Application of graphene derived nanomaterial in microwave absorption has been limited by the issue of excessively high dielectric loss. To address this issue, instead of resorting to burdensome ...compositing with metal and ceramic particles, we put forward the idea of approaching impedance match by transforming graphene from diamagnetic to ferromagnetic and meanwhile suppress the conductivity. In this study, we synthesized the Nitrogen-doped graphene (NG) by a facile hydrothermal method with graphene oxide (GO) and urea as precursors. In comparison with GO and reduced GO (rGO), the nitrogen doping along with reduction process boosted the magnetism via a Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism. Pyrrolic-N has been found to dominate the magnetic property induced, which cooperates with the suppression of conductivity to benefit the absorption performance. The reflection loss of nitrogen doped graphene can achieve −11.3 dB absorption maximum at 12.7 GHz and an absorption bandwidth of 12.2–14.3 GHz (reflection loss < −10 dB) at a thickness of 3 mm, which proves to be favourable with respective to the density as compared to existing graphene-based absorbers.
Display omitted
Hybridizing nanocarbons, such as carbon nanotubes (CNT) or graphene, with magnetic metals is a powerful strategy towards designing high-performance microwave absorber due to the resulting synergetic ...loss mechanisms and tunable electromagnetic properties. Herein, CNT and reduced graphene oxide (rGO) have been respectively coupled with amorphous wire through electrodeposition in a complementary fashion. The absorption performance of the hybrid fibers proves to be tunable via controlling the thickness and morphology of the CNT or by regulating the number of oxygen-functional groups of rGO through thermal annealing. The CNT/wire hybrid structure effectively strengthens both the interfacial polarization of CNT through the support of circular-shaped conductive substrate, and the ferromagnetic resonance of wire through the coupling with magnetic impurities in CNT. As for the rGO/wire fiber, dual-band absorption occurs in the sample annealed at 900 °C with an optimal absorption loss of −35 dB at 11.3 GHz, derived from dielectric loss mechanisms such as removal of functional groups and induced defective structure in combination with enhanced magnetic losses in the hybrid structure. Such complementary design opens up new horizons to scale up the excellent assets of nano-carbons into the macroscale and develop functional adaptive materials for high-frequency applications.
Display omitted
Most traditional fillers used in electromagnetic shielding composites require high loading, uniform distribution and complicated structures for modest property enhancement. Here, we propose a simple ...shielding system incorporating magnetic microwires M and graphene fibers G in different arrangements. Integrating both fillers in the composite resulted in superior shielding effectiveness (SE) with respect to incorporating either individual type of filler, due to improved absorption efficiency, impedance matching and polarization triggered by different arrangements of the fillers. Randomly dispersed arrays provided a maximum shielding of 6 dB for equal amount of G and M, in which polarization effects at the interface between the two regions contributed to the SE value. The highest SE of 18 dB (98.4% attenuation) was reached by the MMMGGG periodic arrays with merely 0.059 wt% filler loading enabled by the optimized arrangement and wave attenuation from the microwires dielectric/magnetic response. The normalized SE of this composite was about two to four orders of magnitude higher than that of many other shielding candidate materials. High SE, low loading, simple structure, and multifunctionality make these composites attractive for several applications. Moreover, tailoring topological and structural factors of both fillers would facilitate further SE enhancement without sacrificing the important lightweight advantage.
A set of composite absorbers with ultra-low loading of down to 0.017 wt.% short-cut microwires were prepared and investigated in terms of their magnetic and microwave properties in the X-band ...(8–12 GHz). The key parameters that could factor into the performance of the present absorbers have been systematically studied from micro to macro scale, i.e., the magnetic domain structure modulated by different internal stress scenarios, microwire aspect and composite filling ratio, and relative importance of impedance matching and material loss. Longer wires (9 mm) and wires after suitable treatment lead to the enhancement of microwave absorbing property mainly due to the larger magnetic loss resulted from the natural ferromagnetic resonance, which is induced in the domain rotation and reversal process. The internal stress modification by removal of glass and joule annealing has profound effects in formulating the microwave absorption frequency and intensity of microwire composites by tailoring the domain structure and local anisotropy field. It is found that the composites with microwires annealed at 132 mA for 15 min obtain the minimum reflection loss and broadest absorption bandwidth with reference to −10 dB at 1.5 mm thickness, which is −25.7 dB (0.81 GHz) at 11.39 GHz caused by the relative high attenuation constant and best matching condition where Zreal is 1.026 and Zimag is −0.102. This indicates that impedance matching plays a dominant role in tailoring the microwave absorbing property. Remarkably, the unconventional absorption frequency - matching thickness relation based on the quarter-wavelength model offers possibility to address the limitation of thickness for low frequency absorbing application.
