Abrupt Degradation Research Articles

Differential occurrence of CSF-like activity and transforming activity of Mos during the cell cycle in fibroblasts.

The Xenopus c-mos proto-oncogene product, Mosxe, possesses cytostatic factor (CSF) activity to arrest maturing oocytes in metaphase II and has weak transforming activity in mouse NIH3T3 cells. We show that Mosxe mutants bearing 'stabilizing' penultimate N-terminal amino acids are strongly transforming and can retard progression through the G2-M phases in Mosxe-transformed cells, probably via their CSF activity. On the other hand, a cyclin-Mosxe fusion protein, which undergoes abrupt degradation at the end of mitosis and is restored to its normal levels only after the G1 phase, transforms cells much less efficiently than a mutated cyclin-Mosxe fusion protein that is stable during M-G1 transition. Moreover, in low-serum medium, cells transformed by the unstable cyclin-Mosxe require a long period to enter the S phase, in contrast with the rapid entry into the S phase of cells transformed by the stable cyclin-Mosxe. These results provide strong evidence that unlike the physiological CSF activity, the transforming activity of Mos is exerted in the G1 phase of the cell cycle.

Magnetic and structural properties of melt-spun erbium-iron-boron ribbons

Melt-spun ribbons of Er0.135Fe0.813B0.052 have a relatively large coercivity of nearly 5 kOe. The coercivity is a sharply peaked function of wheel speed (quench rate) with the optimally quenched ribbons having a wheel speed of 14 m/s and a Br of 4 kG. This also coincides with the maximum in energy product of 2.9 MGOe. The abrupt degradation of coercivity with increasing quench rate corresponds precisely to the lack of crystallinity of the ribbons as determined by x-ray powder diffraction.

The effect of carbon on magnetic properties of an Fe-Cr-Co permanent magnet alloy

The effect of carbon on magnetic properties of an Fe- 24Cr-12Co-1Si-1Ti alloy with carbon content from 0.012 to 0.291 percent (by weight) was studied. It has been found that for a carbon content larger than 0.05 percent there is an abrupt degradation in magnetic properties for alloys treated according to a normal procedure to develop the magnetically optimum state. The reasons have been thoroughly explored by optical metallography, X-ray diffractometry, transmission electron microscopy, carbide extraction, and analysis and hardness measurements. Carbon stabilization of the γ phase, the amount of which increases with carbon content, is the main deteriorating factor found in this alloy. Abnormal spinodal decomposition between α phase and non-α-phase regions and Cr-rich carbide precipitated in or near α-phase impair magnetic properties further. It has been shown that prolonged solution treatment at temperatures near the solidus can compensate part of the carbon effect at the expense of (B-H)m value. Hence, for practical purposes, the 0.05 percent C is set to be the upper limit for ensuring (B-H)m value greater than 5.5 MGOe for this alloy, and the 0.05 percent C limitation is suggested to be common to all Fe-Cr-Co permanent magnet alloys.

Abrupt degradation of three types of semiconductor light emitting diodes at high temperature

Abrupt degradation of three types of semiconductor light emitting diodes (LED’s), Ga1−xAlxAs double-heterostructure (DH) LED’s, Ga1−xAlxAs/ GaAs DH LED’s, and LED-operated Ga1−xAlxAs/ GaAs DH lasers operated at high temperature, was studied by electroluminescence topography, photoluminescence topography, and transmission electron microscopy. The following results were obtained from all types of the diodes. Dark regions which included 〈100〉 dark-line defects (DLD’s) and/or 〈110〉 DLD’s were often observed in the electronluminescence or photoluminescence patterns of the active regions. Two phenomena were associated with this type of degradation as follows: (i) generation of high density of dislocations and dislocation loops (in some cases, stacking faults) by dislocation glide motion due to the relaxation of the stress concentrated in the active region. (ii) subsequent development of dislocation dipoles from the glided dislocations (often accompanied with many small dislocation loops). In some of the degraded diodes, the phenomenon (ii) did not occur. There might be a certain threshold for the phenomenon (ii).