Simultaneous determination of ursodeoxycholic acid and its glycine-conjugate in serum as phenacyl esters using multidimensional liquid chromatography

Summary A narrowbore high-performance liquid chromatographic (HPLC) method using column switching is described for the simultaneous determination of ursodeoxycholic acid (UDCA) and glyco-UDCA (GUDCA) from serum samples as their phenacyl esters. Serum samples were subjected to a preliminary clean-up using octadecylsilane reversed-phase extraction and derivatized with phenacylbromide. The purification, fractionation and concentration of UDCA and GUDCA from the esterified serum sample were performed on-line by appropriate switching of columns. Limit of detection (LOD) of UDCA and GUDCA were 5 ng and the absolute mean recoveries averaged 84.4±8.2% and 85.2±8.4%, respectively. This method was successfully applied to the pharmacokinetic study of UDCA in rats and human.     

PHOTO REACTION OF 4,5'',8-TRIMETHYLPSORALEN WITH ADENOSINE

The near-UV induced photoreaction of 4,5',8-trimethylpsoralen (TMP) with adenosine was investigated in a dry film state. Four major photoadducts were isolated and purified by reverse-phase liquid chromatography. The structures of the photoproducts were elucidated on the basis of spectroscopic methods, including UV, FT-IR, mass spectrometry (FAB and EI methods) and 1H-NMR analysis. These photoproducts were characterized to be TMP-adenosine 1:1 adducts, which resulted from the covalent bond formation between the carbon C(4) of TMP and ribose 1' or 5' carbon of adenosine. Of the photoadducts, one photoadduct (V) was the major product, reflecting some selectivity in the photoreaction of TMP with adenosine in the solid state.     

Preparation and characterization of a nanoscale poly(vinyl alcohol) fiber aggregate produced by an electrospinning method

Nanoscale poly(vinyl alcohol) (PVA) fiber (100–500 nm) aggregates were prepared with an electrospinning technique. Additionally, a chemical crosslinking method was used to crosslink the nanoscale PVA fiber aggregates. Differential scanning calorimetry, wide‐angle X‐ray diffraction, and scanning electron microscopy techniques were employed to characterize the PVA fiber aggregates. The different crosslinking densities of the PVA fiber aggregates were obtained through the control of the weight percentage of glyoxal to PVA. The crosslinking densities due to heat treatment and chemical crosslinking were studied. The influence of heat treatment could be neglected in contrast to chemical crosslinking when the curing temperature was 120 °C. The primary factor that affected the crosslinking density was the volume of the chemical crosslinking agent. The results showed that the properly crosslinked PVA fiber aggregates had better antiwater solubility and mechanical properties than the noncrosslinked PVA fiber aggregates. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1261–1268, 2002     

Fully crosslinked poly(styrene‐co‐divinylbenzene) microspheres by precipitation polymerization and their superior thermal properties

Fully crosslinked, stable poly(styrene‐co‐divinylbenzene) microspheres, which are composed of various concentrations of divilylbenzene from 5 to 75 mol % based on styrene monomer, were prepared without a significant particle coagulation by the precipitation polymerization. The number‐average particle diameter ranged from 3.5 to 2.8 μm and decreased with an increasing concentration of divinylbenzene in monomer. In addition, the coefficient of variation of the microspheres was slightly reduced with the increasing concentration of divinylbenzene. The circularity and the measured specific surface area indicated that lesser particles are coagulated because of the improved stability of individual particles at a high divinylbenzene concentration and that the resulting particles have a smooth surface without micropores. The glass‐transition temperature was not observed for all microspheres formed from the range of divinylbenzene concentrations. In addition, the onset of the thermal‐degradation temperature was increased from 339.8 to 376.9 °C upon higher contents of divinylbenzene. On the basis of the DSC and thermogravimetric data, the polymer microspheres prepared by the precipitation polymerization possessed a fully crosslinked structure and highly enhanced thermal stability. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 835–845, 2004     

Analysis of a queueing system with a general service scheduling function,with applications to telecommunication network traffic control

In this paper we analyze a queueing system with a general service scheduling function. There are two types of customer with different service requirements. The service order for customers of each type is determined by the service scheduling function α_k(i, j) where α_k(i, j) is the probability for type-k customer to be selected when there are i type-1 and j type-2 customers. This model is motivated by traffic control to support traffic streams with different traffic characteristics in telecommunication networks (in particular, ATM networks). By using the embedded Markov chain and supplementary variable methods, we obtain the queue-length distribution as well as the loss probability and the mean waiting time for each type of customer. We also apply our model to traffic control to support diverse traffics in telecommunication networks. Finally, the performance measures of the existing diverse scheduling policies are compared. We expect to help the system designers select appropriate scheduling policy for their systems.     

Photoplastic studies of strain distributions in the cold drawing of polycarbonate cylindrical bars: the rate effect

Strain distributions in the cold drawing of polycarbonate cylindrical bars were obtained at three nominal strain rates using the method of photoplasticity. Optical-mechanical constitutive equations were interpreted based on a physical model. The strain distribution in the necked portion of the rod is shown to be nonuniform, regardless of the strain rate. Comparison between the integrated diameters and the measured diameters gives an average error between 4 and 12 percent. An interesting trend in the fringe patterns with and without a central loop has been observed and attributed to the higher strain-rate effect for patterns without a central loop.     

Sasakian manifolds with vanishing C-Bochner curvature tensor

Supported by TGRC-KOSEF.     

On the stability of medial axis transform

Medial axis transform (MAT) is very sensitive to noise, in the sense that, even if a shape is perturbed only slightly, the Hausdorff distance between the MATs of the original shape and the perturbed one may be large. Recently, Choiet al. (2002) showed that MAT is stable for a class of 2D domains called weakly injective, if we view this phenomenon with the one-sided Hausdorff distance, rather than with the two-sided Hausdorff distance. In this paper, we extend this result to general 2D domains with natural boundary regularity. We also present explicit bounds for this general one-sided stability of the 2D MAT.