5,792 research outputs found
Expectile Matrix Factorization for Skewed Data Analysis
Matrix factorization is a popular approach to solving matrix estimation
problems based on partial observations. Existing matrix factorization is based
on least squares and aims to yield a low-rank matrix to interpret the
conditional sample means given the observations. However, in many real
applications with skewed and extreme data, least squares cannot explain their
central tendency or tail distributions, yielding undesired estimates. In this
paper, we propose \emph{expectile matrix factorization} by introducing
asymmetric least squares, a key concept in expectile regression analysis, into
the matrix factorization framework. We propose an efficient algorithm to solve
the new problem based on alternating minimization and quadratic programming. We
prove that our algorithm converges to a global optimum and exactly recovers the
true underlying low-rank matrices when noise is zero. For synthetic data with
skewed noise and a real-world dataset containing web service response times,
the proposed scheme achieves lower recovery errors than the existing matrix
factorization method based on least squares in a wide range of settings.Comment: 8 page main text with 5 page supplementary documents, published in
AAAI 201
A tight linear chromatic bound for ()-free graphs
For two vertex disjoint graphs and , we use to denote the
graph with vertex set and edge set , and use
to denote the graph with vertex set and edge set
. A is the graph
. In this paper, we prove that if is a
()-free graph. This bound is tight when and ,
and improves the main result of Wang and Zhang. Also, this bound partially
generalizes some results of Prashant {\em et al.}.Comment: arXiv admin note: text overlap with arXiv:2308.05442,
arXiv:2307.1194
Improving thermoelectric properties of p-type Bi2Te3-based alloys by spark plasma sintering
AbstractHigh-performance (Bi2Te3)x(Sb2Te3)1βx bulk materials were prepared by combining fusion technique with spark plasma sintering, and their thermoelectric properties were investigated. The electrical resistivity and Seebeck coefficient increase greatly and the thermal conductivity decreases significantly with the increase of Bi2Te3 content, which leads to a great improvement in the thermoelectric figure of merit ZT. The maximum ZT value reaches 1.33 at 398 K for the composition of 20%Bi2Te3-80%Sb2Te3 with 3% (mass fraction) excess Te
Effects of polymer additives in the bulk of turbulent thermal convection
We present experimental evidence that a minute amount of polymer additives
can significantly enhance heat transport in the bulk region of turbulent
thermal convection. The effects of polymer additives are found to be the
\textit{suppression} of turbulent background fluctuations that give rise to
incoherent heat fluxes that make no net contribution to heat transport, and at
the same time to \textit{increase} the coherency of temperature and velocity
fields. The suppression of small-scale turbulent fluctuations leads to more
coherent thermal plumes that result in the heat transport enhancement. The fact
that polymer additives can increase the coherency of thermal plumes is
supported by the measurements of a number of local quantities, such as the
extracted plume amplitude and width, the velocity autocorrelation functions and
the velocity-temperature cross-correlation coefficient. The results from local
measurements also suggest the existence of a threshold value for the polymer
concentration, only above which can significant modification of the plume
coherent properties and enhancement of the local heat flux be observed.
Estimation of the plume emission rate suggests that the second effect of
polymer additives is to stabilize the thermal boundary layers.Comment: 8 figures, 11 page
Nonlocal coherence harvesting from quantum vacuum
It is well known that nonlocal coherence reflects nonclassical correlations
better than quantum entan-glement. Here, we analyze nonlocal coherence
harvesting from the quantum vacuum to particle detectors adiabatically
interacting with a quantum scalar field in Minkowski spacetime. We find that
the harvesting-achievable separation range of nonlocal coherence is larger than
that of quantum entanglement. As the energy gap grows sufficiently large, the
detectors harvest less quantum coherence, while the detectors could extract
more quantum entanglement from the vacuum state. Compared with the linear
configuration and the scalene configuration, the equilateral triangle
configuration is the best model to harvest tripartite coherence. Finally, we
find a monogamous relationship, which means that tripartite l1-norm of
coherence is essentially bipartite types.Comment: 18 pages, 5 figure
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