Effect of electrical double layer on electric conductivity and pressure drop in a pressure-driven microchannel flow

The effect of an electrical double layer (EDL) on microchannel flow has been studied widely, and a constant bulk electric conductivity is often used in calculations of flow rate or pressure drop. In our experimental study of pressure-driven micropipette flows, the pipette diameter is on the same order of magnitude as the Debye length. The overlapping EDL resulted in a much higher electric conductivity, lower streaming potential, and lower electroviscous effect. To elucidate the effect of overlapping EDL, this paper developed a simple model for water flow without salts or dissolved gases (such as CO₂) inside a two-dimensional microchannel. The governing equations for the flow, the Poisson, and Nernst equations for the electric potential and ion concentrations and the charge continuity equation were solved. The effects of overlapping EDL on the electric conductivity, velocity distribution, and overall pressure drop in the microchannel were quantified. The results showed that the average electric conductivity of electrolyte inside the channel increased significantly as the EDL overlaps. With the modified mean electric conductivity, the pressure drop for the pressure-driven flow was smaller than that without the influence of the EDL on conductivity. The results of this study provide a physical explanation for the observed decrease in electroviscous effect for microchannels when the EDL layers from opposing walls overlap.     

新疆伊犁河谷表层土壤容重的空间变异性分析

容重是土壤最基本的物理性状之一,是衡量土壤退化的核心指标,研究其空间变化对防治土壤侵蚀具有重要意义。本文以伊犁河谷为研究对象,运用传统统计学、GIS空间技术和地统计学的Kriging空间插值等方法,分析了表层土壤（0~20cm）容重的空间变异特征。结果表明：表层土壤容重频率分布为正态分布,K-S单样本检验表明,其峰度为0.14,偏度为0.15,变化范围为（1.01~1.50）g/cm³,平均值为1.25g/cm³,变异系数为7.6%,属于弱变异性;表层土壤容重的块金值为0.0056,基台值为0.0083,块金效应为32.5%,为中等相关性;空间尺度上,表层土壤容重由南向北和由西向东逐渐减小;普通克里金（Ordinary Kriging）插值表明,表层土壤容重南北走向呈条带状,东西走向呈斑块状分布格局;气候、母质等自然因素是表层土壤容重变化的内在因素,土地利用加速土壤容重的变化。     

Edge superconductivity in multilayer WTe2 Josephson junction

WTe₂, as a type-II Weyl semimetal, has 2D Fermi arcs on the (001) surface in the bulk and 1D helical edge states in its monolayer. These features have recently attracted wide attention in condensed matter physics. However, in the intermediate regime between the bulk and monolayer, the edge states have not been resolved owing to its closed band gap which makes the bulk states dominant. Here, we report the signatures of the edge superconductivity by superconducting quantum interference measurements in multilayer WTe₂ Josephson junctions and we directly map the localized supercurrent. In thick WTe₂ (, the supercurrent is uniformly distributed by bulk states with symmetric Josephson effect (). In thin WTe₂ (10 nm), however, the supercurrent becomes confined to the edge and its width reaches up to and exhibits non-symmetric behavior . The ability to tune the edge domination by changing thickness and the edge superconductivity establishes WTe₂ as a promising topological system with exotic quantum phases and a rich physics.     

Orientational Order of C60 Molecules in Low-dimensional Lattices

The orientational order is an important concept of the materials composed of large molecules or clusters. Using high-resolution scanning tunneling microscopy, we have studied the orientational order of two kinds of typical low-dimensional C60 lattices: two-dimensional molecules array and C60(111) multi-layer film surface. Due to the change of the crystal field, their orientational orders are distinctly different from those in bulk system, and some unique phenomena appear.     

BAL Quasars without intrinsic X-ray absorption

While observing a sample of quasars with broad absorption line （BAL） in their spectra, Prof. WANG Junxian and his colleagues Prof. WANG Tinggui and Dr. ZHOU Hongyan with the Center for Astrophysics at the University of Science and Technology of China （USTC） discovered that unlike most of BAL quasars, two of the observed do not show intrinsic X-ray absorption, indicating a different composition of matter in their outflows. This might help us better understand how black holes devour and project gases, according to the astronomers.     

