Self-organized neuronal subpopulations and network morphology underlying superbursts

Neural bursts are an important phenomenon that needs to be understood for their relevance to many different neurological diseases as well as neural computations. While there are different types of neuronal bursts, in this study we investigate the nature of population (as opposed to intrinsic cell-level) bursts, in particular, superbursts (SBs) that are a small (∼100 ms) packet of several population bursts (PBs). It has been suggested that neuronal PBs occur when there exists a delicate balance of system-wide excitation and inhibition and when recurrent excitation loops exist in the network. However, there has been no rigorous investigation on the relation between network morphology and (super)burst dynamics. Here we investigate the important issue based on a well-established Izhikevich network model of integrate-fire neurons. We have employed the overall conduction delay as our control parameter for tuning network morphology as well as its matching burst dynamics. Interestingly, we found that initially identical neurons self-organize to develop several distinct neuronal subpopulations, which are characterized by different spike firing patterns as well as local network properties. Moreover, a few different motifs of SB emerge according to a distinct mixture of neuronal subpopulations that, on average, fire at slightly different phases. Our analyses suggest that recurring motifs of different SBs reflect complex yet organized modular structures of different subpopulations

Correlation between local strain and cycle-life performance of AlPO4-coated LiCoO2 cathodes

AlPO4-coated LiCoO2 cathodes display improved cycle-life performance compared with bare LiCoO2. This is attributed to suppression of cobalt dissolution from the cathodes by the AlPO 4-nanoparticle coating. Dissolution of cobalt during cycling with a charge cut-off voltage of 4.6 V leads to structural degradation, and induces a non-uniform distribution of local strain in the cathodes. The strain in coated samples is significantly reduced after 50 cycles, and is correlated with the enhanced cycle-life performance.close353

Direct carbon-black coating on LiCoO2 cathode using surfactant for high-density Li-ion cell

Direct carbon-black coating of the cathode material using a surfactant increases the capacity of a Li-ion cell by similar to10% compared with using bare LiCoO2. The coating method comprises two steps: (i) dispersion of aggregated carbon black using orotano(R)-a polyacrylate dispersant; (ii) carbon-black coating of the cathode material using a gelatin-an amphoteric surfactant. This technology reduces the carbon content in the electrode without sacrificing the cycle-life performance of the cell, and also improves the rate capability of the Li-ion cell. Moreover, the direct carbon-black-coated cathode exhibits excellent capacity recovery and restricted expansion of the cell thickness compared with a bare cathode during storage at 85 degreesC.close403

Effect of AlPO4-nanoparticle coating concentration on high-cutoff-voltage electrochemical performances in LiCoO2

AlPO4 coating thickness on LiCoO2 cathodes was controlled in the range on the order of 10-100 nm by changing the AlPO4-nanoparticle concentration in the coating solution. The specific capacity and cycle-life performance of the coated cathodes had a strong correlation with the AlPO4 coating concentration (thickness). The cycle-life performance of the 1.0 wt % AlPO4-coated cathodes had the best cycling stability, showing 149 mAh/g capacity retention with 4.8 V charge cutoff by 50 cycles at 1 C (=140 mA/g) rate after precycles. However, the bare cathode showed zero capacity retention at the same condition after only 20 cycles. As the coating concentration was increased to 3.2 wt %, the amount of Co dissolution into the electrolyte decreased. In contrast, the 1.0 wt % AlPO4-coated cathode showed the best cycling stability, possibly due to the suppression of Li diffusivity decay and the appropriate electronic conduction.close42

Annealing-temperature effect on various cutoff-voltage electrochemical performances in AlPO4-Nanoparticle-Coated LiCoO2

The electrochemical properties of AlPO4-coated LiCoO2 cathodes were found to be superior to those of bare cathodes at various charge-cutoff voltages (4.3, 4.6, and 4.8 V), and depended on the annealing temperature. The AlPO4-coated cathodes annealed at 600 and 700°C retained a discharge capacity of ∼150 mAh/g even with a 4.8 V charge-cutoff voltage (after 46 cycles at 1 C = 140 mA/g). The bare cathode showed zero capacity retention at the same condition after only 20 cycles. The enhanced electrochemical performance and rate capability in the coated cathodes were attributed to the inhibition of structural degradation during cycling. The AlPO4-nanoparticle coating layer on the LiCoO2 effectively suppressed cobalt dissolution and a nonuniform distribution of local strain in the cathode.close242

