A Global Approach for Solving Edge-Matching Puzzles

We consider apictorial edge-matching puzzles, in which the goal is to arrange a collection of puzzle pieces with colored edges so that the colors match along the edges of adjacent pieces. We devise an algebraic representation for this problem and provide conditions under which it exactly characterizes a puzzle. Using the new representation, we recast the combinatorial, discrete problem of solving puzzles as a global, polynomial system of equations with continuous variables. We further propose new algorithms for generating approximate solutions to the continuous problem by solving a sequence of convex relaxations

High Spatial Resolution BRDFs with Metallic powders Using Wave Optics Analysis

This manuscript completes the analysis of our SIGGRAPH 2013 paper "Fabricating BRDFs at High Spatial Resolution Using Wave Optics" in which photolithography fabrication was used for manipulating reflectance effects. While photolithography allows for precise reflectance control, it is costly to fabricate. Here we explore an inexpensive alternative to micro-fabrication, in the form of metallic powders. Such powders are readily available at a variety of particle sizes and morphologies. Using an analysis similar to the micro-fabrication paper, we provide guidelines for the relation between the particles' shape and size and the reflectance functions they can produce

SPEGTI: Structured Prediction for Efficient Generative Text-to-Image Models

Modern text-to-image generation models produce high-quality images that are both photorealistic and faithful to the text prompts. However, this quality comes at significant computational cost: nearly all of these models are iterative and require running inference multiple times with large models. This iterative process is needed to ensure that different regions of the image are not only aligned with the text prompt, but also compatible with each other. In this work, we propose a light-weight approach to achieving this compatibility between different regions of an image, using a Markov Random Field (MRF) model. This method is shown to work in conjunction with the recently proposed Muse model. The MRF encodes the compatibility among image tokens at different spatial locations and enables us to significantly reduce the required number of Muse prediction steps. Inference with the MRF is significantly cheaper, and its parameters can be quickly learned through back-propagation by modeling MRF inference as a differentiable neural-network layer. Our full model, SPEGTI, uses this proposed MRF model to speed up Muse by 1.5X with no loss in output image quality

Rethinking FID: Towards a Better Evaluation Metric for Image Generation

As with many machine learning problems, the progress of image generation methods hinges on good evaluation metrics. One of the most popular is the Frechet Inception Distance (FID). FID estimates the distance between a distribution of Inception-v3 features of real images, and those of images generated by the algorithm. We highlight important drawbacks of FID: Inception's poor representation of the rich and varied content generated by modern text-to-image models, incorrect normality assumptions, and poor sample complexity. We call for a reevaluation of FID's use as the primary quality metric for generated images. We empirically demonstrate that FID contradicts human raters, it does not reflect gradual improvement of iterative text-to-image models, it does not capture distortion levels, and that it produces inconsistent results when varying the sample size. We also propose an alternative new metric, CMMD, based on richer CLIP embeddings and the maximum mean discrepancy distance with the Gaussian RBF kernel. It is an unbiased estimator that does not make any assumptions on the probability distribution of the embeddings and is sample efficient. Through extensive experiments and analysis, we demonstrate that FID-based evaluations of text-to-image models may be unreliable, and that CMMD offers a more robust and reliable assessment of image quality.Comment: Code is available at: https://github.com/google-research/google-research/tree/master/cmm

Fabricating BRDFs at high spatial resolution using wave optics

Recent attempts to fabricate surfaces with custom reflectance functions boast impressive angular resolution, yet their spatial resolution is limited. In this paper we present a method to construct spatially varying reflectance at a high resolution of up to 220dpi, orders of magnitude greater than previous attempts, albeit with a lower angular resolution. The resolution of previous approaches is limited by the machining, but more fundamentally, by the geometric optics model on which they are built. Beyond a certain scale geometric optics models break down and wave effects must be taken into account. We present an analysis of incoherent reflectance based on wave optics and gain important insights into reflectance design. We further suggest and demonstrate a practical method, which takes into account the limitations of existing micro-fabrication techniques such as photolithography to design and fabricate a range of reflection effects, based on wave interference.United States-Israel Binational Science FoundationIntel Corporation (Intel Collaborative Research Institute for Computational Intelligence)National Science Foundation (U.S.) (CGV 1116303

