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Specimens sandwiched between copper planchettes were plunged up to a depth of 430 mm into coolants used for cryofixation. Hydrated gelatin containing a miniature thermocouple was used to mimic the behaviour of tissue during freezing. Gelatin and red blood cells were used for ice-crystal analysis. Ethane produced the fastest cooling rates and the smallest(More)
It is important for future ultrastructural preservation studies to freeze biological specimens as rapidly as possible. Finite element numerical techniques have been used to compare different cooling block materials used in the quick freeze 'slamming' method. It is concluded that a pure silver block at an optimum initial temperature of about 15.6 K will(More)
A theoretical model is proposed which is used to derive a quantitative relationship between the critical cooling rate and average crystal size at any location within a biological specimen of given shape subject to rapid freezing. The model is applicable to the slamming, plunging or spraying methods of cryofixation provided the ice crystal size is at least 5(More)
An explicit numerical finite difference scheme for defining the thermal history of a cell or group of cells contained within a biological sample of prescribed shape is described. Solutions are presented for three different cases of freezing of biological materials prior to microscopic examination. It is concluded that a surface boundary condition must be(More)
The design and testing of a prototype cryosurgical probe utilizing helium gas precooled with liquid nitrogen are described. An 8-mm-diameter probe produced an ice ball with a diameter of 28 mm after 10 min freezing using a helium gas flow rate of 42 liter/min. This indicated a surface heat transfer coefficient of 0.34 W/cm2 degrees K and temperature of -138(More)
The construction and preliminary testing of a device is described which can be used to freeze biological specimens in any cryogenic liquid at temperatures down to the nitrogen freezing point (63 K) and which can operate in the pressure range 1.3 kNm-2 to 1 MNm-2. Ultra-rapid freezing can be carried out in a subcooled cryogenic liquid either hyperbarically(More)
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