Constrained inverse volume rendering for planetary nebulae

Journal ArticleDetermining the three-dimensional structure of distant astronomical objects is a challenging task, given that terrestrial observations provide only one viewpoint. For this task, bipolar planetary nebulae are interesting objects of study because of their pronounced axial symmetry due to fundamental physical processes. Making use of this symmetry constraint, we present a technique to automatically recover the asymmetric structure of bipolar planetary nebulae from two-dimensional images. With GPU-based volume rendering driving a non-linear optimization, we estimate the nebula's local emission density as a function of its radial and axial coordinates, and we recover the orientation of the nebula relative to Earth. The optimization refines the nebula model and its orientation by minimizing the differences between the rendered image and the original astronomical image. The resulting model enables realistic 3D visualizations of planetary nebulae, e.g. for educational purposes in planetarium shows. In addition, the recovered spatial distribution of the emissive gas allows validating computer simulation results of the astrophysical formation processes of planetary nebulae

Concussion Safety Law Should be Enacted in all Canadian Provinces and Territories

The concussion crisis in sports remains an important public health issue. Indeed, it is cited by 97% of Canadians as a major public health concern

Teacher Blogging Redux: Post with Caution

In the December 2014 issue of School Business Affairs, this column (Russo 2014) addressed a case from Pennsylvania, Munroe v. Central Bucks School District (2014), that explored the free speech rights of public school teachers who blog on the Internet. In Munroe, a school board in Pennsylvania dismissed a tenured high school teacher who posted controversial, derogatory remarks about her students and others on her personal blog. The Third Circuit subsequently affirmed that insofar as the blog entries were disruptive to school operations, the teacher’s dismissal did not violate the First Amendment (Munroe 2015). Munroe highlights the need for school business officials (SBOs) and other education leaders to be vigilant about teachers’ use of social media. Using Munroe as a departure point, this column first reviews the facts and judicial rationale in Munroe, because it provides food for thought for education leaders, and then offers updated recommendations for SBOs, their boards, and other education leaders to consider in developing policies to regulate teacher blogs

Direct Graphene Growth on Insulator

Fabrication of graphene devices is often hindered by incompatibility between the silicon technology and the methods of graphene growth. Exfoliation from graphite yields excellent films but is good mainly for research. Graphene grown on metal has a technological potential but requires mechanical transfer. Growth by SiC decomposition requires a temperature budget exceeding the technological limits. These issues could be circumvented by growing graphene directly on insulator, implying Van der Waals growth. During growth, the insulator acts as a support defining the growth plane. In the device, it insulates graphene from the Si substrate. We demonstrate planar growth of graphene on mica surface. This was achieved by molecular beam deposition above 600{\deg}C. High resolution Raman scans illustrate the effect of growth parameters and substrate topography on the film perfection. Ab initio calculations suggest a growth model. Data analysis highlights the competition between nucleation at surface steps and flat surface. As a proof of concept, we show the evidence of electric field effect in a transistor with a directly grown channel.Comment: 13 pages, 6 figure

Reconstruction and visualization of planetary nebulae

Journal ArticleAbstract-From our terrestrially confined viewpoint, the actual three-dimensional shape of distant astronomical objects is, in general, very challenging to determine. For one class of astronomical objects, however, spatial structure can be recovered from conventional 2D images alone. So-called planetary nebulae (PNe) exhibit pronounced symmetry characteristics that come about due to fundamental physical processes. Making use of this symmetry constraint, we present a technique to automatically recover the axisymmetric structure of many planetary nebulae from photographs. With GPU-based volume rendering driving a nonlinear optimization, we estimate the nebula's local emission density as a function of its radial and axial coordinates and we recover the orientation of the nebula relative to Earth. The optimization refines the nebula model and its orientation by minimizing the differences between the rendered image and the original astronomical image. The resulting model allows creating realistic 3D visualizations of these nebulae, for example, for planetarium shows and other educational purposes. In addition, the recovered spatial distribution of the emissive gas can help astrophysicists gain deeper insight into the formation processes of planetary nebulae

A Method for Determining Optimal Tenant Mix (Including Location) in Shopping Centers

With assumptions like maximally productive lease structure, equilibrium space allocation, a just-saturated retail market, and zero vacancies, store location would be the remaining variable in obtaining “optimal tenant mix.” Here we illustrate an optimization program to maximize tenant location within shopping malls taking into consideration the two complementary effects present in malls: bid rent theory and revised central place theory. Suggested distance and connection matrices for the quadratic assignment program (QAP) solving for an optimal tenant mix are demonstrated

Current-phase relations of few-mode InAs nanowire Josephson junctions

Gate-tunable semiconductor nanowires with superconducting leads have great potential for quantum computation and as model systems for mesoscopic Josephson junctions. The supercurrent, $I$, versus the phase, $\phi$, across the junction is called the current-phase relation (CPR). It can reveal not only the amplitude of the critical current, but also the number of modes and their transmission. We measured the CPR of many individual InAs nanowire Josephson junctions, one junction at a time. Both the amplitude and shape of the CPR varied between junctions, with small critical currents and skewed CPRs indicating few-mode junctions with high transmissions. In a gate-tunable junction, we found that the CPR varied with gate voltage: Near the onset of supercurrent, we observed behavior consistent with resonant tunneling through a single, highly transmitting mode. The gate dependence is consistent with modeled subband structure that includes an effective tunneling barrier due to an abrupt change in the Fermi level at the boundary of the gate-tuned region. These measurements of skewed, tunable, few-mode CPRs are promising both for applications that require anharmonic junctions and for Majorana readout proposals

Canal Seepage Reduction by Soil Compaction

Large-scale tests were conducted of in-place compaction of irrigation district earthen canal bottoms and sides. Five canal pools with sandy loam soils were compacted. Seepage reduction of about 86% was obtained when the sides and bottoms were compacted; reductions of 12 – 31% were obtained when only sides were compacted