23,474 research outputs found
Universal Estimation of Directed Information
Four estimators of the directed information rate between a pair of jointly
stationary ergodic finite-alphabet processes are proposed, based on universal
probability assignments. The first one is a Shannon--McMillan--Breiman type
estimator, similar to those used by Verd\'u (2005) and Cai, Kulkarni, and
Verd\'u (2006) for estimation of other information measures. We show the almost
sure and convergence properties of the estimator for any underlying
universal probability assignment. The other three estimators map universal
probability assignments to different functionals, each exhibiting relative
merits such as smoothness, nonnegativity, and boundedness. We establish the
consistency of these estimators in almost sure and senses, and derive
near-optimal rates of convergence in the minimax sense under mild conditions.
These estimators carry over directly to estimating other information measures
of stationary ergodic finite-alphabet processes, such as entropy rate and
mutual information rate, with near-optimal performance and provide alternatives
to classical approaches in the existing literature. Guided by these theoretical
results, the proposed estimators are implemented using the context-tree
weighting algorithm as the universal probability assignment. Experiments on
synthetic and real data are presented, demonstrating the potential of the
proposed schemes in practice and the utility of directed information estimation
in detecting and measuring causal influence and delay.Comment: 23 pages, 10 figures, to appear in IEEE Transactions on Information
Theor
The Valuation of Service of Recreation Function of Dalinor National Natural Reserve
Dalinor National Natural Reserve is located in the west of Keshketeng Banner of Chifeng City, Inner Mongolia Autonomous Region (IMAR). It covers a total area of 119,413.35 ha, and is in drought or semi-drought continental climatic zone. DNNR is a comprehensive natural reserve made up of different ecosystems including lakes, prairies, wetlands, and forests. Dalinor Lake in DNNR is regarded as the paradise of birds, covering an area of 238 km2 between sandy lands and grasslands. DNNR was established in 1987 as a provincial natural reserve and was upgraded to a National Natural Reserve by the State Council of China in 1997. DNNR not only serves as an ideal resort for eco-tourism but also serves as an important scientific research base. The value of service of recreation function of DNNR depends heavily on the environmental quality that offers tourists various ecosystem amenities and opportunities for viewing wild plants and animals. So it is meaningful to value the recreation function of DNN
Decoy State Quantum Key Distribution With Modified Coherent State
To beat PNS attack, decoy state quantum key distribution (QKD) based on
coherent state has been studied widely. We present a decoy state QKD protocol
with modified coherent state (MCS). By destruction quantum interference, MCS
with fewer multi-photon events can be get, which may improve key bit rate and
security distance of QKD. Through numerical simulation, we show about 2-dB
increment on security distance for BB84 protocol.Comment: 4 pages, 4 figure
Spatial-Temporal Imaging of Anisotropic Photocarrier Dynamics in Black Phosphorus
As an emerging single elemental layered material with a low symmetry in-plane
crystal lattice, black phosphorus (BP) has attracted significant research
interest owing to its unique electronic and optoelectronic properties,
including its widely tunable bandgap, polarization dependent photoresponse and
highly anisotropic in-plane charge transport. Despite extensive study of the
steady-state charge transport in BP, there has not been direct characterization
and visualization of the hot carriers dynamics in BP immediately after
photoexcitation, which is crucial to understanding the performance of BP-based
optoelectronic devices. Here we use the newly developed scanning ultrafast
electron microscopy (SUEM) to directly visualize the motion of photo-excited
hot carriers on the surface of BP in both space and time. We observe highly
anisotropic in-plane diffusion of hot holes, with a 15-times higher diffusivity
along the armchair (x-) direction than that along the zigzag (y-) direction.
