Showing papers by "University of Maryland, Baltimore County published in 1997"
TL;DR: In this article, the Manakov-polarization mode dispersion (PMD) equation is used to model both non-return-to-zero (NRZ) and soliton signal propagation in optical fibers with randomly varying birefringence.
Abstract: We report on our investigations of the Manakov-polarization mode dispersion (PMD) equation which can be used to model both nonreturn-to-zero (NRZ) and soliton signal propagation in optical fibers with randomly varying birefringence We review the derivation of the Manakov-PMD equation from the coupled nonlinear Schrodinger equation, and we discuss the physical meaning of its terms We discuss our numerical approach for solving this equation, and we apply this approach to both NRZ and soliton propagation, We show by comparison with the coupled nonlinear Schrodinger equation, integrated with steps that are short enough to follow the detailed polarization evolution, that our approach is orders of magnitude faster with no loss of accuracy Finally, we compare our approach to the widely used coarse-step method and demonstrate that the coarse-step method is both efficient and valid
432 citations
TL;DR: In this article, the authors propose a conceptual framework for understanding the role of humans in urban ecosystems, which can be used to frame ecosystem research in and associated with urban and metropolitan areas, and the watershed approach can serve as a spatial basis for organizing comparative studies of ecosystems exhibiting differing degrees of urbanization.
Abstract: The need for integrated concepts, capable of satisfying natural and social scientists and supporting integrated research, motivates a conceptual framework for understanding the role of humans in ecosystems. The question is how to add humans to the ecological models used to understand urban ecosystems. The ecosystem concept can serve as the basis, but specific social attributes of humans and their institutions must be added. Learning and feedback between the human and natural components of urban ecosystems are key attributes of the integrated model. Parallels with familiar ecological approaches can help in understanding the ecology of urban ecosystems. These include the role of spatial heterogeneity and organizational hierarchies in both the social and natural components of urban ecosystems. Although urban watersheds are commonly highly altered, the watershed approach can serve as a spatial basis for organizing comparative studies of ecosystems exhibiting differing degrees of urbanization. The watershed concept can also spatially organize the hierarchically scaled linkages by which the integrated human ecosystem model can be applied. The study of urban ecosystems is a relatively new field, and the questions suggested by the integrated framework can be used to frame ecosystem research in and associated with urban and metropolitan areas.
392 citations
TL;DR: The authors found that children whose early encounters with literacy are enjoyable are more likely to develop a predisposition to read frequently and broadly in subsequent years, while parents who believe that reading is a source of entertainment have children with more positive views about reading than do parents who emphasize the skills aspect of reading development.
Abstract: This article reviews the growing literature on home and family influences on children's motivations for reading. Children whose early encounters with literacy are enjoyable are more likely to develop a predisposition to read frequently and broadly in subsequent years. Young children's self-initiated interactions with print at home are important behavioral indexes of emerging motivations for reading. Shared storybook reading plays an important role in promoting reading motivations; when the socioemotional climate is positive, children are more interested in reading and more likely to view it as enjoyable. The beliefs held by children's parents about the purposes of reading and how children learn to read relate to children's motivations for reading. Parents who believe that reading is a source of entertainment have children with more positive views about reading than do parents who emphasize the skills aspect of reading development. These findings have important implications for offering guidance to parents...
390 citations
TL;DR: In this article, a global shallow-water model based on the flux-form semi-lagrangian scheme is described, which is a multidimensional semi-Lagrangian extension of the higher order Godunov-type finite-volume schemes (e.g., the piece-wise parabolic method).
Abstract: A global shallow-water model based on the flux-form semi-lagrangian scheme is described. the mass-conserving flux-form semi-Lagrangian scheme is a multidimensional semi-Lagrangian extension of the higher order Godunov-type finite-volume schemes (e.g., the piece-wise parabolic method). Unlike the piece-wise parabolic methodology, neither directional splitting nor a Riemann solver is involved. A reverse engineering procedure is introduced to achieve the goal of consistent transport of the absolute vorticity and the mass, and hence, the potential vorticity. Gravity waves are treated explicitly, in a manner that is consistent with the forward-in-time flux-form semi-Lagrangian transport scheme. Due to the finite-volume nature of the flux-form semi-lagrangian scheme and the application of the monotonicity constraint, which can be regarded as a subgrid-scale flux parametrization, essentially noise-free solutions are obtained without additional diffusion. Two selected shallow-water test cases proposed by Williamson et al. (1992) and a stratospheric vortex erosion simulation are presented. Discussions on the accuracy and computational efficiency are given based on the comparisons with a Eulerian spectral model and two advective-form semi-implicit semi-Lagrangian models.
