Search

The Wide Field Survey Telescope (WFST) is a dedicated photometric survey facility under construction jointly by the University of Science and Technology of China and Purple Mountain Observatory. It is equipped with a primary mirror of 2.5m in diameter, an active optical system, and a mosaic CCD camera of 0.73 Gpix on the main focus plane to achieve high-quality imaging over a field of view of 6.5 square degrees. The installation of WFST in the Lenghu observing site is planned to happen in the summer of 2023, and the operation is scheduled to commence within three months afterward. WFST will scan the northern sky in four optical bands (u, g, r, and i) at cadences from hourly/daily to semi-weekly in the deep high-cadence survey (DHS) and the wide field survey (WFS) programs, respectively. WFS reaches a depth of 22.27, 23.32, 22.84, and 22.31 in AB magnitudes in a nominal 30-second exposure in the four bands during a photometric night, respectively, enabling us to search tremendous amount of transients in the low-z universe and systematically investigate the variability of Galactic and extragalactic objects. Intranight 90s exposures as deep as 23 and 24 mag in u and g bands via DHS provide a unique opportunity to facilitate explorations of energetic transients in demand for high sensitivity, including the electromagnetic counterparts of gravitational-wave events detected by the second/third-generation GW detectors, supernovae within a few hours of their explosions, tidal disruption events and luminous fast optical transients even beyond a redshift of 1. Meanwhile, the final 6-year co-added images, anticipated to reach g about 25.5 mag in WFS or even deeper by 1.5 mag in DHS, will be of significant value to general Galactic and extragalactic sciences. The highly uniform legacy surveys of WFST will also serve as an indispensable complement to those of LSST which monitors the southern sky., Comment: 46 pages, submitted to SCMPA

Supplementary Material 1

The surface accuracy of the reflector antenna directly affects the antenna efficiency, and is one of the key performance indicators of the telescopes. Near-field radio holography, which features the advantages of high measurement accuracy and convenience, is one of the most commonly used surface alignment methods for millimeter and submillimeter wave radio telescopes. Near-field radio holography under Cassegrain mode can measure the overall deformation error in the optical path of the telescope. The slant-axis mount is more adaptable to the extreme site environment of terahertz telescopes, and can provide better thermal protection and control for the overall telescope. However, the unique rotation characteristics of the slant-axis antennas will introduce additional error factors during the holography measurements, and devoted study on the near-field holography of slant-axis terahertz under Cassegrain mode has not been reported. In this paper, the influence of the reference receiver position and diffraction of the secondary mirror has been analyzed. The near-field holography measurements have been conducted on a 1.2 m slant-axis terahertz antenna. The repeatability of the experimental system has been evaluated to be better than 2.0 μ m RMS (Root Mean Square), and the comparison between near-field holography and photography has been performed to verify the correctness of the error analyses and corrections.

Pointing calibration and sub-reflector focusing are an important task of antenna measurement, which significantly contributes to the observational performance of a radio telescope. According to the requirements on the pointing accuracy and defocusing gain loss of the 5 m Dome A Terahertz Explorer (DATE5), this paper has derived the requirements of signal-to-noise ratio for the pointing and sub-reflector focusing calibration observations, and selected several astronomical radio sources suitable for the pointing and focusing calibrations at the terahertz waveband in Antarctica, which include planets and ultra-compact HII regions. The effects of the atmospheric absorption and the source angular diameter on the accuracy of calibration measurements are analyzed. Simulations show that when the telescope operates in Antarctica, these sources can provide sufficient flux densities for verifying the pre-established pointing model and focusing model.

Additional file 1. The performances of the early detection model in the subgroup analysis including total matched population, unmatched population, colorectal-related benign disease and stratification by age and the comparison between the early detection model and previously reported mSEPT9 model.

