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Unmanned Aerial Vehicles (UAV) may lose control and collide with other objects in the air, thus causing serious flight safety accidents. In this paper, the impact load and damage mechanism of 4.78 ...

The rapid development of high-speed rail requires copper contact wire that simultaneously possesses excellent electrical conductivity, thermal stability and mechanical properties. Unfortunately, these are generally mutually exclusive properties. Here, we demonstrate directional optimization of microstructure and overcome the strength-conductivity tradeoff in copper wire. We use rotary swaging to prepare copper wire with a fiber texture and long ultrafine grains aligned along the wire axis. The wire exhibits a high electrical conductivity of 97% of the international annealed copper standard (IACS), a yield strength of over 450 MPa, high impact and wear resistances, and thermal stability of up to 573 K for 1 h. Subsequent annealing enhances the conductivity to 103 % of IACS while maintaining a yield strength above 380 MPa. The long grains provide a channel for free electrons, while the low-angle grain boundaries between ultrafine grains block dislocation slip and crack propagation, and lower the ability for boundary migration. Strength and electrical conductivity are generally mutually exclusive properties in copper wires, both of which are required in applications such as high-speed rail. Here, rotary swaging is used to manufacture copper wires that combine high strength and conductivity, and are thermally stable.

We analyze the results of Zhao et al . (Reports, 17 September 2021, p. 1363) with a focus on the mechanical properties and microstructural evolution. We conclude that their results, together with the explanations and interpretations, are confusing, misleading, or even wrong.

Background: Ultrafine-grained (UFG) titanium, which is with high yield strength, biocompatibility and corrosion resistance, is widely used in biomedical and industrial applications. However, adiabatic shear localization (ASL) is often observed in UFG materials due to their worse deformation stability under impact loading. This instability will easily result in formation of adiabatic shear bands (ASB), a narrow band located in the ASL zoom, and finally cause the fracture of material. The main objective of this work is to study the adiabatic shear behavior of UFG titanium under impact loading, including macro- and micro-properties, temperature rise, ASB failure, etc. Methods: A synchronization apparatus, which consisted of Kolsky bar system, high-speed camera system and high-speed infrared temperature measuring system, was set up to carry out the in-situ study of the mechanical properties, temperature rise, and adiabatic shear failure process of UFG pure titanium. Microstructure of the material was also analyzed in this work. Results: The critical strain of UFG pure titanium for adiabatic shear localization is about 0.37 and 0.69 for UFG Ti and CG Ti, respectively. The peak shear stress of UFG Ti is 500MPa. The propagation velocity of ASB in UFG titanium is 533~800m/s, and 160~320m/s for CG Ti. The temperature rsie within ASB of UFG titanium is 307~732℃, and 212-556℃ for CG Ti. The intense temperature rise is after the peak stress and the initiation of ASB most of the time. Conclusion: UFG Ti has good mechanical properties, however, it is easier to form ASB and cause adiabatic shear failure under impact loading when compared with CG Ti. Temperature rise may not play a major role in the formation of ASB in UFG Ti, but may be the consequence of ASB. Results of this work will help researchers better understand the failure of UFG metals under impact loading.

Optical glass materials have a lot of superior properties such as outstanding optical transparency, light weight, low manufacturing cost and high impact resistance. Thus, they are widely utilized in the transparent armors, windshields of high-speed train and airplane as well as mobile phone touch screens. Glass structures are often subjected to loading, including quasi-static and dynamic loading during their service. It is well known that the mechanical properties of engineering materials under impact loading are usually much different from those under static loading. To guide the optimal design of glass structures, it is necessary to conduct a thorough and in-depth study of the mechanical properties of glass materials. However, as a kind of typical brittle material, the failure strain of inorganic glass is extremely small. Therefore, measuring the dynamic mechanical properties of glass material has always been a quite difficult problem in the fields of experimental mechanics and impact dynamics. This paper would propose a new experimental technique-electromagnetic split Hopkinson pressure bar (ESHPB) to solve the afore-mentioned problem. In this paper, quasi-static compressive tests were first conducted using the electronic universal testing machine at a strain rate 10–3 s–1, followed by dynamic unidirectional and bidirectional compressive tests by the ESHPB apparatus under an average strain rate of 300 s−1 for soda-lime silicate glass, respectively. During dynamic compressive tests, the ultra-high-speed camera and flashlights were utilized to observe the damage/crack initiation, propagation and fracture process inside the glass samples. The feedback signal of the ultra-high-speed camera is input into the digital acquisition system, aiming to associate accurately the stress history of the sample with the high-speed image and to study the dynamic failure process in depth. The following conclusions are made based on the test results: (1) When using the ESHPB set-up to measure the dynamic mechanical properties of glass materials, stress equilibrium and approximate constant strain rate loading condition can be achieved without using the pulse shaping technique. It provides a simpler and easier test method for studying the dynamic mechanical properties of brittle materials. (2) Compared with the unidirectional loading tests, bidirectional symmetric loading experimental technique can significantly shorten the time duration for achieving the condition of stress equilibrium and constant strain rate deformation. Therefore, more effective information can be obtained from the test results and the accuracy and reliability of the test results can be greatly improved. (3) Compared with the quasi-static test results, it is found that the compressive strength of the tested glass material increases significantly under dynamic impact loading, showing a strong strain rate effect. The dependence of compressive strength on strain rate was quantitatively characterized by the strain rate sensitivity exponent. (4) The deformation images of samples captured by ultra-high-speed camera indicated that when the cracks first appeared, the specimens did not completely lose the load bearing capacity. The cracks continue to nucleate, propagate and converge. When the cracks fill almost the entire sample, the material loses the load bearing capacity completely and breaks into powders. By comparison, the samples are split into a few columns under quasi-static loading.

