Abstract: A shoe has a retractable heel which is normally latched in an upright position and spring biased into an inclined position. A wearer's foot, when the shoe is donned, acts on a floor member, forcing the heel section into the upright position, causing the heel section to latch to the shoe. The shoe is thus maintained in the donned state, and grips the foot without laces or other attachment devices. A release mechanism is operated by a rod projecting from the rear of the shoe. Release is actuated by moving the shoe rear end against any solid object, thus depressing the release rod. A wearer thus dons the shoe by stepping into it, and releases the heel in order to doff the shoe by manipulating the shoe by foot. Thus, a wearer does not need to use his or her hands either to don or doff the shoe.

Abstract: This invention encompasses a water-to-water heat-pipe heat exchanger having vessel, at least one partition dividing said vessel into at least two compartments, at least one of said compartments further having a fresh water input means and a fresh water output means, and a different compartment having a hot waste water input means and a hot waste water output means, and a plurality of heat exchange pipes for transferring heat between said compartments. The invention is generally in heat exchangers, and for dissipating heat in any system by transferring heat from a hot to a cool substance. Such a system may be used to alleviate the excessive heat generated during thermonuclear reactions, wherein cool water is exposed to a vessel containing hot waste water to cool the temperature of the waste water, such that no mixing or interchange of hot and cool water occurs.