On the dynamic stability of eccentrically reinforced circular cylindrical shells Technical report, Sep. 1, 1965 - Jan. 31, 1967

Dynamic stability of eccentrically reinforced circular cylindrical shell

On the Formulation of Equations of Motion of an Eccentrically Stiffened Shallow Circular Cylindrical Shell Semiannual Progress Report, Sep. 1, 1965 - Mar. 1, 1966

Motion equations formulation for eccentrically stiffened shallow circular cylindrical shel

Distribution of survival times of deliberate Plasmodium falciparum infections in tertiary syphilis patients

Survival time data of Plasmodium falciparum infections from deliberate infection of human subjects with P. falciparum between 1940 and 1963 as a treatment for neurosyphilis in the USA (Georgia) have been used to test the fits of five commonly used parametric distributions for survival times using quantile-quantile plots. Our results suggest that the best fit is obtained from the Gompertz or Weibull distributions. This result has important implications for mathematical modelling of malaria, which has for the past century exclusively assumed that the duration of malaria infections has an exponential distribution. It is desirable to know the correct distribution because its shape profoundly influences the length of monitoring needed in an intervention programme for eliminating or reducing malari

The structure of the QED-Vacuum and Electron-Positron Pair Production in Super-Intense, pulsed Laser Fields

We discuss electron-positron pair-production by super-intense, short laser pulses off the physical vacuum state locally deformed by (stripped) nuclei with large nuclear charges. Consequences of non-perturbative vacuum polarisation resulting from such a deformation are shortly broached. Production probabilities per pulse are calculated.Comment: 10 pages, 1 figure, submitted to Journal of Physics

Third rank Killing tensors in general relativity. The (1+1)-dimensional case

Third rank Killing tensors in (1+1)-dimensional geometries are investigated and classified. It is found that a necessary and sufficient condition for such a geometry to admit a third rank Killing tensor can always be formulated as a quadratic PDE, of order three or lower, in a Kahler type potential for the metric. This is in contrast to the case of first and second rank Killing tensors for which the integrability condition is a linear PDE. The motivation for studying higher rank Killing tensors in (1+1)-geometries, is the fact that exact solutions of the Einstein equations are often associated with a first or second rank Killing tensor symmetry in the geodesic flow formulation of the dynamics. This is in particular true for the many models of interest for which this formulation is (1+1)-dimensional, where just one additional constant of motion suffices for complete integrability. We show that new exact solutions can be found by classifying geometries admitting higher rank Killing tensors.Comment: 16 pages, LaTe

Eliciting Touristic Profiles: A User Study on Picture Collections

Eliciting the preferences and needs of tourists is challenging, since people often have difficulties to explicitly express them, especially in the initial phase of travel planning. Recommender systems employed at the early stage of planning can therefore be very beneficial to the general satisfaction of a user. Previous studies have explored pictures as a tool of communication and as a way to implicitly deduce a traveller's preferences and needs. In this paper, we conduct a user study to verify previous claims and conceptual work on the feasibility of modelling travel interests from a selection of a user's pictures. We utilize fine-tuned convolutional neural networks to compute a vector representation of a picture, where each dimension corresponds to a travel behavioural pattern from the traditional Seven-Factor model. In our study, we followed strict privacy principles and did not save uploaded pictures after computing their vector representation. We aggregate the representations of the pictures of a user into a single user representation, i.e., touristic profile, using different strategies. In our user study with 81 participants, we let users adjust the predicted touristic profile and confirm the usefulness of our approach. Our results show that given a collection of pictures the touristic profile of a user can be determined.Comment: Accepted at UMAP 2020 (full paper

Generalized Taub-NUT metrics and Killing-Yano tensors

A necessary condition that a St\"ackel-Killing tensor of valence 2 be the contracted product of a Killing-Yano tensor of valence 2 with itself is re-derived for a Riemannian manifold. This condition is applied to the generalized Euclidean Taub-NUT metrics which admit a Kepler type symmetry. It is shown that in general the St\"ackel-Killing tensors involved in the Runge-Lenz vector cannot be expressed as a product of Killing-Yano tensors. The only exception is the original Taub-NUT metric.Comment: 14 pages, LaTeX. Final version to appear in J.Phys.A:Math.Ge

Emergence of influential spreaders in modified rumor models

The burst in the use of online social networks over the last decade has provided evidence that current rumor spreading models miss some fundamental ingredients in order to reproduce how information is disseminated. In particular, recent literature has revealed that these models fail to reproduce the fact that some nodes in a network have an influential role when it comes to spread a piece of information. In this work, we introduce two mechanisms with the aim of filling the gap between theoretical and experimental results. The first model introduces the assumption that spreaders are not always active whereas the second model considers the possibility that an ignorant is not interested in spreading the rumor. In both cases, results from numerical simulations show a higher adhesion to real data than classical rumor spreading models. Our results shed some light on the mechanisms underlying the spreading of information and ideas in large social systems and pave the way for more realistic diffusion models.Comment: 14 Pages, 6 figures, accepted for publication in Journal of Statistical Physic

Short distance behaviour of the effective string

We study the Polyakov loop correlator in the (2+1) dimensional Z_2 gauge model. An algorithm that we have presented recently, allows us to reach high precision results for a large range of distances and temperatures, giving us the opportunity to test predictions of the effective Nambu-Goto string model. Here we focus on the regime of low temperatures and small distances. In contrast to the high temperature, large distance regime, we find that our numerical results are not well described by the two loop-prediction of the Nambu-Goto model. In addition we compare our data with those for the SU(2) and SU(3) gauge models in (2+1) dimensions obtained by other authors. We generalize the result of L\"uscher and Weisz for a boundary term in the interquark potential to the finite temperature case.Comment: 38 pages, 7 figures, version accepted for publication in JHE