The results of recent research on the dynamic response, failure mechanism, and changes in the load-transfer paths of a half-scale three-story, three-bay, and three-span reinforced concrete frame ...subjected to a series of sudden column removals are presented. Three phases of testing were carried out, including the removal of a corner column and a column adjacent to the corner column along the short span direction, two middle exterior columns along the long span direction, and one interior column. The column removal was enabled by using a gas cannon. The dynamic response at critical locations after the imposed failure of the respective columns was observed. The removal of the corner column followed by the adjacent column resulted in only an essentially elastic response of the structure. The removal of an interior column resulted in only small deflections. The removal of the two first-story exterior columns resulted in significant vertical deflections of the middle exterior columns and significant yielding at adjacent beams that framed into the two middle exterior columns.
SnO2–ZnO hetero-nanofibers were fabricated by a facile electrospinning method and calcination in this study. The SnO2–ZnO nanofibers were characterized by scanning electron microscopy (SEM), ...transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) and X-ray diffraction (XRD). The gas sensor prepared by the SnO2–ZnO hetero-nanofibers revealed better ethanol sensing performance than pure ZnO and pure SnO2 nanofibers, good stability and excellent selectivity at the optimum temperature of 300°C. The response and recovery time to 100ppm ethanol were about 25s and 9s, respectively. The growth mechanism of the hetero-nanofibers was discussed, as well as the ethanol adsorption–desorption mechanism.
ABSTRACT
Glial cells are the most abundant cells in the central nervous system and play crucial roles in neural development, homeostasis, immunity, and conductivity. Over the past few decades, glial ...cell activity in mammals has been linked to circadian rhythms, the 24‐h chronobiological clocks that regulate many physiological processes. Indeed, glial cells rhythmically express clock genes that cell‐autonomously regulate glial function. In addition, recent findings in rodents have revealed that disruption of the glial molecular clock could impact the entire organism. In this review, we discuss the impact of circadian rhythms on the function of the three major glial cell types – astrocytes, microglia, and oligodendrocytes – across different locations within the central nervous system. We also review recent evidence uncovering the impact of glial cells on the body's circadian rhythm. Together, this sheds new light on the involvement of glial clock machinery in various diseases.
The mechanical behaviour of rubber mixed with different types of host sands is investigated from micro- to macro-scales. The change of the mobilized friction angle because of rubber inclusion is ...associated to the change of inter-particle friction angle and the friction angle due to particle rearrangement. The mobilized friction angles at the peak and critical states were obtained from triaxial testing data, and the inter-particle friction angles at different sand and sand-rubber interfaces were measured by means of grain-scale experiments. It is found that: (i) The peak friction angle decreases after adding rubber particles for all host sands, which is more significant for dilative sands. (ii) For smooth and non-breakable sands, adding rubber increases the friction angle at the critical state, due to the increasing inter-particle friction from sand-rubber interfaces, but the reduction of sand-sand contacts weakens the interlocking, leading to easier particle rearrangement. For rough and breakable sands, adding rubber decreases the friction angle at the critical state, since the inter-particle friction of sand-rubber interfaces is lower than that of pure sand interfaces, but leads to less particle breakage and thus harder particle rearrangement. (iii) State parameter works well in assessing the effect of rubber inclusion on the peak strength.
Display omitted
•The peak strength decreases after adding granulated rubber for all host sands.•For smooth and nonbreakable sands, the φ'cs increases after adding rubber.•For rough and breakable sands, the φ'cs decreases after adding rubber.•State parameter works well in assessing the peak strength of sand-rubber mixtures.
ABSTRACT
The observed diversity in Type Ia supernovae (SNe Ia) – the thermonuclear explosions of carbon–oxygen white dwarf stars used as cosmological standard candles – is currently met with a ...variety of explosion models and progenitor scenarios. To help improve our understanding of whether and how often different models contribute to the occurrence of SNe Ia and their assorted properties, we present a comprehensive analysis of seven nearby SNe Ia. We obtained one to two epochs of optical spectra with Gemini Observatory during the nebular phase (>200 d past peak) for each of these events, all of which had time series of photometry and spectroscopy at early times (the first ∼8 weeks after explosion). We use the combination of early- and late-time observations to assess the predictions of various models for the explosion (e.g. double-detonation, off-centre detonation, stellar collisions), progenitor star (e.g. ejecta mass, metallicity), and binary companion (e.g. another white dwarf or a non-degenerate star). Overall, we find general consistency in our observations with spherically symmetric models for SN Ia explosions, and with scenarios in which the binary companion is another degenerate star. We also present an in-depth analysis of SN 2017fzw, a member of the subgroup of SNe Ia which appear to be transitional between the subluminous ‘91bg-like’ events and normal SNe Ia, and for which nebular-phase spectra are rare.
