Experimental study of energy-minimizing point configurations on spheres

In this paper we report on massive computer experiments aimed at finding spherical point configurations that minimize potential energy. We present experimental evidence for two new universal optima (consisting of 40 points in 10 dimensions and 64 points in 14 dimensions), as well as evidence that there are no others with at most 64 points. We also describe several other new polytopes, and we present new geometrical descriptions of some of the known universal optima.Comment: 41 pages, 12 figures, to appear in Experimental Mathematic

Non-perturbative Many-Body Treatment of Molecular Magnets

Molecular magnets have received significant attention because of their potential applications in quantum information and quantum computing. A delicate balance of electron correlation, spin-orbit coupling (SOC), ligand field splitting, and other effects produces a persistent magnetic moment within each molecular magnet unit. The discovery and design of molecular magnets with improved functionalities would be greatly aided by accurate computations. However, the competition among the different effects poses a challenge for theoretical treatments. Electron correlation plays a central role, since d-, or f-element ions, which provide the magnetic states in molecular magnets, often require explicit many-body treatments. SOC, which expands the dimensionality of the Hilbert space, can also lead to non-perturbative effects in the presence of strong interaction. Furthermore, molecular magnets are large, with tens of atoms in even the smallest systems. We show how an $\textit{ab initio}$ treatment of molecular magnets can be achieved with auxiliary-field quantum Monte Carlo (AFQMC), in which electron correlation, SOC, and material specificity are included accurately and on an equal footing. The approach is demonstrated by an application to compute the zero-field splitting of a locally-linear Co$^{2+}$ complex.Comment: 22 pages, 3 figure

Anti-SARS-CoV-2 Antibodies Testing in Recipients of COVID-19 Vaccination: Why, When, and How?

Although universal vaccination is one of the most important healthcare strategies for limiting SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) circulation and averting the huge number of hospitalizations and deaths due to coronavirus disease 2019 (COVID-19), significant inter-individual variability of COVID-19 vaccines\u2019 efficacies has been described, mostly due to heterogeneous immune response in recipients. This opinion paper hence aims to discuss aspects related to the opportunity of monitoring anti-SARS-CoV-2 antibodies before and after COVID-19 vaccination, highlighting the pros and cons of this strategy. In summary, the advantages of anti-SARS-CoV-2 antibodies\u2019 testing in recipients of COVID-19 vaccination encompass an assessment of baseline seroprevalence of SARS-CoV-2 infection in non-vaccinated individuals; early identification of low or non-responders to COVID-19 vaccination; and timely detection of faster decay of anti-SARS-CoV-2 antibody levels. In contrast, potential drawbacks to date include an unproven equivalence between anti-SARS-CoV-2 antibody titer, neutralizing activity, and vaccine efficiency; the lack of cost-effective analyses of different testing strategies; the enormous volume of blood drawings and increase of laboratory workload that would be needed to support universal anti-SARS-CoV-2 antibodies testing. A potential solution entails the identification of cohorts to be prioritized for testing, including those at higher risk of being infected by variants of concern, those at higher risk of unfavorable disease progression, and subjects in whom vaccine immunogenicity may be expectedly lower and/or shorter

The real origin of SARS-CoV-2: does it really matter?

SARS-CoV-2 has likely originated from a bat coronavirus, probably BatCoV-RaTG13, which has been transmitted to another intermediate animal, maybe a pangolin, where the ancestral virus has undergone primary intra-animal recombination. This new virus (e.g., 2019 GX/GD Pangolin) was likely then transmitted to the first human index case, where it then became the SARS-CoV-2 that originated in the first local outbreak. Failure to timely recognize the first diffusion of the virus within a likely circumscribed human niche has enabled further intra-human recombination processes, which then finally generated the highly virulent pathogen that is causing the ongoing pandemic outbreak. This theory is inherently supported by data showing that the virus has circulated at lower virulence much earlier before its first identification in Wuhan. For example, evidence from environmental monitoring suggests that the virus started to circulate in Italy as early as December 2019, while the much larger outbreak was only recorded 2\u20133 months later

Ab initio Calculations in Atoms, Molecules, and Solids, Treating Spin-Orbit Coupling and Electron Interaction on Equal Footing

