Gross plastic deformation of axisymmetric pressure vessel heads

The gross plastic deformation and associated plastic loads of four axisymmetric torispherical pressure vessels are determined by two criteria of plastic collapse: the ASME twice elastic slope (TES) criterion and the recently proposed plastic work curvature (PWC) criterion. Finite element analysis was performed assuming small and large deformation theory and elastic–perfectly plastic and bilinear kinematic hardening material models. Two plastic collapse modes are identified: bending-dominated plastic collapse of the knuckle region in small deformation models and membrane-dominated plastic collapse of the cylinder or domed end in large deformation models. In both circumstances, the PWC criterion indicates that a plastic hinge bending mechanism leads to gross plastic deformation and is used as a parameter to identify the respective plastic loads. The results of the analyses also show that the PWC criterion leads to higher design loads for strain hardening structures than the TES criterion, as it takes account of the effect of strain hardening on the evolution of the gross plastic deformation mechanism

Design by analysis of ductile failure and buckling in torispherical pressure vessel heads

Thin shell torispherical pressure vessel heads are known to exhibit complex elastic-plastic deformation and buckling behaviour under static pressure. In pressure vessel Design by Analysis, the designer is required to assess both of these behaviour modes when specifying the allowable static load. The EN and ASME boiler and pressure vessel codes permit the use of inelastic analysis in design by analysis, known as the direct route in the EN Code. In this paper, plastic collapse or gross plastic deformation loads are evaluated for two sample torispherical heads by 2D and 3D FEA based on an elastic-perfectly plastic material model. Small and large deformation effects are considered in the 2D analyses and the effect of geometry and load perturbation are considered in the 3D analysis. The plastic load is determined by applying the ASME twice elastic slope criterion of plastic collapse and an alternative plastic criterion, the Plastic Work Curvature criterion. The formation of the gross plastic deformation mechanism in the models is considered in relation to the elastic-plastic buckling response of the vessels. It is concluded that in both cases, design is limited by formation of an axisymmetric gross plastic deformation in the knuckle of the vessels prior to formation of non-axisymmetric buckling modes

Investigating the tension between cloud-related actors and individual privacy rights

Historically, little more than lip service has been paid to the rights of individuals to act to preserve their own privacy. Personal information is frequently exploited for commercial gain, often without the person’s knowledge or permission. New legislation, such as the EU General Data Protection Regulation Act, has acknowledged the need for legislative protection. This Act places the onus on service providers to preserve the confidentiality of their users’ and customers’ personal information, on pain of punitive fines for lapses. It accords special privileges to users, such as the right to be forgotten. This regulation has global jurisdiction covering the rights of any EU resident, worldwide. Assuring this legislated privacy protection presents a serious challenge, which is exacerbated in the cloud environment. A considerable number of actors are stakeholders in cloud ecosystems. Each has their own agenda and these are not necessarily well aligned. Cloud service providers, especially those offering social media services, are interested in growing their businesses and maximising revenue. There is a strong incentive for them to capitalise on their users’ personal information and usage information. Privacy is often the first victim. Here, we examine the tensions between the various cloud actors and propose a framework that could be used to ensure that privacy is preserved and respected in cloud systems

