@article{hunt_iliadis_champagne_downen_cooper_2019, title={New measurement of the E-alpha(lab)=0.83 MeV resonance in Ne-22(alpha,gamma)Mg-26}, volume={99}, ISSN={["2469-9993"]}, DOI={10.1103/PhysRevC.99.045804}, abstractNote={The ${E}_{\ensuremath{\alpha}}^{\text{lab}}=0.83$ MeV resonance in the $^{22}\mathrm{Ne}(\ensuremath{\alpha},\ensuremath{\gamma})^{26}\mathrm{Mg}$ reaction strongly impacts the reaction rates in the stellar temperature region crucial for the astrophysical s process. We report on a new measurement of the energy and strength of this resonance using techniques different from previous investigations. We use a blister-resistant $^{22}\mathrm{Ne}$-implanted target and employ $\ensuremath{\gamma}\ensuremath{\gamma}$-coincidence detection techniques. We find values for the resonance energy and strength of ${E}_{\ensuremath{\alpha}}^{\text{lab}}=835.2\ifmmode\pm\else\textpm\fi{}3.0$ keV and $\ensuremath{\omega}\ensuremath{\gamma}=(4.6\ifmmode\pm\else\textpm\fi{}1.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ eV, respectively. Our mean values are higher compared to previous values, although the results overlap within uncertainties. The uncertainty in the resonance energy has been significantly reduced. The spin-parity assignment, based on the present and previous work, is ${J}^{\ensuremath{\pi}}=$ (${0}^{+}$, ${1}^{\ensuremath{-}}$, ${2}^{+}$, ${3}^{\ensuremath{-}}$).}, number={4}, journal={PHYSICAL REVIEW C}, author={Hunt, Sean and Iliadis, Christian and Champagne, Art and Downen, Lori and Cooper, Andrew}, year={2019}, month={Apr} }
 @article{maity_downen_bochinski_clarke_2011, title={Embedded metal nanoparticles as localized heat sources: An alternative processing approach for complex polymeric materials}, volume={52}, ISSN={["1873-2291"]}, DOI={10.1016/j.polymer.2011.01.062}, abstractNote={Metal nanoparticles were utilized as heating elements within nanofibers to demonstrate an alternative approach to thermally process nanostructured polymeric materials. In the photothermal process, resonant light excites the surface plasmon of the nanoparticle and the absorbed energy is converted into heat due to electron-phonon collisions. This heating is efficient and strongly localized, generated from the nanometer-sized metal particles embedded within the polymer. Composite polyethylene oxide (PEO) nanofibers, containing differing concentrations and types of nanoparticles, were fabricated by electrospinning and irradiated by a low intensity laser tuned specifically to the metal nanoparticle surface plasmon absorbance; aggregation of fibers, loss of fibrous structure, and ultimately, complete melting were observed. The photothermal response to irradiation increased with nanoparticle concentration as long as particle aggregation was avoided. Pure PEO nanofibers, or those containing metal nanoparticles possessing a non-resonant surface plasmon, were also irradiated but no melting occurred, demonstrating the controllable specificity of this approach.}, number={7}, journal={POLYMER}, author={Maity, Somsubhra and Downen, Lori N. and Bochinski, Jason R. and Clarke, Laura I.}, year={2011}, month={Mar}, pages={1674–1685} }
 @article{stevens_skau_downen_roman_clarke_2011, title={Finite-size effects in nanocomposite thin films and fibers}, volume={84}, ISSN={["1550-2376"]}, DOI={10.1103/physreve.84.021126}, abstractNote={Monte Carlo simulations of finite-size effects for continuum percolation in three-dimensional, rectangular sample spaces filled with spherical particles were performed. For samples with any dimension less than 10-20 times the particle diameter, finite-size effects were observed. For thin films in the finite-size regime, percolation across the thin direction of the film gave critical volume fraction (p(c)) values that differed from those along the plane of the film. Simulations perpendicular to the film for very thin samples resulted in p(c) values lower than the classical limit of ∼29% (for spheres in a three-dimensional matrix) which increased with film thickness. For percolation along thin films, while holding film thickness constant, p(c) increased with increasing sample size, which is a modification of the finite-sized scaling effect for cubic samples. For samples with a large aspect ratio (fibers) and a finite-sized cross-sectional area, the critical volume fraction increased with sample length, as the sample became quasi-one-dimensional. The results are discussed in the context of adding volume along or perpendicular to the percolation direction. From an experimental perspective, these findings indicate that sample shape, as well as relative size, influences percolation in the finite-size regime.}, number={2}, journal={PHYSICAL REVIEW E}, author={Stevens, D. R. and Skau, E. W. and Downen, L. N. and Roman, M. P. and Clarke, L. I.}, year={2011}, month={Aug} }
 @article{stevens_downen_clarke_2008, title={Percolation in nanocomposites with complex geometries: Experimental and Monte Carlo simulation studies}, volume={78}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.78.235425}, abstractNote={The development of nanocomposites (a matrix, often polymeric, enhanced by a particle with a nanometer-sized dimension) has expanded dramatically in recent years with a particular focus on materials with complex microstructure and nanostructure. Such composites rely on formation of a connected network of particles throughout the sample volume in order to enhance the polymer's mechanical and electrical properties. From a fundamental perspective, this network formation will be governed by a percolation process within the constrained geometry of the particular microstructure. In this paper, the percolation process within a particular complex nanostructure, namely, a mat of electrospun nanofibers with fiber size of $\ensuremath{\approx}100\text{ }\text{nm}$ and high porosity, is studied via continuum Monte Carlo simulations, where the sample geometry (fiber and particle sizes, orientation, and sample porosity) is matched to the mats utilized in our previous experimental work. A good agreement between experimental and computational results is observed. Simulations of spherical dopant in uniform samples, with zero, one, or two sample dimensions similar in size to the particle, were completed to explore the effects of confinement, in particular within a single fiber. These results were compared and contrasted with those from porous fibrous mats to determine the influence of porosity on the critical volume fraction. The results indicate that percolation in fibrous mats occurs via pathways that include sections of many fibers rather than being contained within single fibers which span the sample. The detailed dependence of critical volume fraction on porosity and the sensitivity to fiber number and width is discussed.}, number={23}, journal={PHYSICAL REVIEW B}, author={Stevens, D. R. and Downen, L. N. and Clarke, L. I.}, year={2008}, month={Dec} }