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   PR # 22187
    The present day cluster mass function defines the space density of   
    the largest virialized systems in the universe, which formed from    
    matter perturbations that should appear as fluctuations in the cosmic
    microwave background on the 10' scale.  We propose to measure the    
    mass function for a complete sample of X-ray clusters, and from it,  
    deduce the variance of the mass fluctuations ($\sigma_8$) and the    
    shape of the power spectrum near $10^{15} M_\odot$.  Our second goal 
    is to measure the baryon to total mass ratio and its variation in    
    the same cluster sample.  If the few measured values for this ratio  
    are typical of the universe, it is impossible to reconcile standard  
    Big Bang nucleosynthesis with an $\Omega=1$ universe.  Both the mass 
   function and the baryonic frac
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