Anisotropic Extra Dimensions

We consider the scenario where in a five-dimensional theory, the extra spatial dimension has different scaling than the other four dimensions. We find background maximally symmetric solutions, when the bulk is filled with a cosmological constant and at the same time it has a three-brane embedded in it. These background solutions are reminiscent of Randall-Sundrum warped metrics, with bulk curvature depending on the parameters of the breaking of diffeomorphism invariance. Subsequently, we consider the scalar perturbation sector of the theory and show that it has certain pathologies and the striking feature that in the limit where the diffeomorphism invariance is restored, there remain ghost scalar mode(s) in the spectrum.Comment: 12 pages, no figures, comments and references added, published versio

The relationship between Higher Education and labour market in Greece : the weakest link?

The high level of graduate unemployment, even though it is acknowledged as one of the most distinctive characteristics of the Greek labour market, it has not attracted enough attention in the academic literature. This paper utilizes micro-data from the Labour Force Survey in order to investigate how the employment situation of young (aged 35 and below) graduates varies across fields of study. The findings suggest that graduates of disciplines that have high levels of private sector employment, such as Polytechnics and Computer Science, are in general better off in the Greek labour market. On the other hand, graduates of disciplines that are traditionally related to the needs of the public sector, such as Sociology and Humanities, face poor employment prospects. The findings of this study highlight the need for drastic reforms of the Higher Education system

Instability of brane cosmological solutions with flux compactifications

We discuss the stability of the higher-dimensional de Sitter (dS) brane solutions with two-dimensional internal space in the Einstein-Maxwel theory. We show that an instability appears in the scalar-type perturbations with respect to the dS spacetime. We derive a differential relation which has the very similar structure to the ordinary laws of thermodynamics as an extension of the work for the six-dimensional model [20]. In this relation, the area of dS horizon (integrated over the two internal dimensions) exactly behaves as the thermodynamical entropy. The dynamically unstable solutions are in the thermodynamically unstable branch. An unstable dS compactification either evolves toward a stable configuration or two-dimensional internal space is decompactified. These dS brane solutions are equivalent to the accelerating cosmological solutions in the six-dimensional Einstein-Maxwell-dilaton theory via dimensional reduction. Thus, if the seed higher-dimensional solution is unstable, the corresponding six-dimensional solution is also unstable. From the effective four-dimensional point of view, a cosmological evolution from an unstable cosmological solution in higher dimensions may be seen as a process of the transition from the initial cosmological inflation to the current dark energy dominated Universe.Comment: 11 pages, 3 figures, references added, to appear in CQ

Perturbations of Gauss-Bonnet Black Strings in Codimension-2 Braneworlds

We derive the Lichnerowicz equation in the presence of the Gauss-Bonnet term. Using the modified Lichnerowicz equation we study the metric perturbations of Gauss-Bonnet black strings in Codimension-2 Braneworlds.Comment: 26 pages, no figures, clarifying comments and one reference added, to be published in JHE

Out-of-sample estimation for a branch-and-bound algorithm with growing datasets

In [Sass et al., Eur. J. Oper. Res., 316 (1): 36 – 45, 2024], we proposed a branch-and-bound (B&amp;B) algorithm with growing datasets for the deterministic global optimization of parameter estimation problems based on large datasets. Therein, we start the B&amp;B algorithm with a reduced dataset and augment it until reaching the full dataset upon convergence. However, convergence may be slowed down by a gap between the lower bounds of the reduced and the original problem, in particular for noisy measurement data. Thus, we propose the use of out-of-sample estimation for improving the lower bounds calculated with reduced datasets. Based on this, we extend the deterministic approach and propose two heuristic approaches. The computational performance of all approaches is compared with the standard B&amp;B algorithm as a benchmark based on real-world estimation problems from process systems engineering, biochemistry, and machine learning covering datasets with and without measurement noise. Our results indicate that the heuristic approaches can improve the final lower bounds on the optimal objective value without cutting off the global solution. Aside from this, we prove that resampling can decrease the variance of the lower bounds calculated based on random initial datasets. In our case study, resampling hardly affects the performance of the approaches which indicates that the B&amp;B algorithm with growing datasets does not suffer from large variances.</p

Demonstration of low power and highly uniform 6-bit operation in SiO2-based memristors embedded with Pt nanoparticles

