1,721,041 research outputs found
Numerical Modeling of Chemical Kinetics to Simulate the Conversion of Internal to Kinetics Energy in Nozzle
No full textThe conversion of internal to kinetic energy as typically occurs in many propulsive
nozzles is characterized by atomic recombination of chemical species and by a peculiar
behaviour of the vibrational energy. These phenomena can be simulated by models with
different level of complexity. Here a comparison is shown among models based on the
hypotesis of perfect gas, frozen and nonequilibrium regimes for the chemical reactions,
equilibrium and frozen vibrational energy. From the comparison of the results the
different influence of each phenomenon on the accuracy of the prediction is evaluated
Numerical analysis of flow separation structures in rocket nozzles, AIAA Paper 2007-5473
No full textInfluence of Chemical Kinetics Effects in Nozzles Shape design
No full textTheoretical and experimental studies on axisymmetric nozzles have shown
that two dimensional flow effects have an important role on the nozzle
performances. These effects are enhanced when nozzles operate in the typical
conditions of aerospace applications, since chemical reactions of dissociation
and atomic recombination occur, which may be significantly influenced by the
radial gasdynamic phenomena.
In this paper the influence of the flowfield behaviour on the finite rate
chemical kinetics is analyzed for Single Expansion Ramp Nozzles (SERN), which
display strong unsymmetric flowfields. The analysis is focused on the throat
region, where these effects are stronger, in order to indicate the causes of
the flow behaviour and provide qualitative evaluations of its interaction with
chemical kinetics, and consequently of their influence on the nozzle
performances
Hearing results of ossiculoplasty in Austin-Kartush group A patients.
No full textOBJECTIVE:
To compare hearing results in patients who underwent ossiculoplasty for Austin-Kartush group A impairments (incus erosion, malleus handle present, stapes superstructure present) with the results in patients with an intact ossicular chain who required only myringoplasty. The literature on hearing results of ossiculoplasty with different types of prostheses and different techniques is reviewed.
PATIENTS AND STUDY DESIGN:
This study retrospectively reviews a series of 181 consecutive ossiculoplasties and 204 consecutive myringoplasties.
SETTING:
The study was carried out partly at a private practice and partly in an academic tertiary referral center.
MAIN OUTCOME MEASURES:
This study complies with levels 1 and 2 of the guidelines recommended by the American Academy of Otolaryngology--Head and Neck Surgery (1995).
RESULTS:
When success was defined as a postoperative air-bone gap within 10 dB, the success rate was higher for myringoplasty (81%) than for ossiculoplasty (55%). When success was defined as a postoperative air-bone gap within 20 dB, the success rate was 97% in myringoplasties and 85% in ossiculoplasties. There was no significant deterioration over time of the mean postoperative air-bone gap for any frequency.
CONCLUSION:
Cumulative data from several authors show that -50% of patients undergoing partial ossiculoplasty have a postoperative air-bone gap of 0 to 10 dB, and 80% have a postoperative air-bone gap of 0 to 20 dB. Equally good results may be achieved with autograft (no difference was found between interposition of the incus or the head of the malleus), homograft, or alloplastic partial prostheses. With alloplastic total prostheses, 36% of patients have a postoperative air-bone gap of 0 to 10 dB, and 74% have a postoperative air-bone gap of 0 to 20 dB
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