Generalized early dark energy and its cosmological consequences

We investigate cosmological consequences of a generalized early dark energy (EDE) model where a scalar field behaves as dark energy at various cosmological epochs for a broad range of parameters such as the energy scale and the initial field value. We consider power-law and axion-type potentials for such an EDE field and study how it affects the cosmological evolution. We show that gravitational wave background can be significantly enhanced to be detected in future observations such as LISA and DECIGO in some parameter space. Implications of the EDE model are also discussed for a scenario where a blue-tilted inflationary tensor power spectrum can explain the recent NANOGrav 15-year signal. We argue that the bounds on the reheating temperature can be relaxed compared to the case of the standard thermal history.Comment: 23 pages, 8 figures, references adde

On the Vulnerabilities Due to Manipulative Zero-Stealthy Attacks in Cyber-Physical Systems

In this paper, we analyze the vulnerabilities due to integrity cyber attacks named zero-stealthy attacks in cyber-physical systems, which are modeled as a stochastic linear time invariant (LTI) system equipped with a Kalman filter, an LQG controller, and a χ2 failure detector. The attacks are designed by a sophisticated attacker so that the measurement residual of the compromised system coincides with the healthy one, and thus it is impossible to detect the attacks. First, we characterize and analyze an existence condition of the attacks from an attacker's standpoint. Then, we extend the attacks into an attacker's goal: The scenario when the adversary wishes to manipulate the systems to an objective designed by him/her. Our results provide that the attacker can manipulate the compromised system to the objective without accessing the networks of real-time sensor or actuator data. Finally, we verify the dangerousness of the attacks through a simple numerical example

Reach Set-Based Secure State Estimation against Sensor Attacks with Interval Hull Approximation

This paper deals with the problem of secure state estimation in an adversarial environment with the presence of bounded noises. The problem is given as min-max optimization, that is, the system operator seeks an optimal estimate which minimizes the worst-case estimation error due to the manipulation by the attacker. To derive the optimal estimate, taking the reach set of the system into account, we first show that the feasible set of the state can be represented as a union of polytopes, and the optimal estimate is given as the Chebyshev center of the union. Then, for calculating the optimal state estimate, we provide a convex optimization problem that utilizes the vertices of the union. On the proposed estimator, the estimation error is bounded even if the adversary corrupts any subset of sensors. For the sake of reducing the calculation complexity, we further provide another estimator which resorts to the interval hull approximation of the reach set and properties of zonotopes. This approximated estimator is able to reduce the complexity without degrading the estimation accuracy sorely. Numerical comparisons and examples finally illustrate the effectiveness of the proposed estimators

Development of a Spiral Shaped Soft Holding Actuator Using Extension Type Flexible Pneumatic Actuators

Recently, several pneumatic soft actuators have been applied to wearable and welfare devices to provide nursing care and physical support for the elderly and disabled. In this study, as a wearable soft actuator for holding body, a spiral shaped soft holding actuator that can wrap a user according to their body shape was proposed and tested. The construction and operating principle of the tested soft actuator with circumferential restraint mechanism using three extension type flexible pneumatic actuators (EFPAs) has been discussed. As a result, it was found that the tested actuator could hold elbows and knees when the joint is in motion. An analytical model of the spiral actuator was also proposed to achieve an optimal design. It can be confirmed that the proposed analytical model can predict the shape of the actuator when various EFPAs are pressurized

Feeding of 1-Kestose Induces Glutathione-S-Transferase Expression in Mouse Liver

Functional food ingredients, including prebiotics, have been increasingly developed for human health. The improvement of the human intestinal environment is one of their main targets. Fructooligosaccarides (FOS) are oligosaccharide fructans that are well studied and commercialized prebiotics. 1-Kestose, one of the components of FOS, is considered to be a key prebiotic component in FOS. However, to our knowledge, no studies have been reported on the physiological efficacy of 1-Kestose regarding its anti-oxidative activity. In the present study, we examined the effects of dietary 1-Kestose on gene expression of antioxidative enzymes in the liver, kidney and epididymal adipose tissue of mice by quantitative RT-PCR (qRT-PCR). We demonstrated that a 1-Kestose-rich diet increased mRNA and enzymatic activity levels of glutathione-S-transferase (GST) in mouse liver. These results suggest the possibility that dietary 1-Kestose as a prebiotic may enhance antioxidative activity in mice