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At least 1,243 records · Page 69Linked to original sources
PubMed1990

Accuracy of model surgery: evaluation of an old technique and introduction of a new one.

This article evaluates the ability of 4th-year residents to accurately perform maxillary model surgical repositioning in the conventional manner. Using a special model surgery--measuring platform, measurements of the maxillary dental casts were recorded before and after model surgery was performed by residents in 20 bimaxillary cases. The model surgery was performed in the usual manner described in several texts, using reference lines scored on the casts and measurements made to the incisal pin and upper member of the articulator. Analysis of the differences between the planned movements and the postsurgical position of the maxillary model surgery casts showed statistically significant errors in maxillary repositioning for all measures. This indicates that the manner in which model surgery was performed by the residents, as reported in the literature, was inaccurate. A new technique and instrument for more accurately recording measurements and repositioning the maxillary cast is introduced.

Audiovisual Aids↗
PubMed1992

Nonlinear joint angle control for artificially stimulated muscle.

Designs of both open- and closed-loop controllers of electrically stimulated muscle that explicitly depend on a nonlinear mathematical model of muscle input-output properties are presented and evaluated. The muscle model consists of three factors: a muscle activation dynamics factor, an angle-torque relationship factor, and an angular velocity torque relationship factor. These factors are multiplied to relate output torque to input stimulation and joint angle. An experimental method for the determination of the parameters of this model was designed, implemented, and evaluated. An open-loop nonlinear compensator, based upon this model, was tested in an animal model. Its performance in the control of joint angle in the presence of a known load was compared with a PID controller, and with a combination of the PID controller and the nonlinear compensator. The performance of the nonlinear compensator appeared to be strongly dependent on modeling errors. Its performance was roughly equivalent to that of the PID controller alone: somewhat better when the model was accurate, and somewhat worse when it was inaccurate. Combining the nonlinear open loop compensator with the PID feedback controller improved performance when the model was accurate.

Animals↗
PubMed1999

Surface Complexation Modeling of Organic Acid Sorption to Goethite.

Surface complexation modeling was performed using the Generalized Two-Layer Model for a series of low molecular weight organic acids. Sorption of these organic acids to goethite was investigated in a previous study to assess the influence of particular structural features on sorption. Here, the ability to describe the observed sorption behavior for compounds with similar structural features using surface complexation modeling was investigated. A set of surface reactions and equilibrium constants yielding optimal data fits was obtained for each organic acid over a range of total sorbate concentrations. Surface complexation modeling successfully described sorption of a number of the simple organic acids, but an additional hydrophobic component was needed to describe sorption behavior of some compounds with significant hydrophobic character. These compounds exhibited sorption behavior that was inconsistent with ligand exchange mechanisms since sorption did not decrease with increasing total sorbate concentration and/or exceeded surface site saturation. Hydrophobic interactions appeared to be most significant for the compound containing a 5-carbon aliphatic chain. Comparison of optimized equilibrium constants for similar surface species showed that model results were consistent with observed sorption behavior: equilibrium constants were highest for compounds having adjacent carboxylic groups, lower for compounds with adjacent phenolic groups, and lowest for compounds with phenolic groups in the ortho position relative to a carboxylic group. Surface complexation modeling was also performed to fit sorption data for Suwannee River fulvic acid. The data could be described well using reactions and constants similar to those for pyromellitic acid. This four-carboxyl group compound may be useful as a model for fulvic acid with respect to sorption. Other simple organic acids having multiple carboxylic and phenolic functional groups were identified as potential models for humic substances. Copyright 1999 Academic Press.

Journal Article↗
PubMedDate not supplied

Simultaneous precise chemoradiation under inhalation anesthesia in an experimental mouse tumor model.

BACKGROUND: Performing radiobiological experiments under general anesthesia is, in many cases, superior to treatment in unanesthetized animals or with intraperitoneal (i.p.) anesthesia. This is especially true for experiments where highly fractionated treatment schedules are used. MATERIALS AND METHODS: An anesthesia system was employed to overcome several of the limitations associated with the use of pentobarbital and other i.p.-administered anesthetics in experimental radiotherapy. RESULTS: Several different experiments with a total of 152 mice were performed. The total of all anesthesia exposures amounted to approximately 1,520. The duration of anesthesia ranged from 3 to 5 min per session. No complications related to the anesthetic procedure were observed. CONCLUSION: The present anesthesia/irradiation setup is a simple, safe and perfectly reproducible system where even multiple fractionated treatments can be performed under anesthesia with excellent tolerance. Our system allows easy and fast handling and immobilization and thus reduces experimental times.

