Re-Assessment of Sargassum Beds at Hon Chong Area, Nha Trang Bay, Vietnam

Sargassum beds play an important role in terms of ecology and economic likelihood ("ecosystem services") for coastal communities along the Hon Chong area, in the bay of Nha Trang, Vietnam. It is a matter of concern that the Sargassum beds at Hon Chong, in particular, and Vietnam, in general, have strongly decreased due to anthropogenic perturbations including land reclamation. Our research focused on a reassessment of Sargassum beds including coverage, occupied area, species composition, branch length frequencies and output (production) over the last 30 years. Remotely-obtained (satellite) information and field data processed through GIS software were used during this study. Results show that the area covered by the Sargassum beds was reduced by 49%. In 1980 the coverage of Sargassum was 75% for all the area (30 ha), but now we observed that 75% of the coverage occurred in area of only 2.2 ha. The average length of Sargassum mcclurei and S. serratum branches recorded in 2009 were reduced by 58% and 65%, respectively, compared with data recorded in 1980. Moreover, in 1980 Sargassum crassifolium was very common in this area, however, during this study it was not found

E-Learning Security Risks and its Countermeasures

E-learning, a novel way in the learning process that involves more interaction between the learners and teachers to some extent, in comparison to the traditional education. Moreover, it depends on the Internet technology and executes via web applications. However, network environment is a honey pot to attract many hackers and it may have some potential security risks such as: malicious attacks, hackers and so on. In addition, network security is one of the security issues of E-learning because it is usually concerns with the instructors, learners, trainers who cannot foresee the risks and know how to prevent the threats and the like. This study mainly focuses on the E-learning security issues and the countermeasures to deal with risks towards e-learning-system

Study on the variation of seagrass population in Coastal waters of Khanh Hoa Province, Vietnam

Khanh Hoa is among of a few coastal provinces where seagrasses are very abundant and form the large meadows in littoral zones, bays, lagoons. It is possible to consider that the coastal waters of Khanh Hoa has the most diverse of seagrass composition among areas of Vietnam. The investigation of seagrass beds in Khanh Hoa province (1996-1997) recorded 9 species of seagrasses, some of which were very interesting because of their large distribution areas, high density and biomass. Study on the variation of density, above ground biomass, leaf growth rate and leaf production of Enhalus acoroides and Thalassia hemprichii at two stations My Giang (Vanphong bay) and Dong Ba Thin (Camranh bay) were conducted two times per month in two years 1998, 1999. At My Giang station: the mean values of density and leaf production of E. acoroides were highest in September: 144±5shoots/m^2 and 5.96±0.3gDW/m^2/day, above ground biomass and leaf growth rate were highest in April 158±2gDW/m^2 and 1.57±0.2cm/day (March). The density of T. hemprichii was highest in May: 1050±30shoots/m^2, biomass was highest in October: 148±10gDW/m^2, leaf growth rate and leaf production were highest in September: 0.66±0.02cm/day and 5.55±0.3gDW/m^2/day. At Dong Ba Thin station: the mean values of density of E. acoroides was highest in November: 120±10shoots/m^2. The above ground biomass, leaf growth rate and leaf production were highest in September. The mean values were 383±15gDW/m^2, 1.8±0.2cm/day and 5.24±0.4gDW/m^2/day respectively. The density, biomass, leaf growth rate and leaf production of T. hemprichii were also highest in September, the mean values were 420±30 shoots/m^2, 110±10gDW/m^2, 0.66±0.05cm/day and 3.79±0.2gDW/m^2/day respectively. The studied results showed that the variation of density, above ground biomass, leaf growth rate and leaf production of seagrass beds depend on seasons in year and the environmental conditions. These values were often high in dry, sunny season (March-October) and often low in the rainy season (November-January). During the low tide (May-August) seagrass beds were exposed to the air that caused the decrease of density, biomass, leaf growth rate and leaf production of seagrasses

Analysis on the performance of reconfigurable intelligent surface-aided free-space optical link under atmospheric turbulence and pointing errors

