bluuebunny/crossref_metadata_2025 huggingface dataset:
The occurrence and epidemiology of Salmonella in European pig slaughterhouses
Authors: HALD T. , WINGSTRAND A. , SWANENBURG M. , von ALTROCK A. , THORBERG B.-M.
Published: December 2003

This study was part of an international research project entitled SALINPORK (FAIR CT-950400) initiated in 1996. The objectives were to investigate the occurrence of Salmonella in pig slaughterhouses and to identify risk factors associated with the contamination of pig carcasses. Data was collected from 12 slaughterhouses in five European countries. Isolates were characterized by serotyping, phage typing and antimicrobial susceptibility. In one country, no Salmonella was found. Salmonella was isolated from 5·3% of 3485 samples of pork and from 13·8% of 3573 environmental samples from the seven slaughterhouses in the four remaining countries. The statistical analyses (multi-level logistic regression) indicated that the prevalence was significantly higher during the warmer months and that the environmental contamination increased during the day of slaughter. The polishing (OR 3·74, 95% CI 1·43–9·78) and pluck removal (OR 3·63, 95% CI 1·66–7·96) processes were found to contribute significantly to the total carcass contamination, the latter especially if the scalding water also was contaminated. To reduce carcass contamination, it is recommended to ensure sufficiently high temperatures of scalding water (62 °C) and appropriate cleaning and disinfection of the polishing equipment at least once a day in order to reduce the level of carcass contamination and consequently the prevalence of Salmonella in pork.
Routes for Campylobacter contamination of poultry meat: epidemiological study from hatchery to slaughterhouse
Authors: HERMAN L. , HEYNDRICKX M. , GRIJSPEERDT K. , VANDEKERCHOVE D. , ROLLIER I. , De ZUTTER L.
Published: December 2003

From April 1998 to March 2000, 18 broiler flocks were followed from the hatchery to the slaughterhouse. Campylobacter was not found in the hatchery, 1-day-old chicks or in the rearing house before the arrival of the chicks. The infection of broiler flocks increased continuously during the rearing time, with a total of seven positive flocks at the end of rearing. Farms with Campylobacter-positive broilers were characterized by the circulation of Campylobacter in the environment (puddles, dung hill) and on the footwear of the farmer. The administration of antibiotics did not significantly reduce Campylobacter shedding. With the exception of one flock during rearing and a few flocks in the slaughterhouse with a mixed Campylobacter coli–Campylobacter jejuni infection, C. jejuni exclusively was found both during rearing and on the carcasses. A significant correlation exits between the contamination of the broilers during rearing and the carcasses after processing. No slaughterhouse was able to avoid contamination of carcasses when status-positive animals were delivered. Moreover, six negatively delivered flocks yielded positive carcasses, the result of a supplementary contamination, which occurred during transport and slaughtering.
Outbreaks of Escherichia coli O157 infections at multiple county agricultural fairs: a hazard of mixing cattle, concession stands and children
Authors: CRUMP JOHN A. , BRADEN CHRISTOPHER R. , DEY MEGHAN E. , HOEKSTRA R. MICHAEL , RICKELMAN-APISA JANET M. , BALDWIN DAVID A. , DE FIJTER SIETSKE J. , NOWICKI SCOTT F. , KOCH ELIZABETH M. , BANNERMAN TAMMY L. , SMITH FORREST W. , SARISKY JOHN P. , HOCHBERG NATASHA , MEAD PAUL S.
Published: December 2003

Escherichia coli O157 infections cause an estimated 60 deaths and 73000 illnesses annually in the United States. A marked summer peak in incidence is largely unexplained. We investigated an outbreak of E. coli O157 infections at an agricultural fair in Ohio and implicated consumption of beverages made with fairground water and sold by a geographically localized group of vendors who were all on the same branch of the fairground water distribution system. To examine county fair attendance as a risk factor for infection, we conducted two further epidemiological studies. In the first, we enhanced surveillance for E. coli O157 infections in 15 Northeast Ohio counties during the 2000 agricultural fair season and showed increased risk of E. coli O157 infection among fair attendees. In the second study, we examined Ohio Public Health Laboratory Information Service (PHLIS) data for 1999 using a time-varying covariate proportional hazards model and demonstrated an association between agricultural fairs and E. coli O157 infections, by county. Agricultural fair attendance is a risk factor for E. coli O157 infection in the United States and may contribute to the summer peak in incidence. Measures are needed to reduce transmission of enteric pathogens at agricultural fairs.
Community-based estimates of incidence and risk factors for childhood pneumonia in Western Sydney
Authors: MacINTYRE C. R. , McINTYRE P. B. , CAGNEY M.
Published: December 2003

