Formation of nanowires and their interaction with atomic steps during growth of Bi on Ni(111)

Using low-energy electron microscopy (LEEM) and selective area low-energy electron diffraction, we have characterized both the (7×7) wetting layer and the BiNi9 [2 0 −2 5] nanowires that form during the growth of Bi on Ni(111). The 60 ± 20 nm wide nanowires have lengths up to 10 μm and a height of 4–6 atomic layers. After the formation of the wetting layer and nanowires, quantum size effect driven growth ensues, accompanied by the gradual disappearance of the nanowires and resulting meandering of the substrate steps. The displacements of substrate steps, directly imaged with LEEM, can be traced back to dealloying

Changes in Timing and kinematics of goal directed eye-hand movements in early-stage Parkinson's disease

Objective: Many daily activities involve intrinsic or extrinsic goal-directed eye and hand movements. An extensive visuomotor coordination network including nigro-striatal pathways is required for efficient timing and positioning of eyes and hands. The aim of this study was to investigate how Parkinson's disease (PD) affects eye-hand coordination in tasks with different cognitive complexity.Methods: We used a touch screen, an eye-tracking device and a motion capturing system to quantify changes in eye-hand coordination in early-stage PD patients (H&amp;Y &lt; 2.5) and age-matched controls. Timing and kinematics of eye and hand were quantified in four eye-hand coordination tasks (pro-tapping, dual planning, anti-tapping and spatial memory task).Results: In the pro-tapping task, saccade initiation towards extrinsic goals was not impaired. However, in the dual planning and anti-tapping task initiation of saccades towards intrinsic goals was faster in PD patients. Hand movements were differently affected: initiation of the hand movement was only delayed in the pro-tapping and dual planning task. Overall, hand movements in PD patients were slower executed compared to controls.Interpretation: Whereas initiation of saccades in an extrinsic goal-directed task (pro-tapping task) is not affected, early stage PD patients have difficulty in suppressing reflexive saccades towards extrinsic goals in tasks where the endpoint is an intrinsic goal (e.g. dual planning and anti-tapping task). This is specific for eye movements, as hand movements have delayed responses in the pro-tapping and dual planning task. This suggests that reported impairment of the dorsolateral prefrontal cortex in early-stage PD patients affects only inhibition of eye movements. We conclude that timing and kinematics of eye and hand movements in visuomotor tasks are affected in PD patients. This result may have clinical significance by providing a behavioral marker for the early diagnosis of PD.</p

Changes in Timing and kinematics of goal directed eye-hand movements in early-stage Parkinson's disease

Objective: Many daily activities involve intrinsic or extrinsic goal-directed eye and hand movements. An extensive visuomotor coordination network including nigro-striatal pathways is required for efficient timing and positioning of eyes and hands. The aim of this study was to investigate how Parkinson's disease (PD) affects eye-hand coordination in tasks with different cognitive complexity.Methods: We used a touch screen, an eye-tracking device and a motion capturing system to quantify changes in eye-hand coordination in early-stage PD patients (H&amp;Y &lt; 2.5) and age-matched controls. Timing and kinematics of eye and hand were quantified in four eye-hand coordination tasks (pro-tapping, dual planning, anti-tapping and spatial memory task).Results: In the pro-tapping task, saccade initiation towards extrinsic goals was not impaired. However, in the dual planning and anti-tapping task initiation of saccades towards intrinsic goals was faster in PD patients. Hand movements were differently affected: initiation of the hand movement was only delayed in the pro-tapping and dual planning task. Overall, hand movements in PD patients were slower executed compared to controls.Interpretation: Whereas initiation of saccades in an extrinsic goal-directed task (pro-tapping task) is not affected, early stage PD patients have difficulty in suppressing reflexive saccades towards extrinsic goals in tasks where the endpoint is an intrinsic goal (e.g. dual planning and anti-tapping task). This is specific for eye movements, as hand movements have delayed responses in the pro-tapping and dual planning task. This suggests that reported impairment of the dorsolateral prefrontal cortex in early-stage PD patients affects only inhibition of eye movements. We conclude that timing and kinematics of eye and hand movements in visuomotor tasks are affected in PD patients. This result may have clinical significance by providing a behavioral marker for the early diagnosis of PD.</p

