bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of interseismic slip rates and the potential for significant earthquakes on the Calaveras fault, central California
Authors: Manaker David M. , Bürgmann Roland , Prescott William H. , Langbein John
Published: June 2003

The Calaveras fault is a major component of the San Andreas fault system in the San Francisco Bay area, that generated 13 earthquakes of ML > 5 since 1850. In most recent ML > 5 events, premain shock and postmain shock microseismicity is sparse in the region of coseismic slip. These aseismic areas are believed to represent locked patches of the fault that are accumulating strain to be released in ML > 5 events. We analyze geodetic data to better characterize the spatial distribution of interseismic slip rates on the Calaveras fault, modeling the slip distribution in the seismogenic zone by inversion of over 25 years of surface deformation data. We use a regional fault model with the seismogenic zone of the Calaveras fault discretized into ∼6 km × 3 km elements, employing a weighted least squares approach with smoothing and positivity constraints. Our discretized fault slip model consistently identifies regions of slip deficit in the seismogenic zone of the Calaveras fault that generally correspond to regions of decreased microseismicity and ruptures of previous moderate earthquakes. In particular, we find correspondence with the 1979 Coyote Lake and 1984 Morgan Hill events, as well as regions where historical earthquakes on the Coyote and the Sunol‐San Ramon segments have occurred. Moment magnitude calculations based on the estimated slip deficit, fault area, and recurrence intervals agree with measured magnitudes of modern events and interpreted historical magnitudes. The results suggest that a combination of geodetically derived fault slip models and microseismicity distribution can be used to characterize seismic hazard.
Dehydration and partial melting in subduction zones: Constraints from U‐series disequilibria
Authors: Bourdon Bernard , Turner Simon , Dosseto Anthony
Published: June 2003

We present a critical reappraisal of U‐series data from arc volcanoes to constrain slab dehydration and melting processes using a global subduction zone data set. There is no clear evidence for significant mobilization of Th or Pa in dehydration fluids while the source region of arc rocks is relatively oxidized and mobility of U is strongly enhanced. It is argued that along‐arc U/Th and U/Pa isotope data reflect time‐integrated addition of U from the slab to the mantle wedge. The presence of large Ra‐Th disequilibrium correlated with Ba/Th ratios provides evidence for some very recent fluid addition and fast magma ascent. This is consistent with radiogenic Os isotope signatures in arc lavas that can only be preserved if there is no melt‐peridotite equilibration during melt transport. The 231Pa excesses found in most arc lavas provide clear evidence for a melting signature and require that the timescale of melt production cannot be as short as the timescale of melt migration (<100 annum). We propose a dynamic model in which melting is initiated by fluid fluxing and where melt is rapidly extracted out of the mantle via high‐velocity channels while 231Pa excess is produced at melting rates consistent with literature estimates of melt productivity. An alternative model with continuous flux melting would require a long melting timescale (1–5 Ma), a large melting region and the mobility of Th and Pa in fluids. A model with a time lag between melting and initial dehydration is more consistent with a thermal structure where the wet solidus is not reached before an intermediate depth.
Connectivity of aqueous fluid in eclogite and its implications for fluid migration in the Earth's interior
Authors: Mibe Kenji , Yoshino Takashi , Ono Shigeaki , Yasuda Atsushi , Fujii Toshitsugu
Published: June 2003

The geometrical distribution of the aqueous fluid in textural equilibrium with eclogite was investigated by measurements of the dihedral angles at aqueous fluid‐clinopyroxene‐clinopyroxene (θcc), at aqueous fluid‐garnet‐garnet (θgg) and at aqueous fluid‐clinopyroxene‐garnet (θcg) triple junctions at 3–5 GPa and 700–800°C with a Kawai‐type multianvil high‐pressure apparatus. The dihedral angles, θcc, θgg, and θcg range from 62° to 68° and appear constant within the experimental uncertainties at the pressures and temperatures investigated. The constant dihedral angle values could be explained by the counterbalance of the effects of pressure, temperature, and the difference in Mg/(Mg + Fe) in the minerals and the aqueous fluid. The present results lead to the suggestion that the aqueous fluid in eclogite at pressures from 3 to 5 GPa (corresponding to depths of ∼90–150 km) exists as isolated pores, provided circumstances of chemical and textural equilibrium prevail. It is suggested that up to about 1–2 vol% aqueous fluid could be trapped as an interstitial fluid in eclogite and be transported to the Earth's interior at depths of at least 150 km by the subduction of the oceanic crust and by the delamination of the crustal roots.
Stress field in the subducting lithosphere and comparison with deep earthquakes in Tonga
Authors: Guest A. , Schubert G. , Gable C. W.
Published: June 2003

