bluuebunny/crossref_metadata_2025 huggingface dataset:
The central cluster and X-ray emission from Sgr A*
Authors: Coker Robert F. , Pittard Julian M.
Published: May 2007

At the centre of the Milky Way is Sgr A*, a putative 3 million solar mass black hole with an observed luminosity that is orders of magnitude smaller than that expected from simple accretion theories. The number density of early-type stars is quite high near Sgr A*, so the ensemble of their stellar winds has a significant impact on the black hole's environment.

We present results of 3D hydrodynamic simulations of the accretion of stellar winds onto Sgr A*. Using the LANL/SAIC code, RAGE, we model the central arc-second of the Galaxy, including the central cluster stars (the S-stars) with orbits and wind parameters that match observations. A significant fraction of the winds from the S stars becomes gravitationally bound to the black hole and thus could provide enough hot gas to produce the X-ray emission seen by Chandra. We perform radiative transfer calculations on the 3D hydrodynamic data cubes and present the resulting synthetic X-ray spectrum.
Dynamical evolution of rotating globular clusters with embedded black holes
Authors: Fiestas José , Spurzem Rainer
Published: May 2007

Evolution of rotating globular clusters with embedded black holes is presented. The interplay between velocity diffusion due to relaxation and black hole star accretion is followed together with cluster rotation, using 2-dimensional, in energy and z-component of angular momentum, Fokker Planck numerical methods. Gravogyro and gravothermal instabilities drive the system to a faster evolution leading to shorter collapse times and a faster cluster dissolution in the tidal field of a parent galaxy.

Angular momentum transport and star accretion support the development of central rotation in relaxation time scales. Two-dimensional distribution (in the meridional plane) of kinematical and structural parameters (density, dispersions, rotation) are reproduced, with the aim to enable the use of set of models for comparison with observational data.
A near-infrared view of the 3CR: properties of hosts and nuclei†
Authors: Floyd David , Chiaberge Marco , Perlman Eric S. , Sparks Bill , Macchetto F. Duccio , Madrid Juan , Baum Stefi , O'Dea Chris , Axon David , Quillen Alice , Capetti Alessandro , Miley George , Tinarelli Stefano
Published: May 2007

The 3CR catalogue provides a statistical sampling of the most powerful radio galaxies out to z ∼ 0.3. Over the decade and a half of Hubble observations we have amassed a major multi-wavelength dataset on these sources, discovering amongst other things, new jets, hotspots, dust disks, and faint point-like nuclei. We present here the results of our latest snapshot survey, a near-complete sampling of the 3CR host galaxies at z < 0.3 in the near-IR (H-band). This un-extinguished view of the host galaxies has provided us with an accurate measure of the stellar/spheroid masses of the sources, and an unbiased view of their morphologies. We show that they exhibit an identical Kormendy relation to nearby QSO's and the massive Elliptical population, but are distinct from the Brightest Cluster Members, and mergers. We find that while a few sources exhibit signs of a recent or impending major merger, many more sources have remnants consistent with a gas-rich minor merger in their recent history. We detect unresolved nuclear sources in most (∼80%) of FRI, with their IR luminosities correlating linearly with radio core power. This implies that the IR nuclei are synchrotron radiation produced at the base of the relativistic jet, and confirms that no infrared (thermal) radiation in excess to synchrotron is present in FRIs, unlike in other classes of AGN.
The K-correction for LMXBs: an application to X1822-371 and GX339-4
Authors: Muñoz-Darias T. , Casares J. , Martínez-Pais I. G.
Published: May 2007

We model the K-correction for emission lines formed on the irradiated face of companion stars in compact binaries. We compute this K-correction in a general approach as function of the mass ratio and the disc flaring angle. Our results, combined with the detection of high excitation emission lines arising from the donor star, can be used to set constraints to the masses of neutron stars and black holes in persistent Low Mass X-ray Binaries (LMXBs).

The application of our model to X1822-371 (Muñoz-Darias, Casares & Martínez-Pais 2005) lends strong support to the presence of a massive neutron star in this LMXB (i.e. MNS > 1.6M⊙). Here, we also present the K-correction for the Black Hole binary GX339-4, where we obtain a solid lower limit to the black hole mass of MBH > 5.8M⊙.
Proper motions of thin filaments at the Galactic Center
Authors: Mužić K. , Eckart A. , Schödel R. , Meyer L. , Zensus A.
Published: May 2007

We present the proper motion study of the thin filaments observed in L'-band (3.8 μm) adaptive optics images of the central parsec of the Milky Way. Observed filaments are associated with the mini-spiral and, in some cases, with stars. They can be interpreted as shock fronts formed by the interaction of a central wind with the mini-spiral or extended dusty stellar envelopes.
Long-term and intra-day variability of BL Lacertae since the last great outburst
Authors: Nikolashvili Maria G. , Kurtanidze Omar M.
Published: May 2007

We present the results of optical photometry of BL Lacertae carried out using ST-6 CCD camera attached to the Newtonian focus of the 70 cm meniscus telescope of Abastumani Observatory. On the basis of observations conducted since August 1997 during more than 550 nights about 17000 frames were collected. They have been reduced using Daophot II.

