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Results for “Model explainability”

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At least 487 records · Page 27Linked to original sources

PubMed2006

Intracochlear pressure and organ of corti impedance from a linear active three-dimensional model.

Intracochlear pressure and basilar membrane (BM) velocity are calculated from a physiologically based chinchilla cochlea model . The model includes three-dimensional viscous fluid and the pectinate zone of the elastic BM with dimensional and material property variation along its length. The passive response shows excellent agreement with measurement at high sound pressure levels. The active process is represented by adding the motility of the outer hair cells (OHCs) to the passive model with the feed-forward approximation of the organ of Corti (OC), as was done previously. The current model explains recent observations including: (1) agreement with characteristic frequency (CF)-to-place map, (2) CF shift in the active model, (3) BM displacement gain from OHC motility, (4) lower intracochlear pressure gain than BM displacement gain, and (5) OC impedance (Z(OC)).

Animals↗

PubMed1994

[Variation in drug prescription costs and general practitioners in an area of North-East Italy. The use of current data].

In this paper we analyse all General Practitioners (GP) prescriptions in a Friuli-Venezia Giulia area (North-eastern Italy). The sample included of 181 GPs and 242,564 patients with 1,191,122 prescribed items. The regional Health Data Base is the source of all data. Data analysis was performed according to the multiple regression and LISREL models. We assessed for all GPs the years of medical profession, patients listed, percent of patients exent from prescription rates, patients over 60, number of active compounds prescribed and related drug companies. Two factors, the number of active compounds prescribed and patients listed, significantly contributed to the multiple regression model. The model explained 56% of variation in prescribing pointing out the importance of those factors in influencing the cost per patient. LISREL model shows a causal chain going from the years of medical profession to cost per patient passing through the number of active compounds and drug companies related. In fact, the older the GP the less the cost per patient and number of active compounds used. A main finding is that the cost per patient is highly influenced by the number of different active compounds prescribed. As in other studies the percent of patients exent from prescriptions rates and aged over 60 are somehow fundamental in influencing the cost per patient. Finally we discussed models and literature on the issue.

Aged↗

PubMed1991

[Modeling of the semi-circular canal, application to labyrinthine hydrops].

The angular accelerometer of vertebrates, the semi circular canal, is a pressure gage. The transformation, acceleration to pressure, is due to the inertia of the endolymph. In the 0 to 1 Hz frequency interval, the endolymph-cupula system can be described by a second order, localised parameter model with two real time constants. This mechanical model explains the occurr]nces of the vestibular-ocular reflex during rotatory stimulations. However, some features of the response to caloric stimulations cannot be explained from this unique point of view. To correspond to these features, the SCC has to be considered as an inflatable structure, sensitive to weak pressure variations between the endolymph and perilymph. Different parameters of the mechanical model, the internal radius of the membranous canal, the dimension of the cupula and its elasticity coefficient depend on the inflating pressure. Ménière's disease is caracterised by hydrops, i.e. an increase of the pressure in the membranous SCC. The different mechanisms related to this hydrops, in particular introducing the inflating pressure as a second input to the ampular system, associated to a new concept of the mechanoneural transduction can explain the classical vestibular symptoms of Ménière's disease. Therefore, this overall mechanical model of the SCC indicates that hydrops is the mechanical cause of Ménière's disease and the primary cause is more likely to be a defect in the regulation loop of the inflating pressure.

Biophysical Phenomena↗

PubMed1997

Statistical modeling of methane production from landfill samples.

