1,716 research outputs found
A visualization of the damage in Lead Tungstate calorimeter crystals after exposure to high-energy hadrons
The anticipated performance of calorimeter crystals in the environment
expected after the planned High-Luminosity upgrade of the Large Hadron Collider
(HL-LHC) at CERN has to be well understood, before informed decisions can be
made on the need for detector upgrades. Throughout the years of running at the
HL-LHC, the detectors will be exposed to considerable fluences of fast hadrons,
that have been shown to cause cumulative transparency losses in Lead Tungstate
scintillating crystals. In this study, we present direct evidence of the main
underlying damage mechanism. Results are shown from a test that yields a direct
insight into the nature of the hadron-specific damage in Lead Tungstate
calorimeter crystals exposed to 24 GeV/c protons.Comment: 8 pages, 6 figure
Spin wave excitations in low dimensional systems with large magnetic anisotropy
The low energy excitation spectrum of a two-dimensional ferromagnetic
material is dominated by single-magnon excitations that show a gapless
parabolic dispersion relation with the spin wave vector. This occurs as long as
magnetic anisotropy and anisotropic exchange are negligible compared to
isotropic exchange. However, to maintain magnetic order at finite temperatures,
it is necessary to have sizable anisotropy to open a gap in the spin wave
excitation spectrum. We consider four real two-dimensional systems for which
ferromagnetic order at finite temperature has been observed or predicted.
Density functional theory calculations of the total energy differences for
different spin configurations permit us to extract the relevant parameters and
connect them with a spin Hamiltonian. The corresponding values of the Curie
temperature are estimated using a simple model and found to be mostly
determined by the value of the isotropic exchange. The exchange and anisotropy
parameters are used in a toy model of finite-size periodic chains to study the
low-energy excitation spectrum, including single-magnon and two-magnon
excitations. At low energies we find that single-magnon excitations appear in
the spectrum together with two-magnon excitations. These excitations present a
gap that grows particularly for large values of the magnetic anisotropy or
anisotropic exchange, relative to the isotropic exchange.Comment: 11 pages, 3 figures, 2 table
Absolute Maximal Entanglement and Quantum Secret Sharing
We study the existence of absolutely maximally entangled (AME) states in
quantum mechanics and its applications to quantum information. AME states are
characterized by being maximally entangled for all bipartitions of the system
and exhibit genuine multipartite entanglement. With such states, we present a
novel parallel teleportation protocol which teleports multiple quantum states
between groups of senders and receivers. The notable features of this protocol
are that (i) the partition into senders and receivers can be chosen after the
state has been distributed, and (ii) one group has to perform joint quantum
operations while the parties of the other group only have to act locally on
their system. We also prove the equivalence between pure state quantum secret
sharing schemes and AME states with an even number of parties. This equivalence
implies the existence of AME states for an arbitrary number of parties based on
known results about the existence of quantum secret sharing schemes.Comment: 5 pages, 2 figure
Dynamics of alternative modes of RNA replication for positive-sense RNA viruses
We propose and study nonlinear mathematical models describing the intracellular time dynamics
of viral RNA accumulation for positive sense single-stranded RNA viruses. Our models consider
different replication modes ranging between two extremes represented by the geometric replication
(GR) and the linear stamping machine replication (SMR). We first analyze a model that quantitatively
reproduced experimental data for the accumulation dynamics of both polarities of Turnip
mosaic potyvirus RNAs. We identify a non-degenerate transcritical bifurcation governing the extinction
of both strands depending on three key parameters: the mode of replication (®), the replication
rate (r) and the degradation rate (±) of viral strands. Our results indicate that the bifurcation associated
with ® generically takes place when the replication mode is closer to the SMR, thus suggesting
that GR may provide viral strands with an increased robustness against degradation. This transcritical
bifurcation, which is responsible for the switching from an active to an absorbing regime,
suggests a smooth (i.e., second-order), absorbing-state phase transition. Finally, we also analyze
a simplified model that only incorporates asymmetry in replication tied to differential replication
modes.This work has been funded by the Human Frontier Science
Program Organization grant RGP12/2008, by the Spanish
Ministerio de Ciencia e Innovaci´on grants BIO2008-01986
(JAD) and BFU2009-06993 (SFE), and by the Santa Fe
Institute. FM is the recipient of a predoctoral fellowship
from Universitat Polit`ecnica de Val`encia. We also want to
thank the hospitality and support of the Kavli Institute
for Theoretical Physics (University of California at Santa
Barbara), where part of this work was developed (grant NSF
PHY05-51164).Peer reviewe
Lumped Approach for Flow-Through and Wall-Flow Monolithic Reactors Modelling for Real-Time Automotive Applications
[EN] The increasingly restrictive legislation on pollutant emissions is involving new homologation procedures driven to be representative of real driving emissions. This context demands an update of the modelling tools leading to an accurate assessment of the engine and aftertreatment systems performance at the same time as these complex systems are understood as a single element. In addition, virtual engine models must retain the accuracy while reducing the computational effort to get closer to real-time computation. It makes them useful for pre-design and calibration but also potentially applicable to on-board diagnostics purposes. This paper responds to these requirements presenting a lumped modelling approach for the simulation of aftertreatment systems. The basic principles of operation of flow-through and wall-flow monoliths are covered leading the focus to the modelling of gaseous emissions conversion efficiency and particulate matter abatement, i.e. filtration and regeneration processes. The model concept is completed with the solution of pressure drop and heat transfer processes. The lumped approach hypotheses and the solution of the governing equations for every sub-model are detailed.