This study investigated the surface characteristics and biocompatibility of ultrafine-grain pure titanium (UFG Ti) after sandblasting and acid etching (SLA) treatment to determine an effective method for modification of UFG Ti dental implants. The UFG Ti was processed by equal-channel angular pressing (ECAP). The micromorphology, roughness, and wettability of its surface were studied after SLA modification in different conditions. Rat bone marrow mesenchymal stem cells were subsequently seeded onto the specimens to evaluate the biocompatibility of cell adhesion, proliferation, and differentiation compared with commercially pure titanium (CP Ti). The results showed that surface characteristics of UFG Ti were affected by the pressure of sandblasting and acid etching time in addition to material properties. The favorable hierarchical porous structure that would benefit cell adhesion was formed on the UFG Ti surface when the pressure of sandblasting was 0.6 MPa and the acid etching time was 5 min; at this time, UFG Ti promoted proliferation and differentiation to a greater extent than CP Ti because of its excellent wettability. From this study, it could be seen that UFG Ti can be used as a dental implant material after proper surface modification.

Swainsonine (SW), an indolizidine alkaloid extracted from locoweeds, was shown toxic effects in multiple studies, but the underlying action mechanism remains unclear. SW is known to cause autophagy and apoptosis, but there has been no report on paraptosis mediated cell death. Here, we showed that SW induced rat primary renal tubular epithelial cells (RTECs) death accompanied by vacuolation in vitro. The fluorescence with the endoplasmic reticulum (ER)-Tracker Red and transmission electron microscopy (TEM) results indicated that the vacuoles were of ER origin, typical of paraptosis. The level of ER stress markers, such as polyubiquitinated proteins, Bip, CHOP and cytoplasmic concentration of Ca2+ have drastically increased. Interestingly, autophagy inhibitor could not interrupt but enhanced the induction of cytoplasmic vacuolization. Furthermore, MAPK pathways were activated by SW and inhibitors of ERK and JNK pathways could prevent the formation of cytoplasmic vacuolization. In this study, we confirmed that SW induced cell paraptosis through ER stress and MAPK signaling pathway, thus further laying a theoretical foundation for the study of SW toxicity mechanism.

The aim of this in vitro and in vivo study was to evaluate the fracture strength and osseointegration of an ultrafine-grained pure titanium (UFG-Ti) mini dental implant, prepared by equal channel angular pressing (ECAP) after macro-morphology optimization. UFG-Ti was prepared by ECAP using four passes in route Bc with the internal channel angle of 120° at room temperature. Furthermore, its microstructure and mechanical properties were studied. In optimization, a three-dimensional finite element model (FEM) composed of an UFG-Ti mini implant and alveolar bone was established to improve the implant surface area and decrease the stress distribution. Then, optimized mini implants were fabricated using UFG-Ti, and a fracture strength test was performed. For the in vivo study, UFG-Ti mini implants were inserted into rabbit femurs. A histological assessment and a pull-out test were performed to evaluate its osseointegration ability. The results show that the ultimate tensile strength of UFG-Ti (685 ± 35 MPa) was significantly higher than that of commercial pure titanium (CP-Ti grade 4, 454 ± 27 MPa). After optimization, the surface area of the 2.5 mm diameter mini implant was 19% higher than that of the standard-thread mini implant, and the maximum equivalent stress (Max EQV stress) decreased by 28% in cortical bone and by 33.1% in cancellous bone, when the thread height was 0.3 mm and the pitch was 0.67 mm. The fracture strength of the UFG-Ti mini implants (328 ± 21 N) was significantly higher than that of CP-Ti grade 4 mini implants (197 ± 11 N). The in vivo study showed favorable osseointegration in both the UFG-Ti and CP-Ti groups, but the osseointegration strength of the optimized mini implants was higher than that of the standard-thread mini implants. In conclusion, the fracture and osseointegration strength had been significantly improved for UFG-Ti mini dental implant after optimization. The excellent mechanical properties and osseointegration of the UFG-Ti mini implant suggest its feasibility for clinical application.

