Fe 3 O 4 /α-F e2 O 3 composites were synthesized by a one-step method. The composition and their performances were modified by adjusting the concentration of Fe 3+ (FeCl 3 •6H 2 O) in the precursor solution, effectively. Compared with single-phase Fe 3 O 4 and Fe 2 O 3 , the effective microwave absorbing ability of Fe 3 O 4 /α-Fe 2 O 3 composites is much widened in the range 1−18 GHz, which could stem from the enhanced dipolar polarization and interfacial polarization due to lattice dislocations at the interface of Fe 3 O 4 /α-Fe 2 O 3 . The minimum reflection loss (RL) of Fe 3 O 4 /α-Fe 2 O 3 composites reaches about −43.1 dB at a thickness of 2.0 mm, with the effective absorption band reaching 3.4 GHz (9.8−13.2 GHz). In the thickness of 1.5−3.2 mm, the width of the RL reaches 9.9 GHz (3.5−13.4 GHz). The results demonstrate that Fe 3 O 4 /α-Fe 2 O 3 composites could be a candidate to be used as absorbers with the microwave absorption band much widened.

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Background: The incidence of osteoporotic fractures has increased rapidly, and because of the poor prognosis and high mortality associated with osteoporotic fractures, they remain a prospective research area globally. One way to reduce their incidence is to investigate their intervention risk factors in the elderly. Hence, this study explores the correlation between serum 25-hydroxyvitamin D [25(OH)D] levels and osteoporotic fractures in elderly patients through a meta-analysis. Methods: We conducted our literature search mainly in PubMed and Embase for identifying studies that investigated the relationship between serum 25(OH)D levels and the risk for osteoporotic fractures. We performed categorical analysis, heterogeneity checks, publication bias analysis, and subgroup analyses. Results: In total, 20 studies were included, of which 4 were case-cohort studies and 16 were cohort studies. A total of 41,738 patients from 20 studies were included in the meta-analysis, of which 5916 had fractures, including 3237 hip fractures. By combining the lowest and highest categories of relative risks (RRs) and 95% confidence intervals (CIs), it was suggested that lower serum 25-hydroxyvitamin D levels may be a risk factor for fractures. RR (95% CI) for total and hip fractures were 1.11 (0.99, 1.24) and 0.89 (0.80, 0.98) after adjustments. Conclusions: Our study showed that compared to low serum 25(OH)D levels, high serum 25(OH)D levels reduce the risk of hip fractures in the patients aged 60 years or older. In contrast, serum 25(OH)D has no significant relationship with total fracture risk.

Conclusion: Postmenopausal women with osteoporosis have a lower concentration of serum Mg. However, the association between the concentration of serum Mg and osteopenia needs further confirmation.