It has been shown that optical variability of BL Lacertae is very complex. The maximum variation was observed at long-term scale and is equal to equals to 3.0 mag (rms=0.03) in B band, while the variation in V and R bands are within 2.71 mag (0.02) and 2.53 mag (0.01), respectively. This means that variations are larger at shorter wavelength or the object become bluer in the active phase. It were also demonstrated that BL Lacertae shows intra-day variability within 0.30 mag (0.02), while intra-hour variability within 0.10 mag (0.01) magnitudes.
IR contamination in quiescence X-Ray Novae
Authors: Reynolds Mark T. , Callanan Paul J. , Kelleher Colm
Published: May 2007

We present archival optical-IR observations of a number of short period X-ray novae (XRNe). We use these to show that in contrast to the current paradigm, there is likely significant non stellar flux in the infra-red (IR).
First e-VLBI observations of GRS 1915+105
Authors: Rushton A. , Spencer R. E. , Strong M. , Campbell R. M. , Casey S. , Fender R. P. , Garrett M. A. , Miller-Jones J. C. A. , Pooley G. G. , Reynolds C. , Szomoru A. , Tudose V. , Paragi Z.
Published: May 2007

We present results from the first successful open call e-VLBI science run, observing the X-ray binary GRS 1915+105. e-VLBI science allows the rapid production of VLBI radio maps, within hours of an observation rather than weeks. A total of 6 telescopes observing at 5 GHz across the European VLBI Network (EVN) were correlated in real time at the Joint Institute for VLBI in Europe (JIVE). Throughout this, GRS 1915+105 was observed for a total of 5.5 hours, producing 2.8 GB of visibilities of correlated data. The peak brightness was 10.2 mJy per beam, with a total integrated radio flux of 11.1 mJy.
Marginally stable thick discs orbiting the Kerr–de Sitter black holes: the mass estimates
Authors: Slaný Petr , Stuchlík Zdeněk
Published: May 2007

Basic properties of equipotential surfaces in test perfect fluid tori with uniform distribution of the specific angular momentum orbiting KdS black holes are summarized. The central mass-densities of adiabatic non-relativistic tori, for which the approximation of test fluid is adequate, are given and compared with the typical densities of Giant Molecular Clouds.
A ULX and a giant cloud collision in M 99
Authors: Soria Roberto , Wong Diane Sonya
Published: May 2007

The Sc galaxy M 99 in the Virgo Cluster has been strongly affected by recent tidal interactions, responsible for an asymmetric spiral pattern and a high star formation rate (∼ 10 M⊙ yr−1). We studied the galaxy with XMM-Newton, Keck and the Very Large Array (VLA). The inner disk is dominated by hot plasma with a total X-ray luminosity ≈ 1041 erg s−1. At the outskirts of the galaxy, away from the main star-forming regions, there is an ultraluminous X-ray source (ULX) with an X-ray luminosity ≈ 2 × 1040 erg s−1 and a hard spectrum (power-law photon index Γ ≈ 1.7). This source is close to the location where a massive H I cloud appears to be falling onto the M 99 disk at a relative speed > 100 km s−1. The infalling gas may have been stripped from the nearby “dark galaxy” candidate VIRGOHI 21. We speculate there may be a relation between collisional events, infall of metal-poor gas clouds, and ULX formation.
Near-IR integral field spectroscopy of the NLR of ESO428-G14: the role of the radio jet
Authors: Storchi-Bergmann Thaisa , Riffel Rogemar A. , Barbosa Fausto K. B. , Winge Cláudia
Published: May 2007

We present two-dimensional (2D) gas kinematics and excitation of the inner 300 pc of the Seyfert galaxy ESO428-G14 at a sampling of 14 pc2, from near-infrared spectroscopic observations at R=5900 obtained with the Integral Field Unit of the Gemini Near-Infrared Spectrograph. Blue-shifts of up to 400 km s−1 and velocity dispersions of up to 150 km s−1, are observed in association with the radio jet running from SE to NW along position angle 129°. Both X-rays emitted by the active galactic nucleus and shocks produced by the radio jet can excite the H2 and [Fe ii] emission lines. We use the 2D velocity dispersion maps we estimate upper limits of 90% to the contribution of the radio jet to the excitation of [Fe ii]λ1.257μm, and of 80% to the excitation of H2λ2.121μm in the jet region.
An ITCZ‐like convergence zone over the Indian Ocean in boreal late autumn
Authors: Sato N. , Yoneyama K. , Katsumata M. , Shirooka R. , Takayabu Y. N.
Published: May 2007

We examined the convective activity over the tropical Indian Ocean in boreal autumn using satellite‐observation data. In November and December, we detected an intertropical convergence zone‐like (ITCZ‐like) precipitation zone between Maldives and Somalia that is unobserved in the other periods of the year. It accompanied a high sea‐surface temperature (SST) north of the equator, and a cold tongue near the equator, similar to the ITCZs over the Pacific and Atlantic Oceans. However, the formation mechanism of the SST anomalies over the Indian Ocean is not the same as that in the Pacific and Atlantic Oceans. The high‐SST region forms in early November corresponding to weak sea‐surface wind during the monsoon transition. The low SST along the equator appears, associated with the upwelling of the subsurface water.
Assessment of the magnetospheric contribution to the suprathermal ions in Saturn's foreshock region
Authors: Thomsen M. F. , DiLorenzo J. P. , McComas D. J. , Young D. T. , Crary F. J. , Delapp D. , Reisenfeld D.B. , Andre N.
Published: May 2007

