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### Young Robots in Love: Thrusting MagnetoSperm

Excuse the title, but I couldn't resist.  I mean how often do you get a chance to write about robotic sperm?  That develop thrust?  It's not my fault though!  The researchers involved have named their newly created device MagnetoSperm.  Apparently this was done with great glee, since the term MagnetoSperm is mentioned no fewer than fifty times in their short four page article[1].  Yes, I am channeling my inner 12 year old today.

Researchers at the German University in Cairo, and at the University of Twente, in The Netherlands recently reported on their progress modeling the swimming motion of sperm-flagella with a microbot made of cobalt-nickel and silicon, (see picture above).  The microbot swims in an oscillating magnetic field.  The head of the MagnetoSperm is elliptical in shape and forms a magnetic dipole.  An oscillating magnetic field causes the elliptical head to oscillate which in turn causes the flexible tail to oscillate.  The oscillating tail generates the thrust that moves the entire MagnetoSperm forward.  The speed of the MagnetoSperm increases with the frequency of the oscillating magnetic field from 0 to about 45 Hz.  At frequencies greater than 45 Hz, MagnetoSperm can't move quickly enough to oscillate with the field, and the propulsion thrust is reduced.

Just in case you think is all just a spoof, here's a video of the little 'bot in action: http://youtu.be/msKutVAp2RU

References:
1.  http://dx.doi.org/10.1063/1.4880035

2.  http://youtu.be/msKutVAp2RU

### 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…

### Kids R Kapable

Just a little note to concerned ‘grownups’ everywhere.  If you look at a kid—and I mean really look—I don’t mean notice a person shorter than you, I mean make eye contact, notice their facial expression and observe their body language—If you look at a kid, don’t assume they need your help unless they’re obviously distressed, or ask for it.  You might think this is difficult call to make.  You might think, not having kids of your own, that you’re unable to make this determination.  You are.  You do in fact, already have the skills even if you’ve never been around kids  It’s a remarkably simple call to make, just use the exact same criteria you would for determining if an adult was in distress.  Because, guess what, kids and adults are in fact the same species of animal and communicate in the same way.  Honest.  If someone—adult or child—doesn’t need your help, feel free to say hello, give a wave, give a smile, but don’t—do not—try to force help on anyone that doesn’t want or need it.

Y…