34 research outputs found
Random on-board pixel sampling (ROPS) X-ray Camera
Recent advances in compressed sensing theory and algorithms offer new
possibilities for high-speed X-ray camera design. In many CMOS cameras, each
pixel has an independent on-board circuit that includes an amplifier, noise
rejection, signal shaper, an analog-to-digital converter (ADC), and optional
in-pixel storage. When X-ray images are sparse, i.e., when one of the following
cases is true: (a.) The number of pixels with true X-ray hits is much smaller
than the total number of pixels; (b.) The X-ray information is redundant; or
(c.) Some prior knowledge about the X-ray images exists, sparse sampling may be
allowed. Here we first illustrate the feasibility of random on-board pixel
sampling (ROPS) using an existing set of X-ray images, followed by a discussion
about signal to noise as a function of pixel size. Next, we describe a possible
circuit architecture to achieve random pixel access and in-pixel storage. The
combination of a multilayer architecture, sparse on-chip sampling, and
computational image techniques, is expected to facilitate the development and
applications of high-speed X-ray camera technology.Comment: 9 pages, 6 figures, Presented in 19th iWoRI
Insights into POT1 structural dynamics revealed by cryo-EM.
Telomeres are protein-DNA complexes that protect the ends of linear eukaryotic chromosomes. Mammalian telomeric DNA consists of 5'-(TTAGGG)n-3' double-stranded repeats, followed by up to several hundred bases of a 3' single-stranded G-rich overhang. The G-rich overhang is bound by the shelterin component POT1 which interacts with TPP1, the component involved in telomerase recruitment. A previously published crystal structure of the POT1 N-terminal half bound to the high affinity telomeric ligand 5'-TTAGGGTTAG-3' showed that the first six nucleotides, TTAGGG, are bound by the OB1 fold, while the adjacent OB2 binds the last four, TTAG. Here, we report two cryo-EM structures of full-length POT1 bound by the POT1-binding domain of TPP1. The structures differ in the relative orientation of the POT1 OB1 and OB2, suggesting that these two DNA-binding OB folds take up alternative conformations. Supporting DNA binding studies using telomeric ligands in which the OB1 and OB2 binding sites were spaced apart, show that POT1 binds with similar affinities to spaced or contiguous binding sites, suggesting plasticity in DNA binding and a role for the alternative conformations observed. A likely explanation is that the structural flexibility of POT1 enhances binding to the tandemly arranged telomeric repeats and hence increases telomere protection
Hollow pellet injection for magnetic fusion
Precise delivery of mass to burning plasmas is a problem of growing interest
in magnetic fusion. The answers to how much mass is necessary and sufficient
can vary depending on parameters such as the type of atoms involved, the type
of applications, plasma conditions, mass injector, and injection timing.
Motivated by edge localized mode (ELM) control in H-mode plasmas, disruption
mitigation and other applications in magnetic fusion, we report progress and
new possibilities in mass delivery based on hollow pellets. Here, a hollow
pellet refers to a spherical shell mass structure with a hollow core. Based on
an empirical model of pellet ablation, coupled with BOUT++ simulations of ELM
triggering threshold, hollow pellets are found to be attractive in comparison
with solid spheres for ELM control. By using hollow pellets, it is possible to
tailor mass delivery to certain regions of edge plasmas while minimizing core
contamination and reducing the total amount of mass needed. We also include
experimental progress in mass delivery experiments, in-situ diagnostics and
hollow pellet fabrication, and emphasize new experimental possibilities for ELM
control based on hollow pellets. A related application is the disruption
mitigation scheme using powder encapsulated inside hollow shells. Further
experiments will also help to resolve known discrepancies between theoretical
predictions and experiments in using mass injection for ELM control and lead to
better predictive models for ELM stability and triggering.Comment: Manuscript prepared for reviews by {\it Nuclear Fusion}, following
the initial presentation in the 27th IAEA FEC, Gandhinagar, India, Oct. 22 -
27, 201
Position-sensitive detection of ultracold neutrons with an imaging camera and its implications to spectroscopy
Position-sensitive detection of ultracold neutrons (UCNs) is demonstrated
using an imaging charge-coupled device (CCD) camera. A spatial resolution less
than 15 m has been achieved, which is equivalent to an UCN energy
resolution below 2 pico-electron-volts through the relation . Here, the symbols , , and are the
energy resolution, the spatial resolution, the neutron rest mass and the
gravitational acceleration, respectively. A multilayer surface convertor
described previously is used to capture UCNs and then emits visible light for
CCD imaging. Particle identification and noise rejection are discussed through
the use of light intensity profile analysis. This method allows different types
of UCN spectroscopy and other applications.Comment: 12 figures, 28 pages, accepted for publication in NIM
Gigahertz (GHz) hard x-ray imaging using fast scintillators
Gigahertz (GHz) imaging technology will be needed at high-luminosity X-ray and charged particle sources. It is plausible to combine fast scintillators with the latest picosecond detectors and GHz electronics for multi-frame hard Xray imaging and achieve an inter-frame time of less than 10 ns. The time responses and light yield of LYSO, LaBr_3, BaF_2 and ZnO are measured using an MCP-PMT detector. Zinc Oxide (ZnO) is an attractive material for fast hard X-ray imaging based on GEANT4 simulations and previous studies, but the measured light yield from the samples is much lower than expected
Needs, trends, and advances in scintillators for radiographic imaging and tomography
Scintillators are important materials for radiographic imaging and tomography
(RadIT), when ionizing radiations are used to reveal internal structures of
materials. Since its invention by R\"ontgen, RadIT now come in many modalities
such as absorption-based X-ray radiography, phase contrast X-ray imaging,
coherent X-ray diffractive imaging, high-energy X- and ray radiography
at above 1 MeV, X-ray computed tomography (CT), proton imaging and tomography
(IT), neutron IT, positron emission tomography (PET), high-energy electron
radiography, muon tomography, etc. Spatial, temporal resolution, sensitivity,
and radiation hardness, among others, are common metrics for RadIT performance,
which are enabled by, in addition to scintillators, advances in high-luminosity
accelerators and high-power lasers, photodetectors especially CMOS pixelated
sensor arrays, and lately data science. Medical imaging, nondestructive
testing, nuclear safety and safeguards are traditional RadIT applications.
