Algorithms for time synchronization of wireless structural monitoring sensors     

Ying Lei  Anne S. Kiremidjian  K. Krishnan Nair  Jerome P. Lynch  Kincho H. Law 《地震工程与结构动力学》2005,34(6):555-573

Dense networks of wireless structural health monitoring systems can effectively remove the disadvantages associated with current wire‐based sparse sensing systems. However, recorded data sets may have relative time‐delays due to interference in radio transmission or inherent internal sensor clock errors. For structural system identification and damage detection purposes, sensor data require that they are time synchronized. The need for time synchronization of sensor data is illustrated through a series of tests on asynchronous data sets. Results from the identification of structural modal parameters show that frequencies and damping ratios are not influenced by the asynchronous data; however, the error in identifying structural mode shapes can be significant. The results from these tests are summarized in Appendix A. The objective of this paper is to present algorithms for measurement data synchronization. Two algorithms are proposed for this purpose. The first algorithm is applicable when the input signal to a structure can be measured. The time‐delay between an output measurement and the input is identified based on an ARX (auto‐regressive model with exogenous input) model for the input–output pair recordings. The second algorithm can be used for a structure subject to ambient excitation, where the excitation cannot be measured. An ARMAV (auto‐regressive moving average vector) model is constructed from two output signals and the time‐delay between them is evaluated. The proposed algorithms are verified with simulation data and recorded seismic response data from multi‐story buildings. The influence of noise on the time‐delay estimates is also assessed. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

A comparison of nearby incremental ground level and in plant concentrations of air pollutants emitted from electronics facilities     

P. L. Law M.Sc.  Ph.D.  S. C. Gracie Chong  A. Baharun B.Sc.  Ph.D.  A. Abdul Rahman M.Sc.  Ph.D. 《International Journal of Environmental Science and Technology》2006,3(3):243-250

Air dispersion modeling by was recently conducted to predict the incremental ground level and inplant concentrations of toxic organic chemicals due to stack and fugitive emissions from Sama Jaya Free Industrial Zone (SJFIZ), Kuching, Sarawak, Malaysia. Simulations of organic air pollutants emitted from industrial facilities in SJFIZ from years 1996 to 2001 were carried out in September 2004 by members of Faculty of Engineering, Universiti Malaysia Sarawak (UNIMAS). The results indicated that there were negligible amount of maximum incremental ground level concentrations of less than 3×10^?2 μg/m³ for 365-day average, and less than 18×10^?2 μg/m³ for 24 h. average. For in-plant maximum incremental concentrations, it is found that the simulated results were much lower than TWA values, except xylene. The predicted in plant concentration of xylene was 119.21 (parts per million) ppm as compared to ACGIH TLV-TWA of 100 ppm approximately 19% higher than ACGIH recommended values. From this study, it was concluded that both nearby population and in plant workers were not potentially at risk to exposing organic chemicals far lower than the threshold limit levels set by ACGIH.  相似文献   

Biofilms and Size Sorting of Fine Sediment During Erosion in Intertidal Sands     

Jessica C. Garwood  Paul S. Hill  Brent A. Law 《Estuaries and Coasts》2013,36(5):1024-1036

The goal of this research was to investigate size-specific retention of clay and silt-sized grains by biofilms in sandy intertidal sediments. Sediment cores were collected from an intertidal flat in Cole Harbour, NS, and eroded at increasing shear stresses (0.08–0.60 Pa) with a Gust microcosm. Half of the cores were eroded without undergoing prior treatment, while sodium hypochlorite was added to the other cores to destroy biofilms. The disaggregated inorganic grain size distribution of sediment resuspended by the Gust microcosm was then obtained with a Multisizer^? 3 Coulter Counter®, and each treated core was compared with its corresponding untreated core. Overall, significantly less total sediment mass was resuspended from untreated cores than from treated cores. At intermediate shear stresses, the sediment resuspended from treated cores contained a greater proportion of fine and medium silts than the sediment resuspended from untreated cores. Very fine silts and clays were not retained preferentially by biofilms. The results show that biofilms stabilize the sediment, but they do not necessarily enhance the proportion of finest sediment sizes, as previously proposed.  相似文献   

Limnology of Lake Waikaremoana with special reference to littoral and pelagic primary producers     

Clive Howard‐Williams  Karen Law  Connie L. Vincent  John Davies  Warwick F. Vincent 《新西兰海洋与淡水研究杂志》2013,47(4):583-597

Lake Waikaremoana, the North Island's deepest lake (248 m), lies in a natural forested catchment, but the lake itself has been modified for hydro‐electric power generation and by the introduction of trout, smelt, and adventive aquatic plants. The lake is a warm monomictic water body of low conductivity (82 μS cm^‐1) and a high seasonal water column stability. The waters are oligotrophic, with epilimnetic dissolved reactive phosphorus concentrations typically < 1 mg m^‐3. The concentration of NO₃‐N is seasonally variable but generally high in winter and spring with maximum epilimnetic values approaching 70 mg m ³. This contrasts with other central North Island lakes. Horizontal variability in surface chlorophyll a is low as are the absolute values (< 1–2 mg m^‐3). A notable feature is the formation of a deep chlorophyll maximum within the metalim‐nion comprised largely of Sphaewcystis schweteri as opposed to diatoms and flagellates which normally dominate the epilimnion. Vascular macro‐phytes (maximum biomass 659 g m² dry weight) extended to 9 m and characeans (maximum biomass 447 g m²dry weight) to 16 m. Total phyto‐plankton primary production was calculated as 4524 tCy^‐1 and macrophyte production as 578 t C y^‐1. The proportion of macrophyte to phy‐toplankton production (0.14) is higher than in the other deep lakes of the central North Island.  相似文献   

The use of chemical dispersants to combat oil spills at sea: A review of practice and research needs in Europe   总被引：1，自引：0，他引：1  

Chapman H  Purnell K  Law RJ  Kirby MF 《Marine pollution bulletin》2007,54(7):827-838

In order to better understand the practice of dispersant use, a review has been undertaken of marine oil spills over a 10 year period (1995-2005), looking in particular at variations between different regions and oil-types. This viewpoint presents and analyses the review data and examines a range of dispersant use policies. The paper also discusses the need for a reasoned approach to dispersant use and introduces past cases and studies to highlight lessons learned over the past ten years, focussing on dispersant effectiveness and monitoring; toxicity and environmental effects; the use of dispersants in low salinity waters; response planning and future research needs.  相似文献