ASEAN Journal on Science and Technology for Development
Studies on Fucoidan and its Production from Vietnamese Brown Seaweeds
Sulfated fucans are among the most widely studied of all the sulfated polysaccharides of plant origin that exhibit biological activities in mammalian systems. In this report fucoidans from some Vietnamese Sargassum species such as S. polycystum, S. oligocystum, S. mcclurei, S. swartzii and denticaprum were extracted and fractionated on a DEAE-Sephadex A-25 column. On the basis of chemical and spectral analyses, the fucoidan fractions obtained were found to be the sulfated fucogalactans containing sulfate ester groups and uronic acid, and composed essentially of fucose and galactose, as well as a minor amount of other sugars. The polysaccharide fractions were tested for anticancer activity. The primarily obtained results showed that all fucoidan fractions isolated from S. swartzii demonstrate bioactivity effects against cancer cells, while fraction F5 with a highest sulfate content exhibits the strongest anti-invasion activity. This indicates that sulfate content plays an important role in the anticancer activity of the brown algal fucoidans. A laboratory scale pilot for fucoidan production from Vietnamese brown seaweeds has been set with a capacity of 500 g of crude fucoidan per day. Keywords: Fucoidan, Apoptosis, Seaweed, Sargassum, Anti-invasion activity AJSTD Vol.22(4) pp.371-380 (2005)
The Safety of Building Structures Subject to Unusual Natural and Man-Made Disasters
Previously, we often use the statistical data on natural disasters and mathematical tools such as probabilistic theory, mathematical statistics and random processes to express and analyze natural disasters' phenomena when dealing with the safety problem of building structures subject to natural disasters. However, due to unusual change of the global climate, natural disasters have changed essentially the intensity, frequency and the appearing time so we cannot rely on the statistical data on natural disasters in the past to do that. Therefore, renovation of the thought on selection of plans, calculation, design, and evaluation of safety of building structures to accommodate to natural disasters and man-made disasters is a required task. This paper presents some points of view of the authors, including: (i) Why should we renovate our thought on selection of plans, calculation, design, and evaluation of safety of existing structures? (ii) What are the old thought and the new thought on the safety of building structures? (iii) How to renovate the selection of building plan, calculation, design and evaluation of the safety of building structures? and (iv) How were some building structures in Vietnam decided according to the new thought? Some specific examples on the selection of building plan given in this paper are to illustrate the authors' opinions. AJSTD Vol. 23 Issue 4 pp. 295-306 (2006)
A New Triterpene Glycoside from the Sea Cucumber Holothuria Scabra Collected in Vietnam
Bioassay guided fractionation led to the isolation of a new triterpene glycoside, holothurinogenin B (1) along with three known compounds, holothurin B (2), holothurin A (3), and holothurin A2 (4), from the methanol extract of the Vietnamese sea cucumber Holothuria scabra. Their structures were deduced from the spectral analysis (1D-NMR, 2D-NMR, MS) and chemical evidences. Keywords: Triterpene glycosides, Sea cucumber, Holothuria scabra, Holothurinogenin B. AJSTD Vol. 23 Issue 4 pp. 253-260 (2006)
Development of a Tunable Ultrashort Dye Laser System by Using Molecular Photonic Processes and a Nanosecond Pumping Laser
The paper presents the physical processes and operational characteristics of an original subpicosecond dye laser system which is designed and successfully developed at our laboratory basing on the combination use of three photonic processes of dye molecules: 1) Fast spectrotemporal evolutions in the broadband dye laser emissions; 2) Generation of a chain of ultrashort pulses (spikes) from low-Q micro-cavity dye lasers; and 3) Non-linear resonant interaction between ultrashort laser pulses and highly-saturated dye media. Such a laser system provides a stable generation of single 500 fs pulses with a peak power of 300 MW at 606 nm. Particularly, the whole sub-picosecond laser system is pumped by a single nanosecond laser (Q-switched Nd:YAG laser). The spectral and time processes involved in these pulse-shortening methods are analyzed with a rate-equation model extended to wavelengths. A white light continuum generation was obtained by focusing the 500 fs pulses into 2 cm water cell. As a result, it enables us to produce widely tunable ultrashort laser pulses with a spectral selection and amplification of the supercontinuum spectrum. AJSTD Vol. 23 Issue 4 pp. 275-284 (2006)
