Vertex-disjoint rainbow triangles in edge-colored graphs

Let $G$ be an edge-colored graph of order $n$. The minimum color degree of $G$, denoted by ${\delta }^c\left(G\right)$, is the largest integer $k$ such that for every vertex $v$, there are at least $k$ distinct colors on edges incident to $v$. We say that an edge-colored graph is rainbow if all its edges have different colors. In this paper, we consider vertex-disjoint rainbow triangles in edge-colored graphs. Li (2013) showed that if ${\delta }^c\left(G\right)\ge (n+1)∕2$, then $G$ contains a rainbow triangle and the lower bound is tight. Motivated by this result, we prove that if $n\ge 20$ and ${\delta }^c\left(G\right)\ge (n+2)∕2$, then $G$ contains two vertex-disjoint rainbow triangles. In particular, we conjecture that if ${\delta }^c\left(G\right)\ge (n+k)∕2$, then $G$ contains $k$ vertex-disjoint rainbow triangles. For any integer $k\ge 2$, we show that if $n\ge 16k-12$ and ${\delta }^c\left(G\right)\ge n∕2+k-1$, then $G$ contains $k$ vertex-disjoint rainbow triangles. Moreover, we provide sufficient conditions for the existence of $k$ edge-disjoint rainbow triangles.     

Salient region detection using background priors

In this paper, we introduce a novel salient region detection algorithm by using background priors. Because of the fact that superpixel is perceptually more meaningful than pixel, and which can reduce the complexity of image processing, we use the superpixel algorithm to reprocess original images. In addition, we hold the point that the colors in the image boundary could mainly represent all background colors, hence we compute the color contrast between the intern colors and the boundary colors. Since the nearer the patches are close to center, the more they affect other patches, we propose a new distribution-based model. Finally, experimental results demonstrate that the proposed method outperforms the state-of-the-art approaches.     

Orthogonal Trichromatic Upconversion with High Color Purity in Core-Shell Nanoparticles for a Full-Color Display

Materials with tunable emission colors has attracted increasing interest in both fundamental research and applications. As a key member of light-emitting materials family, lanthanide doped upconversion nanoparticles (UCNPs) have been intensively demonstrated to emit light in any color upon near-infrared excitation. However, realizing the trichromatic emission in UCNPs with a fixed composition remains a great challenge. Here, without excitation pulsed modulation and three different near-infrared pumping, we report an experimental design to fine-control emission in the full color gamut from core–shell-structured UCNPs by manipulating the energy migration through dual-channel pump scheme. We also demonstrate their potential application in full-color display. These findings may benefit the future development of convenient and versatile optical methos for multicolor tuning and open up the possibility of constructing full-color volumetric display systems with high spatiotemporal resolution.     

Multi-Resonance Building-Block-Based Electroluminescent Material: Lengthening Emission Maximum and Shortening Delayed Fluorescence Lifetime

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials are considered a class of organic materials with exceptional electronic and optical properties, which make them promising for the applications in organic light-emitting diodes (OLEDs). In this study, we improved, synthesized, and characterized a multiple-resonance type emitter based on the assembly of MR-building blocks (MR-BBs). By optimizing the geometric arrangement of MR-BBs, we were able to generate narrowband emission in the longer wavelength region and shorten the delayed excited-state lifetime, resulting in improved emission efficiency compared to the parent molecule. Our proof-of-concept molecule, m-DBCz, exhibited narrowband yellowish-green TADF emission with a full width at half-maximum of 32 nm and a small singlet-triplet energy gap of 0.04 eV. The OLED developed using m-DBCz as the emitter demonstrated electroluminescence at 548 nm and achieved a high external quantum efficiency (EQE) of 34.9 %. Further optimization of the device resulted in a high external quantum efficiency of 36.3 % and extremely low efficiency roll-off, with EQE values of 30.1 % and 27.7 % obtained even at high luminance levels of 50 000 and 100 000 cd m⁻². These results demonstrate the full potential of MR-TADF materials for applications on ultrahigh-luminance OLEDs.     

Effect of metal ions on structural,morphological and optical properties of nano-crystallite spinel cobalt-aluminate (CoAl2O4)

The bright blue nano crystallite cobalt aluminate (CoAl₂O₄) was synthesized by sol–gel method using a mixture of chelating agent of glycerol and citric acid. The effects of changing (0.05, 0.075, 0.10, 0.25, 0.50, and 0.75 mol/L) metal ion concentration on the structural, morphological and color properties of synthesized CoAl₂O₄ were characterized by using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), Nanoparticle size analyzer, Simultaneous Thermal Analyzer (STA), UV–vis absorption spectroscopy, and CIE-LAB colorimetric analysis. From the X-ray peak profile analysis, the crystallite size was measured by Debye-Scherrer (D-S) equation, and three different models presenting average crystallite sizes between 88.3 and 125.4 nm.The average lattice strain, dislocation density, lattice constant, cell volume, and zeta potential were between 0.00021 and 0.0058, (1.73 to 12.8) × 10¹⁴ (lines/m²), 8.10658 to 8.11181 Å, 533.60 to 533.81 Å³, ?56.4 to ? 63.5 mV, respectively. Using UV–vis absorption spectroscopy, the band gap was calculated from Kubelka-Munk method, and the values of band gap increasing from 1.82 to 1.84 eV, respectively. The reflectance spectra and the CIE-L*a*b* values of cobalt aluminate is also measured which confirmed the formation of blue nano crystallite cobalt aluminate.     

Reactive Dyeing of Electrospun Cellulose Nanofibers by Pad-steam Method

Based on the functional properties of electrospun cellulose nanofibers(CNF), scientists are showing substantial interest to enhance the aesthetic properties. However, the lower color yield has remained a big challenge due to the higher surface area of nanofibers. In this study, we attempted to improve the color yield properties of CNF by the pad-steam dyeing method. Neat CNF was obtained by deacetylation of electrospun cellulose acetate(CA) nanofibers. Three different kinds of reactive dyes were used and pad-steam dyeing parameters were optimized. SEM images revealed smooth morphology with an increase in the average diameter of nanofibers. FTIR results showed no change in the chemical structure after dyeing of CNF. Color fastness results demonstrated excellent ratings for reactive dyes, which indicate good dye fixation properties and no color loss during the washing process. The results confirm that the pad-steam dyeing method can be potentially considered to improve the aesthetic properties of CNF, which can be utilized for functional garments, such as breathable raincoats and disposable face masks.