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PubMed2002

Etching conditions for resin-modified glass ionomer cement for orthodontic brackets.

This study reports the tensile bond strength of orthodontic eyelets (RMO, Inc, Denver, Colo) bonded to human extracted teeth with a resin-modified glass ionomer cement (RMGIC) (Fuji Ortho LC, GC America, Alsip, Ill) and various acid etchants (Etch-37 and All-Etch, Bisco, Schaumburg, Ill; Ultra Etch, 3M Unitek, St Paul, Minn) for enamel preparation before bonding. The enamel etch conditions were as follows: 37% phosphoric acid with silica; 37% phosphoric acid, silica-free; 10% phosphoric acid, silica-free; 10% polyacrylic acid; and unetched enamel. Bond strength was measured by pulling in tension on the eyelet with a 0.018-in steel wire perpendicular to the enamel surface with a testing machine (Instron model 1125, Canton, Mass) at a speed of 2 mm/min. A light-cured resin cement (Transbond XT, 3M Unitek, Monrovia, Calif) applied to enamel etched with 37% phosphoric acid containing silica served as a control. Each group included 30 specimens. The Weibull distribution (m) was used for statistical analysis with a 90% CI. The different etchants used with RMGIC did not affect tensile bond strength. The resin cement group had the highest tensile strength. Significantly lower bond strengths were observed when glass ionomer cement was used to bond orthodontic attachments to nonetched teeth. However, unlike resin cement, RMGIC can bond effectively to etched teeth in a moist environment without an additional bonding agent.

Acid Etching, Dental↗
PubMed1988

The distribution of Student's t-statistic for small samples from lognormal exposure distributions.

To assess compliance with industrial hygiene exposure criteria (e.g., TLVs), it may be necessary to perform statistical tests of hypotheses based on relatively small samples. For pollutants with long biological half-lives, the parameter most relevant for determining the risk faced by workers is the long-term arithmetic average concentration of the pollutant. In industrial environments it is common for pollutant concentrations to be approximately lognormal. Unfortunately, when based on small samples from lognormal distributions, the ordinary Student's t-statistic has some undesirable characteristics which are not recognized widely by practicing industrial hygienists. The difficulties in using the ordinary Student's t-statistic to evaluate the average exposure have been demonstrated. The properties of alternative test statistics have been explored. Some general observations on the implications of these findings have been made.

Air Pollutants, Occupational↗
PubMed1984

On the statistical estimation of speech-organization distributions from aphasia data.

Statistical methods of estimating speech-organization distributions from aphasia data are presented. Under certain assumptions, estimators for the proportions of individuals with unilateral right-hemisphere speech, unilateral left-hemisphere speech and bilateral speech organization are derived, and the large-sample properties of these estimators are presented. It is shown that useful results can be obtained when the most questionable assumption is relaxed. The general methodology is presented in terms of a specific example--the estimation of speech organization distributions of right- and left-handed adults across the three speech types. Under the relaxed assumptions a test of the hypothesis that all left-handers are unilaterally organized is derived. Conservative bounds on the proportions of unilaterally organized (left- and right-hemisphere) and bilaterally organized left-handers are also derived. As an illustration, the results are applied to aphasia-incidence data from the literature. Several uncertainties and inadequacies of the available data are discussed. Although minor modifications of the present methods might be required for other examples, the main ideas would be the same.

Adult↗
PubMed2001

Statistical inference of progressivity dominance: an application to health care financing distributions.

This paper employs a distribution-free statistical test suitable for comparisons based on dependent samples to analyse changes in health care financing distributions on Finnish data. In distinction to the more general summary index approach used in most studies of progressivity measurement, the difference between the Lorenz curve of income inequality and the concentration curves of various taxes and payments is used to evaluate progressivity dominance and changes in progressivity. Sample weights are applied to account for the effect of sampling design and non-response. The analysis demonstrates that the dominance approach can be successfully applied to various types of distributional problems besides comparisons concerning differences in income distributions. As an empirical application the paper presents estimation results for the progressivity of various health care financing sources using data from the 1987 and 1996 Finnish Health Care Surveys.

Family Characteristics↗
PubMed1991

Selective distribution of aclarubicin to regional lymph nodes with a new dosage form: aclarubicin adsorbed on activated carbon particles.

A new dosage form (ACR-CH) comprising aclarubicin adsorbed on activated carbon particles was designed to sustain release of aclarubicin. ACR-CH or aclarubicin aqueous solution (ACR-sol) was injected subcutaneously into the fore foot-pads of rats. ACR-CH distributed a statistically significantly higher level of aclarubicin to the axillary lymph nodes (detectable up to 7 days after injection) than aclarubicin distributed in an ACR-sol (not detectable after 48 h). To other tissues, ACR-CH distributed statistically significantly low levels of aclarubicin, as compared with ACR-sol.

Aclarubicin↗
PubMed2002

Effects of temporal modelling on the statistical uncertainty of spatiotemporal distributions estimated directly from dynamic SPECT projections.

