Macroparasites of angelfish Brama brama (Bonnaterre, 1788) in the southern Benguela Current ecosystem     

AL Mackintosh  CC Reed  MAI Nunkoo  PH King  CD van der Lingen 《African Journal of Marine Science》2018,40(3):245-252

The angelfish Brama brama is a mesopelagic species distributed circumglobally in temperate to warm-temperate waters, including continental-shelf-edge and upper-slope waters of the Benguela Current ecosystem. Little is known about the parasite assemblage of Benguela B. brama, with only three parasite taxa having previously been documented from this species in the southern Benguela. This study describes the macroparasites recorded from 35 B. brama collected during research surveys off the west coast of South Africa in 2015 and 2016. A total of six macroparasite taxa were documented, including the nematode Anisakis pegreffii, the copepod Hatschekia conifera, the cestode Hepatoxylon trichiuri, an acanthocephalan from the genus Rhadinorhynchus, a monogenean from the family Diclidophoridae, and an unidentified species. Three of these (He. trichiuri, Rhadinorhynchus sp. and the unidentified species) had not previously been found to infect B. brama. The most prevalent macroparasite taxa were A. pegreffii (94%), the unidentified species (71%) and Ha. conifera (60%). Two of the parasites, Ha. conifera and He. trichiuri, showed seasonal variation in infection, and infection with the latter was positively correlated with host length. These findings increase our knowledge of B. brama biology and contribute to our understanding of the biodiversity of the southern Benguela ecosystem.  相似文献   

Characteristics analysis for the flash flood-induced debris flows   总被引：2，自引：1，他引：1  

Chen Chien-Yuan  Chen Lien-Kuang  Yu Fan-Chieh  Lin Sheng-Chi  Lin Yu-Ching  Lee Chou-Lung  Wang Yu-Ting  Cheung Kei-Wai 《Natural Hazards》2008,47(2):245-261

Typhoon Haitang caused landfall on Taiwan during 15–21 July, 2005 and brought 2,279 mm of maximum cumulative rain with a maximum intensity of 176 mm/h. The torrential rain was mainly distributed from the central mountain range to southern Taiwan and triggered 222 slopeland-related hazards. Among the hazard events, there were 17 debris flows, 157 cases of traffic cut-off, three large-magnitude deep-seated landslides, and 10 villages isolated in the off-track mountainous areas. The debris flows initiated in southern Taiwan were associated with torrential rain, short channel length (<2 km), and small basin area (<3 km²), and were speculated to be induced by flash flood. These flash flood-induced debris flows have a higher rainfall intensity-duration threshold for initiation than in other areas. The deep-seated landslides, isolated villages due to traffic cut-off in off-track mountain areas, and recurrent hazards in areas affected by the M_L 7.6 Chi-Chi earthquake in 1999 are characteristics of slopeland hazards in Taiwan in recent years. One of the most urgently needed mitigation strategies in response to slopeland hazards is the plan for enhancing self-rescue disaster resistance in off-track mountainous villages in Taiwan.  相似文献   

Ensemble forecasting of tropical cyclone motion: comparisonbetween regional bred modes and random perturbations     

K. K. W. Cheung 《Meteorology and Atmospheric Physics》2001,78(1-2):23-34

Summary Random perturbations (RPs) and a modified version for breeding of growing modes are used with a regional baroclinic mesoscale model to perform ensemble forecasting of tropical cyclone motion. Based on a sample of six cases, similar conclusions are found as in previous barotropic modeling studies. Even after introducing a larger spatial correlation into the RPs using a multi-quadric analysis scheme, the skill of this ensemble mean track prediction is almost always lower than that of the control forecast in the cases considered. The track prediction performance of the ensemble using regional bred modes (RBMs) as perturbations has a higher average skill. At nearly all forecast intervals except less than 24 h when the initial position error still dominates, the ensemble mean tracks in all six cases are improved over the control forecast. In the 6 h–24 h range, the success rate (ratio of the cases with a forecast improvement to the total number of cases) has a value of 10/24. In the 30 h–48 h range, the success rate increases to 20/24, but drops to 18/24 in the 54 h–72 h range. A relative skill score (RSS) is used to compare the skills of the two perturbation methodologies. It is found that the average RSSs of using RBMs are significantly higher than the corresponding ones of RPs at the 99% confidence level in all three 24-h periods. Note that the above conclusion is only based on ensemble mean forecasts. All of the possibilities from an ensemble-based probabilistic track distribution are not explored in this paper. The ensemble spreads in these RBM ensembles are large enough to include the verifying tracks in all the cases considered. It is also found that the ensemble spread is well correlated with the average error in an ensemble when using RBMs, but not with the ensemble mean forecast error in both methodologies. Received February 7, 2001/Revised April 18, 2001  相似文献   

Community ecology of the metazoan parasites of snoek Thyrsites atun (Euphrasen, 1791) (Perciformes: Gempylidae) off South Africa     

MAI Nunkoo  CC Reed  SE Kerwath 《African Journal of Marine Science》2016,38(3):363-371