331 citations
TL;DR: The relationship between the therapeutic alliance and treatment participation and drinking outcomes during and after treatment was evaluated among alcoholic outpatient and aftercare clients in this paper, showing that ratings of the working alliance, whether provided by the client or therapist, were significant predictors of treatment participation, after a variety of other sources of variance were controlled.
Abstract: The relationship between the therapeutic alliance and treatment participation and drinking outcomes during and after treatment was evaluated among alcoholic outpatient and aftercare clients. In the outpatient sample, ratings of the working alliance, whether provided by the client or therapist, were significant predictors of treatment participation and drinking behavior during the treatment and 12-month posttreatment periods, after a variety of other sources of variance were controlled. Ratings of the alliance by the aftercare clients did not predict treatment participation or drinking outcomes. Therapists ratings of the alliance in the aftercare sample predicted only percentage of days abstinent during treatment and follow-up. The results document the independent contribution of the therapeutic alliance to treatment participation and outcomes among alcoholic outpatients.
302 citations
TL;DR: In this paper, the spontaneous parametric down-conversion (SPDC) of a continuous wave pump is studied for the case of a pulse, where the pump pulse acts like a clock with an uncertainty equal to its width.
Abstract: Spontaneous parametric down-conversion (SPDC) has been extensively studied for the case of a continuous wave pump. In this paper SPDC is studied for the case in which the pump is a pulse. The pump pulse acts like a clock with an uncertainty equal to its width. This makes it possible to distinguish pairs of photons born at sufficiently different depths inside the crystal with a consequent decrease in two-photon interference. We study this effect in detail for degenerate collinear type-II SPDC and degenerate type-I SPDC. It may be possible in the type-II case to eliminate the clock effect of the pump by judicious choice of materials and wavelengths.
259 citations
TL;DR: New methods that allow, for the first time, genetic analysis in Archaea of the genus Methanosarcina are presented and the complete 5467-bp DNA sequence of pC2A was determined.
Abstract: New methods that allow, for the first time, genetic analysis in Archaea of the genus Methanosarcina are presented. First, several autonomously replicating plasmid shuttle vectors have been constructed based on the naturally occurring plasmid pC2A from Methanosarcina acetivorans. These vectors replicate in 9 of 11 Methanosarcina strains tested and in Escherichia coli. Second, a highly efficient transformation system based upon introduction of DNA by liposomes has been developed. This method allows transformation frequencies of as high as 2 × 108 transformants per microgram of DNA per 109 cells or ≈20% of the recipient population. During the course of this work, the complete 5467-bp DNA sequence of pC2A was determined. The implications of these findings for the future of methanoarchaeal research are also discussed.
241 citations
24 Jul 1997
TL;DR: The research presented here finalizes the specification of KQML and provides semantics for the language, and offers the research community a completely defined communication language that can be used for knowledge exchange between software agents.
Abstract: We address the issue of semantics for an agent communication language. In particular, the specification and semantics of Knowledge Query Manipulation Language (KQML), and the logical architecture of KQML-speaking agents are investigated. KQML is a language and protocol to support communication between (intelligent) software agents. First, we present a new specification for the KQML language that corrects a number of outstanding problems. Then, based on ideas from speech act theory, we propose a semantic description for KQML that associates "cognitive" states of the agent with the use of the language's primitives (performatives). We use this approach to describe the semantics for the whole set of reserved KQML performatives. Building on the semantics, we devise the conversation policies, i.e., a formal description of how KQML performatives may be combined into KQML exchanges (conversations), using a Definite Clause Grammar. Finally, we present the code for a Prolog program that shows how the conversation policies can be incorporated in a software agent that speaks KQML.
