function fadein_fast( target ){
	target.fadeIn("fast");
}
function fadeout_fast( target ){
	target.fadeOut("fast");
}
function animate_alpha_0( target ){
	target.stop().animate({
		opacity : 0
	},200)
}
function animate_alpha_10( target ){
	target.stop().animate({
			opacity : 0.1
	},200)
}
function animate_alpha_20( target ){
	target.stop().animate({
			opacity : 0.2
	},200)
}
function animate_alpha_30( target ){
	target.stop().animate({
			opacity : 0.3
	},200)
}
function animate_alpha_40( target ){
	target.stop().animate({
			opacity : 0.4
	},200)
}
function animate_alpha_50( target ){
	target.stop().animate({
			opacity : 0.5
	},200)
}
function animate_alpha_60( target ){
	target.stop().animate({
			opacity : 0.6
	},200)
}
function animate_alpha_70( target ){
	target.stop().animate({
			opacity : 0.7
	},200)
}
function animate_alpha_80( target ){
	target.stop().animate({
			opacity : 0.8
	},200)
}
function animate_alpha_90( target ){
	target.stop().animate({
			opacity : 0.9
	},200)
}
function animate_alpha_100( target ){
	target.stop().animate({
		opacity : 1
	},200)
}
	scroll_flag = false;
	set_scroll_trigger = 100;
	$(window).scroll(function(){
		var scroll_val = $(window).scrollTop();
		if( scroll_val > set_scroll_trigger && scroll_flag == false ){
			fadein_fast( $("#btn_return_top") );
			scroll_flag = true;
		}else if( scroll_val < set_scroll_trigger && scroll_flag == true ){
			fadeout_fast( $("#btn_return_top") );
			scroll_flag = false;
		}
	});
	$("#btn_return_top").mouseover(function(){
		animate_alpha_100( $(this) );
	})
	$("#btn_return_top").mouseout(function(){
		animate_alpha_70( $(this) );
	})
	$("#btn_return_top").click(function(){
		$('html,body').animate({
			scrollTop: 0
		}, 'slow');
		fadeout_fast( $(this) )
	})
	animate_alpha_70( $("#btn_return_top") );