142 research outputs found
Monte Carlo event generator validation and tuning for the LHC
We summarise the motivation for, and the status of, the tools developed by
CEDAR/MCnet for validating and tuning Monte Carlo event generators for the LHC
against data from previous colliders. We then present selected preliminary
results from studies of event shapes and hadronisation observables from e+e-
colliders, and of minimum bias and underlying event observables from the
Tevatron, and comment on the approach needed with early LHC data to best
exploit the potential for new physics discoveries at the LHC in the next few
years.Comment: Prepared for Proceedings of XII Advanced Computing and Analysis
Techniques in Physics Research, November 3-7 2008, Erice, Ital
New developments in event generator tuning techniques
Data analyses in hadron collider physics depend on background simulations
performed by Monte Carlo (MC) event generators. However, calculational
limitations and non-perturbative effects require approximate models with
adjustable parameters. In fact, we need to simultaneously tune many
phenomenological parameters in a high-dimensional parameter-space in order to
make the MC generator predictions fit the data. It is desirable to achieve this
goal without spending too much time or computing resources iterating parameter
settings and comparing the same set of plots over and over again. We present
extensions and improvements to the MC tuning system, Professor, which addresses
the aforementioned problems by constructing a fast analytic model of a MC
generator which can then be easily fitted to data. Using this procedure it is
for the first time possible to get a robust estimate of the uncertainty of
generator tunings. Furthermore, we can use these uncertainty estimates to study
the effect of new (pseudo-) data on the quality of tunings and therefore decide
if a measurement is worthwhile in the prospect of generator tuning. The
potential of the Professor method outside the MC tuning area is presented as
well.Comment: To appear in the proceedings of the 13th International Workshop on
Advanced Computing and Analysis Techniques in Physics Research, ACAT2010,
Jaipur, India, February 22-27, 201
Crystal Structure Analysis of the Polysialic Acid Specific O-Acetyltransferase NeuO
The major virulence factor of the neuroinvasive pathogen Escherichia coli K1 is the K1 capsule composed of Îą2,8-linked polysialic acid (polySia). K1 strains harboring the CUS-3 prophage modify their capsular polysaccharide by phase-variable O-acetlyation, a step that is associated with increased virulence. Here we present the crystal structure of the prophage-encoded polysialate O-acetyltransferase NeuO. The homotrimeric enzyme belongs to the left-handed β-helix (LβH) family of acyltransferases and is characterized by an unusual funnel-shaped outline. Comparison with other members of the LβH family allowed the identification of active site residues and proposal of a catalytic mechanism and highlighted structural characteristics of polySia specific O-acetyltransferases. As a unique feature of NeuO, the enzymatic activity linearly increases with the length of the N-terminal poly-Ď-domain which is composed of a variable number of tandem copies of an RLKTQDS heptad. Since the poly-Ď-domain was not resolved in the crystal structure it is assumed to be unfolded in the apo-enyzme
DAS PROJEKT LOSTART.DE: EINE INTERNET-DATENBANK FĂR KULTURGUTVERLUSTE
Die Suche nach KulturgĂźtern, die infolge des Zweiten Weltkrieges und des Nationalsozialismus geraubt wurden oder verloren gingen, ist auch heute noch eine aktuelle Aufgabe â nicht nur fĂźr Kunsthistoriker, sondern auch fĂźr betroffene Privatpersonen, Institutionen und natĂźrlich die Politik. In diesem Beitrag wird das âLost Artâ-Projekt vorgestellt, in dessen Rahmen eine Web-Datenbank zur UnterstĂźtzung dieser Suche entwickelt wurde. Die Datenbank umfasst eine Vielzahl von Informationen zu den registrierten KulturgĂźtern und erlaubt unterschiedliche Such- und Navigationsmodi in verschiedenen Sprachen. Ausgehend von der Architektur dieses Systems werden Aspekte der Implementierung, der RecherchemĂśglichkeiten sowie des Datenaustausches zwischen der Ăśffentlichen Web-Datenbank und der eigentlichen internen Datenbank beschrieben
A Finely Segmented Semi-Monolithic Detector tailored for High Resolution PET
Preclinical research and organ-dedicated applications require high-resolution
positron emission tomography (PET) detectors to visualize small structures and
understand biological processes at a finer level of detail. Current commercial
systems often employ finely pixelated or monolithic scintillators, each with
its limitations. We present a semi-monolithic detector, tailored for
high-resolution PET applications, and merging concepts of monolithic and
pixelated crystals. The detector features slabs measuring (24 x 10 x 1) sq. mm,
coupled to a 12 x 12 readout channel photosensor with 4 mm pitch. The slabs are
grouped in two arrays of 44 slabs each to achieve a higher optical photon
density. We employ a fan beam collimator for fast calibration to train
machine-learning-based positioning models for all three dimensions, including
