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You searched for +publisher:"Temple University" +contributor:("Sadeghipour, Keya"). Showing records 1 – 2 of 2 total matches.

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Temple University

1. Laksari, Kaveh. Nonlinear Viscoelastic Wave Propagation in Brain Tissue.

Degree: PhD, 2013, Temple University

Mechanical Engineering

A combination of theoretical, numerical, and experimental methods were utilized to determine that shock waves can form in brain tissue from smooth boundary conditions. The conditions that lead to the formation of shock waves were determined. The implication of this finding was that the high gradients of stress and strain that could occur at the shock wave front could contribute to mechanism of brain injury in blast loading conditions. The approach consisted of three major steps. In the first step, a viscoelastic constitutive model of bovine brain tissue under finite step-and-hold uniaxial compression with 10 1/s ramp rate and 20 s hold time has been developed. The assumption of quasi-linear viscoelasticity (QLV) was validated for strain levels of up to 35%. A generalized Rivlin model was used for the isochoric part of the deformation and it was shown that at least three terms (C_10, C_01 and C_11) are needed to accurately capture the material behavior. Furthermore, for the volumetric deformation, a linear bulk modulus model was used and the extent of material incompressibility was studied. The hyperelastic material parameters were determined through extracting and fitting to two isochronous curves (0.06 s and 14 s) approximating the instantaneous and steady-state elastic responses. Viscoelastic relaxation was characterized at five decay rates (100, 10, 1, 0.1, 0 1/s) and the results in compression and their extrapolation to tension were compared against previous models. In the next step, a framework for understanding the propagation of stress waves in brain tissue under blast loading was developed. It was shown that tissue nonlinearity and rate dependence are key parameters in predicting the mechanical behavior under such loadings, as they determine whether traveling waves could become steeper and eventually evolve into shock discontinuities. To investigate this phenomenon, the QLV material model developed based on finite compression results mentioned above was extended to blast loading rates, by utilizing the stress data published on finite torsion of brain tissue at high rates (up to 700 1/s). It was shown that development of shock waves is possible inside the head in response to compressive pressure waves from blast explosions. Furthermore, it was argued that injury to the nervous tissue at the microstructural level could be attributed to the high stress and strain gradients with high temporal rates generated at the shock front and this was proposed as a mechanism of injury in brain tissue. In the final step, the phenomenon of shock wave formation and propagation in brain tissue was further studied by developing a one-dimensional model of brain tissue using the Discontinuous Galerkin finite element method. This model is capable of capturing high-gradient waves with higher accuracy than commercial finite element software. The deformation of brain tissue was investigated under displacement input and pressure input boundary conditions relevant to blast over-pressure reported in the…

Advisors/Committee Members: Darvish, Kurosh;, Sadeghipour, Keya, Margulies, Susan, Seibold, Benjamin, Crandall, Jeff R.;.

Subjects/Keywords: Engineering; Mechanical engineering; Biomechanics;

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Laksari, K. (2013). Nonlinear Viscoelastic Wave Propagation in Brain Tissue. (Doctoral Dissertation). Temple University. Retrieved from http://digital.library.temple.edu/u?/p245801coll10,242293

Chicago Manual of Style (16th Edition):

Laksari, Kaveh. “Nonlinear Viscoelastic Wave Propagation in Brain Tissue.” 2013. Doctoral Dissertation, Temple University. Accessed October 31, 2020. http://digital.library.temple.edu/u?/p245801coll10,242293.

MLA Handbook (7th Edition):

Laksari, Kaveh. “Nonlinear Viscoelastic Wave Propagation in Brain Tissue.” 2013. Web. 31 Oct 2020.

Vancouver:

Laksari K. Nonlinear Viscoelastic Wave Propagation in Brain Tissue. [Internet] [Doctoral dissertation]. Temple University; 2013. [cited 2020 Oct 31]. Available from: http://digital.library.temple.edu/u?/p245801coll10,242293.

