879 research outputs found
Termination Casts: A Flexible Approach to Termination with General Recursion
This paper proposes a type-and-effect system called Teqt, which distinguishes
terminating terms and total functions from possibly diverging terms and partial
functions, for a lambda calculus with general recursion and equality types. The
central idea is to include a primitive type-form "Terminates t", expressing
that term t is terminating; and then allow terms t to be coerced from possibly
diverging to total, using a proof of Terminates t. We call such coercions
termination casts, and show how to implement terminating recursion using them.
For the meta-theory of the system, we describe a translation from Teqt to a
logical theory of termination for general recursive, simply typed functions.
Every typing judgment of Teqt is translated to a theorem expressing the
appropriate termination property of the computational part of the Teqt term.Comment: In Proceedings PAR 2010, arXiv:1012.455
A new numerical method for obtaining gluon distribution functions , from the proton structure function
An exact expression for the leading-order (LO) gluon distribution function
from the DGLAP evolution equation for the proton structure
function for deep inelastic scattering has
recently been obtained [M. M. Block, L. Durand and D. W. McKay, Phys. Rev.
D{\bf 79}, 014031, (2009)] for massless quarks, using Laplace transformation
techniques. Here, we develop a fast and accurate numerical inverse Laplace
transformation algorithm, required to invert the Laplace transforms needed to
evaluate , and compare it to the exact solution. We obtain accuracies
of less than 1 part in 1000 over the entire and spectrum. Since no
analytic Laplace inversion is possible for next-to-leading order (NLO) and
higher orders, this numerical algorithm will enable one to obtain accurate NLO
(and NNLO) gluon distributions, using only experimental measurements of
.Comment: 9 pages, 2 figure
Comparing introductory and beyond-introductory students' reasoning about uncertainty
Uncertainty is an important concept in physics laboratory instruction.
However, little work has examined how students reason about uncertainty beyond
the introductory (intro) level. In this work we aimed to compare intro and
beyond-intro students' ideas about uncertainty. We administered a survey to
students at 10 different universities with questions probing procedural
reasoning about measurement, student-identified sources of uncertainty, and
predictive reasoning about data distributions. We found that intro and
beyond-intro students answered similarly on questions where intro students
already exhibited expert-level reasoning, such as in comparing two data sets
with the same mean but different spreads, identifying limitations in an
experimental setup, and predicting how a data distribution would change if more
data were collected. For other questions, beyond-intro students generally
exhibited more expert-like reasoning than intro students, such as when
determining whether two sets of data agree, identifying principles of
measurement that contribute to spread, and predicting how a data distribution
would change if better data were collected. Neither differences in student
populations, lab courses taken, nor research experience were able to fully
explain the variability between intro and beyond-intro student responses. These
results call for further research to better understand how students' ideas
about uncertainty develop beyond the intro level.Comment: 19 pages, 12 figure
Context affects student thinking about sources of uncertainty in classical and quantum mechanics
Measurement uncertainty is an important topic in the undergraduate laboratory
curriculum. Previous research on student thinking about experimental
measurement uncertainty has focused primarily on introductory-level students'
procedural reasoning about data collection and interpretation. In this paper,
we extended this prior work to study upper-level students' thinking about
sources of measurement uncertainty across experimental contexts, with a
particular focus on classical and quantum mechanics contexts. We developed a
survey to probe students' thinking in the generic question ``What comes to mind
when you think about measurement uncertainty in [classical/quantum]
mechanics?'' as well as in a range of specific experimental scenarios. We found
that students primarily focused on limitations of the experimental setup in
classical mechanics and principles of the underlying physics theory in quantum
mechanics. Our results suggest that students need careful scaffolding to
identify principles in appropriate classical experimental contexts and
limitations in appropriate quantum experimental contexts. We recommend that
future research probe how instruction in both classical and quantum contexts
can help students better understand the range of sources of uncertainty present
in classical and quantum experiments.Comment: 15 pages, 8 figure
The t-tbar cross-section at 1.8 and 1.96 TeV: a study of the systematics due to parton densities and scale dependence
We update the theoretical predictions for the t-tbar production cross-section
at the Tevatron, taking into account the most recent determinations of
systematic uncertainties in the extraction of the proton parton densities.Comment: 12 pages, 1 figure, Late
New perspectives on student reasoning about measurement uncertainty: More or better data
Uncertainty is an important and fundamental concept in physics education.
