Flow-Centric, Back-In-Time Debugging

Conventional debugging tools present developers with means to explore the run-time context in which an error has occurred. In many cases this is enough to help the developer discover the faulty source code and correct it. However, rather often errors occur due to code that has executed in the past, leaving certain objects in an inconsistent state. The actual run-time error only occurs when these inconsistent objects are used later in the program. So-called back-in-time debuggers help developers step back through earlier states of the program and explore execution contexts not available to conventional debuggers. Nevertheless, even back-in-time debuggers do not help answer the question, ``Where did this object come from?'' The Object-Flow Virtual Machine, which we have proposed in previous work, tracks the flow of objects to answer precisely such questions, but this VM does not provide dedicated debugging support to explore faulty programs. In this paper we present a novel debugger, called Compass, to navigate between conventional run-time stack-oriented control flow views and object flows. Compass enables a developer to effectively navigate from an object contributing to an error back-in-time through all the code that has touched the object. We present the design and implementation of Compass, and we demonstrate how flow-centric, back-in-time debugging can be used to effectively locate the source of hard-to-find bugs.

Nonlinear three-dimensional noise filter with low-dose CT angiography: effect on the detection of small high-contrast objects in a phantom model

To study the effect of a nonlinear noise filter on the detection of simulated endoleaks in a phantom with 80- and 100-kVp multidetector computed tomographic (CT) angiography.

Indirectly measuring evaluations of several attitude objects in relation to a neutral reference point

This article presents a new response time measure of evaluations, the Evaluative Movement Assessment (EMA). Two properties are verified for the first time in a response time measure: (a) mapping of multiple attitude objects to a single scale, and (b) centering that scale around a neutral point. Property (a) has implications when self-report and response time measures of attitudes have a low correlation. A study using EMA as an indirect measure revealed a low correlation with self-reported attitudes when the correlation reflected between-subjects differences in preferences for one attitude object to a second. Previously this result may have been interpreted as dissociation between two measures. However, when correlations from the same data reflected within-subject preference rank orders between multiple attitude objects, they were substantial (average r = .64). This result suggests that the presence of low correlations between self-report and response time measures in previous studies may be a reflection of methodological aspects of the response time measurement techniques. Property (b) has implications for exploring theoretical questions that require assessment of whether an evaluation is positive or negative (e.g., prejudice), because it allows such classifications in response time measurement to be made for the first time.