Transmission Holographic Polymer Dispersed Liquid Crystals Based on a Siloxane Polymer

The low surface energy and the great immiscibility of poly (dimethylsiloxane) (PDMS) with liquid crystals (LCs) are used in the fabrication of holographic polymer dispersed liquid crystals (HPDLCs). By adding increasing amounts of PDMS, the extent of the phase separation between the polymer and the LC, the LC channel width, and—eventually—also the diffraction efficiency of the film can be increased, while keeping the droplet size essentially the same. In addition, the presence of PDMS causes a decrease in the switching voltage and an increase in the response time. At an optimum content of PDMS (PUA40), a minimum switching voltage of 4 V μm^?1, a rise time of 0.20 ms, and a decay of 14.75 ms were obtained. Regarding the effect of the LC content, an overshoot of the diffraction efficiency was observed when the amount of LC exceeded 35 %, which can be attributed to droplet coalescence.     

Electrical characteristics of a millisecond pulsed glow discharge

A μs and ms pulsed argon glow discharge was investigated with respect to the breakdown condition (Paschen curve). Moreover, current–voltage profiles were acquired for different discharge frequencies, pulse durations, cathode–anode spacing and discharge pressures. The breakdown voltage was dependent on the cathode material (Cu, steel, Ti and Al). No severe change in the breakdown voltage was observed for a 1 ms pulse at different frequencies. However, the theoretical breakdown curve, calculated based on the Paschen equation did not fit the experimental data. The current plots for different cathode–anode spacing showed a maximum at intermediate distance (8–10 mm). These data were consistent with mass spectrometric data acquired using the same instrument in a GC-GD-TOFMS chemical speciation study.     

The surface rubbing effect on morphologies of LC droplets and electro-optic properties of flexible PDLC films

The flexible polymer dispersed liquid crystal (PDLC) film with threshold voltage V ₁₀ and saturation driving voltage V ₉₀ as low as 0.34 V/μm and 0.77 V/μm, respectively, has been prepared successfully by polymerization induced phase separation (PIPS). The surface rubbing effect on morphologies of liquid crystals (LC) droplets and electro-optic properties of PDLC films has been studied experimentally and theoretically. We use a CVC (Color Video Camera) and a SEM (Scan Electron Microscope) to detect and characterize morphologies of LC droplets in the net of polymer. The result reveals that almost all the smaller LC droplets exhibit in the rubbing direction uniformly, and the texture of PDLC is similar to that of H-PDLC. Meanwhile, compared with the sample of the non-rubbing disposal, the response time declines evidently by 11.2 ms (i.e., the rising time τ_rise) and 27.2 ms (i.e., the decaying time τ_down), and the contrast ratio is improved from 18.5 to 35.9. Such a result can be attributed to the surface rubbing effect.     

松果状纳米氧化铁对液晶电光性能的影响

液晶材料被广泛应用于液晶显示器(LCD)中,但是由于液晶中杂质的存在,导致液晶的应用电压变大,增加了能耗。 为了降低应用中的阈值电压和饱和电压,通常向液晶中添加纳米颗粒来提高电光性能。 本文采用简单的化学沉淀法制备了形貌均一,大小尺寸均匀的松果状氧化铁(P-Fe₂O₃)纳米颗粒。 将其掺杂到向列相液晶4-氰基-4'-戊基联苯(4-cyano-4'-pentylbiphenyl,5CB)中,结果表明,掺杂质量分数为0.5%时,电光性能达到最优,阈值电压和饱和电压分别降低24.8%和45.2%,对比度增大46%,响应时间降低至17.6 ms,此性能优于相同条件下掺杂普通Fe₂O₃纳米颗粒的向列相液晶5CB,其阈值电压和饱和电压分别降低15%和16%。 这归因于松果状Fe₂O₃纳米颗粒可以在向列相液晶5CB中均匀分散,其粗糙的表面吸附了液晶中的杂质离子,减少了杂质离子的屏蔽效应,从而提高了电光性能。     

Polarity Effects of Propylene Carbonate on Breakdown Strength in Microsecond Range

We investigate the polarity effects of the propylene carbonate on the breakdown voltage using the needle-plate electrodes with gaps of 0.5, 1.0, and 2.0 mm. The devices used in this study involve a compact capacitive-energy-storage pulse power source with charging time varying from 5 ms to 20 ms and a test cell with the needle-plate electrodes. The breakdown voltage is recorded by a digital oscilloscope for each gap. The results of these three groups indicate that the positive breakdown voltage is higher than the negative one and the breakdown voltage of the PC increases with the ascending electrode gap. In addition, a simulation isconducted to support this experiment. Some explanations about the polarity effect of the PC are also given.     

