bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and test‐bed implementation of a reconfigurable receiver for navigation applications
Authors: Dovis F. , Gramazio A. , Mulassano P.
Published: December 2002

The geographical location of a wireless device is acquiring a significant importance under the boost of innovative applications in the wireless market, and under the research activities related to the development of a new generation of Global Navigation Satellite Systems (GNSS). In the US a new phase of the Global Positioning System is foreseen, and Europe has decided to proceed with the Galileo program. In addition, different government institutions worldwide are working toward the definition of navigation plans, and regulations will set as mandatory the location identification of mobile users in emergency situations (US E‐911 law and the European E‐112 directive).

Considering all the navigation/positioning systems and techniques that will be available in the near future, it is clear that a central role will be played by the user handset; in fact, if navigation signals from different sources will be available, the unique possibility to obtain the best navigation performance from the user perspective will be the employment of enhanced receivers able to fuse different data.

With this aim, this paper presents the design of an innovative navigation receiver based on Software Defined Radio (SDR) technology. The reconfigurability and flexibility issues are guaranteed by the use of reprogrammable high‐speed hardware (FPGA—Field Programmable Gate Array and DSP—Digital Signal Processor) and thus a deep integration at the raw signal level between GPS and the future Galileo has been obtained. The interoperability issue among different systems is then solved at the receiver level. This paper discusses the implementation of a baseline architecture of a reconfigurable GNSS receiver over a FPGA + DSP prototype platform. The receiver is able to deal with different input Signals‐In‐Space (SIS), and can operate with present GPS ranging signals or with the future Galileo SIS. Copyright © 2002 John Wiley & Sons, Ltd.
Surface circulation in the eastern North Atlantic, from drifters and altimetry
Authors: Martins C. Sena , Hamann M. , Fiúza A. F. G.
Published: December 2002

A description of the near‐surface circulation and its properties is the result of the analysis of a drifting buoy data set in the eastern North Atlantic between the Iberian Peninsula, the Azores, and the Canary Islands. World Ocean Circulation Experiment–Tropical Ocean–Global Atmosphere experiment drifters equipped with holey sock drogues centered at 15 m depth collected a total of 14.4 years of data. The drifters sampled a rather inhomogeneous velocity field with a weak mean flow regime and eddies of different scales. They meandered southward everywhere in the study region, except in the Iberian coastal transition zone north of 41°N where they headed northward. The near‐surface mean velocity field obtained from the drifter data set shows all important mean currents, including the poleward Portugal Coastal Countercurrent during the fall, winter, and early spring off western and northern Iberia, the southward Portugal Coastal Current, the slow offshore southward flow of the Portugal Current during the whole year, the southwestward Canary Current, and the eastward Azores Current, which extends to the vicinity of the African coast near the Gulf of Cadiz. Maps of the eddy kinetic energy field were obtained from the drifters and from satellite altimetry. It provides the largest part of the total kinetic energy. The rate of dispersion is estimated from the Lagrangian statistics of the drifting buoys. The dispersion of the drifters in the study region is well modeled by a simple description of eddy diffusion assuming homogeneous turbulence. Ensemble mean diffusivities K and the Langrangian integral length scales and timescales (L and T) were obtained for the zonal and meridional directions. The sea surface temperature measured along the drifter trajectories is used to produce estimates of the eddy diffusivity, which is compared with the diffusivity estimates obtained from the theory of Taylor. The eddy diffusivity is found to be approximately proportional to the eddy kinetic energy. Discrete eddies and meanders were observed using drifters and altimetry in order to map and describe their geographical distribution and characteristics in the eastern North Atlantic.
Glacial/interglacial variablity in the Benguela upwelling system: Spatial distribution and budgets of organic carbon accumulation
Authors: Mollenhauer Gesine , Schneider Ralph R. , Müller Peter J. , Spieß Volkhard , Wefer Gerold
Published: December 2002

Modern sedimentary total organic carbon (TOC) content as a proxy for surface water export production was mapped on the shelf and on the upper continental slope of the Benguela upwelling system using 137 core tops. Shelf maxima in TOC can be correlated with maxima in surface water productivity. On the slope, high TOC contents are observed offshore from sites of strong modern upwelling. Estimates of modern TOC mass accumulation rates (MAR) show that approximately 85% of the total is accumulating on the shelf. TOC MAR were calculated, mapped, and budgeted for the Holocene and for the Last Glacial Maximum (LGM) using 19 sediment cores from the continental slope. During the LGM, centers of deposition and production have migrated offshore with respect to their Holocene positions. TOC accumulation on the continental slope was approximately 84% higher during the LGM than during the Holocene, possibly reflecting enhanced productivity. The TOC distribution patterns and sediment echo sounding data suggest that undercurrents strongly influence the sedimentation off Namibia. Winnowing and focusing result in great lateral heterogeneity of sedimentation rates and sediment properties. Individual cores therefore do not necessarily reflect general changes in export production. These results highlight the need for detailed regional studies based on a large number of sediment cores for highly heterogeneous high‐productivity areas in order to derive general statements on total fluxes.
Mantle viscosity beneath the Hudson Bay: An inversion based on the Metropolis algorithm
Authors: Cianetti S. , Giunchi C. , Spada G.
Published: December 2002

