Complexity analysis of Bayesian learning of high-dimensional DAG models and their equivalence classes

We consider MCMC methods for learning equivalence classes of sparse Gaussian DAG models when $p = e^{o(n)}$. The main contribution of this work is a rapid mixing result for a random walk Metropolis-Hastings algorithm, which we prove using a canonical path method. It reveals that the complexity of Bayesian learning of sparse equivalence classes grows only polynomially in $n$ and $p$, under some common high-dimensional assumptions. Further, a series of high-dimensional consistency results is obtained by the path method, including the strong selection consistency of an empirical Bayes model for structure learning and the consistency of a greedy local search on the restricted search space. Rapid mixing and slow mixing results for other structure-learning MCMC methods are also derived. Our path method and mixing time results yield crucial insights into the computational aspects of high-dimensional structure learning, which may be used to develop more efficient MCMC algorithms

Lipschitz Continuous Autoencoders in Application to Anomaly Detection

Anomaly detection is the task of finding abnormal data that are distinct from normal behavior. Current deep learning-based anomaly detection methods train neural networks with normal data alone and calculate anomaly scores based on the trained model. In this work, we formalize current practices, build a theoretical framework of anomaly detection algorithms equipped with an objective function and a hypothesis space, and establish a desirable property of the anomaly detection algorithm, namely, admissibility. Admissibility implies that optimal autoencoders for normal data yield a larger reconstruction error for anomalous data than that for normal data on average. We then propose a class of admissible anomaly detection algorithms equipped with an integral probability metric-based objective function and a class of autoencoders, Lipschitz continuous autoencoders. The proposed algorithm for Wasserstein distance is implemented by minimizing an approximated Wasserstein distance with a penalty to enforce Lipschitz continuity with respect to Wasserstein distance. Through ablation studies, we demonstrate the efficacy of enforcing Lipschitz continuity of the proposed method. The proposed method is shown to be more effective in detecting anomalies than existing methods via applications to network traffic and image datasets(1).N

The IPIN 2019 Indoor Localisation Competition—Description and Results

IPIN 2019 Competition, sixth in a series of IPIN competitions, was held at the CNR Research Area of Pisa (IT), integrated into the program of the IPIN 2019 Conference. It included two on-site real-time Tracks and three off-site Tracks. The four Tracks presented in this paper were set in the same environment, made of two buildings close together for a total usable area of 1000 m 2 outdoors and and 6000 m 2 indoors over three floors, with a total path length exceeding 500 m. IPIN competitions, based on the EvAAL framework, have aimed at comparing the accuracy performance of personal positioning systems in fair and realistic conditions: past editions of the competition were carried in big conference settings, university campuses and a shopping mall. Positioning accuracy is computed while the person carrying the system under test walks at normal walking speed, uses lifts and goes up and down stairs or briefly stops at given points. Results presented here are a showcase of state-of-the-art systems tested side by side in real-world settings as part of the on-site real-time competition Tracks. Results for off-site Tracks allow a detailed and reproducible comparison of the most recent positioning and tracking algorithms in the same environment as the on-site Tracks

Order-based Structure Learning without Score Equivalence

We consider the structure learning problem with all node variables having the same error variance, an assumption known to ensure the identifiability of the causal directed acyclic graph (DAG). We propose an empirical Bayes formulation of the problem that yields a non-decomposable posterior score for DAG models. To facilitate efficient posterior computation, we approximate the posterior probability of each ordering by that of a "best" DAG model, which naturally leads to an order-based Markov chain Monte Carlo (MCMC) algorithm. Strong selection consistency for our model is proved under mild high-dimensional conditions, and the mixing behavior of our sampler is theoretically investigated. Further, we propose a new iterative top-down algorithm, which quickly yields an approximate solution to the structure learning problem and can be used to initialize the MCMC sampler. We demonstrate that our method outperforms other state-of-the-art algorithms under various simulation settings, and conclude the paper with a single-cell real-data study illustrating practical advantages of the proposed method

Optical resonance and charge transfer behavior of patterned WO3 microdisc arrays

One- to three-dimensional alignments of semiconductors on the micro- or nanoscale have been achieved to tailor their opto-physicochemical properties and improve their photoelectrochemical (PEC) performance. Here, to the best of our knowledge, we report for the first time the fabrication of vertically aligned, well-ordered WO3 microdisc arrays via an electrodeposition process on lithographically patterned indium tin oxide (ITO) substrates as well as their geometry-specific photoelectrochemical properties. The as-fabricated WO3 microdisc arrays exhibit enhanced light absorption as well as facilitated charge separation, leading to significantly higher PEC performance than WO3 films. A finite-difference time-domain simulation of a single WO3 microdisc indicates that strong optical resonances occur particularly in the central part of the microdisc, leading to enhanced optical absorption. A time-resolved photoluminescence study further reveals that the average lifetime of charge carriers (τ) in a microdisc array is shorter than that in a film by ∼60%. The reductively deposited Au particles are localized on the side of the microdisc and ITO substrate, which suggests that the photogenerated electrons are transferred to the same location. In addition, the oxidative deposition of FeOOH particles on the top surface and side of a microdisc indicates hole transfer pathways at the same location. This downward transfer of electrons and upward transfer of holes lead to efficient charge separation, and the radial direction appears to be the most preferred shortcut for the carriers inside the bulk of a microdisc. © 2016 The Royal Society of Chemistry.1