While inertial pressure drop contributions are computed from the characteristic pressure drop coefficient, the porous medium
effects in wall-flow monoliths are considered separately. Heat transfer sub-model applies a nodal approach to account for heat
exchange and thermal inertia of the monolith substrate and the external canning. In wall-flow monoliths, the filtration and
porous media properties are computed as a function of soot load applying a spherical packed bed approach. The soot oxidation mechanism including adsorption reactant phase is presented. Concerning gaseous emissions, the general scheme
to solve the chemical species transport in the bulk gas and washcoat regions is also described. In particular, it is finally
applied to the modelling of CO and HC abatement in a DOC and DPF brick. The model calibration steps against a set of
steady-state in-engine experiments allowing separate certain phenomena are discussed. As a final step, the model performance is assessed against a transient test during which all modelled processes are taking place simultaneously under
highly dynamic driving conditions. This test is simulated imposing different integration time-steps to demonstrate the model’s potential for real-time applications.This research has been partially supported by FEDER and the Government of Spain through project TRA2016-79185-R and by the European Union’s Horizon 2020 Framework Programme for research, technological development and demonstration under grant agreement number 723976.Payri, F.; Arnau MartÃnez, FJ.; Piqueras, P.; Ruiz Lucas, MJ. (2018). Lumped Approach for Flow-Through and Wall-Flow Monolithic Reactors Modelling for Real-Time Automotive Applications. SAE Technical Papers. https://doi.org/10.4271/2018-01-0954
Hydrodynamic theory of an electron gas
The generalised hydrodynamic theory of an electron gas, which does not rely
on an assumption of a local equilibrium, is derived as the long-wave limit of a
kinetic equation. Apart from the common hydrodynamics variables the theory
includes the tensor fields of the higher moments of the distribution function.
In contrast to the Bloch hydrodynamics, the theory leads to the correct plasmon
dispersion and in the low frequency limit recovers the Navies-Stocks
hydrodynamics. The linear approximation to the generalised hydrodynamics is
closely related to the theory of highly viscous fluids.Comment: 4 pages, revte
APPLICATION OF BIOMECHANICS TO THE PREVENTION OF OVERLOAD INJURIES IN ELITE SOCCER PLAYERS.
Structural alterations of the foot and inadequate design of sports footwear, as well as overtraining, have been determined to be risk factors for overload injuries during sports practice. A biomechanical analysis protocol was designed to study both, the foot and sports footwear statically and dynamically. This protocol was applied on 47 soccer players of the Spanish Premier League. Amongst the results we should point out that 53.3% of the players had cavus feet. 14.8% of the players deformed the boots. 44.7% of the players studied registered high pressures over the metatarsal heads. and 19.1 % registered high ones at the first toe. 44.7% of the players showed an excessive supination pattern. The data obtained gave us information about the static and dynamic patterns of the elite soccer player. With the individual information the assessment of suitable footwear was carried out for each player. The correct application of this protocol could be used in the diagnosis or prevention of overtraining and in the detection of foot and gait pathologies
Robustness of Generalized Linear Mixed Models for Split-Plot Designs with Binary Data.
This paper examined the robustness of the generalized linear mixed model (GLMM). The GLMM estimates fixed and random effects, and it is especially useful when the dependent variable is binary. It is also useful when the dependent variable involves repeated measures, since it can model correlation. The present study used Monte Carlo simulation to analyze the empirical Type I error rates of GLMMs in split-plot designs. The variables manipulated were sample size, group size, number of repeat-ed measures, and correlation between repeated measures. Extreme condi-tions were also considered, including small samples, unbalanced groups, and different correlation in each group (pairing between group size and correlation between repeated measures). For balanced groups, the results showed that the group effect was robust under all conditions, while for unbalanced groups the effect tended to be conservative with positive pair-ing and liberal with negative pairing. Regarding time and interaction ef-fects, the results showed, for both balanced and unbalanced groups, that: (a) The test was robust with low correlation (.2), but conservative for me-dium values of correlation (.4 and .6), and (b) the test tended to be con-servative for positive and negative pairing, especially the latter.Our work was funded by the grants PSI2016-78737-P and PID2020-113191GB-I00 (AEI/FEDER, UE) from the Spanish Ministry of Economy, Industry and Competitiveness, and the Spanish Ministry of Science and Innovation
Interactions of Ar(9+) and metastable Ar(8+) with a Si(100) surface at velocities near the image acceleration limit
Auger LMM spectra and preliminary model simulations of Ar(9+) and metastable
Ar(8+) ions interacting with a clean monocrystalline n-doped Si(100) surface
are presented. By varying the experimental parameters, several yet undiscovered
spectroscopic features have been observed providing valuable hints for the
development of an adequate interaction model. On our apparatus the ion beam
energy can be lowered to almost mere image charge attraction. High data
acquisition rates could still be maintained yielding an unprecedented
statistical quality of the Auger spectra.Comment: 34 pages, 11 figures, http://pikp28.uni-muenster.de/~ducree
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