Pushdown resistance as a measure of robustness in progressive collapse analysis

This paper presents a technique termed ‘pushdown analysis’ that can be used to investigate the robustness of building systems by computing residual capacity and establishing collapse modes of a damaged structure. The proposed method is inspired by the pushover method commonly used in earthquake engineering. Three variants of the technique, termed uniform pushdown, bay pushdown and incremental dynamic pushdown, are suggested and exercised using nonlinear analysis on 10-story steel moment frames designed for moderate and high levels of seismic risk. Simulation results show that the frame designed for high seismic risk is more robust than the corresponding one designed for moderate seismic risk. The improved performance is attributed to the influence of seismic detailing, specifically, the presence of reduced beam sections and stronger columns. It is shown that the dynamic impact factors associated with column removal are significantly lower than the commonly used value of 2.0 and are in line with lower values in the guidelines recently proposed by the US Department of Defense. The study suggests that seismic ‘fuses’ can play a role in the design for robustness and a discussion of the implications of this observation is provided.     

Plant Responses to Herbivory,Wounding, and Infection

Plants have various self-defense mechanisms against biotic attacks, involving both physical and chemical barriers. Physical barriers include spines, trichomes, and cuticle layers, whereas chemical barriers include secondary metabolites (SMs) and volatile organic compounds (VOCs). Complex interactions between plants and herbivores occur. Plant responses to insect herbivory begin with the perception of physical stimuli, chemical compounds (orally secreted by insects and herbivore-induced VOCs) during feeding. Plant cell membranes then generate ion fluxes that create differences in plasma membrane potential (Vm), which provokes the initiation of signal transduction, the activation of various hormones (e.g., jasmonic acid, salicylic acid, and ethylene), and the release of VOCs and SMs. This review of recent studies of plant–herbivore–infection interactions focuses on early and late plant responses, including physical barriers, signal transduction, SM production as well as epigenetic regulation, and phytohormone responses.     

Stress-Induced Lattice Imperfections: the Principal Motive in Enhancing some Physico-Chemical and Electrical Properties of some Quartz Varieties

Silicon - Chemical reactivity, grindability and zeta potential have been measured and correlated for three variably deformed quartz varieties from three different areas. Results show that there is...     

Behavior of bridge girders with corrugated webs under monotonic and cyclic loading

The focus of this study is to investigate the behavior of plate girders with trapezoidally corrugated webs under fatigue loading. Six girders were tested under both monotonic and cyclic four-point loading arrangements. A relationship between the stress range, F_r, and the number of cycles to failure, N, was developed for the girders. The results from the fatigue tests were related to the current AASHTO specifications and compared with the test results of different types of girders carried out by others. Nonlinear finite element analyses were conducted to study the effects of the different geometrical parameters of this type of girders on the stress concentrations at different locations and to explain the findings of the experimental study. Two sources of stress concentration leading to fatigue cracking were isolated and evaluated; one is dependent on the radius of curvature between the web folds and the other depends on the inclination angle of the inclined fold. An analytical technique based on fracture mechanics is also proposed to enable designers to determine the fatigue life of corrugated web steel girders.     

Optical-fibre network system for air-pollution monitoring over a wide area by optical absorption method

A low-loss optical-fibre network system for monitoring air pollution and species concentrations in various environments utilising the differential absorption method is proposed and discussed as a sensitive and economical as well as nonhazardous method. Its feasibility and advantages are also described on the basis of the present state of the art of the relevant technology.     

Trade and the environment: identifying "hot spot" sectors

A prioritization methodology was developed to identify key "hot spot" sectors that are vulnerable to adverse environmental impacts from trade liberalization. The methodology relies on internationally approved analytical techniques and indicators relevant to the trade and environment issue. Key outputs of this research include the identification of appropriate economic and environmental indicators, an information compilation strategy, and a step-wise procedure to perform the prioritization process. The methodology presented may reduce time and expenses previously incurred in identifying environmental hot spots. It also may assist in prioritizing actions to mitigate negative consequences of trade liberalization in specific sectors. Electronic Publication     

Frost formation and heat transfer on a cold surface in ice fog

In this paper a semi-empirical model describing heat and mass transfer on a cold surface in humid air under supersaturated frosting conditions is presented. The lack of psychrometric data in the supersaturated zone of the psychrometric chart has historically impeded the ability of researchers to accurately predict heat and mass transfer in supersaturated air. The work described in this paper has been partially made possible by developing a systematic procedure to compute the properties of supersaturated air, especially in the low temperature zone of the psychrometric chart. Development of such a capability will allow us to predict the amount of frost collected, the frost deposition and heat transfer rates, frost thickness and surface temperature, and other important parameters.     

