Low-power switching of phase-change materials with carbon nanotube electrodes

Phase-change materials (PCMs) are promising candidates for nonvolatile data storage and reconfigurable electronics, but high programming currents have presented a challenge to realize low-power operation. We controlled PCM bits with single-wall and small-diameter multi-wall carbon nanotubes. This configuration achieves programming currents of 0.5 microampere (set) and 5 microamperes (reset), two orders of magnitude lower than present state-of-the-art devices. Pulsed measurements enable memory switching with very low energy consumption. Analysis of over 100 devices finds that the programming voltage and energy are highly scalable and could be below 1 volt and single femtojoules per bit, respectively.     

Biomolecular interactions at phospholipid-decorated surfaces of liquid crystals

The spontaneous assembly of phospholipids at planar interfaces between thermotropic liquid crystals and aqueous phases gives rise to patterned orientations of the liquid crystals that reflect the spatial and temporal organization of the phospholipids. Strong and weak specific-binding events involving proteins at these interfaces drive the reorganization of the phospholipids and trigger orientational transitions in the liquid crystals. Because these interfaces are fluid, processes involving the lateral organization of proteins (such as the formation of protein- and phospholipid-rich domains) are also readily imaged by the orientational response of the liquid crystal, as are stereospecific enzymatic events. These results provide principles for label-free monitoring of aqueous streams for molecular and biomolecular species without the need for complex instrumentation.     

Optical activity and ferroelectricity in liquid crystals

Some liquid-crystalline phases of optically active materials are themselves optically active and have dissymmetric structures. The cholesteric phase and smectics C,I, and F have a helical order of their molecules. Plane-polarized light is rotated by the helix, and when the pitch of the helix is comparable to the wavelength of visible light, these phases will reflect irridescent light of a single color. The smectics phases can exhibit ferroelectricity and have been utilized recently in fast-switching light valves. A relation between the microscopic property of molecular configuration and the macroscopic properties of ferroelectricity and the rotation of plane-polarized light is developed.     

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.     

Self-organized discotic liquid crystals for high-efficiency organic photovoltaics

Self-organization of liquid crystalline and crystalline-conjugated materials has been used to create, directly from solution, thin films with structures optimized for use in photodiodes. The discotic liquid crystal hexa-peri-hexabenzocoronene was used in combination with a perylene dye to produce thin films with vertically segregated perylene and hexabenzocoronene, with large interfacial surface area. When incorporated into diode structures, these films show photovoltaic response with external quantum efficiencies of more than 34 percent near 490 nanometers. These efficiencies result from efficient photoinduced charge transfer between the hexabenzocoronene and perylene, as well as from effective transport of charges through vertically segregated perylene and hexabenzocoronene pi systems. This development demonstrates that complex structures can be engineered from novel materials by means of simple solution-processing steps and may enable inexpensive, high-performance, thin-film photovoltaic technology.     

Principles for measurement of chemical exposure based on recognition-driven anchoring transitions in liquid crystals

The competitive binding of a molecule forming a liquid crystal and a targeted analyte to a common molecular receptor presented at a solid surface possessing nanometer-scale topography is used to trigger an easily visualized surface-driven change in the orientation of a micrometer-thick film of liquid crystal. Diffusion of the targeted analyte from atmosphere to surface-immobilized receptor across the micrometer-thick film of liquid crystal is fast (on the order of seconds), and the competitive interaction of the targeted analyte and liquid crystal with the receptor provides a high level of tolerance to nontargeted species (water, ethanol, acetone, and hexanes). Systems that provide parts-per-billion (by volume) sensitivity to either organoamine or organophosphorus compounds are demonstrated, and their use for imaging of spatial gradients in concentration is reported. This approach does not require complex instrumentation and could provide the basis of wearable personalized sensors for measurement of real-time and cumulative exposure to environmental agents.     

Hydrodefluorination of perfluoroalkyl groups using silylium-carborane catalysts

Carbon-fluorine bonds are among the most unreactive functionalities in chemistry. Interest in their activation arises in part from the high global warming potentials of anthropogenic polyfluoroorganic compounds. Conversion to carbon-hydrogen bonds (hydrodefluorination) is the simplest modification of carbon-fluorine bonds, but efficient catalytic hydrodefluorination of perfluoroalkyl groups has been an unmet challenge. We report a class of carborane-supported, highly electrophilic silylium compounds that act as long-lived catalysts for hydrodefluorination of trifluoromethyl and nonafluorobutyl groups by widely accessible silanes under mild conditions. The reactions are completely selective for aliphatic carbon-fluorine bonds in preference to aromatic carbon-fluorine bonds.     

