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PubMed2001

Use of computer simulation for cycle length adjustment in sequencing batch reactor.

The city of Nowy Targ located in Poland's highland operates the WWTP with classic SBR technology. In winter some decrease in process efficiency was observed. The research described in the paper was aimed at using computer simulation to adjust SBR cycle length and structure in order to minimize the effects of low wastewater temperature on biological CNP removal. The simulations performed at 6 degrees C wastewater temperature showed that switching from 6 to 8 hours cycle and extension of the aeration phase length from 2.75 to 5 hours will increase the effectiveness of biological nitrification and biological phosphorus removal. The change in practice will not affect COD value in the effluent. Based on the simulation results a new SBR operational strategy was proposed for Nowy Targ WWTP.

Bioreactors↗

PubMed1990

Computer simulation of tumor cell motility and proliferation.

Tumor growth is considered to depend on tumor cell proliferation and on tumor cell motility. The present study investigates in which way these two cellular properties influence the evolving morphological pattern. Computer simulations were performed, where cells were either dividing or moving for a variable distance at a present probability. The simulation parameters (probability of motility, maximum moving distance) were set interactively. The resulting patterns were evaluated by binary morphological criteria, 13 of 17 binary criteria showed a significant relationship with the simulation parameters (median test: p = less than 0.05). Discriminant analysis of two sets of simulations with different simulation parameters provided a correct classification with an efficiency of 100% (k-nearest-neighbour method; jack-knife-procedure). The results indicate that cell proliferation and motility affect morphological patterns in a reproducible way and that the patterns in turn provide morphological clues for the quantitative estimation of motility and proliferation.

Cell Division↗

PubMed1995

Computer simulation of human body dynamics.

Understanding human body dynamics is important in many situations, such as automobile and aircraft crashes, aircraft ejections, falls, and other acceleration environments. The design of automobile interiors, cockpits, and safety equipment requires knowledge of the forces and accelerations encountered during an emergency. Because of the limited information available from actual events and the various constraints in testing, computer simulations are often the only means of obtaining detailed information. The Armstrong Laboratory (AL) developed the Articulated Total Body (ATB) model to predict the human body dynamics in many of these environments. This model is a three-dimensional rigid body dynamics program in which the human body is modeled as a series of segments. Forces on the body segments are calculated based on their interaction with the surroundings including seat and cockpit surfaces. The model also calculates the internal joint resistive and constraint forces. Because of this capability to predict both internal and external forces acting on the body, the ATB model can be used in investigating injuries. It is also a valuable design tool for evaluating safety of proposed systems before prototypes are built or costly tests conducted. When testing is conducted, the model provides data that cannot be measured, such as forces within the body, and supplementing test data with parameter variation simulations. To validate the model, tests such as those conducted on the AL impact sled are simulated. Test films and instrumentation data are compared with simulation graphics and quantitative output to gain confidence in the simulation results.

Acceleration↗

PubMed1994

Fibre optic scrambling in light microscopy: a computer simulation and analysis.

Optical fibres bent in two mutually perpendicular planes have proven useful for randomizing illumination in light microscopes. These optical scramblers can increase the resolution and/or contrast obtained with several modes of light microscopy. Here, computer simulations are used to investigate several parameters affecting light randomization in curved optical fibres in order to further the theoretical basis for scrambler design. Light passing through 90 degrees bends of optical fibre of varying radii of curvature was modelled by ray tracing in two dimensions, and scrambling mechanisms were observed. The effects of varying the position and angle of entry of light on the phase and direction of propagation of the emergent light were determined. It was found that (a) thorough scrambling does not necessarily require high numerical aperture (NA) entry of light into the fibre, (b) considerable order persists after a single 90 degrees bend of an idealized fibre and (c) a higher degree of scrambling (at the cost of transmission efficiency) is achieved in more tightly curved fibres. The pathlength variations introduced by scrambling proved smaller than typical laser coherence lengths, requiring temporal scrambling (vibrating the fibre).

Computer Simulation↗

PubMed1994

Increasing the production of generalists: a computer simulation.