The research presented here finalizes the specification of KQML and provides semantics for the language. The accompanying code shows how this research can be used to build KQML agents that make use of all of the powerful features of KQML. Thus, we offer the research community a completely defined communication language that can be used for knowledge exchange between software agents. Also, our research offers methods for: (1) a speech act theory-based semantic description of a language of communication acts, and (2) the specification of the protocols associated with these acts. Languages of communication acts address the issue of communication between software applications at a level of abstraction that could prove particularly useful to the emerging software agents paradigm of software design and development.
218 citations
TL;DR: The energy-enhancement factor, together with the time-bandwidth product and the stretching factor, were calculated as a function of the difference in absolute values of accumulated dispersion in the fiber spans and the interaction strength of the dispersion-managed solitons was found to depend on the stretching factors.
Abstract: We simulated dispersion-managed soliton propagation and interaction in optical fibers. The energy-enhancement factor, together with the time–bandwidth product and the stretching factor, were calculated as a function of the difference in absolute values of accumulated dispersion in the fiber spans. The interaction strength of the dispersion-managed solitons was found to depend on the stretching factor. When this factor is less than 1.5, the interaction is weaker than for ideal solitons. When it is more than 1.5, there is a strong interaction between the pulses, which constrains the energy enhancement for practical applications.
189 citations
TL;DR: In this article, a comprehensive model of the change process and match therapist interventions to the client's readiness for change is proposed to increase motivation to change in resistant clients, and a supportive and collaborative working alliance between therapist and client enhances treatment effects.
Abstract: Many treatment programs for domestic abuse perpetrators rely on consistent, direct, and often intense confrontation of defenses. These interventions may unwittingly increase rather than decrease resistance and defensiveness and may reinforce the belief that relationships are based on coercive influence. Available research suggests that confrontational, hostile, and critical therapist behaviors limit treatment effectiveness and can harm vulnerable clients. Conversely, a supportive and collaborative working alliance between therapist and client enhances treatment effects. Supportive strategies are available to increase motivation to change in resistant clients. These techniques rely on a comprehensive model of the change process and match therapist interventions to the client's readiness for change.
185 citations
TL;DR: A plant expression system where the scFv-proteins are targeted in the ER provides not only the highest accumulation level of active single chain Fv antibodies ever reported but also a short- or long-term storage of the foreign protein in the harvested plant material.
TL;DR: It is shown that the long-step primal potential reduction methods of Nesterov and Todd and the surface-following methods of Wojciech Nemirovskii extend to hyperbolic barrier functions and that there exists a hyperBolic barrier function on every homogeneous cone.
Abstract: Hyperbolic polynomials have their origins in partial differential equations. We show in this paper that they have applications in interior point methods for convex programming. Each homogeneous hyperbolic polynomial p has an associated open and convex cone called its hyperbolicity cone. We give an explicit representation of this cone in terms of polynomial inequalities. The function Fx = -log px is a logarithmically homogeneous self-concordant barrier function for the hyperbolicity cone with barrier parameter equal to the degree of p. The function Fx possesses striking additional properties that are useful in designing long-step interior point methods. For example, we show that the long-step primal potential reduction methods of Nesterov and Todd and the surface-following methods of Nesterov and Nemirovskii extend to hyperbolic barrier functions. We also show that there exists a hyperbolic barrier function on every homogeneous cone.
TL;DR: Tumor challenge studies demonstrate that tumor cells expressing class II without coexpression of Ii or Ii plus DM are highly immunogenic and preferentially present endogenous antigens, while tumors coexpressing class II with Ii and DM are not effective immunogens.
Abstract: We have developed an immunotherapy in which tumor cells transfected with syngeneic major histocompatibility complex (MHC) class II genes are cell-based vaccines for the treatment of established tumor and metastatic disease. If this strategy is to be used clinically, convenient methods for generating class II+ tumor cells are necessary. Interferon-γ treatment or transduction of the class II transactivator (CIITA) gene induces class II expression but also up-regulates the class II-associated accessory molecules, invariant chain (Ii) and DM. To determine if interferon-γ treatment and CIITA transduction are potential immunotherapies, we assessed the tumorigenicity of sarcoma cells expressing combinations of class II, Ii, and DM. Since we hypothesized that class II-transfected tumor cells not coexpressing Ii and DM present endogenously encoded tumor peptides, we have assessed the transfectants for antigen presentation activity to MHC class II-restricted antigen-specific CD4+ T cells. Tumor challenge studies demonstrate that tumor cells expressing class II without coexpression of Ii or Ii plus DM are highly immunogenic and preferentially present endogenous antigens, while tumors coexpressing class II with Ii or Ii plus DM are not effective immunogens. Because tumor rejection correlates with expression of class II without coexpression of Ii and DM, the most efficacious vaccines will express MHC class II without coexpression of Ii and DM and will preferentially present endogenous antigen.
