Kilonovae and Optical Afterglows from Binary Neutron Star Mergers. II. Optimal Search Strategy for Serendipitous Observations and Target-of-opportunity Observations of Gravitational Wave Triggers

In the second work of this series, we explore the optimal search strategy for serendipitous and gravitational-wave-triggered target-of-opportunity (ToO) observations of kilonovae and optical short-duration gamma-ray burst (sGRB) afterglows from binary neutron star (BNS) mergers, assuming that cosmological kilonovae are AT2017gfo-like (but with viewing-angle dependence) and that the properties of afterglows are consistent with those of cosmological sGRB afterglows. A one-day cadence serendipitous search strategy with an exposure time of ∼30 s can always achieve an optimal search strategy of kilonovae and afterglows for various survey projects. We show that the optimal detection rates of the kilonovae (afterglows) are ∼0.3/0.6/1/20 yr−1 (∼50/60/100/800 yr−1) for Zwicky the Transient Facility (ZTF)/Multi-channel Photometric Survey Telescope (Mephisto)/Wide Field Survey Telescope (WFST)/Large Synoptic Survey Telescope (LSST), respectively. A better search strategy for SiTian than the current design is to increase the exposure time. In principle, a fully built SiTian can detect ∼7(2000) yr−1 kilonovae (afterglows). Population properties of electromagnetic (EM) signals detected by serendipitous observations are studied in detail. For ToO observations, we predict that one can detect ∼11 yr−1 BNS gravitational wave (GW) events during the fourth observing run (O4) by considering an exact duty cycle of the third observing run. The median GW sky localization area is expected to be ∼10 deg2 for detectable BNS GW events. For O4, we predict that ZTF/Mephisto/WFST/LSST can detect ∼5/4/3/3 kilonovae (∼1/1/1/1 afterglows) per year, respectively. The GW detection rates, GW population properties, GW sky localizations, and optimistic ToO detection rates of detectable EM counterparts for BNS GW events at the Advanced Plus, LIGO Voyager, and ET&CE eras are detailedly simulated in this paper

Structural behavior analysis of high strength steel-concrete composite girders

In order to study structural behaviors of high strength steel-concrete composite girders, 14 group-components models with different geometry parameters and material properties were built by using ANSYS software under deuce symmetrical loads at mid-span. The analysis result indicates that steel girder bears about 77. 0% of whole vertical shear strength in plastic state, and the ratios of maximum and minimum values of mid-span deflections for different material strength girders in elastic and plastic states are 79. 5% and 28. 0% respectively; the ratios of maximum and minimum values of mid-span deflections for different transverse bar ratios and widthes of concrete slab girders in plastic state are 62. 1% and 53. 3% respectively; the ratios of maximum and minimum values of longitudinal slips for different material strengthes, widthes of concrete slab, transverse bar ratios and thicknesses of concrete deck girders in plastic state are 25. 0%, 41. 9%, 63. 2% and 70. 7% respectively. Therefore, increasing the strength and section size of steel is economic and reasonable method to increase the vertical shear strength of the girders; the steel and concrete strengthes affect little on the mid-span deflection of the girders in elastic state, and the transverse bar ratio and the width of concrete slab have larger effect on the mid-span deflection in plastic state; the geometry parameters and material properties of the girders have little effect on the longitudinal slip in elastic state, but the material strength, width of concrete slab, transverse bar ratio and thickness of concrete deck have obvious effects on the longitudinal slip in plastic state

Optimization of Urban Block Form by Adding New Volumes for Capacity Improvement and Solar Performance Using A Multi-Objective Genetic Algorithm: A Case Study of Nanjing

During urban renewal, multi-story residential blocks face a contradiction of balancing residential capacity improvement and solar constraint. This paper constructed a set of automatic workflows for adding new volumes to existing buildings, and a multi-objective optimization was applied with a Wallacei plug-in in Grasshopper to optimize the solar radiation, solar hours, and block capacity. First, this study established three building addition modes of existing blocks in the horizontal direction, vertical direction, and mixed direction, respectively. Three optimization objectives—maximum floor area ratio, maximum average radiation amount, and minimum solar shade—were defined. Second, the net increase in the floor area ratio of the block was calculated to balance capacity improvement and solar constraint. Third, the advantages of the three addition modes under different orientations were discussed. Among all three modes, the mixed addition mode had the best capacity improvement effect, with a 70% increase in floor area ratio. The vertical addition mode had the least impact on the solar shade of existing buildings. The horizontal addition mode could further improve the floor area ratio in areas where building height was strictly limited. The results can provide insights and inspiring guidelines for the renewal of the existing residential blocks to solve the floor area ratio constraint from solar radiation, as well as achieve urban function reconstruction and vitality regeneration

Characterization of Precipitation in 7055 Aluminum Alloy by Laser Ultrasonics

After different rolling conditions, four 7055 aluminum alloy samples with different precipitation sizes were measured by scanning electron microscope, transmission electron microscope and laser ultrasonic. The attenuation coefficients of ultrasound measured by laser ultrasonic were calculated in the time domain, frequency domain and wavelet denoising, respectively. The relationship between the precipitate size and attenuation coefficient was established. The results show that the attenuation of the ultrasonic wave is related to the size of the precipitated phase; this provides a new method for rapid non-destructive testing of the precipitation of aluminum alloys

Kilonovae and Optical Afterglows from Binary Neutron Star Mergers. II. Optimal Search Strategy for Serendipitous Observations and Target-of-opportunity Observations of Gravitational Wave Triggers

In the second work of this series, we explore the optimal search strategy for serendipitous and gravitational-wave-triggered target-of-opportunity (ToO) observations of kilonovae and optical short-duration gamma-ray burst (sGRB) afterglows from binary neutron star (BNS) mergers, assuming that cosmological kilonovae are AT2017gfo-like (but with viewing-angle dependence) and that the properties of afterglows are consistent with those of cosmological sGRB afterglows. A one-day cadence serendipitous search strategy with an exposure time of ∼30 s can always achieve an optimal search strategy of kilonovae and afterglows for various survey projects. We show that the optimal detection rates of the kilonovae (afterglows) are ∼0.3/0.6/1/20 yr ^−1 (∼50/60/100/800 yr ^−1 ) for Zwicky the Transient Facility (ZTF)/Multi-channel Photometric Survey Telescope (Mephisto)/Wide Field Survey Telescope (WFST)/Large Synoptic Survey Telescope (LSST), respectively. A better search strategy for SiTian than the current design is to increase the exposure time. In principle, a fully built SiTian can detect ∼7(2000) yr ^−1 kilonovae (afterglows). Population properties of electromagnetic (EM) signals detected by serendipitous observations are studied in detail. For ToO observations, we predict that one can detect ∼11 yr ^−1 BNS gravitational wave (GW) events during the fourth observing run (O4) by considering an exact duty cycle of the third observing run. The median GW sky localization area is expected to be ∼10 deg ^2 for detectable BNS GW events. For O4, we predict that ZTF/Mephisto/WFST/LSST can detect ∼5/4/3/3 kilonovae (∼1/1/1/1 afterglows) per year, respectively. The GW detection rates, GW population properties, GW sky localizations, and optimistic ToO detection rates of detectable EM counterparts for BNS GW events at the Advanced Plus, LIGO Voyager, and ET&CE eras are detailedly simulated in this paper