1,815 research outputs found
Particle production in pp collisions at 900 GeV and 7TeV with ALICE
The ALICE experiment started studying pp collisions at the end of 2009. Pions, kaons, protons are identified using the excellent identification capability of the central barrel detectors over a wide momentum range, at central rapidity
(|y| < 0.5). The ALICE detectors were designed to perform such a study by using the energy-loss dependence on momentum in the lower and intermediate pt region and the time-of-flight measurement in the higher pt region. Moreover, the kaon yield is also measured reconstructing the kaon decays through their kinks topology. A comparison between ALICE measurements and Monte Carlo predictions (using several models) is also reported focusing on the features of the observed pt spectra
Non-backtracking Walk Centrality for Directed Networks
The theory of zeta functions provides an expression for the generating function of nonbacktracking walk counts on a directed network. We show how this expression can be used to produce a centrality measure that eliminates backtracking walks at no cost. We also show that the radius of convergence of the generating function is related to the spectrum of a three-by-three block matrix involving the original adjacency matrix. This gives a means to choose appropriate values of the attenuation parameter. We find that three important additional benefits arise when we use this technique to eliminate traversals around the network that are unlikely to be of relevance. First, we obtain a larger range of choices for the attenuation parameter. Second, a natural approach for determining a suitable parameter range is invariant under the removal of certain types of nodes, we can gain computational efficiencies through reducing the dimension of the resulting eigenvalue problem. Third, the dimension of the linear system defining the centrality measures may be reduced in the same manner. We show that the new centrality measure may be interpreted as standard Katz on a modified network, where self loops are added, and where nonreciprocal edges are augmented with negative weights. We also give a multilayer interpretation, where negatively weighted walks between layers compensate for backtracking walks on the only non-empty layer. Studying the limit as the attenuation parameter approaches its upper bound also allows us to propose a generalization of eigenvector-based nonbacktracking centrality measure to this directed network setting. In this context, we find that the two-by-two block matrix arising in previous studies focused on undirected networks must be extended to a new three-by-three block structure to allow for directed edges. We illustrate the centrality measure on a synthetic network, where it is shown to eliminate a localization effect present in standard Katz centrality. Finally, we give results for real networks
When is a Hamiltonian matrix the commutator of two skew-Hamiltonian matrices?
The mapping (Formula presented.) , where the matrices (Formula presented.) are skew-Hamiltonian with respect to transposition, is studied. Let (Formula presented.) be the range of (Formula presented.) : we give an implicit characterization of (Formula presented.) , obtaining results that find an application in algebraic geometry. Namely, they are used in [R. Abuaf and A. Boralevi, Orthogonal bundles and skew-Hamiltonian matrices, Submitted] to study orthogonal vector bundles. We also give alternative and more explicit characterizations of (Formula presented.) for (Formula presented.). Moreover, we prove that for (Formula presented.) , the complement of (Formula presented.) is nowhere dense in the set of (Formula presented.) -dimensional Hamiltonian matrices, denoted by (Formula presented.) , implying that almost all matrices in (Formula presented.) are in (Formula presented.) for (Formula presented.). Finally, we show that (Formula presented.) is never surjective as a mapping from (Formula presented.) to (Formula presented.) , where (Formula presented.) is the set of (Formula presented.) -dimensional skew-Hamiltonian matrices. Along the way, we discuss the connections of this problem with several existing results in matrix theory
Algebraic arctic curves in the domain-wall six-vertex model
The arctic curve, i.e. the spatial curve separating ordered (or `frozen') and
disordered (or `temperate) regions, of the six-vertex model with domain wall
boundary conditions is discussed for the root-of-unity vertex weights. In these
cases the curve is described by algebraic equations which can be worked out
explicitly from the parametric solution for this curve. Some interesting
examples are discussed in detail. The upper bound on the maximal degree of the
equation in a generic root-of-unity case is obtained.Comment: 15 pages, no figures; v2: metadata correcte
A class of quasi-sparse companion pencils
In this paper, we introduce a general class of quasi-sparse potential companion pencils for arbitrary square matrix polynomials over an arbitrary field, which extends the class introduced in [B. Eastman, I.-J. Kim, B. L. Shader, K.N. Vander Meulen, Companion matrix patterns. Linear Algebra Appl. 436 (2014) 255-272] for monic scalar polynomials. We provide a canonical form, up to permutation, for companion pencils in this class. We also relate these companion pencils with other relevant families of companion linearizations known so far. Finally, we determine the number of different sparse companion pencils in the class, up to permutation.This work has been partially supported by theMinisterio de Economía y Competitividad of Spain through grants MTM2015-68805-REDT and MTM2015-65798-P
Terahertz Security Image Quality Assessment by No-reference Model Observers
To provide the possibility of developing objective image quality assessment
(IQA) algorithms for THz security images, we constructed the THz security image
database (THSID) including a total of 181 THz security images with the
resolution of 127*380. The main distortion types in THz security images were
first analyzed for the design of subjective evaluation criteria to acquire the
mean opinion scores. Subsequently, the existing no-reference IQA algorithms,
which were 5 opinion-aware approaches viz., NFERM, GMLF, DIIVINE, BRISQUE and
BLIINDS2, and 8 opinion-unaware approaches viz., QAC, SISBLIM, NIQE, FISBLIM,
CPBD, S3 and Fish_bb, were executed for the evaluation of the THz security
image quality. The statistical results demonstrated the superiority of Fish_bb
over the other testing IQA approaches for assessing the THz image quality with
PLCC (SROCC) values of 0.8925 (-0.8706), and with RMSE value of 0.3993. The
linear regression analysis and Bland-Altman plot further verified that the
Fish__bb could substitute for the subjective IQA. Nonetheless, for the
classification of THz security images, we tended to use S3 as a criterion for
ranking THz security image grades because of the relatively low false positive
rate in classifying bad THz image quality into acceptable category (24.69%).
