Designing a 2D van der Waals oxide with lone-pair electrons as chemical scissorOA

Two-dimensional（2D） van der Waals（vdW） materials are known for their intriguing physical properties,but their rational design and synthesis remain a great challenge for chemists.In this work,we successfully synthesized a new non-centrosymmetric oxide,i.e.InSbMoO₆,with Sb³⁺ lone-pair electrons serving as chemical scissor to generate its 2D vdW crystal structure.Monolayer and few-layer InSbMoO₆ flakes are readily obtained via facile mechanical exfoliation.They exhibit strong second-harmonic generation（SHG）response with an effective second-order nonlinear optical susceptibility χ_eff^（2） of 32.4 pm·V^-1.Meanwhile,the SHG response is in-plane anisotropic and directly proportional to the layer thickness,independent of layer parity.In addition,the InSbMoO₆ flakes exhibit excellent thermal and atmospheric stability,along with pronounced anisotropy in Raman spectroscopy.This work implies that using lone-pair electrons as chemical scissor is an effective strategy for designing and synthesizing new 2D vdW materials for integrated photonic applications.     

卫星电源测试评估系统的初步研究

介绍了卫星电源基本体系结构以及卫星电源测试评估方法 ,建立了基于虚拟仪器概念的卫星电源测试评估系统 ,并对一个简单的非调节母线卫星电源系统模型进行测试 ,给出了结果分析 .     

Analyzing shear stress-induced alignment of actin filaments in endothelial cells with a microfluidic assay

The physiology of vascular endothelial cells is strongly affected by fluid shear stress on their surface. In this study, a microfluidic assay was employed to analyze the alignment of actin filaments in endothelial cells in response to shear stress. When cells were cultured in microfluidic channels and subjected to shear stress, the alignment of filaments in the channel direction was significantly higher than in static cultures. By adding inhibitory drugs, the roles of several signaling proteins in the process of alignment were determined. Thus, it is shown how microfluidic technology can be employed to provide a mechanistic insight into cell physiology.     

Design and optimization of a double-enzyme glucose assay in microfluidic lab-on-a-chip

An electrokinetic driven microfluidic lab-on-a-chip was developed for glucose quantification using double-enzyme assay. The enzymatic glucose assay involves the two-step oxidation of glucose, which was catalyzed by hexokinase and glucose-6-phosphate dehydrogenase, with the concomitant reduction of NADP⁺ to NADPH. A fluorescence microscopy setup was used to monitor the different processes (fluid flow and enzymatic reaction) in the microfluidic chip. A two-dimensional finite element model was applied to understand the different aspects of design and to improve the performance of the device without extensive prototyping. To our knowledge this is the first work to exploit numerical simulation for understanding a multisubstrate double-enzyme on-chip assay. The assay is very complex to implement in electrokinetically driven continuous system due to the involvement of many species, which has different transport velocity. With the help of numerical simulation, the design parameters, flow rate, enzyme concentration, and reactor length, were optimized. The results from the simulation were in close agreement with the experimental results. A linear relation exists for glucose concentrations from 0.01 to 0.10 g l⁻¹. The reaction time and the amount of enzymes required were drastically reduced compared to off-chip microplate analysis.     

Biotinidase deficiency—Diagnosis by enzyme assay and a follow-up study

A 3 month old male child was brought to the hospital with complaints of skin rashes, developmental delay, seizures, seborrheic dermatitis, alopecia and mild, acidosis. The child was subjected to a simple metabolic screening protocol. The result of the screening and the clinical symptoms provided an index pointing towards biotinidase deficiency., a rare autosomal recessive, inherited metabolic disorder. The enzyme was then assayed by using n-biotinylp-aminobenzoate as substrate and the diagnosis confirmed. A follow-up of the case indicated the efficacy, of biotin supplementation in biotinidase deficiency.     

