Ductile structural system reliability analysis using adaptive importance sampling

This paper presents a hybrid technique for efficient system reliability estimation of large ductile framed structures. The proposed procedure starts with a simple enumeration scheme, but quickly changes to an adaptive importance sampling scheme to make the process more efficient and easier to implement. The method solves the problem of including the effect of multiple failure sequences in an importance sampling scheme, for the system reliability estimation of large structures. The enumeration method is used to identify the first complete failure sequence. This failure sequence defines the initial failure domain for starting the adaptive sampling process. A weighted multi-modal sampling density is used to account for the contribution of different regions in the sampling domain to the system failure probability. As the simulation progresses, the failure domain is gradually modified to include the effect of other significant failure sequences and arrive at an accurate estimate of the system failure probability.     

The function of cation-binding agents in the enzymatic treatment of municipal sludge

Treatment of sludge with enzymes has previously been shown to efficiently release organic matter. However, the added enzymes were partially adsorbed to, entrapped by or bound to the sludge structure. Simultaneous decrease of enzymes activities was observed. Reduced adsorption and more effective, lower, enzyme dose was achieved in sludge pre-treated with three cation-binding agents. The enzymatic solubilisation of sludge was improved by 150%, 240% and 290%, by 50mM sodium tripolyphosphate (STPP), 25mM citric acid (CA) or 50mM ethylenediaminetetraacetate (EDTA), respectively. With cation binders, the lower relative enzyme dose 0.2 (13.7mg/g total solids (TS)) released 3.5 times higher COD than enzyme dose 1 (68.5mg/g TS) alone. In the presence of 25mM CA, 75% added protease remained soluble. In the presence of 50mM CA, EDTA or STPP, 50% of alpha-amylase and cellulase remained soluble. At 200mM STPP, alpha-amylase was inactive, and the efficiency of enzymatic sludge hydrolysis decreased. CA was the most effective of the three cation-binding agents tested. It is biodegradable and can be produced endogenously by the microorganisms in sludge. CA has the greatest potential for the practical application to enhance biogas production. This paper reports on the possible mechanisms of enzymes adsorption to the sludge matrix and possible methods of decreasing the adsorption. We suggest that steric hindrances were responsible for the decreased enzymatic sludge solubilisation and that polyvalent metal ions were directly involved in adsorption of enzymes to sludge matrix. The addition of cation binders eliminated both phenomena and thereby improved the enzymatic solubilisation of sludge.     

Scour at Submerged Cylindrical Obstacles under Steady Flow

Results of an experimental study on clear-water scour at submerged cylindrical obstacles (circular cylinders) in uniform bed sediments under steady flow are presented. The scour depths at submerged circular cylinders are compared with the scour depths at corresponding unsubmerged cylinders (extended above the free surface of flow) of the same diameters under similar flow and bed sediment conditions. The scour depth decreases with an increase in submergence ratio. A submergence factor is introduced to determine the scour depth at a submerged cylinder from the information of the scour depth at an unsubmerged cylinder of the same diameter. In addition, the flow fields along the upstream vertical plane of symmetry of unsubmerged and submerged cylinders are presented through vector plots, which reveal that the dimension and strength of the horseshoe vortex decreases with an increase in submergence ratio. The horseshoe vortex circulations, which decrease with an increase in submergence ratio, are computed from the vorticity contours by using the Stokes theorem.     

Lanthanum-exchanged zeolite and clay as anticorrosive pigments for galvanized steel

A wide variety of inhibitive pigments is now being offered as possible alternatives to chromate and lead compounds for painted metals protection. Unfortunately, the most wide spread of these substitute pigments, zinc phosphate, has, at present, raised some environmental concern because phosphate causes the eutrophication of water courses and zinc itself is toxic. The aim of this re-search was to study the anticorrosive performance of a mixture consisting of zinc phosphate, modified zeolite and clay （bentonite） in order to diminish phosphate content in paints. The zeolite and the clay were exchanged with La（III） ions, as inorganic green inhibitor. In the first step, the anticorrosion protection by La（III） ions in solution was assessed by electrochemical tests. In the second step, an epoxy-polyamide paint formulated with the pigment mixture applied on galvanized panels was studied by salt spray test and electro-chemical noise measurements （ENM）. The results showed that it was possible to replace part of the zinc phosphate content in the paint with the exchanged zeolite and the clay.     

