792 research outputs found
Breakdown patterns in Branly's coheror
We use thermal imaging of Joule heating to see for the first time electrical
conducting paths created by the so-called Branly effect in a two-dimensional
metallic granular medium (aluminium). Multiple breakdowns are shown to occur
when the medium is submitted to high voltage increases (more than 500 V) with
rise times close to one hundred of microseconds.Comment: 4 pages, 5 figures, related informations at
http://chemphys.weizmann.ac.il/~damien/index.htm
Lâattraction des investissements directs et des filiales Ă©trangĂšres dans la globalisation.
Angular and Linear Speed Cells in the Parahippocampal Circuits
An essential role of the hippocampal region is to integrate information to compute and update representations. How this transpires is highly debated. Many theories hinge on the integration of self-motion signals and the existence of continuous attractor networks (CAN). CAN models hypothesise that neurons coding for navigational correlates â such as position and direction â receive inputs from cells conjunctively coding for position, direction and self-motion. As yet, such conjunctive coding had not been found in the hippocampal region. Here, we report neurons coding for angular and linear velocity, distributed across the medial entorhinal cortex, the presubiculum and the parasubiculum. These self-motion neurons often conjunctively encoded position and/or direction, yet lacked a structured organisation, calling for the revision of current CAN models. These results offer insights as to how linear/angular speed â derivative in time of position/direction â may allow the updating of spatial representations, possibly uncovering a generalised algorithm to update any representation
Persistence, extinction and spatio-temporal synchronization of SIRS cellular automata models
Spatially explicit models have been widely used in today's mathematical
ecology and epidemiology to study persistence and extinction of populations as
well as their spatial patterns. Here we extend the earlier work--static
dispersal between neighbouring individuals to mobility of individuals as well
as multi-patches environment. As is commonly found, the basic reproductive
ratio is maximized for the evolutionary stable strategy (ESS) on diseases'
persistence in mean-field theory. This has important implications, as it
implies that for a wide range of parameters that infection rate will tend
maximum. This is opposite with present results obtained in spatial explicit
models that infection rate is limited by upper bound. We observe the emergence
of trade-offs of extinction and persistence on the parameters of the infection
period and infection rate and show the extinction time having a linear
relationship with respect to system size. We further find that the higher
mobility can pronouncedly promote the persistence of spread of epidemics, i.e.,
the phase transition occurs from extinction domain to persistence domain, and
the spirals' wavelength increases as the mobility increasing and ultimately, it
will saturate at a certain value. Furthermore, for multi-patches case, we find
that the lower coupling strength leads to anti-phase oscillation of infected
fraction, while higher coupling strength corresponds to in-phase oscillation.Comment: 12page
Hawks and Doves on Small-World Networks
We explore the Hawk-Dove game on networks with topologies ranging from
regular lattices to random graphs with small-world networks in between. This is
done by means of computer simulations using several update rules for the
population evolutionary dynamics. We find the overall result that cooperation
is sometimes inhibited and sometimes enhanced in those network structures, with
respect to the mixing population case. The differences are due to different
update rules and depend on the gain-to-cost ratio. We analyse and qualitatively
explain this behavior by using local topological arguments.Comment: 12 pages, 8 figure
Anomalous Thermal Diffusivity of Amorphous Semiconductor Superlattices
Since the development of amorphous semiconductor superlattice films, the great interesting in fundamental and technological is attracted by their special properties and applications. The optical and electronic properties of the films have been studied by conventional spectroscope, photoluminescence and photoconductance techniques etc. Some anomalous phenomena, such as, the quantum size effect and the permenent photoconductivity (PPC) effect, have been discovered [1â2]. Recently the investigations of the characteristics and parameters of amorphous semiconductor superlattice films by photoacoustic and photothermal techniques are being got attention [3,4]. In this paper, we describe the study of the thermal diffusivity of a series samples of amorphous semiconductor superlattices a-Si:H/a-SiNx:H. The thermal diffusivity of the samples is experimentally measured by using mirage detection technique [5,6]. Up to date, the mirage detection method has been used successfully to determine the thermal diffusivity of both transparent and opaque materials. Specially it is available to measure directly the thermal parameters of thin films which are usually difficalt to be, evaluated. In the theoretical calculation, one dimensional model with â the thormal resistors in series â and â the weighted average â is used. Comparing the experimental and theoretical results, we find that both are in good agreement for the most of the samples. However, some anomalous thermal diffusivity phenomena have been observed in some special samples
Universal behavior at discontinuous quantum phase transitions
Discontinuous quantum phase transitions besides their general interest are
clearly relevant to the study of heavy fermions and magnetic transition metal
compounds. Recent results show that in many systems belonging to these classes
of materials, the magnetic transition changes from second order to first order
as they approach the quantum critical point (QCP). We investigate here some
mechanisms that may be responsible for this change. Specifically the coupling
of the order parameter to soft modes and the competition between different
types of order near the QCP. For weak first order quantum phase transitions
general results are obtained. In particular we describe the thermodynamic
behavior at this transition when it is approached from finite temperatures.
This is the discontinuous equivalent of the non-Fermi liquid trajectory close
to a conventional QCP in a heavy fermion material.Comment: 7 pages, 3 figure
Universal patterns in sound amplitudes of songs and music genres
We report a statistical analysis over more than eight thousand songs.
Specifically, we investigate the probability distribution of the normalized
sound amplitudes. Our findings seems to suggest a universal form of
distribution which presents a good agreement with a one-parameter stretched
Gaussian. We also argue that this parameter can give information on music
complexity, and consequently it goes towards classifying songs as well as music
genres. Additionally, we present statistical evidences that correlation aspects
of the songs are directly related with the non-Gaussian nature of their sound
amplitude distributions.Comment: Accepted for publication as a Brief Report in Physical Review
Cellular automaton rules conserving the number of active sites
This paper shows how to determine all the unidimensional two-state cellular
automaton rules of a given number of inputs which conserve the number of active
sites. These rules have to satisfy a necessary and sufficient condition. If the
active sites are viewed as cells occupied by identical particles, these
cellular automaton rules represent evolution operators of systems of identical
interacting particles whose total number is conserved. Some of these rules,
which allow motion in both directions, mimic ensembles of one-dimensional
pseudo-random walkers. Numerical evidence indicates that the corresponding
stochastic processes might be non-Gaussian.Comment: 14 pages, 5 figure
The âMirageâ Sensor in a Industrial Environment: Optical and Thermal Losses Determinations
Since the first âMirageâ experiment run in the laboratory of ESPCI in 1979 [1], this method has been used by many other laboratories for the determination of optical and thermal properties and for non destructive evaluation [2] [3] [4]
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