341 research outputs found
Discontinuous shear modulus determines the glass transition temperature
A solid - amorphous or crystalline - is defined by a finite shear modulus
while a fluid lacks such. We thus experimentally investigate the elastic
properties of a colloidal glass former near the glass transition: spectroscopy
of vibrational excitations yields the dispersion relations of longitudinal and
transverse phonons in the glassy state. From the long wavelength limit of the
dispersion relation we extract the bulk and the shear modulus. As expected, the
latter disappear in a fluid and we measure a clearly resolved discontinuous
behaviour of the elastic moduli at the glass transition. This not only
determines the transition temperature T_G of the system but also directly
addresses recent discussions about elasticity during vitrification. We show
that low frequency excitations in our system are plane waves such that
continuum elasticity theory can be used to describe the macroscopic behaviour.Comment: 8 pages, 6 figure
Cities and energy:urban morphology and residential heat-energy demand
Our aim is better understanding of the theoretical heat-energy demand of different types of urban form at a scale of 500 m × 500 m. The empirical basis of this study includes samples of dominant residential building typologies identified for Paris, London, Berlin, and Istanbul. In addition, archetypal idealised samples were created for each type through an analysis of their built form parameters and the removal of unwanted ‘invasive’ morphologies. The digital elevation models of these real and idealised samples were run through a simulation that modelled solar gains and building surface energy losses to estimate heat-energy demand. In addition to investigating the effect of macroscale morphological parameters, microscale design parameters, such as U-values and glazing ratios, as well as climatic effects were analysed. The theoretical results of this study suggest that urban-morphology-induced heat-energy efficiency is significant and can lead to a difference in heat-energy demand of up to a factor of six. Compact and tall building types were found to have the greatest heat-energy efficiency at the neighbourhood scale while detached housing was found to have the lowest
Mermin-Wagner fluctuations in 2D amorphous solids
In a recent comment, M. Kosterlitz described how the discrepancy about the
lack of broken translational symmetry in two dimensions - doubting the
existence of 2D crystals - and the first computer simulations foretelling 2D
crystals at least in tiny systems, motivated him and D. Thouless to investigate
melting and suprafluidity in two dimensions [Jour. of Phys. Cond. Matt.
\textbf{28}, 481001 (2016)]. The lack of broken symmetries proposed by D.
Mermin and H. Wagner is caused by long wavelength density fluctuations. Those
fluctuations do not only have structural impact but additionally a dynamical
one: They cause the Lindemann criterion to fail in 2D and the mean squared
displacement not to be limited. Comparing experimental data from 3D and 2D
amorphous solids with 2D crystals we disentangle Mermin-Wagner fluctuations
from glassy structural relaxations. Furthermore we can demonstrate with
computer simulations the logarithmic increase of displacements predicted by
Mermin and Wagner: periodicity is not a requirement for Mermin-Wagner
fluctuations which conserve the homogeneity of space on long scales.Comment: 7 pages, 4 figure
A Relaxation Model for the Non-Isothermal Navier-Stokes-Korteweg Equations in Confined Domains
The Navier-Stokes-Korteweg (NSK) system is a classical diffuse interface
model which is based on van der Waals theory of capillarity. Diffuse interface
methods have gained much interest to model two-phase flow in porous media.
