美科学家发现新的三体原子束缚态

据美国每日科学网7月3日报道,美国堪萨斯州立大学的科学家在原子内部发现了一种新的三体原子束缚态,在这种状态下,三个一模一样的原子松散地依附在一起,这一量子态与以前发现的三体束缚态不同,其既存在于玻色子中又存在于费米子中,因此,有助于科学家们更好地理解物质及其组成。     

低温等离子体技术及其应用研究

等离子体是由自由电子、离子和中性粒子组成的非束缚态宏观体系,是除去固、液及气态外,物质存在的第四态。按照热平衡状态,等离子体可以分为完全热力学平衡等离子体、局部热力学平衡等离子体以及非热力学平衡等离子体。非热力学平衡等离子体(低温等离子体)由于产生装置简单、容易制造、宏观温度低等优势,近年来成为各领域广泛研究的热点。本文重点论述低温等离子体技术在多晶硅行业的应用现状及前景,并结合青藏高原特点,提出低温等离子体技术在青藏高原环保方面的应用。     

铁磁－非磁性杂质－铁磁隧道结磁电阻效应

基于波函数匹配方法,研究了铁磁-非磁性杂质-铁磁系统的隧道结磁电阻,结果表明,在一定条件下两铁磁结之间分子场的存在导致了准束缚态的形成。当电子入射能量接近准束缚态能级时共振隧穿发生,在其电导中出现一个峰值。非磁性杂质和两铁磁体中的电子有效质量对微分电导有明显的影响,包括影响电导的幅度和共振峰的位置。     

宇宙加速膨胀与星系自转曲线异常

关于宇宙加速膨胀和星系自转曲线异常问题,相应领域每年都有大量论文发表。然而,或许只有学习AlphaGo的"思维方式",像AlphaGo那样思考,我们才能找到问题的答案。重新研究了束缚态和非束缚态,以及超星系团因光辐射而产生的质量损失与空间膨胀的关系。我们推测:光子和任何物体之间的引力势能为零;光子和任何粒子之间的引力势能为零;因光辐射不断产生质量损失的两个相邻的互为非束缚态的天体系统,它们之间的引力势能并不会因为光辐射损失质量而减小,也就是说,它们之间的引力势能是守恒的。循着这一思路,得到了两个相邻的(互为非束缚态的)超星系团之间的空间膨胀速度和空间膨胀加速度的方程。对于星系自转曲线异常,我们推测:在旋涡星系中,存在空间膨胀;旋涡星系中的空间膨胀沿着始自于星系中心的螺旋方向;相对于同一观察者,上述螺旋方向与旋涡星系自转方向同为顺时针方向,或同为逆时针方向;旋涡星系中的一个天体所在区域的空间膨胀速度与这个天体到旋涡星系中心的距离(中心距)成正比。目前测得的旋涡星系自转速度,应该是旋涡星系的本动自转速度与旋涡星系内的空间膨胀速度的叠加。两个速度叠加后,就会出现我们现在看到的星系自转曲线呈平坦状的结果。从旋涡星系自转速度中剔除旋涡星系沿螺旋方向的空间膨胀速度,我们得到旋涡星系的本动自转速度-这一运动速度仍然符合牛顿经典理论。因此,旋涡星系中的恒星不会从旋涡星系中逃逸。需要特别注意的是,由于旋涡星系旋臂的指向一般和星系旋转的方向相反,因此旋涡星系中的空间膨胀沿着的螺旋方向与旋涡星系旋臂的螺旋方向一般是不同的(目前仅发现NGC 4622的旋臂指向就是自己旋转的方向)。     

物理所等在铁基超导体中发现类马约拉纳费米子

<正>中科院物理所潘庶亨、丁洪研究组,利用极低温高分辨率的扫描隧道显微镜,在休斯顿大学超导中心研究员吴诤生长的一系列铁基超导体Fe1+(xTe,Se)中发现处于间隙位置的单原子铁杂质上会产生一个非常尖锐的零能电导峰,通过搬运原子的方法,证实了该束缚态确实由铁杂质诱发。这零能束缚态仅仅存在于单个铁杂质原子1 nm范围内,并且是各项同性的。最奇特的是,它的能量非常鲁棒地严格处于零能,即使加上8特斯拉     

