The invention relates to compounds of the formula 1or pharmaceutically acceptable salts, prodrugs, solvates or hydrates thereof, wherein wherein X, R1, and R2 are as defined herein. A lubricant is disposed in a gap formed between a shaft and a sleeve of the bearing assembly such that textured and coated surfaces of the shaft and sleeve alter wetting properties between the lubricant and surfaces. The amplifier further includes a control input, a signal amplifier, at least two audio outputs connected to the signal amplifier, and an audio input for receiving a digital audio signal from a digital music player to be amplified by the signal amplifier. The outer pouch consists of two polymer films sealed together along their periphery and contain a ball able to pierce the inner pouch by manual action from the user. This actuator is notable in that it comprises a sleeve able to accommodate the said screw and extending with clearance inside the said slideway, the said nut being mounted on that end of the said sleeve that is closest to the said motor, and the said first ball end being interposed between the other end of the said sleeve and the said slideway.