Adaptive Trajectory Tracking Control for Nonholonomic Wheeled Mobile Robots:A Barrier Function Sliding Mode Approach

The trajectory tracking control performance of nonholonomic wheeled mobile robots(NWMRs)is subject to nonholonomic constraints,system uncertainties,and external disturbances.This paper proposes a barrier function-based adaptive sliding mode control(BFASMC)method to provide high-precision,fast-response performance and robustness for NWMRs.Compared with the conventional adaptive sliding mode control,the proposed control strategy can guarantee that the sliding mode variables converge to a predefined neighborhood of origin with a predefined reaching time independent of the prior knowledge of the uncertainties and disturbances bounds.Another advantage of the proposed algorithm is that the control gains can be adaptively adjusted to follow the disturbances amplitudes thanks to the barrier function.The benefit is that the overestimation of control gain can be eliminated,resulting in chattering reduction.Moreover,a modified barrier function-like control gain is employed to prevent the input saturation problem due to the physical limit of the actuator.The stability analysis and comparative experiments demonstrate that the proposed BFASMC can ensure the prespecified convergence performance of the NWMR system output variables and strong robustness against uncertainties/disturbances.

Genome-wide identification and characterization of ACBP gene family in Populus reveal salinity alkali-responsive profiles

Acyl-CoA-binding proteins(ACBPs)are important for the transport of acyl groups for macro molecular biosynthesis involved in plant growth,development,and diverse stress(e.g.,cold,drought,salinity,and heavy metals)responses.Here,we report the phylogeny and characteristics of the ACBP family in the woody plant Populus trichocarpa.Eight genes encoding ACBP proteins were identified,and they are distributed on eight chromosomes in P.trichocarpa.These PtACBP genes were divided into four subgroups according to gene structure,conserved motifs and phylogenetic relationship.Promoter analysis revealed that cis-elements were related to stress response,phytohormone response,and physical and reproductive growth regulation.Expression levels of PtACBP genes varied among different organs,with the highest expression in leaves and the lowest in stems.Quantitative real-time PCR(qRT-PCR)analysis showed that under salinity-alkali stresses(i.e.,200 mM NaCl,75 mM Na2CO3,and 100 mM NaHCO3),four(PtACBP1,PtACBP3,PtACBP4 and PtACBP8)of eight PtACBP genes were significantly induced in roots and leaves.These data provide a comprehensive analysis of the ACBPs family in P.trichocarpa,which could be useful for gene function analyses.

Development of a Novel Extrusion Process for Preparing Rice Straw/LLDPE Composites

Straw utilization is a key issue related to agricultural production and air pollution control.In this study,a novel extrusion process was proposed to improve the physical and mechanical properties of the straw-reinforced linear low-density polyethylene(LLDPE)composite.Instead of crushing the straw and mixing it with plastic matrix,the new method mixes straw with plastic matrix in its original form.The intact long rice straws were parallelly spread on the LLDPE film and then rolled up together into a prefabricated roll.The rolls experienced three extrusion processes as follows:(1)twin-screw melting,cooling and crushing,single-screw extruding;(2)twin-screw melting and single-screw extruding;(3)directly single-screw extruding.The testing results showed that the straw/LLDPE composite(with a ratio of 6:4)prepared by Method(2)exhibited optimized properties.Characterization by scanning electron microscopy indicated that the damage to rice straw fibers was relatively minor,the orientation of long fibers was good,and the binding of fibers with the LLDPE matrix was excellent in this case.The results of dynamic mechanical testing(DMA),differential scanning calorimetry(DSC)and thermogravimetric(TG)analysis demonstrated that composites prepared by the new process exhibited significantly improved thermal stability and energy storage modulus,compared with those prepared by conventional processes(e.g.,extruded straw particles/LLDPE composite).The new proposed method yielded significantly enhanced mechanical properties while reducing dust pollution.

Net Present Value Method: A Method Recommended by ISO 15686-5 for Economic Evaluation of Building Life Cycle Costs

The publication of ISO 15686-5 is significant for studies related to the life-cycle costs of buildings. Among the many economic evaluation methods, the NPV method is recommended for use by this standard. This study explains the concept and method of PV, and then provides an explanation of the concept and method of NPV, and points out the limitations in the practical application of the method.

