On Bouncing and Nonsingular Solutions in Einstein-scalar-Gauss-Bonnet Cosmology

It is generically believed that higher-order curvature corrections to the Einstein-Hilbert action might cure the curvature singularities that plague general relativity. Here we consider Einstein-scalar-Gauss-Bonnet gravity, the only four-dimensional, ghost-free theory with quadratic curvature terms. For any choice of the coupling function and of the scalar potential, we show that the theory does not allow for bouncing solutions in the flat and open Friedmann universe. For the case of a closed universe, using a reverse-engineering method, we explicitly provide a bouncing solution which is nevertheless linearly unstable in the scalar gravitational sector. Moreover, we show that the expanding, singularity-free, early-time cosmologies allowed in the theory are unstable. These results rely only on analyticity and finiteness of cosmological variables at early times.Comment: 9 pages, 4 figures; references and discussion added; further minor revision, accepted to PR

Callimachus and Catullus in a Quest for Liberty

Although studies of Callimachus’s crucial influence upon Catullus abound, my thesis purports to provide new insights to an old question. I argue that Callimachus bequeaths a quest for liberty to Catullus. Each of the three chapters devotes its Greek half to one aspect of this Callimachean quest and its Latin half to the way in which Catullus Romanises such a pursuit. Specifically, in chapter 1, I submit that through the combination of two metaphors in the Reply to the Telchines (namely Μοῦσα λεπταλέη and σχοῖνος Περσίς) Callimachus stakes his claim to poetic freedom. Thereafter, I propose that Catullus’s decided adoption of Callimachean λεπτότης through the word lepos does not merely amount to the espousal of a poetic tenet. Rather, it heralds his infringement of the mos maiorum thanks to the social overtones of lepos even if, as poem 16 illustrates, Catullus is aware of his contemporaries’ malevolent reactions. Subsequently, in chapter 2, I set forth that Callimachus refuses to abide by the principle of τὸ πρέπον, which governs the convenient relationship between subject-matter and linguistic register. Thereupon, I propound that Catullus embraces Callimachus’s rebelliousness against the criterion of τὸ πρέπον. In so doing, despite the anxieties about his own attitude, which he voices in the last stanza of poem 51, Catullus conveys his own politically charged noncompliance with two staples of Roman seemliness (honestum otium and utilitas of the written fruits of leisure). Then, in chapter 3, I maintain that Callimachus masterfully succeeds in blending encomiastic poetry in praise of members of the Ptolemaic court with assertions of his poetic excellence. Finally, I put forward that, in his carmina addressed to socially superior individuals, Catullus absorbs and bolsters the Callimachean heritage: he reciprocates respect with poetic gifts and retaliates arrogance by means of vitriolic abuse

Enhanced urinary stability of peptide hormones and growth factors by dried urine microsampling

Volumetric absorptive microsampling (VAMS) and dried urine spot (DUS) strategies were applied for the collection of dried microsamples for anti-doping testing of low-stability peptide hormones and growth factors prohibited by the World Anti-Doping Agency (WADA). Drying, storage and transport conditions, as well as pretreatment steps, were optimised before liquid chromatography - tandem mass spectrometry (LC–MS/MS) analysis. The analytical method has been fully validated in terms of sensitivity (limits of quantitation 0.3−10 ng/mL), precision (RSD% < 6.6 %) and extraction yields (78–91 %). Dried microsample stability studies (90 days) have been performed and compared to fluid urine stability. Significantly higher losses have been observed in fluid urine stored at −20 °C (up to 55 %) and −80 °C (up to 29 %) than in dried urine microsamples stored at room temperature (< 19 %). The final microsampling and analysis protocols allow the collection of urine microvolumes, unlikely to be tampered, stably storable and shippable with no particular precautions for possible anti-doping testing of prohibited peptides and hormones

