The ASCA Spectrum of the Vela Pulsar Jet

ROSAT observations of the Vela pulsar and its surroundings revealed a collimated X-ray feature almost 45' in length (Markwardt & Ogelman 1995), interpreted as the signature ``cocoon'' of a one-sided jet from the Vela pulsar. We report on a new ASCA observation of the Vela pulsar jet at its head, the point where the jet is believed to interact with the supernova remnant. The head is clearly detected, and its X-ray spectrum is remarkably similar to the surrounding supernova remnant spectrum, extending to X-ray energies of at least 7 keV. A ROSAT+ASCA spectrum can be fit by two-component emission models but not standard one-component models. The lower energy component is thermal and has a temperature of 0.29+/-0.03 keV (1 sigma); the higher energy component can be fit by either a thermal component of temperature ~4 keV or a power law with photon index ~2.0. Compared to the ROSAT-only results, the mechanical properties of the jet and its cocoon do not change much. If the observed spectrum is that of a hot jet cocoon, then the speed of the jet is at least 800 km s^-1, depending on the angle of inclination. The mechanical power driving the jet is >10^36 erg s^-1, and the mass flow rate at the head is > 10^-6 M_sun yr^-1. We conclude that the jet must be entraining material all along its length in order to generate such a large mass flow rate. We also explore the possibility that the cocoon emission is synchrotron radiation instead of thermal.Comment: 12 pages, LaTeX in AAS v4.0 preprint style, two PS figures, accepted for publication in the ApJ Letter

Spectral pitch distance and microtonal melodies

We present an experiment designed to test the effectiveness of spectral pitch distance at modeling the degree of “affinity” or “fit” of pairs of successively played tones or chords (spectral pitch distance is the cosine distance between salience-weighted, Gaussian-smoothed, pitch domain embeddings of spectral pitches—typically the first eight to ten partials of a tone). The results of a previously conducted experiment, which collected ratings of the perceived similarity and fit of root-position major and minor triads, suggest the model works well for pairs of triads in standard 12-tone equal temperament tunings. The new experiment has been designed to test the effectiveness of spectral pitch distance at modeling the affinity of tones in microtonal melodies where the partials of the tones can be variably tempered between being perfectly harmonic and perfectly matched to the underlying microtonal tuning. The use of microtonal tunings helps to disambiguate innate perceptual (psychoacoustical) responses from learned (cultural) responses. Participants are presented with a software synthesizer containing two unlabeled controls: one adjusts the precise tuning of the tones; the other adjusts the extent to which the spectrum is tempered to match the tuning (as set by the first control). A selection of microtonal melodies are played in different tunings, and the participants adjust one, or both, controls until they find a “sweet spot” at which the music sounds most “in-tune” and the notes best “fit” together. The results of these experiments will be presented and discussed

Metrics for pitch collections

Models of the perceived distance between pairs of pitch collections are a core component of broader models of the perception of tonality as a whole. Numerous different distance measures have been proposed, including voice-leading, psychoacoustic, and pitch and interval class distances; but, so far, there has been no attempt to bind these different measures into a single mathematical framework, nor to incorporate the uncertain or probabilistic nature of pitch perception (whereby tones with similar frequencies may, or may not, be heard as having the same pitch). To achieve these aims, we embed pitch collections in novel multi-way expectation arrays, and show how metrics between such arrays can model the perceived dissimilarity of the pitch collections they embed. By modeling the uncertainties of human pitch perception, expectation arrays indicate the expected number of tones, ordered pairs of tones, ordered triples of tones and so forth, that are heard as having any given pitch, dyad of pitches, triad of pitches, and so forth. The pitches can be either absolute or relative (in which case the arrays are invariant with respect to transposition). We provide a number of examples that show how the metrics accord well with musical intuition, and suggest some ways in which this work may be developed

Mining Missing Hyperlinks from Human Navigation Traces: A Case Study of Wikipedia

Hyperlinks are an essential feature of the World Wide Web. They are especially important for online encyclopedias such as Wikipedia: an article can often only be understood in the context of related articles, and hyperlinks make it easy to explore this context. But important links are often missing, and several methods have been proposed to alleviate this problem by learning a linking model based on the structure of the existing links. Here we propose a novel approach to identifying missing links in Wikipedia. We build on the fact that the ultimate purpose of Wikipedia links is to aid navigation. Rather than merely suggesting new links that are in tune with the structure of existing links, our method finds missing links that would immediately enhance Wikipedia's navigability. We leverage data sets of navigation paths collected through a Wikipedia-based human-computation game in which users must find a short path from a start to a target article by only clicking links encountered along the way. We harness human navigational traces to identify a set of candidates for missing links and then rank these candidates. Experiments show that our procedure identifies missing links of high quality

Cardiac Specific Gene Expression Changes in Long Term Culture of Murine Mesenchymal Stem Cells

