12,856 research outputs found
The Distance and Age of the SNR Kes 73 and AXP 1E 1841-045
We provide a new distance estimate to the supernova remnant (SNR) Kes 73 and
its associated anomalous X-ray pulsar (AXP) 1E 1841-045. 21 cm HI images and HI
absorption/ emission spectra from new VLA observations, and 13CO emission
spectra of Kes 73 and two adjacent compact HII regions (G27.276+0.148 and
G27.491+0.189) are analyzed. The HI images show prominent absorption features
associated with Kes 73 and the HII regions. The absorption appears up to the
tangent point velocity giving a lower distance limit to Kes 73 of 7.5 kpc,
which has previously been given as the upper limit. Also, G27.276+0.148 and
G27.491+0.189 are at the far kinematic distances of their radio recombination
line velocities. There is prominent HI emission in the range 80--90 km/s for
all three objects. The two HII regions show HI absorption at ~ 84 km/s, but
there is no absorption in the Kes 73 absorption spectrum. This implies an upper
distance limit of ~ 9.8 kpc to Kes 73. This corrected larger distance to Kes
73/ AXP 1E 1841-045 system leads to a refined age of the SNR of 500 to 1000 yr,
and a ~ 50% larger AXP X-ray luminosity.Comment: 10 pages, 2 figures, ApJ, dol:10.1086/"529120
Directed Explicit Model Checking with HSF-SPIN
We present the explicit state model checker HSF-SPIN which is based on the model checker SPIN and its Promela modeling language. HSF-SPIN incorporates directed search algorithms for checking safety and a large class of LTL-specified liveness properties. We start off from the A* algorithm and define heuristics to accelerate the search into the direction of a specified failure situation. Next we propose an improved nested depth-first search algorithm that exploits the structure of Promela Never-Claims. As a result of both improvements, counterexamples will be shorter and the explored part of the state space will be smaller than with classical approaches, allowing to analyze larger state spaces. We evaluate the impact of the new heuristics and algorithms on a set of protocol models, some of which are real-world industrial protocols
Mapping warm molecular hydrogen with Spitzer's Infrared Array Camera (IRAC)
Photometric maps, obtained with Spitzer's Infrared Array Camera (IRAC), can
provide a valuable probe of warm molecular hydrogen within the interstellar
medium. IRAC maps of the supernova remnant IC443, extracted from the Spitzer
archive, are strikingly similar to spectral line maps of the H2 pure rotational
transitions that we obtained with the Infrared Spectrograph (IRS) instrument on
Spitzer. IRS spectroscopy indicates that IRAC Bands 3 and 4 are indeed
dominated by the H2 v=0-0 S(5) and S(7) transitions, respectively. Modeling of
the H2 excitation suggests that Bands 1 and 2 are dominated by H2 v=1-0 O(5)
and v=0-0 S(9). Large maps of the H2 emission in IC433, obtained with IRAC,
show band ratios that are inconsistent with the presence of gas at a single
temperature. The relative strengths of IRAC Bands 2, 3, and 4 are consistent
with pure H2 emission from shocked material with a power-law distribution of
gas temperatures. CO vibrational emissions do not contribute significantly to
the observed Band 2 intensity. Assuming that the column density of H2 at
temperatures T to T+dT is proportional to T raised to the power -b for
temperatures up to 4000 K, we obtained a typical estimate of 4.5 for b. The
power-law index, b, shows variations over the range 3 to 6 within the set of
different sight-lines probed by the maps, with the majority of sight-lines
showing b in the range 4 to 5. The observed power-law index is consistent with
the predictions of simple models for paraboloidal bow shocks.Comment: 27 pages, including 11 figures. Accepted for publication in Ap
How can we help novice child protection social workers to see situations like experienced practitioners? A randomised controlled trial evaluation of the ShadowBox⢠method using pre-recorded video feedback
Background
Protecting children for abuse and neglect is a complex area of decision-making but frequent staff turnover has meant that many frontline child protection social workers are often relatively inexperienced. The ShadoxBoxTM method is an educational intervention that enables novice practitioners to gain decision-making skills quickly.
