厉以宁先生追思会暨厉以宁学术思想研讨会——经济学思想理论创新和实践探索

2023年2月27日,“改革先锋”奖章获得者、经济体制改革的积极倡导者、著名经济学家、杰出的教育家、北京大学哲学社会科学资深教授、光华管理学院创始院长厉以宁先生因病在北京逝世,享年92岁。

A phylogenetic approach identifies patterns of beta diversity and floristic subregions of the Qinghai-Tibet Plateau

Patterns of taxonomic and phylogenetic beta diversity and their relationships with environmental correlates can help reveal the origin and evolutionary history of regional biota.The Qinghai-Tibet Plateau(QTP)harbors an exceptionally diverse flora,however,a phylogenetic perspective has rarely been used to investigate its beta diversity and floristic regions.In this study,we used a phylogenetic approach to identify patterns of beta diversity and quantitatively delimit floristic regions on the Qinghai-Tibet Plateau.We also examined the relationships between multifaceted beta diversity,geographical distance,and climatic difference,and evaluated the relative importance of various factors(i.e.,climate,topography and history)in shaping patterns of beta diversity.Sørensen dissimilarity indices indicated that patterns of species turnover among sites dominated the QTP.We also found that patterns of both taxonomic and phylogenetic beta diversity were significantly related to geographical distance and climatic difference.The environmental factors that contributed most to these patterns of beta diversity include annual precipitation,mean annual temperature,climatic gradients and climatic instability.Hierarchical dendrograms of dissimilarity and non-metric multidimensional scaling ordination based on phylogenetic beta diversity data identified ten floristic subregions in the QTP.Our results suggest that the contemporary environment and historical climate changes have filtered species composition among sites and eventually determined beta diversity patterns of plants in the QTP.

Simulation of transport mechanism of radium isotopes in aquifer on the southern coast of Laizhou Bay

Naturally occurring radium(^(223)Ra,^(224)Ra,^(226)Ra,and^(228)Ra)isotopes have been widely applied as geochemical tracers in marine environments,especially when estimating the submarine groundwater discharge(SGD).In this sense,the influencing factors and transport mechanism of radium isotope activity in aquifers can be key information for SGD estimation.This work evaluates the adsorption/desorption behavior of^(224)Ra and^(226)Ra in the solid-liquid phase through a leaching experiment and analysis of field data.The results suggested that radium isotope activity was positively correlated with salinity and grain size,in the case of abundant sediments.Through ion analysis,we found that the ions(Na^(+),Ca^(2+),Mg^(2+),and Ba^(2+))exchanged with radium isotopes in the process of transport.A 1-D reactive transport model was established to simulate the transport process of radium isotope in aquifers.The model successfully simulated the variation of radium isotope desorption activity with salinity and was subsequently verified in the field.This study contributes to the understanding of the geochemical behavior of radium isotopes in aquifers and provides guidance for selecting a suitable groundwater endmember in SGD estimation.

Distribution of platelet-derived growth factor-alpha receptor expressing oligodendrocyte precursor cells in the adult rat brain

BACKGROUND： Studies have demonstrated that NG2-positive glial cells in the adult rats are predominantly located in the gray and white matter of the cerebral cortex and hippocampus. Platelet-derived growth factor-a receptor （PDGF-αR） cells are a subset of oligodendrocytes, which are not as mature as NG2-positive cells. Distribution and migration of PDGF-αR-positive cells in the rat brain remain poorly understood. OBJECTIVE： Using immunohistochemical methods, the distribution of oligodendrocyte precursor cells （PDGF-αR-positive） was analyzed in the adult rat brain. DESIGN, TIME AND SETTING： Immunohistochemical study was performed at the Department of Histology and Embryology of the Third Military Medical University from September 2007 to September 2008. MATERIALS： Rabbit anti-PDGF-αR polyclonal antibody was purchased from Santa Cruz Biotechnology, USA. Streptomycin-avidin-biotin complex immunohistochemistry kit was purchased from Zhongshan Goldenbridge Biotechnology, China. METHODS： Whole brains from 5 healthy, adult, Wistar rats were collected for immunohistochemistry, and the mean value of PDGF-αR-expressing cells was quantified. The absolute values were translated to ranked data of high, moderate, and low grades （high grade： 10 positive cells; moderate grade： 5-9 cells; low grade： 〈 5 cells in a 400 × visual field）. Based on the number of cell processes and branches, as well as the number of PDGF-αR-positive cells, in different regions, the cells were classified into three categories, i.e., type Ⅰ-Ⅲ. From type I to type Ill, the number of processes gradually increased. MAIN OUTCOME MEARSURES： The number and distribution of PDGF-αR-positive cells in different brain regions of adult rats. RESULTS： PDGF-αR-positive cells were located in the forebrain and midbrain, but not in the cerebellum or brainstem. In the olfactory bulb and hippocampus, a total of 60% PDGF-αR-positive cells were type Ⅰ and these cells were not mature as others. In the cerebral cortex, olfactory system, hippocampus, and optic chiasma, where neuronal bodies aggregated, approximately 40% of the PDGF-αR-positive cells were type Ⅱ, with few type Ⅲ cells. In the white matter, corpus callosum, basal nucleus, and thalamus, PDGF-αR-positive cell density was moderate. In the olfactory bulb and hippocampus, PDGF-αR-positive cell density was high. PDGF-αR-positive cells were not observed in the cerebellum or brainstem CONCLUSION： PDGF-αR-positive cells were aggregated in the olfactory bulb and hippocampus in the adult, rat brain, but few cells were detected in the cerebellum and brainstem.

