The Angular Momentum of Brightest Cluster Galaxies

Massive Brightest Cluster Galaxies (BCGs) are observed to have a range of angular momenta, suggesting a variety of merging historie

Alternative model of the Antonov problem

Astrophysical systems will never be in a real Thermodynamic equilibrium: they undergo an evaporation process due to the fact that the gravity is not able to confine the particles. Ordinarily, this difficulty is overcome by enclosing the system in a rigid container which avoids the evaporation. We proposed an energetic prescription which is able to confine the particles, leading in this way to an alternative version of the Antonov isothermal model which unifies the well-known isothermal and polytropic profiles. Besides of the main features of the isothermal sphere model: the existence of the gravitational collapse and the energetic region with a negative specific heat, this alternative model has the advantage that the system size naturally appears as a consequence of the particles evaporation.Comment: RevTex4, 9 pages, 10 figures, Version Submitted to PR

Charge ordering in extended Hubbard models: Variational cluster approach

We present a generalization of the recently proposed variational cluster perturbation theory to extended Hubbard models at half filling with repulsive nearest neighbor interaction. The method takes into account short-range correlations correctly by the exact diagonalisation of clusters of finite size, whereas long-range order beyond the size of the clusters is treated on a mean-field level. For one dimension, we show that quantum Monte Carlo and density-matrix renormalization-group results can be reproduced with very good accuracy. Moreover we apply the method to the two-dimensional extended Hubbard model on a square lattice. In contrast to the one-dimensional case, a first order phase transition between spin density wave phase and charge density wave phase is found as function of the nearest-neighbor interaction at onsite interactions U>=3t. The single-particle spectral function is calculated for both the one-dimensional and the two-dimensional system.Comment: 15 pages, 12 figure

Capturing architects’ designerly ways of knowing about users: Exploring an ethnographic research approach

Transferring knowledge about diverse users’ experiences from research into architectural design practice is not straightforward. Effective knowledge transfer requires taking into account architects’ design practice. This paper explores a research approach to gain insight into architects’ designerly ways of knowing about users. It discusses why an ethnographic research approach offers a means to study a culture of practice such as architectural design practice. A fieldwork account from a pilot study in an architecture firm provides insight into the experiential issues architects deal with. It illustrates how fieldwork techniques can be applied to map the socio-material aspects (e.g., different stakeholders and design materials) that mediate knowledge about users. Exploiting these aspects of architectural design practice is expected to open new ways of thinking about informing architects about users’ experiences. For instance, there lies an opportunity in engaging architects’ creative representational skills, which challenges architects’ and researchers’ roles in knowledge transfer

Temperature- and quantum phonon effects on Holstein-Hubbard bipolarons

The one-dimensional Holstein-Hubbard model with two electrons of opposite spin is studied using an extension of a recently developed quantum Monte Carlo method, and a very simple yet rewarding variational approach, both based on a canonically transformed Hamiltonian. The quantum Monte Carlo method yields very accurate results in the regime of small but finite phonon frequencies, characteristic of many strongly correlated materials such as, e.g., the cuprates and the manganites. The influence of electron-electron repulsion, phonon frequency and temperature on the bipolaron state is investigated. Thermal dissociation of the intersite bipolaron is observed at high temperatures, and its relation to an existing theory of the manganites is discussed.Comment: 12 pages, 7 figures; final version, accepted for publication in Phys. Rev.

Ferromagnetism in the Infinite-U Hubbard Model

We have studied the stability of the ferromagnetic state in the infinite-U Hubbard model on a square lattice by approximate diagonalization of finite lattices using the density matrix renormalization group technique. By studying lattices with up to 5X20 sites, we have found the ferromagnetic state to be stable below the hole density of 22 percent. Beyond 22 percent of hole doping, the total spin of the ground state decreased gradually to zero with increasing hole density.Comment: 13 pages, RevteX 3.0, seven figures appended in uuencoded form, correcting problems with uuencoded figure

Ideal kink instability of a magnetic loop equilibrium

The force-free coronal loop model by Titov & D\'emoulin (1999} is found to be unstable with respect to the ideal kink mode, which suggests this instability as a mechanism for the initiation of flares. The long-wavelength ($m=1$) mode grows for average twists \Phi\ga3.5\pi (at a loop aspect ratio of $\approx$ 5). The threshold of instability increases with increasing major loop radius, primarily because the aspect ratio then also increases. Numerically obtained equilibria at subcritical twist are very close to the approximate analytical equilibrium; they do not show indications of sigmoidal shape. The growth of kink perturbations is eventually slowed down by the surrounding potential field, which varies only slowly with radius in the model. With this field a global eruption is not obtained in the ideal MHD limit. Kink perturbations with a rising loop apex lead to the formation of a vertical current sheet below the apex, which does not occur in the cylindrical approximation.Comment: Astron. Astrophys. Lett., accepte

Populating architectural design: Introducing scenario-based design in residential care projects

Copyright: © 2019 van der Linden, Dong, & Heylighen. Despite the very aim of designing living environments for people, the perspectives of the end users are underrepresented in architectural design processes. Architects are expected to address the challenges of a diverse and ageing society but, due to increasingly complex design processes, they often have limited access to the perspectives of those they are designing for. This study aims to bring people’s spatial experience to the foreground in architects’ design processes, by turning to techniques developed by related design disciplines. More precisely, it analyses the potential of scenario-based design, a family of techniques for exploring user experience in design, which architects are largely unfamiliar with. Based on elements like personas, scenarios, and user journeys, a scenario-based design approach tailored to architectural design’s particularities was developed. Test workshops were conducted in two architecture firms involved in designing residential care projects, and findings were discussed with an expert panel. Findings illustrate how these workshops offered architects insight into user profiles and themes, facilitated exploring and diversifying potential futures during design development, and supported communication with team members and the client. Additional opportunities and challenges are identified, which can advance the development of an integrated approach to support architects in designing human-centred environments.Flanders Innovation and Entrepreneurship; PhD Fellowship of the Research Foundation–Flanders (FWO)