507 research outputs found
Alien Registration- Shaw, Isaac L. (Perry, Washington County)
https://digitalmaine.com/alien_docs/1553/thumbnail.jp
A subarcsecond resolution near-infrared study of Seyfert and `normal' galaxies: II. Morphology
We present a detailed study of the bar fraction in the CfA sample of Seyfert
galaxies, and in a carefully selected control sample of non-active galaxies, to
investigate the relation between the presence of bars and of nuclear activity.
To avoid the problems related to bar classification in the RC3, e.g.,
subjectivity, low resolution and contamination by dust, we have developed an
objective bar classification method, which we conservatively apply to our new
sub-arcsecond resolution near-infrared imaging data set (Peletier et al. 1999).
We are able to use stringent criteria based on radial profiles of ellipticity
and major axis position angle to determine the presence of a bar and its axial
ratio. Concentrating on non-interacting galaxies in our sample for which
morphological information can be obtained, we find that Seyfert hosts are
barred more often (79% +/- 7.5%) than the non-active galaxies in our control
sample (59% +/- 9%), a result which is at the 2.5 sigma significance level. The
fraction of non-axisymmetric hosts becomes even larger when interacting
galaxies are taken into account. We discuss the implications of this result for
the fueling of central activity by large-scale bars. This paper improves on
previous work by means of imaging at higher spatial resolution and by the use
of a set of stringent criteria for bar presence, and confirms that the use of
NIR is superior to optical imaging for detection of bars in disk galaxies.Comment: Latex, 3 figures, includes aaspptwo.sty, accepted for publication in
the Astrophysical Journa
Long-Lived Double-Barred Galaxies: Critical Mass and Length Scales
A substantial fraction of disk galaxies is double-barred. We analyze the
dynamical stability of such nested bar systems by means of Liapunov
exponents,by fixing a generic model and varying the inner (secondary) bar mass.
We show that there exists a critical mass below which the secondary bar cannot
sustain its own orbital structure, and above which it progressively destroys
the outer (primary) bar-supporting orbits. In this critical state, a large
fraction of the trajectories (regular and chaotic) are aligned with either bar,
suggesting the plausibility of long-lived dynamical states when
secondary-to-primary bar mass ratio is of the order of a few percent.
Qualitatively similar results are obtained by varying the size of the secondary
bar, within certain limits, while keeping its mass constant. In both cases, an
important role appears to be played by chaotic trajectories which are trapped
around (especially) the primary bar for long periods of time.Comment: 7 pages, 1 figure, to be published in Astrophysical Journal Letters
(Vol. 595, 9/20/03 issue). Replaced by revised figure and corrected typo
Mechanisms of MR/N024524/1Scarless Repair at Time of Menstruation: Insights From Mouse Models
The human endometrium is a remarkable tissue which may experience up to 400 cycles of hormone-driven proliferation, differentiation and breakdown during a woman's reproductive lifetime. During menstruation, when the luminal portion of tissue breaks down, it resembles a bloody wound with piecemeal shedding, exposure of underlying stroma and a strong inflammatory reaction. In the absence of pathology within a few days the integrity of the tissue is restored without formation of a scar and the endometrium is able to respond appropriately to subsequent endocrine signals in preparation for establishment of pregnancy if fertilization occurs. Understanding mechanisms regulating scarless repair of the endometrium is important both for design of therapies which can treat conditions where this is aberrant (heavy menstrual bleeding, fibroids, endometriosis, Asherman's syndrome) as well as to provide new information that might allow us to reduce fibrosis and scar formation in other tissues. Menstruation only occurs naturally in species that exhibit spontaneous stromal cell decidualization during the fertile cycle such as primates (including women) and the Spiny mouse. To take advantage of genetic models and detailed time course analysis, mouse models of endometrial shedding/repair involving hormonal manipulation, artificial induction of decidualization and hormone withdrawal have been developed and refined. These models are useful in modeling dynamic changes across the time course of repair and have recapitulated key features of endometrial repair in women including local hypoxia and immune cell recruitment. In this review we will consider the evidence that scarless repair of endometrial tissue involves changes in stromal cell function including mesenchyme to epithelial transition, epithelial cell proliferation and multiple populations of immune cells. Processes contributing to endometrial fibrosis (Asherman's syndrome) as well as scarless repair of other tissues including skin and oral mucosa are compared to that of menstrual repair
Encoding One Logical Qubit Into Six Physical Qubits
We discuss two methods to encode one qubit into six physical qubits. Each of
our two examples corrects an arbitrary single-qubit error. Our first example is
a degenerate six-qubit quantum error-correcting code. We explicitly provide the
stabilizer generators, encoding circuit, codewords, logical Pauli operators,
and logical CNOT operator for this code. We also show how to convert this code
into a non-trivial subsystem code that saturates the subsystem Singleton bound.
