We investigate the spontaneous pair production, including the Schwinger mechanism and the Hawking thermal radiation, of charged scalar particles from the near horizon region of a (near) extremal Reissner-Nordström black hole. The paradigm is equivalent to the dynamics of the charged scalar field in a specific AdS2 × S 2 spacetime with a constant electric field. Two possible boundary conditions are adopted to explicitly compute the corresponding production rate and absorption cross section. It is shown that the Schwinger production rate can be eventually suppressed by the increasing attractive gravitational force as the geometry changes from the extremal to the near extremal black hole. Consequently, the Schwinger mechanism and the Hawking radiation are generically indistinguishable for the near extremal black holes. The holographic description dual to the pair production is also briefly discussed.

Motivated by recent progresses in the holographic descriptions of the Kerr and Reissner-Nordstrøm (RN) black holes, we explore the hidden conformal symmetry of nonextremal uplifted 5D RN black hole by studying the near horizon wave equation of a massless scalar field propagating in this background. Similar to the Kerr black hole case, this hidden symmetry is broken by the periodicity of the associated angle coordinate in the background geometry, but the results somehow testify the dual CFT description of the nonextremal RN black holes. The duality is further supported by matching of the entropies and absorption cross sections calculated from both CFT and gravity sides.

This paper presents a planar triple-band MIMO antenna that meets GSM900/1800 and LTE2600 bands protocols. The antenna element contains three individual meander-line type Inverted-L radiators; the highest frequency band radiator is fed by a transmission line while the other two utilize the proximity coupling feeding mechanism driven by the highest band radiator. The MIMO antenna is incorporated with two symmetric triple-band antenna elements and two physical decoupling devices. The two antenna elements are closely spaced with one-fifteenth wavelength of the lowest band. The two decoupling devices, a T-shape slot and a meandering microstrip-line resonator, are built for the highest and the lowest frequency bands respectively. Meanwhile, a negligible mutual coupling effect in middle band is achieved by using a collinear placed transverse meander-line pair in the MIMO antenna. The antenna prototype measurement results show good impedance matching with low mutual coupling effect. The calculated Envelope Correlation Coefficient verifies the suitability of the proposed antenna for mobile wireless access applications.