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•A new refractory MoNbHfZrTi high-entropy alloy with single BCC phase is prepared.•The single disordered BCC phase has high structural stability.•The compressive yield strength is ...1719MPa at room temperature.•This alloy still has high compression yield strength at elevated temperatures.•The dynamic recrystallization occurs during elevated-temperature compression.
The present paper reports the microstructure, phase stability and mechanical properties of a new refractory MoNbHfZrTi high-entropy alloy. MoNbHfZrTi alloy consists of a disordered body-centered cubic (BCC) solid solution phase in as-cast and homogenized states. Homogenization treatment and DSC analysis indicate that there is no any phase transition below 1743K. At room temperature, the compressive yield strength for the alloy in as-cast and as-homogenized states reaches about 1719MPa and 1575MPa, respectively and the fracture mechanism is brittle quasi-cleavage fracture. At elevated temperatures, this alloy has compression yield strength of 825MPa at 1073K, 728MPa at 1173K, 635MPa at 1273K, 397MPa at 1373K and 187MPa at 1473K and some fine grains form at grain boundaries due to partial dynamic recrystallization.
High-energy photons from the Crab Nebula
The Crab Nebula contains a pulsar that excites the surrounding gas to emit high-energy radiation. The combination of the pulsar's youth and nearby location ...makes the nebula the brightest gamma-ray source in the sky. The LHAASO Collaboration report observations of this source at energies of tera– to peta–electron volts, extending the spectrum of this prototypical object. They combine these data with observations at lower energies to model the physics of the emission process. The multiwave-length data can be explained by a combination of synchrotron radiation and inverse Compton scattering.
Science
, abg5137, this issue p.
425
Detection of the Crab Nebula at peta–electron volt energies constrains the gamma-ray emission mechanism.
The Crab Nebula is a bright source of gamma rays powered by the Crab Pulsar’s rotational energy through the formation and termination of a relativistic electron-positron wind. We report the detection of gamma rays from this source with energies from 5 × 10
−4
to 1.1 peta–electron volts with a spectrum showing gradual steepening over three energy decades. The ultrahigh-energy photons imply the presence of a peta–electron volt electron accelerator (a pevatron) in the nebula, with an acceleration rate exceeding 15% of the theoretical limit. We constrain the pevatron’s size between 0.025 and 0.1 parsecs and the magnetic field to ≈110 microgauss. The production rate of peta–electron volt electrons, 2.5 × 10
36
ergs per second, constitutes 0.5% of the pulsar spin-down luminosity, although we cannot exclude a contribution of peta–electron volt protons to the production of the highest-energy gamma rays.
ABSTRACT
High time resolution and accuracy are of critical importance in the studies of timing analysis and time delay localization of gamma-ray bursts (GRBs), soft gamma-ray repeaters (SGRs) and ...pulsars. The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) consisting of two micro-satellites, GECAM-A and GECAM-B, launched on 2020 December 10, is aimed at monitoring and locating X-ray and GRBs all over the sky. To achieve its scientific goals, GECAM is designed to have the highest time resolution (0.1 $\mu {\rm s}$) among all GRB detectors ever flown. Here, we make a comprehensive time calibration campaign including both on-ground and on-orbit tests to derive not only the relative time accuracy of GECAM satellites and detectors, but also the absolute time accuracy of GECAM-B. Using the on-ground calibration with a $\rm ^{22}Na$ radioactive source, we find that the relative time accuracy between GECAM-A and GECAM-B is about 0.15 $\mu {\rm s}$ (1σ). To measure the relative time accuracy between all detectors of a single GECAM satellite, cosmic-ray events detected on orbit are utilized since they could produce many secondary particles simultaneously record by multiple detectors. We find that the relative time accuracy among all detectors onboard GECAM-B is about 0.12 $\mu {\rm s}$ (1σ). Finally, we use the novel Li-CCF method to perform the absolute time calibration with Crab pulsar and SGR J1935+2154, both of which were jointly observed by GECAM-B and Fermi/GBM, and obtain that the time difference between GECAM-B and Fermi/GBM is 3.06 ± 6.04 $\mu {\rm s}$ (1σ).
