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At least 847 records · Page 47Linked to original sources
PubMed2005

Effect of power density of curing unit, exposure duration, and light guide distance on composite depth of cure.

This in vitro study compared the depth of cure obtained with six quartz tungsten halogen and light-emitting diode curing units at different exposure times and light tip-resin composite distances. Resin composite specimens (Tetric Ceram, A3; diameter 4 mm, height 6 mm) were exposed from 0-, 3-, and 6-mm distance. The curing units (200-700 mW/cm2) were used for standard (20 and 40 s), pulse-delay mode (initial exposure of 3 s at 200 mW/cm2, followed by a resting period of 3 min and a final exposure of 10 or 30 s at 600 mW/cm2), or soft-start curing (40 s; exponential ramping). Curing depth was determined by measurement of Wallace hardness for each half millimeter starting at 0.5 mm from the top surface. For each specimen, a mean H(W) value was calculated from the H(W) values determined at the depths of 2.0 mm and less (0.5, 1.0, 1.5, and 2.0 mm, respectively). The depth of cure for each specimen was found by determining the greatest depth before an H(W) value exceeding the minimal H(W) value by 25% occurred. For all curing units, an increase in exposure time led to significantly higher depth of cure. Increasing the light tip-resin composite distance significantly reduced the depth of cure. With a light tip-resin composite distance of 6 mm, median values of depth of cure varied between 2.0 and 3.5 mm following a 20-s (or 3+10 s) exposure and between 3.0 and 4.5 mm following a 40-s (or 3+30 s) exposure. The composite situated above the depth of cure value cured equally well with all curing units. At both exposure times, Luxomax resulted in the significantly lowest depth of cure, and Astralis 7 yielded significantly higher depth. At both exposure times, a significant linear correlation was found between the determined power densities of the curing units and the pooled depth of cure values obtained. It seems that for the resin composite tested, the recommended exposure time of 40 s per 2-mm increment may be reduced to 20 s, or that increments may be increased from 2 to 3.5 mm. It may be that the absolute values of depth of cure found are material specific, but we believe that the relationships found between curing units, between exposure times, and between light guide distances are universal.

Composite Resins↗
PubMed2005

Relationship between distance of schools from the nearest municipal waste incineration plant and child health in Japan.

In Japan, the main source of dioxins is incinerators. This study examined the relationship between the distance of schools from municipal waste incineration plants and the prevalence of allergic disorders and general symptoms in Japanese children. Study subjects were 450,807 elementary school children aged 6-12 years who attended 996 public elementary schools in Osaka Prefecture in Japan. Parents of school children completed a questionnaire that included items about illnesses and symptoms in the study child. Distance of each of the public elementary schools from all of the 37 municipal waste incineration plants in Osaka Prefecture was measured using geographical information systems packages. Adjustment was made for grade, socioeconomic status and access to health care per municipality. Decreases in the distance of schools from the nearest municipal waste incineration plant were independently associated with an increased prevalence of wheeze, headache, stomach ache, and fatigue (adjusted odds ratios [95% confidence intervals] for shortest vs. longest distance categories =1.08 [1.01-1.15], 1.05 [1.00-1.11], 1.06 [1.01-1.11], and 1.12 [1.08-1.17], respectively). A positive association with fatigue was pronounced in schools within 4 km of the second nearest municipal waste incineration plant. There was no evident relationship between the distance of schools from such a plant and the prevalence of atopic dermatitis or allergic rhinitis. The findings suggest that proximity of schools to municipal waste incineration plants may be associated with an increased prevalence of wheeze, headache, stomach ache, and fatigue in Japanese children.

Age Factors↗
PubMed1992

Time vs. distance as measures of exposure in driving surveys.

