Physical and numerical modeling of cross-flow turbines

Cross-flow (often vertical-axis) turbines (CFTs), despite being thoroughly investigated and subsequently abandoned for large scale wind energy, are seeing renewed interest for smaller scale wind turbine arrays, offshore wind, and marine hydrokinetic (MHK) energy applications. Though they are similar to the large scale Darrieus wind turbines, today\u27s CFT rotors are often designed with higher solidity, or blade chord-to-radius ratios, which makes their behavior more difficult to predict with numerical models. Furthermore, most experimental datasets used for numerical model validation were acquired with low solidity rotors. An experimental campaign was undertaken to produce high quality open datasets for the performance and near-wake flow dynamics of CFTs. An automated experimental setup was developed using the University of New Hampshire\u27s towing tank. The tank\u27s linear motion, control, and data acquisition systems were redesigned and rebuilt to facilitate automated cross-flow turbine testing at large laboratory (on the order of 1 meter) scale. Two turbines were designed and built---one high solidity (dubbed the UNH Reference Vertical-Axis Turbine or UNH-RVAT) and one medium-to-low solidity, which was a scaled model of the US Department of Energy and Sandia National Labs\u27 Reference Model 2 (RM2) cross-flow MHK turbine. A baseline performance and near-wake dataset was acquired for the UNH-RVAT, which revealed that the relatively fast wake recovery observed in vertical-axis wind turbine arrays could be attributed to the mean vertical advection of momentum and energy, caused by the unique interaction of vorticity shed from the blade tips. The Reynolds number dependence of the UNH-RVAT was investigated by varying turbine tow speeds, indicating that the baseline data had essentially achieved a Reynolds number independent state at a turbine diameter Reynolds number $Re_D \sim 10^6$ or chord based Reynolds number $Re_c \sim 10^5$. A similar study was undertaken for the RM2, with similar results. An additional dataset was acquired for the RM2 to investigate the effects of blade support strut drag on overall performance, which showed that these effects can be quite significant---on the order of percentage points of the power coefficient---especially for lower solidity rotors, which operate at higher tip speed ratio. The wake of the RM2 also showed the significance of mean vertical advection on wake recovery, though the lower solidity made these effects weaker than for the UNH-RVAT. Blade-resolved Reynolds-averaged Navier--Stokes (RANS) computational fluid dynamics (CFD) simulations were performed to assess their ability to model performance and near-wake of the UNH-RVAT baseline case at optimal tip speed ratio. In agreement with previous studies, the 2-D simulations were a poor predictor of both the performance and near-wake. 3-D simulations faired much better, but the choice of an appropriate turbulence model remains uncertain. Furthermore, 3-D blade-resolved RANS modeling is computationally expensive, requiring high performance computing (HPC), which may preclude its use for array analysis. Finally, an actuator line model (ALM) was developed to attempt to drive down the cost of 3-D CFD simulations of cross-flow turbines, since previously, the ALM had only been investigated for a very low Reynolds number 2-D CFT. Despite retaining some of the disadvantages of the lower fidelity blade element momentum and vortex methods, the ALM, when coupled with dynamic stall, flow curvature, added mass, and end effects models, was able to predict the performance of cross-flow turbines reasonably well. Near-wake predictions were able to match some of the important qualitative flow features, which warrants further validation farther downstream and with multiple turbines. Ultimately, the ALM provides an attractive alternative to blade-resolved CFD, with computational savings of two to four orders of magnitude for large eddy simulation and RANS, respectively

Experimental investigation of helical cross-flow axis hydrokinetic turbines, including effects of waves and turbulence

A test bed for cross-flow axis (CFA) hydrokinetic turbines for the UNH tow and wave tank was designed and built, and two different turbines were evaluated. The effects of waves and turbulence on performance were also observed. Drag (thrust) and mechanical power output were measured at tow speeds of 0.6--1.5 m/s for a Gorlov Helical Turbine (GHT) and a Lucid Spherical (helical) Turbine (LST), both provided by Lucid Energy Technologies, LLP. Overall, the GHT performed with a higher power and drag coefficient than the LST. GHT performance was enhanced by progressive waves, but waves caused stalling at higher tip speed ratios compared to the steady case. Grid turbulence enabled the GHT to operate at lower tip speed ratios and did not alter maximum power coefficient, but increased drag on the turbine. Performance in a cylinder wake was highly dependent on the cylinder\u27s cross-stream location, ranging from benign to detrimental

One step construction of PCR mutagenized libraries for genetic analysis by recombination cloning

Recombination cloning encompasses a set of technologies that transfer gene sequences between vectors through site-specific recombination. Due in part to the instability of linear DNA in bacteria, both the initial capture and subsequent transfer of gene sequences is often performed using purified recombination enzymes. However, we find linear DNAs flanked by loxP sites recombine efficiently in bacteria expressing Cre recombinase and the lambda Gam protein, suggesting Cre/lox recombination of linear substrates can be performed in vivo. As one approach towards exploiting this capability, we describe a method for constructing large (>1 × 106 recombinants) libraries of gene mutations in a format compatible with recombination cloning. In this method, gene sequences are cloned into recombination entry plasmids and whole-plasmid PCR is used to produce mutagenized plasmid amplicons flanked by loxP. The PCR products are converted back into circular plasmids by transforming Cre/Gam-expressing bacteria, after which the mutant libraries are transferred to expression vectors and screened for phenotypes of interest. We further show that linear DNA fragments flanked by loxP repeats can be efficiently recombined into loxP-containing vectors through this same one-step transformation procedure. Thus, the approach reported here could be adapted as general cloning method

