Experimental investigation of steel frames braced with symmetrical pairs of y-shaped concentric bracings

Concentric bracings composed of three members arranged in y shaped geometry have been traditionally used to provide openings in braced bays. However, simultanous occurance of compression in three braces leads to instability and out of plane buckling of braces accompanied by low hysteretic energy absorption. In order to study the behavior of y-braced frames, a research program including experimental tests was conducted at BHRC† structural engineering laboratory. Quasi-static cyclic loading was applied to specimens including four full-scale two-bay frames with y-bracings of different cross sections and connection types. The bays are braced symmetrically to have a combination of tensile and compressive braces at all loading stages. The results show that out-of-plane buckling with single curvature in braces can be substituted by in plane, double curvature buckling through appropriate detailing of cross sections and connections. Thus, hysteretic energy dissipation of y-bracing is remarkably improved due to spreading of plastic strains in braces. In this paper, seismic performance of y-braced frame specimens and a reference X-braced frame are also assessed by capacity spectrum method.     

Slotted ALOHA performance for FU‐FB in frequency selective fading environment

Slotted ALOHA is a simple and straightforward random multiple access technique, which has been used extensively in data and cellular networks as the protocol for random access. The complexity of state space‐based analysis methods for finite user finite buffer systems increases exponentially with buffer size and number of users. The presence of multipath frequency selective fading channel further adds to the complexity, making the analysis practically intractable. This paper uses an approximate analysis technique called tagged user analysis (TUA) to analyze the performance parameters of slotted ALOHA over multipath and frequency selective fading channels for finite user finite buffer systems. In TUA, the steady state system performance is evaluated from the analysis of a single user. Moreover, the state flow graph of TUA has just four states, thus reducing the complexity of the analysis. Simulation results confirm the validity of the TUA analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

E-banking and customer preferences in Malaysia: An empirical investigation

This paper examines the current trends in the e-commerce revolution that has set in motion in the Malaysian banking sector and reports on an empirical research that was carried out in Malaysia to study the customers’ preference for electronic banking and the factors, which they considered influenced the adoption of electronic banking. Results based on the analysis of data relating to 300 respondents indicate that while there is no significant differences between the age and educational qualifications of the electronic and conventional banking users, some differences exists on other demographic variables. Analysis further reveals that accessibility of Internet, a wareness of e-banking, and customers’ reluctance to change are the factors that significantly affected the usage of e-banking in Malaysia. The paper discusses on the implications of these. Limitations of the study are highlighted and further research directions are suggested.     

A networking laboratory for the developing world

Internet-based communication is assuming an increasingly important role in the developing world. It is thus crucial that students be exposed to contemporary networking equipment in a realistic setting, in order to connect theoretical material taught in lecture courses with the realities of physical hardware. To this end, a large computer networking laboratory has been set up to provide a realistic environment for teaching internetworking concepts. This laboratory provides university-level students with a testbed to experiment with fundamental issues of internetworking in a way that cannot be provided by simulators and to a degree of rigor not possible with the commonly available laboratory setups designed for technicians. We describe the motivations for setting up the laboratory, its network structure and equipment, and the type of experiments students conduct. The laboratory structure is influenced heavily by the limited funds at our disposal - a common problem in the developing world. Many of the problems we faced in setting up our equipment (such as the crucial impact of proper electrical grounding on system performance) are not ordinarily encountered in developed nations. Our experiences are thus likely to be of value to others in the developing world who are contemplating setting up experimental facilities for teaching networking.     

Online 3-D tracking of suspension living cells imaged with phase-contrast microscopy

Neural stem cells/neural progenitors (NSCs/NPs) are cells that give rise to the main cell types of the nervous system: oligodendrocytes, neurons, and astrocytes. Studying NSCs/NPs with time-lapse microscopy is critical to the understanding of the biology of these cells. However, NSCs/NPs are very sensitive to phototoxic damage, and therefore, fluorescent dyes cannot be used to follow these cells. Also, since in most of NSC/NP-related experiments, a large number of cells neesd to be monitored. Consequently, the acquisition of a huge amount of images is required. An additional difficulty is related to our original suspension living, tracking objective, behavior much closer to the natural, in vivo, way of development of the cells. Indeed, unlike adherent cells, suspension cells float freely in a liquid solution, thus, making their dynamics very different from that of adherent cells. As a result, existing visual tracking algorithms that have primarily been developed to track adherent cells are no longer adequate to tackle living cells in suspension. This paper presents a novel automated 3-D visual tracking of suspension living cells for time-lapse image acquisition using phase-contrast microscopy. This new tracking method can potentially strongly impact on current 3-D video microscopy methods, paving the way for innovative analysis of NSCs/NPs and as a result, on the study of neurodegenerative diseases.     

