Moran Model of Spatial Alignment in Microbial Colonies.

We describe a spatial Moran model that captures mechanical interactions and directional growth in spatially extended populations. The model is analytically tractable and completely solvable under a mean-field approximation and can elucidate the mechanisms that drive the formation of population-level patterns. As an example we model a population of E. coli growing in a rectangular microfluidic trap. We show that spatial patterns can arise as a result of a tug-of-war between boundary effects and growth rate modulations due to cell-cell interactions: Cells align parallel to the long side of the trap when boundary effects dominate. However, when cell-cell interactions exceed a critical value, cells align orthogonally to the trap's long side. This modeling approach and analysis can be extended to directionally-growing cells in a variety of domains to provide insight into how local and global interactions shape collective behavior.

Fine and ultrafine particle exposures on 73 trips by car to 65 non-smoking restaurants in the San Francisco Bay Area.

A number of studies indicate cooking is a major source of exposure to particulate matter, but few studies have measured indoor air pollution in restaurants, where cooking predominates. We made 73 visits by car to 65 different non-smoking restaurants in 10 Northern California towns while carrying portable continuous monitors that unobtrusively measured ultrafine (down to 10 nm) and fine (PM2.5 ) particles to characterize indoor restaurant exposures, comparing them with exposures in the car. The mean ultrafine number concentrations in the restaurants on dinner visits averaging 1.4 h was 71 600 particles/cm3 , or 4.3 times the mean concentration on car trips, and 12.3 times the mean background concentration in the residence. Restaurants that cooked dinner in the same room as the patrons had higher ultrafine concentrations than restaurants with separate kitchens. Restaurant PM2.5 mass concentrations averaged 36.3 µg/m3 , ranging from 1.5 to 454 µg/m3 , but were relatively low on most visits: 43% of the indoor means were below 10 µg/m3 and 66% were below 20 µg/m3 , with 5.5% above 100 µg/m3 . Exposure to fine and ultrafine particles when visiting a restaurant exceeded the exposure a person received while traveling by car to and from the restaurant.

Ultrafine particles from electric appliances and cooking pans: experiments suggesting desorption/nucleation of sorbed organics as the primary source.

Ultrafine particles are observed when metal surfaces, such as heating elements in electric appliances, or even empty cooking pans, are heated. The source of the particles has not been identified. We present evidence that particles >10 nm are not emitted directly from the heating elements or the metal surfaces. Using repeated heating of an electric burner, several types of cooking pans, and a steam iron, the increase in the number of particles (>10 nm) can be reduced to 0. After the devices are exposed to indoor air for several hours or days, subsequent heating results in renewed particle production, suggesting that organic matter has sorbed on their surfaces. Also, after a pan has been heated to the point that no increase in particles is observed, washing with detergent results in copious production of particles the next time the pan is heated. These observations suggest that detergent residue and organics sorbed from indoor air are the sources of the particles. We hypothesize that organic compounds are thermally desorbed from the hot surface as gaseous molecules; as they diffuse from the hot air near the pan into cooler air, selected compounds exceed their saturation concentration and nucleation occurs.

First observation of the unbound nucleus 15Ne.

We report on the first observation of the unbound proton-rich nucleus 15Ne. Its ground state and first excited state were populated in two-neutron knockout reactions from a beam of 500 MeV/u 17Ne. The 15Ne ground state is found to be unbound by 2.522(66) MeV. The decay proceeds directly to 13O with simultaneous two-proton emission. No evidence for sequential decay via the energetically allowed 2- and 1- states in 14F is observed. The 15Ne ground state is shown to have a strong configuration with two protons in the (sd) shell around 13O with a 63(5)% (1s1/2)2 component.

Identifying and quantifying secondhand smoke in source and receptor rooms: logistic regression and chemical mass balance approaches.

Identifying and quantifying secondhand tobacco smoke (SHS) that drifts between multiunit homes is critical to assessing exposure. Twenty-three different gaseous and particulate measurements were taken during controlled emissions from smoked cigarettes and six other common indoor source types in 60 single-room and 13 two-room experiments. We used measurements from the 60 single-room experiments for (i) the fitting of logistic regression models to predict the likelihood of SHS and (ii) the creation of source profiles for chemical mass balance (CMB) analysis to estimate source apportionment. We then applied these regression models and source profiles to the independent data set of 13 two-room experiments. Several logistic regression models correctly predicted the presence of cigarette smoke more than 80% of the time in both source and receptor rooms, with one model correct in 100% of applicable cases. CMB analysis of the source room provided significant PM2.5 concentration estimates of all true sources in 9 of 13 experiments and was half-correct (i.e., included an erroneous source or missed a true source) in the remaining four. In the receptor room, CMB provided significant estimates of all true sources in 9 of 13 experiments and was half-correct in another two.

