The present work shows the dielectric properties of (100-X)Ba
2
TiSi
2
O
8
–(X)TiO
2
composites (X in wt%) at radio frequency (RF) region (< 300 MHz). X-ray diffraction and Rietveld’s refinement ...showed the presence of Ba
2
(Ti
7/9
Si
2/9
)
9
O
20
(BTSO) phase in the studied composites. To analyze the relationship between the electrical properties and the microstructure of the matrix and composites, Impedance spectroscopy (IS) was used. The applied model that best describes the behavior found in the samples is the Havriliak–Negami model. From the IS it was observed that the dielectric relative permittivity presented high values in BTS10 (
X
= 10%) and BTS20 (
X
= 20%) which allows classifying them as Colossal permittivity materials. This is an important result due to the potential for applications in new storage systems, capacitive devices and microelectronics. Nyquist diagrams were employed to evaluate the contribution of the grain and grain boundary in the electrical response of the samples and fitted employing an equivalent circuit with two associations of R-CPE (constant phase element). Temperature coefficient of capacitance (TCC) was also obtained and it was possible to observe that there was an increase in the TCC value for the compounds in all frequencies. In addition, IS demonstrated that the activation energy decreasing with TiO
2
addition indicating a decrease in the resistive character of the materials.
Several studies have reported the adverse effects of recalcitrant compounds and emerging contaminants present in industrial effluents, which are not degradable by ordinary biological treatment. Many ...of these compounds are likely to accumulate in living organisms through the lipid layer. At concentrations above the limits of biological tolerance, these compounds can be harmful to the ecosystem and may even reach humans through food chain biomagnification. In this regard, advanced oxidation processes (AOPs) represent an effective alternative for the removal of the pollutants. This study focused on the AOP involving the use of ultraviolet radiation in homogeneous and heterogeneous systems. Based on the literature review, comparisons between natural and artificial light were established, approaching photoreactors constructive and operational characteristics. We concluded that the high availability of solar power in Brazil would make the implementation of the AOP using natural solar radiation for the decontamination of effluents feasible, thereby contributing to clean production and biodiversity conservation. This will serve as an important tool for the enforcement of environmental responsibility among public and private institutions.
This work studies the dielectric properties in the microwave region (MW) of the Ba
2
TiSi
2
O
8
(BTS) ceramic with TiO
2
additions and its applications as a dielectric resonator antenna (DRA). In ...this study, structural characterization through x-ray diffraction (XRD) is performed and the Rietveld refinement is used to confirm the phases formed. Analysis of the morphology of the materials is performed using scanning electron microscopy (SEM). The resonant frequency temperature coefficient (
τ
f
) reveals a variation from − 47.0 ppm°C
−1
to + 16.5 ppm°C
−1
. The dielectric properties in the MW region reveal an increase in the dielectric permittivity (
ε
r
) and a decrease in the loss tangent (tan
δ
) of the samples. Numerical simulation shows good fits of the experimental data, with gain and directivity standing out, ranging from 4 dBi to 6 dBi and radiation efficiency below 80%. The results demonstrate that the samples can operate in C-band electronics, Wi-Fi devices, meteorological radar systems, etc.
This work presents the study of the dielectric properties in the microwave region (MW) of BaMoO4 ceramic and composites with CaTiO3 (CTO). The BaMoO4 matrix was synthesized by solid state reaction ...and characterized by X-ray diffraction. Ceramic composites were obtained by adding 20–80 mol% of CTO in the BaMoO4 matrix. The Silva-Fernandes-Sombra method was used to measure the resonant frequency temperature coefficient (τf), and the BaMoO4 composite with 20% CTO showed an adequate value of relative dielectric permittivity (εr = 8.90), low dielectric loss tangent (tan δ = 9.89.10−4) and τf close to zero (τf = 3.48 ppm °C−1). BMO and its composites were applied as dielectric resonator antennas, and their far-field parameters were obtained through numerical simulation.
•BaMoO4 – CaTiO3 composites demonstrated thermal-stability in the microwave region.•New LTCC materials were obtained based on BaMoO4 and CaTiO3 phases.•DRAs investigated can be used in S and C-band applications.
This work presents the dielectric properties of Ba
2
TiSi
2
O
8
in the Radiofrequency (RF) and Microwave (MW) regions. X-ray diffraction analysis showed that the material was obtained as a ...single-phase without the presence of spurious phases. Complex impedance spectroscopy demonstrated that there was no significant change of permittivity with temperature, whereas the dielectric loss was less than 1. Nyquist diagrams were modelled through an equivalent circuit using two associations of R-CPE related to the grain and the grain boundary effects. The MW analysis showed
ε′
r
= 11.01 and tan
δ
= 4.55 × 10
–2
, values that are close to the results obtained in the RF region. Moreover, the τ
f
value for Ba
2
TiSi
2
O
8
was equal to − 47 ppm/°C which is close to the values adequate for a microwave device application. The numerical simulation demonstrated the operation of the material as a Dielectric Resonator Antenna (DRA), where a reflection coefficient below − 10 dB, a realised gain of 6.739 dBi, a bandwidth of 452.96 MHz and a radiation efficiency around 100% were observed. The results indicate that Ba
2
TiSi
2
O
8
would be an interesting candidate in microwave operating devices in the C-band, as well as in devices operating in RF.
