Sea Power and Current U.S. Military Strategy

National power exists only to serve the national purposes, to help achieve the national aims

Current U.S. Military Strategy

This morning, my assignment is a challenging one indeed: an analysis of current U.S. military strategy and how it supports the participation of our armed forces, either under circumstances of general war or of conflict short of general war

The Present Situation in the Middle East and the Mediterranean Area

I have been asked to talk today on the situation in the Mediterranean and Middle East-and what I shall give you is pretty much of a reporter\u27s story. I have recently been there and have seen a good many of our military, naval, and diplomatic people-­ and many local personalities as well. I\u27ll give you as objective a survey of the existing situation as I can

Essays and leaves from a notebook

295 p., [1] h. de lám

Quantum process tomography via completely positive and trace-preserving projection

We present an algorithm for projecting superoperators onto the set of completely positive, trace-preserving maps. When combined with gradient descent of a cost function, the procedure results in an algorithm for quantum process tomography: finding the quantum process that best fits a set of sufficient observations. We compare the performance of our algorithm to the diluted iterative algorithm as well as second-order solvers interfaced with the popular CVX package for MATLAB, and find it to be significantly faster and more accurate while guaranteeing a physical estimate.Comment: 13pp, 8 fig

Investigation of Variable Stiffness Based Polymer Morphing Structures

Morphing structures have a multitude of potential applications in many engineering fields. Control surfaces for aircraft, pumps and valves for artificial organs or any application where a complex motion is required and can benefit from incorporating a morphing structure. The ability of a morphing structure to change its shape or configuration can potentially allow designs and functionality that would be impossible to realize without morphing. The focus of this thesis is to investigate the feasibility and operation of a structural shape morphing structure. Structural shape morphing is defined as shape change through material modulus changes. This allows fewer actuators, fewer moving parts and lower energy consumption to effect the same change in configuration as a traditional shape change structure. The morphing structure examined was designed and created specifically for this work and is composed almost entirely of polymer materials. The design utilizes electrical voltage to control the structural stiffness and motion of the structure independently. A review of literature covering fabrication and modeling in morphing structures, polymer actuators, variable modulus materials and variable stiffness structures is presented. A conceptual design for a shape morphing structure is fabricated and refined and an analytical model is developed for the structure to predict its response to applied voltages. The morphing structure’s capabilities are measured through experimental testing and the predictions of the analytical model are compared to the results. We demonstrate shape morphing by deforming the structure with an actuator, increasing the effective structural modulus and then removing the actuation force. Our tests show a fixed shape change in the structure of up to 20% of the total deformation. Feasibility is also discussed for real-world applications and suggested areas for further exploration on the topic are presented

Black Hole Polarimetry I: A Signature of Electromagnetic Energy Extraction

In 1977, Blandford and Znajek showed that the electromagnetic field surrounding a rotating black hole can harvest its spin energy and use it to power a collimated astrophysical jet, such as the one launched from the center of the elliptical galaxy M87. Today, interferometric observations with the Event Horizon Telescope (EHT) are delivering high-resolution, event-horizon-scale, polarimetric images of the supermassive black hole M87* at the jet launching point. These polarimetric images offer an unprecedented window into the electromagnetic field structure around a black hole. In this paper, we show that a simple polarimetric observable that quantifies the magnetic field helicity -- the sign of $\angle\beta_2$ in a near-horizon image -- depends on the sign of the electromagnetic energy flux and therefore provides a direct probe of black hole energy extraction. In Boyer-Lindquist coordinates, the Poynting flux for axisymmetric electromagnetic fields is proportional to the product $B^\phi B^r$. The polarimetric observable $\angle\beta_2$ likewise depends on the ratio $B^\phi/B^r$, thereby enabling an observer to experimentally determine the direction of electromagnetic energy flow in the near-horizon environment. Data from the 2017 EHT observations of M87* are consistent with electromagnetic energy outflow. Currently envisioned multi-frequency observations of M87* will achieve higher dynamic range and angular resolution, and hence deliver measurements of $\angle\beta_2$ closer to the event horizon as well as better constraints on Faraday rotation. Such observations will enable a definitive test for energy extraction from the black hole M87*.Comment: 34 pages, 5 figures. Submitted to ApJ