Método para desplazar contaminantes del pesticida diclorometano que interfieren en el análisis de residuos de herbicidas

A procedure developed for analyses of persistant herbicide residues in soil samples was found to give poor recoveries and extra peaks in gas chromatograms from fortified samples after initial studies had shown acceptable recoveries and no extra peaks. The problem was also found in a "solvent only" sample fortified with prometryn and metribuzin. These two herbicides were then shown to be altered by merely mixing with an aged pesticide grade dichloromethane being used for extractions. Contaminant(s), apparently formed in aged solvent to cause the extra peaks, can be removed by extracting dichloromethane, immediately before it is used, with 10% sodium carbonate solution. Chromatograms are presented to illustrate the effects of the contaminant(s) and their removal by such extraction with recoveries of 0 to 50-percent raised to above 75 percent for the two herbicides when clean solvent is used for extractions. With one of the oldest bottles of dichloromethane in stock for 8 years, the odor of dichlormethane was masked by a pungent acidic odor, which was removed by the sodium carbonate extraction. The contaminant(s) may arise with time in the pesticide grade solvent because of lack or degradation of an additive present in some other grades of this solvent. A literature review for data to explain the contaminants revealed numerous inhibitors, stabilizers and preservatives added at varying levels in many grades of dichloromethane but little information available on how these additives function, or whether they or their altered products may interfere in analyses. The data herein reinforce the report that careful evaluation of dichloromethane for additives or degradation must be made before using this solvent for extractions in trace organic analyses.Se encontró que un procedimiento desarrollado para el análisis de residuos de herbicidas persistentes en suelos daba recuperaciones pobres y cromatogramas con señales extras en muestras fortificadas. En los estudios iniciales se lograron recuperaciones y cromatogramas aceptables. El problema surgió también al analizar muestras del disolvente fortalecido con prometryn y metribuzin. Estos dos herbicidas sufren cambios al mezclarlos con diclorometano envejecido, grado herbicida, que se usa para hacer extracciones. Los contaminantes causantes del problema se pueden eliminar mediante extracción del diclorometano con una solución de carbonato de sodio al 10%. Se presentan cromatogramas para demostrar el efecto del contaminante y su remoción mediante extracción, para los dos herbicidas usando un disolvente limpio para las extracciones. Las recuperaciones con disolvente limpio aumentaron a más de 75% comparadas con recuperaciones de 0 a 50% con el disolvente contaminado. En una de las botellas de diclorometano que estuvo almacenada por 8 años, el olor de diclorometano estaba enmascarado por un olor ácido picante, el cual se eliminó en la extracción con la solución de carbonato de sodio. La contaminación puede surgir con el tiempo en el disolvente grado pesticida debido a la ausencia o a la degradación de un aditivo que se encuentra en el disolvente de otros grados de pureza. En la búsqueda de datos en la literatura que explicaran el comportamiento de los contaminantes se encontraron numerosos inhibidores, estabilizadores y preservativos que se añaden en diferentes porporciones al diclorometano de diferentes grados de pureza y se encontró muy poca información de cómo estos aditivos funcionan y si ellos o sus productos degradados interfieren en los análisis. Los datos aquí incluidos y la revisión de bibliografía indican que hay que evaluar el diclorometano cuidadosamente para la presencia de aditivos o sus degradaciones antes de usar el disolvente en el análisis de trazas de compuestos orgánicos

AN EXTRACTION PROCEDURE FOR MALATHION IN FRUIT PASTES

AN EXTRACTION PROCEDURE FOR MALATHION IN FRUIT PASTE

A new heap game

Given $k\ge 3$ heaps of tokens. The moves of the 2-player game introduced here are to either take a positive number of tokens from at most $k-1$ heaps, or to remove the {\sl same} positive number of tokens from all the $k$ heaps. We analyse this extension of Wythoff's game and provide a polynomial-time strategy for it.Comment: To appear in Computer Games 199

