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Results for “computational modeling”

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At least 397 records · Page 22Linked to original sources
PubMed2006

An anatomically based hybrid computational model of the human lung and its application to low frequency oscillatory mechanics.

Lung input impedance measured via forced oscillation over low frequency range has been confirmed as sensitive to the degree and the heterogeneity of lung disease. In this study we advanced an image-based, multi-scale computational model for the human lung, which includes upper and central airways, small airways and alveoli tissue unit. A three-dimensional (3-D) realistic model of the upper airway (reconstructed from MRI images) was combined with an anatomically based 3-D model of the central airways (based on MDCT images) to form a 3-D model of the large airways (from mouth to generation 6, incomplete for generations 4-6). The small airway trees distal to the central branches were based on a hypothetical airway tree for a normal healthy lung. A constant phase viscoelastic model was assumed for the alveolar tissue unit. Unsteady airflows in the large airways were simulated based on computational fluid dynamics (CFD). An experimentally measured broadband forcing flow was applied at the mouth. The impedance of the small airways was computed based on a one-dimensional transmission line model. The computed overall dynamic lung resistance and elastance compared very well with experimental values. Results showed that unsteady 3-D simulation and realistic geometry of the upper and large airways up to generations 4-6 can provide a reasonably accurate estimation of lung input impedance. The impedance of the upper airway constitutes a significant part of the total lung input impedance. The resistance of the upper airway accounts for 45-70% of the total lung resistance at frequencies between 0 and 1 Hz, and 70-81% at frequencies between 1 and 8 Hz.

Biological Clocks↗
PubMedDate not supplied

Computer model of ventricular interaction during left ventricular circulatory support.

The authors used a computer model of the heart and circulation to test the hypothesis that anatomic ventricular interactions are responsible for the observed instances of right ventricular failure during use of a left ventricular assist device. The model predicts that left ventricular pressure-unloading with a LVAD, in the presence of isolated systolic interaction, results in impairment of RV function, whereas with isolated diastolic interaction, RV function is improved. Due to competition between these two interactions, there is a negligible overall effect of ventricular anatomic interactions in determining right ventricular function in the normal heart.

Computer Simulation↗
PubMed1979

A computer model for hydrodynamic shearing of DNA.

A computer simulation model for the hydrodynamic shearing of DNA is presented. In this model the event space consists of a number of positions at which the DNA strand may break. The results of the model compared with the real world result are reported in this paper. Future endeavors to generalize the model would add significantly to the model's value.

Computers↗
PubMed1992

Computer models of hearing aid transducers for integrated circuit design.

Electronic circuit modeling using computer-based simulation tools is well established and device models are available for common electronic components. However, acoustic models of audio transducers for use during integrated circuit design are not readily available. This causes difficulty for designers of audio amplifiers, and increases the uncertainties of a successful silicon integration of a circuit design. This paper reports on a technique for the creation of electroacoustic models of hearing aid microphones and receivers that can be connected to an amplifier under design, and incorporated into PSPICE simulations. Verification of the technique and models was performed by comparing measured frequency response data with graphs created by PSPICE modeling. The conclusions were that the method developed for creating these models, and the models themselves, were accurate enough to be used for acoustic simulations of frequency response performance during amplifier design, and gave results comparable to data obtained from breadboard measurements of the same circuits.

Computer Simulation↗
PubMed2002

Bootstrapping the lexicon: a computational model of infant speech segmentation.

Prelinguistic infants must find a way to isolate meaningful chunks from the continuous streams of speech that they hear. BootLex, a new model which uses distributional cues to build a lexicon, demonstrates how much can be accomplished using this single source of information. This conceptually simple probabilistic algorithm achieves significant segmentation results on various kinds of language corpora - English, Japanese, and Spanish; child- and adult-directed speech, and written texts; and several variations in coding structure - and reveals which statistical characteristics of the input have an influence on segmentation performance. BootLex is then compared, quantitatively and qualitatively, with three other groups of computational models of the same infant segmentation process, paying particular attention to functional characteristics of the models and their similarity to human cognition. Commonalities and contrasts among the models are discussed, as well as their implications both for theories of the cognitive problem of segmentation itself, and for the general enterprise of computational cognitive modeling.

Algorithms↗
PubMed1981

A computer model for epidermal cellular interactions.

A model has been constructed of an assembly of mammalian epidermal cells. The model, simulated by computer, has served as a framework by which experiments can be performed "in machina". Relationships between the various parameters considered have been established. Hypotheses referring to the time at which cells leave the basal layer, and to the simultaneous occurrence of folded basal layer and of a significant number of vertical mitosis in some hyperplastic conditions have been implemented and examined.

Animals↗
PubMedDate not supplied

Computational models for the helix tilt angle.

