A Numerical Investigation of the Dynamic Behaviour of Functionally Graded Foams

Abstract Two Finite Element models approximating the dynamic behaviour of functionally graded foam materials (FGFMs) have been developed under free weight drop impact and Kolsky wave propagation conditions. The FGFM is modeled by discretising the material into a large number of layers through the foam thickness. Each layer is described by a unique constitutive cellular response, which is derived from the initial relative density, ρ * , unique to that layer. Large strain unixial compressive tests at strain rates of 0.001, 0.01 and 0.1/s were performed on expanded polystyrene (EPS) and ALPORAS Aluminium (Al) foam and their σ − ε response was used as input to a modified constitutive model from the literature. Simulations were then performed on both uniform and graded specimens. For both impact and wave propagation conditions it is found that under certain conditions an FGFM can outperform a uniform foam of equivalent density in terms of reducing peak accelerations imparted from an impact, or mitigating stress wave magnitudes through increased plastic deformation. These properties provide significant insight into the hypothesised behaviour of FGFMs and elucidate the potential for the future use in the design of next generation cushioning structures

Measuring Entangled Qutrits and Their Use for Quantum Bit Commitment

We produce and holographically measure entangled qudits encoded in transverse spatial modes of single photons. With the novel use of a quantum state tomography method that only requires two-state superpositions, we achieve the most complete characterisation of entangled qutrits to date. Ideally, entangled qutrits provide better security than qubits in quantum bit-commitment: we model the sensitivity of this to mixture and show experimentally and theoretically that qutrits with even a small amount of decoherence cannot offer increased security over qubits.Comment: Paper updated to match published version; 5 pages, 4 figures, images have been included at slightly lower quality for the archiv

CORRELATIONS BETWEEN HEAD ROTATIONAL KINEMATICS AND BRAIN TISSUE STRAIN FOR LOW AND HIGH LEVEL FOOTBALL HELMET IMPACTS

This study examined the correlation between head angular velocity and acceleration with brain strain for low and high level impacts. Impacts at 2.4m/s (low) and 11m/s (high) were delivered to a American football helmeted Hybrid III headform using a centric/non-centric protocol. A finite element model calculated strain from headform accelerations. The lowlevel impact data were obtained from a previous subset eliciting angular responses occurring at 20g, therefore linear acceleration relationships were not examined. High correlations (r=>0.8) existed for non-centric conditions between strain with angular acceleration and velocity, while centric conditions had moderate relationships (r=0.50.68). This research demonstrates that kinematic-strain relationships are dependent on the impact event, and that a single variable may not represent strain under all conditi

Using Primary Reinforcement to Enhance Translatability of a Human Affect and Decision-Making Judgment Bias Task

Good translatability of behavioral measures of affect (emotion) between human and nonhuman animals is core to comparative studies. The judgment bias (JB) task, which measures "optimistic" and "pessimistic" decision-making under ambiguity as indicators of positive and negative affective valence, has been used in both human and nonhuman animals. However, one key disparity between human and nonhuman studies is that the former typically use secondary reinforcers (e.g., money) whereas the latter typically use primary reinforcers (e.g., food). To address this deficiency and shed further light on JB as a measure of affect, we developed a novel version of a JB task for humans using primary reinforcers. Data on decision-making and reported affective state during the JB task were analyzed using computational modeling. Overall, participants grasped the task well, and as anticipated, their reported affective valence correlated with trial-by-trial variation in offered volume of juice. In addition, previous findings from monetary versions of the task were replicated: More positive prediction errors were associated with more positive affective valence, a higher lapse rate was associated with lower affective arousal, and affective arousal decreased as a function of number of trials completed. There was no evidence that more positive valence was associated with greater "optimism," but instead, there was evidence that affective valence influenced the participants' decision stochasticity, whereas affective arousal tended to influence their propensity for errors. This novel version of the JB task provides a useful tool for investigation of the links between primary reward and punisher experience, affect, and decision-making, especially from a comparative perspective

Nanoparticle Electric Propulsion: Experimental Results

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76874/1/AIAA-2006-4803-539.pd