SEARCH · PubMed Health

Results for “Model performance”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 919 records · Page 51Linked to original sources

PubMed2002

Computer-assisted resection of supra-tentorial cavernous malformation.

INTRODUCTION: Resection of cerebral tumors or vascular lesions requires a precise localization to minimize the skin, bone and cerebral approach. The image-guided surgery is currently considered to be of undisputed value in microneurosurgical technique. METHODS: Between 1998 and 2000, 13 patients were operated in our service for resection of a cavernous malformation deeply located using the MRI assisted image guidance (Sofamor-Danek Neuronavigation Cranial 3 System). RESULTS: The computer-calculated registration accuracy ranged between 0.8 and 2.0 mm (median 1.1 mm). The exact location of the cavernous malformation was possible in all the cases. Total resection of the lesion was always achieved. Operative mortality and transient morbidity were 0 % and 16 %, respectively. DISCUSSION: The image-guided technique offers a better help than the previously used methods (preoperative localization with CT scan or stereotactic implantation of guiding catheters) to resect intracranial lesions, especially if the lesion is deeply situated in the brain or in an eloquent area. Preoperative MRI-based 3D models, performed using special skin markers, and surgical computer-assisted neuronavigation allow us to find and to resect small and deep lesions with minimal mortality and low morbidity rate.

Adolescent↗

PubMed2005

Sulfur hexafluoride's liquid-vapor coexistence curve, interfacial properties, and diffusion coefficients as predicted by a simple rigid model.

We present here molecular-dynamics simulation results of the vapor-liquid coexistence curve, surface tension, and self-diffusion coefficients of sulfur hexafluoride. Sulfur hexafluoride is modeled as a rigid molecule, following the model proposed by Pawley [Mol. Phys. 43, 1321 (1981)]. Vapor-liquid coexistence curve and surface tension are obtained through direct molecular-dynamic simulations in the NVT ensemble. Simulation results are able to reproduce the qualitative shape of the vapor-liquid envelope. However, lower densities, a higher critical temperature, and an overestimated surface tension are obtained here. Those deviations are explained on the basis of the rigidity of the molecular model used. Self-diffusion coefficients are calculated from simulations in the NVE ensemble for different gas states at atmospheric pressure. The rigid model performs better for dynamical properties since simulation results provide very good agreement with available experimental data in this case.

Journal Article↗

PubMed2006

Simultaneous estimation of phase behavior and second-derivative properties using the statistical associating fluid theory with variable range approach.

A modified statistical associating fluid theory (SAFT) with variable range version is presented using the family of m-n Mie potentials. The use of this intermolecular potential for modeling repulsion-dispersion interactions between the monomer segments, together with a new method for optimizing the molecular parameters of the equation of state, is found to give a very accurate description of both vapor-liquid equilibria and compressed liquid bulk properties (volumetric and derivative properties) for long-chain n-alkanes. This new equation improves other SAFT-like equations of state which fail to describe derivative properties such as the isothermal compressibility and the speed of sound in the condensed liquid phase. Emphasis is placed on pointing out that the key for modeling the latter properties is the use of a variable repulsive term in the intermolecular potential. In the case of the n-alkanes series, a clear dependence of the characteristic molecular parameters on increasing chain length is obtained, demonstrating their sound physical meaning and the consistency of the new fitting procedure proposed. This systematic method for optimizing the model parameters includes data on the saturation line as well as densities and speed of sound data in the condensed liquid phase, and the results show undoubtedly that the model performance is enhanced and its range of applicability is now widened, keeping in any case a good balance between the accuracy of the different estimated properties.

Journal Article↗

PubMed2006

A post-Hartree-Fock model of intermolecular interactions: inclusion of higher-order corrections.