Rural Caregivers and Social Isolation: Some Properties and Dimensions

There are an estimated 400,000 people with multiple sclerosis (MS) in the United States. Many rely on an informal caregiver for assistance. Caregivers are more likely than non-caregivers to report feelings of social isolation. Rural MS caregivers are especially prone to these feelings of isolation. We conducted in-depth interviews with rural caregivers of veterans with MS and used a grounded theory approach to data collection and analysis to illustrate some properties and dimensions of social isolation in a rural MS caregiving sample. These properties include: isolation and the rural environment; isolation from family; isolation from friends; and isolation from the person for whom they provide care

Frontiers of Gravity: Astrophysical Environments, Ringdown Nonlinearities and the Semiclassical Approximation

Einstein’s general relativity is based on a tensorial, nonlinear equation for the spacetime metric. The gravitational interaction is however so weak that, in most circumstances, the equations can be solved perturbatively. This is true in early-time cosmology, for the inspiral of binary systems, and even after black holes merge, releasing the equivalent of multiple solar masses in gravitational waves. In this thesis, we analyze a range of problems that can be addressed assuming a background gravitational field and small fluctuations over it. We will progress from problems where the perturbative hypothesis can be tested and holds, to ones that begin to show nonlinear effects, ending with an application of perturbation theory to quantum gravity, where it is only a working hypothesis. We first analyze the dynamics of black hole binaries immersed in a dense gas environment or interacting with a stellar companion. For binaries in a dense environment, we study the effect of accretion and dynamical friction on the gravitational wave emission. We derive the modification of the gravitational wave phase in the assumption of small accretion rates, and assess whether future gravitational wave observatories could detect this effect. For black holes in a binary with a white dwarf, we identify new evolutionary relations and propose a method to infer the black hole and white dwarf masses and their luminosity distance from the gravitational wave signal alone. Next, we study how isolated black holes react to perturbations, in the simplified setting of spherical symmetry and negative cosmological constant. We show that modes belonging to the linear spectrum can be excited nonlinearly. We further find that nonlinear effects can change the black hole mass at percent level, and that this effect can be explained by the flux of characteristic excitations through the black hole horizon. Finally, we propose a new definition of the semiclassical Einstein equations for cosmological spacetimes. We propose that the source on the right hand side of the Einstein equations could be the amount of stress-energy above the instantaneous ground state. In this more speculative application, the linear order semiclassical approximation is not guaranteed to hold. If our hypothesis were confirmed, however, the vacuum stress-energy above the instantaneous ground state would not renormalize the cosmological constant, hinting at a resolution of the longstanding problem connected to its observed value

A new genetic algorithm framework based on Expected Annual Loss for optimizing seismic retrofitting in reinforced concrete frame structures

The design of seismic retrofitting for existing reinforced concrete frame structures concerns the determination of the position and the arrangement of reinforcements. Currently, this design practice is mainly based on trial-and-error attempts and engineers' experience, without a formal implementation of cost/performance optimization. Though, the implementation of this intervention is associated with significant costs, noticeable downtimes, and elevated invasiveness. This paper presents a new genetic algorithm-based framework for the optimization of two different retrofitting techniques (FRP column wrapping and concentric steel braces) that aims at minimizing costs considering indirectly the lessening of expected annual values. The feasibility of each tentative solution is controlled by the outcomes of static pushover analyses in the framework of the N2 method, achieved by a 3D fiber-section model implemented in OpenSees. Application of the framework in a realistic case study structure will show that the sustainability of retrofitting intervention is achievable by employing artificial intelligence aided structural design

Plasma-photon interaction in curved spacetime I: formalism and quasibound states around nonspinning black holes

We investigate the linear dynamics of an electromagnetic field propagating in curved spacetime in the presence of plasma. The dynamical equations are generically more involved and richer than the effective Proca equation adopted as a model in previous work. We discuss the general equations and focus on the case of a cold plasma in the background of a spherically-symmetric black hole, showing that the system admits plasma-driven, quasibound electromagnetic states that are prone to become superradiantly unstable when the black hole rotates. The quasibound states are different from those of the Proca equation and have some similarities with the case of a massive scalar field, suggesting that the linear instability can be strongly suppressed compared to previous estimates. Our framework provides the first step towards a full understanding of the plasma-photon interactions around astrophysical black holes.Comment: 11 pages, 4 figure