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Putting a Cell Together
Published in Thomas M. Nordlund, Peter M. Hoffmann, Quantitative Understanding of Biosystems, 2019
Thomas M. Nordlund, Peter M. Hoffmann
The entire nuclear pore complex (NPC) is large for a porin. The overall diameter is about 120 nm; the hole has an effective diameter of ~9 nm and depth of ~200 nm; the molecular mass is about 120 MD in mammals, with 30 types of proteins in the complex.12 A protein complex of this large size will not likely be found in the Protein Data Bank (PDB) database of X-ray and nuclear magnetic resonance structures. However, electron microscopy, with its resolution of 10 nm or so, is an ideal tool to determine at least a coarse structure. This has been done, and one image is shown in Figure 7.15. The small end of the pore is shown in the diagram. Note that the authors believe the opposite, wider end of the pore is occupied by a particle in transport through the pore. Some other helpful electron microscope–based diagrams and animations of this complex can be seen at http://sspatel.googlepages.com/nuclearporecomplex2. The pore may be able to expand to 25 nm or so to allow passage of larger molecules. Small particles (<30 kDa) are able to pass through the NPC by passive diffusion. Passage of larger molecules through the pore requires several other proteins. Note that at least in the Ostreococcus cell (Figures 7.13 and 7.14), molecules that pass in and out of the nucleus are quite likely to come against or come from another organelle inside the cell; there is not a large free volume of cytosol outside the nucleus.
Two-dimensional analysis of tapered heat flux burner for measuring laminar burning velocity
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2019
Vinod Kumar Yadav, Shriyansh Srivastava, Vinay Yadav
Powling (1949) commenced the concept of development of flat flame which is free from surface contact. The burner designed by Powling accurately measured true burning velocities and limits of flammability provided that the reacting gases flowed with a perfectly uniform velocity distribution and the flow remains undisturbed by the higher temperature products of combustion. It was observed that the establishment of approximately one-dimensional flame was dependent upon equating laminar burning velocity to the velocity of the unburned mixture flowing toward the burner. However, Powling’s burner could develop flat flames over a speed range of 5–10 cm/s (Powling 1949). Botha and Spalding (1954) extended the range of measurement of laminar burning velocities from 4 to 38 cm/s which helped them to study a wider range of mixture ratios as compared to Powling. They performed the experiments on porous plug burner and measured the temperature rise of cooling water flowing through the porous plug burner. They obtained the burning velocity under adiabatic state by extrapolating their results to zero heat loss. There were large uncertainties due to small rise in cooling water temperature. De Goey, Maaren, and Quax (1993) used the heat flux method to quantify the heat lost by flame to the burner plate by measuring the temperature at the surface of the burner plate. The heat loss was balanced by adding a known quantity of heat energy to the unburnt side and obtained the adiabatic flame. This method is suitable for burning velocity up to 60 cm/s. Maaren, Thung, and de Goey (1994) reported that the velocity distribution for unburnt and burnt mixture is practically uniform (inside the 1D area) in the heat flux method. They showed that despite the coarse structure of the burner plate perforation, the flame temperature profile is independent of perforation pattern geometry.