Anesthesia, Inhalation↗
PubMed2007

Population pharmacokinetics of mefloquine in military personnel for prophylaxis against malaria infection during field deployment.

OBJECTIVE: The purpose of this study was to determine the population pharmacokinetics of mefloquine in healthy military personnel during prophylaxis for malaria infections. METHODS: The subjects were 1,111 Australian soldiers participating in two studies: a randomised double-blinded study (group A, 161 subjects) and an open-label study (group B, 950 subjects). Following a loading dose (250 mg mefloquine base daily, 3 days), subjects received an oral weekly maintenance dose of 250 mg over 6 months. Blood was collected after the last split loading dose then at weeks 4, 8 and 16 for group A, and at weeks 13 and 26 for group B. Plasma mefloquine concentrations were measured by high-performance liquid chromatography (HPLC). Pharmacokinetic modelling was performed using NONMEM. RESULTS: A two-compartment model with inter-occasion variability (IOV) for clearance satisfactorily described the pharmacokinetics. Typical values were clearance (CL/F, 2.09 l/h), central volume of distribution (V1/F, 528 l), absorption rate constant (KA, 0.24 h(-1)), inter-compartmental clearance (Q/F, 12.5 l/h), peripheral volume of distribution (V2/F, 483 l) and elimination half-life (t (1/2), 14.0 days). Weight had a positive influence on central volume but was insufficient to warrant dosage adjustments. The inter-individual variability (coefficient of variation, CV%) for CL/F and V1/F was 24.4% and 29.6%, respectively. The IOV for CL/F was 17.8%. The proportional residual error (CV%) for groups A and B was 11.5% and 19.5%, respectively, and the additive error standard deviation (SD) was 57 ng/ml and 149 ng/ml, respectively. CONCLUSION: The typical parameter values were comparable with those estimated in much smaller cohorts of healthy subjects and in malaria patients treated with single-dose mefloquine. The lower unexplained variability in the blinded study suggested these subjects may have been more compliant in taking their medication than soldiers in the open-label study.

Adolescent↗
PubMedDate not supplied

Analysis of indoor concentrations of benzene using an air-quality model.

We performed measurements to determine indoor benzene levels in 26 residential houses in Kuwait, located in zones of different activity levels. Pumped (or active) sampling was conducted via use of 12 sampling tubes over a period of 24 hr for both indoor and outdoor concentrations simultaneously. Time-average indoor concentration varied linearly with time-average outdoor concentration in accordance with a mass-balance-based indoor air-quality model in which source and sink terms were incorporated. We used regression analysis to determine benzene adsorption rates, which appear in the removal and source terms of the model. The removal rate parameter varied between 0.12/hr and 2.16/hr, whereas source term parameter varied between 0.60 mg/hr and 76.07 mg/hr. Houses were then divided into three groups according to their benzene source strengths (i.e., < 1.0 mg/hr, 1-10 mg/hr, and 10-50 mg/hr). Qualitatively, these levels depended on the characteristics of occupants (e.g., smoking and gas cooker use, number of cars, and parking area) and location of the building.

Air Pollutants↗
PubMed1987

Infant speech-sound discrimination testing: effects of stimulus intensity and procedural model on measures of performance.

Performance of infants in a speech-sound discrimination task (/ba/ vs /da/) was measured at three stimulus intensity levels (50, 60, and 70 dB SPL) using the operant head-turn procedure. The procedure was modified so that data could be treated as though from a single-interval (yes-no) procedure, as is commonly done, as well as if from a sustained attention (vigilance) task. Discrimination performance changed significantly with increase in intensity, suggesting caution in the interpretation of results from infant discrimination studies in which only single stimulus intensity levels within this range are used. The assumptions made about the underlying methodological model did not change the performance-intensity relationships. However, infants demonstrated response decrement, typical of vigilance tasks, which supports the notion that the head-turn procedure is represented best by the vigilance model. Analysis then was done according to a method designed for tasks with undefined observation intervals [C. S. Watson and T. L. Nichols, J. Acoust. Soc. Am. 59, 655-668 (1976)]. Results reveal that, while group data are reasonably well represented across levels of difficulty by the fixed-interval model, there is a variation in performance as a function of time following trial onset that could lead to underestimation of performance in some cases.

