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At least 1,063 records · Page 59Linked to original sources
PubMed2003

Biological waste gas treatment with a modified rotating biological contactor. II. Effect of operating parameters on process performance and mathematical modeling.

In the first part of this paper, we introduced a modified rotating biological contactor (RBC) for the biological treatment of waste gas, and demonstrated its feasibility by applying the process to the biodegradation of toluene in a 91-liter reactor containing 20 biofilm support discs with a diameter of 40 cm [1]. We showed that the proposed system allows the unlimited growth of the biofilm to be suppressed, hence eliminating the risk of clogging associated with other biological waste gas treatment systems. Furthermore, we observed stationary long-term performance for more than one year under typical standard operating conditions. In this part of our work, we investigate experimentally the influence of the main process parameters, i.e., gas flow rate, inlet gas concentration, and rotational speed of the biofilm supports on process performance for the same system. Experimental results indicate that the modified RBC system is mass transfer limited for toluene loadings below 150 g/m(3)h, whereas at higher inlet concentrations of the pollutant, it becomes limited by the biodegradation reaction inside the biofilm. Surprisingly, the disc rotational speed is found to have no major effect on process performance for the system under investigation. A time-independent mathematical model of the process is also presented, and predictions are compared with experimental degradation data. In the range of the investigation process parameters, good agreement between the experimental data and simulation results is obtained.

Bacterial Adhesion↗
PubMedDate not supplied

Using a program logic model that focuses on performance measurement to develop a program.

A program logic model is used to make a program ready for an evaluation. It diagrammatically shows the relationships between the objectives of the program, program activities, indicators, and resources. This article describes an expanded logic model that has a greater focus on measurement of program performance. The expanded logic model specifies both outcome and process indicators, whereas other logic models only show service delivery indicators. Also, this article describes how the expanded logic model was used to develop a bicycle safety program. A workgroup established program boundaries and reviewed documents early in the process of developing the logic model. The workgroup developed the logic model which was subsequently reviewed by other stakeholders. The workgroup continually assessed the plausibility of the logic model. Challenges and advantages in using the logic model are discussed.

Accidents, Traffic↗
PubMed2007

Why does placing the question before an arithmetic word problem improve performance? A situation model account.

The aim of this paper is to investigate the controversial issue of the nature of the representation constructed by individuals to solve arithmetic word problems. More precisely, we consider the relevance of two different theories: the situation or mental model theory (Johnson-Laird, 1983; Reusser, 1989) and the schema theory (Kintsch & Greeno, 1985; Riley, Greeno, & Heller, 1983). Fourth-graders who differed in their mathematical skills were presented with problems that varied in difficulty and with the question either before or after the text. We obtained the classic effect of the position of the question, with better performance when the question was presented prior to the text. In addition, this effect was more marked in the case of children who had poorer mathematical skills and in the case of more difficult problems. We argue that this pattern of results is compatible only with the situation or mental model theory, and not with the schema theory.

Analysis of Variance↗
PubMed2006

Linkage analysis with gene-environment interaction: model illustration and performance of ordered subset analysis.

The ordered subset analysis (OSA) method allows for the incorporation of covariates into the linkage analysis of a dichotomous disease phenotype in order to reduce genetic heterogeneity. Complex human diseases may involve gene-environment (G x E) interactions, which represent a special form of heterogeneity. Here, we present results of a simulation study to evaluate the performance of OSA when the disease-generating mechanism includes G x E interaction, in the absence of main effects of gene and environment. First, the complex simulation models are illustrated graphically. Second, we show that OSA is underpowered to detect small to moderate interaction effects, consistent with previous evaluations of other linkage analysis methods. When interaction effects are large enough to produce substantial marginal effects, standard linkage methods have sufficient power to detect significant baseline linkage evidence in the entire dataset. The power of OSA to improve upon a high baseline lod score is then strongly dependent on the underlying genetic model, especially the susceptibility allele frequency. If significant, OSA identifies family subsets that are more efficient for follow-up analysis than the entire dataset, in terms of the proportion of susceptible genotypes among generated marker genotypes. For example, when strong G x E interaction with RR(G x E) = 10 is operating in at least 70% of families in the dataset, OSA has at least 70% power to detect a subset of families with significantly greater linkage evidence, the majority of linked families are captured in the OSA subset, and the per-genotype efficiency in the subset is 20-30% greater than in the entire dataset.

