Against general wisdom in crystallization,the nucleation of InP and Ⅲ-Ⅴ quantum dots (QDs) often dominates their growth.Systematic studies on InP QDs identified the key reason for this:the dense and tight alkanoate-ligand shell around each nanocrystal.Different strategies were explored to enable necessary ligand dynamics—i.e.,ligands rapidly switching between being bonded to and detached from a nanocrystal upon thermal agitation—on nanocrystals to simultaneously retain colloidal stability and allow appreciable growth.Among all the surface-activation reagents tested,2,4-diketones (such as acetylacetone) allowed the full growth of InP QDs with indium alkanoates and trimethylsilylphosphine as precursors.While small fatty acids (such as acetic acid) were partially active,common neutral ligands (such as fatty amines,organophosphines,and phosphine oxides) showed limited activation effects.The existing amine-based synthesis of InP QDs was activated by acetic acid formed in situ.Surface activation with common precursors enabled the growth of InP QDs with a distinguishable absorption peak between ～450 and 650 nm at mild temperatures (140-180 ℃).Furthermore,surface activation was generally applicable for InAs and Ⅲ-Ⅴ based core/shell QDs. 相似文献
Two-dimensional (2D) ultrathin SiC has received intense attention due to its broad band gap and resistance to large mechanical deformation and external chemical corrosion. However, the synthesis and application of ultrasmall 2D SiC quantum dots (QDs) has not been explored. Herein, we synthesize a type of monolayered 2D SiC QDs with advanced photoluminescence (PL) properties via a facile hydrothermal route. Their average size and thickness can be easily adjusted by altering the reaction time. The ultrasmall 2D SiC QDs exhibit a long fluorescence lifetime of 2.59 μs due to efficient quantum confinement. The applications of SiC QDs are demonstrated through labeling A549, HeLa, and NHDF cells and delivering agents for intracellular low-abundant microRNA (miRNA) detection. This advance in preparing photoluminescent SiC QDs is of great significance for broadening their potential in biomedical and optical applications.
In three-dimensional medical imaging, segmentation of specific anatomy structure is often a preprocessing step for computer-aided detection/diagnosis (CAD) purposes, and its performance has a significant impact on diagnosis of diseases as well as objective quantitative assessment of therapeutic efficacy. However, the existence of various diseases, image noise or artifacts, and individual anatomical variety generally impose a challenge for accurate segmentation of specific structures. To address these problems, a shape analysis strategy termed "break-and-repair" is presented in this study to facilitate automated medical image segmentation. Similar to surface approximation using a limited number of control points, the basic idea is to remove problematic regions and then estimate a smooth and complete surface shape by representing the remaining regions with high fidelity as an implicit function. The innovation of this shape analysis strategy is the capability of solving challenging medical image segmentation problems in a unified framework, regardless of the variability of anatomical structures in question. In our implementation, principal curvature analysis is used to identify and remove the problematic regions and radial basis function (RBF) based implicit surface fitting is used to achieve a closed (or complete) surface boundary. The feasibility and performance of this strategy are demonstrated by applying it to automated segmentation of two completely different anatomical structures depicted on CT examinations, namely human lungs and pulmonary nodules. Our quantitative experiments on a large number of clinical CT examinations collected from different sources demonstrate the accuracy, robustness, and generality of the shape "break-and-repair" strategy in medical image segmentation. 相似文献
