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On the Average Genus of a Graph
Not all rational numbers are possibilities for the average genus of an individual graph. The smallest such numbers are determined, and varied examples are constructed to demonstrate that a single value of average genus can be shared by arbitrarily many different graphs. It is proved that the number one is a limit point of the set of possible values for average genus and that the complete graph K4 is the only 3-connected graph whose average genus is less than one. Several problems for future study are suggested
Do logarithmic proximity measures outperform plain ones in graph clustering?
We consider a number of graph kernels and proximity measures including
commute time kernel, regularized Laplacian kernel, heat kernel, exponential
diffusion kernel (also called "communicability"), etc., and the corresponding
distances as applied to clustering nodes in random graphs and several
well-known datasets. The model of generating random graphs involves edge
probabilities for the pairs of nodes that belong to the same class or different
predefined classes of nodes. It turns out that in most cases, logarithmic
measures (i.e., measures resulting after taking logarithm of the proximities)
perform better while distinguishing underlying classes than the "plain"
measures. A comparison in terms of reject curves of inter-class and intra-class
distances confirms this conclusion. A similar conclusion can be made for
several well-known datasets. A possible origin of this effect is that most
kernels have a multiplicative nature, while the nature of distances used in
cluster algorithms is an additive one (cf. the triangle inequality). The
logarithmic transformation is a tool to transform the first nature to the
second one. Moreover, some distances corresponding to the logarithmic measures
possess a meaningful cutpoint additivity property. In our experiments, the
leader is usually the logarithmic Communicability measure. However, we indicate
some more complicated cases in which other measures, typically, Communicability
and plain Walk, can be the winners.Comment: 11 pages, 5 tables, 9 figures. Accepted for publication in the
Proceedings of 6th International Conference on Network Analysis, May 26-28,
2016, Nizhny Novgorod, Russi
Whatâs Sex (Composition) Got to Do with It? The Importance of Sex Composition of Gangs for Female and Male Membersâ Offending and Victimization
Sex composition of groups has been theorized in organizational sociology and found in prior work to structure female and male membersâ behaviors and experiences. Peer group and gang literature similarly finds that the sex gap in offending varies across groups of differing sex ratios. Drawing on this and other research linking gang membership, offending, and victimization, we examine whether sex composition of gangs is linked to sex differences in offending in this sample, further assess whether sex composition similarly structures femalesâ and malesâ victimization experiences, and if so, why. Self-report data from gang members in a multi-site, longitudinal study of 3,820 youths are employed. Results support previous findings about variations in member delinquency by both sex and sex composition of the gang and also indicate parallel variations in membersâ victimization. These results are further considered within the context of facilitating effects such as gender dynamics, gang characteristics, and normative orientation
Comparison of prestellar core elongations and large-scale molecular cloud structures in the Lupus 1 region
Turbulence and magnetic fields are expected to be important for regulating molecular cloud formation and evolution. However, their effects on sub-parsec to 100 parsec scales, leading to the formation of starless cores, are not well understood. We investigate the prestellar core structure morphologies obtained from analysis of the Herschel-SPIRE 350 mum maps of the Lupus I cloud. This distribution is first compared on a statistical basis to the large-scale shape of the main filament. We find the distribution of the elongation position angle of the cores to be consistent with a random distribution, which means no specific orientation of the morphology of the cores is observed with respect to the mean orientation of the large-scale filament in Lupus I, nor relative to a large-scale bent filament model. This distribution is also compared to the mean orientation of the large-scale magnetic fields probed at 350 mum with the Balloon-borne Large Aperture Telescope for Polarimetry during its 2010 campaign. Here again we do not find any correlation between the core morphology distribution and the average orientation of the magnetic fields on parsec scales. Our main conclusion is that the local filament dynamics---including secondary filaments that often run orthogonally to the primary filament---and possibly small-scale variations in the local magnetic field direction, could be the dominant factors for explaining the final orientation of each core
The balloon-borne large-aperture submillimeter telescope for polarimetry: BLAST-Pol
The Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry
(BLAST-Pol) is a suborbital mapping experiment designed to study the role
played by magnetic fields in the star formation process. BLAST-Pol is the
reconstructed BLAST telescope, with the addition of linear polarization
capability. Using a 1.8 m Cassegrain telescope, BLAST-Pol images the sky onto a
focal plane that consists of 280 bolometric detectors in three arrays,
observing simultaneously at 250, 350, and 500 um. The diffraction-limited
optical system provides a resolution of 30'' at 250 um. The polarimeter
consists of photolithographic polarizing grids mounted in front of each
bolometer/detector array. A rotating 4 K achromatic half-wave plate provides
additional polarization modulation. With its unprecedented mapping speed and
resolution, BLAST-Pol will produce three-color polarization maps for a large
number of molecular clouds. The instrument provides a much needed bridge in
spatial coverage between larger-scale, coarse resolution surveys and narrow
field of view, and high resolution observations of substructure within
