Browsing by Subject "Sorting"
- Results Per Page
- Sort Options
Item Open Access Essays on the Dynamic Decisions of Homeowners and Retailers(2016) Jardim, Eduardo FerreiraUrban problems have several features that make them inherently dynamic. Large transaction costs all but guarantee that homeowners will do their best to consider how a neighborhood might change before buying a house. Similarly, stores face large sunk costs when opening, and want to be sure that their investment will pay off in the long run. In line with those concerns, different areas of Economics have made recent advances in modeling those questions within a dynamic framework. This dissertation contributes to those efforts.
Chapter 2 discusses how to model an agent’s location decision when the agent must learn about an exogenous amenity that may be changing over time. The model is applied to estimating the marginal willingness to pay to avoid crime, in which agents are learning about the crime rate in a neighborhood, and the crime rate can change in predictable (Markovian) ways.
Chapters 3 and 4 concentrate on location decision problems when there are externalities between decision makers. Chapter 3 focuses on the decision of business owners to open a store, when its demand is a function of other nearby stores, either through competition, or through spillovers on foot traffic. It uses a dynamic model in continuous time to model agents’ decisions. A particular challenge is isolating the contribution of spillovers from the contribution of other unobserved neighborhood attributes that could also lead to agglomeration. A key contribution of this chapter is showing how we can use information on storefront ownership to help separately identify spillovers.
Finally, chapter 4 focuses on a class of models in which families prefer to live
close to similar neighbors. This chapter provides the first simulation of such a model in which agents are forward looking, and shows that this leads to more segregation than it would have been observed with myopic agents, which is the standard in this literature. The chapter also discusses several extensions of the model that can be used to investigate relevant questions such as the arrival of a large contingent high skilled tech workers in San Francisco, the immigration of hispanic families to several southern American cities, large changes in local amenities, such as the construction of magnet schools or metro stations, and the flight of wealthy residents from cities in the Rust belt, such as Detroit.
Item Open Access Migration, Polarization, and Sorting in the American Electorate(2009) McDonald, Ian R.Geographic clustering has been linked to contemporary political polarization by jour- nalists and other researchers in recent years, most recently and notably by Bishop and Cushing (2008). In these accounts, clustering is motivated, in part, by shared tastes for combinations of place attributes that attract individuals with interrelated values and similar characteristics or skillsets. In order to test whether political pref- erences aligns with location choice, this paper proposes a sorting model based on the composition of migrants' political preferences.
Sorting is defined as the increase in the variation of a parameter of preference distributions of different location, in the absence of individual preference change. The model estimates the separate prob- abilities of party identification in U.S. congressional districts among migrants and non-migrants.
Based on an empirical application using the 2006 Cooperative Congressional Elec- tion Study, I find that a significant number of district satisfy the sorting condition. Aa multinomial logit model predicts that individual ideology is significant explana- tory variable in the partisanship of destination districts among migrants, even after controlling for the partisanship of originating districts.
The final chapter evaluates sorting and polarization in U.S. congressional districts based on intra-decade changes to population size. I show that overall polarization in high growth districts exceeds sorting, and suggest this results from an increase in electoral bias that could result from heavy migration into districts that begin the decade as very homogenous.
Item Open Access Robust 4D-MRI Sorting with Reduced Artifacts Based on Anatomic Feature Matching(2018) Yang, ZiPurpose: Motion artifacts induced by breathing variations are common in 4D-MRI
images. This study aims to reduce the motion artifacts by developing a novel, robust 4DMRI
sorting method based on anatomic feature matching, which is applicable in both
cine and sequential acquisition.
Method: The proposed method uses the diaphragm as the anatomic feature to guide the
sorting of 4D-MRI images. Initially, both abdominal 2D sagittal cine MRI images and
axial MRI images (in both axial cine and sequential scanning modes) were acquired. The
sagittal cine MRI images were divided into 10 phases as ground truth. Next, the phase of
each axial MRI image is determined by matching the diaphragm position in the
intersection plane between the axial MRI and the ground truth cine MRI. Then, those
matched phases axial MRI images were sorted into 10-phase bins identical to the ground
truth cine images. Finally, 10-phase 4D-MRI were reconstructed from these sorted axial
MRI images. The accuracy of reconstructed 4D-MRI data was evaluated in a simulation
study using the 4D eXtended Cardiac Torso (XCAT) digital phantom with a sphere
tumor in the liver. The effects of breathing signal, including both regular (cosine
function) and irregular (patient data), on reconstruction accuracy were investigated by
calculating total relative error (TRE) of the 4D volumes, Volume-Percent-Difference
(VPD) and Center-of-Mass-Shift(COMS) of the simulated tumor between the
reconstructed and the ground truth images.
Results: In both scanning modes, reconstructed 4D-MRI images matched well with the
ground truth except minimal motion artifacts. The averaged TRE of the 4D volume, VPD
and COMS of the EOE phase in both scanning modes were 0.32%/1.20%/±0.05𝑚𝑚 for
regular breathing, and 1.13%/4.26%/±0.21𝑚𝑚 for patient irregular breathing,
respectively.
Conclusion: The preliminary results illustrated the robustness of the new 4D-MRI
sorting method based on anatomic feature matching. This method improved image
quality with reduced motion artifacts in the resulting reconstructed 4D MRI is applicable
for axial MR images acquired using both cine and sequential scanning modes.