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Mathematical Simulations (mathematical + simulation)
Selected AbstractsMathematical simulation of calcimine deliming in the production of gelatinAICHE JOURNAL, Issue 7 2010Karel Kolomazník Abstract Calcimine is a valuable by-product originating during the processing of cured hide into leather. It is used as raw material in the production of gelatin and biodegradable sheets. For further usage, it is necessary to remove calcium hydroxide from calcimine by chemical deliming, which is, from the environmental protection point of view, the most important stage of the entire deliming process. In this article, a mathematical description of chemical deliming is proposed, based on the unreacted nucleus approach. Numerical solution of the model is found, concentration fields of the reacting chemicals described, and the evolution of the acido-basic boundary inside calcimine shown. The model is used to justify a simplified way to determine the effective diffusion coefficient of the deliming agent. The model can also be used as a basis for optimization of the deliming process. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Quantifying the heterogeneous heat response of Escherichia coli under dynamic temperaturesJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2010E. Van Derlinden Abstract Aims:, Non-sigmoid growth curves of Escherichia coli obtained at constant temperatures near the maximum growth temperature (Tmax) were previously explained by the coexistence of two subpopulations, i.e. a stress-sensitive and a stress-resistant subpopulation. Mathematical simulations with a heterogeneous model support this hypothesis for static experiments at 45°C. In this article, the behaviour of E. coli, when subjected to a linearly increasing temperature crossing Tmax, is studied. Methods and Results:, Subpopulation dynamics are studied by culturing E. coli K12 MG1655 in brain heart infusion broth in a bioreactor. The slowly increasing temperature (°C h,1) starting from 42°C results in growth up to 60°C, a temperature significantly higher than the known Tmax. Given some additional presumptions, mathematical simulations with the heterogeneous model can describe the dynamic experiments rather well. Conclusions:, This study further confirms the existence of a stress-resistant subpopulation and reveals the unexpected growth of E. coli at temperatures significantly higher than Tmax. Significance and Impact of the Study:, The growth of the small stress-resistant subpopulation at unexpectedly high temperatures asks for a revision of currently applied models in food safety and food quality strategies. [source] Block of HERG-Carried K+ Currents by the New Repolarization Delaying Agent H 345/52JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 6 2003Gregory J. Amos M.D. Ph.D. Introduction: The aim of this study was to analyze the block of HERG-carried membrane currents caused by H 345/52, a new antiarrhythmic compound with low proarrhythmic activity, in transfected mouse fibroblasts. Methods and Results: Using the whole-cell configuration of the voltage patch clamp technique, it was demonstrated that H 345/52 concentration-dependently blocked HERG-carried currents with an IC50 of 230 nM. H 345/52 preferentially bound to the open channel with unusually rapid kinetics and was trapped by channel closure. Voltage-independent behavior of H 345/52 was observed during both square-pulse and action potential clamp protocols. In contrast, the Class III agents dofetilide (10 nM) and almokalant (250 nM) demonstrated significant membrane potential-dependent effects during square-pulse clamp protocols. When using action potential clamp protocols, voltage dependence was seen with dofetilide but not with almokalant. Mathematical simulations of human ventricular action potentials predicted that the different voltage-dependent behaviors would not produce marked variations in action potential duration prolongation patterns. Conclusion: We propose that block of IKr is the principal mechanism by which H 345/52 delays repolarization in human myocardium. The voltage independence of HERG/IKr block is unlikely to underlie the low proarrhythmic potential, and ancillary effects on other membrane currents must be considered. (J Cardiovasc Electrophysiol, Vol. 14, pp. 651-658, June 2003) [source] A framework for describing the impact of antidepressant medications on population health statusPHARMACOEPIDEMIOLOGY AND DRUG SAFETY, Issue 7 2002Scott B. Patten MD Abstract Background In the absence of strategies for primary prevention, public health initiatives for major depression have generally focused on secondary and tertiary strategies such as case-finding, public and professional education and disease management. Much emphasis has been placed on low reported rates of antidepressant utilization. In principle, increased rates of treatment utilization should lead to improved mental health status at the population level. However, methods for relating antidepressant utilization to population health status have not been described. Methods An incidence,prevalence model was developed using data from a Canadian national survey, supplemented by parameter estimates from literature reviews. The lifetime sick-day proportion (LSP) was used to approximate point prevalence. Results Mathematical simulations using this model produced reasonable approximations of point prevalence for major depression. The model suggests that an improved rate of treatment utilization may not, in itself, lead to substantially reduced prevalence. Reducing the rate of relapse in those with highly recurrent disorders, which can be accomplished by long-term antidepressant treatment, is predicted to have a more substantial impact on population health status. Conclusions The model presented here offers a framework for describing the impact of