Glassiness, Rigidity and Jamming of Frictionless Soft Core Disks

The jamming of bi-disperse soft core disks is considered, using a variety of different protocols to produce the jammed state. In agreement with other works, we find that cooling and compression can lead to a broad range of jamming packing fractions $\phi_J$, depending on cooling rate and initial configuration; the larger the degree of big particle clustering in the initial configuration, the larger will be the value of $\phi_J$. In contrast, we find that shearing disrupts particle clustering, leading to a much narrower range of $\phi_J$ as the shear strain rate varies. In the limit of vanishingly small shear strain rate, we find a unique non-trivial value for the jamming density that is independent of the initial system configuration. We conclude that shear driven jamming is a unique and well defined critical point in the space of shear driven steady states. We clarify the relation between glassy behavior, rigidity and jamming in such systems and relate our results to recent experiments.Comment: 10 pages, 11 figures, significantly expanded version as accepted for publication in PR

Dissipation and Rheology of Sheared Soft-Core Frictionless Disks

We use numerical simulations to investigate the effect of different dissipative models on the shearing rheology of massive soft-core frictionless disks in two dimensions. We show that the presence of Newtonian (overdamped) vs Bagnoldian (inertial) rheology is related to the formation of large connected clusters of disks, and that sharp transitions may exist between the two as system parameters vary. In the limit of strongly inelastic collisions, we find that rheological curves collapse to a well-defined limit when plotted against an appropriate dimensionless strain rate.Comment: 6 pages, 5 figures, revised to published versio

Critical Scaling of Bagnold Rheology at the Jamming Transition of Frictionless Two Dimensional Disks

We carry out constant volume simulations of steady-state, shear driven, rheology in a simple model of bidisperse, soft-core, frictionless disks in two dimensions, using a dissipation law that gives rise to Bagnoldian rheology. We carry out a detailed critical scaling analysis of our resulting data for pressure $p$ and shear stress $\sigma$, in order to determine the critical exponent $\beta$ that describes the algebraic divergence of the Bagnold transport coefficients, as the jamming transition is approached from below. We show that it is necessary, for the strain rates considered in this work, to consider the leading correction-to-scaling term in order to achieve a self-consistent analysis of our data. Our resulting value $\beta\approx 5.0\pm 0.4$ is clearly larger than the theoretical prediction by Otsuki and Hayakawa, and is consistent with earlier numerical results by Peyneau and Roux, and recent theoretical predictions by DeGiuli et al. We have also considered the macroscopic friction $\mu\equiv \sigma/p$ and similarly find results consistent with Peyneau and Roux, and with DeGiuli et al. Our results confirm that the shear driven jamming transition in Bagnoldian systems is well described by a critical scaling theory (as was found previously for Newtonian systems), and we relate this scaling theory to the phenomenological constituent laws for dilatancy and friction.Comment: 20 pages, 21 figures; revised manuscript according to published versio

Finite-Size-Scaling at the Jamming Transition: Corrections to Scaling and the Correlation Length Critical Exponent

We carry out a finite size scaling analysis of the jamming transition in frictionless bi-disperse soft core disks in two dimensions. We consider two different jamming protocols: (i) quench from random initial positions, and (ii) quasistatic shearing. By considering the fraction of jammed states as a function of packing fraction for systems with different numbers of particles, we determine the spatial correlation length critical exponent $\nu\approx 1$, and show that corrections to scaling are crucial for analyzing the data. We show that earlier numerical results yielding $\nu<1$ are due to the improper neglect of these corrections.Comment: 5 pages, 4 figures -- slightly revised version as accepted for Phys. Rev. E Rapid Communication

Hypotension during transsphenoidal pituitary surgery associated with increase in plasma levels of brain injury markers

BACKGROUND: Patients undergoing pituitary surgery may experience short- and long-term postoperative morbidity. Intraoperative factors such as hypotension might be a contributing factor. Our aim was to investigate the association between intraoperative hypotension and postoperative plasma levels of tau, neurofilament light (NfL), and glial fibrillary acidic protein (GFAP) as markers of perioperative brain injury. METHODS: Between June 2016 and October 2017, 35 patients from the Gothenburg Pituitary Tumor Study were included. For tau, NfL, and GFAP, concentrations were measured in plasma samples collected before and immediately following surgery, and on postoperative days 1 and 5. The difference between the highest postoperative value and the value before surgery was used for analysis (∆taupeak , ∆NfLpeak , ∆GFAPpeak ). Intraoperative hypotension was defined as the area under the curve of an absolute threshold below 70 mmHg (AUC70) and a relative threshold below 20% (AUC20%) of the baseline mean arterial blood pressure. RESULTS: Plasma tau and GFAP were highest immediately following surgery and on day 1, while NfL was highest on day 5. There was a positive correlation between AUC20% and both ∆taupeak (r2  = .20, p < .001) and ∆NfLpeak (r2  = .26, p < .001). No association was found between AUC20% and GFAP or between AUC70 and ∆taupeak , ∆NfLpeak or ∆GFAPpeak . CONCLUSION: Intraoperative relative, but not absolute, hypotension was associated with increased postoperative plasma tau and NfL concentrations. Patients undergoing pituitary surgery may be vulnerable to relative hypotension, but this needs to be validated in future prospective studies

Phase-coherence threshold and vortex-glass state in diluted Josephson-junction arrays in a magnetic field

We study numerically the interplay of phase coherence and vortex-glass state in two-dimensional Josephson-junction arrays with average rational values of flux quantum per plaquette $f$ and random dilution of junctions. For $f=1/2$, we find evidence of a phase coherence threshold value $x_s$, below the percolation concentration of diluted junctions $x_p$, where the superconducting transition vanishes. For $x_s < x < x_p$ the array behaves as a zero-temperature vortex glass with nonzero linear resistance at finite temperatures. The zero-temperature critical currents are insensitive to variations in $f$ in the vortex glass region while they are strongly $f$ dependent in the phase coherent region.Comment: 6 pages, 4 figures, to appear in Phys. Rev.