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PubMed1996

Torsional effects on the molecular polarizabilities of the benzothiazole (A)-benzobisthiazole (B) oligomer A-B13-A.

We outline a method for the calculation of multipole moments and molecular dipole-dipole (alpha), dipole-quadrupole (A), and quadrupole-quadrupole (C) polarizabilities, which we have successfully applied to benzothiazole (A)-benzobisthiazole (B) oligomer A-B13-A. Three model rotational isomers have been characterized: (1) the fully planar (000) rotational isomer; (2) a conformation with each unit rotated 10 degrees in the alternate direction (+(-)+), and (3) a rotational isomer with each unit rotated 10 degrees in the same direction (+3). The dipole moment, mu, is smaller for isomers 000 and +(-)+ than for isomer +3. The calculation of alpha A, and C has been performed by use of the interacting induced dipoles polarization model, which calculates tensor effective anisotropic point polarizabilities (method of Applequist). The values of alpha, A, and C are in the same order of magnitude as reference calculations (PAPID) program). The values of A are rather sensitive to mu, which varies under rotation, explaining the greatest value of magnitude of Ax,xx for polar isomer +3. This rotational isomer has the maximum hydrophilic accessible surface, which would improve solubility in water. It is found that small torsional changes can enhance solubility by increasing the hydrophilic accessible surface without too much affecting the values of alpha and C. However, the torsion of the oligomer can vary the value of mu and so modify A.

Benzothiazoles↗
PubMed1996

Relationship between infrared spectra and isomorphous substitution in smectites: a computer simulation study.

Smectites, members of the 2:1 layer silicate family, share the common feature that two tetrahedral sheets sandwich a sheet of octahedrally coordinated metal ion. The diversity of the members of the 2:1 layer silicates occurs because of their capacity for isomorphous substitution of various cations in the octahedral or tetrahedral sheets. Substitution of a divalent metal ion (such as Mg2+) for the trivalent Al3+ or a trivalent metal ion (such as Al3+) for the tetravalent silicon results in a net negative charge, which then undergoes interaction with positive ions (the exchangeable cations) to form an interlayer hydrated phase. Local density functional (LDF) calculations were employed to model isomorphous substitution of Al3+ by Na+, K+, Mg2+, Fe2+, and Fe3+ in the octahedral layer of a dioctahedral smectite clay such as montmorillonite. The energies of the isomorphous substitution were then compared with the experimental observation. The ordering for successful substitution is Al3+ > Fe3+ > Mg2+ > Fe2+ > Na+ < K+. This ordering is consistent with experimental observation. The vibrational frequencies for the isomorphous substituted systems were calculated by LDF calculation and were compared with the experimental IR results. The results match very well with experiment. This understanding will help in successful prediction of the catalytic activity of smectite clays.

Aluminum Silicates↗
PubMed1996

Prediction of high-frequency electron paramagnetic resonance spectra of spin S = 3/2, 5/2 systems.

By the use of the universal EPR simulation program created by the author, spin S = 3/2 and S = 5/2 systems are studied and their simulated EPR spectra at high frequencies (Q-band for 35 GHz and W-band for 95 GHz) are presented here. The mononuclear Fe3+ in rubredoxin, isolated from Pseudomonas oleovorans (which is an S = 5/2 system with D = 1.76 cm-1 and E/D = 0.28), is extensively studied by EPR spectrum simulation at the Q-band, W-band, and "Z"-band. The molybdenum- and iron-containing protein (MoFe protein), which has g values at g = 4.32, 3.65, and 2.01 (S = 3/2, D = 6.0 cm-1, and E/D = 0.055) at the X-band, is also studied by EPR spectrum simulation at high frequencies.

Computer Graphics↗
PubMed1996

Why spin = 1, 2 species have no electron paramagnetic resonance signal under normal conditions: possible detection by electron paramagnetic resonance at frequency close to D value?

A universal EPR simulation program has been created by the author, which is based on the following spin Hamiltonian equation: [equation: see text] where D and E are the axial and rhombic zero-field splitting parameters, respectively. The program can be used for simulation of EPR spectra with half-integer electronic spin (S = n/2, n = 3, 5, 7, 9) systems. In this article, the integer spin (S = n/2, n = 2, 4) systems are also considered. The EPR simulation results show that when D > frequency, no EPR signal can be seen from EPR simulation; when D approximately frequency, whichever X/Q/W-band is used, the EPR signal can be seen on the basis of the simulated EPR results presented.

Computer Graphics↗
PubMed1996

Analytically defined surfaces to analyze molecular interaction properties.

