21,521 research outputs found
Space law and space resources
Space industrialization is confronting space law with problems that are changing old and shaping new legal principles. The return to the Moon, the next logical step beyond the space station, will establish a permanent human presence there. Science and engineering, manufacturing and mining will involve the astronauts in the settlement of the solar system. These pioneers, from many nations, will need a legal, political, and social framework to structure their lives and interactions. International and even domestic space law are only the beginning of this framework. Dispute resolution and simple experience will be needed in order to develop, over time, a new social system for the new regime of space
Fractional Chern insulators of few bosons in a box: Hall plateaus from center-of-mass drifts and density profiles
Realizing strongly-correlated topological phases of ultracold gases is a
central goal for ongoing experiments. And while fractional quantum Hall states
could soon be implemented in small atomic ensembles, detecting their signatures
in few-particle settings remains a fundamental challenge. In this work, we
numerically analyze the center-of-mass Hall drift of a small ensemble of
hardcore bosons, initially prepared in the ground state of the
Harper-Hofstadter-Hubbard model in a box potential. By monitoring the Hall
drift upon release, for a wide range of magnetic flux values, we identify an
emergent Hall plateau compatible with a fractional Chern insulator state: the
extracted Hall conductivity approaches a fractional value determined by the
many-body Chern number, while the width of the plateau agrees with the spectral
and topological properties of the prepared ground state. Besides, a direct
application of Streda's formula indicates that such Hall plateaus can also be
directly obtained from static density-profile measurements. Our calculations
suggest that fractional Chern insulators can be detected in cold-atom
experiments, using available detection methods.Comment: 13 pages, 11 figures; extended version accepted for publicatio
Oil pollution detection and monitoring from space using Skylab
There are no author-identified significant results in this report
Color Magnetic Corrections to Quark Model Valence Distributions
We calculate order color magnetic corrections to the valence quark
distributions of the proton using the Los Alamos Model Potential wavefunctions.
The spin-spin interaction breaks the model SU(4) symmetry, providing a natural
mechanism for the difference between the up and down distributions. For a value
of sufficient to produce the mass splitting, we find up
and down quark distributions in reasonable agreement with experiment.Comment: 25 Pages, LA-UR-93-132
Quark Model Calculations Of Symmetry Breaking in Parton Distributions
Using a quark model, we calculate symmetry breaking effects in the valence
quark distributions of the nucleon. In particular, we examine the breaking of
the quark model SU(4) symmetry by color magnetic effects, and find that color
magnetism provides an explanation for deviation of the ratio
from . Additionally, we calculate the effect of charge symmetry breaking
in the valence quark distributions of the proton and neutron and find, in
contrast to other authors, that the effect is too small to be seen
experimentally.Comment: 6 Pages, 3 postscript figures compressed using uufile
Realization of uniform synthetic magnetic fields by periodically shaking an optical square lattice
Shaking a lattice system, by modulating the location of its sites
periodically in time, is a powerful method to create effective magnetic fields
in engineered quantum systems, such as cold gases trapped in optical lattices.
However, such schemes are typically associated with space-dependent effective
masses (tunneling amplitudes) and non-uniform flux patterns. In this work we
investigate this phenomenon theoretically, by computing the effective
Hamiltonians and quasienergy spectra associated with several kinds of
lattice-shaking protocols. A detailed comparison with a method based on moving
lattices, which are added on top of a main static optical lattice, is provided.
This study allows the identification of novel shaking schemes, which
simultaneously provide uniform effective mass and magnetic flux, with direct
implications for cold-atom experiments and photonics.Comment: 15 pages, 10 eps figure
Topological phases in a two-dimensional lattice: Magnetic field versus spin-orbit coupling
In this work, we explore the rich variety of topological states that arise in
two-dimensional systems, by considering the competing effects of spin-orbit
couplings and a perpendicular magnetic field on a honeycomb lattice. Unlike
earlier approaches, we investigate minimal models in order to clarify the
effects of the intrinsic and Rashba spin-orbit couplings, and also of the
Zeeman splitting, on the quantum Hall states generated by the magnetic field.
In this sense, our work provides an interesting path connecting quantum Hall
and quantum spin Hall physics. First, we consider the properties of each term
individually and we analyze their similarities and differences. Secondly, we
investigate the subtle competitions that arise when these effects are combined.
We finally explore the various possible experimental realizations of our model.Comment: 19 pages, 15 figure
High powered arc electrodes
Nonconsumable metal electric arc electrodes are described capable of being operated in a variety of gases at various pressures, current, and powers. The cathode has a circular annulus tip to spread the emission area for improved cooling
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