Noncontact Method Aligns Liquid Crystal Molecules
- PDF / 370,694 Bytes
- 1 Pages / 612 x 792 pts (letter) Page_size
- 67 Downloads / 212 Views
above room temperature. For lower temperatures, alcohol cooled by dry ice (CO2) or liquid nitrogen were used to lower the temperature of the samples. Samples tested at temperatures above ~1500 K showed ductilities up to 7%, and no work hardening. The yield stresses in that range increased with decreasing temperature. At ~1500 K there was a transition to a brittle behavior, and the fracture stresses decreased with decreasing temperature until ~1050 K. Below ~900 K down to room temperature, ductilities up to 8% were again observed, but the flow stress remained constant in all tests. At lower temperatures, a continuous increase in the flow stress with decreasing temperature appeared, but not as accelerated as in the tests at high temperature. The researchers observed that this behavior is similar to that of Mg2GeO4 olivine and some intermetallics with an Ll2 structure. Observations of a sample tested at room temperature under transmitted polarized light showed evidence of birefringence bands. Plastically deformed samples tested below ~900 K typically exhibit these bands. These features were not detected in samples tested above 1500 K. Studies about the slip systems acting in this ceramic are limited, and subsequent transmission electron microscopy (TEM) observations become necessary to determine the characteristics of the dislocation activity and its relationship with the flow process. Preliminary observations from this investigation show dislocation dipoles and stacking faults. The researchers expect to later present their results on extensive TEM observations performed in these specimens. SIARI S. SOSA
Hassium Confirmed as Group VIII Member in Periodic Table A team of researchers has established that element 108, hassium, forms a gaseous oxide similar to that of osmium, confirming that hassium, like osmium, is a member of Group VIII of the periodic table and should be placed directly under it. Heino Nitsche of Lawrence Berkeley National Laboratory, who is also a professor of chemistry at the University of California—Berkeley, directed the development of a very low temperature technique for separating and detecting oxides from Group VIII. The researchers used a heavy ion accelerator at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany. Hassium does not exist in nature but must be created one atom at a time by fus-
MRS BULLETIN/JULY 2001
ing lighter nuclei. Energetic magnesium-26 projectiles bombarded targets of curium-248, a rare artificial isotope prepared for the experiment. Multiple curium targets were mounted in a rotating wheel system. The hassium atoms formed by impacts between target and beam reacted with oxygen to form hassium oxide molecules. The single molecules were carried through the detector by a stream of helium and immediately condensed on semiconductor diodes, arranged in rows and maintained at temperatures graded from -20°C to -170°C.
Laser Beam with Spiral Interference Pattern Allows Controlled Rotation of Micro-Objects By combining an annular-shaped laser beam with a refere
Data Loading...
