169 research outputs found
A study of the employment of Negroes in social work based upon a study of the present employment of graduates of the Atlanta University School of Social Work from 1930-1940, 1941
No full textNumerical simulations of grass fires using a coupled atmosphere-fire model:Basic fire behavior and dependence on wind speed
No full textNumerical simulations using a fire model, FIRETEC, coupled to an atmospheric dynamics model, HIGRAD, are examined to investigate several fundamental aspects of fire behavior in grasslands, and specifically the dependence of this behavior on the ambient atmospheric winds and on the initial length of the fire line. The FIRETEC model is based on a multi-phase transport approach, and incorporates representations of the physical processes that govern wildfires, such as combustion and radiative and convective heat exchange. Results from the coupled model show that the forward spread of the simulated fires increases with increasing ambient wind speed, and the spread rates are consistent with those observed in field experiments of grass fires; however, the forward spread also depends significantly on the initial length of the fire line, and for a given ambient wind speed the spread rate for long (100 m) lines is greater than that for short (16 m) lines. The spread of the simulated fires in the lateral direction also depends on the ambient wind speed and the length of the fire line, and a possible explanation for this effect is given. For weak ambient winds, the shape of the fire perimeter is dramatically different from that seen with higher wind speeds. The shape of the fire perimeter is also shown to depend on the initial length of the fire line. These differences in fire behavior are attributed to the differences in the nature of the coupled atmosphere-fire interactions among these cases, and are described in terms of the complex interplay between radiative and convective heat transfer. Copyright 2005 by the American Geophysical Union
Effect of Vertical Canopy Architecture on Transpiration, Thermoregulation and Carbon Assimilation
No full textQuantifying the impact of natural and anthropogenic disturbances such as deforestation, forest fires and vegetation thinning among others on net ecosystem—atmosphere exchanges of carbon dioxide, water vapor and heat—is an important aspect in the context of modeling global carbon, water and energy cycles. The absence of canopy architectural variation in horizontal and vertical directions is a major source of uncertainty in current climate models attempting to address these issues. This manuscript demonstrates the importance of considering the vertical distribution of foliage density by coupling a leaf level plant biophysics model with analytical solutions of wind flow and light attenuation in a horizontally homogeneous canopy. It is demonstrated that plant physiological response in terms of carbon assimilation, transpiration and canopy surface temperature can be widely different for two canopies with the same leaf area index (LAI) but different leaf area density distributions, under several conditions of wind speed, light availability, soil moisture availability and atmospheric evaporative demand.</jats:p
Using Computational Fluid Dynamics to Simulate Large Mixing-Limited Fires Such as Wildfires
No full textRetelling racialized violence, remaking white innocence: the politics of interlocking oppressions in transgender day of remembrance
No full textTransgender Day of Remembrance has become a significant political event among those resisting violence against gender-variant persons. Commemorated in more than 250 locations worldwide, this day honors individuals who were killed due to anti-transgender hatred or prejudice. However, by focusing on transphobia as the definitive cause of violence, this ritual potentially obscures the ways in which hierarchies of race, class, and sexuality constitute such acts. Taking the Transgender Day of Remembrance/Remembering Our Dead project as a case study for considering the politics of memorialization, as well as tracing the narrative history of the Fred F. C. Martinez murder case in Colorado, the author argues that deracialized accounts of violence produce seemingly innocent White witnesses who can consume these spectacles of domination without confronting their own complicity in such acts. The author suggests that remembrance practices require critical rethinking if we are to confront violence in more effective ways. Description from publisher's site: http://caliber.ucpress.net/doi/abs/10.1525/srsp.2008.5.1.2
Numerical simulations of grass fires using a coupled atmosphere-fire model: Dynamics of fire spread
No full textNumerical simulations using a coupled atmosphere-fire model (called HIGRAD/FIRETEC) are examined to investigate the dynamics of fire behavior in grasslands, focusing specifically on the relative roles and contributions of radiative and convective heat transfer and the relationships of these processes to the evolution of the solid fuel temperature; the three-dimensional velocity fields in the vicinity of the fire; and the depletion of fuel, fuel moisture, and oxygen. The progression of the fire past a given point in these simulations is divided into a preheating period and an active burning period. The preheating period is characterized by a slowly increasing radiative heating of the fuel that evaporates fuel moisture and raises the temperature of the fuel slightly and by weak convective cooling because the gases flowing over the heated solid fuel are still cooler than the fuel itself. The active burning