We incorporate explicit, non-perturbative treatment of spin-orbit coupling into ab initio auxiliary-field quantum Monte Carlo (AFQMC) calculations. The approach allows a general computational framework for molecular and bulk systems in which materials specificity, electron correlation, and spin-orbit coupling effects can be captured accurately and on equal footing, with favorable computational scaling versus system size. We adopt relativistic effective-core potentials which have been obtained by fitting to fully relativistic data and which have demonstrated a high degree of reliability and transferability in molecular systems. This results in a 2-component spin-coupled Hamiltonian, which is then treated by generalizing the ab initio AFQMC approach. We demonstrate the method by computing the electron affinity in Pb, the bond dissociation energy in Br$_2$ and I$_2$, and solid Bi.Comment: 26 pages, 4 figures, submitted to The Journal of Chemical Physic

Cryptocurrencies in the future of money and monetary policy

The idiosyncratic allure of cryptocurrencies, in particular Bitcoin, has attracted widespread, if reticent, attention in the financial markets. Since Bitcoin’s introduction in 2008 there has been a growing interest in digital assets possibly supplanting traditional payment methods. Two conceptual questions raised regarding cryptocurrencies are firstly, whether cryptocurrencies meet the traditional functions of money; secondly, what is the future of cryptocurrencies? This dissertation seeks to examine the future of cryptocurrency by reference to money and monetary policy. The further question, whether cryptocurrencies meet the traditional functions of money, is tested via a combination of theoretical and empirical analysis. The study explores both statistical and empirical models, in illustrative comparative detail, provided by analysis which included ADF and KPSS test models, alongside an ARMA(p,q)-GARCH(1,1) model. Cryptocurrencies present both significant benefits, alongside immense shortcomings. They provide the novel ability to conduct anonymous international transactions on a decentralised platform with lower transaction fees. However, the very nature of that anonymity could provide their downfall as much as they open a market for illicit activities. In addition, cryptocurrency’s significant energy consumption through the mining of cryptocurrencies is of concern to environmentalists. The empirical section of the dissertation consists of a comparative analysis between Bitcoin/USD time series to the Rand/USD time series, with specific attention devoted to the level of volatility of each time series. This was important in determining whether cryptocurrencies fulfil the store of value function of money. The dissertation concluded that Bitcoin/USD time series exhibited identifiable adverse characteristics of autocorrelation and ARCH effects, thus suggesting that Bitcoin/USD is strongly associated with volatility. The Rand/USD signified the same effects although of significantly lesser order than that of Bitcoin/USD. Consequently, cryptocurrencies are seen to act more as an asset than a currency. Nonetheless, cryptocurrencies seem likely to grow as a medium of exchange as more and more businesses gain knowledge of the innovation and seek to adopt innovative ways to become more efficient and follow technology trends. Currently, fiat currencies remain superior in the financial market, simply because cryptocurrencies are perceived not to fulfil the traditional functions of money. However in the future, the market share of cryptocurrencies is likely to increase, and so the future of the financial markets will surely include a coexistence of both fiat and cryptocurrencies, as people’s preferences determine where they feel safe to hold their money

The influence of aing on the regenerative potential of human adipose derived mesenchymal stem cells

Tissue regeneration using human adipose derived mesenchymal stem cells (hASCs) has significant potential as a novel treatment for many degenerative bone and joint diseases. Previous studies have established that age negatively affects the proliferation status and the osteogenic and chondrogenic differentiation potential of mesenchymal stem cells. The aim of this study was to assess the agerelated maintenance of physiological function and differentiation potential of hASCs in vitro. hASCs were isolated from patients of four different age groups: (1) >20 years (\u1d45b=7), (2) >50 years (\u1d45b=7), (3) >60 years (\u1d45b=7), and (4) >70 years (\u1d45b=7). The hASCs were characterized according to the number of fibroblasts colony forming unit (CFU-F), proliferation rate, population doubling time (PDT), and quantified parameters of adipogenic, chondrogenic, and osteogenic differentiation. Compared to younger cells, aged hASCs had decreased proliferation rates, decreased chondrogenic and osteogenic potential, and increased senescent features. A shift in favor of adipogenic differentiation with increased age was also observed. As many bone and joint diseases increase in prevalence with age, it is important to consider the negative influence of age on hASCs viability, proliferation status, and multilineage differentiation potential when considering the potential therapeutic applications of hASCs