Understanding the Underlying Field Evaporation Mechanism of Pure Water Tips in High Electrical Fields.

We investigated the field evaporation process of frozen water in atom probe tomography (APT) by density functional simulations. In previous experiments, a strong tailing effect was observed for peaks caused by the molecular structure (H2O)nH+, in contrast to other peaks. In purely field-induced and thermally assisted evaporation simulations, we found that chains of protonated water molecules were pulled out of the dielectric surface by up to 6 Å, which are stable over a wide range of field strengths. Therefore, the resulting water clusters experience only part of the acceleration after evaporation compared to molecules evaporating directly from the surface and, thus, exhibit an energy deficit, which explains the tailing effect. Our simulations provide new insight into the complex evaporation behavior of water in high electrical fields and reveal possibilities for adapting the existing reconstruction algorithms.

Evaporation and Fragmentation of Organic Molecules in Strong Electric Fields Simulated with DFT.

Atom probe tomography allows us to measure the three-dimensional composition of materials with up to atomic resolution by evaporating the material using high electric fields. Initially developed for metals, it is increasingly used for covalently bound structures. To aid the interpretation of the obtained fragmentation pattern, we modeled the fragmentation and desorption of self-assembled monolayers of thiolate molecules on a gold surface in strong electrostatic fields using density functional theory. We used a cluster model and a periodic model of amino-undecanethiolate, NH2(CH2)11S, and fluoro-decanethiolate, CF3(CF2)7(CH2)2S. In the former molecule, the fragment CH2NH2+ was found to evaporate at fields of 5.4-7.7 V/nm. It was followed by different hydrocarbon fragments. Fluoro-decanethiolate evaporates CF3+ at fields of 5.7-6.7 V/nm in the cluster model and at 15.4-23.1 V/nm in the periodic model, followed by CF2+ and C2F42+. Detailed analysis of the electronic structure during the evaporation process revealed a stepwise accumulation of the charge in the head groups exposed to the strongest fields, followed by dissociation of covalent bonds. These observations will facilitate the analysis of atom probe experiments of covalently bound structures.

Effect of deep brain stimulation in rats selectively bred for reduced prepulse inhibition.

BACKGROUND: Sensorimotor gating, measured as prepulse inhibition (PPI) of the acoustic startle reaction (ASR), is disturbed in certain neuropsychiatric disorders, such as schizophrenia, obsessive compulsive disorder, and Tourette's syndrome (TS). Deep brain stimulation (DBS) of the centromedian-parafascicular complex (CM-Pf), globus pallidus internus (in rats the entopeduncular nucleus - EPN), and the ventral striatum (in rats the nucleus accumbens - NAC) has been used for treatment in TS. OBJECTIVE: We tested whether DBS of these regions would alleviate breeding-induced low PPI in rats. METHODS: Rats with breeding-induced low and high PPI were bilaterally implanted with electrodes in the CM-Pf, the EPN, or the NAC. After two weeks, they were stimulated or sham stimulated for epochs of 6 days (in the EPN with a current of 20% below the individual threshold for stimulation-induced side effects, in the NAC or CM-Pf with 100 µA and 150 µA). On the 6th day the rats were tested for PPI of ASR. RESULTS: Stimulation in the CM-Pf with 150 µA significantly alleviated PPI, while NAC stimulation was less effective. In PPI low rats electrode implantation in the EPN already improved PPI, while subsequent stimulation had no additional effect. Startle reaction of PPI low rats was not affected by stimulation of either region. CONCLUSION: The CM-Pf and the EPN are important for the modulation of sensorimotor gating in rats with breeding-induced low PPI. These rats may therefore be useful to further investigate the pathophysiological mechanisms of deficient sensorimotor gating and also mechanisms of action of DBS in these circumstances.

Transradial access or Simmons shaped 8F guide enables delivery of flow diverters in patients with large intracranial aneurysms and type III aortic arch: technical case report.

BACKGROUND AND IMPORTANCE: Flow diversion with the pipeline embolization device (PED) is an emerging endovascular technology allowing curative embolization of very large and giant intracranial aneurysms. Many patients with these complex aneurysms are older. The presence of a tortuous type III aortic arch reduces the chances of successful PED delivery and increases the risk of complications. We report 2 technical nuances regarding the delivery of the PED in older patients with a complex aortic arch. CLINICAL PRESENTATION: In case 1, an 87-year-old woman presented with acute-onset left third nerve palsy. Workup demonstrated an 18-mm left posterior carotid wall aneurysm with a large daughter aneurysm on its dome. Endovascular access was complicated by a type III aortic arch with a hyperacute angle at the origin of the left common carotid artery. An 8F Simmons II shaped guide formed a stable platform, allowing successful PED delivery. In case 2, a 76-year-old woman experienced a transient ischemic attack. She harbored a right-sided 20-mm cavernous internal carotid artery aneurysm. She was treated with 2 PEDs deployed via a transradial approach. CONCLUSION: Transradial access or guide support with the 8F Simmons II catheter grants stable access for curative embolization with the PED in elderly patients with a large intracranial aneurysm and a complex aortic arch.