HLA-CSPIF panel on commercial off-the-shelf distributed simulation

Commercial-off-the-shelf (COTS) simulation packages are widely used in many areas of industry. Several research groups are attempting to integrate distributed simulation principles and techniques with these packages to potentially give us COTS distributed simulation. The High Level Architecture-COTS Simulation Package Interoperation Forum (HLA-CSPIF) is a group of researchers and practitioners that are studying methodological and technological issues in this area. This panel paper presents the views of four members of this forum on the technical problems that must be overcome for this emerging field to be realized

Modeling the anchoring and performance of downhole equipment using an extended Gurson model

In oil and gas (O&G) exploration the well casing, in the form of a long steel tube, maintains the opening of the drilled well hole. Mechanical equipment is often inserted into the well for the purpose of well monitoring, pressure control and various operations. This downhole equipment may be mechanically connected to the pipe casing by the outward radial motion of anchoring teeth such that the inner wall casing is indented. The connection between the tool and the casing must support significant mechanical loads in the longitudinal (axial) direction of the casing, i.e. transverse to the direction of indentation, while minimizing the indentation depth in order to preserve the stiffness and strength of the casing. Consequently, a determination of the ultimate strength of the connection is of critical importance. Failure of this connection involves intense shear of the inner wall of the casing, akin to a machining operation. The critical load for axial slip can be determined experimentally or numerically (or by combination of both). In this study, detailed simulations are performed using the shear-extended GTN (Gurson-Tvergaard-Needleman) model. The choice of model is motivated by the need to accurately the extensive plastic deformation associated with indentation as well as shear-dominated ductile failure on a sub-millimeter scale. The shear-extended GTN model requires a careful calibration of the model parameters by an accurate measurement of the material response. Accordingly, the casing steel was characterized by appropriate measurements under a range of stress states. The calibrated model was used to investigate an idealized two-dimensional representation of the anchoring problem, with a focus on the effect of indentation depth upon connection strength. Both the indentation of the casing inner wall by the anchoring teeth and the subsequent shear of the casing wall were simulated in detail to determine the load required to initiate and progress slip of the anchoring teeth. The results of these analyses show that the connection strength increases linearly with increasing indentation depth

Twin-tunnelling-induced ground movements in clay

Modern tunnelling methods aim to reduce ground movements arising from the construction process. In clay strata the usual method of construction is by tunnel boring machine, which allows close control of the tunnelling process; however, any movements have the potential to cause damage to existing structures at, and below, the ground surface. The construction of underground rail systems often comprises two tunnels running in opposite directions. Common practice for assessing construction-generated movements around these tunnels is to make predictions based upon individual tunnel construction and utilise superposition to generate a total deformation profile. This approach does not take into account the strain- or stress-dependent effects between tunnel constructions. A delay may result in unanticipated ground movements generated by the construction of the second tunnel. The effect of this delay on the ground movements arising between the first and the second tunnel construction process was investigated in a series of plane strain centrifuge tests. The ground movements at and below the surface were monitored and were assessed against superposition-based predictions for surface settlement with the outcomes highlighting some inconsistencies. A procedure for predicting both surface and subsurface vertical settlement profiles in the plane transverse to the advancing tunnels in clay is suggested

Feasibility of dynamic T2*-based oxygen-enhanced lung MRI at 3T

PURPOSE: To demonstrate proof-of-concept of a T2 *-sensitized oxygen-enhanced MRI (OE-MRI) method at 3T by assessing signal characteristics, repeatability, and reproducibility of dynamic lung OE-MRI metrics in healthy volunteers. METHODS: We performed sequence-specific simulations for protocol optimisation and acquired free-breathing OE-MRI data from 16 healthy subjects using a dual-echo RF-spoiled gradient echo approach at 3T across two institutions. Non-linear registration and tissue density correction were applied. Derived metrics included percent signal enhancement (PSE), ∆R2 * and wash-in time normalized for breathing rate (τ-nBR). Inter-scanner reproducibility and intra-scanner repeatability were evaluated using intra-class correlation coefficient (ICC), repeatability coefficient, reproducibility coefficient, and Bland-Altman analysis. RESULTS: Simulations and experimental data show negative contrast upon oxygen inhalation, due to substantial dominance of ∆R2 * at TE > 0.2 ms. Density correction improved signal fluctuations. Density-corrected mean PSE values, aligned with simulations, display TE-dependence, and an anterior-to-posterior PSE reduction trend at TE1 . ∆R2 * maps exhibit spatial heterogeneity in oxygen delivery, featuring anterior-to-posterior R2 * increase. Mean T2 * values across 32 scans were 0.68 and 0.62 ms for pre- and post-O2 inhalation, respectively. Excellent or good agreement emerged from all intra-, inter-scanner and inter-rater variability tests for PSE and ∆R2 *. However, ICC values for τ-nBR demonstrated limited agreement between repeated measures. CONCLUSION: Our results demonstrate the feasibility of a T2 *-weighted method utilizing a dual-echo RF-spoiled gradient echo approach, simultaneously capturing PSE, ∆R2 * changes, and oxygen wash-in during free-breathing. The excellent or good repeatability and reproducibility on intra- and inter-scanner PSE and ∆R2 * suggest potential utility in multi-center clinical applications

