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The primate foveola, with its high cone density and magnified cortical representation, is exquisitely specialized for high-resolution spatial vision. However, uncovering the wiring of retinal circuitry responsible for this performance has been challenging due to the difficulty in recording receptive fields of foveal retinal ganglion cells (RGCs) in vivo. In this study, we use adaptive optics scanning laser ophthalmoscopy (AOSLO) to image the calcium responses of RGCs in the living primate, with a stable, high precision visual stimulus that allowed us to localize the receptive fields of hundreds of foveal ganglion cells. This approach revealed a precisely radial organization of foveal RGCs, despite the many distortions possible during the extended developmental migration of foveal cells. By back projecting the line connecting RGC somas to their receptive fields, we have been able to define the 'physiological center' of the foveola, locating the vertical meridian separating left and right hemifields in vivo.

In the retina, several molecules involved in metabolism, the visual cycle, and other roles exhibit intrinsic fluorescence. The overall properties of retinal fluorescence depend on changes to the composition of these molecules and their environmental interactions due to transient functional shifts, especially in disease. This behooves the understanding of the origins and deviations of these properties within the multilayered retina at high lateral and axial resolution. Of particular interest is the fluorescence lifetime, a potential biomarker of function and disease independent of fluorescence intensity that can be measured in the retina with adaptive optics fluorescence lifetime ophthalmoscopy (AOFLIO). This work demonstrates the utility of the phasor method of analysis, an alternate approach to traditional multiexponential fitting, to evaluate photoreceptor two-photon excited AOFLIO data and separate them based on functional differences. Phasor analysis on fluorescence lifetime decay data allowed the repeatable segregation of S from M/L cones, likely from differences in functional or metabolic demands. Furthermore, it is possible to track the lifetime changes in S cones after photodamage. Phasor analysis increases the sensitivity of AOFLIO to functional differences between cells and has the potential to improve our understanding of pathways involved in normal and diseased conditions at the cellular scale throughout the retina.

The retina is the light-sensitive, multilayered tissue at the back of the eye responsible for converting light into electrical impulses for visual perception. Dysfunction in even one cell type or layer can result in partial to total blindness. Observing the structural and functional dynamics that underlie dysfunction, especially before cell death, is critical to understanding retinal diseases, developing new diagnostic metrics, and evaluating novel treatments. Adaptive optics scanning light ophthalmoscopy (AOSLO), which permits near-diffraction limited imaging by correcting the inherent aberrations of the eye, has enabled in vivo subcellular scale evaluations of the retina. Two-photon excited fluorescence (TPEF) imaging allows the optical probing of molecules spectrally inaccessible with single-photon fluorescence that play important roles in metabolism, the visual cycle, and structure. By combining TPEF with AOSLO, it may be possible to evaluate the biochemistry of different cells and layers throughout the living retina and relate those measurements to function. Previous work has established the instrumentation and workflow to perform TPEF adaptive optics fluorescence lifetime ophthalmoscopy (AOFLIO), an AOSLO modality which measures the time-dependent component of fluorescence aggregated from all contributing endogenous and exogenous fluorophores. The goals of this thesis are to determine how lifetime signatures differ between cells and layers and disambiguate the aggregate lifetimes into their constituent molecular species. First, AOFLIO was deployed in macaque photoreceptors. The phasor method of analysis, a method to visualize fluorescence lifetime decays in two-dimensional frequency space, was incorporated into this workflow. This enabled the separation of S cone, M/L cone, and rod photoreceptor lifetime signatures, an improvement in sensitivity over traditional multiexponential fitting. Second, AOFLIO and phasor analysis were applied to other features in the macaque retina. In vivo fluorescence signatures can be compared to those of known retinal fluorophores with a phasor fingerprint, allowing inferences about the dominant contributing sources. Finally, AOFLIO was deployed in rho-/- retinitis pigmentosa (RP) mice whose retinas expressed a fluorescence lifetime-based sensor of glucose concentration. The first evidence of glucose sequestration in the retinal pigment epithelium, the hypothesized mechanism that causes sequential cone death in RP, was observed. This work has advanced the development of TPEF AOFLIO as a noninvasive probe of biochemical composition in the in vivo retina. This may allow subcellular evaluations of the retina in health, throughout the time course of disease, and in response to therapeutics.

Recent advances in contextualized word embeddings have greatly improved semantic tasks such as Word Sense Disambiguation (WSD) and contextual similarity, but most progress has been limited to high-resource languages like English. Vietnamese, in contrast, still lacks robust models and evaluation resources for fine-grained semantic understanding. In this paper, we present ViConBERT, a novel framework for learning Vietnamese contextualized embeddings that integrates contrastive learning (SimCLR) and gloss-based distillation to better capture word meaning. We also introduce ViConWSD, the first large-scale synthetic dataset for evaluating semantic understanding in Vietnamese, covering both WSD and contextual similarity. Experimental results show that ViConBERT outperforms strong baselines on WSD (F1 = 0.87) and achieves competitive performance on ViCon (AP = 0.88) and ViSim-400 (Spearman's rho = 0.60), demonstrating its effectiveness in modeling both discrete senses and graded semantic relations. Our code, models, and data are available at https://github.com/tkhangg0910/ViConBERT

Spin–orbit torque switching using the spin Hall effect in heavy metals and topological insulators has a great potential for ultralow power magnetoresistive random-access memory. To be competitive with conventional spin-transfer torque switching, a pure spin current source with a large spin Hall angle (θSH > 1) and high electrical conductivity (σ > 105 Ω−1 m−1) is required. Here we demonstrate such a pure spin current source: conductive topological insulator BiSb thin films with σ ≈ 2.5 × 105 Ω−1 m−1, θSH ≈ 52 and spin Hall conductivity σSH ≈ 1.3 × 107 \\[ 2e\\]Ω−1 m−1 at room temperature. We show that BiSb thin films can generate a very large spin–orbit field of 2.3 kOe MA–1 cm2 and a critical switching current density as low as 1.5 MA cm–2 in Bi0.9Sb0.1/MnGa bilayers, which underlines the potential of BiSb for industrial applications.

