837 research outputs found
Integrating LHCb workflows on HPC resources: status and strategies
High Performance Computing (HPC) supercomputers are expected to play an
increasingly important role in HEP computing in the coming years. While HPC
resources are not necessarily the optimal fit for HEP workflows, computing time
at HPC centers on an opportunistic basis has already been available to the LHC
experiments for some time, and it is also possible that part of the pledged
computing resources will be offered as CPU time allocations at HPC centers in
the future. The integration of the experiment workflows to make the most
efficient use of HPC resources is therefore essential. This paper describes the
work that has been necessary to integrate LHCb workflows at a specific HPC
site, the Marconi-A2 system at CINECA in Italy, where LHCb benefited from a
joint PRACE (Partnership for Advanced Computing in Europe) allocation with the
other Large Hadron Collider (LHC) experiments. This has required addressing two
types of challenges: on the software application workloads, for optimising
their performance on a many-core hardware architecture that differs
significantly from those traditionally used in WLCG (Worldwide LHC Computing
Grid), by reducing memory footprint using a multi-process approach; and in the
distributed computing area, for submitting these workloads using more than one
logical processor per job, which had never been done yet in LHCb.Comment: 9 pages, submitted to CHEP2019 proceedings in EPJ Web of Conference
On Usage Control for Data Grids: Models, Architectures, and Specifications
This thesis reasons on usage control in Data Grids, by presenting
models, architectures and specifications. This work is a step
toward a continuous monitoring and control of the data access and
usage in a Data Grid. First, the thesis presents a background on
Grids, security, and security for Grids, by making an abstraction
to the current Grid implementations. We argue that usage control
in Data Grids should be considered as a process composed
by two black boxes. We analysed the requirements for Grid security,
and propose a distributed usage control model suitable for
Grids and distributed systems alike. Then, we apply such model
to a Data Grid abstraction, and present a usage control architecture
for Data Grids that uses the functional components of the
currents Grids. We also present an abstract specification for an
enforcing mechanism for usage control policies. To do so, we use
a formal requirement engineering methodology with a bottom-up
approach, that proves that the specification is sound and complete.
With the methodology, we show formally that such abstract specification
can enforce all the different typologies of usage control
policies. Finally, we consider how existing prototypes can fit in
the proposed architecture, and the advantages derived from using
Semantic Grid techologies for the specification of policies subjects
and objects
A Subset of the CERN Virtual Machine File System: Fast Delivering of Complex Software Stacks for Supercomputing Resources
Delivering a reproducible environment along with complex and up-to-date
software stacks on thousands of distributed and heterogeneous worker nodes is a
critical task. The CernVM-File System (CVMFS) has been designed to help various
communities to deploy software on worldwide distributed computing
infrastructures by decoupling the software from the Operating System. However,
the installation of this file system depends on a collaboration with system
administrators of the remote resources and an HTTP connectivity to fetch
dependencies from external sources. Supercomputers, which offer tremendous
computing power, generally have more restrictive policies than grid sites and
do not easily provide the mandatory conditions to exploit CVMFS. Different
solutions have been developed to tackle the issue, but they are often specific
to a scientific community and do not deal with the problem in its globality. In
this paper, we provide a generic utility to assist any community in the
installation of complex software dependencies on supercomputers with no
external connectivity. The approach consists in capturing dependencies of
applications of interests, building a subset of dependencies, testing it in a
given environment, and deploying it to a remote computing resource. We
experiment this proposal with a real use case by exporting Gauss-a Monte-Carlo
simulation program from the LHCb experiment-on Mare Nostrum, one of the top
supercomputers of the world. We provide steps to encapsulate the minimum
required files and deliver a light and easy-to-update subset of CVMFS: 12.4
Gigabytes instead of 5.2 Terabytes for the whole LHCb repository
A singular case of cavernous internal carotid artery aneurysm in patient with cavernous sinus syndrome and bacterial meningitis
AbstractWe report the uncommon case of an acute cavernous sinus syndrome in a patient who was consequently discovered to have both a cavernous internal carotid artery aneurysm and bacterial meningitis. Which came first, the chicken or the egg? Which of the two, the aneurysm or the meningitis, gave rise to the patient’s symptoms? We briefly reviewed the literature of similar cases and tried to analyze the possible pathophysiological relationship between these findings. Moreover, this case highlights the importance of a multidisciplinary management of these patients to better decide between a medical and a surgical and/or endovascular treatment