Surgical outcomes of mini-open Wiltse approach and conventional open approach in patients with single-segment thoracolumbar fractures without neurologic injury

This study aimed to introduce a novel mini-open pedicle screw fixation technique via Wiltse approach, and com- pared it with the traditional posterior open method. A total of 72 cases of single-segment thoracolumbar fractures without neurologic injury underwent pedicle screw fixation via two different approaches. Among them, 37 patients were treated using posterior open surgery, and 35 patients received mini-open operation via Wiltse approach. Crew placement accuracy rate, operative time, blood loss, postoperative drainage, postoperative hospitalization time, radiation exposure time, postoperative improvement in R value, Cobb＇s angle and visual analog scale （VAS） scores of the two methods were compared. There were no significant differences in the accuracy rate of pedicle screw placement, radiation exposure and postoperative R value and Cobb＇s angle improvement between the two groups. However, the mini-open method had obvious advantages over the conventional open method in operative time, blood loss, postoperative drainage, postoperative hospitalization time, and postoperative improvement in VAS. The mini-open pedicle screw technique could be applied in treatment of single-segment thoracolumbar fracture without neurologic injury and had advantages of less tissue trauma, short operative and rehabilitative time on the premise of guaranteed accuracy rate and no increased radiation exposure.

A new free-hand pedicle screw placement technique with reference to the supraspinal ligament

We sought to compare the safety and accuracy of a new free-hand pedicle screw placement technique to that of the conventional technique. One hundred fifty-three consecutive adult patients with simple fracture in the tho- racic or/and lumbar spine were alternately assigned to either the new free-hand or the conventional group. In the new free-hand technique group, preoperative computerized tomography （CT） images were used to calculate the targeted medial-lateral angle of each pedicle trajectory and the pedicle screw was inserted perpendicular to the corresponding supraspinal ligament. In the conventional technique group, the medial-lateral and cranial-caudal angle of each pedicle trajectory was determined by intraoperatively under fluoroscopic guidance. The accuracy rate of pedicle screw placement, the time of intraoperative fluoroscopy, the operating time and the amount of blood loss during operation were respectively compared. All screws were analyzed by using intraoperative ra- diographs, intraoperative triggered electromyography （EMG） monitoring data, postoperative CT data and clinical outcomes. The accuracy rate of pedicle screw placement in the new free-hand technique group and the conven- tional technique group was 96.3% and 94.2% （P 〈 0.05）, respectively. The intraoperative fluoroscopy time of the new technique group was less than that of the conventional technique group （5.37 seconds vs. 8.79 seconds, P 〈 0.05）. However, there was no statistical difference in the operating time and the amount of blood loss during op- eration （P 〉 0.05）. Pedicle screw placement with the free-hand technique which keeps the screw perpendicular to the supraspinal ligament is an accurate, reliable and safe technique to treat simple fracture in the thoracic or lum- bar spine.

Rapid identification of spinal ventral and dorsal roots using a quartz crystal microbalance

The fast and accurate identification of nerve tracts is critical for successful nerve anastomosis. Taking advantage of differences in acetylcholinesterase content between the spinal ventral and dorsal roots, we developed a novel quartz crystal microbalance method to distinguish between these nerves based on acetylcholinesterase antibody reactivity. The acetylcholinesterase antibody was immobilized on the electrode surface of a quartz crystal microbalance and reacted with the acetylcholinesterase in sample solution. The formed antigen and antibody complexes added to the mass of the electrode inducing a change in frequency of the electrode. The spinal ventral and dorsal roots were distinguished by the change in frequency. The ventral and dorsal roots were cut into 1 to 2-mm long segments and then soaked in 250 pL PBS. Acetylcholinesterase antibody was immobilized on the quartz crystal microbalance gold electrode surface. The results revealed that in 10 minutes, both spinal ventral and dorsal roots induced a frequency change; however, the frequency change induced by the ventral roots was notably higher than that induced by the dorsal roots. No change was induced by bovine serum albumin or PBS. These results clearly demonstrate that a quartz crystal microbalance sensor can be used as a rapid, highly sensitive and accurate detection tool for the quick identification of spinal nerve roots intraoperatively.

