Application of a modified Lindstedt–Poincaré method in coupled TDOF systems with quadratic nonlinearity and a constant external excitation

An analytical approach is developed for the nonlinear oscillation of a conservative, two-degree-of-freedom (TDOF) mass-spring system with serial combined linear–nonlinear stiffness excited by a constant external force. The main idea of the proposed approach lies in two categories, the first one is the transformation of two nonlinear differential equations of a two-mass system using suitable intermediate variables into a single nonlinear differential equation. Another is the treatment a quadratic nonlinear oscillator (QNO) by the modified Lindstedt–Poincaré (L-P) method presented recently by the authors. The first-order and second-order analytical approximations for the modified L-P method are established for the QNOs with satisfactory results. After solving the nonlinear differential equation, the displacements of two-mass system can be obtained directly from the governing linear second-order differential equation. Unlike the common perturbation method, the modified L-P method is valid for weak as well as strong nonlinear oscillation systems. On the other hand, the new approach yields simple approximate analytical expressions valid for small as well as large amplitudes of oscillation. In short, this new approach yields extended scope of applicability, simplicity, flexibility in application, and avoidance of complicated numerical integration as compared to the previous approaches such as the perturbation and classical harmonic balance methods. Two examples of nonlinear TDOF mass-spring systems excited by a constant external force are selected and the approximate solutions are verified with the exact solutions derived from the Jacobi elliptic function and also the numerical fourth-order Runge–Kutta solutions.     

An Extremely Simple and Effective Colony PCR Procedure for Bacteria, Yeasts, and Microalgae

An extremely simple and effective colony PCR procedure is established for both gram-negative and gram-positive bacteria, yeasts, and microalgae. Among the four lysis buffers examined, Y-PER is observed to be more effective than Tris/EDTA, 0.2 % SDS, and 10 mM EDTA in the extraction of PCR-quality genomic DNA from those microorganisms. Vortexing or pipetting agitation of the cells in Y-PER for 5–10 s was sufficient to release genomic DNA for all the test bacteria and yeasts, and most microalgae. Additional incubation at 98 °C for 5 min for further cell disruption was essential only for Chlorella vulgaris due to its notoriously rigid cell wall.     

Non-uniform polonium distribution in lead–bismuth eutectic revealed by evaporation experiments

Understanding polonium evaporation from lead-bismuth eutectic (LBE) is required for the design of nuclear installations that use liquid LBE as coolant or spallation target. In the present study we measured the time-dependent release of polonium from LBE samples in Ar/5 %H₂ and Ar between room temperature and 500 °C. Our experiments revealed that the majority of polonium in the samples evaporated according to established temperature correlations for the Henry constant of polonium in LBE. However a small fraction of polonium in the LBE behaved differently, causing a relatively large but transient polonium release at the start of evaporation experiments. We showed that this volatile fraction of polonium was located near the sample surface and was formed after prolonged exposure of the samples to air at room temperature. We speculate that the peculiar evaporation behavior of this surface polonium is caused by enrichment and association with an oxide layer.     

Field-emission properties of patterned ZnO nanowires on 2.5D MEMS substrate

We fabricated a nanowire-based field-emission display (FED) device on a 2.5D substrate using a photolithography, lift-off, thermal-evaporation, and plasma-etching process. We first fabricated a 3×3 array of microholes (diameter = 400???m and depth = 50???m) on a Si substrate and fabricated ZnO nanowires inside the microholes by using a thermal CVD process. The field-emission pattern image of the 3×3 array of microholes was clearly apparent. The threshold emission field was ca. 5.6?V/??m and we obtained considerable brightness when the applied voltage was 1900?V (i.e. 6.3?V/??m). Because the fabrication processes used in this study are standard semiconductor fabrication routes, the study suggests the feasibility of mass producing a nanowire-based FED device.     

Atmospheric stability of surface boundary layer in coastal region of the Wol–Ryong site

In order to provide statistically reliable information of a wind energy site, accurate analysis on the atmospheric stability and climate characteristics in a certain area is a prerequisite. Two 2-D ultrasonic anemometers and one cup anemometer, located perpendicular to the prevailing wind direction, were used to measure the atmospheric wind environment at a height of 4.5 m in coastal region of the Wol–Ryong, Jeju, South Korea. The study is aiming to understand the atmospheric stability about a coastal region, and the effect of roughness length. We calculate the Monin–Obukhov length for division of atmospheric stability about unstable regime, neutral regime and stable regime. The distribution of diurnal Monin–Obukhov length is highly sporadic in the coastal region due to the effect of radiant heat from the surface or other environmental effects. In order to calculate the roughness length in coastal region, three different methods are applied in terms of the surface roughness, flow fluctuation and gust wind, which are called logarithmic profile, standard deviation and gust factor methods. In the study, the atmospheric stability was insignificant when applying these three methods. In the results, three different roughness length scales sufficiently showed the effect of obstacle and surface conditions around the measurement position. On the basis of an overall analysis of the short-term data measured in the Wol–Ryong area, Jeju Island, it is concluded that for the development of future wind energy resources, the Wol–Ryong site could be a good candidate for a future wind energy site.