6,403 research outputs found
Generalised Umbral Moonshine
Umbral moonshine describes an unexpected relation between 23 finite groups
arising from lattice symmetries and special mock modular forms. It includes the
Mathieu moonshine as a special case and can itself be viewed as an example of
the more general moonshine phenomenon which connects finite groups and
distinguished modular objects. In this paper we introduce the notion of
generalised umbral moonshine, which includes the generalised Mathieu moonshine
[Gaberdiel M.R., Persson D., Ronellenfitsch H., Volpato R., Commun. Number
Theory Phys. 7 (2013), 145-223] as a special case, and provide supporting data
for it. A central role is played by the deformed Drinfel'd (or quantum) double
of each umbral finite group , specified by a cohomology class in
. We conjecture that in each of the 23 cases there exists a rule
to assign an infinite-dimensional module for the deformed Drinfel'd double of
the umbral finite group underlying the mock modular forms of umbral moonshine
and generalised umbral moonshine. We also discuss the possible origin of the
generalised umbral moonshine
Wide-field direct CCD observations supporting the Astro-1 Space Shuttle mission's Ultraviolet Imaging Telescope
Wide field direct CCD observations are being obtained to support and complement the vacuum-ultraviolet (VUV) images provided by Astro's Ultraviolet Imaging Telescope (UIT) during a Space Shuttle flight in December 1990. Because of the wide variety of projects addressed by UIT, the fields observed include (1) galactic supernova remnants such as the Cygnus Loop and globular clusters such as Omega Cen and M79; (2) the Magellanic Clouds, M33, M81, and other galaxies in the Local Group; and (3) rich clusters of galaxies, principally the Perseus cluster and Abell 1367. Ground-based observations have been obtained for virtually all of the Astro-1 UIT fields. The optical images allow identification of individual UV sources in each field and provide the long baseline in wavelength necessary for accurate analysis of UV-bright sources. To facilitate use of our optical images for analysis of UIT data and other projects, we plan to archive them, with the UIT images, at the National Space Science Data Center (NSSDC), where they will be universally accessible via anonymous FTP. The UIT, one of three telescopes comprising the Astro spacecraft, is a 38-cm f/9 Ritchey-Chretien telescope on which high quantum efficiency, solar-blind image tubes are used to record VUV images on photographic film. Five filters with passbands centered between 1250A and 2500A provide both VUV colors and a measurement of extinction via the 2200A dust feature. The resulting calibrated VUV pictures are 40 arcminutes in diameter at 2.5 arcseconds resolution. The capabilities of UIT, therefore, complement HST's WFPC: the latter has 40 times greater collecting area, while UIT's usable field has 170 times WFPC's field area
UIT support observations archive
We are in the process of archiving the approximately 1.2Tbytes of imaging data acquired in support of UIT observations. The UIT is one of three telescopes comprising the ASTRO spacecraft and is a 38-cm f/9 Ritchey-Chretien telescope with wavelength coverage 1200 A to 3000 A and a 40 arcminute diameter field-of-view at 4 min FWHM resolution. During the ASTRO shuttle mission, there were 65 different pointings (some with multiple targets) of the UIT and hence 65 fields. Our support data of these fields were obtained with the KPNO and CTIO 0.9m telescopes and several of the 2048x2048 CCD's. Our images are typically about 20 acrminutes on a side and contain the entire UV target except for nearby galaxies, for which mosaiced images were created. All good quality images in the broadband and narrow band filters for every target are being archived. Though all of the UIT targets were well studied astronomical objects, these frames are many of the first large field format images of them and, when combined with the soon to be released UV frames, provide a unique dataset. These data were already used to address a wide variety of astronomical questions. Vacuum ultraviolet (VUV) observations were used to study star formation in a sample of nearby galaxies, since integrated VUV - optical colors provide the most sensitive available measure of the formation rate of massive stars. The blue stages later in stellar evolution are also being studied. These data allow more accurate determination of the helium and metallicities of hothorzontal branch stars. These data are being prepared to release to the public in CD-ROM format through the National Space Science Data Center
An Army of Me: Sockpuppets in Online Discussion Communities
In online discussion communities, users can interact and share information
and opinions on a wide variety of topics. However, some users may create
multiple identities, or sockpuppets, and engage in undesired behavior by
deceiving others or manipulating discussions. In this work, we study
sockpuppetry across nine discussion communities, and show that sockpuppets
