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At least 1,243 records · Page 69Linked to original sources
PubMed2001

Computer simulation of costs and benefits of segregated early weaning (SEW) in a vertical pork production chain.

A simulation model was developed to quantify costs and benefits of segregated early weaning (SEW) compared to standard pork production in a vertically integrated system. The computer model considers the farrowing, fattening and slaughtering stage as well as the transportation of pigs between these stages. Input parameters relate to both biological and economic variables which were varied within a normal bandwith (sensitivity analysis, high and low level). Model output concerns the production costs per slaughter-pig in each stage and for the chain as a whole. With standard pork production the costs per head accounted for [symbol: see text] 131.72. 28% of the total chain production costs were raised by the farrowing stage, 15% by weaning-to-fattening period (28 kg live weight) and 57% by the fattening stage (> 28 until 115 kg). Despite higher expenses for facilities, transportation and labour, SEW reduced the total chain production cost to [symbol: see text] 128.02 (low) and [symbol: see text] 121.32 (high) per head due to higher biological performance, lower medication and reduced fixed costs per unit. N- and P-excretion diminished by 13%. The results indicate that SEW may be an effective and beneficial alternative which meets some of the demands of pig producers and consumers such as effective production, good health and food safety.

Animal Husbandry↗
PubMed1989

[3-dimensional organ representation with ultrasound. Experimental studies--computer simulation].

This is the first report on the 3-dimensional representation of organs with US. The prerequisite for this was a coordinated transducer movement, in such a manner that the organ under examination was represented by US sections differing in only one of the space coordinates. Such transducer movement was made possible by 2 devices. In the first instance, longitudinal movement of the transducer resulted in the production of parallel sections of the organ while, in the other instance, rotation of the transducer head permitted sections arranged around a fixed center-point. Using a special computer program, the sections were contoured in such a manner that only the surface of the organ was represented. These sections were then arranged in space. The 3-dimensional representation can be effected both by binary image representation and by representation with closed (intact) body surface. The advantage of the binary image representation is the fact that the organ surfaces "extracted" from the original US sections are directly incorporated within the 3-dimensional image build-up, with no further computer manipulations. It can be seen that the rotation of the transducer head represents the practicable possibility for the use in the clinical setting.

Computer Simulation↗
PubMed1998

Computer simulation of the effect of changing abdominal thickness on the electrogastrogram.

The effect of different abdominal thickness on cutaneous recordings of gastric electrical activity (GEA) known as electrogastrograms (EGG) have not been adequately studied. The stomach was represented as a truncated conoid in spherical system of coordinates. Gastric electrical field was modelled using previously described methodology. Electrical voltages were calculated in simulated standard cutaneous recordings. The effect of increased thickness of the abdominal layers was quantitatively examined. Changes of the thickness of the abdominal layers significantly affected signal-to-noise ratio of EGG. When the critical abdominal thickness of 7 cm was exceeded, EGGs were quantified as abnormal although the internal GEA was normal. Computer modelling indicated that changeable abdominal thickness caused by the abdominal layers separating the stomach from the recording electrodes significantly influence the EGG recordings even if the layers are homogeneous.

Abdomen↗
PubMed2003

Computer simulation of the skin reflectance spectra.

The reflectance spectra of the human skin in visible and near-infrared (NIR) spectral region have been calculated using the Monte Carlo technique, and the specular and internal reflection on the medium surface is taken into account. Skin is represented as a complex inhomogeneous multi-layered highly scattering and absorbing medium. The model takes into account variations in spatial distribution of blood, index of blood oxygen saturation, volume fraction of water and chromophores content. The simulation of the skin tissues optical properties and skin reflectance spectra are discussed. Comparison of the results of simulation and in vivo experimental results are given.

Biophysical Phenomena↗
PubMed1993

Mathematical analysis and computer simulation of the respiratory system in the newborn infant.

