424 research outputs found
Form Factors for Quasi-particles in c=1 Conformal Field Theory
The non-Fermi liquid physics at the edge of fractional quantum Hall systems
is described by specific chiral Conformal Field Theories with central charge
c=1. The charged quasi-particles in these theories have fractional charge and
obey a form of fractional statistics. In this paper we study form factors,
which are matrix elements of physical (conformal) operators, evaluated in a
quasi-particle basis that is organized according to the rules of fractional
exclusion statistics. Using the systematics of Jack polynomials, we derive
selection rules for a special class of form factors. We argue that finite
temperature Green's functions can be evaluated via systematic form factor
expansions, using form factors such as those computed in this paper and
thermodynamic distribution functions for fractional exclusion statistics. We
present a specific case study where we demonstrate that the form factor
expansion shows a rapid convergence.Comment: 36 pages, 1 postscript figur
Quasi-particles for quantum Hall edges
We discuss a quasi-particle formulation of effective edge theories for the
fractional quantum Hall effect. Fundamental quasi-particles for the Laughlin
state with filling fraction \nu =1/3 are edge electrons of charge -e and edge
quasi-holes of charge +e/3. These quasi-particles satisfy exclusion statistics
in the sense of Haldane. We exploit algebraic properties of edge electrons to
derive a kinetic equation for charge transport between a \nu=1/3 fractional
quantum Hall edge and a normal metal.Comment: Latex, 6 pages, Contribution to the proceedings of the XXXIVth
Rencontres de Moriond `Quantum Physics at Mesoscopic Scale
Short and random: Modelling the effects of (proto-)neural elongations
To understand how neurons and nervous systems first evolved, we need an
account of the origins of neural elongations: Why did neural elongations (axons
and dendrites) first originate, such that they could become the central
component of both neurons and nervous systems? Two contrasting conceptual
accounts provide different answers to this question. Braitenberg's vehicles
provide the iconic illustration of the dominant input-output (IO) view. Here
the basic role of neural elongations is to connect sensors to effectors, both
situated at different positions within the body. For this function, neural
elongations are thought of as comparatively long and specific connections,
which require an articulated body involving substantial developmental processes
to build. Internal coordination (IC) models stress a different function for
early nervous systems. Here the coordination of activity across extended parts
of a multicellular body is held central, in particular for the contractions of
(muscle) tissue. An IC perspective allows the hypothesis that the earliest
proto-neural elongations could have been functional even when they were
initially simple short and random connections, as long as they enhanced the
patterning of contractile activity across a multicellular surface. The present
computational study provides a proof of concept that such short and random
neural elongations can play this role. While an excitable epithelium can
generate basic forms of patterning for small body-configurations, adding
elongations allows such patterning to scale up to larger bodies. This result
supports a new, more gradual evolutionary route towards the origins of the very
first full neurons and nervous systems.Comment: 12 pages, 5 figures, Keywords: early nervous systems, neural
elongations, nervous system evolution, computational modelling, internal
coordinatio
Metal sources for the Katanga Copperbelt deposits (DRC) insights from Sr and Nd isotope ratios
The ore deposits of the Central African Copperbelt formed during a multiphase mineralisation process. The basement underlying the Neoproterozoic Katanga Supergroup that hosts the ore, demonstrates the largest potential as metal source. Various ore deposits that formed during different mineralisation phases are taken as case studies, i.e. Kamoto, Luiswishi, Kambove West, Dikulushi and Kipushi (Democratic Republic of Congo, DRC). The Sr and Nd isotopic compositions of gangue carbonates associated with these deposits is determined and compared with those of rocks from several basement units, bordering or underlying the Copperbelt, to infer the metal sources. The mineralising fluid of diagenetic stratiform Cu-Co mineralisation interacted with felsic basement rocks underlying the region. The Co from these deposits is most likely derived from mafic rocks, but this is not observed in the isotopic signatures. Syn-orogenic, stratabound Cu-Co mineralisation resulted mainly from remobilisation of diagenetic sulphides. A limited, renewed contribution of metals from felsic basement rocks might be indicated by the isotope ratios in the western part of the Copperbelt, where the metamorphic grade is the lowest. The mineralising fluid of syn- and post-orogenic, vein-type mineralisations interacted with local mafic rocks, and with felsic basement or siliciclastic host rocks
The protocol for positive body experience (PBE); introducing a psychomotor therapy intervention based on positive body exposure targeting negative body image in eating disorders
Negative body experience is a core characteristic of eating disorders, and poses a serious risk factor for its development, maintenance and relapse. This underlines the importance of specific therapeutic attention to body experience. In the past ten years a body-oriented treatment protocol with the focus on positive body exposure, called 'Protocol Positive body experience' has been developed. The aim of this paper is to describe the scientific basis of the protocol and to give an impression of its content and structure, illustrated by clinical case vignettes. An important and innovative aspect of the protocol is to enhance not only aesthetic, but also functional and tactile body experience. The protocol enables body-oriented therapists and psychomotor therapists to treat negative body experience in an evidence-based way and facilitates further research to validate the effect of positive body exposure
Modeling spontaneous activity across an excitable epithelium: Support for a coordination scenario of early neural evolution
Internal coordination models hold that early nervous systems evolved in the first place to coordinate internal activity at a multicellular level, most notably the use of multicellular contractility as an effector for motility. A recent example of such a model, the skin brain thesis, suggests that excitable epithelia using chemical signaling are a potential candidate as a nervous system precursor.We developed a computational model and a measure for whole body coordination to investigate the coordinative properties of such excitable epithelia. Using this measure we show that excitable epithelia can spontaneously exhibit body-scale patterns of activation. Relevant factors determining the extent of patterning are the noise level for exocytosis, relative body dimensions, and body size. In smaller bodies whole-body coordination emerges from cellular excitability and bidirectional excitatory transmission alone.Our results show that basic internal coordination as proposed by the skin brain thesis could have arisen in this potential nervous system precursor, supporting that this configuration may have played a role as a proto-neural system and requires further investigation
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