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    PR # 32239                                                                   
     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   m       
     ass function for a complete sample of X-ray clusters, and from it,  d       
     educe the variance of the mass fluctuations ($\sigma_8$) and the    s       
     hape of the power spectrum near $10^{15} M_\odot$.  Our second goal i       
     s to measure the baryon to total mass ratio and its variation in thes       
     ame cluster sample.  If the few measured values for this ratio are  t       
     ypical of the universe, it is impossible to reconcile standard Big  B       
     ang nucleosynthesis with an $\Omega=1$ universe.  Both the mass     f       
    unction and the baryonic fract                                               
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