MPWide: a light-weight library for efficient message passing over wide area networks

We present MPWide, a light weight communication library which allows efficient message passing over a distributed network. MPWide has been designed to connect application running on distributed (super)computing resources, and to maximize the communication performance on wide area networks for those without administrative privileges. It can be used to provide message-passing between application, move files, and make very fast connections in client-server environments. MPWide has already been applied to enable distributed cosmological simulations across up to four supercomputers on two continents, and to couple two different bloodflow simulations to form a multiscale simulation.Comment: accepted by the Journal Of Open Research Software, 13 pages, 4 figures, 1 tabl

COVID-19 as Industry Forcing Function:Challenges for Entrepreneurship in the Post-Pandemic Future

The COVID-19 crisis has changed how firms and industries do business – at least for now. What is uncertain, is the duration of that change. Will the industry change induced by the COVID-19 crisis persist and, if so, for how long? Can a crisis, and particularly the COVID-19 crisis, act as a more permanent change agent and create an environment that mimics the entrepreneurial opportunity that industry forcing functions create? If yes, then there is cause to consider the entrepreneurial opportunity that the COVID-19 crisis provides. In this paper, we review the changes that the pandemic has brought to business practices. Furthermore, we discuss the differences between crisis-based opportunity and entrepreneurial opportunity created by industry forcing functions in order to illuminate the ability of a COVID-19 crisis–induced Low Touch Economy to sustainably create entrepreneurial opportunities. We show examples and list the attributes of industry forcing functions that have already provided sustainable entrepreneurial opportunity. Then, we match these attributes with the factors related to the COVID-19-related Low Touch Economy. We find that the COVID-19 crisis has similarities and differences to traditional industry forcing functions started by disruptive technologies. However, unlike traditional industry forcing functions, the COVID-19 crisis acts in a pan-industrial manner, making the impact of the pandemic more profound. Furthermore, the timing of the pandemic is important: the COVID-19 crisis struck during the emergence of a Schumpeterian wave of Industry 4.0 and accelerated the adoption of its most important harbingers. We provide researchers and practitioners a lens through which to review not only the COVID-19 crisis's possibility of lasting effects, but also how it will affect entrepreneurs

p-Torsion of Abelian varieties in characteristic p

This is a PhD thesis in arithmetic geometry, which means that geometric methods are used to solve various problems with an arithmetic flavour. In particular, we consider Abelian varieties in positive characteristic. In characteristic p there are several possibilities for the group scheme A[p], which gives rise to the Ekedahl-Oort stratification. It is natural to ask which p-torsion group schemes are realised as the p-torsion of the Jacobian of a curve. This question plays a central role in this thesis. In Chapter 3, the curves in consideration are Artin-Schreier covers, which have an automorphism of order p. The approach from Booher and Cais [2020] is generalised to yield bounds not only on the the nullity of the Cartier operator, known as the a-number, but on the nullity of arbitrary powers of the Cartier operator. In Chapter 4, we consider curves with a cyclic morphism of degree p2 to the projective line, satisfying further technical conditions. Using an adaptation of the methods in Farnell and Pries [2013], we prove an upper bound for the a-number of these curves. We show that this bound is sharp under the condition p = 3. Chapter 5 concerns the p-torsion of Abelian varieties that come equipped with a unitary structure of signature (q −2, 2). We investigate which Ekedahl-Oort strata of this unitary Shimura variety intersect the supersingular locus. We present two different methods that both yield progress towards an answer to this question. In Chapter 6, we investigate pairs of genus-2 curves with a D4 action that are doubly isogenous. We show that there are more such pairs than heuristics predict, by presenting families of coincidences, coming from intersections of modular curves. Finally, Chapter 7 concerns descent by a rational 3-isogeny on elliptic curves. Elements of order 3 in the Tate-Shafarevich group are constructed systematically

Low-level contrast statistics are diagnostic of invariance of natural textures

Texture may provide important clues for real world object and scene perception. To be reliable, these clues should ideally be invariant to common viewing variations such as changes in illumination and orientation. In a large image database of natural materials, we found textures with low-level contrast statistics that varied substantially under viewing variations, as well as textures that remained relatively constant. This led us to ask whether textures with constant contrast statistics give rise to more invariant representations compared to other textures. To test this, we selected natural texture images with either high (HV) or low (LV) variance in contrast statistics and presented these to human observers. In two distinct behavioral categorization paradigms, participants more often judged HV textures as “different” compared to LV textures, showing that textures with constant contrast statistics are perceived as being more invariant. In a separate electroencephalogram (EEG) experiment, evoked responses to single texture images (single-image ERPs) were collected. The results show that differences in contrast statistics correlated with both early and late differences in occipital ERP amplitude between individual images. Importantly, ERP differences between images of HV textures were mainly driven by illumination angle, which was not the case for LV images: there, differences were completely driven by texture membership. These converging neural and behavioral results imply that some natural textures are surprisingly invariant to illumination changes and that low-level contrast statistics are diagnostic of the extent of this invariance

Doubly isogenous genus-2 curves with D₄-action

We study the extent to which curves over finite fields are characterized by their zeta functions and the zeta functions of certain of their covers. Suppose C and C are curves over a finite field K, with K-rational base points P and P , and let D and D be the pullbacks (via the Abel–Jacobi map) of the multiplication-by-2 maps on their Jacobians. We say that (C, P) and (C , P ) are doubly isogenous if Jac(C) and Jac(C ) are isogenous over K and Jac(D) and Jac(D ) are isogenous over K. For curves of genus 2 whose automorphism groups contain the dihedral group of order eight, we show that the number of pairs of doubly isogenous curves is larger than na¨ıve heuristics predict, and we provide an explanation for this phenomenon

The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos

We present the results of the "Cosmogrid" cosmological N-body simulation suites based on the concordance LCDM model. The Cosmogrid simulation was performed in a 30Mpc box with 2048^3 particles. The mass of each particle is 1.28x10^5 Msun, which is sufficient to resolve ultra-faint dwarfs. We found that the halo mass function shows good agreement with the Sheth & Tormen fitting function down to ~10^7 Msun. We have analyzed the spherically averaged density profiles of the three most massive halos which are of galaxy group size and contain at least 170 million particles. The slopes of these density profiles become shallower than -1 at the inner most radius. We also find a clear correlation of halo concentration with mass. The mass dependence of the concentration parameter cannot be expressed by a single power law, however a simple model based on the Press-Schechter theory proposed by Navarro et al. gives reasonable agreement with this dependence. The spin parameter does not show a correlation with the halo mass. The probability distribution functions for both concentration and spin are well fitted by the log-normal distribution for halos with the masses larger than ~10^8 Msun. The subhalo abundance depends on the halo mass. Galaxy-sized halos have 50% more subhalos than ~10^{11} Msun halos have.Comment: 15 pages, 18 figures, accepted by Ap