899 research outputs found
Vertex Intrinsic Fitness: How to Produce Arbitrary Scale-Free Networks
We study a recent model of random networks based on the presence of an
intrinsic character of the vertices called fitness. The vertices fitnesses are
drawn from a given probability distribution density. The edges between pair of
vertices are drawn according to a linking probability function depending on the
fitnesses of the two vertices involved. We study here different choices for the
probability distribution densities and the linking functions. We find that,
irrespective of the particular choices, the generation of scale-free networks
is straightforward. We then derive the general conditions under which
scale-free behavior appears. This model could then represent a possible
explanation for the ubiquity and robustness of such structures.Comment: 4 pages, 3 figures, RevTe
Quasielastic Scattering at MiniBooNE Energies
We present our description of neutrino induced charged current quasielastic
scattering (CCQE) in nuclei at energies relevant for the MiniBooNE experiment.
In our framework, the nucleons, with initial momentum distributions according
to the Local Fermi Gas model, move in a density- and momentum-dependent mean
field potential. The broadening of the outgoing nucleons due to nucleon-nucleon
interactions is taken into account by spectral functions. Long range (RPA)
correlations renormalizing the electroweak strength in the medium are also
incorporated. The background from resonance excitation events that do not lead
to pions in the final state is also predicted by propagating the outgoing
hadrons with the Giessen semiclassical BUU model in coupled channels (GiBUU).
We achieve a good description of the shape of the CCQE Q2 distribution
extracted from data by MiniBooNE, thanks to the inclusion of RPA correlations,
but underestimate the integrated cross section when the standard value of MA =
1 GeV is used. Possible reasons for this mismatch are discussed.Comment: 6 pages, 4 figures, Proceedings of the Sixth International Workshop
on Neutrino-Nucleus Interactions in the Few-GeV Region (NuInt09), May 18-22,
Sitges, Barcelona, Spai
MiniBooNE
The physics motivations, design, and status of the Booster Neutrino
Experiment at Fermilab, MiniBooNE, are briefly discussed. Particular emphasis
is given on the ongoing preparatory work that is needed for the MiniBooNE muon
neutrino to electron neutrino oscillation appearance search. This search aims
to confirm or refute in a definitive and independent way the evidence for
neutrino oscillations reported by the LSND experiment.Comment: 3 pages, no figures, to appear in the proceedings of the 9th
International Conference on Astroparticle and Underground Physics (TAUP
2005), Zaragoza, Spain, 10-14 Sep 200
Low loss Ge-on-Si waveguides operating in the 8–14 µm atmospheric transmission window
Germanium-on-silicon waveguides were modeled, fabricated and characterized at wavelengths ranging from 7.5 to 11 µm. Measured waveguide losses are below 5 dB/cm for both TE and TM polarization and reach values of ∼ 1 dB/cm for ≥ 10 µm wavelengths for the TE polarization. This work demonstrates experimentally for the first time that Ge-on-Si is a viable waveguide platform for sensing in the molecular fingerprint spectral region. Detailed modeling and analysis is presented to identify the various loss contributions, showing that with practical techniques losses below 1 dB/cm could be achieved across the full measurement range
Exploring multi-stability in semiconductor ring lasers: theory and experiment
We report the first experimental observation of multi-stable states in a
single-longitudinal mode semiconductor ring laser. We show how the operation of
the device can be steered to either monostable, bistable or multi-stable
dynamical regimes in a controlled way. We observe that the dynamical regimes
are organized in well reproducible sequences that match the bifurcation
diagrams of a two-dimensional model. By analyzing the phase space in this
model, we predict how the stochastic transitions between multi-stable states
take place and confirm it experimentally.Comment: 4 pages, 5 figure
Tunable delay lines in silicon photonics: coupled resonators and photonic crystals, a comparison
In this paper, we report a direct comparison between coupled resonator optical waveguides (CROWs) and photonic crystal waveguides (PhCWs), which have both been exploited as tunable delay lines. The two structures were fabricated on the same silicon-on-insulator (SOI) technological platform, with the same fabrication facilities and evaluated under the same signal bit-rate conditions. We compare the frequency- and time-domain response of the two structures; the physical mechanism underlying the tuning of the delay; the main limits induced by loss, dispersion, and structural disorder; and the impact of CROW and PhCW tunable delay lines on the transmission of data stream intensity and phase modulated up to 100 Gb/s. The main result of this study is that, in the considered domain of applications, CROWs and PhCWs behave much more similarly than one would expect. At data rates around 100 Gb/s, CROWs and PhCWs can be placed in competition. Lower data rates, where longer absolute delays are required and propagation loss becomes a critical issue, are the preferred domain of CROWs fabricated with large ring resonators, while at data rates in the terabit range, PhCWs remain the leading technology
Topological insight into the non-Arrhenius mode hopping of semiconductor ring lasers
We investigate both theoretically and experimentally the stochastic switching
between two counter-propagating lasing modes of a semiconductor ring laser.
Experimentally, the residence time distribution cannot be described by a simple
one parameter Arrhenius exponential law and reveals the presence of two
different mode-hop scenarios with distinct time scales. In order to elucidate
the origin of these two time scales, we propose a topological approach based on
a two-dimensional dynamical system.Comment: 4 pages, 3 figure
Tunable Q-factor silicon microring resonators for ultra-low power parametric processes
A compact silicon ring resonator is demonstrated that allows simple electrical tuning of the ring coupling coefficient and Q-factor and therefore the resonant enhancement of on-chip nonlinear optical processes. Fabrication-induced variation in designed coupling fraction, crucial in the resonator performance, can be overcome using this post-fabrication trimming technique. Tuning of the microring resonator across the critical coupling point is demonstrated, exhibiting a Q-factor tunable between 9000 and 96,000. Consequently, resonantly enhanced four-wave mixing shows tunable efficiency between -40 and -16.3 dB at an ultra-low on-chip pump power of 0.7 m
Ultra-low power generation of twin photons in a compact silicon ring resonator
We demonstrate efficient generation of correlated photon pairs by spontaneous
four wave mixing in a 5 \mu m radius silicon ring resonator in the telecom band
around 1550 nm. By optically pumping our device with a 200 \mu W continuous
wave laser, we obtain a pair generation rate of 0.2 MHz and demonstrate photon
time correlations with a coincidence-to-accidental ratio as high as 250. The
results are in good agreement with theoretical predictions and show the
potential of silicon micro-ring resonators as room temperature sources for
integrated quantum optics applications.Comment: 8 pages, 3 figure
- …