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Not All Bad Apples Spoil the Bunch: Order Effects on the Evaluation of Groups
When group members are encountered in a random sequential order, people expect the first (vs. middle or last) member to be more diagnostic of the group. Therefore, they weigh the performance of the first (vs. middle or last) more heavily in their predictions and decisions about the whole group
A Unified Scaling Law in Spiral Galaxies
We investigate the origin of a unified scaling relation in spiral galaxies.
Observed spiral galaxies are spread on a plane in the
three-dimensionallogarithmic space of luminosity L, radius R and rotation
velocity V. The plane is expressed as in I-passband,
where is a constant. On the plane, observed galaxies are distributed
in an elongated region which looks like the shape of a surfboard. The
well-known scaling relations, L-V (Tully-Fisher relation), V-R (also the
Tully-Fisher relation) and R-L (Freeman's law), can be understood as oblique
projections of the surfboard-like plane into 2-D spaces. This unified
interpretation of the known scaling relations should be a clue to understand
the physical origin of all the relations consistently. Furthermore, this
interpretation can also explain why previous studies could not find any
correlation between TF residuals and radius.
In order to clarify the origin of this plane, we simulate formation and
evolution of spiral galaxies with the N-body/SPH method, including cooling,
star formation and stellar feedback. Initial conditions are set to isolated 14
spheres with two free parameters, such as mass and angular momentum. The CDM
(h=0.5, ) cosmology is considered as a test case. The simulations
provide the following two conclusions: (a) The slope of the plane is well
reproduced but the zero-point is not. This zero-point discrepancy could be
solved in a low density ($\Omega_00.5) cosmology.
(b) The surfboard-shaped plane can be explained by the control of galactic mass
and angular momentum.Comment: Accepted for publication in ApJ Letters. 6 pages including 2 figure
Is AGN feedback necessary to form red elliptical galaxies?
We have used GADGET2 to simulate the formation of an elliptical galaxy in a
cosmological dark matter halo with mass 3x10^12M_Sun/h. Using a stellar
population synthesis model has allowed us to compute magnitudes, colours and
surface brightness profiles. We have included a model to follow the growth of a
central black hole and we have compared the results of simulations with and
without feedback from AGNs. We have studied the interplay between cold gas
accretion and merging in the development of galactic morphologies, the link
between colour and morphology evolution, the effect of AGN feedback on the
photometry of early type galaxies, the redshift evolution in the properties of
quasar hosts, and the impact of AGN winds on the chemical enrichment of the
intergalactic medium (IGM). We have found that the early phases of galaxy
formation are driven by the accretion of cold filamentary flows, which form a
disc at the centre of the dark matter halo. When the dark matter halo is
sufficiently massive to support the propagation of a stable shock, cold
accretion is shut down, and the star formation rate begins to decline. Mergers
transform the disc into an elliptical galaxy, but also bring gas into the
galaxy. Without a mechanism that removes gas from the merger remnants, the
galaxy ends up with blue colours, atypical for its elliptical morphology. AGN
feedback can solve this problem even with a fairly low heating efficiency. We
have also demonstrated that AGN winds are potentially important for the metal
enrichment of the IGM a high redshift.(abridged)Comment: 19 pages and 17 figures, accepted to MNRAS ID: MN-07-1954-MJ.R1 . For
high resolution images please check following link:
http://www.aip.de/People/AKhalatyan/COSMOLOGY/BHCOSMO
Star Formation, Supernovae Feedback and the Angular Momentum Problem in Numerical CDM Cosmogony: Half Way There?
We present a smoothed particle hydrodynamic (SPH) simulation that reproduces
a galaxy that is a moderate facsimile of those observed. The primary failing
point of previous simulations of disk formation, namely excessive transport of
angular momentum from gas to dark matter, is ameliorated by the inclusion of a
supernova feedback algorithm that allows energy to persist in the model ISM for
a period corresponding to the lifetime of stellar associations. The inclusion
of feedback leads to a disk at a redshift , with a specific angular
momentum content within 10% of the value required to fit observations. An
exponential fit to the disk baryon surface density gives a scale length within
17% of the theoretical value. Runs without feedback, with or without star
formation, exhibit the drastic angular momentum transport observed elsewhere.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
Flight-test evaluation of two electronic display formats for approach to landing under instrument conditions
The results of a flight evaluation of two electronic display formats for the approach to landing under instrument conditions are presented. The evaluation was conducted for a base-line electronic display format and for the same format with runway symbology and track information added. The evaluation was conducted during 3 deg, manual straight-in approaches with and without initial localizer offsets. Flight path tracking performance data and pilot subjective comments were examined with regard to the pilot's ability to capture and maintain localizer and glide slope by using both display formats
A real-time digital computer program for the simulation of a single rotor helicopter
A computer program was developed for the study of a single-rotor helicopter on the Langley Research Center real-time digital simulation system. Descriptions of helicopter equations and data, program subroutines (including flow charts and listings), real-time simulation system routines, and program operation are included. Program usage is illustrated by standard check cases and a representative flight case
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