Yi-Chun Kuo

Novel nanostructured biodegradable polymer matrices fabricated by phase separation techniques for tissue regeneration.

Biomimetic nanostructures have a wide range of applications. In particular, biodegradable polymer nanostructures that mimic the subtleties of extracellular matrix may provide favorable cell interactions. In this study, a co-solvent system was developed to configure a thermodynamically metastable biodegradable polymer solution, from which novel nanostructured matrices subsequently formed via wet phase separation (quaternary) or a combination with thermally induced phase separation. Three-dimensional (3D) nanostructured porous matrices were further fabricated by combination with particle-leaching (100-300μm glucose). The new co-solvent system may generate matrices with reproducible nanostructures from a variety of biodegradable polymers such as poly(d,l-lactide) (PLA), poly(ε-caprolactone) (PCL) and PCL-based polyurethane. In vitro cell culture experiments were performed with mouse pre-osteoblasts (MC3T3-E1) and human bone marrow-derived mesenchymal stem cells (hBM-MSC) to evaluate the osteoinductive potential of PLA nanostructures. The results showed that nanofibrous (<100nm) membranes promoted the bone-related marker gene expression and matrix mineralization of MC3T3-E1 at 14days. Nanofibrous 3D matrices seeded with hBM-MSC without osteogenic induction supplements demonstrated a 2.5-fold increase in bone matrix deposition vs. the conventional microporous matrices after 14 and 21days. Antimicrobial nanofibers were further obtained by plasma-assisted coating of chitosan on PLA nanofibers. This study reveals a platform for fabricating novel biodegradable nanofibrous architecture, with potential in tissue regeneration.

Decadal Variation of Wintertime Sea Surface Temperature in the Taiwan Strait

Long-term advanced very-high-resolution radiometer (AVHRR) data with a resolution of 0.04° provided clearer views of sea surface temperature (SST) warming and variation associated with ENSO in the Taiwan Strait (TS) during wintertime (1981-2013). Over the 33 year period, the spatial average of winter SST warming in the TS reached to 3°C. From 1981-2001, the SST exhibited an increasing trend, with the fastest warming taking place from 1991-2001 after which it seemed to pause. From 2002-2012, the SST showed a cooling trend (-0.08°C/yr). Spatial variation of the warming was distinct, with the highest values concentrated in the winter fronts region, formed by the cold China Coastal Current (CCC) and the warm Kuroshio Branch (KB), indicating northwestward movements of the winter fronts. Influence of ENSO events on winter SST was significant, with higher SST in the CCC region in El Nino years. Temporal SST EOF results in modes 1 and 2 show a long-term warming trend and interannual variations, respectively. Consequently, the combined impacts of global ocean warming and climate variability in future will result in increasing the uncertain of SST variability in the TS.

Association of Taiwan’s Rainfall Patterns with Large-Scale Oceanic and Atmospheric Phenomena

A 50-year (1960–2009) monthly rainfall gridded dataset produced by the Taiwan Climate Change Projection and Information Platform Project was presented in this study. The gridded data (5 × 5 km) displayed influence of topography on spatial variability of rainfall, and the results of the empirical orthogonal functions (EOFs) analysis revealed the patterns associated with the large-scale sea surface temperature variability over Pacific. The first mode (65%) revealed the annual peaks of large rainfall in the southwestern mountainous area, which is associated with southwest monsoons and typhoons during summertime. The second temporal EOF mode (16%) revealed the rainfall variance associated with the monsoon and its interaction with the slopes of the mountain range. This pattern is the major contributor to spatial variance of rainfall in Taiwan, as indicated by the first mode (40%) of spatial variance EOF analysis. The second temporal EOF mode correlated with the El Nino Southern Oscillation (ENSO). In particular, during the autumn of the La Nina years following the strong El Nino years, the time-varying amplitude was substantially greater than that of normal years. The third temporal EOF mode (7%) revealed a north-south out-of-phase rainfall pattern, the slowly evolving variations of which were in phase with the Pacific Decadal Oscillation. Because of Taiwan’s geographic location and the effect of local terrestrial structures, climate variability related to ENSO differed markedly from other regions in East Asia.

Typhoon-enhanced upwelling and its influence on fishing activities in the southern East China Sea

Ocean–atmosphere interactions before and after the passage of Typhoons Haitang, Fung-wong, and Morakot across the southern region of the East China Sea (ECS) were examined by assessing satellite measurements of sea surface temperature (SST) and chlorophyll-a (chl-a) concentration in conjunction with wind data. In terms of the satellite-derived data, the SST declined and chl-a concentration increased after the passage of the typhoons, and this could have resulted from the upwelling induced by typhoons via their long-duration, strong winds. According to fisheries data collected after the passing of Typhoon Morakot, the major fishing grounds of the torchlight fishery were found to have shifted northwards from the northern tip of Taiwan to the southern ECS. Moreover, the major target fish species changed from skipjack tuna (pre-typhoon) to squid (post-typhoon), signifying that the typhoon-enhanced upwelling might have caused the skipjack tuna, which typically prefer warm water, to have migrated elsewhere. In contrast, the nutrient-rich, upwelled water might have directly led to increases in chl-a concentrations and contributed the increase in local squid densities. This study suggests that typhoons can cause marked cooling of the sea surface as well as enhance upwelling that previously resulted in not only chl-a increases but also changes of local fish communities and, consequently, fishing activities.

Numerical study on the interactions between the Kuroshio current in the Luzon Strait and a mesoscale eddy

The Luzon Strait (LS) connects the northwestern Pacific Ocean and the South China Sea (SCS) and is the western boundary gap for the Kuroshio current (KC). Satellite observations indicate that a cyclonic mesoscale eddy can trigger westward extension of the KC into the SCS and shed a smaller anticyclonic eddy to the west of the LS. We used a nonlinear reduced-gravity (primitive equation) model to study this phenomenon and analyzed the dynamic process. The location of the collision between the eddy and the KC could be critical for varying the circulation in the LS. The eddy’s deformation rate, associated with its decaying speed, is also closely related to the location of the eddy during collision. When a cyclonic eddy moved from a region to the east of the Luzon Island toward the LS, the KC intruded into the SCS with growing negative vorticity during the collision of the eddy and KC. This tendency for negative vorticity is attributed to the beta effect and squeezing of the planetary vorticity caused by the flow divergence. As the eddy dissipated, the KC in the LS recovered its original pattern. When the collision of the eddy occurred at the center of the LS, the momentum balance of the KC loop was dominated by the inertial term, and the circulation in the LS remained in a leaping state.

Long-term observation on sea surface temperature variability in the Taiwan Strait during the northeast monsoon season

ABSTRACT The sea surface temperature (SST) in the Taiwan Strait (TS) during autumn and winter (October–March) is strongly influenced by the northeast monsoon, which drives the cold China Coastal Current to flow southward into the TS, where it encounters the warm Kuroshio Branch Current coming from the south to form a quasi-steady front. Using Advanced Very High Resolution Radiometer data, this study investigated long-term SST warming phenomena in the TS during the northeast monsoon season in the years 1980–2012. The SST trend demonstrated significant temporal and spatial variations; the SST of the TS increased during the period 1980–2000 and warmed faster in winter and early spring (January–March) than in autumn. Warming of the spatial average SST of the TS in March during this period reached 3°C. The highest warming trend was noted in the SST frontal region, indicating a northwestward movement of the winter fronts; however, the SST of the TS exhibited a decreasing trend after 2000. The interannual and decadal SST variations in the TS are partly in response to a large-scale wind field anomaly during the northeast monsoon season.