Generation of tunable q-switched erbium-doped fiber laser based on graphite flakes saturable absorber

Pulsed fiber laser has tremendous application in laser processing and laser sensor. The key element to produce a passively Q-switched fiber laser is by using a saturable absorber (SA). Passively Q-switched fiber laser is the most desirable pulse in laser technology due to its ability to generate optical pulses in microsecond and nanosecond. The aim of this study is to construct a single ring erbium-doped fiber (EDF) laser based on graphite flakes SA to produce short pulse laser. Graphite flakes SA were prepared by mechanical exfoliation techniques and was transferred onto a fiber ferrule tip. The saturable absorption property of the graphite was measured using twin detector method which resulted in a modulation depth of 23.82% with a saturation intensity of 0.031 MW/cm2. Surface morphology, elemental analysis and absorbance characteristics of the graphite flakes were analyzed by the field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX) and ultraviolet visible spectroscopy (UV-VIS). The result showed that the carbon element on the SA has a very strong peak intensity. The two different EDF coefficient of 6.43 dB/m and 18.93 dB/m (EDF M-5 and EDF I-12) showed a repetition rate of 41.62 kHz and 60.00 kHz with a pulse width of 6.45 μs and 3.38 μs, respectively at a pump power of 268.8 mW. The wavelength tunability of passively Q-switched fiber laser for EDF M-5 and EDF I-12 were optimized at fixed pump power where the tuning range of EDF M-5 occurred between 1544 nm to 1560 nm and 1552 nm to 1570 nm for EDF I-12. The passively Q-switched fiber laser with different EDF coefficients were successfully constructed in a single ring configuration with more selection of wavelength that is up to L band by using higher EDF coefficient

Performance and wake analysis of rotors in axial flight using computational fluid dynamics

Flow field around rotors in axial flight is known to be complex especially in steep descent where the rotor is operating inside its own wake. It is often reported that, in this flight condition, the rotor is susceptible to severe wake interactions causing unsteady blade load, severe vibration, loss of performance, as well as poor control and handling. So far, there is little data from experimental and numerical analysis available for rotors in axial flight. In this paper, the steady Reynolds-Averaged Navier-Stokes Computational Fluid Dynamics solver Helicopter Multi-Block was used to predict the performance of rotors in axial flight. The main objective of this study was to improve the basic knowledge about the subject and to validate the flow solver used. The results obtained are presented in the form of surface pressure, rotor performance parameters, and vortex wake trajectories. The detailed velocity field of the tip vortex for a rotor in hover was also investigated, and a strong self-similarity of the swirl velocity profile was found. The predicted results obtained when compared with available experimental data showed a reasonably agreement for hover and descent rate, suggesting unsteady solution for rotors in vortex-ring state

Determinants of online shopping intention

The internet has become a key medium for the purchase of products and services in virtual markets and has effectively linked all countries and business. It has been estimated that the internet market is worth $300 billion in 1995. Through the internet, electronic commerce offers a tremendously wide variety of electronic business opportunities. One of them is online shopping which has become the third most popular internet activity after e-mail or instant messaging and web browsing. Malaysia is ranked 17th among 27 countries across Europe, Asia-Pacific and North America in terms of the percentage of internet users shopping online. Even though this method has started to win hearts of Malaysian consumers, the factors influencing the willingness to shop online are still unknown. Thus, the general objective of the study is to examine the factors that influence consumer's online shopping intention (dependent variable). The main independent variables are demographic, trusts, quality and loyalty to website visited. A 100 percent response rate was obtained from students sampled randomly. Findings indicate that quality and loyalty contributed 26.8 percent (R2 = 0.268) and 6.1 percent (R2 = 0.061) respectively to the variance in online shopping intention. Implications of the study are discussed

Map online system using internet-based image catalogue

Digital maps carry along its geodata information such as coordinate that is important in one particular topographic and thematic map. These geodatas are meaningful especially in military field. Since the maps carry along this information, its makes the size of the images is too big. The bigger size, the bigger storage is required to allocate the image file. It also can cause longer loading time. These conditions make it did not suitable to be applied in image catalogue approach via internet environment. With compression techniques, the image size can be reduced and the quality of the image is still guaranteed without much changes. This report is paying attention to one of the image compression technique using wavelet technology. Wavelet technology is much batter than any other image compression technique nowadays. As a result, the compressed images applied to a system called Map Online that used Internet-based Image Catalogue approach. This system allowed user to buy map online. User also can download the maps that had been bought besides using the searching the map. Map searching is based on several meaningful keywords. As a result, this system is expected to be used by Jabatan Ukur dan Pemetaan Malaysia (JUPEM) in order to make the organization vision is implemented