Voyager's flyby of Neptune in August of 1989 was the most distant planetary encounter ever achieved. Round trip light travel time was more than eight hours, exceeding view periods at two of the three tracking station sites. Consequently, the majority of radiometric tracking was accomplished by transmitting the uplink from one station, and receiving the downlink at a different station. This procedure defines three-way data. Dependence on three-way data for orbit determination is one distinguishing element of Voyager's successful encounter with Neptune. This paper addresses the performance of three-way range and Doppler data supporting pre-encounter orbit determination and post-encounter orbit reconstruction. Also, calibrations which reduce systematic errors inherent to three-way data are described and analyzed.
The interdental papilla plays an important role in terms of esthetics and function. Management of the interdental papilla, especially around implants can be challenging. One of the factors mentioned in the literature that affects the viability of the papilla is the distance of the interdental contact point from the crest of the bone. The following case report describes a technique to predictably achieve an interdental contact area within the proper distance from the crest of the bone to help maintain the papilla for the long term.
Stress caused by a non-passively fitting implant superstructure may induce bone adaptation, thereby changing the magnitude of static implant loading.In a previous investigation, repeated in vivo strain measurements were conducted on an implant-supported bar to evaluate changes in the magnitude of misfit resulting from bone remodeling processes. Both maximum (445 μm/m) and minimum (383 μm/m) strain values were simulated using a three-dimensional finite element model. The horizontal misfit needed to simulate experimentally determined strain values and the resulting stresses occurring in the restoration and the bone were quantified as von Mises equivalent stress. Additionally, different stages of osseointegration were modeled by altering the elastic modulus of bone immediately surrounding the implants.To simulate the maximum strain value, a horizontal misfit of 83.3 μm had to be introduced, whereas the minimum strain value could be simulated via a horizontal misfit of 71.5 μm. Maximum misfit caused stress magnitudes of 105 MPa in cortical bone and 5.3 MPa in trabecular bone. Minimum misfit caused stress magnitudes of 90 MPa in cortical bone and 4.6 MPa in trabecular bone. The difference between maximum and minimum horizontal misfit was 12 μm and led to a reduction in maximum stress levels of 15 MPa in cortical bone and 0.7 MPa in trabecular bone. Progressing osseointegration affected the stress situation of the supporting implants.Within the limitations of this investigation, it can be concluded that bone adaptation may lead to implant site displacement in the range of several micrometers. Early fixation of non-passively fitting superstructures on implants may lead to greater passivity of fit.
It is generally assumed that passively fitting superstructures are a prerequisite for long-lasting implant success. In the study presented, the strain development of three-unit implant fixed partial dentures (FPDs) was evaluated at the bone surrounding the implant and on the superstructure using a strain gauge technique. Six groups of three-unit FPDs representing the commonly used techniques of bridge fabrication were investigated with 10 samples each, in order to quantify the influence of impression technique, mode of fabrication and retention mechanism on superstructure fit. Two ITI implants (Straumann, Waldenburg, Switzerland) were anchored in a measurement model according to a real-life patient situation and strain gauges were fixed mesially and distally adjacent to the implants and on the bridge pontics. The developing strains were recorded during cement setting and screw fixation. For statistical analysis, multivariate two sample tests were performed setting the level of significance at P=0.1. None of the investigated bridges revealed a truly passive fit without strains occurring. About 50% of the measured strains were found to be due to impression taking and model fabrication, whereas the remaining 50% were related to laboratory inaccuracies. The two impression techniques used did not reveal any significant differences in terms of precision. Both modes of fixation--i.e. cement and screw retention--provoked equally high stress levels. In the fabrication of screw-retained FPDs, similar results were obtained from the use of burn-out plastic copings and the technique of casting wax moulds to premachined components. Bonding bridge frames onto gold cylinders directly on the implants significantly reduces strain development.
We shall study the qualitative properties of the class of self-similar spherically symmetric models with two non-interacting scalar fields with exponential potentials. Numerous scalar fields, and particularly scalar fields with exponential potentials, are known to arise in a variety of theories of the fundamental interactions. In recent investigations of the cosmological implications of these theories a number of novel features has been obtained, including the important assisted inflationary behaviour. In order to study this inflationary scenario, we shall restrict our study here to the so-called `spatially' self-similar models. We derive the governing system of evolution equations for the model, which is an autonomous five-dimensional system of ordinary differential equations, in terms of appropriately defined bounded variables. A monotonic function is obtained and the local stability of the equilibria is determined, so that global properties of the physical phase space can be deduced. Numerical integrations are also undertaken to complement the qualitative analysis and in order to investigate possible transient behaviour. From our dynamical analysis we find that, depending on the parameters of the models, in general the models begin expanding from a state with two scalar fields which are massless, and subsequently either recollapse and again evolve towards a model with two massless scalar fields or continue expanding towards the assisted inflationary solution. Hence we find that there exists an open set of models that undergo assisted inflation.
