5,311 research outputs found
Accuracy considerations in approximate reanalysis of structures
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76782/1/AIAA-2000-4751-508.pd
Concepts, Developments and Advanced Applications of the PAX Toolkit
The Physics Analysis eXpert (PAX) is an open source toolkit for high energy
physics analysis. The C++ class collection provided by PAX is deployed in a
number of analyses with complex event topologies at Tevatron and LHC. In this
article, we summarize basic concepts and class structure of the PAX kernel. We
report about the most recent developments of the kernel and introduce two new
PAX accessories. The PaxFactory, that provides a class collection to facilitate
event hypothesis evolution, and VisualPax, a Graphical User Interface for PAX
objects
Point configurations that are asymmetric yet balanced
A configuration of particles confined to a sphere is balanced if it is in
equilibrium under all force laws (that act between pairs of points with
strength given by a fixed function of distance). It is straightforward to show
that every sufficiently symmetrical configuration is balanced, but the converse
is far from obvious. In 1957 Leech completely classified the balanced
configurations in R^3, and his classification is equivalent to the converse for
R^3. In this paper we disprove the converse in high dimensions. We construct
several counterexamples, including one with trivial symmetry group.Comment: 10 page
A matrix-valued point interactions model
We study a matrix-valued Schr\"odinger operator with random point
interactions. We prove the absence of absolutely continuous spectrum for this
operator by proving that away from a discrete set its Lyapunov exponents do not
vanish. For this we use a criterion by Gol'dsheid and Margulis and we prove the
Zariski denseness, in the symplectic group, of the group generated by the
transfer matrices. Then we prove estimates on the transfer matrices which lead
to the H\"older continuity of the Lyapunov exponents. After proving the
existence of the integrated density of states of the operator, we also prove
its H\"older continuity by proving a Thouless formula which links the
integrated density of states to the sum of the positive Lyapunov exponents
Eigenvalue Bounds for Perturbations of Schrodinger Operators and Jacobi Matrices With Regular Ground States
We prove general comparison theorems for eigenvalues of perturbed Schrodinger
operators that allow proof of Lieb--Thirring bounds for suitable non-free
Schrodinger operators and Jacobi matrices.Comment: 11 page
DNA binding induces active site conformational change in the human TREX2 3′-exonuclease
The TREX enzymes process DNA as the major 3′→5′ exonuclease activity in mammalian cells. TREX2 and TREX1 are members of the DnaQ family of exonucleases and utilize a two metal ion catalytic mechanism of hydrolysis. The structure of the dimeric TREX2 enzyme in complex with single-stranded DNA has revealed binding properties that are distinct from the TREX1 protein. The TREX2 protein undergoes a conformational change in the active site upon DNA binding including ordering of active site residues and a shift of an active site helix. Surprisingly, even when a single monomer binds DNA, both monomers in the dimer undergo the structural rearrangement. From this we have proposed a model for DNA binding and 3′ hydrolysis for the TREX2 dimer. The structure also shows how TREX proteins potentially interact with double-stranded DNA and suggest features that might be involved in strand denaturation to provide a single-stranded substrate for the active site
Isolated Non-Compaction of the Left Ventricle in a Patient with New-Onset Heart Failure: Morphologic and Functional Evaluation with Cardiac Multidetector Computed Tomography
We describe a case of new-onset heart failure in a patient in whom cardiac CT enabled the non-invasive diagnosis of isolated non-compaction and associated functional abnormalities of the left ventricle with the concomitant evaluation of coronary arteries. This case highlights the utility of cardiac CT for the morphological and functional evaluation of the heart as a single imaging modality
The relative and absolute timing accuracy of the EPIC-pn camera on XMM-Newton, from X-ray pulsations of the Crab and other pulsars
Reliable timing calibration is essential for the accurate comparison of
XMM-Newton light curves with those from other observatories, to ultimately use
them to derive precise physical quantities. The XMM-Newton timing calibration
is based on pulsar analysis. However, as pulsars show both timing noise and
glitches, it is essential to monitor these calibration sources regularly. To
this end, the XMM-Newton observatory performs observations twice a year of the
Crab pulsar to monitor the absolute timing accuracy of the EPIC-pn camera in
the fast Timing and Burst modes. We present the results of this monitoring
campaign, comparing XMM-Newton data from the Crab pulsar (PSR B0531+21) with
radio measurements. In addition, we use five pulsars (PSR J0537-69, PSR
B0540-69, PSR B0833-45, PSR B1509-58 and PSR B1055-52) with periods ranging
from 16 ms to 197 ms to verify the relative timing accuracy. We analysed 38
XMM-Newton observations (0.2-12.0 keV) of the Crab taken over the first ten
years of the mission and 13 observations from the five complementary pulsars.
All the data were processed with the SAS, the XMM-Newton Scientific Analysis
Software, version 9.0. Epoch folding techniques coupled with \chi^{2} tests
were used to derive relative timing accuracies. The absolute timing accuracy
was determined using the Crab data and comparing the time shift between the
main X-ray and radio peaks in the phase folded light curves. The relative
timing accuracy of XMM-Newton is found to be better than 10^{-8}. The strongest
X-ray pulse peak precedes the corresponding radio peak by 306\pm9 \mus, which
is in agreement with other high energy observatories such as Chandra, INTEGRAL
and RXTE. The derived absolute timing accuracy from our analysis is \pm48 \mus.Comment: 16 pages, 9 figures. Accepted for publication on A&
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