However, for the numerical solution of the NSK equations two major challenges
have to be faced. First, an extended numerical stencil is required due to a
third-order term in the linear momentum and the total energy equations. In
addition, the dispersive contribution in the linear momentum equations prevents
the straightforward use of contact angle boundary conditions. Secondly, any
real gas equation of state is based on a non-convex Helmholtz free energy
potential which may cause the eigenvalues of the Jacobian of the first-order
fluxes to become imaginary numbers inside the spinodal region. In this work, a
thermodynamically consistent relaxation model is presented which is used to
approximate the NSK equations. The model is complimented by thermodynamically
consistent non-equilibrium boundary conditions which take contact angle effects
into account. Due to the relaxation approach, the contribution of the Korteweg
tensor in the linear momentum and total energy equations can be reduced to
second-order terms which enables a straightforward implementation of contact
angle boundary conditions in a numerical scheme. Moreover, the definition of a
modified pressure function enables to formulate first-order fluxes which remain
strictly hyperbolic in the entire spinodal region. The present work is a
generalization of a previously presented parabolic relaxation model for the
isothermal NSK equations
\u27Harlem Exchange\u27 Relies on Letters Between Friends of Three Decades
News release announces the Harlem Exchange, an epistolary play, will be presented at the University of Dayton
Update on DLR's OSIRIS program and first results of OSIRISv1 on Flying Laptop
Optical satellite links have gained increasing attention throughout the last years. Especially for the application of optical satellite downlinks. Within the OSIRIS program, DLR's Institute of Communications and Navigation develops optical terminals and systems which are optimized for small satellites. After the successful qualification and launch of two precursor terminals, DLR currently develops OSIRISv3, a 3rd generation OSIRIS terminal with up to 10 Gbps downlink rate, and OSIRIS4Cubesat, a miniaturized version optimized for Cubesat Applications. The University of Stuttgart's Institute of Space Systems develops small satellites, which are used to demonstrate novel technologies in the Space domain. Together, DLR and University of Stuttgart integrated the first OSIRIS generation onboard the Flying Laptop satellite, which was launched in July 2017 and has been successfully operated since. This paper will give an overview about DLR's OSIRIS program. Furthermore, it will show first results of OSIRISv1 on Flying Laptop. Therefore, the Flying Laptop satellite and OSIRISv1 will be explained. Preliminary results from the validation campaign, where optical downlinks have been demonstrated, will be given. © 2019 SPIE. Downloading of the abstract is permitted for personal use only
A framework for using self-organising maps to analyse spatiotemporal patterns, exemplified by analysis of mobile phone usage
We suggest a visual analytics framework for the exploration and analysis of spatially and temporally referenced values of numeric attributes. The framework supports two complementary perspectives on spatio-temporal data: as a temporal sequence of spatial distributions of attribute values (called spatial situations) and as a set of spatially referenced time series of attribute values representing local temporal variations. To handle a large amount of data, we use the self-organising map (SOM) method, which groups objects and arranges them according to similarity of relevant data features. We apply the SOM approach to spatial situations and to local temporal variations and obtain two types of SOM outcomes, called space-in-time SOM and time-in-space SOM, respectively. The examination and interpretation of both types of SOM outcomes are supported by appropriate visualisation and interaction techniques. This article describes the use of the framework by an example scenario of data analysis. We also discuss how the framework can be extended from supporting explorative analysis to building predictive models of the spatio-temporal variation of attribute values. We apply our approach to phone call data showing its usefulness in real-world analytic scenarios
Selbstentwurf. Das Architektenhaus von der Renaissance bis zur Gegenwart
Der Band vereint Beiträge von Architekturhistorikern und praktizierenden Architekten zum Thema des Architektenhauses, das durch eine kritische Rezeption aktueller Ansätze aus der kunsthistorischen Selbstporträt-Forschung neu konturiert wird.
In dem vom Architekten für sich selbst entworfenen Wohnhaus verdichten sich in einzigartiger Komplexität Aspekte des künstlerischen Schaffens, eines oft ostentativen Selbstbezuges und der Verortung in kulturellen und sozialen Gefügen. Die seit dem 15. Jahrhundert überlieferten Entwürfe besitzen nicht selten einen experimentellen Charakter, sie dienten ebenso als ökonomisches Instrument wie als Manifest und utopischer Ausblick. Die paradoxe Vielfalt der Interessen wird in diesem Band unter den pointierten Begrifflichkeiten der jüngeren Forschungen zum Selbstporträt neu beleuchtet, indem nach der Rolle eines derartigen ›Selbstentwurfes‹ zur Selbstvergewisserung gefragt wird
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