16,822 research outputs found
Three-frequency resonances in dynamical systems
We investigate numerically and experimentally dynamical systems having three
interacting frequencies: a discrete mapping (a circle map), an exactly solvable
model (a system of coupled ordinary differential equations), and an
experimental device (an electronic oscillator). We compare the hierarchies of
three-frequency resonances we find in each of these systems. All three show
similar qualitative behaviour, suggesting the existence of generic features in
the parameter-space organization of three-frequency resonances.Comment: See home page http://lec.ugr.es/~julya
Thermal analysis applied to estimation of solidification kinetics of Al–Si aluminium alloys
Evaluation of solidification kinetics by thermal analysis is a useful tool for quality control of Al–Si melts before pouring provided it is rapid and highly reproducible. Series of thermal analysis records made with standard cups are presented that show good reproducibility. They are evaluated using a Newton’s like approach to get the instantaneous heat evolution and from it solidification kinetics. An alternative way of calculating the zero line is proposed which is validated by the fact that the latent heat of solidification thus evaluated is within 5% of the value calculated from thermodynamic data. Solidification kinetics was found highly reproducible provided appropriate experimental conditions were achieved: high enough casting temperature for the cup to heat up to the metal temperature well before solidification starts; and equal and homogeneous temperatures of the metal and of the cup at any time in the temperature range used for integration
Exact time-reversal focusing of acoustic and quantum excitations in open cavities: The perfect inverse filter
The time-reversal mirror (TRM) prescribes the reverse playback of a signal to
focalize an acoustic excitation as a Loschmidt echo. In the quantum domain, the
perfect inverse filter (PIF) processes this signal to ensure an exact reversion
provided that the excitation originated outside the cavity delimited by the
transducers. We show that PIF takes a simple form when the initial excitation
is created inside this cavity. This also applies to the acoustical case, where
it corrects the TRM and improves the design of an acoustic bazooka. We solve an
open chaotic cavity modeling a quantum bazooka and a simple model for a
Helmholtz resonator, showing that the PIF becomes decisive to compensate the
group velocities involved in a highly localized excitation and to achieve
subwavelength resolution.Comment: 6 pages, 2 figure
Uniform non-stoichiometric titanium nitride thin films for improved kinetic inductance detector array
We describe the fabrication of homogeneous sub-stoichiometric titanium
nitride films for microwave kinetic inductance detector (mKID) arrays. Using a
6 inch sputtering target and a homogeneous nitrogen inlet, the variation of the
critical temperature over a 2 inch wafer was reduced to <25 %. Measurements of
a 132-pixel mKID array from these films reveal a sensitivity of 16 kHz/pW in
the 100 GHz band, comparable to the best aluminium mKIDs. We measured a noise
equivalent power of NEP = 3.6e-15 W/Hz^(1/2). Finally, we describe possible
routes to further improve the performance of these TiN mKID arrays.Comment: 7 pages, 4 figures, submitted to Journal of low temperature physics,
Proceedings of LTD-1
Visual attention mechanisms in happiness vs. trustworthiness processing of facial expressions
A happy facial expression makes a person look (more) trustworthy. Do perceptions of happiness and trustworthiness rely on the same face regions and visual attention processes? In an eye-tracking study, eye movements and fixations were recorded while participants judged the un/happiness or the un/trustworthiness of dynamic facial expressions in which the eyes and/or the mouth unfolded from neutral to happy or vice versa. A smiling mouth and happy eyes enhanced perceived happiness and trustworthiness similarly, with a greater contribution of the smile relative to the eyes. This comparable judgement output for happiness and trustworthiness was reached through shared as well as distinct attentional mechanisms: (a) entry times and (b) initial fixation thresholds for each face region were equivalent for both judgements, thereby revealing the same attentional orienting in happiness and trustworthiness processing. However, (c) greater and (d) longer fixation density for the mouth region in the happiness task, and for the eye region in the trustworthiness task, demonstrated different selective attentional engagement. Relatedly, (e) mean fixation duration across face regions was longer in the trustworthiness task, thus showing increased attentional intensity or processing effort
Floquet interface states in illuminated three-dimensional topological insulators
Recent experiments showed that the surface of a three dimensional topological
insulator develops gaps in the Floquet-Bloch band spectrum when illuminated
with a circularly polarized laser. These Floquet-Bloch bands are characterized
by non-trivial Chern numbers which only depend on the helicity of the
polarization of the radiation field. Here we propose a setup consisting of a
pair of counter-rotating lasers, and show that one-dimensional chiral states
emerge at the interface between the two lasers. These interface states turn out
to be spin-polarized and may trigger interesting applications in the field of
optoelectronics and spintronics.Comment: 5 pages with 3 figures + supplemental materia
Geometric magic numbers of sodium clusters: Interpretation of the melting behaviour
Putative global minima of sodium clusters with up to 380 atoms have been
located for two model interatomic potentials. Structures based upon the Mackay
icosahedra predominate for both potentials, and the magic numbers for the
Murrell-Mottram model show excellent agreement with the sizes at which maxima
in the latent heat and entropy change at melting have been found in experiment.Comment: 4 pages, 2 figure
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