Freezing and thawing effects of sand-silt mixtures on elastic waves

Freezing and thawing during the winter season change soil properties such as density. The density change in the particulate media influences soil stiffness. In addition, freezing of partially or fully saturated soils changes the soil matrix from a particulate media to a continuum. The goal of this study is to investigate the cyclic freezing and thawing effects on elastic waves. Sand-silt mixtures with 10% silt fraction in weight and 40% saturation are prepared. The sand-silt mixtures are placed in a nylon cell, onto which a pair of bender elements and a pair of piezoelectric disk elements are installed for the measurement of shear and compressional waves, respectively. The temperature of the mixtures decreases from 20 ℃ to -10 ℃ to freezing. The frozen sample is gradually thawed at room temperature （20 ℃）, These freezing-thawing processes are repeated three times. The test result shows that the shear and compressional wave velocities significantly increase when the specimen is frozen. When the temperature is greater than 0 ℃, the elastic wave velocities are lower during thawing than during freezing due to soil structure change. This study demonstrates that soil strucre change during the winter season may be effectively estimated from elastic waves.

Dynamical control of nanoscale light-matter interactions in low-dimensional quantum materials

Tip-enhanced nano-spectroscopy and-imaging have significantly advanced our understanding of low-dimensional quantum materials and their interactions with light,providing a rich insight into the underlying physics at their natural length scale.Recently,various functionalities of the plasmonic tip expand the capabilities of the nanoscopy,enabling dynamic manipulation of light-matter interactions at the nanoscale.In this review,we focus on a new paradigm of the nanoscopy,shifting from the conventional role of imaging and spectroscopy to the dynamical control approach of the tip-induced light-matter interactions.We present three different approaches of tip-induced control of light-matter interactions,such as cavity-gap control,pressure control,and near-field polarization control.Specifically,we discuss the nanoscale modifications of radiative emissions for various emitters from weak to strong coupling regime,achieved by the precise engineering of the cavity-gap.Furthermore,we introduce recent works on light-matter interactions controlled by tip-pressure and near-field polarization,especially tunability of the bandgap,crystal structure,photoluminescence quantum yield,exciton density,and energy transfer in a wide range of quantum materials.We envision that this comprehensive review not only contributes to a deeper understanding of the physics of nanoscale light-matter interactions but also offers a valuable resource to nanophotonics,plasmonics,and materials science for future technological advancements.

Deep-learning-based gas identification by timevariant illumination of a single micro-LEDembedded gas sensor

Electronic nose(e-nose)technology for selectively identifying a target gas through chemoresistive sensors has gained much attention for various applications,such as smart factory and personal health monitoring.To overcome the crossreactivity problem of chemoresistive sensors to various gas species,herein,we propose a novel sensing strategy based on a single micro-LED(μLED)-embedded photoactivated(μLP)gas sensor,utilizing the time-variant illumination for identifying the species and concentrations of various target gases.A fast-changing pseudorandom voltage input is applied to the μLED to generate forced transient sensor responses.A deep neural network is employed to analyze the obtained complex transient signals for gas detection and concentration estimation.The proposed sensor system achieves high classification(~96.99%)and quantification(mean absolute percentage error~31.99%)accuracies for various toxic gases(methanol,ethanol,acetone,and nitrogen dioxide)with a single gas sensor consuming 0.53 mW.The proposed method may significantly improve the efficiency of e-nose technology in terms of cost,space,and power consumption.