X-ray imaging with amorphous silicon active matrix flat-panel imagers (AMFPIs)

Recent advances in thin-film electronics technology have opened the way for the use of flat-panel imagers in a number of medical imaging applications. These novel imagers offer real time digital readout capabilities ( ∼ 30(∼30 frames per second), radiation hardness (>106 cGy),(>106cGy), large area (30×40 cm2)(30×40cm2) and compactness ( ∼ 1 cm).(∼1cm). Such qualities make them strong candidates for the replacement of conventional x-ray imaging technologies such as film-screen and image intensifier systems. In this report, qualities and potential of amorphous silicon based active matrix flat-panel imagers are outlined for various applications such as radiation therapy, radiography, fluoroscopy and mammography. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87833/2/241_1.pd

Session D5: Case Studies of Fish Passages for High Dams in China

Abstract: High dams created benefits for China in flood control, power capacity, navigation and irrigation. Along with the development of environmental regulations, development of fish passage structures at high dams are of high interest in China. There are hundreds of fish passage structures will be built in the near future for fish upstream migrating across high dams. We present one fish collection system and one fish lift design for dams higher than 100m and discuss the technical challenges during design. The fish collection system consists of a floating barge, guidance net, light and bubble curtain at the bank, together with a reserved navigation route matched with bubble curtain and strobe light exclusion system which allow passage of boats but not fish. The fish lift concept consists of fish attraction channel, holding pool crowder hoist, tank hoist, with a track that transports fish for more than 100m. Both fish passage facilities were designed with the procedures including: 1) requirement by government, 2) fish population survey, 3) evaluation with respect to site hydraulics and hydrology to model the working situations for fish passage, 4) structure design for fish passage, 5) planned biological evaluation as part of the design process. Although these designs have utilized knowledge from western world and are expected to help fish conservation with positive results, a huge gap between knowledge of fish behavior and fish passage design make the success of the proposed fish passage structures uncertain, and the very limited fish population at the site also questions the necessity of fish passage. Further, no downstream passages were considered for the high dams till now

Diurnal, seasonal and inter-annual variability of fish density and distribution in the Three Gorges Reservoir (China) assessed with hydroacoustics

Environment conservation of the Three Gorges Reservoir (TGR) requires reliable assessment of fish resources and variation of their distribution. The goal of this study was to determine the best season and the diurnal period to estimate fish density in the TGR using acoustic surveys as a monitoring tool. To find out diurnal migration pattern of fishes in the TGR, we conducted reduplicated 24-h hydroacoustical surveys in the forequarter of the TGR, which covered different habitats (mainstream, tributary bay), seasons (summer, winter) and years (2012-2015). Measurements were performed using SIMRAD EY60 split beam echosounder with frequency 120 kHz. Additionally, zooplankton and environmental parameters were measured. The results showed more than ten times differences between the day and night fish density estimates, probably resulting either from the horizontal migrations between the littoral and open water or vertical migrations. Differences were higher during winter than during summer, and higher in the tributary bay than in the mainstream. Clear vertical migrations were observed both in the tributary bay (amplitude 15 m) and in the mainstream (amplitude 35 m), but only during winter time. Inter-annual estimates of fish density showed generally decreasing trend with years. especially well pronounced in the tributary bay. We also observed high seasonal and diurnal variability in fish distributions, which can significantly affect the accuracy and precision of biomass estimate, indicating importance of choosing appropriate timing for fish monitoring. According to our results, in order to receive the most reliable estimates of fish density in the TGR, hydroacoustic surveys should be performed during summer at night time. (C) 2017 Elsevier GmbH. All rights reserved.</p

Population survey showing hope for population recovery of the critically endangered Yangtze finless porpoise

