Complex Optical Surfaces Formed by Replica Molding Against Elastomeric Masters

Complex, optically functional surfaces in organic polymers can be fabricated by replicating relief structures present on the surface of an elastomeric master with an ultraviolet or thermally curable organic polymer, while the master is deformed by compression, bending, or stretching. The versatility of this procedure for fabricating surfaces with complex, micrometer- and submicrometer-scale patterns was demonstrated by the production of (i) diffraction gratings with periods smaller than the original grating; (ii) chirped, blazed diffraction gratings (where the period of a chirped grating changes continuously with position) on planar and curved surfaces; (iii) patterned microfeatures on the surfaces of approximately hemispherical objects (for example, an optical surface similar to a fly's eye); and (iv) arrays of rhombic microlenses. These topologically complex, micropatterned surfaces are difficult to fabricate with other techniques.     

Alignment of liquid crystals with patterned isotropic surfaces

The molecules of a nematic liquid crystal exposed to an isotropic surface adopt a mean tilt relative to the normal but have no in-plane alignment-that is, they are free to have any azimuthal orientation in the surface plane. Pursuing the theoretical suggestion by Meyer that, in spite of this azimuthal degeneracy, spatially inhomogeneous isotropic surfaces combine with liquid crystal elastic anisotropy to produce alignment, we show that a boundary line between two isotropic regions that differ in mean tilt does indeed align the liquid crystal. The boundaries on a patterned surface of distinct isotropic regions thus act as a system of lines that the molecular orientation locally follows. This enables the development of liquid crystal alignment surfaces based on printing or lithographic patterning.     

Correlation between surface free energy and surface constitution

Self-assembled monolayers (SAMs) of alkylsiloxanes on elastomeric PDMS (polydimethylsiloxane) were used as model systems to study interactions between surfaces. Surface free energies (gammasv) of these chemically modified surfaces were estimated by measuring the deformations that resulted from the contact between small semispherical lenses and flat sheets of the elastomer under controlled loads. The measured surface free energies correlated with the surface chemical compositions of the SAMs and were commensurate with the values estimated from the measurements of contact angles. This study provides direct experimental evidence for the validity of estimates of the surface free energies of low-energy solids obtained from contact angles.     

毛乌素沙地不同下垫面地表凝结水形成过程

水分是制约干旱半干旱地区植物生长的主要因子。土壤凝结水数量虽小,但作为一种持续稳定的水源,对于维持干旱半干旱地区的生态平衡至关重要。为了深入了解下垫面差异对地表凝结水形成过程的影响,于2014年7—8月采用称质量法,在毛乌素沙地使用微渗仪对裸沙地、油蒿林地、沙柳林地的地表凝结水形成进行观测,并对相关气象因子和土壤温度进行同步监测。结果表明:1)地表凝结水形成在日落后即刻开始,而在日出约1 h后停止,3种下垫面地表凝结水形成规律近似;油蒿和沙柳林地的地表凝结水结束时间晚于裸沙地,有助于延长林地隐花植物和微生物对凝结水的吸收时间。2)在观测期(17 d),裸沙地、油蒿林地、沙柳林地的地表凝结水总量依次为3.332、2.382、1.817 mm,裸沙地日均凝结水量显著大于油蒿和沙柳林地(P0.05),表明灌丛覆盖会改变近地面性质和林内小气候,导致地表凝结水量减少。3)地表凝结水量与空气相对湿度呈极显著正相关关系(P0.01),与气温呈极显著负相关关系(P0.01),与风速呈显著负相关关系(P0.05)。以上研究结果可为毛乌素沙地潜在水资源评估和生态系统管理提供依据。      

Surface analysis and atomic physics with slow positron beams

Recent advances in slow positron beam techniques are making it possible to study the interactions of low-energy positrons with gas molecules and solid surfaces and to measure the properties of free positronium atoms. New surface related results include the observation of surfaces with negative positron affinity and the thermionic emission of slow positronium atoms, low-energy positron diffraction measurements, and the sensitive detection of near-surface crystalline imperfections. Two recent successful experiments in atomic physics are the formation of the positronium negative ion and the optical excitation of positronium for high precisin spectroscopy. Prospects for a positron microscope and the study of exotic antimatter systems such as the two-component Fermi gas are based on the imminent possibility of enormous increases in the brightness and instantaneous intensity of positron beams.     