Helium Shell Detonations on Low Mass White Dwarfs as a Possible Explanation for SN 2005E

Recently several type Ib supernovae (SNe; with the prototypical SN 2005E) have been shown to have atypical properties. These SNe are faint (absolute peak magnitude of ~ -15) and fast SNe that show unique composition. They are inferred to have low ejecta mass (a few tenths of a solar mass) and to be highly enriched in calcium, but poor in silicon elements and nickel. These SNe were therefore suggested to belong to a new class of calcium-rich faint SNe explosions. Their properties were proposed to be the result of helium detonations that may occur on helium accreting white dwarfs. In this paper we theoretically study the scenario of helium detonations, and focus on the results of detonations in accreted helium layers on low mass carbon-oxygen (CO) cores. We present new results from one dimensional simulations of such explosions, including their light curves and spectra. We find that when the density of the helium layer is low enough the helium detonation produces large amounts of intermediate elements, such as calcium and titanium, together with a large amount of unburnt helium. Our results suggest that the properties of calcium-rich faint SNe could indeed be consistent with the helium-detonation scenario on small CO cores. Above a certain density (larger CO cores) the detonation leaves mainly 56Ni and unburnt helium, and the predicted spectrum will unlikely fit the unique features of this class of SNe. Finally, none of our studied models reproduces the bright, fast evolving light curves of another type of peculiar SNe suggested to originate in helium detonations (SNe 1885A, 1939B and 2002bj).Comment: 15 pages, 8 figure

Sub-Chandrasekhar Mass Models For Type Ia Supernovae

For carbon-oxygen white dwarfs accreting hydrogen or helium at rates in the range ~1-10 x 10^(-8) Msun/y, a variety of explosive outcomes is possible well before the star reaches the Chandrasekhar mass. These outcomes are surveyed for a range of white dwarf masses (0.7 - 1.1 Msun), accretion rates (1 - 7 x 10^(-8) Msun/y), and initial white dwarf temperatures (0.01 and 1 Lsun). The results are particularly sensitive to the convection that goes on during the last few minutes before the explosion. Unless this convection maintains a shallow temperature gradient, and unless the density is sufficiently high, the accreted helium does not detonate. Below a critical helium ignition density, which we estimate to be 5 - 10 x 10^5 g cm^(-3), either helium novae or helium deflagrations result. The hydrodynamics, nucleosynthesis, light curves, and spectra of a representative sample of detonating and deflagrating models are explored. Some can be quite faint indeed, powered at peak for a few days by the decay of 48Cr and 48V. Only the hottest, most massive white dwarfs considered with the smallest helium layers, show reasonable agreement with the light curves and spectra of common Type Ia supernovae. For the other models, especially those involving lighter white dwarfs, the helium shell mass exceeds 0.05 Msun and the mass of the 56Ni that is synthesized exceeds 0.01 Msun. These explosions do not look like ordinary Type Ia supernovae, or any other frequently observed transient.Comment: submitted to Ap

EcoliWiki: a wiki-based community resource for Escherichia coli

EcoliWiki is the community annotation component of the PortEco (http://porteco.org; formerly EcoliHub) project, an online data resource that integrates information on laboratory strains of Escherichia coli, its phages, plasmids and mobile genetic elements. As one of the early adopters of the wiki approach to model organism databases, EcoliWiki was designed to not only facilitate community-driven sharing of biological knowledge about E. coli as a model organism, but also to be interoperable with other data resources. EcoliWiki content currently covers genes from five laboratory E. coli strains, 21 bacteriophage genomes, F plasmid and eight transposons. EcoliWiki integrates the Mediawiki wiki platform with other open-source software tools and in-house software development to extend how wikis can be used for model organism databases. EcoliWiki can be accessed online at http://ecoliwiki.net

Binary systems and their nuclear explosions

Peer ReviewedPreprin