116 research outputs found
Competition and Selection Among Conventions
In many domains, a latent competition among different conventions determines
which one will come to dominate. One sees such effects in the success of
community jargon, of competing frames in political rhetoric, or of terminology
in technical contexts. These effects have become widespread in the online
domain, where the data offers the potential to study competition among
conventions at a fine-grained level.
In analyzing the dynamics of conventions over time, however, even with
detailed on-line data, one encounters two significant challenges. First, as
conventions evolve, the underlying substance of their meaning tends to change
as well; and such substantive changes confound investigations of social
effects. Second, the selection of a convention takes place through the complex
interactions of individuals within a community, and contention between the
users of competing conventions plays a key role in the convention's evolution.
Any analysis must take place in the presence of these two issues.
In this work we study a setting in which we can cleanly track the competition
among conventions. Our analysis is based on the spread of low-level authoring
conventions in the eprint arXiv over 24 years: by tracking the spread of macros
and other author-defined conventions, we are able to study conventions that
vary even as the underlying meaning remains constant. We find that the
interaction among co-authors over time plays a crucial role in the selection of
them; the distinction between more and less experienced members of the
community, and the distinction between conventions with visible versus
invisible effects, are both central to the underlying processes. Through our
analysis we make predictions at the population level about the ultimate success
of different synonymous conventions over time--and at the individual level
about the outcome of "fights" between people over convention choices.Comment: To appear in Proceedings of WWW 2017, data at
https://github.com/CornellNLP/Macro
Anatomical labeling of intracranial arteries with deep learning in patients with cerebrovascular disease
Brain arteries are routinely imaged in the clinical setting by various modalities, e.g., time-of-flight magnetic resonance angiography (TOF-MRA). These imaging techniques have great potential for the diagnosis of cerebrovascular disease, disease progression, and response to treatment. Currently, however, only qualitative assessment is implemented in clinical applications, relying on visual inspection. While manual or semi-automated approaches for quantification exist, such solutions are impractical in the clinical setting as they are time-consuming, involve too many processing steps, and/or neglect image intensity information. In this study, we present a deep learning-based solution for the anatomical labeling of intracranial arteries that utilizes complete information from 3D TOF-MRA images. We adapted and trained a state-of-the-art multi-scale Unet architecture using imaging data of 242 patients with cerebrovascular disease to distinguish 24 arterial segments. The proposed model utilizes vessel-specific information as well as raw image intensity information, and can thus take tissue characteristics into account. Our method yielded a performance of 0.89 macro F1 and 0.90 balanced class accuracy (bAcc) in labeling aggregated segments and 0.80 macro F1 and 0.83 bAcc in labeling detailed arterial segments on average. In particular, a higher F1 score than 0.75 for most arteries of clinical interest for cerebrovascular disease was achieved, with higher than 0.90 F1 scores in the larger, main arteries. Due to minimal pre-processing, simple usability, and fast predictions, our method could be highly applicable in the clinical setting
Theory of dynamic crack branching in brittle materials
The problem of dynamic symmetric branching of an initial single brittle crack
propagating at a given speed under plane loading conditions is studied within a
continuum mechanics approach. Griffith's energy criterion and the principle of
local symmetry are used to determine the cracks paths. The bifurcation is
predicted at a given critical speed and at a specific branching angle: both
correlated very well with experiments. The curvature of the subsequent branches
is also studied: the sign of , with being the non singular stress at the
initial crack tip, separates branches paths that diverge from or converge to
the initial path, a feature that may be tested in future experiments. The model
rests on a scenario of crack branching with some reasonable assumptions based
on general considerations and in exact dynamic results for anti-plane
branching. It is argued that it is possible to use a static analysis of the
crack bifurcation for plane loading as a good approximation to the dynamical
case. The results are interesting since they explain within a continuum
mechanics approach the main features of the branching instabilities of fast
cracks in brittle materials, i.e. critical speeds, branching angle and the
geometry of subsequent branches paths.Comment: 41 pages, 15 figures. Accepted to International Journal of Fractur
Patterns and Collective Behavior in Granular Media: Theoretical Concepts
Granular materials are ubiquitous in our daily lives. While they have been a
subject of intensive engineering research for centuries, in the last decade
granular matter attracted significant attention of physicists. Yet despite a
major efforts by many groups, the theoretical description of granular systems
remains largely a plethora of different, often contradicting concepts and
approaches. Authors give an overview of various theoretical models emerged in
the physics of granular matter, with the focus on the onset of collective
behavior and pattern formation. Their aim is two-fold: to identify general
principles common for granular systems and other complex non-equilibrium
systems, and to elucidate important distinctions between collective behavior in
granular and continuum pattern-forming systems.Comment: Submitted to Reviews of Modern Physics. Full text with figures (2Mb
pdf) avaliable at
http://mti.msd.anl.gov/AransonTsimringReview/aranson_tsimring.pdf Community
responce is appreciated. Comments/suggestions send to [email protected]
Thermonuclear Burning Regimes and the Use of SNe Ia in Cosmology
The calculations of the light curves of thermonuclear supernovae are carried
out by a method of multi-group radiation hydrodynamics. The effects of spectral
lines and expansion opacity are taken into account. The predictions for UBVI
fluxes are given. The values of rise time for B and V bands found in our
calculations are in good agreement with the observed values. We explain why our
results for the rise time have more solid physical justification than those
obtained by other authors. It is shown that small variations in the chemical
composition of the ejecta, produced in the explosions with different regimes of
nuclear burning, can influence drastically the light curve decline in the B
band and, to a lesser extent, in the V band. We argue that recent results on
positive cosmological constant Lambda, found from the high redshift supernova
observations, could be wrong in the case of possible variations of the
preferred mode of nuclear burning in the earlier Universe.Comment: 20 pages, 5 figures, presented at the conference "Astronomy at the
Eve of the New Century", Puschino, May 17-22, 1999. A few references and a
table added, typos correcte
Computational Models of Stellar Collapse and Core-Collapse Supernovae
Core-collapse supernovae are among Nature's most energetic events. They mark
the end of massive star evolution and pollute the interstellar medium with the
life-enabling ashes of thermonuclear burning. Despite their importance for the
evolution of galaxies and life in the universe, the details of the
core-collapse supernova explosion mechanism remain in the dark and pose a
daunting computational challenge. We outline the multi-dimensional,
multi-scale, and multi-physics nature of the core-collapse supernova problem
and discuss computational strategies and requirements for its solution.
