Echo State Network With Probabilistic Regularization for Time Series Prediction

Recent decades have witnessed a trend that the echo state network(ESN)is widely utilized in field of time series prediction due to its powerful computational abilities.However,most of the existing research on ESN is conducted under the assumption that data is free of noise or polluted by the Gaussian noise,which lacks robustness or even fails to solve real-world tasks.This work handles this issue by proposing a probabilistic regularized ESN(PRESN)with robustness guaranteed.Specifically,we design a novel objective function for minimizing both the mean and variance of modeling error,and then a scheme is derived for getting output weights of the PRESN.Furthermore,generalization performance,robustness,and unbiased estimation abilities of the PRESN are revealed by theoretical analyses.Finally,experiments on a benchmark dataset and two real-world datasets are conducted to verify the performance of the proposed PRESN.The source code is publicly available at https://github.com/LongJinlab/probabilistic-regularized-echo-state-network.

基于桐油热处理的竹材理化性质研究

寻求绿色、可持续发展的改性方法来生产耐用竹材制品,是目前竹产业面临的挑战。本文将桐油热处理技术应用于竹材改性,探讨了桐油热处理过程中桐油在竹材中的渗透行为和分布,研究了桐油与热处理的协同作用对竹材化学性质、物理性质、力学性质的影响以及相互作用机制。结果表明,桐油热处理不仅可以增强竹材的疏水性能和尺寸稳定性,改善竹材的防霉性能,而且竹材可以保持其良好的力学性能。与未处理竹材相比,200℃桐油热处理后竹材的饱水膨胀率从3.17%下降至2.42%,200℃桐油热处理后竹材径切面的接触角在300 s时仍可保持在100°以上。桐油热处理后竹材性能的改善归因于竹材化学成分的变化、纤维结晶度的增加、竹材外表面和细胞腔内表面油膜的形成。因此,桐油热处技术在竹材工业改性中具有良好的发展前景。

Fabrication and characterization of AlGaN/GaN HEMTs with high power gain and efficiency at 8 GHz

State-of-the-art AlGaN/GaN high electron mobility structures were grown on semi-insulating 4H-SiC substrates by MOCVD and X-band microwave power high electron mobility transistors were fabricated and characterized.Hall mobility of 2291.1 cm^(2)/(V·s)and two-dimensional electron gas density of 9.954×10^(12)cm^(-2)were achieved at 300 K.The HEMT devices with a 0.45-μm gate length exhibited maximum drain current density as high as 1039.6 mA/mm and peak extrinsic transconductance of 229.7 mS/mm.The f_(T)of 30.89 GHz and f_(max)of 38.71 GHz were measured on the device.Load-pull measurements were performed and analyzed under(-3.5,28)V,(-3.5,34)V and(-3.5,40)V gate/drain direct current bias in class-AB,respectively.The uncooled device showed high linear power gain of 17.04 dB and high power-added efficiency of 50.56%at 8 GHz when drain biased at(-3.5,28)V.In addition,when drain biased at(-3.5,40)V,the device exhibited a saturation output power dens-ity up to 6.21 W/mm at 8 GHz,with a power gain of 11.94 dB and a power-added efficiency of 39.56%.Furthermore,the low f_(max)/f_(T)ratio and the variation of the power sweep of the device at 8 GHz with drain bias voltage were analyzed.

Effective Increase of Crystal Area during Sublimation Growth of 6H-SiC by Using the Cone-shaped Baffle

A novel design of crucible is proposed in this paper for the growth of SiC crystals. The relation between grown crystal shape and temperature distribution in a growth chamber was discussed. It is pointed out that the crystal shape had a close relationship with temperature distribution. The calculations suggested that the radial temperature field of the growing crystal became homogenous by setting up the cone-shaped baffle in the growth chamber. By modifying the crucible design and temperature distribution in the growth chamber, it is possible to enhance the enlargement of crystal, and also possible to keep grown surface flat.

Research progress of large size SiC single crystal materials and devices

SiC semiconductor is the focus of recent international research.It is also an important raw material for China to achieve carbon emission peak and carbon neutrality.After nearly 20 years of research and development,we focus on the three types SiC crystals,n-type,p-type and semi-insulating,indicating the development of Shandong University for crystal growth.And defects control,electrical property,atomic polishing,and corresponding device authentication all obtain great progress.Total dislocation density of 6-inch n-type substrates decreases to 2307 cm^(-2),where BPD(Basal Plane Dislocation)lowers to 333 cm^(-2) and TSD(Threading Screw Dislocation)19 cm^(-2).The full width at half maximum(FWHM)(0004)rocking curves is only 14.4 arcsec.The resistivity reaches more than 1E+12Ω·cm for semi-insulating SiC and lower than 20 mΩ·cm for n-type SiC.The impurity concentrations in 6-inch high-purity semi-insulating(HPSI)SiC crystals reach extreme low levels.The devices made of various substrate materials have good performance.

