Prospects for a Psi-Net: the fourth quantum advance in psychiatry.
Explore the source record for details and available documents.
Computers↗
SEARCH · PubMed Health
Results for “quantum computing”
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Density resolution in quantitative computed tomography of foam and lung.
This study was performed to assess density resolution in quantitative computed tomography (CT) of foam and lung. Density resolution, a measure for the ability to discriminate materials of different density in a CT number histogram, is normally determined by quantum noise. In a cellular solid, variations in mass in the volumes sampled by CT cause an additional degradation of density resolution by the linear partial volume effect. The sample volume, which is directly related to spatial resolution, can be varied by choosing different section thicknesses and reconstruction filters. Several polyethene (PE) foams, as simple models of lung tissue, and five patients were investigated using various sample volumes. For the uniform PE foams, density resolution could be directly determined as the full width at half maximum of CT number histograms. Density resolution for foams with cell sizes of 0.8-1.5 mm was dominated by effects caused by the limited sample size, not by quantum noise. The relative magnitudes of density resolution could roughly be explained with a model for a hypothetic random cellular solid. Since lungs are not of uniform density, analysis of patient data was more complicated. A combined convolution least-squares fit procedure, together with information obtained in the studies of foam, were used to determine density resolution in lung studies. Density resolution, both for foams and lung, was strongly dependent on sample volume, and was quite poor for thin sections and sharp filters. Consequently, histogram-shape related parameters are sensitive to the spatial resolution chosen on CT. Thin section densitometry, using a 1-mm section with a standard or high resolution filter, is not recommended except in determining average density. When using thicker sections, an in-plane spatial resolution similar to section thickness is advised.
Humans↗
CT reconstruction by using the MLS-ART technique and the KCD imaging system--I: low-energy X-ray studies.
We investigated the use of the kinestatic charge detector (KCD) combined with the multilevel scheme algebraic reconstruction technique (MLS-ART) for X-ray computer tomography (CT) reconstruction. The KCD offers excellent detective quantum efficiency and contrast resolution. These characteristics are especially helpful for applications in which a limited number of projections are used. In addition, the MLS-ART algorithm offers better contrast resolution than does the conventional convolution backprojection (CBP) technique when the number of projections is limited. Here we present images of a Rando-head phantom that was reconstructed by using the KCD and MLS-ART. We also present, for comparison, the images reconstructed by using the CBP technique. The combination of MLS-ART and the KCD yielded satisfactory images after just one or two iterations.
Algorithms↗
Pyrroloquinolinone methylderivatives, furocoumarin analogues: interaction with biomolecules and computer-aided studies.
Pyrroloquinolinones, furocoumarin analogues, contain a divinilbenzene moiety, suggesting possible photoreactivity. Quantum mechanics calculations indicate that the pyrrole-side double bond exhibits strong photoreactivity, while the pyridone-side double bond is only poorly photoreactive. Intercalation models obtained by molecular mechanics calculations suggest that, in the cis-syn intercalation arrangement, the pyridone-side double bond is well aligned with the nearby thymine, supporting possible C4-cycloaddition with the 5,6 double bond of thymine, while the pyrrole-side double bond assumes an unfavourable position for photobinding. These data suggest that photoreaction between the pyridone-side and thymine double bonds may takes place, although with very low yield. Experimental evidence concerning DNA-photobinding exhibited by 2,6-dimethyl-9-methoxy-4H-pyrroloquinolinone (Compound I) confirms theoretical predictions. The formation of C4-cycloadducts between the pyridone side double bond and thymine also takes place with very low yield. Compound I shows marked BSA photobinding, suggesting that pyrroloquinolinones may photoreact with proteins. The three pyrroloquinolinones examined show high yields of singlet oxygen generation, suggesting that photobiological effects may be obtained through this photodynamic pathway, rather than through DNA photobinding.
Base Sequence↗
Three-dimensional triple quantum-filtered 23Na imaging of rabbit kidney with weighted signal averaging.
