Standard molar enthalpies of formation and phase changes of Tetra-N-phenylbenzidine and 4,4′-Bis (N-carbazolyl)-1,1′-biphenyl

Journal of Thermal Analysis and Calorimetry - The values of the standard molar energies of combustion of Tetra-N-phenylbenzidine and 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl in solid phase...     

Two-stage pricing for custom-made products

A commonly observed two-stage pricing strategy for a custom-made product involves a pre-purchase entry fee for a potential consumer and a purchase price if he decides to buy the product. We solve and compare two settings: In the first, the firm does not commit in advance to the second-stage price and in the second, the firm does. We show that without a commitment mechanism, the two price points are strategic complements, in that the higher pre-product fee implies a higher post-product price. With commitment, the two price points are strategic substitutes and the firm can improve profit over the no-commitment case by offering a low purchase price in the second stage and extracting the surplus through an entry fee. When the production cost is low, the commitment solution benefits both the firm and the consumer.     

The Origins of the Field Concept in Physics

The term, “field,” made its first appearance in physics as a technical term in the mid-nineteenth century. But the notion of what later came to be called a field had been a long time in gestation. Early discussions of magnetism and of the cause of the ocean tides had long ago suggested the idea of a “zone of influence” surrounding certain bodies. Johannes Kepler's mathematical rendering of the orbital motion of Mars encouraged him to formulate what he called “a true theory of gravity” involving the notion of attraction. Isaac Newton went on to construct an eminently effective dynamics, with attraction as its primary example of force. Was his a field theory? Historians of science disagree. Much depends on whether a theory consistent with the notion of action at a distance ought qualify as a “field” theory. Roger Boscovich and Immanuel Kant later took the Newtonian concept of attraction in new directions. It was left to Michael Faraday to propose the “physical existence” of lines of force and to James Clerk Maxwell to add as criterion the presence of energy as the ontological basis for a full-blown “field theory” of electromagnetic phenomena.     

Fast determination of prominent carotenoids in tomato fruits by CEC using methacrylate ester-based monolithic columns

In this study, the major carotenoids (beta-carotene and lycopene) present in tomato fruits were analyzed by CEC with a methacrylate ester-based monolithic column. The effects of the porogenic solvent ratio, and the hydrophobicity of bulk monomer employed were examined on carotenoids separations. A fast separation of these analytes was achieved in less than 5.0 min in a mobile phase containing 35% THF, 30% ACN, 30% methanol, and 5% of a 5 mM Tris aqueous buffer, pH 8, with lauryl methacrylate-based monoliths. The CEC method was evaluated in terms of detection limit and reproducibility (retention time, area, and column preparation) with values below 1.6 microg/mL and 7.2%, respectively. The proposed procedure was successfully applied to the determination of both carotenoids in fruits of several tomato-related species and its usefulness to analyze large series of samples for nutritional quality screening trials in tomato breeding programs is demonstrated. To our knowledge, this is the first work that exploits the powerful and user-friendly monolithic technology for quality breeding and germplasm evaluation program purposes.     

固态荧光碳点的制备

荧光碳点由于其具有无毒、制备成本低以及独特的光致发光性能而引起人们极大的研究兴趣,但是通常碳点的制备和使用均是在溶液中,而且随着碳点浓度的增加其荧光强度可能会降低甚至猝灭,通过简单干燥后得到的固态粉末则常常缺少荧光性质。因此,固态荧光碳点制备及其相关应用的研究相对较少。本文综述了固态荧光碳点的制备方法,包括后处理法(基质分散法、表面工程法)和前驱体直接合成法;对比了各种调控手段处理前后碳点荧光性能的变化情况,总结了各种固态碳点在制备过程中和使用过程中存在的主要问题。最后,针对固态发光碳点的制备方法、性能调控及发展方向进行了展望。开发具有聚集诱导发射增强的碳点是至关重要的,也为固态碳点的发展提供了新思路。     

Modulating the Differentiation of Kinetically Controlled Supramolecular Polymerizations through the Alkyl Bridge Length

The synthesis and self-assembling features of N-annulated perylenebisimides (N-PBIs) 2 – 4 are reported and compared with the complex self-assembly of N-PBI 1 . The studies presented herein demonstrate that increasing the length of the alkyl spacer separating the central aromatic core of the dye and the peripheral side chains cancels the differentiation on the corresponding supramolecular polymerization. Thus, only 2 is able to form two different supramolecular polymorphs. The formation of kinetically trapped monomeric species is observed for all the N-PBIs 2 – 4 . These metastable species, constituted by intramolecularly H-bonded pseudocycles of 7, 8, 9, or 10 members for compounds 1 , 2 , 3 , and 4 , respectively, provoke kinetically controlled supramolecular polymerizations that can be accelerated by the addition of seeds. The results presented herein shed light on the intricate process of differentiation in self-assembly.