scholarly journals On arc characteristics in high pressure helium atmosphere.

1988 ◽  
Vol 6 (1) ◽  
pp. 86-91 ◽  
Author(s):  
Yasuo Suga ◽  
Atsushi Hasui
Author(s):  
Xiaohuan Chen ◽  
Yinan Geng ◽  
Jie Wang

The High Temperature Gas-cooled Reactor (HTGR) designed by Tsinghua university is under development in China. The electrical equipment in Pressure Vessel, such as magnetic bearings and helium circulator are operating in the high pressure helium environment. Design research of insulation property of the electrical device in helium under high pressure is necessary. Nevertheless, it is challenging to investigate by experimental technique. We propose a similarity law, converting the high pressure to a lower pressure to simplify the experimental conditions. Similarity theory of gas discharge is that two geometrically similar gaps with scaling coefficients of k, based on the same product number of pressure p and the gas length d, have the similar discharge characteristics. We research the validity of discharge similarity theory by simulation. A fluid model of direct-current discharge in helium atmosphere was established, referencing experimental results. And the discharge models of gaps were solved by finite-element method respectively. Four geometrically similar gaps were designed, the prototype gap is 2cm long and operating at a pressure of 600Pa while the pressure of three similar gaps are 300Pa, 200Pa, and 120Pa, and corresponding to the length of gaps are 4cm, 6cm and 10cm, with scaled-down factor k of 2, 3, and 5 respectively. The simulation results show that as long as the scaled-down factor of pressure k is less than 5 and the reduced length relation meets the condition p1d1 = p2d2, the discharge characteristics of two geometrically similar gaps are similar. As a result, it is realizable to predict the insulation property of electrical device in helium with similarity law.


Sadhana ◽  
2019 ◽  
Vol 44 (3) ◽  
Author(s):  
Shaojie Wu ◽  
Shan Gong ◽  
Hongming Gao

Author(s):  
Marek Malecki ◽  
James Pawley ◽  
Hans Ris

The ultrastructure of cells suspended in physiological fluids or cell culture media can only be studied if the living processes are stopped while the cells remain in suspension. Attachment of living cells to carrier surfaces to facilitate further processing for electron microscopy produces a rapid reorganization of cell structure eradicating most traces of the structures present when the cells were in suspension. The structure of cells in suspension can be immobilized by either chemical fixation or, much faster, by rapid freezing (cryo-immobilization). The fixation speed is particularly important in studies of cell surface reorganization over time. High pressure freezing provides conditions where specimens up to 500μm thick can be frozen in milliseconds without ice crystal damage. This volume is sufficient for cells to remain in suspension until frozen. However, special procedures are needed to assure that the unattached cells are not lost during subsequent processing for LVSEM or HVEM using freeze-substitution or freeze drying. We recently developed such a procedure.


Author(s):  
Robert Corbett ◽  
Delbert E. Philpott ◽  
Sam Black

Observation of subtle or early signs of change in spaceflight induced alterations on living systems require precise methods of sampling. In-flight analysis would be preferable but constraints of time, equipment, personnel and cost dictate the necessity for prolonged storage before retrieval. Because of this, various tissues have been stored in fixatives and combinations of fixatives and observed at various time intervals. High pressure and the effect of buffer alone have also been tried.Of the various tissues embedded, muscle, cartilage and liver, liver has been the most extensively studied because it contains large numbers of organelles common to all tissues (Fig. 1).


Author(s):  
R.E. Crang ◽  
M. Mueller ◽  
K. Zierold

Obtaining frozen-hydrated sections of plant tissues for electron microscopy and microanalysis has been considered difficult, if not impossible, due primarily to the considerable depth of effective freezing in the tissues which would be required. The greatest depth of vitreous freezing is generally considered to be only 15-20 μm in animal specimens. Plant cells are often much larger in diameter and, if several cells are required to be intact, ice crystal damage can be expected to be so severe as to prevent successful cryoultramicrotomy. The very nature of cell walls, intercellular air spaces, irregular topography, and large vacuoles often make it impractical to use immersion, metal-mirror, or jet freezing techniques for botanical material.However, it has been proposed that high-pressure freezing (HPF) may offer an alternative to the more conventional freezing techniques, inasmuch as non-cryoprotected specimens may be frozen in a vitreous, or near-vitreous state, to a radial depth of at least 0.5 mm.


Author(s):  
William P. Sharp ◽  
Robert W. Roberson

The aim of ultrastructural investigation is to analyze cell architecture and relate a functional role(s) to cell components. It is known that aqueous chemical fixation requires seconds to minutes to penetrate and stabilize cell structure which may result in structural artifacts. The use of ultralow temperatures to fix and prepare specimens, however, leads to a much improved preservation of the cell’s living state. A critical limitation of conventional cryofixation methods (i.e., propane-jet freezing, cold-metal slamming, plunge-freezing) is that only a 10 to 40 μm thick surface layer of cells can be frozen without distorting ice crystal formation. This problem can be allayed by freezing samples under about 2100 bar of hydrostatic pressure which suppresses the formation of ice nuclei and their rate of growth. Thus, 0.6 mm thick samples with a total volume of 1 mm3 can be frozen without ice crystal damage. The purpose of this study is to describe the cellular details and identify potential artifacts in root tissue of barley (Hordeum vulgari L.) and leaf tissue of brome grass (Bromus mollis L.) fixed and prepared by high-pressure freezing (HPF) and freeze substitution (FS) techniques.


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