Effect of existence state of asphaltenes on the asphaltenes-wax interaction in wax deposition

Asphaltenes are the most elusive substances in waxy crude oil,especially the complex structures,which leads to significant precipitation and aggregation characteristics of asphaltenes,and affects the asphaltenes-wax interaction.In this study,the concept of the existence state of asphaltenes was introduced to semi-quantitatively investigate the precipitation and aggregation characteristics of asphaltenes.On this basis,the influence of the existence state of asphaltenes on wax deposition was studied by coldfinger device and high-temperature gas chromatography,and the composition and properties of the deposits were analyzed.Four main findings were made:(1)As the asphaltene concentration increases,the existence state of asphaltenes gradually transitions from dispersed state to aggregated state,and the asphaltene concentration of 0.30 wt%in this study is the starting point of the transition.(2)The existence state of asphaltenes in crude oil does affect the process of wax deposition,as shown in the fact that the dispersed asphaltenes promote the occurrence of wax deposition,while the aggregated asphaltenes can inhibit wax deposition.(3)In the presence of the aggregated asphaltenes,that is,when the asphaltene concentration is higher than 0.30 wt%,the shedding phenomenon of deposit layer was observed,and with the increase of aggregated asphaltenes,the deposit layer fell off earlier.(4)With the increase of the dispersed asphaltenes,the wax appearance temperature(WAT)and wax content of the deposits all showed an increasing trend,while with the appearance of the aggregated asphaltenes,the above situation was reversed.The findings of this study can help for better understanding of the interaction between the asphaltenes and wax in wax deposition.

Cinnamic acid regulates the intestinal microbiome and short-chain fatty acids to treat slow transit constipation

BACKGROUND Slow transit constipation(STC)is a disorder with delayed colonic transit.Cinnamic acid(CA)is an organic acid in natural plants,such as Radix Scrophulariae(Xuan Shen),with low toxicity and biological activities to modulate the intestinal microbiome.AIM To explore the potential effects of CA on the intestinal microbiome and the primary endogenous metabolites-short-chain fatty acids(SCFAs)and evaluate the therapeutic effects of CA in STC.METHODS Loperamide was applied to induce STC in mice.The treatment effects of CA on STC mice were assessed from the 24 h defecations,fecal moisture and intestinal transit rate.The enteric neurotransmitters:5-hydroxytryptamine(5-HT)and vasoactive intestinal peptide(VIP)were determined by the enzyme-linked immunosorbent assay.Hematoxylin-eosin and Alcian blue and Periodic acid Schiff staining were used to evaluate intestinal mucosa's histopathological performance and secretory function.16S rDNA was employed to analyze the composition and abundance of the intestinal microbiome.The SCFAs in stool samples were quantitatively detected by gas chromatography-mass spectrometry.RESULTS CA ameliorated the symptoms of STC and treated STC effectively.CA ameliorated the infiltration of neutrophils and lymphocytes,increased the number of goblet cells and acidic mucus secretion of the mucosa.In addition,CA significantly increased the concentration of 5-HT and reduced VIP.CA significantly improved the diversity and abundance of the beneficial microbiome.Furthermore,the production of SCFAs[including acetic acid(AA),butyric acid(BA),propionic acid(PA)and valeric acid(VA)]was significantly promoted by CA.The changed abundance of Firmicutes,Akkermansia,Lachnoclostridium,Monoglobus,UCG.005,Paenalcaligenes,Psychrobacter and Acinetobacter were involved in the production of AA,BA,PA and VA.CONCLUSION CA could treat STC effectively by ameliorating the composition and abundance of the intestinal microbiome to regulate the production of SCFAs.

Emerging weak antilocalization effect in Ta_(0.7)Nb_(0.3)Sb_(2)semimetal single crystals

Weak antilocalization(WAL)effect is commonly observed in low-dimensional systems,three-dimensional(3D)topological insulators and semimetals.Here,we report the growth of high-quality Ta_(0.7)Nb_(0.3)Sb_(2)single crystals via the chemical vapor transport(CVT).Clear sign of the WAL effect is observed below 50 K,probably due to the strong spin–orbital coupling in 3D bulk.In addition,it is worth noting that a relatively large MR of 120%appears under 1 T magnetic field at T=2 K.Hall measurements and two-band model fitting results reveal high carrier mobility(>1000 cm^(2)·V^(–1)·s^(–1)in 2–300 K region),and off-compensation electron/hole ratio of~8:1.Due to the angular dependence of the WAL effect and the fermiology of the Ta_(0.7)Nb_(0.3)Sb_(2)crystals,interesting magnetic-field-induced changes of the symmetry of the anisotropic magnetoresistance(MR)from two-fold(≤0.6 T)to four-fold(0.8–1.5 T)and finally to two-fold(≥2 T)are observed.This phenomenon is attributed to the mechanism shift from the low-field WAL dominated MR to WAL and fermiology co-dominated MR and finally to high-field fermiology dominated MR.All these signs indicate that Ta_(0.7)Nb_(0.3)Sb_(2)may be a topological semimetal candidate,and these magnetotransport properties may attract more theoretical and experimental exploration of the(Ta,Nb)Sb_(2)family.