20 cm VLA Radio-Continuum Study of M31 - Images and Point Source Catalogues DR2: Extraction of a supernova remnant sample

We present Data Release 2 of the Point Source Catalogue created from a series of previously constructed radio-continuum images of M31 at lambda=20 cm (nu=1.4 GHz) from archived VLA observations. In total, we identify a collection of 916 unique discrete radio sources across the field of M31. Comparing these detected sources to those listed by Gelfand et al. (2004) at lambda=92 cm, the spectral index of 98 sources has been derived. The majority (73%) of these sources exhibit a spectral index of alpha <-0.6, indicating that their emission is predominantly non-thermal in nature, which is typical for background objects and Supernova Remnants (SNRs). Additionally, we investigate the presence of radio counterparts for some 156 SNRs and SNR candidates, finding a total of only 13 of these object in our images within a 5 arcsec search area. Auxiliary optical, radio and X-ray catalogs were cross referenced highlighting a small population of SNR and SNR candidates common to multi-frequency domains

The number of independent sets in a graph with small maximum degree

Let ${\rm ind}(G)$ be the number of independent sets in a graph $G$. We show that if $G$ has maximum degree at most $5$ then $${\rm ind}(G) \leq 2^{{\rm iso}(G)} \prod_{uv \in E(G)} {\rm ind}(K_{d(u),d(v)})^{\frac{1}{d(u)d(v)}}$$ (where $d(\cdot)$ is vertex degree, ${\rm iso}(G)$ is the number of isolated vertices in $G$ and $K_{a,b}$ is the complete bipartite graph with $a$ vertices in one partition class and $b$ in the other), with equality if and only if each connected component of $G$ is either a complete bipartite graph or a single vertex. This bound (for all $G$) was conjectured by Kahn. A corollary of our result is that if $G$ is $d$-regular with $1 \leq d \leq 5$ then $${\rm ind}(G) \leq \left(2^{d+1}-1\right)^\frac{|V(G)|}{2d},$$ with equality if and only if $G$ is a disjoint union of $V(G)/2d$ copies of $K_{d,d}$. This bound (for all $d$) was conjectured by Alon and Kahn and recently proved for all $d$ by the second author, without the characterization of the extreme cases. Our proof involves a reduction to a finite search. For graphs with maximum degree at most $3$ the search could be done by hand, but for the case of maximum degree $4$ or $5$, a computer is needed.Comment: Article will appear in {\em Graphs and Combinatorics

Wage theft is widespread, but politics and policies can play a powerful role in reducing it.

Wage theft is pervasive in America; in a new study of low-wage workers across the US, Daniel J. Galvin finds that 16 percent were paid less than their state’s minimum wage. He also finds that workers in those states which had greater employment law protections tended to have a lower chance of experiencing wage theft, and that those protections tended to be in states with unified Democratic governments. With Donald Trump’s Labor Department unlikely to do much to address the problem, he writes that workers’ advocates will need to build coalitions and work with Democrats at the state and city level in order to ensure workers are protected from wage theft

Mandarin speech perception in combined electric and acoustic stimulation.

For deaf individuals with residual low-frequency acoustic hearing, combined use of a cochlear implant (CI) and hearing aid (HA) typically provides better speech understanding than with either device alone. Because of coarse spectral resolution, CIs do not provide fundamental frequency (F0) information that contributes to understanding of tonal languages such as Mandarin Chinese. The HA can provide good representation of F0 and, depending on the range of aided acoustic hearing, first and second formant (F1 and F2) information. In this study, Mandarin tone, vowel, and consonant recognition in quiet and noise was measured in 12 adult Mandarin-speaking bimodal listeners with the CI-only and with the CI+HA. Tone recognition was significantly better with the CI+HA in noise, but not in quiet. Vowel recognition was significantly better with the CI+HA in quiet, but not in noise. There was no significant difference in consonant recognition between the CI-only and the CI+HA in quiet or in noise. There was a wide range in bimodal benefit, with improvements often greater than 20 percentage points in some tests and conditions. The bimodal benefit was compared to CI subjects' HA-aided pure-tone average (PTA) thresholds between 250 and 2000 Hz; subjects were divided into two groups: "better" PTA (&lt;50 dB HL) or "poorer" PTA (&gt;50 dB HL). The bimodal benefit differed significantly between groups only for consonant recognition. The bimodal benefit for tone recognition in quiet was significantly correlated with CI experience, suggesting that bimodal CI users learn to better combine low-frequency spectro-temporal information from acoustic hearing with temporal envelope information from electric hearing. Given the small number of subjects in this study (n = 12), further research with Chinese bimodal listeners may provide more information regarding the contribution of acoustic and electric hearing to tonal language perception

