Browsing by Subject "elasticity"
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Item Competition between B-Z and B-L transitions in a single DNA molecule: Computational studies(2016-02) Kwon, Ah Young; Nam, Gi Moon; Johner, Albert; Kim, Seyong; Hong, Seok Cheol; Lee, Nam Kyung; Nam, Gi MoonUnder negative torsion, DNA adopts left-handed helical forms, such as Z-DNA and L-DNA. Using the random copolymer model developed for a wormlike chain, we represent a single DNA molecule with structural heterogeneity as a helical chain consisting of monomers which can be characterized by different helical senses and pitches. By Monte Carlo simulation, where we take into account bending and twist fluctuations explicitly, we study sequence dependence of B-Z transitions under torsional stress and tension focusing on the interaction with B-L transitions. We consider core sequences, (GC)(n) repeats or (TG)(n) repeats, which can interconvert between the right-handed B form and the left-handed Z form, imbedded in a random sequence, which can convert to left-handed L form with different (tension dependent) helical pitch. We show that Z-DNA formation from the (GC)(n) sequence is always supported by unwinding torsional stress but Z-DNA formation from the (TG)(n) sequence, which are more costly to convert but numerous, can be strongly influenced by the quenched disorder in the surrounding random sequence.Item Effective Elastic Properties of Additively Manufactured Metallic Lattice Structures: Unit-Cell Modeling(University of Texas at Austin, 2019) Fashanu, O.; Murphy, D.; Spratt, M.; Newkirk, J.; Chandrashekhara, K.Lattice structures are lightweight materials, which exhibit a unique combination of properties such as air and water permeability, energy and acoustic absorption, low thermal conductivity, and electrical insulation. In this work, unit-cell homogenization was used to predict the effective elastic moduli of octet-truss (OT) lattice structures manufactured using selective laser melting (SLM). OT structures were manufactured using a Renishaw AM 250 SLM machine with various relative densities. Compression test was carried out at strain rate 5 × 10-3 m-1 using an MTS frame. Finite element analysis was used in the determination of the OT’s effective elastic properties. Results from the finite element analysis were validated using experiments. It was observed that the finite element predictions were in good agreement with the experimental results.Item Induced Dynamic Nonlinear Ground Response at Garner Valley, California(2008-06) Lawrence, Zack; Bodin, Paul; Langston, Charles A.; Pearce, Fred; Gomberg, Joan; Johnson, Paul A.; Menq, Farn-Yuh; Brackman, Thomas; Menq, Farn-YuhWe present results from a prototype experiment in which we actively induce, observe, and quantify in situ nonlinear sediment response in the near surface. This experiment was part of a suite of experiments conducted during August 2004 in Garner Valley, California, using a large mobile shaker truck from the Network for Earthquake Engineering Simulation (NEES) facility. We deployed a dense accelerometer array within meters of the mobile shaker truck to replicate a controlled, laboratory-style soil dynamics experiment in order to observe wave-amplitude-dependent sediment properties. Ground motion exceeding 1g acceleration was produced near the shaker truck. The wave field was dominated by Rayleigh surface waves and ground motions were strong enough to produce observable nonlinear changes in wave velocity. We found that as the force load of the shaker increased, the Rayleigh-wave phase velocity decreased by as much as similar to 30% at the highest frequencies used (up to 30 Hz). Phase velocity dispersion curves were inverted for S-wave velocity as a function of depth using a simple isotropic elastic model to estimate the depth dependence of changes to the velocity structure. The greatest change in velocity occurred nearest the surface, within the upper 4 m. These estimated S-wave velocity values were used with estimates of surface strain to compare with laboratory-based shear modulus reduction measurements from the same site. Our results suggest that it may be possible to characterize nonlinear soil properties in situ using a noninvasive field technique.Item Physical Properties of Dense Concrete as Determined by the Relative Quantity of Cement(University of Texas at Austin, 1918-03-10) University of Texas at Austin