生物质和塑料加氢脱氧制备燃料和化学品的双金属催化剂研究进展

在全球致力于实现碳中和的大背景下,生物质和废弃塑料的高值化利用已成为科研领域的研究热点.加氢脱氧反应(HDO),作为实现这一目标的重要途径之一,通过精准解离C-O/C-C键,为生产燃料和化学品提供了有效方法.在HDO过程中,C-O键的氢解及不饱和键的氢化是主要步骤,而C-C键的氢解则是需要避免的副反应.与简单的氢化反应相比,HDO过程需要具有双功能特性的催化剂,特别是当目标产物为含氧化合物时,催化剂的区域选择性至关重要.近年来,双金属催化剂在生物质及其衍生物以及含氧塑料废弃物和聚合物的HDO过程中的应用受到广泛关注.通过深入理解金属纳米颗粒与金属氧化物之间的协同作用和强相互作用,双金属催化剂的理性设计取得了显著进展.特别是,部分金属氧化物(如ReO_(x),WO_(x),MoO_(x),FeO_(x))与贵金属(如Ir,Pt,Ru)之间存在的强相互作用,不仅促进了C-O键的断裂,还有效保留了C-C键,为催化剂的高活性和高选择性奠定了基础.通过调整催化剂组成、使用小比表面积的载体等方法,可以进一步优化催化剂性能.本综述聚焦于金属氧化物改性的贵金属催化剂在HDO反应中的最新研究进展,特别是总结了Ir、Pt和Ru基催化剂在HDO反应中的应用.由于这类催化剂的结构和性能能够精确控制,并且每种催化剂都具备独特的选择性,因此被广泛应用于生物质衍生物和塑料废弃物的HDO过程中.本文总结了双金属催化剂的结构特点、HDO反应机制、催化剂结构与催化性能之间的关联,以及这些催化剂在高附加值化学品生产中的实际应用.我们以甘油和1,2-丙二醇的氢解为模型反应,深入探讨了基于Ir、Pt和Ru的双金属催化剂的催化性能、结构特点和催化机理.这些催化剂在温和条件下实现了高效的氢脱氧反应,有效抑制了C-C键的断裂,并优化了化学选择性和区域选择性.双金属催化剂在生物质精炼和塑料/聚合物转化方面展现出广泛的适用性.本文还介绍了其在木质纤维素衍生原料、羰基化合物以及聚碳酸酯等塑料中的应用.然而,双金属催化剂的稳定性在实际应用中仍面临挑战,如金属烧结、浸出、积碳及金属-金属氧化物界面的重构等问题.因此,未来的研究重点是开发高效的再生方法和高度稳定的催化剂.综上所述,金属氧化物改性的贵金属催化剂在HDO反应中展现出巨大潜力.通过深入研究和优化,有望为生物质和塑料的高值化利用提供有效解决方案.本文旨在为双金属催化剂的理性设计和优化提供参考,以期推动生物质和塑料的高值化利用技术的进一步发展和应用.

A stable implicit nodal integration-based particle finite element method(N-PFEM)for modelling saturated soil dynamics

In this study,we present a novel nodal integration-based particle finite element method(N-PFEM)designed for the dynamic analysis of saturated soils.Our approach incorporates the nodal integration technique into a generalised Hellinger-Reissner(HR)variational principle,creating an implicit PFEM formulation.To mitigate the volumetric locking issue in low-order elements,we employ a node-based strain smoothing technique.By discretising field variables at the centre of smoothing cells,we achieve nodal integration over cells,eliminating the need for sophisticated mapping operations after re-meshing in the PFEM.We express the discretised governing equations as a min-max optimisation problem,which is further reformulated as a standard second-order cone programming(SOCP)problem.Stresses,pore water pressure,and displacements are simultaneously determined using the advanced primal-dual interior point method.Consequently,our numerical model offers improved accuracy for stresses and pore water pressure compared to the displacement-based PFEM formulation.Numerical experiments demonstrate that the N-PFEM efficiently captures both transient and long-term hydro-mechanical behaviour of saturated soils with high accuracy,obviating the need for stabilisation or regularisation techniques commonly employed in other nodal integration-based PFEM approaches.This work holds significant implications for the development of robust and accurate numerical tools for studying saturated soil dynamics.

