17,137 research outputs found
Spending time with money: from shared values to social connectivity
This article has been made available through the Brunel Open Access Publishing Fund.There is a rapidly growing momentum driving the development of mobile payment systems for co-present interactions, using near-field communication on smartphones and contactless payment systems. The design (and marketing) imperative for this is to enable faster, simpler, effortless and secure transactions, yet our evidence shows that this focus on reducing transactional friction may ignore other important features around making payments. We draw from empirical data to consider user interactions around financial exchanges made on mobile phones. Our findings examine how the practices around making payments support people in making connections, to other people, to their communities, to the places they move through, to their environment, and to what they consume. While these social and community bonds shape the kinds of interactions that become possible, they also shape how users feel about, and act on, the values that they hold with their co-users. We draw implications for future payment systems that make use of community connections, build trust, leverage transactional latency, and generate opportunities for rich social interactions
Superfluid-Insulator and Roughening Transitions in Domain Walls
We have performed quantum Monte Carlo simulations to investigate the
superfluid behavior of one- and two-dimensional interfaces separating
checkerboard solid domains. The system is described by the hard-core
Bose-Hubbard Hamiltonian with nearest-neighbor interaction. In accordance with
Ref.1, we find that (i) the interface remains superfluid in a wide range of
interaction strength before it undergoes a superfluid-insulator transition;
(ii) in one dimension, the transition is of the Kosterlitz-Thouless type and is
accompanied by the roughening transition, driven by proliferation of charge 1/2
quasiparticles; (iii) in two dimensions, the transition belongs to the 3D U(1)
universality class and the interface remains smooth. Similar phenomena are
expected for domain walls in quantum antiferromagnets.Comment: 6 pages, 7 figures; references added, typo corrected in fig
Level crossings in a cavity QED model
In this paper I study the dynamics of a two-level atom interacting with a
standing wave field. When the atom is subjected to a weak linear force, the
problem can be turned into a time dependent one, and the evolution is
understood from the band structure of the spectrum. The presence of level
crossings in the spectrum gives rise to Bloch oscillations of the atomic
motion. Here I investigate the effects of the atom-field detuning parameter. A
variety of different level crossings are obtained by changing the magnitude of
the detuning, and the behaviour of the atomic motion is strongly affected due
to this. I also consider the situation in which the detuning is oscillating in
time and its impact on the atomic motion. Wave packet simulations of the full
problem are treated numerically and the results are compared with analytical
solutions given by the standard Landau-Zener and the three-level Landau-Zener
models.Comment: 12 pages, 10 figure
Symmetry conserving non-perturbative s-wave renormalization of the pion in hot and baryon dense medium
A non-perturbative s-wave renormalization of the pion in a hot and baryon
rich medium is presented. This approach proceeds via a mapping of the canonical
pion into the axial Noether's charge. The mapping was made dynamical in the
Hartree-Fock-Bogoliubov random phase approximation (HFB-RPA). It is shown that
this approach, while order mixing, is still symmetry conserving both in the
baryon free and baryon rich sectors, at zero as well as finite temperature. The
systematic character of this approach is emphasized and it is particularly
argued that it may constitute an interesting alternative for the
non-perturbative assessment of the nuclear matter saturation properties.Comment: Latex, 22 pages, 3 figure
Phonon Bloch oscillations in acoustic-cavity structures
We describe a semiconductor multilayer structure based in acoustic phonon
cavities and achievable with MBE technology, designed to display acoustic
phonon Bloch oscillations. We show that forward and backscattering Raman
spectra give a direct measure of the created phononic Wannier-Stark ladder. We
also discuss the use of femtosecond laser impulsions for the generation and
direct probe of the induced phonon Bloch oscillations. We propose a gedanken
experiment based in an integrated phonon source-structure-detector device, and
we present calculations of pump and probe time dependent optical reflectivity
that evidence temporal beatings in agreement with the Wannier-Stark ladder
energy splitting.Comment: PDF file including 4 figure
Propagators in Coulomb gauge from SU(2) lattice gauge theory
A thorough study of 4-dimensional SU(2) Yang-Mills theory in Coulomb gauge is
performed using large scale lattice simulations. The (equal-time) transverse
gluon propagator, the ghost form factor d(p) and the Coulomb potential V_{coul}
(p) ~ d^2(p) f(p)/p^2 are calculated. For large momenta p, the gluon propagator
decreases like 1/p^{1+\eta} with \eta =0.5(1). At low momentum, the propagator
is weakly momentum dependent. The small momentum behavior of the Coulomb
potential is consistent with linear confinement. We find that the inequality
\sigma_{coul} \ge \sigma comes close to be saturated. Finally, we provide
evidence that the ghost form factor d(p) and f(p) acquire IR singularities,
i.e., d(p) \propto 1/\sqrt{p} and f(p) \propto 1/p, respectively. It turns out
that the combination g_0^2 d_0(p) of the bare gauge coupling g_0 and the bare
ghost form factor d_0(p) is finite and therefore renormalization group
invariant.Comment: 10 pages, 7 figure
Spin-orbit coupled Bose-Einstein condensate in a tilted optical lattice
Bloch oscillations appear for a particle in a weakly tilted periodic
potential. The intrinsic spin Hall effect is an outcome of a spin-orbit
coupling. We demonstrate that both these phenomena can be realized
simultaneously in a gas of weakly interacting ultracold atoms exposed to a
tilted optical lattice and to a set of spatially dependent light fields
inducing an effective spin-orbit coupling. It is found that both the spin Hall
as well as the Bloch oscillation effects may coexist, showing, however, a
strong correlation between the two. These correlations are manifested as a
transverse spin current oscillating in-phase with the Bloch oscillations.Comment: 12 pages, 7 figure
Measuring the temporal coherence of an atom laser beam
We report on the measurement of the temporal coherence of an atom laser beam
extracted from a Rb Bose-Einstein condensate. Reflecting the beam from a
potential barrier creates a standing matter wave structure. From the contrast
of this interference pattern, observed by magnetic resonance imaging, we have
deduced an energy width of the atom laser beam which is Fourier limited by the
duration of output coupling. This gives an upper limit for temporal phase
fluctuations in the Bose-Einstein condensate.Comment: 4 pages, 3 figure
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