Artefacts can result when reconstructing a dynamic image sequence from inconsistent single photon emission computed tomography (SPECT) projection data acquired by a slowly rotating gantry. The artefacts can lead to biases in kinetic parameters estimated from time-activity curves generated by overlaying volumes of interest on the images. Insufficient sampling and truncation of projections by cone-beam collimators can cause additional artefacts. To overcome these sources of bias in conventional image based dynamic data analysis, we have been investigating the estimation of time-activity curves and kinetic model parameters directly from dynamic SPECT projection data by modelling the spatial and temporal distribution of the radiopharmaceutical throughout the projected field of view. In the present work, we perform Monte Carlo simulations to study the effects of the temporal modelling on the statistical variability of the reconstructed spatiotemporal distributions. The simulations utilize fast methods for fully four-dimensional (4D) direct estimation of spatiotemporal distributions and their statistical uncertainties, using a spatial segmentation and temporal B-splines. The simulation results suggest that there is benefit in modelling higher orders of temporal spline continuity. In addition, the accuracy of the time modelling can be increased substantially without unduly increasing the statistical uncertainty, by using relatively fine initial time sampling to capture rapidly changing activity distributions.

Algorithms↗
PubMed2004

Optimized prostate biopsy via a statistical atlas of cancer spatial distribution.

A methodology is presented for constructing a statistical atlas of spatial distribution of prostate cancer from a large patient cohort, and it is used for optimizing needle biopsy. An adaptive-focus deformable model is used for the spatial normalization and registration of 100 prostate histological samples, which were provided by the Center for Prostate Disease Research of the US Department of Defense, resulting in a statistical atlas of spatial distribution of prostate cancer. Based on this atlas, a statistical predictive model was developed to optimize the needle biopsy sites, by maximizing the probability of detecting cancer. Experimental results using cross-validation show that the proposed method can detect cancer with a 99% success rate using seven needles, in these samples.

Algorithms↗
PubMed1977

Applications of the Mantel-Haenszel statistic to the comparison of survival distributions.

In comparing two survival distributions, a Mantel-Haenszel statistic can be computed after each death as a non-linear two-sample rank statistic. The distributions of both the maximum and terminal statistics in such a sequence are studied numerically, in the absence of censoring, and appropriate critical values are determined. The maximum statistic is applied to simultaneous inference, and both the maximum and terminal statistics are used as the basis for early stopping procedures (especially in the pseudo-sequential context). Procedures based on the two statistics are compared for power and for early decision properties such as stopping index and (for exponential distributions) stopping time.

Biometry↗
PubMed2004

Statistical model with a standard Gamma distribution.

We study a statistical model consisting of N basic units which interact with each other by exchanging a physical entity, according to a given microscopic random law, depending on a parameter lambda. We focus on the equilibrium or stationary distribution of the entity exchanged and verify through numerical fitting of the simulation data that the final form of the equilibrium distribution is that of a standard Gamma distribution. The model can be interpreted as a simple closed economy in which economic agents trade money and a saving criterion is fixed by the saving propensity lambda. Alternatively, from the nature of the equilibrium distribution, we show that the model can also be interpreted as a perfect gas at an effective temperature T(lambda), where particles exchange energy in a space with an effective dimension D(lambda).

Journal Article↗
PubMed2005

Collisional cross sections and momentum distributions in astrophysical plasmas: dynamics and statistical mechanics link.

We show that in stellar core plasmas, the one-body momentum distribution function is strongly dependent, at least in the high velocity regime, on the microscopic dynamics of ion elastic collisions and therefore on the effective collisional cross sections if a random force field is present. We take into account two cross sections describing ion-dipole and ion-ion screened interactions. Furthermore, we introduce a third unusual cross section to link statistical distributions and a quantum effect originated by the energy-momentum uncertainty owing to many-body collisions. We also propose a possible physical interpretation in terms of a tidal-like force. We show that each collisional cross section gives rise to a slight peculiar correction on the Maxwellian momentum distribution function in a well defined velocity interval. We also find a possible link between microscopic dynamics of ions and statistical mechanics in interpreting our results in the framework of nonextensive statistical mechanics.

Journal Article↗
PubMed1996

Distribution-free graphical and statistical analysis of serial dependence in neuronal spike trains.

Two-dimensional 'joint' interval distributions of sequential interspike (ISIs) are a commonly used tool in neuronal spike train analysis. We present and evaluate here a modification of the joint interval plot using ranked ISIs. This modification provides clearer graphical evaluation of serial dependence in ISI sequences, a distribution-free basis for isolating changes in serial dependence across experimental treatments from changes in ISI distributions, and a basis for unambiguous statistical tests of serial dependence and stationarity. To validate this method and illustrate the advantages of its use we have applied it to both single-neuron spike trains recorded from cultured mammalian spinal cord neurons and artificial spike trains generated by stochastic models with defined burst envelopes and serial dependencies.

