Hydration Energies of Deprotonated Amino Acids from Gas Phase Equilibria Measurements

Singly hydrated clusters of deprotonated amino acids were studied using an electrospray high-pressure mass spectrometer equipped with a pulsed ion-beam reaction chamber. Thermochemical data, ΔHo, ΔSo, and ΔGo, for the hydration reaction [AA − H]− + H2O = [AA − H]−·(H2O) were obtained from gas-phase equilibria determinations for AA = Gly, Ala, Val, Pro, Phe, Lys, Met, Trp, Gln, Arg, and Asp. The hydration free-energy changes are found to depend significantly on the side-chain substituents. The water binding energy in [AA − H]−·(H2O) increases with the gas-phase acidity of AA. The anionic hydrogen bond strengths in [AA − H]−·(H2O) are compared with those of the cationic bonds in the corresponding AAH+·(H2O) systems

Twitter Sentiments and Stock Prices: An Event Study on the Role of Influencers

For many companies, some consumers enthusiastically follow brands and may have insights rivaling those of professional financial analysts based on their knowledge of the companies. Often, these brand-loyal consumers express their thoughts and opinions on social media may be received by others in their communities, driving users to follow them based on the perception of expertise and trustworthiness. In academic literature, such users are referred to as Social Media Influencers (SMI). The present study investigates the relationship between sentiments of Twitter posts and abnormal stock price returns. It further explores if source credibility operationalized as followership affects this relationship. SMIs are perceived to have higher source credibility, and it is expected that the relationship is stronger with SMIs than with non-SMI users. Sentiment analysis categorizes tweets into positive, neutral, and negative based on pre-trained models and machine learning. Tweets made between 2017 and 2022 for four specific firms are analyzed using an event study approach. Events are identified using an automated algorithm, and abnormal returns are estimated using the Market model. Tweets are split based on percentile rankings of posting authors’ follower counts. The study finds that positive sentiments are generally statistically significant in identifying positive cumulative abnormal returns. Furthermore, the novel approach of gradually including fractiles of follower numbers shows that the significance of abnormal returns is not homogenous across all users. Contrary to expectations, statistical significance is stronger for a longer duration around identified events with tweets posted by users at the bottom 30% of followership. In contrast, tweets made by the users with more followers are not statistically significant until 80%. This finding suggests that the sentiments of tweets from users with a lower number of followers are more strongly related to the abnormal returns of stock prices. This study shifts the focus of most extant research by using a broader set of tweets from “ordinary” users instead of investment-oriented users in exploring the relationship. The study also contributes to the relatively underexplored effect of SMI by taking an iterative approach to studying tweets through comparative analysis across different numbers of followers

Factors affecting dose distributions in brachytherapy of coronary arteries with P-32 linear source

BackgroundLong-term results of brachytherapy of coronary arteries may be influenced by inhomogeneity of the dose distribution. The dose distribution perturbations due to the presence of stent struts, guide wires and calcium deposits were therefore investigated.AimThe aim of the study was to investigate dose distribution perturbations due to the presence of stent struts, guide wire and calcium deposits during the irradiation. Both experimental and calculational techniques were applied to elucidate these influences.Materials/MethodsThe measurements were carried out with radiochromic foil in a phantom in the presence and absence of the stent and the guide wire. Due to the measurements being limited by the thickness of the detecting foil, the radial dose distribution with or without the metallic stent components were also performed using the MCNP Monte Carlo code. The same code was used to measure the influence of cholesterol plaques on dose distribution in the vessel walls.ResultsA large dose reduction in the area shielded by the guide wire was observed. The presence of the stent caused a 15% dose reduction behind the struts. The dose reduction caused by calcium deposits ranged from 11% to 32%.ConclusionsThese facts may increase the probability of late restenosis after irradiation due to underdosage. The inhomogeneity occurring behind the guide wire, stent struts and calcium deposits should be taken into account in the analysis of dose distributions for clinical applications

Thermochemistry of Microhydration of Sodiated and Potassiated Monosaccharides

The thermochemical properties ΔHon , ΔSon, and ΔGon for the hydration of sodiated and potassiated monosaccharides (Ara = arabinose, Xyl = xylose, Rib = ribose, Glc = glucose, and Gal = galactose) have been experimentally studied in the gas phase at 10 mbar by equilibria measurements using an electrospray high-pressure mass spectrometer equipped with a pulsed ion beam reaction chamber. The hydration enthalpies for sodiated complexes were found to be between −46.4 and −57.7 kJ/mol for the first, and −42.7 and −52.3 kJ/mol for the second water molecule. For potassiated complexes, the water binding enthalpies were similar for all studied systems and varied between −48.5 and −52.7 kJ/mol. The thermochemical values for each system correspond to a mixture of the α and β anomeric forms of monosaccharide structures involved in their cationized complexes

WACCM-D Whole Atmosphere Community Climate Model with D-region ion chemistry

Energetic particle precipitation (EPP) and ion chemistry affect the neutral composition of the polar middle atmosphere. For example, production of odd nitrogen and odd hydrogen during strong events can decrease ozone by tens of percent. However, the standard ion chemistry parameterization used in atmospheric models neglects the effects on some important species, such as nitric acid. We present WACCM-D, a variant of the Whole Atmosphere Community Climate Model, which includes a set of lower ionosphere (D-region) chemistry: 307 reactions of 20 positive ions and 21 negative ions. We consider realistic ionization scenarios and compare the WACCM-D results to those from the Sodankylä Ion and Neutral Chemistry (SIC), a state-of-the-art 1-D model of the D-region chemistry. We show that WACCM-D produces well the main characteristics of the D-region ionosphere, as well as the overall proportion of important ion groups, in agreement with SIC. Comparison of ion concentrations shows that the WACCM-D bias is typically within ±10% or less below 70 km. At 70–90 km, when strong altitude gradients in ionization rates and/or ion concentrations exist, the bias can be larger for some groups but is still within tens of percent. Based on the good agreement overall and the fact that part of the differences are caused by different model setups, WACCM-D provides a state-of-the-art global representation of D-region ion chemistry and is therefore expected to improve EPP modeling considerably. These improvements are demonstrated in a companion paper by Andersson et al