bluuebunny/crossref_metadata_2025 huggingface dataset:
Filtered arc deposition
Authors: Bergmann Erich , Gorokowsky Vladimir
Published: December 2002

Eine Einführung in die Bedeutung der Transportprozesse bei Beschichtungen führt zur Definition des Phasenwandlers als Überbegriff für Filter für die Lichtbogenverdampfer. Einer kurzen Übersicht über Filtervarianten folgt eine Darstellung der industriellen Lösung, der rechteckigen Plasmaleitkammer. Einige Anwendungsbeispiele und ein qualitativer Vergleich mit anderen Verfahren ergänzen die Darstellung.
Triangular backgrounds shift line bisection performance in hemispatial neglect: The critical point
Authors: Esterman Michael , Mcglinchey-Berroth Regina , Alexander Michael P. , Milberg William
Published: December 2002

Isosceles triangular backgrounds influence line bisection performance in normal control participants and patients with hemispatial neglect. When the triangles are oriented asymmetrically with the vertex in 1 visual field, and the base in the other, the perceived midpoint of horizontal lines within the triangle is shifted towards the base, and away from the vertex. The current study examines this illusion further by systematically varying the extent of the triangle presented. With only fragments of the triangle in the background of the line, the vertex is the critical component driving the illusory shift in perceived midpoint. Patients with neglect and controls are equally sensitive to the illusion. Similar geometric illusions that are also intact in neglect, along with these results, suggest that preattentive, implicit visual processing is preserved in neglect and drives these illusions.
Igneous activity in the southern highlands of the Moon
Authors: Hawke B. Ray , Giguere Thomas A. , Blewett D. T. , Lucey Paul G. , Smith G. A. , Taylor G. J. , Spudis P. D.
Published: December 2002

Detailed investigations of both endogenic and exogenic dark‐haloed craters can provide critical information concerning the geology, composition, and evolution of portions of the lunar surface. Several dark‐haloed and dark‐rayed craters have been identified in the Maurolycus region in the southeastern nearside highlands. Clementine and Galileo multispectral imagery as well as Earth‐based remote‐sensing data were used to investigate the composition and origin of dark‐haloed craters in the region. A striking albedo anomaly is associated with Buch B crater, which exhibits both a dark halo and dark rays. The result of a morphologic analysis clearly indicated that Buch B is an impact structure, not a volcanic vent. The optical maturity image shows that the Buch B ejecta deposits are immature and the radar and thermal data indicate a high abundance of fresh rocks and fragments in the 1–50 cm size range. FeO and TiO2 data as well as five point spectra extracted from Clementine UV‐VIS images indicate that the dark ejecta is composed of immature mare‐like material and may contain minor amounts of highland debris. Buch B excavated either an isolated cryptomare or, more likely, a mafic intrusion. One or more dikes of basaltic composition are possible candidates. Minor low‐albedo anomalies have been identified around three other impact craters (Maurolycus A and B and Barocius M) in the region. While small FeO enhancements are seen in portions of the ejecta deposits associated with these craters, they do not approach the FeO values (12–14 wt.%) exhibited by the dark deposits of Buch B, and they do fall within the range of FeO abundances (5–9 wt.%) exhibited by highland terrain in the Maurolycus region. Hence the presence of a basaltic component is not required, and it cannot be concluded that either cryptomare or mafic intrusions were present in the target sites of these craters.
Turnover and storage of C and N in five density fractions from California annual grassland surface soils
Authors: Baisden W. T. , Amundson R. , Cook A. C. , Brenner D. L.
Published: December 2002

We measured 14C/12C in density fractions from soils collected before and after atmospheric thermonuclear weapons testing to examine soil organic matter (SOM) dynamics along a 3 million year California soil chronosequence. The mineral‐free particulate organic matter (FPOM; <1.6 g cm−3) mainly contains recognizable plant material, fungal hyphae, and charcoal. Mineral‐associated light fractions (1.6–2.2 g cm−3) display partially or completely humified fine POM, while the dense fraction (>2.2 g cm−3) consists of relatively OM‐free sand and OM‐rich clays. Three indicators of decomposition (C:N, δ13C, and δ15N) all suggest increasing SOM decomposition with increasing fraction density. The Δ14C‐derived SOM turnover rates suggest that ≥90% of FPOM turns over in <10 years. The four mineral‐associated fractions contain 69–86% “stabilized” (decadal) SOM with the remainder assumed to be “passive” (millenial) SOM. Within each soil, the four mineral‐associated fractions display approximately the same residence time (34–42 years in 200 kyr soil, 29–37 years in 600 kyr soil, and 18–26 years in 1–3 Myr soils), indicating that a single stabilized SOM “pool” exists in these soils and may turn over primarily as a result of soil disruption.
Nucleation of rupture under slip dependent friction law: Simple models of fault zone
Authors: Ampuero J.‐P. , Vilotte J.‐P. , Sánchez‐Sesma F. J.
Published: December 2002

