694 research outputs found
An inefficient dwarf: Chemical abundances and the evolution of the Ursa Minor dwarf spheroidal galaxy
We present detailed chemical element abundance ratios of 17 elements in three
metal poor stars in the Ursa Minor dwarf spheroidal galaxy, which we combine
with extant data from the literature to assess the predictions of a novel suite
of galaxy chemical evolution models. The spectroscopic data were obtained with
the Keck/HIRES instrument and revealed low metallicities of [Fe/H]=-2.12, -2.13
and -2.67 dex. While the most metal poor star in our sample shows an
overabundance of [Mn/Fe] and other Fe-peak elements, our overall findings are
in agreement with previous studies of this galaxy: elevated values of the
[alpha/Fe] ratios that are similar to, or only slightly lower than, the halo
values but with SN Ia enrichment at very low metallicity, as well as an
enhancement of the ratio of first to second peak neutron capture elements
[Y/Ba] with decreasing metallicity. The chemical evolution models which were
tailored to reproduce the metallicity distribution function of the dSph,
indicate that UMi had an extended star formation which lasted nearly 5 Gyr with
low efficiency and are able to explain the [Y/Ba] enhancement at low
metallicity for the first time. In particular, we show that the present day
lack of gas is probably due to continuous loss of gas from the system, which we
model as winds.Comment: 10 pages, 7 figures, table
Hippocampus and retrosplenial cortex combine path integration signals for successful navigation
The current study used fMRI in humans to examine goal-directed navigation in an open field environment. We designed a task that required participants to encode survey-level spatial information and subsequently navigate to a goal location in either first person, third person, or survey perspectives. Critically, no distinguishing landmarks or goal location markers were present in the environment, thereby requiring participants to rely on path integration mechanisms for successful navigation. We focused our analysis on mechanisms related to navigation and mechanisms tracking linear distance to the goal location. Successful navigation required translation of encoded survey-level map information for orientation and implementation of a planned route to the goal. Our results demonstrate that successful first and third person navigation trials recruited the anterior hippocampus more than trials when the goal location was not successfully reached. When examining only successful trials, the retrosplenial and posterior parietal cortices were recruited for goal-directed navigation in both first person and third person perspectives. Unique to first person perspective navigation, the hippocampus was recruited to path integrate self-motion cues with location computations toward the goal location. Last, our results demonstrate that the hippocampus supports goal-directed navigation by actively tracking proximity to the goal throughout navigation. When using path integration mechanisms in first person and third person perspective navigation, the posterior hippocampus was more strongly recruited as participants approach the goal. These findings provide critical insight into the neural mechanisms by which we are able to use map-level representations of our environment to reach our navigational goals
Analysis of return distributions in the coherent noise model
The return distributions of the coherent noise model are studied for the
system size independent case. It is shown that, in this case, these
distributions are in the shape of q-Gaussians, which are the standard
distributions obtained in nonextensive statistical mechanics. Moreover, an
exact relation connecting the exponent of avalanche size distribution
and the q value of appropriate q-Gaussian has been obtained as q=(tau+2)/tau.
Making use of this relation one can easily determine the q parameter values of
the appropriate q-Gaussians a priori from one of the well-known exponents of
the system. Since the coherent noise model has the advantage of producing
different tau values by varying a model parameter \sigma, clear numerical
evidences on the validity of the proposed relation have been achieved for
different cases. Finally, the effect of the system size has also been analysed
and an analytical expression has been proposed, which is corroborated by the
numerical results.Comment: 14 pages, 3 fig
Modeling Islamist Extremist Communications on Social Media using Contextual Dimensions: Religion, Ideology, and Hate
Terror attacks have been linked in part to online extremist content. Although
tens of thousands of Islamist extremism supporters consume such content, they
are a small fraction relative to peaceful Muslims. The efforts to contain the
ever-evolving extremism on social media platforms have remained inadequate and
mostly ineffective. Divergent extremist and mainstream contexts challenge
machine interpretation, with a particular threat to the precision of
classification algorithms. Our context-aware computational approach to the
analysis of extremist content on Twitter breaks down this persuasion process
into building blocks that acknowledge inherent ambiguity and sparsity that
likely challenge both manual and automated classification. We model this
process using a combination of three contextual dimensions -- religion,
ideology, and hate -- each elucidating a degree of radicalization and
highlighting independent features to render them computationally accessible. We
utilize domain-specific knowledge resources for each of these contextual
dimensions such as Qur'an for religion, the books of extremist ideologues and
preachers for political ideology and a social media hate speech corpus for
hate. Our study makes three contributions to reliable analysis: (i) Development
of a computational approach rooted in the contextual dimensions of religion,
ideology, and hate that reflects strategies employed by online Islamist
extremist groups, (ii) An in-depth analysis of relevant tweet datasets with
respect to these dimensions to exclude likely mislabeled users, and (iii) A
framework for understanding online radicalization as a process to assist
counter-programming. Given the potentially significant social impact, we
evaluate the performance of our algorithms to minimize mislabeling, where our
approach outperforms a competitive baseline by 10.2% in precision.Comment: 22 page
ALONE: A Dataset for Toxic Behavior among Adolescents on Twitter
The convenience of social media has also enabled its misuse, potentially resulting in toxic behavior. Nearly 66% of internet users have observed online harassment, and 41% claim personal experience, with 18% facing severe forms of online harassment. This toxic communication has a significant impact on the well-being of young individuals, affecting mental health and, in some cases, resulting in suicide. These communications exhibit complex linguistic and contextual characteristics, making recognition of such narratives challenging. In this paper, we provide a multimodal dataset of toxic social media interactions between confirmed high school students, called ALONE (AdoLescents ON twittEr), along with descriptive explanation. Each instance of interaction includes tweets, images, emoji and related metadata. Our observations show that individual tweets do not provide sufficient evidence for toxic behavior, and meaningful use of context in interactions can enable highlighting or exonerating tweets with purported toxicity
Effect of cutting parameters and tool geometry on the performance analysis of one-shot drilling process of AA2024-t3
Drilling is an important machining process in various manufacturing industries. High-quality holes are possible with the proper selection of tools and cutting parameters. This study investigates the effect of spindle speed, feed rate, and drill diameter on the generated thrust force, the formation of chips, post-machining tool condition, and hole quality. The hole surface defects and the top and bottom edge conditions were also investigated using scan electron microscopy. The drilling tests were carried out on AA2024-T3 alloy under a dry drilling environment using 6 and 10 mm uncoated carbide tools. Analysis of Variance was employed to further evaluate the influence of the input parameters on the analysed outputs. The results show that the thrust force was highly influenced by feed rate and drill size. The high spindle speed resulted in higher surface roughness, while the increase in the feed rate produced more burrs around the edges of the holes. Additionally, the burrs formed at the exit side of holes were larger than those formed at the entry side. The high drill size resulted in greater chip thickness and an increased built-up edge on the cutting tools
Self-organization in dissipative optical lattices
We show that the transition from Gaussian to the q-Gaussian distributions
occurring in atomic transport in dissipative optical lattices can be
interpreted as self-organization by recourse to a modified version of
Klimontovich's S-theorem. As a result, we find that self-organization is
possible in the transition regime, only where the second moment is
finite. Therefore, the nonadditivity parameter q is confined within the range
1<q<5/3, although whole spectrum of q values i.e., 1<q<3, is considered
theoretically possible. The range of q values obtained from the modified
S-theorem is also confirmed by the experiments carried out by Douglas et al.
[Phys. Rev. Lett. 96, 110601 (2006)].Comment: 9 pages, 1 fi
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