The CAFE (Census of warm-hot intergalactic medium, Accretion, and Feedback Explorer) and LyRIC (Lyman UV Radiation from Interstellar medium and Circum-galactic medium) have been proposed to the space agencies in China respectively. CAFE was first proposed in 2015 as a joint scientific CAS-ESA small space mission. LyRIC was proposed in 2019 as an independent external payload operating on the Chinese Space Station. Both missions are dedicated to mapping the Lyman UV emission (ionized oxygen (O VI) resonance lines at 103.2 and 103.8 nm, and Lyman series) for the diffuse sources in our Galaxy and the circum-galactic mediums of the nearby galaxies. We present the primary science objectives, mission concepts, the enabling technologies, as well as the current status., Comment: 9 pages, 6 figures, SPIE Astronomical Telescopes + Instrumentation 2020 conference Paper No. 11444-4

Limited by the working temperature of the test equipment, most of high-precision surface figure measurement techniques cannot be put into application under a cryogenic environment. This paper reports the first attempt to measure the surface figure of a high-precision terahertz reflector panel under low temperatures based on photogrammetry. The measurement employs a high-resolution industrial camera sitting on the automatic testing platform which enables photos been taken in an automatic fashion inside a climate chamber. A repeatable accuracy of 2.1 μ m (rms) is achieved under the cryogenic environment. Furthermore, the surface figure measured by a three-coordinate measuring machine under the room temperature is used to calibrate the thickness differences of the targets. By this technique, the surface figure of an aluminum prototype panel of the 5 meter Dome A Terahertz Telescope (DATE5) is measured from room temperature down to −55°C to obtain the rule of variation of surface deformation of the panel under low temperatures.

High-precision tiling technology is an effective way to fabricate large-aperture astronomical telescope. Based on the application of micro-displacement actuator in the area of large-aperture astronomical telescope, the principle of tiling mirrors and the characteristic of micro-displacement actuator were presented at first. Secondly, the mechanical structures and working principles of typical micro-displacement actuators were reviewed according to the ground-based large-aperture astronomical telescope constructed. The key technologies for micro-displacement actuator in polar low-temperature environment were analyzed emphatically, which include mechanical structure design in low-temperature, anti-ice and deicing technology, material for micro-displacement actuator, lubrication technology in low-temperature and control of actuator. Moreover, the key technologies that should be solved were summarized for the application of micro-displacement actuator in Antarctic astronomical telescope and the prospect for the micro-displacement actuator in Antarctic area was proposed in terms of the future development trend.

With development well underway, 5G is envisioned as an enabler of lighting fast mobile services, such as virtual reality, augmented reality, live video analytics, and etc. In particular, multi-cell Mobile Edge Clouds (MEC) with 5G base stations endowed with computing capability are able to promote the Quality of Services (QoS) of mobile users by executing tasks in the edge cloud. Due to the varying 5G network conditions and limited computation capacity of each base station in the multi-cell MEC, as well as the stringent QoS requirements, a fundamental and challenging problem is how to offload user tasks to the edge cloud, such that the energy consumption of mobile devices is minimized. In this paper, we first formulate the offline and online location-aware mobile task offloading problems in a multi-cell MEC. For the offline location-aware mobile task offloading problem, we then develop an exact solution and an approximation algorithm with an approximation ratio. For the online problem, we thirdly propose a novel deep reinforcement learning-based offloading algorithm for mobile users to obtain the optimal offloading policy. We finally conduct extensive experiments by simulations to evaluate the proposed algorithms against existing benchmarks. The experimental results show that the proposed algorithms are promising and outperform the benchmark algorithms by significantly reducing energy cost of mobile devices and delays experienced by mobile users.

Due to its unique rotation mechanism, a slant-axis mount provides a better adaptability for the extreme site conditions, such as those in Antarctica, compared to traditional equatorial and altazimuth mounts. However, the study devoted to the motion characteristics of slant-axis mount has not been reported yet. In this paper, the advantages and disadvantages of the slant-axis mount are first discussed. The transformation relations between the slant-axis coordinate system and the horizontal and equatorial coordinate systems are then derived, based on this the motion characteristics of slant-axis mount during a normal sidereal tracking are studied, and compared with those of altazimuth mounts. The image rotation behavior of slant-axis mount is also studied, and its influence on the reflector holographic measurement is analyzed. Finally, a pointing model including seven error terms and suitable for slant-axis telescopes is derived.

In this paper, a conjugate interference filter which could be used in gas sensing is presented .The filter consists of two large spot collimators and a gas etalon which has two separate cells:absorption gas chamber and non-absorption gas chamber. When cascading the broadband light to the filter , only light absorbed by the target gas can pass through the filter and the spectrum of output light matches well with the absorption spectrum of target gas.By changing the target gas in the absorption chamber ,filter for various kind of gases can be implemented. In this paper, acetylene is selected as the target gas and the spectrum of light through the filter completely matches the absorption peak of acetylene after parameter adjustments.

