Academic Bibliography

Abstract: All regions and communities have areas where we go when we are not at home. These are places where economic, social, and civic activity, as well as key infrastructure assets, are concentrated. These clusters of activity, or activity centers, are the building blocks of our economy.

Developing an accurate picture of activity centers requires a quantitative analysis. Historically, however, planners and researchers have used very narrow definitions of activity based solely on the locations of residences and jobs. Researchers at Brookings Metro have developed a new approach to identifying activity centers based on a broader definition of activity that takes into account community, consumption, tourism, and institutional assets, as well as economic assets, in measuring activity.

This PAS Memo explores this new activity centers methodology as a potentially valuable tool for planners seeking to better understand the hierarchy of places in their localities and to focus investment and development where it can have the most regional impact. It offers step-by-step guidance in performing an activity center analysis of a locality or region and action steps for making use of a completed analysis in planning practice. Planners and decision makers can use this information to support and expand their communities’ economic productivity, sustainability, and equity.

Abstract: This report seeks to help readers understand how the pandemic’s long-term effects on the types of trips Americans make have produced both challenges and opportunities for U.S. transit systems. Public transit remains essential in large metro areas—not just as a social service or transport of last resort, but as a necessary part of safe, productive, climate-friendly regions. Rather than focusing solely on getting remote workers to return to taking the bus or train to downtown offices, U.S. transit agencies should focus on building public transportation networks that can serve all trips—not just commutes—in the areas where features such as density, mixtures of uses, walkable and well-connected street grids, and low automobile ownership make these transportation modes most viable.

The report focuses on the six large metro areas where the 2017 National Household Travel Survey (NHTS) found that more than 5% of all trips were made by public transportation: Boston, Chicago, New York, San Francisco, Seattle, and Washington, D.C. Between them, these metro areas were home to 56% of all U.S. public transit trips in 2017, despite housing only 15% of the country’s population. These “high-ridership metro areas” range from the nation’s largest (New York) to its 15th-largest (Seattle); we will compare them to the remainder of the 20 largest metro areas, which had 2017 transit mode shares ranging from 3.8% (Baltimore) to 0.4% (Tampa, Fla.).

Abstract: In this report, we argue that office-to-residential conversions are one potential remedy in some circumstances. But the public interest in conversion and the potential beneficiaries must be clearly defined in order to justify any public financial support. It is still early in the shift to hybrid work and many market forces (e.g., office buildings repricing to lower rents) have yet to play out. Governments rushing to provide financial support for conversions could inadvertently subsidize the wrong behavior. Office-to-residential conversions are not a panacea, but rather one tool in a much broader toolkit for downtown revitalization.

This report begins by identifying the five common arguments made by proponents for converting offices into housing. It then evaluates the myths and realities of each argument, using data from cities across the United States. It concludes with six recommendations for what cities should do about conversions and what other long-term strategies they could adopt.

Abstract: Community investment patterns are often influenced by race as well as wealth. Analyzing the distribution of grocery stores in several large U.S. cities, we find that premium grocery stores are less likely to be located in Black-majority neighborhoods, regardless of the average household income of those neighborhoods, and are substantially more likely to be located in neighborhoods where the Black population share is less than 10%.

In other words, businesses and the broader real estate and financing sectors are not investing even in prospering Black-majority neighborhoods, which devalues these communities and hinders opportunities for growth.

Abstract: In this report, we introduce a new methodology to locate and characterize activity centers: places within regions where economic, physical, social, and civic assets cluster at a clearly defined hyperlocal scale. We present a typology of activity centers, map their locations within the 110 U.S. metropolitan statistical areas (MSAs) with at least 500,000 residents using census block groups, and analyze those centers to help planners, real estate professionals, and elected leaders better understand how and why they matter.

Data Download: https://github.com/BrookingsMetro/activity-centers-data

Interactive Map: https://www.brookings.edu/articles/activity-centers/#metropolitan-area-activity-centers

Abstract: The United States began the 20^th century as a rural nation, evolved into a nation of cities, and ended the century with a suburban majority. The first half of this transition—from a nation of farmers to one of urban workers—was part of a global trend, as economies shifted from agrarian to manufacturing to services. The second half—from a nation of cities to a nation of suburbs—was especially pronounced in the U.S. due to government policies that invested in suburbanization. These policies included federal subsidies for suburban mortgages, tax subsidies that favored sprawl, and the construction of urban highways that destroyed dense neighborhoods of color while speeding suburban commuters to downtown jobs. By dispersing and isolating different people and assets, these policies supersized segregation and left behind a fragile, unjust infrastructure landscape.

