G_2 Domain Walls in M-theory

M-theory is considered in its low-energy limit on a G_2 manifold with non-vanishing flux. Using the Killing spinor equations for linear flux, an explicit set of first-order bosonic equations for supersymmetric solutions is found. These solutions describe a warped product of a domain wall in four-dimensional space-time and a deformed G_2 manifold. It is shown how these domain walls arise from the perspective of the associated four-dimensional N=1 effective supergravity theories. We also discuss the inclusion of membrane and M5-brane sources.Comment: 30 pages, Late

The Aged Retinal Pigment Epithelium/Choroid: A Potential Substratum for the Pathogenesis of Age-Related Macular Degeneration

Although the statement that age is the greatest risk factor for Age-related macular degeneration (AMD) is widely accepted, the cellular and molecular explanations for that clinical statement are not generally known. A major focus of AMD research is the retinal pigment epithelium (RPE)/choroid. The purpose of this study was to characterize the changes in the RPE/choroid with age that may provide a background for the development of AMD.We compared the transcriptional profiles, key protein levels and histology of the RPE/choroid from young and old mice. Using three statistical methods, microarray data demonstrated marked changes in the old mouse. There were 315 genes differentially expressed with age; most of these genes were related to immune responses and inflammatory activity. Canonical pathways having significant numbers of upregulated genes in aged RPE/choroid included leukocyte extravasation, complement cascades, natural killer cell signaling and IL-10 signaling. By contrast, the adjacent neural retina showed completely different age-related changes. The levels of proteins that participate in leukocyte extravasation and complement pathways were consistently increased in the normal, aged RPE/choroid. Furthermore, there was increased gene expression and protein levels of leukocyte attracting signal, chemokine ligand 2 (Ccl2) in aged RPE/choroid. In old animals, there was marked extravasation and accumulation of leukocytes from the choroidal circulation onto Bruch's membrane and into the RPE.These phenotypic changes indicate that the RPE/choroid in the normal, old mouse has become an immunologically active tissue. There are signals from the normal, aged RPE/choroid which recruit leukocytes from the circulation and activate the complement cascade. These age-related changes that occur in the RPE/choroid with age, to the extent that they occur in the human retina, may provide the background for an error in regulation of immunological activity to cause AMD to appear in an elderly individual

Towards interpretable quantum machine learning via single-photon quantum walks

Variational quantum algorithms represent a promising approach to quantum machine learning where classical neural networks are replaced by parametrized quantum circuits. However, both approaches suffer from a clear limitation, that is a lack of interpretability. Here, we present a variational method to quantize projective simulation (PS), a reinforcement learning model aimed at interpretable artificial intelligence. Decision making in PS is modeled as a random walk on a graph describing the agent's memory. To implement the quantized model, we consider quantum walks of single photons in a lattice of tunable Mach-Zehnder interferometers trained via variational algorithms. Using an example from transfer learning, we show that the quantized PS model can exploit quantum interference to acquire capabilities beyond those of its classical counterpart. Finally, we discuss the role of quantum interference for training and tracing the decision making process, paving the way for realizations of interpretable quantum learning agents.Comment: 11+8 pages, 6+9 figures, 2 tables. F. Flamini and M. Krumm contributed equally to this wor

Removing the twin image in digital holography by segmented filtering of in-focus twin image

We propose and investigate a new digital method for the reduction of twin-image noise from digital Fresnel holograms. For the case of in-line Fresnel holography the unwanted twin is present as a highly corruptive noise when the object image is numerically reconstructed. We propose to firstly reconstruct the unwanted twin-image when it is in-focus and in this plane we calculate a segmentation mask that borders this in focus image. The twin-image is then segmented and removed by simple spatial filtering. The resulting digital wavefield is the inverse propagated to the desired object image plane. The image is free of the twin-image resulting in improved quality reconstructions. We demonstrate the segmentation and removal of the unwanted twin-image from in-line digital holograms containing real-world macroscopic objects. We offer suggestions for its rapid computational implementation