Direct Integration of Micromachined Pipettes in a Flow Channel for Single DNA Molecule Study by Optical Tweezers

We have developed a micromachined flow cell consisting of a flow channel integrated with micropipettes. The flow cell is used in combination with an optical trap setup (optical tweezers) to study mechanical and structural properties of λ-DNA molecules. The flow cell was realized using silicon micromachining including the so-called buried channel technology to fabricate the micropipettes, the wet etching of glass to create the flow channel,\ud and the powder blasting of glass to make the fluid connections. The volume of the flow cell is 2 µl. The pipettes have a length of 130 m, a width of 5–10 µm, a round opening of 1 um and can be processed with different shapes. Using this flow cell we stretched single molecules (λ-DNA) showing typical force-extension curves also found with conventional techniques. These pipettes can be\ud also used for drug delivery, for injection of small gas bubbles into a liquid flow to monitor the streamlines, and for the mixing of liquids to study diffusion effects. The paper describes the design, the fabrication and testing of the flow cell

Cytosolic enzymes with a mitochondrial ancestry from the anaerobic chytrid Piromyces sp. E2

The anaerobic chytrid Piromyces sp. E2 lacks mitochondria, but contains hydrogen-producing organelles, the hydrogenosomes. We are interested in how the adaptation to anaerobiosis influenced enzyme compartmentalization in this organism. Random sequencing of a cDNA library from Piromyces sp. E2 resulted in the isolation of cDNAs encoding malate dehydrogenase, aconitase and acetohydroxyacid reductoisomerase. Phylogenetic analysis of the deduced amino acid sequences revealed that they are closely related to their mitochondrial homologues from aerobic eukaryotes. However, the deduced sequences lack N-terminal extensions, which function as mitochondrial leader sequences in the corresponding mitochondrial enzymes from aerobic eukaryotes. Subcellular fractionation and enzyme assays confirmed that the corresponding enzymes are located in the cytosol. As anaerobic chytrids evolved from aerobic, mitochondria-bearing ancestors, we suggest that, in the course of the adaptation from an aerobic to an anaerobic lifestyle, mitochondrial enzymes were retargeted to the cytosol with the concomitant loss of their N-terminal leader sequences

Probing Crystallinity and Grain Structure of 2D Materials and 2D-Like Van der Waals Heterostructures by Low-Voltage Electron Diffraction

4D scanning transmission electron microscopy (4D-STEM) is a powerful method for characterizing electron-transparent samples with down to sub-Ångstrom spatial resolution. 4D-STEM can reveal local crystallinity, orientation, grain size, strain, and many more sample properties by rastering a convergent electron beam over a sample area and acquiring a transmission diffraction pattern (DP) at each scan position. These patterns are rich in information about the atomic structure of the probed volume, making this technique a potent tool to characterize even inhomogeneous samples. 4D-STEM can also be used in scanning electron microscopes (SEMs) by placing an electron-sensitive camera below the sample. 4D-STEM-in-SEMs is ideally suited to characterize 2D materials and 2D-like van der Waals heterostructures (vdWH) due to their inherent thickness of a few nanometers. The lower accelerating voltage of SEMs leads to strong scattering even from monolayers. The large field of view and down to sub-nm spatial resolution of SEMs are ideal to map properties of the different constituents of 2D-like vdWH by probing their combined sample volume. A unique 4D-STEM-in-SEM system is applied to reveal the single crystallinity of MoS2 exfoliated with gold-mediation as well as the crystal orientation and coverage of both components of a C60/MoS2 vdWH are determined.Peer Reviewe