We present a numerical model of the subducting lithosphere that provides an alternative explanation for stresses causing deep earthquakes. Our model lithosphere is composed of α olivine, β spinel, γ spinel, and perovskite + magnesiowüstite. The heat conduction equation is solved to determine temperature conditions in the slab and to locate the equilibrium phase transformations in pressure‐temperature space. Volumetric strains in the subducting lithosphere are calculated from the density of individual phases and from the heat released or consumed in the phase changes. These strains are used as sources of stress in the subducting lithosphere. Dislocation creep and Peierls stress creep laws are included in the viscoelastic rheology. Volumetric reductions due to equilibrium phase transformations cause high shear stress in the transition zone because of the variable viscosity inside the subducting slab. Aspects of the model shear stresses are in agreement with observations of high seismic activity in the Tonga‐Wadati Benioff zone. Compression is oriented along the dip of the slab, and extension is oriented in the plane perpendicular to the compression axis. Since our model stresses agree with the seismic observations, and because the model stresses are larger than those caused by buoyancy forces, our model provides a possible explanation of stresses causing deep earthquakes. Also, our model does not need metastability of olivine to explain the occurrence of high shear stress in the transition zone.
Size‐dependent scavenging efficiencies of multicomponent atmospheric aerosols in clouds
Authors: Sellegri K. , Laj P. , Dupuy R. , Legrand M. , Preunkert S. , Putaud J.‐P.
Published: June 2003

The size‐dependent scavenging efficiencies of inorganic and carbonaceous fractions of aerosol have been investigated in clouds present at the Puy de Dôme (1465 m above sea level, France) in winter. In‐cloud interstitial aerosols and residues of evaporated cloud droplets are separated by a round jet impactor (RJI) collecting the interstitial phase and a counterflow virtual impactor (CVI) collecting cloud droplets hereinafter evaporated. In addition, interstitial and droplet phases are collected together in a whole air inlet. Particles (interstitial aerosol and evaporated cloud droplets) are subsequently sampled using low‐pressure cascade impactors, weighted, and analyzed for major ions, organic (OC) and elemental (EC) carbon. RJI and CVI data provide mass‐scavenging efficiencies of the different aerosol components. The scavenged fraction of inorganic species ions (εinorg) is 0.76 ± 0.07 on a first accumulation mode (0.2 ± 0.1 μm geometric diameter (GMD) (Acc1) and 0.93 ± 0.03 on a second (0.5 ± 0.2 μm GDM) accumulation mode. Instead, the scavenged fraction of organic carbon (εOC) is much lower with averaged values of 0.14 ± 0.07 on both modes. These differences are clearly indicative of a high degree of external mixing between inorganic and organic aerosols. Gravimetric data confirm these values of εOC and εinorg with total mass scavenging efficiency of 0.41 ± 0.07 and 0.54 ± 0.07 for Acc1 and Acc2 modes, respectively. Higher mass scavenging efficiencies are obtained for EC than OC (εEC(Acc1) = 0.33 ± 0.09 and εEC (Acc2) = 0.74 ± 0.09). This suggests either internal mixing between black carbon and more soluble species such as sulfate or nitrate or presence on the surface of EC particle of species containing more hygroscopic properties.
Spatiotemporal variability of the relation between African Easterly Waves and West African Squall Lines in 1998 and 1999
Authors: Fink Andreas H. , Reiner Andreas
Published: June 2003

This study investigates the spatiotemporal variability of the relationship between African Easterly Waves (AEWs) and the lifecycle and characteristics of Squall Lines (SLs) over West Africa for the two six‐month periods May–October 1998 and 1999. In all, 81 AEWs have been tracked using analyses from the European Centre for Medium‐Range Weather Forecasts (ECMWF) and 344 SLs have been identified by localizing their leading edges mainly from passive microwave rain rate retrievals. It is found that the area west of the AEW trough is a favorable location for SL generation over the entire tropical West Africa. In the Sahel, a secondary peak around the region of maximum AEW‐related southerlies is observed. In these wave phases, 42% of all 344 SLs were identified and defined as “AEW‐forced”. According to this definition, the contribution of AEWs to SL generation increases from 20% around 15°E to 68% at the West African coast (15°W), and is larger for the Sahel than for the Guinea Coast/Soudanian region. Furthermore, the impact of AEWs on SL genesis is greater at the height of the Sahelian rainy season (July–September) than in the remaining early and late monsoon months. Few SLs form after midnight and in the morning hours, but if so, they mostly belong to the sample of AEW‐forced SLs. Since AEW‐forced SLs exhibit no extraordinary characteristics (lifetime, propagation speed, size, and rain rate) compared to the remaining SLs, it is suggested that the impact of AEWs is largely restricted to SL initiation and organization processes. Finally, some potential physical mechanisms responsible for the AEW/SL genesis relationship are discussed.
Long‐term variation (1992–1999) of gross‐beta, 210Pb and 90Sr concentrations in rainwater and deposition to ground
Authors: Dueñas C. , Fernández M. C. , Carretero J. , Liger E. , Cañete S.
Published: June 2003

