Engineering Commons^™

Fast Neutron Assay Of Elemental Content Of Bulk Samples, Calder Emerson Lane

UNLV Theses, Dissertations, Professional Papers, and Capstones

The purpose of this research was to analyze the capabilities of fast neutrons in the detection and analysis of various isotopes in bulk samples. The deuterium-tritium (DT) fusion reaction generates highly penetrating, high-energy (14.1-MeV) neutrons which induce nuclear reactions in irradiated targets. Neutrons and gamma rays are generated in these reactions. Emitted gamma rays are characteristic of the emitter; the gamma spectrum enables stoichiometric identification of the assayed samples. Neutron backscattering can also be used for identification of the elemental composition of the sample.

This work had three objectives. The first objective was to develop a computational technique to model …

On-Chip Terahertz Modulation And Emission With Integrated Graphene Junctions, Joshua O. Island, Peter Kissin, Jacob Schalch, Xiaomeng Cui, Sheikh Rubaiat Ui Haque, Alex Potts, Takashi Taniguchi, Kanji Watanabe, Richard D. Averitt, Andrea F. Young

Physics & Astronomy Faculty Research

The efficient modulation and control of ultrafast signals on-chip is of central importance in terahertz (THz) communications and a promis- ing route toward sub-diffraction limit THz spectroscopy. Two-dimensional (2D) materials may provide a platform for these endeavors. We explore this potential, integrating high-quality graphene p–n junctions within two types of planar transmission line circuits to modulate and emit picosecond pulses. In a coplanar strip line geometry, we demonstrate the electrical modulation of THz signal transmission by 95%. In a Goubau waveguide geometry, we achieve complete gate-tunable control over THz emission from a photoexcited graphene junction. These studies inform the development …

Buckling Of Blue Phosphorus Nanotubes Under Axial Compression: Insights From Molecular Dynamics Simulations, Shiping Jiang, Huiling Wu, Liangzhi Kou, Chun Tang, Chengyuan Wang, Changfeng Chen

Physics & Astronomy Faculty Research

We report on mechanical properties of blue phosphorus nanotubes (BluePNTs) from systematic molecular dynamics simulations, adopting a Stillinger-Weber potential with parameters determined by fitting to energetic and structural data from first-principles calculations. Our results corroborate the previously reported bending poison effect and size-dependent buckling behaviors. Under axial compression, current simulations predict a shell-to-column buckling mode transition for BluePNTs with increasing aspect ratios; further compression of BluePNTs with large aspect ratios results in a column-to-shell buckling mode transition. Associated critical buckling strains can be described by the continuum mechanics theory. We also simulated buckling behavior of black phosphorus nanotubes (BlackPNTs) and …