Arousal↗
PubMed1998

Automatic stimulus-response translation in dual-task performance.

In bottleneck models of overlapping-task performance, stimulus-response translation for secondary tasks is postponed until the primary response is selected. If this is so, then compatibility between the secondary and primary responses, or between the secondary response and the primary stimulus, should not affect primary-task performance. Yet such effects were demonstrated in 5 dual-task experiments combining primary manual and secondary vocal tasks: Pronounced effects of compatibility between the secondary and primary response and between the secondary response and primary stimulus were found on primary-task performance. The latter effect was also found with the lowest level of an extensive stimulus onset asynchrony variation, when the secondary task was not speeded, and even when the 2 tasks were performed on different trials. Findings suggest that secondary responses were activated before primary response selection was completed and thus support an automatic-translation hypothesis holding that, although eventual response selection may be serial, stimulus-response translation is performed in parallel.

Adolescent↗
PubMed1995

Daily validation procedure of chromatographic assay using gaussoexponential modelling.

High performance liquid chromatography is one of the most successful analytical methods used for the quantitative determination of drugs in biological samples. However, this method is marked by a lack of performance reproducibility: chromatographic peaks become wider and even asymmetrical as the column ages. These progressive changes in the chromatographic parameters have to be taken into account when evaluating the validation criteria for the method. These criteria change with the ageing process of the column leading to the need for new estimations to assure the quality of the results. Procedures are proposed for the daily determination of some validation criteria using the exponentially modified Gaussian (EMG) model of the chromatographic peak. This modelling has been studied on simulated chromatographic peaks in order to obtain the relationships between chromatographic measurements and EMG parameters.

Chromatography, High Pressure Liquid↗
PubMed2000

An examination of the psychometric properties of the Test of Reading Performance using structural equation modeling.

The present purpose was to investigate the psychometric properties of the Test of Reading Performance, a new scale designed to evaluate the reading performance of Greek elementary school students. The sample consisted of 181 elementary school students, attending Grades 1-6 at two elementary schools in the area of Thessaloniki. The Test of Reading Performance was hypothesized to measure six constructs, namely, letter knowledge, phoneme blending, word identification, morphology knowledge, syntactic knowledge, and passage comprehension. Each construct was defined by two to four measured variables. The chosen structural model supported the multidimensional nature of reading and the relationship between the measured variables and constructs. Estimates of discriminant and convergent validity using confirmatory factor analytic procedures were satisfactory although these was multicollinearity for the measures morphology-syntax and morphology-comprehension. Internal consistency was also satisfactory for the full scale (alpha = .83).

Achievement↗
PubMed1998

Observational learning and the fearful child: influence of peer models on swimming skill performance and psychological responses.

This study examined the role of peer mastery and coping models on children's swimming skills, fear, and self-efficacy. Children (N = 24; M age = 6.2 years), who were identified as fearful of the water, were matched to control, peer-mastery, or peer-coping model conditions. Day 1 included a preintervention assessment. Days 2-4 included exposure to model conditions followed by a 20-min swimming lesson, Day 5 consisted of postintervention assessments, and a follow-up test was conducted 4 days later. Data were analyzed in a series of 3 x 3 (Model Type x Assessment Period) repeated measures analyses of variance on the dependent variables. Results revealed differences between modeling and control groups at postintervention and follow-up, but the small sample size and large within-group variability compromised many statistically significant findings. Calculation of effect sizes indicated moderate-to-large pre- to posintervention differences between control and modeling groups on skill, self-efficacy, and fear of swimming. These findings suggest that a modeling intervention combined with swimming lessons is a more effective behavior change agent for fearful children than swimming lessons alone.

Adaptation, Psychological↗
PubMed2005

The National Health Performance Framework: an evaluation model for use by psychiatrists.

OBJECTIVES: To demonstrate the use of the National Health Performance Framework as an evaluation framework for clinical interventions and service outcomes in mental health. CONCLUSIONS: Evaluation is not a complex process. What is required is a willingness to be accountable for outcomes of care. It does not require complex data systems but openness to scrutiny through reflective practices and a commitment to continue to explore the possibilities of making things better.

Australia↗
PubMed2000

Performance appraisal reactions: measurement, modeling, and method bias.

