We study the introduction of a third material, namely Zr, within a nanometric periodic Mg/Co structure designed to work as optical component in the extreme UV (EUV) spectral range. Mg/Co, Mg/Zr/Co, ...Mg/Co/Zr and Mg/Zr/Co/Zr multilayers are designed, and then characterized in terms of structural quality and optical performances through X-ray and EUV reflectometry measurements, respectively. For the Mg/Co/Zr structure, the reflectance value is equal to 50% at 25.1 nm and 45° of grazing incidence and reaches 51.3% upon annealing at 200°C. Measured EUV reflectivity values of tri-layered systems are discussed in terms of material order within a period and compared to the predictions of the theoretical model of Larruquert. Possible applications are pointed out.
A light ray tracing model and a heat transfer model were built to analyse the heat flux distribution and heat transfer in a 1m cavity receiver tube with Parabolic Trough Collectors as the ...concentrator. The numerical methods were used to simulate the thermal stress and deformation of the receiver tube. The temperature fields of the receiver tube and the thermal stress distribution in the steel tube at the cross section and along the fluid flowing direction were presented. It is obtained from this study that non-uniform heat flux distribution is absorbed at the receiver tube outer surface due to the structure of the cavity receiver tube. Temperature fields in the steel receiver tube at the inlet and the outlet match well with the incident solar radiation. An eccentric circle temperature gradient is observed at cross section of the outlet fluid. The equivalent stress is a complex result of solar heating flux, energy transfer inside the PTC and the fluid and steel characteristics. Highest deformation is 3.1mm at 0.82m. On increasing the fluid mass flow rate, higher fluid mass flow rate results in higher equivalent stress along the absorber tube.
ABSTRACT
The study of blazar jet has been performed for several decades via VLBI technique, while its generation and propagation stay unclear. In the present work, we compiled a sample of 407 VLBI ...detected Fermi blazars (VFBs) and studied the correlations between apparent velocity (${\rm log}\, \beta _{\rm app}$) and jet/accretion disc properties. We found a positive correlation between γ-ray luminosity (${\rm log}\, L_{\rm \gamma }$) and ${\rm log}\, \beta _{\rm app}$; the correlation suggests that the apparent motion of jet knot is related to the jet power. The correlations between ${\rm log}\, \beta ^{\rm max}_{\rm app}$ and the jet radiation power (${\rm log}\, L_{\rm rad}$), and between ${\rm log}\, \beta ^{\rm max}_{\rm app}$ and the jet extended region luminosity at 5 GHz (${\rm log}\, L_{\rm 5GHz}^{\rm ext}$), which is an indicator of jet kinetic power, reveal that the knots apparent motion is correlated with both jet radiation power and the kinetic power. But this indication is not held for flat-spectrum radio quasar (FSRQs) in terms of the correlation ${\rm log}\, L_{\rm 5GHz}^{\rm ext}\, versus \, {\rm log}\, \beta ^{\rm max}_{\rm app}$. Besides, ${\rm log}\, \beta ^{\rm max}_{\rm app}$ has a moderate correlation with accretion disc luminosity (${\rm log}\, L_{\rm Disk}$) and the normalized accretion disc luminosity ${\rm log}\, (L_{\rm Disk}/L_{\rm Edd})$, which may suggest both the power of accretion disc and the accretion rate are critical to generate knots and to accelerate them. In addition, we found the VFBs have larger average values of γ-ray luminosity (${\rm log}\, L_{\rm \gamma }$), γ-ray photon index (αph), and variability index (${\rm log}\, VI$) than the rest of Fermi blazars. Through Gaussian mixture models method, we generated a criteria, ${\rm log}\, L_{\rm \gamma } \gt 45.40$, αph > 2.24, and ${\rm log}\, VI \gt 1.71$ to find VFB candidates, selected 228 VFB candidates from the rest of Fermi blazar.
Mining activities generate spoils and effluents that are harmful to ecosystems and human health due to their extremely high toxic metal concentrations. Plants have been planted on these spoils to ...uptake heavy metal and to revegetate for phytoremediation. Soil obtained from Pb/Zn mine tailing areas was used to conduct a greenhouse pot experiment to compare the growth and toxic metal accumulation of six tree species for afforestation in southern China. One year growth indicated that the six species tolerated toxic metals and their accumulation differed with plant species, their parts and kinds of metals. Height and biomass of Betula alnoideswere significantly greater than the rest of the species. Alnus nepalerms had the highest translocation (0.86 in root and 0.69 in shoot) and bioconcentration (0.62 in root and 0.51 in shoot) factor values for Pb, while Pinus yunnanensis had higher translocation and bioconcentration factor values (0.78, 0.45 in root and 0.84, 0.48 in shoot respectively) for Zn. Alnus nepalensis was the best candidate species for phytoremediation of Pb/Zn mine tailing areas due to its good nitrogen fixation, greater translocation and bioconcentration factor values and larger biomass, accumulating an average of 4.70 mg Pb and 6.92 mg Zn.