We have previously demonstrated that the dipole moment of the exchange hole can be used to derive intermolecular C(6) dispersion coefficients [J. Chem. Phys. 122, 154104 (2005)]. This was subsequently the basis for a novel post-Hartree-Fock model of intermolecular interactions [J. Chem. Phys. 123, 024101 (2005)]. In the present work, the model is extended to include higher-order dispersion coefficients C(8) and C(10). The extended model performs very well for prediction of intermonomer separations and binding energies of 45 van der Waals complexes. In particular, it performs twice as well as basis-set extrapolated MP2 theory for dispersion-bound complexes, with minimal computational cost.

Journal Article↗

PubMed2004

Erythropoietin mediates tissue protection through an erythropoietin and common beta-subunit heteroreceptor.

The cytokine erythropoietin (Epo) is tissue-protective in preclinical models of ischemic, traumatic, toxic, and inflammatory injuries. We have recently characterized Epo derivatives that do not bind to the Epo receptor (EpoR) yet are tissue-protective. For example, carbamylated Epo (CEpo) does not stimulate erythropoiesis, yet it prevents tissue injury in a wide variety of in vivo and in vitro models. These observations suggest that another receptor is responsible for the tissue-protective actions of Epo. Notably, prior investigation suggests that EpoR physically interacts with the common beta receptor (betacR), the signal-transducing subunit shared by the granulocyte-macrophage colony stimulating factor, and the IL-3 and IL-5 receptors. However, because betacR knockout mice exhibit normal erythrocyte maturation, betacR is not required for erythropoiesis. We hypothesized that betacR in combination with the EpoR expressed by nonhematopoietic cells constitutes a tissue-protective receptor. In support of this hypothesis, membrane proteins prepared from rat brain, heart, liver, or kidney were greatly enriched in EpoR after passage over either Epo or CEpo columns but covalently bound in a complex with betacR. Further, antibodies against EpoR coimmunoprecipitated betacR from membranes prepared from neuronal-like P-19 cells that respond to Epo-induced tissue protection. Immunocytochemical studies of spinal cord neurons and cardiomyocytes protected by Epo demonstrated cellular colocalization of Epo betacR and EpoR. Finally, as predicted by the hypothesis, neither Epo nor CEpo was active in cardiomyocyte or spinal cord injury models performed in the betacR knockout mouse. These data support the concept that EpoR and betacR comprise a tissue-protective heteroreceptor.

Animals↗

PubMed2006

A molecular correlate to the Gleason grading system for prostate adenocarcinoma.

Adenocarcinomas of the prostate can be categorized into tumor grades based on the extent to which the cancers histologically resemble normal prostate glands. Because grades are surrogates of intrinsic tumor behavior, characterizing the molecular phenotype of grade is of potential clinical importance. To identify molecular alterations underlying prostate cancer grades, we used microdissection to obtain specific cohorts of cancer cells corresponding to the most common Gleason patterns (patterns 3, 4, and 5) from 29 radical prostatectomy samples. We paired each cancer sample with matched benign lumenal prostate epithelial cells and profiled transcript abundance levels by microarray analysis. We identified an 86-gene model capable of distinguishing low-grade (pattern 3) from high-grade (patterns 4 and 5) cancers. This model performed with 76% accuracy when applied to an independent set of 30 primary prostate carcinomas. Using tissue microarrays comprising >800 prostate samples, we confirmed a significant association between high levels of monoamine oxidase A expression and poorly differentiated cancers by immunohistochemistry. We also confirmed grade-associated levels of defender against death (DAD1) protein and HSD17 beta4 transcripts by immunohistochemistry and quantitative RT-PCR, respectively. The altered expression of these genes provides functional insights into grade-associated features of therapy resistance and tissue invasion. Furthermore, in identifying a profile of 86 genes that distinguish high- from low-grade carcinomas, we have generated a set of potential targets for modulating the development and progression of the lethal prostate cancer phenotype.

Adenocarcinoma↗

PubMed1978

Beneficial and detrimental modeling effects on creative response production.

