32,551 research outputs found
An FPT 2-Approximation for Tree-Cut Decomposition
The tree-cut width of a graph is a graph parameter defined by Wollan [J.
Comb. Theory, Ser. B, 110:47-66, 2015] with the help of tree-cut
decompositions. In certain cases, tree-cut width appears to be more adequate
than treewidth as an invariant that, when bounded, can accelerate the
resolution of intractable problems. While designing algorithms for problems
with bounded tree-cut width, it is important to have a parametrically tractable
way to compute the exact value of this parameter or, at least, some constant
approximation of it. In this paper we give a parameterized 2-approximation
algorithm for the computation of tree-cut width; for an input -vertex graph
and an integer , our algorithm either confirms that the tree-cut width
of is more than or returns a tree-cut decomposition of certifying
that its tree-cut width is at most , in time .
Prior to this work, no constructive parameterized algorithms, even approximated
ones, existed for computing the tree-cut width of a graph. As a consequence of
the Graph Minors series by Robertson and Seymour, only the existence of a
decision algorithm was known.Comment: 17 pages, 3 figure
Recognizing hyperelliptic graphs in polynomial time
Recently, a new set of multigraph parameters was defined, called
"gonalities". Gonality bears some similarity to treewidth, and is a relevant
graph parameter for problems in number theory and multigraph algorithms.
Multigraphs of gonality 1 are trees. We consider so-called "hyperelliptic
graphs" (multigraphs of gonality 2) and provide a safe and complete sets of
reduction rules for such multigraphs, showing that for three of the flavors of
gonality, we can recognize hyperelliptic graphs in O(n log n+m) time, where n
is the number of vertices and m the number of edges of the multigraph.Comment: 33 pages, 8 figure
Disease recurrence and rejection following liver transplantation for autoimmune chronic active liver disease
Autoimmune chronic active liver disease (ACALD), a major indication for liver transplantation, is associated strongly with antigenic determinants HLA-B8 and DR3. A retrospective analysis of 43 patients who underwent OLTx for putative ACALD and who, as well as their tissue organ donors, were typed, was performed. Disease recurrence and graft rejection episodes were determined by chart review and histopathological review of all material available. Disease recurrence was histologically documented in 11 (25.6%) of these 43 cases. Graft rejection episodes occurred in 24 (66.8%). All recurrences were in recipients of HLA-DR3-negative grafts. Nine of the recurrences were in HLA-DR3-poeitive recipients (odds ratio: 6.14, P<0.03). Two of 11 cases of disease recurrence were in recipients who were HLA-DR3-negative. Nine of these 11 had received HLA-DR3-negative grafts. Rejection occurred in 13 HLA-B8-positive recipients, 12 of whom received HLA-B8-negative grafts. Eleven HLA-B8-negative recipients experienced at least one rejection episode and 9 of these had received HLA-B8-negative grafts. Based upon these data we conclude: 1) that recurrence of putative ACALD is more likely to occur in HLA-DR3-positive recipients of HLA-DR3-negative grafts; (2) that recurrences were not seen in recipients of HLA-DR3-positive grafts; (3) that BXA-B8 status does not affect disease recurrence; and (4) that neither the HLA-B8 nor the DR3 status of the graft or recipient has an effect on the observed frequency of rejection. ©1992 by Williams & Wilkins
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Cats with thermal burn injuries from California wildfires show echocardiographic evidence of myocardial thickening and intracardiac thrombi.
Recent increases in the prevalence and severity of wildfires in some regions have resulted in an increased frequency of veterinary burn patients. Few studies exist regarding diagnostics and management of burn wounds in veterinary patients and current knowledge is extrapolated from human literature and research models. Post-burn cardiac injury is a common finding and predictor of mortality in human patients and echocardiography is an important tool in monitoring response to therapy and predicting outcome. We describe the notable findings from cats naturally exposed to California wildfires in 2017 and 2018. Domestic cats (n = 51) sustaining burn injuries from the Tubbs (2017) and Camp (2018) wildfires were prospectively enrolled and serial echocardiograms and cardiac troponin I evaluations were performed. Echocardiograms of affected cats revealed a high prevalence of myocardial thickening (18/51) and spontaneous echocardiographic contrast and thrombi formation (16/51). Forty-two cats survived to discharge and 6 died or were euthanized due to a possible cardiac cause. For the first time, we describe cardiovascular and coagulation effects of thermal burn and smoke inhalation in cats. Further studies in veterinary burn victims are warranted and serve as a translational research opportunity for uncovering novel disease mechanisms and therapies
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Re: the role of radiology in anatomy teaching in UK medical schools: a national survey. A reply.
Sir – We thank Raja and colleagues1 for their interest in our article and share their enthusiasm for the integration of radiology in anatomy teaching. This is something that we feel passionate about. Two of our authors are full-time practicing consultant radiologists with additional roles as medical educators in anatomy teaching at the University of Cambridge medical school
Fast Algorithms for Join Operations on Tree Decompositions
Treewidth is a measure of how tree-like a graph is. It has many important
algorithmic applications because many NP-hard problems on general graphs become
tractable when restricted to graphs of bounded treewidth. Algorithms for
problems on graphs of bounded treewidth mostly are dynamic programming
algorithms using the structure of a tree decomposition of the graph. The
bottleneck in the worst-case run time of these algorithms often is the
computations for the so called join nodes in the associated nice tree
decomposition.