核心能力战略危机预警系统设计原理与方法

核心能力战略的实施与运作过程中因为各种因素的扰动,难免发生偏差。设计核心能力战略危机预警系统的目的就在于及时发现和预见偏差以便实施控制,保证核心能力战略的可持续性和高效性。基于此,本文探讨了核心能力战略的危机预警系统设计原理与方法。     

学科服务设计与实践的微创新研究--北京师范大学图书馆学科服务发展历程

“微创新”理念的实质是用户需求导向的创新,这一理念与学科服务发展的理念有异曲同工之妙。北京师范大学图书馆在启动新一轮的学科服务过程中,通过对学科服务的格局、模式和过程设计的微创新;通过开展全程跟踪式的学科资源支持、嵌入式信息素养教育、高端课题咨询等微创新服务;通过对技术平台应用以及营销推广方式的微创新,优化用户服务体验,快速的推动学科服务向纵深发展。     

An algorithm for modeling the sinusoidal input/steady-state response behavior of nonlinear systems over a set of frequencies and amplitudes

An algorithm for constructing a black box model of the sinusoidal input/steady-state response behavior of nonlinear time-invariant systems over a set of frequencies and amplitudes is presented. It is assumed that the steady-state response is periodic of the same fundamental frequency as the excitation, and that the Fourier coefficients are continuous functions of amplitude and square-integrable functions of frequency. The algorithm converges, in a mean-square sense, to an exact representation of the first N harmonics of the steady-state response minus its d.c. component. The model constructed by the algorithm admits a relatively simple physical realization characterized by 2NM+1 linear dynamic elements, and N(2M+1)+1 nonlinear static elements. The underlying mathematical structure of the model is an orthogonal series expansion relative to time whose coefficients are themselves truncated orthogonal expansions relative to frequency. Here M, the number of harmonics used for frequency interpolation, is determined by the algorithm. Of the N(2M+1)+1 memoryless nonlinearities which characterize the model, N of these are specified ahead of time (Tchebysheff polynomials), and 2NM+1 are parameters which mold the representation to the specific system being modeled. Each of these functions of a single variable can be obtained in a pointwise manner directly from steady-state measurements. The algorithm was implemented on a digital computer, and forced versions of the classic equations of van der Pol and Duffing were run as examples. An additional analytic example of a frequency multiplier of prescribed bandwidth was also presented.     

基于机器视觉的SMD晶振上片点胶机的设计和实现

利用机器视觉、自动控制和机械技术,设计并开发了一种高速高精度的SMD晶振点胶上片一体化机器人.系统通过标定模块建立完整的绝对坐标体系,通过图像处理和模式识别技术,系统能逻辑上判断分析晶体和晶体基座的绝对位置,并补偿机械运动的精度,完成满足工艺精度的点胶和上片动作.     

Estimation of the levels of atrial natriuretic peptide (ANP) in cardiac blood samples by a simple and indigenous enzyme linked immunosorbent assay

Levels of Atrial Natriuretic Peptide (ANP) were estimated in twenty four blood samples collected from the right and the left ventricles of the patients undergoing cardiac catheterization by an Enzyme Linked Immunosorbent Assay (ELISA) developed to the sensitivity of 5 pp/well and within 10% of interassay coeficient of variance. Simultaneously, levels of ANP in plasma samples from the systemic venous blood of seventy five normal subjects were also estimated which ranged between 25–60 pg/ml.     

运用大协调学构建高效益的和谐社会

大协调学(Macro-coordinationScience),是研究人类同自然与社会各环节大尺度交叉协调规律及其应用的科学,主要帮助人们扩大视野,在大尺度上认识和解决或预防社会经济发展与生态、环境、资源不协调的问题,是人类同自然宏观协调不可缺少的科学。大协调学涉及约140门文理工学科,主要的功能是为宏观决     

Bifurcation analysis in a predator-prey system with stage-structure and harvesting

In this paper, we consider a predator-prey model with stage-structure and harvesting. This model is the same as the one developed by Kar and Pahari (2007) [9], but we make bifurcation analysis more general than their work. In particular, using the approach of Beretta and Kuang (2002) [4], we show that the positive steady state can be destabilized through a Hopf bifurcation. We also investigate the stability and direction of periodic solutions bifurcating from Hopf bifurcation by using the normal form theory and the center manifold theorem presented in Hassard et al. (1981) [8]. Numerical simulations are then carried out as supporting evidences of our analytical results.     

