13,382 research outputs found
A review of Lee, A. and Danby, S. (2012) Reshaping Doctoral Education: international approaches and pedagogies
Development of cost-optimized insulation system for use in large solid rocket motors. Volume 4, task 4 - 260 in. dia motor insulation system design and process plan Final report
Design, weight, cost, and tooling concepts for cost optimized insulation system for 260 in. dia solid rocket moto
Do Salaries Improve Worker Performance?
We establish the effects of salaries on worker performance by exploiting a natural experiment in which some workers in a particular occupation (football referees) switch from short-term contracts to salaried contracts. Worker performance improves among those who move onto salaried contracts relative to those who do not. The finding is robust to the introduction of worker fixed effects indicating that it is not driven by better workers being awarded salary contracts. Nor is it sensitive to workers sorting into or out of the profession. Improved performance could arise from the additional effort workers exert due to career concerns, the higher income associated with career contracts (an efficiency wage effect) or improvements in worker quality arising from off-the-job training which accompanies the salaried contracts.
Custodial Symmetry, Flavor Physics, and the Triviality Bound on the Higgs Mass
The triviality of the scalar sector of the standard one-doublet Higgs model
implies that this model is only an effective low-energy theory valid below some
cut-off scale Lambda. We show that the experimental constraint on the amount of
custodial symmetry violation implies that the scale Lambda must be greater than
of order 7.5 TeV. The underlying high-energy theory must also include flavor
dynamics at a scale of order Lambda or greater in order to give rise to the
different Yukawa couplings of the Higgs to ordinary fermions. This flavor
dynamics will generically produce flavor-changing neutral currents. We show
that the experimental constraints on the neutral D-meson mass difference imply
that Lambda must be greater than of order 21 TeV. For theories defined about
the infrared-stable Gaussian fixed-point, we estimate that this lower bound on
Lambda yields an upper bound of approximately 460 GeV on the Higgs boson's
mass, independent of the regulator chosen to define the theory. We also show
that some regulator schemes, such as higher-derivative regulators, used to
define the theory about a different fixed-point are particularly dangerous
because an infinite number of custodial-isospin-violating operators become
relevant.Comment: 15 pages, 7 ps/eps embedded figures, talk presented at the 1996
International Workshop on Perspectives of Strong Coupling Gauge Theories
(SCGT 96), Nagoya, Japa
Topcolor in the LHC Era
Ongoing LHC searches for the standard model Higgs Boson in WW or ZZ decay
modes strongly constrain the top-Higgs state predicted in many models with new
dynamics that preferentially affects top quarks. Such a state couples strongly
to top-quarks, and is therefore produced through gluon fusion at a rate that
can be greatly enhanced relative to the rate for the standard model Higgs
boson. As we discuss in this talk, a top-Higgs state with mass less than 300
GeV is excluded at 95% CL if the associated top-pion has a mass of 150 GeV, and
the constraint is even stronger if the mass of the top-pion state exceeds the
top-quark mass or if the top-pion decay constant is a substantial fraction of
the weak scale. These results have significant implications for theories with
strong top dynamics, such as topcolor-assisted technicolor, top-seesaw models,
and certain Higgsless models
Factorization of correlations in two-dimensional percolation on the plane and torus
Recently, Delfino and Viti have examined the factorization of the three-point
density correlation function P_3 at the percolation point in terms of the
two-point density correlation functions P_2. According to conformal invariance,
this factorization is exact on the infinite plane, such that the ratio R(z_1,
z_2, z_3) = P_3(z_1, z_2, z_3) [P_2(z_1, z_2) P_2(z_1, z_3) P_2(z_2,
z_3)]^{1/2} is not only universal but also a constant, independent of the z_i,
and in fact an operator product expansion (OPE) coefficient. Delfino and Viti
analytically calculate its value (1.022013...) for percolation, in agreement
with the numerical value 1.022 found previously in a study of R on the
conformally equivalent cylinder. In this paper we confirm the factorization on
the plane numerically using periodic lattices (tori) of very large size, which
locally approximate a plane. We also investigate the general behavior of R on
the torus, and find a minimum value of R approx. 1.0132 when the three points
are maximally separated. In addition, we present a simplified expression for R
on the plane as a function of the SLE parameter kappa.Comment: Small corrections (final version). In press, J. Phys.
Detecting Stellar Spots by Gravitational Microlensing
During microlensing events with a small impact parameter, the amplification
of the source flux is sensitive to the surface brightness distribution of the
source star. Such events provide a means for studying the surface structure of
target stars in the ongoing microlensing surveys, most efficiently for giants
in the Galactic bulge. In this work we demonstrate the sensitivity of
point-mass microlensing to small spots with radii source
radii. We compute the amplification deviation from the light curve of a
spotless source and explore its dependence on lensing and spot parameters.
During source-transit events spots can cause deviations larger than 2%, and
thus be in principle detectable. Maximum relative deviation usually occurs when
the lens directly crosses the spot. Its numerical value for a dark spot with
sufficient contrast is found to be roughly equal to the fractional radius of
the spot, i.e., up to 20% in this study. Spots can also be efficiently detected
by the changes in sensitive spectral lines during the event. Notably, the
presence of a spot can mimic the effect of a low-mass companion of the lens in
some events.Comment: 18 pages with 7 Postscript figures, to appear in ApJ, January 2000;
discussion expanded, references added, minor revisions in tex
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