2,878 research outputs found
High Speed Peltier Calorimeter for the Calibration of High Bandwidth Power Measurement Equipment
Accurate power measurements of electronic components operating at high
frequencies are vital in determining where power losses occur in a system such
as a power converter. Such power measurements must be carried out with
equipment that can accurately measure real power at high frequency. We present
the design of a high speed calorimeter to address this requirement, capable of
reaching a steady state in less than 10 minutes. The system uses Peltier
thermoelectric coolers to remove heat generated in a load resistance, and was
calibrated against known real power measurements using an artificial neural
network. A dead zone controller was used to achieve stable power measurements.
The calibration was validated and shown to have an absolute accuracy of +/-8 mW
(95% confidence interval) for measurements of real power from 0.1 to 5 W
Optimisation of the parameters of an extended defect model applied to non-amorphizing implants
In this paper, we present the optimisation of the parameters of a physical model of the kinetics of extended defects and applied the model with the optimised parameters to non-amorphizing implants. The model describes the small clusters, the {113} defects and the dislocation loops. In the first part, we determine the formation energies of the small clusters, the fault energy of the {113} defects, their Burgers vector and the self-diffusivity of silicon using TEM measurements and extractions of the supersaturation from the spreading of boron marker layers in low-dose implanted silicon. The improvements of the simulations are presented for the fitted experiments and for other wafers annealed at intermediate temperatures. In the second part, we increase the dose and energy of the non-amorphizing implant, leading to the transformation of {113} defects into dislocation loops. The predictions obtained with the optimised model are shown to be in agreement with the measurements. (c) 2005 Elsevier B.V. All rights reserved
Entropic Inflation
One of the major pillars of modern cosmology theory is a period of
accelerating expansion in the early universe. This accelerating expansion, or
inflation, must be sustained for at least 30 e--foldings. One mechanism used to
drive the acceleration is the addition of a new energy field, called the
Inflaton; often this is a scalar field. We propose an alternative mechanism
which, like our approach to explain the late-time accelerating universe, uses
the entropy and temperature intrinsic to information holographically stored on
a surface enclosing the observed space. The acceleration is due in both cases
to an emergent entropic force, naturally arising from the information storage
on the horizon.Comment: 12 pages; version to appear in IJMP
Heralding two- and four-photon path entanglement on chip
Generating quantum entanglement is not only an important scientific endeavor,
but will be essential to realizing quantum-enhanced technologies, in
particular, quantum-enhanced measurements with precision beyond classical
limits. We investigate the heralded generation of multiphoton entanglement for
quantum metrology using a reconfigurable integrated waveguide device in which
projective measurement of auxiliary photons heralds the generation of
path-entangled states. We use four and six-photon inputs, to analyze the
heralding process of two- and four-photon NOON states-a superposition of N
photons in two paths, capable of enabling phase supersensitive measurements at
the Heisenberg limit. Realistic devices will include imperfections; as part of
the heralded state preparation, we demonstrate phase superresolution within our
chip with a state that is more robust to photon loss
Spinflation
We study the cosmological implications of including angular motion in the DBI
brane inflation scenario. The non-canonical kinetic terms of the
Dirac-Born-Infeld action give an interesting alternative to slow roll
inflation, and cycling branes can drive periods of accelerated expansion in the
Universe. We present explicit numerical solutions demonstrating brane inflation
in the Klebanov-Strassler throat. We find that demanding sufficient inflation
takes place in the throat is in conflict with keeping the brane's total energy
low enough so that local gravitational backreaction on the Calabi-Yau manifold
can be safely ignored. We deduce that spinflation (brane inflation with angular
momentum) can ease this tension by providing extra e-foldings at the start of
inflation. Cosmological expansion rapidly damps the angular momentum causing an
exit to a more conventional brane inflation scenario. Finally, we set up a
general framework for cosmological perturbation theory in this scenario, where
we have multi-field non-standard kinetic term inflation.Comment: 29 pages, 6 figures, minor changes, typos fixed, to appear in JCA
Circumventing the eta problem in building an inflationary model in string theory
The eta problem is one of the most significant obstacles to building a
successful inflationary model in string theory. Planck mass suppressed
corrections to the inflaton potential generally lead to inflaton masses of
order the Hubble scale and generate contributions of order unity to the eta
slow roll parameter rendering prolonged slow roll inflation impossible. We
demonstrate the severity of this problem in the context of brane anti-brane
inflation in a warped throat of a Calabi-Yau flux compactification with all
phenomenologically dangerous moduli stabilized. Using exact numerical solutions
we show that the eta problem can be avoided in scenarios where the inflaton is
non-minimally coupled to gravity and has Dirac-Born-Infeld (DBI) kinetic term.
We show that the resulting cosmic microwave background (CMB) observables such
as measures of non-gaussianites can, in principle, serve as a probe of
scalar-gravity couplings.Comment: 8 pages, 3 figures; title changed and reference added to match
published version in PR
Renormalon disappearance in Borel sum of the 1/N expansion of the Gross-Neveu model mass gap
The exact mass gap of the O(N) Gross-Neveu model is known, for arbitrary ,
from non-perturbative methods. However, a "naive" perturbative expansion of the
pole mass exhibits an infinite set of infrared renormalons at order 1/N,
formally similar to the QCD heavy quark pole mass renormalons, potentially
leading to large perturbative ambiguities. We examine the
precise vanishing mechanism of such infrared renormalons, which avoids this
(only apparent)contradiction, and operates without need of (Borel) summation
contour prescription, usually preventing unambiguous separation of perturbative
contributions. As a consequence we stress the direct Borel summability of the
(1/N) perturbative expansion of the mass gap. We briefly speculate on a
possible similar behaviour of analogous non-perturbative QCD quantities.Comment: 16 pp., 1 figure. v2: a few paragraphs and one appendix added, title
and abstract slightly changed, essential results unchange
Modular converter system for low-cost off-grid energy storage using second life Li-ion batteries
Lithium ion batteries are promising for small off- grid energy storage
applications in developing countries because of their high energy density and
long life. However, costs are prohibitive. Instead, we consider 'used' Li-ion
batteries for this application, finding experimentally that many discarded
laptop cells, for example, still have good capacity and cycle life. In order to
make safe and optimal use of such cells, we present a modular power management
system using a separate power converter for every cell. This novel approach
allows individual batteries to be used to their full capacity. The power
converters operate in voltage droop control mode to provide easy charge
balancing and implement a battery management system to estimate the capacity of
each cell, as we demonstrate experimentally.Comment: Presented at IEEE GHTC Oct 10-14, 2014, Silicon Valle
Continuous Flow Multi-Step Organic Synthesis
Using continuous flow techniques for multi-step synthesis enables multiple reaction steps to be combined into a single continuous operation. In this mini-review we discuss the current state of the art in this field and highlight recent progress and current challenges facing this emerging area
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