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At least 271 records · Page 15Linked to original sources
PubMed2003

Lens optics as an optical computer for group contractions.

It is shown that the one-lens system in para-axial optics can serve as an optical computer for contraction of Wigner's little groups and an analog computer that transforms analytically computations on a spherical surface to those on a hyperbolic surface. It is shown possible to construct a set of Lorentz transformations which leads to a 2x2 matrix whose expression is the same as those in the para-axial lens optics. It is shown that the lens focal condition corresponds to the contraction of the O(3)-like little group for a massive particle to the E(2)-like little group for a massless particle, and also to the contraction of the O(2,1)-like little group for a spacelike particle to the same E(2)-like little group. The lens-focusing transformations presented in this paper allow us to continue analytically the spherical O(3) world to the hyperbolic O(2,1) world, and vice versa. Since the traditional role of Wigner's little groups has been to dictate the internal space-time symmetries of massive, massless, and imaginary-mass particles, the one-lens system provides a unification of those symmetries.

Journal Article↗
PubMed1995

Polyiodinated triglyceride analogs as potential computed tomography imaging agents for the liver.

A series of glyceryl 2-oleoyl 1,3-bis[omega-(3-amino-2,4,6-triiodophenyl)] alkanoates was synthesized, radioiodinated with iodine-125, emulsified, and evaluated for their ability to selectively localize in the liver for potential use as hepatographic agents in computed tomography. All seven analogs displayed rapid liver uptake wherein between 65 and 78% of the injected dose accumulated in the liver by 30 min. Liver values ranged from 46 to 93% 3 h after injection which corresponded to liver to blood ratios ranging from 21 to 450. Moreover, subsequent elimination of radioactivity from the liver was nearly linear with respect to alkyl chain length. Analogs with longer alkyl chain length were eliminated from the liver more rapidly than their shorter chain counterparts. Because of their biochemical similarities to naturally occurring triglycerides, these novel analogs may prove useful not only for high-resolution anatomic imaging of focal liver lesions, but also for evaluating a variety of diffuse diseases known to affect hepatic function and biochemistry.

Animals↗
PubMed1999

Article for analog vector algebra computation.

We introduce the concept of an analog neural network represented by chemical operations performed on strands of DNA. This new type of DNA computing has the advantage that it should be fault tolerant and thus more immune to DNA hybridization errors than a Boolean DNA computer. We describe a particular set of DNA operations to effect the interconversion of electrical and DNA data and to represent the Hopfield associative memory and the feed-forward neural network of Rumelhart et al. We speculate that networks containing as many as 10(9) neurons might be feasible.

Animals↗
PubMed1987

Computation, rhythm, and cerebral slow waves.

The trajectories of data and modelling from formerly divergent research efforts now seem to be converging to an unexpected region of the phase space of neuroscience. Computational network theory and simulation assume that temporal rhythm may be a significant parameter for the successful organization of nonlinear analog computation effected by hierarchical sets of biological neurons and of nonbiological circuitry alike. For neurobiology, the apparently chaotic rhythms of cerebral compound field potentials--the electroencephalogram (EEG) and slow waves of event related brain potentials (ERBP)--have long been a phenomenological embarrassment, of only marginal clinical utility. But recent data from molecular biophysics, nonlinear dynamics, artificial intelligence, and scalp-conducted human electrocorticography suggest a possible functional role in the serial gating of neural network computations for the familiar theta-alpha-beta rhythms of the EEG clinic.

Auditory Perception↗
PubMed1982

Impedance loading servo pump system for excised canine ventricle.

To investigate ventricular-arterial system interaction, we have developed a hybrid-computer-controlled impedance loading servo pump system that enables us to impose a simulated arterial hydraulic impedance on an excised canine ventricle. An analog computer programmed to simulate a three-element Windkessel model of the arterial system computes instantaneous aortic flow from the instantaneous ventricular pressure. The time integral of this flow is used to command a volume servo pump system that controls the instantaneous ventricular volume. All parameter values in the loading system are controlled by a digital computer. The actual impedance spectrum generated by the system was reasonably close to that expected from the arterial model. The unique features of this system are the following. 1) The instantaneous volume of the ventricle, which is crucial information, can be measured. 2) If needed, the arterial impedance model can easily be reprogrammed to generate more complex impedance spectra. 3) The vascular parameters can be made nonlinear or time varying through the digital computer control.

Animals↗
PubMed1980

On-line computation of dead space and nitrogen clearance curve.

This work is aimed at getting on-line values of dead space and nitrogen clearance curves during washout experiments performed during continuous oxygen inhalation. An analog computer was built and connected to standard numeric implements, sending to them the processed signals from the measuring instruments. This solution seems to give at the same time good accuracy and good versatility at the lowest cost both in time and money.

