1,084 research outputs found
Crack Sizing by the Time-of-Flight Diffraction Method, in the Light of Recent International Round-Robin Trials, (UKAEA, DDT and PISC II)
In 1980–81, Harwell developed a mini-computer controlled multi-probe defect detection and sizing system(l) based on the ultrasonic time-of-light/diffraction principle introduced by Silk(2). This system proved to be capable of fully automatic data collection from the PWR girth-weld simulation Plates 1 and 2 in the Defect Detection Trials of 1981–82. The speed of collection and subsequent analysis was such that a report on the defects found could be filed within 48 hours. The mode of operation adopted simulated minimum time of access to the defects, and was intended to define that dimension of a defect which has greatest significance, ie the through-thickness dimension
Nebular-Phase Spectra of Nearby Type Ia Supernovae
We present late-time spectra of eight Type Ia supernovae (SNe Ia) obtained at
days after peak brightness using the Gemini South and Keck telescopes.
All of the SNe Ia in our sample were nearby, well separated from their host
galaxy's light, and have early-time photometry and spectroscopy from the Las
Cumbres Observatory (LCO). Parameters are derived from the light curves and
spectra such as peak brightness, decline rate, photospheric velocity, and the
widths and velocities of the forbidden nebular emission lines. We discuss the
physical interpretations of these parameters for the individual SNe Ia and the
sample in general, including comparisons to well-observed SNe Ia from the
literature. There are possible correlations between early-time and late-time
spectral features that may indicate an asymmetric explosion, so we discuss our
sample of SNe within the context of models for an offset ignition and/or white
dwarf collisions. A subset of our late-time spectra are uncontaminated by host
emission, and we statistically evaluate our nondetections of H emission
to limit the amount of hydrogen in these systems. Finally, we consider the
late-time evolution of the iron emission lines, finding that not all of our SNe
follow the established trend of a redward migration at days after
maximum brightness.Comment: 20 pages, 8 figures, 9 tables; accepted to MNRA
Physiology and Pharmacology Ca V 3.1 T-Type Ca 2þ Channels Contribute to Myogenic Signaling in Rat Retinal Arterioles
PURPOSE. Although L-type Ca 2þ channels are known to play a key role in the myogenic reactivity of retinal arterial vessels, the involvement of other types of voltage-gated Ca 2þ channels in this process remains unknown. In the present study we have investigated the contribution of T-type Ca 2þ channels to myogenic signaling in arterioles of the rat retinal microcirculation. METHODS. Confocal immunolabeling of whole-mount preparations was used to investigate the localization of Ca V 3.1-3 channels in retinal arteriolar smooth muscle cells. T-type currents and the contribution of T-type channels to myogenic signaling were assessed by whole-cell patchclamp recording and pressure myography of isolated retinal arteriole segments. RESULTS. Strong immunolabeling for Ca V 3.1 was observed on the plasma membrane of retinal arteriolar smooth muscle cells. In contrast, no expression of Ca V 3.2 or Ca V 3.3 could be detected in retinal arterioles, although these channels were present on glial cell end-feet surrounding the vessels and retinal ganglion cells, respectively. TTA-A2-sensitive T-type currents were recorded in retinal arteriolar myocytes with biophysical properties distinct from those of the L-type currents present in these cells. Inhibition of T-type channels using TTA-A2 or ML-218 dilated isolated, myogenically active, retinal arterioles. CONCLUSIONS. Ca V 3.1 T-type Ca 2þ channels are functionally expressed on arteriolar smooth muscle cells of retinal arterioles and play an important role in myogenic signaling in these vessels. The work has important implications concerning our understanding of the mechanisms controlling blood flow autoregulation in the retina and its disruption during ocular disease
Optical and Ultraviolet Observations of the Very Young Type IIP SN 2014cx in NGC 337
Extensive photometric and spectroscopic observations are presented for SN
2014cx, a type IIP supernova (SN) exploding in the nearby galaxy NGC 337. The
observations are performed in optical and ultraviolet bands, covering from -20
to +400 days from the peak light. The stringent detection limit from
prediscovery images suggests that this supernova was actually detected within
about 1 day after explosion. Evolution of the very early-time light curve of SN
2014cx is similar to that predicted from a shock breakout and post-shock
cooling decline before reaching the optical peak. Our photometric observations
show that SN 2014cx has a plateau duration of ~ 100 days, an absolute V-band
magnitude of ~ -16.5 mag at t~50 days, and a nickel mass of 0.056+-0.008 Msun.