Controlled experiments measuring personal exposure to PM2.5 in close proximity to cigarette smoking.

Few measurements of exposure to secondhand smoke (SHS) in close proximity to a smoker are available. Recent health studies have demonstrated an association between acute (<2 h) exposures to high concentrations of SHS and increased risk of cardiovascular and respiratory disease. We performed 15 experiments inside naturally ventilated homes and 16 in outdoor locations, each with 2-4 non-smokers sitting near a cigarette smoker. The smoker's and non-smokers' real-time exposures to PM2.5 from SHS were measured by using TSI SidePak monitors to sample their breathing zones. In 87% of the residential indoor experiments, the smoker received the highest average exposure to SHS, with PM2.5 concentrations ranging from 50-630 µg/m(3) . During the active smoking period, individual non-smokers sitting within approximately 1 m of a smoker had average SHS exposures ranging from negligible up to >160 µg/m(3) of PM2.5 . The average incremental exposure of the non-smokers was higher indoors (42 µg/m(3) , n = 35) than outdoors (29 µg/m(3) , n = 47), but the overall indoor and outdoor frequency distributions were similar. The 10-s PM2.5 averages during the smoking periods showed great variability, with multiple high concentrations of short duration (microplumes) both indoors and outdoors.

Radioactive materials in biosolids: dose modeling.

The Interagency Steering Committee on Radiation Standards (ISCORS) has recently completed a study of the occurrence within the United States of radioactive materials in sewage sludge and sewage incineration ash. One component of that effort was an examination of the possible transport of radioactivity from sludge into the local environment and the subsequent exposure of humans. A stochastic environmental pathway model was applied separately to seven hypothetical, generic sludge-release scenarios, leading to the creation of seven tables of Dose-to-Source Ratios (DSR), which can be used in translating from specific activity in sludge into dose to an individual. These DSR values were then combined with the results of an ISCORS survey of sludge and ash at more than 300 publicly owned treatment works, to explore the potential for radiation exposure of sludge workers and members of the public. This paper provides a brief overview of the pathway modeling methodology employed in the exposure and dose assessments and discusses technical aspects of the results obtained.

Mathematical models for predicting indoor air quality from smoking activity.

Much progress has been made over four decades in developing, testing, and evaluating the performance of mathematical models for predicting pollutant concentrations from smoking in indoor settings. Although largely overlooked by the regulatory community, these models provide regulators and risk assessors with practical tools for quantitatively estimating the exposure level that people receive indoors for a given level of smoking activity. This article reviews the development of the mass balance model and its application to predicting indoor pollutant concentrations from cigarette smoke and derives the time-averaged version of the model from the basic laws of conservation of mass. A simple table is provided of computed respirable particulate concentrations for any indoor location for which the active smoking count, volume, and concentration decay rate (deposition rate combined with air exchange rate) are known. Using the indoor ventilatory air exchange rate causes slightly higher indoor concentrations and therefore errs on the side of protecting health, since it excludes particle deposition effects, whereas using the observed particle decay rate gives a more accurate prediction of indoor concentrations. This table permits easy comparisons of indoor concentrations with air quality guidelines and indoor standards for different combinations of active smoking counts and air exchange rates. The published literature on mathematical models of environmental tobacco smoke also is reviewed and indicates that these models generally give good agreement between predicted concentrations and actual indoor measurements.

Thyroid volume and urinary iodine in European schoolchildren: standardization of values for assessment of iodine deficiency.

