Soft Contract Verification

Behavioral software contracts are a widely used mechanism for governing the flow of values between components. However, run-time monitoring and enforcement of contracts imposes significant overhead and delays discovery of faulty components to run-time. To overcome these issues, we present soft contract verification, which aims to statically prove either complete or partial contract correctness of components, written in an untyped, higher-order language with first-class contracts. Our approach uses higher-order symbolic execution, leveraging contracts as a source of symbolic values including unknown behavioral values, and employs an updatable heap of contract invariants to reason about flow-sensitive facts. We prove the symbolic execution soundly approximates the dynamic semantics and that verified programs can't be blamed. The approach is able to analyze first-class contracts, recursive data structures, unknown functions, and control-flow-sensitive refinements of values, which are all idiomatic in dynamic languages. It makes effective use of an off-the-shelf solver to decide problems without heavy encodings. The approach is competitive with a wide range of existing tools---including type systems, flow analyzers, and model checkers---on their own benchmarks.Comment: ICFP '14, September 1-6, 2014, Gothenburg, Swede

Size-Change Termination as a Contract

Termination is an important but undecidable program property, which has led to a large body of work on static methods for conservatively predicting or enforcing termination. One such method is the size-change termination approach of Lee, Jones, and Ben-Amram, which operates in two phases: (1) abstract programs into "size-change graphs," and (2) check these graphs for the size-change property: the existence of paths that lead to infinite decreasing sequences. We transpose these two phases with an operational semantics that accounts for the run-time enforcement of the size-change property, postponing (or entirely avoiding) program abstraction. This choice has two key consequences: (1) size-change termination can be checked at run-time and (2) termination can be rephrased as a safety property analyzed using existing methods for systematic abstraction. We formulate run-time size-change checks as contracts in the style of Findler and Felleisen. The result compliments existing contracts that enforce partial correctness specifications to obtain contracts for total correctness. Our approach combines the robustness of the size-change principle for termination with the precise information available at run-time. It has tunable overhead and can check for nontermination without the conservativeness necessary in static checking. To obtain a sound and computable termination analysis, we apply existing abstract interpretation techniques directly to the operational semantics, avoiding the need for custom abstractions for termination. The resulting analyzer is competitive with with existing, purpose-built analyzers

Naltrexone and Bupropion Combination: A New Promising Therapy for Long Term Weight Loss

Background: Being overweight or obese is a growing health concern not just in the United States, but worldwide. In 2009-2010, 2 out of 3 adults are considered overweight or obese, and 1 out of 3 adults are considered obese in the U.S. Overweight and obesity acts as a major risk in cardiovascular diseases, diabetes, cancer, and arthritis, and carries an overwhelming economic burden. With a 5-10% weight loss, patients can benefit from reduced metabolic and cardiovascular risks; however, this is a challenging goal to achieve and maintain. Naltrexone is a medication commonly used for opioid addiction and alcohol dependence, and bupropion is commonly used for depression. Separately, these two medications have been shown to reduce weight weakly; this review aims to evaluate the benefits of naltrexone and bupropion used in combination for weight loss. Method: An exhaustive literature search using the search engines Medline-OVID, CINAHL, and Web of Science combining keywords naltrexone, bupropion, and weight loss was conducted. Eligible criteria include research with naltrexone and bupropion combination therapy comparing to mono-therapy, other weight loss therapy, or placebo. Only randomized controlled trials (RTC) were selected for maximum validity. Excluded from this analysis were articles with animal subjects or other languages except English. Selected articles were assessed for quality using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE). Results: Three articles met the criteria and were included in this systematic review. In Greenway et al, enrolled were 419 participants in this randomized, placebo and monotherapy controlled, double blind trial. In general, at week 24, participants in most combination drug groups showed statistically significant weight loss compared to monotherapy and placebo. In the COR-I study, 1742 participants enrolled in this randomized, double blind, placebo controlled phase 3 trial. At week 56, mean change in body weight was statistically significant in combination drug groups compared to placebo. In the COR-II study, a randomized, double blind, placebo controlled study of 1,496 participants, the combination drug group achieved and maintained weight loss at a more pronounced rate than placebo group at the completion of the 28 week trial. Conclusion: Naltrexone and bupropion combination therapy shows promising evidence as a drug therapy for long-term weight loss as evidenced by these studies. While this combination therapy is a safe alternative, further research is needed to assess naltrexone and bupropion combination therapy against other current FDA approved weight loss therapy and its effects on patients with complicated obesity

How do students engage with computer-based assessments: impact of study breaks on intertemporal engagement and pass rates