Nineteen months of Cassini Plasma Spectrometer measurements are surveyed for episodes of suprathermal ions upstream from Saturn's bow shock. A total of 45 hours of mass‐resolved observations are obtained. Suprathermal ions (between 3 and 50 keV/q) in Saturn's foreshock are found to be dominantly comprised of H+ and ions with m/q = 2, presumably solar wind He++, with no detectable contribution from magnetospheric water group ions. In light of the dominant contribution of water group ions to the hot plasma of the outer magnetosphere, it thus appears that magnetospheric leakage is not a significant source of upstream ions in this energy range. One implication is that the more energetic O+ ions reported recently most likely originate from direct leakage of already‐energized magnetospheric particles, rather than from their upstream acceleration by bow shock‐related processes.
Phase separation and convection in heterogeneous porous media: Implications for seafloor hydrothermal systems
Authors: Emmanuel Simon , Berkowitz Brian
Published: May 2007

We examine experimentally the effect of phase separation of a binary fluid on convection and heat transfer in porous domains with heterogeneous permeability fields. In mid‐ocean ridge hydrothermal systems, a dense brine phase and a coexisting vapor phase form during the phase separation of seawater at supercritical conditions; this process strongly influences the chemistry of vents and the convective transfer of heat. Furthermore, convection and phase separation are likely to occur in oceanic crust that is highly heterogeneous in nature. Because of high temperatures and pressures required for phase separation in saline systems, a binary fluid [H2O‐2‐butoxyethanol], with a lower consolute point of 48.5°C, was used as a proxy for seawater. A saturated pseudo‐two‐dimensional porous domain containing high permeability [k] zones embedded in a lower permeability matrix was heated from below and cooled from above. As with homogeneous systems, chemical stratification develops in heterogeneous domains, with dense fluid accumulating in low‐velocity regions at the bottom of the porous matrix. Furthermore, in both types of porous media, the efficiency of thermal transport is reduced relative to single‐phase systems. Heterogeneities in the permeability field, however, can act to amplify these effects; in systems with vertical high‐k zones, the thickness of the dense‐phase layer increases in the low‐k regions, and thermal transport is suppressed even more. Also, the experiments show that regions of both high and low permeabilities can act as a store for brines and facilitate the formation of much thicker brine layers than are otherwise predicted by models based on homogeneous oceanic crust.
Precision requirements for space‐based data
Authors: Miller C. E. , Crisp D. , DeCola P. L. , Olsen S. C. , Randerson J. T. , Michalak A. M. , Alkhaled A. , Rayner P. , Jacob D. J. , Suntharalingam P. , Jones D. B. A. , Denning A. S. , Nicholls M. E. , Doney S. C. , Pawson S. , Boesch H. , Connor B. J. , Fung I. Y. , O'Brien D. , Salawitch R. J. , Sander S. P. , Sen B. , Tans P. , Toon G. C. , Wennberg P. O. , Wofsy S. C. , Yung Y. L. , Law R. M.
Published: May 2007

Precision requirements are determined for space‐based column‐averaged CO2 dry air mole fraction data. These requirements result from an assessment of spatial and temporal gradients in the relationship between precision and surface CO2 flux uncertainties inferred from inversions of the data, and the effects of biases on the fidelity of CO2 flux inversions. Observational system simulation experiments and synthesis inversion modeling demonstrate that the Orbiting Carbon Observatory mission design and sampling strategy provide the means to achieve these data precision requirements.
Characterizing arid region alluvial fan surface roughness with airborne laser swath mapping digital topographic data
Authors: Frankel Kurt L. , Dolan James F.
Published: May 2007

Range‐front alluvial fan deposition in arid environments is episodic and results in multiple fan surfaces and ages. These distinct landforms are often defined by descriptions of their surface morphology, desert varnish accumulation, clast rubification, desert pavement formation, soil development, and stratigraphy. Although quantifying surface roughness differences between alluvial fan units has proven to be difficult in the past, high‐resolution airborne laser swath mapping (ALSM) digital topographic data are now providing researchers with an opportunity to study topography in unprecedented detail. Here we use ALSM data to calculate surface roughness on two alluvial fans in northern Death Valley, California. We define surface roughness as the standard deviation of slope in a 5‐m by 5‐m moving window. Comparison of surface roughness values between mapped fan surfaces shows that each unit is statistically unique at the 99% confidence level. Furthermore, there is an obvious smoothing trend from the presently active channel to a deposit with cosmogenic 10Be and 36Cl surface exposure ages of ∼70 ka. Beyond 70 ka, alluvial landforms become progressively rougher with age. These data suggest that alluvial fans in arid regions smooth out with time until a threshold is crossed where roughness increases at greater wavelength with age as a result of surface runoff and headward tributary incision into the oldest surfaces.
Attenuation of cosmic ray flux in temperate forest
Authors: Plug L. J. , Gosse J. C. , McIntosh J. J. , Bigley R.
Published: May 2007

