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1.
Food Chem ; 366: 130609, 2022 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-34311231

RESUMO

Several grains such as wheat, rice, corn, oat, barley and rye are cultivated throughout the world. They are converted to variety of food products using a multitude of processing technologies to quench the growing organoleptic demands and consumers' preferences. Among them, corn, ranking third in wide consumption, is cost-effective and has long-term storability. Herein, ready-to-eat corn flours with variable starch digestion have been developed by processing at high temperature with shear using a twin screw continuous processor. The influence of processing temperature (121, 145 and 160°C) and moisture (25, 30 and 35%) has been studied. Results suggest both processing temperature and moisture modulate the rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) amounts of the flours. The presence or absence of oil in the flour further controls the starch digestion. The outcome is deemed to be helpful to design and develop healthy and palatable functional food products in addition to furthering the current market share for corn and other grains.


Assuntos
Farinha , Oryza , Digestão , Amido , Zea mays
2.
Anal Chem ; 2021 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-34637621

RESUMO

Sensitive and precise determination of chloramphenicol (CAP) is of great significance for human health due to its high risk in trace amounts. Solid-state artificial nanochannels are expected to be highly promising sensing devices owing to single-molecule sensitivity, target-specific selectivity, and portability. Herein, we report an aptamer self-assembly-functionalized artificial nanochannel-based sensor for highly sensitive and precise determination of CAP. Aptamer self-assembly (AAs) served as the specific recognition component and were in situ grown on the surface of stable anodic aluminum oxide (AAO) nanochannels to develop an AAs@AAO nanochannel-based sensor. Selective interaction with CAP led to the disassembly of AAs and sensitive current change of AAs@AAO nanochannels, allowing sensitive and precise sensing of CAP in complex food samples. The developed AAs@AAO nanochannel-based sensor showed a wide linear range from 0.32 to 1600 pg. mL-1, low limit of detection (LOD) of 0.1 pg. mL-1, high precision with relative standard deviation of 2.9%, and quantitative recoveries of 93.4-102.2% for CAP in milk, milk powder, and honey samples. This work proposes a versatile nanochannel-based platform for facile, sensitive, and precise sensing of hazardous residues in food samples.

3.
BMC Neurol ; 21(1): 373, 2021 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-34610800

RESUMO

BACKGROUND: The prognostic value of serum bilirubin in stroke is controversial, since bilirubin has both neuroprotective and neurotoxic properties. We aimed to investigate the association between serum bilirubin, including total bilirubin (TBIL), direct bilirubin (DBIL) and indirect bilirubin (IBIL) and poor functional outcomes in patients with acute ischemic stroke (AIS) or transient ischemic attack (TIA). METHODS: All patients with AIS or TIA were recruited from the Third China National Stroke Registry. The poor functional outcomes included modified Rankin Scale (mRS) score 2-6 and 3-6 at 3 months and 1 year. Multivariable logistic regression was used to investigate the associations of TBIL, DBIL, and IBIL with poor functional outcomes. RESULTS: Among 11,121 enrolled patients, the median (interquartile range) of TBIL, DBIL, and IBIL was 13.30 (9.90-17.70), 3.80 (2.70-5.30), and 9.30 (6.70-12.80) µmol/L. After adjustment for conventional confounding factors, patients in the highest TBIL quartile had the highest proportion of mRS score 2-6 at 3 months (odds ratio [OR], 1.37; 95 % confidence interval [CI], 1.19-1.59) and 1 year (OR, 1.31; 95 % CI, 1.13-1.52), and mRS score 3-6 at 3 months (OR, 1.33; 95 % CI, 1.11-1.59) and 1 year (OR, 1.28; 95 % CI, 1.07-1.53), when compared to patients in the lowest TBIL quartile. Similar results were observed for DBIL and IBIL. We also found J-shaped associations between serum bilirubin levels and each outcome. CONCLUSIONS: Elevated levels of serum bilirubin were significantly associated with poor functional outcomes in patients with AIS or TIA at 3 months and 1 year.

