Study of the Magnetic Properties of the Zn-Doped Spinel LiV2O4 Materials

The magnetic properties of spinel Zn _x Li_1?x V₂O₄ systems are studied by using the probability law, and high-temperature series expansions in the range 0≤x≤1. The nearest-neighboring J ₁(x) and the next-neighboring super-exchange J ₂(x) interactions are obtained. The intra-planar and the inter-planar exchange interaction are obtained. The corresponding classical exchange energy for the magnetic structure is obtained. The high-temperature series expansion combined with the Padé approximants method has been applied to the spinel Zn _x Li_1?x V₂O₄ systems to determine the magnetic phase diagram. The critical exponents associated with the magnetic susceptibility γ and with the correlation lengths ν are deduced.     

Synthesis and Magnetic Properties of Bulk Ferrites Spinels Ni0.5Zn0.5Fe2O4: Experimental an Ab-Initio Study

Polycrystalline Ni_0.5Zn_0.5Fe₂O₄ ferrites have been prepared using the solid-state reaction technique. The structure of ferrite was measured using an X-ray diffractometer (XRD). It is shown that the structure of Ni_0.5Zn_0.5Fe₂O₄ ferrites is a single spinel structure. The magnetic properties of the samples were tested at room temperature by a superconducting quantum interference device (SQUID) to determine magnetic properties versus temperature and applied magnetic field. Based on first-principles spin-density functional calculations, using the Korringa–Kohn–Rostoker method (KKR) combined with the coherent potential approximation (CPA), the ferromagnetic and half-metallic behaviors was observed with LDA (local density approximation) and LDA–SIC (local density approximation-self-interaction correction) approximation.     

Magnetic Properties and Phase Transitions in a Diluted Ferromagnet: Ising,XY, and Heisenberg Models

The magnetic properties and phase transition of a ferromagnetic spin-S disordered diluted thin film with a face-centred cubic lattice are investigated using the high-temperature series expansion technique extrapolated with Padé approximant method for Heisenberg, XY and Ising models. The reduced critical temperature of the system t_c=\frack_BT_c2S(S+1)J_b\tau_{\mathrm{c}}=\frac{k_{\mathrm{B}}T_{\mathrm{c}}}{2S(S+1)J_{\mathrm{b}}} is studied as the function of the thickness of the thin film and the exchange interactions in the bulk, and within the surfaces J _b,J _s and J _⊥, respectively. It is found that τ _c increases with the exchange interactions of surface. The magnetic phase diagrams (τ _c versus the dilution x) and the percolation threshold are obtained. The shifts of the critical temperatures T _c(L) from the bulk value (\fracT_c(￥)T_c(L)-1)(\frac{T_{\mathrm{c}}(\infty )}{T_{\mathrm{c}}(L)}-1) can be described by a power law L ^−λ , where λ is the inverse of the correlation length exponent.     

Congestion Control and Contention Elimination in Optical Burst Switching

Optical burst switching (OBS) is a proposed new communications technology that seeks to expand the use of optical technology in switching systems. However, many challenging issues have to be solved in order to pave the way for an effective implementation of OBS. Contention, which may occur when two or more bursts compete for the same wavelength on the same link, is a critical issue. Many contention resolution methods have been proposed in the literature but many of them are very vulnerable to network load and may suffer severe loss in case of heavy traffic. Basically, this problem is due to the lack of information at the nodes and the absence of global coordination between the edge routers. In this work, we propose another approach to avoid contention and decrease the loss. In this scheme, the intermediate nodes report the loss observed to the edge nodes so that they can adjust the traffic at the sources to meet an optimal network load. Furthermore, we propose a combination of contention reduction through congestion control and bursts retransmission to eliminate completely bursts loss. This new approach achieves fairness among all the edge nodes and enhances the robustness of the network. We also show through simulation that the proposed protocol is a viable solution for effectively reducing the conflict and increasing the bandwidth utilization for optical burst switching.     

