18,997 research outputs found
THE CLINICAL IMPORTANCE OF HYPERKALAEMIA FOLLOWING SUXAMETHONIUM ADMINISTRATION
SUMMARY A 3-year-old child with severe tetanus, at the end of the third week of illness, developed circulatory arrest after suxamethonium injection. A similar incident also occurred in an adult patient with tetanus. Both incidents were attributable to acute hyperkalacmia induced by suxamethonium. In another patient with severe tetanus, after injection of suxamethonium 100 mg, the potassium level rose within 2 minutes from 3.8 m.equiv/l. to 7.4 m.equiv/l. Cardiac arrest followed suxamethonium injection also in two patients with uraemia. One further patient developed ventricular fibrillation when given suxa-methonium three weeks after a road accident in which he sustained multiple injuries. It is suggested that in these last three instances the increase of serum potassium caused by the injected suxamethonium was responsible for the circulatory arres
Dynamic fracture of icosahedral model quasicrystals: A molecular dynamics study
Ebert et al. [Phys. Rev. Lett. 77, 3827 (1996)] have fractured icosahedral
Al-Mn-Pd single crystals in ultrahigh vacuum and have investigated the cleavage
planes in-situ by scanning tunneling microscopy (STM). Globular patterns in the
STM-images were interpreted as clusters of atoms. These are significant
structural units of quasicrystals. The experiments of Ebert et al. imply that
they are also stable physical entities, a property controversially discussed
currently. For a clarification we performed the first large scale fracture
simulations on three-dimensional complex binary systems. We studied the
propagation of mode I cracks in an icosahedral model quasicrystal by molecular
dynamics techniques at low temperature. In particular we examined how the shape
of the cleavage plane is influenced by the clusters inherent in the model and
how it depends on the plane structure. Brittle fracture with no indication of
dislocation activity is observed. The crack surfaces are rough on the scale of
the clusters, but exhibit constant average heights for orientations
perpendicular to high symmetry axes. From detailed analyses of the fractured
samples we conclude that both, the plane structure and the clusters, strongly
influence dynamic fracture in quasicrystals and that the clusters therefore
have to be regarded as physical entities.Comment: 10 pages, 12 figures, for associated avi files, see
http://www.itap.physik.uni-stuttgart.de/~frohmut/MOVIES/emitted_soundwaves.avi
and
http://www.itap.physik.uni-stuttgart.de/~frohmut/MOVIES/dynamic_fracture.av
Vertical quantum wire realized with double cleaved-edge overgrowth
A quantum wire is fabricated on (001)-GaAs at the intersection of two
overgrown cleaves. The wire is contacted at each end to n+ GaAs layers via
two-dimensional (2D) leads. A sidegate controls the density of the wire
revealing conductance quantization. The step height is strongly reduced from
2e^2/h due to the 2D-lead series resistance. We characterize the 2D density and
mobility for both cleave facets with four-point measurements. The density on
the first facet is modulated by the substrate potential, depleting a 2um wide
strip that defines the wire length. Micro-photoluminescence shows an extra peak
consistent with 1D electron states at the corner.Comment: 4 pages, 4 figure
Quasicrystalline Order in Binary Dipolar Systems
Motivated by recent experimental findings, we investigate the possible
occurrence and characteristics of quasicrystalline order in two-dimensional
mixtures of point dipoles with two sorts of dipole moments. Despite the fact
that the dipolar interaction potential does not exhibit an intrinsic length
scale and cannot be tuned a priori to support the formation of quasicrystalline
order, we find that configurations with long--range quasicrystallinity yield
minima in the potential energy surface of the many particle system. These
configurations emanate from an ideal or perturbed ideal decoration of a binary
tiling by steepest descent relaxation. Ground state energy calculations of
alternative ordered states and parallel tempering Monte-Carlo simulations
reveal that the quasicrystalline configurations do not correspond to a
thermodynamically stable state. On the other hand, steepest descent relaxations
and conventional Monte-Carlo simulations suggest that they are rather robust
against fluctuations. Local quasicrystalline order in the disordered
equilibrium states can be strong.Comment: 10 pages, 7 figure
Fracture of complex metallic alloys: An atomistic study of model systems
Molecular dynamics simulations of crack propagation are performed for two
extreme cases of complex metallic alloys (CMAs): In a model quasicrystal the
structure is determined by clusters of atoms, whereas the model C15 Laves phase
is a simple periodic stacking of a unit cell. The simulations reveal that the
basic building units of the structures also govern their fracture behaviour.
