Design and implementation of 2-dimensional wavelength/time codes for OCDMA

In this paper, two-dimensional (2D) wavelength/time codes are designed and implemented. The 2D codes are constructed by a technique based on folding of Golomb rulers. The performance evaluation of OCDMA system based on wavelength/time code has been analyzed by measuring the values of bit error rates and eye diagrams for different number of active users. It is shown that eye opening decreases and BER increases with increase in number of active users. It is also shown that BER further increases with increase in number of active users when number of decoders increases on receiver side. Hence, it is concluded that multiple access interference (MAI) is the dominant source of BER and there is graceful degradation in system performance when number of simultaneously active users increases. The received optical power is also measured at different transmission distance. It has been observed that received optical power decreases with increase in length of fiber due to attenuation.     

Magnetostrictions and Curie temperature measurements of (Fe–Co)91−xMo8Cu1Bx alloys with varying Co/Fe ratio

Amorphous rapidly quenched ribbons of (Fe–Co)₇₉Mo₈Cu₁B₁₂ and (Fe–Co)₇₆Mo₈Cu₁B₁₅ with the ratio of Co/Fe from 0 to 1 and 0 to 2, respectively, were prepared by planar flow casting. The dependence of Curie temperature T_C on Co/Fe ratio was determined from temperature dependencies of sample dilatation measured using a special dilatometer designed for these materials. Due to the presence of the invar effect, it was possible to measure the spontaneous volume magnetostriction in the temperature interval between 300 K and T_C, which is of the order of 10⁻³. Using special disc-shaped samples field dependencies of magnetostriction in parallel and perpendicular directions of the applied magnetic field were obtained by direct measurement. Subsequently, saturation magnetostriction and volume magnetostriction as well as forced magnetostriction were computed. Saturation magnetostriction λ_S increases with increasing Co/Fe ratio from 0 up to 15 and from 0 up to 17 ppm for both alloy systems, respectively, depending both on the Co/Fe ratio and on the shift of T_C with composition. After attaining the maximal value and further increase of the Co/Fe ratio the saturation magnetostriction decreases. Both alloy systems with ratio Co/Fe=0 exhibit T_C near room temperature and the system passes into paramagnetic state. T_C for higher Co/Fe ratios approaches the glass transition region. In paramagnetic state the field dependencies of magnetostriction are practically linear functions of applied field and approach saturation only for high-field values.     

用于光码分多址系统的一种3—D地址码

在构造2—D码的基础上,提出并构造了一种用于OCDMA系统的新的空域／频域／时域     

Analysis of (π K<Superscript>+</Superscript>) and (K<Superscript>-</Superscript>, K<Superscript>+</Superscript>) hypernuclear production spectra in distorted-wave impulse approximation

We study the hyperon-nucleus potential with distorted-wave impulse wave approximation (DWIA) using the Green's function method. In order to include the nucleon and hyperon potential effects in Fermi averaging, we introduce the local optimal momentum approximation of target nucleons. We can describe the quasi-free Λ , Σ and Ξ production spectra in a better way than in the standard Fermi-averaged t -matrix treatments.     

High-frequency response of nanostructured magnetic materials

This paper reports a brief overview on recent developments regarding the high-frequency response in the GHz range of nanostructured magnetic materials. Emphasis is placed on the linear regime in the frequency domain characterized by the dynamic susceptibility spectrum. Some modeling tools and experimental probes allowing determination of the dynamic susceptibility spectrum are first rapidly reviewed and their respective advantages and disadvantages are discussed. Next, some illustrative examples of the high-frequency response of nanopatterned materials based on recent works are presented. The role played by the shape of the element on the characteristics of excitation spectrum is underlined. Lastly, some prospects are proposed and promising trends are highlighted.     

Determination of anisotropy constants of protein encapsulated iron oxide nanoparticles by electron magnetic resonance

Angle-dependent electron magnetic resonance was performed on 4.9, 8.0, and 19 nm iron oxide nanoparticles encapsulated within protein capsids and suspended in water. Measurements were taken at liquid nitrogen temperature after cooling in a 1 T field to partially align the particles. The angle dependence of the shifts in the resonance field for the iron oxide nanoparticles (synthesized within Listeria-Dps, horse spleen ferritin, and cowpea chlorotic mottle virus) all show evidence of a uniaxial anisotropy. Using a Boltzmann distribution for the particles’ easy-axis direction, we are able to use the resonance field shifts to extract a value for the anisotropy energy, showing that the anisotropy energy density increases with decreasing particle size. This suggests that surface anisotropy plays a significant role in magnetic nanoparticles of this size.     

Permeability enhancement of soft magnetic films through metamaterial structures

The present article proposes a structure consisting of a single magnetic film enclosed in a metamaterial. This planar structure can be manufactured using conventional deposition and patterning techniques commonly utilized in the silicon industry. One example of such a structure was manufactured, and its permeability was measured in a wide frequency range and compared to the permeability of its core. Theoretical investigations of this structure were performed in order to establish its permeability as a function of the frequency, and an excellent agreement between the predicted and measured values was observed. Parametrical studies revealed that the metafilm exhibited two resonances; one below the gyromagnetic resonance frequency of the magnetic core, and one at a much higher frequency. Metafilms are attractive negative permeability materials since they exhibit large negative permeability levels within a wide frequency range, and since they are readily adjustable. In this respect, they combine the advantages of metamaterials and of their magnetic cores.     

