From today's featured article

From today's featured article
Silent Hill 4: The Room is a survival horror video game, the fourth installment in the Silent Hill series developed by Konami Computer Entertainment Tokyo. It was published by Konami and translated by Jeremy Blaustein. The game and its soundtrack were released in Japan in June 2004, and in North America and Europe the following September, for the PlayStation 2, Xbox and Microsoft Windows. In 2012, it was released on the Japanese PlayStation Network. Unlike the previous installments, which were set primarily in the town of Silent Hill, this game is set in the fictional town of South Ashfield, and follows Henry Townshend as he attempts to escape from his locked-down apartment. During the course of the game, Henry explores a series of supernatural worlds and finds himself in conflict with an undead serial killer. The fourth installment in the series features an altered gameplay style with third-person navigation and plot elements taken from previous installments. Upon its release, the game received generally positive critical reaction, with mixed reaction to its deviations from the rest of the series. (Full article...)

Explanation of permeability.

In electromagnetism, the auxiliary magnetic field
H represents how a magnetic field B influences
the organization of magnetic dipoles in a given
medium, including dipole migration and
magnetic dipole reorientation. Its relation to
permeability is
where the permeability, μ, is a scalar if the
medium is isotropic or a second rank tensor for
an anisotropic medium.
In general, permeability is not a constant, as it
can vary with the position in the medium, the
frequency of the field applied, humidity ,
temperature, and other parameters. In a
nonlinear medium , the permeability can depend
on the strength of the magnetic field.
Permeability as a function of frequency can take
on real or complex values. In ferromagnetic
materials, the relationship between B and H
exhibits both non-linearity and hysteresis : B is
not a single-valued function of H , [2] but
depends also on the history of the material. For
these materials it is sometimes useful to
consider the incremental permeability defined as
This definition is useful in local linearizations of
non-linear material behavior, for example in a
Newton–Raphson iterative solution scheme that
computes the changing saturation of a magnetic
circuit.