Synthesis and Characterization of Pure-Silicazeolite- Beta Membrane
The semiconductor industry needs low dielectric constant (low k-value) materials to more advance microprocessor and chips by reducing the size of the device features. In fabricate this context, a new material with lower k value than conventional silica ( k = 3.9 - 4.2 ) is needed in order to improve the circuit performance. As per the recent International Semiconductor Technology plan, a low-k material with a k = 1.6 will be needed by 2010. The choice of the inorganic zeolite membrane is an attractive option for low k material and suitable for microprocess application. In the present study, a pure silica zeolite beta membrane coated on the non-porous stainless steel support was synthesized using in situ crystallization of a gel with the composition of SiO2 : 0.6 TEAOH : 0.6 HF : 10.1 H2O. The crystallization was carried in the presence of tetraethylammonium hydroxide TEA(OH) as structure directing agent, fumed silica, HF and deionized water at pH value of 9. The crystallization under hydrothermal conditions at 130°C was carried out for the time period of 14 days. The membrane was characterized by X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA), Nitrogen Adsorption and Scanning Electron Microscope (SEM). SEM micrographs show highly crystalline, truncated square bipyramidal morphology of pure silica zeolite beta was coated on the non-porous stainless steel support. The membrane dielectric constant, k-value was measured as 2.64 which makes it suitable for the microprocessor applications. Keywords: Zeolite membrane, zeolite BETA and microprocessor AJSTD Vol. 23 Issue 4 pp. 285-293 (2006)
Compact 3U as a Novel Artificial Lighting Source for Gloxinia (Sinningia spp.) and Potato (Solanum tuberosum) Micropropagation
An efficient lighting system (Compact 3U) was successfully applied to the micropropagation of gloxinia and potato plants. To compare the in vitro growth of plantlets under Neon and Compact 3U lighting systems, gloxinia and potato shoots were cultured on suitable media at different light intensities: (1) 45 μmol m-2s-1 (under Neon lighting system as a control); (2) 45 μmol m-2s-1, (3) 60 μmol m-2s-1, and (4) 75 μmol m-2s-1 (under Compact 3U lighting systems). The results obtained after 3 weeks of in vitro culture and 6 weeks of acclimatization in a greenhouse showed that the growth of plantlets cultured under the Compact 3U system was better than that under Neon lighting system. The Compact 3U lighting source had a highly significant effect on the growth and development of gloxinia and potato plantlets. Besides, the data in our study also indicated that gloxinia and potato plantlets adapted differently to different lighting sources and light intensities. Keywords: Compact 3U, gloxinia, Neon, potato AJSTD Vol. 23 Issue 4 pp. 333-341 (2006)
Metal Composites Behaviour under Biaxial Stresses
For this study, different volume fraction (vol.%) of particulate alumina (Al2O3) reinforced aluminium alloy (Al 6061) with 5 vol.%, 15 vol.% and 25 vol.% are produced by powder metallurgy method. These samples were subjected to biaxial stresses in order to investigate the behaviour of the metal matrix composites (MMCs). Microstructure analysis on the individual sample before and after loading was performed under scanning electron microscopy. The small particles of 2 μm in size have exhibited strong interfacial bonding with the matrix. The particles of 5 μm in size have shown fractures and debonding interface. Large particles of above 20 μm in size have revealed severe fractures and particles pulled out. Behavior of the MMC was explained by relating the microstructures and displacement directions of the undeformed and deformed samples. Some understandings on the behaviour of the MMCs with different vol.% of Al2O3 due to biaxial stresses have been established. Keywords: Metal matrix composites, biaxial stresses, microstructures, displacement, fracture, debonding AJSTD Vol. 23 Issue 4 pp. 307-321 (2006)
Mapping QTLs Associated with Root Traits Related to Drought Resistance in Vietnamese Upland Rice