A mathematical model of neonatal respiratory control is proposed which can be used to stimulate the system under different physiological conditions. The model consists of a continuous plant and a discrete controller. Included in the plant are lungs, body tissue, brain tissue, a cerebrospinal fluid compartment, and central and peripheral receptors. The effect of shunt in the lungs is included in the model and the lung volume and the dead space are time varying. The controller utilizes outputs from peripheral and central receptors to adjust the depth and rate of breathing and the effects of prematurity of peripheral receptors are included in the system. Hering-Breuer type reflexes are embodied in the controller to accomplish respiratory synchronization. The model is examined and its simulation results under test conditions in hypoxia and hypercapnia are presented.

Blood Gas Analysis↗
PubMed2004

DNA sequence-dependent deformability--insights from computer simulations.

The article reviews some recent developments in studying DNA sequence-dependent deformability, with emphasis on computer modeling. After a brief outline of available experimental techniques, we proceed to computational methods and focus on atomic-resolution molecular dynamics (MD) simulations. A sequence-dependent local (base-pair step) force field inferred from MD is compared with force fields obtained by other techniques. Various methods for establishing global (flexible-rod) DNA elastic constants are reviewed, including an approach based on atomic resolution MD. The problem of defining the global deformation variables, as well as the question of anisotropy and nonlocal effects, are discussed. As an example, both local and global deformability calculations from atomic-resolution MD of EcoRI dodecamer are presented.

Base Sequence↗
PubMed2004

Dosimetric comparison at FiR 1 using microdosimetry, ionisation chambers and computer simulation.

Tissue equivalent proportional counter microdosimetry has been applied in the dosimetry of epithermal neutron beams as they can provide an independent and accurate method to determine gamma ray and neutron absorbed doses. Dosimetric comparison has been performed using a tissue equivalent proportional counter, dual ionisation chambers and DORT computer code at FiR 1 boron neutron capture therapy facility in Espoo, Finland. The three methods were applied to determine neutron and gamma ray absorbed doses at 25, 40, 60 and 120 mm depths along the beam centerline in a water-filled PMMA phantom. The determined absorbed doses were found to agree within the limits of the estimated uncertainties.

Boron Neutron Capture Therapy↗
PubMed1993

Computer simulation of fractionated radiotherapy: further results and their relevance to percutaneous irradiation and brachytherapy.

Based on previous papers, the present communication considers the simulation of the radiotherapeutic treatments of glioblastoma multiforme, rectum adenocarcinoma, and gynaecological tumors of cervix uteri (squamous and adenocarcinoma) in spheroid culture. Starting with a single tumor cell in a nutrient medium and after the corresponding growth of the tumor spheroids, varying irradiation schemes are applied to the carcinoma and are compared with regard to tumor kill effectiveness using the LQ-model. The two first-mentioned carcinoma are exposed to the dose fractionation schemes standard-, super-, hyperfractionation, and weekly high single dose. The result is that hyperfractionation (3 x 1.5 Gy/day) and weekly high single dose (1 x 6 Gy/week) yield the most effective tumor cell kill. The weekly high single dose may be realized by some different irradiation techniques, e. g. stereotactic irradiation or interstitial high dose rate brachytherapy. The treatment of the cervix uteri tumors is performed by a combined therapy form (high dose rate brachytherapy and percutaneous irradiation). A comparing simulation of two typical regimens yields a nearly equivalent tumor kill effectiveness. By the integration of in vitro tumor growth and clinical treatment schemes in a computer model, the possibility is made available to test the effectiveness of variable regimens with the help of computer experiments.

Administration, Cutaneous↗
PubMed1976

Computer-simulated urea reflection coefficients in human red cells.

Relative volume curves for human red cells were generated with a computer program to simulate the experimental results obtained by rapidly mixing red cells and urea. Known values for the permeability variables were used in the Kedem and Katchalsky (Biochim. Biophys. Acta (1958) 27, 229-246) solute and solvent flux equations. The different values used for the reflection coefficient, o, were 0.62, 0.75 and 1.0. The theoretical computer curves with o = 0.75 compared closely with the experimental stopped-flow curves.

