5,088 research outputs found

    Estimating a pressure dependent thermal conductivity coefficient with applications in food technology

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    In this paper we introduce a method to estimate a pressure dependent thermal conductivity coefficient arising in a heat diffusion model with applications in food technology. To address the known smoothing effect of the direct problem, we model the uncertainty of the conductivity coefficient as a hierarchical Gaussian Markov random field (GMRF) restricted to uniqueness conditions for the solution of the inverse problem established in Fraguela et al. Furthermore, we propose a Single Variable Exchange Metropolis-Hastings algorithm to sample the corresponding conditional probability distribution of the conductivity coefficient given observations of the temperature. Sensitivity analysis of the direct problem suggests that large integration times are necessary to identify the thermal conductivity coefficient. Numerical evidence indicates that a signal to noise ratio of roughly 1000 suffices to reliably retrieve the thermal conductivity coefficient

    The truth about freedom of choi

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    El presente es un an谩lisis de los principales rasgos y tendencias que caracterizan hoy a la triada Sociedad-Estado-Mercado. Hace 茅nfasis en la hegemon铆a del mercado y ofrece un recuento anal铆tico de los hechos que la acompa帽an como son: la transnacionalizaci贸n de la cadena de valor, el ascenso de la sociedad del conocimiento, el protagonismo oligop贸lico de la empresa transnacional, la nueva divisi贸n social transnacional del trabajo, el proceso de reconfiguraci贸n cultural, la exclusi贸n social y la subordinaci贸n del Estado, entre otros. El planteamiento que subyace a estas consideraciones es lo que ac谩 se denomina 鈥渓a verdad sobre la libertad de elegir鈥, con lo cual se quiere hacer referencia al hecho de que las relaciones Sociedad-Estado se encuentran hoy mediatizadas por el mercado, arrojando, como consecuencia, una involuci贸n heter贸noma de la Sociedad y del mismo Estado liberal.The actual is an academic analysis of the main features on the day has the triad Society, State and Market. It emphasizes the market hegemony and offers an analytical recount of the facts that go with, as the value chain internationalization, the knowledge society rise, the translational enterprise powerful mark up, the new international social labour division, the cultural reshape process, the social exclusion, the State subordination, among others. The underlying outlining these issues is what the author calls 鈥淭he truth under the free to choose鈥, as a reference to the fact that the relationships between the Society and the State are hindered by the Market with a heteronomous society involution as consequence

    A Natural Rank Problem for Homogeneous Polynomials and Connections with the Theory of Functions of Several Complex Variables

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    We study a natural extremal problem about the vector space consisting of all homogeneous polynomials of degree dd in n+1n+1 variables with real coefficients, together with the zero polynomial. We define the {\it rank} of a polynomial to be the number of distinct monomials appearing in the polynomial with non-zero coefficient. We are particularly interested in those homogeneous polynomials whose quotient with the homogeneous polynomial x0+x1++xnx_0+x_1+\cdots+x_n is a polynomial of degree d1d-1 with maximal rank. For each degree dd, we seek the minimum rank for an element of this subfamily and we seek to describe those polynomials with minimum rank. We call such polynomials {\it sharp} polynomials. These problems have a simple solution for polynomials in one and two variables. The three-variable case is interesting and non-trivial, but well-understood. This research question has its roots in the study of proper polynomial mappings between balls in complex Euclidean spaces of different dimensions and the degree estimates problem. D\u27Angelo, Kos and Riehl \cite{degree} and Lebl and Peters \cite{hyperplaneq} used a graph-theoretic approach to solve this problem in the case of proper monomial mappings. Lebl and Peters give a minimum rank estimate that answers our question in the three variable case. A family of sharp polynomials was described by D\u27Angelo and has been extensively studied. Brooks and Grundmeier \cite{notes} provided a new proof of the minimum rank theorem in the three-variable case using a commutative algebra approach. They reformulate the problem as a question about homogeneous ideals and address it by studying the Hilbert function and the graded Betti number of certain ideals. Using the same method as Brooks and Grundmeier, we give a sharp estimate for the minimum rank of homogeneous polynomials of our subfamily in four variables as well as a family of sharp polynomials. Moreover, we state a general result on the minimum rank for polynomials in n+1n+1 variables. Although this estimate is sharp in the three- and four- variable cases, the estimate is not sharp when the number of variables is greater than four

