Impulse Properties

As expected from the scaling property, the Fourier transform of an impulse is a function that is infinitely stretched , that is, the Fourier Transform is 1 at all frequencies. Using the duality principle, a signal x(t) = 1 for all t will have a Fourier transform of 6( ), that is, an impulse at time 00 = 0. This is to be expected - a constant signal (a d.c. signal in electrical terms) has no variation and hence no information at frequencies other than 0. 

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Oxidizers. The characteristics of the oxidizer affect the baUistic and mechanical properties of a composite propellant as well as the processibihty. Oxidizers are selected to provide the best combination of available oxygen, high density, low heat of formation, and maximum gas volume in reaction with binders. Increases in oxidizer content increase the density, the adiabatic flame temperature, and the specific impulse of a propellant up to a maximum. The most commonly used inorganic oxidizer in both composite and nitroceUulose-based rocket propellant is ammonium perchlorate. The primary combustion products of an ammonium perchlorate propellant and a polymeric binder containing C, H, and O are CO2, H2, O2, and HCl. Ammonium nitrate has been used in slow burning propellants, and where a smokeless exhaust is requited. Nitramines such as RDX and HMX have also been used where maximum energy is essential. 

The principal physical properties influencing ink performance ate surface tension and viscosity. High surface tension is desired for good droplet formation and capillary refill in dtop-on-demand ink jet. Low viscosity is desired because less energy is required to pump and eject ink. Conductivity is also an important parameter. Continuous ink-jet inks must have some conductivity to allow for charging. Low conductivity is generally preferred for impulse, particularly thermal ink jet, because excess ions can cause corrosion of the printhead. 

Automa-ticity. Special cardiac cells, such as SA and AV nodal cells, His-bundle cells, and Purkinje fibers, spontaneously generate an impulse. This is the property of automaticity. Ectopic sites can act as pacemakers if the rate of phase 4 depolarization or resting membrane potential is increased, or the threshold for excitation is reduced. 

Conductivity. Conductivity is an electrical property of excitable tissue which ensures that if one area of a membrane is excited to full activity, that area excites adjacent areas. Conduction of an impulse varies direcdy with the rate of development of phase 0 and the ampHtude of the action potential. Phase 0 is faster, and ampHtude of the action potential is greater, the more negative the transmembrane potential at the time of initiation of the impulse. Conduction velocity is faster when phase 0 is fast. 

Figure 9-6. Schematic of an Impulse turbine showing the variation of the thermodynamic and fluid mechanic properties.

It is possible to deteraiine the eumulative residenee time distribution funetion F(t) from either a traeer step-ehange or a traeer impulse response. From its definition, the properties of F(t) are ... 

Without the influence of burning rate catalysts most of these hydrocarbon prop bits have similar burning rates and ballistic behavior. They may differ significantly in mechanical properties, particularly as a function of temp. Most hydrocarbon-based composites are used in larger rockets because of their ease of fabrication and high specific impulse. Polaris first and second stages, the Titan 3C booster rocket and Mlnuteman are all powered with composite proplnts... 

R.C. Oliver et al, USDeptCom, Office Tech-Serv ..AD 265822,(1961) CA 60, 10466 (1969) Metal additives for solid proplnts formulas for calculating specific impulse and other proplnt performance parameters are given. A mathematical treatment of the free-energy minimization procedure for equilibrium compn calcns is provided. The treatment is extended to include ionized species and mixing of condensed phases. Sources and techniques for thermodynamic-property calcns are also discussed... 

The cardiac muscle (myocardium) has attributes of both nerve and muscle and therefore has the properties of both. Some cardiac arrhythmias are caused by the generation of an abnormal number of electrical impulses... 

The impulse function is rarely defined in the conventional sense, but rather via its important property in an integral ... 

For composite propellants the properties depend on the proportion of binder, and also on whether high energy fuels such as aluminium have been added. Figure 19.5, taken from Barrere, Jaumotte, de Veubeke and Vandenkerckhove, shows how the specific impulse depends on these factors. 

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