Vietnam Academy of Science and Technology: Journals Online
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ÁP DỤNG MÔ HÌNH SWAN DỰ BÁO TRƯỜNG SÓNG VEN BỜ BIỂN HẢI PHÒNG
Get PDFThis paper presents some results of studying the SWAN model, and application of SWAN model to simulate wave field representative of the rainy season and dry season in the coastal area of Hai Phong. During the dry season, the dominant wave direction is in a range from 60o to 100o, maximum height of waves near shore is in a range from 1,0 m to 1,5 m with wavelength of about 2,0 m to 5,0 m, maximum height of waves offshore is in a range from 2,0 m to 2,5 m with wavelength of about 6,0 m to 16 m. During the rainy season, wave height near shore is in a range from 0,2 m to 0,6 m, and that offshore is in a range from 0,8 m to 1,4 m, maximum height of waves is about 3,4 m, predominant wave directions in this season are E, SE and S. In this scenario that predicts waves generated by storms, wave height offshore is in a range from 8,0 m to 10 m with wavelength of about 60 m, and that near shore is in a range from 2,0 m to 4,0 m with wavelength of about 10–20 m.Bài báo trình bày các kết qủa nghiên cứu về mô hình SWAN, và áp dụng mô hình SWAN để mô phỏng trường sóng đại diện cho mùa mưa và mùa khô của khu vực ven biển Hải Phòng. Trong mùa khô, hướng sóng chiếm ưu thế nằm trong khoảng 600-1000, độ cao sóng lớn nhất ở khu vực ven bờ khoảng 1,0-1,5m với độ dài bước sóng khoảng 2,0-5,0m, khu vực ngoài khơi khoảng độ cao sóng lớn nhất khoảng 2,0-2,5m với độ dài bước sóng khoảng 6,0-16m. Trong mùa mưa, độ cao sóng vùng bờ nằm trong khoảng từ 0,2m – 0,6m, ở ngoài khơi độ cao sóng vào khoảng 0,8m-1,4m, độ cao sóng lớn nhất có thể đạt 3,4m, hướng sóng chiếm ưu thế trong mùa này là Đông, Đông Nam và Nam. Trong kịch bản dự báo sóng trong bão, độ cao sóng ở khu vực ngoài khơi khoảng 8,0-10m với độ dài bước sóng khoảng 60m, ở các khu vực ven bờ độ cao sóng trong khoảng 2,0-4,0m với độ dài bước sóng khoảng 10-20m
Species composition and distribution characteristic of seaweeds on seagrass beds in Phu Quoc island
Get PDFSeagrass beds in Phu Quoc are a favorable environment for seaweed development (bottom-living and epiphytic species). The surveys at 18 sites along the coastal line in Phu Quoc island showed that 69 species belonging to 4 phyla of seaweed were recorded on seagrass beds in Phu Quoc island. Among them, there are 27 species of Rhodophytes (comprising 37% of total species), 19 Chlorophytes (28%), 16 Ochrophytes (24%) and 7 Cyanobacteriophytes (11%). We identified 12 species of epiphytic algae including three species on seagrass and nine species on both seagrass and the substratum. The characteristics of substratum may play an important role for diversity and distribution of the bottom-living seaweed. For epiphytic algae on bigger size seagrass, the diversity of epiphytic species on the top of seagrass leaf is higher than on the root and other parts of leaf
Geo-chemical fractionations of arsenic and lead in the surface sediments of Thuy Trieu lagoon, Khanh Hoa province
Get PDFThe sequential extraction method of Tessier et al. was applied to identify the phase associations of As and Pb in the surface sediment of Thuy Trieu lagoon. The results showed that these two metals were mainly found in the residual fractions. Meanwhile, the carbonate fractions stayed at the lowest portions. Levels of arsenic and lead as Fe-Mn oxide fractions were higher than those as organic fractions and exchangeable fractions. Exchangeable fractions and carbonate fractions of two elements seemed to increase in rainy season. Generally, the mobility of Pb was higher than that of As. In the sediments of Thuy Trieu lagoon, Pb levels cannot currently cause adverse effects on the ecosystems. On the contrary, the risk of As was assessed as moderate level
Development of a Short Pulse Broadband and Narrow Linewidth Ultraviolet Laser Using Ce:LiCAF Crystal
No full textWe report the successful development of an all-solid state laser based on a Czochralski method-grown cerium-doped lithium calcium aluminum fluoride (Ce3+:LiCaAlF6 or Ce:LiCAF) crystal as the gain medium. Results for the broadband, narrow linewidth and short pulse laser emission are obtained by pumping the crystal with 7 ns pulses from the fourth harmonics (266 nm) of a Nd:YAG laser operating at 10 Hz. The effects of output coupler reflectivity, resonator length and pump energy on the laser pulse duration were explored. With broadband configuration, a maximum output pulse energy of 3.4 mJ and a slope efficiency of about 33% were achieved. By optimizing the parameters of the resonator and pump laser energy, 450 ps UV laser pulses were generated from resonator transient conditions of low-Q and short resonator under a near threshold pump energy. With narrow linewidth configuration, where the end mirror is replaced by a grating, tunability from 281 nm to 299 nm is also achieved with a linewidth of about 0.2 nm
Parameter Assessment of Beam Transport Line for Nuclear Physics Research
Get PDFThe IBA CP30 cyclotron was installed at the 108 Central Hospital in Hanoi, Vietnam. A proton beam with energy range from 15 to 30 MeV can be delivered by this facility. Currently, facility is mainly used for medical radioactive isotope production. There is an idea to use this accelerator for scientific research as well. For this purpose, a new beam line should be designed. A high energy resolution with minimum momentum spread is a key point for designing. A preliminary design of the beam line using matrix codes, modeling 3D optical elements, magnetic field calculations, and beam dynamics analysis is presented in this paper
An enhanced nodal gradient finite element for non-linear heat transfer analysis
