Determination of successive ionization constants: A computer assisted laboratory experiment

1970 ◽  
Vol 47 (2) ◽  
pp. 147 ◽  
Author(s):  
R. E. Jensen ◽  
R. G. Garvey ◽  
B. A. Paulson
Keyword(s):  
Laboratory Experiment ◽  
Ionization Constants ◽  
Computer Assisted

Computer-Assisted High-Re Solution TEM

1990 ◽  
Vol 48 (1) ◽  
pp. 162-163
Author(s):  
F.A. Ponce ◽  
H. Hikashi
Keyword(s):  
Signal To Noise Ratio ◽  
Accurate Determination ◽  
Computer Software ◽  
Video Camera ◽  
Image Contrast ◽  
Objective Lens ◽  
Computer Assisted ◽  
Optical Parameters ◽  
Astigmatism Correction

The determination of the atomic positions from HRTEM micrographs is only possible if the optical parameters are known to a certain accuracy, and reliable through-focus series are available to match the experimental images with calculated images of possible atomic models. The main limitation in interpreting images at the atomic level is the knowledge of the optical parameters such as beam alignment, astigmatism correction and defocus value. Under ordinary conditions, the uncertainty in these values is sufficiently large to prevent the accurate determination of the atomic positions. Therefore, in order to achieve the resolution power of the microscope (under 0.2nm) it is necessary to take extraordinary measures. The use of on line computers has been proposed [e.g.: 2-5] and used with certain amount of success.We have built a system that can perform operations in the range of one frame stored and analyzed per second. A schematic diagram of the system is shown in figure 1. A JEOL 4000EX microscope equipped with an external computer interface is directly linked to a SUN-3 computer. All electrical parameters in the microscope can be changed via this interface by the use of a set of commands. The image is received from a video camera. A commercial image processor improves the signal-to-noise ratio by recursively averaging with a time constant, usually set at 0.25 sec. The computer software is based on a multi-window system and is entirely mouse-driven. All operations can be performed by clicking the mouse on the appropiate windows and buttons. This capability leads to extreme friendliness, ease of operation, and high operator speeds. Image analysis can be done in various ways. Here, we have measured the image contrast and used it to optimize certain parameters. The system is designed to have instant access to: (a) x- and y- alignment coils, (b) x- and y- astigmatism correction coils, and (c) objective lens current. The algorithm is shown in figure 2. Figure 3 shows an example taken from a thin CdTe crystal. The image contrast is displayed for changing objective lens current (defocus value). The display is calibrated in angstroms. Images are stored on the disk and are accessible by clicking the data points in the graph. Some of the frame-store images are displayed in Fig. 4.

Determination of the tertiary structure of glycoprotein hormones by computer-assisted modelling of hCG

1986 ◽  
Vol 113 (1_Suppl) ◽  
pp. S134-S135
Author(s):  
K.P. WILLEY ◽  
M. R. LUCK ◽  
F. LEIDENBERGER
Keyword(s):  
Tertiary Structure ◽  
Computer Assisted ◽  
Glycoprotein Hormones

Determination of Nitrate and Nitrite in Water by Capillary Electrophoresis: An Undergraduate Laboratory Experiment

1998 ◽  
Vol 75 (12) ◽  
pp. 1588 ◽  
Author(s):  
David S. Hage ◽  
Anuja Chattopadhyay ◽  
Carrie A. C. Wolfe ◽  
Julie Grundman ◽  
Paul Kelter
Keyword(s):  
Capillary Electrophoresis ◽  
Laboratory Experiment ◽  
Undergraduate Laboratory ◽  
Nitrate And Nitrite
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