Creation of a complex butterfly attractor using a novel Lorenz-type system

A novel Lorenz-type system of nonlinear differential equations is proposed. Unlike the original Lorenz system, where the chaotic dynamics remain confined to the positive half-space with respect to the Z state variable due to a limiting threshold effect, the proposed system enables bipolar swing of this state variable. In addition, the classical set of parameters (a, b, c) controlling the behavior of the Lorenz system are reduced to a single parameter, namely a. Two possible modes of operation are admitted by the system; switching between these two modes results in the creation of a complex butterfly chaotic attractor. Numerical simulations and results from an experimental setup are presented

Surfing the high energy output branch of nonlinear energy harvesters

Hysteresis and multistability are fundamental phenomena of driven nonlinear oscillators, which, however, restrict many applications such as mechanical energy harvesting. We introduce an electrical control mechanism to switch from the low to the high energy output branch of a nonlinear energy harvester by exploiting the strong interplay between its electrical and mechanical degrees of freedom. This method improves the energy conversion efficiency over a wide bandwidth in a frequency-amplitude-varying environment using only a small energy budget. The underlying effect is independent of the device scale and the transduction method and is explained using a modified Duffing oscillator model.

Frequency adjustable MEMS vibration energy harvester

Ambient mechanical vibrations offer an attractive solution for powering the wireless sensor nodes of the emerging "Internet-of-Things". However, the wide-ranging variability of the ambient vibration frequencies pose a significant challenge to the efficient transduction of vibration into usable electrical energy. This work reports the development of a MEMS electromagnetic vibration energy harvester where the resonance frequency of the oscillator can be adjusted or tuned to adapt to the ambient vibrational frequency. Micro-fabricated silicon spring and double layer planar micro-coils along with sintered NdFeB micro-magnets are used to construct the electromagnetic transduction mechanism. Furthermore, another NdFeB magnet is adjustably assembled to induce variable magnetic interaction with the transducing magnet, leading to significant change in the spring stiffness and resonance frequency. Finite element analysis and numerical simulations exhibit substantial frequency tuning range (25% of natural resonance frequency) by appropriate adjustment of the repulsive magnetic interaction between the tuning and transducing magnet pair. This demonstrated method of frequency adjustment or tuning have potential applications in other MEMS vibration energy harvesters and micromechanical oscillators.

Unconjugated bile acids influence expression of circadian genes: a potential mechanism for microbe-host crosstalk

Disruptions to circadian rhythm in mice and humans have been associated with an increased risk of obesity and metabolic syndrome. The gut microbiota is known to be essential for the maintenance of circadian rhythm in the host suggesting a role for microbe-host interactions in the regulation of the peripheral circadian clock. Previous work suggested a role for gut bacterial bile salt hydrolase (BSH) activity in the regulation of host circadian gene expression. Here we demonstrate that unconjugated bile acids, known to be generated through the BSH activity of the gut microbiota, are potentially chronobiological regulators of host circadian gene expression. We utilised a synchronised Caco-2 epithelial colorectal cell model and demonstrated that unconjugated bile acids, but not the equivalent tauro-conjugated bile salts, enhance the expression levels of genes involved in circadian rhythm. In addition oral administration of mice with unconjugated bile acids significantly altered expression levels of circadian clock genes in the ileum and colon as well as the liver with significant changes to expression of hepatic regulators of circadian rhythm (including Dbp) and associated genes (Per2, Per3 and Cry2). The data demonstrate a potential mechanism for microbe-host crosstalk that significantly impacts upon host circadian gene expression. Disruptions to circadian rhythm in mice and humans have been associated with an increased risk of obesity and metabolic syndrome. The gut microbiota is known to be essential for the maintenance of circadian rhythm in the host suggesting a role for microbe-host interactions in the regulation of the peripheral circadian clock. Previous work suggested a role for gut bacterial bile salt hydrolase (BSH) activity in the regulation of host circadian gene expression. Here we demonstrate that unconjugated bile acids, known to be generated through the BSH activity of the gut microbiota, are potentially chronobiological regulators of host circadian gene expression. We utilised a synchronised Caco-2 epithelial colorectal cell model and demonstrated that unconjugated bile acids, but not the equivalent tauro-conjugated bile salts, enhance the expression levels of genes involved in circadian rhythm. In addition oral administration of mice with unconjugated bile acids significantly altered expression levels of circadian clock genes in the ileum and colon as well as the liver with significant changes to expression of hepatic regulators of circadian rhythm (including Dbp) and associated genes (Per2, Per3 and Cry2). The data demonstrate a potential mechanism for microbe-host crosstalk that significantly impacts upon host circadian gene expression.