X-ray diffraction and computation yield the structure of alkanethiols on gold(111)

The structure of self-assembled monolayers (SAMs) of long-chain alkyl sulfides on gold(111) has been resolved by density functional theory-based molecular dynamics simulations and grazing incidence x-ray diffraction for hexanethiol and methylthiol. The analysis of molecular dynamics trajectories and the relative energies of possible SAM structures suggest a competition between SAM ordering, driven by the lateral van der Waals interaction between alkyl chains, and disordering of interfacial Au atoms, driven by the sulfur-gold interaction. We found that the sulfur atoms of the molecules bind at two distinct surface sites, and that the first gold surface layer contains gold atom vacancies (which are partially redistributed over different sites) as well as gold adatoms that are laterally bound to two sulfur atoms.     

Deep UV photochemistry of chemisorbed monolayers: patterned coplanar molecular assemblies

Deep ultraviolet (UV) irradiation is shown to modify organosilane self-assembled monolayer (SAM) films by a photocleavage mechanism, which renders the surface amenable to further SAM modification. Patterned UV exposure creates alternating regions of intact SAM film and hydrophilic, reactive sites. The exposed regions can undergo a second chemisorption reaction to produce an assembly of SAMs in the same molecular plane with similar substrate attachment chemistry. The UV-patterned films are used as a template for selective buildup of fluorophores, metals, and biological cells.     

Self-assembled organic monolayers: model systems for studying adsorption of proteins at surfaces

Self-assembled monolayers (SAMs) of omega-functionalized long-chain alkanethiolates on gold films are excellent model systems with which to study the interactions of proteins with organic surfaces. Monolayers containing mixtures of hydrophobic (methyl-terminated) and hydrophilic [hydroxyl-, maltose-, and hexa(ethylene glycol)-terminated] alkanethiols can be tailored to select specific degrees of adsorption: the amount of protein adsorbed varies monotonically with the composition of the monolayer. The hexa(ethylene glycol)-terminated SAMs are the most effective in resisting protein adsorption. The ability to create interfaces with similar structures and well-defined compositions should make it possible to test hypotheses concerning protein adsorption.     

Voyager 2 in the uranian system: imaging science results

Voyager 2 images of the southern hemisphere of Uranus indicate that submicrometersize haze particles and particles of a methane condensation cloud produce faint patterns in the atmosphere. The alignment of the cloud bands is similar to that of bands on Jupiter and Saturn, but the zonal winds are nearly opposite. At mid-latitudes (-70 degrees to -27 degrees ), where winds were measured, the atmosphere rotates faster than the magnetic field; however, the rotation rate of the atmosphere decreases toward the equator, so that the two probably corotate at about -20 degrees . Voyager images confirm the extremely low albedo of the ring particles. High phase angle images reveal on the order of 10(2) new ringlike features of very low optical depth and relatively high dust abundance interspersed within the main rings, as well as a broad, diffuse, low optical depth ring just inside the main rings system. Nine of the newly discovered small satellites (40 to 165 kilometers in diameter) orbit between the rings and Miranda; the tenth is within the ring system. Two of these small objects may gravitationally confine the e ring. Oberon and Umbriel have heavily cratered surfaces resembling the ancient cratered highlands of Earth's moon, although Umbriel is almost completely covered with uniform dark material, which perhaps indicates some ongoing process. Titania and Ariel show crater populations different from those on Oberon and Umbriel; these were probably generated by collisions with debris confined to their orbits. Titania and Ariel also show many extensional fault systems; Ariel shows strong evidence for the presence of extrusive material. About halfof Miranda's surface is relatively bland, old, cratered terrain. The remainder comprises three large regions of younger terrain, each rectangular to ovoid in plan, that display complex sets of parallel and intersecting scarps and ridges as well as numerous outcrops of bright and dark materials, perhaps suggesting some exotic composition.     

