2,097 research outputs found
Experimental observation of the 'Tilting Mode' of an array of vortices in a dilute Bose-Einstein Condensate
We have measured the precession frequency of a vortex lattice in a
Bose-Einstein condensate of 87Rb atoms. The observed mode corresponds to a
collective motion in which all the vortices in the array are tilted by a small
angle with respect to the z-axis (the symmetry axis of the trapping potential)
and synchronously rotate about this axis. This motion corresponds to excitation
of a Kelvin wave along the core of each vortex and we have verified that it has
the handedness expected for such helical waves, i.e. precession in the opposite
sense to the rotational flow around the vortices. The experimental method used
to excite this collective mode closely resembles that used to study the
scissors mode and excitation of the scissors mode for a condensate containing a
vortex array was used to determine the angular momentum of the system. Indeed,
the collective tilting of the array that we have observed has previously been
referred to as an `anomalous' scissors mode.Comment: 5 pages, 7 figures to be published in PR
A Bayesian approach for estimating the probability of trigger failures in the stop-signal paradigm
Response inhibition is frequently investigated using the stop-signal paradigm, where participants perform a two-choice response time task that is occasionally interrupted by a stop signal instructing them to withhold their response. Stop-signal performance is formalized as a race between a go and a stop process. If the go process wins, the response is executed; if the stop process wins, the response is inhibited. Successful inhibition requires fast stop responses and a high probability of triggering the stop process. Existing methods allow for the estimation of the latency of the stop response, but are unable to identify deficiencies in triggering the stop process. We introduce a Bayesian model that addresses this limitation and enables researchers to simultaneously estimate the probability of trigger failures and the entire distribution of stopping latencies. We demonstrate that trigger failures are clearly present in two previous studies, and that ignoring them distorts estimates of stopping latencies. The parameter estimation routine is implemented in the BEESTS software (Matzke et al., Front. Quantitative Psych. Measurement, 4, 918; 2013a) and is available at http://dora.erbe-matzke.com/software.html
Prostate cancer survivorship care: if not now, when?
Prostate cancer is the most common cancer diagnosed in Australian men, excluding non-melanoma skin cancer, and it is estimated that there are over 220 000 Australian men living with a diagnosis of prostate cancer [1]. Survival for men with prostate cancer is excellent in countries that have accessible screening and treatment services, and in Australia 5-year relative survival is over 95% [1]. High incidence, coupled with improving long-term survival, leads to a correspondingly high prevalence rate and high community disease burden. Many men with prostate cancer experience long-term decrements in their mental and physical quality of life, overall they have a greater suicide risk than their non-cancer peers, and unmet supportive care needs are pervasive [2]. In this context, survivorship care for men with prostate cancer is crucial in both the short and long term. The recent development of a Prostate Cancer Survivorship Essentials Framework in the Australian and New Zealand setting provides an example of a regional response to this issue that delivers guidance for policy makers, clinicians, community and consumers on what is essential for step change in prostate cancer survivorship outcomes [3]
Experimental demonstration of painting arbitrary and dynamic potentials for Bose-Einstein condensates
There is a pressing need for robust and straightforward methods to create
potentials for trapping Bose-Einstein condensates which are simultaneously
dynamic, fully arbitrary, and sufficiently stable to not heat the ultracold
gas. We show here how to accomplish these goals, using a rapidly-moving laser
beam that "paints" a time-averaged optical dipole potential in which we create
BECs in a variety of geometries, including toroids, ring lattices, and square
lattices. Matter wave interference patterns confirm that the trapped gas is a
condensate. As a simple illustration of dynamics, we show that the technique
can transform a toroidal condensate into a ring lattice and back into a toroid.
The technique is general and should work with any sufficiently polarizable
low-energy particles.Comment: Minor text changes and three references added. This is the final
version published in New Journal of Physic
“I Wouldn’t Want to Be a Gender Expert:” Gender Experts in Peace Mediation
Peace mediation is a professional practice that is increasingly reliant on thematic technical experts, including gender experts. The strategy of including gender expertise in peace mediation reflects the Women, Peace and Security agenda and the call to include dedicated gender expertise in all peacemaking efforts. Based on interviews with peace mediation practitioners, the article analyzes the role of gender experts in peace mediation. We argue that there is a tension between the art of mediation and the art of gender expertise that reflects the gendered power dynamics of peace mediation. We conclude that the strategy of appointing gender experts to peace mediation teams will not “dismantle the master’s house.” However, we acknowledge that without a gender expert very little will be accomplished on this issue. For peace mediation to address the gendered foundations of conflict we argue for the development of an alternate feminist peace mediation practice
SN 1987A's Circumstellar Envelope, II: Kinematics of the Three Rings and the Diffuse Nebula
We present several different measurements of the velocities of structures
within the circumstellar envelope of SN 1987A, including the inner, equatorial
ring (ER), outer rings (ORs), and the diffuse nebulosity at radii < 5 pc, based
on CTIO 4m and HST data. A comparison of STIS and WFPC2 [N II]6583 loci for the
rings show that the ER is expanding in radius at 10.5+-0.3 km/s, with the
northern OR expanding along the line of sight at about 26 km/s, and for the
southern OR, about 23 km/s. Similar results are found with CTIO 4m data.
Accounting for inclination, the best fit to all data show both ORs with an
expansion from the SN of 26 km/s. The ratio of the ER to OR velocities is
nearly equal to the ratio of ER to OR radii, so the rings are roughly
homologous, all having kinematic ages corresponding to about 20,000 yr before
the SN explosion. This makes previously reported, large compositional
differences between the ER and ORs difficult to understand. Additionally, a
grid of longslit 4m/echelle spectra centered on the SN shows two velocity
components over a region roughly coextensive with the outer circumstellar
envelope extending about 5 pc (20 arcsec) from the SN. One component is
blueshifted and the other redshifted from the SN centroid by about 10 km/s
each. These features may represent a bipolar flow expanding from the SN, in
which the ORs are propelled 10-15 km/s faster than that of the surrounding
envelope into which they propogate. The kinematic timescale for the entire
nebula is at least about 350,000 yr. The kinematics of these various structures
constrain possible models for the evolution of the progenitor and its formation
of a mass loss nebula.Comment: 25 pages AASTeX text plus 12 figures. ApJ, in pres
Finding the depth of radioactivity in construction materials
A key challenge in disposing of nuclear legacy facilities and planning a new nuclear plant is how to assess the extent or likelihood of radioactive contamination in construction materials and the ground. This paper summarises the status of two techniques based on the analysis of emitted radiation from materials that comprise such structures, and describes how this analysis can be used to infer the depth of contamination without the need to penetrate the structure or to destroy it in the process. Two experimental facilities have been developed to test the efficacy of these techniques, and data are provided for the most widespread contaminant experienced in the sector: caesium-137. Finally, the influence on the technique of the likely variety of silica-based media to be encountered in the nuclear industry is described, together with a summary of challenges to be addressed in future research
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