如何在PHP中设置名称空间正确？

I have load file index.php in server in directory public_html. In this file I set namespace and use like as:

namespace public_html;

error_reporting(E_ALL);
ini_set('memory_limit', '-1');

set_time_limit(0);

use public_html\Helper\Curl\CurlHeaders;
use public_html\Helper\Curl\Curl as Curl;
use public_html\Helper\Pdo\FacadeQuery as Db;

So, all files that you see are located in root directory public_html

When I run script I get error:

Fatal error: Class 'public_html\Helper\Pdo\FacadeQuery' not found in /home/bulud/public_html/parse.php on line 34