Up to 1992, most European countries used to be moderately to severely iodine deficient. The present study aimed at evaluating possible changes in the status of iodine nutrition in 12 European countries during the past few years. Thyroid volume was measured by ultrasonography in 7599 schoolchildren aged 7-15 years in one to fifteen sites in The Netherlands. Belgium, Luxemburg, France, Germany, Austria, Italy, Poland, the Czech and Slovak Republics, Hungary and Romania. The concentrations of urinary iodine were measured in 5709 of them. A mobile unit (ThyroMobil van) equipped with a sonographic device and facilities for the collection of urine samples visited all sites in the 12 countries. All ultrasounds and all urinary iodine assays were performed by the same investigators. The status of iodine nutrition in schoolchildren has markedly improved in many European countries and is presently normal in The Netherlands, France and Slovakia. It remains unchanged in other countries such as Belgium. There is an inverse relationship between urinary iodine and thyroid volume in schoolchildren in Europe. Goiter occurs as soon as the urinary iodine is below a critical threshold of 10 micrograms/dl. Its prevalence is up to 10 to 40% in some remote European areas. This work produced updated recommendations for the normal volume of the thyroid measured by ultrasonography as a function of age, sex and body surface area in iodine-replete schoolchildren in Europe. This study proposes a method for a standardized evaluation of iodine nutrition on a continental basis, which could be used in other continents.

Primary cesarean section: factors related to postpartum infection.

Four hundred sixty-five primary cesarean sections (10.4% of total deliveries) performed during 1977 and 1978 were reviewed and compared with 465 vaginal deliveries to ascertain factors that may be related to postpartum infection. The overall morbidity (19.7%) related to postpartum infection in the primary cesarean section group was statistically different from the 2.4% morbidity in the vaginal group. Cross comparisons of the effect of membrane status, use of internal electronic monitoring, development of postpartum anemia, duration of active labor, and difference in patient populations showed that internal monitoring had little or no effect on the development of postpartum endometritis. However, the development of postpartum anemia, increased time between membrane rupture and delivery, and, most important, a significant difference in patient populations were believed to be related to the development of postpartum endometritis in both groups.

Primary cesarean section: a critical analysis.

A detailed analysis of 465 primary cesarean sections (10.4% of total deliveries) performed at St. Mary's Health Center during 1977 and 1978 was undertaken. Cephalopelvic disproportion, malpresentation, and fetal distress were the 3 most common primary indications for cesarean section. An analysis of the effects of fetal monitoring seemed to indicate that the procedure was not a significant factor in increased use of cesarean section.

Clinical application of fetal weight determination by real-time ultrasound measurements.

The weights of 101 neonates delivered within 72 hours of real-time ultrasound examination were compared with the weight calculated from the ultrasonically measured biparietal diameter and abdominal circumference. A high degree of correlation (4 = .9624) was found between actual and calculated weights. This method of weight estimation has been clinically useful, especially in infants weighing less than 1500 g.

Defining altered fetal growth by second-trimester sonography.

A method of predicting birth weight from a single ultrasound examination between 18-28 weeks' gestation was evaluated prospectively in 315 obstetric patients with singleton pregnancies. Estimated fetal weight at the time of the ultrasound examination was used to predict actual birth weight. At delivery, the percent difference between the projected and actual birth weights was then used to define whether an infant was small, appropriate, or large for gestational age. This method appeared to be accurate and showed identical relationships to the presence of abnormal fetal heart rate patterns in growth-retarded infants as did the traditional birth-weight-for-gestational-age method of defining intrauterine growth retardation.

Fetal femur length, neonatal crown-heel length, and screening for intrauterine growth retardation.

Early ultrasonic diagnosis of intrauterine growth retardation (IUGR) can be very beneficial. However, most methods of ultrasonic diagnosis require an accurate knowledge of gestational age. The current study was designed to prospectively evaluate the relationship between fetal femur length and neonatal crown-heel length, and to study the femur length/abdominal circumference ratio as a method of screening for IUGR. Three hundred twenty-six infants who had undergone real-time ultrasound examination within 72 hours before birth were used for the study. Fetal femur length was compared with neonatal crown-heel length, although the most accurate relationship was geometric (r2 = .7474), and a strong linear relationship was also observed: y(crown-heel length) = 11.887 + 5.158 X (femur length), (r2 = .7067; SD = 3.34 cm). Mean femur length/abdominal circumference ratios were significantly different for average-for-gestational-age (22.33 +/- 1.86%), small-for-gestational-age (23.34 +/- 1.89%), and large-for-gestational-age (20.99 +/- 1.32%) infants, but did not reveal a discriminatory value for the diagnosis of IUGR as positive as that reported by Hadlock et al. The femur length/abdominal circumference ratio should be evaluated further as a screening tool in the diagnosis of IUGR.

Accurate gestational dating.