differ from ordinary users in terms of their posting behavior, linguistic
traits, as well as social network structure. Sockpuppets tend to start fewer
discussions, write shorter posts, use more personal pronouns such as "I", and
have more clustered ego-networks. Further, pairs of sockpuppets controlled by
the same individual are more likely to interact on the same discussion at the
same time than pairs of ordinary users. Our analysis suggests a taxonomy of
deceptive behavior in discussion communities. Pairs of sockpuppets can vary in
their deceptiveness, i.e., whether they pretend to be different users, or their
supportiveness, i.e., if they support arguments of other sockpuppets controlled
by the same user. We apply these findings to a series of prediction tasks,
notably, to identify whether a pair of accounts belongs to the same underlying
user or not. Altogether, this work presents a data-driven view of deception in
online discussion communities and paves the way towards the automatic detection
of sockpuppets.Comment: 26th International World Wide Web conference 2017 (WWW 2017
The Value of College Athletics in the Labor Market: Results from a Resume Audit Field Experiment
Employers may favor applicants who played college sports if athletics participation contributes to leadership, conscientiousness, discipline, and other traits that are desirable for labor-market productivity. We conduct a resume audit to estimate the causal effect of listing collegiate athletics on employer callbacks and test for subgroup effects by ethnicity, gender, and sport type. We applied to more than 450 jobs on a large, well-known job board. For each job listing we submitted two fictitious resumes, one of which was randomly assigned to include collegiate varsity athletics. Overall, listing a college sport does not produce a statistically significant change in the likelihood of receiving a callback or interview request. However, among non-white applicants, athletes are 3.2 percentage points less likely to receive an interview request (p = .04) relative to non-athletes. We find no statistically significant differences among males or females
Prevalence of Tidal Interactions among Local Seyfert Galaxies
No mechanisms have hitherto been conclusively demonstrated to be responsible
for initiating optically-luminous nuclear (Seyfert) activity in local disk
galaxies. Only a small minority of such galaxies are visibly disturbed in
optical starlight, with the observed disturbances being at best marginally
stronger than those found in matched samples of inactive galaxies. Here, we
report the first systematic study of an optically-selected sample of
twenty-three active galaxies in atomic hydrogen (HI) gas, which is the most
sensitive and enduring tracer known of tidal interactions. Eighteen of these
galaxies are (generally) classified as Seyferts, with over half (and perhaps
all) having [OIII] luminosities within two orders of magnitude of Quasi-Stellar
Objects. Only ~28% of these Seyfert galaxies are visibly disturbed in optical
DSS2 images. By contrast, ~94% of the same galaxies are disturbed in HI, in
nearly all cases not just spatially but also kinematically on galactic (>~20
kpc) scales. In at least ~67% and perhaps up to ~94% of cases, the observed HI
disturbances can be traced to tidal interactions with neighboring galaxies
detected also in HI. The majority of these neighboring galaxies have projected
separations of <~ 100 kpc and differ in radial velocities by <~100 km/s from
their respective Seyfert galaxies, and many have optical luminosities ranging
from the Small to Large Magellanic Clouds. In a companion paper, we show that
only ~15% of a matched control sample of inactive galaxies display comparable
HI disturbances. Our results suggest that: i) most Seyfert galaxies (with high
nuclear luminosities) have experienced tidal interactions in the recent past;
ii) in most cases, these tidal interactions are responsible for initiating
events that lead to their nuclear activity.Comment: 64 pages, 44 figures, accepted for publication in ApJ. Changes:
Nothing is changed except that the paper was compiled differently to reduce
the number of pages. To be friendly to the Earth forest, you could also
choose to only print the text part of the paper and view images on line. (see
http://www.astro.virginia.edu/~ck2v/paper/
Two-body Cabibbo-suppressed Decays of Charmed Baryons into Vector Mesons and into Photons
The heavy quark effective theory and the factorization approximation are used
to treat the Cabibbo-suppressed decays of charmed baryons to vector mesons,
,
and . The input from two recent experimental results on
decays allows the estimation of the branching ratios for these modes, which
turn out to be between and . The long distance contribution
of these transitions via vector meson dominance to the radiative weak processes
, and
leads to quite small branching ratios,
; the larger value holds if a sum rule between the coupling
constants of the vector mesons is broken.Comment: 11 pages, latex, no figure
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