The aim was to estimate the community incidence and risk factors for all-cause pneumonia in children in Western Sydney, Australia. A cross-sectional randomized computer-assisted telephone interview was conducted in July 2000, in Western Sydney. Parents of 2020 children aged between 5 and 14 years were interviewed about their child's respiratory health since birth. No verification of reported diagnosis was available. Logistic regression analysis was used to determine risk factors for pneumonia. A lifetime diagnosis of pneumonia was reported in 137/2020 (6·8%) children, giving an estimated incidence in the study sample of 7·6/1000 person-years. Radiological confirmation was reported in 85% (117/137). Hospitalization was reported in 41% (56/137) and antibiotic therapy in 93% (127/137) of cases. Using logistic regression modelling, statistically significant associations with pneumonia were a reported history of either asthma, bronchitis or other lung problems and health problems affecting other systems. In most cases, the diagnosis of asthma preceded the diagnosis of pneumonia. The community incidence of all causes of pneumonia is not well enumerated, either in adults or in children. This study provides community-based incidence data. The incidence of hospitalization for pneumonia in this study is comparable to estimates from studies in comparable populations, suggesting that retrospective parental report for memorable events is likely to be valid. We found a relationship between pneumonia and childhood respiratory diseases such as asthma, which has implications for targeted vaccination strategies.
Effect of clinical and socio-economic factors on the rate of clustering of Mycobacterium tuberculosis clinical isolates in Elche (Spain)
Authors: RUIZ M. , NAVARRO J. F. , RODRÍGUEZ J. C. , LARROSA J. A. , ROYO G.
Published: December 2003

We studied the association that exists between the epidemiological type clustering of isolates of Mycobacterium tuberculosis and certain clinical, epidemiological and socio-economic characteristics of tuberculosis patients in the Elche health district of Spain. A total of 144 patients diagnosed between 1993 and 1999 and whose isolates had been genotyped by IS6110–RFLP in an earlier study were included. Multivariate analysis showed that the independent variables associated with clustering of strain types were: age (1–25 years, OR 2·92, 95% CI 0·83–10·3), a high percentage of infection in the first circle of contacts (OR 2·89, 95% CI 0·96–8·68), urban dwelling (OR 2·12, 95% CI 0·73–6·2), use of bronchoscopy to obtain samples (OR 16·3, 95% CI 2·3–11·5) and working contact with many people (OR 2·81, 95% CI 0·94–8·3). These data contribute to a better understanding of the epidemiology of tuberculosis and improved systems of control.
Community-acquired Legionnaires' Disease in Nottingham – too many cases?
Authors: LIM W. S. , SLACK R. , GOODWIN A. , ROBINSON J. , LEE J. V. , JOSEPH C. , NEAL K.
Published: December 2003

The aim of this study was to compare the incidence of community-acquired Legionnaires' Disease in Nottingham with England and Wales and to explore reasons for any difference observed. Based on data from the National Surveillance Scheme for Legionnaires' Disease (1980–1999), the rate of infection in England and Wales was 1·3 per million/year compared with 6·6 per million/year in Nottingham. Domestic water samples were obtained from 41 (95%) of 43 Nottingham cases between 1997 and 2000. In 16 (39%) cases, Legionella sp. were cultured in significant quantities. Proximity to a cooling tower was examined using a 1[ratio ]4 case-controlled analysis. No significant difference in the mean distance between place of residence to the nearest cooling tower was noted (cases 2·7 km vs. controls 2·3 km; P=0·5). These data suggest that Nottingham does have a higher rate of legionella infection compared to national figures and that home water systems are a source.
Homocystinuria due to cystathionine β‐synthase deficiency: Novel biochemical findings and treatment efficacy
Authors: Orendáč M. , Zeman J. , Stabler S. P. , Allen R. H. , Kraus J. P. , Bodamer O. , Stöckler‐Ipsiroglu S. , Kvasnička J. , Kožich V.
Published: December 2003

Summary: To explore the pathogenesis of cystathionine β‐synthase (CBS) deficiency and to test the efficacy of pharmacological therapy we examined a panel of metabolites in nine homocystinuric patients under treated and/or untreated conditions. Off pharmacological treatment, the biochemical phenotype was characterized by accumulation of plasma total homocysteine (median 135 µmol/L) and blood S‐adenosylhomocysteine (median 246 nmol/L), and by normal levels of guanidinoacetate and creatine. In addition, enhanced remethylation was demonstrated by low serine level (median 81 µmol/L), and by increased concentration of methionine (median 76 µmol/L) and N‐methylglycine (median 6.8 µmol/L). Despite the substantially blocked transsulphuration, which was evidenced by undetectable cystathionine and severely decreased total cysteine levels (median 102 µmol/L), blood glutathione was surprisingly not depleted (median 1155 µmol/L). In 5 patients in whom pharmacological treatment was withdrawn, the differences of median plasma total homocysteine levels (125 µmol/L after withdrawal versus 33 µmol/L under treatment conditions), total cysteine levels (139 versus 211 µmol/L) and plasma serine levels (53 versus 103 µmol/L) on and off treatment demonstrated the efficacy of long‐term pyridoxine/betaine administration (p<0.05). The treatment also decreased blood S‐adenosylhomocysteine level (133 versus 59 nmol/L) with a borderline significance. In summary, our study shows that conventional treatment of CBS deficiency by diet and pyridoxine/betaine normalizes many but not all metabolic abnormalities associated with CBS deficiency. We propose that the finding of low plasma serine concentration in untreated CBS‐deficient patients merits further exploration since supplementation with serine might be a novel and safe component of treatment of homocystinuria.
Molecular genetic analysis of glycogen storage disease type Ia in 26 Chinese patients
Authors: Qiu W. J. , Gu X. F. , Ye J. , Han L.Sh. , Zhang Y. F. , Liu X. Q.
Published: December 2003

