favalli G. , Franceschi D. , Lauciani V. , Mavonga G. , Monachesi G. , Pagliuca N.M. , Sorrentino D. , Yalire M.
Published: May 2007

On 17 January 2002, the Nyiragongo volcano (1.52°S, 29.25°E, 3469 meters above sea level), located about 18 kilometers north of Lake Kivu in the Democratic Republic of Congo, erupted, releasing a volume of 14–34 million cubic meters of lava. Lava flows originated from north‐south oriented fractures that rapidly developed along the southern flank of the volcano. Two lava flows divided the nearby city of Goma (∼500,000 people) into two parts, forcing a rapid exodus of the population into Rwanda. One of these lava flows ran into Lake Kivu, encroaching 60 meters below lake level with a submerged lava volume of 1 million cubic meters. About 15% of the town was directly affected, leaving approximately 120,000 people homeless. At least 170 people died as a direct consequence of the eruption.
Global look at salt giants
Authors: Hübscher Christian , Cartwright Joe , Cypionka Heribert , DeLange Gert J. , Robertson Alastair , Suc Jean‐Pierre , Urai Janos L.
Published: May 2007

Water basins with narrow outlets can preserve vast thicknesses of evaporites, known as salt giants, which are thought to form when marginal basins or subbasins are cut off from the main oceanic basin and the water evaporates. Sea salt precipitates and is deposited on the basin floor. They are potential frontiers for challenging research on structural, tectonic, biogenic, and fluid dynamic evolution. These structures are of global importance because they strongly affect the structural, chemical, and biological evolution of sedimentary basins.
Thermospheric targets
Authors: Rishbeth Henry
Published: May 2007

Recent decades have seen great progress in computer modeling of the global thermosphere‐ionosphere system. The models are derived by solving simultaneously the conservation equations of mass, momentum, and energy that govern the concentrations, velocities, and temperatures of the ions, electrons, and neutral gases. Typically they cover heights from 80–100 to 500–700 kilometers, with resolutions of 100–1000 kilometers horizontally, 10 kilometers vertically, and tens of minutes in time; they do not deal with smallscale structure such as plasma instabilities. Some models extend down into the mesosphere (30–80 kilometers) or up to the protonosphere, the region where the dominant constituents are thermal protons and electrons. The input parameters include photochemical and transport rate coefficients and the fluxes of solar ionizing radiation and energetic particles, and the models can be run for general levels of solar and geomagnetic activity or for specific dates. Calibrated with real data, the models mimic well the behavior of the real thermosphere and ionosphere and have contributed much to understanding, besides helping the practical task of ‘near‐real‐time modeling,’ which is important for communications. They differ from purely descriptive ‘empirical’ models, which merely seek to describe the upper atmosphere and ionosphere, not to explain it.
Modeling the influence of Greenland ice sheet melting on the Atlantic meridional overturning circulation during the next millennia
Authors: Driesschaert E. , Fichefet T. , Goosse H. , Huybrechts P. , Janssens I. , Mouchet A. , Munhoven G. , Brovkin V. , Weber S. L.
Published: May 2007

A three‐dimensional Earth system model of intermediate complexity including a dynamic ice sheet component has been used to investigate the long‐term evolution of the Greenland ice sheet and its effects on the Atlantic meridional overturning circulation (AMOC) in response to a range of stabilized anthropogenic forcings. Our results suggest that the Greenland ice sheet volume should experience a significant decrease in the future. For a radiative forcing exceeding 7.5 W m−2, the modeled ice sheet melts away within 3000 years. A number of feedbacks operate during this deglaciation, implying a strong non‐linear relationship between the radiative forcing and the melting rate. Only in the most extreme scenarios considered, the freshwater flux from Greenland into the surrounding oceans (of ca. 0.1 Sv during a few centuries) induces a noticeable weakening of the AMOC in the model.
Formation regions of Subantarctic Mode Water detected by OFES and Argo profiling floats
Authors: Aoki Shigeru , Hariyama Mieko , Mitsudera Humio , Sasaki Hideharu , Sasai Yoshikazu
Published: May 2007

We investigated the distribution of the deep mixed layer in the Southern Ocean, where Subantarctic Mode Water (SAMW) forms, by using Argo profiling floats and the ocean general circulation model for the Earth simulator (OFES). The mixed‐layer depth (MLD) generally increased eastward from 50°–180°E and from 180°–80°W, with distinct local maxima near major bathymetric features. A sudden transition from deep to shallow mixed layer was found along the equatorward limit of the deep mixed layer. This diagnosed MLD front coincides with the line of ug · ∇σs = 0, indicating the distributions of the general deepening and local maxima of MLD were affected by near‐surface geostrophic flow. The flow is steered by the major bottom topographies, and the local MLD maxima occurred where the flow direction was deflected southward. This implies a link between the bathymetric features and formation of thick SAMW.
Contrasting patterns of seed and root colonization by bacteria from the genus Chryseobacterium and from the family Oxalobacteraceae
Authors: Green Stefan J , Michel Frederick C , Hadar Yitzhak , Minz Dror
Published: May 2007

