16,544 research outputs found
Duesing\u27s Adoniram Judson: A Bicentenial Appreciation of the Pioneer American Missionary (Book Review)
Thermal and stress analysis of an Attached Inflatable Decelerator /AID/ deployed in the Mars and Earth atmospheres
Trajectory, thermodynamic, and stress analyses of spacecraft inflatable decelerators in Mars and Earth atmosphere
Social Class in art and design education: a significant omission
This chapter investigate the way ‘classed’ practices permeate art and design education. It provides the wider context in both art and education, exploring contemporary sociological approaches to thinking about class and briefly outlining our methodology and focuses on A&D PGCE students’ complex and contradictory self-understandings in relation to class and their reflections on its impact on their educational journey. The chapter discusses implications for Initial Teacher Education and proffers ways in which art and design educators might be encouraged to refuse conformity, challenge unspoken ‘classism’ and work towards cultural democracy. Teachers are constantly encouraged to consider the significance of race, gender, Special Educational Needs and disability for an inclusive learning environment and heteronormativity and mental health; class is invariably omitted in the art curriculum. In 2002, the German sociologist Ulrich Beck famously stated that class had become a ‘Zombie Category’
Distributed SUSY Breaking: Dark Energy, Newton's Law and the LHC
We identify the underlying symmetry mechanism that suppresses the low-energy
effective 4D cosmological constant within 6D supergravity models, leading to
results suppressed by powers of the KK scale relative to the much larger masses
associated with particles localized on codimension-2 branes. In these models
the conditions for unbroken supersymmetry can be satisfied locally everywhere
within the extra dimensions, but are obstructed by global conditions like flux
quantization or the mutual inconsistency of boundary conditions at the various
branes. Consequently quantities forbidden by supersymmetry cannot be nonzero
until wavelengths of order the KK scale are integrated out, since only such
long wavelength modes see the entire space and so know that supersymmetry
breaks. We verify these arguments by extending earlier rugby-ball calculations
of one-loop vacuum energies to more general pairs of branes within two warped
extra dimensions. The predicted effective 4D vacuum energy density can be of
order C (m Mg/4 pi Mp)^4, where Mg (Mp) is the rationalized 6D (4D) Planck
scale and m is the heaviest brane-localized particle. Numerically this is C
(5.6 x 10^{-5} eV)^4 if we take m = 173 GeV and take Mg as small as possible
(10 TeV corresponding to KK size r < 1 micron), consistent with supernova
bounds. C is a constant depending on details of the bulk spectrum, which could
be ~ 500 for each of hundreds of fields. The value C ~ 6 x 10^6 gives the
observed Dark Energy density
Gravitational Forces on a Codimension-2 Brane
We compute the gravitational response of six dimensional gauged, chiral
supergravity to localized stress energy on one of two space-filling branes,
including the effects of compactifying the extra dimensions and brane
back-reaction. We find a broad class of exact solutions, including various
black-brane solutions. Several approximate solutions are also described, such
as the near-horizon geometry of a small black hole which is argued to be
approximately described by a 6D Schwarzschild (or Kerr) black hole, with event
horizon appropriately modified to encode the brane back-reaction. The general
linearized far-field solutions are found in the 4D regime very far from the
source, and all integration constants are related to physical quantities
describing the branes and the localized energy source. The localized source
determines two of these, corresponding to the source mass and the size of the
strength of a coupling to a 4D scalar mode whose mass is parametrically smaller
than the KK scale. At large distances the solutions agree with those of 4D
general relativity, but for an intermediate range of distances (larger than the
KK scale) the solutions better fit a Brans-Dicke theory. For a realistic choice
of parameters the KK scale could lie at a micron, while the crossover to
Brans-Dicke behaviour could occur at around 10 microns. While allowed by
present data this points to potentially measurable changes to Newton's Law
arising at distances larger than the KK scale.Comment: 31 pages + appendices, 2 figure
On the Naturalness of Higgs Inflation
We critically examine the recent claim that the Standard Model Higgs boson
could drive inflation in agreement with observations if has a strong coupling to the Ricci curvature scalar. We
first show that the effective theory approach upon which that claim is based
ceases to be valid beyond a cutoff scale , where is the
reduced Planck mass. We then argue that knowing the Higgs potential profile for
the field values relevant for inflation () requires knowledge of the ultraviolet completion of the SM beyond
. In absence of such microscopic theory, the extrapolation of the pure
SM potential beyond is unwarranted and the scenario is akin to other
ad-hoc inflaton potentials afflicted with significant fine-tuning. The
appealing naturalness of this minimal proposal is therefore lost.Comment: 9 pages. Replaced with published version, plus a footnote clarifying
the use of power counting estimate
Running with Rugby Balls: Bulk Renormalization of Codimension-2 Branes
We compute how one-loop bulk effects renormalize both bulk and brane
effective interactions for geometries sourced by codimension-two branes. We do
so by explicitly integrating out spin-zero, -half and -one particles in
6-dimensional Einstein-Maxwell-Scalar theories compactified to 4 dimensions on
a flux-stabilized 2D geometry. (Our methods apply equally well for D dimensions
compactified to D-2 dimensions, although our explicit formulae do not capture
all divergences when D>6.) The renormalization of bulk interactions are
independent of the boundary conditions assumed at the brane locations, and
reproduce standard heat-kernel calculations. Boundary conditions at any
particular brane do affect how bulk loops renormalize this brane's effective
action, but not the renormalization of other distant branes. Although we
explicitly compute our loops using a rugby ball geometry, because we follow
only UV effects our results apply more generally to any geometry containing
codimension-two sources with conical singularities. Our results have a variety
of uses, including calculating the UV sensitivity of one-loop vacuum energy
seen by observers localized on the brane. We show how these one-loop effects
combine in a surprising way with bulk back-reaction to give the complete
low-energy effective cosmological constant, and comment on the relevance of
this calculation to proposed applications of codimension-two 6D models to
solutions of the hierarchy and cosmological constant problems.Comment: 42 pages + appendices. This is the final version which appears in
JHE
Magnetic Field Rotations in the Solar Wind at Kinetic Scales
The solar wind magnetic field contains rotations at a broad range of scales,
which have been extensively studied in the MHD range. Here we present an
extension of this analysis to the range between ion and electron kinetic
scales. The distribution of rotation angles was found to be approximately
log-normal, shifting to smaller angles at smaller scales almost self-similarly,
but with small, statistically significant changes of shape. The fraction of
energy in fluctuations with angles larger than was found to drop
approximately exponentially with , with e-folding angle at
ion scales and at electron scales, showing that large angles
() do not contain a significant amount of energy at kinetic
scales. Implications for kinetic turbulence theory and the dissipation of solar
wind turbulence are discussed
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