4,077 research outputs found
Subpixel Spatial Resolution of the X-Ray Charge-Coupled Device Based on the Charge Cloud Shape
When an X-ray photon lands into a pixel (event pixel), the primary charge is
mainly collected into the event pixel. If the X-ray landing position is
sufficiently close to the pixel boundary, the primary charge spills over to the
adjacent pixel forming split events. We can easily understand that there are
three parameters coupled together; the X-ray landing position inside the pixel,
the X-ray event pattern and the primary charge cloud shape. We can determine
any one of them from the other two parameters. Since we know the charge cloud
shape using the multi-pitch mesh experiment, we can calculate the X-ray landing
position with subpixel resolution using the event pattern. We applied our
method to Ti-K X-rays for the charge-coupled device with m square
pixel. Once the primary charge splits into the adjacent pixel, we can determine
the X-ray landing position with subpixel resolution. Using three- or four-pixel
split events, we can determine the X-ray landing position with an accuracy of
less than m. For a two-pixel split event, we obtained a similar position
accuracy in the split direction with no improvement in the direction
perpendicular to it. We will discuss the type of CCD which can achieve the
subpixel resolution for the entire area of the CCD.Comment: 16pages, 5 figures. To appear in Jpn. J. Appl. Phys. March, 200
Nonthermal emission properties of the northwestern rim of supernova remnant RX J0852-4622
The supernova remnant (SNR) RX J0852-4622 (Vela Jr., G266.6-1.2) is one of
the most important SNRs for investigating the acceleration of multi-TeV
particles and the origin of Galactic cosmic rays because of its strong
synchrotron X-ray and TeV gamma-ray emission, which show a shell-like
morphology similar to each other. Using the XMM-Newton archival data consisting
of multiple pointing observations of the northwestern rim of the remnant, we
investigate the spatial properties of the nonthermal X-ray emission as a
function of distance from an outer shock wave. All X-ray spectra are well
reproduced by an absorbed power-law model above 2 keV. It is found that the
spectra show gradual softening from a photon index 2.56 in the rim region to
2.96 in the interior region. We show that this radial profile can be
interpreted as a gradual decrease of the cutoff energy of the electron spectrum
due to synchrotron cooling. By using a simple spectral evolution model that
includes continuous synchrotron losses, the spectral softening can be
reproduced with the magnetic field strength in the post-shock flow to less than
several tens of uG. If this is a typical magnetic field in the SNR shell,
gamma-ray emission would be accounted for by inverse Compton scattering of
high-energy electrons that also produce the synchrotron X-ray emission. Future
hard X-ray imaging observations with Nustar and ASTRO-H and TeV gamma-ray
observations with the Cherenkov Telescope Array (CTA) will allow to us to
explore other possible explanations of the systematic softening of the X-ray
spectra.Comment: accepted by A&
Exploring Fine Subpixel Spatial Resolution of Hybrid CMOS Detectors
When an X-ray is incident onto the silicon absorber array of a detector, it
liberates a large number of electrons, which tend to diffuse outward into what
is referred to as the charge cloud. This number can vary from tens to thousands
across the soft X-ray bandpass (0.1 - 10 keV). The charge cloud can then be
picked up by several pixels, and forms a specific pattern based on the exact
incident location of the X-ray. We present experimental results on subpixel
resolution for a custom H2RG with 36 micron pixels, presented in Bray 2018, and
compare the data to simulated images . We then apply the model simulation to a
prototype small pixel hybrid CMOS detector (HCD) that would be suitable for the
Lynx X-ray surveyor. We also discuss the ability of a small pixel detector to
obtain subpixel resolution
Histone H3 lysine 56 acetylation by Rtt109 is crucial for chromosome positioning
Peer reviewedPublisher PD
Overabundance of Calcium in the young SNR RX J08524622: evidence of over-production of Ti
Recently, COMPTEL has detected -rays of 1157 keV from Ti in
the direction of the SNR RX J08524622 (Iyudin et al. 1998). Since Ti
is a product of explosive nucleosynthesis and its half lifetime \tau\sb{1/2}
is about 60 yrs, RX J08524622 must be a young supernova remnant and
radiation is dominated by the ejecta rather than by interstellar matter. We
have detected an X-ray emission line at keV which is thought to
come from highly ionized Ca. The emission line is so far only seen in the
north-west shell region of RX J08524622. The X-ray spectrum can be well
fitted with that of thin hot plasma of cosmic abundances except that of Ca,
which is overabundant by a factor of . Assuming that most of Ca is
Ca, which originates from Ti by radioactive decay, we estimate a
total Ca mass of about . Combining the amount of
Ca and the observed flux of the Ti -ray line, the age of
RX J08524622 is around 1000 yrs.Comment: 14 pages, 5figures, accepted for publication of PAS
Vacancy Ordering in Vanadium Carbides Based on V_6C_5
The ordered arrangement of carbon vacancies in vanadium carbides near V_6C_5 has been analysed by means of selected-area electron diffraction and high-voltage electron microscopy. A new type of ordered distribution of carbon vacancies is found at non-stoichiometric compositions between V_6C_5 and V_8C_7. This structure can be expressed as a long-period structure consisting of the enantiomorphic domains based on the structure V_6C_5 which was determined by Billingham, Bell and Lewis (1972). The periodic domain boundaries with spacing eleven times the nearest-neighbour interatomic distance are directly observed by electron microscopy
The Interplay of Metaphor and Iconicity: A Cognitive Approach to Poetic Texts
This essay attempts to clarify the interrelationship between the notions of metaphor and iconicity in the theory of cognitive metaphor, particularly in the model of βblendingβ (Turner and Fauconnier 1995, in press, Fauconnier and Turner 1996, Turner 1996, 1998, among others). In cognitive and semiotic terms, βiconsβ and βmetaphorsβ share that property of signification βmotivatedβ by similarity. Connecting things of similarity is one of the basic operations of the human mind. The treatment of metaphor and iconicity in an interrelated fashion will provide a more cohesive and integrated explanation of various linguistic phenomena. The list of such phenomena includes word formation, word order, grammaticalisation, semantic change, poetic discourse, signed languages and writing systems, as manifestations of the interplay between metaphor and iconicity. This study shows that poetic texts, in particular, serve as an optimal example in this exploration because in poetic discourse, the interplay of metaphor and iconicity is foregrounded rather than backgrounded as in everyday discourse (Jakobson and Waugh 1979). This paper, therefore, aims to contribute in the following two issues. Firstly, theoretical clarification of the interplay of metaphor and iconicity will be given in cognitive terms. Particularly, with the model of blending, we can specify which part(s) of the metaphorical process - whether the input, generic, or blended spaces - relate(s) to the iconic mapping of form and meaning. Secondly, the analysis will demonstrate how the interplay of metaphor and iconicity is manifested in linguistic signs in general, and in poetic texts in particular. It will be claimed that there are two major types of manifestation: (i) that there are iconic moments in metaphor; and (ii) that a form acquires an iconic meaning via metaphor
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