Set Of Boundaries Research Articles

Collimation of plasma-produced x-rays by spherical crystals: Ray-tracing simulations and experimental results

Ray-tracing simulations, validated by experimental results, demonstrate that high intensity collimated x-ray beams can be produced from an isotropic x-ray source. A spherically bent mica crystal was used to collimate and monochromatize x rays emitted by a femtosecond laser-produced plasma. The result is a short pulse x-ray beam with a high degree of collimation (less than 1 mrad divergence), good spectral resolution (10−2<Δλ/λ<10−4), and tunability over a wide spectral range. The role of the experimental parameters in the resulting beam divergence is thoroughly analyzed by ray-tracing modeling. These simulations are validated by test experiments. The ray-tracing calculations define a set of boundaries in the experimental parameters, which will guarantee the achievement of collimated beams better than 1 mrad in further experiments.

Boundaries in the Drosophila wing imaginal disc organize vein-specific genetic programs.

Previous studies have suggested that vein primordia in Drosophila form at boundaries along the A/P axis between discrete sectors of the larval wing imaginal disc. Genes involved in initiating vein development during the third larval instar are expressed either in narrow stripes corresponding to vein primordia or in broader 'provein' domains consisting of cells competent to become veins. In addition, genes specifying the alternative intervein cell fate are expressed in complementary intervein regions. The regulatory relationships between genes expressed in narrow vein primordia, in broad provein stripes and in interveins remains unknown, however. In this manuscript, we provide additional evidence for veins forming in narrow stripes at borders of A/P sectors. These experiments further suggest that narrow vein primordia produce secondary short-range signal(s), which activate expression of provein genes in a broad pattern in neighboring cells. We also show that crossregulatory interactions among genes expressed in veins, proveins and interveins contribute to establishing the vein-versus-intervein pattern, and that control of gene expression in vein and intervein regions must be considered on a stripe-by-stripe basis. Finally, we present evidence for a second set of vein-inducing boundaries lying between veins, which we refer to as paravein boundaries. We propose that veins develop at both vein and paravein boundaries in more 'primitive' insects, which have up to twice the number of veins present in Drosophila. We present a model in which different A/P boundaries organize vein-specific genetic programs to govern the development of individual veins.

An adaptive finite element procedure for the image segmentation problem

The image segmentation problem in computer vision is considered. Given a two-dimensional domain D and a function defined on it (the original image), the problem is to obtain a 'cartoon' associated with this function, namely to find a set of inner boundaries which divide D into subdomains (objects) in an optimal way. The optimality criterion used here is given by the Mumford-Shah (MS) and Blake-Zisserman model, which leads to a strongly non-linear problem. Related problems appear in multiphase continuum mechanics. An iterative procedure based on an h-adaptive finite element method is proposed for the solution of this problem. The mesh adaptivity enables an efficient solution technique, with the use of basic coarse discretization and a few local regions of high resolution where needed.

Hierarchical Modeling in Geographic Information Systems: Population Interpolation over Incompatible Zones

When inference is desired regarding some attribute of a particular geographic region, it often happens that data are not directly available for that region. However, it may be that data are available over the same general area, but reported according to a different set of regional boundaries. Recently, powerful computer programs called geographic information systems (GIS's) have enabled the simultaneous display of such "misaligned" datasets, but these systems address only the descriptive needs of the user, leaving the inferential goal unmet. In this article we describe a hierarchical Bayes approach, implemented via Markov chain Monte Carlo methods, which provides a natural solution to this problem through its ability to sensibly combine information from several sources of data and available prior information. After presenting a simple, idealized example to illustrate the method, we apply it to a dataset on leukemia rates in Tompkins County, New York, wherein we use block group-level covariate information to interpolate disease counts given only aggregate (census tract-level) summaries. We display our results graphically, using both statistical (S-plus) and GIS (ARC/INFO, MapInfo) software packages. The approach emerges as flexible, accurate, and suggestive of promising related methods for spatial smoothing of underlying relative risks.

