Sol–gel synthesis, X-ray photoelectron spectroscopy and electrical conductivity of Co-doped (La, Sr)(Ga, Mg)O3−δ perovskites

La0.8Sr0.2Ga0.8Mg0.2−xCoxO3−δ (LSGMC) powders containing different amounts of Co (x = 0.05 and 0.085) were prepared by a citrate sol–gel method. The powders were used to prepare highly phase-pure LSGMC sintered pellets with controlled composition and fractional densities larger than 95%. For the first time, LSGMC materials were subjected to X-ray photoelectron spectroscopy (XPS) characterization. XPS data confirmed the presence of the dopants in the material and allowed to identify two different chemical states for Sr2+ and oxygen, both related to the oxygen-deficient perovskite structure of LSGMC. The conductivity of LSGMC sintered pellets containing different amounts of Co ions in the B sites of the perovskite lattice was assessed by electrochemical impedance spectroscopy (EIS) in the 250–750 °C temperature range. Conductivity values and apparent activation energies were in good agreement with previously published data referring to materials with same composition, but prepared by solid-state route. Therefore, the physicochemical and electrochemical characterization clearly demonstrated the ability of sol–gel methods to produce high-purity Co-doped LSGM perovskites, which represent promising solid electrolytes for intermediate-temperature SOFCs

Conflict-Directed Graph Coverage

Abstract. Many formal method tools for increasing software reliability apply Satisfiability Modulo Theories (SMT) solvers to enumerate feasible paths in a program subject to certain coverage criteria. Examples include inconsistent code detection tools and concolic test case generators. These tools have in common that they typically treat the SMT solver as a black box, relying on its ability to efficiently search through large search spaces. However, in practice the performance of SMT solvers often degrades significantly if the search involves reasoning about complex control-flow. In this paper, we open the black box and devise a new algorithm for this problem domain that we call conflict-directed graph coverage. Our algorithm relies on two core components of an SMT solver, namely conflict-directed learning and deduction by propagation, and applies domain-specific modifications for reasoning about controlflow graphs. We implemented conflict-directed coverage and used it for detecting code inconsistencies in several large Java open-source projects with over one million lines of code in total. The new algorithm yields significant performance gains on average compared to previous algorithms and reduces the running times on hard search instances from hours to seconds

Book Review: Viet Cong at Wounded Knee: The Trail of a Blackfeet Activist

Woody Kipp\u27s life story is a reflection of a new generation of Native writers and activists. His autobiography has nothing to do with trying to save the white world from itself or to explain Indians to a curious and perhaps even sympathetic white audience. The white world literally and figuratively took aim at Woody Kipp (and a number of other American Indian Vietnam veterans) for daring to oppose the injustices he saw in Indian life. He became, as the title of his book indicates, the then-current enemy of the American state. He was, ironically, a domestic version of the Viet Cong he had fought as a young Marine in Vietnam