Characterization of moisture mobility and diffusion in fresh tobacco leaves during drying by the TG–NMR analysis

This paper presents the stabilization effects of inorganic filler, cerium-doped lead zirconate titanate on high-density polyethylene. The filler was loaded in two concentrations (1 and 3 wt%). The dopant contents in PbZrO₃ were 0, 0.05, 0.075, 0.1 and 0.125 mol%. The degradation of hybrid samples was accomplished by γ-irradiation at various doses up to 200 kGy. The isothermal and nonisothermal chemiluminescence (CL) and thermal analysis (TG-DSC) were applied for the thermal stability characterization of modified HDPE samples. The mechanistic considerations and radiochemical consequences caused by the variation of filler concentration and doping level are discussed. The results demonstrate that the filler acts efficiently as stabilizer at low concentration of additive when the lower filler amount is present. The start of degradation precedes melting by four processes through which the chain scission and radical oxidation represent the essential degradation stage. The filler concentration influences the degradation due to the intimate interaction between solid-state defects and free radicals. The polymer protection against oxidation is based on the scavenging of radicals by the doping elements, that is, they trap and block radicals delaying material aging. The present results open a new perspective in the quality amelioration of organic products toward high durability.

     

A general theory on spectral properties of state-homogeneous finite-state quasi-birth–death processes

In this paper a spectral theory pertaining to Quasi-Birth–Death Processes (QBDs) is presented. The QBD, which is a generalization of the birth–death process, is a powerful tool that can be utilized in modeling many stochastic phenomena. Our theory is based on the application of a matrix polynomial method to obtain the steady-state probabilities in state-homogeneous finite-state QBDs. The method is based on finding the eigenvalue–eigenvector pairs that solve a matrix polynomial equation. Since the computational effort in the solution procedure is independent of the cardinality of the counting set, it has an immediate advantage over other solution procedures. We present and prove different properties relating the quantities that arise in the solution procedure. By also compiling and formalizing the previously known properties, we present a formal unified theory on the spectral properties of QBDs, which furnishes a formal framework to embody much of the previous work. This framework carries the prospect of furthering our understanding of the behavior the modeled systems manifest.     

Antioxidant coumarin and pyrone derivatives from the insect-associated fungus Aspergillus Versicolor

Abstract

Two new compounds, versicolones A and B (1 and 2), and three known pyrone derivatives (3?5) were isolated from the insect-associated fungus Aspergillus versicolor. Their structures were elucidated through a combination of HRESIMS and NMR spectroscopic analysis. Versicolone A (1) was revealed as a coumarin derivative with the rare 5-alkyl side chain substitution. Compound 5 exhibited significant antioxidant activity with EC₅₀ value of 8.0?μM in the ABTS (2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid) assay, which was more than 2-fold potency of the positive control trolox.     

An arbitrary-shaped acoustic cloak with merits beyond the internal and external cloaks

Based on transformation acoustics, an arbitrary-shaped acoustic cloak capable of functioning as an information exchange-enabling internal cloak and a movement-allowing external cloak is presented. The general expressions of material parameters for the acoustic cloaks with arbitrarily conformal or non-conformal boundaries are derived, and then the performances of developed cloaks are validated by full-wave simulations. Finally, the different characteristics of the linear and nonlinear transformations-based cloaks are compared and analyzed. The proposed cloak could lead to wider applications beyond that of normal cloaks, since it effectively compensates the insufficiencies of traditional internal and external cloaks. Besides, this work also provides a new method to design bifunctional device and suggests an alternative way to make a large object invisible.     

Synthesis,thermal property and antifungal evaluation of pyrazine esters

Synthesis, thermal properties, as well as antifungal assessment of pyrazine esters were handed in this work. The metal-free esterification of pyrazinyl methanol and acid chloride derivatives in a stoichiometric ratio yielded the following compounds: pyrazin-2-ylmethyl benzoate (3a), (5-methylpyrazin-2-yl) methyl benzoate (3b), 1-(pyrazin-2-yl) ethyl benzoate (3c), 2-(pyrazin-2-yl) ethyl benzoate (3d), pyrazin-2-ylmethyl pivalate (3e). The spectral results totally showed that the synthesis conditions used permitted the compounds to be produced with great yield. The characterization included ¹H NMR, ¹³C NMR, IR, HRMS and organoleptic tests. Their thermal degradation process was examined by using the TG (thermogravimetry) and DSC (differential scanning calorimeter) methods. The pyrolysis products of the pyrazine esters in inert and oxidative atmospheres were analyzed by the Py-GC/MS (pyrolysis–gas chromatography/mass spectrometry) method. It revealed that 3a–3e were totally evaporated throughout the pyrolysis experiments at low temperatures. And they evaporated with high relative contents in pure nitrogen (86.12%–94.17%) and oxidative (75.01%–88.85%) atmospheres, with only a small amount decomposing into a series of substances. Additionally, the in vitro antifungal effects of compounds 3a–3e against R. solani, P. nicotianae, F. oxysporum, F. graminearum, and F. moniliforme were further investigated using the mycelial growth rate methodology. The findings shown that compound 3c has 94% and 80% inhibitor rates at 0.5 mg/ml against R. solani and P. nicotianae, respectively, with an EC₅₀ value (half maximum effective concentration) of 0.0191 mg/ml and 0.1870 mg/ml, respectively. Similarly, that of compounds 3a and 3b exhibited 82% and 91% at 0.5 mg/ml against R. solani, with an EC₅₀ value of 0.0209 mg/ml and 0.0218 mg/ml, respectively. The molecular docking of compound 3c with SDH (Succinate dehydrogenase) was preliminarily performed to reveal the binding modes in active pocket and analyze the interactions between the molecules and the protein.     