Carbon emission reduction:Contribution of photovoltaic power and practice in China

As a clean and renewable form of energy,photovoltaic(PV)power generation converts solar energy into electrical energy,reducing the consumption of fossil fuels and significantly lowering greenhouse gas emissions.Amidst the global transition towards cleaner forms of energy,countries all around the world are vigorously developing PV technology.

Confirmation of a Sub-Saturn-size Transiting Exoplanet Orbiting a G Dwarf:TOI-1194 b and a Very Low Mass Companion Star: TOI-1251 B from TESS

We report the confirmation of a sub-Saturn-size exoplanet,TOI-1194 b,with a mass of about 0.456+0.055-0.051M_(J),and a very low mass companion star with a mass of about 96.5±1.5 MJ,TOI-1251 B.Exoplanet candidates provided by the Transiting Exoplanet Survey Satellite(TESS)are suitable for further follow-up observations by ground-based telescopes with small and medium apertures.The analysis is performed based on data from several telescopes worldwide,including telescopes in the Sino-German multiband photometric campaign,which aimed at confirming TESS Objects of Interest(TOIs)using ground-based small-aperture and medium-aperture telescopes,especially for long-period targets.TOI-1194 b is confirmed based on the consistent periodic transit depths from the multiband photometric data.We measure an orbital period of 2.310644±0.000001 days,the radius is 0.767+0.045-0.041RJ and the amplitude of the RV curve is 69.4_(-7.3)^(+7.9)m s^(-1).TOI-1251 B is confirmed based on the multiband photometric and high-resolution spectroscopic data,whose orbital period is 5.963054+0.000002-0.000001days,radius is 0.947+0.035-0.033 R_(J) and amplitude of the RV curve is 9849_(-40)^(+42)ms^(-1).

Heavy ion energy influence on multiple-cell upsets in small sensitive volumes:from standard to high energies

The 28 nm process has a high cost-performance ratio and has gradually become the standard for the field of radiation-hardened devices.However,owing to the minimum physical gate length of only 35 nm,the physical area of a standard 6T SRAM unit is approximately 0.16μm^(2),resulting in a significant enhancement of multi-cell charge-sharing effects.Multiple-cell upsets(MCUs)have become the primary physical mechanism behind single-event upsets(SEUs)in advanced nanometer node devices.The range of ionization track effects increases with higher ion energies,and spacecraft in orbit primarily experience SEUs caused by high-energy ions.However,ground accelerator experiments have mainly obtained low-energy ion irradiation data.Therefore,the impact of ion energy on the SEU cross section,charge collection mechanisms,and MCU patterns and quantities in advanced nanometer devices remains unclear.In this study,based on the experimental platform of the Heavy Ion Research Facility in Lanzhou,low-and high-energy heavy-ion beams were used to study the SEUs of 28 nm SRAM devices.The influence of ion energy on the charge collection processes of small-sensitive-volume devices,MCU patterns,and upset cross sections was obtained,and the applicable range of the inverse cosine law was clarified.The findings of this study are an important guide for the accurate evaluation of SEUs in advanced nanometer devices and for the development of radiation-hardening techniques.

Dynamics modeling and optimal control for multi-information diffusion in Social Internet of Things

As an ingenious convergence between the Internet of Things and social networks,the Social Internet of Things(SIoT)can provide effective and intelligent information services and has become one of the main platforms for people to spread and share information.Nevertheless,SIoT is characterized by high openness and autonomy,multiple kinds of information can spread rapidly,freely and cooperatively in SIoT,which makes it challenging to accurately reveal the characteristics of the information diffusion process and effectively control its diffusion.To this end,with the aim of exploring multi-information cooperative diffusion processes in SIoT,we first develop a dynamics model for multi-information cooperative diffusion based on the system dynamics theory in this paper.Subsequently,the characteristics and laws of the dynamical evolution process of multi-information cooperative diffusion are theoretically investigated,and the diffusion trend is predicted.On this basis,to further control the multi-information cooperative diffusion process efficiently,we propose two control strategies for information diffusion with control objectives,develop an optimal control system for the multi-information cooperative diffusion process,and propose the corresponding optimal control method.The optimal solution distribution of the control strategy satisfying the control system constraints and the control budget constraints is solved using the optimal control theory.Finally,extensive simulation experiments based on real dataset from Twitter validate the correctness and effectiveness of the proposed model,strategy and method.

