Influence of laser pulse shape both on temperature profile and hardened layer depth

This paper presents a mathematical modelling and numerical calculations of heat conduction problems where laser generated heat is assumed as a surface heat source. Also the effect of a laser time structure on a hardened layer depth is examined. Temperature profiles for different laser pulse shapes are determined from the solution of a linear one-dimensional heat conduction equation for semi-infinite medium and discussed in terms of the parameters evolution such as dimensionless: temperature, heat flux, hardening depth, laser impulse duration and increasing time of triangular pulse shape.     

Adiabatic divergence of the chaotic layer width and acceleration of chaotic and noise-induced transport

We show that, in spatially periodic Hamiltonian systems driven by a time-periodic coordinate-independent (AC) force, the upper energy of the chaotic layer grows unlimitedly as the frequency of the force goes to zero. This remarkable effect is absent in any other physically significant systems. It gives rise to the divergence of the rate of the spatial chaotic transport. We also generalize this phenomenon for the presence of a weak noise and weak dissipation. We demonstrate for the latter case that the adiabatic AC force may greatly accelerate the spatial diffusion and the reset rate at a given threshold.     

Influence of bath composition and deposition parameters on nanostructure and thermal stability of gold

Nanocrystalline gold is electrodeposited from a stable nontoxic bath, in which Au⁺ is stabilized by complex formation with 3-mercapto-1-propanesulfonic acid sodium salt. Nanoscaling is achieved by pulse techniques. The crystallite size is strongly dependent on physical and chemical process parameters, such as pulse duration, current density, bath temperature, type, and amount of additives; especially, we observe a decrease of the crystallite size down to 16 nm by the proper choice of current density and temperature, and down to 7 nm by the use of additives. The thermal stability of nanocrystalline gold is investigated by in situ high-temperature X-ray diffraction; nanogold exhibits a thermal stability up to 673 K. An activation energy of 37 kJ mol⁻¹ is determined for the grain-growth kinetics.Paper presented at the “Jahrestagung der Fachgruppe Angewandte Electrochemie der Gesellschaft Deutscher Chemiker, Düsseldorf, 11.–14.06.2005”     

Exact formulae for determination of the mean temperature and wear during braking

This paper deals with the one-dimensional transient heat conductivity contact problem of a sliding two semi-spaces, which induces effects of friction, heat generation and water during braking. In the present temperature analysis the capacity of the frictional source on the contact plane dependent on the time of braking. The problem solved exactly using the Laplace transform technique. Numerical results for the temperature are obtained for the different values of the input parameter, which characterise the duration of the increase of the contact pressure during braking from zero to the maximum value. An analytical formulae for the abrasive wear of the contact plane is obtained in the assumption, that the wear coefficient is the linear function of the contact temperature. Received on 8 September 1998     

The influence of distribution intensity form of heat flux on the temperature by the local quasi-stationary heating on external surface of the ring

The solution of the mixed quasi-stationary heat conduction problem for the ring has been obtained by using a finite Fourier transformation. The heating on the external side surface of the ring due to any locally distributed heat flux, as well as the convective cooling from internal side surface and from the end faces are considered. It has been proved that for some special geometrical and thermo-physical parameters of problem the received solution agrees with well known studies. The influence of some distribution intensity form of heat flux on the maximum temperature was studied.     

Distribution of the friction heat between two stationary pins and a rotating disc

A closed-form model for the computation of heat fluxes distribution between two motionless cylindrical pins and a fast rotating disc is investigated. Based on a finite Fourier transform technique and an asymptotic analysis, a series solution for the disc surface temperature is obtained. The solution for the pin is trivial. By matching the average temperatures over the contact areas the coefficients of the heat distribution between a pin and a disc are found. It is demonstrated that the present analysis covers the previously known case of one pin as well as new results are obtained. Received on 4 November 1996     

Divergence of the chaotic layer width and strong acceleration of the spatial chaotic transport in periodic systems driven by an adiabatic ac force

We show for the first time that a weak perturbation in a Hamiltonian system may lead to an arbitrarily wide chaotic layer and fast chaotic transport. This generic effect occurs in any spatially periodic Hamiltonian system subject to a sufficiently slow ac force. We explain it and develop an explicit theory for the layer width, verified in simulations. Chaotic spatial transport as well as applications to the diffusion of particles on surfaces, threshold devices, and others are discussed.     

Drastic facilitation of the onset of global chaos

We show that the onset of global chaos in a time periodically perturbed Hamiltonian system may occur at unusually small magnitudes of perturbation if the unperturbed system possesses more than one separatrix. The relevant scenario is the combination of the overlap in the phase space between resonances of the same order and their overlap in energy with chaotic layers associated with separatrices of the unperturbed system. We develop the asymptotic theory and verify it in simulations.