The pool boiling characteristics of dilute dispersions of alumina, zirconia and silica nanoparticles in water were studied. These dispersions are known as nanofluids. Consistently with other nanofluid studies, it was found that a significant enhancement in Critical Heat Flux (CHF) can be achieved at modest nanoparticle concentrations (<0.1% by volume). Buildup of a porous layer of nanoparticles on the heater surface occurred during nucleate boiling. This layer significantly improves the surface wettability, as shown by a reduction of the static contact angle on the nanofluid-boiled surfaces compared with the pure-water-boiled surfaces. CHF theories support the nexus between CHF enhancement and surface wettability changes. This represents a first important step towards identification of a plausible mechanism for boiling CHF enhancement in nanofluids.
In vitro embryogenic callus is a critical factor for genetic transformation of rice, especially for indica varieties. In this study, we investigated the relationship between polyamines, including putrescine (Put), spermidine (Spd) and spermine (Spm), and callus browning, and we studied the effect of exogenous Put on callus regeneration and on the content of endogenous polyamines. In addition, the expression levels of arginine decarboxylase gene (Adcl) and S-adenosylmethionine decarboxylase gene (Samdc) in embryogenic callus were studied by quantitative Real-time PCR analysis. The results showed that the contents of endogenous Put and Spd in the browning callus were significantly lower than those in normal callus. Exogenous Put could effectively improve the growing state of callus of indica rice and enhance the development of embryogenic callus. The content of endogenous polyamines in embryogenic callus, especially Spd and Spm, was increased after addition of exogenous Put. Additionally, exogenous Put also had an obvious impact on the expression levels of Adcl but partial effect on the expression levels of Samdc gene. This study could increase the knowledge of both embryogenic callus induction and polyamine catabolism in callus in indica rice.