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Porosity is a significant issue when conducting laser welding (LW) of aluminum (Al) alloys. Laser oscillating welding appears a good choice for suppressing porosity, but it is accompanied by energy losses. To address the above issues, this paper proposes an innovative power-modulated LW system that simultaneously achieved porosity suppression, power modulation, and energy loss reduction. To demonstrate the effectiveness of the system, comparative experiments were performed using three welding modes: conventional LW, constant power (CP) laser oscillating welding, and gradient power (GP) laser oscillating welding. The results of the experiments indicated that the GP mode was more effective at reducing porosity and the weld depth was greater than that of the CP mode. Numerical simulations were conducted to describe this process. The results showed that changes in the molten pool (MP) flow behavior of the GP mode determined the welding effect. The physical mechanism by which the GP mode suppressed porosity and reduced energy losses was revealed.

Due to sensitivity to heat, laser welding of aluminum alloys is always accompanied by serious defects such as porosity and cracks, which restricts their wide application for structures of lightweight applications. Beam oscillating welding can potentially eliminate these defects to a large extent but with shortcoming of low heat utilization rate. For better solution, a Full Domain Power Modulation (FDPM) system was promoted to conduct bead-on-plate welding tests of 6061 aluminum alloys using circular oscillation. The impact of three welding modes (traditional Laser Welding, Constant Power (CP), Gradient Power (GP)) and oscillation frequency on the weld morphology, porosity, and microstructure was examined by Optical Microscopy (OM), Electron backscatter diffraction patterns (EBSD) and industrial Computed Tomography (CT). The results demonstrated that at the same frequency, the weld depth-to-width ratio in GP mode exceeded the CP mode. The strong stirring effect promoted the pores to escape and increased the heterogeneous nucleated particles of the molten pool, which yielded the lowest weld porosity and the largest equiaxed crystal ratio in GP mode. The mechanism of porosity removal and grain refinement was determined based on the calculated energy distribution. This study provides a brand new approach for porosity inhibition and microstructure optimization of laser-welded aluminum alloys.

The service areas of the BeiDou Navigation Satellite System (BDS) are China, the Asia–Pacific, and the world via three stages of development. The BDS constellation is designed to maintain a geostationary Earth orbit (GEO), inclined geosynchronous orbit (IGSO), and medium Earth orbit (MEO). These orbital maneuvers yield certain difficulties for data processing, especially for the BeiDou satellites, such as a decrease in the real-time service performance, which causes a missing precise orbit product from the maneuvered satellites. The frequencies of the orbital maneuvers for the GEO and IGSO satellites are higher than those for the MEO satellites. The maneuvering time and strategy cannot be obtained by common users due to secrecy, which can yield a decline in the service performance of the BDS. Thus, in this study, we analyzed the variation in the orbital semimajor axis for the satellites. The long-term variation in the orbital semimajor axis changes linearly. The short-term variation in the orbital semimajor axis also has periodicity, which can be described by the sum of sine functions. According to the long-term variation in the orbital semimajor axis for the satellites, we propose a detection method for in-plane orbital maneuvering of the GEO, IGSO, and MEO satellites. We then propose a detection method for out-of-plane maneuvering of the GEO satellites. BDS and Global Positioning System (GPS) data from the broadcast ephemeris were analyzed to verify the proposed methods. The experimental results from 2013 to 2019 show that the frequency of orbital maneuvering is approximately once a month for the GEO satellites, once every six months for the IGSO satellites, and once every 1.4 years for the MEO satellites.

We investigated the effects of supplemental chitosan on digestibility of feed nutrients, intestinal histology and digestive enzyme activity in the pancreas, duodenum and jejunoileum in Leiothrix lutea.Sixty-four adult birds were randomly allotted to one of four dietary treatments (basal diet supplemented with 0%, 0.1%, 0.5% and 1% chitosan). The experiment lasted for 30 days, of which the last 4 days involved metabolic experiments. Compared with the control group, the addition of 0.5% chitosan enhanced the apparent metabolism rate of dry matter, metabolisable energy, crude fat and phosphorus, and decreased apparent metabolism rate of calcium; crude protein was unaffected. Compared with the control group, the villous height of the duodenum and ileum supplemented with 0.5% chitosan increased by 12.11% and 15.03%, while the crypt depth in the duodenum deepened by 6.48%. Supplemental chitosan decreased lipase and amylase activities; trypsin and chymotrypsin activities increased first and then decreased as the level of chitosan increased. These data suggest that dietary chitosan (0.5%) may improve the digestive physiology of L. luteain captivity by increasing the apparent metabolic rate of most nutrients, improving intestinal health and enhancing digestive enzyme activity.

