Sparse Image Reconstruction for Contrast Enhanced Cardiac Ultrasound using Diverging Waves

Assessing cardiac function with trans-thoracic ultrasound is a challenging task, mainly due to its fast motion and its anatomical position which only allows for a narrow intercostal imaging window. These factors often lead to the use of diverging waves, even when contrast agents are employed. While capable of achieving a very high frames rate, an acquisition with diverging waves from a narrow aperture suffers from serious image quality degradation. In this regard, it is often impossible to mitigate this problem using common processing methods, such as coherent compounding. In this study, we cast the problem of reconstructing the contrast enhanced ultrasound images as regularised inverse problem, analogous to the compressed sensing one, where the sensing matrix is fundamentally described by the delay operator associated with the time of flight. The results show that this framework can improve the Signal to Noise Ratio (SNR) of the image by up to 5.85dB compared to delay and sum (DAS) and is therefore a promising way to reconstruct contrast enhanced cardiac images. The experiments also highlight that the way noise is modelled has a significant impact on the final image quality © 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including eprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other work

The Effect of High Energy (HZE) Particle Radiation (40Ar) on Aging Parameters of Mouse Hippocampus and Retina

Eight month old C57BL6 mice were exposed (head only) to 0.5 rad or 50 rads of Argon particles at the Lawrence Berkeley Radiation Facility, CA. Neuromotor performance was assessed monthly for six months beginning twelve weeks post-irradiation using a \u27\u27string test . The decline in motor performance was dose-related and none of the animals was able to complete the task after four months of testing. Morphological changes were monitored six and twelve months post-irradiation by light and electron microscopy. The synaptic density in the CA-1 area of the hippocampus decreased six and twelve months after irradiation. The decrease after twelve months was less than after six months. The width of the outer nuclear layer (ONL) of the retina increased with increasing dose. The number of blood vessels between the ONL and the ganglion layer decreased twelve months after irradiation and this area did not show significant accumulation of age pigment

Dynamic Key-Value Memory Networks for Knowledge Tracing

Knowledge Tracing (KT) is a task of tracing evolving knowledge state of students with respect to one or more concepts as they engage in a sequence of learning activities. One important purpose of KT is to personalize the practice sequence to help students learn knowledge concepts efficiently. However, existing methods such as Bayesian Knowledge Tracing and Deep Knowledge Tracing either model knowledge state for each predefined concept separately or fail to pinpoint exactly which concepts a student is good at or unfamiliar with. To solve these problems, this work introduces a new model called Dynamic Key-Value Memory Networks (DKVMN) that can exploit the relationships between underlying concepts and directly output a student's mastery level of each concept. Unlike standard memory-augmented neural networks that facilitate a single memory matrix or two static memory matrices, our model has one static matrix called key, which stores the knowledge concepts and the other dynamic matrix called value, which stores and updates the mastery levels of corresponding concepts. Experiments show that our model consistently outperforms the state-of-the-art model in a range of KT datasets. Moreover, the DKVMN model can automatically discover underlying concepts of exercises typically performed by human annotations and depict the changing knowledge state of a student.Comment: To appear in 26th International Conference on World Wide Web (WWW), 201