Upland rice grows on 19 million ha, about 15% of the world's rice plantation [2]. The production of upland rice is crucial to agricultural economy of many countries [15]. The yield of upland rice is very low with an average of about 1 t/ha. Drought is a major constraint to the productivity of upland rice. In this paper, we present the results on mapping QTLs for root traits related to drought resistance (maximum root length, root thickness, root weight to shoot and deep root weight to shoot ratios) in upland rice using a recombinant inbreed (RI) population derived from a cross between Vietnamese upland rice accessions. The first molecular linked of Vietnamese upland rice were constructed. The map consists of 239 markers (36 SSR and 203 AFLP markers) mapped to all 12 rice chromosomes. This map covered 3973.1 cM of rice genome with an average distance of 16.62 cM between the markers. Twenty three putative QTLs were detected. Among them, four QTLs for MRL, four QTLs for R/SR, four QTLs for DR/SR, two QTL for RN, two QTLs for RT, two for PH, and five QTLs for TN were recorded. There are several SSR markers such as RM250, RM270, RM263, RM242, RM221 linked to QTL regions. They could be very useful for drought resistant selection in rice. Some common QTLs for maximum root length and deep root weight to shoot ratio were observed in different genetic background (RDB09 × R2021 and IR64 × Azorean populations) and ecological locations (IRRI and Vietnam). These QTLs could be very useful for precise locating drought resistant gene(s) and marker-assisted selection. AJSTD Vol. 23 Issue 4 pp. 323-332 (2006)
Characteristics of Solid-State Calcium Ion Sensors Based on Photocurableand Selfplasticising Polyacrylate Matrices
New membrane materials based on cross-linked poly(n-butyl acrylate) (nBA), have been used successfully as calcium ion-selective membranes. These membrane materials possess selfplasticising property and hence do not require plasticisers. The photocurability and good adhesion characteristics of these polymer matrices enable workable solid-state calcium ion sensors to be fabricated by simple photocure procedures employing the calcium ionophore ETH5234 and a lipophilic additive as ion sensing components. The calcium ion-selectivity of the sensors can be controlled by varying the chemical composition of the photocured membrane. An optimum amount of the cross-linker 2,2-hexanedioldiacrylate (HDDA) and the incorporation of n-heptyl acrylate (nHA) led to improvement in the calcium ion-selectivity. The best calcium ion-selectivity was obtained from a copolymer membrane with composition: nBA = 74 wt-%, nHA = 20 wt-% and HDDA = 0.1 wt-%. The selectivity coefficients of calcium over major cations were: LogKCa NaPot, = -4.4, LogKCa KPot, = -3.6, Log Ca LiPot = -5.9, LogKCa MgPot , = -4.4 with a Nernstian slope (29.1 ± 0.8 mV/decade) under buffered conditions. This potentiometric performance is comparable to other solid-state calcium ion sensors with various plasticised polymer membranes. AJSTD Vol. 23 Issue 4 pp. 261-273 (2006)
Influence of Nitrogen Gas Flow Rate on the Microstructural and Mechanical Properties of Tin Deposited Carbon Steel Synthesized by CAE PVD Technique
This paper reports on the preparation of titanium nitride (TiN) thin films on carbon steel plates, using cathodic arc evaporation CAE PVD technique. We studied and discussed the effect of various nitrogen gas flow rates on microstructural and mechanical properties of TiN-coated carbon steel plates. The coating properties investigated in this work included the surface morphology, thickness of deposited coating, adhesion between the coating and substrate, coating composition, coating crystallography, hardness and surface characterization using a field emission scanning electron microscope (FE-SEM) with energy dispersive X-ray (EDX), Xray diffraction (XRD) with glazing incidence angle (GIA) technique, scratch tester, hardness testing machine, surface roughness tester and atomic force microscope (AFM). SEM analyses showed that all the films had columnar and dense structures with clearly defined substrate-film interfacial layers. The hardness of TiN-coated carbon steel was noted six times more than the hardness of uncoated one. An increase in nitrogen gas flow rate showed; decrease in the formation of macro-droplets, average roughness (Ra) and root-mean-square (RMS) values in CAE PVD technique. During XRD-GIA studies, it was observed that by increasing the nitrogen gas flow rate, the main peak [1,1,1] shifted toward the lower angular position. Microhardness of TiN-coated carbon steel showed about six times increase in hardness than the uncoated one. Scratch tester results showed an average adhesion between the coating material and substrate. Thanks to the high resolution power could be observed that by increasing nitrogen gas flow rate there was percentage increase in the bearing ratio while percentage decrease in histogram. Keywords: TiN, PVD, carbon steel, microstructure, hardness, surface roughness, adhesion AJSTD Vol. 23 Issue 4 pp. 239-251 (2006)
