A valve for controlling a flow of abrasive particles suspended in a pressurized carrier fluid has at least two apertured valve seats in face to face contact. In one embodiment, a plurality of task icons, each of which represents a respective one task, are shown in defined positions in a view on the computer system, and these defined positions of the task icons are used to determine the order in which the tasks are to be executed by the computer system. Then a charge of polymerization initiator, and a mixture of multiple-vinyl aromatic monomer and mono-vinyl aromatic monomer are added. Embodiments may also include limiting a model based reverberation equalizer using a temporal constraint for direct sound distortions, the model based reverberation equalizer configured to generate one or more outputs, based upon, at least in part, at signal least one of the first audio signal and the reverberation audio signal.