A Viewing Angle - Kinetic Luminosity Unification Scheme For BL Lacertae Objects

We propose a unified classification for BL Lac objects (BLs), focusing on the synchrotron peak frequency of the spectral energy distribution. The unification scheme is based on the angle Theta that describes the orientation of the relativistic jet and on the electron kinetic luminosity Lambda of the jet. We assume that Lambda scales with the size of the jet r in a self-similar fashion (Lambda propto r^2), as supported by observational data. The jets are self-similar in geometry and have the same pressure and median magnetic field at the inlet, independent of size. The self-similarity is broken for the highest energy electrons, which radiate mainly at high frequencies, since for large sources they suffer more severe radiative energy losses over a given fraction of the jet length. We calculate the optically thin synchrotron spectrum using an accelerating inner jet model based on simple relativistic gas dynamics and show that it can fit the observed infrared to X-ray spectrum of PKS 2155--304. We couple the accelerating jet model to the unification scheme and compare the results to complete samples of BLs. The negative apparent evolution of X-ray selected BLs is explained as a result of positive evolution of the jet electron kinetic luminosity $\Lambda_{kin}$. We review observational arguments in favor of the existence of scaled-down accretion disks and broad emission-line regions in BLs. The proposed unification scheme can explain the lack of observed broad emission lines in X-ray selected BLs, as well as the existence of those lines preferentially in luminous radio-selected BLs. Finally, we review observational arguments that suggest the extension of this unification scheme to all blazars.Comment: 32 pages, 8 figures, to be published in the ApJ (Oct 20, 1998

The role of morphological markedness in the processing of number and gender agreement in Spanish: an event-related potential investigation

Current morphological theory assumes that feature values, such as masculine and feminine or singular and plural, are asymmetrically represented. That is, one member of the opposition (e.g. feminine for gender, plural for number) is assumed to be marked, and the other one, unmarked. The present study examines how these asymmetries impact agreement resolution in Spanish. Agreement was manipulated between a noun acting as head of a relative clause and an adjective located inside the relative clause (e.g. catedral que parecía inmensa “cathedral that looked huge”). Half of the nouns were feminine (marked) and the other half, masculine (unmarked). Half of the nouns were used in the plural (marked) and the other half, in the singular (unmarked). Twenty-seven Spanish native speakers read 240 sentences while their brain activity was recorded with EEG and performed a grammaticality judgment. Results showed that both number and gender violations elicited a central-posterior P600, a component associated with syntactic repair, and a late anterior negativity, argued to reflect working memory costs. Only the P600 was affected by markedness. It started earlier for violations where the mismatching feature was marked. Moreover, it was larger for errors where the mismatching feature was marked, although this amplitude modulation only emerged for number, possibly due to differences in how number and gender cues were realized (i.e. both masculine and feminine showed overt inflection, but singular was uninflected relative to plural). These results suggest that the parser is sensitive to markedness asymmetries in the course of online processing

Spectral optical monitoring of 3C390.3 in 1995-2007: I. Light curves and flux variation of the continuum and broad lines

Here we present the results of the long-term (1995-2007) spectral monitoring of the broad line radio galaxy \object{3C~390.3}, a well known AGN with the double peaked broad emission lines, usually assumed to be emitted from an accretion disk. To explore dimensions and structure of the BLR, we analyze the light curves of the broad H$\alpha$ and H$\beta$ line fluxes and the continuum flux. In order to find changes in the BLR, we analyze the H$\alpha$ and H$\beta$ line profiles, as well as the change in the line profiles during the monitoring period. First we try to find a periodicity in the continuum and H$\beta$ light curves, finding that there is a good chance for quasi-periodical oscillations. Using the line shapes and their characteristics (as e.g. peaks separation and their intensity ratio, or FWHM) of broad H$\beta$ and H$\alpha$ lines, we discuss the structure of the BLR. Also, we cross-correlate the continuum flux with H$\beta$ and H$\alpha$ lines to find dimensions of the BLR. We found that during the monitoring period the broad emission component of the H$\alpha$ and H$\beta$ lines, and the continuum flux varied by a factor of $\approx$4-5. Also, we detected different structure in the line profiles of H$\alpha$ and H$\beta$. It seems that an additional central component is present and superposed to the disk emission. In the period of high activity (after 2002), H$\beta$ became broader than H$\alpha$ and red wing of H$\beta$ was higher than the one of H$\alpha$. We found time lags of $\sim$95 days between the continuum and H$\beta$ flux, and about 120 days between the continuum and H$\alpha$ flux. Variation in the line profiles, as well as correlation between the line and continuum flux during the monitoring period is in the favor of the disk origin of the broad lines with the possible contribution of some additional region and/or some kind of perturbation in the disk.Comment: 32 pages, accepted to A&A, typos correcte