270 research outputs found
Permutability of Matrices over Bipotent Semirings
We study permutability properties of matrix semigroups over commutative
bipotent semirings (of which the best-known example is the tropical semiring).
We prove that every such semigroup is weakly permutable (a result previous
stated in the literature, but with an erroneous proof) and then proceed to
study in depth the question of when they are strongly permutable (which turns
out to depend heavily on the semiring). Along the way we classify monogenic
bipotent semirings and describe all isomorphisms between truncated tropical
semirings.Comment: 19 page
Tropical Representations and Identities of the Stylic Monoid
We exhibit a faithful representation of the stylic monoid of every finite
rank as a monoid of upper unitriangular matrices over the tropical semiring.
Thus, we show that the stylic monoid of finite rank generates the
pseudovariety , which corresponds to the class of
all piecewise testable languages of height , in the framework of Eilenberg's
correspondence. From this, we obtain the equational theory of the stylic
monoids of finite rank, show that they are finitely based if and only if , and that their identity checking problem is decidable in linearithmic
time. We also establish connections between the stylic monoids and other
plactic-like monoids, and solve the finite basis problem for the stylic monoid
with involution.Comment: 22 pages. Added results on the finite basis problem for the stylic
monoid with involution and updated reference
Lattices of varieties of plactic-like monoids
We study the equational theories and bases of meets and joins of several
varieties of plactic-like monoids. Using those results, we construct
sublattices of the lattice of varieties of monoids, generated by said
varieties. We calculate the axiomatic ranks of their elements, obtain
plactic-like congruences whose corresponding factor monoids generate varieties
in the lattice, and determine which varieties are joins of the variety of
commutative monoids and a finitely generated variety. We also show that the
hyposylvester and metasylvester monoids generate the same variety as the
sylvester monoid.Comment: 36 pages, 3 figures, 1 tabl
Integrating Metaliteracy into the Design of a Collaborative Online International Learning (COIL) Course in Digital Storytelling
This paper explores the redesign of a course in Digital Storytelling that integrates metaliteracy to advance Collaborative Online International Learning (COIL). Students from the United States and Prague, Czech Republic are active participants in this fully online global course as they learn to produce digital stories. The metaliteracy framework encourages metacognitive reflection and the active participation in social information environments. A collaborative teaching team from the United States and Europe redesigned this course to integrate metaliteracy into the learning activities and self-assessments. As students learn to become digital storytellers, they self-identify with specific metaliterate learner roles (producer, collaborator, researcher, etc.), assess their learning through four domains of metaliterate learning (affective, behavioural, cognitive, and metacognitive), and lastly reflect on their work in the course through the metaliteracy characteristics (collaborative, open, reflective, civic-minded, etc.). The internationalization of education in this COIL course is enhanced by the novel combination of metaliteracy and digital storytelling.</p
Excess AGN Activity in the z=2.30 Protocluster in HS 1700+64
We present the results of spectroscopic, narrow-band and X-ray observations
of a z=2.30 protocluster in the field of the QSO HS 1700+643. Using a sample of
BX/MD galaxies, which are selected to be at z~2.2-2.7 by their rest-frame
ultraviolet colours, we find that there are 5 protocluster AGN which have been
identified by characteristic emission-lines in their optical/near-IR spectra;
this represents an enhancement over the field significant at ~98.5 per cent
confidence. Using a ~200 ks Chandra/ACIS-I observation of this field we detect
a total of 161 X-ray point sources to a Poissonian false-probability limit of
4x10^{-6} and identify 8 of these with BX/MD galaxies. Two of these are
spectroscopically confirmed protocluster members and are also classified as
emission-line AGN. When compared to a similarly selected field sample the
analysis indicates this is also evidence for an enhancement of X-ray selected
BX/MD AGN over the field, significant at ~99 per cent confidence. Deep Lya
narrow-band imaging reveals that a total of 4/123 Lya emitters (LAEs) are found
to be associated with X-ray sources, with two of these confirmed protocluster
members and one highly likely member. We do not find a significant enhancement
of AGN activity in this LAE sample over that of the field (result significant
at only 87 per cent confidence). The X-ray emitting AGN fractions for the BX/MD
and LAE samples are found to be 6.9_{-4.4}^{+9.2} and 2.9_{-1.6}^{+2.9} per
cent, respectively, for protocluster AGN with L_{2-10 keV}>4.6x10^{43} erg
s^{-1} at z=2.30. These findings are similar to results from the z=3.09
protocluster in the SSA 22 field found by Lehmer et al. (2009), in that both
suggest AGN activity is favoured in dense environments at z>2.Comment: 8 pages, 2 figures. Accepted for publication in MNRAS
The role of environment in low-level active galactic nucleus activity: no evidence for cluster enhancement
We use the AMUSE-Virgo and AMUSE-Field surveys for nuclear X-ray emission in
early-type galaxies to conduct a controlled comparison of low-level
supermassive black hole activity within cluster and field spheroids. While both
the Virgo and the Field samples feature highly sub-Eddington X-ray luminosities
(log L_x/L_Edd between -8 and -4), we find that after accounting for the
influence of host galaxy stellar mass, the field early-type galaxies tend
toward marginally greater (0.38+/-0.14 dex) nuclear X-ray luminosities, at a
given black hole mass, than their cluster counterparts. This trend is
qualitatively consistent with the field black holes having access to a greater
reservoir of fuel, plausibly in the form of cold gas located near the nucleus.