Summary: Sequence analysis of 26 patients from Mainland China with glycogen storage disease type Ia revealed a high frequency of two mutations in the glucose‐6‐phosphatase gene. These mutations, 727G>T and R83H, were also found to be in linkage disequilibrium with a polymorphism at position 1176. These findings have implications for carrier detection and prenatal diagnosis of this disease in the Chinese population.
Clinical heterogeneity in patients with mutations in the NDUFS4 gene of mitochondrial complex I
Authors: Budde S. M. S. , van den Heuvel L. P. W. J. , Smeets R. J. P. , Skladal D. , Mayr J. A. , Boelen C. , Petruzzella V. , Papa S. , Smeitink J. A. M.
Published: December 2003

Summary: A comparison of the clinical presentation, disease course and results of laboratory and imaging studies of all patients so far published with a NDUFS4 mutation are presented. This reveals marked clinical heterogeneity, even in patients with the same genotype.
Global Predictability of Chaotic Epidemiological Dynamics in Coupled Populations
Authors: Davison Matt , Essex C. , Shiner J. S.
Published: December 2003

When the dynamics of an epidemic are chaotic, detailed prediction is effectively impossible, except perhaps in the short term. However, a probability distribution underlying the motion does allow for the long term prediction of statistical measures such as the mean or the standard deviation. Even this weaker long term predictability might be lost if distinct populations with chaotic dynamics are coupled. We show that such coupling can result in a phenomenon we call “sensitive dependence on neglected dynamics”. In light of this phenomenon, it is somewhat surprising that when two logistic maps are coupled, the long term predictability of the mean and standard deviation is maintained. This is true even though the probability distribution describing the time series depends on the coupling strength. The coupling-strength dependence does reveal itself in the loss of predictability of higher order moments such as skewness and kurtosis.
Self-Organizing Approach for Automated Gene Identification
Authors: Zinovyev Andrey Yu. , Gorban Alexander N. , Popova Tatyana G.
Published: December 2003

Self-training technique for automated gene recognition both in entire genomes and in unassembled ones is proposed. It is based on a simple measure (namely, the vector of frequencies of non-overlapping triplets in sliding window), and needs neither predetermined information, nor preliminary learning. The sliding window length is the only one tuning parameter. It should be chosen close to the average exon length typical to the DNA text under investigation. An essential feature of the technique proposed is preliminary visualization of the set of vectors in the subspace of the first three principal components. It was shown, the distribution of DNA sites has the bullet-like structure with one central cluster (corresponding to non-coding sites) and three or six flank ones (corresponding to protein-coding sites). The bullet-like structure itself revealed in the distribution seems to be very interesting illustration of triplet usage in DNA sequence. The method was examined on several genomes (mitochondrion of P.wickerhamii, bacteria C.crescentus and primitive eukaryot S.cerevisiae). The percentage of truly predicted nucleotides exceeds 90%.
Minimal Work for Separation Processes of Binary Mixtures
Authors: Amelkin S. A. , Tsirlin A. M. , Burzler J. M. , Schubert S. , Hoffmann K. H.
Published: December 2003

The work expenditures for both perfect and imperfect separation processes are well known for the reversible case; yet such a description is often far from reality. Real processes operate at finite times and non-zero rates leading to an additional, irreversible energy expenditure. This paper employs an idealized van t'Hoff chamber as a theoretical model to derive lower bounds for the irreversible work in real separation processes such as membrane separation. Methods of optimal control for open systems and nonlinear programming of averaged problems are used to calculate the optimal mass transfer kinetics for the finite-time separation of binary mixtures of ideal gases.
On Some Nonendoreversible Engine Models with Nonlinear Heat Transfer Laws
Authors: Arias-Hernández L. A. , de Parga G. Ares , Angulo-Brown F.
Published: December 2003

In this work, we analyze a nonendoreversible thermal engine model with a nonlinear heat transfer law between the heat reservoirs and the working fluid under two optimization criteria: the maximum power regime and the so-called ecological criterion. We find that this nonendoreversible model has a similar behaviour to that shown by De Vos (Am. J. Phys. 53, 570 (1985)) for endoreversible models with two thermal conductances with only one superior conductance and with only one inferior conductance, respectively. The model is compared with two sets of real power plants, the first one containing power plants of old design (before 1960's) and the second one being formed by modern nuclear power plants. Our results suggest that the first group was designed under conditions which are reminiscent of a maximum power regime and the second one under an ecological-like criterion. We also study some general properties of nonendoreversible thermal engine models.
Performance Optimization of a Combined Heat Pump Cycle
Authors: Chen Lingen , Bi Yuehong , Sun Fengrui , Wu Chih
Published: December 2003

A steady flow combined heat pump cycle model with heat resistance, heat leakage and internal irreversibility is built in this paper. The optimal performance of the model is studied. The relation between optimal heating load and coefficient of performance (COP), as well as the maximum COP and the corresponding heating load are derived.
Thermodynamic Analysis on Thermoacoustic Self-Excited Oscillation
Authors: Li Qing , Wu Feng , Guo Fangzhong , Wu Chili , Wu Jihao
Published: December 2003

Thermodynamic mechanism of thermoacoustic self-excited oscillation is analyzed in this paper. The law of minimizing entropy flow is obtained basing on the fundamentals of finite-time thermodynamics. The results obtained here show that the thermoacoustic self-excited oscillation, which is a non-isentropic oscillation with power-output corresponding to a limit cycle in the phase space takes place when hot temperature Th exceeds a threshold value [Formula: see text]. The effect of nonlinear terms on the system will lead to the second harmonic wave.
Oxygen isotope content of CO2 in nocturnal ecosystem respiration: 2. Short‐term dynamics of foliar and soil component fluxes in an old‐growth ponderosa pine forest
Authors: Bowling D. R. , McDowell N. G. , Welker J. M. , Bond B. J. , Law B. E. , Ehleringer J. R.
Published: December 2003

