5,113 research outputs found
Green Grass, High Cotton: Reflections on the Evolution of the Journal of Advertising
This article reflects on my time as the fifth editor of the Journal of Advertising, makes observations about the evolution of scholarship in the Journal over the past decades, offers suggestions for how JA might advance in the coming years, and provides some “words of wisdom” to advertising researchers. Because it is the first in an invited article series of editor reflections, a bit of historical context is provided
Past, Present, and Future of Simultaneous Localization And Mapping: Towards the Robust-Perception Age
Simultaneous Localization and Mapping (SLAM)consists in the concurrent
construction of a model of the environment (the map), and the estimation of the
state of the robot moving within it. The SLAM community has made astonishing
progress over the last 30 years, enabling large-scale real-world applications,
and witnessing a steady transition of this technology to industry. We survey
the current state of SLAM. We start by presenting what is now the de-facto
standard formulation for SLAM. We then review related work, covering a broad
set of topics including robustness and scalability in long-term mapping, metric
and semantic representations for mapping, theoretical performance guarantees,
active SLAM and exploration, and other new frontiers. This paper simultaneously
serves as a position paper and tutorial to those who are users of SLAM. By
looking at the published research with a critical eye, we delineate open
challenges and new research issues, that still deserve careful scientific
investigation. The paper also contains the authors' take on two questions that
often animate discussions during robotics conferences: Do robots need SLAM? and
Is SLAM solved
Search for nearby stars among proper motion stars selected by optical-to-infrared photometry. I. Discovery of LHS 2090 at spectroscopic distance of d=6pc
We present the discovery of a previously unknown very nearby star - LHS 2090
at a distance of only d=6 pc. In order to find nearby (i.e. d < 25 pc) red
dwarfs, we re-identified high proper motion stars ( 0.18 arcsec/yr) from
the NLTT catalogue (Luyten \cite{luyten7980}) in optical Digitized Sky Survey
data for two different epochs and in the 2MASS data base. Only proper motion
stars with large colour index and with relatively bright infrared
magnitudes () were selected for follow-up spectroscopy. The
low-resolution spectrum of LHS 2090 and its large proper motion (0.79
arcsec/yr) classify this star as an M6.5 dwarf. The resulting spectroscopic
distance estimate from comparing the infrared magnitudes of LHS 2090
with absolute magnitudes of M6.5 dwarfs is pc assuming an
uncertainty in absolute magnitude of 0.4 mag.Comment: 3 pages, 1 figure, accepted for publication in Astronomy and
Astrophysics Letter
Hypervelocity Collisions of Binary Stars at the Galactic Centre
Recent surveys have identified seven hypervelocity stars (HVSs) in the halo
of the Milky Way. Most of these stars may have originated from the breakup of
binary star systems by the nuclear black hole SgrA*. In some instances, the
breakup of the binary may lead to a collision between its member stars. We
examine the dynamical properties of these collisions by simulating thousands of
different binary orbits around SgrA* with a direct N-body integration code. For
some orbital parameters, the two stars collide with an impact velocity lower
than their escape velocity and may therefore coalesce. It is possible for a
coalescing binary to have sufficient velocity to escape the galaxy.
Furthermore, some of the massive S-stars near Sgr A* might be the merger
remnants of binary systems, however this production method can not account for
most of the S-stars.Comment: 5 pages, 2 figures, accepted for publication in MNRA
New neighbours: V. 35 DENIS late-M dwarfs between 10 and 30 parsecs
This paper reports updated results on our systematic mining of the DENIS
database for nearby very cool M-dwarfs (M6V-M8V, 2.0<I-J<3.0, photometric
distance within 30 pc), We calibrate the DENIS (M_I, I-J) colour-luminosity
relationship from M dwarfs with well measured parallaxes (HIP, GCTP,...),
obtaining distance errors for single dwarfs of 25%. Using proper motions
measured on archive Schmidt plates for stars that meet the photometric
selection criteria, we eliminate the giants by a Reduced Proper Motion cutoff,
which is significantly more selective than a simple proper motion cutoff.
Here we present new data for 62 red dwarf candidates selected over 5700
square degrees in the DENIS database. 26 of those originate in the 2100 square
degrees analysed in Paper I, with improved parameters here, and 36 were found
in 3600 additional square degrees. 25 of those are new nearby dwarfs. We
determine from that sample of 62 stars a stellar density for 12.0<M_I<14.0 of
2.2(+-0.4)E-3 stars/pc^3/mag. This value is consistent with photometric
luminosity functions measured from deeper and smaller-field observations, but
not with the nearby star luminosity function. In addition we cross-identified
the NLTT and DENIS catalogues to find 15 similar stars, in parts of the sky not
yet covered by the colour-selected search.Comment: Accepted by Astronomy & astrophysics. 17 pages, 8 figure
The nuclear star cluster of the Milky Way: proper motions and mass
Nuclear star clusters (NSCs) are located at the photometric and dynamical
centers of the majority of galaxies. They are among the densest star clusters
in the Universe. The NSC in the Milky Way is the only object of this class that
can be resolved into individual stars. We measured the proper motions of more
than 6000 stars within ~1.0 pc of the supermassive black hole Sgr A*. The full
data set is provided in this work. We largely exclude the known early-type
stars with their peculiar dynamical properties from the dynamical analysis. The
cluster is found to rotate parallel to Galactic rotation, while the velocity
dispersion appears isotropic (or anisotropy may be masked by the cluster
rotation). The Keplerian fall-off of the velocity dispersion due to the point
mass of Sgr A* is clearly detectable only at R <~ 0.3 pc. Nonparametric
isotropic and anisotropic Jeans models are applied to the data. They imply a
best-fit black hole mass of 3.6 (+0.2/-0.4) x 10^6 solar masses. Although this
value is slightly lower than the current canonical value of 4.0x10^6 solar
masses, this is the first time that a proper motion analysis provides a mass
for Sagittarius A* that is consistent with the mass inferred from orbits of
individual stars. The point mass of Sagittarius A* is not sufficient to explain
the velocity data. In addition to the black hole, the models require the
presence of an extended mass of 0.5-1.5x10^6 solar masses in the central
parsec. This is the first time that the extended mass of the nuclear star
cluster is unambiguously detected. The influence of the extended mass on the
gravitational potential becomes notable at distances >~0.4 pc from Sgr A*.
