Cheetahs

Sponsor/Developing Organization LLNL. Developer. Laurence E. Fried LLNL, P.O. Box 808 Livermore, CA 94551, E-mail cheetah llnl.gov. Hardware-. IBM-PC or clone, Windows 3.1, Windows 95, Mac OS 7.x or later, SUN and SGI workstations, 4.3 MB of hard disk. Software ANSI C. Run execution time for typical problem (CPU or real time). Standard run About 30 seconds on a Power Macintosh 6100/80. Cost None from LLNL. Source code is available, with the stipulations that all modifications be preapproved and forwarded to the sponsor for tracking... 

Protein dynamics—the action of enzymes and molecular motors—provides the key to understanding the biochemistry of this cheetah and the grasses through which it runs. (Frank Lane/Parfitt/Tony Stone Images)... 

Setchell, K.D.R., Gossehn, S.J., and Welsh, M.B. et al. (1987). Dietary estrogens—a probable cause of infertility and liver-disease in captive cheetahs. Gastroenterology 93, 225-233. 

We shall start by clustering animals and scientists (separately). Living creatures display a remarkable diversity some species have few features in common, while others are very alike. An elephant is not much like an amoeba, beyond the fact that they are both alive, but leopards and cheetahs share many characteristics. 

Caro, T.M. (1994) Cheetah of the Serengeti plains, Chicago Univ. Press, USA. Demanze, C. (1996) Natural Waxes in Oils and Fats Manual, Vol. I (original Manual des corps gras, 1992) (Ed. Karleskind, A.), Intercept Ltd., USA. 

Poddar-Sarkar M. and Brahmachary, R.L. (1997) Putative semiochemicals in the African Cheetah Acinonyx jubatus). J.Lipid Mediator and Cell Signalling 15, 285-287. 

Exp-6 potential models can be validated through several independent means. Fried and Howard33 have considered the shock Hugoniots of liquids and solids in the decomposition regime where thermochemical equilibrium is established. As an example of a typical thermochemical implementation, consider the Cheetah thermochemical code.32 Cheetah is used to predict detonation performance for solid and liquid explosives. Cheetah solves thermodynamic equations between product species to find chemical equilibrium for a given pressure and temperature. From these properties and elementary detonation theory, the detonation velocity and other performance indicators are computed. 

In addition to the intermolecular potential, there is an intramolecular portion of the Helmholtz free energy. Cheetah uses a polyatomic model to account for this portion including electronic, vibrational, and rotational states. Such a model can be expressed conveniently in terms of the heat of formation, standard entropy, and constant-pressure heat capacity of each species. 

The thermodynamic theory for exp-6 mixtures of polar materials is now implemented in the thermochemical code Cheetah.32 We considered first the major polar detonation products H20, NH3, CO, and HF. The optimal exp-6 parameters and dipole moment values for these species were determined by fitting to a variety of available experimental data. We find, for example, that a dipole moment of 2.2 Debye for water reproduces very well all available experiments. Incidentally, this value is in very good agreement with values typically used to model supercritical water.50... 

A comparison of our Cheetah polar water model predictions with both high-pressure Hugoniot data,51 and low-density (steam at 800 K) experimental data52 is presented in Figure 6. The agreement is very good for both cases. 

The newly developed equation of state was applied to the calculation of detonation properties. In this context, one stringent test of any equation of state is the prediction of detonation velocities as a function of initial densities, and we chose for this purpose PETN. The Cheetah results are shown in Figure 7 along with the experimental data.53 The agreement is again very good. 

Figure 7 PETN detonation velocity as a function of initial density experiments (symbols) and Cheetah calculation (line).

Predictions of high explosive detonation based on the new approach yield excellent results. A similar theory for ionic species model43 compares very well with MD simulations. Nevertheless, high explosive chemical equilibrium calculations that include ionization are beyond the current abilities of the Cheetah code, because of the presence of multiple minima in the free energy surface. Such calculations will require additional algorithmic developments. In addition, the possibility of partial ionization, suggested by first principles simulations of water discussed below, also needs to be added to the Cheetah code framework. 

Because of the lack of high-pressure experimental reaction rate data for HMX and other explosives with which to compare, we produce in Figure 15 a comparison of dominant species formation for decomposing HMX that have been obtained from entirely different theoretical approaches. The concentration of species at chemical equilibrium can be estimated through thermodynamic calculations with the Cheetah thermochemical code.32,109... 

The results of the MD simulation compare well with the formation of H20, N2, and HNCO predicted by Cheetah. The relative concentrations of CO and C02, however, are reversed, possibly because of the limited time duration of the simulation. Another discrepancy is that Cheetah predicts carbon in the diamond phase is in equilibrium with the other species at a concentration of 4.9-mol/kg HMX. No condensed carbon was observed in the simulation. Several other products and intermediates with lower concentrations, common to the two methods, have also been identified, including HCN, NH3, N20, CH3OH, and CH20. A comparison between... 

Snowmass, Colorado, (1998). Kinetic Modeling of Non-ideal Explosives with Cheetah. 

In contrast to the other large cats, the urine of the cheetah, A. jubatus, is practically odorless to the human nose. An analysis of the organic material from cheetah urine showed that diglycerides, triglycerides, and free sterols are possibly present in the urine and that it contains some of the C2-C8 fatty acids [95], while aldehydes and ketones that are prominent in tiger and leopard urine [96] are absent from cheetah urine. A recent study [97] of the chemical composition of the urine of cheetah in their natural habitat and in captivity has shown that volatile hydrocarbons, aldehydes, saturated and unsaturated cyclic and acyclic ketones, carboxylic acids and short-chain ethers are compound classes represented in minute quantities by more than one member in the urine of this animal. Traces of 2-acetylfuran, acetaldehyde diethyl acetal, ethyl acetate, dimethyl sulfone, formanilide, and larger quantities of urea and elemental sulfur were also present in the urine of this animal. Sulfur was found in all the urine samples collected from male cheetah in captivity in South Africa and from wild cheetah in Namibia. Only one organosulfur compound, dimethyl disulfide, is present in the urine at such a low concentration that it is not detectable by humans [97]. 

The presence of elemental sulfur in the urine is quite surprising. Until more information has been obtained, it is speculated that sulfur could possibly be a cheetah pheromone. There could, however, also be another reason for the presence of sulfur in the animal s urine and the almost total absence of organosulfur compounds. Although the cheetah can reach speeds of more than 110 km per hour in short bursts, it is not very powerful and cannot defend itself against the lion and hyena. The conversion of organosulfur compounds to elemental sulfur could therefore be a mechanism to avoid detection by stronger predators. 

Although too little information on the composition of the urine of the large cats is at present available to reach any final conclusion, there seem to be some similarities between the urine of the cheetah and that of the spotted hyena, Croatia crocuta [99]. 

It may however, be noted that these values for different parameters are influenced by purity, morphology and particle size of the sample. The calculated values of VOD for FOX-7 and RDX are 9090ms 1 and 8940 ms 1 respectively (Cheetah Thermochemical Code). Based on these results, it was concluded that FOX-7 is better than RDX which is used as a benchmark explosive for comparison with other explosives. Consequently, it is an attractive ingredient for application in high performance IM compliant explosive formulations. FOX-7 also increases the burning-rate in propellants and as a natural consequence, is of interest for high performance propellants. 

And if the cheetah is now an endangered species, it is because the price of a cheetah pelt is just right for some people to hunt one animal after the other (p. 17). 

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