Determining nonuniformities of core-shell nanoparticle coatings by analysis of the inelastic background of X-ray photoelectron spectroscopy survey spectra

Most real core-shell nanoparticle (CSNP) samples deviate from an ideal core-shell structure potentially having significant impact on the particle properties. An ideal structure displays a spherical core fully encapsulated by a shell of homogeneous thickness, and all particles in the sample exhibit the same shell thickness. Therefore, analytical techniques are required that can identify and characterize such deviations. This study demonstrates that by analysis of the inelastic background in X-ray photoelectron spectroscopy (XPS) survey spectra, the following types of deviations can be identified and quantified: the nonuniformity of the shell thickness within a nanoparticle sample and the incomplete encapsulation of the cores by the shell material. Furthermore, CSNP shell thicknesses and relative coverages can be obtained. These results allow for a quick and straightforward comparison between several batches of a specific CSNP, different coating approaches, and so forth. The presented XPS methodology requires a submonolayer distribution of CSNPs on a substrate. Poly(tetrafluoroethylene)-poly(methyl methacrylate) and poly(tetrafluoroethylene)-polystyrene polymer CSNPs serve as model systems to demonstrate the applicability of the approach.     

Synthesis,structural analysis,and photophysical properties of bi-1,2,3-triazoles

Structural Chemistry - Structural insights of a group of bi-1,2,3-triazoles derived from oxidative CuAAC are described through an X-ray crystallography study, distinguishing a dihedral angle which...     

Palladium‐Catalyzed Chlorocarbonylation of Aryl (Pseudo)Halides Through In Situ Generation of Carbon Monoxide

An efficient palladium‐catalyzed chlorocarbonylation of aryl (pseudo)halides that gives access to a wide range of carboxylic acid derivatives has been developed. The use of butyryl chloride as a combined CO and Cl source eludes the need for toxic, gaseous carbon monoxide, thus facilitating the synthesis of high‐value products from readily available aryl (pseudo)halides. The combination of palladium(0), Xantphos, and an amine base is essential to promote this broadly applicable catalytic reaction. Overall, this reaction provides access to a great variety of carbonyl‐containing products through in situ transformation of the generated aroyl chloride. Combined experimental and computational studies support a reaction mechanism involving in situ generation of CO.     

Electroclinic properties of chiral smectic a liquid crystalline polymers and block copolymers

The scope for the synthesis and investigation of chiral smectic A liquid crystalline (LC) polymers and block copolymers is discussed. LC block copolymers can combine the molecular order of liquid crystals and the supramolecular order typical of block copolymers, thus allowing to attain information on mesomorphic responses in restricted geometries. We present a general overview on several aspects of the syntheses and properties of LC block copolymers, specifically those obtained by starting from azomacroinitiators. These materials can exhibit an electroclinic effect, that is an electrically induced molecular tilt, which is characterized by a linear dependence on the applied field and a very fast response time in the paraelectric smectic A phase. The current progress in their potential application in electrooptics is outlined.     

Optimization of Hydrogen‐Evolving Photochemical Molecular Devices

A molecular photocatalyst consisting of a Ru^II photocenter, a tetrapyridophenazine bridging ligand, and a PtX₂ (X=Cl or I) moiety as the catalytic center functions as a stable system for light‐driven hydrogen production. The catalytic activity of this photochemical molecular device (PMD) is significantly enhanced by exchanging the terminal chlorides at the Pt center for iodide ligands. Ultrafast transient absorption spectroscopy shows that the intramolecular photophysics are not affected by this change. Additionally, the general catalytic behavior, that is, instant hydrogen formation, a constant turnover frequency, and stability are maintained. Unlike as observed for the Pd analogue, the presence of excess halide does not affect the hydrogen generation capacity of the PMD. The highly improved catalytic efficiency is explained by an increased electron density at the Pt catalytic center, this is confirmed by DFT studies.     

