U Mass Logo

T.W.I.G.S.
The "What Is ...?" Graduate Seminar

Room 1634, Lederle Graduate Research Tower
University of Massachusetts, Amherst
ComplexCubicUnitAction
The Seminar meets on most Wednesdays, 3:00-4:00 in 1634 LGRT.    
Driving Directions   and   Campus Maps
Overview of the Seminar
Maintained by Farshid Hajir.

NOTE Here are the schedules for TWIGS Fall 2002, TWIGS Spring 2003, TWIGS Fall 2003, and TWIGS Spring 2004.

Fall Schedule
  27 September Ivan Mirkovic, UMass Amherst
3:00-4:00   What is a triangulated category? [Joint with Representation Theory seminar; note special day and time]

  29 September Farshid Hajir, UMass Amherst
3:00-4:00   What Is MathSciNet?

  6 October Tom Weston, UMass Amherst
3:00-4:00   What is cohomology?

  13 October Robin Young, UMass Amherst
3:00-4:00   What Is A Shock Wave?

  20 October Farshid Hajir, UMass Amherst
3:00-4:00   What Is the Herglotz Trick?

  27 October Luc Rey-Bellet, UMass Amherst
3:00-4:00   What Is Entropy?

  10 November Amit Khetan, UMass Amherst
3:00-4:00   What Is Lagrange Inversion?

  17 November Jessica Sidman, Mt Holyoke
3:00-4:00   What Is A Rational Normal Scroll?

  1 December Eric Sommers, UMass Amherst
3:00-4:00   What Is A Hyperplane Arrangement?


Abstracts
27 September
Ivan Mirkovic, UMass Amherst
What is a triangulated category?

Abstract
Loosely speaking, Homological Algebra is a mechanism for systematic use of the ``hidden'' information on mathematical objects. The notion of a triangulated category provides the standard setting for homological algebra. A simple example is that if one tries to extend the the duality for finite dimensional vector spaces to modules over a given ring, there are obvious problems and it does not work. However, if one looks at a larger picture, a suitable triangulated category of modules, there is a satisfactory duality. The moral is that the right object to look at (in various situations) is the triangulated category. This lesson has been driven home by discovery that seemingly very different mathematical settings may have the same triangulated category, which makes them for practical purposes the same.


29 September
Farshid Hajir, UMass Amherst
What Is MathSciNet?

Abstract
When you want to study a mathematical problem, how do you determine what is already known about the problem? Since 1940, the AMS has been maintaining a database of short (and sometimes not-so-short) reviews of mathematical publications called the Math Reviews. Certain European archives date even further back. When I was a graduate student, I spent quite a bit of time in the library becoming familiar with the intricacies of navigating the Math Reviews. These days, all the Math Reviews are available via an internet service known as MathSciNet. I'll talk about various cool features of this most useful research tool.


6 October
Tom Weston, UMass Amherst
What is cohomology?

Abstract
Cohomology is a tool for converting mathematics (which is hard) into linear algebra (which is relatively easy). Although there are many different kinds of cohomology in all different fields of mathematics, all cohomology theories share various formal similarities. In this lecture we will attempt to illuminate these general properties via the specific examples of singular homology and group cohomology.
TOP


13 October
Robin Young, UMass Amherst
What is a shock wave?

Abstract
I will describe shock waves and simple waves in one-dimensional systems of conservation laws, and describe some of their interactions. We will mostly consider the coupling between different fields and show how multiple wave interactions can lead to nonexistence of solutions.
TOP


20 October
Farshid Hajir , UMass Amherst
What Is the Herglotz Trick?

Abstract
I'll describe a very neat idea of Gustav Herglotz (an important mathematical physicist and analytic number theorist) for proving an infinite-series representation of the cotangent function, followed by some applications of the formula to evaluating the Riemann Zeta Function at even positive integers.


27 October
Luc Rey-Bellet, UMass Amherst
What Is Entropy?

Abstract
The answer to the question is: "I am not sure". Entropy is a somewhat vague concept in the sense that the word is used to name various objects in very different situations. Quite generally entropy can be seen as a quantitative measure of "information". I will illustrate this concept by considering several examples from various fields.


10 November
Amit Khetan, UMass Amherst
What Is Lagrange Inversion?

Abstract
Generating functions are powerful tools to record and compute combinatorial data. Here we give a formula to find the "compositional inverse" of a generating function. As an example we derive the famous Cayley Prufer formula counting the number of trees on n nodes.


17 November
Jessica Sidman, Mt. Holyoke
What Is A Rational Normal Scroll?

Abstract
Rational normal scrolls are an important family of examples in algebraic geometry. I will show how to construct a scroll from two rational normal curves. I will also discuss how to think about a rational normal scroll as a determinantal variety and as a toric variety.


The picture above was created by Paul Gunnells. It visualizes the natural action of the group of units of a complex cubic field on 3-space. Consult Paul for more details.

Last modified: Feb 2004 by Farshid Hajir