Microstructure and mechanical properties of AZ91-Ca magnesium alloy cast by different processes

The microstructure and mechanical properties of magnesium （Mg） alloys are significantly influenced by the casting process. In this paper, a comparative study on microstructure and mechanical properties at ambient and elevated temperatures of AZ91-2wt.% Ca （AZX912） Mg alloy samples prepared by gravity casting （GC）, squeeze casting （SC） and rheo-squeeze casting （RSC）, respectively, was carried out. The results show that mMg grains in SC and RSC samples are significantly refined compared to the GC sample. The average secondary dendritic arm spacing of AZX912 alloy samples decreases in the order of GC, SC and RSC. As testing temperature increases from 25 ~C to 200 ~C, strength of AZX912 alloy samples is reduced, while their elongation is increased continuously. Compared to GC and SC processes, RSC process can improve the mechanical properties of AZX912 alloy at both ambient and elevated temperatures. The enhancement of mechanical properties of RSC sample over GC and SC samples mainly results from grain refinement in the as-cast microstructure of AZX912 alloy.

谐波减速器用柔性轴承疲劳寿命实验与失效分析

柔性轴承是谐波齿轮减速器的重要组成部分。为了研究柔性轴承的失效特性,研制了一种可进行柔性轴承疲劳寿命实验的专用试验机。该试验机的加载装置能够与柔性轴承的内圈一起旋转,并可在外圈主轴两端同步施加载荷。通过对四套柔性轴承进行疲劳寿命试验,观察到了几种柔性轴承的失效现象。实验后测量了沟道的宽度,深度和表面粗糙度。实验结果表明:柔性轴承的内圈仅在主轴末端出现磨损和疲劳剥落现象,而外圈可能出现疲劳断裂和剥落现象。此外,还发现柔性轴承套圈沟道的磨损是不均匀的。

Effect of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3Al-(1,2,3)Sn alloys

The effects of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3Al-(1,2,3)Sn(wt.%)alloys were investigated by X-ray diffractometry(XRD),optical microscopy(OM),scanning electron microscopy(SEM)and tensile test.It is found that,as-cast Mg-8Li-3Al-(1,2,3)Sn alloys consist ofα-Mg+β-Li duplex matrix,MgLiAl2 and Li2Mg Sn phases.Increasing Sn content leads to grain refinement ofα-Mg dendrites and increase in content of Li2MgSn phase.During hot extrusion,complete dynamic recrystallization(DRX)takes place inβ-Li phase while incomplete DRX takes place inα-Mg phase.As Sn content is increased,the volume fraction of DRXedα-Mg grains is increased and the average grain size of DRXedα-Mg grains is decreased.Increasing Sn content is beneficial to strength but harmful to ductility for as-cast Mg-8Li-3Al-(1,2,3)Sn alloys.Tensile properties of Mg-8Li-3Al-(1,2,3)Sn alloys are improved significantly via hot extrusion and Mg-8Li-3Al-2Sn alloy exhibits the best tensile properties.

Microstructure and mechanical properties of as-extruded Mg-Sn-Zn-Ca alloy with different extrusion ratios

The effect of extrusion ratio on microstructure and mechanical properties of as-extruded Mg-6Sn-2Zn-1Ca （TZX621）（mass fraction, %） alloy was investigated. It is found that incomplete dynamic recrystallization （DRX） took place in as-extrudedTZX621 alloy. As the extrusion ratio was increased from 6 to 16, both fraction of un-DRXed grains and average size of DRXedgrains in as-extruded TZX621 alloy decreased and the basal texture was weakened. Coarse CaMgSn phase was broken into particlesand fine Mg2Sn phase precipitated from α-Mg matrix during hot extrusion. Yield strength, ultimate tensile strength and elongation ofas-extruded TZX621 alloy with extrusion ratio of 16 reached 226.9 MPa, 295.6 MPa and 18.1%, which were improved by 36.0%,17.7% and 13.5%, respectively, compared to those of as-extruded TZX621 alloy with extrusion ratio of 6.

Construction of daily precipitation series and the observational characteristics of extreme precipitation in Tianjin,China during 1888-2022

Given the difficulties in rescuing and ensuring the quality of long-term climate data,current studies on century-scale climate change are usually limited to annual and monthly data,resulting in the poor detection of extreme climate events and their changes before 1950.In this study,we reconstructed a daily precipitation series for Tianjin from 15 September 1887 to 31 December 2022 on the basis of the most comprehensive daily precipitation records collected from the Tianjin Meteorological Archive,China,and in reference to the precipitation analysis results based on the datasets developed by the Climatic Research Unit Time-Series version 4.06,Global Precipitation Climatology Centre and University of Delaware along with the application of various homogenisation methods for climate series.Our approach provides a complete and reliable century-long daily precipitation series for the study of regional or local extreme weather and climate events.The reconstructed daily dataset reveals that the annual precipitation amount and R95 intensity in Tianjin during 1888-2022 lack significant trends and have values of 0.74±6.99 and-1.84±3.22 mm per decade,respectively.On the annual and seasonal scales,the precipitation amount and R95 intensity,particularly those in autumn,have increased since the latter half of the 20th century relative to those in 1888-1950.However,the increase in precipitation amount and R95 intensity is relatively limited compared with that in atmospheric water vapour content due to surface warming,indicating the highly sensitive response of extreme precipitation events to warming.In addition,the estimates for the return periods of 5,10,20,50 and 100 years covering 1888-2022,1888-1950 and 1951-2022 depict that the intensity of heavy rain and above magnitude was highest in 1888-1950 and decreased in 1951-2022.

