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Nov 21, 2004

The prevalence and characterization of implant-related findings in panoramic radiographs

Introduction: In Colombia, the last oral health study showed that about 70% of the population has partial edentulism while 5.2% will have lost all their teeth between the age of 65 and 79. Rehabilitation with implants is an increasingly used option, which requires clinical and radiographic follow-up. Panoramic radiography is a low-cost option, in which it is possible to observe areas of bone loss, mesiodistal angulation of the implant, relationship with anatomical structures and lesions suggestive of peri-implantitis. Reports and analysis of relevant data on radiographic findings associated with dental implants are required to determine the risk factors for their success in patients who use them. Objective: To determine the prevalence and characterize the findings associated with osseointegration implants in panoramic radiographs. Methods: A descriptive cross-sectional observational study was carried out with 10,000 digital panoramic radiographs selected by convenience from radiological centers in the city of Bogota, Colombia, of which 543 corresponded to the sample analyzed for the presence of implants. The following were evaluated for each implant: location, position, angulation and distances to adjacent structures, using the Clínicalview® program (Orthopantomograph OP200D, Instrumentarium, USA). Results: The frequency of radiographs with implants was 5.43% with a total of 1,791 implants, with an average of 3.2 per radiograph. They were found in greater proportion in the upper jaw with a supracrestal location and an angulation of 10.3 degrees. 32% had implant/tooth or implant/implant distances that were less than optimal. 40.9% were restored and 1.2% showed lesions compatible with periimplantitis. Conclusions: A high percentage of the implants reviewed have a risk factor that affects their long-term viability, either due to angulation, supracrestal or crestal position, proximity to teeth or other implants, or because they are not restorable.

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Jan 1, 1970

Imaging properties of radiative multi-sub mirror array structure

Based on the characteristics of liquid lens sparse aperture imaging, a radiative multiplet array structure is proposed; a simplified model of sparse aperture imaging is given, and the analytical expression of the modulation transfer function is derived from the optical pupil function of the multiplet array structure; the specific distribution form of this multiplet array structure is given, and the structure parameters are approximated by the dimensionless method; the two types of radiative multiplet array structures are discussed, and the filling factor, redundancy, modulation transfer function and other characteristic parameters are calculated. The physical phenomena exhibited by the parametric scan are discussed, and the structural features and imaging characteristics of these two arrays are compared. The results show that the type-II structure with larger actual equivalent aperture and actual cutoff frequency and lower redundancy is selected when the average modulation transfer function and the IF characteristics of the modulation transfer function of the two structures are close to each other; the type-II structure has certain advantages in imaging; the conclusion is suitable for arbitrary enclosing circle size because the liquid lens-based multiplet array structure adopts dimensionless approximation parameters; compared with the composite toroidal structure, the radiative multiplet mirror structure has a larger actual cut-off frequency and actual equivalent aperture when the filling factor is the same.

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Sept 26, 2021

Research on Optimization of collector module of new flat plate heat pipe PV/T heat pump system

The mathematical model of a new flat plate heat pipe PV/T heat pump system is established. The experimental data of the system under various working conditions are obtained through experimental measurement, and the accuracy and reliability of the model are verified. Based on the verified mathematical model, the thermal performance, electrical performance and the performance of the heat pump system are simulated. The results show that under winter conditions, the daily average thermal power, electrical power and COP of the system are 274.5 W, 93.5 W and 2.7 W respectively. Due to the low outdoor ambient temperature in winter, during winter operation, the heat collection system will lose a lot of heat to the surrounding environment through the photovoltaic panel surface, resulting in the heat collection of the system cannot meet the heat demand of the heat pump side, which is intuitively shown as the water temperature of the heat collection tank on the evaporation side shows a downward trend throughout the day. Therefore, the collector module of the system is optimized by adding a collector. After optimization, the daily average thermal power of the system is increased to 654.2 W and the COP is increased to 6.9.

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May 18, 2021

Determination of overall heat transfer coefficients comparing LMTD and ε-NTU methods

Thermal energy transfer processes are important problems to be solved in the field of engineering. In this field, heat exchangers are one of the most used equipment in the industry. The present investigation was carried out in an operating hydrogen sulfide cooler system, with the objective of determining the overall heat transfer coefficients by two methods, applying the passive experimentation procedure. With the Logarithmic Mean Temperature Difference (LMTD)

method, values ranging from 11.1 to 73.3 W/(m² ·K) were obtained, compared to 11.0 to 58.9 W/(m² ·K) when applying the Effectiveness-Number of Transfer Units (ε-NTU) method. Although the results obtained were similar, for the thermal evaluation of the chiller system studied, it was recommended to employ the LMTD approach, used by most researchers.

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Apr 11, 2019

Rising incomes and inequality of access to infrastructure among Latin American Households

The question of infrastructure needs is a crucial policy one in Latin America, given evidence of large access shortfalls across all major types of infrastructure, and the increase in demand linked to the rapid growth in households’ income over the past two decades. However, how much and how fast countries should invest in each of the main infrastructure areas are largely speculative, as to date, literature on investment needs has relied exclusively on aggregate data and cross-country regressions, ignoring both potential policy and supply-side differences across settings, and variations in demand along the income distribution. This paper addresses these shortcomings, providing building blocks to better assess infrastructure investment needs across the region. It does so documenting access to services and ownership of infrastructure-related durables in the water, energy, telecom, and transport areas, based on harmonized household survey data covering 1.6 million households in 14 Latin American countries from 1992 to –2012. It provides a systematic disaggregation of access and ownership rates at different levels of income and over time, and econometrically derives the country infrastructure premium, a measure of how much a household benefits from simply being located in a given country. Within countries, the results show extensive inequality of access across the income distribution, but this is also the case for households at similar levels of income across countries. Few country fundamentals appear to be significant in explaining this variability, pointing to differences in policy choices and local constraints as important determinants. The paper derives disaggregated income elasticity measures for the full set of infrastructure indicators and uses these to estimate the time that would be needed to close the remaining gap for households at different levels of the income distribution in each country under a “business as usual” hypothesis. Under that scenario, universal access appears to still be decades away for many countries in the region. The last part discusses the policy challenges, arguing that in a context in which public budgets face strong constraints and significant increases in private investment are unlikely to be forthcoming, a large part of the solution lies in refocused investment strategies, better demand management, and improved public spending efficiency.

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Aug 3, 2020

Subnanophase coatings as new type low-dimensional nanomaterials: Ultra-high-vacuum synthesis, properties and application

In this paper, a classification of low-dimensional nanomaterials is given, and new type of these nanomaterials — subnanophase coatings are proposed. Experimental results on the formation of a wetting layer of a transition metal on a silicon substrate by physical deposition in vacuum and results of this layer identification by the EELS method are given. Based on these results, a new approach to the formation of subnanophase coatings has been proposed by creation of an interface stresses structuring WL. The possible properties and application prospects of subnanophase coatings are considered.

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