Mössbauer study of iron ore from El Hobo,Huila, Colombia

Iron ore from the El Hobo municipality located in the Huila department in Colombia (2^°35^′7^″N 75^°13^′27^″E) was studied by Mössbauer spectroscopy. The material was quite inhomogeneous, consisting of light brown and dark brown concretions of up to about a centimeter in size, and a sandy fraction. Mössbauer spectra at ambient temperature and at 4.2 K were taken of the two kinds of concretions and the sandy fraction. The concretions contain iron mainly as goethite with only a few percent of hematite. The sandy fraction contains goethite and hematite in roughly equal amounts and a minor fraction of divalent iron that splits magnetically at 4.2 K and may be an impure kind of siderite.     

Neutron imaging at PSI: a promising tool in materials science and technology

Neutron imaging as a method for non-destructive studies takes advantage of the alternative contrast mechanism of neutrons compared to X-rays: most of the light elements feature high contrast, whereas heavy elements are relatively transparent to neutrons. In the previous decade, the neutron imaging technique has made substantial progress in well-tailored and well-equipped beam lines, in improvements of the image recording quality and efficiency by new and modern imaging techniques, and in modern image processing tools.     

The Homogeneous Hamilton–Jacobi and Bernoulli Equations Revisited, II

It is shown that the admissible solutions of the continuity and Bernoulli or Burgers' equations of a perfect one-dimensional liquid are conditioned by a relation established in 1949–1950 by Pauli, Morette, and Van Hove, apparently, overlooked so far, which, in our case, stipulates that the mass density is proportional to the second derivative of the velocity potential. Positivity of the density implies convexity of the potential, i.e., smooth solutions, no shock. Non-elementary and symmetric solutions of the above equations are given in analytical and numerical form. Analytically, these solutions are derived from the original Ansatz proposed in Ref. 1 and from the ensuing operations which show that they represent a particular case of the general implicit solutions of Burgers' equation. Numerically and with the help of an ad hoc computer program, these solutions are simulated for a variety of initial conditions called compatible if they satisfy the Morette–Van Hove formula and anti-compatible if the sign of the initial velocity field is reversed. In the latter case, singular behaviour is observed. Part of the theoretical development presented here is rephrased in the context of the Hopf–Lax formula whose domain of applicability for the solution of the Cauchy problem of the homogeneous Hamilton–Jacobi equation has recently been enlarged.     

Maximum feasibility guideline in the design and analysis of protein folding potentials

Protein folding potentials are expected to have the lowest energy for the native shape. The Linear Programming (LP) approach achieves exactly that goal for a training set, or indicates that this goal is impossible to obtain. If a solution cannot be found (i.e., the problem is infeasible) two possible routes are possible: (a) choosing a new functional form for the potential, (b) finding the best potential with a feasible subset of the data, and (or) detecting inconsistent subset of the data in the training set. Here, we explore option (b). A simple heuristic for finding an approximate solution to an infeasible set of linear inequalities is outlined. An approximately feasible solution is obtained iteratively, starting from a certain initial guess, by computing a series of analytic centers of the polyhedra defined by all the inequalities satisfied at the subsequent iterations. Standard interior point algorithms for Linear Programming can be used to compute efficiently the analytic center of a polyhedron. We demonstrate how this procedure can be used for the design of folding potentials that are linear in their parameters. The procedure shows an improvement in the quality of the potentials and sometimes points to flaws in the original data.     

US Environmental Protection Agency Method 326.0, a new method for monitoring inorganic oxyhalides and optimization of the postcolumn derivatization for the selective determination of trace levels of bromate

The development of US Environmental Protection Agency (EPA) Method 317.0 provided a more sensitive, acceptable alternative to EPA Method 300.1 to be proposed as one of the recommended compliance monitoring methods for Stage II of the Disinfectants/Disinfection By-Products (DBP) Rule. This work was initiated to evaluate other postcolumn reagents (PCRs) that might be utilized to provide an additional, alternative method in order to augment compliance monitoring flexibility for inorganic oxyhalide DBP anions. Modifications of the method reported by Salhi and von Gunten, which included adjustment and optimization of flow-rates, reaction temperature, and delivery of the PCR, improved the method performance. Method 326.0 incorporates an acidic solution of potassium iodide containing catalytic amounts of molybdenum(VI) as the PCR and provides acceptable precision and accuracy for all analytes and a postcolumn bromate detection limit in reagent water of 0.17 microg/l.     

Light-induced decarboxylation of (o-acylphenyl)acetic acids

Near-UV irradiation of both o-acetylphenyl- and o-benzoylphenylacetic acids in benzene solution results in their efficient decarboxylation. Their meta and para isomers do not undergo this process. The O-deuterated acids yield deuterated o-acyltoluene products, suggesting the possibility of an intramolecular proton transfer step in the decarboxylation process, although intermolecular deuteration would achieve the same result. The corresponding esters and amides are essentially photoinert and, like the acids, do not undergo the benzocyclobutenol formation expected of o-alkylphenyl ketones.     

Exclusive measurement of the pp --> pppi(+)pi(-) reaction near threshold

The pp-->pp pi(+) pi(-) reaction has been measured exclusively near threshold at CELSIUS. The total cross sections are nearly an order of magnitude lower than expected from previous inclusive measurements. The differential cross sections reveal pp-->pp(*)(1440)-->pp sigma = pp(pi(+)pi(-))(I = l = 0) as the dominant process as well as significant contributions from p(*)-->Delta(++)pi(-)-->psigma. The observed anisotropy in the proton angular dependence is consistent with heavy-meson exchange. In the invariant mass spectra, no narrow structures of statistical relevance (3sigma) are found.     

On the fundamental solutions of the operators of S. Timoshenko and R. D. Mindlin

Our recent paper about some new fundamental solutions is complemented by a representation of the fundamental solution of certain evolution operators of fourth order in terms of a family of fundamental solutions of operators of second order. By applying this to the operators of vibrating beams and plates we deduce representations of their fundamental solutions as simple definite integrals over tabulated functions.     

Crowns,cutsets, and valuable partial orders

We consider the problem of recognizing those partial orders which admit a valuation: this is a linear-algebraic condition which arises naturally in an algebraic/geometric context. We show that a partial order has at most one valuation (which is integer-valued) and present various structural conditions which are either necessary or sufficient for a partial order to be valuable. The first main result is a reduction theorem which allows us to restrict attention to those partial orders which do not have a bounded cutset. We use this and a theorem of Kelly and Rival to prove the second main result: that every contraction of a bounded partial order is fibre-valuable if and only if the partial order is a dismantlable lattice. This result has a geometric interpretation.This research was supported by the Natural Sciences and Engineering Research Council of Canada under operating grant OGP0105392.