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At least 613 records · Page 34Linked to original sources
PubMed2001

Three-dimensional quantification of color-marked occlusal paths on anatomically oriented casts.

STATEMENT OF PROBLEM: The analysis of occlusal contacts on mounted diagnostic casts is an important task in prosthetic diagnostics. However, it is still restricted mainly to qualitative aspects because existing measuring techniques fail to provide 3-dimensional data for more than a few single points in acceptable time. PURPOSE: The aim of this study was to develop a method for quantifying occlusal contacts and paths by using anatomically oriented diagnostic casts and to design the method to allow fast acquisition of digital 3-dimensional coordinates. MATERIAL AND METHODS: Plaster casts with color-marked contacts were digitized optically with a profilometric system based on the fringe projection technique. Digital camera images taken simultaneously were used to define the contact areas by marking them either manually or automatically with the help of image-processing routines. Three-dimensional coordinates were determined by finding the corresponding points within the profilometric data set. RESULTS: Color-marked contact areas on diagnostic casts were successfully digitized with a computer-controlled, automatic setup in approximately 30 seconds. The accuracy of the acquired 3-dimensional data was estimated to be better than 60 microm in lateral and 30 microm in height resolution. The data set was visualized and evaluated in a skull related coordinate system. SUMMARY: This study verified the use of a new tool to quantify color-marked occlusal contacts on diagnostic casts in terms of spatial coordinates. The resulting digital data may be stored easily and analyzed numerically as well as visualized 3-dimensionally with computer graphic equipment. Because the anatomic orientation of the casts is maintained throughout the measurement process, it is possible to compare the data with electronically registered condyle paths and therefore to investigate, for example, their relation to the corresponding guidance paths of the frontal teeth and the canines in dynamic occlusion.

Color↗
PubMed2002

An enquiry into rainfall data measurement and processing for model use in urban hydrology.

Rain data are collected all over the world because water is of paramount importance to all human life. WMO has provided standards for collection and standardized data processing of daily rainfall measurements. Currently no such standards are available for gauges with a resolution suitable for urban hydrology, where the resolution in time must not exceed a few minutes. The Group on Urban Rainfall under the International Water Association has made a comparison of national standards by means of a survey of 77 questions sent to 44 countries. The paper discusses the first results of the answers of the survey. Currently tipping bucket gauges are the dominating method of obtaining high resolution rain data, but the numbers of weighing gauges and radar measurements are rapidly growing. It is necessary to try to increase the awareness of documentation of current standards and to agree on standards for measurements and data processing on an international level in the future.

Cities↗
PubMed2004

Assessing cortical functional connectivity by linear inverse estimation and directed transfer function: simulations and application to real data.

OBJECTIVE: To test a technique called Directed Transfer Function (DTF) for the estimation of human cortical connectivity, by means of simulation study and human study, using high resolution EEG recordings related to finger movements. METHODS: The method of the Directed Transfer Function (DTF) is a frequency-domain approach, based on a multivariate autoregressive modeling of time series and on the concept of Granger causality. Since the spreading of the potential from the cortex to the sensors makes it difficult to infer the relation between the spatial patterns on the sensor space and those on the cortical sites, we propose the use of the DTF method on cortical signals estimated from high resolution EEG recordings, which exhibit a higher spatial resolution than conventional cerebral electromagnetic measures. The simulation study was followed by an analysis of variance (ANOVA) of the results obtained for different levels of Signal to Noise Ratio (SNR) and temporal length, as they have been systematically imposed on simulated signals. The whole methodology was then applied to high resolution EEG data recorded during a visually paced finger movement. RESULTS: The statistical analysis performed returns that during simulations, DTF is able to estimate correctly the imposed connectivity patterns under reasonable operative conditions, i.e. when data exhibit a SNR of at least 3 and a length of at least 75 s of non-consecutive recordings at 64 Hz of sampling rate, equivalent, more generally, to 4800 data samples. CONCLUSIONS: Functional connectivity patterns of cortical activity can be effectively estimated under general conditions met in any practical EEG recordings, by combining high resolution EEG techniques, linear inverse estimation and the DTF method. SIGNIFICANCE: The estimation of cortical connectivity can be performed not only with hemodynamic measurements, by using functional MRI recordings, but also with modern EEG recordings treated with advanced computational techniques.

Analysis of Variance↗
PubMed2001

Correlation of topographic surface and volume data from three-dimensional electron microscopy.