In this study, the authors attempted to comprehensively examine the measurement of performance appraisal reactions. They first investigated how well the reaction scales, representative of those used in the field, measured their substantive constructs. A confirmatory factor analysis indicated that these scales did a favorable job of measuring appraisal reactions, with a few concerns. The authors also found that the data fit a higher order appraisal reactions model. In contrast, a nested model where the reaction constructs were operationalized as one general factor did not adequately fit the data. Finally, the authors tested the notion that self-report data are affectively driven for the specific case of appraisal reactions, using the techniques delineated by L. J. Williams, M. B. Gavin, and M. L. Williams (1996). Results indicated that neither positive nor negative affect presented method biases in the reaction measures, at either the measurement or construct levels.

Adult↗
PubMed1998

Comparison of multiple prediction models for ambulation following spinal cord injury.

Few studies have properly compared predictive performance of different models using the same medical data set. We developed and compared 3 models (logistic regression, neural networks, and rough sets) in the in prediction of ambulation at hospital discharge following spinal cord injury. We used the multi-center Spinal Cord Injury Model System database. All models performed well and had areas under the receiver operating characteristic curve in the 0.88-0.91 range. All models had sensitivity, specificity, and accuracy greater than 80% at ideal thresholds. The performance of neural network and logistic regression methods was not statistically different (p = 0.48). The rough sets classifier performed statistically worse than either the neural network or logistic regression models (p-values 0.002 and 0.015 respectively).

Acute Disease↗
PubMed1992

In vivo patency of endothelial cell-lined expanded polytetrafluoroethylene prostheses in an ovine model.

The performance of small-diameter vascular prostheses may be improved by implantation of grafts lined with endothelial cells. Expanded polytetrafluoroethylene (ePTFE) prostheses (4 mm x 40 mm) were coated with fibronectin (20 micrograms/ml), seeded with endothelial cells, and cultured for 48 h to produce a confluent, autologous endothelial cell lining. They were implanted as carotid interposition grafts in sheep. Seeded ePTFE grafts were compared with nonseeded ePTFE grafts and autologous carotid artery grafts. No anticoagulant or antiplatelet therapy was administered, making this a stringent test model for the thromboresistance of a small-diameter prosthesis. After 13 weeks the patencies of seeded, nonseeded, and autologous artery grafts were 16% (1/6), 0% (0/6), and 100% (6/6), respectively. The one seeded graft that was patent was fully lined with endothelial cells and showed no stenosis. The remaining five seeded grafts were occluded by fibrous tissue and displayed substantial spindle cell hyperplasia. There was no apparent difference between the autologous artery grafts and normal arterial tissue, and the anastomoses showed no stenosis. The ovine model provides a conservative test of prosthesis survival and may be useful for study of graft failure.

Anastomosis, Surgical↗
PubMed1995

Effective hospital leadership for quality: theory and practice.

Hospitals need excellent leadership to be efficient in the use of scarce stakeholder resources and to be effective in the competitive provision of services to multiple customers. This study was conducted with the cooperation of the executive team at a large government-funded hospital in Brisbane. It focused on understanding the conceptual models of leadership held by members of the executive and comparing this model with an externally derived model of leadership. Performance on the local model was estimated by cross-linking performance assessment on the external model. Members of the executive espoused, and were also rated by others in the hospital as practising, to a moderate degree, a transformational style of leadership. An overall evaluation of quality practice in the hospital revealed the use of data, the understanding of processes and the formation of supplier partnerships as the areas of hospital activity most limiting the ability to improve. The implications of the conceptual model and performance levels are discussed in relation to the introduction of quality management practice in the hospital, and in terms of management development. A complementary paper focusing on quality implementation as perceived at different staff levels in the hospital is in preparation.

Australia↗
PubMed1990

A mathematical model of retrieval system performance.

There have been a number of major evaluations of the performance of retrieval systems against large full text and surrogate (bibliographic) databases. These evaluations have concentrated on the experimental determination of the Precision Ratio, the fraction of retrieved items that are relevant to an information request, and the Recall Ratio, the fraction of the total number of relevant items that were actually retrieved. While these measures have met with general acceptance, they have also generated much controversy. The purpose of this article is to review the results of several of the largest evaluations and to propose a simple model for the performance of such systems that may help explain the relationship between these measures and user behavior.

Evaluation Studies as Topic↗