739 research outputs found
Cosmic sound: Measuring the Universe with baryonic acoustic oscillations
No full textDuring the last ten to fifteen years cosmology has turned from a data-starved to
a data-driven science. Several key parameters of the Universe have now been measured with an accuracy better than 10%. Surprisingly, it has been found that instead of slowing down, the expansion of the Universe proceeds at an ever increasing rate. From this we infer the existence of a negative pressure component -- the so-called Dark Energy (DE) -- that makes up more than two thirds of the total matter-energy content of our Universe. It is generally agreed amongst cosmologists and high energy physicists that understanding the nature of the DE poses one of the biggest challenges for the modern theoretical physics.
Future cosmological datasets, being superior in both quantity and quality to currently existing data, hold the promise for unveiling many of the properties of the mysterious DE component. With ever larger datasets, as the statistical errors decrease, one needs to have a very good control over the possible systematic uncertainties. To make progress, one has to concentrate the observational effort towards the phenomena that are theoretically best understood and also least ``contaminated'' by complex astrophysical processes or several intervening foregrounds. Currently by far the cleanest cosmological information has been obtained through measurements of the angular temperature fluctuations of the Cosmic Microwave Background (CMB). The typical angular size of the CMB temperature fluctuations is determined by the distance the sound waves in the tightly coupled baryon-photon fluid can have traveled since the Big Bang until the epoch of recombination. A similar scale is also expected to be imprinted in the large-scale matter distribution as traced by, for instance, galaxies or galaxy clusters. Measurements of the peaks in the CMB angular power spectrum fix the physical scale of the sound horizon with a high precision. By identifying the corresponding features in the low redshift matter power spectrum one is able to put constraints on several cosmological parameters.
In this thesis we have investigated the prospects for the future wide-field SZ cluster surveys to detect the acoustic scale in the matter power spectrum, specifically concentrating on the possibilities for constraining the properties of the DE. The core part of the thesis is concerned with a power spectrum analysis of the SDSS Luminous Red Galaxy (LRG) sample. We have been able to detect acoustic features in the redshift-space power spectrum of LRGs down to scales of ~ 0.2 hMpc^{-1}, which approximately corresponds to the seventh peak in the CMB angular spectrum. Using this power spectrum measurement along with the measured size of the sound horizon, we have carried out the maximum likelihood cosmological parameter estimation using Markov chain Monte Carlo techniques. The precise measurement of the low redshift sound horizon in combination with the CMB data has enabled us to measure, under some simplifying assumptions, the Hubble constant with a high precision: H_0 = 70.8 {+1.9} {-1.8} km/s/Mpc. Also we have shown that a decelerating expansion of the Universe is ruled out at more than 5-sigma confidence level
Unearthing the Real Process Behind the Event Data The Case for Increased Process Realism
No full textThis book is a revised version of the PhD dissertation written by the author at Hasselt University in Belgium.This dissertation introduces the concept of process realism. Process realism is approached from two perspectives in this dissertation. First, quality dimensions and measures for process discovery are analyzed on a large scale and compared with each other on the basis of empirical experiments. It is shown that there are important differences between the different quality measures in terms of feasibility, validity and sensitivity. Moreover, the role and meaning of the generalization dimension is unclear. Second, process realism is also tackled from a data point of view. By developing a transparent and extensible tool-set, a framework is offered to analyze process data from different perspectives. From both perspectives, recommendations are made for future research, and a call is made to give the process realism mindset a central place within process mining analyses.
In 2020, the PhD dissertation won the “BPM Dissertation Award”, granted to outstanding PhD theses in the field of Business Process Management
Can AGN and galaxy clusters explain the surface brightness fluctuations of the cosmic X-ray background?
