 Theory and Applications of Categories (TAC)  Robert Rosebrugh, Ed.; Mount Allison University
The allelectronic, refereed journal on Category Theory, categorical methods and their applications in the mathematical sciences. The scope of the journal includes: all areas of pure category theory, including higher dimensional categories; applications
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 Theory of Tieknots  Yong Mao
The mathematical theory behind tying a necktie, with illustrations of the Four in Hand, the Pratt Knot, the HalfWindsor, and the FullWindsor, and a classification of necktie knots with respect to size and shape. Tying a tie knot is equivalent to a persistent
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 There are trisectable angles that are not constructible  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
Why certain angles that are trisectable cannot be constructed by traditional methods.
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 Thermicks  P. Zuidema
A Matlab routine for 2D thermal analysis.
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 Theron J. Hitchman
Scholarship and teaching by a professor of mathematics at the University of Northern Iowa. Hitchman's research focuses on differential and metric geometry, dynamical systems, and Lie theory, with particular interest in discrete subgroups of semisimple
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 These are Times that Try Mathematicians' Souls  David Brooks
Spurred by the Unabomber arrest, David Brooks, Science Editor, says it's time to stand on our desktops and shout to the world: "Say it out loud, I like math and I'm proud!" Previously published in The Telegraph (Nashua, NH).
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 The Theta Foundation
A scientific and notforprofit organisation, promoting mathematical knowledge, based in Romania.
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 A Thing In Common  Cut the Knot!, Alexander Bogomolny
Two applets, both of which use the Pythagorean theorem: a puzzle (Draw an {N/D} star polygon  a polygon whose N vertices are uniformly distributed on a circle, but each vertex is connected to its Dth neighbor. Regular polygons correspond to D = 1, and
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 Things I Made From Yarn  Alan Eliasen
Futureboy's online calculators include a blackjack strategy table, a model solar system calculator (create your own model solar system of any scale), a sun locator (find current position of the sun), a historical currency converter (find out "how much
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 Things Impossible  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
Essays on impossible things, including trisecting an angle, doubling a cube, squaring a circle, moving pegs five places in one direction (via checkerjumps), finding the center of a given circle with the straightedge alone, representing the square root
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 Think & Derive  Chris Long
Monthly mathematical columns from May 1994 through April 1996 written for Central New Jersey Mensa's Forvm. Problems and puzzles, many with solutions.
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 ThinkFun  ThinkFun, Inc.
The makers of Spin Out and Rush Hour seek to "push [you] farther, probe deeper and think more creatively through game play." Brainteaser games include Math Dice, which challenges you to use addition, subtraction, multiplication, division, and exponents
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 Thinking Mathematics!  James Tanton
Tanton writes wordless volumes of creative and surprising math puzzles, accessible approaches to calculus suitable for standardized test preparation, and curriculum "tidbits." Download his free guides to fractions and "to everything quadratic," and watch
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 ThinkNum  Gregory Ugwi
A webbased financial data analysis engine. Use regression, curve trades, and other quantitative trading algorithms from scipy, numpy, and similar open source libraries to analyze economic information from hundreds of sources ranging from the ADO National
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 ThinkWave.com
A free web community that provides secure internetbased communication for parents, students, and teachers: realtime information about attendance, assignments, grades, and school curriculum.
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 Third Apex to Fractovia  Juan Luis Martínez
Several galleries, each with up to 18 fractal images, and discussions on fractals as art. Also an uptodate list of freeware fractal generators, screen savers, and fractal music software, with links and reviews.
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 thnik again!  Jan Nordgreen
"Silly mathematical dialogues aimed to confuse." Nordgreen's daily blog of brain teasers and quotes dates back to November, 2007.
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 Thomas Harriot's manuscripts  MacTutor Math History Archives
Linked essay: Thomas Harriot died in 1621. He had published no mathematical or astronomical works during his lifetime, but he left his papers in reasonably good order and set out his wishes in his will that they should be properly edited and published.
