Nonlinear vibrations and time delay control of an extensible slowly rotating beam

Nonlinear Dynamics - This paper investigates the time-varying formation tracking (TVFT) problem of multiple heterogeneous Euler–Lagrange agents (MHELAs) with predefined-time convergence...     

Magnetorheological damping and semi-active control of an autoparametric vibration absorber

A numerical study of an application of magnetorheological (MR) damper for semi-active control is presented in this paper. The damper is mounted in the suspension of a Duffing oscillator with an attached pendulum. The MR damper with properties modelled by a hysteretic loop, is applied in order to control of the system response. Two methods for the dynamics control in the closed-loop algorithm based on the amplitude and velocity of the pendulum and the impulse on–off activation of MR damper are proposed. These concepts allow the system maintaining on a desirable attractor or, if necessary, to change a position from one attractor to another. Additionally, the detailed bifurcation analysis of the influence of MR damping on the number of periodic solutions and their stability is shown by continuation method. The influence of MR damping on the chaotic behavior is studied, as well.     

Nucleation of diamond powder particles in an RF methane plasma

The author examined the structure of powder particles obtained in the gas phase by decomposition of methane in an RF electric field. The powders are not nucleated on the substrates. They are formed when the process duration is long enough (i.e. dozens of minutes) at a large flow of methane gas. By means of TEM it was found that the powder obtained consisted of superfine crystallites of a diamond structure. The author presumes that the powders were formed in the gas phase. It seems that superfine diamond crystallites present in the powder particles may also have formed directly in the gas phase since the growth conditions are suitable for sp³ electron hybridization, and the Laplace pressure (the surface energy effect) is of the order GPa, especially in crystallites of a nanometer size.     

A collecting and analysing system for the determination of chlorinated hydrocarbons in working place atmospheres

Conclusion The method allows to collect and analyse a wide range of chlorinated hydrocarbons in longtime measurements with good results. It works with the gaseous chloromethane (b. p. –23.8°C) as well as with the high-boiling hexachloro-1,3-butadiene (b.p. 215°C) and the reactive 1 -chloro-2,3-epoxy-propane. If the concentration of volatile compounds is very high it may be necessary to shorten the sampling time in order to prevent overloading, but in general sampling during a full shift of 8 h is possible.

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Sammel- und Analysensystem zur Bestimmung von CKW in der Luft am Arbeitsplatz

     

Nanocrystalline Diamond Coatings

Carbon—in the form of diamond coatings (nanocrystalline diamond—NCD) on suitable substrates—has attractive properties for biomedical applications. The excellent chemical inertness of NCD films makes them a promising material for medical implants, cardiovascular surgery and for coating of certain components of artificial heart valves.

The medical applications of carbon films impose some special requirements on their quality, purity, phase content and the state of the surface. Of particular importance is the smoothness of the surface and good adhesion of the coatings to the substrate. We have investigated carbon films which were synthesized by Radio Frequency Plasma Chemical Vapour Deposition (RF–PCVD).

The specimens obtained have been tested to show their structure and their biological, mechanical and chemical resistance. Additional investigations of the NCD films were carried out by micro-X-ray spectroscopy, Raman spectroscopy, AFM, Auger spectroscopy, corrosion tests, breakdown tests and clinical investigations. Nanocrystalline diamond (NCD) layers obtained by a new method of RF dense plasma CVD onto AISI-316L steel used in surgery were investigated to determine their suitability as biomaterials.     

Time delay Duffing’s systems: chaos and chatter control

The effect of a delay feedback control (DFC), realized by displacement in the Duffing oscillator, for parameters which generate strange chaotic Ueda attractor is investigated in this paper. First, the classical Duffing system without time delay is analysed to find stable and especially unstable periodic orbits which can be stabilized by means of displacement delay feedback. The periodic orbits are found with help of the continuation method using the AUTO97 software. Next, the DFC is introduced with a time delay and a feedback gain parameters. The proper time delay and feedback gain are found in order to destroy the chaotic attractor and to stabilize the periodic orbit. Finally, chatter generated by time delay component is suppressed with help of an external excitation.     

Dynamics of a laminated composite beam with delamination and inclusions

In this work numerical and experimental study of the dynamic behaviour of a composite laminated beam having delamination is presented. The model of delamination takes into account a contact interaction between sublaminates including normal forces, shear forces and additional damping. In order to verify the model special samples of multilayered beams have been manufactured. Small parts of adjacent layers have been cut and replaced by inclusions from different materials modelling delamination. The mechanical properties of the inclusions have been considered during the numerical calculations. The beams were subjected to a short pulse loading and then their response was registered. The results from the numerical simulation were in a good agreement with the experimental results. The significance of the additional damping due to delamination on the response of the beam was confirmed numerically and experimentally.     

Investigation of a new method to control thin-film growth

Results of investigations of a possible application of RHEED azimuthal plots of characterize in situ epitaxially grown thin films are described. Dynamically calculated and measured azimuthal plots for Si(111) are compared. A set of azimuthal plots experimentally collected at different stages of preparation of a Si/YSi_2-x/Si(111)-7×7 layered structure are presented.