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A Tobias

Publications and source records attributed to A Tobias.

At least 19 recordsLinked to original sources
PubMed2005

Q2 dependence of the neutron spin structure function g2(n) at low Q2.

We present the first measurement of the Q2 dependence of the neutron spin structure function g2(n) at five kinematic points covering 0.57 (GeV/c)2 < or = Q2 < or = 1.34 (GeV/c)2 at x approximately = 0.2. Though the naive quark-parton model predicts g2 = 0, nonzero values occur in more realistic models of the nucleon which include quark-gluon correlations, finite quark masses, or orbital angular momentum. When scattering from a noninteracting quark, g2(n) can be predicted using next-to-leading order fits to world data for g1(n). Deviations from this prediction provide an opportunity to examine QCD dynamics in nucleon structure. Our results show a positive deviation from this prediction at lower Q2, indicating that contributions such as quark-gluon interactions may be important. Precision data obtained for g1(n) are consistent with next-to-leading order fits to world data.

Journal Article↗
PubMed2004

Precision measurement of the neutron spin asymmetryA(n)(1) and spin-flavor decomposition in the valence quark region.

We have measured the neutron spin asymmetry A(n)(1) with high precision at three kinematics in the deep inelastic region at x=0.33, 0.47, and 0.60, and Q(2)=2.7, 3.5, and 4.8 (GeV/c)(2), respectively. Our results unambiguously show, for the first time, that A(n)(1) crosses zero around x=0.47 and becomes significantly positive at x=0.60. Combined with the world proton data, polarized quark distributions were extracted. Our results, in general, agree with relativistic constituent quark models and with perturbative quantum chromodynamics (PQCD) analyses based on the earlier data. However they deviate from PQCD predictions based on hadron helicity conservation.

Journal Article↗
PubMed2001

Measurement of the electric form factor of the neutron through d-->(e-->,e(')n)p at Q2 = 0.5 (GeV/c)(2).

We report the first measurement using a solid polarized target of the neutron electric form factor G(n)(E) via d-->(e-->,e(')n)p. G(n)(E) was determined from the beam-target asymmetry in the scattering of longitudinally polarized electrons from polarized deuterated ammonia ( 15ND3). The measurement was performed in Hall C at Thomas Jefferson National Accelerator Facility in quasifree kinematics with the target polarization perpendicular to the momentum transfer. The electrons were detected in a magnetic spectrometer in coincidence with neutrons in a large solid angle segmented detector. We find G(n)(E) = 0.04632+/-0.00616(stat)+/-0.00341(syst) at Q2 = 0.495 (GeV/c)(2).

Journal Article↗
PubMed2001

Clinical importance of Alternaria exposure in children.

The fungus Alternaria is known to be allergenic and is one of the most common fungi worldwide. We investigated the extent to which exposure to Alternaria increases the severity of asthma. We undertook a prospective cohort study in Australia of 399 school children who had positive skin tests to one or more aeroallergens. Airway responsiveness to histamine, wheeze, and bronchodilator use in 1 mo was measured five times between 1997 and 1999. Airway hyperresponsiveness was defined as PD(20)FEV(1) = 3.9 micromol histamine. Airborne concentrations of Alternaria spores were measured throughout the study, and mean daily concentrations over 1 mo ranged from 2.2 to 307.7 spores/m(3) of ambient air. Using generalized estimating equations, we found that airway responsiveness, wheeze, and bronchodilator use increased significantly in association with increased spore concentrations and that the increase in airway responsiveness was greater in children sensitized to Alternaria than in other children (p = 0.01). The odds ratio for airway hyperresponsiveness in children sensitized to Alternaria was 1.26 (95% CI, 1.14 to 1.39) after an increase in mean exposure of 100 spore/m(3)/d over 1 mo. These results suggest that Alternaria allergens contribute to severe asthma in regions where exposure to the fungus is high.

Allergens↗
PubMed2001

Use of poisson regression and box-jenkins models to evaluate the short-term effects of environmental noise levels on daily emergency admissions in Madrid, Spain.

