16,959 research outputs found
Noncommutative geometry and motives: the thermodynamics of endomotives
We combine aspects of the theory of motives in algebraic geometry with
noncommutative geometry and the classification of factors to obtain a
cohomological interpretation of the spectral realization of zeros of
-functions. The analogue in characteristic zero of the action of the
Frobenius on l-adic cohomology is the action of the scaling group on the cyclic
homology of the cokernel (in a suitable category of motives) of a restriction
map of noncommutative spaces. The latter is obtained through the thermodynamics
of the quantum statistical system associated to an endomotive (a noncommutative
generalization of Artin motives). Semigroups of endomorphisms of algebraic
varieties give rise canonically to such endomotives, with an action of the
absolute Galois group. The semigroup of endomorphisms of the multiplicative
group yields the Bost-Connes system, from which one obtains, through the above
procedure, the desired cohomological interpretation of the zeros of the Riemann
zeta function. In the last section we also give a Lefschetz formula for the
archimedean local L-factors of arithmetic varieties.Comment: 52 pages, amslatex, 1 eps figure, v2: final version to appea
EXCITATION of COUPLED STELLAR MOTIONS in the GALACTIC DISK by ORBITING SATELLITES
We use a set of high-resolution N-body simulations of the Galactic disk to study its interactions with the population of cosmologically predicted satellites. One simulation illustrates that multiple passages of massive satellites with different velocities through the disk generate a wobble, which has the appearance of rings in face-on projections of the stellar disk. They also produce flares in the outer disk parts and gradually heat the disk through bending waves. A different numerical experiment shows that an individual satellite as massive as the Sagittarius dwarf galaxy passing through the disk will drive coupled horizontal and vertical oscillations of stars in underdense regions with small associated heating. This experiment shows that vertical excursions of stars in these low-density regions can exceed 1 kpc in the Solar neighborhood, resembling the recently locally detected coherent vertical oscillations. They can also induce non-zero vertical streaming motions as large as 10-20 km s-1, which is consistent with recent observations in the Galactic disk. This phenomenon appears as a local ring with modest associated disk heating. © 2016. The American Astronomical Society. All rights reserved
Effect of wing bend on the experimental force and moment characteristics of an oblique wing
Static longitudinal and lateral/directional force and moment characteristics are presented for an elliptical oblique wing mounted on top of a Sears-Haack body of revolution. The wing had an aspect ratio of 6 (based on the unswept span) and was tested at various sweep angles relative to the body axis ranging from 0 to 60 deg. In an attempt to create more symmetrical spanwise wing stalling characteristics, both wing panels were bent upward to produce washout on the trailing wing panel and washing on the leading wing panel. Small fluorescent tufts were attached to the wing surface to indicate the stall progression on the wing. The tests were conducted throughout a Mach number range from 0.6 to 1.4 at a constant unit Reynolds number of 8.2 x 10 per meter. The test results indicate that upward bending of the wing panels had only a small effect on the linearity of the moment curves and would require an impractical wing-pivot location at low lift to eliminate the rolling moment resulting from this bending
Microprogram scheme for automatic recovery from computer error
Microprogram scheme enables computer to recover from failure in one of its two central processing units during time duration of instruction in which failure occurs. Microprogram advantages include - /1/ built-in interpretive capability, /2/ selection of processing interrupts by priority, and /3/ economical use of bootstrap sequence
The Phoenix Deep Survey: X-ray properties of faint radio sources
In this paper we use a 50ks XMM-Newton pointing overlapping with the Phoenix
Deep Survey, a homogeneous radio survey reaching muJy sensitivities, to explore
the X-ray properties and the evolution of star-forming galaxies. UV, optical
and NIR photometry is available and is used to estimate photometric redshifts
and spectral types for radio sources brighter than R=21.5mag (total of 82).
Sources with R<21.5mag and spiral galaxy SEDs (34) are grouped into two
redshift bins with a median of z=0.240 and 0.455 respectively. Stacking
analysis for both the 0.5-2 and 2-8keV bands is performed on these subsamples.