In this piece, we analyze urban-to-suburban population shifts over the last 70 years to underscore how wealth and jobs moved out of American cities and left behind segregated, disinvested communities. A solution, we conclude, can be found through a broad coalition of pro-growth as well as racial and environmental justice groups to advance region-wide prosperity through reinvesting in urban cores.

Abstract: While pedestrian-oriented urban places have been identified as beneficial in a number of fields, including public health and climate change, there is a shortage of quantitative studies of such places covering large geographic areas. This study characterizes neighborhoods in US metropolitan areas based on built environment and density variables derived from the American Community Survey, Longitudinal Employer-Household Dynamics Origin-Destination Employment Statistics, National Land Cover Database, and OpenStreetMaps datasets.

Neighborhoods and metropolitan areas as a whole are typologized based on this data using k-means analysis. The resulting neighborhood and metro area types are analyzed in connection with metro area history, the distributions of residents by race and jobs by income, and qualitative perceptions of density. Finally, the implications of these results for public transportation are discussed, and it is shown that transit commute share in US metro areas is strongly correlated with the number of jobs in dense central business districts.

Thesis Supervisor: Prof. Dillon Mahmoudi, University of Maryland, Baltimore County Department of Geography and Environmental Systems

Abstract: The full effects of the COVID-19 pandemic on U.S. retail may not be fully clear for months. Many stores and restaurants have closed permanently, but some—especially those located in residential neighborhoods where more people are working from home—may benefit from the changes to people’s routines. What is clear is that that these new and powerful impacts on the sector are coming on top of much longer-term changes in how and where people shop.

Post-pandemic, every metropolitan area—but especially metro areas in the Midwest and the Southeast—will find themselves with surplus retail space in need of major capital investment for adaptive reuse. Short-term strategies to stabilize department-store-anchored malls will not last against long-term trends, and long-standing racial disparities in access to retail will reinforce structural racism at a time when the nation is crying out for racial justice. The industry and policymakers should view this as an opportunity to work together to create new opportunities for housing, institutional uses, and locally empowered retail entrepreneurship.

Abstract: Density is one of the most fundamental properties of urban areas: what makes a city different from a suburb, and suburbs different from rural areas is chiefly how many people there are, and how close they are to each other. However, measuring the number of people or jobs per square mile does not reflect the effect of street networks on density as observed by a pedestrian.

Most neighborhoods in American metro areas don’t have ideal street grids, however: winding roads and cul-de-sacs force pedestrians to take indirect trips, and bodies of water, hills, freeways, industrial areas, and superblocks often pose barriers, reducing the number of destinations that can be reached by walking a given distance. In this article, I present a statistic called “Percent Ideal Walkshed” that takes this into account by measuring the fraction of locations within a half mile of the center a block group that are actually within a half-mile walk of it.

Abstract: A series of studies report elevated rates of autism and autistic characteristics among gender-diverse youth seeking gender services. Although youth with the co-occurrence present with complex care needs, existing studies have focused on co-occurrence rates. Further, clinical commentaries have emphasized provider-centered interpretations of clinical needs rather than key stakeholder-driven clinical approaches. This study aimed to employ community-based participatory research methodologies to develop a key stakeholder-driven clinical group program.

Autistic/neurodiverse gender-diverse (A/ND-GD) youth (N = 31), parents of A/ND-GD youth (N = 46), A/ND-GD self-advocates (N = 10), and expert clinical providers (N = 10) participated in a multi-stage community-based participatory procedure. Needs assessment data were collected repeatedly over time from A/ND-GD youth and their parents as the youth interacted with one another through ongoing clinical groups, the curriculum of which was developed progressively through the iterative needs assessments.

Separate adolescent and parent needs assessments revealed key priorities for youth (e.g., the importance of connecting with other A/ND-GD youth and the benefit of experiencing a range of gender-diverse role models to make gender exploration and/or gender affirmation more concrete) and parents (e.g., the need for A/ND-related supports for their children as well as provision of an A/ND-friendly environment that fosters exploration of a range of gender expressions/options). Integration and translation of youth and parent priorities resulted in 11 novel clinical techniques for this population.

With generally high acceptability ratings for each component of the group program, this study presents a community-driven clinical model to support broad care needs and preferences of A/ND-GD adolescents.

Abstract: While both molecular fluorine (F₂) and xenon difluoride (XeF₂) fluorinate Si(100)2×1 surfaces at coverages up to one monolayer, fluorine is unable to cleave Si-Si bonds that ultimately leads to etching silicon at coverages above one monolayer (reaction probability 9×10^–4) while XeF₂ does so readily (reaction probability 0.6). Previous studies have demonstrated that both fluorine and xenon difluoride react with silicon via atom-abstraction mechanisms at low coverages, and that the XeF radicals produced by atom abstraction from xenon difluoride dissociate in the gas phase, producing a source of F radicals that may contribute to Si-Si bond cleavage by formation of multiple F-Si bonds. In addition, it has been shown that van der Waals clusters of F₂ with a Xe atom and with a Kr atom have reaction probabilities with silicon at one monolayer of fluorine coverage of roughly 0.9 and 0.04, respectively, suggesting that the effect of mass of the incident gas molecules is important in activating the cleavage of silicon-silicon bonds through a multiple collision process.

