20,655 research outputs found
Gaia Stellar Kinematics in the Head of the Orion A Cloud: Runaway Stellar Groups and Gravitational Infall
This work extends previous kinematic studies of young stars in the Head of
the Orion A cloud (OMC-1/2/3/4/5). It is based on large samples of infrared,
optical, and X-ray selected pre-main sequence stars with reliable radial
velocities and Gaia-derived parallaxes and proper motions. Stellar kinematic
groups are identified assuming they mimic the motion of their parental gas.
Several groups are found to have peculiar kinematics: the NGC 1977 cluster and
two stellar groups in the Extended Orion Nebula (EON) cavity are caught in the
act of departing their birthplaces. The abnormal motion of NGC 1977 may have
been caused by a global hierarchical cloud collapse, feedback by massive Ori
OB1ab stars, supersonic turbulence, cloud-cloud collision, and/or slingshot
effect; the former two models are favored by us. EON groups might have
inherited anomalous motions of their parental cloudlets due to small-scale
`rocket effects' from nearby OB stars. We also identify sparse stellar groups
to the east and west of Orion A that are drifting from the central region,
possibly a slowly expanding halo of the Orion Nebula Cluster. We confirm
previously reported findings of varying line-of-sight distances to different
parts of the cloud's Head with associated differences in gas velocity.
Three-dimensional movies of star kinematics show contraction of the groups of
stars in OMC-1 and global contraction of OMC-123 stars. Overall, the Head of
Orion A region exhibits complex motions consistent with theoretical models
involving hierarchical gravitational collapse in (possibly turbulent) clouds
with OB stellar feedback.Comment: Accepted for publication in MNRAS. 26 pages, 13 figures. The two 3-D
stellar kinematic movies, aimed as Supplementary Materials, can be found on
YouTube at: https://youtu.be/B4GHCVvCYfo (`restricted' sample) and
https://youtu.be/6fUu8sP0QFI (`full' sample
Towards Semantic Integration of Heterogeneous Sensor Data with Indigenous Knowledge for Drought Forecasting
In the Internet of Things (IoT) domain, various heterogeneous ubiquitous
devices would be able to connect and communicate with each other seamlessly,
irrespective of the domain. Semantic representation of data through detailed
standardized annotation has shown to improve the integration of the
interconnected heterogeneous devices. However, the semantic representation of
these heterogeneous data sources for environmental monitoring systems is not
yet well supported. To achieve the maximum benefits of IoT for drought
forecasting, a dedicated semantic middleware solution is required. This
research proposes a middleware that semantically represents and integrates
heterogeneous data sources with indigenous knowledge based on a unified
ontology for an accurate IoT-based drought early warning system (DEWS).Comment: 5 pages, 3 figures, In Proceedings of the Doctoral Symposium of the
16th International Middleware Conference (Middleware Doct Symposium 2015),
Ivan Beschastnikh and Wouter Joosen (Eds.). ACM, New York, NY, US
Optimizing photon indistinguishability in the emission from incoherently-excited semiconductor quantum dots
Most optical quantum devices require deterministic single-photon emitters.