Enhancement of creativity through various educational "training" methods or external factors fostering creative production has long been demonstrated. The assumption has been that creativity exists as a given quantity in trait form, or that progressive learning takes place. Social observational modeling is investigated here as a technique that can both increase and decrease level of creative production in the individual despite every opportunity presented to respond freely and without (a) resort to any direct education or reinforcement methods or (b) the presence of environmental constraints. One hundred and twenty female university students were assessed for creativity on one figural and one verbal task of the Torrance Tests of Creative Thinking and the components of fluence, flexibility, originality, and elaboration. Ss then observed either high, low, or no figural creative model performance based on normative responses of past Ss and were reassessed on alternate test forms. Reassessment showed both predicted increases and decreases in component verbal creativity scores.

Creativity↗

PubMed2000

Optimum DNA curvature using a hybrid approach involving an artificial neural network and genetic algorithm.

In the present paper, a hybrid technique involving artificial neural network (ANN) and genetic algorithm (GA) has been proposed for performing modeling and optimization of complex biological systems. In this approach, first an ANN approximates (models) the nonlinear relationship(s) existing between its input and output example data sets. Next, the GA, which is a stochastic optimization technique, searches the input space of the ANN with a view to optimize the ANN output. The efficacy of this formalism has been tested by conducting a case study involving optimization of DNA curvature characterized in terms of the RL value. Using the ANN-GA methodology, a number of sequences possessing high RL values have been obtained and analyzed to verify the existence of features known to be responsible for the occurrence of curvature. A couple of sequences have also been tested experimentally. The experimental results validate qualitatively and also near-quantitatively, the solutions obtained using the hybrid formalism. The ANN-GA technique is a useful tool to obtain, ahead of experimentation, sequences that yield high RL values. The methodology is a general one and can be suitably employed for optimizing any other biological feature.

Algorithms↗

PubMed2006

Normative data for triceps and subscapular skinfold thicknesses of Chinese infants.

UNLABELLED: Skinfold thickness is a validated parameter of subcutaneous fat accumulation. Data on triceps and subscapular skinfold thicknesses were collected from 10,043 (5318 males, 4725 females) singletons at 12 hospitals with gestation 31-42 wk. The LMS method using maximum penalized likelihood was used to perform model fitting of the anthropometric centiles for these parameters. Both triceps and subscapular skinfold thicknesses were greater in girls than in boys. Racial differences were found when comparing with other populations. The triceps subscapular skinfold thicknesses of Chinese infants were significantly lower than those of US white infants but larger than those of African-American infants, Israeli infants, Spanish infants and Indian infants. CONCLUSION: This study provides the first set of references for the triceps and subscapular skinfold thicknesses of Chinese infants by gestation and gender. These data are helpful in determining the nutritional status of infants at birth and in assessing the postnatal growth of Chinese infants.

China↗

PubMed2003

An environmental decision-making tool for evaluating ground-level ozone-related health effects.

A computer model called the Ozone Risk Assessment Model (ORAM) was developed to evaluate the health effects caused by ground-level ozone (O3) exposure. ORAM was coupled with the U.S. Environmental Protection Agency's (EPA) Third-Generation Community Multiscale Air Quality model (Models-3/CMAQ), the state-of-the-art air quality model that predicts O3 concentration and allows the examination of various scenarios in which emission rates of O3 precursors (basically, oxides of nitrogen [NOx] and volatile organic compounds) are varied. The principal analyses in ORAM are exposure model performance evaluation, health-effects calculations (expected number of respiratory hospital admissions), economic valuation, and sensitivity and uncertainty analysis through a Monte Carlo simulation. As a demonstration of the system, ORAM was applied to the eastern Tennessee region, and the entire O3 season was simulated for a base case (typical emissions) and three different emission scenarios. The results indicated that a synergism occurs when reductions in NOx emissions from mobile and point sources were applied simultaneously. A 12.9% reduction in asthma hospital admissions is expected when both mobile and point source NOx emissions are reduced (50 and 70%, respectively) versus a 5.8% reduction caused by mobile source and a 3.5% reduction caused by point sources when these emission sources are reduced individually.

