Radiative transfer modelling of parsec-scale dusty warped discs

Warped discs have been found on (sub-)parsec scale in some nearby Seyfert nuclei, identified by their maser emission. Using dust radiative transfer simulations we explore their observational signatures in the infrared in order to find out whether they can partly replace the molecular torus. Strong variations of the brightness distributions are found, depending on the orientation of the warp with respect to the line of sight. Whereas images at short wavelengths typically show a disc-like and a point source component, the warp itself only becomes visible at far-infrared wavelengths. A similar variety is visible in the shapes of the spectral energy distributions. Especially for close to edge-on views, the models show silicate feature strengths ranging from deep absorption to strong emission for variations of the lines of sight towards the warp. To test the applicability of our model, we use the case of the Circinus galaxy, where infrared interferometry has revealed a highly elongated emission component matching a warped maser disc in orientation and size. Our model is for the first time able to present a physical explanation for the observed dust morphology as coming from the AGN heated dust. As opposed to available torus models, a warped disc morphology produces a variety of silicate feature shapes for grazing lines of sight, close to an edge-on view. This could be an attractive alternative to a claimed change of the dust composition for the case of the nearby Seyfert 2 galaxy NGC 1068, which harbours a warped maser disc as well.Comment: accepted by MNRA

The Vacancy Rate and Rent Levels in the Commercial Office Market

This paper develops and estimates a cross-sectional model of the commercial office market in which the building vacancy rate is a key factor in the determination of rents. Individual buildings in Greensboro, North Carolina are used as the unit of analysis and simultaneous equation procedures are employed to produce estimates of rent per square foot. The estimates confirm that the vacancy rate must be included when estimating the price of commercial office space.

Anthropogenic Disturbances in Estuarine Ecosystems: The Effects of Altered Freshwater Inflow, Introduction of Invasive Species, and Habitat Alteration in the Loxahatchee River, FL

With the majority of Earth’s population living in coastal areas, estuarine ecosystems have been particularly affected by anthropogenic disturbances. My dissertation research focused on three interrelated types of human disturbance that affect estuaries: Anthropogenic alteration of freshwater inflow, the introduction of invasive species, and habitat alteration. Using the LoxahatcheeRiver(Jupiter, FL) as a model system, my goal was to understand how these disturbances affect estuarine organisms, particularly fishes. One of the most ecologically harmful disturbances affecting estuaries is anthropogenic alteration of freshwater inflow (and resulting changes in salinity patterns). To identify effects of freshwater inflow on the behavior of an ecologically and economically important fish (common snook Centropomus undecimalis), I conducted a 19-month acoustic telemetry study. Common snook were more abundant and made more frequent upstream migrations during the wet season, but freshwater inflow did not appear to be the proximate cause for these behaviors. Increased estuarine salinity resulting from anthropogenic flow alteration may have facilitated the second type of disturbance that I address in this dissertation; the invasion of non-native Indo-Pacific lionfish into estuarine habitats. During the course of my dissertation research, I documented the first ever estuarine invasion by non-native lionfish. Using mark-recapture, I identified high site fidelity in lionfish, a trait that may aid future control efforts. The extremely low minimum salinity tolerance that I identified in lionfish appears to have allowed the species to colonize far upriver in estuaries with anthropogenically modified salinity patterns. Anthropogenic salinity alteration has also led to a severe degradation of oyster reef habitats in theLoxahatcheeRiver. As a foundation species, oysters provide food, shelter, and nursery habitat for a wide variety of estuarine organisms, including many ecologically and economically important fishes. Increasingly, degraded oyster reef habitats have been the focus of restoration efforts. I identified a relatively rapid (\u3c 2 years) convergence between restored and natural oyster reef communities, and documented the importance of vertical relief in restoration success. My dissertation research is critical for the management and conservation of coastal rivers inFlorida, while more broadly informing restoration and management decisions in many other estuarine and coastal ecosystems

The Earnings of REALTORS: Some Empirical Evidence

This paper explores the factors that influence the earnings of REALTORS. It presents estimates of a human capital earnings model estimated on the basis of a nationwide survey of REALTORS collected by the National Association of REALTORS in 1984. Estimates of this model are compared to previous studies that have been based on surveys of REALTORS in individual states.

Provision of ecosystem services by human-made structures in a highly impacted estuary

Water filtration is one of the most important ecosystem services provided by sessile organisms in coastal ecosystems. As a consequence of increased coastal development, human-made shoreline structures (e.g., docks and bulkheads) are now common, providing extensive surface area for colonization by filter feeders. We estimate that in a highly urbanized sub-tropical estuary, water filtration capacity supported by filter feeding assemblages on dock pilings accounts for 11.7 million liters of water h−1, or ~30% of the filtration provided by all natural oyster reef throughout the estuary. Assemblage composition, and thus filtration capacity, varied as a function of piling type, suggesting that the choice of building material has critical implications for ecosystem function. A more thorough depiction of the function of coastal ecosystems necessitates quantification of the extensive ecosystem services associated with human-made structures

Atypicalities and Apartment Rent Concessions

This paper examines the use and value of rental concession using a 1988 sample of apartment rents in the Greensboro/High Point/Winston-Salem (North Carolina) MSA. The first section develops an approach to the problem and the second section estimates a logit model to predict the use of concessions as a pricing strategy based on characteristics of the apartment. The third section employs a hedonic pricing model to measure the average value of rental concessions in the Greensboro market. The final section summarizes relevant findings.

The Role of Commission Rates and Specialization in the Determination of Real Estate Agent Income

This paper explores the performance of residential real estate agents and the commission structure under which they operate. This study reveals the interrelationship among the number of properties sold by an agent, the dollar volume of sales, and real estate agent income. This research shows that the ability to generate listings is essential to generating higher levels of income in residential real estate sales. The listings become the platform from which agents leverage their human capital in the generation of income. However, the ability to generate listings is a skill related to experience, as well as to the firm and market environment

Single-Family Housing and Wealth Portfolios

This paper explores the risk and return of a portfolio of single-family housing during 1978:1-2001:4 in the context of a portfolio of financial assets. Homeownership offers higher returns to those who have higher tax brackets, longer investment horizons and use more financial leverage. Housing returns are positively correlated with large-stock returns and negatively correlated with returns on small stocks and debt securities. Portfolio allocation to housing is large in a minimum variance portfolio, and it increases with longer holding periods and higher tax brackets. Homeownership risk and return vary widely among the forty-two MSAs studied, and within an MSA, housing returns exhibit substantial variation

A Note on Agency Size and Brokerage Commission Splits

This paper develops a model to explain the commission split among cooperating real estate brokers operating within a multiple listing service where individual agencies are free to negotiate. The paper provides theoretical and empirical evidence that suggests that the amount of the total commission paid to a cooperating broker is a negative function of the size of the agency that lists the property for sale.

Systems Integration and Test of the Lunar Flashlight Spacecraft

Lunar Flashlight is a 6U CubeSat launching in late 2022 or early 2023 that will search for surface water ice content in permanently shadowed regions at the south pole of the Moon using infrared relative reflectance spectroscopy. The mission will act as a technology demonstration of an Advanced Spacecraft Energetic NonToxic (ASCENT) green propulsion system and active laser spectroscopy within the CubeSat form-factor. This paper provides an overview of the entire Systems Integration and Test campaign which took place at the Jet Propulsion Laboratory and the Georgia Institute of Technology. From initial testing of the isolated avionics and payload subsystems to the final tests with a fully integrated spacecraft, the project’s integration and test campaign is reviewed, with a focus on lessons learned