Shaving Sword introduced the 'bonded blade' razor, which consisted of a single blade housed in a plastic cartridge. Gillette followed in 1971 with its Trac II cartridge razor that utilised two blades. Gillette built on this twin blade design for a time, introducing new razors with added features such as a pivoting head, lubricating strip, and spring-mounted blades until their 1998 launch of the triple-bladed Mach3 razor. Schick launched a four-blade Quattro razor later the same year, and in 2006 Gillette launched the five-blade Fusion. Since then, razors with six and seven blades have been introduced. Wholly disposable razors gained popularity
Mach reflection convex away from the oncoming flow, and the slip plane slopes towards the reflecting surface. By new results there is a new configuration of shock waves - configuration with a negative angle of reflection in steady flow. In Pseudo-steady flows, the triple point moves away from the reflecting surface and the reflection is a direct-Mach reflection. In unsteady flows, it is also possible that the triple point remains stationary relative to the reflecting surface (stationary-Mach reflection), or moves toward the reflecting surface (inverse-Mach reflection). In inverse Mach reflection, the Mach stem is convex toward the oncoming flow, and the slip