Evolution of Magnetic Properties in Ferrites: Trends of Single- Sample and Multi-Sample Sintering

Microstructure of magnetic materials greatly influences the performance of magnetic properties, and sintering has been used as an agent to tailor the microstructure of these magnetic materials especially ferrites. Nanostructured ferrites prepared by high-energy milling method are often inherently unstable owing to their small constituent sizes, non-equilibrium cation distribution, disordered spin configuration, and high chemical activity. Therefore, sintering of the milled ferrites recrystallizes the nanostructure and causes its transition from an excited metastable (activated) state into the low-energy crystalline state. A better understanding of the response of nanoscale ferrites with changes in temperature is crucial not only for basic science (the development of an atomistic and microscopic theory of the mechanochemical processes) but also because of the technological high-temperature applications in catalysis, ferrofluids and information storage. This chapter discusses on two different sintering schemes, which are a commonly applied multi-sample sintering and a rarely adopted single-sample sintering. Experimental results of single-sample and multi-sample sintering of NiZn ferrites and yttrium iron garnet (YIG) were highlighted, and their microstructural consequences on the magnetic properties were also discussed

Microwave sintering of Ni-Cr doped strontium hexaferrite synthesized via sol-gel method

The magnetic behavior of Strontium hexaferrite ceramics with nominal composition SrFe12-2xNixCrxO19 (where x = 0.2, 0.4, 0.6, 0.8) samples are reported in this paper. Four samples were synthesized by the sol-gel method. The XRD analysis confirms the single phase and various parameters such as lattice constants (a and c), are calculated from the XRD data. Magnetic properties, such as specific saturation magnetization (Ms) and coercivity (Hc) are calculated from the hysteresis loops. Values of coercivity are found to increase up to the substitution level of x = 0.0-0.2 and then decreases continuously while that of saturation magnetization decrease continuously with increase in Ni-Cr concentration. The results show that microwave sintering requires about 75% less processing time than required by conventional method and still provides better magnetic properties

Assessing the Risk of Dengue Fever based on the Epidemiological, Environmental and Entomological Variables

AbstractDengue fever is an infectious vector-borne disease in Malaysia. Descriptive spatial analysis indicated the DF infection was normally distributed in urban area. As for the environmental attributes, there was no significant difference except for the existence of abandoned houses across the study area. As for breeding index, it was found to be high in all temporal indices in the locality. However, it was noteworthy that there was a significant difference in the preferred breeding containers in all temporal risk indices. As a conclusion, the risk factors for Aedes mosquito breeding sites should be considered in carrying an effective vector control

Coupling of remote sensing data and environmental-related parameters for dengue transmission risk assessment in Subang Jaya, Malaysia.

In Malaysia, the endemic level of dengue fever (DF) has already changed morbidity indicators, and the magnitude of these incidences in the last few years has surpassed the incidences of all other diseases of compulsory notification. The reasons for the dramatic emergence of DF are complex and not well understood. There are many factors that contribute to the epidemiological conditions that favour viral transmission by the main mosquito vector. This study, therefore, is filling this gap by analysing the impact of dengue incidence at a local (Subang Jaya) scale using environmental factors. Meteorological data and land-use pattern were consolidated using geographic information system (GIS) and its components as an analytical tool. We have shown that weather variables (relative humidity, temperature and precipitation) have significant correlation with DF incidence with seasonal variation. Besides land-use pattern, DF incidence shows the higher distribution in the residential area, followed by commercial and industrial area. This is due to the higher population density in residential area as well as favourable places for the breeding of dengue-carrying Aedes mosquitos created by humans in the residential area, especially one-storey houses. The analysis on the trends of DF incidence towards various housing types indicate that most of the victims’ houses fall into interconnection houses and mixed houses types compared to the independent houses area. The outcome driven from this analysis suggested that each character of the environmental factors has their own risk towards dengue incidence. In line with that, it is possible to develop a dynamic model of DF transmission using the knowledge produced by this comprehensive time series data and the results provided by the different analyses

Recent developments of smart electromagnetic absorbers based polymer-composites at gigahertz frequencies

