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At least 1,729 records · Page 96Linked to original sources
PubMed1995

A modified ROC analysis for the selection of cut-off values and the definition of intermediate results of serodiagnostic tests.

A total number of 50 sera from clinically confirmed cases of canine Borrelia (B.) burgdorferi infection and 44 negative control sera were tested with a B. burgdorferi specific antibody ELISA. The data were submitted to the 'two-graph receiver operating characteristic' (TG-ROC) analysis which is a plot of the test sensitivity (Se) and specificity (Sp) against the threshold (cut-off) value assuming the latter to be an independent variable. Thus, in contrast to the conventional ROC analysis, valid pairs of Se and Sp can be read for pre-assigned threshold values directly from the TG-ROC plots. A cut-off that realises equal test parameters (Se = Sp = theta 0 (theta-zero)) can be obtained as the intersection point of the two graphs. Since the value for theta 0 is below a preselected accuracy level (95% or 90%), two cut-off values are selected that represent the bounds of an 'intermediate range' (IR). IR can be considered as a 'borderline' range for the clinical interpretation of test results. The proportion of the measurement range (MR) that gives unambiguous test results can be expressed using IR as the 'valid range proportion' (VRP = (MR-IR)/MR). VRP and theta 0 are useful parameters for test comparison since they do not depend upon the selection of a single cut-off point. In addition, the selection of cut-off values is supported by graphical displays of efficiency, Youden's index and likelihood ratios which can be considered as functions of the pre-assigned cut-off value. TG-ROC was derived as a user-defined template for a commercially available spreadsheet programme (MS-EXCEL, Microsoft).

Animals↗
PubMed1992

Influence of tooth contact on the path of condylar movements.

The correlation between condylar inclination and tooth guidance was tested by comparison of recordings of condylar movement in right and left parasagittal planes during lateral excursion, opening, and protrusive movements in 13 subjects with temporomandibular joint (TMJ) clicks and 15 subjects without TMJ clicks. The characteristic tracing of mandibular movements at the condyle with tooth-guided versus non-tooth-guided conditions were investigated by use of a computerized Axiograph graph. The generated tracings of each subject were graphed and analyzed to calculate the horizontal condylar inclinations as related to the axis orbital reference plane. Information from a standardized questionnaire provided evidence of a definite correlation between the presence of TMJ clicking and a specific prior medical event (tonsillectomy). The data from computerized tracings of all subjects revealed no significant difference (p 0.05) in the mean angles of condylar guidance at any of the millimeter intervals examined regardless of whether the craniomandibular contact was an articulation of natural teeth or an articulation of maxillary natural teeth against a tray clutch. These results do not suggest that dynamic interarch tooth guidance or the change in vertical dimension reflect a significant alteration in the recordings of condylar guidance in clicking or nonclicking groups.

Adolescent↗
PubMed1990

Topological analysis of metabolic control.

A topological approach is presented for the analysis of control and regulation in metabolic pathways. In this approach, the control structure of a metabolic pathway is represented by a weighted directed graph. From an inspection of the topology of the graph, the control coefficients of the enzymes are evaluated in a heuristic manner in terms of the enzyme elasticities. The major advantage of the topological approach is that it provides a visual framework for (1) calculating the control coefficients of the enzymes, (2) analyzing the cause-effect relationships of the individual enzymes, (3) assessing the relative importance of the enzymes in metabolic regulation, and (4) simplifying the structure of a given pathway, from a regulatory viewpoint. Results are obtained for (a) an unbranched pathway in the absence of feedback the feedforward regulation and (b) an unbranched pathway with feedback inhibition. Our formulation is based on the metabolic control theory of Kacser and Burns (1973) and Heinrich and Rapoport (1974).

Enzymes↗
PubMed1991

The principle of interval constraints: a generalization of the symmetric Dirichlet distribution.