4.
FEBS Open Bio ; 2021 Sep 12.
Artigo em Inglês | MEDLINE | ID: mdl-34510818

RESUMO

MreC is a scaffold protein required for cell shape determination through interactions with proteins related to cell wall synthesis. Here, we determined the crystal structure of the major periplasmic part of MreC from Escherichia coli at 2.1 Å resolution. The periplasmic part of MreC contains a coiled coil domain and two six-stranded barrel domains. The coiled coil domain is essential for dimer formation, and the two monomers are prone to relative motion that is related to the small interface of ß-barrel domains. In addition, MreC forms an antiparallel filament-like structure along the coiled coil direction, which is different to the helical array structure in Pseudomonas aeruginosa. Our structure deepens our understanding of polymer formation of MreC.

6.
Ann Palliat Med ; 2021 Aug 30.
Artigo em Inglês | MEDLINE | ID: mdl-34498480

RESUMO

BACKGROUND: Previous studies found that lactate dehydrogenase (LDH) levels predicted poor outcomes in hemorrhagic stroke, but the prognostic role of LDH in ischemic stroke (IS) remains unclear. The aim of this study is to investigate the association between LDH and adverse clinical outcomes in patients with acute ischemic stroke (AIS) or transient ischemic attack (TIA). METHODS: All patients were enrolled from the Third China National Stroke Registry (CNSR-III). Adverse outcomes included all-cause death and poor functional outcomes [defined as modified Rankin Scale (mRS) score 3-6 and 2-6] at 3 months and 1 year. Multivariable Cox proportional hazards models and logistic regressions were used to evaluate the association of LDH with risk of all-cause death and poor functional outcomes, respectively. RESULTS: Among 9,796 included patients, the median [interquartile range (IQR)] of LDH was 175.00 (151.00-205.40) U/L. After adjustment for confounding factors, patients in the highest LDH quartile had a higher risk of all-cause death [hazard ratio (HR), 2.23; 95% confidence interval (CI), 1.27-3.90], and a higher proportion of mRS score 3-6 (odds ratio (OR), 1.54; 95% CI, 1.26-1.90) and mRS score 2-6 (OR, 1.56; 95% CI, 1.32-1.84) at 3 months. We also observed a J-shaped association between LDH and risk of each outcome. Consistent results were found at 1 year. CONCLUSIONS: Higher LDH levels are independently associated with adverse outcomes in patients with AIS or TIA.

7.
Molecules ; 26(18)2021 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-34577164

RESUMO

Many enzymes, particularly in one single family, with highly conserved structures and folds exhibit rather distinct substrate specificities. The underlying mechanism remains elusive, the resolution of which is of great importance for biochemistry, biophysics, and bioengineering. Here, we performed a neutron scattering experiment and molecular dynamics (MD) simulations on two structurally similar CYP450 proteins; CYP101 primarily catalyzes one type of ligands, then CYP2C9 can catalyze a large range of substrates. We demonstrated that it is the high density of salt bridges in CYP101 that reduces its structural flexibility, which controls the ligand access channel and the fluctuation of the catalytic pocket, thus restricting its selection on substrates. Moreover, we performed MD simulations on 146 different kinds of CYP450 proteins, spanning distinct biological categories including Fungi, Archaea, Bacteria, Protista, Animalia, and Plantae, and found the above mechanism generally valid. We demonstrated that, by fine changes of chemistry (salt-bridge density), the CYP450 superfamily can vary the structural flexibility of its member proteins among different biological categories, and thus differentiate their substrate specificities to meet the specific biological needs. As this mechanism is well-controllable and easy to be implemented, we expect it to be generally applicable in future enzymatic engineering to develop proteins of desired substrate specificities.

