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31.
Richard P. Mied William J. Schulz Robert A. Handler Charlotte M. Snow Robert A. Fusina John H. Porter 《Continental Shelf Research》2010
The effects of local and remote wind forcing of water level heights in the Virginia Coast Reserve (VCR) are examined in order to determine the significant forces governing estuarine motions over subtidal time scales. Recent (1996–2008) data from tide and wind stations in the lagoon, a tide station to the north at Sandy Hook, NJ, and one offshore wind station at the Chesapeake Light Tower are examined. Sea surface height spectrum calculations reveal significant diurnal and semidiurnal tidal effects along with subtidal variations, but a suppressed inertial signal. Sea-surface heights (SSH) with 2–5 day periods at Wachapreague, VA are coherent with those at Sandy Hook and lag them in time, suggesting that southward-propagating continental shelf waves provide subtidal variability within the lagoon. The coherence between lagoon winds and sea surface height, as well as between winds and cross-lagoon sea height gradient, were significant at a relatively small number of frequency and wind direction combinations. The frequencies at which this wind forcing occurs are the tidal and subtidal bands present to the north, so that lagoon winds selectively augment existing SSH signals, but do not generate them. The impact of the wind direction is closely related to the geometry of the lagoon and bounding landmasses. The effect of wind stress is also constrained by geometry in affecting the cross-lagoon water height gradient. Water levels at subtidal frequencies are likely forced by a combination of local wind forcing, remote wind forcing and oceanic forcing modified by the complex topography of the lagoon, shelf, and barrier islands. 相似文献
32.
Keith Porter 《地震工程与结构动力学》2016,45(5):819-833
Second‐generation performance‐based earthquake engineering (PBEE‐2) requires a library of component fragility functions to estimate probabilistic damage to a wide variety of building components. The present work draws on a large body of (mostly) post‐earthquake reconnaissance and (some) post‐earthquake survey observations of traction elevators to create fragility functions useful in PBEE‐2. Two surveys provide detailed observations of 115 representative elevators at 12 hospitals shaken in the 1989 Loma Prieta and 1994 Northridge earthquakes and selected without regard to or foreknowledge of damage. Of these, 55 failed and 60 did not. Approximately half were installed after an important code change of 1972, so one can distinguish the performance of pre‐1973 and post‐1973 elevator construction. They experienced a range of strong motion: 22 with peak ground acceleration (PGA) < 0.25 g, 93 with 0.25 g < PGA < 0.85 g. The hospitals had elevator failure rates as low as 0% and as high as 100%. A third survey describes damage qualitatively for six sites with PGA ≤ 0.25 and per‐site failure rates of 0% to perhaps 30%. Fragility functions are offered where the damage state is the loss of functionality of the elevator. The elevators in these surveys exhibit a median capacity of PGA ≈ 0.35 g with a logarithmic standard deviation of 0.40. Capacity is modestly sensitive to whether the elevator was installed before or after 1973. Using building‐specific intensity measures such as Sa(T1) does not improve the fragility functions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
33.
Leesun Kim Ian E. Galbally Nichola Porter Ian A Weeks Sarah J Lawson 《Journal of Atmospheric Chemistry》2011,68(3):265-279
Emissions of biogenic volatile organic compounds (BVOCs) from mechanical wounding of leaves and branches of plants can contribute
to the atmospheric burden of volatile organic compounds (VOCs) in both (a) urban airsheds (from urban garden maintenance)
and (b) the global atmosphere (from large scale forest harvesting). These emissions of BVOCs are poorly understood and quantified,
and their role in urban and global emissions inventories neglected. This paper presents measurements of the magnitude, duration
and composition of emissions of BVOCs, carbon dioxide (CO2) and methane (CH4) from freshly cut leaf mulch and wood chips derived from a common eucalypt tree, Eucalyptus sideroxylon (red ironbark), found in southeastern Australian forests and gardens. The emissions of BVOCs from freshly cut and shredded
leaves and wood of E. sideroxylon were found to be 2.3 ± 0.6 and 0.05 ± 0.04 mg g-1 DM (Dry Mass) from leaf mulch and wood chips respectively and to last typically for 1 day following cutting. Three sampling
techniques were used for VOC speciation and the 12 most abundant BVOCs released from the mulch materials were identified.
The specific BVOCs emitted in order of decreasing abundance from leaf mulch are: (a) stored plant oils, 1,8-cineole, α–pinene
and o-cymene which make up the major part of the emissions, (b) a minor contribution from chemicals associated with environmental
stress and wound defence, (Z)–3–hexenyl acetate, (E)-2-hexenal and (Z)-3-hexen-1-ol, and (c) a second minor contribution from
metabolic products, acetaldehyde and acetone. The observed integrated emissions of BVOCs from leaves following mulching are
equivalent to more than half and perhaps all of the likely stored plant oils in the leaves. For the two comparable studies
available, one of a plant with stored oils (this study) and one of a plant without stored plant oils, the emissions of leaf
wound defence BVOCs are in the same range for both plants. In the plant with stored plant oils, the plant oil emissions are
about a factor of 11 larger in emission rate than the plant wound defence BVOCs. A compilation of available leaf wounding
BVOC emission studies indicates that for plants with stored plant oils, plant oil emissions dominate, whereas with other plants,
leaf wound defence BVOCs dominate the emissions. 相似文献
34.