A structure for representing problems in decision analysis and in expert systems, which reason under uncertainty, is the influence diagram or causal network. A causal network consists of an underlying joint probability distribution and a directed acyclic graph in which a propositional variable that represents a marginal distribution is stored at each vertex in the graph. This paper is concerned with two of the problems in applications that use causal networks. The first problem is the determination of the conditional probabilities of the values of remaining propositional variables in the network given that certain variables are instantiated for particular values. This is called probability propagation. The second problem is the determination of the most probable, second most probable, third most probable, and so on sets of values of a particular set of variables (called the explanation set) given that certain variables are instantiated for particular values. This problem is called abductive inference. There exists a class of causal networks in which each variable has only two parents, for which the time is required, by any known method, for probability propagation is exponential relative to the number of vertices in the network. The determination of a new method that would be efficient for all causal networks appears unlikely, because probability propagation has been shown to be #P-complete. In many medical applications, networks are often large and not sparsely connected. Therefore a method for the exact determination of probability values appears unlikely for such applications, and the development of approximation methods seems to be the best solution. The current approximation methods obtain interval bounds for the probability values. When such intervals are obtained, it is not possible in general to rank the alternatives. In this paper, a method is developed for obtaining expected values for the point probabilities from interval constraints on the probabilities. The method is based on an application of the principle of indifference to the probability values themselves. The distributions obtained with the principle of indifference are a generalization of the symmetric Dirichlet distribution in which prior ignorance is assumed.

Decision Making↗
PubMed1996

Measures of concurrency in networks and the spread of infectious disease.

An investigation is made into the impact of concurrent partnerships on epidemic spread. Starting from a definition of concurrency on the level of individuals, the authors define ways to quantify concurrency on the population level. An index of concurrency based on graph theoretical considerations is introduced, and the way in which it is related to the degree distribution of the contact graph is demonstrated. Then the spread of an infectious disease on a dynamic partnership network is investigated. The model is based on a stochastic process of pair formation and separation and a process of disease transmission within partnerships of susceptible and infected individuals. Using Monte Carlo simulation, the spread of the epidemic is compared for contact patterns ranging from serial monogamy to situations where individuals can have many partners simultaneously. It is found that for a fixed mean number of partners per individual the distribution of these partnerships over the population has a major influence on the speed of the epidemic in its initial phase and consequently in the number of individuals who are infected after a certain time period.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Xeroradiography in root fracture diagnosis.

Root fracture is a clinical problem that often is difficult to diagnose. The purpose of this study was to compare diagnostic value of conventional radiographic and xeroradiographic images of experimentally fractured teeth. Forty-five extracted human single-rooted teeth were used. The roots of the teeth were coated with wax to simulate periodontal ligament and invested in acrylic to the cementoenamel junction. An access cavity was prepared and para-post, size 4 to 12 mm, was placed into the root canal. Each tooth with post was placed on the load cell table of an Instron testing machine. The Instron continuously recorded load on a moving graph paper. The load was increased until the tooth fractured. Determination of fracture was made by the sound of a sharp "crack" and by a sudden release of load on the post, as seen on the Instron recording graph. After fracture, conventional radiograph and xeroradiograph were obtained for each tooth by use of the paralleling technique. The x-ray beam angle, film distance, and tooth placement were held constant in both techniques by use of a Rinn instrument. All films were evaluated by use of light from a masked viewbox, while all of the xeroradiographs were viewed in reflected light. A magnifying glass was used to aid in the examination process. The samples were examined and categorized for root fracture by the examiners with the use of the following scores: 0 = unacceptably poor, 1 = poor but diagnostic, 2 = adequate for diagnostic information, and 3 = optimal for diagnostic information.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Stress Analysis↗
PubMedDate not supplied

Genetic and environmental influences on lifespan and diseases in Han:Wistar rats.

In a longevity study with SPF rats of the Han:Wistar outbred stock, 320 virgin males and 320 virgin females of marked littermates were maintained in a barrier-type animal house under highly standardized conditions from weaning until their natural end of life. Diseased and dead animals were sectioned and examined using histological, bacteriological and virological methods. The mortality of the rats is low up to the 18th month of life. Thereafter the mortality graph inclines steadily. The course of the graph is determined by very few diseases only, such as pituitary adenomas in both sexes, adenocarcinomas of the uterine glands in the females, and in the third and fourth year nephropathies in the males. Because of the high number of adenocarcinomas of the uterine glands the median life expectancy is between 30 and 33 months for the females, somewhat lower than between the 33rd and the 36th months for the males. The disease spectrum consists generally of tumor lesions, but out of the large tumor spectrum only single alterations exceed the 5% border. As shown by analysis of variance and estimation of the heritability coefficients (h2), mortality and the most important tumorous lesions underlie high genetic effects. The cage environments are found to have no influence upon mortality and diseases. Under the given standardized environmental conditions, the present results can be looked upon--because of the strong genetic effects on mortality and diseases - to be representative for correspondingly selected populations of future generations of the Han:Wistar stock.

