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PubMed1991

Solid state 2H-NMR as a method for determining the orientation of cannabinoid analogs in membranes.

In order to investigate the correlation between the pharmacological activities of cannabinoids and the geometric features of their interactions with membranes, we have calculated the molecular orientations of five analogs in model membrane bilayers. The studies involved the stereospecific 2H-labeling of each analog in different positions and the use of solid state 2H-NMR. The cannabinoids included in our study are (-)-delta 9-tetrahydrocannabinol (THC), (-)-delta 8-THC and its methylated ether analog (-)-O-methyl-delta 8-THC, as well as two hexahydrocannabinols (HHC) having an additional hydroxyl in the 11-position, (-)-11-OH-9 alpha-HHC and (-)-11-OH-9 beta-HHC. A new algorithm is used to circumvent the problem of deuterium quadrupolar splitting signs. The method has general applicability for calculating the orientation of a molecule in a anisotropic environment. Our calculations show that the biological inactive O-methyl-delta 8-THC orients with its long axis parallel to the lipid acyl chains, whereas the psychoactive cannabinoids assume "awkward" orientations in which the hydroxyl groups are pointing towards the bilayer interface, presumably to maximize the amphipathic interaction with the membrane. To produce their biological effects, cannabinoids may need to acquire an appropriate location and orientation in the membrane bilayer so that, through lateral diffusion, they can reach their sites of action and interact productively with these sites.

Cannabinoids↗
PubMed1995

A parallel neural network simulator on the connection machine CM-5.

We here present a parallel implementation of artificial neural networks on the connection machine CM-5 and compare it with other parallel implementations on SIMD and MIMD architectures. This parallel implementation was developed with the goal of efficiently training large neural networks with huge training pattern sets for applications in molecular biology, in particular the prediction of coding regions in DNA sequences. The implementation uses training pattern parallelism and makes use of the parallel I/O facilities of the CM-5 and its efficient reduction operations available within the control network to achieve a high scalability. The parallel simulator obtains a maximum speed of 149.25 MCUPS for training feedforward networks with backpropagation on a 512 processor CM-5 system without using the CM-5 vector facility. The implementation poses no restriction on the type of network topology and works with different batch training algorithms like BP. Quickprop and Rprop.

Algorithms↗
PubMed1999

The incipient stage in thrombin-induced fibrin polymerization detected by FCS at the single molecule level.

We used fluorescence correlation spectroscopy (FCS) to study the activation of fibrinogen by thrombin and the subsequent aggregation of fibrin monomers into fibrin polymers at a very low and at physiological fibrinogen concentrations. In the labeling procedure used the fibrinogen was randomly labeled and the label was bound to the fibrinopeptide A and/or to the part of fibrinogen which after activation takes part in fibrin formation. We measured a diffusion coefficient for fibrinogen of 2.48 x 10(-7) +/- 0.10 x 10(-7) cm2/s. After activation with thrombin both fibrinopeptide A and fibrin polymerization products could be demonstrated. From our findings we suggest a model for the formation of a three-dimensional network as two parallel processes, elongation and branching and that fibrin oligomers are not only intermediates in the polymerization process but also are substrates for branching.

Algorithms↗
PubMed2000

Forecasts using neural network versus Box-Jenkins methodology for ambient air quality monitoring data.

This study explores ambient air quality forecasts using the conventional time-series approach and a neural network. Sulfur dioxide and ozone monitoring data collected from two background stations and an industrial station are used. Various learning methods and varied numbers of hidden layer processing units of the neural network model are tested. Results obtained from the time-series and neural network models are discussed and compared on the basis of their performance for 1-step-ahead and 24-step-ahead forecasts. Although both models perform well for 1-step-ahead prediction, some neural network results reveal a slightly better forecast without manually adjusting model parameters, according to the results. For a 24-step-ahead forecast, most neural network results are as good as or superior to those of the time-series model. With the advantages of self-learning, self-adaptation, and parallel processing, the neural network approach is a promising technique for developing an automated short-term ambient air quality forecast system.

Air Pollution, Indoor↗
PubMed1988

Interaction of carotid chemoreceptor and baroreceptor reflexes in anesthetized dogs.

Interaction between baroreceptors and chemoreceptors during simultaneous activation of the reflexes was studied in eight pentobarbital sodium-anesthetized vagotomized dogs. The carotid sinus reflexogenic area was isolated and perfused at controlled carotid sinus pressure (CSP), PO2, and PCO2. Random combinations of CSP, PO2, and PCO2 were delivered to the carotid sinus. Results were analyzed by multiple linear regression. For the arterial pressure response, increasing CO2 resulted in an upward shift of the baroreceptor reflex response curve and an increased slope of the linear portion of the curve. The heart rate-CSP curve was also shifted upward by CO2, with the effect being greatest at high levels of CSP. The respiratory frequency-CO2 relationship had an increased slope and was shifted upward when CSP was decreased. The responses of tidal volume and ventilation (VE) depended on all three inputs. At any level of PO2, decreasing CSP resulted in a parallel shift of the VE-CO2 relationship. The results indicate that there is a significant interaction between chemoreceptor and baroreceptor reflex sensitivities.

