Dielectric materials are eternal jewels in the view of research due to their strong dissipation ability, low density and higher stability compared to those of magnetic materials. Regarding the ...significance of permittivity to characterize the dielectric properties of dielectrics, an in-depth and systematical investigation of dielectric polarization process has become quite necessary. Updated and critical surveys of the key factors determining permittivity, dielectric polarization in single-component system, dielectric polarization in multi-component system and related polarization relaxation are all highlighted. In addition, the challenges for dielectric polarization and polarization relaxation, the prospects for further exploration in electromagnetic wave absorption are also discussed. In short, this review provides a brief but systematic introduction to dielectric polarization and related polarization relaxation in electromagnetic wave absorption, which motivates further study of dielectric absorbers in microwave absorption field.
•Key factors determining permittivity are discussed.•Dielectric polarizations in single-component system are discussed.•Dielectric polarizations in multi-component system are discussed.•Related polarization relaxations are also highlighted.•The prospects for further exploration in electromagnetic wave absorption are proposed.
In this work, SiO
2
/CNTs nano-composites were synthesized by the modified Stöber method for exploring the microwave absorbing performance at gradient temperatures. The SEM results show that the ...as-prepared SiO
2
particles have spherical morphology, with a diameter of 100 nm, and the carbon nanotubes in the powder are interlaced. With increasing temperature, more and more SiO
2
spheres were seen to attach to the carbon nanotubes, and the increase in conductivity was ascribed to the increase in carrier concentration. Ascribed to the enhanced conductivity and the increasing interface between the SiO
2
particles and the carbon nanotubes, the real and imaginary parts of the complex permittivity were seen to gradually increase, contributing to the improving attenuation. Hence, the sample tested at 400 °C exhibited optimal microwave absorbing performance with a minimum reflection loss (RL) of − 9.76 dB and a bandwidth (RL < − 4 dB) of 4.1 GHz at a thickness of 2 mm, which basically covers the entire 8.2–12.4 GHz (X-band).
With extensive use of electronic devices and communication equipment, serious issue of electromagnetic wave pollution needs to be addressed as one of the priorities that demand social efforts. In ...this work, carbon black (CB)/SiO
2
composites were synthesized via facile and reliable route and applied for microwave absorption at high-temperature environment around 673 K. Variations of complex permittivity and microwave absorption performance of composites under X-band of 8.2–12.4 GHz and temperature range of 298–673 K were analyzed in detail. Results showed that complex permittivity improved continuously with the increase in CB content and temperature. By elevating the temperature to 673 K, the composite with 10 wt.% of CB can achieve full coverage of effective absorption (
RL
<− 10 dB) over X-band with thin thickness of 2.9 mm. Therefore, this new composite material has good application prospect as high-temperature microwave absorber, considering its extraordinary properties and easy preparation.
Low infrared emissivity coatings were prepared by using polyurethane (PU) and aluminum (Al) as adhesives and fillers, respectively. Due to increasing the electrical conductivity with increasing Al ...content, the infrared emissivity is decreasing obviously. Mechanical properties of PU/Al composite coatings were studied by using adhesion test and impact strength test. We found the relationship between the Al content and mechanical properties presents a “U” type, and PU/Al composite coating has good adherence and impact strength at Al content of 40
wt.%. Moreover, the composite coatings were tested for the corrosion behavior with potentiodynamic polarization. Corrosion test results showed that the Al
2O
3 from Al oxidation do not sacrifice the corrosion resistance of PU itself, and the low emissivity composite coatings exhibited favorable corrosion resistance.
•Ge/ZnS 1DHPC was successfully prepared by optical coating technology.•The 1DHPC has infrared spectrally selective low emissivity at the wavelength of 3–18μm.•The 1DHPC may unify the infrared stealth ...and effective cooling of the aircraft.
Ge/ZnS one-dimensional heterostructure photonic crystal (1DHPC) was successfully prepared by alternating thin films of Ge and ZnS on the quartz substrate by using the optical coating technology. The microstructure and spectral emissivity of as-prepared 1DHPC were characterized by using scanning electron microscopy (SEM) and fourier transform infrared spectrometer (FTIR), respectively. The test result of spectral emissivity shows that the average emissivities of as-prepared Ge/ZnS 1DHPC in the atmospheric windows of 3–5μm and 8–14μm can be as low as 0.046 and 0.190, respectively, but the average emissivity in the non-atmospheric window of 5–8μm can be as high as 0.579. The results indicate that the as-prepared Ge/ZnS 1DHPC has obviously infrared spectrally selective low emissivity characteristic, basically meets the requirements of our design. The as-prepared 1DHPC with infrared spectrally selective low emissivity is promising for use as a material to unify the infrared stealth and effective cooling of the aircraft.