We then prove that a six-qubit code without entanglement assistance cannot
simultaneously possess a Calderbank-Shor-Steane (CSS) stabilizer and correct an
arbitrary single-qubit error. A corollary of this result is that the Steane
seven-qubit code is the smallest single-error correcting CSS code. Our second
example is the construction of a non-degenerate six-qubit CSS
entanglement-assisted code. This code uses one bit of entanglement (an ebit)
shared between the sender and the receiver and corrects an arbitrary
single-qubit error. The code we obtain is globally equivalent to the Steane
seven-qubit code and thus corrects an arbitrary error on the receiver's half of
the ebit as well. We prove that this code is the smallest code with a CSS
structure that uses only one ebit and corrects an arbitrary single-qubit error
on the sender's side. We discuss the advantages and disadvantages for each of
the two codes.Comment: 13 pages, 3 figures, 4 table
Why Buckling Stellar Bars Weaken in Disk Galaxies
Young stellar bars in disk galaxies experience a vertical buckling
instability which terminates their growth and thickens them, resulting in a
characteristic peanut/boxy shape when viewed edge on. Using N-body simulations
of galactic disks embedded in live halos, we have analyzed the bar structure
throughout this instability and found that the outer third of the bar dissolves
completely while the inner part (within the vertical inner Lindblad resonance)
becomes less oval. The bar acquires the frequently observed peanut/boxy-shaped
isophotes. We also find that the bar buckling is responsible for a mass
injection above the plane, which is subsequently trapped by specific 3-D
families of periodic orbits of particular shapes explaining the observed
isophotes, in line with previous work. Using a 3-D orbit analysis and surfaces
of sections, we infer that the outer part of the bar is dissolved by a rapidly
widening stochastic region around its corotation radius -- a process related to
the bar growth. This leads to a dramatic decrease in the bar size, decrease in
the overall bar strength and a mild increase in its pattern speed, but is not
expected to lead to a complete bar dissolution. The buckling instability
appears primarily responsible for shortening the secular diffusion timescale to
a dynamical one when building the boxy isophotes. The sufficiently long
timescale of described evolution, ~1 Gyr, can affect the observed bar fraction
in local universe and at higher redshifts, both through reduced bar strength
and the absence of dust offset lanes in the bar.Comment: 7 pages, 4 figures, ApJ Letters, in pres
Nested Bars in Disk Galaxies: No Offset Dust Lanes in Secondary Nuclear Bars
Under certain conditions, sub-kpc nuclear bars form inside large-scale
stellar bars of disk galaxies. These secondary bars spend a fraction of their
lifetime in a dynamically-decoupled state, tumbling in the gravitational field
of the outer bars. We analyze the flow pattern in such nested bar systems and
find that secondary bars differ fundamentally from their large-scale
counterparts. In particular the gas flow across the bar-bar interface in these
systems can be more chaotic or more regular in nature, and, contrary to
predictions, has no difficulty in penetrating the secondary bars. The outer
parts of both short and long nuclear bars (with respect to their corotation)
appear to be depopulated of gas, while deep inside them the flow exhibits low
Mach numbers and follows ovally-shaped orbits with little dissipation. We find
that gas-dominated and star-dominated nuclear bars avoid the bar-bar interface,
making both types of bars short relative to their corotation. Furthermore, our
earlier work has shown that dynamically-coupled secondary bars exhibit a
similarly relaxed low-dissipation flow as well. Therefore, no large-scale
shocks form in the nuclear bars, and consequently, no offset dust lanes are
expected there. We find that offset dust lanes cannot be used in the search for
secondary (nuclear) bars.Comment: 13 pages, 8 figures, to be published in ApJ 564, January 10, 200
Single cell RNA sequencing and lineage tracing confirm mesenchyme to epithelial transformation (MET) contributes to repair of the endometrium at menstruation
