416,315 research outputs found
Discrete Time from Quantum Physics
't Hooft has recently developed a discretisation of (2+1) gravity which has a
multiple-valued Hamiltonian and which therefore admits quantum time evolution
only in discrete steps. In this paper, we describe several models in the
continuum with single-valued equations of motion in classical physics, but with
multiple-valued Hamiltonians. Their time displacements in quantum theory are
therefore obliged to be discrete. Classical models on smooth spatial manifolds
are also constructed with the property that spatial displacements can be
implemented only in discrete steps in quantum theory. All these models show
that quantization can profoundly affect classical topology.Comment: 21 pages with 2 figures, SU-4240-579 (figures corrected in this
version
The emerging structure of the Extended Evolutionary Synthesis: where does Evo-Devo fit in?
The Extended Evolutionary Synthesis (EES) debate is gaining ground in contemporary evolutionary biology. In parallel, a number of philosophical standpoints have emerged in an attempt to clarify what exactly is represented by the EES. For Massimo Pigliucci, we are in the wake of the newest instantiation of a persisting Kuhnian paradigm; in contrast, Telmo Pievani has contended that the transition to an EES could be best represented as a progressive reformation of a prior Lakatosian scientific research program, with the extension of its Neo-Darwinian core and the addition of a brand-new protective belt of assumptions and auxiliary hypotheses. Here, we argue that those philosophical vantage points are not the only ways to interpret what current proposals to âextendâ the Modern Synthesis-derived âstandard evolutionary theoryâ (SET) entail in terms of theoretical change in evolutionary biology. We specifically propose the image of the emergent EES as a vast network of models and interweaved representations that, instantiated in diverse practices, are connected and related in multiple ways. Under that assumption, the EES could be articulated around a paraconsistent network of evolutionary theories (including some elements of the SET), as well as models, practices and representation systems of contemporary evolutionary biology, with edges and nodes that change their position and centrality as a consequence of the co-construction and stabilization of facts and historical discussions revolving around the epistemic goals of this area of the life sciences. We then critically examine the purported structure of the EESâpublished by Laland and collaborators in 2015âin light of our own network-based proposal. Finally, we consider which epistemic units of Evo-Devo are present or still missing from the EES, in preparation for further analyses of the topic of explanatory integration in this conceptual framework
Integrated care and the working record
By default, many discussions and specifications of electronic health records or integrated care records often conceptualize the record as a passive information repository. This article presents data from a case study of work in a medical unit in a major metropolitan hospital. It shows how the clinicians tailored, re-presented and augmented clinical information to support their own roles in the delivery of care for individual patients. This is referred to as the working record: a set of complexly interrelated clinician-centred documents that are locally evolved, maintained and used to support delivery of care in conjunction with the more patient-centred chart that will be stored in the medical records department on the patientâs discharge. Implications are drawn for how an integrated care record could support the local tailorability and flexibility that underpin this working record and hence underpin practice
Exact Solutions for the Intrinsic Geometry of Black Hole Coalescence
We describe the null geometry of a multiple black hole event horizon in terms
of a conformal rescaling of a flat space null hypersurface. For the prolate
spheroidal case, we show that the method reproduces the pair-of-pants shaped
horizon found in the numerical simulation of the head-on-collision of black
holes. For the oblate case, it reproduces the initially toroidal event horizon
found in the numerical simulation of collapse of a rotating cluster. The
analytic nature of the approach makes further conclusions possible, such as a
bearing on the hoop conjecture. From a time reversed point of view, the
approach yields a description of the past event horizon of a fissioning white
hole, which can be used as null data for the characteristic evolution of the
exterior space-time.Comment: 21 pages, 6 figures, revtex, to appear in Phys. Rev.
Developmental Systems Theory as a Process Theory
Griffiths and Russell D. Gray (1994, 1997, 2001) have argued that the fundamental unit of analysis in developmental systems theory should be a process â the life cycle â and not a set of developmental resources and interactions between those resources. The key concepts of developmental systems theory, epigenesis and developmental dynamics, both also suggest a process view of the units of development. This chapter explores in more depth the features of developmental systems theory that favour treating processes as fundamental in biology and examines the continuity between developmental systems theory and ideas about process in the work of several major figures in early 20th century biology, most notable C.H Waddington
On the Probabilistic Interpretation of the Evolution Equations with Pomeron Loops in QCD
We study some structural aspects of the evolution equations with Pomeron
loops recently derived in QCD at high energy and for a large number of colors,
with the purpose of clarifying their probabilistic interpretation. We show
that, in spite of their appealing dipolar structure and of the self-duality of
the underlying Hamiltonian, these equations cannot be given a meaningful
interpretation in terms of a system of dipoles which evolves through
dissociation (one dipole splitting into two) and recombination (two dipoles
merging into one). The problem comes from the saturation effects, which cannot
be described as dipole recombination, not even effectively. We establish this
by showing that a (probabilistically meaningful) dipolar evolution in either
the target or the projectile wavefunction cannot reproduce the actual evolution
equations in QCD.Comment: 31 pages, 2 figure
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