21,878 research outputs found
High temperature onset of field-induced transitions in the spin-ice compound Dy2Ti2O7
We have studied the field-dependent ac magnetic susceptibility of single
crystals of Dy2Ti2O7 spin ice along the [111] direction in the temperature
range 1.8 K - 7 K. Our data reflect the onset of local spin ice order in the
appearance of different field regimes. In particular, we observe a prominent
feature at approximately 1.0 T that is a precursor of the low-temperature
metamagnetic transition out of field-induced kagome ice, below which the
kinetic constraints imposed by the ice rules manifest themselves in a
substantial frequency-dependence of the susceptibility. Despite the relatively
high temperatures, our results are consistent with a monopole picture, and they
demonstrate that such a picture can give physical insight to the spin ice
systems even outside the low-temperature, low-density limit where monopole
excitations are well-defined quasiparticles
Balancing the competing requirements of saltatorial and fossorial specialisation: burrowing costs in the spinifex hopping mouse, Notomys alexis
© The Company of BiologistsSemi-fossorial animals (burrowing surface foragers) need to balance the competing morphological requirements of terrestrial and burrowing locomotion. These species rarely show the same degree of claw, forelimb and pectoral girdle structural development that fully fossorial forms (burrowing subterranean foragers) do, but nevertheless invest considerable amounts of energy in burrow systems. The compromise between terrestrial and burrowing locomotion was investigated by measuring net costs of burrowing and pedestrian transport in the spinifex hopping mouse, Notomys alexis, a species that forages in open areas in arid environments and is adapted for saltatorial locomotion. The net cost of transport by burrowing of hopping mice was found to be more expensive than for specialised fossorial species, and burrows were estimated to represent an energy investment equivalent to the terrestrial locomotion expected to be incurred in 17–100 days. A phylogenetically independentcontrasts approach revealed that morphological specialisation for burrowing was associated with low maximum running speeds in fossorial mammals and, for non-fossorial rodents and marsupials, maximum running speed was positively correlated with an index of habitat structure that ranged from arboreal to open desert. The high terrestrial speeds attainable by this semi-fossorial species by saltatory locomotion apparently outweigh the energetic savings that would be associated with burrowing specialisation.Craig R. White, Philip G. D. Matthews, and Roger S. Seymou
Lesbian, gay, bisexual, transgender and queer experiences of homelessness and identity : insecurity and home(o)normativity
Homelessness among the young lesbian, gay, bisexual and trans* (LGBT+) population is becoming an increasing societal concern, with alarmist reporting of high rates of homelessness compared to heterosexual people. This paper presents qualitative evidence from research with 20 LGBT + people who had experienced homelessness in Scotland. Significantly, it moves discussion of LGBT + homelessness out of a concern with public health and social work, to understand it in terms of homelessness research and housing theory. The analysis also brings in queer theory to our discussions of homelessness and housing. As a result, rather than understanding our participants as passive victims of a homophobic or transphobic society, we focus on their agency in developing a queer identity alongside their experiences of insecure accommodation. In their experiences of homelessness people were carrying out ‘edgework’ at the margins of heteronormative society. Routes out of homelessness were thus associated with people becoming more comfortable within their identities. We conclude by arguing that experiences of homelessness interacted in complex ways with sexual and gender identity, and that tailored mainstream housing provision is required for LGBT + homeless people
Faint Infrared Flares from the Microquasar GRS 1915+105
We present simultaneous infrared and X-ray observations of the Galactic
microquasar GRS 1915+105 using the Palomar 5-m telescope and Rossi X-ray Timing
Explorer on July 10, 1998 UT. Over the course of 5 hours, we observed 6 faint
infrared (IR) flares with peak amplitudes of mJy and durations
of seconds. These flares are associated with X-ray
soft-dip/soft-flare cycles, as opposed to the brighter IR flares associated
with X-ray hard-dip/soft-flare cycles seen in August 1997 by Eikenberry et al.
(1998). Interestingly, the IR flares begin {\it before} the X-ray oscillations,
implying an ``outside-in'' origin of the IR/X-ray cycle. We also show that the
quasi-steady IR excess in August 1997 is due to the pile-up of similar faint
flares. We discuss the implications of this flaring behavior for understanding
jet formation in microquasars.Comment: 10 pages, 4 figures Accepted for publication in ApJ Letter
High-Latitude HI in the Low Surface Brightness Galaxy UGC7321
From the analysis of sensitive HI 21-cm line observations, we find evidence
for vertically extended HI emission (|z|<~2.4 kpc) in the edge-on, low surface
brightness spiral galaxy UGC7321. Three-dimensional modelling suggests that the
HI disk of UGC7321 is both warped and flared, but that neither effect can fully
reproduce the spatial distribution and kinematics of the highest z-height gas.
We are able to model the high-latitude emission as an additional HI component
in the form of a ``thick disk'' or ``halo'' with a FWHM~3.3 kpc. We find
tentative evidence that the vertically extended gas declines in rotational
velocity as a function of z, although we are unable to completely rule out
models with constant V(z). In spite of the low star formation rate of UGC7321,
energy from supernovae may be sufficient to sustain this high-latitude gas.
However, alternative origins for this material, such as slow, sustained infall,
cannot yet be excluded.Comment: to appear in the August 20 Astrophysical Journal; 17 pages; version
with full resolution figures available at
http://cfa-www.harvard.edu/~lmatthew
Watching a superfluid untwist itself: Recurrence of Rabi oscillations in a Bose-Einstein condensate
The order parameter of a condensate with two internal states can continuously
distort in such a way as to remove twists that have been imposed along its
length. We observe this effect experimentally in the collapse and recurrence of
Rabi oscillations in a magnetically trapped, two-component Bose-Einstein
condensate of ^87Rb
Computer generated animation and movie production at LARC: A case study
The process of producing computer generated 16mm movies using the MOVIE.BYU software package developed by Brigham Young University and the currently available hardware technology at the Langley Research Center is described. A general overview relates the procedures to a specific application. Details are provided which describe the data used, preparation of a storyboard, key frame generation, the actual animation, title generation, filming, and processing/developing the final product. Problems encountered in each of these areas are identified. Both hardware and software problems are discussed along with proposed solutions and recommendations
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