Particle water and pH are predicted using meteorological observations (relative humidity (RH), temperature (T)), gas/particle composition, and thermodynamic modeling (ISORROPIA-II). A comprehensive ...uncertainty analysis is included, and the model is validated. We investigate mass concentrations of particle water and related particle pH for ambient fine-mode aerosols sampled in a relatively remote Alabama forest during the Southern Oxidant and Aerosol Study (SOAS) in summer and at various sites in the southeastern US during different seasons, as part of the Southeastern Center for Air Pollution and Epidemiology (SCAPE) study. Particle water and pH are closely linked; pH is a measure of the particle H+ aqueous concentration and depends on both the presence of ions and amount of particle liquid water. Levels of particle water, in turn, are determined through water uptake by both the ionic species and organic compounds. Thermodynamic calculations based on measured ion concentrations can predict both pH and liquid water but may be biased since contributions of organic species to liquid water are not considered. In this study, contributions of both the inorganic and organic fractions to aerosol liquid water were considered, and predictions were in good agreement with measured liquid water based on differences in ambient and dry light scattering coefficients (prediction vs. measurement: slope = 0.91, intercept = 0.5 μg m−3, R2 = 0.75). ISORROPIA-II predictions were confirmed by good agreement between predicted and measured ammonia concentrations (slope = 1.07, intercept = −0.12 μg m−3, R2 = 0.76). Based on this study, organic species on average contributed 35% to the total water, with a substantially higher contribution (50%) at night. However, not including contributions of organic water had a minor effect on pH (changes pH by 0.15 to 0.23 units), suggesting that predicted pH without consideration of organic water could be sufficient for the purposes of aqueous secondary organic aerosol (SOA) chemistry. The mean pH predicted in the Alabama forest (SOAS) was 0.94 ± 0.59 (median 0.93). pH diurnal trends followed liquid water and were driven mainly by variability in RH; during SOAS nighttime pH was near 1.5, while daytime pH was near 0.5. pH ranged from 0.5 to 2 in summer and 1 to 3 in the winter at other sites. The systematically low pH levels in the southeast may have important ramifications, such as significantly influencing acid-catalyzed reactions, gas–aerosol partitioning, and mobilization of redox metals and minerals. Particle ion balances or molar ratios, often used to infer pH, do not consider the dissociation state of individual ions or particle liquid water levels and do not correlate with particle pH.
Electron-electron (e-e) collisions can impact transport in a variety of surprising and sometimes counterintuitive ways. Despite strong interest, experiments on the subject proved challenging because ...of the simultaneous presence of different scattering mechanisms that suppress or obscure consequences of e-e scattering. Only recently, sufficiently clean electron systems with transport dominated by e-e collisions have become available, showing behaviour characteristic of highly viscous fluids. Here we study electron transport through graphene constrictions and show that their conductance below 150 K increases with increasing temperature, in stark contrast to the metallic character of doped graphene. Notably, the measured conductance exceeds the maximum conductance possible for free electrons. This anomalous behaviour is attributed to collective movement of interacting electrons, which 'shields' individual carriers from momentum loss at sample boundaries. The measurements allow us to identify the conductance contribution arising due to electron viscosity and determine its temperature dependence. Besides fundamental interest, our work shows that viscous effects can facilitate high-mobility transport at elevated temperatures, a potentially useful behaviour for designing graphene-based devices.
The hot deformation characteristics of dynamic recrystallization (DRX) of the MoNbHfZrTi refractory high-entropy alloy (HEA) was investigated using the isothermal compression tests in the strain rate ...of 0.001–0.1s−1 at the temperature range of 800–1200°C. Scanning electron microscope (SEM) with the electron backscatter diffraction (EBSD) technique was used to study the effect of deformation temperature and strain rate on the stress–strain behavior, microstructure evolution and dynamic recrystallization (DRX) during hot deformation. At 800°C, the stress–strain curve exhibits a work-hardening stage until fracture at the strain rate of 0.1s−1 and 0.01s−1. Under other deformation conditions, the stress–strain curves exhibit the typical DRX characteristics. On the whole, the stress decreases with the increase of deformation temperature and decrease of the strain rate. The initial dendritic structure gradually disappears and more dynamic recrystallized grains form with the decrease of strain rate and the increase of the deformation temperature. The nucleation mechanism of discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) occurred simultaneously for the MoNbHfZrTi alloy during hot deformation. The effect of CDRX was weakened with the increase of deformation temperature and with the decrease of strain rate.
This paper reported the effect of Cr addition on microstructure, phase constitutes and mechanical properties of the Hf0.5Mo0.5NbTiZr refractory high-entropy alloy. The CrxHf0.5Mo0.5NbTiZr (x = 0.1, ...0.2, 0.3, 0.4 and 0.5) alloys were composed of one BCC solid solution phase and one CrMoZr-typed Laves phase. This alloy system exhibited the typical dendritic structure after casting. The dendritic structure was refined with the Cr addition. The strength of CrxHf0.5Mo0.5NbTiZr alloys increased and the plasticity also was improved with small amount addition of Cr elements, the strength continued to increase while the plasticity decreased as the concentration of Cr element increased. The homogenization treatment promoted more formation of Laves phase, which significantly increased the strength.