Regionality of food consumption

Understanding food consumption patterns around the United States is important for food marketers and researchers. A cluster analysis of the food purchases in 126 categories across 54 markets found 11 market groupings that are quite different from those commonly used in demand studies. These new regions were consistent with the findings from some cultural geographers and explained more of the regional variation in food consumption than the standard set of geographic boundaries. Food marketers could use these clusters to balance experiments, identify local marketing opportunities, and segment the US market into geographies with similar food demand patterns. © 1998 John Wiley & Sons, Inc.

On a class of free boundary problems for the Laplace equation in two dimensions

The problem of determining a simple boundary from given Cauchy data is studied. This problem may be relevant in two-dimensional electrical impedance tomography where reconstructions of both the conductivity and the boundary are sought. It is found that under certain restrictions on the data, a one-parameter set of boundaries can be obtained in closed form. An immediate consequence of this result is that this problem does not have a unique solution. We make some comments on how to solve the problem with more generalized Cauchy data that do not necessarily obey the restrictions given.

Defining boundaries between words: A tightly-focused approach to the analysis of naturally-occurring text

This paper describes the linguistic basis for the operation of a computer program which performs a particular type of grammatical/syntactic analysis—the assigning of structural “boundaries” between orthographic words in written English text. While the nature of the “boundary” as a linguistic element is implicitly recognized—as with the functional/systemic grammar word → above; group → above; clause hierarchy—an explicit definition of the “boundary” as a linguistic entity, together a set of potential boundaries, is an area in the analysis of language which has not been explored. The linguistic description in this paper forms a part of a study which has been primarily for the computer analysis of language. It is suggested that the concept of boundaries as linguistic entities is, however, also worth investigating for its intrinsic linguistic merit. In order to put the concept of the “boundary” into perspective, some background is necessary on the computer analysis of language; this is kept to a minimum, however.

Shape-based tracking of left ventricular wall motion

An approach for tracking and quantifying the nonrigid, nonuniform motion of the left ventricular (LV) endocardial wall from two-dimensional (2-D) cardiac image sequences, on a point-by-point basis over the entire cardiac cycle, is presented. Given a set of boundaries, motion computation involves first matching local segments on one contour to segments on the next contour in the sequence using a shape-based strategy. Results from the match process are incorporated with a smoothness term into an optimization functional. The global minimum of this functional is found, resulting in a smooth flow field that is consistent with the match data. The computation is performed for all pairs of frames in the temporal sequence and equally sampled points on one contour are tracked throughout the sequence, resulting in a composite flow field over the entire sequence. Two perspectives on characterizing the optimization functional are presented which result in a tradeoff resolved by the confidence in the initial boundary segmentation. Experimental results for contours derived from diagnostic image sequences of three different imaging modalities are presented. A comparison of trajectory estimates with trajectories of gold-standard markers implanted in the LV wall are presented for validation. The results of this comparison confirm that although cardiac motion is a three-dimensional (3-D) problem, two-dimensional (2-D) analysis provides a rich testing ground for algorithm development.

Political district determination using large-scale network optimization

Political redistricting involves the amalgamation of a large number of geographic or statistical units into a smaller set of electoral districts such that the districts satisfy various criteria prescribed by law, judicial mandate, or historical precedent. This paper describes a network-based optimization model that is currently being used by governmental decision-makers in New Zealand to assist in the preliminary stages of determining Parliamentary district boundaries. The model is capable of solving large-scale problems. In the New Zealand case, the procedure has been applied to problems involving over 35,000 geographic units (called “meshblocks”) and 95 Parliamentary districts. The model generates electoral districts that have roughly equal population and are generally compact in shape. One of the key features of the model is its flexibility. On the one hand, it can take into account currently existing features such as topographic terrain or previously existing electoral boundaries. On the other hand, it can also be used to generate an entirely new set of political boundaries as was mandated by the voters in a recent referendum in New Zealand.

