Physics tutorials

Use these tutorials to introduce quantitative sciences perspectives to your biological work. You can use this curriculum to prepare for introductory courses in undergraduate math, science, and systems biology. Know how to explain the canonical model for protein dynamics when it appears on the first day of systems biology 101. Understand why some systems of interacting molecules oscillate. Know how to estimate uncertainties and perform curve fitting. Know the difference between a normal and log-normal distribution and which is more intuitively expected in biology. If you find these tutorials helpful, these external resources and textbooks might interest you as well.

Pre-algebra, algebra, geometry, and precalculus

Topic Slides Video Description
"What is a number?" PPTX slides MP4 video Street numbers, money in bank accounts, points on number lines, quantum particles
as contrasted with distinguishable manipulatives
For our purposes, infinity is not a number
Algebra PPTX slides MP4 video Variables: At once arbitrary, yet specific and particular (a.s.a.p.)
Functions, composition, and inverse
f(x) is not a function. f(x) is not the function f. f(x) is the particular value associated, in the big picture of the function f, with x, a number that is at once arbitrary, yet particular and specific
Inverse functions do not always exist
First glimpse at the complex plane and i := √ -1 

Additional activity for this module

Quadratic equation PPTX slides MP4 video Linear combination of terms in a polynomial
Zeroes or "roots" of a function
Completing the square
Euclidean geometry and trigonometry PPTX slides MP4 video Flat space, curved space, non-embedded curved space
Pythagorean theorem (ca. 300 BCE)
The unit-radius circle, the unit-hypotenuse triangle, jya-ardha (sine), koti-jya (cosine) (ca. 510)
Geometric construction for approximating π
Angle-sum identities

Additional activity for this module

Summation PPTX slides MP4 video Geometric series
Harmonic series; sums do not always exist
Gauss summation trick
Enumerative combinatorics PPTX slides MP4 video Permutations and factorials
Combinations
Binomial theorem
Small parameter expansion

Calculus (ca. 1700s)

In this unit we define constructions in calculus (derivatives and integrals) so that we can eventually identify them, using explicit and concrete figures and words, with the processes of (1) describing the kinetic processes and (2) inferring long-term time-course outcomes for collections of chemically reacting biological molecules. This line of discussion presents differential equation models of biology as potentially useful approximations. Biochemistry is not always idiomatic for calculus; in fact, cellular biochemistry is an example of where applying calculus can be very dicey.

Limits PPTX slides MP4 video ε-δ definition of limit, notion of "arbitrarily close"
Example of calculating a limit
Limits do not always exist
Differentiation PPTX slides MP4 video Slopes and derivatives
Derivatives do not always exist
Common derivatives: power law, chain rule, product rule, quotient rule, sine, and cosine
Infinitessimals describe processes; in this course they are not numbers
Taylor expansions PPTX slides MP4 video Second derivative and curvature
Local approximations and Taylor series
(Successful) power-series representations do not always exist
Power-series expansion of sine and cosine, iterative calculation of π
Taylor expansions II l'Hôpital's rule ("0/0" version)
Newton-Raphson method for approximating zeros of a function
Integration PPTX slides MP4 video Anti-derivatives, Riemann sums, and integrals
Example kosher calculation of a simple integral
Deductive inference of integral by definition as anti-derivative
"Backwards chain rule"--u substitution
Integration II Integration by parts
Integration III Integrals do not always exist
Triangle/trigonometric substitution
Partial fractions
Separation of variables PPTX slides MP4 video Two wrongs make a right
Tear two differentials apart as though they retained meaning in isolation
Slap on the smooth S integral sign as though it were a unit of meaning itself, even without a differential
You get the same integral expression you would obtain long-hand using u-substitution or "change of variables" in integrals
Euler's number PPTX slides MP4 video Euler's number 1a: Compound interest
Compounding interest with arbitrarily short compounding periods
Power series representation of ex
MP4 video Euler's number 1b: e to the zero
e0 = 1
MP4 video Euler's number 1c: Exponent multiplication identity
(ex)p = epx
MP4 video Euler's number 1d: Exponent addition identity
exey = ex+y
MP4 video Euler's number 1e: Andrew Jackson
Mnemonic for memorizing e = 2.718281828459045...
MP4 video Euler's number 1f: Natural logarithm
The natural logarithm is the inverse of the exponential
ln(ex) = eln(x) = 1
MP4 video Euler's number 1g: Integral of 1/x
∫(1/x)dx = ln(x) + C
Euler's number projects day Make a slide rule
Equal-tempered tuning in European musical tradition