•CrxHf0.5Mo0.5NbTiZr alloy system was composed of one BCC solid solution phase and one CrMoZr-typed Laves phase.•The strength of CrxHf0.5Mo0.5NbTiZr alloys increased and the plasticity also increased with small amount of Cr elements.•The homogenization treatment promoted more formation of the Laves phase, leading to the increase of the strength.
Aim To investigate the value of hepatic extracellular volume fractions (fECVs) measured using routine liver computed tomography (CT) evaluating liver fibrosis (LF). Materials and methods A total of ...60 patients (male:female ratio, 39:21; mean age, 42.4 years) histologically diagnosed with LF underwent routine liver CT. Absolute enhancement (in Hounsfield units) of the liver parenchyma (Eliver ) and aorta (Eaorta ) 3 minutes after contrast medium administration was calculated using precontrast and equilibrium phase scans. The fECV was calculated using the following equation: fECV (%)=Eliver × (100 − haematocrit %)/Eaorta . Correlation between fECV and LF stage was evaluated using the Spearman correlation coefficient. The fECVs were compared between each stage of LF. The diagnostic performance of fECV was assessed using receiver operating characteristic (ROC) curve analysis. Results The difference among the groups was statistically significant ( p <0.05). The fECVs were significantly different ( p <0.05) between F0 versus F4, F1 versus F4, and F2 versus F4. The fECVs showed a significant correlation with pathological LF staging ( r =0.468, p =0.001). The sensitivity and specificity were 0.76 and 0.68 for severe LF (F≥3); and 0.89 and 0.63 for cirrhosis (F=4). The areas under the ROC curve (AUCs) for F≥3 and F=4 were 0.757 and 0.775, respectively. Conclusions Calculation of fECV during routine contrast-enhanced liver CT may provide a non-invasive means of assessing LF.
Abstract
We report the discovery of an ultrahigh-energy (UHE) gamma-ray source, LHAASO J2108+5157, by analyzing the LHAASO-KM2A data of 308.33 live days. A significant excess of gamma ray–induced ...showers is observed in both energy bands of 25−100 and >100 TeV with 9.5
σ
and 8.5
σ
, respectively. This source is not significantly favored as an extended source with an angular extension smaller than the point-spread function of KM2A. The measured energy spectrum from 20 to 200 TeV can be approximately described by a power-law function with an index of −2.83 ± 0.18
stat
. A harder spectrum is demanded at lower energies considering the flux upper limit set by Fermi-LAT observations. The position of the gamma-ray emission is correlated with a giant molecular cloud, which favors a hadronic origin. No obvious counterparts have been found, and deeper multiwavelength observations will help to cast new light on this intriguing UHE source.
Aims
The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama transmits the bacterium ‘Candidatus Liberibacter asiaticus’ (Las), which causes citrus huanglongbing (HLB) disease. Although many ...studies have been conducted on the biology of ACP on different host plants, few have taken the plant, Las bacteria and the vector insect within one context to evaluate the effects of Las on the fitness of ACP under field conditions. Understanding the relationship between Las and ACP is critical for both ACP and HLB disease management.
Methods and Results
We estimated the development and survival of ACP immatures, the longevity and fecundity of ACP female adults in four treatments (Las‐positive or ‐negative ACP on Las‐infected and ‐free citrus plants). Las‐positive ACP immatures developed significantly faster on Las‐infected citrus than those on Las‐free plants. The fecundity and longevity of Las‐positive female adults were also greater, or longer on Las‐infected citrus shoots, whereas the survival of Las‐positive immatures was significantly lower on Las‐infected citrus shoots, compared to those that developed on Las‐free plants. Similarly, the intrinsic rate of population increase (rm) was highest (0·1404) when Las‐positive ACP fed on Las‐infected citrus shoots and the lowest (0·1328) when the Las‐negative ACP fed on Las‐free citrus shoots.
Conclusions
Both the Las infection in ACP and citrus plants had obvious effects on the biology of ACP. When compared to the Las infection in ACP insects, the Las infection in citrus shoots had a more significant effect on the fitness of ACP.
Significance and Impact of the Study
To efficiently prevent the occurrence and spread of HLB disease, it is critical to understand the ecological basis of vector outbreaks and disease incidence, especially under field conditions. Thus, this study has increased our understanding of the epidemiology of HLB transmitted by psyllids in nature.
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