Cell Membrane Permeability↗
PubMed2006

Computer simulation of proton solvation and transport in aqueous and biomolecular systems.

The excess proton in aqueous media is critical to many aspects of chemistry, biology, and materials science. This species is at the heart of the most elementary of chemical (e.g., acid-base) and biological (e.g., bioenergetics) concepts, yet to this day, it remains mysterious, surprising, and often misunderstood. In this Account, our efforts to describe excess proton solvation and transport through computer modeling and simulation will be described. Results will be summarized for several important systems, as obtained from the multistate empirical valence bond (MS-EVB) approach, which allows for the explicit treatment of (Grotthuss) proton shuttling and charge delocalization.

Biological Transport↗
PubMed1995

Computer simulation of the temperature- and hydration-dependent lateral diffusion of phosphatidylcholine in lipid bilayers.

A lattice model of a lipid bilayer near the so-called main phase transition between the liquid crystalline (L alpha) and the gel (L beta) phase is presented. It is based on a two-state model. Jump dynamics are defined for the lattice molecules to simulate lateral diffusion. The temperature and hydration dependence of the lateral diffusion coefficients of the model are calculated for the L alpha phase using Monte Carlo simulation techniques. The results obtained allow the estimation of the hydration dependent part of the lateral diffusion activation energy by thermodynamical quantities. We compare these results with measured activation energies of dipalmitoylphosphatidylcholine (DPPC) and propose a model to describe the total lateral diffusion activation energy of such systems.

Chemical Phenomena↗
PubMed2005

Calculation of absolute protein-ligand binding free energy from computer simulations.

A general methodology for calculating the equilibrium binding constant of a flexible ligand to a protein receptor is formulated on the basis of potentials of mean force. The overall process is decomposed into several stages that can be computed separately: the free ligand in the bulk is first restrained into the conformation it adopts in the bound state, position, and orientation by applying biasing potentials, then it is translated into the binding site, where it is released completely. The conformational restraining potential is based on the root-mean-square deviation of the peptide coordinates relative to its average conformation in the bound complex. Free energy contributions from each stage are calculated by means of free energy perturbation potential of mean force techniques by using appropriate order parameters. The present approach avoids the need to decouple the ligand from its surrounding (bulk solvent and receptor protein) as is traditionally performed in the double-decoupling scheme. It is believed that the present formulation will be particularly useful when the solvation free energy of the ligand is very large. As an application, the equilibrium binding constant of the phosphotyrosine peptide pYEEI to the Src homology 2 domain of human Lck has been calculated. The results are in good agreement with experimental values.

Binding Sites↗
PubMed1998

Computer simulation of the impact of different dimensions of the stomach on the validity of electrogastrograms.

The impact of the dimensions of the stomach on cutaneous recordings of gastric electrical activity (GEA) has not been adequately studied. The stomach was represented as a truncated conoid in a spherical coordinate system. The gastric electric field was modelled using a previously described methodology. Electrical potentials were calculated from sets of points simulating standard cutaneous recordings. The frequency of the signals was maintained at 3 cycles min-1 (period of repetition: 20 s), while the velocity of propagation of the depolarisation waves was reduced relative to the reduction in gastric dimensions. The signals were digitally contaminated with a random artificial artefact with a constant amplitude range of 0.2 mV, while the dimensions of the conoid (the circumferential radii and the length of the central axis) were decreased by factors of 1.5, two, four, six and eight. Simulated EGG signals were evaluated quantitatively. Simulated EGG records contaminated with random signals recorded from stomachs with decreasing dimensions exhibited non-linearly increasing standard deviations (p < 0.001). Randomly contaminated EGGs calculated from stomachs with dimensions reduced four, six and eight times were abnormal according to previously established quantitative criteria. Computer modelling indicated that gastric dimensions can significantly influence the validity of EGGs. These findings could be particularly important in a paediatric electrogastrography.

Computer Simulation↗