TL;DR: In this paper, a conceptual model using Jenny's (1941) state factor approach for human impact on soil formation details the "anthroposequence," the benchmark anthroposity model may be applied to studying soil systems along urban-rural land use gradients.
Abstract: This paper discusses the concept of soil in both urban and rural environments, and along the urban-rural land use gradient, to illustrate the obvious need to increase our understanding of urban soils. Spatial variability of the urban landscape is illustrated with "Soil series - Urban land complexes" from Baltimore County, Maryland. The World Reference Base for Soil Resources (ISSS-ISRIC-FAO, 1994) proposed Anthrosol and Regosol major soil groups are discussed to show modern approaches to soil classification and to illustrate how the classification of urban soils is essentially undeveloped. Models of soil genesis help identify the processes and functions of the soil system. A conceptual model using Jenny's (1941) state factor approach for human impact on soil formation details the "anthroposequence." The benchmark anthroposequence model may be applied to studying soil systems along urban-rural land use gradients. The process of "anthropedogenesis" is supported to quantify the role of human activity in changing the "natural" direction of soil formation. Future directions of soil research in the urban landscape should involve large scale soil mapping (e.g. 1:6000), benchmark anthroposequences, improved soil classification, and refined characterization of the role of human activities in soil formation.
TL;DR: The studies show that the laminated appearance of cartilage in MRI is caused by T2 anisotropy of the tissue, and the structure of the cartilage tissue indicates that the collagen meshwork defines this T2Anisotography.
Abstract: To understand the origin of the laminated appearance of cartilage in MRI (the magic angle effect), microscopic MRI (mu MRI) experiments were performed at 14-microns pixel resolution on normal canine articular cartilage from the shoulder joints. Two-dimensional images of the spin-spin relaxation time (T2) of the cartilage-bone plug at two angles (0 degree and 55 degrees) were calculated quantitatively. A distinct T2 anisotropy was observed as a function of the cartilage tissue depth. The surface and the deep regions exhibit strong orientational dependence of T2, whereas the upper-middle region exhibits little orientational dependence of T2. These three mu MRI regions correspond approximately to the three histologic zones in cartilage tissue. The results from the bulk T2 measurements agreed with these mu MRI results. Our studies show that the laminated appearance of cartilage in MRI is caused by T2 anisotropy of the tissue. We further suggest that the molecular origin of the T2 anisotropy is the nuclear dipolar interaction. The structure of the cartilage tissue indicates that the collagen meshwork defines this T2 anisotropy. The results show that the T2 anisotropy provides an indirect but sensitive indicator for the orientation of macromolecular structures in cartilage. The clinical implications of this anisotropy are discussed.
TL;DR: In this article, a patch approach is proposed to evaluate tree cover for an entire urban area that is based on patch dynamics, and Treed patches are classified by their origin, structure, and management intensity.
Abstract: Analysis of urban tree cover is generally limited to inventories of tree structure and composition on public lands. This approach provided valuable information for resource management. However, it does not account for all tree cover within an urban landscape, thus providing insufficient information on ecological patterns and processes. We propose evaluating tree cover for an entire urban area that is based on patch dynamics. Treed patches are classified by their origin, structure, and management intensity. A patch approach enables ecologists to evaluate ecological patterns and processes for the entire urban landscape and to examine how social patterns influence these ecological patterns and processes.
TL;DR: In this paper, the transtheoretical model of change is applied to the problem of domestic violence, specifically to group treatment for abuse perpetrators, and clinical suggestions are provided that are appropriate to each stage of change (precontemplation, contemplation, preparation, action, and maintenance).
Journal Article•
TL;DR: The discussion of the experimental testing and numerical analysis of plaque is directed toward summarizing the current knowledge of plaque material properties, and how the knowledge can be used to enhance the reliability of interventional procedures.
