13,450 research outputs found
3-manifolds with(out) metrics of nonpositive curvature
In the context of Thurstons geometrisation program we address the question
which compact aspherical 3-manifolds admit Riemannian metrics of nonpositive
curvature. We show that non-geometric Haken manifolds generically, but not
always, admit such metrics. More precisely, we prove that a Haken manifold
with, possibly empty, boundary of zero Euler characteristic admits metrics of
nonpositive curvature if the boundary is non-empty or if at least one atoroidal
component occurs in its canonical topological decomposition. Our arguments are
based on Thurstons Hyperbolisation Theorem. We give examples of closed
graph-manifolds with linear gluing graph and arbitrarily many Seifert
components which do not admit metrics of nonpositive curvature.Comment: 16 page
Interaction analysis and stability concept as a means for understanding complex systems-application to vertical migration of zooplankton.
Linear Quadratic Zero-Sum Two-Person Differential Games
International audienceAs in optimal control theory, linear quadratic (LQ) differential games (DG) can be solved, even in high dimension, via a Riccati equation. However, contrary to the control case, existence of the solution of the Riccati equation is not necessary for the existence of a closed-loop saddle point. One may " survive " a particular, non generic, type of conjugate point. An important application of LQDG's is the so-called H∞-optimal control, appearing in the theory of robust control
Stimulation of endothelial adenosine Al receptors enhances adhesion of neutrophils in the intact guinea pig coronary system
Objective: The primary aim was to determine the action of pathophysiologically relevant adenosine concentrations (0.1-1 μM) on adhesion of neutrophils to coronary endothelium. Further aims were to evaluate the nature and localisation of the adenosine receptor involved. and to assess the effect of endogenous adenosine.
Methods: Adhesion was studied in isolated perfused guinea pig hearts by determining the number of cells emerging in the coronary effluent after intracoronary bolus injections of 600 000 neutrophils prepared from guinea pig or human blood. The system was characterised by the use of the proadhesive stimulus thrombin.
Results: A 5 rnin infusion of adenosine (0.1-0.3 μM) or the A1 receptor agonist N6-cyclopentyladenosine (CPA, 0.01 μM) significantly increased adhesion from about 20% (control) to 30%. This effect was prevented by the A1 receptor antagonist dipropyl-8-cyclopentylxanthine (DPCPX. 0.1 μM). It was not diminished by cessation of adenosine infusion 90 s prior to neutrophil injection. At a higher concentration of adenosine (1 μM), adhesion did not seem to be enhanced. However, coinfusion of the A2 receptor antagonist 3,7-dimethyl-1-propargylxanthine (DMPX. 0.1 μM) with 1 μM adenosine unmasked the A1 action, adhesion rising to 39%. Adenosine had a quantitatively identical effect on adhesion of human neutrophils. Total ischaemia of 15 min duration raised adhesion of subsequently applied neutrophils to 35%. This effect was completely blocked by DPCPX, as well as by ischaemic preconditioning (3 X 3 min). Preconditioning raised initial postischaemic coronary effluent adenosine from about 0.8 μM to 1.5 μM.
Conclusions: The findings suggest a bimodal participation of adenosine in the development of postischaemic dysfunction by an endothelium dependent modulation of neutrophil adhesion. Stimulation occurs via endothelial A1 receptors at submicromolar adenosine levels, whereas cardioprotection by adenosine may in part relate to the use of pharmacologically high concentrations of adenosine or enhanced endogenous production after preconditioning
A Monte Carlo Renormalization Group Approach to the Bak-Sneppen model
A recent renormalization group approach to a modified Bak-Sneppen model is
discussed. We propose a self-consistency condition for the blocking scheme to
be essential for a successful RG-method applied to self-organized criticality.
A new method realizing the RG-approach to the Bak-Sneppen model is presented.
It is based on the Monte-Carlo importance sampling idea. The new technique
performs much faster than the original proposal. Using this technique we
cross-check and improve previous results.Comment: 11 pages, REVTex, 2 Postscript figures include
Application of Peptides Containing the Cleavage Sequence of Pro-TNFα in Assessing TACE Activity of Whole Cells
Tumor necrosis factor-α (TNFα) is presumably shed from cell membranes by TNFα-cleaving enzyme (TACE). The peptides SPLAQAVRSSSR and Dabcyl-LAQAVRSSSR-Edans, each encompassing the cleavage sequence of pro-TNFα recognized by TACE, were applied to intact umbilical vein endothelium (HUVEC), peripheral blood leukocytes (PBL) and the mast cell line HMC-1, which express TACE, to homogenates of rat heart tissue and to membrane and cytoplasmic extracts of PBL. Formation of SPLAQA (specific cleavage) was determined by HPLC, while cleavage (specific plus non-specific) of Dabcyl-TNFα-Edans was followed over time by measuring fluorescence. Participation of TACE was assessed from inhibition due to the drug TAPI-2. Incubation with recombinant human TACE gave specific cleavage, fully inhibitable by TAPI-2 (IC50<0.1 μM). HUVEC rapidly degraded TNFα-peptide, but in a non-specific manner (no SPLAQA detectable) and 50 μM TAPI-2 was without effect. Fluorescence was evoked when Dabcyl-
LAQAVRSSSR-Edans was incubated with HMC-1 or PBL and also with cytoplasmic and membrane fractions of lysed PBL, but in no case was there significant inhibition by TAPI-2. However, marginal (10%) inhibition of fluorescence by 50 μM TAPI-2 was observed with homogenized heart tissue. This contained TACE, about 75% of which was without the inhibitory cysteine switch (Western blot). In conclusion, simple peptide analogs of pro-TNFα cannot be employed as substrates for measuring membrane TACE activity, largely due to extensive non-specific proteolytic cleavage by whole cells and cell extracts
Muon-spin-rotation study of the magnetic structure in the tetragonal antiferromagnetic state of weakly underdoped BaKFeAs
With muon spin rotation (SR) we studied the transition between the
orthorhombic antiferromagnetic (o-AF) and the tetragonal antiferromagnetic
(t-AF) states of a weakly underdoped BaKFeAs
single crystal. We observed some characteristic changes of the magnitude and
the orientation of the magnetic field at the muon site which, due to the fairly
high point symmetry of the latter, allow us to identify the magnetic structure
of the t-AF state. It is the so-called, inhomogeneous double-
magnetic structure with -axis oriented moments which has a vanishing
magnetic moment on half of the Fe sites.Comment: 5 pages, 4 figures. Supplementary Material: 8 figure
Learning Blind Motion Deblurring
As handheld video cameras are now commonplace and available in every
smartphone, images and videos can be recorded almost everywhere at anytime.
However, taking a quick shot frequently yields a blurry result due to unwanted
camera shake during recording or moving objects in the scene. Removing these
artifacts from the blurry recordings is a highly ill-posed problem as neither
the sharp image nor the motion blur kernel is known. Propagating information
between multiple consecutive blurry observations can help restore the desired
sharp image or video. Solutions for blind deconvolution based on neural
networks rely on a massive amount of ground-truth data which is hard to
acquire. In this work, we propose an efficient approach to produce a
significant amount of realistic training data and introduce a novel recurrent
network architecture to deblur frames taking temporal information into account,
which can efficiently handle arbitrary spatial and temporal input sizes. We
demonstrate the versatility of our approach in a comprehensive comparison on a
number of challening real-world examples.Comment: International Conference on Computer Vision (ICCV) (2017
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