High-Tc superconductor Fe(Se,Te) monolayer: an intrinsic,scalable and electrically tunable Majorana platform

Iron-based superconductors have been identified as a novel platform for realizing Majorana zero modes (MZMs) without heterostructures, due to their intrinsic topological properties and high-T_c superconductivity. In the two-dimensional limit, the FeTe_1−xSe_x monolayer, a topological band inversion has recently been experimentally observed. Here, we propose to create MZMs by applying an in-plane magnetic field to the FeTe_1−xSe_x monolayer and tuning the local chemical potential via electric gating. Owing to the anisotropic magnetic couplings on edges, an in-plane magnetic field drives the system into an intrinsic high-order topological superconductor phase with Majorana corner modes. Furthermore, MZMs can occur at the domain wall of chemical potentials at either one edge or certain type of tri-junction in the two-dimensional bulk. Our study not only reveals the FeTe_1−xSe_x monolayer as a promising Majorana platform with scalability and electrical tunability and within reach of contemporary experimental capability, but also provides a general principle to search for realistic realization of high-order topological superconductivity.     

哈尔滨城市园林树木绿地土壤肥力质量调查

选择市区主要园林树木绿地采样调查,研究哈尔滨市城市园林树木绿地土壤物理、化学特性,主要包括绿地土壤质地、容重、孔隙度、pH、有机质、全氮、全磷、全钾、碱解氮、有效磷、速效钾等含量测定,根据测定结果评价哈尔滨城市园林树木绿地土壤肥力质量,并与耕作土壤进行对比,揭示城市园林树木绿地土壤存在的主要问题。     

Hydrolysis and oxidation in supercritical water

The continuity of the liquid and gaseous states, and the existence of critical temperatures for specific gases, was discovered by Thomas Andrews in 1861. This had important implications for the liquefaction of the supposedly ‘permanent’ gases and the creation of an important new industry. Currently, the chemistry of reactions in supercritical fluids, especially water, is the subject of much research, especially in the context of treating industrial waste.     

谁是“全球变暖”的主因——碳的自然排放源与地球化学循环及气候变化主因研究评述

通常认为,导致地球大气圈CO2温室气体增加的主要原因是人类对化石燃料的燃烧。笔者研究表明,导致地球大气圈CO2气体的增加还有更重要的来源,即自然因素。它们是火山气体、泥火山气体、矿床中的气体(金属矿、盐矿、煤矿、石油天然气藏等),与地震、海啸、洋中脊、洋壳蛇纹石化有关的气体,以及与森林大火有关的地球排气等等。而海洋—大气、土壤—大气的碳循环作为CO2与CH4的汇涉及到CO2、CH4的演化与循环。相比之下,人类活动在碳循环中的作用是很小的。只有全世界科学家通力合作,观测研究CO2、CH4气体的源与汇及其通量,进而对温室气体CO2与CH4做半定量、定量的评价,才能确定人类活动与地球排气对环境的影响孰主孰次。     

Influence of technology on science: a comment on some experiences at IBM research

The stimulation of technological development by scientific discovery is a widely accepted premise. Somewhat less recognized is the inverse relationship, the stimulation of science by technology. Examples of the latter are the advances in thermodynamics following the development of the steam engine by Watt; and the advancement of the understanding of thermionic emission into gases, by Langmuir, following his own invention of the nitrogen-filled electric bulb.In this paper, we discuss several examples of contributions to science at IBM Research which were generated by our technological effort. These are of two types. The first one comprises scientific investigation stimulated by the need to understand some technological problems. Examples are the ‘two-dimensional electron gas’ investigations inspired by the desire to understand the physical properties of the planar field-effect transistors; or contributions to the theory of magnetism stimulated by the advent of ‘magnetic bubbles’ as a promising storage medium. The second type of stimulation of science by technology is the creation of new tools for scientific investigation. Examples are advances in electron-beam microscopy, originating from a search for improved microfabrication techniques; or the development of tunable lasers, coming out of a search for new devices, not necessarily with a computer orientation, and finding a wide range of applications in physics, chemistry and biology.Beyond enumerating several examples such as the above, we have made an attempt to identify factors contributing to the cross-fertilization of science and technology. We propose three as among the most important ones: strong interactions among scientists and technologists; novelty of the technology involved; and initiative coupled with a searching attitude for underlying principes and phenomena on the part of the researchers involved.     