The Groebner basis of the ideal of vanishing polynomials

We construct an explicit minimal strong Groebner basis of the ideal of vanishing polynomials in the polynomial ring over Z/m for m>=2. The proof is done in a purely combinatorial way. It is a remarkable fact that the constructed Groebner basis is independent of the monomial order and that the set of leading terms of the constructed Groebner basis is unique, up to multiplication by units. We also present a fast algorithm to compute reduced normal forms, and furthermore, we give a recursive algorithm for building a Groebner basis in Z/m[x_1,x_2,...,x_n] along the prime factorization of m. The obtained results are not only of mathematical interest but have immediate applications in formal verification of data paths for microelectronic systems-on-chip.Comment: 15 pages, 1 table, 2 algorithms (corrected version with new Prop. 3.8 and proof); Journal of Symbolic Computation 46 (2011

Books on Language, Words, Etc.

A compilation of books about language, words, etc

On polynomial functions (mod m)

AbstractIn this paper, we obtain a canonical representation for those polynomials (with integer coefficients) which vanish (mod m), a canonical representation for each polynomial function (mod m) and an expression for the number of polynomial functions (mod m). This number turns out to be (weakly) multiplicative in m

Tunable compression of template banks for fast gravitational-wave detection and localisation

One strategy for reducing the online computational cost of matched-filter searches for gravitational waves is to introduce a compressed basis for the waveform template bank in a grid-based search. In this paper, we propose and investigate several tunable compression schemes for a general template bank. Through offline compression, such schemes are shown to yield faster detection and localisation of signals, along with moderately improved sensitivity and accuracy over coarsened banks at the same level of computational cost. This is potentially useful for any search involving template banks, and especially in the analysis of data from future space-based detectors such as eLISA, for which online grid searches are difficult due to the long-duration waveforms and large parameter spaces.Comment: Published versio

An Evolutionary Approach for Solving the Rubik’s Cube Incorporating Exact Methods

Abstract. Solutions calculated by Evolutionary Algorithms have come to surpass exact methods for solving various problems. The Rubik’s Cube multiobjective optimization problem is one such area. In this work we present an evolutionary approach to solve the Rubik’s Cube with a low number of moves by building upon the classic Thistlethwaite’s approach. We provide a group theoretic analysis of the subproblem complexity in-duced by Thistlethwaite’s group transitions and design an Evolutionary Algorithm from the ground up including detailed derivation of our cus-tom fitness functions. The implementation resulting from these observa-tions is thoroughly tested for integrity and random scrambles, revealing performance that is competitive with exact methods without the need for pre-calculated lookup-tables.

Morphological and Structural Characterization of Cro2/Cr2o3 Films Grown by Laser-CVD

This work reports on the synthesis of chromium (III, IV) oxides films by KrF laser-assisted CVD. Films were deposited onto sapphire substrates at room temperature by photodissociation of Cr(CO)6 in dynamic atmospheres containing oxygen and argon. A study of the processing parameters has shown that partial pressure ratio of O2 to Cr(CO)6 and laser fluence are the prominent parameters that have to be accurately controlled in order to co-deposit both crystalline oxide phases. Films consistent with such a two-phase system were synthesised for a laser fluence of 75 mJ cm-2 and a partial pressure ratio about 1. PACS: 81.15.Fg, 81.15.Kk, 81.05.JeComment: 17 pages, 4 figure

Two examples of minimal Cheeger sets in the plane

We construct two minimal Cheeger sets in the Euclidean plane, i.e., unique minimizers of the ratio \u201cperimeter over area\u201d among their own measurable subsets. The first one gives a counterexample to the so- called weak regularity property of Cheeger sets, as its perimeter does not coincide with the 1-dimensional Hausdorff measure of its topological boundary. The second one is a kind of porous set, whose boundary is not locally a graph at many of its points, yet it is a weakly regular open set admitting a unique (up to vertical translations) nonparametric solution to the prescribed mean curvature equation, in the extremal case corresponding to the capillarity for perfectly wetting fluids in zero gravity