We revisit the problem of inferring mantle viscosity from postglacial relative sea level (RSL) data across the Hudson Bay. We invert a recently revised data set using the Metropolis algorithm together with an annealing schedule: this method, which is well established in geophysics, is applied here for the first time to the glacial isostatic adjustment problem. The Metropolis algorithm performs a search, which is not limited to downhill moves in the model space and thus is less influenced by local minima of the misfit than traditional inverse approaches. Furthermore, its CPU requirements are far superior to Monte Carlo methods. The major drawbacks include slow convergence and the need for careful tuning of crucial variables such as the temperature schedule and the increment in the model space. When all the Hudson Bay RSL data are considered, and the viscosity of the upper mantle above the 670 km discontinuity is inverted, the best fitting solution is characterized by a viscosity close to 2 × 1020 Pa s. However, when the shallow upper mantle and transition zone viscosity are separately inverted, other less traditional solutions with a more complex viscosity structure are found to be equally possible. A stable feature is the lower mantle viscosity, which is generally found to be close to the value of 1021 Pa s in all of the stochastic inversions we have performed. The solutions agree with previous findings concerning both postglacial rebound observables and global geodynamics signatures.
Modeling postbreakup landscape development and denudational history across the southeast African (Drakensberg Escarpment) margin
Authors: van der Beek Peter , Summerfield Michael A. , Braun Jean , Brown Roderick W. , Fleming Alastair
Published: December 2002

We employ a numerical surface processes model to study the controls on postbreakup landscape development and denudational history of the southeast African margin. Apatite fission track data, presented in the companion paper, suggest that the Drakensberg Escarpment formed by rapid postbreakup river incision seaward of a preexisting drainage divide, located close to its present position, and subsequently retreated at rates of only ∼100 m m.y.−1. Numerical modeling results support such a scenario and show that the prebreakup topography of the margin has exerted a fundamental control on subsequent margin evolution. The rheology of the lithosphere, lithological variations in the eroding upper crust, and inland base level falls provided secondary controls. A relatively low flexural rigidity of the lithosphere (Te ≈ 10 km) is required to explain the observed pattern of denudation as well as the observed geological structure of the southeast African margin. Lithological variations have contributed to the formation of flat‐topped ridges buttressing the main escarpment, as well as major fluvial knickpoints. Both these features have previously been interpreted as supporting significant Cenozoic uplift of the margin. An inland base level fall, possibly related to back‐cutting of the Orange River drainage system and occurring 40–50 m.y. after breakup, explains the observed denudation inland of the escarpment as well as the development of inland drainage parallel to the escarpment. Our model results suggest that in contrast to widely accepted inferences from classical geomorphic studies, the southeast African margin has remained tectonically stable since breakup and escarpment retreat has been minimal (<25 km).
Fault structure and kinematics of the Long Valley Caldera region, California, revealed by high‐accuracy earthquake hypocenters and focal mechanism stress inversions
Authors: Prejean Stephanie , Ellsworth William , Zoback Mark , Waldhauser Felix
Published: December 2002

We have determined high‐resolution hypocenters for 45,000+ earthquakes that occurred between 1980 and 2000 in the Long Valley caldera area using a double‐difference earthquake location algorithm and routinely determined arrival times. The locations reveal numerous discrete fault planes in the southern caldera and adjacent Sierra Nevada block (SNB). Intracaldera faults include a series of east/west‐striking right‐lateral strike‐slip faults beneath the caldera's south moat and a series of more northerly striking strike‐slip/normal faults beneath the caldera's resurgent dome. Seismicity in the SNB south of the caldera is confined to a crustal block bounded on the west by an east‐dipping oblique normal fault and on the east by the Hilton Creek fault. Two NE‐striking left‐lateral strike‐slip faults are responsible for most seismicity within this block. To understand better the stresses driving seismicity, we performed stress inversions using focal mechanisms with 50 or more first motions. This analysis reveals that the least principal stress direction systematically rotates across the studied region, from NE to SW in the caldera's south moat to WNW–ESE in Round Valley, 25 km to the SE. Because WNW–ESE extension is characteristic of the western boundary of the Basin and Range province, caldera area stresses appear to be locally perturbed. This stress perturbation does not seem to result from magma chamber inflation but may be related to the significant (∼20 km) left step in the locus of extension along the Sierra Nevada/Basin and Range province boundary. This implies that regional‐scale tectonic processes are driving seismic deformation in the Long Valley caldera.
Along‐arc structural variation of the plate boundary at the Japan Trench margin: Implication of interplate coupling
Authors: Tsuru Tetsuro , Park Jin‐Oh , Miura Seiichi , Kodaira Shuichi , Kido Yukari , Hayashi Tsutomu
Published: December 2002

At the Japan Trench convergent margin, many large interplate earthquakes of greater than M7.5 frequently occur. Their epicenters have uneven distribution, mostly located in the northern area. To investigate the relationship between this distribution and tectonic structures, we have conducted multichannel seismic surveys since 1996. Our data show two kinds of interplate sedimentary units: a wedge‐shaped unit and a channel‐like unit. Both units have a lower P wave velocity than the basal part of the overriding island arc crust. The wedge‐shaped unit having a velocity of 2–3 km/s is widely distributed over the forearc region in the northern area. Its thickness decreases with depth, becoming several hundred meters at a depth of ∼12 km. The channel‐like unit having a velocity of 3–4 km/s is observed in the southern area, extending in the downdip direction. Its thickness reaches ∼2 km at a depth of ∼12 km. If the low velocity of these units results from the existence of fluid, as many authors assume, the units being thick implies higher fluid content assuming constant porosity. Considering that fluid reduces basal friction and with an assumption that fluid available at a specific interface is proportional to the total fluid content in the sediment, the thickness variation of the units would cause different degrees of coupling at the plate boundary along the arc. This may provide one explanation for the regional disparity in the interplate earthquake occurrence in the margin. Furthermore, we attempt to call attention to the possibility that the channel‐like sediment works as a shear stress releaser.
Low‐frequency variability of the North Pacific Ocean: The roles of boundary‐ and wind‐driven baroclinic Rossby waves
Authors: Fu Lee‐Lueng , Qiu Bo
Published: December 2002

