An experimental program including study has been conducted to investigate buckling behavior of 7A04 high-strength (HS) aluminum alloy columns under axial compression, in which 42 L-shaped extruded ...specimens were designed and tested. The specimens involved two sections and seven slenderness ratios varying from 15 to 100. The test results were compared with design results in accordance with American Aluminum Design Manual, GB 50429-2007 and Eurocode 9. A finite element (FE) model of the tested specimens under axial compression has been developed by using general finite element software ANSYS, and was verified by using the test results reported herein and other experimental results presented in the literature. By using this FE model, an extensive body of parametric analyses were conducted to clarify the effects of width-to-thickness ratio of angle legs, initial imperfections and material strengths on the buckling resistance of the 7A04 angle columns. Based on the test and FE analyses results, a modified design method was proposed for predicting the buckling resistance of 7A04 high-strength aluminum alloy columns more accurately.
•Tests are conducted on high strength aluminum alloy angle columns.•Test results are compared with three current design standards.•A FE model is developed and verified by test results.•An extensive body of parametric analyses are conducted to study three factors.•A modified design method is proposed which can predict results more accurately.
The aim of this paper is to characterize both microstructural evolution and thixoformability during partial melting of semi-solid 319s alloy. The thixoformability criteria of 319s was initially ...investigated by thermodynamic analysis. In-situ observation of partial re-melting was performed by a Confocal Laser Scanning Microscope to determine the effect of heating rate on melting characteristics. Meanwhile, the microstructural evolution of 319s alloy at extremely low heating rate was also investigated in order to understand the mechanism of re-melting process. The studies demonstrated that 319s alloy is suitable for thixocasting because of the controllable liquid fraction in the operating window of 15 °C. The process window was effected by both temperature and heating time. The primary particles evolution in 319s alloy can be divided into four stages, and the coarsening rate during isothermal test is 227 μm3/s. The effective method to obtain desirable microstructure is to manage the time in the semi-solid state by controlling heating rate and soaking time.
•The thixoformability of 319s is discussed by using SPSC and thermodynamic analysis.•The re-melting processes at different heating rate are in-situ observed.•We identified the four stages of microstructural evolution during re-melting.•The coarsening rate K for 319s during isothermal test is identified.•The variation tendency of Si particle size with increasing time is reported.
The focal plane camera is the core component of the Wide Field-of-view Cherenkov/fluorescence Telescope Array (WFCTA) of the Large High-Altitude Air Shower Observatory (LHAASO). Because of the ...capability of working under moonlight without aging, silicon photomultipliers (SiPM) have been proven to be not only an alternative but also an improvement to conventional photomultiplier tubes (PMT) in this application. Eighteen SiPM-based cameras with square light funnels have been built for WFCTA. The telescopes have collected more than 100 million cosmic ray events and preliminary results indicate that these cameras are capable of working under moonlight. The characteristics of the light funnels and SiPMs pose challenges (e.g. dynamic range, dark count rate, assembly techniques). In this paper, we present the design features, manufacturing techniques and performances of these cameras. Finally, the test facilities, the test methods and results of SiPMs in the cameras are reported here.
Nano-SiCp/AZ91 magnesium matrix composite was fabricated by stir casting. The as-cast ingots were extruded at 350°C, then processed by equal channel angular pressing (ECAP) at various temperatures ...(250°C, 300°C and 350°C). Grains are significantly refined after the extrusion and the ECAP. A basal fibre texture was detected by neutron diffraction after the extrusion, which inclines about 45° to the extrusion direction (ED) after the ECAP. Nano-scaled SiC particles agglomerate in the as-cast composite. After the extrusion, the agglomeration tends to form continuous or discontinuous strips along the extrusion direction. By application of the ECAP, the agglomerated SiC particles are partly dispersed and the strips formed during the extrusion tend to be thinner and broken with the increasing pass number. The yield tensile strength (YTS) and the ultimate tensile strength (UTS) of the composite are dramatically increased after the extrusion. ECAP for one pass at various temperatures further increases the strength, however, the YTS decreases with the increasing ECAP temperature and the pass number. The Orowan equations predict the maximum YTS of the composite may be up to 400MPa providing SiC particles are homogenously distributed in the matrix.
•Nano-scaled SiC particles were successfully added into AZ91 by stirring casting.•Agglomeration of nano-particles were improved by extrusion and ECAP.•Yield strength of the composite is 328MPa after one pass of ECAP.•Further ECAP process with optimized parameters may fully disperse nano-particles.•Yield strength is predicted to up to 400MPa when particles are fully dispersed.
We present the measurements of all-particle energy spectrum and mean logarithmic mass of cosmic rays in the energy range of 0.3-30 PeV using data collected from LHAASO-KM2A between September 2021 and ...December 2022, which is based on a nearly composition-independent energy reconstruction method, achieving unprecedented accuracy. Our analysis reveals the position of the knee at 3.67±0.05±0.15 PeV. Below the knee, the spectral index is found to be -2.7413±0.0004±0.0050, while above the knee, it is -3.128±0.005±0.027, with the sharpness of the transition measured with a statistical error of 2%. The mean logarithmic mass of cosmic rays is almost heavier than helium in the whole measured energy range. It decreases from 1.7 at 0.3 PeV to 1.3 at 3 PeV, representing a 24% decline following a power law with an index of -0.1200±0.0003±0.0341. This is equivalent to an increase in abundance of light components. Above the knee, the mean logarithmic mass exhibits a power law trend towards heavier components, which is reversal to the behavior observed in the all-particle energy spectrum. Additionally, the knee position and the change in power-law index are approximately the same. These findings suggest that the knee observed in the all-particle spectrum corresponds to the knee of the light component, rather than the medium-heavy components.