slab identification and depth-of-interaction (DOI), utilizing gradient tree
boosting (GTB). Energy calculation was based on a position-dependent energy
calibration. Using an analytical timing calibration, time skews were corrected
for coincidence timing resolution (CTR) estimation. Leveraging
machine-learning-based calibration in all three dimensions, we achieved high
detector spatial resolution: down to 1.18 mm full width at half maximum (FWHM)
detector spatial resolution and 0.75 mm mean absolute error (MAE) in the
planar-monolithic direction along the slabs, and 2.14 mm FWHM and 1.03 mm MAE
for depth-of-interaction (DOI) at an energy window of (435-585) keV. Correct
slab interaction identification exceeded 80%, alongside an energy resolution of
13.8% and a CTR of 450 ps FWHM. Therewith, the introduced finely segmented,
high-resolution slab detector demonstrates an appealing performance suitable
for high-resolution PET applications. The current benchtop-based detector
calibration routine allows these detectors to be used in PET systems.Comment: 14 pages, 11 figures, IEEE NSS MIC RTSD 202
WESSBAS: extraction of probabilistic workload specifications for load testing and performance predictionâa model-driven approach for session-based application systems
The specification of workloads is required in order to evaluate performance characteristics of application systems using load testing and model-based performance prediction. Defining workload specifications that represent the real workload as accurately as possible is one of the biggest challenges in both areas. To overcome this challenge, this paper presents an approach that aims to automate the extraction and transformation of workload specifications for load testing and model-based performance prediction of session-based application systems. The approach (WESSBAS) comprises three main components. First, a system- and tool-agnostic domain-specific language (DSL) allows the layered modeling of workload specifications of session-based systems. Second, instances of this DSL are automatically extracted from recorded session logs of production systems. Third, these instances are transformed into executable workload specifications of load generation tools and model-based performance evaluation tools. We present transformations to the common load testing tool Apache JMeter and to the Palladio Component Model. Our approach is evaluated using the industry-standard benchmark SPECjEnterprise2010 and the World Cup 1998 access logs. Workload-specific characteristics (e.g., session lengths and arrival rates) and performance characteristics (e.g., response times and CPU utilizations) show that the extracted workloads match the measured workloads with high accuracy
Antiferromagnetic gap in the Hubbard model
We compute the temperature dependence of the antiferromagnetic order
parameter and the gap in the two dimensional Hubbard model at and close to half
filling. Our approach is based on truncations of an exact functional
renormalization group equation. The explicit use of composite bosonic degrees
of freedom permits a direct investigation of the ordered low temperature phase.
We show that the Mermin--Wagner theorem is not practically applicable for the
spontaneous breaking of the continuous spin symmetry in the antiferromagnetic
state. The critical behavior is dominated by the fluctuations of composite
Goldstone bosons.Comment: new discussion of critical behavior 4 pages,2 figures, LaTe
Systematic event generator tuning for the LHC
In this article we describe Professor, a new program for tuning model
parameters of Monte Carlo event generators to experimental data by
parameterising the per-bin generator response to parameter variations and
numerically optimising the parameterised behaviour. Simulated experimental
analysis data is obtained using the Rivet analysis toolkit. This paper presents
the Professor procedure and implementation, illustrated with the application of
the method to tunes of the Pythia 6 event generator to data from the LEP/SLD
and Tevatron experiments. These tunes are substantial improvements on existing
standard choices, and are recommended as base tunes for LHC experiments, to be
themselves systematically improved upon when early LHC data is available.Comment: 28 pages. Submitted to European Physical Journal C. Program sources
and extra information are available from
http://projects.hepforge.org/professor
Halogenated Rocaglate Derivatives: Pan-antiviral Agents against Hepatitis E Virus and Emerging Viruses
The synthesis of a library of halogenated rocaglate derivatives belonging to the flavagline class of natural products, of which silvestrol is the most prominent example, is reported. Their antiviral activity and cytotoxicity profile against a wide range of pathogenic viruses, including hepatitis E, Chikungunya, Rift Valley Fever virus and SARS-CoV-2, were determined. The incorporation of halogen substituents at positions 4â˛, 6 and 8 was shown to have a significant effect on the antiviral activity of rocaglates, some of which even showed enhanced activity compared to CR-31-B and silvestrol
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