A survey of drivers carried out in Ontario in 1988 has provided data on time spent driving as well as the distances driven for licensed drivers of both sexes in six age groups and three regions. Substantial differences were found in times, distances, and distance/time ratios among these groups. Men drove 50% greater distances, but spent only 30% more time driving than women; speed, averaged over each day's driving, was lower for older drivers than for younger drivers. Differences in speed reflect differences in the driving done in urban or rural areas, and differences in the opportunity for road crashes; such differences, whether based on units of time or distance, will also affect both the comparisons of accident rates and the perceptions of risk among different groups of drivers. A definition of exposure to risk of road crash is required that considers both time and distance appropriately.

Accidents, Traffic↗
PubMed1995

Distance from an intrauterine hydrophone as a factor affecting intrauterine sound pressure levels produced by the vibroacoustic stimulation test.

OBJECTIVE: The purpose of this study was to determine whether intrauterine sound pressure levels produced by vibroacoustic stimulation were associated with distance from an intrauterine hydrophone in human parturients and to evaluate the effects of distance on the spectrum of the stimulus. STUDY DESIGN: Measurements of intrauterine sound were taken in eight volunteer parturients in normal active-phase labor by use of an intrauterine hydrophone. Vibroacoustic stimulation was performed on the maternal abdomen directly overlying the hydrophone; at distance of 5, 10, 15, 20, and 25 cm from the hydrophone; and at the maternal sternum. Intrauterine sound pressure levels were tape-recorded for later analysis. Fetal heart rate and fetal movement were assessed with each vibroacoustic stimulation. Spectral analyses were performed by taking the fast Fourier transform of the tape-recorded stimulation at each position. RESULTS: Analysis of variance with repeated measures indicated a statistically significant decrease (F = 4.1, p = 0.004) in the sound pressure levels as distance increased. Spectral analysis indicated large variability between and within subjects. CONCLUSION: Sound exposure of the fetal ear is on average decreased as the distance between the ear and the vibroacoustic stimulation is increased. The spectrum of the stimulus produced with vibroacoustic stimulation is highly variable.

Acoustic Stimulation↗
PubMed1986

Effective stimulation distance for current from macroelectrodes.

Effective spread of stimulating current from macroelectrodes was measured using antidromic responses of axons of the pyramidal tract as an indicator of excitation. Both monopolar and concentric bipolar electrode configurations were tested with stimulating distances as large as 7mm. The effective stimulation distance was greater from monopolar electrodes especially at greater current strengths, but differences between the two configurations were frequently small and reversals of this trend occurred. There was no statistically significant difference between the estimates of effective stimulation distance made using large and small axons. The shape of current-distance curves was approximately parabolic using both bipolar and monopolar stimulation. A current strength of 0.5 to 1.0 mA will confine effective current from a monopolar electrode to a sphere of 2-mm radius, but will not stimulate all elements within that area. Even in a brain area as homogeneous as the pyramidal tract, there is still a great deal of variability from mean values in effective stimulation distance. Presumably, the variability would be even greater in more heterogeneous regions.

Animals↗
PubMed1992

Fetal binocular distance as a predictor of menstrual age.

The relation between fetal binocular distance and menstrual age was determined by cross-sectional analysis of 555 normal fetuses (14-40 weeks) using real-time sonography. Mathematical modelling of the data demonstrated that the binocular distance growth curve, similar to the biparietal diameter, is nonlinear. Predicted binocular values at various points in gestation were comparable to the results of other investigators. Predicted menstrual age in weeks for specific binocular distance measurements in millimeters were calculated and are reported in tabular form. The variability (+/- 2 SD) associated with predicting menstrual age from binocular distance is +/- 14 days between 14 and 27 weeks, but between 29 and 40 weeks the variability is +/- 24 days. Binocular distance can be used as an adjunct in estimating menstrual age and may be useful in the diagnosis of some abnormalities, e.g. hypotelorism or hypertelorism.

Analysis of Variance↗
PubMed1984

Polypeptide secondary structure determination by nuclear magnetic resonance observation of short proton-proton distances.

