Comment on "Orientational Distribution of Free O-H Groups of Interfacial Water is Exponential"

In a recent letter (PRL,121,246101,2018), Sun et al. reported that combined MD simulation and sum frequency generation vibrational spectroscopy (SFG-VS) measurements led to conclusions of a broad and exponentially decaying orientational distribution, and the presence of the free O-H group pointing down to the bulk at the air/water interface. In this comment, we show that their main conclusions are based on questionable interpretation of the SFG-VS data presented in the letter [1], and are also contrary to the established data analysis and interpretations in the literature [2-5].Comment: 2 pages, 0 figure

Spectroscopic Evidence for the Specific Na+ and K+ Interactions with the Hydrogen-bonded Water Molecules at the Electrolyte Aqueous Solution Surfaces

Sum frequency generation vibrational spectra of the water molecules at the NaF and KF aqueous solution surfaces showed significantly different spectral features and different concentration dependence. This result is the first direct observation of the cation effects of the simple alkali cations, which have been believed to be depleted from the aqueous surface, on the hydrogen bonding structure of the water molecules at the electrolyte solution surfaces. These observations may provide important clue to understand the fundamental phenomenon of ions at the air/water interface.Comment: 15 pages, 2 figure

New predictions on the mass of the 1−+1^{-+} light hybrid meson from QCD sum rules

We calculate the coefficients of the dimension-8 quark and gluon condensates in the current-current correlator of $1^{-+}$ light hybrid current $g\bar{q}(x)\gamma_{\nu}iG_{\mu\nu}(x)q{(x)}$. With inclusion of these higher-power corrections and updating the input parameters, we re-analyze the mass of the $1^{-+}$ light hybrid meson from Monte-Carlo based QCD sum rules. Considering the possible violation of factorization of higher dimensional condensates and variation of $\langle g^3G^3\rangle$, we obtain a conservative mass range 1.72--2.60\,GeV, which favors $\pi_{1}(2015)$ as a better hybrid candidate compared with $\pi_{1}(1600)$ and $\pi_{1}(1400)$.Comment: 12pages, 2 figures, the version appearing in JHE

Experimental study on behaviour of retrofitted square hollow section slender columns under axial compression

An experimental investigation was conducted in this study on axially loaded square hollow section (SHS) slender columns retrofitted by carbon fiber reinforced polymer (CFRP). A total of seven specimens with identical cross section dimensions and raw material properties were compressed between pinned ends to identify the influence of the CFRP, in which six specimens were retrofitted by the CFRP. The effects of many influential factors including different layers of the CFRP, retrofitting directions of the CFRP and retrofitting sequences of the CFRP on the behaviour of the CFRP strengthened SHS slender columns were carefully evaluated. The column strengths obtained from the experimental investigation are compared with the design strengths calculated using the design equations given in the British Standard (CIRIA) and the equations modified based on the section conversion method proposed by Canadian Standard (CAN/CSA-S16-01). It is shown from the comparison that the ultimate strengths of the SHS slender columns were enhanced by retrofitting with the CFRP. The retrofitting directions of the CFRP in the longitudinal directions were found to have a great influence on the ultimate strengths of the CFRP strengthened SHS slender columns. Furthermore, a correction factor (βc) is proposed in this paper for the stability of the CFRP retrofitted SHS slender columns under axial compression

A Comprehensive Analysis on Repeating Fast Radio Bursts

About 900 fast radio burst (FRB) sources have been detected till now, among which 29 FRBs are found to burst out repeatedly. Although a firm connection between at least some FRBs and magnetars has been established, the trigger mechanism and radiation process in these enigma phenomena are still highly controversial. In this study, we build a sample of 16 repeating FRBs from which at least five bursts have been detected, including the most active four repeaters of FRBs 20121102A, 20180916B, 20190520B and 20201124A. Various key parameters of their bursts are collected from the literature, which include the trigger time, pulse width, dispersion measure (DM), Faraday rotation measure (RM), bandwidth, waiting time, peak flux and fluence. The distribution and time evolution of these parameters are investigated. Potential correlations between various parameter pairs are also extensively explored. The behaviors of different repeaters are then compared. It is found that the DM of FRB 20121102A seems to increase continuously on a long timescale. While the $DM$ of most repeaters varies in a narrow range of $\pm 3$ cm$^{-3}$ pc, FRB 20190520B is found to have a large variation range of $\pm 12$ cm$^{-3}$ pc. A linear correlation between $DM$ and the star formation rate is established. $RM$ evolves with time in a much more chaos behavior in different repeaters. Generally, the waiting time shows a bimodal distribution in each source. The implications of these features to the underlying physics are discussed.Comment: 47 pages, 51 figures, 8 table

Differentiation of Eight Commercial Mushrooms by Electronic Nose and Gas Chromatography-Mass Spectrometry

Volatile profiles of eight mushrooms were characterized by gas chromatography-mass spectrometry and electronic nose analysis. Volatile compounds including 11 alcohols, 11 ketones, 15 aldehydes, 3 sulfur compounds and alkenes, 8 terpenes, 7 acid and esters, 5 heterocyclic compounds, 20 aromatic compounds, and 4 other compounds were identified. The overall aroma properties of the mushrooms were analyzed by the electronic nose. Results indicated that the e-nose sensors have the ability to accurately respond to different mushrooms with similar fingerprint chromatograms. The relationship between the GC-MS data and e-nose responses of different mushrooms was modeled by principal component analysis and partial least squares regression. This combination for the volatile analysis with chemometric methods can be applied to distinguish different mushrooms successfully. Furthermore, it is concluded that the volatile composition of commercial mushrooms could benefit a finger spectrum by e-nose to identify the species of edible fungi