Forests alter secondary cosmic radiation (CR) to the ground by (1) diminishing it owing to absorption by trees, (2) inducing spatial and temporal variability because biomass distribution is heterogeneous, and (3) lengthening the apparent mean attenuation length at ground level because nucleons are shielded over muons. We model CR flux through three‐dimensional simulated forests with properties drawn from old‐growth plots in Nova Scotia, Canada (Acadian forest) and the Olympic Peninsula, Washington state (coastal rain forest). For exposure durations of ≥105, conservative mean shielding in rain forest is 7.3 ± 2.3%, canopy and floor biomass included. Acadian/boreal forest has mean shielding 2.3 ± 0.6%. These long‐timescale mean values are similar to previous estimates from treating forest biomass as a layer of constant thickness. Ground flux varies significantly between sites within a forest, ranging from 1 to 100% of nonforested flux for short timescales if some trees are large (diameters ≥1.5 m) because the position of the sample site relative to individual large trees is important. Temperate rain forests have large trees and disturbance/regeneration intervals approaching 103 y; hence, CR flux and resultant terrestrial cosmogenic nuclide (TCN) concentrations vary by 1.5% after 8000 y but only 0.2% after 80,000 y. These results are for a forest that is statistically uniform through time; changes in biomass heterogeneity through time and/or space, owing to climate, wind‐throw, or localized recruitment, would increase the inherent variability of TCN production. TCN dating experiments on timescales much shorter than 80 secondary successions of the forest will have significant uncertainty in effective production rates but catchment‐wide average erosion experiments will not.
Long‐term sea surface temperature and climate change in the Australian–New Zealand region
Authors: Barrows Timothy T. , Juggins Steve , De Deckker Patrick , Calvo Eva , Pelejero Carles
Published: May 2007

We compile and compare data for the last 150,000 years from four deep‐sea cores in the midlatitude zone of the Southern Hemisphere. We recalculate sea surface temperature estimates derived from foraminifera and compare these with estimates derived from alkenones and magnesium/calcium ratios in foraminiferal carbonate and with accompanying sedimentological and pollen records on a common absolute timescale. Using a stack of the highest‐resolution records, we find that first‐order climate change occurs in concert with changes in insolation in the Northern Hemisphere. Glacier extent and inferred vegetation changes in Australia and New Zealand vary in tandem with sea surface temperatures, signifying close links between oceanic and terrestrial temperature. In the Southern Ocean, rapid temperature change of the order of 6°C occurs within a few centuries and appears to have played an important role in midlatitude climate change. Sea surface temperature changes over longer periods closely match proxy temperature records from Antarctic ice cores. Warm events correlate with Antarctic events A1–A4 and appear to occur just before Dansgaard‐Oeschger events 8, 12, 14, and 17 in Greenland.
Model and laboratory study of dispersion in flows with submerged vegetation
Authors: Murphy E. , Ghisalberti M. , Nepf H.
Published: May 2007

Vegetation is ubiquitous in rivers, estuaries, and wetlands, strongly influencing water conveyance and mass transport. The plant canopy affects mean and turbulent flow structure, and thus both advection and dispersion. Accurate prediction for the transport of nutrients, microbes, dissolved oxygen and other scalars depends on our ability to quantify the impact of vegetation. In this paper, we focus on longitudinal dispersion, which traditionally has been modeled in vegetated channels by drawing analogy to rough boundary layers. This approach is inappropriate in many cases, as the vegetation provides a significant dead zone, which may trap scalars and augment dispersion. The dead zone process is not captured in the rough boundary model. This paper describes a new model for longitudinal dispersion in channels with submerged vegetation, and it validates the model with experimental observations.
New images of turbulent Venusian atmosphere
Authors: Zielinski Sarah
Published: May 2007

The European Space Agency's Venus Express has sent back new images of atmospheric turbulence and cloud features that may help explain what causes the planet's violent winds. Using infrared wavelengths, the spacecraft's Ultraviolet, Visible, and Near‐Infrared Mapping Spectrometer can see through the thick layer of clouds covering the planet's atmosphere and take images at various depths. The new images show that clouds are irregular and bubble‐shaped at the equator, become more regular and streaky at mid‐latitudes, and enter a vortex shape at the poles. In addition, images over clouds over a region called Alpha Regio—characterized by troughs and ridges that can b e up to 4 kilometers high—indicate that surface topography may influence local atmospheric turbulence. The images are available at http://www.esa.int/esaCP/SEM9N77DWZE_index_0.html
Computer failure caused loss of Mars spacecraft
Authors: Zielinski Sarah
Published: May 2007

A computer error that occurred 5 months before NASA lost contact with the Mars Global Surveyor on 2 November 2006 led to the spacecraft's eventual battery failure and subsequent loss of orientation. This is according to a 13 April preliminary report from an internal NASA review board. The report,“Mars Global Surveyor Spacecraft Loss of Contact,” is available at http://www.nasa.gov/mission_pages/mgs/
Scientific ocean drilling behind the assessment of geo‐hazards from submarine slides, Barcelona, Spain, 25–27 October 2006
Authors: Urgeles Roger , Camerlenghi Angelo , Ercilla Gemma , Anselmetti Flavio , Brückmann Warner , Canals Miquel , Gràcia Eulàlia , Locat Jacques , Krastel Sebastian , Solheim Anders
Published: May 2007

Submarine slope instability represents a geo‐hazard for its destructive potential on nearshore structures and life and offshore seabed structures. Submarine slides may bear a tsunamigenic potential and are capable of methane gas release into the seawater and atmosphere. A recent workshop sponsored by the European Science Foundation (ESF; http://www.esf.org), “Scientific Ocean Drilling Behind the Assessment of Geo‐hazards From Submarine Slides,” held in Barcelona, Spain, 25–27 October 2006, reviewed the current state of knowledge on submarine slope failures and how scientific drilling can improve our knowledge of the process and help to mitigate the derived risks (a report with full details of participants and program can be found at http://www.geohazards.no/IGCP511/). The workshop gathered 50 scientists and representatives of private companies, mainly from the European area, representing a wide spectrum of disciplines such as geophysics, stratigraphy sedimentology paleoceanography marine geotechnology, geotechnical engineering, and tsunami modeling.

