122 research outputs found
Multipath propagation model for high altitude platform (HAP) based on circular straigh cone geometry
A geometric model that describes a multipath
propagation for a fixed wireless communication system between a
High Altitude Platform and a fixed terrestrial user is presented.
The model describes the propagation of the reflected signals that
are able to reach the receiver as a consequence of all the
scatterers located inside the system coverage area. The
establishment of a particular geometry characterizing the system
coverage area allows the behavior of the multipath phenomenon
effects to be modeled accurately.Postprint (published version
Influence of Modularity and Regularity on Disparity of Atelostomata Sea Urchins
A modularity approach is used to study disparity rates and evolvability of sea urchins belonging to the Atelostomata superorder. For this purpose, the pentameric sea urchin architecture is partitioned into modular spatial components and the interference between modules is quantified using areas and a measurement of the regularity of the spatial partitions. This information is used to account for the variability through time (disparity) and potential for morphological variation and evolution (evolvability) in holasteroid echinoids. We obtain that regular partitions of the space produce modules with high modular integrity, whereas irregular partitions produce low modular integrity; the former ones are related with high morphological disparity (facilitation hypothesis). Our analysis also suggests that a pentameric body plan with low regularity rates in Atelostomata reflects a stronger modular integration among modules than within modules, which could favors bilaterality against radial symmetry. Our approach constitutes a theoretical platform to define and quantify spatial organization in partitions of the space that can be related to modules in a morphological analysis
Severe and common mental disorders and risk of emergency hospital admissions for ambulatory care sensitive conditions among the UK Biobank cohort
BACKGROUND: People with mental disorders have worse physical health compared with the general population, which could be attributable to receiving poorer quality healthcare. AIMS: To examine the relationship between severe and common mental disorders and risk of emergency hospital admissions for ambulatory care sensitive conditions (ACSCs), and factors associated with increased risk. METHOD: Baseline data for England ( N = 445 814) were taken from UK Biobank, which recruited participants aged 37-73 years during 2006-2010, and linked to hospital admission records up to 31 December 2019. Participants were grouped into those with a history of either schizophrenia, bipolar disorder, depression or anxiety, or no mental disorder. Survival analysis was used to assess the risk of hospital admission for ACSCs among those with mental disorders compared with those without, adjusting for factors in different domains (sociodemographic, socioeconomic, health and biomarkers, health-related behaviours, social isolation and psychological). RESULTS: People with schizophrenia had the highest (unadjusted) risk of hospital admission for ACSCs compared with those with no mental disorder (hazard ratio 4.40, 95% CI 4.04-4.80). People with bipolar disorder (hazard ratio 2.48, 95% CI 2.28-2.69) and depression or anxiety (hazard ratio 1.76, 95% CI 1.73-1.80) also had higher risk. Associations were more conservative when including all admissions, as opposed to first admissions only. The observed associations persisted after adjusting for a range of factors. CONCLUSIONS: People with severe mental disorders have the highest risk of preventable hospital admissions. Ensuring people with mental disorders receive adequate ambulatory care is essential to reduce the large health inequalities they experience
Experimental realization of the classical Dicke model
We report the experimental implementation of the Dicke model in the
semiclassical approximation, which describes a large number of two-level atoms
interacting with a single-mode electromagnetic field in a perfectly reflecting
cavity. This is managed by making use of two non-linearly coupled active,
synthetic LC circuits, implemented by means of analog electrical components.
