新型化学反应法制备SiC/Al2O3复相陶瓷涂层

陶瓷涂层材料以其高硬度、耐腐蚀、耐高温、抗氧化等一系列优点,在航空航天、武器装备、核工业、石油化工等领域具有广阔的应用前景.SiC/Al_2O_3复相陶瓷在常温和高温下都具有较好耐磨性和化学稳定性,是一种极具工程应用前景的复合陶瓷材料.本研究采用优质陶瓷先驱体聚合物PCS,添加惰性填料SiC纳米颗粒和活性填料金属Al粉共同作用,克服了先驱体法制备陶瓷材料中存在较大体积收缩的缺点,在金属基体上制备了单层厚度可达50 μm的致密SiC/Al_2O_3复相陶瓷涂层,复相陶瓷涂层中的SiC来自于先驱体PCS热解转化的SiC和添加的纳米SiC颗粒;其中的Al_2O_3来自于金属Al粉的氧化.该化学反应方法在金属基体上成功地制备出连续、致密的SiC/Al_2O_3复相陶瓷涂层,既简单又方便,表现出极大的应用潜力.     

Residential mobility of Chinese immigrants: An analysis of housing conditions and tenure structure

For a long period of time, immigrants have played an important role in the development of Hong Kong. With an influx of over 50,000 immigrants from mainland China on a yearly basis, this is truer than ever in Hong Kong. The behavior of these immigrants is a worthwhile topic for researcher. This study focuses on various aspects of housing, ranging from the tenure choices and housing conditions to the residential mobility of new Chinese immigrants in Hong Kong. Thus far, the literature has rarely explored situations that arise when immigrants have the same racial background as the people in the host cities. This research is intended to fill this gap in knowledge. Our findings reveal that Chinese immigrant households tend to start off overwhelmingly as private renters in the housing market. They also tend to live in inferior housing. However, as the duration of their residence in Hong Kong lengthens, the types of tenure become more diverse and the quality of their housing improves, indicating an upward mobility in terms of housing conditions.     

COMPARISON OF ANTIMICROBIAL ACTIONS OF MONOLAURIN AND SORBIC ACID

The antimicrobial effects of monolaurin and sorbic acid were compared in laboratory media, cottage cheese and a pork homogenate. Sorbic acid (250–1000 ppm) was more effective than monolaurin (250–1000 ppm) in inhibiting the growth of Staphylococcus aureus S-6 and Salmonella enteritidis 13076 in pH 5.2 trypticase soy broth. Monolaurin was more effective than sorbic acid against the growth of S. typhimurium 13311 under similar conditions. No synergistic effects were observed when combinations of monolaurin and sorbic acid were tested. In the cottage cheese study, 800 ppm sorbic acid effectively inhibited the growth of coliforms and yeasts and molds, but only slightly inhibited the growth of psychrotrophs. Monolaurin at 800 ppm was ineffective in controlling the growth of any of the microorganisms tested. The use of 3000 ppm monolaurin in a pork homogenate had no effect on the outgrowth and gas formation by Clostridium sporogenes PA3679, whereas 3000 ppm sorbic acid delayed outgrowth and gas formation. Combinations of monolalurin and sorbic acid indicated that sorbic acid was the active anticlostridial agent.     

DYNAMICS OF ASSISTED HOMEOWNERSHIP IN SINGAPORE

ABSTRACT: This study aims to first investigate if the market‐force hypothesis and upgrading hypothesis still hold in explaining the demand for first‐hand housing development board (HDB) flats in Singapore. Then, simulations are carried out via system dynamics models to assess how policy changes, differentiated in scales and frequencies, affect such demand. The findings, while refuting the market‐force hypothesis, extend the upgrading hypothesis, as capital appreciations through selling in the resale HDB market not only contribute to the upgrading of properties among HDB owners, but also provide incentives for nonhomeowners to make the first move in realizing the “Singapore Dream.” Further, simulations point out that either too few or too many institutional changes in response to market adjustments render the HDB system unhealthy. The former induces fluctuating demand, while the latter likely generates extra administrative cost that could cause long‐term effects on the financial position of the HDB.