Converting harmonic oscillations into chaos

A new simple model of a system with chaotic dynamics, based on the equations of bistable systems, is considered. The possibility of converting harmonic signals into chaotic oscillations, which represent intermittent irregular and switching quasi-regular motions, is demonstrated by numerical methods. The mechanism of chaotization is analyzed using the results of numerical calculations.     

Influence of lead on the wear resistance of cast composites of the Fe-Cr-Cu-Ti-C system in sliding friction

The positive influence of lead (2.5%) on the original structure of a cast composite of the Fe-Cr-Cu-C-Ti system, its wear rate, friction coefficient, and the formation of secondary structures is established under the conditions of dry friction and friction with boundary lubrication. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 6, pp. 73–80, November–December, 2006.     

A controllable chaotic system based on inductively coupled bistable oscillators

A mathematical model of a new controllable autooscilatory chaotic system based on inductively coupled Chua’s oscillators is described. Numerical simulations show that, using a chaotizing feedback algorithm, chaotic oscillations in this system can be excited in regimes where only regular oscillations are generated otherwise.     

Bulk micromachining of silicon in TMAH-based etchants for aluminum passivation and smooth surface

The fabrication of silicon based micromechanical sensors often requires bulk silicon etching after aluminum metallization. All wet silicon etchants including ordinary undoped tetramethyl ammonium hydroxide (TMAH)-water solution attack the overlaying aluminum metal interconnect during the anisotropic etching of (100) silicon. This paper presents a TMAH-water based etching recipe to achieve high silicon etch rate, a smooth etched surface and almost total protection of the exposed aluminum metallization. The etch rate measurements of (100) silicon, silicon dioxide and aluminum along with the morphology studies of etched surfaces are performed on both n-type and p-type silicon wafers at different concentrations (2, 5, 10 and 15%) for undoped TMAH treated at various temperatures as well as for TMAH solution doped separately and simultaneously with silicic acid and ammonium peroxodisulphate (AP). It is established through a detailed study that 5% TMAH-water solution dual doped with 38 gm/l silicic acid and 7 gm/l AP yields a reasonably high (100) silicon etch rate of 70 μm/h at 80 °C, very small etch rates of SiO₂ and pure aluminum (around 80 Å/h and 50 Å/h, respectively), and a smooth surface (±7 nm) at a bath temperature of 80 °C. The etchant has been successfully used for fabricating several MEMS structures like piezoresistive accelerometer, vaporizing liquid micro-thruster and flow sensor. In all cases, the bulk micromachining is carried out after the formation of aluminum interconnects which is found to remain unaffected during the prolonged etching process at 80 °C. The TMAH based etchant may be attractive in industry due to its compatibility with standard CMOS process.     

Friction and Thermal Effects of Engineering Plastics Sliding Against Steel and DLN-Coated Counterfaces

Polymers are increasingly used in tribological applications, because of their self-lubricating ability, corrosion resistance and chemical compatibility. However, their performance depends strongly on the parameters of the total tribological system. Not only polymer characteristics, but also counterface properties become important because of their influence on friction and wear, on surface energy and on the thermal conductivity of the total system. Applying a Diamond-Like Nanocomposite (DLN) coating on a steel counterface can improve the tribological behaviour of the sliding couple under certain conditions. In the case of metal sliding against DLN, the high hardness and the wear resistance of the coating is advantageous for better tribological properties. However, for polymers sliding against DLN, the lower thermal conductivity of the DLN coating compared with a steel mating surface dominates friction and wear. In case of polyamides this results in worse tribological performance in contact with the DLN coating, because of polymer melting. In the case of more rigid polymers, such as, e.g., POM-H and PETP, lower coefficients of friction lead to lower frictional heat generation. In these cases, the thermal characteristics of the counterface are less important and the lower surface energy of the DLN coating is favourable for decreased adhesion between the polymer and the coating and consequently better tribological properties.     

Multimode self-sustained oscillatory system with additional autoparametric feedback

A new mathematical model of a delayed self-sustained oscillatory system with additional feedback is considered; this feedback provides autoparametric self-action in the system. Results of numerical analysis of the proposed model are presented. It is shown that, if autoparametric self-action is used, the chaotization of oscillations becomes more developed and is realized even if just regular oscillations are excited without additional feedback.     

Thermodynamics of carbon dioxide hydrate formation in media with broad pore-size distributions

Equilibrium pressures for the dissociation of carbon dioxide hydrates confined in silica gel pores of nominal radii 7.5, 5.0, and 3.0 nm were measured over a wide temperature range and were observed to be higher than those for bulk carbon dioxide hydrate. Models that have been previously reported in the literature are used to determine the pore radius involved in each equilibrium associated with these data, exactly reproducing the experimental equilibrium pressure. Based on these models, pore volume distributions are reconstructed and compared to those obtained from nitrogen desorption isotherms. This comparison indicates that in the nominal 7.5 nm pores the hydrate formed nearly uniformly in the available pores, while in the nominal 5.0 and 3.0 nm pores it did not.     

Characterization of laser and laser/thermal annealed semiconducting iron silicide thin films

-FeSi₂ is an important semiconducting silicide which is being studied extensively. In this paper, we report our results of the effect of laser and laser-thermal annealing on the properties of -FeSi₂. 5N purity Fe was deposited on Si substrate and was subsequently irradiated by CW and pulsed laser separately followed by thermal annealing to reduce the laser induced damage. The samples were then characterized by sheet resistance, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), optical reflectance and absorption studies. Lastly, -FeSi₂/n-Si heterojunctions were fabricated and the effect of laser treatment on the junction ideality factor was investigated. All these characterizations indicated the formation of good quality -FeSi₂, particularly after pulsed laser followed by thermal treatment.     

Multimode self-oscillating systems with a filter in a delayed feedback circuit

A chaotic self-oscillating system based on a delayed oscillator containing a filter in the feedback loop is considered. Results of the numerical analysis of equations describing such an oscillator are presented for symmetric and asymmetric amplitude characteristics enabling variation in their nonlinearity within wide limits. The mechanism of transition to chaos is considered. A two-stage delayed oscillator containing a filter between partial amplifiers is studied.     

Controlled oscillations in an autostochastic system

Processes in a nonautonomous autostochastic system possessing an attractor of the Chen type were analyzed by numerical methods. The system was described by a set of equations for coupled oscillators with inertia. It is demonstrated that autooscillations can be controlled when a regular signal acts unidirectionally upon chaotic oscillations or, vice versa, when chaotic oscillations act upon the regular ones.