56 research outputs found
Simplicial blowups and discrete normal surfaces in simpcomp
simpcomp is an extension to GAP, the well known system for computational
discrete algebra. It allows the user to work with simplicial complexes. In the
latest version, support for simplicial blowups and discrete normal surfaces was
added, both features unique to simpcomp. Furthermore, new functions for
constructing certain infinite series of triangulations have been implemented
and interfaces to other software packages have been improved to previous
versions.Comment: 10 page
Stacked polytopes and tight triangulations of manifolds
Tightness of a triangulated manifold is a topological condition, roughly
meaning that any simplexwise linear embedding of the triangulation into
euclidean space is "as convex as possible". It can thus be understood as a
generalization of the concept of convexity. In even dimensions,
super-neighborliness is known to be a purely combinatorial condition which
implies the tightness of a triangulation.
Here we present other sufficient and purely combinatorial conditions which
can be applied to the odd-dimensional case as well. One of the conditions is
that all vertex links are stacked spheres, which implies that the triangulation
is in Walkup's class . We show that in any dimension
\emph{tight-neighborly} triangulations as defined by Lutz, Sulanke and Swartz
are tight.
Furthermore, triangulations with -stacked vertex links and the centrally
symmetric case are discussed.Comment: 28 pages, 2 figure
simpcomp -- A GAP toolbox for simplicial complexes
simpcomp is an extension (a so called package) to GAP, the well known system
for computational discrete algebra. The package enables the user to compute
numerous properties of (abstract) simplicial complexes, provides functions to
construct new complexes from existing ones and an extensive library of
triangulations of manifolds.Comment: 4 page
A novel feature-scrambling approach reveals the capacity of convolutional neural networks to learn spatial relations
Convolutional neural networks (CNNs) are one of the most successful computer
vision systems to solve object recognition. Furthermore, CNNs have major
applications in understanding the nature of visual representations in the human
brain. Yet it remains poorly understood how CNNs actually make their decisions,
what the nature of their internal representations is, and how their recognition
strategies differ from humans. Specifically, there is a major debate about the
question of whether CNNs primarily rely on surface regularities of objects, or
whether they are capable of exploiting the spatial arrangement of features,
similar to humans. Here, we develop a novel feature-scrambling approach to
explicitly test whether CNNs use the spatial arrangement of features (i.e.
object parts) to classify objects. We combine this approach with a systematic
manipulation of effective receptive field sizes of CNNs as well as minimal
recognizable configurations (MIRCs) analysis. In contrast to much previous
literature, we provide evidence that CNNs are in fact capable of using
relatively long-range spatial relationships for object classification.
Moreover, the extent to which CNNs use spatial relationships depends heavily on
the dataset, e.g. texture vs. sketch. In fact, CNNs even use different
strategies for different classes within heterogeneous datasets (ImageNet),
suggesting CNNs have a continuous spectrum of classification strategies.
Finally, we show that CNNs learn the spatial arrangement of features only up to
an intermediate level of granularity, which suggests that intermediate rather
than global shape features provide the optimal trade-off between sensitivity
and specificity in object classification. These results provide novel insights
into the nature of CNN representations and the extent to which they rely on the
spatial arrangement of features for object classification
Hamiltonian submanifolds of regular polytopes
We investigate polyhedral -manifolds as subcomplexes of the boundary
complex of a regular polytope. We call such a subcomplex {\it -Hamiltonian}
if it contains the full -skeleton of the polytope. Since the case of the
cube is well known and since the case of a simplex was also previously studied
(these are so-called {\it super-neighborly triangulations}) we focus on the
case of the cross polytope and the sporadic regular 4-polytopes. By our results
the existence of 1-Hamiltonian surfaces is now decided for all regular
polytopes.
Furthermore we investigate 2-Hamiltonian 4-manifolds in the -dimensional
cross polytope. These are the "regular cases" satisfying equality in Sparla's
inequality. In particular, we present a new example with 16 vertices which is
highly symmetric with an automorphism group of order 128. Topologically it is
homeomorphic to a connected sum of 7 copies of . By this
example all regular cases of vertices with or, equivalently, all
cases of regular -polytopes with are now decided.Comment: 26 pages, 4 figure
A gut bacterial signature in blood and liver tissue characterizes cirrhosis and hepatocellular carcinoma
BackgroundHCC is the leading cause of cancer in chronic liver disease. A growing body of experimental mouse models supports the notion that gut-resident and liver-resident microbes control hepatic immune responses and, thereby, crucially contribute to liver tumorigenesis. However, a comprehensive characterization of the intestinal microbiome in fueling the transition from chronic liver disease to HCC in humans is currently missing.MethodsHere, we profiled the fecal, blood, and liver tissue microbiome of patients with HCC by 16S rRNA sequencing and compared profiles to nonmalignant cirrhotic and noncirrhotic NAFLD patients.ResultsWe report a distinct bacterial profile, defined from 16S rRNA gene sequences, with reduced α-and β-diversity in the feces of patients with HCC and cirrhosis compared to NAFLD. Patients with HCC and cirrhosis exhibited an increased proportion of fecal bacterial gene signatures in the blood and liver compared to NAFLD. Differential analysis of the relative abundance of bacterial genera identified an increased abundance of Ruminococcaceae and Bacteroidaceae in blood and liver tissue from both HCC and cirrhosis patients compared to NAFLD. Fecal samples from cirrhosis and HCC patients both showed a reduced abundance for several taxa, including short-chain fatty acid-producing genera, such as Blautia and Agathobacter. Using paired 16S rRNA and transcriptome sequencing, we identified a direct association between gut bacterial genus abundance and host transcriptome response within the liver tissue.ConclusionsOur study indicates perturbations of the intestinal and liver-resident microbiome as a critical determinant of patients with cirrhosis and HCC
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Dietary lipids fuel GPX4-restricted enteritis resembling Crohn’s disease
Abstract: The increased incidence of inflammatory bowel disease (IBD) has become a global phenomenon that could be related to adoption of a Western life-style. Westernization of dietary habits is partly characterized by enrichment with the ω-6 polyunsaturated fatty acid (PUFA) arachidonic acid (AA), which entails risk for developing IBD. Glutathione peroxidase 4 (GPX4) protects against lipid peroxidation (LPO) and cell death termed ferroptosis. We report that small intestinal epithelial cells (IECs) in Crohn’s disease (CD) exhibit impaired GPX4 activity and signs of LPO. PUFAs and specifically AA trigger a cytokine response of IECs which is restricted by GPX4. While GPX4 does not control AA metabolism, cytokine production is governed by similar mechanisms as ferroptosis. A PUFA-enriched Western diet triggers focal granuloma-like neutrophilic enteritis in mice that lack one allele of Gpx4 in IECs. Our study identifies dietary PUFAs as a trigger of GPX4-restricted mucosal inflammation phenocopying aspects of human CD
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