Resistência à tração de barras de aço corroídas

Among the pathological manifestations associated with reinforced concrete, corrosion of the reinforcement is one of the most serious issues since it is related to the durability of the structures and the safety of the users. Although the reinforcement in the structural components is protected by a covering layer, carbonation or the presence of chlorides in the concrete generates necessary conditions for corrosion of the reinforcement. This causes a reduction in the cross section and the generation of products that, due to their volumetric expansion, cause cracks in the interior of the concrete. This work evaluates the effects of corrosion on mechanical properties of corroded reinforcements through accelerated conditions in the laboratory. Steel bars installed inside cylindrical concrete specimens are subjected to accelerated corrosion, immersed in a saline solution with the application of an electric current for periods of 1, 3, 5 and 7 d. After corrosion, the steel bars are removed and their weight loss, degree of corrosion and tensile strength are evaluated. The results demonstrate an increased degree of corrosion with exposure time to the saline solution and the non-uniform reduction of the tensile strength of the bars due to the formation of corrosion pits with varying depth along the bar.

Microcrystal alignment in drawn fiber over sub-meter to kilometer length scales

This paper describes a method for aligning stiff, high-aspect-ratio microcrystals over macro-length scales using a polymer fiber drawing process. A composite preform was constructed with an interfacial, liquid shell layer of grapeseed oil suspending ytterbium-doped potassium lutetium fluoride microcrystals (30% Yb:K2LuF5, KLF) between adjacent cylindrical surfaces of acrylic (polymethyl methacrylate, PMMA). The mean length of synthesized KLF microcrystals was 67 microns, and the mean aspect ratio, equivalent to crystal length divided by diameter, was eight. The acrylic-host preform was drawn into fiber, resulting in uniform reduction of all cross-sectional dimensions by a factor of approximately 20 in the final fiber. A corresponding width reduction of the interstitial liquid-filled gap, containing microcrystals between the polymer surfaces, constrains the microcrystals and causes alignment of the crystal long axes parallel to the axis of the drawn composite fiber. Alignment was best for clearly separated microcrystals and improved even further with the longest lengths, or highest aspect-ratio microcrystals.

A Novel Elastic Wrap for Syndesmotic Reduction with Post-Operative CT Scan Analysis

Category: Ankle, Trauma Introduction/Purpose: Syndesmosis malreductions occur in up to 50% of patients. Several studies concluded that the position of the reduction tines of the periarticular clamp determines the final fibular position. The purpose of this study was to determine if an elastic wrap would provide a more uniform reduction force resulting in an anatomic syndesmosis reduction. We hypothesized that the force applied to the ankle by an elastic wrap would be relatively low and uniform circumferentially around the ankle medially and laterally. Furthermore we thought the ankle wrap would negate the dependency of clamp tine placement and circumferentialy reduce the syndesmosis perfectly. In this series Syndesmotic injuries were treated with the wrap for reduction, screw fixation and post-operative CT scan verification. Methods: Syndesmosis malreductions occur in up to 50% of patients. Several studies concluded that the position of the reduction tines of the periarticular clamp determines the final fibular position. The purpose of this study was to determine if an elastic wrap would provide a more uniform reduction force resulting in an anatomic syndesmosis reduction. We hypothesized that the force applied to the ankle by an elastic wrap would be relatively low and uniform circumferentially around the ankle medially and laterally. Furthermore we thought the ankle wrap would negate the dependency of clamp tine placement and circumferentialy reduce the syndesmosis perfectly. In this series Syndesmotic injuries were treated with the wrap for reduction, screw fixation and post-operative CT scan verification. Results: In a grossly unstable cadaver ankle model the ankle wrap achieved a perfect reduction every time it was trialed. The pressure film component of this study confirmed a uniform reduction force circumferentially at the ankle under the ankle wrap device of 5-9 pounds per square inch. Post-operative CT scans in 5 cases confirmed anatomic reduction of the syndesmosis in those cases treated surgically with the wrap and screw fixation. Conclusion: Malreduction of the syndesmosis can be avoided by using an elastic wrap instead of the standard peri-articular clamp in common clinical practice today.

Air quality in the eastern United States and Eastern Canada for 1990–2015: 25 years of change in response to emission reductions of SO₂ and NO_x in the region

