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91.
基于1951—2018年哈德里中心海温资料、美国气象环境预报中心和美国国家大气研究中心再分析资料和第四代欧洲中心汉堡模式, 针对1994年、2018年等西北太平洋热带气旋(TC)生成异常多的年份, 研究了引起TC增加的海表温度异常(SSTA)模态及其影响机制。结果表明, 北半球热带中太平洋增暖与印度洋变冷是夏季西北太平洋TC生成频数增加的主要原因, 北大西洋负三极型式SSTA促使TC生成的进一步增加。热带中太平洋增暖与印度洋冷却在菲律宾以东激发出西风异常和气旋性环流异常。北大西洋负三极型式SSTA在我国南海、菲律宾至东南沿岸激发出气旋性环流异常。前者在西北太平洋中部, 后者在南海产生有利于TC生成的局地环境。1994年和2018年夏季热带中太平洋出现暖SSTA、印度洋为冷SSTA、北大西洋呈现负三极型式SSTA, 西北太平洋TC生成频数极端增多。近30年来, 当出现热带中太平洋增暖和印度洋冷却时, 北大西洋表现出比1989年以前更强的负三极型式SSTA, 使西北太平洋TC生成频数和北半球热带印度洋-太平洋SSTA梯度的线性相关更显著。 相似文献
92.
93.
When travelling, people are accustomed to taking and uploading photos on social media websites, which has led to the accumulation of huge numbers of geotagged photos. Combined with multisource information (e.g. weather, transportation, or textual information), these geotagged photos could help us in constructing user preference profiles at a high level of detail. Therefore, using these geotagged photos, we built a personalised recommendation system to provide attraction recommendations that match a user's preferences. Specifically, we retrieved a geotagged photo collection from the public API for Flickr (Flickr.com) and fetched a large amount of other contextual information to rebuild a user's travel history. We then created a model-based recommendation method with a two-stage architecture that consists of candidate generation (the matching process) and candidate ranking. In the matching process, we used a support vector machine model that was modified for multiclass classification to generate the candidate list. In addition, we used a gradient boosting regression tree to score each candidate and rerank the list. Finally, we evaluated our recommendation results with respect to accuracy and ranking ability. Compared with widely used memory-based methods, our proposed method performs significantly better in the cold-start situation and when mining ‘long-tail’ data. 相似文献
94.
文中介绍陆地影像图与港口航道图镶嵌的制图工艺,影像图与港口航道图镶嵌后的成图质量评价。简单阐述了作者在绘制该图种过程中的一些体会,以及影像图取代现有港口航道图上陆地地形的可行性。 相似文献
95.
一种准确通用的台风路径预报模式 总被引:1,自引:0,他引:1
应用天气学理论,对台风云图的晴空区轴线制约台风移动的规律进行物理解释。根据台风云团与晴空区之间存在的干、湿梯度力和推动台风前进的惯性力的互相关系,建立台风移向预报方程和轨迹预报方程,分析论证了台风移向变化的物理过程,把影响台风移动的复杂因子转化为单一的预报因子。 相似文献
96.
The effect of ambient currents on nearshore nonlinear wave–wave energy transfer in random waves is studied with the use of a nonlinear frequency domain wave–current interaction model. We focus on the phenomenon of wave recurrence as a classical nonlinear phenomenon whose characteristics are well established for systems truncated to small numbers of frequency modes. The model used for this study is first extended to enhance accuracy; comparisons of permanent form solutions to analytical forms confirm the model accuracy. Application of the model to a highly truncated system confirmed the model’s consistency with published results for both positive (following) and negative (adverse) currents. Propagation of random wave spectra over a flat bottom was performed with the model, with the intent of determining the prevalence of recurrence between the spectral peak and its harmonics. For spectra of moderate Ursell number, it was found that positive currents extended the length scale of recurrence relative to the case with no currents; conversely, negative currents reduced the recurrence lengths. However, beyond a propagation distance of ≈40 wavelengths of the spectral peak, recurrence becomes almost completely damped as the spectra becomes broad and the spectral energies equilibrate. For spectra of high Ursell number, in contrast, recurrence is almost immediately damped, suggesting that the nonlinearity is sufficient to allow immediate spectral broadening and equilibration and overwhelming any preferential interactions among the spectral peak and its harmonics, regardless of current magnitude or direction. 相似文献
97.
