### Memories

Two-year-old No. 3 and my stumbling crash a few weeks back has become shared legend between she and I.  I got to hang out with the gang all day today, and when we arrived at soccer practice, three weeks, and one-and-a-half blocks East of our tumble on the sidewalk, she pointed down the road and said "That's where we tumbled, and went crrsshhccc."

I said, "Yeah, and where'd you land?"

"On my backpack."  Then unexpectedly, she said, "You landed on your cheek."  I had completely forgotten that she'd been looking right at me as she landed!  Her attention to detail during our crash is astounding!  I had landed on my cheek.

Later in the afternoon, No. 3 and I headed back out to pick up chicken at our local market.  As we rounded the corner to our bus stop, a woman said "Hi Diana!"

The kids have lots of friends in the neighborhood I don't know thanks to their daily roamings.  I introduced myself and we started to talk.  It turns out that she knew Diana from when she used to go, frequently tucked inside a wrap, to the Chinese story time at our local library.  I love our neighborhood!

### Cool Math Tricks: Deriving the Divergence, (Del or Nabla) into New (Cylindrical) Coordinate Systems

The following is a pretty lengthy procedure, but converting the divergence, (nabla, del) operator between coordinate systems comes up pretty often. While there are tables for converting between common coordinate systems, there seem to be fewer explanations of the procedure for deriving the conversion, so here goes!

What do we actually want?

To convert the Cartesian nabla

to the nabla for another coordinate system, say… cylindrical coordinates.

What we’ll need:

1. The Cartesian Nabla:

2. A set of equations relating the Cartesian coordinates to cylindrical coordinates:

3. A set of equations relating the Cartesian basis vectors to the basis vectors of the new coordinate system:

How to do it:

Use the chain rule for differentiation to convert the derivatives with respect to the Cartesian variables to derivatives with respect to the cylindrical variables.

The chain rule can be used to convert a differential operator in terms of one variable into a series of differential operators in terms of othe…

### The Valentine's Day Magnetic Monopole

There's an assymetry to the form of the two Maxwell's equations shown in picture 1.  While the divergence of the electric field is proportional to the electric charge density at a given point, the divergence of the magnetic field is equal to zero.  This is typically explained in the following way.  While we know that electrons, the fundamental electric charge carriers exist, evidence seems to indicate that magnetic monopoles, the particles that would carry magnetic 'charge', either don't exist, or, the energies required to create them are so high that they are exceedingly rare.  That doesn't stop us from looking for them though!

Keeping with the theme of Fairbank[1] and his academic progeny over the semester break, today's post is about the discovery of a magnetic monopole candidate event by one of the Fairbank's graduate students, Blas Cabrera[2].  Cabrera was utilizing a loop type of magnetic monopole detector.  Its operation is in concept very simpl…