Examples of growing or emerging applications include space, additive
manufacturing, machine vision, and virtual reality or `metaverse'. Scintillator
metrics such as light yield and decay time are correlated to RadIT metrics.
More than 160 kinds of scintillators and applications are presented during the
SCINT22 conference. New trends include inorganic and organic scintillator
heterostructures, liquid phase synthesis of perovskites and m-thick films,
use of multiphysics models and data science to guide scintillator development,
structural innovations such as photonic crystals, nanoscintillators enhanced by
the Purcell effect, novel scintillator fibers, and multilayer configurations.
Opportunities exist through optimization of RadIT with reduced radiation dose,
data-driven measurements, photon/particle counting and tracking methods
supplementing time-integrated measurements, and multimodal RadIT.Comment: 45 pages, 43 Figures, SCINT22 conference overvie
A multilayer surface detector for ultracold neutrons
A multilayer surface detector for ultracold neutrons (UCNs) is described. The
top B layer is exposed to the vacuum chamber and directly captures UCNs.
The ZnS:Ag layer beneath the B layer is a few microns thick, which is
sufficient to detect the charged particles from the B(n,)Li
neutron-capture reaction, while thin enough so that ample light due to
and Li escapes for detection by photomultiplier tubes. One-hundred-nm thick
B layer gives high UCN detection efficiency, as determined by the mean
UCN kinetic energy, detector materials and others. Low background, including
negligible sensitivity to ambient neutrons, has also been verified through
pulse-shape analysis and comparisons with other existing He and B
detectors. This type of detector has been configured in different ways for UCN
flux monitoring, development of UCN guides and neutron lifetime research.Comment: 21 pages, 10 figure
Automated vulnerability discovery and exploitation in the internet of things
Recently, automated software vulnerability detection and exploitation in Internet of Things (IoT) has attracted more and more attention, due to IoT’s fast adoption and high social impact. However, the task is challenging and the solutions are non-trivial: the existing methods have limited effectiveness at discovering vulnerabilities capable of compromising IoT systems. To address this, we propose an Automated Vulnerability Discovery and Exploitation framework with a Scheduling strategy, AutoDES that aims to improve the efficiency and effectiveness of vulnerability discovery and exploitation. In the vulnerability discovery stage, we use our Anti-Driller technique to mitigate the “path explosion” problem. This approach first generates a specific input proceeding from symbolic execution based on a Control Flow Graph (CFG). It then leverages a mutation-based fuzzer to find vulnerabilities while avoiding invalid mutations. In the vulnerability exploitation stage, we analyze the characteristics of vulnerabilities and then propose to generate exploits, via the use of several proposed attack techniques that can produce a shell based on the detected vulnerabilities. We also propose a genetic algorithm (GA)-based scheduling strategy (AutoS) that helps with assigning the computing resources dynamically and efficiently. The extensive experimental results on the RHG 2018 challenge dataset and the BCTF-RHG 2019 challenge dataset clearly demonstrate the effectiveness and efficiency of the proposed framework
Gigahertz (GHz) hard x-ray imaging using fast scintillators
Gigahertz (GHz) imaging technology will be needed at high-luminosity X-ray and charged particle sources. It is plausible to combine fast scintillators with the latest picosecond detectors and GHz electronics for multi-frame hard Xray imaging and achieve an inter-frame time of less than 10 ns. The time responses and light yield of LYSO, LaBr_3, BaF_2 and ZnO are measured using an MCP-PMT detector. Zinc Oxide (ZnO) is an attractive material for fast hard X-ray imaging based on GEANT4 simulations and previous studies, but the measured light yield from the samples is much lower than expected