The Viability of Lactobacillus rhamnosus GG and Lactobacillus acidophilus NCFM Following Double Encapsulation in Alginate and Maltodextrin

Lactobacillus rhamnosus GG (LGG) and Lactobacillus acidophilus NCFM (LNCFM) were encapsulated in alginate microgel particles (microbeads) by a novel dual aerosols method. The encapsulated probiotics in microbead gel matrix were further stabilized in maltodextrin solids by either spray or freeze-drying to form probiotic microcapsule powders. The free cells of probiotics were also sprayed and freeze-dried in maltodextrin only without microgel encapsulation. After rehydration of microgel-encapsulated powder, gel particles regained their shape. There was no difference in the loss of viability between encapsulated and unencapsulated probiotics during spray drying or freeze-drying. For LNCFM, spray-dried bacteria with or without gel encapsulation exhibited less death (3.03 and 3.07 log CFU/g reduction, respectively) than those of freeze-dried bacteria (4.36 and 4.89 log CFU/g reduction, respectively) after 6 months storage at 4 °C. The same trend was also observed in spray-dried LGG without gel encapsulation which showed 5.87 log CFU/g reduction in viability after 6 months at 4 °C; however, freeze-dried LGG without gel encapsulation exhibited a rapid reduction in viability of 5.91 log CFU/g within just 2 months. Gel-encapsulated LGG which was freeze-dried exhibited less death (3.32 log CFU/g reduction) after 6 months at 4 °C. This work shows that spray drying results in improved subsequent probiotic survivability compared to freeze-drying and that alginate gel encapsulation can improve the survivability following freeze-drying in a probiotic-dependent manner.     

Crystallization analysis fractionation of poly(ethylene-co-styrene) produced by metallocene catalysts

Ethylene homo polymer and ethylene–styrene copolymers were synthesized using Cp₂ZrCl₂ (1)/methyl aluminoxane (MAO) and rac-silylene-bis (indenyl) zirconium dichloride (2)/MAO catalyst systems by varying styrene concentration and reaction conditions. Crystallization analysis fractionation (CRYSTAF), DSC, FTIR and ¹H NMR spectroscopy were used for characterizing the synthesized polymers. Interestingly, styrene was able to increase the activity of 1/MAO and 2/MAO catalyst systems at low concentrations, but at higher concentrations the activity decreases. The 1/MAO system at low and high pressure was unable to incorporate styrene, and the final product was pure polyethylene. On the other hand, with 2/MAO polymerization of ethylene and styrene yielded copolymer containing both styrene and ethylene. Results obtained from CRYSTAF and DSC reveal that on using 1/MAO system at high pressure, the resulting polymer in the presence of styrene has similar crystallinity as the polymer produced without styrene. Using both 1/MAO at low pressure and 2/MAO leads to decrease in crystallinity with increase in styrene concentration, even though the former does not incorporate styrene.     

Friction and wear behaviour of electron beam modified PTFE filled EPDM compounds

The friction and wear of non-modified and electron beam modified polytetrafluoroethylene (PTFE) filled ethylene–propylene–diene–monomer (EPDM) rubber investigated with the help of pin on disk tribometer showed different behaviour during the sliding contact with hard spherical steel-ball. The friction coefficient (μ) and specific wear rate (k) of modified PTFE filled EPDM increased with an absorbed dose of PTFE powder while non-modified PTFE filled EPDM showed the lowest μ and k values. This variation in friction and wear behaviour of PTFE filled EPDM compounds is caused by the influence of radiation induced chemical changes in PTFE powder on the radical initiated peroxide crosslinking. It results from the lower crosslinking efficiency and consequently in the deterioration of the bulk properties. The electron modification of PTFE powder reduces the hardness (modulus) and increases the energy dissipation (tan delta) of compounds. Beside other factors, these variations in bulk properties have been shown to have deleterious effects on the friction and wear properties of electron beam modified PTFE filled EPDM.