Injector fouling and its impact on engine emissions and spray characteristics in gasoline direct injection engines

In Gasoline Direct Injection engines, direct exposure of the injector to the flame can cause combustion products to accumulate on the nozzle, which can result in increased particulate emissions. This research observes the impact of injector fouling on particulate emissions and the associated injector spray pattern and shows how both can be reversed by utilising fuel detergency. For this purpose multi-hole injectors were deliberately fouled in a four-cylinder test engine with two different base fuels. During a four hour injector fouling cycle particulate numbers (PN) increased by up to two orders of magnitude. The drift could be reversed by switching to a fuel blend that contained a detergent additive. In addition, it was possible to completely avoid any PN increase, when the detergent containing fuel was used from the beginning of the test. Microscopy showed that increased injector fouling coincided with increased particulate emissions. Based on these results a selection of the injectors was installed in a laboratory injection chamber and the spray patterns were investigated with a high speed camera. Injectors corresponding to the largest PN drift produced the thinnest spray jets with the deepest penetration. These factors amplify the risk of wall wetting and provide an explanation for the increase of PN. The positive effect of the detergent was also reflected in the spray pattern analysis, which illustrates the potential benefits of such fuel additives

Structural basis for Fullerene geometry in a human endogenous retrovirus capsid

The HML2 (HERV-K) group constitutes the most recently acquired family of human endogenous retroviruses, with many proviruses less than one million years old. Many maintain intact open reading frames and provirus expression together with HML2 particle formation are observed in early stage human embryo development and are associated with pluripotency as well as inflammatory disease, cancers and HIV-1 infection. Here, we reconstruct the core structural protein (CA) of an HML2 retrovirus, assemble particles in vitro and employ single particle cryogenic electron microscopy (cryo-EM) to determine structures of four classes of CA Fullerene shell assemblies. These icosahedral and capsular assemblies reveal at high-resolution the molecular interactions that allow CA to form both pentamers and hexamers and show how invariant pentamers and structurally plastic hexamers associate to form the unique polyhedral structures found in retroviral cores

Change and Aging Senescence as an adaptation

Understanding why we age is a long-lived open problem in evolutionary biology. Aging is prejudicial to the individual and evolutionary forces should prevent it, but many species show signs of senescence as individuals age. Here, I will propose a model for aging based on assumptions that are compatible with evolutionary theory: i) competition is between individuals; ii) there is some degree of locality, so quite often competition will between parents and their progeny; iii) optimal conditions are not stationary, mutation helps each species to keep competitive. When conditions change, a senescent species can drive immortal competitors to extinction. This counter-intuitive result arises from the pruning caused by the death of elder individuals. When there is change and mutation, each generation is slightly better adapted to the new conditions, but some older individuals survive by random chance. Senescence can eliminate those from the genetic pool. Even though individual selection forces always win over group selection ones, it is not exactly the individual that is selected, but its lineage. While senescence damages the individuals and has an evolutionary cost, it has a benefit of its own. It allows each lineage to adapt faster to changing conditions. We age because the world changes.Comment: 19 pages, 4 figure

Apparatus for centrifuge modelling of twin-tunnel construction

In urban areas it is common for pairs of tunnels to be used as a method for building rapid transit systems. Driven by an increasing population and demand for services, tunnels are more widespread in their use than at any previous time. Construction of any form of tunnel causes ground movements which have the potential to damage existing surface and sub-surface structures. Modern tunnelling practice aims to reduce these movements to a minimum but there is still a requirement for accurate assessments of possible damage to structures resulting from settlements. For tunnels driven in clay, superposition of settlement predictions made by considering a single tunnel is an accepted method used to estimate movements around pairs of tunnels. Previous research, particularly numerical studies, has indicated that this may not necessarily be sufficient. In this paper a series of centrifuge model tests designed to investigate settlements related to twin-tunnel construction are described. The development of the experimental apparatus for sequential twin-tunnel construction with variable centre-to-centre spacing and volume loss is described in detail