9,298 research outputs found
Spectral Properties From Lyman-alpha to H-alpha For An Essentially Complete Sample of Quasars I: Data
We have obtained quasi-simultaneous ultraviolet-optical spectra for 22 out of
23 quasars in the complete PG-X-ray sample with redshift, z<0.4, and M_B<-23.
The spectra cover rest-frame wavelengths from at least Lyman-alpha to H-alpha.
Here we provide a detailed description of the data, including careful
spectrophotometry and redshift determination. We also present direct
measurements of the continua, strong emission lines and features, including
Lyman-alpha, SiIV+OIV], CIV, CIII], SiIII], MgII, H-beta, [OIII],
He5876+NaI5890,5896, H-alpha, and blended iron emission in the UV and optical.
The widths, asymmetries and velocity shifts of profiles of strong emission
lines show that CIV and Lyman-alpha are very different from H-beta and H-alpha.
This suggests that the motion of the broad line region is related to the
ionization structure, but the data appears not agree with the radially
stratified ionization structure supported by reverberation mapping studies, and
therefore suggest that outflows contribute additional velocity components to
the broad emission line profiles.Comment: 42 pages, 10 figures, 13 tables. Accepted by AJ. Supplemental figures
not included. Full version available at
http://physics.uwyo.edu/~shang/pgxpaper/ShangPaper.pd
Near-field interaction between domain walls in adjacent Permalloy nanowires
The magnetostatic interaction between two oppositely charged transverse
domain walls (DWs)in adjacent Permalloy nanowires is experimentally
demonstrated. The dependence of the pinning strength on wire separation is
investigated for distances between 13 and 125 nm, and depinning fields up to 93
Oe are measured. The results can be described fully by considering the
interaction between the full complex distribution of magnetic charge within
rigid, isolated DWs. This suggests the DW internal structure is not appreciably
disturbed by the pinning potential, and that they remain rigid although the
pinning strength is significant. This work demonstrates the possibility of
non-contact DW trapping without DW perturbation and full continuous flexibility
of the pinning potential type and strength. The consequence of the interaction
on DW based data storage schemes is evaluated.Comment: 4 pages, 4 figures, 1 page supplimentary material (supporting.ps
Measuring a photonic qubit without destroying it
Measuring the polarisation of a single photon typically results in its
destruction. We propose, demonstrate, and completely characterise a
\emph{quantum non-demolition} (QND) scheme for realising such a measurement
non-destructively. This scheme uses only linear optics and photo-detection of
ancillary modes to induce a strong non-linearity at the single photon level,
non-deterministically. We vary this QND measurement continuously into the weak
regime, and use it to perform a non-destructive test of complementarity in
quantum mechanics. Our scheme realises the most advanced general measurement of
a qubit: it is non-destructive, can be made in any basis, and with arbitrary
strength.Comment: 4 pages, 3 figure
Mobile Access in the Library: Some New Developments in Ireland
New insights provided by a range of specialists in the areas of social science, cognitive research and computer science research have led to increased developments and advances in the architectures for interactive and mobile learning environments. The most exciting results indicate that mobile technologies can be used to revolutionize learning and provided discontinuous rather than incremental learning opportunities in libraries and campuses worldwide. Mobile learning corroborates the view of educational philosophers such as Dewey and McLuhan that there is an intrinsic connection between communication, information provision and the learner community. Nevertheless, despite the rapid and continuing adoption of mobile devices, there has, to date, been little activity in integrating these technologies into the realm of mobile learning and the learning and library/information environments. A paradigm shift is occurring in the access people have to educational materials due to the ubiquitous availability of these materials brought about by the mobility and pervasiveness factors, which are inherent to mobile technologies. The potential for mobile technologies in education is enormous and the challenge for the e-learning community is to harness these devices for the benefit of education. One such benefit is the ever-increasing availability of educational content such as e-books on mobile devices. The availability of e-books will greatly support mobile access in the library
Changing social contracts in climate-change adaptation
Risks from extreme weather events are mediated through
state, civil society and individual action
1
,
2
. We propose evolving
social contracts as a primary mechanism by which adaptation
to climate change proceeds. We use a natural experiment
of policy and social contexts of the UK and Ireland affected
by the same meteorological event and resultant flooding in
November 2009. We analyse data from policy documents and
from household surveys of 356 residents in western Ireland and
northwest England. We find significant differences between
perceptions of individual responsibility for protection across
the jurisdictions and between perceptions of future risk from
populations directly affected by flooding events. These explain
differences in stated willingness to take individual adaptive
actions when state support retrenches. We therefore show
that expectations for state protection are critical in mediating
impacts and promoting longer-term adaptation. We argue
that making social contracts explicit may smooth pathways to
effective and legitimate adaptation
Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi: I. Early X-ray emission from the shocked ejecta and red giant wind
RS Ophiuchi began its latest outburst on 2006 February 12. Previous outbursts
have indicated that high velocity ejecta interact with a pre-existing red giant
wind, setting up shock systems analogous to those seen in Supernova Remnants.