Comparative Proteomic Analysis of Cucumber Fruits Under Nitrogen Deficiency At the Fruiting Stage

Nitrogen deficiency is a major factor that affects the yield and quality of horticultural crops.Differentially expressed proteins were identified in cucumber fruit under nitrogen deficiency treatment,and are expected to be highly useful for dissecting carbon,nitrogen and ascorbate metabolism in cucumber and for improving nitrogen fertilizer utilization.Cucumber plants grown hydroponically in Hoagland solution were transferred to nitrogen-free conditions for 3 or 5 d after the blossom of female flowers.Fruit proteome profiles were assessed using twodimensional electrophoresis.The relative expression of the genes encoding 50 selected differentially expressed proteins and 4 key enzymes in carbon metabolism was analyzed by qRT-PCR.Resulted showed that most of the identified differentially expressed proteins were mainly associated with carbon metabolism,amino acid biosynthesis,ascorbate metabolism,and proteasomes.Glucose phosphorylation was enhanced,while the pentose phosphate pathway was inhibited.Carbon metabolism and the synthesis of most amino acids was affected significantly,and ascorbate might be accumulated under nitrogen deficiency in cucumber fruit.

多层级手性结构生物丝束力学性能的理论模拟

高度有序的多层级手性结构赋予肌腱、韧带和植物卷须等生物丝束优异的力学性能.然而,多层级手性结构如何影响丝束的力学性能尚不清楚.本文建立了具有自相似多层级手性结构的生物丝束的理论模型.基于此模型,研究了丝束载荷传递机制、材料手性和手性组装形式及结构层级数对生物丝束的模量、刚度等力学性能的影响.结果表明,丝束的力学性能显著依赖于纤维的材料手性和多层级手性结构.材料手性可以使纤维更加柔软,多层级手性结构使丝束能够承受大的拉伸变形.此工作不仅加深了对生物丝束结构-性能关系的理解,还有助于人造肌肉和柔性致动器、传感器等的设计.

Spectrum structure and decay rate estimates on the Landau equation with Coulomb potential

In this paper we first deduce the estimates on the linearized Landau operator with Coulomb potential and then analyze its spectrum structure by using semigroup theory and linear operator perturbation theory.Based on these estimates,we give the precise time decay rate estimates on the semigroup generated by the linearized Landau operator so that the optimal time decay rates of the nonlinear Landau equation follow.In addition,we present a similar result for the non-angular cutoff Boltzmann equation with soft potentials.

NUMERICAL SIMULATION OF CRACK GROWTH IN BRITTLE MATRIX OF PARTICLE REINFORCED COMPOSITES USING THE XFEM TECHNIQUE

Crack growth in particle reinforced composites is significantly influenced by the character of the reinforcement particles.To accurately deal with such problems,the extended finite element method （XFEM） was employed and improved.The simulations are accomplished by using a new domain expression of an interaction integral for evaluating stress intensity factors （SIFs）,and by adopting the maximum hoop stress criterion for crack-growth direction prediction.Crack deflection/attraction mechanisms and their associated energy release rate variations are investigated.It is shown that the applied numerical method allows a considerable flexibility and can be used in more general situations.The crack-tip shielding and amplifying behaviors are clearly observed.

手性失配细长丝的拉伸行为

手性细长丝在人工和生物材料中普遍存在.由于具有手性微结构,手性丝通常表现出优异的弹性和拉伸-扭转耦合变形等性能.然而,手性微结构如何影响细长丝的弹性行为尚不清楚.本文提出了一种考虑手性微结构和手性失配的精细弹性细杆模型.基于此模型,研究了单股螺旋和双股螺旋等手性丝组装结构在拉伸过程中的力-位移关系和结构手性变化.结果表明,手性失配会导致明显的弯曲-扭转耦合变形,使杆在拉伸时柔性更大.手性长丝在拉伸时还表现出类似DNA的反常扭转行为,可用结构手性的非线性变化来解释.该研究表明手性失配可用于调控手性丝的性能,有助于柔性执行器和软机器等柔性器件的设计.

Steady formation analysis onmulti-robot systems

In this paper,a controller is designed for a group of cooperative robots to achieve the stable displacements.Communication network among the robots is assumed unavailable and each robot can only measure the displacements relative to their neighbours.The controller will enable the robots to move to a predefined formation or a special formation under a suitable protocol which we will design.We will discuss the effect of different sizes of the multi-vehicle system and conduct simulations to verify the effectiveness of the proposed controller and the formation protocols.