Algorithms↗
PubMed2001

Detection of motion in hybrid PET/SPECT imaging based on the correlation of partial sinograms.

This paper describes a motion detection method specific to hybrid positron emission tomography/single photon emission computed tomography systems. The method relies on temporal fractionation of the acquisition into three data sets followed by an algorithm based on the cross correlation (CC) of partial sinograms from successive sets at different rotations of the camera. Spatial inconsistencies due to motion are detected by decreases in the CC between two sets. This permits to separate data into premotion and postmotion sets of consistent data that are reconstructed independently then registered and summed. Rigid motions greater than 1-cm translation or 10 degrees rotation were detected with this method from experimental data obtained by manually moving phantoms made of radioactive spheres as well as from a patient lung study corrupted by artificial motion. The different motion studies showed that the image contrast does not seem to be a limiting factor and that the motion is best detected when the gantry is parallel to the direction of motion. The registration and fusion of the reconstructed premotion and postmotion sets lead in all cases to a reduction of the motion artifacts and an increase in signal-to-noise ratio.

Algorithms↗
PubMed1990

Image analysis techniques for automatic evaluation of two-dimensional electrophoresis.

Techniques for automatic analysis of two-dimensional electrophoresis gels by computer-aided image analysis are described. Original gels or photographic films are scanned using a laser scanner and the files are transferred to a microcomputer. The program package first performs a compression and preevaluation of the files. Spot identification and quantification is performed by the chain code algorithm after appropriate zooming and cutting. Labeling facilitates spot identification and quantification in numerical and graphical (pseudocolor) representation on peripheral devices for camera ready output. Interpolation between measured basepoints is performed by cubic spline algorithms which are automatically switched on and off, depending on the need by the program. High speed analysis and graphic representation is achieved using fast Assembler language routines rather than high level languages. One-dimensional gels can be analyzed using the same software. Spot matching between parallel two-dimensional gels has not yet been implemented.

Electrophoresis, Gel, Two-Dimensional↗
PubMed1996

On-line laser-photometric monitoring of aerosol deposition in ventilated rabbit lungs.

A photometric technique was developed for on-line measurement of aerosol deposition in isolated, ventilated, and perfused rabbit lungs. A jet nebulizer was used for aerosolization of saline (hygroscopic particles) and di(2-ethylhexyl) sebacate (nonhygroscopic particles). Aerosol concentration (laser photometer, constructed for measurements in rabbit lungs) and flow rate (commercial pneumotachograph) were continuously monitored at the inlet of the tracheal cannula. Computer-assisted data processing allowed the breath-by-breath calculation of inhaled and exhaled aerosol mass, thus providing the deposition fraction. With the use of hygroscopic particles, however, this approach was hampered by the humidity-induced particle growth in the airways, leading to an overestimation of the aerosol concentration in exhaled air. This effect was corrected by an algorithm using a "particle growth factor" derived breath by breath from the photometer signal. To test the reliability of this approach, saline particles carrying technetium-99m label were aerosolized into rabbit lungs with the use of various ventilator settings, and the aerosol deposition was assessed in parallel by photometry and by radioactivity detection over the lung and over a trap in the exhaled-air circuit. Superimposable curves of cumulative aerosol deposition, with changes in kinetics dependent on the ventilator mode, were obtained. For a given ventilator setting, absolute values of the deposition fraction were 0.32 +/- 0.04 (radiotracer quantification) and 0.36 +/- 0.04 (photometry; means +/- SD; n = 4). We conclude that the presented laser-photometric technique allows reliable on-line monitoring of the deposition of both nonhygroscopic and hygroscopic aerosol particles in ventilated lungs.

Aerosols↗
PubMed1994

[Pathogenetic rationale and diagnostic methods in allergic tuberculous synovitis of the knee joint].

The pathogenesis of tuberculous allergic synovitis was specified in the experiments on 44 rabbits by applying original simulation methods, including bivalent sensibilization, parallel study of the synovial fluid and serum of laboratory animals. A role of the synovial layer as an organ of immunogenesis and its impact on antibody titers were defined. A new diagnostic test, involving a diagnostic parameter and an equation for its calculation was developed. An algorithm was proposed for examining patients with synovitis (arthritis) of unknown etiology, which includes a set of significant clinical and laboratory parameters. Its testing in 64 patients enabled the tuberculous nature of the disease to be identified in 30% of cases.

