469 research outputs found
Revisiting van der Waals like behavior of f(R) AdS black holes via the two point correlation function
Van der Waals like behavior of AdS black holes is revisited via two
point correlation function, which is dual to the geodesic length in the bulk.
The equation of motion constrained by the boundary condition is solved
numerically and both the effect of boundary region size and gravity are
probed. Moreover, an analogous specific heat related to is
introduced. It is shown that the graphs of AdS black holes
exhibit reverse van der Waals like behavior just as the graphs do. Free
energy analysis is carried out to determine the first order phase transition
temperature and the unstable branch in curve is removed by a
bar . It is shown that the first order phase transition temperature is
the same at least to the order of for different choices of the
parameter although the values of free energy vary with . Our result
further supports the former finding that charged AdS black holes behave
much like RN-AdS black holes. We also check the analogous equal area law
numerically and find that the relative errors for both the cases
and are small enough. The fitting functions between and for both cases are also
obtained. It is shown that the slope is around 3, implying that the critical
exponent is about . This result is in accordance with those in former
literatures of specific heat related to the thermal entropy or entanglement
entropy.Comment: Revised version. Match the published version. 14pages,5figure
Probe optimization for quantum metrology via closed-loop learning control
Experimentally achieving the precision that standard quantum metrology
schemes promise is always challenging. Recently, additional controls were
applied to design feasible quantum metrology schemes. However, these approaches
generally does not consider ease of implementation, raising technological
barriers impeding its realization. In this paper, we circumvent this problem by
applying closed-loop learning control to propose a practical controlled
sequential scheme for quantum metrology. Purity loss of the probe state, which
relates to quantum Fisher information, is measured efficiently as the fitness
to guide the learning loop. We confirm its feasibility and certain
superiorities over standard quantum metrology schemes by numerical analysis and
proof-of-principle experiments in a nuclear magnetic resonance (NMR) system
In-wheel motor vibration control for distributed-driven electric vehicles:A review
Efficient, safe, and comfortable electric vehicles (EVs) are essential for the creation of a sustainable transport system. Distributed-driven EVs, which often use in-wheel motors (IWMs), have many benefits with respect to size (compactness), controllability, and efficiency. However, the vibration of IWMs is a particularly important factor for both passengers and drivers, and it is therefore crucial for a successful commercialization of distributed-driven EVs. This paper provides a comprehensive literature review and state-of-the-art vibration-source-analysis and -mitigation methods in IWMs. First, selection criteria are given for IWMs, and a multidimensional comparison for several motor types is provided. The IWM vibration sources are then divided into internally-, and externally-induced vibration sources and discussed in detail. Next, vibration reduction methods, which include motor-structure optimization, motor controller, and additional control-components, are reviewed. Emerging research trends and an outlook for future improvement aims are summarized at the end of the paper. This paper can provide useful information for researchers, who are interested in the application and vibration mitigation of IWMs or similar topics
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