A high-speed gas-specific approach for gas detection is proposed and experimentally demonstrated. It is based on a conjugated interferometer which transforms the absorption spectrum of the sample gas to a conjugated emission spectrum. By combining such conjugated interferometer with broadband optical gain medium, a comb light source which emits light at gas absorption lines is produced. The absorption of the conjugated interference source is very weak for other types of gases whose absorption lines are typically different, but is relatively strong for the same type of gas used in the conjugated interferometer. A high sensitivity, high speed, and high specificity gas sensor is produced with the conjugated interference source.

The structure, phase stability, and electrical properties of BaCe1−xYxO3−δ (x = 0–0.4) in humidity air and CO2 atmosphere are investigated. XRD results indicate that the BaCe0.9Y0.1O3−δ sample has a symmetric cubic structure, and its phase changes to tetragonal as the Y3+ doping amount increases to 20 mol%. The conductivity of BaCe1−xYxO3−δ increases with temperature, and it depends on the amount of yttrium doping and the atmosphere. BaCe0.8Y0.2O3−δ exhibits the highest conductivity of 0.026 S cm−1 at 750 °C. The activation energy for conductivity depends on yttrium doping amount and temperature. The conductivity of BaCe0.8Y0.2O3−δ is 0.025 S cm−1 in CO2 atmosphere at 750 °C which is 3.8% lower than that in air due to reactions with CO2 and BaCO3 and the CeO2 impure phases formed. The structure of BaCe0.8Y0.2O3−δ is unstable in water and decomposes to Ba(OH)2 and CeO2 phases. It is found that the activation energy of samples in CO2 atmosphere is higher than that of sample in air. Sr-doped Ba1−ySryCe0.8Y0.2O3−δ (y = 0–0.2) is prepared to improve the phase stability of BaCe0.8Y0.2O3−δ in water. The conductivity of Ba0.9Sr0.1Ce0.8Y0.2O3−δ is 0.023 S cm−1 at 750 °C which was 11% lower than that of BaCe0.8Y0.2O3−δ, however, the phase stability of Ba0.9Sr0.1Ce0.8Y0.2O3−δ is much better than that of BaCe0.8Y0.2O3−δ in water.

Through surveying current development situations and existing problems of planting and processing of Ziziphus jujuba in south Xinjiang, this paper discussed planting, processing mode of Ziziphus jujube in south Xinjiang and development direction of enterprises in Ziziphus jujube production. It is expected to ensure and increase quality and sales volume of Ziziphus jujube and promote sound and sustainable development of Ziziphus jujube industrial chain in south Xinjiang.

Research on air impingement drying of line pepper was carried out using an air impingement drying dryer.7 different mathematical drying models were compared by some evaluation targets such as coefficient of determination (R2), root mean square error(RMSE), X2 and standard error(SE). The results showed that the Modified Page mathematical drying model was the fittest, which was related to the drying temperature and air velocity. The expression and values of model parameters were also obtained subsequently. It showed that the Modified Page mathematical drying model could sufficiently predict and control the drying process of line pepper, according to the comparison values and calculated values.

A method based on magneto-acoustic technique is developed to measure bioelectric currents non-invasively. Theoretically, vibrations of particles in the medium are produced due to the Lorentz force when oscillatory currents flow through medium in a steady magnetic field. These vibrations contain information of the bioelectric currents and can be detected by surface contact detector. An experimental setup is presented to detect the microampere level currents in saline and tissue. The results show the linear relationship between the acoustic signal and the current.

In this paper, the author will discuss the system design of one portable myocardial infarction monitoring system which processes the functions of general ECG monitoring and the alarm and emergency of acute myocardial infarction. This system can also provide real-time ECG signal parameters for clinical diagnosis.

In the present paper, the electron transport equation has been applied to study the phenomena of cavity ionization. It has been shown that the effect of the cavity on the energy spectrum of electron inside it can be attributed to an equivalent electron source uniformly distributed in the cavity. A formula for the energy spectrum of the equivalent electron source is obtained. The deposited energy of the equivalent electron source in the cavity of a plate chamber has been calculated. As compared with the Spencer-Attix theory, the present theory is shown to be in better agreement with experiment for describing phenomena of the cavity ionization.