Change In Direction Of Rotation Research Articles

Ion thinning of TEM cross sections under beam switching control

Ion milled, cross sectional TEM specimens are used extensively to study the microstructure of multilayered materials. Unfortunately, it is difficult to get all the layers in a cross section equally electron transparent because usually they mill at different rates and have different atomic numbers. Differential thinning can be minimized by milling at low angles so that the slow milling layers protect the fast milling layers from the ion beam. However, even at low angles uneven milling can still occur when the ion beam travels along the multilayer interface (glue line). This problem can be partially overcome by using a shield to cut off the ion beam in these directions. However, this solution is not completely satisfactory because material sputtered from the edge of the shield can contaminate the specimen. A better solution, is to rock the specimen over a range of angles while the ion beam is centered approximately about the perpendicular to the glue line. With this method there is a possibility of uneven milling at both ends of the rocking angle where the beam is stationary for a short period during the change in direction of specimen rotation. Another solution, which is reported here, is to rotate the specimen continuously in the normal way and to switch off the ion beam as it passes by along the specimen glue line.

Contingent aftereffects: Lateral interactions between color and motion

A randomly dotted yellow disk was rotated at a speed of 5 rpm, alternating in direction every 10 sec. Its change in direction of rotation was paired with a change in surround color, which was either red or green. After 15 min of exposure, observers reported vivid motion aftereffects contingent on the color of both the stationary disk and the surround, even though during adaptation only motion or color was associated with either alone. In further experiments, it was established that a change in color (or direction of motion) of the disk could be associated with a change in direction of motion (or color) of the surround. Such lateral effects were found even when a wide (5 degree) annulus was introduced between the disk and the surround during adaptation and testing. Furthermore, the aftereffects generalized to the annulus, which was not associated with either color or motion during adaptation. However, when the disk alone was adapted to color and motion, no generalization to the surround was found (and vice versa), suggesting that the effects are not produced by adaptation of large receptive fields or by scatter of light within the eye. The results appear to conflict with the ideas that contingent aftereffects are confined to the adapted area of the retina and that they are built up by links between single-duty neurones, and with an extreme view of the segregation of color and motion early in human vision.

New aspect of giant exciton Faraday rotation in Cd1-xMnx Te semimagnetic compomd: Fundamentals and applications

Wavelength, magnetic field, and temperature dependences of Faraday rotation (FR) in various compositions of the dilute magnetic semiconductors Cd1-xMn Te and Zn1-xMn Te have been experimentally investigated. Regularities of the Faraday effect dispersion connected with the change of rotation direction as a function of temperature and Mn concentration in the compound have been revealed. Deviation in FR saturation at helium temperatures and high magnetic fields is observed. According to the FR temperature dependence, the spontaneous Faraday effect is assumed to be a characteristic of the spin glass state of semimagnetic semiconductors. A rapid magnetic field sensor system as a possible application of this material has been proposed.

Pausing, switching and speed fluctuation of the bacterial flagellar motor and their relation to motility and chemotaxis

Wild-type Escherichia coli and Salmonella typhimurium cells, tethered to glass by their flagella, rotate with brief intermittent pauses, the prevalence of which is decreased by attractants and increased by repellents. By attaching latex beads to filaments of a S. typhimurium mutant having straight rather than helical flagella, it was established that the flagella on free cells also pause intermittently. Pausing is therefore an intrinsic feature of the motor and not an artifact associated with tethering. In tethered cells of wild-type strains and non-chemotactic mutants defective in transducers, chemotaxis proteins, or the flagellar switch, both the classical response to chemotactic stimuli (change in direction of rotation from counterclockwise to clockwise or vice versa), and the pausing response to such stimuli, were linked together. No separate signal for pausing was found. In comparing different strains under different stimulation conditions, it was found that cells that never reversed seldom if ever paused, while cells that reversed frequently paused frequently. It is suggested that pausing is the result of futile switching events. A modified description of tumbling and chemotaxis is provided in which pausing, as well as reversal, has a role. Suppression of reversals and pauses by attractant stimuli commonly resulted in an increase in the speed of counterclockwise rotation; this may be because of suppression of pauses or reversals that are too brief to be detected. The clockwise rotation rate of unstimulated cells, which commonly was faster than their counterclockwise rate, was not further increased by repellent stimuli. The rotation rate of any given cell under any given condition was found to fluctuate on all time-scales measured. The study also revealed that some of the common repellents of E. coli and S. typhimurium slow down or stop the motor; these effects are not mediated by the chemotaxis machinery or intracellular pH.

Vertical Variations of Tidal Currents in Shallow Land Fast Ice-Covered Regions

Arctic tidal currents with periods near the local inertial period are strongest and rotate clockwise at mid-depth, and decrease in amplitude towards the bottom and ice-cover, experiencing a change in direction of rotation of the current vector to counterclockwise near the boundaries. Such observations are explained by analytical solutions to a simple model in which the current vector of frequency ω is the sum of oppositely rotating components. The frictional boundary layer thickness is proportional to (ω±f)−1, and therefore is markedly different for the two components. In the case of semidiurnal tidal components at high latitudes, the positive rotary component has a thin boundary layer and dominates near the boundaries, whereas the negative rotary component with a much larger boundary layer dominates at mid-depth. For a two-layered ocean, a set of particular solutions is used to verify the observed vertical variations in velocity components with maxima occurring at the interface between the two layers (pycnocline). A general solution consisting of the sum of particular and homogeneous solutions is also presented for the condition when the maxima in velocity components occurs away from the interface.

Change in direction of flagellar rotation is the basis of the chemotactic response in Escherichia coli.

BERG and Anderson1 recently argued from existing evidence that bacteria swim by rotation of their helical flagella. Silver-man and Simon2 have now provided a clear demonstration of this. By means of antibodies specific for flagellar components, they tethered cells to microscope slides or to each other and observed rotation of the cell bodies. The cells were able to stop and to rotate in either direction. It seemed possible, as they proposed2, that cessation, or reversal of flagellar rotation might be involved in bacterial chemotaxis. Accordingly, we used wild-type and chemotaxis-defective mutant cells of Escherichia coli tethered to microscope slides in a manner similar to that of Silverman and Simon2, and stimulated them by sudden increases of chemotactic agents. We found that changes in the direction of flagellar rotation indeed constitute the basis of chemotaxis: addition of attractants causes counter clockwise (CCW) rotation, whereas repellents cause clockwise (CW) rotation.

Drifting and Rifting of Africa

THE purpose of my recent article1 was to bring together various geophysical data relating to the development and evolution of the East African rift system. I do not deduce a clockwise rotation of Africa from palaeomagnetic data alone as Brock presumes in the previous communication. All I say is “… there is some suggestion of a change in direction of rotation of Africa … consistent with the interpretation of the magnetic anomalies over the Red Sea …” and the question mark in Fig. 5 emphasizes this. I also discussed the difficulty of separating polar wander from continental movement.