Curcumin Inhibits Lipopolysaccharide-lnduced Mucin 5AC Hypersecretion and Airway Inflammation via Nuclear Factor Erythroid 2-Related Factor 2

Background： Excess mucus production is an important pathophysiological feature of chronic inflammatory airway diseases. Effective therapies are currently lacking. The aim of the study was to evaluate the effects ofcurcumin （CUR） on lipopolysaccharide （LPS）-induced mucus secretion and inflammation, and explored the underlying mechanism in vivo and in vitro. Methods： For the in vitro study, human bronchial epithelial （NCI-H292） cells were pretreated with CUR or vehicle for 30 min, and then exposed to LPS for 24 h. Next, nuclear factor erythroid 2-related factor 2 （Nrf2） was knocked down with Nrf2 small interfering RNA （siRNA） to confirm the specific role of Nrf2 in mucin regulation of CUR in NCI-H292 cells. In vivo, C57BL/6 mice were randomly assigned to three groups （n = 7 for each group）： control group, LPS group, and LPS ＋ CUR group. Mice in LPS and LPS ＋ CUR group were injected with saline or CUR （50 mg/kg） intraperitoneally 2 h before intratracheal instillation with LPS （ 100 μg/ml） for 7 days. Cell lysate and lung tissue were obtained to measured Mucin 5AC （MUC5AC） and Nrf2 mRNA and protein expression by a real-time polymerase chain reaction and Western blotting. Bronchoalveolar lavage fluid （BALF） was collected to enumerate total cells and neutrophils. HistopathologicaI changes of the lung were observed. Data were analyzed by one-way analysis of variance. Student＇s t-test was used when two groups were compared. Results： CUR significantly decreased the expression ofMUC5AC mRNA and protein in NCI-H292 cells exposed to LPS. This effect was dose dependent （2.424 ± 0.318 vs. 7.169 ± 1.785, t = 4.534, and 1.060 ± 0.197 vs. 2.340 ± 0.209, t = 7.716; both P 〈 0.05, respectively） and accompanied by increased mRNA and protein expression of Nrf2 （1.952 ± 0.340 vs. 1.142 ± 0.176, t = -3.661, and 2.010 ± 0.209 vs. 1.089 ±0. 132, t = -6.453; both P 〈 0.05, respectively）. Furthermore, knockdown of Nrf2 with siRNA increased MUC5A C mRN A expression by 47.7%, compared with levels observed in the siRNA-negative group （6.845 ± 1.478 vs. 3.391 ± 0.517, t = -3.821, P 〈 0.05）. Knockdown of Nrf2 with siRNA also markedly increased MUC5A C protein expression in NCI-H292 cells. CUR also significantly decreased LPS-induced mRNA and protein expression of MUC5A C in mouse lung （ 1.672 ± 0.721 vs. 5.961 ± 2.452, t = 2.906, and 0.480 ± 0.191 vs. 2.290 ± 0.834, t = 3.665, respectively; both P 〈 0.05）. Alcian blue/periodic acid-Schiff staining also showed that CUR suppressed mucin production. Compared with the LPS group, the numbers of inflammatory cells （247 ± 30 vs. 334 ± 24, t = 3.901, P 〈 0.05） and neutrophils （185 ± 22 vs. 246 ± 20, t = 3.566, P 〈 0.05） in BALF decreased in the LPS ＋ CUR group, as well as reduced inflammatory cell infiltration in lung tissue. Conclusion： CUR inhibits LPS-induced airway mucus hypersecretion and inflammation through activation of Nrf2 possibly.

How do groups of red imported fire ants （Hymenoptera： Formicidae） feed on a droplet of sugar water？

Many previous studies have focused on the foraging behaviors and strategies of the red imported fire ants, Solenopsis invicta Buren on solid food or granular bait; little attention has been paid to how liquid sugar is fed upon. In the present study, behavioral responses ofS. invicta to 25% sucrose water droplets were observed. Five foraging patterns were identified in S. invicta colonies under laboratory conditions： （i） no feeding, no sucrose water feeding was observed; （ii） surround feeding, ants surrounded and fed along the edge of the sucrose droplet; （iii） stacked feeding, ants stacked and fed along the edge of the sucrose droplet; （iv） droplet-break feeding, ants broke the liquid droplet and sucked sucrose water that spread on surface of the substance or soil particles previously transported by ants; and （v） cover feeding, whole surface of the sucrose droplet was covered by layers of feeding ants. This is the first time cover feeding in S. invicta has been reported, which obviously requires more ants compared to the other patterns. In addition, individual ants were tracked in videos under laboratory conditions, and behavioral repertoires that led to stacking, covering and droplet-breaking were identified and described. The field investigation showed that surround feeding was most frequently performed by S. invicta foragers; however, cover feeding was not observed under field conditions during this study. Both laboratory and field studies showed colony-level variations in sugar-water feeding.

