German cuisine widely available, but do not play an important role. Meat is usually braised; fried dishes also exist, but these recipes usually originate from France and Austria. Several cooking methods used to soften tough cuts have evolved into national specialties, including "Sauerbraten" (sour roast), involving marinating beef, horse meat or venison in a vinegar or wine vinegar mixture over several days. A long tradition of sausage-making exists in Germany; more than 1,500 different types of sausage () are made. Most "Wurst" is made with natural casings of pork, sheep or lamb intestines. Among the most popular and most common are "Bratwurst",
Slowly varying envelope approximation Slowly varying envelope approximation In physics, the slowly varying envelope approximation (SVEA, sometimes also called slowly varying amplitude approximation or SVAA) is the assumption that the envelope of a forward-travelling wave pulse varies slowly in time and space compared to a period or wavelength. This requires the spectrum of the signal to be narrow-banded—hence it also referred to as the narrow-band approximation. The slowly varying envelope approximation is often used because the resulting equations are in many cases easier to solve than the original equations, reducing the order of—all or some of—the highest-order partial derivatives. But the validity of the