No full textFluctuations of the surface brightness of cosmic X-ray background (CXB) carry unique information about faint and low-luminosity source populations, which is inaccessible for conventional large-scale structure (LSS) studies based on resolved sources. We used XBOOTES (5ks deep Chandra X-rayObservatoryACIS-I maps of the similar to 9 deg(2) Bootes field of the NOAO Deep Wide-Field Survey) to conduct the most accurate measurement to date of the power spectrum of fluctuations of the unresolved CXB on the angular scales of 3 arcsec-17 arcmin. We find that at sub-arcmin angular scales, the power spectrum is consistent with the active galactic nucleus ( AGN) shot noise, without much need for any significant contribution from their onehalo term. This is consistent with the theoretical expectation that low-luminosity AGN reside alone in their dark matter haloes. However, at larger angular scales, we detect a significant LSS signal above the AGN shot noise. Its power spectrum, obtained after subtracting the AGN shot noise, follows a power law with the slope of -0.8 +/- 0.1 and its amplitude is much larger than what can be plausibly explained by the two-halo term of AGN. We demonstrate that the detected LSS signal is produced by unresolved clusters and groups of galaxies. For the flux limit of the XBOOTES survey, their flux-weighted mean redshift equals z similar to 0.3, and the mean temperature of their intracluster medium (ICM), T approximate to 1.4 keV, corresponds to the mass of M500 similar to 10(13.5) M-circle dot. The power spectrum of CXB fluctuations carries information about the redshift distribution of these objects and the spatial structure of their ICM on the linear scales of up to similar to Mpc, i. e. of the order of the virial radius.International Max Planck Research School (IMPRS) on Astrophysics at the Ludwig-Maximilians University of Munich (LMU); China Postdoctoral Science Foundation [2016M590012]; Russian Scientific Foundation (RNF) [14-22-00271]SCI(E)ARTICLE33035-305946
Authorship as cultural performance: new perspectives in authorship studies
No full textThis article proposes a performative model of authorship, based on the historical alternation between predominantly 'weak' and 'strong' author concepts and related practices of writing, publication and reading. Based on this model, we give a brief overview of the historical development of such author concepts in English literature from the Middle Ages to the twentieth century. We argue for a more holistic approach to authorship within a cultural topography, comprising social contexts, technological and media factors, and other cultural developments, such as the distinction between privacy and the public sphere
A resilience assessment framework for complex engineered systems using graphical evaluation and review technique (GERT)
No full textSystem resilience characterizes the capability of maintaining the required functionality under disruptions, which is of great significance in evaluating the productivity and safety of complex engineered systems. Although most studies conduct resilience assessment from qualitative and quantitative perspectives, system functionality that reflects functional requirements for complex engineered systems needs to be elaborated. In addition, given that complex engineered systems achieve dynamic performance during disruptions, measuring the actual performance under uncertainty is imperative. To this end, this paper develops a quantitative framework to assess the resilience of complex engineered systems. The developed framework comprises three phases, functionality analysis, performance evaluation, and resilience assessment. Firstly, system functionality is analyzed using a functional tree illustrating the relationship between functions. The overall objective, primary functions, and sub-functions are identified according to task requirements. Secondly, system performance is quantified considering uncertain factors through Graphical Evaluation and Review Technique (GERT). Probabilistic branches and network logic are employed to represent the implementation of various functions. Finally, resilience assessment is carried out from the perspectives of anticipation, absorption, adaptation, and restoration abilities. A case study on the satellite network shows the effectiveness of the developed framework. The developed framework determines system functionality based on task requirements, evaluates system performance with limited information, and accurately assesses system resilience.Safety and Security Scienc
Recent advances on graphical evaluation and review techniques
No full textGraphical evaluation and review techniques (GERT) is a technique to study the stochastic nature of networks consists of different branches. In GERT, all branches are explained in terms of the probability that the branch is traversed and the tile to traverse the branch in case it is realized. This paper presents recent advances of the implementation of GERT in various industries. The study presents a comprehensive description of GERT and recent advances on the implementation of GERT in various industries over the period 2002-2017.Peer reviewedFinal article published.Network designGERTGraphical evaluation and review technique
Secularization – an empirically consolidated narrative in the face of an increasing influence of religion on politics
No full textWith this research Gert Pickel proposes an updated version of secularization’s narrative, contrasting it with the growing phenomena of religious pluralism, secular-religious polarization, and religiosity’s politicization in Europe. This article focuses especially on the European religious landscape of the late twentieth and early twenty-first century, analyzing the empirical developments in its indices of secularization, namely at the individual level. For this purpose, the author calls upon several statistical data that consider individuals’ attitudes towards religion, bearing in mind the different levels of modernization, as well as the political, religious and historical-cultural vicissitudes of the different countries. Despite religious affair’s proliferation in public debate, this article concludes that secularization remains empirically more convincing than the narrative of the return of religions. However, we are still far from speaking of a secular Europe
Corrigendum to “Rapid vacuum-driven monolayer assembly of microparticles on the surface of perforated microfluidic devices” [Powder Technology 390 (2021), 330–338] (Powder Technology (2021) 390 (330–338), (S0032591021004885), (10.1016/j.powtec.2021.05.079))
No full textThe authors regret to inform that they would like to change the corresponding author in the Elsevier system from Gert Desmet to Ignaas S. M. Jimidar. All authors have given their consent to make this change. See earlier correspondence and collected signatures from the authors. The authors would like to apologise for any inconvenience caused.</p
History of the Graeco-Latin fable /
No full text"This edition has been revised and updated by the author and Gert-Jan van Dijk."Includes bibliographical references and indexes.v. 1. Introduction and, From the origins to to the Hellenistic age -- v. 2. The fable during the Roman Empire and in the Middle Ages -- v. 3. Inventory and documentation of the Graeco-Latin fable
Corrigendum to A detailed study of the interaction between levitated microspheres and the target electrode in a strong electric field [Powder Technology 383 (2021), 292–301] (Powder Technology (2021) 383 (292–301), (S0032591021000528), (10.1016/j.powtec.2021.01.036))
No full textThe authors regret to inform that they would like to change the corresponding author in the Elsevier system from Gert Desmet to Ignaas Jimidar. All authors have given their consent to make this change. See earlier correspondence and collected signatures from the authors. The authors would like to apologise for any inconvenience caused
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