The use of proton-proton nuclear Overhauser enhancement (NOE) distance information for identification of polypeptide secondary structures in non-crystalline proteins was investigated by stereochemical studies of standard secondary structures and by statistical analyses of the secondary structures in the crystal conformations of a group of globular proteins. Both regular helix and beta-sheet secondary structures were found to contain a dense network of short 1H-1H distances. The results obtained imply that the combined information on all these distances obtained from visual inspection of the two-dimensional NOE (NOESY) spectra is sufficient for determination of the helical and beta-sheet secondary structures in small globular proteins. Furthermore, cis peptide bonds can be identified from unique, short sequential proton-proton distances. Limitations of this empirical approach are that the exact start or end of a helix may be difficult to define when the adjoining residues form a tight turn, and that unambiguous identification of tight turns can usually be obtained only in the hairpins of antiparallel beta-structures. The short distances between protons in pentapeptide segments of the different secondary structures have been tabulated to provide a generally applicable guide for the analysis of NOESY spectra of proteins.

Aprotinin↗
PubMed1986

Application of molecular dynamics with interproton distance restraints to three-dimensional protein structure determination. A model study of crambin.

The applicability of restrained molecular dynamics for the determination of three-dimensional protein structures on the basis of short interproton distances (less than 4 A) that can be realistically determined from nuclear magnetic resonance measurements in solution is assessed. The model system used is the 1.2 A resolution crystal structure of the 46 residue protein crambin, from which a set of 240 approximate distance restraints, divided into three ranges (2.5 +/- 0.5, 3.0+0.5(-1.0) and 4 +/- 1 A), is derived. This interproton distance set comprises 159 short-range ([i-j] less than or equal to 5) and 56 ([i-j] greater than 5) long-range inter-residue distances and 25 intra-residue distances. Restrained molecular dynamics are carried out using a number of different protocols starting from two initial structures: a completely extended beta-strand; and an extended structure with two alpha-helices in the same positions as in the crystal structure (residues 7 to 19, and 23 to 30) and all other residues in the form of extended beta-strands. The root-mean-square (r.m.s.) atomic differences between these two initial structures and the crystal structure are 43 A and 23 A, respectively. It is shown that, provided protocols are used that permit the secondary structure elements to form at least partially prior to folding into a tertiary structure, convergence to the correct final structure, both globally and locally, is achieved. The r.m.s. atomic differences between the converged restrained dynamics structures and the crystal structure range from 1.5 to 2.2 A for the backbone atoms and from 2.0 to 2.8 A for all atoms. The r.m.s. atomic difference between the X-ray structure and the structure obtained by first averaging the co-ordinates of the converged restrained dynamics structures is even smaller: 1.0 A for the backbone atoms and 1.6 A for all atoms. These results provide a measure with which to judge future experimental results on proteins whose crystal structures are unknown. In addition, from an examination of the dynamics trajectories, it is shown that the convergence pathways followed by the various simulations are different.

Hydrogen Bonding↗
PubMed1992

Solution structure of a DNA octamer containing the Pribnow box via restrained molecular dynamics simulation with distance and torsion angle constraints derived from two-dimensional nuclear magnetic resonance spectral fitting.