Aim:
This study was an RCT evaluation of an educational intervention for novice social workers that used the ShadoxBoxTM method adapted to include pre-recorded video feedback from an expert panel to test whether novice decision making would become more similar to experienced practitioners.
Methods:
The study was an RCT in which participants completed complex scenarios in a computer lab in control and intervention groups. The training method involved participants receiving feedback from highly experienced practitioners at each decision point within the scenarios. The intervention group received pre-recorded video feedback from a panel of highly experienced practitioners while the control group received no feedback.
Participants and Setting
Participants (n=83) were trainee social workers from a London university randomly allocated to control and intervention groups. Data was collected on computer stations using Qualtrics.
Results
Undertaking the scenarios improved both groups but greater improvement was seen in participants who had received video feedback from a panel of experienced practitioners. The results were promising, with participant accuracy increasing by 44% (from 31% to 75%) in the intervention group compared to an increase of 31% (from 32% to 63%) in the control group.
Considerable improvements were noted in both intervention and control groups, which suggest that scenario-based interventions can be a promising educational method as learning is rooted in real life scenarios and participants have the opportunity to reflect upon their decisions.
The qualitative findings are that novice participants make predictable errors, including:
⢠Making shallow assumptions
⢠Focusing exclusively on the parents rather than the child.
⢠Jumping to early conclusions with insufficient information.
Conclusions
⢠ShadoxBoxTM training appears to be a promising intervention for improving decision making.
⢠Novices benefitted from having concentrated exposure to complex scenarios focused on assessing risk and making professional judgements.
⢠When this was augmented by direct feedback from a panel of highly experienced practitioners, these benefits were increased considerably.
⢠The complexity of the scenarios also exposed the novices to real life pressures rather than the simplified versions used in decision research
The Paths to Choreography Extraction
Choreographies are global descriptions of interactions among concurrent
components, most notably used in the settings of verification (e.g., Multiparty
Session Types) and synthesis of correct-by-construction software (Choreographic
Programming). They require a top-down approach: programmers first write
choreographies, and then use them to verify or synthesize their programs.
However, most existing software does not come with choreographies yet, which
prevents their application.
To attack this problem, we propose a novel methodology (called choreography
extraction) that, given a set of programs or protocol specifications,
automatically constructs a choreography that describes their behavior. The key
to our extraction is identifying a set of paths in a graph that represents the
symbolic execution of the programs of interest. Our method improves on previous
work in several directions: we can now deal with programs that are equipped
with a state and internal computation capabilities; time complexity is
dramatically better; we capture programs that are correct but not necessarily
synchronizable, i.e., they work because they exploit asynchronous
communication
Spontaneous soliton formation and modulational instability in Bose-Einstein condensates
The dynamics of an elongated attractive Bose-Einstein condensate in an
axisymmetric harmonic trap is studied. It is shown that density fringes caused
by self-interference of the condensate order parameter seed modulational
instability. The latter has novel features in contradistinction to the usual
homogeneous case known from nonlinear fiber optics. Several open questions in
the interpretation of the recent creation of the first matter-wave bright
soliton train [Strecker {\it et al.} Nature {\bf 417} 150 (2002)] are
addressed. It is shown that primary transverse collapse, followed by secondary
collapse induced by soliton--soliton interactions, produce bursts of hot atoms
at different time scales.Comment: 4 pages, 3 figures. Phys. Rev. Lett. in pres
Discriminating cool-water from warm-water carbonates and their diagenetic environments using element geochemistry: the Oligocene Tikorangi Formation (Taranaki Basin) and the dolomite effect
