Design, characterization, and fabrication of solar-retroreflective cool-wall materials

Raising urban albedo increases the fraction of incident sunlight returned to outer space, cooling cities and their buildings. We evaluated the angular distribution of solar radiation incident on exterior walls in 17 U S. climates to develop performance parameters for solar-retroreflective walls, then applied first-principle physics and ray-tracing simulations to explore designs. Our analysis indicates that retroreflective walls must function at large incidence angles to reflect a substantial portion of summer sunlight, and that this will be difficult to attain with materials that rely on total internal reflection. Gonio-spectrophotometer measurements of the solar spectral bi-directional reflectivity of a bicycle reflector showed little to no retroreflection at large incidence angles. Visual comparisons of retroreflection to specular first-surface reflection for four different retroreflective safety films using violet and green lasers suggest their retroreflection to be no greater than 0.09 at incidence angles up to 45°, and no greater than 0.30 at incidence angles of up to 70°. Attempts to produce a two-surface retroreflector with orthogonal mirror grooves by cutting and polishing an aluminum block indicate that residual surface roughness impedes retroreflection. Ongoing efforts focus on forming orthogonal surfaces with aluminized Mylar film, a material with very high specular reflectance across the solar spectrum. We investigated (1) folding or stamping a free film; (2) adhering the film to a pre-shaped substrate; or (3) attaching the film to a flat ductile substrate, then shaping. The latter two methods were more successful but yielded imperfect right angles

Plasmonically Enhanced Reflectance of Heat Radiation from Low-Bandgap Semiconductor Microinclusions

Increased reflectance from the inclusion of highly scattering particles at low volume fractions in an insulating dielectric offers a promising way to reduce radiative thermal losses at high temperatures. Here, we investigate plasmonic resonance driven enhanced scattering from microinclusions of low-bandgap semiconductors (InP, Si, Ge, PbS, InAs and Te) in an insulating composite to tailor its infrared reflectance for minimizing thermal losses from radiative transfer. To this end, we compute the spectral properties of the microcomposites using Monte Carlo modeling and compare them with results from Fresnel equations. The role of particle size-dependent Mie scattering and absorption efficiencies, and, scattering anisotropy are studied to identify the optimal microinclusion size and material parameters for maximizing the reflectance of the thermal radiation. For composites with Si and Ge microinclusions we obtain reflectance efficiencies of 57 - 65% for the incident blackbody radiation from sources at temperatures in the range 400 - 1600 {\deg}C. Furthermore, we observe a broadbanding of the reflectance spectra from the plasmonic resonances due to charge carriers generated from defect states within the semiconductor bandgap. Our results thus open up the possibility of developing efficient high-temperature thermal insulators through use of the low-bandgap semiconductor microinclusions in insulating dielectrics.Comment: Main article (8 Figures and 2 Tables) + Supporting Information (8 Figures

Predictors of First Mental Health Service Utilization among Homeless and Runaway Adolescents

Purpose: To describe and explain variations in first mental health service utilization before and after running away from home for homeless adolescents. Methods: Survey interviews were conducted with homeless and runaway youth in several Midwestern locations. The effects of family of origin factors and street experiences on the likelihood of seeing a mental health professional for the first time before running away and after running away for the first time were examined. Bivariate and multivariate logistic regression methods are used to analyze these data. Interactions are tested across race and gender sub-groups. Results: Caretaker education, caretaker rejection, and family transitions increase the probability that an adolescent first sees a mental health professional before running away from home. Post-run intervention is more likely for females, younger runaways, shelter users, youths with social support networks, and youths abused by their caretakers. A gender gap in first service use exists for Whites but not for minority youth. Minority youth who experienced family abuse were less likely than abused Whites to report ever seeing a mental health professional. Conclusions: Analyses indicate homeless youth’s utilization patterns are differentiated by family of origin factors, street experiences, timing of first utilization, and by race and gender interactions. Our findings suggest that youths whose first contact with mental health service use follows running away for the first time may experience higher levels of mental distress compared with other homeless runaways. The significant differences in first service use across race and gender subgroups should be further explored. The racial-ethnic gap in first mental health intervention for abused youths indicates this sub-group is not receiving services that are available to other homeless youths. Our findings suggest that homelessness does not homogenize racial/ethnic differences in first mental health service utilization

Copycat dynamics in leaderless animal group navigation

Background: Many animals are known to have improved navigational efficiency when moving together as a social group. One potential mechanism for social group navigation is known as the 'many wrongs principle', where information from many inaccurate compasses is pooled across the group. In order to understand how animal groups may use the many wrongs principle to navigate, it is important to consider how directional information is transferred and shared within the group. Methods: Here we use an individual-based model to explore the information-sharing and copying dynamics of a leaderless animal group navigating towards a target in a virtual environment. We assume that communication and information-sharing is indirect and arises through individuals partially copying the movement direction of their neighbours and weighting this information relative to their individual navigational knowledge. Results: We find that the best group navigation performance occurs when individuals directly copy the direction of movement of a subset of their neighbours while only giving a small (6%) weighting to their individual navigational knowledge. Surprisingly, such a strategy is shown to be highly efficient regardless of the level of individual navigational error. We find there is little relative improvement in navigational efficiency when individuals copy from more than 7 influential neighbours. Conclusions: Our findings suggest that we would expect navigating group-living animals to predominantly copy the movement of others rather than relying on their own navigational knowledge. We discuss our results in the context of individual and group navigation behaviour in animals

