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91.
In the recent paper by Tai-Wen Hsu, John R.-C. Hsu, Wen-Kai Weng, Swun-Kwang Wang, and Shan-Hwei Ou (Coastal Engineering, 53, 865–877, 2006), the authors derived theoretical formulations for calculating the wave setup and setdown induced by obliquely incident waves on a beach. The derivation of an expression for setdown contains errors which would lead to an imbalance in longshore momentum flux outside the surfzone. We correct their derivation and give results in terms of the radiation stress concept in a general case including an oblique wave incidence. We also point out that the correct form of wave setdown is important to describe the zero-net force in the momentum balance outside the surfzone. 相似文献
92.
Damage costs from hurricanes have increased dramatically as hurricane strikes, populations, and property values have increased along the U.S. southeastern and Gulf Coast states. Federal expenditures in hurricane affected areas and coastal property insurance costs have increased as well. We discuss current public and private sector actions that impact damage costs and consider ways to mitigate future damage costs and government financial exposure. Encouraging adaptive and avoidance measures through market signals and government policies, and protecting areas such as wetlands which mitigate storm damage will help limit damage from hurricanes. 相似文献
93.
Andrew J. Davies Max Wisshak James C. Orr J. Murray Roberts 《Deep Sea Research Part I: Oceanographic Research Papers》2008,55(8):1048-1062
Ecological-niche factor analysis (ENFA) was applied to the reef framework-forming cold-water coral Lophelia pertusa. The environmental tolerances of this species were assessed using readily available oceanographic data, including physical, chemical, and biological variables. L. pertusa was found at mean depths of 468 and 480 m on the regional and global scales and occupied a niche that included higher than average current speed and productivity, supporting the theory that their limited food supply is locally enhanced by currents. Most records occurred in areas with a salinity of 35, mean temperatures of 6.2–6.7 °C and dissolved oxygen levels of 6.0–6.2 ml l−1. The majority of records were found in areas that were saturated with aragonite but had low concentration of nutrients (silicate, phosphate, and nitrate). Suitable habitat for L. pertusa was predicted using ENFA on a global and a regional scale that incorporated the north-east Atlantic Ocean. Regional prediction was reliable due to numerous presence points throughout the area, whereas global prediction was less reliable due to the paucity of presence data outside of the north-east Atlantic. However, the species niche was supported at each spatial scale. Predicted maps at the global scale reinforced the general consensus that the North Atlantic Ocean is a key region in the worldwide distribution of L. pertusa. Predictive modelling is an approach that can be applied to cold-water coral species to locate areas of suitable habitat for further study. It may also prove a useful tool to assist spatial planning of offshore marine protected areas. However, issues with eco-geographical datasets, including their coarse resolution and limited geographical coverage, currently restrict the scope of this approach. 相似文献
94.
Power spectra based on Pioneer 6 interplanetary magnetic field data in early 1966 exhibit a frequency dependence of f
–2 in the range 2.8 × 10–4 to 1.6 × 10–2 cps for periods of both quiet and disturbed field conditions. Both the shape and power levels of these spectra are found to be due to the presence of directional discontinuities in the microstructure (< 0.01 AU) of the interplanetary magnetic field. Power spectra at lower frequencies, in the range of 2.3 × 10–6 to 1.4 × 10–4 cps, reflect the field macrostructure (> 0.1 AU) and exhibit a frequency dependence roughly between f
–1 and f
–3/2. The results are related to theories of galactic cosmic-ray modulation and are found to be consistent with recent observations of the modulation. 相似文献
95.
Laboratory experiments show that albedoes as low as those on the Moon can be produced by vacuum vitrification and associated chemical fractionation of ordinary terrestrial basaltic material. Vitrification is established as an unequivocal process that can account for the low albedo and apparent local darkening with age of the lunar surface. The spectral reflectance curves of glass powders are significantly different than those of the parent rock mineralogy; thus, the presence of ubiquitous glass in lunar surface material complicates compositional determinations by interpretation of spectral reflectance curves. Vitrification of rocks on the Moon may highly modify the chemical composition of the resulting glass; thus, glass fragments found in lunar fines cannot be assumed to represent bulk parent rock material. Progressive impact vitrification of lunar surface material throughout the Moon's history may have led to a fine-grain, opaque, refractory-rich material we call ultimate glass. This unidentified and, at this point, hypothetical component may exist in dark regolith material; if found, it may be a useful indicator of regolith maturity.Paper dedicated to Prof. Harold C. Urey on the occasion of his 80th birthday on 29 April 1973. 相似文献
96.
97.
James W. Warwick 《Solar physics》1968,4(4):446-452
During a period of intense decametric continuum arising near the center of the sun, there occurred additional very strong emission closely associated with the flare beginning at 1522 UT on August 28, 1966. Owing to strong ionospheric absorption from about 1527 UT on, which eliminated telecommunications interference, the frequency range over which the flare-associated emission appears is unusually large, from the upper limit of the spectrograph, 41 MHz, to about 11 MHz, where external reflection cuts off the solar signals. Strong bursts of Type III (fast drift) occur from 1527 to 1531 UT, and a complex Type II (slow drift) from 1532 to 1547 UT. As the Type-II burst progresses at frequencies from 15 to 25 MHz, Northward position shifts of many solar radii probably take place; at higher frequencies the burst moves in a complicated pattern through a much narrower range of distances to the North of the sun. Type-IV emission, from 1540 UT on, moves a large distance to the sun's North, and then, after 1600 UT, returns to a stable position quite close to the sun. 相似文献
98.
Computations of the equivalent widths of absorption lines as a function of planetary phase angle are made for a homogeneous cloud with particles having the properties (shape, refractive index, and size distribution) deduced from polarimetry of Venus. The computed equivalent widths show an “inverse phase effect” comparable to that which is observed for CO2 lines on Venus. This result verifies a recent suggestion of Regas et al. that the existence of an inverse phase effect does not by itself imply the presence of multiple layers of scattering particles in the atmosphere of Venus. 相似文献
99.
100.
Over 3000 predominantly small-scale fishers have exited the New Zealand's quota management system (QMS) between its inception in 1986 and 2000. This study, based on the Ministry of Fisheries database and a questionnaire sent to the exiters, establishes that compliance costs in general, and those specifically related to the QMS, were one of the most consistent reasons for exit. Uncertainty about future QMS policy and the high cost of quota were also significant factors. It appears that the small fishers’ perception of high compliance cost can be supported by industry data. 相似文献