NMR elastometry of fluid membranes in the mesoscopic regime

In solid-state 2H NMR of fluid lipid bilayers, quasielastic deformations at MHz frequencies are detected as a square-law dependence of the nuclear spin-lattice (R1Z) relaxation rates and order parameters (SCD). The signature square-law slope is found to decrease progressively with the mole fraction of cholesterol and with the acyl chain length, due to a stiffening of the membrane. The correspondence to thermal vesicle fluctuations and molecular dynamics simulations implies that a broad distribution of modes is present, ranging from the membrane size down to the molecular dimensions

La manteca de karité

A bibliographical review of the extraction, composition properties and applications of shea butter is made.Se hace una revisión bibliográfica sobre la extracción, composición, propiedades y aplicaciones de la manteca de karité

Os cariótipos de Trinomys moojeni (Pessôa, Oliveira & Reis, 1992) e de Trinomys setosus elegans (Lund, 1841) (Rodentia, Echimyidae) de Minas Gerais, leste do Brasil

Two new karyotypes of species in the genus Trinomys are described from specimens collected recently in Morro do Pilar and Santa Bárbara, Minas Gerais State (MG), Brazil. Trinomys moojeni from Morro do Pilar had 2n=56 and FN=106 and T. setosus elegans from Santa Bárbara had 2n=56 and FN=104. Besides the differences in FN, different morphologies in the sex chromosomes also had been detected. These results at chromosomal level corroborate findings from the mitochondrial genome that suggest that T. s. elegans belongs to a clade composed by T. s. setosus and T. s. denigratus. The chromosomal data corroborated the inclusion of T. moojeni in this clade, as previously suggested on the basis of cranial morphology evidence.Dois novos cariótipos são descritos para espécies do gênero Trinomys com base em coletas recentes nos municípios de Morro do Pilar e Santa Bárbara no Estado de Minas Gerais (MG). Trinomys moojeni de Morro do Pilar apresentou o cariótipo com número diplóide (2n) igual a 56 e número fundamental (NF) igual a 106 e T. setosus elegans de Santa Bárbara apresentou 2n=56 e NF=104. Além da diferença nos valores de NF, diferenças na morfologia cromossômica do par sexual também foram detectadas. Os resultados no nível cromossômico corroboram aqueles encontrados com base no genoma mitocondrial, que evidenciou que T. s. elegans pertence a um clado composto por T. setosus setosus e T. s. denigratus. Os dados cromossômicos corroboraram a inclusão de T. moojeni neste clado, como previamente sugerido com base em evidências da morfologia craniana

Performance of a Tungsten-Cerium Fluoride Sampling Calorimeter in High-Energy Electron Beam Tests

A prototype for a sampling calorimeter made out of cerium fluoride crystals interleaved with tungsten plates, and read out by wavelength-shifting fibres, has been exposed to beams of electrons with energies between 20 and 150 GeV, produced by the CERN Super Proton Synchrotron accelerator complex. The performance of the prototype is presented and compared to that of a Geant4 simulation of the apparatus. Particular emphasis is given to the response uniformity across the channel front face, and to the prototype's energy resolution.Comment: 6 pages, 6 figures, Submitted to NIM

Ensayos para refinación física de la manteca de karité

Assays for physical refining of shea butter. The best conditions for the refining of shea butter used-in cosmetic industries are defined. The objective is to obtain a bleached, deodorized fat, with a 3% maximum free acidity and a high amount of unsaponifiable matter having minimal losses with respect to the initial sample. The following variables have been studied: phosphoric acid proportion in degumming, bleaching clays and active carbon percentages in bleaching, and temperature/time in the stage of deodorization. The results demonstrate that good quality shea butter can be obtained by physical refining if the level of free fatty acid in the initial sample is lower than 5%. Otherwise, a neutralization is necessary, which should be partial in order to reduce the loss of unsaponifiable matter.Se estudian las condiciones más adecuadas en la refinación de la manteca de karité para su uso en cosmética. El objetivo es conseguir un producto decolorado, desodorizado con acidez libre inferior al 3% e insaponificable elevado, con pérdidas mínimas sobre el existente en la muestra inicial. Se han estudiado las siguientes variables: proporción de ácido fosfórico en la fase de desgomado, cantidad de tierras decolorantes y carbón activo en la decoloración y temperatura/tiempo en la desodorización. Los resultados demuestran que puede obtenerse una grasa de buena calidad mediante refinación física cuando las muestras contienen menos de un 5% de acidez. En caso contrario es necesario una neutralización previa que debe ser parcial para disminuir al mínimo las pérdidas de compuestos del insaponificable

On the fraction of dark matter in charged massive particles (CHAMPs)

From various cosmological, astrophysical and terrestrial requirements, we derive conservative upper bounds on the present-day fraction of the mass of the Galactic dark matter (DM) halo in charged massive particles (CHAMPs). If dark matter particles are neutral but decay lately into CHAMPs, the lack of detection of heavy hydrogen in sea water and the vertical pressure equilibrium in the Galactic disc turn out to put the most stringent bounds. Adopting very conservative assumptions about the recoiling velocity of CHAMPs in the decay and on the decay energy deposited in baryonic gas, we find that the lifetime for decaying neutral DM must be > (0.9-3.4)x 10^3 Gyr. Even assuming the gyroradii of CHAMPs in the Galactic magnetic field are too small for halo CHAMPs to reach Earth, the present-day fraction of the mass of the Galactic halo in CHAMPs should be < (0.4-1.4)x 10^{-2}. We show that redistributing the DM through the coupling between CHAMPs and the ubiquitous magnetic fields cannot be a solution to the cuspy halo problem in dwarf galaxies.Comment: 21 pages, 2 figures. To appear in JCA

Crossover in the nature of the metallic phases in the perovskite-type RNiO_3

We have measured the photoemission spectra of Nd$_{1-x}$Sm$_{x}$NiO$_{3}$, where the metal-insulator transition and the N\'{e}el ordering occur at the same temperature for $x \lesssim 0.4$ and the metal-insulator transition temperature ($T_{MI}$) is higher than the N\'{e}el temperature for $x \gtrsim 0.4$. For $x \le 0.4$, the spectral intensity at the Fermi level is high in the metallic phase above $T_{MI}$ and gradually decreases with cooling in the insulating phase below $T_{MI}$ while for $x > 0.4$ it shows a pseudogap-like behavior above $T_{MI}$ and further diminishes below $T_{MI}$. The results clearly establish that there is a sharp change in the nature of the electronic correlations in the middle ($x \sim 0.4$) of the metallic phase of the $R$NiO$_3$ system.Comment: 4 pages, 4 figure, submitted to Phys. Rev.

First order transition and phase separation in pyrochlores with colossal-magnetoresistance

Tl$_{2}$Mn$_{2}$O$_{7}$ pyrochlores present colossal magnetoresistance (CMR) around the long range ferromagnetic ordering temperature (T$_{C}$). The character of this magnetic phase transition has been determined to be first order, by purely magnetic methods, in contrast to the second order character previously reported by Zhao et al. (Phys. Rev. Lett. 83, 219 (1999)). The highest CMR effect, as in Tl$_{1.8}$Cd$_{0.2}$Mn$_{2}$O$_{7}$, corresponds to a stronger first order character. This character implies a second type of magnetic interaction, besides the direct superexchange between the Mn$^{4+}$ ions, as well as a phase coexistence. A model is proposed, with a complete Hamiltonian (including superexchange and an indirect interaction), which reproduce the observed phenomenology.Comment: 6 pages. Figures include