364 research outputs found
Affine actions on non-archimedean trees
We initiate the study of affine actions of groups on -trees for a
general ordered abelian group ; these are actions by dilations rather
than isometries. This gives a common generalisation of isometric action on a
-tree, and affine action on an -tree as studied by I. Liousse. The
duality between based length functions and actions on -trees is
generalised to this setting. We are led to consider a new class of groups:
those that admit a free affine action on a -tree for some .
Examples of such groups are presented, including soluble Baumslag-Solitar
groups and the discrete Heisenberg group.Comment: 27 pages. Section 1.4 expanded, typos corrected from previous versio
Quantum Sign Permutation Polytopes
Convex polytopes are convex hulls of point sets in the -dimensional space
\E^n that generalize 2-dimensional convex polygons and 3-dimensional convex
polyhedra. We concentrate on the class of -dimensional polytopes in \E^n
called sign permutation polytopes. We characterize sign permutation polytopes
before relating their construction to constructions over the space of quantum
density matrices. Finally, we consider the problem of state identification and
show how sign permutation polytopes may be useful in addressing issues of
robustness
The development of visuotactile congruency effects for sequences of events.
Abstract Sensitivity to the temporal coherence of visual and tactile signals increases perceptual reliability and is evident during infancy. However, it is not clear how, or whether, bidirectional visuotactile interactions change across childhood. Furthermore, no study has explored whether viewing a body modulates how children perceive visuotactile sequences of events. Here, children aged 5–7 years (n = 19), 8 and 9 years (n = 21), and 10–12 years (n = 24) and adults (n = 20) discriminated the number of target events (one or two) in a task-relevant modality (touch or vision) and ignored distractors (one or two) in the opposing modality. While participants performed the task, an image of either a hand or an object was presented. Children aged 5–7 years and 8 and 9 years showed larger crossmodal interference from visual distractors when discriminating tactile targets than the converse. Across age groups, this was strongest when two visual distractors were presented with one tactile target, implying a "fission-like" crossmodal effect (perceiving one event as two events). There was no influence of visual context (viewing a hand or non-hand image) on visuotactile interactions for any age group. Our results suggest robust interference from discontinuous visual information on tactile discrimination of sequences of events during early and middle childhood. These findings are discussed with respect to age-related changes in sensory dominance, selective attention, and multisensory processing
Determining eigenstates and thermal states on a quantum computer using quantum imaginary time evolution
The accurate computation of Hamiltonian ground, excited, and thermal states
on quantum computers stands to impact many problems in the physical and
computer sciences, from quantum simulation to machine learning. Given the
challenges posed in constructing large-scale quantum computers, these tasks
should be carried out in a resource-efficient way. In this regard, existing
techniques based on phase estimation or variational algorithms display
potential disadvantages; phase estimation requires deep circuits with ancillae,
that are hard to execute reliably without error correction, while variational
algorithms, while flexible with respect to circuit depth, entail additional
high-dimensional classical optimization. Here, we introduce the quantum
imaginary time evolution and quantum Lanczos algorithms, which are analogues of
classical algorithms for finding ground and excited states. Compared to their
classical counterparts, they require exponentially less space and time per
iteration, and can be implemented without deep circuits and ancillae, or
high-dimensional optimization. We furthermore discuss quantum imaginary time
evolution as a subroutine to generate Gibbs averages through an analog of
minimally entangled typical thermal states. Finally, we demonstrate the
potential of these algorithms via an implementation using exact classical
emulation as well as through prototype circuits on the Rigetti quantum virtual
machine and Aspen-1 quantum processing unit.Comment: 18 pages, 7 figures; improved figures and tex
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HDAC9 is implicated in atherosclerotic aortic calcification and affects vascular smooth muscle cell phenotype.
Aortic calcification is an important independent predictor of future cardiovascular events. We performed a genome-wide association meta-analysis to determine SNPs associated with the extent of abdominal aortic calcification (n = 9,417) or descending thoracic aortic calcification (n = 8,422). Two genetic loci, HDAC9 and RAP1GAP, were associated with abdominal aortic calcification at a genome-wide level (P < 5.0 × 10-8). No SNPs were associated with thoracic aortic calcification at the genome-wide threshold. Increased expression of HDAC9 in human aortic smooth muscle cells promoted calcification and reduced contractility, while inhibition of HDAC9 in human aortic smooth muscle cells inhibited calcification and enhanced cell contractility. In matrix Gla protein-deficient mice, a model of human vascular calcification, mice lacking HDAC9 had a 40% reduction in aortic calcification and improved survival. This translational genomic study identifies the first genetic risk locus associated with calcification of the abdominal aorta and describes a previously unknown role for HDAC9 in the development of vascular calcification
EGFRvIII upregulates DNA mismatch repair resulting in increased temozolomide sensitivity of MGMT promoter methylated glioblastoma
The oncogene epidermal growth factor receptor variant III (EGFRvIII) is frequently expressed in glioblastomas (GBM) but its impact on therapy response is still under controversial debate. Here we wanted to test if EGFRvIII influences the sensitivity towards the alkylating agent temozolomide (TMZ). Therefore, we retrospectively analyzed the survival of 336 GBM patients, demonstrating that under standard treatment, which includes TMZ, EGFRvIII expression is associated with prolonged survival, but only in patients with O6-methylguanine-DNA methyltransferase (MGMT) promoter methylated tumors. Using isogenic GBM cell lines with endogenous EGFRvIII expression we could demonstrate that EGFRvIII increases TMZ sensitivity and results in enhanced numbers of DNA double-strand breaks and a pronounced S/G2-phase arrest after TMZ treatment. We observed a higher expression of DNA mismatch repair (MMR) proteins in EGFRvIII+ cells and patient tumor samples, which was most pronounced for MSH2 and MSH6. EGFRvIII-specific knockdown reduced MMR protein expression thereby increasing TMZ resistance. Subsequent functional kinome profiling revealed an increased activation of p38- and ERK1/2-dependent signaling in EGFRvIII expressing cells, which regulates MMR protein expression downstream of EGFRvIII. In summary, our results demonstrate that the oncoprotein EGFRvIII sensitizes a fraction of GBM to current standard of care treatment through the upregulation of DNA MMR
Subtypes of children with attention disabilities.
Subtypes of children with attentional problems were investigated using cluster analysis. Subjects were 9-year-old-elementary school children (N = 443). The test battery administered to these children comprised a comprehensive set of common attention tests, covering different aspects of attentional functioning, and a test of reading comprehension. Cluster analysis of these data yielded eight stable and reproducible clus¬ters. The test profiles of two subgroups were indicative of distinct attentional problems. One group ap¬peared deficient in speed of processing, the other in attentional control. A third subgroup showed a reading deficit. Two additional clusters had very poor and excellent performance on the whole battery, respec¬tively. Finally, three clusters were found with minor variations approximating average performance. The internal validity, that is, the adequacy and stability of the cluster solution, appeared to be reasonably good, as indicated by a variety of measures. The long-term stability over an 18-month period was also checked and found to be satisfactory
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