Abstract: Atherosclerosis is the leading cause of death in the U.S. In balloon angioplasty, pressure is applied directly to atherosclerotic plaque to reopen the occluded blood vessel. The mechanical behavior of the plaque often determines the outcome of the angioplasty. Little information on the material properties of atherosclerotic plaque is available, yet the properties govern the plaque's behavior. Our discussion of the experimental testing and numerical analysis of plaque is directed toward summarizing the current knowledge of plaque material properties. Atherosclerotic plaque exhibits a wide range of behaviors consistent with the variability in the underlying composition. Overall, plaques exhibit nonlinear and inelastic mechanical behavior, although geometry and material properties are not well known. The histomorphological composition is critical in determining the plaque's mechanical response. Finite element approximations have been used to study the stresses developed in the diseased vessel; however, material properties are a critical component of a finite element analysis: the predictive capabilities depend on how accurately the material is modeled. When more information on plaque behavior is generated through careful and extensive experimental investigations, better models will be constructed to more accurately predict plaque responses. As the biomechanics community learns about plaque mechanics, we can use the knowledge to enhance the reliability of interventional procedures.
TL;DR: In this paper, two types of interference were observed using two-photon spontaneous parametric radiation from two nonlinear interaction regions: Young and Mach-Zehnder interferometers.
Abstract: Two types of interference were observed using two-photon spontaneous parametric radiation from two nonlinear interaction regions. Two experimental setups analogous to the Young and Mach-Zehnder interferometers were used. An interesting feature of the two-photon Young interference is the opposite conditions for its observation by two different methods: by measuring intensity of light at a single frequency and by measuring correlation of intensities at two conjugated frequencies (method of coincidences). Two-photon Mach-Zehnder interference resembles the Ramsey method of separated fields, which is used in beam spectroscopy. A simple macroscopic quantum model agrees well with the experimental results and enables their interpretation in terms of ``biphotons'' carrying information about the pump phase.
TL;DR: In this paper, a discussion of studies on parents' beliefs about the nature and causes of childhood disability, and their ideas about treatment among various cultural groups, is proposed that parental beliefs is a means by which culture affects child development.
Abstract: This paper examines studies on the interface of culture, parental beliefs, and childhood disability, within an ecological framework. Through a discussion of studies on parents’ beliefs about the nature and causes of childhood disability, and their ideas about treatment among various cultural groups, it is proposed that parental beliefs is a means by which culture affects child development. Parents’ beliefs about childhood disability provide the structure and context to the development of a child with a disability. Parents’ beliefs about the nature and causes of disability likewise provide the context for parents’ beliefs about treatment and intervention. The studies also revealed that parents held both biomedical and sociocultural views, reflecting duality in beliefs. Conceptual and methodological considerations for future research on culture, parental beliefs, and childhood disability are discussed. The linkages between parents’ ideas and intervention has implications for clinical practice, part...
TL;DR: MALDI, combined with enzymatic reactions and protein chemistry, provides information on molecular masses, peptide maps, and primary structure.
Abstract: MALDI, combined with enzymatic reactions and protein chemistry, provides information on molecular masses, peptide maps, and primary structure.
TL;DR: Results suggested that early interventions focus on training mothers to attend to maintain, and repair mother-child interactions to more closely approximate normal levels of interactive coordination.
Abstract: Interactive coordination was observed in laboratory play interactions of pairs of 29 clinically depressed and 14 nondepressed mothers and their 13-29-m onth-old children (M = 18.9 months). Nondepressed mothers and their children displayed more interactive coordination than depressed-m other dyads ( p < .001). Depressed mothers were less likely to repair interrupted interactions, and their toddlers were less likely to maintain interactions than nondepressed controls. Toddlers m atched their nondepressed but not their depressed m others’ negative behavior rates. Results suggested that early interventions focus on training mothers to attend to, maintain, and repair m other-child interactions to more closely approxim ate normal levels of interactive coordination. Adaptive success in infancy requires develop ment of the baby’s ability to coordinate activi ties in the social and physical environment while maintaining affective equilibrium (Tronick & Cohn, 1989). In normal social devel opment, infants are helped by their mothers to develop effective strategies to coordinate their actions with those of interactional partners in a mutually satisfying manner. Tronick (1986) described interactions as coordinated when participants achieve a joint focus of attention on a mutual goal over a majority of the inter action period. Coordination may be accom plished by maintaining the interaction over an extended period of time with few breaks in Videotaped interactions analyzed in this study came from a longitudinal study directed by authors Gelfand and Teti and supported by NIM H grant num ber 41474. W e thank participants and the maternal depression research group,
Journal Article•
TL;DR: It is shown that both large and small vessel endothelial cells chronically exposed to inflammatory cytokines produce and release bioactive bFGF in the absence of cell death, and a mechanism by which these cytokines can cooperate in the induction of KS is suggested.
