 sudden contact hot ga cold solid sudden contact hot ga cold solid flow induc sudden contact semi-infinit expans ga solid initi temperatur examin basi linear continuum theori time larg compar time molecular collis ga veloc pressur disturb concentr wave front propag interfac ambient isentrop sound speed whilst interfac disturb small ga temperatur equal predict classic constant pressur heat conduct theori signific connect reflect shock wave techniqu measur high temperatur ga properti comment 