1,858 research outputs found
Full-scale Investigation of Cooling Shroud and Ejector Nozzle for a Turbojet Engine : Afterburner Installation
A full-scale ejector cooling investigation was made on a turbojet engine - afterburner installation in the NACA Lewis altitude wind tunnel. Ejector performance was studied at primary exhaust-gas temperatures from 2700 degrees to 3400 degrees R (corresponding to ejector temperature ratios from 2.0 to 5.0), primary pressure ratios from 1.79 to 3.4, secondary air flows up to 29 percent of the primary gas flow, and for diameter ratios from 1.08 to 1.42 and spacing ratios from 0.04 to 1.16. In addition, variations were made in the primary exhaust-nozzle area. Ejectors with large diameter ratios permit the attainment of high gas flow ratios, but the jet-thrust losses become prohibitive as the spacing ratio is increased from 0 to 0.16. As the ejector diameter is reduced, the obtainable gas-flow ratio and the thrust loss are reduced. Previous results showing that data obtained at a temperature ratio of 1.0 could not be extrapolated to determine ejector performance at high temperature ratios by the application of the temperature ratio factor to the gas-flow ratios are substantiated by the present investigation
41Ca in tooth enamel. part I: A biological signature of neutron exposure in atomic bomb survivors
The detection of 41Ca atoms in tooth enamel using accelerator mass spectrometry is suggested as a method capable of reconstructing thermal neutron exposures from atomic bomb survivors in Hiroshima and Nagasaki. In general, 41Ca atoms are produced via thermal neutron capture by stable 40Ca. Thus any 41Ca atoms present in the tooth enamel of the survivors would be due to neutron exposure from both natural sources and radiation from the bomb. Tooth samples from five survivors in a control group with negligible neutron exposure were used to investigate the natural 41Ca content in tooth enamel, and 16 tooth samples from 13 survivors were used to estimate bomb-related neutron exposure. The results showed that the mean 41Ca/Ca isotope ratio was (0.17 ± 0.05) × 10-14 in the control samples and increased to 2 × 10-14 for survivors who were proximally exposed to the bomb. The 41Ca/Ca ratios showed an inverse correlation with distance from the hypocenter at the time of the bombing, similar to values that have been derived from theoretical free-in-air thermal-neutron transport calculations. Given that γ-ray doses were determined earlier for the same tooth samples by means of electron spin resonance (ESR, or electron paramagnetic resonance, EPR), these results can serve to validate neutron exposures that were calculated individually for the survivors but that had to incorporate a number of assumptions (e.g. shielding conditions for the survivors).Fil: Wallner, A.. Ludwig Maximilians Universitat; Alemania. Universitat Technical Zu Munich; Alemania. Universidad de Viena; AustriaFil: Ruhm, W.. Helmholtz Center Munich German Research Center For Environmental Health; Alemania. Ludwig Maximilians Universitat; AlemaniaFil: Rugel, G.. Ludwig Maximilians Universitat; Alemania. Universitat Technical Zu Munich; AlemaniaFil: Nakamura, N.. Radiation Effects Research Foundation; JapónFil: Arazi, Andres. Universitat Technical Zu Munich; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Faestermann, T.. Universitat Technical Zu Munich; AlemaniaFil: Knie, K.. Universitat Technical Zu Munich; Alemania. Ludwig Maximilians Universitat; AlemaniaFil: Maier, H. J.. Ludwig Maximilians Universitat; AlemaniaFil: Korschinek, G.. Universitat Technical Zu Munich; Alemani
On-the-fly memory compression for multibody algorithms.
