Taxing hard-to-tax markets

Tax enforcement costs constrain the government s ability to observe economic transactions, giving rise to hard-to-tax (HTT) markets. In these markets transactions are untaxed and consumers are better o¤ than in taxed markets. This paper studies a novel approach to combat evasion in HTT markets: consumer auditing, which rewards consumers for re- questing transaction receipts. We develop a Hotelling-type spatial model of sales taxation to analyze the welfare and distributional e¤ects of the implementation of this policy. We and that consumer auditing allows for a lower tax rate and greater provision of the public good in the economy. We show that this policy not only can enhance welfare, but also equalize utilities of consumers across markets

Efeitos da hard accountability na gestão das escolas públicas estaduais brasileiras

Este estudo avalia os impactos das políticas de hard accountability sobre a gestão das escolas estaduais das redes públicas brasileiras. Para isto, foi elaborado um indicador de gestão com base nas informações da Prova Brasil dos anos de 2007 e 2013. Posteriormente, através da metodologia diferenças-em-diferenças, foi estimada a relação entre os programas de incentivo via bonificação e a gestão, isolando-se os efeitos distintos entre escolas por meio de variáveis de controles desenhadas para captar o ambiente escolar. Os resultados sugerem que a hard accountability é estatisticamente significativa sobre a gestão das escolas e seu efeito é negativo. Resultados nessa linha também foram encontrados ao segmentar estas escolas de acordo com a experiência dos diretores e nível de proficiência. Adicionalmente, os impactos da hard accountability e gestão foram estudados tendo a proficiência como variável dependente. A hard accountability apresentou efeito positivo sobre a proficiência do 9º ano em Matemática. O indicador de gestão, por sua vez, mostrou relação positiva com as notas médias de todas as séries e disciplinas avaliadas.

Estudo da molhabilidade de ligas de adição à base de prata sobre insertos cerâmicos para aplicação em brocas perfuração de poços de petróleo

Metal-ceramic interfaces are present in tricone drill bits with hard ceramic inserts for oil well drilling operations. The combination of actions of cutting, crushing and breaking up of rocks results in the degradation of tricone drill bits by wear, total or partial rupture of the drill bit body or the ceramic inserts, thermal shock and corrosion. Also the improper pressfitting of the ceramic inserts on the bit body may cause its total detachment, and promote serious damages to the drill bit. The improvement on the production process of metal-ceramic interfaces can eliminate or minimize some of above-mentioned failures presented in tricone drill bits, optimizing their lifetime and so reducing drilling metric cost. Brazing is a widely established technique to join metal-ceramic materials, and may be an excellent alternative to the common mechanical press fitting process of hard ceramic inserts on the steel bit body for tricone drill bit. Wetting phenomena plays an essential role in the production of metal/ceramic interfaces when a liquid phase is present in the process. In this work, 72Silver-28Copper eutectic based brazing alloys were melted onto zirconia, silicon nitride and tungsten carbide/Co substrates under high vacuum. Contact angle evolution was measured and graphically plotted, and the interfaces produced were analysed by SEM-EDX. The AgCu eutectic alloy did not wet any ceramic substrates, showing high contact angles, and so without chemical interaction between the materials. Better results were found for the systemns containing 3%wt of titanium in the AgCu alloy. The presence os titanium as a solute in the alloy produces wettable cand termodinamically stable compounds, increasing the ceramics wetting beahviour

Influence of shot peening and hard chromium electroplating on the fatigue strength of 7050-T7451 aluminum alloy

Chromium electrodeposition is a technique for the production of functional coatings on engineering components. These coatings are extensively micro-cracked and present high level of hardness, resistance to corrosion and wear and low coefficient of friction. In this paper the shot peening influence on the fatigue strength of aluminum 7050-T7451 alloy chromium electroplated, was investigated.The shot peening process was carried out to create residual stresses using ceramic and glass shots. A hard chromium electroplated coating of 100 mu m thickness was performed on the base material and the shot peened base material surfaces. S-N curves were obtained in axial and bending fatigue tests and compared with the 7050-T7451 aluminum alloy. In order to study the influence of residual stresses on fatigue life, the behavior of compressive residual stress field was measured by an X-ray tensometry.An increase in the axial fatigue strength of 25% and 50% of ceramic and glass shots, respectively, was observed. The lower performance in fatigue life for ceramic-shot peening may be attributed to higher surface damage, as a consequence of the overpeening intensity performed. However, in bending fatigue the behavior was practically equivalent for both processes. Fracture surface analysis by scanning electron microscopy was used to observe crack origin sites from shot peened and chromium electroplated samples. (C) 2006 Elsevier Ltd. All rights reserved.

