Magnetoresistance Devices Based on Single Walled Carbon Nanotubes

We demonstrate the physical principles for the construction of a nanometer sized magnetoresistance device based on the Aharonov-Bohm effect. The proposed device is made of a short single-walled carbon nanotube (SWCNT) placed on a substrate and coupled to a tip. We consider conductance due to motion of electrons along the circumference of the tube (as opposed to motion parallel to its axis). We find that the circumference conductance is sensitive to magnetic fields threading the SWCNT due to the Aharonov-Bohm effect, and show that by retracting the tip, so that its coupling to the SWCNT is reduced, very high sensitivity to the threading magnetic field develops. This is due to the formation of a narrow resonance through which the tunneling current flows. Using a bias potential the resonance can be shifted to low magnetic fields, allowing the control of conductance with magnetic fields of the order of 1 Tesla.Comment: 4 pages, 3 figure

Analytical Continuation Approaches to Electronic Transport: The Resonant Level Model

The analytical continuation average spectrum method (ASM) and maximum entropy (MaxEnt) method are applied to the dynamic response of a noninteracting resonant level model within the framework of the Kubo formula for electric conductivity. The frequency dependent conductivity is inferred from the imaginary time current-current correlation function for a wide range of temperatures, gate voltages and spectral densities representing the leads, and compared with exact results. We find that the MaxEnt provides more accurate results compared to the ASM over the full spectral range.Comment: 6 pages, 5 figure

Fuel consumption prediction methodology for early stages of naval ship design

Thesis (S.M. in Mechanical Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M. in Naval Architecture and Marine Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 72).In recent years, fuel consumption has increased in importance as a design parameter in Navy ships. Economical fuel consumption is important not only for operating cost measures but also for ship endurance tankage requirements. Minimizing fuel consumption has many benefits for both naval and commercial ships. This thesis work will suggest a new comprehensive approach to early-stage ship design to determine fuel consumption for the whole system. A hull must be designed to work harmoniously with an optimized propulsor and propulsion plant to ensure best performance and to comply with imposed design requirements. Thus, this work will address three main aspects of the fuel consumption equation: -- Ship's resistance is calculated using a computational fluid dynamics simulation of the vessel in calm water at various speeds up to maximum speed. -- Propeller performance is based on propeller curves for the chosen propulsor. -- Efficiencies of the drive train and electrical production and distribution system are calculated for all operating conditions. Note that for an electric-drive ship, the non-propulsion electrical loads must be included in the calculations. These three major components of the ship efficiency equation are assessed for each speed and battle condition of the mission profile. In addition, the corresponding operating conditions for each piece of machinery will be specified to estimate the total fuel consumption and tankage required. In this thesis work, I will suggest a design methodology to determine hull resistance and total power for a given ship with a specified operational profile. The total power for the operational profile will be translated to fuel consumption, thus producing annual fuel consumption requirements and recommended tankage to support the operational needs.by Eran Gheriani.S.M.in Naval Architecture and Marine EngineeringS.M.in Mechanical Engineerin

Stochastic Resolution of Identity for Real-Time Second-Order Green's Function: Ionization Potential and Quasi-Particle Spectrum.

We develop a stochastic resolution of identity approach to the real-time second-order Green's function (real-time sRI-GF2) theory, extending our recent work for imaginary-time Matsubara Green's function [ Takeshita et al. J. Chem. Phys. 2019 , 151 , 044114 ]. The approach provides a framework to obtain the quasi-particle spectra across a wide range of frequencies and predicts ionization potentials and electron affinities. To assess the accuracy of the real-time sRI-GF2, we study a series of molecules and compare our results to experiments as well as to a many-body perturbation approach based on the GW approximation, where we find that the real-time sRI-GF2 is as accurate as self-consistent GW. The stochastic formulation reduces the formal computatinal scaling from O(Ne5) down to O(Ne3) where Ne is the number of electrons. This is illustrated for a chain of hydrogen dimers, where we observe a slightly lower than cubic scaling for systems containing up to Ne ≈ 1000 electrons