Biomedical subjects

Wei Gai

Publications and source records attributed to Wei Gai.

3 recordsLinked to original sources

PubMed2003

Dipole-mode wakefields in dielectric-loaded rectangular waveguide accelerating structures.

By applying different symmetric boundary conditions, we found that the transverse wakefields generated by an electron bunch traveling through a partially loaded rectangular dielectric structure at an off center position can be decomposed into corresponding orthogonal longitudinal section electric (LSE) and longitudinal section magnetic (LSM) modes for guided waves as in the case of longitudinal wakefields treated previously. The wakefields are characterized using the normalized shunt impedance R/Q, a function of the geometry of the accelerating structure, for both LSE and LSM modes. A numerical example is given for an X-band waveguide structure and detailed results are given for the several leading transverse wakefield terms. The analytic results obtained are in agreement with the results from the time domain simulation tool MAFIA.

Journal Article↗

PubMed2003

The exothermal behavior in the hydration process of calcium phosphate cement.

The exothermal behavior in the hydration process of calcium phosphate cement (CPC) and their effect factors were investigated systematically. One CPC formulation is composed of tetracalcium phosphate (TECP) and dicalcium phosphate anhydrous (DCPA), and its hydration reaction is an exothermic reaction. Hydration includes five processes, namely, the start, induction, acceleration, deceleration and the terminating process. The introduction of hydroxyapatite (HAP) as crystal seed shortens induction and advances on the reaction peak position, which resulted from the introduction of crystal seed that reduced the activation energy of heterogeneous nucleation. The increase in temperature not only makes the reaction advance but also enlarges it. The activation energy of the hydration reaction is 176kJ/mol by calculation. The particle size of the raw material and the ratio of calcium to phosphate in the specimen have large effects on the hydration process. Decrease in particle size of TECP and in the ratio of calcium to phosphate resulted in marked acceleration of reaction and made the reaction peak advance evidently, but the effect of particle size of DCPA is not so remarkable. Based on the heat liberation in the hydration of CPC specimens taking Ca/P as 1.5 and 1.67, the standard mole enthalpies of formation of TECP and calcium-deficient hydroxyapatite are -5908 and -11,119kJmol(-1), respectively.

Biocompatible Materials↗

PubMed2001

Field analysis of a dielectric-loaded rectangular waveguide accelerating structure.

Recently, there has been some interest in planar or rectangular dielectric accelerating structures for future high-gradient linear accelerators. In this paper, we present a detailed analysis of the modes of a dielectric-loaded rectangular waveguide accelerating structure based on a circuit model approximation and mode matching method. In general, the acceleration field in a synchronous acceleration mode is nonuniform in the two transverse dimensions. We show, however, that by using a series of rectangular structures successively rotated by 90 degrees, the net accelerating force can be made almost uniform. Characteristic parameters such as R/Q, group velocity, and attenuation constant for X- and W-band accelerators are calculated. The longitudinal wakefields experienced by a relativistic charged particle beam in these structures are also presented. These analytical results are also compared with numerical calculations using the MAFIA code suite demonstrating the validity of our analytic approach.

Journal Article↗