bluuebunny/crossref_metadata_2025_split huggingface dataset:
N : P ratios in terrestrial plants: variation and functional significance
Authors: Güsewell Sabine 
Published: October 2004

SummaryNitrogen (N) and phosphorus (P) availability limit plant growth in most terrestrial ecosystems. This review examines how variation in the relative availability of N and P, as reflected by N : P ratios of plant biomass, influences vegetation composition and functioning. Plastic responses of plants to N and P supply cause up to 50‐fold variation in biomass N : P ratios, associated with differences in root allocation, nutrient uptake, biomass turnover and reproductive output. Optimal N : P ratios – those of plants whose growth is equally limited by N and P – depend on species, growth rate, plant age and plant parts. At vegetation level, N : P ratios <10 and >20 often (not always) correspond to N‐ and P‐limited biomass production, as shown by short‐term fertilization experiments; however long‐term effects of fertilization or effects on individual species can be different. N : P ratios are on average higher in graminoids than in forbs, and in stress‐tolerant species compared with ruderals; they correlate negatively with the maximal relative growth rates of species and with their N‐indicator values. At vegetation level, N : P ratios often correlate negatively with biomass production; high N : P ratios promote graminoids and stress tolerators relative to other species, whereas relationships with species richness are not consistent. N : P ratios are influenced by global change, increased atmospheric N deposition, and conservation managment.

Contents

Summary
243

I
Introduction
244

II
Variability of N : P ratios in response to nutrient  supply
244

III
Critical N : P ratios as indicators of nutrient  limitation
248

IV
Interspecific variation in N : P ratios
252

V
Vegetation properties in relation to N : P ratios
255

VI
Implications of N : P ratios for human impacts  on ecosystems
258

VII
Conclusions
259

Acknowledgements
259

References
260
Time Dependent Properties and Performance of a Tubular Solid Oxide
Fuel Cell
Authors: Ju Gang , Reifsnider Kenneth , Huang Xinyu , Du Yanhai 
Published: October 2004

Abstract
Time dependent properties and performance of tubular solid oxide fuel cells were studied numerically and experimentally. The numerical model incorporated local characteristics such as porosity, tortuosity, grain size, and conductivity and was used to evaluate the specific and relative changes in performance caused by the effect of time-dependent material changes of those characteristics. A 500 hour experimental study was conducted at 800°C in 97%H2∕3%H2O on an extruded LSCo-La0.6Sr0.4CoO3∕LSGM∕Ni electrolyte-supported tubular SOFC made in our laboratory. Changes in current density with time (at constant voltage) formed a curve with initial convex (upward) curvature, becoming monotonic decreasing. The microstructure of the constituent layers was examined by scanning electron microscopy. Comparisons between model predictions and experimental observations were made. For the situation modeled and tested, the porosity and ionic conductivity were found to be most influential on performance. More importantly, the effect of porosity is a trade-off between the influence on gas transport and the mixed conductor influence on the electrochemical reactions at the electrode.
Predictors of hearing threshold levels and distortion product otoacoustic emissions among noise exposed young adults
Authors: Seixas N S , Kujawa S G , Norton S , Sheppard L , Neitzel R , Slee A 
Published: October 2004