Computers↗
PubMed2004

Computation in gene networks.

Genetic regulatory networks have the complex task of controlling all aspects of life. Using a model of gene expression by piecewise linear differential equations we show that this process can be considered as a process of computation. This is demonstrated by showing that this model can simulate memory bounded Turing machines. The simulation is robust with respect to perturbations of the system, an important property for both analog computers and biological systems. Robustness is achieved using a condition that ensures that the model equations, that are generally chaotic, follow a predictable dynamics.

Algorithms↗
PubMed1995

Predicting ligand binding to proteins by affinity fingerprinting.

BACKGROUND: There are many ways to represent a molecule's properties, including atomic-connectivity drawings, NMR spectra, and molecular orbital models. Prior methods for predicting the biological activity of compounds have largely depended on these physical representations. Measuring a compound's binding potency against a small reference panel of diverse proteins defines a very different representation of the molecule, which we call an affinity fingerprint. Statistical analysis of such fingerprints provides new insights into aspects of binding interactions that are shared among a wide variety of proteins. These analyses facilitate prediction of the binding properties of these compounds assayed against new proteins. RESULTS: Affinity fingerprints are reported for 122 structurally-diverse compounds using a reference panel of eight proteins that collectively are able to generate unique fingerprints for about 75% of the small organic compounds tested. Application of multivariate regression techniques to this database enables the creation of computational surrogates to represent new proteins that are surprisingly effective at predicting binding potencies. We illustrate this for two enzymes with no previously recognizable similarity to each other or to any of the reference proteins. Fitting of analogous computational surrogates to four other proteins confirms the generality of the method; when applied to a fingerprinted library of 5000 compounds, several sub-micromolar hits were correctly predicted. CONCLUSIONS: An affinity fingerprint database, which provides a rich source of data defining operational similarities among proteins, can be used to test theories of cryptic homology unexpected from current understanding of protein structure. Practical applications to drug design include efficient pre-screening of large numbers of compounds against target proteins using fingerprint similarities, supplemented by a small number of empirical measurements, to select promising compounds for further study.

Chromatography, Affinity↗
PubMed1973

Analyses of breath-by-breath responses of ventilation to CO 2 employing V-PCO 2 loops.

Computer techniques were employed to construct a respiratory control model in which the variables treated were programmed according to a series of mathematical equations, with the purpose of eliciting the relationship of V-PCO2 (minute ventilation-partial pressure of carbon dioxide) on a transient time basis. It was discovered that the transient V-PCO2 relationship has the shape of a loop half of which is for on-CO2 and the other half for off-CO2. Breath-by-breath ventilation was calculated by means of a home-made computer and the V-PCO2 relationship was monitored on an XY plotter. The transient V-PCO2 course also showed a loop which was quite similar in the general shape to the one traced employing theoretical analysis with an analog computer. This V-PCO2 loop may have potential usefulness to reveal mechanisms of respiratory control which may not be shown by the conventional V-PCO2 response curves.

Brain↗
PubMed1987

(A)GGG(A), (A)CCC(A) and other potential 3' splice signals in primate nuclear pre-mRNA sequences.

Several 3' splice signals in nuclear precursor mRNAs have already been known for some time: the AG doublet on the left-hand side of the splice and a run of pyrimidines just upstream of it. More recently it has been noted that the YNYTRAY sequence (where Y is a pyrimidine, R a purine and N any base) is a branching-sequence participating in formation of a lariat structure. Keller and Noon have shown the existence of several putative consensus sequences at this site. In this work, extensive computations of the distributions of 256 quartets in all primate nuclear pre-mRNA intron sequences present in GenBank have been carried out. Several putative signals upstream and downstream of the 3' splice have been detected. These have been compared with the results obtained in analogous computations carried out on all nuclear pre-mRNA introns present in a combined eukaryotic file containing mammal, non-mammalian vertebrate, invertebrate and plant sequences. The distributions of the more interesting oligomers are shown here. Of particular interest are the putative (A)GGG(A) signal 60 nucleotides upstream of the 3' splice site and (A)CCC(A) 3-40 nucleotides downstream of it. A possible splicing model explaining these data and involving formation of alternative hairpin loop structures is proposed.

Animals↗
PubMed1976

[On-line, high-speeded data analysis of cardiovascular function using hybrid systems (author's transl)].

In recent years application of computer techniques to various problems in biology has increased. In the field of anesthesia, where rapid changes appearing in a short time must be followed, the conventional, mannual methods are not applicable. So we have developed on-line computer analytical methods of cardiovascular function. Hybrid systems are the preferred methods in many biological problems, either because of efficiency and lower cost, or because of real time, on-line, closed-loop capabilities for direct use during experiments. As a computer output we used a graphic display computer and cathod ray tube devices. We applied these systems to analize and calculate cardiac work with other circulatory parameters. We got a ventricular function curve in visible form on CRT within 30 seconds after introducing the signals of left ventricular work and ventricular end-diastolic pressure into the analog computer. It was also useful to calculate vascular input impedence and myocardial maximal velocity of shortening. Finally causes of input errors in these analytical methods were discussed.

