Abstract: A cooling system employs a single-acting positive displacement bellows pump to transfer a cryogenic liquid such as liquid nitrogen from a storage dewar to a heat exchanger coupled to a measurement chamber of an instrument, wherein cooling takes place by vaporizing the liquid. Preferably, the capacity of the pump is greater than the maximum cooling requirement of the instrument, wherein both vapor resulting from vaporizing of the cryogenic liquid circulated through the heat exchanger and liquid that does not vaporize when circulated through the heat exchanger are returned to the storage dewar, wherein the vapor is subsequently vented from the dewar. Preferably, with the aid of a weir in a return line, the level of liquid in the heat exchanger is maintained full and constant, and the cooling demands are automatically met without the need for other control of the flow rate or level of the liquid.

Abstract: A cooling system employs a single-acting positive displacement bellows pump to transfer a cryogenic liquid such as liquid nitrogen from a storage dewar to a heat exchanger coupled to a measurement chamber of an instrument, wherein cooling takes place by vaporizing the liquid. Preferably, the capacity of the pump is greater than the maximum cooling requirement of the instrument, wherein both vapor resulting from vaporizing of the cryogenic liquid circulated through the heat exchanger and liquid that does not vaporize when circulated through the heat exchanger are returned to the storage dewar, wherein the vapor is subsequently vented from the dewar. Preferably, with the aid of a weir in a return line, the level of liquid in the heat exchanger is maintained full and constant, and the cooling demands are automatically met without the need for other control of the flow rate or level of the liquid.

Abstract: A writing utensil configurable between retracted and extended configurations is provided. The writing utensil includes a body having an interior volume and an aperture. A reciprocally movable nib assembly is located in the body and includes a nib that, when in the extended configuration, traverses the aperture. To prevent the nib from drying when in the retracted configuration, a sealing element seals the aperture. In an embodiment, the sealing element is a resilient valve element that can be opened by a sleeve slidably engaging the nib assembly. After the sleeve opens the valve, the sleeve slides with respect to the nib assembly to expose the nib. In another embodiment, the sealing element can be a sliding door that is attached to the nib assembly and overlays the aperture. When the nib assembly is moved to the extended configuration, the sliding door slides in a manner that opens the aperture.