31,166 research outputs found
Hierarchical information clustering by means of topologically embedded graphs
We introduce a graph-theoretic approach to extract clusters and hierarchies
in complex data-sets in an unsupervised and deterministic manner, without the
use of any prior information. This is achieved by building topologically
embedded networks containing the subset of most significant links and analyzing
the network structure. For a planar embedding, this method provides both the
intra-cluster hierarchy, which describes the way clusters are composed, and the
inter-cluster hierarchy which describes how clusters gather together. We
discuss performance, robustness and reliability of this method by first
investigating several artificial data-sets, finding that it can outperform
significantly other established approaches. Then we show that our method can
successfully differentiate meaningful clusters and hierarchies in a variety of
real data-sets. In particular, we find that the application to gene expression
patterns of lymphoma samples uncovers biologically significant groups of genes
which play key-roles in diagnosis, prognosis and treatment of some of the most
relevant human lymphoid malignancies
Competing Ordered States in Bilayer Graphene
We use a perturbative renormalization group approach with short-range
continuum model interactions to analyze the competition between isotropic
gapped and anisotropic gapless ordered states in bilayer graphene, commenting
specifically on the role of exchange and on the importance of spin and valley
flavor degeneracy. By comparing the divergences of the corresponding
susceptibilities, we conclude that this approach predicts gapped states for
flavor numbers N=1,2,4. We also comment briefly on the related gapped states
expected in chiral (ABC) trilayer graphene.Comment: 12 pages, 7 figures and 1 tabl
Cosmological HII Bubble Growth During Reionization
We present general properties of ionized hydrogen (HII) bubbles and their
growth based on a state-of-the-art large-scale (100 Mpc/h) cosmological
radiative transfer simulation. The simulation resolves all halos with atomic
cooling at the relevant redshifts and simultaneously performs radiative
transfer and dynamical evolution of structure formation. Our major conclusions
include: (1) for significant HII bubbles, the number distribution is peaked at
a volume of at all redshifts. But, at ,
one large, connected network of bubbles dominates the entire HII volume. (2)
HII bubbles are highly non-spherical. (3) The HII regions are highly biased
with respect to the underlying matter distribution with the bias decreasing
with time. (4) The non-gaussianity of the HII region is small when the universe
becomes 50% ionized. The non-gaussianity reaches its maximal near the end of
the reionization epoch . But at all redshifts of interest there is a
significant non-gaussianity in the HII field. (5) Population III galaxies may
play a significant role in the reionization process. Small bubbles are
initially largely produced by Pop III stars. At even the largest HII
bubbles have a balanced ionizing photon contribution from Pop II and Pop III
stars, while at Pop II stars start to dominate the overall ionizing
photon production for large bubbles, although Pop III stars continue to make a
non-negligible contribution. (6) The relationship between halo number density
and bubble size is complicated but a strong correlation is found between halo
number density and bubble size for large bubbles.Comment: 10 pages, 14 figures; accepted version; higher resolution figures and
supplementary material can be found at
http://www.astro.princeton.edu/~msshin/reionization/web.ht
Technical Barriers to Interstate Trade: Noxious Weed Regulations
We focus on regulations controlling the spread of noxious weeds, especially the trade effects of regulatory differences across U.S. states. We specify a gravity model for each state’s seed, nursery product, and commodity trade with each other state. Within the gravity model, we examine the role of cross-state regulatory congruence arising from ecological and agronomic characteristics and interest-group lobbying. A spatial-autoregressive Tobit model is estimated with a modified expectation-maximization algorithm. Results show that weed regulatory congruence positively affects interstate trade. By fostering cross-state regulatory differences, consumer and commodity-producer lobbying reduce the value of interstate trade by about two percent per annum.interstate trade, invasive species, rent-seeking, Agribusiness, Community/Rural/Urban Development, Food Consumption/Nutrition/Food Safety, Land Economics/Use, Political Economy, Public Economics, Research Methods/ Statistical Methods, F1, H7, Q5,
Is there an association between bone mineral density and mammographic density? A systematic review
Tunnel spin polarization of Ni80Fe20/SiO2 probed with a magnetic tunnel transistor
The tunnel spin polarization of Ni80Fe20/SiO2 interfaces has been investigated using a magnetic tunnel transistor (MTT). The MTT with a Ni80Fe20/SiO2 emitter shows a magnetocurrent of 74% at 100 K, corresponding to a tunnel spin polarization of the Ni80Fe20/SiO2 interface of 27%. This is only slightly lower than the value of 34% for Ni80Fe20/Al2O3 interfaces determined in similar MTT structures. This suggests that SiO2 can be applied in semiconductor spintronic devices, for example in ferromagnet/SiO2/Si tunnel contacts for spin injection.\ud
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