The initiation of frictional instability is investigated for simple models of fault zone using a linearized perturbation analysis. The fault interface is assumed to obey a linear slip‐weakening law. The fault is initially prestressed uniformly at the sliding threshold. In the case of antiplane shear between two homogeneous linearly elastic media, space‐time and spectral solutions are obtained and shown to be consistent. The nucleation is characterized by (1) a long‐wavelength unstable spectrum bounded by a critical wave number; (2) an exponential growth of the unstable modes; and (3) an induced off‐fault deformation that remains trapped within a bounded zone in the vicinity of the fault. These phenomena are characterized in terms of the elastic parameters of the surrounding medium and a nucleation length that results from the coupling between the frictional interface and the bulk elasticity. These results are extended to other geometries within the same formalism and implications for three‐dimensional rupture are discussed. Finally, internal fault structures are investigated in terms of a fault‐parallel damaged zone. Spectral solutions are obtained for both a smooth and a layered distribution of damage. For natural faults the nucleation is shown to depend strongly on the existence of a internal damaged layer. This nucleation can be described in terms of an effective homogeneous model. In all cases, frictional trapping of the deformation out of the fault can lead to the property that arbitrarily long wavelengths remain sensitive to the existence of a fault zone.
Self‐sealing in sedimentary basins
Authors: Deming David , Cranganu Constantin , Lee Youngmin
Published: December 2002

Over the last decade, the picture that has emerged from several geologic disciplines is that the Earth's crust is permeable to great depths and that fluids are more or less constantly moving, transporting both heat and mass and affecting virtually every geologic process. In contrast, workers in the petroleum industry have maintained that sections of the crust contain impermeable pressure seals and hydraulically sealed compartments. We show that these starkly different conceptions can be reconciled by a theory of self‐sealing through gas generation in sedimentary basins. The model especially applies to older sedimentary basins where overpressuring cannot be readily explained as the result of ongoing sedimentation and compaction disequilibrium. In our conceptual model, overpressuring is created by catagenic gas generation and maintained by a combination of vertical and horizontal gas capillary seals. Data from the Anadarko Basin in Oklahoma provide support for the self‐sealing hypothesis. Well logs reveal the presence of 9 or 10 gas‐water interfaces over a 30‐m overpressured interval. Capillary pressure measurements show that the force necessary for gas to displace water from a shale is ∼3 × 106 Pa, a pressure equivalent to that exerted by a column of water 300 m high. A theory of self‐sealing explains the anomalous overpressuring observed in some older sedimentary basins by invoking known mechanisms and forces; it is both parsimonious and falsifiable.
Finite element modeling of neotectonics in New Zealand
Authors: Liu Zhen , Bird Peter
Published: December 2002

Thin‐shell finite element methods that incorporate faults, realistic rheology, laterally varying heat flow and topography, and plate velocity boundary conditions have been used to model the neotectonics of New Zealand. We find that New Zealand's faults have effective friction of ∼0.17, comparable to that found in other Pacific Rim regions. The long‐term average slip rate of the Alpine fault varies along strike, generally increasing northeastward until slip is partitioned among the strands of the Marlborough system. The average slip rate, ∼30 mm/yr, when combined with published geodetic results and historical seismicity, strongly suggests a high probability of future large earthquakes. Tectonic deformation of North Island is controlled by a balance between differential topographic pressure and traction from the Hikurangi subduction thrust. The Hikurangi forearc is an independent plate sliver moving relative to the Pacific and Australian plates. There is a complicated zone of slip partitioning in the transition from the Alpine fault to the Puysegur trench. An offshore thrust fault, the southern segment of which may correspond to the Waipounamou fault system, parallels to the SE coast of South Island and needs to be included in seismic hazard estimates.
A model study of the seasonal variability and formation mechanisms of the barrier layer in the eastern equatorial Indian Ocean
Authors: Masson Sébastien , Delecluse Pascale , Boulanger Jean‐Philippe , Menkes Christophe
Published: December 2002

By modifying mixed layer thickness, the barrier layer (BL) may have a significant impact on air–sea interactions. In the tropical Indian Ocean, thermohaline observations are lacking over most of the basin, despite a few BL observations in the Bay of Bengal and off Sumatra. A 15‐yearlong model simulation is used to investigate the seasonal variations and formation mechanisms of the BL. In the eastern equatorial area, the model thermohaline structure is in close agreement with observations and simulates a realistic seasonal variability. A robust and thick BL (of more than 40 m) is observed seasonally with a maximum horizontal extent (of about 1500 km) in November. This BL corresponds to the merging of two BLs that undergo different formation mechanisms. The first is formed as the Wyrtki Jet propagates eastward, deepening the thermocline while zonally advecting a salinity subsurface maximum. At the same time, northward wind stresses induce a northward advection of a thin fresh water layer toward the equator. This combination decouples salinity from temperature, and a BL is formed. Later, as the jet penetrates further toward the fresh pool, a second BL appears off Sumatra. This one is controlled by two different mechanisms. A westward surface current trapped in the thin mixed layer off Sumatra advects fresh water from the coastal precipitation area. Then, significant upwelling associated with the westward current further raises the halocline. In situ observations confirm the realism of these simulated formation mechanisms. From year to year, the timing, thickness, and shape of the BLs follow the strong interannual variability of the Wyrtki Jet. Despite these variations, the formation mechanisms remain unchanged.
Segmentation of temperature microstructure
Authors: Chen Huey‐Long , Hondzo Miki , Rao A. Ramachandra
Published: December 2002