In-situ-reduced synthesis of cyano group modified g-C_(3)N_(4)/CaCO_(3) composite with highly enhanced photocatalytic activity for nicotine elimination

Graphite carbon nitride has many excellent properties as a two-dimensional semiconductor material so that it has a wide application prospect in the field of photocatalysis.However,the traditional problems such as high recombination rate of photogenerated carriers limit its application.In this work,we introduce nitrogen deficiency into g-C_(3)N_(4)to solve this problem a simple and safe in-situ reduction method.g-C_(3)N_(4)/CaCO_(3)was obtained by a simple and safe one-step calcination method with industrial-grade micron particles CaCO_(3).Cyano group modification was in-situ reduced during the thermal polymerization process,which would change the internal electronic structure of g-C_(3)N_(4).The successful combination of g-C_(3)N_(4)and CaCO_(3)and the introduction of cyanide have been proved by Fourier transform infrared spectroscopy and X-ray photoelectron spectrometer.The formation of the cyano group,an electron-absorbing group,promotes the effective separation of photogenic electron hole pairs and inhibits the recombination of photogenic carriers.These advantages result in the generation of more·O_(2)-and1O_(2)in the catalytic system,which increases the photocatalytic efficiency of nicotine degradation by ten times.Furthermore,the degradation process of nicotine has been studied in this work to provide a basis for the degradation of nicotine organic pollutants in the air.

Robust Co_(3)O_(4)nanocatalysts supported on biomass-derived porous N-doped carbon toward low-pressure hydrogenation of furfural

The catalytic conversion of biomass platform chemicals using abundant non-noble metal nanocatalysts is a challenging topic.Here,high-density cobalt oxide nanoparticles loaded on biomass-derived porous N-doped carbon(NC)was fabricated by a tandem hydrothermal pyrolysis and mild nitrate decomposition process,which is a green and cheap preparation method.The Co_(3)O_(4) nanoparticles with the average size of 12 nm were uniformly distributed on the porous NC.The nanocomposites also possessed large surface area,high N content,good dispersibility in isopropanol,and furfural absorbability.Due to these characteristics,the novel cobalt nanocatalyst exhibited high catalytic activity for producing furfuryl alcohol,yielding 98.7%of the conversion and 97.1%of the selectivity at 160℃ for 6 h under 1 bar H2.The control experiments implied that both direct hydrogenation and transfer hydrogenation pathways co-existed in the hydrogenation reaction.The excellent catalytic activity of Co_(3)O_(4)@NC was attributed to the cooperative effects of porous NC and Co_(3)O_(4) nanoparticles.This approach provides a new idea to design effective high-density nonnoble metal oxide nanocatalysts for hydrogenation reactions,which can make full use of sustainable natural biomass.

Facile fabrication of superior antibacterial cotton fabric based on ZnO nanoparticles/quaternary ammonium salts hybrid composites and mechanism study

In the research for the safe and efficiently antibacterial cotton fabrics to minimize risk for human health,an organic–inorganic hybrid material of ZnO nanoparticles(NPs)and quaternary ammonium salt(QAS)was employed to modify cotton fabrics by a dipping–padding–drying method.The synergistic effects of ZnO NPs and QAS on the structure and antibacterial properties of cotton fabrics were studied in detail.Results displayed that the QAS and ZnO NPs were immobilized firmly in cotton fabric by the formation of chemical covalent bonds and silica gel structure.ZnO/QAS/cotton had a good inhibitory effect on the growth of E.coli and S.aureus,with superior antibacterial efficiency of>99.99%.ZnO/QAS/cotton preserved good mechanical property,water absorbability,and limpness.We also provided a detailed analysis of antibacterial mechanism for the hybrid materials.The contact mechanism and the Zn2+release were considered as the main mechanisms for the ZnO/QAS/cotton,while the reactive oxygen species(ROS)generation only had a little contribution to the antibacterial activity.In short,the excellent integrated properties endowed the hybrid cotton fabrics as potential application in many fields,like healthcare,food packaging.

Demonstration of epitaxial growth of strain-relaxed GaN films on graphene/SiC substrates for long wavelength light-emitting diodes

Strain modulation is crucial for heteroepitaxy such as GaN on foreign substrates.Here,the epitaxy of strain-relaxed GaN films on graphene/SiC substrates by metal-organic chemical vapor deposition is demonstrated.Graphene was directly prepared on SiC substrates by thermal decomposition.Its pre-treatment with nitrogen-plasma can introduce C–N dangling bonds,which provides nucleation sites for subsequent epitaxial growth.The scanning transmission electron microscopy measurements confirm that part of graphene surface was etched by nitrogen-plasma.We study the growth behavior on different areas of graphene surface after pre-treatment,and propose a growth model to explain the epitaxial growth mechanism of GaN films on graphene.Significantly,graphene is found to be effective to reduce the biaxial stress in GaN films and the strain relaxation improves indium-atom incorporation in InGaN/GaN multiple quantum wells(MQWs)active region,which results in the obvious red-shift of light-emitting wavelength of InGaN/GaN MQWs.This work opens up a new way for the fabrication of GaN-based long wavelength light-emitting diodes.

Anomalous Resistivity in Vanadium-Doped Semi-Insulating 4H-SiC Wafers

The resistivities of vanadium-doped semi-insulating 4H-SiC wafers were measured by a contactless resistivity measurement system. Anomalous resistivity was found in semi-insulating 4H-SiC wafer. Raman spectra of semi-insulating4H-SiC wafer indicated that the anomalous resistivity was caused by polytype inclusion. Based on the activation energies of different SiC polytypes calculated from resistivity versus temperature data measured by COREMA-VT, the resistivities in the vanadium-doped semi-insulating 4H-SiC wafer with 6H polytype inclusion were calculated. The calculated resistivities are quite consistent with the measured resistivities. Furthermore, the compensation mechanism for the formation of anomalous resistivity was proposed.