Graph-based discovery and analysis of atomic-scale one-dimensional materials

Recent decades have witnessed an exponential growth in the discovery of low-dimensional materials (LDMs), benefiting from our unprecedented capabilities in characterizing their structure and chemistry with the aid of advanced computational techniques. Recently, the success of two-dimensional compounds has encouraged extensive research into one-dimensional (1D) atomic chains. Here, we present a methodology for topological classification of structural blocks in bulk crystals based on graph theory, leading to the identification of exfoliable 1D atomic chains and their categorization into a variety of chemical families. A subtle interplay is revealed between the prototypical 1D structural motifs and their chemical space. Leveraging the structure graphs, we elucidate the self-passivation mechanism of 1D compounds imparted by lone electron pairs, and reveal the dependence of the electronic band gap on the cationic percolation network formed by connections between structure units. This graph-theory-based formalism could serve as a source of stimuli for the future design of LDMs.     

Experimental determination of the flame temperatures of complex mixtures of combustible gases and a method for calculating them

The flame temperatures of mixtures of hydrogen, or methane, or carbon monoxide containing various amounts of nitrogen and carbon dioxide, with air, have been determined. The flame temperatures of a number of complex mixtures of combustible gases and industrial gases have also been determined. A method of calculating the maximum flame temperature of any mixed gas is described. Good agreement is found between the calculated and determined temperatures of the gases used in this investigation.     

中国稻田温室气体的排放与减排

中国是世界上最大的水稻生产国, 水稻种植面积占全球总种植面积的30%。水稻生产在粮食安全方面起着重要的作用, 稻田却是温室气体甲烷(CH₄)和氧化亚氮(N₂O)的重要排放源。文章综述了稻田CH₄和N₂O的产生过程、影响因素及时空变异规律, 总结了近年来我国稻田CH₄和N₂O排放总量的估算结果, 并提出了针对性的温室气体减排措施。     

Characterization of two-dimensional cellular automata over ternary fields

The set of papers [3], [4], [6] and [7] (Chattopadhyay et al., 1999; Dihidar and Choudhury, 2004; Khan et al., 1997, 1999) deals with the behavior of the uniform two-dimensional cellular automata over binary fields (Z₂). Some structural properties and precise mathematical models using matrix algebra over the field Z₂ are reported for characterizing the behavior of two-dimensional nearest neighborhood linear cellular automata with null and periodic boundary conditions [3], [4], [6] and [7] (Chattopadhyay et al., 1999; Dihidar and Choudhury, 2004; Khan et al., 1997, 1999). In this paper, we characterize two-dimensional linear cellular automata transformations by using matrix algebra built on Z₃. We analyze some results for two-dimensional CA with rule numbers 2460N and 2460P. Finally, we investigate the dimension of the kernel of two-dimensional cellular automata defined by the rule number 2460N.     