Multiple-regression analysis was conducted to evaluate the simultaneous effects of 10 environmental factors on the rate of methane production (MR) from 38 municipal solid-waste (MSW) samples collected from the Fresh Kills landfill, which is the world's largest landfill. The analyses showed that volatile solids (VS), moisture content (MO), sulfate (SO(inf4)(sup2-)), and the cellulose-to-lignin ratio (CLR) were significantly associated with MR from refuse. The remaining six factors did not show any significant effect on MR in the presence of the four significant factors. With the consideration of all possible linear, square, and cross-product terms of the four significant variables, a second-order statistical model was developed. This model incorporated linear terms of MO, VS, SO(inf4)(sup2-), and CLR, a square term of VS (VS(sup2)), and two cross-product terms, MO x CLR and VS x CLR. This model explained 95.85% of the total variability in MR as indicated by the coefficient of determination (R(sup2) value) and predicted 87% of the observed MR. Furthermore, the t statistics and their P values of least-squares parameter estimates and the coefficients of partial determination (R values) indicated that MO contributed the most (R = 0.7832, t = 7.60, and P = 0.0001), followed by VS, SO(inf4)(sup2-), VS(sup2), MO x CLR, and VS x CLR in that order, and that CLR contributed the least (R = 0.4050, t = -3.30, and P = 0.0045) to MR. The SO(inf4)(sup2-), VS(sup2), MO x CLR, and CLR showed an inhibitory effect on MR. The final fitted model captured the trends in the data by explaining vast majority of variation in MR and successfully predicted most of the observed MR. However, more analyses with data from other landfills around the world are needed to develop a generalized model to accurately predict MSW methanogenesis.

Journal Article↗

PubMed1985

Simulation modelling of the population dynamics of cereal aphids.

A simulation model explaining the population dynamics of the grain aphid (Sitobion avenae), a serious pest of wheat in Western Europe, is described. The model includes the effects of crop development and some natural enemies on the biology of the aphid. It is concluded that although much of the population dynamics of the aphid, especially in relation to its host plant, is now well understood, many uncertainties still remain concerning natural enemies. As these organisms seem able to prevent cereal aphid outbreaks, in some years, these gaps are presently preventing the development of a reliable forecasting scheme.

Animals↗

PubMed1993

Applying the "Model of recovering alcoholics' behavior stages and goal setting" to nursing practice.

In 1990, the author developed the Model of Recovering Alcoholics' Behavior Stages and Goal Setting as a result of grounded theory research. The model explains the natural progression of recovery through four behavior stages. Each stage is characterized by specific patient goals. Application of the model provides a framework for nursing care planning that is both stage-focused and patient-centered. In this article, the author discusses nursing intervention in relation to the model.

Alcoholism↗

PubMed2002

Models of eukaryotic gradient sensing: application to chemotaxis of amoebae and neutrophils.

Eukaryotic cells can detect shallow gradients of chemoattractants with exquisite precision and respond quickly to changes in the gradient steepness and direction. Here, we describe a set of models explaining both adaptation to uniform increases in chemoattractant and persistent signaling in response to gradients. We demonstrate that one of these models can be mapped directly onto the biochemical signal-transduction pathways underlying gradient sensing in amoebae and neutrophils. According to this scheme, a locally acting activator (PI3-kinase) and a globally acting inactivator (PTEN or a similar phosphatase) are coordinately controlled by the G-protein activation. This signaling system adapts perfectly to spatially homogeneous changes in the chemoattractant. In chemoattractant gradients, an imbalance between the action of the activator and the inactivator results in a spatially oriented persistent signaling, amplified by a substrate supply-based positive feedback acting through small G-proteins. The amplification is activated only in a continuous presence of the external signal gradient, thus providing the mechanism for sensitivity to gradient alterations. Finally, based on this mapping, we make predictions concerning the dynamics of signaling. We propose that the underlying principles of perfect adaptation and substrate supply-based positive feedback will be found in the sensory systems of other chemotactic cell types.

Amoeba↗

PubMed1992

Generation of activity-rest patterns by dual circadian pacemaker systems: a model.

