Determination of midodrine in human plasma by high-performance liquid chromatography with fluorescence detection.

A simple and sensitive fluorometric high-performance liquid chromatographic method was developed for the determination of midodrine in human plasma. After liquid-liquid extraction from plasma, the drug and 2-phenylglycinol (internal standard) were convened into the corresponding fluorescent derivatives by reaction with 3,4-dihydro-6,7-dimethoxy-4-methyl-3-oxoquinoxaline-2-carbonyl chloride, a fluorescence derivatization reagent for amines. The derivatives were separated within 30 min on a reversed-phase column using isocratic elution with acetonitrile-methanol-water (10:30:60, v/v) and were detected spectrofluorometrically at 485 nm with excitation at 400 nm. The detection limit for midodrine was 0.3 pmol (76 pg) per mL plasma at a signal-to-noise ratio of 3.     

Electromagnetophoretic force measurement of a single binding interaction between lectin and yeast cell surfaces.

A novel measurement method of the binding force between a micrometer-sized particle and a solid surface in an electrolyte solution has been established by using the electromagnetophoretic buoyancy on the particle. By this method, we investigated the binding force between a yeast cell surface and an oligosaccharide-binding protein, concanavalin A (Con A), fixed on a silica capillary wall. The force measurement was carried out up to 60 pN. In a lower surface concentration of Con A, yeast cells could be desorbed by a force less than 60 pN. However, in a higher surface concentration after treated by 1 mg ml(-1) solution, yeast cells were adsorbed with a force stronger than 60 pN. In this case, the addition of 10 mg ml(-1) D-mannose solution to the medium reduced the binding force to less than 60 pN. The observed adsorption force of yeast cells ranged within 30 - 40 pN, regardless of the interfacial amount of Con A. This force was thought to be the single binding force between a mannose group of the cell surface and an active site of Con A. Moreover, the dissociation rate constant of the single binding of yeast cell and Con A complex was determined as 4.6 x 10(-3) s(-1) and the increment of the binding distance at the transition state as 0.33 nm from the desorption kinetic experiments of yeast cell under the constant pulling conditions of 10, 20 and 30 pN. Such satisfactory results demonstrate the novel advantages of the present method.     

Atomistic phenomena in dense fluid shock waves

The shock structure problem is one of the classical problems of fluid mechanics and at least for non-reacting dilute gases it has been considered essentially solved. Here we present a few recent findings, to show that this is not the case. There are still new physical effects to be discovered provided that the numerical technique is general enough to not rule them out a priori. While the results have been obtained for dense fluids, some of the effects might also be observable for shocks in dilute gases.     

Approximation of transient temperatures in complex geometries using fractional derivatives

It is shown that time-dependent temperatures in a transient, conductive system can be approximately modeled by a fractional-order differential equation, the order of which depends on the Biot number. This approximation is particularly suitable for complex shapes for which a first-principles approach is too difficult or computationally time-consuming. Analytical solutions of these equations can be written in terms of the Mittag-Leffler function. The approximation is especially useful if a suitable fractional-order controller is to be designed for the system.     

Damage and fracture evaluation of granular composite materials by digital image correlation method

This paper presents the applications of digital image correlation technique to the mesoscopic damage and fracture study of some granular based composite materials including steelfiber reinforced concrete, sandstone and crystal-polymer composite. The deformation fields of the composite materials resulted from stress localization were obtained by the correlation computation of the surface images with loading steps and thus the related damage prediction and fracture parameters were evaluated. The correlation searching could be performed either directly based on the gray levels of the digital images or from the wavelet transform (WT) coefficients of the transform spectrum. The latter was developed by the authors and showed higher resolution and sensitivity to the singularity detection. Because the displacement components came from the rough surfaces of the composite materials without any coats of gratings or fringes of optical interferometry, both surface profiles and the deformation fields of the composites were visualized which was helpful to compare each other to analyze the damage of those heterogeneous materials. The project supported by the National Natural Science Foundation of China (10125211 and 10072002), the Scientific Committee of Yunnan Province for the Program of Steel Fiber Reinforced Concrete, and the Institute of Chemical Materials, CAEP at Mianyang