On-wafer, cryogenic characterization of ultra-low noise HEMT devices

Significant advances in the development of high electron-mobility field-effect transistors (HEMT's) have resulted in cryogenic, low-noise amplifiers (LNA's) whose noise temperatures are within an order of magnitude of the quantum noise limit (hf/k). Further advances in HEMT technology at cryogenic temperatures may eventually lead to the replacement of maser and superconducting insulator superconducting front ends in the 1- to 100-GHz frequency band. Key to identification of the best HEMT's and optimization of cryogenic LNA's are accurate and repeatable device measurements at cryogenic temperatures. This article describes the design and operation of a cryogenic coplanar waveguide probe system for the characterization and modeling of advanced semiconductor transistors at cryogenic temperatures. Results on advanced HEMT devices are presented to illustrate the utility of the measurement system

Parameterized optimized effective potential for atoms

The optimized effective potential equations for atoms have been solved by parameterizing the potential. The expansion is tailored to fulfill the known asymptotic behavior of the effective potential at both short and long distances. Both single configuration and multi configuration trial wave functions are implemented. Applications to several atomic systems are presented improving previous works. The results here obtained are very close to those calculated in either the Hartree-Fock and the multi configurational Hartree-Fock framework.Comment: 8 pages, 3 figure

A Self-Consistent Model for Positronium Formation from Helium Atoms

The differential and total cross sections for electron capture by positrons from helium atoms are calculated using a first-order distorted wave theory satisfying the Coulomb boundary conditions. In this formalism a parametric potential is used to describe the electron screening in a consistent and realistic manner. The present procedure is self consistent because (i) it satisfies the correct boundary conditions and post-prior symmetry, and (ii) the potential and the electron binding energies appearing in the transition amplitude are consistent with the wave functions describing the collision system. The results are compared with the other theories and with the available experimental measurements. At the considered range of collision energies, the results agree reasonably well with recent experiments and theories. [Note: This paper will be published on volume 42 of the Brazilian Journal of Physics

Teaching and Learning of Calculus

This survey focuses on the main trends in the field of calculus education. Despite their variety, the findings reveal a cornerstone issue that is strongly linked to the formalism of calculus concepts and to the difficulties it generates in the learning and teaching process. As a complement to the main text, an extended bibliography with some of the most important references on this topic is included. Since the diversity of the research in the field makes it difficult to produce an exhaustive state-of-the-art summary, the authors discuss recent developments that go beyond this survey and put forward new research questions

The use of diode lasers in non-surgical therapy of periodontitis

Introduction. Periodontitis is a disease of multifactorial etiology and complex clinical manifestation. Removal of subgingival bacterial biofilm is a fundamental procedure in the treatment of periodontitis. Scaling and root planing (SRP) is currently the gold standard in the treatment of periodontitis, but in some cases such a procedure does not provide satisfactory results. The use of lasers in the treatment of periodontitis is one of the alternative adjunctive methods that has recently become more popular. Objective. The aim of the study was to evaluate the effectiveness of diode lasers in the treatment of periodontitis, based on the literature found in the Medline, Pubmed and Scopus databases published from June 2013 – June 2020. Results were based on a comparison of the effectiveness of SRP treatment in combination with photodynamic therapy or SRP in combination with laser irradiation of periodontal pockets. Results. The majority of studies confirmed the effectiveness of periodontal treatment combining SRP with photodynamic therapy or SRP with laser irradiation, compared to an SRP alone. Conclusions. Based on the recent literature, it can be concluded that SRP combined with photodynamic therapy or SRP in combination with a diode laser irradiation are effective methods to improve the outcomes of non-surgical periodontal treatment