A high confidence level signal (>3.5sigma) is detected in the 0.5-2keV band
corresponding to a mean flux of ~3e-16cgs for both subsamples. This flux
translates to mean luminosities of ~5e40 and 1.5e41cgs for the z=0.240 and
0.455 subsamples respectively. Only a marginally significant signal (2.6sigma)
is detected in the 2-8keV band for the z=0.455 subsample. We argue that the
stacked signal above is dominated by star-formation. The mean L_X/L_B ratio and
the mean L_X of the two subsamples are found to be higher than optically
selected spirals and similar to starbursts. We also find that the mean L_X and
L_1.4 of the faint radio sources studied here are consistent with the L_X-L_1.4
correlation of local star-forming galaxies. Moreover, the X-ray emissivity of
sub-mJy sources to z~0.3 is found to be elevated compared to local HII
galaxies. The observed increase is consistent with L_X evolution of the form
(1+z)^3. Assuming that our sample is indeed dominated by starbursts this is
direct evidence for evolution of such systems at X-ray wavelengths. Using an
empirical L_X to SFR conversion we estimate a global SFR density at z~0.3 of
\~0.029M_o/yr/Mpc in agreement with previous studies.Comment: 12 pages, 6 figures, accepted for publication in MNRA
The Phoenix Deep Survey: spectroscopic catalog
The Phoenix Deep Survey is a multi-wavelength survey based on deep 1.4 GHz
radio imaging, reaching well into the sub-100 microJy level. One of the aims of
this survey is to characterize the sub-mJy radio population, exploring its
nature and evolution. In this paper we present the catalog and results of the
spectroscopic observations aimed at characterizing the optically ``bright''
(R<~ 21.5 mag) counterparts of faint radio sources. Out of 371 sources with
redshift determination, 21% have absorption lines only, 11% show AGN
signatures, 32% are star-forming galaxies, 34% show narrow emission lines that
do not allow detailed spectral classification (due to poor signal-to-noise
ratio and/or lack of diagnostic emission lines) and the remaining 2% are
identified with stars. For the star-forming galaxies with a Balmer decrement
measurement we find a median extinction of A(Ha)=1.9 mag, higher than that of
optically selected samples. This is a result of the radio selection, which is
not biased against dusty systems. Using the available spectroscopic
information, we estimate the radio luminosity function of star-forming galaxies
in two independent redshift bins at z~0.1 and 0.3 respectively. We find direct
evidence for strong luminosity evolution of these systems consistent with L(1.4
GHz) ~ (1+z)^(2.7).Comment: 39 pages, 12 figures. References added, and minor changes to reflect
published versio
How Much Mass do Supermassive Black Holes Eat in their Old Age?
We consider the distribution of local supermassive black hole Eddington
ratios and accretion rates, accounting for the dependence of radiative
efficiency and bolometric corrections on the accretion rate. We find that black
hole mass growth, both of the integrated mass density and the masses of most
individual objects, must be dominated by an earlier, radiatively efficient,
high accretion rate stage, and not by the radiatively inefficient low accretion
rate phase in which most local supermassive black holes are currently observed.
This conclusion is particularly true of supermassive black holes in elliptical
host galaxies, as expected if they have undergone merger activity in the past
which would fuel quasar activity and rapid growth. We discuss models of the
time evolution of accretion rates and show that they all predict significant
mass growth in a prior radiatively efficient state. The only way to avoid this
conclusion is through careful fine-tuning of the accretion/quasar timescale to
a value that is inconsistent with observations. Our results agree with a wide
range of observational inferences drawn from the quasar luminosity function and
X-ray background synthesis models, but our approach has the virtue of being
independent of the modeling of source populations. Models in which black holes
spend the great majority of their time in low accretion rate phases are thus
completely consistent both with observations implying mass gain in relatively
short, high accretion rate phases and with the local distribution of accretion
rates.Comment: 11 pages, 4 figures, matches version accepted to Ap
Vortex nucleation in Bose-Einstein condensates in an oblate, purely magnetic potential
We have investigated the formation of vortices by rotating the purely
magnetic potential confining a Bose-Einstein condensate. We modified the bias
field of an axially symmetric TOP trap to create an elliptical potential that
rotates in the radial plane. This enabled us to study the conditions for vortex
nucleation over a wide range of eccentricities and rotation rates.Comment: 4 pages 4 figure
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