122 research outputs found
Experimental investigation of corrosion of IG-110 graphite by steam
In the framework of a cooperation between the Japan Atomic Energy Research Institute (JAERI) and the Research Centre of Julien (KFA) experiments on the corrosion of the Japanese graphite IG-110 by water vapour were carried out. The temperature of the graphite samples and the water vapour partial pressure were kept constant at 1000°C/474 mbar. The total pressure in the test loop using helium as carrier gas was varied between 3 and 55 bar. Burn-off and pressure dependent reaction rates and density profiles in corroded samples were measured. As expected, the burn-off dependence of the reaction rate decreased with increasing pressure, while only a comparably low pressure dependence of the reaction rate was found. The latter indicates that the influence of the Knudsen diffusion is giveneven for the highest pressure. This finding is in fair agreement with the results of density profile measurements carried out at a couple of corroded samples, which also revealed a relatively small pressure dependence of the "penetration depth". Correlations for the caculation of reaction rates and the penetration depth are given
An experimental investigation on mass transfer in presence of chemical reactions on a graphite cylinder in crossflow
In connection with analyses of hypothetical massive air ingress accidents in HTGR (igh emperature as-Cooled eactor), in which it is assumed that the air is transported through the hot region of graphite core support posts, experiments on mass transfer and in-pore diffusion with homogeneous and heterogeneous chemical reactions were performed on a graphite cylinder in crossflow. Two BLMR (oundary ayer ass transfer controlled egime) runs and two runs in an intermediate regime between BLMR and IPDR (n-ore-iffusion controlled egime) were executed at atmospheric pressures, Reynolds numbers ranging from 533 to 2490, and cylinder temperatures from 848°C to 1120°C. The nuclear grade graphite cylinder having a diameter of 100 mm and a porosity of 21.2 % was corroded in a nitrogen gas flow containing approximately 5 % oxygen. Mean and local mass transfer coefficients and corrosion rates were obtained to examine the influences of the chemical reactions on the mass transfer. As a result it can be concluded that the chemical reactions and small changes in shape do not significantly influence the mass transfer under conditions to be expected in HTGR air ingress accidents and that thus the analogy between heat and mass transfer can be used for safety calculations
Thermal photons as a measure for the rapidity dependence of the temperature
The rapidity distribution of thermal photons produced in Pb+Pb collisions at
CERN-SPS energies is calculated within scaling and three-fluid hydrodynamics.
It is shown that these scenarios lead to very different rapidity spectra. A
measurement of the rapidity dependence of photon radiation can give cleaner
insight into the reaction dynamics than pion spectra, especially into the
rapidity dependence of the temperature.Comment: 3 Figure
Second Order Dissipative Fluid Dynamics for Ultra-Relativistic Nuclear Collisions
The M\"uller-Israel-Stewart second order theory of relativistic imperfect
fluids based on Grad's moment method is used to study the expansion of hot
matter produced in ultra-relativistic heavy ion collisions. The temperature
evolution is investigated in the framework of the Bjorken boost-invariant
scaling limit. The results of these second-order theories are compared to those
of first-order theories due to Eckart and to Landau and Lifshitz and those of
zeroth order (perfect fluid) due to Euler.Comment: 5 pages, 4 figures, size of y-axis tick marks for Figs. 3 and 4 fixe
a randomized controlled study
Background Uncertainty persists regarding the optimal ventilatory strategy in
trauma patients developing acute respiratory distress syndrome (ARDS). This
work aims to assess the effects of two mechanical ventilation strategies with
high positive end-expiratory pressure (PEEP) in experimental ARDS following
blunt chest trauma. Methods Twenty-six juvenile pigs were anesthetized,
tracheotomized and mechanically ventilated. A contusion was applied to the
right chest using a bolt-shot device. Ninety minutes after contusion, animals
were randomized to two different ventilation modes, applied for 24 h: Twelve
pigs received conventional pressure-controlled ventilation with moderately low
tidal volumes (VT, 8 ml/kg) and empirically chosen high external PEEP
(16cmH2O) and are referred to as the HP-CMV-group. The other group (n = 14)
underwent high-frequency inverse-ratio pressure-controlled ventilation (HFPPV)
involving respiratory rate of 65breaths · min−1, inspiratory-to-expiratory-
ratio 2:1, development of intrinsic PEEP and recruitment maneuvers, compatible
with the rationale of the Open Lung Concept. Hemodynamics, gas exchange and
respiratory mechanics were monitored during 24 h. Computed tomography and
histology were analyzed in subgroups. Results Comparing changes which occurred
from randomization (90 min after chest trauma) over the 24-h treatment period,
groups differed statistically significantly (all P values for group effect
<0.001, General Linear Model analysis) for the following parameters (values
are mean ± SD for randomization vs. 24-h): PaO2 (100 % O2) (HFPPV 186 ± 82 vs.