The electroremoval of copper from dilute waste solutions using Swiss-roll electrode cell

Copper is usually present in concentrations less than 5 g/L⁻¹ in dilute waste solutions. The low concentrations make these solutions unsuitable for the electro-flow owinning processes via conventional electrolysis cells. Unconventional, two-and three-dimensional electrode cells with relatively large cathodic area are essential for such treatment. Different types of cells are mentioned in the literature. Among these cells, the two-dimensional Swiss-roll cell (SR) is considered in this study. The effects of cathodic current densities, initial copper concentrations, free sulfuric acid concentration, the presence of iron and zinc cations, and the rate of flow of the solution on both the cathodic current efficiency and power consumption were studied. Copper was removed from synthetic and industrial mixtures of Cu/Fe/Zn sulfate solutions to less than 5 ppm with power consumptions of 10.326 kWh/kg⁻¹ and 8.61 kWh/kg⁻¹, respectively. The correlation between the SR cell and packed-column cell on such treatment was also considered.     

Graft polymerization of acrylic acid onto starch using potassium permanganate acid (redox system)

Graft polymerization of acrylic acid (AA) onto rice starch using postassium permanganate/acid redox system as initiator was investigated. When starch was reacted with KMnO₄ solution, MnO₂ was deposited onto starch. The dependence of MnO₂ amount deposited was directly related to KMnO₄ concentration. Subjecting the MnO₂-containing starch to a solution consisting of monomer (AA) and acid (citric, tartaric, oxalic and hydrochloric acid) formed poly(AA)–starch graft copolymers. The graft yield, expressed as meq COOH/100 g starch, was measured by the amount of MnO₂ deposited, AA concentration, material-to-liquor ratio, kind and concentration of acid, as well as temperature and duration. Finally, the newly prepared poly(AA)–starch graft copolymers were applied to cotton textiles to determine their suitability as sizing agents. The highest graft yield was obtained with citric acid and the least with hydrochloric acid, with tartaric and oxalic acid in between. The graft yield increased by increasing the concentration of acid to a certain concentration beyond which grafting leveled off. A similar trend was observed when the magnitude of grafting was related to the amount of MnO₂ deposited. The graft yield increased by increasing the polymerization temperature from 30° to 50°C. Increasing the temperature to 60°C is accompanied by decreased grafting. On the other hand, fabric samples sized with poly(AA)–starch graft copolymers acquire higher tensile strength, elongation at break, and abrasion resistance than that sized with native rice starch, i.e., poly(AA)–starch graft copolymers serve as good sizing agents for cotton textiles. A tentative mechanism for grafting rice starch with AA using the KMnO₄/acid redox system was elucidated. © 1995 John Wiley & Sons, Inc.     

Mode of zero wear in mechanical systems with dry contact

A theoretical and experimental analysis of a mechanical system with dry contact and subject to harmonic excitation is made. The adopted model is a two-degree-of-freedom system representing two sub-structures in dry contacts from their flat ground surfaces. It is theoretically shown that the two sub-structures move in phase with equal amplitudes at a particular frequency of oscillation. This particular frequency is called the frequency of virtual sticking and depends upon the physical properties of the two contacting sub-structures as well as the ratio between the amplitudes of external forces applied on these two structures in the direction of their friction sliding. Zero wear of contact surfaces can thus be established since relative velocity between encountered asperities of sub-structure surfaces becomes zero. It is shown, theoretically and experimentally, that when one of the applied harmonic forces is zero, the frequency of virtual sticking is equal to the natural frequency of the unforced sub-structure. The displacement ratio of the two contacting structures under the effect of harmonic excitation in their sliding direction is investigated within a frequency range up to 400 Hz. The tangential contact stiffness and the dynamic contact rigidity are theoretically determined and experimentally predicted from the measured forced displacement ratio.