Optimizing the power conversion processes in diluted donor/acceptor heterojunctions towards 19.4%efficiency all-polymer solar cells

All polymer solar cells(all-PSCs)promise mechanically-flexible and morphologically-stable organic photovoltaics and have aroused increased interests very recently.However,due to their disorderly conformation structures within the photoactive film,inefficient charge generation and carrier transport are observed which lead to inferior photovoltaic performance compared to smaller molecular acceptor-based photovoltaics.Here,by diluting PM6 with a cutting-edge polymeric acceptor PY-IT and diluting PY-IT with PM6 or D18,donor-dominating or acceptor-dominating heterojunctions were prepared.Synchrotron X-ray and multiple spectrometer techniques reveal that the diluted heterojunctions receive increased structural order,translating to enhanced carrier mobility,improved exciton diffusion length,and suppressed non-radiative recombination loss during the power conversion.As the results,the corresponding PM6+1%PY-IT/PY-IT+1%D18 and PM6+1%PY-IT/PY-IT+1%PM6 devices fabricated by layer-by-layer deposition received superior power conversion efficiency(PCE)of 19.4%and 18.8%respectively,along with enhanced operational lifetimes in air,outperforming the PCE of 17.5%in the PM6/PY-IT reference device.

HWD-YOLO:A New Vision-Based Helmet Wearing Detection Method

It is crucial to ensure workers wear safety helmets when working at a workplace with a high risk of safety accidents,such as construction sites and mine tunnels.Although existing methods can achieve helmet detection in images,their accuracy and speed still need improvements since complex,cluttered,and large-scale scenes of real workplaces cause server occlusion,illumination change,scale variation,and perspective distortion.So,a new safety helmet-wearing detection method based on deep learning is proposed.Firstly,a new multi-scale contextual aggregation module is proposed to aggregate multi-scale feature information globally and highlight the details of concerned objects in the backbone part of the deep neural network.Secondly,a new detection block combining the dilate convolution and attention mechanism is proposed and introduced into the prediction part.This block can effectively extract deep featureswhile retaining information on fine-grained details,such as edges and small objects.Moreover,some newly emerged modules are incorporated into the proposed network to improve safety helmetwearing detection performance further.Extensive experiments on open dataset validate the proposed method.It reaches better performance on helmet-wearing detection and even outperforms the state-of-the-art method.To be more specific,the mAP increases by 3.4%,and the speed increases from17 to 33 fps in comparison with the baseline,You Only Look Once(YOLO)version 5X,and themean average precision increases by 1.0%and the speed increases by 7 fps in comparison with the YOLO version 7.The generalization ability and portability experiment results show that the proposed improvements could serve as a springboard for deep neural network design to improve object detection performance in complex scenarios.

Reconceptualization of immune checkpoint inhibitor-associated gastritis

In recent years,with the extensive application of immunotherapy in clinical practice,it has achieved encouraging therapeutic effects.While enhancing clinical efficacy,however,it can also cause autoimmune damage,triggering immunerelated adverse events(irAEs).Reports of immunotherapy-induced gastritis have been increasing annually,but due to its atypical clinical symptoms,early diagnosis poses a certain challenge.Furthermore,it can lead to severe complications such as gastric bleeding,elevating the risk of adverse outcomes for solid tumor patients if immunotherapy is interrupted.Therefore,gaining a thorough understanding of the pathogenesis,clinical manifestations,diagnostic criteria,and treatment of immune-related gastritis is of utmost importance for early identification,diagnosis,and treatment.Additionally,the treatment of immune-related gastritis should be personalized according to the specific condition of each patient.For patients with grade 2-3 irAEs,restarting immune checkpoint inhibitors(ICIs)therapy may be considered when symptoms subside to grade 0-1.When restarting ICIs therapy,it is often recommended to use different types of ICIs.For grade 4 irAEs,permanent discontinuation of the medication is necessary.