8.
J Sep Sci ; 2021 Sep 12.
Artigo em Inglês | MEDLINE | ID: mdl-34514725

RESUMO

Red and yellow pigments are the major ingredients of safflower, often used to color food and cosmetics. Carthamin was the main component of red pigment and hydroxysafflor yellow A and anhydrosafflower yellow B were representative components of yellow pigment. Plant metabolomics and semi-quantitative analysis were used to analyze the changes of pigment composition during the blooming period, especially these characteristic components. Carthamin, hydroxysafflor yellow A, anhydrosafflower yellow B, and other components were screened out as differential metabolites based on plant metabolomics. Then semi-quantitative analysis was used to quantify these three representative components of pigments. Experimental results showed that the content of pigments has dynamic changes along with flowering, in the early blooming period, yellow pigment accumulated much and red pigment was low in content. In the middle period, the accumulation rate of the yellow pigment slowed down and content was stabilized. In the next step, the content of yellow pigments gradually decreased, and the content of red pigments gradually increased. Later, the level of yellow pigment decreased significantly, and the accumulation rate of red pigment increased significantly. Last, the appearance color of safflower was red, with yellow parts barely visible, and accumulation of red pigment was the highest and of the yellow pigment was the lowest in content.

9.
Transl Oncol ; 14(12): 101214, 2021 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-34500231

RESUMO

P-glycoprotein (P-gp) acts as a pump to transport cytotoxic drugs out of cells and is upregulated in cancer cells. Suppressing the expression of P-gp is an effective strategy to overcome multidrug resistance in cancer chemotherapy. Temozolomide (TMZ) is the recommended drug for the standard treatment of patients with glioblastoma, but its clinical application is restricted due to drug resistance. Transient receptor potential channel-5 (TRPC5), a Ca2+-permeable channel, has been attributed to a different drug resistance mechanism except DNA repair system; therefore, we aimed to elucidate the mechanism regarding the role of TRPC5 in TMZ resistance. TRPC5 and P-glycoprotein (P-gp) are upregulated in TMZ-resistant glioblastoma cell lines. The downregulation of TRPC5 inhibited P-gp expression and led to a significant reversal of TMZ resistance in TMZ-resistant cell lines. TRPC5-siRNA restricted the growth of tumour xenografts in an athymic nude mouse model of TMZ-resistant cells. In specimens from patients with recurrent glioblastoma, TRPC5 was found to be highly expressed, accompanied by the upregulation of P-gp expression. The nuclear factor of activated T cell isoform c3 (NFATc3), which acts as a transcriptional factor, bridges TRPC5 activity to P-gp induction. In conclusion, these results demonstrate the functional role of the TRPC5-NFATc3-P-gp signalling pathway in TMZ resistance in glioblastoma cells.

10.
Analyst ; 146(20): 6178-6186, 2021 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-34553726

RESUMO

This work designed a novel dioctyl phthalate (DOP) photoelectrochemical (PEC) sensor based on a molecularly imprinted polymer (MIP) modified Cu3(BTC)2@Cu2O heterostructure. In this work, a metal organic framework (MOF), Cu3(BTC)2, was coated on Cu2O through a simple immersion method to form a Cu3(BTC)2@Cu2O heterostructure. The heterostructure exhibited strong light adsorption ability, good stability and enhanced photocurrent under visible light irradiation. Using the Cu3(BTC)2@Cu2O heterostructure as the photoelectric converter, a PEC sensor was constructed by imprinting DOP on the heterostructure. Under the optimal experimental conditions, the PEC sensor showed a wide linear range from 25.0 pM-0.1 µM and a low detection limit of 9.15 pM. This method with good sensitivity, stability, selectivity and reproducibility in actual sample analyses showed promising applications of the MOF-based heterostructure in photoelectrochemical analysis fields.