Animals↗
PubMed1987

Retinal wholemounts: a simple method for precise mapping.

A simple and inexpensive method to analyse retinal wholemounts is described. It allows the definition of regularly spaced sites to map regional specializations of the retina under light microscopy. After attaching a piece of translucent millimetre graph paper behind the slide holding the preparation, the two grid patterns of the graph paper and of the eye-piece grid are used in combination for the definition of sites for analysis and the return to specific areas as small as 50-100 microns2. The present method is simpler and offers several advantages when compared to others based on X-Y movements of the microscope stage or on photographic montage.

Evaluation Studies as Topic↗
PubMed1991

Methods for viral isolation and DNA extraction for a penaeid shrimp baculovirus.

Procedures for the purification of virions and nucleocapsids of Baculovirus penaei (BP) of penaeid shrimp and subsequent extraction of the viral nucleic acid are described. BP-infected hepatopancrata, from two species of shrimp from different geographical locations in the Americas, were removed and homogenized in a solution of TN buffer (0.01 M Tris-HCl, 0.10 M NaCl, pH 8.0). The homogenized mixture was strained through a 100-mesh screen to remove large pieces of tissue and centrifuged to concentrate the remaining material. The pellet was suspended in TN buffer and layered on to a handmade CsCl gradient. Fractions were collected according to the bands observed in the gradient, and the optical density at 254 nm was recorded for each fraction. The resultant data was tabulated and graphed. Additionally, each fraction was examined by transmission electron microscopy to determine relative numbers of viral particles present. Large amounts of virus consistently corresponded to a specific band in the gradient, which produced a peak when the spectrophometric data was graphed. Nucleic acid was then extracted from the purified viral particles. Removal of polysaccharides was accomplished with the addition of CTAB/NaCl. The BP DNA was visualized on an agarose gel with phage lambda DNA markers for size estimation, and a preliminary endonuclease digestion was performed using BamHI.

Animals↗
PubMed1986

The effect of bulk hydrogen ion concentration upon the apparent kinetic parameters of purified pig liver catechol O-methyltransferase.

In order to investigate the pH dependence of catechol O-methyltransferase (S-adenosyl-L-methionine:catechol O-methyltransferase, EC 2.1.1.6), kinetic parameters have been determined for the highly purified enzyme from pig liver over the pH range 6.75-8.20 using the substrates S-adenosylmethionine (AdoMet) and 3,4-dihydroxyphenylacetic acid (DOPAC). The Km for AdoMet was found to be invariant with pH while the Km for DOPAC decreased sharply with increasing pH. The group responsible for the latter has a pK of approx. 7.1. The logarithmic (Dixon) plot of Km against pH for both substrates and that of Vmax/Km against pH for DOPAC mirror the kinetic behaviour revealed by linear plots. However, for other parameters, linear graphs indicate peaks too narrow to be explicable by a simple kinetic mechanism, whereas logarithmic plots of these parameters produce graphs apparently not reflecting this behaviour. We conclude that these results are not the products of random error or artefactual data analysis but are too complex to be explicable by a simple model of kinetic behaviour. Possible explanations (adherence of catechol O-methyltransferase to a higher-order mechanism or a dual mode of substrate binding) are advanced.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1986

ODDC and MULTIGRAPH: programs for spectrophotometer data collection and manipulation using a microcomputer.

