Complete wetting from polymer mixtures

Coexisting polymer phases are characterized by very small interfacial energies, even well below their critical solution temperature. This situation should readily lead to the exclusion of one of the phases from any interface that favors the other. Such complete wetting behavior from a binary mixture of statistical olefinic copolymers is reported. By means of a self-regulating geometry, it is found that the thickness of a wetting layer of one of the phases at the polymer-air interface, growing from the other coexisting phase, attains macroscopic dimensions, increasing logarithmically with time. These results indicate that binary polymer mixtures could be attractive models for the study of wetting phenomena.     

LIQUID CRYSTALS: New Banana Phases

Liquid crystals-materials that flow like a fluid but are optically anisotropic like a crystal-exhibit large responses to modest external disturbances. In his Perspective, Lubensky discusses the advances reported in two papers in this issue, both of which involve liquid crystals made from V-shaped or bent-core molecules. Walba et al. report a synthetic strategy for producing a ferroelectric phase from achiral bent-core molecules. Pratibha et al. show that new liquid crystalline phases form when bent-core molecules are mixed with a particular class of rodlike molecules. These papers introduce new molecular designs that yield new liquid crystalline phases with controlled structure and properties.     

Sequential interplay of nicotinic and GABAergic signaling guides neuronal development

GABA (gamma-aminobutyric acid), the major inhibitory transmitter in the brain, goes through a transitory phase of excitation during development. The excitatory phase promotes neuronal growth and integration into circuits. We show here that spontaneous nicotinic cholinergic activity is responsible for terminating GABAergic excitation and initiating inhibition. It does so by changing chloride transporter levels, shifting the driving force on GABA-induced currents. The timing of the transition is critical, because the two phases of GABAergic signaling provide contrasting developmental instructions. Synergistic with nicotinic excitation, GABAergic inhibition constrains neuronal morphology and innervation. The results reveal a multitiered activity-dependent strategy controlling neuronal development.     

Disorder-sensitive phase formation linked to metamagnetic quantum criticality

Condensed systems of strongly interacting electrons are ideal for the study of quantum complexity. It has become possible to promote the formation of new quantum phases by explicitly tuning systems toward special low-temperature quantum critical points. So far, the clearest examples have been appearances of superconductivity near pressure-tuned antiferromagnetic quantum critical points. We present experimental evidence for the formation of a nonsuperconducting phase in the vicinity of a magnetic field-tuned quantum critical point in ultrapure crystals of the ruthenate metal Sr3Ru2O7, and we discuss the possibility that the observed phase is due to a spin-dependent symmetry-breaking Fermi surface distortion.     

Quantum criticality: competing ground states in low dimensions

Small changes in an external parameter can often lead to dramatic qualitative changes in the lowest energy quantum mechanical ground state of a correlated electron system. In anisotropic crystals, such as the high-temperature superconductors where electron motion occurs primarily on a two-dimensional square lattice, the quantum critical point between two such lowest energy states has nontrivial emergent excitations that control the physics over a significant portion of the phase diagram. Nonzero temperature dynamic properties near quantum critical points are described, using simple theoretical models. Possible quantum phases and transitions in the two-dimensional electron gas on a square lattice are discussed.     

Two-dimensional rare gas solids

Monolayers of rare gas atoms adsorbed onto the basal planes of graphite play the same prototype role in two dimensions that rare gas liquids and solids do in three dimensions. In recent experiments such novel phenomena as continuous melting, the lack of true crystallinity in two dimensions, orientationally ordered fluid phases, and melting from a solid to a reentrant fluid with decreasing temperature have been observed. Because the forces in these rare gas monolayers are simple and well understood, by studying them the investigator can examine a direct interface between experiment and first principles. In order to understand the phases and phase transitions that occur in such materials, it is necessary to consider the geometrical matching of the rare gas overlayer to the graphite substrate. It turns out that in two dimensions both the local and the long-distance behavior are important. These two-dimensional rare gas solids may be effectively probed with synchrotron x-ray techniques, and the results of a series of synchrotron x-ray scattering studies of these solids are presented.     