antidepressant treatment on population health status. Mathematical models may assist with decision-making and priority setting in the public health sphere, as illustrated by the model presented here, which challenges some commonly held assumptions. Copyright © 2002 John Wiley & Sons, Ltd. [source] Notochordal intervertebral disc cells: Sensitivity to nutrient deprivationARTHRITIS & RHEUMATISM, Issue 4 2009Thorsten Guehring Objective The nucleus pulposus (NP) of the intervertebral disc develops from the notochord. Humans and other species in which notochordal cells (NCs) disappear to be replaced by chondrocyte-like mature NP cells (MNPCs) frequently develop disc degeneration, unlike other species that retain NCs. The reasons for NC disappearance are unknown. In humans, the change in cell phenotype (to MNPCs) coincides with changes that decrease nutrient supply to the avascular disc. We undertook this study to test the hypothesis that the consequent nutrient stress could be associated with NC disappearance. Methods We measured cell densities and metabolic rates in 3-dimensional cultures of porcine NCs and bovine MNPCs, and we determined survival rates under conditions of nutrient deprivation. We used scanning electron microscopy to examine end plate porosity of discs with NCs and those with MNPCs. Nutrient,metabolite profiles and cell viability were calculated as a function of cell density and disc size in a consumption/diffusion mathematical model. Results NCs were more active metabolically and more susceptible to nutrient deprivation than were MNPCs. Hypoxia increased rates of glycolysis in NCs but not in MNPCs. Higher end plate porosity in discs with NCs suggested greater nutrient supply in keeping with higher nutritional demands. Mathematical simulations and experiments using an analog disc diffusion chamber indicated that a fall in nutrient concentrations resulting from increased diffusion distance during growth and/or a fall in blood supply through end plate changes could instigate NC disappearance. Conclusion NCs demand more energy and are less resistant to nutritional stress than MNPCs, which may shed light on the fate of NCs in humans. This provides important information about prospective NC tissue engineering approaches. [source] Predicting unit plot soil loss in Sicily, south ItalyHYDROLOGICAL PROCESSES, Issue 5 2008V. Bagarello Abstract Predicting soil loss is necessary to establish soil conservation measures. Variability of soil and hydrological parameters complicates mathematical simulation of soil erosion processes. Methods for predicting unit plot soil loss in Sicily were developed by using 5 years of data from replicated plots. At first, the variability of the soil water content, runoff, and unit plot soil loss values collected at fixed dates or after an erosive event was investigated. The applicability of the Universal Soil Loss Equation (USLE) was then tested. Finally, a method to predict event soil loss was developed. Measurement variability decreased as the mean increased above a threshold value but it was low also for low values of the measured variable. The mean soil loss predicted by the USLE was lower than the measured value by 48%. The annual values of the soil erodibility factor varied by seven times whereas the mean monthly values varied between 1% and 244% of the mean annual value. The event unit plot soil loss was directly proportional to an erosivity index equal to , being QRRe the runoff ratio times the single storm erosion index. It was concluded that a relatively low number of replicates of the variable of interest may be collected to estimate the mean for both high and particularly low values of the variable. The USLE with the mean annual soil erodibility factor may be applied to estimate the order of magnitude of the mean soil loss but it is not usable to estimate soil loss at shorter temporal scales. The relationship for estimating the event soil loss is a modified version of the USLE-M, given that it includes an exponent for the QRRe term. Copyright © 2007 John Wiley & Sons, Ltd. [source] Designing an Inducer-Feeding Schedule To Enhance Production of Recombinant Protein in Escherichia coli by Microbial Reaction EngineeringBIOTECHNOLOGY PROGRESS, Issue 3 2008Jesus M. Gonzalez Metabolic constraints during the production of recombinant protein in Escherichia coli impede the efficient utilization of resources by the cells, thus reducing their production potential. In order to minimize these adverse effects, we have proposed to segregate the cell population into two groups: the first one formed by non-induced cells, growing at a high specific growth rate and rapidly contributing cells to the system, and the second one formed by fully induced cells, growing slowly but using the cell machinery to express the target protein. An adequate balance between these two populations should maximize the protein expression in a given system. This segregation is accomplished experimentally by taking advantage of the "all or none" phenomenon, in which at subsaturated inducer conditions the cells are either fully induced or fully uninduced. Based on this two-population theory, a mathematical model was developed in which a parameter , was defined as the fraction of the fully induced cells in the total population. In this study three different induction strategies were investigated and their effect on the protein production was established. It was found that the linear increase of this fraction, achieving maximum induction (, = 1) only at the end of the fermentation and with a slope m = 0.15 gave the best results. Finally these results were validated experimentally with the finding that they closely match the mathematical simulation with a 26% increase in protein production with respect to the conventional induction approach described. [source] Quantifying the heterogeneous heat response of