Memory and bandwidth demands challenge developers of particle-based codes that have to scale on new architectures, as the growth of concurrency outperforms improvements in memory access facilities, as the memory per core tends to stagnate, and as communication networks cannot increase bandwidth arbitrary. We propose to analyse each particle of such a code to find out whether a hierarchical data representation storing data with reduced precision caps the memory demands without exceeding given error bounds. For admissible candidates, we perform this compression and thus reduce the pressure on the memory subsystem, lower the total memory footprint and reduce the data to be exchanged via MPI. Notably, our analysis and transformation changes the data compression dynamically, i.e. the choice of data format follows the solution characteristics, and it does not require us to alter the core simulation code
Effect of Compressor-outlet Bleedoff on Turbojet-engine Performance
An investigation was conducted in the NACA Lewis altitude wind tunnel to determine the effect of compressor-outlet bleedoff on the performance of an axial-flow turbojet engine equipped with a variable-area exhaust nozzle. Results presented indicate the effect of compressor-outlet bleedoff on performance at altitudes of 25,000 and 40,000 feet and a flight Mach number of 0.53. Variation of performance with bleedoff flow is indicated for operation with fixed- and variable-area exhaust nozzles. Temperature and pressure losses through the bleedoff ducting system are also discussed
From Gravitons to Gravity: Myths and Reality
There is a general belief, reinforced by statements in standard textbooks,
that: (i) one can obtain the full non-linear Einstein's theory of gravity by
coupling a massless, spin-2 field self-consistently to the total
energy momentum tensor, including its own; (ii) this procedure is unique and
leads to Einstein-Hilbert action and (iii) it only uses standard concepts in
Lorentz invariant field theory and does not involve any geometrical
assumptions. After providing several reasons why such beliefs are suspect --
and critically re-examining several previous attempts -- we provide a detailed
analysis aimed at clarifying the situation. First, we prove that it is
\textit{impossible} to obtain the Einstein-Hilbert (EH) action, starting from
the standard action for gravitons in linear theory and iterating repeatedly.
Second, we use the Taylor series expansion of the action for Einstein's theory,
to identify the tensor , to which the graviton field
couples to the lowest order. We show that the second rank tensor
is {\it not} the conventional energy momentum tensor
of the graviton and provide an explanation for this feature. Third, we
construct the full nonlinear Einstein's theory with the source being spin-0
field, spin-1 field or relativistic particles by explicitly coupling the spin-2
field to this second rank tensor order by order and summing
up the infinite series. Finally, we construct the theory obtained by self
consistently coupling to the conventional energy momentum tensor
order by order and show that this does {\it not} lead to Einstein's
theory. (condensed).Comment: revtex; 19 pages; no figure
Search for supernova-produced 60Fe in a marine sediment
An 60Fe peak in a deep-sea FeMn crust has been interpreted as due to the
signature left by the ejecta of a supernova explosion close to the solar system
2.8 +/- 0.4 Myr ago [Knie et al., Phys. Rev. Lett. 93, 171103 (2004)]. To
confirm this interpretation with better time resolution and obtain a more
direct flux estimate, we measured 60Fe concentrations along a dated marine
sediment. We find no 60Fe peak at the expected level from 1.7 to 3.2 Myr ago.
However, applying the same chemistry used for the sediment, we confirm the 60Fe
signal in the FeMn crust. The cause of the discrepancy is discussed.Comment: 15 pages, 5 figures, submitted to PR
The Ni(n,) cross section measured with DANCE
The neutron capture cross section of the s-process branch nucleus Ni
affects the abundances of other nuclei in its region, especially Cu and
Zn. In order to determine the energy dependent neutron capture cross
section in the astrophysical energy region, an experiment at the Los Alamos
National Laboratory has been performed using the calorimetric 4 BaF
array DANCE. The (n,) cross section of Ni has been determined
relative to the well known Au standard with uncertainties below 15%.
Various Ni resonances have been identified based on the Q-value.
Furthermore, the s-process sensitivity of the new values was analyzed with the
new network calculation tool NETZ.Comment: 11 pages, 13 page
Reality Conditions and Ashtekar Variables: a Different Perspective
We give in this paper a modified self-dual action that leads to the
-ADM formalism without having to face the difficult second class
constraints present in other approaches (for example if one starts from the
Hilbert-Palatini action). We use the new action principle to gain some new
insights into the problem of the reality conditions that must be imposed in
order to get real formulations from complex general relativity. We derive also
a real formulation for Lorentzian general relativity in the Ashtekar phase
space by using the modified action presented in the paper.Comment: 22 pages, LATEX, Preprint CGPG-94/10-
Self-paced part-list cuing
Ironically, the presentation of a subset of studied material as retrieval cues at test often impairs recall of the remaining (target) material—an effect known as part-list cuing impairment. Part-list cues are typically provided at the beginning of the recall period, a time when nearly all individuals would be able to recall at least some studied items on their own. Across two experiments, we examined the effects of part-list cuing when student participants could decide on their own when the cues were presented during the recall period. Results showed that participants activated the cues relatively late in the recall period, when recall was already close to asymptote. Critically, such delayed cuing no longer impaired recall performance. The detrimental effect of part-list cuing, as it has been demonstrated numerous times in the memory literature, thus seems to depend on presentating the cue items (too) early in the recall period
- …