Simulation of water and nitrogen dynamics as affected by drip fertigation strategies

The aim of drip fertigation is synchronising the application of water and nutrients with crop requirements, and maintaining the proper concentration and distribution of nutrient and water in the soil. The wetting patterns and nutrient distributions under drip fertigation have been proved to be closely related to the fertigation strategies. In order to find out the critical factors that affect the nutrient distribution under different drip fertigaiton strategies, a computer simulation model HYDRUS2D/3D was used to simulate the water and nitrate distribution for various fertigation strategies from a surface point source. Simulation results were compared with the observed ones from our previous studies. A 15° wedge-shaped plexiglass container was used in our experiment to represent one-twenty-fourth of the complete cylinder. The height of container is 40 cm, and the radius is 41 cm. The ammonium nitrate solution was added through a no. 7 needle connected to a Mariotte tube with a flexible hose. The soil water content, nitrate and ammonium concentrations were measured. The comparison of simulated and observed data demonstrated that the model performed reliably. The numerical analysis for various fertigation strategies from a surface point source showed that:(1) The total amount of irrigation water, the concentration of the fertilizer solution and the amount of pure water used to flush the pipeline after fertilizer solution application are the three critical factors influencing the distribution of water and fertilizer nitrogen in the soil.(2) The fresh water irrigation duration prior to fertigation has no obvious effect on nitrate distribution. The longer flushing time period after fertigation resulted in nitrate accumulation closer to the wetting front. From the point of avoiding the possibility of nitrate loss from the root zone, we recommended that the flushing time period should be as shorter as possible.(3) For a given amount of fertilizer, higher concentration of the fertilizer applied solution reduces the potential of nitrate leaching in drip irrigation system. While, lower concentration of the fertilizer solution resulted in an uniform distribution of nitrate band closer to the wetted front.     

Deconfined quantum critical points

The theory of second-order phase transitions is one of the foundations of modern statistical mechanics and condensed-matter theory. A central concept is the observable order parameter, whose nonzero average value characterizes one or more phases. At large distances and long times, fluctuations of the order parameter(s) are described by a continuum field theory, and these dominate the physics near such phase transitions. We show that near second-order quantum phase transitions, subtle quantum interference effects can invalidate this paradigm, and we present a theory of quantum critical points in a variety of experimentally relevant two-dimensional antiferromagnets. The critical points separate phases characterized by conventional "confining" order parameters. Nevertheless, the critical theory contains an emergent gauge field and "deconfined" degrees of freedom associated with fractionalization of the order parameters. We propose that this paradigm for quantum criticality may be the key to resolving a number of experimental puzzles in correlated electron systems and offer a new perspective on the properties of complex materials.     

Quantum phase transition in organic charge-transfer complexes

A phase transition in an organic charge-transfer complex, which originates from the neutral-ionic valence instability, can be tuned toward zero kelvin with use of external pressure or chemical modification as a control parameter. The phase diagram and observed dielectric behaviors are typical of quantum paraelectricity, yet this zero-kelvin transition point namely, the quantum critical point, accompanies large quantum fluctuation of the molecular charge, as demonstrated by the molecular vibrational mode spectra. The result indicates that the pi-electron transfer between donor and acceptor molecules is coupled with the zero-point lattice dynamics around the quantum critical point.     

Macroscopic separation of dense fluid phase and liquid phase of phosphorus

Structural transformation between a dense molecular fluid and a polymeric liquid of phosphorus that occurred at about 1 gigapascal and 1000 degrees C was investigated by in situ x-ray radiography. When the low-pressure fluid was compressed, dark and round objects appeared in the radiograph. X-ray diffraction measurements confirmed that these objects were the highpressure liquid. The drops grew and eventually filled the sample space. Decompressing caused the reverse process. The macroscopic phase separation supported the existence of a first-order phase transition between two stable disordered phases besides the liquid-gas transition. X-ray absorption measurements revealed that the change in density at the transition corresponds to about 40% of the density of the high-pressure liquid.     

