Search

In this letter, a new reliability phenomenon, named early-stage resistance fluctuation (ERF), in analog resistive random-access memory (RRAM) devices and its impact on the neuromorphic computing are investigated. ERF is found to be a non-negligible random fluctuation behavior of RRAM resistance within ~10,000s after verification due to stochastic migration of vacancies. As a result, ERF can induce weight noise in RRAM-based neural network even with write-verify operation and cause a significant (~42%) drop of recognition accuracy on the MNIST dataset recognition tasks. An approach incorporating automatic early-stop and dropout during training is proposed to reduce the impacts of ERF. Results show that the recognition accuracy with ERF can be improved from 58% to 96% after adopting the proposed optimization method.

Nanofibers possess high surface area to volume ratios and are particularly attractive for a variety of applications including tissue regeneration, drug delivery, fiber-reinforced composites, filtration, and protective clothing. Though the production of nanofibers from common thermoplastic polymers is relatively well-demonstrated, processing constraints have limited high throughput manufacturing of nanofibers from high performance polymers. This has in turn limited broad technological exploitation of polymer nanofibers in areas such as hot chemical filtration or high-performance lightweight composites for aerospace and defense applications. We report here that nanofibers can be produced in a solventless high throughput process from polymers such as poly(butylene terephthalate) (PBT) using a newly developed technology termed "Forcespinning" that employs centrifugal force to attenuate fibers. Our investigations also show that these nanofibers have a high crystallinity and enhanced molecular orientation which is important for realizing desirable physical and chemical properties of many high-performance polymer fibers.

Purpose Ovarian cancer (OC) is the most common malignancy in women with high mortality. Increasing studies have revealed that long non-coding RNA (lncRNA) MNX1-AS1 has a promoting effect on various cancers. However, the mechanisms of MNX1-AS1 in OC are still unclear. Therefore, this study focused on exploring the mechanisms of MNX1-AS1 in OC. Materials and methods The expression of SOX12 at the protein level was detected by western blot. Cell proliferation was detected by CCK8 assay and colony formation assay. Cell cycle and cell apoptosis were detected by flow cytometry. Wound-healing assay, transwell assay and western blot were used to detect the ability of cell migration and invasion. The target binding was confirmed through the luciferase reporter assay. Results The expression of MNX1-AS1 was increased in OC tumor tissues and cells. Elevated MNX1-AS1 expression is associated with advanced stage and lower overall survival rate. Knockdown of MNX1-AS1 inhibited cell proliferation, migration and invasion, blocked cell cycle, and promoted cell apoptosis in SKOV-3 and OVCAR-3 cells. MNX1-AS1 was competitively binding with miR-744-5p, and its downstream target gene was SOX12. miR-544-5p expression was decreased, while SOX12 expression was increased in OC tumor tissues and cells. Overexpression of miR-744-5p inhibited cell proliferation, migration, invasion and promoted cell apoptosis in SKOV-3 and OVCAR-3 cells. Conclusion MNX1-AS1 promoted the development of OC through miR-744-5p/SOX12 axis. This study revealed a novel mechanism of MNX1-AS1 in OC, which may provide a new treatment or scanning target for OC.

BACKGROUND Worldwide, ovarian cancer has a high mortality rate due to the difficulty in diagnosing early-stage disease and resistance to chemotherapy agents. Costunolide is a plant-derived sesquiterpene lactone with anti-oxidant properties. This study aimed to investigate the effects of costunolide on cell growth, apoptosis, autophagy, the production of reactive oxygen species (ROS), cleaved caspase-3, and cleaved caspase-9 on the multidrug-resistant ovarian cancer cell line, OAW42-A. MATERIAL AND METHODS The MTT assay determined the proliferation rate of OAW42-A multidrug-resistant ovarian cancer cells and the apoptosis rate was determined using propidium iodide (PI) staining. Autophagy was detected by measuring the expression of LC3 II. Fluorescence flow cytometry was used to measure the levels of reactive oxygen species (ROS) and the mitochondrial membrane potential. Protein expression of LC3 II, beclin 1, cleaved caspase-3, and cleaved caspase-9 were measured by Western blot. RESULTS Costunolide treatment inhibited the growth of OAW42-A cells with an IC₅₀ of 25 µM, resulted in apoptotic cell death, increased the expression of Bax, and decreased the expression of Bcl-2. Confocal electron microscopy showed that costunolide induced autophagy in the OAW42-A cells. Western blot showed that costunolide treatment of OAW42-A cells increased the expression of the LC3 II, beclin 1, cleaved caspase-3, and cleaved caspase-9. Costunolide treatment significantly increased the levels of ROS and reduced the OAW42-A cell mitochondrial membrane potential. CONCLUSIONS Costunolide inhibited growth, apoptosis, ROS generation, and was associated with loss of mitochondrial membrane potential of OAW42-A multidrug-resistant ovarian cancer cells.

