Seasonal variation of particle-induced oxidative potential of airborne particulate matter in Beijing

An in vitro plasmid scission assay (PSA), the cell apoptosis assay, and ICP-MS were employed to study the oxidative potentials and trace element compositions of the airborne particulate matter (PM) in Beijing during a one year-long field campaign from June 2010 to June 2011. The cell damages induced by PM reveled by the cell apoptosis assay showed a similar variation pattern to the DNA damages obtained by PSA, verifying the feasibility of the PSA in analyzing the oxidative capacity of PM samples. The PSA experiments showed that the particle-induced DNA damage was highest in summer, followed by spring, winter and autumn in descending order. The percentages of the oxidative damages to plasmid DNA induced by the water-soluble fractions of PM under the particle doses from 10 to 250 μg/ml were generally lower than 45%, with some values peaking at above 50%. The peak values were frequently present in late spring (i.e. April and May) and early summer (i.e. June) but they were scarcely observed in other seasons. These peak values were mostly associated with haze days or the days with low wind speed (less than 4 m/s), indicating that the PM samples during haze had higher oxidative potential than those during non-haze periods. The oxidative potential induced by the water-soluble fraction of the PM displayed a significant positive correlation with the concentrations of the water-soluble elements Cd, Cs, Pb, Rb, Zn, Be and Bi, demonstrating that the particle-induced oxidative potentials were mainly sourced from these elements. The exposure risk represented by the mass concentration of these elements in unit volume of atmosphere was higher in summer and winter, and lower in autumn and spring. The haze day PM samples not only had higher level of oxidative potentials but also had higher concentrations of water-soluble elements

Cross-sectional optimization of cold-formed steel channels to Eurocode 3

Cold-formed steel structural systems are widely used in modern construction. However, identifying optimal cross section geometries for cold-formed steel elements is a complex problem, since the strength of these members is controlled by combinations of local, distortional, and global buckling. This paper presents a procedure to obtain optimized steel channel cross-sections for use in compression or bending. A simple lipped C-shape is taken as a starting point, but the optimization process allows for the addition of double-fold (return) lips, inclined lips and triangular web stiffeners. The cross-sections are optimized with respect to their structural capacity, determined according to the relevant Eurocode (EN1993-1-3), using genetic algorithms. All plate slenderness limit values and all limits on the relative dimensions of the cross-sectional components, set by the Eurocode, are thereby taken into account as constraints on the optimization problem. The optimization for compression is carried out for different column lengths and includes the effects of the shift of the effective centroid induced by local buckling. Detailed finite element models are used to confirm the relative gains in capacity obtained through the optimization process

Modal decomposition of coupled instabilities: The method of the equivalent nodal forces

A solution to the ‘modal decomposition problem’ encountered within the context of the stability analysis of thin-walled structural members is presented. The proposed method achieves decomposition of a randomly deformed shape into a number of constituent modes, which have the physical meaning of the classical local, distortional and global buckling modes, augmented with two additional classes of shear and transverse extension modes. The basis vectors of these five classes are created by defining sets of nodal forces which, when applied to the member in a first order linear elastic problem, generate shapes commensurate with specific mechanical criteria defining the local, distortional, global, shear and transverse extension modes. In a second step the basis vectors of a given class are used to define a constrained stability problem, where the solution is restricted to a linear combination of these basis vectors, in order to obtain the buckled shapes under a given loading. The full set of buckling modes spanning the five classes forms an orthonormal basis of the complete deformation space. Consequently, decomposition can be achieved by projecting the shape which is to be decomposed onto the basis vectors. Two examples are provided to illustrate the method

Optimum design of cold-formed steel beams using Particle Swarm Optimisation method

Applying optimisation techniques to the design of cold-formed steel (CFS) sections can lead to more economical and efficient design solutions. However, a crucial factor in such an optimisation is to arrive at a solution which is practical and fits within the constraints of the fabrication and construction industries. Targeting this objective, a comprehensive investigation was conducted on the practical optimisation of CFS beams using a Particle Swarm Optimisation (PSO) method. Six different CFS channel section prototypes were selected and then optimised with respect to their flexural strength, determined according to the effective width based provisions of Eurocode 3 (EC3) part 1–3. Comparing the capacities of the optimised sections to those of the original channel sections with the same amount of structural material, significant improvements were obtained. The accuracy of the optimisation procedure was assessed using experimentally validated nonlinear Finite Element (FE) analyses accounting for the effect of imperfections. The results indicated that, using the same amount of material, the optimum sections offered up to 25% and 75% more flexural strength for laterally braced and unbraced CFS beams, respectively, while they also satisfied predefined manufacturing and design constraints. Therefore, the proposed optimisation methodology has the potential to prove useful in practical design applications

Experimental study of the cross-sectional capacity of cold-formed steel built-up columns

