5,325 research outputs found
Quantum Hysteresis in Coupled Light-Matter Systems
We investigate the non-equilibrium quantum dynamics of a canonical
light-matter system, namely the Dicke model, when the light-matter interaction
is ramped up and down through a cycle across the quantum phase transition. Our
calculations reveal a rich set of dynamical behaviors determined by the cycle
times, ranging from the slow, near adiabatic regime through to the fast, sudden
quench regime. As the cycle time decreases, we uncover a crossover from an
oscillatory exchange of quantum information between light and matter that
approaches a reversible adiabatic process, to a dispersive regime that
generates large values of light-matter entanglement. The phenomena uncovered in
this work have implications in quantum control, quantum interferometry, as well
as in quantum information theory.Comment: 9 pages and 4 figure
A USB3.0 FPGA Event-based Filtering and Tracking Framework for Dynamic Vision Sensors
Dynamic vision sensors (DVS) are frame-free sensors
with an asynchronous variable-rate output that is ideal for hard
real-time dynamic vision applications under power and latency
constraints. Post-processing of the digital sensor output can
reduce sensor noise, extract low level features, and track objects
using simple algorithms that have previously been implemented
in software. In this paper we present an FPGA-based framework
for event-based processing that allows uncorrelated-event noise
removal and real-time tracking of multiple objects, with dynamic
capabilities to adapt itself to fast or slow and large or small
objects. This framework uses a new hardware platform based on
a Lattice FPGA which filters the sensor output and which then
transmits the results through a super-speed Cypress FX3 USB
microcontroller interface to a host computer. The packets of
events and timestamps are transmitted to the host computer at
rates of 10 Mega events per second. Experimental results are
presented that demonstrate a low latency of 10us for tracking
and computing the center of mass of a detected object.Ministerio de Economía y Competitividad TEC2012-37868-C04-0
An Expanding HI Photodissociated Region Associated with the Compact HII Region G213.880-11.837 in the GGD 14 Complex
We present high angular and spectral resolution HI 21~cm line observations
toward the cometary-shaped compact HII region G213.880-11.837 in the GGD~14
complex.The kinematics and morphology of the photodissociated region, traced by
the HI line emission, reveal that the neutral gas is part of an expanding flow.
The kinematics of the HI gas along the major axis of G213.880-11.837 shows that
the emission is very extended toward the SE direction, reaching LSR radial
velocities in the tail of about 14 km/s. The ambient LSR radial velocity of the
molecular gas is 11.5 km/s, which suggests a champagne flow of the HI gas. This
is the second (after G111.61+0.37) cometary HII/HI region known.Comment: Accepted for publication in the Astronomical Journal (10 pages, 4
figures, 1 table
Quantum Phase Transitions detected by a local probe using Time Correlations and Violations of Leggett-Garg Inequalities
In the present paper we introduce a way of identifying quantum phase
transitions of many-body systems by means of local time correlations and
Leggett-Garg inequalities. This procedure allows to experimentally determine
the quantum critical points not only of finite-order transitions but also those
of infinite order, as the Kosterlitz-Thouless transition that is not always
easy to detect with current methods. By means of simple analytical arguments
for a general spin- Hamiltonian, and matrix product simulations of
one-dimensional and anisotropic models, we argue that
finite-order quantum phase transitions can be determined by singularities of
the time correlations or their derivatives at criticality. The same features
are exhibited by corresponding Leggett-Garg functions, which noticeably
indicate violation of the Leggett-Garg inequalities for early times and all the
Hamiltonian parameters considered. In addition, we find that the infinite-order
transition of the model at the isotropic point can be revealed by the
maximal violation of the Leggett-Garg inequalities. We thus show that quantum
phase transitions can be identified by purely local measurements, and that
many-body systems constitute important candidates to observe experimentally the
violation of Leggett-Garg inequalities.Comment: Minor changes, 11 pages, 11 figures. Final version published in Phys.
Rev.
