Abstract Graphene/silicon nitride ( GR /Si 3 N 4 ) ceramic composites with uniformly dispersed GR sheets were prepared using spark plasma sintering. The effects of GR content on the microstructure and electrical properties of the composites were investigated in detail. With the GR content rising, the conductive GR network was formed in the composites, leading to the appearance of a percolation phenomenon, and the conductive mechanism also changed from hopping conductivity to metal‐like conductivity. When the GR content reached the percolation threshold, the composites showed a negative permittivity behavior, which resulted from the low frequency plasmonic state generated by the formative conducting GR networks. The increasing GR content resulted in a higher plasma frequency and larger magnitude of negative permittivity, which was consistent with the analysis of Drude model. A relatively high dielectric loss was observed in the composites and mainly induced by the high leakage current among GR sheets. Our work is beneficial to expound the regulation mechanism of negative permittivity, and the obtained ceramic composites present some potential applications in microwave absorption, shielding and capacitors.
Coronavirus disease 2019 (COVID-19) due to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has been associated with cardiovascular features, which may be deteriorated in patients with cancer. However, cardiac outcomes of cancer patients with COVID-19 have not been closely examined. We retrospectively assessed 1,244 patients with COVID-19 from February 1 to August 31, 2020 (140 cancer and 1,104 noncancer patients). Demographic and clinical data were obtained and compared between cancer and noncancer groups. Including the cardiac biomarkers, we also analyzed laboratory findings between these two groups. Risk factors for in-hospital mortality were identified by multivariable Cox regression models. For cancer group, 56% were in severe and critical status with more diabetes and immune deficiency, whereas the proportion was 10% for noncancer group. Patients with cancer had increased levels of leukocyte, neutrophil count, and blood urea nitrogen (BUN) (all P < 0.01), whereas lymphocyte count was significantly lower (P < 0.001). The most common solid tumor types were gastrointestinal cancer (26%), lung cancer (21%), and breast and reproductive cancer (both 19%). There is a rising for cardiac biomarkers, including pro-B-type natriuretic peptide (Pro-BNP), sensitive troponin I (cTnI), myoglobin (MYO), creatine kinase-MB (CK-MB), as well as D-Dimer in COVID-19 cancer population, especially in deceased subjects with cancer. The 30-day in-hospital mortality in cancer group was dramatically raised than that in noncancer group (12.9% vs. 4.0%, P < 0.01). In multivariable Cox regression models, fever, disease severity status, and underlying diseases were risk factors for mortality. COVID-19 patients with cancer relate to deteriorating conditions and poor cardiac outcomes accompanied by a high in-hospital mortality, which warrants more aggressive treatment.NEW & NOTEWORTHY Our study indicates that the 30-day mortality is higher in COVID-19 patients with cancer; more COVID-19 patients with cancer are in severe and critical status; age, respiratory rate, neutrophil count, AST, BUN, MYO, Pro-BNP, disease severity status, underlying diseases, and fever are risk factors for in-hospital mortality among COVID-19 cancer cases; COVID-19 patients with cancer display severely impaired myocardium, damaged heart function, and imbalanced homeostasis of coagulation; what is more, those with both cancer and CVD have more significantly increased Pro-BNP and D-Dimer level.
Spatially resolved elastic strains in the bulk interior of a laminated Ti-Al metal composite were studied during in situ tensile loading at strains up to 1.66% by a synchrotron-based micro-diffraction technique, namely differential aperture X-ray microscopy (DAXM). For both Al and Ti grains, deviatoric elastic strains were estimated based on polychromatic X-ray microbeam diffraction, while lattice strains along the normal direction of the tensile sample were directly measured using monochromatic X-ray microbeam diffraction. The estimated deviatoric strains show large spatial variations, and the mean values are consistent with the external loading conditions, i.e., increasing tensile strain along the tensile direction and increasing compressive strain along the sample normal with increasing loading. The directly measured lattice strains also show large spatial variations, although the magnitude of this variation is smaller than that for the estimated deviatoric strain. The directly measured lattice strains in Ti grains are largely consistent with the external loading, whereas those in Al grains are in contradiction with the external loading. The causes of the experimental results are discussed and related to both the laminated microstructure of the composite material and the limitations of the techniques.
The effect of 0−1.0 at.% Al additions on grain refinement and phase transformation of the Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn (at.%) alloy containing a long period stacking ordered (LPSO) phase was investigated in this work. The addition of Al promoted the formation of the Al2RE phase in the Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn (at.%) alloy, and the dominant secondary phases in the as-cast Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn-1.0Al (at.%) alloy were the Mg3RE phase, LPSO phase, and Al2RE phase. With increased Al addition, the area fraction of the Al2RE phase increased monotonously, while the area fraction of LPSO phase and Mg3RE phase decreased gradually. The orientation relationship between the Al2RE phase and the α-Mg matrix was determined to be <112>Al2RE//<112¯0>α-Mg, {101}Al2RE//{101¯0}α-Mg, which was not affected by Zn and Mn concentrations in the Al2RE phase. Since the Al2RE particles with a size more than 6 μm located at the center of grains could act as nucleants for α-Mg grains, the average grain size of the as-cast alloys decreased from 276 μm to 49 μm after 1.0% Al addition. The effect of the Al addition on the grain refinement of the Mg-2.0Gd-1.2Y-0.5Zn-0.2Mn alloy was comparable to that of the Zr refined counterpart.
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