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At least 1,441 records · Page 80Linked to original sources
PubMed2002

The study on automorphism group of ESESOC.

It is necessary to generate the automorphism group of a chemical graph in computer-aided structure elucidation. In this paper, an algorithm was developed by the all-paths topological symmetry algorithm to build the automorphism group of a chemical graph. A comparison of several topological symmetry algorithms reveals that the all-paths algorithm (APA) could yield the correct class of a chemical graph. It lays a foundation for the ESESOC system in computer-aided structure elucidation.

Journal Article↗
PubMed1997

Analysis of forces developed during obturations. Comparison of three gutta-percha techniques.

The aim of this study was to compare the forces developed during three obturation techniques: warm vertical compaction (WVC), lateral condensation (LC), and thermomechanical compaction (TMC). A force-analyzer device allowed us to record and analyze the forces exerted during the obturations. The different methods, which varied in instrumentation, duration, and compaction load, were studied from graphs representing the force application sequences. In addition, the graphs resulting from specific modifications in the LC technique (use of a single spreader) and deliberately induced failures with TMC (with a too-small condensor or with excessive load) were analyzed. The mean values for the vertical forces for WVC, LC, and TMC were, respectively, 2.5 +/- 0.4 kg, 1.1 +/- 0.3 kg, and 1.65 +/- 0.2 kg. The mean values for the lateral forces were, respectively, 0.85 +/- 0.2 kg, 0.35 +/- 0.1 kg, and 0.5 +/- 0.2 kg. The use of graphs provides a new approach to the analysis of obturation methods and may find its greatest application in the teaching of these techniques. It also has the potential to improve research into obturation technique.

Analysis of Variance↗
PubMed1998

Analysis of forces developed during obturations. Wedging effect: Part II.

The aim of this study was to use a force analyzer device, the modified Endographe with a new cupule, to compare the forces and wedging effects developed in the root canal using four obturation techniques: warm vertical compaction, lateral condensation, thermomechanical compaction, and Thermafil condensation. The different methods--that varied in instrumentation, duration, and compaction load--were studied from graphs representing the force application sequences. In addition, the graphs resulting from modifications in technique (such as using an undersized spreader and pluggers that were either too small or too big) and deliberately induced failures in technique (by use of a too small condenser or a too small master cone) were studied. The mean values for the wedging effect for warm vertical compaction, lateral condensation, thermomechanical compaction, and Thermafil condensation were, respectively, 0.65 +/- 0.07 kg, 0.8 +/- 0.1 kg, 0.6 +/- 0.08 kg, and 0.03 +/- 0.01 kg. The use of graphs provides a new approach to the analysis of obturation techniques.

Analysis of Variance↗
PubMed2002

A new WIN32 computer program for estimating immunoassay variance functions.

A new WIN32 computer program for estimating immunoassay variance functions is described. It replaces and enhances an MS-DOS version written more than a decade ago. Input data can consist of either runs of raw replicated measurements (maximum: 40,000 observations) or sets of values of N, mean and SD (maximum: 20,000 sets). Data can be imported from Paradox, dBase, Foxpro or Access database tables, from text files, or via the Windows clipboard. The program produces histogram plots of sets of replicates and plots containing up to 12 variance functions expressed in terms of variance, SD or CV(%) versus the mean (imprecision profiles). Any specified view of a variance function graph can be inset into any other view. Interactive point and click design dialogues give virtually complete control over graph appearance. Graphs can be exported to external applications via the clipboard or disk files, in either bitmap or Windows enhanced metafile format.

Analysis of Variance↗
PubMedDate not supplied

Conducting and interpreting interface pressure evaluations of clinical support surfaces.

Interface pressure measurement is a common method to compare various mattresses, operating room beds, or other clinical support surfaces used for patients. The colorful graphs create a good visual display of information. Unfortunately, no standard method exists for performing the measurements or displaying the information. Because the graph is such a good visual representation of the data, many clinicians rely on the look of the graph. However, altering its appearance by simple manipulations of the display characteristics is very easy. This manipulation can lead to inaccurate conclusions about the product and consequent purchase of products that are inappropriate, less effective, or more expensive than others. This article provides basic information about interface pressure measurement and interpretation so that clinicians can make informed decisions about various clinical surfaces.

