6,043 research outputs found
Breathers and kinks in a simulated crystal experiment
We develop a simple 1D model for the scattering of an incoming particle
hitting the surface of mica crystal, the transmission of energy through the
crystal by a localized mode, and the ejection of atom(s) at the incident or
distant face. This is the first attempt to model the experiment described in
Russell and Eilbeck in 2007 (EPL, v. 78, 10004). Although very basic, the model
shows many interesting features, for example a complicated energy dependent
transition between breather modes and a kink mode, and multiple ejections at
both incoming and distant surfaces. In addition, the effect of a heavier
surface layer is modelled, which can lead to internal reflections of breathers
or kinks at the crystal surface.Comment: 15 pages, 12 figures, based on a talk given at the conference
"Localized Excitations in Nonlinear Complex Systems (LENCOS)", Sevilla
(Spain) July 14-17, 200
Butcher & Oemler Cluster A2111: A Head-on Merger at z = 0.23
We present ROSAT PSPC and HRI observations of A2111, the richest galaxy
cluster photometrically surveyed by Butcher & Oemler (1984). The cluster
contains a distinct comet-shaped X-ray subcomponent, which appears hotter than
the rest of the cluster. The galaxy and X-ray surface brightness distributions
of the cluster show a similarly elongated morphology. These results suggest
that the cluster is undergoing a head-on subcluster merger. This merger may
also be responsible for the high fraction of gas-rich blue galaxies observed in
the cluster. We have further detected a poor cluster along the merging axis and
at a projected distance of about 5 Mpc from A2111.Comment: To be published in MNRAS, 16 pages, plus 13 figures in the GIF or
jpeg format (uuencoded). Black & white postscript files of the figures are
available at http://www.astro.nwu.edu/astro/wqd/paper/a2111
Tests of Profiled Steel Decks with V-stiffeners
The size and position of intermediate stiffeners in the compression flanges of thin-walled profiled steel decks exerts a strong influence on the dominant buckling mode of the flange. The ability of the deck to provide both high load carrying capacity before the onset of elastic buckling and a high ultimate load capacity may therefore be affected. A programme of tests to determine the effectiveness of intermediate stiffeners in controlling buckling modes has been undertaken. A series of specimens were loaded in pure bending resulting in various buckling waveforms prior to ultimate failure through a plastic collapse mechanism. All specimens were brake-pressed to designs that were chosen to ensure that the primary buckling took place in the elastic range and was not affected by plasticity. The experimentally determined buckling stresses were found to be comparable with studies performed using a computer analysis based on the finite strip method in which both local and distortional buckling modes were predicted. The test rig developed for the programme successfully approximated the boundary conditions implicit in the numerical model and prevented premature failure due to localised stressing at the specimen ends. A simplified design procedure for distortional buckling is proposed. The existing design procedure for local buckling in the Australian Standard AS1538-1988 is confirmed
Determinants of prehospital lactate in trauma patients:A retrospective cohort study
Background: Point of care serum lactate measurement is emerging as an adjunct to prehospital clinical assessment and has the potential to guide triage and advanced treatment decision-making. In this study we aimed to assess which factors potentially affect prehospital lactate levels.Methods: We performed a retrospective cohort study of all trauma patients attended by the Air Ambulance, Kent, Surrey & Sussex (AAKSS) between July 2017 and April 2018 in whom a pre-hospital lactate was measured. Lactate was measured before AAKSS treatments were commenced, but generally after prehospital treatment by ground ambulance crews was initiated. Primary endpoint of interest was the association of various patient- and treatment characteristics with prehospital lactate levels. Results: During the study period, lactate was measured in 156 trauma patients. Median lactate was 3.0 [2.0-4.1] mmol/l. Patients with an elevated lactate more often had deranged indices of end organ perfusion- and oxygenation (shock index 0.80 [0.58-1.03] vs 0.61 [0.40-0.82], p < 0.001, SpO2 96 [89-100%] vs 98 [96-100%], p = 0.025). They more often suffered from head injuries (62% vs 41%, p = 0.008), and received less analgesia prior to arrival of the AAKSS team (51.6% vs 67.2%, p = 0.03). In multivariate analysis, indices of end organ perfusion- and oxygenation only explained 15% of the variation in lactate levels. Conclusions: Prehospital lactate levels are not solely associated with indices of end organ perfusion- and oxygenation. Injury type, treatments given on scene and many other (unmeasured) factors likely play an important role as well. This should be taken into account when lactate is used in clinical algorithms to guide prehospital triage or treatment.</p
Determinants of prehospital lactate in trauma patients:A retrospective cohort study
Background: Point of care serum lactate measurement is emerging as an adjunct to prehospital clinical assessment and has the potential to guide triage and advanced treatment decision-making. In this study we aimed to assess which factors potentially affect prehospital lactate levels.Methods: We performed a retrospective cohort study of all trauma patients attended by the Air Ambulance, Kent, Surrey & Sussex (AAKSS) between July 2017 and April 2018 in whom a pre-hospital lactate was measured. Lactate was measured before AAKSS treatments were commenced, but generally after prehospital treatment by ground ambulance crews was initiated. Primary endpoint of interest was the association of various patient- and treatment characteristics with prehospital lactate levels. Results: During the study period, lactate was measured in 156 trauma patients. Median lactate was 3.0 [2.0-4.1] mmol/l. Patients with an elevated lactate more often had deranged indices of end organ perfusion- and oxygenation (shock index 0.80 [0.58-1.03] vs 0.61 [0.40-0.82], p < 0.001, SpO2 96 [89-100%] vs 98 [96-100%], p = 0.025). They more often suffered from head injuries (62% vs 41%, p = 0.008), and received less analgesia prior to arrival of the AAKSS team (51.6% vs 67.2%, p = 0.03). In multivariate analysis, indices of end organ perfusion- and oxygenation only explained 15% of the variation in lactate levels. Conclusions: Prehospital lactate levels are not solely associated with indices of end organ perfusion- and oxygenation. Injury type, treatments given on scene and many other (unmeasured) factors likely play an important role as well. This should be taken into account when lactate is used in clinical algorithms to guide prehospital triage or treatment.</p
Dark matter annihilation and non-thermal Sunyaev-Zel'dovich effect: II. dwarf spheroidal galaxy
We calculate the CMB temperature distortion due to the energetic electrons
and positrons produced by dark matter annihilation (Sunyaev-Zel'dovich effect),
in dwarf spheroidal galaxies (dSphs). In the calculation we have included two
important effects which were previously ignored. First we show that the
electron-positron pairs with energy less than GeV, which were neglected in
previous calculation, could contribute a significant fraction of the total
signal. Secondly we also consider the full effects of diffusion loss, which
could significantly reduce the density of electron-positron pairs at the center
of cuspy halos. For neutralinos, we confirm that detecting such kind of SZ
effect is beyond the capability of the current or even the next generation
experiments. In the case of light dark matter (LDM) the signal is much larger,
but even in this case it is only marginally detectable with the next generation
of experiment such as ALMA. We conclude that similar to the case of galaxy
clusters, in the dwarf galaxies the SZ_2DM} effect is not a strong probe of
DM annihilations.Comment: 22 pages, 9 figures, version accepted by JCA
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