Image recovery from rotational and translational invariants

We introduce a framework for recovering an image from its rotationally and translationally invariant features based on autocorrelation analysis. This work is an instance of the multi-target detection statistical model, which is mainly used to study the mathematical and computational properties of single-particle reconstruction using cryo-electron microscopy (cryo-EM) at low signal-to-noise ratios. We demonstrate with synthetic numerical experiments that an image can be reconstructed from rotationally and translationally invariant features and show that the reconstruction is robust to noise. These results constitute an important step towards the goal of structure determination of small biomolecules using cryo-EM.Comment: 5 pages, 3 figure

Multi-target detection with rotations

We consider the multi-target detection problem of estimating a two-dimensional target image from a large noisy measurement image that contains many randomly rotated and translated copies of the target image. Motivated by single-particle cryo-electron microscopy, we focus on the low signal-to-noise regime, where it is difficult to estimate the locations and orientations of the target images in the measurement. Our approach uses autocorrelation analysis to estimate rotationally and translationally invariant features of the target image. We demonstrate that, regardless of the level of noise, our technique can be used to recover the target image when the measurement is sufficiently large.Comment: 20 pages, 5 figure

Getting the message straight: effects of a brief hepatitis prevention intervention among injection drug users

To redress gaps in injection drug users' (IDUs) knowledge about hepatitis risk and prevention, we developed a brief intervention to be delivered to IDUs at syringe exchange programs (SEPs) in three US cities. Following a month-long campaign in which intervention packets containing novel injection hygiene supplies and written materials were distributed to every client at each visit, intervention effectiveness was evaluated by comparing exposed and unexposed participants' self-reported injection practices. Over one-quarter of the exposed group began using the novel hygiene supplies which included an absorbent pad ("Safety Square") to stanch blood flow post-injection. Compared to those unexposed to the intervention, a smaller but still substantial number of exposed participants continued to inappropriately use alcohol pads post-injection despite exposure to written messages to the contrary (22.8% vs. 30.0%). It should also be noted that for those exposed to the intervention, 8% may have misused Safety Squares as part of pre-injection preparation of their injection site; attention should be paid to providing explicit and accurate instruction on the use of any health promotion materials being distributed. While this study indicates that passive introduction of risk reduction materials in injection drug users through syringe exchange programs can be an economical and relatively simple method of changing behaviors, discussions with SEP clients regarding explicit instructions about injection hygiene and appropriate use of novel risk reduction materials is also needed in order to optimize the potential for adoption of health promotion behaviors. The study results suggest that SEP staff should provide their clients with brief, frequent verbal reminders about the appropriate use when distributing risk reduction materials. Issues related to format and language of written materials are discussed

Moment-based metrics for molecules computable from cryo-EM images

Single particle cryogenic electron microscopy (cryo-EM) is an imaging technique capable of recovering the high-resolution 3-D structure of biological macromolecules from many noisy and randomly oriented projection images. One notable approach to 3-D reconstruction, known as Kam's method, relies on the moments of the 2-D images. Inspired by Kam's method, we introduce a rotationally invariant metric between two molecular structures, which does not require 3-D alignment. Further, we introduce a metric between a stack of projection images and a molecular structure, which is invariant to rotations and reflections and does not require performing 3-D reconstruction. Additionally, the latter metric does not assume a uniform distribution of viewing angles. We demonstrate uses of the new metrics on synthetic and experimental datasets, highlighting their ability to measure structural similarity.Comment: 21 Pages, 9 Figures, 2 Algorithms, and 3 Table

Evolution of the pairing pseudogap in the spectral function with interplane anisotropy

We study the pairing pseudogap in the spectral function as a function of interplane coupling. The analytical expressions for the self-energy in the critical regime are obtained for any degree of anisotropy. The frequency dependence of the self-energy is found to be qualitatively different in two and three dimensions, and the crossover from two to three dimensional behavior is discussed. In particular, by considering the anisotropy of the Fermi velocity and gap along the Fermi surface, we can qualitatively explain recent photoemission experiments on high temperature superconductors concerning the temperature dependent Fermi arcs seen in the pseudogap phase.Comment: 20 pages, revtex, 5 encapsulated postscript figures include