Single-Cell RNA Sequencing of hESC-Derived 3D Retinal Organoids Reveals Novel Genes Regulating RPC Commitment in Early Human Retinogenesis.

The development of the mammalian retina is a complicated process involving the generation of distinct types of neurons from retinal progenitor cells (RPCs) in a spatiotemporal-specific manner. The progression of RPCs during retinogenesis includes RPC proliferation, cell-fate commitment, and specific neuronal differentiation. In this study, by performing single-cell RNA sequencing of cells isolated from human embryonic stem cell (hESC)-derived 3D retinal organoids, we successfully deconstructed the temporal progression of RPCs during early human retinogenesis. We identified two distinctive subtypes of RPCs with unique molecular profiles, namely multipotent RPCs and neurogenic RPCs. We found that genes related to the Notch and Wnt signaling pathways, as well as chromatin remodeling, were dynamically regulated during RPC commitment. Interestingly, our analysis identified that CCND1, a G1-phase cell-cycle regulator, was coexpressed with ASCL1 in a cell-cycle-independent manner. Temporally controlled overexpression of CCND1 in retinal organoids demonstrated a role for CCND1 in promoting early retinal neurogenesis. Together, our results revealed critical pathways and novel genes in early retinogenesis of humans

NANOPARTICLE FLOTATION COLLECTORS

Flotation is a critical operation in the isolation of valuable minerals from natural ore. Before flotation, chemical collectors are routinely added to ground ore slurries. Collectors selectively bind to mineral-rich particles, increasing their hydrophobicity thus promoting selective flotation. Conventional collectors are small surfactants with a short hydrocarbon tail (2-6 carbons) and a head group, such as xanthate. In this work, much larger hydrophobic polystyrene nanoparticles are evaluated as potential flotation collectors. Experiments involving both clean model mineral suspensions and complex ultramafic nickel ores confirm that conventional water-soluble molecular collectors could be partially or completely replaced by colloidal hydrophobic nanoparticle flotation collectors. The ability of nanoparticles to induce flotation has been demonstrated by floating hydrophilic, negatively charged glass beads with cationic polystyrene nanoparticle collectors. Mechanisms and key parameters such as nanoparticle hydrophobicity and nanoparticle adsorption density have been identified. Electrostatic attraction promotes the spontaneous deposition of the nanoparticles on the glass surfaces raising the effective contact angle to facilitate the adhesion of beads to air bubbles. The pull-off force required to detach a glass sphere from the air/water interface of a bubble into the water was measured by micromechanics. Coating with nanoparticles allows the beads to attach remarkably firmly on the air bubble. As little as 10% coverage of the bead surfaces with the most effective nanoparticles could promote high flotation efficiencies, whereas conventional molecular collector requires 25% or higher coverage for a good recovery. Contact angle measurements of modified glass surfaces with a series of nanoparticles that covered a range of surface energies were used to correlate the nanoparticle surface properties with their ability to promote flotation of glass beads. Factors influencing nanoparticle deposition on glass, such as nanoparticle dosage, nanoparticle size, conditioning time have been investigated with a quartz crystal microbalance (QCM). Deposition kinetics has been analyzed according to Langmuir kinetics model. Surface functionalized nanoparticles enhance the ability of nanoparticle collectors to selectively deposit onto surfaces of the desired mineral particles in the presence of gangue materials. Poly (styrene-co-vinylimidazole) based nanoparticle collectors have been developed to selectively deposit onto nickel mineral (pentlandite) in the presence of Mg/Si slime. Flotation tests of ultramafic nickel ores with these nanoparticle collectors have shown improvements in both pentlandite recovery and selectivity.Doctor of Philosophy (PhD

Ultra-efficient frequency comb generation in AlGaAs-on-insulator microresonators

Recent advances in nonlinear optics have revolutionized integrated photonics, providing on-chip solutions to a wide range of new applications. Currently, state of the art integrated nonlinear photonic devices are mainly based on dielectric material platforms, such as Si₃N₄ and SiO₂. While semiconductor materials feature much higher nonlinear coefficients and convenience in active integration, they have suffered from high waveguide losses that prevent the realization of efficient nonlinear processes on-chip. Here, we challenge this status quo and demonstrate a low loss AlGaAs-on-insulator platform with anomalous dispersion and quality (Q) factors beyond 1.5 × 10⁶. Such a high quality factor, combined with high nonlinear coefficient and small mode volume, enabled us to demonstrate a Kerr frequency comb threshold of only ∼36 µW in a resonator with a 1 THz free spectral range, ∼100 times lower compared to that in previous semiconductor platforms. Moreover, combs with broad spans (>250 nm) have been generated with a pump power of ∼300 µW, which is lower than the threshold power of state-of the-art dielectric micro combs. A soliton-step transition has also been observed for the first time in an AlGaAs resonator

Research on the Effectiveness of China's Rural Land Ownership Policy

The confirmation of rural land rights and the "separation of three rights" have opened the prelude to the deepening reform of China's agricultural land system, and are of great significance to the implementation of rural revitalization and agricultural security strategy in the new era. Based on existing literature studies, this paper summarizes and analyzes the effect of land ownership confirmation on farmers' income, land circulation, scale management, urbanization, rural governance and other aspects of China's rural land ownership confirmation. The research shows that land ownership confirmation can improve farmers' income, promote land circulation and scale management to a certain extent, but the effect is limited. The impact on urbanization and rural governance is still unclear