Non-dimensionalization

Stochasticity PPTX slides MP4 video (This section is a prerequisite for "protein dynamics 101"). Many of the homework problems from undergraduate calculus and differential equations involve notions of stochasticity.
* For-real stochasticity: Fundamental indeterminism
* Fake stochasticity: Periodic, deterministic hidden variables
* Fake stochasticity: Aperiodic, deterministic (chaos)
Markov models

Additional activity for this module

Protein dynamics 101 PPTX slides MP4 video This is a canonical worked problem from introductory systems biology (Alon, Ch. 2.4, pp. 18-21). We will explain one way to fantasize about the classic protein dynamics equation dx/dt = β - αx and analytically demonstrate that protein "rise time" depends on degradation rate only.
Mass action Why mass action reaction rates look like terms from polynomials
Cooperativity of the simple kind
Hill functions
Gompertzian dynamics PDF notes A given trajectory can often be easily accommodated by a variety of physically inconsistent microscopic models
Derivation from time-invariant, resource-limited governing equation
Derivation from time-variant governing equation
Negative sign floating around in Gompertzian age distribution (1825)

Linear algebra

LA I PPTX slides Motivating example: Modeling dynamics of web start-up company customer base
Vector space and basis
Linear operator and representation
Matrix multiplication
Using eigenvalues and eigenvectors to avoid computational inefficiency

Additional activity for this module

Euler's number II Small-argument expansion
Euler's formula: Expanding the exponential function in terms of sine and cosine
LA II Euclidean rotation matrix
Complex eigenvectors and eigenvalues
LA III Orthogonality, dot product, and length
Determinants
Invertibility
Euclidean rotation matrix
Quasispecies Simple quasispecies eigendemographics and eigenrates

Differential equations

DEs I PPTX slides Direction fields, quiver plots, and integral curves
Numerical integration of systems of differential equations
DEs II Integrating factor method
Solution by power-series expansion
DEs III Eigenvector-eigenrate solution method for canonical 2-by-2 system of linear differential equations with constant coefficients
Phase portrait stability analysis
Transcription-translation Canonical mRNA-protein system from systems biology 101
DEs IV Using linear algebra to study nonlinear differential equations
Local linearization: Jacobian
DEs V PPTX slides Intuitive introduction to 2-d oscillations (Romeo and Juliet)
Twisting nullclines
Time-delays
Stochastic resonance
Adaptation Adaptation is not absence of change; instead it is the presence of eventually compensatory changes
Biological oscillators
Evolutionary game theory Replicator dynamics
Prisoner's dilemma
Simultaneous survival of the relatively most fit with decrease in overall fitness
Additional homework TBA

Ignoring small parameters (guess and check)
Fourier analysis
Example: Audio compression (irrelevance coding) on iPods and other MP3 players

Probability, statistics, and stochastic processes

Coin toss Bernoulli (ca. 1700s) coin-toss process
Binomial distribution
Limit of rare events Poisson distribution
Luria-Delbrück fluctuation analysis P0 method
Limit of many independent parts Stirling's approximation
Statement of central limit theorem, heuristic study of binomial distribution in limit of many coin tosses
Biology's central limit theorem: Log-normal distributions
Working with brackets Variances of independently fluctuating variables add
Experimental uncertainty propagation
Parameters and sample estimators Standard deviation vs. sample standard deviation
Mean vs. sample mean
Standard deviation of the mean vs. standard error of the mean
Apparent sample size "I quantitated staining intensity for 1 million cells in contiguous fields of view, everything I measure is statistically significant!" Your data quite possibly fail to meet the fine print permitting application of the √ N  formula for calculating the standard error.
Curve fitting Reduced chi-square χ2
Best-fit parameters are not independent (Gutenkunst, Sorger)
Describing heterogeneity Why on earth have we multiple measurements of distribution heterogeneity?
Some measures increase, some flatline, and some decrease with "effective number" size
  • Standard deviation
  • Coefficient of variation
  • Fano factor
  • Entropy, Shannon information, diversity

