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891.
Sidney Borowitz 《Physics in Perspective (PIP)》2008,10(3):287-294
I sketch the lives and work of the Norwegian physicist Kristian Birkeland (1867–1917) and the English mathematician Sydney
Chapman (1888–1970), focusing particularly on Chapman’s controversy with Birkeland over the origin and development of auroras,
a controversy that Chapman conducted with Birkeland for more than fifty years after Birkeland’s death.
Sidney Borowitz is Professor Emeritus of Physics at New York University. 相似文献
892.
在电离层释放电子吸附类中性气体能够引起电离层电子密度耗空,在释放之后快速形成"电离层洞";同时,由于释放气体的快速膨胀,挤压背景等离子体,在电离层洞的外边缘产生"壳状"电子密度增强结构,电离层洞和电子密度增强结构同时存在是释放早期试验效应的显著特征.本文研究了电离层中性气体释放的早期试验效应,建立了释放早期电子密度的时空演化物理模型,仿真了释放早期电子密度的时空演化过程,同时采用射线追踪方法研究了释放后10 s和120 s不同频率信号在扰动区的传播效应,并反演得到了电离层垂直探测电离图,反演结果与一次火箭喷焰的实际观测结果吻合较好,初步验证了本模型的正确性. 相似文献
893.
The properties of polar optical phonon vibrations in a quasi-zero- dimensional (Q0D) anisotropic wurtzite cylindrical quantum dot (QD) are analyzed based on the dielectric continuum model and Loudon's uniaxial crystal model.The analytical electrostatic potentials of the phonon vibrations in the systems are deduced and solved exactly. The result shows that there exist four types of polar mixing optical phonon modes in the Q0D wurtzite cylindrical QD systems. The dispersive equations and electron-phonon coupling function for the quasi-confined-half-space (QC-HS) mixing modes are derived and discussed. It is found that once the radius or the height of the QD approach infinity, the dispersive equations of the QC-HS mixing modes in the Q0D cylindrical QD can naturally reduce to those of the QC and HS modes in Q2D QWs or Q1D QWWs systems. This has been analyzed reasonably from both of physical and mathematical viewpoints. 相似文献
894.
Luis Eduardo Mosquera Narvaez Lindalva Maria de Meneses Costa Ferreira Suellen Sanches Desire Alesa Gyles Jos Otvio Carrra Silva-Júnior Roseane Maria Ribeiro Costa 《Molecules (Basel, Switzerland)》2022,27(9)
New strategies for the delivery of bioactives in the deeper layers of the skin have been studied in recent years, using mainly natural ingredients. Among the strategies are organogels as a promising tool to load bioactives with different physicochemical characteristics, using vegetable oils. Studies have shown satisfactory skin permeation, good physicochemical stability mainly due to its three-dimensional structure, and controlled release using vegetable oils and low-molecular-weight organogelators. Within the universe of natural ingredients, vegetable oils, especially those from the Amazon, have a series of benefits and characteristics that make them unique compared to conventional oils. Several studies have shown that the use of Amazonian oils brings a series of benefits to the skin, among which are an emollient, moisturizing, and nourishing effect. This work shows a compilation of the main Amazonian oils and their nutraceutical and physicochemical characteristics together with the minority polar components, related to health benefits, and their possible effects on the synthesis of organogels for cosmetic purposes. 相似文献
895.
Xiaojun Zhang Yimeng Liu Chengguan Chen Hua Guo Qingtian Zeng 《Entropy (Basel, Switzerland)》2022,24(8)
The Belief Propagation (BP) algorithm has the advantages of high-speed decoding and low latency. To improve the block error rate (BLER) performance of the BP-based algorithm, the BP flipping algorithm was proposed. However, the BP flipping algorithm attempts numerous useless flippings for improving the BLER performance. To reduce the number of decoding attempts needed without any loss of BLER performance, in this paper a metric is presented to evaluate the likelihood that the bits would correct the BP flipping decoding. Based on this, a BP-Step-Flipping (BPSF) algorithm is proposed which only traces the unreliable bits in the flip set (FS) to flip and skips over the reliable ones. In addition, a threshold is applied when the magnitude of the log–likelihood ratio (LLR) is small, and an enhanced BPSF (EBPSF) algorithm is presented to lower the BLER. With the same FS, the proposed algorithm can reduce the average number of iterations efficiently. Numerical results show the average number of iterations for EBPSF-1 decreases by 77.5% when N = 256, compared with the BP bit-flip-1 (BPF-1) algorithm at = 1.5 dB. 相似文献
896.
897.
898.
Rorijs Dobulans Daiga Cepite Egils Fonavs Inta Muzikante Andrey Tokmakov Donats Erts Boris Polakov 《Macromolecular Symposia》2004,212(1):421-426
In this work betaine-type molecules were investigated. As a result of the asymmetry of charge distribution, molecules possess in the ground state a considerable permanent dipole moment. The decay of surface potential of poled polymer films is dependent at least on two relaxation processes. The influence of glass transition of PMMA on thermal dependence of the surface potential is shown. The transition temperature, where no changes of the surface potential appeared, is related to glass transition temperature of the host-guest system. The topography of the film surface was obtained by AFM. 相似文献
899.
900.
Xuan Sun Li Xu Huijiao Yan Peng Li Hidayat Hussain Jiguo Liu Jinjie Zhang Daijie Wang 《Journal of separation science》2023,46(19):2300238
Gynostemma pentaphyllum (Thunb.) Makino represents the popular health food and supplemental product with broad pharmacological activities. The highly polar glycosides, including flavonoids and saponins, are major effective active components that contain diverse sugar positions and quantities, which result in diverse chemical polarities, making it challenging to separate and isolate these components. The present work described the rapid and efficient linear gradient counter-current chromatography to preparatively separate glycosides from aboveground parts of G. pentaphyllum. Besides, the ethyl acetate and n-butanol binary mobile phases were achieved through adjusting associated proportions. Six glycosides, including quercetin-3-O-neohesperidoside ( 1 ), kaempferol-3-O-robinobioside ( 2 ), kaempferol-3-O-neohesperidoside ( 3 ), gypenoside LVI ( 4 ), ginsenoside Rb3 ( 5 ), and gypenoside XLVI ( 6 ), were isolated at the purities greater than 98%. Moreover, electrospray ionization mass spectrometry and nuclear magnetic resonance tandem mass spectrometry were conducted for structural identification. According to our findings, the established linear gradient counter-current chromatography was an efficient approach to separate the highly polar glycosides from aboveground parts of G. pentaphyllum. Our proposed strategy can be used to separate active compounds from other complex natural products. 相似文献