The effects of the sea level variability along the eastern boundary of the North Pacific Ocean, including those associated with El Niño Southern Oscillation, have been considered an important factor in determining the low‐frequency large‐scale variability of the ocean interior through Rossby waves generated at the eastern boundary. This hypothesis is examined in this study using 8 years worth of the sea surface height observations made by the TOPEX/Poseidon satellite. The timescales of interest are longer than 90 days with the annual cycle removed. The results indicate that the influence of the eastern boundary of the North Pacific Ocean has limited offshore extent, varying from 3000–4000 km at 10°N to 200–300 km at 50°N. The variability in the ocean interior is primarily driven by wind with only a minor influence from the boundary. Simulations of a linear two‐layer model of the ocean driven by wind stress curl are correlated with the observations. The effects of wind forcing accumulate along the characteristics of long nondispersive Rossby waves in the time‐longitude domain. These wind‐driven Rossby waves overwhelm the boundary‐driven waves in the ocean interior, where there are only some small residual effects of the boundary‐driven waves, however. These small effects become clearer after the simulated wind‐driven variability is removed from the observations.
Stratospheric Aerosol and Gas Experiment (SAGE) III measurements: A study on the retrieval of ozone, nitrogen dioxide, and aerosol extinction coefficients
Authors: Brogniez C. , Bazureau A. , Lenoble J. , Chu W. P.
Published: December 2002

This paper presents the inversion algorithms that we propose to apply to the Stratospheric Aerosol and Gas Experiment (SAGE) III measurements for retrieving the aerosol and gas components of the Earth atmosphere. SAGE III is an upgraded version of SAGE II: The main improvements are the larger number of channels, including several resolved channels and a channel centered near 1.55 μm, and a higher vertical resolution. The species retrieval from the transmission measurements can be achieved via the inversion algorithm that we developed at Laboratoire d'Optique Atmosphérique for SAGE II with only minor changes, in which all the channels are handled altogether for species separation by using an iterative method. For SAGE III, ozone and nitrogen dioxide can also be retrieved independently from two specific resolved channels by using their spectral signature over a small wavelength range; this second inversion leads only to the ozone and nitrogen dioxide concentrations and to the aerosols at two wavelengths. Since these later O3 and NO2 retrievals are shown to be of better quality, it is further possible to use them in the first algorithm, in a combined analysis, for aerosol separation in the other channels. The performances of these three inversions have been compared for various atmospheric models, accounting for some probable measurement errors. The three methods perform very well in the case of nominal data. When errors are added to the measurements, the combined analysis leads generally to better retrieval for O3 and NO2, while there is almost no improvement for the aerosols. For random measurement error, the retrieved profiles exhibit no bias with respect to the input profiles, except at high altitude. The accuracy of the results is shown to be dependent on the species and on the atmospheric model.
General circulation model simulations of recent cooling in the east‐central United States
Authors: Robinson Walter A. , Ruedy Reto , Hansen James E.
Published: December 2002

In ensembles of retrospective general circulation model (GCM) simulations, surface temperatures in the east‐central United States cool between 1951 and 1997. This cooling, which is broadly consistent with observed surface temperatures, is present in GCM experiments driven by observed time varying sea‐surface temperatures (SSTs) in the tropical Pacific, whether or not increasing greenhouse gases and other time varying climate forcings are included. Here we focus on ensembles with fixed radiative forcing and with observed varying SST in different regions. In these experiments the trend and variability in east‐central U.S. surface temperatures are tied to tropical Pacific SSTs. Warm tropical Pacific SSTs cool U.S. temperatures by diminishing solar heating through an increase in cloud cover. These associations are embedded within a year‐round response to warm tropical Pacific SST that features tropospheric warming throughout the tropics and regions of tropospheric cooling in midlatitudes. Precipitable water vapor over the Gulf of Mexico and the Caribbean and the tropospheric thermal gradient across the Gulf Coast of the United States increase when the tropical Pacific is warm. In observations, recent warming in the tropical Pacific is also associated with increased precipitable water over the southeast United States. The observed cooling in the east‐central United States, relative to the rest of the globe, is accompanied by increased cloud cover, though year‐to‐year variations in cloud cover, U.S. surface temperatures, and tropical Pacific SST are less tightly coupled in observations than in the GCM.
Validation of the physical modeling approach for braided rivers
Authors: Rosatti Giorgio
Published: December 2002

Laboratory channels are often used to study the complexity of braiding mechanisms for the advantages with respect to field studies. Nevertheless, the extensive use of experimental data raises the question of how representative laboratory braided channels are as compared to real braided rivers. This study verifies to what extent laboratory braided patterns reproduce the main features of braided rivers. Experimental data display isotropic and anisotropic scaling of braided patterns, state‐space plot of total widths, anisotropic scaling of islands, and statistical distribution of island areas that are similar to those observed in real rivers. Moreover, the data reveals scaling in the perimeter‐area relation. These results support both the reliability of experimental braided channels as physical models of braided rivers and also the possibility of investigating some aspects of braiding in the laboratory that are difficult to address in the field. The lack of preferential scales in island characteristics suggests that other phenomena must play a key role in generating island shapes besides classical sediment transport‐based mechanisms which tend to select well‐defined length scales.
A metahillslope model based on an analytical solution to a linearized Boussinesq equation for temporally variable recharge rates
Authors: Pauwels Valentijn R. N. , Verhoest Niko E. C. , De Troch François P.
Published: December 2002