    M 122.01: College Trigonometry

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    Energy prices in Europe. Evidence of persistence across markets

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    This paper deals with the behavior of energy price changes and how their shocks exert an impact on suppliers and consumers in different markets. For this purpose, a fractional integration model is used to evaluate the persistence and mean reversion in prices across the major European markets (Germany, France, Italy, UK, Spain). We compare the results with other major players as the US and Japan, to understand, first, if the European behavior is different, and second, if geopolitical shocks that are affecting this market are expected to be permanent. Empirical results show evidence of mean reversion properties in European prices, though some minor differences arise from market to market that apparently, are not associated with the energy generation strategies followed by each country. Thus, it will likely be expected following the current energy shocks the series will recover due to natural market forces, without the need for additional policies

    The Effect Of Type-III Antifreeze Proteins (AFPs) On CO2 Hydrate Slurry Formation

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    CO2 hydrate slurry is a favourable direct coolant of fresh products due to its large latent heat and phase change temperature around 5掳C. Continuous production of this slurry is, however, difficult to realise due to the high rate of hydrate formation. The use of additives is proposed with the purpose of decreasing the formation rate so that the controllability of the process is improved. Type-III Antifreeze Proteins (AFPs) are non-poisonous additives which have proven to be inhibitors of hydrate formation. These additives have also shown to protect the bio-cells of fresh products from damaging by freezing. The effect of these additives on the CO2 hydrate formation rate is experimentally investigated. The experiments have been performed in a coil heat exchanger with 6 mm internal diameter under operating conditions corresponding to hydrate formation conditions. The concentration of Type-III AFPs has been varied: no additives, 5 ppm and 10 ppm. The mixture of additives and CO2-water solution is cooled down until the hydrate formation conditions are attained. The growth rate of hydrates on the wall of the heat exchanger has been derived from the variation of the overall heat transfer coefficient with time. Results show that the addition of AFPs changes the supersaturation degree of CO2 water solution needed to initiate the hydrate formation process. A low concentration of the proposed additives is sufficient to slow down the formation rate of CO2 hydrate improving significantly the controllability of the hydrate production process

    The role of vitamin D as a potential adjuvant for COVID-19 vaccines

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    Quasars Clustering at z approx 3 on Scales less sim 10 h^{-1} Mpc

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    We test the hypothesis whether high redshift QSOs would preferentially appear in small groups or pairs, and if they are associated with massive, young clusters. We carried out a photometric search for \Ly emitters on scales 10h1\lesssim 10 h^{-1} Mpc, in the fields of a sample of 47 z3z\approx3 known QSOs. Wide and narrow band filter color-magnitude diagrams were generated for each of the 6.66.66'.6\times6'.6 fields. A total of 13 non resolved objects with a significant color excess were detected as QSO candidates at a redshift similar to that of the target. All the candidates are significantly fainter than the reference QSOs, with only 2 of them within 2 magnitudes of the central object. Follow-up spectroscopic observations have shown that 5, i.e., about 40% of the candidates, are QSOs at the same redshift of the target; 4 are QSOs at different z (two of them probably being a lensed pair at z = 1.47); 2 candidates are unresolved HII galaxies at z\sim0.3; one unclassified and one candidate turned out to be a CCD flaw. These data indicate that at least 10% of the QSOs at z\sim3 do have companions. We have also detected a number of resolved, rather bright \Ly Emitter Candidates. Most probably a large fraction of them might be bright galaxies with [OII] emission, at z\approx 0.3. The fainter population of our candidates corresponds to the current expectations. Thus, there are no strong indication for the existence of an overdensity of \Ly galaxies brighter than m \approx 25 around QSOs at zz\approx 3.Comment: 29 pages, 8 figures, tar gzip LaTex file, accepted to appear in Ap
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