Abstract: A semiconductor memory device may include a cell substrate including a cell array region and an extension region, a first mold structure on the cell substrate, a second mold structure on the first mold structure, a channel structure passing through the first and second mold structures on the cell array region, and a cell contact structure passing through the first and second mold structures on the extension region. The first mold structure and the second mold structure respectively include first gate electrodes and second gate electrodes sequentially stacked on the cell array region and stacked in a stepwise manner on the extension region. The cell contact structure includes a lower conductive pattern connected to one of the first gate electrodes, an upper conductive pattern connected to one of the second gate electrodes, and an insulating pattern separating the lower conductive pattern from the upper conductive pattern.

Abstract: A vertical memory device includes a channel and gate electrodes. The channel extends in a vertical direction with respect to a top surface of a substrate. The gate electrodes are disposed on an outer sidewall of the channel. The gate electrodes includes a ground selection line (GSL), a word line, a string selection line (SSL) and a first dummy word line sequentially stacked from the top surface of the substrate in the vertical direction to be spaced apart from each other. The channel includes an impurity region at a portion adjacent to the SSL.

Abstract: A power transmission device of a land rowing machine which generates a propelling force to be applied to wheels by pulling and pushing levers or moving a seat forward and backward is disclosed. The levers having uni-directional ratchet wheels A are installed at opposite ends of a motive shaft which passes through a side surface portion of the propelling part. A seat lever which has a uni-directional ratchet wheel B in the same direction as that of the uni-directional ratchet wheels A and interlocks with the seat is disposed on the motive shaft between the levers. A passive gear which is engaged with a motive gear installed on the motive shaft is installed on a passive shaft with the rear wheel part mounted thereon.

Abstract: A rowing bike operated in a manner similar to a rowing boat. The rowing bike includes a body frame, a handle part having both a front wheel and a foothold, and rear wheels provided at the back of the body frame. The body frame has two parallel guide rods oriented in a longitudinal direction. The rowing bike further includes two drive levers, one provided on each side of the body frame, so that, when the drive levers are repeatedly levered upwards, the driving force of the drive levers is transmitted to the rear wheels. The rowing bike further includes a seat movable along the guide rods. A rack having a spur gear is mounted to the seat. Thus, when the seat is linearly reciprocated forwards and backwards, the driving force of the seat is transmitted to the rear wheels through a gear mechanism engaging with the rack gear.