The Friedberg–Lee symmetry and minimal seesaw model

The Friedberg–Lee (FL) symmetry is generated by a transformation of a fermionic field q to q+ξz. This symmetry puts very restrictive constraints on allowed terms in a Lagrangian. Applying this symmetry to N fermionic fields, we find that the number of independent fields is reduced to N−1 if the fields have gauge interaction or the transformation is a local one. Using this property, we find that a seesaw model originally with three generations of left- and right-handed neutrinos, with the left-handed neutrinos unaffected but the right-handed neutrinos transformed under the local FL translation, is reduced to an effective theory of minimal seesaw which has only two right-handed neutrinos. The symmetry predicts that one of the light neutrino masses must be zero.     

Preparation and Compatibility of EVM/TPU Blend

The preparation of EVM (ethylene‐vinyl acetate copolymer rubber)/TPU (thermoplastic polyurethane) blends with various ratios and their compatibility were investigated. The influence of mixing technology, filler type and content, the VA content in EVM (40 and 70 wt.%) and the addition of compatibilizers on the mechanical properties and the compatibility of the EVM/TPU blends were systematically studied.

The test results showed that in preparation of the blend, fillers should be added to the blend to improve the processability and that among the fillers used, silica showed the best reinforcing effect on the blends. The best parameters for blending EVM and TPU in a HAAKE rheometer was: mixing temperature 160°C, rotor speed 45 rpm and mixing time 15 min. The test results also showed that the compatibility of EVM 700 (VA=70%) with TPU was better than that of EVM400 (VA=40%). The addition of a compatibilizer EVM‐g‐MAH and EVM‐g‐FME improved the processability of the blends. The addition of EVM‐g‐MAH also improved the compatibility of EVM 700/TPU blend; both the mechanical properties and hot‐air aging properties of the blends were improved. However, the addition of EVM‐g‐FME did not improve the compatibility of EVM/TPU blends.     

Fluid friction in incompressible laminar convection: Reynolds' analogy revisited for variable fluid properties

The Reynolds' analogy between the Stanton number (St) and the skin friction coefficient (c_f) is popularly believed to hold when St increases with increasing c_f, for simple situations. In this investigation, the validity of Reynolds' analogy between St and c_f for micro-convection of liquids with variations in fluid properties is re-examined. It is found that the Sieder-Tate's property-ratio method for obtaining Nusselt number corrections is theoretically based on the validity of Reynolds' analogy. The inverse dependence of Reynolds number and skin friction coefficient is the basis for validity of the Reynolds' analogy, in convective flows with fluid property variations. This leads to the unexpected outcome that Reynolds' analogy now results in St increasing with decreasing c_f. These results and their analyses indicate that the validity of Reynolds' analogy is based on deeper foundations, and the well-known validity criterion is a special case.     

Influence of microstructures on exchange bias behaviors of La0.7Sr0.3MnO3/La0.33Ca0.67MnO3 bilayers

Ferromagnetic La_0.7Sr_0.3MnO₃ (LSMO) and antiferromagnetic La_0.33Ca_0.67MnO₃ (LCMO) layers were grown on SrTiO₃ (STO) substrates by the pulsed laser deposition technique. LSMO films had rougher surfaces and larger grain sizes than LCMO films. Fully strained bilayers, in which each layer was as thin as 10 nm, were prepared by changing their stacking sequences, i.e. LSMO/LCMO/STO and LCMO/LSMO/STO. The former had higher T_C (350 K) than the latter (300 K), and exchange bias effects were only observed in the former bilayers. This revealed that microstructures could play an important role in the transport and magnetic properties of manganese oxide thin films.     

New properties of magnon density in uniaxial anisotropic ferromagnet on the background of spin wave

The N-soliton solutions of magnetization in uniaxial anisotropic ferromagnet on the background of spin wave are presented by using the effective Darboux transformation method. With the analytical solutions new properties of magnon density is studied in detail. On the ground state background the magnon density is constant for the spin wave solution and the magnetic soliton, respectively. However, on the spin wave background the magnon density possesses of temporal or spatial periodic oscillation. Moreover, the soliton solution possess the breather character in its propagation along the ferromagnet. These results show that during soliton propagation a periodic magnon exchange occurs between the magnetic soliton and the spin wave background.     

Magnetic vortex driven by non-uniform injection of spin-polarized current in nano-scale spin valves

We demonstrate that a current pulse of a non-uniform spin-polarized current density in a nanomagnet can drive, apart from magnetization reversal a static magnetic vortex. This vortex configuration can be achieved in low shape anisotropy spin valves of elliptical cross-sectional area. These non-uniform configurations exist also in presence of either ion mill damages below the nano-aperture or thermal effects at low temperature. We performed a numerical experiment of spin-torque driven ferromagnetic resonance in a magnetic vortex configuration, our results predict a frequency response with a few maxima and minima related to small oscillation of the vortex state around its equilibrium configuration.