292 research outputs found
Limiting fragmentation in heavy-ion collisions and percolation of strings
The observed limiting fragmentation of charged particle distributions in
heavy ion collisions is difficult to explain as it does not apply to the proton
spectrum itself. On the other hand, string percolation provides a mechanism to
regenerate fast particles, eventually compensating the rapidity shift (energy
loss) of the nucleons. However a delicate energy-momentum compensation is
required, and in our framework we see no reason for limiting fragmentation to
be exact. A prediction, based on percolation arguments, is given for the
charged particle density in the full rapidity interval at LHC energy .Comment: 9 pages, 2 figures (2 eps files), late
Precoder and combiner design for generalized spatial modulation based multiuser MIMO systems
Multiple input multiple output (MIMO) schemes based on generalized spatial modulations (GSM) have been widely considered as potential candidate techniques for next-generation wireless networks, as they can improve both spectral and energy efficiency. In this paper we propose a multi-user MIMO system, where a base station transmits precoded GSM symbols to several receivers. In the adopted GSM approach, multiple antennas transmit different high-level QAM symbols simultaneously. The precoder is designed in order to remove interference between users while an iterative algorithm is applied at the receiver to accomplish single-user GSM detection. Simulation results show that the presented GSM MU-MIMO approach is capable to effectively exploit a large number of transmit antennas deployed at the transmitter and also provide performance gains over conventional MU-MIMO schemes with identical spectral efficiencies.info:eu-repo/semantics/acceptedVersio
Precoded generalized spatial modulation for downlink MIMO transmissions in beyond 5G networks
The design of multiple input multiple output (MIMO) schemes capable of achieving both
high spectral and energy efficiency constitutes a challenge for next-generation wireless networks.
MIMO schemes based on generalized spatial modulations (GSM) have been widely considered as a powerful technique to achieve that purpose. In this paper, a multi-user (MU) GSM MIMO system is proposed, which relies on the transmission of precoded symbols from a base station to multiple receivers. The precoder’s design is focused on the removal of the interference between users and allows the application of single-user GSM detection at the receivers, which is accomplished using a low-complexity iterative algorithm. Link level and system level simulations of a cloud radio access network (C-RAN) comprising several radio remote units (RRUs) were run in order to evaluate the performance of the proposed solution. Simulation results show that the proposed GSM MU-MIMO approach can exploit efficiently a large number of antennas deployed at the transmitter.
Moreover, it can also provide large gains when compared to conventional MU-MIMO schemes with identical spectral efficiencies. In fact, regarding the simulated C-RAN scenario with perfect channel estimation, system level results showed potential gains of up to 155% and 139% in throughput and coverage, respectively, compared to traditional cellular networks. The introduction of imperfect channel estimation reduces the throughput gain to 125%.info:eu-repo/semantics/publishedVersio
Identification of low energy neutral and charged cosmic ray events in large wide field observatorie
The lower energy thresholds of large wide-field gamma-ray observatories are
often determined by their capability to deal with the very low-energy cosmic
ray background. In fact, in observatories with areas of tens or hundreds of
thousands of square meters, the number of background events generated by the
superposition of random, very low energy cosmic rays is huge and may exceed by
far the possible signal events. In this article, we argue that a trigger
strategy based on pattern recognition of the shower front can significantly
reject the background, keeping a good efficiency and a good angular accuracy
(few square degrees) for gamma rays with energies as low as tens of GeV. In
this way, alerts can be followed or emitted within time lapses of the order of
the second, enabling wide-field gamma-ray observatories to better contribute to
global multi-messenger networks of astrophysical observatories.Comment: 9 pages, 14 figure
Particle production azimuthal asymmetries in a clustering of color sources model
The collective interactions of many partons in the first stage of the
collisions is the usual accepted explanation of the sizable elliptical flow.
The clustering of color sources provides a framework of partonic interactions.
In this scheme, we show a reasonable agreement with RHIC data for pT<1.5 GeV/c
in both the dependence of v2 transverse momentum and in the shape of the
nuclear modified factor on the azimuthal angle for different centralities. We
show the predictions at LHC energies for Pb-Pb. In the case of proton-proton
collisions a sizable v2 is obtained at this energy.Comment: To appear in Journal of Physics
Perinatal insults and neurodevelopmental disorders may impact Huntington's disease age of diagnosis
INTRODUCTION:
The age of diagnosis of Huntington's disease (HD) varies among individuals with the same HTT CAG repeat expansion size. We investigated whether early-life events, like perinatal insults or neurodevelopmental disorders, influence the diagnosis age.