After the end of atmospheric nuclear weapons tests and after the Chernobyl accident, the deposition characteristics of radionuclides changed from a predominant wet deposition to the present resuspension mechanism characterised by predominant dry deposition. To study the deposition, monthly deposition data from a collector located at a coastal station (Málaga, South Spain) were compared from 1992 to 1999. The measurement of artificial and natural radionuclide activity concentrations in bulk deposition material by non‐destructive ultra low‐level gamma‐ray spectrometry and long‐term deposition fluxes at this sampling site are reported. The range in annual fluxes for gross‐beta is 60.1–97.2 Bq m−2 yr−1. A measure of the annual deposition velocity for the total beta activity has been obtained using specific concentrations in air and deposition fluxes. The annual total deposition fluxes of 210Pb varied between 12.4 Bq m−2 [1998] and 464.15 Bq m−2 [1996], showing a minimum in the years 1994, 1995 and 1999. The average atmospheric fallout value for 210Pb (135.7 Bq m−2 yr−1) measured over 8 years (1992–1999) is compared with values from other stations. The annual total deposition fluxes of 90Sr varied between <2.15 Bq m−2 [1999] and 13.3 Bq m−2 [1994], showing a significant decrease as expected for natural removal and radioactive decay and no new releases from nuclear facilities or weapons testing.
Numerical simulation of Martian dust devils
Authors: Toigo Anthony D. , Richardson Mark I. , Ewald Shawn P. , Gierasch Peter J.
Published: June 2003

Large eddy simulations of vertical convective vortices and dust devils in the Martian convective boundary layer are presented, employing a version of the Mars MM5 mesoscale model, adapted to use periodic boundary conditions and run at resolutions of 10 to 100 m. The effects of background horizontal wind speed and shear on dust devil development are studied in four simulations, each extending over the daytime portion of one Martian day. The general vorticity development in all cases is similar, with roughly equal positive and negative vorticity extrema. Two dust devils were found to develop in the highest wind speed case and in a case run without background wind. The dust devil structures were found to agree well qualitatively with terrestrial dust devil observations, including the prediction of greatly diminished vertical velocities in the vortex core. Thermodynamic scaling theory of dust devils was found to provide good prediction of the relationship between central pressure and temperature in the modeled vortices. Examination of the turbulent kinetic energy budgets suggests balance between buoyancy generation and loss through dissipation and transport. The vorticity for the dust devils is provided by twisting of horizontal vorticity into the vertical. The horizontal vorticity originates from horizontal variations in temperature at the lower boundary (thermal buoyancy). While the horizontal winds generated by the modeled dust devils were likely insufficient to lift dust, this study provides a solid starting point for dynamic modeling of what may be an important component of the Martian dust cycle.
Dust impact on marine biota and atmospheric CO2 during glacial periods
Authors: Bopp Laurent , Kohfeld Karen E. , Le Quéré Corinne , Aumont Olivier
Published: June 2003

We assess the impact of high dust deposition rates on marine biota and atmospheric CO2 using a state‐of‐the‐art ocean biogeochemistry model and observations. Our model includes an explicit representation of two groups of phytoplankton and colimitation by iron, silicate, and phosphate. When high dust deposition rates from the Last Glacial Maximum (LGM) are used as input, our model shows an increase in the relative abundance of diatoms in today's iron‐limited regions, causing a global increase in export production by 6% and an atmospheric CO2 drawdown of 15 ppm. When the combined effects of changes in dust, temperature, ice cover, and circulation are included, the model reproduces roughly our reconstruction of regional changes in export production during the LGM based on several paleoceanographic indicators. In particular, the model reproduces the latitudinal dipole in the Southern Ocean, driven in our simulations by the conjunction of dust, sea ice, and circulation changes. In the North Pacific the limited open ocean data suggest that we correctly simulate the east‐west gradient in the open ocean, but more data are needed to confirm this result. From our model‐data comparison and from the timing of the dust record at Vostok, we argue that our model estimate of the role of dust is realistic and that the maximum impact of high dust deposition on atmospheric CO2 must be <30 ppm.
Role of tropics in changing the response to Milankovich forcing some three million years ago
Authors: Philander S. George , Fedorov Alexey V.
Published: June 2003

Throughout the Cenozoic the Earth experienced global cooling that led to the appearance of continental glaciers in high northern latitudes around 3 Ma ago. At approximately the same time, cold surface waters first appeared in regions that today have intense oceanic upwelling: the eastern equatorial Pacific and the coastal zones of southwestern Africa and California. There was furthermore a significant change in the Earth's response to Milankovich forcing: obliquity signals became large, but those associated with precession and eccentricity remained the same. The latter change in the Earth's response can be explained by hypothesizing that the global cooling during the Cenozoic affected the thermal structure of the ocean; it caused a gradual shoaling of the thermocline. Around 3 Ma the thermocline was sufficiently shallow for the winds to bring cold water from below the thermocline to the surface in certain upwelling regions. This brought into play feedbacks involving ocean‐atmosphere interactions of the type associated with El Niño and also mechanisms by which high‐latitude surface conditions can influence the depth of the tropical thermocline. Those feedbacks and mechanisms can account for the amplification of the Earth's response to periodic variations in obliquity (at a period of 41K) without altering the response to Milankovich forcing at periods of 100,000 and 23,000 years. This hypothesis is testable. If correct, then in the tropics and subtropics the response to obliquity variations is in phase with, and corresponds to, El Niño conditions when tilt is large and La Niña conditions when tilt is small.
RADARSAT 1 synthetic aperture radar observations of Antarctica: Modified Antarctic Mapping Mission, 2000
Authors: Jezek K. C. , Farness K. , Carande R. , Wu X. , Labelle‐Hamer N.
Published: June 2003