近30年河北省小麦育成品种产量性状分析

以河北省区试对照品种的更换时间为界,将近30年的小麦育种历程划分为5个阶段,对每阶段育成品种的产量性状研究得出：1975—1979年泰山4号作对照和1980—1988年冀麦7号作对照的两个育种阶段为产量育种稳步提高阶段;1989—1992年冀麦24作对照的育种阶段为产量育种飞跃阶段;1993—1998年以冀麦36为对照和1999至今石4185为对照的两个育种阶段为产量育种攻坚阶段。对每阶段的产量成因分析认为：中等穗数、重穗粒、重品种类型的选育,是高产育种的突破口,穗粒数、千粒重的同时改良,增产潜力大,容易找到理想结合点,更有利于产量突破。     

Pairing and phase separation in a polarized Fermi gas

We report the observation of pairing in a gas of atomic fermions with unequal numbers of two components. Beyond a critical polarization, the gas separates into a phase that is consistent with a superfluid paired core surrounded by a shell of normal unpaired fermions. The critical polarization diminishes with decreasing attractive interaction. For near-zero polarization, we measured the parameter beta = -0.54 +/- 0.05, describing the universal energy of a strongly interacting paired Fermi gas, and found good agreement with recent theory. These results are relevant to predictions of exotic new phases of quark matter and of strongly magnetized superconductors.     

管道内天然气水合物沉积演化进程数值模拟

传统的双欧拉流体模型将水合物颗粒近似为流体相进行两相流动沉积预测,并未考虑流动过程中由相变导致颗粒生成的影响.为了解决该问题,在OpenFoam4.0开源计算软件植入双流体模型、界面面积传输方程、对流换热方程,在考虑水合物颗粒聚并、破碎效率的同时,引入关键的相变源项,根据管内温度场分布实时模拟计算水合物生成量,并在之后...     

Metal-insulator transition in disordered two-dimensional electron systems

We present a theory of the metal-insulator transition in a disordered two-dimensional electron gas. A quantum critical point, separating the metallic phase, which is stabilized by electronic interactions, from the insulating phase, where disorder prevails over the electronic interactions, has been identified. The existence of the quantum critical point leads to a divergence in the density of states of the underlying collective modes at the transition, causing the thermodynamic properties to behave critically as the transition is approached. We show that the interplay of electron-electron interactions and disorder can explain the observed transport properties and the anomalous enhancement of the spin susceptibility near the metal-insulator transition.     

The onset of turbulence in pipe flow

Shear flows undergo a sudden transition from laminar to turbulent motion as the velocity increases, and the onset of turbulence radically changes transport efficiency and mixing properties. Even for the well-studied case of pipe flow, it has not been possible to determine at what Reynolds number the motion will be either persistently turbulent or ultimately laminar. We show that in pipes, turbulence that is transient at low Reynolds numbers becomes sustained at a distinct critical point. Through extensive experiments and computer simulations, we were able to identify and characterize the processes ultimately responsible for sustaining turbulence. In contrast to the classical Landau-Ruelle-Takens view that turbulence arises from an increase in the temporal complexity of fluid motion, here, spatial proliferation of chaotic domains is the decisive process and intrinsic to the nature of fluid turbulence.     

Superconductivity in dense lithium

Superconductivity in compressed lithium is observed by magnetic susceptibility and electrical resistivity measurements. A superconducting critical temperature (Tc) is found ranging from 9 to 16 kelvin at 23 to 80 gigapascals. The pressure dependence of Tc suggests multiple phase transitions, consistent with theoretical predictions and reported x-ray diffraction results. The observed values for Tc are much lower than those theoretically predicted, indicating that more sophisticated theoretical treatments similar to those proposed for metallic hydrogen may be required to understand superconductivity in dense phases of lithium.     