Air Pollution↗

PubMed2006

The phylogeny of early eureptiles: comparing parsimony and Bayesian approaches in the investigation of a basal fossil clade.

For the first time the phylogenetic relationships of early eureptiles, consisting of captorhinids, diapsids, and protorothyridids, are investigated in a modern phylogenetic context using both parsimony and Bayesian approaches. Ninety parsimony-informative characters and 25 taxa were included in the analyses. The Bayesian analysis was run with and without a gamma-shape parameter allowing for variable rates across characters. In addition, we ran two more Bayesian analyses that included 42 autapomorphies and thus parsimony-uninformative characters in order to test the effect of variable branch lengths. The different analyses largely converged to the same topology, suggesting that the "protorothyridid" Coelostegus is the sister taxon of all other eureptiles and that the remaining "protorothyridids" are paraphyletic. Also, there is a close relationship between diapsids and Anthracodromeus, Cephalerpeton, and Protorothyris, a grouping of Thuringothyris with captorhinids, and a variable position of the "protorothyridids" Brouffia, Hylonomus, and Paleothyris. The lack of resolution in some parts of the tree might be due to "hard polytomies" and short divergence times between the respective taxa. The tree topology is consistent with the hypothesis that the temporal fenestrations of diapsid reptiles appear to be the consequence of a more lightly built skeleton, indicating a significant ecological shift in the early stages of diapsid evolution. Bayesian analysis is a very useful additional approach in studies of fossil taxa in which more traditional statistical support like the bootstrap is often weak. However, the exclusive use of the Mk model appears suitable only if autapomorphic characters are included, whereas the Mk+gamma model performed well with or without autapomorphies.

Animals↗

PubMedDate not supplied

GASTON: an architecture for the acquisition and execution of clinical guideline-application tasks.

Recently, studies have shown the benefits of using clinical guidelines in the practice of medicine. There have been numerous efforts to develop clinical decision support systems that support guideline-based care in an automated fashion, covering a wide range of clinical settings and tasks. Despite these efforts, only a few systems progressed beyond the prototype stage and the research laboratory. For guideline-based clinical decision support systems to be successful, a balance must be made between intuitive but imprecise representations usually encountered by most of today's systems and representations that support a strong underlying clinical performance model. The project described in this paper tries to achieve such a balance. It presents the GASTON architecture that contains a set of reusable software components for the application of guidelines, including design-time components to facilitate the guideline authoring process based on guideline representation models along with execution-time components for building decision support systems that incorporate these guidelines. This architecture was used to develop several guideline representation models such as a rule-based representation to model rule-based guidelines and guideline representation models that address more complex tasks. Also, decision support systems that incorporate these models were developed with the architecture. For the representation and application of various classes of guidelines, rules were also viewed as instances of more complex tasks. By identifying similar characteristics of sets of rules, we developed several tasks such as a drug intera ction and drug contraindication task. Based on these models, we have developed and validated guidelines and decision support systems for use in several application domains such as intensive care, family physicians and psychiatry. In order to be able to represent more complex time-oriented plans, new guideline representation models are being developed.

Algorithms↗

PubMed1993

The effect of respirator dead space and lung retention on exposure estimates.

This paper develops, tests, and applies equations that predict the magnitude of the effect of lung retention and respirator dead space on average inhalation concentration and other related quantities. The equations were validated by numerical simulation and experimental measurement with a respirator on a mannequin connected to a breathing machine. Experimental data are presented verifying the applicability of the equations. The authors present applications of the equations and procedures to various types of respirator performance measurements and to a predictive respirator performance model. Graphs are presented giving correction factors. In all cases the correction factors are less than 2. Under typical conditions of workplace protection factor measurement with half-mask respirators, average inhalation concentration will be 105% to 125% of full-cycle average concentration.

