35,905 research outputs found
Topology of Entanglement in Multipartite States with Translational Invariance
The topology of entanglement in multipartite states with translational
invariance is discussed in this article. Two global features are foundby which
one can distinguish distinct states. These are the cyclic unit and the
quantised geometric phase. Furthermore the topology is indicated by the
fractional spin. Finally a scheme is presented for preparation of these types
of states in spin chain systems, in which the degeneracy of the energy levels
characterises the robustness of the states with translational invariance.Comment: major revision. accepted by EPJ
Characterizing time series : when Granger causality triggers complex networks
In this paper, we propose a new approach to characterize time series with noise perturbations in both the time and frequency domains by combining Granger causality and complex networks. We construct directed and weighted complex networks from time series and use representative network measures to describe their physical and topological properties. Through analyzing the typical dynamical behaviors of some physical models and the MIT-BIH* human electrocardiogram data sets, we show that the proposed approach is able to capture and characterize various dynamics and has much potential for analyzing real-world time series of rather short length
Radiance and Doppler shift distributions across the network of the quiet Sun
The radiance and Doppler-shift distributions across the solar network provide
observational constraints of two-dimensional modeling of transition-region
emission and flows in coronal funnels. Two different methods, dispersion plots
and average-profile studies, were applied to investigate these distributions.
In the dispersion plots, we divided the entire scanned region into a bright and
a dark part according to an image of Fe xii; we plotted intensities and Doppler
shifts in each bin as determined according to a filtered intensity of Si ii. We
also studied the difference in height variations of the magnetic field as
extrapolated from the MDI magnetogram, in and outside network. For the
average-profile study, we selected 74 individual cases and derived the average
profiles of intensities and Doppler shifts across the network. The dispersion
plots reveal that the intensities of Si ii and C iv increase from network
boundary to network center in both parts. However, the intensity of Ne viii
shows different trends, namely increasing in the bright part and decreasing in
the dark part. In both parts, the Doppler shift of C iv increases steadily from
internetwork to network center. The average-profile study reveals that the
intensities of the three lines all decline from the network center to
internetwork region. The binned intensities of Si ii and Ne viii have a good
correlation. We also find that the large blue shift of Ne viii does not
coincide with large red shift of C iv. Our results suggest that the network
structure is still prominent at the layer where Ne viii is formed in the quiet
Sun, and that the magnetic structures expand more strongly in the dark part
than in the bright part of this quiet Sun region.Comment: 10 pages,9 figure
Upflows in the upper transition region of the quiet Sun
We investigate the physical meaning of the prominent blue shifts of Ne VIII,
which is observed to be associated with quiet-Sun network junctions (boundary
intersections), through data analyses combining force-free-field extrapolations
with EUV spectroscopic observations. For a middle-latitude region, we
reconstruct the magnetic funnel structure in a sub-region showing faint
emission in EIT-Fe 195. This funnel appears to consist of several smaller
funnels that originate from network lanes, expand with height and finally merge
into a single wide open-field region. However, the large blue shifts of Ne VIII
are generally not associated with open fields, but seem to be associated with
the legs of closed magnetic loops. Moreover, in most cases significant upflows
are found in both of the funnel-shaped loop legs. These quasi-steady upflows
are regarded as signatures of mass supply to the coronal loops rather than the
solar wind. Our observational result also reveals that in many cases the
upflows in the upper transition region (TR) and the downflows in the middle TR
are not fully cospatial. Based on these new observational results, we suggest
different TR structures in coronal holes and in the quiet Sun.Comment: 4 pages, 4 figures, will appear in the Proceedings of the Solar wind
12 conferenc
Exceptional del Pezzo hypersurfaces
We compute global log canonical thresholds of a large class of quasismooth
well-formed del Pezzo weighted hypersurfaces in
. As a corollary we obtain the existence
of orbifold K\"ahler--Einstein metrics on many of them, and classify
exceptional and weakly exceptional quasismooth well-formed del Pezzo weighted
hypersurfaces in .Comment: 149 pages, one reference adde
High Stellar FUV/NUV Ratio and Oxygen Contents in the Atmospheres of Potentially Habitable Planets
Recent observations of several planet-hosting M dwarfs show that most have
FUV/NUV flux ratios 1000 times greater than that of the Sun. Here we show that
the atmospheric oxygen contents (O2 and O3) of potentially habitable planets in
this type of UV environment could be 2~3 orders of magnitude greater than those
of their counterparts around Sun-like stars as a result of decreased photolysis
of O3, H2O2, and HO2. Thus detectable levels of atmospheric oxygen, in
combination with the existence of H2O and CO2, may not be the most promising
biosignatures on planets around stars with high FUV/NUV ratios such as the
observed M dwarfs
Room temperature InGaAs/InP distributed feedback laser directly grown on silicon
We report an optically pumped room-temperature O-band DFB laser, based on the buffer-less epitaxial growth of high quality InGaAs/InP waveguides directly on silicon wafer
Theoretical Wood Densitometry: III. Mean Density and Density Variation on Stem Cross-Sections
Wood densitometry measures micro-scale densities in specimens that are subsamples drawn from trees receiving various treatments. However, forestry research often requires macro-scale wood density in experimental units for testing for significance of treatment effects. Acquisition of desired macro-scale wood density expressions necessitates mathematical manipulation. To facilitate direct calculation of mean density and density variation in an individual segment or in an arbitrary aggregate of segments and to derive indirect estimation of density mean and variation in annuli and cross-sections, wood density profiles have been modeled as continuous functions whose values are linearly interpolated. Theoretical macro-scale wood density expressions have been derived from applying normalization procedures and both linear and quadratic weights to micro-scale densities. Examples demonstrate the use of newly developed equations to calculate density means and root-mean-squares in single and multiple densitometric data sets
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