Relativistic accretion onto compact objects

The present PhD thesis summarises results on analytical accretion models obtained during my PhD studies in 2014a 2018. I present a new ansatz for specific angular momentum-angular velocity dependence for perfect fluid in circular motion around a Kerr black hole. With this ansatz new solutions for toroidal configurations were obtained. I discuss here in detail the dynamical properties of these configurations and results of their application as initial conditions for accretion simulations with 2-D HARM code. For the case of circular motion in the NUT spacetime I present my results on characteristic circular geodesics radii in it. These results are further used for modelling perfect fluid tori with constant specific angular momentum (Polish Doughnuts). Characteristic changes in the patterns of circular motion of perfect fluid due to presence of the NUT parameter are discussed. The last part of the work presents a pre-study of accretion of spinning particles/fluids onto Kerr black holes. I discuss our results on spin-induced advance in last stable orbits and its relevance for accretion models

Evaluation of social network user sentiments based on fuzzy sets

The article introduces social network user sentiment evaluation with proposed technique based on fuzzy sets. The advantage of proposed technique consists in ability to take into account user's influence as well as the fact that a user could be an author of several messages. Results presented in this paper can be used in mechanical engineering to analyze reviews on products as well as in robotics for developing user communication interface. The paper contains experimental data and shows the steps of sentiment value calculation of resulting messages on a certain topic. Application of proposed technique is demonstrated on experimental data from Twitter social network

Estimation of social network user's influence in a given area of expertise

Nowadays social networks are frequently used to express personal opinion on a topic of interest. Some users' opinion has more informational influence than others do. These users are called influential users. There are services that allow evaluating how popular and influential users are; however, any information on evaluation methods is proprietary and represents know-how of such software services. Furthermore, most services could not provide extensive data on the influential users within the specified area of knowledge. This article proposes the method of evaluating a user influence index within a social network in a given area of expertise

A Search for Jet Handedness in Hadronic Z0Z^0 Decays

We have searched for signatures of polarization in hadronic jets from $Z^0 \to q \bar{q}$ decays using the ``jet handedness'' method. The polar angle asymmetry induced by the high SLC electron-beam polarization was used to separate quark jets from antiquark jets, expected to be left- and right-polarized, respectively. We find no evidence for jet handedness in our global sample or in a sample of light quark jets and we set upper limits at the 95% C.L. of 0.063 and 0.099 respectively on the magnitude of the analyzing power of the method proposed by Efremov {\it et al.}Comment: Revtex, 8 pages, 2 figure

Terrestrial Very-Long-Baseline Atom Interferometry:Workshop Summary

This document presents a summary of the 2023 Terrestrial Very-Long-Baseline Atom Interferometry Workshop hosted by CERN. The workshop brought together experts from around the world to discuss the exciting developments in large-scale atom interferometer (AI) prototypes and their potential for detecting ultralight dark matter and gravitational waves. The primary objective of the workshop was to lay the groundwork for an international TVLBAI proto-collaboration. This collaboration aims to unite researchers from different institutions to strategize and secure funding for terrestrial large-scale AI projects. The ultimate goal is to create a roadmap detailing the design and technology choices for one or more km-scale detectors, which will be operational in the mid-2030s. The key sections of this report present the physics case and technical challenges, together with a comprehensive overview of the discussions at the workshop together with the main conclusions

Rationale and design of the PeriOperative ISchemic Evaluation-3 (POISE-3): a randomized controlled trial evaluating tranexamic acid and a strategy to minimize hypotension in noncardiac surgery

Background For patients undergoing noncardiac surgery, bleeding and hypotension are frequent and associated with increased mortality and cardiovascular complications. Tranexamic acid (TXA) is an antifibrinolytic agent with the potential to reduce surgical bleeding; however, there is uncertainty about its efficacy and safety in noncardiac surgery. Although usual perioperative care is commonly consistent with a hypertension-avoidance strategy (i.e., most patients continue their antihypertensive medications throughout the perioperative period and intraoperative mean arterial pressures of 60 mmHg are commonly accepted), a hypotension-avoidance strategy may improve perioperative outcomes. Methods The PeriOperative Ischemic Evaluation (POISE)-3 Trial is a large international randomized controlled trial designed to determine if TXA is superior to placebo for the composite outcome of life-threatening, major, and critical organ bleeding, and non-inferior to placebo for the occurrence of major arterial and venous thrombotic events, at 30 days after randomization. Using a partial factorial design, POISE-3 will additionally determine the effect of a hypotension-avoidance strategy versus a hypertension-avoidance strategy on the risk of major cardiovascular events, at 30 days after randomization. The target sample size is 10,000 participants. Patients ≥45 years of age undergoing noncardiac surgery, with or at risk of cardiovascular and bleeding complications, are randomized to receive a TXA 1 g intravenous bolus or matching placebo at the start and at the end of surgery. Patients, health care providers, data collectors, outcome adjudicators, and investigators are blinded to the treatment allocation. Patients on ≥ 1 chronic antihypertensive medication are also randomized to either of the two blood pressure management strategies, which differ in the management of patient antihypertensive medications on the morning of surgery and on the first 2 days after surgery, and in the target mean arterial pressure during surgery. Outcome adjudicators are blinded to the blood pressure treatment allocation. Patients are followed up at 30 days and 1 year after randomization. Discussion Bleeding and hypotension in noncardiac surgery are common and have a substantial impact on patient prognosis. The POISE-3 trial will evaluate two interventions to determine their impact on bleeding, cardiovascular complications, and mortality. Trial registration ClinicalTrials.gov NCT03505723. Registered on 23 April 2018

Relativistische Akkretion auf Kompakte Objekte

The present PhD thesis summarises results on analytical accretion models obtained during my PhD studies in 2014a 2018. I present a new ansatz for specific angular momentum-angular velocity dependence for perfect fluid in circular motion around a Kerr black hole. With this ansatz new solutions for toroidal configurations were obtained. I discuss here in detail the dynamical properties of these configurations and results of their application as initial conditions for accretion simulations with 2-D HARM code. For the case of circular motion in the NUT spacetime I present my results on characteristic circular geodesics radii in it. These results are further used for modelling perfect fluid tori with constant specific angular momentum (Polish Doughnuts). Characteristic changes in the patterns of circular motion of perfect fluid due to presence of the NUT parameter are discussed. The last part of the work presents a pre-study of accretion of spinning particles/fluids onto Kerr black holes. I discuss our results on spin-induced advance in last stable orbits and its relevance for accretion models