COMPLETE KAHLER METRICS WITH POSITIVE HOLOMORPHIC SECTIONAL CURVATURES ON CERTAIN LINE BUNDLES(RELATED TO A COHOMOGENEITY ONE POINT OF VIEW ON A YAU CONJECTURE)

In this article,we study Kahler metrics on a certain line bundle over some compact Kahler manifolds to find complete Kahler metrics with positive holomorphic sectional(or bisectional)curvatures.Thus,we apply a strategy to a famous Yau conjecture with a co-homogeneity one geometry.

Direct scaling of residual displacements for bilinear and pinching oscillators

The estimation of residual displacements in a structure due to an anticipated earthquake event has increasingly become an important component of performance-based earthquake engineering because controlling these displacements plays an important role in ensuring cost-feasible or cost-effective repairs in a damaged structure after the event.An attempt is made in this study to obtain statistical estimates of constant-ductility residual displacement spectra for bilinear and pinching oscillators with 5%initial damping,directly in terms of easily available seismological,site,and model parameters.None of the available models for the bilinear and pinching oscillators are useful when design spectra for a seismic hazard at a site are not available.The statistical estimates of a residual displacement spectrum are proposed in terms of earthquake magnitude,epicentral distance,site geology parameter,and three model parameters for a given set of ductility demand and a hysteretic energy capacity coefficient in the case of bilinear and pinching models,as well as for a given set of pinching parameters for displacement and strength at the breakpoint in the case of pinching model alone.The proposed scaling model is applicable to horizontal ground motions in the western U.S.for earthquake magnitudes less than 7 or epicentral distances greater than 20 km.

THE LOGARITHMIC SOBOLEV INEQUALITY FOR A SUBMANIFOLD IN MANIFOLDS WITH ASYMPTOTICALLY NONNEGATIVE SECTIONAL CURVATURE

In this note,we prove a logarithmic Sobolev inequality which holds for compact submanifolds without a boundary in manifolds with asymptotically nonnegative sectional curvature.Like the Michale-Simon Sobolev inequality,this inequality contains a term involving the mean curvature.

Distribution and correlation of refractive parameters in children with different corneal curvatures in southeast China

AIM:To analyze the distribution of refractive status in school-age children with different corneal curvatures(CC)and the correlation between CC and refractive status.METHODS:A total of 2214 school-aged children of grade 4 in Hangzhou who were screened for school myopia were included.Uncorrected distance visual acuity(UCDVA),non-cycloplegic refraction,axial length(AL),horizontal and vertical corneal curvature(K1,K2)were measured and spherical equivalent(SE),corneal curvature radius(CCR)and axial length/corneal radius of curvature ratio(AL/CR)were calculated.UCDVA<5.0 and SE≤-0.50 D were classified as school-screening myopia.According to the different CCRs,the patients were divided into the lower corneal curvature(LCC)group(CCR≥7.92)and the higher corneal curvature(HCC)group(CCR<7.92).Each group was further divided into the normal AL subgroup and the long AL subgroup.The refractive parameters were compared to identify any differences between the two groups.RESULTS:Both SE and AL were greater in the LCC group(P=0.013,P<0.001).The prevalence of myopia was 38% in the LCC group and 44% in the HCC group(P<0.001).The proportion of children without screening myopia was higher in the LCC group(62%)than in the HCC group(56%).Among these children without screening myopia,the proportion of long AL in the LCC group(24%)was significantly higher than that in the HCC group(0.012%;P<0.001).The change of SE in the LCC group was less affected by the increase of AL than that in the HCC group.CONCLUSION:School-aged children in the LCC group have a lower incidence of screening myopia and longer AL.Low CC can mask SE reduction and AL growth to some extent,and the change of AL growth change more in children with low CC than high CC.Before the onset of myopia,its growth rate is even faster than that after the onset of myopia.

拟常曲率黎曼流形中极小子流形的Pinching定理

讨论了局部对称拟常曲率黎曼流形N^(n+p)中的紧致极小子流形M^(n),在ξ∈Γ(TM)时,得到了第二基本形式模长平方的Pinching常数,推广了定理A。

A DIFFERENTIABLE SPHERE THEOREM WITH PINCHING INTEGRAL RICCI CURVATURE

In this article, we introduce the Hausdorff convergence to derive a differentiable sphere theorem which shows an interesting rigidity phenomenon on some kind of manifolds.

