Opera hat which means hat, and "claque", which means "tap" or "click". The "chapeau claque" is thus a hat that folds with a click, and unfolds likewise. In English the hat model is usually referred to as a "collapsible top-hat", "gibus" or more often "opera hat"- The construction may originally have been inspired by an historical hat model called "chapeau bras" ("arm hat"), made as bicorne or tricorne to be carried folded under the arm On May 5, 1812, a London hatter called Thomas Francis Dollman patented a design for "an elastic round hat" supported by ribs and springs. His patent was
Top-hat filter theoretically possible. Top-hat filters can be constructed by chaining theoretical low-band and high-band filters. In practice, an approximate top-hat filter can be constructed in analogue hardware using approximate low-band and high-band filters. In Fourier space, a top hat filter selects a band of signal of desired frequency by the specification of a lower and upper bounding frequencies. Top-hat filters are particularly easy to implement digitally. The top hat function can be generated by differentiating a linear ramp function of width formula_1. The limit of formula_1 then becomes the Dirac delta function. Its real-space form is the same as the moving