The Development of a Technique for Sensitizing Cells of Various Origins for Biotechnological Purposes

The functional activity stimulation of cell cultures was tested in MDBK cell culture, photobacteria AliivibriofischeriandHalobacteriumhalobium. Theaim of the investigation was to increase the ”yield” of the cells using an environmentallysafe stimulant and membrane-tropic agent that isalso safe for the experimenter. Ultrasonicwaves were used.Experimental ultrasonic exposure varied within the following limits: time from 1 to 300 sec, SATA-intensity of 0.01–2.0 W/cm2, generation frequency of 0.88 or 2.64 MHz, standing or traveling wave. The modulation frequency range was within 0.1–150 Hz. The devices used were: UST-1-01F, UST-5 and UST1.02C. The modulating generators were G3–112 and CP–110.Stimulation of MDBK cell growth was initiated by US-intensity of 0.03–0.05 W/cm2 , with an exposure of 5–30 sec.Exposure to ultrasound with an intensity of 0.2–0.4 W/cm2 (for 3 min) had a stimulating effect on bioluminescence and was associated with an increase in the growth rate ofA. fischeri. The findings indicated that 0.4 W/cm2ultrasonic intensity and modulation frequencies from 0.25 to 0.7 Hz can stimulate the growth of archaea.It was revealed that the maximum proliferation index in all cases of stimulant application was noted in cultures with minimal initial proliferative activity in the control.The authors expect thatthese results on the possibilities of acoustic continuous and modulated waves can be applied for biotechnological purposes to develop a new biotechnological method. Keywords: cell culture, ultrasound, proliferation, stimulation

Secondary Faraday waves in microgravity

Recent microgravity experiments have demonstrated that Faraday waves can arise in a secondary instability over the primary columnar patterns that develop after the frozen wave instability. While some numerical studies have investigated this phenomenon, theoretical analyses are only found in the works of Shevtsova et al. (2016) [1] and Lyubimova et al. (2019) [2]. Here, we extend these efforts by analysing the stability of a three-layer system, and derive the critical onset of Faraday waves, which appear via Hopf bifurcation. Numerical simulations — based on a model that reproduces the frozen wave mode with lowest wavenumber — are carried out to test this result and to analyse the character of the bifurcation. The predicted Hopf bifurcation is confirmed, which constitutes the first observation of modulated secondary Faraday waves. The abrupt growth of these modulated waves above onset indicates that the primary bifurcation is subcritical and is accompanied by a saddle-node bifurcation of periodic orbits that stabilises the (branch of) unstable solutions created in the subcritical Hopf bifurcation. Further above onset, these modulated waves are destroyed via a saddle-node heteroclinic bifurcation. Results for an N-layer configuration, which represents a more general frozen wave pattern, are also presented and compared with the three-layer case.

Effect of Crack Closure on Magnitude of Modulated Wave

Fatigue cracks generated by repeated loads cause structural failures. Such cracks grow continuously and at an increasing speed owing to the concentration of stresses near the crack tips. Therefore, the early detection of fatigue cracks is imperative in the field of structural-health monitoring for the safety of structures exposed to dynamic loading. In particular, the detection of those cracks subjected to compression is known as a challenging problem in the nondestructive inspection area. The nonlinear ultrasonic modulation technique is effective for the detection of microcracks smaller than the size of a wavelength because this technique uses the deformation of waves passing through the crack surfaces. However, the technique has not been thoroughly verified for detecting cracks subjected to external forces. In this study, nonlinear ultrasonic modulation tests are performed on two types of crack specimens under compressive forces. The results show that in fatigue-cracked specimens, the cracks can be detected using modulated waves even under strong compressions. With artificial cracks, buckling occurs at a relatively low compression, and the amounts of modulated waves rapidly increase due to the bending of the specimen before buckling failure takes place. In this study, the crack detection methodology under compression is proposed and experimentally verified. The proposed method might be beneficial to find cracks under compression in various structural components.

Detection of Micro-Cracks in Metals Using Modulation of PZT-Induced Lamb Waves

The ultrasonic modulation technique, developed by inspecting the nonlinearity from the interactions of crack surfaces, has been considered very effective in detecting fatigue cracks in the early stage of the crack development due to its high sensitivity. The wave modulation is the frequency shift of a wave passing through a crack and does not occur in intact specimens. Various parameters affect the modulation of the wave, but quantitative analysis for each variable has not been comprehensively conducted due to the complicated interaction of irregular crack surfaces. In this study, specimens with a constant crack width are manufactured, and the effects of various excitation parameters on modulated wave generation are analyzed. Based on the analysis, an effective crack detection algorithm is proposed and verified by applying the algorithm to fatigue cracks. For the quantitative analysis, tests are repeatedly conducted by varying parameters. As a result, the excitation intensity shows a strong linear relationship with the amount of modulated waves, and the increase of modulated wave is expected as crack length increases. However, the change in the dynamic characteristics of the specimen with the crack length is more dominant in the results. The excitation frequency is the most dominant variable to generate the modulated waves, but a direct correlation is not observed as it is difficult to measure the interaction of crack surfaces. A numerical analysis technique is developed to accurately simulate the movement and interaction of the crack surface. The crack detection algorithm, improved by using the observations from the quantitative analyses, can distinguish the occurrence of modulated waves from the ambient noises, and the state of the specimens is determined by using two nonlinear indexes.