Separable Multipartite Mixed States - Operational Asymptotically Necessary and Sufficient Conditions

We introduce an operational procedure to determine, with arbitrary probability and accuracy, optimal entanglement witness for every multipartite entangled state. This method provides an operational criterion for separability which is asymptotically necessary and sufficient. Our results are also generalized to detect all different types of multipartite entanglement.Comment: 4 pages, 2 figures, submitted to Physical Review Letters. Revised version with new calculation

Massive perturbers and the efficient merger of binary massive black holes

We show that dynamical relaxation in the aftermath of a galactic merger and the ensuing formation and decay of a binary massive black hole (MBH), are dominated by massive perturbers (MPs) such as giant molecular clouds or clusters. MPs accelerate relaxation by orders of magnitude relative to 2-body stellar relaxation alone, and efficiently scatter stars into the binary MBH's orbit. The 3-body star-binary MBH interactions shrink the binary MBH to the point where energy losses from the emission of gravitational waves (GW) lead to rapid coalescence. We model this process based on observed and simulated MP distributions and take into account the decreased efficiency of the star-binary MBH interaction due to acceleration in the galactic potential. We show that mergers of gas-rich galactic nuclei lead to binary MBH coalescence well within the Hubble time. Moreover, lower-mass binary MBHs (<10^8 Msun) require only a few percent of the typical gas mass in a post-merger nucleus to coalesce in a Hubble time. The fate of a binary MBH in a gas poor galactic merger is less certain, although massive stellar structures (e.g. clusters, stellar rings) could likewise lead to efficient coalescence. These coalescence events are observable by their strong GW emission. MPs thus increase the cosmic rate of such GW events, lead to a higher mass deficit in the merged galactic core and suppress the formation of triple MBH systems and the resulting ejection of MBHs into intergalactic space.Comment: 14 pages, 4 figures, 3 tables. More detailed explanations and changes in structure. Section on hypervelocity stars moved to another paper (in preparation). Results and conclusions unchanged. Accepted to Ap

Algorithm Engineering in Robust Optimization

Robust optimization is a young and emerging field of research having received a considerable increase of interest over the last decade. In this paper, we argue that the the algorithm engineering methodology fits very well to the field of robust optimization and yields a rewarding new perspective on both the current state of research and open research directions. To this end we go through the algorithm engineering cycle of design and analysis of concepts, development and implementation of algorithms, and theoretical and experimental evaluation. We show that many ideas of algorithm engineering have already been applied in publications on robust optimization. Most work on robust optimization is devoted to analysis of the concepts and the development of algorithms, some papers deal with the evaluation of a particular concept in case studies, and work on comparison of concepts just starts. What is still a drawback in many papers on robustness is the missing link to include the results of the experiments again in the design

Tidal spin-up of stars in dense stellar cusps around massive black holes

We show that main-sequence stars in dense stellar cusps around massive black holes are likely to rotate at a significant fraction of the centrifugal breakup velocity due to spin-up by hyperbolic tidal encounters. We use realistic stellar structure models to calculate analytically the tidal spin-up in soft encounters, and extrapolate these results to close and penetrating collisions using smoothed particle hydrodynamics simulations. We find that the spin-up falls off only slowly with distance from the black hole because the increased tidal coupling in slower collisions at larger distances compensates for the decrease in the stellar density. We apply our results to the stars near the massive black hole in the Galactic Center. Over their lifetime, ~1 Msol main sequence stars in the inner 0.3 pc of the Galactic Center are spun-up on average to ~10%--30% of the centrifugal breakup limit. Such rotation is ~20--60 times higher than is usual for such stars and may affect their subsequent evolution and their observed properties.Comment: 25 pages, 7 figures. Submitted to Ap

CoRoT 101186644: A transiting low-mass dense M-dwarf on an eccentric 20.7-day period orbit around a late F-star

We present the study of the CoRoT transiting planet candidate 101186644, also named LRc01_E1_4780. Analysis of the CoRoT lightcurve and the HARPS spectroscopic follow-up observations of this faint (m_V = 16) candidate revealed an eclipsing binary composed of a late F-type primary (T_eff = 6090 +/- 200 K) and a low-mass, dense late M-dwarf secondary on an eccentric (e = 0.4) orbit with a period of ~20.7 days. The M-dwarf has a mass of 0.096 +/- 0.011 M_Sun, and a radius of 0.104 +0.026/-0.006 R_Sun, which possibly makes it the smallest and densest late M-dwarf reported so far. Unlike the claim that theoretical models predict radii that are 5%-15% smaller than measured for low-mass stars, this one seems to have a radius that is consistent and might even be below the radius predicted by theoretical models.Comment: Accepted for publication in Astronomy & Astrophysics, 8 pages, 10 figure

Irish attitudes toward COVID tracker app & privacy: sentiment analysis on Twitter and survey data

