The limiting equilibrium of shallow shells reinforced by ribs

International Applied Mechanics -     

Stability and Fracture of Plates with a Central and an Edge Crack under Tension

We report on the results of experimental study into the local buckling and fracture of plates with a central and an edge crack under tension. Analyses are made of the buckling mechanisms, the associated critical stresses, and the effect of plate bulging on their strength.     

Solution of two-dimensional problems of unsteady heavy-fluid seepage into unsaturated porous soil on the basis of an instantaneous saturation model

Two-dimensional problems of the unsteady seepage of a heavy fluid into a uniform unsaturated porous soil from a single channel and from an infinite periodic system of identical channels are solved. The fluid level in the channel is a known function of timet, which simulates the propagation of the fluid along a furrow normal to the plane of the problem. Seepage into the soil, which occupies the space outside (mainly below) the channel, takes place under the influence of the force of gravity and begins at the momentt=0 after it is instantaneously filled with fluid. On the interval 0 <t < t₁ the height of the fluid in the channel is constant, and whent=t ₁ it falls instantaneously to some other level, also constant. This may be the zero level, which coincides with the bottom of the channel. The problem in which the fluid level in the channel rises is also considered.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 86–94, January–February, 1992.In conclusion the authors wish to thank V. A. Vostretsov for his assistance.     

Allowance for nonstationary heat and mass transfer in the propagation of small perturbations in a liquid with bubbles

The propagation of small perturbations in a liquid with vapor-gas bubbles is studied. Heat and mass transfer between the phases is taken into account on the basis of the exact equations of heat conduction and diffusion. The aim of the present investigation is to make more precise the results of an earlier paper [1] of the author and verify the applicability of using fixed coefficients of heat and mass transfer for nonstationary heat and mass transfer between a pulsating bubble and the liquid.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 157–162, July–August, 1979.     

Vibrational distribution functions and relaxation rate in anharmonic-oscillator systems

Analytical expressions were derived for the vibrational distribution function in a system of anharmonic oscillators under conditions where the supply of vibrational energy considerably exceeded the equilibrium value. Distribution was found by considering the effect of vibrational-vibrational and vibrational-translational energy exchange, as well as spontaneous radiative transitions. Analytical expressions were also obtained for the relaxation rate of vibrational energy. It was shown that where there is a strong deviation from equilibrium this rate can significantly exceed the corresponding value for a model of harmonic oscillators and is determined by the probability of vibrational-vibrational exchange in the molecules.     

Forced nonlinear oscillations of a gas bubble in a large spherical flask (resonator) filled with a fluid

Radial oscillations of a gas bubble in a large spherical flask filled with a fluid are considered. We derive an equation of the change of the bubble radius by the known law of pressure variation at the boundary of the liquid volume (the law of motion of the piston) for a period of time during which, repeatedly reflected from the piston, the leading front of the reflected-from-the bubble perturbations reaches the bubble. For further calculations of the change of the bubble radius, recurrent relations which include the wave reflected from the bubble in the previous cycle and its subsequent reflection from the piston are obtained. Under harmonic action of the piston on the fluid-bubble system, a certain periodic regime with a package of bubble oscillations is established. Institute of Mechanics, Ural Scientific Center, Russian Academy of Sciences, Ufa 450000. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 5, pp. 77–87, September–October, 1998.     

Heteromolecular structures in aqueous solutions of dimethylformamide and tetrahydrofuran,according to molecular dynamics data

The complex dielectric permittivity of aqueous solutions of tetrahydrofuran and dimethylformamide in wide ranges of temperature (220–300 K) and pressure (0.1–12 MPa) is studied by means of molecular dynamics. The autocorrelation functions of the dipole moments of molecules are calculated. Dielectric permittivity spectra are obtained. The dielectric relaxation times are determined as functions of the tetrahydrofuran and dimethylformamide concentrations in the indicated binary mixtures. The dielectric relaxation frequency shifts toward low frequencies in the range of tetrahydrofuran and dimethylformamide concentrations x ≤ 0.5 molar fraction, due to the formation of heteromolecular structures with hydrogen bonds. This is confirmed by the negative values of the excess dielectric permittivities of binary solutions at x ～ 0.3–0.4 molar fraction.     

4-Methoxy-3-methylgoniothalamin from marine-derived fungi of the genus Penicillium

The new styrylpyrone derivative, viz. 4-methoxy-3-methylgoniothalamin (1), and the known compound sulochrin were isolated from the marine-derived fungi Penicillium glabrum and P. implicatum. The structure of compound 1 was determined by X-ray diffraction, 2D NMR spectroscopy, and high-resolution mass spectrometry. It was shown for the first time that sulochrin increases expression of the protein Hsp70.