SPHERE (which stands for Spectro-Polarimetric High-contrast Exoplanet REsearch) is a second-generation Very Large Telescope (VLT) instrument dedicated to high-contrast direct imaging of exoplanets whose first-light is scheduled for 2011. Within this complex instrument one of the central components is the apodized Lyot coronagraph (ALC). The principal aim of this paper is to report the first laboratory experiment of the ALC designed for the SPHERE instrument. The performance and sensitivity of the optical configuration was first numerically studied with an end-to-end approach (see the results in paper I subtitled ??Detailed numerical study??). Made confident by the results, we then tested a prototype on an infrared coronagraphic bench. We measured the transmission profiles of the apodizer prototype and the coronagraphic performance of the apodized Lyot coronagraph in Y, J, and H bands. The coronagraph sensitivity to lateral and longitudinal misalignments of its three main components (apodizer, coronagraphic mask and Lyot stop) was finally studied in H band. We can conclude that the prototype meets the SPHERE technical requirements for coronagraphy. 相似文献
When a high-speed body with cavity passes through water-air free surface and exits water, its mechanical environment and dynamic characteristics change significantly due to the great difference in density and viscosity between water and air. With focusing on this problem, the Computational Fluid Dynamics (CFD) method is applied to perform numerical calculation on the process of this vapor-liquid-gas flow during the water exit of a high-speed cylinder, with the Volume of Fraction (VOF) multiphase flow interface-capturing techniques and the overset grid technology. After the verification and validation of the CFD model through mesh convergence study and a water-entry experiment, cavity evolution and flow characteristics including pressure and velocity distribution during the water exit are analyzed. The effects of different initial velocities on the pressure distribution and drag characteristics of the cylinder are investigated. Calculated results show that the cavity collapse during water exit causes strong pressure fluctuation on the cylinder; when the cylinder exits water enveloped in a supercavity, the pressure distribution on its wall surface and surrounding water region is relatively uniform, and the drag changes gently, and thus the cylinder has good motion stability.
In this paper, the transient fluid resonance phenomenon inside a narrow gap between two adjacent boxes excited by the incident focused waves with various spectral peak periods and focused wave amplitudes is simulated by utilizing the open-sourced computational fluid dynamics software, OpenFOAM. The weather-side box is allowed to heave freely under the action of waves, and the lee-side box keeps fixed. This paper mainly focuses on how both the spectral peak period and the focused wave amplitude affect the free-surface amplification inside the gap, the motion of the weather-side box, and the wave loads (including the vertical and the horizontal wave forces) acting on both boxes. For comparison, another two-box system with both boxes fixed is also considered as a control group. It is found that the motion of the weather-side box significantly changes the characteristics of the transient gap resonance, and it would cause that the fluid resonant period becomes 1.4–1.6 times that of the two-box system with both boxes fixed. All the concerned physical quantities (i.e., the free-surface amplification in the gap, the motion of the weather-side box, the wave loads) are found to closely depend on both the spectral peak period and the focused wave amplitude.
