To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
An upper limit on the space density of quasars at z > 5 is obtained independent of any optical magnitude limit, from the complete identification of a large sample of flat-spectrum radio sources. This upper limit is below the observed space density at z ≃ 2 − 3, showing that the turnover in space density is real and not merely due to obscuration.
Email your librarian or administrator to recommend adding this to your organisation's collection.