Boronate Covalent and Hybrid Organic Frameworks Featuring PIII and P=O Lewis Base Sites

Two covalent organic frameworks comprising Lewis basic P^III centers and Lewis acidic boron atoms were prepared by poly-condensation reactions of newly obtained tris(4-diisopropoxyborylphenyl)phosphine with 2,3,6,7,10,11-hexahydroxytriphenylene and 2,3,6,7-tetrahydroxy-9,10-dimethylanthracene. Obtained materials exhibit significant sorption of dihydrogen (100 cm³ g⁻¹ at 1 bar at 77 K), methane (20 cm³ g⁻¹ at 1 bar at 273 K) and carbon dioxide (50 cm³ g⁻¹ at 1 bar at 273 K). They were exploited as solid-state ligands for coordination of Pd⁰ centers. Alternatively, in a bottom-up approach, boronated phosphine was treated with Pd₂dba₃ and poly-condensated, yielding hybrid materials where the polymer networks are formed by means of covalent boronate linkages and coordination P−Pd bonds. In addition, the analogous materials based on phosphine oxide were synthesized. The DFT calculations on framework–guest interactions revealed that the behavior of adjacent boron and phosphorus/phosphine oxide centers is reminiscent of that found in Frustrated Lewis Pairs and may improve sorption of selected molecules.     

Microsolvation of small cations and anions

Recent advances in the theoretical treatment of microsolvation of small ions, a problem with practical implications in chemistry, physics, and biology, are exposed. In particular, we discuss sound stochastic approaches to sample complex energy landscapes and delve into the nature of bonding interactions that dictate both structural and energetical preferences. An in-depth analysis of the effect of formal charges in the surrounding network of solvent to solvent hydrogen bonds is also presented. The problem, as expected, is more complicated than simple definitions may forecast.     

Orientational–deformational nature of flow birefringence in solutions of rigid-chain polymers

The orientational–deformational nature of flow birefringence (FB) in solutions of rigid-chain polymers is confirmed experimentally. The possibility of a direct determination of the internal viscosity parameter by the dependence of the FB relaxation time on the solvent viscosity is demonstrated. Indirect manifestation of internal viscosity in the FB relaxation time is confirmed by the dependence of the form factor on the degree of coiling. © 1993 John Wiley & Sons, Inc.     

不同科学史设计对高一学生科学本质观发展的影响——以原子结构发现史为例

科学史是促进学生科学本质观发展的重要策略。本研究以181名高一学生为研究对象,采用准实验设计,探讨了在原子结构教学中,不同科学史设计对学生科学本质观发展的影响。结果表明：无论何种教学设计对学生科学本质观发展都有影响,但影响的方面和程度不同;采用“认识型”、“反思型”的科学史设计效果要明显优于“知识型”。     

1. 5-环辛二烯-3, 7-二炔(C~8H~4)结构和光谱性质的理论研究

采用量子化学从头算方法研究了1,5-环辛二烯-3,7-二炔(C~8H~4)的结构和光谱性质,根据等键反应分析和自然键轨道方法研究了它的稳定性、成键情况和共轭性。结果表明1,5-环辛二烯-3,7-二炔(C~8H~4)分子为平面刚性结构,可能稳定存在。分子中C≡C键与C=C键存在一定程度的共轭,可能具有芳香性。     

CTA成像在下肢血管闭塞病变中的应用及与血管腔内疗效的关系

本文探讨计算机体层扫描血管造影(CTA)检查在下肢血管闭塞病变中的应用价值及与血管腔内疗效的关系。选取经数字减影血管造影(DSA)确诊的93例下肢血管闭塞病变患者,采用CTA检查,分析CTA诊断病变部位结果、血管狭窄程度及与DSA诊断结果的一致性,并探讨CTA征象与患者血管腔内疗效的关系。结果显示,CTA诊断下肢血管闭塞病变部位、狭窄程度与DSA诊断结果均具有较高一致性(P<0.05);病变血管长度>1.41 cm、血管狭窄程度4级、病变血管远端CT值>62.65 Hu、钙化性斑块是下肢血管闭塞病变血管腔内治疗失败的危险因素(P<0.05)。CTA检查是诊断下肢血管闭塞病变的可靠方法,通过检查患者病变血管长度、血管狭窄程度、远端CT值及管腔内粥样斑块性质,有助于降低治疗盲目性,提高血管腔内治疗成功率。     

