Research Progress on Synthesis and Application of Cyclodextrin Polymers

Cyclodextrins (CDs) are a series of cyclic oligosaccharides formed by amylose under the action of CD glucosyltransferase that is produced by Bacillus. After being modified by polymerization, substitution and grafting, high molecular weight cyclodextrin polymers (pCDs) containing multiple CD units can be obtained. pCDs retain the internal hydrophobic-external hydrophilic cavity structure characteristic of CDs, while also possessing the stability of polymer. They are a class of functional polymer materials with strong development potential and have been applied in many fields. This review introduces the research progress of pCDs, including the synthesis of pCDs and their applications in analytical separation science, materials science, and biomedicine.     

Restriction of Intramolecular Motion(RIM): Investigating AIE Mechanism from Experimental and Theoretical Studies

Mechanistic studies promote scientific development from phenomena to theories.Aggregation-induced emission(AIE),as an unusual photophysical phenomenon,builds the bridge between molecular science and aggregate mesoscience.With the twenty-year development of AIE,restriction of intramolecular motion(RIM)has been verified as the working mechanism of AIE effect.In this review,these mechanistic works about RIM are summarized from experimental and theoretical perspectives.Thereinto,the experimental studies are introduced from three parts:external rigidification,structural modification and structural characterization.In the theoretical part,calculations on the low-frequency motion of AIEgens have been performed to prove the RIM mechanism.By virtue of the theoretical calculations,some new mechanisms are proposed to supplement the RIM,such as restriction of access to conical intersection,suppression of Kasha transition,restriction of access to dark state,etc.It is foreseeable that the RIM mechanism will unify the photophysical theories for both molecules and aggregates,and inspire more progress in aggregate science.     

美国《科学教师培养标准(2020年版)》述评*

美国《科学教师培养标准(2020年版)》针对《新一代科学教育标准》的推行而修订,立足于科学教育最新研究成果,尤其突出学科内容知识的重要性,补充对科学本质和科学文化的要求,强化对工程和技术、交叉概念、学科观念的理解,突出学习进阶规律在科学教师培养中的应用。此外,在学科教学法、学习环境、安全、对学生学习的影响等维度做出相应的改动。该标准启示我国:借鉴国际改革趋势出台中国特色的科学教师培养标准,但科学教师培养也要本土化;学科内容知识对科学教师专业发展非常重要;科学教师的培养应立足于学习进阶的规律;职前科学教师培养需要注重学习环境建设。     

探究镁与氯化钠溶液反应的微观过程*

镁在常温下和水发生反应的速率较慢,这是因为镁表面存在氢氧化镁附着层的保护作用,但是镁可以和NaCl溶液发生较快的反应,在产生大量气泡的同时生成白色固体。通过对白色固体进行分析发现,在有Cl^-的环境下氢氧化镁会逐渐转化为碱式氯化镁,同时也会导致溶液pH的升高。经过实验探究发现,镁在不同浓度NaCl溶液中的反应现象存在差异,在反应过程中溶解氧含量也会下降。     

Influence of surface heterogeneity in electroosmotic flows—Implications in chromatography, fluid mixing, and chemical reactions in microdevices

We analyze the influence of surface heterogeneity, inducing a random ζ-potential at the walls in electroosmotic incompressible flows. Specifically, we focus on how surface heterogeneity modifies the physico-chemical processes (transport, chemical reaction, mixing) occurring in microchannel and microreactors. While the macroscopic short-time features associated with solute transport (e.g. chromatographic patterns) do not depend significantly on ζ-potential heterogeneity, spatial randomness in the surface ζ-potential modifies the spectral properties of the advection-diffusion operator, determining different long-term properties of transport/reaction phenomena compared to the homogeneous case. Examples of physical relevance (chromatography, infinitely fast reactions) are addressed.     