Chromosome Mapping↗
PubMedDate not supplied

A model for peak performance.

This study identified major factors that contributed to peak performance among eight nursing educators. The peak performers were interviewed 3 times over 8 years. Intense commitment to a mission, continual performance assessment, concentration on satisfaction and rewards, and the ability to set priorities and seek social support were delineated as factors in peak performance. Commitment to a personal mission that aligns with the demands of the university was a peak performer's ultimate personal investment and service to students and the university.

Faculty, Nursing↗
PubMed2005

Non-monotonic changes in performance with eccentricity modeled by multiple eccentricity-dependent limitations.

Eccentricity-dependent resolution losses are sometimes compensated for in psychophysical experiments by magnifying (scaling) stimuli at each eccentricity. The use of either pre-selected scaling factors or unscaled stimuli sometimes leads to non-monotonic changes in performance as a function of eccentricity. We argue that such non-monotonic changes arise when performance is limited by more than one type of constraint at each eccentricity. Building on current methods developed to investigate peripheral perception [e.g., Watson, A. B. (1987). Estimation of local spatial scale. Journal of the Optical Society of America A, 4 (8), 1579-1582; Poirier, F. J. A. M., & Gurnsey, R. (2002). Two eccentricity dependent limitations on subjective contour discrimination. Vision Research, 42, 227-238; Strasburger, H., Rentschler, I., & Harvey Jr., L. O. (1994). Cortical magnification theory fails to predict visual recognition. European Journal of Neuroscience, 6, 1583-1588], we show how measured scaling can deviate from a linear function of eccentricity in a grating acuity task [Thibos, L. N., Still, D. L., & Bradley, A. (1996). Characterization of spatial aliasing and contrast sensitivity in peripheral vision. Vision Research, 36(2), 249-258]. This framework can also explain the central performance drop [Kehrer, L. (1989). Central performance drop on perceptual segregation tasks. Spatial Vision, 4, 45-62] and a case of "reverse scaling" of the integration window in symmetry [Tyler, C. W. (1999). Human symmetry detection exhibits reverse eccentricity scaling. Visual Neuroscience, 16, 919-922]. These cases of non-monotonic performance are shown to be consistent with multiple sources of resolution loss, each of which increases linearly with eccentricity. We conclude that most eccentricity research, including "oddities", can be explained by multiple-scaling theory as extended here, where the receptive field properties of all underlying mechanisms in a task increase in size with eccentricity, but not necessarily at the same rate.

Contrast Sensitivity↗
PubMed2002

Measurement and modeling of optical performance of wire grids and liquid-crystal displays utilizing grid polarizers.

We studied the optical performance of a reflective wire-grid polarizer designed for visible light. The polarizer reflects E polarization and transmits H polarization with low losses. The studies of transmission and reflectivity of nonpolarized and polarized light from single grids and stacked grids show that the optical performance of wire-grid polarizers can be adequately described by representing the polarizer as an effective uniaxial medium with anisotropic absorption. The description facilitates the incorporation of the polarizers in modeling procedures widely used in the design of liquid-crystal devices. We present the modeling and measurement results of twisted-nematic devices with wire-grid polarizers serving simultaneously as reflective polarizers, alignment layers, and back electrodes. The application of wire-grid polarizers for reflective liquid-crystal devices provides brightness enhancement, high contrast ratio at wide viewing angles, and elimination of viewing parallax.

Journal Article↗
PubMed1993

Shortening-length diagram: a new method of modeling skeletal muscle performance.

Muscle shortening is usually characterized in terms of force-velocity and length-active tension properties. We have examined a third relationship, that between shortening and initial length to further characterize muscle performance. This analysis shows that optimal shortening is achieved at a length (Ls) different from the length (Lo) of optimal tension development. Moreover, the analysis reveals discrepancies between results expected (using classical modeling) and experimental findings and these discrepancies increase with age. This effect of age on shortening has not been previously identified. Diaphragm muscle strips were dissected from male Fischer 344 rats of 3 and 24 months of age. Muscles were subjected, in vitro, to isotonic loads of either 30% or 50% of peak isometric tension (Po*) and shortened from initial lengths ranging from 80% to 130%Lo. The relationship between shortening and initial length was fitted by a second order polynomial using linear regression analysis. Results at 30% P/Po* indicate a difference in ability to shorten of 7% at Lo between muscles of young and elderly rats. The age-related change was enhanced under a load of 50% P/Po*, with a 46% difference in ability to shorten between young and old rats. The results show an age-related decrease in shortening of the diaphragm that is not predicted using classical muscle mechanics. Factors other than the length-tension relation and load must therefore be explored to explain decrements of shortening with age.