Abstract: Inflammatory cytokines including TNF-alpha, IL-1beta, and IFN-gamma are increased in sera and lesions of Kaposi's sarcoma (KS) patients. Previous data have indicated that the combination of these cytokines as found in conditioned media from activated T cells induces normal endothelial cells to acquire the features of KS spindle cells (KS cells) including spindle morphology, marker expression, and the responsiveness to the effects of HIV-1 Tat protein. Conditioned media from activated T cells or the single cytokines also induce AIDS-KS cells to produce and release basic fibroblast growth factor (bFGF). bFGF is highly expressed also by in situ KS cells and mediates KS-like lesion formation after inoculation of the cells in nude mice. Here we show that both large and small vessel endothelial cells chronically exposed to inflammatory cytokines produce and release bioactive bFGF in the absence of cell death. In addition, after this treatment, endothelial cells acquire angiogenic capability and induce KS-like lesions after inoculation in nude mice. Production and release of bFGF is induced in a synergistic fashion by TNF-alpha, IL-1beta, and IFN-gamma, and its release is further promoted by low cell density and by the serine proteases plasmin and thrombin. These results indicate that inflammatory cytokines induce endothelial cells to export bFGF and to acquire angiogenic properties, a key feature of the KS cell phenotype, and suggest a mechanism by which these cytokines can cooperate in the induction of KS.
TL;DR: The 3-oxo-Δ5-steroid isomerase (EC 5331) was solved by multidimensional heteronuclear magnetic resonance spectroscopy as mentioned in this paper.
Abstract: The three-dimensional structure of the enzyme 3-oxo-Δ5-steroid isomerase (EC 5331), a 28-kilodalton symmetrical dimer, was solved by multidimensional heteronuclear magnetic resonance spectroscopy The two independently folded monomers pack together by means of extensive hydrophobic and electrostatic interactions Each monomer comprises three α helices and a six-strand mixed β-pleated sheet arranged to form a deep hydrophobic cavity Catalytically important residues Tyr14(general acid) and Asp38 (general base) are located near the bottom of the cavity and positioned as expected from mechanistic hypotheses An unexpected acid group (Asp99) is also located in the active site adjacent to Tyr14, and kinetic and binding studies of the Asp99 to Ala mutant demonstrate that Asp99 contributes to catalysis by stabilizing the intermediate
TL;DR: An a posterior least squares orthogonal subspace projection (LSOSP) derived from OSP is presented on the basis of an a posteriori model so that the abundances of signatures can be estimated through observations rather than assumed to be known as in the a priori model.
Abstract: One of the primary goals of imaging spectrometry in Earth remote sensing applications is to determine identities and abundances of surface materials. In a recent study, an orthogonal subspace projection (OSP) was proposed for image classification. However, it was developed for an a priori linear spectral mixture model which did not take advantage of a posteriori knowledge of observations. In this paper, an a posterior least squares orthogonal subspace projection (LSOSP) derived from OSP is presented on the basis of an a posteriori model so that the abundances of signatures can be estimated through observations rather than assumed to be known as in the a priori model. In order to evaluate the OSP and LSOSP approaches, a Neyman-Pearson detection theory is developed where a receiver operating characteristic (ROC) curve is used for performance analysis. In particular, a locally optimal Neyman-Pearson's detector is also designed for the case where the global abundance is very small with energy close to zero a case to which both LSOSP and OSP cannot be applied. It is shown through computer simulations that the presented LSOSP approach significantly improves the performance of OSP.