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 Thorleif's SOMA page  Thorleif Bundgard, Denmark
Over a thousand figures for these cubes: standard figures (176, all solved); McFarrens figure set (798, all possible); and more. An index of all figures is available. With some SOMA history and a link to a newsletter.
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 Those Amazing Flying Mathematicians  Keith Devlin (Devlin's Angle)
October is the month when those of us living in the United States see migrating birds moving south for the winter. How do they know which direction to fly?... Assuming that the average bird is not the mathematical equivalent of a college math major, how
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 Thot / Nouvelles de la formation à distance  Denys Lamontagne, Directeur et Rédacteur en Chef
Une base de données de rubriques: cours, logiciels, références, technologies, didactique, arguments, actions, institutions, revue médias, et communiqués. Aussi, des forums animé et archivés.
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 Threedimensional Geometry (The Geometry Junkyard)  David Eppstein, Theory Group, ICS, UC Irvine
An extensive annotated list of links to material on threedimensional geometry.
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 The Three Jugs Problem  Cut the Knot!, Alexander Bogomolny
Two friends who have an eightquart jug of water wish to share it evenly. They also have two empty jars, one holding five quarts, the other three. How can they each measure exactly 4 quarts of water? ... The description of the 3 Jugs problem as a triple
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 Three Years of Computing: Final Report On The Palindrome Quest  John Walker
A 1990 report on computations on the 196 problem: "Pick a number. Reverse its digits and add the resulting number to the original number. If the result isn't a palindrome, repeat the process. Do all numbers in base 10 eventually become palindromes through
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 Thue Equations  Clemens Heuberger
A special family of equations F(X,Y) = m, where F is an irreducible homogeneous form of degree n at least 3 and m is a nonzero integer. With a list of special cases that have been solved.
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 TI83 / TI84 Games and Programs  Bill Paetzke
Bill Paetzke offers TI83/TI84 Plus programs to help students and teachers be more efficient in using their calculators. The programs are organized under these categories: Algebra, Finance, Geometry, Physics, Programs, Statistics, Trigonometry, and Tutorials.
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 TI84 Basic Programs
Programs for the Ti84 or Ti83+. Available subjects include: limits, derivates, integrals, differential equations, vector plotting, vector calculating, complex numbers. Also for control systems: Nyquist diagrams and many programs for electrical engineering.
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 ticalc.org
The unofficial TIcalculator home page. A nonprofit, collaborative effort geared toward fans of Texas Instruments' graphing calculators, acting as a headquarters for all available information on the subject. It is also the home of ZShell and Fargo, assembly
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 Tickling the Mind  Ivars Peterson (MathTrek)
... Different math teachers may use different styles and methods, and they may favor different topics. However, they all share the goal of building an appreciation of both the usefulness and the intellectual wonder of mathematics. Much of the current
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 Tides and Tide Prediction  Tony Phillips; Dept. of Mathematics, SUNYStony Brook
General information about tides and tide prediction: Priming/Lagging: a calculus with calculators exercise demonstrating the priming and lagging of the tides at Stony Brook. Samples of current tide predictions from the National Ocean Service. TideSounds:
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 TierneyLab Puzzles  John Tierney
Challenging word problems that "put ideas in science to the test," from The New York Times' science columnist. Solve and comment on the puzzles and their extra credit extensions. See also Tierney's blog entries on mathematics.
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 Tiled CA  Brian Prentice
An interesting variation on the traditional 2D Cellular Automata simulators, for Windows.
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 Tile.Net  ListUniverse.com
A comprehensive Internet reference site for finding discussion lists (mailing lists); Usenet newsgroups; FTP sites; computer products and vendors; and Internet and Web design companies. Search mailing lists by keyword (algebra, calculus, etc.) to find
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 Tiletris  Oktay Haracci
A tiling program for aperiodic or periodic tiling. Freeware, for PCs only, running Win 9x/2000. Help, including instructions, available on the site.
