Covalency and the metal-insulator transition in titanate and vanadate perovskites

A combination of density functional and dynamical mean-field theory is applied to the perovskites SrVO$_3$, LaTiO$_3$ and LaVO$_3$. We show that DFT+DMFT in conjunction with the standard fully localized-limit (FLL) double-counting predicts that LaTiO$_3$ and LaVO$_3$ are metals even though experimentally they are correlation-driven ("Mott") insulators. In addition, the FLL double counting implies a splitting between oxygen $p$ and transition metal $d$ levels which differs from experiment. Introducing into the theory an \textit{ad hoc} double counting correction which reproduces the experimentally measured insulating gap leads also to a $p$-$d$ splitting consistent with experiment if the on-site interaction $U$ is chosen in a relatively narrow range ($\sim 6\pm 1$ eV). The results indicate that these early transition metal oxides will serve as critical test for the formulation of a general \textit{ab initio} theory of correlated electron metals.Comment: 5 pages, 3 figure

Mars methane engine

The feasibility of an internal combustion engine operating on a mixture of methane, carbon dioxide, and oxygen has been verified by previous design groups for the Mars Methane Engine Project. Preliminary stoichiometric calculations examined the theoretical fuel-air ratios needed for the combustion of methane. Installation of a computer data acquisition system along with various ancillary components will enable the performance of the engine, running on the described methane mixture, to be optimized with respect to minimizing excess fuel. Theoretical calculations for stoichiometric combustion of methane-oxygen-carbon dioxide mixtures yielded a ratio of 1:2:4.79 for a methane-oxygen-carbon dioxide mixture. Empirical data shows the values to be closer to 1:2.33:3.69 for optimum operation

Increased gene expression of a facilitated diffusion urea transporter in the skin of the African lungfish (Protopterus annectens) during massively elevated post-terrestrialization urea excretion

The full-length cDNA sequence of a putative urea transporter (IfUl) of the facilitated diffusion UT-A type has been cloned from the African lungfish Protopterus annectens. The IFUTcDNA is 1990bp in length and its open reading frame encodes a 409 amino acid long protein, with a calculated molecular mass of 44,723 Da. The sequence is closest to those of amphibians (∼65% amino acid homology), followed by mammals and elasmobranchs (∼60%), and then teleosts (∼50%). IfUT was clearly expressed in gill, kidney, liver, skeletal muscle and skin. Upon re-immersion in water after 33days of air exposure (\u27terrestrialization\u27), lungfish exhibited a massive rise in urea-N excretion which peaked at 12-30h with rates of 2000-5000μmol-N kg-1 h -1 (versus normal aquatic rates of \u3c130μmol-Nkg -1h-1) and persisted until 70h. This appears to occur mainly through the skin. Total \u27excess\u27 urea-N excretion amounted to ∼81,000-91,000 μmol-N kg-1 over 3 days. By real-time PCR, there was no difference in IfUT expression in the ventral abdominal skin between aquatic ammoniotelic controls and terrestrialized lungfish immediately after return to water (0h), and no elevation of urea-N excretion at this time. However, skin biopsies revealed a significant 2.55-fold elevation of IfUT expression at 14h, coincident with peak urea-N excretion. At 48h, there was no longer any significant difference in IFUT mRNA levels from those at 0 and 14h, or from aquatic fed controls. In accordance with earlier studies, which identified elevated urea-N excretion w\u27athe skin of P. dolloi with pharmacology typical of UT-A carriers, these results argue that transcriptional activation of a facilitated diffusion type urea transporter (IfUT) occurs in the skin during re-immersion. This serves to clear the body burden of urea-N accumulated during terrestrialization

Supply chain security certification and operational performance:The role of upstream complexity

Supply chain security (SCS) incidents increasingly cause financial losses to manufacturing facilities and logistics service providers. Thus, supply chain security certification can have implications for production economics, particularly for importing firms who rely on a smooth logistics flow across country borders. However, it largely remains unknown regarding how such certification could influence a firm's operational performance. To this end, we empirically examine whether and how the adoption of Customs-Trade Partnership Against Terrorism (C-TPAT) certification, initiated by the U.S. Customs and Border Protection (CBP), could improve operational performance in adopter firms. This study draws upon signaling theory to empirically investigate the value of C-TPAT certification on U.S. publicly-traded importer firms' operational performance by analyzing the longitudinal data of properly-matched sample-control groups. The data come from multiple sources: public announcements of C-TPAT certification from the News Retrieval Service database, import data from lading records, and financial data from Standard & Poor's COMPUSTAT database. Employing a coarsened exact matching (CEM) method and a difference-in-difference (DID) analysis, we find that C-TPAT certified importers have better operational performance than that of non-certified importers. We also find that the level of upstream supply chain complexity (detail, dynamic, and spatial complexity) enhances the operational performance derived from C-TPAT certification. This study sheds light on the performance value of a management standard that is attributed to the non-process mechanism (not due to process improvements) enabled by the signaling effectiveness incorporating the upstream supply chain complexities. Our findings have important theoretical and practical implications for production economics and supply chain management studies