University of Maryland, Baltimore County

About: University of Maryland, Baltimore County is a education organization based out in Baltimore, Maryland, United States. It is known for research contribution in the topics: Population & Galaxy. The organization has 8749 authors who have published 20843 publications receiving 795706 citations. The organization is also known as: UMBC.

A conceptual framework for the study of human ecosystems in urban areas

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.

Gamma-ray light curves and variability of bright fermi-detected blazars

Abstract: This paper presents light curves as well as the first systematic characterization of variability of the 106 objects in the high-confidence Fermi Large Area Telescope Bright AGN Sample (LBAS) Weekly light curves of this sample, obtained during the first 11 months of the Fermi survey (2008 August 4–2009 July 4), are tested for variability and their properties are quantified through autocorrelation function and structure function analysis For the brightest sources, 3 or 4 day binned light curves are extracted in order to determine power density spectra (PDSs) and to fit the temporal structure of major flares More than 50% of the sources are found to be variable with high significance, where high states do not exceed 1/4 of the total observation range Variation amplitudes are larger for flat spectrum radio quasars and low/intermediate synchrotron frequency peaked BL Lac objects Autocorrelation timescales derived from weekly light curves vary from four to a dozen of weeks Variable sources of the sample have weekly and 3–4 day bin light curves that can be described by 1/f α PDS, and show two kinds of gamma-ray variability: (1) rather constant baseline with sporadic flaring activity characterized by flatter PDS slopes resembling flickering and red noise with occasional intermittence and (2)—measured for a few blazars showing strong activity—complex and structured temporal profiles characterized by long-term memory and steeper PDS slopes, reflecting a random walk underlying mechanism The average slope of the PDS of the brightest 22 FSRQs and of the 6 brightest BL Lacs is 15 and 17, respectively The study of temporal profiles of well-resolved flares observed in the 10 brightest LBAS sources shows that they generally have symmetric profiles and that their total duration vary between 10 and 100 days Results presented here can assist in source class recognition for unidentified sources and can serve as reference for more detailed analysis of the brightest gamma-ray blazars

Maker fringes revisited: second-harmonic generation from birefringent or absorbing materials

Abstract: We present a new formulation of Maker fringes in parallel-surface films, using self-consistent boundary conditions for reflections and allowing for any degree of refractive-index dispersion. This treatment of the second-harmonic reflections and dispersion, unlike a number of previous derivations, leads correctly to the expected form for the effective second-harmonic d coefficients. Complete expressions with physically meaningful factors are given for the generated second-harmonic power for either absorbing or birefringent films including reflections for the case of no pump depletion. A comparison with the isotropic approximation is given, and practical considerations in the use of these expressions for the fitting of experimental data are discussed.

Highly structured slow solar wind emerging from an equatorial coronal hole

Abstract: During the solar minimum, when the Sun is at its least active, the solar wind1,2 is observed at high latitudes as a predominantly fast (more than 500 kilometres per second), highly Alfvenic rarefied stream of plasma originating from deep within coronal holes. Closer to the ecliptic plane, the solar wind is interspersed with a more variable slow wind3 of less than 500 kilometres per second. The precise origins of the slow wind streams are less certain4; theories and observations suggest that they may originate at the tips of helmet streamers5,6, from interchange reconnection near coronal hole boundaries7,8, or within coronal holes with highly diverging magnetic fields9,10. The heating mechanism required to drive the solar wind is also unresolved, although candidate mechanisms include Alfven-wave turbulence11,12, heating by reconnection in nanoflares13, ion cyclotron wave heating14 and acceleration by thermal gradients1. At a distance of one astronomical unit, the wind is mixed and evolved, and therefore much of the diagnostic structure of these sources and processes has been lost. Here we present observations from the Parker Solar Probe15 at 36 to 54 solar radii that show evidence of slow Alfvenic solar wind emerging from a small equatorial coronal hole. The measured magnetic field exhibits patches of large, intermittent reversals that are associated with jets of plasma and enhanced Poynting flux and that are interspersed in a smoother and less turbulent flow with a near-radial magnetic field. Furthermore, plasma-wave measurements suggest the existence of electron and ion velocity-space micro-instabilities10,16 that are associated with plasma heating and thermalization processes. Our measurements suggest that there is an impulsive mechanism associated with solar-wind energization and that micro-instabilities play a part in heating, and we provide evidence that low-latitude coronal holes are a key source of the slow solar wind. Measurements from the Parker Solar Probe show that slow solar wind near the Sun’s equator originates in coronal holes.

Home and family influences on motivations for reading

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...