Algorithms↗
PubMed2000

Enhanced 3D PET OSEM reconstruction using inter-update Metz filtering.

We present an enhancement of the OSEM (ordered set expectation maximization) algorithm for 3D PET reconstruction, which we call the inter-update Metz filtered OSEM (IMF-OSEM). The IMF-OSEM algorithm incorporates filtering action into the image updating process in order to improve the quality of the reconstruction. With this technique, the multiplicative correction image--ordinarily used to update image estimates in plain OSEM--is applied to a Metz-filtered version of the image estimate at certain intervals. In addition, we present a software implementation that employs several high-speed features to accelerate reconstruction. These features include, firstly, forward and back projection functions which make full use of symmetry as well as a fast incremental computation technique. Secondly, the software has the capability of running in parallel mode on several processors. The parallelization approach employed yields a significant speed-up, which is nearly independent of the amount of data. Together, these features lead to reasonable reconstruction times even when using large image arrays and non-axially compressed projection data. The performance of IMF-OSEM was tested on phantom data acquired on the GE Advance scanner. Our results demonstrate that an appropriate choice of Metz filter parameters can improve the contrast-noise balance of certain regions of interest relative to both plain and post-filtered OSEM, and to the GE commercial reprojection algorithm software.

Algorithms↗
PubMed1995

Estimation of shape characteristics of surface muscle signal spectra from time domain data.

Myoelectric manifestations of muscle fatigue have been described by monitoring the first-order moment (mean frequency) of the power spectral density function during voluntary or electrically elicited sustained contractions. Higher order central moments provide additional information about the width, skewness, and kurtosis of the spectrum and its shape changes, thereby providing a description of slow nonstationarities more accurate than that allowed by the mean frequency alone. In 1986, B. Saltzberg introduced a method of representing the moments of the power spectral density function of band limited signals, without computing the Fourier transform, as weighted sums of samples of the autocorrelation function. If we allow for oversampling of the signal (and therefore of its autocorrelation function), more efficient weighted sums can be found which give Saltzberg's formula as a limiting case. The faster rate of decay of the weights implies a faster convergence of the estimates and the need to compute fewer samples of the autocorrelation function. The algorithm is particularly suitable for: 1) analysis of evoked potentials (M-waves), because it does not need zero padding to increase resolution and operates on any number of samples, and 2) on-line implementation by dedicated microprocessors performing simultaneous spectral moment analysis on a number of parallel channels.

Electrophysiology↗
PubMed1993

Optoelectronic implementation of neural networks.

The performance of electronic neural networks will eventually be limited by the capacity of their interconnections as operating speeds are increased. The use of optical connections to link electronic elements offers a way to overcome this problem. In particular, spatial optic techniques are especially suited to neural systems because of their parallel structure. Three experimental optoelectronic networks are described that employ holographic components and arrays of high-speed optical modulators. These of a network to 64 x 8 connections with optical fan-out. A hybrid networks have been used to demonstrate operation at 50 MHz, novel training algorithms and the expansion technique for integrating optoelectronic systems is also being developed.

Algorithms↗
PubMed2000

Impact of antiandrogen treatment on the fatty acid profile of neutral lipids in human meibomian gland secretions.

The purpose of this study was to determine whether the use of antiandrogen medications is associated with significant alterations in the fatty acid (FA) profiles of neutral lipids in human meibomian gland secretions. Meibomian gland secretions were obtained from both eyes of patients receiving antiandrogen therapy and from age-related controls. Samples were processed for high-performance liquid chromatography/mass spectrometry and an evaluation of the mass/charge ratios of neutral lipid FA. Our results demonstrate that antiandrogen therapy is associated with significant and consistent alterations in the mass/charge ratios of neutral lipid fractions of meibomian gland secretions. Patients taking antiandrogen medications had significant changes in the occurrence of numerous diglyceride, triglyceride, and wax/cholesterol ester FA products, compared with age-matched controls. Statistical analyses of data within groups demonstrated very high correlation coefficients, and cross-correlation analyses revealed characteristic shifts in FA patterns between groups. Our findings show that antiandrogen use is paralleled by significant changes in the FA profiles of neutral lipid fractions in meibomian gland secretions.

Aged↗
PubMed1988

Regional variation and function of nucleotide and amino acid sequence.

Two methods of qualitative analysis of sequence distribution in DNA and protein are presented. The first method is based on the finding that the frequency of occurrence of each nucleotide in a defined sequence with functional significance more or less deviates from uniform distribution. The deviation found in this defined sequence seems to parallel the function of this sequence. In the second method, two model compounds (trypsin and its inhibitor) have been used to see the topological fit between their local structures. Acrophilicity parameter for amino acid was used to construct the topological structure. Both methods may find practical application in algorithms to design functional DNA and protein molecules.

