### SPESIF 2012 and Getting Around at the University of Maryland

I'm attending SPESIF 2012 this week at the University of Maryland. I'm learning a few tricks for getting around the area easily since I'm using solely public transportation on this trip.

Getting from the Airport to the University:
The B30 metro bus leaves the airport every 40 minutes or so [pdf]. It costs \$6 and you have to have exact change. It will take you directly to the Greenbelt Metro station. From there, you can ride one stop on the metro train to the College Park Metro station.

University of Maryland College Park Shuttle System:
From here on out, you can get a remarkable number of places on the UMD shuttle bus system. Make sure to check the complete schedule and maps [really big pdf[ to see if where you're headed is on a route. You can also use the excellent NextBus application on your phone. Just click on the NextBus logo in the upper right corner of the UMD transit web page.

To get from the College Park Metro Station to campus, hop on the 104 in front of the station. The bus will drop you off at the Stamp Student Union building.

On several of the shuttle routes a student ID card is not required. I've never been asked for one on the 104 for example. The good news is that even if you're not a student, you can go to the transportation office in the Regent's parking garage, (see map below), and ask for a letter that lets you on the shuttles for \$4 a day, (I hear). That brings us to the great news. If you're the student of any university, you can use your ID to get on any of the shuttles for free.

View UMD Transit in a larger map

### 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…

### Lab Book 2014_07_10 More NaI Characterization

Summary: Much more plunking around with the NaI detector and sources today.  A Pb shield was built to eliminate cosmic ray muons as well as potassium 40 radiation from the concreted building.  The spectra are much cleaner, but still don't have the count rates or distinctive peaks that are expected.
New to the experiment?  Scroll to the bottom to see background and get caught up.
Lab Book Threshold for the QVT is currently set at -1.49 volts.  Remember to divide this by 100 to get the actual threshold voltage. A new spectrum recording the lines of all three sources, Cs 137, Co 60, and Sr 90, was started at approximately 10:55. Took data for about an hour.
Started the Cs 137 only spectrum at about 11:55 AM

Here’s the no-source background from yesterday
In comparison, here’s the 3 source spectrum from this morning.

The three source spectrum shows peak structure not exhibited by the background alone. I forgot to take scope pictures of the Cs137 run. I do however, have the printout, and…

### Unschooling Math Jams: Squaring Numbers in their own Base

Some of the most fun I have working on math with seven year-old No. 1 is discovering new things about math myself.  Last week, we discovered that square of any number in its own base is 100!  Pretty cool!  As usual we figured it out by talking rather than by writing things down, and as usual it was sheer happenstance that we figured it out at all.  Here’s how it went.

I've really been looking forward to working through multiplication ala binary numbers with seven year-old No. 1.  She kind of beat me to the punch though: in the last few weeks she's been learning her multiplication tables in base 10 on her own.  This became apparent when five year-old No. 2 decided he wanted to do some 'schoolwork' a few days back.

"I can sing that song... about the letters? all by myself now!"  2 meant the alphabet song.  His attitude towards academics is the ultimate in not retaining unnecessary facts, not even the name of the song :)

After 2 had worked his way through the so…