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   PR # 22171
    ROSAT observations show that the difference between radio-loud and   
    radio-quiet quasars X-ray spectra increases with the redshift.       
    However, the PSPC data cannot discriminate between two alternative   
    interpretations: a) evolution in the environment of radio-loud       
    quasars; b) evolution of the emission spectrum of radio-quiet        
    quasars.  Three radio-loud high-z quasars have been already observed 
    by {\it Asuka} in the PV and AO1 phases. We propose to observe two   
    high-z {\em radio-quiet} quasars. Our 2 targets are 4 times brighter 
    in X-ray than the next best candidates. These observations can have  
    large implications on the study of the physical evolution of quasars.
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