Three-dimensional(3D) reconstructions from tilt series in an electron microscope show in general an anisotropic resolution due to an instrumentally limited tilt angle. As a consequence, the information in the z direction is blurred, thus making it difficult to detect the boundary of the reconstructed structures. In contrast, high-resolution topography data from microscopic surface techniques provide exactly complementary information. The combination of topographic surface and volume data leads to a better understanding of the 3D structure. The new correlation procedure presented determines both the height scaling of the topographic surface and the relative position of surface and volume data, thus allowing information to be combined. Experimental data for crystalline T4 bacteriophage polyheads were used to test the new method. Three-dimensional volume data were reconstructed from a negatively stained tilt series. Topographic data for both surfaces were obtained by surface relief reconstruction of electron micrographs of freeze-dried and unidirectionally metal-shadowed polyheads. The combined visualization of volume data with the scaled and aligned surface data shows that the correlation technique yields meaningful results. The reported correlation method may be applied to surface data obtained by any microscopic technique yielding topographic data.

Algorithms↗
PubMed2000

Probing contacts between the ribonuclease H domain of HIV-1 reverse transcriptase and nucleic acid by site-specific photocross-linking.

Cys(38) and Cys(280) of p66/p51 human immunodeficiency virus type 1 reverse transcriptase (HIV-1 RT) can be converted to Ser without affecting enzyme function. We have exploited this feature to construct and purify "monocysteine" RT derivatives for site-specific modification with the photoactivable cross-linking agent, p-azidophenacyl bromide. Acylation of a unique cysteine residue introduced at the extreme C terminus of the p66 subunit (C(561)) with an azidophenacyl group allowed us to probe contacts between residues C-terminal to alpha-helix E' of the RNase H domain and structurally divergent nucleic acid duplexes. In a binary complex of RT and template-primer, we demonstrate efficient cross-linking to primer nucleotides -21 to -24/-25, and template nucleotides -18 to -21. Cross-linking specificity was confirmed by an analogous evaluation following limited primer extension, where the profile is displaced by the register of DNA synthesis. Finally, contact with a DNA primer hybridized to an isogenic RNA or DNA template indicates subtle alterations in cross-linking specificity, suggesting differences in nucleic acid geometry between duplex DNA and RNA/DNA hybrids at the RNase H domain. These data exemplify how site-specific acylation of HIV-1 RT can be used to provide high resolution structural data to complement crystallographic studies.

Azides↗
PubMed2001

A new approach to data reduction and evaluation in high-resolution time-of-flight mass spectrometry using a time-to-digital convertor data-recording system.

A new effective and robust approach to the detection of incompletely resolved peaks, and evaluation of their parameters in high-resolution time-of-flight mass spectra for time-to-digital convertor (TDC) data acquisition mode, is described. The method is based on fast construction of a smoothed continuous curve that approximates the initial data (transformed to a constant relative width of time intervals for ion counting) with respect to precision of measurements. The first derivative of this curve is used for correction of skewness of the peak shape as far as possible. A contribution of the second derivative is subtracted from the smoothed curve for better resolution of partially resolved peaks. The comparison of local maxima of this resulting final curve with those for the initial smoothed curve allows reliable detection of the peaks and to test whether or not they are spoiled by overlapping. Ion counting performed by TDC gives an opportunity to estimate standard deviations of peak locations and their intensities. These values proved to be close to theoretically minimal standard deviations for these parameters for single fully resolved peaks. Thus, estimates of the main parameters of mass peaks by the described method are close to statistically efficient estimators for these parameters.

Journal Article↗
PubMed2003

Dehydration converts DsbG crystal diffraction from low to high resolution.

Diffraction quality crystals are essential for crystallographic studies of protein structure, and the production of poorly diffracting crystals is often regarded as a dead end in the process. Here we show a dramatic improvement of poorly diffracting DsbG crystals allowing high-resolution diffraction data measurement. Before dehydration, the crystals are fragile and the diffraction pattern is streaky, extending to 10 A resolution. After dehydration, there is a spectacular improvement, with the diffraction pattern extending to 2 A resolution. This and other recent results show that dehydration is a simple, rapid, and inexpensive approach to convert poor quality crystals into diffraction quality crystals.

Crystallography, X-Ray↗
PubMed1996

Crystallization of a soluble form of the Kex1p serine carboxypeptidase from Saccharomyces cerevisiae.

