1,674 research outputs found
Enhancement of thrust reverser cascade performance using aerodynamic and structural integration
This paper focuses on the design of a cascade within a cold stream thrust reverser during the early, conceptual stage of the product development process. A reliable procedure is developed for the exchange of geometric and load data between a two dimensional aerodynamic model and a three dimensional structural model. Aerodynamic and structural simulations are carried out using realistic operating conditions, for three different design configurations with a view to minimising weight for equivalent or improved aerodynamic and structural performance. For normal operational conditions the simulations show that total reverse thrust is unaffected when the performance of the deformed vanes is compared to the un-deformed case. This shows that for the conditions tested, the minimal deformation of the cascade vanes has no significant affect on aerodynamic efficiency and that there is scope for reducing the weight of the cascade. The pressure distribution through a two dimensional thrust reverser section is determined for two additional cascade vane configurations and it is shown that with a small decrease in total reverse thrust, it is possible to reduce weight and eliminate supersonic flow regimes through the nacelle section. By increasing vane sections in high pressure areas and decreasing sections in low pressure areas the structural performance of the cascade vanes in the weight reduced designs, is improved with significantly reduced levels of vane displacement and stress
Solid State Neutral Particle Analyzer Array on NSTX
A Solid State Neutral Particle Analyzer (SSNPA) array has been installed on the National Spherical Torus Experiment (NSTX). The array consists of four chords viewing through a common vacuum flange. The tangency radii of the viewing chords are 60, 90, 100, and 120 cm. They view across the three co-injection neutral beam lines (deuterium, 80 keV (typ.) with tangency radii 48.7, 59.2, and 69.4 cm) on NSTX and detect co-going energetic ions. A silicon photodiode used was calibrated by using a mono-energetic deuteron beam source. Deuterons with energy above 40 keV can be detected with the present setup. The degradation of the performance was also investigated. Lead shots and epoxy are used for neutron shielding to reduce handling any hazardous heavy metal. This method also enables us to make an arbitrary shape to be fit into the complex flight tube
Chandra Observations and the Nature of the Anomalous Arms of NGC 4258 (M 106)
This paper presents high resolution X-ray observations with Chandra of NGC
4258 and infers the nature of the so called ``anomalous arms'' in this galaxy.
The anomalous arms dominate the X-ray image; diffuse X-ray emission from the
``plateaux'' regions, seen in radio and H imaging, is also found. X-ray
spectra have been obtained at various locations along the anomalous arms and
are well described by thermal (mekal) models with kT in the range 0.37 - 0.6
keV. The previously known kpc-scale radio jets are surrounded by cocoons of hot
X-ray emitting gas for the first 350 pc of their length. The radio jets, seen
in previous VLBA and VLA observations, propagate perpendicular to the compact
nuclear gas disk (imaged in water vapor maser emission). The angle between the
jets and the rotation axis of the galactic disk is 60. The jets shock
the normal interstellar gas along the first 350 pc of their length, causing the
hot, X-ray emitting cocoons noted above. At a height of z = 175 pc from the
disk plane, the jets exit the normal gas disk and then propagate though the low
density halo until they reach ``hot spots'' (at 870 pc and 1.7 kpc from the
nucleus), which are seen in radio, optical line and X-ray emission. These jets
must drive mass motions into the low density halo gas. This high velocity halo
gas impacts on the dense galactic gas disk and shock heats it along and around
a ``line of damage'', which is the projection of the jets onto the galactic gas
disk as viewed down the galaxy disk rotation axis. However, because NGC 4258 is
highly inclined ( = 64), the ``line of damage'' projects on the
sky in a different direction to the jets themselves. We calculate the expected
p.a. of the ``line of damage'' on the sky and find that it coincides with the
anomalous arms to within 2. (Abstract truncated).Comment: 12 pages plus 9 figures, to be published in the Astrophysical
Journal, v560, nr 1, pt 1 (Oct 10, 2001 issue
Galactic-Scale Outflow and Supersonic Ram-Pressure Stripping in the Virgo Cluster Galaxy NGC 4388
The Hawaii Imaging Fabry-Perot Interferometer (HIFI) on the University of
Hawaii 2.2m telescope was used to map the Halpha and [O III] 5007 A
emission-line profiles across the entire disk of the edge-on Sb galaxy NGC
4388. We confirm a rich complex of highly ionized gas that extends ~4 kpc above
the disk of this galaxy. Low-ionization gas associated with star formation is
also present in the disk. Evidence for bar streaming is detected in the disk
component and is discussed in a companion paper (Veilleux, Bland-Hawthorn, &
Cecil 1999; hereafter VBC). Non-rotational blueshifted velocities of 50 - 250
km/s are measured in the extraplanar gas north-east of the nucleus. The
brighter features in this complex tend to have more blueshifted velocities. A
redshifted cloud is also detected 2 kpc south-west of the nucleus. The velocity
field of the extraplanar gas of NGC 4388 appears to be unaffected by the
inferred supersonic (Mach number M ~ 3) motion of this galaxy through the ICM
of the Virgo cluster. We argue that this is because the galaxy and the high-|z|
gas lie behind a Mach cone with opening angle ~ 80 degrees. The shocked ICM
that flows near the galaxy has a velocity of ~ 500 km/s and exerts insufficient
ram pressure on the extraplanar gas to perturb its kinematics. We consider
several explanations of the velocity field of the extraplanar gas. Velocities,
especially blueshifted velocities on the N side of the galaxy, are best
explained as a bipolar outflow which is tilted by > 12 degrees from the normal
to the disk. The observed offset between the extraplanar gas and the radio
structure may be due to buoyancy or refractive bending by density gradients in
the halo gas. Velocity substructure in the outflowing gas also suggests an
interaction with ambient halo gas.Comment: 29 pages including 5 figures, Latex, requires aaspp4.sty, to appear
in ApJ, 520 (July 20, 1999 issue
A Kinematic Link between Boxy Bulges, Stellar Bars, and Nuclear Activity in NGC 3079 & NGC 4388
We present direct kinematic evidence for bar streaming motions in two active
galaxies with boxy stellar bulges. The Hawaii Imaging Fabry-Perot
Interferometer was used on the Canada-France-Hawaii 3.6-m telescope and the
University of Hawaii 2.2-m telescope to derive the two-dimensional velocity
field of the line-emitting gas in the disks of the Sc galaxy NGC 3079 and the
Sb galaxy NGC 4388. In contrast to previous work based on long-slit data, the
detection of the bar potential from the Fabry-Perot data does not rely on the
existence of inner Lindblad resonances or strong bar-induced shocks. Simple
kinematic models which approximate the intrinsic gas orbits as nonintersecting,
inclined elliptical annuli that conserve angular momentum characterize the
observed velocity fields. Box-shaped bulges in both NGC 3079 and NGC 4388 are
confirmed using new near-infrared images to reduce dust obscuration.