Polyurethane/Cu composite coatings with low infrared emissivity near to 0.10 at the wavelength of 8–14
μm were prepared by a simple and convenient process. The influences of the content of Cu powder, ...surface roughness, coating thickness and temperature on infrared emissivity of the coatings were systematically investigated. The results indicated that the emissivity decreases significantly with increasing content of Cu powder and coating thickness. The coatings with smooth surface exhibit lower emissivity values than those with rough coatings. Moreover, we found the relationship between the emissivity of coatings and temperature presents a “U” type, and the emissivity reaches to the minimum at about 380
K. The mechanisms of low emissivity were proposed by optical theories, which are found to be in a good agreement with the experimental results.
The complex life cycle of Plasmodium falciparum requires coordinated gene expression regulation to allow host cell invasion, transmission, and immune evasion. Increasing evidence now suggests a major ...role for epigenetic mechanisms in gene expression in the parasite. In eukaryotes, many lncRNAs have been identified to be pivotal regulators of genome structure and gene expression. To investigate the regulatory roles of lncRNAs in P. falciparum we explore the intergenic lncRNA distribution in nuclear and cytoplasmic subcellular locations. Using nascent RNA expression profiles, we identify a total of 1768 lncRNAs, of which 718 (~41%) are novels in P. falciparum. The subcellular localization and stage-specific expression of several putative lncRNAs are validated using RNA-FISH. Additionally, the genome-wide occupancy of several candidate nuclear lncRNAs is explored using ChIRP. The results reveal that lncRNA occupancy sites are focal and sequence-specific with a particular enrichment for several parasite-specific gene families, including those involved in pathogenesis and sexual differentiation. Genomic and phenotypic analysis of one specific lncRNA demonstrate its importance in sexual differentiation and reproduction. Our findings bring a new level of insight into the role of lncRNAs in pathogenicity, gene regulation and sexual differentiation, opening new avenues for targeted therapeutic strategies against the deadly malaria parasite.
This study presents a novel method for designing and preparing a visible light-infrared-compatible camouflage sample based on the shape, size of the visible band’s color unit and the infrared band’s ...material coatings. The coatings were prepared by using the cold spray method on 1 m × 1 m aluminum substrates with a color unit of the regular hexagonal sample (M1) and regular quadrilateral sample (M2). Then the color difference, the temperature difference and image salience value methods were used to analyze the effectiveness of camouflage samples through the real-scene tests. The results indicate that designed and prepared compatible camouflage samples are effective in their surrounding environment. Meanwhile, it can be concluded that M1 has high fusion with a background in visible and infrared bands compared to M2, M1 has 90.6% color similarity and only 0.8% temperature difference, the M2 has 85.4% color similarity and 1.6% temperature difference with the green background. These findings indicate that the cold spray method could compensate for conventional visible light camouflage design limitations. The combination of camouflage color unit design and visible/infrared material coating could be helpful in optical camouflage research. Furthermore, to improve the military equipment’s survival time on the battlefield.
Low infrared emissivity coatings were prepared by using epoxy-polyurethane (EPU) and bronze as adhesives and fillers, respectively. Due to the increasing electrical conductivity with increasing ...bronze content, the infrared emissivity is decreasing obviously. Mechanical properties of EPU/bronze composite coatings were studied by using adhesion test and impact strength test. We found that EPU/bronze composite coating had good adherence and impact strength at bronze content below 50wt.%, and then the mechanical properties decreased in the bronze content range from 50wt.% to 60wt.%. Moreover, the composite coatings were tested for the corrosion behavior with potentiodynamic polarization. Corrosion test results showed that the low emissivity EPU/bronze composite coatings exhibited favorable corrosion resistance. By comparing EPU/bronze, PU/Cu, (ball-milled Ag–Cu)/PU and PU/Al coatings, the EPU/bronze coatings with 40wt.% bronze have the best adherence, low infrared emissivity and good corrosion resistance.
► Low infrared emissivity coatings were obtained by using epoxy-polyurethane (EPU) and bronze as adhesives and fillers, respectively. ► The effect of bronze content on the infrared emissivity, mechanical properties and corrosion resistance properties of EPU/bronze composite coatings was studied. ► The EPU/bronze composite coating was compared to PU/Cu, (ball-milled Ag-Cu)/PU and PU/Al coatings.
Magnetoelectric nano-composites (1 - x)CoFe2O4 + (x)BaTiO3 with x varies as, 0.,0.65 and 1.0 in molar ratio were prepared by molten-salt synthesis method. The structural analysis carried out by X-ray ...diffraction (XRD) technique has confirmed that both phases are present in all the nano-composites powders and ceramic composites. The TEM images show that the nano-particle crystallite size is about 50-80 nm, which is consistent to the result calculated by XRD. The dielectric constant was studied as a function of frequency for ceramic composites sintered by using those nano-composite powders. The saturation magnetization (Ms) and remnant polarization (Pr) were calculated from the magnetic hysteresis loop and electric hysteresis loop, respectively. And a large ME coefficient of about 17.04 mV cm-1 Oe-1 was observed for 0.5CoFe2O4 + 0.5BaTiO3 ME composite under the ac superimposed magnetic signal with 20 kHz frequency by using the lock-in technique.