Molecular surfaces are widely used for characterizing molecules and displaying and quantifying their interaction properties. Here we consider molecular surfaces defined as isocontours of a function (a sum of exponential functions centered on each atom) that approximately represents electron density. The smoothness is advantageous for surface mapping of molecular properties (e.g., electrostatic potential). By varying parameters, these surfaces can be constructed to represent the van der Waals or solvent-accessible surface of a molecular with any accuracy. We describe numerical algorithms to operate on the analytically defined surfaces. Two applications are considered: (1) We define and locate extremal points of molecular properties on the surfaces. The extremal points provide a compact representation of a property on a surface, obviating the necessity to compute values of the property on an array of surface points as is usually done; (2) a molecular surface patch or interface is projected onto a flat surface (by introducing curvilinear coordinates) with approximate conservation of area for analysis purposes. Applications to studies of protein-protein interactions are described.

Computer Graphics↗
PubMed1996

Knowledge-based modeling of a legume lectin and docking of the carbohydrate ligand: the Ulex europaeus lectin I and its interaction with fucose.

Ulex europaeus isolectin I is specific for fucose-containing oligosaccharide such as H type 2 trisaccharide alpha-L-Fuc (1-->2) beta-D-Gal (1-->4) beta-D-GlcNAc. Several legume lectins have been crystallized and modeled, but no structural data are available concerning such fucose-binding lectin. The three-dimensional structure of Ulex europaeus isolectin I has been constructed using seven legume lectins for which high-resolution crystal structures were available. Some conserved water molecules, as well as the structural cations, were taken into account for building the model. In the predicted binding site, the most probable locations of the secondary hydroxyl groups were determined using the GRID method. Several possible orientations could be determined for a fucose residue. All of the four possible conformations compatible with energy calculations display several hydrogen bonds with Asp-87 and Ser-132 and a stacking interaction with Tyr-220 and Phe-136. In two orientations, the O-3 and O-4 hydroxyl groups of fucose are the most buried ones, whereas two other, the O-2 and O-3 hydroxyl groups are at the bottom of the site. Possible docking modes are also studied by analysis of the hydrophobic and hydrophilic surfaces for both the ligand and the protein. The SCORE method allows for a quantitative evaluation of the complementarity of these surfaces, on the basis of molecular lipophilicity calculations. The predictions presented here are compared with known biochemical data.

Artificial Intelligence↗
PubMed1996

Modeling polysaccharides: present status and challenges.

The most recent tools that have been developed for modeling the three-dimensional features of polysaccharides and carbohydrate polymers are presented. The presentation starts with a description of the conformations of the monosaccharides, and of the flexible rings such as in the case of five-membered rings, and a thorough description of the conformational space that is available for a disaccharide unit, either in vacuo or in an aqueous phase. The extension to the modeling of the parent polysaccharides is addressed, based on the assumption that owing to the size and relative rigidity of the intervening monosaccharides units, the rotations at a particular linkage can be, under some conditions, considered as independent of nearest neighbor interactions. Appropriate modeling techniques are described that can provide insights into the dimensions of the chain in a solution which is best described as a random coil accompanied by the occurrence of local "helical" regions. With the help of such descriptors such as helical parameters, the ordered state of polysaccharide strands can be readily characterized. The generation of double or triple helices can be then attempted in order to explore the occurrence of such multi-stranded arrangements that may be energetically stable. The final step in the determination of the structure of polysaccharides in the ordered state, is the investigation of the interactions of different helices. This may lead to either the best arrangement(s) between two polymeric chains, or to the prediction of the dimensions, and the symmetry of a three-dimensional lattice. Some of the tools which have been developed should allow automatic scarches for meaningful correlations between structures and functions, through exploratory data analysis. Structure-function or structure-property correlation could be then used to model changes arising from structural alterations. This would open the field of polysaccharide engineering.

Carbohydrate Conformation↗
PubMed1997

Computed intraoperative navigation guidance--a preliminary report on a new technique.

OBJECTIVE: To assess the value of a computer-assisted three-dimensional guidance system (Virtual Patient System) in maxillofacial operations. DESIGN: Laboratory and open clinical study. SETTING: Teaching Hospital, Austria. SUBJECTS: 6 patients undergoing various procedures including removal of foreign body (n=3) and biopsy, maxillary advancement, and insertion of implants (n=1 each). INTERVENTIONS: Storage of computed tomographic (CT) pictures on an optical disc, and imposition of intraoperative video images on to these. The resulting display is shown to the surgeon on a micromonitor in his head-up display for guidance during the operations. MAIN OUTCOME MEASURES: To improve orientation during complex or minimally invasive maxillofacial procedures and to make such operations easier and less traumatic. RESULTS: Successful transferral of computed navigation technology into an operation room environment and positive evaluation of the method by the surgeons involved. CONCLUSIONS: Computer-assisted three-dimensional guidance systems have the potential for making complex or minimally invasive procedures easier to do, thereby reducing postoperative morbidity.