Atoms in the Laves phase play a comparable role to the clusters in the
quasicrystal. Although the latter are not rigid units, they have to be regarded
as significant physical entities.Comment: 6 pages, 4 figures, for associated avi file, see
http://www.itap.physik.uni-stuttgart.de/~frohmut/MOVIES/C15.LJ.011.100.av
Experimental study of fingered flow through initially dry sand
International audienceWater infiltration into coarse textured dry porous media becomes instable depending on flow conditions characterized through dimensionless quantities, i.e. the Bond number and the Capillary number. Instable infiltration fronts break into flow fingers which we investigate experimentally using Hele-Shaw cells. We further developed a light transmission method to measure the dynamics of water within flow fingers in great detail with high spatial and temporal resolution. The method was calibrated using x-ray absorption and the measured light transmission was corrected for scattering effects through deconvolution with a point spread function. Additionally we applied a dye tracer to visualize the velocity field within flow fingers. We analyzed the dynamics of water within the finger tips, along the finger core behind the tip, and within the fringe of the fingers during radial growth. Our results confirm previous findings of saturation overshoot in the finger tips and revealed a saturation minimum behind the tip as a new feature. The finger development was characterized by a gradual increase in water content within the core of the finger behind this minimum and a gradual widening of the fingers to a quasi-stable state which evolves on time scales that are orders of magnitudes longer than those of fingers' evolution. In this state, a sharp separation into a core with fast convective flow and a fringe with exceedingly slow flow was detected. All observed phenomena could by consistently explained based on the hysteretic behavior of the soil- water characteristic and on the positive pressure induced at the finger tip by the high flow velocity
A dynamical trichotomy for structured populations experiencing positive density-dependence in stochastic environments
Positive density-dependence occurs when individuals experience increased
survivorship, growth, or reproduction with increased population densities.
Mechanisms leading to these positive relationships include mate limitation,
saturating predation risk, and cooperative breeding and foraging. Individuals
within these populations may differ in age, size, or geographic location and
thereby structure these populations. Here, I study structured population models
accounting for positive density-dependence and environmental stochasticity i.e.
random fluctuations in the demographic rates of the population. Under an
accessibility assumption (roughly, stochastic fluctuations can lead to
populations getting small and large), these models are shown to exhibit a
dynamical trichotomy: (i) for all initial conditions, the population goes
asymptotically extinct with probability one, (ii) for all positive initial
conditions, the population persists and asymptotically exhibits unbounded
growth, and (iii) for all positive initial conditions, there is a positive
probability of asymptotic extinction and a complementary positive probability
of unbounded growth. The main results are illustrated with applications to
spatially structured populations with an Allee effect and age-structured
populations experiencing mate limitation
Mean-field analysis of the stability of a K-Rb Fermi-Bose mixture
We compare the experimental stability diagram of a Fermi-Bose mixture of K-40
and Rb-87 atoms with attractive interaction to the predictions of a mean-field
theoretical model. We discuss how this comparison can be used to give a better
estimate of the interspecies scattering length, which is currently known from
collisional measurements with larger uncertainty.Comment: 5 pages, 4 figure
Evidence for phase formation in potassium intercalated 1,2;8,9-dibenzopentacene
We have prepared potassium intercalated 1,2;8,9-dibenzopentacene films under
vacuum conditions. The evolution of the electronic excitation spectra upon
potassium addition as measured using electron energy-loss spectroscopy clearly
indicate the formation of particular doped phases with compositions
Kdibenzopentacene ( = 1,2,3). Moreover, the stability of these phases as
a function of temperature has been explored. Finally, the electronic excitation
spectra also give insight into the electronic ground state of the potassium
doped 1,2;8,9-dibenzopentacene films.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1201.200
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