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PubMedDate not supplied

Some neural network applications in environmental sciences. Part II: advancing computational efficiency of environmental numerical models.

A new generic neural network (NN) application-improving computational efficiency of certain processes in numerical environmental models-is considered. This approach can be used to accelerate the calculations and improve the accuracy of the parameterizations of several types of physical processes which generally require computations involving complex mathematical expressions, including differential and integral equations, rules, restrictions and highly nonlinear empirical relations based on physical or statistical models. It is shown that, from a mathematical point of view, such parameterizations can usually be considered as continuous mappings (continuous dependencies between two vectors) and, therefore, NNs can be used to replace primary parameterization algorithms. In addition to fast and accurate approximation of the primary parameterization, NN also provides the entire Jacobian for very little computation cost. Four particular real-life applications of the NN approach are presented here: for oceanic numerical models, a NN approximation of the UNESCO equation of state of the sea water (NN for the density of the seawater) and an inversion of this equation (NN for the salinity of the seawater); for atmospheric numerical models, a NN approximation for long wave radiative transfer code; and for wave models, a NN approximation for the nonlinear wave-wave interaction. In all considered applications a significant acceleration of numerical computations has been achieved. The first two of these NN applications have already been implemented in the multi-scale ocean forecast system at NCEP. The NN approach introduced in this paper can provide numerically efficient solutions to a wide range of problems in numerical models where lengthy, complicated calculations, which describe physical, chemical and/or biological processes, must be repeated frequently.

Environment↗
PubMed2001

Probabilistic approaches to the use of higher order clone relationships in physical map assembly.

UNLABELLED: Physical map assembly is the inference of genome structure from experimental data. Map assembly depends on the integration of diverse data including sequence tagged site (STS) marker content, clone sizing, and restriction digest fingerprints (RDF). As experimentally measured data, these are uncertain and error prone. Physical map assembly from error free data is straightforward and can be accomplished in linear time in the number of clones, but the assembly of an optimal map from error prone data is an NP-hard problem. We present an alternative approach to physical map assembly that is based on a probabilistic view of the data and seeks to identify those features of the map that can be reliably inferred from the available data. With this approach, we achieve a number of goals. These include the use of multiple data sources, appropriate representation of uncertainties in the underlying data, the use of clone length information in fingerprint map assembly, and the use of higher order information in map assembly. By higher order information, we mean relationships that are not expressible in terms of neighbouring clone relationships. These include triplet and multiple clone overlaps, the uniqueness of STS position, and fingerprint marker locations. In a probabilistic view of physical mapping, we assert that all of the many possible map assemblies are equally likely a priori. Given experimental data, we can only state which assemblies are more likely than others given the experimental observations. Parameters of interest are then derived as likelihood weighted averages over map assemblies. Ideally these averages should be sums or integrals over all possible map assemblies, but computationally this is not feasible for real-world map assembly problems. Instead, sampling is used to asymptotically approach the desired parameters. Software implementing our probabilistic approach to mapping has been written. Assembly of mixed RDF and STS maps containing up to 60 clones can be accomplished on a desktop PC with run times under an hour. AVAILABILITY: http://stl.wustl.edu/software/gibbsmap/.

Cloning, Molecular↗
PubMed2001

Fitness portfolio calibration for first- through sixth-grade children.

The purpose of this study was to develop and calibrate health-relatedfitness portfolios for 1st-6th grade students using the many-faceted Rasch model, and examine advantages and disadvantages of a portfolio assessment system based on Rasch calibration. Nine hundred ninety-five studentsfrom 23 schools infirst-sixth grade, who completed three-six of nine health-related fitness portfolios, participated in this study. Ten physical education teachers performed the grading across various portfolios and grade levels. Students'portfolios were rated using 23 predeveloped rubrics, and their scores linked through several common portfolios that were used across schools. The rating scores were analyzed using the many-faceted Rasch model, with four defined facets: portfolio, rubric, student, and rater The model-data fit was very good, and a consistent grade difference wasfound, that is, older students scored higher in fitness knowledge than younger ones. With Rasch calibration, measurement problems in conventional portfolio assessments can be eliminated, and a valid and reliable assessment system can be developed. In addition, several other measurement advantages are provided by Rasch calibration (e.g., related facets can be examined and controlled simultaneously). A large sample size and a more complex process, however, are required in the calibration stage of developing such a system using the Rasch model.