The rapid increase in electromagnetic interference has received a serious attention from researchers who responded by producing a variety of radar absorbing materials especially at high gigahertz frequencies. Ongoing investigation is being carried out in order to find the best absorbing materials which can fulfill the requirements for smart absorbing materials which are lightweight, broad bandwidth absorption, stronger absorption etc. Thus, to improve the absorbing capability, several important parameters need to be taken into consideration such as filler type, loading level, type of polymer matrix, physical thickness, grain sizes, layers and bandwidth. Therefore, this article introduces the electromagnetic wave absorption mechanisms and then reveals and reviews those parameters that enhance the absorption performance

Molecular characterization of aedes albopictus (diptera:culicidae) from hot spot dengue-infested areas / Siti Nazrina Camalxaman, Prof Madya Rodziah Ismail and Dr. Nazri Che Dom

Laboratory work and thesis writing has been completed within one and a half years. The aim of this study is to characterize the genetic diversity and evolutionary relationship of Ae. albopictus collected from dengue cluster areas based on the CO1 gene as a genetic marker. Local sequences will be amplified and compared, results obtained will help determine the genetic diversity, geographic origin and future expansion of Ae. albopictus. The distribution and infection frequencies of Wolbachia in local Ae. albopictus is currently unknown also forms the basis of this study. Broadly, findings from this study are expected to provide a new perspective aimed to improve current vector control and surveillance program. One of the approaches that could mitigate the spread and threat of dengue would be by improving the current understanding of the vector biology and enhancing vector control strategies. This in turn necessitates the need to characterize the vector itself, and the determination of the prevalence of Wolbachia in these vectors for biological control based approaches (Bonizzoni, Gasperi, Chen, & James, 2013). Wolbachia is an endosymbiotic alpha-proteobacteria that infects more than 70% of insect species worldwide including a variety of arthropods (Miller, 2013). The potential of Wolbachia to manipulate various functional systems of its hosts affects several aspects of host biology, physiology, immunity, ecology and evolution as well as reproductive properties including feminization, parthenogenesis, male killing and most commonly, cytoplasmic incompatibility (CI) (Werren, 1997). This intracellular bacteria functions as reproductive parasites and has been proposed for the future development of a symbiont-based control approach to tackle Ae. albopictus population (Bourtzis et al., 2014). In tandem, data regarding the natural infection frequency of Wolbachia in Ae. albopictus and the effectiveness of its transmission rates are essential to evaluate its use as a candidate vehicle to modify vector populations (Mains, Brelsfoard, Crain, Huang, & Dobson, 2013). Morphological characterization using DNA barcoding methods that utilize cytochrome oxidase subunit I (CO1) gene has been widely used in the past to attain information regarding mosquito taxonomy (Besansky, Severson, & Ferdig, 2003; Meier & Zhang, 2008). In addition, it has also been used for diagnostic purposes of specific target species. Most research to date focuses on spatial distribution and abundance of Aedes vectors, but scarce information exists regarding the phylogenetic and evolutionary relationship among the vectors at specific localities in Malaysia. Recently, a temporal model using climate variables was developed to forecast dengue cases in Subang Jaya (Dom, Ahmad, Latif, & Ismail, 2013). This model proved to be useful in predicting dengue cases and reinforces previous studies using different modalities and risk assessment methods (Dom, Ahmad, Latif, Ismail, & Pradhan, 2012a; Dom, Latif, Ahmad, Ismail, & Pradhan, 2012b). Such hotspots described by Dom et al. (2013) could now serve as a platform to determine the prevalence and distribution of both the DENV and the vector of choice

Dependence of developing magnetic hysteresis characteristics on stages of evolving microstructure in polycrystalline yttrium iron garnet

