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At least 1,315 records · Page 73Linked to original sources
PubMed2001

Spatially modulated illumination microscopy: online visualization of intensity distribution and prediction of nanometer precision of axial distance measurements by computer simulations.

During the last years, measurements considerably beyond the conventional "Abbe-Limit" of optical resolution in far field light microscopy were realized by several light microscopical approaches. Point spread function (PSF) engineering, spectral precision distance microscopy (SPDM), and related methods were used to demonstrate the feasibility of such measurements. SPDM allows the measurement of position and multiple distances between point-like fluorescent objects of different spectral signatures far below the optical resolution criterion as defined by the full width at half maximum of the PSF. Here, we report a software method to obtain online visualization of light distribution in the lateral and axial direction of any object detected in a spatially modulated illumination (SMI) microscope. This strongly facilitates routine application of SMI microscopy. The software was developed using Microsoft Visual C++ running on Windows NT. Furthermore, some aspects of the theoretical limits of the SPDM method were studied by virtual microscopy. For the case of SMI microscopy the precision of axial distance measurements was studied, taking into account photon statistics and image analysis procedures. The results indicate that even under low fluorescence intensity conditions typical for biological structure research, precise distance measurements in the nanometer range can be determined, and that axial distances in the order of 40 nm are detectable with such precision.

Computer Simulation↗
PubMed2005

Computational simulation of human upper airway collapse using a pressure-/state-dependent model of genioglossal muscle contraction under laminar flow conditions.

A three-element, pressure- and state (sleep and wake) -dependent contraction model of the genioglossal muscle was developed based on the microstructure of skeletal muscle and the cross-bridge theory. This model establishes a direct connection between the contractile forces generated in muscle fibers and the measured electromyogram signals during various upper airway conditions. This effectively avoids the difficulty of determining muscle shortening velocity during complex pharyngeal conditions when modeling the muscle's contractile behaviors. The activation of the genioglossal muscle under different conditions was then simulated. A sensitivity analysis was performed to determine the effects of varying each modeled parameter on the muscle's contractile behaviors. This muscle contraction model was then incorporated into our anatomically correct, two-dimensional computational model of the pharyngeal airway to perform a finite-element analysis of air flow, tissue deformation, and airway collapse. The model-predicted muscle deformations are consistent with previous observations regarding upper airway behavior in normal subjects.

Airway Obstruction↗
PubMedDate not supplied

Formulation of controlled release microspheres containing nicardipine: the role of pharmacokinetic modeling and computer simulation.

Nicardipine is an antihypertensive drug of the dihydropyridine series. It has high solubility in an acidic and low solubility in an alkaline medium. It is rapidly absorbed, extensively presystemically metabolized and excreted in the urine and faeces, mainly as inactive metabolites. Since the duration of its action can be extended by prolonging the absorption interval, the design of controlled release formulation is reasonable. The aim of the present study was to prepare microspheres which would release nicardipine at a decreased rate in gastric and increased rate in intestinal juice during a 12 h interval. Pharmacokinetic modeling based on compartment analysis and supported by analog computer and digital simulation technique showed that the target steady state peak plasma concentrations of 32 microg/l and trough plasma concentration of 7 microg/l would be maintained if nicardipine were incorporated in a formulation releasing the drug as follows: 25% after 1 h, 40% after 2 h, 65% after 4 h, 80% after 6 h, 90% after 8 h and 100% by 12 h. Microspheres have been prepared from hydroxypropylmethylcellulose phthalate polymer using the solvent evaporation method. Drug content, scanning electron micrographs, particle size distribution and dissolution profile were determined. In vitro nicardipine release was described by a biphasic square root of time kinetics and was in accordance with the above values relating to the dissolution. Furthermore, a composed first-pass pharmacokinetic model with derived release function as an input was developed to predict nicardipine plasma concentrations after single- and 12 h multiple-dosage-regimen scheme administration of controlled release microspheres.

Antihypertensive Agents↗
PubMed1996

Computer simulations of proteolysis of Marburg and Ebola-Zaire filovirus coded proteins to generate nonapeptides with motifs of known HLA class I haplotypes and detection of antigenic domains in the viral glycoproteins.

The primary amino acid sequences of the proteins coded by Marburg and Ebola-Zaire filoviruses were studied by computer programs to search for putative proteolytic cleavages which yield nonapeptides with motifs of binding to known HLA class I haplotypes. The computer analyses predicted that numerous nonapeptides with motifs to bind HLA class I A68 and A2 haplotypes were detected. A few nonapeptides with motifs HLA class I A24, B8, B27 and B35 were predicted in Marburg virus proteins. A similar finding is reported for Ebola-Zaire viral proteins (the viral polymerase was not studied). The search for antigenic domains that may induce the humoral immune response in the viral glycoproteins was based on computer analyses of the physical properties and antigenicity predictions of amino acids in certain domains of the primary amino acid sequences. Twelve putative antigenic domains were detected in Marburg virus glycoprotein and 11 putative antigenic domains in Ebola-Zaire virus glycoprotein. Despite the marked differences in the primary amino acid sequences in the putative antigenic domains of the two viral glycoproteins, 8 antigenic domains were found to have similar locations in the viral glycoproteins of the two viruses. Each pair of antigenic domains resemble each other in the physical properties of the amino acids that are different. These computer analyses may provide an approach to developing synthetic peptides capable of induction of both the cellular and humoral responses to protect against infection with Marburg or Ebola viruses.