Theoretical analysis of localized heating in human skin subjected to high voltage pulses

Electroporation, the increase in the permeability of bilayer lipid membranes by the application of high voltage pulses, has the potential to serve as a mechanism for transdermal drug delivery. However, the associated current flow through the skin will increase the skin temperature and might affect nearby epidermal cells, lipid structure or even transported therapeutic molecules. Here, thermal conduction and thermal convection models are used to provide upper and lower bounds on the local temperature rise, as well as the thermal damage, during electroporation from exponential voltage pulses (70 V maximum) with a 1 ms and a 10 ms pulse time constant. The peak temperature rise predicted by the conduction model ranges from 19 degrees C for a 1 ms time constant pulse to 70 degrees C for the 10 ms time constant pulse. The convection (mass transport) model predicts a 18 degrees C peak rise for 1 ms time constant pulses and a 51 degrees C peak rise for a 10 ms time constant pulse. The convection model compares more favorably with previous experimental studies and companion observations of the local temperature rise during electroporation. Therefore, it is expected that skin electroporation can be employed at a level which is able to transport molecules transdermally without causing significant thermal damage to the tissue.     

Investigation of electro-optical characteristics of photo-aligned TN-LCDs on PCEMA surfaces

In this work, a novel photo-alignment material, poly(cinnamolyethyl methacrylate) (PCEMA), was synthesized by photo-dimerization. We investigated the electro-optical characteristics of twisted nematic (TN)-liquid crystal displays (LCDs) photo-aligned with linearly polarized UV light irradiation at normal direction on the PCEMA surfaces. Excellent voltagetransmittance characteristics were observed. The threshold voltage of the photo-aligned TN-LCD decreases with increasing UV irradiation time. Additionally, response times are almost the same as for a rubbing-aligned TN-LCD.     

Investigation of electro-optical characteristics of photo-aligned TN-LCDs on PCEMA surfaces

In this work, a novel photo-alignment material, poly(cinnamolyethyl methacrylate) (PCEMA), was synthesized by photo-dimerization. We investigated the electro-optical characteristics of twisted nematic (TN)-liquid crystal displays (LCDs) photo-aligned with linearly polarized UV light irradiation at normal direction on the PCEMA surfaces. Excellent voltagetransmittance characteristics were observed. The threshold voltage of the photo-aligned TN-LCD decreases with increasing UV irradiation time. Additionally, response times are almost the same as for a rubbing-aligned TN-LCD.     

Electro-optical properties of holographically patterned polymer-stabilized cholesteric liquid crystals

Electro-optical properties of cholesteric liquid crystals (LCs) with holographically patterned polymer stabilization were examined. It is hypothesized that increasing the LC domain size in a single dimension, relative to a random three-dimensional network of LC pockets separated by polymer strands, will allow enhanced electro-optical properties of the final device. Prior to holographic patterning, polymer stabilization with large elastic memory was generated by way of high irradiation intensities and optimized material choices. High irradiation intensities are required for the holographic patterning process to maintain polymer layer formation. At optimized conditions, polymer patterning of the stabilization allowed for an approximate 20% increase in the clear state transmission of the device, and allowed for an approximate 3 V µm^-1 reduction in the overall switching voltage as compared to an analogous floodlit irradiated sample. Switching times were increased at most threefold with holographic patterning, but all relaxation times were below 20 ms. The enhanced electro-optical properties appear to stem from a single dimension domain size increase, which allows for a reduction in the LC/polymer interaction.     

A rapid transportation facility for irradiation with thermal and fast neutrons

A rapid vertical transportation system for irradiation with thermal and fast neutrons is devised and partly constructed for inserting samples into the central thimble of our TRIGA MARK II reactor. Fast neutrons will be produced by a⁶LiD-converter, so that the energy distribution of neutrons is hardened by absorption of thermal and by the production of 14 MeV neutrons. In pulse irradiation, the 14 MeV-neutron flux is expected to be in the order of 10¹²/s. The transportation time is to be below 30ms to enable determination of short-lived nuclides down to 15ms. Helium will be used as propelling gas.     

