Structural and immunologic studies of Proteus mirabilis 033 O-specific polysaccharide

A variety of adrenal imaging agents have been used in nuclear medicine, but no agent has been developed for magnetic resonance (MR) imaging. The authors have previously observed accumulation of aminated macromolecules in adrenal glands. They now report the synthesis of a model polymeric aminated contrast agent for enhanced MR imaging of the adrenal glands. The model agent consisted of a poly-L-lysine conjugate (molecular weight, 245 kd) that had 70% free epsilon amino groups and 30% diethylenetriaminepentaacetic acid (DTPA)-derivatized amino groups to bind indium-111 or gadolinium. One hour after intravenous administration of this compound, adrenal uptake was 10.1% +/- 0.7 of injected dose per gram of tissue. When all free epsilon amino groups of the polylysine were completely substituted with DTPA, adrenal uptake was 3.4 times lower, indicating the importance of free amino groups for adrenal uptake. MR imaging in rats showed that a dose of 0.08 mmol of gadolinium per kilogram of the agent was sufficient to enhance the signal intensity of adrenal glands. There hours after intravenous administration of the agent, signal intensity of the adrenal glands was 186% of precontrast values (liver, 165%; kidney, 91%). Fluorescence microscopy showed that the agent accumulated primarily in the cortical zona glomerulosa and in the adrenal medulla. These initial studies demonstrate the feasibility of designing contrast agents for MR imaging of the adrenal glands.     

Phase Transformation Temperatures, γ–γ′ Lattice Parameter Misfit,and γ′ Precipitate Morphology in Co–Ti–V Alloys

In the context of developing tungsten free cobalt alloys, the physical metallurgical properties of γ′ precipitate strengthened Co–Ti–V alloys were investigated. In this study, few alloys were cast and heat treated to study systematic effects on the properties. The addition of V to the Co–Ti system decreases γ′ solvus temperature, whereas it increases solidus temperature. The γ–γ′ lattice parameter misfit decreases with V addition. The γ′ precipitates have cuboidal with round corners morphology, and the extent of roundedness of corners increases with V addition. Density functional theory calculations were performed to understand the experimental observation of phase transformation temperatures, lattice misfit, and γ′ precipitate morphology. The calculations indicate that magnitude of the heat of formation of Co₃(Ti,V) in the L1₂ crystal structure decreases with V addition. The γ–γ′ interfacial energy at 0 K is predicted to increase with V addition to the Co–Ti system.

     

Plastic mechanisms database for thin-walled cold-formed steel members in compression and bending

Short members of thin-walled cold-formed (TWCF) steel sections, in compression and bending, fail by forming local plastic mechanisms. Taking into account the localised buckling pattern, the collapse of slender members, due to the interaction between local and overall buckling modes, is always characterised by local plastic mechanism failure mode. Based on these two observations, the ultimate strength in interactive buckling of these members can be regarded as an interaction between localised plastic mode and overall elastic one.The yield line mechanism method has been widely used to predict the sectional strength (e.g. local) of thin-walled cold-formed steel members that involve failure mode characterized by local collapse mechanisms. This method can be also used to study post-collapse behaviour and to evaluate the load-carrying capacity, ductility and energy absorption.This paper is based on previous studies and some latest investigations of authors, as well as the literature collected data. It represents an attempt to make an inventory, classify and range geometrical and analytical models for the local-plastic mechanisms aiming to characterize the ultimate capacity of some of the most used cold-formed steel sections in structural applications.     

