JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The National Institute of Environmental Health Sciences (NIEHS) andBrogan & Partners are collaborating with JSTOR to digitize, preserve and extend access to Environmental Health Perspectives.Five statistical procedures were used to partial the correlation between waterborne asbestos and digestive site cancer for the putative effects of population density. These include: analysis based on a data subset with roughly homogeneous population density; standard residual analysis (partial correlation); conditional probability integral transformation; analysis based upon ranked data, and use of logarithmic transformation.Nonparametric regression graphical techniques are applied to examine the nature or shape of the asbestos-cancer dose-response curve. Evidence is presented that suggests that there is considerable difference between analyses involving nonhigh-density tracts and non-San Francisco tracts. Evidence is also presented that the modal-type nonparametric regression curve forks or bifurcates when adjustment is made for population density.

The literature describes several applications where Aphron fluid technology has been applied in both drilling and re-entry scenarios and includes an extensive description of how this fluid system works. A highly efficient leak-off prevention mechanism makes aphron based fluid systems beneficial for certain completion and workover applications as well, where formation damage could be avoided by the practical elimination of fluid-fluid or fluid-rock interaction or where simply the workover objectives can be achieved by obtaining efficient circulation of fluid to surface. Completion and workover applications for this fluid system have not been extensively reported. This paper reviews three applications of Aphron fluid technology in different completion and workover scenarios. The selected cases were reviewed to present some of the technical and operational lessons learned and to some extent discuss the observed formation cleanup behavior. The following three applications were reviewed: completion of a dual string sour gas well, using an oil based aphron system for kill fluid, with practically no kill fluid loss to a hydraulically fractured formation; the completion of additional zones within a depleted dolomitic limestone formation on two wells where the method of Aphron fluid placement was found to significantly affect fluid losses; and finally, the enabling of the provision of annular pressure support at pressures which approached the hydraulic fracture opening pressure of a shallow zone while hydraulically fracturing a deeper zone through tubing with a packer. Introduction The mechanisms by which the Aphron fluid system operates make it a reliable tool for certain completion and workover applications. These mechanisms have been described extensively in the literature (Brookey 1998; Ivan et al 2001; Growcock et al. 2005a; Catalin et al. 2002; Hoff, O'Connor and Growcock 2005). Moreover, the presentation of field performance data for Aphron fluids in drilling and re-entry operations is also extensively published (Ivan et al. 2001; White et al. 2003; Brookey et al. 2003; Rea et al. 2003 and Kinchen et al. 2001). Lessons learned from the performance of Aphron fluids in a wide range of applications have caused a specific profile to evolve for the effective use of this fluid technology. Brookey (1998) showed that the high low shear rate viscosity (HLSRV) of the Aphron fluid system, which provides the proper environment for aphron bubble formation and survival, also provides a high resistance to flow under low shear conditions, which significantly inhibits initial fluid loss to the formation. Brookey (1998), supported by Ramirez et al. (2002) showed that the creation of aphron aggregates is an effective filtrate control mechanism which further reduces fluid loss. Formation damage prevention is attributed to the inert gas which makes up the majority of an aphron aggregate, combined with the limited amount of fluid invasion into a potential leakoff zone. Adverse fluid-fluid and fluid-rock reactions are prevented because the completion and workover fluid is not available as a reactant or contaminant.

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A description of ISIS can be found in [7]. In this paper we describe a fundamental element of a new system called HORUS 1 being built at Cornell. HORUS has evolved from ISIS after much experience with building practical fault-tolerant distributed systems.This work was motivated by a trend in the use of ISIS process groups that has become apparent over the last eight years. The process group paradigm is popular with ISIS applications programmers; almost every major application written using ISIS makes extensive use of process groups. In their original design, process groups were intended as a coarse grain transport mechanism for communicating with multiple processes. Process groups were used to represent a replicated service. However, the paradigm has proven popular for more fine grain uses. Over the last few years applications written using ISIS have used process groups to represent objects rather than services. This trend has impacted the original design in several ways and has lead us to focus our attention on providing light-weight process groups.The architecture of HORUS was influenced by microkernel design concepts, in which several light-weight mechanisms are provided in user space. The most obvious of these is the light-weight process or thread abstraction [8,15]. Another well-known, older abstraction is memory allocation. These abstractions not only allow easier resource management by sharing most of a core environment, but also provide a portable interface across different environments.The basic idea behind the light-weight process group (LWG) abstraction is that many LWGs are mapped to a single core group (or set of core groups) as implemented by the kernel of HORUS. Thus, these LWGs share the same security environment (much like threads share the same address space), and the same failure model, while their messages are multiplexed over a single core group transport. The benefit of this approach is that membership changes to the core group automatically affect large numbers of LWGs, amortizing the cost of maintaining membership information over what the application considers a large number of independent groups. The ISIS system lacks such a facility, forcing many application programmers to develop equivalent mechanisms.We have built a prototype of LWGs on top of ISIS V3.0.6 and the initial results show significant improvements in performance. In particular, the LWG subsystem allows LWGs to share the same failure detection protocol execution thereby resulting in faster reaction to member failures and reduced network load. Execution times for typical group operations are also improved: the initial prototype has a speed-up factor of nine for the group create operation (the resulting speed is about SIn Egyptian mythology, HORUS is the son of ISIS. TRENDS IN THE USE OF PROCESS GROUPS3 30 ms), and even higher speed-ups for group joins and leaves.To motivate the problem, we present several examples of how fine grain process groups help solve problems present in distributed applications. We then briefly presen...

This report has been reviewed by the Information Office (0!) and is releasable to the National Technical Information Service (NTIS). At NTIS, it will be available to the general public, including foreign nations. This technical report has been reviewed and is approved for publication. FOR THE COMMANDER