A software package is described that collects, graphs, performs peak sensing, and prints data from a spectrophotometer interfaced to an Apple II microcomputer with an ADALAB analog-to-digital converter card. Data collection and storage is performed by an interpreted BASIC program with machine language subroutines. Recalling, graphing, and printout of the data is accomplished by a separate compiled BASIC program. Both of these programs, as well as assisting utility programs, are under control of a menu program. The programs take advantage of all available memory in the 64-K Apple II computer to allow for storage of up to 12 600 data points (7 hours of data collection at a sampling rate of 1 sample every 2 s). As the data collection program provides peak sensing, and the capability of annotating various time points, the programs are ideally suited for use in column chromatography.

Chromatography↗
PubMed1987

Computer programs for the analysis of protein fluorescence quenching data.

Educational computer programs for analysis of fluorescence quenching studies of proteins have been developed. The program is written according to the classical Stern-Volmer equation and some modified Stern-Volmer equations. The static and dynamic quenching constants as well as the accessibility of the quencher molecules to the fluorescence groups are calculated. The experimental data are plotted on a high resolution graph. The calculated data or the graphs can be printed out to obtain a hard copy for filing.

Kinetics↗
PubMed1986

Graphical analysis of multivariate pain data in analgesic trials.

In order to compare analgesic treatments effectively one must measure pain over time. In a single-dose clinical analgesic trial one typically obtains repeated pain measurements from each patient during a relatively short period (4-6 hours). Such measurements constitute multivariate data, which are usually reduced by simple addition to a single derived pain measure for analysis of between-treatment differences. In this article we consider graphical procedures for the display of multivariate, clinical analgesic data. The first of these are the traditional time-effect curves, with added "standard error bars." We also examine a multivariate display, the biplot, which is based on principal component analysis. This technique provides a representation of the raw pain scores at each time of measurement by a vector originating from the origin of a two-dimensional graph. The multivariate pain scores of individual patients are summarized by points on the graph. Differences in pain scores over time (or between treatment groups) may be examined by relating points (or ellipses representing treatment groups) to different vectors. Using actual data from a postsurgical analgesic trial, we compare the two approaches and show that the multivariate approach is a useful addition to the standard technique for display of such data.

Analgesics↗
PubMed1994

Modification of aminoacyl-tRNA synthetases with pyridoxal-5'-phosphate. Identification of the labeled amino acid residues.

The isotopic [32P]PPi-ATP exchange activity of isoleucyl-, valyl-, histidyl-, tyrosyl- and methionyl-tRNA synthetases from Escherichia coli are lost upon incubation in the presence of pyridoxal-5'-phosphate (PLP). When the residual activity of either isoleucyl-, valyl- or methionyl-tRNA synthetase (monomeric truncated form) was plotted as a function of the number of PLP molecules incorporated per enzyme molecule, the plots obtained appeared biphasic. Below 50% inactivation of these enzymes, PLP incorporation varied linearly with the isotopic exchange measurements, and extrapolation of the first half of the plot indicated a stoichiometry of 1.10 +/- 0.05 mol of PLP incorporated per mol of 100% inactivated synthetase. Beyond 50% inactivation, the graph deviated from its initial slope, and up to 4-5 mol of PLP were incorporated per mol of synthetase at the highest used PLP concentrations. In the cases of homodimeric histidyl- and tyrosyl-tRNA synthetases, extrapolation of the graph at 100% inactivation indicated 2.8 +/- 0.1 and 2.4 +/- 0.1 mol of PLP incorporated per mol of enzyme, respectively. PLP-labeled peptides were obtained through trypsin digestion and RPLC purification, prior to Edman degradation analysis. PLP-labeled residues were identified as lysines 132, 332, 335 and 402 of monomeric methionyl-tRNA synthetase, lysines 332, 335, 402, 465, 596 and 640 of native dimeric methionyl-tRNA synthetase, lysines 22, 117, 601, 604 and 645 of isoleucyl-tRNA synthetase, lysines 554, 557, 559, 593 and 909 of valyl-tRNA synthetase, lysines 2, 118, 369 and 370 of histidyl-tRNA synthetase, and lysine 237 of tyrosyl-tRNA synthetase. In addition, the amino terminal residue of the polypeptide chain(s) of either isoleucyl-, valyl-, histidyl- or methionyl-tRNA synthetases was found labeled. Among these residues, lysines 332, 335 and 402 of monomeric methionyl-tRNA synthetase as well as lysines 332, 335, 402 and 596 of dimeric methionyl-tRNA synthetase, lysines 601, 604 and 645 of isoleucyl-tRNA synthetase, lysines 554, 557 and 559 of valyl-tRNA synthetase, lysines 2, 369 and 370 of histidyl-tRNA synthetase, and lysine 237 of tyrosyl-tRNA synthetase were labeled in the presence of PLP concentrations smaller than or equal to 1 mM, and are shown to be critical for the activity of the enzymes. It is concluded that these residues participate to the binding sites of the phosphates of ATP on the studied synthetases.

