Background

A higher slow vital capacity (VC) compared with forced vital capacity (FVC) indicates small airway collapse and air trapping. We hypothesized that a larger difference between VC and FVC (VC-FVC) would predict impaired exercise capacity in patients with chronic obstructive pulmonary disease (COPD).

Methods

Pulmonary function and incremental cardiopulmonary exercise responses were assessed in 97 COPD patients. Patients were then divided into two groups: one in which VC > FVC (n = 77) and the other in which VC ≤ FVC (n = 20).

Results

Patients with VC > FVC had lower FEV1 and peak oxygen uptake (VO2/kg) compared with patients with VC ≤ FVC. There was a significant inverse correlation for the entire group between VC-FVC and peak VO2/kg (r = -0.404; p < 0.001). There was also a direct correlation between FEV1% pred and peak VO2/kg (r = 0.418; p < 0.001). The results of the multivariate regression analysis with peak VO2/kg as the dependent variable showed that VC-FVC, FEV1(% pred) and age were all significant independent predictors of peak VO2/kg. The model explained 35.9% of the peak VO2/kg variance.

Conclusions

The difference between VC and FVC, easily measured by spirometry, can be used not only as an index of severity of airflow limitation, but also to predict exercise performance in COPD patients.

Ordered self-assembled arrays or superstructures of nanocrystals (NCs) have attracted intense research interest due to their ability to translate valuable nanoscale properties to larger length scales. Numerous techniques have been explored to induce self-assembly into various superstructures. Here we investigated a simple kinetic approach to form self-assembled one-dimensional perovskite CsPbX₃ (X: halides) nanocrystal arrays templated inside a pod shaped inert lead sulfate (PbSO₄) scaffold. Both the solvent effects, and the self-assembly process and mechanism, are systematically studied based on a uniform procedure developed to generate CsPbX₃ nanocrystal superlattices with different sizes and compositions. The formation of one-dimensional (1D) chains of NCs within a half-cylindrical pod of PbSO₄ reflects a balance between solvophobicity and solvophilicity of the components. By reducing the size of NCs, we successfully realized 2D superlattices with two or three rows of close-packed CsPbBr₃ NCs, in addition to single string-of-pearl type 1D assemblies. The superlattices can be assembled both inside and outside of the half-cylindrical shells by regulating the reaction conditions. The self-assembly behavior is reminiscent of the host-guest systems of organic molecular species where supramolecular recognition rules apply to give well-defined complexes. The current study opens a door for controlling self-assembled nanostructures of CsPbX₃ NCs, and provides an attainable platform for future optoelectronic devices.

Despite the exceptional optoelectronic characteristics of the emergent perovskite nanocrystals, the ionic nature greatly limits their stability, and thus restricts their potential applications. Here we have adapted a self-assembly strategy to access a rarely reported nanorod suprastructure that provide excellent encapsulation of perovskite nanocrystals by polymer-grafted graphene oxide layers. Polyacrylic acid-grafted graphene oxide (GO-g-PAA) was used as a surface ligand during the synthesis of the CsPbX₃ perovskite nanocrystals (NCs), yielding particles (5-12 nm) with tunable halide compositions that were homogeneously embedded in the GO-g-PAA matrix. The resulting NC-GO-g-PAA exhibits a higher photoluminescence quantum yield than previously reported encapsulated NCs while maintaining an easily tunable bandgap, allowing for emission spanning the visible spectrum. The NC-GO-g-PAA hybrid further self-assembles into well-defined nanorods upon solvent treatment. The resulting nanorod morphology imparts extraordinary chemical stability toward protic solvents such as methanol and water and much enhanced thermal stability. The introduction of barrier layers by embedding the perovskite NCs in the GO-g-PAA matrix, together with its unique assembly into nanorods, provides a novel strategy to afford robust perovskite emissive materials with environmental stability that may meet or exceed the requirement for optoelectronic applications.

Si-Sn-C nanocomposites were synthesized via a facile mechanical milling method. Phase composition and morphologies of the asproduced Si-Sn-C nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. Both XRD and Raman studies revealed the amorphization of Si after mechanical milling process, while Sn remained as the crystalline phase in both Si-Sn and Si-Sn-C nanocomposites. Meanwhile, the particle size was significantly reduced, but Si tended to agglomerate during the milling and it was alleviated through the addition of carbon. The galvanostatic charge/discharge measurements were carried out to evaluate the electrochemical performance. Compared to milled Si, Si-Sn nanocomposites, Si-Sn-C nanocomposites exhibited a higher initial capacity of ∼1000 mAh/g, and its capacity was retained at ∼80% after 50 cycles. The possible buffering effect of Sn and carbon at different operating potentials during the lithiation/delithiation process was discussed.

Abstract: We demonstrate the guiding principles behind simple two dimensional self‐assembly of MOF nanoparticles (NPs) and oleic acid capped iron oxide (Fe3O4) NCs into a uniform two‐dimensional bi‐layered superstructure. This self‐assembly process can be controlled by the energy of ligand–ligand interactions between surface ligands on Fe3O4 NCs and Zr6O4(OH)4(fumarate)6 MOF NPs. Scanning transmission electron microscopy (TEM)/energy‐dispersive X‐ray spectroscopy and TEM tomography confirm the hierarchical co‐assembly of Fe3O4 NCs with MOF NPs as ligand energies are manipulated to promote facile diffusion of the smaller NCs. First‐principles calculations and event‐driven molecular dynamics simulations indicate that the observed patterns are dictated by combination of ligand–surface and ligand–ligand interactions. This study opens a new avenue for design and self‐assembly of MOFs and NCs into high surface area assemblies, mimicking the structure of supported catalyst architectures, and provides a thorough fundamental understanding of the self‐assembly process, which could be a guide for designing functional materials with desired structure.