The microstructures of four different AlTiC master alloys produced through a new method involving the reaction of pure Ti and carbon in an Al melt have been examined using XRD, SEM, EPMA, and TEM, and their re ning ef ciencies tested. Individual TiC particles were found to be single crystals with polyhedral or spherical morphologies. In addition to the aluminium matrix, Al -5Ti -0 . 3C (wt-%) re ners contain TiC and TiAl 3 phases, whereas Al -8 . 4Ti -1 . 8C contains only TiC. Three types of agglomerating behaviour of TiC particles, namely discrete particles, homogeneously distributed clusters, and compact blocks along grain boundaries, were found in master alloys produced at different temperatures, and these further in uence the re ning performances. Ti was found to play an important role in the re nement of Al by AlTiC re ners; observation of grain centres showed that TiC particles are located at the grain centre and the excess Ti segregates to them and forms a roselike structure around them. It is clear that the re nement of Al by AlTiC results from the combined action of TiC and Ti, and it is possible that AlTiC and AlTiB share some common rules in re ning Al. Possible re nement mechanisms have been discussed based on microstructure observations and previous studies. MST/5542The authors are in the Key

It was found that silver nanoparticles could strongly enhance the chemiluminescence (CL) of the luminol-KIO 4 system in the presence of Co 2+ . The most intensive CL signals were obtained with silver nanoparticles in diameter of 22 nm. The studies of UV-visible spectra and CL spectra were carried out to explore the possible CL enhancement mechanism. Moreover, the influences of 17 amino acids and 25 organic compounds on the luminol-KIO 4 -Co 2+ -Ag NPs CL system were studied by a flow injection procedure, which led to an effective method to detect these compounds. KeywordsFlow Injection, Luminol, Chemiluminescence, Silver Nanoparticle * Corresponding author. nanoparticles, especially metal nanoparticles, as catalysts for the chemiluminescence system has attracted considerable interest.Recently, the combination of nanoparticles with chemiluminescence has attracted substantial interest because the noble metal nanoparticles have been found to participate in CL reactions as a catalyst, reductant, luminophor, and energy acceptor [20] [21]. For example, Lin et al. [22] [23] have reported that metal nanoparticles can enhance the CL of the luminol-H 2 O 2 and NaHCO 3 -H 2 O 2 system. Cui's group applied noble metal nanoparticles to the CL reactions of lucigenin and potassium permanganate system [24] [25].In this study, we examined the response of Ag NPs for CL intensity of the luminol-KIO 4 -Co 2+ system. The prepared Ag NPs displayed much stronger catalytic activity in presence of Co 2+ on the luminol CL than single Ag NPs or Co 2+ . The effects of reaction conditions on the CL intensity were examined. Moreover, the possible enhancement mechanism of Ag NPs on luminol-KIO 4 -Co 2+ CL reaction was investigated in terms of the UVvisible and CL spectra in detail. In addition, the influences of amino acids and organic compounds on the luminol-KIO 4 -Co 2+ -Ag NPs CL system were reported in extension. Experimental Section Reagents and MaterialsAll chemicals and reagents were analytically pure and used without further purification, and the deionized and triple-distilled water was used throughout.A 2.5 × 10 −2 mol•L −1 stock solution of luminol (3-aminophthalhydrazide) was prepared by dissolving luminol (Fluka) in 0.1 mol•L −1 sodium hydroxide solution. Working solutions of luminol were prepared by diluting the stock solution with water. The 1.0 × 10 −2 mol•L −1 stock solution of periodate was prepared by dissolving 0.23 g KIO 4 (Shanghai, China) in 0.01 mol•L −1 sodium hydroxide solution, and stored in a brown bottle to avoid photochemical decomposition. Silver nitrate, trisodium citrate, hydroborate, amino acids and organics were obtained from Sinopharm Group Chemical Reagent Co. Ltd. (Shanghai, China).

Potassium ions enhance photosynthetic tolerance to salt stress. We hypothesized that potassium ions, by minimizing the trans‐thylakoid proton diffusion potential difference, can alleviate over‐reduction of the photosynthetic electron transport chain and maintain the functionality of the photosynthetic apparatus. This study investigated the effects of exogenous potassium on the transcription level and activity of proteins related to the photosynthetic electron‐transport chain of tobacco seedlings under salt stress. Salt stress retarded the growth of seedlings and caused an outflow of potassium ions from the chloroplast. It also lowered qP (indicator of the oxidation state of QA, the primary quinone electron acceptor in Photosystem II (PSII) and YPSII (average photochemical yield of PSII in the light‐adapted state) while increasing YNO+NF (nonregulatory energy dissipation in functional and nonfunctional PSII), accompanied by decreased expression of most light‐harvesting, energy‐transduction, and electron‐transport genes. However, exogenous potassium prevented these effects due to NaCl. Interestingly, lincomycin (an inhibitor of the synthesis of chloroplast‐encoded proteins in PSII) significantly diminished the alleviation effect of exogenous potassium on salt stress. We attribute the comprehensive NaCl‐induced downregulation of transcription and photosynthetic activities to retrograde signaling induced by reactive oxygen species. There probably exist at least two types of retrograde signaling induced by reactive oxygen species, distinguished by their sensitivity to lincomycin. Exogenous potassium appears to exert its primary effect by ameliorating the trans‐thylakoid proton diffusion potential difference via a potassium channel, thereby accelerating ATP synthesis and carbon assimilation, alleviating over‐reduction of the photosynthetic electron transport chain, and maintaining the functionality of photosynthetic proteins.