The spectral evolution of SN 2014cx resembles that of normal SNe IIP like SN
1999em and SN 2004et, except that it has a slightly higher expansion velocity
(~ 4200 km/s at 50 days). From the cooling curve of photospheric temperature,
we derive that the progenitor has a pre-explosion radius of ~ 640 Rsun,
consistent with those obtained from SNEC modeling (~ 620 Rsun) and
hydrodynamical modeling of the observables (~ 570 Rsun). Moreover, the
hydrodynamical simulations yield a total explosion energy of ~ 0.4*10e51 erg,
and an ejected mass of ~ 8 Msun. These results indicate that the immediate
progenitor of SN 2014cx is likely a red supergiant star with a mass of ~ 10
Msun.Comment: 47 pages, 12 figures and 7 tables. Accepted by Ap
SN~2012cg: Evidence for Interaction Between a Normal Type Ia Supernova and a Non-Degenerate Binary Companion
We report evidence for excess blue light from the Type Ia supernova SN 2012cg
at fifteen and sixteen days before maximum B-band brightness. The emission is
consistent with predictions for the impact of the supernova on a non-degenerate
binary companion. This is the first evidence for emission from a companion to a
SN Ia. Sixteen days before maximum light, the B-V color of SN 2012cg is 0.2 mag
bluer than for other normal SN~Ia. At later times, this supernova has a typical
SN Ia light curve, with extinction-corrected M_B = -19.62 +/- 0.02 mag and
Delta m_{15}(B) = 0.86 +/- 0.02. Our data set is extensive, with photometry in
7 filters from 5 independent sources. Early spectra also show the effects of
blue light, and high-velocity features are observed at early times. Near
maximum, the spectra are normal with a silicon velocity v_{Si} = -10,500$ km
s^{-1}. Comparing the early data with models by Kasen (2010) favors a
main-sequence companion of about 6 solar masses. It is possible that many other
SN Ia have main-sequence companions that have eluded detection because the
emission from the impact is fleeting and faint.Comment: accepted to Ap
Hubble Space Telescope and Ground-Based Observations of the Type Iax Supernovae SN 2005hk and SN 2008A
We present Hubble Space Telescope (HST) and ground-based optical and
near-infrared observations of SN 2005hk and SN 2008A, typical members of the
Type Iax class of supernovae (SNe). Here we focus on late-time observations,
where these objects deviate most dramatically from all other SN types. Instead
of the dominant nebular emission lines that are observed in other SNe at late
phases, spectra of SNe 2005hk and 2008A show lines of Fe II, Ca II, and Fe I
more than a year past maximum light, along with narrow [Fe II] and [Ca II]
emission. We use spectral features to constrain the temperature and density of
the ejecta, and find high densities at late times, with n_e >~ 10^9 cm^-3. Such
high densities should yield enhanced cooling of the ejecta, making these
objects good candidates to observe the expected "infrared catastrophe," a
generic feature of SN Ia models. However, our HST photometry of SN 2008A does
not match the predictions of an infrared catastrophe. Moreover, our HST
observations rule out a "complete deflagration" that fully disrupts the white
dwarf for these peculiar SNe, showing no evidence for unburned material at late
times. Deflagration explosion models that leave behind a bound remnant can
match some of the observed properties of SNe Iax, but no published model is
consistent with all of our observations of SNe 2005hk and 2008A.Comment: 20 pages, 15 figure
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