Topological defects and phase transitions in the early universe

Imperial Users onl

Classical theory of radiating strings

The divergent part of the self force of a radiating string coupled to gravity, an antisymmetric tensor and a dilaton in four dimensions are calculated to first order in classical perturbation theory. While this divergence can be absorbed into a renormalization of the string tension, demanding that both it and the divergence in the energy momentum tensor vanish forces the string to have the couplings of compactified N = 1 D = 10 supergravity. In effect, supersymmetry cures the classical infinities

String mediated phase transitions

It is demonstrated from first principles how the existence of string-like structures can cause a system to undergo a phase transition. In particular, the role of topologically stable cosmic string in the restoration of spontaneously broken symmetries is emphasized. How the thermodynamic properties of strings alter when stiffness and nearest neighbor string-string interactions are included is discussed

Using Remote Infrared Sensors to Detect Changes in Moisture Conditions on Natural Watersheds

Foreword: This report summarizes the results of laboratory measurements of the infrared reflectance of selected living plants typical of the natural watersheds in northern Utah. Data indicate that the IR reflectance decreases as the moisture content of the soil decreases and the moisture tension in the soil increases. Additional data will be collected in the field to confirm the results and to further tests the feasibility of using IR reflectance of vegetation as an indicator of soil moisture conditions on the watershed. Mr. Briscoe, Research Physicist, has been responsible for the gathering of laboratory data and has written the manuscript for this report. Introduction: The continuing world-wide population explosion is placing an ever-increasing demand on present usable water supplies, and water shortages are becoming more severe. While scientists and engineers are working to produce additional fresh water by weather control or desalination, much can be done to alleviate water shortages by better management of our watershed areas. In order to make optimum use of our watersheds, we must develop improved methods of determining the water conditions within them. An important contribution toward improved watershed management would be made if some method could be devised which would facilitate data aquisition of watershed parameters. The purpose of this study has been to investigate the feasibility of measuring these parameters by remote reconnaissance methods. The remote sensing technique has been applied, to some extent, in the science of hydrology. Although some of the measurements taken have indicated that various hydrological factors influence the data received, comprehensive results are not available relating to quantitative measurements of water conditions. The procedure followed in this study was to conduct a literature survey of data available at all regions of the electromagnetic spectrum, and then to perform laboratory spectral measurements on certain areas which showed promise

Booster Obsolescence and Life Extension (BOLE) for Space Launch System (SLS)

A human mission to the moon and Mars is the stated space exploration goal of the United States and the international community. To achieve these goals, NASA is developing the Space Launch System (SLS) and the Orion crew capsule as key elements in the architecture for missions to the moon and Mars. As part of the SLS Booster Obsolescence and Life Extension (BOLE) program, Northrop Grumman Space Systems is working to address booster obsolescence issues in design and manufacturing. The upgraded boosters will also provide increased performance that will benefit future lunar campaigns, science missions, and the eventual Mars campaign

Quantum tunneling of superconducting string currents

We investigate the decay of current on a superconducting cosmic string through quantum tunneling. We construct the instanton describing tunneling in a simple bosonic string model, and estimate the decay rate. The tunneling rate vanishes in the limit of a chiral current. This conclusion, which is supported by a symmetry argument, is expected to apply in general. It has important implications for the stability of chiral vortons.Comment: 16 pages, 2 figure

Q Rings

We show the existence of new stable ring-like localized scalar field configurations whose stability is due to a combination of topological and nontopological charges. In that sense these defects may be called semitopological. These rings are Noether charged and also carry Noether current (they are superconducting). They are local minima of the energy in scalar field theories with an unbroken U(1) global symmetry. We obtain numerical solutions of the field configuration corresponding to large rings and derive virial theorems demonstrating their stability. We also derive the minimum energy field configurations in 3D and simulate the evolution of a finite size Q ring on a three dimensional lattice thus generalizing our demonstration of stability.Comment: 4 double column pages including 2 figure

Pavement Thickness Evaluation by GPR Survey in Idaho

In 1995 and 1996, the Idaho Transportation Department (lTD) conducted a series of ground-penetrating radar (GPR) surveys as a nondestructive testing (NDT) method to evaluate the thickness of asphalt and Portland cement concrete (AC/PCC) pavements in Idaho. GPR surveys employed both air-coupled and combination air and ground coupled systems with their associated equipment and software. A total of 30 miles of AC/PCC pavements were evaluated by GPR surveys. The results obtained were correlated with the site-specific ground-truth data from borings. Knowledge of pavement layer thickness is needed to predict pavement performance, establish load carrying capacities and develop maintenance and rehabilitation priorities. In addition, for new construction, it is important to ensure that the thickness of materials being placed by the contractor is acceptably close to specification. Core sampling and test pits are destructive to the pavement system, expensive, time consuming and intrusive to traffic. The objective of the lTD study was to evaluate, compare and assess the ability of these two GPR systems to accurately measure the thickness of multiple pavement layers, and document the data nondestructively. This paper reviews the findings of these surveys and provides statistically based data for both AC and PCC pavements. The overall study has shown that reasonably accurate, dependable determination of pavement thickness can be achieved by using GPR survey for conditions encountered in Idaho

Booster Obsolescence and Life Extension (BOLE) for Space Launch System (SLS)

A human mission to the moon and Mars is the stated space exploration goal of the United States and the international community. To achieve these goals, NASA is developing the Space Launch System (SLS) and the Orion crew capsule as key elements in the architecture for missions to the moon and Mars. As part of the SLS Booster Obsolescence and Life Extension (BOLE) program, Northrop Grumman Innovation Systems is working to address booster obsolescence issues in design and manufacturing. The upgraded boosters will also provide increased performance that will benefit future lunar campaigns, science missions, and the eventual Mars campaign

Oscillation damping of chiral string loops

Chiral cosmic string loop tends to the stationary (vorton) configuration due to the energy loss into the gravitational and electromagnetic radiation. We describe the asymptotic behaviour of near stationary chiral loops and their fading to vortons. General limits on the gravitational and electromagnetic energy losses by near stationary chiral loops are found. For these loops we estimate the oscillation damping time. We present solvable examples of gravitational radiation energy loss by some chiral loop configurations. The analytical dependence of string energy with time is found in the case of the chiral ring with small amplitude radial oscillations.Comment: 10 pages, 2 figures. Accepted for publication in Physical Review