Activity-rest patterns displayed by an animal under various circumstances are suggested to result from the combined influences of two virtually identical circadian pacemaker components. Increased output of each component proportionally increases the probability of activity of the animal. Such a dual circadian pacemaker model explains much of the phenomenology of activity-rest records. Under normal light-dark schedules, the two components of the model have a similar phase relationship to the Zeitgeber. Differential synchronization of the components to dawn and dusk is not assumed.

Journal Article↗

PubMed2004

K+ channels and their modulation by 5-HT in Drosophila photoreceptors: a modelling study.

In order to clarify the role of inactivating and noninactivating K+ conductances in nonspiking neurons, we developed an isopotential model of the Drosophila photoreceptor membrane based on Hodgkin-Huxley-type equations. The model includes voltage dependent potassium conductances, the shaker (gKA) and the delayed rectifier (gKs). The model parameters were derived from published results by Hardie and coworkers and nearly identical model was used also in our previous work (J. E. Niven, M. Vähäsöyrinki, M. Kauranen, R. C. Hardie, M. Juusola, and M. Weckström. The Contribution of shaker K+ channels to the information capacity of Drosophila photoreceptors. Nature. 421:630-634, 2003). The model explains how the two types of channels function together to define the voltage dependent properties of the photoreceptor membrane. Additionally the model enables us to run simulations of conditions which are difficult to achieve in patch clamp, like prolonged membrane depolarizations by light adaptation. Effects of the activation of the delayed rectifier type conductance were found to be in accordance with published experimental work but the inactivation of the shaker channels, in addition to its importance in the determination of the resting potential, produced voltage amplification over equivalent passive membrane under dark adapted conditions. This phenomenon was not present in light adapted conditions. The modulation of the voltage dependence of the conductances as reported by serotonin (5-HT) caused the shaker to act essentially like the delayed rectifier conductance.

Animals↗

PubMed2004

Explaining fruit and vegetable consumption: the theory of planned behaviour and misconception of personal intake levels.

The influence of individuals' misconceptions in assessing fruit and vegetable consumption on the ability of the theory of planned behaviour to explain variance in the consumption of these foods was studied. Dutch women (mean age 41, n=159) completed a questionnaire assessing the theory's constructs with regard to the daily consumption of at least two pieces of fruit and 200 gram of vegetables. Consumption was assessed using a self-rated measure and more objectively with a food-frequency questionnaire. Both measures were combined to classify participants according to the accuracy of their self-assessed intake levels ('realists' vs. 'overestimators'). The model explained variation in objective fruit and vegetable intake much better among realists (R2 = 45% for fruits and 39% for vegetables) than among overestimators (R2 = 18% and 5%, respectively). Perceived behavioural control was the strongest predictor of intentions and behaviour. When plasma vitamin C and carotenoid concentrations were used as objective indicators for fruit and vegetable intake, the explanatory value of the model was lower, but again more variance was explained among realists than among overestimators. We conclude that awareness of personal behaviour should be taken into account when applying the theory of planned behaviour to explain dietary behaviours as well as to design health education interventions.

Adult↗

PubMed2005

Morphology and productivity of filamentous fungi.

Cultivation processes involving filamentous fungi have been optimised for decades to obtain high product yields. Several bulk chemicals like citric acid and penicillin are produced this way. A simple adaptation of cultivation parameters for new production processes is not possible though. Models explaining the correlation between process-dependent growth behaviour and productivity are therefore necessary to prevent long-lasting empiric test series. Yet, filamentous growth consists of a complex microscopic differentiation process from conidia to hyphae resulting in various macroscopically visible appearances. Early approaches to model this morphologic development are recapitulated in this review to explain current trends in this area of research. Tailoring morphology by adjusting process parameters is one side of the coin, but an ideal morphology has not even been found. This article reviews several reasons for this fact starting with nutrient supply in a fungal culture and presents recent advances in the investigation of fungal metabolism. It illustrates the challenge to unfold the relationship between morphology and productivity.

Acremonium↗

PubMed2005

Relationships between patient, family, and significant other disposition preferences in psychiatric emergency services and the clinical symptom ratings and disposition decisions of psychiatrists.

