1,145 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
TRANSIENT BUBBLE GROWTH IN A HOMOGENEOUS REACTOR
A mechanism for shutting off a power excursion in a homogeneotns reactor by the rapid formation of bubbles was investigated. Equations are derived which give upper and lower bounds for the radius of a bubble, as a function of time, under conditions present in a reactor. Deduction of the bubble nuclei growth rate from observations of void volume and pressure can be made. (auth
Insulin secretory and antidiabetic actions of Heritiera fomes bark together with isolation of active phytomolecules
In folklore, Heritiera fomes (H. fomes) has been extensively used in treatment of various ailments such as diabetes, cardiac and hepatic disorders. The present study aimed to elucidate the antidiabetic actions of hot water extract of H. fomes (HWHF), including effects on insulin release from BRIN BD11 cells and isolated mouse islets as well as glucose homeostasis in high-fat-fed rats. Molecular mechanisms underlying anti-diabetic activity along with isolation of active compounds were also evaluated. Non-toxic concentrations of HWHF stimulated concentration-dependent insulin release from isolated mouse islets and clonal pancreatic β-cells. The stimulatory effect was potentiated by glucose and isobutyl methylxanthine (IBMX), persisted in presence of tolbutamide or a depolarizing concentration of KCl but was attenuated by established inhibitors of insulin release such as diazoxide, verapamil, and Ca(2+) chelation. HWHF caused depolarization of the β-cell membrane and increased intracellular Ca(2+). The extract also enhanced glucose uptake and insulin action in 3T3-L1 differentiated adipocytes cells and significantly inhibited in a dose-dependent manner starch digestion, protein glycation, DPP-IV enzyme activity, and glucose diffusion in vitro. Oral administration of HWHF (250 mg/5ml/kg b.w.) to high-fat fed rats significantly improved glucose tolerance and plasma insulin responses and it inhibited plasma DPP-IV activity. HWHF also decreased in vivo glucose absorption and intestinal disaccharidase activity while increasing gastrointestinal motility and unabsorbed sucrose transit. Compounds were isolated from HWHF with similar molecular weights to quercitrin (C(21) H(20) O(11)) ranging from 447.9 to 449.9 Da which stimulated the insulin release in vitro and improved both glucose tolerance and plasma insulin responses in mice. In conclusion, H. fomes and its water-soluble phytochemicals such as quercitrin may exert antidiabetic actions mediated through a variety of mechanisms which might be useful as dietary adjunct in the management of type 2 diabetes
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
- …