The oxygen isotope contents (δ18O) of soil, xylem, and leaf water and ecosystem respiration were studied in a ponderosa pine forest during summer 2001. Our goal was to assess whether δ18O of CO2 could be used to quantify the relative contributions of soil and foliar respiration to total nocturnal ecosystem respiration. The δ18O in leaf and soil water showed enrichment over a 2‐week sampling period as the weather became hot and dry (leaves 0.9 to 15.0‰, and soil −10.4 to −3.1‰), while δ18O of xylem water remained constant (−12.9‰). Water in the soil was enriched in 18O near the soil surface (−6.4‰ at 5 cm depth) relative to greater depths (−11.1‰ at 20 cm). The δ18O of ecosystem respiration became gradually enriched over the 2‐week sampling period (from 24.2 initially to 32.9‰ at the end, VSMOW scale). Soil respiration contributed 80 ± 12 percent to the total respiratory flux, close to estimates from scaled‐up chamber data (77% [Law et al., 2001a]). Quantitative application of the isotopic approach to determine respiratory proportions required direct measurement of δ18O of soil and xylem water, air and soil temperature, and humidity. Better estimates of the isotopic signatures of component fluxes could be achieved with additional measurements and more detailed modeling. Results demonstrate that (1) there is variability in δ18O of precipitation inputs to ecosystems, (2) immediately following a precipitation event, δ18O of ecosystem respiration may reflect δ18O of precipitation, (3) periods of hot dry weather can substantially enrich ecosystem water pools and subsequently alter the isotope content of CO2 in ecosystem respiration, and (4) stable oxygen isotopes in CO2 can be used to quantify the foliar and soil components of ecosystem respiration.
Active phases and pauses during the installation of the West African monsoon through 5‐day CMAP rainfall data (1979–2001)
Authors: Louvet S. , Fontaine B. , Roucou P.
Published: December 2003

Objective diagnostic analyses based on PCA decomposition, Varimax rotation and low‐pass filters (≥1 month) are performed on the 5‐day CMAP rainfall data over West Africa. The northward excursion of the rainbelt can be divided into 4 basic subperiods each composed of an equilibrium period (pause) followed by a rapid increase (active phase) of the system. We suggest easy criteria to automatically detect these events and propose a calendar for the 23 years. The pauses are centered around 27–28 March (pause #1), between 29 April and 2 May (pause #2), 11 June (pause #3) and 24 July (pause # 4) with standard deviations of 7–11 days. The phase of any pause impacts on the phase of other pauses. Pause #4, starting earlier, is preceded by earlier pauses #2 and #3, then is followed by an earlier annual rainfall maximum and more abundant June–August amounts.
Modeled spectral optical properties for smoke aerosols in Amazonia
Authors: Procopio A. S. , Remer L. A. , Artaxo P. , Kaufman Y. J. , Holben B. N.
Published: December 2003

The optical properties of aerosols from biomass burning in Brazil were derived from measurements by the AERONET sun photometer network in Amazonia. A dynamical aerosol model was constructed from Mie Theory calculations, using as input a constant complex refractive index and the average size distribution of aerosols for 12 ranges of aerosol optical thickness. The aerosol optical properties were described for 24 wavelengths in the spectral range of 0.20–3.00 μm. The model was used to simulate radiances and irradiances and the results agreed well with the measurements. The derived optical model is immediately applicable to estimate aerosol forcing by biomass burning aerosol emitted on the development frontier in Amazonia.
On the transmission line model for lightning return stroke representation
Authors: Baba Y. , Rakov V. A.
Published: December 2003

The widely used transmission‐line (TL) model of lightning return stroke in a vertical channel is most rigorously represented by a vertical phased array of current sources that produce a spherical transverse electromagnetic (TEM) wave in the case of return‐stroke speed v equal to the speed of light c. If the radius of the lightning channel were equal to zero, the equivalent representation could be obtained by applying a hypothetical infinitesimal source of pure spherical TEM wave at the bottom of the channel. A non‐zero‐radius vertical wire above ground excited by a practical source at its bottom end cannot support unattenuated current waves, and the associated electromagnetic field structure is non‐TEM.
Widespread persistent near‐surface ozone depletion at northern high latitudes in spring
Authors: Zeng Tao , Wang Yuhang , Chance Kelly , Browell Edward V. , Ridley Brian A. , Atlas Elliot L.
Published: December 2003