The human endometrium experiences repetitive cycles of tissue wounding characterised by piecemeal shedding of the surface epithelium and rapid restoration of tissue homeostasis. In this study, we used a mouse model of endometrial repair and three transgenic lines of mice to investigate whether epithelial cells that become incorporated into the newly formed luminal epithelium have their origins in one or more of the mesenchymal cell types present in the stromal compartment of the endometrium. Using scRNAseq, we identified a novel population of PDGFRb + mesenchymal stromal cells that developed a unique transcriptomic signature in response to endometrial breakdown/repair. These cells expressed genes usually considered specific to epithelial cells and in silico trajectory analysis suggested they were stromal fibroblasts in transition to becoming epithelial cells. To confirm our hypothesis we used a lineage tracing strategy to compare the fate of stromal fibroblasts (PDGFRa+) and stromal perivascular cells (NG2/CSPG4+). We demonstrated that stromal fibroblasts can undergo a mesenchyme to epithelial transformation and become incorporated into the re-epithelialised luminal surface of the repaired tissue. This study is the first to discover a novel population of wound-responsive, plastic endometrial stromal fibroblasts that contribute to the rapid restoration of an intact luminal epithelium during endometrial repair. These findings form a platform for comparisons both to endometrial pathologies which involve a fibrotic response (Ashermanâs syndrome, endometriosis) as well as other mucosal tissues which have a variable response to wounding
Aging modulates the effects of ischemic injury upon mesenchymal cells within the renal interstitium and microvasculature
Abstract The renal mesenchyme contains heterogeneous cells, including interstitial fibroblasts and pericytes, with key roles in wound healing. Although healing is impaired in aged kidneys, the effect of age and injury on the mesenchyme remains poorly understood. We characterized renal mesenchymal cell heterogeneity in young vs old animals and after ischemiaâreperfusionâinjury (IRI) using multiplex immunolabeling and single cell transcriptomics. Expression patterns of perivascular cell markers (αâSMA, CD146, NG2, PDGFRâα, and PDGFRâÎČ) correlated with their interstitial location. PDGFRâα and PDGFRâÎČ coâexpression labeled renal myofibroblasts more efficiently than the current standard marker αâSMA, and CD146 was a superior murine renal pericyte marker. Three renal mesenchymal subtypes; pericytes, fibroblasts, and myofibroblasts, were recapitulated with data from two independently performed single cell transcriptomic analyzes of murine kidneys, the first dataset an aging cohort and the second dataset injured kidneys following IRI. Mesenchymal cells segregated into subtypes with distinct patterns of expression with aging and following injury. Baseline uninjured old kidneys resembled postâischemic young kidneys, with this phenotype further exaggerated following IRI. These studies demonstrate that age modulates renal perivascular/interstitial cell marker expression and transcriptome at baseline and in response to injury and provide tools for the histological and transcriptomic analysis of renal mesenchymal cells, paving the way for more accurate classification of renal mesenchymal cell heterogeneity and identification of ageâspecific pathways and targets
Toward Silicon-Matched Singlet Fission: Energy-Level Modifications Through Steric Twisting of Organic Semiconductors
Singlet fission (SF) is a potential avenue for augmenting the performance of silicon photovoltaics, but the scarcity of SF materials energy-matched to silicon represents a barrier to the commercial realization of this technology. In this work, a molecular engineering approach is described to increase the energy of the S1 and T1 energy levels of diketopyrrolopyrrole derivatives such that the energy-level requirements for exothermic SF and energy-transfer to silicon are met. Time-resolved photoluminescence studies show that the silicon-matched materials are SF active in the solid state, forming a correlated triplet pair 1(TT) â a crucial intermediate in the SF process â as observed through Herzberg-Teller emission from 1(TT) at both 77 K and room temperature. Transient electron paramagnetic resonance studies show that the correlated triplet pair does not readily separate into the unbound triplets, which is a requirement for energy harvesting by silicon. The fact that the triplet pair do not separate into free triplets is attributed to the intermolecular crystal packing within the thin films. Nevertheless, these results demonstrate a promising route for energy-tuning silicon-matched SF materials
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