Correlation between ionic conductivity and7Li-NMR of polyether-polyurethane networks containing lithium perchlorate

Summary The effect of temperature on the ionic conductivity and the⁷Li NME line width of a polyether-polyurethane network containing lithium perchlorate was studied. A treatment of the results based on free-volume principles yielded a linear correlation between the logarithm of the reduced conductivity, _T /_{T 0}, and the logarithm of the reduced⁷Li NMR line width, _T/_{T 0}, for a given reference temperature, T_o=323 K.     

Hydrocarbons and polychlorinated biphenyls from the unsaponifiable fraction of anhydrous milk fat

Using a combination of gas-liquid chromatography and mass spectrometry, the presence of 39 aliphatic hydrocarbons was firmly established in the unsaponifiable fraction of anhydrous milk fat. The hydrocarbons were the C(14) to C(27) and the C(29) to C(31) straight-chain paraffins, their monoolefin analogs, and the C(25) to C(29) branched alkanes. Phytene (3,7,11,15-tetramethyl-n-hexadec-2-ene), identified for the first time in milk fat, was isolated and identified by high-resolution mass spectrometry and infrared analysis. The total hydrocarbon content amounted to 30 ppm of the milk fat. Polychlorinated biphenyls also were detected in trace amounts in the area of the chromatogram between the C(18) and the C(23) hydrocarbons.     

Crystal growth and structure of BiVO4

Large crystals of BiVO₄ were grown. Extensive twinning can be related to the ferroelastic transition at 528K. The structure of BiVO₄ was refined at 4.5, 295 and 566K from powder neutron diffraction data and at 295K from powder X-ray diffraction data by the Rietveld profile technique. Space groups of $\text{I}\text{4}{}_1\text{a}$ above and $\text{I}\text{2}\text{b}$ below 528K were confirmed. It is suggested that the transition in BiVO₄ is driven by the lone-pair cation Bi³⁺. The Bi-O polyhedron is regular above the transition but becomes significantly distorted below the transition. This lone-pair distortion increases on cooling from 295 to 4.5K. The V-O tetrahedron remains regular at all temperatures.     

Hydrogen storage in a beryllium substituted TiFe compound

The TiFe_0.8Be_0.2 alloy was prepared and its hydrogen absorption capacity was investigated. The highest hydrogen quantity occluded at 100 atm by the alloy corresponds to the nominal composition TiFe_0.8Be_0.2H_1.34. The equilibrium pressures between the α and β phases at 21, 50, 80 and 125°C are respectively 0.7, 2.5, 7 and 10–20 atm. For every absorption-desorption isotherm, the hysteresis cycle is very narrow if compared to that found for the TiFe compound.     

A modified heil-prausnitz equation for excess gibbs energy

An equation for the Gibbs excess energy, similar to that of Heil-Prausnitz, is derived on the basis of the lattice theory of fluids. This equation takes into account both the enthalpic and entropic contributions to G^E for liquid mixtures, and in addition uses the α_ij parameter of Renon-Prausnitz. It is compared in the one- and two-parameter forms with the analogous equations of Wilson, NRTL and Heil-Prausnitz for 44 binary liquid-vapour systems, and with the NRTL equation for 2 ternary liquid-liquid systems. Rules are given for calculating the α_ij parameter. Methods are also reported for predictive calculations of the binary interaction parameter g₁₂ based on the properties of the pure fluids.     

Formule di quadratura con funzione di influenza di segno costante

Sommario Si espongono tre procedimenti per costruire formule di quadratura, relative ad un integrale col pesog(x)≥0, che abbiano la funzione di influenza di segno costante.

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Summary Three procedures are exposed to construct quadrature formulae, relative to an integral with a weightg(x)≥0, whose influence function doesn't change sign.

