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At least 505 records · Page 28Linked to original sources

PubMed2000

Prediction of pesticide concentrations in the atmosphere using an atmospheric diffusion model (linear source plume model).

The foundational model to predict concentration of pesticides in the atmosphere outside of the sprayed area was developed using the results of measured concentration in the atmosphere, in reference to the atmospheric diffusion model utilized for the air pollution prediction model. The atmospheric diffusion model assumes that the applied area was a topographically flat farmland, that wind direction and wind speeds were constant, and the pesticide was constantly discharged from the emission line sources. Therefore the linear source plume model (LSPLM) was developed. The concentration in the atmosphere was predicted by assigning the property of the pesticides and various conditions of measurements of the model, and compared with the measured them, then the adaptability of the model was examined. As a result, the correlation between the measured value and the predicted value in paddy and forested areas was significant (P < 0.01) although deviations in the order of tens were observed, the measured value and the predicted value were generally in agreement.

Agriculture↗

PubMed2001

A novel platelet-rich arterial thrombosis model in rabbits. Simple, reproducible, and dynamic real-time measurement by using double-opposing inverted-sutures model.

Though numerous animal thrombosis models have been introduced, an easy, reliable, and reproducible arterial thrombosis model remains a continuing challenge prior to a thrombolytic study. In an effort to evaluate the efficiency of various recombinant thrombolytic agents with specific affinity to activated platelets in vivo, we developed a novel double-opposing inverted-sutures model to create a platelet-rich thrombus in the femoral artery of rabbits. The arteriotomy was done semicircumferentially, and variously sized microsurgical sutures were introduced intraluminally in a double-opposing inverted manner. The animals were divided into three groups according to the double-opposing inverted-sutures used: Group 1 with 10-0 nylon (n=6), Group 2 with 9-0 nylon (n=6), and Group 3 with 8-0 nylon (n=22). The superficial epigastric branch was cannulated with a thin polyethylene (PE) tube for intraarterial administration of the studied thrombolytic agent. The blood flow was continuously measured with a real-time ultrasonic flow meter. Within 2 h of installation of the sutures, there was no thrombus formation in either Group 1 or 2. In Group 3, the thrombosis rate was 91% (20 of 22) under a steady baseline flow (with an average of 12.23+/-2.40 ml/min). It was highly statistically significant with a P-value of .0000743 using Fisher's Exact Test. The averaged time to thrombosis was 21.8+/-9.8 min. The ultrasonic flow meter to record the dynamic real-time measurement of blood flow was a guideline for thrombus formation or dissolution, which was correlated with the morphological findings of stenotic status of the vessel detected by the Doppler sonography. The components of the thrombus were proven to be platelet-rich predominant by histological examination via hematoxylin and eosin (H&E) stain and transmission electron microscopy (TEM). To confirm that the double-opposing inverted-sutures model would be useful for a study of thrombolytic agents, we evaluated the effects of recombinant tissue-type plasminogen activator (rt-PA) and streptokinase-human plasminogen (SK-HPlg). The average time to thrombolysis post rt-PA infusion was 16.0+/-8.2 min and that of SK-HPlg was 79.6+/-23.1, which were similar to the previous reports. In conclusion, the novel double-opposing inverted-sutures (8-0 nylon) model provides a simple, reliable, and reproducible platelet-rich arterial thrombosis model with noninvasive and dynamic real-time measurement. It may be applied in assessing the efficiency of the recombinant thrombolytic agents and offers many advantages of an arterial platelet-rich in vivo thrombosis model.

Animals↗

PubMed2001

A field-based population model for the sediment toxicity test organism Leptocheirus plumulosus: II. Model application.

