<?xml version="1.0" encoding="UTF-8"?><?xml-stylesheet type="text/xsl" href="static/style.xsl"?><OAI-PMH xmlns="http://www.openarchives.org/OAI/2.0/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/ http://www.openarchives.org/OAI/2.0/OAI-PMH.xsd"><responseDate>2026-09-21T02:58:13Z</responseDate><request verb="GetRecord" identifier="oai:dspace.mit.edu:1721.1/151508" metadataPrefix="dim">https://dspace.mit.edu/server/oai/request</request><GetRecord><record><header><identifier>oai:dspace.mit.edu:1721.1/151508</identifier><datestamp>2023-08-01T03:08:13Z</datestamp><setSpec>com_1721.1_7582</setSpec><setSpec>com_1721.1_7581</setSpec><setSpec>col_1721.1_131022</setSpec></header><metadata><dim:dim xmlns:dim="http://www.dspace.org/xmlns/dspace/dim" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:doc="http://www.lyncode.com/xoai" xsi:schemaLocation="http://www.dspace.org/xmlns/dspace/dim http://www.dspace.org/schema/dim.xsd">
   <dim:field mdschema="dc" element="contributor" qualifier="advisor">Hintz, Peter</dim:field>
   <dim:field mdschema="dc" element="contributor" qualifier="author">Sussman, Ethan W.</dim:field>
   <dim:field mdschema="dc" element="contributor" qualifier="department">Massachusetts Institute of Technology. Department of Mathematics</dim:field>
   <dim:field mdschema="dc" element="date" qualifier="accessioned">2023-07-31T19:45:07Z</dim:field>
   <dim:field mdschema="dc" element="date" qualifier="available">2023-07-31T19:45:07Z</dim:field>
   <dim:field mdschema="dc" element="date" qualifier="issued">2023-06</dim:field>
   <dim:field mdschema="dc" element="date" qualifier="submitted">2023-05-24T14:46:51.942Z</dim:field>
   <dim:field mdschema="dc" element="identifier" qualifier="uri">https://hdl.handle.net/1721.1/151508</dim:field>
   <dim:field mdschema="dc" element="description" qualifier="abstract">In this thesis, we examine the transition between Legendrian regularity and ellipticity at infinity for two PDEs, the Schrödinger–Helmholtz equation with an attractive long range potential and the Klein–Gordon equation. In the former case, the transition occurs as the spectral parameter 𝐸 → 0⁺, and thus describes the ionization of Hydrogenic atoms, and in the latter case the transition occurs at null infinity, where the phase in the asymptotic tails becomes singular. Using novel microlocal tools, we work in the variable coefficient setting throughout.</dim:field>
   <dim:field mdschema="dc" element="description" qualifier="degree">Ph.D.</dim:field>
   <dim:field mdschema="dc" element="publisher">Massachusetts Institute of Technology</dim:field>
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   <dim:field mdschema="dc" element="title">Scattering at threshold in massive wave propagation and ionization</dim:field>
   <dim:field mdschema="dc" element="type">Thesis</dim:field>
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   <dim:field mdschema="mit" element="thesis" qualifier="degree">Doctoral</dim:field>
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   	&lt;Title>Scattering at threshold in massive wave propagation and ionization&lt;/Title>
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   	&lt;PublicationDate>2023-06&lt;/PublicationDate>
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        	&lt;DisplayName>Sussman, Ethan W.&lt;/DisplayName>
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            &lt;DisplayName>Massachusetts Institute of Technology&lt;/DisplayName>
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   	&lt;Abstract>In this thesis, we examine the transition between Legendrian regularity and ellipticity at infinity for two PDEs, the Schrödinger–Helmholtz equation with an attractive long range potential and the Klein–Gordon equation. In the former case, the transition occurs as the spectral parameter 𝐸 → 0⁺, and thus describes the ionization of Hydrogenic atoms, and in the latter case the transition occurs at null infinity, where the phase in the asymptotic tails becomes singular. Using novel microlocal tools, we work in the variable coefficient setting throughout.&lt;/Abstract>
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