A model based on a classical harmonic oscillator linked via a variable damping term to the thermal energy of the lattice is proposed to test the importance of the mass of the gas molecules to energy transfer and the duration of the vibrational excitation of the silicon-silicon lattice bonds. Computer simulations using this model suggest that the mass of the gas molecule does not affect the overall energy transferred to the silicon. However, the heavy mass and the resulting multiple collisions do extend the duration of the silicon excitation and the duration during which the gas molecule is in contact with the vibrationally excited silicon lattice.

The techniques that have been used to study the reactivity of fluorine compounds with silicon are potentially of use to the study of another problem: why triplet molecular oxygen (O₂) is able to dissociatively chemisorb across singlet silicon-silicon dimer bonds to form the singlet Si-O product. Several mechanisms, including atom abstraction and non-adiabatic ladder climbing of (O₂)₂ van der Waals dimers are suggested to explain this reaction and a series of experiments to test the hypothesized mechanisms are proposed.

In addition, a detailed account of the ultra-high-vacuum molecular beam surface scattering apparatus used for these studies is provided, including a detailed description of its operation and maintenance procedures.

Thesis Supervisor: Prof. Sylvia T. Ceyer, MIT Department of Chemistry

Abstract: While both molecular fluorine (F₂) and xenon difluoride (XeF₂) fluorinate Si(100)2×1 surfaces at coverages up to one monolayer, fluorine is unable to cleave Si-Si bonds that ultimately leads to etching silicon at coverages above one monolayer (reaction probability 9×10^–4) while XeF₂ does so readily (reaction probability 0.6). Experimental work presented here demonstrate that van der Waals clusters of F₂ with a Xe atom and with a Kr atom have reaction probabilities with silicon at one monolayer of fluorine coverage of roughly 0.9 and 0.04, respectively, suggesting that the effect of mass of the incident gas molecules is important in activating the cleavage of silicon-silicon bonds through a multiple collision process.

Abstract: There is significant interest in improved sensitivity and decreased measurement times for nuclear magnetic resonance and magnetic resonance imaging of small molecules, especially those with ¹³C and ¹⁵N spin labels. A source of spin polarizations of order unity is spin-exchange optical pumping, which produces ¹²⁹Xe with fractional polarization of order unity, about 10⁵ higher than is achieved at equilibrium in high field.

The research presented is the development and testing of components of an apparatus intended to bring target molecules, such as acetic acid, into the close (near 1 nm) contact with hyperpolarized ¹²⁹Xe atoms as needed to effect rapid equalization of their spin temperatures through dipolar couplings. Specifically, an apparatus has been designed and is being built with the intention of rapidly depositing a gaseous mixture of xenon and the target molecule as a homogeneous solid under a strong magnetic field, then dropping the field strength to allow spin equalization through dipolar couplings followed by rapid production of a liquid sample of the target molecule at room temperature.

Thesis Advisor: Prof. Daniel P. Weitekamp, Caltech Department of Chemistry

Abstract: Light pollution is artificially-produced light which serves no useful purpose. It may be light directed toward places that do not need illumination or light that is directed directly into the sky. There are many different sources of light pollution. One way in which light pollution sources differ is their spectra—different light sources have different spectra and thus alter the night time sky glow in different ways. One can determine the proportions of light pollution produced by different light sources.

Spectra were taken in three directions: Baltimore, MD, Washington, DC, and Annapolis, MD. It should be noted that Laurel and Columbia, MD are in the same general direction as Baltimore and that Bowie, MD is in the same general direction as Annapolis, MD. Spectra of Washington were also taken both in the early evening and around midnight. Lines produced by sodium, mercury, scandium, thorium, lithium, oxygen, neon, and high-pressure sodium were detected. Sodium D lines and scandium lines were stronger in Baltimore than in any other city, suggesting that low pressure sodium and metal halide lamps are more prevalent there. Mercury and sodium lines increased over the course of the night, suggesting that the proportion of the sky glow produced by mercury vapor and high pressure sodium lamps increases over the course of the night. This study showed that the breakdown of light pollution spectra does change over the course of a night and that different cities do produce different sky glow spectra

Thesis Advisor: Ronald J. Oliversen, NASA Goddard Space Flight Center