On the Equivalence of Cellular Automata and the Tile Assembly Model

In this paper, we explore relationships between two models of systems which are governed by only the local interactions of large collections of simple components: cellular automata (CA) and the abstract Tile Assembly Model (aTAM). While sharing several similarities, the models have fundamental differences, most notably the dynamic nature of CA (in which every cell location is allowed to change state an infinite number of times) versus the static nature of the aTAM (in which tiles are static components that can never change or be removed once they attach to a growing assembly). We work with 2-dimensional systems in both models, and for our results we first define what it means for CA systems to simulate aTAM systems, and then for aTAM systems to simulate CA systems. We use notions of simulate which are similar to those used in the study of intrinsic universality since they are in some sense strict, but also intuitively natural notions of simulation. We then demonstrate a particular nondeterministic CA which can be configured so that it can simulate any arbitrary aTAM system, and finally an aTAM tile set which can be configured so that it can be used to simulate any arbitrary nondeterministic CA system which begins with a finite initial configuration.Comment: In Proceedings MCU 2013, arXiv:1309.104

Privacy, Self-Sovereign Identity Technology and the Willingness to Provide Personal Information

The internet has caused an unprecedented increase in the amount of personal information that is available online. This personal information has been harnessed directly by companies, to provide targeted marketing to 3rd parties. It can also be used for a company's own internal marketing communication practices. Further highlighting the importance of personal information, some companies have emerged whose business models depend on the accurate collection, and monetisation of this personal information (Streitfeld, 2018). This has led to interest and concern over the misuse of personal information, and the extent companies should benefit from the acquisition of personal information of consumers and 3rd parties. Technological innovation, specifically Blockchain Technology has created the possibility to eliminate these actual or perceived abuses of consumer data, and allow consumers to exercise greater control over their personal data. Blockchain Technology can be simply understood as a Microsoft Excel spreadsheet where hundreds of participants continuously verify each entry in the spreadsheet so that no incorrect or fraudulent inputs are made. Specifically, SelfSovereign Identity Technology, currently in its early stages, may allow consumers to have full control of their consumer data via the Blockchain. This includes, access, distribution and may even allow consumers to monetise their own personal information. If consumers fully embrace Self-Sovereign Identity Technology, businesses will have to rethink and overhaul their data collection, marketing practices and business models. On the other hand, consumers will have to decide what they will do, with the data relating to their digital identity and how they might exchange it for their benefit. Despite its potential to disrupt the collection of personal information by companies, a scholarly analysis of the use Self-Sovereign Identity Technology and its relationship with a consumer's willingness to share personal information has not yet happened. Thus the aim of this thesis is two-fold. Firstly, to understand what drives a consumer to disclose personal information over the internet. Secondly, to understand the connection between this willingness to disclose personal information, and the use of Self-Sovereign Identity Technology. This is investigated using a survey analysis and primary data. This study aspires to create an academic basis for the examination of Self-Sovereign Identity Technology and its relationship with the willingness of consumers to provide personal information. In this study several factors were found to affect a South African consumer's willingness to provide personal information online. Based on the prior work of Schoenbachler and Gordon (2010) and Phelps, Nowak and Ferrel (2000) several perceived risk factors and trust factors were hypothesised to affect this willingness to provide personal information. The trust factors included: past experience with a company, reputation of a company and perception of dependability. The perceived risk factors included: type of personal information requested, consequences and benefits, individual consumer characteristics and consumer control over information. All of these factors were found to be significant except for the perception of dependability, which was not supported. Furthermore, perceived functional value was found to moderate the relationship between individual consumer characteristics and the willingness to provide personal information. Lastly, this study found evidence that a relationship exists between the willingness to provide personal information online and the willingness to use SSI technology. This relationship was found to be strong, and negative

Insights from the Outskirts: Chemical and Dynamical Properties in the outer Parts of the Fornax Dwarf Spheroidal Galaxy

We present radial velocities and [Fe/H] abundances for 340 stars in the Fornax dwarf spheroidal from R~16,000 spectra. The targets have been obtained in the outer parts of the galaxy, a region which has been poorly studied before. Our sample shows a wide range in [Fe/H], between -0.5 and -3.0 dex, in which we detect three subgroups. Removal of stars belonging to the most metal-rich population produces a truncated metallicity distribution function that is identical to Sculptor, indicating that these systems have shared a similar early evolution, only that Fornax experienced a late, intense period of star formation (SF). The derived age-metallicity relation shows a fast increase in [Fe/H] at early ages, after which the enrichment flattens significantly for stars younger than ~8 Gyr. Additionally, the data indicate a strong population of stars around 4 Gyr, followed by a second rapid enrichment in [Fe/H]. A leaky-box chemical enrichment model generally matches the observed relation but does not predict a significant population of young stars nor the strong enrichment at late times. The young population in Fornax may therefore originate from an externally triggered SF event. Our dynamical analysis reveals an increasing velocity dispersion with decreasing [Fe/H] from sigma_sys 7.5 km/s to >14 km/s, indicating an outside-in star formation history in a dark matter dominated halo. The large velocity dispersion at low metallicities is possibly the result of a non-Gaussian velocity distribution amongst stars older than ~8 Gyr. Our sample also includes members from the Fornax GCs H2 and H5. In agreement with past studies we find [Fe/H]=-2.04+-0.04 and a mean radial velocity RV=59.36+-0.31 km/s for H2 and [Fe/H]=-2.02+-0.11 and RV=59.39+-0.44 km/s for H5. Overall, we find large complexity in the chemical and dynamical properties, with signatures that additionally vary with galactocentric distance.Comment: 21 pages, 18 figures, 4 tables, accepted for publication in A&