METHODS:
We used data from 13,856 participants from REGISTRY and Enroll-HD, two large international multicenter observational studies. Disease-free survival analyses of mutation carriers with an HTT CAG repeat expansion size above and including 36 were computed through Kaplan-Meier estimates of median time until an HD diagnosis. Comparisons between groups were computed using a Cox proportional hazard survival model adjusted for CAG-repeat expansion length. We also assessed whether the group effect depended on gender and the affected parent.
RESULTS:
Insults in the perinatal period were associated with an earlier median age of diagnosis of 45.00 years (95%CI: 42.07–47.92) compared to 51.00 years (95%CI: 50.68–51.31) in the reference group, with a CAG-adjusted hazard ratio of 1.61 (95%CI: 1.26–2.06). Neurodevelopmental disorders were also associated with an earlier median age of diagnosis than the reference group of 47.00 years (95% CI: 43.38–50.62) with a CAG-adjusted hazard ratio of 1.42 (95%CI: 1.16–1.75). These associations did not change significantly with gender or affected parent.
CONCLUSIONS:
These results, derived from large observational datasets, show that perinatal insults and neurodevelopmental disorders are associated with earlier ages of diagnosis of magnitudes similar to the effects of known genetic modifiers of HD. Given their clear temporal separation, these early events may be causative of earlier HD onset, but further research is needed to prove causation
Percolation of Color Sources and the determination of the Equation of State of the Quark-Gluon Plasma (QGP) produced in central Au-Au collisions at \sqrt S_{NN}= 200 GeV
The Color String Percolation Model (CSPM) is used to determine the equation
of state (EOS) of the QGP produced in central Au-Au collisions at
= 200 A GeV using STAR data at RHIC. When the initial density
of interacting colored strings exceeds the 2D percolation threshold a cluster
is formed, which defines the onset of color deconfinement. These interactions
also produce fluctuations in the string tension which transforms the Schwinger
particle (gluon) production mechanism into a maximum entropy thermal
distribution. The single string tension is determined by identifying the known
value of the universal hadron limiting temperature = 167.7 2.6
MeV with the CSPM percolation temperature at the critical threshold
=1.2. At mid-rapidity the initial Bjorken energy density and the initial
temperature determine the number of degrees of freedom consistent with the
formation of a 2+1 flavor QGP. An analytic expression for the equation
of state, the sound velocity is obtained in CSPM. The CSPM
and the bulk thermodynamic values and are in excellent agreement in the phase transition region with recent
lattice QCD simulations (LQCD) by the HotQCD Collaboration.Comment: 4 pages, 3 figure
Detection of the Cherenkov light diffused by Sea Water with the ULTRA Experiment
The study of Ultra High Energy Cosmic Rays represents one of the most
challenging topic in the Cosmic Rays and in the Astroparticle Physics fields.
The interaction of primary particles with atmospheric nuclei produces a huge
Extensive Air Shower together with isotropic emission of UV fluorescence light
and highly directional Cherenkov photons, that are reflected/diffused
isotropically by the impact on the Earth's surface or on high optical depth
clouds. For space-based observations, detecting the reflected Cherenkov signal
in a delayed coincidence with the fluorescence light improves the accuracy of
the shower reconstruction in space and in particular the measurement of the
shower maximum, giving a strong signature for discriminating hadrons and
neutrinos, and helping to estimate the primary chemical composition. Since the
Earth's surface is mostly covered by water, the ULTRA (UV Light Transmission
and Reflection in the Atmosphere)experiment has been designed to provide the
diffusing properties of sea water, overcoming the lack of information in this
specific field. A small EAS array, made up of 5 particle detectors, and an UV
optical device, have been coupled to detect in coincidence both electromagnetic
and UV components. The detector was in operation from May to December, 2005, in
a small private harbor in Capo Granitola (Italy); the results of these
measurements in terms of diffusion coefficient and threshold energy are
presented here.Comment: 4 pages, 3 figures, PDF format, Proceedings of 30th ICRC,
International Cosmic Ray Conference 2007, Merida, Yucatan, Mexico, 3-11 July
200
Application of Information Theory in Nuclear Liquid Gas Phase Transition
Information entropy and Zipf's law in the field of information theory have
been used for studying the disassembly of nuclei in the framework of the
isospin dependent lattice gas model and molecular dynamical model. We found
that the information entropy in the event space is maximum at the phase
transition point and the mass of the cluster show exactly inversely to its
rank, i.e. Zipf's law appears. Both novel criteria are useful in searching the
nuclear liquid gas phase transition experimentally and theoretically.Comment: 5 pages, 5 figure
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