The relationship between environmental factors and hospital admissions has usually been analysed without taking into account the influence of a factor closely related to traffic in big cities, that is, environmental noise levels. We analysed the relationship between environmental noise and emergency admissions, for all causes and specific causes in Madrid (Spain), for the study period 1995-1997, using two statistical methods for the analysis of epidemiological time series data: Poisson autoregressive models and Box Jenkins (ARIMA) methodology. Both methods produce a clear association between emergency admissions for all and specific causes and environmental noise levels. We found very similar results from both methods for all and circulatory causes, but slightly different for respiratory causes. Around 5% of all emergency admissions can be attributed to high noise levels, with a lower figure for specific causes. Current levels of environmental noise have a considerable epidemiological impact on emergency admissions in Madrid. A reduction of environmental noise levels could be accompanied by a possible reduction in the number of emergency admissions.

Air Pollutants↗
PubMed2001

Atmospheric pressure and sudden infant death syndrome in Cook County, Chicago.

We investigated daily deaths from sudden infant death syndrome (SIDS) in Cook County, Chicago, from 1 January 1986 to 31 December 1990. The daily SIDS rate was 0.54 deaths/day. Mean daily atmospheric pressure ranged from 952 to 1007 mb. We found a weak link with barometric pressure, whereby an increase of 10 mb was associated with an increased risk of 12% [95% CI 0.1%, 24%]. Cross-tabulation revealed that the highest SIDS rates were associated with a drop from high to low pressure. Possible reasons for this are discussed.

Atmospheric Pressure↗
PubMed2001

Symptoms of asthma, bronchial responsiveness and atopy in immigrants and emigrants in Europe. European Community Respiratory Health Survey.

Migration studies on asthma may provide information on its environmental causes. The European Community Respiratory Health Survey has potential advantages due to the number of countries involved, standardized collection of information, assessment of directionality of migration, and availability of physiological data on bronchial responsiveness and atopy. Prevalence rates of symptoms associated with asthma were compared for immigrants, emigrants and nonmigrants living in centres mostly in western Europe. Similar analyses were carried out for bronchial responsiveness (provocative concentration causing a 20% fall in forced expiratory volume in one second and slope) and atopy. Medication and use of health services were also explored. Overall, 1,678 (8.6%) of 19,516 participants were immigrants in the 18 countries participating in the study, of whom 581 were emigrants from one of the participating countries. Rates of asthma symptoms were higher in immigrants (odds ratio (OR): 1.21, 95% confidence interval (CI): 1.00-1.51) and emigrants (OR: 1.31, 95% CI: 0.96-1.51) compared to nonmigrants after controlling for area, sex, age and smoking status. However, bronchial responsiveness and atopy were equally distributed between immigrants, emigrants and nonmigrants. Use of health services was observed to be similar in migrants and nonmigrants with asthma. In the European Community Respiratory Health Survey, migrants reported more asthma symptoms, but had similar bronchial responsiveness, atopy, and use of health services when compared with the nonmigrant population.

Adult↗
PubMed1999

A GEE moving average analysis of the relationship between air pollution and mortality for asthma in Barcelona, Spain.

Several studies have assessed the association between air pollution and hospital admissions or emergency room visits for asthma. Because of both the presence of missing data and the small number of observations, the relationship between air pollution and mortality for respiratory causes has been rarely analysed, and when it has, the results are very inconclusive or even inconsistent. The objective of this study is to assess the relation between levels of air pollutants (black smoke, sulphur dioxide, nitrogen dioxide and ozone), meteorological variables (24th average temperature and relative humidity) and daily mortality for asthma (ICD-9 493, 2 to 45 years old) in Barcelona, Spain, during the period 1986-1989. Since the range of daily mortality for asthma (2 to 45 years old) during the period 1986-1989 was 0-1), we have preferred to consider this variable as dichotomous. First, the relationship between air pollutants, meteorological variables and daily mortality (controlled for the occurrence of asthma epidemics) was estimated using logistic regression models. As was expected, the residuals from this regression were autocorrelated, showing a complex moving average (MA) structure. If covariates were not time dependent the so-called generalized linear mixed models, could be applied. In our case the covariates vary. As a consequence the likelihood is numerically intractable because it involves the evaluation of n-fold integral. An alternative method that avoids these numerical problems is the generalized estimating equations method (GEE). It is a multivariate analogue of quasi-likelihood estimation. In the absence of a likelihood function the parameters can be estimated by solving a multivariate analogue of the quasi score function. We have modified the GEE method in this paper, allowing for a different structure in the error covariance matrix (MA). Both air pollutants and meteorological variables are related with the occurrence of a death for asthma. In this sense, nitrogen dioxide, NO(2) (ss=0.037, p<0. 05), ozone, O(3) (ss=0.021, p<0.06) and high temperature (the ss's were in the range (0.098-0.182), p<0.05) increased the probability of dying for asthma in Barcelona during the period 1986-1989.