Increasing Solidification Rate of M2 High-Speed Steel Ingot by Fusible Metal Mold

As one of the most popular used high-speed steels, M2 possesses excellent hardness and toughness as cutting tools. Networks of eutectic carbides distributing in the inter-dendritic region are academically considered to be the typical microstructure of M2, which can be refined by increasing cooling rate. In this paper, a novel casting method named fusible metal mold （FMM） is employed to refine the microstructure of M2 high-speed steel. Results show that FMM casting method can improve cooling rate by 100% without any contamination of the melts＇ composition.

Leakage current characteristics of SrTiO_(3)/LaNiO_(3)/Ba_(0.67)Sr_(0.33)TiO_(3)/SrTiO_(3 )heterostructure thin films

There is an urgent demand to explore new approaches of improving the electric breakdown strength of the ferroelectric thin-film capacitor without the degradation of the high dielectric constant.In this work,LaNiO_(3)/Ba_(0.67)Sr_(0.33)TiO_(3)(LNO/BST) thin film and SrTiO_(3)(STO)/LNO/BST/SrTiO_(3)(STO) were prepared by using radio frequency(RF) magnetron sputtering technique and ultrathin STO insulator layers were inserted between the LNO/BST and metal electrodes(Au or Pt) to improve the electric breakdown strength and the leakage current of the LNO/BST thin film.X-ray diffraction(XRD) and scanning electron microscopy(SEM) investigations revealed that these multilayer thin films show compact,smooth and uniform morphologies.The leakage current density of STO/LNO/BST/STO thin film was decreased by one order of magnitude and breakdown strength of STO/LNO/BST/STO thin film was enhanced from 0.72 to 1.26 MV-cm-1compared with that of LNO/BST thin film.Moreover,the dielectric constant of the STO/LNO/BST/STO thin film keeps at the same level as that of LNO/BST thin film,and dielectric loss of the STO/LNO/BST/STO thin film was decreased slightly compared with that of LNO/BST thin film.

Effect of maternal lipid profile,C-peptide,insulin,and HBA1c levels during late pregnancy on large-for-gestational age newborns

Background:Large-for-gestational age(LGA)newborns can increase the risk of metabolic syndrome.Previous studies have shown that the levels of maternal blood lipids,connecting peptide(C-peptide),insulin and glycosylated hemoglobin(HbA_(1c))were significantly different between LGA and appropriate-for-gestational age(AGA)newborns.This study aimed to determine the effect of the levels of maternal lipids,C-peptide,insulin,and HbA_(1c) during late pregnancy on LGA newborns.Methods:This study comprised 2790 non-diabetic women in late pregnancy.Among their newborns,2236(80.1%)newborns were AGA,and 554(19.9%)newborns were LGA.Maternal and neonatal characteristics were obtained from questionnaires and their case records.The levels of maternal fasting serum apolipoprotein A1(ApoA1),triglyceride(TG),total cholesterol(TC),high-density lipoprotein cholesterol(HDL-C),low-density lipoprotein cholesterol(LDL-C),C-peptide,insulin and blood HbA_(1c) were measured.The chi-square and Mann-Whitney U test were used to analyze categorical variables and continuous variables between the AGA and LGA groups,respectively.Binary logistic regression analysis was made to determine the independent risk factors for LGA newborns.Results:Maternal TG,C-peptide,insulin and HbA_(1c) levels were signifi cantly higher in the LGA group than in the AGA group(P<0.05).The LGA group had signifi cantly lower levels of maternal TC,HDL-C and LDL-C than the AGA group(P<0.05).After adjustment for confounding variables,including maternal age,pre-pregnancy body mass index,education,smoking,annual household income,amniotic fluid volume,gestational hypertension,newborn gender and gestational age at blood collection,high maternal TG levels remained signifi cantly associated with LGA newborns(P<0.05).Conclusion:High maternal TG level during late pregnancy is signifi cantly associated with LGA newborns.

Phase Separation and Crystallization Induced by Electron Irradiation in Nanoscale Fe_(56.5)Mn_(11)Cr_(8.5)Ni_4Si_(10)C_(10) Metallic Glass

A nanoscale Fe56.5Mn11Cr8.5Ni4Si10C10 metallic glass was irradiated by electron beam in a 200 kV trans- mission electron microscope. Structure evolution in the metallic glass was investigated in situ during continuous irradi- ation, where phase separation was observed after irradiation for 5 min and crystallization was observed after 33.5 min. Based on the analysis of irradiation effect, atomic displacement is believed to be the main reason for the structure rearrangement. Accumulation of atomic displacement increases the energy of the sample and promotes atomic diffusion during transformation. On the other hand, the large specific surface area of the sample also contributes to increasing free energy and atomic diffusion.