The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis), has experienced rapid declines in recent decades. We estimate its abundance based on surveys conducted between November and December 2017 in the main-stem of the Yangtze River and adjacent Poyang and Dongting Lakes. We compare these to published abundance estimates from 2006 and 2012, using a bootstrap resampling approach to make inference about population change over the 2006-2017 time period. Encounter rates of porpoise from additional surveys during this period provided another index for evaluating temporal changes in abundance in Poyang and Dongting Lakes. As of December 2017, free-ranging populations of this species are estimated at 1012 (95%CI: 791-1233) individuals of which 445 (95%CI: 295-595) occur in the main stem of the Yangtze River, 457 (95%CI: 329-634) in Poyang Lake, and 110 (95%CI: 65-187) in Dongting Lake. Porpoise numbers in main-stem of the Yangtze River and Dongting Lake declined rapidly from 2006 to 2012 (mean annual rates of -14% and -12%, respectively). These rates of decline greatly eased from 2012 to 2017 (-2.5% and +3% annual growth, respectively). In Poyang Lake, the encounter rates of porpoise have remained relatively stable between 2006 and 2017. This improved population trajectory was likely a joint consequence of government and public conservation efforts. However, fragmentation of porpoise populations in Yangtze River main-stem and significantly reduced migratory movements between the two adjoining lakes and the Yangtze main stem pose a continued threat to the long-term viability of this species. Further actions to improve habitat connectivity are urgently needed.</p

Quantitative assessment of fish passage efficiency at a vertical-slot fishway on the Daduhe River in Southwest China

Fish passage facilities are constructed to enable fish to pass anthropogenic barriers such as dams though their efficiency varies across species and location. There are a number of studies that assess the efficiency of fish passage facilities, yet rarely have such assessments been conducted in Asia. We conducted one of the first quantitative assessments of the efficiency of a vertical-slot fishway in Asia on the Daduhe River in Southwest China. Quantitative assessment of fish passage efficiency was conducted using a combination of methods, including fish sampling, video recordings and a Passive Integrated Transponder (PIT) system for tracking individually-tagged fish (N = 69 of 6 species). Fish sampling revealed 40 species assembled downstream of the dam. Fish captured closer to the fishway tended to be larger than fish caught more distant from the fishway. Half of the fish species observed downstream of the fishway were also observed at the entrance to the fishway (i.e. 153 individuals across 20 species). Video records revealed that overall passage rates were 71.2% based on the number of fish observed at the exit of the viewing chamber relative to that observed passing the entrance viewing chamber. Most fish passed the fishway at night with peak passage occurring in June. PIT technology results revealed that passage efficiency among the six tagged species ranged from 0% to 60% (four species successfully ascended the fishway). Transit time from the fishway entrance to exit was variable both among and within species that successfully ascended the fishway (i.e. 17.9–20.3 h for Schizothorax davidi, 6.4–88.8 h for Schizothorax preuanti, 46.4 h for Silurus meridionalis, 22.1–53.9 h Semilabeo prochilus). Fishway performance varied by species such that there is evidence that the fishway may be useful for maintaining river connectivity for some species. However, passage was often restricted during periods when there was sufficient flow in the fishway. Additional research is needed to put these findings in an ecological context given the overall low number of fish that passed the dam

Passive acoustic survey of Yangtze finless porpoises using a cargo ship as a moving platform

In order to periodically investigate the population and distribution of the Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) in its main distribution range in the Yangtze River, a passive acoustic system deployed on a cargo ship as a moving platform, rather than a dedicated research ship, was developed. A stereo acoustic event data-logger (A-tag) was installed on the cargo ship to passively detect phonating animals. In three surveys carried out in the Yangtze River from Wuhan to Shanghai, an average of 6059 clicks in each survey and 284 porpoises in total were acoustically detected along an 1100-km stretch. The animals were detected frequently in most of the survey range except two &quot;gap sections&quot; with 40 and 60 km lengths, respectively, where no animals were detected in all three surveys. Detected group sizes of the animals in each 120-s time window were not significantly different among the surveys, but the distribution pattern was different and suggested seasonal migration. The cargo ship based passive acoustic survey was effective in detecting phonating animals and can potentially monitor the distribution and population trend over time. Compared to surveys that used dedicated research ships, the present method is more cost effective. (C) 2011 Acoustical Society of America. [DOI: 10.1121/1.3625257