The so‐called indirect method of estimating the kinetic energy dissipation rate, a key parameter in environmental fluid mechanics, involves fitting the observed spectrum to the theoretical Batchelor spectrum. This requires the statistically nonstationary temperature gradient profiles to be split onto statistically stationary segments. This comparative study of segmentation algorithms uses synthetic temperature gradient series and the temperature gradient profiles that are measured in an inland lake. The results of segmentation based on autoregressive (AR) models and wavelet analysis are compared. The bias in estimating the Batchelor spectrum from nonstationary segments, which have changes in the spectral shape or the spectral magnitude, is demonstrated. The estimated spectra of the resulting stationary segments should be stationary in both the shape and the magnitude of the spectra. A modified AR‐based test and a proposed wavelet‐based test are sensitive to changes in both the spectral shape and the spectral magnitude. An empirical segmentation technique sensitive to changes in the spectral shape only is not recommended for use.
Fire dynamics and implications for nitrogen cycling in boreal forests
Authors: Harden Jennifer W. , Mack Michelle , Veldhuis Hugo , Gower S. T.
Published: December 2002

We used a dynamic, long‐term mass balance approach to track cumulative carbon (C) and nitrogen (N) losses to fire in boreal Manitoba over the 6500 years since deglaciation. Estimated C losses to decomposition and fire, combined with measurements of N pools in mature and burned forest floors, suggest that loss of N by combustion has likely resulted in a long‐term loss that exceeds the amount of N stored in soil today by 2 to 3 times. These estimates imply that biological N fixation rates could be as high as 5 to 10 times atmospheric deposition rates in boreal regions. At the site scale, the amount of N lost is due to N content of fuels, which varies by stand type and fire severity, which in turn vary with climate and fire dynamics. The interplay of fire frequency, fire severity, and N partitioning during regrowth are important for understanding rates and sustainability of nutrient and carbon cycling over millenia and over broad regions.
Model studies on the sensitivity of upper tropospheric chemistry to heterogeneous uptake of HNO3 on cirrus ice particles
Authors: Meier Andreas , Hendricks Johannes
Published: December 2002

A chemistry box model is applied to investigate potential chemical perturbations in the midlatitude upper troposphere caused by the reactive and nonreactive uptake of trace gases on cirrus ice particles. Chemical implications of denoxification caused by heterogeneous reactions with HNO3 as a product and adsorption of gas phase HNO3 on ice surfaces are the special focus. The role of denitrification due to gravitational settling of ice particles is investigated. The simulations suggest that cirrus cloud chemistry has the potential to induce strong local reductions in upper tropospheric HNO3 and NOx. Because of NO reduction the OH/HO2 ratio and the OH concentration decrease. As a consequence of these effects a significant reduction in the net ozone production rate is modeled. Sensitivity studies were performed varying the HNO3 adsorption efficiency, the particle sedimentation efficiency, and the ambient NOx concentration. The sensitivity experiments reveal that the modeled cirrus cloud impacts are mainly driven by the nonreactive uptake of HNO3 on ice particles and the subsequent particle sedimentation. The effects strongly depend on the efficiency of HNO3 adsorption. If a very efficient uptake of HNO3 is assumed, decreases in the ozone mixing ratio up to 14% are modeled. The simulations also suggest that the cirrus cloud impact on ozone is sensitive to the ambient NOx concentration. The heterogeneous reactions on ice with HNO3 as a product appear to be of secondary importance in the upper troposphere. Chlorine activation due to heterogeneous reactions on cirrus ice particles has a minor effect on model ozone chemistry under the conditions regarded. The model calculations further suggest that chemical perturbations caused by the uptake of OH, HO2, and H2O2 on ice are potentially significant only in periods of high cirrus cloud activity. Since observational data on cirrus chemical impacts in the upper troposphere are currently too sparse to perform a detailed model validation, it remains unclear whether the potentially large chemical perturbations caused by HNO3 adsorption on cirrus ice particles are of relevance for the real atmosphere.
Chemical, microphysical, and optical properties of polar stratospheric clouds
Authors: Schreiner J. , Voigt C. , Weisser C. , Kohlmann A. , Mauersberger K. , Deshler T. , Kröger C. , Rosen J. , Kjome N. , Larsen N. , Adriani A. , Cairo F. , Di Donfrancesco G. , Ovarlez J. , Ovarlez H. , Dörnbrack A.
Published: December 2002

A balloonborne gondola for a comprehensive study of polar stratospheric clouds (PSCs) was launched on 25 January 2000 near Kiruna/Sweden. Besides an aerosol composition mass spectrometer, the gondola carried optical particle counters, two backscatter sondes, a hygrometer, and several temperature and pressure sensors. A mountain wave induced PSC was sampled between 20 and 23 km altitude. Strongly correlated PSC particle properties were detected with the different instruments. A large variability of particle types was measured in numerous PSC layers, and PSC development was followed for about two hours. Liquid ternary PSC layers were found at temperatures near the ice frost point. A large fraction of the sampled cloud layers consisted of nitric acid trihydrate (NAT) particles with a molar ratio H2O:HNO3 close to 3 at temperatures near and below the equilibrium temperature TNAT. The median radius of the NAT particle size distribution was between 0.5 and 0.75 μm at concentrations around 0.5 cm−3. Below the NAT layers and above TNAT, thin cloud layers containing a few large particles with radii up to 3.5 μm coexisted with smaller solid or liquid particles. The molar ratio in this region was found to be close to two.
A Parameterization of cirrus cloud formation: Homogeneous freezing including effects of aerosol size
Authors: Kärcher B. , Lohmann U.
Published: December 2002