Springtime near‐surface ozone depletion has been observed at northern high latitudes. Due to limited observations, the spatial and temporal extent of low O3 concentrations near the surface is still unknown. A regional 3‐D chemistry and transport model is applied to simulate surface O3 depletion catalyzed by bromine radicals at northern high latitudes in March and April 2000. Satellite observations of BrO column by the ESA Global Ozone Monitoring Experiment (GOME) were processed to specify the BrO concentrations in the lower troposphere. In view of the GOME measurement and model uncertainties, the model results show an adequate agreement with the O3 depletion events observed at two surface sites, Alert, Canada (82.5°N, 62.3°W) and Barrow, Alaska (71.3°N, 156.6°W), and by airborne in situ and DIAL instrument during the TOPSE experiments at northern high latitudes. Low O3 events at Alert appear to be mostly driven by transport of O3‐poor air from high BrO regions. Model results indicate that low O3 concentrations (<20 ppbv) near the surface cover ∼60% of the northern high latitudes and that the depleted O3 concentrations (<10 ppbv) cover ∼20% of the region in April. The high BrO events tend to be large‐scale and persistent (1–2 weeks). We find that they are correlated with low temperature, a condition conducive for heterogeneous reactions on frozen snow or aerosol surfaces.
A correspondence of altimetric gravity texture to abyssal hill morphology along the flanks of the Southeast Indian Ridge
Authors: Goff John A. , Smith Walter H. F.
Published: December 2003

We examine the relationship between altimetric gravity and abyssal hill textures along the flanks of Southeast Indian Ridge, where previous studies observed a progressive west‐to‐east increase in abyssal hill roughness and scales. Such a relationship is often considered unlikely because abyssal hills are typically smaller than upward continuation filter scales. However, our results, which exclude ridges, fracture zones and large pseudofaults, show that altimetric gravity roughness and characteristic scales in this region also increase from west to east and, at the largest scales, gravity texture exhibits ridge‐parallel lineaments. Synthetic profiles also demonstrate how the texture parameters of a filtered field are related to those of the unfiltered field, particularly where the characteristic scale of the latter is smaller than the filter length.
Does the aurora provide evidence for the occurrence of antiparallel magnetopause reconnection?
Authors: Sandholt P. E. , Farrugia C. J.
Published: December 2003

Antiparallel merging at the magnetopause predicts a longitudinal bifurcation of the cusp during intervals of southeast or southwest interplanetary magnetic field (IMF) orientation. In the aurora this should manifest itself as a longitudinal gap in the midday sector, bracketed by bright auroral forms on either side. With the purpose of testing this prediction, we searched for an auroral signature in our database from the arctic islands of Svalbard, focusing on strong, isolated auroral brightenings belonging to the category of events which has been previously established as a signature of transient magnetopause reconnection (flux transfer events (FTEs)). We found some very interesting events, showing clear brightenings in the eastern and western parts of the field of view (FOV), with a gap in between. In this paper we present a 1 hour long interval of auroral observations in the 1100–1400 MLT sector, showing two strong, isolated auroral events, which were separated by 20 min. The IMF was steady and directed southeast (By = 3 nT; Bz = −3 nT; clock angle = 135°), in a solar wind of low speed (370 km s−1) and low dynamic pressure (0.2 nPa). Each auroral event is characterized by an initial, strong brightening of the cusp equatorward boundary, previously referred to as equatorward boundary intensification (EBI), which is followed by a westward and poleward moving auroral form (PMAF). The main point here is that the initial brightening is longitudinally bifurcated, with near‐simultaneous auroral brightenings in the eastern (1300–1400 MLT) and western (1100–1130 MLT) parts of the all‐sky camera FOV being separated by a ∼500 km wide “gap.” The brightening event is discussed as a possible signature of transient, antiparallel reconnection, taking place at high magnetopause latitudes, while the “gap” aurora is attributed to quasi steady component reconnection in the subsolar region.
Yucatan Channel flow: Observations versus CLIPPER ATL6 and MERCATOR PAM models
Authors: Candela Julio , Tanahara Sorayda , Crepon Michel , Barnier Bernard , Sheinbaum Julio
Published: December 2003

The statistical properties of the flow structure in the Yucatan Channel's main section based on 2 years of continuous observations (August 1999 to June 2001) are compared with those simulated by the Océan Parallélisé (OPA) primitive equation model in two different configurations: the ATL6 configuration from the CLIPPER project (the whole Atlantic domain with a 1/6° resolution), and the Prototype Atlantique Méditerranée (PAM) configuration from the MERCATOR project (the North Atlantic domain with 1/12° resolution). While the observed 2‐year mean transport into the Gulf of Mexico is 23.06 Sv, ATL6 has a 5‐year mean of 27.49 Sv and PAM has a 3‐year mean of 29.06 Sv. Apart from this discrepancy in the mean transport both simulations are able to reproduce well, in structure and magnitude, details of the mean current and its variability. Features like the Yucatan Current core and the deep countercurrents in the Yucatan and Cuban sides are both well reproduced, as is the presence of a minimum surface current variability at the center of the channel. The two principal empirical modes of current variability, which are related to the passage of eddies through the channel, are also reproduced by the simulations. The observed and simulated transports above and below the 6°C isotherm show no coherency at any frequency except for a significant coherent peak at a period around 20 days, which we interpret as a first baroclinic Kelvin mode between the two layers. As in the observations, the shedding of eddies by the Loop Current in the simulations is preceded by periods of diminished negative horizontal vorticity flux into the Gulf of Mexico.
Reactive organic species in the northern extratropical lowermost stratosphere: Seasonal variability and implications for OH
Authors: Scheeren H. A. , Fischer H. , Lelieveld J. , Hoor P. , Rudolph J. , Arnold F. , Bregman B. , Brühl C. , Engel A. , van der Veen C. , Brunner D.
Published: December 2003