The RADARSAT 1 Antarctic Mapping Project (RAMP) is a collaboration between NASA and the Canadian Space Agency to map Antarctica using synthetic aperture radar (SAR). RAMP comprises two distinct mapping missions. The first Antarctic Mapping Mission was successfully completed in October 1997. Data from the acquisition phase of the 1997 campaign have been used to achieve the primary goal of producing the first high‐resolution SAR image map of the entire Antarctic continent. The Modified Antarctic Mapping Mission (MAMM) occurred during the fall of 2000. The acquisition strategy concentrated on collecting highest‐resolution RADARSAT 1 data of Antarctica's fast glaciers for change detection, feature tracking estimates of surface velocity, and interferometric analysis of velocity and coherence over the entire viewable region, which extends north of 80.1°S latitude. This paper reviews the MAMM project and describes the techniques to be used in processing the data. An example of data acquired over the Drygalski ice tongue, Antarctica illustrates how MAMM data will further benefit investigations of the icy continent.
Advanced microwave sounding unit cloud and precipitation algorithms
Authors: Weng Fuzhong , Zhao Limin , Ferraro Ralph R. , Poe Gene , Li Xiaofan , Grody Norman C.
Published: June 2003

Although the advanced microwave sounding unit (AMSU) on board the NOAA 15 and NOAA 16 satellites is primarily designed for profiling atmospheric temperature and moisture, the products associated with clouds and precipitation are also derived using its window channel measurements with a quality similar to those derived from microwave imagers such as the Special Sensor Microwave Imager. However, the AMSU asymmetry in radiance along the scan was found to be obvious at its window channels and could severely degrade the quality of cloud and precipitation products if not properly corrected. Thus a postlaunch calibration scheme is developed for these channels, and the causes of the asymmetry are analyzed from the AMSU instrument model. A preliminary study shows that the asymmetry may be caused by either the AMSU polarization misalignment or the antenna pointing angle error. A generic radiative transfer model is developed for a single‐layered cloud using a two‐stream approximation and can be utilized for the retrievals of cloud liquid water (L) and total precipitable water (V), cloud ice water path (IWP), and particle effective diameter (De). At the AMSU lower frequencies the scattering from cloud liquid is neglected, and therefore the retrieval of L and V is linearly derived using 23.8 and 31.4 GHz. However, for ice clouds the radiative transfer model is simplified by neglecting the thermal emission, and therefore the retrieval of IWP and De is analytically derived using the AMSU millimeter wavelength channels at 89 and 150 GHz. These cloud algorithms are tested for the AMSU on board the NOAA 15 and NOAA 16 satellites, and the results are rather promising. It is also found that the AMSU‐derived cloud ice water path is highly correlated with the surface rain rates and is now directly used to monitor surface precipitation throughout the world.
Solution of time domain electric field integral equation for arbitrarily shaped dielectric bodies using an unconditionally stable methodology
Authors: Chung Young‐seek , Sarkar Tapan K. , Jung Baek Ho
Published: June 2003

In this work, we present a new and efficient numerical method to obtain an unconditionally stable solution for the time domain electric field integral equation (TD‐EFIE) for arbitrary homogeneous dielectric bodies, derived utilizing the surface equivalence principle. This novel method does not utilize the customary marching‐on in time solution method often used to solve a hyperbolic partial differential equation. Instead we solve the wave equation by expressing the transient behaviors in terms of weighted Laguerre polynomials. By using these orthonormal basis functions for the temporal variation, the time derivatives in the TD‐EFIE formulation can be handled analytically. Since these weighted Laguerre polynomials converge to zero as time progresses, the induced electric and magnetic currents when expanded in a series of weighted Laguerre polynomials also converge to zero. In order to solve the wave equation, we introduce two separate testing procedures, a spatial and temporal testing. By introducing first the temporal testing procedure, the marching‐on in time procedure is replaced by a recursive relation between the different orders of the weighted Laguerre polynomials. The other novelty of this approach is that through the use of the entire domain Laguerre polynomials for the expansion of the temporal variation of the currents, the spatial and the temporal variables can be separated. For convenience, we use the Hertz vector as the unknown variable instead of the equivalent electric current density. However, we use the equivalent magnetic current density as it is. To verify our method, we apply the proposed method to various dielectric scatterers and compare the results of an inverse Fourier transform of a frequency domain EFIE.
FDTD surface impedance models for electrically thick dispersive material coatings
Authors: Kärkkäinen Mikko
Published: June 2003

