Experimental verification on the effectiveness of random vibration testing with controlling acceleration and velocity kurtosis

Random vibration tests for packages are conducted to confirm the safety of these packages during shipping. In our previous study, a method of generating the random vibration controlling the power spectral density and kurtosis of acceleration and the kurtosis of velocity was proposed. The aim of the present study is to verify the effectiveness of the proposed method. Three vibrations were generated in this study and compared with the real vibration, which replicates the truck bed. In the first case, control of the acceleration and velocity kurtosis was neglected. In the second case, the vibration controlling the acceleration kurtosis was considered. The third case corresponded to the vibration controlling both the acceleration and velocity kurtosis generated by the proposed method. In the present study, an aluminum plate simulating the product was fixed to a table for evaluating the vibrations. The natural frequency of the plate was varied by varying the mass of the weight placed on the plate. The relative displacement of the plate was calculated from the difference between the readings of two laser displacement meters. The vibrations were evaluated via the root mean square, kurtosis, and skewness of the relative displacements of the plate. Kurtosis and skewness of the relative displacement of the proposed method were similar to those of the real vibration. However, the kurtosis and skewness of the other generated vibrations were far from those of the real vibration. Results provided experimental verification that the kurtosis of velocity is an important factor for random vibration tests

A Method for Generating Random Vibration Using Acceleration Kurtosis and Velocity Kurtosis

Random vibration tests for packaging are conducted to confirm safety during shipping by truck. However, there is a difference between the traditional random vibration tests and the real vibrations on the truck bed. One reason for this difference is the shock caused by road roughness. Hence, many studies have been conducted to improve random vibration testing. In these studies, the root mean square, power spectral density, kurtosis, and probability density of acceleration are considered. In this study, we show that the kurtosis and probability density of velocity are also important factors for such tests and propose a new method for generating vibrations with arbitrary kurtosis of acceleration and velocity. By bringing the kurtosis and probability density of velocity closer to those of real vibration, it is possible to conduct more accurate vibration tests

Topological enhancement of non-normality in non-Hermitian skin effects

The non-Hermitian skin effects are representative phenomena intrinsic to non-Hermitian systems: the energy spectra and eigenstates under the open boundary condition (OBC) drastically differ from those under the periodic boundary condition (PBC). Whereas a non-trivial topology under the PBC characterizes the non-Hermitian skin effects, their proper measure under the OBC has not been clarified yet. This paper reveals that topological enhancement of non-normality under the OBC accurately quantifies the non-Hermitian skin effects. Correspondingly to spectrum and state changes of the skin effects, we introduce two scalar measures of non-normality and argue that the non-Hermitian skin effects enhance both macroscopically under the OBC. We also show that the enhanced non-normality correctly describes phase transitions causing the non-Hermitian skin effects and reveals the absence of non-Hermitian skin effects protected by average symmetry. The topological enhancement of non-normality governs the perturbation sensitivity of the OBC spectra and the anomalous time-evolution dynamics through the Bauer-Fike theorem.Comment: 33 pages, 14 figure

A new thin sectioning method for observation of higher resolution images in bone histomorphology

A new thin sectioning method for observation of higher resolution images in bone histomorpholog