第一讲信息的产生与获得(上)

信息是物质运动本身的属性．通过大自然发出的信息理解宇宙，发现自然规律，是科学永恒的主题．现代信息科学技术使人们能够超越感觉器官和神经系统的生理极限，以前所未有的方式获取自然的信息．文章回溯了人类获取自然信息的历史过程及其不同发展阶段的科学内涵与技术特征，阐述了信息对科学发展的决定性意义，概括地介绍了人类探寻科学信息的某些前沿活动，讨论了它们对探索者的启示．     

含氮氟化类金刚石(FN-DLC)薄膜的研究：(Ⅲ)疏水性能分析

不同沉积条件下，在单晶硅基底上沉积了含氮氟化类金刚石(FN-DLC)薄膜，用静滴接触角/表面张力测量仪测量了水与FN-DLC膜表面的接触角.用X射线光电子能谱、Raman光谱和傅里叶变换吸收红外光谱(FTIR)分析了薄膜的组分和结构.用原子力显微镜观测了薄膜的表面形貌.结果表明，FN-DLC薄膜疏水性能主要取决于薄膜表面的化学结构、薄膜表面极化强度的强弱、以及薄膜的表面粗糙度的大小.sp³/sp²的比值减小，CF₂基团含量增加，薄膜粗糙度增加，接触角增大；反之，则接触角减小.在工艺上，沉积温度和功率的减小，气体流量比r(r=CF4/［CF₄+CH₄］)的增加，都会使水的浸润性变差，接触角增大. 关键词： 氟化类金刚石膜 疏水性 接触角     

Scaling and memory in the non-Poisson process of limit order cancelation

The order submission and cancelation processes are two crucial aspects in the price formation of stocks traded in order-driven markets. We investigate the dynamics of order cancelation by studying the statistical properties of inter-cancelation durations, defined as the waiting times between consecutive order cancelations of 22 liquid stocks traded on the Shenzhen Stock Exchange of China in year 2003. Three types of cancelations are considered, including cancelation of any limit orders, of buy limit orders and of sell limit orders. We find that the distributions of the inter-cancelation durations of individual stocks can be well modeled by Weibulls for each type of cancelation, and the distributions of rescaled durations of each type of cancelations exhibit a scaling behavior for different stocks. Complex intra-day patterns are also unveiled in the inter-cancelation durations. The detrended fluctuation analysis (DFA) and the multifractal DFA show that the inter-cancelation durations possess long-term memory and multifractal nature, which are not influenced by the intra-day patterns. No clear crossover phenomenon is observed in the detrended fluctuation functions with respect to the time scale. These findings indicate that the cancelation of limit orders is a non-Poisson process, which has potential worth in the construction of order-driven market models.     

Modified entropic gravitation in superconductors

Verlinde recently developed a theoretical account of gravitation in terms of an entropic force. The central element in Verlinde’s derivation is information and its relation with entropy through the holographic principle. The application of this approach to the case of superconductors requires to take into account that information associated with superconductor’s quantum vacuum energy is not stored on Planck size surface elements, but in four volume cells with Planck-Einstein size. This has profound consequences on the type of gravitational force generated by the quantum vacuum condensate in superconductors, which is closely related with the cosmological repulsive acceleration responsible for the accelerated expansion of the Universe. Remarkably this new gravitational type force depends on the level of breaking of the weak equivalence principle for cooper pairs in a given superconducting material, which was previously derived by the author starting from similar principles. It is also shown that this new gravitational force can be interpreted as a surface force. The experimental detection of this new repulsive gravitational-type force appears to be challenging.