In a previous study, we have derived an approximate, physically based parameterization of cirrus cloud formation by homogeneous freezing, applying to a wide class of supercooled aerosols in the upper troposphere and tropopause region. In this study, the parameterization scheme is extended to include the effects of aerosol size on the freezing process in adiabatically rising air parcels. Aerosol size effects become important when the timescale of the freezing event is fast compared to the timescale of depositional growth of the pristine ice particles. The generalized parameterization scheme is validated with parcel model simulations and can directly be applied in models that do not explicitly resolve the ice nucleation process, such as cloud‐resolving models, weather forecast models, and climate models. The relationship between aerosol and ice crystal number concentrations in cirrus clouds formed by homogeneous freezing is discussed. This relationship is much weaker than in liquid water clouds. It is shown that even freezing of enhanced levels of sulfate aerosol originating from strong volcanic eruptions is unlikely to exert a sensible influence on cirrus formation.
Weathering reactions and hyporheic exchange controls on stream water chemistry in a glacial meltwater stream in the McMurdo Dry Valleys
Authors: Gooseff Michael N. , McKnight Diane M. , Lyons W. Berry , Blum Alex E.
Published: December 2002

In the McMurdo Dry Valleys, Antarctica, dilute glacial meltwater flows down well‐established streambeds to closed basin lakes during the austral summer. During the 6–12 week flow season, a hyporheic zone develops in the saturated sediment adjacent to the streams. Longer Dry Valley streams have higher concentrations of major ions than shorter streams. The longitudinal increases in Si and K suggest that primary weathering contributes to the downstream solute increase. The hypothesis that weathering reactions in the hyporheic zone control stream chemistry was tested by modeling the downstream increase in solute concentration in von Guerard Stream in Taylor Valley. The average rates of solute supplied from these sources over the 5.2 km length of the stream were 6.1 × 10−9 mol Si L−1 m−1 and 3.7 × 10−9 mol K L−1 m−1, yielding annual dissolved Si loads of 0.02–1.30 mol Si m−2 of watershed land surface. Silicate minerals in streambed sediment were analyzed to determine the representative surface area of minerals in the hyporheic zone subject to primary weathering. Two strategies were evaluated to compute sediment surface area normalized weathering rates. The first applies a best linear fit to synoptic data in order to calculate a constant downstream solute concentration gradient, dC/dx (constant weathering rate contribution, CRC method); the second uses a transient storage model to simulate dC/dx, representing both hyporheic exchange and chemical weathering (hydrologic exchange, HE method). Geometric surface area normalized dissolution rates of the silicate minerals in the stream ranged from 0.6 × 10−12 mol Si m−2 s−1 to 4.5 × 10−12 mol Si m−2 s−1 and 0.4 × 10−12 mol K m−2 s−1 to 1.9 × 10−12 mol K m−2 s−1. These values are an order of magnitude lower than geometric surface area normalized weathering rates determined in laboratory studies and are an order of magnitude greater than geometric surface area normalized weathering rates determined in a warmer, wetter setting in temperate basins, despite the cold temperatures, lack of precipitation and lack of organic material. These results suggest that the continuous saturation and rapid flushing of the sediment due to hyporheic exchange facilitates weathering in Dry Valley streams.
Estimate of transport properties of porous media by microfocus X‐ray computed tomography and random walk simulation
Authors: Nakashima Yoshito , Watanabe Yoshinori
Published: December 2002

The transport properties (porosity, surface‐to‐volume ratio of the pore space, diffusion coefficient, and permeability) of a porous medium were calculated by image analysis and random walk simulation using the digital image data on the pore structure of a bead pack (diameter 2.11 mm). A theory developed for laboratory experiments of nuclear magnetic resonance was applied to the random walk simulation. The three‐dimensional data set (2563 voxels) of the bead pack was obtained by microfocus X‐ray computed tomography at a spatial resolution of 0.053 mm. An original cluster labeling program, Kai3D.m, was used to estimate the porosity and surface‐to‐volume ratio. The surface‐to‐volume ratio and diffusion coefficient were calculated by an original random walk program, RW3D.m. The calculations were completed on a personal computer in reasonable time (≤13 hours). The permeability was estimated by substituting the results of Kai3D.m and RW3D.m into the Kozeny‐Carman equation. The results for the porosity, surface‐to‐volume ratio, and diffusion coefficient were within 5–8% of measured values, whereas the calculated permeability involved an error of 35%. The promising results of the present study indicate that it is possible to estimate the permeability of porous media with reasonable accuracy by the diffusometry and random walk simulation. Because, in principle, the diffusometry could be performed by proton nuclear magnetic resonance logging, the method of estimating the transport properties presented here is applicable to the in situ measurement of strata. We open the original Mathematica® programs (Kai3D.m and RW3D.m) used to calculate the porosity, surface‐to‐volume ratio, and diffusion coefficient at the authors' home page to facilitate the personal‐computer‐based study of porous media using X‐ray computed tomography.
Unsaturated flow through a fracture–matrix network: Dynamic preferential pathways in mesoscale laboratory experiments
Authors: Glass R. J. , Nicholl M. J. , Pringle S. E. , Wood T. R.
Published: December 2002