450 ± 59 mmHg; HP-CMV 249 ± 73 vs. 243 ± 81 mmHg), venous admixture (HFPPV 34
± 9.8 vs. 11.2 ± 3.7 %; HP-CMV 33.9 ± 10.5 vs. 21.8 ± 7.2 %), PaCO2 (HFPPV
46.9 ± 6.8 vs. 33.1 ± 2.4 mmHg; HP-CMV 46.3 ± 11.9 vs. 59.7 ± 18.3 mmHg) and
normally aerated lung mass (HFPPV 42.8 ± 11.8 vs. 74.6 ± 10.0 %; HP-CMV 40.7 ±
8.6 vs. 53.4 ± 11.6 %). Improvements occurring after recruitment in the HFPPV-
group persisted throughout the study. Peak airway pressure and VT did not
differ significantly. HFPPV animals had lower atelectasis and inflammation
scores in gravity-dependent lung areas. Conclusions In this model of ARDS
following unilateral blunt chest trauma, HFPPV ventilation improved
respiratory function and fulfilled relevant ventilation endpoints for trauma
patients, i.e. restoration of oxygenation and lung aeration while avoiding
hypercapnia and respiratory acidosis
Evolution of Baryon-Free Matter Produced in Relativistic Heavy-Ion Collisions
A 3-fluid hydrodynamic model is introduced for simulating heavy-ion
collisions at incident energies between few and about 200 AGeV. In addition to
the two baryon-rich fluids of 2-fluid models, the new model incorporates a
third, baryon-free (i.e. with zero net baryonic charge) fluid which is created
in the mid-rapidity region. Its evolution is delayed due to a formation time
, during which the baryon-free fluid neither thermalizes nor interacts
with the baryon-rich fluids. After formation it thermalizes and starts to
interact with the baryon-rich fluids. It is found that for =0 the
interaction strongly affects the baryon-free fluid. However, at reasonable
finite formation time, =1 fm/c, the effect of this interaction turns out
to be substantially reduced although still noticeable. Baryonic observables are
only slightly affected by the interaction with the baryon-free fluid.Comment: 17 pages, 3 figures, submitted to the issue of Phys. of Atomic Nuclei
dedicated to S.T. Belyaev on the occasion of his 80th birthday, typos
correcte
Nonequilibrium fluid-dynamics in the early stage of ultrarelativistic heavy-ion collisions
To describe ultrarelativistic heavy-ion collisions we construct a three-fluid
hydrodynamical model. In contrast to one-fluid hydrodynamics, it accounts for
the finite stopping power of nuclear matter, i.e. for nonequilibrium effects in
the early stage of the reaction. Within this model, we study baryon dynamics in
the BNL-AGS energy range. For the system Au+Au we find that kinetic equilibrium
between projectile and target nucleons is established only after a time
. Observables which are
sensitive to the early stage of the collision (like e.g. nucleon flow)
therefore differ considerably from those calculated in the one-fluid model.Comment: 36 pages, Late
Hydrodynamical assessment of 200 AGeV collisions
We are analyzing the hydrodynamics of 200 A GeV S+S collisions using a new
approach which tries to quantify the uncertainties arising from the specific
implementation of the hydrodynamical model. Based on a previous
phenomenological analysis we use the global hydrodynamics model to show that
the amount of initial flow, or initial energy density, cannot be determined
from the hadronic momentum spectra. We additionally find that almost always a
sizeable transverse flow deve- lops, which causes the system to freeze out,
thereby limiting the flow velocity in itself. This freeze-out dominance in turn
makes a distinction between a plasma and a hadron resonance gas equation of
state very difficult, whereas a pure pion gas can easily be ruled out from
present data. To complete the picture we also analyze particle multiplicity
