Real single ion solvation free energies with quantum mechanical simulation

Single ion solvation free energies are one of the most important properties of electrolyte solutions and yet there is ongoing debate about what these values are. Only the values for neutral ion pairs are known. Here, we use DFT interaction potentials with molecular dynamics simulation (DFT-MD) combined with a modified version of the quasi-chemical theory (QCT) to calculate these energies for the lithium and fluoride ions. A method to correct for the error in the DFT functional is developed and very good agreement with the experimental value for the lithium fluoride pair is obtained. Moreover, this method partitions the energies into physically intuitive terms such as surface potential, cavity and charging energies which are amenable to descriptions with reduced models. Our research suggests that lithium's solvation free energy is dominated by the free energetics of a charged hard sphere, whereas fluoride exhibits significant quantum mechanical behavior that cannot be simply described with a reduced model.Comment: 13 pages, 4 figure

Electrostatic solvation free energies of charged hard spheres using molecular dynamics with density functional theory interactions

Determining the solvation free energies of single ions in water is one of the most fundamental problems in physical chemistry and yet many unresolved questions remain. In particular, the ability to decompose the solvation free energy into simple and intuitive contributions will have important implications for models of electrolyte solution. Here, we provide definitions of the various types of single ion solvation free energies based on different simulation protocols. We calculate solvation free energies of charged hard spheres using density functional theory interaction potentials with molecular dynamics simulation (DFT-MD) and isolate the effects of charge and cavitation, comparing to the Born (linear response) model. We show that using uncorrected Ewald summation leads to unphysical values for the single ion solvation free energy and that charging free energies for cations are approximately linear as a function of charge but that there is a small non-linearity for small anions. The charge hydration asymmetry (CHA) for hard spheres, determined with quantum mechanics, is much larger than for the analogous real ions. This suggests that real ions, particularly anions, are significantly more complex than simple charged hard spheres, a commonly employed representation.Comment: 28 pages, 5 figure

George Floyd AFUM Scholarship Announcement

Fundraising plea from University President Joan Ferrini-Mundy and AFUM President Lisa K. Neuman, to all UMaine staff, introducing the George Floyd AFUM Scholarship established at the University of Maine Foundation by individuals concerned about the violent death of George Floyd, an African-American man, while in police custody on May 25, 2020 in Minneapolis, Minnesota

George Floyd AFUM Scholarship Announcement

Fundraising plea from University President Joan Ferrini-Mundy and AFUM President Lisa K. Neuman, to all UMaine staff, introducing the George Floyd AFUM Scholarship established at the University of Maine Foundation by individuals concerned about the violent death of George Floyd, an African-American man, while in police custody on May 25, 2020 in Minneapolis, Minnesota.https://digitalcommons.library.umaine.edu/racial_justice/1135/thumbnail.jp

Smoothed Dissipative Particle Dynamics model for mesoscopic multiphase flows in the presence of thermal fluctuations

Thermal fluctuations cause perturbations of fluid-fluid interfaces and highly nonlinear hydrodynamics in multiphase flows. In this work, we develop a novel multiphase smoothed dissipative particle dynamics model. This model accounts for both bulk hydrodynamics and interfacial fluctuations. Interfacial surface tension is modeled by imposing a pairwise force between SDPD particles. We show that the relationship between the model parameters and surface tension, previously derived under the assumption of zero thermal fluctuation, is accurate for fluid systems at low temperature but overestimates the surface tension for intermediate and large thermal fluctuations. To analyze the effect of thermal fluctuations on surface tension, we construct a coarse-grained Euler lattice model based on the mean field theory and derive a semi-analytical formula to directly relate the surface tension to model parameters for a wide range of temperatures and model resolutions. We demonstrate that the present method correctly models the dynamic processes, such as bubble coalescence and capillary spectra across the interface

The impact of shocks on the chemistry of molecular clouds: high resolution images of chemical differentiation along the NGC1333-IRAS2A outflow