In this work, an optimized method was implemented for attaining stable multibit operation with low energy consumption in a two-terminal memory element made from the following layers: Ag/Pt nanoparticles (NPs)/SiO2/TiN in a 1-Transistor-1-Memristor configuration. Compared to the reference sample where no NPs were embedded, an enlarged memory window was recorded in conjunction with reduced variability for both switching states. A comprehensive numerical model was also applied to shed light on this enhanced performance, which was attributed to the spatial confinement effect induced by the presence of the Pt NPs and its impact on the properties of the percolating conducting filaments (CFs). Although 5-bit precision was demonstrated with the application of the incremental-step-pulse-programming (ISPP) algorithm, the reset process was unreliable and the output current increased abnormally when exceeded the value of 150 uA. As a result, the multibit operation was limited. To address this issue, a modified scheme was developed to accurately control the distance between the various resistance levels and achieve highly reliable 6-bit precision. Our work provides valuable insights for the development of energy-efficient memories for applications where a high density of conductance levels is required

Water-food-energy nexus for transboundary cooperation in Eastern Africa

This is the author accepted manuscript. The final version is available on open access from IWA Publishing via the DOI in this recordEstablishing cooperation in transboundary rivers is challenging especially with the weak or non-existent river basin institutions. A nexus-based approach is developed to explore cooperation opportunities in transboundary river basins while considering system operation and coordination under uncertain hydrologic river regimes. The proposed approach is applied to the Nile river basin with a special focus on the Grand Ethiopian Renaissance Dam (GERD), assuming two possible governance positions: with or without cooperation. A cooperation mechanism is developed to allocate additional releases from the GERD when necessary, while a unilateral position assumes that the GERD is operated to maximize hydropower generation regardless of downstream users' needs. The GERD operation modes were analysed considering operation of downstream reservoirs and varying demands in Egypt. Results show that average basin-wide hydropower generation is likely to increase by about 547 GWh/year (1%) if cooperation is adopted when compared to the unilateral position. In Sudan, hydropower generation and water supply are expected to enhance in the unilateral position and would improve further with cooperation. Furthermore, elevated low flows by the GERD are likely to improve the WFE nexus outcomes in Egypt under full cooperation governance scenario with a small reduction in GERD hydropower generation (2,000 GWh/year (19%)).Ministry of Higher Education (MoHE), EgyptUniversity of Exete

Early prediction of COVID-19 outcome using artificial intelligence techniques and only five laboratory indices

We aimed to develop a prediction model for intensive care unit (ICU) hospitalization of Coronavirus disease-19 (COVID-19) patients using artificial neural networks (ANN). We assessed 25 laboratory parameters at first from 248 consecutive adult COVID-19 patients for database creation, training, and development of ANN models. We developed a new alpha-index to assess association of each parameter with outcome. We used 166 records for training of computational simulations (training), 41 for documentation of computational simulations (validation), and 41 for reliability check of computational simulations (testing). The first five laboratory indices ranked by importance were Neutrophil-to-lymphocyte ratio, Lactate Dehydrogenase, Fibrinogen, Albumin, and D-Dimers. The best ANN based on these indices achieved accuracy 95.97%, precision 90.63%, sensitivity 93.55%. and F1-score 92.06%, verified in the validation cohort. Our preliminary findings reveal for the first time an ANN to predict ICU hospitalization accurately and early, using only 5 easily accessible laboratory indices

The international face of Thessaloniki: the “Greek crisis,” the entrepreneurial mayor, and mainstream media discourses

Thessaloniki and its mayor have been portrayed quite favourably in international mainstream media compared to the Greek state after the 2008 economic crisis. The dominant (media) discourses on Greece interpret the crisis as the result of the failure of the Greek state to reform due to the prevalence of a traditional political culture over a modern one and the moral failures of the population. In the international media representations of Thessaloniki, the local government has been described as “exceptional” in its crisis management compared to the state and other local governments, and the city's mayor, Yiannis Boutaris, has been portrayed as a reform hero, due to the implemented entrepreneurial development strategy and the revamp of the city's image through place branding. Analysing the key role of international media in the production and reproduction of a place-branding campaign of Thessaloniki in international media by employing critical discourse analysis, the paper questions the favourable representations of the city compared to the Greek state during the same period. I argue that the serial repetition of positive images contributed to Thessaloniki being perceived as an example to be followed by other Greek local governments and the central state, acting as a best practice example for transformations envisioned on wider scales. The paper contributes to place-branding debates by illustrating the important role of international media in the dissemination of place brands, and by analysing how media representations of place may serve the legitimation of processes of neoliberalisation on scales wider than the concrete urban setting where they occur