Ptychography

Ptychography is a computational imaging technique. A detector records an extensive data set consisting of many inference patterns obtained as an object is displaced to various positions relative to an illumination field. A computer algorithm of some type is then used to invert these data into an image. It has three key advantages: it does not depend upon a good-quality lens, or indeed on using any lens at all; it can obtain the image wave in phase as well as in intensity; and it can self-calibrate in the sense that errors that arise in the experimental set up can be accounted for and their effects removed. Its transfer function is in theory perfect, with resolution being wavelength limited. Although the main concepts of ptychography were developed many years ago, it has only recently (over the last 10 years) become widely adopted. This chapter surveys visible light, x-ray, electron, and EUV ptychography as applied to microscopic imaging. It describes the principal experimental arrangements used at these various wavelengths. It reviews the most common inversion algorithms that are nowadays employed, giving examples of meta code to implement these. It describes, for those new to the field, how to avoid the most common pitfalls in obtaining good quality reconstructions. It also discusses more advanced techniques such as modal decomposition and strategies to cope with three-dimensional () multiple scattering

Vertical structure and color of Jovian latitudinal cloud bands during the Juno era

The identity of the coloring agent(s) in Jupiter's atmosphere and the exact structure of Jupiter's uppermost cloud deck are yet to be conclusively understood. The Crème Brulée model of Jupiter's tropospheric clouds, originally proposed by Baines et al. and expanded upon by Sromovsky et al. and Baines et al., presumes that the chromophore measured by Carlson et al. is the singular coloring agent in Jupiter's troposphere. In this work, we test the validity of the Crème Brulée model of Jupiter's uppermost cloud deck using spectra measured during the Juno spacecraft's fifth perijove pass in 2017 March. These data were obtained as part of an international ground-based observing campaign in support of the Juno mission using the New Mexico State University Acousto-optic Imaging Camera at the 3.5 m telescope at Apache Point Observatory in Sunspot, NM, USA. We find that the Crème Brulée model cloud-layering scheme can reproduce Jupiter's visible spectrum both with the Carlson et al. chromophore and with modifications to its imaginary index of refraction spectrum. While the Crème Brulée model provides reasonable results for regions of Jupiter's cloud bands such as the North Equatorial Belt and Equatorial Zone, we find that it is not a safe assumption for unique weather events, such as the 2016–2017 Southern Equatorial Belt outbreak that was captured by our measurements

Pathways of cerebrospinal fluid outflow: a deeper understanding of resorption

Cerebrospinal fluid (CSF) absorption has long been held to predominantly entail drainage into the venous outflow system via the intracranial arachnoid granulations. Newer data suggest pathways involving spinal arachnoid granulations and lymphatic channels may also make substantial contributions to CSF outflow