Strategies to Overcome Network Congestion in Infrastructure Systems

Networked Infrastructure systems deliver services and/or products from point to point along the network. They include transportation networks (e.g., rails, highways, airports, sea ports), telecommunication networks (by frequency-bounded airwaves or cables), and utilities (e.g., electric power, water, gas, oil, sewage). Each is a fixed capacity system having marked time-of-day and day-of-week patterns of demand. Usually, the statistics of demand, including hourly patterns (i.e., means and variances) are well known and often correlated with outside factors such as weather (short term) and the general economy (longer term)

Implementing Congestion Pricing on Metropolitan Highway Networks with Self-Financing Public-Private Partnerships

This paper presents a new public-private partnership model for road pricing applications either at the facility level or on a region-wide highway network. The model addresses issues of monopoly power and efficiency of delivery of transportation services. The paper also addresses issues relating to financial self-sufficiency of integrated multimodal pricing strategies and assesses the financial self-sufficiency of an ambitious region-wide pricing concept that integrates multimodal mobility choices

The Role of GIS to Enable Public-Sector Decision Making Under Conditions of Uncertainty

Uncertainty is inherent in environmental planning and decision making. For example, water managers in arid regions are attuned to the uncertainty of water supply due to prolonged periods of drought. To contend with multiple sources and forms of uncertainty, resource managers implement strategies and tools to aid in the exploration and interpretation of data and scenarios. Various GIS capabilities, such as statistical analysis, modeling and visualization are available to decision makers who face the challenge of making decisions under conditions of deep uncertainty. While significant research has lead to the inclusion and representation of uncertainty in GIS, existing GIS literature does not address how decision makers implement and utilize GIS as an assistive technology to contend with deep uncertainty. We address this gap through a case study of water managers in the Phoenix Metropolitan Area, examining how they engage with GIS in making decisions and coping with uncertainty. Findings of a qualitative analysis of water mangers reveal the need to distinguish between implicit and explicit uncertainty. Implicit uncertainty is linked to the decision-making process, and while understood, it is not displayed or revealed separately from the data. In contrast, explicit uncertainty is conceived as separate from the process and is something that can be described or displayed. Developed from twelve interviews with Phoenix-area water managers in 2005, these distinctions of uncertainty clarify the use of GIS in decision making. Findings show that managers use the products of GIS for exploring uncertainty (e.g., cartographic products). Uncertainty visualization emerged as a current practice, but definitions of what constitutes such visualizations were not consistent across decision makers. Additionally, uncertainty was a common and even sometimes helpful element of decision making; rather than being a hindrance, it is seen as an essential component of the process. These findings contradict prior research relating to uncertainty visualization where decision makers often express discomfort with the presence of uncertainty.

Shifted distinct-part partition identities in arithmetic progressions

The partition function $p(n)$, which counts the number of partitions of a positive integer $n$, is widely studied. Here, we study partition functions $p_S(n)$ that count partitions of $n$ into distinct parts satisfying certain congruence conditions. A shifted partition identity is an identity of the form $p_{S_1}(n-H) = p_{S_2}(n)$ for all $n$ in some arithmetic progression. Several identities of this type have been discovered, including two infinite families found by Alladi. In this paper, we use the theory of modular functions to determine the necessary and sufficient conditions for such an identity to exist. In addition, for two specific cases, we extend Alladi's theorem to other arithmetic progressions

Chemical Evolution in Hierarchical Models Of Cosmic Structure I: Constraints on the Early Stellar Initial Mass Function

I present a new Galactic chemical evolution model motivated by and grounded in the hierarchical theory of galaxy formation, as expressed by a halo merger history of the Galaxy. This model accurately reproduces the "metallicity distribution function" (MDF) for Population II stars residing today in the Galactic halo. The observed MDF and the apparent absence of true Population III stars from the halo strongly imply that there is some critical metallicity, Z_crit <~ 10^-4 Z_sun, below which low-mass star formation is inhibited, and perhaps impossible. The observed constraints from the halo MDF, relative metal abundances from Galactic halo stars, and the ionizing photon budget needed to reionize the IGM together imply a stellar IMF that is peaked in the range of massive stars that experience core-collapse supernovae, with mean mass = 8 - 42 Msun. This mass range is similar to the masses predicted by models of primordial star formation that account for formation feedback. The model also implies that metal-poor halo stars below [Fe/H] <~ -3 had only 1 - 10 metal-free stars as their supernova precursors, such that the relative abundances in these halo stars exhibit IMF-weighted averages over the intrinsic yields of the first supernovae. This paper is the first part of a long term project to connect the high-redshift in situ indicators of early star formation with the low-z, old remnants of the first stars.Comment: Submitted to ApJ, 22 pages in emulate ApJ format, uncompressed figures available from http://astro.uchicago.edu/~tumlinso/fs.htm

Place Attachment and Willingness to Pay: How Do Visitors Value State Parks?

Abstract State parks provide benefits for members of the public who may not have access to natural environments. In this context, it is critical to understand how minority groups value and depend on state parks. To better understand these issues research was conducted during the summers of 2009 and 2010 at three state parks in north Georgia. Intercept surveys were administered to 929 state park visitors. Data pertaining to whether or not visitors perceived themselves as being dependent on state parks and were willing to pay for parks were collected. Results of an exploratory factor analysis suggested that place dependency varied by race/ethnicity, education and income. Results revealed a positive relationship between willingness to pay and place dependency. Results of this study may provide Georgia state park managers with a better understanding of how visitors, in particular minorities, value state parks