Specifically, we highlight the axisymmetric (2D) radiation-MHD code VULCAN/2D
and present results obtained from the first full-2D angle-dependent neutrino
radiation-hydrodynamics simulations of the post-core-bounce supernova
evolution. We then go on to discuss the new code Zelmani which is based on the
open-source HPC Cactus framework and provides a scalable AMR approach for 3D
fully general-relativistic modeling of stellar collapse, core-collapse
supernovae and black hole formation on current and future massively-parallel
HPC systems. We show Zelmani's scaling properties to more than 16,000 compute
cores and discuss first 3D general-relativistic core-collapse results.Comment: 16 pages, 5 figures, to appear in the proceedings of the DOE/SciDAC
2009 conference. A version with high-resolution figures is available from
http://stellarcollapse.org/papers/Ott_SciDAC2009.pd
Acoustic-Friction Networks and the Evolution of Precursory Rupture Fronts in Laboratory Earthquakes
We show that the mesoscopic and transport characteristics of networks follow
the same trends for the same type of the shear ruptures in terms of rupture
speed while also comparing the results of three different friction
experiments.The classified fronts obtained from a saw cut Westerly granite
fault regarding friction network parameters show a clear separation into two
groups indicating two different rupture fronts. With respect to the scaling of
local ruptures durations with the networks parameters we show that the gap is
related to the possibility of a separation between slow and regular fronts
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
A faint type of supernova from a white dwarf with a helium-rich companion
Supernovae (SNe) are thought to arise from two different physical processes.
The cores of massive, short-lived stars undergo gravitational core collapse and
typically eject a few solar masses during their explosion. These are thought to
appear as as type Ib/c and II SNe, and are associated with young stellar
populations. A type Ia SN is thought to arise from the thermonuclear detonation
of a white dwarf star composed mainly of carbon and oxygen, whose mass
approaches the Chandrasekhar limit. Such SNe are observed in both young and old
stellar environments. Here we report our discovery of the faint type Ib SN
2005E in the halo of the nearby isolated galaxy, NGC 1032.
The lack of any trace of recent star formation near the SN location (Fig. 1),
and the very low derived ejected mass (~0.3 M_sun), argue strongly against a
core-collapse origin for this event. Spectroscopic observations and the derived
nucleosynthetic output show that the SN ejecta have high velocities and are
dominated by helium-burning products, indicating that SN 2005E was neither a
subluminous nor a regular SN Ia (Fig. 2). We have therefore found a new type of
stellar explosion, arising from a low-mass, old stellar system, likely
involving a binary with a primary white dwarf and a helium-rich secondary. The
SN ejecta contain more calcium than observed in any known type of SN and likely
additional large amounts of radioactive 44Ti. Such SNe may thus help resolve
fundamental physical puzzles, extending from the composition of the primitive
solar system and that of the oldest stars, to the Galactic production of
positrons.Comment: Revised to reflect published version in Nature, May 20th, 2010.
Additional data and analysis are include
Eyes wide open: perceived exploitation and its consequences
Drawing on the array of literature on exploitation from several social science disciplines, we propose a new way of seeing employer-employee relationships by introducing the concept of perceived exploitative employee-organization relationships, distinguish it from related concepts, and conduct five studies to develop a scale and test our theoretical model of the effects of such employee perceptions. Contributing to the Employee-Organization Relationships and workplace emotions literatures, perceived exploitation is defined as employees’ perceptions that they have been purposefully taken advantage of in their relationship with the organization, to the benefit of the organization itself. We propose and find that such perceptions are associated with both outward-focused emotions of anger and hostility toward the organization and inward-focused ones of shame and guilt at remaining in an exploitative job. In two studies including construction workers and a time-lagged study of medical residents, we find that the emotions of anger and hostility partially mediate the effects of perceived exploitation on employee engagement, revenge against the organization, organizational commitment, and turnover intentions, whereas the emotions of shame and guilt partially mediate the effects of perceived exploitation on employee burnout, silence, and psychological withdrawal
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