Our results provide direct evidence of anisotropic hot carrier transport in BP
and demonstrate the capability of SUEM to resolve ultrafast hot carrier
dynamics in layered two-dimensional materials.Comment: 21 pages, 6 figure
Heteroepitaxy of N-type β-Ga2O3 Thin Films on Sapphire Substrate by Low Pressure Chemical Vapor Deposition
This paper presents the heteroepitaxial growth of ultrawide bandgap β-Ga2O3 thin films on c-plane sapphire substrates by low pressure chemical vapor deposition. N-type conductivity in silicon (Si)-doped β-Ga2O3 films grown on sapphire substrate is demonstrated. The thin films were synthesized using high purity metallic gallium (Ga) and oxygen (O2) as precursors. The morphology, crystal quality, and properties of the as-grown thin films were characterized and analyzed by field emission scanning electron microscopy, X-ray diffraction, electron backscatter diffraction, photoluminescence and optical, photoluminescence excitation spectroscopy, and temperature dependent van der Pauw/Hall measurement. The optical bandgap is ∼4.76 eV, and room temperature electron mobility of 42.35 cm2/V s was measured for a Si-doped heteroepitaxial β-Ga2O3 film with a doping concentration of 1.32 × 1018 cm−3
Effect of Binary Source Companions on the Microlensing Optical Depth Determination toward the Galactic Bulge Field
Currently, gravitational microlensing survey experiments toward the Galactic
bulge field utilize two different methods of minimizing blending effect for the
accurate determination of the optical depth \tau. One is measuring \tau based
on clump giant (CG) source stars and the other is using `Difference Image
Analysis (DIA)' photometry to measure the unblended source flux variation.
Despite the expectation that the two estimates should be the same assuming that
blending is properly considered, the estimates based on CG stars systematically
fall below the DIA results based on all events with source stars down to the
detection limit. Prompted by the gap, we investigate the previously
unconsidered effect of companion-associated events on determination.
Although the image of a companion is blended with that of its primary star and
thus not resolved, the event associated with the companion can be detected if
the companion flux is highly magnified. Therefore, companions work effectively
as source stars to microlensing and thus neglect of them in the source star
count could result in wrong \tau estimation. By carrying out simulations based
on the assumption that companions follow the same luminosity function of
primary stars, we estimate that the contribution of the companion-associated
events to the total event rate is ~5f_{bi}% for current surveys and can reach
up to ~6f_{bi}% for future surveys monitoring fainter stars, where f_{bi} is
the binary frequency. Therefore, we conclude that the companion-associated
events comprise a non-negligible fraction of all events. However, their
contribution to the optical depth is not large enough to explain the systematic
difference between the optical depth estimates based on the two different
methods.Comment: 4 pages, 1 figure, 1 table, ApJ, submitte
Improved Detection Rates for Close Binaries Via Astrometric Observations of Gravitational Microlensing Events
In addition to constructing a Galactic matter mass function free from the
bias induced by the hydrogen-burning limit, gravitational microlensing allows
one to construct a mass function which is less affected by the problem of
unresolved binaries (Gaudi & Gould). However, even with the method of
microlensing, the photometric detection of binaries is limited to binary
systems with relatively large separations of of their combined
Einstein ring radius, and thus the mass function is still not totally free from
the problem of unresolved binaries. In this paper, we show that by detecting
distortions of the astrometric ellipse of a microlensing event with high
precision instruments such as the {\it Space Interferometry Mission}, one can
detect close binaries at a much higher rate than by the photometric method. We
find that by astrometrically observing microlensing events, of
binaries with separations of can be detected with the detection
threshold of 3%. The proposed astrometric method is especially efficient at
detecting very close binaries. With a detection threshold of 3% and a rate of
10%, one can astrometrically detect binaries with separations down to .Comment: total 14 pages, including 5 Figures and no Table (For figure 1,
please send a request mail to [email protected]), accepted to
ApJ (Vol 525, 000), updated versio
Fundamental Cycles and Graph Embeddings
In this paper we present a new Good Characterization of maximum genus of a
graph which makes a common generalization of the works of Xuong, Liu, and Fu et
al. Based on this, we find a new polynomially bounded algorithm to find the
maximum genus of a graph
Surface plasmon polaritons assisted diffraction in periodic subwavelength holes of metal films with reduced interplane coupling
Metal films grown on Si wafer perforated with a periodic array of
subwavelength holes have been fabricated and anomalous enhanced transmission in
the mid-infrared regime has been observed. High order transmission peaks up to
Si(2,2) are clearly revealed due to the large dielectric constant contrast of
the dielectrics at the opposite interfaces. Si(1,1) peak splits at oblique
incidence both in TE and TM polarization, which confirms that anomalous
enhanced transmission is a surface plasmon polaritons (SPPs) assisted
diffraction phenomenon. Theoretical transmission spectra agree excellently with
the experimental results and confirm the role of SPPs diffraction by the
lattice.Comment: 4 pages, 5 figures, 26 reference
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