During the workshop, it was agreed that scientific drilling offers the possibility of answering a number of scientific questions, among them, (1) What is the frequency of submarine slides? (2) What was the tsunamigenic potential of past submarine slides, and what is the tsunamigenic potential of unfailed submarine slopes? (3) Do precursory phenomena of slope failure exist? (4) Can we monitor sea‐floor gravitational movements such as creep? (5) What makes up weak layers in midlatitude continental margins? And (6) when and under what circumstances do weak layers form? Scientific drilling also offers the possibility of testing at least two existing hypotheses on basic mechanisms of submarine slide generation and of massive releases of gas: (1) focusing of fluids and lateral transfer of stresses under variable overburden on permeable layers and (2) proving the link between methane emissions during rapid climatic changes and submarine slides.
New author choice for open access
Authors: Anonymous
Published: May 2007

AGU journals now offer authors the opportunity to make their articles open for others to read for free. Authors choosing this option pay a fee based on article length and number of figures; these charges are designed to offset the potential loss of subscription income. This new option, called Author Choice, provides · Unlimited access to the article for all readers from the moment of publication. · Permission to deposit the PDF version in institutional repositories so long as the repository accepts AGU copyright permissions. · Continued copyright protection to prevent unauthorized uses of the author's work.
New borehole strain system detects uplift at Campi Flegrei
Authors: Scarpa Roberto , Amoruso Antonella , Crescentini Luca , Romano Pierdomenico , De Cesare Walter , Martini Marcello , Scarpato Giovanni , Linde Alan T. , Sacks Selwyn I.
Published: May 2007

Campi Flegrei and Mount Vesuvius are active Italian volcanoes though presently in aquiescent stage. The last eruption of Mount Vesuvius occurred during the spring of 1944. Campi Flegrei last erupted in 1538 but experienced a subsidence trend from the early 1900s to 1970, which was followed by episodes of ground uplift accompanied by seismic swarms [see, e.g., Aster et al., 1992].

Over the past 37 years at Campi Flegrei, about 4 meters of maximum ground uplift has occurred followed by about 1 meter of subsidence, as measured near the center of the caldera in two episodes during 1970–1972 and 1982–1984. This deformation has occurred close to the harbor of the town of Pozzuoli, putting about 400,000 people at heightened risk. From 1985 to 2004, Campi Flegrei's caldera showed gradual subsidencethat was interrupted by five mini‐uplift episodesin 1976, 1989, 1995, 2000, and, most recently, 2004–2006, each amounting to a few centimeters of uplift [Pingue et al., 2006]. The caldera is generally aseismic during gradual subsidence, but small swarms of microearthquakes are produced during periods of elevated strain rates associated with the mini‐uplift episodes [Saccorotti et al., 2001 ].
New research site to launch in June
Authors: Zielinski Sarah
Published: May 2007

Thirteen science and technology societies will launch a new Web site (http://www.scitopia. org) in June that will enable users to search more than three million journal articles, conference proceedings, and patents at once.

“Scitopia.org's aim is to provide powerful, focused aggregation and an additional access point to the highest quality scientific research available on the Web today... [The site] will offer the most direct route to the very latest research, within hours of it appearing on the Web,” said Terry Hulbert, head of Electronic Development and Strategy at the Institute of Physics Publishing (IOP), one of the participating organizations.
Latitudinal variation of aerosol optical depths from northern Arabian Sea to Antarctica
Authors: Vinoj V. , Anjan Anjit , Sudhakar M. , Satheesh S. K. , Srinivasan J. , Moorthy K. Krishna
Published: May 2007

Measurements of the spectral aerosol optical depths (AODs) were made over the Arabian Sea, Indian Ocean, Southern Ocean, and Antarctica during a trans‐continental cruise experiment conducted during January to April 2006. Our investigations show that AODs (at 500 nm) remain low (≤0.1) and steady in the Southern Indian Ocean (20°S to 40°S). In contrast, large latitudinal gradients exist north of 20°S. The AODs increase nearly exponentially from ∼0.1 near Antarctica to reach a value as high as 0.7 in the northern Arabian Sea (∼15°N). The latitudinal gradients were larger in summer than in winter. The comparison of measured daily optical depths with those retrieved from MODIS satellite sensor showed good agreement (within ∼0.02) for regions north of 40°S. The AODs were higher over remote oceans between 40°S to 60°S (MODIS observations) latitudes as a result of enhanced sea‐salt production due to high winds associated with the ‘Roaring Forties.’
First principles investigation of the postspinel transition in Mg2SiO4
Authors: Yu Yonggang G. , Wentzcovitch Renata M. , Tsuchiya Taku , Umemoto Koichiro , Weidner Donald J.
Published: May 2007

We have investigated the dissociation of iron free ringwoodite, Mg2SiO4γ‐spinel, into MgO periclase and MgSiO3 perovskite using quasi‐harmonic free energy computations within the local density approximation (LDA) and generalized gradient approximation (GGA). The transition pressure, Ptr, obtained from GGA is higher and in much better agreement with experimental measurements than its LDA counterpart. This can be rationalized by close inspection of GGA and LDA functional forms. The Clapeyron slope obtained from this calculation is −2.9 − −2.6 MPa/K. Surprisingly, we find a small decrease in bulk sound velocity across this transition. Our results are consistent with 64 ± 12% ringwoodite volume fraction at the bottom of the transition zone.
Regional body‐wave attenuation using a coda source normalization method: Application to MEDNET records of earthquakes in Italy
Authors: Walter William R. , Mayeda Kevin , Malagnini Luca , Scognamiglio Laura
Published: May 2007