Control of AlPO4-nanoparticle coating on LiCoO2 by using water or ethanol

The electrochemical properties of AlPO4-coated LiCoO 2 cathodes prepared in a water or ethanol solvent were characterized with the view of stabilizing LiCoO2 at charge-cutoff voltages of 4.6 and 4.8 V. Under the influence of the AlPO4 crystallinity, the coated LiCoO2 prepared in ethanol had better capacity retention than those prepared in water. This enhancement also correlated with the improved suppression of Li-diffusivity decay in the coated cathode from the ethanol compared to that from water. In addition, the differential scanning calorimetry (DSC) results of the AlPO4 nanoparticle-coated LiCoO2 with ethanol showed an enhanced thermal stability.close212

Efficient protein digestion using highly-stable and reproducible trypsin coatings on magnetic nanofibers

Protein digestion, using an enzyme called trypsin (TR), is one of the key steps in proteomic analysis. The current technology of protein digestion in proteomic analysis is time-consuming, tedious and not automated due to the poor stability and autolysis of trypsin. To improve the protein digestion process, trypsin was immobilized and stabilized on polymer nanofibers entrapping superparamagnetic nanoparticles (magnetic nanofibers, NP-NFs). By electrospinning the homogeneous mixture of superparamagnetic nanoparticles (NPs) and polystyrene-poly(styrene-co-maleic anhydride), NPs could be effectively entrapped within polymer nanofibers, generating magnetically-separable nanofibers with high surface area for trypsin immobilization via the approach of enzyme coatings. Trypsin coatings on magnetic nanofibers (EC-TR/NP-NFs; EC-TR), fabricated via simple attachment of crosslinked trypsin molecules onto NP-NFs, were highly stable and could be recycled via facile magnetic separation. EC-TR showed negligible loss of trypsin activity even after incubation in an aqueous buffer under rigorous shaking (200 rpm) for 80 days, while the control samples of covalently-attached trypsin on NP-NFs (CA-TR/NP-NFs; CA-TR) and free trypsin lost more than 90% of their initial activities within 11 and 6 days, respectively. When highly-stable and magnetically-separable EC-TR was employed for the repetitive digestions of enolase under recycled uses for the duration of 50 days and even after treatment with another protease (chymotrypsin) for 32 h, the performance of enolase digestion was successfully maintained. The use of EC-TR for the enolase digestion in the ultra-sonication system resulted in fast (similar to 10 min) and efficient digestions with reproducible performance under recycled uses.115Nsciescopu

Effective Antifouling Using Quorum-Quenching Acylase Stabilized in Magnetically-Separable Mesoporous Silica

Highly effective antifouling was achieved by immobilizing and stabilizing an acylase, disrupting bacterial cell-to-cell communication, in the form of cross-linked enzymes in magnetically separable mesoporous silica. This so-called “quorum-quenching” acylase (AC) was adsorbed into spherical mesoporous silica (S-MPS) with magnetic nanoparticles (Mag-S-MPS), and further cross-linked for the preparation of nanoscale enzyme reactors of AC in Mag-S-MPS (NER-AC/Mag-S-MPS). NER-AC effectively stabilized the AC activity under rigorous shaking at 200 rpm for 1 month, while free and adsorbed AC lost more than 90% of their initial activities in the same condition within 1 and 10 days, respectively. When applied to the membrane filtration for advanced water treatment, NER-AC efficiently alleviated the biofilm maturation of Pseudomonas aeruginosa PAO1 on the membrane surface, thereby enhancing the filtration performance by preventing membrane fouling. Highly stable and magnetically separable NER-AC, as an effective and sustainable antifouling material, has a great potential to be used in the membrane filtration for water reclamation