BACKGROUND & OBJECTIVES: The Association of American Medical Colleges set a goal for US medical schools to produce 50% of their graduates as generalists. Methods for achieving this goal have not been established. METHODS: We developed a computer simulation to gauge the effect of interventions that could occur at five different points during medical school education. Each intervention would improve by 10% the proportion of trainees choosing a generalist career. RESULTS: Our model predicts that 24.1% of 1992 medical school graduates will ultimately become generalists. Any of the interventions we evaluated increased generalist production to the 25%-26.5% range. If class size is held constant and if a 10% annual improvement occurred in all of the other intervention points for 3 years, our model still predicts only 44.8% generalists. CONCLUSIONS: Computerized "what-if" analysis can effectively project specialty outcomes after various interventions. The best intervention increased generalist production 2.6 times more than did less effective interventions. The loss of primary care residents into subspecialty fellowships is substantial. Even if 100% of current medical graduates could be directed into family practice, internal medicine, and pediatric residencies in their current proportions, only a 43.7% generalist outcome would be achieved because of attrition of internists and pediatricians into subspecialties. Family practice is the most efficient producer of generalists but currently lacks either the capacity or the marketability to be the nation's sole supplier. More effective interventions are needed to achieve a 50% generalist outcome.

Career Choice↗

PubMed1990

Delayed detection of hypoxic events by pulse oximeters: computer simulations.

There is a variable delay between a reduction in alveolar PO2 and the decrease in arterial oxygen saturation recorded on a pulse oximeter. The decrease in arterial oxygen saturation in response to disconnexion of a paralysed patient from the breathing system, oxygen supply failure with continued mechanical ventilation and disconnexion of the fresh gas supply to Mapleson D and circle absorption breathing systems were studied by simulations on the MacPuf computer model of the cardiorespiratory system. The simulations revealed that there were marked differences between the rate of arterial desaturation which resulted from each of the three types of oxygen supply failure and that arterial oxygen saturation may reach dangerous levels before a pulse oximeter alarm is activated.

Computer Simulation↗

PubMed1997

Computer simulation of subchondral bone adaptation to mechanical loading in an incongruous joint.

BACKGROUND: We hypothesized that the typically bicentric distribution of subchondral bone density (i.e., two maxima) in incongruous joints with deeper sockets could be predicted by a computer simulation employing a concavely incongruous finite-element model and current bone remodeling theory. Additional objectives were to assess the uniqueness of the solution with respect to assumed model parameters and initial conditions and to determine the relationship between contact areas, subchondral bone stress, and subchondral bone density patterns. METHODS: An idealized model of the humeroulnar joint was constructed with a quantitatively realistic representation of its natural incongruity. A currently accepted remodeling theory was implemented with a finite-element code using a node-based approach. RESULTS: The simulation predicted a dense subchondral bone plate after application of 3,000 daily load cycles for 300 days. The pronounced bicentric distribution of subchondral mineralization emerged. The solution was virtually independent of the initial density distribution and other assumed model parameters. Furthermore, the model predicted high tensile stresses in the subchondral bone, when the joint socket was spread apart during loading. Therefore, the locations of maximal strain energy density in the subchondral bone did not correspond with areas of joint contact. CONCLUSIONS: The results of the bone remodeling simulations are consistent with patterns of subchondral bone density determined experimentally. Furthermore, the solutions exhibited a high degree of uniqueness, were rather insensitive to changes in cartilage stiffness, moderately sensitive to number of applied loading cycles, and highly sensitive to loading magnitude. Tensile stresses seem to play a dominant role in subchondral bone remodeling due to bending in the subchondral bone plate. Thus, we conclude that, in the case of an incongruous joints with deeper sockets, the density of the subchondral bone cannot be regarded as a direct measure of the adjacent articular pressure.

Adaptation, Physiological↗

PubMed1984

The slow inward current, isi, in the rabbit sino-atrial node investigated by voltage clamp and computer simulation.

The properties of the slow inward current, isi, in the sino-atrial (s.a.) node of the rabbit have been investigated using two microelectrodes to apply voltage clamp to small, spontaneously beating, preparations. Many of the experimental results can be closely simulated using the computer model of s.a. node electrical activity (Noble & Noble 1984) which has been developed from models of Purkinje fibre activity (Noble 1962; DiFrancesco & Noble 1984). Comparison of the computed reconstructions with experimental results provides a test of the validity of the modelling. Experiments using paired depolarizing clamp pulses show that inactivation of isi is calcium-entry dependent although, unlike the inactivation of Ca2+ currents in some other systems, it also shows some voltage-dependence. Re-availability (recovery from inactivation) of isi in s.a. node is much slower than inactivation at the same potential, showing that isi is not controlled by a single first order process. This very slow recovery from inactivation of isi in the s.a. node and the slow time course of its activation and inactivation at voltages near threshold (-40 to -50 mV) can be closely modelled by assuming that there are two components of 'total isi': a fast inward current, iCa,f' representing the 'gated' fraction and a second, slower, inward current component, iNaCa which, we propose, is caused by the sodium-calcium exchange that ensues when the initial Ca2+ -entry triggers the release of stored intracellular Ca2+. When repetitive trains of clamp pulses are given, a 'staircase' of isi magnitude is seen which can be increasing ('positive') or decreasing ('negative') according to the potential level and frequency of the pulse train given. When computer reconstructions of such staircases are made, it is found that the positive staircases (which, in contrast to negative staircases, imply that more complex processes than simple inactivation are present) can be closely simulated by a model which incorporates slower processes (suggested Na-Ca exchange current) in the total isi in addition to the gated current component.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2006

