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At least 1,279 records · Page 71Linked to original sources
PubMed1999

A simple predictive model for the structure of the oceanic pycnocline

A simple theory for the large-scale oceanic circulation is developed, relating pycnocline depth, Northern Hemisphere sinking, and low-latitude upwelling to pycnocline diffusivity and Southern Ocean winds and eddies. The results show that Southern Ocean processes help maintain the global ocean structure and that pycnocline diffusion controls low-latitude upwelling.

Journal Article↗
PubMed1998

Comprehensive evaluation of long-term trends in occupational exposure: Part 2. Predictive models for declining exposures.

OBJECTIVES: To explore the effects of various factors related to the industry, the contaminant, and the period and type of sampling on long term declining trends in occupational exposure. METHODS: Linear regression analyses were used to assess the relation between reductions in exposure and geographical location, industrial sector, type of contaminant, type of monitoring, carcinogenic classification, calendar period, duration of sampling, and number of reductions in the threshold limit value during the sampling period. Both univariable and multivariable models were applied. RESULTS: Based on univariable analyses, the findings suggest that exposures declined more rapidly in manufacturing than in mining, more rapidly for aerosol contaminants than for vapours, and more rapidly when biological, rather than airborne, monitoring was conducted. Exposures collected more recently (first year of sampling in 1972 or later) fell more rapidly than exposures first evaluated during earlier periods. Irrespective of when the data were collected, the results also suggest that the longer the duration of sampling the slower the rate of decline. Taken together, we found that characteristics related to the contaminant, the industry, the sampling period, and the type of sampling explained a substantial proportion of the variability for exposures evaluated before 1972 (R2 = 0.78) and for sites evaluated both before and after 1972 (R2 = 0.91), but explained essentially no variation for data gathered exclusively after 1972 (R2 = 0.04). CONCLUSIONS: By identifying factors that have affected the rates of reduction in a consistent fashion, the results should guide investigators in estimating historical levels when studies assessing exposure-response relations are carried out.

Analysis of Variance↗
PubMed1982

Use of prediction models to forecast and analyse airborne spread during the foot-and-mouth disease outbreaks in Brittany, Jersey and the Isle of Wight in 1981.

Between March 4 and 26, 1981 the French veterinary authorities reported a series of 14 outbreaks of disease due to type O foot-and-mouth (FMD) virus, 13 in Brittany and one in Normandy. The United Kingdom reported FMD type O in Jersey on March 19 and in the Isle of Wight on March 22. The field and laboratory investigations on the farm in the Isle of Wight are outlined. The way in which short and long range numerical models were used to forecast the airborne spread of FMD from Brittany to the UK and then to assess the risk of further airborne spread within the UK is described.

Air Microbiology↗
PubMed1980

A predictive model study of the visual contribution to canine postural control.

Dogs were trained to stand on a movable table and their quiet stance was perturbed by osccillation of the table during normal sighted condition and during blindfolded condition. The data formed the frequency response characteristic (describing function) for postural control with and without visual input. A feedback model was tested to assess the effect of visual input during the perturbation of quiet stance. The results of the tests of the model indicate that the effect of a visual input depends on the context of the multiple sensory factors influencing postural control. The effectiveness of the visual input increases if there is a conflict between the visually derived body position cues and the other cues that indicate the orientation of the body.

Animals↗
PubMed1997

A prediction model for functional recovery in stroke.

BACKGROUND AND PURPOSE: Stroke-related physical disability can diminish quality of daily living, place care burden on families, and increase need for long-term institutionalization. We developed a prognostic index for use in research and with potential for adaptation to clinical practice that establishes the likelihood of an individual achieving a specific stage of functional recovery after stroke rehabilitation. METHODS: We constructed the index using logistic regression based on 3760 patient records from 96 rehabilitation facilities in 31 states. The stage, as measured by the Functional Independence Measure, includes achievement of the following: independence in eating, grooming, and dressing the upper body; continence in bowel and bladder; and transfer between a bed and chair with supervision only. RESULTS: This stage was achieved by 26.1% of patients functioning below it at rehabilitation admission. Disability onset of less than 60 days was associated with more than a 3-fold increase in the likelihood of achieving the stage (adjusted odds ratio, 3.5; 95% confidence interval, 2.0 to 6.0). Each eight-point increase in an eight-item activities of daily living score, measured at admission to rehabilitation, increased the odds 2.5-fold (95% confidence interval, 2.3 to 2.8). For those living alone or employed before the stroke, the odds of achieving the stage increased by factors of 1.3 and 2.2, respectively. The index showed minimal shrinkage on cross validation. The achievement of this profile of function is important because 95.3% of stroke patients who achieved or exceeded it were discharged home, as opposed to only 66.8% of those who did not achieve it. CONCLUSIONS: The index can be used to establish prognoses for individual stroke patients at admission to rehabilitation with regard to achieving this stage. Achievement of the stage is associated with a high likelihood of discharge to home.

Activities of Daily Living↗
PubMed2000

Quantitative assessment of peripheral arterial obstruction in Raynaud's phenomenon: development of a predictive model of obstructive arterial cross-sectional area and validation with a Doppler blood flow study.