molecular cloud cores. The first science flight will be from McMurdo Station,
Antarctica in December 2010.Comment: 14 pages, 9 figures Submitted to SPIE Astronomical Telescopes and
Instrumentation Conference 201
Shifting perspectives on coastal impacts and adaptation
The Intergovernmental Panel on Climate Change reports reflect evolving attitudes in adapting to
sea-level rise by taking a systems approach and recognizing that multiple responses exist to achieve a
less hazardous coast.info:eu-repo/semantics/publishedVersio
Excitation of the molecular gas in the nuclear region of M82
We present high resolution HIFI spectroscopy of the nucleus of the
archetypical starburst galaxy M82. Six 12CO lines, 2 13CO lines and 4
fine-structure lines are detected. Besides showing the effects of the overall
velocity structure of the nuclear region, the line profiles also indicate the
presence of multiple components with different optical depths, temperatures and
densities in the observing beam. The data have been interpreted using a grid of
PDR models. It is found that the majority of the molecular gas is in low
density (n=10^3.5 cm^-3) clouds, with column densities of N_H=10^21.5 cm^-2 and
a relatively low UV radiation field (GO = 10^2). The remaining gas is
predominantly found in clouds with higher densities (n=10^5 cm^-3) and
radiation fields (GO = 10^2.75), but somewhat lower column densities
(N_H=10^21.2 cm^-2). The highest J CO lines are dominated by a small (1%
relative surface filling) component, with an even higher density (n=10^6 cm^-3)
and UV field (GO = 10^3.25). These results show the strength of multi-component
modeling for the interpretation of the integrated properties of galaxies.Comment: Accepted for publication in A&A Letter
Detection of hydrogen fluoride absorption in diffuse molecular clouds with Herschel/HIFI: a ubiquitous tracer of molecular gas
We discuss the detection of absorption by interstellar hydrogen fluoride (HF)
along the sight line to the submillimeter continuum sources W49N and W51. We
have used Herschel's HIFI instrument in dual beam switch mode to observe the
1232.4762 GHz J = 1 - 0 HF transition in the upper sideband of the band 5a
receiver. We detected foreground absorption by HF toward both sources over a
wide range of velocities. Optically thin absorption components were detected on
both sight lines, allowing us to measure - as opposed to obtain a lower limit
on - the column density of HF for the first time. As in previous observations
of HF toward the source G10.6-0.4, the derived HF column density is typically
comparable to that of water vapor, even though the elemental abundance of
oxygen is greater than that of fluorine by four orders of magnitude. We used
the rather uncertain N(CH)-N(H2) relationship derived previously toward diffuse
molecular clouds to infer the molecular hydrogen column density in the clouds
exhibiting HF absorption. Within the uncertainties, we find that the abundance
of HF with respect to H2 is consistent with the theoretical prediction that HF
is the main reservoir of gas-phase fluorine for these clouds. Thus, hydrogen
fluoride has the potential to become an excellent tracer of molecular hydrogen,
and provides a sensitive probe of clouds of small H2 column density. Indeed,
the observations of hydrogen fluoride reported here reveal the presence of a
low column density diffuse molecular cloud along the W51 sight line, at an LSR
velocity of ~ 24kms-1, that had not been identified in molecular absorption
line studies prior to the launch of Herschel.Comment: 4 pages, 3 figures, A&A Letter special issue, accepted on 07/13/201
The Atacama Cosmology Telescope: The polarization-sensitive ACTPol instrument
The Atacama Cosmology Telescope (ACT) is designed to make high angular
resolution measurements of anisotropies in the Cosmic Microwave Background
(CMB) at millimeter wavelengths. We describe ACTPol, an upgraded receiver for
ACT, which uses feedhorn-coupled, polarization-sensitive detector arrays, a 3
degree field of view, 100 mK cryogenics with continuous cooling, and meta
material anti-reflection coatings. ACTPol comprises three arrays with separate
cryogenic optics: two arrays at a central frequency of 148 GHz and one array
operating simultaneously at both 97 GHz and 148 GHz. The combined instrument
sensitivity, angular resolution, and sky coverage are optimized for measuring
angular power spectra, clusters via the thermal Sunyaev-Zel'dovich and kinetic
Sunyaev-Zel'dovich signals, and CMB lensing due to large scale structure. The
receiver was commissioned with its first 148 GHz array in 2013, observed with
both 148 GHz arrays in 2014, and has recently completed its first full season
of operations with the full suite of three arrays. This paper provides an
overview of the design and initial performance of the receiver and related
systems
Improving Photoelectron Counting and Particle Identification in Scintillation Detectors with Bayesian Techniques
Many current and future dark matter and neutrino detectors are designed to
measure scintillation light with a large array of photomultiplier tubes (PMTs).
The energy resolution and particle identification capabilities of these
detectors depend in part on the ability to accurately identify individual
photoelectrons in PMT waveforms despite large variability in pulse amplitudes
and pulse pileup. We describe a Bayesian technique that can identify the times
of individual photoelectrons in a sampled PMT waveform without deconvolution,
even when pileup is present. To demonstrate the technique, we apply it to the
general problem of particle identification in single-phase liquid argon dark
matter detectors. Using the output of the Bayesian photoelectron counting
algorithm described in this paper, we construct several test statistics for
rejection of backgrounds for dark matter searches in argon. Compared to simpler
methods based on either observed charge or peak finding, the photoelectron
counting technique improves both energy resolution and particle identification
of low energy events in calibration data from the DEAP-1 detector and
simulation of the larger MiniCLEAN dark matter detector.Comment: 16 pages, 16 figure
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