58 research outputs found
On the minimum number of inversions to make a digraph -(arc-)strong
The {\it inversion} of a set of vertices in a digraph consists of
reversing the direction of all arcs of . We study
(resp. ) which is the minimum number of inversions
needed to transform into a -arc-strong (resp. -strong) digraph and
sinv'_k(n) = \max\{sinv'_k(D) \mid D~\mbox{is a 2kn}\}. We show :
;
for any fixed positive integers and , deciding whether a given
oriented graph satisfies (resp.
) is NP-complete ;
if is a tournament of order at least , then , and ;
for some
tournament of order ;
if is a tournament of order at least (resp. ), then
(resp. );
for every , there exists such that for every tournament on at least
vertices
Maximum Independent Set when excluding an induced minor: and
Dallard, Milani\v{c}, and \v{S}torgel [arXiv '22] ask if for every class
excluding a fixed planar graph as an induced minor, Maximum Independent Set
can be solved in polynomial time, and show that this is indeed the case when
is any planar complete bipartite graph, or the 5-vertex clique minus one
edge, or minus two disjoint edges. A positive answer would constitute a
far-reaching generalization of the state-of-the-art, when we currently do not
know if a polynomial-time algorithm exists when is the 7-vertex path.
Relaxing tractability to the existence of a quasipolynomial-time algorithm, we
know substantially more. Indeed, quasipolynomial-time algorithms were recently
obtained for the -vertex cycle, [Gartland et al., STOC '21] and the
disjoint union of triangles, [Bonamy et al., SODA '23].
We give, for every integer , a polynomial-time algorithm running in
when is the friendship graph ( disjoint edges
plus a vertex fully adjacent to them), and a quasipolynomial-time algorithm
running in when is (the
disjoint union of triangles and a 4-vertex cycle). The former extends a
classical result on graphs excluding as an induced subgraph [Alekseev,
DAM '07], while the latter extends Bonamy et al.'s result.Comment: 15 pages, 2 figure
Small But Unwieldy
We show that for any natural number , there is a constant and a
subgraph-closed class having, for any natural , at most graphs on
vertices up to isomorphism, but no adjacency labeling scheme with labels of
size at most . In other words, for every , there is a small (even
tiny) monotone class without universal graphs of size . Prior to this
result, it was not excluded that every small class has an almost linear
universal graph, or equivalently a labeling scheme with labels of size
. The existence of such a labeling scheme, a scaled-down
version of the recently disproved Implicit Graph Conjecture, was repeatedly
raised [Gavoille and Labourel, ESA '07; Dujmovi\'{c} et al., JACM '21; Bonamy
et al., SIDMA '22; Bonnet et al., Comb. Theory '22]. Furthermore, our small
monotone classes have unbounded twin-width, thus simultaneously disprove the
already-refuted Small conjecture; but this time with a self-contained proof,
not relying on elaborate group-theoretic constructions.Comment: 24 pages, 1 figure, shortened abstrac
A tamed family of triangle-free graphs with unbounded chromatic number
We construct a hereditary class of triangle-free graphs with unbounded
chromatic number, in which every non-trivial graph either contains a pair of
non-adjacent twins or has an edgeless vertex cutset of size at most two. This
answers in the negative a question of Chudnovsky, Penev, Scott, and Trotignon.
The class is the hereditary closure of a family of (triangle-free) twincut
graphs such that has chromatic number . We also
show that every twincut graph is edge-critical
Imaging of Vascular Aphasia
Brain imaging is essential for the diagnosis of acute stroke and vascular aphasia. Magnetic resonance imaging (MRI) is the modality of choice for the etiological diagnosis of aphasia, the assessment of its severity, and the prediction of recovery. Diffusion weighted imaging is used to detect, localize, and quantify the extension of the irreversibly injured brain tissue called ischemic core. Perfusion weighted imaging (from MRI or CT) is useful to assess the extension of hypoperfused but salvageable tissue called penumbra. Functional imaging (positron emission tomography (PET), functional MRI (fMRI)) may help predicting recovery and is useful for the understanding of language networks and individual variability. This chapter is meant to review the state of the art of morphological and functional imaging of vascular aphasia and to illustrate the MRI profiles of different aphasic syndromes
How can we combat multicenter variability in MR radiomics? Validation of a correction procedure
International audienc
New insights into the genetic etiology of Alzheimer's disease and related dementias
Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele
Multiancestry analysis of the HLA locus in Alzheimer’s and Parkinson’s diseases uncovers a shared adaptive immune response mediated by HLA-DRB1*04 subtypes
Across multiancestry groups, we analyzed Human Leukocyte Antigen (HLA) associations in over 176,000 individuals with Parkinson’s disease (PD) and Alzheimer’s disease (AD) versus controls. We demonstrate that the two diseases share the same protective association at the HLA locus. HLA-specific fine-mapping showed that hierarchical protective effects of HLA-DRB1*04 subtypes best accounted for the association, strongest with HLA-DRB1*04:04 and HLA-DRB1*04:07, and intermediary with HLA-DRB1*04:01 and HLA-DRB1*04:03. The same signal was associated with decreased neurofibrillary tangles in postmortem brains and was associated with reduced tau levels in cerebrospinal fluid and to a lower extent with increased Aβ42. Protective HLA-DRB1*04 subtypes strongly bound the aggregation-prone tau PHF6 sequence, however only when acetylated at a lysine (K311), a common posttranslational modification central to tau aggregation. An HLA-DRB1*04-mediated adaptive immune response decreases PD and AD risks, potentially by acting against tau, offering the possibility of therapeutic avenues
Analyse des perturbations orbitales d'un satellite autour de Mars / Orbital perturbations analysis of a spacecraft around Mars
Mars est entourée d'une atmosphère ténue, composée à 95% de dioxyde de carbone (CO2). Au cours d'une année martienne, des transferts de masse (jusqu'à 30% du CO2 atmosphérique) entre l'atmosphère et les calottes polaires produisent des variations temporelles à très grande longueur d'onde du champ de gravité, notamment des harmoniques zonaux de
son développement en harmoniques sphériques (de fait les coefficients "composites" de degré 2 et 3). D'un autre côté, le potentiel gravitationnel du Soleil induit des déformations, dites de marée, du volume martien. Ces déformations produisent un potentiel perturbateur en tout point extérieur à la planète, proportionnel à son nombre de Love de degré 2 k2. k2 traduit la réponse élastique de la planète au potentiel solaire et permet de
caractériser physiquement le noyau de Mars (sa nature, solide ou liquide, et son rayon). Une manière de quantifier les transferts de la masse
atmosphérique et l'état du noyau est de déterminer les perturbations inhérentes sur le mouvement d'un satellite artificiel.
Le cycle saisonnier du CO2 et l'état du noyau impliquent aussi des variations de la rotation de Mars. Une autre manière de quantifier les transferts de la masse atmosphérique et l'état du noyau est donc d'observer leurs effets sur la rotation.
Des simulations d'observations de trajectographie de satellites (comme celles de Mars Global Surveyor, MGS, Odyssey, MODY) et/ou de la position d'un réseau de stations à la surface de Mars (comme dans l'expérience NEIGE) nous ont permis de voir s'il est possible de restituer précisément les variations des harmoniques zonaux de gravité de bas degré et/ou la rotation.
Avec les observations réelles de trajectographie des missions américaines MGS et MODY, on a restitué les variations des harmoniques zonaux de gravité de bas degré et k2.(PHYS 3)--UCL, 200
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