Environmental Exposure↗

PubMed2002

The validity of a social indicator approach to substance misuse needs assessment.

Factors other than the magnitude of a community's drug- or alcohol-use-related problems may play a large role in resource allocation. Needs assessment approaches such as key informant interviews and household surveys can contribute to a more informed process. An additional approach to needs assessment, social indicator modeling, addresses the high cost of surveys and the potential subjectivity of key informant interviews. This paper discusses the history of social indicator approaches to needs assessment and reviews recent equitable distribution approaches. An equitable distribution model of alcohol- and other drug-use-related problems was created and validated. The drug model accounted for close to 50% of the variation in estimates of lifetime diagnosis of drug dependence or misuse. The alcohol model performed less successfully, accounting for 21% of the variation in lifetime diagnosis of alcohol-use-related problems.

Adolescent↗

PubMed1992

Estimation of effective dose to the patient during medical x-ray examinations from measurements of the dose-area product.

Effective dose is likely to be used as a dose index for patient exposures in diagnostic radiology. Calculation of effective dose requires estimates of doses to many organs. In the absence of such dose data it would be useful to be able to directly estimate effective dose from a quantity that can be easily measured in the x-ray room. Relationships between effective dose and each of entrance surface dose, entrance air kerma and dose-area product were studied for common radiographic projections using the organ dose data from Monte Carlo modelling performed at the National Radiological Protection Board, UK. Dose-area product proved to be the best quantity for estimating effective dose and these data are presented. For typical peak generating potentials, estimates of effective dose can be made from dose-area product using a small number of conversion coefficients. For cervical spine, chest, kidneys, abdomen, lumbar spine and pelvis AP projections, the conversion coefficient 0.21 mSv per Gy cm2 will estimate effective dose within 30% of the value obtained using specific organ doses. Conversion coefficients for lateral and PA projections of the trunk are approximately half this value. These coefficients allow the direct estimation of effective dose with sufficient accuracy for most purposes.

Humans↗

PubMed2004

Construction of robust prognostic predictors by using projective adaptive resonance theory as a gene filtering method.

MOTIVATION: For establishing prognostic predictors of various diseases using DNA microarray analysis technology, it is desired to find selectively significant genes for constructing the prognostic model and it is also necessary to eliminate non-specific genes or genes with error before constructing the model. RESULTS: We applied projective adaptive resonance theory (PART) to gene screening for DNA microarray data. Genes selected by PART were subjected to our FNN-SWEEP modeling method for the construction of a cancer class prediction model. The model performance was evaluated through comparison with a conventional screening signal-to-noise (S2N) method or nearest shrunken centroids (NSC) method. The FNN-SWEEP predictor with PART screening could discriminate classes of acute leukemia in blinded data with 97.1% accuracy and classes of lung cancer with 90.0% accuracy, while the predictor with S2N was only 85.3 and 70.0% or the predictor with NSC was 88.2 and 90.0%, respectively. The results have proven that PART was superior for gene screening. AVAILABILITY: The software is available upon request from the authors. CONTACT: honda@nubio.nagoya-u.ac.jp

Algorithms↗

PubMed2026

Using high-dimensional environmental covariates to study genotype by environment interaction for reproductive traits in Duroc boars.