The concept of hydrophobic imbalance and that of hydrophobic and hydrophilic centers are used along with side chain models in the computation of helix orientation and tilt angle in or near a membrane. Rotamer statistics are used to infer typical side chain positions and chain length for each amino acid, and the results are used in fast computation of helix orientation. Sliding windows are used to compute local tilt angles on long alpha-helices that defy idealized modeling and generate tilt angle profiles. Seven different procedures based on different formulas and hydrophobicity scales are used for comparison. These procedures generated very similar tilt angle profiles. These profiles provide insights into helix deformation, membrane destabilization, and similarity and differences between membrane proteins.

Algorithms↗
PubMed2004

Towards computational models of cells for environmental toxicology.

This paper outlines an approach to the development of computational models of cells for marine environmental toxicology. Exposure of cells to pollutants can lead to lysosomal damage and dysfunction, augmented autophagy, cellular dysfunction and atrophy and ultimately tissue pathology and organ damage. The application of carbon and nitrogen based models of intra cellular vesicular traffic for simulating the autophagic and lysosomal response of the hepatopancreatic digestive cells of marine molluscs is described. Two numerical models of the vesicular transport of carbon and nitrogen in the cell are presented. These demonstrate the importance of endocytotic uptake as a driver of lysosomal dynamics and the need to recognize and model it as a discrete process. Conceptual and mathematical models of the toxic impact of polycyclic aromatic hydrocarbons on the digestive gland are presented. The role of experimental research and the need to integrate it with modelling is highlighted.

Animals↗
PubMed2005

A computer model of the auditory-nerve response to forward-masking stimuli.

A computer model of the auditory periphery is used to study the involvement of auditory-nerve (AN) adaptation in forward-masking effects. An existing model is shown to simulate published AN recovery functions both qualitatively and quantitatively after appropriate parameter adjustments. It also simulates published data showing only small threshold shifts when a psychophysical forward-masking paradigm is applied to AN responses. The model is extended to simulate a simple but physiologically plausible mechanism for making threshold decisions based on coincidental firing of a number of AN fibers. When this is used, much larger threshold shifts are observed of a size consistent with published psychophysical observations. The problem of how stimulus-driven firing can be distinguished from spontaneous activity near threshold is also addressed by the same decision mechanism. Overall, the modeling results suggest that poststimulatory reductions in AN activity can make a substantial contribution to the raised thresholds observed in many psychophysical studies of forward masking.

Acoustic Stimulation↗
PubMedDate not supplied

A parametric algorithm for computing model period and cohort human survival functions.

A parametric algorithm was developed for computing model cohort and period survival functions used in making projections of human populations. Two levels of parameters were used in developing the algorithm. The algorithm provides a method for calculating model period survival functions as a function of an expectation of life at birth; model cohort survival functions are calculated as a function of a time series of period expectations of life at birth. Expectations of life at birth ranging from about 35 to 110 years in both sexes may be accommodated by the algorithm.

Actuarial Analysis↗
PubMed1999

A computer model for describing the effect of urethral afferents on simulated lower urinary tract function.

A computer model of mechanical properties of the bladder, the urethra and the rhabdosphincter, as well as their neural control is presented in this paper. The model has a rather simple design and processes sensory information from both the bladder wall tension and urethral stretch. It is assumed that afferent signals from the urethra are involved in a sacral excitatory reflex and a supraspinal inhibitory reflex. Pressure and flow signals that resemble experimentally measured normal human behaviour could be simulated with this model. From these simulations the relation between the neural control mechanisms used in the model and the neural control mechanism in vivo cannot be judged entirely because similar behaviour could be simulated with models that are bas ed on different neural control mechanisms. Also behaviour that resembles detrusor overactivity was simulated with our model after an externally induced rise in detrusor pressure was added. Detrusor overactivity, sometimes in combination with urethral relaxation, can occur during a urodynamic investigation. A possible explanation for this detrusor overactivity might be that the micturition reflex is triggered by unknown disturbances and is inhibited immediately after by the same mechanism that normally ceases voiding. The described model provides such a mechanism. Based on these simulations, therefore, it is concluded that urethral afferent signals might be important in lower urinary tract control.

Afferent Pathways↗
PubMed1995

A computer model of health status and costs in national health planning.

We developed a computer model which measures the impact of disease on a population, has the ability to track changes in disease incidence over time, and incorporates costs of disease prevention and treatment. This model was developed with data for Malaysia and used by the Ministry of Health in the development of their national health plan. The model uses the DHLL (DALY) measure which incorporates morbidity and mortality impacts of disease. The ability of the model to adjust for changes in disease incidence over a period of years allows health planners to accurately reflect demographic and development related changes in disease incidence. This model is of value to health planners because in incorporates information on population health status, costs of prevention and treatment, and changes in health status over time. It produces an evaluation of the cost effectiveness of possible interventions that can be used by health planners in making decisions on resource allocation.