In this work, a novel random number generator with adjustable adaptability is demonstrated based on the intrinsic fluctuation of resistive random access memory (RRAM). Experimental data shows the standard deviation of resistance state has a negative dependence on compliance current (CC), thus an adaptive random number generator (ARNG) can be realized by controlling the CC in RRAM set process. Benchmarking results show that the RRAM based ARNG can achieve same performance compared with software ARNG in reinforcement learning process of zebra finch’s singing pattern.

In this study, the key factors for controlling the average fiber diameter and diameter distribution of fibers made via simultaneous centrifugal spinning and UV initiated polymerization are elucidated. Through systematic investigation, it was found that the average fiber diameter has a strong dependence on monomer delivery rate through the orifice, which can be intuitively linked to both the orifice diameter and monomer mixture viscosity. On the other hand, the breadth of the fiber diameter distribution can be controlled by the spin speed of the rotating spinneret. Carefully tuning these process parameters allows near independent control of average fiber diameter and its distribution, which could provide access to a widely tailorable range of fibers appropriate for different applications. Finally, under optimized process conditions, crosslinked fibers with average diameters of approximately 1.5 μm can be produced, which are one to two orders of magnitude smaller than photocured fibers fabricated in previous reports and comparable with the smallest melt blown nonwoven fibers produced commercially. Coupled with the advantages of cross-linked fibers made by in-situ photopolymerization, the capability to produce small fibers with tailored diameter distributions by centrifugal spinning could further establish this technology as a competitive alternative to existing approaches.

The history of the development of Ultra-High Performance Concrete (UHPC) shear walls and the current status of today’s research as well as the future development prospects are comprehensively collated. The analysis process and conclusive results of the present-day domestic and international research on UHPC shear walls are highlighted. The load displacement curves, hysteresis curves and skeleton lines of ultra-high performance concrete shear walls under different experimental loads are collated and compared. Integrate the corresponding equations for shear bearing capacity and equations for the overall specimen load displacement curves. A finite element model of the ultra-high performance concrete shear wall is established to simulate and perform non-linear finite element analysis of its force process under unidirectional horizontal loading.

In this paper, the transient behavior of RRAM device under pulse-SET operation is used to mimic neuron action potential accurately. By studying the effect of pulse parameters including rising time, holding time and falling time on the output voltage waveform, we summarized a method to mimic the action potential of real neuron by adjusting proper bias on resistive device precisely. Since this RRAM device resistance hasn’t been changed after pulse operating, so there is no need to generate reverse RESET voltage, which reduces the complexity of peripheral circuits. In addition, only one single RRAM device is involved in this operation, indicating that this method is capable to minimize the number of devices to form electronic neurons without increasing the complexity of circuit and the area of chip.

Random telegraph noise (RTN) in resistive random access memory (RRAM) introduces variation in resistance which might cause errors in RRAM based logic circuits. In this paper, we find multiple RTN patterns in RRAM devices and build a simulation model. Using this model, noise immunity of a RRAM based IMP logic circuit is evaluated and method to suppress RTN’s effect is proposed.

High-resistance state instability (HRSI) is one of the major challenges that obstruct the application of resistive random access memory (RRAM) in commercial markets. In this letter, we studied the mechanism of HRSI of TaOx-based RRAM with a statistical methodology. During DC sweep, the model is able to calculate the defect numbers when the endurance degradation and short-term HRSI occur. Our result reveals that these two kinds of HRSI both have a strong connection with the change of defect numbers which play an important role in current conduction. According to our analysis, the endurance degradation is caused by the increase in fixed defect numbers, while short-term HRSI originates from the relaxation induced by reduction of defect numbers.