Viral-Bacterial Interactions in Cystic Fibrosis Lung Disease

Pseudomonas aeruginosa is a Gram-negative, opportunistic pathogen that chronically infects approximately 80% of cystic fibrosis (CF) patients by early adulthood, accounting for the majority of morbidity and mortality in these patients. The development of chronic P. aeruginosa infections in the CF lung involves the formation of highly recalcitrant biofilm communities. Clinical observations have noted a correlation between respiratory virus infection and the acquisition of chronic P. aeruginosa infection by CF patients, but the mechanism underlying this interaction in the CF lung is not understood. In this dissertation, we hypothesized that respiratory viral co-infection promotes P. aeruginosa biofilm formation on airway epithelial cells (AECs). We demonstrate that in the presence of respiratory syncytial virus (RSV) co-infection, P. aeruginosa biofilm growth is significantly increased. We observed that RSV infection increased the release of iron-bound transferrin, suggesting that RSV infection disrupts iron homeostasis in the airway epithelium. Iron is an essential nutrient for P. aeruginosa biofilm growth, and both iron chelation and depletion of transferrin from apical secretions collected from AECs blocked the biofilm stimulatory effect of RSV co-infection. We also demonstrate that RSV infection promotes the apical release of extracellular vesicles (EVs) from AECs, which increases the availability of iron-loaded transferrin in the apical secretions of AECs. Interestingly, purified EVs stimulate P. aeruginosa biofilm growth, suggesting that host-derived EVs interact with a bacterium to promote chronic bacterial infections. Finally, the innate immune response to virus infection, measured by type I and type III (IFN-beta and -lambda, respectively) interferon production, peaks at the same time as virus-induced biofilms growth, and treatment of AECs with either IFN replicates the enhanced biofilm growth observed during virus co-infection. Our data suggest a novel mechanism by which the host response to viral infection contributes to the development of chronic pulmonary P. aeruginosa infection and provide mechanistic insight into our understanding of nutritional immunity in the lung

On the quotient of the homology cobordism group by Seifert spaces

We prove that the quotient of the integer homology cobordism group by the subgroup generated by the Seifert fibered spaces is infinitely generated.Comment: 21 pages, 11 figures. Comments welcome

The metal-poor Knee in the Fornax Dwarf Spheroidal Galaxy

We present alpha-element abundances of Mg, Si, and Ti for a large sample of field stars in two outer fields of the Fornax dwarf spheroidal galaxy (dSph), obtained with VLT/GIRAFFE (R~16,000). Due to the large fraction of metal-poor stars in our sample, we are able to follow the alpha-element evolution from [Fe/H]=-2.5 continuously to [Fe/H]=-0.7 dex. For the first time we are able to resolve the turnover from the Type II supernovae (SNe) dominated, alpha-enhanced plateau down to subsolar [alpha/Fe] values due to the onset of SNe Ia, and thus to trace the chemical enrichment efficiency of the galaxy. Our data support the general concept of an alpha-enhanced plateau at early epochs, followed by a well-defined "knee", caused by the onset of SNe Ia, and finally a second plateau with sub-solar [alpha/Fe] values. We find the position of this knee to be at [Fe/H]=-1.9 and therefore significantly more metal-poor than expected from comparison with other dSphs and standard evolutionary models. Surprisingly, this value is rather comparable to the knee in Sculptor, a dSph about 10 times less luminous than Fornax. Using chemical evolution models, we find that both the position of the knee as well as the subsequent plateau at sub-solar level can hardly be explained unless the galaxy experienced several discrete star formation events with a drastic variation in star formation efficiency, while a uniform star formation can be ruled out. One possible evolutionary scenario is that Fornax experienced one or several major accretion events from gas-rich systems in the past, so that its current stellar mass is not indicative of the chemical evolution environment at ancient times. If Fornax is the product of several smaller building blocks, this may also have implications of the understanding on the formation process of dSphs in general.Comment: 10 pages, 6 Figures, accepted for publication in Ap