11.
Bioengineered ; 12(1): 7964-7974, 2021 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-34565286

RESUMO

Long non-coding RNAs (lncRNAs) play important regulatory roles in hepatocellular carcinoma (HCC). However, the function of LOC107985656 in HCC progression remains unclear. The lncRNA, mRNA and miRNA levels in HCC tissues or cells were measured using real-time quantitative polymerase chain reaction (RT-qPCR). The proliferation of cancer cells was evaluated using 3-(4, 5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) viability and colony formation assays. Bioinformatics prediction, dual luciferase assay and RNA pull-down assay were performed to analyze the relationships between LOC107985656 and miR-106b-5p, or miR-106b-5p and large tumor suppressor 1 (LATS1). The protein expression levels were detected using Western blot. Results showed that LncRNA LOC107985656 was downregulated in HCC tissues and cells. Upregulation of LOC107985656 inhibited the proliferation of HCC cells, whereas its knockdown promoted this phenomenon. LOC107985656 could activate the tumor-suppressive Hippo pathway by repressing yes association protein (YAP) and WW domain-containing transcription regulator protein 1 (WWTR1, also known as TAZ) (two homologs of Yki) protein expression in HCC. Further investigation suggested that LOC107985656 regulated the expression of LATS1 by acting as a sponge for absorbing miR-106b-5p in HCC cells. In conclusion, this study unraveled the role of LOC107985656 following a ceRNA (competing endogenous RNAs) mechanism for the miR-106b-5p/LATS1 axis in HCC. The results indicate potential diagnostic and therapeutic applications of LOC107985656 in HCC.Abbreviations:HCC: hepatocellular carcinoma; LncRNA: long non-coding RNA; LATS1: large tumor suppressor 1; MTT: 3-(4, 5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide; YAP: yes association protein; WWTR1: WW domain-containing transcription regulator protein 1; cDNA: single-stranded complementary DNA; RT-qPCR: real-time quantitative polymerase chain reaction; Radio-Immunoprecipitation Assay (RIPA); BCA: bicinchoninic acid; ASO: antisense oligonucleotide; MST1/2: Ste20-like kinases 1/2; TEAD: TEA domain transcription factor; ceRNA: competing endogenous RNAs.

12.
J Fluoresc ; 2021 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-34546469

RESUMO

Using two-dimensional (2D) nickel-based metal organic framework (Ni-MOF) nanosheets as a matrix, Eu3+ and Ag+ were incorporated to synthesize Ag/Eu@Ni-MOF with double luminescence centers of Eu3+ ion (615 nm) and organic ligand (524 nm). And a ratiometric luminescence sensor is constructed based on Ag/Eu@Ni-MOF for sensitive detection of biothiols in aqueous solutions. The dual-emissive fluorescence properties can be tuned by changing the amounts of Ag+ ions doping. The results of temperature and pH effects on the fluorescence of Ag/Eu@Ni-MOF indicates that the Ag/Eu@Ni-MOF is a temperature-sensitive material and the fluorescence of Ag/Eu@Ni-MOF can keep stable over a wide pH range. Due to the binding of -SH in cysteine (Cys) and glutathione (GSH) with Ag+, the ligand luminescence was significantly inhibited by weakening the Ag + influence on the energy transfer process in the MOFs. Therefore, ratiometric fluorescent sensing of biomolecular thiols was realized based on the dual-emission Ag/Eu@Ni-MOF. More importantly, the fluorescence color change can be observed with naked eyes to realize visual detection. The ratiometric fluorescent sensor exhibits high performance for Cys and GSH detection with a wide linear range of 5-250 µM and a relatively low detection limit of 0.20 µM and 0.17 µM, respectively. Furthermore, the biothiols content in human serum was determined with satisfactory results. It proves the Ni-MOF nanosheets can be used as a stable matrix for construction luminescent MOFs for the first time, and validate the great potential of Ag/Eu@Ni-MOF as a ratiometric fluorescent probe for point-of-care testing (POCT) in disease diagnosis.