Aim:To examine the relations between noise exposure and other risk factors with hearing function as measured by audiometric thresholds and distortion product otoacoustic emissions.Methods:A total of 456 subjects were studied (393 apprentices in construction trades and 63 graduate students). Hearing and peripheral auditory function were quantified using standard, automated threshold audiometry, tympanometry, and distortion product otoacoustic emissions (DPOAEs). The analysis addressed relations of noise exposure history and other risk factors with hearing threshold levels (HTLs) and DPOAEs at the baseline test for the cohort.Results:The cohort had a mean age of 27 (7) years. The construction apprentices reported more noise exposure than students in both their occupational and non-occupational exposure histories. A strong effect of age and years of work in construction was observed at 4, 6, and 8 kHz for both HTLs and DPOAEs. Each year of construction work reported prior to baseline was associated with a 0.7 dB increase in HTL or 0.2 dB decrease DPOAE amplitude. Overall, there was a very similar pattern of effects between the HTLs and DPOAEs.Conclusions:This analysis shows a relatively good correspondence between the associations of noise exposures and other risk factors with DPOAEs and the associations observed with pure-tone audiometric thresholds in a young adult working population. The results provide further evidence that DPOAEs can be used to assess damage to hearing from a variety of exposures including noise. Clarifying advantages of DPOAEs or HTLs in terms of sensitivity to early manifestations of noise insults, or their utility in predicting future loss in hearing will require longitudinal follow up.
Exposure to cobalt in the production of cobalt and cobalt compounds and its effect on the heart
Authors: Linna A , Oksa P , Groundstroem K , Halkosaari M , Palmroos P , Huikko S , Uitti J 
Published: October 2004

Aims:To investigate whether exposure to cobalt in cobalt plants has any measurable effect on the cardiovascular system.Methods:Occupational, cross sectional study, using a self administered questionnaire, blood pressure measurement, electrocardiography, and laboratory tests in which 203 male workers with at least one year of exposure to cobalt and 94 unexposed controls participated. Echocardiography was performed on a subset of 122 most highly exposed cobalt workers, of which 109 were analysed, and on 60 controls, of which 57 were analysed. Analysis of covariance and a multiple regression analysis were used to evaluate the data.Results:Two of the echocardiography parameters measured were associated with cobalt exposure. In the higher exposure group the left ventricular isovolumic relaxation time (mean 53.3, 49.1, and 49.7 ms in the high exposure, low exposure, and control groups respectively) and the deceleration time of the velocity of the early rapid filling wave (mean 194.3, 180.5, and 171.7 ms for those in the high exposure, low exposure, and control groups respectively) were prolonged, indicating altered left ventricular relaxation and early filling.Conclusion:Cumulative exposure to cobalt was found to be associated with the results of Doppler echocardiography measurements, indicating altered diastole. This finding supports the hypothesis that cobalt accumulation in the myocardium could affect myocardial function. Whether this finding has clinical implications remains to be evaluated.
An occupational health intervention programme for workers at risk for early retirement; a randomised controlled trial
Authors: de Boer A G E M , van Beek J-C , Durinck J , Verbeek J H A M , van Dijk F J H 
Published: October 2004

Aims:To evaluate an occupational health intervention programme for workers at risk for early retirement.Methods:Between April 1997 and May 1998, 116 employees of a large company who were older than 50 years indicated that they would not be able to work up to their retirement. They were randomly assigned to an intervention (n = 61) or control group (n = 55). The intervention programme lasted six months and was executed by an occupational physician. Job position and number of sick leave days after two years were collected from the company’s computer database. A questionnaire was sent to the employees at baseline, after six months, and after two years; it included the Work Ability Index, the Utrecht Burn Out Scale, and the Nottingham Health Profile measuring quality of life.Results:Fewer employees (11%) in the intervention group retired early than in the control group (28%). The total average number of sick leave days in two years was 82.3 for the intervention group and 107.8 for the control group. Six months after baseline, employees in the intervention group had better work ability, less burnout, and better quality of life than employees in the control group. Two years after randomisation no differences between the two groups were found.Conclusions:This occupational health intervention programme proved to be a promising intervention in the prevention of early retirement.
Use of a crop and job specific exposure matrix for estimating cumulative exposure to triazine herbicides among females in a case-control study in the Central Valley of California
Authors: Young H A , Mills P K , Riordan D , Cress R 
Published: October 2004