A New Encryption-Then-Compression Scheme on Gray Images Using the Markov Random Field

Compressing encrypted images remains a challenge.As illustrated in our previous work on compression of encrypted binary images,it is preferable to exploit statistical characteristics at the receiver.Through this line,we characterize statistical correlations between adjacent bitplanes of a gray image with the Markov random field(MRF),represent it with a factor graph,and integrate the constructed MRF factor graph in that for binary image reconstruction,which gives rise to a joint factor graph for gray images reconstruction(JFGIR).By exploiting the JFGIR at the receiver to facilitate the reconstruction of the original bitplanes and deriving theoretically the sum-product algorithm(SPA)adapted to the JFGIR,a novel MRF-based encryption-then-compression(ETC)scheme is thus proposed.After preferable universal parameters of the MRF between adjacent bitplanes are sought via a numerical manner,extensive experimental simulations are then carried out to show that the proposed scheme successfully compresses the first 3 and 4 most significant bitplanes(MSBs)for most test gray images and the others with a large portion of smooth area,respectively.Thus,the proposed scheme achieves significant improvement against the state-of-the-art leveraging the 2-D Markov source model at the receiver and is comparable or somewhat inferior to that using the resolution-progressive strategy in recovery.

Validation of American Joint Committee on Cancer 8th edition of TNM staging in resected distal pancreatic cancer

BACKGROUND In order to improve risk stratification and clinical management of the pancreatic ductal adenocarcinoma(PDAC),the American Joint Committee on Cancer(AJCC)has published its eighth edition staging manual.Some major changes have been introduced in the new staging system for both T and N categories.Given the rarity of resectable disease,distal pancreatic cancer is likely underrepresented in the published clinical studies,and how the impact of the staging system actually reflects on to clinical outcomes remain unclear.AIM To validate the AJCC 8th edition of TNM staging in distal PDAC.METHODS A retrospective cohort study was performed in seven academic medical centers in the United States.Clinicopathological prognostic factors associated with progression-free survival(PFS)and overall survival(OS)were evaluated through univariate and multivariate analyses.RESULTS Overall,454 patients were enrolled in the study,and were divided into 2 subgroups:Invasive intraductal papillary mucinous neoplasms(IPMN)(115 cases)and non-IPMN associated adenocarcinoma(339 cases).Compared to invasive IPMN,non-IPMN associated adenocarcinomas are more common in relatively younger patients,have larger tumor size,are more likely to have positive lymph nodes,and are associated with a higher tumor(T)stage and nodal(N)stage,lymphovascular invasion,perineural invasion,tumor recurrence,and a worse PFS and OS.The cohort was predominantly categorized as stage 3 per AJCC 7th edition staging manual,and it’s more evenly distributed based on 8th edition staging manual.T and N staging of both 7th and 8th edition sufficiently stratify PFS and OS in the entire cohort,although dividing into N1 and N2 according to the 8th edition does not show additional stratification.For PDAC arising in IPMN,T staging of the 7th edition and N1/N2 staging of the 8th edition appear to further stratify PFS and OS.For PDAC without an IPMN component,T staging from both versions fails to stratify PFS and OS.CONCLUSION The AJCC 8th edition TNM staging system provides even distribution for the T staging,however,it does not provide better risk stratification than previous staging system for distal pancreatic cancer.

Pesticides Could Alleviate the Symptoms of Sweet Potato Virus Disease(SPVD)

In recent years, sweet potato virus disease （SPVD） has severely affected the production of sweet potato in China. In order to select chemical agents to prevent sweet potato from being infected with SPVD, 14 pesticides were sprayed on the plants of sweet potato infected with SPVD, and the relative mRNA level of the viruses in the leaves and physiological indicators of sweet potato plants were detected. The results showed that after the application of most of the pesticides, the relative mRNA level of the two viruses that caused SPVD decreased, and the chlorophyll content and biomass of sweet potato infected with SPVD increased significantly or extremely significantly. Among the pesticides, BASF virus liquid, 0.1% physcion and Aolike powder for cucumber virus were proved to be the best, as the chlorophyll content and stem length of sweet potato increased significantly. The experiment indicated that the pesticides could reduce the harm of SPVD to sweet potato.

大熊猫(Ailuropoda melanoleuca)miRNA研究进展

MicroRNA(miRNA)是一类广泛存在于真核生物、长约22 nt的内源性非编码RNA。miRNA通过与靶基因mRNA特异性结合影响基因的表达,进而参与调控多种生物学过程。大熊猫(Ailuropoda melanoleuca)是我国特有的珍稀动物,备受全世界的关注。近年来,随着二代测序技术(next-generation sequencing,NGS)的普及,大熊猫miRNA陆续被发现和鉴定。本文综述了miRNA在大熊猫免疫反应、乳腺发育、精子冷冻耐受及其他生物学过程的研究进展,并探讨了大熊猫miRNA的研究前景,以期为深入研究大熊猫miRNA的调控机制和促进大熊猫繁育与保护工作提供科学参考和新思路。