We conducted two laboratory experiments at the meter scale in which water was applied to the top of an initially dry, uncemented wall composed of porous bricks. One experiment (Experiment 1) encouraged evaporation and resulting mineral precipitation, while the other (Experiment 2) was designed to minimize these processes. In both cases, processes acting within the fracture network controlled early time behavior, forming discrete pathways and demonstrating fractures to act as both flow conductors and capillary barriers. At a later time, evaporation–mineral precipitation in Experiment 1 constrained flow, strengthening some pathways and starving others. In Experiment 2, the wetted structure took on the appearance of a diffuse plume; however, individual pathways persisted within the wetted structure and interacted, displaying erratic outflow over a wide range of timescales, including switching between pathways. Thus, under conditions of constant supply and both with and without evaporation–mineral precipitation, unsaturated flow through fractured rock can create dynamic preferential pathways.
Nitrogen in rock: Occurrences and biogeochemical implications
Authors: Holloway JoAnn M. , Dahlgren Randy A.
Published: December 2002

There is a growing interest in the role of bedrock in global nitrogen cycling and potential for increased ecosystem sensitivity to human impacts in terrains with elevated background nitrogen concentrations. Nitrogen‐bearing rocks are globally distributed and comprise a potentially large pool of nitrogen in nutrient cycling that is frequently neglected because of a lack of routine analytical methods for quantification. Nitrogen in rock originates as organically bound nitrogen associated with sediment, or in thermal waters representing a mixture of sedimentary, mantle, and meteoric sources of nitrogen. Rock nitrogen concentrations range from trace levels (<200 mg N kg−1) in granites to ecologically significant concentrations exceeding 1000 mg N kg−1in some sedimentary and metasedimentary rocks. Nitrate deposits accumulated in arid and semi‐arid regions are also a large potential pool. Nitrogen in rock has a potentially significant impact on localized nitrogen cycles. Elevated nitrogen concentrations in water and soil have been attributed to weathering of bedrock nitrogen. In some environments, nitrogen released from bedrock may contribute to nitrogen saturation of terrestrial ecosystems (more nitrogen available than required by biota). Nitrogen saturation results in leaching of nitrate to surface and groundwaters, and, where soils are formed from ammonium‐rich bedrock, the oxidation of ammonium to nitrate may result in soil acidification, inhibiting revegetation in certain ecosystems. Collectively, studies presented in this article reveal that geologic nitrogen may be a large and reactive pool with potential for amplification of human impacts on nitrogen cycling in terrestrial and aquatic ecosystems.
Mercury and methylmercury contamination related to artisanal gold mining, Suriname
Authors: Gray John E. , Labson Victor F. , Weaver Jean N. , Krabbenhoft David P.
Published: December 2002

Elemental Hg‐Au amalgamation mining practices are used widely in many developing countries resulting in significant Hg contamination of surrounding ecosystems. We have measured total Hg and methyl‐Hg concentrations in sediment and water collected from artisanal Au mines and these are the first Hg speciation data from such mines in Suriname. Total Hg and methyl‐Hg contents in mine‐waste sediment and water are elevated over local uncontaminated baselines. Total Hg (10–930 ng/L) and methyl‐Hg (0.02–3.8 ng/L) are highly elevated in mine waters. Increasing total Hg contents in discharged mine waters correlate with increasing water turbidity indicating that most Hg transport is on suspended particulates. Our Hg results are similar to those found in artisanal Au mines in the Amazon basin, where Hg contamination has led to adverse effects on tropical ecosystems.
Dependence of the surface climate interannual variability on spatial scale
Authors: Giorgi Filippo
Published: December 2002

This paper examines the scale dependence of surface climate interannual variability over six regions of the world using a gridded observed dataset of precipitation and surface air temperature for the period 1961–1990. The scales analysed cover the range of 0.5 to 3.5 degrees in longitude/latitude. The interannual variability of precipitation exhibits a strong sensitivity to spatial scale, especially at the finer scales analysed, while the interannual variability of temperature shows a weak sensitivity to spatial scale. The scale sensitivity of interannual variability is maximum in warm climate regimes, such as over tropical and sub‐tropical regions and in the summer season. These results have important implications for climate predictability (e.g., at seasonal and longer temporal scales) and for the identification of climatic trends and changes. They indicate that the prediction and detection of precipitation changes becomes a substantially more difficult task as the scale of interest is increasingly refined. Conversely, for temperature, since the variability is characterized by broader spatial scales, scale refinement is a less important factor.
An assessment of SeaWinds on QuikSCAT wind retrieval
Authors: Draper David W. , Long David G.
Published: December 2002