Animals↗
PubMed1981

Computer-assisted electrocoagulation: bipolar vs. monopolar in the treatment of experimental canine gastric ulcer bleeding.

A prospective, randomized, controlled experiment using a canine model of severely bleeding gastric ulcer was performed to compare the hemostatic efficacy and tissue damage produced by one bipolar and two monopolar electrodes. Both monopolar electrodes were insulated to their tips; they differed with respect to their surface area (3 mm2 vs. 4 mm2). The force of electrode application was controlled. An analog computer monitored the energy per electrode application and predetermined the duration of each application. Fifty-nine standard acute bleeding ulcers were made and treated one at a time in six heparinized foxhounds at sterile laparotomy. Treatment was randomized to the bipolar or to one of the monopolar electrodes within each of three bleeding strata. No significant difference was observed in hemostatic efficacy among the three electrodes. Treated ulcers were examined histologically after 5 to 7 days to determine the maximum tissue damage produced: Bipolar electrocoagulation caused significantly less damage than electrocoagulation with either monopolar electrode. We conclude that with these electrodes, bipolar electrocoagulation is equally effective for stopping bleeding but results in less tissue injury than monopolar electrocoagulation in this experimental model.

Animals↗
PubMed2002

Computational drug design accommodating receptor flexibility: the relaxed complex scheme.

A novel computational methodology for drug design that accommodates receptor flexibility is described. This "relaxed-complex" method recognizes that ligand may bind to conformations that occur only rarely in the dynamics of the receptor. We have shown that the ligand-enzyme binding modes are very sensitive to the enzyme conformations, and our approach is capable of finding the best ligand-enzyme complexes. This new method serves as the computational analog of the experimental "SAR by NMR" and "tether" methods, which permit a building block approach for constructing a very potent drug.

Algorithms↗
PubMed2000

A neural network architecture for visual selection.

This article describes a parallel neural net architecture for efficient and robust visual selection in generic gray-level images. Objects are represented through flexible star-type planar arrangements of binary local features which are in turn star-type planar arrangements of oriented edges. Candidate locations are detected over a range of scales and other deformations, using a generalized Hough transform. The flexibility of the arrangements provides the required invariance. Training involves selecting a small number of stable local features from a predefined pool, which are well localized on registered examples of the object. Training therefore requires only small data sets. The parallel architecture is constructed so that the Hough transform associated with any object can be implemented without creating or modifying any connections. The different object representations are learned and stored in a central module. When one of these representations is evoked, it "primes" the appropriate layers in the network so that the corresponding Hough transform is computed. Analogies between the different layers in the network and those in the visual system are discussed. Furthermore, the model can be used to explain certain experiments on visual selection reported in the literature.

Algorithms↗
PubMed1961

Computer solutions for photosynthesis rates from a two pigment model.

A kinetic model for a two pigment mechanism of photosynthesis based on observations made on the red alga Porphyridium cruentum is developed. The model supposes that different products are formed by chlorophyll and phycobilin pigments and that these products react to produce oxygen. The product of the chlorophyll reaction is also rapidly utilized for O(2) consumption both in light and in the dark. Rate equations based on the model reactions were derived and put into an analog computer. The effect of varying parameters on the time course curves for oxygen exchange resulting from the model was studied. Appropriate selection of parameters yielded computer curves which resembled fairly closely the oxygen exchange curves obtained using Porphyridium. The model showed the Emerson enhancement effect, chromatic transients, "respiratory stimulation," and other effects observed with live algae.

Chlorophyll↗
PubMedDate not supplied

Effect of mastoid cavity modification on middle ear sound transmission.

The modified radical mastoidectomy and intact canal wall mastoidectomy are the two most popular procedures used today for the treatment of chronic middle ear and mastoid disease. Their effects on the anatomy of the middle ear and mastoid cavity are quite different and it might also be expected that they would modify middle ear sound transmission in different ways. This paper describes experiments with human temporal bones and a middle ear computer analog model that attempt to define acoustic differences produced by cavity modifications in these two procedures. The temporal bone studies showed that blocking the aditus (as in modified radical mastoidectomy) produced improved sound transmission in the 1,500- to 4,000-Hz range and decreased transmission below 1,000 Hz when compared to the enlarged aditus and enlarged mastoid condition (as in intact canal wall mastoidectomy). Computer model showed better transmission at all frequencies with the intact canal wall mastoidectomy simulation.

Acoustic Stimulation↗
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↗