Spin state transition in LaCoO3 by variational cluster approximation

The variational cluster approximation is applied to the calculation of thermodynamical quantities and single-particle spectra of LaCoO3. Trial self-energies and the numerical value of the Luttinger-Ward functional are obtained by exact diagonalization of a CoO6 cluster. The VCA correctly predicts LaCoO3 as a paramagnetic insulator and a gradual and relatively smooth increase of the occupation of high-spin Co3+ ions causes the temperature dependence of entropy and magnetic susceptibility. The single particle spectral function agrees well with experiment, the experimentally observed temperature dependence of photoelectron spectra is reproduced satisfactorily. Remaining discrepancies with experiment highlight the importance of spin orbit coupling and local lattice relaxation.Comment: Revtex file with 10 eps figure

Correlated band structure of NiO, CoO and MnO by variational cluster approximation

The variational cluster approximation proposed by Potthoff is applied to the calculation of the single-particle spectral function of the transition metal oxides MnO, CoO and NiO. Trial self-energies and the numerical value of the Luttinger-Ward functional are obtained by exact diagonalization of a TMO6-cluster. The single-particle parameters of this cluster serve as variational parameters to construct a stationary point of the grand potential of the lattice system. The stationary point is found by a crossover procedure which allows to go continuously from an array of disconnected clusters to the lattice system. The self-energy is found to contain irrelevant degrees of freedom which have marginal impact on the grand potential and which need to be excluded to obtain meaningful results. The obtained spectral functions are in good agreement with experimental data.Comment: 14 pages, 17 figure

Guidance and Control in a Josephson Charge Qubit

In this paper we propose a control strategy based on a classical guidance law and consider its use for an example system: a Josephson charge qubit. We demonstrate how the guidance law can be used to attain a desired qubit state using the standard qubit control fields.Comment: 9 pages, 5 figure

Certain physiological and pathological effects of feeding various levels of fluorine and alleviators to lambs

The fluorine problem in livestock feeding is one of increasing importance. Fluorosis has been commonly defined as “chronic poisoning with fluorine” (American Illustrated Medical Dictionary). To some, the word may mean the condition that results when the abnormal ingestion of fluorine is sufficient to harm the animal (i.e., as the term is defined medically). To others, the word may mean the condition resulting from any ingestion of fluorine above normal levels. Fluorosis in livestock has been encountered in several ways, one of which is the use of mineral supplements containing fluorine. These minerals are the different varieties of phosphate rock which contain 3 to 4 percent fluorine, and phosphatic limestones which contain fluorine in proportion to the amount of phosphorus present. In the manufacture of superphosphate from phosphate rock, approximately one-fourth to two-thirds of the fluorine is driven off by volatilization as hydrogen fluoride or as silicon tetrafluoride, as reported by Mitchell and Edman (1951). Chronic fluorosis in farm animals has been reported from many countries in areas adjacent to industrial plants emitting fluorine-containing gasses and dusts. The production of acid phosphate and defluorinated phosphate, the electrolytic production of aluminum, the manufacture of bricks from fluorine-bearing clays, the calcimining of ironstone, and certain enameling processes have been chiefly involved. However, even the fumes from coal-burning furnaces may contribute to the industrial hazard, since coal and shales associated with coal contain from forty to several hundred parts per million fluorine, according to Churchill et al. (1948). Since fluorine is very active chemically and does not occur in a free state, the fluorine-bearing fumes from factories processing fluorine-containing ores may be largely hydrofluoric acid, ad the fluorine-bearing dusts may consist of fluorides, such as sodium fluoride or cryolite, which have been volatilized and then condensed in the cooler surrounding air. The leaves of plants may absorb the gas and collect some of the dust on their surfaces, according to Mitchell and Edman (1952). The extent of contamination of the forage, therefore, will depend on several factors, such as the amount of the fluorine-containing materials being emitted, weather conditions, prevailing winds, topography of surrounding terrain, and type of vegetation

Probabilistic analysis of unreinforced brick masonry walls subjected to horizontal bending

Published online on April 11, 2017Unreinforced masonry walls subjected to out-of-plane horizontal bending can fail by two alternate modes: stepped failure along the brick-mortar bond, or line failure cutting directly through the bricks. Because of random variations in material properties throughout a panel and the tendency for failure to occur across the weaker elements, vertical cracks will generally exhibit a combination of the two modes. This paper develops a pair of analytical methodologies that treat this phenomenon using a stochastic approach. The first part deals with calculating the ultimate moment capacity by allowing for the weakening effect associated with the mixed (stepped and line) mode of failure. This effect is quantified in terms of strength-reduction factors for mean and characteristic (0.05 quantile) values of strength, which may be applied toward generic ultimate strength design. The second part deals with estimating the relative probability of each failure mode and the probability distribution for the relative proportions of each failure mode along a crack. This is of particular relevance to seismic performance because the two failure modes lead to significantly different postcracking behavior.Jaroslav Vaculik and Michael C. Griffit

On the Interface Between LENS® Deposited Stainless Steel 304L Repair Geometry and Cast or Machined Components

Laser Engineered Net Shaping™ (LENS®) is being evaluated for use as a metal component repair/modification process. A component of the evaluation is to better understand the characteristics of the interface between LENS deposited material and the substrate on which it is deposited. A processing and metallurgical evaluation was made on LENS processed material fabricated for component qualification tests. A process parameter evaluation was used to determine optimum build parameters and these parameters were used in the fabrication of tensile test specimens to study the characteristics of the interface between LENS deposited material and several types of substrates. Analyses of the interface included mechanical properties, microstructure, and metallurgical integrity. Test samples were determined for a variety of geometric configurations associated with interfaces between LENS deposited material and both wrought base material or previously deposited LENS material. Thirteen different interface configurations were fabricated for evaluation representing a spectrum of deposition conditions from complete part build, to hybrid substrate-LENS builds, to repair builds for damaged or re-designed housings. Good mechanical properties and full density were observed for all configurations. When tested to failure, fracture occurred by ductile microvoid coalescence. The repair and hybrid interfaces showed the same metallurgical integrity as, and had properties similar to, monolithic LENS deposits.Mechanical Engineerin