578 research outputs found
The developmental dynamics of terrorist organizations
We identify robust statistical patterns in the frequency and severity of
violent attacks by terrorist organizations as they grow and age. Using
group-level static and dynamic analyses of terrorist events worldwide from
1968-2008 and a simulation model of organizational dynamics, we show that the
production of violent events tends to accelerate with increasing size and
experience. This coupling of frequency, experience and size arises from a
fundamental positive feedback loop in which attacks lead to growth which leads
to increased production of new attacks. In contrast, event severity is
independent of both size and experience. Thus larger, more experienced
organizations are more deadly because they attack more frequently, not because
their attacks are more deadly, and large events are equally likely to come from
large and small organizations. These results hold across political ideologies
and time, suggesting that the frequency and severity of terrorism may be
constrained by fundamental processes.Comment: 28 pages, 8 figures, 4 tables, supplementary materia
The 1999 international emergency humanitarian evacuation of the Kosovars to Canada: A qualitative study of service providers' perspectives at the international, national and local levels
BACKGROUND: In response to the Kosovo crisis, Canada received 5,500 Albanian Kosovar refugees in 1999 as part of the emergency humanitarian evacuation and settlement effort. This study attempts to describe the experiences of service providers at the international, national, and local levels, involved in the organization and delivery of health and settlement services in Canada for the Kosovar refugees. METHODS: A qualitative case study design using key informant interviews was used. Nominated sampling was used to identify 17 individuals involved in the organization and delivery of health and settlement. Key themes were identified and recommendations made to provide a framework for the development of policy to guide response to future humanitarian emergencies. RESULTS: Six themes emerged: (1) A sense of being overwhelmed, (2) A multitude of health issues, (3) critical challenges in providing health care, (4) access to health and settlement services, (5) overall successes and (6) need for a coordinated approach to migration health. CONCLUSIONS: For those involved, the experience was overwhelming but rewarding. Interviewees' major concerns were the need for a more comprehensive and coordinated approach to the flow of medical information and handling of specific health problems
Single Spin Measurement using Single Electron Transistors to Probe Two Electron Systems
We present a method for measuring single spins embedded in a solid by probing
two electron systems with a single electron transistor (SET). Restrictions
imposed by the Pauli Principle on allowed two electron states mean that the
spin state of such systems has a profound impact on the orbital states
(positions) of the electrons, a parameter which SET's are extremely well suited
to measure. We focus on a particular system capable of being fabricated with
current technology: a Te double donor in Si adjacent to a Si/SiO2 interface and
lying directly beneath the SET island electrode, and we outline a measurement
strategy capable of resolving single electron and nuclear spins in this system.
We discuss the limitations of the measurement imposed by spin scattering
arising from fluctuations emanating from the SET and from lattice phonons. We
conclude that measurement of single spins, a necessary requirement for several
proposed quantum computer architectures, is feasible in Si using this strategy.Comment: 22 Pages, 8 Figures; revised version contains updated references and
small textual changes. Submitted to Phys. Rev.
Directly Imaging Rocky Planets from the Ground
Over the past three decades instruments on the ground and in space have
discovered thousands of planets outside the solar system. These observations
have given rise to an astonishingly detailed picture of the demographics of
short-period planets, but are incomplete at longer periods where both the
sensitivity of transit surveys and radial velocity signals plummet. Even more
glaring is that the spectra of planets discovered with these indirect methods
are either inaccessible (radial velocity detections) or only available for a
small subclass of transiting planets with thick, clear atmospheres. Direct
detection can be used to discover and characterize the atmospheres of planets
at intermediate and wide separations, including non-transiting exoplanets.