A stage-structured population model has been developed for the estuarine amphipod Leptocheirus plumulosus to provide interpretive guidance for sediment toxicity tests with this species. This time-varying, field-based model includes several matrices to reflect seasonal changes in demographics. In this paper, we conduct sensitivity analysis of the model to identify which life history parameters have the greatest potential impact on population growth rate (lambda). Results indicate seasonal variability in the relative demographic importance of vital rates. Over winter, annual population growth is most sensitive to the persistence of juveniles and adults and growth from the juvenile to the adult stage. In spring and fall, changes in fecundity are likely to have large effects on population dynamics. In addition, we demonstrate the applicability of the model by using it to interpret toxicological data from an assessment of sediment contamination in Baltimore Harbor, MD. The model was parameterized with survival data from acute toxicity tests with L. plumulosus to project effects on population growth rate (lambda). Results of these model simulations indicate that relatively small changes in survival can result in large changes in lambda, indicating high risk to benthic populations. Furthermore, population projections mirror observed abundances of L. plumulosus at the test sites. These analyses provide a first indication of the usefulness of the Leptocheirus population model as a tool for exploring ecological effects of sediment contamination.

Animals↗

PubMed2000

Body modeling and model-based tracking for neuroethology.

The accurate tracking of an animal's movements and postures through time has broad applicability to questions in neuroethology and animal behavior. In this paper we describe methods for precision body modeling and model-based tracking of non-rigid animal movements without the use of external markers. We describe the process of obtaining high-fidelity urethane casts of a model organism, the weakly electric knifefish Apteronotus albifrons, and the use of a stylus-type 3-D digitizer to create a polygonal model of the animal from the cast. We describe the principles behind markerless model-based tracking software that allows the user to translate, rotate, and deform the polygon model to fit it to digitized video images of the animal. As an illustration of these methods, we discuss how we have used model-based tracking in the study of prey capture in nocturnal weakly electric fish to estimate sensory input during behavior. These methods may be useful for bridging between the analytical approaches of quantitative neurobiology and the synthetic approaches of integrative computer simulations and the building of biomimetic robots.

Animals↗

PubMed2000

Derivation of [(11)C]WAY-100635 binding parameters with reference tissue models: effect of violations of model assumptions.

In several positron-emission tomography studies of human subjects, analyses of data from the 5-hydroxytryptamine(1A) (5-HT(1A)) receptor radioligand, [(11)C]WAY-100635 ¿[carbonyl-(11)C]N-(2-(4-methoxy-phenyl)-1-piperazin-1-yl)ethyl)-N -(2 -pyridyl)cyclohexanecarboxamide¿ have shown a discrepancy between the outcome measure k(3)/k(4) (binding potential normalized to cerebellum) as estimated by the simplified reference region method and results obtained by conventional kinetic modeling with an arterial input function. The reference region method has yielded results that are lower than the conventional approach, with the relative underestimation appearing to be an increasing function of k(3)/k(4). We performed simulations on idealized data to identify the source of the discrepancy. Both the simplified reference tissue model (SRTM) and the original full reference tissue model (FRTM) were tested to determine (a) if the error in estimated k(3)/k(4) is dependent on the blood flow in the region of interest relative to the blood flow in the region of reference (R(1)) and on the receptor density in the region of interest (true k(3)/k(4)), and (b) which violation of the reference model assumptions were responsible for this effect. FRTM returned parameter estimates that were independent and accurate if the reference region was constructed precisely as a one-tissue compartment model. SRTM overestimated k(3)/k(4) when the reference region was constructed as a one-tissue compartment model and underestimated k(3)/k(4) when the reference region was constructed as a two-tissue compartment model (which is the case for [(11)C]WAY-100635). In both cases, the magnitude of the error in k(3)/k(4) returned by SRTM was dependent on true R(1) and true k(3)/k(4). In conclusion, the SRTM is associated with a bias in the derivation of k(3)/k(4) that is not a simple scaling factor. This magnitude of these errors should be carefully evaluated for each new radioligand.

Carbon Radioisotopes↗

PubMed1999

The tachycardia-induced dog model of atrial fibrillation. clinical relevance and comparison with other models.

In the past, investigators have relied extensively on acute in vivo models of atrial fibrillation (AF), in which AF was induced either pharmacologicly or by vagal stimulation. More recently, there is a need and desire for more clinically relevant models that can only be achieved with the use of chronically instrumented animals. One of these models is the atrial tachycardia-induced AF dog model, which is the main focus of this review. The model produces a persistent AF in 80% of animals paced at 400 beats/min for 6 weeks. Atrial tachycardia also induces various pathophysiologic and ultrastructural changes that often resemble electrical remodeling of atria in patients that have a high susceptibility to AF. This model can also be used to evaluate drug efficacy with respect to attenuation of AF duration or conversion of AF to sinus rhythm. The model may therefore be used to provide further insights into the discovery of new therapeutic approaches to modifying this atrial arrhythmic disorder in man.