Timely identification of disaster-prone neighborhoods and examination of disparity in disaster exposure are critical for policymakers to plan efficient disaster management strategies. Many studies have investigated racial, ethnic, and geographic disparities and populations most vulnerable to disasters. However, little attention has been paid to the development of easily accessible and reusable tools to enable: (1) the prompt identification of vulnerable neighborhoods; and (2) the examination of social disparity in disaster impact. In this research, we have developed a visual analytics tool that allows users to: (1) delineate neighborhoods based on their selection of variables; and (2) explore which neighborhoods are susceptible to the impacts of disasters based on specific socioeconomic and demographic characteristics. Through an exploration of COVID-19 data in the case study, we revealed that the tool can provide new insights into the identification of vulnerable neighborhoods that need immediate attention for disaster control, management, and relief. 相似文献
This study provides new insights for the hatchery released Chinese shrimp (Fenneropenaeus chinensis), including proportion, dynamic migration route, after they were released into nature for stock enhancement using a new strategy quite different than ever. Chinese shrimp were sampled at 22 survey stations during two investigation voyages acrossing 74 survey stations in the Bohai Sea from July 16 to August 9 in 2015. Among 289 sampled individuals during the second voyage, totally 155 shrimps were identified as hatchery shrimp released into the Laizhou Bay at mid-May in 2015 based on finger-print of eight SSR (simple sequence repeats) markers, and the proportion of hatchery released shrimp in recapture samples were from 41.30%–85.71% in each station with an average value 53.63%, which verified a previous view point that up to 90% of autumn season Chinese shrimp landing in the Bohai Sea were composed of hatchery released. Meanwhile, the dynamic migration route of hatchery released shrimp revealed that part of released shrimp migrated heading northwest along the west coast of the Bohai Sea up to the Bohai Bay but just remained at the Laizhou Bay until over-wintering migration at mid-October when they initiate over-wintering migration. Present unnatural spring season shrimp fishing model cut the throat of spawner shrimp chance to swim back to their respective spawning plants at each spring, it still no chance to clarify whether the hatchery released shrimp could replenish to the reproduce population and complete a whole life cycle as same as their natural relatives. 相似文献
Content and density of soil organic carbon(SOC) and labile and stable SOC fractions in peat mire soil in wetland, soybean field and rice paddy field reclaimed from the wetland around Xingkai Lake in Northeast China were studied. Studies were designed to investigate the impact of reclamation of wetland for soybean and rice farming on stability of SOC. After reclamation, SOC content and density in the top 0–30 cm soil layer decreased, and SOC content and density in soybean field were higher than that in paddy field. Content and density of labile SOC fractions also decreased, and density of labile SOC fractions and their ratios with SOC in soybean field were lower than that observed in paddy field. In the 0–30 cm soil layer, densities of labile SOC fractions, namely, dissolved organic carbon(DOC), microbial biomass carbon(MBC), readily oxidized carbon(ROC) and readily mineralized carbon(RMC), in both soybean field and paddy field were all found to be lower than those in wetland by 34.00% and 13.83%, 51.74% and 35.13%, 62.24% and 59.00%, and 64.24% and 17.86%, respectively. After reclamation, SOC density of micro-aggregates( 0.25 mm) as a stable SOC fraction and its ratio with SOC in 0–5, 5–10, 10–20 and 20–30 cm soil layers increased. SOC density of micro-aggregates in the 0–30 cm soil layer in soybean field was 50.83% higher than that in paddy field. Due to reclamation, SOC density and labile SOC fraction density decreased, but after reclamation, most SOC was stored in a more complex and stable form. Soybean farming is more friendly for sustainable SOC residence in the soils than rice farming. 相似文献
The multifractal measure enables an examination of the characteristics of a quantity distributed over a domain. This study examined the multifractal properties of turbulent intensities obtained from jet discharge experiments, where three types of nozzle geometries were examined in terms of the velocity fields and turbulent characteristics using particle image velocimetry. Depending on the nozzle geometry, the experimental results showed that the distribution of turbulent intensities and resulting dilution exhibited different behaviors. The experiment also showed that the transversal velocity profiles are similar to each other regardless of the outfall nozzle shapes and demonstrates the traditional similarity assumption at the same time. The multifractal exponents of the turbulent intensities were obtained with Box Count Method in a two-dimensional space. The results showed that the turbulent intensities obtained in two-dimensional space have a common multifractal spectrum, which was not the case for the velocity or shear stress observed in the same space. Although the transversal velocity profiles are similar, the multifractal exponent clearly shows a difference depending on the outfall geometries. In particular, the minimum value of the Lipschitz–Hölder exponent (αmin) and the entropy dimension (α1) tends to increase as turbulent intensity and dilution increase. These results suggest that the multifractal properties can be utilized potentially to categorize and evaluate the discharge outfall capabilities in terms of the resulting dilution. 相似文献
