A simple design of a broadband multifunctional polarization converter using an anisotropic metasurface for X-band application is proposed. The proposed polarization converter consists of a periodic ...array of the two-corner-cut square patch resonators based on the FR-4 substrate that achieves both cross-polarization and linear-to-circular polarization conversions. The simulated results show that the polarization converter displays the linear cross-polarization conversion in the frequency range from 8 to 12 GHz with the polarization conversion efficiency above 90%. The efficiency is kept higher than 80% with wide incident angle up to 45°. Moreover, the proposed design achieves the linear-to-circular polarization conversion at two frequency bands of 7.42-7.6 GHz and 13-13.56 GHz. A prototype of the proposed polarization converter is fabricated and measured, showing a good agreement between the measured and simulated results. The proposed polarization converter exhibits excellent performances such as simple structure, multifunctional property, and large cost-efficient bandwidth and wide incident angle insensitivity in the linear cross polarization conversion, which can be useful for X-band applications. Furthermore, this structure can be extended to design broadband polarization converters in other frequency bands.
We report a numerical study on the design of a broadband metamaterial absorber (MMA) with a single layer of metal–dielectric–metal based on an FR-4 substrate for X-band applications. The MMA ...structure consists of a periodic array of a split circle ring and lumped resistors coupled within split segments. The MMA structure achieves a broadband absorption response in the frequency range of 7.8–12.6 GHz with an absorptivity of above 90% under normal incidence for all polarization angles. The absorptivity remains above 70% in the frequency range of 6.8–11.8 GHz at wide incident angles from 0° to 30° for both transverse electric and transverse magnetic polarizations. The physical mechanism of the absorber is explained by the electric and the surface current distributions that, in turn, are significantly affected by magnetic resonance.
Developing a simple structure using low-cost material that enables both large-scale fabrication and broadband absorption response is highly desirable but very challenging for achieving ...high-performance metamaterial absorber. Herein, we propose and numerically investigate an ultra-broadband and wide-angle insensitive perfect metamaterial absorber in the ultraviolet to near-infrared (UV–NIR) region based on a simple metal–dielectric–metal structure. The proposed absorber structure consists of a periodic array of a tungsten hexagonal prism and a tungsten ground plane separated by a silicon dioxide dielectric substrate. The proposed absorber achieves an ultra-broadband absorption response in the range of 275–1000 nm with an absorptivity above 90
%
and a relative bandwidth of 106.8
%
at normal incidence, which covers from the UV to NIR region. The absorption efficiency is maintained with the figure of merit
η
OBW
higher than 90
%
for a wide incident angle up to 40
o
for transverse electric (TE) polarization and 65
o
for transverse magnetic (TM) polarization. The effects of structural parameters and different metallic materials on the absorption performance are presented. In addition, the physical mechanism is analyzed using the surface density and distributions of electric and magnetic fields that are attributed to both localized surface plasmon (LSP) and propagating surface plasmon (PSP) resonances. Owing to outstanding merits of simple structure, low cost, and high absorption performance, the designed absorber can be suitable for many applications in the UV–NIR spectrum such as thermal emitters and solar cells.