The DNA octamer [d(GTATAATG].[(CATATTAC)], containing the prokaryotic upstream consensus recognition sequence, has been examined via proton homonuclear two-dimensional nuclear Overhauser effect (2D NOE) and double-quantum-filtered correlation (2QF-COSY) spectra. All proton resonances, except those of H5' and H5" protons, were assigned. A temperature dependence study of one-dimensional nuclear magnetic resonance (NMR) spectra, rotating frame 2D NOE spectroscopy (ROESY), and T1 rho measurements revealed an exchange process that apparently is global in scope. Work at lower temperatures enabled a determination of structural constraints that could be employed in determination of a time-averaged structure. Simulations of the 2QF-COSY cross-peaks were compared with experimental data, establishing scalar coupling constant ranges of the individual sugar ring protons and hence pucker parameters for individual deoxyribose rings. The rings exhibit a dynamic equilibrium of N and S-type conformers with 80 to 100% populations of the latter. A program for iterative complete relaxation matrix analysis of 2D NOE spectral intensities, MARDIGRAS, was employed to give interproton distances for each mixing time. According to the accuracy of the distance determination, upper and lower distance bounds were chosen. The distance bounds define the size of a flat-well potential function term, incorporated into the AMBER force-field, which was employed for restrained molecular dynamics calculations. Torsion angle constraints in the form of a flat-well potential were also constructed from the analysis of the sugar pucker data. Several restrained molecular dynamics runs of 25 picoseconds were performed, utilizing 184 experimental distance constraints and 80 torsion angle constraints; three different starting structures were used: energy minimized A-DNA, B-DNA, and wrinkled D-DNA, another member of the B-DNA family. Convergence to similar structures obtained with root-mean-square deviations between resulting structures of 0.37 to 0.92 A for the central hexamer of the octamer. The average structure from the nine different molecular dynamics runs was subjected to final restrained energy minimization. The resulting final structure was in good agreement with the structures derived from different molecular dynamics runs and exhibited a substantial improvement in the 2D NOE sixth-root residual index in comparison with the starting structures. An approximation of the structure in the terminal base-pairs, which displayed experimental evidence of fraying, was made by maintaining the structure of the inner four base-pairs and performing molecular dynamics simulations with the experimental structural constraints observed for the termini.(ABSTRACT TRUNCATED AT 400 WORDS)

Base Sequence↗
PubMed1990

Intercanthal and interpupillary distance in the black population.

Intercanthal distance is an important measurement in the evaluation of congenital deformities and posttraumatic telecanthus. In this study 100 black patients (71 female and 29 male) were measured for intercanthal and interpupillary distance. For the overall group the mean intercanthal distance was 33.9 +/- 3.0 mm; previous studies of white persons and mixed populations indicate an average of 32 +/- 3 mm. The mean interpupillary distance for this study was 63.7 +/- 3.7 mm; previous studies indicate an average of 63 +/- 3 mm. This study suggests that the intercanthal and interpupillary distances in blacks are similar to findings of previous studies on whites and mixed populations.

Black People↗
PubMed1986

An improved approach to the analysis of drug-protein binding by distance geometry.

The calculation of side chain centers of coordinates and the subsequent generation of side chain-side chain and side chain-backbone distance matrices is suggested as an improved method for viewing interactions inside proteins and for the comparison of protein structures. The use of side chain distance matrices is demonstrated with free PTI, and the use of difference distance matrices for side chains is shown for free and trypsin-bound PTI as well as for the X-ray structures of trypsin complexes with PTI and with benzamidine. It is found that conformational variations are reflected in the side chain distance matrices much more than in the standard C-C distance representations.

Benzamidines↗
PubMed1991

Distance changes at the regulatory and catalytic sites on Escherichia coli glutamine synthetase: a spin label study on the effect of substrate(s) binding.

A spin-labeled ATP analogue, 2,2,6,6-tetramethylpiperidine-1-oxyl adenosine triphosphatase (Tempo-ATP) is used to adenylate Escherichia coli glutamine synthetase (L-glutamine: ammonia ligase (ADP-forming), EC 6.3.1.2). The Tempo adenylylated glutamine synthetase (Tempo-GS) exhibits similar catalytic properties, pH profile and inhibitor susceptibility as those of glutamine synthetase adenylylated with normal ATP. Using the spin label on the enzyme as a probe and employing the spin-spin interactions between the label probe and paramagnetic Mn2+, the distances from the nitroxyl moiety of the covalently bound Tempo-AMP to the two Mn2+ binding sites, n1 and n2 were determined. The n1 site is the structural site and n2 is located at the catalytic site. The distances from Mn2+ at n1 and n2 sites to the nitroxyl radical are 19 and 16 A, respectively. Binding of the substrate, L-Glu, causes a protein conformational change which is reflected by the reduction of approximately 2 A for the n1 to Tempo-AMP distance and lengthening of approximately 2 A for the n2 to the Tempo-AMP distance. Addition of ATP to the Tempo-GS/L-Glu complex increases the distance between n1 and Tempo-AMP, and n2 and Tempo-AMP by 4 and 3 A, respectively.