     

A fast preconditioner for the incompressible Navier Stokes Equations

The pressure matrix method is a well known scheme for the solution of the incompressible Navier–Stokes equations by splitting the computation of the velocity and the pressure fields (see, e.g., [17]). However, the set-up of effective preconditioners for the pressure matrix is mandatory in order to have an acceptable computational cost. Different strategies can be pursued (see, e.g., [6, 22 , 4, 7, 9]). Inexact block LU factorizations of the matrix obtained after the discretization and linearization of the problem, originally proposed as fractional step solvers, provide also a strategy for building effective preconditioners of the pressure matrix (see [23]). In this paper, we present numerical results about a new preconditioner, based on an inexact factorization. The new preconditioner applies to the case of the generalized Stokes problem and to the Navier–Stokes one, as well. In the former case, it improves the performances of the well known Cahouet–Chabard preconditioner (see [2]). In the latter one, numerical results presented here show an almost optimal behavior (with respect to the space discretization) and suggest that the new preconditioner is well suited also for flexible or inexact strategies, in which the systems for the preconditioner are solved inaccurately.     

Are loss functions all the same?

In this letter, we investigate the impact of choosing different loss functions from the viewpoint of statistical learning theory. We introduce a convexity assumption, which is met by all loss functions commonly used in the literature, and study how the bound on the estimation error changes with the loss. We also derive a general result on the minimizer of the expected risk for a convex loss function in the case of classification. The main outcome of our analysis is that for classification, the hinge loss appears to be the loss of choice. Other things being equal, the hinge loss leads to a convergence rate practically indistinguishable from the logistic loss rate and much better than the square loss rate. Furthermore, if the hypothesis space is sufficiently rich, the bounds obtained for the hinge loss are not loosened by the thresholding stage.     

Detection and quantification of lanthanide complexes in cell lysates by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Gadolinium (III) complexes are under intense scrutiny as contrast agents for magnetic resonance imaging. Although currently used mainly as extracellular agents, there is a growing interest to exploit their contrast enhancing ability in the intracellular environment. To ascertain the preservation of their chemical integrity upon the intracellular entrapment, it is necessary to have a method for their dosage in the cell lysates. Herein, a mass spectrometric method for detection and quantification of gadolinium complexes in cell lysates is reported. The detection by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was carried out by using a non-acidic matrix (2,4,6-trihydroxyacetophenone), which does not allow any leakage of gadolinium from the complex. Quantification has been possible by using as an internal standard an ytterbium complex with the same ligand of the analyte. Ytterbium was chosen because, among the lanthanides, it is the one with the isotopic distribution pattern the most similar to that of gadolinium. Sensitivity was enough to detect low micromolar quantities of a cationic complex and high micromolar quantities of a neutral complex in cell lysates of rat hepatoma cells. In the case of anionic complexes, sensitivity was too low for quantitative analysis. To the best of our knowledge, this is the first report concerning the quantification of metal complexes by MALDI-TOF-MS.     

From hypergravity to microgravity: Choosing the suitable simulator

Cardiovascular system functions are impaired in altered gravity conditions. In particular endothelial cells play a major role being responsible for the integrity of the vascular wall. Due to obvious difficulties in performing continuous and exhaustive experiments in space, most of the available data have been obtained so far using various simulators of hypergravity and microgravity (µg) conditions. The consistency of the data resides on the reliability of the simulator, being a critical point in the development of the research. We exposed the cell cultures to 1) hypergravity (launch condition) using MidiCAR at Dutch Experiment Support Center (DESC, NL); 2) simulated µg using the Rotating Wall Vessel (RWV) and the Random Positioning Machine (RPM). We used two different cellular models: human umbilical vein endothelial cells (HUVEC) and human leukocytes (U937). Only few experiments on cells using RPM have been reported. To assess the RPM best operative parameters we considered data from experiments in space on U937 as reference standard. Differently, cultures in modelled µg using RWV have been extensively reported. Our data on HUVEC indicate that the two µg simulators provide analogous results in terms of proliferation and cytoskeletal organization. Finally, to investigate the effects of spaceflight on different human cells, we developed a spaceflight-like protocol consisting of an initial hypergravity phase (launch), followed by a µg simulation (orbital flight). Using this protocol, results show that hypergravity limits in our models the effects on proliferation induced by modelled µg.