4,275 research outputs found
High-Velocity Features in Type Ia Supernova Spectra
We use a sample of 58 low-redshift (z <= 0.03) Type Ia supernovae (SNe Ia)
having well-sampled light curves and spectra near maximum light to examine the
behaviour of high-velocity features (HVFs) in SN Ia spectra. We take advantage
of the fact that Si II 6355 is free of HVFs at maximum light in all SNe Ia,
allowing us to quantify the strength of HVFs by comparing the structure of
these two lines. We find that the average HVF strength increases with
decreasing light-curve decline rate, and rapidly declining SNe Ia (dm_15(B) >=
1.4 mag) show no HVFs in their maximum-light spectra. Comparison of HVF
strength to the light-curve colour of the SNe Ia in our sample shows no
evidence of correlation. We find a correlation of HVF strength with the
velocity of Si II 6355 at maximum light (v_Si), such that SNe Ia with lower
v_Si have stronger HVFs, while those SNe Ia firmly in the "high-velocity"
(i.e., v_Si >= 12,000 km/s) subclass exhibit no HVFs in their maximum-light
spectra. While v_Si and dm_15(B) show no correlation in the full sample of SNe
Ia, we find a significant correlation between these quantities in the subset of
SNe Ia having weak HVFs. In general, we find that slowly declining (low
dm_15(B)) SNe Ia, which are more luminous and more energetic than average SNe
Ia, tend to produce either high photospheric ejecta velocities (i.e., high
v_Si) or strong HVFs at maximum light, but not both. Finally, we examine the
evolution of HVF strength for a sample of SNe Ia having extensive pre-maximum
spectroscopic coverage and find significant diversity of the pre-maximum HVF
behaviour.Comment: Version accepted by MNRA
Providing the Third Dimension: High-resolution Multibeam Sonar as a Tool for Archaeological Investigations - An Example from the D-day Beaches of Normandy
In general, marine archaeological investigations begin in the archives, using historic maps, coast surveys, and other materials, to define submerged areas suspected to contain potentially significant historical sites. Following this research phase, a typical archaeological survey uses sidescan sonar and marine magnetometers as initial search tools. Targets are then examined through direct observation by divers, video, or photographs. Magnetometers can demonstrate the presence, absence, and relative susceptibility of ferrous objects but provide little indication of the nature of the target. Sidescan sonar can present a clear image of the overall nature of a target and its surrounding environment, but the sidescan image is often distorted and contains little information about the true 3-D shape of the object. Optical techniques allow precise identification of objects but suffer from very limited range, even in the best of situations. Modern high-resolution multibeam sonar offers an opportunity to cover a relatively large area from a safe distance above the target, while resolving the true three-dimensional (3-D) shape of the object with centimeter-level resolution. A clear demonstration of the applicability of highresolution multibeam sonar to wreck and artifact investigations occurred this summer when the Naval Historical Center (NHC), the Center for Coastal and Ocean Mapping (CCOM) at the University of New Hampshire, and Reson Inc., collaborated to explore the state of preservation and impact on the surrounding environment of a series of wrecks located off the coast of Normandy, France, adjacent to the American landing sectors The survey augmented previously collected magnetometer and high-resolution sidescan sonar data using a Reson 8125 high-resolution focused multibeam sonar with 240, 0.5° (at nadir) beams distributed over a 120° swath. The team investigated 21 areas in water depths ranging from about three -to 30 meters (m); some areas contained individual targets such as landing craft, barges, a destroyer, troop carrier, etc., while others contained multiple smaller targets such as tanks and trucks. Of particular interest were the well-preserved caissons and blockships of the artificial Mulberry Harbor deployed off Omaha Beach. The near-field beam-forming capability of the Reson 8125 combined with 3-D visualization techniques provided an unprecedented level of detail including the ability to recognize individual components of the wrecks (ramps, gun turrets, hatches, etc.), the state of preservation of the wrecks, and the impact of the wrecks on the surrounding seafloor
Recommended from our members
Synthetic peripherally-restricted cannabinoid suppresses chemotherapy-induced peripheral neuropathy pain symptoms by CB1 receptor activation.