In hydrology the slow, subsurface component of the discharge is usually referred to as base flow. One method to model base flow is the conceptual approach, in which the complex physical reality is simplified using hypotheses and assumptions, and the various physical processes are described mathematically. The purpose of this paper is to develop and validate a conceptual method, based on hydraulic theory, to calculate the base flow of a catchment, under observed precipitation rates. The governing groundwater equation, the Boussinesq equation, valid for a unit width sloping aquifer, is linearized and solved for a temporally variable recharge rate. The solution allows the calculation of the transient water table profile in and the outflow from an aquifer under temporally variable recharge rates. When a catchment is considered a metahillslope, the solution can be used, when coupled to a routing model, to calculate the catchment base flow. The model is applied to the Zwalm catchment and four subcatchments in Belgium. The results suggest that it is possible to model base flow at the catchment scale, using a Boussinesq‐based metahillslope model. The results further indicate that it is sufficient to use a relatively simple formulation of the infiltration, overland flow, and base flow processes to obtain reasonable estimates of the total catchment discharge.
Energy partitioning between latent and sensible heat flux during the warm season at FLUXNET sites
Authors: Wilson Kell B. , Baldocchi Dennis D. , Aubinet Marc , Berbigier Paul , Bernhofer Christian , Dolman Han , Falge Eva , Field Chris , Goldstein Allen , Granier Andre , Grelle Achim , Halldor Thorgeirsson , Hollinger Dave , Katul Gabriel , Law B. E. , Lindroth Anders , Meyers Tilden , Moncrieff John , Monson Russ , Oechel Walter , Tenhunen John , Valentini Riccardo , Verma Shashi , Vesala Timo , Wofsy Steve
Published: December 2002

The warm season (mid‐June through late August) partitioning between sensible (H) and latent (LE) heat flux, or the Bowen ratio (β = H/LE), was investigated at 27 sites over 66 site years within the international network of eddy covariance sites (FLUXNET). Variability in β across ecosystems and climates was analyzed by quantifying general climatic and surface characteristics that control flux partitioning. The climatic control on β was quantified using the climatological resistance (Ri), which is proportional to the ratio of vapor pressure deficit (difference between saturation vapor pressure and atmospheric vapor pressure) to net radiation (large values of Ri decrease β). The control of flux partitioning by the vegetation and underlying surface was quantified by computing the surface resistance to water vapor transport (Rc, with large values tending to increase β). There was a considerable range in flux partitioning characteristics (Rc, Ri and β) among sites, but it was possible to define some general differences between vegetation types and climates. Deciduous forest sites and the agricultural site had the lowest values of Rc and β (0.25–0.50). Coniferous forests typically had a larger Rc and higher β (typically between 0.50 and 1.00 but also much larger). However, there was notable variability in Rc and Ri between coniferous site years, most notably differences between oceanic and continental climates and sites with a distinct dry summer season (Mediterranean climate). Sites with Mediterranean climates generally had the highest net radiation, Rc, Ri, and β. There was considerable variability in β between grassland site years, primarily the result of interannual differences in soil water content and Rc.
Atmospheric methanol budget and ocean implication
Authors: Heikes Brian G. , Chang Wonil , Pilson Michael E. Q. , Swift Elijah , Singh Hanwant B. , Guenther Alex , Jacob Daniel J. , Field Brendan D. , Fall Ray , Riemer Daniel , Brand Larry
Published: December 2002

Methanol is a biogeochemically active compound and a significant component of the volatile organic carbon in the atmosphere. It influences background tropospheric photochemistry and may serve as a tracer for biogenic emissions. The mass of methanol in the atmospheric reservoir, the annual mass flux of methanol from sources to sinks, and the estimated atmospheric lifetime of methanol in the free troposphere, marine boundary layer, continental boundary layer, and in‐cloud, are evaluated. The atmosphere contains approximately 4 Tg (terragrams, 1012 g) of methanol. Estimates of global methanol sources and sinks total 340 and 270 Tg methanol yr−1, respectively, and are in balance given their estimated precision. Sink terms were evaluated using observed methanol distributions; the total loss is approximately a factor of 5 larger than prior estimates. The adopted source is a factor of 3 larger than its prior estimate. Recent net flux observations and the magnitude of the estimated sink suggest biogenic methanol emissions to be near their current estimated upper limit, >280 Tg methanol yr−1, and this value was adopted. The methanol source will be larger with the inclusion of an argued for oceanic gross emission of 30 Tg methanol yr−1, but a major uncertainty concerns whether the oceans are a major net sink or source of methanol, an issue which will not be resolved without new measurements. Other large uncertainties are the estimates of primary biogenic emissions and gas surface deposition. The first loss estimates of methanol by in‐cloud chemistry and precipitation are presented. They are approximately equal at 10 Tg methanol yr−1, each. These are small in comparison to the surface loss and gas phase photochemical loss estimated here but would be significant additional losses in earlier budgets. Surface exchange processes dominate the atmospheric budget of methanol and its distribution. The atmospheric deposition of methanol and the argued for methanol produced in the upper ocean are ubiquitous sources of C1 substrate capable of sustaining methylotrophic organisms throughout the surface ocean.
Anomalous atmospheric circulation over the Weddell Sea, Antarctica during the Austral summer of 2001/02 resulting in extreme sea ice conditions
Authors: Turner John , Harangozo Stephen A. , Marshall Gareth J. , King John C. , Colwell Steve R.
Published: December 2002