Aging↗
PubMed2000

Interdisciplinary shared governance: a partnership model for high performance in a managed care environment.

Today's managed care environment is forcing hospitals to seek new and innovative ways to deliver a seamless continuum of high-quality care and services to defined populations at lower costs. Many are striving to achieve this goal through the implementation of shared governance models that support point-of-service decision making, interdisciplinary partnerships, and the integration of work across clinical settings and along the service delivery continuum. The authors describe the key processes and strategies used to facilitate the design and successful implementation of an interdisciplinary shared governance model at The University Hospital, Cincinnati, Ohio. Implementation costs and initial benefits obtained over a 2-year period also are identified.

Cost-Benefit Analysis↗
PubMedDate not supplied

Assessing the performance of neural encoding models in the presence of noise.

An analytical method is introduced for evaluating the performance of neural encoding models. The method addresses a critical question that arises during the course of the development and validation of encoding models: is a given model near optimal in terms of its accuracy in predicting the stimulus-elicited responses of a neural system, or can the predictive accuracy be improved significantly by further model development? The evaluation method is based on a derivation of the minimum mean-square error between actual responses and modeled responses. It is formulated as a comparison between the mean-square error of the candidate model and the theoretical minimum mean-square error attainable through an optimal model for the system. However, no a priori information about the nature of the optimal model is required. The theoretically minimum error is determined solely from the coherence function between pairs of system responses to repeated presentations of the same dynamic stimulus. Thus, the performance of the candidate model is judged against the performance of an optimal model rather than against that of an arbitrarily assumed model. Using this method. we evaluated a linear model for neural encoding by mechanosensory cells in the cricket cercal system. At low stimulus intensities, the best-fit linear model of encoding by single cells was found to be nearly optimal, even though the coherence between stimulus-response pairs (a commonly used measure of system linearity) was low. In this low-stimulus-intensity regime, the mean square error of the linear model was on the order of the power of the cell responses. In contrast, at higher stimulus intensities the linear model was not an accurate representation of neural encoding. even though the stimulus-response coherence was substantially higher than in the low-intensity regime.

Action Potentials↗
PubMedDate not supplied

Performance improvement: one model to reduce length of stay.

Dedicated quality professionals are tired of quick fixes, Band-Aids, and other first-aid strategies that offer only temporary relief of nagging problems rather than a long-term cure. Implementing strategies that can produce permanent solutions to crucial problems is a challenge confronted by organizations striving for continuous performance improvement. One vehicle, driven by data and customer requirements, that can help to solve problems and sustain success over time is the storyboard. This article illustrates the use of the storyboard as the framework for reducing length of stay--one of the most important problems facing healthcare organizations today.

Data Display↗
PubMed2000

Mechanisms of human motion perception: combining evidence from evoked potentials, behavioural performance and computational modelling.

Based on single cell recordings in monkey, it has been suggested that neural activity can be related directly to psychophysically measured threshold behaviour. Here, we investigated in humans whether evoked potentials correlate with behavioural measurements like discrimination thresholds and reaction time. Subjects were asked to report the perceived direction of object motion stimuli which contained variable amounts of coherent motion. Simultaneously, we recorded evoked potentials with a multielectrode array, or measured the reaction time. We show here that motion coherence had a strong influence on both amplitude and latency of the evoked potential. Stronger motion signals evoked stronger and faster cortical responses. The latency reduction of the motion onset response with increasing coherence correlated very well with the concurrent decrease in reaction time. Taken together, these results suggest that temporal integration is an important step in analysing motion signals to generate a reliable behavioural response. We stimulated a two-dimensional array of correlation-type motion detectors with the same motion sequences, and analysed the distribution of local motion signals according to signal detection theory. Performance resembled that of human subjects when the decision strategy was optimized so as to exclude small signals and, in particular, when the ideal observer had some knowledge about a region of interest in which the object was to be expected.

Cerebral Cortex↗
PubMed2006

Single- versus dual-process models of lexical decision performance: insights from response time distributional analysis.

