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Creators/Authors contains: "Shi, Ying"

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  1. Free, publicly-accessible full text available July 1, 2024
  2. Free, publicly-accessible full text available August 1, 2024
  3. Abstract

    Despite decades of studies, the nature of the glass transition remains elusive. In particular, the sharpness of the dynamical arrest of a melt at the glass transition is captured by its fragility. Here, we reveal that fragility is governed by the medium-range order structure. Based on neutron-diffraction data for a series of aluminosilicate glasses, we propose a measurable structural parameter that features a strong inverse correlation with fragility, namely, the average medium-range distance (MRD). We use in-situ high-temperature neutron-scattering data to discuss the physical origin of this correlation. We argue that glasses exhibiting lowMRDvalues present an excess of small network rings. Such rings are unstable and deform more readily with changes in temperature, which tends to increase fragility. These results reveal that the sharpness of the dynamical arrest experienced by a silicate glass at the glass transition is surprisingly encoded into the stability of rings in its network.

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    Silicate glasses have no long-range order and exhibit a short-range order that is often fairly similar to that of their crystalline counterparts. Hence, the out-of-equilibrium nature of glasses is largely encoded in their medium-range order. However, the ring size distribution—the key feature of silicate glasses’ medium-range structure—remains invisible to conventional experiments and, hence, is largely unknown. Here, by combining neutron diffraction experiments and force-enhanced atomic refinement simulations for two archetypical silicate glasses, we show that rings of different sizes exhibit a distinct contribution to the first sharp diffraction peak in the structure factor. On the basis of these results, we demonstrate that the ring size distribution of silicate glasses can be determined solely from neutron diffraction patterns, by analyzing the shape of the first sharp diffraction peak. This method makes it possible to uncover the nature of silicate glasses’ medium-range order. 
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  6. Abstract

    Although multisensory integration is crucial for sensorimotor function, it is unclear how visual and proprioceptive sensory cues are combined in the brain during motor behaviors. Here we characterized the effects of multisensory interactions on local field potential (LFP) activity obtained from the superior parietal lobule (SPL) as non-human primates performed a reaching task with either unimodal (proprioceptive) or bimodal (visual-proprioceptive) sensory feedback. Based on previous analyses of spiking activity, we hypothesized that evoked LFP responses would be tuned to arm location but would be suppressed on bimodal trials, relative to unimodal trials. We also expected to see a substantial number of recording sites with enhanced beta band spectral power for only one set of feedback conditions (e.g. unimodal or bimodal), as was previously observed for spiking activity. We found that evoked activity and beta band power were tuned to arm location at many individual sites, though this tuning often differed between unimodal and bimodal trials. Across the population, both evoked and beta activity were consistent with feedback-dependent tuning to arm location, while beta band activity also showed evidence of response suppression on bimodal trials. The results suggest that multisensory interactions can alter the tuning and gain of arm position-related LFP activity in the SPL.

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  7. null (Ed.)
    Traditional software reliability growth models only consider defect discovery data, yet the practical concern of software engineers is the removal of these defects. Most attempts to model the relationship between defect discovery and resolution have been restricted to differential equation-based models associated with these two activities. However, defect tracking databases offer a practical source of information on the defect lifecycle suitable for more complete reliability and performance models. This paper explicitly connects software reliability growth models to software defect tracking. Data from a NASA project has been employed to develop differential equation-based models of defect discovery and resolution as well as distributional and Markovian models of defect resolution. The states of the Markov model represent thirteen unique stages of the NASA software defect lifecycle. Both state transition probabilities and transition time distributions are computed from the defect database. Illustrations compare the predictive and computational performance of alternative approaches. The results suggest that the simple distributional approach achieves the best tradeoff between these two performance measures, but that enhanced data collection practices could improve the utility of the more advanced approaches and the inferences they enable. 
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