Adolescent↗
PubMed1999

Occupational asthma in Europe and other industrialised areas: a population-based study. European Community Respiratory Health Survey Study Group.

BACKGROUND: There are no large population-based studies on occupational asthma, and few estimates of the proportion of asthma attributed to occupation, even though asthma is the most common occupational respiratory disorder in industrialised countries. METHODS: We assessed data on 15,637 people aged 20-44, randomly selected from the general population of 26 areas in 12 industrialised countries. Asthma was assessed by methacholine challenge test and by questionnaire data on respiratory symptoms and use of medication. Occupation was defined by job-titles and a job exposure matrix was constructed. FINDINGS: Highest risk of asthma, defined as bronchial hyperresponsiveness and reported asthma symptoms or medication, was shown for farmers (odds ratio 2.62 [95% CI 1.29-5.35]), painters (2.34 [1.04-5.28]), plastic workers (2.20 [0.59-8.29]), cleaners (1.97 [1.33-2.92]), spray painters (1.96 [0.72-5.34]), and agricultural workers (1.79 [1.02-3.16]). Similar risks were shown for asthma defined as reported asthma symptoms or medication. The most consistent results across countries were shown for farmers and cleaners. Excess asthma risk was associated with high exposure to biological dusts, mineral dusts, and gases and fumes. The proportion of asthma among young adults attributed to occupation was 5%-10%. INTERPRETATION: The prevalence of occupational asthma in women and in specific occupations has been underestimated. Given a mean prevalence of asthma of about 5%, about 0.2%-0.5% of young adults become asthmatics or have their asthma exacerbated because of their occupations.

Adult↗
PubMed1999

Generational increase of self-reported first attack of asthma in fifteen industrialized countries. European Community Respiratory Health Study (ECRHS).

The prevalence of asthma has increased worldwide. However, there is only local evidence for changes in incidence. Data from the European Community Respiratory Heath Survey (ECRHS) can be analysed to reconstruct trends in incidence from 1946-1991 in cohorts born between 1946-1971 in 35 areas corresponding to 15 countries. The authors report the time trends in self-reported first occurrence of asthma and its geographical distribution. All centres completed the same cross-sectional study in 1991-92. A total of 17,613 individuals (63% of those randomly selected) were included. Recall of age of first asthma attack was recorded at an interview at one point in time in subjects aged 20-44 yrs. Relative risk of asthma by cohort was estimated using survival methods with age as the time scale. Yearly incidence of asthma increased progressively by birth cohort. The relative risks were 1.12 (0.94-1.34), 1.39 (1.17-1.66), 2.01 (1.60-2.51), and 2.33 (1.81-2.98) for the cohorts born in the years 1951-55, 1956-60, 1961-65, and 1966-71, respectively, in comparison with the cohort born in the years 1946-50. The increase occurred concurrently in most of the countries, in both males and females, and both in childhood and adulthood onset asthma. These results are consistent with a generational increase in asthma incidence during the previous decades (explained by both a period and/or a cohort effect), although some of the findings could be explained by generational increases in asthma diagnosis.

Adult↗
PubMed1998

Genes and regulatory sites of the "host-takeover module" in the terminal redundancy of Bacillus subtilis bacteriophage SPO1.