The scatterometer ocean wind retrieval process produces several possible solutions or ambiguities at each point, requiring a separate ambiguity selection step to infer a unique wind vector field. An ambiguity selection error occurs when the selected wind vector is not the closest ambiguity to the true wind. The current ambiguity selection routine for SeaWinds is ad hoc, but performs well under most circumstances. Factors such as instrument noise and rain can also cause the estimated wind flow to deviate from the true wind. A quality assurance (QA) analysis is performed to assess the ambiguity selection effectiveness and noise level of the retrieved wind using a low‐order wind field model. The wind field model is data‐driven and shown to be rather insensitive to the training data set. The QA analysis demonstrates that the SeaWinds ambiguity selection process is at least 95% effective. Ambiguity selection errors are correlated with storms and rain corruption. A subjective analysis on a set of cyclonic storm passes confirms that the wind retrieval is somewhat less effective in storm regions.
Effect of vertically extended strike object on the distribution of current along the lightning channel
Authors: Rachidi F. , Rakov V. A. , Nucci C. A. , Bermudez J. L.
Published: December 2002

On the basis of a distributed‐source representation of the lightning channel, the mathematical formulations of the so‐called engineering lightning return stroke models are generalized to take into account the presence of a vertically extended strike object. The strike object is modeled as a lossless uniform transmission line, and the reflection coefficients are all assumed to be constant. The distribution of current along the lightning channel for each model is expressed in terms of the “undisturbed” current, object height, and current reflection coefficients at the top and the bottom of the object. The undisturbed current is defined as the current that would flow in the channel if the current reflection coefficients at the extremities of the strike object were equal to zero, that is, the characteristic impedances of the lightning channel and the strike object were equal to each other and equal to the grounding impedance of the strike object. The distributed‐source representation of the lightning channel adopted in this study allows for a more general and straightforward formulations of the generalized return‐stroke models than the traditional representations implying a lumped current source at the bottom of the channel, including a self‐consistent treatment of the impedance discontinuity at the tower top.
Siberian Lena River hydrologic regime and recent change
Authors: Yang Daqing , Kane Douglas L. , Hinzman Larry D. , Zhang Xuebin , Zhang Tingjun , Ye Hengchun
Published: December 2002

The long‐term (1935–1999) monthly records of temperature, precipitation, stream flow, river ice thickness, and active layer depth have been analyzed in this study to examine Lena River hydrologic regime and recent change. Remarkable hydrologic changes have been identified in this study. During the cold season (October–April), significant increases (25–90%) in stream flow and decrease in river ice thickness have been found due to warming in Siberia. In the snowmelt period (May–June), strong warming in spring leads to an advance of snowmelt season into late May and results in a lower daily maximum discharge in June. During summer months (July–September) the changes in stream flow hydrology are less significant in comparison to those for winter and spring seasons. A slight stream flow increase is discovered for both July and August, mainly owing to precipitation increase in May and June. Discharge in September has a slight downward trend due to precipitation decrease and temperature increase in August. The magnitudes of changes in stream flow and river ice thickness identified in this study are large enough to alter the hydrologic regime. Investigation into the hydrologic response of the Lena River to climate change and variation reveals strong linkages of stream flow with temperature and precipitation. We therefore believe that Lena River hydrologic regime changes are mainly the consequence of recent climate warming over Siberia and also closely related to changes in permafrost condition.
Conditions for flow in the continental crust
Authors: McKenzie Dan , Jackson James
Published: December 2002

Earthquake focal depth distributions and effective elastic thickness variations on the continents suggest that in old cold regions such as shields, the lower continental crust can be stronger than the upper mantle, and imply that the upper mantle can flow even when the lower crust does not. However, in other places substantial flow in the lower crust does occur, particularly near extensional metamorphic core complexes. We suggest that the lower crust only flows when its viscosity is significantly reduced, either by heating from igneous intrusions or by the addition of water. In both cases, the important characteristics of the flow are a consequence of the limited time over which the viscosity reduction occurs. The timescale is controlled either by conductive cooling of intrusions, or by the separation of melt from its matrix, which removes the water.
Regulation of Endothelial Cell Adhesion Molecule Expression in an Experimental Model of Cerebral Malaria
Authors: BAUER PHILLIPE R. , van der HEYDE HENRI C. , SUN GUANG , SPECIAN ROBERT D. , GRANGER D. NEIL
Published: December 2002

Objective: Plasmodium falciparum malaria in humans and animal models of this disease have revealed changes in the infected host that are consistent with a systemic inflammatory response. Although it has been proposed that endothelial cell adhesion molecules (CAM) contribute to the adhesive interactions of Plasmodium‐infected erythrocytes and immune cells with vascular endothelial cells, ECAM expression has not been systematically studied in Plasmodium‐infected animals.

Methods: In this study, the dual radiolabeled monoclonal antibody method was used to quantify the expression of different ECAMs (ICAM‐1, VCAM‐1, P‐selectin, E‐selectin) in different regional vascular beds of Plasmodium berghei ANKA‐inffected mice (PbA), a well‐recognized model of human cerebral malaria. The roles of T lymphocytes and certain cytokines (TNF‐α, IL‐12, IFN‐γ) in mediating the infection‐induced expression of ICAM‐1 and P‐selectin were assessed by using relevant mutant mice.