Computational simulation of renal biopsy accuracy in focal segmental glomerulosclerosis.

The goal of this study was to estimate the diagnostic and prognostic accuracy of renal biopsies in focal segmental glomerulosclerosis (FSGS), accounting for the focal nature of affected glomeruli. Computational simulations were performed on a total of 138,600 virtual kidneys, across a range of FSGS involvement. Simulations were designed to address the diagnostic accuracy of renal biopsies, and the biopsy characteristics required to reflect accurately the true degree of involvement of FSGS in the entire kidney or just the juxtamedullary (JM) region. The diagnostic accuracy of renal biopsies for the detection of at least one FSGS glomerulus exceeded 80% when 10-20% of the kidney was affected by FSGS. Hundreds to thousands of biopsy glomeruli were required to characterize reliably the true extent of FSGS when fewer than 75% of the kidney's glomeruli were affected. Renal biopsies with an average of 20 glomeruli did not accurately reflect the extent of FSGS in kidneys until at least 80% of all glomeruli in the kidney were affected. Targeting JM glomeruli did not result in significant improvements in the prognostic performance characteristics of renal biopsies. These findings suggest that conventional renal biopsies might be inadequate for characterizing the extent of FSGS.

Biopsy↗

PubMed1998

Simultaneous variation of temperature and gradient steepness for reversed-phase high-performance liquid chromatography method development. I. Application to 14 different samples using computer simulation.

The optimized reversed-phase HPLC separation of 14 different samples is reported, based on simultaneous changes in temperature and gradient steepness. Four experimental runs are required for each sample, following which preferred conditions can be predicted using computer simulation software (DryLab). The overall accuracy and effectiveness of this method development approach is discussed, with particular attention to the use of resolution maps provided by the software. These maps are useful for maximizing resolution for the total sample, for optimizing the separation of a smaller number of selected sample compounds, and as an initial step in the separation of more demanding samples.

Adrenal Cortex Hormones↗

PubMed1999

Breast cancer: computer simulation method for estimating optimal intervals for screening.

PURPOSE: To develop and evaluate a mathematic method that can be used to determine the optimal screening interval for detection of breast cancer prior to distant metastatic spread. MATERIALS AND METHODS: A computer simulation was developed with the use of biologically based data from the literature on the rates of tumor growth and spread, which can be used to calculate the course of breast cancer growth and metastasis. RESULTS: On the basis of the data available at this time, the results of the simulations suggested that a screening interval of 2 years would result in a 22% reduction in the rate of distant metastatic disease, an interval of 1 year would result in a 51% reduction, and an interval of 6 months would result in an 80% reduction. CONCLUSION: These findings suggest that more frequent screening could dramatically reduce the death rate from breast cancer.

Appointments and Schedules↗

PubMed2005

Accuracy of popular automatic QT interval algorithms assessed by a 'gold standard' and comparison with a Novel method: computer simulation study.

