2,443 research outputs found
Envelopes and principal component regression
Envelope methods offer targeted dimension reduction for various models. The
overarching goal is to improve efficiency in multivariate parameter estimation
by projecting the data onto a lower-dimensional subspace known as the envelope.
Envelope approaches have advantages in analyzing data with highly correlated
variables, but their iterative Grassmannian optimization algorithms do not
scale very well with ultra high-dimensional data. While the connections between
envelopes and partial least squares in multivariate linear regression have
promoted recent progress in high-dimensional studies of envelopes, we propose a
more straightforward way of envelope modeling from a novel principal components
regression perspective. The proposed procedure, Non-Iterative Envelope
Component Estimation (NIECE), has excellent computational advantages over the
iterative Grassmannian optimization alternatives in high dimensions. We develop
a unified NIECE theory that bridges the gap between envelope methods and
principal components in regression. The new theoretical insights also shed
light on the envelope subspace estimation error as a function of eigenvalue
gaps of two symmetric positive definite matrices used in envelope modeling. We
apply the new theory and algorithm to several envelope models, including
response and predictor reduction in multivariate linear models, logistic
regression, and Cox proportional hazard model. Simulations and illustrative
data analysis show the potential for NIECE to improve standard methods in
linear and generalized linear models significantly
Remote information concentration and multipartite entanglement in multilevel systems
Remote information concentration (RIC) in -level systems (qudits) is
studied. It is shown that the quantum information initially distributed in
three spatially separated qudits can be remotely and deterministically
concentrated to a single qudit via an entangled channel without performing any
global operations. The entangled channel can be different types of genuine
multipartite pure entangled states which are inequivalent under local
operations and classical communication. The entangled channel can also be a
mixed entangled state, even a bound entangled state which has a similar form to
the Smolin state, but has different features from the Smolin state. A common
feature of all these pure and mixed entangled states is found, i.e., they have
common commuting stabilizers. The differences of qudit-RIC and qubit-RIC
() are also analyzed.Comment: 10 pages, 3 figure
Molecular Lines of 13 Galactic Infrared Bubble Regions
We investigated the physical properties of molecular clouds and star
formation processes around infrared bubbles which are essentially expanding HII
regions. We performed observations of 13 galactic infrared bubble fields
containing 18 bubbles. Five molecular lines, 12CO (J=1-0), 13CO (J=1-0),
C18O(J=1-0), HCN (J=1-0), and HCO+ (J=1-0), were observed, and several publicly
available surveys, GLIMPSE, MIPSGAL, ATLASGAL, BGPS, VGPS, MAGPIS, and NVSS,
were used for comparison. We find that these bubbles are generally connected
with molecular clouds, most of which are giant. Several bubble regions display
velocity gradients and broad shifted profiles, which could be due to the
expansion of bubbles. The masses of molecular clouds within bubbles range from
100 to 19,000 solar mass, and their dynamic ages are about 0.3-3.7 Myr, which
takes into account the internal turbulence pressure of surrounding molecular
clouds. Clumps are found in the vicinity of all 18 bubbles, and molecular
clouds near four of these bubbles with larger angular sizes show shell-like
morphologies, indicating that either collect-and-collapse or radiation-driven
implosion processes may have occurred. Due to the contamination of adjacent
molecular clouds, only six bubble regions are appropriate to search for
outflows, and we find that four of them have outflow activities. Three bubbles
display ultra-compact HII regions at their borders, and one of them is probably
responsible for its outflow. In total, only six bubbles show star formation
activities in the vicinity, and we suggest that star formation processes might
have been triggered.Comment: 55 Pages, 32 figures. Accepted for publication in A
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