A simple one-pot chemical reduction
synthesis is provided to prepare a novel metal–graphene nanostructure,
in which surface-oxidized amorphous Fe nanoparticles grow uniformly
on reduced graphene oxide (rGO) sheets to form amorphous-Fe/rGO nanocomposites.
A relatively low coercivity of 60.2 Oe is achieved in these magnetic
graphene-based nanosheets supported with uniformly distributed amorphous
Fe nanoparticles. The dielectric properties of amorphous-Fe/rGO nanocomposites
are effectively tuned by suitable rGO additions. Improved impedance
matching resulting from balanced magnetic and dielectric loss can
be obtained in the Fe/5 wt % rGO nanocomposites, which results in
their good wave absorption performance containing a high maximum reflection
loss (−72.8 dB at 4.48 GHz) for a 3.26 mm thickness and a wide
absorption bandwidth (5.90 GHz, <−10 dB). The simple synthesis,
high structural stability, low density, and excellent wave absorption
properties for amorphous-Fe/rGO nanocomposites enable their significant
latent applications in lightweight electromagnetic microwave absorbers.
Duffing-Van der Pol equation with the fifth nonlinear-restoring force is investigated. The bifurcation structure and chaotic motion under the periodic perturbation are obtained by numerical simulations. Numerical simulations, including bifurcation diagrams, Lyapunov exponents, phase portraits and Poincaré maps, exhibit some new complex dynamical behaviors of the system. Different routes to chaos, such as period doubling and quasi-periodic routes, and various kinds of strange attractors are also demonstrated.
With two new tortoise coordinate transformations, Hawking effect from a dynamical Kinnersley black hole is investigated by using the improved Damour-Ruffini method. After the tortoise coordinate transformation, the Klein-Gordon equation can be written in the standard form at the event horizon. Then extending the outgoing wave from outside to inside of the horizon analytically, the surface gravity and the Hawking temperature can be obtained automatically. It is found that Hawking temperature of different points on the surface are different. There is a problem of dimension in the usual tortoise coordinate and the results are different from those of the same black hole by using two different tortoise coordinate transformations. The results obtained by using two new tortoise coordinate transformations are still different.
Using a new tortoise coordinate transformation, we discuss the quantum nonthermal radiation characteristics near an event horizon by studying the Hamilton-Jacobi equation of a scalar particle in curved space-time, and obtain the event horizon surface gravity and the Hawking temperature on that event horizon. The results show that there is a crossing of particle energy near the event horizon. We derive the maximum overlap of the positive and negative energy levels. It is also found that the Hawking temperature of a black hole depends not only on the time, but also on the angle. There is a problem of dimension in the usual tortoise coordinate, so the present results obtained by using a correct-dimension new tortoise coordinate transformation may be more reasonable.
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