High Precision in Fluidic Control Provides Needed and Reliable Accuracy in Ligand Induced Current Responses of Acetylcholine and GABA Receptors

The pharmacology of a γ-aminobutyric acid (GABA) receptor on the cell body of an identified motor neuron of the cockroach ( Periplaneta americana ) was investigated by current-clamp and voltage-clamp methods. Iontophoretic application of GABA increased membrane conductance to chloride ions, and prolonged application resulted in desensitization. Hill coefficients, determined from dose–response data, indicated that binding of at least two GABA molecules was required to activate the chloride channel. Differences between vertebrate GABA A receptors and insect neuronal GABA receptors were detected. For the GABA receptor of motor neuron D f , the following rank order of potency was observed: isoguvacine > muscimol ≽ GABA > 3-aminopropanesulphonic acid. The GABA B receptor agonist baclofen was inactive. Of the potent vertebrate GABA receptor antagonists (bicuculline, pitrazepin, RU5135 and picrotoxin), only picrotoxin (10 –7 M) produced a potent, reversible block of the response to GABA of motor neuron D f . Both picrotoxinin and picrotin also blocked GABA-induced currents. Bicuculline hydrochloride (10 –4 M) and bicuculline methiodide (10 –4 M) were both ineffective when applied at resting membrane potential (–65 mV), although at hyper-polarized levels partial block of GABA-induced current was sometimes observed. Pitrazepin (10 –4 M) caused a partial, voltage-independent block of GABA-induced current. The steroid derivative RU5135 was inactive at 10 –5 M. In contrast to the potent competitive blockade of vertebrate GABA A receptors by bicuculline, pitrazepin and RU5135, none of the weak antagonism caused by these drugs on the insect GABA receptor was competitive. Flunitrazepam (10 –6 M) potentiated GABA responses, providing evidence for a benzodiazepine site on an insect GABA-receptor–chloride-channel complex.

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Automatic measurement of SAED patterns from asbestos minerals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100106296 ◽

1988 ◽

Vol 46 ◽

pp. 846-847

Author(s):

J. C. Russ ◽

T. Taguchi ◽

P. M. Peters ◽

E. Chatfield ◽

J. C. Russ ◽

...

Keyword(s):

Diffraction Pattern ◽

High Precision ◽

Diffraction Data ◽

Automatic Measurement ◽

Automatic Method ◽

Important Method ◽

X Ray ◽

Integrated Intensity ◽

Asbestiform Minerals ◽

True Center

Conventional SAD patterns as obtained in the TEM present difficulties for identification of materials such as asbestiform minerals, although diffraction data is considered to be an important method for making this purpose. The preferred orientation of the fibers and the spotty patterns that are obtained do not readily lend themselves to measurement of the integrated intensity values for each d-spacing, and even the d-spacings may be hard to determine precisely because the true center location for the broken rings requires estimation. We have implemented an automatic method for diffraction pattern measurement to overcome these problems. It automatically locates the center of patterns with high precision, measures the radius of each ring of spots in the pattern, and integrates the density of spots in that ring. The resulting spectrum of intensity vs. radius is then used just as a conventional X-ray diffractometer scan would be, to locate peaks and produce a list of d,I values suitable for search/match comparison to known or expected phases.

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On effects of non-systematic reflections on weak-beam images of partial dislocations

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100087756 ◽

1991 ◽

Vol 49 ◽

pp. 688-689

Author(s):

K. Z. Botros ◽

S. S. Sheinin

Keyword(s):

High Precision ◽

Stacking Fault ◽

Important Application ◽

Stacking Fault Energy ◽

Sharp Peak ◽

Weak Beam ◽

Partial Dislocations ◽

Deviation Parameter ◽

Beam Diffraction

The main features of weak beam images of dislocations were first described by Cockayne et al. using calculations of intensity profiles based on the kinematical and two beam dynamical theories. The feature of weak beam images which is of particular interest in this investigation is that intensity profiles exhibit a sharp peak located at a position very close to the position of the dislocation in the crystal. This property of weak beam images of dislocations has an important application in the determination of stacking fault energy of crystals. This can easily be done since the separation of the partial dislocations bounding a stacking fault ribbon can be measured with high precision, assuming of course that the weak beam relationship between the positions of the image and the dislocation is valid. In order to carry out measurements such as these in practice the specimen must be tilted to "good" weak beam diffraction conditions, which implies utilizing high values of the deviation parameter Sg.