Robust resource allocation for NOMA-assisted heterogeneous networks

As a promising technology to improve spectrum efficiency and transmission coverage,Heterogeneous Network(HetNet)has attracted the attention of many scholars in recent years.Additionally,with the introduction of the Non-Orthogonal Multiple Access(NOMA)technology,the NOMA-assisted HetNet cannot only improve the system capacity but also allow more users to utilize the same frequency band resource,which makes the NOMA-assisted HetNet a hot topic.However,traditional resource allocation schemes assume that base stations can exactly estimate direct link gains and cross-tier link gains,which is impractical for practical HetNets due to the impact of channel delays and random perturbation.To further improve energy utilization and system robustness,in this paper,we investigate a robust resource allocation problem to maximize the total Energy Efficiency(EE)of Small-Cell Users(SCUs)in NOMA-assisted HetNets under imperfect channel state information.By considering bounded channel uncertainties,the robust resource optimization problem is formulated as a mixed-integer and nonlinear programming problem under the constraints of the cross-tier interference power of macrocell users,the maximum transmit power of small base station,the Resource Block(RB)assignment,and the quality of service requirement of each SCU.The original problem is converted into an equivalent convex optimization problem by using Dinkelbach's method and the successive convex approximation method.A robust Dinkelbach-based iteration algorithm is designed by jointly optimizing the transmit power and the RB allocation.Simulation results verify that the proposed algorithm has better EE and robustness than the existing algorithms.

Relations among Main Operating Parameters of Gasifier in IGCC

Gasification unit is one of the key subsystems in the IGCC power system;the operating parameters of gasifier directly affect syngas quality and performance of whole IGCC system. The system model of gasification unit with coal water slurry gasifier was simulated and calculated using THERMOFLEX software, and the relations of oxygen coal ratio (Roc), water coal ratio (Rsc), gasification pressure, gasification temperature and cold gas efficiency were mostly researched. The results show that Roc and Rsc have effect of mutual restriction on gasification temperature, cold gas efficiency and syngas composition. Gasification pressure mainly determines the capacity of the gasifier, little effects on syngas composition.

Precise trajectory tracking of mecanum-wheeled omnidirectional mobile robots via a novel fixed-time sliding mode control approach

This paper proposes a novel fixed-time sliding mode control approach for trajectory-tracking tasks of a mecanum-wheeled omnidirectional mobile robot.First,the idea of two-phase attractors is introduced into the domain of sliding mode control,and a new fixed-time sliding surface is proposed.Then,according to this sliding surface,a new type of nonsingular fast terminal sliding mode control algorithm is designed for the omnidirectional mobile robot,which can realize a fast fixed-time convergence property.The stability of the control system is proven scrupulously,and a guideline for control-parameter tuning is expounded.Finally,experiments are implemented to test the trajectory-tracking performance of the robot.Experimental results demonstrate the superiority of the proposed sliding surface and the corresponding control scheme in comparison with benchmark controllers.

新时期高校网络教育治理体系的结构与关键制度

新时期高校网络教育改革面临新挑战,需要构建新的治理结构、搭建新的制度环境以提供支撑。本研究基于新时期高校网络教育双轮驱动的新定位,依据教育治理现代化的基本方向、互联网时代教育的基本规律、服务全民终身学习的根本目标,尝试构建了新时期高校网络教育治理的基本结构,即政府主导、学校自治以及行业企业和社会第三方等多元主体参与的治理结构,并进一步明晰了治理结构调整的三项主要任务。根据"结构+制度"作为完善治理体系的建设内容,提出新时期高校网络教育治理所需的关键性制度,即质量保证制度、资历框架制度、学习成果认证制度和学分银行制度。文章期望提升新时期高校网络教育的治理能力,为"十四五"时期高校网络教育高质量发展提供参考。

高校网络教育质量保证分析框架与动力机制研究

高校开展网络教育质量保证是确保教育教学质量、提升办学声誉的关键措施。关于高校网络教育质量保证体系应该涵盖的维度和要点以及现存问题形成原因的系统研究相对欠缺,且高校内部也没有形成完善的质量保证体系,导致高校网络教育质量保证水平参差不齐。本研究采用文献分析、访谈和文本分析方法,从业务质量实施、内部质量控制和外部质量评估、组织架构以及层级安排四个维度构建高校网络教育质量保证分析框架,总结出高校网络教育质量保证的三种形态(被动保守型、稳步推进型和主动进取型)及其发展规律。从驱动高校开展网络教育质量保证的内外因素角度,提出了由内驱力(领导质量意识)、拉力(政策引导、行业氛围和学生需求)和压力(生存发展压力)构成的高校网络教育质量保证动力机制,该动力机制能够很好地解释高校网络教育质量保证形态和发展规律形成的原因。最后,针对目前高校网络教育质量保证给出改进建议。研究有助于进一步完善远程教育质量保证相关理论,并为实践者以及各级教育行政部门构建完善的高校网络教育质量保证体系提供参考。

