Search

The reaction pathways and potential energy profiles are theoretically explored for H-abstraction, addition and addition–dissociation reactions of methyl formate (MF, HC(＝O)OCH3) + NO2 using the high level quantum chemical compound method CCSD(T)/cc-pVxZ(x = T, Q)//M062X/6-311+G(2df,2p). Notably, three different HNO2 isomers (cis-HONO, trans-HONO and HNO2) are all considered in each reaction pathway. The corresponding temperature- and pressure-dependent rate constants are then computed by RRKM/ME simulations with one-dimensional hindered rotor approximation and asymmetric Eckart tunneling corrections. The calculations show that the rate constants are pressure independent. Although trans-HONO is the most stable HNO2 isomer, the results reveal that the dominant channels are cis-HONO + HC(＝O)OCH2/C(＝O)OCH3 and cis-HC(O)(ONO)OCH3 for the H-abstraction and addition, respectively. Moreover, the lowest energy barrier for the H-abstraction channel (cis-abs) is 11.2 kcal mol−1 lower than the addition channel (cis-add), and thus the addition channel is less kinetically favored. The computed rate constants for the MF + NO2 reaction are then incorporated into a kinetic model and the importance of the title reaction in predicting the ignition behavior of MF/NO2 mixtures is demonstrated by kinetic modeling. The detailed reaction kinetics in this work will be helpful for kinetic model development of other ester-based fuels. [ABSTRACT FROM AUTHOR]

Atomic-like emitters in the solid state serve as important resources in the advancement of future quantum networks. In particular, intra-4f optical transitions of rare earth ions exhibit excellent coherence properties thanks to the shielding effect of outer electrons. Still, the presence of various dephasing channels in solid state hosts introduces additional decoherence beyond the radiative decay, causing the coherence time of most rare earth doped materials to be over an order of magnitude lower than the radiative limit. Such obstacle prevents the emission of indistinguishable photons from rare earth ions, which is an essential requirement for various quantum applications. In this work, we perform optical coherence study on erbium ions doped in thin-film lithium niobate by patterning photonic crystal resonators with quality factor around 100 k and sub- λ 3 mode volume. Leveraging the combination of long coherence and strong Purcell enhancement in the cavity, we show that the coherence time measured with photon echo approaches the radiative limit (80%), representing a 50-fold improvement compared to the waveguide case. Our results present promising prospects toward utilizing rare earth doped materials as quantum repeaters and sources of indistinguishable photons. [ABSTRACT FROM AUTHOR]

Electrostatic control and van der Waals integration are useful methods for 2D materials to help modulate their properties. Here, we constructed nine types of monolayer and multilayer Janus structures based on group-III monochalcogenides and investigated their atomic and electronic structures from first-principles calculations. We found the existence of an intrinsic electric field at Janus structures by comparing their average vacuum electron potentials at two surfaces. Careful charge analyses reveal that the electric field at monolayer Janus structures is mainly due to the dipole of the bond that connects group-III elements of weaker negativity and group-VI elements of stronger negativity. The E-filed at multilayer Janus structures maintains owing to the superposition of dipole at each layer when layer numbers (LN) are not very large, and the electric field starts to reduce when LN is large enough and obvious charge transfer happens between two surfaces of Janus multilayers. Electronic structure calculations at Janus structures demonstrate that the electric field can hardly modulate the charge density population in the monolayer case, while the electric field will significantly bend the bands in multilayer cases and make the charge density of the valence band maximum and the conduction band minimum always located at two separating surfaces, which promotes electron–hole to separate. Furthermore, we investigated the band alignment of isolated monolayer pristine group-III monochalcogenides and isolated Janus group-III monochalcogenides of monolayer, bilayer, and trilayer, and constructed van der Waals (vdW) heterostructures with one pristine monolayer and one Janus monolayer. The results show that the surface termination of Janus structures at the interface can significantly influence the band offset and electronic structures of vdW heterostructures. These results can not only provide a new understanding of the intrinsic electric field of monolayer and multilayer 2D Janus structures but also give a guide that uses electrostatic to modulate the properties of group-III monochalcogenides and other 2D materials. [ABSTRACT FROM AUTHOR]

The various rhapsodies or poetic expositions of the Han dynasty known as Han fu are replete with passages from the classic Chinese poetry collection the Shijing , or Book of Poetry. The reverse is also true: Shijing scholarship has likewise cited Han fu in many of its exegetical works. As a result, the various editions of the Han fu are important sources in the study of the Confucian classics, a discipline commonly known in Chinese as jingxue. The classical citations of the Shijing throughout the Han fu can be placed into one of two categories: "language citation" and "meaning citation", while the "ironic citation" of Han fu in exegeses of the Shijing that is prevalent in the interpretative system of the Confucian classics can be further broken down into three types: "meaning and principle", "verification and justification" and "language and exposition". In the meaning-based citations of the Shijing by the Han fu – especially those of "persuasive remonstrance" and "hymns and eulogies" – the conveyed messages were ironically cited by later generations of interpreters of Confucian classics, which helped form new meanings and principles. The main themes, subject matter, emotional expression and language style of Han fu are lifted heavily from the Shijing. Later generations of Confucian scholars then cited text from the Han fu , thereby constructing new forms of language and exposition. The unique characteristics of fu to "describe things and express themselves clearly" and reference a wide range of "names and things" were used by later Confucian scholars who sought to better understand a whole host of signifiers referred to in the classic texts, from herbs, trees and birds, to beasts, insects and fish. Meanwhile, the perception of fu as knowledge-laden texts inspired Confucian scholars to carry out textual research on them. Scholarly comparisons in premodern China between the Shijing as a Confucian classic, the Shijing as a literary corpus, and Han fu developed during a process of ordinary citation and ironic citation. This resulted in the practice of "complementary citations" of meaning and principle, verification and justification, and language and exposition. A scholarship cycle was thus formed in which the classics were used to revere the fu , then the classics were used to enrich the fu , and interpretations of the fu started to be used to transmit canonical messages. It was a cycle that was imbued with a cross-permeation of neo-Confucian, historical and literary dimensions, eventually resulting in the construction of a new interpretative system for premodern Chinese scholarship of classic texts. [ABSTRACT FROM AUTHOR]