23,637 research outputs found
Anomalies in Universal Intensity Scaling in Ultrarelativistic Laser-Plasma Interactions
Laser light incident on targets at intensities such that the electron
dynamics is ultrarelativistic gives rise to a harmonic power spectrum extending
to high orders and characterized by a relatively slow decay with the harmonic
number m that follows a power law dependence, m^{-p}. Relativistic similarity
theory predicts a universal value for p = 8/3 up to some cut-off m = m*. The
results presented in this work suggest that under conditions in which plasma
effects contribute to the emission spectrum, the extent of this contribution
may invalidate the concept of universal decay. We report a decay with harmonic
number in the ultrarelativistic range characterised by an index 5/3 < p < 7/3,
significantly weaker than that predicted by the similarity model.Comment: 5 pages, 4 figure
Remarks on Form Factor Bounds
Improved model independent upper bounds on the weak transition form factors
are derived using inclusive sum rules. Comparison of the new bounds with the
old ones is made for the form factors h_{A_1} and h_V in B -> D* decays.Comment: 8 pages, 2 figures, title changed and typos corrected for journal
publicatio
Scalable reconstruction of density matrices
Recent contributions in the field of quantum state tomography have shown
that, despite the exponential growth of Hilbert space with the number of
subsystems, tomography of one-dimensional quantum systems may still be
performed efficiently by tailored reconstruction schemes. Here, we discuss a
scalable method to reconstruct mixed states that are well approximated by
matrix product operators. The reconstruction scheme only requires local
information about the state, giving rise to a reconstruction technique that is
scalable in the system size. It is based on a constructive proof that generic
matrix product operators are fully determined by their local reductions. We
discuss applications of this scheme for simulated data and experimental data
obtained in an ion trap experiment.Comment: 9 pages, 5 figures, replaced with published versio
Raman gain against a background of non-thermal ion fluctuations in a plasma
A complex stimulated Raman scattering event against a background of non-thermal ion acoustic waves in an inhomogeneous plasma is described. We obtain analytic forms for the Raman gain due to a five-wave interaction consisting of conventional three-wave Raman scattering followed by the decay of the Raman Langmuir wave into a second Langmuir wave (or a second scattered light wave) and an ion acoustic wave. Very modest levels of ion waves produce a. significant effect on Raman convective gain. A combination of plasma inhomogeneity and suprathermal ion fluctuations may offer a means for the control of Raman gain
Bubble Growth in Superfluid 3-He: The Dynamics of the Curved A-B Interface
We study the hydrodynamics of the A-B interface with finite curvature. The
interface tension is shown to enhance both the transition velocity and the
amplitudes of second sound. In addition, the magnetic signals emitted by the
growing bubble are calculated, and the interaction between many growing bubbles
is considered.Comment: 20 pages, 3 figures, LaTeX, ITP-UH 11/9
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
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