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81.
For the appropriate management and restoration of rivers, isolated vegetation is often a practical means for improving stream habitat and ecology. The effect of a finite vegetation patch on flow and bed morphology in an open channel was investigated using laboratory experiments. The patch containing emergent and submerged vegetation was modeled using circular cylinders and located mid‐channel along a side wall. Several configurations of the patch and submergence ratio (i.e. water depth to the height of vegetation), and two flow conditions (i.e. below and above the sediment motion threshold) were considered. For flows below the sediment motion threshold, erosion occurred primarily on the opposite side of the patch and near the leading edge of the patch. The degree of scouring depth observed in both these regions was affected by the submergence ratio and it increased with the non‐dimensional flow blockage (i.e. the product of the patch density and width). In contrast, for flows above the sediment motion threshold, sediment accumulated within and around the patch due to a reduction in bed shear stress, which was strongly influenced by the flow blockage and the obstruction ratio (i.e. the ratio of patch width to channel width). The eroded area observed within the patch was consistent with the interior adjustment region where the deceleration and diversion of flow occurred through the patch. As the flow blockage increased or as the obstruction ratio decreased, the deposition rate within and behind the patch decreased. Furthermore, the deposition rate increased with an increase in the ratio of flow rate through the patch to total flow rate regardless of the submergence ratio. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
82.
Kazuho Horiuchi Tomoko Uchida Yuko Sakamoto Aoi Ohta Hiroyuki Matsuzaki Yasuyuki Shibata Hideaki Motoyama 《Quaternary Geochronology》2008,3(3):253-261
The cosmogenic nuclide 10Be was analyzed by using accelerator mass spectrometry on an ice core drilled at the Dome Fuji station, inland Antarctica, for 700–1900 yr CE. The measured concentration of 10Be in the Dome Fuji ice core and the derived 10Be flux show similar fluctuations, with both increasing at known solar-activity minima over the last millennium in agreement with earlier observations of 10Be and 14C. Based on the similar nature of the 10Be flux to the reconstructed 14C production rate patterns, a 10Be–14C correlation age model for the Dome Fuji ice core was successfully constructed. This age model agrees well with the initial version of the tephrochronology of the core. The 10Be-flux record contains information on variability in the amount of cosmic radiation incident on the atmosphere, which is mainly attributable to high-frequency change in solar activity and low-frequency background intensity adjustment of the geomagnetic field. High-resolution 10Be analyses of the Dome Fuji ice cores promise to provide potentially important information on the history of cosmic radiation intensity over the past several hundred thousand years. 相似文献
83.
Miyake Y Jiang Q Yuan W Hanari N Okazawa T Wyrzykowska B So MK Lam PK Yamashita N 《Marine pollution bulletin》2008,57(6-12):357-364
Dietary intake is one of the important routes of human exposure to brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs). The use of PBDEs may also result in exposure to polybrominated dibenzo-p-dioxins and dibenzofurans (PBDDs/DFs), as these compounds are impurities in technical mixtures of BFRs and can also be formed unintentionally by the same processes that generate chlorinated dioxins. This study determined the concentrations of polybrominated compounds in common seafood in Guangzhou and Zhoushan, and assessed the health risks of these chemicals via consumption of contaminated seafood. Seafood samples (fish, bivalves, shrimp, crab, and cephalopods) purchased from local markets in 2003 and 2004 were analyzed for PBDEs and PBDDs/DFs. The highest concentration of total PBDEs (46.3 ng g(-1) lipid wt.) was detected in fish from Guangzhou, in which BDEs 47 and 209 were the two predominant congeners. The total daily intakes of PBDEs, PBDDs, and PBDFs were, 946, 6.39, and 6.54 pg kg(-1) body weight (bw) in Guangzhou, and 489, 4.99, and 7.65 pg kg(-1) bw in Zhoushan, respectively. The hazard ratios for PBDDs and PBDFs were both greater than unity, indicating that these compounds may pose some health risks to the local population. 相似文献
84.
Simulation of a storm surge caused by Typhoon 9918 in the Yatsushiro Sea, Kyushu, Japan was hindcasted by the synchronous
coupled wind-wave-surge model composed of a Meso-scale meteorological model (MM5) for the wind and sea surface pressure, a
spectral third-generation wind-wave model (Wavewatch III) for waves, and the coastal ocean model (Princeton Ocean Model).
Inclusion of the whitecap wave breaking stresses (whitecap dissipation stress) in the coastal ocean model made it possible
to reproduce the extreme surge height in the extremely shallow bay. 相似文献
85.
Bernhard Schnetger Yasuyuki Muramatsu Satoshi Yoshida 《Geostandards and Geoanalytical Research》1998,22(2):181-186
Analytical results for iodine in twenty six geological reference materials (RM) are presented. Bromine, fluorine and chlorine were also determined in some samples. Pyrohydrolysis in a heated quartz tube under a wet oxygen flow was used for the separation of the halogens from the matrix and the evolved gas was absorbed in a trap solution. The halogens were measured by ICP-MS and ion chromatography (IC). All four halogens can be collected in the trap solution from one combustion procedure. The analysed samples range in type from igneous rocks to terrestrial and marine sediments. Precision, detection limits, and accuracy are also presented. 相似文献
86.
87.
Hiromi Yamashita 《Ocean & Coastal Management》2009,52(7):327-335
Developments in coastal regions often entail invisible, complex and uncertain aspects of risk. This paper examines: (1) what kinds of environmental risk information are generally “invisible” or difficult to understand; (2) whether or not there is specific “invisible” risk information especially related to coastal development; and (3) what would be bases of risk education in coastal communities in the future. It discusses these by looking at successful and unsuccessful attempts to make some “invisible” risk information visible, using examples from Japan and elsewhere. 相似文献
88.
Aierken Sidike Nuerrula Jilili S. Kobayashi K. Atobe Nobuhiko Yamashita 《Physics and Chemistry of Minerals》2010,37(2):83-89
The photoluminescence (PL) spectra, optical excitation spectra and PL decay curves of anthophyllite from Canada were obtained
at 300 and 10 K. The MnO content in the sample, determined using an electron probe microanalyzer, was high at 5.77 wt%. In
the PL spectra obtained under 410-nm excitation, bright red bands with peaks at 651 and 659 nm were observed at 300 and 10 K,
respectively. The origin of the red luminescence was ascribed to Mn2+ in anthophyllite from the analysis of the excitation spectra and PL decay times of 6.1–6.6 ms. In the PL spectra obtained
under 240-nm excitation at 300 K, a small violet band with a peak at 398 nm was observed. On the violet band at 10 K, a vibronic
structure was observed. The origin of the violet luminescence was attributed to a minor impurity in anthophyllite. 相似文献
89.
Distribution of perfluorinated compounds in surface seawaters between Asia and Antarctica 总被引:3,自引:0,他引:3
Wei S Chen LQ Taniyasu S So MK Murphy MB Yamashita N Yeung LW Lam PK 《Marine pollution bulletin》2007,54(11):1813-1818
90.
Richard Saunders Rüdiger Kneissl Keith Grainge William F. Grainger Michael E. Jones Alessia Maggi Rhiju Das † Alastair C. Edge Anthony N. Lasenby G. G. Pooley Shigeru J. Miyoshi Taisuke Tsuruta Koujun Yamashita Yuzuru Tawara Akihiro Furuzawa Akihiro Harada Izamu Hatsukade 《Monthly notices of the Royal Astronomical Society》2003,341(3):937-940