Improved resolution crystal structure of Acanthamoeba actophorin reveals structural plasticity not induced by microgravity

Actophorin, a protein that severs actin filaments isolated from the amoeba Acanthamoeba castellanii, was employed as a test case for crystallization under microgravity. Crystals of purified actophorin were grown under microgravity conditions aboard the International Space Station (ISS) utilizing an interactive crystallization setup between the ISS crew and ground-based experimenters. Crystals grew in conditions similar to those grown on earth. The structure was solved by molecular replacement at a resolution of 1.65 Å. Surprisingly, the structure reveals conformational changes in a remote β-turn region that were previously associated with actophorin phosphorylated at the terminal residue Ser1. Although crystallization under microgravity did not yield a higher resolution than crystals grown under typical laboratory conditions, the conformation of actophorin obtained from solving the structure suggests greater flexibility in the actophorin β-turn than previously appreciated and may be beneficial for the binding of actophorin to actin filaments.

Experimental Investigation of Heat Transfer on the Internal Tip Wall in a Rotating Two-Pass Rectangular Channel

The tip turn region within the gas turbine blade experienced severe thermal issues related to temperature variations and temperature gradients. The current study experimentally measured the heat transfer distribution of the internal blade tip wall in a rotating cooling channel. The aspect ratio of this rectangular channel was 1:4, and the hydraulic diameter was 25.6 mm. Due to the impact of the 180 deg turn, complex three-dimensional flow significantly affected the heat transfer on the internal tip surface. The steady-state liquid crystal method was used to obtain a detailed distribution of heat transfer on the internal tip surface. In this study, the leading and trailing surfaces of the channel wall were either smooth or roughened with 45 deg angled ribs. The Reynolds number inside the pressurized cooling channel ranged from 10,000 to 30,000, and the rotation number was up to 0.53. Furthermore, two-channel orientations (90 deg and 135 deg) with respect to the rotation direction were tested. The tip heat transfer from the smooth channel wall was more sensitive to rotation, and the largest heat transfer enhancement caused by rotation was 68%. Channel orientation of 90 deg produced higher heat transfer compared to the orientation of 135 deg.

Steady RANS of Flow and Heat Transfer in a Smooth and Pin-Finned U-Duct With a Trapezoidal Cross Section

Steady Reynolds-averaged Navier--Stokes (RANS) simulations were performed to examine the ability of four turbulence models—realizable k–ε (k–ε), shear-stress transport (SST), Reynolds stress model with linear pressure strain (RSM-LPS), and stress-omega RSM (RSM-τω)—to predict the turbulent flow and heat transfer in a trapezoidal U-duct with and without a staggered array of pin fins. Results generated for the heat-transfer coefficient (HTC) were compared with experimental measurements. For the smooth U-duct, the maximum relative error in the averaged HTC in the up-leg is 2.5% for k–ε, SST, and RSM-τω and 9% for RSM-LPS. In the turn region, the maximum is 50% for k–ε and RSM-LPS, 14.5% for RSM-τω, and 29% for SST. In the down-leg, SST gave the best predictions and RSM-τω being a close second with maximum relative error less than 10%. The ability to predict the separated flow downstream of the turn dominated the performance of the models. For the U-duct with pin fins, SST and RSM-τω predicted the best, and k–ε predicted the least accurate HTCs. For k–ε, the maximum relative error is about 25%, whereas it is 15% for the SST and RSM-τω, and they occur in the turn. In the turn region, the staggered array of pin fins was found to behave like guide vanes in turning the flow. The pin fins also reduced the size of the separated region just after the turn.

Steady RANS of Flow and Heat Transfer in a Smooth and Pin-Finned U-Duct With a Trapezoidal Cross Section

Steady RANS were performed to examine the ability of four turbulence models — realizable k-ε (k-ε), shear-stress transport (SST), Reynolds stress model with linear pressure strain (RSM-LPS), and stress-omega RSAM (RSM-τω) — to predict the turbulent flow and heat transfer in a U-duct with a trapezoidal cross section and with and without a staggered array of pin fins. Results generated for the heat-transfer coefficient (HTC) were compared with experimentally measured values. For the smooth U-duct, the maximum relative error in the averaged HTC in the up-leg is 2.5% for k-ε, SST, and RSM-τω and 9% for RSM-LPS. In the turn region, that maximum is 14.5% for RSM-τω, 29% for SST, and 50% for k-ε and RSM-LPS. In the down-leg, SST gave the best predictions and RSM-τω being a close second with maximum relative error less than 10%. The ability to predict the secondary flow in the turn region and the separated flow downstream of the turn dominated in how well the models predict the HTC. For the U-duct with pin fins, k-ε predicted the lowest and the least accurate HTCs, and SST and RSM-τω predicted the best. For k-ε, the maximum relative error in the averaged HTC is about 25%, whereas it is 15% for the SST and RSM-τω, and they occur in the turn. In the turn region, the staggered array of pin fins was found to behave like guide vanes in turning the flow. The pin fins also reduced the size of the separated region just after the turn.

Dihydrochalcone molecules destabilize Alzheimer's amyloid-β protofibrils through binding to the protofibril cavity

Dihydrochalcone molecules destabilize Aβ17–42protofibrils by disrupting the N-terminal β1 region and the turn region through binding to the protofibril cavity.

Numerical Simulation of Flow and Heat Transfer in Rotating Cooling Passage With Turning Vane in Hub Region

Numerical simulation of three-dimensional turbulent flow and heat transfer was performed in a multipass rectangular (AR = 2:1) rotating cooling channel with and without turning vane in the hub region under various flow conditions, with two different Reynolds numbers of 10,000 and 25,000, two different channel orientations of 45-deg and 90-deg, and the rotation number varies from 0 to 0.2. This study shows that the addition of the turning vane in the hub turn region does not cause much impact to the flow before the hub. However, it significantly alters the flow reattachment and vortex distribution in the hub turn region and after the hub turn portion. The local heat transfer is deeply influenced by this complex flow field and this turning vane effect lasts from the hub turn region to the portion after it.