Beds↗
PubMed2001

Graphical presentation of the range of hip and knee rotations for clinical evaluation of gait.

OBJECTIVE: This paper reports a method of using a multi-axis graph to represent the range of rotations at the hip and knee joints during gait for clinical evaluation of a patient's performance. DESIGN AND METHODS: The multi-axis graph uses 12 symmetrically arranged axes to represent each component of range of rotations at the hip and knee joints of both legs. The range of joint rotations of thirteen normal subjects and two patients were measured using an electromagnetic motion tracking system with four foot switches. RESULTS: The range of joint rotations of normal subjects shows a symmetrical star in the multi-axis graph. Abnormal function of a patient shows an asymmetrical star. CONCLUSIONS: This representation provides a simple way to examine a patient's performance in a time effective manner. Relevance. In clinical practice, the multi-axis representation of joint rotations can be used as an initial evaluation of a patient's performance to identify problems for further investigation.

Adult↗
PubMedDate not supplied

Diagrammatic representations for modelling biological knowledge.

The contemporary research and development context in multidisciplinary biology has a serious requirement for integrating knowledge from disparate sources, and facilitating much-needed inter- and intra-disciplinary dialogue. A multiplicity of models arises when pluralistic approaches to modelling are followed, and also when there is not only a requirement to model systems and data, but also knowledge of systems and data. The challenges of addressing this multiplicity do not only include articulating the structure of complex systems, but also placing modelling within the framework of a process as well as a product. The graph representations presented here facilitate dialogue, modelling, clarification and specification of concepts, and the sharing of terms. This paper explores relationships between collections of graph representations. It is hoped that in future, when readers look at a node or a process in a graph, they will have a much deeper appreciation of relationships and context.

Data Display↗
PubMed1979

Spectrofluorimetric determination of dipyridamole in serum--a comparison of two methods.

Two spectrofluorimetric methods for the determination of dipyridamole in plasma are described. The thin-layer chromatographic-fluoridensitometric method utilizes 1 ml of plasma which is extracted at pH 10 with diethyl ether-dichloromethane (80:20). The organic phase is evaporated to dryness, reconstituted in 250 microliter dichloromethane and 5 microliter are spotted on a silica gel 60 plate. The plate is developed in ethyl acetate-methanol-ammonia (85:10:5), dried, dipped in a paraffin wax solution, dried, and scanned using 380 nm as excitation wavelength, a 430 nm cut-off filter, and collecting all emitted light on the photomultiplier. Quantitation was done by the external standard method, peak heights being measured and a calibration graph constructed. For the spectrofluorimetric method 1 ml of plasma is extracted at pH 10 with 8 ml of hexane-isoamyl alcohol (95:5) and the organic phase used directly for the measurement of the fluorescence intensity (excitation 405 nm, emission 495 nm). Quantitation was done by measuring the fluorescence of standards that were treated as above and constructing a calibration graph of concentration versus fluorescence intensity. Concentrations of unknowns were found by interpolation from this graph. The two methods were found to exhibit good correlation but the spectrofluorimetric method proved to be more amenable to the analysis of a large number of samples.

Chromatography, Thin Layer↗
PubMed2003

Novel map descriptors for characterization of toxic effects in proteomics maps.

We consider a novel numerical characterization of proteomics maps based on the construction of a graph obtained by connecting all protein spots in a proteomics map that are at distance equal to, or smaller than, a critical distance D(c). We refer to the so constructed graph as a cluster graph and we calculate four associated characteristic matrices, previously considered in the literature: (1) the Euclidean-distance matrix ED; (2) the neighborhood-distance matrix ND; (3) the path-distance matrix based on the shortest paths between connected spots PD; and (4) the quotient matrix Q, the elements of which are given as the quotient of the corresponding elements of ED and ND matrices. Numerical descriptors for proteomics maps include in particular the leading eigenvalue of the Q matrix and the family of associated "higher order" matrices defined as powers of Q. These map descriptors show considerable sensitivity to perturbations of proteomics maps by toxicants.

Animals↗
PubMed1997

Clique-detection algorithms for matching three-dimensional molecular structures.

