function faderimg() {
   $('.sicon').mouseover(function(){
      $(this).animate({opacity: '1'}, {duration: 400});
   }); 
   $('.sicon').mouseout(function(){
      $(this).animate({opacity: '.5'}, {duration: 400});
   });
}

$(document).ready(function(){                           
        $('.sicon').animate({opacity: '.4'}, {duration: 100});
        faderimg();    

});