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

Why is timing of bird migration advancing when individuals are not?

Recent advances in spring arrival dates have been reported in many migratory species but the mechanism driving these advances is unknown. As population declines are most widely reported in species that are not advancing migration, there is an urgent need to identify the mechanisms facilitating and constraining these advances. Individual plasticity in timing of migration in response to changing climatic conditions is commonly proposed to drive these advances but plasticity in individual migratory timings is rarely observed. For a shorebird population that has significantly advanced migration in recent decades, we show that individual arrival dates are highly consistent between years, but that the arrival dates of new recruits to the population are significantly earlier now than in previous years. Several mechanisms could drive advances in recruit arrival, none of which require individual plasticity or rapid evolution of migration timings. In particular, advances in nest-laying dates could result in advanced recruit arrival, if benefits of early hatching facilitate early subsequent spring migration. This mechanism could also explain why arrival dates of short-distance migrants, which generally return to breeding sites earlier and have greater scope for advance laying, are advancing more rapidly than long-distance migrants

Automated operation of a home made torque magnetometer using LabVIEW

In order to simplify and optimize the operation of our home made torque magnetometer we created a new software system. The architecture is based on parallel, independently running instrument handlers communicating with a main control program. All programs are designed as command driven state machines which greatly simplifies their maintenance and expansion. Moreover, as the main program may receive commands not only from the user interface, but also from other parallel running programs, an easy way of automation is achieved. A program working through a text file containing a sequence of commands and sending them to the main program suffices to automatically have the system conduct a complex set of measurements. In this paper we describe the system's architecture and its implementation in LabVIEW.Comment: 6 pages, 7 figures, submitted to Rev. Sci. Inst

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