The parasite assemblage of snoek Thyrsites atun, a commercially important fish in the Benguela system, was examined over a one-year period. In all, 16 parasite taxa including eight new host records (Bolbosoma vasculosum, Caligus coryphaenae, Caligus dakari, Corynosoma australe, Hatschekia conifera, Nothobomolochus fradei, Rhadinorhynchus cadenati, Tentacularia coryphaenae) and four new locality records (B. vasculosum, C. dakari, Molicola uncinatus, Pseudoterranova sp.) were recovered from 210 specimens. The dominance of larval helminths in the component community suggests that T. atun occupies an intermediate position in the food web. The ‘nestedness metric based on overlap and decreasing fill’ (NODF) indicated that the parasite assemblage exhibited no nestedness (NODF = 73.3, p = 0.103). Generalised additive mixed modelling results indicated that host length is the main determinant of parasite species richness in T. atun. PERMANOVA and ANOSIM suggested that infracommunity structure varied little with respect to the sex, length, seasonality and capture region of the host. The stability and randomness in parasite acquisition, as indicated by the lack of nestedness of the parasite assemblage, can be ascribed to the opportunistic feeding behaviour and nomadic movement of T. atun in the southern Benguela. The homogeneity of the community structure of long-lived endoparasites suggests that a single T. atun stock occurs off South Africa.  相似文献   

Mesoscale simulation and moisture budget analyses of a heavy rain event over southern Taiwan in the Meiyu season     

L. T.-C. Chang  G. T.-J. Chen  K. K. W. Cheung 《Meteorology and Atmospheric Physics》2008,101(1-2):43-63

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华北南缘古元古代末岩墙群侵位的磁组构证据   总被引：7，自引：3，他引：4  

侯贵廷  王传成  李乐 《岩石学报》2010,26(1):318-324

华北克拉通南缘的中条山及邻区广泛发育元古宙放射状基性岩墙群,与五台山-恒山和大同地区的北北西向基性岩墙群以及熊耳中条拗拉谷的火山岩在时空分布和地球化学方面均具有密切的相关性。中条山及邻区放射状基性岩墙群的宏观和微观流动构造(包括捕虏体、冲痕构造、矿物线理和定向斑晶)指示岩墙群以一定的仰角向北西侵位。通过该区岩墙群磁化率各向异性(AMS)测量得到磁组构的最大磁化率长轴优势方位分布图和磁组构各向异性特征分析进一步指示华北南缘古元古代末岩墙群从熊耳中条拗拉谷的底部向北西侵位。岩墙群的流动构造和磁组构的统计成果夯实了华北克拉通古元古代末基性岩墙群与熊耳中条拗拉谷的成生联系。  相似文献   

Magnetic activity of the spotted dwarf AP149 in the α Persei open cluster     

Sze-Leung Cheung  Ho-Keung Hui  Chi-Tai Kwok  Kam-Cheung Leung 《中国天文和天体物理学报》2010,10(3)

The simultaneous photometric and spectroscopic observations of the spotted G dwarf AP149 in the young open cluster α Persei are analyzed here.We reconstruct the observed light curves with a two-starspot model by means of a light curve modeling technique,and find that the active regions shift oppositely along longitude on a time scale of one day.Combining with the observational data obtained by other groups,we discuss the evolution of spotted regions in the photosphere,and find that its starspots evolve not ...  相似文献   

Boundary element method with exterior collocation in two-dimensional elastodynamic problems     

T. M. Fu  J. G. Xiong  Y. K. Cheung 《地震工程与结构动力学》1995,24(1):99-108

In the present paper, the boundary element method with exterior collocation was applied to two-dimensional elastodynamic problems. The stability of the numerical solution was discussed and the collocation rule of source points outside the region being studied was investigated in the frequency domain by means of the computed error in the boundary displacement and the condition number of the coefficient matrix for two typical wave propagation problems. The achieved results are helpful to the practical application of this method to earthquake ground motion analysis.  相似文献   

Monitoring interannual dynamics of desertification in Minqin County,China, using dense Landsat time series     

Xiaolin Zhu  Kwok Huen Leung  Wing Sze Li  Lek Kin Cheung 《International Journal of Digital Earth》2020,13(8):886-898

ABSTRACT

Minqin County in northwestern China is highly affected by desertification. Campaigns have been initiated in recent decades to combat desertification in Minqin. To assess the effectiveness of these campaigns, this study used a dense Landsat time series from 1987 to 2017 to investigate the interannual dynamics of vegetation coverage and greenness over the past 31 years. First, this study applied an advanced technology to reconstruct a high-quality Landsat annual time series. Specifically, one image in the vegetation-peak season was selected as the base image in each year, and then problematic pixels were interpolated by the neighborhood similar pixel interpolator using ancillary images in the same year. Second, the land cover map and the enhanced vegetation index (EVI) were derived from all reconstructed images. Third, the change of vegetation coverage and EVI values over the 31 years were analyzed. The results show that the total vegetation coverage and greenness increased during the 31 years. Linking this change trend to other factors suggests that vegetation in Minqin County is highly affected by agriculture and groundwater supply rather than by climate. To mitigate desertification in a sustainable way, agriculture should be well managed to avoid overconsumption of natural resources such as underground water.  相似文献   

Incremental time—space finite strip method for non-linear structural vibrations     

Y. K. Cheung  S. L. Lau 《地震工程与结构动力学》1982,10(2):239-253

Based on an incremental Hamilton's principle a versatile and systematic computer method for analysing non-linear structural vibrations is developed in this paper. The essence of the proposed method can be regarded as an incremental harmonic balance method associated with a finite strip procedure in the time-space domain. Only linearized equations in terms of frequency increment, amplitude increments, etc. have to be formulated and solved in each incremental step. This method is applicable to highly non-linear problems and may be generalized to related non-linear periodic structural motions such as dynamic stability, flutter and some motions of a rotating body, etc. To show the effectiveness and versatility of this method, a typical time-space finite strip for beam problems is worked out and examples for a wide variety of vibration problems including free and forced vibrations, super- and sub-harmonic resonances, and complicated phenomena such as internal resonance are computed. Comparisons with previous results are also made.  相似文献