Frost Durability and Strength of Concrete Prepared with Crushed Sand of Different Characteristics

The influences of fines content, methylene blue (MB) value, and lithology of crushed sand (CS) on frost durability and strength of concrete were investigated, and the frost durability and strength of crushed sand concrete (CSC) and river sand concrete (RSC) were compared. The results show that inclusion of fines improves CSC compressive strength and reduces frost durability of C30 CSC when fines content reaches 10%, whereas it has little negative influence on frost durability of C60 CSC. Increasing MB value does not negatively affect compressive strength of C30 CSC but decreases compressive strength of C60 CSC and frost durability of CSC, and the reduction is more pronounced when MB value exceeds 1.0. Lithology has no prominent influence on frost durability and compressive strength of CSC within the lithologies (dolomite, limestone, granite, basalt, and quartz) studied. Though compressive strength of CSC is a little higher than RSC under equal water to cement ratio, frost durability of CSC is no better than RSC especially for C30 CSC, and air-entraining agent is suggested for enhancing frost durability of C30 CSC exposed to freezing environment

Study on Yield Stress and Thixotropy of Hydroxypropyl Distarch Phosphate Paste

In order to study the yield stress and thixotropic behavior of the hydroxypropyl distarch phosphate (HPDSP) paste, HPDSP respectively derived from corn starch (CS) and waxy corn starch (WS) with different ratios of amylopectin were investigated. The critical mass fractions, yield stress, and thixotropic behavior of HPDSP pastes under various temperatures were studied. The results showed that, the critical mass fractions for the transition of the HPDSP solution at 5 ℃ from dilute to semi-dilute, and from semi-dilute to concentrated were 3wt% and 6wt%, respectively. The yield stress of 5wt% corn starch-hydroxypropyl distarch phosphate (CS-HPDSP) and waxy corn starch-hydroxypropyl distarch phosphate (WS-HPDSP) paste both showed weak correlations with temperature. However, at 6wt% concentration, the yield stress significantly decreased (P<0.05) by 69.52% and 77.95% respectively at 85 ℃. Additionally, the thixotropic behavior of HPDSP was influenced by both mass fraction and temperature. At 5 ℃, 5wt% CS-HPDSP and WS-HPDSP showed limited thixotropy, while at 6wt% of mass fraction, the areas of thixotropic loops of CS-HPDSP and WS-HPDSP were 163.49 and 85.00 Pa/s, respectively, and decreased by 86.38% and 92.18% at 85 ℃, respectively. WS-HPDSP exhibited less thixotropic behavior than CS-HPDSP, and showed better stability in three interval thixotropy test (3iTT). In conclusion, WS-HPDSP showed less yield stress and thixotropy compared with CS-HPDSP. This study provides theoretical supports for practical application of HPDSP as thickening agents in food products

Geometry and optics calibration of WFCTA prototype telescopes using star light

The Large High Altitude Air Shower Observatory project is proposed to study high energy gamma ray astronomy ( 40 GeV-1 PeV ) and cosmic ray physics ( 20 TeV-1 EeV ). The wide field of view Cherenkov telescope array, as a component of the LHAASO project, will be used to study energy spectrum and compositions of cosmic ray by measuring the total Cherenkov light generated by air showers and shower maximum depth. Two prototype telescopes have been in operation since 2008. The pointing accuracy of each telescope is crucial to the direction reconstruction of the primary particles. On the other hand the primary energy reconstruction relies on the shape of the Cherenkov image on the camera and the unrecorded photons due to the imperfect connections between photomultiplier tubes. UV bright stars are used as point-like objects to calibrate the pointing and to study the optical properties of the camera, the spot size and the fractions of unrecorded photons in the insensitive areas of the camera.Comment: 5 pages, 6 figures, submitted to Chinese Physics

The LEGUE Input Catalogue for Dark Night Observing in the LAMOST Pilot Survey

We outline the design of the dark nights portion of the LAMOST Pilot Survey, which began observations in October 2011. In particular, we focus on Milky Way stellar candidates that are targeted for the LEGUE (LAMOST Experiment for Galactic Understanding and Exploration) survey. We discuss the regions of sky in which spectroscopic candidates were selected, and the motivations for selecting each of these sky areas. Some limitations due to the unique design of the telescope are discussed, including the requirement that a bright (V < 8) star be placed at the center of each plate for wavefront sensing and active optics corrections. The target selection categories and scientific goals motivating them are briefly discussed, followed by a detailed overview of how these selection functions were realized. We illustrate the difference between the overall input catalog - Sloan Digital Sky Survey (SDSS) photometry - and the final targets selected for LAMOST observation.Comment: 11 pages, 7 figures, accepted for publication in RA

An Algorithm for Preferential Selection of Spectroscopic Targets in LEGUE

We describe a general target selection algorithm that is applicable to any survey in which the number of available candidates is much larger than the number of objects to be observed. This routine aims to achieve a balance between a smoothly-varying, well-understood selection function and the desire to preferentially select certain types of targets. Some target-selection examples are shown that illustrate different possibilities of emphasis functions. Although it is generally applicable, the algorithm was developed specifically for the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) survey that will be carried out using the Chinese Guo Shou Jing Telescope. In particular, this algorithm was designed for the portion of LEGUE targeting the Galactic halo, in which we attempt to balance a variety of science goals that require stars at fainter magnitudes than can be completely sampled by LAMOST. This algorithm has been implemented for the halo portion of the LAMOST pilot survey, which began in October 2011.Comment: 17 pages, 7 figures, accepted for publication in RA

