On concentration of the empirical measure for general transport costs

Let $\mu$ be a probability measure on $\mathbb{R}^d$ and $\mu_N$ its empirical measure with sample size $N$. We prove a concentration inequality for the optimal transport cost between $\mu$ and $\mu_N$ for cost functions with polynomial local growth, that can have superpolynomial global growth. This result generalizes and improves upon estimates of Fournier and Guillin. The proof combines ideas from empirical process theory with known concentration rates for compactly supported $\mu$. By partitioning $\mathbb{R}^d$ into annuli, we infer a global estimate from local estimates on the annuli and conclude that the global estimate can be expressed as a sum of the local estimate and a mean-deviation probability for which efficient bounds are known

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Department of Energy EngineeringElectronic skins (e-skins) enabling to detect various mechanical/chemical stimuli and environmental conditions by converting into various electrical and optical signals have attracted much attentions for various fields including wearable electronics, intelligent/medical robotics, healthcare monitoring devices, and haptic interfaces. Conventional e-skins have been widely used for the realization of these applications, however it is still considered that new e-skins with enhanced sensor performances (i.e. sensitivity, flexibility, multifunctionality, etc.) should be developed. In accordance with these demands, two approaches to explore novel functional materials or to modify device architectures have been introduced for enhancing sensor performance and acquiring multifunctional sensing capabilities. Firstly, a synthesis of multifunctional materials combined with conductive fillers (carbon nanotube, graphene oxide) and functional polymer matrix (i.e. ferroelectric polymer, elastomer) can provide the multimodal sensing capability of various stimuli and stretchability. Secondly, controlling design of device structures into various micro/nanostructures enables a significant improvement on sensing capabilities of e-skins with sensitivity and multidirectional force sensing, resulting from structural advantages such as large surface area, effective stress propagation, and anisotropic deformation. Therefore, a demonstration of e-skin combined with the functional composites and uniquely designed microstructures can offer a powerful platform to realize ideal sensor systems for next generation applications such as wearable electronics, healthcare devices, acoustic sensor, and haptic interface devices. In this thesis, we introduce the novel multifunctional and high performance electronic skins combined with various types of composite materials and nature-inspired 3D microstructures. Firstly, Chapter 1 briefly introduces various types of e-skins and the latest research trends of microstructured e-skins and summarizes the key components for their promising application fields. In chapters 2 and 3, mimicked by interlocking system between epidermal and dermal layers in human skin, we demonstrate the piezoresistive e-skins based on CNT/PDMS composite materials with interlocked microdome arrays for great pressure sensitivity and multidirectional force sensing capabilities. In chapter 4, we conduct in-depth study on giant tunneling piezoresistance in interlocking system and investigate systematically on the geometrical effect of microstructures on multidirectional force sensitivity and selectivity in interlocking sensor systems. In chapter 5, we demonstrate the ferroelectric e-skin that can detect and discriminate the static/dynamic touches and temperature inspired by multi-stimuli detection of various mechanoreceptors in human skin. Using the multifunctional sensing capabilities, we demonstrated our e-skin to the temperature-dependent pressure monitoring of artery vessel, high-precision acoustic sound detection, and surface texture recognition of various surfaces. In chapter 6, we demonstrate the linear and wide range pressure sensor with multilayered composite films having interlocked microdomes. In chapter 7, we present a new-concept of e-skin based on mechanochromic polymer and porous structures for overcoming limitations in conventional mechanochromic systems with low mechanochromic performances and limited stretchability. In addition, our mechanochromic e-skins enable the dual-mode detection of static and dynamic forces without any external power. Our e-skins based on functional composites and uniquely designed microstructures can provide a solid platform for next generation eskin in wearable electronics, humanoid robotics, flexible sensors, and wearable medical diagnostic systems.clos

Piezoresistive tactile sensor discriminating multidirectional forces

Flexible tactile sensors capable of detecting the magnitude and direction of the applied force together are of great interest for application in human-interactive robots, prosthetics, and bionic arms/feet. Human skin contains excellent tactile sensing elements, mechanoreceptors, which detect their assigned tactile stimuli and transduce them into electrical signals. The transduced signals are transmitted through separated nerve fibers to the central nerve system without complicated signal processing. Inspired by the function and organization of human skin, we present a piezoresistive type tactile sensor capable of discriminating the direction and magnitude of stimulations without further signal processing. Our tactile sensor is based on a flexible core and four sidewall structures of elastomer, where highly sensitive interlocking piezoresistive type sensing elements are embedded. We demonstrate the discriminating normal pressure and shear force simultaneously without interference between the applied forces. The developed sensor can detect down to 128 Pa in normal pressure and 0.08 N in shear force, respectively. The developed sensor can be applied in the prosthetic arms requiring the restoration of tactile sensation to discriminate the feeling of normal and shear force like human skin.open0

Comment on "Amplified emission and lasing in photonic time crystals"

Lyubarov et al. (Research Articles, 22 July 2022, p. 425) claim that the spontaneous emission rate of an atom vanishes at the momentum gap edges of photonic Floquet media. We show that their theoretical prediction is based on assumptions that result in misleading interpretations on the spontaneous emission rate in photonic Floquet media

A Triple-Mode Flexible E-Skin Sensor Interface for Multi-Purpose Wearable Applications

This study presents a flexible wireless electronic skin (e-skin) sensor system that includes a multi-functional sensor device, a triple-mode reconfigurable readout integrated circuit (ROIC), and a mobile monitoring interface. The e-skin device's multi-functionality is achieved by an interlocked micro-dome array structure that uses a polyvinylidene fluoride and reduced graphene oxide (PVDF/RGO) composite material that is inspired by the structure and functions of the human fingertip. For multi-functional implementation, the proposed triple-mode ROIC is reconfigured to support piezoelectric, piezoresistance, and pyroelectric interfaces through single-type e-skin sensor devices. A flexible system prototype was developed and experimentally verified to provide various wireless wearable sensing functions-including pulse wave, voice, chewing/swallowing, breathing, knee movements, and temperature-while their real-time sensed data are displayed on a smartphone

Transparent and conductive nanomembranes with orthogonal silver nanowire arrays for skin-attachable loudspeakers and microphones

We demonstrate ultrathin, transparent, and conductive hybrid nanomembranes (NMs) with nanoscale thickness, consisting of an orthogonal silver nanowire array embedded in a polymer matrix. Hybrid NMs significantly enhance the electrical and mechanical properties of ultrathin polymer NMs, which can be intimately attached to human skin. As a proof of concept, we present a skin-attachable NM loudspeaker, which exhibits a significant enhancement in thermoacoustic capabilities without any significant heat loss from the substrate. We also present a wearable transparent NM microphone combined with a micropyramid-patterned polydimethylsiloxane film, which provides excellent acoustic sensing capabilities based on a triboelectric voltage signal. Furthermore, the NM microphone can be used to provide a user interface for a personal voice-based security system in that it can accurately recognize a user???s voice. This study addressed the NM-based conformal electronics required for acoustic device platforms, which could be further expanded for application to conformal wearable sensors and health care devices