Wave maps on (1+2)-dimensional curved spacetimes

In this article we initiate the study of 1+ 2 dimensional wave maps on a curved spacetime in the low regularity setting. Our main result asserts that in this context the wave maps equation is locally well-posed at almost critical regularity. As a key part of the proof of this result, we generalize the classical optimal bilinear L^2 estimates for the wave equation to variable coefficients, by means of wave packet decompositions and characteristic energy estimates. This allows us to iterate in a curved X^{s,b} space.Comment: 100 pages, 1 figur

Review of \u3ci\u3eBirds of Prey of the West: A Field Guide,\u3c/i\u3e by Brian K. Wheeler

Birds of prey epitomize much of what attracts us to birding. Many are large and easy to observe, particularly in open landscapes. Their predatory nature and behavior give them an added aura of wildness; their migrations can be spectacular. And even veteran birders should enjoy the challenge of identifying the myriad of plumage variations shown by different ages, sexes, subspecies, and color morphs. With his newest effort, Birds of Prey of the West, Brian Wheeler has compiled a comprehensive and enhanced field guide with illustrations that stunningly capture that variation, combined with enough additional context to make it a valuable desk reference for birders of all levels. The geographic scope of this book is the United States north of Mexico and west of the Mississippi River, and Canada west of Manitoba and the western shore of Hudson Bay, north into Nunavut and across western Canada and Alaska. It covers nearly all the regularly occurring raptors of North America, excluding only the Snail Kite (Rostrhamus sociabilis) of the southeast and a few species of Eurasian and Mexican vagrants (e.g., Steller’s Sea Eagle [Haliaeetus pelagicus] and Roadside Hawk [Rupornis magnirostris]). As such, it may appeal to birders beyond the geography covered, although a companion volume is also available for the East (Wheeler 2018). This informative, richly illustrated book certainly deserves a place on the bookshelf of anyone interested in birds of prey or in the intricacies of bird identification in general

Strongly non embeddable metric spaces

Enflo constructed a countable metric space that may not be uniformly embedded into any metric space of positive generalized roundness. Dranishnikov, Gong, Lafforgue and Yu modified Enflo's example to construct a locally finite metric space that may not be coarsely embedded into any Hilbert space. In this paper we meld these two examples into one simpler construction. The outcome is a locally finite metric space $(\mathfrak{Z}, \zeta)$ which is strongly non embeddable in the sense that it may not be embedded uniformly or coarsely into any metric space of non zero generalized roundness. Moreover, we show that both types of embedding may be obstructed by a common recursive principle. It follows from our construction that any metric space which is Lipschitz universal for all locally finite metric spaces may not be embedded uniformly or coarsely into any metric space of non zero generalized roundness. Our construction is then adapted to show that the group $\mathbb{Z}_\omega=\bigoplus_{\aleph_0}\mathbb{Z}$ admits a Cayley graph which may not be coarsely embedded into any metric space of non zero generalized roundness. Finally, for each $p \geq 0$ and each locally finite metric space $(Z,d)$, we prove the existence of a Lipschitz injection $f : Z \to \ell_{p}$.Comment: 10 page

Progressive Network Deployment, Performance, and Control with Software-defined Networking

The inflexible nature of traditional computer networks has led to tightly-integrated systems that are inherently difficult to manage and secure. New designs move low-level network control into software creating software-defined networks (SDN). Augmenting an existing network with these enhancements can be expensive and complex. This research investigates solutions to these problems. It is hypothesized that an add-on device, or shim could be used to make a traditional switch behave as an OpenFlow SDN switch while maintaining reasonable performance. A design prototype is found to cause approximately 1.5% reduction in throughput for one ow and less than double increase in latency, showing that such a solution may be feasible. It is hypothesized that a new design built on event-loop and reactive programming may yield a controller that is higher-performing and easier to program. The library node-openflow is found to have performance approaching that of professional controllers, however it exhibits higher variability in response rate. The framework rxdn is found to exceed performance of two comparable controllers by at least 33% with statistical significance in latency mode with 16 simulated switches, but is slower than the library node-openflow or professional controllers (e.g., Libfluid, ONOS, and NOX). Collectively, this work enhances the tools available to researchers, enabling experimentation and development toward more sustainable and secure infrastructur

Refinancing the American dream : a modern history of federal policy aimed at ending America’s housing crisis

textThis report seeks to outline recent federal policy regarding home mortgage finance, specifically the Home Affordable Refinance Program (HARP), the main tool of the Making Home Affordable Program (MHA), which is aimed at helping the United States recover from the housing crisis it has been experiencing ever since the mid-late 2000s. A modern history of federal policy on home mortgage finance will help to set the stage for the reader for what has been one of the most difficult housing disasters that America has ever seen. After outlining HARP’s background, the background of the housing crisis, the roles of Government-sponsored entities, and the effectiveness of the most current federal responses to the crisis, this report will detail policy recommendations and changes to the current programs that may help to further alleviate the problems discussed in this report, and more effectively achieve the stated goals of the MHA and HARP.Community and Regional Plannin

A Grism Design Review and the as-built performance of the silicon grisms for JWST-NIRCAM

Grisms are dispersive transmission optics that find their most frequent use in instruments that combine imaging and spectroscopy. This application is particularly popular in the infrared where imagers frequently have a cold pupil in their optical path that is a suitable location for a dispersive element. In particular, several recent and planned space experiments make use of grisms in slit-less spectrographs capable of multi-object spectroscopy. We present an astronomer-oriented general purpose introduction to grisms and their use in current and future astronomical instruments. We present a simple, step-by-step procedure for adding a grism spectroscopy capability to an existing imager design. This procedure serves as an introduction to a discussion of the device performance requirements for grisms, focusing in particular on the problems of lithographically patterned silicon devices, the most effective grism technology for the 1.1-8 micron range. We begin by summarizing the manufacturing process of monolithic silicon gratings. We follow this with a report in detail on the as-built performance of parts constructed for a significant new space application, the NIRCam instrument on JWST and compare these measurements to the requirements.Comment: Accepted for publication in PAS

Characterization of Adsorption Processes in High-Temperature CO2 Sorbents

The proposed work aims to develop novel membrane technology for efficient, high selective high-temperature carbon dioxide and simultaneous carbon dioxide and sulfur dioxide capture. Realization of high-performance membranes for such applications is widely recognized as a potentially revolutionary technology for continuous carbon capture. The research focuses on two materials: sodium oxide promoted alumina and silicalite-1. The main objectives involve synthesizing and characterizing the materials. Membranes will then be modeled, synthesized, and characterized. Success of this program should lead to novel practical and fundamental insight and, potentially, the establishment of a new paradigm for membrane based carbon sequestration.https://preserve.lehigh.edu/undergrad-scholarship-freed-posters/1021/thumbnail.jp