Retina shows an extremely high signal processing efficiency because of its specific signal processing strategy which called computing in sensor. In retina, photoreceptor cells encode light signals into spikes and ganglion cells finish the shape perception process. In order to realize the neuromorphic vision sensor, the one-transistor-one-memristor (1T1M) structure which formed by one memristor and one MOSFET in serial is used to construct photoreceptor cell and ganglion cell. The voltage changes between two terminals of memristor and MOSFET can mimic the changes of membrane potential caused by spikes and illumination respectively. In this paper, the tunable memristive neurons with 1T1M structures are built. According to the concept of receptive field of ganglion cells (GCs) in the retina, the artificial shape perception retina network is constructed with these memristive neurons. The final results show that the artificial retina can extract shape information from the image and transfer it into spike frequency realizing the function of computing in sensor.

In this study, the fabrication of crosslinked nonwoven fibers via simultaneous thiol-ene photopolymerization and spinning of monomer jets has been demonstrated in centrifugal Forcespinning for the first time. We observed that simultaneous Forcespinning and photopolymerization resulted in a wide variety of fiber morphologies including beads, beads-on-string, uniform fiber, fused fibers, and well-cured fibers. To elucidate the underlying mechanisms and parameter interactions that give rise to these morphologies, we systematically varied the light intensity, solution elasticity, and spin speed of the Forcespinning process. From these experimental results, an operating diagram was constructed based on the measured process parameters, their respective timescales, and observed effects on fiber morphology. While numerous parameters can individually affect fiber formation and morphology, the interplay between curing kinetics, solution viscoelasticity, and orifice-to-collector processing time window is also crucial in this process. Smooth and well-cured fibers were formed only when the photopolymerization occurred sufficiently quickly, before both the breakup of fibers into droplets due to a surface tension driven Rayleigh instability and the deposition of fibers on the collector. Our findings can serve as a predictive guideline for the fabrication of crosslinked fibers with desired morphology, the implementation of the in-situ polymerization and spinning concept into other commercial fiber manufacturing technologies, and the adaptation of other functional or high performance monomer systems.

As one of the emerging memory device, Ta 2 O 5 based RRAM has shown various outstanding features, such as low power consumption, high reliability and excellent scalability. In Ta 2 O 5 RRAM, the formation and the migration of oxygen vacancies are crucial to the resistive switching characteristics, reliability and uniformity of the device. In this paper, we used the first-principle simulation to study the properties of oxygen vacancies including forming energy and migration barrier in amorphous tantalum pentoxide. The β-Ta 2 O 5 supercell was built and annealing algorithm was used for generating amorphous Ta 2 O 5 in Material Studio. The band structure and DOS of both materials were studied by Vienna Ab initio simulation program (VASP). We also calculated the formation energy and migration barrier of oxygen vacancies, and discussed the mechanism of conductive path formation in amorphous Ta 2 O 5 . Finally, we proposed a new microscopic model of resistive switching mechanism in amorphous Ta 2 O 5 RRAM device.

Aim: We aimed to explore the roles of circular RNAs (circRNAs) in extracellular vesicles (EVs) isolated from serum of patients with endometrial cancer. Materials & methods: EVs were isolated from serum samples of three patients with stage III adenocarcinoma aged 50–60 years and three matched healthy controls. RNA was extracted from the EVs and analyzed using RNA-seq technique. Results: We got 209 upregulated circRNAs and 66 downregulated circRNAs. Kyoto Encyclopedia of Genes and Genomes pathway analysis indicated that the differentially expressed circRNAs were enriched in five pathways. The expression level of hsa_circ_0109046 and hsa_circ_0002577 was confirmed using real-time quantitative PCR. Conclusion: We identified 275 differentially expressed circRNAs and the expression level of two circRNAs was confirmed using real-time quantitative PCR.

