Differential Equations and Oscillations
Many problems in physics are described by differential equations. As a complete discussion of differential equations is beyond the scope of this chapter we will deal only with linear first and second order ordinary differential equations.
http://www.physics.orst.edu/~rubin/nacphy/ComPhys/DIFFEQ/mydif2/

Differential Forms in Electromagnetic Theory
BYU Electromagnetic Field Theory and Differential Forms Research Group
http://www.ee.byu.edu/ee/forms/forms-home.html

ATI - Amplifier Technologies Inc.
Manufacturers of preamp/processor, stereo, multi channel and distribution amplifiers utilizing differential drive amplifier technology.
http://www.ati-amp.com/

Matisse
Makes mono block and stereo amplifiers, pre-amplifiers, phono pre-amplifiers and cables.
http://www.signatureaudio.com/matisse.html

Advantech
Manufacturer of Solid State High Power Amplifiers (SSPA) and Low Noise Amplifiers (LNA) and associated redundancy equipment. Also manufactures broadband amplifiers and multiplexers.
http://www.advantech.ca/

Topics in Integral and Differential Calculus
An explanation and demonstration of the differential formulas, including an applet.
http://www.ma.utexas.edu/users/kawasaki/mathPages.dir/index.html

Exterior Differential Calculus
Mathematica Packages for Exterior Differential Calculus
http://www.inp.demokritos.gr/~sbonano/EDC/ExteriorDifferentialCalculus.html

TransducerSales.com
BIOPAC Transducers for life science data acquisition: airflow, oxygen saturation, blood pressure, differential pressure, temperature, force transducers; goniometers, laser doppler flow probes, stroboscopes, accelerometers, amplifiers, and electrodes.
http://store.transducersales.com

Mapletree Audio Design
Manufacturers of stereo and multi-channel tube audio amplifiers, line pre-amplifiers, headphone/phono amplifiers and line router.
http://hollowstate.netfirms.com/

Differential Geometry
Several books by Peter W. Michor et al. including "Foundations of Differential Geometry", "Natural operations in differential geometry" (corrected version), "Transformation Groups", and "Gauge theory for fiber bundles" plus papers by the author in postscript.
http://www.mat.univie.ac.at/~michor/listpubl.html