The radio continuum emission of star forming galaxies at low to high redshift

In this thesis, the radio-continuum emission of starburst galaxies is explored to understand the physical processes that trace star formation. Separating and constraining these processes require a broad, densely sampled spectral energy distribution that can be used to apply and constrain various radiative transfer models. Existing tracers of star formation include a suite of multi-wavelength diagnostics, including UV, optical, infrared, nebular transitions, and radio continuum. At present, optical and near infrared observations have been the most successful at probing the high redshift volume and constraining the star formation at the earliest epochs of the Universe. However, such approaches are critically awed in that they are subject to the effects of dust obscuration, requiring sophisticated methods to recover the intrinsic luminosities of the optical tracers of star formation. In the high redshift Universe, these corrections are increasingly compromised and uncertain. Radio-continuum measurements of star formation have the potential to be the most reliable in this high redshift regime because they are not affected by the presence of dust, allowing observers to acquire uncompromised measures of star formation. At frequencies below _ 2 GHz, the radio continuum is made up overwhelmingly by non-thermal synchrotron emission, produced by near light speed cosmic rays interacting with the large-scale magnetic structure of a galaxy. Although this type of emission is not a direct product of stars, it has been reasonably well calibrated to exploit the far-infrared to radio correlation to obtain a measure of star formation. Our current understanding of the far-infrared to radio correlation suggests that there should be an evolution as a function of redshifts; however, observationally evidence both confirms and rejects this evolution hypothesis. As the far-infrared to radio correlation is the foundation of star formation rate indicators based on the radio continuum for frequencies where synchrotron emission is a significant component of the observed spectrum, there is a requirement to investigate, and if necessary repair, radio-based star formation rate measures in preparation for radio telescopes like the Square Kilometre Array. Throughout my candidature, I have studied the spectral energy distribution of 30 local galaxies that were selected based on their high star formation rates, as indicated by their radio and infrared emission data collected from existing surveys. Across a broad frequency range spanning 80MHz to 50 GHz, the underlying physical processes driving the radio continuum have been disentangled. By comparing these products to other multi-wavelength indicators of star formation, we can begin to understand the radio-based tracers for faint star forming galaxies at high redshift that the next generation of radio telescopes will reveal

The role of modularity in knowledge protection and diffusion: The case of Nokia and Ericsson

When network externalities are important for a product, there is often a move to introduce standards on the basis of product modularity such that product interfaces remain constant over time and across brands. This allows other firms to develop complementary products and services. However, introducing standardization can lead to a weakening of the technology developer?s competitive position. Standardization makes much of the underlying product knowledge accessible, reducing barriers to entry such that other manufacturers are able to quickly develop comparable products. Thus in cases where network externalities are important and standardization needs to occur, there are also needs to protect knowledge that may form the basis for the developer?s competitive position within the industry. To review the differing approaches to managing technical knowledge we deconstruct product architectures into clusters of technical knowledge that we refer to as information structures. We use the notion of knowledge structures to study how different components of a product architecture can be made open in the form of standards, whereas other elements can be heavily protected. To study these issues, we chose the mobile phone industry. Nokia and Ericsson were instrumental in developing the GSM standard and pushing for its institutionalising across Europe. However, both of these firms still remain dominant in the manufacture of mobile phones. Thus we sought to observe how they managed various clusters of technical knowledge such that the standard was open, a range of firms has produced complementary products, and yet Nokia and Ericsson?s competitive position within the industry has not been diminished