The magnetic and compressive properties of the ternary Ni
40.6
Fe
36.4
Ti
23
eutectic alloys solidified under electromagnetic levitation condition were investigated. An undercooling range from 32 to ...141 K was achieved, and a ternary eutectic consisting of a fibrous Fe
2
Ti phase and lamellar γ-Fe(Ni) + Ni
3
Ti phases formed. In the ternary eutectic, the γ-Fe(Ni) and Ni
3
Ti phases kept cooperative growth, while the Fe
2
Ti phase grew either cooperatively with these two phases or sometimes independently. Theoretical calculations showed that there existed a vertical flow field and temperature gradient in the center of the levitated alloy droplet, contributing to the directional growth behavior of eutectic grain. The growth velocity of primary Ni
3
Ti dendrite increased by 2.4 times, while that of ternary eutectic increased by 77% as undercooling rose, and consequently, the microstructures were significantly refined. The temperature stability of coercivity and residual magnetization below ambient temperature was improved once alloy undercooling reached 128 K, ascribed to the enhancement of the exchange coupling effect between the magnetic domains inside refined grains. The fracture strain of the ternary eutectic alloy increased with undercooling because microcrack propagation was further hindered and the plastic deformation was more homogeneous. Meanwhile, the fracture was dominated by transgranular (TG) mode at an undercooling of 132 K because the bonding force of grain boundaries became stronger.
► The focus is simultaneous determination of seven neonicotinoid residues in grains. ► It is a rapid and reliable method that we have developed to analyse seven pesticides. ► It is the first time to ...analyse seven neonicotinoid residues in maize, millet and oat.
A method using dispersive solid-phase extraction and dispersive liquid–liquid micro-extraction cleanup followed by high performance liquid chromatography (HPLC) has been established for determination of seven neonicotinoid insecticides residues in grains including brown rice, maize, millet and oat. Based on an appraisal of the characteristics of HPLC, validation experiments were conducted for seven neonicotinoid insecticides. In the method, dispersive solid-phase extraction was carried out using PSA and bonded C18 coupled with graphitised carbon black with acetonitrile as the eluted solvent. In the linear range of each pesticide, the correlation coefficient was R2⩾0.99. At the low, medium and high three fortification levels of 0.05–0.8mgkg−1, recoveries fell within 76–123%. The relative standard deviation was between 0.9% and 12.6% for seven neonicotinoid pesticides. Low limits of detection (0.002–0.005mgkg−1) and quantification (0.007–0.018mgkg−1) were readily achieved with this method for all tested pesticides.
Background
Extensive research was conducted to analyze the ultrasonic fatigue behavior of ASGU-T64 cast aluminum alloy under different humidity environments. The study placed particular emphasis on ...investigating the factors influencing crack initiation, as well as the propagation of both short and long cracks. By examining the alloy's performance in various moisture conditions, a comprehensive understanding of its fatigue behavior was achieved.
Objective
The primary objective is to elucidate the mechanism underlying crack initiation and accurately predict the lifespan of short and long cracks. The ultimate goal is to determine how crack initiation size affects the percentage of crack initiation life in relation to the overall fatigue life.
Method
Scanning Electron Microscope (SEM) and Electron Back Scatter Diffraction (EBSD) were employed and provided valuable insights into the characteristics of the facets. Furthermore, computational methods were utilized, employing the Paris crack growth law, to accurately determine the growth lives of both short and long cracks. By combining experimental and computational approaches, a comprehensive understanding of the fracture behavior and crack growth mechanisms was achieved, contributing to the advancement of knowledge in this field.