Get PDFThe present work is devoted to the analysis of non-linear heat transfer problems using the recent development of consective-interpolation procedure. Approximation of temperature is enhanced by taking into account both the nodal values and their averaged nodal gradients, which results in an improved finite element model. The novel formulation possesses many desirable properties including higher accuracy and higher-order continuity, without any change of the total number of degrees of freedom. The non-linear heat transfer problems equation is linearized and iteratively solved by the Newton-Raphson scheme. To show the accuracy and efficiency of the proposed method, several numerical examples are hence considered and analyzed
SYNTHESIS OF SULFUR-CONTAINED MICROCAPSULES AND POTENTIAL APPLICATION IN RUBBER
Get PDFMicrocapsule-based material is potentially utilized in a variety of fields such as pharmaceuticals, food, biology, self-healing materials, etc. More remarkedly, in the rubber-related fields, this outstanding material is able to have a crucial role to play as an alternative of sulfur in compounding and vulcanizing process with regard to the self-healing ability after cracking. In this research, the interface polymerization was applied to generate microcapsules, whose shell was synthesized from Urea-formaldehyde pre-polymer modified by 0.25 wt% melamine containing sulfur (S) as a core substance. When the synthesizing process was carried out at 80 C and stirring rate of 300 rpm in 2 hours, the microcapsule product was spherical with the average size of 115 m and contained 60% of core content that was examined by FTIR, DLS, SEM, TGA and experimented the potential application. As a result, the amount of 8 phr of produced microcapsules utilized in NBR rubber compounds necessitated a longer time to vulcanize rubber at 160 C compared to using 5 phr free S. Besides, the mechanical strength of the microcapsules-contained product was insignificantly changed but bloom-like phenomenon on the rubber surface was markedly improved. It is noticeable that the vulcanized NBR rubber with the presence of these microcapsules are well able to heal its crack or cut when heated up to 150 C in 10 minutes while the free S-vulcanized NBR rubber is definitely unable to be self-healing in the same conditions
Pythagorean Picture Fuzzy Sets, Part 1- basic notions
Get PDFPicture fuzzy set (2013) is a generalization of the Zadeh‟ fuzzy set (1965) and the Antanassov‟intuitionistic fuzzy set. The new concept could be useful for many computational intelligentproblems. Basic operators of the picture fuzzy logic were studied by Cuong, Ngan [10,11 ].Newconcept –Pythagorean picture fuzzy set ( PPFS) is a combination of Picture fuzzy set with theYager‟s Pythagorean fuzzy set [12-14].First, in the Part 1 of this paper, we consider basic notionson PPFS as set operators of PPFS‟s , Pythagorean picture relation, Pythagorean picture fuzzy softset. Next, the Part 2 of the paper is devoted to main operators in fuzzy logic on PPFS: picturenegation operator, picture t-norm, picture t-conorm, picture implication operators on PPFS.As aresult we will have a new branch of the picture fuzzy set theory
Geographical variation in morphological leaf traits of Huperzia serrata (lycopodiaceae) from Vietnam
Get PDFMorphological leaf traits can be used to assess adaptive responses of plants to environmental conditions. To assess how the representation of Huperzia serrata leaf traits, such as leaf length (LL), leaf width (LW) and leaf area (LA) response to changes in mean annual temperature (MAT), sunshine duration (SuH), mean annual precipitation (MAP), air humidity (Hu), intraspecific variation of the morphological leaf traits of the species was analyzed along a geographical gradient of Vietnam. The results showed that among the three populations at the three sites, leaf sizes increased with MAT and MAP. Huperzia serrata, climatic factors, morphological leaf traits, Vietnam.
Testing the -theory of Gravity
Get PDFA procedure of testing the -theory of gravity is discussed. The latter is an extension of the general theory of relativity (GR). In order this extended theory (in some variant) to be really confirmed as a more precise theory it must be tested. To do that we first have to solve an equation generalizing Einstein's equation in the GR. However, solving this generalized Einstein's equation is often very hard, even it is impossible in general to find an exact solution. It is why the perturbation method for solving this equation is used. In a recent work \cite{Ky:2018fer} a perturbation method was applied to the -theory of gravity in a central gravitational field which is a good approximation in many circumstances. There, perturbative solutions were found for a general form and some special forms of . These solutions may allow us to test an -theory of gravity by calculating some quantities which can be verified later by the experiment (observation). In \cite{Ky:2018fer} an illustration was made on the case . For this case, in the present article, the orbital precession of S2 orbiting around Sgr A* is calculated in a higher-order of approximation. The -theory of gravity should be also tested for other variants of not considered yet in \cite{Ky:2018fer}. Here, several representative variants are considered and in each case the orbital precession is calculated for the Sun--Mercury- and the Sgr A*--S2 gravitational systems so that it can be compared with the value observed by a (future) experiment. Following the same method of \cite{Ky:2018fer} a light bending angle for an model in a central gravitational field can be also calculated and it could be a useful exercise