During the Austral summer of 2001/02 exceptionally heavy sea ice conditions were experienced over the eastern Weddell Sea. Satellite microwave imagery showed that large negative (positive) ice anomalies were present from October 2001 to January 2002 over the north‐western Weddell Sea (off the coast of Dronning Maud Land). These were a result of anomalously high (low) atmospheric pressure over the South Atlantic (southern Weddell Sea and Bellingshausen Sea), which gave strong north to north‐westerly cyclonic flow over the northern and eastern Weddell Sea. This resulted in convergence of sea ice into the southern Weddell Sea and inhibited ice advection along the coast of Dronning Maud land. The atmospheric anomalies around the Weddell Sea were part of an Antarctic‐wide amplification of the mean wavenumber 3 pattern resulting in more intrusions of mid‐latitude air into the interior of the continent, giving rise to near‐record warm temperatures at several locations.
Observation of migrating and nonmigrating diurnal tides in the equatorial lower thermosphere
Authors: Oberheide J. , Gusev O. A.
Published: December 2002

During 9 November 1994, the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment measured vertical profiles of temperature up to an altitude of 120 km. Temperatures above 75 km are retrieved from 15 μm CO2 emissions, accounting for the deviation from the local thermodynamical equilibrium (non‐LTE, NLTE). This study presents the first amplitude and phase measurements of global temperature tides in a region of Earth's atmosphere where prior to CRISTA no daytime and nighttime temperature measurements were available. The migrating and 8 nonmigrating components of the diurnal tide are analyzed from 75–120 km and at 7.5°N. Combined amplitudes exceed 80 K with the nonmigrating components dominant above ∼90 km.
The minimum depth of fault failure in compressional environments
Authors: Stanislavsky Eyal , Garven Grant
Published: December 2002

The absence of very shallow seismicity in thrust faults could be due to either a layered pore pressure/depth profile or to heterogeneous lithology of the crust. Poroelasticity equations were solved by the finite element discretization of a two‐dimensional plane strain cross‐section simulating a thrust environment. Although the modeled faults are actively compacting during thrusting, our numerical results show that the pore pressure accumulation in the basement is faster than in the fault zone and therefore the fluid flow is directed into the fault. The combination of heterogeneous rheology, with the existence of hydrostatic fluid, retards failure near the land surface. A layered pore pressure/depth profile, where the pore pressure is hydrostatic in the sediments and near lithostatic in the basement, magnifies this result and failure occurs faster. In fact, with this pore pressure/depth profile, failure is reached at the same depth regardless of the crustal structure we assume.
Mercury concentrations in coastal California precipitation: Evidence of local and trans‐Pacific fluxes of mercury to North America
Authors: Steding Douglas J. , Flegal A. Russell
Published: December 2002

Because of mercury's (Hg) relatively high vapor pressure and long (0.5–2 years) atmospheric residence, there is the potential for long‐range transport of contaminant Hg. Many studies have focused on that transport and deposition in central and eastern North America, Europe, and the Arctic, but there has been little research on the cycling of Hg in the western coast of North America. That deficiency is addressed in this preliminary study, which indicates there is long‐range transport of Hg across the North Pacific. This transport is evidenced by the elevated (relative to equatorial and theoretical baseline) Hg concentrations in rainwater collected on the coast of California, as well as by the positive correlation between North Pacific storm tracks and Hg concentrations, with maximum concentrations associated with storms from 20°–40° latitude. Those tracks trace air masses containing industrial emissions with peak O3 concentrations moving eastward off the Asian continent. The Asian fluxes appear to enhance Hg concentrations both directly, through the emission of particle‐bound Hg and reactive Hg2+, and indirectly, by increasing the rate of oxidation of Hg0 in the atmosphere. Superimposed on the trans‐Pacific background of industrial Hg is a local signal, with elevated concentrations at the urban site relative to the more pristine coastal site in California. This secondary enrichment is tentatively attributed to elevated local emissions of redox species, including O3 and its precursors, which increase oxidation rates of Hg0 in the atmosphere and Hg concentrations in precipitation.
Ribavirin Quantification in Combination Treatment of Chronic Hepatitis C
Authors: Larrat Sylvie , Stanke-Labesque Françoise , Plages Agnès , Zarski Jean-Pierre , Bessard Germain , Souvignet Claude
Published: December 2002