Early in infection of Bacillus subtilis by bacteriophage SPO1, the synthesis of most host-specific macromolecules is replaced by the corresponding phage-specific biosyntheses. It is believed that this subversion of the host biosynthetic machinery is accomplished primarily by a cluster of early genes in the SPO1 terminal redundancy. Here we analyze the nucleotide sequence of this 11.5-kb "host-takeover module," which appears to be designed for particularly efficient expression. Promoters, ribosome-binding sites, and codon usage statistics all show characteristics known to be associated with efficient function in B. subtilis. The promoters and ribosome-binding sites have additional conserved features which are not characteristic of their host counterparts and which may be important for competition with host genes for the cellular biosynthetic machinery. The module includes 24 genes, tightly packed into 12 operons driven by the previously identified early promoters PE1 to PE12. The genes are smaller than average, with half of them having fewer than 100 codons. Most of their inferred products show little similarity to known proteins, although zinc finger, trans-membrane, and RNA polymerase-binding domains were identified. Transcription-termination and RNase III cleavage sites were found at appropriate locations.

Amino Acid Sequence↗
PubMed1998

Effect of the method of administration, mail or telephone, on the validity and reliability of a respiratory health questionnaire. The Spanish Centers of the European Asthma Study.

The European Community Respiratory Health Survey (ECRHS), a multinational survey, assesses and compares the prevalence of asthma among subjects, aged 20 to 44, in several European areas. In Spain, some participating centers have used mail and telephone as methods of questionnaire administration. The objective of the present study was to determine whether the validity and reliability of the questionnaire differed by method of administration. Reliability of the questionnaire was measured with the kappa index and the odds ratio of agreement, and validity with the sensitivity and specificity. This study found differences in the reliability of the questionnaires although these differences were more related to the questions themselves than to the method of administration. Among men, but not women, mailed questionnaires were more sensitive and telephone questionnaires more specific. We hypothesize that these differences in validity were due to the self-selection to more severe symptomatic subjects replying earlier and therefore to the mailed questionnaire. Combining different methods of administration was useful as it increased participation and was an adequate procedure to obtain information of good quality.

Adult↗
PubMed1998

Pulmonary ventilatory defects and occupational exposures in a population-based study in Spain. Spanish Group of the European Community Respiratory Health Survey.

We assessed the association between occupational exposures and symptoms of chronic bronchitis and pulmonary ventilatory defects in a general population-based study of five areas in Spain. This study forms part of the European Community Respiratory Health Study (ECRHS). Subjects (n = 1,735; age range, 20-44 yr; 52.4% of those initially selected) completed a respiratory questionnaire on symptoms and occupation and underwent baseline spirometry. Occupation was translated with an ad hoc developed job-exposure matrix (EM) into none, low, and high exposure to biological dust, mineral dust, and gases and fumes. Exposure to high levels of biological dust was associated with cough for more than 3 mo (odds ratio [OR], 1.9; p = 0.07), a reduction in FEF(25-27) to 478 ml/s (SD 178), and a reduction in FEV1 to 151 mL (SD 71). These associations remained after excluding subjects with asthma symptoms or bronchial responsiveness. Smokers tended to have a higher risk for respiratory symptoms, but smoking did not modify the association of occupation with pulmonary function. Exposure to mineral dust and gases/fumes was less consistently related to pulmonary function or to respiratory symptoms and this association further decreased after excluding subjects with asthma. In conclusion, exposure to high levels of biological dust in young adults is associated with symptoms of chronic bronchitis and pulmonary ventilatory defects, independently of asthma and smoking.

Adult↗
PubMed1998

Respiratory symptoms, lung function and use of health services among unemployed young adults in Spain. Spanish Group of the European Community Respiratory Health Survey.

