Publication des couches en provenance de geoserver via OpenLayers

Code:
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<h:body >
        <div id="map" style=" clear: both;
             position: relative;width: 800px; height: 500px;   border: 1px solid black;
             "></div>
             <script defer="defer" type="text/javascript">
 
 
                // Création d'un objet map
                var map = new OpenLayers.Map('map');
                var wms = new OpenLayers.Layer.WMS("North America sample imagery",
                        "http://localhost:8080/geoserver/wms", {
                            srs: 'EPSG:4326',
                            width: '800',
                            styles: '',                            
                            height: '500',                            
                            layers: 'nurc:Img_Sample',
                            transparent: "true",
                            format: 'application/openlayers'
 
                        },
                {singleTile: true, opacity: 0.5, isBaseLayer: false}
 
                );
              var dm_wms = new OpenLayers.Layer.WMS(
                        "mosaic",
                        "http://localhost:8080/geoserver/wms",
                        {
                            srs: 'EPSG:4326',
                            width: '800',
                            styles: '',
                            height: '500',                            
                            layers: "nurc:mosaic",
                            transparent: "true",
                            format: "image/png"
                        },
                {isBaseLayer: false}
                );
                map.addLayers([wms,dm_wms]);
                map.zoomToMaxExtent();
 
        </script>
 
    </h:body>
lorsque j'utilise ce code , au moment de l'execution , la couche n'apparait pas , y aurait une erreur , SVP aidez moi