Constraints on the distribution of this extended mass are weak. The extended
mass can be explained well by the mass of the stars that make up the cluster.Comment: accepted for publication in Astronomy & Astrophysics; please contact
first author for higher quality figure
The Anisotropic Spatial Distribution of Hypervelocity Stars
We study the distribution of angular positions and angular separations of
unbound hypervelocity stars (HVSs). HVSs are spatially anisotropic at the
3-sigma level. The spatial anisotropy is significant in Galactic longitude, not
in latitude, and the inclusion of lower velocity, possibly bound HVSs reduces
the significance of the anisotropy. We discuss how the observed distribution of
HVSs may be linked to their origin. In the future, measuring the distribution
of HVSs in the southern sky will provide additional constraints on the spatial
anisotropy and the origin of HVSs.Comment: 4 pages, accepted to ApJ Letter
Artful Thinking: Critical and Creative Thinking in Primary and Secondary Visual Arts Education
This study is an investigation into critical and creative thinking in visual arts education. It is often claimed that the development of critical and creative thinking amongst students is a central concern of arts education. Moreover, it is frequently assumed that critical and creative thinking result naturally from arts education because the discipline is innately creative. However, educational research suggests otherwise; namely, a more deliberate teacher-directed approach is required to foster these thinking skills amongst students. While a number of studies have highlighted the value of arts learning in promoting these kinds of higher order thinking skills, little has been documented about the educational approaches or strategies used to foster them. This thesis begins to fill this gap in the research by documenting perspectives and practices associated with critical and creative thinking in the visual arts classroom. The study explores the perspectives and practices of four experienced and competent art teachers and their students. Specifically, ethnographic case study methods are used to gather, analyse and triangulate significant data. Four different cases – two in primary and two in secondary school – are included in the study. Data was collected through observation records and interviews with teachers and students in these case groups. Through field-based data collection and subsequent data analyses, a series of descriptive portraits are created that illustrate different pedagogical approaches to teaching critical and creative thinking through the visual arts. These portraits reflect teacher practitioners' theories and the value they ascribe to training critical and creative thinking through art. In addition, they reflect the ways these teachers' theories and beliefs impact on education practices in their classrooms. While the four case studies could not possibly represent the realities of the broader field of art education, they are able to capture some of the diversity that exists in art teaching practices
Massive Stars: Their Birth Sites and Distribution
The stellar IMF has been found to be an invariant Salpeter power-law
(alpha=2.35) above about 1 Msun, but at the same time a massive star typically
has more than one companion. This constrains the possible formation scenarios
of massive stars, but also implies that the true, binary-star corrected stellar
IMF could be significantly steeper than Salpeter, alpha>2.7. A significant
fraction of all OB stars are found relatively far from potential birth sites
which is most probably a result of dynamical ejections from cores of
binary-rich star clusters. Such cores form rapidly due to dynamical mass
segregation, or they are primordial. Probably all OB stars thus form in stellar
clusters together with low-mass stars, and they have a rather devastating
effect on the embedded cluster by rapidly driving out the remaining gas leaving
expanding OB associations and bound star clusters. The distributed population
of OB stars has a measured IMF with alpha about 4, which however, does not
necessarily constitute a different physical mode for isolated star formation. A
steep field-star IMF is obtained naturally because stars form in clusters which
are distributed according to a power-law cluster mass function.Comment: 12 pages, New Astronomy Reviews, accepted, minor changes to text for
consistency with published versio
The curious case of (caffeine).(benzoic acid): how heteronuclear seeding allowed the formation of an elusive cocrystal
Cocrystals are modular multicomponent solids with exceptional utility in synthetic chemistry and materials science. A variety of methods exist for the preparation of cocrystals yet, some promising cocrystal phases have proven to be intractable synthetic targets. We describe a strategy for the synthesis of the pharmaceutically relevant (caffeine).(benzoic acid) cocrystal (1), which persistently failed to form using a broad range of established techniques. State-of-the-art crystal structure prediction methods were employed to assess the possible existence of a thermodynamically stable form of 1, and to identify appropriate heteronuclear seeds for corystallization. Once introduced, the designed heteronuclear seeds facilitated the formation of 1 and, significantly, continued to act as long-lasting laboratory .contaminants., which encouraged cocrystal formation even when present at such low levels as to evade detection. The seeding technique described thus enables the synthesis of cocrystals regarded as unobtainable under desired conditions, and potentially signifies a new direction in the field of materials research
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