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811.
This paper considers issues of designing a gas-turbine engine in the helicopter system at the early design stages. The optimum and rational values of engine working process parameters at different flight speeds of the flight vehicle (FV) are analyzed. Several characteristics of mathematical models (MM) that form the helicopter–engine system, are described. 相似文献
812.
The paper provides a method for multi-criteria selection of the optimal structural layout option based on a fuzzy logic inference that allows for uncertainties in engineering and operates with heterogeneous information of the qualitative and quantitative nature for the systems being designed. 相似文献
813.
Chi-Ming Lee Chung-Yen Kuo Jian Sun Tzu-Pang Tseng Kwo-Hwa Chen Wen-Hau Lan C.K. Shum Tarig Ali Kuo-En Ching Philip Chu Yuanyuan Jia 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(3):1280-1288
Global sea level rise due to an increasingly warmer climate has begun to induce hazards, adversely affecting the lives and properties of people residing in low-lying coastal regions and islands. Therefore, it is important to monitor and understand variations in coastal sea level covering offshore regions. Signal-to-noise ratio (SNR) data of Global Navigation Satellite System (GNSS) have been successfully used to robustly derive sea level heights (SLHs). In Taiwan, there are a number of continuously operating GNSS stations, not originally installed for sea level monitoring. They were established in harbors or near coastal regions for monitoring land motion. This study utilizes existing SNR data from three GNSS stations (Kaohsiung, Suao, and TaiCOAST) in Taiwan to compute SLHs with two methods, namely, Lomb–Scargle Periodogram (LSP)-only, and LSP aided with tidal harmonic analysis developed in this study. The results of both methods are compared with co-located or nearby tide gauge records. Due to the poor quality of SNR data, the worst accuracy of SLHs derived from traditional LSP-only method exceeds 1?m at the TaiCOAST station. With our procedure, the standard deviations (STDs) of difference between GNSS-derived SLHs and tide gauge records in Kaohsiung and Suao stations decreased to 10?cm and the results show excellent agreement with tide gauge derived relative sea level records, with STD of differences of 7?cm and correlation coefficient of 0.96. In addition, the absolute GNSS-R sea level trend in Kaohsiung during 2006–2011 agrees well with that derived from satellite altimetry. We conclude that the coastal GNSS stations in Taiwan have the potential of monitoring absolute coastal sea level change accurately when our proposed methodology is used. 相似文献
814.
G. Ghirlanda L. NavaG. Ghisellini 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Short and long GRBs are thought to be two distinct classes based on their different duration and spectrum. Through the spectral analysis of two similarly selected samples of BATSE short and long GRBs, we show that short GRBs are harder than long events, confirming what found from the comparison of their hardness ratio. However, this spectral diversity seems to be due to a harder low energy spectral component of short GRBs, rather than a (slightly higher) peak energy. Interestingly short GRBs have a spectrum which is similar to the spectrum of the emission of the first 1–2 s of long events. We find evidence that short GRBs are inconsistent with the Epeak–Eiso correlation defined by long bursts while they follow the same Epeak–Liso correlation of long GRBs. These results, coupled to the similar variability timescale of short events and the first seconds of long ones, suggest that a common (or similar) dissipation mechanism could operate in both classes. The difference in the duration would then be due mainly to the central engine lifetime. 相似文献
815.
B. Rizk C. Drouet dAubigny C.W. Hergenrother B.J. Bos D.R. Golish R. Malhotra D.S. Lauretta J. Butt J. Patel M. Fitzgibbon C. May E.B. Bierhaus S. Freund M. Fisher S. Cambioni C.A. Bennett S.S. Balram-Knutson K. Harshman M. Moreau 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(1):672-691
We analyzed high-angular rate streaks first recorded by OSIRIS-REx’s MapCam during a 2017 search for Earth Trojan asteroids. We interpret them as water-ice particles that translated across the imager’s field of view, originating from the spacecraft itself. Their translation velocities approximated 0.1–1?m/s based on reasonable conclusions about their range. Pursuing several lines of investigation to seek a coherent hypothesis, we conclude that the episodic releases of the water ice particles are associated with spacecraft attitudes that resulted in solar illumination of previously shadowed regions. This correlation suggests that the OSIRIS-REx spacecraft itself possesses micro-climatic zones consisting of hot regions and cold traps that may temporarily potentially pass volatiles back and forth before losing most of them. 相似文献
816.
Stephen K. Reed 《Spatial Cognition & Computation》2019,19(1):1-45
I apply my proposed modification of Soar/Spatial/Visual System and Kosslyn’s (1983) computational operations on images to problems within a 2 × 2 taxonomy that classifies research according to whether the coding involves static or dynamic relations within an object or between objects (Newcombe & Shipley, 2015). I then repeat this analysis for problems that are included in mathematics and science curricula. Because many of these problems involve reasoning from diagrams Hegarty’s (2011) framework for reasoning from visual-spatial displays provides additional support for organizing this topic. Two more relevant frameworks specify reasoning at different levels of abstraction (Reed, 2016) and with different combinations of actions and objects (Reed, 2018). The article concludes with suggestions for future directions. 相似文献
817.
818.
819.
In this paper, we consider an example of estimating and comparing the efficiency of different concepts for a high-altitude unmanned aerial vehicle (UAV) under diversity of efficiency criteria. 相似文献
820.
B. A. Antuf’ev 《Russian Aeronautics (Iz VUZ)》2016,59(3):303-307
This study proposes an approximate solution to a contact problem of dynamic deformation of a cyclically symmetrical discretely ring-stiffened cylindrical shell, the side surface of which is subjected to an evenly distributed inertia live load. The solution of the problem assumes the quasistatic mode of deformation of the structure. Several critical velocities of the live load have been found. A number of examples are presented. 相似文献