A Novel Strategy to Eliminate the Influence of Water Adsorption on Quartz Surfaces on Piezoelectric Dynamometers

Piezoelectric dynamometers are out of use in high humidity. Experimental results showed that piezoelectric coefficients measured by the force-induced charges method initially fluctuated in a small range and then was unstable, and they could not be measured at high relative humidity (RH). The traditional shielding method-insulation paste was not quiet convenient, and it even added the weight of piezoelectric dynamometers. In this paper, a novel strategy that eliminates the influence of water adsorption with quartz surfaces on piezoelectric dynamometers was proposed. First, a water-quartz model was developed to analyze the origin of the RH effect. In the model, water vapor, which was adsorbed by the quartz sheet side surface, was considered. Second, equivalent sheet resistor of the side surface was researched, while the relationship of the three R’s (Roughness, RH, and Resistor) was respectively discussed based on the adsorption mechanism. Finally, fluorination technology was skillfully adapted to each surface of quartz sheets to shield the water vapor. The experiment verified the fluorination strategy and made piezoelectric dynamometers work in high humidity up to 90%RH successfully. The results showed that the presented model above was reasonable. In addition, these observations also drew some useful insights to change the structure of piezoelectric dynamometers and improve the properties

Hierarchical assembly of NiFe-PB-derived bimetallic phosphides on 3D Ti3C2 MXene ribbon networks for efficient oxygen evolution

The development of MXene-based heterostructures for electrocatalysis has garnered significant attention owing to their potential as high-performance catalysts that play a pivotal role in hydrogen energy. Herein, we present a multistep strategy for the synthesis of a Ti3C2 MXene ribbon/NiFePx @graphitic N-doped carbon (NC) heterostructure that enables the formation of three-dimensional (3D) Ti3C2 MXene ribbon networks and bimetallic phosphide nanoarrays. With the assistance of HF etching and KOH shearing, the MXene sheets were successfully transformed into 3D MXene networks with interlaced MXene ribbons. Notably, a hydrothermal method, ion exchange route, and phosphorization process were used to anchor NiFePx@NC nanocubes derived from Ni(OH)2/NiFe-based Prussian blue (NiFe-PB) onto the MXene ribbon network. The resulting MXene ribbon/NiFePx@NC heterostructure demonstrated enhanced oxygen evolution reaction (OER) activity, characterized by a low overpotential (164 mV at a current density of 10 mA cm−2) and a low Tafel slope (45 mV dec−1). At the same time, the MXene ribbons/NiFePx@NC heterostructure exhibited outstanding long-term stability, with a 12 mV potential decay after 5000 cyclic voltammetry (CV) cycles. This study provides a robust pathway for the design of efficient MXene-based heterostructured electrocatalysts for water splitting

WIPP: Wi-Fi Compass for Indoor Passive Positioning with Decimeter Accuracy

In recent decades, the proliferation of smart phones, tablets, and wireless networks has fostered a growing interest in indoor passive positioning. The Wi-Fi-based passive positioning systems can provide Location-Based Services (LBSs) to the third party such as market and security departments. Most of the existing systems are based on the Receive Signal Strength Indication (RSSI) information, which are generally time-consuming and susceptible to environmental change. To overcome this problem, we propose the Wi-Fi compass for indoor passive positioning system (WIPP), an Angle of Arrival (AOA) based passive positioning system using the existing commodity Wi-Fi network. In this paper, we first propose a new algorithm for the joint estimation of AOA and Time of Arrival (TOA) measurements based on the fine-grained Channel State Information (CSI), which is collected by an off-the-shelf Wi-Fi device equipped with only three antennas. Second, we use the affinity propagation clustering algorithm to identify the direct signal path from the target to each Wi-Fi Access Point (AP). Finally, we deploy the WIPP in an actual indoor environment to conduct the performance comparison with the well-known radio-frequency (RF) based system for locating and tracking users inside buildings (RADAR), as well as the conventional passive positioning system using the AOA solely. The experimental results show that the WIPP is able to achieve the median positioning error 0.7 m, which is much lower than the ones by the RADAR system and the conventional system using the AOA solely

Low‐Voltage, High‐Performance, Indium‐Tin‐Zinc‐Oxide Thin‐Film Transistors Based on Dual‐Channel and Anodic‐Oxide

Abstract Oxide semiconductor thin‐film transistors (TFTs) with low‐voltage operation, excellent device performance, and bias stability are highly desirable for portable and wearable electronics. Here, the development of low‐voltage indium‐tin‐zinc‐oxide (ITZO) TFTs with excellent device performance and bias stability based on a dual‐channel layer and an anodic‐oxide dielectric layer are reported. An ultra‐thin anodic AlxOy film as a gate dielectric layer is prepared using an anodization process. The dual‐channel layer consists of an oxygen‐uncompensated channel layer and an oxygen‐compensated capping layer. It is confirmed that the dual‐channel structure is effective for enhancing device performance and bias stability in comparison with the single‐channel structure. As a result, the dual‐channel ITZO TFT gated with anodic AlxOy exhibits an effective saturation mobility of 12.56 cm2 Vs−1, a threshold voltage of 0.28 V, a subthreshold swing of 76 mV dec−1, a low‐voltage operation of 1 V, and good operational stability (threshold voltage shift (ΔVTH) < −0.03 V under a negative gate bias stress and ΔVTH < 0.15 under positive gate bias stress of 3600 s). The work shows that the ITZO TFTs, based on a dual‐channel layer and an anodic‐oxide gate dielectric layer, have great potential for low‐power, portable, and wearable electronics

Empirical Phase Diagram for Three-layer Neural Networks with Infinite Width

Substantial work indicates that the dynamics of neural networks (NNs) is closely related to their initialization of parameters. Inspired by the phase diagram for two-layer ReLU NNs with infinite width (Luo et al., 2021), we make a step towards drawing a phase diagram for three-layer ReLU NNs with infinite width. First, we derive a normalized gradient flow for three-layer ReLU NNs and obtain two key independent quantities to distinguish different dynamical regimes for common initialization methods. With carefully designed experiments and a large computation cost, for both synthetic datasets and real datasets, we find that the dynamics of each layer also could be divided into a linear regime and a condensed regime, separated by a critical regime. The criteria is the relative change of input weights (the input weight of a hidden neuron consists of the weight from its input layer to the hidden neuron and its bias term) as the width approaches infinity during the training, which tends to $0$, $+\infty$ and $O(1)$, respectively. In addition, we also demonstrate that different layers can lie in different dynamical regimes in a training process within a deep NN. In the condensed regime, we also observe the condensation of weights in isolated orientations with low complexity. Through experiments under three-layer condition, our phase diagram suggests a complicated dynamical regimes consisting of three possible regimes, together with their mixture, for deep NNs and provides a guidance for studying deep NNs in different initialization regimes, which reveals the possibility of completely different dynamics emerging within a deep NN for its different layers.Comment: arXiv admin note: text overlap with arXiv:2007.0749