Amino Acid Sequence↗
PubMed1993

Computation of biopolymers: a general approach to different problems.

A comparative analysis of some effective algorithms widely used in analysis, computation and comparison of chain molecules is presented. A notion of a stream in an oriented hypergraph is introduced, which generalizes a notion of a path in a graph. All considered algorithms looking over exponential sets of structures in polynomial time can be described as variants of a general algorithm of analysis of paths in graphs and of streams in oriented hypergraphs.

Algorithms↗
PubMed1984

Na+/K+-ATPase from Xenopus laevis (Daudin) kidney and epidermis: high sensitivity towards regulatory compounds.

Na+/K+-ATPase was prepared from Xenopus laevis epidermis. Purification was obtained by ultracentrifugation on sucrose discontinuous gradient. The maximum of enzyme-containing membranes was concentrated in the denser sucrose layer, exhibiting a good and long-lasting activity (specific activity about 55 mumoles of ATP hydrolyzed/mg of protein/hour). The Kd for the ouabain of kidney and epidermis enzymes were very low (in purified preparations respectively 16 nM for kidney enzyme and 4 nM for skin enzyme), indicating a very high sensitivity toward the cardioglycoside. The dose-response graphs of kidney and skin Na+/K+-ATPase vs ouabain concentrations show that at ouabain concentrations ranging from 1 nM and 1 pM the inhibition elicited by the cardioglycoside disappears and is replaced by an activatory effect. At cardioglycoside concentrations higher than 1 nM, the graphs show the typical inhibition curve.

Animals↗
PubMed1985

Characterization of sheep liver and lung microsomal ethylmorphine N-demethylase.

Ethylmorphine N-demethylase activity of the sheep liver and lung microsomes was reconstituted in the presence of solubilized microsomal cytochrome P-450, NADPH-cytochrome c reductase and synthetic lipid, phosphatidylcholine dilauroyl. The Km of the lung microsomal ethylmorphine N-demethylase was calculated to be 4.84 mM ethylmorphine from its Lineweaver-Burk graph and lung enzyme was inhibited by its substrate, ethylmorphine, when its concn was 25 mM and above, reaching to 67% inhibition at 50 mM concn. The Lineweaver-Burk and Eadie-Hofstee plots of the liver enzyme were found to be curvilinear. From these graphs, two different Km values were calculated for the liver enzyme as 4.17 mM and 0.40 mM ethylmorphine. Ethylmorphine N-demethylase activities of both liver and lung microsomes were inhibited by NiCl2, CdCl2 and ZnSO4. Ethylalcohol inhibited N-demethylation of ethylmorphine in lung and liver microsomes. Acetone (5%) slightly enhanced the N-demethylase activity of the liver enzyme, whereas 5% acetone completely inhibited the lung enzyme. Phenylmethylsulfonyl fluoride at 0.10 mM and 0.25 mM concn had no effect on liver enzyme activity, while at these concns, it inhibited the activity of the lung enzyme by about 35%.

Acetone↗
PubMed1985

Aging of the immune system.

A review of the literature shows that the thymus is the major reason for aging of the immune system. A graph of the mouse thymus mass is linear with age after puberty. However, T cell function is determined by thymic hormone factors and serum thymic factors. The net result is that T cell function is so affected that there is a deficit in T cell responsiveness. For humans a graph of 1-I (I is immunological efficiency) versus age is a straight line on a semi-log plot. The slope of the line is about the same as the incidence of class I cancer incidence vs. age.

Aging↗