A soluble form of the killer factor and prohormone-processing carboxypeptidase, "Kex1 delta p," from Saccharomyces cerevisiae, has been crystallized in 17-22% poly(enthylene glycol) methyl ether (average M(r) = 5,000), 100 mM ammonium acetate, 5% glycerol, pH 6.5, at 20 degrees C. A native data set (2.8 A resolution) and four derivative data sets (3.0-3.2 A resolution) were collected at the Photon Factory (lambda = 1.0 A). The crystals belong to space group P2(1)2(1)2(1) with a =56.6 A, b = 84.0 A, c = 111.8 A. Freezing a Kex1 delta p crystal has facilitated the collection of a 2.4-A data set using a rotating anode source (lambda = 1.5418 A). Molecular replacement models have been built based on the structures of wheat serine carboxypeptidase (CPDW-II; Liao DI et al., 1992, Biochemistry 31:9796-9812) and yeast carboxypeptidase Y.

Animals↗
PubMed2005

High-resolution iterative frequency identification for NMR as a general strategy for multidimensional data collection.

We describe a novel approach to the rapid collection and processing of multidimensional NMR data: "high-resolution iterative frequency identification for NMR" (HIFI-NMR). As with other reduced dimensionality approaches, HIFI-NMR collects n-dimensional data as a set of two-dimensional (2D) planes. The HIFI-NMR algorithm incorporates several innovative features. (1) Following the initial collection of two orthogonal 2D planes, tilted planes are selected adaptively, one-by-one. (2) Spectral space is analyzed in a rigorous statistical manner. (3) An online algorithm maintains a model that provides a probabilistic representation of the three-dimensional (3D) peak positions, derives the optimal angle for the next plane to be collected, and stops data collection when the addition of another plane would not improve the data model. (4) A robust statistical algorithm extracts information from the plane projections and is used to drive data collection. (5) Peak lists with associated probabilities are generated directly, without total reconstruction of the 3D spectrum; these are ready for use in subsequent assignment or structure determination steps. As a proof of principle, we have tested the approach with 3D triple-resonance experiments of the kind used to assign protein backbone and side-chain resonances. Peaks extracted automatically by HIFI-NMR, for both small and larger proteins, included approximately 98% of real peaks obtained from control experiments in which data were collected by conventional 3D methods. HIFI-NMR required about one-tenth the time for data collection and avoided subsequent data processing and peak-picking. The approach can be implemented on commercial NMR spectrometers and is extensible to higher-dimensional NMR.

Animals↗
PubMed2003

High-resolution structure of phenol hydroxylase and correction of sequence errors.

The crystal structure model of phenol hydroxylase has been corrected for 11 sequence errors and refined against new data to 1.7 A resolution. The higher resolution data together with careful exploitation of non-crystallographic symmetry restraints and the use of many small groups for refinement of anisotropic displacement parameters resulted in a large decrease in the crystallographic R factor. The final crystallographic free R factor is 18.0%, which should be compared with the values of 27.8% for the previously published model (PDB code 1foh). The rebuilding and re-refinement procedure is described. A comparison with the previously published model was performed and possible biochemical implications are discussed. No large differences suggesting gross errors in the earlier model were found. The actual differences between these two models give an indication of the level of ambiguity and inaccuracy that may be found in a well refined protein model at 2.4 A resolution.

Crystallography, X-Ray↗
PubMed2004

MAP estimation for hyperspectral image resolution enhancement using an auxiliary sensor.

This paper presents a novel maximum a posteriori estimator for enhancing the spatial resolution of an image using co-registered high spatial-resolution imagery from an auxiliary sensor. Here, we focus on the use of high-resolution panchomatic data to enhance hyperspectral imagery. However, the estimation framework developed allows for any number of spectral bands in the primary and auxiliary image. The proposed technique is suitable for applications where some correlation, either localized or global, exists between the auxiliary image and the image being enhanced. To exploit localized correlations, a spatially varying statistical model, based on vector quantization, is used. Another important aspect of the proposed algorithm is that it allows for the use of an accurate observation model relating the "true" scene with the low-resolutions observations. Experimental results with hyperspectral data derived from the airborne visible-infrared imaging spectrometer are presented to demonstrate the efficacy of the proposed estimator.

Algorithms↗
PubMed1991

Mathematical isolation of component spectra in HPLC/UV-vis and GC-MS. How unique are the resolved spectra?