Ferroelectric columnar liquid crystal featuring confined polar groups within core-shell architecture

Ferroelectric liquid crystals are materials that have a remnant and electrically invertible polar order. Columnar liquid crystals with a ferroelectric nature have potential use in ultrahigh-density memory devices, if electrical polarization occurs along the columnar axis. However, columnar liquid crystals having an axial nonzero polarization at zero electric field and its electrical invertibility have not been demonstrated. Here, we report a ferroelectric response for a columnar liquid crystal adopting a core-shell architecture that accommodates an array of polar cyano groups confined by a hydrogen-bonded amide network with an optimal strength. Under an applied electric field, both columns and core cyano groups align unidirectionally, thereby developing an extremely large macroscopic remnant polarization.     

非热电磁生物效应特性与液晶电流体动力不稳定性的对比研究

采用液晶生物膜模型，将非热电磁生物效应与液晶电流体动力不稳定性的特性进行了对比研究，提出非热电磁生物效应的关键机理是液晶生物膜的电流体不稳定性假说。并用此假说对非热电磁生物效应的非线性特性、协同性、相干性、“窗”特性、阈值特性等重要特性都作了很好的解释。     

Oxygen activation and reduction in respiration: involvement of redox-active tyrosine 244

Cytochrome oxidase activates and reduces O(2) to water to sustain respiration and uses the energy released to drive proton translocation and adenosine 5'-triphosphate synthesis. A key intermediate in this process, P, lies at the junction of the O(2)-reducing and proton-pumping functions. We used radioactive iodide labeling followed by peptide mapping to gain insight into the structure of P. We show that the cross-linked histidine 240-tyrosine 244 (His240-Tyr244) species is redox active in P formation, which establishes its structure as Fe(IV) = O/Cu(B)2+-H240-Y244. Thus, energy transfer from O2 to the protein moiety is used as a strategy to avoid toxic intermediates and to control energy utilization in subsequent proton-pumping events.     

免疫酶组化法对病料中多杀性巴氏杆菌定型的研究

本文采用自制的 B、A、D、E 定型酶抗体及由其组成的全价酶标抗体,以免疫酶直接法染色检查了20株多杀性巴氏杆菌及10株其它对照细菌感染致死小鼠脏器标本触片.并与脏器标本触片的免疫酶间接法染色,常规染色法及细菌分离培养鉴定等方法作了比较.建立了多杀性巴氏杆菌诊断和定型的一种特异快速的方法.     

施用专用叶面肥对荔枝座果率和产量的效应

以有机营养物质、中微量元素和植物生长物质组配的荔枝专用叶面肥在广东省3市(县)5个品种上进行肥效试验,结果表明:施用荔枝专用叶面肥有极显著的增产、提高品质和提高座果率的效果,增产幅度达11.1%~37.6%,达极显著水平。多数试验点增产效果优于常用保果剂,增产达3.22%~11.87%。具有提高荔枝果实维生素C、可溶糖、可溶性固形物含量,降低有机酸含量的效应。谢花后40天座果率和收获期的座果率分别比对照提高2.70~23.80个百分点和3.15~13.79个百分点。多数试验点和品种的座果率比常用保果剂处理分别提高2.01~15.81个百分点和2.19~6.25个百分点,达显著水平。     

免疫酶组化法对病料中多杀性巴氏杆菌定型的研究

 本文采用自制的B、A、D、E定型酶抗体及由其组成的全价酶标抗体,以免疫酶直接法染色检查了20株多杀性巴氏杆菌及10株其它对照细菌感染致死小鼠脏器标本触片.并与脏器标本触片的免疫酶间接法染色,常规染色法及细菌分离培养鉴定等方法作了比较.建立了多杀性巴氏杆菌诊断和定型的一种特异快速的方法.     