Animals↗

PubMed2005

Social stress in tree shrews as an animal model of depression: an example of a behavioral model of a CNS disorder.

Animal models are invaluable in preclinical research on human psychopathology. Valid animal models to study the pathophysiology of depression and specific biological and behavioral responses to antidepressant drug treatments are of prime interest. In order to improve our knowledge of the causal mechanisms of stress-related disorders such as depression, we need animal models that mirror the situation seen in patients. One promising model is the chronic psychosocial stress paradigm in male tree shrews. Coexistence of two males in visual and olfactory contact leads to a stable dominant/subordinate relationship, with the subordinates showing obvious changes in behavioral, neuroendocrine, and central nervous activity that are similar to the signs and symptoms observed during episodes of depression in patients. To discover whether this model, besides its "face validity" for depression, also has "predictive validity," we treated subordinate animals with the tricyclic antidepressant clomipramine and found a time-dependent recovery of both endocrine function and normal behavior. In contrast, the anxiolytic diazepam was ineffective. Chronic psychosocial stress in male tree shrews significantly decreased hippocampal volume and the proliferation rate of the granule precursor cells in the dentate gyrus. These stress-induced changes can be prevented by treating the animals with clomipramine, tianeptine, or the selective neurokinin receptor antagonist L-760,735. In addition to its apparent face and predictive validity, the tree shrew model also has a "molecular validity" due to the degradation routes of psychotropic compounds and gene sequences of receptors are very similar to those in humans. Although further research is required to validate this model fully, it provides an adequate and interesting non-rodent experimental paradigm for preclinical research on depression.

Animals↗

PubMedDate not supplied

Pseudoreceptor models and 3D-QSAR for imidazobenzodiazepines at GABA A/BzR subtypes alphaxbeta3gamma2 [x = 1-3, 5, and 6] via flexible atom receptor model.

Since benzodiazepines have been used widely in the treatment of anxiety, sleeplessness, and epilepsy, the receptor sites for the benzodiazepine are of prime importance. Quantitative structure-activity relationship (QSAR) studies and receptor modeling via Flexible Atom Receptor Model (FLARM) for the binding affinities of a series of imidazobenzodiazepines at five recombinant receptor subtypes were carried out successfully. The 3D-QSAR models for all five receptor subtypes were examined by a set of test set and demonstrated their high predictability for affinities of imidazobenzodiazepines at five receptor subtypes. The pseudoreceptors yielded by FLARM were compared to the united pharmacophore/receptor model. The result shows that two hydrogen bonds and other regions in the united pharmacophore/receptor model are presented in the pseudoreceptors, which demonstrates the receptor modeling capability of FLARM. The models and pseudoreceptors can help design high affinity ligands on the GABA(A)/BZ receptor and understand the GABA(A) receptor.

Benzodiazepines↗

PubMed2003

Impacts of lindane usage in the Canadian prairies on the Great Lakes ecosystem. 1. Coupled atmospheric transport model and modeled concentrations in air and soil.

A coupled atmospheric transport, soil-air, water-air exchange model was developed to investigate the impacts of gamma-hexachlorocyclohexane (gamma-HCH or lindane) usage in the Canadian prairies over the Great Lakes region. The fate of gamma-HCH in air and soil is governed by atmospheric dynamics and physical and chemical processes that are described by the coupled model. These processes include transport and turbulent diffusion in the atmosphere, dry and wet deposition, exchange at the interfacial boundaries of air-water and soil-air, and removal processes from the soil such as diffusion, leaching, and degradation. Numerical experiments were conducted for the period of May 1, 1998-April 30, 1999, starting with application of lindane in the spring. The coupled model was executed with two lindane emission (usage) inventories in the model domain. The first scenario contained all known fresh emission sources in Canada-98% was usage in the prairies; the second excluded emission sources from Ontario and Quebec. The model showed that, in the absence of the reemission from past application of lindane, usage of lindane in Ontario and Quebec has a negligible impact on air concentrations in these regions and that the lindane budget in the Great Lakes ecosystem is mostly attributed to applications of lindane in the canola fields in Canadian prairie provinces. Model-predicted air concentrations and seasonal trends agreed well with measured data over the same time period for several background sites operated under the Integrated Atmospheric Deposition Network. Air temperature was shown to play a key role on surface-air exchange dynamics of gamma-HCH. A future paper will assess loadings to the Great Lakes based on these validated model results.

