Impact Testing of Orbiter Thermal Protection System Materials

This viewgraph presentation reviews the impact testing of the materials used in designing the shuttle orbiter thermal protection system (TPS). Pursuant to the Columbia Accident Investigation Board recommendations a testing program of the TPS system was instituted. This involved using various types of impactors in different sizes shot from various sizes and strengths guns to impact the TPS tiles and the Leading Edge Structural Subsystem (LESS). The observed damage is shown, and the resultant lessons learned are reviewed

Applying Block Chain Technologies to Digital Voting Algorithms

Voting is a fundamental aspect to democracy. Many countries have advanced voting systems in place, but many of these systems have issues behind them such as not being anonymous or verifiable. Additionally, most voting systems currently have a central authority in charge of counting votes, which can be prone to corruption. We propose a voting system which mitigates many of these issues. Our voting system attempts to provide decentralization, pseudoanonymity, and verifiability. For our system, we have identified the requirements, implemented the backbone of the system, recognized some of its shortcomings, and proposed areas of future work on this voting system

The Returns to formality and Informality in Urban Africa

This paper addresses the question as to why we observe such large differentials in earnings in urban African labour markets after controlling for observable human capital. We first use a three year panel across Ghana and Tanzania and find common patterns for both countries assuming that movement between occupations is exogenous. Unobserved individual market ability is by far the most important factor explaining the variance of earnings. Sector differences do matter even with controls for ability and the sectoral gap between private wage employment and civil servants is about 50 per cent, once we control for unobserved time-invariant factors. Wage earners earn the same as the selfemployed in both Ghana and Tanzania. An additional important aspect of formality is enterprise size. At most half of the OLS effect of size on earnings can be explained by unobservable ability. Workers in largest firms are the high earners with wage rates which exceed those of civil servants. We then use an extension of the Ghana panel to five years to assess the extent of possible biases from the assumption of exogenous movement. We find evidence that this is important and that OLS may be understating the extent of both the size effect and the private sector wage (negative) premium. The implications of our results for understanding the nature of formal and informal employment in Africa are discussed.

Shields for Enhanced Protection Against High-Speed Debris

A report describes improvements over the conventional Whipple shield (two thin, spaced aluminum walls) for protecting spacecraft against high-speed impacts of orbiting debris. The debris in question arises mainly from breakup of older spacecraft. The improved shields include exterior "bumper" layers composed of hybrid fabrics woven from combinations of ceramic fibers and high-density metallic wires or, alternatively, completely metallic outer layers composed of high-strength steel or copper wires. These shields are designed to be light in weight, yet capable of protecting against orbital debris with mass densities up to about 9 g/cubic cm, without generating damaging secondary debris particles. As yet another design option, improved shields can include sparsely distributed wires made of shape memory metals that can be thermally activated from compact storage containers to form shields of predetermined shape upon arrival in orbit. The improved shields could also be used to augment shields installed previously

Solar Radiation Pressure and Deviations from Keplerian Orbits

Newtonian gravity and general relativity give exactly the same expression for the period of an object in circular orbit around a static central mass. However, when the effects of the curvature of spacetime and solar radiation pressure are considered simultaneously for a solar sail propelled satellite, there is a deviation from Kepler's third law. It is shown that solar radiation pressure affects the period of this satellite in two ways: by effectively decreasing the solar mass, thereby increasing the period, and by enhancing the effects of other phenomena, rendering some of them detectable. In particular, we consider deviations from Keplerian orbits due to spacetime curvature, frame dragging from the rotation of the sun, the oblateness of the sun, a possible net electric charge of the sun, and a very small positive cosmological constant.Comment: 4 pages, minor typo corrected, additional comment

GARField: Group Anything with Radiance Fields

Grouping is inherently ambiguous due to the multiple levels of granularity in which one can decompose a scene -- should the wheels of an excavator be considered separate or part of the whole? We present Group Anything with Radiance Fields (GARField), an approach for decomposing 3D scenes into a hierarchy of semantically meaningful groups from posed image inputs. To do this we embrace group ambiguity through physical scale: by optimizing a scale-conditioned 3D affinity feature field, a point in the world can belong to different groups of different sizes. We optimize this field from a set of 2D masks provided by Segment Anything (SAM) in a way that respects coarse-to-fine hierarchy, using scale to consistently fuse conflicting masks from different viewpoints. From this field we can derive a hierarchy of possible groupings via automatic tree construction or user interaction. We evaluate GARField on a variety of in-the-wild scenes and find it effectively extracts groups at many levels: clusters of objects, objects, and various subparts. GARField inherently represents multi-view consistent groupings and produces higher fidelity groups than the input SAM masks. GARField's hierarchical grouping could have exciting downstream applications such as 3D asset extraction or dynamic scene understanding. See the project website at https://www.garfield.studio/Comment: Project site: https://www.garfield.studio/ First three authors contributed equall

Self-Supervised Visuo-Tactile Pretraining to Locate and Follow Garment Features

Humans make extensive use of vision and touch as complementary senses, with vision providing global information about the scene and touch measuring local information during manipulation without suffering from occlusions. While prior work demonstrates the efficacy of tactile sensing for precise manipulation of deformables, they typically rely on supervised, human-labeled datasets. We propose Self-Supervised Visuo-Tactile Pretraining (SSVTP), a framework for learning multi-task visuo-tactile representations in a self-supervised manner through cross-modal supervision. We design a mechanism that enables a robot to autonomously collect precisely spatially-aligned visual and tactile image pairs, then train visual and tactile encoders to embed these pairs into a shared latent space using cross-modal contrastive loss. We apply this latent space to downstream perception and control of deformable garments on flat surfaces, and evaluate the flexibility of the learned representations without fine-tuning on 5 tasks: feature classification, contact localization, anomaly detection, feature search from a visual query (e.g., garment feature localization under occlusion), and edge following along cloth edges. The pretrained representations achieve a 73-100% success rate on these 5 tasks.Comment: RSS 2023, site: https://sites.google.com/berkeley.edu/ssvt

How close is the dose? Manipulation of 10 mg hydrocortisone tablets to provide appropriate doses to children

This study explores the methodology advised by healthcare professionals and the methods used by parents/carers to identify whether there is a best practice method for manipulation of 10 mg hydrocortisone tablets to provide an accurate dose to children. Bespoke surveys were used to identify methods recommended and used in manipulation of tablets. Hydrocortisone tablets were manipulated to provide a specified dose by both naïve participants and parents/carers. The accuracy of manipulation was assessed using HPLC analysis. Competed surveys were received from 159 parent/carers reporting doses that ranged from 0.25 to 15 mg. Parents/carers most commonly reported splitting the tablet and administering the solid fraction; however more than 30% of those reporting physically splitting tablets were preparing doses that were not simply halving or quartering tablets. In a naïve population the dose accuracy, defined as percent of doses within 20% of the theoretical dose ranged from 57 to 58% depending on the tablet brand and the method of manipulation used. Almost three-quarters (74.1%) of parent/carers (n = 27) were able to produce a dose within 20% of the theoretical value and the most accurate method was to split tablets and administer the solid fraction. This study shows that a lack of age-appropriate medicines results in children being at risk of sub-optimal dosing