data, which suggest that chemical equilibrium is not reached with respect to
the strange particles. However, the over- population of pions seems to be at
most moderate, with a pion chemical potential far away from the Bose
divergence.Comment: 19 pages, 11 figs in separate uuencoded file, for LateX, epsf.tex,
dvips, TPR-94-5 and BNL-(no number yet
1+1 Dimensional Hydrodynamics for High-energy Heavy-ion Collisions
A 1+1 dimensional hydrodynamical model in the light-cone coordinates is used
to describe central heavy-ion collisions at ultrarelativistic bombarding
energies. Deviations from Bjorken's scaling are taken into account by choosing
finite-size profiles for the initial energy density. The sensitivity of fluid
dynamical evolution to the equation of state and the parameters of initial
state is investigated. Experimental constraints on the total energy of produced
particles are used to reduce the number of model parameters. Spectra of
secondary particles are calculated assuming that the transition from the
hydrodynamical stage to the collisionless expansion of matter occurs at a
certain freeze-out temperature. An important role of resonances in the
formation of observed hadronic spectra is demonstrated. The calculated rapidity
distributions of pions, kaons and antiprotons in central Au+Au collisions at
the c.m. energy 200 GeV per NN pair are compared with experimental data of the
BRAHMS Collaboration. Parameters of the initial state are reconstructed for
different choices of the equation of state. The best fit of these data is
obtained for a soft equation of state and Gaussian-like initial profiles of the
energy density, intermediate between the Landau and Bjorken limits.Comment: 43 pages, 27 figure
Impact of Anxiety During Hospitalization on the Clinical Outcome of Patients With Osteoporotic Thoracolumbar Vertebral Fracture
STUDY DESIGN: Multicenter prospective cohort study.
OBJECTIVES: Anxiety in combination with osteoporotic vertebral compression fractures (OVCFs) of the spine remains understudied. The purpose of this study was to analyze whether anxiety has an impact on the short-term functional outcome of patients with an OVCF. Furthermore, a direct impact of the fracture on the patient's anxiety during hospitalization should be recognized.
METHODS: All inpatients with an OVCF of the thoracolumbar spine from 2017 to 2020 were included. Trauma mechanism, analgetic medication, anti-osteoporotic therapy, timed-up-and-go test (TuG), mobility, Barthel index, Oswestry-Disability Index (ODI) and EQ5D-5L were documented.For statistical analysis, the U test, chi-square independence test, Spearman correlation, General Linear Model for repeated measures, Bonferroni analysis and Wilcoxon test were used. The item anxiety/depression of the EQ5D-5L was analyzed to describe the patients' anxiousness.
RESULTS: Data from 518 patients from 17 different hospitals were evaluated. Fracture severity showed a significant correlation (r = .087, P = .0496) with anxiety. During the hospital stay, pain medication (P < .001), anti-osteoporotic medication (P < .001), and initiation of surgical therapy (P < .001) were associated with less anxiety. The anxiety of a patient at discharge was negatively related to the functional outcomes at the individual follow-up: TuG (P < .001), Barthel index (P < .001), ODI (P < .001) and EQ5D-5L (P < .001).
CONCLUSIONS: Higher anxiety is associated with lower functional outcome after OVCF. The item anxiety/depression of the EQ5D-5L provides an easily accessible, quick and simple tool that can be used to screen for poor outcomes and may also offer the opportunity for a specific anxiety intervention
- …