We present C2–C6 nonmethane hydrocarbon (NMHC) measurements from canister samples obtained in the extratropical lower stratosphere during the fall (November/December 1995), winter (March 1997), and summer seasons (July 1998) as part of the stratosphere‐troposphere experiments by aircraft measurements campaign. The flights were carried out from Amsterdam (Netherlands, 52°N, 4.5°E) during fall, from Kiruna (Sweden, 68°N, 20°E) during winter, and from Timmins (Canada, 48.2°N, 70.3°W) during summer. The NMHC measurements have been evaluated along with concurrent in situ measurements of acetone (CH3COCH3), CO, O3, N2O, and CFC‐12 (CCl2F2). The vertical distributions of NMHC and acetone as a function of O3 and potential temperature in the lowermost stratosphere show a strong seasonality. Enhanced concentrations of NMHC + CH3COCH3 were found during July up to potential temperatures of Θ = 370 K, whereas during March this was limited to Θ = 340 K, in agreement with stronger isentropic cross‐tropopause transport during summer. Increasing methyl chloride (CH3Cl) concentrations with altitude were measured during July, pointing to mixing at the subtropical tropopause. During summer and fall, mean NMHC + acetone concentrations were more than a factor of 2 higher than that during winter. Box model calculations indicate that the observed acetone levels of 0.5–1 ppbv can explain 30–50% of the enhanced OH radical concentrations in the summertime lowermost stratosphere. Using mass balance calculations, we show that a significant tropospheric fraction (≤30%) was present up to Θ = 370 K in the summertime lowermost stratosphere. During winter, the tropospheric fraction approached zero at about Θ = 350 K. The time between selected troposphere‐to‐stratosphere mixing events and the aircraft measurements has been estimated at 3–14 days. Our results emphasize that isentropic cross‐tropopause transport can be a fast process occurring on timescales of days to weeks.
Variability in surface ozone background over the United States: Implications for air quality policy
Authors: Fiore A. , Jacob D. J. , Liu H. , Yantosca R. M. , Fairlie T. D. , Li Q.
Published: December 2003

The U.S. Environmental Protection Agency (EPA) presently uses a 40 ppbv background O3 level as a baseline in its O3 risk assessments. This background is defined as those concentrations that would exist in the absence of North American emissions. Lefohn et al. [2001] have argued that frequent occurrences of O3 concentrations above 50–60 ppbv at remote northern U.S. sites in spring are of stratospheric origin, challenging the EPA background estimate and implying that the current O3 standard (84 ppbv, 8‐hour average) may be unattainable. We show that a 3‐D global model of tropospheric chemistry reproduces much of the observed variability in U.S. surface O3 concentrations, including the springtime high‐O3 events, with only a minor stratospheric contribution (always <20 ppbv). We conclude that the previous interpretations of a stratospheric source for these events underestimated the role of regional and hemispheric pollution. While stratospheric intrusions might occasionally elevate surface O3 at high‐altitude sites, our results indicate that these events are rare and would not compromise the O3 air quality standard. We find that the O3 background is generally 15–35 ppbv, with some incidences of 40–50 ppbv in the west in spring at high‐elevation sites (>2 km). It declines from spring to summer and further decreases during O3 pollution episodes. The 40 ppbv background assumed by EPA thus actually underestimates the risk associated with O3 during polluted conditions. A better definition would represent background as a function of season, altitude, and total surface O3 concentration. Natural O3 levels are typically 10–25 ppbv and never exceed 40 ppbv. International controls to reduce the hemispheric pollution background would facilitate compliance with an AOT40‐type standard (cumulative exposure to O3 above 40 ppbv) in the United States.
Effect of wind speed on columnar aerosol optical properties at Midway Island
Authors: Smirnov A. , Holben B. N. , Eck T. F. , Dubovik O. , Slutsker I.
Published: December 2003

Aerosol optical properties over Midway Island in the central Pacific Ocean are considered in conjunction with the information on surface wind speed. In general, optical conditions over Midway resemble aerosol found over other maritime locations in the Pacific Ocean (Lanai, Tahiti, and Nauru). The most frequently occurring values of aerosol optical depth at 500‐nm wavelength and Angstrom parameter are 0.06 and ∼0.40, respectively. Empirical relationships are established between columnar aerosol optical properties and surface wind speed. Increased emission of sea‐salt aerosols at greater wind speeds primarily influenced aerosol optical depth at infrared wavelengths. The correlation coefficient between 24 hour average surface wind speed and aerosol optical depth, although not high (0.52 at a 1020 nm wavelength), is statistically significant at a 99% confidence level. Wind speed anticorrelates with the Angstrom parameter owing to an influx of large particles from the surface. Wind speed influences primarily the coarse fraction (radius > 0.5 μm) concentration of the retrieved columnar size distribution (correlation coefficient 0.56). Effective radii of the retrieved fine and coarse modes are found to be independent of wind speed. Average size distributions for various wind speed bins can be very well simulated with the maritime aerosol component model.
How do the strongest radio pulses from thunderstorms relate to lightning flashes?
Authors: Jacobson Abram R.
Published: December 2003

