In order to examine the structure of bleomycin-induced DNA double-strand breaks, defined-sequence DNA was labeled in each strand at a single restriction site and treated with bleomycin. Various double-stranded fragments resulting from bleomycin-induced double-strand breaks were isolated, denatured, and run on sequencing gels to determine the sites of cleavage in each strand. For virtually every double-strand break, the cleavage site in one strand was a pyrimidine in a G-Py sequence, reflecting a specificity similar to that of bleomycin-induced single-strand cleavage. However, the cleavage site in the complementary strand was seldom a G-Py sequence, and was usually a site where single-strand cleavage was infrequent. When the sequence at the double-strand break was G-Py-Py', the break at Py was usually accompanied by a break at the base directly opposite Py, resulting in blunt ends. When the sequence was G-Py-Pu, the break at Py was usually accompanied by a break at the base opposite Pu, resulting in single-base 5' extensions. Double-strand breaks with 3' extensions, such as would result from cleavage of two C residues in a self-complementary G-C sequence, were conspicuously absent. These data provide further evidence that bleomycin-induced double-strand breaks do not result from coincidence of independent site-specific single-strand breaks.(ABSTRACT TRUNCATED AT 250 WORDS)
Composed of a soft polymer matrix and magnetic filler particles, ferrogel is a smart material responsive to magnetic fields. Due to the viscoelasticity of the matrix, the behaviors of ferrogel are usually rate-dependent. Very few models with coupled magnetic field and viscoelasticity exist in the literature, and even fewer are capable of reliable predictions. Based on the principles of non-equilibrium thermodynamics, a field theory is developed to describe the magneto-viscoelastic property of ferrogel. The theory provides a guideline for experimental characterizations and structural designs of ferrogel-based devices. A specific material model is then selected and the theory is implemented in a finite element code. Through numerical examples, the responses of a ferrogel in uniform and non-uniform magnetic fields are analyzed. The dynamic response of a ferrogel to cyclic magnetic fields is also studied, and the prediction agrees with our experimental results. In the reversible limit, our theory recovers existing models for elastic ferrogel, and is capable of capturing some instability phenomena.
Filled with certain amount of magnetic particles, an elastomer can be made magneto active for numerous applications. When a magneto-active elastomer (MAE) is subject to a homogeneous magnetic field, both magnetostriction and field-stiffening effect can be observed. Inspired by experimental observations and microstructure simulations in the literature, this paper presents a simplified phenomenological model for MAEs by considering a uniaxial deformation state. The model hypothesizes the field-stiffening effect to be a direct consequence of the inverse magnetostriction, i.e., the strain-dependent magnetization, in the context of finite deformation. By taking the elastic energy to be independent of magnetic field and the magnetization energy to be strain dependent, the model can capture both magnetostriction and field stiffening of an MAE. The functional form of the strain-dependent magnetization energy is determined by the underlying microstructure. MAEs with different microstructures exhibit different magnetostriction and field-stiffening behaviors. To predict the behavior of a specific MAE, one only needs to measure the effective permeability of an MAE as a function of the axial strain. The mathematical simplicity of the model could enable simulation and optimization of MAEbased devices under complex loading conditions.
Ferrogels are low stiffness polymer materials with embedded magnetic powder filler, giving them the capability to strain in a magnetic field. The large strains, high energy densities and fast responses that have been reported make these materials attractive for actuator applications; however, a full understanding of the dynamic behavior is lacking. This paper presents an experimental study of the cyclic behavior of these materials under various frequencies in both the upright and inverted configurations. A 1D phenomenological magneto-viscoelastic model is developed and used to capture this behavior. The trends in stiffness, viscosity and density are described and then used to predict the amplitude of the strain at different frequencies.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.