Stress State Required for Pyramidal Dislocation Movement in Zinc

A tension or compression stress in such a direction that basal slip is minimized can produce second-order pyramidal slip bands in zinc single crystals. The stress required to initiate pyramidal dislocation motion is not sensitive to temperature. However, dislocation velocity at a given stress is sensitive to temperature and the very small dislocation velocity at low temperatures has lead to an erroneous estimate of a ``starting stress'' for pyramidal dislocations. Dislocation velocity at a constant temperature was found to be a function of the magnitude, but not the sense of the resolved shear stress

Twinning and Slip in Zinc by Indentation

Observations of twinning and slip deformation caused by indentation of zinc reveal that extensive slip on the basal and second-order pyramidal systems takes place at loads up to 5 kg. Prismatic punching through 1-cm crystals is observed at indentation loads in excess of about 2.5 kg. It is concluded that the stress at the tip of the twins cannot be obtained by use of an elastic stress analysis

Orientation Dependence of a Dislocation Etch for Zinc

The dislocation etch for (101-[bar]0] surfaces of zinc reported by Brandt, Adams, and Vreeland have been further explored. Additional surface orientations have been found where dislocation etching takes place. These orientations cover an area located between 3 degrees and 12.2 degrees to the [0001], and the area is symmetric about that axis. Attempts to produce dislocation etching on within 2 degrees of (0001) were generally unsuccessful. This is in contrast to etching of many crystals which takes place only within a few degrees of a low index plane

Dislocation velocity on the {1212}<1213> slip systems of zinc

Dislocation velocity on the {1212} slip systems of zinc monocrystals was deduced from the rate of growth of slip bands. Near 77°K dislocation velocity is directly proportional to stress, and screw dislocations move more rapidly than edge dislocations. The difference between edge and screw dislocation velocity can be interpreted in two ways. The pre-exponential factors in a thermal activation model may differ by a factor 4 while the common activation energy is 0.21 eV, or the pre-exponential factors are the same, but the activation energy for edge dislocations (0.22 eV) exceeds that for screws by 5%. Other experiments will be required to establish the appropriate model. The authors favor the second alternative since extra activation energy might be needed to change the core structure of the edge dislocations (which lie on the basal planes) to make them glissile. Near room temperature, dislocation velocity decreases and cross-glide increases with increasing temperature. It is suggested that dragging dipoles and debris caused by their dissociation are responsible for the decrease in dislocation velocity. Finally, it is shown that the temperature dependence of both the yield strength and the plastic modulus is similar to the temperature dependence of the stress required to produce a constant dislocation velocity

Dislocation Velocity on the {1212}〈1213〉Slip System of Zinc

Dislocation velocity on the {1212}〈1213〉slip systems of zinc monocrystals was deduced from the rate of growth of slip bands. Near 77°K dislocation velocity is directly proportional to stress, and screw dislocations move more rapidly than edge dislocations. The pre-exponential factor in a thermal activation model is the same for edge and screw dislocations, but the activation energy for edge dislocations (0.22eV) exceeds that for screws by 5%. It is postulated that the larger activation energy for edge dislocations is due to their dissociation in the basal plane. Near room temperature dislocation velocity decreases and cross-glide increases with increasing temperature. It is suggested that dragging dipoles are responsible for the decrease in dislocation velocity. Finally, it is shown that the temperature dependence of both the yield strength and the plastic modulus is similar to the temperature dependence of the stress required to produce a constant dislocation velocity

Second Order Pyramidal Slip in Zinc

Measurements of strain, dislocation density, and dislocation velocity have been made in 99.999% Zn stressed in compression along the hexagonal axis, [0001]. Slip bands on the second order pyramid,〈1213〉{1212}, system were observed. The average dislocation density increases linearly with strain. The velocity of edge dislocations in slip bands obeys the relation v = (Γ/ Γ_0)^n with v in in. / sec, n = 8.7, Γ_0 = 870 lb/in.^2, and Γ the resolved shear stress in lb/in^2. These observations together with measurements of the strain rate sensitivity of the flow stress show that the stress dependence of the density of moving dislocations is more important than the stress dependence of the dislocation velocity as they affect the strain rate

Loss of heterozygosity and SOSTDC1 in adult and pediatric renal tumors

<p>Abstract</p> <p>Background</p> <p>Deletions within the short arm of chromosome 7 are observed in approximately 25% of adult and 10% of Wilms pediatric renal tumors. Within Wilms tumors, the region of interest has been delineated to a 2-Mb minimal region that includes ten known genes. Two of these ten candidate genes, <it>SOSTDC1 </it>and <it>MEOX2</it>, are particularly relevant to tumor development and maintenance. This finding, coupled with evidence that SOSTDC1 is frequently downregulated in adult renal cancer and regulates both Wingless-Int (Wnt)- and bone morphogenetic protein (BMP)-induced signaling, points to a role for SOSTDC1 as a potential tumor suppressor.</p> <p>Methods</p> <p>To investigate this hypothesis, we interrogated the Oncomine database to examine the SOSTDC1 levels in adult renal clear cell tumors and pediatric Wilms tumors. We then performed single nucleotide polymorphism (SNP) and sequencing analyses of <it>SOSTDC1 </it>in 25 pediatric and 36 adult renal tumors. Immunohistochemical staining of patient samples was utilized to examine the impact of <it>SOSTDC1 </it>genetic aberrations on SOSTDC1 protein levels and signaling.</p> <p>Results</p> <p>Within the Oncomine database, we found that SOSTDC1 levels were reduced in adult renal clear cell tumors and pediatric Wilms tumors. Through SNP and sequencing analyses of 25 Wilms tumors, we identified four with loss of heterozygosity (LOH) at 7p and three that affected <it>SOSTDC1</it>. Of 36 adult renal cancers, we found five with LOH at 7p, two of which affected <it>SOSTDC1</it>. Immunohistochemical analysis of SOSTDC1 protein levels within these tumors did not reveal a relationship between these instances of <it>SOSTDC1 </it>LOH and SOSTDC1 protein levels. Moreover, we could not discern any impact of these genetic alterations on Wnt signaling as measured by altered beta-catenin levels or localization.</p> <p>Conclusions</p> <p>This study shows that genetic aberrations near <it>SOSTDC1 </it>are not uncommon in renal cancer, and occur in adult as well as pediatric renal tumors. These observations of <it>SOSTDC1 </it>LOH, however, did not correspond with changes in SOSTDC1 protein levels or signaling regulation. Although our conclusions are limited by sample size, we suggest that an alternative mechanism such as epigenetic silencing of <it>SOSTDC1 </it>may be a key contributor to the reduced SOSTDC1 mRNA and protein levels observed in renal cancer.</p