Structural Complexity and Decay in FLOSS Systems: An Inter-Repository Study

Past software engineering literature has firmly established that software architectures and the associated code decay over time. Architectural decay is, potentially, a major issue in Free/Libre/Open Source Software (FLOSS) projects, since developers sporadically joining FLOSS projects do not always have a clear understanding of the underlying architecture, and may break the overall conceptual structure by several small changes to the code base. This paper investigates whether the structure of a FLOSS system and its decay can also be influenced by the repository in which it is retained: specifically, two FLOSS repositories are studied to understand whether the complexity of the software structure in the sampled projects is comparable, or one repository hosts more complex systems than the other. It is also studied whether the effort to counteract this complexity is dependent on the repository, and the governance it gives to the hosted projects. The results of the paper are two-fold: on one side, it is shown that the repository hosting larger and more active projects presents more complex structures. On the other side, these larger and more complex systems benefit from more anti-regressive work to reduce this complexity

Dual position locking joint design for a medical walker

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 19).In this thesis we analyzed a joint created for a medical walker currently in the prototyping stage of development. The walker is designed to help a user stand up from a seated position. The joint holds two legs of the walker together in an 'x' shape. It must be able to lock in two positions and support the full weight of the user while he or she is getting up. We looked at four different locking mechanisms including a spring loaded pull pin, a friction bearing, a clutch, and an electronic solenoid. After weighing the pros and cons of each mechanism we recommend and present a design using the pull pin. In order to determine the strength and deflection of the loaded pin we modeled it both as a cantilevered beam, and a simply supported beam with three points of contact. We compared the hand calculations to FEA of solid models and found that modeling the pin as a simply supported beam is more accurate than the cantilever representation.by Eric M. Beecher.S.B

Privatization, Monopoly, and Structured Competition in the Water Industry: Is There a Role for Regulation

This paper provides an overview of privatization andcompetition in the water industry from a public policyvantage point. In particular, it contrasts the contractoperations model with the private ownership withregulation model. Advantages and disadvantages ofeach model are summarized. The monopolistic natureof the water industry and the potential need forstructured competition and economic regulation arediscussed

S-adenosyl-L-methionine: (S)-scoulerine 9-O-methyltransferase, a highly stereo- and regio-specific enzyme in tetrahydroprotoberberine biosynthesis

Suspension cultures of Berberis species are useful sources for the detection and isolation of a new enzyme which transfers the methyl group from S-adenosyl-L-methionine specifically to the 9-position of the (S)-enantiomer of scoulerine, producing (S)-tetrahydrocolumbamine. The enzyme was enriched 27-fold; it is not particle bound, has a pH optimum of 8.9, a molecular weight of 63 000 and shows a high degree of substrate specificity