The representation of chemical and biological molecules by means of graphs permits the use of a maximum common subgraph (MCS) isomorphism algorithm to identify the structural relationships existing between pairs of such molecular graphs. Clique detection provides an efficient way of implementing MCS detection, and this article reports a comparison of several different clique-detection algorithms when used for this purpose. Experiments with both small molecules and proteins demonstrate that the most efficient of these particular applications, which typically involve correspondence graphs with low edge densities, is the algorithm described by Carraghan and Pardalos. This is shown to be two to three times faster than the Bron-Kerbosch algorithm that has been used previously for MCS applications in chemistry and biology. However, the latter algorithm enables all substructures common to a pair of molecules to be identified, and not just the largest ones, as with the other algorithms considered here. The two algorithms can usefully be combined to increase the efficiency of database-searching systems that use the MCS as a measure of structural similarity.

Algorithms↗
PubMed2004

Raman anisotropic bandwidth study of C=O stretching vibration of methyl isobutyl ketone: role of van der Waals' volume of the interacting systems.

The bandwidth (FWHM) of the anisotropic component (Gamma(aniso)) of methyl isobutyl ketone (MIBK) for different concentrations of solvents varying from 10 to 90% was measured and was plotted as a function of solvent concentrations. In lower solvent concentration, the graph shows a curvature with a discontinuity which occurs between 40 and 60% and in higher solvent concentration, the graph shows a straight line for most of the solvents. In order to interpret the complicated behaviour we have taken into accounts the van der Waals' volume (V(w)) of the sphere of influence in solute dissolved in all solvents. Considering the role of van der Waals' volume in these systems the parameter Gamma(omega)=ln(Gamma(aniso)/V(w)) was plotted at different solvent concentrations. The graph shows a straight line for the entire region. In order to study the influence of screening effect on the bandwidth, the capacitances of the liquid mixture at different solvent concentrations varying from 10 to 90% were measured for all the solvents. The plot of capacitance at different solvent concentrations for each solvent shows a discontinuity around 50% of solvent concentration.

Anisotropy↗
PubMed2002

Birth weight by gestational age for Albertan liveborn infants, 1985 through 1998.

OBJECTIVES: (1) To provide percentile tables and graphs of birth weight by gestational age and by gender, for singleton and twin liveborn neonates. (2) To determine changes in birth weight relative to gestational age over the study period. METHODS: Data on 556,775 singletons and 12,125 twins, born alive in Alberta from 1985 through 1998, were obtained from Alberta Registries - Vital Statistics. Mean birth weights for individual and grouped years were compared by independent two-tailed t-tests. Linear trends in birth weight over the 14-year period were obtained using one-way analyses of variance. RESULTS: Four tables and corresponding graphs showing birth weight for gestational age by gender for 21 through 44 completed weeks gestation provide data for the 1st to 99th percentile. Changes in birth weight for the combined gestational ages included an increase for singletons (male, F 17.6, p < 0.001; female, F 53.3, p < 0.001), and a decrease for female twins (F 5.8, 0.004). The increase for singletons was seen at 38 through 42 weeks gestation for both genders. No change occurred under 38 weeks except in singleton females of 33 to 35 weeks with a decrease in birth weight observed from 2636 +/- 539 g, 1985 to 2576 +/- 479 g, 1998; t 2.5, p = 0.002. CONCLUSIONS: The graphs and tables established in this study represent a specific geographic area and population. They may be relevant as a reference for other geographic regions and populations. The clinical significance of the observed increased birth weight among term, but not preterm newborns, requires critical evaluation.

Adult↗
PubMedDate not supplied

Downstream process synthesis for biochemical production of butanol, ethanol, and acetone from grains: generation of optimal and near-optimal flowsheets with conventional operating units.

Manufacturing butanol, ethanol, and acetone through grain fermentation has been attracting increasing research interest. In the production of these chemicals from fermentation, the cost of product recovery constitutes the major portion of the total production cost. Developing cost-effective flowsheets for the downstream processing is, therefore, crucial to enhancing the economic viability of this manufacturing method. The present work is concerned with the synthesis of such a process that minimizes the cost of the downstream processing. At the outset, a wide variety of processing equipment and unit operations, i.e., operating units, is selected for possible inclusion in the process. Subsequently, the exactly defined superstructure with minimal complexity, termed maximal structure, is constructed from these operating units with the rigorous and highly efficient graph-theoretic method for process synthesis based on process graphs (P-graphs). Finally, the optimal and near-optimal flowsheets in terms of cost are identified.

