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A systematic investigation to understand the use of a novel axial impeller as a part of counter-rotating axial compressor to compress water vapor as refrigerant was undertaken. Blade angle was investigated at first to understand this novel impeller’s geometry. A commercial CFD package, which solves the Reynolds-averaged Navier–Stokes equations, was used to compute the complex flow field of the impeller. Two hub/shroud tip ratios with different speed ratios were numerically simulated. The numerical simulation focused on the water vapor flow from compressor impeller inlet to outlet and the overall performance level and range were predicted. The numerical investigation revealed that at hub/shroud tip ratio of 0.54, maximum pressure ratio reached about 1.24 with isentropic efficiency around 75\% at its design point. Detailed investigation into flow structure showed that a serious secondary flow exists between span ranges of 30–50\%. An enlargement of hub/shroud tip ratio to 0.75 showed that pressure ratio had been improved significantly. By comparing different speed ratios and hub/shroud tip ratios, the study shows potential to utilize this novel axial impeller to compress water vapor as refrigerant.

The authors discuss the problem of hedging between the natural gas and electric power markets. Based on multiple forecasts for natural gas prices, natural gas demand, and electricity prices, a stochastic optimization model advises a decision maker on when to buy or sell natural gas and when to transform gas into electricity. For relatively small models, branch-and-bound solves the problem to optimality. Larger models are solved using Benders decomposition and Lagrangian relaxation. They apply their approach to the system of an electric utility and succeed in solving problems with 50000 binary variables in less than 4 min to within 1.16% of the optimal value.

The neurobiological processes involved in establishing sleep regulation are vulnerable to environmental exposures as early as seven weeks of gestation. Studies have linked in utero pesticide exposure to childhood sleep-disordered breathing. However, the impact of in utero pesticide exposure on the sleep health of adolescents remains unexplored.Data from 137 mother-adolescent pairs from a Mexico City cohort were analyzed. We used maternal urinary 3-phenoxybenzoic acid (3-PBA, pyrethroid metabolite) and 3, 5, 6-trichloro-2-pyridinol (TCPy, chlorpyrifos metabolite) from trimester three to estimate in utero pesticide exposure. Among adolescents, we obtained repeated measures of objectively assessed sleep duration, midpoint, and fragmentation using wrist-actigraphy devices for 7 consecutive days in 2015 and 2017. Unstratified and sex-stratified associations between maternal urinary 3-PBA and TCPy and adolescent sleep measures were examined using generalized linear mixed models (GLMMs). We also examined the interactive effects of maternal pesticide exposure and offspring sex on sleep outcomes.3-PBA and TCPy were detected in 44.4% and 93% of urine samples, respectively. Adjusted findings demonstrated that higher exposure to maternal TCPy was associated with longer sleep duration and later sleep timing. Findings from interaction tests between maternal pesticide exposure and offspring sex were not statistically significant, although adjusted sex-stratified findings showed that the association between TCPy with duration and midpoint was evident only among female offspring. To illustrate, those in the highest tertile of exposure had a 59 minute (95% CI: 12.2, 104.8) (p, trend = 0.004) longer sleep duration and a 0.6 hour (95% CI: 0.01, 1.3) (p, trend = 0.01) later sleep midpoint. We found no significant associations between 3-PBA and sleep outcomes.Within a cohort of mother-adolescent pairs, we found associations between maternal prenatal pesticide exposure and longer sleep duration and later sleep timing among adolescent offspring. Further, this association may be female-specific.

A duct flow generated by a planar jet at the inlet and affected by a magnetic field perpendicular to the jet's plane is analyzed in high-resolution numerical simulations. The case of very high Reynolds and Hartmann numbers is considered. It is found that the flow structure is drastically modified in the inlet area. It becomes determined by three new planar jets oriented along the magnetic field lines: two near the walls and one in the middle of the duct. The downstream evolution of the flow includes the Kelvin-Helmholtz instability of the jets and slow decay of the resulting quasi-two-dimensional turbulence.

Research on the evolutionary ecology of urban areas reveals how human-induced evolutionary changes affect biodiversity and essential ecosystem services. In a rapidly urbanizing world imposing many selective pressures, a time-sensitive goal is to identify the emergent issues and research priorities that affect the ecology and evolution of species within cities. Here, we report the results of a horizon scan of research questions in urban evolutionary ecology submitted by 100 interdisciplinary scholars. We identified 30 top questions organized into six themes that highlight priorities for future research. These research questions will require methodological advances and interdisciplinary collaborations, with continued revision as the field of urban evolutionary ecology expands with the rapid growth of cities.

Through means of 3-D CFD (Computational Fluid Dynamics) method, a novel axial compressor with different impeller shapes compressing water vapor as refrigerant was investigated. The numerical simulation focuses on the fluid flow from compressor impeller inlet to outlet. The overall performance level and range are predicted. Different blade patterns with different hub sizes were compared regarding the aerodynamic performance. Independent of the blade pattern, in this numerical investigation the largest hub diameter shows the highest pressure ratio and efficiency at narrowest operating range.

Reference EPFL-ARTICLE-229565doi:10.1016/j.applthermaleng.2017.03.140View record in Web of Science Record created on 2017-07-10, modified on 2017-07-10

Climate change decoupling mutualism Many coevolved species have precisely matched traits. For example, long-tongued bumblebees are well adapted for obtaining nectar from flowers with long petal tubes. Working at high altitude in Colorado, Miller-Struttmann et al. found that long-tongued bumblebees have decreased in number significantly over the past 40 years. Short-tongued species, which are able to feed on many types of flowers, are replacing them. This shift seems to be a direct result of warming summers reducing flower availability, making generalist bumblebees more successful than specialists and resulting in the disruption of long-held mutualisms. Science , this issue p. 1541