Efficient model chemistries for peptides. I. Split-valence Gaussian basis sets and the heterolevel approximation in RHF and MP2

We present an exhaustive study of more than 250 ab initio potential energy surfaces (PESs) of the model dipeptide HCO-L-Ala-NH2. The model chemistries (MCs) used are constructed as homo- and heterolevels involving possibly different RHF and MP2 calculations for the geometry and the energy. The basis sets used belong to a sample of 39 selected representants from Pople's split-valence families, ranging from the small 3-21G to the large 6-311++G(2df,2pd). The reference PES to which the rest are compared is the MP2/6-311++G(2df,2pd) homolevel, which, as far as we are aware, is the more accurate PES of a dipeptide in the literature. The aim of the study presented is twofold: On the one hand, the evaluation of the influence of polarization and diffuse functions in the basis set, distinguishing between those placed at 1st-row atoms and those placed at hydrogens, as well as the effect of different contraction and valence splitting schemes. On the other hand, the investigation of the heterolevel assumption, which is defined here to be that which states that heterolevel MCs are more efficient than homolevel MCs. The heterolevel approximation is very commonly used in the literature, but it is seldom checked. As far as we know, the only tests for peptides or related systems, have been performed using a small number of conformers, and this is the first time that this potentially very economical approximation is tested in full PESs. In order to achieve these goals, all data sets have been compared and analyzed in a way which captures the nearness concept in the space of MCs.Comment: 54 pages, 16 figures, LaTeX, AMSTeX, Submitted to J. Comp. Che

Integrable Quasiclassical Deformations of Algebraic Curves

A general scheme for determining and studying integrable deformations of algebraic curves is presented. The method is illustrated with the analysis of the hyperelliptic case. An associated multi-Hamiltonian hierarchy of systems of hydrodynamic type is characterized.Comment: 28 pages, no figure

Where do women birth during a pandemic? Changing perspectives on Safe Motherhood during the COVID-19 pandemic

During the coronavirus disease 2019 (COVID-19) pandemic, health systems all over the world are either stressed to their maximum capacity or anticipating becoming overwhelmed. The population is advised not to attend hospital unless strictly necessary, yet this advice seems to apply to all but healthy women during childbirth. Specialized hospital care during childbirth can be lifesaving in case of obstetric complications or for COVID-19 symptomatic women, while strong evidence suggests the appropriateness of midwifery units that are integrated into the healthcare system for eligible women. We must ask ourselves whether obstetric units are the appropriate birthing facilities for healthy women during the pandemic. We have learned from previous crises that the needs of women and children are often badly served during disasters. The COVID-19 pandemic raises concerns over escalation of mistreatment and abuse media are already reporting on restrictions to the rights of birthing women in Europe and the US. In addition, concerns have emerged over increased risk of infection to COVID-19 among birthing women and familied by concentrating all women in obstetric units and lack of optimal care due to pressure on staff and resources. Women's rights in childbirth are being threatened by lack of care during labor, restrictions on accompaniment, unnecessary interventions including inductions, separation of mother and baby and prohibition on breastfeeding. An effective response to the crisis depends on strong and coordinated health care systems where mothers can birth safely, and the needs of the newborn babies are met. The interpretation of what constitute safe care is a stimulus for a strong debate between those who argue for strengthening community and primary care services and those who recommend for centralization of all births in hospitals. This debate is particularly salient during this pandemic and in preparation of future pandemics. We propose a strategic response in the face of the pandemic by expanding the use of midwifery units both alongside the obstetric unit and freestanding (in the community). Where midwifery units are absent pop-up units can be created quickly following the example of the Netherlands. This strategy in high income countries is evidence-based and also serves as a response to the surge in requests of safe childbirths pathways away from the obstetric unit by concerned women at unprecedented rates. We urge policy makers to consider replicating this model in low- and middle-income countries where hospital conditions are more precarious. A strong collaboration between midwives, nurses, obstetricians and neonatologists and the integration of primary care and acute services could ensure safety while maximizing the rational use of resources. Immediate strategic action would ensure that women are able to access appropriate care at the appropriate time, while hospitals continue to respond to the COVID-19 crisis and obstetric units are kept for women needing specialist care

Nonlinear Dynamics on the Plane and Integrable Hierarchies of Infinitesimal Deformations

A class of nonlinear problems on the plane, described by nonlinear inhomogeneous $\bar{\partial}$-equations, is considered. It is shown that the corresponding dynamics, generated by deformations of inhomogeneous terms (sources) is described by Hamilton-Jacobi type equations associated with hierarchies of dispersionless integrable systems. These hierarchies are constructed by applying the quasiclassical $\bar{\partial}$-dressing method.Comment: 30 pages, tcilate

Hydrodynamic reductions and solutions of a universal hierarchy

The diagonal hydrodynamic reductions of a hierarchy of integrable hydrodynamic chains are explicitly characterized. Their compatibility with previously introduced reductions of differential type is analyzed and their associated class of hodograph solutions is discussed.Comment: 19 page