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Tools for efficient analysis of concurrent software systems
The ever increasing use of distributed computing as a method of providing added computing power and reliability has sparked interest in methods to model and analyze concurrent hardware/ software systems. Efficient automated analysis tools are needed to aid designers of such systems. The Distributed Systems Project at UCI has been developing a suite of tools (dubbed the P-NUT system) which supports efficient analysis of models of concurrent software. This paper presents the principles which guide the development of P-NUT tools and discusses the development of one of the tools: the Reachability Graph Builder (RGB). The P-NUT approach to tool development has resulted in the production of a highly efficient tool for constructing reachability graphs. The careful design of data structures and associated algorithms has significantly enlarged the class of models which can be analyzed
Fundamental structures of dynamic social networks
Social systems are in a constant state of flux with dynamics spanning from
minute-by-minute changes to patterns present on the timescale of years.
Accurate models of social dynamics are important for understanding spreading of
influence or diseases, formation of friendships, and the productivity of teams.
While there has been much progress on understanding complex networks over the
past decade, little is known about the regularities governing the
micro-dynamics of social networks. Here we explore the dynamic social network
of a densely-connected population of approximately 1000 individuals and their
interactions in the network of real-world person-to-person proximity measured
via Bluetooth, as well as their telecommunication networks, online social media
contacts, geo-location, and demographic data. These high-resolution data allow
us to observe social groups directly, rendering community detection
unnecessary. Starting from 5-minute time slices we uncover dynamic social
structures expressed on multiple timescales. On the hourly timescale, we find
that gatherings are fluid, with members coming and going, but organized via a
stable core of individuals. Each core represents a social context. Cores
exhibit a pattern of recurring meetings across weeks and months, each with
varying degrees of regularity. Taken together, these findings provide a
powerful simplification of the social network, where cores represent
fundamental structures expressed with strong temporal and spatial regularity.
Using this framework, we explore the complex interplay between social and
geospatial behavior, documenting how the formation of cores are preceded by
coordination behavior in the communication networks, and demonstrating that
social behavior can be predicted with high precision.Comment: Main Manuscript: 16 pages, 4 figures. Supplementary Information: 39
pages, 34 figure
Locally embedded presages of global network bursts
Spontaneous, synchronous bursting of neural population is a widely observed
phenomenon in nervous networks, which is considered important for functions and
dysfunctions of the brain. However, how the global synchrony across a large
number of neurons emerges from an initially non-bursting network state is not
fully understood. In this study, we develop a new state-space reconstruction
method combined with high-resolution recordings of cultured neurons. This
method extracts deterministic signatures of upcoming global bursts in "local"
dynamics of individual neurons during non-bursting periods. We find that local
information within a single-cell time series can compare with or even
outperform the global mean field activity for predicting future global bursts.
Moreover, the inter-cell variability in the burst predictability is found to
reflect the network structure realized in the non-bursting periods. These
findings demonstrate the deterministic mechanisms underlying the locally
concentrated early-warnings of the global state transition in self-organized
networks
Expected properties of the Two-Point Autocorrelation Function of the IGM
Recent analyses of the fluctuations of the soft Diffuse X-ray Background
(DXB) have provided indirect detection of a component consistent with the
elusive Warm Hot Intergalactic Medium (WHIM). In this work we use theoretical
predictions obtained from hydrodynamical simulations to investigate the angular
correlation properties of the WHIM in emission and assess the possibility of
indirect detection with next-generation X-ray missions. Our results indicate
that the angular correlation signal of the WHIM is generally weak but dominates
the angular correlation function of the DXB outside virialized regions. Its
indirect detection is possible but requires rather long exposure times [0.1-1]
Ms, large (~1{\deg} x1{\deg}) fields of view and accurate subtraction of
isotropic fore/background contributions, mostly contributed by Galactic
emission. The angular correlation function of the WHIM is positive for {\theta}
< 5' and provides limited information on its spatial distribution. A
satisfactory characterization of the WHIM in 3D can be obtained through
spatially resolved spectroscopy. 1 Ms long exposures with next generation
detectors will allow to detect ~400 O VII+O VIII X-ray emission systems that we
use to trace the spatial distribution of the WHIM. We predict that these
observations will allow to estimate the WHIM correlation function with high
statistical significance out to ~10 Mpc h^-1 and characterize its dynamical
state through the analysis of redshift-space distortions. The detectable WHIM,
which is typically associated with the outskirts of virialized regions rather
than the filaments has a non-zero correlation function with slope {\gamma} =
-1.7 \pm 0.1 and correlation length r0 = 4.0 \pm 0.1 Mpc h^-1 in the range r =
[4.5, 12] Mpc h^-1. Redshift space distances can be measured to assess the
dynamical properties of the gas, typically infalling onto large virialized
structures.Comment: 17 pages, 2 tables, 11 figures, Final version, accepted for
publication on MNRA
How accurately can the SZ effect measure peculiar cluster velocities and bulk flows?
