The concept of mass (mass, energy, relativity)

You definitely saw this at least once

 In most school, college and undergraduate courses of  Special Theory of Relativity (STR) there is a misconception that uses this formula to infer a particle mass from the particle's full energy, for example a mass is assigned to a moving photon which is a particle of zero mass. Actually, the mass is an invariant. There is a well written explanation of a conception of mass in Special Theory of Relativity written by a russian theoretical physicist L.B. Okun .

For English speaking readers follow this link The concept of mass ( mass, energy, relativity )

For Russian speaking readers follow this link Понятие массы ( масса, энергия, относительность )

Setup and hold time for D flip-flop

For those interested in nature of setup and hold time for D flip-flop there is a good explanation at www.edn.com,  just follow the link Understanding the basics of setup and hold time

I borrowed two illustrations that show the reason for setup and hold time

Reason for SETUP Time:

The time it takes data D to reach node Z is called the setup time.

Reason for HOLD Time:

The darkened line shows the conducting path for hold time.

For the reference the definition for propagation and contamination delays borrowed from here ( (c) 6004 MIT )

  Altogether,  the illustrations from here ( (c) Nilesh Goel )

Setup and Hold Time for D flip-flop

Combinational Propagation and Contamination Delay

Is Microsoft serious about IoT?

It looks like they are not as they do not have plans to release symbol files for windows IoT.
No plans to release symbol files.

UDATE. This is true only for Windows IoT based on Windows 8.1 which is used on Intel Galileo.

Why you need a special theory for complex numbers.

  There is a big flaw in teaching the complex number theory. The first lecture or book's first paragraph usually starts with a boring description of what is complex number and its representation in different forms followed by the introduction of the theory. It does not answer the question - Why do we need a special theory and what is wrong with the real numbers algebra when applied to complex numbers?

   I believe that after defining a complex number it must be stressed that it is not possible to introduce ordering ( see Order_theory ) in the complex number space while you have a natural ordering for real numbers ( for irrational numbers introduced via nested intervals with rational borders the order is easily introduced ). This is the difference that does not allow to map a complex number space on a real number space and use a familiar real number algebra. So you need a new theory.

   It looks like that this is a common belief that this idea of lack of ordering in complex space is too complicated for first-year or second-year students and it is not possible to prove it at the level of introductory course.