13.
Acta Pharm Sin B ; 2021 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-34522576

RESUMO

The spread of coronavirus disease 2019 (COVID-19) throughout the world has resulted in stressful healthcare burdens and global health crises. Developing an effective measure to protect people from infection is an urgent need. The blockage of interaction between angiotensin-converting enzyme 2 (ACE2) and S protein is considered an essential target for anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) drugs. A full-length ACE2 protein could be a potential drug to block early entry of SARS-CoV-2 into host cells. In this study, a therapeutic strategy was developed by using extracellular vesicles (EVs) with decoy receptor ACE2 for neutralization of SARS-CoV-2. The EVs embedded with engineered ACE2 (EVs-ACE2) were prepared; the EVs-ACE2 were derived from an engineered cell line with stable ACE2 expression. The potential effect of the EVs-ACE2 on anti-SARS-CoV-2 was demonstrated by both in vitro and in vivo neutralization experiments using the pseudovirus with the S protein (S-pseudovirus). EVs-ACE2 can inhibit the infection of S-pseudovirus in various cells, and importantly, the mice treated with intranasal administration of EVs-ACE2 can suppress the entry of S-pseudovirus into the mucosal epithelium. Therefore, the intranasal EVs-ACE2 could be a preventive medicine to protect from SARS-CoV-2 infection. This EVs-based strategy offers a potential route to COVID-19 drug development.

14.
Artigo em Inglês | MEDLINE | ID: mdl-34398374

RESUMO

Bletilla striata (Thunb.) Reichb.f. has shown rather extraordinary medicinal and economic value in recent years. However, the artificial cultivation of B. striata faces quite a lot of obstacles, especially the quality degradation and heavy metal pollution problems. Cadmium (Cd) in particular, is reported to generally exceed the standard in the artificial cultivation of B. striata. So far, little attention has been paid to analyze the effects of heavy metals on the growth and the medicinal treatment efficacy of B. striata. Herein, we investigate the physio-ecological response of B. striata under gradient Cd concentration treatment: Control (0.285 mg kg-1); Tr-1 (0.655 mg kg-1); Tr-2 (1.285 mg kg-1); Tr-3 (7.675 mg kg-1); Tr-4 (54.885 mg kg-1), so as to provide a reference for the study of the Cd response regulation on B. striata. In this work, we examined the biomass, total carbon, total nitrogen, and content of B. striata polysaccharides (BSP, the functional component of B. striata), as well as the absorption proportion of Cd in B. striata. Based on the preliminary research, ecological risk assessment and human health risk assessment were allocated. Experiments were conducted in two batches (2018 and 2019, sampling in the same season) with the following findings: (1) The biomass showed no pronounced differences between the treatments or the sampling dates, only reached significant decrease at 54.885 mg kg-1 (Tr-4) soil Cd concentration in 2019; (2) The total carbon of B. striata under Cd treatment was in line with the Hormesis effect and reached a peak at 0.655 mg kg-1 (Tr-1) soil Cd concentration; (3) The total nitrogen content was generally promoted under Cd treatment with the highest content at 1.225 mg kg-1 (Tr-2); (4) The total BSP content in two sampling years are both sorted in decreasing order: Tr-4 < Tr-3 < Tr-2 < Tr-1 < Control; (5) The Cd content in Bletillae Rhizoma (tuber of B. striata) under 0.655 mg kg-1 soil Cd treatment was within the threshold stipulated in Chinese Pharmacopoeia in 2018 batch and in 2019 batch, only the control group was qualified with a safe plantation limit of Cd. The results of ecological risk assessment showed moderate toxic risk under Tr-1 (0.655 mg Cd kg-1) and the human health risk assessment indicated negligible toxic effects on human health. Overall, the soil Cd concentration should be lower than 0.655 mg kg-1, if safe cultivation, medicinal effect of B. striata and human health risk are taken into consideration.

