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排序方式: 共有273条查询结果,搜索用时 0 毫秒
1.
Vladimir Rozenshtein Alexander Berg Haim Levanon Uwe Krueger Dietmar Stehlik Yuri Kandrashkin Art Van Der Est 《Israel journal of chemistry》2003,43(3-4):373-381
Light-induced spin-polarized transient EPR spectra are reported for several water-soluble copper porphyrins. The spectra are assigned to the doublet ground state, with emissive spin polarization resulting from photoexcitation and subsequent electronic relaxation. In contrast to other systems for which polarization of a doublet ground state has been observed, the exchange interactions in the copper porphyrins are strong and the geometry is fixed. It is proposed that intersystem crossing from the photoexcited trip-doublet to the trip-quartet state can lead to net polarization of the spin system and that this polarization is maintained during electronic decay, possibly via charge-transfer and exciplex states. The intensity of the observed spin polarization is essentially independent of the molecular orientation in the external field, but is strongly dependent on the nature of the charged peripheral groups. Possible reasons for this behavior are discussed. 相似文献
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Bituminous coal piles stored in the open air can undergo autocatalytic heating accompanied by the emission of small but appreciable amounts of molecular hydrogen. When the coal is contained in a confined space and the temperature reaches 40°C, accumulation of hydrogen is expected. This process has been observed for a wide variety of bituminous coals. The amount of hydrogen gas expected to accumulate in the air pocket above the coal cargo in ship holds (assuming that the coal's temperature approaches 40°C during the voyage) has been calculated. The results clearly indicate that in most cases the hydrogen concentration will be appreciably above the lower explosion limit in air. Hence when bituminous coals are stored in a confined space (e.g. a ship hold), the explosive risk of hydrogen should be taken into account. 相似文献
4.
Avner Adini Irit Adini Etty Grad Yuval Tal Haim D. Danenberg Peter M. Kang Benjamin D. Matthews Robert J. DAmato 《International journal of molecular sciences》2021,22(10)
Myocardial infarction (MI) remains the leading cause of death in the western world. Despite advancements in interventional revascularization technologies, many patients are not candidates for them due to comorbidities or lack of local resources. Non-invasive approaches to accelerate revascularization within ischemic tissues through angiogenesis by providing Vascular Endothelial Growth Factor (VEGF) in protein or gene form has been effective in animal models but not in humans likely due to its short half-life and systemic toxicity. Here, we tested the hypothesis that PR1P, a small VEGF binding peptide that we developed, which stabilizes and upregulates endogenous VEGF, could be used to improve outcome from MI in rodents. To test this hypothesis, we induced MI in mice and rats via left coronary artery ligation and then treated animals with every other day intraperitoneal PR1P or scrambled peptide for 14 days. Hemodynamic monitoring and echocardiography in mice and echocardiography in rats at 14 days showed PR1P significantly improved multiple functional markers of heart function, including stroke volume and cardiac output. Furthermore, molecular biology and histological analyses of tissue samples showed that systemic PR1P targeted, stabilized and upregulated endogenous VEGF within ischemic myocardium. We conclude that PR1P is a potential non-invasive candidate therapeutic for MI. 相似文献
5.
This work presents experimental results on pickup velocity (critical velocity) measurements for a variety of particulate solids. The present experiments together with previously published experiments of a number of researchers encompass about 100 measurements of 24 materials for a wide range of particle sizes, shapes and densities. Based on the experimental results, three zones are defined by establishing simple relationships between the Reynolds and Archimedes numbers. The empirical relationships were further modified by taking into account the pipe diameter and particle shape (sphericity). The three-zone model was shown to reasonably correlate to Geldart's classification groups. 相似文献
6.
Changchun?Liu Michael?G.?Mauk Haim?H.?BauEmail author 《Microfluidics and nanofluidics》2011,11(2):209-220
An inexpensive, disposable, integrated, polymer-based cassette for loop-mediated isothermal amplification (LAMP) of target
nucleic acids was designed, fabricated, and tested. The LAMP chamber was equipped with single-use, thermally actuated valves
made with a composite consisting of a mixture of PDMS and expandable microspheres. The effect of the composite composition
on its expansion was investigated, and the valve’s performance was evaluated. In its closed state, the valve can hold pressures
as high as 200 kPa without any significant leakage. Both the LAMP chamber and the valves were actuated with thin film heaters.
