No abstract

Through the use of conditional compilation and related tools, many software projects can be used to generate a huge number of related programs. The problem of typing such variational software is difficult. The brute-force strategy of generating all variants and typing each one individually is: (1) usually infeasible for efficiency reasons and (2) produces results that do not map well to the underlying variational program. Recent research has focused mainly on efficiency and addressed only the problem of type checking. In this work we tackle the more general problem of variational type inference and introduce variational types to represent the result of typing a variational program. We introduce the variational lambda calculus (VLC) as a formal foundation for research on typing variational programs. We define a type system for VLC in which VLC expressions are mapped to correspondingly variational types. We show that the type system is correct by proving that the typing of expressions is preserved over the process of variation elimination, which eventually results in a plain lambda calculus expression and its corresponding type. We identify a set of equivalence rules for variational types and prove that the type unification problem modulo these equivalence rules is unitary and decidable; we also present a sound and complete unification algorithm. Based on the unification algorithm, the variational type inference algorithm is an extension of algorithm W . We show that it is sound and complete and computes principal types. We also consider the extension of VLC with sum types, a necessary feature for supporting variational data types, and demonstrate that the previous theoretical results also hold under this extension. Finally, we characterize the complexity of variational type inference and demonstrate the efficiency gains over the brute-force strategy.

To meet the energy demand for flexible and miniaturized green electronics, it is highly desirable to develop a portable, cost-effective, lightweight, and sustainable power source through a facile and environment friendly approach. Herein, we report a portable, flexible, and low-cost selfcharging power system (SCPS) consisting of a paper-based triboelectric nanogenerator (P-TENG) with high output power density as the energy harvester and a paper-based supercapacitor (P-SC) with a great areal capacitance as the energy storage device. A cellulose paper/polypyrrole composite with a low sheet resistance of 7.8 Ω sq −1 replaced the conventional metal electrodes and positive friction material in the P-TENG, as well as the capacitive material in the P-SC. The portable SCPS is capable of driving various miniaturized electronics such as a temperature/humidity indicator, thus demonstrating its potential as a sustainable power source for flexible and miniaturized green electronics.

Our aim in this study was to probe into the factors of team members' team commitment in order to determine if members' teamwork behaviors significantly influence their trust, and if the members' perception of team support influences their attitude or behavior within a team. A total of 548 questionnaires were distributed to teams participating in competitions, and 206 valid samples were collected (rate of return = 38%). The results of structural equation modeling showed that teamwork behaviors, trust, and perceived team support significantly influenced team commitment, teamwork behaviors significantly influenced trust among the members, and perceived team support significantly influenced teamwork behaviors, trust, and team commitment.