20,220 research outputs found
Nonlinear plasmonics at high temperatures
We solve the Maxwell and heat equations self-consistently for metal
nanoparticles under intense continuous wave (CW) illumination. Unlike previous
studies, we rely on {\em experimentally}-measured data for the metal
permittivity for increasing temperature and for the visible spectral range. We
show that the thermal nonlinearity of the metal can lead to substantial
deviations from the predictions of the linear model for the temperature and
field distribution, and thus, can explain qualitatively the strong nonlinear
scattering from such configurations observed experimentally. We also show that
the incompleteness of existing data of the temperature dependence of the
thermal properties of the system prevents reaching a quantitative agreement
between the measured and calculated scattering data. This modelling approach is
essential for the identification of the underlying physical mechanism
responsible for the thermo-optical nonlinearity of the metal and should be
adopted in all applications of high temperature nonlinear plasmonics,
especially for refractory metals, both for CW and pulsed illumination
Constrain intergalactic medium from the SZ effect map
In this paper, we try to detect the SZ effect in the 2MASS DWT clusters and
less bound objects in order to constrain the warm-hot intergalactic medium
distribution on large scales by cross-correlation analysis. The results of both
observed WMAP and mock SZ effect map indicate that the hot gas distributes from
inside as well as outside of the high density regions of galaxy clusters, which
is consistent with the results of both observation and hydro simulation.
Therefore, the DWT measurement of the cross-correlation would be a powerful
tool to probe the missing of baryons in the Universe.Comment: 9 pages,2 figures. Accepted for publication in Mod. Phys. Lett.
Probing dipole-forbidden autoionizing states by isolated attosecond pulses
We propose a general technique to retrieve the information of
dipole-forbidden resonances in the autoionizing region. In the simulation, a
helium atom is pumped by an isolated attosecond pulse in the extreme
ultraviolet (EUV) combined with a few-femtosecond laser pulse. The excited wave
packet consists of the , , and states, including the background
continua, near the doubly excited state. The resultant electron
spectra with various laser intensities and time delays between the EUV and
laser pulses are obtained by a multilevel model and an ab initio time-dependent
Schr\"odinger equation calculation. By taking the ab initio calculation as a
"virtual measurement", the dipole-forbidden resonances are characterized by the
multilevel model. We found that in contrast to the common assumption, the
nonresonant coupling between the continua plays a significant role in the
time-delayed electron spectra, which shows the correlation effect between
photoelectrons before they leave the core. This technique takes the advantages
of ultrashort pulses uniquely and would be a timely test for the current
attosecond technology.Comment: 10 pages, 6 figure
Unbiased Offline Evaluation of Contextual-bandit-based News Article Recommendation Algorithms
Contextual bandit algorithms have become popular for online recommendation
systems such as Digg, Yahoo! Buzz, and news recommendation in general.
\emph{Offline} evaluation of the effectiveness of new algorithms in these
applications is critical for protecting online user experiences but very
challenging due to their "partial-label" nature. Common practice is to create a
simulator which simulates the online environment for the problem at hand and
then run an algorithm against this simulator. However, creating simulator
itself is often difficult and modeling bias is usually unavoidably introduced.
In this paper, we introduce a \emph{replay} methodology for contextual bandit
algorithm evaluation. Different from simulator-based approaches, our method is
completely data-driven and very easy to adapt to different applications. More
importantly, our method can provide provably unbiased evaluations. Our
empirical results on a large-scale news article recommendation dataset
collected from Yahoo! Front Page conform well with our theoretical results.
Furthermore, comparisons between our offline replay and online bucket
evaluation of several contextual bandit algorithms show accuracy and
effectiveness of our offline evaluation method.Comment: 10 pages, 7 figures, revised from the published version at the WSDM
2011 conferenc
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