The resolution of overlapping spectra in GC-MS and HPLC/UV-vis is fundamentally limited by the quality of the experimental data. The narrowness of the solution range depends on the degree of overlap between components. If the components are dissimilar, the solutions obtained by all mathematical methods are robust. Small perturbations in the observations do not change the calculated solution very much. Alternating regression (AR) is a useful tool in the analysis of overlapping spectra because AR can be calculated very rapidly. The robustness of the solution can be easily checked with AR. The mathematical analysis is repeated several times after adding different sets of noise. Each time different random spectra are used as a starting point. The range of solutions thus obtained reflects the quality of the data for resolution purposes.

Chemistry Techniques, Analytical↗
PubMed2004

Phylogenetics of barbets (Aves: Piciformes) based on nuclear and mitochondrial DNA sequence data.

A combination of nuclear (beta-fibrinogen intron 7; 938 bp) and mitochondrial (cytochrome b; 1045 bp) DNA sequence data analyzed with model-based phylogenetic methods yields a hypothesis of barbet and toucan relationships supported by high Bayesian posterior probabilities and several synapomorphic indels in the nuclear intron data. The basal topology differs from previous morphology and mitochondrial DNA sequence based hypotheses, but is consistent with DNA-DNA hybridization results. The mitochondrial DNA sequence data provide resolution at the tips of the tree, but when analyzed alone, yield a different basal topology than the combined data. However, the basal nodes in the mitochondrial-based tree have little statistical support. Combined data analysis produced strong statistical support at basal nodes and a relatively simple geographic structure. Barbets from each of the three tropical regions are monophyletic, but the Old World barbets are paraphyletic. The African and New World clades are sister taxa, and the Asian clade is basal. This geographic structure indicates that similarities in plumage, voice, and behavior between Gymnobucco and Calorhamphus are convergent. The data are not conclusive, but suggest paraphyly of the New World barbets. Only 4% of the Bayesian posterior distribution unites Semnornis with the other New World barbets.

Animals↗
PubMed1999

Taking MAD to the extreme: ultrafast protein structure determination.

Multiwavelength anomalous diffraction data were measured in 23 min from a 16 kDa selenomethionyl substituted protein, producing experimental phases to 2.25 A resolution. The data were collected on a mosaic 3 x 3 charge-coupled device using undulator radiation from the Structural Biology Center 19ID beamline at the Argonne National Laboratory's Advanced Photon Source. The phases were independently obtained semiautomatically by two crystallographic program suites, CCP4 and CNS. The quality and speed of this data acquisition exemplify the opportunities at third-generation synchrotron sources for high-throughput protein crystal structure determination.

Base Sequence↗
PubMed1995

Comparative role of omeprazole in the treatment of gastroesophageal reflux disease.

OBJECTIVE: To review gastroesophageal reflux disease (GERD) and its treatment, with emphasis on the use and place of omeprazole, a proton pump inhibitor. DATA SOURCES: A compilation prepared by the National Library of Medicine's Interactive Retrieval Services (Medlars II) for the period 1987 to 1994 was used as the data source. STUDY SELECTION: Focus was placed on human comparative clinical studies with well-accepted measures of esophageal healing (endoscopy) and symptom resolution. Safety data were compiled from the clinical trials literature and large postmarketing data studies. Pharmacoeconomic studies selected were judged to meet the criteria of good design, presence of sensitivity testing, and statement of perspective. DATA EXTRACTION: Data were obtained from double-blind, controlled clinical studies. Other data were extracted from pertinent literature of good design and significant results. DATA SYNTHESIS: Overall, the clinical trials of omeprazole for the treatment of patients with erosive GERD demonstrate that omeprazole provides superior therapy in terms of esophageal healing symptom resolution and patient compliance when compared with histamine2-receptor antagonists (H2RAs) and antacids. In addition, studies also indicate that omeprazole is the most effective agent for the treatment of patients with GERD refractory to other treatments. Dosage adjustment is not necessary in patients with impaired renal or hepatic function or in the elderly. Finally, although the acquisition drug cost for daily treatment of patients with GERD is highest with the use of omeprazole, pharmacoeconomic studies indicate that treatment is more cost-effective with the use of omeprazole than with H2RA or antacid treatment alone or combined with nonpharmacologic approaches. CONCLUSIONS: Based on efficacy, safety, and cost-effectiveness, omeprazole is the drug of choice for the treatment of patients with endoscopically confirmed erosive GERD.