Members of the genus Aeromonas are opportunistic pathogen of a variety of aquatic animals that exhibits multidrug resistance, phenotypes, virulence genes and virulence. The present study described ...the species distribution and the potential pathogenicity of Aeromonas isolated from healthy Northern snakehead (Channa argus) in China. Molecular identification revealed that A. veronii biovar veronii (69/167; 41·3%) and A. hydrophila (41/167; 24·6%) were the most common species found in Northern snakehead intestine based on sequencing of the 16S rRNA gene and DNA gyrase subunit B protein. The distribution of seven virulence factors including aer (84·4%), act (80·8%), ser (40·1%), Aha (27·5%), lip (23·4%), exu (15·0%) and LuxS (12·6%) were determined exclusively in Aeromonas isolates. All the seven virulence genes were present in 9·6% (16/167), among which 11 strains were identified as A. veronii biovar veronii. For the strains harbouring seven virulence genes, the 50% lethal doses (LD50) of isolates were lower compared to the isolates carrying two virulence genes. The challenge tests revealed that isolate W31 had the lowest lethal dose, causing 50% mortality at 4·5 × 103 colony‐forming units (CFU) per ml. Furthermore, histopathology of Northern snakehead infected with Aeromonas strains showed necrosis and congestion in liver, spleen and kidney and also damage to the intestine. This study confirms that the Aeromonas strains isolated from healthy Northern snakehead may be a cause of concern for public health.
Significance and Impact of the Study
Aeromonas species are widely distributed in aquatic environments and have considerable virulence potential. The aim of this study was to identify Aeromonas strains isolated from healthy Northern snakehead, and to investigate if Aeromonas species isolated from healthy fish potential pathogenicity with special reference to virulence and epidemiology studies.
Significance and Impact of the Study: Aeromonas species are widely distributed in aquatic environments and have considerable virulence potential. The aim of this study was to identify Aeromonas strains isolated from healthy Northern snakehead, and to investigate if Aeromonas species isolated from healthy fish potential pathogenicity with special reference to virulence and epidemiology studies.
Aim
To examine the association between depression and impaired glucose regulation, newly diagnosed diabetes and previously diagnosed diabetes in middle‐aged and elderly Chinese people, and whether ...depression was associated with different treatment regimens or durations of diabetes.
Methods
A cross‐sectional study was performed among 229 047 adults living in the community aged ≥ 40 years from 25 centres in China. The self‐reported depression rating scale Patient Health Questionnaire 9 (PHQ–9) was used to diagnose probable and sub‐threshold depression. Glucose metabolism status was determined according to World Health Organization 1999 diagnostic criteria.
Results
The numbers of participants with normal glucose regulation, impaired glucose regulation, newly diagnosed diabetes and previously diagnosed diabetes were 120 458, 59 512, 24 826 and 24 251, respectively. The prevalence of sub‐threshold depression in the total sample of participants was 4.8% (4.8%, 4.8%, 4.4% and 5.6% from normal glucose regulation to previously diagnosed diabetes, respectively), and the prevalence of probable depression was 1.1% (1.1%, 1.0%, 0.9% and 1.8% from normal glucose regulation to previously diagnosed diabetes, respectively). Compared with participants with normal glucose regulation, those with previously diagnosed diabetes had increased odds of probable depression odds ratio (OR) = 1.61, 95% confidence interval (CI) 1.39–1.87 and sub‐threshold depression (OR = 1.14, 95% CI 1.06–1.24), after adjustment for multiple confounding factors. Newly diagnosed diabetes or impaired glucose regulation was not associated with depression. Among those with previously diagnosed diabetes, insulin treatment was associated with greater odds of depression compared with no treatment or oral anti‐diabetic medicine.
Conclusion
Previously diagnosed diabetes, but not newly diagnosed diabetes or impaired glucose regulation, was associated with a higher prevalence of depression. Patients receiving insulin were more likely to have depression than those not receiving treatment or being treated with oral anti‐diabetic medicine.
What's new?
Using a nationwide sample of middle‐aged and elderly Chinese people, we showed that patients with previously diagnosed diabetes had a higher prevalence of depression, compared with those with normal glucose regulation. Newly diagnosed diabetes or impaired glucose regulation were not associated with depression.
Patients with diabetes treated with insulin had greater odds of suffering from depression than those who were treated with oral medicine or were untreated. Duration of diabetes was not associated with depression, after accounting for the role of different treatments.
