An Interference Cancellation Scheme for TFI-OFDM in Time-Variant Large Delay Spread Channel

In the mobile radio environment, signals are usually impaired by fading and multipath delay phenomenon. In such channels, severe fading of the signal amplitude and inter-symbol-interference (ISI) due to the frequency selectivity of the channel cause an unacceptable degradation of error performance. Orthogonal frequency division multiplexing (OFDM) is an efficient scheme to mitigate the effect of multipath channel. Since it eliminates ISI by inserting guard interval (GI) longer than the delay spread of the channel. In general, the GI is usually designed to be longer than the delay spread of the channel, and is decided after channel measurements in the desired implementation scenario. However, the maximum delay spread is longer than GI, the system performance is significantly degraded. The conventional time-frequency interferometry (TFI) for OFDM does not consider timevariant channel with large delay spread. In this paper, we focus on the large delay spread channel and propose the ISI and inter-carrier-interference (ICI) compensation method for TFI-OFDM

Chemically stable magnetic nanoparticles for metal adsorption and solid acid catalysis in aqueous media

Accepted 07 Feb 2014We have developed a magnetically collectable, reusable adsorbent and a catalyst for concentrating heavy metal ions in acidic aqueous solutions and solid acid catalysis in aqueous media. Chemically stable, magnetic rattle-type core-shell particles, comprising metallic cobalt nanoparticles in hollow silica microspheres, were prepared by the sol-gel reaction of alkylsilyl trichlorides around water droplets in a water-in-oil emulsion. Sulfonic groups were immobilized on the external surface of the core-shell particles through silylation with 3-mercaptopropyl(trimethoxysilane) and subsequent oxidization of the thiol groups by nitric acid. The sulfonic groups acted as adsorption sites for Zn and Pb ions under acidic conditions and as catalytically active sites for the hydrolysis of ethyl acetate in aqueous media. The enclosed Co was not eroded during the regeneration of the adsorbent/catalyst by 1 M HCl. The chemical stability arose from the dense non-porous shell, which prevents the passage of solvents.ArticleJOURNAL OF MATERIALS CHEMISTRY A. 2(16):5751-5758 (2014)journal articl

Magnetic and electronic properties of bimagnetic materials comprising cobalt particles within hollow silica decorated with magnetite nanoparticles

Bimagnetic materials were fabricated by decorating the external surface of rattle-type hollow silica microspheres (which themselves contain metallic cobalt nanoparticles) with magnetite nanoparticles; thus, each magnetic substance was spatially isolated by the silica shell. The amount of magnetite decoration on the co-occluded hollow silica was varied from 1 to 17 mass %. Magnetic and electronic properties of the resulting bimagnetic materials were characterized by superconducting quantum interference device measurements and X-ray absorption spectroscopy, respectively. The ferrous iron in the bimagnetic sample was slightly more oxidized than in the magnetite reference, probably from some charge-transfer because of the SiO2 surface contact, although the overall oxidation state of the samples is very similar to that of magnetite. The temperature dependence of the sample magnetization recorded with Zero Field Cooling and Field Cooling resulted in blocking temperatures for the bimagnetic materials that were close to that of magnetite nanoparticles (176K) and were lower than that for the bare Co-occluded hollow silica (which was above room temperature). Values of coercive force and exchange bias at 300K became quite small after decoration with only minimal amounts of magnetite nanoparticles (1-3 mass %) and were lower than those of magnetite. This is the first example of enhancing superparamagnetism by spatial separation of both Co and magnetite magnetic nanoparticles using a thin wall of diamagnetic silica.ArticleJOURNAL OF APPLIED PHYSICS. 114(12):124304 (2013)journal articl

Magnetic and electronic properties of bimagnetic materials comprising cobalt particles within hollow silica decorated with magnetite nanoparticles

Bimagnetic materials were fabricated by decorating the external surface of rattle-type hollow silica microspheres (which themselves contain metallic cobalt nanoparticles) with magnetite nanoparticles; thus, each magnetic substance was spatially isolated by the silica shell. The amount of magnetite decoration on the co-occluded hollow silica was varied from 1 to 17 mass %. Magnetic and electronic properties of the resulting bimagnetic materials were characterized by superconducting quantum interference device measurements and X-ray absorption spectroscopy, respectively. The ferrous iron in the bimagnetic sample was slightly more oxidized than in the magnetite reference, probably from some charge-transfer because of the SiO2 surface contact, although the overall oxidation state of the samples is very similar to that of magnetite. The temperature dependence of the sample magnetization recorded with Zero Field Cooling and Field Cooling resulted in blocking temperatures for the bimagnetic materials that were close to that of magnetite nanoparticles (176K) and were lower than that for the bare Co-occluded hollow silica (which was above room temperature). Values of coercive force and exchange bias at 300K became quite small after decoration with only minimal amounts of magnetite nanoparticles (1-3 mass %) and were lower than those of magnetite. This is the first example of enhancing superparamagnetism by spatial separation of both Co and magnetite magnetic nanoparticles using a thin wall of diamagnetic silica.ArticleJOURNAL OF APPLIED PHYSICS. 114(12):124304 (2013)journal articl

Preparation of porous thin-film polymethylsiloxane microparticles in a W/O emulsion system

Porous thin-film polymethylsiloxane microparticles have been prepared successfully from octyltrichlorosilane and methyltrichlorosilane in (water/oil) W/O emulsion systems by using several oil phases and changing the amount of the silanes or of the surfactant Span 60. Hollow microspheres of various shell thicknesses (120-180 nm) and high surface area were prepared by using four types of nonpolar solvents as the oil phase of the W/O emulsion system. The diameter of the spheres can also be controlled (1-1.6 mu m) by using different oil phases. The results of thermal analysis, nitrogen adsorption isotherm, infrared spectra and X-ray diffraction data showed that hollow microspheres of amorphous polymethylsiloxane with high surface area (360-385 m(2)g(-1)) can be obtained by heating the spheres in air at 673 K; the polymethylsiloxane microspheres become nonporous silica particles after calcination at 873 K for 3 h. Cup-shape microparticles of polymethylsiloxane with nano-order thickness (20-120 nm) were prepared by reducing the amount of silanes in the mixture. Small hollow particles were prepared by replacing a portion of the octyltrichlorosilane with Span 60.ArticlePOLYMER JOURNAL. 47(6): 449-455 (2015)journal articl

Thickness dependent structural and magnetic properties of ultra-thin Fe/Al structures

The structural and magnetic properties of electron beam evaporated ultra-thin Fe/Al structures are studied as a function of Fe layer thickness, while keeping the Al layer thickness constant. The grazing incidence X-ray reflectivity measurements carried out on the structures having Fe layer thickness ≤20 Å show substantial intermixing between the layers during deposition, indicated by a loss of periodicity. These structures resemble a composite single layer film consisting of Fe and Al clusters. However, for thicker Fe layers (≥30 Å), the appearance of a first order Bragg peak in the reflectivity patterns indicates the formation of a better-multilayered structure. These results are also supported by AFM and resistivity measurements. The X-ray diffraction measurements show that in all the multilayer films, deposited Fe layers are textured mainly along (110) direction. The corresponding magnetic measurements show a soft magnetic behaviour of the films with an in-plane easy direction of the magnetization. The observed soft magnetic behaviour in these samples is explained in terms of (i) weak crystalline magnetic anisotropy due to small crystal grains and magnetostriction and (ii) the morphological and structural changes occurring due to the variation in the Fe layer thickness below the critical value in the deposited structures. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200668.65.Ac Multilayers, 75.70.-i Magnetic properties of thin films, surfaces, and interfaces,