Search

Self-healing materials represent a paradigm shift from traditional materials development, enabling intrinsic repair of functionality (such as strength) after a catastrophic failure as opposed to part replacement. Several healing mechanisms have been demonstrated in polymeric and ceramic materials, but few in metallic systems. This study demonstrates a novel liquid-assisted self-healing metal-matrix composite (MMC) designed to be capable of over 90% strength recovery after a healing cycle. The aluminum (Al)-based matrix is reinforced with continuous nickel-titanium (NiTi) shape-memory alloy (SMA) reinforcements. Using a tailored heat treatment for healing, a paired effect of crack closure from the SMA reinforcement and partial liquefaction of the matrix occurs. These effects result in a compressive force across the crack surface, and, coupled with increased diffusion rates from the liquefied matrix, produces consolidation and healing in the composite structure. This work provides experimental and computational evidence for the healing mechanism under both tensile and fatigue conditions.

International audience; The Upper Jurassic volcanic rocks of the Pre-Cordillera and High Andes of northern Chile (26 - 31°S) represent a back-arc magmatic chain formed during an earlier stage of Andean subduction. After the Callovian, the back-arc basin gradually changed from marine to continental conditions and was characterized by basaltic to rhyolitic rocks erupted along two belts, parallel to the coeval arc. The western belt comprises the Picudo and Algarrobal formations, whereas the eastern belt comprises the Lagunillas Formation and the Quebrada Vicuñita Beds. New major and trace elements data, along with whole rock Sr, Nd and Pb isotopes are presented for these volcanic belts and compared to the geochemical features of the Jurassic and Early Cretaceous arc magmatism. Ar-Ar and U-Pb ages constrain the back arc volcanism to have evolved between 163.9 ± 1.4 and 148.9 ± 1.2 Ma.Rocks belonging to the western belt have steep multi-element patterns and low concentrations of HREE, suggesting the presence of garnet in the source, and a more radiogenic isotopic composition than the arc magmatism. Parental magmas of these back-arc lavas would have been generated through melting of a depleted mantle, although less depleted than the sub-arc mantle, and interacted with minor amounts of Paleozoic crust. The geochemical composition of the rocks belonging to the eastern belt is more heterogeneous and suggests involvement of different magmatic sources, including depleted mantle as well as an OIB-type mantle within the wedge. In spite the fact that the Jurassic Andean arc was built over a continental plate, the architecture of the volcanic chains and geochemical variations observed among the arc and back-arc rocks in northern Chile resemble those in modern island arcs, and thus support the hypothesis that early Andean subduction developed under extensional tectonic conditions.

During the last forty years, Santiago has experienced a series of drastic changes in public transport policies. These changes have ranged widely, from total deregulation to processes that concentrated the management of public transport within the hands of the public sector. From traditional forms of regulations and policies within a framework that is common throughout Latin America, the system then migrated to complete deregulation. Later, it made a return to more traditional regulations, although tendering for concessions was introduced as an innovation. Finally, after a new intervention in 2007, a highly planned system was introduced with a strongly centralized organization of authority. These four major changes, over four decades, leads to the conclusion that Santiago has become a true laboratory for public transport policies and management. However, and regardless of these changes, certain elements have remained unaltered, such as the almost complete dominance of private ownership in the operation of the system (except for the minor public company, which ended during the 1970's), the absence of subsidies for operations (except in the last period) and with authority lying with the national government as opposed to local government. This article reviews the practices of these forty years, analyzing the components of their policies, results and evaluations, as well as the foundations on which these changes are built.

To determine the factors responsible for the dramatic fall in cholesterol levels after coronary artery bypass surgery (CABG), the authors reviewed, in a retrospective study, the cholesterol levels of 36 patients who underwent CABG surgery during 1987 and compared their levels with those of a control group of 30 patients who underwent cholecystectomies during the same time. In a prospective study, the authors measured the lipids and the hematocrit levels of 15 patients undergoing CABG surgery before the initiation of cardiopulmonary bypass, after 5 minutes of extracorporeal circulation (ECC), and at the end of ECC. In the CABG group, the plasma cholesterol level fell from 211 +/- 63 mg/dl (mean +/- SE) to 70 +/- 48 mg/dl (p less than 0.01), a 77% decrease within 24 hours of surgery. In the cholecystectomy group, the plasma cholesterol fell from 192.3 +/- 8.9 mg/dl to 158 +/- 76 mg/dl (p less than 0.01), an 18% decrease within 24 hours of surgery. To estimate the contribution of hemodilution or blood loss to the fall in cholesterol, changes in hematocrit were recorded. In the CABG group, hematocrit fell from 39.5 +/- 0.7% to 23.5 +/- 0.7% 24 hours after surgery (41% decrease) (p less than 0.01), whereas in the cholecystectomy group hematocrit fell from 39.4 +/- 0.8% to 37.1 +/- 0.9% on the first postoperative day (6% decrease). There was a positive correlation between the fall in cholesterol and the fall in hematocrit in the CABG group (correlation coefficient 0.472), suggesting that hemodilution was a major factor in the decrease in cholesterol levels.(ABSTRACT TRUNCATED AT 250 WORDS)