Urban growth and development caused by urbanization influence the urban heat island (UHI) phenomenon. With the rapid development of urbanization, China's major cities are facing more serious climate ...change problems, especially the UHI phenomenon. Proper planning and urban design of compact cities may improve the ventilation of street canyons and change the heat balance in the urban canopy and thus mitigate the UHI phenomenon. The aim of this study is to evaluate and discuss the mitigation of UHI with different types of land-use and land-cover (LUCC), as well as different development patterns for compact cities. To this end, we applied the weather research and forecasting model (WRF) with urban canopy model (WRF/UCM) in this study. To evaluate the impact of LUCC changes on the UHI, we set 2 cases based on land use and land cover statistical data from 1965 and 2008 of Wuhan. Also, to evaluate the impact of urban morphology changes on the UHI, we designed 2 hypothetical cases based on 2 different urban developing patterns, one is high rise case and another is high density case, to simulate the impact of urban morphology on the UHI. As for the results of this study, with different LUCC of 1965 and 2008, UHI intensity of Wuhan increased by 0.2 °C–0.4 °C in average. Moreover, the critical wind speed which can mitigate UHI of case 1965 is much lower than case 2008. With different urban morphology, the high-rise case may lead to lower UHI intensity at the pedestrian level due to the shading effects of high-rise buildings. However, the critical value of wind speed in the high-rise case was almost 1.5–2 times greater than that of the high-density case, which illustrates the reduced possibility of mitigating the UHI phenomenon for high-rise buildings in Wuhan City.
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•When the lake area decreased by 130 km2 in the built-up area of Wuhan, UHI intensity increased by 0.2 °C–0.4 °C.•When the lake area decreased by 130 km2, the critical value of wind speed needed to mitigate the UHI doubled at 04:00.•Air temperature differences between these two development patterns can reach 1 °C and that at 12:00 and 17:00, respectively.•The critical values of wind speed in the high-density case were 1.5 and 2 times higher than those of the high-rise case.•The T2 in the high-density case was 0.5 ºC higher, however, wind speed of high-rise case was 70% of high-density case.
Thermal-stable dielectric capacitors with high energy density and power density have attracted increasing attention in recent years. In this work, (1 – x)Bi0.5Na0.5TiO3–xNaTaO3 (1 – x)BNT–xNT, x = ...0–0.30 lead-free relaxor ferroelectric ceramics are developed for capacitor applications. The x = 0.20 ceramic exhibits superior thermal stability of discharged energy density (W D) with a variation of less than 10% in an ultrawide temperature range of −50 to 300 °C, showing a significant advantage compared with the previously reported ceramic systems. The W D reaches 4.21 J/cm3 under 38 kV/mm at room temperature. Besides, a record high of power density (P D ≈ 89.5 MW/cm3) in BNT-based ceramics is also achieved in x = 0.20 ceramic with an excellent temperature insensitivity within 25–160 °C. The x = 0.20 ceramic is indicated to be an ergodic relaxor ferroelectric with coexisted R3c nanodomains and P4bm polar nanoregions at room temperature, greatly inducing large maximum polarization, maintaining low remnant polarization, and thus achieving high W D and P D. Furthermore, the diffuse phase transition from R3c to P4bm phase on heating is considered to be responsible for the superior thermal stability of the high W D and P D. These results imply the large potential of the 0.80BNT–0.20NT ceramic in temperature-stable dielectric capacitor applications.
NaNbO
3
-based lead-free ceramics show great potential in energy storage and piezoelectric applications due to the antiferroelectric and ferroelectric features. However, pure NaNbO
3
usually shows ...lossy hysteresis loops because of the metastable antiferroelectric phase at room temperature. In this work, Bi(Zn
2/3
Nb
1/3
)O
3
was introduced into NaNbO
3
to modulate the phase structure, dielectric, and energy storage properties. The addition of Bi(Zn
2/3
Nb
1/3
)O
3
changed the phase structure from orthorhombic to pseudo-cubic, decreased the grain size from ~ 20 μm to ~ 1 μm, shifted the temperature of dielectric peak from 360℃ to room temperature, and led to much-reduced polarization hysteresis and improved breakdown strength. With the addition of 9 mol% Bi(Zn
2/3
Nb
1/3
)O
3
, the maximum recoverable energy density of 3.3 J/cm
3
was achieved under 33.5 kV/mm. These results provide a feasible route to design and fabricate new NaNbO
3
-based energy storage ceramics.
Hydrogen can contribute significantly to the energy mix of the near future, as it is an attractive replacement for fossil fuels due to its high energy density and low greenhouse gas emission. A ...fascinating approach is to use the polarization change of a ferroelectric due to an applied stress or temperature change to achieve piezo- or pyro-catalysis for both H2 generation and wastewater treatment. We exploit low Curie temperature (Tc) ferroelectrics for polarization-driven electrochemical reactions, where the large changes in polarization and high activity of a ferroelectric near its Tc provides a novel avenue for such materials. We present experimental evidence for enhanced water splitting and rhodamine B degradation via piezo-catalysis by ultrasonic excitation at its Tc. Such work provides an effective strategy for water splitting/treatment systems that employ low Tc ferroelectrics under the action of mechanical stress or/and thermal fluctuations.