Acetone↗
PubMedDate not supplied

On finding nonisomorphic connected subgraphs and distinct molecular substructures.

The problem of finding all nonisomorphic subgraphs of a given graph (all distinct substructures of a given molecular structure) is discussed. A computer program is introduced that first generates all connected subgraphs and then uses a combination of well-discriminating graph invariants to eliminate duplicates. The program is broadly applicable, in particular for molecular graphs which may or may not contain unsaturation or heteroatoms. The number of distinct substructures (Ns), proposed earlier as a measure of a compound's complexity which takes into account its symmetry, is thus automatically obtained. As was to be expected, due to the nature of the problem the computational effort increases exponentially with problem size, whence in most cases complexity measures other than Ns are to be preferred.

Journal Article↗
PubMedDate not supplied

The overall Wiener index--a new tool for characterization of molecular topology.

Recently, the concept of overall connectivity of a graph G, TC(G), was introduced as the sum of vertex degrees of all subgraphs of G. The approach of more detailed characterization of molecular topology by accounting for all substructures is extended here to the concept of overall distance OW(G) of a graph G, defined as the sum of distances in all subgraphs of G, as well as the sum of eth-order terms, (e)OW(G), with e being the number of edges in the subgraph. Analytical expressions are presented for OW(G) of several basic classes of graphs. The overall distance is analyzed as a measure of topological complexity in acyclic and cyclic structures. The potential usefulness of the components of this generalized Wiener index in QSPR/QSAR is evaluated by its correlation with a number of properties of C3-C8 alkanes and by a favorable comparison with models based on molecular connectivity indices.

Journal Article↗
PubMedDate not supplied

Step-by-step calculation of all maximum common substructures through a constraint satisfaction based algorithm.

In this paper we propose a new algorithm for subgraph isomorphism based on the representation of molecular structures as colored graphs and the representation of these graphs as vectors in n-dimensional spaces. The presented process that obtains all maximum common substructures is based on the solution of a constraint satisfaction problem defined as the common m-dimensional space (m< or =n) in which the vectors representing the matched graphs can be defined.

Journal Article↗
PubMedDate not supplied

From Wiener index to molecules.

In this paper we present an algorithm for the generation of molecular graphs with a given value of the Wiener index. The high number of graphs for a given value of the Wiener index is reduced thanks to the application of a set of heuristics taking into account the structural characteristics of the molecules. The selection of parameters as the interval of values for the Wiener index, the diversity and occurrence of atoms and bonds, the size and number of cycles, and the presence of structural patterns guide the processing of the heuristics generating molecular graphs with a considerable saving in computational cost. The modularity in the design of the algorithm allows it to be used as a pattern for the development of other algorithms based on different topological invariants, which allow for its use in areas of interest, say as involving combinatorial databases and screening in chemical databases.

Journal Article↗
PubMedDate not supplied

ErG: 2D pharmacophore descriptions for scaffold hopping.

An extended reduced graph approach (ErG) is presented that uses pharmacophore-type node descriptions to encode the relevant molecular properties. The basic idea of the method can be described as a hybrid approach of reduced graphs (Gillet et al. J. Chem. Inf. Comput. Sci. 2003, 43, 338-345) and binding property pairs (Kearsley et al. J. Chem. Inf. Comput. Sci. 1996, 36, 118-127). However, specific extension modifications to correctly describe the pharmacophoric properties, size, and shape of the molecules under study result in a very stable and good performance as compared to DAYLIGHT fingerprints (DFP). This is exemplified for 11 activity classes of the MDL Drug Data Report database, for which ErG performs as well or better than DFP in 10 cases. On the basis of the example data sets, the ability of ErG to switch from one chemotype to another (often referred to as "scaffold hopping") is highlighted. Additionally, possible pitfalls of reduced graph approaches as well as suitable solutions are discussed with the help of example structures. Overall, it is shown that ErG is a widely applicable method capable of identifying structurally diverse actives for a given active search query. This diversity is achieved by a high degree of molecular abstraction, which in turn results in a low dimensional descriptor vector that allows very low computation times for similarity searches.

Journal Article↗