In this paper, we review two different approaches that have appeared in the
literature about computations for the join nodes: one using fast zeta and
M\"obius transforms and one using fast Fourier transforms. We combine these
approaches to obtain new, faster algorithms for a broad class of vertex subset
problems known as the [\sigma,\rho]-domination problems. Our main result is
that we show how to solve [\sigma,\rho]-domination problems in arithmetic operations. Here, t is the treewidth, s is the
(fixed) number of states required to represent partial solutions of the
specific [\sigma,\rho]-domination problem, and n is the number of vertices in
the graph. This reduces the polynomial factors involved compared to the
previously best time bound (van Rooij, Bodlaender, Rossmanith, ESA 2009) of arithmetic operations. In particular, this removes
the dependence of the degree of the polynomial on the fixed number of
states~.Comment: An earlier version appeared in "Treewidth, Kernels, and Algorithms.
Essays Dedicated to Hans L. Bodlaender on the Occasion of His 60th Birthday"
LNCS 1216
Multidimensional Binary Vector Assignment problem: standard, structural and above guarantee parameterizations
In this article we focus on the parameterized complexity of the
Multidimensional Binary Vector Assignment problem (called \BVA). An input of
this problem is defined by disjoint sets , each
composed of binary vectors of size . An output is a set of disjoint
-tuples of vectors, where each -tuple is obtained by picking one vector
from each set . To each -tuple we associate a dimensional vector by
applying the bit-wise AND operation on the vectors of the tuple. The
objective is to minimize the total number of zeros in these vectors. mBVA
can be seen as a variant of multidimensional matching where hyperedges are
implicitly locally encoded via labels attached to vertices, but was originally
introduced in the context of integrated circuit manufacturing.
We provide for this problem FPT algorithms and negative results (-based
results, [2]-hardness and a kernel lower bound) according to several
parameters: the standard parameter i.e. the total number of zeros), as well
as two parameters above some guaranteed values.Comment: 16 pages, 6 figure
Psychosocial perception of adults with onychomycosis: a blinded, controlled comparison of 1,017 adult Hong Kong residents with or without onychomycosis
BACKGROUND: A survey was conducted amongst 1,017 Hong Kong residents ages 18 and over to determine their knowledge of fungal nail infections (onychomycosis) and the psychosocial impact of the disease on the relationships, social lives and careers of sufferers. METHODS: The Fungal Nail Perception Survey was conducted by email and online between May 29th and June 10th, 2013. Participants were shown three photographs of people with and without onychomycosis of the toenails. Respondents were asked ten questions (repeated for each picture) to ascertain their perceptions of the people in the pictures. Questions were related to perceptions around the ability of sufferers and non-sufferers to form relationships with others, social activities of sufferers and non-sufferers, perceptions of the effect of the disease on the potential for career success, and awareness of fungal nail disease and health. The sub-population who themselves suffered from onychomycosis were asked about self-perception as well as their perception of others with onychomycosis. RESULTS: Compared with non-sufferers, survey respondents perceived those with onychomycosis as less likely to be able to form good relationships. They also indicated that they would be more likely to exclude sufferers than non-sufferers from social activities and that they would be more likely to feel uncomfortable when sitting or standing beside an infected person than beside an uninfected person. Respondents perceived people with onychomycosis to be less able to perform well in their chosen career than with someone without onychomycosis. Interestingly, those respondents who themselves were infected felt socially excluded, upset and embarrassed by their infection. CONCLUSIONS: Onychomycosis may lead to stigmatization and social exclusion. Misconceptions of onychomycosis are high and education about the disease needs to be improved. Early recognition and treatment of the disease is essential to avoid complications and improve treatment outcomes, which would lead to reduced psychosocial impact on those with fungal nail infections
Edge Shear Flows and Particle Transport near the Density Limit in the HL-2A Tokamak
Edge shear flow and its effect on regulating turbulent transport have long
been suspected to play an important role in plasmas operating near the
Greenwald density limit . In this study, equilibrium profiles as well as
the turbulent particle flux and Reynolds stress across the separatrix in the
HL-2A tokamak are examined as is approached in ohmic L-mode discharges.
As the normalized line-averaged density is raised, the
shearing rate of the mean poloidal flow drops, and the
turbulent drive for the low-frequency zonal flow (the Reynolds power ) collapses. Correspondingly, the turbulent particle
transport increases drastically with increasing collision rates. The geodesic
acoustic modes (GAMs) gain more energy from the ambient turbulence at higher
densities, but have smaller shearing rate than low-frequency zonal flows. The
increased density also introduces decreased adiabaticity which not only
enhances the particle transport but is also related to a reduction in the
eddy-tilting and the Reynolds power. Both effects may lead to the cooling of
edge plasmas and therefore the onset of MHD instabilities that limit the plasma
density
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