period is characterized by the presence of a strong pulse of convective heating and continued radiative heating, accompanied by the development of large vertical velocities and a rapid increase in fuel temperature that causes the reaction rates to increase and the fuel to begin to burn, producing heat and increasing the rates of depletion of fuel and oxygen. In all simulations, the magnitude of the convective heat transfer is greater than that of the radiative heat transfer; however, these processes and their relationships to the three-dimensional structure and evolution of the fire are shown to depend both on the ambient wind speed and on the specific location along the fire front (e.g., at the head of the fire where the fire is spreading in the direction of the ambient wind, or on the flank of the fire where the fire is spreading in the direction almost perpendicular to the ambient wind. Copyright 2007 by the American Geophysical Union
Pathways to Spatial Instability in Models of Fire Propagation
No full textAn equilibrium solution to a time-dependent system is considered stable if small disturbances decay in time and the solution eventually returns to its original form, perhaps up to a translation. Instability, on the other hand, is characterized by disturbances that grow exponentially and cause the solution to transition to a new, qualitatively different form. Often, the onset of instability leads to the formation of spatially patterned states. This type of spatial patterning is characteristic of a number of emergent phenomena in the field of wildland fire science. In order to understand the onset of instability in models of fire propagation and characterize the resulting spatially structured solutions, we study pathways to instability in two systems: a reaction-diffusion model of temperature and fuel concentration with a spatially dependent wind and a model of fluid flow over a heat source with a constant wind. Using tools from geometric dynamical systems, we extend existing theory concerning the existence and stability of traveling wave solutions to reaction-diffusion systems to include systems with spatial dependence in the advection coefficient. An interesting result is that, in a system with spatial dependence constructed to model the fire-induced wind, traveling wave solutions exist for a continuum of wave speeds instead of a single, unique speed. We identify this range of speeds and explain how both the speed and shape of the traveling waves is influenced by the magnitude and sign of the imposed wind. We develop a selection mechanism to identify the one-dimensional fronts that are most likely to persist in nature and identify regions of transverse instability. Taken together, these results allow us to classify parameter regimes for which unstable two-dimensional fronts exist and visualize the resulting patterned states. Lastly, we examine an analogue of the classic model for Rayleigh-B\'enard convection, adapted to the fire application by the addition of a crosswind term, and identify the conditions necessary for spatial patterning in a system that lacks the mechanisms of combustion and fuel consumption. The pattern-forming mechanism in the first system is the interplay between the diffusing heat and the combustion reaction; in the second system, it is thermally-driven buoyancy and the resulting fluid dynamics. We find regions of two-dimensional instability in both systems, suggesting that neither mechanism alone is responsible for the generation of spatial structure. However, our findings demonstrate that the existence of a spatially dependent, first-order forcing term capturing the dynamics of the local wind velocity leads to the emergence of patterned front solutions. The fact that the spatial patterning that develops in the fluids model resembles this forcing term strongly suggests that the spatially dependent wind is a key component contributing to the onset of pattern formation.Doctor of Philosoph
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Eaten: A Novel
No full textThis novel operates on two levels. First, it is a story concerning the fate of a young woman named Raven Adams, who is prompted into journeying westward after witnessing what she believes to be an omen. On another level, however, the novel is intended to be a philosophical questioning of western modes of “science-based” singular conceptualizations of reality, which argue that there is only one “real world” and anyone who deviates from this is “crazy,” “stupid,” or “wrong.” Raven as a character sees the world in terms of what might be called “magical thinking” in modern psychology; her closest relationship is with a living embodiment of a story, the ancient philosopher Diogenes, which she believes is capable of possessing others and directing her journey. As the story continues the reader comes to understand Raven’s perceptions of her reality, leading to a conceptualization of reality as being “multi-layered.” Eventually these layers are collapsed and unified in the final chapters. The novel makes use of many reference points including philosophy, classical mythology, folklore, religion, and internet social media in order to guide the reader along Raven’s story
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The Nature of Things
No full textThe Nature of Things is a collection of stories and a preface that examine character motivation. The author is concerned with unexpected reactions and surprising outcomes. The stories are independent of each other and involve a wide range of characters
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