LENS® and SFF: Enabling Technologies for Optimized Structures

Optimized, lightweight, high-strength structures are needed in many applications from aerospace to automotive. In pursuit of such structures, there have been proposed analytical solutions and some specialized FEA solutions for specific structures such as automobile frames. However, generalized 3D optimization methods have been unavailable for use by most designers. Moreover, in the cases where optimized structural solutions are available, they are often hollow, curving, thin wall structures that cannot be fabricated by conventional manufacturing methods. Researchers at Sandia National Laboratories and the University of Rhode Island teamed to solve these problems. The team has been pursuing two methods of optimizing models for generalized loading conditions, and also has been investigating the methods needed to fabricate these structures using Laser Engineered Net Shaping™ (LENS®) and other rapid prototyping methods. These solid freeform fabrication (SFF) methods offer the unique ability to make hollow, high aspect ratio features out of many materials. The manufacturing development required for LENS to make these complex structures has included the addition of rotational axes to Sandia’s LENS machine bringing the total to 5 controlled axes. The additional axes have required new efforts in process planning. Several of the unique structures that are only now possible through the use of SFF technology are shown as part of the discussion of this exciting new application for SFF.Mechanical Engineerin

Hybrid Superconductor-Quantum Point Contact Devices using InSb Nanowires

Proposals for studying topological superconductivity and Majorana bound states in nanowires proximity coupled to superconductors require that transport in the nanowire is ballistic. Previous work on hybrid nanowire-superconductor systems has shown evidence for Majorana bound states, but these experiments were also marked by disorder, which disrupts ballistic transport. In this letter, we demonstrate ballistic transport in InSb nanowires interfaced directly with superconducting Al by observing quantized conductance at zero-magnetic field. Additionally, we demonstrate that the nanowire is proximity coupled to the superconducting contacts by observing Andreev reflection. These results are important steps for robustly establishing topological superconductivity in InSb nanowires

Children's play space and safety management: rethinking the role of play equipment standards

The provision of stimulating and engaging play space for children and young people is increasingly recognized as an important societal goal, not the least because it provides the young with opportunities to develop and gain experience in experimenting with risk. Research in several disciplines now suggests that achievement of this goal has however been impeded in recent decades, and reasons commonly cited have included fear of injury and avoidance of litigation. International standards on play equipment have also been promulgated and justified in terms of securing young people’s “safety,” most usually narrowly defined as injury reduction. There appears to be a widespread presumption that measures aimed at injury prevention are necessarily beneficial overall for young people’s welfare. In this article, we subject European standards for play equipment and surfacing to scrutiny. In particular, we examine underlying motives, consistency of purpose, use of evidence, philosophical leanings, scope, practicalities of application, systems of management, and legal ramifications. From this, we identify a number of fundamental issues that suggest that as a consequence of compartmentalized thinking and misunderstandings, these standards have invaded areas of decision making beyond their legitimate territory. The consequence of this is that play provision is skewed away from what are properly play provision objectives. In such circumstances, local decision makers are often disempowered, and their ability to provide optimal play spaces thereby circumscribed

Deep optical imaging of nova remnants II. A southern-sky sample

We present an optical imaging study of 20 southern-sky nova remnants which has resulted in the discovery of four previously unknown nova shells -- V842 Cen, RR Cha, DY Pup and HS Pup. The study has also revealed previously unobserved features in three other known shells -- those of BT Mon, CP Pup and RR Pic. The images of BT Mon, V842 Cen, RR Cha, DY Pup and HS Pup have been processed using several deconvolution algorithms (Richardson-Lucy, maximum entropy and clean) in addition to straightforward point-source subtraction in an attempt to resolve the shells from the central stars. The use of four different methods enables us to make a qualitative judgement of the results. Notably, the shell of RR Pic displays tails extending outwards from clumps in the main ejecta similar to those previously detected in DQ Her.Comment: Accepted for publication by MNRA

EPR entanglement strategies in two-well BEC

Criteria suitable for measuring entanglement between two different potential wells in a Bose- Einstein condensation (BEC) are evaluated. We show how to generate the required entanglement, utilizing either an adiabatic two-mode or dynamic four-mode interaction strategy, with techniques that take advantage of s-wave scattering interactions to provide the nonlinear coupling. The dynamic entanglement method results in an entanglement signature with spatially separated detectors, as in the Einstein-Podolsky-Rosen (EPR) paradox.Comment: 4 pages, 4 figure

Optimal Bell tests do not require maximally entangled states

Any Bell test consists of a sequence of measurements on a quantum state in space-like separated regions. Thus, a state is better than others for a Bell test when, for the optimal measurements and the same number of trials, the probability of existence of a local model for the observed outcomes is smaller. The maximization over states and measurements defines the optimal nonlocality proof. Numerical results show that the required optimal state does not have to be maximally entangled.Comment: 1 figure, REVTEX