Reactant Gas Pressure This parameter indicates the ambient vapor pressure of the hydrocarbon precursor used as a source of carbon inside the reaction chamber for the synthesis of CNT. Usually the reactant gas pressure is maintained between 1-40 mTorr. A good website for learning pressure conversions  is available here. Reactant Gas Temperature This parameter denotes the temperature (in degrees Celsius) of the reaction gas and the value is usually maintained between 400 - 900ºC. It is the ambient (global) temperature and must not be confused with the local temperature at the reaction site which is dependent on the exothermic/ endothermic nature of the reaction. Mass of Gas Molecule The mass of the gaseous molecule must be given in atomic mass units (a.m.u.). One a.m.u is defined to be 1/12 of the mass of one atom of carbon-12. More generally, an atom or molecule that contains n nucleons (# protons + # neutrons) will have a mass approximately equal to n a.m.u. For example, the mass of a water molecule is approximately 18 a.m.u. (Can you figure that out?) Nanotube Diameter This value is approximated to the diameter of the catalyst metal nanoparticle which is assumed to be spherical. A widely accepted growth mechanism suggests that the CNTs nucleate at the ledges that develop at the surface of these metal nanoparticles. However, it must be noted that this assumption is very idealistic as it neglects faceting of the catalyst nanoparticle which may render it non-spherical. Moreover, impurities in the catalyst particle surface may make that region ineffective as a reaction site thus decreasing the net surface area available for reaction, effectively decreasing the nanotube diameter. Number of Walls This parameter determines if the CNT is single-walled or multi-walled. Sticking Coefficient When a single acetylene molecule dissociates it gives rise to two carbon atoms. The sticking co-efficient is an empirical parameter which is the measure of the probability of an acetylene molecule dissociating and the resulting carbon atoms participating in the CNT growth process. Impingement Rate This quantity determines the rate at which molecules (acetylene) descend on unit area of the catalyst surface (here 1 nm2). It is calculated from assumptions involved in the Kinetic Theory of Gases namely the consideration that the gas behaves ideally and the velocity of gas molecules obeys the Maxwell-Boltzmann distribution. Linear Density Determines the number of carbon atoms per unit length of the nanotube. Depends on the CNT diameter and the number of nanotube walls. Catalyst Cap Surface Area Assumes that the catalyst is spherical and so calculates the surface area of the "exposed" hemisphere.