Two mod-p Johnson filtrations

We consider two mod-p central series of the free group given by Stallings and Zassenhaus. Applying these series to definitions of Dennis Johnson's filtration of the mapping class group we obtain two mod-p Johnson filtrations. Further, we adapt the definition of the Johnson homomorphisms to obtain mod-p Johnson homomorphisms. We calculate the image of the first of these homomorphisms. We give generators for the kernels of these homomorphisms as well. We restrict the range of our mod-p Johnson homomorphisms using work of Morita. We finally prove the announced result of Perron that a rational homology 3-sphere may be given as a Heegaard splitting with gluing map coming from certain members of our mod-p Johnson filtrations.Comment: 35 pages, 1 figure; added referenc

Entertainment — The painful process of rethinking consent

The principal focus of this article will be upon an area of activity that has over the past decade seen a significant amount of growth in popularity, namely, the infliction of pain and/or injury for the purposes of entertainment, as pioneered by the US TV series and spin-off films Jackass and widely copied in the UK by, for example, Dirty Sanchez and the double act ‘The Pain Men’ on Channel 4’s programme, Balls of Steel. Until recently, and despite its popularity, this type of entertainment has attracted minimal comment from academics or practitioners on the legality of such conduct. However, a campaign begun by Mediawatch in 2010 has brought to prominence some interesting and potentially difficult questions about the ability of a person to consent to injuries caused in the name of entertainment. As the parameters of legally valid consent are both unstable and contested, it is unclear whether the types of conduct under discussion here are capable of being consented to and whether the associated reasons for inflicting the pain and sometimes injury provide any justification for what might otherwise be criminal behaviour. In analysing the application of the criminal law to instances of what is referred to here as ‘painful entertainment’ this article challenges traditional approaches to the categorisation of consensual activities and proposes a rethinking of how the law of offences against the person could be applied to novel situations

A metaphysical consideration of nature

Thesis (Ph.D.)--Boston Universit

Shuttle orbiter radar cross-sectional analysis

Theoretical and model simulation studies on signal to noise levels and shuttle radar cross section are described. Pre-mission system calibrations, system configuration, and postmission system calibration of the tracking radars are described. Conversion of target range, azimuth, and elevation into radar centered east north vertical position coordinates are evaluated. The location of the impinging rf energy with respect to the target vehicles body axis triad is calculated. Cross section correlation between the two radars is presented

Compacton Solutions in a Class of Generalized Fifth Order Korteweg-de Vries Equations

We study a class of generalized fifth order Korteweg-de Vries (KdV) equations which are derivable from a Lagrangian L(p,m,n,l) which has variable powers of the first and second derivatives of the field with powers given by the parameters p,m,n,l. The resulting field equation has solitary wave solutions of both the usual (non-compact) and compact variety ("compactons"). For the particular case that p=m=n+l, the solitary wave solutions have compact support and the feature that their width is independent of the amplitude. We discuss the Hamiltonian structure of these theories and find that mass, momentum, and energy are conserved. We find in general that these are not completely integrable systems. Numerical simulations show that an arbitrary compact initial wave packet whose width is wider than that of a compacton breaks up into several compactons all having the same width. The scattering of two compactons is almost elastic, with the left over wake eventually turning into compacton-anticompacton pairs. When there are two different compacton solutions for a single set of parameters the wider solution is stable, and this solution is a minimum of the Hamiltonian.Comment: 13 pages (8 embedded figures), RevTeX (plus macro), uses eps

Sketch-Based Interfaces to Support Collaborative Conceptual Design Learning

In order to gain a better understanding of online collaborative conceptual design processes this paper investigates how student designers make use of Lyceum, a shared virtual synchronous environment when engaged in conceptual design. The software enables users to talk to each other and share sketches when they are remotely located. The paper describes a novel methodology for observing and analysing collaborative design processes by adapting the concepts of grounded theory. Rather than concentrating on narrow aspects of the final artefacts, emerging 'themes' are generated that provide a broader picture of collaborative design process and context descriptions. Findings on the themes of 'grounding – mutual understanding' and 'support creativity' complement findings from other research, while important themes associated with 'near-synchrony' have not been emphasised in other research. From the study, a series of design recommendations are made for the development of tools to support online computer-supported collaborative work in design using a shared virtual environment

"Managed Care, Physician Incentives, and Norms of Medical Practice: Racing to the Bottom or Pulling to the Top?"

The incentive contracts that managed care organizations write with physicians have generated considerable controversy. Critics fear that if informational asymmetries inhibit patients from directly assessing the quality of care provided by their physician, competition will lead to a "race to the bottom" in which managed care plans induce physicians to offer only minimal levels of care. To analyze this issue we propose a model of competition between managed care organizations. The model serves for both physician incentive contracts and HMO product market strategies in an environment of extreme information asymmetry--physicians perceive quality of care perfectly, and patients don't perceive it at all. We find that even in this stark setting, managed care organizations need not race to the bottom. Rather, the combination of product differentiation and physician practice norms causes managed care organizations to race to differing market niches, with some providing high levels of care as a means of assembling large physician networks. We also find that relative physician practice norms, defined endogenously by the standards of medical care prevailing in a market, exert a "pull to the top" that raises the quality of care provided by all managed care organizations in the market. We conclude by considering the implications of our model for public policies designed to limit the influence of HMO incentive systems.

Technologies for aerobraking

Aerobraking is one of the largest contributors to making both lunar and Mars missions affordable. The use of aerobraking/aeroassist over all propulsive approaches saves as much as 60 percent of the initial mass required in low earth orbit (LEO); thus, the number and size of earth to orbit launch vehicles is reduced. Lunar transfer vehicles (LTV), which will be used to transport personnel and materials from LEO to lunar outpost, will aerobrake into earth's atmosphere at approximately 11 km/sec on return from the lunar surface. Current plans for both manned and robotic missions to Mars use aerocapture during arrival at Mars and at return to Earth. At Mars, the entry velocities will range from about 6 to 9.5 km/sec, and at Earth the return velocity will be about 12.5 to 14 km/sec. These entry velocities depend on trajectories, flight dates, and mission scenarios and bound the range of velocities required for the current studies. In order to successfully design aerobrakes to withstand the aerodynamic forces and heating associated with these entry velocities, as well as to make them efficient, several critical technologies must be developed. These are vehicle concepts and configurations, aerothermodynamics, thermal protection system materials, and guidance, navigation, and control systems. The status of each of these technologies are described, and what must be accomplished in each area to meet the requirements of the Space Exploration Initiative is outlined