59 research outputs found
Mean Field Theory of Josephson Junction Arrays with Charge Frustration
Using the path integral approach, we provide an explicit derivation of the
equation for the phase boundary for quantum Josephson junction arrays with
offset charges and non-diagonal capacitance matrix. For the model with nearest
neighbor capacitance matrix and uniform offset charge , we determine,
in the low critical temperature expansion, the most relevant contributions to
the equation for the phase boundary. We explicitly construct the charge
distributions on the lattice corresponding to the lowest energies. We find a
reentrant behavior even with a short ranged interaction. A merit of the path
integral approach is that it allows to provide an elegant derivation of the
Ginzburg-Landau free energy for a general model with charge frustration and
non-diagonal capacitance matrix. The partition function factorizes as a product
of a topological term, depending only on a set of integers, and a
non-topological one, which is explicitly evaluated.Comment: LaTex, 24 pages, 8 figure
Activism and radical politics in the digital age: Towards a typology
This article aims to develop a typology for evaluating different types of activism in the digital age, based on the ideal of radical democracy. Departing from this ideal, activism is approached in terms of processes of identification by establishing conflictual frontiers to outside Others as either adversaries or enemies. On the basis of these discussions, we outline a typology of four kinds of activists: the salon activist, the contentious activist, the law-abiding activist, and the Gandhian activist. The typologyâs first axis, between antagonism and agonism, is derived from normative discussions in radical democracy concerning developing frontiers. The second axis, about readiness to engage in civil disobedience, is derived from a review of studies of different forms of online activism. The article concludes by suggesting that the different forms of political engagement online have to be taken into account when studying how online activism can contribute to social change
Magnetic trapping of ultracold neutrons
Three-dimensional magnetic confinement of neutrons is reported. Neutrons are
loaded into an Ioffe-type superconducting magnetic trap through inelastic
scattering of cold neutrons with 4He. Scattered neutrons with sufficiently low
energy and in the appropriate spin state are confined by the magnetic field
until they decay. The electron resulting from neutron decay produces
scintillations in the liquid helium bath that results in a pulse of extreme
ultraviolet light. This light is frequency downconverted to the visible and
detected. Results are presented in which 500 +/- 155 neutrons are magnetically
trapped in each loading cycle, consistent with theoretical predictions. The
lifetime of the observed signal, 660 s +290/-170 s, is consistent with the
neutron beta-decay lifetime.Comment: 17 pages, 18 figures, accepted for publication in Physical Review
Quantum computation based on d-level cluster states
The concept of qudit (a d-level system) cluster state is proposed by
generalizing the qubit cluster state (Phys. Rev. Lett. \textbf{86}, 910 (2001))
according to the finite dimensional representations of quantum plane algebra.
We demonstrate their quantum correlations and prove a theorem which guarantees
the availability of the qudit cluster states in quantum computation. We
explicitly construct the network to show the universality of the one-way
computer based on the defined qudit cluster states and single-qudit
measurement. And the corresponding protocol of implementing one-way quantum
computer can be suggested with the high dimensional "Ising" model which can be
found in many magnetic systems.Comment: Revtex4, 15 pages, 3 eps figure
IR studies of the oxygen and carbon precipitation processes in electron irradiated tin-doped silicon
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