Tumores en ganado ovino sacrificado en matadero

Trabajo presentado al: XL Congreso Nacional y el XVI Congreso Internacional de la Sociedad Española de Ovinotecnia y Caprinotecnia. (Castellón de la Plana, España, 16-18 septiembre 2015).Peer Reviewe

<i>In Situ </i>Studies of Arylboronic Acids/Esters and R₃SiCF₃ Reagents: Kinetics, Speciation, and Dysfunction at the Carbanion–Ate Interface

[Image: see text] Reagent instability reduces the efficiency of chemical processes, and while much effort is devoted to reaction optimization, less attention is paid to the mechanistic causes of reagent decomposition. Indeed, the response is often to simply use an excess of the reagent. Two reaction classes with ubiquitous examples of this are the Suzuki–Miyaura cross-coupling of boronic acids/esters and the transfer of CF(3) or CF(2) from the Ruppert–Prakash reagent, TMSCF(3). This Account describes some of the overarching features of our mechanistic investigations into their decomposition. In the first section we summarize how specific examples of (hetero)arylboronic acids can decompose via aqueous protodeboronation processes: Ar–B(OH)(2) + H(2)O → ArH + B(OH)(3). Key to the analysis was the development of a kinetic model in which pH controls boron speciation and heterocycle protonation states. This method revealed six different protodeboronation pathways, including self-catalysis when the pH is close to the pK(a) of the boronic acid, and protodeboronation via a transient aryl anionoid pathway for highly electron-deficient arenes. The degree of “protection” of boronic acids by diol-esterification is shown to be very dependent on the diol identity, with six-membered ring esters resulting in faster protodeboronation than the parent boronic acid. In the second section of the Account we describe (19)F NMR spectroscopic analysis of the kinetics of the reaction of TMSCF(3) with ketones, fluoroarenes, and alkenes. Processes initiated by substoichiometric “TBAT” ([Ph(3)SiF(2)][Bu(4)N]) involve anionic chain reactions in which low concentrations of [CF(3)](−) are rapidly and reversibly liberated from a siliconate reservoir, [TMS(CF(3))(2)][Bu(4)N]. Increased TMSCF(3) concentrations reduce the [CF(3)](−) concentration and thus inhibit the rates of CF(3) transfer. Computation and kinetics reveal that the TMSCF(3) intermolecularly abstracts fluoride from [CF(3)](−) to generate the CF(2), in what would otherwise be an endergonic α-fluoride elimination. Starting from [CF(3)](−) and CF(2), a cascade involving perfluoroalkene homologation results in the generation of a hindered perfluorocarbanion, [C(11)F(23)](−), and inhibition. The generation of CF(2) from TMSCF(3) is much more efficiently mediated by NaI, and in contrast to TBAT, the process undergoes autoacceleration. The process involves NaI-mediated α-fluoride elimination from [CF(3)][Na] to generate CF(2) and a [NaI·NaF] chain carrier. Chain-branching, by [(CF(2))(3)I][Na] generated in situ (CF(2) + TFE + NaI), causes autoacceleration. Alkenes that efficiently capture CF(2) attenuate the chain-branching, suppress autoacceleration, and lead to less rapid difluorocyclopropanation. The Account also highlights how a collaborative approach to experiment and computation enables mechanistic insight for control of processes

Maritime Perspective of Panama Interoceanic Railway

In 1977, when the American historian David McCullough wrote a book called ”The Path Between the Seas: The Creation of the Panama Canal, 1870-1914”, about the social and geographical environment during the Panama Canal construction, he described the transisthmic railway as a complement of the engineering department that French’s company did not know how to take advantage of, because with the Californian gold fever decadence and with the Canal works it would not have had any commercial purpose other than the ridiculous price of passenger tickets. He never imagined that 100 years later this complement will be a key fact in the supply chain of the Latin-American and worldwide trade. In this paper, we will focus in the logistical map of America, where Panama is the centre. Being the way to connect Asia and America, also both coasts of the American Continent, and the begin/end place of four of the five Feeders highways of Latin America, it turns in the link with the others and with the rest of the world. But they are separated by 76 kilometres that a logistical system converts this distance into a one-hour travel to the next connection. The challenges of this system are raising everyday as result of di_erent regional trade facts. The Panamanian complex is playing an important role with the trade balances, the growing economies and transoceanic services with stop in Panama, generating disequilibrium (empty containers problem). The empty containers must follow the empty container cycle since the container is emptied and the customer returns it to the owner, it’s taken to the depot for maintenance, step that is mandatory in order to return to the cycle of export

Carbon and oxygen in HII regions of the Magellanic Clouds: abundance discrepancy and chemical evolution

