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Response patterns of phytoplankton growth to variations in resuspension in the German Bight revealed by daily MERIS data in 2003 and 2004

Su J., Tian T., Krasemann H., Schartau M., Wirtz K.

Oceanologia

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2015

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No. 57 (4)

328--341

EN

Chlorophyll (chl a) concentration in coastal seas exhibits variability on various spatial and temporal scales. Resuspension of particulate matter can somewhat limit algal growth, but can also enhance productivity because of the intrusion of nutrient-rich pore water from sediments or bottom water layers into the whole water column. This study investigates whether characteristic changes in net phytoplankton growth can be directly linked to resuspension events within the German Bight. Satellite-derived chl a were used to derive spatial patterns of net rates of chl a increase/decrease (NR) in 2003 and 2004. Spatial correlations between NR and mean water column irradiance were analysed. High correlations in space and time were found in most areas of the German Bight (R2 > 0.4), suggesting a tight coupling between light availability and algal growth during spring. These correlations were reduced within a distinct zone in the transition between shallow coastal areas and deeper offshore waters. In summer and autumn, a mismatch was found between phytoplankton blooms (chl a > 6 mg m−3) and spring-tidal induced resuspension events as indicated by bottom velocity, suggesting that there is no phytoplankton resuspension during spring tides. It is instead proposed here that frequent and recurrent spring-tidal resuspension events enhance algal growth by supplying remineralized nutrients. This hypothesis is corroborated by a lag correlation analysis between resuspension events and in-situ measured nutrient concentrations. This study outlines seasonally different patterns in phytoplankton productivity in response to variations in resuspension, which can serve as a reference for modelling coastal ecosystem dynamics.

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Preparation and bioactivity of embedded-style hydroxyapatite-titania nanotube arrays

Xiao X. F., Liu R. F., Tian T.

Materials Science Poland

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2009

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Vol. 27, No. 1

23--31

EN

Embedded-style hydroxyapatite-titania nanotube arrays were successfully prepared by anodic oxidation of titanium substrate and centrifugal filling hydroxyapatite precursor sol into hollow nanotubes. The morphology, microstructure and thermal stability of the samples were characterized by X-ray diffraction, environmental scanning electron microscopy, and energy dispersive X-ray analysis. The results show that the structure of titania nanotube arrays is stable at 500 °C or below, and the crystallized hydroxyapatite could be formed from hydroxyapatite precursor sol after calcining at 500 °C for 4 h. The optimum calcining temperature for this material is 500 °C. An obvious apatite layer formed on the surface of the embedded- style material after soaking in simulated body fluid for 5 days, indicating that the material possesses a good in vitro apatite forming ability on its surface.

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Biomimetic growth of apatite on titania nanotube arrays fabricated by titanium anodization in NH4F/H2SO4 electrolyte

Tian T., Xiao Xiu-feng, She Hou-de, Liu Rong-fang

Materials Science Poland

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2008

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Vol. 26, No. 3

487--494

EN

In the present work, the titania nanotube arrays was fabricated by anodizing titanium in NH4F/H2SO4 electrolyte. The crystal structure and the apatite-forming ability of the titania nanotube arrays were investigated. The samples were examined by ESEM, XRD and FT-IR. The results indicate that the crystal structure of the titania nanotube arrays occurred transformation from amorphous to anatase and rutile as the annealed temperature rised. The surface structure of the nanotube could enhance the bioactivity of titania. The bioactivity of titania nanotube arrays lies on its the crystal structure, ranked in following series: mixture of anatase and rutile structure > anatase > amorphous.