3,870 research outputs found
GPU-based Online Track Reconstruction for the ALICE TPC in Run 3 with Continuous Read-Out
In LHC Run 3, ALICE will increase the data taking rate significantly to 50
kHz continuous read-out of minimum bias Pb-Pb collisions. The reconstruction
strategy of the online-offline computing upgrade foresees a first synchronous
online reconstruction stage during data taking enabling detector calibration
and data compression, and a posterior calibrated asynchronous reconstruction
stage. Many new challenges arise, among them continuous TPC read-out, more
overlapping collisions, no a priori knowledge of the primary vertex and of
location-dependent calibration in the synchronous phase, identification of
low-momentum looping tracks, and sophisticated raw data compression. The
tracking algorithm for the Time Projection Chamber (TPC) will be based on a
Cellular Automaton and the Kalman filter. The reconstruction shall run online,
processing 50 times more collisions per second than today, while yielding
results comparable to current offline reconstruction. Our TPC track finding
leverages the potential of hardware accelerators via the OpenCL and CUDA APIs
in a shared source code for CPUs and GPUs for both reconstruction stages. We
give an overview of the status of Run 3 tracking including performance on
processors and GPUs and achieved compression ratios.Comment: 8 pages, 7 figures, contribution to CHEP 2018 conferenc
Track Reconstruction in the ALICE TPC using GPUs for LHC Run 3
In LHC Run 3, ALICE will increase the data taking rate significantly to
continuous readout of 50 kHz minimum bias Pb-Pb collisions. The reconstruction
strategy of the online offline computing upgrade foresees a first synchronous
online reconstruction stage during data taking enabling detector calibration,
and a posterior calibrated asynchronous reconstruction stage. We present a
tracking algorithm for the Time Projection Chamber (TPC), the main tracking
detector of ALICE. The reconstruction must yield results comparable to current
offline reconstruction and meet the time constraints like in the current High
Level Trigger (HLT), processing 50 times as many collisions per second as
today. It is derived from the current online tracking in the HLT, which is
based on a Cellular automaton and the Kalman filter, and we integrate missing
features from offline tracking for improved resolution. The continuous TPC
readout and overlapping collisions pose new challenges: conversion to spatial
coordinates and the application of time- and location dependent calibration
must happen in between of track seeding and track fitting while the TPC
occupancy increases five-fold. The huge data volume requires a data reduction
factor of 20, which imposes additional requirements: the momentum range must be
extended to identify low-pt looping tracks and a special refit in uncalibrated
coordinates improves the track model entropy encoding. Our TPC track finding
leverages the potential of hardware accelerators via the OpenCL and CUDA APIs
in a shared source code for CPUs, GPUs, and both reconstruction stages. Porting
more reconstruction steps like the remainder of the TPC reconstruction and
tracking for other detectors will shift the computing balance from traditional
processors to GPUs.Comment: 13 pages, 10 figures, proceedings to Connecting The Dots Workshop,
Seattle, 201
Time Optimal Control of Coupled Qubits Under Non-Stationary Interactions
In this article, we give a complete characterization of all the unitary
transformations that can be synthesized in a given time for a system of coupled
spin-1/2 in presence of general time varying coupling tensor. Our treatment is
quite general and our results help to characterize the reachable set at all
times for a class of bilinear control systems with time varying drift and
unbounded control amplitude. These results are of fundamental interest in
geometric control theory and have applications to control of coupled spins in
solid state NMR spectroscopy.Comment: 4 page
Kerr effect as a tool for the investigation of dynamic heterogeneities
We propose a dynamic Kerr effect experiment for the distinction between
dynamic heterogeneous and homogeneous relaxation in glassy systems. The
possibility of this distinction is due to the inherent nonlinearity of the Kerr
effect signal. We model the slow reorientational molecular motion in
supercooled liquids in terms of non-inertial rotational diffusion. The Kerr
effect response, consisting of two terms, is calculated for heterogeneous and
for homogeneous variants of the stochastic model. It turns out that the
experiment is able to distinguish between the two scenarios. We furthermore
show that exchange between relatively 'slow' and 'fast' environments does not
affect the possibility of frequency-selective modifications. It is demonstrated
how information about changes in the width of the relaxation time distribution
can be obtained from experimental results.Comment: 23 pages incl. 6 figures accepted for publication in The Journal of
Chemical Physic
Conformationally selective multidimensional chemical shift ranges in proteins from a PACSY database purged using intrinsic quality criteria
We have determined refined multidimensional chemical shift ranges for intra-residue correlations ([superscript 13]Câ[superscript 13]C, [superscript 15]Nâ[superscript 13]C, etc.) in proteins, which can be used to gain type-assignment and/or secondary-structure information from experimental NMR spectra. The chemical-shift ranges are the result of a statistical analysis of the PACSY database of >3000 proteins with 3D structures (1,200,207 [superscript 13]C chemical shifts and >3 million chemical shifts in total); these data were originally derived from the Biological Magnetic Resonance Data Bank. Using relatively simple non-parametric statistics to find peak maxima in the distributions of helix, sheet, coil and turn chemical shifts, and without the use of limited âhand-pickedâ data sets, we show that ~94 % of the [superscript 13]C NMR data and almost all [superscript 15]N data are quite accurately referenced and assigned, with smaller standard