应用新型量子粒子群优化算法求解PFSP问题

为了提高粒子群算法在求解调度问题时的搜索能力和优化效率以及避免早熟收敛。通过采用了一种新颖的量子粒子群算法,用量子位的概率幅对粒子位置编码,用量子旋转门实现粒子移动,完成粒子搜索;并采用量子非门来实现变异,从而提高种群多样性。由于每个量子都有两个概率幅,因此每个粒子实际占据两个粒子位置,所以在粒子数目相等的情况下,能加速粒子的搜索进程。仿真实验结果表明,在求解置换流水线生产调度问题时优于基本粒子群算法。     

物理学家称或将发现奇异粒子和额外时空维度

物理学家认为奇异粒子和额外的时空维度是物理学的下一个探索目标,奇异粒子是一些亚原子粒子,其参与强相互作用和弱相互作用,来自英国伯明翰大学的物理学家大卫·查尔顿认为这些奇异粒子将填补粒子物理标准模型的空白。     

多波束粒子群深度零点轨迹信息搜索效率优化

传统的基于粒子群算法的前馈神经网络训练系统进行数据库访问时,易陷入局部极值,产生零点轨迹信息搜索效率较低,局部极小点和搜索方向紊乱。提出一种改进的粒子群优化算法。构建基于误差反传的神经网络系统结构,引入混沌映射概念,提出了一种根据粒子搜索状态,动态调整粒子飞行速度和位置的粒子群优化算法,提高多波束粒子群深度零点轨迹信息的提取的搜索效率,根据粒子的轨迹信息,研究如何动态调整粒子的搜索速度和方向,提高了训练和控制精度与效益。仿真实验表明,该算法进行多波束粒子零点轨迹信息搜索,效率较高,通过外力的干涉尝试调整粒子的方向,使得粒子可以逃离这个稳定阶段,提高了粒子收敛速度,提高控制搜索精度,运行时间较短。算法在智能控制等领域具有较好的应用价值。     

锯齿形微通道结构参数对布朗粒子分离的影响研究

微通道粒子分离技术通过设计特殊的微通道结构对布朗粒子构成特定的熵势阱,同时施加一定的外力影响,从而实现粒子分离。本文研究了恒定外力和熵势的共同作用下,锯齿型微通道结构参数对微通道中不同粒径大小的粒子分离特性的影响。分析了不同粒径粒子的速度差,两种粒径大小不同粒子大小以及改变左壁斜率大小的情况下,对粒子的分离效果的影响,并得出相应的最优分离方案。这些研究结果有利于促进微通道粒子分离技术的进一步发展。     

暗物质假说

在大爆炸的前期,宇宙处于极高温、极高压的状态,每个粒子都含有一种能够反射光、发射光的粒子(称为介粒子)。宇宙中心的温度极高,达到要发光的状态。由于这种介粒子可以自由地进入粒子,且粒子对它的束缚力不相同,所以,在任何粒子中含量有很大区别。这时,介粒子流动集中到宇宙中     

影响脂肪族化合物构象的因素

分析探讨了分子内ｖａｎ ｄｅｒ Ｗａａｌｓ 作用力、成键轨道电子云相互作用、分子内氢键、分子内偶极相互作用、分子间偶极相互作用和溶剂化作用六种因素对脂肪族化合物分子构象的影响．在诸多影响因素中必然会有一种因素对分子的优势构象起主要作用     

