The case for metadata harvesting

Metadata harvesting is an increasingly popular model of interaction between the mutually autonomous parties of medium, medium-large federations of digital library services. With a harvesting protocol, in particular, resource descriptions locally available at each party can be served to remote applications for the implementation of federated services, such as resource discovery. This article offers a systematic explanation of the success of the model and its standard implementations in the context of current initiatives for national and international federations

A (comparative) catalogue: images, observed moments, buildings

For some years this practice was, as many others have been, immersed in small architecture – alterations and additions to existing houses and buildings. In these projects an intensity of connection between building, architect and client fostered a search for references and for connections at a small scale. This developed into a continuous catalogue of moments rather than complete buildings which is in the process of further development through a step into larger commissions. The real interest relates to the idea of a catalogue, not of patterns or models but of moments, a sense of the building captured in one frame, its unexpectedness and sometimes the beauty in its awkwardness. Early projects rely on the pre-existing to create separation and connection. In later projects, new buildings are often formed through an invented context. Rarely is the building considered complete but rather an ambiguous sense of suspension is strived for. Throughout, the re-appropriation of catalogue images sourced from within the work becomes apparent. In this way the distillation of images and projects leads to a more complete resolution. It is through (these) moments that a design is held together - light through a void, tunnel, or a distant horizon. The creation of these moments is not about systems or forms and stand in lieu of the complete building. This is an illustration of a continued distillation of certain similar, recurrent moments in the work

Hybrid applications over XML - integrating the declarative and navigational approaches

We discuss the design of a quasi-statically typed language for XML in which data may be associated with different structures and different algebras in different scopes, whilst preserving identity. In declarative scopes, data are trees and may be queried with the full flexibility associated with XML query algebras. In procedural scopes, data have more conventional structures, such as records and sets, and can be manipulated with the constructs normally found in mainstream languages. For its original form of structural polymorphism, the language offers integrated support for the development of hybrid applications over XML, where data change form to re flct programming expectations and enable their enforcement

Probing bulk viscosity in relativistic flows

We derive an analytical connection between kinetic relaxation rate and bulk viscosity of a relativistic fluid in d spatial dimensions, all the way from the ultra-relativistic down to the near non-relativistic regime. Our derivation is based on both Chapman-Enskog asymptotic expansion and Grad's method of moments. We validate our theoretical results against a benchmark flow, providing further evidence of the correctness of the Chapman-Enskog approach; we define the range of validity of this approach and provide evidence of mounting departures at increasing Knudsen number. Finally, we present numerical simulations of transport processes in quark gluon plasmas, with special focus on the effects of bulk viscosity which might prove amenable to future experimental verification

Relativistic dissipation obeys Chapman-Enskog asymptotics: analytical and numerical evidence as a basis for accurate kinetic simulations

We present an analytical derivation of the transport coefficients of a relativistic gas in (2+1) dimensions for both Chapman-Enskog (CE) asymptotics and Grad's expansion methods. Moreover, we develop a systematic calibration method, connecting the relaxation time of relativistic kinetic theory to the transport parameters of the associated dissipative hydrodynamic equations. Comparison between the analytical results and numerical simulations, shows that the CE method correctly captures dissipative effects, while Grad's method does not. The resulting calibration procedure based on the CE method opens the way to the quantitative kinetic description of dissipative relativistic fluid dynamics under fairly general conditions, namely flows with strongly non-linearities, in non-ideal geometries, across both ultra-relativistic and near-non-relativistic regimes

Selective suppression of local interneuron circuits in human motor cortex contributes to movement preparation.

Changes in neural activity occur in the motor cortex prior to movement, but the nature and purpose of this preparatory activity is unclear. To investigate this in the human (male and female) brain non-invasively, we used transcranial magnetic stimulation (TMS) to probe the excitability of distinct sets of excitatory inputs to corticospinal neurones during the warning period of various reaction time tasks. Using two separate methods (H-reflex conditioning and directional effects of TMS), we show that a specific set of excitatory inputs to corticospinal neurones are suppressed during motor preparation, whilst another set of inputs remain unaffected. To probe the behavioural relevance of this suppression, we examined whether the strength of the selective preparatory inhibition in each trial was related to reaction time. Surprisingly, the greater the amount of selective preparatory inhibition, the faster the reaction time was. This suggests that the inhibition of inputs to corticospinal neurones is not involved in preventing release of movement but may in fact facilitate rapid reactions. Thus, selective suppression of a specific set of motor cortical neurones may be a key aspect of successful movement preparation.Significance statementMovement preparation evokes substantial activity in the motor cortex despite no apparent movement. One explanation for the lack of movement is that motor cortical output in this period is gated by an inhibitory mechanism. This notion was supported by previous non-invasive TMS studies of human motor cortex indicating a reduction of corticospinal excitability. On the contrary, our data supports the idea that there is a coordinated balance of activity upstream of the corticospinal output neurones. This includes a suppression of specific local circuits that supports, rather than inhibits, the rapid generation of prepared movements. Thus, the selective suppression of local circuits appears to be an essential part of successful movement preparation, instead of an external control mechanism

A Lattice Boltzmann Method for relativistic rarefied flows in (2+1) dimensions

We propose an extension to recently developed Relativistic Lattice Boltzmann solvers (RLBM), which allows the simulation of flows close to the free streaming limit. Following previous works Ambruş and Blaga (2018), we use product quadrature rules and select weights and nodes by separately discretizing the radial and the angular components. This procedure facilitates the development of quadrature-based RLBM with increased isotropy levels, thus improving the accuracy of the method for the simulation of flows beyond the hydrodynamic regime. In order to quantify the improvement of this discretization procedure over existing methods, we perform numerical tests of shock waves in one and two spatial dimensions in various kinetic regimes across the hydrodynamic and the free-streaming limits.</p

Beyond moments: relativistic Lattice-Boltzmann methods for radiative transport in computational astrophysics

We present a new method for the numerical solution of the radiative-transfer equation (RTE) in multidimensional scenarios commonly encountered in computational astrophysics. The method is based on the direct solution of the Boltzmann equation via an extension of the Lattice Boltzmann (LB) equation and allows to model the evolution of the radiation field as it interacts with a background fluid, via absorption, emission, and scattering. As a first application of this method, we restrict our attention to a frequency independent ("grey") formulation within a special-relativistic framework, which can be employed also for classical computational astrophysics. For a number of standard tests that consider the performance of the method in optically thin, optically thick and intermediate regimes with a static fluid, we show the ability of the LB method to produce accurate and convergent results matching the analytic solutions. We also contrast the LB method with commonly employed moment-based schemes for the solution of the RTE, such as the M1 scheme. In this way, we are able to highlight that the LB method provides the correct solution for both non-trivial free-streaming scenarios and the intermediate optical-depth regime, for which the M1 method either fails or provides inaccurate solutions. When coupling to a dynamical fluid, on the other hand, we present the first self-consistent solution of the RTE with LB methods within a relativistic-hydrodynamic scenario. Finally, we show that besides providing more accurate results in all regimes, the LB method features smaller or comparable computational costs compared to the M1 scheme.Comment: 22 pages, 16 figures, matches version accepted in MNRA