Mechanism for multiplication of atmospheric ice crystals: apparent charge distribution on laboratory crystals

Replication of ice crystals with vapor of methyl 2-cyanoacrylate has produced evidence of whiskers on them; an additional mechanism for the necessary multiplication of ice crystals in the atmosphere is suggested. This replication technique also confirms crystal clustering in the atmosphere and appears to confirm the distribution of electrical charge on ice crystals.     

High-resolution EM of colloidal nanocrystal growth using graphene liquid cells

We introduce a new type of liquid cell for in situ transmission electron microscopy (TEM) based on entrapment of a liquid film between layers of graphene. The graphene liquid cell facilitates atomic-level resolution imaging while sustaining the most realistic liquid conditions achievable under electron-beam radiation. We employ this cell to explore the mechanism of colloidal platinum nanocrystal growth. Direct atomic-resolution imaging allows us to visualize critical steps in the process, including site-selective coalescence, structural reshaping after coalescence, and surface faceting.     

PC开关电源启动电路的探讨

对于PC开关电源,无论是自激式还是他激式都存在一简单的启动电路.该电路直接影响电源启动的成败,尤其在电路中元件参数处于临界状态时,电源启动成败变成随机性.本文对部分常见的PC开关电源启动电路及故障现象进行探讨.     

Topographic mapping of the quantum hall liquid using a few-electron bubble

A scanning probe technique was used to obtain a high-resolution map of the random electrostatic potential inside the quantum Hall liquid. A sharp metal tip, scanned above a semiconductor surface, sensed charges in an embedded two-dimensional (2D) electron gas. Under quantum Hall effect conditions, applying a positive voltage to the tip locally enhanced the 2D electron density and created a "bubble" of electrons in an otherwise unoccupied Landau level. As the tip scanned along the sample surface, the bubble followed underneath. The tip sensed the motions of single electrons entering or leaving the bubble in response to changes in the local 2D electrostatic potential.     

鸡组织中泰拉霉素残留的高效液相色谱-串联质谱法检测

【目的】建立鸡血浆、肌肉、肝脏、肾脏中泰拉霉素残留的高效液相色谱-串联质谱(HPLC-MS/MS)检测方法。【方法】制备鸡血浆、肌肉、肝脏、肾脏泰拉霉素加标样品,经乙腈提取,SCX固相萃取小柱净化后,40℃氮气吹干,用乙腈-1mL/L甲酸水溶液(体积比为1∶1)定容,Luna C18(2)色谱柱分离,以乙腈-1mL/L甲酸水溶液(体积比为90∶10)为流动相进行梯度洗脱,通过质谱分析进行外标法定量,再通过试验确定HPLC-MS/MS的检出限和定量限,并对血浆和肌肉、肝脏、肾脏分别进行10,20,50μg/L和10,20,50μg/kg 3个水平的泰拉霉素添加回收试验。【结果】在5~200μg/L血浆样品和5~200μg/kg肌肉、肝脏、肾脏样品中,泰拉霉素含量与峰面积呈良好的线性关系(R0.99),血浆和肌肉、肝脏、肾脏样品中的泰拉霉素检出限依次为0.8μg/L和0.5,0.8,0.5μg/kg,定量限依次为2.0μg/L和1.0,2.0,1.0μg/kg。添加回收试验的平均回收率为80.3%~104.4%,日内相对标准偏差为5.0%~9.2%,日间相对标准偏差为5.2%~12.7%。【结论】HPLC-MS/MS方法简便、快速、准确,可用于鸡组织中泰拉霉素药物残留的确证和定量检测。     

液相色谱-安培法检测养殖水体中的几种染料类抗菌剂

利用液相色谱—安培法检测分析养殖水体中3种染料—孔雀石绿、结晶紫、亚甲基蓝及其代谢物,无需衍生,养殖水样品采用阳离子反相混合模式MCX小柱富集,色谱柱为Waters Xettra C18(250×4.6 mm,5μm)流动相采用70%甲醇[甲醇∶0.1 mol.L-1乙酸钠=7∶3(V/V),pH4.5],流速为1 mL.min-1。采用直流安培检测,氧化电位1.4 V,工作电极为玻碳电极。3种染料及其代谢物在0.05~100μg.mL-1范围内具有良好的线性关系,检测限在0.2~0.5μg.L-1范围内,回收率为66%~101%,方法的精密度在0.5%~4.8%。该方法具有灵敏度高、选择性好的优点。