The mini-JPAS: A study of the wavelength dependence of the photon response nonuniformity of the JPAS-pathfinder camera

Understanding the origins of small-scale flats of CCDs and their wavelength-dependent variations plays an important role in high-precision photometric, astrometric, and shape measurements of astronomical objects. Based on the unique flat data of 47 narrowband filters provided by JPAS-Pathfinder, we analyze the variations of small-scale flats as a function of wavelength. We find moderate variations (from about 1.0% at 390 nm to 0.3% at 890 nm) of small-scale flats among different filters, increasing toward shorter wavelengths. Small-scale flats of two filters close in central wavelengths are strongly correlated. We then use a simple physical model to reproduce the observed variations to a precision of about ±0.14% by considering the variations of charge collection efficiencies, effective areas, and thicknesses between CCD pixels. We find that the wavelength-dependent variations of the small-scale flats of the JPAS-Pathfinder camera originate from inhomogeneities of the quantum efficiency (particularly charge collection efficiency), as well as the effective area and thickness of CCD pixels. The former dominates the variations in short wavelengths, while the latter two dominate at longer wavelengths. The effects on proper flat-fielding, as well as on photometric/flux calibrations for photometric/slitless spectroscopic surveys, are discussed, particularly in blue filters/wavelengths. We also find that different model parameters are sensitive to flats of different wavelengths, depending on the relations between the electron absorption depth, photon absorption length, and CCD thickness. In order to model the wavelength-dependent variations of small-scale flats, a small number (around 10) of small-scale flats with well-selected wavelengths are sufficient to reconstruct small-scale flats in other wavelengths. © 2021. The American Astronomical Society. All rights reserved.he PRNU model adopted in this work was developed as part of Mr. Baocun Chen's undergraduate thesis work under the supervision of H.Z. This work is supported by the National Natural Science Foundation of China through projects NSFC 12173007 and 11603002, the National Key Basic R&D Program of China via 2019YFA0405503, and Beijing Normal University grant No. 310232102. We acknowledge the science research grants from the China Manned Space Project with Nos. CMS-CSST-2021-A08 and CMS-CSST2021-A09. Based on observations made with the JST/T250 telescope and JPCam at the Observatorio Astrofisico de Javalambre (OAJ) in Teruel, owned, managed, and operated by the Centro de Estudios de Fisica del Cosmos de Aragon (CEFCA). We acknowledge the OAJ Data Processing and Archiving Unit (UPAD) for reducing and calibrating the OAJ data used in this work. Funding for the JPAS Project has been provided by the Governments of Spain and Aragon through the Fondo de Inversion de Teruel, European FEDER funding, and the Spanish Ministry of Science, Innovation and Universities, as well as by the Brazilian agencies FINEP, FAPESP, and FAPERJ and the National Observatory of Brazil. Additional funding was also provided by the Tartu Observatory and the JPAS Chinese Astronomical Consortium. With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709

LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) The survey science plan

We describe the current plans for a spectroscopic survey of millions of stars in the Milky Way galaxy using the Guo Shou Jing Telescope (GSJT, formerly the Large Area Multi-Object Spectroscopic Telescope - LAMOST). The survey will obtain spectra for 2.5 million stars brighter than $r<19$ during dark/grey time, and 5 million stars brighter than $r<17$ or $J<16$ on nights that are moonlit or have low transparency. The survey will begin in fall of 2012, and will run for at least four years. The telescope design constrains the optimal declination range for observations to $10^\circ<\delta<50^\circ$, and site conditions lead to an emphasis on stars in the direction of the Galactic anticenter. The survey is divided into three parts with different target selection strategies: disk, anticenter, and spheroid. The resulting dataset will be used to study the merger history of the Milky Way, the substructure and evolution of the disks, the nature of the first generation of stars through identification of the lowest metallicity stars, and star formation through study of open clusters and the OB associations. Detailed design of the LEGUE survey will be completed after a review of the results of the pilot survey in summer 2012.Comment: 19 pages, 1 figure, accepted for publication in RA

Laboratory observation of ion acceleration via reflection off laser-produced magnetized collisionless shocks

Fermi acceleration by collisionless shocks is believed to be the primary mechanism to produce high energy charged particles in the Universe,where charged particles gain energy successively from multiple reflections off the shock front.Here,we present the first direct experimental evidence of ion energization from reflection off a supercritical quasi perpendicular collisionless shock,an essential component of Fermi acceleration in a laser produced magnetized plasma. We observed a quasi monoenergetic ion beam with 2,4 times the shock velocity in the upstream flow using time of flight method. Our related kinetic simulations reproduced the energy gain and showed that these ions were first reflected and then accelerated mainly by the motional electric field associated with the shock. This mechanism can also explain the quasi monoenergetic fast ion component observed in the Earth's bow shock