Study breaks and exam revision weeks are increasingly embedded in learning design under the assumption that students would make use of this time to catch up with their study or prepare for upcoming assessment tasks. However, there remains a paucity of empirical evidence to evaluate to what extent the implementation of study breaks, preparation and exam revision weeks impact students’ engagement and academic performance. By applying learning analytics in a Computer-Based Assessment (CBA) setting, this study investigates how study break weeks and assessment preparation weeks impacted the odds of passing a module using a mixed effect logistic regression on 123,916 undergraduate students in 205 modules over several semesters from 2015-2017 at the Open University. Furthermore, we investigated the intertemporal characteristics of student engagement during preparation weeks for a final assessment in an Introductory Business course over three semesters. A mixed-effect logistic regression was used to model behavioural engagement of 3,385 students on the VLE (i.e. click counts) over three semesters during the assessment preparation weeks. Our findings indicated a positive association between study breaks and the odds of passing a course, while there was no statistically significant effect in relation to the number of assessment preparation and revision weeks. Analysis of behavioural engagement on the VLE suggested that there was a higher proportion of passed students remained active during preparation and exam revision weeks compared to failed students. Compared to the pass group, the fail group also exhibited a stronger pattern of procrastination. This study offers new insights that could help institution management and course designer to evaluate the efficacy of using of study breaks and exam preparation weeks to improve student retention

CFD Analysis of Airflow for Capture Efficiency of Residential Range-Hoods

HVAC ventilation systems play an important role in maintaining healthy indoor air quality levels by removing air pollutants to the outdoors. In order to evaluate the ability of domestic range-hoods to remove contaminated air from kitchen environments, the American Society for Testing and Materials (ASTM) developed the ASTM-E3087 standard (Standard Test Method for Measuring Capture Efficiency of Domestic Range-Hoods). This standard was used to build and develop a well-instrumented test chamber at the RELLIS Energy Efficiency Laboratory (REEL) for the purpose of measuring and evaluating the capture efficiency (CE) of different range-hoods following procedures that comply with the standard. A shortcoming of evaluating range-hood capture efficiency by using the test facility is that the experiments are time consuming. In addition, parts of the test facility and the ASTM standard procedures, may in fact need further evaluations for improvements. Therefore, this study focused on designing and developing a computational fluid dynamics (CFD) model based on the CE test procedures specified in ASTM-E3087, with the goal of simulating the space environment and the boundary conditions of the actual test chamber located at REEL. An important step before the CFD model can be applied is validating it, which means showing that there is good agreement between the simulation model output and experimental measurements of CE. In support of this study and the above CFD model validation, multiple CE experiments were conducted on a typical residential kitchen range-hood. For this purpose, a Venmar under-cabinet range-hood, Inspira IU600ES30BL, was selected for testing and modeling. These tests and simulations were performed at three different experimental test conditions, representing three fan operating speeds and thus different air flowrates (in CFM, cubic-feet-per-minute) and CO2 gas injection rates (in standard l/m, liters-per-minute). During each experimental test, CO2 concentrations were measured using three sensors placed at three different locations according to the ASTM E3087-18 standard. These measured CO2 concentrations were in turn used to calculate the capture efficiencies at the special test conditions. Next, the CFD simulation model was used to predict values of CO2 concentrations at the same three test conditions, followed by calculations of CE values. Of special importance are the CE differences between the results of the CFD simulations and the experiments for the three cases, which were found to be 0.01%, 2.73%, and 0.14%. Based on the closeness of these results, the CFD model was consider validated, so that it could in fact be used as a tool for analyzing and evaluating CE methodologies and test facilities. Once the CFD model was validated, it was then used to analyze the distribution of CO¬2 concentration inside the chamber for the purpose of evaluating the optimum chamber location for CO2 trace gas sampling, based on a location where the sample value is representative of the chamber as a whole. The results of this evaluation showed that the sampling location that is specified in the ASTM-E3087 standard is in fact in a region of uniform CO2 distributions, meaning the standard location is representative of the chamber as a whole. Quantitatively, the capture efficiency at the standard-specified location is about 3% to 5% higher than those CE values based on sampling locations near the walls and door of the chamber. A second study that made use of the validated CFD simulation model was to investigate the effect that the volume of the test chamber has on CE testing and measurements. This investigation was extremely important because the ASTM-E3087 standard does not specify exact chamber dimensions or volumes, and tests performed on the same range-hood at the same test conditions in two different facilities of different volumes produced significantly different CE values, which was a surprising outcome. Using the CFD simulation model, CE values were determined for several chambers with different volumes, and the results showed that measured capture efficiency decreases as the volume of the chamber increases. In one example, as the volume was decreased by 65%, the capture efficiency went up by as much as 27 %. This particular example of a volume decrease was a comparison of the actual REEL test chamber and the smaller standard minimum-dimensions chamber specified in ASTM-E3087, which is a volume lower limit. Based on this important result, it is highly recommended that the standard specifies an exact chamber size for CE tests rather than specifying a minimum-size chamber