Structural evolution of protein-biofilms: Simulations and experiments

The control of biofilm formation is a challenging goal that has not been reached yet in many aspects. One unsolved question is the role of van der Waals forces and another is the importance of mutual interactions between the adsorbing and the adsorbed biomolecules ("critical crowding"). In this study, a combined experimental and theoretical approach is presented, which fundamentally probes both aspects. On three model proteins-lysozyme, α-amylase, and bovine serum albumin-the adsorption kinetics is studied experimentally. Composite substrates are used enabling a separation of the short- and the long-range forces. Although usually neglected, experimental evidence is given for the influence of van der Waals forces on the protein adsorption as revealed by in situ ellipsometry. The three proteins were chosen for their different conformational stabilities in order to investigate the influence of conformational changes on the adsorption kinetics. Monte Carlo simulations are used to develop a model for these experimental results by assuming an internal degree of freedom to represent conformational changes. The simulations also provide data on the distribution of adsorption sites. By in situ atomic force microscopy we can also test this distribution experimentally, which opens the possibility to, e.g., investigate the interactions between adsorbed proteins.     

Coexistence of plastic and partially diffusive phases in a helium-methane compound

Helium and methane are major components of giant icy planets and are abundant in the universe. However, helium is the most inert element in the periodic table and methane is one of the most hydrophobic molecules, thus whether they can react with each other is of fundamental importance. Here, our crystal structure searches and first-principles calculations predict that a He₃CH₄ compound is stable over a wide range of pressures from 55 to 155 GPa and a HeCH₄ compound becomes stable around 105 GPa. As nice examples of pure van der Waals crystals, the insertion of helium atoms changes the original packing of pure methane molecules and also largely hinders the polymerization of methane at higher pressures. After analyzing the diffusive properties during the melting of He₃CH₄ at high pressure and high temperature, in addition to a plastic methane phase, we have discovered an unusual phase which exhibits coexistence of diffusive helium and plastic methane. In addition, the range of the diffusive behavior within the helium-methane phase diagram is found to be much narrower compared to that of previously predicted helium-water compounds. This may be due to the weaker van der Waals interactions between methane molecules compared to those in helium-water compounds, and that the helium-methane compound melts more easily.     

The 2001 Benjamin Franklin Medal in Earth Science presented to Rob Van der Voo

The Franklin Institute, Philadelphia, Pennsylvania, awarded the 2001 Benjamin Franklin Medal in Earth Science to Rob Van der Voo for his outstanding contributions to the field of paleomagnetism and his reconstruction of ancient continental positions that have lead to a better understanding of plate tectonic processes for the past billion years of Earth history.     

有限理性与竞争情报

博弈论是竞争情报领域影响最大的理论,但它对情报工作的实际意义不大,原因是它的分析是基于“人是完全理性的”这一假设,而现实中的人不是完全理性的。本文尝试将西方行为经济学的“有限理性”的理论引入竞争情报领域。本文阐述了有限理性在收集信息、理解信息和（人们）日常行为中的表现,提出了利用该理论克服信息收集和分析中的缺陷,更有效地分析竞争对手和提供情报报告的方法。     

Modeling of dielectrophoretic transport of myoglobin molecules in microchannels

Myoglobin is one of the premature identifying cardiac markers, whose concentration increases from 90 pg∕ml or less to over 250 ng∕ml in the blood serum of human beings after minor heart attack. Separation, detection, and quantification of myoglobin play a vital role in revealing the cardiac arrest in advance, which is the challenging part of ongoing research. In the present work, one of the electrokinetic approaches, i.e., dielectrophoresis (DEP), is chosen to separate the myoglobin. A mathematical model is developed for simulating dielectrophoretic behavior of a myoglobin molecule in a microchannel to provide a theoretical basis for the above application. This model is based on the introduction of a dielectrophoretic force and a dielectric myoglobin model. A dielectric myoglobin model is developed by approximating the shape of the myoglobin molecule as sphere, oblate, and prolate spheroids. A generalized theoretical expression for the dielectrophoretic force acting on respective shapes of the molecule is derived. The microchannel considered for analysis has an array of parallel rectangular electrodes at the bottom surface. The potential and electric field distributions are calculated using Green’s theorem method and finite element method. These results also compared to the Fourier series method, closed form solutions by Morgan et al. [J. Phys. D: Appl. Phys. 34, 1553 (2001)] and Chang et al. [J. Phys. D: Appl. Phys. 36, 3073 (2003)]. It is observed that both Green’s theorem based analytical solution and finite element based numerical solution for proposed model are closely matched for electric field and square electric field gradients. The crossover frequency is obtained as 40 MHz for given properties of myoglobin and for all approximated shapes of myoglobin molecule. The effect of conductivity of medium and myoglobin on the crossover frequency is also demonstrated. Further, the effect of hydration layer on the crossover frequency of myoglobin molecules is also presented. Both positive and negative DEP effects on myoglobin molecules are obtained by switching the frequency of applied electric field. The effect of different shapes of myoglobin on DEP force is studied and no significant effect on DEP force is observed. Finally, repulsion of myoglobin molecules from the electrode plane at 1 KHz frequency and 10 V applied voltage is observed. These results provide the ability of applying DEP force for manipulating nanosized biomolecules such as myoglobin.     

