Ray Tracing Displacement Mapped Surface

Displacement mapping is a technique in computer graphics which allows a simple base surface to be deformed into a more complex surface by applying a texture to change the geometry. This is achieved by applying to each point on the surface a displacement, specified by a displacement function, with a magnitude specified by a height field. This technique makes it possible to transform the simple primitives used in computer graphics today into visually rich and geometrically complex surfaces. Displacement mapping is a texture mapping technique in which the texture is the height field defining the displacement magnitudes. But, unlike any other form of texture mapping, displacement mapping alters the surface geometry. This has many implications for the rendering of displacement mapped surfaces. It must be considered early in the rendering process during the visibility calculations (since it defines the actual geometry of the surface). This is in contrast to other forms of texture mapping which are applied after the visibility of the surface is known. This fact accounts for much of the power and complexity involved in rendering displacement mapped surfaces This thesis provides an investigation into ways to render such surfaces by the use of ray tracing. It is commonly believed that displacement mapped surfaces are too complex to be ray-traced due to the complex nature of the geometry they define. This myth is disproved by the algorithms contained herein. Three algorithms are presented which tackle the ray-surface intersection problem for displacement mapped surfaces (this being the core calculation in a ray tracer). The first algorithm tackles the problem geometrically by analysing the geometry of the intersection calculation. This approach provides a fast algorithm but with limited applicability. It is only suitable for simple base surfaces where the underlying geometry can be easily analysed. The second algorithm reduced the intersection calculation to a system of non-linear equations and applies existing numerical techniques to solve these. This approach, although very general, proves to unsuccessful due to the enormous amount of computation involved. The third approach polygonalises the displacement-mapped surface as it is rendered and calculates the intersections with the generated polygons. This, combined with a system to allow the efficient generation, storage and processing of the generated polygons, provides the first practical system for ray tracing displacement mapped surfaces

Lifting lockdown policies: A critical moment for COVID-19 stigma

COVID-19 'lockdown' policies may have unintended consequences for individuals, households and country economies. Hence lockdown may be unsustainable despite the risk of a resurgence of new COVID-19 infections. The repeal and alteration of lockdown policies mark a symbolic transfer of responsibility for epidemic control from state to individual. This has the potential to catalyse fear, blame and judgement within and between populations. We draw on experience from the HIV pandemic to show that this will worsen during later phases of the pandemic if COVID-19 stigma increases, as we fear it could. We suggest policy recommendations for 'lockdown lifting' to limit COVID-19 stigma. We suggest three policy priorities to minimise potential increases in COVID-19 stigma: limit fear by strengthening risk communication, engage communities to reduce the emergence of blaming, and emphasise social justice to reduce judgement. 'Lockdown' policies cannot continue uninterrupted. However, lifting lockdown without unintended consequences may prove harder than establishing it. This period has the potential to see the emergence of fear, blame and judgement, intersecting with existing inequalities, as governments seek to share responsibility for preventing further Sars-Cov-2 transmission. As we have learned from HIV, it is critical that a wave of COVID-19 stigma is prevented from flourishing

Bound feature combinations in visual short-term memory are fragile but influence long-term learning

We explored whether individual features and bindings between those features in VSTM tasks are completely lost from trial to trial or whether residual memory traces for these features and bindings are retained in long-term memory. Memory for arrays of coloured shapes was assessed using change detection or cued recall. Across trials, either the same colour-shape (integrated object) combinations were repeated or one feature was repeated while the other varied. Observers became sensitive to the repetition of bindings, but only if it occurred on every trial. Repetition of single features only led to learning in the cued-recall task, and was weak compared to whole-object repetitions. Results suggest that representations in visual short-term memory comprise integrated objects rather than individual features. These representations are readily displaced by new representations formed on subsequent trials. However, when a given representation is not displaced, longer term residual traces can be generated to support long-term learning, and any learning that does occur is based on integrated objects, not individual features

Glucocorticoid-Mediated Inhibition of Angiogenic Changes in Human Endothelial Cells Is Not Caused by Reductions in Cell Proliferation or Migration

Glucocorticoid-mediated inhibition of angiogenesis is important in physiology, pathophysiology and therapy. However, the mechanisms through which glucocorticoids inhibit growth of new blood vessels have not been established. This study addresses the hypothesis that physiological levels of glucocorticoids inhibit angiogenesis by directly preventing tube formation by endothelial cells.Cultured human umbilical vein (HUVEC) and aortic (HAoEC) endothelial cells were used to determine the influence of glucocorticoids on tube-like structure (TLS) formation, and on cellular proliferation (5-bromo-2'-deoxyuridine (BrdU) incorporation), viability (ATP production) and migration (Boyden chambers). Dexamethasone or cortisol (at physiological concentrations) inhibited both basal and prostaglandin F(2α) (PGF(2α))-induced and vascular endothelial growth factor (VEGF) stimulated TLS formation in endothelial cells (ECs) cultured on Matrigel, effects which were blocked with the glucocorticoid receptor antagonist RU38486. Glucocorticoids had no effect on EC viability, migration or proliferation. Time-lapse imaging showed that cortisol blocked VEGF-stimulated cytoskeletal reorganisation and initialisation of tube formation. Real time PCR suggested that increased expression of thrombospodin-1 contributed to glucocorticoid-mediated inhibition of TLS formation.We conclude that glucocorticoids interact directly with glucocorticoid receptors on vascular ECs to inhibit TLS formation. This action, which was conserved in ECs from two distinct vascular territories, was due to alterations in cell morphology rather than inhibition of EC viability, migration or proliferation and may be mediated in part by induction of thrombospodin-1. These findings provide important insights into the anti-angiogenic action of endogenous glucocorticoids in health and disease