The Pinching Theorem of Global Umbilic Submanifolds in a Riemannian Manifold with Quasi Constant Curvature

We study the global umbilic submanifolds with parallel mean curvature vector fields in a Riemannian manifold with quasi constant curvature and get a local pinching theorem about the length of the second fundamental form.

RANDERS SPACES WITH SCALAR FLAG CURVATURE

Let(M, F) be an n-dimensional Randers space with scalar flag curvature. In this paper, we will introduce the definition of a weak Einstein manifold. We can prove that if(M, F) is a weak Einstein manifold, then the flag curvature is constant.

A CLASS OF INVERSE QUOTIENT CURVATURE FLOW IN THE ADS-SCHWARZSCHILD MANIFOLD

In this paper,we study the asymptotic behavior of a class of inverse quotient curvature flow in the anti-de Sitter-Schwarzschild manifold.We prove that under suitable convex conditions for the initial hypersurface,one can get the long-time existence for the inverse curvature flow.Moreover,we also get that the principal curvatures of the evolving hypersurface converge to 1 when t→+∞.

Microcurvature landscapes induce neural stem cell polarity and enhance neural differentiation

Tissue curvature has long been recognized as an important anatomical parameter that affects intracellular behaviors,and there is emerging interest in applying cell-scale curvature as a designer property to drive cell fates for tissue engineering purposes.Although neural cells are known to undergo dramatic and terminal morphological changes during development and curvature-limiting behaviors have been demonstrated in neurite outgrowth studies,there are still crucial gaps in understanding neural cell behaviors,particularly in the context of a three-dimensional(3D)curvature landscape similar to an actual tissue engineering scaffold.In this study,we fabricated two substrates of microcurvature(curvature-substrates)that present a smooth and repeating landscape with focuses of either a concave or a convex pattern.Using these curvature-substrates,we studied the properties of morphological differentiation in N2a neuroblastoma cells.In contrast to other studies where two-dimensional(2D)curvature was demonstrated to limit neurite outgrowth,we found that both the concave and convex substrates acted as continuous and uniform mechanical protrusions that significantly enhanced neural polarity and differentiation with few morphological changes in the main cell body.This enhanced differentiation was manifested in various properties,including increased neurite length,increased nuclear displacement,and upregulation of various neural markers.By demonstrating how the micron-scale curvature landscape induces neuronal polarity,we provide further insights into the design of biomaterials utilizing the influence of surface curvature in neural tissue engineering.

Variable Curvature Modeling Method of Soft Continuum Robots with Constraints

The inherent compliance of continuum robots holds great promise in the fields of soft manipulation and safe human–robot interaction.This compliance reduces the risk of damage to the manipulated object and its surroundings.However,continuum robots possess theoretically infinite degrees of freedom,and this high flexibility usually leads to complex deformations when subjected to external forces and positional constraints.Describing these complex deformations is the main challenge in modeling continuum robots.In this study,we investigated a novel variable curvature modeling method for continuum robots,considering external forces and positional constraints.The robot configuration curve is described using the developed mechanical model,and then the robot is fitted to the curve.A ten-section continuum robot prototype with a length of 1 m was developed in order to validate the model.The feasibility and accuracy of the model were verified by the ability of the robot to reach target points and track complex trajectories with a load.This work was able to serve as a new perspective for the design analysis and motion control of continuum robots.

Trimmable bandgap reference circuit with exponential curvature compensation

This paper proposes an improved exponential curvature-compensated bandgap reference circuit to exploit the exponential relationship between the current gainβof the bipolar junction transistor(BJT)and the temperature as well as reduce the influence of resistance-temperature dependency.Considering the degraded circuit performance caused by the process deviation,the trimmable module of the temperature coefficient(TC)is introduced to improve the circuit stability.The circuit has the advantages of simple structure,high linear stability,high TC accuracy,and trimmable TC.It consumes an area of 0.09 mm^(2)when fabricated by using the 0.25-μm complementary metal-oxide-semiconductor(CMOS)process.The proposed circuit achieves the simulated power supply rejection(PSR)of about-78.7 dB@1 kHz,the measured TC of~4.7 ppm/℃over a wide temperature range from-55℃to 125℃with the 2.5-V single-supply voltage,and the tested line regulation of 0.10 mV/V.Such a high-performance bandgap reference circuit can be widely applied in high-precision and high-reliability electronic systems.