Amino Acid Sequence↗
PubMed1984

Potential use of computer simulation in treatment of burns with special regard to oedema formation.

The potential usefulness of computer-based 'patient-simulators' in burn care is discussed and illustrated in the special case of oedema formation in three patients with severe thermal injuries. The present model was derived from a model by Wiederhielm (1978), and modified to be applicable to thermal injuries. The model seems to describe accurately the oedema formation as well as the distribution and composition of local and general oedema. Following thermal injuries the general oedema is characterized by typical disturbances in the circulatory state variables such as capillary pressure and plasma colloid osmotic pressure. The net water flow is increased because of an increase in filtration rate and a decrease in reabsorption rate. The resulting interstitial oedema leads to dilution of the free water proteins and a decrease in interstitial colloid osmotic pressure. The elevation of interstitial pressure leads to an increase in lymph flow. The local oedema is caused by changes in both the circulatory system and the interstitial space. There is an increase in both water and protein net flows. The latter is due to increased protein leakage to the interstitium. This results in an interstitial oedema with a higher protein concentration in free water than in general oedema. Because of the higher protein concentration in free water, the interstitial colloid osmotic pressure is at all times larger than the corresponding pressure in general oedema. In all three patients the general shape of the simulated and measured oedema curve were the same, but with minor differences in numerical values. It is interesting to note that the general oedema was larger than the local oedema in all three extensively burned patients. The results from the present investigation indicate the importance of monitoring either the total plasma protein concentration or the plasma colloid osmotic pressure and small vein pressure for guidance of a proper fluid resuscitation. The steady state 'oedema vs. venous pressure'-diagram obtained may also be used for evaluating the dynamic effects on general oedema formation due to changes in venous pressure and plasma protein concentration. It thus turned out that for a typical thermal injury with a decreased small vein pressure a continuous colloid infusion is to be preferred instead of an intermittent model of administration.

Blood Proteins↗
PubMed2003

Computer simulation: how can it help the surgeon optimize implant position?

Component placement critically affects the performance and longevity of total hip replacements (THRs). Because of limitations of observation and anatomic orientation imposed by the operative site, selection of the correct size, and position of the acetabular and femoral components is best done through preoperative planning. Currently, this is done by comparing two-dimensional templates of prosthetic components with clinical radiographs; however, this method has the inherent limitation that AP and lateral radiographs each provide one projection of the pelvis and the femur. Computer technology makes it possible to observe implantation of the femoral and acetabular components in three dimensions. This approach allows surgeons to template with superior accuracy, while providing an intimate view of the fit of the components in the implantation site. Additionally, computer routines can predict the functional outcome of a preoperative plan before its implementation. Restoration of leg length, center of rotation, ROM of the joint during various activities, and points of bony and prosthetic impingement can be analyzed preoperatively by the surgeon. This is a valuable tool for surgical navigation and surgeon training. With emerging technologic advances in surgical technique, computer-based preoperative planning tools should prove all the more essential to reliable component placement.

Arthroplasty, Replacement, Hip↗
PubMed2000

Nucleic acids: theory and computer simulation, Y2K.

Molecular dynamics simulations on DNA and RNA that include solvent are now being performed under realistic environmental conditions of water activity and salt. Improvements to force-fields and treatments of long-range interactions have significantly increased the reliability of simulations. New studies of sequence effects, axis bending, solvation and conformational transitions have appeared.

Chemical Phenomena↗
PubMed1991

Spontaneous degradation and enzymatic repair of aspartyl and asparaginyl residues in aging red cell proteins analyzed by computer simulation.

The inherent instability of proteins may be a limiting factor in the longevity of an organism. Spontaneously altered forms may themselves be toxic, or their accumulation may simply crowd out normal proteins. Two of the major sites of nonenzymatic degradation are aspartyl and asparaginyl residues, which are susceptible to an intramolecular reaction that results in the deamidation of asparaginyl residues and the isomerization and racemization of both aspartyl and asparaginyl residues. In all eucaryotic cells examined so far, an enzyme is present that can recognize at least some of these damaged sites and initiate their conversion to normal forms. This enzyme, the type II protein carboxyl methyltransferase, catalyzes the methyl esterification of L-isoaspartyl and D-aspartyl residues, enabling them to spontaneously revert to their normal L-aspartyl configurations. In this study, we utilize data on the rates of spontaneous degradation and enzymatic methylation in a computer program that simulates these reactions in the intact human erythrocyte. The results show that the methyltransferase may have an important role in limiting the accumulation of proteins containing altered aspartyl and asparaginyl residues.