Chemotherapy-induced peripheral neuropathy (CIPN) is a severe and dose-limiting side effect of cancer treatment that affects millions of cancer survivors throughout the world and current treatment options are extremely limited by their side effects. Cannabinoids are highly effective in suppressing pain symptoms of chemotherapy-induced and other peripheral neuropathies but their widespread use is limited by central nervous system (CNS)-mediated side effects. Here, we tested one compound from a series of recently developed synthetic peripherally restricted cannabinoids (PRCBs) in a rat model of cisplatin-induced peripheral neuropathy. Results show that local or systemic administration of 4-{2-[-(1E)-1[(4-propylnaphthalen-1-yl)methylidene]-1H-inden-3-yl]ethyl}morpholine (PrNMI) dose-dependently suppressed CIPN mechanical and cold allodynia. Orally administered PrNMI also dose-dependently suppressed CIPN allodynia symptoms in both male and female rats without any CNS side effects. Co-administration with selective cannabinoid receptor subtype blockers revealed that PrNMI's anti-allodynic effects are mediated by CB1 receptor (CB1R) activation. Expression of CB2Rs was reduced in dorsal root ganglia from CIPN rats, whereas expression of CB1Rs and various endocannabinoid synthesizing and metabolizing enzymes was unaffected. Daily PrNMI treatment of CIPN rats for two weeks showed a lack of appreciable tolerance to PrNMI's anti-allodynic effects. In an operant task which reflects cerebral processing of pain, PrNMI also dose-dependently suppressed CIPN pain behaviors. Our results demonstrate that PRCBs exemplified by PrNMI may represent a viable option for the treatment of CIPN pain symptoms
A blinded determination of from low-redshift Type Ia supernovae, calibrated by Cepheid variables
Presently a tension exists between values of the Hubble constant
derived from analysis of fluctuations in the Cosmic Microwave Background
by Planck, and local measurements of the expansion using calibrators of type Ia
supernovae (SNe Ia). We perform a blinded reanalysis of Riess et al. 2011 to
measure from low-redshift SNe Ia, calibrated by Cepheid variables and
geometric distances including to NGC 4258. This paper is a demonstration of
techniques to be applied to the Riess et at. 2016 data. Our end-to-end analysis
starts from available CfA3 and LOSS photometry, providing an independent
validation of Riess et al. 2011. We obscure the value of throughout our
analysis and the first stage of the referee process, because calibration of SNe
Ia requires a series of often subtle choices, and the potential for results to
be affected by human bias is significant. Our analysis departs from that of
Riess et al. 2011 by incorporating the covariance matrix method adopted in SNLS
and JLA to quantify SN Ia systematics, and by including a simultaneous fit of
all SN Ia and Cepheid data. We find (stat)
(sys) km s Mpc with a three-galaxy (NGC 4258+LMC+MW) anchor. The
relative uncertainties are 4.3% statistical, 1.1% systematic, and 4.4% total,
larger than in Riess et al. 2011 (3.3% total) and the Efstathiou 2014
reanalysis (3.4% total). Our error budget for is dominated by statistical
errors due to the small size of the supernova sample, whilst the systematic
contribution is dominated by variation in the Cepheid fits, and for the SNe Ia,
uncertainties in the host galaxy mass dependence and Malmquist bias.Comment: 38 pages, 13 figures, 13 tables; accepted for publication in MNRA
The SkyMapper Transient Survey
The SkyMapper 1.3 m telescope at Siding Spring Observatory has now begun
regular operations. Alongside the Southern Sky Survey, a comprehensive digital
survey of the entire southern sky, SkyMapper will carry out a search for
supernovae and other transients. The search strategy, covering a total
footprint area of ~2000 deg2 with a cadence of days, is optimised for
discovery and follow-up of low-redshift type Ia supernovae to constrain cosmic
expansion and peculiar velocities. We describe the search operations and
infrastructure, including a parallelised software pipeline to discover variable
objects in difference imaging; simulations of the performance of the survey
over its lifetime; public access to discovered transients; and some first
results from the Science Verification data.Comment: 13 pages, 11 figures; submitted to PAS
PromoterPlot: a graphical display of promoter similarities by pattern recognition
PromoterPlot (http://promoterplot.fmi.ch) is a web-based tool for simplifying the display and processing of transcription factor searches using either the commercial or free TransFac distributions. The input sequence is a TransFac search (public version) or FASTA/Affymetrix IDs (local install). It uses an intuitive pattern recognition algorithm for finding similarities between groups of promoters by dividing transcription factor predictions into conserved triplet models. To minimize the number of false-positive models, it can optionally exclude factors that are known to be unexpressed or inactive in the cells being studied based on microarray or proteomic expression data. The program will also estimate the likelihood of finding a pattern by chance based on the frequency observed in a control set of mammalian promoters we obtained from Genomatix. The results are stored as an interactive SVG web page on our serve
PromoterPlot: a graphical display of promoter similarities by pattern recognition
PromoterPlot () is a web-based tool for simplifying the display and processing of transcription factor searches using either the commercial or free TransFac distributions. The input sequence is a TransFac search (public version) or FASTA/Affymetrix IDs (local install). It uses an intuitive pattern recognition algorithm for finding similarities between groups of promoters by dividing transcription factor predictions into conserved triplet models. To minimize the number of false-positive models, it can optionally exclude factors that are known to be unexpressed or inactive in the cells being studied based on microarray or proteomic expression data. The program will also estimate the likelihood of finding a pattern by chance based on the frequency observed in a control set of mammalian promoters we obtained from Genomatix. The results are stored as an interactive SVG web page on our server
- …