University of Macau

About: University of Macau is a education organization based out in Macao, Macau, China. It is known for research contribution in the topics: Computer science & Population. The organization has 6636 authors who have published 18324 publications receiving 327384 citations. The organization is also known as: UM & UMAC.

Log-polar wavelet energy signatures for rotation and scale invariant texture classification

Abstract: Classification of texture images is important in image analysis and classification This paper proposes an effective scheme for rotation and scale invariant texture classification using log-polar wavelet signatures The rotation and scale invariant feature extraction for a given image involves applying a log-polar transform to eliminate the rotation and scale effects, but at same time produce a row shifted log-polar image, which is then passed to an adaptive row shift invariant wavelet packet transform to eliminate the row shift effects So, the output wavelet coefficients are rotation and scale invariant The adaptive row shift invariant wavelet packet transform is quite efficient with only O(n /spl middot/ log n) complexity A feature vector of the most dominant log-polar wavelet energy signatures extracted from each subband of wavelet coefficients is constructed for rotation and scale invariant texture classification In the experiments, we employed a Mahalanobis classifier to classify a set of 25 distinct natural textures selected from the Brodatz album The experimental results, based on different testing data sets for images with different orientations and scales, show that the proposed classification scheme using log-polar wavelet signatures outperforms two other texture classification methods, its overall accuracy rate for joint rotation and scale invariance being 908 percent, demonstrating that the extracted energy signatures are effective rotation and scale invariant features Concerning its robustness to noise, the classification scheme also performs better than the other methods

Two-dimensional Ruddlesden–Popper layered perovskite solar cells based on phase-pure thin films

Abstract: Two-dimensional Ruddlesden–Popper layered metal-halide perovskites have attracted increasing attention for their desirable optoelectronic properties and improved stability compared to their three-dimensional counterparts. However, such perovskites typically consist of multiple quantum wells with a random well width distribution. Here, we report phase-pure quantum wells with a single well width by introducing molten salt spacer n-butylamine acetate, instead of the traditional halide spacer n-butylamine iodide. Due to the strong ionic coordination between n-butylamine acetate and the perovskite framework, a gel of a uniformly distributed intermediate phase can be formed. This allows phase-pure quantum well films with microscale vertically aligned grains to crystallize from their respective intermediate phases. The resultant solar cells achieve a power conversion efficiency of 16.25% and a high open voltage of 1.31 V. After keeping them in 65 ± 10% humidity for 4,680 h, under operation at 85 °C for 558 h, or continuous light illumination for 1,100 h, the cells show <10% efficiency degradation. Two-dimensional Ruddlesden–Popper layered metal-halide perovskites show better performance over three-dimensional versions, but are typically based on quantum wells with random width distribution. Liang et al. show that introducing molten salt spacers gives phase-pure quantum wells and improved solar cell performance.

Nanoscale Metal–Organic Particles with Rapid Clearance for Magnetic Resonance Imaging-Guided Photothermal Therapy

Abstract: Nanoscale metal-organic particles (NMOPs) are constructed from metal ions and organic bridging ligands via the self-assembly process. Herein, we fabricate NMOPs composed of Mn(2+) and a near-infrared (NIR) dye, IR825, obtaining Mn-IR825 NMOPs, which are then coated with a shell of polydopamine (PDA) and further functionalized with polyethylene glycol (PEG). While Mn(2+) in such Mn-IR825@PDA-PEG NMOPs offers strong contrast in T1-weighted magnetic resonance (MR) imaging, IR825 with strong NIR optical absorbance shows efficient photothermal conversion with great photostability in the NMOP structure. Upon intravenous injection, Mn-IR825@PDA-PEG shows efficient tumor homing together with rapid renal excretion behaviors, as revealed by MR imaging and confirmed by biodistribution measurement. Notably, when irradiated with an 808 nm laser, tumors on mice with Mn-IR825@PDA-PEG injection are completely eliminated without recurrence within 60 days, demonstrating the high efficacy of photothermal therapy with this agent. This study demonstrates the use of NMOPs as a potential photothermal agent, which features excellent tumor-targeted imaging and therapeutic functions, together with rapid renal excretion behavior, the latter of which would be particularly important for future clinical translation of nanomedicine.

Multiresponsive Graphene-Aerogel-Directed Phase-Change Smart Fibers.

Abstract: Wearable devices and systems demand multifunctional units with intelligent and integrative functions. Smart fibers with response to external stimuli, such as electrical, thermal, and photonic signals, etc., as well as offering energy storage/conversion are essential units for wearable electronics, but still remain great challenges. Herein, flexible, strong, and self-cleaning graphene-aerogel composite fibers, with tunable functions of thermal conversion and storage under multistimuli, are fabricated. The fibers made from porous graphene aerogel/organic phase-change materials coated with hydrophobic fluorocarbon resin render a wide range of phase transition temperature and enthalpy (0-186 J g-1 ). The strong and compliant fibers are twisted into yarn and woven into fabrics, showing a self-clean superhydrophobic surface and excellent multiple responsive properties to external stimuli (electron/photon/thermal) together with reversible energy storage and conversion. Such aerogel-directed smart fibers promise for broad applications in the next-generation of wearable systems.

Monotonicity of effect sizes: Questioning kappa-squared as mediation effect size measure.

Abstract: Mediation analysis is important for research in psychology and other social and behavioral sciences. Great progress has been made in testing mediation effects and in constructing their confidence intervals. Mediation effect sizes have also been considered. Preacher and Kelley (2011) proposed and recommended κ² as an effect size measure for a mediation effect. In this article, we argue that κ² is not an appropriate effect size measure for mediation models, because of its lack of the property of rank preservation (e.g., the magnitude of κ² may decrease when the mediation effect that κ² represents increases). Furthermore, κ² can lead to paradoxical results in multiple mediation models. We show that the problem of κ² is due to (a) the improper calculation of the maximum possible value of the indirect effect, and (b) mathematically, the maximum possible indirect effect is infinity, implying that the definition of κ² is mathematically incorrect. At this time, it appears that the traditional mediation effect size measure PM (the ratio of the indirect effect to the total effect), together with some other statistical information, should be preferred for basic mediation models. But for inconsistent mediation models where the indirect effect and the direct effect have opposite signs, the situation is less clear. Other considerations and suggestions for future research are also discussed.