An Evaluation of Drapeability of Jute Fabric

From the very inception of the Indian Jute Industry, jute fiber has proved its superiority over other fibers particularly in the area of packaging for food grains, in terms of its functionality and reusability due to its considerable tensile strength, low extensibility, and good dimensional stability, which is obviously the natural choice for packaging. One of the growing alternatives in today’s context is the emergence of technical textiles made out of natural fibers which includes geotextile products for geotechnical applications, agrotextile products as well as other such relevant areas. Jute geotextile can certainly be considered as a potential aspirant replacing majority of today’s popular synthetic products which are posing severe threats to our environment thereby adversely affecting the eco-congruity. During the application of jute fabrics of different types at the sites and even in designing garments in the Apparel Sector, it has been observed that the ability of the fabric to assume a graceful appearance of the contour is very crucial conveying the significance of drapeability of the jute fabric. An attempt has been made in this paper to study the effect of relevant property parameters and their comparative analysis on the drapeability of jute fabric as well as synthetic woven and nonwoven fabrics with respect to their end-use requirements.     

Impacts of community-based fish culture in seasonal floodplains on income,food security and employment in Bangladesh

This paper examines the impact of community based fish culture in seasonal floodplains on fish production, consumption, income, and food security of the participating households in Bangladesh. An analysis was performed using a randomly selected 46 % of the households from the three project and control floodplains; data were collected using longitudinal surveys on a seasonally, quarterly and monthly basis for the years 2007, 2008 and 2009. Fish production, income and food security of the participating households was improved due to the adoption of an equitable and inclusive multi-stakeholder approach introduced by the project. Average fish production increased from 124 kg/ha/yr. to 464 kg/ha/yr. The introduced community-based fish culture approach generated 3.74 times more fish income for households in the project sites in comparison to the control sites. Per capita monthly fish consumption increased from 1.26 kg to 2.31 kg in the project sites, which was 32 % higher than the control sites. Project implementation reduced the vulnerability of local beneficiaries, particularly of the landless and poor fishermen, by creating additional fishing opportunity for up to 6 months of the year. Promotion of the community based fish culture in seasonal floodplains may thus be useful in bringing about positive changes in the overall floodplain productivity and livelihood gains for the poor people of Bangladesh.     

Generalized optical gain analysis in nonparabolic semiconductor laser

A simple generalized theory is developed for optical gain of nonparabolic semiconductor lasers based on the three‐band model of Kane, by taking into account the wave‐vector () dependence of the optical matrix element. The gain in laser of nonparabolic semiconductors is demonstrated, by taking InAs, InSb, Hg_1−xCd_xTe and In_1−xGa_xAs_yP_1−y lattice matched to InP as examples, and it has been found that the peak of the gain spectra for a given carrier density is higher in the three‐band model of Kane than those with parabolic energy band approximations in all the cases. The difference between the peak of gain spectra for three‐band model and the parabolic band model is greater for laser of narrow band gap materials in comparisons with that of laser of wide band gap materials, thereby reveals the necessity for inclusion of the nonparabolicity in modeling lasers of small band gap materials. The well‐known results for wide band gap materials having parabolic energy bands has also been obtained from our generalized formulation under certain limiting condition. Copyright © 2013 John Wiley & Sons, Ltd.     

Clear-Water Scour at Piers in Sand Beds with an Armor Layer of Gravels

Clear-water scour at circular and square piers, embedded in a sand bed overlain by a thin armor layer of gravels, was experimentally studied. Depending on the pier width, flow depth, armor gravel, and bed-sand sizes, three cases of scour holes at piers in armored beds were recognized. A comparison of the experimental data shows that the scour depth at a pier with an armor layer under limiting stability of the surface particles is greater than that without an armor layer for the same bed sediments, if the secondary armoring formed within the scour hole is scattered. The equations of maximum equilibrium scour depths at piers in armored beds for these cases are proposed. On the other hand, the scour depth with an armor layer is less than that without an armor layer for the same bed sediments, when the scour hole is shielded by the compact secondary armor layer.