98.
This paper deals with the application of nonparametric system identification to a nonlinear maneuvering model for large tankers using artificial neural network method. The three coupled maneuvering equations in this model for large tankers contain linear and nonlinear terms and instead of attempting to determine the parameters (i.e. hydrodynamic derivatives) associated with nonlinear terms, all nonlinear terms are clubbed together to form one unknown time function per equation which are sought to be represented by the neural network coefficients. The time series used in training the network are obtained from simulated data of zigzag maneuvers and the proposed method has been applied to these data. The neural network scheme adopted in this work has one middle or hidden layer of neurons and it employs the Levenberg–Marquardt algorithm. Using the best choices for the number of hidden layer neurons, length of training data, convergence tolerance etc., the performance of the proposed neural network model has been investigated and conclusions drawn. 相似文献
99.
Enrique Mateos-Naranjo Susana Redondo-Gmez Carlos J. Luque Eloy M. Castellanos Anthony J. Davy M. Enrique Figueroa 《Estuarine, Coastal and Shelf Science》2008,79(4):727-732
The South American cordgrass, Spartina densiflora, has invaded a range of different habitats that can support different native species assemblages on salt marshes in the Gulf of Cadiz, Spain. Little is known about the mechanisms of invasion. We examined the potential for seed germination and recruitment in a field transplant experiment, representing a wide range of environments, on elevational gradients across marshes with muddy and sandy sediments. The biotic resistance of native, perennial vegetation (where present) to recruitment of the alien was also investigated. Spartina densiflora seeds were able to germinate over a greater than 2-m range of elevation in the tidal frame. Germination success on unvegetated muddy sediments was related to sediment redox potential, with poor germination at strongly negative redox potentials on the lower sites. On sandy, well-drained sediments, germination was apparently constrained by water availability at the highest elevations. Comparison of vegetated and cleared plots on the upper marsh showed that there was a negative relationship between the presence of Atriplex portulacoides and germination on the muddy sediments. Recruitment (survival of seedlings for 12 weeks) was seen only on unvegetated muddy sediments at the highest elevation. Hence the invasive success and wide elevational tolerance of S. densiflora on the marshes of the Gulf of Cadiz are not reflected in its short-term ability to become established from its prolific seed production. Colonization of sub-optimal habitats may be largely by vegetative propagules and clonal growth. 相似文献
100.
Dissolved inorganic carbon (DIC) and its carbon isotopic composition in sediment pore waters from the Shenhu area,northern South China Sea 总被引:2,自引:0,他引:2
Tao Yang Shao-Yong Jiang Jing-Hong Yang Ge Lu Neng-You Wu Jian Liu Dao-Hua Chen 《Journal of Oceanography》2008,64(2):303-310
The Shenhu area is one of the most favorable places for the occurrence of gas hydrates in the northern continental slope of
the South China Sea. Pore water samples were collected in two piston cores (SH-A and SH-B) from this area, and the concentrations
of sulfate and dissolved inorganic carbon (DIC) and its carbon isotopic composition were measured. The data revealed large
DIC variations and very negative δ
13C-DIC values. Two reaction zones, 0–3 mbsf and below 3 mbsf, are identified in the sediment system. At site SH-A, the upper
zone (0–3 mbsf) shows relatively constant sulfate and DIC concentrations and δ
13C-DIC values, possibly due to bioturbation and fluid advection. The lower zone (below 3 mbsf) displays good linear gradients
for sulfate and DIC concentrations, and δ
13C-DIC values. At site SH-B, both zones show linear gradients, but the decreasing gradients for δ
13C-DIC and SO4
2− in the lower zone below 3 mbsf are greater than those from the upper zone, 0–3 mbsf. The calculated sulfate-methane interface
(SMI) depths of the two cores are 10.0 m and 11.1 m, respectively. The depth profiles of both DIC and δ
13C-DIC showed similar characteristics as those in other gas hydrate locations in the world oceans, such as the Blake Ridge.
Overall, our results indicate an anaerobic methane oxidation (AMO) process in the sediments with large methane flux from depth
in the studied area, which might be linked to the formation of gas hydrates in this area. 相似文献