Structures and Photoelectron Spectra of Helium Nano Clusters

The ionization energies and photoelectron spectra of van der Waals (vdW) helium nano clusters (He_<i>n</i>) were studied in this work. Clusters with different numbers of helium atoms, in the range from <i>n</i> = 2 to <i>n</i> = 100, and belonging to different symmetry point groups were selected. Density functional theory (DFT) employing the CAM-B3LYP functional and the 6-31+G­(d) basis set was used for optimizing the structures. Symmetry adapted cluster-configuration interaction (SAC-CI) methodology and the 6-31+G­(3df) basis set were also used to calculate the ionization energies and their intensities. The calculated ionization energies and their intensities were used to simulate the photoelectron spectrum of each structure. It was found that the clustering of He atoms decreases the first ionization energy of the cluster compared to the isolated helium atom in the gas phase. The variation of the first ionization energies of the nanostructures were plotted versus their sizes and fitted into a mathematical equation. The simulated photoelectron spectra of the nano clusters were compared with each other comprehensively to investigate the change in the shape of the spectrum with the size of the cluster. The calculated ionization bands of each cluster were assigned using natural bonding orbital (NBO) analysis, and their changes with the size were studied. Also, it was studied how much the ionization processes are governed by the electron correlation, and the effect of the size on the electron correlation was examined

CTA analysis and assessment of morphological factors related to rupture in 413 posterior communicating artery aneurysms

Posterior communicating artery (PcomA) aneurysms are frequently encountered, but there are few publications on their morphology. A growing number of aneurysms are incidental findings, which makes evaluation of rupture risk important. Our goal was to identify morphological features and anatomical variants associated with PComA aneurysms and to assess parameters related to rupture. We studied CT angiographies of 391 consecutive patients treated between 2000 and 2014 at a single institution. We determined clinically important morphological parameters and performed univariate and multivariate analysis. There were a total of 413 PComA aneurysms: 258 (62%) were ruptured and 155 (38%) unruptured. Ruptured PComA aneurysms had the potential to cause severe bleeding with IVH and/or temporal ICH (n = 170, 66% of ruptured). The main types of PComA origin were classified as follows: (1) separate (32%), (2) side by side (21%) and (3) a joint neck with the aneurysm (6%). After the multivariate logistic regression, the morphological parameters related to PComA aneurysm rupture were an irregular aneurysm dome, neck diameter, and aspect ratio > 1.5. The most marked morphological features of the PComA aneurysms were: saccular nature (99%), infero-posterior dome orientation (42%), infrequency of large or giant aneurysms (4%), narrow neck compared to the aneurysm size, PComA originating directly from the aneurysm neck or the dome (28%), and fetal or dominant PComA on the side of the aneurysm (35%). There were location-related parameters that were more strongly associated with PComA aneurysm rupture than aneurysm size: an irregular aneurysm dome, larger diameter of the aneurysm neck and aspect ratio > 1.5.Peer reviewe