var Arc = function (materialOptions) {
  var geometry = new THREE.Geometry(),
      R1       = ETHER.Config.R1,
      R2       = ETHER.Config.R2,
      SUBDIV   = ETHER.Config.SUBDIV,
      SPEED    = ETHER.Config.SPEED,
      PERIOD   = ETHER.Config.PERIOD,
      SPACING  = ETHER.Config.SPACING;

  // create vertices
  for (var i = 0; i <= SUBDIV; i++) {

    var
      j = i - SUBDIV / 2,
      s = Math.sin(2 * Math.PI * j / SUBDIV),
      c = Math.cos(2 * Math.PI * j / SUBDIV);

    geometry.vertices.push(
      new THREE.Vector3(R1 * s, R1 * c - 3, 0),
      new THREE.Vector3(R2 * s, R2 * c - 3, 0)
    );

  }

  // create faces
  for (var i = 1; i <= SUBDIV; i++) {

    var ii = i * 2;

    geometry.faces.push(
      new THREE.Face3(ii, ii - 1, ii - 2),
      new THREE.Face3(ii, ii + 1, ii - 1)
    );

  }

  // map texture
  var material = new THREE.MeshBasicMaterial(materialOptions);

  geometry.faceVertexUvs[0] = [];

  for (var i = 0; i < SUBDIV; i++) {

    var j = i * 2;
        k = 1 - i / SUBDIV,
        l = 1 - (i + 1) / SUBDIV;

    geometry.faceVertexUvs[0][j] =
      [ new THREE.Vector2(l, 0),
        new THREE.Vector2(k, 1),
        new THREE.Vector2(k, 0), ];

    geometry.faceVertexUvs[0][j + 1] =
      [ new THREE.Vector2(l, 0),
        new THREE.Vector2(l, 1),
        new THREE.Vector2(k, 1), ];

  }

  // set pivot point
  geometry.applyMatrix(new THREE.Matrix4().makeTranslation(0, 3, 0));

  // combine geometry and material
  return new THREE.Mesh(geometry, material);

};