A Note on Directed 5-Cycles in Digraphs

In this note, it is proved that if α≥0.24817, then any digraph on n vertices with minimum outdegree at least αn contains a directed cycle of length at most 5.

Luminescent ionic lattice occupation and wide tunable emission spectra of La_(2)MgZrO_(6):Bi^(3+),Eu^(3+)double perovskite phosphors for white light LED

La_(2)Mg_(1-x/2)Zr_(1-x/2)O_(6):xBi^(3+)(x=0.01-0.035,abbreviated as LMZ:Bi^(3+))and La_(2-y)Mg_(0.99)Zr_(0.99)O_(6):0.02Bi^(3+),yEu^(3+)(y=0.1-0.11,abbreviated as LMZ:Bi^(3+),Eu^(3+))double-perovskite phosphors were prepared through high-temperature solid-phase method.The emission spectrum of LMZ:xBi^(3+)(x=0.01-0.035)phosphors excited at 353 nm is asymmetric in the range between 375 and 650 nm,showing strong green light.There are two luminescent centers of[Mg1/Zr2-O_(6)]and[Mg2/Zr1-O_(6)]for Bi^(3+)occupation,which were analyzed through different excitation wavelengths,Gaussian fitting peaks,fluorescence decay curves and Rietveld refinement of powder X-ray diffraction data.Through deep study of the luminescent lattices in the LMZ matrix,the green to blue tunning-emission is observed by different excitation wavelengths.In addition,red emission is obtained by co-doping Bi^(3+)/Eu^(3+),and adjustable emission was investigated by changing the content of Eu^(3+)in the co-doped phosphor formulation,so it is converted from green emission to red emission.The above results demonstrate how to tune emission color by co-doping rare earth ions in the double perovskite phosphor,which is attractive for future applications.

Review of the direct thermochemical conversion of lignocellulosic biomass for liquid fuels

Increased demand for liquid transportation fuels, environmental concerns and depletion of petroleum resources requires the development of efficient conversion technologies for production of second-generation biofuels from non-food resources. Thermochemical approaches hold great potential for conversion of lignocellulosic biomass into liquid fuels. Direct thermochemical processes convert biomass into liquid fuels in one step using heat and catalysts and have many advantages over indirect and biological processes, such as greater feedstock flexibility, integrated conversion of whole biomass, and lower operation costs. Several direct thermochemical processes are employed in the production of liquid biofuels depending on the nature of the feedstock properties: such as fast pyrolysis/liquefaction of lignocellulosic biomass for bio-oil, including upgrading methods, such as catalytic cracking and hydrogenation. Owing to the substantial amount of liquid fuels consumed by vehicular transport, converting biomass into drop-in liquid fuels may reduce the dependence of the fuel market on petroleumbased fuel products. In this review, we also summarize recent progress in technologies for large-scale equipment for direct thermochemical conversion. We focus on the technical aspects critical to commercialization of the technologies for production of liquid fuels from biomass,including feedstock type, cracking catalysts, catalytic cracking mechanisms, catalytic reactors, and biofuel properties. We also discuss future prospects for direct thermochemical conversion in biorefineries for the production of high grade biofuels.

Liquefaction of bamboo biomass and production of three fractions containing aromatic compounds

Depolymerization of lignin to produce value-added aromatic monomers has attracted increasing attention since these monomers can be used as phenol replacement in production of phenolic resins.Here a one-pot depolymerization of bamboo lignin was investigated to obtain aromatic platforms with low molecular weight using acidic catalyst and ethanol.Three fractions(1#,2#,and 3#)containing different molecular weight distributions of aromatic compounds could be efficiently extracted using water-organic solvent system via a stepwise fractionation process by gradual removal of solvent.The fractions distribution was found to be primarily dependent on the reaction temperature and time.When the temperature was increased from 160°C to 200°C,the yield of fractions containing aromatic products increased significantly from 19.1 wt%to 27 wt%,the same change trend was found by changing the time,and the yield of aromatic products increased from 22.4%to 26.7%with an increase of time from 10 min to 30 min.The bioproducts were characterized by using gas chromatography/mass spectrometry(GC-MS),gel permeation chromatography(GPC)and two-dimensional heteronuclear single-quantum coherence(2D HSQC NMR).As evidenced by GC-MS spectra,the three fractions were mainly comprised of phenolic derivatives,and the relative contents of phenolic compounds took up about 80%of the total area of each fraction.With the similar physiochemical properties of the fractions,aromatic platforms could provide a new paradigm of bamboo lignin utilization for renewable energy and value-added biochemicals.

Mechanism of Preparation of Platform Compounds from Lignocellulosic Biomass Liquefaction Catalyzed by Bronsted Acid: A Review

Over the past two decades, research on transforming lignocellulosic biomass into small molecule chemicals byusing catalytic liquefaction has made great progress. Notably, in recent years it has been found the production of smallmolecule chemicals through directional liquefaction of lignocellulosic biomass. Understanding the liquefactionmechanism of lignocellulosic biomass is highly important. In this review, the liquefaction mechanism of lignocellulosicbiomass and model compounds of cellulose are described, and some problems and suggestions to address them aredescribed.