Numerical simulation of a truncated cladding negative curvature fiber sensor based on the surface plasmon resonance effect

A refractive index(RI)sensor based on the surface plasmon resonance effect is proposed using a truncated cladding negative curvature fiber(TC-NCF).The influences of the TC-NCF structure parameters on the sensing performances are investigated and compared with the traditional NCF.The simulation results show that the proposed TC-NCF RI sensor has an ultra-wide detection range from 1.16 to 1.43.The maximum wavelength sensitivity reaches 12400 nm/RIU,and the corresponding R^(2)of the polynomial fitting equation is 0.9999.The maximum and minimum resolutions are 2.56×10^(-5)and 8.06×10^(-6),respectively.In addition,the maximum amplitude sensitivity can reach-379.1 RIU^(-1)when the RI is chosen as 1.43.The proposed TC-NCF RI sensor could be useful in biochemical medicine,environmental monitoring,and food safety.

GLOBAL RIGIDITY THEOREMS FOR SUBMANIFOLDS WITH PARALLEL MEAN CURVATURE

In this paper,we mainly study the global rigidity theorem of Riemannian submanifolds in space forms.Let Mn(n≥3)be a complete minimal submanifold in the unit sphere Sn+p(1).Forλ∈[0,n2−1/p),there is an explicit positive constant C(n,p,λ),depending only on n,p,λ,such that,if∫MSn/2dM<∞,∫M(S−λ)n/2+dM<C(n,p,λ),then Mn is a totally geodetic sphere,where S denotes the square of the second fundamental form of the submanifold and∫+=max{0,f}.Similar conclusions can be obtained for a complete submanifold with parallel mean curvature in the Euclidean space Rn+p.

Passability test and simulation of sand control string with natural gas hydrates completion in large curvature hole

To meet the requirements of marine natural gas hydrate exploitation,it is necessary to improve the penetration of completion sand control string in the large curvature borehole.In this study,large curvature test wells were selected to carry out the running test of sand control string with pre-packed screen.Meanwhile,the running simulation was performed by using the Landmark software.The results show that the sand control packer and screen can be run smoothly in the wellbore with a dogleg angle of more than 20°/30 m and keep the structure stable.Additionally,the comprehensive friction coefficient is 0.4,under which and the simulation shows that the sand control string for hydrate exploitation can be run smoothly.These findings have important guiding significance for running the completion sand control string in natural gas hydrate exploitation.

基于新的改进Bouc-Wen模型的预制RC桥墩滞回模型研究

Bouc-Wen-Baber-Noori(BWBN)模型是改进的Bouc-Wen模型。BWBN模型可以较好地描述钢筋混凝土结构在强震作用下的捏缩效应,但由于BWBN模型中“捏缩效应”函数复杂且参数较多,其计算效率较低。针对该问题,该文基于近似狄拉克δ函数构建更简单、高效的“捏缩效应”函数,进而提出了新的改进Bouc-Wen(MBW)模型,它可以用更少的参数来实现捏缩效应。基于预制RC桥墩的拟静力试验数据来验证MBW模型的有效性,利用MATLAB遗传算法工具箱对BWBN模型和MBW模型进行参数识别,结果表明,该文提出的MBW模型具有更高的计算精度。