Ribavirin in combination with alpha 2 interferon is the consensus treatment for chronic hepatitis C. However, recent preliminary pharmacological studies have suggested that the bioavailability of ribavirin displays great interindividual variability. In order to monitor serum ribavirin levels during combination treatment, we developed and validated a quantitative assay using an approach adaptable for routine hospital laboratories. The method involved solid-phase extraction on phenyl boronic acid cartridges followed by high-performance liquid chromatography with a C
18
-bonded silica column and a mobile phase containing 10 mM ammonium phosphate buffer (with the pH adjusted to 2.5) and UV detection (207 nm). The sensitivity, recovery, linearity of the calibration curve, intra- and interassay accuracies, precision, and stability at 4°C were consistent with its use in the laboratory routine. In addition, other nucleoside analogues sometimes used with ribavirin in patients coinfected with hepatitis C virus (HCV) and human immunodeficiency virus did not interfere with the quantification of ribavirin levels. The ribavirin concentration was quantified in 24 serum samples from patients with chronic hepatitis C treated with a combination of ribavirin and alpha 2 interferon. The mean serum ribavirin concentration was 2.67 ± 1.06 μg/ml (
n
= 24) at week 12 of treatment (W12) and 3.24 ± 1.35 μg/ml (
n
= 24) at week 24 of treatment (W24). In addition, ribavirin concentrations displayed high interindividual variabilities: the coefficients of variation of the serum ribavirin concentrations adjusted to the administered dose were 44 and 48% at W12 and W24, respectively. Moreover, the ribavirin concentration was higher in patients with a sustained virological response (
n
= 11) than in patients with treatment failure (
n
= 13), with significant intergroup differences at W12 (
P
= 0.030) and W24 (
P
= 0.049). The present study describes a simple analytical method for the quantification of ribavirin in human serum that could be a useful tool for the monitoring of ribavirin concentrations in HCV-infected patients in order to improve the efficacy and safety of therapy with ribavirin plus interferon.
Comparative Molecular Analysis of Community- or Hospital-Acquired Methicillin-Resistant
Staphylococcus aureus
Authors: Fey P. D. , Saïd-Salim B. , Rupp M. E. , Hinrichs S. H. , Boxrud D. J. , Davis C. C. , Kreiswirth B. N. , Schlievert P. M.
Published: December 2002

Community-acquired methicillin-resistant
Staphylococcus aureus
(CA-MRSA) is a growing public health concern that has been associated with pediatric fatalities. It is hypothesized that the evolution of CA-MRSA is a recent event due to the acquisition of
mec
DNA by previously methicillin-susceptible strains that circulated in the community. This study investigated the genetic relatedness between CA-MRSA, hospital-associated MRSA (HA-MRSA), and nonmenstrual toxic shock syndrome (nmTSS) isolates. Thirty-one of 32 CA-MRSA isolates were highly related as determined by pulsed-field gel electrophoresis and
spa
typing yet were distinguishable from 32 HA-MRSA strains. The 31 related CA-MRSA isolates produced either staphylococcal enterotoxin B (
n
= 5) or C (
n
= 26), and none made TSS toxin 1. All CA-MRSA isolates tested contained a type IV staphylococcal cassette chromosome
mec
(SCC
mec
) element. In comparison, none of the HA-MRSA isolates (
n
= 32) expressed the three superantigens. Antibiotic susceptibility patterns were different between the CA-MRSA and HA-MRSA isolates; CA-MRSA was typically resistant only to β-lactam antibiotics. Six of twenty-one nmTSS isolates were indistinguishable or highly related to the CA-MRSA isolates. MnCop, an nmTSS isolate obtained in Alabama in 1986, was highly related to the CA-MRSA isolates except that it did not contain an SCC
mec
element. These data suggest that CA-MRSA strains may represent a new acquisition of SCC
mec
DNA in a previously susceptible genetic background that was capable of causing nmTSS. CA-MRSA poses a serious health risk not only because it is resistant to the antibiotics of choice for community-acquired staphylococcal infections but also because of its ability to cause nmTSS via superantigen production.
Garenoxacin (BMS-284756) and Moxifloxacin in Experimental Meningitis Caused by Vancomycin-Tolerant Pneumococci
Authors: Rodriguez-Cerrato Violeta , McCoig Cindy C. , Saavedra Jesus , Barton Tess , Michelow Ian C. , Hardy Robert D. , Bowlware Karen , Iglehart Janie , Katz Kathy , McCracken George H.
Published: December 2002

The emergence of multidrug-resistant strains of
Streptococcus pneumoniae
drives the development and evaluation of new antipneumococcal agents, especially for the treatment of bacterial meningitis. The aims of the present study were to assess the antibacterial effectiveness of two new quinolones, garenoxacin (BMS; BMS-284756) and moxifloxacin (MOX) in experimental meningitis caused by a vancomycin (VAN)-tolerant
S. pneumoniae
strain and to compare the results with those obtained by therapy with VAN and ceftriaxone (CRO) in combination. Meningitis was induced in young male New Zealand White rabbits by intracisternal inoculation of a VAN-tolerant pneumococcal strain (strain Tupelo) from a child with meningitis. Sixteen hours after inoculation, therapy was given by intravenous administration of BMS at 20 mg/kg of body weight, followed 5 h later by administration at a dosage of 10 mg/kg (
n
= 9 animals) or MOX as two doses of 20 mg/kg every 5 h (
n
= 8 animals). For comparison, we studied the following groups: (i) animals treated with VAN (20 mg/kg every 5 h, three doses) and CRO (125 mg/kg, one dose) (
n
= 9), (ii) animals infected with a VAN-tolerant strain but not treated (
n
= 8), (iii) animals infected with a VAN-tolerant pneumococcus isolated from the nasopharynx of a carrier and treated with BMS (
n
= 8), and (iv) animals infected with a cephalosporin-resistant type 6B
S. pneumoniae
strain and treated with BMS (
n
= 6). The MICs of penicillin, CRO, VAN, BMS, and MOX for the Tupelo strain were 2, 1, 0.5, 0.06, and 0.03 μg/ml, respectively. The rates of killing of strain Tupelo (the change in the log
10
number of CFU per milliliter per hour) in cerebrospinal fluid at 5 h were −0.70 ± 0.35, −0.61 ± 0.44, and −0.49 ± 0.36 for BMS, MOX, and VAN-CRO, respectively. Therapy with BMS and MOX was as effective as therapy with VAN-CRO against VAN-tolerant pneumococcal meningitis in rabbits.
Combination of Drug Level Measurement and Parasite Genotyping Data for Improved Assessment of Amodiaquine and Sulfadoxine-Pyrimethamine Efficacies in Treating
Plasmodium falciparum
Malaria in Gabonese Children
Authors: Aubouy Agnès , Bakary Mohamed , Keundjian Annick , Mbomat Bernard , Makita Jean Ruffin , Migot-Nabias Florence , Cot Michel , Le Bras Jacques , Deloron Philippe
Published: December 2002

