Sequential Adaptive Detection for In-Situ Transmission Electron Microscopy (TEM)

We develop new efficient online algorithms for detecting transient sparse signals in TEM video sequences, by adopting the recently developed framework for sequential detection jointly with online convex optimization [1]. We cast the problem as detecting an unknown sparse mean shift of Gaussian observations, and develop adaptive CUSUM and adaptive SSRS procedures, which are based on likelihood ratio statistics with post-change mean vector being online maximum likelihood estimators with $\ell_1$. We demonstrate the meritorious performance of our algorithms for TEM imaging using real data

Neuronopathic Gaucher disease in the mouse: viable combined selective saposin C deficiency and mutant glucocerebrosidase (V394L) mice with glucosylsphingosine and glucosylceramide accumulation and progressive neurological deficits

Gaucher disease is caused by defective acid β-glucosidase (GCase) function. Saposin C is a lysosomal protein needed for optimal GCase activity. To test the in vivo effects of saposin C on GCase, saposin C deficient mice (C−/−) were backcrossed to point mutated GCase (V394L/V394L) mice. The resultant mice (4L;C*) began to exhibit CNS abnormalities ∼30 days: first as hindlimb paresis, then progressive tremor and ataxia. Death occurred ∼48 days due to neurological deficits. Axonal degeneration was evident in brain stem, spinal cord and white matter of cerebellum accompanied by increasing infiltration of the brain stem, cortex and thalamus by CD68 positive microglial cells and activation of astrocytes. Electron microscopy showed inclusion bodies in neuronal processes and degenerating cells. Accumulation of p62 and Lamp2 were prominent in the brain suggesting the impairment of autophagosome/lysosome function. This phenotype was different from either V394L/V394L or C−/− alone. Relative to V394L/V394L mice, 4L;C* mice had diminished GCase protein and activity. Marked increases (20- to 30-fold) of glucosylsphingosine (GS) and moderate elevation (1.5- to 3-fold) of glucosylceramide (GC) were in 4L;C* brains. Visceral tissues had increases of GS and GC, but no storage cells were found. Neuronal cells in thick hippocampal slices from 4L;C* mice had significantly attenuated long-term potentiation, presumably resulting from substrate accumulation. The 4L;C* mouse mimics the CNS phenotype and biochemistry of some type 3 (neuronopathic) variants of Gaucher disease and is a unique model suitable for testing pharmacological chaperone and substrate reduction therapies, and investigating the mechanisms of neuronopathic Gaucher disease

Impurity and texture driven HCP-to-FCC transformations in Ti-X thin films during in situ TEM annealing and FIB milling

A hexagonal close-packed (HCP) to face-centered cubic (FCC) phase transition has been observed in freestanding alpha-titanium (α-Ti) thin foils under two separate conditions: (1) after focused ion beam (FIB) irradiation, and (2) during in situ heating in a transmission electron microscope (TEM). The FCC phase is not found on the Ti single-component equilibrium phase diagram, however, both FCC structures were found to be stable after formation under these conditions. Here, we combine analytical TEM and Atom Probe Tomography (APT) investigations into the chemical nature of these anomalous FCC Ti-X phases. Both occurrences of the FCC phase were observed in thin films containing (initial) prismatic HCP surface plane texturing and appear to be facilitated by hydrogen and oxygen impurities. Our results suggest that the FIB-induced FCC Ti-X is a form of titanium hydride (δ-TiH2 and/or γ-TiH), while the thermally-induced FCC Ti-X appears to be tied to the incorporation of oxygen

Multiple Twinning and Stacking Faults in Silver Dendrites

Detailed defect structure of dendrite formation was studied in order to connect the mesoscopic with the atomistic structure. It was demonstrated that twinning and stacking fault formation play a central role in the growth of electrodeposited Ag dendrites. The broad faces of Ag dendrites and the main trunk growth direction were found to be ((1) over bar 11) and [(1) over bar1 (2) over bar], respectively. Dendrite branches also formed and grew from the main trunk parallel to the [12 (1) over bar] and [(211) over bar] crystallographic directions. Twins and stacking faults were found to reside on the {111} crystallographic planes, as expected for a face centered cubic (FCC) Ag crystal. Using electron back scattered diffraction (EBSD) we found two variants of in-plane 60 degrees rotational twin domains in the ((1) over bar 11) broad dendrite surface plane. The intersections of twins and stacking faults with dendrite arm surfaces are perpendicular to the (112) arm growth directions. However, occasionally twins on the {111} planes parallel to the (112) arm growth directions were also observed. Although defect assisted dendrite growth is facilitated by twinning and stacking fault formation on {111} planes, the growth directions of the trunk and branches are not of the (111) type, but rather close to (112). The (112) growth directions are maintained by breaking dendrite facets into thermodynamically stable 111 and 200 steps and structural ledges of different length

In situ TEM observation of FCC Ti formation at elevated temperatures

Pure Ti traditionally exhibits the hexagonal closed packed (HCP) crystallographic structure under ambient conditions and the body centered cubic (BCC) structure at elevated temperatures. In addition to these typical structures for Ti alloys, the presence of a face centered cubic (FCC) phase associated with thin films, interfaces, or high levels of plastic deformation has occasionally been reported. Here we show that small FCC precipitates form in freestanding thin foils during in situ transmission electron microscope (TEM) heating and we discuss the potential origins of the FCC phase in light of the in situ observations. This FCC phase was found to be stable upon cooling and under ambient conditions, which allowed us to explore its mechanical properties and stability via nanomechanical in situ TEM testing. It was found that FCC platelets within the HCP matrix phase were stable under mechanical deformation and exhibited similar mechanical deformation behavior as the parent HCP phase