12,231 research outputs found
Evaluation of the impact of solder die attach versus epoxy die attach in a state of the art power package
Subject of this paper is the thermal investigation of epoxy (EDA) and solder
(SDA) die attaches by a comparison of an ASIC with multiple heat sources in
different package assemblies. Static and transient thermal measurements and
simulations were performed to investigate the thermal behavior of two samples
in a state of the art QFP power package differing only in the die attach
material (EDA and SDA).Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
A (Bounded) Bestiary of Feynman Integral Calabi-Yau Geometries
We define the rigidity of a Feynman integral to be the smallest dimension
over which it is non-polylogarithmic. We argue that massless Feynman integrals
in four dimensions have a rigidity bounded by 2(L-1) at L loops, and we show
that this bound may be saturated for integrals that we call marginal: those
with (L+1)D/2 propagators in (even) D dimensions. We show that marginal Feynman
integrals in D dimensions generically involve Calabi-Yau geometries, and we
give examples of finite four-dimensional Feynman integrals in massless
theory that saturate our predicted bound in rigidity at all loop orders.Comment: 5+2 pages, 11 figures, infinite zoo of Calabi-Yau manifolds. v2
reflects minor changes made for publication. This version is authoritativ
Point-contact spectroscopy in heavy-fermion superconductors
We develop a minimal model to calculate point-contact spectra between a
metallic tip and a superconducting heavy-fermion system. We apply our tunneling
model to the heavy fermion CeCoIn5, both in the normal and superconducting
state. In point-contact and scanning tunneling spectroscopy many heavy-fermion
materials, like CeCoIn5, exhibit an asymmetric differential conductance, dI/dV,
combined with a strongly suppressed Andreev reflection signal in the
superconducting state. We argue that both features may be explained in terms of
a multichannel tunneling model in the presence of localized states near the
interface. We find that it is not sufficient to tunnel into two itinerant bands
of light and heavy electrons to explain the Fano line shape of the differential
conductance. Localized states in the bulk or near the interface are an
essential component for quantum interference to occur when an electron tunnels
from the metallic tip of the point contact into the heavy-fermion system.Comment: 13 pages, 9 figures. Accepted for publication in Physical Review
A supersymmetric multicritical point in a model of lattice fermions
We study a model of spinless fermions with infinite nearest-neighbor
repulsion on the square ladder which has microscopic supersymmetry. It has been
conjectured that in the continuum the model is described by the superconformal
minimal model with central charge c=3/2. Thus far it has not been possible to
confirm this conjecture due to strong finite-size corrections in numerical
data. We trace the origin of these corrections to the presence of unusual
marginal operators that break Lorentz invariance, but preserve part of the
supersymmetry. By relying mostly on entanglement entropy calculations with the
density-matrix renormalization group, we are able to reduce finite-size effects
significantly. This allows us to unambiguously determine the continuum theory
of the model. We also study perturbations of the model and establish that the
supersymmetric model is a multicritical point. Our work underlines the power of
entanglement entropy as a probe of the phases of quantum many-body systems.Comment: 16 pages, 8 figure
The Elliptic Double-Box Integral: Massless Amplitudes Beyond Polylogarithms
We derive an analytic representation of the ten-particle, two-loop double-box
integral as an elliptic integral over weight-three polylogarithms. To obtain
this form, we first derive a four-fold, rational (Feynman-)parametric
representation for the integral, expressed directly in terms of
dual-conformally invariant cross-ratios; from this, the desired form is easily
obtained. The essential features of this integral are illustrated by means of a
simplified toy model, and we attach the relevant expressions for both integrals
in ancillary files. We propose a normalization for such integrals that renders
all of their polylogarithmic degenerations pure, and we discuss the need for a
new 'symbology' of iterated elliptic/polylogarithmic integrals in order to
bring them to a more canonical form.Comment: 4+2 pages, 2 figures. Explicit results are included as ancillary
files. v2: minor changes made for clarification; references adde
Imaging the formation of high-energy dispersion anomalies in the actinide UCoGa
We use angle-resolved photoemission spectroscopy (ARPES) to image the
emergence of substaintial dispersion anomalies in the electronic
renormalization of the actinide compound UCoGa which was presumed to belong
to a conventional Fermi liquid family. Kinks or abrupt breaks in the slope of
the quasiparticle dispersion are detected both at low (130 meV) and high
(1 eV) binding energies below the Fermi energy, ruling out any
significant contribution of phonons. We perform numerical calculations to
demonstrate that the anomalies are adequately described by coupling between
itinerant fermions and spin fluctuations arising from the particle-hole
continuum of the spin-orbit split states of uranium. These anomalies are
resemble the `waterfall' phenomenon of the high-temperature copper-oxide
superconductors, suggesting that spin fluctuations are a generic route toward
multiform electronic phases in correlated materials as different as
high-temperature superconductors and actinides.Comment: 10 pages including supplementary material, Accepted for publication
in PR
An Infrared Study of the Circumstellar Material Associated with the Carbon Star R Sculptoris
The asymptotic giant branch (AGB) star R Sculptoris (R Scl) is one of the
most extensively studied stars on the AGB. R Scl is a carbon star with a
massive circumstellar shell () which
is thought to have been produced during a thermal pulse event years
ago. To study the thermal dust emission associated with its circumstellar
material, observations were taken with the Faint Object InfraRed CAMera for the
SOFIA Telescope (FORCAST) at 19.7, 25.2, 31.5, 34.8, and 37.1 m. Maps of
the infrared emission at these wavelengths were used to study the morphology
and temperature structure of the spatially extended dust emission. Using the
radiative transfer code DUSTY and fitting the spatial profile of the emission,
we find that a geometrically thin dust shell cannot reproduce the observed
spatially resolved emission. Instead, a second dust component in addition to
the shell is needed to reproduce the observed emission. This component, which
lies interior to the dust shell, traces the circumstellar envelope of R Scl. It
is best fit by a density profile with where
and dust mass of
. The strong departure from an
law indicates that the mass-loss rate of R Scl has not been constant.
This result is consistent with a slow decline in the post-pulse mass-loss which
has been inferred from observations of the molecular gas.Comment: 10 pages, 10 figures, accepted to Ap
Color Transparent GPDs?
The relation between GPD's and color transparency is explored. The discovery
of color transparency in pionic diffractive dissociation reactions allows us to
make specific predictions for the behavior of the pion generalized parton
distribution, and provide a further test of any model of the pion form factor.Comment: 12 pages, 3 figure
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