Effectiveness of Selected Entomopathogenic Fungi in Packed Rice Grain at Room Temperature against Corcyra cephalonica Stainton
Eight isolates of entomopathogenic fungi were evaluated as dried conidia against the rice moth, Corcyra cephalonica. In bioassays two isolates of Beauveria bassiana (BbGc and BbPs) and one isolate of Metarhizium anisopliae (MaPs) consistently gave high mortality to C. cephalonica larvae. Formulations in either kaolin, talc or tapioca flour (20 % w/w a.i.) thoroughly mixed with long grain rice in plastic cups (8 cm diameter by 5 cm) gave complete larval mortality by the 12th day of treatment. However, in general those formulated in kaolin and talc were more efficacious and faster to kill compared to those formulated in tapioca flour or the unformulated control. Even at the lowest rate of 0.05 g BbGc in kaolin provided 100% mortality 7 days after introduction compared with other dust formulations. Isolate BbGc in kaolin and talc administered at 0.4 g a.i. in 200 g rice packed in plastic kept at room temperature provided protection against the rice moth up to 4 months of storage. Larval mortality in excess of 90% was obtained 15 days after introduction. Formulations of MaPs was effective only within the first month of storage beyond which infectivity rapidly declined. Keywords: entomopathogenic fungi, dust formulation, rice moth, storage AJSTD Vol.23(3) pp.183-192 (2006)
Timing Synchronization for MC-CDMA Systems using a Time-Multiplexed Synchronization Channel
In this paper, we present a synchronization algorithm for Multi-Carrier CDMA (MC-CDMA) systems using a time-multiplexed synchronization channel. The simulations results show that a system using proposed algorithm has much higher timing detection probability than using other algorithms, especially in exponential decay multipath fading. AJSTD Vol.23(3) pp.231-237 (2006)
Effects of Habitat Fragmentation on Genetic Diversity in Cycas balansae (Cycadaceae)
Habitat fragmentation is a serious threat to species survival. In Vietnam, Cycas balansae has been considered as threatened species because of the reduction and fragmentation of its habitats and over-exploitation. We assessed genetic variability and the pattern of population structure among six populations sampled in four provinces: Hoa Binh, Ha Nam, Ninh Binh and Quang Ninh. Polyacrylamide gel electrophoresis was performed on leaf tissues from 152 individuals representing 6 populations of C. balansae. Six of twelve enzyme systems were used to estimate genetic diversity at population and species levels. Eleven loci were examined. The allozyme data showed high levels of genetic diversity within all populations, ranging from 0.538 in Ba Sao to 0.628 in Tan Dan (average 0.576). The maintenance of high levels of expected heterozygosity (average 0.571) and low in observed heterozygosity (average 0.347) might be related to great heterozygote deficiency and increased frequencies of rare alleles. Genetic differentiation among populations was low (Dst = 0.036 and Gst = 0.064), indicating high level of gene flow (Nm = 3.22). Isolation by geographical distance was observed, however, no significant relationship between genetic distances and geographical distances was recorded. Our studies suggest small population sizes of cycads brought about by fragmentation of its habitats, over-exploitation, and increasing number of inbred individuals within populations. Keywords: Habitat fragmentation, Cycas balansae, genetic variation, allozymes, conservation AJSTD Vol.23(3) pp.193-205 (2006)
Investigation on the Behaviour of Rigid Polyvinylchloride Pipes Subjected to Uniaxial Compression Loads
The objective of this research was to investigate the capability of rigid Polyvinylchloride (PVC-U) pipes to sustain axial loads. The behavior of PVC-U pipes specimens subjected to short-term uniaxial compression loads were experimentally investigated. Results of the load-displacement tests on pipes of different wall thickness, diameter, and specimen heights were recorded. The experimental test results show that the PVC-U pipes are capable of supporting loads greater than the required design load (3.4 kN). Increasing the pipe specimen height decreases the pipe strength for supporting the axial loads. Euler buckling was observed in the pipe specimens with small diameter and long axial height. Furthermore, an attempt has been made to utilize the ANSYS finite element commercial package to model the pipe system using eight noded brick element and the results were compared with those obtained from the experimental tests. Good agreement was found between the two sets of results, within the elastic range of the load-displacement curve. Keywords: PVC-U pipes, polyvinylchloride, uniaxial load, models AJSTD Vol.23(3) pp.145-160 (2006)