A previous paper examined the relationship between 10 clinical ratings made by psychiatrists and 465 psychiatric emergency service (PES) dispositions. A logistic regression model explained 52% of the variance in the psychiatrist's decisions to admit to inpatient services or release. The 5 clinical ratings in the model, rated on 8-point scales, were severity of danger to self, psychosis, inability to care for self, impulse control, and depression. The current paper examines the relationships between patient and family/significant other dispositional preferences expressed in the PES, and the psychiatrist's disposition decision and the 10 clinical ratings. It found that the dispositional preferences of the patient, family, and other individuals (community clinician, police, or ambulance driver) were very consistent with the actual decision made by the PES psychiatrist. Further, it found that these preferences explained an additional 35% of the variability in the psychiatrist's decision to admit or release. Finally, the ten clinical ratings made by the PES psychiatrist explained only a small amount of the variance in the dispositional preferences, and some of the significant coefficients were in the opposite direction expected. Patient, family and other significant individuals' expressed preferences and expectations in the PES are important and should be routinely recorded in the charts. The small relationships between clinical ratings and preferences suggests that the reasons the family/significant other and the patient seeks hospital admission or release may differ with psychiatrists' reasons for disposition.

Choice Behavior↗

PubMed1995

Accrual to the Breast Cancer Prevention Trial by participating Community Clinical Oncology Programs: a panel data analysis.

In 1992 patient accrual to the National Cancer Institute-sponsored Breast Cancer Prevention Trial was initiated in the United States and Canada. The Trial will involve 16,000 women who are evaluated to be at high risk of developing breast cancer. Nearly 250 health care organizations are participating in the Trial, including over 40 Community Clinical Oncology Program (CCOP) organizations, which are a component of the NCI's national clinical trials program. A previous NCI-funded evaluation conducted by the University of North Carolina showed the CCOP program to be an effective means of transferring the latest cancer technology, particularly cancer treatments, to the community setting. This paper describes a study designed to evaluate the performance of CCOP organizations in the Breast Cancer Prevention Trial. Using data from the first fifteen months of the Trial, the ability of CCOPs to accrue women is assessed using panel data estimation techniques. An attempt is made to predict accrual by structural, process, and environmental characteristics of participating CCOPs. Factors predictive of accrual include month in which accrual occurred and the extent of competition for trial participants in the CCOP service area. The hypothesized model explains slightly over 19 percent of the variation in accrual performance. The analysis demonstrates the utility of a panel data approach to modeling the dynamics of CCOP participation in a chemoprevention clinical trial.

Breast Neoplasms↗

PubMed1996

Quantal Ca2+ release and inactivation in a model of the inositol 1,4,5-trisphosphate receptor involving transformation of the ligand by the receptor.

A model explaining quantal Ca2+ release as an intrinsic property of the inositol 1,4,5-triphosphate (IP3) receptor has been put forward. The model is based on the hypothesis that the IP3 receptor can catalyze a transformation of the IP3 molecule differing from its conventional metabolism. A simple kinetic mechanism is considered, in which IP3-induced Ca2+ channel opening is followed by the step of IP3 conversion and channel closure. Examination of the resulting mathematical model shows that it can reproduce well both partial release of stored Ca2+ and the same responsiveness to subsequent IP3 additions. On incorporation of an additional closed state of the channel, the model describes also a time-dependent channel inactivation at a high IP3 dose. Temperature sensitivity of the catalytic step accounts for the reported elimination of quantal responses and inactivation at low temperature. The transformation product is surmised to be a positional or stereo isomer of IP3.

Calcium↗

PubMed2005

Modeling pathways to affective barriers on colorectal cancer screening among Japanese Americans.