Photoelectrochemical hydrogen production on silicon microwire arrays overlaid with ultrathin titanium nitride

p-Si wire arrays overlaid with an ultrathin titanium nitride (TiN) film are developed and demonstrated to be an efficient and robust photocathode for hydrogen production. Arrays of vertically aligned 20 μm long p-Si microwires of varying diameters (1.6-14.6 μm) are fabricated via a photolithographic technique, and then the wires are coated with a TiN nanolayer 2-20 nm thick by low-temperature plasma-enhanced atomic layer deposition. The optimized heterojunction consisting of 1.6 μm-thick wires covered by 10 nm thick TiN exhibits significantly improved performance for hydrogen evolution reaction under simulated sunlight (AM 1.5G, 100 mW cm-2). It displays a photocurrent onset potential of ∼+0.4 V vs. reversible hydrogen electrode (RHE), and a faradaic efficiency of nearly 100% at 0 V vs. RHE over 20 h of reaction. Time-resolved photoluminescence decay reveals that the lifetime (τ) of the photogenerated charge carriers in the optimized wire/TiN heterojunction is ∼60% shorter than those using thicker wires, suggesting significantly faster charge transfer. Such remarkable performance is attributed to enhanced transfer of the minority carriers in the radial direction of the wires. TiN performs the triple roles of antireflection, protection of the Si surface, and electrocatalysis of hydrogen production. Finite-difference time-domain simulation reveals a significant increase in the absorptance of wire arrays with TiN film, and that long wavelength photons are more effectively absorbed by the wire/TiN arrays. © 2016 The Royal Society of Chemistry.

Photoelectrochemical hydrogen production on silicon microwire arrays overlaid with ultrathin titanium nitride

p-Si wire arrays overlaid with an ultrathin titanium nitride (TiN) film are developed and demonstrated to be an efficient and robust photocathode for hydrogen production. Arrays of vertically aligned 20 mu m long p-Si microwires of varying diameters (1.6-14.6 mm) are fabricated via a photolithographic technique, and then the wires are coated with a TiN nanolayer 2-20 nm thick by low-temperature plasma-enhanced atomic layer deposition. The optimized heterojunction consisting of 1.6 mu m-thick wires covered by 10 nm thick TiN exhibits significantly improved performance for hydrogen evolution reaction under simulated sunlight (AM 1.5G, 100 mW cm(-2)). It displays a photocurrent onset potential of similar to+0.4 V vs. reversible hydrogen electrode (RHE), and a faradaic efficiency of nearly 100% at 0 V vs. RHE over 20 h of reaction. Time-resolved photoluminescence decay reveals that the lifetime (tau) of the photogenerated charge carriers in the optimized wire/TiN heterojunction is similar to 60% shorter than those using thicker wires, suggesting significantly faster charge transfer. Such remarkable performance is attributed to enhanced transfer of the minority carriers in the radial direction of the wires. TiN performs the triple roles of antireflection, protection of the Si surface, and electrocatalysis of hydrogen production. Finite-difference time-domain simulation reveals a significant increase in the absorptance of wire arrays with TiN film, and that long wavelength photons are more effectively absorbed by the wire/TiN arrays.1185sciescopu

Effects of Interleukin-4 and Interleukin-12b Gene Polymorphisms on Hepatitis B Virus Vaccination

Approximately 10% of individuals do not respond to hepatitis B virus (HBV) vaccination, i.e. non-responders (NRs). We aimed to investigate the association of interleukin (IL)-4 and IL-12B gene polymorphisms with responsiveness to the HBV vaccine in Korean infants. Among 300 healthy infants (9-12 month), SNPs for the IL-4 gene (rs2243250, rs2070874, and rs2227284) and for the IL-12B gene (rs3213094 and rs17860508) were compared between subgroups in terms of the response to HBV vaccination. The percentages of NRs ( 6 months from the 3rd dose (n = 87) and ≤ 6 months from the 3rd dose (n = 213). In the ≤ 6 month subjects, rs2243250C and rs2227284G were significantly frequent in the lower-titer individuals (NRs + LR) than HRs (40.1 vs. 25.9%, p = 0.014 and 45.1 vs. 33.0%, p = 0.018, respectively), and the rs2243250C and rs2227284G frequencies were significantly different among the three subgroups (13.2 vs. 26.9 vs. 25.9%, p = 0.040 and 15.5 vs. 29.6 vs. 33.0%, p = 0.038, respectively). In conclusion, those results suggest that IL-4 gene polymorphisms may play a role in the response to the HBV vaccine in Korean infants