Influence Of Thermal Excitation Research Articles

Nonlinear dynamic analysis of ring truss antenna equivalent to the cylindrical shell with thermal excitation

In this paper, the nonlinear dynamic analysis of the circular truss equivalent to the cylindrical shell under the influence of the thermal excitation and the damping coefficient are studied. The annular truss structure is equivalent to the cylindrical shell structure based on the previous equivalent process, and the nonlinear dynamic equations of the equivalent cylindrical shell considering the effect of thermal excitation are established by using the first-order shear deformation theory. The natural frequencies and modes of the equivalent cylindrical shell are analyzed by the finite element method, and the frequency ratio between modes is calculated. Considering the fixed boundary condition of the equivalent cylindrical shell in the generatrix direction, the torsional mode function and the bending mode function of the equivalent cylindrical shell are selected by the Chebyshev polynomial approximation method and are truncated by Galerkin method. Based on the nonlinear ordinary differential equations of two degrees of freedom, the amplitude-frequency responses, bifurcation, and chaotic characteristics of the system are analyzed. The results show that under the influence of thermal excitation, the motions of the system are complex, and when the excitation amplitude is large, the system appears chaotic motion. The damping coefficient limits the possibility of complex motions of the system. With the influence of the damping coefficient, the motion of the system tends to be stable.

Influence of thermal excitation on magnetization states and switching routes of magnetic multilayer rings

The low temperature magnetic switching behavior of micron scale NiFe/Cu/Co circular ring elements has been investigated using micromagnetic simulations and magnetoresistance (MR) measurements. The rings were patterned, so that two different contact configurations could be used to measure MR simultaneously. By comparing these measurements with the simulation results, the rings’ magnetization states and switching routes were determined at both 1.7 and 300 K. It was found that at 1.7 K the rings exhibited multiple switching routes and also showed more metastable states and broader transitions between states than was observed at 300 K. The rings’ behavior at low temperature is explained as the result of an increase in the strength of magnetocrystalline and magnetoelastic anisotropies combined with an absence of thermal excitation which would usually aid the nucleation and depinning of domain walls.

Relaxation-Induced Suppression of Vortex Disturbances in a Molecular Gas

The influence of thermal excitation on a finite-amplitude vortex disturbance in a shear flow of a molecular gas is studied in a model problem. The evolution of such vortex structures is typical of both the nonlinear stage of the laminar–turbulent transition and for developed turbulence. Since the excitation level was assumed to be comparatively low, full Navier–Stokes equations for a compressible heat-conducting gas were used in calculations; nonequilibrium was taken into account by the coefficient of bulk viscosity. As the bulk viscosity increases in the range of realistic values, the disturbance-energy damping rate in a weakly compressible flow increases approximately by 10%. The increase in the Mach number enhances the effect of disturbance suppression.

Resistivity due to Domain Wall Excitation in Thin Wires of Ferromagnetic Metals

We study the influence of thermal excitation of a domain wall (DW) on resistivity in thin wires of disordered ferromagnetic metals. The negative correction for local conductivity δσ due to the DW e...

Fragmentation, charge transfer and chemical reactions in C60+/C70+–SF6 collisions

Collisions of C60+ and C70+ with SF6 were investigated in a time of flight mass spectrometer and compared with the results of collisions with Ar and Xe. Reaction cross sections were determined as a function of the center of mass collision energy between 25 and 300 eV. The influence of thermal excitation on fragmentation was examined. The effects of additional vibrational degrees of freedom in the case of SF6 on the fragmentation cross sections are discussed. Charge transfer reactions producing C602+ or C702+ were observed only with SF6. Thermal electron emission from highly excited C60− was used for the formation of an intense neutral C60 beam with 1 keV kinetic energy which was used to investigate charge transfer in neutral C60+SF6 collisions. Reaction products CnF+, n=1–11, were found in SF6 collisions.

LEED structural analysis of Al(111)-K-( sqrt 3 x sqrt 3 )R30 degrees: Identification of stable and metastable adsorption sites.

A detailed low energy electron diffraction analysis has been performed to investigate the adsorption of potassium on Al(111) at 90 K and at 300 K. At each temperature a (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 )R30\ifmmode^\circ\else\textdegree\fi{} structure is formed, however, the adsorbate positions are different. For absorption at 90 K the adatoms occupy on-top sites and at 300 K they occupy substitutional sites, both geometries have hitherto been regarded as very unusual. An irreversible phase transition from the former to the latter stable structure occurs on warming to 300 K. The obtained interatomic distances and surface relaxations are discussed in terms of an interplay of the electrostatic repulsion between adatoms and substrate screening as well as coordination number. An approximate scheme for including the effect of anisotropic atomic motions under the influence of thermal excitation was applied. It is found that the R factors for the on-top site are significantly improved whereas no improvement is found for the substitutional site.

Anisotropic atomic motions in structural analysis by low energy electron diffraction.

The structure of the \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 R30\ifmmode^\circ\else\textdegree\fi{} overlayer formed by CO molecules adsorbed on a Ru(0001) was analyzed by low energy electron diffraction. Anisotropic atomic motions under the influence of thermal excitation were taken into account by adopting the concept of split positions. Apart from considerable improvement in the structural refinement this technique provides information about dynamic processes. In particular, the molecular axis of the CO molecules was found to be tilted on the average by (12\ifmmode\pm\else\textpm\fi{}3\ifmmode^\circ\else\textdegree\fi{} at 150 K, which is attributed to excitation of the bending mode vibration (i.e., frustrated translation).