Stochastic models and their implementation in MatLab

Master equation and SSA PPTX slides Interpretation of master equation
Derivation of exponential distribution of waiting times
Numerical stochastic simulation PPTX slides Pseudo-random number generators
Example stochastic birth-death process script
Langevin integration method PPTX slides Stochastic differential equations
Gaussian white noise
Path integrals

Spatially-resolved models

Fast-Fourier transform
Efficient computation of local linear interactions FFT convolution trick

Newtonian physics

Vectors Review of vector addition and vector calculus
Force Velocity v := dx/dt
Momentum p := mv
Momentum exchange for an isolated pair of bodies
Superposition of pairwise momentum exchange
FNET = ma
Newtonian gravitation r2-law
Approximate uniform gravitational acceleration for small relative changes in radii
Uniformly accelerated motion
Non-fundamental forces Normal force
Tension
Kinetic and static friction

Simple-harmonic-oscillation (pendulum)

Lab: Measuring the gravitational field with a pendulum

Elastic materials (Hookean)
Elastic modulus
Propagation of vibrations on a taut string
Standing waves
Lab: Measure the speed of sound using a flute
Lab: Build a graduated cylinder water harmonica (equal-tempered tuning)

Derivation of the shape of a suspension bridge
Lab: Calculate the linear mass-density of the Golden Gate bridge

Momentum conservation
Work and energy conservation

Newton's law of gravitation
Rocket science
Electricity and magnetism

Modern physics

Light has wave-like properties

Lab: Location of phantom laser spots seen while wearing diffraction-grating glasses

Postulates of quantum mechanics
Heisenberg uncertainty relationship (not a principle, but a result): You postulate that eigenvalues of Hermitian operators represent experimental measurement outcomes; you define some operators in terms of other operators in ways such that they necessarily cannot share eigenvectors, and then you are surprised that dispersion in some observables can only be squished at the expense of precision in other observables
Ehrenfest theorem and correspondence principle, Newtonian physics from quantum mechanics
Particle in a box

Hydrogen atom Single-electron solution
Multi-electron atom Taylor-expansion of interaction potential
See also: http://arxiv.org/abs/physics/0407126
Multi-electron molecules

Symmetries, conserved quantities, and extremized quantities
Path-integral formulation of quantum mechanics and wave optics, extremizing functions of path
Entanglement, Einstein-Podolsky-Rosen paradox, and Bell's inequalities

General relativity

Sine-Gordon equation and solitons

Statistical physics

Modern statistical mechanics Heuristic justification of equal a priori probability postulate
Second "law" of thermodynamics
Boltzmann distribution PPTX slides Ways of sharing energy between a small system and a large reservoir
Entropy
Free energy
Ising model Phase transition
Hysteresis
Bose-Einstein statistics Bose-Einstein systems obey Boltzmann distributions! A quantum index need not be interpreted as referring to a collection of distinct particles.
Lagrange multiplier

Blackbody radiation
Diffusion, Brownian motion, and fluctuation-dissipation (Smoluchowski treatment)
Self-organized criticality
Chaos is not a lack of determinism

Biological physics and biophysics

Optical coherence microscopy
Fluorescence correlation spectroscopy and auto-correlation function
Lateral displacement mechanical flow cell sorter (Loutherback-Sturm)

Introduction to population dynamics topics PPTX slides See table below
Fancy name Descriptive name Example insight
Fixation time of mutants Allele proportions fluctuate stochastically in finite populations of true-breeding replicators Rapid loss of heterogeneity is possible in small populations
Quasispecies Interplay between dispersive forces that generate genotypic heterogeneity and populating forces that favor replication of fit genotypes determine whether populations expand, maintain heterogeneity, or disperse throughout genotypic space and lose macroscopic population numbers Fitness, in the sense of rapid net production of progeny, is not sufficient to ensure survival. It also matters whether the progeny actually look like their parents.
Evolutionary game theory Collections of (mostly) true-breeding cell subpopulations interact by modulating each other's net replication rates in a pairwise, linear manner In a population where population composition influences the absolute fitness of both relatively unfit and relatively fit subpopulations, survival of the relatively fit can lead to decline in fitness for all individuals. The rich and the poor both get poorer.
Cellular automata Probabilistic or deterministic prescription for changing the discrete state of a lattice point into the future is a function of the current configuration of its local spatial neighborhood Cell subpopulations that would otherwise die out in a well-mixed population can survive by huddling together and minimizing their interactions with hostile neighbors. Spatiality can help sustain diversity.