Results
Through this study, it was discovered that fatigue cracks in the AS7GU-T64 alloy consistently initiated on the surface of the sample, primarily due to the presence of persistent slip bands (PSBs). Each facet observed on the fracture surface corresponded to an entire grain within the short crack area. While the stress intensity factor fell within the range of 3.5 to 10 MPa·√m for all three environments, it was found that the stress intensity factor in dry air exceeded that of saturated air and distilled water conditions. Importantly, the percentage of fatigue life attributed to crack initiation was found to be heavily dependent on the humidity of the testing environment and the applied stress amplitude. These insights highlight the intricate relationship between environmental conditions, stress intensity factor, crack initiation, and the overall fatigue life of the AS7GU-T64 alloy.
Conclusion
Humidity negatively affects the ultrasonic fatigue life of the AS7GU-T64 alloy. Furthermore, the size of crack initiation was identified as a significant factor influencing the percentage of crack initiation life in relation to the overall fatigue life.
A third-generation Al–Li alloy AA2198 has been successfully welded by bobbin tool friction stir welding. The stirred zone, displaying an hourglass shape, consists of recrystallized Al grains and ...precipitates remaining in solution. Joint line remnants have been found in all etched welds. Symmetrical hardness profiles have been obtained in the thickness direction, which indicates that the joints have homogenous through-thickness mechanical properties. As the rotational speed increases, the grain size of the stirred zone increases, whereas the density of strengthening particles decreases; the joint line remnants become compressed remarkably in the shoulder-dominated zone while less changes occur in the probe-dominated zone; the softest region shrinks and shifts outward, the average hardness of the stirred zone increases and the hardness profile along the cross section of the joint changes from the U-shaped to W-shaped. The tensile strength of the joint initially increases with rotational speed and then decreases with the maximal strength efficiency reaching 80%; three fracture modes have been observed and cracking initiates at the joint line remnant propagating towards the heat-affected zone, and finally to the border between the thermal-mechanically affected zone and stirred zone.
Display omitted
•The latest Al–Li alloy 2198 is welded by bobbin tool friction stir welding.•With increasing rotational speed the hardness changes from the U- to W-shaped.•Joint line remnants exist in all welds and compressed at a higher rotational speed.•Joint efficiency depends on the rotational speed and has a highest value of 80%.•Three typical fracture modes are defined based on the cracking initiation site.
Dehydration and anatexis of ultrahigh‐pressure (UHP) metamorphic rocks during continental collision are two key processes that have great bearing on the physicochemical properties of deeply subducted ...continental crust at mantle depths. Determining the time and P–T conditions at which such events take place is needed to understand subduction‐zone tectonism. A combined petrological and zirconological study of UHP metagranite from the Sulu orogen reveals differential behaviours of dehydration and anatexis between two samples from the same UHP slice. The zircon mantle domains in one sample record eclogite facies dehydration metamorphism at 236 ± 5 Ma during subduction, exhibiting low REE contents, steep MREE–HREE patterns without negative Eu anomalies, low Th, Nb and Ta contents, low temperatures of 651–750 °C and inclusions of quartz, apatite and jadeite. A second mantle domain records high‐T anatexis at 223 ± 3 Ma during exhumation, showing high REE contents, steeper MREE–HREE patterns with marked negative Eu anomalies, high Hf, Nb, Ta, Th and U contents, high temperatures of 698–879 °C and multiphase solid inclusions of albite + muscovite + quartz. In contrast, in a second sample, one zircon mantle domain records limited hydration anatexis at 237 ± 3 Ma during subduction, exhibiting high REE contents, steep MREE–HREE patterns with marked negative Eu anomalies, high Hf, Nb, Ta, Th and U contents, medium temperatures of 601–717 °C and multiphase solid inclusions of albite + muscovite + hydrohalite. A second mantle domain in this sample records a low‐T dehydration metamorphism throughout the whole continental collision in the Triassic, showing low REE contents, steep MREE–HREE patterns with weakly negative Eu anomalies, low Th, Nb and Ta contents, low temperatures of 524–669 °C and anhydrite + gas inclusions. Garnet, phengite and allanite/epidote in these two samples also exhibit different variations in texture and major‐trace element compositions, in accordance with the zircon records. The distinct P–T–t paths for these two samples suggest separate processes of dehydration and anatexis, which are ascribed to the different geothermal gradients at different positions inside the same crustal slice during continental subduction‐zone metamorphism. Therefore, the subducting continental crust underwent variable extents of dehydration and anatexis in response to the change in subduction‐zone P–T conditions.
PDF
