Windham Regional Community Council

Abstract Dedicated to Prof. Dr. Akimitsu Kurita on his 70th birthdayIn current bridge design codes or specifications, the dynamic effects of vehicles are considered by using a dynamic amplification factor (DAF) or dynamic load allowance (IM). However, a DAF is defined based on the ratio of the maximum dynamic load responses to the static load responses, and it is more appropriate for maximum value‐based strength design. For fatigue design, stress cycles other than the maximum stress ranges could contribute to fatigue damage accumulations. Meanwhile, on the capacity side, a reduction in fatigue strength due to structural deterioration, which is related to local environmental conditions, including temperature, humidity, etc., could introduce more uncertainties into structural safety and reliability evaluation. However, such multiple stress range effects and structural deterioration are not included in current bridge fatigue design. To evaluate the vehicular dynamic effects for the life cycle fatigue design of short‐span bridges, the present study proposes a new dynamic amplification factor for life cycle bridge fatigue design (DALC), which is defined as the ratio of the life cycle nominal live load stress range to the maximum static stress range. In contrast to other traditionally defined dynamic factors, the newly defined DALC includes information about both the structural loading and the structural capacity. Therefore, the multiple stress cycles from vehicle‐induced vibrations and the structural deteriorations from road surface conditions and corrosion of structural members are included. Parametric studies of DALC were carried out for multiple parameters and variables in the bridge's design life cycle, for instance, possible faulting days in each year, fatigue strength exponent, corrosion parameters and corrosion level. The stochastic properties and uncertainties from these variables are also considered in the DALC calculation.

Four percent articaine local anesthetic has been successfully used to attain local anesthesia for dental procedures. Mandibular block anesthesia may consume longer time to attain and have a higher failure of local anesthesia compared to infiltration. Mandibular facial infiltration has been reported to successfully attain effective local anesthesia for dental procedures. This study involved only several tooth sites and found that 1.8 cc of 4% articaine facial infiltration in the mandible may be effective when the facial mandibular cortex is <2.0–3.0 mm. A waiting time of 5–10 minutes may be required for effective anesthesia. An additional 1.8 cc of dose may be required to attain anesthesia if an initial 1.8 cc of dose fails. The need for additional anesthetic may be predicted by a measurement of the facial cortex using cone beam computerized tomography. A study of mandibular sites is needed to delineate the anatomical dimensions, density of cortical bone, and apical neural location for ensuring successful local anesthetic infiltration.

Dental implants are used to retain and support fixed and removable dental prostheses. In many clinical situations, local bone morphology requires dental implants that have a diameter that is significantly smaller than the typical implant diameters. In these cases, the fatigue life of the smaller diameter implants becomes a critical therapeutic parameter. However, this fatigue life depends on the implant itself, on the physical properties of the bone, as well as on other morphological characteristics that are patient dependent. In other words, this fatigue life varies greatly with each newly placed implant, but the capability to predict the fatigue life of dental implants does not exist today. In this paper, we present the first steps towards establishing such a methodology. We develop a finite element based fatigue model for rigidly mounted dental implants, and correlate its results with both analytical predictions as well as physical measurements. This implies that such a model can be used as a valid predictor of fatigue life of dental implants themselves, and can be used as a valuable implant design tool. Furthermore, we present the design of a cost effective device to measure the fatigue life of dental implants that can be either rigidly or bone mounted (in vitro). This device was used to measure the fatigue life of an initial sample of nine dental implants, and we show that the results predicted by the finite element model correlated well with our initial experimental results.

Summary This article describes how a teacher changed her method of teaching after acquiring knowledge about graphing calculators in a Professional development program. It describes one particular unit on understanding variables and graph interpretation taught in a seventh-grade science and math class. The use of graphing calculators proved to be effective in increasing student understanding of relationships between variables, graphing, and experimental design. The teacher in our project also found graphing calculators to be effective tools for teaching constructively. Our study implies that math and science teaching can be improved through the use of graphing calculators.