Deck Prisms and Vault Lights

Sometime around 1800 sailing ships started using large pieces of glass embedded in the deck to bring much-needed illumination to the “tween decks” region. It was a simple and elegant solution to a common problem. The pieces of glass used were too thick to fracture easily, and they made use of an otherwise unwanted by-product of the glass industry. But why do the reproductions that are now sold in gift stores feature what must have been a rather dangerous downward-protruding sharp point in something that was to be used in the notoriously low-ceilinged lower deck? How did these Deck Prisms develop, and what is their relationship to the similar Vault Lights used in cities around the same time?

Local Optimization for Robust Signed Distance Field Collision

Signed distance fields (SDFs) are a popular shape representation for collision detection. This is due to their query efficiency, and the ability to provide robust inside/outside information. Although it is straightforward to test points for interpenetration with an SDF, it is not clear how to extend this to continuous surfaces, such as triangle meshes. In this paper, we propose a per-element local optimization to find the closest points between the SDF isosurface and mesh elements. This allows us to generate accurate contact points between sharp point-face pairs, and handle smoothly varying edge-edge contact. We compare three numerical methods for solving the local optimization problem: projected gradient descent, Frank-Wolfe, and golden-section search. Finally, we demonstrate the applicability of our method to a wide range of scenarios including collision of simulated cloth, rigid bodies, and deformable solids.

Investigation of Anisotropic Subsequent Yield Behavior for 45 Steel by the Distortional Yield Surface Constitutive Model

The subsequent anisotropic yield behavior of 45 steel was predicted by the distortional yield surface constitutive model, which can describe the anisotropic subsequent yield and the cross effect of metal associating with loading history. The yield characteristics and plastic hardening behaviors of the 45 steel were simulated under three preloading paths including pre-torsion, pre-tension, and pre-tension–torsion. Based on the comparison between the experimental yield stresses and the simulation by the classical Chaboche model, the proposed model can describe the remarkable anisotropic yield behavior related to the loading history, which can effectively describe the sharp point of yield surface in pre-loading direction and the smaller curvature near its opposite direction. It was successfully simulated by the constitutive model proposed that the subsequent distortional yield surface defined by small offset strain and the degradation process of the distortion feature defined by large offset strain.

Directional Sharp-Point Failure Mechanism of Rocks Surrounding Underground Circular Cavities Subjected to Large-Scale Failure

Large-scale expansion of failure areas in rocks surrounding underground cavities causes severe destruction of the underground space and may trigger serious disasters. To study the large-scale failure mechanism and expansion laws of rocks surrounding underground cavities, we performed a theoretical study of the distribution characteristics of the stress field around a circular cavity and determined the directional sharp-point failure mechanism by analysing the stress destructive power using the three elements of the Mohr circle. Results showed that, along the circumferential direction, the stress destructive power increases first and then decreases, showing a sharp-angular distribution. Rock with any properties will suffer priority damage at the stress sharp point. The direction criterion of the stress sharp points was proposed, and the direction of these points showed a convergent behaviour in the radial direction of the cavity, tending to be stable at 40°-50° beyond five times the cavity radius. In addition, the results were verified by FLAC3D numerical simulation. The theoretical analysis for the ideal circular cavity may provide references to study the damage laws of rocks surrounding other irregular-shaped space, as well as providing a theoretical basis for the prevention and control of underground engineering disasters.

Bulbophyllum chrysolabium (Orchidaceae, Epidendroideae, Malaxideae), a new species from Yunnan, China

Bulbophyllumchrysolabium, a new species belonging to section Racemosae from Yunnan, China is described and illustrated. The species is related to B.orientale and B.morphologorum, but differs by having the following set of characters: obliquely broadly-based triangular petals with a long filiform apex; lip densely glandular papillose and conspicuously ciliolate along margins; lip auricles well developed, narrowly falcate, tapering to a long sharp point at the apex; stelidia subulate and twisted inwards, slightly exceeding operculum. The conservation status of B.chrysolabium is assessed and taxonomic notes are provided.

A legal analysis in context: The Regulation of Gatherings Act – a hindrance to the right to protest?

South Africa has seen a groundswell of protests in the past few years. The number of arrests during protest action has likewise increased. In June 2017 the Social Justice Coalition (SJC) challenged the constitutionality of the Regulation of Gatherings Act 205 of 1993 in the Western Cape High Court. This was an appeal from the magistrates’ court in which 21 members of the SJC were convicted of contravening the Regulation of Gatherings Act for failing to provide notice. This is the first court challenge to the constitutionality of the Regulation of Gatherings Act. Although the challenge was brought on restricted grounds, it highlights the Regulation of Gatherings Act as a sharp point of controversy. This article will consider the regulatory provisions and the extent to which they restrict the constitutional right to protest, particularly in light of the important role played by protest in South Africa’s constitutional democracy.

Dynamic Resistivity Changes of Diesel Contamination Plume in Simulated Aquifer

Hydrocarbon contamination to subsurface from petroleum spills and underground tank leaking has become more and more concerned. In this study, the vertical migration processes of diesel was simulated in a scaled beach sand aquifer model using a cylinder Plexiglas tank and monitored by self-made automatic resistivity monitoring system. It was shown that the resistivity change curves were dissimilar among unsaturated zone, capillary fringe and saturated zone. Through the measurements of the soil samples, the water content and oil content variability were consistent with the resistivity changes. From the sharp point of resistivity change curves, the thickness of the accumulated oil zone could be estimated. It provides an effective method to dynamically monitor the light oil plume migration in ground aquifer after leaking and determine the location of the oil lens.

Modeling of Flow Fields of Different Delivery Chamfers in Spray Forming Process

The computational fluid dynamic (CFD) software was used to calculate the velocity field in atomization chamber of spray forming equipment. The relationship between melt flow rates, gas aspiration of the atomizer and operating pressure are complex, and the above mentioned parameters are closely related to the atomization process. The influences of different delivery chamfers on gas flow field, which is determined by atomizer structure, were analyzed. Using K-epsilon model with a symmetrical domain, the gas dynamic of different delivery chamfer conditions were investigated. The results indicate that the sharp point of delivery tube causes detachment of flow field, and 56°, 45° and 34° chamfer conditions have same diffusion angle. Gas was aspirated from delivery tube when chamfer was 0°, which is beneficial to liquid metal flow in atomization process.

Cutting Force Model for Diamond Cutting Microstructured Surfaces

The depth of cut changed periodically along the contour of the cutting surfaces. The diamond tool of sharp point tip was used in diamond cutting microstructured surfaces with Fast Tool Serve (FTS). All reported the cutting force model were not suitable for accurately predicting cutting force. A cutting forces model concerned with edge radius, spring back and dynamic shear angle was proposed for diamond cutting microstructured surfaces. The model was verified with a series of experimental results. The results showed that the proposed model was able to exactly predict the cutting force.