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1.
A review is given on theoretical studies of roles of the spindegree of freedom in transport through a quantum dot with thetotal spin S for N electrons and for N+1electrons in the ground state. The conductance and the phasecoherency are expressed in terms of universal functions ofS, , and the spin splitting at small tunnelingrates in the absence of spin-orbit interactions and are shownto exhibit the correlation between tunnelings of electronswith opposite spins and the dephasing due to spin flips.  相似文献   

2.
In the present work, the thermal behavior of a thin slab, under the effect of a fluctuating volumetric thermal disturbance described by the dual-phase-lag heat conduction model is investigated. It is found that the use of the dual-phase-lag heat conduction model is essential at large frequencies of the volumetric disturbance. It is found that the hyperbolic wave model deviates from the diffusion model when and the dual-phase-lag model deviates from the diffusion model when . where is the angular velocity of the fluctuating wall temperature, is the phase-lag in the heat flux vector and is the phase-lag in the temperature gradient vector.  相似文献   

3.
4.
This paper studies the phenomenon of spontaneous boiling-up of polymeric liquids on heating at rates up to 107 K·s–1. A model of the thermal equation of state for (polymer + monomer) systems and a procedure for determination of the spontaneous boiling-up temperature T* for polymeric liquids, taking decomposition into account, are proposed. The experimental data on T * for a number of polymer melts are compared with results calculated from the model.  相似文献   

5.
The validity of using the microscopic hyperbolic heat conduction model under a harmonic fluctuating boundary heating source is investigated. It is found that using the microscopic hyperbolic heat conduction model is essential when . The phase shift between the electron-gas and solid-lattice temperatures is found to be . This phase shift reaches a fixed value of 1.5708 rad at very large values of . It is found that the use of the microscopic hyperbolic heat conduction model is essential when ¯>1×109 rads–1 for most metallic layers independent of their thickness.  相似文献   

6.
Two types of positive temperature coefficient of resistance (PTCR) ceramics with relatively low room-temperature resistivity were prepared using the four-component system (Ba, Sr, Ca, Pb)TiO3 with lanthanum oxide (La2O3) as the donor dopant and boron nitride (BN) as the sintering aid. The first type of materials was sintered at 1080 °C for 2 h. It has a Curie point , a room-temperature resistivity of 58 cm and a resistivity jump of around . For the second type of materials that were sintered at 1100 °C for 20 min, , and . These PTCR ceramics are considered to be suitable materials for fabricating multilayer PTCR devices by the co-firing process. Factors associated with the composition that influence the PTCR property of the materials are discussed.  相似文献   

7.
The electrical properties and thermal stability of (hereafter referred to as ) Schottky contacts to n-GaN as a function of the Ge concentration and annealing temperature are studied. Upon rapid thermal annealing the /n-GaN Schottky diode is formed at 300 °C and is stable up to 650 °C. At 700 °C the agglomeration occurs in the films. For the Cu-25 at % Ge films the ideality factor, n, barrier height, , and flat band barrier height, , of the /n-GaN diodes are in the ranges of 1.22–1.36, 0.53–0.72 eV, and 0.65–0.97 eV, respectively, being decreased with the annealing temperature. Higher Ge concentration in the Cu-35 at % Ge films results in larger n, , and of /n-GaN Schottky diodes. The film is expected to be a suitable candidate for stable Schottky contacts to n-GaN at elevated temperatures.  相似文献   

8.
Perovskite phase formation and dielectric characteristics of ceramic system with addition of were investigated in order to examine the influence of . The ceramic system powders were synthesized via a B-site precursor route. Peculiar behaviors of frequency dispersion in dielectric constant spectra in the paraelectric region were observed due to increasing conductivity. Lattice parameters, dielectric maximum temperatures, and maximum dielectric constants increased with increasing content.  相似文献   

9.
In this work, an attempt is made to study system with x=0.0125, 0.025, 0.050, 0.075 and 0.1. It was shown that there is limited solid solubility (0.625 mol %) of or 1.25 mol % of in PZT(53/47). For higher levels of dopant, mainly two other extra second phases were detected. The first was a Zr-rich phase in which some and small amounts of was dissolved. The second one was a Pb solid solution composed of mainly PbO, and which was initially also seen in calcined samples. The formation of Zr-rich phase is thought possibly to originate due to the sublimation of Pb from source during the sintering process. For higher x values, a structural shift towards Ti-rich region of PZT's phase diagram is seen. All piezoelectric parameters of the doped samples such as , are seen to decline sharply compared to that of undoped samples. Increasing the level of dopant gave rise to the increase of conductivity and dielectric loss of sintered samples. The formation of non-ferroelectric extra phases, and the Zr/Ti change of the main formed phase is believed to be responsible for this behavior.  相似文献   

10.
The microwave dielectric properties of (AMT) ceramics and the design of small coplanar waveguide fed antenna (CPWFA) have been investigated. ( and ( have orthorhombic and tetragonal structure, respectively. As ( concentration increased, AMT ceramics transformed into the tetragonal structure. Specimens having tetragonal single phase could be obtained above x=0.6. As ( concentration increased, the grain size, dielectric constant and quality factor (Q) significantly increased and the temperature coefficient of resonant frequency changed from negative to positive. The of was realized at x=0.65 and the Q · f O value and for this composition were 112 470 GHz and 26.1, respectively. Newly developed dielectric materials were used for 1.5 GHz band CPWFA design and fabrication. The size of the CPWFA can be reduced by using high dielectric constant AMT ceramics, insetting slits into the patch, and fabricating CPW feed line in the ground plane. The slits play a role in not only lowering a center frequency but also fine tuning for the proposed antenna together with the open stub of CPW feed line. The CPWFA with slits has a lower center frequency than the conventional CPWFA, which suggests that the antenna size can be reduced by as much as 16.3%. The structure simulations of the CPWFAs have been performed to obtain impedance matching and to investigate the effects of slits. Experimental results of the fabricated device were in good agreement with the simulation.  相似文献   

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