Contact tracing apps used in tracing and mitigating the spread of COVID-19 have sparked discussions and controversies worldwide. The major concerns in relation to these apps are around privacy. Ireland was in general praised for the design of its COVID tracker app, and the transparency through which privacy issues were addressed. However, the "voice" of the Irish public was not really heard or analysed. This study aimed to analyse the Irish public sentiment towards privacy and COVID tracker app. For this purpose we have conducted sentiment analysis on Twitter data collected from public Twitter accounts from Republic of Ireland. We collected COVID-19 related tweets generated in Ireland over a period of time from January 1, 2020 up to December 31, 2020 in order to perform sentiment analysis on this data set. Moreover, the study performed sentiment analysis on the feedback received from a national survey on privacy conducted in Republic of Ireland. The findings of the study reveal a significant criticism towards the app that relate to privacy concerns, but other aspects of the app as well. The findings also reveal some positive attitude towards the fight against COVID-19, but these are not necessarily related to the technological solutions employed for this purpose. The findings of the study contributed to the formulation of useful recommendations communicated to the relevant Irish actors

The Privacy Paradox - investigating people's attitude towards privacy in a time of COVID-19

The advent of digital technologies used as a mechanism to deal with the Covid-19 global pandemic, has raised serious concerns around privacy and security issues. Despite these concerns and the potential risk of data misuse, including third party use, countries around the world have pushed the use and proliferation of contact-tracing applications. However, the success of these contact-tracing applications relies on their adoption and use. A well known phenomenon referred to as privacy paradox is defined as the discrepancy between the expressed privacy concern and the actual behaviour of users when it comes to protect their privacy. In this context, this paper presents a study investigating the privacy paradox in the context of a global pandemic. A national survey has been conducted and the data is analysed to examine people's privacy risk perception. The results show inconsistencies between people's privacy concerns and their actual behaviour that is reflected in their attitude shift of sharing their mobile data during a global pandemic. The study also compiles a list of recommendations for policymakers

PRIVATT - a closer look at people’s data privacy attitudes in times of COVID-19

The current Covid-19 global pandemic led to a proliferation of contact-tracing applications meant to help control and suppress the spread of the virus. However, the success of these contact-tracing apps relies on obtaining access to sensitive data stored on citizen’s mobile devices. The approaches taken are different around the world. While the countries with a strong democratic and civil liberty ethos are encouraging voluntary adoption of contact-tracing apps by their citizens, other countries opted for forced mass surveillance methods that limit individual freedoms. As a result, the attempt to fight the global pandemic is actually testing people’s attitudes towards privacy and government surveillance. In this context, this research introduces a pilot study examining people’s privacy concerns in a time of Covid-19. The results show that people are willing to share their personal data in the interest of controlling the spread of the virus and save lives

Privacy in times of COVID-19: a pilot study in the Republic of Ireland

Contact tracing apps used in tracing and mitigating the spread of COVID-19 have sparked discussions and controversies worldwide with major concerns around privacy. COVID Tracker app used in the Republic of Ireland was praised in general for the way it addressed privacy and was used as baseline for other contact tracing apps worldwide. The success of the app is dependent on the general public uptake, hence their voice and attitude is the one that really matters. This paper focuses on developing a survey and the methods aiming to examine the attitudes toward privacy during COVID-19 of the general public in the Republic of Ireland and their impact on the uptake of the COVID tracker app. Various privacy models are used and health belief model as well in this purpose. A pilot study with 286 participants show a change in attitude towards privacy during COVID-19 pandemic, with more people willing to share their data in the interest of saving lives. However, privacy attitudes are shown to have impacted the adoption of the app in Ireland

When are anti-fat attitudes understood as prejudice versus truth? An experimental study of social influence effects

Background/Objectives If people who hold anti-fat attitudes believe these attitudes to be true, then anti-prejudice appeals are likely to be unsuccessful, if only because the targets will not see their attitudes as in need of change. The current study examined processes that may lead people to see their anti-fat attitudes as 'truth' or as 'prejudice'. Subjects/Methods Participants (N = 482) read anti-fat statements and were then presented with an interpretation of these statements as 'truth' or 'prejudice'. The source of this interpretation was either an (i) in-group or out-group member and (ii) expert or non-expert. Participants' judgements of the statements were expected to vary such that in-group others and experts would exert more influence than would out-group others and non-experts. Results Participants aligned their own interpretations of an anti-fat statement with those of an expert, but not with those of a non-expert, F(1,466) = 8.97, p <0.05, eta(2)(p) = 0.02. The group membership variable had no effect on judgements of 'truth' or 'prejudice' of the anti-fat statement. Conclusion The expressions that people believe constitute anti-fat prejudice versus truth about people described as overweight are influenced by exposure to expert opinion (in this case, by medical doctors). Implications for the success of weight-based anti-prejudice appeals and for healthcare provision are discussed