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 Tiling and Packing results  Torsten Sillke
Packing problems, mostly, in English, with some in German. Packing Polycubes and Polyspheres; Tilings with Matching Conditions; links.
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 Tiling Plane and Fancy  Steve Edwards
The 17 wallpaper groups identify the plane symmetry groups and link to background patterns illustrating them. Tiling Definitions define, with examples, the terms fundamental region, isohedral tiling (isohedral and nonisohedral), isogonal tiling, lattice,
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 Tilings and Geometric Ornament  Kaplan, Salesin
A project designed to explore the intersection between computer graphics, geometry, and ornamental design. Papers and illustrations on Escherization, Islamic Star Patterns, Parquet Deformations, Symmetrohedra, and Voronoi Diagrams.
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 Tilings (Graphics Archive, Special Topics)  The Geometry Center
Regular subdivisions of the plane or space.
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 Tilings (The Geometry Junkyard)  David Eppstein, Theory Group, ICS, UC Irvine
An extensive annotated list of links to material on tilings. One way to define a tiling is a partition of an infinite space (usually Euclidean) into pieces having a finite number of distinct shapes. Tilings can be divided into two types, periodic and
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 Tiling with Polyominoes  Ivars Peterson (MathTrek)
"Mathematicians have proved that the general question of whether it's possible to cover the plane with identical copies of a given finite set of tiles is, in principle, computationally undecidable. In other words, there's no cookbook recipe or handbook
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 TiltAWhirl Chaos  Ivars Peterson (MathTrek)
The amusement park TiltAWhirl spins its passengers in one direction, then another... A rider never knows exactly what to expect next. Yet these complicated, surprising movements arise from a remarkably simple geometry. A passenger rides in one of seven
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 TI Math  Texas Instruments, Inc. (TI)
Activities (by subject and technology type), events, research, professional development, and resources, for the high school crowd and beyond.
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 Timelines and Scales of Measurement  Niel Brandt
TEX, DVI, PDF, Postscript, and ASCII files: Science / Technology History Timeline; Evolutionary / Geological Timeline; Cosmological Timeline; Scales of Measurement.
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 Time Series Analysis and Forecasting; AUTOBOX  Automatic Forecasting Systems (AFS) Corporation
Autobox for Windows provides forecasting based on the BoxJenkins modelbuilding process, implemented for both ARIMA (univariate) modeling and Transfer Function (multivariate or regression) modeling. Features, prices, faqs, support, and mathematical information
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 TINspire: Taking Learning to New Heights  Marc Garneau
A blog about the TINspire™ graphing calculator, and its use in the classroom. Includes Garneau's handout from the T^3 International Conference in Seattle, 2009, on Tips and Tricks for the TINspire.
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 Tips & Tricks to Gothic Geometry  Joe Chiffriller; NewYorkCarver.com
The geometry of gothic cathedrals: how to construct a trifoil design, an ogee arch, and a rose window. With links to cathedral and castle tours.
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 Tomoko Fuse Origami Quilts  Jeff Kerwood
These origami quilts were designed and made by Jeff Kerwood, using the modules developed by Tomoko Fuse, a Japanese origami artist universally acknowledged as the master of modular or unit origami. In modular origami, the model is built up from multiple
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 Tomás Oliveira e Silva
From an assistant professor in the Electronics and Telecommunications Department of the University of Aveiro, Portugal. On the Collatz problem: maximum number tested (N): 91·2^50 = 102456891522678784.
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 Tony Phillips  Dept. of Mathematics, SUNYStony Brook
Ongoing Web math projects: Honors Calculus; Visualizing Women in Mathematics, the Physical Sciences and Technology; Calculus Reform; Geometry of the Binary Tetrahedral Group in SU(2); Mazes; Tides; Integrating Research and Education (RAIRE); Math Photo
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 Tools for Decision Analysis: Analysis of Risky Decisions  Hossein Arsham
Decision making under risk is presented in the context of decision analysis using different decision criteria for public and private decisions based on decision criteria, type, and quality of available information, together with risk assessment. Also
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