15.
Obes Surg ; 31(10): 4436-4451, 2021 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-34373988

RESUMO

PURPOSE: This study aims to investigate the effectiveness of the transtheoretical model (TTM)-based exercise training on TTM variables, exercise adherence, and physical function in patients in the early stages after bariatric surgery (BS). MATERIALS AND METHODS: We conducted a single-blinded, prospective, randomized controlled trial (RCT) to evaluate the effects of TTM-based exercise training on BS patients immediately after surgery. Participants (n = 120) were randomized into a TTM-based exercise training group (n = 60) and a control group (n = 60). Main outcomes included TTM variables (measured by exercise stages of change (ESCs), exercise self-efficacy (ESE), and decisional balance), exercise adherence, and physical function (determined by the 6-min walk distance (6MWD)). Secondary outcomes were physical activity, anthropometrics, and body composition. We performed all analyses in accordance with the intention-to-treat principle. RESULTS: Retention rates for the interventions were 91.7% for the intervention group and 90.0% for the control group. Compared with the control group, the 12-week TTM-based intervention significantly helped participants advance through ESCs, demonstrate higher ESE, perceive more benefits and fewer barriers to exercise, and show higher exercise adherence and better physical function afterward (all P < 0.05). However, we observed no statistically significant difference between the two groups in anthropometric parameters or body composition after intervention. CONCLUSION: The TTM-based exercise intervention had significant positive effects on the TTM variables, which could further help increase patients' exercise adherence and physical function immediately after BS. TRIAL REGISTRATION: This study was retrospectively registered at the Chinese Clinical Trial Registry (website: www.chictr.org.cn , registry number: ChiCTR2000039319).

16.
J Mol Neurosci ; 71(9): 1944-1950, 2021 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-34218423

RESUMO

Progressive myoclonic epilepsy is a group of neurodegenerative diseases with complex clinical and genetic heterogeneity, which is associated with spontaneous or action-induced myoclonus and progressive neurodegeneration. Since 2020, 4 families with progressive myoclonic epilepsy-11 [OMIM#618876] have been reported with a very limited spectrum of SEMA6B pathogenic variants. In our study, whole-exome sequencing was used in a proband from a nonconsanguineous Chinese family presenting with growth retardation and recurrent atonic seizures. A deletion mutation (c.1960_1978del, p.Leu654Argfs*25) in the last exon of SEMA6B was detected, which is a de novo variant and pathogenic. The new genetic evidence we reported here strengthened the gene-disease relationship, and the gene curation level between SEMA6B and progressive myoclonic epilepsy-11 became "strong" following the ClinGen SOP. Therefore, the results of this study broaden the mutation spectrum of SEMA6B in different ethnic groups and strengthen the gene-disease relationship between SEMA6B and progressive myoclonic epilepsy-11.

17.
Eur J Surg Oncol ; 2021 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-34325940

RESUMO

BACKGROUND: Frailty is common in patients who undergo digestive system tumor surgery. This review aimed to explore the effects of preoperative frailty on multiple outcomes following surgery among patients with digestive system tumors. METHODS: PubMed (Medline), Embase, Web of Science, and other databases were searched from the inception of each database to April 2021. Meta-analysis or qualitative synthesis was performed to examine the relationship between preoperative frailty and adverse postoperative outcomes. RESULTS: A total of 29 studies encompassing 122,548 patients were included. Through meta-analysis, frailty was associated with an increased risk of total complications (risk ratio [RR] 1.44; 95 % confidence interval [CI] 1.39 to 1.50), major complications (RR 1.72; 95 % CI 1.51 to 1.95), 30-d mortality (RR 2.40; 95 % CI 2.14 to 2.70), and 5-year mortality (RR 1.74; 95 % CI 1.35 to 2.24). Through qualitative synthesis, compared with non-frail patients, two studies found that frail patients had a worse quality of life, and three studies reported that frail patients experienced greater rates of non-home discharge. However, two studies demonstrated inconsistent conclusions regarding the relationship between frailty and functional status. CONCLUSIONS: Preoperative frailty was an important risk factor for multiple adverse postoperative outcomes of patients with digestive system tumors, including objective clinical outcomes and patient-centered outcomes. Future studies focusing on the effects of frailty on patient-centered outcomes such as quality of life and functional status are needed.

