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气体放电击穿过程的物理和数值研究 总被引:1,自引:0,他引:1
胡希伟 《核聚变与等离子体物理》1994,14(1):44-50
本文对低气压(10^-2Pa)热阴极气体放电的击穿过程给出了物理描述和相应的双流体数学型,并发展了一种选择和调整未知初始条件的有效算法,可以通过伴随试射法得到对初始条件十分敏感的非线性两点边值常微分方程组的数值解,从而给出这类气体放电中击穿过程的定量描述。 相似文献
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周锡伟 《影像科学与光化学》2020,(2):206-210
本文对不同月经周期乳腺增生的超声图像特征进行了分析。研究对象为选取2017年6月~2019年6月本院乳腺增生患者102例,所有患者均于不同月经周期(月经期、增殖期、分泌期)给予彩色多普勒超声检查,并检测性激素[雌二醇(E2)、孕酮(P)],分析不同月经周期乳腺增生的超声图像特征。结果显示,102例乳腺增生患者中,彩色多普勒超声诊断符合98例,符合率为96.08%,与病理结果比较,差异无统计学意义(P>0.05);乳腺增生患者增殖期乳腺腺体层厚度、导管宽度、乳房胀痛率、E2水平均明显高于月经期、分泌期,增殖期P水平明显低于分泌期但明显高于月经期,差异有统计学意义(P<0.05),分泌期乳腺腺体层厚度、导管宽度、乳房胀痛率、E2水平均高于月经期,但差异无统计学意义(P>0.05)。本文证实了彩色多普勒超声对乳腺增生具有良好的诊断价值,且不同月经周期乳腺增生的超声图像特征存在差异,可有效评价患者月经周期与性激素、增生性病变的关系。 相似文献
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Generalized signcryption can adaptively work as an encryption scheme, a signature scheme or a signcryption scheme with only one algorithm. It is very suitable for storage-constrained environments. In this paper, we introduce a formal security model for certificateless generalized signcryption schemes secure against the malicious-but-passive key generation center attacks and propose a novel scheme. Our scheme is proved to be IND-CCA2 secure under the GBDH assumption and CDH assumption and existentially unforgeable under the GDH’ assumption and CDH assumption in random oracle model. Furthermore, performance analysis shows the proposed scheme is efficient and practical. 相似文献
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Previous reports have seldom concerned about the RTILs (Room temperature ionic liquids), and their effects on derivatization
reaction or derivatives. In this study, we reported that the effects of four different RTILs, i.e., [EMIM]PF6, [BMIM]PF6, [HMIM]PF6 and [OMIM]PF6, on fluorescence spectra of 17 β-estradiol (E2), and its derivatization solvent dansyl chloride (DNSCl) and the derivative.
[BMIM]PF6 had a significant quenching effect on the fluorescence intensity of E2, suggesting the formation of [BMIM]PF6/E2 complexes and possible buried E2 molecular in a more hydrophobic microenvironment. The estimated Stern-Volmer quenching
constant (Ksv = 0.3519) proved that E2 quenching caused by [BMIM]PF6 was a dynamic quenching process. Four RTILs, with different alkyl chain-length in imidazolium cation, resulted in different
quenching intensities to E2 as follows: [EMIM]PF6 > [BMIM]PF6 > [HMIM]PF6 > [OMIM]PF6. At 5 mg L−1 of DNSCl, [BMIM]PF6, [HMIM]PF6 and [OMIM]PF6 increased the fluorescence intensities of E2 in water by 8.5, 7.6 and 6.1 times, respectively, and a 37-nm hypsochromic shift
occurred. The fluorescence intensity for [BMIM]PF6-extracted derivative of E2 increased more than two times compared with that for the control. In conclusion, this study demonstrated
that above four hexafluorophosphate salt ionic liquids could be used in derivatization reaction to enhance fluorescent sensitivity
in E2 trace residual analysis. 相似文献
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In this article, we propose an unbiased estimating equation approach for a two-component mixture model with correlated response data. We adapt the mixture-of-experts model and a generalized linear model for component distribution and mixing proportion, respectively. The new approach only requires marginal distributions of both component densities and latent variables. We use serial correlations from subjects’ subgroup memberships, which improves estimation efficiency and classification accuracy, and show that estimation consistency does not depend on the choice of the working correlation matrix. The proposed estimating equation is solved by an expectation-estimating-equation (EEE) algorithm. In the E-step of the EEE algorithm, we propose a joint imputation based on the conditional linear property for the multivariate Bernoulli distribution. In addition, we establish asymptotic properties for the proposed estimators and the convergence property using the EEE algorithm. Our method is compared to an existing competitive mixture model approach in both simulation studies and an election data application. Supplementary materials for this article are available online. 相似文献
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Two-dimensional Jamus van der Waals(vdW)heterojunctions,referring to the junction containing at least one Janus material,are found to exhibit tuneable electronic structures,wide light adsorption spectra,controllable contact resistance,and sufficient redox potential due to the intrinsic polarization and unique interlayer coupling.These novel structures and properties are promising for the potential applications in eleetronics and energy conversion devices.To provide a comprehensive picture about the research progress and guide the following investigations,here we summarize their fundamental properties of different types of two-dimensional Janus vdW heterostruct ures including electronic struc-ture,interface contact and optical properties,and discuss the potential applications in electronics and energy conversion devices.The further challenges and possible research directions of the novel heterojunctions are discussed at the end of this review. 相似文献
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Cai J Jie J Jiang P Wu D Xie C Wu C Wang Z Yu Y Wang L Zhang X Peng Q Jiang Y 《Physical chemistry chemical physics : PCCP》2011,13(32):14663-14667
Gallium-doped n-type CdS nanowires (NWs) were successfully synthesized via a thermal evaporation method. The conductivities of the CdS NWs were dramatically improved by nearly nine orders of magnitude after Ga doping, and could be further tuned over a wide range by adjusting the doping level. High-performance metal-insulator-semiconductor field-effect transistors (MISFETs) were constructed based on the single CdS : Ga NW with high-κ Si(3)N(4) dielectrics and top-gate geometries. In contrast to back-gate FETs, the MISFETs revealed a substantial improvement in device performance. Nano-light emitting diodes (nanoLEDs) were fabricated from the CdS : Ga NWs by using a n-NW/p(+)-Si substrate hybrid device structure. The nanoLEDs showed a bright yellow emission at a low forward bias. It is expected that the Ga-doped CdS NWs with controlled electrical transport properties will have important applications in nano-optoelectronic devices. 相似文献