Students are often first exposed to uncertainty in introductory labs, expand
their knowledge across lab courses, and then are introduced to quantum
mechanical uncertainty in upper-division courses. This study is part of a
larger project evaluating student thinking about uncertainty across these
contexts. In this research, we investigate advanced physics student thinking
about uncertainty by asking them conceptual questions about how a hypothetical
distribution of measurements would change if `more' or `better' data were
collected in four different experimental scenarios. The scenarios include both
classical and quantum experiments, as well as experiments that theoretically
result in an expected single value or an expected distribution. This
investigation is motivated by our goal of finding insights into students'
potential point- and set-like thinking about uncertainty and of shining light
on the limitations of those binary paradigms.Comment: 15 pages, 5 figures, accepted to Physical Review Physics Education
Researc
Lunar lander conceptual design
This paper is a first look at the problems of building a lunar lander to support a small lunar surface base. A series of trade studies was performed to define the lander. The initial trades concerned choosing number of stages, payload mass, parking orbit altitude, and propellant type. Other important trades and issues included plane change capability, propellant loading and maintenance location, and reusability considerations. Given a rough baseline, the systems were then reviewed. A conceptual design was then produced. The process was carried through only one iteration. Many more iterations are needed. A transportation system using reusable, aerobraked orbital transfer vehicles (OTV's) is assumed. These OTV's are assumed to be based and maintained at a low Earth orbit (LEO) space station, optimized for transportation functions. Single- and two-stage OTV stacks are considered. The OTV's make the translunar injection (TLI), lunar orbit insertion (LOI), and trans-Earth injection (TEI) burns, as well as midcourse and perigee raise maneuvers
The impact of new neutrino DIS and Drell-Yan data on large-x parton distributions
New data sets have recently become available for neutrino and antineutrino
deep inelastic scattering on nuclear targets and for inclusive dimuon
production in pp pd interactions. These data sets are sensitive to different
combinations of parton distribution functions in the large-x region and,
therefore, provide different constraints when incorporated into global parton
distribution function fits. We compare and contrast the effects of these new
data on parton distribution fits, with special emphasis on the effects at large
x. The effects of the use of nuclear targets in the neutrino and antineutrino
data sets are also investigated.Comment: 24 pages, 13 figure
Weak-scale phenomenology of models with gauge-mediated supersymmetry breaking
We study in some detail the spectral phenomenology of models in which
supersymmetry is dynamically broken and transmitted to the supersymmetric
partners of the quarks, leptons and gauge bosons, and the Higgs bosons
themselves, via the usual gauge interactions. We elucidate the parameter space
of what we consider to be the minimal model, and explore the regions which give
rise to consistent radiative electroweak symmetry breaking. We include the
weak-scale threshold corrections, and show how they considerably reduce the
scale dependence of the results. We examine the sensitivity of our results to
unknown higher-order messenger-sector corrections. We compute the superpartner
spectrum across the entire parameter space, and compare it to that of the
minimal supergravity-inspired model. We delineate the regions where the
lightest neutralino or tau slepton is the next-to-lightest supersymmetric
particle, and compute the lifetime and branching ratios of the NLSP. In
contrast to the minimal supergravity-inspired model, we find that the lightest
neutralino can have a large Higgsino component, of order 50%. Nevertheless, the
neutralino branching fraction to the gravitino and the light Higgs boson
remains small, < 10^{-4}, so the observation of such a decay would point to a
non-minimal Higgs sector.Comment: 22 pages, 16 figures, published versio
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