Load-capacity estimation and collapse analysis of thin-walled beams and columns—recent advances

The present paper is devoted to the recent results of research in the area of load-capacity and post-failure behaviour of thin-walled beams and columns (among them thin-walled cold-formed profiles). It deals with ultimate load and collapse of box-section girders (tubes) of different cross-sections under bending, as well as of lipped and plain channel-section beam-columns. The paper contains the presentation of theoretical analysis and experimental investigation of plastic mechanisms of failure and collapse behaviour of these thin-walled sections. The short review of results obtained in recent years in general precedes those obtained by the Department of Strength of Materials and Structures, TUL. The problem of post-failure behaviour is solved using the rigid-plastic theory adopted and modified for the purposes of the solution taking into consideration strain-hardening of the member’s material. On the basis of experimental investigations theoretical models of plastic mechanisms of failure are produced for different sections. Theoretical analysis is based on the principle of virtual velocities. The problem is solved in an analytical–numerical way. The particular attention has been paid to the influence of the strain-hardening of the material after yielding upon the collapse structural behaviour and also to the influence of cross-section shape and dimensions on the character of collapse. The upper-bound estimation of the load-carrying capacity of analysed thin-walled sections by combining results of non-linear, elastic post-buckling analysis with the results of plastic mechanism analysis is carried out. Results are presented in diagrams showing post-failure curves as well as curves representing structural behaviour in the whole range of loading up to and beyond the ultimate load. Some results are compared with experimental results and those obtained from FE analysis. A comparison of lower- and upper-bound estimation of the load-carrying capacity is discussed and illustrated in diagrams. Conclusions dealing with the influence of strain-hardening phenomenon displayed by the material upon the load-carrying capacity and collapse behaviour of examined sections are derived. Also conclusions concerning different upper- and lower-bound estimations of the load-carrying capacity of analysed sections are presented.     

Web crippling behaviour of thin-walled lipped channel beams

This paper presents the results of an investigation into web crippling behaviour—conducted on cold-formed thin-walled steel lipped channel beams subjected to Interior-One-Flange (IOF), Interior-Two-Flange (ITF), End-One-Flange (EOF) and End-Two-Flange (ETF) loading conditions as defined by the American Iron and Steel Institute (AISI). An experimental program was designed to obtain the load-deformation characteristics of beam members with varying cross-sectional and loading parameters under the three web crippling loading conditions. The results obtained from the experiments comprised of the ultimate web crippling strength values and displacements of the thirty-six beam specimens tested. Nonlinear finite element models were developed to simulate web crippling failure of the two loading conditions considered in the experimental program. Also, a combination of elastic analysis with a plastic mechanism approach was employed to investigate the load-deformation characteristics of lipped channel members subjected to the IOF loading condition. The comparison of experimental, finite element and plastic mechanism approach results revealed that the nonlinear finite element models were best capable of closely simulating the web crippling failure behaviour observed in the experiments for all ranges of displacement. Web crippling strength predicted from the Eurocode 3, Part 1.3 [1], and the Polish PN-B-0327 [2] design specifications were also compared with the experimental results and the comparisons indicated considerable underestimations for the range of specimens under EOF and ETF loading conditions.     

Plastic strength of thin-walled plated members—Alternative solutions review

The paper presents results of the comparative theoretical study into plastic strength of thin-walled plated structures (plates and columns) using two different approaches: energy method and equilibrium strip method. Two types of members, a thin plate and a channel section column subjected to compression, were under investigation. Numerical results obtained using both methods, together with FE simulation are presented in load-deformation diagrams. Experimental verification of theoretical analysis (using two methods under investigation together with standards strength predictions) focused on stub columns (lipped channel sections) is presented.     

Influence of load-non-uniformity and eccentricity on the stability and load carrying capacity of orthotropic tubular columns of regular hexagonal cross-section

The paper contains an analysis of the influence of non-uniformity and eccentricity of compressive loads on global and local buckling, on interactive buckling, and on the load-carrying capacity of thin-walled columns. Isotropic and orthotropic tubular columns of regular hexagonal cross-section have been examined. Equilibrium equations for the first and the second order non-linear approximation have been solved using the asymptotic Byskov–Hutchinson method. Numerical calculations have been performed for numerous different loading modes of isotropic columns and also for several loading modes of orthotropic columns. The results are presented in diagrams with some conclusions.