Asymptotic Properties of the Empirical Spatial Extremogram

The extremogram, proposed by Davis and Mikosch (2008), is a useful tool for measuring extremal dependence and checking model adequacy in a time series. We define the extremogram in the spatial domain when the data is observed on a lattice or at locations distributed as a Poisson point process in d-dimensional space. Under mixing and other conditions, we establish a central limit theorem for the empirical spatial extremogram. We show these conditions are applicable for max-moving average processes and Brown-Resnick processes and illustrate the empirical extremogram's performance via simulation. We also demonstrate its practical use with a data set related to rainfall in a region in Florida.Comment: 30 pages, 6 fugure

Agile Product Testing with Constrained Prototypes

The means to acquire reliable functional information is a critical factor that differentiates product development time and cost. Thanks to advances in solid freeform fabrication techniques, industries can produce geometrically complex parts within dramatically reduced time and cost. Even though industries can save significant efforts by performing functional tests rapid prototypes, they still prefer full-scale product tests, especially in later design phases, due to inherent limitations in traditional similarity methods (TSM). This paper describes a new method to perform reliable functional tests with rapid prototypes that cannot be properly handled by the TSM.Mechanical Engineerin

Gravitational waves from BH-NS binaries: Effective Fisher matrices and parameter estimation using higher harmonics

Inspiralling black hole-neutron star (BH-NS) binaries emit a complicated gravitational wave signature, produced by multiple harmonics sourced by their strong local gravitational field and further modulated by the orbital plane's precession. Some features of this complex signal are easily accessible to ground-based interferometers (e.g., the rate of change of frequency); others less so (e.g., the polarization content); and others unavailable (e.g., features of the signal out of band). For this reason, an ambiguity function (a diagnostic of dissimilarity) between two such signals varies on many parameter scales and ranges. In this paper, we present a method for computing an approximate, effective Fisher matrix from variations in the ambiguity function on physically pertinent scales which depend on the relevant signal to noise ratio. As a concrete example, we explore how higher harmonics improve parameter measurement accuracy. As previous studies suggest, for our fiducial BH-NS binaries and for plausible signal amplitudes, we see that higher harmonics at best marginally improve our ability to measure parameters. For non-precessing binaries, these Fisher matrices separate into intrinsic (mass, spin) and extrinsic (geometrical) parameters; higher harmonics principally improve our knowledge about the line of sight. For the precessing binaries, the extra information provided by higher harmonics is distributed across several parameters. We provide concrete estimates for measurement accuracy, using coordinates adapted to the precession cone in the detector's sensitive band.Comment: 19 pages, 11 figure

Giant Cell Tumor of Bone: Documented Progression over 4 Years from Its Origin at the Metaphysis to the Articular Surface.

The exact location of origin for giant cell tumors of bone (GCTB) remains controversial, as lesions are not routinely imaged early but rather late when the tumor is large and clinically symptomatic. At the time of diagnosis, GCTB are classically described as lucent, eccentric lesions with nonsclerotic margins, located within the epiphysis to a greater extent than the metaphysis. Here we present a case of a biopsy proven GCTB initially incidentally seen on MRI as a small strictly metaphyseal lesion, which over the course of several years expanded across a closed physis to involve the epiphysis and abut the articular surface/subchondral bone plate

Building a continuum of care through boundary spanning and organizational change : corrections and HIV/AIDS supported housing in Massachusetts

Thesis (M.C.P.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 2000.Includes bibliographical references (leaves 103-105).In the current context of federal devolution, practitioners in supported housing systems and other diverse organizational contexts increasingly face the challenge of fostering coordination and managing conflicts of values and perspectives within organizations tied together in networks. Such coordination is problematic, just as conflicts are inevitable, within such networks and other inter-organizational systems because of the historically evolved structures and specialization of organizations. These specialized structures or 'domains' imply certain boundaries defining what activities can be considered internally coherent and consistent with organizational goals. Yet it is too often the case that these structures are "incomplete" in fulfilling all of society's needs. In situations where this is the case, "'gaps" can be said to exist between the domains of two organizations, and can have serious consequences for individuals and communities proximate to them. In this light, homelessness as a result of de-institutionalization, or unemployment among post-secondary school youth, may be seen as social problems generated by structural gaps between organizational domain boundaries. Solving these problems, I argue, requires that practitioners undertake roles in their own organizations that are 'boundary spanning.' Boundary spanning becomes a means of building ties across vast inter-organizational distances, inventing programmatic solutions to structural problems, and creating organizational change. In this thesis, I examine organizational change as it occurred within a specific interorganizational network of providers and institutions: a continuum of care for ex-offenders living with HIV/AIDS in Massachusetts. The case presented here is one in which I am both an observer/researcher and a practitioner. Reflecting upon the activities of myself and others working to expand access to HIV/AIDS supported and other housing opportunities, I analyze the attributes of our boundary spanning roles as examples of successful practice in creating organizational change towards our goal of homelessness prevention among ex offenders living with HIV/AIDS. From these attributes emerges a theory of practice for boundary spanning towards organizational change.by Richard S. Cho.M.C.P

Scaling laws for light weight optics, studies of light weight mirrors mounting and dynamic mirror stress, and light weight mirror and mount designs

Scaling laws for light-weight optical systems are examined. A cubic relationship between mirror diameter and weight has been suggested and used by many designers of optical systems as the best description for all light-weight mirrors. A survey of existing light-weight systems in the open literature was made to clarify this issue. Fifty existing optical systems were surveyed with all varieties of light-weight mirrors including glass and beryllium structured mirrors, contoured mirrors, and very thin solid mirrors. These mirrors were then categorized and weight to diameter ratio was plotted to find a best curve for each case. A best fitting curve program tests nineteen different equations and ranks a goodness-to-fit for each of these equations. The resulting relationship found for each light-weight mirror category helps to quantify light-weight optical systems and methods of fabrication and provides comparisons between mirror types

EFFECTS OF THE CANADIAN WHEAT BOARD ON THE U.S. WHEAT INDUSTRY

The practices of the Canadian Wheat Board (CWB) are an important issue in U.S. - Canada trade disputes and WTO negotiations. This study analyzes the CWB?s effect on U.S. producers by reviewing findings from previous research and developing models to analyze CWB wheat exports to the United States and the competitive structure of Canadian wheat exports in the world market. U.S. grain producers could benefit from the removal of the CWB as the United States could become more competitive in export markets. However, elimination of the CWB could also result in an increase in Canadian wheat exports to the United States as Canadian producers near the border could sell directly to the United States to take advantage of market opportunities. The net effect is difficult to quantify. The net benefits may be significant in the short run, but reduced significantly in the long run. Similarly, if Canada reforms its wheat board by eliminating trade-distorting subsidies, the United States may increase its exports and Canadian exports to the United States may increase. The net benefits from reforming the CWB could be greater than those from eliminating it. However, the United States could benefit the most from complete elimination of state trading enterprises (STEs), since they have elements distorting trade flows and the United States competes with several STEs in the world wheat market.Canadian Wheat Board, state trading enterprises, price discrimination, wheat exports, Crop Production/Industries, International Relations/Trade,