This paper reviews the dielectric properties of Sr
2
TiSi
2
O
8
(STS) ceramic in the radio frequency (RF) and microwave (MW) regions. X-ray diffraction (XRD) analysis is used to demonstrate that a ...small secondary phase of SrTiO
3
is present in a synthesised STS ceramic. Complex impedance spectroscopy is performed, and the typical permittivity values of ceramic materials are observed. Nyquist diagrams are fitted based on an equivalent circuit using two associations of R-CPE related to the grain and the grain boundary effects. A dependence study of the changes in AC conductivity with frequency at different temperatures demonstrates that the conduction process is thermally activated, and a value of 1.0 eV is obtained for the activation energy. In the MW range, we observe values of
ε
r
= 12.7, tan
δ
= 1.3 × 10
–2
, and
τ
f
= − 6.1 ppm/°C, indicating interesting properties for applications in devices that operate in the MW region. A numerical simulation is employed to evaluate STS ceramic as a dielectric resonator antenna, and we observe a reflection coefficient of below − 10 dB, a realised gain of 4.6 dBi, a bandwidth of 475 MHz, and a radiation efficiency of around 75%. The properties of the STS matrix presented here indicate that this ceramic would be a suitable candidate for the operation of devices in the C-band, as well as in devices operating in the RF range.
•The synergic effect between ZnO and NaX was positive, which increased its activity.•The best results were obtained at pH 3 and 9 with ZnO/NaX and at pH 3 with Nb2O5/AC.•High degradation and ...considerable mineralization were attained with 10% ZnO/NaX.•ZnO and Nb2O5 supported on NaX and AC are promising alternatives as photocatalysts.
This study aimed to evaluate the photocatalytic activity of ZnO and Nb2O5 catalysts, both supported on NaX zeolite and activated charcoal (AC). The synergistic effect between oxide and support and the influence of solution pH (3, 7 and 9) on photocatalytic degradation of reactive blue 5G (C.I. 222) were analyzed. The catalysts Nb2O5/NaX, Nb2O5/AC and ZnO/NaX, ZnO/AC with 5 and 10% (wt%) were prepared by wet impregnation. The results showed that the catalysts exhibit quite different structural and textural properties. The synergic effect between ZnO and NaX support was higher than that with the activated charcoal, showing that these catalysts were more efficient. The most photoactive catalyst was 10% ZnO/NaX which showed 100% discoloration of the dye solution at pH 3, 7 and 9 after 0.5, 5 and 2h of irradiation, respectively. The hydrolytic nature of zeolite favored the formation of surface hydroxyl radicals, which increased the activity of the photocatalyst. Thus, catalysts supported on NaX zeolite are promising for use in photocatalysis.
Hansen's disease (leprosy) remains an important health problem in Brazil, where 34,894 new cases were diagnosed in 2010, corresponding to 15.3% of the world's new cases detected in that year. The ...purpose of this study was to use home visits as a tool for surveillance of Hansen's disease in a hyperendemic area in Brazil. A total of 258 residences were visited with 719 individuals examined. Of these, 82 individuals had had a previous history of Hansen's disease, 209 were their household contacts and 428 lived in neighboring residences. Fifteen new Hansen's disease cases were confirmed, yielding a detection rate of 2.0% of people examined. There was no difference in the detection rate between household and neighbor contacts (p = 0.615). The two groups had the same background in relation to education (p = 0.510), household income (p = 0.582), and the number of people living in the residence (p = 0.188). Spatial analysis showed clustering of newly diagnosed cases and association with residential coordinates of previously diagnosed multibacillary cases. Active case finding is an important tool for Hansen's disease control in hyperendemic areas, enabling earlier diagnosis, treatment, decrease in disability from Hansen's disease and potentially less spread of Mycobacterium leprae.
Aim
To report the evidence on the effect of mechanical and/or chemical plaque control in the simultaneous management of gingivitis and caries.
Material and Methods
A protocol was designed to identify ...randomized (RCTs) and controlled (CCTs) clinical trials, cohort studies and prospective case series (PCS), with at least 6 months of follow‐up, reporting on plaque, gingivitis and caries. Relevant information was extracted from full papers, including quality and risk of bias. Meta‐analyses were performed whenever possible.
Results
After the screening of 1,373 titles, 15 RCTs, 10 CCTs and 2 PCS were included. Low to moderate evidence support that combined professional and self‐performed mechanical plaque control significantly reduces standardized plaque index n = 4; weighted mean difference (WMD) = 1.294; 95% CI (0.445; 2.144); p = 0.003 and gingivitis scores n = 4; WMD = 1.728; 95% CI (0.631; 2.825); p = 0.002. The addition of fluoride to mechanical plaque control is relevant for caries management n = 5; WMD = 1.159; 95% CI (0.145; 2.172); p = 0.025 while chlorhexidine rinses are relevant for gingivitis.
Conclusion
Mechanical plaque control procedures are effective in reducing plaque and gingivitis. The addition of fluoride to mechanical plaque control is significant for caries management. Chlorhexidine rinse has a positive effect on gingivitis and inconclusive role in caries.
In this work, the influence of the addition of Bi
2
O
3
on the dielectric properties in the microwave range of BiCu
3
Ti
3
FeO
12
(BCTFO) ceramic matrix and its potential application as a dielectric ...resonator antenna are analysed. X-ray diffraction shows that a reaction between BCTFO and Bi
2
O
3
occurs that results in the formation of new crystalline phases. The morphology of the samples is studied by field-emission scanning electron microscopy and demonstrates a dependence of the grain size on the Bi
2
O
3
content. From the Mössbauer spectroscopic analysis, it is found that the Fe
3+
ions replace the Ti
4+
in the crystalline structure. The addition of Bi
2
O
3
also reduces the dielectric permittivity (ϵ
r
), dielectric loss (tan δ) and the coefficient of the resonance frequency (τ
f
) values. Finally, numerical simulations are carried out in order to obtain the antenna parameters and they demonstrate that BCTFO could be a potential candidate for devices operating in the S-band.
PDF
