Finding Critical Nuclei in Phase Transformations by Shrinking Dimer Dynamics and its Variants

AbstractWe investigate the critical nuclei morphology in phase transformation by combining two effective ingredients, with the first being the phase field modeling of the relevant energetics which has been a popular approach for phase transitions and the second being shrinking dimer dynamics and its variants for computing saddle points and transition states. In particular, the newly formulated generalized shrinking dimer dynamics is proposed by adopting the Cahn-Hilliard dynamics for the generalized gradient system. As illustrations, a couple of typical cases are considered, including a generic system modeling heterogeneous nucleation and a specific material system modeling the precipitate nucleation in FeCr alloys. While the standard shrinking dimer dynamics can be applied to study the non-conserved case of generic heterogeneous nucleation directly, the generalized shrinking dimer dynamics is efficient to compute precipitate nucleation in FeCr alloys due to the conservation of concentration. Numerical simulations are provided to demonstrate both the complex morphology associated with nucleation events and the effectiveness of generalized shrinking dimer dynamics based on phase field models.

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EXPRESS: Spectral Considerations for Standoff Infrared Detection of RDX on Reflective Aluminum

Applied Spectroscopy ◽

10.1177/00037028211053865 ◽

2021 ◽

pp. 000370282110538

Author(s):

Kevin J Major ◽

Jas Sanghera ◽

Mikella E. Farrell ◽

Ellen L Holthoff ◽

Paul M Pellegrino ◽

...

Keyword(s):

Surface Concentration ◽

Thin Layers ◽

Infrared Detection ◽

Aluminum Surface ◽

Material System ◽

Spectral Signatures ◽

Spectral Changes ◽

Standoff Detection ◽

Infrared Spectrometer ◽

Specific Material

This paper examines infrared spectroscopic effects for the standoff detection of an explosive material, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), inkjet printed on an aluminum surface. Results of a spectroscopic study are described, using multiple optical setups. These setups were selected to explore how variations in the angles of incidence and collection from the surface of the material result in corresponding variations in the spectral signatures. The goal of these studies is to provide an understanding of these spectral changes, since it affects standoff detection of hazardous materials on a reflective substrate. We demonstrate that variations in spectral effects are dependent on the relative surface concentration of the deposited RDX. We also show that it is reasonable to use spectroscopic data collected in a standard laboratory infrared spectrometer outfitted with a variable angle reflectometer set at 0ï° as reference spectra for data collected in a standoff configuration. These results are important to provide a systematic approach to understanding IR spectra collection using standoff systems in the field, and to allow for comparison between such data, and data collected in the laboratory. Though the precise results are constrained to a specific material system (thin layers on a reflective substrate), the approach and general discussion provided are applicable to a broad range of IR standoff sensing techniques and applications.

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Phase-field modeling of the microstructure evolution and heterogeneous nucleation in solidifying ternary Al–Cu–Ni alloys

Acta Materialia ◽

10.1016/j.actamat.2014.09.057 ◽

2015 ◽

Vol 83 ◽

pp. 448-459 ◽

Cited By ~ 3

Author(s):

Julia Kundin ◽

Evgeny Pogorelov ◽

Heike Emmerich

Keyword(s):

Microstructure Evolution ◽

Phase Field ◽

Heterogeneous Nucleation ◽

Phase Field Modeling ◽

Ni Alloys ◽

Field Modeling

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Fabrication and Characterization of Electrospun Pristine and Fluorescent Composite Poly (acrylic acid) Ultra-Fine Fibers

Journal of Engineered Fibers and Fabrics ◽

10.1177/155892501200702s08 ◽

2012 ◽

Vol 7 (2_suppl) ◽

pp. 155892501200702 ◽

Cited By ~ 1

Author(s):

Jennifer S. Atchison ◽

Caroline L. Schauer

Keyword(s):

Acrylic Acid ◽

Charged Droplet ◽

Material System ◽

Composite Fibers ◽

Fine Fiber ◽

Specific Material ◽

Nanofabrication Technique ◽

Fibrous Assemblies ◽

Small Clusters ◽

Poly Acrylic Acid

Electrospinning is a facile nanofabrication technique that produces fibrous assemblies of ultra-fine fibers, 20–1000 nm in diameter, from a charged droplet of spinning solution. Optimization of the fiber diameter of a specific material system is dependent on the solution and process variables. The electrospinning parameters for poly (acrylic acid) (PAA), a synthetic polyelectrolyte, were systematically investigated and consistent nanofiber diameters with uniform morphology were achieved. The optimization matrix included several solvent systems including ethanol, aqueous NaCl and aqueous NaOH. Optimized spinning parameters were then applied to electrospinning fluorescent fibrous assembles of quantum dot-PAA ultra-fine fiber composites. Ultrafine composite fibers were prepared by electrospinning aqueous solutions of 6wt% PAA loaded with 0.05, 0.10, 0.15 and 0.20%v/v, carboxylic acid functionalized CdSe/ZnS nanoparticles (SNPs). The resulting composite fibers exhibited uniform fiber morphologies with increasing fiber diameters corresponding to increasing SNP loading. Fluorescence micrographs reveal luminescent fibers with evenly distributed fluorophores in the higher loaded samples. Moreover, laser excited fibers manifest SNP intermittency correlated with small clusters and single SNPs suggesting excellent dispersion in the PAA matrix.

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