Adult↗
PubMed1997

Virtual reality for orthognathic surgery: the augmented reality environment concept.

PURPOSE: The objective of this study was to apply virtual reality technology to osteotomies of the facial skeleton. MATERIALS AND METHODS: Augmented reality can be considered a hybrid of virtual and real environment spaces, which are coregistered and simultaneously visualized. Using a see-through HMD (head-mounted display) and Interventional Video Tomography intraoperatively, partial visual immersion into a patient-related virtual data space augments the surgeon's perception as shown in an experimental study and clinical applications. RESULTS: Without limiting the surgical judgment, offering continuous observation of the operating field, the presented technology additionally provides visual access to invisible data of anatomy, physiology, and function and thus guarantees unencumbered and fluent surgery. CONCLUSION: Despite current shortcomings, augmented reality technology proved to be particularly well suited for use in osteotomies of the facial skeleton.

Anatomy, Cross-Sectional↗
PubMed2000

Human motor development and hand laterality: a kinematic analysis of drawing movements.

This study examines the developmental profiles of basic 'open-loop' drawing movements on the non-dominant hand (ND) in comparison with the dominant hand (D). Fifty-three right-handed children aged 7-14 years and 15 adults aged 27-43 years were examined. Each subject drew lines and circles of different sizes at maximum velocity with a pressure-sensitive pen on a computer graphics tablet. Small lines were drawn at 90 degrees to the axis of the forearm (lines using wrist movements (LWM)) and along the axis of the forearm (lines using elbow movements (LEM)). Larger lines were drawn at 90 degrees to the axis of the forearm (LEM). At both extremities, the movement frequencies of the proximally generated drawing movements increased in a parallel fashion at different levels. In LWM, the right-left-differences (RLD) were high in 7- to 8-year-old children; until puberty, the ND hand reached almost the performance of the D hand. In contrast, the RLD of the LFM increased at the same time. As adulthood approaches, frequencies of all drawings increased further while the LWM on the ND side remained stable. In adults, there were similar RLD for all line drawings involving predominantly flexion and extension movements. When drawing circles, the RLD were highest, though stable in all age groups. Hand laterality of pen use changes over time; these changes are dependent on complexity (combined/sequential cf. flexion-extension muscle activation) and on topography (proximal cf. distal movements). Distinct developmental profiles of motoneuronal populations of the cortex may be responsible for the distinct hand laterality effects and the decreasing variability of motor patterns. The drawing abilities and developmental changes on the untrained ND hand indicate that effector-specific practice plays a minor role.

Adolescent↗
PubMed1984

Preliminary study of the upper limb with the use of ultrasound transmission imaging.

A biologically safe, noninvasive method for visualizing bone and soft tissue relationships has been developed recently. Termed the ultrasonic transmission imaging system, its advantages include visualization of soft tissues in real time while motion is underway. The image can be correlated to standard x-ray films, but since no ionizing radiation is involved, repeated risk-free visualization of extremities for either diagnostic assessment or biomechanical studies is permitted. Resolution of 1 mm and a depth of field of 8 mm are adequate for visualization of neurovascular bundles, tendons, ligaments, bones, and joints. The image can be digitized and stored for later analysis on computer graphic systems. Pilot studies have correlated the ultrasonic anatomy of normal and abnormal living and cadaver hands with known anatomic structures. The benefits to biomechanical analysis include the ability to visualize and accurately measure in a noninvasive manner the in vivo changes of position of tendons and other structures during movement. These initial efforts indicate the growing diagnostic and analytic capabilities of this instrument.

Evaluation Studies as Topic↗
PubMed1986

Computer analysis of optokinetic nystagmus for clinical usefulness.

A computer program was developed for on-line analysis of nystagmus parameters using a microcomputer (SORD M243EX). In this paper, the clinical utilities of microcomputer analysis of optokinetic nystagmus (OKN) were described, and quantitative analysis of each parameter of OKN was performed in 20 normal subjects and 49 patients with central nervous system (CNS) disorders. The average gain was accurately measured and the maximal stimulus velocity during which time the gain was more than 0.8, was termed as the "optokinetic adaptation limit (OAL)," and used as a clinical index for evaluation of OKN abnormalities. All patients in the present study showed a remarkable decrease in OAL. The differences in OAL among these patients at each level of lesion site, however, proved to be statistically insignificant. The relationship between the direction of OKN limitation and the lesion side was investigated. In all patients who had lesions on the thalamus, midbrain, and cerebellum, OKN limitation was observed toward the lesion side. The OKN limitation, however, was seen toward the intact side in 7 of 11 patients with medullary lesions and in 2 of 11 patients with cerebellopontine angle (CPA) tumors. hence, OKN in a useful diagnostic tool for the assessment of infratentorial lesions and computer analysis of OKN may be clinically useful.