However, in the previous outburst in 1985, X-ray observations did not commence
until 55 days after the initial explosion. Here we report on Swift observations
covering the first month of the 2006 outburst with the Burst Alert (BAT) and
X-ray Telescope (XRT) instruments. RS Oph was clearly detected in the BAT 14-25
keV band from t=0 to days. XRT observationsfrom 0.3-10 keV, started at
3.17 days after outburst. The rapidly evolving XRT spectra clearly show the
presence of both line and continuum emission which can be fitted by thermal
emission from hot gas whose characteristic temperature, overlying absorbing
column, , and resulting unabsorbed total flux decline monotonically
after the first few days. Derived shock velocities are in good agreement with
those found from observations at other wavelengths. Similarly, is in
accord with that expected from the red giant wind ahead of the forward shock.
We confirm the basic models of the 1985 outburst and conclude that standard
Phase I remnant evolution terminated by days and the remnant then
rapidly evolved to display behaviour characteristic of Phase III. Around t=26
days however, a new, luminous and highly variable soft X-ray source began to
appear whose origin will be explored in a subsequent paper.Comment: 20 pages, 4 figures (2 updated), accepted by Ap
Quantum Non-demolition Measurements on Qubits
We discuss the characterization and properties of quantum non-demolition
(QND) measurements on qubit systems. We introduce figures of merit which can be
applied to systems of any Hilbert space dimension thus providing universal
criteria for characterizing QND measurements. We discuss the controlled-NOT
gate and an optical implementation as examples of QND devices for qubits. We
also discuss the QND measurement of weak values
Hubble Space Telescope Imaging of the Expanding Nebular Remnant of the Recurrent Nova RS Ophiuchi (2006)
We report Hubble Space Telescope imaging obtained 155 days after the 2006
outburst of RS Ophiuchi. We detect extended emission in both [O III] and [Ne V]
lines. In both lines, the remnant has a double ring structure. The E-W
orientation and total extent of these structures (580+-50 AU at d=1.6kpc) is
consistent with that expected due to expansion of emitting regions imaged
earlier in the outburst at radio wavelengths. Expansion at high velocity
appears to have been roughly constant in the E-W direction (v_{exp} = 3200+-300
km/s in the plane of the sky), with tentative evidence of deceleration N-S. We
present a bipolar model of the remnant whose inclination is consistent with
that of the central binary. The true expansion velocities of the polar
components are then v = 5600+-1100 km/s. We suggest that the bipolar morphology
of the remnant results from interaction of the outburst ejecta with a
circumstellar medium that is significantly denser in the equatorial regions of
the binary than at the poles. This is also consistent with observations of
shock evolution in the X-ray and the possible presence of dust in the infrared.
Furthermore, it is in line with models of the shaping of planetary nebulae with
close binary central systems, and also with recent observations relating to the
progenitors of Type Ia supernovae, for which recurrent novae are a proposed
candidate. Our observations also reveal more extended structures to the S and E
of the remnant whose possible origin is briefly discussed.Comment: 13 pages, 2 figures, accepted for publication in ApJ
Testing the standard fireball model of GRBs using late X-ray afterglows measured by Swift
We show that all X-ray decay curves of GRBs measured by Swift can be fitted
using one or two components both of which have exactly the same functional form
comprised of an early falling exponential phase followed by a power law decay.
The 1st component contains the prompt gamma-ray emission and the initial X-ray
decay. The 2nd component appears later, has a much longer duration and is
present for ~80% of GRBs. It most likely arises from the external shock which
eventually develops into the X-ray afterglow. In the remaining ~20% of GRBs the
initial X-ray decay of the 1st component fades more slowly than the 2nd and
dominates at late times to form an afterglow but it is not clear what the
origin of this emission is.
The temporal decay parameters and gamma/X-ray spectral indices derived for
107 GRBs are compared to the expectations of the standard fireball model
including a search for possible "jet breaks". For ~50% of GRBs the observed
afterglow is in accord with the model but for the rest the temporal and
spectral indices do not conform to the expected closure relations and are
suggestive of continued, late, energy injection. We identify a few possible jet
breaks but there are many examples where such breaks are predicted but are
absent.
The time, T_a, at which the exponential phase of the 2nd component changes to
a final powerlaw decay afterglow is correlated with the peak of the gamma-ray
spectrum, E_peak. This is analogous to the Ghirlanda relation, indicating that
this time is in some way related to optically observed break times measured for
pre-Swift bursts.Comment: submitted to Ap
GMRT Observations of the 2006 outburst of the Nova RS Ophiuchi: First detection of emission at radio frequencies < 1.4 GHz
The first low radio frequency (<1.4 GHz) detection of the outburst of the
recurrent nova RS Ophiuchi is presented in this letter. Radio emission was
detected at 0.61 GHz on day 20 with a flux density of ~48 mJy and at 0.325 GHz
on day 38 with a flux density of ~ 44 mJy. This is in contrast with the 1985
outburst when it was not detected at 0.327 GHz even on day 66. The emission at
low radio frequencies is clearly non-thermal and is well-explained by a
synchrotron spectrum of index alpha ~ -0.8 (S propto nu^alpha) suffering
foreground absorption due to the pre-existing, ionized, warm, clumpy red giant
wind. The absence of low frequency radio emission in 1985 and the earlier
turn-on of the radio flux in the current outburst are interpreted as being due
to higher foreground absorption in 1985 compared to that in 2006, suggesting
that the overlying wind densities in 2006 are only ~30% of those in 1985.Comment: 14 pages, 1 figure. Accepted for publication in ApJ
- …