Investigation of Projectile Impact Behaviors of Graphene Aerogel Using Molecular Dynamics Simulations

Graphene aerogel(GA),as a novel solid material,has shown great potential in engineering applications due to its unique mechanical properties.In this study,the mechanical performance of GA under high-velocity projectile impacts is thoroughly investigated using full-atomic molecular dynamics(MD)simulations.The study results show that the porous structure and density are key factors determining the mechanical response of GA under impact loading.Specifically,the impact-induced penetration of the projectile leads to the collapse of the pore structure,causing stretching and subsequent rupture of covalent bonds in graphene sheets.Moreover,the effects of temperature on the mechanical performance of GA have been proven to be minimal,thereby highlighting the mechanical stability of GA over a wide range of temperatures.Finally,the energy absorption density(EAD)and energy absorption efficiency(EAE)metrics are adopted to assess the energy absorption capacity of GA during projectile penetration.The research findings of this work demonstrate the significant potential of GA for energy absorption applications.

A Multi-AGV Routing Planning Method Based on Deep Reinforcement Learning and Recurrent Neural Network

Dear Editor,This letter presents a multi-automated guided vehicles(AGV) routing planning method based on deep reinforcement learning(DRL)and recurrent neural network(RNN), specifically utilizing proximal policy optimization(PPO) and long short-term memory(LSTM).

Carbon emission reduction: Contribution of geothermal energy and practice in China

As a kind of natural energy from the earth’s interior,geothermal energy is characterized by large reserve,wide distribution,good stability,high utilization coefficient,and positive effects of energy-saving and emission-reduction.It is of great significance for promoting green and low-carbon energy transition,reducing greenhouse gas emission,and achieving global climate goals and sustainable economic development.Hence,it has been highly recognized and valued by lots of countries around the world,and has become one of the most important clean energy sources that countries are accelerating to develop and utilize.The potential of the global geothermal energy resource is estimated to be 1.25×1027 J,equivalent to 4.27×10^(16) t of standard coal,among which the geothermal resource between 0 km and 5 km is 1.45×10^(26) J,equivalent to 4.95×1015 t of standard coal(China Geological Survey,2018).

Efficacy of scleral buckling for the treatment of rhegmatogenous retinal detachment using a novel foldable capsular buckle

●AIM:To evaluate the effectiveness and safety of scleral buckling for the treatment of rhegmatogenous retinal detachment(RRD)using a novel foldable capsular buckle(FCB).●METHODS:This was a series of case observation studies.Eighteen patients(18 eyes)who visited our ophthalmology department between August 2020 and August 2022 and were treated for RRD with scleral buckling using FCB were included.The procedure was similar to conventional scleral buckling,while a balloon-like FCB was placed onto the retinal break with balanced salt solution filling for a broad,external indentation instead of the silicone buckle.The retinal reattachment rate,best corrected visual acuity(BCVA),intraocular pressure(IOP),refractive dioptre and astigmatism degree,and complications were evaluated and recorded.●RESULTS:There were 7 males and 11 females aged 19-58y.The average time course of RRD was 12d,ranging from 7-20d.The retinal break was located in the superior quadrants in 8 eyes and in the inferior quadrants in 10 eyes,with macula-off detachments in 12 eyes.The patients were followed-up for at least 6mo.The final retinal reattachment rate was 100%.The BCVA was significantly improved compared with the baseline(P<0.05).There was no significant change in refractive dioptre or astigmatism degree at each follow-up(all P>0.05).Three patients had transiently high IOPs within one week after surgery.Mild diplopia occurred in 5 patients after surgery and then disappeared after the balloon fluid was removed.●CONCLUSION:The success rate of FCB scleral buckling for RRD is satisfactory.This procedure can be expected to be applied in new,uncomplicated cases of RRD.

Research on Quantitative Identification of Three-Dimensional Connectivity of Fractured-Vuggy Reservoirs

The fractured-vuggy carbonate oil resources in the western basin of China are extremely rich.The connectivity of carbonate reservoirs is complex,and there is still a lack of clear understanding of the development and topological structure of the pore space in fractured-vuggy reservoirs.Thus,effective prediction of fractured-vuggy reservoirs is difficult.In view of this,this work employs adaptive point cloud technology to reproduce the shape and capture the characteristics of a fractured-vuggy reservoir.To identify the complex connectivity among pores,fractures,and vugs,a simplified one-dimensional connectivity model is established by using the meshless connection element method(CEM).Considering that different types of connection units have different flow characteristics,a sequential coupling calculation method that can efficiently calculate reservoir pressure and saturation is developed.By automatic history matching,the dynamic production data is fitted in real-time,and the characteristic parameters of the connection unit are inverted.Simulation results show that the three-dimensional connectivity model of the fractured-vuggy reservoir built in this work is as close as 90%of the fine grid model,while the dynamic simulation efficiency is much higher with good accuracy.