We develop a new methodology to determine apparent attenuation for the regional seismic phases Pn, Pg, Sn, and Lg using coda‐derived source spectra. The apparent Q, combining path and site attenuation, is determined from the difference between the geometrical spreading‐corrected amplitude and the independently determined source spectra derived from the coda methodology. We apply the technique to 50 earthquakes with magnitudes greater than 4 in central Italy as recorded by MEDNET broadband stations around the Mediterranean at local‐to‐regional distances. A power law attenuation of the form Q(f) = Qofγ fit all the phases quite well over the 0.5 to 8 Hz band. The measured apparent Q values are quite repeatable from event to event. Finding the attenuation function in this manner guarantees a close match between inferred source spectra from direct waves and coda techniques. This is important if coda and direct wave amplitudes are to produce consistent seismic results.
Influence of the lower hybrid drift instability on the onset of magnetic reconnection
Authors: Ricci Paolo , Brackbill J. U. , Daughton W. , Lapenta Giovanni
Published: May 2007

Two-dimensional and three-dimensional kinetic simulation results reveal the importance of the lower-hybrid drift instability (LHDI) to the onset of magnetic reconnection. Both explicit and implicit kinetic simulations show that the LHDI heats electrons anisotropically and increases the peak current density. Linear theory predicts these modifications can increase the growth rate of the tearing instability by almost two orders of magnitude and shift the fastest growing modes to significantly shorter wavelengths. These predictions are confirmed by nonlinear kinetic simulations in which the growth and coalescence of small scale magnetic islands leads to a rapid onset of large scale reconnection.
Criteria for second stability for ballooning modes in stellarators
Authors: Hudson S. R. , Hegna C. C.
Published: May 2007

An expression determining how variations in the pressure gradient and average magnetic shear affect ballooning stability for a stellarator equilibrium is presented. The procedure for determining the marginal stability boundaries, for each field line, depends only on the equilibrium and a single ballooning eigenfunction calculation. This information is sufficient to determine if increasing pressure gradient is stabilizing or destabilizing and to predict whether the configuration possesses a second stable region.
Nonlinear Lagrangian theory of envelope electrostatic plasma waves in a two-electron-temperature plasma
Authors: Kourakis I. , Shukla P. K.
Published: May 2007

An analytical model based on Lagrangian variables is presented for the description of ion-acoustic waves propagating in an unmagnetized, collisionless, three-component plasma composed of inertial positive ions and two thermalized electron populations, characterized by different temperatures. The wave’s amplitude is shown to be modulationally unstable. Different types of localized envelope electrostatic excitations are shown to exist, and their forms are analytically and numerically investigated in terms of the plasma dispersion and nonlinearity laws. These results are in qualitative agreement with satellite observations in the magnetosphere.
Derivatives of the polarization propagator including orbital relaxation effects
Authors: Tisko Edmund L. , Hunt Katharine L. C.
Published: May 2007

In this article, we relate derivatives of the polarization propagator used in many-body theory to the nonlinear (quadratic) polarization propagator, and we relate derivatives of the quadratic polarization propagator to the nonlinear propagator of the next higher order, the cubic polarization propagator. We restrict the analysis to differentiation with respect to parameters η for which the derivative of the Hamiltonian can be written as a sum of one-electron operators. Geometrical derivatives are obtained by specializing to the parameter η to the α coordinate of nucleus I. We treat orbital relaxation explicitly by allowing for the η dependence of creation and annihilation operators in the propagators. This treatment entails an extension of the geometrical derivative relations among response functions proven by Olsen and Jørgensen [J. Chem. Phys. 82, 3235 (1985)], because the propagator derivatives may involve changes in the one-electron orbitals that do not appear in the susceptibility derivatives. These results underlie the relations between Raman intensities and electric-field shielding tensors, which have been explained in terms of nonlocal polarizability and hyperpolarizability densities. The results suggest an alternative computational route to geometrical or other derivatives of both linear- and nonlinear-response functions: these derivatives can be evaluated without numerical differentiation, directly from the propagator of the next higher order.
Influence of the insertion of a nano-oxide layer on the interfacial magnetism of FeMn∕NiFe∕Cu∕NiFe spin valves
Authors: Tafur Miguel , Alayo W. , Munayco P. , Baggio-Saitovitch E. , Nascimento V. P. , Alvarenga A. D. , Brewer W. D.
Published: May 2007

We have studied the influence of an inserted nano-oxide layer (NOL) on the interfacial magnetism in spin-valve systems showing the giant magnetoresistance effect. Specifically, we performed a magnetic depth profile of these structures with and without a NOL, using the x-ray magnetic circular dichroism technique. We found that insertion of a NOL into the spin-valve structure is correlated with a stronger reduction of the magnetic moments at the ferromagnetic (FM)∕NOL∕FM interface in comparison with a spin valve without NOL.
Electromagnetic fields induced by a cuboidal inclusion with uniform spontaneous polarization and magnetization
Authors: Wang X. , Pan E.
Published: May 2007