Adenosine Diphosphate↗
PubMed1993

Energy-transfer measurements of the Cys35-Cys84 distance in bovine cardiac troponin C.

Bovine cardiac troponin C (cTnC) has cysteine residues located in the non-functional Ca(2+)-binding loop I (Cys-35) and at the N-terminal end of the central helix (Cys-84) near site II, the regulatory Ca(2+)-binding site. Recently, we reported that the excimer fluorescence resulting from the dimerization of adjacent pyrene groups attached to the two Cys residues is reduced by Ca2+ binding to site II (Liou, Y.-M. and Fuchs, F. (1992) Biophys. J. 61, 892-901). This result would suggest that Ca2+ binding causes a separation of the two Cys residues, a conclusion at variance with predictions from molecular modeling studies (Herzberg, O., Moult, J. and James, M.N.G. (1986) J. Biol. Chem. 261, 2638-2644). Alternatively, the reduction in excimer fluorescence could be accounted for by an immobilization of the pyrene attached to Cys-84 by a Ca(2+)-induced hydrophobic pocket. To arrive at a more definitive interpretation of these experiments, we carried out steady-state fluorescence resonance energy-transfer measurements of the Cys35-Cys84 distance. We used three different donor-acceptor pairs: 2-(4'-(iodoacetamido)anilino) naphthalene-6-sulfonic acid (IAANS) and 4-dimethylamino-phenylazophenyl-4-maleimide (DABMI), IAANS and N-(4-(dimethyl-amino)-3,5-dinitrophenyl) maleimide (DDPM), and 5-((((2-iodoacetyl)amino)ethyl)amino)naphthalene-1-sulfonic acid (IAEDANS) and DDPM. At pCa 8.0, the distances were 23.8, 21.0, and 22.0 A with the donor-acceptor pairs, IAANS-DABMI, IAANS-DDPM and IAEDAN-DDPM, respectively. At pCa 4.0, the distances were 25.8, 24.1 and 21.2 A. The distances at pCa 8 and pCa 4.0 were not significantly altered when labeled cTnC was complexed with cardiac troponin I (cTnI). Thus, Ca2+ has little, if any, effect on the Cys35-Cys84 distance. These results are consistent with a model in which Ca2+ binding induces a separation of helices B and C from helix D, without any relative movement of the two N-terminal Ca(2+)-binding domains.

Adenosine Triphosphatases↗
PubMed1992

A set of BASIC programs to evaluate relationships among protein sequences by optimum alignment and distance matrix analysis.

These six programs evaluate relationships among a number (> 2) of protein (or DNA) sequences. Program 1 automatically computes optimum alignments and total distances for all pairwise sequence combinations over any user desired range of the two gap penalties. Programs 2, 3 and 4 generate a square, symmetrical distance matrix, which can be exported for cluster analysis, or further analysed with programs 5 and 6 to give specific distances between sequences and extract sequence relationships. Data and results are exchanged among these programs, which are written in BASIC and compiled to run on Macintosh (68020/030/040) type machines with coprocessor and at least one MB of RAM. BASIC graphics commands or those for the Macintosh interface are avoided to facilitate use on other machines. Two groups of sequences are used to demonstrate (a) alignment, inter sequence distance calculation and dendrogram generation and (b) specific distance calculation and its usage in detecting sub groups of related sequences in dendrograms.

Algorithms↗
PubMed1984

The relationship between distance from inpatient facilities and the rate of psychiatric admissions in Western Australia.

Western Australia is the largest and most sparsely populated state in Australia with all its specialised psychiatric inpatient facilities in Perth, the capital city. This study tested a number of hypotheses concerning the effect of distance from Perth, firstly, on total hospitalisation rates for psychiatric illness of the rural population and secondly, on the proportion who were hospitalized in Perth. High rates of alcoholism in males and of neuroses in females, together with local conditions in various rural centres, rather than distance from Perth, were major determining factors affecting both total hospitalisation and th proportion sent to Perth. The major exception was that the proportion of male alcoholics admitted to Perth hospitals decreased the further the patient lived from Perth. These findings were contrary to those reported in the literature. However the distances from Perth were much greater than those usually reported elsewhere. It was concluded that beyond a certain distance from psychiatric facilities, distance per se was not a major factor governing admissions to these facilities.