Aims:To determine if a job exposure matrix (JEM) could be developed using the California Department of Pesticide Regulation Pesticide Usage Database in conjunction with crop, time, and county specific self reported work history and to determine if this was a feasible method to obtain exposure estimates to triazine herbicides.Methods:Agricultural work histories were gathered from women enrolled in a population based case-control study of ovarian cancer cases and random controls. The work histories were used in conjunction with the database to construct job exposure matrices which took into account weightings for job type, work location, and crop.Results:Cumulative exposure estimates were determined for 98 study subjects. Mean exposure estimates were similar for cases and controls. The exposure estimates were robust and insensitive to varying job weight assumptions. The estimates from the original weights were highly correlated with those constructed using the conservative and maximum weights. Estimates from all three schemes produced similar multivariate age adjusted odds ratios comparing cases and controls. There was a high degree of agreement in categorised quartiles of exposure between the original and conservative, and original and maximum weights.Conclusions:The exposure estimate from the JEM provides a ranking of exposure within the study population that can be utilised as an “exposure score” with which to compare groups. Although it is not an absolute exposure measurement, it does offer a substantial advance over dichotomous categories based on self report of herbicide use, particularly when subjects are unlikely to recall specific names and dates of use of herbicides.
Contrasting patterns of mortality and hospital admissions during hot weather and heat waves in Greater London, UK
Authors: Kovats R S , Hajat S , Wilkinson P 
Published: October 2004

Background:Epidemiological research has shown that mortality increases during hot weather and heat waves, but little is known about the effect on non-fatal outcomes in the UK.Aims and Methods:The effects of hot weather and heat waves on emergency hospital admissions were investigated in Greater London, UK, for a range of causes and age groups. Time series analyses were conducted of daily emergency hospital admissions, 1 April 1994 to 31 March 2000, using autoregressive Poisson models with adjustment for long term trend, season, day of week, public holidays, the Christmas period, influenza, relative humidity, air pollution (ozone, PM10), and overdispersion. The effects of heat were modelled using the average of the daily mean temperature over the index and previous two days.Results:There was no clear evidence of a relation between total emergency hospital admissions and high ambient temperatures, although there was evidence for heat related increases in emergency admissions for respiratory and renal disease, in children under 5, and for respiratory disease in the 75+ age group. During the heat wave of 29 July to 3 August 1995, hospital admissions showed a small non-significant increase: 2.6% (95% CI −2.2 to 7.6), while daily mortality rose by 10.8% (95% CI 2.8 to 19.3) after adjusting for time varying confounders.Conclusions:The impact of hot weather on mortality is not paralleled by similar magnitude increases in hospital admissions in the UK, which supports the hypothesis that many heat related deaths occur in people before they come to medical attention. This has evident implications for public health, and merits further enquiry.
Daily variation in fine and ultrafine particulate air pollution and urinary concentrations of lung Clara cell protein CC16
Authors: Timonen K L , Hoek G , Heinrich J , Bernard A , Brunekreef B , de Hartog J , Hämeri K , Ibald-Mulli A , Mirme A , Peters A , Tiittanen P , Kreyling W G , Pekkanen J 
Published: October 2004

Background:Daily variations in ambient particulate air pollution have been associated with respiratory mortality and morbidity.Aims:To assess the associations between urinary concentration of lung Clara cell protein CC16, a marker for lung damage, and daily variation in fine and ultrafine particulate air pollution.Methods:Spot urinary samples (n = 1249) were collected biweekly for six months in subjects with coronary heart disease in Amsterdam, Netherlands (n = 37), Erfurt, Germany (n = 47), and Helsinki, Finland (n = 47). Ambient particulate air pollution was monitored at a central site in each city.Results:The mean 24 hour number concentration of ultrafine particles was 17.3×103cm−3in Amsterdam, 21.1×103cm−3in Erfurt, and 17.0×103cm−3in Helsinki. The mean 24 hour PM2.5concentrations were 20, 23, and 13 μg/m3, respectively. Daily variation in ultrafine particle levels was not associated with CC16. In contrast, CC16 concentration seemed to increase with increasing levels of PM2.5in Helsinki, especially among subjects with lung disorders. No clear associations were observed in Amsterdam and Erfurt. In Helsinki, the CC16 concentration increased by 20.2% (95% CI 6.9 to 33.5) per 10 μg/m3increase in PM2.5concentration (lag 2). The respective pooled effect estimate was 2.1% (95% CI −1.3 to 5.6).Conclusion:The results suggest that exposure to particulate air pollution may lead to increased epithelial barrier permeability in lungs.
A cross-sectional study of triallate exposure and neurological health among workers at a pesticide manufacturing and formulating facility
Authors: Sathiakumar N , Delzell E , MacLennan P A , Anne M , Rosenberg N L , Cheng H , Myers S L 
Published: October 2004