We present C and O abundances in the Magellanic Clouds derived from deep spectra of HII regions. The data have been taken with the Ultraviolet-Visual Echelle Spectrograph at the 8.2-m VLT. The sample comprises 5 HII regions in the Large Magellanic Cloud (LMC) and 4 in the Small Magellanic Cloud (SMC). We measure pure recombination lines (RLs) of CII and OII in all the objects, permitting to derive the abundance discrepancy factors (ADFs) for O^2+, as well as their O/H, C/H and C/O ratios. We compare the ADFs with those of other HII regions in different galaxies. The results suggest a possible metallicity dependence of the ADF for the low-metallicity objects, but more uncertain for high-metallicity objects. We compare nebular and B-type stellar abundances and we find that the stellar abundances agree better with the nebular ones derived from collisionally excited lines (CELs). Comparing these results with other galaxies we observe that stellar abundances seem to agree better with the nebular ones derived from CELs in low-metallicity environments and from RLs in high-metallicity environments. The C/H, O/H and C/O ratios show almost flat radial gradients, in contrast with the spiral galaxies where such gradients are negative. We explore the chemical evolution analysing C/O vs. O/H and comparing with the results of HII regions in other galaxies. The LMC seems to show a similar chemical evolution to the external zones of small spiral galaxies and the SMC behaves as a typical star-forming dwarf galaxy.Comment: Accepted for publication in MNRAS, 17 pages, 11 figures, 8 table

Nonlinear field theories during homogeneous spatial dilation

The effect of a uniform dilation of space on stochastically driven nonlinear field theories is examined. This theoretical question serves as a model problem for examining the properties of nonlinear field theories embedded in expanding Euclidean Friedmann-Lema\^{\i}tre-Robertson-Walker metrics in the context of cosmology, as well as different systems in the disciplines of statistical mechanics and condensed matter physics. Field theories are characterized by the speed at which they propagate correlations within themselves. We show that for linear field theories correlations stop propagating if and only if the speed at which the space dilates is higher than the speed at which correlations propagate. The situation is in general different for nonlinear field theories. In this case correlations might stop propagating even if the velocity at which space dilates is lower than the velocity at which correlations propagate. In particular, these results imply that it is not possible to characterize the dynamics of a nonlinear field theory during homogeneous spatial dilation {\it a priori}. We illustrate our findings with the nonlinear Kardar-Parisi-Zhang equation

Lump solitons in a higher-order nonlinear equation in 2+1 dimensions

We propose and examine an integrable system of nonlinear equations that generalizes the nonlinear Schrodinger equation to 2 + 1 dimensions. This integrable system of equations is a promising starting point to elaborate more accurate models in nonlinear optics and molecular systems within the continuum limit. The Lax pair for the system is derived after applying the singular manifold method. We also present an iterative procedure to construct the solutions from a seed solution. Solutions with one-, two-, and three-lump solitons are thoroughly discussed

The impact of chemical differentiation of white dwarfs on thermonuclear supernovae

Gravitational settling of 22Ne in cooling white dwarfs can affect the outcome of thermonuclear supernovae. We investigate how the supernova energetics and nucleosynthesis are in turn influenced by this process. We use realistic chemical profiles derived from state-of-the-art white dwarf cooling sequences. The cooling sequences provide a link between the white dwarf chemical structure and the age of the supernova progenitor system. The cooling sequence of a 1 M_sun white dwarf was computed until freezing using an up-to-date stellar evolutionary code. We computed explosions of both Chandrasekhar mass and sub-Chandrasekhar mass white dwarfs, assuming spherical symmetry and neglecting convective mixing during the pre-supernova carbon simmering phase to maximize the effects of chemical separation. Neither gravitational settling of 22Ne nor chemical differentiation of 12C and 16O have an appreciable impact on the properties of Type Ia supernovae, unless there is a direct dependence of the flame properties (density of transition from deflagration to detonation) on the chemical composition. At a fixed transition density, the maximum variation in the supernova magnitude obtained from progenitors of different ages is ~0.06 magnitudes, and even assuming an unrealistically large diffusion coefficient of 22Ne it would be less than ~0.09 mag. However, if the transition density depends on the chemical composition (all other things being equal) the oldest SNIa can be as much as 0.4 magnitudes brighter than the youngest ones (in our models the age difference is 7.4 Gyr). In addition, our results show that 22Ne sedimentation cannot be invoked to account for the formation of a central core of stable neutron-rich Fe-group nuclei in the ejecta of sub-Chandrasekhar models, as required by observations of Type Ia supernovae.Comment: 8 pages, 8 figures, 3 tables, accepted for Astronomy and Astrophysics. Revised version with corrected typo