Identification of twist-angle-dependent excitons in WS2/WSe2 heterobilayers

Stacking atomically thin films enables artificial construction of van der Waals heterostructures with exotic functionalities such as superconductivity, the quantum Hall effect, and engineered light-matter interactions. In particular, heterobilayers composed of monolayer transition metal dichalcogenides have attracted significant interest due to their controllable interlayer coupling and trapped valley excitons in moiré superlattices. However, the identification of twist-angle-modulated optical transitions in heterobilayers is sometimes controversial since both momentum-direct (K–K) and -indirect excitons reside on the low energy side of the bright exciton in the monolayer constituents. Here, we attribute the optical transition at ∼1.35 eV in the WS₂/WSe₂ heterobilayer to an indirect Γ–K transition based on a systematic analysis and comparison of experimental photoluminescence spectra with theoretical calculations. The exciton wavefunction obtained by the state-of-the-art GW-Bethe-Salpeter equation approach indicates that both the electron and hole of the excitons are contributed by the WS₂ layer. Polarization-resolved k-space imaging further confirms that the transition dipole moment of this optical transition is dominantly in-plane and is independent of the twist angle. The calculated absorption spectrum predicts that the so-called interlayer exciton peak coming from the K–K transition is located at 1.06 eV, but with a much weaker amplitude. Our work provides new insight into the steady-state and dynamic properties of twist-angle-dependent excitons in van der Waals heterostructures.     

On electron optics

For many experiments in physics and in some engineering applications, it is necessary to produce electron bundles, or as they are often called, “electron beams” of considerable intensities.Various methods have been used for directing a cloud of electrons evaporated from an emitting surface into a beam and then concentrating this beam to a desired degree. The concentration of electron beam in high vacuum depends entirely upon fields of force, either electric or magnetic, while in low vacuum or in rarified rare gas it depends also upon the action of the field of ionized gas molecules.In high vacuum the fields of force act upon the electron beam in a manner similar to the action of lenses upon a beam of light. An improperly shaped field produces effects similar to spherical aberration in poorly corrected lenses; non-uniform velocity of electrons in the beam results in effects similar to chromatic aberration of light.This optical analogy is not perfect.In the case of the electron beam the velocity varies continuously throughout most of the path and indices of refraction employed usually are greater than in the optical case. Moreover, space charge in beams of high intensity limits the concentration attainable; consequently, even theoretically, an electron beam can never be brought up to a mathematical point as in the case of light optics. Many secondary effects are present which complicate the problem still further.In focusing electron beams, both electrostatic and electromagnetic methods have been used extensively. The electrostatic method, however, seems to be preferable, especially when the beam is to be deflected. Precautions should be taken not to destroy the focusing of the beam during deflection.     

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.     

C60分子在低维晶格中的取向序

取向序是由大分子或团簇构成的新型材料的一个重要概念。利用高分辨扫描隧道显微镜 ,对两种典型的低维C60 分子晶格体系的取向序进行了研究 :二维C60 分子阵列和C60 分子多层膜(111)表面。由于外部晶场环境的改变 ,这两种体系的分子取向序与宏观C60 晶体材料有着明显不同 ,并且出现了一些特殊现象。