Low signal-to-noise ratio (SNR) has been the main obstacle to multiple quantum-filtered 23Na imaging becoming an important technique for biologic and clinical applications. Through computer simulations and phantom experiments, we show that the SNR in 23Na imaging can be substantially improved by weighted signal averaging. Three-dimensional single quantum and triple quantum (TQ)-filtered 23Na images of an externalized rabbit kidney were collected with this technique. The TQ-filtered image did not show any signal when the animal was alive. However, upon sacrificing the animal, the renal cortex became clearly visible without any significant increase in signal from the medullary region. This increase in TQ-filtered signal in the renal cortex may be caused by an increased concentration of intracellular Na+ in the large intracellular space present herein, compared with the medulla. To our knowledge, this study represents the first example of three-dimensional TQ-filtered 23Na image of a biological sample.
Animals↗
Modelling the catalytic reaction in human aldose reductase.
Aldose reductase (ALR2) has received considerable attention due to its possible link to long-term diabetic complications. Although crystal structures and kinetic data reveal important aspects of the reaction mechanism, details of the catalytic step are still unclear. In this paper a computer simulation study is presented that utilizes the hybrid quantum mechanical and molecular mechanical (QM-MM) potential to elucidate the nature of the hydride and proton transfer steps in the reduction of D-glyceraldehyde by ALR2. Several reaction pathways were investigated in two models with either Tyr48 or protonated His110+ acting as the potential proton donor in the active site. Calculations show that the substrate binds to ALR2 through hydrogen bonds in an orientation that facilitates the stereospecific catalytic step in both models. It is established that in the case that His110 is present in the protonated form in the native complex, it is the energetically favored proton donor compared with Tyr48 in the active pocket with neutral His110. The reaction mechanisms in the different models are discussed based on structural and energetic considerations.
Aldehyde Reductase↗
Conformational properties of molecules by ab initio quantum mechanical energy minimization.
The recent literature on the determination of minimum energy conformations by ab initio quantum mechanical techniques is reviewed. The availability of computer-coded analytical first and second derivatives of the Hartree-Fock energy makes possible calculations that will be of significant assistance in structure determination of molecules. A short review of recent progress in empirical energy minimization and molecular dynamics is provided.
Models, Chemical↗
Determination of structure-activity relationships for salicylaldehydes using CNDO and EHT calculations.
EHT and CNDO calculations have been performed on a series on fungicidal salicylaldehyde derivatives. Correlations are found between the inhibitory activity and several quantum-mechanical indices.
Aldehydes↗
Characterization of functional interactions of imidazoquinoxaline derivatives with benzodiazepine-gamma-aminobutyric acidA receptors.
U-78875 [imidazo[1,5-a]quinoxalin-4(5H)-one, 3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-5-(1-methylethyl)] belongs to a series of imidazoquinoxaline derivatives, recently discovered ligands with high affinity for benzodiazepine receptors. In this study, we have examined the drug and its analogs for their modes of interaction with the receptors, with a particular emphasis on finding molecular determinants for their functional properties. Changes in the substituents on N5 and C6 of the heterocyclic ring produced no major effects on binding characteristics but yielded drugs of widely varying efficacy (antagonist to full agonist), measured as gamma-aminobutyric acid (GABA)-mediated 36Cl- uptake and t-butylbicyclophosphoro[35S]thionate binding in rat cerebrocortical membranes. The relative binding affinity and efficacy of the analogs measured in brain membranes were similar to those in cloned GABAA receptors of the alpha 1 beta 2 gamma 2 (type I) and alpha 3 beta 2 gamma 2 (type II) subtypes. The imidazoquinoxalines showed no marked subtype selectivity. Their Ki value against [3H]flunitrazepam binding for type I was only 2-3 times lower than that for type II, and their rank order for agonistic activity was the same in the two subtypes, measured as GABA-mediated Cl- currents in human kidney cells (A293) expressing the subtypes of GABAA receptors. According to computational modeling of the drugs using both molecular and quantum mechanics, the agonistic activity of the imidazoquinoxaline derivatives depends on the presence of a bulky alkyl substituent at N5 and the deformation of the substituted portion of the otherwise planar ring system induced by a bulky moiety at N5 or C6. With a fixed N5 substituent (isopropyl), the relative efficacy in the brain membranes, as well as in the cloned receptors, appeared to be dependent on the degree of the ring deformation. This out-of-plane portion of the imidazoquinoxalines can be assigned to the general region occupied by the 5-phenyl group of diazepam and other agonistic functional groups of several nonbenzodiazepine ligands. It seems that this region, apparently common to various agonistic ligands, interacts with an agonistic pocket in type I and type II subtypes of the benzodiazepine receptors in the brain. Our results also provide direct support for the view that the agonists and nonagonists share largely overlapping binding regions in the benzodiazepine receptor, which has been proposed earlier from in vivo efficacy measurements of other series of ligands.