Algorithms↗
PubMedDate not supplied

Differences due to collimator blurring in cardiac images with use of circular and elliptic camera orbits.

BACKGROUND: In cardiac imaging systems, an elliptic acquisition orbit about the patient can be used to enhance resolution of single photon emission computed tomography (SPECT) images by minimizing the distance between the object imaged and the rotating detector system. In this study artifacts from images acquired with the standard circular acquisition are compared with those acquired with various elliptic acquisitions. METHODS AND RESULTS: With the use of elliptic camera orbits of different eccentricities, simulated projection data were generated from a slice through the left ventricle (LV). The projection data included a simulation of the degradation due to the depth-dependent response of the collimator. As is common in many clinical systems, SPECT images were reconstructed with the standard filtered backprojection algorithm without correction for the collimator response. When the ratio of the major-to-minor axis of the acquisition arc is changed from 1 (circular) to 1.5 (elliptic), reconstructed SPECT images show an additional loss of counts (about 10%) in the apical region of the LV. The severity of the apical defect is also dependent on the starting angle of the acquisition arc. When the starting angle is changed from 0 degrees (detector parallel to the major axis of the LV) to 60 degrees, the ratio between the minimum count in the apical region and the maximum count in the left ventricular myocardial wall decreases by as much as 20%. CONCLUSIONS: SPECT image artifacts from elliptic acquisitions are significantly more severe than those from circular acquisitions. Because of the significant difference in images reconstructed from circular and elliptic acquisitions, standardized normal files acquired from circular acquisitions should not be used for comparisons with patient data acquired from elliptic acquisitions.

Algorithms↗
PubMed1998

Power deposition in the head and neck of an anatomically based human body model for plane wave exposures.

At certain frequencies, when the human head becomes a resonant structure, the power absorbed by the head and neck, when the body is exposed to a vertically polarized plane wave propagating from front to back, becomes significantly larger than would ordinarily be expected from its shadow cross section. This has possible implications in the study of the biological effects of electromagnetic fields. Additionally the frequencies at which these resonances occur are not readily predicted by simple approximations of the head in isolation. In order to determine these resonant conditions an anatomically based model of the whole human body has been used, with the finite-difference time-domain (FDTD) algorithm to accurately determine field propagation, specific absorption rate (SAR) distributions and power absorption in both the whole body and the head region (head and neck). This paper shows that resonant frequencies can be determined using two methods. The first is by use of the accurate anatomically based model (with heterogeneous tissue properties) and secondly using a model built from parallelepiped sections (for the torso and legs), an ellipsoid for the head and a cylinder for the neck. This approximation to the human body is built from homogeneous tissue the equivalent of two-thirds the conductivity and dielectric constant of that of muscle. An IBM SP-2 supercomputer together with a parallel FDTD code has been used to accommodate the large problem size. We find resonant frequencies for the head and neck at 207 MHz and 193 MHz for the isolated and grounded conditions, with absorption cross sections that are respectively 3.27 and 2.62 times the shadow cross section.

Adult↗
PubMedDate not supplied

Solution structure of bovine heart fatty acid-binding protein (H-FABPc).

Fatty acid-binding protein (FABP) from bovine heart, a 15 kDa cytoplasmic protein has been investigated by multi-dimensional homonuclear and heteronuclear NMR-spectroscopy. Perdeuterated palmitic acid has been used as fatty acid ligand. The tertiary structure has been determined from distance geometry calculations with the variable target functions algorithm (DIANA) utilizing 1027 interproton distance constraints, which were obtained from 1H-homonuclear NOESY spectra. Overlapping NOE crosspeaks were assigned by heteronuclear multidimensional NMR-experiments with a 15N-labelled sample. The tertiary structure resembles a beta-barrel (beta-clam) consisting of ten anti-parallel beta-strands and a short helix-turn-helix motif. The beta-strands are arranged in two nearly orthogonal beta-sheets composed of 5 strands each. The solution structure is compared with the x-ray crystal structure of bovine heart and rat intestinal FABPs.

Animals↗
PubMed2000

The electrochemistry of ubiquinone-10 in a phospholipid model membrane.

The electrochemistry of ubiquinone-10, UQ, incorporated over a phospholipid layer adsorbed on a mercury drop electrode has been investigated over a wide pH range. It is shown that the position of the quinone headgroup in relation to the lipid determines the reversibility of the redox chemistry. For pH <7, the reaction follows a disproportionation route involving the ubiquione radical. There is evidence for the presence of a parallel reaction sequence. The bifurcation point appears to occur for the UQ molecule, which disproportionates after protonation and reduction, in parallel with direct electron transfer to yield the UQ--radical anion. The incorporation of UQ in a lipid monolayer makes its reduction very irreversible for pH > 7.

Algorithms↗