«Horions», roman (extraits) ; suivi de Les fonctions extra-narratives dans "Trou de mémoire" d’Hubert Aquin

Ce mémoire de recherche-création porte sur les fonctions extra-narratives telles que définies par Gérard Genette, soit les fonctions de régie, testimoniale, de communication et idéologique, dans le contexte d’un récit à narrateurs multiples. Deux approches ont été privilégiées ici : l’écriture d’un roman comportant plusieurs instances de narration, et l’analyse d’un roman offrant un type comparable de structure narrative, soit Trou de mémoire d’Hubert Aquin. Ainsi, la partie création comprend des extraits d’Horions, roman hybride combinant les formes romanesque, poétique et dramatique, et dont ne figurent dans ce mémoire que des extraits des passages romanesques. Une instance narrative d’abord anonyme, puis nommée à la toute fin, retrace son passé en prêtant une voix à des êtres qui l’habitent, notamment un homme violent et un fils aphasique. Ces personnages-narrateurs exercent, outre la fonction narrative, d’autres fonctions qui justifient en quelque sorte leur présence : l’un est témoin de l’intrigue qu’il rapporte, l’autre communique avec un narrataire intra-diégétique, un troisième rend compte des émotions du protagoniste… Quant à la partie réflexion, elle se fonde sur les notions de narrateur, de narrataire et de situation narrative, mais se concentre sur les fonctions extra-narratives exercées par les diverses instances prenant la parole au fil du récit. Ces notions permettent de rendre compte de la structure narrative d’ensemble du roman Trou de mémoire d’Hubert Aquin, lequel juxtapose plusieurs voix, soit celles de Pierre X. Magnant, Rachel Ruskin, Olympe Ghezzo-Quénum et Charles-Édouard Mullahy. Un bref retour sur l’écriture d’Horions et sur les enjeux du récit à plusieurs narrateurs se prévalant des diverses fonctions extra-narratives complète la démarche

The yeast S phase checkpoint enables replicating chromosomes to bi-orient and restrain spindle extension during S phase distress

The budding yeast S phase checkpoint responds to hydroxyurea-induced nucleotide depletion by preventing replication fork collapse and the segregation of unreplicated chromosomes. Although the block to chromosome segregation has been thought to occur by inhibiting anaphase, we show checkpoint-defective rad53 mutants undergo cycles of spindle extension and collapse after hydroxyurea treatment that are distinct from anaphase cells. Furthermore, chromatid cohesion, whose dissolution triggers anaphase, is dispensable for S phase checkpoint arrest. Kinetochore–spindle attachments are required to prevent spindle extension during replication blocks, and chromosomes with two centromeres or an origin of replication juxtaposed to a centromere rescue the rad53 checkpoint defect. These observations suggest that checkpoint signaling is required to generate an inward force involved in maintaining preanaphase spindle integrity during DNA replication distress. We propose that by promoting replication fork integrity under these conditions Rad53 ensures centromere duplication. Replicating chromosomes can then bi-orient in a cohesin-independent manner to restrain untimely spindle extension

PIASy-dependent SUMOylation regulates DNA topoisomerase IIα activity

SUMOylation of TopoIIα inhibits its decatenation activity, preventing resolution of tangled DNA at centromeres before anaphase onset

The SUMO Isopeptidase Ulp2p Is Required to Prevent Recombination-Induced Chromosome Segregation Lethality following DNA Replication Stress

SUMO conjugation is a key regulator of the cellular response to DNA replication stress, acting in part to control recombination at stalled DNA replication forks. Here we examine recombination-related phenotypes in yeast mutants defective for the SUMO de-conjugating/chain-editing enzyme Ulp2p. We find that spontaneous recombination is elevated in ulp2 strains and that recombination DNA repair is essential for ulp2 survival. In contrast to other SUMO pathway mutants, however, the frequency of spontaneous chromosome rearrangements is markedly reduced in ulp2 strains, and some types of rearrangements arising through recombination can apparently not be tolerated. In investigating the basis for this, we find DNA repair foci do not disassemble in ulp2 cells during recovery from the replication fork-blocking drug methyl methanesulfonate (MMS), corresponding with an accumulation of X-shaped recombination intermediates. ulp2 cells satisfy the DNA damage checkpoint during MMS recovery and commit to chromosome segregation with similar kinetics to wild-type cells. However, sister chromatids fail to disjoin, resulting in abortive chromosome segregation and cell lethality. This chromosome segregation defect can be rescued by overproducing the anti-recombinase Srs2p, indicating that recombination plays an underlying causal role in blocking chromatid separation. Overall, our results are consistent with a role for Ulp2p in preventing the formation of DNA lesions that must be repaired through recombination. At the same time, Ulp2p is also required to either suppress or resolve recombination-induced attachments between sister chromatids. These opposing defects may synergize to greatly increase the toxicity of DNA replication stress