The effect of WC-17Co thermal spray coating by HVOF and hard chromium electroplating on the fatigue life and abrasive wear resistance of AISI 4340 high strength steel

One of the most interesting alternatives for replacement of hard chrome plating is tungsten carbide thermal spray coating applied by the high velocity oxy-fuel (HVOF) process which presents a safer, cleaner and less expensive alternative to chromium plating. The objective of this research is to compare the influence of the tungsten carbide-17cobalt (WC- 17Co) coating applied by high velocity oxy fuel (HVOF) process with that of hard-chromium electroplating on the fatigue strength and abrasive wear of AISI 4340 steel.

Scanning electron microscopy evaluation of the hard tissue barrier after pulp capping with calcium hydroxide, mineral trioxide aggregate (MTA) or ProRoot MTA

The aim of this study was to investigate the morphology and localisation of calcium hydroxide- and mineral trioxide aggregate (MTA)-induced hard tissue barriers after pulpotomy in dogs' teeth. Pulpotomies were performed on maxillary and mandibular premolars of five dogs. The teeth were assigned into three groups according to the pulp-capping agent used. The pulpal wounds were capped with calcium hydroxide (Ca(OH)(2) - control), MTA or ProRoot MTA, and the cavities were restored with amalgam. After a 90-day follow-up period, the dogs were euthanised and the teeth were examined under scanning electron microscopy (SEM). An image-processing and analysis software was used to delimit the perimeters of the root canal area and the hard tissue barrier to determine the percentage of root canal obliteration. SEM data were used to assess the morphology, localisation and extension of the reparative hard tissue barriers. ProRoot MTA was statistically different from MTA and Ca(OH)(2) (P < 0.05) regarding tissue barrier morphology. Localisation data showed that ProRoot MTA was significantly different from Ca(OH)(2) (P < 0.05) and similar to MTA (P > 0.01; P > 0.05). No statistically significant difference (P > 0.01; P > 0.05) was observed between MTA and Ca(OH)(2). A larger number of complete (centroperipheral) hard tissue barriers with predominance of dentinal tubules was observed to the ProRoot MTA when compared with the Ca(OH)(2) group.

Linear dimensional changes of denture base and hard chair-side reline resins after disinfection

Objectives: This study evaluated the effect of disinfection by immersion in sodium perborate (50 degrees C/10 min) or microwave irradiation (650 W/6 min) on the linear dimensional change (LDC) of four reline resins (Kooliner-K, New Truliner-N, Tokuso Rebase Fast-T, Ufi Gel Hard-U) and one heat-polymerizing denture base resin (Lucitone 550-L). Methods: Specimens (50.0 mm diameter, 0.5 mm thickness) were made using a split mold with reference points, and divided into two controls and four test groups (u = 8). The distances between the points were measured on the mold (baseline readings), and compared to those obtained from the specimens after: polymerization or immersion in water (37 degrees C) for 7 days (controls); 2 or 7 cycles of disinfection by immersion or microwave irradiation. Results: the two-way ANOVA and Tukey's test (alpha = 0.05) showed that microwave disinfection significantly increased the mean LDC of materials L (-1.43%), N (-1.27%) and K (-1.06%). Material N also exhibited a significant increase in LDC after two cycles of chemical disinfection (-0.73%). For U (-0.47%) and T (-0.21%) materials, no significant changes in LDC were found. Conclusions: Microwave disinfection increases the shrinkage of materials L, N, and K. The dimensional stability of resins U and T was not affected by the disinfection methods evaluated. (c) 2006 Wiley Periodicals, Inc.