Results: Wild‐type (WT) mice exhibited highly significant increases in the expression of ICAM‐1, VCAM‐1, and P‐selectin (but not E‐selectin) in all vascular beds on the 6th day of PbA infection. The PbA‐induced upregulation of ICAM‐1 was significantly blunted in mice that were either deficient in IFN‐α, IL‐12 (but not TNF1b) or T lymphocytes (Rag‐1 deficiency); however, these responses were tissue specific.

Conclusions: These findings indicate that vascular endothelial cells in most regional circulations assume an inflammatory phenotype and that cytokines and immune cells mediate this response in a tissue‐specific manner.
Development of Mouse Cremaster Transplantation Model for Intravital Microscopic Evaluation
Authors: OZER KAGAN , ZIELINSKI MACIEJ , UNSAL MURAT , SIEMIONOW MARIA
Published: December 2002

Objective: In this study, we investigated the possibility of transplanting cremaster muscle in mice. After transplantation, we measured the microcirculatory parameters and compared with the cremaster‐control values with no transplantation.

Methods: In group 1 (n = 10, C57BL/6N), normal cremaster microcirculation parameters were measured without transplantation. In group 2 (n = 6), isograft transplantations were performed between C57BL/6N mice. After transplantation, standard microcirculatory parameters were measured for 3 hours in both groups.

Results: The procedure was performed with a 95% success rate and 75 minutes of ischemia time. Functional capillary perfusion, diameters, and red blood cell velocities of the first‐, second‐, and third‐order arterioles and veins showed significant decreases in the isograft group within the first 2 hours (p < 0.05) but returned to normal values at the third hour. The number of rolling, adhering, and transmigrating leukocytes and lymphocytes also showed an increase in the isograft group within the first and second hours (p < 0.05, compared to cremaster control).

Conclusions: Leukocyte/endothelial interaction and hemodynamic parameters of muscle flap circulation displayed the effects of ischemia in the isograft group. The cremaster muscle transplantation in mice was found to be a reliable and reproducible model offering the unique possibility of observing and studying the leukocyte‐endothelial interaction during ischemia/reperfusion injury and allograft rejection using intravital microscopy.
Mechanisms of Heterogeneous Endothelial Cytoplasmic Calcium Increases in Venular Microvessels
Authors: MCKNIGHT T.R. , CURRY F.E.
Published: December 2002

Objective: Localized inflammatory leaky sites form at regions of the microvessel wall with the largest increase in endothelial cell cytoplasmic calcium concentration, [Ca2+]i. We investigated the mechanisms that modulate localized increases in [Ca2+]i in individual endothelial cells of microvessels after exposure to ATP.

Methods: [Ca2+]i was measured by using digital fluorescence microscopy and fura‐2 in the endothelial cells forming the walls of individually perfused frog mesenteric microvessels. The spread of [Ca2+]i from a localized mechanical stimulus was also measured.

Results: The peak [Ca2+]i after ATP showed marked heterogeneity, ranging from 227 to 1469 nM from resting values of 69 ± 5 nM. After depolarization with high‐potassium solutions, the endothelial cells with the largest peak increase in [Ca2+]i had the largest fractional reduction. Localized increases in [Ca2+]i due to mechanical stimulus did not spread.

Conclusion: The key mechanism regulating the heterogeneity in initial peak increase in [Ca2+]i is a calcium‐dependent process regulated by the calcium influx itself. One such mechanism, the calcium‐dependent opening of additional potassium channels leading to membrane hyperpolarization and increased driving force for calcium entry through passive conductance pathways, accounts for a significant amount of the heterogeneity of [Ca2+]i in our experiments. Further investigations of both localized calcium influx and membrane potentials in the endothelial cells of intact microvessels in both frog and mammals using the imaging methods developed for these investigations are needed to understand the formation of localized leaky sites in inflamed microvessels.
Microcirculation as a Target for the Anti‐inflammatory Properties of Statins
Authors: SCALIA ROSARIO , STALKER TIMOTHY J.
Published: December 2002

Statins are inhibitors of the 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase, a ubiquitous enzyme critical for the biosynthesis of cholesterol. Because of their cholesterol‐lowering properties, statins are extensively used in medical practice, and large clinical trials have shown that statins effectively reduce cardiovascular related morbidity and mortality. In the past 5 years, an important, new concept suggesting that the cardioprotective effects of statins are not necessarily related to cholesterol‐lowering actions has emerged. Indeed, in vivo findings have clearly shown that statins exert anti‐inflammatory and immunomodulatory effects and that they modulate vascular remodeling under normocholesterolemic conditions. These pleiotropic properties of statins affect important molecules in vascular biology and help preserve endothelial function in acute and chronic inflammatory states of the cardiovascular system, including coronary and cerebral artery diseases, diabetes, and atherosclerosis. Emerging evidence indicates that the microcirculation is a crucial target for the pleiotropic actions of statins because of its important role in regulating blood flow, leukocyte‐endothelium interactions, and vascular remodeling. Accordingly, this review focuses on the role that the microcirculation plays in the vascular protective action of statins.
Cytochromeb558–Dependent NAD(P)H Oxidase–Phox Units in Smooth Muscle and Macrophages of Atherosclerotic Lesions
Authors: Kalinina Natalia , Agrotis Alex , Tararak Eduard , Antropova Yulia , Kanellakis Peter , Ilyinskaya Olga , Quinn Mark T. , Smirnov Vladimir , Bobik Alex
Published: December 2002

Objective—Despite studies implicating superoxide anion–producing oxidases in atherosclerosis, their characteristics, expression, and regulation in cells of lesions are poorly understood. We examined the following: (1) whether cytochromeb558–dependent NAD(P)H oxidase–phox peptides are expressed by intimal smooth muscle cells (iSMCs) and macrophages of human aortic atherosclerotic lesions and their regulation and (2) whether cytochromeb558–dependent NAD(P)H oxidase represents a major NAD(P)H oxidase in iSMCs.