deviations (0.2 and 0.8 ppm, respectively) than recognized previously. On the other hand, approximately 6 % of the [superscript 13]C chemical shift data in the PACSY database are shown to be clearly misreferenced, mostly by ca. â2.4 ppm. The removal of the misreferenced data and other outliers by this purging by intrinsic quality criteria (PIQC) allows for reliable identification of secondary maxima in the two-dimensional chemical-shift distributions already pre-separated by secondary structure. We demonstrate that some of these correspond to specific regions in the Ramachandran plot, including left-handed helix dihedral angles, reflect unusual hydrogen bonding, or are due to the influence of a following proline residue. With appropriate smoothing, significantly more tightly defined chemical shift ranges are obtained for each amino acid type in the different secondary structures. These chemical shift ranges, which may be defined at any statistical threshold, can be used for amino-acid type assignment and secondary-structure analysis of chemical shifts from intra-residue cross peaks by inspection or by using a provided command-line Python script (PLUQin), which should be useful in protein structure determination. The refined chemical shift distributions are utilized in a simple quality test (SQAT) that should be applied to new protein NMR data before deposition in a databank, and they could benefit many other chemical-shift based tools.National Institutes of Health (U.S.) (Grant GM066976
Interactive Learning of Probabilistic Decision Making by Service Robots with Multiple Skill Domains
This thesis makes a contribution to autonomous service robots, centered around two aspects. The first is modeling decision making in the face of incomplete information on top of diverse basic skills of a service robot. Second, based on such a model, it is investigated, how to transfer complex decision-making knowledge into the system. Interactive learning, naturally from both demonstrations of human teachers and in interaction with objects, yields decision-making models applicable by the robot
Ion and polymer dynamics in polymer electrolytes PPO-LiClO4: II. 2H and 7Li NMR stimulated-echo experiment
We use 2H NMR stimulated-echo spectroscopy to measure two-time correlation
functions characterizing the polymer segmental motion in polymer electrolytes
PPO-LiClO4 near the glass transition temperature Tg. To investigate effects of
the salt on the polymer dynamics, we compare results for different ether oxygen
to lithium ratios, namely, 6:1, 15:1, 30:1 and infinity. For all compositions,
we find nonexponential correlation functions, which can be described by a
Kohlrausch function. The mean correlation times show quantitatively that an
increase of the salt concentration results in a strong slowing down of the
segmental motion. Consistently, for the high 6:1 salt concentration, a high
apparent activation energy E_a=4.1eV characterizes the temperature dependence
of the mean correlation times at Tg < T< 1.1T_g, while smaller values E_a=2.5eV
are observed for moderate salt contents. The correlation functions are most
nonexponential for 15:1 PPO-LiClO4, whereas the stretching is reduced for
higher and lower salt concentrations. A similar dependence of the correlation
functions on the evolution time in the presence and in the absence of ions
indicates that addition of salt hardly affects the reorientational mechanism.
For all compositions, mean jump angles of about 15 degree characterize the
segmental reorientation. In addition, comparison of results from 2H and 7Li NMR
stimulated-echo experiments suggests a coupling of ion and polymer dynamics in
15:1 PPO-LiClO4.Comment: 14 pages, 12 figure
Gas hydrate occurrences along the Haida Gwaii margin - Constraints on the geothermal regime and implications for fluid flow
Seismic-reflection data along the Haida Gwaii margin collected from 1967 to 2013 were used to identify gas hydrateârelated bottom-simulating reflectors (BSRs). The BSRs occur along the Queen Charlotte Terrace only, within more strongly folded and tectonically deformed sedimentary ridges. The BSRs are absent within well-bedded and sediment-filled minibasins. The BSR is modeled as the base of the phase boundary of the methane hydrate (structure I) stability zone and is used to estimate geothermal gradients. The P-wave velocity structure required to convert observed depths of the BSR in two-way time to meters below seafloor was constrained from ocean-bottom seismometers. The BSR-derived gradients are lower than data from heat-probe deployments in the region, as well as predicted values from previous modeling of the large-scale tectonic thermal regime. Lower values of the BSR-derived thermal gradients may be due to topographic effects across the ridges where BSRs were observed. The previously identified landward decrease in thermal gradients across the terrace was also identified to a lesser extent from the BSRs, in accordance with the effects of oblique convergence of the Pacific plate with the North American plate. Geothermal gradients decreased from south to north by a factor of two, which is likely an effect of plate cooling due to an increase in age of the underlying plate (ca. 8 Ma off southern Haida Gwaii to ca. 12 Ma at Dixon Entrance) as well as the fact that sediments triple in thickness over the same distance. This may be due to downward flexure of the underlying crust during transpression and/or a high flux of sediments through Dixon Entrance
Die Spektren der Protonen aus (d,p)-Reaktionen an schweren Kernenbei Deuteronenenergien unter 12 MeV.
The proton spectra of the (d,p)-reactions on heavy nuclei show, in addition to the low energy continuum and the gross structure at higher energies, a pronounced proton group. The relative intensity of the proton group increases with decreasing energy of the primary deuterons. The dependence of the spectra on the atomic number of the target and the energy dependence and angular distribution for gold have been measured. The results are explained in terms of the properties of the nuclear surface
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