The purpose of this study was to assess the influence of Er:YAG laser pulse repetition rate on the thermal alterations occurring during laser ablation of sound and demineralized primary dentin. The morphological changes at the lased areas were examined by scanning electronic microscopy (SEM). To this end, 60 fragments of 30 sound primary molars were selected and randomly assigned to two groups (n = 30); namely A sound dentin (control) and B demineralized dentin. Each group was divided into three subgroups (n = 10) according to the employed laser frequencies: I-4 Hz; II-6 Hz, and III-10 Hz. Specimens in group B were submitted to a pH-cycling regimen for 21 consecutive days. The irradiation was performed with a 250 mJ pulse energy in the noncontact and focused mode, in the presence of a fine water mist at 1.5 mL/min, for 15 s. The measured temperature was recorded by type K thermocouples adapted to the dentin wall relative to the pulp chamber. Three samples of each group were analyzed by SEM. The data were submitted to the nonparametric Kruskal-Wallis test and to qualitative SEM analysis. The results revealed that the temperature increase did not promote any damage to the dental structure. Data analysis demonstrated that in group A, there was a statistically significant difference among all the subgroups and the temperature rise was directly proportional to the increase in frequency. In group B, there was no difference between subgroup I and II in terms of temperature. The superficial dentin observed by SEM displayed irregularities that augmented with rising frequency, both in sound and demineralized tissues. In conclusion, temperature rise and morphological alterations are directly related to frequency increment in both demineralized and sound dentin. 相似文献
Modern compilers apply various code transformation algorithms to improve the quality of the target code. However, a complex problem is to determine which transformation algorithms must be utilized. This is difficult because of three reasons: a number of transformation algorithms, various combination possibilities, and several configuration possibilities. Over the last few years, various intelligent systems were presented in the literature. The goal of these systems is to search for transformation algorithms and thus apply them to a certain program. This paper proposes a flexible, low-cost and intelligent system capable of identifying transformation algorithms for an input program, considering the program’s specific features. This system is flexible for parameterization selection and has a low-computational cost. In addition, it has the capability to maximize the exploration of available computational resources. The system was implemented under the Low Level Virtual Machine infrastructure and the results indicate that it is capable of exceeding, up to 21.36%, performance reached by other systems. In addition, it achieved an average improvement of up to 17.72% over the most aggressive compiler optimization level of the Low Level Virtual Machine infrastructure. 相似文献
In this study we tested a Bayesian model based on a conjugate gamma/Poisson pair associated with environmental variables derived from satellite data such as sea surface temperature (SST) and its derived gradient fields from Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra, chlorophyll-a concentration from Sea Viewing Wide field of View Sensor (SEAWiFS)/SeaStar and surface winds and Ekman pumping from SeaWinds/Quick Scatterometer (QuikSCAT) to predict weekly catch estimates of the skipjack tuna in the South Brazil Bight. This was achieved by confronting the fishery data with model estimates and regressing the results on the satellite data. The fishery data were expressed by an index of catch per unit effort (CPUE) calculated as the weight of fish caught (in tonnes) by fishing week, and were divided into two series, called historical series (1996–1998; 2001), and validation year (2002). The output of model CPUE estimates is in good agreement with the historical weekly CPUE and generated updated weekly estimates that explained up to 62% of weekly CPUE from 2002. In general, the best proxy for the Bayesian weekly estimates is the gradient zonal SST field. The results refined previous knowledge of the influence of SST on the occurrence of skipjack tuna. 相似文献
We are interested in the finite element solution of elliptic problems with a right-hand side of the single layer distribution type. Such problems arise when one aims at accounting for a physical hypersurface (or line, for bi-dimensional problem), but also in the context of fictitious domain methods, when one aims at accounting for the presence of an inclusion in a domain (in that case the support of the distribution is the boundary of the inclusion). The most popular way to handle numerically the single layer distribution in the finite element context is to spread it out by a regularization technique. An alternative approach consists in approximating the single layer distribution by a combination of Dirac masses. As the Dirac mass in the right hand side does not make sense at the continuous level, this approach raises particular issues. The object of the present paper is to give a theoretical background to this approach. We present a rigorous numerical analysis of this approximation, and we present two examples of application of the main result of this paper. The first one is a Poisson problem with a single layer distribution as a right-hand side and the second one is another Poisson problem where the single layer distribution is the Lagrange multiplier used to enforce a Dirichlet boundary condition on the boundary of an inclusion in the domain. Theoretical analysis is supplemented by numerical experiments in the last section. 相似文献
L605 (20Cr-15W-10Ni wt pct) and CCM (28Cr-6Mo wt pct) cobalt-based superalloys are candidates for a wide range of applications, from gas turbine components to biomedical implants. Attention is currently focused on the optimization of grain structure as an appropriate approach to increase yield stress without affecting significantly the ductility. In this study, the Laser Ultrasonics for Metallurgy (LUMet) technology is used to examine in situ the evolution of the mean grain size associated with recrystallization and grain growth during heat treatments from the cold-rolled state. The recrystallization process is completed at 1373 K (1100 °C) for L605 and 1273 K (1000 °C) for CCM. The subsequent grain growth rate in L605 is larger compared to CCM. Continuous measurements of the grain size evolution are found to be consistent with grain growth affected by solute drag. Through in situ measurements, the laser ultrasonic technology significantly accelerates the determination of metallurgical parameters allowing for fast optimization of process parameters required to meet specific applications.
Transformation-induced plasticity in a ceria-stabilized-zirconia based composite was studied in four-point bending, with particular emphasis on nucleation and growth of tetragonal-to-monoclinic transformation bands. They initiated on the side in tension at a given value of stress and grow in size and number with increased applied load. The spacing between them was related to samples’ thickness: thicker samples led to a smaller number of larger/deeper bands. Residual stresses around indentations, placed on the tensile surface of some samples, triggered transformation bands nucleation but had no significant effect on the final total number of bands. A simple stress shielding model suggests that wide bands hinder adjacent thinner bands to propagate and expand because of stress shielding around them. Nucleation of a given transformation band is thus related to: (i) stress concentrations at the surface, (ii) geometry (stress-field inside the sample) and (iii) a shielding effect from the bands already present. 相似文献