Action Potentials↗
PubMed2006

Photodissociation of Mg+-XCH3 (X=F, Cl, Br, and I) complexes. II. Fragment angular and energy distributions.

Angular and energy distributions of photofragments from Mg+-XCH3 (X=F, Cl, Br, and I) were deduced from time-of-flight (TOF) profiles measured by rotating the polarization direction of the dissociation laser with respect to ion beam direction. The TOF profiles of ICH3+ and MgI+ fragment ions produced from Mg+-ICH3 complex with 266 and 355 nm photons showed clear but opposite recoil anisotropy to each other. In addition, BrCH3+ formed by a dissociation of the Mg+-BrCH3 complex at a photolysis wavelength of 266 nm also showed an anisotropic distribution in the TOF profile which had the same behavior as the profile of ICH3+. For Mg+-FCH3 complex, CH3+ and MgF+ formed with a 266 nm photon had also spatial anisotropy, in which the TOF profile of MgF+ was almost opposite to that of MgI+. These anisotropic distributions were explained by (1) local excitation on the Mg+ ion, (2) rapid dissociation compared with a rotational period of the parent complex, and (3) geometrical structures of the parent complexes. Anisotropy beta parameter values were determined to be +1.30(ICH3+), -0.50(MgI+), +0.74(BrCH3+), and +0.75(CH3+ and MgF+). This dependence on the halogen atom observed in beta values was qualitatively explained by both the geometrical parameters and classical rotational periods of parent complexes. In the product energy distribution, 46%, 40%, 21%, 16%, and 16% of available energies were found to be transferred into translational energies of ICH3+, MgI+, BrCH3 +, CH3+, and MgF+, respectively. These values were compared with energy distributions estimated by a statistical prior distribution and a nonstatistical impulsive model. For ICH3+ and MgI+, the translational energies determined from the measurement had values between those estimated from statistical and nonstatistical models. On the other hand, the energy partitioning for the product ions of BrCH3+, CH3+, and MgF+ was found to be almost statistical. From these considerations, we concluded that nonstatistical processes were more important in the dissociation of Mg+-ICH3 than in other systems.

Journal Article↗
PubMed1997

[Incidence of lunar position in the distribution of deliveries. A statistical analysis].

OBJECTIVE: To point out the influence of the lunar position on the distribution of deliveries. METHODS: We examined all the full-term spontaneous deliveries that occurred at the Civil Hospital in Fano (March) throughout 24 synodic months in a 2-year period (1993-1994). In order to perform the statistical analysis, each delivery was considered as a single measure. We used techniques of circular statistics to execute data analysis. RESULTS: A significant relationship between lunar position and distribution of deliveries was pointed out in multigravidae (in detail, the deliveries resulted clustered around the full moon phase). On the contrary, no significant relation was observed in primigravidae. CONCLUSIONS: The observed results evidence a significant influence of the position of the moon on the distribution of deliveries, especially in multigravidae.

Delivery, Obstetric↗
PubMed1994

Focal abnormalities of P3 ERPs unveiled in patients with cortical lesions and primary progressive aphasia by average reference recordings.

Event related potentials (ERPs) to an auditory odd-ball paradigm were recorded with the linked earlobe reference (LER) and with a computer calculated average reference (AR), excluding the two linked earlobe derivations. The study was performed in 30 patients with lesions of frontal, parietal, occipital cortex, unilateral and bilateral lesions of the medial temporal lobe (MTL), in four patients affected by Primary Progressive Aphasia (PPA) and in 56 age matched controls. Latencies, amplitudes and scalp distribution of the earlier ERP components (P1, N1, P2, N2) were within normal limits for both LER and AR recordings. P3 scalp distribution in patients was normal when LER was used, with the exception of two patients affected by bilateral MTL lesions. When P3 was recorded using AR, the scalp distribution was statistically different from normal distributions in all patients. A negativity, instead of the positive P3 observed in controls, was recorded in patients from leads corresponding to the affected areas. This finding might have clinical applications, and confirms earlier studies suggesting that P3 is generated simultaneously from different cortical areas.

Aged↗
PubMed1995

P300 asymmetries in focal brain lesions are reference dependent.

In 6 patients with lesions of frontal, parietal and temporal lobe, in 4 patients affected by primary progressive aphasia (PPA) and in 56 age-matched controls, event-related potentials (ERPs) to an auditory odd-ball paradigm were recorded with the linked earlobe reference (LER) and with a computer calculated average reference (AR), excluding the two linked earlobe derivations. Latencies, amplitudes and scalp distribution of the earlier ERP components (P1, N1, P2, N2) were within normal limits for both LER and AR recordings. P300 scalp distribution in patients was normal when LER was used. When P300 was recorded using AR, the scalp distribution was statistically different from normal distributions in all patients. A negativity, instead of the positive P300 observed in controls, was recorded in patients from leads corresponding to the affected hemisphere.

Acoustic Stimulation↗