Circuits with light at nanoscales: optical nanocircuits inspired by metamaterials

A form of optical circuitry is overviewed in which a tapestry of subwavelength nanometer-scale metamaterial structures and nanoparticles may provide a mechanism for tailoring, patterning, and manipulating local optical electric fields and electric displacement vectors in a subwavelength domain, leading to the possibility of optical information processing at the nanometer scale. By exploiting the optical properties of metamaterials, these nanoparticles may play the role of "lumped" nanocircuit elements such as nanoinductors, nanocapacitors, and nanoresistors, analogous to microelectronics. I show that this concept of metamaterial-inspired nanoelectronics ("metactronics") can bring the tools and mathematical machinery of the circuit theory into optics, may link the fields of optics, electronics, plasmonics, and metamaterials, and may provide road maps to future innovations in nanoscale optical devices, components, and more intricate nanoscale metamaterials.     

Tetraplex formation of a guanine-containing nonameric DNA fragment

A combination of spectroscopic and calorimetric techniques has been used to characterize the structures formed by a family of short, guanine-containing DNA single strands of the form d[GGTTXTTGG], X = A, C, G, T. In 1 molar NaCl at low temperatures, these molecules do not behave like single strands, but rather exhibit properties consistent with tetraplex formation. The standard state enthalpies, entropies, and free energies for formation of each tetraplex have been measured, as have preliminary nuclear magnetic resonance (NMR) spectra. In 1 molar KCl, the melting behavior of the structure or structures is more complex than in 1 molar NaCl. This observation may be related to the recently proposed "sodium-potassium switch."     

“森林—竹子—大熊猫”非线性动力系统的周期解与混沌奇怪吸引子

为从理论上研究＂森林—竹子—大熊猫＂三位一体的保护栖息地理念,考虑了竹子开花的影响,把竹子和森林分成两个阶段,建立了一个描述＂森林—竹子—大熊猫＂的非线性动力系统。利用Mawhin重合度理论可以证明此系统存在一个周期解,利用计算机数值模拟画出了此动力系统的周期解随时间的变化规律和相图。数值模拟显示脉冲的影响非常复杂,进...     

The equatorial ridges of Pan and Atlas: terminal accretionary ornaments?

In the outer regions of Saturn's main rings, strong tidal forces balance gravitational accretion processes. Thus, unusual phenomena may be expected there. The Cassini spacecraft has recently revealed the strange "flying saucer" shape of two small satellites, Pan and Atlas, located in this region, showing prominent equatorial ridges. The accretion of ring particles onto the equatorial surfaces of already-formed bodies embedded in the rings may explain the formation of the ridges. This ridge formation process is in good agreement with detailed Cassini images showing differences between rough polar and smooth equatorial terrains. We propose that Pan and Atlas ridges are kilometers-thick "ring-particle piles" formed after the satellites themselves and after the flattening of the rings but before the complete depletion of ring material from their surroundings.     

Electrorheological fluids

Suspensions of polarizable particles in nonpolarizable solvents form fibrillated structures in strong electric fields. The resulting increase in viscosity of these "electrorheological" fluids can couple electrical to hydraulic components in a servomechanism. The physical properties of these fluids are unusual owing to the long-range, anisotropic nature of the interparticle forces. Immediately after the electric field is applied, elongated chains or columns of particles form parallel to the field. This structure then coarsens as a result of thermal forces between the columns. In shear flows, fluids show yielding behavior at low stresses followed by shear-thinning behavior at higher stresses.     

密度依赖口袋常数下奇异夸克物质及奇异星

在有效质量口袋模型(EMBM)下采用密度依赖口袋常数描述奇异夸克物质,研究了口袋常数的密度依赖性对奇异夸克物质的状态方程及奇异星性质的影响.结果表明,密度依赖口袋常数在低密度处较大,随着密度增大而明显变小,很好地体现了低密度处色禁闭、高密度处夸克退紧闭的量子色动力学(QCD)基本精神.与常数口袋常数的情形相比,密度依赖口袋常数下奇异夸克物质的状态方程变硬,奇异星的引力质量和对应的半径均有明显变大,且均在脉冲星的观测值范围内,表明该模型适合于描述质量和半径较大的奇异星内的夸克物质.     