The split Hopkinson bar (SHB) has been widely used for testing the dynamic mechanical behavior of materials. However, it is hard to involve complex stress conditions in traditional SHB due to its intrinsic characteristics. The Electromagnetic Hopkinson bar (E-Hopkinson bar) has been recently proposed as a solution. Different from the traditional SHB, the stress pulse of the E-Hopkinson bar is generated directly by the electromagnetic force. Therefore, the stress pulse that loads the specimen can be accurately controlled. With this advantage, some experiments that cannot be done with traditional SHB can be conducted by the E-Hopkinson bar technique. In this review, we introduced briefly the basic principles of the E-Hopkinson bar. Some lasted tests, such as symmetrically dynamic compression/tension of materials, interlaminar fracture of composites, dynamic Bauschinger effect of metals, intermediate strain rate tests, and dynamic multi-axial tests were also introduced. This new technique will be helpful for those researchers in the field of solid mechanics, especially when the strain rate and complex stress condition are involved.

In dairy cows, fatty liver is one of the most common metabolic diseases that occurs during the periparturient period. Angiopoietin-like protein 4 (ANGPTL4) is a well-known downstream target of peroxisome proliferator-activated receptors (PPARs), which regulate the glucose and fatty acid metabolisms. The inhibition of lipoprotein lipase (LPL) activity interferes with the storage of triglycerides (TG) in adipocytes, which plays an essential role in lipid metabolism in rodents. However, it remains unclear whether ANGPTL4 is involved in the pathological process of fatty liver in dairy cows as a result of the regulation of the hepatocellular lipid transport system. This study intended to investigate the effect of ANGPTL4 on the very-low-density lipoprotein (VLDL) assembly and secretion in bovine hepatocytes. Bovine hepatocytes were isolated using a modified two-step perfusion and collagenase digestion process, and treated with different concentrations of ANGPTL4 (0, 4, 12, and 24 ng/ml) for 24 hr. The results showed that a high concentration of ANGPTL4 could significantly increase the extracellular concentration of VLDL while reducing the intracellular content of TG. Thus, it was confirmed that ANGPTL4 could promote the transport of TG in the form of VLDL by partially regulating the expression of related proteins in hepatocytes, thereby contributing to the partial adaptive regulation of lipid transport in dairy cows.

Swainsonine (SW), an indolizidine alkaloid, is the primary toxin in locoweeds that causes toxicity syndrome in livestock. Current research shows that SW can induce both apoptosis and autophagy. However, the relationship between, and regulatory mechanism of, autophagy and apoptosis in SW-mediated cytotoxicity remain unclear. In this study, we investigated the role of autophagy and apoptosis in SW-induced cytotoxicity in rat primary renal tubular epithelial cells (RTECs). We examined the effect of SW on lysosomal function using western blotting, transmission electron microscopy, fluorescent microscopy, and flow cytometry. The results showed that SW induced both autophagy and apoptosis, and autophagy protected RTECs from cellular damage. Activating autophagy using rapamycin (Rapa) inhibited apoptosis, while suppressing autophagy using bafilomycin A1 (Baf A1) greatly enhanced SW-induced apoptosis. SW treatment suppressed the expression of lysosomal-related proteins, and co-incubation with SW and aloxistatin (E64d) further promoted apoptosis and LC3-II accumulation in RTECs. These results suggest that SW causes toxicity by disrupting lysosomal dysfunction, inhibiting autophagic degradation, and promoting apoptosis.