We investigated the potential of incorporating grid-cell-based environmental covariates (ECs) in the genetic evaluation of total sperm count (TSC), sperm motility (MOT), and sperm morphology (MOR) for Duroc boars. A total of 188,665 records derived from 3,684 genotyped boars, born between December 2018 and October 2024 and raised in three stud farms located in different U.S. states, were analyzed using multi-trait linear-threshold repeatability models. To account for genotype by environment interactions (GE), we constructed an interaction matrix as the Hadamard product of the genomic relationship matrix and an environmental (co)variance matrix. The environmental groups were defined in three ways: farm, farm-season, and farm-year-season. The (co)variance matrix was constructed based on daily ECs obtained from the NASA POWER database for each environmental group. Of all available ECs, those significantly associated with TSC, MOT, and MOR (temperature, relative humidity, atmospheric pressure, and wind speed and direction) were retained. We evaluated five models with different GE structures: M1 represented the baseline without accounting for GE, in M2 the GE included farm as environmental groups, in M3 the GE included farm-season as environmental groups, in M4 the GE included farm-year-season as environmental groups, and M5 involved M3 with an additional random effect of the farm-season. Estimates of heritability for TSC, MOT, and MOR ranged from 0.03 to 0.04, 0.05 to 0.08, and 0.04 to 0.08, respectively. Corresponding repeatability ranged from 0.15 to 0.23, 0.28 to 0.49, and 0.28 to 0.49. The proportion of phenotypic variance attributed to GE variance ranged from 0.00 to 0.32, 0.00 to 0.44, and 0.00 to 0.44. Lastly, estimates of genetic correlation, TSC-MOT, TSC-MOR, and MOT-MOR ranged from 0.27 to 0.31, 0.24 to 0.31, and 0.98 to 0.99, respectively, with minor differences across models. We assessed the predictive ability of models using the linear regression validation. Across traits and models, bias ranged from -0.05 to 0.02 standard deviations, slope varied from 0.88 to 0.99, the correlation ranged from 0.75 to 0.84, and accuracy from 0.41 to 0.53. Overall, building the GE matrix considering grid-cell-based ECs helped to account for GE, thereby reducing the proportion of phenotypic variance attributed to genetic components; however, it did not improve the validation metrics. Additional on-farm records for ECs may improve the model performance.

Animals↗

PubMed1998

Early extubation following cardiac surgery in a veterans population.

BACKGROUND: Early tracheal extubation is an important component of the "fast track" cardiac surgery pathway. Factors associated with time to extubation in the Department of Veterans Affairs (DVA) population are unknown. The authors determined associations of preoperative risk and intraoperative clinical process variables with time to extubation in this population. METHODS: Three hundred four consecutive patients undergoing coronary artery bypass graft, valve surgery, or both on a fast track clinical pathway between October 1, 1993 and September 30, 1995 at a university-affiliated DVA medical center were studied retrospectively. After univariate screening of a battery of preoperative risk and intraoperative clinical process variables, stepwise logistic regression was used to determine associations with tracheal extubation < or = 10 h (early) or > 10 h (late) after surgery. Postoperative lengths of stay, complications, and 30-day and 6-month mortality rates were compared between the two groups. RESULTS: One hundred forty-six patients (48.3%) were extubated early; one patient required emergent reintubation (0.7%). Of the preoperative risk variables considered, only age (odds ratio, 1.80 per 10-yr increment) and preoperative intraaortic balloon pump (odds ratio, 7.88) were multivariately associated with time to extubation (model R) ("late" association is indicated by an odds ratio >1.00; "early" association is indicated by an odds ratio <1.00). Entry of these risk variables into a second regression model, followed by univariately significant intraoperative clinical process variables, yielded the following associations (model R-P): age (odds ratio, 1.86 per 10-yr increment), sufentanil dose (odds ratio, 1.54 per 1-microg/kg increment), major inotrope use (odds ratio, 5.73), platelet transfusion (odds ratio, 10.03), use of an arterial graft (odds ratio, 0.32), and fentanyl dose (odds ratio, 1.45 per 10-microg/kg increment). Time of arrival in the intensive care unit after surgery was also significant (odds ratio, 1.42 per 1-h increment). Intraoperative clinical process variables added significantly to model performance (P < 0.001 by the likelihood ratio test). CONCLUSIONS: In this population, early tracheal extubation was accomplished in 48% of patients. Intraoperative clinical process variables are important factors to be considered in the timing of postoperative extubation after fast track cardiac surgery.

Adult↗