Building Water Models, A Different Approach

Simplified, classical models of water are an integral part of atomistic molecular simulations, especially in biology and chemistry where hydration effects are critical. Yet, despite several decades of effort, these models are still far from perfect. Presented here is an alternative approach to constructing point charge water models - currently, the most commonly used type. In contrast to the conventional approach, we do not impose any geometry constraints on the model other than symmetry. Instead, we optimize the distribution of point charges to best describe the "electrostatics" of the water molecule, which is key to many unusual properties of liquid water. The search for the optimal charge distribution is performed in 2D parameter space of key lowest multipole moments of the model, to find best fit to a small set of bulk water properties at room temperature. A virtually exhaustive search is enabled via analytical equations that relate the charge distribution to the multipole moments. The resulting "optimal" 3-charge, 4-point rigid water model (OPC) reproduces a comprehensive set of bulk water properties significantly more accurately than commonly used rigid models: average error relative to experiment is 0.76%. Close agreement with experiment holds over a wide range of temperatures, well outside the ambient conditions at which the fit to experiment was performed. The improvements in the proposed water model extend beyond bulk properties: compared to the common rigid models, predicted hydration free energies of small molecules in OPC water are uniformly closer to experiment, root-mean-square error < 1kcal/mol

Point Charges Optimally Placed to Represent the Multipole Expansion of Charge Distributions

We propose an approach for approximating electrostatic charge distributions with a small number of point charges to optimally represent the original charge distribution. By construction, the proposed optimal point charge approximation (OPCA) retains many of the useful properties of point multipole expansion, including the same far-field asymptotic behavior of the approximate potential. A general framework for numerically computing OPCA, for any given number of approximating charges, is described. We then derive a 2-charge practical point charge approximation, PPCA, which approximates the 2-charge OPCA via closed form analytical expressions, and test the PPCA on a set of charge distributions relevant to biomolecular modeling. We measure the accuracy of the new approximations as the RMS error in the electrostatic potential relative to that produced by the original charge distribution, at a distance the extent of the charge distribution–the mid-field. The error for the 2-charge PPCA is found to be on average 23% smaller than that of optimally placed point dipole approximation, and comparable to that of the point quadrupole approximation. The standard deviation in RMS error for the 2-charge PPCA is 53% lower than that of the optimal point dipole approximation, and comparable to that of the point quadrupole approximation. We also calculate the 3-charge OPCA for representing the gas phase quantum mechanical charge distribution of a water molecule. The electrostatic potential calculated by the 3-charge OPCA for water, in the mid-field (2.8 Å from the oxygen atom), is on average 33.3% more accurate than the potential due to the point multipole expansion up to the octupole order. Compared to a 3 point charge approximation in which the charges are placed on the atom centers, the 3-charge OPCA is seven times more accurate, by RMS error. The maximum error at the oxygen-Na distance (2.23 Å ) is half that of the point multipole expansion up to the octupole order

Epidemiological and Clinical Aspects of COVID-19; a Narrative Review

There are significant misconceptions and many obstacles in the way of illuminating the epidemiological and clinical aspects of COVID-19 as a new emerging epidemic. In addition, usefulness of some evidence published in the context of the recent epidemic for decision making in clinic as well as public health is questionable. However, misinterpreting or ignoring strong evidence in clinical practice and public health probably results in less effective and somehow more harmful decisions for individuals as well as subgroups in general populations of countries in the initial stages of this epidemic. Accordingly, our narrative review appraised epidemiological and clinical aspects of the disease including genetic diversity of coronavirus genus, mode of transmission, incubation period, infectivity, pathogenicity, virulence, immunogenicity, diagnosis, surveillance, clinical case management and also successful measures for preventing its spread in some communities. Keywords:COVID-19; severe acute respiratory syndrome coronavirus 2; epidemiology; public health; communicable diseases; emergin

A novel laryngeal palpatory scale (LPS) in patients with muscle tension dysphonia

Objectives: Laryngeal palpation is a routine clinical method for evaluation of patients with muscle tension dysphonia (MTD). The aim of this study was to develop a new comprehensive valid and reliable “laryngeal palpatory scale” (LPS), based on psychometric criteria. Methods: The scale items were selected based on an in-depth analysis of the literature and an expert focus group. Scale item generation and item reduction were followed by a psychometric assessment. Qualitative and quantitative content validity (the content validity ratio (CVR), content validity index (CVI)), the qualitative face validity, and the inter-rater reliability were determined. For this purpose, 531 patients were assessed and finally 55 patients with primary MTD (26 women, mean age: 40.8 years, SD: 12.5; 29 male, mean age: 41.6 years, SD: 11.8) participated in the study. A weighted kappa (k*) statistic was used to examine the inter-rater reliability for each single item. Results: Based on the CVR, three items were omitted because they had a score of less than 0.62. The CVI for all remaining items was greater than 0.79 and the scale CVI was equal to 0.96. The final 45 items were a result of the study. The inter-rater reliability for each single item ranged from 0.41 to 1, indicating moderate to almost perfect agreement. Conclusions: The LPS is a reliable and valid instrument for assessing patients with MTD. However, future studies are needed to provide adequate data on sensitivity, specificity, concurrent validity, and cutoff scores

Comparison of laryngeal palpatory scale (LPS), with surface electromyographic measures in patients with muscle tension dysphonia

OBJECTIVES : The aim of this study was to examine the laryngeal palpatory scale (LPS) to ascertain possible correlation with neck surface electromyography (sEMG). METHODS : Two otolaryngologists and one certified speech-language pathologist assessed 21 participants (seven women and 14 men; with a mean age of 42.8 years; ranged: 21 to 70 years) with muscle tension dysphonia (MTD) diagnosed with the current version of the LPS rating system. Consequently, relationships between LPS and objective measures of sEMG were evaluated using Spearman's rank correlation coefficient (r). RESULTS : The results show that there was a low to moderate between correlations, (statistically positive and significant in 10 correlations among the examined items/states). CONCLUSIONS : In conclusion, low-moderate positive correlations between sEMG and LPS ratings were found with particular strength for LPS ratings of tightness and ratings made during dynamic tasks. Further investigations can provide useful evidence for researchers and clinicians to document treatment outcomes by using LPS and sEMG in patients with MTD and leading to the more standardized care and improved information about patient progress.http://www.journals.elsevier.com/journal-of-voicehj2023Speech-Language Pathology and Audiolog