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Digital differential hysteresis iimage processing displays what the microscope acquires but the eye can't see

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100139585 ◽

1995 ◽

Vol 53 ◽

pp. 642-643

Author(s):

Klaus-Ruediger Peters

Keyword(s):

Image Processing ◽

Visual System ◽

High Precision ◽

Image Data ◽

Processing Technology ◽

Output Data ◽

Contrast Resolution ◽

Pixel Intensity ◽

Data Reading ◽

Hysteresis Properties

Differential hysteresis processing is a new image processing technology that provides a tool for the display of image data information at any level of differential contrast resolution. This includes the maximum contrast resolution of the acquisition system which may be 1,000-times higher than that of the visual system (16 bit versus 6 bit). All microscopes acquire high precision contrasts at a level of <0.01-25% of the acquisition range in 16-bit - 8-bit data, but these contrasts are mostly invisible or only partially visible even in conventionally enhanced images. The processing principle of the differential hysteresis tool is based on hysteresis properties of intensity variations within an image.Differential hysteresis image processing moves a cursor of selected intensity range (hysteresis range) along lines through the image data reading each successive pixel intensity. The midpoint of the cursor provides the output data. If the intensity value of the following pixel falls outside of the actual cursor endpoint values, then the cursor follows the data either with its top or with its bottom, but if the pixels' intensity value falls within the cursor range, then the cursor maintains its intensity value.

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Electron beam induced current study of thin silicon layers on insulator substrate

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100176228 ◽

1990 ◽

Vol 48 (4) ◽

pp. 618-619

Author(s):

A. Buczkowski ◽

Z. J. Radzimski ◽

J. C. Russ ◽

G. A. Rozgonyi

Keyword(s):

Electron Beam ◽

Energy Loss ◽

Beam Energy ◽

Collection Efficiency ◽

Silicon Layer ◽

Depletion Layer ◽

Incident Electron Energy ◽

Induced Current ◽

Electron Hole ◽

Electron Beam Induced Current

If a thickness of a semiconductor is smaller than the penetration depth of the electron beam, e.g. in silicon on insulator (SOI) structures, only a small portion of incident electrons energy , which is lost in a superficial silicon layer separated by the oxide from the substrate, contributes to the electron beam induced current (EBIC). Because the energy loss distribution of primary beam is not uniform and varies with beam energy, it is not straightforward to predict the optimum conditions for using this technique. Moreover, the energy losses in an ohmic or Schottky contact complicate this prediction. None of the existing theories, which are based on an assumption of a point-like region of electron beam generation, can be used satisfactorily on SOI structures. We have used a Monte Carlo technique which provide a simulation of the electron beam interactions with thin multilayer structures. The EBIC current was calculated using a simple one dimensional geometry, i.e. depletion layer separating electron- hole pairs spreads out to infinity in x- and y-direction. A point-type generation function with location being an actual location of an incident electron energy loss event has been assumed. A collection efficiency of electron-hole pairs was assumed to be 100% for carriers generated within the depletion layer, and inversely proportional to the exponential function of depth with the effective diffusion length as a parameter outside this layer. A series of simulations were performed for various thicknesses of superficial silicon layer. The geometries used for simulations were chosen to match the "real" samples used in the experimental part of this work. The theoretical data presented in Fig. 1 show how significandy the gain decreases with a decrease in superficial layer thickness in comparison with bulk material. Moreover, there is an optimum beam energy at which the gain reaches its maximum value for particular silicon thickness.

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