The KELT Follow-Up Network And Transit False-Positive Catalog: Pre-Vetted False Positives For TESS

The Kilodegree Extremely Little Telescope (KELT) project has been conducting a photometric survey of transiting planets orbiting bright stars for over 10 years. The KELT images have a pixel scale of ~23\u27\u27 pixel⁻¹—very similar to that of NASA\u27s Transiting Exoplanet Survey Satellite (TESS)—as well as a large point-spread function, and the KELT reduction pipeline uses a weighted photometric aperture with radius 3\u27. At this angular scale, multiple stars are typically blended in the photometric apertures. In order to identify false positives and confirm transiting exoplanets, we have assembled a follow-up network (KELT-FUN) to conduct imaging with spatial resolution, cadence, and photometric precision higher than the KELT telescopes, as well as spectroscopic observations of the candidate host stars. The KELT-FUN team has followed-up over 1600 planet candidates since 2011, resulting in more than 20 planet discoveries. Excluding ~450 false alarms of non-astrophysical origin (i.e., instrumental noise or systematics), we present an all-sky catalog of the 1128 bright stars (6 \u3c V \u3c 13) that show transit-like features in the KELT light curves, but which were subsequently determined to be astrophysical false positives (FPs) after photometric and/or spectroscopic follow-up observations. The KELT-FUN team continues to pursue KELT and other planet candidates and will eventually follow up certain classes of TESS candidates. The KELT FP catalog will help minimize the duplication of follow-up observations by current and future transit surveys such as TESS

Effects of exposure to facial expression variation in face learning and recognition.

Facial expression is a major source of image variation in face images. Linking numerous expressions to the same face can be a huge challenge for face learning and recognition. It remains largely unknown what level of exposure to this image variation is critical for expression-invariant face recognition. We examined this issue in a recognition memory task, where the number of facial expressions of each face being exposed during a training session was manipulated. Faces were either trained with multiple expressions or a single expression, and they were later tested in either the same or different expressions. We found that recognition performance after learning three emotional expressions had no improvement over learning a single emotional expression (Experiments 1 and 2). However, learning three emotional expressions improved recognition compared to learning a single neutral expression (Experiment 3). These findings reveal both the limitation and the benefit of multiple exposures to variations of emotional expression in achieving expression-invariant face recognition. The transfer of expression training to a new type of expression is likely to depend on a relatively extensive level of training and a certain degree of variation across the types of expressions

HIV, Gender, Race, Sexual Orientation, and Sex Work: A Qualitative Study of Intersectional Stigma Experienced by HIV-Positive Women in Ontario, Canada

Mona Loutfy and colleagues used focus groups to examine experiences of stigma and coping strategies among HIV-positive women in Ontario, Canada

PDGF-C Induces Maturation of Blood Vessels in a Model of Glioblastoma and Attenuates the Response to Anti-VEGF Treatment

Recent clinical trials of VEGF inhibitors have shown promise in the treatment of recurrent glioblastomas (GBM). However, the survival benefit is usually short-lived as tumors escape anti-VEGF therapies. Here we tested the hypothesis that Platelet Derived Growth Factor-C (PDGF-C), an isoform of the PDGF family, affects GBM progression independent of VEGF pathway and hinders anti-VEGF therapy.We first showed that PDGF-C is present in human GBMs. Then, we overexpressed or downregulated PDGF-C in a human GBM cell line, U87MG, and grew them in cranial windows in nude mice to assess vessel structure and function using intravital microscopy. PDGF-C overexpressing tumors had smaller vessel diameters and lower vascular permeability compared to the parental or siRNA-transfected tumors. Furthermore, vessels in PDGF-C overexpressing tumors had more extensive coverage with NG2 positive perivascular cells and a thicker collagen IV basement membrane than the controls. Treatment with DC101, an anti-VEGFR-2 antibody, induced decreases in vessel density in the parental tumors, but had no effect on the PDGF-C overexpressing tumors.These results suggest that PDGF-C plays an important role in glioma vessel maturation and stabilization, and that it can attenuate the response to anti-VEGF therapy, potentially contributing to escape from vascular normalization