Gestational age by four ultrasonic parameters (biparietal diameter, head circumference, abdominal circumference, and femur length) was calculated for 210 normal obstetric patients divided into four gestational age groups based on time of first ultrasound examination. Accuracy of the calculations was determined by comparison of each technique and a simple arithmetic average of the four techniques to the gestational age calculated from the Dubowitz examination of the neonate after delivery. The analysis indicated that each ultrasonic technique has certain advantages and disadvantages, but that the simple arithmetic average of the four techniques had the lowest systematic and random error.

Ultrasonic diagnosis of altered fetal growth by use of a normal ultrasonic fetal weight curve.

A previously developed normal ultrasonic fetal weight curve was used for antenatal diagnosis of altered fetal growth in 595 patients who had undergone real-time ultrasound examination within 72 hours before birth. Fetal weight was estimated using biparietal diameter and abdominal circumference and plotted on the normal curve. The diagnosis of small for gestational age (SGA) or large for gestational age (LGA) was based on whether the ultrasonic weight fell below or above the normal limits. After delivery, infants were classified as SGA, LGA, or average for gestational age (AGA) by birth weight, and the postnatal diagnosis was compared to the antenatal ultrasound diagnosis. The sensitivity of the technique for the diagnosis of SGA infants was 89.9%; for LGA it was 73.5%. The overall specificity of the technique was 79.8%.

Analysis of variables affecting perinatal mortality: St. Louis City Hospital, 1969-1975.

A marked drop in perinatal mortality at St. Louis City Hospital No. 1 (SLCH) from 1974 to 1975 (39.7 vs 20.6 per 1000 births) prompted a detailed analysis of various factors which might have effected the change. Comparisons were also made between SLCH and St. Mary's Health Center (SMHC), a private hospital affiliated with St. Louis University. The significant drop in perinatal mortality at SLCH in 1975 seems to be due to a combination of various factors: 1) improvement in antepartum care, 2) increase use of cesarean sections, and 3) the influence of intrapartum fetal monitoring.

Vacuum extraction.

In the past twenty years, the vacuum extractor has gained wide use in Europe with an associated decrease in perinatal mortality. There, its use is considered by many to be much safet than a forceps delivery. Certain complications are associated with its use, but in general these are minor and transitory. On analysis, most of the serious complications reported in the literature are considered to be due to other associated factors, or to misuse of the vacuum extractor. Experience with the vacuum extractor in the United States has been minimal, and most authors feel that there are few indications for its use. Perhaps it is time that obstetricians in the United States take a more careful look at the European experience, and give the vacuum extractor a fair trial.

The current status of intrapartum fetal monitoring.

Intensive intrapartum fetal monitoring, using direct fetal EKG leads and intrauterine pressure sensing transducers, seems to add another level of care for the fetus. As with other laboratory aids or devices, fetal monitoring data should not be exclusively relied on in decision making processes. When used with other modern monitor aids, such as scalp pH, it can aid immensely in the management of both normal and complicated labors. When fetal heart rate patterns remain normal throughout labor there can be a high degree of confidence that the fetal outcome will be good. If abnormal patterns occur, however, great care should be taken in interpreting these data, and it should be combined with the overall status of the mother and the fetus, and used together with the clinical acumen of the physician in determining a method of approach to the management of intrapartum situations. Continuous monitoring techniques can and should be applied in the neonatal nursery for intensive neonatal management and care (79,80). As experience is gained in clinical fetal monitoring and as new techniques and methods become available, intensuve intrapartum fetal monitoring will become an increasingly important and significant technique for management of labor (4, 139).

Human exposure assessment: the birth of a new science.

I am honored to have been selected to receive the 1995 Weselowski Award for Career Achievement in Exposure Assessment. When I think back to my friendship with Jerry Weselowski, I remember our discussions in 1991 about the need to define exposure rigorously and quantitatively. In fact, I sent Jerry a letter on that topic--the quantitative definition of exposure--on November 7, 1991. I think it is fitting, therefore, that I select one of the topics in my talk today from that letter. Jerry always welcomed full and open scientific debate and discussion, and I feel that the need to define exposure and to understand what it means is a topic of great importance in exposure assessment. I also want to offer some observations about the importance of our field for the public and the regulatory community and to suggest the directions that exposure assessment might take as it evolves as a profession. Finally, I hope to provide an up-to-date listing of some selected scientific papers that are relevant to our field.