Asparagine↗
PubMed2004

Computer simulation tool for rhinoplasty planning.

Rhinoplasty is a collection of surgical procedures performed on nose for the purpose of correcting functional and shape deformities. Nose is a facial feature which naturally draws attention during everyday contact. Any operation performed on nose has to blend well with the other facial features of the face. For this reason rhinoplasty is a type of surgery which requires artistic skills from surgeon as well as surgical skills. In this paper we present an artistic simulation tool which manipulates the shape of the nose on the bases of rhinoplasty procedures to be used during the surgery. Unlike other artistic simulation tools which can modify shape with no constraints, this tool simulates the effect of individual operations. Simulation tool can be valuable only if it predicts the outcome of the surgery with accuracy. Ultimately the outcome of the simulation depends largely on the experience of the surgeon. This is also the case with the tool presented in this study, so with experience the tool can be useful for predicting outcome more and more accurately. In this paper, the mechanical model of the nose and tools used for simulation are discussed. The simulation results are compared with actual rhinoplasty results to see the fidelity of the approach. A flowchart of the decision process and how rhinoplastic simulation together with the ideal nose data can be used to aid actual rhinoplastic surgery is given at the end.

Computer Simulation↗
PubMed1993

New version of LSTSIM for computer simulation of Amblyomma americanum (Acari: Ixodidae) population dynamics.

A previous version of Lone Star Tick Simulation Model (LSTSIM) for a wildlife ecosystem was revised and expanded to include a beef cattle forage area and improved handling of tick-host-habitat interactions. Relationships between environmental and biological variables were also refined in the new version. General validity of the revised model was established by comparing simulated and observed host-seeking populations of Amblyomma americanum (L.) at five geographic locations, three in Oklahoma and two in Kentucky-Tennessee. Additional validity was indicated from comparisons of simulated and observed seasonality of lone star ticks at one location in Kentucky. The model produced acceptable values for initial population growth rate, generation time, and 15-yr population density when historical weather files for 14 locations in the United States were used. The model of A. americanum population dynamics was used to study the relationship between tick density and density of white-tailed deer, Odocoileus virginianus (Zimmerman), and cattle. The revised model can be used for additional simulation studies on effects of tick control technologies and integrated management strategies.

Animals↗
PubMed1992

A computer simulation of the influence of selection and breakage of food on the chewing efficiency of human mastication.

The reduction of food particle sizes during mastication is considered to be the composite result of a selection and breakage process. The chance of a food particle being selected between the teeth was assumed to increase as a power function of the particle's size, whereas the breakage of food particles was described by a cumulative distribution function. The selection and breakage functions were combined with matrix algebra, resulting in a matrix model. By use of this model, particle-size distributions could be calculated after various numbers of chewing cycles. From these distributions, the decrease of the median particle size was determined as a function of the number of chewing cycles. The calculations were performed for various sets of physiologically relevant selection and breakage variables. The number of chewing cycles, N1/2, needed for the initial particle size to be halved was taken as an indication of chewing efficiency. This number varied approximately inversely with both the selection coefficient and the breakage variable. The initial particle size appeared to have the largest influence on N1/2. The theoretical results from the simulation study were also compared with data obtained from experiments on human chewing efficiency.

Computer Simulation↗
PubMed2003

Computer simulation of convective and diffusive transport of controlled-release drugs in the vitreous humor.

PURPOSE: Biodistribution of drugs in the eye is central to the efficacy of pharmaceutical ocular therapies. Of particular interest to us is the effect of intravitreal transport on distribution of controlled-released drugs within the vitreous. METHODS: A computer model was developed to describe the three-dimensional convective-diffusive transport of drug released from an intravitreal controlled release source. Unlike previous studies, this work includes flow of aqueous from the anterior to the posterior of the vitreous. The release profile was based on in vitro release of gentamicin from poly(L-lactic acid) microspheres into vitreous. RESULTS: For small drugs, convection plays a small role, but for large (slower diffusing) drugs, convection becomes more important. For the cases studied, the predicted ratio of drug reaching the retina to drug cleared by the aqueous humor was 2.4 for a small molecule but 13 for a large molecule. Transport in neonatal mouse eye, in contrast, was dominated by diffusion, and the ratio decreased to 0.39. CONCLUSIONS: The interaction among convection, diffusion, and geometry causes significant differences in biodistribution between large and small molecules or across species. These differences should be considered in the design of delivery strategies or animal studies.

Animals↗