As a generic property, all substances transfer heat through microscopic collisions of constituent particles . A solid conducts heat through both transverse and longitudinal acoustic phonons, but a liquid employs only longitudinal vibrations. As a result, a solid is usually thermally more conductive than a liquid. In canonical viewpoints, such a difference also serves as the dynamic signature distinguishing a solid from a liquid. Here, we report liquid-like thermal conduction observed in the crystalline AgCrSe. The transverse acoustic phonons are completely suppressed by the ultrafast dynamic disorder while the longitudinal acoustic phonons are strongly scattered but survive, and are thus responsible for the intrinsically ultralow thermal conductivity. This scenario is applicable to a wide variety of layered compounds with heavy intercalants in the van der Waals gaps, manifesting a broad implication on suppressing thermal conduction. These microscopic insights might reshape the fundamental understanding on thermal transport properties of matter and open up a general opportunity to optimize performances of thermoelectrics.
Reactions of H atoms with N2O have two product channels yielding NH+NO and OH+N2. Both channels were observed via NH A 3Π←X 3∑ and OH A 2∑←X 2Π laser-induced fluorescence spectra. Photoinitiated reactions with N2O–HI complexes yield a much lower [NH]/[OH] ratio than under the corresponding bulk conditions at the same photolysis wavelength. For hot D-atom reactions with N2O, this effect is somewhat more pronounced. These results can be interpreted in terms of entrance channel geometric specificity, namely, biasing hydrogen attack toward the oxygen. Another striking observation is that the OH and OD rotational level distributions (RLD) obtained under bulk conditions differ markedly from those obtained under complexed conditions, while the NH as well as the ND RLD are similar for the two environments. In addition, OH Doppler profiles change considerably in going from bulk to complexed conditions, while such an effect is not observed for NH. The changes observed with the OH RLD are most likely due to OH–halogen interactions and/or entrance channel specificity. Under bulk conditions, the Doppler shift measurements indicate a large amount of N2 internal excitation (i.e., ∼25 000 cm−1) for the OH (v=0) levels monitored. This is consistent with a reaction mechanism involving an HNNO° intermediate. The hot hydrogen atom first attaches to the terminal nitrogen of N2O and forms an excited HNNO° intermediate having a relatively elongated N–N bond compared with N2O. Then the H atom migrates from nitrogen to oxygen and exits to the N2+OH product channel, leaving N2 vibrationally excited. A simple Franck–Condon model can reconcile quantitatively the large amount of N2 vibrational excitation.
The size effect theory was proposed by Frossard and co-workers for evaluating the shear strength of rockfill material. However, this theory has not been validated in a general stress path, in which the intermediate principal stress may be different from the minor principal stress. A series of true triaxial compression tests on rockfill material A (RFM-A, a small-sized particle) and rockfill material B (RFM-B, a larger-sized particle) were carried out to validate the size effect theory in the general stress state. It was found that the predictions by the size effect theory, based on the material constants from the strength data of RFM-A, were in good agreement with the strength data of RFM-B.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.