Escherichia coli under dynamic temperaturesJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2010E. Van Derlinden Abstract Aims:, Non-sigmoid growth curves of Escherichia coli obtained at constant temperatures near the maximum growth temperature (Tmax) were previously explained by the coexistence of two subpopulations, i.e. a stress-sensitive and a stress-resistant subpopulation. Mathematical simulations with a heterogeneous model support this hypothesis for static experiments at 45°C. In this article, the behaviour of E. coli, when subjected to a linearly increasing temperature crossing Tmax, is studied. Methods and Results:, Subpopulation dynamics are studied by culturing E. coli K12 MG1655 in brain heart infusion broth in a bioreactor. The slowly increasing temperature (°C h,1) starting from 42°C results in growth up to 60°C, a temperature significantly higher than the known Tmax. Given some additional presumptions, mathematical simulations with the heterogeneous model can describe the dynamic experiments rather well. Conclusions:, This study further confirms the existence of a stress-resistant subpopulation and reveals the unexpected growth of E. coli at temperatures significantly higher than Tmax. Significance and Impact of the Study:, The growth of the small stress-resistant subpopulation at unexpectedly high temperatures asks for a revision of currently applied models in food safety and food quality strategies. [source] A comparison of Ktrans measurements obtained with conventional and first pass pharmacokinetic models in human gliomasJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2004Hamied A. Haroon MSc Abstract Purpose To compare in a group of patients with cerebral gliomas the estimates of Ktrans between a conventionally established pharmacokinetic model and a recently developed first pass method. Materials and Methods Glioma patients (23) were studied using T1 -weighted dynamic contrast-enhanced magnetic resonance imaging (MRI), and two alternative pharmacokinetic models were used for analysis to derive the volume transfer constant Ktrans. These were a modified version of the established model (yielding KTK) and a recently published method based on first pass leakage profile (FP) of contrast bolus (yielding Kfp). Results We found a strong correlation between intra-tumoral median KTK and Kfp (rho = 0.650, P < 0.01), but the values from the conventional model were consistently and significantly higher (mean of inter-tumoral Kfp and KTK medians were 0.018 minute,1 and 0.284 minute,1, respectively, P < 0.001). The spatial distribution of KTK and Kfp showed poor correlation in the presence of large vascular structures and good correlation elsewhere. Conclusion KTK and Kfp produce similar biologic information within voxels not dominated by vascular tissue. The FP method avoids erroneous overestimation of Ktrans in areas of significant intravascular contrast. Findings are in keeping with the predictions of previous mathematical simulations. J. Magn. Reson. Imaging 2004;19:527,536. © 2004 Wiley-Liss, Inc. [source] Odontocete suction feeding: Experimental analysis of water flow and head shapeJOURNAL OF MORPHOLOGY, Issue 12 2006Alexander J. WerthArticle first published online: 13 NOV 200 Abstract The role of cranial morphology in the generation of intraoral and oropharyngeal suction pressures in odontocetes was investigated by manipulating the jaw and hyolingual apparatus of submerged heads of three species presenting varied shapes. Hyoid and gular muscles were manually employed to depress and retract the tongue. Pressures were recorded at three locations in the oral cavity, as gape and site, speed, and force of pull were varied. A biomechanical model was also developed to evaluate pressure data. The species with the shortest, bluntest head and smallest mouth opening generated greater negative pressures. Suction generation diminished sharply as gape increased. Greatest negative pressures attained were around ,45 mmHg (,6,000 Pa), a magnitude deemed suitable for capture of small live prey. Odontocetes utilizing this bidirectional flow system should profit by evolution of a rounder mouth opening through progressive shortening and widening of the rostrum and jaws, a trend evident in cranial measurements from fossil and recent odontocetes. Blunt heads correlate with anatomical, ecological, and behavioral traits associated with suction feeding. Small-gape suction (with minimally opened jaws) could be used by odontocetes of all head and oral shapes to draw prey sufficiently close to the mouth for suction ingestion or grasping via dentition. Principal limitations of the experimental and mathematical simulations include assumption of a stationary odontocete with static (open or closed) jaws and potential scaling issues with differently sized heads and gapes. J. Morphol., 2006. © 2006 Wiley-Liss, Inc. [source] Specific interactions in ternary system quaternized polysulfone/mixed solventPOLYMER ENGINEERING & SCIENCE, Issue 1 2009Anca Filimon Theoretical and experimental aspects on the specific interactions developed via electrostatic interactions and hydrogen-bonding in a ternary system formed of a proton-donor solvent (N,N -dimethylformamide or methanol), a proton-acceptor solvent (water), and a quaternized polysulfone with various contents of ionic chlorine, which indicates a proton-acceptor character, are investigated. Thus, the interactions of the ternary systems are corrected on the basis of the association phenomena defined through association constants. Numerical values for these constants were evaluated as a function of the system composition, by mathematical simulations for an accurate adjustment of preferential adsorption, determined by the Flory,Huggins,Pouchly theoretical approach applied to the experimental data. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers [source] | |||||||||||||