2,504 research outputs found
Metaphor, Objects, and Commodities
This article is a contribution to a symposium that focuses on the ideas of Margaret Jane Radin as a point of departure, and particularly on her analyses of propertization and commodification. While Radin focuses on the harms associated with commodification of the person, relying on Hegel's idea of alienation, we argue that objectification, and in particular objectification of various features of the digital environment, may have important system benefits. We present an extended critique of Radin's analysis, basing the critique in part on Gadamer's argument that meaning and application are interrelated and that meaning changes with application. Central to this interplay is the speculative form of analysis that seeks to fix meaning, contrasted with metaphorical thought that seeks to undermine some fixed meanings and create new meanings through interpretation. The result is that speculative and metaphorical forms are conjoined in an interactive process through which new adaptations emerge. Taking this critique an additional step, we use examples from contemporary intellectual property law discourse to demonstrate how an interactive approach, grounded in metaphor, can yield important insights
Role of the Ground State in Electron-Atom Double Ionization
Recently, absolute measurements have been reported for double ionization of helium by 5.6 keV electron-impact. At this high energy, one would think that the first Born approximation for the interaction of the projectile with the atom would be valid. However, on the basis of a lowest-order implementation of a Faddeev-type approach, Berakdar concluded that the approximation was not valid. Here we argue that (i) it is valid at this energy and (ii) the previous discrepancy between calculations in the first Born approximation and the overall magnitude of the measurements was due to a poor description of the ground state
Slow Convergence of the Born Approximation for Electron-Atom Ionization
It is usually assumed that the first-Born approximation for electron-atom ionization becomes valid for the fully differential cross section at sufficiently high impact energies, at least for asymmetric collisions where the projectile suffers only a small energy loss and is scattered by a small angle. Here we investigate this assumption quantitatively for ionization of hydrogen atoms. We find that convergence of the Born approximation to the correct nonrelativistic result is generally achieved only at energies where relativistic effects start to become important. Consequently, the assumption that the Born approximation becomes valid for high energy is inaccurate, since by the time it converges, nonrelativistic scattering theory is not valid
Creation of a monopole in a spinor condensate
We propose a method to create a monopole structure in a spin-1 spinor
condensate by applying the basic methods used to create vortices and solitons
experimentally in single-component condensates. We show, however, that by using
a two-component structure for a monopole, we can simplify our proposed
experimental approach and apply it also to ferromagnetic spinor condensates. We
also discuss the observation and dynamics of such a monopole structure, and
note that the dynamics of the two-component monopole differs from the dynamics
of the three-component monopole.Comment: The focus of the paper is shifted towards creation and observation of
monopole
Three-Body Models of Electron-Hydrogen Ionization
In this paper, we report calculations of electron-hydrogen ionization whereby the final-state wave Function is approximated by recently reported analytical three-body wave functions. In a first model we use the wave function of Alt and Mukhamedzhanov [Phys. Rev. A 47, 2004 (1993)], and in a second model we use the wave function of Berakdar [Phys. Rev. A 53, 2314 (1996)]
Spin-Resolved (e,2e) Coincidences for Heavy Rare-Gas Targets
It has been well established that the Coulomb force alone can produce spin-dependent effects for electron-impact excitation of heavy rare-gas atoms if the incident electrons are spin polarized and the final J state of the atom is resolved. This effect has become known as the fine-structure effect. Here we demonstrate that the same type of effect may be expected for electron-impact ionization
Perturbative and Nonperturbative Calculations of Electron-Hydrogen Ionization
We compare calculations of the fully differential cross section for ionization of atomic hydrogen by electron impact using two different theories-the perturbative CDW-EIS (continuum distorted wave with eikonal initial state) approximation and the nonperturbative ECS (exterior complex scaling) method. For this comparison, we chose an impact energy of 54.4 eV, since this is near the lowest energy that our perturbative approach would be applicable and near the highest energy that can be tackled by the ECS method with our present computational resources. For the case of equal-energy outgoing electrons investigated here, the two theories predict nearly identical results except that CDW-EIS underestimates the ECS values nearly uniformly by about 30%. Interestingly, when initial-state projectile-target interactions are neglected by replacing the eikonal initial state with the unperturbed initial state (the approximation of Brauner, Briggs, and Klar @J. Phys. B 22, (2265) (1989:]). the cross section oscillates by ±50% about the ECS values
Treatment of Ion-Atom Collisions using a Partial-Wave Expansion of the Projectile Wavefunction
We present calculations of ion-atom collisions using a partial-wave expansion of the projectile wavefunction. Most calculations of ion-atom collisions have typically used classical or plane-wave approximations for the projectile wavefunction, since partial-wave expansions are expected to require prohibitively large numbers of terms to converge scattering quantities. Here we show that such calculations are possible using modern high-performance computing. We demonstrate the utility of our method by examining elastic scattering of protons by hydrogen and helium atoms, problems familiar to undergraduate students of atomic scattering. Application to ionization of helium using partial-wave expansions of the projectile wavefunction, which has long been desirable in heavy-ion collision physics, is thus quite feasible
Vortex lattices for ultracold bosonic atoms in a non-Abelian gauge potential
The use of coherent optical dressing of atomic levels allows the
coupling of ultracold atoms to effective non-dynamical gauge fields. These can be
used to generate effective magnetic fields, and have the potential
to generate non-Abelian gauge fields. We consider a model of a gas
of bosonic atoms coupled to a gauge field with symmetry, and
with constant effective magnetic field. We include the effects of
weak contact interactions by applying Gross-Pitaevskii mean-field
theory. We study the effects of a non-Abelian gauge field on the vortex
lattice phase induced by a uniform effective magnetic field,
generated by an Abelian gauge field or, equivalently, by rotation of
the gas. We show that, with increasing non-Abelian gauge field, the
nature of the groundstate changes dramatically, with structural
changes of the vortex lattice. We show that the
effect of the non-Abelian gauge field is equivalent to the introduction of effective
interactions with non-zero range. We also comment on the
consequences of the non-Abelian gauge field for strongly correlated fractional quantum Hall
states
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