Morphological analysis of starlight in these galaxies is combined with the gas
kinematics derived from the Fabry-Perot spectra to test evolutionary models of
stellar bars that involve transitory boxy bulges, and to quantify the
importance of such bars in fueling active nuclei. Our data support the
evolutionary bar models, but fail to prove convincingly that the stellar bars
in NGC 3079 and NGC 4388 directly trigger or sustain the nuclear activity.
(abridged)Comment: 31 pages, 18 figures, Latex, requires aaspp4.sty. Accepted for the
Astronomical Journal (November issue
Neutrons from multiplicity-selected La-La and Nb-Nb collisions at 400A MeV and La-La collisions at 250A MeV
Triple-differential cross sections for neutrons from high-multiplicity La-La
collisions at 250 and 400 MeV per nucleon and Nb-Nb collisions at 400 MeV per
nucleon were measured at several polar angles as a function of the azimuthal
angle with respect to the reaction plane of the collision. The reaction plane
was determined by a transverse-velocity method with the capability of
identifying charged-particles with Z=1, Z=2, and Z > 2. The flow of neutrons
was extracted from the slope at mid-rapidity of the curve of the average
in-plane momentum vs the center-of-mass rapidity. The squeeze-out of the
participant neutrons was observed in a direction normal to the reaction plane
in the normalized momentum coordinates in the center-of-mass system.
Experimental results of the neutron squeeze-out were compared with BUU
calculations. The polar-angle dependence of the maximum azimuthal anisotropy
ratio was found to be insensitive to the mass of the colliding
nuclei and the beam energy. Comparison of the observed polar-angle dependence
of the maximum azimuthal anisotropy ratio with BUU calculations for
free neutrons revealed that is insensitive also to the
incompressibility modulus in the nuclear equation of state.Comment: ReVTeX, 16 pages, 17 figures. To be published in Physical Review
Spectroscopic factors for bound s-wave states derived from neutron scattering lengths
A simple and model-independent method is described to derive neutron
single-particle spectroscopic factors of bound s-wave states in nuclei from neutron scattering lengths. Spectroscopic factors
for the nuclei ^{13}C, ^{14}C, ^{16}N, ^{17}O, ^{19}O, ^{23}Ne, ^{37}Ar, and
^{41}Ar are compared to results derived from transfer experiments using the
well-known DWBA analysis and to shell model calculations. The scattering length
of ^{14}C is calculated from the ^{15}C_{g.s.} spectroscopic factor.Comment: 9 pages (uses revtex), no figures, accepted for publication in PRC,
uuencoded tex-files and postscript-files available at
ftp://is1.kph.tuwien.ac.at/pub/ohu/Thermal.u
Neutrons from multiplicity-selected Au-Au collisions at 150, 250, 400, and 650 AMeV
We measured neutron triple-differential cross sections from
multiplicity-selected Au-Au collisions at 150, 250, 400, and 650 \AMeV. The
reaction plane for each collision was estimated from the summed transverse
velocity vector of the charged fragments emitted in the collision. We examined
the azimuthal distribution of the triple-differential cross sections as a
function of the polar angle and the neutron rapidity. We extracted the average
in--plane transverse momentum and the normalized
observable , where is the neutron
transverse momentum, as a function of the neutron center-of-mass rapidity, and
we examined the dependence of these observables on beam energy. These
collective flow observables for neutrons, which are consistent with those of
protons plus bound nucleons from the Plastic Ball Group, agree with the
Boltzmann--Uehling--Uhlenbeck (BUU) calculations with a momentum--dependent
interaction. Also, we calculated the polar-angle-integrated maximum azimuthal
anisotropy ratio R from the value of .Comment: 20 LaTeX pages. 11 figures to be faxed on request, send email to
sender's addres
- âŠ