9,244 research outputs found
The Complex of Solutions of the Nested Bethe Ansatz. The A_2 Spin Chain
The full set of polynomial solutions of the nested Bethe Ansatz is
constructed for the case of A_2 rational spin chain. The structure and
properties of these associated solutions are more various then in the case of
usual XXX (A_1) spin chain but their role is similar
Discovery of three z>6.5 quasars in the VISTA Kilo-degree Infrared Galaxy (VIKING) survey
Studying quasars at the highest redshifts can constrain models of galaxy and
black hole formation, and it also probes the intergalactic medium in the early
universe. Optical surveys have to date discovered more than 60 quasars up to
z~6.4, a limit set by the use of the z-band and CCD detectors. Only one z>6.4
quasar has been discovered, namely the z=7.08 quasar ULAS J1120+0641, using
near-infrared imaging. Here we report the discovery of three new z>6.4 quasars
in 332 square degrees of the Visible and Infrared Survey Telescope for
Astronomy Kilo-degree Infrared Galaxy (VIKING) survey, thus extending the
number from 1 to 4. The newly discovered quasars have redshifts of z=6.60,
6.75, and 6.89. The absolute magnitudes are between -26.0 and -25.5, 0.6-1.1
mag fainter than ULAS J1120+0641. Near-infrared spectroscopy revealed the MgII
emission line in all three objects. The quasars are powered by black holes with
masses of ~(1-2)x10^9 M_sun. In our probed redshift range of 6.44<z<7.44 we can
set a lower limit on the space density of supermassive black holes of
\rho(M_BH>10^9 M_sun) > 1.1x10^(-9) Mpc^(-3). The discovery of three quasars in
our survey area is consistent with the z=6 quasar luminosity function when
extrapolated to z~7. We do not find evidence for a steeper decline in the space
density of quasars with increasing redshift from z=6 to z=7.Comment: 14 pages, 9 figures. Published in Ap
The Northern Sky Optical Cluster Survey II: An Objective Cluster Catalog for 5800 Square Degrees
We present a new, objectively defined catalog of candidate galaxy clusters
based on the galaxy catalogs from the Digitized Second Palomar Observatory Sky
Survey (DPOSS). This cluster catalog, derived from the best calibrated plates
in the high latitude (|b|>30) Northern Galactic Cap region, covers 5,800 square
degrees, and contains 8,155 candidate clusters. A simple adaptive kernel
density mapping technique, combined with the SExtractor object detection
algorithm, is used to detect galaxy overdensities, which we identify as
clusters. Simulations of the background galaxy distribution and clusters of
varying richnesses and redshifts allow us to optimize detection parameters, and
measure the completeness and contamination rates for our catalog. Cluster
richnesses and photometric redshifts are measured, using integrated colors and
magnitudes for each cluster. An extensive spectroscopic survey is used to
confirm the photometric results.
This catalog, with well-characterized sample properties, provides a sound
basis for future studies of cluster physics and large scale structure.Comment: 49 pages, 16 figures. Accepted to AJ; appearing in April. Version
with full resolution figures, and full length tables available at
http://dposs.caltech.edu:8080/NoSOCS.htm
An investigation of vegetation and other earth resource/feature parameters using LANDSAT and other remote sensing data. A: LANDSAT. B: Remote sensing of volcanic emissions
There are no author-identified significant results in this report
Discovery of Extreme Examples of Superclustering in Aquarius
We report the discovery of two highly extended filaments and one extremely
high density knot within the region of Aquarius. The supercluster candidates
were chosen via percolation analysis of the Abell and ACO catalogs and include
only the richest clusters (R >= 1). The region examined is a 10x45 degree strip
and is now 87% complete in cluster redshift measurements to mag_10 = 18.3. In
all, we report 737 galaxy redshifts in 46 cluster fields. One of the
superclusters, dubbed Aquarius, is comprised of 14 Abell/ACO clusters and
extends 110h^-1Mpc in length only 7 degrees off the line-of-sight. On the
near-end of the Aquarius filament, another supercluster, dubbed Aquarius-Cetus,
extends for 75h^-1Mpc perpendicular to the line-of-sight. After fitting
ellipsoids to both Aquarius and Aquarius-Cetus, we find axis ratios (long-to-
midlength axis) of 4.3 for Aquarius and 3.0 for Aquarius-Cetus. We fit
ellipsoids to all N>=5 clumps of clusters in the Abell/ACO measured-z cluster
sample. The frequency of filaments with axis ratios >=3.0 (~20%) is nearly
identical with that found among `superclusters' in Monte Carlo simulations of
random and random- clumped clusters, however, so the rich Abell/ACO clusters
have no particular tendency toward filamentation. The Aquarius filament also
contains a `knot' of 6 clusters at Z ~0.11, with five of the clusters near
enough togeteher to represent an apparent overdensity of 150. There are
three other R >= 1 cluster density enhancements similar to this knot at lower
redshifts: Corona Borealis, the Shapely Concentration, and another grouping of
seven clusters in Microscopium. All four of these dense superclusters appear
near the point of breaking away from the Hubble Flow, and some may now be in
collapse, but there is little evidence of any being virialized.Comment: 45 pages (+ e-tables), 7 figures, AASTeX Accepted for Publication in
Ap
Cluster Correlation in Mixed Models