Free-space optical (FSO) communication can provide the cost-efficient, secure, high data-rate communication links required for applications. For example, it provides broadband Internet access and backhauling for the fifth-generation (5G) and the sixth-generation (6G) communication networks. However, previous solutions to deal with signal loss caused by obstructions and atmospheric turbulence. In these solutions, reconfigurable intelligent surfaces (RISs) are considered hardware technology to improve the performance of optical wireless communication systems. This study investigates the pointing error effects for RIS-aided FSO links under atmospheric turbulence channels. We analyze the performance of RIS-aided FSO links influenced by pointing errors, atmospheric attenuation, and turbulence for the subcarrier quadrature amplitude modulation (SC-QAM) technique. Atmospheric turbulence is modeled using log-normal distribution for weak atmospheric turbulence. Several numerical outcomes obtained for different transmitter beam waist radius and pointing error displacement standard deviation are shown to quantitatively illustrate the average symbol error rate (ASER)

Contribution to The Study of Gracilaria and relative genera (Gracilariales, Rhodophyta) from Vietnam

More than 1500 specimens of Gracilaria sensu lato (Gracilaria, Gracilariopsis, and Hydropuntia) collecting by previous authors along the coast of Vietnam and our new material, which are deposited in the herbaria of the Institute of Oceanography, Nhatrang (ION), Institute of Material Science, Nhatrang Branch (IMS) and Institute of Oceanology, Hai Phong Branch (IOH), have been studied. We re-examined almost herbarium specimens of 33 Gracilaria taxa had been published by Dawson (1954); Pham Hoang Ho (1969), Nguyen Huu Dinh (1992), Nguyen Huu Dinh et al (1993) and Nguyen Van Tien (1994). Some of them were misidentified or misapplied names. In this paper, 19 Vietnamese species of Gracilaria sensu lato were discussed and critically adjusted. The structure of male and female reproductive organs, particularly the formation of spermatangia has been studied carefully. Five of the nineteen were added for the flora: Gracilaria rubra, G. cuneifolia, G. longirostric, G. yamamotoi, and Hydropuntia divergens

E-learning módszerek a 21. században

Az E-learning kifejezés egy új oktatási módszert takar. Növeli a tanulás és tanítás hatékonyságát, öszszehasonlítva a hagyományos oktatással. Mindez általában érinti a tanárok, tanulók, oktatók széles skáláját, akik a közvetlen használják az Internet-technológia és a web alkalmazások adta lehetőségeket. Ez a tanulmány bemutatja, a vietnámi diákok hatékonyságát és hozzáállását a különféle e-learning rendszerek alkalmazása esetén, cserélhetők-e a régi, hagyományos tanítási módszerek vagy sem a 21. században, továbbá ebben a kutatásban azt is bemutatjuk, milyen e-learning hatások jelentkeznek a vietnami diákok különböző tanulási módszereiben

Catalytic Performance of La-Ni/Al2O3 Catalyst for CO2 Reforming of Ethanol

Bio-derived ethanol has been considered as an attractive and alternative feedstock for dry or steam reforming reactions to generate renewable hydrogen, which may be used for replacement of conventional fossil fuels. Ethanol dry reforming (EDR) is an environmentally-friendly process since it transforms greenhouse gas, CO2 to value-added products and ethanol can be easily obtained from biomass which is free of catalyst poisons (i.e. sulphur-containing compounds). However, there are currently limited studies regarding syngas production from EDR [1, 2]. Ni-based catalysts are commonly used for reforming reactions due to its capability of C-C bond rupture, relatively low cost and high availability compared to precious metals [2]. Nevertheless, carbonaceous deposition may considerably deteriorate catalytic activity and stability of Ni-based catalysts. La promoter reportedly hindered carbon deposition and improved catalytic activity [3]. Hence, the objective of this research was to investigate the effect of La promotion on 10%Ni/Al2O3 catalyst for EDR

Average symbol error rate analysis of reconfigurable intelligent surfaces based free-space optical link over Weibull distribution channels

Optical wireless communication (OWC) enables wireless connectivity using ultraviolet bands, infrared or visible. With its advantages features as high bandwidth, low cost, and operation in an unregulated spectrum. Free-space optical (FSO) communication systems are near terrestrial as a communication link between transceivers, the link is line-of-sight and successfully transmitted optical signals. Nevertheless, the optical signals transmissions over the FSO channels bring challenges to the system. To overcome the challenges posed by the FSO channels, the most common technique is to use relay stations, the most recent is the reconfigurable intelligent surfaces (RISs) technique. This study introduces a Weibull distribution model for a free-space optical communication link with RISs assisted, the parameter used to evaluate the performance of the system is the average symbol error rate (ASER). The RISs effect is examined by considering the influence of the transmitter beam waist radius, shape parameter, aperture radius, scale parameter, and signal-to-noise ratio on the ASER