The effects of oscillatory temperature on HaCaT keratinocyte behaviors

BACKGROUND: Keratinocytes are exposed to a thermal gradient throughout epidermal layers in human skin depending on environmental temperatures. OBJECTIVE: Here, the effect of cyclic temperature changes (ΔT) on HaCaT cell behaviors was explored. METHODS: HaCaT cells were cultured at constant temperature (37 °C or 25 °C) or under ΔT conditions. The morphology, mechanics, cell cycle progression, proliferation, and lipid synthesis of HaCaT cells were determined. RESULTS: ΔT conditions led to the inhomogeneous arrangement of the cytoskeleton in HaCaT cells, which resulted in enlarged size, rounder shape, and increased stiffness. Accumulation in the G2/M phase in the cell cycle, a decreased proliferation rate, and a delayed lipogenesis were detected in HaCaT cells cultured under ΔT conditions. CONCLUSIONS: ΔT conditions resulted in the re-arrangement of the cytoskeleton in HaCaT cells, which showed similarity to the temperature-induced disassemble and re-assemble of cytoskeletons in keratinocyte in vivo. The altered cytoskeleton arrangement resulted in the cell enlargement and stiffening, which reflected the changes in cellular functions. The application of oscillatory temperature in the in vitro culture of keratinocytes provides a way to gain more insights into the role of skin in response to environmental stimuli and maintaining its homeostasis in vivo.

Rheological Characterization of Starch Gelatinization: Effects of plasticizer/starch ratio and clay content in corn-starch/glycerol thermoplastic starch (TPS)

ABSTRACTThis work presents a systematic rheological study of the gelatinization process of corn-starch plasticized with glycerol, showing the effects of the glycerol/starch ratio, water/starch ratio, and clay (montmorillonite) content. Gelatinization temperatures at different heating rates in rheological oscillatory temperature-sweep experiments were determined for different corn-starch/glycerol/clay formulations. The influences of the different formulation variables on the gelatinization processes and on the gel properties are analyzed. Some hypotheses postulating how the different intermolecular interactions present in the composites are responsible for these effects are discussed.

Temperature Advection by Tropical Instability Waves

A numerical model of the tropical Pacific Ocean is used to investigate the processes that cause the horizontal temperature advection of tropical instability waves (TIWs). It is found that their temperature advection cannot be explained by the processes on which the mixing length paradigm is based. Horizontal mixing of temperature across the equatorial SST front does happen, but it is small relative to the “oscillatory” temperature advection of TIWs. The basic mechanism is that TIWs move water back and forth across a patch of large vertical entrainment. Outside this patch, the atmosphere heats the water and this heat is then transferred into the thermocline inside the patch. These patches of strong localized entrainment are due to equatorial Ekman divergence and due to thinning of the mixed layer in the TIW cyclones. The latter process is responsible for the zonal temperature advection, which is as large as the meridional temperature advection but has not yet been observed. Thus, in the previous observational literature the TIW contribution to the mixed layer heat budget may have been underestimated significantly.

Effect of Modulation on Thermal Convection Instability

The linear stability problem for a fluid in a classic Benard configuration is considered. The applied temperature gradient is the sum of a steady component and a time-dependent periodic component. Only infinitesimal disturbances are considered. The time-dependent perturbation is expressed in Fourier series. The shift in critical Rayleigh number is calculated and the modulating effect of the oscillatory temperature gradient on the stability of the fluid layer is examined. Some comparison is made with known results.