X-ray Damage to CF3CO2-Terminated Organic Monolayers on Si/Au: Principal Effect of Electrons

The relative importance of x-rays alone and of x-ray-generated primary and secondary electrons in damaging organic materials was explored by use of self-assembled monolayers (SAMs) on multilayer thin-film supports. The substrates were prepared by the deposit of thin films of silicon (0, 50, 100, and 200 angstroms) on thick layers of gold (2000 angstroms). These systems were supported on chromium-primed silicon wafers. Trifluoroacetoxy-terminated SAMs were assembled on these substrates, and the samples were irradiated with common fluxes of monochromatic aluminum K(alpha) x-rays. The fluxes and energy distributions of the electrons generated by interactions of the x-rays with the various substrates, however, differed. The substrates that emitted a lower flux of electrons exhibited a slower loss of fluorine from the SAMs. This observation indicated that the electrons-and not the x-rays themselves-were largely responsible for the damage to the organic monolayer.     

脉冲偏压电弧离子镀CrN薄膜的表面形貌和性能研究

采用脉冲偏压电弧离子镀技术沉积了CrN薄膜,并考察了在不同偏压下薄膜的表面形貌、相结构、显微硬度和耐磨性．随着偏压的增加,CrN薄膜表面颗粒逐渐变少,表面粗糙度降低,结晶度增大,偏压为-100V的CrN薄膜具有致密的表面结构,较高的硬度,最佳的抗磨性能．     

Polar orientation of dyes in robust multilayers by zirconium phosphate-phosphonate interlayers

Polar orientation of molecules in solids leads to materials with potentially useful properties such as nonlinear optical and electrooptical activity, electrochromism, and pyroelectricity. A simple self-assembly procedure for preparing such materials is introduced that yields multiple polar dye monolayers on solid surfaces joined by zirconium phosphate-phosphonate interlayers. Second harmonic generation (SHG) shows that the multilayers have polar order that does not decrease with increasing numbers (up to a large number) of monolayers in the film. The inorganic interlayers, as determined by SHG, impart excellent orientational stability to the dye molecules, with the onset of orientational randomization above 150 degrees C.     

Cu2+胁迫诱导花鲢血细胞凋亡的研究

以花鲢Aristichthys nobilis（Rich）血细胞为研究对象,选用不同浓度的铜离子Cu^2＋进行不同时间的胁迫诱导,通过瑞士姬姆萨染色和AO/EB荧光染色,在光学和荧光显微镜下观察细胞形态变化,并统计凋亡率。结果表明：在Cu^2＋的胁迫作用下,花鲢血细胞呈现细胞变圆、核变圆、核边缘化、形成凋亡小体等凋亡形态特征,且凋亡细胞随着Cu^2＋浓度的增加和作用时间的延长而增加。表明Cu^2＋能诱导花鲢血细胞发生典型的凋亡,而且细胞凋亡率与Cd^2＋的浓度和处理时间成明显的剂量-效应关系。     

Crystal Structure of the Solid Electrolyte, RbAg4I5

The crystal structure of the solid electrolyte RbAg(4)I(5) has been determined from single-crystal x-ray diffraction counter data. There are four RbAg(4)I(5) in a cubic unit cell with a = 11.24 A. The structure refinement, by least squares, is based on space group P4(1)3 (O(7)). The arrangement of the iodide ions is similar to that of the manganese atoms in beta-manganese, and provides 56 iodide tetrahedra per unit cell, which share faces in such manner as to provide diffusion paths for the silver ions. The occurrence of the two low-temperature phases of RbAg(4)I(5) has been established by x-ray diffraction and optical examination.     

