1,598 research outputs found
Neutron diffraction in a model itinerant metal near a quantum critical point
Neutron diffraction measurements on single crystals of Cr1-xVx (x=0, 0.02,
0.037) show that the ordering moment and the Neel temperature are continuously
suppressed as x approaches 0.037, a proposed Quantum Critical Point (QCP). The
wave vector Q of the spin density wave (SDW) becomes more incommensurate as x
increases in accordance with the two band model. At xc=0.037 we have found
temperature dependent, resolution limited elastic scattering at 4
incommensurate wave vectors Q=(1+/-delta_1,2, 0, 0)*2pi/a, which correspond to
2 SDWs with Neel temperatures of 19 K and 300 K. Our neutron diffraction
measurements indicate that the electronic structure of Cr is robust, and that
tuning Cr to its QCP results not in the suppression of antiferromagnetism, but
instead enables new spin ordering due to novel nesting of the Fermi surface of
Cr.Comment: Submitted as a part of proceedings of LT25 (Amsterdam 2008
Near-infrared integral field spectroscopy of Massive Young Stellar Objects
We present medium resolution () -band integral field
spectroscopy of six MYSOs. The targets are selected from the RMS survey, and we
used the NIFS on the Gemini North telescope. The data show various spectral
line features including Br, CO, H, and \mbox{He\,{\sc i}}. The
Br line is detected in emission in all objects with
-- 200 kms. V645 Cyg shows a high-velocity
P-Cygni profile between -800 kms and -300 kms. We performed
three-dimensional spectroastrometry to diagnose the circumstellar environment
in the vicinity of the central stars using the Br line. We measured the
centroids of the velocity components with sub-mas precision. The centroids
allow us to discriminate the blueshifted and redshifted components in a roughly
east--west direction in both IRAS 18151--1208 and S106 in Br. This lies
almost perpendicular to observed larger scale outflows. We conclude, given the
widths of the lines and the orientation of the spectroastrometric signature,
that our results trace a disc wind in both IRAS 18151--1208 and S106. The CO
absorption lines at low transitions are detected in IRAS
18151--1208 and AFGL 2136. We analysed the velocity structure of the neutral
gas discs. In IRAS 18151--1208, the absorption centroids of the blueshifted and
redshifted components are separated in a direction of north-east to south-west,
nearly perpendicular to that of the larger scale jet. The
position-velocity relations of these objects can be reproduced with central
masses of 30 M_{\sun} for IRAS 18151--1208 and 20 M_{\sun} for AFGL 2136.
We also detect CO bandhead emission in IRAS 18151--1208, S106 and
V645 Cyg. The results can be fitted reasonably with a Keplerian rotation model,
with masses of 15, 20 and 20 M_{\sun} respectively.Comment: 17 pages, 10 figures, accepted by MNRA
Recommended from our members
A longitudinal evaluation of the acceptability and impact of a diet diary app for older adults with age-related macular degeneration
Ongoing advances in technology are increasing the scope for enhancing and supporting older adults’ daily living. The digital divide between older and younger adults raises concerns, however, about the suitability of technological solutions for older adults, especially for those with impairments. Taking older adults with Age-Related Macular Degeneration (AMD) as a case study, we used user-centred and participatory design approaches to develop an assistive mobile app for self-monitoring their intake of food [12,13]. In this paper we report on findings of a longitudinal field evaluation of our app that was conducted to investigate how it was received and adopted by older adults with AMD and its impact on their lives. Demonstrating the benefit of applying inclusive design methods for technology for older adults, our findings reveal how the use of the app raises participants’ awareness and facilitates self-monitoring of diet, encourages positive (diet) behaviour change, and encourages learning
Probing discs around massive young stellar objects with CO first overtone emission
We present high resolution (R~50,000) spectroastrometry over the CO 1st
overtone bandhead of a sample of seven intermediate/massive young stellar
objects. These are primarily drawn from the red MSX source (RMS) survey, a
systematic search for young massive stars which has returned a large, well
selected sample of such objects. The mean luminosity of the sample is
approximately 5 times 10^4 L_\odot, indicating the objects typically have a
mass of ~15 solar masses. We fit the observed bandhead profiles with a model of
a circumstellar disc, and find good agreement between the models and
observations for all but one object. We compare the high angular precision
(0.2-0.8 mas) spectroastrometric data to the spatial distribution of the
emitting material in the best-fitting models. No spatial signatures of discs
are detected, which is entirely consistent with the properties of the
best-fitting models. Therefore, the observations suggest that the CO bandhead
emission of massive young stellar objects originates in small-scale disks, in
agreement with previous work. This provides further evidence that massive stars
form via disc accretion, as suggested by recent simulations.Comment: Accepted for publication in MNRA
Singlet-triplet dispersion reveals additional frustration in the triangular dimer compound BaMnO
We present single crystal inelastic neutron scattering measurements of the
S=1 dimerized quasi-two-dimensional antiferromagnet BaMnO. The
singlet-triplet dispersion reveals nearest-neighbor and next-nearest-neighbor
ferromagnetic interactions between adjacent bilayers that compete against each
other. Although the inter-bilayer exchange is comparable to the intra-bilayer
exchange, this additional frustration reduces the effective coupling along the
c-axis and leads to a quasi-two dimensional behavior. In addition, the obtained
exchange values are able to reproduce the four critical fields in the phase
diagram.Comment: 4 pages, 3 color figures, submitted to an APS physical review journa
Doping Dependence of Spin Dynamics in Electron-Doped Ba(Fe1-xCox)2As2
The spin dynamics in single crystal, electron-doped Ba(Fe1-xCox)2As2 has been
investigated by inelastic neutron scattering over the full range from undoped
to the overdoped regime. We observe damped magnetic fluctuations in the normal
state of the optimally doped compound (x=0.06) that share a remarkable
similarity with those in the paramagnetic state of the parent compound (x=0).
In the overdoped superconducting compound (x=0.14), magnetic excitations show a
gap-like behavior, possibly related to a topological change in the hole Fermi
surface (Lifshitz transition), while the imaginary part of the spin
susceptibility prominently resembles that of the overdoped cuprates. For the
heavily overdoped, non-superconducting compound (x=0.24) the magnetic
scattering disappears, which could be attributed to the absence of a hole
Fermi-surface pocket observed by photoemission.Comment: 6 pages, 5 figures, published versio
- …