Air Movements↗

PubMed2006

A generalized model for aerobic granule-based sequencing batch reactor. 1. Model development.

A generalized model was established for simulating an aerobic granule-based sequencing batch reactor (SBR) with considerations of biological processes, reactor hydrodynamics, mass transfer, and diffusion. Methodology of discretization was effectively used forthe model development and calculations. The activated sludge model no.1 was modified to describe the biological processes within the granules. Based on the difference between the calculated and measured results, the model structure was further improved through introducing simultaneous consumption of soluble substrates by storage and heterotrophs growth with a changeable reaction rate. Model calculations were conducted using a MATLAB program. The calculation results show the respective contributions of granules in different size fractions and slices to the overall change of model component concentrations. Moreover, oxygen concentration profiles within granules and oxygen consumption rate varied in one operating cycle. This confirms the applicability and validity of the discretization method and the model structure.

Aerobiosis↗

PubMed2004

GSSI, a general model for solute-solvent interactions. 1. Description of the model.

A novel, semiempirical approach for the general treatment of solute-solvent interactions (GSSI) was developed to enable the prediction of solution-phase properties (e.g., free energies of desolvation, partition coefficients, and membrane permeabilities). The GSSI approach is based on the principle that all solution-phase processes can be modeled in terms of one or more gas-to-solution transfer processes. The free energy of each gas-to-solution transfer process is calculated as the sum of the free energy of cavity formation and the free energy of solute-solvent interaction. The solute's contributions to these free energies are modeled on the basis of various quantities computed from the solute's three-dimensional (3D) structure, whereas the solvent's contributions are modeled by empirically determined regression coefficients. More specifically, the free energy of cavity formation is modeled on the basis of the total solvent-accessible surface area of the solute. The enthalpy of solute-solvent interaction is modeled on the basis of intermolecular interaction potentials calculated at many uniformly distributed points on the solvent-accessible surface of the solute. The entropy of solute-solvent interaction is modeled on the basis of an effective number of rotatable bonds in the solute and by the regression coefficients characteristic of the solvent. The potential utility of the GSSI approach was demonstrated by modeling the free energy of gas-to-solution transfer for 111 solutes in water, 250 solutes in hexadecane, and 84 solutes in octanol.

Kinetics↗

PubMed2000

Sequential logistic models for 30 days mortality after CABG: pre-operative, intra-operative and post-operative experience--The Israeli CABG study (ISCAB). Three models for early mortality after CABG.

OBJECTIVES: The goal of this paper was to examine the added effect of operative and post-operative variables on 30 days mortality, in addition to patients' case-mix factors. SETTING AND DESIGN: A prospective study of 4835 patients, 95% of all Israeli patients who underwent coronary artery bypass grafting (CABG) in 1994. Information related to risk of death was collected at admission to hospital (preceding the operation), at time of the operation and in the immediate post-operative period. Deaths were independently ascertained. METHOD: Data collectors followed every patient from admission to discharge. Sequential logistic models were constructed for the 'case-mix', 'operative' and the 'post-operative' periods in chronological order. Each model incorporated and adjusted for the risk estimated at the previous point in time, by forcing individual risk scores. RESULTS: Significant pre-operative risk factors for 30 days mortality, in the case-mix model included mainly severity of illness characteristics, such as, left ventricular dysfunction and emergency admission, (c-statistic 78.8%). Model 2 (the 'operation' model) included in addition to the case-mix score, excessive duration of the operation per graft, bleeding, etc. (c-statistic 85.3%). The post-operative model showed the added effect of the post-operative factors such as low haemoglobin, additional surgery, and excessive time on respirator, (c-statistic 92.4%). CONCLUSIONS: The sequential analysis was an efficient method for updating patients' risk over time, where the number of events was small, relative to the number of risk factors. The addition of peri-operative factors increased significantly the predictive power of the model, adding clinical insights to the role of the hospital experience on 30 days mortality.

