arXiv subjects

Amy L. Graves

Publications and source records attributed to Amy L. Graves.

4 recordsLinked to original sources

arXiv2022

Jammed solids with pins: Thresholds, Force networks and Elasticity

The role of fixed degrees of freedom in soft/granular matter systems has broad applicability and theoretical interest. Here we address questions of the geometrical role that a scaffolding of fixed particles plays in tuning the threshold volume fraction and force network in the vicinity of jamming. Our 2d simulated system consists of soft particles and fixed "pins", both of which harmonically repel overlaps. On one hand, we find that many of the critical scalings associated with jamming in the absence of pins continue to hold in the presence of even dense pin latices. On the other hand, the presence of pins lowers the jamming threshold, in a universal way at low pin densities and a geometry-dependent manner at high pin densities, producing packings with lower densities and fewer contacts between particles. The onset of strong lattice dependence coincides with the development of bond-orientational order. Furthermore, the presence of pins dramatically modifies the network of forces, with both unusually weak and unusually strong forces becoming more abundant. The spatial organization of this force network depends on pin geometry and is described in detail. Using persistent homology we demonstrate that pins modify the topology of the network. Finally, we observe clear signatures of this developing bond-orientational order and broad force distribution in the elastic moduli which characterize the linear response of these packings to strain.

cond-mat.soft↗

arXiv2020

Structured randomness: Jamming of soft discs and pins

Simulations are used to find the zero temperature jamming threshold, $ϕ_j$, for soft, bidisperse disks in the presence of small fixed particles, or "pins", arranged in a lattice. The presence of pins leads, as one expects, to a decrease in $ϕ_j$. Structural properties of the system near the jamming threshold are calculated as a function of the pin density. While the correlation length exponent remains $ν= 1/2$ at low pin densities, the system is mechanically stable with more bonds, yet fewer contacts than the Maxwell criterion implies in the absence of pins. In addition, as pin density increases, novel bond orientational order and long-range spatial order appear, which are correlated with the square symmetry of the pin lattice.

cond-mat.soft↗

arXiv2017

Swimming against the tide: Gender bias in the physics classroom

This study examines physics students' evaluations of identical, video-recorded lectures performed by female and male actors playing the role of professors. The results indicate that evaluations by male students show statistically significant overall biases with male professors rated more positively than female professors. Female students tended to be egalitarian, except in two areas. Female students evaluated female professors' interpersonal/communicative skills more positively than male professors'. They evaluated female professors' scientific knowledge and skills less positively than that of male professors just as male students did. These findings are relevant to two areas of research on bias in evaluation: rater-ratee similarity bias and stereotype confirmation bias. Results from this study have important implications for efforts focused on educating students and mentoring faculty members in order to increase the representation of women in the physical sciences.

physics.ed-ph↗

arXiv2016

Pinning Susceptibility: The effect of dilute, quenched disorder on jamming

We study the effect of dilute pinning on the jamming transition. Pinning reduces the average contact number needed to jam unpinned particles and shifts the jamming threshold to lower densities, leading to a pinning susceptibility, $χ_p$. Our main results are that this susceptibility obeys scaling form and diverges in the thermodynamic limit as $χ_p \propto |ϕ- ϕ_c^\infty|^{-γ_p}$ where $ϕ_c^\infty$ is the jamming threshold in the absence of pins. Finite-size scaling arguments yield these values with associated statistical (systematic) errors $γ_p = 1.018 \pm 0.026 (0.291) $ in $d=2$ and $γ_p =1.534 \pm 0.120 (0.822)$ in $d=3$. Logarithmic corrections raise the exponent in $d=2$ to close to the $d=3$ value, although the systematic errors are very large.

cond-mat.soft↗