Phase transformations induced by spherical indentation in ion-implanted amorphous silicon

The deformation behavior of ion-implanted (unrelaxed) and annealed ion-implanted (relaxed) amorphous silicon(a-Si) under spherical indentation at room temperature has been investigated. It has been found that the mode of deformation depends critically on both the preparation of the amorphous film and the scale of the mechanical deformation.Ex situmeasurements, such as Raman microspectroscopy and cross-sectional transmission electron microscopy, as well as in situ electrical measurements reveal the occurrence of phase transformations in all relaxed a-Si films. The preferred deformation mode of unrelaxed a-Si is plastic flow, only under certain high load conditions can this state of a-Si be forced to transform. In situ electrical measurements have revealed more detail of the transformation process during both loading and unloading. We have used ELASTICA simulations to obtain estimates of the depth of the metallic phase as a function of load, and good agreement is found with the experiment. On unloading, a clear change in electrical conductivity is observed to correlate with a “pop-out” event on load versus penetration curves

Certain Adenylated Non-Coding RNAs, Including 5′ Leader Sequences of Primary MicroRNA Transcripts, Accumulate in Mouse Cells following Depletion of the RNA Helicase MTR4

RNA surveillance plays an important role in posttranscriptional regulation. Seminal work in this field has largely focused on yeast as a model system, whereas exploration of RNA surveillance in mammals is only recently begun. The increased transcriptional complexity of mammalian systems provides a wider array of targets for RNA surveillance, and, while many questions remain unanswered, emerging data suggest the nuclear RNA surveillance machinery exhibits increased complexity as well. We have used a small interfering RNA in mouse N2A cells to target the homolog of a yeast protein that functions in RNA surveillance (Mtr4p). We used high-throughput sequencing of polyadenylated RNAs (PA-seq) to quantify the effects of the mMtr4 knockdown (KD) on RNA surveillance. We demonstrate that overall abundance of polyadenylated protein coding mRNAs is not affected, but several targets of RNA surveillance predicted from work in yeast accumulate as adenylated RNAs in the mMtr4KD. microRNAs are an added layer of transcriptional complexity not found in yeast. After Drosha cleavage separates the pre-miRNA from the microRNA\u27s primary transcript, the byproducts of that transcript are generally thought to be degraded. We have identified the 5′ leading segments of pri-miRNAs as novel targets of mMtr4 dependent RNA surveillance

Giant pop-ins and amorphization in germanium during indentation

Sudden excursions of unusually large magnitude (>1 μm), “giant pop-ins,” have been observed in the force-displacement curve for high load indentation of crystalline germanium(Ge). A range of techniques including Raman microspectroscopy, focused ion-beam cross sectioning, and transmission electron microscopy, are applied to study this phenomenon. Amorphous material is observed in residual indents following the giant pop-in. The giant pop-in is shown to be a material removal event, triggered by the development of shallow lateral cracks adjacent to the indent. Enhanced depth recovery, or “elbowing,” observed in the force-displacement curve following the giant pop-in is explained in terms of a compliant response of plates of material around the indent detached by lateral cracking. The possible causes of amorphization are discussed, and the implications in light of earlier indentation studies of Ge are considered

Nanoindentation-induced deformation of Ge

The deformation mechanisms of crystalline (100) Ge were studied using nanoindentation, cross sectional transmission electron microscopy (XTEM) and Raman microspectroscopy. For a wide range of indentation conditions using both spherical and pointed indenters, multiple discontinuities were found in the force–displacement curves on loading, but no discontinuities were found on unloading. Raman microspectroscopy, measured from samples which had plastically deformed on loading, showed a spectrum shift from that in pristine Ge, suggesting only residual strain. No evidence (such as extra Raman bands) was found to suggest that any pressure-induced phase transformations had occurred, despite the fact that the material had undergone severe plastic deformation.Selected area diffraction pattern studies of the mechanically damaged regions also confirmed the absence of additional phases. Moreover, XTEM showed that, at low loads, plastic deformation occurs by twinning and dislocation motion. This indicates that the hardness of Gemeasured by indentation is not primarily dominated by phase transformation, rather by the nucleation and propagation of twin bands and/or dislocations