A new accurate finite‐difference time‐domain model of dielectric and conductive layers on metal surfaces is developed. The model is based on higher‐order surface impedance boundary conditions (SIBC). Several improvements to the existing numerical SIBC models are presented. The most important features of the proposed model are the inclusion of the tangential variations of the fields into the model and a considerably more accurate approximation of the impedance function than in the earlier works. In addition to the usual dielectric and conductive layers, the model can also handle layers of Lorentz, Debye, or Drude media. It is shown that the range of applicability of the proposed SIBC model is greatly increased as compared with the earlier models. Verification of the model is performed with one‐ and two‐dimensional simulations. The results are compared with the exact results in both time and frequency domains. Also, a comparison with an earlier model is provided.
Water vapor transport in the vicinity of imbibing saline plumes: Homogeneous and layered unsaturated porous media
Authors: Weisbrod Noam , Niemet Michael R. , McGinnis Thomas , Selker John S.
Published: June 2003

Water vapor transport in the vicinity of imbibing saline solutions was investigated in two‐dimensional (2‐D) chambers using a light transmission technique. Concentrated NaNO3 solutions (brines) were applied as point sources to the surface of homogenous packs of prewetted silica sand for four different sand grades. The same solutions were applied to layered systems, where two horizontal fine layers were embedded within a coarser matrix, mimicking stratified sedimentary deposits. Water vapor transport from the residually saturated sand into the imbibing brine was observed in all sand grades and geometries. Pure water applied to sand prewetted with brine migrated into the surrounding residual brine. Water vapor stripping was found to enhance the lateral transport of brine in layered sand, where capillary barrier effects play a major role. Our observations suggest that osmotic potential and vapor density lowering in saline solutions, often neglected in predictive models, should be taken into account when predicting the transport of brines in the vadose zone.
Path‐based methods for the determination of nondispersive drainage directions in grid‐based digital elevation models
Authors: Orlandini Stefano , Moretti Giovanni , Franchini Marco , Aldighieri Barbara , Testa Bruno
Published: June 2003

Path‐based methods for the determination of nondispersive drainage directions in grid‐based digital elevation models are presented. These methods extend the descriptive capabilities of the classical D8 method by cumulating the deviations between selected and theoretical drainage directions along the drainage paths. It is shown that either angular or transversal deviations can be employed. Accordingly, two classes of methods designated D8‐LAD (eight drainage directions, least angular deviation) and D8‐LTD (eight drainage directions, least transversal deviation) are developed. Detailed tests on four synthetic drainage systems of known geometry and on the Liro catchment (central Italian Alps) indicate that the proposed methods provide significant improvement over the D8 method for the determination of drainage directions and drainage areas.
Column water vapor from diffuse irradiance
Authors: Kiedron P. , Berndt J. , Michalsky J. , Harrison L.
Published: June 2003

We investigate the possibility of measuring water vapor column from diffuse irradiance, and thus the extension of optical retrievals to cloudy days. Data from the rotating shadowband spectroradiometer (RSS) during its winter deployment at the North Slope of Alaska (NSA) site are used: 20 days in March 1999 that include clear, partly cloudy and overcast days. During these days water vapor column varied between one and five mm according to the NSA site's microwave radiometer (MWR). The diffuse transmittance in the 760‐nm oxygen absorption band is used to obtain the effective air mass. The end result is a correlation of 0.97 and 0.95 between MWR and RSS retrievals using 820‐nm and 940‐nm diffuse transmittances, respectively. These results, which are based on empirical data analysis only, imply that the diffuse irradiance may contain sufficient information to retrieve water vapor column.
Properties of jet engine combustion particles during the PartEmis experiment: Hygroscopicity at subsaturated conditions
Authors: Gysel M. , Nyeki S. , Weingartner E. , Baltensperger U. , Giebl H. , Hitzenberger R. , Petzold A. , Wilson C. W.
Published: June 2003

Hygroscopic properties of combustion particles were measured online with a Hygroscopicity Tandem Differential Mobility Analyzer (H‐TDMA) during PartEmis jet engine combustor experiments. The combustor was operated at old and modern cruise conditions with fuel sulfur contents (FSC) of 50, 410 and 1270 μg g−1, and hygroscopic growth factors (HGF) of particles with different dry diameters were investigated at relative humidities RH ≤ 95%. HGFs increased strongly with increasing FSC (HGF[95% RH, 50 nm, modern cruise] = 1.01 and 1.16 for low and high FSC, respectively), and decreased with increasing particle size at fixed FSC, whereas no significant difference was detected between old and modern cruise. HGFs agreed well with a two‐parameter theoretical model which provided an estimate of the sulfuric acid content of dry particles, indicating a nearly linear dependence on FSC.
Is there any structure inside the liquid outer core?
Authors: Souriau Annie , Teste Alexandra , Chevrot Sébastien
Published: June 2003

The anomalous splitting of some core‐sensitive eigenmodes suggests the presence of a structure in the liquid core. Geodynamical considerations rule out density heterogeneities, however they do not rule out the possibility of anisotropy in the liquid core. The seismic polar paths through the anisotropic inner core, which are anomalously fast, also sample the liquid core inside the cylinder tangent to the inner core, a structure insulated from the rest of the core during rotation. We investigate the possibility that anisotropy be present in that part of the liquid core, using PKPbc waves which have a long path inside the tangent cylinder, but which do not sample the inner core. We also investigate the possibility of heterogeneities which could have deposited beneath the polar caps, using differential travel times of S3KS‐SKKS waves. The data do not reveal heterogeneity or anisotropy inside the tangent cylinder, nor the presence of anomalous polar caps.
Mars Orbiter Laser Altimeter pulse width measurements and footprint‐scale roughness
Authors: Neumann G. A. , Abshire J. B. , Aharonson O. , Garvin J. B. , Sun X. , Zuber M. T.
Published: June 2003