Animals↗
[Operator's systemic quanta under psychoregulating acts].
The aim of this study is to examine psychoregulatory effects for computer operator's rehabilitation. K. V. Sudakov's systemic quantum behavior conception as a methodological basis for human activity study. The comparison of quantum characteristics, such as motivation, activity result and its physiological cost up prior to and after psychoregulation for different groups of human biotypology has shown that the systemic quantum of the operator's activity is the reliable indicator of a functional condition. It has indicated that this way for rehabilitation is more effective for human beings who have predominantly parasympathicotonia and rather high initial motivation levels.
Adolescent↗
Physical imaging performance of a compact computed radiography acquisition device.
A comprehensive investigation of the physical imaging performance of a Philips AC3 computed radiography system using fifth-generation image plate technology has been undertaken. Measurements include characteristic response, modulation transfer function (MTF) and Wiener spectra (WS) for standard and high resolution image plates sampled at 10 pixels/mm. These results were used to calculate noise equivalent quanta (NEQ) and detective quantum efficiency (DQE) spectral descriptions of system performance. Luminescence noise and x-ray quantum noise components were separated. From an estimate of the luminescence noise power, the average system gain was calculated and results show a substantial improvement over earlier generations of computed radiography systems for standard image plates.
Calibration↗
The implementation of ab initio quantum chemistry calculations on transporters.
The RHF and geometry optimization sections of the ab initio quantum chemistry code, GAMESS, have been optimized for a network of parallel microprocessors, Inmos T800-20 transputers, using both indirect and direct SCF techniques. The results indicate great scope for implementation of such codes on small parallel computer systems, very high efficiencies having been achieved, particularly in the cases of direct SCF and geometry optimization with large basis sets. The work, although performed upon one particular parallel system, the Meiko Computing Surface, is applicable to a wide range of parallel systems with both shared and distributed memory.
Computers↗
QMView: a computational chemistry three-dimensional visualization tool at the interface between molecules and mankind.
QMView is designed to facilitate the visualization and interpretation of quantum mechanical data. Capabilities include display of chemical structure, animation of quantum mechanically determined vibrational modes, and depiction of electronic properties and three-dimensional molecular orbitals. QMView has a user-friendly interface that allows users to interactively manipulate many features of the molecular structure and/or property, including positioning and structure representation, via mouse-activated dialog boxes. Although the interface allows input from results of any of the popularly used quantum mechanical software, we have focused on GAMESS, a widely distributed quantum chemistry code. QMView has been designed with the special feature of working in distributed mode with GAMESS, the latter running on a supercomputer, the former running on a Silicon Graphics platform. Ancillary programs provide a method of obtaining output of graphic images in various media, including hardcopy, PostScript files, slide, and/or video. These and other original features discussed in this article provide a graphic interface that is unique compared to others that are currently available. Examples of images produced by QMView are presented.
Computer Graphics↗
Quantum leaps in technology transfer.
Explore the source record for details and available documents.