Metal-organic frameworks-derived hierarchical ZnO structures as efficient sensing materials for formaldehyde detection

Semiconducting metal oxides have been considered as effective approach for designing high-performance chemical sensing materials. In this paper, a kind of metal-organic frameworks ZIF-8 was used as sacrificed template to prepare porous ZnO hollow nanocubes for the application in gas sensing. It is found that changing calcination temperature and solvent can greatly influence the morphology of the material, which finally affects the gas sensing performance. Acetylene-sensing properties of the sensors were investigated in detail. It can be clearly seen that the material used methanol as reaction solvent with the decomposition at 350 °C for 2 h (ZnO-350-M) showed the optimal formaldehyde-sensing behaviors compared with other materials prepared in this experiment. The dynamic transients of the ZnO-350-M-based sensors demonstrated a high response value (about 10), fast response and recovery rate (4 s and 4 s, respectively) and good selectivity towards 100 ppm (part per million) formaldehyde as well as a low detectable limit (1 ppm). As exemplified for the sensing investigation towards formaldehyde, the porous ZnO hollow nanocubes showed a significantly improved chemical sensitivity due to the highly synergistic effects from the well exposed surfaces, defect states and the robust ZnO.     

Investigation of agricultural residues pyrolysis behavior under inert and oxidative conditions

Three samples of biomass including rice straw, corn straw and corncob were analyzed by using TG–MS analyzer. The relevance of the oxidizing versus inert atmosphere to the conversion of Chinese typical agricultural residues are discussed and analyzed. Firstly the effect of oxygen concentration on three biomass conversion pathway is discussed. Secondly the releasing temperature and quantities of major non-condensable gases and tar components are analyzed, and finally the kinetic parameters is calculated and compared.The results show that the oxygen concentration and fuel type play an important role in biomass conversion pathway. All the detected non-condensable gases are favored by oxidative conditions for three samples. With the increase of oxygen concentration, all the condensable gases except H₂ are released over narrower temperature ranges under oxidizing conditions. All the tar components mainly evolve within 300–700 °C, with the increase of oxygen concentration, these major tar components show different features: except that benzene and phenol quickly decreases, other tar components basically changes moderately. The Coats and Redfern integral method is used for kinetic modeling, and Malek method is adopted to select the proper mechanism function. Most of experimental data can be simulated by F1 mechanism model. For the first temperature range of all samples, the values of the activation energy and of the reaction order are lower compared to the case of inert pyrolysis.     

Rapid and Sensitive Determination of Five Amine Biomarkers in Plasma Samples from Stroke Patients by MEKC with Precolumn Derivatization

The current diagnosis of stroke remains hampered and delayed due to lack of a suitable mechanism for the rapid, accurate, and analytically sensitive biomarker-based testing methods. In the present study, a MEKC method coupled with highly sensitive laser-induced fluorescence detection and precolumn derivatization was originally described for the rapid, sensitive determination of five amine biomarkers including homocysteine (Hcy), glutamic acid (Glu), putrescine (Put), spermine (Spm) and spermidine (Spd) of stroke in plasma samples from stroke patients. 3-(2-Furoyl)quinoline-2-carboxaldehyde (FQ) was selected as the fluorescence reagent and optimized for the advantageous high-throughput derivatization with total 30 μL reaction system in 384-well microplates for the rapid determination of the targeted analytes. Results showed that the proposed derivatization reaction approach coupled with MEKC-LIF was an efficient method for the rapid determination of five amine biomarkers of stroke in plasma samples.

     

Characterization,determination and elimination technologies for sulfur from petroleum: Toward cleaner fuel and a safe environment

Sulfur-containing compounds are the most abundant compounds in crude oil. Sulfur in liquid fuel oil leads to the emission of sulfur oxides and sulfate particulate matter which not only endangers health and community property but also reduces the life of the catalysts and engines due to corrosion. Various methods, with a high level of precision and sensitivity, have been developed to analyze sulfur-containing compounds. On the other side, the removal and characterization of sulfur-containing compounds in crude oils and petroleum products is of great importance, not only for the downstream refining process, control/optimization, and environmental compliance, but also for upstream geochemical studies for exploration and production. This review summarizes the analytical strategies and some of the most important and promising technologies for the removal of sulfur from oil.