We evaluate the dependence of the cluster correlation length r_c on the mean
intercluster separation D_c, for three models with critical matter density,
vanishing vacuum energy (Lambda = 0) and COBE normalized: a tilted CDM (tCDM)
model (n=0.8) and two blue mixed models with two light massive neutrinos
yielding Omega_h = 0.26 and 0.14 (MDM1 and MDM2, respectively). All models
approach the observational value of sigma_8 (and, henceforth, the observed
cluster abundance) and are consistent with the observed abundance of Damped
Lyman_alpha systems. Mixed models have a motivation in recent results of
neutrino physics; they also agree with the observed value of the ratio
sigma_8/sigma_25, yielding the spectral slope parameter Gamma, and nicely fit
LCRS reconstructed spectra. We use parallel AP3M simulations, performed in a
wide box (side 360/h Mpc) and with high mass and distance resolution, enabling
us to build artificial samples of clusters, whose total number and mass range
allow to cover the same D_c interval inspected through APM and Abell cluster
clustering data. We find that the tCDM model performs substantially better than
n=1 critical density CDM models. Our main finding, however, is that mixed
models provide a surprisingly good fit of cluster clustering data.Comment: 22 pages + 10 Postscript figures. Accepted for publication in Ap
From arbitrariness to ambiguities in the evaluation of perturbative physical amplitudes and their symmetry relations
A very general calculational strategy is applied to the evaluation of the
divergent physical amplitudes which are typical of perturbative calculations.
With this approach in the final results all the intrinsic arbitrariness of the
calculations due to the divergent character is still present. We show that by
using the symmetry properties as a guide to search for the (compulsory) choices
in such a way as to avoid ambiguities, a deep and clear understanding of the
role of regularization methods emerges. Requiring then an universal point of
view for the problem, as allowed by our approach, very interesting conclusions
can be stated about the possible justifications of most intriguing aspect of
the perturbative calculations in quantum field theory: the triangle anomalies.Comment: 16 pages, no figure
Artesunate reduces but does not prevent posttreatment transmission of Plasmodium falciparum to Anopheles gambiae.
Combination therapy that includes artemisinin derivatives cures most falciparum malaria infections. Lowering transmission by reducing gametocyte infectivity would be an additional benefit. To examine the effect of such therapy on transmission, Gambian children with Plasmodium falciparum malaria were treated with standard regimens of chloroquine or pyrimethamine-sulfadoxine alone or in combination with 1 or 3 doses of artesunate. The infectivity to mosquitoes of gametocytes in peripheral blood was determined 4 or 7 days after treatment. Infection of mosquitoes was observed in all treatment groups and was positively associated with gametocyte density. The probability of transmission was lowest in those who received pyrimethamine-sulfadoxine and 3 doses of artesunate, and it was 8-fold higher in the group that received pyrimethamine-sulfadoxine alone. Artesunate reduced posttreatment infectivity dramatically but did not abolish it completely. The study raises questions about any policy to use pyrimethamine-sulfadoxine alone as the first-line treatment for malaria
Deer reduce habitat quality for a woodland songbird: evidence from settlement patterns, demographic parameters, and body condition.
Understanding avian responses to ungulate-induced habitat modification is important because deer populations are increasing across much of temperate Europe and North America. Our experimental study examined whether habitat quality for Blackcaps (Sylvia atricapilla) in young woodland in eastern England was affected by deer, by comparing Blackcap behavior, abundance, and condition between paired plots (half of each pair protected from deer). The vegetation in each pair of plots was the same age. The Blackcap is an ideal model species for testing effects of deer on avian habitat quality because it is dependent on dense understory vegetation and is abundant throughout much of Europe. We compared timing of settlement, abundance, age structure (second-year vs. after-second-year), and phenotypic quality (measured as a body condition index, body mass divided by tarsus length) between experimental and control plots. We used point counts to examine Blackcap distribution, and standardized mist netting to collect demographic and biometric data. Incidence of singing Blackcaps was higher in nonbrowsed than in browsed plots, and singing males were recorded in nonbrowsed plots earlier in the season, indicating earlier and preferential territory establishment. Most Blackcaps, both males and females, were captured in vegetation prior to canopy closure (2–4 years of regrowth). Body condition was superior for male Blackcaps captured in nonbrowsed plots; for second-year males this was most marked in vegetation prior to canopy closure. We conclude that deer browsing in young woodland can alter habitat quality for understory-dependent species, with potential consequences for individual fitness and population productivity beyond the more obvious effects on population density
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