Multi-link laser interferometry architecture for interspacecraft displacement metrology     

Samuel P. Francis  Timothy T.-Y. Lam  David E. McClelland  Daniel A. Shaddock 《Journal of Geodesy》2018,92(3):241-251

Targeting a future Gravity Recovery and Climate Experiment (GRACE) mission, we present a new laser interferometry architecture that can be used to recover the displacement between two spacecraft from multiple interspacecraft measurements. We show it is possible to recover the displacement between the spacecraft centers of mass in post-processing by forming linear combinations of multiple, spatially offset, interspacecraft measurements. By canceling measurement error due to angular misalignment of the spacecraft, we remove the need for precise placement or alignment of the interferometer, potentially simplifying spacecraft integration. To realize this multi-link architecture, we propose an all-fiber interferometer, removing the need for any ultrastable optical components such as the GRACE Follow-On mission’s triple mirror assembly. Using digitally enhanced heterodyne interferometry, the number of links is readily scalable, adding redundancy to our measurement. We present the concept, an example multi-link implementation and the signal processing required to recover the center of mass displacement from multiple link measurements. Finally, in a simulation, we analyze the limiting noise sources in a 9 link interferometer and ultimately show we can recover the \(80\;\text {nm}/\sqrt{\text {Hz}}\) displacement sensitivity required by the GRACE Follow-On laser ranging interferometer.  相似文献   

Susceptibility assessment of the precursor stage of a landslide threatening Haivan Railway Station,Vietnam     

Lam Huu Quang  Doan Huy Loi  Kyoji Sassa  Kaoru Takara  Hirotaka Ochiai  Khang Dang  Shinro Abe  Shiho Asano  Do Ngoc Ha 《Landslides》2018,15(2):309-325

Haivan Station is an important station on the North-South railway line in central Vietnam. Field investigation has identified a precursor stage of a landslide that would threaten this railway. Therefore, a landslide susceptibility assessment for Haivan Station was urgently needed to protect passenger safety and the national railway. Conducted investigations included air-photo interpretation, drilling, ground water and inclinometer monitoring, laboratory testing, and landslide simulation. This research applied the undrained dynamic loading ring shear apparatus ICL-2 to drill-core samples from the precursor landslide. Samples for ring shear tests were taken from sandy soil layers found at depths of ~21, ~31, and ~50 m in the cores. Each of these was believed to be a possible sliding surface of a landslide, and all were tested to shear failure in the ICL-2 apparatus. The boundary between highly weathered granitic rock and weathered granitic rock was identified at about 50 m depth. The inclinometer monitoring detected slight movement at this depth. Therefore, the present day risk of a landslide forming at 50 m is higher than for one forming at either 21 or 31 m. The landslide dynamic parameters obtained from the ring shear test of the 50-m-deep sample were used in an integrated numerical simulation model LS-RAPID. The simulation result gave the critical pore-pressure ratio for landslide occurrence, and landslide’s likely maximum speed, total volume, and depth of landslide debris that could cover the railway. These estimates serve to raise awareness of the vulnerability of the Vietnam national railway sector to landslide impact.  相似文献   

A fast algorithm for finding K shortest paths using generalized spur path reuse technique     

Bi Yu Chen  Xiao‐Wei Chen  Hui‐Ping Chen  William H. K. Lam 《Transactions in GIS》2021,25(1):516-533

The problem of finding the K shortest paths (KSPs) between a pair of nodes in a road network is an important network optimization problem with broad applications. Yen's algorithm is a classical algorithm for exactly solving the KSP problem. However, it requires numerous shortest path searches, which can be computationally intensive for real large networks. This study proposes a fast algorithm by introducing a generalized spur path reuse technique. Using this technique, shortest paths calculated during the KSP finding process are stored. Accordingly, many shortest path searches can be avoided by reusing these stored paths. The results of computational experiments on several large‐scale road networks show that the introduced generalized spur path reuse technique can avoid more than 98% of shortest path searches in the KSP finding process. The proposed algorithm speeds up Yen's algorithm by up to 98.7 times in experimental networks.  相似文献   

Geographic information science and technology at Louisiana State University     

Michael Leitner  Nina N.S. Lam  Fahui Wang  Lei Wang  Shelley Meng  Joshua Kent 《制图学和地理信息科学》2015,42(4):84-90

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Development of Rapid Consolidation Equipment for Cohesive Soil   总被引：1，自引：1，他引：0  

Khairul Anuar Kassim  Ahmad Safuan A. Rashid  Ahmad Beng Hong Kueh  Chong Siaw Yah  Lam Chee Siang  Norhazilan Mohd Noor  Hossein Moayedi 《Geotechnical and Geological Engineering》2015,33(1):167-174

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A Detailed Study on the Equal Arrival Time Surface Effect in Gamma-Ray Burst Afterglows     

Yong-Feng Huang Ye Lu Anna Yuen Lam Wong Kwong Sang Cheng 《中国天文和天体物理学报》2007,7(3):397-404

Due to the relativistic motion of gamma-ray burst remnant and its deceleration in the circumburst medium, the equal arrival time surfaces at any moment are not spherical, rather, they are distorted ellipsoids. This will leave some imprints in the afterglows. We study the effect of equal arrival time surfaces numerically for various circumstances, i.e., isotropic fireballs, collimated jets, density jumps and energy injection events. For each case, a direct comparison is made between including and not including the effect. For isotropic fireballs and jets viewed on axis, the effect slightly hardens the spectra and postpones the peak time of the afterglows, but does not change the shapes of the spectra and light curves significantly. In the cases of a density jump or an energy injection, the effect smears out the variations in the afterglows markedly.  相似文献   

Concentrations of Persistent Organic Pollutants in Surface Sediments of the Mudflat and Mangroves at Mai Po Marshes Nature Reserve, Hong Kong   总被引：4，自引：0，他引：4  

Gene J. Zheng  Michael H. W. Lam  Paul K. S. Lam  Bruce J. Richardson  Ben K. W. Man  Ashley M. Y. Li 《Marine pollution bulletin》2000,40(12):1210-1214

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Reservoirs: Brian Henderson-Sellers Macmillans,London, 1979, £3.95     

D.C.L. Lam 《Advances in water resources》1980,3(2):95

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Fixing the wheel the carpetbaggers broke     

Martin M  Lam PK  Richardson BJ 《Marine pollution bulletin》2003,46(7):918-920

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Exposure and time dependent DNA strand breakage in hepatopancreas of green-lipped mussels (Perna viridis) exposed to Aroclor 1254, and mixtures of B[a]P and Aroclor 1254     

Siu WH  Hung CL  Wong HL  Richardson BJ  Lam PK 《Marine pollution bulletin》2003,46(10):1285-1293

Green-lipped mussels (Perna viridis) were exposed to Aroclor 1254 (0.5, 5 and 50 microgl(-1)) and a mixture of benzo[a]pyrene (B[a]P) and Aroclor 1254 (0.3+0.5 and 3+5 microgl(-1)) for 12 days. On day 0, 1, 3, 6 and 12, the levels of DNA strand breaks in the mussel hepatopancreas were monitored using an alkaline unwinding assay. The results were compared to the findings of a previous study in which the levels of DNA strand breakage in the same species were measured following exposure to various concentrations of B[a]P (0.3, 3 and 30 microgl(-1)). The results indicated that Aroclor 1254 at a concentration 相似文献