Calibration↗
PubMedDate not supplied

Attitudes of contemporary parents toward behavior management techniques used in pediatric dentistry.

PURPOSE: The objective of this study was to examine parental attitudes toward behavior management techniques currently used in pediatric dentistry. METHODS: Fifty-five parents viewed videotaped scenes of 8 behavior management techniques being used during actual pediatric dental treatment. The 8 techniques shown were: (1) tell-show-do; (2) nitrous oxide sedation; (3) passive restraint; (4) voice control; (5) hand-over-mouth; (6) oral premedication (sedation); (7) active restraint; and (8) general anesthesia. Parents rated their acceptance of each technique using a visual analogue scale (VAS). RESULTS: Forty-six parents completed survey forms for analysis. Tell-show-do was rated as the most acceptable technique, followed (in order of decreasing acceptance) by: (1) nitrous oxide sedation; (2) general anesthesia; (3) active restraint; (4) oral premedication; (5) voice control; (6) passive restraint; and (7) hand-over-mouth. The following groups emerged with statistically similar means: (1) tell-show-do and nitrous oxide sedation; (2) nitrous oxide sedation, general anesthesia, and active restraint; and (3) general anesthesia, active restraint, oral premedication, and voice control. Hand-over-mouth and passive restraint were rated as the least acceptable techniques, and the ratings for both techniques were significantly different from all other techniques and from each other. Overall, hand-over-mouth was the least acceptable technique. Acceptance of each behavior management technique was not related to parental age, gender, education level, or social status. CONCLUSIONS: The mean parental acceptance rating was in the acceptable range for all behavior management techniques examined in this study except for hand-over-mouth. General anesthesia was ranked as the third most acceptable technique. This high level of acceptance of general anesthesia compared to earlier studies may suggest that parental acceptance of this technique is increasing.

Adult↗
PubMed1979

Physical growth: National Center for Health Statistics percentiles.

Anthropometry is an effective and frequently performed child health and nutrition screening procedure. The value of physical growth data depends on their accuracy and reliability, how they are recorded and interpreted, and what follow-up efforts are made after identification of growth abnormality. The new National Center for Health Statistics percentiles can be used to improve identification of potential health and nutritional problems and to facilitate the epidemological comparison of one group of children with others.

Adolescent↗
PubMed2005

Magnetic pulse affects a putative magnetoreceptor mechanism.

Clusters of superparamagnetic (SP) magnetite crystals have recently been identified in free nerve endings in the upper-beak skin of homing pigeons and are interpreted as being part of a putative magnetoreceptor system. Motivated by these findings, we developed a physical model that accurately predicts the dynamics of interacting SP clusters in a magnetic field. The main predictions are: 1), under a magnetic field, a group of SP clusters self-assembles into a chain-like structure that behaves like a compass needle under slowly rotating fields; 2), in a frequently changing field as encountered by a moving bird, a stacked chain is a structurally more stable configuration than a single chain; 3), chain-like structures of SP clusters disrupt under strong fields applied at oblique angles; and 4), reassemble on a timescale of hours to days (assuming a viscosity of the cell plasma eta approximately 1 P). Our results offer a novel mechanism for magnetic field perception and are in agreement with the response of birds observed after magnetic-pulse treatments, which have been conducted in the past to specifically test if ferrimagnetic material is involved in magnetoreception, but which have defied explanation so far. Our theoretical results are supported by experiments on a technical SP model system using a high-speed camera. We also offer new predictions that can be tested experimentally.

Animals↗
PubMed1999

The rational clinical examination. Is this patient hypovolemic?