P-type perovskite oxides La1-xSrxCoO3 (x=,0.1) have been prepared by solid state reactions and sol-gel processes. The Seebeck coefficient, electrical conductivity and thermal conductivity of the ...samples have been investigated. It is found that substitution of Sr for La significantly improved the electrical conductivity but reduced the Seebeck coefficients and thermal conductivity. The samples with the same composition prepared from different routes distinguished from each other in morphologies but exhibited similar conductive mechanism and had the same energy gap Eg and motional enthalpy DeltaHm. The effects of density on electrical and thermal conductivity were obvious. The room-temperature ZT value of the sol-gel derived La0.9Sr0.1CoO3 was 0.046, which is comparable to that of the single crystal NaCo2O4 (ZT=0.03).
Fatigue crack growth has been observed recently in ferroelectrics under cyclic electric loading. Does the crack grow by electric breakdown, or by the stress field near the crack tip? The present ...paper provides a mechanistic explanation for the electric-field-induced fatigue crack growth. The non-uniform electric field near an insulated crack tip might cause domain switching which in turn produces a concentrated stress field characterized by a stress intensity factor. For ferroelectrics poled along a direction perpendicular to the crack, we are able to show quantitatively that: (1) the stress intensity factor under a negative electric field is nine times as large as the stress intensity factor under a positive electric field; (2) the crack starts to grow if the stress intensity factor is higher than the fracture toughness of the material, but the stress intensity factor decreases as the crack extends and eventually results in crack arrest; (3) by reversing the electric field, the stress intensity factor is increased and crack growth resumes; and (4) this model can predict the extent of fatigue crack growth. In contrast to the conventional perception of (mechanical) fatigue, the fatigue crack growth in ferroelectrics under cyclic electric loading is a step by step cleavage process caused by a domain switching sequence that generates a cyclic driving stress field near the crack tip.
Interface adhesion between cast iron substrate and oxide layer formed during dry unidirectional sliding wear was studied by using thermo-mechanically processed 4.8Ni–1.5Cr cast iron. The purpose of ...the present work is to reveal the difference of the adhesion behaviour between martensitic matrix with a higher hardness and austenitic matrix with low hardness. The 4.8Ni–1.5Cr alloy was sandwiched as a middle layer with low carbon steel as outer layers and thermo-mechanically processed via (1) hot rolling (HR), (2) hot rolling and heat treatment (HT), and (3) hot rolling, heat treatment and hot compression (HC), respectively. The applied normal loads were 20 and 40N, and the sliding speeds were 45 and 78mm/s in sliding wear test. The durations of the wear test were 2 and 7min, respectively for different testing rounds. It was found that the wear after running-in was always mild under the conditions of 20N and 45mm/s or 20N and 78mm/s for all the tested samples. Prior to the transition into mild oxidational wear, negative displacements of pins were observed for HT and HC samples when the applied load was raised to 40N at the sliding speed of 78mm/s. No similar response was observed for HR sample under the same testing condition. The possible mechanisms for the negative displacement of pin in the test are discussed in terms of the microstructure and phases of the testing samples. The effect of the hardness of the substrate on the growth and integrity of the oxide film formed during the sliding and the interface adhesion between the oxide film and substrate are also discussed.
Since the stability of the power grid and the quality of electricity supply can be affected, the intermittent and unpredictable features make the renewable energy generation cannot be absorbed by the ...power grid easily and completely. "Abandoning the wind and solar power" phenomenon also becomes more serious in recent years. As an efficient thermoelectric conversion device, the heat pump system can couple thermal energy and electricity to eliminate excess electricity of the system theoretically. However, the influence of the heat pump technology on the microgrid system which needs to be analysed case by case lacks a unified evaluation method. Therefore, based on the Energy PLAN, an energy microgrid model of an ecological region in Qingdao is established to study the impact on the renewable energy integration and the enhancement of renewable energy utilization through applying the air-source heat pump system. The simulation results showed that the maximum photovoltaic penetration rate in the region is 19.23% initially. After applying the air-source heat pump, the photovoltaic capacity corresponding to the critical point of 100% renewable energy utilization is in direct proportion to the heat pump capacity. Additionally, the maximum photovoltaic penetrations can reach 25%. In this paper, we also propose relevant suggestions for the designing and building of the micro-net energy system.
High hardness in a nanocrystalline Mg97Y2Zn1 alloy Youssef, K.M.; Wang, Y.B.; Liao, X.Z. ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
09/2011, Letnik:
528, Številka:
25-26
Journal Article
Recenzirano
► Synthesis of nc (21nm) Mg97Y2Zn1 alloy using a modified mechanical alloying. ► Annealing at 573K increases the grain size to 28nm with a hardness of 2.4GPa. ► This is the highest value for hardness ...yet reported for a Mg-base (>95% Mg) alloy. ► The excellent strength of this alloy is discussed throughout the article.
A nanocrystalline Mg97Y2Zn1 alloy was prepared with an average grain size of 21nm by mechanical alloying of elemental powders. The structure of the alloy was characterized by X-ray diffraction and transmission electron microscopy. The hardness of the alloy as-milled for 8h at room temperature was 2.1GPa. After compaction and annealing at 573K, the average grain size slightly increases to 28nm with an increase in hardness to 2.4GPa. These are the highest values for hardness yet reported for a crystalline Mg-based (>95% Mg) alloy. Possible factors leading to this high strength are discussed.
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