BACKGROUND: Accurate measurement of the QT interval is very important from a clinical and pharmaceutical drug safety screening perspective. Expert manual measurement is both imprecise and imperfectly reproducible, yet it is used as the reference standard to assess the accuracy of current automatic computer algorithms, which thus produce reproducible but incorrect measurements of the QT interval. There is a scientific imperative to evaluate the most commonly used algorithms with an accurate and objective 'gold standard' and investigate novel automatic algorithms if the commonly used algorithms are found to be deficient. METHODS: This study uses a validated computer simulation of 8 different noise contaminated ECG waveforms (with known QT intervals of 461 and 495 ms), generated from a cell array using Luo-Rudy membrane kinetics and the Crank-Nicholson method, as a reference standard to assess the accuracy of commonly used QT measurement algorithms. Each ECG contaminated with 39 mixtures of noise at 3 levels of intensity was first filtered then subjected to three threshold methods (T1, T2, T3), two T wave slope methods (S1, S2) and a Novel method. The reproducibility and accuracy of each algorithm was compared for each ECG. RESULTS: The coefficient of variation for methods T1, T2, T3, S1, S2 and Novel were 0.36, 0.23, 1.9, 0.93, 0.92 and 0.62 respectively. For ECGs of real QT interval 461 ms the methods T1, T2, T3, S1, S2 and Novel calculated the mean QT intervals(standard deviations) to be 379.4(1.29), 368.5(0.8), 401.3(8.4), 358.9(4.8), 381.5(4.6) and 464(4.9) ms respectively. For ECGs of real QT interval 495 ms the methods T1, T2, T3, S1, S2 and Novel calculated the mean QT intervals(standard deviations) to be 396.9(1.7), 387.2(0.97), 424.9(8.7), 386.7(2.2), 396.8(2.8) and 493(0.97) ms respectively. These results showed significant differences between means at >95% confidence level. Shifting ECG baselines caused large errors of QT interval with T1 and T2 but no error with Novel. CONCLUSION: The algorithms T2, T1 and Novel gave low coefficients of variation for QT measurement. The Novel technique gave the most accurate measurement of QT interval, T3 (a differential threshold method) was the next most accurate by a large margin. The objective and accurate 'gold standard' presented in this paper may be useful to assess new QT measurement algorithms. The Novel algorithm may prove to be more accurate and reliable method to measure the QT interval.

Algorithms↗

PubMed1989

Computer simulation of respiratory impedance and flow transfer functions during high frequency oscillations.

The usefulness of measuring respiratory flow in the airway and at the chest wall and of measuring respiratory input impedance (Z) to monitor high frequency ventilation was investigated by computer simulation using a monoalveolar 10-coefficient model. The latter included a central airway with its resistance (Rc) and inertance (lc), a resistive peripheral airway (Rp), a lumped bronchial compliance (Cb), alveolar gas compliance (Cgas), lung tissue with its resistance (RL) and compliance (CL), and chest wall resistance (RW), inertance (lw) and compliance (Cw). Gas flow in the peripheral airway (Vp), shunt flow through Cb (Vb), gas compression flow (Vgas) and rate of volume change of the lung (VL) and of the chest (VW) were computed and expressed as a function of gas flow in the central airway (Vc). For normal values of the coefficients, Vp/Vc was found to decrease moderately with increasing frequency and was still 0.75 at 20 Hz. Peripheral airway obstruction (Rp x 5) considerably decreased Vp/Vc, particularly at high frequency. It did not change the relationship between the two measurable flows, Vc and Vw, but increased the effective resistance at low frequency and shifted the reactance curve to the right. A reduced lung or chest wall compliance produced little change in Vp/Vc and Z except at very low frequencies; however, it decreased the phase lag between Vw and Vc. Finally, an increased airway wall compliance decreased Vp/Vc, but had little effect on Z and Vw/Vc. It is concluded that measuring respiratory impedance may help in detecting some, but not all of the conditions in which peripheral flow convection is decreased during high frequency oscillations.

Airway Obstruction↗

PubMed1983

Radiofrequency-induced hyperthermia: computer simulation of specific absorption rate distributions using realistic anatomical models.

A description is given of a computer simulation technique which predicts the specific absorption rate (SAR) distribution within the human body resulting from the application of radiofrequency electromagnetic energy. The method uses an extension to the principle of over-relaxation of electric potentials and the basis of the simulation is a realistic three-dimensional model derived from both dielectric and anatomical data. Two of the principal means of applying radiofrequency hyperthermia, namely the use of capacitive electrodes and inductive coils, have been provided for. The accuracy of the simulation has been favourably tested using an agar split-phantom and an infrared thermograph camera. The simulations can be used to assist the design and clinical use of radiofrequency applicators, and examples are given of the application of both an inductive coil and switched capacitive electrodes to heat the thorax.

Computers↗

PubMed2006

High-resolution computer simulations of stacking of weak bases using a transient pH boundary in capillary electrophoresis. 1. Concept and impact of sample ionic strength.