Chapter 3 An anatomical model of cerebellar modules

Publisher Summary This chapter presents a view of cerebellar organization in which the entire cortex is subdivided into a reproducible array of very small modules. The working hypothesis is that bands of Purkinje cells plus their afferent climbing fibers, with a clear origin early in cerebellar embryology, are further subdivided into microzones/patches by the mossy fiber afferents. A predictable structural compartmentation down to the units of the order ∼102 Purkinje cells and associated interneurons implies that these modules may function as single processing units. The afferent topography of the cerebellum is complex and stereotyped, and multiple afferent pathways terminate in precise receiving areas, bands, and patches. The cerebellar cortex is subdivided parasagittally into bands, which may be further split; and orthogonal to the zebrin compartments is a second set of boundaries, revealed by the lobulation, developmental defects in mouse mutants and wrinkles in the granular layer. Each module receives a particular pattern of mossy fiber innervation and projects onto a topographically organized Purkinje cell layer above.

IS IT ROSLYN OR IS IT CICELY? REPRESENTATION AND THE AMBIGUITY OF PLACE

Representations or images of place are widely recognized as contributing to how people understand the places in which they live, work, and study. Increasingly they are being seen to contribute to the production of places as well. This paper addresses the relationships between representation and place as social processes by examining the blurring of Cicely, the Alaskan town in the television show Northern Exposure, and Roslyn, the town in Washington state where outdoor scenes of Northern Exposure are shot. Two main points are raised. First, the production of place-images by the entertainment industry has material repercussions for the residents of places. Second, the relationship between Roslyn and Cicely helps advance an epistemology of place that recognizes that the entire set of boundaries we use to define places limits our understanding of places as open, ambiguous, and, therefore, political social processes.

Image registration based on boundary mapping

A new two-stage approach for nonlinear brain image registration is proposed. In the first stage, an active contour algorithm is used to establish a homothetic one-to-one map between a set of region boundaries in two images to be registered. This mapping is used in the second step: a two-dimensional transformation which is based on an elastic body deformation. This method is tested by registering magnetic resonance images to atlas images.

Compression of mixed images using an image representation formed via segmentation

Abstract— This paper presents an approach for the compression of mixed‐image data (images which include text) using a segmentation‐based image representation. The mixed image to be compressed is approximated as a set of uniform regions encoded as a set of region boundaries (contours) and descriptions of the region interiors. In order to improve the visual quality of textual portions in the image approximation, coarsely quantized approximation error (corresponding only to the textual portions) is also encoded. The segmentation method used to form this representation combines a Gaussian texture model and a Gibbs‐Markov contour model in order to find regions with boundaries which correspond closely to the objects in the image. A mixed image, in general, is difficult for conventional transform coding methods because these methods typically discard high‐frequency components or quantize them coarsely. Structures such as edges in the image, however, are dependent upon these high‐frequency components. Therefore, the visual quality of structures such as text (which consists mostly of high‐contrast edges) in the image is severely degraded by conventional transform coding methods. Due to its ability to capture the semantically important structure in the image, segmentation‐based coding is a promising approach for these images. The effectiveness of the proposed approach for the compression of mixed images is demonstrated through experimental results.

The Clinical Boundaries of Posttraumatic Stress Disorder

Three sets of clinical boundaries exist for posttraumatic stress disorder (PTSD), as for all concepts of psychiatric disorder. The first involves the border with normal psychology in general, and with the normal psychology of stress response in particular. This boundary can be surveyed from a number of vantage points and the maps which result will not necessarily correspond. The second boundary issue involves internal boundaries between psychiatric disorders, specifically between PTSD and other concepts of disorder. The high level of comorbidity documented in PTSD has ensured that this aspect of boundary setting is particularly contentious. The third set of boundaries is concerned with subtyping within the global construct of PTSD. The validity and extent of subtyping would be based on the degree to which phenomenological differences exist in relation to PTSD syndromes occurring in the wake of certain types of traumatic events. Such clinical subtyping might however need to be buttressed by external validity indicators such as differential treatment responses or outcome. A final boundary issue of major significance to therapists involves the need to place oneself unambiguously on the side of the trauma survivor in the struggle to resolve the traumatic experiences. The pivotal position of PTSD in the psychopathological arena is discussed.