Effect of microwave disinfection on the flexural strength of hard chairside reline resins

Objectives: This study investigated the effect of microwave disinfection (650 W/6 min) on the flexural strength of five hard chairside reline resins (Kooliner, Duraliner II, Tokuso Rebase Fast, Ufi Get Hard, New Truliner) and one denture base resin (Lucitone 550).Methods: Thirty-two specimens (3.1x10x64 mm) from each acrylic resin were produced and divided into four groups of eight specimens each. The flexural test was performed after polymerization (G1), after two cycles of microwave disinfection (G2), after 7 days storage in water at 37 degrees C (G3) and after seven cycles of microwave disinfection (G4). Specimens from group G4 were microwaved daily being stored in water at 37 degrees C between exposures. The specimens were placed in three-point bend fixture in a MTS machine and loaded until failure. The flexural values (MPa) were submitted to ANOVA and Tukey's test (p=0.05).Results: Two cycles of microwave disinfection promoted a significant increase in flexural strength for materials Kooliner and Lucitone 550. After seven cycles of microwave disinfection, materials Kooliner and New Truliner showed a significant increase (p<0.05) in flexural values. The flexural strength of the material Tokuso Rebase was not significantly affected by microwave irradiation. Seven cycles of microwave disinfection resulted in a significant decrease in the flexural strength of material Duraliner II. Material Ufi Get Hard was the only resin detrimentally affected by microwave disinfection after two and seven cycles.Conclusions: Microwave disinfection did not adversely affect the flexural strength of all tested materials with the exception of material Ufi Get Hard. (c) 2005 Elsevier Ltd. All rights reserved.

Bonding strength between a hard chairside reline resin and a denture base material as influenced by surface treatment

Direct relining of dentures made with hard chairside reline resins is faster than laboratory-processed reline systems and the patient is not without the prosthesis for the time necessary to perform the laboratory procedures. However, a weak bond between the autopolymerizing acrylic reline resins and the denture base material has been observed. This study evaluated the effect of six different surface treatments on the bond strength between a hard chairside reline acrylic resin and ia heat-cured acrylic resin. Specimens of the heat-cured acrylic resin were divided into seven groups. one of these groups remained intact. In the other groups, a 10-mm square section was removed from the centre of each specimen. The bonding surfaces were then treated with (i) methyl methacrylate monomer, (ii) isobutyl methacrylate monomer, (iii) chloroform, (iv) acetone, (v) experimental adhesive and (vi) no surface treatment-control group. Kooliner acrylic resin was packed,into the square sections and polymerized. The bonding strength was evaluated by a three-point loading test. The results were submitted to one-way analysis of variance (ANOVA) followed by a Tukey multiple range test at a 5% level of significance. No significant difference was found between the surface treatment with Lucitone 550 monomer or chloroform, but both were stronger than the majority of the other groups. The bond strength provided by all the surface treatments was lower than that of the intact heat-cured resin.

Effect of thermal cycling on microleakage between hard chairside relines and denture base acrylic resins

Objectives:Microleakage is a pre-stage of debonding between hard chairside relines and denture base acrylic resins. Therefore, it is important to assess them with regard to the longevity of the relined denture. This study investigated the effect of thermal cycling on the microleakage at the interface of three hard chairside reline resins and three denture base resins.Material and methods:Rectangular bars (12 mm x 3 mm x 3 mm) of Lucitone 550, Acron MC and QC 20 were made and relined with Kooliner, Tokuyama Rebase Fast II and Ufi Gel Hard, Lucitone 550, Acron MC and QC 20 resins. Specimens were divided into one control and two test groups (n = 10). In specimens of the control group, the microleakage was performed after the reline procedure. In Test Group 1, the specimens were stored for 24 h in distilled water at room temperature and in Test Group 2; the specimens were thermal cycled from 5 to 55 degrees C for 5000 cycles with a 30-s dwell time. Subsequently, all specimens were immersed in 50% silver nitrate solutions for 24 h. All specimens were sectioned longitudinally into three fractions and the lateral sections were examined (n = 20). Silver nitrate stain penetration was examined under a stereoscopic lens with x30 magnification, and the images were captured. Leica Qwin image analysis software was used to determine microleakage at the interface of the materials. Data were analysed using the Kruskal-Wallis test at a 95% level of significance.Results:For all cycles, there were no statistically significant differences between thermal cycled and non-thermal cycled groups (p > 0.05).Conclusion:It can be concluded that thermal cycling had no effect on the microleakage.

Glass transition temperature of hard chairside reline materials after post-polymerisation treatments

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)