Aims:To evaluate the relation between an indicator of cumulative exposure to triallate and selected measures of neurological function, including nerve conduction, the prevalence of certain neurological deficits as determined by a medical examination, and vibration perception threshold testing in workers at a pesticide manufacturing plant.Methods:Subjects were 50 workers with high estimated triallate exposure (“high triallate” group) and 50 workers with no or low triallate exposure (“no/low triallate” group). Industrial hygienists used existing work histories and personal knowledge of plant operations to develop a triallate score. In-person interviews elicited information on past medical history and on occupational and non-occupational exposures. A neurologist carried out nerve conduction tests of the sural and the peroneal nerves, a standardised neurological examination, and vibration sensation testing.Results:Differences between the high and the no/low triallate groups were minimal for all but one of the six nerve conduction tests, for the prevalence of neurological abnormalities, and for vibration sensation perception. The high triallate group had lower mean sural nerve peak amplitude than the no/low triallate group (11.7v15.2 µV, p = 0.03). This difference was reduced when adjusted for other potential risk factors (12.5v14.5 µV, p = 0.25) and was not associated with cumulative triallate score. We also noted several associations between factors other than triallate and nerve conduction measures.Conclusion:The results were consistent with the absence of an association between triallate and measures of neurological function.
Do factors in the psychosocial work environment mediate the effect of socioeconomic position on the risk of myocardial infarction? Study from the Copenhagen Centre for Prospective Population Studies
Authors: Andersen I , Burr H , Kristensen T S , Gamborg M , Osler M , Prescott E , Diderichsen F 
Published: October 2004

Aim:To investigate whether the effect of socioeconomic position on risk of myocardial infarction (MI) is mediated by differential exposure or differential susceptibility to psychosocial work environment.Methods:Data were used from three prospective population studies conducted in Copenhagen. A total of 16 214 employees, 44% women, aged 20–75 years, with initial examination between 1974 and 1992 were followed until 1996 for incident (hospital admission or death) MI. Register based information on job categories was used. Psychosocial job exposures were measured indirectly by means of a job exposure matrix based on the Danish Work Environment Cohort Study 1990.Results:During follow up, 731 subjects were diagnosed with an MI: 610 men and 121 women (35% fatal). The hazards by socioeconomic position showed a graded effect with a hazard ratio (HR) of 1.57 (95% CI 1.23 to 2.03) for unskilled workers compared to executive managers. Despite a strong and graded association in risk of MI related to decision authority and skill discretion, only skill discretion mediated the effect of socioeconomic position. The HR for unskilled workers was reduced to 1.47 (0.93 to 2.31) after adjustment for decision authority and other cardiovascular risk factors, and to 1.07 (0.72 to 1.60) after adjustment for skill discretion and cardiovascular risk factors. No sign of synergy was found.Conclusions:Decision authority and skill discretion were strongly related to socioeconomic position; and the effect on risk of MI was partially mediated by skill discretion. Improvements in psychosocial work environment, especially possibilities for skill discretion, might contribute to reducing the incidence of MI and social inequality in MI.
The impact of exposure categorisation for grouped analyses of cohort data
Authors: Richardson D B , Loomis D 
Published: October 2004