The objective of this study was to develop a method for the analytical assessment of arterial obstruction in conditions of Raynaud's phenomenon capable of providing diagnostic criteria. Numerous attempts have been made to determine and quantify arterial obstruction in terms of Doppler ultrasound measurements of arterial blood velocity. Absent from these methods is a formulation that allows an assessment of arterial obstruction based on the obstructed area as derived from direct measurement. The authors used spectral analysis of velocity signals from a pulsed, range-gated Doppler ultrasonic instrument to make quantitative measurements of arterial blood flow velocity in hands of normal subjects and persons with Raynaud's phenomenon. They measured the peak and mean velocity during the cardiac cycle and the time integral of the velocity signal over the cardiac cycle. These measurements for two distinct hemodynamic states induced by temperature changes allowed them to calculate the fractional change in arterial cross-sectional area produced by the change in temperature through the application of a hydraulic model of digital arterial circulation. They found an equation expressing fractional obstructed area expressed as: dA/A = 2 (dD - taudv - vtau)/(D + vdtau), where D is the time integral of the velocity signal; tau is the blood flow interval, v is the blood velocity; and dD, dtau and dv are the differences in D, tau, and v at two different hemodynamic states produced by two different temperature states. Their findings suggest that over a temperature range of 35 degrees-25 degrees C, normal subjects experience 0.05/ degrees C reduction in cross-sectional area while Raynaud subjects experience a reduction of 5.8%/degrees C. The results, based on findings in 13 subjects, suggest that Doppler ultrasound can differentiate persons with Raynaud's phenomenon from normal subjects. Additionally, the hydraulic model appears to offer the potential of assessing relative stenotic area in other arterial obstructive diseases.

Adult↗
PubMed2005

Probabilities and predictions: modeling the development of scientific problem-solving skills.

The IMMEX (Interactive Multi-Media Exercises) Web-based problem set platform enables the online delivery of complex, multimedia simulations, the rapid collection of student performance data, and has already been used in several genetic simulations. The next step is the use of these data to understand and improve student learning in a formative manner. This article describes the development of probabilistic models of undergraduate student problem solving in molecular genetics that detailed the spectrum of strategies students used when problem solving, and how the strategic approaches evolved with experience. The actions of 776 university sophomore biology majors from three molecular biology lecture courses were recorded and analyzed. Each of six simulations were first grouped by artificial neural network clustering to provide individual performance measures, and then sequences of these performances were probabilistically modeled by hidden Markov modeling to provide measures of progress. The models showed that students with different initial problem-solving abilities choose different strategies. Initial and final strategies varied across different sections of the same course and were not strongly correlated with other achievement measures. In contrast to previous studies, we observed no significant gender differences. We suggest that instructor interventions based on early student performances with these simulations may assist students to recognize effective and efficient problem-solving strategies and enhance learning.

Aptitude↗
PubMed2005

Seasonality and children's blood lead levels: developing a predictive model using climatic variables and blood lead data from Indianapolis, Indiana, Syracuse, New York, and New Orleans, Louisiana (USA).

On a community basis, urban soil contains a potentially large reservoir of accumulated lead. This study was undertaken to explore the temporal relationship between pediatric blood lead (BPb), weather, soil moisture, and dust in Indianapolis, Indiana; Syracuse, New York; and New Orleans, Louisiana. The Indianapolis, Syracuse, and New Orleans pediatric BPb data were obtained from databases of 15,969, 14,467, and 2,295 screenings, respectively, collected between December 1999 and November 2002, January 1994 and March 1998, and January 1998 and May 2003, respectively. These average monthly child BPb levels were regressed against several independent variables: average monthly soil moisture, particulate matter < 10 microm in diameter (PM10), wind speed, and temperature. Of temporal variation in urban children's BPb, 87% in Indianapolis (R2 = 0.87, p = 0.0004), 61% in Syracuse (R2 = 0.61, p = 0.0012), and 59% in New Orleans (R2 = 0.59, p = 0.0000078) are explained by these variables. A conceptual model of urban Pb poisoning is suggested: When temperature is high and evapotranspiration maximized, soil moisture decreases and soil dust is deposited. Under these combined weather conditions, Pb-enriched PM10 dust disperses in the urban environment and causes elevated Pb dust loading. Thus, seasonal variation of children's Pb exposure is probably caused by inhalation and ingestion of Pb brought about by the effect of weather on soils and the resulting fluctuation in Pb loading.

Child, Preschool↗
PubMed1998

The U.S. National Toxicology Program evaluation of transgenic mice as predictive models for identifying carcinogens.

National Institute of Environmental Health Sciences researchers have invested considerable effort in exploring the utility of transgenic mice to detect carcinogens and study mechanisms of carcinogenesis. Work has assessed several mouse models genetically altered to enhance their expression of chemically induced tumors. Results with the p53def (hemizygous for the tumor-suppressor gene) and the Tg.AC (carrier of an activated H-ras oncogene) mice have been used as a basis for a proposed new strategy for identifying chemical carcinogens and assessing risk. The U.S. National Toxicology Program is conducting a series of studies with these two transgenic strains to further examine their strengths and weaknesses for identification of documented rodent and human carcinogens and to explore their ability to provide information concerning the effective dosimetry for target organ mutation.

Animals↗