融合空间和统计特征的CNN-GRU臭氧浓度预测模型研究

近年来,空气污染问题备受关注,近地面臭氧逐渐成为我国部分城市的首要污染物,因此对臭氧浓度的精准预测尤为重要.为了进一步提高臭氧浓度预测的精度,提出一种融合空间特征和统计特征的卷积神经网络和门控循环单元(Convolutional Neural Networks and Gate Recurrent Unit,CNN-GRU)臭氧浓度组合预测模型.首先,通过对时空因素以及其他大气污染物与臭氧浓度进行相关性分析,利用基于统计域的方法和克里金插值法对臭氧浓度时序数据进行预处理来提取臭氧浓度数据的时空特征,采用并联杂交CNN和GRU结构的组合预测模型得到最终的臭氧浓度预测结果.实验结果表明,CNN-GRU组合预测模型预测未来一小时的臭氧浓度可决系数、均方根误差和均方误差的值分别为0.9598,11.9508和8.2753,未来两小时的臭氧浓度可决系数、均方根误差和均方误差的值分别为0.8985,18.5373和13.0045,优于独立的CNN、长短期记忆(LongShortTermMemory,LSTM)网络、GRU、卷积-长短期记忆网络(Convolutional LSTM Network,ConvLSTM)、CNN-LSTM和CNN-GRU预测模型,这是由于CNN-GRU组合预测模型融合了空间和统计特征,可以多角度提取特征并采用并联杂交的网络结构,所以预测精度较高,且具备较好的鲁棒性.

Response of the sensorimotor cortex of cerebral palsy rats receiving transplantation of vascular endothelial growth factor 165-transfected neural stem cells

Neural stem cells are characterized by the ability to differentiate and stably express exogenous ge- nes. Vascular endothelial growth factor plays a role in protecting local blood vessels and neurons of newborn rats with hypoxic-ischemic encephalopathy. Transplantation of vascular endothelial growth factor-transfected neural stem cells may be neuroprotective in rats with cerebral palsy. In this study, 7-day-old Sprague-Dawley rats were divided into five groups： （1） sham operation （control）, （2） cerebral palsy model alone or with （3） phosphate-buffered saline, （4） vascular en- dothelial growth factor 165 ＋ neural stem cells, or （5） neural stem cells alone. The cerebral palsy model was established by ligating the left common carotid artery followed by exposure to hypox- ia. Phosphate-buffered saline, vascular endothelial growth factor ＋ neural stem cells, and neural stem cells alone were administered into the sensorimotor cortex using the stereotaxic instrument and microsyringe. After transplantation, the radial-arm water maze test and holding test were performed. Immunohistochemistry for vascular endothelial growth factor and histology using hematoxylin-eosin were performed on cerebral cortex. Results revealed that the number of vas- cular endothelial growth factor-positive cells in cerebral palsy rats transplanted with vascular endothelial growth factor-transfected neural stem cells was increased, the time for finding water and the finding repetitions were reduced, the holding time was prolonged, and the degree of cell degeneration or necrosis was reduced. These findings indicate that the transplantation of vascu- lar endothelial growth factor-transfected neural stem cells alleviates brain damage and cognitive deficits, and is neuroprotective in neonatal rats with hypoxia ischemic-mediated cerebral palsy.

Triterpenoid saponin biosynthesis genes and their expression patterns during the development of sea cucumber Apostichopus japonicus

Sea cucumbers are echinoderm species with a leathery skin and an elongated body.Natural compounds,including saponins,have been previously isolated from sea cucumber.The majority of saponins derived from this organism typically belong to the triterpene glycosides,which exhibit various biological effects(e.g.,antifungal,cytotoxic,hemolytic,and cytostatic immunomodulatory activities).In the present study,30 saponin biosynthesis enzymes,namely 2 AACTs,2 FPSs,2 HMGSs,2 OSCs,1 SS,2 SEs,and 19 UGTs,were found in the genome of sea cucumber Apostichopus japonicus.Compared with upstream saponin biosynthesis enzymes(i.e.,AACTs,FPSs,HMGSs,OSCs,and SSs),the downstream saponin biosynthesis enzymes(SEs and UGTs)shared lower amino acid sequence similarity with the corresponding genes in other echinoderms.It was proposed that the enzyme structures comprised bothα-helices andβ-sheets.Notably,only a low percentage ofβ-sheets were present in FPSs,OSCs,and SS.The saponin biosynthesis enzymes showed dynamic expression patterns during five critical developmental stages of A.japonicus(fertilized oocytes,blastula,gastrula,doliolaria,and penractula).The present study involved elucidation of putative saponin biosynthesis pathways in sea cucumber and provides a valuable platform for further investigation of saponin biosynthesis in echinoderms.

Theoretical investigations on the growth of graphene by oxygenassisted chemical vapor deposition

Recently,graphene has drawn considerable attention in the field of electronics,owing to its favorable conductivity and high carrier mobility.Crucial to the industrialization of graphene is its high-quality microfabrication via chemical vapor deposition.However,many problems remain in its preparation,such as the not fully understood cracking mechanism of the carbon source,the mechanism of its substrate oxidation,and insufficient defect repair theory.To help close this capability gap,this study leverages density functional theory to explore the role of O in graphene growth.The effects of Cu substrate oxidation on carbon source cracking,nucleation barriers,crystal nucleus growth,and defect repairs are discussed.OCu was found to reduce energy change during dehydrogenation,rendering the process easier.Moreover,the adsorbed O in graphene or its Cu substrate can promote defect repair and edge growth.

Thermally conductive MWCNTs/Fe_(3)O_(4)/Ti_(3)C_(2)T_(x) MXene multi-layer films for broadband electromagnetic interference shielding

The Ti_(3)C_(2)T_(x)MXene is thought to be a promising candidate for next-generation electromagnetic interference(EMI) shielding materials.However,its broadband shielding capability and thermal conduction performance are insufficient to meet the growing demands.Herein,we reported a layer-by-layer composite film composed of Ti_(3)C_(2)T_(x)MXene,multi-walled carbon nanotubes(MWCNTs),and Fe_(3)O_(4)nanoparticles.Benefitting from the architecture and the synergistic effect of components,the obtained composite film exhibited high comprehensive performance.Specifically,the introduction of Fe_(3)O_(4)magnetic nanoparticles effectively reduced the impedance mismatch between the composite film and air and enhanced the magnetic loss of the composite film.The layered structure prolonged the transmission path of electromagnetic waves inside the composite film and constructed a rich conductive network,causing interfacial polarization and ohmic loss.The results indicated that the composite film(52 μm) delivered a high EMI shielding effectiveness of 49 dB in the frequency range from X-band to Ku-band.Furthermore,the MWCNTs layers in the composite films provided numerous heat transfer channels,reducing phonon scattering during heat transfer and resulting in a maximum thermal conductivity of 8.241 W/(m K).