A new megastigmane glycoside, (3S,4R,7E)-megastigma-5,7-diene-9-one-3,4-diol 3-O-β-D-apiofuranosyl-(1→2)-β-D-glucopyranoside (1) and a new cyanogenic glycosyl derivative, ...(S)-2-(6′-O-R-rosmarinoyl-β-D-glucopyranosyloxy)-phenylacetonitrile (2) were isolated from the methanol extract of the Elsholtzia ciliata together with twelve known compounds, 1-O-β-D-glucopyranosyl-2-hydroxy-4-allylbenzene (3), citrusin C (4), 1,2-di-O-β-D-glucopyranosyl-4-allylbenzene (5), manglieside B (6), 4-allyl-2-hydroxyphenyl 1-O-β-D-apiofuranosyl-(1→6)-β-D-glucopyranoside (7), (-)-isolariciresinol 3α-β-D-glucopyranoside (8), 7R,8R-threo-4,7,9-trihydroxy-3,3′-dimethoxy-8-O-4′-neolignan-9′-O-β-D-glucopyranoside (9), 7R,8R-threo-4,7,9,9′-tetrahydroxy-3-methoxy-8-O-4′-neolignan-9′-O-β-D-glucopyranoside (10), cedrusin-4-O-β-D-glucopyranoside (11), icariside E
3
(12), everlastoside L (13) and rosmarinic acid (14). Their chemical structures were elucidated on the basic of extensive 1D and 2D-NMR experiments, as well as their mass spectroscopic data. The absolute configurations of the compounds 1 and 2 were successfully indicated by both theoretical and calculated CD spectra. Compounds 3-7, 9 and 10 potential inhibited NO production in LPS-activated RAW264.7 cells with IC
50
values of 6.71, 8.97, 12.38, 14.27, 16.13, 13.54, 16.27 µM, respectively, compared to that of the positive control of N
G
-monomethyl-L-arginine acetate (L-NMMA), IC
50
= 32.51 µM.
Alkaloid-enriched extract of Huperzia serrata (Thunb.) Trevis (Lycopodiaceae) (HsAE) can potentially be used to manage neuronal disorders.
This study determines the anti-neuroinflammatory effects of ...HsAE on lipopolysaccharide (LPS)-stimulated BV-2 microglial cells and the underlying mechanisms.
BV-2 cells were pre- or post-treated with different concentrations of HsAE (25-150 µg/mL) for 30 min before or after LPS induction. Cell viability was assessed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and no cytotoxicity was found. Nitric oxide (NO) concentration was determined using Griess reagent. The levels of prostaglandin E2 (PGE2), tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 were determined using enzyme-linked immunosorbent assay. The levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 and the phosphorylation of mitogen-activated protein kinase (MAPK) were analyzed using western blotting.
HsAE reduced LPS-induced NO production with half-maximal inhibitory concentration values of 99.79 and 92.40 µg/mL at pre- and post-treatment, respectively. Pre-treatment with HsAE at concentrations of 50, 100, and 150 µg/mL completely inhibited the secretion of PGE2, TNF-α, IL-6, and IL-1β compared to post-treatment with HsAE. This suggests that prophylactic treatment is better than post-inflammation treatment. HsAE decreased the expression levels of iNOS and COX-2 and attenuated the secretion of pro-inflammatory factors by downregulating the phosphorylation of p38 and extracellular signal-regulated protein kinase in the MAPK signaling pathway.
HsAE exerts anti-neuroinflammatory effects on LPS-stimulated BV-2 cells, suggesting that it may be a potential candidate for the treatment of neuroinflammation in neurodegenerative diseases.
We report a wideband and polarization-/wide-angle insensitive metamaterial absorber based on a symmetry structure associated with surface mount resistors. The proposed structure consists of a ...periodic array of a top metal symmetry resonator loading with four lumped resistors and a continuous metal ground plane separated by a dielectric substrate of FR-4. A prototype of the proposed absorber is fabricated and measured, confirming a good agreement between the measurement and simulation results. The proposed absorber shows polarization-insensitive behavior and the absorption response in a frequency range from 8-18 GHz covering the entire X- and Ku- bands with an absorptivity above 80<inline-formula><tex-math notation="LaTeX">\%</tex-math></inline-formula> for a wide incident angle up to 40<inline-formula><tex-math notation="LaTeX">^{\circ }</tex-math></inline-formula> for both transverse electric and transverse magnetic polarizations. Compared with the reported broadband absorbers using lumped resistors, our proposed absorber exhibits excellent characteristics in terms of compact and simple structure, high relative absorption bandwidth, and polarization and wide-incident insensitivity. Therefore, this design shows promising potential for both X- and Ku-band applications.