In the application of magnetic refrigeration technology, magnetocaloric materials are required to possess large magnetocaloric effect and broad working temperature range with good thermal ...conductivity and mechanical properties. To address this elusive combination of properties, we prepared Ni-Mn-Ga/Al magnetocaloric composites via hot pressing method. Phase composition and element distribution revealed the influence of sintering temperature on composites' microstructure. The magnetic properties and magnetocaloric effect of hot pressed Ni-Mn-Ga alloy and Ni-Mn-Ga/Al composites were studied, indicating their largely broadened working temperature range of 71 K and maximum magnetic entropy change of 2.2–3.0 J/(kg K). Based on thermomagnetic measurements, critical behavior was investigated via modified Arrott plots and Kouvel-Fisher method, and mean-field theory model could best explain the samples' critical behavior. The Ni-Mn-Ga/Al composite also possessed enhanced fracture stress of 306 MPa, much higher than that of bulk Ni-Mn-Ga alloy by arc melting. The good magnetocaloric response of the composites, which is comparable or even better than that of many other Ni-Mn-Ga particle and microwire counterparts, is accompanied by improved thermal conductivity and mechanical properties, extending the applicability of magnetocaloric materials with large specific surface area. The novel findings of this systematic study offer new insights into magnetocaloric composites and provide an approach to reach a significant balance when fulfilling multiple requirements of magnetic refrigeration technology.
Display omitted
•Hot pressed Ni-Mn-Ga/Al was thoroughly studied in view of refrigeration application.•HP samples had good MCE comparable to their counterparts with reduced length scale.•MAP and KF method were used to compute critical exponents and study critical behavior.•Order of phase transition was ascertained by both Banerjee criterion and exponent n.•Thermal conductivity and mechanical properties were improved after making composites.
•Magnetic properties of Ni2MnGa nanowires are systematically studied for the first time.•Griffith phase theory explains anomalous magnetic behavior disobeying Curie-Weiss law.•Qualitative and ...quantitative methods determine second order magnetic phase transition.•Ni2MnGa nanowires have broad (150 K) and shallow (0.35 J/kgK) magnetic entropy change.•Magnetocaloric response is analyzed by constructing phenomenological universal curves.
Heusler alloys are favorable candidates for fabricating functional devices and sensors due to their characteristic structural and magnetic properties, which vary at different length scales. In this paper, for the sake of expanding the fields of application and systematically studying the mechanisms at the nanoscale, Ni2MnGa Heusler alloy nanowires were fabricated via the electrospinning method followed by optimized heat treatments. While the nanowires exhibited ferromagnetic-paramagnetic transition near room temperature, anomalies in magnetic behaviors were observed by power fitting of χ−1-T curves disobeying Curie-Weiss law. The Ni2MnGa nanowires exhibited maximum isothermal entropy change of 0.35 J/kgK accompanied by extremely wide working temperature region (150 K), with a peak temperature (305 K) suitable for room temperature applications. Arrott plots and quantitative analysis of field/temperature dependence of magnetic entropy change determined second order magnetic phase transition in the nanowires. Construction of phenomenological universal curves addressed demagnetizing effect on magnetocaloric response, which was compared to the multiphase composition obtained by structural analysis. These novel findings in Ni-Mn-Ga nanowires enrich our knowledge of structure and magnetism of Heusler alloys at the nanoscale and could be taken as reference facilitating future relevant research.
► GMI effect is closely related to annealed microstructures observed by HRTEM. ► Twin-zone Joule-heated annealing (TJHA) as a novel effective annealing treatment. ► TJHA wires have relatively larger ...GMI ratio and field sensitivity. ► From HRTEM perspective to explain the GMI peaks feature of different states wires. ► TJHA wires are useful for high-resolution magnetic sensor applications.
The influence of twin-zone Joule annealing (TJA) on the microstructure and magnetic properties of melt-extracted Co68.2Fe4.3B15Si12.5 amorphous microwires has been investigated. Experimental results indicated that twin-zone Joule annealing treatment improved the GMI property of as-cast wires to a greater extent comparing with Joule annealing (JA) and conventional vacuum annealing (CVA) techniques. At 15MHz, e.g., the maximum GMI ratio ΔZ/Z0max of a TJA wire increases to 104.29%, which is more than 5 times of 20.49% for the as-cast wire, nearly two times of 56.47% for the JA wire, while the CVA wire has a decreased GMI ratio; the field response sensitivity of the TJA wire increased to 171.62%/Oe from 80.32%/Oe for the as-cast wire, exceeding the values of 140.76%/Oe for the JA wire and of 39.17%/Oe for the CVA wire. The stress or structural relaxation in TJA wire increases circumferential permeability, and magnetic moment achieves a critical state of excitation for overcoming eddy-current damping or “nail-sticked” action in rotational magnetization process at relatively high frequency. From the microstructural point of view, the role of regularly arranged atomic micro-regions (RAAM) and of medium range order region (MROR) determines the efficiency of various annealing techniques. Conclusively, TJA is established as an efficient annealing technique to enhance the GMI effect of wires, which can subsequently be used for detecting weak magnetic field at relatively wider working range (±2.0Oe).
PDF
