Linear growth of spiral SASI modes in core-collapse supernovae

Two-dimensional axisymmetric simulations have shown that the post-bounce accretion shock in core collapse supernovae is subject to the Spherical Accretion Shock Instability, or SASI. Recent three-dimensional simulations have revealed the existence of a non-axisymmetric mode of the SASI as well, where the postshock flow displays a spiral pattern. Here we investigate the growth of these spiral modes using two-dimensional simulations of the post-bounce accretion flow in the equatorial plane of a core-collapse supernova. By perturbing a steady-state model we are able to excite both one, two and three-armed spiral modes that grow exponentially with time, demonstrating that these are linearly unstable modes closely related to the original axisymmetric sloshing modes. By tracking the distribution of angular momentum, we show that these modes are able to efficiently separate the angular momentum of the accretion flow (which maintains a net angular momentum of zero), leading to a significant spin-up of the underlying accreting proto-neutron star.Comment: To be published in The Astrophysical Journa

Data handling methods and target detection results for multibeam and sidescan data collected as part of the search for SwissAir Flight 111

The crash of SwissAir Flight 111, off Nova Scotia in September 1998, triggered one of the largest seabed search surveys in Canadian history. The primary search tools used were sidescan sonars (both conventional and focussed types) and multibeam sonars. The processed search data needed to be distributed on a daily basis to other elements of the fleet for precise location of divers and other optical seabed search instruments (including laser linescan and ROV video). As a result of the glacial history of the region, many natural targets, similar in gross nature to aircraft debris were present. These included widespread linear bedrock outcrop patterns together with near ubiquitous glacial erratic boulders. Because of the severely broken-up nature of the remaining aircraft debris, sidescan imaging alone was often insufficient to unambiguously identify targets. The complementary attributes of higher resolution, but poorly located, sidescan imagery together with slightly lower resolution, but excellently navigated multibeam sonar proved to be one of critical factors in the success of the search. It proved necessary to rely heavily on the regional context of the seabed (provided by the multibeam sonar bathymetry and backscatter imagery) to separate natural geomorphic targets from anomalous anthropogenic debris. In order to confidently prove or disprove a potential target, the interpreter required simultaneous access to the full resolution sidescan data in the geographic context of the multibeam framework. Specific software tools had to be adapted or developed shipboard to provide this capability. Whilst developed specifically for this application, these survey tools can provide improved processing speed and confidence as part of more general mine hunting, hydrographic, engineering or scientific surveys

Contrast-enhanced ultrasound identifies early extrahepatic collateral contributing to residual hepatocellular tumor viability after transarterial chemoembolization.

The mainstay of treatment for unresectable hepatocellular carcinoma is locoregional therapy including percutaneous ablation and transarterial chemo- and radioembolization. While monitoring for tumor response after transarterial chemoembolization is crucial, current imaging strategies are suboptimal. The standard of care is contrast-enhanced magnetic resonance imaging or computed tomography imaging performed at least 4 to 6 weeks after therapy. We present a case in which contrast-enhanced ultrasound identified a specific extra-hepatic collateral from the gastroduodenal artery supplying residual viable tumor and assisting with directed transarterial management

The Value of the Cosmological Constant

We make the cosmological constant, {\Lambda}, into a field and restrict the variations of the action with respect to it by causality. This creates an additional Einstein constraint equation. It restricts the solutions of the standard Einstein equations and is the requirement that the cosmological wave function possess a classical limit. When applied to the Friedmann metric it requires that the cosmological constant measured today, t_{U}, be {\Lambda} ~ t_{U}^(-2) ~ 10^(-122), as observed. This is the classical value of {\Lambda} that dominates the wave function of the universe. Our new field equation determines {\Lambda} in terms of other astronomically measurable quantities. Specifically, it predicts that the spatial curvature parameter of the universe is {\Omega}_{k0} \equiv -k/a_(0)^(2)H^2= -0.0055, which will be tested by Planck Satellite data. Our theory also creates a new picture of self-consistent quantum cosmological history.Comment: 6 pages. This article received Third Prize in the 2011 Gravity Research Foundation Awards for Essays on Gravitatio

SIMD Tree Algorithms for Image Correlation

This paper examines the applicability of fine-grained tree-structured SIMD machines, which are amenable to highly efficient VLSI implementation to image correlation which is a representative of image window-based operations. Several algorithms are presented for image shifting and correlation operations. A particular massively parallel machine called NON-VON is used for purposes of explication and performance evaluation. Although the most recent version of the NON-VON architecture also supports other interconnection topologies and execution modes, only its tree-structured communication capabilities and its SIMD mode of execution are considered in this paper. Novel algorithmic techniques are described, such as vertical pipelining, subproblem partitioning, associative matching, and data duplication that effectively exploit the massive parallelism available in fine-grained SIMD tree machines while avoiding communication bottlenecks. Simulation results are presented and compared with results obtained or forecast for other highly parallel machines. The relative advantages and limitations of the class of machines under consideration are then outlined

Evaluation of Hepatocellular Carcinoma Transarterial Chemoembolization using Quantitative Analysis of 2D and 3D Real-time Contrast Enhanced Ultrasound.

Quantitative 2D and 3D contrast-enhanced ultrasound (CEUS) was assessed to evaluate early transarterial chemoembolization (TACE) treatment response. Seventeen patients scheduled for TACE for the treatment of hepatocellular carcinoma participated in the study. 2D and 3D CEUS were performed for each patient at three time points: Prior to TACE, 1-2 weeks post TACE, and 1 month post TACE. Peak-intensities of the tumor and surrounding liver tissue were calculated from 2D and 3D data before and after TACE and used to evaluate tumor treatment response. Residual tumor percentages were calculated from 2D and 3D CEUS acquired 1-2 weeks and 1 month post TACE and compared with results from MRI 1 month post TACE. Nine subjects had complete response while 8 had incomplete response. Peak-intensities of the tumor from 3D CEUS prior to TACE were similar between the complete and incomplete treatment groups (p = 0.70), while 1-2 weeks (p \u3c 0.01) and 1 month post treatment (p \u3c 0.01) were significantly lower in the complete treatment group than in the incomplete treatment group. For 2D CEUS, only the peak-intensity values of the tumor from 1 month post TACE were significantly different (p \u3c 0.01). The correlation coefficients between 2D and 3D residual tumor estimates 1-2 weeks post TACE and the estimates from MRI were 0.73 and 0.94, respectively, while those from 2D and 3D CEUS 1 month post TACE were 0.66 and 0.91, respectively. Quantitative analysis on 2D and 3D CEUS shows potential to differentiate patients with complete versus incomplete response to TACE as early as 1-2 weeks post treatment