The simplicity and versatility of our platform allows us not only to
experimentally explore the coexistence of regular and chaotic trajectories in
the Dicke model but also to directly observe the so-called ground-state and
excited-state ``quantum'' phase transitions. In this analysis, the trajectories
in phase space, Lyapunov exponents and the recently introduced
Out-of-Time-Order-Correlator (OTOC) are used to identify the different
operating regimes of our electronic device. Exhaustive numerical simulations
are performed to show the quantitative and qualitative agreement between theory
and experiment
Experimental observation of phase transitions of a deformed Dicke model using a reconfigurable, bi-parametric electronic platform
We experimentally study the infinite-size limit of the Dicke model of quantum
optics with a parity-breaking deformation strength that couples the system to
an external bosonic reservoir. We focus on the dynamical consequences of such
symmetry-breaking, which makes the classical phase space asymmetric with
non-equivalent energy wells. We present an experimental implementation of the
classical version of the deformed Dicke model using a state-of-the-art
bi-parametric electronic platform. Our platform constitutes a playground for
studying representative phenomena of the deformed Dicke model in electrical
circuits with the possibility of externally controlling parameters and initial
conditions. In particular, we investigate the dynamics of the ground state,
various phase transitions, and the asymmetry of the energy wells as a function
of the coupling strength and the deformation strength in the
resonant case. Additionally, to characterize the various behavior regimes, we
present a two-dimensional phase diagram as a function of the two intrinsic
system parameters. The onset of chaos is also analyzed experimentally. Our
findings provide a clear connection between theoretical predictions and
experimental observations, demonstrating the usefulness of our bi-parametric
electronic setup
Reconfigurable Network for Quantum Transport Simulation
In 1981, Richard Feynman discussed the possibility of performing quantum
mechanical simulations of nature. Ever since, there has been an enormous
interest in using quantum mechanical systems, known as quantum simulators, to
mimic specific physical systems. Hitherto, these controllable systems have been
implemented on different platforms that rely on trapped atoms, superconducting
circuits and photonic arrays. Unfortunately, these platforms do not seem to
satisfy, at once, all desirable features of an universal simulator, namely
long-lived coherence, full control of system parameters, low losses, and
scalability. Here, we overcome these challenges and demonstrate robust
simulation of quantum transport phenomena using a state-of-art reconfigurable
electronic network. To test the robustness and precise control of our platform,
we explore the ballistic propagation of a single-excitation wavefunction in an
ordered lattice, and its localization due to disorder. We implement the
Su-Schrieffer-Heeger model to directly observe the emergence of
topologically-protected one-dimensional edge states. Furthermore, we present
the realization of the so-called perfect transport protocol, a key milestone
for the development of scalable quantum computing and communication. Finally,
we show the first simulation of the exciton dynamics in the B800 ring of the
purple bacteria LH2 complex. The high fidelity of our simulations together with
the low decoherence of our device make it a robust, versatile and promising
platform for the simulation of quantum transport phenomena
Comparison of GPS analysis strategies for high-accuracy vertical land motion
Tide gauges measure sea level changes relative to land. To separate absolute changes in sea level from vertical land movements tide gauges are often co-located with Continuous GPS (CGPS). In order to achieve an accuracy of better than 1 mm/yr, as required for sea level studies in the global change context, vertical land motion needs to be determined with the same accuracy. This is an ambitious goal for CGPS and needs a carefully designed analysis strategy. We have compared the independent results from six different analysis centres, using three different GPS processing softwares and a number of different analysis strategies. Based on the comparison, we discuss the achieved accuracy and the quality of the different strategies. The data analysed are from the CGPS network of the European Sea Level Service and cover the time window from the beginning of 2000 until the end of 2003. The comparison reveals large differences in the day-to-day variations of the coordinate time series and also in the seasonal cycle contained in these. The trends show systematic differences, depending on software and strategy used. To a large extent, the latter deviations can be explained by differences in the realisation of the reference frame, while some parts may be due to other, as yet, unidentified contributions. The results suggest that the reference frame and its relation to the center of mass of the Earth system may be the main limitation in achieving the accuracy goal for the secular velocity of vertical land motion.Peer ReviewedPostprint (published version
Structural, morphological, and magnetic characterizations of (FexMn1-x)2O3 nanocrystals: A comprehensive stoichiometric determination
Iron manganese trioxide (FexMn1-x)2O3 nanocrystals were synthesized by the
sol-gel method. The 80 K Mossbauer spectrum was well-fitted using two doublets
representing the 8b and 24d crystallographic sites of the (FexMn1-x)2O3 phase
and two weak extra sextets which were attributed to crystalline and amorphous
hematite. Our findings showed formation of a bixbyite primary phase. The Raman
spectrum exhibits six Raman active modes, typical of (Fe,Mn)2O3, and two extra
Raman modes associated with the secondary hematite phase. X-ray photoelectron
spectroscopy analysis confirmed the presence of oxygen vacancy onto the
(FexMn1-x)2O3 particle surface, with varying oxidation states. X-band magnetic
resonance data revealed a single broad resonance line in the whole temperature
range (3.8 K - 300 K). The temperature dependence of both resonance field and
resonance linewidth shows a remarkable change in the range of 40 - 50 K, herein
credited to surface spin glass behavior. The model picture used assumes
(FexMn1-x)2O3 nanoparticles with a core-shell structure. Results indicate that
below about 50 K the spin system of shell reveals a paramagnetic to spin
glass-like transition upon cooling, with a critical temperature estimated at 43
K. In the higher temperature range, the superparamagnetic hematite (secondary)
phase contributes remarkably to the temperature dependence of the resonance
linewidth. Zero-field-cooled (ZFC) and fieldcooled (FC) data show strong
irreversibility and a peak in the ZFC curve at 33 K, attributed to a
paramagnetic-ferrimagnetic transition of the main phase. Hysteresis curve at 5
K shows a low coercive field of 4 kOe, with the magnetization not reaching
saturation at 70 kOe, suggesting the occurrence of a ferrimagnetic core with a
magnetic disorder at surface, characteristic of core-shell spin-glass-like
behavior
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