4,935 research outputs found
Characterisation of an aperture-stacked patch antenna for ultra-wideband wearable radio systems
This paper presents, for the first time, the time-domain characteristics of an aperture-stacked patch antenna (ASPA) for ultra-wideband (UWB) wearable devices. The methodology of antennas characterization for UWB radio systems is also outlined. The antenna operates within the 3-6 GHz frequency band. Time- and frequency-domain characteristics of this antenna are presented in transmission mode (Tx), receiving mode (Rx) and for 2-antenna (Tx-Rx) system. The pulse driving the antenna has duration of 0.65 ns. In the Tx mode, pulses radiated in different directions of the H-plane have very similar shapes. Fidelity factors are as high as 91.6-99.9%. For 2-antenna system, pulses received in normal and end-fire-like directions have the fidelity of 69.5%. As it was found, antenna does not behave "reciprocal" comparing Tx and Rx modes. For normal propagation direction, radiated pulse is the 2nd derivative of the input waveform, but in the Rx mode, received pulse is the 1st derivative of the incident plane wave. This antenna can be used for transmission of short-pulses, even 0.65-1 ns in duration. It is also small (patch planar dimensions 32/19 mm) and compact. Microstrip configuration allows further integration of active devices on the same board. Taking into account above results we can say that ASPA is a good candidate for UWB non-invasive wireless body area network (WBAN) applications
Theory of Coherent -Axis Josephson Tunneling between Layered Superconductors
We calculate exactly the Josephson current for -axis coherent tunneling
between two layered superconductors, each with internal coherent tight-binding
intra- and interlayer quasiparticle dispersions. Our results also apply when
one or both of the superconductors is a bulk material, and include the usually
neglected effects of surface states. For weak tunneling, our results reduce to
our previous results derived using the tunneling Hamiltonian. Our results are
also correct for strong tunneling. However, the -axis tunneling results of
Tanaka and Kashiwaya are shown to be incorrect in any limit. In addition, we
consider the -axis coherent critical current between two identical layered
superconductors twisted an angle about the -axis with respect to
each other. Regardless of the order parameter symmetry, our coherent tunneling
results using a tight-binding intralayer quasiparticle dispersion are
inconsistent with the recent -axis twist bicrystal
BiSrCaCuO twist junction experiments of Li {\it et
al.}Comment: 11 pages, 13 figures, submitted to Physical Review
Stable and unstable attractors in Boolean networks
Boolean networks at the critical point have been a matter of debate for many
years as, e.g., scaling of number of attractor with system size. Recently it
was found that this number scales superpolynomially with system size, contrary
to a common earlier expectation of sublinear scaling. We here point to the fact
that these results are obtained using deterministic parallel update, where a
large fraction of attractors in fact are an artifact of the updating scheme.
This limits the significance of these results for biological systems where
noise is omnipresent. We here take a fresh look at attractors in Boolean
networks with the original motivation of simplified models for biological
systems in mind. We test stability of attractors w.r.t. infinitesimal
deviations from synchronous update and find that most attractors found under
parallel update are artifacts arising from the synchronous clocking mode. The
remaining fraction of attractors are stable against fluctuating response
delays. For this subset of stable attractors we observe sublinear scaling of
the number of attractors with system size.Comment: extended version, additional figur
Cultural transmission and optimization dynamics
We study the one-dimensional version of Axelrod's model of cultural
transmission from the point of view of optimization dynamics. We show the
existence of a Lyapunov potential for the dynamics. The global minimum of the
potential, or optimum state, is the monocultural uniform state, which is
reached for an initial diversity of the population below a critical value.
Above this value, the dynamics settles in a multicultural or polarized state.
These multicultural attractors are not local minima of the potential, so that
any small perturbation initiates the search for the optimum state. Cultural
drift is modelled by such perturbations acting at a finite rate. If the noise
rate is small, the system reaches the optimum monocultural state. However, if
the noise rate is above a critical value, that depends on the system size,
noise sustains a polarized dynamical state.Comment: 11 pages, 10 figures include
Causality Violation and Naked Time Machines in AdS_5
We study supersymmetric charged rotating black holes in AdS, and show
that closed timelike curves occur outside the event horizon. Also upon lifting
to rotating D3 brane solutions of type IIB supergravity in ten dimensions,
closed timelike curves are still present. We believe that these causal
anomalies correspond to loss of unitarity in the dual , D=4 super
Yang-Mills theory, i.e. the chronology protection conjecture in the AdS bulk is
related to unitarity bounds in the boundary CFT. We show that no charged or
uncharged geodesic can penetrate the horizon, so that the exterior region is
geodesically complete. These results still hold true in the quantum case,
i.~e.~the total absorption cross section for Klein-Gordon scalars propagating
in the black hole background is zero. This suggests that the effective
temperature is zero instead of assuming the naively found imaginary value.Comment: 22 pages, Latex, uses JHEP.cls, 1 figure. v3: comments on unitarity
in CFT and 2 references added. v4: changes in final remarks, final version to
appear in JHE
Competition in the presence of aging: order, disorder, and synchronized collective behavior
We study the stochastic dynamics of coupled states with transition
probabilities depending on local persistence, this is, the time since a state
has changed. When the population has a preference to adopt older states the
system orders quickly due to the dominance of the old state. When preference
for new states prevails, the system can show coexistence of states or
synchronized collective behavior resulting in long ordering times. In this
case, the magnetization of the system oscillates around .
Implications for social systems are discussed.Comment: 5 pages, 5 figures, lette
Temporal networks: slowing down diffusion by long lasting interactions
Interactions among units in complex systems occur in a specific sequential
order thus affecting the flow of information, the propagation of diseases, and
general dynamical processes. We investigate the Laplacian spectrum of temporal
networks and compare it with that of the corresponding aggregate network.
First, we show that the spectrum of the ensemble average of a temporal network
has identical eigenmodes but smaller eigenvalues than the aggregate networks.
In large networks without edge condensation, the expected temporal dynamics is
a time-rescaled version of the aggregate dynamics. Even for single sequential
realizations, diffusive dynamics is slower in temporal networks. These
discrepancies are due to the noncommutability of interactions. We illustrate
our analytical findings using a simple temporal motif, larger network models
and real temporal networks.Comment: 5 pages, 2 figures, v2: minor revision + supplemental materia
Mass measurement in boosted decay systems at hadron colliders
We report a new possibility of using the \mct2 (Constransverse mass)
variable for mass measurement in single step decay chains involving missing
particles with moderate transverse momentum. We show that its experimental
feasibility is enhanced compared to the corresponding \mt2-kink method. We
apply this method to reconstruct a pair of chargino decay chains.Comment: 6 pages, 12 figures, published in PRD,
http://link.aps.org/doi/10.1103/PhysRevD.84.03501
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