A VLBI experiment using a remote atomic clock via a coherent fibre link
We describe a VLBI experiment in which, for the first time, the clock reference is delivered from a National Metrology Institute to a radio telescope using a coherent fibre link 550 km long. The experiment consisted of a 24-hours long geodetic campaign, performed by a network of European telescopes; in one of those (Medicina, Italy) the local clock was alternated with a signal generated from an optical comb slaved to a fibre-disseminated optical signal. The quality of the results obtained with this facility and with the local clock is similar: interferometric fringes were detected throughout the whole 24-hours period and it was possible to obtain a solution whose residuals are comparable to those obtained with the local clock. These results encourage further investigation of the ultimate VLBI performances achievable using fibre dissemination at the highest precision of state-of-the-art atomic clocks
Comparing Remote Atomic Clocks via VLBI Networks and Fiber Optic Links: the LIFT/MetGeSp Perspective
Very Long Baseline Interferometry experiments require an extremely precise synchronization between the atomic clocks keeping the time and frequency standards at radiotelescope observatories. Recently the availability of fiber optic links from a few radio observatories and their national metrological institutes has made the streaming of extremely stable frequency standards via optical atomic clocks possible (even two orders of magnitudes better than Rubidium or Hydrogen maser standards). Firstly, we present the infrastructure of the Italian Link for Frequency and Time (LIFT) and results of the MetGeSp project aimed at finally creating a common clock between two of the antennas of the VLBI Italian Network. Secondly, the results are shown from VLBI experiments in which the rms phase noise was used to accurately compare the synchronicity of atomic clocks located at a few European stations (Medicina, Noto, Yebes, Torun, and Matera). VLBI clock timing proves a valid alternative to satellite-based techniques such as the Global Navigation Satellite System or the Two-Way Satellite Time and Frequency Transfer
The First Geodetic VLBI Field Test of LIFT: a 550-km-long Optical Fiber Link for Remote Antenna Synchronization
We present the first field test of the implementation of a coherent optical fiber link for remote antenna synchronization realized in Italy between the Italian Metrological Institute (INRIM) and the Medicina radio observatory of the National Institute for Astrophysics (INAF). The Medicina VLBI antenna participated in the EUR137 experiment carried out in September 2015 using, as reference systems, both the local H-maser and a remote H-maser hosted at the INRIM labs in Turin, separated by about 550 km. In order to assess the quality of the remote clock, the observed radio sources were split into two sets, using either the local or the remote H-maser. A system to switch automatically between the two references was integrated into the antenna field system. The observations were correlated in Bonn and preliminary results are encouraging since fringes were detected with both time references along the full 24 hours of the session. The experimental set-up, the results, and the perspectives for future radio astronomical and geodetic experiments are presented
Optical Fiber Links Used in VLBI Networks and Remote Clock Comparisons: the LIFT/MetGesp Project
The synchronization between atomic clocks
plays an important part in both radio astronomical
and geodetic Very Long Baseline Interferometry, as
the clocks are responsible for providing time and
frequency reference at radio stations. The availability
of highly stable optical fiber links from a few radio
observatories and their national metrological institutes
has recently allowed the streaming of frequencies from
optical clocks based on the Sr/Yb lattice technology
(even two order of magnitudes more stable than
H-maser clocks). We will present the current status of
the Italian Link for Frequency and Time (LIFT) and
the ongoing e orts to realize a geodetic experiment
utilizing the radio stations in Medicina and Matera
connected in common clock via the optical fiber link.
We will then show the results from the latest VLBI
clock timing experiments also making use of the LIFT
link to compare atomic clocks of the three italian radio
VLBI antennas (Mc, Sr and Nt) using the rms noise in
the interferometric phase. VLBI clock timing proves
more e ective than Global Navigation Satellite System
and less expensive than Two-Way Satellite Frequency
and Time Transfer in synchronizing remote clocks
A Coherent Optical Fiber Link for Very Long Baseline Interferometry
We realize a phase-stabilised optical fiber backbone that connects the Italian National Metrology Institute with two radio telescopes over a 600 km baseline. This allows referencing of Very Long Baseline Interferometry (VLBI) facilities with the best atomic frequency standards available today and the implementation of a common-clock architecture, which we are now using to assess VLBI ultimate performances
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