Design and implementation of a rectangular frequency invariant beamformer with a full azimuth angle coverage

A novel design of the frequency invariant beamformer based on a rectangular array is proposed with two unique features: there are no taped delay-lines (TDLs) or any other temporal processing involved and the resultant beamformer has a full 360° azimuth angle coverage. This leads to a wideband beamformer with complex-valued coefficients and its implementation is not as straightforward as the traditional ones. Depending on whether the input signal is complex-valued or real-valued, special arrangements and structures are required for its effective implementation. Several design examples are provided with a satisfactory frequency invariant property. Two sets of implementation results are given based on both simulations and data collected by a planar microphone array system.     

以更伸展的历史眼光和更宽广的世界眼光透视中国当代改革

当代中国改革是整个中国改革历史长河的一段,是世界改革历史长河的一隅。有必要建立一种＂大改革观＂,将当代中国改革放在中外改革史的经纬坐标中整体反思,走出＂两个历史宿命＂和＂两个历史循环＂。     

Asymmetry of red blood cell motions in a microchannel with a diverging and converging bifurcation

In microcirculation, red blood cells (RBCs) flowing through bifurcations may deform considerably due to combination of different phenomena that happen at the micro-scale level, such as: attraction effect, high shear, and extensional stress, all of which may influence the rheological properties and flow behavior of blood. Thus, it is important to investigate in detail the behavior of blood flow occurring at both bifurcations and confluences. In the present paper, by using a micro-PTV system, we investigated the variations of velocity profiles of two working fluids flowing through diverging and converging bifurcations, human red blood cells suspended in dextran 40 with about 14% of hematocrit level (14 Hct) and pure water seeded with fluorescent trace particles. All the measurements were performed in the center plane of rectangular microchannels using a constant flow rate of about 3.0 × 10⁻¹² m³/s. Moreover, the experimental data was compared with numerical results obtained for Newtonian incompressible fluid. The behavior of RBCs was asymmetric at the divergent and convergent side of the geometry, whereas the velocities of tracer particles suspended in pure water were symmetric and well described by numerical simulation. The formation of a red cell-depleted zone immediately downstream of the apex of the converging bifurcation was observed and its effect on velocity profiles of RBCs flow has been investigated. Conversely, a cell-depleted region was not formed around the apex of the diverging bifurcation and as a result the adhesion of RBCs to the wall surface was enhanced in this region.     

历史悠久影响重大 政府支持人才荟萃——第90届印度科学大会介绍

<正> 第90届印度科学大会于2003年1月3日至7日在印度南部新型科技城市——班加罗尔举行。该会议是由印度国内重要的非政府学术组织——印度科学大会协会主办的系列性学术年会。应第90届印度科学大会秘书处的邀请,以中国科协书记处书记冯长根同志为团长的中国科协代表团一行,于2003年1月专程赴印度访问,出席并考察了印度科学大会。我作为团员有幸随团出访,对印方的有关工作进行了调查了解,现简要介绍如下。     

具有纳米结构表层的纯铁和38CrMoAl钢的渗氮

通过表面机械研磨技术(SMAT),在纯铁和38CrMoAl钢样品表面产生大量的塑性应变,致使其表层晶粒细化至纳米量级.随后的气体渗氮实验表明,纳米纯铁和38CrMoAl钢发生渗氮反应的温度大大低于传统粗晶材料(＞500℃),分别降至约300℃和400℃.这种低温渗氮过程不仅有利于降低渗氮工件的变形和能耗,也为选择性渗氮技术的实现提供了新途径.