Computer Communication Networks↗
Quantum simulation of ferrocytochrome c.
The dramatic progress in the understanding of the dynamics of biomolecules has been largely fuelled by computer simulations based on the law of classical mechanics. However in some respects biomolecules are at the borders of the domain of applicability of classical mechanics. The role of quantum mechanical effects in biomolecular structure and function is therefore worth investigating. Here we present preliminary results from a quantum simulation of a protein and contrast them with results from full classical simulations. The most significant differences are found in motions of high frequency, such as bond stretching or the torsional oscillation of groups that bear hydrogen atoms. The amplitudes of such motions are significantly increased by the penetration of atoms into classically forbidden regions. These differences will directly influence the rates of such processes as proton and electron transfer.
Cytochrome c Group↗
Azapsoralens-DNA interactions: crystal structure characterization of furan-side monoadduct and computer-aided studies.
In this paper a theoretical study, concerning molecular mechanics optimised structures, obtained by quantum mechanics as well as molecular mechanics calculations was carried out with the aim of correlating the theoretical model of the interactions between azapsoralens and DNA with the data experimentally obtained. The theoretical model suggests that both furan-side and pyrone-side double bonds may be involved in the cycloaddition with pyrimidines (although the cycloaddition at the level of furan is preferred), and is in line with the capacity of these compounds to form inter-strand cross-links. Moreover, concerning the theoretical intercalation model calculations on 3,4,4',5'-tetramethylazapsoralen intercalated inside a polynucleotide, they suggest a cis-syn arrangement between furan-side of the intercalated ligand and the above situated thymine, with which, under light activation, a cycloadduct may take place, having a cis-syn steric arrangement. Also this datum is in agreement with the cis-syn regio and stereochemistry of the isolated 4,4',5'-trimethylazapsoralen-thymine cycloadduct. Finally, from theoretical data, the role of nitrogen seems not important: in fact only small differences were found with the corresponding methylpsoralens so that the small differences observed may be mainly attributed to steric rather than to electronic effects. In general a good correlation between the theoretical model and the experimental data was observed.
Chromatography, High Pressure Liquid↗
Three-dimensional molecular illustrations I: Isoelectron density contours and isoelectrostatic energy contours.
A method of depicting dimensional illustrations of molecules in vacuo that are sensitive to small electronic perturbations was attempted. This method would be useful in determining the effects of either perturbing groups from other molecules or changes produced by the addition or modification of an existing atom or chemical group on the same molecule. Isoelectron density contours for small molecules such as benzene, ammonia, and formaldehyde were first considered using the CNDO/2 molecular approximation method and then extended to the use of deorthogonalized CNDO/2 eigenvectors. These methods were similar in molecular projections but insensitive to electronic alterations. Therefore, the electrostatic potential energy was considered in developing contour surfaces of several of the molecules studied. In this case, acute and visually discernible changes were evidenced by electron exchange in the three-dimensional illustration of formaldehyde. The effect on the two-dimensional contour map of ammonia was strikingly altered by the addition of a proton, further substantiating the sensitivity of electrostatic contours to perturbing influences. These methods are considered and amplified in this report.
Ammonia↗
Multiple echoes, multiple quantum coherence, and the dipolar field: demonstrating the significance of higher order terms in the equilibrium density matrix.
It is well known that dipolar field effects lead to multiple spin echoes in a simple two-RF pulse experiment (the MSE experiment). We show here that coherence transfer echoes (which identify the existence of multiple quantum coherences in liquid NMR) and multiple spin echoes have a common origin. Using density matrix theory we have calculated the phase and timing of multiple spin echoes from all quadrature phase combinations of RF pulses. We show for the MSE experiment that there is a one-to-one correspondence between the time domain echo order and the multiple quantum coherence order. The experimental confirmation of these phase predictions shows that multiple spin echoes provide independent evidence for the breakdown of the high temperature approximation as proposed by Warren et al. (Science 262, 2005 (1993)).
Artifacts↗