Influence of Baseline Fluctuation Cancellation on Automatic Measurement of Motor Unit Action Potential Duration
The aim of this work is to analyze the influence of a method for baseline fluctuation (BLF) cancellation for electromyographic (EMG) signals on automatic methods for measurement of the motor unit action potential (MUAP) duration. These methods include four conventional automatic methods (CAMs) and a recently published wavelet transform method (WTM). A set of 182 MUAPs from 170 EMG recordings were studied. The CAMs and the WTM were applied to the MUAPs before and after applying BLF cancellation to the recordings. A gold standard of duration marker positions (GSP) ws manually established. The accuracy of each algorithm was estimated as the dfference between its positions and the GSP. Accuracies were compared for the 5 methods and for each method before and after BLF cancellation. A significant difference between accuracy pre- and post-BLF removal was found in two CAMs; markers were closer to the GSP after BLF removal. For all MUAPs, the differences between WTM markers and the GSP were the smallest, and significant differences were not found for the WTM before and after BLF cancellation. The management of BLF is an important issue in EMG signal processing and BLF removal must be considered in extraction and analyse of MUAP waveforms. The BLF removal method improved the performance of two CAMs for MUAP duration measurement. The WTM was the most accurate and was not affected by BLF.
Dynamics of Entanglement and the Schmidt Gap in a Driven Light-Matter System
The ability to modify light-matter coupling in time (e.g. using external
pulses) opens up the exciting possibility of generating and probing new aspects
of quantum correlations in many-body light-matter systems. Here we study the
impact of such a pulsed coupling on the light-matter entanglement in the Dicke
model as well as the respective subsystem quantum dynamics. Our dynamical
many-body analysis exploits the natural partition between the radiation and
matter degrees of freedom, allowing us to explore time-dependent
intra-subsystem quantum correlations by means of squeezing parameters, and the
inter-subsystem Schmidt gap for different pulse duration (i.e. ramping
velocity) regimes -- from the near adiabatic to the sudden quench limits. Our
results reveal that both types of quantities indicate the emergence of the
superradiant phase when crossing the quantum critical point. In addition, at
the end of the pulse light and matter remain entangled even though they become
uncoupled, which could be exploited to generate entangled states in
non-interacting systems.Comment: 15 pages, 4 figures, Accepted for publication in Journal of Physics
B, special issue Correlations in light-matter interaction
Estudio de la marcha en la infancia
El análisis de la marcha se ha visto reforzado por la
aparición de sistemas de invetigación de nueva tecnología
como son las plataformas de fuerzas monitorizadas
que permiten estudiar, con alta precisión, el desarrollo
cinético y en parte cinemático de la marcha. Con este
sistema hemos estudiado el paso de 62 niños de 5 y 6
años de edad, para determinar los valores de normalidad
de los parámetros temporoespaciales y las magnitudes
de las fuerzas de reacción pie-suelo en los tres
ejes de plano espaciales.
Hemos encontrado diferencias estadísticamente significativas
entre estas edades para la longitud de paso,
tiempo de doble apoyo y la mayoría de las fuerzas de
reacción del suelo, indicando una evolución de la marcha
en este periodo
Motor differences in cadet taekwondo athletes according to competition level
El objetivo de este estudio es observar las diferencias entre atletas cadetes de Taekwondo de diferentes niveles competitivos en términos antropométricos, de potencia muscular, flexibilidad y velocidad de reacción. Veinte atletas varones fueron analizados, divididos en dos grupos: medallistas nacionales y no medallistas nacionales. Para cada atleta se tomaron datos antropométricos, de velocidad de reacción, potencia muscular y rango de movimiento articular de la articulación coxofemoral. Los atletas medallistas mostraron valores significativamente menores en altura, envergadura, tiempo de reacción óculo-podal, y tiempo de reacción óculo-manual con mano no dominante; y valores mayores para longitud de piernas, flexión pasiva de cadera, y abducción de cadera tanto activa como pasiva. Las leves diferencias observadas entre grupos en potencia muscular, grasa corporal y flexión activa de cadera no concuerdan con estudios previos. Conocer está información podría ser de interés para los entrenadores para llevar a cabo programas de detección de talentosThe aim of this study was to determine the differences between Taekwondo cadet athletes belonging to different competition levels in terms of anthropometry, legs power, flexibility and reaction time. Twenty male athletes were analysed, divided in two groups: national medallist and non-national medallist. Data of every athlete’s anthropometric measurements, reaction speed ability, leg power and hip ROM (range of movement) were taken. Medallist athletes showed significantly lower values for height, arm span, foot reaction time (dominant and non-dominant) and non-dominant hand reaction time; and higher values for leg length, passive hip flexion, active hip abduction and passive hip abduction in ROM tests. Slight differences observed between medallists and non-medallists in leg power (CMJ), body fat (Σ skinfolds) and active hip flexion do not agree with previous studies. Knowing this information could be interesting for coaches in order to carry out talent detection program
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