1. A skateboard comprising a front board and a rear board that are connected at a predetermined distance and casters fixed to bottoms of the front and rear boards,
wherein a hollow cover body is fitted in assembly holes of housings formed beneath the bottoms of the front board and the rear board,
a first propeller shaft having a cam-shaped joint portion at one end thereof and fitted in the assembly hole at the front board and a second propeller shat having a cam-shaped joint portion at one end thereof and fitted in the assembly hole at the rear board are inserted in the hollow cover body in contact with each other by the cam-shaped joint portions, and
the first and second propeller shafts horizontally and elastically expandcontract in rolling motion of the front board and the rear board.
2. A skateboard comprising a front board and a rear board that are connected at a predetermined distance and casters fixed to bottoms of the front arid rear boards,
wherein a hollow cover body is fitted in assembly holes of housings formed beneath the bottoms of the front board and the rear board, a first propeller shaft fitted in the assembly hole at the front board and a second propeller shaft fitted in the assembly hole at the rear board are inserted in the hollow cover body in contact with each other by cam-shaped joint portions, and the first and second propeller shafts horizontally and elastically expandcontact in rolling motion of the front board and the rear board, and
wherein the joint portion of each of the first and second propeller shafts has a depressed portion and a protrusion, the depressed portions and the protrusions of the first and second propeller shafts face each other to be engaged with each other, respectively, and the first and second propeller shafts are connected with a spring therebetween such that the first and second propeller shafts are elastically spaced or return.
3. The skateboard according to claim 2, wherein a groove where the spring is seated is formed in the first propeller shaft, a rod extending and protruding from the second propeller shaft is inserted in the groove, and the spring is fitted on the rod and fixed by a nut to provide elastic force between the first and second propeller shafts.
4. A skateboard comprising a front board and a rear board that are connected at a predetermined distance and casters fixed to bottoms of the front and rear boards,
wherein a hollow cover body is fitted in assembly holes of housings formed beneath the bottoms of the front board and the rear board, a first propeller shaft fitted in the assembly hole at the front board and second propeller shaft fitted in the assembly hole at the rear board are inserted in the hollow cover body in contact with each other by cam-shaped joint portions, and the first and second propeller shafts horizontally and elastically expandcontract in rolling motion of the front board and the rear board, and
wherein a groove where a spring is seated is formed in the first propeller shaft, a rod extending and protruding from the second propeller shaft is inserted in the groove, and the spring is fitted on the rod and fixed by a nut to provide elastic force between the first and second propeller shafts.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A light-emitting device comprising:
a substrate; and
a quantum well active layer formed on the substrate in a first direction, comprising a first semiconductor material and a second semiconductor material alternatively arranged with each other in a second direction perpendicular to the first direction in a cross-section view, wherein the first semiconductor material is different from the second semiconductor material.
2. The light-emitting device of claim 1, wherein the first and the second semiconductor materials comprise GayIn1-yN.
3. The light-emitting device of claim 1, wherein the quantum well active layer is free of holes.
4. The light-emitting device of claim 1, wherein the first semiconductor material and the second semiconductor material have different bandgaps.
5. The light-emitting device of claim 1, wherein the first semiconductor material and the second semiconductor material have different refraction indices.
6. The light-emitting device of claim 1, wherein the quantum well active layer comprises one or two-dimensional photonic crystal structure.
7. A light-emitting device, comprising:
an upper semiconductor layer having a bottom surface; and
an active layer of an epitaxial structure, having an upmost surface connected to the bottom surface, and a refraction index variation merely varied in the epitaxial structure and along the upmost surface.
8. The light-emitting device of claim 7, wherein the refraction index variation has one or more periods.
9. The light-emitting device of claim 7, wherein the refraction index variation has a one or two dimensional pattern.
10. The light-emitting device of claim 7, wherein the active layer has a material composition variation on the upmost surface.
11. The light-emitting device of claim 7, wherein the active layer has a dielectric constant change on the upmost surface.
12. The light-emitting device of claim 7, wherein the active layer comprises a photonic crystal structure.
13. The light-emitting device of claim 7, wherein the active layer is formed on the upper semiconductor layer in a first direction, the refraction index variation is varied in a second direction substantially perpendicular to the first direction.
14. An active layer of an epitaxial structure, comprising:
an upmost surface;
a lowermost surface;
a right surface smaller than the upmost surface; and
a refraction index variation varied in the epitaxial structure and along the upmost surface.
15. The active layer of claim 14, wherein the refraction index variation is varied on the upmost surface.
16. The active layer of claim 14, wherein the refraction index variation is varied on the right surface.
17. The active layer of claim 14, wherein the refraction index variation has one or more periods.
18. The active layer of claim 14, wherein the refraction index variation has a one or two dimensional pattern.
19. The active layer of claim 14, wherein the refraction index variation is varied to form a photonic crystal structure in the epitaxial structure.
20. The active layer of claim 14, wherein the upmost surface is faced to the lowermost surface in a first direction, the refraction index variation is varied in a second direction substantially not parallel to the first direction.