University of CaliforniaSanta Barbara

University of Technology of Compiègne, France

University of CaliforniaSanta Barbara

University of Technology of Compiègne, France
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Cortes A.,University of CaliforniaSanta Barbara | Macintyre S.,University of CaliforniaSanta Barbara | Sadro S.,University of CaliforniaSanta Barbara
Limnology and Oceanography | Year: 2017

The extent to which snowmelt flowing into ice-covered lakes spreads horizontally and mixes vertically influences retention of solutes derived from the landscape. To quantify these transport processes and retention, we combine time series temperature and specific conductance measurements in Toolik Lake (Alaska) and its major inflow, with measurements of discharge and meteorology, and profiles of specific conductance, temperature, fluorescence, chlorophyll a, and dissolved organic carbon (DOC) in spring of 3 yr. During early snowmelt, the concentration of DOC in the stream was 750 μM, twice that in the lake. During slow melt (discharge (Q)<4 m3 s-1), the incoming solute-rich intrusion spread lakewide below the ice. During melt with Q>6 m3 s-1, the incoming water partially flushed the inlet basin and the more dilute water flowed over the original intrusion with a preferential flowpath to the outlet. Penetrative convection was restricted by the increased density gradients from the incoming plume and initially constrained to shallow mixing zones associated with the step changes in density. As ice thickness decreased to less than 1 m, heating caused density instabilities at the base of the intrusions that mixed solutes ∼ 10 m vertically, contributing to retention. Near-surface layers enriched with DOC persisted for ∼ 10 d during a rapid melt and for over 3 weeks when the melt was slow. Retention, of order 10-20%, also depended on the rapidity of melt and magnitude of discharge. © 2017 Association for the Sciences of Limnology and Oceanography.


Shi W.,University of CaliforniaSanta Barbara | Li W.,University of CaliforniaSanta Barbara | Delaney K.T.,University of CaliforniaSanta Barbara | Fredrickson G.H.,University of CaliforniaSanta Barbara | And 4 more authors.
Journal of Polymer Science, Part B: Polymer Physics | Year: 2015

Here, we report the morphology variation in a series of PS-b-PI-b-PS' asymmetric triblock copolymer and PS homopolymer (hPS) blends, where PS' and PS are polystyrene blocks with a molecular weight ratio of approximately 0.11 and PI is poly(isoprene). We find that adding a small amount of hPS results in significant order-order transition (OOT) boundary deflection toward higher PS volume fractions fPS, which is accompanied by morphology re-entry. For example, the neat triblock copolymer with a PS+PS' volume fraction of fPS=0.38 exhibits a lamellar microphase; adding a small amount of hPS reverts the morphology into a hexagonal phase with PS cylinders, while further increasing the hPS fraction leads to normal OOTs from PS cylinders to lamellae, to PI cylinders and finally to spheres. The morphology variation reported here is significantly different from that reported in binary blends of diblock or symmetric triblock copolymer with homopolymer. While the domain features of the LAM structure can be correctly reproduced by self-consistent field theory (SCFT), the observed morphology re-entry is absent in the theoretical SCFT phase diagram. © 2015 Wiley Periodicals, Inc.

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