Optical Resonance of a Three-Level System in Semiconductor Quantum Dots
The optical resonance of a three-level system of the strongly correlated electrons in the two-level semiconductor quantum dot interacting with the linearly polarized monochromatic electromagnetic radiation is studied. With the application of the Green function method the expressions of the state vectors and the energies of the stationary states of the system in the regime of the optical resonance are derived. The Rabi oscillations of the electron populations at different levels as well as the Rabi splitting of the peaks in the photon emission spectra are investigated. PACS numbers: 71.35.-y, 78.55.-m, 78.67.Hc Keywords: quantum dot, optical resonance, Rabi oscillation, population flopping AJSTD Vol.23(3) pp.161-181 (2006)
Role of Sawdust in the Removal of Iron from Aqueous Solution
Sawdust, inexpensive material has been utilized as an absorbent for the removal of iron from aqueous solution for their safe disposal. The adsorption experiments of untreated sawdust (SD) and treated sawdust (SDC) have been carried out at room temperature using the batch test. The Langmuir and Freundlich isotherms were used to observe sorption phenomena of sawdust in the removal of iron. The results indicate that the sawdust was capable in removing iron in aqueous solution. The results have shown that the Langmuir isotherm was found well fitted into the experimental data as compared to the Freundlich isotherm. It was found that, chemisorptions and physisorption were the prime mechanism for the process of adsorption to occur between the sawdust and iron. The results also proved that the acid sulphuric treated sawdust is much better than that of untreated sawdust as an adsorbent for iron. AJSTD Vol.23(3) pp.223-229 (2006)
A Fuzzy logic Based Method for Analysing Test Results
Network operators must perform many tasks to ensure smooth operation of the network, such as planning, monitoring, etc. Among those tasks, regular testing of network performance, network errors and troubleshooting is very important. Meaningful test results will allow the operators to evaluate network performanceof any shortcomings and to better plan for network upgrade. Due to the diverse and mainly unquantifiable nature of network testing results, there is a needs to develop a method for systematically and rigorously analysing these results. In this paper, we present STAM (System Test-result Analysis Method) which employs a bottom-up hierarchical processing approach using Fuzzy logic. STAM is capable of combining all test results into a quantitative description of the network performance in terms of network stability, the significance of various network erros, performance of each function blocks within the network. The validity of this method has been successfully demonstrated in assisting the testing of a VoIP system at the Research Instiute of Post and Telecoms in Vietnam. The paper is organized as follows. The first section gives an overview of fuzzy logic theory the concepts of which will be used in the development of STAM. The next section describes STAM. The last section, demonstrating STAM’s capability, presents a success story in which STAM is successfully applied. AJSTD Vol.23(3) pp.217-222 (2006)
Crossflow Ultrafiltration for Removing Direct-15 Dye from Waste Water of Textile Industry
Ultrafiltration membrane was used to treat the effluent from textile industries. Crossflow ultrafiltration using GN polymeric membrane was used to remove the dye from textile effluent. A synthetic textile effluent of Direct-15 dye was used. The study focused through the effect of feed concentration, transmembrane pressure and solution’s pH on the permeate flux and percentage of dye removal were investigated. Dye concentration had significant effects on flux values. Under the fixed pressures and pH, the flux decreased while the dye rejection increased with increasing feed concentration. Transmembrane pressure also had significant effect on flux values. Under the fixed feed concentration and pH, the flux increased while dye rejection decreased with increasing pressure. Experiment data showed that the highest flux was observed at pH 4 (acidic condition) while the highest dye removal observed at pH 7. Data collection could be used to improve the effectiveness of dye removal from textile industry wastewater using membrane technology. Keywords: Ultrafiltration, membrane separation, dye, crossflow ultrafiltration, cake resistance AJSTD Vol.23(3) pp.207-216 (2006)