Synthesis of two-dimensional polymers

A synthetic pathway is described to construct "in bulk" two-dimensional (2D) polymers shaped as molecular sheets. A chiral oligomeric precursor is used that contains two reactive sites, a polymerizable group at one terminus and a reactive stereogenic center near the middle of the molecule. The bulk reaction yields bilayer 2D polymers of molecular weight in the order of millions and a monodisperse thickness of 50.2 angstroms. The 2D molecular objects form through molecular recognition by the oligomers, which self-organize into layers that place the reactive groups within specific planes. The oligomers become catenated by two different stitching reactions involving the reactive sites. At room temperature, stacks of these molecular objects can organize as single crystals and at higher temperatures melt into smectic liquid crystals. Nonlinear optical experiments reveal that solid films containing the 2D polymers form structures that are thermally and temporally more stable than those containing analogous 1D polymers. This observation suggests that the transformation of common polymers from a 1D to a 2D architecture may produce generations of organic materials with improved properties.     

混沌动力系统特性的可视化分析

混沌动力系统内部具有非线性、复杂性、无序性、初值敏感性、时间序列的不规则性和有奇怪吸引子。本文编制了混沌动力系统仿真分析程序，用可视化方法对混沌动力系统的这些特性进行分析研究，可直观地理解和分析混沌动力系统的运动轨迹特性。     

High levels of intracellular bombesin characterize human small-cell lung carcinoma

"Small cells" or "oat cells" characterize a virulent form of lung cancer and share many biochemical properties with peptide-secreting neurones. The neuropeptide bombesin is present in all small-cell lines examined, but not in other lung cancer cell lines, suggesting that bombesinergic precursor cells in lung may give rise to this disease.     

Information and the ecology of scholars

Groups of scholars often behave in ways that are startlingly reminiscent of the behavior of groups of plants and animals in a biological ecosystem. I have tried to show that the parallel may have its basis in two fundamental considerations: (i) the similar properties of stable dissipative structures in a wide variety of contexts and (ii) the mathematical similarity of information to chemical (nutrient) free energy. A particularly intriguing problem is that of successional trends arising from the kinetic limitation of information flow through the intellectual and social structures created by scholars. The "strategy of ecosystem development" may have implications for the strategy of academic administration. In this connection, it is worth bearing in mind Marglef's dictum (6, p. 77): "Probably the hypothesis holds everywhere that the less mature ecosystem feeds the more mature structures around it."     

Packing C60 in boron nitride nanotubes

We have created insulated C60 nanowire by packing C60 molecules into the interior of insulating boron nitride nanotubes (BNNTs). For small-diameter BNNTs, the wire consists of a linear chain of C60 molecules.With increasing BNNT inner diameter, unusual C60 stacking configurations are obtained (including helical, hollow core, and incommensurate) that are unknown for bulk or thin-film forms of C60.C60 in BNNTs thus presents a model system for studying the properties of dimensionally constrained "silo" crystal structures. For the linear-chain case, we have fused the C60 molecules to form a single-walled carbon nanotube inside the insulating BNNT.     

SOME REFLECTIONS CONCERNING VALENCE VARIATION AND ATOMIC STRUCTURE

In bringing to a conclusion these few scattered reflections concerning valence variation and atomic structure, may I be permitted to say this: He who is experimentally inclined may henceforth take heart and he need not be quite so timid in interpreting strange chemical reactions on the assumption of possible anomaly in the valence of the reactants. The physicist has no hesitation in speaking of the temporary existence, at the higher temperature employed in spectroscopic work, of such molecules as BaCl, AlO, (HO), CH(+), CH(2), MgF, etc. Is it not possible that under the influence of surface forces somewhat similar valence variation may not be excluded even at lower temperatures? That these strange compounds are thermodynamically unstable may be true. Nevertheless, they may function as the mysterious catalysts, or as initiators of chain reactions.     

Jets in extragalactic radio sources

Observations now require that there be a continuous supply of energy to the giant extragalactic radio sources. These observations also suggest that this energy input may be in the form of streams or jets of gas emanating from the centers of galaxies and quasi-stellar objects. Current data indicate that the large-scale jet structures are not moving with relativistic speeds, as previously proposed. Slow-moving jets, which possess turbulent interiors and are dominated by relatively cool gas, can account for the observed jet properties at optical and radio wavelengths. Extremely small-scale jets observed adjacent to the central energy source may or may not be in relativistic motion.     

Oscillatory kinetics and spatio-temporal self-organization in reactions at solid surfaces

Chemical reactions far from equilibrium on solid surfaces may exhibit typical phenomena of nonlinear dynamics, as exemplified by the catalytic oxidation of carbon monoxide on a platinum(110) single-crystal surface. Depending on the external parameters (temperature and partial pressures of the reactants), the temporal variation of the reaction rate may become oscillatory or even chaotic. In a parallel way, the concentration distributions of the adsorbed species on the surface form spatio-temporal patterns including propagating and standing waves, rotating spirals, as well as irregular and rapidly changing structures denoted "chemical turbulence."     

