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Rays
\"Dscover facts about rays, including physical features, habitat, life cycle, food, and threats to these ocean creatures. Photos, captions, and keywords supplement the narrative of this informational text\"-- Provided by publisher.
Book
Implant Restorations
The fourth edition of Implant Restorations: A Step-by-Step Guide provides a wealth of updated and expanded coverage on detailed procedures for restoring dental implants. Focusing on the most common treatment scenarios, it offers concise literature reviews for each chapter and easy-to-follow descriptions of the techniques, along with high-quality clinical photographs demonstrating each step. Comprehensive throughout, this practical guide begins with introductory information on incorporating implant restorative dentistry in clinical practice. It covers diagnosis and treatment planning and digital dentistry, and addresses advances in cone beam computerized tomography (CBCT), treatment planning software, computer generated surgical guides, rapid prototype printing and impression-less implant restorative treatments, intra-oral scanning, laser sintering, and printing/milling polymer materials. Record-keeping, patient compliance, hygiene regimes, and follow-up are also covered. * Provides an accessible step-by-step guide to commonly encountered treatment scenarios, describing procedures and techniques in an easy-to-follow, highly illustrated format * Offers new chapters on diagnosis and treatment planning and digital dentistry * Covers advances in cone beam computerized tomography (CBCT), computer generated surgical guides, intra-oral scanning, laser sintering, and more An excellent and accessible guide on a burgeoning subject in modern dental practice by one of its most experienced clinicians, Implant Restorations: A Step-by-Step Guide, Fourth Edition will appeal to prosthodontists, general dentists, implant surgeons, dental students, dental assistants, hygienists, and dental laboratory technicians.
eBook
In-orbit Background and Sky Survey Simulation Study of POLAR-2/LPD
The Low-Energy X-ray Polarization Detector (LPD) is one of the payloads in the POLAR-2 experiment, designed as an external payload for the China Space Station deployment in early 2026. LPD is specifically designed to observe the polarization of gamma-ray burst (GRB) prompt emission in the energy range of 2–10 keV, with a wide field of view (FoV) of 90° in preliminary design. This observation is achieved using an array of X-ray photoelectric polarimeters based on gas pixel detectors. Due to the wide FoV configuration, the in-orbit background count rate in the soft X-ray range is high, while GRBs themselves also exhibit high flux in this energy band. In order to assess the contribution of various background components to the total count rate, we conducted detailed simulations using the GEANT4 C++ package. Our simulations encompassed the main interactions within the instrument materials and provided insights into various background components within the wide-FoV scheme. The simulation results reveal that among the background components, the primary contributors are the cosmic X-ray background (CXB) and bright X-ray sources. The total background count rate of LPD, after applying the charged particle background rejection algorithm, is approximately 0.55 counts cm–2 s–1 on average, and it varies with the detector’s orbit and pointing direction. Furthermore, we performed comprehensive simulations and comparative analyses of the CXB and X-ray bright sources under different FoVs and detector pointings. These analyses provide valuable insights into the background characteristics for soft X-ray polarimeter with wide FoV.
Journal Article
An In-depth Study of Gamma Rays from the Starburst Galaxy M82 with VERITAS
Assuming Galactic cosmic rays originate in supernovae and the winds of massive stars, starburst galaxies should produce very-high-energy (VHE; E > 100 GeV) gamma-ray emission via the interaction of their copious quantities of cosmic rays with the large reservoirs of dense gas within the galaxies. Such VHE emission was detected by VERITAS from the starburst galaxy M82 in 2008–09. An extensive, multiyear campaign followed these initial observations, yielding a total of 254 hr of good-quality VERITAS data on M82. Leveraging modern analysis techniques and the larger exposure, these VERITAS data show a more statistically significant VHE signal (∼6.5 standard deviations, σ). The corresponding photon spectrum is well fit by a power law (Γ = 2.3 ± 0.3stat ± 0.2sys), and the observed integral flux is F (>450 GeV) = (3.2 ± 0.6stat ± 0.6sys) × 10−13 cm−2 s−1, or ∼0.4% of the Crab Nebula flux above the same energy threshold. The improved VERITAS measurements, when combined with various multiwavelength data, enable modeling of the underlying emission and transport processes. A purely leptonic scenario is found to be a poor representation of the gamma-ray spectral energy distribution (SED). A lepto-hadronic scenario with cosmic rays following a power-law spectrum in momentum (index s ≃ 2.25) and with significant bremsstrahlung below 1 GeV provides a good match to the observed SED. The synchrotron emission from the secondary electrons indicates that efficient nonradiative losses of cosmic-ray electrons may be related to advective escape from the starburst core.
Journal Article
Einstein Probe Discovery of EP J005245.1−722843: A Rare Be–White Dwarf Binary in the Small Magellanic Cloud?
On 2024 May 27, the Wide-field X-ray Telescope on board the Space Sciences, University of Chinese Academy of Einstein Probe (EP) mission detected enhanced X-ray emission from a new transient source in the Small Magellanic Cloud during its commissioning phase. Prompt follow-up with the EP Follow-up X-ray Telescope, the Swift X-ray Telescope. and NICER have revealed a very soft, thermally emitting source (kT ~ 0.1 keV at the outburst peak) with an X-ray luminosity of L ~ 4 × 1038 erg s−1, labeled EP J005245.1−722843. This supersoft outburst faded very quickly in a week's time. Several emission lines and absorption edges were present in the X-ray spectrum, including deep nitrogen (0.67 keV) and oxygen (0.87 keV) absorption edges. The X-ray emission resembles the supersoft source phase of typical nova outbursts from an accreting white dwarf (WD) in a binary system, despite the X-ray source being historically associated with an O9-B0e massive star exhibiting a 17.55 day periodicity in the optical band. The discovery of this supersoft outburst suggests that EP J005245.1−722843 is a BeWD X-ray binary: an elusive evolutionary stage where two main-sequence massive stars have undergone a common envelope phase and experienced at least two episodes of mass transfer. In addition, the very short duration of the outburst and the presence of Ne features hint at a rather massive, i.e., close to the Chandrasekhar limit, Ne–O WD in the system.
Journal Article
Rays of the world
\"This book is the first complete pictorial atlas of the world's ray fauna. It also provides general identifying features and distributional information about this iconic, but surprisingly poorly known, group of fishes\"-- Introduction.
BOOK
Galactic Superaccreting X-Ray Binaries as Super-PeVatron Accelerators
The extension of the cosmic-ray (CR) spectrum well beyond 1 PeV necessitates the existence of a population of accelerators in the Milky Way, which we refer to as super-PeVatrons. Identifying the nature of these sources remains a challenge to the paradigm of Galactic CRs. Galactic superaccreting X-ray binaries (XRBs), where the compact object accretes at a rate near or above the Eddington limit, can meet the energy requirement to supply the high-energy population of Galactic CRs. We demonstrate that the transrelativistic jets and/or winds of these powerful objects with kinetic power exceeding 1039 erg s−1 can accelerate protons to energies above several PeV. Detection of such superaccreting XRBs through their ultrahigh-energy gamma-ray “halos” and large-scale nebulae is also discussed.
Journal Article