Operational significance of the deviation equation in relativistic geodesy

Deviation equation: Second order differential equation for the 4-vector which measures the distance between reference points on neighboring world lines in spacetime manifolds. Relativistic geodesy: Science representing the Earth (or any planet), including the measurement of its gravitational field, in a four-dimensional curved spacetime using differential-geometric methods in the framework of Einstein's theory of gravitation (General Relativity).Comment: 9 pages, 4 figures, contribution to the "Encyclopedia of Geodesy". arXiv admin note: text overlap with arXiv:1811.1047

Gravitational lens optical scalars in terms of energy-momentum distributions

This is a general work on gravitational lensing. We present new expressions for the optical scalars and the deflection angle in terms of the energy-momentum tensor components of matter distributions. Our work generalizes standard references in the literature where normally stringent assumptions are made on the sources. The new expressions are manifestly gauge invariant, since they are presented in terms of curvature components. We also present a method of approximation for solving the lens equations, that can be applied to any order.Comment: 17 pages, 2 figures. Titled changed. Small improvements. References added. Final version published in Phys.Rev.

Parallel-propagated frame along null geodesics in higher-dimensional black hole spacetimes

In [arXiv:0803.3259] the equations describing the parallel transport of orthonormal frames along timelike (spacelike) geodesics in a spacetime admitting a non-degenerate principal conformal Killing-Yano 2-form h were solved. The construction employed is based on studying the Darboux subspaces of the 2-form F obtained as a projection of h along the geodesic trajectory. In this paper we demonstrate that, although slightly modified, a similar construction is possible also in the case of null geodesics. In particular, we explicitly construct the parallel-transported frames along null geodesics in D=4,5,6 Kerr-NUT-(A)dS spacetimes. We further discuss the parallel transport along principal null directions in these spacetimes. Such directions coincide with the eigenvectors of the principal conformal Killing-Yano tensor. Finally, we show how to obtain a parallel-transported frame along null geodesics in the background of the 4D Plebanski-Demianski metric which admits only a conformal generalization of the Killing-Yano tensor.Comment: 17 pages, no figure

Pharmacology and toxicology of xylazine: quid novum?

The current opioid overdose crisis is characterized by the presence of unknown psychoactive adulterants. Xylazine is an alpha-2 receptor agonist that is not approved for human use but is commonly used in veterinary medicine due to its sedative and muscle-relaxant properties. Cases of human intoxication due to accidental or voluntary use have been reported since the 1980s. However, reports of adulteration of illicit opioids (heroin and illicit fentanyl) with xylazine have been increasing all over Western countries. In humans, xylazine causes respiratory depression, bradycardia, and hypotension-posing individuals, using xylazine-adulterated opioids. We present a narrative review of the latest intoxication cases related to xylazine, to bring awareness to readers and also to help pathologists to detect and deal with xylazine cases

On the Significance of the Weyl Curvature in a Relativistic Cosmological Model

The Weyl curvature includes the Newtonian field and an additional field, the so-called anti-Newtonian. In this paper, we use the Bianchi and Ricci identities to provide a set of constraints and propagations for the Weyl fields. The temporal evolutions of propagations manifest explicit solutions of gravitational waves. We see that models with purely Newtonian field are inconsistent with relativistic models and obstruct sounding solutions. Therefore, both fields are necessary for the nonlocal nature and radiative solutions of gravitation.Comment: 15 pages, incorporating proof correction

