333 research outputs found
Inverse probability weighting for covariate adjustment in randomized studies
Covariate adjustment in randomized clinical trials has the potential benefit of precision gain. It also has the potential pitfall of reduced objectivity as it opens the possibility of selecting a 'favorable' model that yields strong treatment benefit estimate. Although there is a large volume of statistical literature targeting on the first aspect, realistic solutions to enforce objective inference and improve precision are rare. As a typical randomized trial needs to accommodate many implementation issues beyond statistical considerations, maintaining the objectivity is at least as important as precision gain if not more, particularly from the perspective of the regulatory agencies. In this article, we propose a two-stage estimation procedure based on inverse probability weighting to achieve better precision without compromising objectivity. The procedure is designed in a way such that the covariate adjustment is performed before seeing the outcome, effectively reducing the possibility of selecting a 'favorable' model that yields a strong intervention effect. Both theoretical and numerical properties of the estimation procedure are presented. Application of the proposed method to a real data example is presented
Preparation and Photocatalytic Properties of SnO 2
SnO2 nanoparticles coated on nitrogen-doped carbon nanotubes were prepared successfully via a simple wet-chemical route. The as-obtained SnO2/CNx composites were characterized using X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. The photocatalytic activity of as-prepared SnO2/CNx for degradation Rhodamine B under UV light irradiation was investigated. The results show that SnO2/CNx nanocomposites have a higher photocatalytic activity than pure SnO2 and SnO2/CNTs nanocomposites. This enhanced photoresponse indicates that the photoinduced electrons in the SnO2 prefer separately transferring to the CNx, which has a high degree of defects. As a consequence, the radiative recombination of the electron-hole pairs is hampered and the photocatalytic activity is significantly enhanced for the SnO2/CNx photocatalysts
Developing Dipole-scheme Heterojunction Photocatalysts
The high recombination rate of photogenerated carriers is the bottleneck of
photocatalysis, severely limiting the photocatalytic efficiency. Here, we
develop a dipole-scheme (D-scheme for short) photocatalytic model and materials
realization. The D-scheme heterojunction not only can effectively separate
electrons and holes by a large polarization field, but also boosts
photocatalytic redox reactions with large driving photovoltages and without any
carrier loss. By means of first-principles and GW calculations, we propose a
D-scheme heterojunction prototype with two real polar materials, PtSeTe/LiGaS2.
This D-scheme photocatalyst exhibits a high capability of the photogenerated
carrier separation and near-infrared light absorption. Moreover, our
calculations of the Gibbs free energy imply a high ability of the hydrogen and
oxygen evolution reaction by a large driving force. The proposed D-scheme
photocatalytic model is generalized and paves a valuable route of significantly
improving the photocatalytic efficiency.Comment: 10 pages, 5 figure
Stabilization of Ferroelectric Hf0.5Zr0.5O2 Epitaxial Films via Monolayer Reconstruction Driven by Interfacial Redox Reaction
The binary fluorite oxide Hf0.5Zr0.5O2 tends to grab a significant amount of
notice due to the distinct and superior ferroelectricity found in its
metastable phase. Stabilizing the metastable ferroelectric phase and
delineating the underlying growth mechanism, however, are still challenging.
Recent discoveries of metastable ferroelectric Hf0.5Zr0.5O2 epitaxially grown
on structurally dissimilar perovskite oxides have triggered intensive
investigations on the ferroelectricity in materials that are nonpolar in bulk
form. Nonetheless, the growth mechanism for the unique fluorite/perovskite
heterostructures has yet to be fully explored. Here we show that the metastable
ferroelectric Hf0.5Zr0.5O2 films can be stabilized even on a
one-unit-cell-thick perovskite La0.67Sr0.33MnO3 buffer layer. In collaboration
with scanning transmittance electron microscopy (STEM) based characterizations,
we show that monolayer reconstruction driven by interfacial redox reactions
plays a vital role in the formation of a unique heterointerface between the two
structurally dissimilar oxides, providing the template monolayer that
facilitates the epitaxial growth of the metastable HZO films. Our findings
offer significant insights into the stabilization mechanism of the
ferroelectric Hf0.5Zr0.5O2, and this mechanism could be extended for exploring
functional metastable phases of various metal oxides
Femtosecond laser nanostructuring in glass with sub-50nm feature sizes
We report on controllable production of nanostructures embedded in a porous
glass substrate by femtosecond laser direct writing. We show that a hollow
nano-void with a lateral size of ~40 nm and an axial size of ~1500 nm can be
achieved by manipulating the peak intensity and polarization of the writing
laser beam. Our finding enables direct construction of 3D nanofluidics inside
glass.Comment: 15 pages, 4 figure
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