Spike‐Timing‐Dependent Plasticity in Memristors

The spike‐timing‐dependent plasticity (STDP) characteristic of the memristor plays an important role in the development of neuromorphic network computing in the future. The STDP characteristics were observed in different memristors based on different kinds of materials. The investigation regarding the influences of device hysteresis characteristic, the initial conductance of the memristors, and the waveform of the voltage pulses applied to the memristor as preneuron voltage spike and postneuron voltage spike on the STDP behavior of memristors are reviewed

A comparative study of discriminating human heart failure etiology using gene expression profiles

BACKGROUND: Human heart failure is a complex disease that manifests from multiple genetic and environmental factors. Although ischemic and non-ischemic heart disease present clinically with many similar decreases in ventricular function, emerging work suggests that they are distinct diseases with different responses to therapy. The ability to distinguish between ischemic and non-ischemic heart failure may be essential to guide appropriate therapy and determine prognosis for successful treatment. In this paper we consider discriminating the etiologies of heart failure using gene expression libraries from two separate institutions. RESULTS: We apply five new statistical methods, including partial least squares, penalized partial least squares, LASSO, nearest shrunken centroids and random forest, to two real datasets and compare their performance for multiclass classification. It is found that the five statistical methods perform similarly on each of the two datasets: it is difficult to correctly distinguish the etiologies of heart failure in one dataset whereas it is easy for the other one. In a simulation study, it is confirmed that the five methods tend to have close performance, though the random forest seems to have a slight edge. CONCLUSIONS: For some gene expression data, several recently developed discriminant methods may perform similarly. More importantly, one must remain cautious when assessing the discriminating performance using gene expression profiles based on a small dataset; our analysis suggests the importance of utilizing multiple or larger datasets

Dual functional states of working memory realized by memristor-based neural network

Working memory refers to the brain's ability to store and manipulate information for a short period. It is disputably considered to rely on two mechanisms: sustained neuronal firing, and “activity-silent” working memory. To develop a highly biologically plausible neuromorphic computing system, it is anticipated to physically realize working memory that corresponds to both of these mechanisms. In this study, we propose a memristor-based neural network to realize the sustained neural firing and activity-silent working memory, which are reflected as dual functional states within memory. Memristor-based synapses and two types of artificial neurons are designed for the Winner-Takes-All learning rule. During the cognitive task, state transformation between the “focused” state and the “unfocused” state of working memory is demonstrated. This work paves the way for further emulating the complex working memory functions with distinct neural activities in our brains

3D printable ionic conductive hydrogels with super stretch and self-adhesion performances for flexible sensors

Ionic conductive hydrogels (ICHs) have emerged as a landmark soft material for a wide range of applications, such as flexible wearable sensors and electronic skins. However, to achieve a super-stretchability, high strength, and self-adhesion simultaneously by 3D printing remains a significant challenge. In the construction of a hydrogel, ionic liquids (ILs) and tannic acid (TA) have been successfully introduced in the copolymerization of acrylamide (AAm) and poly(ethylene glycol) (diol) diacrylate (PEGDA) to form a p(AAm-co-PEGDA) hydrogel (PAP) system. The PAP hydrogel showed super-stretching (4300%), high strength, and self-adhesion properties. More specifically, the 3D printing of the ICHs provided an effective and flexible way to manufacture flexible wearable sensors, thus greatly simplifying the device fabrication process. In addition, the sensors could be specified by a customized production and were, thus, adapted to a wider range of applications. It is believed that the here presented hydrogel integration with 3D printing will inspire new ideas on how to prepare novel flexible sensors, thus promoting further research on the construction of electronic skins, human-computer interactions, and advanced materials

Area Dependence of Effective Electromechanical Coupling Coefficient Induced by On-Chip Inductance in LiNbO₃-Based BAW Resonators

