arXiv subjects

Patrick Walker

Publications and source records attributed to Patrick Walker.

3 recordsLinked to original sources

arXiv2026

Low Energy Neutrinos in Milky Way and Cloud-9

We study low-energy galactic neutrinos in the Milky Way under two descriptions of gravity and show that they can prove gravity underlying nature. If gravity is quantum, its long-range interaction produces an atom-like bound neutrino structure. However, we find that withing 292 kpc, this structure contributes only 10 to the -29 of the galaxy dark matter, ruling it out as a deark-matter candidate. Its detection would nevertheless provide direct evidence for quantum gravity mediated by gravitons. If gravity instead arises from spacetime curvature, neutrinos interact only through the short-range weak force and behave as free, collisionless classical particles orbiting the galaxy. In this regime, they do not experience Fermi pressure and can form a sufficiently compact population to reproduce the Milky Way rotation curve. We further model Cloud-9 dark-matter compoent as free, collisionless neutrinos. Because neutrino-antinetrino annihilation cross section is extremely small, neutrinos and antineutrinos may remai near equilibrium over cosmological timescales, potentially relating this framework to the observed matter-antimatter assymmetry.

hep-ph↗

arXiv2025

Multimodal Optical Imaging Platform for Quantitative Burn Assessment

Accurate assessment of burn severity at injury onset remains a major clinical challenge due to the lack of objective methods for detecting subsurface tissue damage. This limitation is critical in battlefield and mass-casualty settings, where rapid and reliable evaluation of burn depth is essential for triage and surgical decision-making. We present a multimodal optical imaging framework that establishes the foundation for a compact, low-size, weight, and power (low-SWaP) field-deployable device for quantitative burn assessment. The system integrates broadband hyperspectral imaging (VSWIR, 400 -- 2100 nm) with laser speckle contrast imaging to jointly evaluate biochemical composition and microvascular perfusion. Using short-wave infrared (SWIR, >1000 nm) wavelengths, we developed and validated novel deep-tissue parameters linked to water, lipid, and collagen absorption features that enhance burn-tissue separability and burn severity classification. We implemented and validated unsupervised learning methods for spectral feature extraction, band down-selection, and clustering against histology, establishing a foundation for a rugged, data-driven device for early quantitative burn evaluation in austere environments.

eess.IV↗

arXiv2022

Consideration of the Intricacies Inherent in Molecular Beam Epitaxy of the NaCl/GaAs System

The high cost of substrates for III-V growth can be cost limiting for technologies that require large semiconductor areas. Thus, being able to separate device layers and reuse the original substrate is highly desirable, but existing techniques to lift off a film from a substrate have substantial drawbacks. This work discusses some of the complexities with the growth of a water-soluble, alkali-halide salt thin film between a III-V substrate and overlayer. Much of the difficulty stems from the growth of GaAs on an actively decomposing NaCl surface at elevated temperatures. Interestingly, the presence of an in-situ electron beam incident on the NaCl surface, prior to and during GaAs deposition, affects the crystallinity and morphology of the III-V overlayer. Here we investigate a wide range of growth temperatures and the timing of the impinging flux of both elemental sources and high energy electrons at different points during the growth. We show that an assortment of morphologies (discrete islands, porous material, and fully dense layers with sharp interfaces) and crystallinity (amorphous, crystalline, and highly textured) occur depending on the specific growth conditions, driven largely by changes in GaAs nucleation which is greatly affected by the presence of the reflection high energy electron diffraction beam.

cond-mat.mtrl-sci↗