$lastvisitors_array[] =  "<img class='uk-widget-top-avatar uk-border-circle' src='". $avatar_src ."' width='35' height='35'> <div class='uk-width-expand'>". $username . "</div>";

$lastvisitors_array[] =  `<img class="uk-widget-top-avatar uk-border-circle" src="{$avatar_src}" width="35" height="35"> <div class="uk-width-expand">{$username}</div>`;