Fractal surfaces of proteins

Fractal surfaces can be used to characterize the roughness or irregularity of protein surfaces. The degree of irregularity of a surface may be described by the fractal dimension D. For protein surfaces defined with probes in the range of 1.0 to 3.5 angstroms in radius, D is approximately 2.4 or intermediate between the value for a completely smooth surface (D = 2) and that for a completely space-filling surface (D = 3). Individual regions of proteins show considerable variation in D. These variations may be related to structural features such as active sites and subunit interfaces, suggesting that surface texture may be a factor influencing molecular interactions.     

Current issues and problems in the chemical vapor deposition of diamond

Current issues and problems in the chemical vapor deposition (CVD) of diamond are those which relate to its characterization, its nucleation on foreign surfaces, the question of its formation in preference to the other phases of solid carbon (for example, graphite, chaoite, or lonsdaleite), why different morphologies and crystallographic orientations (textures) are seen in different experiments or with different parameters in the same experiment, and finally whether well-crystallized metastable phases can be obtained by CVD in other material systems or are only a peculiarity of carbon chemistry. Whether a given carbon coating is justly described as diamond has been such an issue, and coatings should clearly show evidence for diamond by x-ray diffraction and Raman spectroscopy before the claim of diamond is made. Experimental results have not been consistent in many cases, and much work remains to be done before an accurate assessment can be made of the technological impact of the development.     

佛山市高明区生态安全格局和建设用地扩展预案

城市生态环境问题已上升到生态安全的层面.以人类生存安全和理想人居环境为目标,基于空间数据和统计资料,利用景观安全格局原理和地理信息系统空间分析方法,构建了包含基本保障格局-缓冲格局-最优格局3个级别的水安全格局、地质灾害安全格局、大气安全格局、生物保护安全格局和农田安全格局,叠加得到高明区综合生态安全格局,在此基础上提出了高明区建设用地扩展最优方案和生态功能分区.结果显示,并非生态安全格局水平越高,城乡发展模式越优,缓冲生态安全格局下的高明区建设用地扩展模式,最可能实现生态安全保护与城镇扩展的和谐发展.综合生态安全格局明确了区域的生态环境敏感区和生态服务功能重要区,为区域生态功能分区提供了新的思路.     

Chondrules with peculiar REE patterns: implications for solar nebular condensation at high C/O

Rare earth element (REE) data from two ordinary chondrite chondrules show distinct negative chondrite-normalized concentration anomalies of samarium, europium, and ytterbium. The peculiar patterns may be the result of REE gas/solid fractionation at an oxygen fugacity lower than has been assumed for the canonical solar nebula. We suggest that the two ordinary chondrite chondrules acquired the fractionated REE patterns by incorporation of highly reduced, ultrarefractory condensates in their precursors. This interpretation implies that high-temperature condensation processes occurred in nebular environments with a strong deficit in oxygen, such as regions with an enhanced carbon/oxygen ratio.     

The Effect of Surface Roughness on Triton's Volatile Distribution

Calculations of radiative equilibrium temperatures on Triton's rough surface suggest that significant condensation of N(2) may be occurring in the northern equatorial regions, despite their relatively dark appearance. The bright frost is not apparent in the Voyager images because it tends to be concentrated in relatively unilluminated facets of the surface. This patchwork of bright frost-covered regions and darker bare ground may be distributed on scales smaller than that of the Voyager resolution; as a result the northern equatorial regions may appear relatively dark. This hypothesis also accounts for the observed wind direction in the southern hemisphere because it implies that the equatorial regions are warmer than the south polar regions.     

Far-field optical hyperlens magnifying sub-diffraction-limited objects

The diffraction limit of light, which is causd by the loss of evanescent waves in the far field that carry high spatial frequency information, limits the resolution of optical lenses to the order of the wavelength of light. We report experimental demonstration of the optical hyperlens for sub-diffraction-limited imaging in the far field. The device magnifies subwavelength objects by transforming the scattered evanescent waves into propagating waves in an anisotropic medium and projects the high-resolution image at far field. The optical hyperlens opens up possibilities in applications such as real-time biomolecular imaging and nanolithography.