The tail of the contact force distribution in static granular materials

We numerically study the distribution P(f) of contact forces in frictionless bead packs, by averaging over the ensemble of all possible force network configurations. We resort to umbrella sampling to resolve the asymptotic decay of P(f) for large f, and determine P(f) down to values of order 10^{-45} for ordered and disordered systems in two and three dimensions. Our findings unambiguously show that, in the ensemble approach, the force distributions decay much faster than exponentially: P(f) ~ exp(-f^{\alpha}), with alpha \approx 2.0 for 2D systems, and alpha \approx 1.7 for 3D systems.Comment: 4 pages, 4 figures, submitted to Phys. Rev.

Qualitative, quantitative, and data mining methods for analyzing log data to characterize students' learning strategies and behaviors [discussant]

This symposium addresses how different classes of research methods, all based upon the use of log data from educational software, can facilitate the analysis of students’ learning strategies and behaviors. To this end, four multi-method programs of research are discussed, including the use of qualitative, quantitative-statistical, quantitative-modeling, and educational data mining methods. The symposium presents evidence regarding the applicability of each type of method to research questions of different grain sizes, and provides several examples of how these methods can be used in concert to facilitate our understanding of learning processes, learning strategies, and behaviors related to motivation, meta-cognition, and engagement

Plate fixation of clavicle fractures:comparison between early and delayed surgery

Background: The optimal treatment strategy for clavicle fractures remains a topic of debate. We evaluated our step-wise treatment protocol for patients with clavicle fractures to determine our success rate of conservative treatment. In addition, we evaluated the incidence of complications after clavicle plate fixation in patients undergoing acute surgery vs. delayed surgery. Methods: This was a retrospective analysis in which we registered all patients aged 14 years or older with a clavicle fracture between January 2010 and May 2018 and at least 6 weeks' follow-up. Patients who underwent surgery were included from a prospectively maintained database. Functional outcomes were measured by Disabilities of the Arm, Shoulder and Hand and Constant-Murley scores 6 weeks after surgery. Results: Conservative treatment was successful in 1627 of 1748 patients (93%). Primary fixation was performed in 73 patients (61%) and delayed fixation in 48 (39%). In 8 patients (6.6%), radiologic widening of the acromioclavicular (AC) joint was present after surgery, suggestive of AC injury. The incidence of complications was significantly higher among patients who underwent delayed fixation vs. those who underwent primary fixation: 15 of 48 patients (31.3%) vs. 9 of 73 patients (12.3%). Conclusion: Most patients with clavicle fractures have an excellent outcome using conservative management. Acute surgery can be performed in high-demand patients, resulting in high performance scores. Delayed surgery is associated with a higher risk of complications, although the outcome is generally good. Associated AC joint dislocation found on postoperative radiographs does not influence outcomes. Shared decision making is key, and patients should be well aware of the potential risks and benefits of surgery