Interestingly, due to the specific property of THz image, the average pixel
intensity gave the best performance than the above complicated IQA algorithms,
with the PLCC, SROCC and RMSE of 0.9001, -0.8800 and 0.3857, respectively. This
study will help the users such as researchers or security staffs to obtain the
THz security images of good quality. Currently, our research group is
attempting to make this research more comprehensive.Comment: 13 pages, 8 figures, 4 table
New Eco-gas mixtures for the Extreme Energy Events MRPCs: results and plans
The Extreme Energy Events observatory is an extended muon telescope array,
covering more than 10 degrees both in latitude and longitude. Its 59 muon
telescopes are equipped with tracking detectors based on Multigap Resistive
Plate Chamber technology with time resolution of the order of a few hundred
picoseconds. The recent restrictions on greenhouse gases demand studies for new
gas mixtures in compliance with the relative requirements. Tetrafluoropropene
is one of the candidates for tetrafluoroethane substitution, since it is
characterized by a Global Warming Power around 300 times lower than the gas
mixtures used up to now. Several mixtures have been tested, measuring
efficiency curves, charge distributions, streamer fractions and time
resolutions. Results are presented for the whole set of mixtures and operating
conditions, %. A set of tests on a real EEE telescope, with cosmic muons, are
being performed at the CERN-01 EEE telescope. The tests are focusing on
identifying a mixture with good performance at the low rates typical of an EEE
telescope.Comment: 8 pages, 6 figures, proceedings for the "XIV Workshop on Resistive
Plate Chambers and Related Detectors" (19-23 February 2018), Puerto Vallarta,
Jalisco State, Mexic
A simulation tool for MRPC telescopes of the EEE project
The Extreme Energy Events (EEE) Project is mainly devoted to the study of the
secondary cosmic ray radiation by using muon tracker telescopes made of three
Multigap Resistive Plate Chambers (MRPC) each. The experiment consists of a
telescope network mainly distributed across Italy, hosted in different building
structures pertaining to high schools, universities and research centers.
Therefore, the possibility to take into account the effects of these structures
on collected data is important for the large physics programme of the project.
A simulation tool, based on GEANT4 and using GEMC framework, has been
implemented to take into account the muon interaction with EEE telescopes and
to estimate the effects on data of the structures surrounding the experimental
apparata.A dedicated event generator producing realistic muon distributions,
detailed geometry and microscopic behavior of MRPCs have been included to
produce experimental-like data. The comparison between simulated and
experimental data, and the estimation of detector resolutions is here presented
and discussed
The Extreme Energy Events HECR array: status and perspectives
The Extreme Energy Events Project is a synchronous sparse array of 52
tracking detectors for studying High Energy Cosmic Rays (HECR) and Cosmic
Rays-related phenomena. The observatory is also meant to address Long Distance
Correlation (LDC) phenomena: the network is deployed over a broad area covering
10 degrees in latitude and 11 in longitude. An overview of a set of preliminary
results is given, extending from the study of local muon flux dependance on
solar activity to the investigation of the upward-going component of muon flux
traversing the EEE stations; from the search for anisotropies at the sub-TeV
scale to the hints for observations of km-scale Extensive Air Shower (EAS).Comment: XXV ECRS 2016 Proceedings - eConf C16-09-04.
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