Adult↗

PubMed1995

Incorporation of first-order uptake rate constants from simple mammillary models into blood-flow limited physiological pharmacokinetic models via extraction efficiencies.

Incorporation of First-Order Uptake Rate Constants from Simple Mammillary Models into Blood-Flow Limited Physiological Pharmacokinetic Models via Extraction Efficiencies. W. L. Roth, L. W. D. Weber, and K. Rozman (1995). Pharm. Res. 263-269. First-order rate constants obtained from classical pharmacokinetic models correspond to mammillary systems in which all of the blood (or plasma) is assumed to be located in a central compartment. In such models the rate at which chemicals are transported out of this pool and into another compartment is the product of the mass of chemical in the central compartment multiplied by a rate constant, which is not limited in magnitude by the blood flow, or the rate at which chemicals from the blood are delivered to the peripheral compartment. Most of the physiologically-based models published to date dispense with some of the information available from mammillary models by assuming that all of the chemical delivered by the flow of blood rapidly equilibrates and can be taken up by the tissue under the control of a "partition coefficient" (Rij = Cj/Ci). We show that the partition coefficient alone does not retain the uptake rate (kji) information available from a classical mammillary model, but that the uptake rate information can be incorporated via unitless extraction efficiency parameters, epsilon j.

Blood Volume↗

PubMed2006

Microarray analysis of a reversible model and an irreversible model of anti-Thy-1 nephritis.

A single intravenous injection of anti-Thy-1 monoclonal antibody (mAb) 1-22-3 is known to cause reversible mesangial proliferative glomerulonephritis. However, mAb 1-22-3 injection followed by unilateral nephrectomy leads to progressive glomerulosclerosis and tubulointerstitial change with an irreversible course. To identify genes that play an important role in the irreversible progression of renal injury, we used microarray technology to identify differences in gene expression between these models. Rats were intravenously injected with mAb 1-22-3 1 week after unilateral nephrectomy (irreversible model) or a sham operation (reversible model), and rats were killed on days 4, 7, 14, 42, and 56 after the injection. complementary DNA probes prepared from kidney messenger RNAs were hybridized with oligonucleotide microarrays containing 4854 rat genes. The microarray identified 189 differentially expressed genes, having at least a two-fold difference in expression level between the two models, and they were classified into five clusters. One of the clusters consisted of genes whose expression was markedly upregulated in the irreversible model. This cluster included the genes encoding osteopontin, kidney injury molecule-1, and thymosin beta10. Increased expression of thymosin beta10 was localized mainly in macrophages in the fibrotic interstitium, and upregulation of thymosin beta10 expression was also observed in a unilateral ureteral obstruction model. The microarray analysis yielded information on the molecular mechanisms responsible for the difference in disease progression between the reversible and irreversible model of anti-Thy-1 nephritis. Thymosin beta10 may play an important role in the progression of kidney disease.

Animals↗

PubMed2006

Software tools that facilitate kinetic modelling with large data sets: an example using growth modelling in sugarcane.

A solution to manage cumbersome data sets associated with large modelling projects is described. A kinetic model of sucrose accumulation in sugarcane is used to predict changes in sucrose metabolism with sugarcane internode maturity. This results in large amounts of output data to be analysed. Growth is simulated by reassigning maximal activity values, specific to each internode of the sugarcane plant, to parameter attributes of a model object. From a programming perspective, only one model definition file is required for the simulation software used; however, the amount of input data increases with each extra interrnode that is modelled, and likewise the amount of output data that is generated also increases. To store, manipulate and analyse these data, the modelling was performed from within a spreadsheet. This was made possible by the scripting language Python and the modelling software PySCeS through an embedded Python interpreter available in the Gnumeric spreadsheet program.

Algorithms↗

PubMedDate not supplied

[A validated finite element model of the human spine--description of the model and initial application].