This report describes the direct melt processing of inorganic tin fluorophosphate (TFP) glass fibers with average diameters ranging from 2 to 4 µm via centrifugal Forcespinning. This was accomplished by using a TFP glass with low glass transition temperature (T g) and the melt processing capability of Forcespinning. The thermal behavior of TFP glass fibers was investigated by differential scanning calorimetry and thermogravimetric analysis, while the compositional evolution of the fibers was studied using energy-dispersive spectrometry and Fourier-transform infrared spectroscopy. These fibers exhibited excellent thermal stability after thermal post-treatment at 300 °C. The T g of the thermally treated fibers increased by 100 °C compared to the bulk material. The fibers were found to undergo dehydration and loss of fluorine during thermal treatment, resulting in a rigid and crosslinked glass network with enhanced thermal stability and increased T g. The enhanced thermal stability demonstrated the potential of TFP fibers for high temperature catalysis and chemical filtration applications.

Animals’ survival is dependent on their abilities to adapt to the changing environment by adjusting their behaviours, which is related to the ubiquitous learning behaviour, nonassociative learning. Thus mimicking the indispensable learning behaviour in organisms based on electronic devices is vital to better achieve artificial neural networks and neuromorphic computing. Here a three terminal device consisting of an oxide-based memristor and a NMOS transistor is proposed. The memristor with gradual conductance tuning inherently functions as the synapse between sensor neurons and motor neurons and presents adjustable synaptic plasticity, while the NMOS transistor attached to the memristor is utilized to mimic the modulatory effect of the neuromodulator released by inter neurons. Such a memristor-based multi-terminal device allows the practical implementation of significant nonassociative learning based on a single electronic device. In this study, the experience-induced modification behaviour, both habituation and sensitization, was successfully achieved. The dependence of the nonassociative behavioural response on the strength and interval of presented stimuli was also discussed. The implementation of nonassociative learning offers feasible and experimental advantages for further study on neuromorphic systems based on electronic devices.

Inspired by the computing architecture of human brain, neuromorphic computing promises massively parallel, energy efficient and fault tolerant computation compared with conventional von Neumann approaches. In order to achieve this ambitious goal, one of the crucial tasks is to make devices that can emulate the functions of biological synapses at the physical level. Here we fabricated a novel Pt/TaOx/Ta memristor with recessed Ta bottom electrodes, where the TaOx film was formed by thermal oxidation of the bottom electrode and thus had a constantly ascending concentration of oxygen vacancies from the Pt/TaOx interface to the TaOx/Ta interface. Such cell geometry and ion distribution profile gave rise to highly incremental and uniform resistive switching that emulated the potentiation or depression process of synapses. Furthermore, important synaptic learning rules, such as spike timing dependent plasticity, could also be implemented by these devices, making them well suited for electronic synapses in neuromorphic systems.

Memory unit, especially the non-volatile memory (NVM), is an indispensable component in a high performance electronic systems which aims at efficient information processing and storage. Resistive random access memory (RRAM) is one of the most promising candidates among the emerging memory technologies. However, optimization of the variability introduced by the intrinsic stochastic nature of filament formation remains a tough problem. In this paper, both operation voltage and resistance of the device with localized implantation show significant improvement of uniformity compared with uniformly doped device, which can be attributed to the further undermine of the randomness due to localized doping instead of uniformly doping.

An all-optical signal up-conversion scheme using a directly modulated DFB semiconductor laser and an optoelectronic oscillator is proposed and experimentally demonstrated. By directly modulating a DFB semiconductor laser, a higher modulation efficiency and a lower conversion loss are achieved comparing with the modulators based schemes. The 40 Mb/s 16QAM signal working at 1 GHz is successfully up-converted to 10.68 GHz. The conversion loss is independent of the frequency and the power of the intermediate-frequency signal.

We propose a novel approach of fast tunable laser, which uses high-speed driving circuit and DFB semiconductor laser array to achieve the fast switching of wavelength. We use single chip microcomputer and FPGA to form the control system, and a high-speed driving circuit to ensure the switching speed. The 8-channel DFB laser array was fabricated based on reconstruction-equivalent-chirp (REC) technique. The experimental result shows that the switching time of the wavelength is about 30 ns.

