Inverse gas chromatography of lignocellulosic fibers coated with a thermosetting polymer: Use of peak maximum and conder and young methods

The Conder and Young (CY) and the peak maximum (PM) methods were used to estimate the retention time of n-alkane probes on chemithermomechanical pulp (CTMP) wood fibers treated with a low molecular weight grade phenol-formaldehyde resin (PFR). Thermodynamic functions (ΔH_a^o, ΔG_a^o, and ΔS_a^o) and the London dispersive component of the surface energy were derived from these retention times. Treated wood fibers show a high energy surface due to the presence of the thermoset resin on their surface. Values of ΔH_a^o obtained from the CY method were higher than those obtained with the PM method at relatively high temperatures and with relatively low molecular weight alkanes. The results from the two methods were identical at low temperature (293 K) and with the relatively high molecular weight alkane n-undecane.     

New Sphingolipids and Other Constituents of Pancovia laurentii

Phytochemical investigation of the bark and leaves of Pancovia laurentii (Sapindaceae) resulted in the isolation of a new ceramide and a new cerebroside, named pancoviamide ( 1 ), and pancovioside ( 2 ) respectively, together with six known compounds: uracil, (R)‐N‐[(1S,2S,3R)‐2,3‐dihydroxy‐1‐(hydroxymethyl)heptadec‐5‐en‐1‐yl]‐2‐hydroxytetracosanamide, stigmasta‐7,22‐dien‐3‐ol, β‐stitosterol, β‐sitosterol 3‐O‐β‐D ‐glucopyranoside, and 2,3‐dihydroxypropyl pentadecanoate. The structures of 1 and 2 were determined by means of spectroscopic methods. Compounds 1 and 2 were tested in vitro for their antiprotozoal properties against several protozoa and for their cytotoxicity.     

Backscatter factor and absorption ratio of fibrous zirconia media in the visible

Fibrous thermal insulations are widely used to conserve energy in ambient to high temperature applications including buildings, solar collectors, heat exchangers, furnaces and thermal protection systems of reusable launch vehicles. It has long been recognised that zirconia has the lowest thermal conductivity of commercial refractories. The thermal conductivity of a zirconia fibrous medium is strongly dependent of its bulk density; high bulk densities of zirconia fibers provide the most effective insulation at high temperatures. Lee's theory for radiative transfer through fibrous media is used in this paper. The two-flux model is applied to determine the backward and forward parameters of a medium of zirconia fibers oriented in parallel planes. Theoretical calculations of the backscatter factor and absorption ratio of this medium are carried out in the visible spectrum for different size parameters of the fibers and for three different temperatures. Our results show that the backscatter factor of zirconia fibrous insulations is maximum, and therefore the heat transfer by the fibrous medium is the lowest, for a size parameter of 0.45 for all the temperatures studied. We also observed that the backscatter factor decreases with increasing temperature.     

Afzeliixanthones A and B, two new prenylated xanthones from Garcinia afzelii ENGL. (Guttiferae)

Two new prenylated xanthones, afzeliixanthones A (1) and B (2), together with three known xanthones (3-5) and two phytosterols, beta-sitosterol and stigmasterol, were isolated from the CH2Cl2/MeOH (1:1) extract of the stem bark of Garcinia afzelii ENGL. collected in the South West Province of Cameroon. Structures were mainly established using one and two-dimensional NMR and mass spectroscopies. The antioxidant activities of the crude extracts as well as the new compounds (1) and (2) were evaluated.     

Models for capacitated lot-sizing problem with backlogging,setup carryover and crossover

Setup operations are significant in some production environments. It is mandatory that their production plans consider some features, as setup state conservation across periods through setup carryover and crossover. The modelling of setup crossover allows more flexible decisions and is essential for problems with long setup times. This paper proposes two models for the capacitated lot-sizing problem with backlogging and setup carryover and crossover. The first is in line with other models from the literature, whereas the second considers a disaggregated setup variable, which tracks the starting and completion times of the setup operation. This innovative approach permits a more compact formulation. Computational results show that the proposed models have outperformed other state-of-the-art formulation.     

Sharp estimates for the CDF of quadratic forms of MPE random vectors

In this paper we develop an efficient analytical expansion of the cumulative distribution function (cdf) XBX^t where X=(X₁,…,X_n+1) with n≥2, follows a multivariate power exponential distribution (MPE). Our approach provides a sharp estimate of the cumulative distribution function of a quadratic form of MPE, together with explicit error estimates.     

Triterpenoids from Drypetes chevalieri Beille (euphorbiaceae)

The CH2Cl2/CH3OH (1/1) extract of the dried stem of Drypetes chevalieri Beille afforded two new triterpeno?ds named drypechevalin A (11-oxo-beta-amyrin-3beta-ylcaffeate) and drypechevalin B (3,7-dioxo-D:A-friedooleanan-24-al) along with five known compounds: lupeol, lupeone, erythrodiol, putranjivadione, friedelin. Their structures were established on the basis of spectroscopic analysis and chemical evidence.