SO2 and NOx are precursors to form sulfate, nitrate and ammonium particles, which account for more than 50 % of PM2.5 mass in the eastern US and Eastern Canada, and are dominant components of PM2.5 during many smog events. H2SO4 and HNO3, formed from oxidation of SO2 and NOx respectively, are the main sources of acid deposition through wet and dry depositions. NOx is also a precursor to the formation of tropospheric O3, which is an important atmospheric oxidant and is also essential for the formation of other atmospheric oxidants, such as OH and H2O2. In the past 26 years from 1990 to 2015, emissions of SO2 and NOx in US were significantly reduced from 23.1 and 25.2 million tons/year in 1990 to 3.7 and 11.5 million tons/year in 2015 respectively. In Canada, SO2 and NOx were reduced by 63 % and 33 % from 1990 to 2014. In response to the significant reduction of SO2 and NOx emissions, air quality in the eastern US and Eastern Canada improved tremendously during 1990–2015. In this study, we analyzed surface air concentrations of SO42−, NO3−, NH4+, HNO3 and SO2 measured weekly by the Clean Air Status and Trends Network (CASTNET) in the US and measured daily from the Canadian Air and Precipitation Monitoring Network (CAPMoN) in Canada to reveal the temporal and spatial changes of each species during the 25-year period. For the whole the eastern US and Eastern Canada, the annual mean concentrations of SO42−, NO3−, NH4+, HNO3, SO2 and TNO3 (NO3− + HNO3, expressed as the mass of equivalent NO3−) were reduced by 73.3 %, 29.1 %, 67.4 %, 65.8 %, 87.6 % and 52.6 % respectively from 1990 to 2015. In terms of percentage, reduction of all species except NO3− was spatially uniform; reduction of SO2 and HNO3 was similar in warm season (May–October) and cold season (November–April), and reduction of SO42−, NO3− and NH4+ was more significant in warm season than in cold season. Reduction of SO42− and SO2 mainly occurred in 1989–1995 and 2007–2015 during warm season, and in 1989–1995 and 2005–2015 during cold season. Reduction of NO3− mainly occurred in the Midwest after 2000. Other than in the Midwest, NO3− had very little change during cold season for the period. The reduction of NH4+ generally followed the reduction trend of SO42−, especially after 2000 the temporal trend of NH4+ was almost identical to that of SO42−. The ratio of S in SO42− to total S in SO42− and SO2, as well as the ratio of NO3− to TNO3 increased by more than 50 % during the period. This indicates that much more percentage of SO2 was oxidized to SO42−, and much more percentage of HNO3 was neutralized to NH4NO3 in the region near the end of the period.

The effect of increased concentration of organic matter on the rock properties

Rocks enriched with organic matter (OM) are considered: Baltic combustible shale-kukersites and domanic deposits of the Volga-Ural basin, in which organic matter is one of the rock-forming components. The discrepancy between the volume and weight ratios of organic and mineral matter of rocks is noted. The volume significance of the OM of these rocks in the thickness of shale formations and domanic sediments is shown. The high content of OM determines the reduced strength of such rocks. The variability of OM concentrations and other irregularities of shale formations and Domanic rocks (texture, nodule bodies, etc.) are factors of mosaic distribution of areas with different density-strength properties and, as a result, non-uniform reduction of layers and their deformation in case of loss (full or partial) of organic matter.

RECIPROCAL DUMPING AND ENVIRONMENTAL POLICES

In a reciprocal dumping model of trade we analyse the effect of environmental policy reform on welfare in the presence of unemployment and repatriated profits. Pollution quota, used by the government in each country, restricts the local production and reduces the social harmful pollution. However, this quota is a barrier of trade which inhibits the employment and consumers surplus benefit. Bearing in mind this, both countries agree an infinitesimal and proportionate uniform reduction in pollution quota. In both cases global welfare will increase if marginal disutility of pollution is larger than the cost for abating pollution. The effect on each country will depend on the market size and marginal technological costs. Under the same conditions, when both countries agree harmonisation in pollution quotas the global welfare increase but the effect on the welfare of each country will be different.

Neotropical human–landscape interactions, fire, and atmospheric CO2 during European conquest

Neotropical biomass burning reconstructions synthesized from soil and sedimentary charcoal records indicate a period of reduced biomass burning sustained for several centuries after ~500 cal. yr BP. Proxy records of solar irradiance, El Niño events, temperature, and precipitation document regionally variable climate-related trends that do not account for the uniform reduction in burning across the Neotropics. Decreased human ignition resulting from pandemic-induced mortality offers an alternative, geographically comprehensive explanation. In addition, natural (solar-volcanic) factors can explain only ~1.3 ppm out of the rapid 6–10 ppm CO2 decrease between ad 1525 and the early 1600s. Reforestation following land abandonment due to population collapse has the potential to account for the rest of this CO2 decline, and variations in the 13C/12C of atmospheric CO2 and CH4 are consistent with both a major reduction in Neotropical landscape management by fire and massive reforestation. Our findings are demonstrative of the scale at which pre-industrial human activities influenced Earth’s atmospheric greenhouse gas budget.

Real-time Control System for Improved CMP Pad Profiles

Chemical mechanical planarization (CMP) pads require conditioning to maintain the surfaces yielding optimal performance. However, conditioning not only regenerates the pad surface but also wears away the pad material and slurry transport grooves. Non-optimized conditioning may result in non-uniform pad profiles, limiting the productive lifetimes of pads. A new approach to conditioning uses closed-loop control (CLC) of conditioning sweep to enable uniform groove depth removal across the pad, throughout pad life. A sensor integrated into the conditioning arm enables the pad stack thickness to be monitored in situ and in real time. Feedback from the thickness sensor is used to modify pad conditioner dwell times across the pad surface, correcting for drifts in the pad profile that may arise as the pad and disk age. Pad profile CLC enables uniform reduction in groove depth with continued conditioning, providing longer consumables lifetimes and reduced operating costs.