The utility of the cassette was demonstrated by carrying out LAMP of Escherichia coli DNA target and reverse transcribed loop meditated isothermal amplification (RT-LAMP) of RNA targets. The amplicons were detected
in real time with a portable, compact detector. The system was capable of detecting as few as 10 target molecules per sample
in well under 1 h. The portable, integrated cassette system described here is particularly suited for applications at the
point of care and in resource-poor countries, where funds and trained personnel are in short supply. 相似文献
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The conversion behavior of 2MEP4FS, a polymer with thermally reversible Diels–Alder cross-links, is modeled. A processing method is developed to create small, homogeneous prepolymer samples. The glass transition temperature of the prepolymer is estimated using temperature modulated differential scanning calorimetry and equated with the conversion of the polymer. Comparing the measured energy with the literature and computational estimates, the fully cured polymer appears to have a large portion of its moieties unreacted. An autocatalytic model is considered to approximate the reaction rate of 2MEP4FS as a function of conversion and temperature. Outside of the fitted temperature range, the model underpredicts the reaction rates at room temperature and 100 °C. Manual mixing of the monomers is determined to be inadequate to obtain a maximum level of cross-linking. Viscosity measurements made at room temperature and elevated temperatures are correlated with the conversion of the prepolymer. 相似文献
9.
在分析光谱测试仪器检测设备发展现状的前提下,为解决光栅分辨率测试仪器中存在的电路复杂、探测器灵敏度低、结构可变通性差等问题,设计了一种以线阵CCD ILX554B为探测器的、以STM32F103为主控单元的线阵CCD光谱分辨率检测系统。系统利用片上高速时钟产生线阵CCD所需的驱动时序,经片上ADC采样后获取实时的光谱数据,将采集的数据经USB接口上传给上位机进行处理,获得最终的被测分光器件的光谱分辨率信息。最后,分别以汞灯和氩灯为光源,利用所设计的系统对光栅分辨率进行了测试,实验数据表明,在500 k Hz的驱动频率下,系统光谱分辨率可以达到0.01nm。系统满足低成本、高精度、稳定和可靠等要求。 相似文献
10.
Direct evaluation of stress intensity factors for curved cracks using Irwin's integral and XFEM with high‐order enrichment functions 下载免费PDF全文
Yongxiang Wang Haim Waisman Isaac Harari 《International journal for numerical methods in engineering》2017,112(7):629-654
This paper presents a comprehensive study on the use of Irwin's crack closure integral for direct evaluation of mixed‐mode stress intensity factors (SIFs) in curved crack problems, within the extended finite element method. The approach employs high‐order enrichment functions derived from the standard Williams asymptotic solution, and SIFs are computed in closed form without any special post‐processing requirements. Linear triangular elements are used to discretize the domain, and the crack curvature within an element is represented explicitly. An improved quadrature scheme using high‐order isoparametric mapping together with a generalized Duffy transformation is proposed to integrate singular fields in tip elements with curved cracks. Furthermore, because the Williams asymptotic solution is derived for straight cracks, an appropriate definition of the angle in the enrichment functions is presented and discussed. This contribution is an important extension of our previous work on straight cracks and illustrates the applicability of the SIF extraction method to curved cracks. The performance of the method is studied on several circular and parabolic arc crack benchmark examples. With two layers of elements enriched in the vicinity of the crack tip, striking accuracy, even on relatively coarse meshes, is obtained, and the method converges to the reference SIFs for the circular arc crack problem with mesh refinement. Furthermore, while the popular interaction integral (a variant of the J‐integral method) requires special auxiliary fields for curved cracks and also needs cracks to be sufficiently apart from each other in multicracks systems, the proposed approach shows none of those limitations. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献