The Mars Orbiter Laser Altimeter (MOLA) measured the pulse width and energy of altimetric laser returns during the course of two Mars years of operations. As secondary science objectives, MOLA obtains the footprint‐scale roughness and the bidirectional reflectivity of Mars. MOLA underwent extensive preflight calibration and pulse measurements were monitored continuously in flight, but anomalous values of roughness have been inferred. A calibration of pulse widths using inflight data yields a slope‐corrected roughness over ∼75‐m‐diameter footprints that may be used for quantitative geomorphic surface characterization, required, for example, for landing site selection. The recalibration uses a total least‐squares estimation of pulse characteristics that generalizes the method of Abshire et al. [2000]. This method, utilizing the timing at voltage threshold crossings and the area between crossings, accounts for observation errors and shows that surface roughness as small as 1 m can be resolved.
Emergence of a band‐limited power law in the aftershock decay rate of a slider‐block model
Authors: Narteau C. , Shebalin P. , Hainzl S. , Zöller G. , Holschneider M.
Published: June 2003

In order to elucidate how structural heterogeneities affect the aftershock decay rate, we examine the aftershock sequences produced by a slider‐block model of seismicity. In this model, the geometry of the seismic zone is the only free parameter and all aspects of the system are known. The power law aftershock decay rate holds only for smooth faults. A band‐limited power law emerges at intermediate fault complexity. For rough faults, only a transient regime toward an exponential decay is observed. In all fault geometries examined, a band‐limited power law model fits the synthetic aftershock decay rate better than the Modified Omori Law. Then, as the connected seismic elements form a simpler localised surface, we show that the power law aftershock decay rate extends over longer time, and that the power law exponent increases. These results support the inference that the correlation time of the power law aftershock decay rate increases as the deformation localises along dominant major faults.
Climate variations since the last interglacial recorded in Czech loess
Authors: Shi Caidong , Zhu Rixiang , Glass Billy P. , Liu Qingsong , Zeman A. , Suchy V.
Published: June 2003

Magnetic susceptibility, organic matter content, and grain size were measured on a loess/palaeosol sequence deposited since the last interglacial at the Dolni Vestonice section in the Czech Republic. High values in magnetic susceptibility and organic matter content in palaeosols PK0, PK2, and PK3 indicate that they were strongly influenced by long‐term pedogenesis and high vegetation density linked to interglacials or interstadials. Grain‐size variations record a series of cold wind‐strengthened events during the last glacial, which we interpret as a record of the distinctive ‘Younger Dryas’ episode and millennial‐scale climate oscillations that correlate with the GRIP ice core δ18O record and North Atlantic Heinrich events. These climate events, as indicated by grain‐size peaks, combined with previous climate records at French Massif Central and Lago Grande di Monticchio in Italy, suggest that the climate over these areas might have undergone synchronous oscillations with the shifts in sea‐surface temperatures of the North Atlantic and air temperature changes above Greenland.
Solar and geospace connections of energetic particle events
Authors: Gopalswamy N.
Published: June 2003

A Coordinated Data Analysis Workshop (CDAW) was conducted recently to study the solar and geospace connections of large solar energetic particle (SEP) events of solar cycle 23 (up to the end of 2001). This paper summarizes the properties these events, the scientific issues discussed, and some of the results obtained during the workshop.
Interannual‐to‐interdecadal sea surface temperature variability along the western coast of South America
Authors: Montecinos A. , Purca S. , Pizarro O.
Published: June 2003

Interannual and interdecadal regional‐scale sea surface temperature (SST) variability along Peru and Chile are described based on 9 coastal stations and global SST in the period 1951–1999. ENSO‐related interannual variability dominates the low‐passed time series along the coast, with maximum amplitudes in the tropics decreasing southward. At tropical latitudes interdecadal variance is about one‐third of the interannual variance while they are of similar amplitude in the midlatitudes (36°S). The correlation between the low frequency coastal modes and the Pacific and Atlantic SST suggests that the coastal SST variability comprises two main large‐scale climate processes: the ENSO cycle at interannual timescale, and a basin‐wide, perhaps even a global‐scale, interdecadal oscillation.
Importance of direct and indirect triggered seismicity in the ETAS model of seismicity
Authors: Helmstetter Agnès , Sornette Didier
Published: June 2003

Using the simple ETAS branching model of seismicity, which assumes that each earthquake can trigger other earthquakes, we quantify the role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as the overall level of seismicity in the presence of a constant external seismicity source. We show that, in this model, the fraction of earthquakes in the population that are aftershocks is equal to the fraction of aftershocks that are indirectly triggered and is given by the average number of triggered events per earthquake. Previous observations that a significant fraction of earthquakes are triggered earthquakes therefore imply that most aftershocks are indirectly triggered by the mainshock.
Sensitivity studies of the effect of increased aerosol concentrations and snow crystal shape on the snowfall rate in the Arctic
Authors: Lohmann U. , Zhang J. , Pi J.
Published: June 2003