AIM: To generate a finite-element model of the human cervical spine and evaluate the first application of the model to the analysis of new c-spine implants. METHODS: CT-data were used to generate a three-dimensional, anisotrophic, linear model of the human C4-C7 motion segments using the software ANSYS 5.4. As a next step, anterior cervical fusion and plate fixation using mono- and bicortical screws was simulated in the model. Loading of the finite-element models was simulated using pure moments of +/- 2.5 Nm in flexion/extension, axial left/right rotation, and left/right lateral bending. The range of motion was calculated. The results were compared to the results of an in vitro study using human cadaveric c-spine segments C4-C7, with the same implants and moments on both the intact and surgically treated specimens. RESULTS: The results obtained by the finite-element model were always within one standard deviation of the results of the in vitro study. CONCLUSION: Keeping in mind the simplifications of such a mathematical model, it may be used for a first analysis of the shape of new c-spine implants or to predict the initial stability of a new device.

Adult↗

PubMed2004

Modeling the water use efficiency of soybean and maize plants under environmental stresses: application of a synthetic model of photosynthesis-transpiration based on stomatal behavior.

Understanding the variability of plant WUE and its control mechanism can promote the comprehension to the coupling relationship of water and carbon cycle in terrestrial ecosystem, which is the foundation for developing water-carbon coupling cycle model. In this paper, we made clear the differences of net assimilation rate, transpiration rate, and WUE between the two species by comparing the experiment data of soybean (Glycine max Merr.) and maize (Zea mays L.) plants under water and soil nutrient stresses. WUE of maize was about two and a half times more than that of soybean in the same weather conditions. Enhancement of water stresses led to the marked decrease of Am and Em of two species, but water stresses of some degree could improve WUE, and this effect was more obvious for soybean. WUE of the two species changed with psiL in a second-order curve relation, and the WUE at high fertilization was higher than that at low fertilization, this effect was especially obvious for maize. Moreover, according to the synthetic model of photosynthesis-transpiration based on stomatal behavior (SMPTSB) presented by Yu et al. (2001), the WUE model and its applicability were discussed with the data measured in this experiment. The WUE estimated by means of the model accorded well with the measured values. However, this model underestimated the WUE for maize slightly, thus further improvement on the original model was made in this study. Finally, by discussing some physiological factors controlling Am and WUE, we made clear the physiological explanation for differences of the relative contributions of stomata- and mesophyll processes to control of Am and WUE, and the applicability of WUE model between the two species. Because the requirement to stomatal conductance by unit change of net assimilation rate is different, the responses of opening-closing activity of stomata to environmental stresses are different between the two species. To obtain the same level of net assimilation rate, soybean has to open its stomata more widely to keep small stomatal resistance, as compared with maize.

Ecosystem↗

PubMed2000

Assessment of the nested grid model estimates for driving regional visibility models in the southwestern United States.

The Nested Grid Model (NGM) is a primitive-equation meteorological model that is routinely exercised over North America for forecasting purposes by the National Meteorological Center. While prognostic meteorological models are being increasingly used to drive air quality models, their use in conducting annual simulations requires significant resources. NGM estimates of wind fields and other meteorological variables provide an attractive alternative since they are typically archived and readily available for an entire year. Preliminary evaluation of NGM winds during the summer of 1992 for application to the region surrounding the Grand Canyon National Park showed serious shortcomings. The NGM winds along the borders between California, Arizona and Mexico tend to be northwesterly with a speed of about 6 m/sec, while the observed flow is predominantly southerly at about 2-5 m/sec. The mesoscale effect of a thermal low pressure area over the highly heated Southern California and western Arizona deserts does not appear to be represented by the NGM because of its coarse resolution and the use of sparse observations in that region. Tracer simulations and statistical evaluation against special high resolution observations of winds in the southwest United States clearly demonstrate the northwest bias in NGM winds and its adverse effect on predictions of an air quality model. The "enhanced" NGM winds, in which selected wind observations are incorporated in the NGM winds using a diagnostic meteorological model provide additional confirmation on the primary cause of the northwest bias. This study has demonstrated that in situations where limited resources prevent the use of prognostic meteorological models, previously archived coarse resolution wind fields in which additional observations are incorporated to correct known biases provide an attractive option.

Aerosols↗