The Sunyaev-Zel'dovich effect is a powerful tool for cosmology that can be
used to measure the radial peculiar velocities of galaxy clusters, and thus to
test, and constrain, theories of structure formation and evolution. This
requires, in principle, an accurate measurement of the effect, a good
separation between the Sunyaev-Zel'dovich components, and a good understanding
of the sources contributing to the signal and their effect on the measured
velocity. In this study, we evaluate the error in the individual radial
peculiar velocities determined with Sunyaev-Zel'dovich measurements. We
estimate, for three cosmological models, the errors induced by the major
contributing signals (primary Cosmic Microwave Background anisotropies,
Sunyaev-Zel'dovich effect due to the background cluster population, residuals
from component separation and instrumental noise). We generalise our results to
estimate the error in the bulk velocity on large scales. In this context, we
investigate the limitation due to the Sunyaev-Zel'dovich source (or spatial)
confusion in a Planck-like instrumental configuration. Finally, we propose a
strategy based on the future all-sky Sunyaev-Zel'dovich survey, that will be
provided by the Planck mission, to measure accurately the bulk velocities on
large scales up to redshift 1, or more.Comment: 24 pages, 8 figures, revised version of an article submitted to
Astronomy and Astrophysics (in referee style
CMBPol Mission Concept Study: Foreground Science Knowledge and Prospects
We report on our knowledge of Galactic foregrounds, as well as on how a CMB
satellite mission aiming at detecting a primordial B-mode signal (CMBPol) will
contribute to improving it. We review the observational and analysis techniques
used to constrain the structure of the Galactic magnetic field, whose presence
is responsible for the polarization of Galactic emissions. Although our current
understanding of the magnetized interstellar medium is somewhat limited,
dramatic improvements in our knowledge of its properties are expected by the
time CMBPol flies. Thanks to high resolution and high sensitivity instruments
observing the whole sky at frequencies between 30 GHz and 850 GHz, CMBPol will
not only improve this picture by observing the synchrotron emission from our
galaxy, but also help constrain dust models. Polarized emission from
interstellar dust indeed dominates over any other signal in CMBPol's highest
frequency channels. Observations at these wavelengths, combined with
ground-based studies of starlight polarization, will therefore enable us to
improve our understanding of dust properties and of the mechanism(s)
responsible for the alignment of dust grains with the Galactic magnetic field.
CMBPol will also shed new light on observations that are presently not well
understood. Morphological studies of anomalous dust and synchrotron emissions
will indeed constrain their natures and properties, while searching for
fluctuations in the emission from heliospheric dust will test our understanding
of the circumheliospheric interstellar medium. Finally, acquiring more
information on the properties of extra-Galactic sources will be necessary in
order to maximize the cosmological constraints extracted from CMBPol's
observations of CMB lensing. (abridged)Comment: 43 pages, 7 figures, 2 table
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