function dwr_ajax(request_url , params , callback_function){
	var fatal_error_ret = ['false' , 'fatal error!']
	new Ajax.Request(request_url, {parameters: params , asynchronous:true, evalScripts:true , 
		onFailure:function(){
		callback_function.apply(null , [fatal_error_ret]);
	},
	onException:function(){
		callback_function.apply(null , [fatal_error_ret]);
	},
	onSuccess:function(transport){
		var ret_value;
		var flag = true;
		try{
			//alert("cool value is " + transport.responseText);
			ret_value = eval(transport.responseText);
		}catch(e){
			flag = false;
			callback_function.apply(null , [fatal_error_ret]);
		}
		if(flag){
			callback_function.apply(null , [ret_value]);
		}
	}
	});
}