Alcoholism↗
PubMedDate not supplied

Accurate estimation of inter-atomic distances in large proteins by NMR.

Recently a method was proposed which permits the extraction of the exact interatomic distance information from the measurement of the evolution of a single cross-peak relative to the mixing time in a NOESY experiment. This is performed through a careful multi-exponential analysis allowing the extraction of the relaxation parameter, and, consequently, the inter-proton distance. We investigate in the present paper whether this technique, already evaluated theoretically, can be used in a real experimental case. We have recorded and analyzed a set of 56 NOESY experiments on a lysozyme sample. Some 81 nOe build-up curves obtained from these data were analyzed in terms of distance. It is shown that the correlation between the measured distances and the reference distances obtained from crystallographic studies, is quite good. An accuracy of the order of 10% is obtained.

Magnetic Resonance Spectroscopy↗
PubMed1993

The effect of facial growth, attrition, and age on the distance from the cementoenamel junction to the alveolar bone crest in the deciduous dentition.

The aim of this study was to describe the distances from the cementoenamel junction to the alveolar bone crest (CEJ-ABC) in the deciduous dentition and to relate them to age, facial, and tooth structure in 72 dry human skulls. Age correlated significantly with anterior face height (AntFH), the distance from condyle to gnathion (Co-Gn), lateral face height (LatFH), molar anatomic crown (MAC), and molar space (MS). The CEJ-ABC per skull and for the molars correlated with age, LatFH, AntFH, Co-Gn, MS, and MAC. The CEJ-ABC for the canines and the incisors correlated with age, LatFH, AntFH, and Co-GN. Multiple regression analysis on the effect of age, AntFH, LatFH, Co-Gn, and MAC on the CEJ-ABC distances indicated that they account for 36.3% of the CEJ-ABC distance per skull, 68.8% for the molars, 34.3% for the canines, and 44.2% for the incisors. The effect of each variable while controlling for the others indicated that age, LatFH, and MAC had a significant effect on the CEJ-ABC of the molars, whereas only age had a significant effect on the CEJ-ABC of the canines and incisors. These results indicate that there is a site-specific effect of facial growth and attrition on the CEJ-ABC distances in the deciduous dentition.

Age Factors↗
PubMed2004

Healing of implanted expanded polytetrafluoroethylene vascular access grafts with different internodal distances: a histologic study in dogs.

OBJECTIVE: We assessed characteristics of healing, over time, of two types of expanded polytetrafluoroethylene grafts. STUDY DESIGN: An experimental histological study in dogs. METHODS: The graft types studied had the same internal diameter (5 mm) but different internodal distances. In one, the internodal distance was 60 microm in the external surface and 20 microm in the luminal surface. In the other, the internodal distance was 30 microm throughout the material. Sixteen grafts of each type were implanted between the femoral artery and vein in 16 dogs; explanted 1, 2, 4 or 12 weeks later; and examined histologically. RESULTS: In both graft types, infiltrating-cell density and maximum cell-penetration depth increased significantly between 1 and 2 weeks after implantation, but no significant increases occurred after 2 weeks. The number of inflammatory cells peaked 1 week after implantation and decreased significantly by 2 weeks. Subsequently, there were no significant changes in inflammatory cell numbers, suggesting that the inflammatory phase was over by 2 weeks after implantation and the grafts had become attached to surrounding tissue. There were no significant differences between the two graft types in cell density, cell-penetration depth, or number of inflammatory cells at any assessment time. CONCLUSION: Our results provide histologic support for guidelines recommending that synthetic vascular grafts for hemodialysis access should not be cannulated until 2 weeks after implantation. Since increasing the internodal distance to 60 microm in the external surface had no effect on graft healing, methods other than manipulation of internodal distance should be used in developing a graft suitable for early cannulation.

Animals↗