Goodness-of-fit tests for a semiparametric model under random double truncation

Doubly truncated data are commonly encountered in areas like medicine, astronomy, economics, among others. A semiparametric estimator of a doubly truncated random variable may be computed based on a parametric specification of the distribution function of the truncation times. This semiparametric estimator outperforms the nonparametric maximum likelihood estimator when the parametric information is correct, but might behave badly when the assumed parametric model is far off. In this paper we introduce several goodness-of-fit tests for the parametric model. The proposed tests are investigated through simulations. For illustration purposes, the tests are also applied to data on the induction time to acquired immune deficiency syndrome for blood transfusion patients.     

The Group of Automorphisms of the Rational Group Algebra of a Finite Metacyclic Group

We investigate the group of automorphisms Aut(? G) of a rational group algebra ? G of a finite metacyclic group G by first describing the simple components of the Wedderburn decomposition of ? G and then investigating when two of these simple components are isomorphic.     

A Berry-Esseen type bound in kernel density estimation for strong mixing censored samples

In this paper, we discuss the estimation of a density function based on censored data by the kernel smoothing method when the survival and the censoring times form a stationary α-mixing sequence. A Berry-Esseen type bound is derived for the kernel density estimator at a fixed point x. For practical purposes, a randomly weighted estimator of the density function is also constructed and investigated.     

An accurate calibration method for high pressure vibrating tube densimeters in the density interval (700 to 1600) kg · m−3

A calibration procedure of vibrating tube densimeters for density measurement of liquids in the intervals (700 to 1600) kg · m^?3, (283.15 to 323.15) K, and (0.1 to 60) MPa is presented. It is based on the modelization of the vibrating tube as a thick-tube clamped at one end (cantilever) whose stress and thermal behaviour follows the ideas proposed in the Forced Path Mechanical Calibration model (FPMC). Model parameters are determined using two calibration fluids with densities certified at atmospheric pressure (dodecane and tetracholoroethylene) and a third one with densities known as a function of pressure (water). It is applied to the Anton Paar 512P densimeter, obtaining density measurements with an expanded uncertainty less than 0.2 kg · m^?3 in the working intervals. This accuracy comes from the combination of several factors: densimeter behaves linearly in the working density interval, densities of both calibration fluids cover that interval and they have a very low uncertainty, and the mechanical behaviour of the tube is well characterized by the considered model. The main application of this method is the precise measurement of high density fluids for which most of the calibration procedures are inaccurate.     

Excess molar properties for binary systems of alkylimidazolium-based ionic liquids + nitromethane. Experimental results and ERAS-model calculations

Density, isobaric molar heat capacity, and excess molar enthalpy were experimentally determined at atmospheric pressure for a set of binary systems ionic liquid + nitromethane. The studied ionic liquids were: 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylpyridinium tetrafluoroborate, 1-ethyl-3-methylimidazolium ethylsulfate, 1-butyl-3-methylimidazolium methylsulfate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, and 1-butyl-3-methylimidazolium trifluoromethanesulfonate. Density and heat capacity were obtained within the temperature range (293.15 to 318.15) K whereas excess molar enthalpy was measured at 303.15 K; excess molar volume and excess molar isobaric heat capacity were calculated from experimental data. The ERAS-model was applied in order to study the microscopic mechanisms involved in the mixing process. Although the studied compounds are not self-associated, ERAS-model describe adequately the experimental results if cross-association between both compounds is considered.     

An efficient preparation of stereospecific β-hydroxy nitriles

The cyanide-ring opening of thionocarbonates with NaCN in DMF and TBACN in THF is described. This reaction occurred regioselectively to afford β-hydroxy nitrile with preserved stereochemistry of the hydroxy group in high yield.     

Enzymatic metabolism of ergosterol by cytochrome p450scc to biologically active 17alpha,24-dihydroxyergosterol

We demonstrate the metabolism of ergosterol by cytochrome P450scc in either a reconstituted system or isolated adrenal mitochondria. The major reaction product was identified as 17alpha,24-dihydroxyergosterol. Purified P450scc also generated hydroxyergosterol as a minor product, which is probably an intermediate in the synthesis of 17alpha,24-dihydroxyergosterol. In contrast to cholesterol and 7-dehydrocholesterol, cleavage of the ergosterol side chain was not observed. NMR analysis clearly located one hydroxyl group to C24, with evidence that the second hydroxyl group is at C17. 17alpha,24-Dihydroxyergosterol inhibited cell proliferation of HaCaT keratinocytes and melanoma cells. Thus, in comparison with cholesterol and 7-dehydrocholesterol, the 24-methyl group and the C22-C23 double bond of ergosterol prevent side chain cleavage by P450scc and change the enzyme's hydroxylase activity from C22 and C20, to C24 and C17, generating bioactive product.     

Organometalloidal derivatives of the transition metals : XXX. Mass spectrometry of transition metal substituted disilanes

Mass spectral fragmentation of a series of transition metal substituted disilanes, LMSiMe₂SiMe₂ML, LM = (η⁵-C₅H₅)Fe(CO)₂- (Fp), (η⁵-C₅H₅)Fe(η⁵-C₅H₄)- (Fc), RFe(CO)₂(η⁵-C₅H₄), are reported. They exhibit significant distinctions depending on the nature of LM. Direct cleavage of the Si---Si bond occurs in the order Fc å Fp å RFe(CO)₂(η⁵-C₅H₄) owing to the capacity of the LM fragment to stabilize positive charge. For complexes containing a direct Fe---Si bond, i.e. Fp-SiMe₂SiMe₂ML, disilene complexed ions are observed, and those complexes containing both an Fp group and a (η⁵-C₅H₄-SiMe₂SiMe₂) group exhibit significant formation of (C₅H₄=Si=SiMe₂) complexed ions. Little disproportionation is observed for any of the complexes studied, in contrast to organodisilanes.     

Density and refractive index in mixtures of ionic liquids and organic solvents: Correlations and predictions

Correlations between volumetric properties and refractive index of binary mixtures of room temperature ionic liquids (RTILs) and organic solvents were examined. To this end, the density and refractive index for a set of these systems were measured at atmospheric pressure at 298.15 K throughout the composition range. These data were used to calculate excess volumes and refractive index deviations by using expressions firmly based on the physical significance of each quantity, fact that allowed the expected relations between the two quantities to be confirmed. Based on these results, the molar refraction and free or void volume of the mixtures are calculated with a view to estimating the relative contribution of both quantities to the excess molar volume. Once molar refraction was confirmed to exhibit a near-ideal behaviour in all mixtures, a method for predicting the density and refractive index of RTIL + organic solvent mixtures was developed; the results show that this procedure can be a highly useful alternative to the usually complex experimental methods available for the thermophysical characterization of these systems.