Street centrality and land use intensity in Baton Rouge, Louisiana

This paper examines the relationship between street centrality and land use intensity in Baton Rouge, Louisiana. Street centrality is calibrated in terms of a node's closeness, betweenness and straightness on the road network. Land use intensity is measured by population (residential) and employment (business) densities in census tracts, respectively and combined. Two CIS-based methods are used to transform data sets of centrality (at network nodes) and densities (in census tracts) to one unit for correlation analysis. The kernel density estimation (KDE) converts both measures to raster pixels, and the floating catchment area (FCA) method computes average centrality values around census tracts. Results indicate that population and employment densities are highly correlated with street centrality values. Among the three centrality indices, closeness exhibits the highest correlation with land use densities, straightness the next and betweenness the last. This confirms that street centrality captures location advantage in a city and plays a crucial role in shaping the intraurban variation of land use intensity. (C) 2010 Elsevier Ltd. All rights reserved

Cooling curves and initial models for low-mass white dwarfs (<0.25 Msun) with helium core

We present a detailed calculation of the evolution of low-mass ($< 0.25~M_\odot$) helium white dwarfs. These white dwarfs (the optical companions to binary millisecond pulsars) are formed via long-term, low-mass binary evolution. After detachment from the Roche lobe, the hot helium cores have a rather thick hydrogen layer with mass between 0.01 to 0.06$~M_\odot$. Due to mixing between the core and outer envelope, the surface hydrogen content is 0.5 to 0.35, depending on the initial value of the heavy element (Z) and the initial secondary mass. We found that the majority of our computed models experience one or two hydrogen shell flashes. We found that the mass of the helium dwarf in which the hydrogen shell flash occurs depends on the chemical composition. The minimum helium white dwarf mass in which a hydrogen flash takes place is 0.213$~M_\odot$ (Z=0.003), 0.198$~M_\odot$ (Z=0.01), 0.192$~M_\odot$ (Z=0.02) or 0.183$~M_\odot$ (Z=0.03). The duration of the flashes (independent of chemical composition) is between few $\times 10^6$ years to few $\times 10^7$ years. In several flashes the white dwarf radius will increase so much that it forces the model to fill its Roche lobe again. Our calculations show that cooling history of the helium white dwarf depends dramatically on the thickness of the hydrogen layer. We show that the transition from a cooling white dwarf with a temporary stable hydrogen-burning shell to a cooling white dwarf in which almost all residual hydrogen is lost in a few thermal flashes (via Roche-lobe overflow) occurs between 0.183-0.213$~M_\odot$ (depending on the heavy element value).Comment: 15 pages, 11 figures, 6 tables, submitted to MNRA

Hurricane Andrew and pregnancies in Louisiana

There are anecdotal accounts about the possible impact of a pregnant woman\u27s mental health on her unborn fetus. This thesis investigates the possible association between hurricane-related stress experienced by pregnant women living in the area afflicted by Hurricane Andrew in Louisiana in 1992 and poor pregnancy outcomes such as preterm and Low Birth Weight (LBW) births. This is an important topic of research because by investigating past events one can better understand the pregnancy-related health issues for areas affected by extreme weather events such as Hurricanes Katrina and Rita. This research analyzed birth data from Louisiana both before and after Hurricane Andrew. Two areas were compared: the area affected by the hurricane and a non-affected area. The affected area was within the hurricane-force winds zone, suffered damage, and had an order or recommendation to evacuate. The non-affected area was used as a control; it was outside of the hurricane\u27s track, sustained no damage, and it had no mandatory evacuation order. Analogous statistical analyses were used to analyze birth data for both areas, namely, Chi-squared analysis, which was applied to find if there were statistically significant changes in the number of LBW and preterm deliveries for the periods following the hurricane compared to a period preceding Hurricane Andrew, which was considered a baseline for the analysis. Results of the analyses have shown that hurricane-related stress while affecting preterm births, does not seem to have the same affect on LBW deliveries. Ultimately, this research will lessen the negative health impact of the hurricanes, which in turn will lessen the economic burden on a society by decreasing total medical costs associated with caring for LBW and preterm babies

