43 research outputs found
Resource Allocation in User-Centric Optical Wireless Cellular Networks based on Blind Interference Alignment
Visible light communications (VLC) have been recently proposed to enhance the capacity of next generation of wireless services. Moreover, VLC networks usually comprise a large number of overlapping optical access points (APs). Moreover, each of these APs provides a small and confined area of coverage in order to generate satisfactory illumination. In this work, a user-centric (UC) clustering formation based on the K-means algorithm is proposed to manage the inter-cell interference (ICI) and enhance the performance of VLC networks. Moreover, assuming that each user is equipped with a reconfigurable photodetector, the use of blind interference alignment (BIA) in each UC cluster is considered. Notice that the data rate demands are not the same for all the users. We formulate an optimization problem to maximize the utility of the network resources allocated to the users based on their demands. After that, a centralized algorithm is proposed to obtain an optimal solution through exhaustive search, which is subject to high complexity. To reduce the complexity of this optimization problem, the problem is divided into sub-problems based on the number of constructed UC clusters. Then, a distributed algorithm via Lagrangian multipliers is proposed within each UC cluster with the aim of providing a near optimal solution to the centralized algorithm. Simulation results demonstrate that the proposed resource allocation algorithms provide higher performance than a uniform resource allocation scheme among users.The work of Ahmad Adnan Qidan and Jaafar M. H. Elmirghani has been supported by the Engineering and Physical Sciences Research Council (EPSRC), in part by the INTERNET project under Grant EP/H040536/1, in part by the STAR project under Grant P/K016873/1, and in part by the TOWS project under Grant EP/S016570/1. All data are provided in full in the results section of this paper. The work of MĂĄximo Morales-CĂ©spedes and Ana GarcĂa Armada was supported by the Spanish National Project TERESAADA (TEC2017-90093-C3-2-R) (MINECO/AEI/FEDER, UE) and the project GEOVEOLUZ-CM-UC3M. The work of MĂĄximo Morales-CĂ©spedes was also supported by the Juan de la Cierva IncorporacioĂn under Grant IJC2019-040317-I
Advanced functionality for radio analysis in the Offline software framework of the Pierre Auger Observatory
The advent of the Auger Engineering Radio Array (AERA) necessitates the
development of a powerful framework for the analysis of radio measurements of
cosmic ray air showers. As AERA performs "radio-hybrid" measurements of air
shower radio emission in coincidence with the surface particle detectors and
fluorescence telescopes of the Pierre Auger Observatory, the radio analysis
functionality had to be incorporated in the existing hybrid analysis solutions
for fluoresence and surface detector data. This goal has been achieved in a
natural way by extending the existing Auger Offline software framework with
radio functionality. In this article, we lay out the design, highlights and
features of the radio extension implemented in the Auger Offline framework. Its
functionality has achieved a high degree of sophistication and offers advanced
features such as vectorial reconstruction of the electric field, advanced
signal processing algorithms, a transparent and efficient handling of FFTs, a
very detailed simulation of detector effects, and the read-in of multiple data
formats including data from various radio simulation codes. The source code of
this radio functionality can be made available to interested parties on
request.Comment: accepted for publication in NIM A, 13 pages, minor corrections to
author list and references in v
Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory
The Pierre Auger Collaboration has reported evidence for anisotropy in the
distribution of arrival directions of the cosmic rays with energies
eV. These show a correlation with the distribution
of nearby extragalactic objects, including an apparent excess around the
direction of Centaurus A. If the particles responsible for these excesses at
are heavy nuclei with charge , the proton component of the
sources should lead to excesses in the same regions at energies . We here
report the lack of anisotropies in these directions at energies above
(for illustrative values of ). If the anisotropies
above are due to nuclei with charge , and under reasonable
assumptions about the acceleration process, these observations imply stringent
constraints on the allowed proton fraction at the lower energies
Search for First Harmonic Modulation in the Right Ascension Distribution of Cosmic Rays Detected at the Pierre Auger Observatory
We present the results of searches for dipolar-type anisotropies in different
energy ranges above eV with the surface detector array of
