Quasiperiodic forced vibrations of a beam interacting with a nonlinear spring

Summary A simply supported beam with fixed ends and an attached strongly nonlinear spring is considered. As the forced bending vibrations of the beam have moderate amplitudes, the stretching force is a nonlinear function of the deflection. The vibrations are presented as a series with respect to the modes of the beam without attachment. Applying the Bubnov-Galerkin procedure, an infinite system of ordinary differential equations is derived. Using the multiple scales method, the quasiperiodic vibrations in the region of the combination resonance are analyzed in the paper. The system vibrations, when the nonlinear spring is attached in different points, are analyzed. Applicability of the nonlinear spring for mitigation of a combination resonance is discussed.     

STW resonator with organo-functionalized metallic nanoparticle film for vapor sensing

A 1 GHz surface transverse wave resonator on 36° Y-cut quartz plate coated with organothiol-functionalized gold nanoparticle film has been studied as a chemical gas sensor. Considerable sensitivity of the resonant frequency to vapors of ethanol, methanol, chloroform, and acetic acid has been found. Owing to the high short-term stability of the oscillator built, the detection limit is in the low ppm range. The results qualitatively confirm previous results on the same film type obtained by conductivity measurements. In the present case, the conductivity effect resulting from variable separation of nanoparticles is accompanied with surface-attached mass of the absorbed gas. The film matrix exhibits considerable capacity to absorb large amounts of molecules at high gas concentrations.     

Dynamics of shallow shells with geometrical nonlinearity interacting with fluid

The vibrations of the shallow shell with geometrical nonlinearity submerged in a fluid are considered. Interaction of the shell with a fluid is described by linear hypersingular integral equation, which is solved by the boundary element method. The vibrations of the shell are described by the nonlinear finite-degree-of-freedom system. The vibrations are studied by the Shaw–Pierre nonlinear modes.     

Bifurcations of parametric oscillations of beams with three equilibria

Summary. Nonlinear curvature and nonlinear inertia are taken into account in the beam model. The constant part of the parametric force is proposed to be greater than the buckling one, therefore the beam has three equilibria. One-mode approximation of the beam oscillations is used. Bifurcations of the beam oscillations are analyzed by Melnikov's method. Moreover, beam oscillations close to the stable equilibriums are studied by the multiple scales method.     

Thermal stability and electrical conductivity of Ge20As14(Se x S1-x )52I14 glasses

Investigations of five-component glasses of the Ge₂₀As₁₄(Se _x S_1-x )₅₂I₁₄ type are reviewed for the temperature interval from room temperature to 1273 K. Thermogravimetric analyses enable the determination of the mechanism of thermal decomposition, as well as the range of amorphous phase existence. Electroconductivity was followed by the method of four points under a direct current regime. Semiconductive character was evaluated, as well as the energies of the corresponding energy gaps. The effect of sulphur (i.e. selen) concentrations on the electrical characteristics was also discussed, along with some of the elements significant for determining the mechanisms of electrical conductivity. Results on optical energy gaps were also redetermined.     

A coupling-of-modes approach to the analysis of STW devices

The dispersion characteristics of surface transverse waves (STW) on 36° rotated Y-cut quartz have been analyzed numerically. A closed form dispersion relation has been derived and introduced in the equations of the coupling-of-modes (COM) theory to account for the variation of energy trapping with frequency. The transmission and reflection coefficients at the finger edges have been determined from the stopband characteristics. Through the introduction of an electromechanical coupling which varies linearly with the electrode mass loading, quantitative agreement with experimental results on two different types of two-port STW resonators has been achieved, and characteristic features have been explained     

Aorto-enteric fistula as a rare manifestation of rupture of an abdominal aortic aneurysm--case report

Aortoenteric fistula represents a communication between aortic and duodenal lumen. It is a very rare complication of aortic aneurysmal disease as well as aortic prosthetic surgery. There are only few surgeons who have seen more than one case of aortoenteric fistula. At the Institute of Surgery one case of aortoenteric fistula was treated. It was well diagnosed at the Institute for Internal Medicine, and then presented to the vascular surgeon who operated immediately. The whole diagnostic and therapeutic procedure was well done, but stenosing carcinoma of ascendent colon was found during the operation. Resection were done leading to the dehiscence of bowel anastomosis and fatal outcome for the patient. This case is instructive in a diagnostic and surgical manner.     

The formation of amorphous and crystalline condensates from the vapour phase

An electron microprobe technique is described for determining the thickness of SiO₂ and Si₃N₄ in wafers and devices. The technique is based on the measurement of oxygen and silicon X-ray intensities at 2.5 kV and 10 kV through the nitride overlay. At the lower accelerating voltage, both intensities decrease with increasing nitride thickness owing to absorption and silicon distribution in depth. The SiO₂ thickness, however, is obtained by measuring the oxygen X-ray intensity at the higher voltage (10 kV), because at this voltage the oxygen intensity is not dependent on the nitride thickness.Empirical relationships expressing Si₃N₄ thickness in terms of Si and O X-ray intensities and SiO₂ thickness are derived.     

Structural Optimization of Waffle Shell Sections in Launch Vehicles

Strength of Materials - A new approach to optimizing the waffle shell sections of the launch vehicle is proposed. The waffle cantilever cylindrical shells are considered under the action of the...