The dynamics of focusing weak bases using a transient pH boundary was examined via high-resolution computer simulation software. Emphasis was placed on the mechanism and impact that the presence of salt, namely, NaCl, has on the ability to focus weak bases. A series of weak bases with mobilities ranging from 5 x 10(-9) to 30 x 10(-9) m2/V x s and pKa values between 3.0 and 7.5 were examined using a combination of 65.6 mM formic acid, pH 2.85, for the separation electrolyte, and 65.6 mM formic acid, pH 8.60, for the sample matrix. Simulation data show that it is possible to focus weak bases with a pKa value similar to that of the separation electrolyte, but it is restricted to weak bases having an electrophoretic mobility of 20 x 10(-9) m2/V x s or quicker. This mobility range can be extended by the addition of NaCl, with 50 mM NaCl allowing stacking of weak bases down to a mobility of 15 x 10(-9) m2/V x s and 100 mM extending the range to 10 x 10(-9) m2/V x s. The addition of NaCl does not adversely influence focusing of more mobile bases, but does prolong the existence of the transient pH boundary. This allows analytes to migrate extensively through the capillary as a single focused band around the transient pH boundary until the boundary is dissipated. This reduces the length of capillary that is available for separation and, in extreme cases, causes multiple analytes to be detected as a single highly efficient peak.

Computer Simulation↗

PubMed1991

A mathematical model and computer simulation study of insulin sensitive glucose transporter regulation.

A mathematical model of insulin sensitive glucose transporter regulation is developed. Model structure is based on experimental evidence from adipocytes and myocytes. Model parameters correspond with known cellular processes. As an example, computer simulation results are compared with data from rat adipocytes. Cellular processes explicitly represented in the model include state-dependent glucose transporter synthesis and degradation rates, insulin sensitive glucose transporter translocation rates, and a glucose transporter endocytosis rate. Most of these processes are represented as first-order events. Using more complex representations of the model structure (e.g. higher order rate constants or saturable pathways) or alternative structures did not result in qualitatively better results. The model is able to accurately simulate the insulin sensitive, insulin concentration dependent, reversible translocation of glucose transporters observed in normal adipocytes. The model is also able to accurately simulate the changes in regulation of glucose transporter translocation observed with increases in cell surface area. Finally, the model can simulate pathogenic states which induce impairment of glucose transporter regulation (e.g. altered glucose transporter regulation in adipocytes from rats on high fat diets, rats with streptozotocin induced diabetes, and fasted rats). Since the structure of our model is sufficient to explain glucose transporter regulation in both normal and pathological states, it may aid in understanding the post-receptor components of insulin resistance (decreased sensitivity or responsiveness to insulin) seen in pathological states such as obesity and diabetes mellitus.

Adipose Tissue↗

PubMed1998

Computer simulation as a tool in evaluating intracellular spatial arrangement of an organelle using random section data.

A random profile of a cell gives a highly biased presentation of the location of various organelles within an intracellular space. The technique combining mathematical modeling and computer simulation presented here is aimed to overcome this bias and interpret intracellular spatial arrangement of an organelle using two-dimensional (2-D) observations from random sections. It allows to simulate random sectioning of a cell whose shape approximates to an ellipsoid of rotation, and to obtain the coordinates for the center of an organelle profile located within a cell profile. The pilot study was performed to investigate the influence of different three-dimensional (3-D) scattering patterns of an organelle on the coordinates of an organelle profile's center. Computer tests were carried out on a personal computer using the original software written in Pascal. It was ascertained that statistical properties of a sample of organelle profile's center coordinates allow for a quantitative estimation of some 3-D features, including the position of an organelle with respect to a cell center and specific characteristics of an organelle position (e.g., its fixity or randomness).

Cells↗

PubMed1999

Multiple-task performance on a computer-simulated life support system during a space mission simulation.

This paper presents an experiment which examined the effects of isolation and confinement during a simulation of a short-term space mission. During the 7-day spaceflight simulation, four Canadian astronauts were tested daily on a 30-min performance task. The task, CAMS (Cabin Air Management System), represents a computer-based simulation of a generic life support system. As a multiple-task environment, it allows the measurement of a wide range of task management variables such as primary and secondary task performance, and system control activities. Measures of subjective state variables were also taken. The results did not show any evidence of serious performance decrements for any crew member. The analysis revealed different adjustment patterns with which crew members responded as a function of mission duration and variations in workload. Among the secondary tasks employed, prospective memory was found to be more sensitive than reaction time to increases in workload. The paper concludes with a discussion of the utility of spaceflight simulations and computer-based simulations of space work.

Adaptation, Psychological↗