# Elemetry Spin Immersed in a Magnetic Field

##### Landau-Lifshitz Equation: time evolution of ferromagnetic materials

Consider an elementary ferromagnet which has an average magnetic moment, for example, a small sphere of iron, fixed in space. When immersed in an external magnetic field (H), the sample's magnetic moment (M) will dynamically reorient according to the Landau-Lifshitz equations. One observes both a circular precession about the magnetic field axis, and losses which dampen the motion until the spin comes into alignment with the magnetic field.

# Epidemic Modeling

##### Dynamics of Infectious Deseases with the SIR model

The SIR (Susceptible, Infected, Recovered) models are a class of differential equations for modeling the spread of infectious diseases. In the model, the population is divided into groups which may transition to other groups. Susceptible becomes infected at a certain rate, infected becomes recovered (and immune) at a certain rate, and this relation is written (S->I->R). Variations and modifications of this simple model help inform the spread of various recurrent epidemic illnesses such as measles and influenza, and now much more recently, Covid 19. Dimensional analysis on infection rates can establish how virulant the diseases is, and whether `Epidemic' will (may) occur. Presented above is the phase diagram and some example trajectories of the S->I->R->S model, where the recovered population loses its immunity to the illness at a certain rate. Here one observes, absent any external input, that the infected population settles down to a constant nonzero value, and the illness is not eradicated.

# Traveling Wave

##### Viscous Burgers Equation

The Viscous Burgers Equation is one of the simplest nonlinear advection diffusion equations. Analytical solutions exist via the Cole-Hopf transformation. Interestingly, it is known to admit a simple traveling wave solution under certain conditions. Pictured right, numerical solution of the traveling wave via explicit forward-Euler method.