Maternal influence in learning by observation in kittens

Kittens who observed their mothers perform a stimulus-controlled response (lever pressing to a visual stimulus for food) acquired and discriminated that response sooner than kittens who observed a strange female cat's performance. Kittens exposed to a trial and error condition never acquired the response. Initial differences in attentiveness to demonstrator performances disappeared by the second day. "Altruism" (food sharing) and other forms of social behavior were exhibited by both mother and stranger demonstrators.     

Supracolloidal reaction kinetics of Janus spheres

Clusters in the form of aggregates of a small number of elemental units display structural, thermodynamic, and dynamic properties different from those of bulk materials. We studied the kinetic pathways of self-assembly of "Janus spheres" with hemispherical hydrophobic attraction and found key differences from those characteristic of molecular amphiphiles. Experimental visualization combined with theory and molecular dynamics simulation shows that small, kinetically favored isomers fuse, before they equilibrate, into fibrillar triple helices with at most six nearest neighbors per particle. The time scales of colloidal rearrangement combined with the directional interactions resulting from Janus geometry make this a prototypical system to elucidate, on a mechanistic level and with single-particle kinetic resolution, how chemical anisotropy and reaction kinetics coordinate to generate highly ordered structures.     

Simulating the self-assembly of gemini (dimeric) surfactants

The morphologies and dynamics of aggregates formed by surfactant molecules are known to influence strongly performance properties spanning biology, household cleaning, and soil cleanup. Molecular dynamics simulations were used to investigate the morphology and dynamics of a class of surfactants, the gemini or dimeric surfactants, that are of potential importance in several industrial applications. Simulation results show that these surfactants form structures and have dynamic properties that are drastically different from those of single-chain surfactants. At the same weight fraction, single-chain surfactants form spherical micelles whereas gemini surfactants, whose two head groups are coupled by a short hydrophobic spacer, form thread-like micelles. Simulations at different surfactant concentrations indicate the formation of various structures, suggesting an alternative explanation for the unexpected viscosity behavior of gemini surfactants.     

Two-dimensional electronic excitations in self-assembled conjugated polymer nanocrystals

Several spectroscopic methods were applied to study the characteristic properties of the electronic excitations in thin films of regioregular and regiorandom polythiophene polymers. In the regioregular polymers, which form two-dimensional lamellar structures, increased interchain coupling strongly influences the traditional one-dimensional electronic properties of the polymer chains. The photogenerated charge excitations (polarons) show two-dimensional delocalization that results in a relatively small polaronic energy, multiple absorption bands in the gap where the lowest energy band becomes dominant, and associated infrared active vibrations with reverse absorption bands caused by electron-vibration interferences. The relatively weak absorption bands of the delocalized polaron in the visible and near-infrared spectral ranges may help to achieve laser action in nanocrystalline polymer devices using current injection.     

中国农业和农村经济爬的是什么坡

<正> 处于爬坡阶段,这是党中央、国务院对我国农业和农村经济现状的基本判断。爬坡,意味着“长期向好,短困增加”,那么,我国农业和农村经济爬得是什么坡? 首先,爬的是陡坡。之所以称为陡坡,指的是今后一个历史阶段我国农业和农村经济的发展将越来越难。一、市场对农产品的品质要求越来越高。目前农产品供大于求,出现了阶段性和结构性的过剩,农产品要卖的贵,卖的多,卖的快,就必须以质取胜。增营养保健康的优质农产品比普通农产品开价一般     

荒诞的梦幻与超验的真实——残雪《山上的小屋》解读

残雪的小说怪异晦涩,常常被人们称为另类,《山上的小屋》以其独有的梦魇、荒诞的形式让人读罢不禁感觉到毛骨悚然,不知所云。她的小说有着令人困惑又让人着迷的残酷的魔力,灵魂不仅把人推向人类深渊的边缘,而且还难以测出藏在其中的底蕴。要完全读懂这篇小说,必须以一种全新的审美眼光破译她这种反常的形式。《山上的小屋》深刻地揭示了现代人的生存状态和人的生存受到他人(异己力量)的包围而产生的孤独恐惧感,以及人的脆弱的灵魂无法面对又无力回避他人的宿命情结。