Murine MSCs are a readily available source of adult stem cells enabling extensive in vitro study of this cell population. MSCs have been described as multipotent, and have been proven capable of differentiation into several connective tissue types. Furthermore some studies have suggested an ability to differentiate into non-connective tissue cell types such as the cardiomyocyte. The aim of this study was to differentiate murine MSCs toward cardiac lineage with the commonly used method of culture with 5’ Azacytidine. Critically, baseline analysis of gene expression of passage four MSCs demonstrated expression of key cardiac markers including cardiac troponin T and I, and the ryanodine receptor. Furthermore, expression analysis of these genes changed with time in culture and passage number. However, there was no significant alteration when cells were subjected to a differentiation protocol. This study therefore highlights the importance of analyzing baseline cells extensively, and indicates the limitations in extrapolating data for comparison between species. Furthermore this data brings into question the efficacy of cardiac differentiation using MSCs

Panax ginseng has no effect on indices of glucose regulation following acute or chronic ingestion in healthy volunteers

In the absence of effective pharmacotherapy for diabetes there has been an increase in the use of, and research into, alternative treatment strategies. These include exercise, dietary interventions and the use of supplements including extracts of ginseng. Two separate, placebo-controlled, double-blind, cross-over studies investigating the effects of chronic ingestion of Panax ginseng (study 1 used G115, study 2 used Cheong Kwan Jang) on glycated Hb (HbA1c; study 1, n 18; study 2, n 11), fasting plasma insulin (study 1, n 17; study 2, n 12), fasting plasma glucose and postprandial response (following breakfast) (study 1, n 23; study 2, n 14) in healthy volunteers are reported. In both studies it was found that Panax ginseng had no effect on any gluco-regulatory parameter investigated. These results are not consistent with those reported for a diabetic sample (albeit using slightly different outcomes). These results would suggest that chronic use of Panax ginseng by non-diabetic individuals will have little long-term effect on glucose regulation. The benefits to glucose regulation associated with long-term ginseng use may only be present in populations with compromised glucose control; however, further research is needed to confirm such a speculation

Deformations of elliptic fibre bundles in positive characteristic

We study deformation theory of elliptic fibre bundles over curves in positive characteristics. As applications, we give examples of non-liftable elliptic surfaces in charactertic two and three, which answers a question of Katsura and Ueno. Also, we construct a class of elliptic fibrations, whose liftability is equivalent to a conjecture of F. Oort concerning the liftability of automorphisms of curves. Finally, we classify deformations of bielliptic surfaces.Comment: Many typos fixed (thanks to the referee). Minor improvements in presentatio

New Constraints on the Energetics, Progenitor Mass, and Age of the Supernova Remnant G292.0+1.8 Containing PSR J1124-5916

We present spatially resolved spectroscopy of the supernova remnant (SNR) G292.0+1.8 with the Chandra X-ray observatory. This SNR contains the 135 ms pulsar, J1124-5916. We apply non-equilibrium ionization (NEI) models to the data. By comparing the derived abundances with those predicted from nucleosynthesis models, we estimate a progenitor mass of 30-40 solar masses. We also derive the intrinsic parameters of the supernova explosion such as its energy, the age of the SNR, the blast wave velocity, and the swept-up mass. In the Sedov interpretation, our estimated SNR age of 2,600 years is close to the pulsar's characteristic age of 2,900 years. This confirms the pulsar/SNR association and relaxes the need for the pulsar to have a non-canonical value for the braking index, a large period at birth or a large transverse velocity. We discuss the properties of the pulsar wind nebula (PWN) in the light of the Kennel and Coroniti model and estimate the pulsar wind magnetization parameter. We also report the first evidence for steepening of the power law spectral index with increasing radius from the pulsar.Comment: 5 pages, 3 figures. To appear in ApJL, Feb 1 2003 (submitted Oct 9 2002, accepted Dec 19 2002

Radio Emission from the Composite Supernova Remnant G326.3-1.8 (MSH15-56)

High resolution radio observations of the composite supernova remnant (SNR) G326.3-1.8 or MSH 15-56 with the Australia Telescope Compact Array show details of both the shell and the bright plerion which is offset about 1/3 of the distance from the center of the SNR to the shell. The shell appears to be composed of thin filaments, typical of older shell SNRs. The central part of the elongated plerion is composed of a bundle of parallel ridges which bulge out at the ends and form a distinct ring structure on the northwestern end. The magnetic field with a strength of order 45 microGauss, is directed along the axis of the ridges but circles around the northwestern ring. This plerion is large and bright in the radio but is not detected in x-ray or optical wavelengths. There is, however, a faint hard x-ray feature closer to the shell outside the plerion. Perhaps if the supernova explosion left a rapidly moving magnetar with large energy input but initially rapid decay of both relativistic particles and magnetic field, the observed differences with wavelength could be explained.Comment: 15 pages, 10 figures, accepted by Ap

Radio Observations of the Supernova Remnant Candidate G312.5-3.0

The radio images from the Parkes-MIT-NRAO (PMN) Southern Sky Survey at 4850 MHz have revealed a number of previously unknown radio sources. One such source, G312.5-3.0 (PMN J1421-6415), has been observed using the multi-frequency capabilities of the Australia Telescope Compact Array (ATCA) at frequencies of 1380 MHz and 2378 MHz. Further observations of the source were made using the Molonglo Observatory Synthesis Telescope (MOST) at a frequency of 843 MHz. The source has an angular size of 18 arcmin and has a distinct shell structure. We present the reduced multi-frequency observations of this source and provide a brief argument for its possible identification as a supernova remnant.Comment: 5 pages, 5 figures, Accepted for publication in MNRA