Studies on the transesterification of glycerides: I. The methanolysis of tripalmitin catalysed by diorganotin(IV) compounds

The potential of diorganotin compounds, in particular alkoxides and phenoxides, to function as neutral and non‐corrosive catalysts in the methanolysis of tripalmitin (the main triglyceride in palm oil) to methyl palmitate has been investigated. The compounds reveal a strong dependence of catalytic activity on the nature of the organic moiety on tin, the ring‐borne substituent on the phenoxyl group and the chain length of the alkoxyl fragment, as well as the ring size in cyclic alkoxides derived from bifunctional ligands such as diethanolamine. Kinetic studies, based on detailed compositional analysis of the reaction mixture by gas chromatography, were performed typically at 70.0 ± 0.1 °C in mixed methanol–tetrahydrofuran (3:2, v/v) medium and at 1.0 mol% catalyst concentration with respect to tripalmitin. The catalysts used for the kinetic studies were dibutyl bis( p‐chlorophenoxyl)tin 1, dibutyl bis(phenoxyl)tin 2, 1,1‐dibutyl‐5‐aza‐2,8‐dioxo‐1‐stannacyclo‐octane 3, 2,2‐dibutyl‐2‐stanna‐1,3‐benzdioxane 4 and dioctyltin oxide 5. The methanolysis was shown to proceed by a consecutive reaction pathway. Numerical analysis of the rate data yielded values of the three rate constants k₁, k₂ and k₃ corresponding to the respective conversions, tripalmitin → dipalmitin → monopalmitin → glycerol. Based on t values ranging from 7.2 to 22.3 h⁻¹, the following order of catalytic activity was established: 1 > 2 > 3 ≫ 5 ≫ 4; for catalyst 4 the t value was close to that of the uncatalysed reaction. A six‐fold increase in rate was observed when the catalyst concentration was raised from 1.0 to 3.0 mol% for 3. ¹¹⁹Sn NMR analysis of the chloroform extracts of the pot residue following solvent removal at the end of 24 h of the transesterification reaction revealed that the catalysts 1 and 3 essentially retained their chemical integrity. Copyright © 2000 John Wiley & Sons, Ltd.     

The Immuno-Modulatory Activities of Pentaherbs Formula on Ovalbumin-Induced Allergic Rhinitis Mice via the Activation of Th1 and Treg Cells and Inhibition of Th2 and Th17 Cells

Allergic rhinitis (AR) is a highly prevalent allergic disease induced by immunoglobulin (Ig) E-mediated hypersensitivity reaction at the nasal epithelium against inhaled allergens. Previous studies have demonstrated that Pentaherbs formula (PHF), a modified herbal formula comprising five herbal medicines (Flos Lonicerae, Herba Menthae, Cortex Phellodendri, Cortex Moutan and Rhizoma Atractylodis), could suppress various immune effector cells to exert anti-inflammatory and anti-allergic effects in allergic asthma and atopic dermatitis. The present study aimed to further determine the anti-inflammatory activities of PHF in an ovalbumin (OVA)-induced AR BALB/c mouse model. Nasal symptoms such as sneezing and nose rubbing were recorded and the serum total IgE and OVA-specific IgG1, as well as interleukin (IL)-4, IL-5, IL-10, IL-13, chemokines CXCL9 CXCL10, and tumor necrosis factor (TNF)-α concentrations in nasal lavage fluid (NALF) were measured during different treatments. Effects of PHF on the expression of inflammatory mediators in the sinonasal mucosa were quantified using real-time QPCR. PHF was found to suppress allergic symptoms, infiltration of inflammatory cells, and hyperplasia of goblet cells in the nasal epithelium of the OVA-induced AR mice. PHF could reduce OVA-specific IgG1 level in serum, and TNF-α and IL-10 in nasal lavage fluid (NALF), significantly up-regulate the splenic regulatory T (Treg) cell level, increase the Type 1 helper T cell (Th1)/Type 2 helper T cell (Th2) ratio, and reduce the Th17 cells (all p < 0.05). PHF could also alleviate in situ inflammation in sinonasal mucosa of OVA-induced AR mice. In conclusion, oral treatment of PHF showed immuno-modulatory activities in the OVA-induced AR mice by regulating the splenic T cell population to suppress the nasal allergy symptoms and modulating inflammatory mediators, implicating that PHF could be a therapeutic strategy for allergic rhinitis.     

Measurement of slow (micros-ms) time scale dynamics in protein side chains by (15)N relaxation dispersion NMR spectroscopy: application to Asn and Gln residues in a cavity mutant of T4 lysozyme.

A new NMR experiment is presented for the measurement of micros-ms time scale dynamics of Asn and Gln side chains in proteins. Exchange contributions to the (15)N line widths of side chain residues are determined via a relaxation dispersion experiment in which the effective nitrogen transverse relaxation rate is measured as a function of the number of refocusing pulses in constant-time, variable spacing CPMG intervals. The evolution of magnetization from scalar couplings and dipole-dipole cross-correlations, which has limited studies of exchange in multi-spin systems in the past, does not affect the extraction of accurate exchange parameters from relaxation profiles of NH(2) groups obtained in the present experiment. The utility of the method is demonstrated with an application to a Leu --> Ala cavity mutant of T4 lysozyme, L99A. It is shown that many of the side chain amide groups of Asn and Gln residues in the C-terminal domain of the protein are affected by a chemical exchange process which may be important in facilitating the rapid binding of hydrophobic ligands to the cavity.     