Dynamics of Discs in a Nematic Liquid Crystal

In this thesis, a new way of simulating a two-way coupling between a liquid crystal and an immersed object is proposed. It can be used for objects of various geometries and can be expanded to be used for an object of any geometry. Additionally, a simple yet effective model was suggested for calculations of transmitted light through a nematic liquid crystal sample. This model allowed us to clarify the behavior of a ferromagnetic disc in a nematic liquid crystal observed in experiments and incorrectly interpreted at that time. Our simulations have demonstrated the following: in the absence of external forces and torques, discs with homeotropic (perpendicular) anchoring align with their surface normal parallel to the director of the nematic liquid crystal. In the presence of a weak magnetic field, a ferromagnetic disc will rotate to equilibrate the elastic torque due to the distortion of the nematic director and the magnetic torque. When the magnetic field rotates the disc so that the angle between normal to the surface of the disc and director of the liquid crystal becomes greater than 90 degrees, the disc flips around the axis perpendicular to the rotation axis, thus resolving the distortion in the liquid crystal. An analysis of this behavior was performed in Chapter 3. In particular, we look at the impact of the disc thickness, and conditions on the edges of the object, on defect creation and the flipping transition. We also analyze the importance of backflow (i.e. coupling of tensor order parameter with velocity field). We also study the same system under the action of fast rotating weak magnetic fields, that demonstrates a different behavior: the disc avoids flipping via creation of two symmetric defects on the sides. Some results on disc pairs are presented in Chapter 4. Interactions between discs, their motion and final position strongly depend on the distance between them, and the magnitude and angular velocity of the rotating magnetic field. Depending on the initial configuration of the system, different stable structures of discs result

Land use, individual attributes, and travel behavior in Baton Rouge, Louisiana

Although the interrelationship between land use and travel behavior was given more than scant attention in the past, urban planners are far from a solution to reduce commuting and travel by car. One of the reasons is that studies of this kind are often conducted at the aggregate scale limiting one’s probabilities of making inferences of individual/household-level travel behavior. Using 1997 Baton Rouge Personal Transportation Survey (BRPTS) data this study attempts to overcome this limitation. First, a multi-level modeling (MLM) approach is applied to investigate the geographical effect of a place and the role of population composition in accounting for place-to-place differentiation in commuting. The models examined the degree of association between several aspects of land use and travel behavior, considered alone and controlling for socio-economic factors. Results of the study indicate that land use remains significant even after accounting for socio-economic factors. Thus, spatial proximity of jobs determines commuting in a significant way. Second, urban structure and its effect on commuting in the Baton Rouge region of Louisiana were examined. Job concentrations in the study area in 1990 and 2000 were defined and changes examined from 1990 to 2000. Commuting patterns both from the perspectives of monocentric and polycentric urban structures were investigated. Results indicate that the polycentric system contributes to a reduction in individual commuting times and distances in the study area. Lastly, individual-level trip data for the Baton Rouge metropolitan area was used to examine the relationship between land use and trip chaining behavior. Specifically, land use measures were used to explain the likelihood of combining activities into multi-stop trip chains by residents of Baton Rouge region. In addition, the impact of travelers’ employment status was also considered. Models of the ordinary logistic regression, and one accounting for correlation among individual observations were compared. In all models tested, inclusion of land use measures improved the model. Results indicate the significant land use impact on a traveler’s decision regarding trip chaining. The study findings are consistent with the literature, however, they illustrate the difference that exists between by workers and non-workers

Advanced mathematical programming tools for alternative energy systems design

The goal of this thesis is to provide a systematic mathematical decision-support tool for the design of energy systems. Nowadays the society is becoming increasingly conscious about ecological problems originated by anthropogenic factors. In response to this situation, the authorities are taking measures with the purpose to restrict the actual and further environmental load related to human activity. Here, energy efficiency and renewable energies play an important role. Particularly, one of the measures with considerable potential is the retrofit of standard industrial processes through the incorporation of renewable energies in order to reduce the environmental impact related to the use of natural fossil fuels. The general problem we aim to solve in this thesis is the design of environmentally friendly energy systems with the lowest possible cost. To illustrate the capabilities of our approach, we consider a case study: a desalination plant located in the Tarragona region. Our methodology is general enough to be applied to other energy systems, and aims to guide decisions-makers towards the adoption of alternatives with less environmental impact