This article evaluates 2 competing models that address the decision-making processes mediating word recognition and lexical decision performance: a hybrid 2-stage model of lexical decision performance and a random-walk model. In 2 experiments, nonword type and word frequency were manipulated across 2 contrasts (pseudohomophone-legal nonword and legal-illegal nonword). When nonwords became more wordlike (i.e., BRNTA vs. BRANT vs. BRANE), response latencies to nonwords were slowed and the word frequency effect increased. More important, distributional analyses revealed that the Nonword Type = Word Frequency interaction was modulated by different components of the response time distribution, depending on the specific nonword contrast. A single-process random-walk model was able to account for this particular set of findings more successfully than the hybrid 2-stage model.

Adult↗
PubMed1983

Rowing performance, a mathematical model based on analysis of body dimensions as exemplified by body weight.

The theory of body dimensional influence on muscular work is employed for calculating the racing time of heavy- and lightweight male, and female rowers. The developed equation predicts racing results with an accuracy of 1 s +/- 1.7 (SE). The prediction of a 2.6% advantage of the heavyweights (average bodyweight) 93 kg over the lightweights (70 kg) is in excellent agreement with observations (2.5%). Significant implications of the equation would be to row without a coxswain, to reduce boat weight to a minimum, and to increase racing distance e.g., for females to the racing distance rowed by the males (2,000 m) in order to reduce the influence of body dimensions on rowing performance.

Aerobiosis↗
PubMed2001

Expression of presumed specific early and late factors associated with liver regeneration in different rat surgical models.

Experiments performed on the portal branch ligation (PBL) model indicate that early changes observed after surgery are not related to the regenerative process because they also occur in atrophying lobes. To further confirm the lack of specificity of the early events and to exclude the influence of circulatory factors released by proliferating lobes on their occurrence, we investigated this response after sham operation (SO) and portacaval shunt (PCS), a model characterized by liver atrophy. We also attempted to determine expression of later events associated specifically with regeneration, ie, expression of p53 or c-Ha-ras, or inhibition of proliferation, ie, interleukin-1beta (IL-1beta) and transforming growth factor-beta1 (TGF-beta1) after partial (PH) and temporary partial (TPH) hepatectomy, SO and PCS. Nuclear factor-kappaB (NF-kappaB) and signal transducer and activator of transcription 3 (STAT3) DNA binding were assessed by electrophoretic mobility shift assay (EMSA), interleukin-6 (IL-6) mRNA by reverse transcription-polymerase chain reaction (RT-PCR), c-myc and c-jun mRNAs by Northern blot analysis at 0.5 and 2 hours, p53 and c-Ha-ras mRNAs by Northern blot analysis at 8 and 24 hours, and IL-1beta and TGF-beta1 by RT-PCR at 24 hours. The early response including an increase of NF-kappaB, STAT3, IL-6, and immediate-early genes expression was present after PH, PCS, and SO. In SO, slight differences were observed in comparison with PH: no NF-kappaB p65/p50 DNA binding was observed, only three of six SO rats were positive for IL-6, and immediate-early genes induction showed differences in the intensity of the response. At later times, p53 mRNA increased at 8 hours after PH and TPH, c-Ha-ras mRNA at 24 hours after PH, and IL-1beta mRNA at 24 hours after PCS. Early events are not specifically associated with the reduction of liver mass or with the regenerative process, are not predictive of future cell fate, and are most likely related to surgical stress. p53 and c-Ha-ras induction is closely associated with cell cycle progression whereas IL-1beta, but not TGF-beta1, appears to be one of the negative growth regulators that might play an important role in atrophy.

Animals↗
PubMed2003

Multiple-object working memory--a model for behavioral performance.

In a psychophysics experiment, monkeys were shown a sequence of two to eight images, randomly chosen out of a set of 16, each image followed by a delay interval, the last image in the sequence being a repetition of any (one) of the images shown in the sequence. The monkeys learned to recognize the repetition of an image. The performance level was studied as a function of the number of images separating cue (image that will be repeated) from match for different sequence lengths, as well as at fixed cue-match separation versus length of sequence. These experimental results are interpreted as features of multi-item working memory in the framework of a recurrent neural network. It is shown that a model network can sustain multi-item working memory. Fluctuations due to the finite size of the network, together with a single extra ingredient, related to expectation of reward, account for the dependence of the performance on the cue-position, as well as for the dependence of performance on sequence length for fixed cue-match separation.

Animals↗