Polyhedral oligomeric silsesquioxanes (POSS) are versatile inorganic-organic hybrid building blocks that have potential applications as reinforcement nanofillers, thermal stabilizers, and catalyst supports for metal nanoparticles. However, fabrication of fibrous materials with high POSS content has been a challenge because of the aggregation and solubility limits of POSS units. In this paper, we describe a robust and environmentally friendly fabrication approach of inorganic-organic hybrid POSS fibers by integrating UV initiated thiol-ene polymerization and centrifugal fiber spinning. The use of monomeric liquids in this approach not only reduces the consumption of heat energy and solvent, but it also promotes homogeneous mixing of organic and inorganic components that allows integration of large amount of POSS (up to 80 wt %) into the polymer network. The POSS containing thiol-ene fibers exhibited enhanced thermomechanical properties compared to purely organic analogs as revealed by substantial increases in residual weight and a factor of 4 increase in modulus after thermal treatment at 1000 °C. This simple fabrication approach combined with the tunability in fiber properties afforded by tailoring monomer composition make POSS containing thiol-ene fibers attractive candidates for catalyst supports and filtration media, particularly in high-temperature and harsh environments.

Neuromorphic engineering offers a promising route toward intelligent and low power computing systems that may find applications in artificial intelligence and the Internet. Construction of neuromorphic systems, however, requires scalable nanodevices that could implement the key functionalities of biological synapses. Here, we demonstrate an artificial synaptic device consisting of a Ti/yttria-stabilized-zirconia (ZrO2:Y)/Pt memristive structure, where the loss microstructure, high oxygen vacancy concentration, and resultant high ionic conductivity in ZrO2:Y facilitate the oxygen vacancy migration and filament evolution in the devices, leading to a bipolar artificial synapse with low forming and operation voltages. As the thickness of ZrO2:Y film increases, a transition from bipolar to unipolar resistive switching was observed, which can be ascribed to the competing vertical and radial ion transport dynamics. The emergence of unipolar switching has in turn allowed the device to exhibit metaplasticity, a history dependent plasticity that is important for memory and learning functions. This work thus demonstrates on-demand manipulation of ionic transport properties for building synaptic elements with rich functionalities.

In this paper, the impacts of random telegraph noise (RTN) on delay and energy of digital logic circuits are studied. The conventional method of extracting logic gate delay is found inaccurate due to the bias dependency of RTN amplitude. Thus an appropriate measuring strategy is proposed, based on which the impact of single RTN on circuit delay is investigated, and non-monotonous trend against trap energy level Et is found. Furthermore, the impacts of multi RTN on Energy-Delay(ED) curves are discussed. It is found that RTN is unneglectable when performing an ED optimization. Otherwise, under-design phenomenon would occur considering delay constraint, and over-design would occur considering energy constraint. This result provide helpful guidelines for circuit design.

A novel vertical 3D RRAM structure with greatly improved reliability behavior is proposed and experimentally demonstrated through basically compatible process featuring self-localized switching region by sidewall electrode oxidation. Compared with the conventional structure, due to the effective confinement of the switching region, the newly-proposed structure shows about two orders higher endurance (>108 without verification operation) and better retention (>180h@150 °C), as well as high uniformity. Corresponding model is put forward, on the base of which thorough theoretical analysis and calculations are conducted as well, demonstrating that, resulting from the physically-isolated switching from neighboring cells, the proposed structure exhibits dramatically improved reliability due to effective suppression of thermal effects and oxygen vacancies diffusion interference, indicating that this novel structure is very promising for future high density 3D RRAM application.

Memristor has attracted significant attention in recent years because of its capability to act as artificial synapse in neuromorphic systems. In this paper, a memristor is demonstrated based on tantalum oxide. Multiple resistance states can be achieved. The resistance switching mechanism of continuous sets and resets is discussed. The essential synaptic behaviors of potentiation and depression are achieved.

Spike-timing-dependent-plasticity (STDP) is an important leaning rule in organisms. In the application of neural computation, it is meaningful to apply symmetric STDP to associative learning. In this paper, an electronic synapse with symmetric STDP features was demonstrated. Meanwhile, taking Pavlov's experiment as an example, a model of neural network was built with this electronic synapse and successfully simulated the Pavlov's experiment, indicating the proposed symmetric STDP synaptic circuit can mimic the working principle of associative learning.