The association of respiratory symptoms, lung function and use of health services with employment status was examined in Spain, a country with a high rate of unemployment. A population sample comprising 179 unemployed and 1,868 employed subjects aged 20-44 yrs in 1993, was randomly selected from a base population of about 170,000 people in five urban and rural areas of Spain. Subjects completed a questionnaire on respiratory symptoms, sociodemographic and lifestyle factors, occupational exposure and use of health services, and performed a forced spirometry, a methacholine challenge test and blood tests. Unemployed subjects had a higher risk of simple chronic bronchitis (odds ratio=2.06, 95% confidence interval 1.30-3.24) and of bronchitis-type symptoms, than those who were employed. These risks were, in part, due to the higher prevalence of smoking, poorer housing and prior occupational exposures among unemployed than among employed people. Smaller differences were found between employed and unemployed subjects for asthma-type symptoms, atopia and lung function tests. Use of health services among subjects with respiratory symptoms was similar among employed and unemployed subjects, except that the latter consistently reported less frequent contact with specialized practitioners. Unemployed subjects had a higher risk of bronchitis-type symptoms than employed subjects. In Spain's national, free-access healthcare system, the differential use of specialized health services by employment status is likely to imply differences in the characteristics of the healthcare provided.

Adult↗
PubMed1997

Short-term effects of ambient oxidant exposure on mortality: a combined analysis within the APHEA project. Air Pollution and Health: a European Approach.

The Air Pollution and Health: a European Approach (APHEA) project is a coordinated study of the short-term effects of air pollution on mortality and hospital admissions using data from 15 European cities, with a wide range of geographic, sociodemographic, climatic, and air quality patterns. The objective of this paper is to summarize the results of the short-term effects of ambient oxidants on daily deaths from all causes (excluding accidents). Within the APHEA project, six cities spanning Central and Western Europe provided data on daily deaths and NO2 and/or O3 levels. The data were analyzed by each center separately following a standardized methodology to ensure comparability of results. Poisson autoregressive models allowing for overdispersion were fitted. Fixed effects models were used to pool the individual regression coefficients when there was no evidence of heterogeneity among the cities and random effects models otherwise. Factors possibly correlated with heterogeneity were also investigated. Significant positive associations were found between daily deaths and both NO2 and O3. Increases of 50 micrograms/m3 in NO2 (1-hour maximum) or O3 (1-hour maximum) were associated with a 1.3% (95% confidence interval 0.9-1.8) and 2.9% (95% confidence interval 1.0-4.9) increase in the daily number of deaths, respectively. Stratified analysis of NO2 effects by low and high levels of black smoke or O3 showed no significant evidence for an interaction within each city. However, there was a tendency for larger effects of NO2 in cities with higher levels of black smoke. The pooled estimate for the O3 effect was only slightly reduced, whereas the one for NO2 was almost halved (although it remained significant) when two pollutant models including black smoke were applied. The internal validity (consistency across cities) as well as the external validity (similarities with other published studies) of our results on the O3 effect support the hypothesis of a causal relation between O3 and all cause daily mortality. However, the short-term effects of NO2 on mortality may be confounded by other vehicle-derived pollutants. Thus, the issue of independent NO2 effects requires additional investigation.

Europe↗
PubMed1997

Smoking and bronchial responsiveness in nonatopic and atopic young adults. Spanish Group of the European Study of Asthma.

BACKGROUND: Smoking may influence the response of the lungs to other inhaled substances. A study was undertaken to assess the effect of the interaction between smoking and the immunoresponse to common aeroallergens (atopy) on bronchial responsiveness. METHODS: A random sample was selected from the general population census of five areas of Spain (Albacete, Barcelona, Galdakao, Huelva, and Oviedo). A total of 1169 (35%) subjects completed a face-to-face respiratory questionnaire, a methacholine bronchial responsiveness challenge, and underwent measurements of total and specific serum IgE levels to mites, pets and moulds. A survival model (Weibull) was used to examine the methacholine dose-response relation, adjusting for bronchial obstruction. RESULTS: Smokers showed greater bronchial responsiveness than never smokers (p < 0.05) at any dose of methacholine, but only among non-atopic individuals. Atopy had a large effect on responsiveness at low levels of methacholine, but smoking did not increase responsiveness in atopic subjects. There were no differences in intensity or cessation of smoking between atopic and non-atopic subjects, suggesting that smoking self-selection does not fully explain these results. CONCLUSIONS: The association between smoking and bronchial responsiveness varies with atopy, which may be explained by different immunological and/or inflammatory effects of smoking on atopy.

Adult↗