To solve the problem of filter bandwidth in 5G communication, it is urgent to develop an acoustic resonator with a large effective electromechanical coupling coefficient (Keff2). In this paper, the dependence between the resonance area and the performance of the bulk acoustic wave (BAW) resonator is studied. The solidly mounted resonators (SMRs) based on 43° Y cut lithium niobate (LN) were fabricated by the wafer transfer technique. The on-chip inductor was integrated with the BAW resonator through a pad electrode. Resonators with different resonant areas were fabricated and tested. Finite element modeling (FEM) simulation of acoustic resonators and electromagnetic (EM) simulation of layout were carried out, respectively. The Modified Butterworth Van Dyke (MBVD) model was used to analyze the results, and simulation of the Mason model was adopted. The results show that the dependency relationship between the resonant area and the effective electromechanical coupling coefficient can be induced by on-chip inductance. In the resonant area range of 20 × 20 μm2~160 × 160 μm2, the Keff2 increases from 11.97% to 43.28%

Residual stress in AlN films grown on sapphire substrates by molecular beam epitaxy

Residual stress in AlN films grown by molecular beam epitaxy (MBE) has been studied by Raman scattering spectroscopy. A strain-free Raman frequency and a biaxial stress coefficient for E-2(high) mode are experimentally determined to be 657.8 +/- 0.3 cm(-1) and 2.4 +/- 0.2 cm(-1) /GPa, respectively. By using these parameters, the residual stress of a series of AlN layers grown under different buffer layer conditions has been investigated. The residual compressive stress is found to be obviously decreased by increasing the Al/N beam flux ratio of the buffer layer, indicating the generation of tensile stress due to stronger coalescence of AlN grains, as also confirmed by the in-situ reflection high energy electron diffraction (RHEED) monitoring observation. The stronger coalescence does lead to improved quality of AlN films as expected. (C) 2016 Elsevier Ltd. All rights reserved.National Basic Research Program of China [2012CB619300, 2013CB632800]; National Natural Science Foundation of China [61225019, 61521004, 61376060, 61361166007]; Open Fund of the State Key Laboratory on Integrated OptoelectronicsSCI(E)[email protected]; [email protected]

Memristive Synapse Based on Single‐Crystalline LiNbO3 Thin Film with Bioinspired Microstructure for Experience‐Based Dynamic Image Mask Generation

Abstract One of the key steps toward constructing neuromorphic systems is to develop reliable bio‐realistic synaptic devices. Here, memristors based on single‐crystalline LiNbO3 (SC‐LNO) thin film are fabricated as artificial synapses. A reservoir of oxygen vacancies is induced by Ar+ irradiation to resemble synaptic vesicles containing neurotransmitters. Phenomena of saturation and adaptivity, short‐term plasticity, paired‐pulse facilitation, paired‐pulse depression, and long‐term potentiation are successfully mimicked. The dynamic transition from sensory memory to short‐term memory, and further to long‐term memory, is also successfully emulated for multipattern memorization. In addition, first, taking advantage of short‐ and long‐term synaptic plasticity is proposed, to realize experience‐based image mask generation with different stimuli schemes. During the experience‐based generation process, memristive multi‐value masks (MMVMs) are generated with different numbers of stimuli applied to the memristor at each pixel, which corresponds to the times the region occurred in the history image set. The experience‐based memristive multi‐value mask successfully extracts multiple regions of interest with different priorities. This work demonstrates that the memristor based on Ar+‐irradiated SC‐LNO thin film with bioinspired microstructure shows great potential in future neuromorphic systems for experience‐based intelligent image processing

A Memristor‐Based Bioinspired Multimodal Sensory Memory System for Sensory Adaptation of Robots

Sensory adaptation plays a critical role in humans interacting with the environment. Inspired by humans, realization of sensory adaptation on robots can make them adapt to the environment gradually. The gradual change of sensitivity that depends on recent experience of external stimuli is the most important process for the adaptation. To realize sensory adaptation, such change of sensitivity needs to be realized. It is proposed to fabricate the memristor based on single‐crystalline LiNbO3 thin film. The resistance of the memristor can be changed monotonically and gradually with the increase in the number of voltage pulses, which can be ascribed to the property of single‐crystalline thin films. Based on the characteristic, it is proposed to use the memristor as artificial synapse of the proposed bioinspired system, using conductance of the memristor to denote susceptibility value to realize the gradual change of sensitivity by recent external stimuli. A novel general excitation method of signals from multimodal sensors on memristor is proposed and utilized in the signal‐coupling module of the system, which makes the system realize sensory adaptation for different stimuli accepted by multimodal sensors. Using artificial sensory memory systems, sensory adaptation on robot is realized for the first time herein