3-Dimensional Electron Microscopy of Biological Specimens

Three-dimensional (3D) imaging is an important tool in electron microscopy, especially in biological specimens where the main focus is the structure of the cells. Many times important information is lost because the exact orientation of a specimen is unknown. We tested two different 3D imaging techniques, focused ion beam (FIB) slice and view, and cryo-FIB thinning of samples for use in cryo transmission electron tomography (cryo-TEM) and cryo-electron tomography (cryo-ET). We began our research with room temperature FIB slice and view, with an intention to move onto slice and view at cryogenic temperatures. We found this technique to be difficult to control and the time required to produce results was simply too high. We moved on to investigating cryo-FIB milling as a tool for thinning cryo-ET specimens. Advances in cryo-ET have enabled high-resolution 3D imaging of complex assemblies and determination of cellular architectures in their close-to-native states. However, one major limitation, the accessible specimen thickness, has hindered its broader application in cellular biology. Recent efforts have been made to create thin, frozen-hydrated sections using cryo-ultramicrotomy, but with many mechanical artifacts and low yields. Here, we report a method that applies a focused ion beam (FIB) at cryogenic temperature (cryo-FIB) to reduce the thickness of frozen-hydrated cells, including mammalian cells, to a degree suitable for cryo-ET

Detecting malingered posttraumatic stress disorder using the Morel Emotional Numbing Test-Revised (MENT-R) and the Miller Forensic Assessment of Symptoms Test (M-FAST)

From feigning psychosis to avoid prosecution to claiming an anxiety disorder to receive disability insurance, people from all socioeconomic and educational backgrounds have been suspected of or found to be malingering (Rogers, 1997). The present study investigated the utility of two assessment measures in detecting malingered PTSD: the Morel Emotional Numbing Test-Revised (MENT-R) and Miller Forensic Assessment of Symptoms Test (M-FAST). The Detailed Assessment of Posttraumatic Stress (DAPS) was used as the criterion variable for the following groups: clinical PTSD, subclinical PTSD, honest responders, and coached malingerers. Total scores on the MENT-R distinguished among the four groups of participants. The three groups responding honestly averaged fewer than 3.5 errors, while malingerers missed over 5 times that number. Scores on the M-FAST were also higher for the group of participants malingering. Although the MENT-R and M-FAST correctly identified 63% and 78% of coached malingerers respectively, the combined use of both measures resulted in the correct classification of over 90% of the participants instructed to malinger PTSD

Sub-gap spectroscopy of thermally excited quasiparticles in a Nb contacted carbon nanotube quantum dot

We present electronic transport measurements of a single wall carbon nanotube quantum dot coupled to Nb superconducting contacts. For temperatures comparable to the superconducting gap peculiar transport features are observed inside the Coulomb blockade and superconducting energy gap regions. The observed temperature dependence can be explained in terms of sequential tunneling processes involving thermally excited quasiparticles. In particular, these new channels give rise to two unusual conductance peaks at zero bias in the vicinity of the charge degeneracy point and allow to determine the degeneracy of the ground states involved in transport. The measurements are in good agreement with model calculations.Comment: 5 pages, 4 figure

Direct observation of band-gap closure for a semiconducting carbon nanotube in a large parallel magnetic field

We have investigated the magnetoconductance of semiconducting carbon nanotubes (CNTs) in pulsed, parallel magnetic fields up to 60 T, and report the direct observation of the predicted band-gap closure and the reopening of the gap under variation of the applied magnetic field. We also highlight the important influence of mechanical strain on the magnetoconductance of the CNTs.Comment: 4 pages, 4 figure

Normal metal - insulator - superconductor interferometer

Hybrid normal metal - insulator - superconductor microstructures suitable for studying an interference of electrons were fabricated. The structures consist of a superconducting loop connected to a normal metal electrode through a tunnel barrier . An optical interferometer with a beam splitter can be considered as a classical analogue for this system. All measurements were performed at temperatures well below 1 K. The interference can be observed as periodic oscillations of the tunnel current (voltage) through the junction at fixed bias voltage (current) as a function of a perpendicular magnetic field. The magnitude of the oscillations depends on the bias point. It reaches a maximum at energy $eV$ which is close to the superconducting gap and decreases with an increase of temperature. Surprisingly, the period of the oscillations in units of magnetic flux $\Delta \Phi$ is equal neither to $h/e$ nor to $h/2e$, but significantly exceeds these values for larger loop circumferences. The origin of the phenomena is not clear.Comment: 11 pages and 8 figure

Bistability in superconducting rings containing an inhomogeneous Josephson junction

We investigate the magnetic response of a superconducting Nb ring containing a ferromagnetic PdNi Josephson junction and a tunnel junction in parallel. A doubling of the switching frequency is observed within certain intervals of the external magnetic field. Assuming sinusoidal current-phase relations of both junctions our model of a dc-SQUID embedded within a superconducting ring explains this feature by a sequence of current reversals in the ferromagnetic section of the junction in these field intervals. The switching anomalies are induced by the coupling between the magnetic fluxes in the two superconducting loops.Comment: 5 pages, 4 figure