Growth Response and Recovery of Corynebacterium glutamicum Colonies on Single-Cell Level Upon Defined pH Stress Pulses

Bacteria respond to pH changes in their environment and use pH homeostasis to keep the intracellular pH as constant as possible and within a small range. A change in intracellular pH influences enzyme activity, protein stability, trace element solubilities and proton motive force. Here, the species Corynebacterium glutamicum was chosen as a neutralophilic and moderately alkali-tolerant bacterium capable of maintaining an internal pH of 7.5 ± 0.5 in environments with external pH values ranging between 5.5 and 9. In recent years, the phenotypic response of C. glutamicum to pH changes has been systematically investigated at the bulk population level. A detailed understanding of the C. glutamicum cell response to defined short-term pH perturbations/pulses is missing. In this study, dynamic microfluidic single-cell cultivation (dMSCC) was applied to analyze the physiological growth response of C. glutamicum to precise pH stress pulses at the single-cell level. Analysis by dMSCC of the growth behavior of colonies exposed to single pH stress pulses (pH = 4, 5, 10, 11) revealed a decrease in viability with increasing stress duration w. Colony regrowth was possible for all tested pH values after increasing lag phases for which stress durations w were increased from 5 min to 9 h. Furthermore, single-cell analyses revealed heterogeneous regrowth of cells after pH stress, which can be categorized into three physiological states. Cells in the first physiological state continued to grow without interruption after pH stress pulse. Cells in the second physiological state rested for several hours after pH stress pulse before they started to grow again after this lag phase, and cells in the third physiological state did not divide after the pH stress pulse. This study provides the first insights into single-cell responses to acidic and alkaline pH stress by C. glutamicum.

Electrical Properties of PZT Under High-Pressure Stress Pulse Effects of Loading Frequency and Circuit Load

The research on the discharge characteristics of PZT under conventional applications has made good progress. In theory, the piezoelectric equation can be used to describe the relationship between stress and electrical output. However, existing studies have shown that the relationship becomes nonlinear under high-pressure stress pulses. To study the effect of loading frequency and circuit load on the electrical output performance of PZT under high-pressure stress pulse, the experiment was carried out based on the split Hopkinson pressure bar and a dynamic & static universal test machine. The effects of different circuits load on the output voltage under high-frequency and low-frequency high-pressure stress pulses are analyzed. Both theory and experiments prove that the critical open-circuit measurement resistance (Rcritial) of PZT decreases with the load frequency. The output voltage is positively correlated with the load resistance when the load resistance is less than Rcritial. It is confirmed by loading different circuits (diodes are added in different positions) that reverse positive charge appears at the negative pole of the material during the stress unloading stage. PZT have the maximum dischargeable strain Tunder the high-pressure stress pulses. PZT no longer generates induced charges when the strain is greater than h. When constant strain rate loading makes PZT completely release energy, its open-circuit output voltage is proportional to the strain rate.

Effect of stress pulse shape on the dynamic fracture of soda-lime glass

The goal of this paper is to evaluate the tensile strength and fracture behavior of the soda lime glass under static and dynamic loading using Brazilian tests. The evaluation of the static tensile strength was performed using the universal testing machine; the fracture behavior under dynamic loading was studied using the Hopkinson Split Pressure Bar (HSPB) Technique. The dynamic loading is realized using the stress pulses of the different shape. In order to obtain the different loading stress pulses impact strikes made from four different materials (Steel, Teflon, Beech, and Polymer) were used. The high-speed camera in both static and dynamic tests was used to obtain some detail view on the failure process of specimens. Experimental results showed that the dynamic tensile strength was at least three times higher than the static one. The initiation of the dynamic fracture occurs when some parameters of the loading stress pulse reaches critical values. These parameters are independent on the stress pulse shape.

Research the Effect of Stress-Pulse Regulation on the Process of Manual Arc Welding Technological Plates Made of AMg6 Alloy Sheet Material 4mm Thickness

The result of the effect of stress-pulse regulation on the process of manual arc welding with the connection of pulse generator is presented. Technology of stress-pulse regulation is accessible and easy to use: the equipment is so small that it can be applied in any convenient place. At the same time, there is a practical alignment of the microhardness of the zone of the base metal of the welded plates, the transition zone and the zone of the weld, which indicates the absence of residual stresses of the welded parts. The results of the research confirm the effectiveness and prospects stress-pulse regulation in any production.

Design guidelines for the striker and transfer flange of a split Hopkinson tension bar and the origin of spurious waves

Characteristics of the stress pulse generated by impact of a hollow striker on the flange of a split Hopkinson tension bar are investigated via an explicit finite element analysis. Design guidelines are extracted for the hollow striker and flange from the viewpoint of eliminating spurious waves located between the incident and reflected pulses. According to design guidelines, it is desirable to have a striker cross-sectional area the same as that of the flange. It is also desirable to make the cross-sectional area of the striker (flange) the same as that of the bar. As for the flange length, it is recommended to be comparable to the diameter of the bar. The magnitude and duration of the primary stress pulse are consistent with the results of a one-dimensional analysis even when spurious waves are present; meanwhile, overly long spurious waves should be avoided to eliminate their superposition with the reflected pulse. Spurious waves appear when general impedance of the striker is higher than the bar. The origin of spurious waves is a series of step-wise residual pulses generated by multiple cycles of striker impact that make the striker keep compressing the flange after the first cycle of impact. Step-wise residual pulses appear in two forms (continuous waves and discrete waves) in spurious waves due to the secondary impacts during the entrance process of step-wise residual pulses to the flange. The consequences of spurious waves in the use of split Hopkinson tension bars are discussed.