中国温室气体排放研究——中国科学院战略性先导科技专项“应对气候变化的碳收支认证及相关问题”之排放清单任务群研究进展

温室气体排放清单一直是气候模型构建、各国减排政策制定及国际谈判与博弈的重要基础。2011年中科院启动战略性先导科技专项"应对气候变化的碳收支认证及相关问题",其中设置了"排放清单任务群"4个项目,以建立我国温室气体参数及排放数据库。文章介绍了"排放任务群"中"能源消费与水泥生产过程排放"、"土地利用与畜牧业的甲烷和氧化亚氮排放"、"自然过程碳排放"和"卫星反演的‘净排放’"4个项目的主要研究进展,结果发现,中国2013年二氧化碳实际排放总量比前期估计值低近15%,该成果近期发表于Nature。本文同时针对温室气体排放的需求,提出了今后的发展方向。     

A three-dimensional text image watermarking model based on multilayer overlapping of extracted two-dimensional information

Aiming at the problem that watermark information is easy to be lost in two-dimensional text image watermarking, a three-dimensional text image watermarking model is proposed based on multilayer overlapping of extracted two-dimensional information, and a specific method is accordingly realized by means of embedding, extracting and overlapping of multiple watermarks in sequence. We discuss the influence of the sequence order, positional distancing and color difference of the extracted multiple two-dimensional information on displaying a three-dimensional text watermark image. In addition, considering the crucial evaluation indices of the invisibility and robustness for the watermarking algorithm, the selection method for superior embedding regions of multiple watermarks is also constructed to enhance the robust performance of watermarks under the premise of effective invisibility. Moreover, we embed the multiple two-dimensional information into the host image by using the undecimated dual-tree complex wavelet transforms - bidiagonal singular value decomposition algorithm. In this way, the extracted multiple two-dimensional information is automatically overlapped to generate the three-dimensional text watermarking according to the optimal matching parameters. We use standard image processing data set to carry out experiments, the results show that the peak signal to noise ratio before and after embedded watermarks is higher than 39 dB, and the peak signal to noise ratio between the original watermarks and the extracted watermarks is more than 37 dB, which is superior to the current reported watermark model. Therefore, it is suggested that the proposed model shows good invisibility and robustness and can reduce the loss of watermark during transmission and attack as much as possible.     

Development of time-limited model reduction technique for one-dimensional and two-dimensional systems with error bound via balanced structure

In this article, the two-dimensional model is decomposed into two one-dimensional models using the minimal rank-decomposition condition, and the model reduction is conducted on these two one-dimensional models using time-limited Gramians. The proposed framework works for both one-dimensional and two-dimensional systems. The suggested approach addresses the primary flaw in Gawronski & Juang’s problem of reduced-order model instability. Researchers revealed some stability preservation solutions to address this key flaw, which ensure the stability of one-dimensional reduced-order systems; nevertheless, these strategies result in large approximation errors. However, to the best of the authors’ knowledge, there is no literature available for the stability preserving time-limited-intervals Gramians based model reduction framework for the two-dimensional discrete-time systems. In comparison to other stability-preserving strategies, the proposed framework provides an a priori error-bound formulation that is easily computable. The simulation results show that the proposed framework performs well compared to other existing stability-preserving methods, demonstrating its usefulness.     

自然资源综合观测视角下的土壤肥力评价指标

土壤肥力是土壤的基本属性和质的特征,其评价指标体系的建立是实现自然资源综合观测和统一管理的重要支撑,然而,目前仍然没有建立一个统一的标准和指标体系。本文基于文献计量的方法,对CNKI库中相关文献进行统计分析,总结了国内学者对土壤肥力质量评价所选用的主要指标,并分别从土壤化学、土壤物理和土壤生物学3个不同性质方面进行探讨。结果表明,有机质、全氮和速效钾等是土壤化学性状的重要指标,容重、土壤含水率和质地等是土壤物理性状的重要指标,脲酶、转化酶和代谢熵等是土壤生物学性状的重要指标。在此基础上,以全国自然资源综合观测和统一管理的需求为导向,遵循综合性、稳定性、独立性和获取性的指标选用原则,提出了土壤肥力评价指标体系的初步构建方案,旨在为开展土壤资源长期定位观测和质量评价提供科学依据。     

Powders—gaseous, liquid and solid

Powders can float like a gas; flow like a liquid; or support a weight in the same way as hard-packed snow. They behave rather like gases when in the form of smoke or dust in the atmosphere; rather like liquids when poured or conveyed during manufacturing processes; and rather like solids when compressed into blocks by subjecting them to pressure.