On the Radio Polarization Signature of Efficient and Inefficient Particle Acceleration in Supernova Remnant SN 1006

We present a radio polarization study of SN 1006, based on combined VLA and ATCA observations at 20 cm that resulted in sensitive images with an angular resolution of 10 arcsec. The fractional polarization in the two bright radio and X-ray lobes of the SNR is measured to be 0.17, while in the southeastern sector, where the radio and non-thermal X-ray emission are much weaker, the polarization fraction reaches a value of 0.6 +- 0.2, close to the theoretical limit of 0.7. We interpret this result as evidence of a disordered, turbulent magnetic field in the lobes, where particle acceleration is believed to be efficient, and a highly ordered field in the southeast, where the acceleration efficiency has been shown to be very low. Utilizing the frequency coverage of our observations, an average rotation measure of ~12 rad/m2 is determined from the combined data set, which is then used to obtain the intrinsic direction of the magnetic field vectors. While the orientation of magnetic field vectors across the SNR shell appear radial, a large fraction of the magnetic vectors lie parallel to the Galactic Plane. Along the highly polarized southeastern rim, the field is aligned tangent to the shock, and therefore also nearly parallel to the Galactic Plane. These results strongly suggest that the ambient field surrounding SN 1006 is aligned with this direction (i.e., from northeast to southwest) and that the bright lobes are due to a polar cap geometry. Our study establishes that the most efficient particle acceleration and generation of magnetic turbulence in SN 1006 is attained for shocks in which the magnetic field direction and shock normal are quasi-parallel, while inefficient acceleration and little to no generation of magnetic turbulence obtains for the quasi-perpendicular case.Comment: Accepted for publication in Astronomical Journa

Exploratory Study on Selected Philippine Agricultural Commodity Import Statistics vis-Ã -vis Export Statistics of the Exporting Countries

Using the import data compiled by the Philippines and comparing these with data as reported by the exporting countries, this study aims to determine the disparity of the statistics from the two sources on the quantity and value of selected agricultural commodities for the years 2000 to 2005. The products covered by this study consist of wholly or semi-milled rice, maize (corn), live poultry, domestic fowls, ducks, geese, frozen meat of bovine animals, apples, oranges, onions and shallots, and garlic. The differences in statistics on the bilateral transactions─in terms of FOB values, quantities, and derived unit prices─are examined by using percentage differences, the implicit minimal measurement error (IMME), and the Wilcoxon Matched-Pair Signed-Ranks (Wilcoxon-MPSR) test. Results show that considerable discrepancies between import and export statistics do exist. The discrepancy may reflect both legitimate conceptual differences between Philippine imports and exports statistics of the exporting countries, as well as errors in reporting. The discrepancy is further substantiated by the results of the Wilcoxon-MPSR test, which show that these differences are significant.

Punk in Translation: A Music and Fashion History of Punk

Senior Project submitted to The Division of Social Studies of Bard College

A New Bispectral Test for Nonlinear Serial Dependence

Bispectrum, nonlinearity, time series analysis

Synchronous and asynchronous teacher electronic feedback and learner uptake in ESL composition

We know little about how teacher feedback and student revisions are influenced when feedback is given electronically. This study contributes to a better understanding of teacher electronic feedback (TEF) in second language writing by investigating its effectiveness in face-to-face and online ESL writing classes in which TEF was offered asynchronously, as Word comments and track changes in electronic drafts, as well as in synchronous text chats between teachers and students. TEF was extracted from 93 drafts written by 64 students and 93 chats in which they conferenced with their teachers. Students’ perceptions about TEF were then solicited via a survey. Additionally, the three participating teachers were interviewed about their use of TEF. Findings show that most TEF was successfully implemented or attempted, and that it was focused on content. Important conclusions are that TEF is effective, and synchronous TEF effectively reinforces asynchronous TEF

On A* Graph Search Algorithm Heuristics Implementation Towards Efficient Path Planning in the Presence of Obstacles

Nowadays it has become more and more important to reach a destination in a short time, in the shortest path between all the options and possibilities. This need is addressed by different search engines like google maps for example and it is common sense that the user is expecting the result in the least amount of time. The scope of this publication, is to help the reader understand the mechanism behind pathfinding algorithms integrated with heuristics and on how to choose between them in a given case study. Moreover, this paper aims at illustrating, after pathfinding algorithm selection, how to tweak and improve it in order to better fit the given setup scenario. With this respect, it will be shown how the A* algorithm computationally performs in a graph theoretic grid setup, initially in a small one and then, in a graph grid with a 10-fold increase of the initial setup dimensions. This experimental study compares two different heuristics in A* implementation, the Euclidean distance heuristic and the Chebyshev heuristic. Computational time results are compared with respect to the time taken to produce a final result in each case. Moreover, the total number of nodes involved in the path as well as the total cost estimated are considered per each case. These results are further compared with the ones derived when obstacles are introduced in the graph grid setup and how the algorithm will handle such scenarios is illustrated. This paper aims at providing information to researchers so that to understand what analysis needs to be done when selecting heuristics associated with pathfinding algorithms heuristics, and at providing relevant performance metrics regarding shortest path planning estimation between two predefined nodes in a graph grid setup. Moreover, aims at providing information on how the heuristics define the decision-making process in the A* algorithm and on how to weight the time/cost factors importance based on specific use cases

The symbiotic binary system RX Puppis: a possible recurrent nova with a Mira companion

We present an analysis of photometric and spectroscopic observations of the symbiotic binary system RX Pup with the aims of developing a reliable binary for the system and identifying mechanisms responsible for its spectacular activity. The binary is composed of a long-perod Mira variable surrounded by a thick dust shell and a hot white dwarf companion. The hot component produces practically all activity observed in the UV, optical and radio range, while variable obscuration of the Mira by circumstellar dust is responsible for long-term changes in the near-IR magnitudes. The observations show RX Pup underwent a nova-like eruption during the last three decades. The hot component contracted in radius at roughly constant luminosity from 1975 to 1986, and was the source of a strong stellar wind which prevented it from accreting material lost in the Mira wind. Around 1988/9 the hot component turned over in the HR diagram and by 1991 its luminosity had faded by a factor of about 30 with respect to the maximum plateau value and the hot wind had practically ceased. By 1995 the nova remnant started to accrete material from the Mira wind, as indicated by a general increase in intensity of the optical continuum and HI emission. The quiescent spectrum resembles the quiescent spectra of symbiotic recurrent novae, and its intensity indicates the hot component must accrete as much as about 1 per cent of the Mira wind, which is more or less the amount predicted by Bondi-Hoyle theory. The earliest observational records from the 1890s suggest that another nova-like eruption of RX Pup occurred around 1894.Comment: 23 pages, 12 figues, MNRAS - accepte