Stability and Strain in Hisactophilin and Mechanism of the Myristoyl Switch

Hisactophilin is a myristoylated, histidine-rich, pH-dependent actin- and membrane-binding protein. In response to cellular changes in pH, this β-trefoil protein reversibly switches between cytosolic and membrane- bound forms. A key feature of the reversible membrane-binding is the covalent acylation of the N-terminal glycine with a C14 myristoyl group. At pH > 6.9, the myristoyl group favours sequestration in the barrel of the β-trefoil, whereas at pH < 6.9, the myristoyl group favours increased solvent accessibility and eventually anchors hisactophilin to the inner leaflet of the cell membrane. In Dictyostelium discoideum, membrane-bound hisactophilin also binds and bundles actin, contributing to cell locomotion. Despite widespread myristoylation of eukaryotic proteins, its effects on protein folding, stability, and function are still poorly understood and limits our understanding of a broader set of switches and the ability to design them. Combining equilibrium denaturation, folding kinetics, variable temperature and variable pH nuclear magnetic resonance (NMR), chemical shift perturbations, and reverse micelle encapsulation, we use hisactophilin as a model for characterizing the determinants of finely tuned myristoyl switches. Equilibrium stability measurements identified hisactophilin mutants with broken switches—in which pH ceases influencing conformational switching—and switches with tuned sensitivities. In a few cases, stunningly small changes to amino acid side chains broke the pH-dependent myristoyl switch. Interestingly, a thermodynamic switch broken by one mutation may be repaired by making additional mutations, illustrating novel synergistic contributions to global stability and switching. Studying the mutants also revealed that a predominant effector of switching appears to be strain from an overpacked core when the myristoyl group is sequestered in the binding pocket. Altering strain through changing the geometry of the myristoyl binding pocket offers a new approach for tuning the sensitivity of hisactophilin and other switch proteins, as well as to inform future design efforts. The temperature dependence of amide proton chemical shifts localized myristoyl-induced strain to a set of residues in wild-type hisactophilin’s myristoyl-binding pocket. The mutants with broken switches (I85L, which favours the accessible state, and F6L/I85L/I93L, which favours the sequestered state), however, no longer show evidence of strain. Nonlinear temperature dependence of chemical shifts indicate that dynamics in residues that report on switching adjacent to the myristoyl group are also attenuated in broken-switch mutants. Thus, the strained residues in the protein core appear to form part of the communication network between the proton binding site(s) and the myristoyl group. Apparent pKas of backbone amide protons for I85L and LLL obtained by NMR-monitored pH titrations further support the decoupling of residues adjacent to the myristoyl group from switching. While we have achieved a high resolution and unrivalled look at the mechanism of hisactophilin’s pH-dependent myristoyl switch, we have also shown the validity and utility of chemical shift temperature dependences for characterizing small, functionally relevant local stability changes and gaining insight to the near-native energy landscape and its relation to protein function. Myristoyl switches participate in important cell signalling cascades by forming reversible protein- membrane or protein-protein interactions in response to environmental stimuli. Notwithstanding their prevalence, the high sensitivity and cooperativity of myristoyl switches complicates their study, resulting in poorly understood determinants and mechanisms. By employing thermodynamic measurements and developing a new, general application of an NMR technique, we have developed a detailed picture of the mechanism of a pH-dependent myristoyl switch

Evaluating plastic loads in torispherical heads using a new criterion of collapse

In ASME Design by Analysis, the plastic load of pressure vessels is established using the Twice Elastic Slope criterion of plastic collapse. This is based on a characteristic load-deformation plot obtained by inelastic analysis. This study investigates an alternative plastic criteria based on plastic work dissipation where the ratio of plastic to total work is monitored. Two sample analyses of medium thickness torispherical pressure vessels are presented. Elastic-perfectly plastic and strain hardening material models are considered in both small and large deformation analyses. The calculated plastic loads are assessed in comparison with experimental results from the literature

First results from the asymmetric O(a) improved Fermilab action

We present first results from calculations using O(a) improved (FNAL) space-time asymmetric action on a 12^3 x 24 quenched lattice at \beta = 5.7 and c_SW = 1.57. The asymmetry parameter is determined non-perturbatively from the energy-momentum dispersion relation. This improvement scheme is mass dependent, and the calculations have been done in the charm and bottom quark mass sectors since it is at these heavier masses that the asymmetry is expected to be relevant.Comment: 3 pp. LaTeX2e, 6PostScript figures, uses espcrc2.sty. Contribution to Lattice99 (Pisa) proceedings (Improvement and Renormalisation