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

Discovering Motion Flow by Temporal-Informational Correlations in Sensors

A method is presented for adapting the sensors of a robot to its current environment and to learn motion flow detection by observing the informational relations between sensors and actuators. Examples are shown where the robot learns to detect motion flow from sensor data generated by its own movement

Trading CDS Indices vs. Equity Index Futures – A pairs trade

In this thesis we use a unique data set to show that there is a cointegrating relationship between the EURO STOXX 50 index and the Markit iTraxx Europe index that can be exploited through trading. As far as we know, we are the first ones to write about trading this pair in an academic paper. On our way we deal with various peculiarities in the data set before we manage to find cointegration. The cointegration is evident enough to be utilized when trading the pair. We deal with many practical issues when simulating the trading environment, like marking-to-market of CDS index positions. We successively add more layers of reality to the trading simulation, such as bid-offer-spreads and even in the last step our strategies are highly profitable. Finally, we benchmark our strategies against indices and show that they have low market correlation. This is achieved by introducing an alternative beta measure, customized for the involved assets

Investigation of High-Level Language Support in a Resource-Constrained Embedded Environment

Personal computers have gained a significant boost in computational power and digital storage space at a reduced cost in the last decade. In the search of increased programmer productivity and cross platform portability, language popularity has shifted from lower level languages such as C to higher level languages such as Java and C#. Many of today’s embedded systems are experiencing the same development as the personal computers did. However, most companies dealing with embedded devices still use C. We investigated what effect a shift like this would have at Axis Communications. The study was done by setting up C# and Java on a camera and conducting performance tests on it. The analysis showed that when using C# as a replacement for C, we saw improvements in programmer productivity whilst still upholding performance for some applications. For the most performance intense use cases, the performance requirements were not satisfied. With the growth of high-level languages, we do see a bright future for the support for them in embedded systems

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

Group assessment challenges in project-based learning – Perceptions from students in higher engineering courses

Industry and society want to recruit students who can work in team-based projects. Thus the task for educators in higher education is to prepare and provide such learning environments. However, assessment is one major challenge associated with enacting these learning environments. The literature advocates active team learning but then supports individual assessment modes. The purpose of this paper is to identify and elaborate on group assessment challenges for students and educators in project-based learning. The research is based on a literature review in the field of project-based learning and group assessment. It is empirically supported by action research in three classes of university engineering students. The findings point to an assessment dilemma, which requires a change in mind-set from individual to team/group grading. The students prefer group learning over written exams. However, when it comes to assessment, the majority want individual grading. Individual assessment is perceived as more fair but unnecessary for learning. Furthermore, a challenge identified by educators is to ensure that all individuals have achieved the learning outcomes. At the same time, they find it frustrating to make individual assessments when the course is based on group learning