19,389 research outputs found
Emergence of Complex Spatio-Temporal Behavior in Nonlinear Field Theories
We investigate the emergence of time-dependent nonperturbative configurations
during the evolution of nonlinear scalar field models with symmetric and
asymmetric double-well potentials. Complex spatio-temporal behavior emerges as
the system seeks to establish equipartition after a fast quench. We show that
fast quenches may dramatically modify the decay rate of metastable states in
first order phase transitions. We briefly suggest possible applications
incondensed matter systems and early universe cosmology.Comment: 6 pages, 8 figure
Resonant emergence of global and local spatiotemporal order in a nonlinear field model
We investigate the nonequilibrium evolution of a scalar field in (2+1)
dimensions. The field is set in a double-well potential in contact (open) or
not (closed) with a heat bath. For closed systems, we observe the synchronized
emergence of coherent spatiotemporal configurations, identified with oscillons.
This initial global ordering degenerates into localized order until all
oscillons disappear. We show that the synchronization is driven by resonant
parametric oscillations of the field's zero mode and that local ordering is
only possible outside equipartition. None of these orderings occur for open
systems.Comment: 4 pages, 5 figures, LaTeX, minor corrections to eqs. 1,3,
Efficient high-dimensional entanglement imaging with a compressive sensing, double-pixel camera
We implement a double-pixel, compressive sensing camera to efficiently
characterize, at high resolution, the spatially entangled fields produced by
spontaneous parametric downconversion. This technique leverages sparsity in
spatial correlations between entangled photons to improve acquisition times
over raster-scanning by a scaling factor up to n^2/log(n) for n-dimensional
images. We image at resolutions up to 1024 dimensions per detector and
demonstrate a channel capacity of 8.4 bits per photon. By comparing the
classical mutual information in conjugate bases, we violate an entropic
Einstein-Podolsky-Rosen separability criterion for all measured resolutions.
More broadly, our result indicates compressive sensing can be especially
effective for higher-order measurements on correlated systems.Comment: 10 pages, 7 figure
Cross-Phase Modulation Enhancement Via a Resonating Cavity: Semiclassical Description
We evaluate the advantages of performing cross-phase modulation (XPM) on a
very-far-off-resonance atomic system. We consider a ladder system with a weak
(few-photon level) control coherent field imparting a conditional nonlinear
phase shift on a probe beam. We find that by coupling to an optical resonator
the optimal XPM is enhanced proportional to the finesse of the resonator by a
factor of . We present a semi-classical description of the system and
show that the phenomenon is optimal in the self-defined condition of
off-resonance-effective-cooperativity equal to one
Fringe counter for interferometers Patent
Digital sensor for counting fringes produced by interferometers with improved sensitivity and one photomultiplier tube to eliminate alignment proble
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The (Mis)appropriation of HIV/AIDS advocacy strategies in Global Mental Health: towards a more nuanced approach
Background: Mental health is increasingly finding a place on global health and international development agendas. Advocates for Global Mental Health (GMH), and international organizations such as the World Health Organization (WHO) and the World Bank, argue that treatments available in high-income countries should also be made available in low- and middle-income countries. Such arguments are often made by comparing mental health to infectious diseases, including the relative disease and economic burdens they impose, and pointing to the applicability of the right to access treatment for mental health, not only infectious diseases. HIV/AIDS advocacy in particular has been held up by GMH advocates as offering an appropriate strategy for generating global commitment.
Discussion: There is a need to assess how health issues are framed not only in relation to social goods outside of health (such as human rights, security or development), but also in relation to other health or disease models, and how health policy and practice is shaped as a result. The article debates the merits and consequences of likening mental health to HIV/AIDS, and identifies four major problems with the model for GMH advocacy being developed through these analogies: 1. An inappropriately universalizing global approach to context-specific problems; 2. A conception of human rights that focuses on the right to access treatment at the expense of the right to refuse it; 3. A tendency to treat poverty as a psychiatric issue, rather than recognizing that mental distress can be the result of poverty and other forms of inequality; 4. The prioritization of destigmatization of disease over social justice models.
Conclusion: There are significant problems with the wholesale adoption of an (often simplified) version of HIV/AIDS advocacy as a model for GMH. Yet critical engagement with the important and nuanced differences between HIV/AIDS and mental health may nevertheless point to some possibilities for productive engagement and cross-fertilisation between advocates, activists and scholars in both fields
Paraxial ray optics cloaking
Despite much interest and progress in optical spatial cloaking, a
three-dimensional (3D), transmitting, continuously multidirectional cloak in
the visible regime has not yet been demonstrated. Here we experimentally
demonstrate such a cloak using ray optics, albeit with some edge effects. Our
device requires no new materials, uses isotropic off-the-shelf optics, scales
easily to cloak arbitrarily large objects, and is as broadband as the choice of
optical material, all of which have been challenges for current cloaking
schemes. In addition, we provide a concise formalism that quantifies and
produces perfect optical cloaks in the small-angle (`paraxial') limit
Intermittency in the transition to turbulence
It is commonly known that the intermittent transition from laminar to turbulent flow in pipes occurs because, at intermediate values of a prescribed pressure drop, a purely laminar flow offers too little resistance, but a fully turbulent one offers too much. We propose a phenomenological model of the flow, which is able to explain this in a quantitative way through a hysteretic transition between laminar and turbulent states, characterized by a disturbance amplitude variable that satisfies a natural type of evolution equation. The form of this equation is motivated by physical observations and derived by an averaging procedure, and we show that it naturally predicts disturbances having the characteristics of slugs and puffs. The model predicts oscillations similar to those which occur in intermittency in pipe flow, but it also predicts that stationary biphasic states can occur in sufficiently short pipes
Paraxial full-field cloaking
We complete the `paraxial' (small-angle) ray optics cloaking formalism
presented previously [Choi and Howell, Opt. Express 22, 29465 (2014)], by
extending it to the full-field of light. Omnidirectionality is then the only
relaxed parameter of what may be considered an ideal, broadband, field cloak.
We show that an isotropic plate of uniform thickness, with appropriately
designed refractive index and dispersion, can match the phase over the whole
visible spectrum. Our results support the fundamental limits on cloaking for
broadband vs. omnidirectionality, and provide insights into when anisotropy may
be required
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