Effect of alloy type and surface conditioning on roughness and bond strength of metal brackets

The effect of 5 different surface conditioning methods on bonding of metal brackets to cast dental alloys was examined. The surface conditioning methods were fine (30-µm) or rough (125-µm) diamond bur, sandblasting (50-µm or 110-µm aluminum oxide [Al2O3]), and silica coating (30-µm silica). Fifty disc-shaped specimens of 5 different alloys (gold-silver, palladium-silver, nickel-chromium, cobaltchromium, and titanium) were ground with 1200-grit silicone carbide abrasive and polished before being reused for each conditioning method. Polished surfaces were used as negative controls. After measuring surface roughness (RZ), metal brackets were bonded to the conditioned alloys with a self-curing resin composite. Specimens were thermocycled (5000 times, 5°–55°C, 30 seconds), and shear bond tests were performed. Significantly higher (P .001) surface roughnesses were observed with use of the rough diamond bur (RZ ~33 µm), 110-µm Al2 O3 (RZ ~14 µm), and fine diamond bur (RZ ~10 µm), compared with the controls (RZ ~1 µm). Silica coating (RZ ~4 µm) and 50-µm Al2 O3 (RZ ~4 µm) demonstrated no significant difference (P > .001) in roughness when compared with the controls. The control group showed no resistance to shear forces (0 MPa). Bond values were greater (19 MPa) when silica coating was used, compared with 50-µm Al2O3 (7 MPa) and 110-µm Al2O3 (8 MPa) for all alloys tested. However, interaction between alloys and conditioning methods exhibited significant differences (P > .0001)

A Quasiperiodic Gibbons--Hawking Metric and Spacetime Foam

We present a quasiperiodic self-dual metric of the Gibbons--Hawking type with one gravitational instanton per spacetime cell. The solution, based on an adaptation of Weierstrassian $\zeta$ and $\sigma$ functions to three dimensions, conforms to a definition of spacetime foam given by Hawking.Comment: 14 pages, Late

N=2 Supersymmetric Model with Dirac-Kahler Fermions from Generalized Gauge Theory in Two Dimensions

We investigate the generalized gauge theory which has been proposed previously and show that in two dimensions the instanton gauge fixing of the generalized topological Yang-Mills action leads to a twisted N=2 supersymmetric action. We have found that the R-symmetry of N=2 supersymmetry can be identified with the flavour symmetry of Dirac-Kahler fermion formulation. Thus the procedure of twist allows topological ghost fields to be interpreted as the Dirac-Kahler matter fermions.Comment: 22 pages, LaTe

Prevalence and Predictors of Tobacco Use Among School Adolescents in Zakho, Kurdistan Region of Iraq

Knowledge regarding the smoking prevalence among the Kurdistan general population is not clear, at least for males. Here in the Kurdistan Youth Smoking Survey and Behaviours (KYSS&B) we tried to further expand our knowledge about the smoking profile of school students across Kurdistan. Five hundred students from four Zakho male basic schools were taken to participate in the study to determine the prevalence of smoking and socio-demographical factors associating with smoking among students aged 12 to 15 years. The KYSS&B questionnaire included various parameters such as age, gender, friends, parent history and blood groups. This study showed that the prevalence of students who ever tried smoking was 74%; about 65% of them started at age 12 years or less. Although the majority of participants (95%) knew that smoking is harmful and had negative impact on human health, 18% of them thought that they will never quit smoking. The study concluded that there was no strong association between family monthly income, parent education level and blood groups. On the other hand, the three most critical factors connected with smoking habit reported by students were age, peer influence and father smoking

A Large Hadron Electron Collider at CERN

This document provides a brief overview of the recently published report on the design of the Large Hadron Electron Collider (LHeC), which comprises its physics programme, accelerator physics, technology and main detector concepts. The LHeC exploits and develops challenging, though principally existing, accelerator and detector technologies. This summary is complemented by brief illustrations of some of the highlights of the physics programme, which relies on a vastly extended kinematic range, luminosity and unprecedented precision in deep inelastic scattering. Illustrations are provided regarding high precision QCD, new physics (Higgs, SUSY) and electron-ion physics. The LHeC is designed to run synchronously with the LHC in the twenties and to achieve an integrated luminosity of O(100) fb$^{-1}$. It will become the cleanest high resolution microscope of mankind and will substantially extend as well as complement the investigation of the physics of the TeV energy scale, which has been enabled by the LHC

Privacy-Preserving Release of Spatio-temporal Density

International audienceIn today’s digital society, increasing amounts of contextually rich spatio-temporal information are collected and used, e.g., for knowledge-based decision making, research purposes, optimizing operational phases of city management, planning infrastructure networks, or developing timetables for public transportation with an increasingly autonomous vehicle fleet. At the same time, however, publishing or sharing spatio-temporal data, even in aggregated form, is not always viable owing to the danger of violating individuals’ privacy, along with the related legal and ethical repercussions. In this chapter, we review some fundamental approaches for anonymizing and releasing spatio-temporal density, i.e., the number of individuals visiting a given set of locations as a function of time. These approaches follow different privacy models providing different privacy guarantees as well as accuracy of the released anonymized data. We demonstrate some sanitization (anonymization) techniques with provable privacy guarantees by releasing the spatio-temporal density of Paris, in France. We conclude that, in order to achieve meaningful accuracy, the sanitization process has to be carefully customized to the application and public characteristics of the spatio-temporal data