Syntheses of L‐Glutamic Acid Analogues for Neuroexcitatory Activity Studies

Starting from D–serine, (2S,3S)‐, (2S,3R)‐substituted‐L‐glutamic acids were prepared via Claisen rearrangement methodology. A variety of the substituents can be introduced at the C‐3 of the L‐glutamic acid backbone.     

Intelligent resource simulation for an airport check-in counterallocation system

The objective of resource allocation systems is to assign valuable corporate resources to meet business demands. However, in applications involving stochastic events, demands cannot be determined explicitly beforehand. For those applications, computer simulation is often used to predict resource demands. The paper describes research in developing a knowledge based simulation system to predict resource requirements at an international airport. Our intelligent resource simulation system (IRSS) determines how many check-in counters should be allocated to each departure flight while providing passengers with sufficient quality of service. This predicted resource requirement is then used by a constraint-based resource allocation system to allocate the actual check-in counters. Because IRSS considers many more factors than a human can, the resulting allocation schedule is more efficient. These factors include: 1) different service rates for different destinations, airlines, or handling agents; 2) different passenger arrival rates for different times of the day or days of the week; and 3) different requirements for different service levels, etc. Our experiments show that there are substantial resource savings by combining a resource allocation system with an intelligent resource simulation system     

Epi-拓扑的某些性质

Throughout this paper R denotes the set of all real numbers.An extended real valued function j f X-[--oo, +oc] is called lower semicontinuouson X if fOr each real Q, {x' f(x) > o} is open in X. Clearly, f is lower semicontinuous ifand only if, its epigraph eghf = {(x, a) f f(x) 5 cr} is closed in X x R. f is caJ1ed proper ifit is somewhere finite, and its values lie in (--co, +oc]. We denote by LSC(X) the set of ajlproper lower semicontinuous functions.In the sequel, we identify lower se…     

Domain decomposition for radial basis meshless methods

Both overlapping and nonoverlapping domain decomposition methods (DDM) on matching and nonmatching grid have been developed to couple with the meshless radial basis function (RBF) method. Example shows that overlapping DDM with RBF can achieve much better accuracy with less nodal points compared to FDM and FEM. Numerical results also show that nonmatching grid DDM can achieve almost the same accuracy within almost the same iteration steps as the matching grid case; hence our method is very attractive, because it is much easier to generate nonmatching grid just by putting blocks of grids together (for both overlapping and nonoverlapping), where each block grid can be generated independently. Also our methods are showed to be able to handle discontinuous coefficient. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 20: 450–462, 2004.     

Disturbing,but not surprising: Did Gödel surprise Einstein with a rotating universe and time travel?

The question is raised as to the kind of methodology required to deal with foundational issues. A comparative study of the methodologies of Gödel and Einstein reveals some similar traits which reflect a concern with foundational problems. It is claimed that the interest in foundational problems stipulates a certain methodology, namely, the methodology of limiting cases.In honor of Professor Max Jammer on the occasion of his 80th birthday.This paper was completed while I was a DAAD (Deutscher Akademischer Austauschdienst) fellow at the Zentrum Philosophie und Wissenschaftstheorie, Universität Konstanz, Germany. I gratefully acknowledge the generous assistance of the DAAD. Special thanks are due to Martin Carrier, Olivier Darrigol, and Gereon Wolters.     

Formation dynamics of Bragg phase gratings in photosensitiveoptical fibers

A double-well potential model based on the local two-photon absorption photobleaching mechanism in blue-green wavelength region by oxygen-deficient Ge-Si bonds is presented and analyzed for describing the photostructural changes of a germanosilicate optical fiber. The growth dynamics are also derived from the coupled wave analysis, which describes the overall temporal behaviors of the grating reflectance and transmittance during the grating formations     

An efficient convolutional coding/decoding strategy for channelswith memory

Many digital communication channels are affected by errors that tend to occur in bursts. A great deal of work has been devoted to finding good burst-error-correcting codes and developing burst-error-correcting schemes. However, burst-error-correcting codes are generally not effective for long bursts. Some burst-error-correcting schemes suffer long delay in decoding. Others are very sensitive to random errors in the guard space. Most of these schemes are not adaptive to channel conditions. A new adaptive scheme is proposed to overcome these drawbacks. The scheme employs a combination of two complementary punctured convolutional (CPC) codes. One of the codes is used for burst detection and for channel state estimation, and both codes are used for error correction. The proposed scheme is analyzed over a two state Markov chain channel model. Unlike existing burst-error-correcting schemes, it is shown that the proposed scheme is adaptive to channel conditions and less sensitive to errors in the guard space. For the same delay, the proposed scheme offers better performance than the interleaving schemes. When the channel is heavily corrupted by bursts, the improvement is even more pronounced