Brain Diseases↗
PubMed2001

Measuring extraocular muscle volume using dynamic contours.

The effect of medical treatment on extraocular muscle enlargement in thyroid associated ophthalmopathy (TAO) may be monitored by measuring the change in volume of the extraocular muscles on serial orbital MRI examinations. In theory, 3D image sets offer the opportunity to minimise errors due to poor repositioning and partial volume effects. This study describes an automated technique for estimating extraocular muscle volumes from 3D datasets. Operator input is minimal and the technique is robust. Verification of the technique on both simulated and real datasets is described. For simulated image sets, both automated segmentation and manual outlining produced estimates of volume which were on average 4% less than "true" volume. For real patient data, extraocular muscle volumes measured by the automated technique were 1.6% (SD 13%) less than volumes measured by manual outlining. Coefficient of variation for repeat outlining of the same image dataset for the automated technique was 1.0%, compared with 4% for manual outlining. The manual technique took an experienced operator approximately 20 min to perform, compared to 7 min for the automated technique. The automated method is therefore rapid, reproducible and at least as accurate as other available methods.

Algorithms↗
PubMedDate not supplied

A new method for estimating T2 distributions from NMR measurements.

A semi-continuous relaxation model is constructed using sums of gamma functions and non-negative least squares for the inversion of Carr-Purcell-Meiboom-Gill (CPMG) echo data. No regularization is necessary for this approach, and yet the solution is stable even with noisy data. Test results derived from 60 echo trains are presented. Computational advantages of the method are presented.

Computer Graphics↗
PubMed1999

Computer-assisted animation of atrial tachyarrhythmias recorded with a 64-electrode basket catheter.

OBJECTIVES: The aim of this study was to assess the value of a new mapping technique based on computer-assisted animation of multielectrode basket catheter (BC) recordings in patients with atrial arrhythmias. BACKGROUND: The three-dimensional activation patterns of cardiac arrhythmias are not completely understood owing to limitations of conventional mapping techniques. METHODS: The study included 32 patients with atrial tachycardia (AT) and 38 patients with atrial flutter (AFL). A software program was developed to analyze the activation patterns based on 56 bipolar electrograms recorded with a 64-electrode BC deployed in the right atrium (RA). RESULTS: The total time needed for the animation of activation patterns of atrial arrhythmias was 5 +/- 0.8 min. In 22 patients with right AT, the animated maps revealed that arrhythmia was unifocal in 15 patients, multifocal in 2 patients, polymorphic in 4 patients and reentrant in 1 patient. In 10 patients with left AT, breakthroughs on the right side of the septum (2 in 8 patients and 1 in 2 patients) and a left-to-right activation of the RA were demonstrated. In patients with typical AF, the reentrant excitation was a broad activation front with preferential propagation around the tricuspid annulus. In patients with atypical AFL, the reentry circuit involved one of the venae cavae and a line of block located in the posterior wall. CONCLUSIONS: The computer-assisted animation of multiple electrograms recorded with a BC is a valuable mapping tool that delineates the three-dimensional activation patterns of various atrial arrhythmias. The technique is appropriate for complex, short-lived or unstable arrhythmias.

Adult↗
PubMed1987

[Programmed injection of liquid volatile anesthetics into the system. A plea for a tightly closed circuit].

Severinghaus et Lowe have given us a precise means of knowing what the patient's anaesthetic needs are under volatile anaesthesia. The parameters of the well-known formula for calculating the unit dose, Qan = 2 [Qc (dl).lambda.1.3 MAC], are recorded in the microprocessor of a computerized syringe: 1) the patient's body weight to the power 0.75 and multiplied by 2, i.e. cardiac output (Qc); 2) the nature of the selected volatile, i.e. the product of elements other than the Qc. The microprocessor calculates also the rate per minute according to the information obtained from the clock and the principle that the rate of anaesthetic is inversely proportional to the square root of the time the anaesthesia lasts. A numerical panel gives information on the following: injection time, injected anaesthetic volume per minute, cumulative quantity of liquid anaesthetic injected. The syringe is set in such a manner as to face upwards to prevent the development of bubbles. A rapidly stable alveolar concentration is obtained, proving Lowe right.

Anesthesia, Closed-Circuit↗
PubMed1999

Potpourri II.

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Computer Graphics↗