Schemes so far demonstrated in the solid state imply an energy relaxation which
tends to spoil the coherent nature of the time evolution, and with it the
photon indistinguishability. We focus our theoretical investigation on
semiconductor quantum dots embedded in microcavities. Simple and general
relations are identified between the photon indistinguishability and the
collection efficiency. The identification of the key parameters and of their
interplay provides clear indications for the device optimization
Counter-Intuitive Vacuum-Stimulated Raman Scattering
Vacuum-stimulated Raman scattering in strongly coupled atom-cavity systems
allows one to generate free-running single photon pulses on demand. Most
properties of the emitted photons are well defined, provided spontaneous
emission processes do not contribute. Therefore, electronic excitation of the
atom must not occur, which is assured for a system adiabatically following a
dark state during the photon-generation process. We experimentally investigate
the conditions that must be met for adiabatic following in a time-of-flight
driven system, with atoms passing through a cavity and a pump beam oriented
transverse to the cavity axis. From our results, we infer the optimal intensity
and relative pump-beam position with respect to the cavity axis.Comment: 4 pages, 4 figure
Influence of temperature probe sheathing materials during ultrasonic heating
Journal ArticleThe influence of sheathing materials upon temperature probes used during the monitoring of ultrasonic heating was measured. The measurements show that the sheathing can be heated in a manner not representative of the temperature rise occurring in the surrounding material, altering the probe readings
Control in the technical societies: a brief history
By the time control engineering emerged as a coherent body of knowledge and practice (during and just after WW2) professional engineering societies had existed for many decades. Since control engineering is an interdisciplinary branch of the profession, new sections devoted to control were quickly established within the various existing technical societies. In addition, some new bodies devoted specifically or primarily to control were established. This article, a revised version of a paper presented at the IEEE 2009 Conference on the History of Technical Societies, describes how control engineering as a distinct branch of engineering became represented in technical societies in a number of countries
Regional inequalities and transnational solidarity in the European Union
Amid the eurocrisis, scholars and policy makers sought to establish an EU-wide layer of social policy, aiming to ensure common standards through the EU and to
provide a degree of common social protection. While public support for European social policy has been extensively studied, we don’t know how regional (i.e.,
subnational) inequalities relate to preferences for European social policy. We analyse the effect of regional differences in socio-economic and institutional contexts on
public preferences for European social policy in general and support for European unemployment insurance in particular. Combining original survey data collected in
2018 in 12 European countries with regional-level economic and political indicators, we find that regional-level self-interest impacts individual preferences but that
the effect is not always clear-cut. Contrary to expectations, people in richer regions are more supportive of EU social policy than people in poorer regions, while
citizens of politically more autonomous regions tend to have a generally more positive view of EU social policy. A conjoint experiment on support for different policy
variants of European unemployment insurance sheds light on these counterintuitive findings: Citizens in richer regions are indeed more supportive of EU-level social
policy, but only when it has limited redistributive implications and instead affects standards; conversely citizens in poorer regions are willing to forego their op-
position to EU social policy for redistributive programs
Regional inequalities and transnational solidarity in the European Union
Amid the eurocrisis, scholars and policy makers sought to establish an EU-wide layer of social policy, aiming to ensure common standards through the EU and to provide a degree of common social protection. While public support for European social policy has been extensively studied, we don't know how regional (i.e., subnational) inequalities relate to preferences for European social policy. We analyse the effect of regional differences in socio-economic and institutional contexts on public preferences for European social policy in general and support for European unemployment insurance in particular. Combining original survey data collected in 2018 in 12 European countries with regional-level economic and political indicators, we find that regional-level self-interest impacts individual preferences but that the effect is not always clear-cut. Contrary to expectations, people in richer regions are more supportive of EU social policy than people in poorer regions, while citizens of politically more autonomous regions tend to have a generally more positive view of EU social policy. A conjoint experiment on support for different policy variants of European unemployment insurance sheds light on these counterintuitive findings: Citizens in richer regions are indeed more supportive of EU-level social policy, but only when it has limited redistributive implications and instead affects standards; conversely citizens in poorer regions are willing to forego their opposition to EU social policy for redistributive programs
High precision determination of the -evolution of the Bjorken Sum
We present a significantly improved determination of the Bjorken Sum for
0.64.8 GeV using precise new and
data taken with the CLAS detector at Jefferson Lab. A higher-twist analysis of
the -dependence of the Bjorken Sum yields the twist-4 coefficient
. This leads to the color
polarizabilities and
. The strong force coupling is determined to be
\alpha_{s}^{\overline{\mbox{ MS}}}(M_{Z}^{2})=0.1124\pm0.0061, which has an
uncertainty a factor of 1.5 smaller than earlier estimates using polarized DIS
data. This improvement makes the comparison between extracted from
polarized DIS and other techniques a valuable test of QCD.Comment: Published in Phys. Rev. D. V1: 8 pages, 3 figures. V2: Updated
references; Included threshold matching in \alpha_s evolution. Corrected a
typo on the uncertainty for \Lambda_QCD. V3: Published versio
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