Scroll expander is suitable for small-scale organic Rankine cycle system. In this article, a detailed mathematical model describing the stable and dynamic process of scroll expander is built, an experiment system is set up, and the performance of scroll expander is tested. The results show that the p−V diagram of simulation and experiment show good agreement. The volumetric efficiency of scroll expander increases with rotating speed, and the maximum value is 63% under the tested condition. The isentropic efficiency increases at low rotating speed but then decreases, and the maximum value is 36.4%. Both the stable rotating speed and stable time of scroll expander increase with the electric resistance; here the stable time is defined as the elapsed time when the scroll expander varies from one stable condition to another. Although the transient rotating speed varies periodically with running time when the scroll expander runs stably, the variable quantity can be ignored. The total efficiency of expander and system efficiency first increase with the rotating speed and then decrease, and the maximum values are 41% and 2.9%, respectively, when the Carnot efficiency is 21.2% and the maximum theoretical efficiency is 8%.

The swing state of high–altitude platform (HAP) may critically impact the communication links of HAP stations (HAPS). Current studies have significant limitations and, therefore, do not accurately reflect the actual situation. This paper considers the impact platform swing has on wireless links through modelling. A wireless link model reflecting the swing state of HAP is proposed, and the problems associated with HAPs' instability are resolved. Furthermore, in this study issues concerning inefficient and poor communication quality, caused by significant random validation in receiving and transmitting signal in case of platform swing, are also solved. Finally, the validity of the proposed model is confirmed through numerical analysis and simulation.

Three new naphthoquinones, astropaquinones A?-?C ( 1- 3), were isolated from cultures of the freshwater fungus ASTROSPHAERIELLA PAPUANA YMF 1.01181, together with the known compound, 6-hydroxy-2,4-dimethoxy-7-methylanthraquinone ( 4). The structures of the compounds were settled mainly by interpretation of their 1D and 2D?NMR spectra. Astropaquinone B ( 2) and C ( 3) were found to possess a rare pyranonaphthoquinone skeleton containing a lactol ring. Furthermore, compounds 1- 4 showed moderate antagonistic activity against nine fungi and four bacterial strains. [ABSTRACT FROM AUTHOR]

Recently, our institute, in conjunction with the Development Division of the Ministry of Foreign Trade and Economic Cooperation (MOFTEC), organized its staff to conduct a survey of foreign-trade, industrial-trade, and foreign-funded enterprises. The subjects of this study comprised 1,400 enterprises specializing in foreign trade, the largest 500 enterprises in China in which foreign capitalists have made investments, and 100 enterprises that conduct export-import business on their own. The combined total of imports and exports made by these three types of enterprises accounts for more than 80 percent of our country's annual exports and imports. The results of this investigation and study, therefore, to a significant extent reflect the impact that the [Asian] financial crisis has exerted on our country's overall export trade.

Summary: Impedance pulmonary arterial pressure (PAP) measuring instrument with a microcomputer was designed and manufactured. It performs the functions of graphic analysis, logic judgment and mean pulmonary arterial pressure (PAP) measurement. Impedance information obtained by impedance PAP measuring instrument with a microcomputer was consistent with that by type HB-3COG apparatus. This new instrument has many advantages, such as reliability, saving of time and efforts as well as simplicity in operation.

Association rules mining (ARM) is one of the most important problems in knowledge discovery and data mining. Given a transaction database that has a large number of transactions and items, the task of ARM is to acquire consumption habits of customers by discovering the relationships between itemsets (sets of items). In this paper, we address ARM in the quantum settings and propose a quantum algorithm for the key part of ARM, finding frequent itemsets from the candidate itemsets and acquiring their supports. Specifically, for the case in which there are M(k)f frequent k-itemsets in the M(k)c candidate k-itemsets (M(k)f≤M(k)c), our algorithm can efficiently mine these frequent k-itemsets and estimate their supports by using parallel amplitude estimation and amplitude amplification with complexity O(kM(k)cM(k)√f/ε), where ε is the error for estimating the supports. Compared with the classical counterpart, i.e., the classical sampling-based algorithm, whose complexity is O(kM(k)c/ε²), our quantum algorithm quadratically improves the dependence on both ε and M(k)c in the best case when M(k)f≪M(k)c and on ε alone in the worst case when M(k)f≈M(k)c. [ABSTRACT FROM AUTHOR]