110 research outputs found
SU(5) Gravitating Monopoles
Spherically symmetric solutions of the SU(5) Einstein-Yang-Mills-Higgs system
are constructed using the harmonic map ansatz \cite{IS}. This way the problem
reduces to solving a set of ordinary differential equations for the appropriate
profile functions.Comment: 12 pages, 3 Figure
Repeatability of brain phase-based magnetic resonance electric properties tomography methods and effect of compressed SENSE and RF shimming
Magnetic resonance electrical properties tomography (MREPT) is an emerging imaging modality to noninvasively measure tissue conductivity and permittivity. Implementation of MREPT in the clinic requires repeatable measurements at a short scan time and an appropriate protocol. The aim of this study was to investigate the repeatability of conductivity measurements using phase-based MREPT and the effects of compressed SENSE (CS), and RF shimming on the precision of conductivity measurements. Conductivity measurements using turbo spin echo (TSE) and three-dimensional balanced fast field echo (bFFE) with CS factors were repeatable. Conductivity measurement using bFFE phase showed smaller mean and variance that those measured by TSE. The conductivity measurements using bFFE showed minimal deviation with CS factors up to 8, with deviation increasing at CS factors > 8. Subcortical structures produced less consistent measurements than cortical parcellations at higher CS factors. RF shimming using full slice coverage 2D dual refocusing echo acquisition mode (DREAM) and full coverage 3D dual TR approaches further improved measurement precision. BFFE is a more optimal sequence than TSE for phase-based MREPT in brain. Depending on the area of the brain being measured, the scan can be safely accelerated with compressed SENSE without sacrifice of precision, offering the potential to employ MREPT in clinical research and applications. RF shimming with better field mapping further improves precision of the conductivity measures
Space of kink solutions in SU(N)\times Z_2
We find distinct classes (``generations'') of kink solutions in an
field theory. The classes are labeled by an integer . The
members of one class of kinks will be globally stable while those of the other
classes may be locally stable or unstable. The kink solutions in the
class have a continuous degeneracy given by the manifold ,
where is the unbroken symmetry group and is the group under which the
kink solution remains invariant. The space is found to contain
incontractable two spheres for some values of , indicating the possible
existence of certain incontractable spherical structures in three dimensions.
We explicitly construct the three classes of kinks in an SU(5) model with
quartic potential and discuss the extension of these ideas to magnetic monopole
solutions in the model.Comment: 11 pages, 3 figures. Several minor changes made. Matches the version
accepted to PR
Regulatory Taking: A Contract Approach
This Article begins by defining the parameters of the fifth amendment\u27s taking clause. The Article then reviews the various tests used in determining whether governmental action constitutes a taking, and discusses the recent Supreme Court decisions within the framework of case law as it has evolved since the Court\u27s 1922 landmark decision, Pennsylvania Coal Co. v. Mahon. Finally, the Article suggests a formula based on well-established contract principles for analyzing the impact of land use regulation on private property interests
An Attempt to Construct the Standard Model with Monopoles
We construct a model in which stable magnetic monopoles have magnetic charges
that are identical to the electric charges on leptons and quarks and the
colored monopoles are confined by strings in color singlets.Comment: 10 pages; LaTeX Added clarifying remarks, a Comment on the scattering
of particles, acknowledgements and references. Version to be publishe
Is there a monopole problem?
We investigate the high temperature behavior of SU(5) in its minimal version.
We show that there exists a range of parameters of the Higgs potential for
which the symmetry remains broken at high temperature, thus avoiding the phase
transition that gives rise to the overproduction of monopoles . We also show
that in such scenario the thermal production of monopoles can be suppressed in
a wide range of parameters, keeping their number density below the cosmological
limits.Comment: Latex, 12 pages, revised version as appeared in Physical Review
Letters. Minor corrections, comments and two references adde
Features of Motion Around Global Monopole in Asymptotically dS/AdS Spacetime
In this paper, we study the motion of test particle and light around the
Global Monopole in asymptotically dS/AdS spacetime. The motion of a test
particle and light in the exterior region of the global monopole in dS/AdS
spacetime has been investigated. Although the test particle's motion is quite
different from the case in asymptotically flat spacetime, the behaviors of
light(null geodesic) remain unchanged except a energy(frequency) shift. Through
a phase-plane analysis, we prove analytically that the existence of a periodic
solution to the equation of motion for a test particle will not be altered by
the presence of cosmological constant and the deficit angle, whose presence
only affects the position and type of the critical point on the phase plane. We
also show that the apparent capture section of the global monopole in dS/AdS
spacetime is quite different from that in flat spacetime.Comment: 15 pages, 4 PS figures, accepted for publication in Class. Quantum
Gra
Global Monopole in Asymptotically dS/AdS Spacetime
In this paper, we investigate the global monopole in asymptotically dS/Ads
spacetime and find that the mass of the monopole in the asymptotically dS
spacetime could be positive if the cosmological constant is greater than a
critical value. This shows that the gravitational field of the global monopole
could be attractive or repulsive depending on the value of the cosmological
constant.Comment: 5 pages, 1 figure, to appear in Phys. Rev.
Cratering Soil by Impinging Jets of Gas, with Application to Landing Rockets on Planetary Surfaces
Several physical mechanisms are involved in excavating granular materials beneath a vertical jet of gas. These occur, for example, beneath the exhaust plume of a rocket landing on the soil of the Moon or Mars. A series of experiments and simulations have been performed to provide a detailed view of the complex gas/soil interactions. Measurements have also been taken from the Apollo lunar landing videos and from photographs of the resulting terrain, and these help to demonstrate how the interactions extrapolate into the lunar environment. It is important to understand these processes at a fundamental level to support the ongoing design of higher-fidelity numerical simulations and larger-scale experiments. These are needed to enable future lunar exploration wherein multiple hardware assets will be placed on the Moon within short distances of one another. The high-velocity spray of soil from landing spacecraft must be accurately predicted and controlled lest it erosively damage the surrounding hardware
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