Methods and Results—Using a combination of immunochemical and reverse transcription–polymerase chain reaction procedures, we demonstrate that p22phoxand gp91phox(cytochromeb558) expression in normal intima was restricted to a quarter of the iSMCs. In fatty streaks, a similar fraction of iSMCs expressed cytochromeb558, whereas macrophages also expressed low levels of p47phoxand p67phox. In fibrofatty lesions, the majority of iSMCs expressed the cytochromeb558subunits; p67phoxwas also detected. Macrophages and macrophage-derived foam cells expressed the 4 phox subunits that constitute superoxide-producing cytochromeb558–dependent NAD(P)H oxidase. These were upregulated by transforming growth factor-β1and interferon-γ. Aortic lesions also expressed Thox1 and Nox4, and although their expression also increases with lesion severity, their expression is less frequent than that of gp91phox.

Conclusions—In human aortic fibrofatty lesions, a cytochromeb558–dependent NAD(P)H oxidase appears to be a major iSMC and macrophage oxidase whose expression is upregulated by cytokines.
Blood Pressure Increase and Incidence of Hypertension in Relation to Inflammation-Sensitive Plasma Proteins
Authors: Engström Gunnar , Janzon Lars , Berglund Göran , Lind Peter , Stavenow Lars , Hedblad Bo , Lindgärde Folke
Published: December 2002

Objective—

The reasons for the relationship between inflammation-sensitive plasma proteins (ISPs) and incidence of cardiovascular diseases are poorly understood. This study explored the hypothesis that ISPs are associated with future hypertension and age-related blood pressure increase.

Method and Results—

Blood pressure and plasma levels of fibrinogen, α1-antitrypsin, haptoglobin, ceruloplasmin, and orosomucoid were determined in 2262 healthy men aged 35 to 50 years, initially without treatment for hypertension. The cohort was re-examined after 15.7 (±2.2) years. Incidence of hypertension and blood pressure increase was studied in relation to number of elevated proteins (ie, in the top quartile) at baseline. Among men without treatment for hypertension at follow-up, mean (±SD) increase in systolic blood pressure was 18.8±17, 19.2±17, 19.3±17, and 22.1±18 mm Hg, respectively, for men with 0, 1, 2, and ≥3 elevated proteins (
P
for trend=0.02, adjusted for confounders). The corresponding values for pulse pressure increase was 15.5±14, 15.8±14, 17.4±14, and 17.8±15 mm Hg, respectively (
P
=0.02). Incidence of hypertension (≥160/95 mm Hg or treatment) and future blood pressure treatment showed similar associations with ISPs. Increase in diastolic blood pressure showed no association with ISPs.

Conclusions—

Plasma levels of ISPs are associated with a future increase in blood pressure. This could contribute to the relationship between ISP levels and cardiovascular disease.
PlAPolymorphism of Integrin β3Differentially Modulates Cellular Migration on Extracellular Matrix Proteins
Authors: Sajid Mansoor , Vijayan K. Vinod , Souza Shiloe , Bray Paul F.
Published: December 2002

Objective—Cell migration is central to multiple physiological and pathologic processes and involves interactions between integrins on the cell surface and the extracellular matrix. The Leu33Pro (PlA) polymorphism of integrin β3has been reported to be associated with a greater rate of restenosis after angioplasty, a process involving endothelial and smooth muscle cell migration. We have addressed the possibility that the Leu33Pro polymorphism could modify the migratory behavior of Chinese hamster ovary (CHO) cells expressing the β3-containing integrin complexes.

Methods and Results—Haptotactic migratory responses of CHO αIIbβ3cells to fibronectin and vitronectin were not statistically different between the Leu33 and Pro33 cells. However, CHO cells with the Pro33 (PlA2) polymorphism had an enhanced haptotactic migratory response to fibrinogen and von Willebrand Factor. This enhanced migration (1) could be blocked by the αIIbβ3-complex–specific neutralizing mAb 10E5, by 7E3, a neutralizing mAb specific for the β3integrin, and by the αIIbβ3-blocking peptide Integrilin; (2) was not observed with a CHO cell line expressing an activating β3Cys435 to Ala mutation; and (3) was attributable to increased activity of mitogen-activated protein kinase and cyclooxygenase. CHO cell lines expressing the Pro33 isoform of αvβ3had an enhanced haptotactic migratory response to vitronectin and osteopontin but not fibrinogen.

Conclusions—The Leu33Pro polymorphism alters the migratory behavior of cells on extracellular matrix substrates, and the α subunit influences the substrate specificity of this genetic effect.