Many African countries currently use a sulfadoxine-pyrimethamine combination (SP) or amodiaquine (AQ) to treat uncomplicated
Plasmodium falciparum
malaria. Both drugs represent the last inexpensive alternatives to chloroquine. However, resistant
P. falciparum
populations are largely reported in Africa, and it is compulsory to know the present situation of resistance. The in vivo World Health Organization standard 28-day test was used to assess the efficacy of AQ and SP to treat uncomplicated
falciparum
malaria in Gabonese children under 10 years of age. To document treatment failures, molecular genotyping to distinguish therapeutic failures from reinfections and drug dosages were undertaken. A total of 118 and 114 children were given AQ or SP, respectively, and were monitored. SP was more effective than AQ, with 14.0 and 34.7% of therapeutic failures, respectively. Three days after initiation of treatment, the mean level of monodesethylamodiaquine (MdAQ) in plasma was 149 ng/ml in children treated with amodiaquine. In those treated with SP, mean levels of sulfadoxine and pyrimethamine in plasma were 100 μg/ml and 212 ng/ml, respectively. Levels of the three drugs were higher in patients successfully treated with AQ (MdAQ plasma levels) or SP (sulfadoxine and pyrimethamine plasma levels). Blood concentration higher than breakpoints of 135 ng/ml for MdAQ, 100 μg/ml for sulfadoxine, and 175 ng/ml for pyrimethamine were associated with treatment success (odds ratio: 4.5, 9.8, and 11.8, respectively; all
P
values were <0.009). Genotyping of merozoite surface proteins 1 and 2 demonstrated a mean of 4.0 genotypes per person before treatment. At reappearance of parasitemia, both recrudescent parasites (represented by common bands in both samples) and newly inoculated parasites (represented by bands that were absent before treatment) were present in the blood of most (51.1%) children. Only 3 (6.4%) therapeutic failures were the result not of treatment inefficacy but of new infection. In areas where levels of drug resistance and complexity of infections are high, drug dosage and parasite genotyping may be of limited interest in improving the precision of drug efficacy measurement. Their use should be weighted according to logistical constraints.
Genetic and Functional Analysis of the Chromosome-Encoded Carbapenem-Hydrolyzing Oxacillinase OXA-40 ofAcinetobacter baumannii
Authors: Héritier Claire , Poirel Laurent , Aubert Daniel , Nordmann Patrice
Published: December 2002

Clinical isolateAcinetobacter baumanniiCLA-1 was resistant to a series of antibiotic molecules, including carbapenems. Cloning and expression of the β-lactamase gene content of this isolate inEscherichia coliDH10B identified a chromosome-encoded oxacillinase, OXA-40, that differed by one or two amino acid changes from OXA-24, -25, and -26 and an AmpC-type cephalosporinase. The OXA-40 β-lactamase had a mainly narrow-spectrum hydrolytic profile, but it included ceftazidime and imipenem. Its activity was resistant to inhibition by clavulanic acid, tazobactam, sulbactam, and, like most of the other carbapenem-hydrolyzing oxacillinases, NaCl. OXA-40 had an FGN triad replacing a YGN motif at class D β-lactamase (DBL) positions 144 to 146. Site-directed DNA mutagenesis leading to a Phe-to-Tyr change at DBL position 144 in OXA-40 gave a mutant enzyme with increased hydrolytic activity against most β-lactams, including imipenem. Conversely, with a gene encoding the narrow-spectrum oxacillinase OXA-1 as the template, a nucleotide substitution leading to a Tyr-to-Phe change in the YGN motif of OXA-1 gave a mutant enzyme with decreased hydrolytic activity without an increase in carbapenem-hydrolyzing activity. Thus, the Phe residue in the FGN motif was not associated with carbapenem-hydrolyzing activity by itself but instead was associated with weak overall hydrolytic activity. Finally, this Phe residue in OXA-40 explained resistance to inhibition by NaCl whereas a Tyr residue in motif YGN was related to susceptibility to NaCl.
In Vitro Activities of Daptomycin, Vancomycin, Quinupristin- Dalfopristin, Linezolid, and Five Other Antimicrobials against 307 Gram-Positive Anaerobic and 31
Corynebacterium
Clinical Isolates
Authors: Goldstein Ellie J. C. , Citron Diane M. , Merriam C. Vreni , Warren Yumi A. , Tyrrell Kerrin L. , Fernandez Helen T.
Published: December 2002