残疾人群体终身学习现状的实证研究

2019年第四届全球学习型城市大会将全纳作为建设终身学习和可持续发展城市的基本原则。残疾人群体是弱势群体的典型代表,是建设学习型城市、贯彻全纳原则应首要关注的群体。互联网技术的发展为残疾人群体参与终身学习提供了新的契机。本研究采用问卷调查法,以北京市794名残疾人为样本,对成年残疾人群体终身学习和继续教育现状进行了调查。研究发现:(1)残疾人群体对终身学习的认可度较高,但认识程度有待提升;(2)残疾人群体终身学习动机以身心发展为主;(3)残疾人群体终身学习方式和内容趋于多样化,但仍以传统的学习形式为主;(4)残疾人群体应用信息技术工具的熟练程度相对较低,时间、课程和学费问题凸显;(5)残疾人群体的终身学习受到身体性因素和发展性因素的影响。基于上述研究结果,进一步提出促进残疾人群体参与终身学习的建议。

Mirror-enhanced super-resolution microscopy

Axial excitation confinement beyond the diffraction limit is crucial to the development of next-generation,super-resolution microscopy.STimulated Emission Depletion(STED)nanoscopy offers lateral super-resolution using a donut-beam depletion,but its axial resolution is still over 500 nm.Total internal reflection fluorescence microscopy is widely used for single-molecule localization,but its ability to detect molecules is limited to within the evanescent field of~100 nm from the cell attachment surface.We find here that the axial thickness of the point spread function(PSF)during confocal excitation can be easily improved to 110 nm by replacing the microscopy slide with a mirror.The interference of the local electromagnetic field confined the confocal PSF to a 110-nm spot axially,which enables axial super-resolution with all laser-scanning microscopes.Axial sectioning can be obtained with wavelength modulation or by controlling the spacer between the mirror and the specimen.With no additional complexity,the mirror-assisted excitation confinement enhanced the axial resolution six-fold and the lateral resolution two-fold for STED,which together achieved 19-nm resolution to resolve the inner rim of a nuclear pore complex and to discriminate the contents of 120 nm viral filaments.The ability to increase the lateral resolution and decrease the thickness of an axial section using mirror-enhanced STED without increasing the laser power is of great importance for imaging biological specimens,which cannot tolerate high laser power.

Binding between Prion Protein and Aβ Oligomers Contributes to the Pathogenesis of Alzheimer’s Disease

A plethora of evidence suggests that protein misfolding and aggregation are underlying mechanisms of various neurodegenerative diseases,such as prion diseases and Alzheimer's disease(AD).Like prion diseases,AD has been considered as an infectious disease in the past decades as it shows strain specificity and transmission potential.Although it remains elusive how protein aggregation leads to AD,it is becoming clear that cellular prion protein(PrP^c)plays an important role in AD pathogenesis.Here,we briefly reviewed AD pathogenesis and focused on recent progresses how PrP^c contributed to AD development.In addition,we proposed a potential mechanism to explain why infectious agents,such as viruses,conduce AD pathogenesis.Microbe infections cause AD deposition and upregulation of PrP^c,which lead to high affinity binding between AD oligomers and PrP^c.The interaction between PrP^c and AP oligomers in turn activates the Fyn signaling cascade,resulting in neuron death in the central nervous system(CNS).Thus,silencing PrP^c expression may turn out be an effective treatment for PrP^c dependent AD.

Computational methods in super-resolution microscopy

The broad applicability of super-resolution microscopy has been widely demonstrated in various areas and disciplines. The optimization and improvement of algorithms used in super-resolution microscopy are of great importance for achieving optimal quality of super-resolution imaging. In this review, we comprehensively discuss the computational methods in different types of super-resolution microscopy, including deconvolution microscopy, polarization-based super-resolution microscopy, structured illumination microscopy, image scanning microscopy, super-resolution optical fluctuation imaging microscopy, single-molecule localization microscopy, Bayesian super-resolution microscopy, stimulated emission depletion microscopy, and translation microscopy. The development of novel computational methods would greatly benefit super-resolution microscopy and lead to better resolution, improved accuracy, and faster image processing.