During a June 1996 cruise in the northern Red Sea, we studied spatial distributions of alkaline phosphatase (AP) activities in different plankton size fractions and in the aqueous fraction which passes through 0.2 pm filters. AP proved to be a highly stable compound In the Red Sea and has potential use as an indicator for inorganic P-availability to planktonic communities. Depth profiles showed that aqueous and particulate alkaline phosphatase activities were highest in surface waters. The contribution of the aqueous fraction to total alkaline phosphatase activity varied between 42 and 74 Oh. The bulk of particulate alkaline phosphatase activity was associated wlth picoplankton (50 to 71 1; ") at all sampling sites. A good correlation was found between depth distributions of alkaline phosphatase activities and Synechococcus, suggesting that this abundant picoplanktonic cyanobacterium is a significant contributor to the enzyme activity in the northern half of the Gulf of Aqaba. Chlorophyll aspecific alkaline phosphatase activities were highest for plankton communities in the surface layers of the northern half of the Gulf. Alkahne phosphatase activities increased in the Gulf of Aqaba in water bodies traveling north, further away from the Straits of Tlran. At t h~s narrow and shallow entrance to the Gulf, local turbulent conditions and coral reef flats inject phosphate into the productive layer. Plankton communities immediately north of the Straits showed basal levels of alkaline phosphatase activity, and phosphate supply presumably satisfied their P-demands. Based on the regulat~on of alkaline phosphatase synthesis, its secretion and stabhty, we proposed the use of alkaline phosphatase activities for a (partial) assessment of the P-status of marine planktonic communities. Such an assessment indicated that inorganic phosphate availability in the waters of the northern Gulf of Aqaba was persistently low durlng the period prior to sampling.

This paper examines the linkages between the two emerging stock exchanges in mainland China and the established markets in Hong Kong and in the US by a multivariate GARCH approach. We use a four-variable asymmetric GARCH in the line of the BEKK model proposed by Engle and Kroner (1995) to account for the regularities documented in the share price indices and test for the transmission of returns and volatility across the markets. While we do not find any evidence of a direct linkage between the stock exchanges in mainland China and the US market, we find evidence of uni-directional volatility spillovers from the stock exchange in Hong Kong to those in Shanghai and Shenzhen. However, the magnitude of the volatility linkages between the mainland and Hong Kong is small, indicating a weak integration of the Chinese stock exchanges with the regional developed market. The implication of the weak integration is that overseas investors will benefit from the reduction of diversifiable risk, and thus total portfolio risk, by adding the mainland Chinese stocks to their investment portfolio.

Ultrathin SWCNT transparent and conductive films on flexible and transparent substrates are prepared via repeatedly halving the directly grown SWCNT films and flexible and transparent supercapacitors with excellent performance were fabricated.

No abstract

Layered tungsten disulfide nanostructures are of both fundamental and technological interest. The widths of currently synthesized WS 2 ribbons are in the microscale. By using single-walled carbon nanotubes and double-walled carbon nanotubes as templates, we fabricate WS 2 nanoribbons with smooth zigzag edges and uniform widths down to 1-3 nm and layer numbers down to 1-3, dependent on the nanotube diameter. Although bulk WS 2 is a nonmagnetic semiconductor, the ultra-narrow freestanding zigzag-edged WS 2 nanoribbons turn out to be magnetic or nonmagnetic metals depending on the edge passivation way according to our first-principles calculations, whereas the ultra-narrow armchair-edged WS 2 nanoribbons remain nonmagnetic semiconductors with a narrow gap. Results and discussionFormation of WS 2 was confirmed by Raman scattering measurements. Remarkable Raman signals (E 2g 1 mode, 350 cm À1

No abstract

No abstract

No abstract