OBJECTIVE: To review, systematically, the physical diagnosis of hypovolemia in adults. METHODS: We searched MEDLINE (January 1966-November 1997), personal files, and bibliographies of textbooks on physical diagnosis and identified 10 studies investigating postural vital signs or the capillary refill time of healthy volunteers, some of whom underwent phlebotomy of up to 1150 mL of blood, and 4 studies of patients presenting to emergency departments with suspected hypovolemia, usually due to vomiting, diarrhea, or decreased oral intake. RESULTS: When clinicians evaluate adults with suspected blood loss, the most helpful physical findings are either severe postural dizziness (preventing measurement of upright vital signs) or a postural pulse increment of 30 beats/min or more. The presence of either finding has a sensitivity for moderate blood loss of only 22% (95% confidence interval [CI], 6%-48%) but a much greater sensitivity for large blood loss of 97% (95% CI, 91%-100%); the corresponding specificity is 98% (95% CI, 97%-99%). Supine hypotension and tachycardia are frequently absent, even after up to 1150 mL of blood loss (sensitivity, 33%; 95% CI, 21%-47%, for supine hypotension). The finding of mild postural dizziness has no proven value. In patients with vomiting, diarrhea, or decreased oral intake, the presence of a dry axilla supports the diagnosis of hypovolemia (positive likelihood ratio, 2.8; 95% CI, 1.4-5.4), and moist mucous membranes and a tongue without furrows argue against it (negative likelihood ratio, 0.3; 95% CI, 0.1-0.6 for both findings). In adults, the capillary refill time and poor skin turgor have no proven diagnostic value. CONCLUSIONS: A large postural pulse change (> or =30 beats/min) or severe postural dizziness is required to clinically diagnose hypovolemia due to blood loss, although these findings are often absent after moderate amounts of blood loss. In patients with vomiting, diarrhea, or decreased oral intake, few findings have proven utility, and clinicians should measure serum electrolytes, serum blood urea nitrogen, and creatinine levels when diagnostic certainty is required.

Aged↗
PubMed1997

A sequential design for psychophysical experiments: an application to estimating timing of sensory events.

An experimental subject sequentially receives different levels of a stimulus, and data are recorded on response or non-response to the stimulus. To ensure that the subject cannot predict the next stimulus level based on previous stimulus levels, a randomized design, based on a generalized Pólya urn model, is used to allocate the stimulus levels. The goal of the experiment is to elicit information efficiently about the relationship between stimulus level and response (either for an individual subject or a group of independent subjects), by estimating quantiles of the stimulus-response curve. Our design allocates stimulus levels unimodally and symmetrically around the unknown median of the stimulus-response curve. We discuss estimation under a broad family of distributions and also fully discuss design issues and options. This design was used for an experiment in neurophysiology in humans to estimate the timing of onset of kinesthetic stimuli. Such psychophysical studies can increase our understanding of normal and pathological function. We present data from that experiment.

Adult↗
PubMed2007

LongCriSP: a test for bump hunting in longitudinal data.

We propose an extension of the Harezlak and Heckman (J. Comput. Graph. Statist. 2001; 10(4): 713-729) test for detecting local extrema to the longitudinal data setting. We use penalized spline regression techniques (Statist. Sci. 1996; 11:89-102) to provide a computationally efficient method of testing for relatively large data sets. We estimate the p-values of our test, LongCriSP, with a smoothed bootstrap. Our simulation studies indicate that the test is generally conservative and has power exceeding 70 per cent at the alpha = 0.1 nominal level in most considered settings. Finally, we apply our testing procedure to the longitudinal measurements of body mass index of former prisoners of war in Vietnam and conclude that the mean population curve exhibits non-monotone behaviour.

Body Mass Index↗
PubMed1993

Impact of a breast cancer screening community intervention.

BACKGROUND: Efforts to detect breast cancer in its early stages are necessary to reduce breast cancer-associated mortality. This study evaluated the impact of a multicomponent intervention implemented between 1987 and 1990 to increase a community's utilization of breast cancer screening by women over 50 years of age. METHODS: The study used a pretest/post-test two-community design, with one community assigned as the intervention community and the other as the comparison. The intervention consisted of a comprehensive physician involvement component and a community education effort. To assess the overall impact of the interventions, we measured women's participation in screening via random digit dial telephone surveys at three time points, each approximately 18 months apart. RESULTS: Over the course of the study, there were dramatic improvements in breast cancer screening participation in both communities. However, the intervention city showed more improvement in selected variables than did the comparison community in the early phases of the project between baseline and midpoint. These included increased advice by physicians to have mammograms, increased awareness that screening is necessary in the absence of symptoms, increased awareness that many women over 50 have mammograms, decreased perception of barriers to clinical breast exam, and an increase in the proportion of women having a clinical breast exam. In addition, significantly fewer women in the intervention city than in the comparison city reported never having had a mammogram at midpoint. CONCLUSIONS: The findings demonstrate limited impact of a community intervention during a period of increasing adoption of mammography screening, in part, due to this rapidly rising secular trend. Additionally, increased activities in the comparison community were documented. Therefore, as incidence of screening increases, targeted activities aimed at population subgroups are warranted, and evaluation designs need to include multiple comparison groups or broader geographic random samples.