牡丹花芽的形态发生及其生命周期的观察

牡丹花芽是一个混合芽。它的形成和分化是由腋芽原基开始,历时三个年周期大约25个月的发育结束其生命周期。在三年发育过程中,顺序形成腋芽原始体,花原基和种子及果实。在器管建造过程中可以区分为营养生长和生殖生长两个大的阶段。由叶原基产生结束到苞片原基开始产生为其质变的临界点。如果此时的营养条件和成花激素都是合适的。腋芽原基就会继续发育而成混合芽。否则,发育就终止在叶原基形成阶段,只能形成叶芽。任何一年的处在第二个年周期的混合芽都要产生子一代芽的原始体。子一代芽又在它的第二个周期中产生子二代芽的原始体,一代接一代,依次类推的发育下去。利用花芽形成的规律可以解决牡丹栽培上的一些实际问题。     

On the thermodynamic stability of confined thin films under shear

Thin films of monatomic fluid constrained between two plane-parallel structured solid walls have been modeled by Monte Carlo simulation under conditions (fixed temperature, chemical potential, and normal stress or load) prevailing in high-precision measurements of surface forces. Several states of the film, corresponding to different numbers of layers of fluid parallel with the walls, are generally consistent with these conditions, but only one is thermodynamically stable; the others are metastable. When the walls are properly aligned, epitaxial solid phases are stable. These melt under shear, eventually becoming metastable, whereupon a drainage (or imbibition) transition occurs, leading to a stable phase with fewer (or more) layers.     

Anisotropic violation of the Wiedemann-Franz law at a quantum critical point

A quantum critical point transforms the behavior of electrons so strongly that new phases of matter can emerge. The interactions at play are known to fall outside the scope of the standard model of metals, but a fundamental question remains: Is the basic concept of a quasiparticle-a fermion with renormalized mass-still valid in such systems? The Wiedemann-Franz law, which states that the ratio of heat and charge conductivities in a metal is a universal constant in the limit of zero temperature, is a robust consequence of Fermi-Dirac statistics. We report a violation of this law in the heavy-fermion metal CeCoIn5 when tuned to its quantum critical point, depending on the direction of electron motion relative to the crystal lattice, which points to an anisotropic destruction of the Fermi surface.     

利用河南-海南两地三季生态差异鉴定玉米品种丰产稳产性

【目的】加快高产稳产广适性玉米杂交种的筛选鉴定。【方法】在河南郑州-海南三亚设置6种鉴定试验环境,于2011—2012 年对11个玉米新品种（组合）进行3个生产周期的试验研究,通过与2011年河南9个试验点鉴定试验结果的对比,研究了两地生态环境条件的差异以及两地三季玉米主要性状的生态稳定性和相关性。【结果】河南-海南两地生态环境条件差异较大,与河南相比,玉米生长期间海南一期和海南二期光照时数较河南分别增加2.69%和11.17%,平均温度分别增加-0.39%和11.02%,降雨量分别减少15.49%和8.15%。两地的能量来源河南以短波辐射为主,海南一期、海南二期以长波辐射为主。11个品种（组合）生育期海南一期、海南二期平均分别较河南延长5.7 d和缩短7.02 d。玉米主要性状在两地的表现存在一定的相关关系。利用海南的自然条件可对品种的生育期、株高、穗粗、秃尖长、穗行数、雄穗分枝、穗位叶长和基部第三茎节长进行有效鉴定,且除出籽率之外,在海南二期选择更有效。对穗位高、穗长、行粒数、穗粒数、千粒重、产量、茎节数、穗位叶宽、基部第三节茎粗等的选择标准应适当放宽,选择应以河南为主。青枯病、锈病适合在海南鉴定,叶斑病、粗缩病适合在河南鉴定。鉴定结果河南-海南两地表现一致。6种鉴定试验环境中,河南适宜密度、海南二期旱瘠处理鉴定效果最好,兼具较强的鉴别力和较好的代表性,海南二期正常管理和海南一期正常管理次之,河南高密度和海南一期旱瘠处理适合淘汰稳定性差的品种。不同品种产量在各鉴定环境条件下表现差异较大。仅仅利用一种生态环境或者任意一种鉴定环境都不能对品种的综合性能进行很好地评价。【结论】在海南对玉米新品种（组合）部分性状的选择是有效的,利用河南-海南一年两地三季相结合的方法能够对玉米新品种（组合）的丰产稳产性进行更有效地鉴定。