S135钻杆接头螺纹三维参数化建模及力学特性分析

S135钢级钻杆在矿井勘探、探放水、瓦斯抽采等钻孔施工中得到了广泛使用。然而,由于钻杆接头螺纹承受轴向拉压、扭转、弯曲及其复合载荷的循环作用,导致接头螺纹的使用寿命远远低于其设计寿命,是整个钻杆结构中最薄弱的环节。因此,通过万能拉伸试验获得钻杆接头材料的力学性能参数,经计算转化得到其本构参数,对钻杆接头进行有限元分析。为了提高有限元分析效率,推导垂直于钻杆接头轴线的螺纹截面轮廓几何表达式,基于旋转、抬升、缩径和连接节点的设计思路,提出了一种考虑钻杆接头锥度和台肩的三维螺纹参数化建模方法,并根据单元和节点之间的关系开发了钻杆接头连接的参数化三维六面体网格建模程序,通过与交互式建模方法计算结果的对比验证了其有效性和可行性。此外,对上扣扭矩、压扭及压弯扭复合载荷作用下接头外螺纹的力学特性进行了分析。结果表明:3种工况下钻杆接头外螺纹上的应力近似呈现“浴盆”形态,第1螺纹牙上的应力最大;随着圈次的增加,螺纹牙上的应力迅速下降,最后一圈螺纹牙上的应力呈现上升趋势;在弯矩的作用下,螺纹牙上的应力具有非对称特征。在接头螺纹设计时,必须考虑井眼曲率的影响并且需要重点关注接头压缩边第1螺纹牙上的应力。

覆岩导水裂隙带发育高度动态演化规律研究

为了研究覆岩导水裂隙带发育高度动态演化规律,以小保当矿区2^(-2)煤层为研究对象,通过理论分析、相似模拟实验及实例验证的方法,对导水裂隙带动态发育高度进行研究;借助概率积分法预计其上部岩层移动变形的理论公式,给出了1种基于覆岩曲率变形的导水裂隙带动态发育高度预计方法。研究表明:导水裂隙带上部岩层下沉系数是1个与挠度及下部自由空间高度相关的分段函数,上部岩层曲率变形大小是决定导水裂隙带发育高度的关键因素;导水裂隙带发育高度与工作面推进长度相关;理论预计小保当矿区2^(-2)煤层导水裂隙带发育高度为160.8 m,相似模拟实验发育高度为155 m,现场实测发育高度为152.01~175.57 m。

TEB算法中机器人平稳避障策略研究

时间弹性带(Time Elastic Band,TEB)算法由于其具有运动学约束、最快路径约束的特点被广泛用于实时局部路径规划和避障,但是在非结构化的动态社会环境进行导航的情况下,强转弯时存在速度输出不稳定的问题,这对于移动机器人的整个前进过程是非常不利的。为了解决这一问题,将轨迹曲率作为一种新的约束引入TEB算法,提出了基于曲率速度控制的时间弹性带(Curve Speed Control TEB,CSC-TEB)算法。在CSC-TEB算法中,移动机器人在实时避障时的最大瞬时速率能够根据其与行进路径的航向变化程度做出一定调整。实验结果表明,应用CSC-TEB算法能够使移动机器人在躲避障碍物时具有更加平稳的速度,同时输出较平滑的轨迹曲线,避免了原始TEB算法中的速度抖动现象。在静态和动态场景中,移动机器人躲避障碍物时具有更加稳定的速度曲线,保证机器人在安全避障的前提下路径总耗时降低了15.02%,从整体上提升了路径规划效率。

Z箍缩动力学行为及其直接驱动型脉冲源研究进展

Z箍缩在惯性约束聚变、强脉冲辐射效应等前沿科技和国家安全领域发挥着重要作用。该文综述了Z箍缩等离子体动力学行为及其直接驱动型脉冲源关键技术方面的研究进展。首先,总结Z箍缩等离子体的实验诊断技术的发展,特别是激光汤姆逊散射流场诊断方法以及基于磁旋光效应的磁场诊断方法;其次,分析Z箍缩消融、内爆等过程中磁场演化图像及其作用机理的研究进展;再次,面向提升内爆品质的需求,总结预脉冲电流调控质量分布、外施轴向磁场调控等对丝阵Z箍缩内爆动力学行为的影响。同时,面向功率百太瓦级的大型Z箍缩装置建设,概述直接驱动型脉冲源新技术路线中的快直线型变压器支路技术、触发技术以及单路脉冲源的主要进展。最后,总结并提出下一步需要重点攻克的研究方向,主要包括长内爆时间下等离子体不稳定性抑制方法、大型直接驱动型脉冲源电磁能高效传输汇聚方法以及可靠运行技术等。