Council of Science Editors:

Laksari K. Nonlinear Viscoelastic Wave Propagation in Brain Tissue. [Doctoral Dissertation]. Temple University; 2013. Available from: http://digital.library.temple.edu/u?/p245801coll10,242293


Temple University

2. Bezares, Francisco Javier. Pulsed Laser Deposition of Eu-doped Multilayer Thin Films for Spectral Storage Applications.

Degree: PhD, 2010, Temple University

Physics

This thesis studies different Eu optical centers in MgS:Eu and CaS:Eu thin films produced by Chemically Controlled Pulse Laser Deposition (CCPLD) and evaluates their suitability for the development of spectral storage devices of the future. The produced thin films consist of one or more optically active layer(s), MgS:Eu, CaS:Eu or a similar material, and a corresponding ZnS capping layer that functions as a protecting barrier for the other layers and preserves their composition and integrity. Given that the synthesis of the materials used to produce the multilayer structures in this work proved a great challenge, careful attention was given to the optimization of all fabrication parameters. Mass Spectrometry was used during the deposition of the thin films and the data obtained resulted on improvements and optimization of the deposition process. Scanning electron microscopy studies of these thin films were conducted to study degradation upon long-term storage. Microscopy results show that the morphology of the produced thin films is correlated to the growth environment during deposition and deterioration of the deposited materials could be initiated by nano-gaps and cracks in the capping layer of the thin films. In addition to optical centers in MgS:Eu and CaS:Eu, new centers were created by changing the thin film growth environment inside a hi-vacuum chamber, modifying the composition of the ablation target material, or both. For example, introducing O2, or alternatively HCl, inside the CCPLD chamber while producing MgS:Eu thin films results in the formation of impurity associated centers across lattice sites throughout the deposited structures. In another method of impurity doping studied, Cl- and Na+ were introduced into the MgS:Eu and CaS:Eu lattices by mixing trace amounts of the impurity ions into these materials in polycrystalline form and making this mixture a deposition target by hi-pressure cold compression technique. The introduction of these impurity ions will alter the crystal field environment around the Eu ions thus creating new optical centers with a shift in energy of their characteristic Zero Phonon Line. After extensive characterization of the optical properties of the thin films produced, laser-induced fluorescence spectroscopy and absorption spectroscopy measurements confirm that they are suitable candidates to be used in conjunction with power-gated spectral holeburning technique and could potentially provide ultrahigh, terabits per square inch, storage densities.

Temple University – Theses

Advisors/Committee Members: Hasan, Zameer U., Gawlinski, Edward T., Riseborough, Peter, Sadeghipour, Keya, Helferty, John J..

Subjects/Keywords: Physics, Condensed Matter; Physics, Optics; Europium Doping; Multilayer Thin Films; Pulsed Laser Deposition; Rare Earths; Spectral Storage; ZnS Thin Films

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Bezares, F. J. (2010). Pulsed Laser Deposition of Eu-doped Multilayer Thin Films for Spectral Storage Applications. (Doctoral Dissertation). Temple University. Retrieved from http://digital.library.temple.edu/u?/p245801coll10,70042

Chicago Manual of Style (16th Edition):

Bezares, Francisco Javier. “Pulsed Laser Deposition of Eu-doped Multilayer Thin Films for Spectral Storage Applications.” 2010. Doctoral Dissertation, Temple University. Accessed October 31, 2020. http://digital.library.temple.edu/u?/p245801coll10,70042.

MLA Handbook (7th Edition):

Bezares, Francisco Javier. “Pulsed Laser Deposition of Eu-doped Multilayer Thin Films for Spectral Storage Applications.” 2010. Web. 31 Oct 2020.

Vancouver:

Bezares FJ. Pulsed Laser Deposition of Eu-doped Multilayer Thin Films for Spectral Storage Applications. [Internet] [Doctoral dissertation]. Temple University; 2010. [cited 2020 Oct 31]. Available from: http://digital.library.temple.edu/u?/p245801coll10,70042.

Council of Science Editors:

Bezares FJ. Pulsed Laser Deposition of Eu-doped Multilayer Thin Films for Spectral Storage Applications. [Doctoral Dissertation]. Temple University; 2010. Available from: http://digital.library.temple.edu/u?/p245801coll10,70042

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