2,038 research outputs found
Orbital-transverse density-wave instabilities in iron-based superconductors
Besides the conventional spin-density-wave (SDW) state, a new kind of
orbital-transverse density-wave (OTDW) state is shown to exist generally in
multi-orbital systems. We demonstrate that the orbital character of Fermi
surface nesting plays an important role in density responses. The relationship
between antiferromagnetism and structural phase transition in LaFeAsO (1111)
and BaFeAs (122) compounds of iron-based superconductors may be
understood in terms of the interplay between the SDW and OTDW with a
five-orbital Hamiltonian. We propose that the essential difference between 1111
and 122 compounds is crucially determined by the presence of the
two-dimensional -like Fermi surface around (0,0) being only in 1111
parent compounds.Comment: several parts were rewritten for clarity. 6 pages, 3 figures, 1 tabl
Emergence of Blind Areas in Information Spreading
Recently, contagion-based (disease, information, etc.) spreading on social
networks has been extensively studied. In this paper, other than traditional
full interaction, we propose a partial interaction based spreading model,
considering that the informed individuals would transmit information to only a
certain fraction of their neighbors due to the transmission ability in
real-world social networks. Simulation results on three representative networks
(BA, ER, WS) indicate that the spreading efficiency is highly correlated with
the network heterogeneity. In addition, a special phenomenon, namely
\emph{Information Blind Areas} where the network is separated by several
information-unreachable clusters, will emerge from the spreading process.
Furthermore, we also find that the size distribution of such information blind
areas obeys power-law-like distribution, which has very similar exponent with
that of site percolation. Detailed analyses show that the critical value is
decreasing along with the network heterogeneity for the spreading process,
which is complete the contrary to that of random selection. Moreover, the
critical value in the latter process is also larger that of the former for the
same network. Those findings might shed some lights in in-depth understanding
the effect of network properties on information spreading
HyperBO+: Pre-training a universal prior for Bayesian optimization with hierarchical Gaussian processes
Bayesian optimization (BO), while proved highly effective for many black-box
function optimization tasks, requires practitioners to carefully select priors
that well model their functions of interest. Rather than specifying by hand,
researchers have investigated transfer learning based methods to automatically
learn the priors, e.g. multi-task BO (Swersky et al., 2013), few-shot BO
(Wistuba and Grabocka, 2021) and HyperBO (Wang et al., 2022). However, those
prior learning methods typically assume that the input domains are the same for
all tasks, weakening their ability to use observations on functions with
different domains or generalize the learned priors to BO on different search
spaces. In this work, we present HyperBO+: a pre-training approach for
hierarchical Gaussian processes that enables the same prior to work universally
for Bayesian optimization on functions with different domains. We propose a
two-step pre-training method and analyze its appealing asymptotic properties
and benefits to BO both theoretically and empirically. On real-world
hyperparameter tuning tasks that involve multiple search spaces, we demonstrate
that HyperBO+ is able to generalize to unseen search spaces and achieves lower
regrets than competitive baselines.Comment: Full version of the workshop paper at 2022 NeurIPS Workshop on
Gaussian Processes, Spatiotemporal Modeling, and Decision-making System
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