Fields portrayed within bivariate element plots have been used to distinguish between carbonates formed in warm- (tropical) water and cool- (temperate) water depositional settings. Here, element concentrations (Ca, Mg, Sr, Na, Fe, and Mn) have been determined for the carbonate fraction of bulk samples from the late Oligocene Tikorangi Formation, a subsurface, mixed dolomite-calcite, cool-water limestone sequence in Taranaki Basin, New Zealand. While the occurrence of dolomite is rare in New Zealand Cenozoic carbonates, and in cool-water carbonates more generally, the dolomite in the Tikorangi carbonates is shown to have a dramatic effect on the "traditional" positioning of cool-water limestone fields within bivariate element plots. Rare undolomitised, wholly calcitic carbonate samples in the Tikorangi Formation have the following average composition: Mg 2800 ppm; Ca 319 100 ppm; Na 800 ppm; Fe 6300 ppm; Sr 2400 ppm; and Mn 300 ppm. Tikorangi Formation dolomite-rich samples (>15% dolomite) have average values of: Mg 53 400 ppm; Ca 290 400 ppm; Na 4700 ppm; Fe 28 100 ppm; Sr 5400 ppm; and Mn 500 ppm. Element-element plots for dolomite-bearing samples show elevated Mg, Na, and Sr values compared with most other low-Mg calcite New Zealand Cenozoic limestones. The increased trace element contents are directly attributable to the trace element-enriched nature of the burial-derived dolomites, termed here the "dolomite effect". Fe levels in the Tikorangi Formation carbonates far exceed both modern and ancient cool-water and warm-water analogues, while Sr values are also higher than those in modern Tasmanian cool-water carbonates, and approach modern Bahaman warm-water carbonate values. Trace element data used in conjunction with more traditional petrographic data have aided in the diagenetic interpretation of the carbonate-dominated Tikorangi sequence. The geochemical results have been particularly useful for providing more definitive evidence for deep burial dolomitisation of the deposits under the influence of marine-modified pore fluids
The Distances of SNR W41 and overlapping HII regions
New HI images from the VLA Galactic Plane Survey show prominent absorption
features associated with the supernovae remnant G23.3-0.3 (SNR W41). We
highlight the HI absorption spectra and the CO emission spectra of eight
small regions on the face of W41, including four HII regions, three non-thermal
emission regions and one unclassified region. The maximum velocity of
absorption for W41 is 782 km/s and the CO cloud at radial velocity
955 km/s is behind W41. Because an extended TeV source, a diffuse X-ray
enhancement and a large molecular cloud at radial velocity 775 km/s are
also projected at the center of W41, these yield the kinematic distance of 3.9
to 4.5 kpc for W41. For HII regions, our analyses reveal that both G23.42-0.21
and G23.07+0.25 are at the far kinematic distances (9.9 kpc and
10.6 kpc respectively) of their recombination-line velocities (1030.5 km/s
and 89.62.1 km/s respectively), G23.07-0.37 is at the near kinematic
distance (4.40.3 kpc) of its recombination-line velocity (82.72.0
km/s), and G23.27-0.27 is probably at the near kinematic distance (4.10.3
kpc) of its recombination-line velocity (76.10.6 km/s).Comment: 11 pages, 3 figs., 2 tables, accepted by A
Generating ring currents, solitons, and svortices by stirring a Bose-Einstein condensate in a toroidal trap
We propose a simple stirring experiment to generate quantized ring currents
and solitary excitations in Bose-Einstein condensates in a toroidal trap
geometry. Simulations of the 3D Gross-Pitaevskii equation show that pure ring
current states can be generated efficiently by adiabatic manipulation of the
condensate, which can be realized on experimental time scales. This is
illustrated by simulated generation of a ring current with winding number two.
While solitons can be generated in quasi-1D tori, we show the even more robust
generation of hybrid, solitonic vortices (svortices) in a regime of wider
confinement. Svortices are vortices confined to essentially one-dimensional
dynamics, which obey a similar phase-offset--velocity relationship as solitons.
Marking the transition between solitons and vortices, svortices are a distinct
class of symmetry-breaking stationary and uniformly rotating excited solutions
of the 2D and 3D Gross-Pitaevskii equation in a toroidal trapping potential.
Svortices should be observable in dilute-gas experiments.Comment: 8 pages, 4 figures; accepted for publication in J. Phys. B (Letters
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