2,052 research outputs found
Non-metric chaotic inflation
We consider inflation within the context of what is arguably the simplest
non-metric extension of Einstein gravity. There non-metricity is described by a
single graviscalar field with a non-minimal kinetic coupling to the inflaton
field , parameterized by a single parameter . We discuss the
implications of non-metricity for chaotic inflation and find that it
significantly alters the inflaton dynamics for field values , dramatically changing the qualitative behaviour in this regime.
For potentials with a positive slope non-metricity imposes an upper bound on
the possible number of e-folds. For chaotic inflation with a monomial
potential, the spectral index and the tensor-to-scalar ratio receive small
corrections dependent on the non-metricity parameter. We also argue that
significant post-inflationary non-metricity may be generated.Comment: 7 pages, 1 figur
Creep of a fracture line in paper peeling
The slow motion of a crack line is studied via an experiment in which sheets
of paper are split into two halves in a ``peel-in-nip'' (PIN) geometry under a
constant load, in creep. The velocity-force relation is exponential. The
dynamics of the fracture line exhibits intermittency, or avalanches, which are
studied using acoustic emission. The energy statistics is a power-law, with the
exponent . Both the waiting times between subsequent
events and the displacement of the fracture line imply complicated stick-slip
dynamics. We discuss the correspondence to tensile PIN tests and other similar
experiments on in-plane fracture and the theory of creep for elastic manifolds
Photoelectron Emission from Metal Surfaces Induced by VUV-emission of Filament Driven Hydrogen Arc Discharge Plasma
Photoelectron emission measurements have been performed using a
filament-driven multi-cusp arc discharge volume production H^- ion source
(LIISA). It has been found that photoelectron currents obtained with Al, Cu,
Mo, Ta and stainless steel (SAE 304) are on the same order of magnitude. The
photoelectron currents depend linearly on the discharge power. It is shown
experimentally that photoelectron emission is significant only in the short
wavelength range of hydrogen spectrum due to the energy dependence of the
quantum efficiency. It is estimated from the measured data that the maximum
photoelectron flux from plasma chamber walls is on the order of 1 A per kW of
discharge power
An Experimental Study of Waveguide Coupled Microwave Heating with Conventional Multicusp Negative Ion Source
Negative ion production with conventional multicusp plasma chambers utilizing
2.45 GHz microwave heating is demonstrated. The experimental results were
obtained with the multicusp plasma chambers and extraction systems of the
RFdriven RADIS ion source and the filament driven arc discharge ion source
LIISA. A waveguide microwave coupling system, which is almost similar to the
one used with the SILHI ion source, was used. The results demonstrate that at
least one third of negative ion beam obtained with inductive RF-coupling
(RADIS) or arc discharge (LIISA) can be achieved with 1 kW of 2.45 GHz
microwave power in CW mode without any modification of the plasma chamber. The
co-extracted electron to H^- ratio and the optimum pressure range were observed
to be similar for both heating methods. The behaviour of the plasma implies
that the energy transfer from the microwaves to the plasma electrons is mainly
an off-resonance process
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