On selection criteria for problems with moving inhomogeneities

We study mechanical problems with multiple solutions and introduce a thermodynamic framework to formulate two different selection criteria in terms of macroscopic energy productions and fluxes. Studying simple examples for lattice motion we then compare the implications for both resting and moving inhomogeneities.Comment: revised version contains new introduction, numerical simulations of Riemann problems, and a more detailed discussion of the causality principle; 18 pages, several figure

Die Nederduitsch Hervormde Kerk van Afrika as volkskerk: Oorsig en herbesinning

The Nederduitsch Hervormde Kerk van Afrika as “volkskerk”: Overview and evaluationThe Church Order of the Nederduitsch Hervormde Kerk van Afrika (NHKA) states in Ordinance 4 that the NHKA is a “volkskerk”, meaning a Church that is ethnically based and focused on the ministry to Afrikaans speaking people. This article examines the history of the relationship between NHKA and Afrikaners that prevailed since the early 19th century. It argues that the establishment of separate and ethnically based churches in South Africa was, initially, the result of a specific understanding of Afrikaner nationalism and liberty. Only after the Second World War, due to criticism levelled at separate development and separate churches by the ecumenical movement, it was based on theological reflection. This article concludes that the term “volkskerk” has become theologically obsolete as well as practically unusable

On the emergence of Lorentzian signature and scalar gravity

In recent years, a growing momentum has been gained by the emergent gravity framework. Within the latter, the very concepts of geometry and gravitational interaction are not seen as elementary aspects of Nature but rather as collective phenomena associated to the dynamics of more fundamental objects. In this paper we want to further explore this possibility by proposing a model of emergent Lorentzian signature and scalar gravity. Assuming that the dynamics of the fundamental objects can give rise in first place to a Riemannian manifold and a set of scalar fields we show how time (in the sense of hyperbolic equations) can emerge as a property of perturbations dynamics around some specific class of solutions of the field equations. Moreover, we show that these perturbations can give rise to a spin-0 gravity via a suitable redefinition of the fields that identifies the relevant degrees of freedom. In particular, we find that our model gives rise to Nordstrom gravity. Since this theory is invariant under general coordinate transformations, this also shows how diffeomorphism invariance (albeit of a weaker form than the one of general relativity) can emerge from much simpler systems.Comment: 10 pages, revtex4. Replaced with the published versio

Automated mass spectrometer/analysis system: A concept

System performs rapid multiple analyses of entire compound classes or individual compounds on small amounts of sample and reagent. Method will allow screening of large populations for metabolic disorders and establishment of effective-but-safe levels of therapeutic drugs in body fluids and tissues

Die kerkregtelike posisie van die kind in die Nederduitsch Hervormde Kerk van Afrika, met besondere verwysing na lidmaatskap, dpop, nagmaal en tug

The position of the child in the Nederduitsch Hervormde Kerk van Afirika with specific reference to membership, baptism, eucharist and discipline The position of the child in the church has been taken for granted for many years. This article gives a historical perspective on the church orders of Calvin, Bucer, the Netherlands and the Nederduitsch Hervormde Kerk van Afrika, and analizes those articles that shed any light on the position of the child in the church. Matters such as children’s membership of the church, infant baptism, children’s communion and discipline are discussed from the viewpoint of church order

Quasinormal Modes, the Area Spectrum, and Black Hole Entropy

The results of canonical quantum gravity concerning geometric operators and black hole entropy are beset by an ambiguity labelled by the Immirzi parameter. We use a result from classical gravity concerning the quasinormal mode spectrum of a black hole to fix this parameter in a new way. As a result we arrive at the Bekenstein - Hawking expression of $A/4 l_P^2$ for the entropy of a black hole and in addition see an indication that the appropriate gauge group of quantum gravity is SO(3) and not its covering group SU(2).Comment: 4 pages, 2 figure

Die Nederduitsch Hervormde Kerk van Afrika as volkskerk: Oorsig en herbesinning

The Nederduitsch Hervormde Kerk van Afrika as “volkskerk”: Overview and evaluation The Church Order of the Nederduitsch Hervormde Kerk van Afrika (NHKA) states in Ordinance 4 that the NHKA is a “volkskerk”, meaning a Church that is ethnically based and focused on the ministry to Afrikaans speaking people. This article examines the history of the relationship between NHKA and Afrikaners that prevailed since the early 19th century. It argues that the establishment of separate and ethnically based churches in South Africa was, initially, the result of a specific understanding of Afrikaner nationalism and liberty. Only after the Second World War, due to criticism levelled at separate development and separate churches by the ecumenical movement, it was based on theological reflection. This article concludes that the term “volkskerk” has become theologically obsolete as well as practically unusable

Riemann solvers and undercompressive shocks of convex FPU chains

We consider FPU-type atomic chains with general convex potentials. The naive continuum limit in the hyperbolic space-time scaling is the p-system of mass and momentum conservation. We systematically compare Riemann solutions to the p-system with numerical solutions to discrete Riemann problems in FPU chains, and argue that the latter can be described by modified p-system Riemann solvers. We allow the flux to have a turning point, and observe a third type of elementary wave (conservative shocks) in the atomistic simulations. These waves are heteroclinic travelling waves and correspond to non-classical, undercompressive shocks of the p-system. We analyse such shocks for fluxes with one or more turning points. Depending on the convexity properties of the flux we propose FPU-Riemann solvers. Our numerical simulations confirm that Lax-shocks are replaced by so called dispersive shocks. For convex-concave flux we provide numerical evidence that convex FPU chains follow the p-system in generating conservative shocks that are supersonic. For concave-convex flux, however, the conservative shocks of the p-system are subsonic and do not appear in FPU-Riemann solutions

Framing energetic top-quark pair production at the LHC

Top-quark pair production is central to many facets of LHC physics. At leading order, the top and anti-top are produced in a back-to-back topology, however this topology accounts only for a minority of $t \bar t$ events with TeV-scale momentum transfer. The remaining events instead involve the splitting of an initial or final-state gluon to $t \bar t$. We provide simple quantitative arguments that explain why this is the case and examine the interplay between different topologies and a range of variables that characterise the event hardness. We then develop a method to classify the topologies of individual events and use it to illustrate our findings in the context of simulated events, using both top partons and suitably defined fiducial tops. For events with large $t \bar t$ invariant mass, we comment on additional features that have important experimental and theoretical implications.Comment: 23 pages + 2 appendice

Lagrangian and Hamiltonian two-scale reduction

Studying high-dimensional Hamiltonian systems with microstructure, it is an important and challenging problem to identify reduced macroscopic models that describe some effective dynamics on large spatial and temporal scales. This paper concerns the question how reasonable macroscopic Lagrangian and Hamiltonian structures can by derived from the microscopic system. In the first part we develop a general approach to this problem by considering non-canonical Hamiltonian structures on the tangent bundle. This approach can be applied to all Hamiltonian lattices (or Hamiltonian PDEs) and involves three building blocks: (i) the embedding of the microscopic system, (ii) an invertible two-scale transformation that encodes the underlying scaling of space and time, (iii) an elementary model reduction that is based on a Principle of Consistent Expansions. In the second part we exemplify the reduction approach and derive various reduced PDE models for the atomic chain. The reduced equations are either related to long wave-length motion or describe the macroscopic modulation of an oscillatory microstructure.Comment: 40 page