Mark L. Porter Marcel G. Schaap Dorthe Wildenschild 《Advances in water resources》2009,32(11):1632-1640
Hysteresis in the relationship between capillary pressure (Pc), wetting phase saturation (Sw) and nonwetting–wetting interfacial area per volume (anw) is investigated using multiphase lattice-Boltzmann simulations of drainage and imbibition in a glass bead porous system. In order to validate the simulations, the Pc–Sw and anw–Sw main hysteresis loops were compared to experimental data reported by Culligan et al. [Culligan KA, Wildenschild D, Christensen BS, Gray WG, Rivers ML, Tompson AB. Interfacial area measurements for unsaturated flow through porous media. Water Resour Res 2004;40:W12413]. In general, the comparison shows that the simulations are reliable and capture the important physical processes in the experimental system. Pc–Sw curves, anw–Sw curves and phase distributions (within the pores) show good agreement during drainage, but less satisfactory agreement during imbibition. Drainage and imbibition scanning curves were simulated in order to construct Pc–Sw–anw surfaces. The root mean squared error (RMSE) and mean absolute error (MAE) between drainage and imbibition surfaces was 0.10 mm−1 and 0.03 mm−1, respectively. This small difference indicates that hysteresis is virtually nonexistent in the Pc–Sw–anw relationship for the multiphase system studied here. Additionally, a surface was fit to the main loop (excluding scanning curves) of the drainage and imbibition Pc–Sw–anw data and compared to the surface fit to all of the data. The differences between these two surfaces were small (RMSE = 0.05 mm−1 and MAE = 0.01 mm−1) indicating that the Pc–Sw–anw surface is adequately represented without the need for the scanning curve data, which greatly reduces the amount of data required to construct the non-hysteretic Pc–Sw–anw surface for this data. 相似文献
35.
36.
Megan Damon Masanori C. Kameyama Michael Knox David H. Porter Dave Yuen Erik O. D. Sevre 《Visual Geosciences》2008,13(1):49-57
The current availability of thousands of processors at many high performance computing centers has made it feasible to carry
out, in near real time, interactive visualization of 3D mantle convection temperature fields, using grid configurations having
10–100 million unknowns. We will describe the technical details involved in carrying out this endeavor, using the facilities
available at the Laboratory of Computational Science and Engineering (LCSE) at the University of Minnesota. These technical
details involve the modification of a parallel mantle convection program, ACuTEMan; the usage of client–server socket based
programs to transfer upwards of a terabyte of time series scientific model data using a local network; a rendering system
containing multiple nodes; a high resolution PowerWall display, and the interactive visualization software, DSCVR. We have
found that working in an interactive visualizastion mode allows for fast and efficient analysis of mantle convection results.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
37.
Limiting accessibility to a fishing area can reduce fishing effort effectively and may therefore promote local recovery of depleted stocks. In January 2002, beach driving was banned in South Africa, thereby reducing angler access to large areas of the coastline, particularly in less-developed areas. In November 2001 a project had been established in the St Lucia Marine Reserve, on the east coast of South Africa, to compare surf-zone fish populations inside a no-take sanctuary zone with those in an adjacent exploited area. Subsequent to the ban, the aim of the project was adapted such that surf-zone fish populations were monitored for potential recovery in what had been the exploited area, located to the north of Cape Vidal, which anglers could no longer access easily, because of the prohibition on beach driving. Standardised research fishing was conducted at two sites in the previously exploited area and two sites in the no-take sanctuary. Conventional stock-status indicators showed evidence of recovery in the four most common species caught in the previously exploited area, in terms of both abundance and biomass. Generalised additive mixed models were used to account for the influence of targeting specific species; however, subtle differences in habitat between the sampling sites, improved angling skill over time, variability in recruitment, and differential species-specific responses complicated interpretation of results. The implications of the findings are discussed in terms of the future monitoring and management of marine protected areas both within the St Lucia Marine Reserve and farther afield. 相似文献
38.
T. J. G. Francis I. T. Porter R. D. Lane P. J. Osborne J. E. Pooley P. K. Tomkins 《Marine Geophysical Researches》1975,2(3):195-213
The ocean bottom seismograph described in this paper has been developed primarily for recording earthquakes on the mid-oceanic ridges. The instrument is suitable for dropping onto the most rugged areas of the ocean floor. Acoustic tracking with the ship's precision echo sounder enables it to be located there relative to both the topography of the sea bed and the ship. The outputs of a 3-component seismometer and a hydrophone are recorded in FM form on a low-power magnetic tape recorder designed specifically for the instrument. 相似文献
39.
This article presents a US perspective on the influence of government policies on the nature and development of advanced marine electronic instrumentation (MEI) technologies in Europe. US firms traditionally have enjoyed a strong international competitive advantage in the MEI field, but European institutions are undergoing rapid changes that may affect the competitive position of firms in advanced technology industries. These include the consolidation of firms in specific markets and the increased emphasis on centralized, collaborative ‘technology transfer’ research efforts across sectors and across national borders. We expect broadly defined marine markets to grow in Europe. The best policy for US firms may well be one of cautious optimism and close attention to the potential for business relationships with established and emerging European firms. 相似文献
40.
Commercial whaling is highly contentious, angering animal rights groups and conservation organizations, who threaten boycotts. Proponents of whaling argue that many whale stocks are plentiful enough to support sustainable harvests. In terms of economic efficiency, a nation's decision to engage in whaling depends on rents from the whaling industry, ecological and market linkages, and the potential for boycotts. We analyze the tradeoffs involved in a nation's decision to engage in whaling, whale-watching, and fishing. Scenarios exist in which whaling is economically rational. Indeed, sometimes it makes economic sense to subsidize whaling. In other circumstances, market pressures make commercial whaling inefficient. 相似文献