Photolysis of polymers using the medium pressure mercury lamp: Part 1—Photolysis and product analysis apparatus and the effect of some experimental variables

A photolysis cell, designed for irradiation of a polymer film deposited on a stainless steel support under closely controlled temperature conditions, is described. Using an evacuated system, detection and estimation of small amounts of volatile products may be carried out by subambient thermal volatilisation analysis (SATVA). Illustrative SATVA results are presented for the photolyses of poly(methyl acrylate) and poly(2-ethylhexyl acrylate). Each product appears as a peak on the SATVA trace, which is a record of rate of transfer of volatile material as a function of time, as products are allowed to warm up slowly from ?196°C to ambient temperature. The area under a given SATVA peak measures the amount of substance volatilised. Calibration data are given, relating peak area to moles of material for each of the various products.The effect of lamp to sample distance, film thickness and irradiation time on the yield of condensable volatile products has been tested for poly(methyl acrylate) in order to establish optimum conditions for use of the apparatus.     

ZIF-8对向列相液晶电-光性能的提升

ZIF-8（沸石咪唑酯骨架结构材料）是一种金属有机物骨架结构材料,因其极高的比表面积、出色的热稳定性而被广泛应用于各种性质研究中。ZIF-8通过传统的水热法在甲醇溶液中合成,其颗粒尺寸约为250nm,形貌为菱形十二面体。研究发现,合成的ZIF-8材料具有良好的热稳定性及相当大的比表面积。将其掺杂进液晶中会增强液晶的电-光性能,增强效果与掺杂浓度有关。在向列相液晶4-氰基-4'-戊基联苯（5CB）中,ZIF-8可以吸附杂质离子,抑制屏蔽效应,最终使液晶驱动电压降低,响应加快。在掺杂浓度为0.05%（w,质量分数）时,液晶体系的电-光性能改善最明显,阈值电压（V_th）最小达到0.92 V,饱和电压（V_sat）达到1.31 V,响应时间仅为10.04 ms。而当掺杂浓度大于0.05%（w）时,ZIF-8在液晶盒中发生团聚,影响液晶分子的有序排布,同时吸附杂质离子减少,不利于液晶电-光性能的改善。     

不同光滑度立方体氧化铁对液晶电光性能的改善

向列相液晶被广泛应用于液晶显示中,但是由于杂质的存在,会导致液晶的驱动电压变大,增加能耗。 为了降低阈值电压和饱和电压,通常向液晶中添加纳米颗粒来提高电光性能。 本文利用水热法制备了表面粗糙和光滑的两种立方体Fe₂O₃纳米颗粒,其形貌均匀,尺寸约550 nm。 将二者分别掺杂到向列相液晶E7中,结果表明,粗糙立方体Fe₂O₃/E7复合体系具有比光滑立方体Fe₂O₃/E7复合体系和向列相液晶E7更优的电光性能,且在掺杂质量分数为0.4%时,其电光性能达到最优,阈值电压和饱和电压分别降低9.9%和11.6%,对比度增大80%,响应时间降低至6.0 ms。 这归因于粗糙立方体Fe₂O₃具有足够的表面积和表面所带电荷更多,所以会更易吸附体系中的杂质离子和减弱杂质离子的屏蔽作用,从而提高了电光性能。     

Dip-coating deposition of resistive BiVO<Subscript>4</Subscript> thin film and evaluation of their photoelectrochemical parameters under distinct sources illumination

Resistive monoclinic bismuth vanadate (BiVO₄) nanocrystals in the form of thin films were obtained by the solution combustion synthesis coupled with the dip-coating deposition process. The structure, morphology, and optical properties of BiVO₄ nanocrystals were characterized by means of x-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis spectroscopy. The photoelectrochemical properties were obtained by cyclic voltammetry and chronoamperometry techniques in potassium chloride (KCl) electrolyte solution under distinct visible light sources irradiation condition. Under blue InGaN light emitting diode (LED) irradiation, the electrode has a better efficiency, faster response time (260 ms), and faster decay time (65 ms), when compared with the irradiation by dichroic lamp. Besides, the photocurrent density (j _ph) is approximately 39 times higher than j _ph obtained under dichroic lamp. The performance analysis based on the methylene blue degradation reaction has shown that the BiVO₄ material has higher electroactivity under InGaN LED irradiation condition, with estimated k _obs value of 200 × 10^?4 min^?1, which is a little higher than the value obtained with dichroic lamp illumination. In the dark condition, the BiVO₄ presented much lower photocatalytic activity.     

