Assessment of Particle Candidates for Falling Particle Receiver Applications Through Irradiance and Thermal Cycling

Falling particle receiver (FPR) systems are a rapidly developing technology for concentrating solar power applications. Solid particles are used as both the heat transfer fluid and system thermal energy storage media. Through the direct irradiation of the solid particles, flux and temperature limitations of tube-bundle receives can be overcome, leading to higher operating temperatures and energy conversion efficiencies. Candidate particles for FPR systems must be resistant to changes in optical properties during long term exposure to high temperatures and thermal cycling using highly concentrated solar irradiance. Five candidate particles, CARBOBEAD HSP 40/70, CARBOBEAD CP 40/100, including three novel particles, CARBOBEAD MAX HD 35, CARBOBEAD HD 350, and WanLi Diamond Black, were tested using simulated solar flux cycling and tube furnace thermal aging. Each particle candidate was exposed for 10 000 cycles (simulating the exposure of a 30-year lifetime) using a shutter to attenuate the solar simulator flux. Feedback from a pyrometer temperature measurement of the irradiated particle surface was used to control the maximum temperatures of 775 °C and 975 °C. Particle solar-weighted absorptivity and emissivity were measured at 2000 cycle intervals. Particle thermal degradation was also studied by heating particles to 800 °C, 900 °C, and 1000 °C for 300 hours in a tube furnace purged with bottled unpurified air. Here particle absorptivity and emissivity were measured at 100-hour intervals. Measurements taken after irradiance cycling and thermal aging were compared to measurements taken from as-received particles. WanLi Diamond Black particles had the highest initial value for solar weighted absorptance, 96%, but degraded up to 4% in irradiance cycling and 6% in thermal aging. CARBOBEAD HSP 40/70 particles currently in use in the prototype FPR at the National Solar Thermal Test Facility had an initial value of 95% solar absorptance with up to a 1% drop after irradiance cycling and 4% drop after 1000 °C thermal aging.

Dimeric heat shock protein 40 binds radial spokes for generating coupled power strokes and recovery strokes of 9 + 2 flagella

T-shape radial spokes regulate flagellar beating. However, the precise function and molecular mechanism of these spokes remain unclear. Interestingly, Chlamydomonas reinhardtii flagella lacking a dimeric heat shock protein (HSP) 40 at the spokehead–spokestalk juncture appear normal in length and composition but twitch actively while cells jiggle without procession, resembling a central pair (CP) mutant. HSP40− cells begin swimming upon electroporation with recombinant HSP40. Surprisingly, the rescue doesn't require the signature DnaJ domain. Furthermore, the His-Pro-Asp tripeptide that is essential for stimulating HSP70 adenosine triphosphatase diverges in candidate orthologues, including human DnaJB13. Video microscopy reveals hesitance in bend initiation and propagation as well as irregular stalling and stroke switching despite fairly normal waveform. The in vivo evidence suggests that the evolutionarily conserved HSP40 specifically transforms multiple spoke proteins into stable conformation capable of mechanically coupling the CP with dynein motors. This enables 9 + 2 cilia and flagella to bend and switch to generate alternate power strokes and recovery strokes.

Specificity of Class II Hsp40 Sis1 in Maintenance of Yeast Prion [RNQ +]

Sis1 and Ydj1, functionally distinct heat shock protein (Hsp)40 molecular chaperones of the yeast cytosol, are homologs of Hdj1 and Hdj2 of mammalian cells, respectively. Sis1 is necessary for propagation of the Saccharomyces cerevisiae prion [RNQ + ]; Ydj1 is not. The ability to function in [RNQ + ] maintenance has been conserved, because Hdj1 can function to maintain Rnq1 in an aggregated form in place of Sis1, but Hdj2 cannot. An extended glycine-rich region of Sis1, composed of a region rich in phenylalanine residues (G/F) and another rich in methionine residues (G/M), is critical for prion maintenance. Single amino acid alterations in a short stretch of amino acids of the G/F region of Sis1 that are absent in the otherwise highly conserved G/F region of Ydj1 cause defects in prion maintenance. However, there is some functional redundancy within the glycine-rich regions of Sis1, because a deletion of the adjacent glycine/methionine (G/M) region was somewhat defective in propagation of [RNQ + ] as well. These results are consistent with a model in which the glycine-rich regions of Hsp40s contain specific determinants of function manifested through interaction with Hsp70s.