How can i select the next element?

How can i select the next element?

Here is the html code:

<form method="post" action="" id="product_form">
    <table width="100%" cellpadding="2" cellspacing="0" border="1" bordercolor="#666666">
        <tbody>
                 <tr bgcolor="#F3F3F3">
    <th><p>Item No.</p></th>
<th><p>P.order#:</p></th>
<th><p>Description</p></th>
<th><p>Qty</p></th>
<th><p>U.price</p></th>
<th><p>Amount</p></th>

</tr>
            <tr class="mytr">
                <td id="orders">
                    <input type="text" name="product[]" class="products" id="product" size="10">
                    <button class="add" type="button">+</button>
                </td>
               
                <td align="right">
                    <input type="text" name="porder[]" class="porder" id="porder" size="5">
                </td>
               <td align="right">
                    <input type="text" name="description[]" class="description" id="description" size="50">
                </td>
                <td align="right">
                    <input type="text" name="qty[]" class="qty" id="qty" size="5">
                </td>
                <td align="right">
                    <input type="text" name="uprice[]" class="uprice" id="uprice" size="5">
                </td>
                <td align="right">
                    <input type="text" name="amount[]" class="amount" id="amount" size="5">
                </td>
            </tr>
        </tbody>
    </table>
</form>



Here is the jquery code:
$('#product_form').on("keyup", "td .uprice", function (e) {
 
 $(this).parent().next('td .amount').val(50);
  
  
  
   });




http://jsfiddle.net/boajay/p3sFh/23/