71 research outputs found
Policy, Principle, or Values: An Exploration of Judicial Decision-Making
The article reveals the values underpinning judicial decisions in three cases in which the complexity and legal uncertainty divided the court and argues that the language of public policy is used to frame a decision based on judicial values
Spherically Symmetric, Self-Similar Spacetimes
Self-similar spacetimes are of importance to cosmology and to gravitational
collapse problems. We show that self-similarity or the existence of a
homothetic Killing vector field for spherically symmetric spacetimes implies
the separability of the spacetime metric in terms of the co-moving coordinates
and that the metric is, uniquely, the one recently reported in [cqg1]. The
spacetime, in general, has non-vanishing energy-flux and shear. The spacetime
admits matter with any equation of state.Comment: Submitted to Physical Review Letter
Uniqueness of Self-Similar Asymptotically Friedmann-Robertson-Walker Spacetime in Brans-Dicke theory
We investigate spherically symmetric self-similar solutions in Brans-Dicke
theory. Assuming a perfect fluid with the equation of state , we show that there are no non-trivial solutions which approach
asymptotically to the flat Friedmann-Robertson-Walker spacetime if the energy
density is positive. This result suggests that primordial black holes in
Brans-Dicke theory cannot grow at the same rate as the size of the cosmological
particle horizon.Comment: Revised version, 4 pages, no figures, Revtex, accepted for
publication in Physical Review
Grassmann Variables and the Jaynes-Cummings Model
This paper shows that phase space methods using a positive P type
distribution function involving both c-number variables (for the cavity mode)
and Grassmann variables (for the two level atom) can be used to treat the
Jaynes-Cummings model. Although it is a Grassmann function, the distribution
function is equivalent to six c-number functions of the two bosonic variables.
Experimental quantities are given as bosonic phase space integrals involving
the six functions. A Fokker-Planck equation involving both left and right
Grassmann differentiation can be obtained for the distribution function, and is
equivalent to six coupled equations for the six c-number functions.
The approach used involves choosing the canonical form of the (non-unique)
positive P distribution function, where the correspondence rules for bosonic
operators are non-standard and hence the Fokker-Planck equation is also
unusual. Initial conditions, such as for initially uncorrelated states, are
used to determine the initial distribution function. Transformations to new
bosonic variables rotating at the cavity frequency enables the six coupled
equations for the new c-number functions (also equivalent to the canonical
Grassmann distribution function) to be solved analytically, based on an ansatz
from a 1980 paper by Stenholm. It is then shown that the distribution function
is the same as that determined from the well-known solution based on coupled
equations for state vector amplitudes of atomic and n-photon product states.
The treatment of the simple two fermion mode Jaynes-Cummings model is a
useful test case for the future development of phase space Grassmann
distribution functional methods for multi-mode fermionic applications in
quantum-atom optics.Comment: 57 pages, 0 figures. Version
Gravitational Collapse of Phantom Fluid in (2+1)-Dimensions
This investigation is devoted to the solutions of Einstein's field equations
for a circularly symmetric anisotropic fluid, with kinematic self-similarity of
the first kind, in -dimensional spacetimes. In the case where the radial
pressure vanishes, we show that there exists a solution of the equations that
represents the gravitational collapse of an anisotropic fluid, and this
collapse will eventually form a black hole, even when it is constituted by the
phantom energy.Comment: 10 page
The Similarity Hypothesis in General Relativity
Self-similar models are important in general relativity and other fundamental
theories. In this paper we shall discuss the ``similarity hypothesis'', which
asserts that under a variety of physical circumstances solutions of these
theories will naturally evolve to a self-similar form. We will find there is
good evidence for this in the context of both spatially homogenous and
inhomogeneous cosmological models, although in some cases the self-similar
model is only an intermediate attractor. There are also a wide variety of
situations, including critical pheneomena, in which spherically symmetric
models tend towards self-similarity. However, this does not happen in all cases
and it is it is important to understand the prerequisites for the conjecture.Comment: to be submitted to Gen. Rel. Gra
Research and Innovation As a Catalyst For Food System Transformation
Background Food systems are associated with severe and persistent problems worldwide. Governance approaches aiming to foster sustainable transformation of food systems face several challenges due to the complex nature of food systems.
Scope and approach In this commentary we argue that addressing these governance challenges requires the development and adoption of novel research and innovation (R&I) approaches that will provide evidence to inform food system transformation and will serve as catalysts for change. We first elaborate on the complexity of food systems (transformation) and stress the need to move beyond traditional linear R&I approaches to be able to respond to persistent problems that affect food systems. Though integrated transdisciplinary approaches are promising, current R&I systems do not sufficiently support such endeavors. As such, we argue, we need strategies that trigger a double transformation – of food systems and of their R&I systems.
Key Findings and Conclusions Seizing the opportunities to transform R&I systems has implications for how research is done – pointing to the need for competence development among researchers, policy makers and society in general – and requires specific governance interventions that stimulate a systemic approach. Such interventions should foster transdisciplinary and transformative research agendas that stimulate portfolios of projects that will reinforce one another, and stimulate innovative experiments to shape conditions for systemic change. In short, a thorough rethinking of the role of R&I as well as how it is funded is a crucial step towards the development of the integrative policies that are necessary to engender systemic change – in the food system and beyond
A Systems Approach to Research and Innovation for Food System Transformation
This policy brief of the European Union (EU) Think Tank – part of the FIT4FOOD2030 Coordination and Support Action (CSA) of the FOOD 2030 initiative – is a response and contribution to growing pleas for a ‘systems approach’ to transform food systems for Food and Nutrition Security (FNS) for present and future generations. This policy brief specifically focusses on the necessity of the adoption of a systems approach to Research and Innovation (R&I) in order to foster the transformation of food systems
Research and Innovation Supporting the Farm to Fork Strategy of the European Commission
The EU Think Tank (as part of the FIT4FOOD2030 Coordination andSupport Action) strongly supports the development of the Farm toFork Strategy as a key component of the European Green Deal,recognising the need to transform the food system as a whole
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