Abstract
For decades, supernova remnants (SNRs) have been considered the prime sources of Galactic cosmic rays (CRs). But whether SNRs can accelerate CR protons to PeV energies and thus dominate CR ...flux up to the knee is currently under intensive theoretical and phenomenological debate. The direct test of the ability of SNRs to operate as CR PeVatrons can be provided by ultrahigh-energy (UHE;
E
γ
≥ 100 TeV)
γ
-rays. In this context, the historical SNR Cassiopeia A (Cas A) is considered one of the most promising targets for UHE observations. This paper presents the observation of Cas A and its vicinity by the LHAASO KM2A detector. The exceptional sensitivity of LHAASO KM2A in the UHE band, combined with the young age of Cas A, enabled us to derive stringent model-independent limits on the energy budget of UHE protons and nuclei accelerated by Cas A at any epoch after the explosion. The results challenge the prevailing paradigm that Cas A–type SNRs are major suppliers of PeV CRs in the Milky Way.
•Fructose derived MF and DMF biofuels improve the lubricity of commercial gasoline.•A physicochemical mechanism for the lubricity is proposed.•The mechanism is reliant on the number of functional ...methyl groups and the blend ratio.
2-Methylfuran (MF) and 2,5-dimethylfuran’s (DMF) combustion characteristics have confirmed their validity as appropriate gasoline replacement and enhancement fuels. However, the performance of fuel injection equipment is dependant on the tribological performance of these fuels lubricity testing of MF, DMF and their blends with gasoline was undertaken using the high frequency reciprocating rig method, based on ASTM D6079 . Results showed that both MF and DMF possessed greater lubricity and wear resistance characteristics than those of gasoline when tested as pure substances. Their blends with gasoline at 2, 4, 6, 8, 10, 20 and 50 percent volume (%vol) showed improved tribological performance also. DMF was found to possess greater lubricating properties than that of MF. As little as 2%vol reduced the wear scar diameter by 46% and 47% for MF and DMF respectively showing even a small addition of these biofuels could greatly improve the tribological performance of the fuel within the engine. This was mainly due to the polar functional groups of MF and DMF bonding to the bearing surfaces during testing, creating a tribo-film that protected the surface, reducing both wear and friction. These effects were greatest for the DMF blends, with two methyl groups leading to stronger polarity and a resulting higher bonding strength to the metal surfaces. The reduction in friction coefficients with the addition of the biofuels showed that utilisation of these blends would reduce frictional losses along the fuel line, improving the overall engine efficiency.
Summary
To investigate the effects of different concentrations of various cryoprotectants (CPs) on the cell viability as well as expression of spermatogenesis‐related genes, such as CREM, Stra8 and ...HSP70‐2 in frozen–thawed bovine calf testicular tissue, immature bovine (Qinchuan cattle) calf testicular tissue was collected and cryopreserved in the cryomedia containing different concentrations (5%, 10%, 15% and 20%) of the following three CPs: glycerol, ethylene glycol (EG) and dimethyl sulphoxide (DMSO) respectively. After 1 month cryopreservation in liquid nitrogen, cell viability was evaluated using Trypan blue exclusion under a bright‐field microscope. The mRNA expression of the three genes was also evaluated using qRT‐PCR. The results indicated that different concentrations of glycerol, EG and DMSO in cryomedia during cryopreservation could protect bovine calf testicular tissue in various ways to avoid freezing or cryopreservation‐induced expression changes in spermatogenesis‐related genes. The highest cell viability and the three spermatogenesis‐related genes (CREM, Stra8 and HSP70‐2) expression level came from the cryomedia containing glycerol, EG and DMSO at 10% concentration respectively (p < .05). Meanwhile, compared with the other CPs, the frozen–thawed bovine calf testicular tissue treated with 10% DMSO exhibited the highest cell viability and mRNA expression level of the spermatogenesis‐related genes (CREM, Stra8 and HSP70‐2).
Deformation mechanisms of an Ni-based superalloy during low-cycle fatigue at various temperatures were studied. A new configuration of cross-slip dislocation was observed in the γ matrix during the ...deformation at 760 and 900°C, which is an important component of the slip band at 900°C. Slip bands with different morphologies were observed at room temperature and 900°C, corresponding to the obvious work-hardening. It was observed that stacking faults spread throughout the γ/γ′ interface.
Abstract
The Global Navigation Satellite System radio occultation technique provides materials for the validation of a mathematical description of the topside ionosphere up to the low Earth orbit ...(LEO) satellite altitude. An attempt to represent the topside electron density profile is using
α
‐Chapman function with a continuously varying scale height. In this study, the Vary‐Chap scale height profiles are obtained based on Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) electron density profiles from 1 January 2008 to 31 December 2013 and fitted by a shape function composed of two weighted patterns representing the ion and electron contributions of lower and higher altitudes. The associated fitting parameters
a
and
b
are analyzed to reveal their temporal and spatial features and variations along with enhancement of solar activity. The prominent dependence on latitudes, longitudes, the local time, the season, and the solar cycle shown in the parameters inspires future modeling of the Vary‐Chap scale height in constructing empirical topside ionospheric models.
Key Points
The Vary‐Chap scale height is retrieved from the COSMIC electron density profiles
A shape function composed of two weighted patterns is proposed to fit the Vary‐Chap scale height profile
Fitting coefficients and key parameters are analyzed to probe their spatial and temporal features
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