Microbial colonization of plant seeds and roots is a highly complex process in which soil and plant type can influence the composition of the root-associated and rhizosphere microbial communities. Amendment of compost, a common agricultural technique, introduces exogenous nutrients and microorganisms to the soil–plant environment, and can further influence microbial community composition in the plant environment. Although compost amendments can strongly influence soil and rhizosphere microbial communities, there is evidence that with increasing proximity to the root, plant influences predominate over soil effects. We hypothesized that the ‘rhizosphere effect’ observed with proximity to plant surfaces does not act equally on all microorganisms. To explore this issue, we examined two bacterial taxa that reproducibly colonized seed and root surfaces in an experiment examining the influence of compost amendment on plant-associated bacterial communities. Population-specific analyses revealed striking differences in the ecology of bacteria from the genus Chryseobacterium and the family Oxalobacteraceae in potting mix and plant-associated environments. Seed- and root-colonizing Oxalobacteraceae populations were highly sensitive to plant effects, and phylogenetic analyses of root-colonizing Oxalobacteraceae revealed the presence of root-associated populations that were highly similar, regardless of treatment, and differed from the potting mix populations detected at the same sampling points. Conversely, Chryseobacterium community composition was found to be essentially invariant within treatments, but was strongly influenced by compost amendment. This persistence and stable nature of the Chryseobacterium community composition demonstrates that rhizosphere selection is not the exclusive factor involved in determining the composition of the cucumber spermosphere and rhizosphere communities.
On the geometry of nonholonomic mechanical systems with vertical distribution
Authors: Bejancu Aurel
Published: May 2007

Let (Q,g) be the configuration space of a nonholonomic mechanical system, where g is a Riemannian metric on Q. Suppose the horizontal distribution D on Q admits a vertical distribution D¯, that is D¯ is an integrable complementary (not necessarily orthogonal) distribution to D in TQ. We prove the existence and uniqueness of a linear connection on (Q,g) subject to some conditions on its torsion and on the covariant derivative of g. Then we show that the solutions of the Lagrange-d’Alembert equations are the geodesics of ∇ and vice versa. All the local components of the torsion and curvature tensor fields of ∇ with respect to an adapted frame field are determined. Finally, two examples are given to illustrate the theory we develop in the paper.
Relaxation theory of the electronic spin of a complexed paramagnetic metal ion in solution beyond the Redfield limit
Authors: Fries Pascal H. , Belorizky Elie
Published: May 2007

The relaxation of the electronic spin S of a paramagnetic metal ion with fully quenched orbital angular momentum in its ground state is investigated in an external magnetic field through a systematic study of the time correlation functions governing the evolution of the statistical operator (density matrix). Let ω0 be the Larmor angular frequency of S. When the relaxation is induced by a time-fluctuating perturbing Hamiltonian ℏH1(t) of time correlation τc, it is demonstrated that after a transient period the standard Redfield approximation is relevant to calculate the evolution of the populations of the spin states if ∥H1∥2τc2∕(1+ω02τc2)⪡1 and that this transient period becomes shorter than τc at sufficiently high field for a zero-field splitting perturbing Hamiltonian. This property, proven analytically and confirmed by numerical simulation, explains the surprising success of several simple expressions of the longitudinal electronic relaxation rate 1∕T1e derived from the Redfield approximation well beyond its expected validity range ∥H1∥τc⪡1. It has favorable practical consequences on the interpretation of the paramagnetic relaxation enhancement of nuclei used for structural and dynamic studies.
Magnetotransport properties in near-stoichiometric hydride films of YH2+δ under weak fields
Authors: Sakai M. , Nanbo T. , Nakamura O. , Tajima H. , Uwatoko Y.
Published: May 2007

We have investigated the basic characteristics of mobile carriers in as-deposited thin films of hexagonal-close-packed Y and hydrogenated films of face-centered-cubic YH2+δ. Hall resistance and transverse magnetoresistance measurements were carried out under magnetic fields of up to 1 T at room temperature. The Hall coefficient in YH2+δ showed a minimum value of ∼5×10−12 m3/C when the δ value reached ∼−0.1, in accordance with the δ dependence of resistivity reported previously. Quantitative analysis based on the present measurements revealed that YH2+δ is a compensated metal whose carrier density and mobility were determined to be ∼1.4×1027 (∼1.9×1027) m−3 and ∼3.5×10−3 (∼3.1×10−3) m2 V−1 s−1, respectively, for δ=0.04(−0.03) for both electrons and holes. These carrier parameters were found to account concurrently for the reflection spectral line shapes observed. The compensation observed in YH2+δ is at variance with a simple criterion used previously [E. Fawcett and W. A. Reed, Phys. Rev. 131, 2463 (1963)].
Reagents for electrophilic amination: A quantum Monte Carlo study
Authors: Amador-Bedolla Carlos , Salomón-Ferrer Romelia , Lester William A. , Vázquez-Martínez José Alfredo , Aspuru-Guzik Alán
Published: May 2007

Electrophilic amination is an appealing synthetic strategy to construct carbon-nitrogen bonds. The authors explore the use of the quantum Monte Carlo method and a proposed variant of the electron pair localization function—the electron pair localization function density—as a measure of the nucleophilicity of nitrogen lone pairs as a possible screening procedure for electrophilic reagents.
Purging of dropwise condensate by electrowetting
Authors: Kim J. , Kaviany M.
Published: May 2007

The onset of motion of a dropwise condensate (on inclined substrate) under applied direct current potential (with an overhanging electrode) is studied experimentally and described based on overcoming of the static three-phase contact line (TCL) friction by electrowetting. Electrowetting phenomenon exerts a radial electrostatic force on the TCL, causing an imbalance in the TCL surface tension forces, thus initiating the surface droplet motion (by an applied threshold, local electric field intensity). The experimental results using overhanging wire electrodes have identified three regimes (gravity dominated, intermediate, and surface force dominated) and show significant lowering of the critical inclination angle for the liquid droplet. In the intermediate Bond number regime (both gravity and surface liquid-gas tension are significant), the critical (for onset of motion) electrostatic potential is predicted and good agreement is found with experiments.