A simulation of the cluster structures in Ge-Se vitreous chalcogenide semiconductors

A structure of germanium selenide glasses is simulated by the featured clusters built from the tetrahedral GeSe4 units up to the clusters with six germanium atoms (Ge6Se16H4 and Ge6Se16H8). Quantum chemical calculations at the DFT level with effective core potentials for Ge and Se atoms for the clusters of different composition reveal their relative stability and optical properties.Comment: 5 pages, 3 Figures include

Evolution of magnetic Dirac bosons in a honeycomb lattice

We examine the presence and evolution of magnetic Dirac nodes in the Heisenberg honeycomb lattice. Using linear spin theory, we evaluate the collinear phase diagram as well as the change in the spin dynamics with various exchange interactions. We show that the ferromagnetic structure produces bosonic Dirac and Weyl points due to the competition between superexchange interactions. Furthermore, it is shown that the criteria for magnetic Dirac nodes are coupled to the magnetic structure and not the overall crystal symmetry, where the breaking of inversion symmetry greatly affects the antiferromagnetic configurations. The tunability of the nodal points through variation of the exchange parameters leads to the possibility of controlling Dirac symmetries through an external manipulation of the orbital interactions.Comment: 9 pages, 7 figures, Submitted for publicatio

Results of Radical Surgical Treatment of Cholangiocarcinoma

Radical operations of cholangiocarcinomas are connected with the great number of post-operative complications, and lethality reaches 15-30 %. The most debatable questions remain the choice of the operation type depending on localization and spreading of a tumor and also the expedience of using mini-invasive technologies as a preoperational preparation to the radical surgical treatment. We would like to share the little experience of the radical surgical treatment of cholangiocarcinomas.The research aim is to analyze results of radical surgical treatment of patients with cholangiocarcinoma.Matherials and methods. We have analyzed the outcomes of surgical treatment in 18 patients with cholangiocarcinomas. Tumor localization was determined according to the Bismuth-Corlett classification. Type 1 tumors were found in 2 (11.1 %), type 2 in 4 (22.2 %), type 3А in 5 (27.8 %), type 3B in 4 (22.2 %), type 4 in 1 (5.6 %), and distal localization in 2 (11.1 %) patients. As biliary decompression, 9 (50 %) patients underwent percutaneous transhepatic biliary duct drainage (PTBD), and another 9 (50 %) patients were operated without preoperative biliary decompression Pre-operative embolization of portal vein branches with the aim to increase the low volume of liver after anticipated resection was performed in 4 (22.2 %) patients.Results. After the embolization of portal vein branches, the estimated residual volume of hepatic parenchyma increased from 33.4 % to 45.7 %. Patients with cholagiocarcinomas of different localization performed the radical operations: isolated hepaticocholedochus resection in 5 (27.8 %) patients, hepaticocholedochus resection combined with Taj Mahal hepatic resection in 1 (5.6 %), right hemihepatectomy in 5 (27.8 %), left hemihepatectomy in 4 (22.2 %), extended right hemihepatectomy in 1 (5.6 %), and pancreoduodenal resection in 2 (11.1 %) patients. Complications of radical surgeries were observed in 4 (22.2 %) patients. Lethal outcomes occurred in 3 (16.7 %) patients.Conclusions. Radical operations are attended with complications in 22,2 % and lethality in 16,7 %. As a preoperative preparation it is possible to use mini-invasive interventions for the biliary decompression and increase of hepatic parenchyma volume

Optimization of quantum cascade laser operation by geometric design of cascade active band in open and closed models

Using the effective mass and rectangular potential approximations, the theory of electron dynamic conductivity is developed for the plane multilayer resonance tunnel structure placed into a constant electric field within the model of open nanosystem, and oscillator forces of quantum transitions within the model of closed nanosystem. For the experimentally produced quantum cascade laser with four-barrier active band of separate cascade, it is proven that just the theory of dynamic conductivity in the model of open cascade most adequately describes the radiation of high frequency electromagnetic field while the electrons transport through the resonance tunnel structure driven by a constant electric field.Comment: 10 pages, 2 figure