Linked Fate: Justice and the Criminal Legal System During the COVID-19 Pandemic

The concept of “linked fate” has taken on new meaning in the face of the COVID-19 pandemic. People all over the world – from every walk of life, spanning class, race, gender, and nationality – face a potentially deadly threat requiring cooperation and sacrifice. The plight of the most vulnerable among us affects the capacity of the larger community to cope with, recover, and learn from COVID-19’s devastating impact. COVID-19 makes visible and urgent the need to embrace our linked fate, “develop a sense of commonality and shared circumstances,” and unstick dysfunctional and inequitable political and legal systems. Nowhere is the hazard of failing to recognize linked fate more urgent than in the criminal legal system. COVID-19 pandemic has hit people who live and work in correctional institutions particularly hard. The government bears legal and moral responsibility for people incarcerated in prisons, jails, and juvenile detention facilities, who cannot leave and must depend for their survival of the pandemic on the state. The movement in and out of correctional facilities by those employed to fulfill government’s responsibility also ensures the spread of infection. One study, for example, found that increases in a county\u27s jail incarceration rate were associated with significant rates of infectious disease deaths. The collective failure to attend to the circumstances that enmesh people in the criminal legal system – poverty, racial discrimination, poor health and mental care health care – also make prisons and jails a ground zero of the pandemic\u27s spread

Gravitational Wave Propagation in Isotropic Cosmologies

We study the propagation of gravitational waves carrying arbitrary information through isotropic cosmologies. The waves are modelled as small perturbations of the background Robertson-Walker geometry. The perfect fluid matter distribution of the isotropic background is, in general, modified by small anisotropic stresses. For pure gravity waves, in which the perturbed Weyl tensor is radiative (i.e. type N in the Petrov classification), we construct explicit examples for which the presence of the anisotropic stress is shown to be essential and the histories of the wave-fronts in the background Robertson-Walker geometry are shear-free null hypersurfaces. The examples derived in this case are analogous to the Bateman waves of electromagnetic theory.Comment: 27 pages, accepted for publication in Phys.Rev.

Relativistic tidal compressions of a star by a massive black hole

Aims: We investigate the stellar pancake mechanism during which a solar-type star is tidally flattened within its orbital plane passing close to a 10^6 solar masses black hole. We simulate the relativistic orthogonal compression process and follow the associated shock waves formation. Methods: We consider a one-dimensional hydrodynamical stellar model moving in the relativistic gravitational field of a non-rotating black hole. The model is numerically solved using a Godunov-type shock-capturing source-splitting method in order to correctly reproduce the shock waves profiles. Results: Simulations confirm that the space-time curvature can induce several successive orthogonal compressions of the star which give rise to several strong shock waves. The shock waves finally escape from the star and repeatedly heat up the stellar surface to high energy values. Such a shock-heating could interestingly provide a direct observational signature of strongly disruptive star - black hole encounters through the emission of hard X or soft gamma-ray bursts. Timescales and energies of such a process are consistent with some observed events such as GRB 970815.Comment: 8 pages, 11 figures, submitted to Astron. Astrophy

Homicide or suicide? A probabilistic approach for the evaluation of the manner of death in sharp force fatalities

The role of forensic science can be defined as providing relevant opinions to assist investigators and courts of law in answering questions. The Likelihood Ratio (LR) provides a quantitative and logical approach to communicating the strength of expert evidence. We reviewed existing forensic literature on sharp force fatalities, focusing on studies reporting the manner of death and the frequency of some characteristics that are traditionally assessed. Four studies were included, resulting in a database of 173 suicides and 354 homicides. The LR of each of the characteristic under both hypotheses (suicide and homicide) was obtained. Subsequently, the LR was computed in six fatalities with known manner of death, three suicides and three homicides, by multiplying the corresponding LR of each individual characteristic. LR ranged from 115 to 140,250 in suicidal cases and from 9 to 2728 in homicidal cases. Compared to other fields of forensic science where LR is used extensively, the values obtained in our cases of sharp force fatalities is low. However, in forensic pathology there is evidence that is outside the expert's opinion, and it is for the trier of fact, such as the judge or jury, to draw conclusions. Nevertheless, the LR serves as a tool for interpreting and weighing evidence while maintaining the distinct roles of the trier of fact and the expert. To comprehensively apply the LR in the field of sharp force deaths, it will be necessary to standardize the methodology of investigation and data collection in descriptive studies