The design of a lightweight and ultra‐wideband absorber for C and X bands is still a challenge as the dimension of the absorber is relatively large in such a relatively low‐frequency band. Herein, an ...ultra‐wideband and lightweight metamaterial absorber (MMA) is presented for C‐ and X‐band applications. The unit cell of the proposed MMA consists of four copper sectors loaded by lumped resistors and a continuous copper ground plane, which is printed on two FR‐4 substrates. Furthermore, an airgap separating the FR‐4 layers is used as the active substrate medium of the MMA to achieve both ultra‐wideband absorption spectra and lightweight design. The MMA is investigated by simulation and measurement, showing that a good agreement is achieved. The result indicates that the absorptivity of the MMA under both transverse electric (TE) and transverse magnetic (TM) polarizations is greater than 90% in a wide range from 3.7 to 13.6 GHz for all polarization angles. Compared to other reported broadband absorbers, the proposed MMA shows an ultra‐wide absorption bandwidth and a lightweight design, which demonstrates a great potential for C‐and X‐band applications.
Herein, a lightweight, ultra‐wideband, and polarization‐insensitive metamaterial absorber is designed and fabricated. The designed absorber exhibits absorption response with absorptivity greater than 90% in a wide range from 3.7 to 13.6 GHz and a relative bandwidth of 114.5% for all polarization angles, which entirely covers both the C and X bands.
In the present article, the synthesis of spherical hollow cobalt ferrite and application as an electrode modifier were demonstrated. The synthesis of cobalt ferrite was conducted using carbonaceous ...microspheres prepared from a glucose solution as a sacrificial template, followed by subsequent heat treatment. The Fe/Co molar ratio in cobalt ferrite depends significantly on the initial Fe/Co molar ratio. The Fe/Co molar ratio as 1/1 could provide the stoichiometric cobalt ferrite (CoFe
2
O
4
) with a hollow sphere structure and large saturation magnetization. The simultaneous quantification of ascorbic acid (ASA), acetaminophen (ACE), and caffeine (CAF) was performed utilizing the differential pulse anodic stripping voltammetric method with CoFe
2
O
4
modified glassy carbon electrode. The detection limits in the linear range of 0.2–4.4 µM are 0.313, 0.267, and 0.226 µM for ASA, ACE, and CAF, respectively. This proposed method enables the simultaneous detection of ASA, ACE, and CAF in pharmaceutical formulations and beverage samples. The determined concentration of the analytes is comparable with that obtained with HPLC.
Fever of unknown origin (FUO) is a challenge for clinicians treating patients with HIV/AIDS. CD4 counts can be helpful in the diagnosis and treatment. This study aimed to determine several common ...etiologies of FUO stratified by CD4 count levels in HIV/AIDS patients.
A cross-sectional retrospective and prospective study was conducted in 195 HIV/AIDS patients with FUO admitted to the National Hospital for Tropical Diseases from January 2016 to June 2019. Clinical parameters, immune status, and etiologies for each patient were recorded. Odds ratios were calculated to compare the distributions of common etiologies in groups with two different CD4 count levels: < 50 cells/mm
and ≥ 50 cells/mm
.
The proportions of opportunistic infections and noninfectious etiologies were 93.3% and 3.6%, respectively. Tuberculosis was the most common opportunistic infection (46.7%), followed by talaromycosis (29.2%) and Pneumocystis jiroveci (PCP) infection (20.5%). Tuberculosis was predominant in all CD4 level groups. Most patients with talaromycosis had CD4 counts below 50 cells/mm
. In total, 53.8% of the patients were infected by one pathogen. The risks of tuberculosis and talaromycosis in FUO-HIV patients were high when their CD4 counts were below 50 cells/mm
.
Opportunistic infections, especially tuberculosis, are still the leading cause of FUO in HIV/AIDS patients. Tuberculosis and Talaromyces marneffei (TM) infection should be considered in patients with CD4 cell counts < 50 cells/mm
. This study implies that guidelines for appropriate testing to identify the etiology of FUO in HIV/AIDS patient based on the CD4 cell count should be developed, thereby reducing resource waste.
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