The mesoscale model GESIMA is used to simulate microphysical properties of Arctic clouds and their effect on radiation. Different case studies during the FIRE ACE/SHEBA project show that GESIMA is able to simulate the cloud boundaries, ice and liquid water content, and effective radii in good agreement with observations. For two different aerosol scenarios, the simulation results show that the anthropogenic aerosol can alter microphysical properties of Arctic clouds, and consequently modify surface precipitation. Borys et al. [2000] proposed that anthropogenically induced decreases in cloud droplet size inhibit the riming process. On the contrary, we find that the accretion of snow crystals with cloud droplets is increased in the polluted cloud owing to its higher cloud droplet number concentration. Instead, the autoconversion rate of cloud droplets and accretion of drizzle by snow decreases caused by the shutdown of the collision‐coalescence process in the polluted cloud. The amount of precipitation reaching the surface as snow depends crucially on the crystal shape. If aggregates are assumed, then a tenfold increase in aerosol concentration leads to an increase in accumulated snow by 40% after 7 hours of simulation whereas the snow amount decreases by 30% when planar crystals are assumed because of the larger accretion efficiency of snow crystals with cloud droplets in case of aggregates.
Cadaveric organ donor recruitment at Los Angeles County Hospital: improvement after formation of a structured clinical, educational and administrative service
Authors: Roth Bradley J , Sher Linda , Murray James A , Belzberg Howard , Mateo R , Heeran A , Romero Javier , Mone Tom , Chan Linda , Selby Rick
Published: June 2003

Abstract: Background/Aims: There remains a critical shortage of cadaveric organs. At a large inner city level one trauma centre, several strategies were devised and combined to (a) optimize the physiologic status of potential donors, (b), promote awareness of the donation process among health care professionals and (c) perform quality control on the organ donation system − all in an effort to improve organ donation rates. Resuscitative and maintenance protocols were devised and implemented through a multidisciplinary team approach for patients diagnosed with brain death. We report the effect this approach has had on organ donation in a single centre.

Method: A death record review (DRR) by the local organ procurement agency (OPO) was used to identify the number of patients diagnosed with brain death at Los Angeles County Hospital each year from 1995 through 2001. Data were collected to determine the number of these potential donors that eventually underwent organ donation. Data were collected for two time intervals: Phase I (1995–98) and Phase II (1999–2001). During Phase I, there was no focused institutional programme for the approach to potential donors. During Phase II, an institutional programme including the following characteristics was implemented: 1) donor resuscitation protocol, 2) assignment of a dedicated OPO coordinator liaison to interact with families, hospital personnel and the coroner's office, 3) assignment of the primary role of stabilization and care of potential donors and the integration of all medical services to the trauma service, and 4) biweekly conferences to review policies, protocols, and outcomes of donor management strategies.

Results: From 1995 to 2001 there was a large increase in patient referrals for donor evaluation from 86 (Phase I) to 124 (Phase II). There was a smaller increase in the number of suitable donors: Phase I (mean: 51/year) and Phase II (mean: 63/year). There was, however, an increase in the mean number of actual organ donors from 14.2/year to 25.7/year from Phase I to Phase II and an increase in organs donated from 29 to 49. Organ donor declines decreased from 53% (Phase I) to 39% (Phase II).

Conclusions: Strategies to increase the number of cadaveric organs available for organ transplantation are crucial. A strategy combining prompt identification of potential organ donors, institution of resuscitative protocols, a multidisciplinary team approach, educational activities and utilization of personnel expert in organ procurement led to a marked increase in the number of organ donors and the number of organs donated at a single institution. Wider application of this approach should prove successful in increasing organ donation in a similar fashion in other institutions.
Cold ischaemia time added to kidneys can be minimized by completing the final cross‐match before organs are taken from the operating room
Authors: Bryan Christopher F ,   for the Midwest Transplant Network Organ Procurement Organization Organ Procurement Coordinators,   Renal Placement Coordinators,   Histocompatibility Medical Technologists,   Pilots
Published: June 2003

Abstract: Purpose:Minimizing the amount of cold ischaemia time (CIT) added to cadaveric kidneys before their transplantation is an important goal since longer CIT is associated with worse long‐term graft outcome. Our organ procurement organization (OPO) and HLA laboratories have taken the approach of performing the histocompatibility testing, including the final cross‐match, as early in the donor process as possible.

Methods:The data in this study were collected from all consecutive final cross‐matches done for cadaveric kidney (n = 113) and simultaneous pancreas + kidney (SPK) (n = 25) transplants done with organs recovered from donors in the Midwest Transplant Network OPO from 1 January 2001 to 9 May 2002. We evaluated the time the final cross‐match was completed from when the kidneys from that donor were taken from the operating room (OR) and compared that time with CIT.