Lipid peroxidation plays a crucial role in early brain injury (EBI) after subarachnoid hemorrhage (SAH), and cystine/glutamate antiporter system Xc- has been proved to be associated with glutathione (GSH) synthesis, which protects cells against oxidative damage. Antioxidant effect of system Xc- is mediated by Beclin 1 (BECN1). Therefore, this study aimed to determine whether administration of BECN1 small interfering RNA (siRNA) could attenuate EBI after SAH experiment, specifically through suppressing lipid peroxidation and increasing system Xc- activity. Endovascular perforation was performed to induce SAH in a rat model and BECN1 siRNA was administered through intracerebroventricular injection. Neurological score, brain edema, lipid peroxidation (malondialdehyde, MDA), and antioxidation system, containing GSH, glutathione peroxidase (GSH-Px), glutathione reductase (GR), and anti-reactive oxygen species (anti-ROS), were examined. The expression of BECN1 and light chain of system Xc- (xCT) was detected by western blot, immunoprecipitation, and immunofluorescence staining. This study confirmed that SAH induced neurological deficits and brain edema, which was accompanied by the increase of BECN1 expression and lipid peroxidation, and the decrease of xCT expression and antioxidative capacity. However, downregulation of BECN1 by siRNA could decrease the formation of the BECN1-xCT complex and lipid peroxidation, enhance antioxidative capacity, and ameliorate neurological deficits and brain edema in SAH rats. The results suggested that inhibition of BECN1 suppresses accumulation of lipid peroxidation by increasing system Xc- activity in EBI after SAH, and BECN1 may be a new effective target for EBI treatment after SAH.

The plastic deformation and failure behavior of metals is significantly affected by loading conditions such as stress state, strain rate, temperature and etc. In this study, the tensile behavior of a dual-phase Ti-6Al-4V alloy was investigated and the influences of stress triaxiality, strain rate and temperature were characterized. Specimens with various initial stress triaxialities (0.33, 0.43, 0.52, 0.62, and 0.74 in this work) were designed and tested under quasi-static and dynamic tension. Digital image correlation (DIC) technique was used to accurately determine the local strain on the surface of the specimen during the process of deformation. Combined experimental-numerical method was adopted to acquire the maximum local strain as well as the local stress triaxiality. Results show that the critical point of the specimen always hides in the center of the cylinder and it is unpractical to measure these values directly, therefore calibration is required for both failure strain and stress triaxiality. Moreover, our results indicate that the flow stress of Ti-6Al-4V is significantly affected by the stress condition. The notched specimens display enhanced engineering flow stress (or load capacity) compared with the smooth cylinder. On the contrary, after calibrated by Bridgman’s theory, their true equivalent stresses are actually lower. These findings remind the researchers that special attention should be paid to the effects of stress triaxiality, even the general trend might be wrong.

Introduction The objective of the study was to identify trends in incidence of adult diffuse gliomas in the United States and evaluate the contribution of age, period, and cohort effects to the trends. Methods Using the Surveillance, Epidemiology, and End Results 9 database, primary diffuse glioma patients (≥20 years old) diagnosed from 1973 to 2014 were identified. Incidence trends were analyzed using joinpoint regression and age‐period‐cohort modeling. Results Overall, the incidence for adult glioma decreased slowly from 1985 to 2014 (annual percent change [APC] = 0.5%, 95% confidence intervals [CI], 0.3%‐0.6%). In histology subtype‐stratified analysis, glioblastoma and nonglioblastoma exhibited opposite trends. The incidence for glioblastoma increased from 1978 to 2014 (APC for year 1978‐1992 = 2.7%, 95% CI, 1.8%‐3.6%; APC for 1992‐2014 = 0.3%, 95% CI, 0%‐0.6%), while the incidence for nonglioblastoma decreased significantly from 1982 to 2014 (APC = 2.2%, 95% CI, 2.0%‐2.5%). Age‐period‐cohort modeling revealed significant period and cohort effects, with the patterns for glioblastoma and nonglioblastoma distinctive from each other. Compared with adults born 1890s, those born 1920s had approximately 4‐fold the risk of glioblastoma after adjustment of age and period effects, while the risk of nonglioblastoma was reduced by half in individuals in the 1939 cohort as compared with those in the 1909 cohort. Conclusions The results support the hypothesis of etiological heterogeneity of diffuse gliomas by histology subtypes. The established risk factors cannot fully explain the distinct patterns by histology subtypes, which necessitate further epidemiological studies.

Measurement of the impact strength of brittle solids is traditionally conducted by split Hopkinson pressure bar (SHPB), where one stress wave is generated and loads on the specimen (uniaxial-unidirectional, UD). What if this single stress wave is split into two (or more) smaller pulses that load on the same specimen? Based on the classical one dimensional elastic stress wave theory, nothing different would happen. However, our experiments revealed the opposite results. Electromagnetic split Hopkinson pressure bar (ESHPB), a newly developed technique that can launch two stress pulses simultaneously in opposite directions along the coaxial bars (uniaxial-bidirectional, BD), was developed to test the compressive strength of a glass. Results indicated that the loading stress waves largely determined the measured compressive strength, with all other conditions identical. Significant discrepancy (as large as 69.1%) was observed between UD and BD strength. Possible reason for this discrepancy was proposed by high-speed photography.