Universidade Federal de Santa Maria

About: Universidade Federal de Santa Maria is a education organization based out in Santa Maria, Brazil. It is known for research contribution in the topics: Population & Context (language use). The organization has 21178 authors who have published 35632 publications receiving 371665 citations.

Stereoselective synthesis of enynes by nickel-catalyzed cross-coupling of divinylic chalcogenides with alkynes.

Abstract: (Z,Z)- and (E,E)-divinylic selenides and telurides undergo direct coupling with terminal alkynes in the presence of a nickel/CuI catalyst at room temperature to give (Z)- and (E)-enyne systems in good yields and with complete retention of configuration.

The Endocrown: An Alternative Approach for Restoring Extensively Damaged Molars

Abstract: Endocrown-type restorations are single prostheses fabricated from reinforced ceramics that can be acid etched, indicated for endodontically treated molar teeth that have significant loss of coronal structure. Endocrowns are formed from a monoblock containing the coronal portion integrated into the apical projection that fills the pulp chamber space, and possibly the root canal entrances. In this study, the proposal was to discuss the indication and use of the endocrown to replace single crowns with intraradicular retention, and to present a clinical case report on the 3-year follow-up of an endocrown-type restoration, fabricated from injected lithium disilicate ceramic (IPS e.Max Press/Ivoclar Vivadent) in a mandibular first molar with extensive coronal destruction from fracture. It was found that endocrown restorations could be made following the development of reinforced ceramics that can be acid etched, that have aggregate strength and esthetics, that bond to the dental structure, and that have developed from broader knowledge of the biomechanical behavior of depulped teeth restored with and without intraradicular posts. Clinical studies have shown that the endocrown has functional longevity, and has become a promising alternative in the esthetic and functional recovery of endodontically treated molar teeth. CLINICAL SIGNIFICANCE It should be borne in mind that endocrowns offer advantages for the restoration of depulped molar teeth, insofar as they promote adequate function and offer adequate esthetics, and also maintain the biomechanical integrity of the compromised structure of non-vital posterior teeth. By eliminating the use of a post and filling core, the number of adhesive bond interfaces is reduced, thus making the restoration less susceptible to the adverse effects of degradation of the hybrid layer. In this clinical case, the 3-year survival of the endocrown restoration may be considered successful. (J Esthet Restor Dent 25:383-391, 2013)

Low-temperature degradation of a Y-TZP ceramic after surface treatments.

Abstract: The purpose of this study was to evaluate the influence of zirconia surface treatments on low-temperature degradation (LTD). Disc-shaped specimens were subjected to one of four surface treatments, denoted as C (control-no surface treatment), Si (air abrasion with 30 µm silica-modified alumina particles), Al (air abrasion with 30 µm alumina particles), and Gr (grinding with 120 grit diamond discs). Half of the samples were submitted to autoclave treatment for 12 h (127°C, 1.5 bar). Samples were characterized by x-ray diffraction and profilometer analysis and were subjected to biaxial flexural strength test. All of the groups exhibited an increase in the amount of monoclinic phase (m-phase) after LTD. The t→m transformation was remarkable for the specimens from the C group, which also exhibited a significant increase in strength. The Gr group also exhibited an increase in strength but lower initial roughness, which probably suppressed LTD on the zirconia surface. The specimens subjected to air abrasion exhibited higher initial amounts of m-phase and a small increase in m-phase after LTD; the strength was not affected in these groups. The effects of LTD were different with each surface treatment applied. Apparently, LTD may be suppressed by smoother surfaces or the presence of an initial amount of m-phase on zirconia surface.

Comparison of digital control techniques with repetitive integral action for low cost PWM inverters

Abstract: This paper presents a comparison among digital control techniques with repetitive integral action applied to voltage-source PWM inverters. As a result of the repetitive integral action, these digital control schemes can reduce steady-state errors and distortions caused by unknown periodic disturbances, which usually result from the input source and output load. Moreover, these digital control schemes measure only the output voltage, decreasing the amount of sensors and the overall system cost. The control laws, stability analysis, common and distinguishing features of these control algorithms are discussed. Experimental results from a PWM inverter (110 V/sub RMS/, 1 kVA) controlled by a low cost microcontroller are presented to demonstrate the control techniques performance under different load conditions, output filters and command strategies.