Results:For kidney transplants, 72% of the final cross‐matches were complete before the kidneys were taken from the OR. The CIT of that group (10.4 ± 3.8 h) was significantly lower than that of the group of kidney transplant patients whose final cross‐match was done after the kidneys were taken from the OR (15.5 ± 5.8 h) (P < 0.001). Similarly, for SPK transplants, 88% of the final cross‐matches were completed before the organs left the OR and the CIT of that group (10.2 ± 3.4 h) was less than in the group whose final cross‐match was done after the organs left the OR (14.3 ± 4.8 h) (P > 0.1).

Conclusions:These data show that the practice of completing the final cross‐match as early in the donor process as possible helps to minimize the amount of cold ischaemia time added to the kidneys and pancreata before transplantation. That should reduce the detrimental influence that longer CIT has on short‐ and long‐term function in kidney as well as SPK transplantation.
Management of complications of simultaneous kidney–pancreas transplantation with temporary venting jejunostomy
Authors: Boykin Kevin N , Zibari Gazi B
Published: June 2003

Abstract: Background/Aims: The majority of simultaneous kidney–pancreas (SPK) transplants are being performed with portal‐enteric drainage, which does not allow easy access to the donor pancreas. By adding a temporary venting jejunostomy (TVJ) we have been able to closely monitor patients for bleeding, anastomotic leak and rejection.

Methods: Retrospective chart review of 29 patients undergoing SPK with PE drainage from December 1996 to December 2001.

Results: Median follow‐up was 32 months. Patient, kidney and pancreas graft survival were 93%, 90% and 93%, respectively. The most common early complications were wound infections and bleeding. No patient suffered vessel thrombosis. The most common late (greater than 3 months post‐transplant) complication was gastro‐intestinal bleeding. Adequate tissue was obtained for biopsy in 100% of patients with suspected pancreatic rejection. The TVJ allowed one patient to undergo donor pancreas ERCP that demonstrated the site of a pancreatic duct leak. Duodenal stump leak and anastomotic bleeding were diagnosed in one patient each via the TVJ. The median time to takedown of the TVJ was 14 months.

Conclusion: TVJ allows patients an easy method of graft surveillance, is well tolerated, and has an acceptable complication rate. The TVJ allows access to diagnose anastomotic leak, cauterize bleeding mucosa, perform ERCP and biopsy the pancreas allograft.
Long‐term experience with simultaneous kidney–pancreas transplantation with portal‐enteric drainage and tacrolimus/mycophenolate mofetil‐based immunosuppression
Authors: Stratta Robert J , Shokouh‐Amiri M H , Egidi M Francesca , Grewal Hani P , Lo Agnes , Kizilisik A Tarik , Nezakatgoo Nosratollah , Gaber Lillian W , Gaber A. Osama
Published: June 2003

Abstract: Background/Aims: Refinements in surgical techniques and advances in clinical immunosuppression have led to steadily improving results in pancreas transplantation (PTX). Although there is renewed interest in enteric exocrine drainage, most PTXs are performed with systemic venous delivery of insulin. To improve the physiology of PTX, we developed a novel technique of portal venous delivery of insulin and enteric drainage of the exocrine secretions (portal‐enteric [P‐E]). The purpose of the study was to analyse outcomes in patients undergoing PTX with P‐E drainage and contemporary immunosuppression.

Materials and methods: From January 1997 through September 2002, we performed 67 primary simultaneous kidney–PTXs (SKPT) with P‐E drainage. Maintenance immunosuppression consisted of tacrolimus (TAC), mycophenolate mofetil (MMF) and steroids. No antibody induction therapy occurred in 33 patients (49%) with the remainder receiving daclizumab (n = 15), basiliximab (n = 2), or thymoglobulin (n = 14) induction therapy. The patient group included 38 males and 29 females with a mean age of 39.7 year (range 23–58) and a mean duration of pretransplant diabetes of 24.5 year (9–46). Fourteen patients (21%) were African‐American.

Results:The mean waiting time for SKPT was 3.3 months (range 0.1–10). Mean kidney and pancreas cold ischaemia times were 15.1 and 15.4 h, respectively. Patient, kidney and pancreas graft survival rates were 97%, 92.5% and 82%, respectively, with a mean follow‐up of 20 months (range 1–56). Two deaths (one sepsis, one cardiac event) occurred at 1 month after SKPT; both patients died with functioning grafts (DWFG). Three patients (4.5%) had delayed renal allograft function and received temporary dialysis after SKPT. Five kidney graft losses occurred (two DWFG, one thrombosis, two chronic rejection). All but four patients (6%) had immediate PTX function. A total of 12 pancreas graft losses occurred (two DWFG, five thrombosis, five chronic rejection). The incidence of acute rejection was 28%, but no grafts were lost due to isolated acute rejection. The incidence of major infection was 51%, but only five patients (7.5%) developed cytomegalovirus infection. A total of 19 patients (28%) underwent early relaparotomy within 3 months of SKPT. The composite endpoint of no rejection, graft loss, or mortality was attained by 63% of patients. At present, 58 patients (87%) are both dialysis and insulin‐independent (including four retransplants).

Conclusion:These findings suggest that SKPT with P‐E drainage and contemporary immunosuppression may result in excellent intermediate‐term outcomes.