A resistive switching device with inherent nonlinear characteristics through a delicately engineered interfacial layer is an ideal component to be integrated into passive crossbar arrays for the suppression of sneaking current, especially in ultra-dense 3D integration. In this paper, we demonstrated a TaOx-based bipolar resistive switching device with a nearly symmetrical bi-directional nonlinear feature through interface engineering. This was accomplished by introducing an ultra-thin interfacial layer (SiO2-x) with unique features, including a large band gap and a certain level of negative heat of oxide formation between the top electrode (TiN) and resistive layer (TaOx). The devices exhibit excellent nonlinear property under both positive and negative bias. Modulation of the inherent nonlinearity as well as the resistive switching mechanism are comprehensively studied by scrutinizing the results of the experimental control groups and the extensive characterizations including detailed compositional analysis, which suggests that the underlying mechanism of the nonlinear behavior is associatively governed by the serially connected metallic conductive filament and Flower-Nordheim tunneling barrier formed by the SiO2-x interface layer. The proposed device in this work has great potential to be implemented in future massive storage memory applications of high-density selector-free crossbar structure.

TaOx-based resistive random access memory (RRAM) attracts considerable attention for the development of next generation nonvolatile memories. However, read current noise in RRAM is one of the critical concerns for storage application, and its microscopic origin is still under debate. In this work, the read current noise in TaOx-based RRAM was studied thoroughly. Based on a noise power spectral density analysis at room temperature and at ultra-low temperature of 25 K, discrete random telegraph noise (RTN) and continuous average current fluctuation (ACF) are identified and decoupled from the total read current noise in TaOx RRAM devices. A statistical comparison of noise amplitude further reveals that ACF depends strongly on the temperature, whereas RTN is independent of the temperature. Measurement results combined with conduction mechanism analysis show that RTN in TaOx RRAM devices arises from electron trapping/detrapping process in the hopping conduction, and ACF is originated from the thermal activatio...

Here we propose a novel encapsulated vertical 3D RRAM structure with each resistive switching cell encapsulated by dielectric layers, contributing to both the reliability improvement of individual cells and thermal disturbance reduction of adjacent cells due to the effective suppression of unwanted oxygen vacancy diffusion. In contrast to the traditional vertical 3D RRAM, encapsulated bar-electrodes are adopted in the proposed structure substituting the previous plane-electrodes, thus encapsulated resistive switching cells can be naturally formed by simply oxidizing the tip of the metal bar-electrodes. In this work, TaO x -based 3D RRAM devices with SiO2 and Si3N4 as encapsulation layers are demonstrated, both showing significant advantages over traditional unencapsulated vertical 3D RRAM. Furthermore, it was found thermal conductivity and oxygen blocking ability are two key parameters of the encapsulation layer design influencing the scalability of vertical 3D RRAM. Experimental and simulation data show that oxygen blocking ability is more critical for encapsulation layers in the relatively large scale, while thermal conductivity becomes dominant as the stacking layers scale to the sub-10 nm regime. Finally, based on the notable impacts of the encapsulation layer on 3D RRAM scaling, an encapsulation material with both excellent oxygen blocking ability and high thermal conductivity such as AlN is suggested to be highly desirable to maximize the advantages of the proposed encapsulated structure. The findings in this work could pave the way for reliable ultrahigh-density storage applications in the big data era.

In this paper, we present an analysis of single-mode fiber resonators with 2×2 directional single-mode couplers, using signal flow graphs. Our method is more simple than conventional methods. Furthermore, a novel compound fiber resonator constructed by two cross-coupling fiber resonators, which is shown to be useful for line narrowing in fiber lasers, is investigated.

Forty-four NH(3) absorption spectral lines of the combination tones of the vibration-rotation transitions were observed at 1.4988-1.5520 microm with a 1.5-microm grating-external-cavity semiconductor laser. The linewidth and absorption rate of NH(3) absorption spectral lines were measured. Also, the changes of center frequency and linewidth of the NH(3) absorption spectral line with the our knowledge the first time.