We use yearlong vertical temperature profile time‐series (seven thermistors at evenly spaced depth intervals from 10 to 70 cm) from five sites in and around the Deep Hole thermal area, southeast of Stevenson Island, Yellowstone Lake, to investigate heat and mass fluxes across the lake floor. The records demonstrate that thermal gradients in surficial sediments are modulated by a rich spectrum of bottom water temperature variations generated by hydrodynamic processes, and that sites inside the thermal area also respond to hydrothermal variations. We develop and implement a new method for estimating the sediment effective thermal diffusivity and pore fluid vertical flow rate that exploits the full spectrum of observed temperature variations to generate the parameter estimates, uncertainties, and metrics to assess statistical significance. Sediments at sites outside thermal areas have gradients of ∼7.5°C/m, in situ thermal diffusivities of ∼1.6 × 10−7 m2/s consistent with highly porous (80–90%) siliceous sediments, and experience hypolentic flow in the upper ∼20 cm. Sites inside the Deep Hole thermal area exhibit considerable spatial and temporal variability, with gradients of 1–32°C/m, and higher thermal diffusivities of ∼2–12 × 10−7 m2/s, consistent with hydrothermal alteration of biogenic silica to clays, quartz, and pyrite. Upward pore fluid flow at these sites is observed across multiple depth intervals, with maximum values of ∼3 cm/day. The observed spatial and temporal variability within the thermal area is consistent with upward finger flow combined with short wavelength convection within the porous sediments above a steam reservoir.
We present a mechanism for thermal cycling that does not require electricity; instead, the device functions as a heat engine and requires only a generic heat source and a shape memory alloy (SMA) spring. The SMA spring mechanically translates to a low-temperature reservoir when heated, and the subsequent cooling of the spring causes translation back to a high-temperature reservoir. The usefulness of the mechanism is displayed by performing the quantitative polymerase chain reaction (qPCR), an important biological assay that requires thermal cycling for amplification of nucleic acids. The ability to perform qPCR with a generic heat source enables a variety of significant health diagnostic tests to be performed in resource limited settings, where electricity access may not be available or reliable. We demonstrate robust thermal cycling using a direct flame, sunlight, and electricity as heat sources, with maximum heating and cooling rates of 4.4 °C s−1and −2.7 °C s−1, respectively.
more » « less- Award ID(s):
- 1719875
- NSF-PAR ID:
- 10303192
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Smart Materials and Structures
- Volume:
- 29
- Issue:
- 4
- ISSN:
- 0964-1726
- Page Range / eLocation ID:
- Article No. 045038
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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