Article: The net quality of a ground reflection depends on the topography of the surface. When the irregularities of the surface are much smaller than the wavelength, we are in the regime of specular reflection, and the receiver sees both the real antenna and an image of the antenna under the ground due to reflection. But if the ground has irregularities not small compared to the wavelength, reflections will not be coherent but shifted by random phases. With shorter wavelengths (higher frequencies), this is generally the case.

Question: What frequencies is associated with shorter wavelengths?
Ans: higher frequencies


Article: When an electromagnetic wave strikes a plane surface such as the ground, part of the wave is transmitted into the ground and part of it is reflected, according to the Fresnel coefficients. If the ground is a very good conductor then almost all of the wave is reflected (180° out of phase), whereas a ground modeled as a (lossy) dielectric can absorb a large amount of the wave's power. The power remaining in the reflected wave, and the phase shift upon reflection, strongly depend on the wave's angle of incidence and polarization. The dielectric constant and conductivity (or simply the complex dielectric constant) is dependent on the soil type and is a function of frequency.

Question: what is reflected and transmitted into the ground when a plane surface is struck?
Ans: electromagnetic wave


Article: However, the early Ming government enacted a law, later rescinded, which forbade Han Chinese to learn the tenets of Tibetan Buddhism. There is little detailed evidence of Chinese—especially lay Chinese—studying Tibetan Buddhism until the Republican era (1912–1949). Despite these missions on behalf of the Hongwu Emperor, Morris Rossabi writes that the Yongle Emperor (r. 1402–1424) "was the first Ming ruler actively to seek an extension of relations with Tibet."

Question: Who worked towards obtaining a extension of relations with Tibet?
Ans: the Yongle Emperor


Article: The first truth explains the nature of dukkha. Dukkha is commonly translated as "suffering", "anxiety", "unsatisfactoriness", "unease", etc., and it is said to have the following three aspects:

Question: What is Dukkha?
Ans:
"suffering", "anxiety", "unsatisfactoriness", "unease", etc.