Effect of ion implantation energy for the synthesis of Ge nanocrystals in SiN films with HfO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> stack tunnel dielectrics for memory application

Ge nanocrystals (Ge-NCs) embedded in SiN dielectrics with HfO₂/SiO₂ stack tunnel dielectrics were synthesized by utilizing low-energy (≤5 keV) ion implantation method followed by conventional thermal annealing at 800°C, the key variable being Ge⁺ ion implantation energy. Two different energies (3 and 5 keV) have been chosen for the evolution of Ge-NCs, which have been found to possess significant changes in structural and chemical properties of the Ge⁺-implanted dielectric films, and well reflected in the charge storage properties of the Al/SiN/Ge-NC + SiN/HfO₂/SiO₂/Si metal-insulator-semiconductor (MIS) memory structures. No Ge-NC was detected with a lower implantation energy of 3 keV at a dose of 1.5 × 10¹⁶ cm^-2, whereas a well-defined 2D-array of nearly spherical and well-separated Ge-NCs within the SiN matrix was observed for the higher-energy-implanted (5 keV) sample for the same implanted dose. The MIS memory structures implanted with 5 keV exhibits better charge storage and retention characteristics compared to the low-energy-implanted sample, indicating that the charge storage is predominantly in Ge-NCs in the memory capacitor. A significant memory window of 3.95 V has been observed under the low operating voltage of ± 6 V with good retention properties, indicating the feasibility of these stack structures for low operating voltage, non-volatile memory devices.     

Study of the Magnetic Properties of the Zn-Doped Spinel CdV2O4 Materials

The magnetic properties of spinel Cd_1?x Zn _x V₂O₄ systems in the range 0≤x≤1 are studied by mean field theory and high-temperature series expansions (HTSE). The nearest neighboring and the next-neighboring superexchange interactions J ₂(x) and J ₂(x) are given. The intra-planar and the inter-planar interaction are deduced. The HTSE theory is applied in the spinel Cd_1?x Zn _x V₂O₄ systems, combined with the Padé approximants method, to determine the magnetic phase diagrams (T _N versus dilution x) in the range 0≤x≤1. The critical exponents associated with the magnetic susceptibility γ and the correlation lengths ν are deduced.     

Poly(ethylene terephthalate‐co‐isophthalate) copolyesters obtained from ethylene terephthalate and isophthalate oligomers

A series of poly(ethylene terephthalate‐co‐isophthalate) copolyesters containing upto 50%‐mole of isophthalic units were prepared by polycondensation from ethylene terephthalate and ethylene isophthalate fractions of linear oligomers containing from 5 to 6 repeating units in average. The polyesters were obtained in good yields and with high‐molecular‐weights. The microstructure of the copolyesters was studied as a function of reaction time by ¹³C‐NMR showing that a random distribution of the comonomers was achieved since the earlier stages of polycondensation. The melting temperature and enthalpy of the copolyesters decreased with the content of isophthalic units so that copolyesters containing more than 25% of these units were amorphous. Isothermal crystallization studies made on crystalline copolyesters revealed that the crystallization rate of copolyesters decreased with the content in isophthalic units. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Analysis of multiple types of voice recordings in cepstral domain using MFCC for discriminating between patients with Parkinson’s disease and healthy people

In this study, we wanted to discriminate between two groups of people. The database used in this study contains 20 patients with Parkinson’s disease (PD) and 20 healthy people. Three types of sustained vowels (/a/, /o/ and /u/) were recorded from each participant and then the analyses were done on these voice samples. The technique used in this study is to extract voiceprint from each voice samples by using mel frequency cepstral coefficients (MFCCs). The extracted MFCC were compressed by calculating their average value in order to extract the voiceprint from each voice recording. Subsequently, a classification method was performed using leave one subject out (LOSO) validation scheme along with support vector machines (SVMs). We also used an independent test to validate our results by using another database which contains 28 PD patients. Based on the research result, the best obtained classification accuracy using LOSO on the first dataset was 82.50 % using MLP kernel of SVM on sustained vowel /u/. And the maximum classification accuracy using the independent test was 100 % using sustained vowel /a/ with polynomial kernel of the SVM and with MLP kernel of the SVM. This result was also achieved using sustained vowel /o/ with polynomial kernel of the SVM.