The study aimed to identify the mechanisms through which colorectal cancer (CRC)-specific affective barriers, including fear of finding CRC, embarrassment, and concerns for screening discomfort, can be reduced to guide the development of interventions aimed at the secondary prevention of CRC. A model explaining these affective barriers was developed and tested among a random sample of 305 asymptomatic Japanese Americans using a path analysis. The model suggested that affective barriers could be reduced by increasing CRC-related knowledge, which could be enhanced by acculturation, social support, and physician recommendation. Interventions that focus on increasing CRC-related knowledge could reduce affective barriers to CRC screening for this population when taking the enhancement of communication skills and interpersonal interactions into account.

Acculturation↗

PubMed1991

Leading a high-commitment high-performance organization.

This article conducts a thorough review of the extensive literature on executive leadership. It provides a definition for the concept of superior executive leadership and then presents a model explaining the key roles and attributes required to perform effectively in top management ranks. The article then discusses the implications of this model for senior executives and describes how it can be used to assess the quality of executive performance.

Administrative Personnel↗

PubMed2006

Task analysis of patients' medication-taking practice and the role of making sense: a grounded theory study.

BACKGROUND: Patients on long-term medications have varied medication-taking practices and complex and often unmet medication information needs. OBJECTIVES: The objective of this qualitative study was to describe from the patient's perspective the medication-taking tasks performed by patients currently receiving long-term medications and then to hypothesize how these tasks relate to patients' medication information needs. METHODS: In-depth semistructured interviews were conducted with individuals between the ages of 18 and 65, who had a college or university education, and who were on at least one long-term medication. Grounded theory approach was used for data gathering and data analysis. Maximum variation and theoretical sampling were used and the sample size was determined when theoretical saturation was reached in the core category. Interpretive and theoretical validity were ensured through member checking, through the use of the constant comparative method, and by a review of the results by a panel of pharmacists and physicians. RESULTS: Ten participants aged between 41 and 64 years were included in the study sample. The participants had between one and 7 chronic illnesses, duration of these illnesses to date varied from 1 year to 40 years, and each participant was taking between one and 13 medications. A model was developed that consists of 4 thematic categories: (a) making sense of medication taking, (b) medication-taking acts, (c) mediation-taking self-assessment, and (d) context of medication taking. The main category was making sense of medication taking that consisted of 3 subcategories: (a) nonproblematic mode, (b) problematic mode, and (c) stunned mode. The model explains how and why a patients' need for medication-taking education may vary because their medication-taking practices changes. The model also connects each category to medication information that people may need. CONCLUSIONS: Findings contribute to our understanding of medication-taking practice of individuals on long-term medication and have implication for patient education.

Adult↗

PubMed1991

A photophysical model for diphenylhexatriene fluorescence decay in solvents and in phospholipid vesicles.

The fluorescence decay of 1,6-diphenyl-1,3,5-hexatriene (DPH) in pure solvents and in phospholipid vesicles has been measured using frequency domain fluorometry. Data analysis uses a model with two energetically close excited states. The model explains the high quantum yield and the double exponential decay of DPH observed in some pure solvents and in phospholipid vesicles. This model assumes that after excitation to a first excited state, there is a rapid interconversion to a lower excited state and that most of the emission occurs from this state. The interconversion rates between the two excited states determine the average lifetime. For DPH in solvents, we find that the interconversion rates are solvent and temperature dependent. For DPH in phospholipid vesicles, we find that the back reaction rate from excited state 2 to excited state 1 (R12) is what determines the fluorescence properties. The phospholipid phase transition affects only this back reaction rate. The model was analyzed globally for a range of solvents, temperatures and vesicle composition. Of the six parameters of the model, only two, the interconversion rates between the two excited states, varied in all different samples examined. For DPH in phospholipid vesicles, there is an additional feature of the model, which is related to the apparent distribution of the rate R12. Significantly better fits were obtained using a continuous lorentzian distribution of interconversion rates. The resulting lifetime distribution was asymmetric and showed a definite narrowing above the phase transition.

Diphenylhexatriene↗