Leibniz University of Hanover

About: Leibniz University of Hanover is a education organization based out in Hanover, Niedersachsen, Germany. It is known for research contribution in the topics: Finite element method & Computer science. The organization has 14283 authors who have published 29845 publications receiving 682152 citations.

Nonequilibrium Cation Distribution, Canted Spin Arrangement, and Enhanced Magnetization in Nanosized MgFe2O4 Prepared by a One-Step Mechanochemical Route

Abstract: A single-step synthesis of magnesium ferrite (MgFe2O4) nanoparticles with an average crystallite size of about 8.5 nm synthesized via mechanochemical processing of binary oxide precursors at room temperature is reported. The study highlights the nature of the cation disorder and of the spin arrangement in mechanosynthesized MgFe2O4 as well as its response to changes in temperature. An unusual property of the magnetization enhancement in nanoscale mechanosynthesized MgFe2O4 is reported. Whereas the inner core of a MgFe2O4 nanoparticle exhibits a partly inverse spinel structure with a Neel type collinear spin alignment, the major features of the ionic and spin configurations in the grain boundary (surface) region are a nonequilibrium cation distribution and a canted spin arrangement. Although the spin-canting effect tends to reduce the magnetic moment, the magnetization enhancement exhibited by mechanosynthesized MgFe2O4 is attributed to the nearly random distribution of magnetic cations in the surface regi...

Matter imprints in waveform models for neutron star binaries: tidal and self-spin effects

Abstract: The combined observation of gravitational and electromagnetic waves from the coalescence of two neutron stars marks the beginning of multimessenger astronomy with gravitational waves (GWs). The development of accurate gravitational waveform models is a crucial prerequisite to extract information about the properties of the binary system that generated a detected GW signal. In binary neutron star systems (BNS), tidal effects also need to be incorporated in the modeling for an accurate waveform representation. Building on previous work [Phys. Rev. D 96, 121501 (2017)], we explore the performance of inspiral-merger waveform models that are obtained by adding a numerical relativity (NR) based approximant for the tidal part of the phasing ($\mathrm{NRTidal}$) to existing models for nonprecessing and precessing binary black hole systems, as implemented in the LSC Algorithm Library Suite. The resulting BNS waveforms are compared and contrasted to a set of target waveforms which we obtain by hybridizing NR waveforms (covering the last $\ensuremath{\sim}10$ orbits up to the merger and extending through the postmerger phase) with inspiral waveforms calculated from 30 Hz obtained with a state-of-the-art effective-one-body waveform model. While due to the construction procedure of the target waveforms, there is no error budget available over the full frequency range accessible by advanced GW detectors, the waveform set presents only an approximation of the real signal. We probe that the combination of the self-spin terms and of the $\mathrm{NRTidal}$ description is necessary to obtain minimal mismatches ($\ensuremath{\lesssim}0.01$) and phase differences ($\ensuremath{\lesssim}1\text{ }\text{ }\mathrm{rad}$) with respect to the target waveforms. We also discuss possible improvements and drawbacks of the $\mathrm{NRTidal}$ approximant in its current form.

Using personal examples to improve risk communication for security & privacy decisions

Abstract: IT security systems often attempt to support users in taking a decision by communicating associated risks. However, a lack of efficacy as well as problems with habituation in such systems are well known issues. In this paper, we propose to leverage the rich set of personal data available on smartphones to communicate risks using personalized examples. Examples of private information that may be at risk can draw the users' attention to relevant information for a decision and also improve their response. We present two experiments that validate this approach in the context of Android app permissions. Private information that becomes accessible given certain permissions is displayed when a user wants to install an app, demonstrating the consequences this installation might have. We find that participants made more privacy-conscious choices when deciding which apps to install. Additionally, our results show that our approach causes a negative affect in participants, which makes them pay more attention.

What makes student entrepreneurs? : On the relevance (and irrelevance) of the university and the regional context for student start-ups

Abstract: Student start-ups are a significant part of overall university entrepreneurship. Yet, we know little about the determinants of this type of start-ups and, specifically, the relevance of context effects. Drawing on organizational and regional context literature, we develop and test a model that aims to explain student entrepreneurship in a contextual perspective. Based on unique micro-data and using multi-level techniques, we analyse nascent and new entrepreneurial activities of business and economics students at 41 European universities. Our analysis reveals that individual and contextual determinants influence students’ propensity to start a business. While peoples’ individual characteristics are most important, the organizational and regional contexts also play a role and have a differentiated effect, depending on the source of the venture idea and the stage of its development. Organizational characteristics, like the prevalence of fellow students who have attended entrepreneurship education, influence whether students take action to start a new firm (nascent entrepreneurship) but do not seem to support the actual establishment of a new firm. In contrast, the latter is less dependent on the university context but more strongly influenced by regional characteristics. Overall, our study contributes to our understanding of the emergence of start-ups in the organizational context of universities and has implications for initiatives and programs that aim at encouraging students to become entrepreneurs.