This paper presents a detailed study of the chemistry in the outflow associated with the low-mass protostar NGC1333-IRAS2A down to 3" (650 AU) scales. Millimeter-wavelength aperture-synthesis observations from the OVRO and BIMA interferometers and (sub)millimeter single-dish observations from the Onsala 20m telescope and CSO are presented. The interaction of the highly collimated protostellar outflow with a molecular condensation ~15000 AU from the central protostar is clearly traced by molecular species such as HCN, SiO, SO, CS, and CH3OH. Especially SiO traces a narrow high velocity component at the interface between the outflow and the molecular condensation. Multi-transition single-dish observations are used to distinguish the chemistry of the shock from that of the molecular condensation and to address the physical conditions therein. Statistical equilibrium calculations reveal temperatures of 20 and 70 K for the quiescent and shocked components, respectively, and densities near 10^6 cm^{-3}. Significant abundance enhancements of two to four orders of magnitude are found in the shocked region for molecules such as CH3OH, SiO and the sulfur-bearing molecules. HCO+ is seen only in the aftermath of the shock consistent with models where it is destroyed through release of H2O from grain mantles in the shock. N2H+ shows narrow lines, not affected by the outflow but rather probing the ambient cloud. Differences in abundances of HCN, H2CO and CS are seen between different outflow regions and are suggested to be related to differences in the atomic carbon abundance. Compared to the warm inner parts of protostellar envelopes, higher abundances of in particular CH3OH and SiO are found in the outflows, which may be related to density differences between the regions.Comment: 18 pages, 13 figures. Accepted for publication in A&

Mass Density Fluctuations in Quantum and Classical descriptions of Liquid Water

First principles molecular dynamics simulation protocol is established using revised functional of Perdew-Burke-Ernzerhof (revPBE) in conjunction with Grimme's third generation of dispersion (D3) correction to describe properties of water at ambient conditions. This study also demonstrates the consistency of the structure of water across both isobaric (NpT) and isothermal (NVT) ensembles. Going beyond the standard structural benchmarks for liquid water, we compute properties that are connected to both local structure and mass density uctuations that are related to concepts of solvation and hydrophobicity. We directly compare our revPBE results to the Becke-Lee-Yang-Parr (BLYP) plus Grimme dispersion corrections (D2) and both the empirical fixed charged model (SPC/E) and many body interaction potential model (MB-pol) to further our understanding of how the computed properties herein depend on the form of the interaction potential

Dual role for the latent transforming growth factor-beta binding protein in storage of latent TGF-beta in the extracellular matrix and as a structural matrix protein

The role of the latent TGF-beta binding protein (LTBP) is unclear. In cultures of fetal rat calvarial cells, which form mineralized bonelike nodules, both LTBP and the TGF-beta 1 precursor localized to large fibrillar structures in the extracellular matrix. The appearance of these fibrillar structures preceded the appearance of type I collagen fibers. Plasmin treatment abolished the fibrillar staining pattern for LTBP and released a complex containing both LTBP and TGF-beta. Antibodies and antisense oligonucleotides against LTBP inhibited the formation of mineralized bonelike nodules in long-term fetal rat calvarial cultures. Immunohistochemistry of fetal and adult rat bone confirmed a fibrillar staining pattern for LTBP in vivo. These findings, together with the known homology of LTBP to the fibrillin family of proteins, suggest a novel function for LTBP, in addition to its role in matrix storage of latent TGF-beta, as a structural matrix protein that may play a role in bone formation

Reflections on belonging and a law student pledge

In 2017, the School of Law at the University of Wollongong commenced an experimental initiative through the introduction of a Law Student Pledge. It was designed as a symbolic statement to students that from the day they begin their law studies they become a member of the legal professional community. In this way, it invited First Year Students to commit to core values, attitudes and practices seen as important to developing a positive professional identity. This article reports on learnings following the implementation of the Pledge over 3 iterations and reflects upon its impact on shaping students’ sense of belonging. As an empirical project, this research incorporates both the student voice as well as the academic perspective, via the methodology of reflective practice. The research will consider whether the Pledge provided an opportunity for students to engage in a community of shared identity or became a perceived ‘imposed’ requirement to belong

Vienna Circle and Logical Analysis of Relativity Theory

In this paper we present some of our school's results in the area of building up relativity theory (RT) as a hierarchy of theories in the sense of logic. We use plain first-order logic (FOL) as in the foundation of mathematics (FOM) and we build on experience gained in FOM. The main aims of our school are the following: We want to base the theory on simple, unambiguous axioms with clear meanings. It should be absolutely understandable for any reader what the axioms say and the reader can decide about each axiom whether he likes it. The theory should be built up from these axioms in a straightforward, logical manner. We want to provide an analysis of the logical structure of the theory. We investigate which axioms are needed for which predictions of RT. We want to make RT more transparent logically, easier to understand, easier to change, modular, and easier to teach. We want to obtain deeper understanding of RT. Our work can be considered as a case-study showing that the Vienna Circle's (VC) approach to doing science is workable and fruitful when performed with using the insights and tools of mathematical logic acquired since its formation years at the very time of the VC activity. We think that logical positivism was based on the insight and anticipation of what mathematical logic is capable when elaborated to some depth. Logical positivism, in great part represented by VC, influenced and took part in the birth of modern mathematical logic. The members of VC were brave forerunners and pioneers.Comment: 25 pages, 1 firgure