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•First demonstration of the positive impact of operating near Tc for piezo-catalysis•Ultrasound applied to achieve piezo-catalysis near Tc•High hydrogen production rate and degradation rate were achieved at the Tc•Piezo-catalysis is a new avenue for low Tc and lead-free ferroelectrics
Catalysis; Electrochemical Energy Production; Ceramics
We demonstrate that trimethylamine borane can exhibit desirable piezoelectric and pyroelectric properties. The material was shown to be able operate as a flexible film for both thermal sensing, ...thermal energy conversion and mechanical sensing with high open circuit voltages (>10 V). A piezoelectric coefficient of d33≈10–16 pC N−1, and pyroelectric coefficient of p≈25.8 μC m−2 K−1 were achieved after poling, with high pyroelectric figure of merits for sensing and harvesting, along with a relative permittivity of ϵ33σ≈
6.3.
Pyroelectrics are borane: Plasticity and mechanical flexibility in trimethylamine borane are harnessed to generate a piezoelectric and pyroelectric flexible film for sensing and energy harvesting applications.
Summer extreme high-temperatures occur frequently in large cities; urban spatial form is the primary factor affecting the urban thermal environment. Thus, planning and arranging urban spaces is a key ...approach to regulating urban microclimates. Studies into how urban spatial forms influence the formation of urban microclimates have been carried out for multiple cities in warm and hot regions; however, few studies of this kind have been carried out for cities in cold regions. In this study, we analyze Zhengzhou, a city located in a cold region of China, using summer 2017 measurement data to determine why high temperatures develop in cold areas. We investigated how temperature and humidity vary during the morning, at noon, and in the evening given different land use properties (commercial and residential) and different spatial forms (building height, building density, green coverage rate, and plot ratio); we then studied the correlation between urban spatial form and the urban thermal environment. Our research results indicate that the commercial district’s thermal microclimate was related to PR and BH in the afternoon and GCR in the morning and at night. In the residential district, the key urban morphology factors related to its thermal microclimates were BD, PR, and GCR during almost the whole day.
Lead-free piezoelectric ceramics featuring high piezoelectricity and fatigue resistance are extremely important in practical applications. In this work, 0.85Bi
0.5
Na
0.5
TiO
3
–0.11Bi
0.5
K
0.5−
x
...Rb
x
TiO
3
–0.04BaTiO
3
(
x
= 0–0.20) ceramics are developed, and the effects of Rb content on the crystalline phase, domain structure, electric property, and fatigue resistance are investigated. XRD results show that all the ceramics exhibit the rhombohedral/tetragonal morphotropic phase boundary. The introduction of Rb at A-sites induces enhanced relaxor characteristics. Increasing the Rb content leads to apparently decreased size and increased dynamics of ferroelectric domains, as revealed by the PFM and TEM observations. Notably, the fatigue resistance of ceramics is greatly improved with the introduction of Rb. In particular, the composition of
x
= 0.10 exhibits almost fatigue-free behaviors in conjunction with high piezoelectricity of
d
33
~ 203 pC/N, which can be attributed to the formation of tweed-like nanodomains with a size of 10–20 nm and stripe-like nanodomains with an average width of ~ 3.5 nm.
In piezoceramics, the Curie temperature (TC) and piezoelectric coefficient (d33) are often inversely proportional, so it is very difficult to optimize high piezoelectricity and TC simultaneously. In ...addition, the high and temperature‐insensitive piezoelectric strain coefficient (d33*) with small hysteresis is also a longstanding obstacle in the development of lead‐free ceramics. In this work, a facile approach of donor doping strategy is adopted to replace Ba2+ with Yb3+, Y3+, Sm3+, and Nd3+ as a result, a high TC of 450 °C and outstanding d33 of 422–436 pC N−1 is achieved by a novel magnetic poling method. Thermally‐stable and outstanding piezoelectric strain performance (d33* ≈ 520–550 pm V−1 and ΔST ≈ 10%) with small strain hysteresis (H < 20%) results are highly encourageable in lead‐free ceramics. The main factors contributing to high piezoelectricity are the morphotropic phase boundary, suppression of defect charges by donor doping, thermal quenching, mesoscale nanodomain size, and novel poling method. The excellent piezoelectric performance and high TC of this work are superior to those of state‐of‐the‐art piezoceramics. The synergistic approaches of compositional design strategy and novel poling process in this work are highly beneficial for temperature‐insensitive piezoelectric sensor and actuator applications.
Normally, the piezoelectric constant (d33) and Curie temperature (TC) are inversely proportional. In this work, simultaneously high TC of 450 °C and excellent piezoelectric performance (d33 ≈ 436 ± 5 pC N−1) are achieved in lead‐free BiFeO3–BaTiO3 ceramics. This high d33 value is obtained by applying a novel poling method inside a strong magnetic field.
Inconel 718 (IN718) nickel-based superalloy is widely used in aerospace and nuclear applications owing to its excellent comprehensive mechanical properties, oxidation resistance, and hot corrosion ...resistance. However, the elemental segregation caused by heterogeneous solidification during casting has great influence on the mechanical properties. Therefore, accurately characterizing the segregation behavior is necessary. Traditional quantitative characterization of elemental segregation uses various sampling methods, in which only macroscopic segregation results are obtained. In this study, micro-beam X-ray fluorescence (μ-XRF) is used for the quantitative characterization of element micro-segregation in IN718 superalloy. The concentration distributions of Cr, Fe, Mo, Nb, and Ti in IN718 alloy are determined with optimized testing parameters, and the degree of elemental segregation in different regions of the analytical area is calculated. It is found that the segregation degree of Nb and Ti in the testing area is larger than other alloying elements. The correlation between the microstructure distribution and the segregation degree of Nb and Ti has been studied using scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS). There is severe segregation of Nb and Ti in areas where Nb-containing precipitates are accumulated. The distribution of abnormal signals of Nb with a high fluorescence intensity has a close relationship with the area of precipitates-enriched Nb.
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