Quarry Evaluation and Control of Bench Blasting
Potential sites of quarries were evaluated by numerical rating techniques. There are 3 groups of implied rating factors on the rock deposits in surveyed quarry sites: the resource characteristics, resource economics, and the optimal excavation. A final result for each potential site was recorded and compared. In case of ongoing quarries, the planning steps for bench blasting were also suggested. By using the written packed program, the output results can be automatically demonstrated. Further trial processes can be done and the optimized blast plan view is obtained. Keywords: Potential sites, Implied rating factors, Planning steps, Optimized blast plan. AJSTD Vol.23(1&2) pp.19-26 (2006)
Numerical Investigation of Turbulent Swirling Flows through an Abrupt Expansion Tube
A numerical investigation of turbulent swirling flows through an abrupt expansion tube is reported. The TEFESS code, based on a staggered Finite Volume approach with the standard k-ε model and first-order numerical schemes built-in, was used to carry out all the computations. The code has been modified in the present work to incorporate the ASM and two second-order numerical schemes. The ASM, which includes the non-gradient convection terms arising from the transformation from Cartesian to cylindrical coordinates, was investigated for isothermal flows by applying it to the flow through an abrupt expansion tube with or without swirl flows. In addition, to investigate the effects of numerical diffusion on the predicted results, two second-order differencing schemes, namely, second-order upwind and the quadratic upstream interpolation, were used to compare with the first-order hybrid scheme. An abrupt expansion tube with non-swirling flow, predicted results using both the k-ε model and the ASM were in good agreement with measurements. For swirling flows, the calculated results suggested that the use of the ASM with a second-order numerical scheme leads to better agreement between the numerical results and experimental data, while the k-ε model is incapable of capturing the stabilizing effect of the swirl. Keywords: Algebraic Reynolds stress model (ASM), k-ε turbulence model, abrupt expansion tube, Swirl flow. AJSTD Vol.23(1&2) pp.55-70 (2006)
G-Jitter Induced Free Convection over a Vertical Flat Plate
The effect of the periodic oscillation of the gravitational field, known as g-jitter, on the free convection from a vertical plate is investigated in the present paper. The problem has been simplified by the laminar boundary layer and Boussinesq approximations. The fully implicit finite-difference scheme is used to solve the dimensionless system of the governing equations. The results for laminar flow of air (Pr = 0.72) and water (Pr = 7.00) are presented for different values of the amplitudes and frequencies of the g-jitter. The results presented show the steady periodic variation of Nusselt number and the friction coefficient with the amplitude and frequency of the gravitational acceleration oscillation. It is found that the Prandtl number as well as the amplitude and the frequency of the oscillating gravitational acceleration affect considerably the periodic oscillation of the Nusselt number and the skin friction on the vertical plate. AJSTD Vol.23(1&2) pp.133-143 (2006)
Hedge Algebras: An Algebraic Approach to Domains of Linguistic Variables and their Applicability
The paper is an overview on an algebraic approach to domains of linguistic variables and some first applications to show the applicability of this new approach. In this approach, each linguistic domain can be considered as a hedge algebra (HA for short) and based on the structure of HAs, a notion of fuzziness measure of linguistic hedges and terms can be defined. In order to apply hedge algebras to those problems, the results of which are needed, a notion of semantically quantifying mappings (SQMs) will be introduced. It shown that there is a closed connection between SQMs and fuzziness measure of hedge and primary terms (the generators of linguistic domains). To show the applicability of this approach, new methods to solve a Fuzzy Multiple Conditional Reasoning problem, the problem of Balancing an Inverted Pendulum will be presented. AJSTD Vol.23(1&2) pp.1-18 (2006)