悬浮液进样-液体阴极辉光放电原子发射光谱法测定高纯氮化硅粉体中微量杂质元素

针对高纯氮化硅粉体中的9种微量杂质元素(Al、Ca、Co、Fe、K、Mg、Mn、Na、Ni),建立了悬浮液进样-液体阴极辉光放电原子发射光谱定量分析方法.考察了制备稳定悬浮液对样品颗粒度的要求,并通过六通阀将悬浮液引入液体阴极辉光放电原子发射光谱装置检测.本方法采用水溶液标准进行定量分析,无需对悬浮液的pH值进行精确调节,能够保持液体阴极辉光等离子体的稳定性.研究了仪器装置的操作电压、载液流速、光电倍增管积分时间等因素对检出限的影响.优化后得到的最佳实验条件为操作电压1080 V,载液流速1.2 mL/min,光电倍增管积分时间800 ms.利用六通阀进样系统对原有的液体阴极辉光放电原子发射光谱装置进行改进,从而实现悬浮液直接进样检测.用此装置对氮化硅实际样品进行检测,得到各种元素的检出限在0.2~53 mg/kg之间,RSD在1.1%~5.0%之间.通过对氮化硅标准参考物质ERM-ED101进行分析,其测定结果与高温高压消解-电感耦合等离子体发射光谱法一致,并与标准参考值吻合,表明此方法可用于氮化硅粉体的悬浮液直接进样检测,结果准确可靠,灵敏度高,具备应用价值.     

Activated ion electron capture dissociation (AI ECD) of proteins: Synchronization of infrared and electron irradiation with ion magnetron motion

Here, we show that to perform activated ion electron capture dissociation (AI-ECD) in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer equipped with a CO₂ laser, it is necessary to synchronize both infrared irradiation and electron capture dissociation with ion magnetron motion. This requirement is essential for instruments in which the infrared laser is angled off-axis, such as the Thermo Finnigan LTQ FT. Generally, the electron irradiation time required for proteins is much shorter (ms) than that required for peptides (tens of ms), and the modulation of ECD, AI ECD, and infrared multiphoton dissociation (IRMPD) with ion magnetron motion is more pronounced. We have optimized AI ECD for ubiquitin, cytochrome c, and myoglobin; however the results can be extended to other proteins. We demonstrate that pre-ECD and post-ECD activation are physically different and display different kinetics. We also demonstrate how, by use of appropriate AI ECD time sequences and normalization, the kinetics of protein gas-phase refolding can be deconvoluted from the diffusion of the ion cloud and measured on the time scale longer than the period of ion magnetron motion.     

Microwave-assisted Oxidation of Alcohols and Polyarenes with Cetyltrimethylammonium Bromochromate

An efficient and mild methodology for oxidation of alcohols and polyarenes was described using cetyltrimethylammonium bromochromate (CTMABC) under microwave irradiation. Primary and secondary alcohols and polyarenes could be selectively oxidized under microwave irradiation into the corresponding aldehydes and ketones in high yields and short reaction time, using commercially available and magnetically retrievable oxidative material (CTMABC).     

Photoluminescence Properties of Surface-Modified Nanocrystalline ZnS : Mn

DBS surface-modified nanocrystalline ZnS : Mn was prepared by a precipitation method. Photoluminescence spectra and decay curves were measured and compared to those of unmodified samples. For both kinds of samples, luminescence decay curves of 600 nm emission consist of two components with nanosecond (ns) and millisecond (ms) lifetimes. The nanosecond component is attributed to zinc vacancies luminescence, with peak located at 440 nm. While the millisecond component is attributed to Mn(2+) luminescence and its decay time changes with Mn(2+) concentration and surface modification. The surface-modified sample has a longer lifetime compared to unmodified samples. The photoaging of surface-modified samples is slow. Particle size effects on photoaging were also examined. For nanocrystalline ZnS : Mn photoaging is more noticeable than that of bulk material. After UV irradiation, photoluminescence intensity of the modified sample is several times larger than that of the unmodified sample, because the surface-active reagent decreases surface defects and depresses radiationless transitions. XPS yields direct evidence of the surface-modification effect on the surface structure. Copyright 2000 Academic Press.     

Preparation of nanosized gold particles in a biopolymer using UV photoactivation

Gold nanoparticles have been prepared by UV photoactivation in the presence of a biopolymer, sodium alginate. The particles are characterized by UV-vis spectra and TEM studies. Both particle size and the UV-visible absorption peak are dependent on the sodium alginate concentration. The effects of various other parameters such as change of light source, cell material of the reaction chamber, heating effect, irradiation time, and HAuCl4 concentration are studied. The particles are spherical and in situ stabilized by the biopolymer. The method is very simple and reproducible.     

An automatic NAA analyzer for short-lived nuclides

An automatic activation analyzer with sample changer, pneumatic transfer system and fast pulse counting with real time pulse pile-up and dead time compensation is described. Transfer times between 80 and 300 ms from irradiation position to measurement station can be obtained. Counting losses are corrected within 10% up to total count rates of 120 kc/s.