PopArt: Efficient Sparse Regression and Experimental Design for Optimal Sparse Linear Bandits

In sparse linear bandits, a learning agent sequentially selects an action and receive reward feedback, and the reward function depends linearly on a few coordinates of the covariates of the actions. This has applications in many real-world sequential decision making problems. In this paper, we propose a simple and computationally efficient sparse linear estimation method called PopArt that enjoys a tighter $\ell_1$ recovery guarantee compared to Lasso (Tibshirani, 1996) in many problems. Our bound naturally motivates an experimental design criterion that is convex and thus computationally efficient to solve. Based on our novel estimator and design criterion, we derive sparse linear bandit algorithms that enjoy improved regret upper bounds upon the state of the art (Hao et al., 2020), especially w.r.t. the geometry of the given action set. Finally, we prove a matching lower bound for sparse linear bandits in the data-poor regime, which closes the gap between upper and lower bounds in prior work.Comment: 10 pages, 1 figures, to be published in 2022 Conference on Neural Information Processing System

Utilization of a combined EEG/NIRS system to predict driver drowsiness

The large number of automobile accidents due to driver drowsiness is a critical concern of many countries. To solve this problem, numerous methods of countermeasure have been proposed. However, the results were unsatisfactory due to inadequate accuracy of drowsiness detection. In this study, we introduce a new approach, a combination of EEG and NIRS, to detect driver drowsiness. EEG, EOG, ECG and NIRS signals have been measured during a simulated driving task, in which subjects underwent both awake and drowsy states. The blinking rate, eye closure, heart rate, alpha and beta band power were used to identify subject’s condition. Statistical tests were performed on EEG and NIRS signals to find the most informative parameters. Fisher’s linear discriminant analysis method was employed to classify awake and drowsy states. Time series analysis was used to predict drowsiness. The oxy-hemoglobin concentration change and the beta band power in the frontal lobe were found to differ the most between the two states. In addition, these two parameters correspond well to an awake to drowsy state transition. A sharp increase of the oxy-hemoglobin concentration change, together with a dramatic decrease of the beta band power, happened several seconds before the first eye closure

High-Efficiency Blue Organic Light-Emitting Diodes Using C60 as a Surface Modifier on Indium Tin Oxide

C60 was introduced as a modifier on indium tin oxide (ITO) and the effect of C60 modification on light-emitting efficiency of blue organic light-emitting didoes was investigated. Device performances of C60 modified devices were greatly dependent on ITO surface properties and C60 thickness. Power efficiency of blue devices was improved by 80% by C60 buffer layer on ITO because of low driving voltage and balanced electron-hole recombinatio

Lifetime improvement of green phosphorescent organic light-emitting diodes by charge confining device structure

Lifetime improvement of green phosphorescent organic light-emitting diodes by charge confinement inside an emitting layer was investigated. Excitons were confined within the emitting layer by using a charge confining structure with a high doping concentration at the center of the emitting layer. The lifetime of green devices could be improved by more than five times by confining the excitons at the center of the emitting layer

Efficient electron injection in organic light-emitting diodes using lithium quinolate/Ca/Al cathodes

Device performances of green devices with cathode structure of lithium quinolate Liq /Ca/Al were investigated and electron injection mechanism was studied using ultraviolet photoelectron spectroscopy. Power efficiency could be improved by 70% by using Liq/Ca/Al cathode structure due to efficient electron injection, and interfacial energy barrier lowering by Liq/Ca/Al metal cathode was observed

Improvement in Power Efficiency in Organic Light Emitting Diodes Through Intermediate Mg:Ag Layer in LiF/Mg:Ag/Al Cathodes

Effects of Mg:Ag interlayer between LiF and Al on electron injection and device performances of organic light-emitting diodes OLEDs were investigated. Thickness of Mg:Ag layer was changed from 0 to 10 nm and the relationship between interlayer thickness and device performances was studied. Current density of OLEDs was increased due to efficient electron injection from cathode to organic layer by Mg:Ag interlayer. In addition, power efficiency of OLEDs was improved by more than 50% due to low driving voltage and high recombination efficiency and it showed a maximum value at a Mg:Ag thickness of 1.0 nm

High efficiency phosphorescent organic light-emitting diodes using carbazole-type triplet exciton blocking layer

Device performances of green phosphorescent organic light-emitting diodes using 4,4 -N,N -dicarbazole biphenyl CBP and N,N -dicarbazolyl-3,5-benzene mCP as an exciton blocking layer were investigated. CBP and mCP were introduced between hole transport layer and emitting layer to block triplet exciton quenching and efficient hole transport to emitting layer. The efficiency of green devices could be improved by more than three times by using mCP exciton blocking layer

Relationship Between Host Energy Levels and Device Performances of Phosphorescent Organic Light-Emitting Diodes with Triplet Mixed Host Emitting Structure

Green phosphorescent organic light-emitting diodes (PHOLEDs) with a triplet mixed host emitting layer were developed and device performances were studied by changing host materials in light-emitting layer. Power efficiency of green PHOLEDs could be improved from 12.7 to 29.1 lm/W by using triplet mixed host emitting layer. Combination of hole-transport-type host with good hole injection properties and electron-transport-type host with good electron injection properties was effective to get high efficiency in triplet mixed host devices