221,615 research outputs found
Heat kernel transform for nilmanifolds associated to the Heisenberg group
We study the heat kernel transform on a nilmanifold of the Heisenberg
group. We show that the image of under this transform is a direct
sum of weighted Bergman spaces which are related to twisted Bergman and
Hermite-Bergman spaces.Comment: Revised version; to appear in Revista Mathematica Iberoamericana, 28
Stochastic Block Transition Models for Dynamic Networks
There has been great interest in recent years on statistical models for
dynamic networks. In this paper, I propose a stochastic block transition model
(SBTM) for dynamic networks that is inspired by the well-known stochastic block
model (SBM) for static networks and previous dynamic extensions of the SBM.
Unlike most existing dynamic network models, it does not make a hidden Markov
assumption on the edge-level dynamics, allowing the presence or absence of
edges to directly influence future edge probabilities while retaining the
interpretability of the SBM. I derive an approximate inference procedure for
the SBTM and demonstrate that it is significantly better at reproducing
durations of edges in real social network data.Comment: To appear in proceedings of AISTATS 201
Variations in radiocarbon ages of various organic fractions in core sediments from Erhai Lake, SW China
Radiocarbon dating was performed for the extracted organic fractions (cellulose-rich and humic acid fractions of plant fragment; fulvic acid, humic acid and humin fractions of humus substance) and shell from core sediments of the Erhai Lake, SW China. The C-14 dating results reveal that there are considerable differences, but there apparently is a humic acid less than or equal to humin < fulvic acid fraction sequence of C-14 age increase. The variability in radiocarbon ages of organic fraction of lake sediment suggests that special caution is necessary when radiocarbon ages of bulk sediments are used.
The linear correlation between C-14 age of allochthonous terrestrial macrofossil (plant fragment and shell) and depth indicates roughly a constant sedimentation rate of ca. 0.7 rum yr(-1) in central Erhai Lake since 4500 yr BP. The C-14 ages of the autochthonous humic acid fraction are 210similar to4800 yr shift from "the true C-14 age" obtained by interpolating the corresponding horizontal level to the above C-14 age-depth correlation. Such age difference may be alternatively attributed to a uniform reservoir effect (most likely ca. 300 yr). The period with large C-14 age shift synchronizes with the period of changes in (delta(13)C and ARM intensity and ARM/susceptibility values
Narrow double-peaked emission lines of SDSS J131642.90+175332.5: signature of a single or a binary AGN in a merger, jet-cloud interaction, or unusual narrow-line region geometry
We present an analysis of the active galaxy SDSS J131642.90+175332.5, which
is remarkable because all of its narrow emission lines are double-peaked, and
because it additionally shows an extra broad component (FHWM ~ 1400 km/s) in
most of its forbidden lines, peaking in between the two narrow systems. The
peaks of the two narrow systems are separated by 400--500 km/s in velocity
space. The spectral characteristics of double-peaked [O III] emission have
previously been interpreted as a signature of dual or binary active galactic
nuclei (AGNs), among other models. In the context of the binary scenario, SDSS
J131642.90+175332.5 is a particularly good candidate because not just one line
but all of its emission lines are double-peaked. However, we also discuss a
number of other scenarios which can potentially account for double-peaked
narrow emission lines, including projection effects, a two-sided outflow,
jet-cloud interactions, special narrow-line region (NLR) geometries (disks,
bars, or inner spirals), and a galaxy merger with only one AGN illuminating two
NLRs. We argue that the similarity of the emission-line ratios in both systems,
and the presence of the very unusual broad component at intermediate velocity,
makes a close pair of unrelated AGNs unlikely, and rather argues for processes
in a single galaxy or merger. We describe future observations which can
distinguish between these remaining possibilities.Comment: ApJ Letters, 705, L20-L24, 2009 (November 1 issue); incl. 2 colour
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Discontinuous resistance change and domain wall scattering in patterned NiFe wires with a nanoconstriction
A nonlinear current-voltage (I-V) characteristic was observed in patterned NiFe wires with a central "bow-tie" point contact constriction. By passing a dc current through the wire, a sharp resistance drop was obtained for current densities in the range of 1.1-1.4 x 10(7) A/cm(2). This is attributed to current-induced domain wall drag, resulting in displacement of a domain wall away from the constriction. A maximum current-induced resistance change of 0.079% was obtained for a 100-nm constriction, which is comparable with the magnetoresistance due to domain wall scattering in NiFe
Personalized Degrees: Effects on Link Formation in Dynamic Networks from an Egocentric Perspective
Understanding mechanisms driving link formation in dynamic social networks is
a long-standing problem that has implications to understanding social structure
as well as link prediction and recommendation. Social networks exhibit a high
degree of transitivity, which explains the successes of common neighbor-based
methods for link prediction. In this paper, we examine mechanisms behind link
formation from the perspective of an ego node. We introduce the notion of
personalized degree for each neighbor node of the ego, which is the number of
other neighbors a particular neighbor is connected to. From empirical analyses
on four on-line social network datasets, we find that neighbors with higher
personalized degree are more likely to lead to new link formations when they
serve as common neighbors with other nodes, both in undirected and directed
settings. This is complementary to the finding of Adamic and Adar that neighbor
nodes with higher (global) degree are less likely to lead to new link
formations. Furthermore, on directed networks, we find that personalized
out-degree has a stronger effect on link formation than personalized in-degree,
whereas global in-degree has a stronger effect than global out-degree. We
validate our empirical findings through several link recommendation experiments
and observe that incorporating both personalized and global degree into link
recommendation greatly improves accuracy.Comment: To appear at the 10th International Workshop on Modeling Social Media
co-located with the Web Conference 201
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