Diffraction Analysis of 2-D Pupil Mapping for High-Contrast Imaging

Pupil-mapping is a technique whereby a uniformly-illuminated input pupil, such as from starlight, can be mapped into a non-uniformly illuminated exit pupil, such that the image formed from this pupil will have suppressed sidelobes, many orders of magnitude weaker than classical Airy ring intensities. Pupil mapping is therefore a candidate technique for coronagraphic imaging of extrasolar planets around nearby stars. Unlike most other high-contrast imaging techniques, pupil mapping is lossless and preserves the full angular resolution of the collecting telescope. So, it could possibly give the highest signal-to-noise ratio of any proposed single-telescope system for detecting extrasolar planets. Prior analyses based on pupil-to-pupil ray-tracing indicate that a planet fainter than 10^{-10} times its parent star, and as close as about 2 lambda/D, should be detectable. In this paper, we describe the results of careful diffraction analysis of pupil mapping systems. These results reveal a serious unresolved issue. Namely, high-contrast pupil mappings distribute light from very near the edge of the first pupil to a broad area of the second pupil and this dramatically amplifies diffraction-based edge effects resulting in a limiting attainable contrast of about 10^{-5}. We hope that by identifying this problem others will provide a solution.Comment: 23 pages, 13 figures, also posted to http://www.orfe.princeton.edu/~rvdb/tex/piaaFresnel/ms.pd

Is it too late to turn back the clock of managerialism and neoliberalism?

The esteemed health economist, Gavin Mooney, who died in tragic circumstances in December 2012, devoted his last book The Health of Nations: Towards a New Political Economy[1] to exposing the pernicious effects of neoliberalism on healthcare. He argued compellingly that the consequences of ‘neoliberalism’ – in his usage, the reliance on market mechanisms to address all the needs of a society in the areas of healthcare, education, social welfare and even the arts – have been disastrous for the health system and have exacerbated inequalities in access to care at both the national and global levels. They have led to inappropriate and perverse social outcomes, distorted the kinds of medicines and technologies that are employed, increased the equity gap, and exacerbated environmental destruction. He posed the question of whether it is possible to reverse what has, until now, been largely assumed to be an inexorable trend and, using case studies drawn from both developed and developing countries, drew attention to several possible alternative strategies for designing and delivering the sort of healthcare that may enrich communities, increase equity and properly address the social determinants of health

Diffraction tomography using power extinction measurements

We propose a new method for determining structures of semitransparent media from measurements of the extinguished power in scattering experiments. The method circumvents the problem of measuring the phase of the scattered field. We illustrate how this technique may be used to reconstruct both deterministic and random scatterers

Statistical generalizations of the optical cross-section theorem with application to inverse scattering

A fundamental result of scattering theory, the so-called optical theorem, applies to situations where the field incident on the scatterer is a monochromatic plane wave and the scatterer is deterministic. We present generalizations of the theorem to situations where either the incident field or the scatterer or both are spatially random. By using these generalizations we demonstrate the possibility of determining the structure of some random scatterers from the knowledge of the power absorbed from two plane waves incident on it

Rapid assessment of drug use and sexual HIV risk patterns among vulnerable drugusing populations in Cape Town, Durban and Pretoria, South Africa

This exploratory study examines the links between drug use and high-risk sexual practices and HIV in vulnerable drug-using populations in South Africa, including commercial sex workers (CSWs), men who have sex with men (MSM), injecting drug users (IDUs) and non-injecting drug users who are not CSWs or MSM (NIDUs). A rapid assessment ethnographic study was undertaken using observation, mapping, key informant interviews and focus groups in known ‘hotspots\' for drug use and sexual risk in Cape Town, Durban and Pretoria. Key informant (KI) and focus group interviews involved drug users and service providers. Purposeful snowball sampling and street intercepts were used to recruit drug users. Outcome measures included drug-related sexual HIV risk behaviour, and risk behaviour related to injection drug use, as well as issues relate to service use. HIV testing of drug-using KIs was conducted using the SmartCheck Rapid HIV-1 Antibody Test. Non-injection drug use (mainly cannabis, methaqualone, crack cocaine and crystal methamphetamine) and injection drug use (mainly heroin) was occurring in these cities. Drug users report selling sex for money to buy drugs, and CSWs used drugs before, during and after sex. Most (70%) of the drug-using KIs offered HIV testing accepted and 28% were positive, with rates highest among CSWs and MSM. IDUs reported engaging in needle sharing and needle disposal practices that put them and others at risk for contracting HIV. There was a widespread lack of awareness about where to access HIV treatment and preventive services, and numerous barriers to accessing appropriate HIV and drug- intervention services were reported. Multiple risk behaviours of vulnerable populations and lack of access to HIV prevention services could accelerate the diffusion of HIV. Targeted interventions could play an important role in limiting the spread of HIV in and through these under-reached and vulnerable populations. Keywords: Drug use, sexual risk behaviour, HIV/AIDS, South Africa.SAHARA-J Vol. 5 (3) 2008: pp. 113-11

Convergence and Stability of the Inverse Scattering Series for Diffuse Waves

We analyze the inverse scattering series for diffuse waves in random media. In previous work the inverse series was used to develop fast, direct image reconstruction algorithms in optical tomography. Here we characterize the convergence, stability and approximation error of the serie

Fermion zero modes at the boundary of superfluid 3He-B

Superfluid 3He-B belongs to the important special class of time-reversal invariant topological superfluids. It has Majorana fermions as edge states on the surface of bulk 3He-B. On the rough wall these fermion zero modes have finite density of states at E=0. It is possible that Lancaster experiments with a wire vibrating in 3He-B have already probed Majorana fermions living on the surface of the wire.Comment: 4 pages, no Figures, JETP Letters style, version to be published in JETP Letter

Anderson Localization of Polar Eigenmodes in Random Planar Composites

Anderson localization of classical waves in disordered media is a fundamental physical phenomenon that has attracted attention in the past three decades. More recently, localization of polar excitations in nanostructured metal-dielectric films (also known as random planar composite) has been subject of intense studies. Potential applications of planar composites include local near-field microscopy and spectroscopy. A number of previous studies have relied on the quasistatic approximation and a direct analogy with localization of electrons in disordered solids. Here I consider the localization problem without the quasistatic approximation. I show that localization of polar excitations is characterized by algebraic rather than by exponential spatial confinement. This result is also valid in two and three dimensions. I also show that the previously used localization criterion based on the gyration radius of eigenmodes is inconsistent with both exponential and algebraic localization. An alternative criterion based on the dipole participation number is proposed. Numerical demonstration of a localization-delocalization transition is given. Finally, it is shown that, contrary to the previous belief, localized modes can be effectively coupled to running waves.Comment: 22 pages, 7 figures. Paper was revised and a more precise definition of the participation number given, data for figures recalculated accordingly. Accepted to J. Phys.: Cond. Mat