Spin orbit torque (SOT) magnetization switching of ferromagnets with large perpendicular magnetic anisotropy has a great potential for the next generation non-volatile magnetoresistive random-access memory (MRAM). It requires a high performance pure spin current source with a large spin Hall angle and high electrical conductivity, which can be fabricated by a mass production technique. In this work, we demonstrate ultrahigh efficient and robust SOT magnetization switching in fully sputtered BiSb topological insulator and perpendicularly magnetized Co/Pt multilayers. Despite fabricated by the magnetron sputtering instead of the laboratory molecular beam epitaxy, the topological insulator layer, BiSb, shows a large spin Hall angle of θ SH  = 10.7 and high electrical conductivity of σ  = 1.5 × 10 5 Ω −1  m −1 . Our results demonstrate the feasibility of BiSb topological insulator for implementation of ultralow power SOT-MRAM and other SOT-based spintronic devices.

The large spin Hall effect in topological insulators (TIs) is very attractive for ultralow-power spintronic devices. However, evaluation of the spin Hall angle and spin–orbit torque (SOT) of TIs is usually performed on high-quality single-crystalline TI thin films grown on dedicated III-V semiconductor substrates. Here, we report on room-temperature ultralow power SOT magnetization switching of a ferrimagnetic layer by non-epitaxial BiSb TI thin films deposited on Si/SiO 2 substrates. We show that non-epitaxial BiSb thin films outperform heavy metals and other epitaxial TI thin films in terms of the effective spin Hall angle and switching current density by one to nearly two orders of magnitude. The critical SOT switching current density in BiSb is as low as 7 × 10 4  A/cm 2 at room temperature. The robustness of BiSb against crystal defects demonstrate its potential applications to SOT-based spintronic devices.

Topological materials, such as topological insulators (TIs), have great potential for ultralow power spintronic devices, thanks to their giant spin Hall effect. However, the giant spin Hall angle ( θ SH  > 1) is limited to a few chalcogenide TIs with toxic elements and low melting points, making them challenging for device integration during the silicon Back-End-of-Line (BEOL) process. Here, we show that by using a half-Heusler alloy topological semi-metal (HHA-TSM), YPtBi, it is possible to achieve both a giant θ SH up to 4.1 and a high thermal budget up to 600 °C. We demonstrate magnetization switching of a CoPt thin film using the giant spin Hall effect of YPtBi by current densities lower than those of heavy metals by one order of magnitude. Since HHA-TSM includes a group of three-element topological materials with great flexibility, our work opens the door to the third-generation spin Hall materials with both high θ SH and high compatibility with the BEOL process that would be easily adopted by the industry.

Spin injection using ferromagnetic semiconductors at room temperature is a building block for the realization of spin-functional semiconductor devices. Nevertheless, this has been very challenging due to the lack of reliable room-temperature ferromagnetism in well-known group IV and III-V based semiconductors. Here, we demonstrate room-temperature spin injection by using spin pumping in a BiSb/(Ga,Fe)Sb heterostructure, where (Ga,Fe)Sb is a ferromagnetic semiconductor (FMS) with high Curie temperature ( T C ) and BiSb is a topological insulator (TI). Despite the very small magnetization of (Ga,Fe)Sb at room temperature (45 emu/cc), we detected spin injection from (Ga,Fe)Sb by utilizing the large inverse spin Hall effect (ISHE) in BiSb. Our study provides the first demonstration of spin injection at room temperature from a FMS.

Plant uptake and metabolism of pesticides are complex and dynamic processes, which contribute to the overall toxicity of the pesticides. We investigated the metabolic fate of cyantraniliprole, a new diamide class of insecticide, during various growth stages of tomato. Cyantraniliprole was the major residue in leaves, flowers, and fruits, with the relative metabolite-to-parent ratios maintained at < 10% up to 28 days after treatment (DAT). Mature leaves contained consistently higher residues of cyantraniliprole than young leaves throughout the study. Flowers contained the highest cyantraniliprole residues up to 21 DAT, then gradually decreased. Immature green fruits had the highest cyantraniliprole residues (5.3 ± 0.7 ng/g; 42 DAT), and decreased toward red ripening stages (1.4 ± 0.2 ng/g; 84 DAT). Metabolism of cyantraniliprole primarily occurred in the foliage, where 21 metabolites were tentatively identified. Flowers and fruits contained 14 and four of these metabolites, respectively. Major transformation pathways were characterized by ring closure, followed by N -demethylation, and glycosylation. Additionally, plant metabolism of cyantraniliprole was also associated with several minor phase-I, phase-II, and breakdown metabolites. The occurrence of these metabolites in plants varied as a function of tissue types and their developmental stages. Our study highlights a tissue-specific biotransformation and accumulation of metabolites of cyantraniliprole in tomato.