We present a statistical analysis of thunderstorm radio frequency and optical data from the FORTE satellite to examine the relationship of strong radio frequency pulsed emissions to more conventional signals from lightning. The study is built on a FORTE database of intracloud pulsed radio signals from storms whose geolocation is provided either by coincidence with the FORTE optical imager or by coincidence with ground‐based lightning‐detection arrays. We show statistically that intracloud radio emissions with peak power >40 kW in the FORTE low band (26–48 MHz) have unique characteristics compared to weaker emissions, including: occurring either in isolation or at the start of leader progression but never within a progressing leader; occurring without light emission detectable by FORTE; sometimes occurring in association with a rapid (10 μs) relaxation of the electric charge; and being followed by an upward progressing leader in the cases where a leader is initiated. These strong intracloud radio pulses appear to be associated with an intracloud discharge process that is physically distinct from conventional leader progression.
Nonlinear modeling of mean flow redistribution in curved open channels
Authors: Blanckaert Koen , de Vriend Huib J.
Published: December 2003

Phenomena concerning flow, morphology, and water quality in rivers are often investigated by means of a depth‐integrated flow model, coupled to a sediment transport model and a water quality model. In such depth−integrated models, the vertical structure of the flow is represented by a closure submodel, which mainly has to account for the secondary circulation, which (1) redistributes by advection the flow, the boundary shear stresses, the sediment transport, and dissolved and suspended matter, (2) causes the direction of the bed shear stress to deviate from the direction of the depth‐averaged velocity and thereby influences the bed topography, and (3) gives rise to additional friction losses as compared with straight uniform flow. The commonly used linear closure submodels are shown to fail in reproducing essential features in moderately to strongly curved flow, because they neglect the feedback between the downstream velocity and the secondary circulation. A nonlinear closure submodel taking this feedback into account is proposed and shown to yield results that compare well with experimental data, even for very strongly curved flow. The feedback effects turn out to be controlled almost exclusively by a single parameter, which enables their parameterization in a relatively simple way. This control parameter also helps to objectively distinguish weak, moderate, and strongly curved flows. The proposed closure submodel has the potential of improving the performance of depth‐integrated flow‐sediment‐water quality models without much extra computational effort.
A travel time based hydraulic tomographic approach
Authors: Brauchler R. , Liedl R. , Dietrich P.
Published: December 2003

Hydraulic tomography is a method to identify the three‐dimensional spatial distribution of hydraulic properties in the subsurface. We propose a tomographic approach providing the inversion of travel times of hydraulic or pneumatic tests conducted in a tomographic array. The inversion is based on the relation between the peak time of a recorded transient pressure curve and the diffusivity of the investigated system. The development of a transformation factor enables the inversion of further travel times besides the peak time of a transient curve. As the early travel times of the curve are mainly related to preferential flow features while the inversion based on late travel times are reflecting an integral behavior, it can be assumed that the different inversion results reflect the properties of the overall system. By comparing the different reconstructions the system interpretation therefore becomes more comprehensive and reliable. Furthermore, the similarity of the proposed hydraulic tomographic approach to seismic travel time tomography allows us to apply the inversion algorithms which are used for seismic tomography. We therefore apply the method of staggered grids, which enables to refine the grid resulting in a higher nominal resolution, to data from a set of interference tests arranged in a tomographic array. The tests were conducted in an unsaturated fractured sandstone cylinder in the laboratory. The three‐dimensional reconstructions of the diffusivity distribution are found to be highly reliable and robust. In particular, the mapped fracture of the sandstone cylinder coincides with our reconstructed diffusivity distribution.
Miscible displacement of salinity fronts: Implications for colloid mobilization
Authors: Flury Markus , Harsh James B. , Mathison Jon B.
Published: December 2003

Colloids can be mobilized in the subsurface when low ionic strength pore water displaces high ionic strength pore water. Various experiments in saturated porous media, where such a change in ionic strength was used to mobilize colloids, have been reported in the literature. Here we experimentally test the effect of the flow direction on the hydrodynamic stability of the salinity displacement front. A series of experiments was conducted in packed columns where a solution of 1000 mM NaCl was displaced by 1 mM NaNO3 in a saturated porous medium. The flow direction was vertically downward, horizontal, or vertically upward. Nitrate breakthrough curves were determined at the column outflow. Results show that for downward flow of a salinity front the displacement fronts were hydrodynamically stable, but breakthrough curves showed less dispersion than in the case of equimolar miscible displacement. For upward flow of the salinity front the displacement was unstable. Breakthrough curves were not reproducible, and a family of breakthrough curves was observed for repeated experiments. This was caused by the development of distinct fingers at the displacement front. For horizontal flow of the salinity front the displacement was unstable. Repeated breakthrough curves were reproducible, but there was more dispersion than under equimolar displacement, which we attribute to some instability in the displacement front. Front instability inferred from breakthrough curves was consistent with theoretical expectations for miscible displacement.
The enhanced spontaneous activity of the diabetic colon is not the consequence of impaired inhibitory control mechanisms
Authors: Forrest A. , Parsons M.
Published: December 2003

1 Approximately 45% of patients with diabetes mellitus have gastrointestinal complications such as diarrhoea and constipation, but the underlying aetiology is unclear. The present study investigates alterations in spontaneous motility of the colon that may be, in part, responsible for these symptoms using an established animal model of diabetes.

2 Rats were rendered diabetic by a single intraperitoneal injection of streptozotocin and age‐matched controls were injected with citrate buffer. Rats were sacrificed after 8‐weeks and proximal colonic circular muscle tissue mounted in organ baths.

3 Spontaneous activity was observed in both control and diabetic tissues, but this activity was almost doubled in colonic tissue taken from diabetic rats. It was hypothesized that this increase was due to a deficit in inhibitory control of the colon in the diabetic state.