The activities of daptomycin, a cyclic lipopeptide, and eight other agents were determined against 338 strains of gram-positive anaerobic bacteria and corynebacteria by the NCCLS reference agar dilution method with supplemented brucella agar for the anaerobes and Mueller-Hinton agar for the corynebacteria. The daptomycin MICs determined on Ca
2+
-supplemented (50 mg/liter) brucella agar plates were one- to fourfold lower than those determined in unsupplemented media. Daptomycin was highly active (MICs, ≤2 μg/ml) against many strains including 36 of 37 peptostreptococci, 37 of 48 isolates of the
Eubacterium
group, and all strains of
Propionibacterium
spp.,
Clostridium perfringens
,
Clostridium difficile
, and other
Clostridium
spp. It was fourfold or greater more active than vancomycin against
Clostridium innocuum
and 16 of 34 strains of vancomycin-resistant lactobacilli. Three strains of
C. difficile
for which quinupristin-dalfopristin and linezolid MICs were >8 μg/ml were inhibited by <1 μg of daptomycin per ml. Daptomycin MICs were ≥4 μg/ml for most strains of
Clostridium clostridioforme
,
Clostridium paraputrificum
,
Clostridium tertium
, and
Clostridium ramosum
; the isolates were generally more resistant to other antimicrobials. Daptomycin was two- to fourfold less active against
Actinomyces
spp. than vancomycin, quinupristin-dalfopristin, or linezolid. Twenty-nine of 31 strains of
Corynebacterium
spp., including
Corynebacterium jeikeium
,
Corynebacterium amycolatum
, and
Corynebacterium pseudodiphtheriticum
, were inhibited by ≤0.25 μg of daptomycin per ml. For two strains of “
Corynebacterium aquaticum
,” 8 μg of daptomycin per ml was required for inhibition. Daptomycin demonstrated very good activities against a broad range of gram-positive organisms including vancomycin-resistant
C. innocuum
and lactobacillus strains and quinupristin-dalfopristin- and linezolid-resistant
C. difficile
strains.
In Vitro Activities of Linezolid against Clinical Isolates of
Mycobacterium tuberculosis
That Are Susceptible or Resistant to First-Line Antituberculous Drugs
Authors: Alcalá Luis , Ruiz-Serrano María Jesús , Pérez-Fernández Turégano Cristina , García de Viedma Darío , Díaz-Infantes Marisol , Marín-Arriaza Mercedes , Bouza Emilio
Published: December 2002

We evaluated 117 isolates of
Mycobacterium tuberculosis
for susceptibility to linezolid by the proportion and E-test methods. Linezolid showed high in vitro activity, with all the strains inhibited by ≤1 μg of the drug per ml. E-test MICs were at least 4 dilutions lower than their equivalents by the standard proportion method.
Activation and Deactivation of a Broad-Spectrum Antiviral Drug by a Single Enzyme: Adenosine Deaminase Catalyzes Two Consecutive Deamination Reactions
Authors: Wu Jim Zhen , Walker Heli , Lau Johnson Y. N. , Hong Zhi
Published: December 2002

Ribavirin is an approved broad-spectrum antiviral drug. A liver-targeting prodrug of ribavirin, viramidine, is in clinical trial in an attempt to provide a better therapeutic index. The conversion of viramidine to ribavirin, and of ribavirin to an inactive metabolite through adenosine deaminase, is reported. Kinetic analysis indicates that adenosine deaminase is likely involved in activation of viramidine in vivo, and the process is highly pH sensitive. The differential activities of two consecutive deamination reactions are kinetically studied and interpreted based on adenosine deaminase structural information. A comprehensive understanding of the viramidine and ribavirin deamination mechanism should help in designing better nucleoside therapeutics in the future.
Clinical
Trichophyton rubrum
Strain Exhibiting Primary Resistance to Terbinafine
Authors: Mukherjee Pranab K. , Leidich Steven D. , Isham Nancy , Leitner Ingrid , Ryder Neil S. , Ghannoum Mahmoud A.
Published: December 2002

The in vitro antifungal susceptibilities of six clinical
Trichophyton rubrum
isolates obtained sequentially from a single onychomycosis patient who failed oral terbinafine therapy (250 mg/day for 24 weeks) were determined by broth microdilution and macrodilution methodologies. Strain relatedness was examined by random amplified polymorphic DNA (RAPD) analyses. Data obtained from both broth micro- and macrodilution assays were in agreement and revealed that the six clinical isolates had greatly reduced susceptibilities to terbinafine. The MICs of terbinafine for these strains were >4 μg/ml, whereas they were <0.0002 μg/ml for the susceptible reference strains. Consistent with these findings, the minimum fungicidal concentrations (MFCs) of terbinafine for all six strains were >128 μg/ml, whereas they were 0.0002 μg/ml for the reference strain. The MIC of terbinafine for the baseline strain (cultured at the initial screening visit and before therapy was started) was already 4,000-fold higher than normal, suggesting that this is a case of primary resistance to terbinafine. The results obtained by the broth macrodilution procedure revealed that the terbinafine MICs and MFCs for sequential isolates apparently increased during the course of therapy. RAPD analyses did not reveal any differences between the isolates. The terbinafine-resistant isolates exhibited normal susceptibilities to clinically available antimycotics including itraconazole, fluconazole, and griseofulvin. However, these isolates were fully cross resistant to several other known squalene epoxidase inhibitors, including naftifine, butenafine, tolnaftate, and tolciclate, suggesting a target-specific mechanism of resistance. This is the first confirmed report of terbinafine resistance in dermatophytes.