20,136,749 research outputs found
Phase-locking in Multi-Frequency Brillouin Oscillator via Four Wave Mixing
Stimulated Brillouin scattering (SBS) and Kerr-nonlinear four wave-mixing
(FWM) are among the most important and widely studied nonlinear effects in
optical fibres. At high powers SBS can be cascaded producing multiple Stokes
waves spaced by the Brillouin frequency shift. Here, we investigate the complex
nonlinear interaction of the cascade of Stokes waves, generated in a
Fabry-Perot chalcogenide fibre resonator through the combined action of SBS and
FWM. We demonstrate the existence of parameter regimes, in which pump and
Stokes waves attain a phase-locked steady state. Real-time measurements of 40ps
pulses with 8GHz repetition rate are presented, confirming short-and long-term
stability. Numerical simulations qualitatively agree with experiments and show
the significance of FWM in phase-locking of pump and Stokes waves. Our findings
can be applied for the design of novel picosecond pulse sources with GHz
repetition rate for optical communication systems
Creation of Dirac Particles in the Presence of a Constant Electric Field in an Anisotropic Bianchi I Universe
In this article we compute the density of Dirac particles created by a
cosmological anisotropic Bianchi I universe in the presence of a constant
electric field. We show that the particle distribution becomes thermal when one
neglects the electric interaction.Comment: 9 page
The Digital Life of Walkable Streets
Walkability has many health, environmental, and economic benefits. That is
why web and mobile services have been offering ways of computing walkability
scores of individual street segments. Those scores are generally computed from
survey data and manual counting (of even trees). However, that is costly, owing
to the high time, effort, and financial costs. To partly automate the
computation of those scores, we explore the possibility of using the social
media data of Flickr and Foursquare to automatically identify safe and walkable
streets. We find that unsafe streets tend to be photographed during the day,
while walkable streets are tagged with walkability-related keywords. These
results open up practical opportunities (for, e.g., room booking services,
urban route recommenders, and real-estate sites) and have theoretical
implications for researchers who might resort to the use social media data to
tackle previously unanswered questions in the area of walkability.Comment: 10 pages, 7 figures, Proceedings of International World Wide Web
Conference (WWW 2015
The spectroscopic evolution of the symbiotic-like recurrent nova V407 Cygni during its 2010 outburst. I. The shock and its evolution
On 2010 Mar 10, V407 Cyg was discovered in outburst, eventually reaching V< 8
and detected by Fermi. Using medium and high resolution ground-based optical
spectra, visual and Swift UV photometry, and Swift X-ray spectrophotometry, we
describe the behavior of the high-velocity profile evolution for this nova
during its first three months. The peak of the X-ray emission occurred at about
day 40 with a broad maximum and decline after day 50. The main changes in the
optical spectrum began at around that time. The He II 4686A line first appeared
between days 7 and 14 and initially displayed a broad, symmetric profile that
is characteristic of all species before day 60. Low-excitation lines remained
comparatively narrow, with v(rad,max) of order 200-400 km/s. They were
systematically more symmetric than lines such as [Ca V], [Fe VII], [Fe X], and
He II, all of which showed a sequence of profile changes going from symmetric
to a blue wing similar to that of the low ionization species but with a red
wing extended to as high as 600 km/s . The Na I D doublet developed a broad
component with similar velocity width to the other low-ionization species. The
O VI Raman features were not detected. We interpret these variations as
aspherical expansion of the ejecta within the Mira wind. The blue side is from
the shock penetrating into the wind while the red wing is from the low-density
periphery. The maximum radial velocities obey power laws, v(rad,max) t^{-n}
with n ~ 1/3 for red wing and ~0.8 for the blue. (truncated)Comment: Accepted for publication, A&A (submitted: 9 Oct 2010; accepted: 1 Dec
2010) in press; based on data obtained with Swift, Nordic Optical Telescope,
Ondrejov Observatory. Corrected typo, Fermi?LAT detection was at energies
above 100 MeV (with thanks to C. C. Cheung
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
Quark Mixing Matrix Studies and Lepton Flavor Violation Searches Using Rare Decays of Kaons
I review recent results from experiments on rare decays of kaons,
concentrating on searches for lepton flavor violation (LFV) and on measurements
of quark mixing (CKM) matrix elements. The LFV results are the culmination of
15 years of experimentation at Brookhaven National Laboratory and are unlikely
to be improved upon soon. The CKM studies derive from measurements of decay
rates of charged and neutral kaons into lepton anti-lepton pairs, both with and
without a charged or neutral pion. I discuss recent results and prospects for
improved measurements that could provide an unambiguous test of the Standard
Model explanation for CP violation. This paper is the written version of a talk
presented at the Lepton-Photon Conference in August 1999.Comment: Written version of a talk at the 1999 Lepton Photon Conferenc
On the resonances and eigenvalues for a 1D half-crystal with localised impurity
We consider the Schr\"odinger operator on the half-line with a periodic
potential plus a compactly supported potential . For generic , its
essential spectrum has an infinite sequence of open gaps. We determine the
asymptotics of the resonance counting function and show that, for sufficiently
high energy, each non-degenerate gap contains exactly one eigenvalue or
antibound state, giving asymptotics for their positions. Conversely, for any
potential and for any sequences (\s_n)_{1}^\iy, \s_n\in \{0,1\}, and
(\vk_n)_1^\iy\in \ell^2, \vk_n\ge 0, there exists a potential such that
\vk_n is the length of the -th gap, , and has exactly \s_n
eigenvalues and 1-\s_n antibound state in each high-energy gap. Moreover, we
show that between any two eigenvalues in a gap, there is an odd number of
antibound states, and hence deduce an asymptotic lower bound on the number of
antibound states in an adiabatic limit.Comment: 25 page
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