Nanoscale observations of the operational failure for phase-change-type nonvolatile memory devices using Ge2Sb2Te5 chalcogenide thin films

In this study, a phase-change memory device was fabricated and the origin of device failure mode was examined using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Ge₂Sb₂Te₅ (GST) was used as the active phase-change material in the memory device and the active pore size was designed to be 0.5 m. After the programming signals of more than 2×10⁶ cycles were repeatedly applied to the device, the high-resistance memory state (reset) could not be rewritten and the cell resistance was fixed at the low-resistance state (set). Based on TEM and EDS studies, Sb excess and Ge deficiency in the device operating region had a strong effect on device reliability, especially under endurance-demanding conditions. An abnormal segregation and oxidation of Ge also was observed in the region between the device operating and inactive peripheral regions. To guarantee an data endurability of more than 1×10¹⁰ cycles of PRAM, it is very important to develop phase-change materials with more stable compositions and to reduce the current required for programming.     

Scanning tunneling microscopy/spectroscopy on Au nanoparticles assembled using lauryl amine (LAM) and octadecane thiol (ODT)

In this report, we demonstrate scanning tunneling microscopy and spectroscopy on thin films of lauryl amine (LAM) and octadecane thiol (ODT) protected gold nanoparticles. We show that the zero current in the I-V curves (measure of Coulomb blockade (CB) of the nanoparticles) depends on the properties of the spacer molecule. In both the cases the gap voltage and the tunneling current at which the images are obtained are quite different which is further confirmed from the fitting performed based on the orthodox theory. The values for the capacitance and charging energy obtained from the fitting for ODT capped particles are comparable to the values obtained using spherical capacitor model. In contrast, values of these parameters were found to differ for LAM capped nanoparticles. While imaging, ODT capped nanoparticles were observed to drag along the scan direction leading to ordering of particles. Images of LAM capped gold nanoparticles show local ordering in self-assembly of particles although no evidence of large scale ordering in spatial Fourier transform was seen. These observations suggest that nanoparticles with larger CB would be imaged nonevasively in contrast to small CB systems for which tip induced effects will be dominant. In both the systems the current was found to rise faster than theoretical curves based on the orthodox theory suggesting that mechanism of charge transfer in this case may involve field emission rather than tunneling through a rectangular barrier. An attempt has been made to explain charge transfer based on Fowler-Nordheim (F-N) plots of the I-V curves.     

Multifractal detrended fluctuation analysis of derivative and spot markets

We investigate the multifractal properties of price increments in the cases of derivative and spot markets. Through the multifractal detrended fluctuation analysis, we estimate the generalized Hurst and the Renyi exponents for price fluctuations. By deriving the singularity spectrum from the above exponents, we quantify the multifractality of a financial time series and compare the multifractal properties of two different markets. The different behavior of each agent-group in transactions is also discussed. In order to identify the nature of the underlying multifractality, we apply the method of surrogate data to both sets of financial data. It is shown that multifractality due to a fat-tailed distribution is significant.     

Decay rate with coordinate-dependent diffusion coefficients

Using a master equation for the reduced density matrix of open quantum system, the influence of coordinate-dependent microscopical diffusion coefficients on the decay rate from a potential well is studied. For different temperatures, frictions, heights of barrier and ratios of stiffnesses of the potential in the minimum and on the top of the barrier, the quasistationary decay rates are obtained with the sets of coordinate-dependent and -independent microscopical diffusion coefficients, and coordinate-dependent phenomenological diffusion coefficients.     

Transport of waves in disordered waveguides: A potential model

We study the statistical properties of wave transport in a disordered waveguide. We first derive the properties of a “building block” (BB) of length δL starting from a potential model consisting of thin potential slices. We then find a diffusion equation—in the space of transfer matrices that describe our system—which governs the evolution with the length L of the disordered waveguide of the transport properties of interest. The latter depend only on the mean free paths and on no other property of the slice distribution. The universality that arises demonstrates the existence of a generalized central-limit theorem. We have developed a numerical simulation in which the universal statistical properties of the BB found analytically are first implemented numerically, and then the various BBs are combined to construct the full waveguide. The reported results thus obtained are in good agreement with microscopic calculations, for both bulk and surface disorder.