This paper describes a comprehensive experimental programme in which built-up cold-formed steel stub columns with four different cross-sectional geometries were investigated. Twenty built-up sections were fabricated from individual channels and flat plates with nominal thicknesses ranging from 1.2 mm to 2.4 mm and assembled with either bolts or self-drilling screws. The connector spacing was varied among specimens of the same geometry in order to study its effect. The built-up columns were tested between fixed boundary conditions and the load was transmitted through end plates which were attached to the columns with an epoxy resin. Tensile coupons were taken from the corners and flat portions of the constituent sections in order to determine their material properties, while detailed measurements of the geometric imperfections of each specimen were also performed using a laser displacement sensor. The experiments revealed a significant amount of restraint and interaction between the individual components of the columns while buckling, with the connector spacing having a pronounced effect on the observed buckling modes. However, the ultimate cross-sectional capacity was seen to be much less dependent on the connector spacing within the considered range of spacings

Development of optimum cold-formed steel sections for maximum energy dissipation in uniaxial bending

Cold-formed steel (CFS) elements are increasingly used as load-bearing members in construction, including in seismic regions. More conventional hot-rolled steel and concrete building structures are typically allowed by the design standards to exceed their elastic limits in severe earthquakes, rendering parameters indicating ductility and energy dissipation of primordial importance. However, insufficient research has yet been conducted on the energy dissipation of CFS structures. In the majority of previous optimization research on CFS sections the ultimate capacity, as typically controlled by local, distortional and/or global buckling modes, is considered to be the sole optimization criterion. This paper aims to improve the seismic performance of CFS elements by optimising their geometric and material highly non-linear post-buckling behaviour to achieve maximum energy dissipation. A novel shape optimisation framework is presented using the Particle Swarm Optimisation (PSO) algorithm, linked to GMNIA ABAQUS finite element analyses. The relative dimensions of the cross-section, the location and number of intermediate stiffeners and the inclination of the lip stiffeners are considered to be the main design variables. All plate slenderness limit values and limits on the relative dimensions of the cross-sectional components as defined by Eurocode 3, as well as a number of practical manufacturing and construction limitations, are taken into account as constraints in the optimisation problem. It is demonstrated that a substantial improvement in energy dissipation capacity and ductility can be achieved through the proposed optimization framework. Optimized cross-sectional shapes are presented which dissipate up to 60% more energy through plastic deformations than a comparable commercially available lipped channel

Therapy Response Assessment of Pediatric Tumors with Whole-Body Diffusion-weighted MRI and FDG PET/MRI

Background: Whole-body diffusion-weighted (DW) MRI can help detect cancer with high sensitivity. However, the assessment of therapy response often requires information about tumor metabolism, which is measured with fluorine 18 fluorodeoxyglucose (FDG) PET. Purpose: To compare tumor therapy response with whole-body DW MRI and FDG PET/MRI in children and young adults. Materials and Methods: In this prospective, nonrandomized multicenter study, 56 children and young adults (31 male and 25 female participants; mean age, 15 years +/- 4 [standard deviation]; age range, 6-22 years) with lymphoma or sarcoma underwent 112 simultaneous whole-body DW MRI and FDG PET/MRI between June 2015 and December 2018 before and after induction chemotherapy(ClinicalTrials.gov identifier: NCT01542879). The authors measured minimum tumor apparent diffusion coefficients (ADCs) and maximum standardized uptake value (SUV) of up to six target lesions and assessed therapy response after induction chemotherapy according to the Lugano classification or PET Response Criteria in Solid Tumors. The authors evaluated agreements between whole-body DW MRI- and FDG PET/MRI-based response classifications with Krippendorff alpha statistics. Differences in minimum ADC and maximum SUV between responders and nonresponders and comparison of timing for discordant and concordant response assessments after induction chemotherapy were evaluated with the Wilcoxon test. Results: Good agreement existed between treatment response assessments after induction chemotherapy with whole-body DW MRI and FDG PET/MRI (alpha = 0.88). Clinical response prediction according to maximum SUV (area under the receiver operating characteristic curve = 100%; 95% confidence interval [CI]: 99%, 100%) and minimum ADC (area under the receiver operating characteristic curve = 98%; 95% CI: 94%, 100%) were similar (P =.37). Sensitivity and specificity were 96% (54 of 56 participants;95% CI: 86%, 99%) and 100% (56 of 56 participants; 95% CI: 54%, 100%), respectively, for DW MRI and 100% (56 of 56 participants; 95% CI: 93%, 100%) and 100% (56 of 56 participants; 95% CI: 54%, 100%) for FDG PET/MRI. In eight of 56 patients who underwent imaging after induction chemotherapy in the early posttreatment phase, chemotherapy-induced changes in tumor metabolism preceded changes in proton diffusion (P =.002). Conclusion: Whole-body diffusion-weighted MRI showed significant agreement with fluorine 18 fluorodeoxyglucose PET/MRI for treatment response assessment in children and young adults. (C) RSNA, 202