Clinical Trials as Topic↗
PubMed1999

Temporal resolution and temporal masking properties of transient stimuli: data and an auditory model.

Temporal resolution is often measured using the detection of temporal gaps or signals in temporal gaps embedded in long-duration stimuli. In this study, psychoacoustical paradigms are developed for measuring the temporal encoding of transient stimuli. The stimuli consisted of very short pips which, in two experiments, contained a steady state portion. The carrier was high-pass filtered, dynamically compressed noise, refreshed for every stimulus presentation. The first experiment shows that, with these very short stimuli, gap detection thresholds are about the same as obtained in previous investigations. Experiments II and III show that, using the same stimuli, temporal-separation thresholds and duration-discrimination thresholds are better than gap-detection thresholds. Experiment IV investigates the significance of residual spectral cues for the listeners' performance. In experiment V, temporal separation thresholds were measured as a function of the signal-pip sensation level (SL) in both forward- and backward-masking conditions. The separation thresholds show a strong temporal asymmetry with good separation thresholds independent of signal-pip SL in backward-masking conditions and increasing separation thresholds with decreasing signal-pip SL in forward-masking conditions. A model of the auditory periphery is used to stimulate the gap-detection and temporal-separation thresholds quantitatively. By varying parameters like auditory-filter width and transduction time constants, the model provides some insight into how the peripheral auditory system may cope with temporal processing tasks and thus represents a more physiology-related complement to current models of temporal processing.

Adult↗
PubMed2004

Crystallization and preliminary X-ray analysis of an acetone carboxylase from Xanthobacter autotrophicus strain Py2.

Acetone carboxylase from Xanthobacter autotrophicus strain Py2 catalyzes the MgATP-dependent carboxylation of acetone to acetoacetate. Interestingly, during this reaction ATP is hydrolyzed to AMP and inorganic phosphate, suggesting a novel carboxylation mechanism. Acetone carboxylase is a heterohexameric protein comprised of three different polypeptides having molecular weights of 86 342, 78 509 and 19 773 Da arranged in an alpha(2)beta(2)gamma(2) quaternary structure. Here, the crystallization and preliminary X-ray data analysis of acetone carboxylase is reported. The acetone carboxylase isolated from the aerobic microorganism X. autotrophicus strain Py2 crystallizes in a primitive orthorhombic point group P222, with unit-cell parameters a = 76.2, b = 122.0, c = 264.2 A. The Matthews coefficient calculation indicates that one alphabetagamma half of the large protein complex is located in the asymmetric unit in this crystal form. Crystals have been obtained that diffract to better than 2.8 A resolution and data have been collected to 3.2 A resolution.

Adenosine Triphosphate↗
PubMed1999

Systematic review and meta-analysis of corticosteroids for the resolution of malignant bowel obstruction in advanced gynaecological and gastrointestinal cancers. Systematic Review Steering Committee.

BACKGROUND: The objective was to locate, appraise and summarise evidence from scientific studies on intestinal obstruction due to advanced gynaecological and gastrointestinal cancers, in order to assess the efficacy of corticosteroids. MATERIALS AND METHODS. DATA SOURCES: A comprehensive list of studies was provided by an extensive search of electronic databases, relevant journals, bibliographic databases, conference proceedings, reference lists, the grey literature, personal contact and the world wide web. DATA SYNTHESIS: Two researchers extracted the data independently. A qualitative analysis was performed of the dichotomous data of resolution of obstruction and death at one month. Both fixed and random effect models were used. Number needed to treat (with corticosteroids to resolve one episode of bowel obstruction) was derived from the odds ratio. Kaplan-Meier survival curves from individual patient data were also analysed. Studies of lower methodological quality were assessed in a qualitative manner. RESULTS: There is a trend towards resolution of bowel obstruction using corticosteroids but this result does not achieve statistical significance. There is no statistically significant difference in mortality at one month, nor in the Kaplan Meier survival curves. Number needed to treat is 6, though with wide confidence intervals (3-infinity). The results are robust to fixed and random effects models and to 'best' and 'worst case' scenarios on the data from missing patients. The morbidity associated with corticosteroids appears to be very low. CONCLUSIONS: The role of corticosteroids needs further elucidation. More patients need to be recruited in order to obtain more precise results. Further trials should include quality of life measures as primary outcomes as well as most effective type of corticosteroid, dose or dosing regime, route of administration and morbidity.

Adrenal Cortex Hormones↗