Gastric cancer liver metastasis will reduce the efficacy of immunotherapy

Immune checkpoint inhibitors augment the antitumor activity of T cells by inhibiting the negative regulatory pathway of T cells,leading to notable efficacy in patients with non-small cell lung cancer,melanoma,and other malignancies through immunotherapy utilization.However,secondary malignant liver tumors not only lower the liver's sensitivity to immunotherapy but also trigger systemic immune suppression,resulting in reduced overall effectiveness of immune therapy.Patients receiving immunotherapy for non-small cell lung cancer and melanoma experience reduced response rates,progression-free survival,and overall survival when secondary malignant tumors develop in the liver.Through Liu's retrospective analysis,valuable insights are provided for the future clinical management of these patients.Therefore,in patients with gastric cancer(GC),the occurrence of liver metastasis might be indicative of reduced efficacy of immuno-therapy.Overcoming liver immune tolerance mechanisms and their negative impacts allows for the potential benefits of immunotherapy in patients with GC and liver metastasis.INTRODUCTION Gastric cancer(GC)ranks among the prevalent malignancies affecting the digestive system globally.Based on the latest epidemiological data[1,2],it holds the fifth position for incidence and the fourth position for mortality among all malignant tumors.GC cases and fatalities in China make up roughly half of the worldwide figures.Earlier investigations[3]have demonstrated that the median overall survival(mOS)among advanced GC patients left untreated typically ranges from 3 to 4 months.Systemic chemotherapy recipients often experience a mOS of around one year,accompanied by a marked improvement in the quality of life among patients with advanced GC.The mainstay of treatment for advanced GC patients involves chemotherapeutic medications such as fluoropyrimidines,platinum compounds,and taxanes.However,their efficacy in tumor control is constrained by acquired resistance and primary resistance.The rise of personalized precision therapy has propelled immunotherapy into the spotlight as a crucial component of comprehensive treatment[4].By blocking the negative regulatory pathways of T cells,immune checkpoint inhibitors(ICIs)boost the anti-tumor effect of T cells.Immunotherapy has brought about significant therapeutic benefits for patients diagnosed with non-small cell lung cancer,melanoma,and related illnesses[5,6],instilling newfound hope in those with advanced GC[7].However,phase III clinical trial data[8-12]reveals that the incorporation of immunotherapy into chemotherapy regimens improves overall survival(OS)outcomes for patients with advanced GC.The liver's immune-exempt nature renders it less responsive to immunotherapy when secondary malignant tumors are present,fostering systemic immune suppression and yielding unfavorable outcomes in immune therapy[13-15].In retrospective research[16-20]pertaining to non-small cell lung cancer and melanoma,it has been observed that the presence of secondary liver malignancies may lower the response rate,progression-free survival(PFS),and OS rates in patients treated with immunotherapy,independent of factors such as tumor mutation burden and PD-L1 expression.Despite this,there is a paucity of studies examining whether the existence of secondary malignant liver tumors affects the effectiveness of immunotherapy in patients diagnosed with advanced HER-2 negative GC.

头体配穴法埋线治疗心肾不交型失眠的临床研究

目的:观察头体配穴法埋线治疗心肾不交型失眠的临床效果。方法:以2021年4月-2022年4月梅州市第二中医医院康复科门诊收治的符合纳入标准的80例心肾不交型失眠患者为研究对象,并通过随机计数法分为治疗组和对照组。其中,治疗组采用头体配穴法埋线治疗,埋线穴位:心俞穴、肾俞穴、安眠穴、关元穴、太溪穴、百会穴、神庭穴,一周1次,共治疗8周;对照组选取同样的穴位进行针刺治疗,针刺治疗一周3次(星期一、星期三、星期五),共治疗8周。结果:(1)治疗组和对照组的性别、平均年龄和平均病程对比,差异没有显著意义(P>0.05);(2)治疗前两组患者的匹兹堡睡眠质量指数(Pittsburgh Sleep Quality Index,PSQI)评分和睡眠率差异不明显(P>0.05),治疗后两组患者的PSQI评分较治疗前均显著减低(P<0.05),相比对照组,治疗组患者治疗后的PSQI评分比治疗前极显著减低(P<0.01);治疗后两组患者的睡眠率较治疗前均显著升高(P<0.05),相比对照组,治疗组患者治疗后的睡眠率比治疗前极显著升高(P<0.01);(3)治疗组患者的有效率显著高于对照组(P<0.05)。结论:头体配穴法埋线治疗心肾不交型失眠具有显著的临床效果,相比针刺疗法,可以提高睡眠效率、改善睡眠质量,更好地改善患者的睡眠状况,值得临床广泛应用。

