844 research outputs found
Relatively Complete Counterexamples for Higher-Order Programs
In this paper, we study the problem of generating inputs to a higher-order
program causing it to error. We first study the problem in the setting of PCF,
a typed, core functional language and contribute the first relatively complete
method for constructing counterexamples for PCF programs. The method is
relatively complete in the sense of Hoare logic; completeness is reduced to the
completeness of a first-order solver over the base types of PCF. In practice,
this means an SMT solver can be used for the effective, automated generation of
higher-order counterexamples for a large class of programs.
We achieve this result by employing a novel form of symbolic execution for
higher-order programs. The remarkable aspect of this symbolic execution is that
even though symbolic higher-order inputs and values are considered, the path
condition remains a first-order formula. Our handling of symbolic function
application enables the reconstruction of higher-order counterexamples from
this first-order formula.
After establishing our main theoretical results, we sketch how to apply the
approach to untyped, higher-order, stateful languages with first-class
contracts and show how counterexample generation can be used to detect contract
violations in this setting. To validate our approach, we implement a tool
generating counterexamples for erroneous modules written in Racket.Comment: In Proceedings of the 36th annual ACM SIGPLAN conference on
Programming Language Design and Implementation, Portland, Oregon, June 201
A microfabricated sensor for thin dielectric layers
We describe a sensor for the measurement of thin dielectric layers capable of
operation in a variety of environments. The sensor is obtained by
microfabricating a capacitor with interleaved aluminum fingers, exposed to the
dielectric to be measured. In particular, the device can measure thin layers of
solid frozen from a liquid or gaseous medium. Sensitivity to single atomic
layers is achievable in many configurations and, by utilizing fast, high
sensitivity capacitance read out in a feedback system onto environmental
parameters, coatings of few layers can be dynamically maintained. We discuss
the design, read out and calibration of several versions of the device
optimized in different ways. We specifically dwell on the case in which
atomically thin solid xenon layers are grown and stabilized, in cryogenic
conditions, from a liquid xenon bath
Obesity: A Biobehavioral Point of View
Excerpt: If you ask an overweight person, “Why are you fat?’, you will, almost invariably, get the answer, “Because 1 eat too much.” You will get this answer in spite of the fact that of thirteen studies, six find no significant differences in the caloric intake of obese versus nonobese subjects, five report that the obese eat significantly less than the nonobese, and only two report that they eat significantly more
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