Exact closed-form solutions are derived for the electromagnetic fields induced by a cuboidal inclusion with uniform spontaneous polarization and magnetization embedded in an infinite uniaxial multiferroic solid. The method of Green’s function and direct integration are employed to obtain the solution, with the results for the induced electric and magnetic potentials as well as the electric and magnetic fields being in terms of elementary functions. It is observed that all the electric and magnetic field components exhibit logarithmic singularities near the eight corners of the cuboid. There also exist logarithmic singularities for the electric and magnetic fields near certain edges of the cuboid. Numerical results are presented for a typical multiferroic composite to demonstrate the variation of electromagnetic fields in and near the cuboidal inclusion.
Transition from tungsten erosion to carbon layer deposition with simultaneous bombardment of tungsten by helium and carbon
Authors: Bizyukov Ivan , Krieger Karl
Published: May 2007

Simultaneous bombardment of tungsten layers with helium and carbon ions leads to both erosion of tungsten and implantation of carbon. The underlying processes have been investigated numerically and experimentally as a function of the carbon fraction in the incident ion flux for ion energies in the kilo electron volt range. Tungsten layers were deposited on polished single-crystal silicon substrate by magnetron sputter deposition to eliminate the influence of surface roughness on the experimental results. The fluence-dependent dynamics of the surface composition was measured in situ by ion beam analysis. The given projectile-target system is subject only to kinematic processes, and is therefore particularly suitable for benchmarking of purely kinematic simulations based on the binary-collision approximation, as implemented in the TRIDYN code. TRIDYN calculations match the experimental results very well, which demonstrates the validity of the kinematic description. In particular, the simulations allow us to predict the change of surface composition by bombardment with gaseous and nonvolatile ions, as well as the transition point from W erosion to C deposition as function of the carbon fraction in the incident ion flux.
Analysis of strain relaxation by microcracks in epitaxial GaAs grown on Ge∕Si substrates
Authors: Colombo D. , Grilli E. , Guzzi M. , Sanguinetti S. , Marchionna S. , Bonfanti M. , Fedorov A. , von Känel H. , Isella G. , Müller E.
Published: May 2007

A detailed spectroscopic and morphological study of GaAs epitaxial layers grown by molecular beam epitaxy on Ge buffer layers deposited by low energy plasma enhanced chemical vapor deposition on Si is presented. The aim is to understand the nature of thermal strain relaxation induced by crack formation in the epilayers. The comparison of the experimental data on the spatial strain relaxation pattern with the theoretical prediction from a purely elastic model indicates that strain relaxation around cracks arises from two contributions. At short distances the main contribution is essentially plastic, due to the presence of extended defects. At large distances, on the contrary, elastic relaxation seems to dominate. It is also shown that GaAs grown on Ge∕Si substrates is in a state of metastable strain as a consequence of the fact that cracks relax the thermal tensile strain only locally.
Electronic structure of 3C inclusions in 4H SiC
Authors: Miao M. S. , Lambrecht Walter R. L.
Published: May 2007

The band gap, the polarization, and the quantum well states for 3C inclusions in 4H SiC are studied in a systematic way with inclusions of 2–10 cubic layers in a supercell of 12 layers of 4H SiC. The polarization is strongly reduced by screening and correspondingly the effective band gap of the 3C quantum well in a 4H system is never smaller than that of pure 3C. To explain the observation of below 3C gap luminescence in such systems, an increase in exciton binding energy must be invoked.
Low temperature noise spectroscopy of 0.1 μm partially depleted silicon on insulator metal-oxide-semiconductor field effect transistors
Authors: Lartigau I. , Routoure J. M. , Guo W. , Cretu B. , Carin R. , Mercha A. , Claeys C. , Simoen E.
Published: May 2007

The variations of the low frequency noise versus temperature have been used to characterize the traps at the Si/SiO2 interface and in the depletion layer of partially depleted silicon on insulator metal-oxide-semiconductor field effect transistors obtained from recent 0.1 μm processes. For this technology, it is shown that 1/f noise and Lorentzians do not have the same physical origin. Moreover, an additional implantation, which is performed to control the short-channel effects, is shown to increase trap densities in the depletion layer and at the Si/SiO2 interface.
Role of template layer on microstructure, phase formation and polarization behavior of ferroelectric relaxor thin films
Authors: Ranjith R. , Chaudhuri Ayan Roy , Krupanidhi S. B. , Victor P.
Published: May 2007

( 1 − x ) Pb ( Mg 1 / 3 Nb 2 / 3 ) O 3 − ( x ) PbTiO 3 (PMNPT) a relaxor ferroelectric has gained attention due to its interesting physical properties both in the bulk and thin film forms from a technological and fundamental point of view. The PMNPT solid solution at the morphotropic phase boundary composition has superior properties and is potentially used as an electrostrictive actuator, sensor, and in MEMS applications. Deposition of phase pure PMNPT thin films on bare platinized silicon wafers has been an impossible task so far. In this study the role of the LSCO template on the phase formation and the influence of platinum surface on the same have been studied. It was observed that formation of hillocks in Pt coated silicon wafers is associated with an ATG type of instability while roughening through strain relaxation. The hillocks formation was observed only on the troughs of the strain waves on the surface of Pt. The nucleation and growth of the PMNPT films were analyzed using AFM studies and the nucleation nucleates only at the tips of the hillocks and grows along the same direction with a new nucleus adjacent to the first one. A wavy pattern of PMNPT nuclei was observed and later the lateral growth of the islands takes place to cover the surface and minimizes the roughness to 2 nm. Hence, a template layer with a minimum of 40 nm is required to have a complete coverage with a roughness of less than 2 nm. The chemical states of the PMNPT films grown with and without the template layer were analyzed using x-ray photoelectron spectrum. The XPS spectrum of PMNPT deposited on a Pt surface exhibited a reduced oxidation state of niobium ions and a metallic state of Pb at the initial stage of the growth, which effectively destabilizes the perovskite phase of PMNPT in which the charge states and the ordering of Nb and Mg are more crucial to have a stable perovskite structure.
Five-dimensional ab initio potential energy surface and predicted infrared spectra of H2–CO2 van der Waals complexes
Authors: Ran Hong , Zhou Yanzi , Xie Daiqian
Published: May 2007