TL;DR: Data from the Commonwealth Productive Aging Survey confirmed findings of previous research that retirement is not associated with higher rates of volunteering, but nonvolunteers show a heightened receptivity to volunteering in the first and second years following termination of employment.
Abstract: Higher rates of volunteering might be expected of elders in the period immediately after retirement because they tend to be in relatively good health and have fewer competing obliga tions. Data from the Commonwealth Productive Aging Survey, a telephone survey of a repre sentative national sample of 2,999 people 55 years of age and older, confirmed findings of previous research that retirement is not associated with higher rates of volunteering. However, in the first and second years following termination of employment, nonvolunteers show a heightened receptivity to volunteering; that is, they indicate more willingness to take on volunteer assignments and an ability to do so than do elders who are employed or who have been out of the workforce for longer periods. The findings suggest that volunteer coordinators should focus volunteer recruiting efforts on elders who are about to leave jobs or who have recently left jobs.
TL;DR: In this article, the authors present three principal methods: core analysis, historic mapping, and gradient analysis, to link spatial and temporal data for urban ecosystems and applies their use in the Baltimore-Chesapeake region.
Abstract: Understanding contemporary urban landscapes requires multiple sets of spatially and temporally compatible data that can integrate historical land use patterns and disturbances to land cover. This paper presents three principal methods: (1) core analysis; (2) historic mapping; and (3) gradient analysis, to link spatial and temporal data for urban ecosystems and applies their use in the Baltimore-Chesapeake region. Paleoecological evidence derived from the geochronology of sediment cores provides data on long-term as well as recent changes in vegetative land cover. This information, combined with contemporary vegetation maps, provides a baseline for conducting trend analyses to evaluate urbanization of the landscape. A 200-year historical land use database created from historical maps, census data, and remotely sensed data provides a spatial framework for investigating human impacts on the region. A geographic information system (GIS) integrates core analyses with historic data on land use change to yield a comprehensive land use and land cover framework and rates of change. These data resources establish the regional foundation for investigating the ecological components of an urban ecosystem. Urban-rural gradient analyses and patch analyses are proposed as the most appropriate methods for studying the urban ecosystem as they link ecological and social patterns and processes for varying degrees of urbanization.
TL;DR: It is argued that it is more accurate to think of states as specialized political markets in which individuals and groups develop and promote innovative products.
Abstract: States are often touted as "laboratories" for developing national solutions to social problems. In this article we examine the appropriateness of this metaphor for comprehensive health care reform and attempt to draw lessons about policy innovation from recent state actions. We present evidence from six states that enacted major pieces of health care legislation in the late 1980s or early 1990s: Massachusetts, Oregon, Florida, Minnesota, Vermont, and Washington State. The variation in design casts doubt on the proposition that states can invent plans and programs for other states and the federal government to adopt for themselves. Instead, we argue that it is more accurate to think of states as specialized political markets in which individuals and groups develop and promote innovative products. We examine the factors that might create receptive markets for comprehensive health care reforms and conclude that the critical factor these states shared in common was skilled and committed leadership from "policy entrepreneurs" who formulated the plans for system reform and prominent "investors" who contributed substantial political capital to the development of the reforms. We illustrate different strategies that leaders in these states used to carry out the entrepreneurial tasks of identifying a market opportunity, designing an innovation, attracting political investment, marketing the innovation, and monitoring its early production.
TL;DR: This paper investigated the relationship between professional sports franchises and venues and real per capita personal income in 37 Standard Metropolitan Statistical Areas in the United States over the period 1969-1994 and found evidence that some sports franchises reduce the level of personal income and have no effect on the growth in per capita income.
Abstract: This paper investigates the relationship between professional sports franchises and venues and real per capita personal income in 37 Standard Metropolitan Statistical Areas in the United States over the period 1969-1994. Our empirical framework accounts for the entry and departure of professional football, basketball and baseball franchises; the construction of arenas and stadia; and other sports-related factors over this time period. In contrast to other existing studies, we find evidence that some professional sports franchises reduce the level of per capita personal income in metropolitan areas and have no effect on the growth in per capita income, casting doubt on the ability of a new sports franchise or facility to spur economic growth. We also find evidence that results obtained from estimating reduced form relationships, a common practice in the literature, are not robust to alternative statistical model specifications.