We are able to rule out at high confidence the alternative of enhanced X-ray
activity within clusters. Presuming nuclear X-ray emission correlates with the
total energy and momentum output of these weakly accreting black holes, this
indicates that low-level active galactic nucleus feedback is not generally
stronger within typical cluster galaxies than in the field. These results
confirm that for most cluster early-type galaxies (i.e., excluding brightest
cluster galaxies) direct environmental effects, such as gas stripping, are more
relevant in quenching star formation.Comment: Corrected typos and references; 6 pages emulateapj, 2 tables, 3
figures. Published in ApJ Letter
A Holocene record of savanna vegetation dynamics in southern lowland Papua New Guinea
The southern lowlands of Papua New Guinea (PNG) are biogeographically distinct. Vast tracts of savanna vegetation occur there and yet most palaeoecological studies have focused on highlands and/or forest environments. Greater focus on long-term lowland environments provides a rare opportunity to understand and promote the significance of local and regional savannas, ultimately allowing non-forested and forested ecosystem dynamics to be compared. This paper examines palaeoecological and archaeological data from a lowland open savanna site situated on the south-central PNG coastline. The methods used incorporate pollen and micro-charcoal analyses, artefact recovery and sediment descriptions. We conclude with an environmental model of sedimentation and vegetation change for the past c. 5,800 years, revealing a mid to late Holocene savanna interchange between herbaceous and woody plant growth, with fluctuating fire occurrence increasing toward the present day. Increased silt deposition and modified regional hydrology are also recorded. Environmental changes correspond in timing with the start of permanent settlements and human use of fire. In particular, landscape burning for hunting and gardens for agriculture have helped create the open ecosystem still evident today
Breakdown of the Endothelial Barrier Function in Tumor Cell Transmigration
The ability of tumor cells to metastasize is associated with a poor prognosis for cancer. During the process of metastasis, tumor cells circulating in the blood or lymph vessels can adhere to, and potentially transmigrate through, the endothelium and invade the connective tissue. We studied the effectiveness of the endothelium as a barrier against the invasion of 51 tumor cell lines into a three-dimensional collagen matrix. Only nine tumor cell lines showed attenuated invasion in the presence of an endothelial cell monolayer, whereas 17 cell lines became invasive or showed a significantly increased invasion. Endothelial cells cocultured with invasive tumor cells increased chemokine gene expression of IL-8 and Gro-β. Expression of the IL-8 and Gro-β receptor, CXCR2, was upregulated in invasive tumor cells. Addition of IL-8 or Gro-β increased tumor cell invasiveness by more than twofold. Tumor cell variants selected for high CXCR2 expression were fourfold more invasive in the presence of an endothelial cell layer, whereas CXCR2 siRNA knock-down cells were fivefold less invasive. We demonstrate that Gro-β and IL-8 secreted by endothelial cells, together with CXCR2 receptor expression on invasive tumor cells, contribute to the breakdown of the endothelial barrier by enhancing tumor cell force generation and cytoskeletal remodeling dynamics
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