Computer Simulation↗
PubMed2001

A computational model of membrane lipid electronic properties in relation to neural signaling.

We present a computational model of a transiently-organized neural membrane molecular system with possible information-processing capacity. The model examines field-induced dipole and quadrupole moments and polarizability in monomeric, dimeric, and trimeric ethenes. Polarization of the ethenes is strongly indicated. This result is interpreted as a significant electronic feature of a molecular computing system based on organization of membrane lipids into a transient ( approximately 10(-4) s) crystalline state due to lipid-protein hydrophobic mismatch at the membrane-ion-channel interface. Predictive implications of the model's electronic features are briefly discussed.

Animals↗
PubMed2002

Theoretical and computational models of ion channels.

Computational studies can make meaningful contributions to our understanding of biological ion channels. A wide variety of methods, at different levels of approximation, can be used. Over the past few years, progress in the experimental determination of three-dimensional structures has given a fresh impetus to the theorists. Noteworthy progress has been made in carefully constructing realistic models of a number of complex biological channels to address important questions about their function.

Bacterial Proteins↗
PubMed2003

A 3-dimensional computer model to simulate trabecular bone metabolism.

Mechanical loading of trabecular bone affects the bone architecture. Bone mass is correlated to the magnitude of the external load and trabeculae are aligned to the loading direction. Physical exercise increases bone mass while disuse or microgravity decreases it. In previous work we have presented a mathematical model of bone metabolism that could explain the emergence, maintenance and adaptation of trabecular bone under influence of the load imposed, using a 2-dimensional computer model (Huiskes et al., Nature 404 (2000), 704-706). This model was based on hypothetical mathematical descriptions of bone formation by osteoblastic cells, and resorption by osteoclastic cells, both as governed by mechanical stimuli. In order to quantitatively compare the behavior of the proposed regulation mechanism to real trabecular bone metabolism we present a 3-dimensional computer simulation model. The first 3-dimensional simulation results show that the regulatory rules proposed earlier mimic trabecular bone metabolism in a robust way.

Bone Remodeling↗
PubMed1992

Computer modeling of polysaccharide-polysaccharide interactions: an approach to the kappa-carrageenan-mannan case.

A computer program SAINT has been developed for the investigation of the structure and for the prediction of minimum-energy structure of polysaccharide-polysaccharide complexes. The energy minimization is carried out on internal geometrical parameters--namely bond angles, torsional angles, and five parameters describing the mutual orientations of polysaccharide chains. For this purpose, the nonderivative method of conjugated directions is used. This procedure was applied to computer modeling of an idealized model of the binary gelling kappa-carrageenan and galactomannan system. It is shown that the interaction between two chains influences the structure of the individual polysaccharide molecule and that in the minimum-energy structures of the complex, the conformation of the chains does not correspond to the lowest energy.

Carbohydrate Sequence↗
PubMedDate not supplied

A computer model of human ventricular myocardium for simulation of ECG, MCG, and activation sequence including reentry rhythms.

A computer model is presented for simulation of the spread of activation and repolarization in ventricular myocardium. The program calculating the activation sequence is based on an algorithm similar to Huygen's principle of constructing wavefronts. Physiological parameters of the heart, such as areas of early activation on the endocardium, conduction velocity, anisotropy of propagation, duration of action potentials and refractory periods are taken into account. The time-course of ECG and MCG is calculated using the equations of the bidomain model. Simulation of pathologic cases of activation is performed through variation of the physiological heart parameters. The simulations presented here show good agreement of ECG and MCG with measurements in the normal case, the case of bundle branch block and abnormal repolarization. A special feature of the model is the possibility of simulating reentry rhythms following a premature stimulus in ventricular myocardium. Two kinds of reentry are simulated: reentry around an anatomical obstacle and the leading-circle model. The widespread capability for investigating not only ECG but also MCG and various kinds of pathologic activation patterns including reentry rhythms indicates that the model may be useful in studying numerous problems in cardiologic research.

Action Potentials↗
PubMedDate not supplied

A simple computer model for insulin-receptor interactions and insulin dependent glucose uptake by adipocytes.

A simple computer model is described for the simulation of insulin binding to cell surface receptors on adipocytes and the subsequent stimulation of glucose uptake. The model is based on the currently accepted physiology and biochemistry of insulin action. The model successfully simulated changes in sensitivity to insulin with changes in receptor numbers seen with in vitro experiments; it is also consistent with the proposal that an increased rate of insulin-receptor complex internalisation should lead to an insulin-resistant state. The model also suggests that such an insulin-resistant state should not be affected by a subsequent increase in the rate of return of internalised receptors to the outer cell surface.

Adipose Tissue↗