乙基苯胺的转动光谱及分子结构

本文使用傅里叶变换微波谱仪研究了乙基苯胺类物质(邻乙基苯胺,间乙基苯胺,对乙基苯胺)的分子结构. 由于此类分子含氮原子(I¹⁴N=1),因此跃迁谱线中都呈现出核四级裂分. 通过比较实验测定得到的分子结构,可总结苯胺环上不同位置乙基的取代对氨基及分子整体结构的影响.     

Totally Splittable Polytopes

A split of a polytope is a (necessarily regular) subdivision with exactly two maximal cells. A polytope is totally splittable if each triangulation (without additional vertices) is a common refinement of splits. This paper establishes a complete classification of the totally splittable polytopes.     

Design of a contact grating setup for mJ-energy THz pulse generation by optical rectification

According to the recent calculations, more efficient THz pulse generation is possible using relief grating on the front surface of the generating LiNbO₃ (LN) crystal for tilted-pulse-front-excitation rather than imaging the pump spot on a reflection grating into the LN crystal. Very recently, it was shown that—compared to a free-standing LN surface-relief grating—significantly higher diffraction efficiency can be reached if the grating profiles are filled with fused silica. Since realisation of such a setup is technically very challenging, in the present paper, we analyse the case where the input side of the LN grating is immersed into a refractive index matching liquid (RIML) instead of a solid material. Our results showed that the diffraction efficiency remains above 90?% for a refractive index ranging 1.45–1.60 of the applied RIML, and it is as high as 99?% for using the RIML for BK7. For this case, we carried out detailed calculations for various grating parameters. We propose a practical setup applying tilted input and slightly tilted output surfaces resulting in low losses and high diffraction efficiency for the pump. We conclude that a contact grating setup using BK7 RIML is suitable for producing THz pulses even in the mJ-energy range.     

New nonbinary code bounds based on divisibility arguments

For \(q,n,d \in \mathbb {N}\), let \(A_q(n,d)\) be the maximum size of a code \(C \subseteq [q]^n\) with minimum distance at least d. We give a divisibility argument resulting in the new upper bounds \(A_5(8,6) \le 65\), \(A_4(11,8)\le 60\) and \(A_3(16,11) \le 29\). These in turn imply the new upper bounds \(A_5(9,6) \le 325\), \(A_5(10,6) \le 1625\), \(A_5(11,6) \le 8125\) and \(A_4(12,8) \le 240\). Furthermore, we prove that for \(\mu ,q \in \mathbb {N}\), there is a 1–1-correspondence between symmetric \((\mu ,q)\)-nets (which are certain designs) and codes \(C \subseteq [q]^{\mu q}\) of size \(\mu q^2\) with minimum distance at least \(\mu q - \mu \). We derive the new upper bounds \(A_4(9,6) \le 120\) and \(A_4(10,6) \le 480\) from these ‘symmetric net’ codes.     

An investigation of assessment and feedback practices in fully asynchronous online undergraduate mathematics courses

Research suggests it is difficult to learn mathematics in the fully asynchronous online (FAO) instructional modality, yet little is known about associated teaching and assessment practices. In this study, we investigate FAO mathematics assessment and feedback practices in particular consideration of both claims and findings that these practices have a powerful influence on learning.

A survey questionnaire was constructed and completed by 70 FAO undergraduate mathematics instructors, mostly from the USA, who were each asked to detail their assessment and feedback practices in a single FAO mathematics course. Alongside these questions, participants also answered the 16-item version of the Approaches to Teaching Inventory. In addition, a novel feedback framework was also created and used to examine how feedback practices may be related to participants' approaches to teaching.

Results show that assessment and feedback practices are varied and complex: in particular, we found there was not a simple emphasis on summative assessment instruments, nor a concomitant expectation these would always be invigilated. Though richer assessment feedback appears to be emphasized, evidence suggests this feedback may not be primarily directed at advancing student learning. Moreover, we found evidence of a reliance on computer--human interactions (e.g. via computer-assisted assessment systems) and further evidence of a decline in human interactions, suggesting a dynamic that is both consistent with current online learning theory and claims FAO mathematics courses are becoming commodified. Several avenues for further research are suggested.