The origins and evolution of the field of industrial relations in the United States: A review essay

In sum, I am as pessimistic as Kaufman about the ability of existing IR and HR disciplinary institutions to develop a consensus around a different set of intellectual boundaries and a new label. Unfortunately, it will be a very difficult task to corral the energies currently misspent on the creation and defense of ideological and disciplinary territories and to devote them to creating disciplinary institutions that will facilitate the creation and transmission of knowledge about how best to balance the interests of workers with the organizations and societies in which they work. But if we fail as a discipline to take advantage of a favorable external environment that has put human problems on center stage, it will not be because his extremely important work has not clarified the problems and prospects involved in entering a new golden age.

A geometric algorithm finding set of linear decision boundaries

Proposes a geometric algorithm for finding all linear decision boundaries each of which correctly separates two nonoverlapping classes of pattern vectors. When the given T patterns are linearly separable, the algorithm terminates in T iterations, even though the computational time for each iteration tends to increase. When the given T patterns are linearly inseparable, the algorithm is able to detect it in at most T iterations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Rational Prepayments and the Valuation of Collateralized Mortgage Obligations

AbstractThis article presents a procedure for evaluating collateralized mortgage obligation (CMO) tranches. The solution procedure is in the spirit of a dynamic programming problem in which an individual mortgagor's decision to prepay is the feedback control variable―the mortgagor seeks to minimize the value of the mortgage subject to refinancing costs. We employ a two‐step procedure to solve this dynamic programming problem. The first step uses an implicit finite difference backward solution procedure to determine the “optimal” prepayment boundary for a class of mortgagors, each of whom confronts the same proportional refinancing cost. This step is repeated for several different classes of mortgagors that differ in the level of refinancing costs that they confront. The outcome of this first step is a series of prepayment boundaries―one set of boundaries for each level of refinancing costs (i.e., one set of boundaries for each refinancing cost category of mortgagors). In the second step, the prepayment boundaries determined in the first step are used in conjunction with Monte Carlo simulation to value the CMO tranches. The essence of the second step is that when the simulated interest rate hits the boundary for a particular class, it triggers a prepayment scenario for that class of mortgagors. We conduct extensive sensitivity analysis to determine the robustness of this approach (and our solution procedure) to alternative single‐factor models of the term structure of interest rates and to alternative specifications of the distribution of refinancing cost levels confronted by mortgagors. The sensitivity analysis indicates that CMO tranche valuation is not particularly sensitive to alternative models of the term structure so long as the models are consistent with the current yield curve, but, even when alternative specifications of the refinancing cost categories generate nearly identical values for the collateral underlying the CMO (i.e., the generic mortgage‐backed securities), the resulting tranche values can differ widely between the two specifications. The results point out the importance of accurate estimation of the distribution of refinancing costs when the rational valuation model is used for the analysis of CMO tranches.