Aged↗
PubMed2001

Estimation of the gas exchange threshold in humans: a time series approach.

An autoregressive moving average model is presented for detecting the gas exchange threshold (GET) from gas exchange response data taken during an incremental exercise test. The approach has the advantage of modelling the serial correlation in the noise between observations from the same subject. The model is fitted by maximum likelihood and a breakpoint or threshold in the mean function is the estimated GET. It is shown how an estimate of standard error can be obtained by bootstrapping the residuals from the fitted model. To evaluate the approach, gas exchange data on 14 healthy subjects during a ramp exercise test (20 W x min(-1)) to the limits of tolerance, were analysed. The results are compared to the v-slope method and to the method of maximum likelihood assuming independent noise.

Adult↗
PubMed2006

Bivariate survival modeling: a Bayesian approach based on Copulas.

Copula models have become increasingly popular for modeling multivariate survival data. In this paper we review some of the recent work that has been appeared for copula model for bivariate survival data and propose a Bayesian modeling. Our approach is very flexible with respect to the choice of marginal distributions and, depending on the copula model employed, it is possible to have a class of variation for the dependence parameter. We compare some of the copula models using a descriptive diagnostic method and three popular Bayesian model selection criteria. Our methodology is illustrated with the Diabetic Retinopathy Study (1976).

Bayes Theorem↗
PubMed1997

Quantitative assessments from the clinical examination. How should clinicians integrate the numerous results?

OBJECTIVE: To describe strategies for using multiple clinical examination items to estimate disease probabilities; and to evaluate the diagnostic accuracy of each strategy. DESIGN: Prospective observational study. SETTING: Medical preoperative evaluation clinic at a university-affiliated Veterans Affairs Medical Center. PATIENTS: Previously reported consecutive series of patients referred for outpatient medical preoperative risk assessment. MEASUREMENTS AND MAIN RESULTS: Pulmonary clinical examination and spirometry were the measurements. A strategy of using likelihood ratios (LRs) from seven clinical examination items was least accurate (p < .0001). Three alternative strategies were equivalent in diagnostic accuracy (p > or = .2): (1) using the single best clinical examination item and its LR, (2) using the LRs from three clinical examination items chosen by logistic regression, and (3) using the adjusted LRs chosen in strategy 2. When compared with using LRs from all seven items, the strategies of using three LRs chosen by logistic regression or using adjusted likelihood ratios better discriminated patients with airflow limitation from those without (receiver operating characteristic [ROC] areas 0.79 vs 0.69; p = .02). Using the single best clinical finding did not statistically degrade the clinical examination's discriminating ability (ROC areas 0.79 vs 0.75; p = .20). CONCLUSIONS: Describing the rational clinical examination requires evaluating conditional independence of examination components. Conditional independence assumptions were violated when seven clinical examination items were used to estimate posterior probability of airflow limitation. Focusing on clinical examination items identified through logistic models overcame violations of independence; further statistical adjustment did not improve diagnostic accuracy. Clinicians can use the single most predictive clinical examination finding to avoid inaccuracy from violating the independence assumption.

Aged↗
PubMedDate not supplied

Gastric lipid peroxidation, glutathione and calcium channel blockers in the stress-induced ulcer model in rats.

The antiulcer activity of verapamil and its analogues devapamil and gallopamil was studied. All three drugs reduced cold-restraint stress-induced ulcer development. Gallopamil almost abolished gastric ulcers. Verapamil prevented the increase in gastric lipid peroxidation (LP) due to stress. On the other hand, devapamil and gallopamil increased gastric lipid peroxidation and decreased glutathione levels. This effect may be attributed to the increase in oxygen supply due to possible effective vasodilation at gastric mucosa. The second part of this study revealed that stress-induced gastric ulcers in rats rapidly and spontaneously heal and disappear within 24 h. During recovery, gastric LP decreased and glutathione levels increased within 12 h after the withdrawal of stress, preceded by an initial reduction in glutathione. After 72 h, an unexplained increase in gastric LP and a decrease in glutathione were observed. Treatment with verapamil, devapamil and gallopamil promoted healing, gallopamil being again the most effective. Their effects on gastric LP and glutathione levels are in accordance with the results of pretreatment experiments. In conclusion, devapamil and gallopamil are effective antiulcer agents against stress-induced ulcers, but unlike verapamil, antioxidant activity does not seem likely to be among their mechanisms of action.

Animals↗