The evolution of distributed sensing and collective computation in animal populations

Many animal groups exhibit rapid, coordinated collective motion. Yet, the evolutionary forces that cause such collective responses to evolve are poorly understood. Here, we develop analytical methods and evolutionary simulations based on experimental data from schooling fish. We use these methods to investigate how populations evolve within unpredictable, time-varying resource environments. We show that populations evolve toward a distinctive regime in behavioral phenotype space, where small responses of individuals to local environmental cues cause spontaneous changes in the collective state of groups. These changes resemble phase transitions in physical systems. Through these transitions, individuals evolve the emergent capacity to sense and respond to resource gradients (i.e. individuals perceive gradients via social interactions, rather than sensing gradients directly), and to allocate themselves among distinct, distant resource patches. Our results yield new insight into how natural selection, acting on selfish individuals, results in the highly effective collective responses evident in nature.National Science Foundation (NSF)Office of Naval ResearchArmy Research OfficeHuman Frontier Science ProgramNSFJames S McDonnell Foundatio

Row Spacing and Productivity of Russian Wild Rye Pastures in Semiarid Environments

To sustain forage yields in dry years in semiarid climates, row spacings \u3e59cm have been recommended for Russian wild rye [Psathyrostachys juncea (Fisch.) Nevski] (Lawrence & Heinrichs, 1968). However, wide row spacings promote weed invasion, soil erosion, and elevated plant crowns resulting in a rough, washboard ground surface (Kilcher, 1961). Jefferson and Kielly (1998) suggested a 30-cm row spacing for optimum sustainable forage yields in Russian wild rye in the semiarid prairie region of Canada. This study aimed to evaluate the relationship between row spacing and productivity of Russian wild rye at two semiarid sites near Mandan, in the northern Great Plains region of the USA (46º 48\u27 N latitude, 100º 55\u27 W longitude)

ASTM standards for measuring solar reflectance and infrared emittance of construction materials and comparing their steady-state surface temperatures

Numerous experiments on individual buildings in California and Florida show that painting roofs white reduces air conditioning load up to 50%, depending on the thermal resistance or amount of insulation under the roof. The savings, of course, are strong functions of the thermal integrity of a building and climate. In earlier work, the authors have estimated the national energy savings potential from reflective roofs and paved surfaces. Achieving this potential, however, is conditional on receiving the necessary Federal, states, and electric utilities support to develop materials with high solar reflectance and design effective implementation programs. An important step in initiating an effective program in this area is to work with the american Society for Testing and Materials (ASTM) and the industry to create test procedures, rating, and labeling for building and paving materials. A subcommittee of ASTM E06, E06.42, on Cool Construction Materials, was formed as the vehicle to develop standard practices for measuring, rating, and labeling cool construction materials. The subcommittee has also undertaken the development of a standard practice for calculating a solar reflectance index (SRI) of horizontal and low-sloped surfaces. SRI is a measure of the relative steady-state temperature of a surface with respect to a standard white surface (SRI = 100) and a standard black surface (SRI = 0) under standard solar and ambient conditions. This paper discusses the technical issues relating to development of these two ASTM standards

Latitudinal and Longitudinal Adaptation of Switchgrass Populations

Switchgrass (Panicum virgatum L.) is a warmseason native grass, used for livestock feed, bioenergy, soil and wildlife conservation, and prairie restoration in a large portion of the USA. The objective of this research was to quantify the relative importance of latitude and longitude for adaptation and agronomic performance of a diverse group of switchgrass populations. Six populations, chosen to represent remnant prairie populations on two north–south transects, were evaluated for agronomic traits at 12 locations ranging from 36 to 47°N latitude and 88 to 101°W longitude. Although the population × location interactions accounted for only 10 to 31% of the variance among population means, many significant changes in ranking and adaptive responses were observed. Ground cover was greater for northern-origin populations evaluated in hardiness zones 3 and 4 and for southern-origin populations evaluated in hardiness zones 5 and 6. There were no adaptive responses related to longitude (ecoregion). Switchgrass populations for use in biomass production, conservation, or restoration should not be moved more than one hardiness zone north or south from their origin, but some can be moved east or west of their original ecoregion, if results from field tests support broad longitudinal adaptation

Characterization of Testing Locations for Developing Cool-Season Grass Species

The identification of best testing locations facilitates the allocation of resources in a breeding program, allowing emphasis to be placed at the sites best suited for identifying superior plant materials for the target environment. The objective of this study was the identification of best locations for the evaluation and testing of cool-season grass species within the Northern Great Plains and Intermountain regions of the USA. This study also sought to subdivide the locations into meaningful environmental groupings based on similar entry performance. The study characterized initial stand frequency and forage production (over a 3-yr period) of crested wheatgrass [Agropyron cristatum (L.) Gaertn.; A. desertorum (Fisch. ex Link) Schultes; A. fragile (Roth) Candargy], intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey], and smooth bromegrass (Bromus inermis Leyss.) at six locations within these regions. Results suggested the existence of best testing locations and environmental groupings for each of the species. For example, the Ithaca, NE, location was consistently a good location for testing forage production. Although there were some consistencies, generally, the best testing locations and environmental groupings were species and trait specific. Thus, the targeted use of locations appeared to be most useful on an individual species basis, rather than considered across the cool-season grass species