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The mixed spin-2 and spin-5/2 Ising ferrimagnetic system with different anisotropies (DA/z｜J｜) for the spin-2 and (DB/z｜J｜) for the spin-5/2 is studied by the use of the mean-field theory based on the Bogoliubov inequality for the free energy. First, the ground state phase diagram of the system at zero temperature is obtained on the (DA/z｜J｜,DB/z｜J｜) plane. Topologically, different kinds of phase diagrams are achieved by changing the temperature and the values of the single ion anisotropies DA/z｜J｜ and DB/z｜J｜. Besides second-order transition lines, first order phase transition lines terminating at tricritical points, are found. The existence and dependence of a compensation temperature on single-ion anisotropies is also investigated.
The mixed spin-3/2 and spin-2 Ising ferrimagnetic system with
different single-ion anisotropies in the absence of an external magnetic field
is studied within the mean-field theory based on Bogoliubov inequality for the
Gibbs free energy. Second-order critical lines are obtained in the
temperature-anisotropy plane. Tricritical line separating second-order
and first-order lines is found. Finally, the existence and dependence of a
compensation points on single-ion anisotropies is also investigated for the
system. As a result, this mixed-spin model exhibits one, two or three compensation
temperature depending on the values of the anisotropies.
Hydrometallurgical technology offers a unique possibility for developing countries to exploit their mineral resources locally instead of shipping them as concentrates. Production plants may start on a small scale with small capital investment then increase productivity later when the economy permits without financial penalty. This is in contract to smelting operations which necessitates large scale production from the start with high capital investment that may not be available locally.
The magnetic properties of a mixed Ising ferrimagnetic system consisting of spin-3/2 and spin-2 with different single ion anisotropies and under the effect of an applied longitudinal magnetic field are investigated within the mean-field theory based on Bogoliubov inequality for the Gibbs free energy. The ground-state phase diagram is constructed. The thermal behaviours of magnetizations and magnetic susceptibilities are examined in detail. Finally, we find some interesting phenomena in these quantities, due to applied longitudinal magnetic field.
The choice of a wind turbine for a given site is a very significant operation. It is advised to make an in-depth study on the characteristics of the aerogenerator and the implantation site before any installation of a wind farm for choosing well the system best adapted to the energy needs. The objective of this study is to sensitize the users of the wind energy on the various problems involved in the aerogenerator installation on any site and to provide a decision-making aid to the judicious choice of the wind system best adapted. The idea is to estimate, for a selected implantation site, the energy production and the operating time of several wind systems. We can thus select the aerogenerator best adapted by making a compromise between a maximum recovery of energy and a high time of production. The influence height of the aerogenerator on energy profitability is also studied. We apply this step to the twenty six Tunisian synoptic sites by implantation scenarios of seven wind systems of various nominal speeds in function of the height.
A new design for an ultra-low power, low phase noise differential 10 GHz LC voltage-controlled oscillator (VCO) which is biased in the subthreshold regime, is presented in the 0.18 μm CMOS process, for the first time. The designed circuit topology is an NMOS only cross-coupled LC-tank VCO which has an extra symmetric centre tapped inductor between the source ends of the cross-coupled transistors. Using this inductor leads to an improvement of the phase noise of VCO about 3.5 dB. At the supply voltage of 0.46 V, the output phase noise is －107.8 dBc/Hz at 1 MHz offset frequency from the carrier frequency of 10.53 GHz, so that the dc power consumption is only 0.346 mW. Tuning range is between 10.53 GHz to 11.35 GHz which is 7.5% and the figure of merit is －193.8 dB, which this result shows that this is the first VCO design in the subthreshold regime at this frequency. This VCO can be used for multi-standard wireless LAN communication protocols 802.11a/b/g easily by a frequency division of 2 or 4 respectively.
Carbon Nano-Tube Field Effect Transistors (CNTFETS) are the competitor of the conventional MOSFET technology due to their higher current drive capability, ballistic transport, lesser power delay product, higher thermal stability, and so on. Based on these promising properties of CNTFETs, a CNTFET-based millimeter wave ring oscillator operating around 150 GHz and beyond is introduced here in 32 nm technology node. To prevent overestimation, the CNT interconnects between transistors are also included in simulation, which are assumed to be a single layer of ballistic metallic CNTs in parallel. For the sake of simplicity in RF design, the oscillator is based on CNTFET-based inverters. The inverters with DC gain of 87.5 dB are achieved by proper design with the non-loaded delay around 0.6 ps, which is at least one order of magnitude better than the same 32 nm MOSFET-based inverters. The oscillator’s average power consumption is as low as 40 μW with the fundamental harmonic amplitude of around –6.5 dB. These values are, based on our knowledge, for the first time reported in the literature in CNTFET-based oscillator designs. Also, on the average, the performance of the designed oscillator is 5 - 6 times better than MOSFET-based designs.