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Liu, Siqi

Publications and source records attributed to Liu, Siqi.

BigNeuron: a resource to benchmark and predict performance of algorithms for automated tracing of neurons in light microscopy datasets

BigNeuron is an open community bench-testing platform with the goal of setting open standards for accurate and fast automatic neuron tracing. We gathered a diverse set of image volumes across several species that is representative of the data obtained in many neuroscience laboratories interested in neuron tracing. Here, we report generated gold standard manual annotations for a subset of the available imaging datasets and quantified tracing quality for 35 automatic tracing algorithms. The goal of generating such a hand-curated diverse dataset is to advance the development of tracing algorithms and enable generalizable benchmarking. Together with image quality features, we pooled the data in an interactive web application that enables users and developers to perform principal component analysis, t-distributed stochastic neighbor embedding, correlation and clustering, visualization of imaging and tracing data, and benchmarking of automatic tracing algorithms in user-defined data subsets. The image quality metrics explain most of the variance in the data, followed by neuromorphological features related to neuron size. Furthermore, we observed that diverse algorithms can provide complementary information to obtain accurate results and developed a method to iteratively combine methods and generate consensus reconstructions. The consensus trees obtained provide estimates of the neuron structure ground truth that typically outperform single algorithms in noisy datasets. However, specific algorithms may outperform the consensus tree strategy in specific imaging conditions. Finally, to aid users in predicting the most accurate automatic tracing results without manual annotations for comparison, we used support vector machine regression to predict reconstruction quality given an image volume and a set of automatic tracings.

97 MATHEMATICS AND COMPUTING↗

Dynamics of ionic liquids in the presence of polymer-grafted nanoparticles

We incorporated polymer-grafted nanoparticles into ionic and zwitterionic liquids to explore the solvation and confinement effects on their heterogeneous dynamics using quasi-elastic neutron scattering (QENS). 1-Hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMIM-TFSI) mixed with deuterated poly(methyl methacrylate) (d-PMMA)-grafted nanoparticles is studied to unravel how dynamic coupling between PMMA and HMIM-TFSI influence the fast and slow diffusion characteristics of the HMIM + cations. The zwitterionic liquid, 1-butyl-3-methyl imidazole-2-ylidene borane (BMIM-BH 3 ) is critically selected and mixed with PMMA-grafted nanoparticles for comparison in this work as its ions do not self-dissociate and it does not couple with PMMA through ion-dipole interactions as HMIM-TFSI does. We find that long-range unrestricted diffusion of HMIM + cations is higher in well-dispersed particles than in aggregated particle systems, whereas the localized diffusion of HMIM + is measured to be higher in close-packed particles. Translational diffusion dynamics of BMIM-BH 3 is not influenced by any particle structures suggesting that zwitterions do not interact with PMMA. In conclusion, this difference between two ionic liquid types enables us to decouple polymer effects from the diffusion of ionic liquids, which is integral to understand the ionic transport mechanism in ionic liquids confined in polymer-grafted nanoparticle electrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Ordering Polymer‐Grafted Nanoparticles at Oil–Air Interfaces under Magnetic Fields

Abstract Polymer‐grafted magnetic nanoparticles at oil–air interfaces are examined to reveal the role of chain length and anisotropy on particle packing order in thin films. It is found that particles grafted with intermediate chain lengths and sparse grafting densities exhibit enhanced packing order with increasing magnetic field strength. Voronoi tessellation results present an increase in the cell area distribution of these samples, suggesting that chain conformations are affected. For the longest graft length, particles become more disordered under magnetic fields. It is proposed that fluctuations in the bridged chains rearrange particles into less ordered packing with field application and the mechanism of packing order differs for varying graft chain lengths. Grafting anisotropy is found to determine the spatial nanoparticle organization in assembled monolayers.

Liu, Siqi↗

Structure and Entanglement Factors on Dynamics of Polymer-Grafted Nanoparticles

Nanoparticles functionalized with long polymer chains at low graft density are interesting systems to study structure–dynamic relationships in polymer nanocomposites since they are shown to aggregate into strings in both solution and melts and also into spheres and branched aggregates in the presence of free polymer chains. Our work investigates structure and entanglement effects in composites of polystyrene-grafted iron oxide nanoparticles by measuring particle relaxations using X-ray photon correlation spectroscopy. And for particles within highly ordered strings and aggregated systems, they experience a dynamically heterogeneous environment displaying hyperdiffusive relaxation commonly observed in jammed soft glassy systems. Furthermore, particle dynamics is diffusive for branched aggregated structures which could be caused by less penetration of long matrix chains into brushes. These results suggest that particle motion is dictated by the strong interactions of chains grafted at low density with the host matrix polymer.

36 MATERIALS SCIENCE↗

Evolutionary transients in the rice transcriptome.

The number of protein-coding genes predicted from the rice genome remains much larger than the number of genes for Arabidopsis. Most of the excess rice genes show low similarity to Arabidopsis, and eudicots in general. It is difficult to repudiate these genes because even for the 19,079 non-redundant rice cDNAs that have been sequenced, 34.3% are low similarity. Here, we describe a major contributor to this excess of low similarity genes: the frequent and continued occurrence of gene duplications in plants, and the post- duplicative degradation (i.e. relaxed selection) that is typically expected to occur in one of the two gene copies. The salient feature of this degradation is an increase in Ka/Ks for Ks per available site, respectively. We show that low similarity genes are expressed at lower mRNA and protein levels than other genes, and that regions of the encoded proteins are structurally disordered. Indeed, many are evolutionary “transients” that may be destined to die, even if they remain transcriptionally active for millions of years.

59 BASIC BIOLOGICAL SCIENCES↗