The microstructure evolution in several polycrystalline yttrium iron garnet samples as a result of a sintering scheme was studied in detail, in parallel with the changes in their magnetic properties. Samples with nanometer sized starting powder were synthesized by employing the High-Energy Ball Milling technique and then sintering toroidal compacts of the milled powder. Nine sintered samples were obtained, each corresponding to a particular sintering from 600 °C to 1400 °C. The samples were characterized for their evolution in crystalline phases, microstructure and magnetic hysteresis-loops parameters. The results showed an increasing tendency of the saturation magnetization and saturation induction with grain size, which is attributed to crystallinity increase and to reduction of demagnetizing fields in the grains. The variation in coercivity could be related to anisotropy field changes within the samples due to grain size changes. In particular, the starting appearance of room temperature ferromagnetic order suggested by the sigmoid-shaped B–H loops seems to be dependent on a sufficient number of large enough magnetic domain-containing grains having been formed in the microstructure. Viewed simultaneously, the hysteresis loops appear to belong to three groups with different magnetism-type dominance, respectively dependent on phase purity and three different groups of grain size distributions

Sintering temperature dependence of optimized microstructure formation of BaFe12O19 using sol–gel method

In an attempt to obtain the best possible properties of barium hexaferrite (BaFe12O19), the sol–gel synthesis method was chosen and, the optimum sintering conditions were established. The effects of the sintering temperature on the structural, morphological and magnetic properties of hexaferrite were studied. X-ray analysis indicates that the sintered samples (1,000–1,150 °C) remained in the hexagonal structure. From this analysis, no secondary phases are identified. The effect of sintering temperature on the grain growth of BaFeBaFe12O19 is confirmed by the microstructure using HR-SEM and is in good agreement with the XRD analysis based on the peak intensity of the (107) plane. The samples sintered at 1,150 °C showed the densities as ~93 % of theoretical density. Sintering temperature affected the grains in compact samples. The results show that homogeneous and dense BaFeBaFe12O19 ceramics obtained at a lower sintering temperature of 1,150 °C which is lower than the normally reported sintering temperature of ≥1,200 °C. The thermal treatment can markedly affect the grains in compact samples

Integration of GIS-Based Model with Epidemiological data as a Tool for Dengue Surveillance

This study aims to fully integrated and validated spatial temporal statistical model using epidemiological data as a predictive model for surveillance and control of DF cases. Kernel-density estimation (KDE) method was carried out by using spatial union analysis in order to predict and visualize the DF hotspot area by monthly basis in the Subang Jaya area. The generated maps were then verified using Receiver operating characteristics (ROC) was performed to validate the DF hotspot simulation model. Spatial analysis showed that the dengue epidemics in Subang Jaya were spatially dependent. This analysis demonstrated spatial clustering of dengue activity which can facilitate prediction of the magnitude, timing and location of future dengue epidemic. The model developed highlights the adaptation capabilities of the approach where the accuracy assessment result showed accuracy about 60% agreements between the hotspot map and the actual DF location data. It can thus be suggested that any future population increase will be associated with increased DF risk in areas which already accommodate this disease environmentally, climatically and socioeconomically. Future risk could be modelled using the same methods. This would help decision maker in choosing which areas should be under intensive treatment to counter mosquito breeding and reduce prevalence of DF

Magnetic and microwave properties of polycrystalline gadolinium iron garnet

The microwave loss in nanosized GdIG particles synthesized using mechanical alloying technique was investigated. There were very few of research on the microwave properties of nanosized particle GdIG and there is no attempt investigating on the material at C-band frequency range and its correlation with the microstructure. Gadolinium (III) iron oxide and iron (III) oxide, α-Fe2O3 were used as the starting materials. The mixed powder was then milled in a high-energy ball mixer/mill SPEX8000D for 3 hours. The samples were sintered at temperature 1200°C for 10 hours in an ambient air environment. The phase formation of the sintered samples was analyzed using a Philips X’Pert Diffractometer with Cu-Kα radiation. Complex permeability constitutes of real permeability and magnetic loss factor were measured using an Agilent HP4291A Impedance Material Analyzer in the frequency range from 10 MHz to 1 GHz. A PNA-N5227 Vector Network Analyzer (VNA) was used to obtain the information on ferromagnetic linewidth broadening, ΔH that represents the microwave loss in the samples in in frequency range of 4 to 8 GHz (C-band). The ΔH value was calculated from the transmission (S21) data acquired from VNA. The single phase GdIG showed low initial permeability and low magnetic loss when applied with low-frequency range energy. From these data, it is validated that GdIG is a suitable material for microwave devices for the high-frequency range