18.
Artigo em Chinês | MEDLINE | ID: mdl-34304521

RESUMO

Hyperacusis refers to the experience of the sound environment being perceived as overwhelmingly loud or painful, and this can severely affect the patient's quality of life. In China little attention has been paid to hyperacusis, and there has been little research undertaken on the topic. Therefore, this article summarizes the recent research on hyperacusis regarding definition, epidemiology, etiology, mechanism, evaluation and treatment to give directions for future research.


Assuntos
Hiperacusia , Zumbido , China , Humanos , Hiperacusia/epidemiologia , Qualidade de Vida , Som
19.
Huan Jing Ke Xue ; 42(8): 3595-3603, 2021 Aug 08.
Artigo em Chinês | MEDLINE | ID: mdl-34309246

RESUMO

In late August 2020, a period of O3 pollution occurred in the main urban area of Chongqing and lasted for approximately 2 weeks (till early September). Ambient air samples, collected using Summa Canisters and DNPH sampling columns at three observation sites in the main urban area, were used to study the composition, photochemical reaction activity, and source apportionment of volatile organic compounds (VOCs) during the period of O3 pollution. The results showed that the mean volume fraction of TVOCs in the main urban area of Chongqing during the observation period was 45.08×10-9, and the components were ranked by volume fraction in the following order:OVOCs, alkanes, halohydrocarbons, alkenes, aromatics, and alkynes. Formaldehyde, ethylene, and acetone made up the higher volume fraction of VOCs, together accounting for more than 30% of TVOCs. OVOCs and alkenes contributed more to · OH loss rate (Li·OH) and ozone formation potential (OFP) and were the key VOCs components for ozone generation. The main active species in the OVOCs component were formaldehyde, acetaldehyde, and acrolein; the main active species in the alkene component were isoprene, ethylene, and n-butene. The ratio of xylene to ethylbenzene in VOCs was low, and they showed a significant correlation, indicating that the VOCs air mass in the main urban area was highly aging and affected by long-distance transmission from other areas. The source apportionment results of the PMF model showed five main sources of VOCs, namely secondary generation (27.67%), vehicle exhaust (26.56%), industrial emission (17.86%), plant (14.51%), and fossil fuel combustion (13.4%).


Assuntos
Poluentes Atmosféricos , Ozônio , Compostos Orgânicos Voláteis , Poluentes Atmosféricos/análise , China , Monitoramento Ambiental , Ozônio/análise , Emissões de Veículos/análise , Compostos Orgânicos Voláteis/análise
20.
Nanoscale ; 2021 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-34195726

RESUMO

In order to acquire TiAl composites with a multi-scale reinforcing phase, and to improve the microstructure and tensile properties at elevated temperatures, TiAl alloys have been prepared with different added carbon content levels via vacuum arc melting. The results show that when the carbon content is greater than or equal to 1.0 at%, then Ti2AlC forms and the microstructure changes from having a dendrite morphology to an equiaxed crystal morphology. The B2 phase disappears in the Ti2AlC-containing alloys. As the carbon content increases from 0 to 3.0 at%, the lamellar colony size decreases from 148.4 to 32.8 µm and the lamellar width decreases from 441.2 to 117.6 nm. More nanoscale Ti2AlC particles form in the α2 lamellae at a higher carbon content, and there are a lot of dislocations around them. As the carbon content, the Ti2AlC content increases from 0 to 16.8 vol% and the length-diameter ratio decreases from 9.2 to 1.8. The reason for the microstructure refinement is that carbon and carbide act as heterogeneous particles during solidification, and carbide dissolves some alloy elements, improving the microstructure uniformity. Compressive testing shows that the maximum compressive strength is 2324.3 MPa at a carbon content of 1.5%. At a carbon content of 2.5%, the compression strain is higher (28.1%). Tensile testing at elevated temperatures shows that upon increasing the temperature from 750 to 850 °C, the tensile strength increases from 398 to 541 MPa, and the strain increases from 6.1 to 12.2% with a temperature increase from 750 to 950 °C. The increase in the mechanical properties is attributed to the refined lamellar colonies and lamellar width, the solid solution of elements, and the formation of nanoprecipitates.

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