The authors present a new five-dimensional potential energy surface for H2–CO2 including the Q3 normal mode for the ν3 antisymmetric stretching vibration of the CO2 molecule. The potential energies were calculated using the supermolecular approach with the full counterpoise correction at the CCSD(T) level with an aug-cc-pVTZ basis set supplemented with bond functions. The global minimum is at two equivalent T-shaped coplanar configurations with a well depth of 219.68cm−1. The rovibrational energy levels for four species of H2–CO2 (paraH2–, orthoH2–, paraD2–, and orthoD2–CO2) were calculated employing the discrete variable representation (DVR) for radial variables and finite basis representation (FBR) for angular variables and the Lanczos algorithm. Our calculations showed that the off-diagonal intra- and intermolecular vibrational coupling could be neglected, and separation of the intramolecular vibration by averaging the total Hamiltonian with the wave function of a specific vibrational state of CO2 should be a good approximation with high accuracy. The calculated band origin shift in the infrared spectra in the ν3 region of CO2 is −0.113cm−1 for paraH2–CO2 and −0.099cm−1 for orthoH2–CO2, which agrees well with the observed values of −0.198 and −0.096cm−1. The calculated rovibrational spectra for H2–CO2 are consistent with the available experimental spectra. For D2–CO2, it is predicted that only a-type transitions occur for paraD2–CO2, while both a-type and b-type transitions are significant for orthoD2–CO2.
Continuous near-infrared-to-ultraviolet lasing from II-VI nanoribbons
Authors: Zapien J. A. , Liu Y. K. , Shan Y. Y. , Tang H. , Lee C. S. , Lee S. T.
Published: May 2007

The authors show that II-VI nanoribbons are capable of room-temperature lasing covering the complete spectral range from near infrared (NIR) to ultraviolet (UV). This is accomplished by simply using nanoribbons of two ternary compositions, namely, CdSXSe1−X and ZnYCd1−YS. Under optical pumping, CdSXSe1−X nanoribbons lase from NIR (710nm) to green (510nm) as X changes from 0 to 1, while ZnYCd1−YS nanoribbons lase from green (510nm) to UV (340nm) as Y varies from 0 to 1. Furthermore, lasing control shows fine-tuning via composition changes that overlap thermally induced tuning. This demonstrates that II-VI materials can enable lasing at any selected wavelength between 710 and 340nm with continuous tuning capabilities.
Charge exchange and ionization in hydrogen atom-fully stripped ion collisions in Debye plasmas
Authors: Zhang H. , Wang J. G. , He B. , Qiu Y. B. , Janev R. K.
Published: May 2007

The processes of charge exchange and ionization in collisions of ground state hydrogen atom with fully stripped ions in a weakly coupled plasma are studied by the classical trajectory Monte Carlo method in the collision energy range 10–900keV∕amu. The interparticle interactions are described by the Debye-Hückel model with inclusion of dynamical effects associated with the projectile velocity. The microcanonical distribution of initial state electronic coordinates and momenta has been determined by inclusion of plasma screening effects. The cross section dependencies on plasma parameters and ion charge and velocity are investigated. It is shown that plasma effects on charge exchange and ionization cross sections are significant and particularly pronounced at low collision velocities. The results of systematic cross section calculations for different values of Debye screening length (in the range 1–50a0) and ion charges (in the range 1–14) are presented.
Phase shift induces currents in a periodic tube
Authors: Ai Bao-Quan , Liu Liang-Gang
Published: May 2007

The average current of an overdamped Brownian particle moving along the axis of a three-dimensional periodic tube is investigated in the presence of a symmetric potential and a temporally symmetric unbiased external force. Reduction of the spatial dimensionality from two or three physical dimensions to an effective one-dimensional system entails the appearance of not only an entropic barrier but also an effective diffusion coefficient. The authors find that the phase shift between the tube shape and the potential can break the symmetry of the effective potential and can induce net currents. Under optimal condition, the current as a function of temperature and the phase shift possesses many extrema of alternating signs. The current may reverse its direction several times when temperature or the phase shift is changed. The authors’ model is to describe the movement of molecular motors along microtubule.
Low temperature epitaxial growth of GaN films on LiGaO2 substrates
Authors: Sakurada Kento , Kobayashi Atsushi , Kawaguchi Yuji , Ohta Jitsuo , Fujioka Hiroshi
Published: May 2007

GaN films have been grown on LiGaO2 {001} substrates at low substrate temperatures by pulsed laser deposition and their structural properties have been investigated. It is found that the metal-face LiGaO2 substrates are thermally more stable than O-face LiGaO2. It is also found that growth of GaN films proceeds epitaxially, even at room temperature (RT), on metal-face LiGaO2, but polycrystalline GaN films are formed on O-face LiGaO2 at RT. Reduction in growth temperature lessens the interface reactions that have previously been regarded as the most serious problem with this substrate have been revealed by x-ray reflectivity measurements.