Today, a small number of exoplanets have been directly imaged, but they
represent only a rare class of young, self-luminous super-Jovian-mass objects
orbiting tens to hundreds of AU from their host stars. Atmospheric
characterization of planets in the <5 AU regime, where radial velocity (RV)
surveys have revealed an abundance of other worlds, is technically feasible
with 30-m class apertures in combination with an advanced AO system,
coronagraph, and suite of spectrometers and imagers. There is a vast range of
unexplored science accessible through astrometry, photometry, and spectroscopy
of rocky planets, ice giants, and gas giants. In this whitepaper we will focus
on one of the most ambitious science goals --- detecting for the first time
habitable-zone rocky (<1.6 R_Earth) exoplanets in reflected light around nearby
M-dwarfsComment: 8 pages, 1 figure, Astro2020 Science White Pape
Short-lived p-nuclides in the early solar system and implications on the nucleosynthetic role of X-ray binaries
The data available for short-lived -nuclides are used in an open nonlinear
model of the chemical evolution of the Galaxy in order to discuss the origin of
extinct radionuclides, the stellar sources of -nuclides, and the chronology
of solar system formation. It is concluded that the observed abundances of
Tc, Tc, Nb, and Sm in the early solar system are
consistent with nucleosynthesis in type II supernovae during continuous
chemical evolution of the Galaxy and a subsequent short isolation of the
presolar molecular cloud from fresh nucleosynthetic inputs. However, further
work on supernova models is needed before -radionuclides will comprise
reliable cosmochronometers. Despite these limitations, we argue that niobium-92
can be used to test whether the {\it rp}-process contributed to the synthesis
of light {\it p}-nuclides in the Mo-Ru region.Comment: 8 pages, 2 figures. Proceedings of the Nuclear Physics in
Astrophysics Conference, Debrecen, Hungary, 2002, to appear in Nucl. Phys.
Genotyping-by-Sequencing and Ecological Niche Modeling Illuminate Phylogeography, Admixture, and Pleistocene Range Dynamics in Quaking Aspen (Populus Tremuloides)
Populus tremuloides is the widestâranging tree species in North America and an ecologically important component of mesic forest ecosystems displaced by the Pleistocene glaciations. Using phylogeographic analyses of genomeâwide SNPs (34,796 SNPs, 183 individuals) and ecological niche modeling, we inferred population structure, ploidy levels, admixture, and Pleistocene range dynamics of P. tremuloides, and tested several historical biogeographical hypotheses. We found three genetic lineages located mainly in coastalâCascades (cluster 1), eastâslope CascadesâSierra NevadasâNorthern Rockies (cluster 2), and U.S. Rocky Mountains through southern Canadian (cluster 3) regions of the P. tremuloides range, with tree graph relationships of the form ((cluster 1, cluster 2), cluster 3). Populations consisted mainly of diploids (86%) but also small numbers of triploids (12%) and tetraploids (1%), and ploidy did not adversely affect our genetic inferences. The main vector of admixture was from cluster 3 into cluster 2, with the admixture zone trending northwest through the Rocky Mountains along a recognized phenotypic cline (Utah to Idaho). Clusters 1 and 2 provided strong support for the âstableâedge hypothesisâ that unglaciated southwestern populations persisted in situ since the last glaciation. By contrast, despite a lack of clinal genetic variation, cluster 3 exhibited âtrailingâedgeâ dynamics from niche suitability predictions signifying complete northward postglacial expansion. Results were also consistent with the âinland dispersal hypothesisâ predicting postglacial assembly of Pacific Northwestern forest ecosystems, but rejected the hypothesis that Pacificâcoastal populations were colonized during outburst flooding from glacial Lake Missoula. Overall, congruent patterns between our phylogeographic and ecological niche modeling results and fossil pollen data demonstrate complex mixtures of stableâedge, refugial locations, and postglacial expansion within P. tremuloides. These findings confirm and refine previous genetic studies, while strongly supporting a distinct Pacificâcoastal genetic lineage of quaking aspen
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A Systematic Review of Semantic Feature Analysis Therapy Studies for Aphasia
Purpose : The purpose of this study was to review treatment studies of semantic feature analysis (SFA) for persons with aphasia . The review documents how SFA is used, appraises the quality of the included studies and evaluates the efficacy of SFA.
Methods : The following electronic databases were systematically searched (last search February 2017) : Academic Search Complete; CINAHL Plus; E -journals; Health Policy Reference Centre; MEDLINE; PsycART ICLES; PsycINFO; and SocINDEX. The quality of the included studies was rated. Clinical efficacy was determined by calculating effect sizes ( Cohenâs d ) or percent of non-overlapping data when d could not be calculated.
Results: Twenty -one studies were reviewed reporting on 55 persons with aphasia. SFA was used in six different types of studies: confrontation naming of nouns, of verbs , connected speech /discourse, group, multilingual and studies where SFA was compared with other approaches . The quality of included studies was high [ Single Case Experimental Design Scale (SCED S) average (range) =9.55 ( 8.0- 11 )]. Naming of trained items improved for 45 participants ( 81.82%). Effect sizes indicated there was a small treatment effect.
Conclusions: SFA leads to p ositive outcomes despite the variability of treatment procedures, dosage, duration and variations to the traditional SFA protocol. Further research is warranted to examine the efficacy of SFA and generalization effects in larger controlled studies
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