60,543 research outputs found
SurveyMan: Programming and Automatically Debugging Surveys
Surveys can be viewed as programs, complete with logic, control flow, and
bugs. Word choice or the order in which questions are asked can unintentionally
bias responses. Vague, confusing, or intrusive questions can cause respondents
to abandon a survey. Surveys can also have runtime errors: inattentive
respondents can taint results. This effect is especially problematic when
deploying surveys in uncontrolled settings, such as on the web or via
crowdsourcing platforms. Because the results of surveys drive business
decisions and inform scientific conclusions, it is crucial to make sure they
are correct.
We present SurveyMan, a system for designing, deploying, and automatically
debugging surveys. Survey authors write their surveys in a lightweight
domain-specific language aimed at end users. SurveyMan statically analyzes the
survey to provide feedback to survey authors before deployment. It then
compiles the survey into JavaScript and deploys it either to the web or a
crowdsourcing platform. SurveyMan's dynamic analyses automatically find survey
bugs, and control for the quality of responses. We evaluate SurveyMan's
algorithms analytically and empirically, demonstrating its effectiveness with
case studies of social science surveys conducted via Amazon's Mechanical Turk.Comment: Submitted version; accepted to OOPSLA 201
Towards a renewal of the propeller in aeronautics
The reasons for reconsidering the propeller for aircraft propulsion, the areas of application, and necessary developments are considered. Rising fuel costs and an increasing theoretical and experimental data base for turboprop engines have demonstrated that significant cost savings can be realized by the use of propellers. Propellers are well-suited to powering aircraft traveling at speeds up to Mach 0.65. Work is progressing on the development of a 150 seat aircraft which has a cruise speed of Mach 0.8, powered by a turboprop attached to an engine of 15,000 shp. Aeroelasticity analyses ae necessary in order to characterize the behavior of thin profile propfan blades, particularly to predict the oscillations through the entire functional range. High-power reducers must be developed, and the level of cabin noise must be controlled to less than 90 dB. Commercial applications are predicted for turboprops in specific instances
The Singularity in Generic Gravitational Collapse Is Spacelike, Local, and Oscillatory
A longstanding conjecture by Belinskii, Khalatnikov, and Lifshitz that the
singularity in generic gravitational collapse is spacelike, local, and
oscillatory is explored analytically and numerically in spatially inhomogeneous
cosmological spacetimes. With a convenient choice of variables, it can be seen
analytically how nonlinear terms in Einstein's equations control the approach
to the singularity and cause oscillatory behavior. The analytic picture
requires the drastic assumption that each spatial point evolves toward the
singularity as an independent spatially homogeneous universe. In every case,
detailed numerical simulations of the full Einstein evolution equations support
this assumption.Comment: 7 pages includes 4 figures. Uses Revtex and psfig. Received
"honorable mention" in 1998 Gravity Research Foundation essay contest.
Submitted to Mod. Phys. Lett.
Evolution of the Fermi surface of BiTeCl with pressure
We report measurements of Shubnikov-de Haas oscillations in the giant Rashba
semiconductor BiTeCl under applied pressures up to ~2.5 GPa. We observe two
distinct oscillation frequencies, corresponding to the Rashba-split inner and
outer Fermi surfaces. BiTeCl has a conduction band bottom that is split into
two sub-bands due to the strong Rashba coupling, resulting in two
spin-polarized conduction bands as well as a Dirac point. Our results suggest
that the chemical potential lies above this Dirac point, giving rise to two
Fermi surfaces. We use a simple two-band model to understand the pressure
dependence of our sample parameters. Comparing our results on BiTeCl to
previous results on BiTeI, we observe similar trends in both the chemical
potential and the Rashba splitting with pressure.Comment: 6 pages, 5 figure
Prioritized Garbage Collection: Explicit GC Support for Software Caches
Programmers routinely trade space for time to increase performance, often in
the form of caching or memoization. In managed languages like Java or
JavaScript, however, this space-time tradeoff is complex. Using more space
translates into higher garbage collection costs, especially at the limit of
available memory. Existing runtime systems provide limited support for
space-sensitive algorithms, forcing programmers into difficult and often
brittle choices about provisioning.
This paper presents prioritized garbage collection, a cooperative programming
language and runtime solution to this problem. Prioritized GC provides an
interface similar to soft references, called priority references, which
identify objects that the collector can reclaim eagerly if necessary. The key
difference is an API for defining the policy that governs when priority
references are cleared and in what order. Application code specifies a priority
value for each reference and a target memory bound. The collector reclaims
references, lowest priority first, until the total memory footprint of the
cache fits within the bound. We use this API to implement a space-aware
least-recently-used (LRU) cache, called a Sache, that is a drop-in replacement
for existing caches, such as Google's Guava library. The garbage collector
automatically grows and shrinks the Sache in response to available memory and
workload with minimal provisioning information from the programmer. Using a
Sache, it is almost impossible for an application to experience a memory leak,
memory pressure, or an out-of-memory crash caused by software caching.Comment: to appear in OOPSLA 201
Constructing compact 8-manifolds with holonomy Spin(7) from Calabi-Yau orbifolds
Compact Riemannian 7- and 8-manifolds with holonomy G(2) arid Spin(7) were first constructed by the author in 1994-5, by resolving orbifolds T-7/Gamma and T-8/Gamma. This paper describes a new construction of compact 8-manifolds with holonomy Spin(7). We start with a Calabi-Yau 4-orbifold Y with isolated singularities of a special kind. We divide by an antiholomorphic involution a of Y to get a real 8-orbifold Z = Y/. Then we resolve tire singularities of Z to get a compact 8-manifold M, which has metrics with holonomy Spin(7). Manifolds constructed in this way typically have large fourth Betti number b(4)(M).</sigma
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