Age, Growth, And Reproduction Of Tautog Tautoga-Onitis (Labridae, Perciformes) From Coastal Waters Of Virginia

Tautog Tautoga onitis are gaining popularity in Virginia\u27s coastal waters as a recreational and food fish. Adult tautog are seasonally abundant on inshore hard-bottom habitats (1-10 m) and inhabit offshore areas (10-75 m) year-round. Juveniles, especially newly-settled recruits, inhabit vegetated areas in shallow water (usually \u3c 1 m). From March 1979 to July 1986, tautog were collected in lower Chesapeake Bay and nearby coastal waters to examine age, growth, and sexual maturation. Age estimates were determined from annular marks on opercle bones: 82% of the fish were age-10 or younger, 18% exceeded age-10, and 1% were age-20 or older. Marginal increment analysis revealed that annuli formed concurrent with a protracted spawning season (April-July). The von Bertalanffy growth equation, derived from back-calculated mean lengths-at-age, was l(t) = 742 [1-e-0.085 (t-1.816)]. Tautog are long-lived (25+ yr) and attain relatively large sizes (672 mm TL) slowly (K for sexes combined = 0.085). Growth rates of both sexes are similar, although males grow slightly faster (K = 0.090 vs. 0.085 for females). Maturity occurs at age-3 in both sexes. Growth rates for tautog from Virginia are similar to those reported nearly 25 years ago for tautog in Rhode Island. Growth rates for tautog are similar to those of other reef fishes, such as snappers and groupers. Habitat restriction, slow growth, great longevity, and increasing popularity by user groups may contribute to over-exploitation of this species in Virginia waters

An evaluation of a series of sixth grade compositions to determine growth in originality, elaborative thinking, and vocabulary

Thesis (Ed.M.)--Boston Universit

Inhibitory Effects of Ketoconazole on the Oxidation of Linoleic Acid Micelles, Phospholipid Liposomes, and Human Low Density Lipoprotein (h-LDL)

36 leavesSoybean lipoxygenase (SLO) (500-5000 units/ml), Fe(III)Cl3/ascorbate (5-100microM) and hematin (5-100microM) induced oxidative modification of lipids present in micelles of linoleic acid (0.5 mM), liposomes prepared from phospholipid extracts of bovine brain (2.5 mg/ml), and h-LDL (0.5 mg/ml). Oxidation of the lipid substrates was determined by the formation of thiobarbituric acid reactive substances and conjugated dienes. Free iron (Fe(III)Cl3/ascorbate) was the strongest initiator, followed by hematin and SLO. Ketoconazole (KC) attenuated lipid oxidation in a concentration dependent manner at pharmacologically relevant levels (25-100microM) in all three substrates. Pretreatment of liposomes and h-LDL with KC produced greater attenuation of lipid oxidation by the various initiators in comparison to free KC

Formation and growth of nanoindentation-induced high pressure phases in crystalline and amorphous silicon

Nanoindentation-induced formation of high pressure crystalline phases (Si-III and Si-XII) during unloading has been studied by Raman micro-spectroscopy, cross-sectional transmission electron microscopy (XTEM), and postindentation electrical measurements. For indentation in crystalline silicon(c-Si), rapid unloading (∼1000 mN∕s) results in the formation of amorphous silicon(a-Si) only; a result we have exploited to quench the formation of high pressure phases at various stages during unloading to study their formation and evolution. This reveals that seed volumes of Si-III and Si-XII form during the early stages of unloading with substantial volumes only forming after the pop-out event that occurs at about 50% of the maximum load. In contrast, high pressure phases form much more readily in an a-Si matrix, with substantial volumes forming without an observable pop-out event with rapid unloading. Postindentation electrical measurements have been used to further investigate the end phases and to identify differences between indentations which otherwise appear to be identical from the XTEM and Raman analyses.This research was funded by the Australian Research Council and by WRiota Pty. Ltd