Mapping and energization in the magnetotail: 1. Magnetospheric boundaries

A set of boundaries was chosen to model the principal observed magnetospheric regions. Those regions which extended out to the distant magnetotail were defined at xsm = −20 RE. The Tsyganenko (1989) magnetic field model (T89) was used to project the boundaries down to the ionosphere. It was found that all field lines which passed within 3 RE of the magnetopause projected to the dayside ionosphere. Dayside arcs therefore generally map to the low‐latitude boundary layer, the cusp/cleft, or the entry layer. The nightside auroral zone, and therefore field lines associated with the substorm current diversion process, primarily traced to portions of the plasma sheet that do not come in direct contact with flowing solar wind plasma. Several mapping problems were encountered. The first involved identifying certain boundaries in the magnetosphere model. The flanks of the magnetotail are not modeled realistically. As a result, we had difficulty in defining a T89 magnetopause in the equatorial plane. Other problems were that some magnetotail boundaries may have no ionospheric signature, and that some boundaries are influenced by cross‐field plasma drift. Plasma boundaries are not tangent to field lines when drift is present, but all mapping was done by following field lines. Uncertainties of about 1° of latitude in the resulting ionospheric projections were found for each 1 RE of drift near midnight at xsm = −20 RE. The steady state magnetotail then was subdivided out to xsm = −22 RE according to the expected characteristics of charged particle orbits. Orbits were traced in the modified Harris magnetic field model, with parameters adjusted to approximate the shapes of T89 magnetic field lines. The one‐dimensional Harris model was used to eliminate some drift effects. This permitted a detailed study of each separate subregion. Curves defining various orbit types were projected to the ionosphere. It is suggested that low‐ or middle‐altitude satellites may be able to detect regions of quasi‐adiabatic and nonadiabatic equatorial orbits by monitoring the loss cones. For these highly field aligned loss cone particles, we found that the net effect of the complex interaction with the current sheet can be explained by an extremely simple model. The model involves shifting all generally field‐aligned ions as a block through an energy‐dependent “scatter” angle. When viewed microscopically, the resulting pitch angle changes are highly structured. Macroscopically it may be possible to describe the process in terms of pitch angle diffusion.

The Database System GONIAT—A tool for research on systematics and evolution of Paleozoic ammonoids

The Database System GONIAT will provide not only determinations on the base of morphological criteria but also reports on occurrence, duration, literature and phylogenetic relationships of every taxon of the generic and species level. It is developed with dBASE IV. It consists of the six separate databases BOUND, LIT, LOC, TAX, MORPHA and MORPHB, which are linked by relational techniques. BOUND includes a set of biostratigraphical boundaries, which represent the time planes expressed in terms of biostratigraphical zonation as well as in absolute dating as actually assumed. The databases LIT and LOC include complete information on literature and localities, respectively. The databases TAX, MORPHA and MORPHB include the taxonomic data as well as the whole set of morphological descriptors (more than 200 in each MORPH) of all significant characters which are important for the identification of the taxa. MORPHA is restricted to general (or adult) characters, MORPHB includes early and middle ontogenetic stages of the forms in which they can be recognized. GONIAT is designed to serve as a tool for investigations on the systematics and the evolution of the diversity of the ammonoids and their paleogeographic distribution during Devonian until Permian.

High Resolution Biostratigraphy of Oligo-Miocene Leon and Chama Formations: An Integrated Approach for Sequence Stratigraphy Analysis

Based on foraminiferal and palynological high resolution studies, a set of Sequence Boundaries (SB) and Maximum Flooding Surfaces (MSF) were identified for the Venezuelan Northwestern Andean Foothills Leon and Chama formations. Changes in abundance patterns of forminifera palynomorphs, in faunal/floral composition and distribution, together with quantitative studies of particulate organic matter allowed picking SB 30, 21 and 15.5 (very low values of fossil abundance and faunal discontinuities, recognized by a rapid stratigraphic change in biofacies and faunal assemblage and the associated mineralogical contents) and MFS 18.5, 16, and 15 (abundant fossils). The Leon Formation represents coastal plain and swamp deposits with some minor fluctuations in the seawater level. The top of the Leon Formation shaly unit is bounded by SB 30, according to Hag B.U. et al (version 1992), marked by a decrease in fossil abundance. An increase in faunal/floral content close to the top of the section coincides with the MFS 18.5. The upper part of the formation is marked by a sandy unit with SB 16.5, characterized again by a decrease in fossil abundance at its top. The Chama Formation was deposited in a transitional environment, with minor seawater level fluctuations. Climate type was tropical humid, with seasonalmore » precipitations, except at the Early Miocene arid or semiarid phase. Mangrove and rain forest vegetation dominated throughout the Early to Middle Miocene. MFS 16 was picked on the basis of a high abundance of microforams and glauconite.« less