Equation of State and Thermodynamic Properties of BCC Metals
The moment method in statistical dynamics is used to study the equation of state and thermodynamic properties of the bcc metals taking into account the anharmonicity effects of the lattice vibrations and hydrostatic pressures. The explicit expressions of the lattice constant, thermal expansion coefficient, and the specific heats CV CP of the bcc metals are derived within the fourth order moment approximation. The thermodynamic quantities of W, Nb, Fe, and Ta metals are calculated as a function of the pressure, and they are in good agreement with the corresponding results obtained from the first principles calculations and experimental results. The effective pair potentials work well for the calculations of bcc metals. AJSTD Vol.23(1&2) pp.27-42 (2006)
Effect of Gender on Human Performance under the Impact of a Polluted Mobile Human-Computer-Interaction Environment
This paper presents findings of two experimental studies that were carried out to evaluate the impact of gender, environmental pollution and vibration induced stresses on human performance when the subjects performed readability task in a mobile Human-Computer-Interaction (HCI), environment. Eleven subjects (7 males and 4 females) and 4 male subjects participated in the first and second studies respectively. In the first study the gender and the levels of vibration were kept as independent variables whereas, the environmental pollution and the levels of vibration were taken as independent variables in the second study. The dependant variable in both the studies was the average number of literal characters read per minute, which was taken as the measure of human performance. The data obtained was analyzed using two factor analysis of variance (ANOVA). The results indicated that the variable gender, levels of vibration, and pollution were all statistically significant at a significance level of 0.05. The findings of the present work are discussed in the light of previous studies undertaken on the topic and a few conclusions are drawn on the basis of results of the studies. Keywords: Human-Computer-Interaction; Vibration; Pollution; Human Performance; Analysis of Variance. AJSTD Vol.23(1&2) pp.43-53 (2006) The full text is not available at this time. Please contact the author.
Effect of the Reciprocating Mass of Slider-Crank Mechanism on Torsional Vibrations of Diesel Engine Systems
The torsional vibration phenomenon in the running gear of reciprocating engine systems is usually dealt with by considering a series of constant inertias connected by sections of massless shafting. However in reality, a slider crank mechanism is a vibrating system with varying inertia because the effective inertia of the total oscillating mass of each crank assembly varies twice per revolution of the crankshaft. Large variations in inertia torques can give rise to the phenomenon of secondary resonance in torsional vibration of modern marine diesel engines which can not be explained by conventional theory incorporating only the mean values of the varying inertias. In the past associated secondary resonances and regions of instability tended to be dismissed by most engineers as interesting but of no importance. The situation changed in recent years since there is evidence of the existence of the secondary resonance effects which could have contributed to a number of otherwise inexplicable crankshaft failures in large slow speed marine engines. The cyclic variation of the polar moment of inertia of the reciprocating parts during each revolution causes a periodic variation of frequency and corresponding amplitude of vibration of reciprocating engine systems. It also causes an increase in the speed range over which resonance effects are experienced and only a partial explanation of the behaviour of the systems has been worked out. It is impossible to avoid these instabilities by changes in the design, unless of course the variations in mass and spring constant can be made zero. In the present paper a critical appraisal of the regions of instability as determined from the equation of motion which takes into account variation of inertia is given. The motion in the form of complex waveforms is studied at different speeds of engine rotation. A comparison of theoretical results with Goldsbrough’s experimental results and Gregory’s analysis is included. AJSTD Vol.23(1&2) pp.71-81 (2006)
