THE EFFICACY OF A FLUORIDE-CONTAINING ORTHODONTIC PRIMER IN PREVENTING DEMINERALIZATION

Purpose: To evaluate the efficacy of a fluoride-containing orthodontic primer in preventing demineralization adjacent to brackets and compare the quality of enamel on tooth surfaces that received interproximal reduction (IPR). Methods: Patients at the VCU Orthodontic clinic who consented to orthodontic treatment involving extraction of at least 2 premolars were recruited to this pilot clinical study. Brackets were bonded to premolars using one of two primers, fluoride-containing experimental or control. IPR was also performed, and the experimental primer was applied to randomly selected teeth. Extracted teeth were analyzed visually for the presence of white spot lesions (WSLs). Micro-CT analyses were also performed to evaluate demineralization and measure the lesions. Results: A total of 18 teeth from 6 subjects were included in the following analyses. Based on micro-CT imaging, lesions were found on 89% of teeth treated with the experimental primer compared to 67% with the control primer, but this difference was not statistically significant (p=0.5765). There was also no significant difference between the depths of the lesions (p=1.00), handedness (p=0.5765), hygiene (p=0.7804), or time in the mouth (p=0.5601). According to visual examination, there was no significant difference in the incidence of WSLs between the two groups (89% and 89%; p=1.00) Also, there was no association with treatment (p=1.00), handedness (p=1.00), hygiene (p=0.1373), or time in the mouth (p=0.2987). No differences were noted on the microstructural characteristics of enamel at the IPR sites. Conclusion: Fluoride-containing primers do not seem to provide any additional benefit over conventional non-fluoride primers in orthodontic patients

Explicit generation of the branching tree of states in spin glasses

We present a numerical method to generate explicit realizations of the tree of states in mean-field spin glasses. The resulting study illuminates the physical meaning of the full replica symmetry breaking solution and provides detailed information on the structure of the spin-glass phase. A cavity approach ensures that the method is self-consistent and permits the evaluation of sophisticated observables, such as correlation functions. We include an example application to the study of finite-size effects in single-sample overlap probability distributions, a topic that has attracted considerable interest recently.Comment: Version accepted for publication in JSTA

Wear rates in urban rail systems

A significant part of maintenance costs in urban rail systems (metro, tram, light rapid transit/light metro) is due to wheel-rail wear. Wear rates - measured for example as depth of wear per kilometre run (rolling stock) or per train passage (rails) - depend in a complex manner on several influence factors. Among the most important are key design factors of the rolling stock (wheel profiles, suspension characteristics), of the track (distribution of curve radii, characteristics of switches and crossings, rail profiles), of the wheel-rail interface (lubrication, materials in contact, ambient characteristics), and of operations (frequency of traction and braking, trainset inversion policy, maintenance policy etc.). When designing an urban rail system, all of these factors have to be under control in order to limit the costs due to wheel/rail reprofiling/grinding and replacement. The state of the art allows the calculation of wear rates given quantitative input regarding the above factors. However, it is difficult to find in the literature experimental values for calibration of wear models and indications on what is a reasonable state-of-the-art wear rate for any given type of urban rail system. In this paper we present a structured analysis of flange wear rates found in the literature and derived from the experience of the authors, for a variety of cases, including metros and mainline rail systems. We compare the wear rates and explain their relationship with the influence factors. We then relate the wear rates with the needs in terms of wheel reprofiling/replacement. We estimate ranges for the calibration coefficients of wear models. We present the results in a way as to allow the designer of urban rail systems to derive values for target wear rates according to their specific conditions without the need for complex simulations

Helioseismology and the solar age

The problem of measuring the solar age by means of helioseismology hasbeen recently revisited by Guenther & Demarque (1997) and by Weiss & Schlattl (1998). Different best values for $t_{\rm seis}$ and different assessment of the uncertainty resulted from these two works. We show that depending on the way seismic data are used, one may obtain the value $t_{\rm seis}\approx 4.6$ Gy, close to the age of the oldest meteorites, $t_{\rm met}=4.57$ Gy, like in the first paper, or above 5 Gy like in the second paper. The discrepancy in the seismic estimates of the solar age may be eliminated by assuming higher than the standard metal abundance and/or an upward revision of the opacities in the solar radiative interior.We argue that the most accurate and robust seismic measure of the solar age are the small frequency separations, $D_{\ell,n}=\nu_{l,n}-\nu_{\ell+1,n-1}$, for spherical harmonic degrees $\ell=0,2$ and radial orders $n\gg\ell$.The seismic age inferred by minimization of the sum of squared differences between the model and the solar small separations is $t_{\rm seis}=4.66\pm0.11$, a number consistent with meteoritic data.Our analysis supports earlier suggestions of using small frequency separations as stellar age indicators.Comment: 8 pages + 4 ps figures included, LaTeX file with l-aa.sty, submitted to Astronomy and Astrophysic

On the Use of Optimized Monte Carlo Methods for Studying Spin Glasses

We start from recently published numerical data by Hatano and Gubernatis cond-mat/0008115 to discuss properties of convergence to equilibrium of optimized Monte Carlo methods (bivariate multi canonical and parallel tempering). We show that these data are not thermalized, and they lead to an erroneous physical picture. We shed some light on why the bivariate multi canonical Monte Carlo method can fail.Comment: 6 pages, 5 eps figures include