Background:Poisson regression is routinely used in occupational and environmental epidemiology. For typical Poisson regression analyses, person-time and events are tabulated by categorising predictor variables that were originally measured on a continuous scale. In order to estimate a dose-response trend, a researcher must decide how to categorise exposures and how to assign scores to exposure groups.Aims:To investigate the impact on regression results of decisions about exposure categorisation and score assignment.Methods:Cohort data were generated by Monte Carlo simulation methods. Exposure categories were defined by quintiles or deciles of the exposure distribution. Scores were assigned to exposure groups based on category midpoint and mean exposure levels. Estimated exposure-disease trends derived via Poisson regression were compared to the “true” association specified for the simulation.Results:Under the assumption that exposures conform to a lognormal or exponential distribution, trend estimates tend to be negatively biased when scores are assigned based on category midpoints and positively biased when scores are assigned based on cell specific mean values. The degree of bias was greater when exposure categories were defined by quintiles of the exposure distribution than when categories were defined by deciles of the exposure distribution.Conclusions:The routine practice of exposure categorisation and score assignment introduces exposure misclassification that may be differential with respect to disease status and, consequently, lead to biased exposure-disease trend estimates. When using the Poisson regression method to evaluate exposure-disease trends, such problems can be minimised (but not necessarily eliminated) by forming relatively refined exposure categories based on percentiles of the exposure distribution among cases, and by assigning scores to exposure categories that reflect person-time weighted mean exposure levels.
Decreased fecundity among male lead workers
Authors: Shiau C-Y , Wang J-D , Chen P-C 
Published: October 2004

Aims:To investigate time to pregnancy (TTP) in male lead workers in order to determine the dose-response relation between blood lead and decreased fecundity.Methods:A total of 163 currently employed married male lead battery workers were classified into five categories of exposure based on questionnaire information and annual individual blood lead measurement. Information pertaining to the TTP was collected using personal interviews with 133 men and their spouses, with 280 valid pregnancies. The fecundability ratios (FRs) were calculated with the Cox discrete proportional hazard regression technique to evaluate the effects of lead exposure.Results:After other factors associated with TTP were controlled for, there was a dose-response relation between blood lead level and TTP. The measured FRs were 0.90 (95% CI 0.61 to 1.34), 0.72 (0.46 to 1.11), 0.52 (0.35 to 0.77), and 0.40 (0.27 to 0.59) for concurrent blood lead levels of <20, 20–29, 30–39, and ⩾40 μg/dl, respectively. Paired self comparison was also performed for 41 couples that had pregnancies prior to lead exposure and pregnancies with male occupational lead exposure. The TTP was prolonged for 0.15 cycles by a 1 μg/dl increase in blood lead.Conclusions:These results corroborate the hypothesis that a raised blood lead level affects fecundity. A blood lead level of less than 40 μg/dl may still significantly prolong TTP.
THE MINIMAL SUPERSYMMETRIC STANDARD MODEL
Authors: CSÁKI CSABA 
Published: October 2004

The structure of the MSSM is reviewed. We first motivate the particle content of the theory by examining the quantum numbers of the known standard model particles and by the requirement of anomaly cancellation. Once the particle content is fixed we can write down the most general renormalizable superpotential. However such a superpotential will contain terms breaking lepton and baryon number which leads us to the concept of R-parity conservation. The question of supersymmetry breaking is discussed next. We list the possible soft breaking terms. However the Lagrangian involving the most general soft breaking terms is phenomenologically intractable because of the appearance of many new parameters. It also leads to some unacceptable predictions. To reduce the number of parameters we restrict ourselves to the case with universal soft breaking terms at the GUT scale. We motivate the need for universal soft breaking terms by the apparent unification of gauge couplings in the MSSM and by the absence of flavor changing neutral currents. Then we discuss radiative electroweak symmetry breaking. Radiative breaking arises because the one-loop corrections involving the large top Yukawa coupling change the sign of the soft breaking mass parameter of the up-type Higgs doublet, this way introducing a nontrivial minimum in the Higgs potential. Finally we give an overview of the possible mixings in the MSSM and enumerate the physical (mass eigenstate) fields together with the mass matrices.