Anomalous curving of Arrhenius plots for data obtained from electro-thermal vaporization at atmospheric pressure

Arrhenius plots are often used in electrothermal atomization atomic absorption spectroscopy (ETA-AAS) to obtain activation energies (E_a) of vaporization processes. However, these plots are often nonlinear, and the exact cause of the curvature is not clear. This phenomenon has been attributed to multiple generation functions, diffusion of atoms through the graphite walls, changes in the size of the generating particles, changes in the surface coverage and interferences of the removal function with the supply function. This paper examines several other possibilities using computer simulations on a micro-computer. These possibilities include the effects of diffusion, errors in the assumed order of the reaction and small systematic errors. These can create curving very similar to that observed in typical ETA-AAS and should be considered before assigning the curvature to other chemical or physical properties of the system.     

双中心全息记录的矢量分析与记录方向优化

对描述双掺杂晶体非挥发性全息记录动力学过程的Kukhtarev方程进行了矢量分析,分析中考虑了体光生伏特效应和外加电场的作用。在小信号近似的基础上给出了双中心全息记录中记录与固定阶段空间电荷场的矢量解析解。在综合考虑空间电荷场的各向异性以及晶体有效电光系数的各向异性后,给出了双中心全息记录的优化记录方向。结果表明,对(Fe,Mn)∶LiNbO3晶体633nm寻常光记录,优化记录方向主要由有效电光系数决定,光栅波矢与光轴夹角为22°,方位角为30°;对(Fe,Mn)∶LiNbO3晶体633nm非寻常光记录,优化记录方向主要由固定空间电荷场决定,光栅波矢与光轴夹角为44°,方位角为90°。     

Two Equivalent Reduction of Copper(I) Complexes; Evidence of an Anionic Copper Species

Reactive copper solutions have been prepared by a cold temperature, two equivalent lithium naphthalenide reduction of copper(I) complexes. One equivalent of organic halides react with one equivalent of the anionic copper to yield organocopper reagents.     

Comparison of phantom materials for use in quality assurance of microbeam radiation therapy

Microbeam radiation therapy (MRT) is a promising radiotherapy modality that uses arrays of spatially fractionated micrometre‐sized beams of synchrotron radiation to irradiate tumours. Routine dosimetry quality assurance (QA) prior to treatment is necessary to identify any changes in beam condition from the treatment plan, and is undertaken using solid homogeneous phantoms. Solid phantoms are designed for, and routinely used in, megavoltage X‐ray beam radiation therapy. These solid phantoms are not necessarily designed to be water‐equivalent at low X‐ray energies, and therefore may not be suitable for MRT QA. This work quantitatively determines the most appropriate solid phantom to use in dosimetric MRT QA. Simulated dose profiles of various phantom materials were compared with those calculated in water under the same conditions. The phantoms under consideration were RMI457 Solid Water (Gammex‐RMI, Middleton, WI, USA), Plastic Water (CIRS, Norfolk, VA, USA), Plastic Water DT (CIRS, Norfolk, VA, USA), PAGAT (CIRS, Norfolk, VA, USA), RW3 Solid Phantom (PTW Freiburg, Freiburg, Germany), PMMA, Virtual Water (Med‐Cal, Verona, WI, USA) and Perspex. RMI457 Solid Water and Virtual Water were found to be the best approximations for water in MRT dosimetry (within ±3% deviation in peak and 6% in valley). RW3 and Plastic Water DT approximate the relative dose distribution in water (within ±3% deviation in the peak and 5% in the valley). PAGAT, PMMA, Perspex and Plastic Water are not recommended to be used as phantoms for MRT QA, due to dosimetric discrepancies greater than 5%.     

Dependence of electrical performance on structural organization in polymer field effect transistors

Organic semiconductors (OSCs) are strong contenders for use in printed, flexible electronics. Although organic electronic materials have been studied for many years, the physics of charge transport is still under investigation. This is in part due to variability resulting from the large variety of molecules that can be synthesized and inconsistency in electrical characterization due to device and processing conditions. Molecular ordering in OSCs is known to alter the charge transport characteristics and attention to long range and short range ordering provides clues as to the nature of transport pathways. Here, we study ordered regioregular poly(3‐hexylthiophene‐2,5‐diyl) films carefully prepared to obtain a set of three samples with incrementally increasing order on identical transistor architectures. Ordering was characterized using a variety of short and long range techniques to probe the coherence and number of crystallites formed during processing, and the correlation between these different measures of order are quantified. We observe three changes in transistor behavior that show a shift from non‐ideal to more textbook‐like characteristics with increasing order: reduction of the contact resistance, shift to field‐independent mobility, and a shift from a diode‐like (S‐shaped) to linear response at low lateral fields. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1063–1074     

Cold crystallization behavior of polyamide 6 in PS‐g‐PA6 graft copolymers

TEM micrographs show that the PA grafts of PS‐g‐PA6 graft copolymers, which are obtained directly by extracting homo‐PA6 out from the homo‐PA6/PS‐g‐PA6 blends, are in the form of wormlike structure. The wormlike PA6 domains can shrink into droplets after annealing at 250 °C for 15 min. The diameter of the droplet determined by TEM and SAXS is in the range of 50–60 nm. This article reports on a unique crystallization behavior of the PA6 grafts in PS‐g‐PA6 graft copolymers. In a DSC cooling scan, PA6 grafts do not crystallize from the melt with a cooling rate of 10 °C/min. However, there is a cold crystallization peak around 65 °C in the subsequent heating scan. This cold crystallization phenomenon, which has not yet been reported in the literature till now, follows well the homogeneous nucleation mechanism and is depressed at relatively slow cooling rates (2 °C/min) or even completely eliminated after annealing within a specific temperature range. It may be caused by the slow diffusion or transport rate of the less flexible PA6 grafts to the crystal fronts when crystallization takes place around its glass transition temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 65–73, 2010     

Quantifying induced electric field strengths during gene transfer to the intact rat vasculature

The application of appropriate electric fields to cells and tissues, termed electroporation, can result in efficient and safe gene transfer. We have shown previously that this approach results in high level gene transfer to and expression in the vasculature of living animals. This paper presents the results of an electric field distribution study of a rat mesenteric vasculature model using the Finite-Element Time-Domain (FETD) technique. A novelty of this work is the use of Debye dispersive dielectric parameters, as the electrical response of biological tissues is inherently frequency-dependent. The results compare fairly well with experimental findings.