Effect of Electrolyte Disturbance on Prognosis of Patients with Traumatic Brain Injury

Objective:To investigate the prognostic value of electrolyte disturbances in patients with traumatic brain injury(TBI).Methods:Cases of TBI patients admitted to the Department of Neurosurgery at Dezhou Second People’s Hospital from September 2015 to September 2021 were analyzed to examine the impact of electrolyte disturbances on patient prognosis and to establish a risk prediction model.Results:Patients with electrolyte disturbances had poorer prognoses,with serum sodium and serum calcium levels significantly affecting the outcomes of patients with traumatic brain injury.Conclusion:Serum sodium and calcium levels may serve as potential prognostic markers in patients with traumatic brain injury.

Exponential Estimation of the Lyapunov Function for Delay-Coupled Neural Networks with Integral Terms

This paper investigates a class of coupled neural networks with delays and ad-dresses the exponential synchronization problem using delay-compensatory impulsive control. Razumikhin-type inequalities involving some destabilizing delayed impulse gains are proposed, along with a new delay-compensatory concept demonstrating two crucial roles in system stability. Based on the constructed inequalities and the introduced delay-compensatory concept, sufficient stability and synchronization criteria for globally exponential synchronization of coupled neural networks are provided. To address the exponential synchronization problem in coupled neural networks. Utilizing delay-compensatory impulsive control and Razumikhin-type inequalities. The Lyapunov function for coupled neural networks with delays and integral terms exhibits exponential estimates.

机构投资者合作如何促进公司创新?——基于基金网络社区结构的研究视角

“公司大股东话语权过强,机构投资者话语权不足”是阻碍单独机构投资者参与公司治理的突出问题,而机构投资者之间的合作行为能够有效地提升治理意愿、强化治理水平。本文首次从理论和实证上分析了机构投资者通过信息交流合作来强化公司治理的作用机制和经济效果。本文构造了一个序贯博弈模型均衡来刻画共同基金的行为机制,理论结果显示基金合作会形成具有社区分布特征的信息网络结构,处于同一社区中的关联配对基金会对持股公司形成合作治理关系,从而提升双方的治理意愿与治理效果。进而本文基于2007—2021年上市公司创新数据和基金持股数据进行了实证分析,结果显示基金在网络社区结构下的治理合作关系能够显著激励公司未来的创新活动。进一步的分析发现:第一,配对基金之间的社区合作关系呈现出独特的治理效应,这一效应不能被以往的网络信息度和抱团持股指标所解释,在考虑因果识别以及稳健性检验后结论依然成立;第二,本文在社区结构中识别了两类具体的基金合作行为,即“共同调研”和“同步交易”,两者分别代表机构投资者通过“用手投票”和“用脚投票”渠道的合作治理机制;第三,基金的主动监督意愿会影响合作治理的效果,有更高监督意愿的基金会更积极频繁地参与共同调研活动,对公司创新活动有更好的治理效果。本文研究有助于理解机构投资者治理机制、推进公司治理,并为资本市场高质量发展提供有益的政策启示。

空气过滤用驻极体纤维材料研究进展

驻极体纤维过滤材料是口罩、空气净化器、暖通空调系统过滤器等空气过滤产品的核心滤层材料,驻极纤维滤材可利用纤维与气溶胶颗粒间的静电力捕集气溶胶颗粒,表现出高效低阻过滤性能。文中介绍了驻极过滤材料的静电吸附机理、电荷表征方法,分析了驻极原料、驻极工艺和存放环境等影响驻极过滤材料电荷稳定性的因素,从构建复合膜结构、添加纳米颗粒两方面阐述了提升驻极材料带电能力和电荷稳定性的研究现状,最后提出了驻极体纤维过滤材料目前存在的问题及未来发展方向。