Fine Time Synchronization Algorithm for MIMO-OFDM
In this paper, we propose a fine time synchronization for a Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system. The proposed algorithm uses one more IFFT to find the timing offset, then correct it. The simulations show that comparing to the conventional algorithm using cross-correlation method, the proposed algorithm has a higher timing detection probability. AJSTD Vol.23(1&2) pp.83-87 (2006)
Creep Analysis of Bimaterial Microcantilever Beam for Sensing Device using Artificial Neural Network (ANN)
In this study, a feed-forward back-propagation Artificial Neural Network (ANN) is used to predict the stress relaxation and behavior of creep for bimaterial microcantilever beam for sensing device. Results obtained from ANSYS® 8.1 finite element (FE) simulations, which show good agreement with experimental work [1], is used to train the neural network. Parametric studies are carried out to analyze the effects of creep on the microcantilever beam in term of curvature and stress developed with time. It is shown that ANN accurately predicts the stress level for the microcantilever beam using the trained ANSYS® simulation results due to the fact that there is no scattered data in the FE simulation results. ANN takes a small fraction of time and effort compared to FE prediction. AJSTD Vol.23(1&2) pp.89-96 (2006)
Characterisation of Multicrystalline Solar Cells
The evaluation and assessment of the performance of photovoltaic (PV) cells in terms of measurable parameters requires the measurement of the current as a function of voltage, temperature, intensity, wind speed and spectrum. Most noticeable of all these parameters is the PV conversion efficiency η, defined as the maximum electrical power Pmax produced by the PV cell divided by the incident photon power Pin which is measured with respect to standard test conditions (STC). These conditions refer to the spectrum (AM 1.5), solar radiation intensity (1000 Wm-2), cell temperature (25 ± 2°C) and wind speed (2 mph). Tests under STC are carried out in the laboratory at a controlled environment. There have been several studies that analyze uncertainties in the laboratory measurement of solar cell efficiencies using different solar simulators and their transference to operational situations. Our preliminary results demonstrate that the short circuit current (ISC) of the solar cell decreases when irradiance is less than 1000 Wm-2 irrespective of the working temperature of the cell. Keywords: Outdoor testing of solar cells by I-V and P-V; Photovoltaics, Multicrystalline AJSTD Vol.23(1&2) pp.97-106 (2006)
On a solution to Improve the Object Detection Ability of Radars by Dynamic Polarization Method
One of the most important problems of modern radar is increasing object detection, object distinction ability. In the last years, the used traditional radar signal processing methods are seem to use up. For solving this question, specialists are interested in analyzing the fine structure of radar signal, and the first is polarization structure. The use of polarization information allows to raise the information ability of radar systems and provides high probability of radar objects detection, high contrast of small-scale man-made objects on the radar map and radar objects classification. The article deals with the detection of radar objects by exploiting the information on polarization based on the scattering matrix (SM) of the object. A solution to improve the object detection ability of radars by dynamic polarization method (to modify the polarization of radiative wave) is introduced. AJSTD Vol.23(1&2) pp.107-112 (2006)
Effect of Fly Ash Particle Reinforcement on Microstructure, Porosity and Hardness in Al-(Si-Mg) Cast Composites
The microstructure of cast Al-4Si-Mg reinforced with fly ash particles at various particle contents has been studied. The composites were fabricated by stir casting process and characterized by optical microscopy, image analyzer, scanning electron microscopy and hardness measurements. The results showed that particle contents affected to the presence of porosities and hardness of the composites. It was observed that increasing the fly ash content increase the porosity in the composites, with the matrix alloy reinforced with 15 wt.% of fly ash particles having the highest porosity and lowest hardness. Keywords: Particle contents; Stir casting process; Hardness; Porosities AJSTD Vol.23(1&2) pp.113-122 (2006)