4 Possible alterations in nitrergic and vasoactive intestinal polypeptide (VIP)ergic control were investigated using a range of pharmacological tools.

5 Sodium nitroprusside, VIP and antioxidants (reduced glutathione, ascorbate and α‐tocopherol) inhibited the spontaneous activity, but the level of inhibition observed was not different in diabetic tissue compared with control.

6 Arginine, [d‐p‐Cl‐Phe6, Leu17]‐VIP and α‐chymotrypsin had no effect on spontaneous activity in either sets of tissue.

7 N‐nitro‐l‐arginine produced a small, but significant, increase in the level of spontaneous activity, but the degree of increase was not different between control and diabetic tissues.

8 Western blots demonstrated that there was no inducible‐nitric oxide synthase (iNOS) in control or diabetic tissues and that the levels of endothelial‐NOS (eNOS) and neuronal‐NOS (nNOS) detected were not statistically significantly different. The [3H]‐citrulline assay established that the functionality of the NOS isoforms present were unaltered in the diabetic state.

9 This study demonstrates that there is a marked alteration in motility in the colon taken from diabetic animals. However, the change in motility is unlikely to be due to a change in inhibitory control mechanisms and may be due to an increased excitability.
Adenosine affects the calcium dynamics of rat portal vein
Authors: Telang R. S. , Tripathi H. C. , Mishra S. K. , Raviprakash V.
Published: December 2003

1 The present study was carried out to characterize the effect of adenosine on calcium dynamics in the rat portal vein. Isolated portal vein of male albino rats was used as the experimental model as it exhibits autorhythmicity. Adenosine and its analogues 2‐CAD, N6‐CHA and NECA were used to characterize the type of adenosine receptor involved and 2‐CAD was used along with adenosine throughout the other part of study to characterize the effect of adenosine on Ca2+ dynamics.

2 Adenosine and its analogues were found to inhibit the spontaneous contractions of rat portal vein in a concentration‐related manner. The order of potency was NECA > 2‐CAD > N6‐CHA > adenosine. Incubation of the tissue with CGS∼15943A, an adenosine receptor antagonist, had a per se enhancing effect on autorhythmicity. Adenosine and 2‐CAD failed to reverse the contractile response produced by hypertonic KCl (80 or 30 mm). Whereas adenosine and 2‐CAD effectively relaxed the tissues contracted with phenylephrine (10−5 m).

3 Preincubation of the tissue with 2‐CAD (10−4, 10−5 or 10−6 m) for 5 min raised the threshold concentration of CaCl2 to evoke contractile response and also significantly increased the mean EC50 values of CaCl2. Nifedipine was found to be more potent than 2‐CAD on Ca2+ channels.

4 The results of the present study suggest that the endogenous adenosine plays a significant role in producing vascular relaxation through the participation of A2 receptor subtype. This effect may be due to its inhibitory effect on release of Ca2+ from the intracellular stores. Further to this effect, 2‐CAD had a major inhibitory effect on voltage‐operated Ca2+ channels compared with receptor‐operated Ca2+ channels.

5 It can be concluded that adenosine through its A2 receptor produces vasorelaxant effect by interfering with the release of Ca2+ from the intracellular stores coupled with influx of Ca2+ from the extracellular sources.
Regulation of the resistance and resilience of periparturient ewes to infection with gastrointestinal nematode parasites by dietary supplementation
Authors: Kahn L. P.
Published: December 2003

Control of gastrointestinal nematode (GIN) parasites has traditionally been based on the premise of chemotherapeutic control with the resultant consequence being the development of anthelmintic resistance by GIN. An alternative premise to the management of GIN parasites is to improve the resistance and resilience of sheep to GIN infection by manipulating the nutritional environment at key periods of a sheep's life. One key period, is the periparturient phase in the reproductive cycle when ewes experiences a temporary loss, or diminution, of immunity to GIN parasites. This phase is associated with an increased requirement for both metabolisable energy (ME) and metabolisable protein (MP). The increased requirement being greater for MP. The loss of immunity to GIN is associated with a diminished cell-mediated immune response in the gut mucosa, the magnitude of which can be regulated by protein nutrition, or more specifically the supply of MP. Experimental studies that have increased MP supply, in housed and grazing periparturient ewes, have demonstrated significant improvements in resistance to GIN infection. Positive gut immune responses to an increased MP supply are believed to occur because the increased MP supply counters the combined pathological consequences of GIN infection per se and the host's immune response, namely a net loss of amino acids. Susceptibility to GIN infection in the periparturient ewe may also be a function of a low priority for use of MP toward immune function but evidence from young animals suggests a disproportionate partitioning of amino acids to the gastrointestinal tract during GIN infection. It is proposed that the priorities for use of MP that predispose the ewe to GIN infection are altered following infection to favour a gut immune response. Despite being under the regulation of MP supply and genetic selection, the loss of immunity during the periparturient period cannot be fully restored by either approaches suggesting that other unidentified factors are involved in the periparturient loss of immunity. Resilience to GIN infection is responsive to both ME and MP supply. The practice of supplementing periparturient ewes to increase MP and ME supply, in order to enhance resistance and resilience to GIN infection, is gaining favour with graziers within some regions of Australia. Other benefits (e.g. increased reproductive rates) arise from such supplementation strategies that improve the cost effectiveness of this approach.