the Pierre Auger Observatory, reporting on both the phase and the amplitude
measurements of the first harmonic modulation in the right-ascension
distribution. Upper limits on the amplitudes are obtained, which provide the
most stringent bounds at present, being below 2% at 99% for EeV
energies. We also compare our results to those of previous experiments as well
as with some theoretical expectations.Comment: 28 pages, 11 figure
The Power Board of the KM3NeT Digital Optical Module: design, upgrade, and production
The KM3NeT Collaboration is building an underwater neutrino observatory at
the bottom of the Mediterranean Sea consisting of two neutrino telescopes, both
composed of a three-dimensional array of light detectors, known as digital
optical modules. Each digital optical module contains a set of 31 three inch
photomultiplier tubes distributed over the surface of a 0.44 m diameter
pressure-resistant glass sphere. The module includes also calibration
instruments and electronics for power, readout and data acquisition. The power
board was developed to supply power to all the elements of the digital optical
module. The design of the power board began in 2013, and several prototypes
were produced and tested. After an exhaustive validation process in various
laboratories within the KM3NeT Collaboration, a mass production batch began,
resulting in the construction of over 1200 power boards so far. These boards
were integrated in the digital optical modules that have already been produced
and deployed, 828 until October 2023. In 2017, an upgrade of the power board,
to increase reliability and efficiency, was initiated. After the validation of
a pre-production series, a production batch of 800 upgraded boards is currently
underway. This paper describes the design, architecture, upgrade, validation,
and production of the power board, including the reliability studies and tests
conducted to ensure the safe operation at the bottom of the Mediterranean Sea
throughout the observatory's lifespa
Silica Gel Template for Calcium Phosphates Crystallization.
Synthetic calcium phosphates exhibit good properties as biomaterials, such as biocompatibility, bioactivity, and
osteoconductivity, and they have important applications in the fields of bone tissue engineering and orthopedic therapies. In this
work, we performed an extensive characterization of the composite calcium phosphates/silica synthesized in gel by varying the
pH and density of the silica solution. As a function of the pH values, brushite, octacalcium phosphate, hydroxyapatite, and
monetite crystallization have been obtained, while changing the silica solution density the crystals are covered by different
amounts of silica which results differently structured as a function of the pH. These materials have been analyzed using several
experimental techniques (X-ray diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy,
transmission electron microscopy, scanning electron microscopy, and field emission scanning electron microscopy). Large
brushite crystals present amorphous silica both embedded within them and deposited on the crystal surfaces. The resulting
calcium phosphate-silica composite is deposited as a powder, but it can be also easily molded into monolithic forms. The results
of this study could be of significance in the field of biomaterials for considerable improvements of performance of bone implants
in terms of osteointegration and in possible association to set up calcium phosphates-silica biocomposites
Cobalt hexacyanoferrate supported on Sb-doped SnO2 as a non-noble catalyst for oxygen evolution in acidic medium
This study investigates the activity and stability of a Prussian blue analogue (PBA) as an inexpensive anode catalyst for Polymer Electrolyte Membrane Water Electrolysis (PEMWE). While some PBAs have recently been reported to catalyze the oxygen evolution reaction (OER) in acidic electrolytes, the present study focuses on their integration in a PEMWE device. Cobalt hexacyanoferrate nanoparticles were interfaced with an electrically conductive support that withstands the PEMWE anodic conditions, namely Sb-doped SnO2. The OER activity of the composite materials was first verified in liquid electrolytes and then in PEMWE. A promising current density of 50â100 mA cm- 2 was reached at 2 V cell voltage. The PBA/Sbâ SnO2 anode was stable up to 1.9 V, but showed more and more instability at higher potentials. Increasing leaching rates of Sn and Sb observed above 1.9 V suggest that the material instability above 1.9 V can mainly be assigned to Sb-doped SnO2 conductive support. These results are overall promising for the use of PBAs as catalytic sites at the anode of PEMWE. The study also identifies the need for more active PBAs in order to reach a higher current density at a cell voltage of 1.6â1.9 V, a potential range necessary for an acceptable energy efficiency of the PEMWE