4,001 research outputs found
The Two-Point Correlation of 2QZ Quasars and 2SLAQ LRGs: From a Quasar Fueling Perspective
Public data from the 2dF quasar survey (2QZ) and 2dF/SDSS LRG & QSO (2SLAQ),
with their vast reservoirs of spectroscopically located and identified sources,
afford us the chance to more accurately study their real space correlations in
the hopes of identifying the physical processes that trigger quasar activity.
We have used these two public databases to measure the projected cross
correlation, , between quasars and luminous red galaxies. We find the
projected two-point correlation to have a fitted clustering radius of and a slope, on scales from
0.7-27Mpc.
We attempt to understand this strong correlation by separating the LRG sample
into 2 populations of blue and red galaxies. We measure at the cross
correlation with each population. We find that these quasars have a stronger
correlation amplitude with the bluer, more recently starforming population in
our sample than the redder passively evolving population, which has a
correlation that is much more noisy and seems to flatten on scales Mpc. We compare this result to published work on hierarchical models.
The stronger correlation of bright quasars with LRGs that have undergone a
recent burst of starformation suggests that the physical mechanisms that
produce both activities are related and that minor mergers or tidal effects may
be important triggers of bright quasar activity and/or that bright quasars are
less highly biased than faint quasars.Comment: Accepted for publication in Ap
The Key Role of Heavy Precipitation Events in Climate Model Disagreements of Future Annual Precipitation Changes in California
Climate model simulations disagree on whether future precipitation will increase or decrease over California, which has impeded efforts to anticipate and adapt to human-induced climate change. This disagreement is explored in terms of daily precipitation frequency and intensity. It is found that divergent model projections of changes in the incidence of rare heavy (\u3e60 mm day−1) daily precipitation events explain much of the model disagreement on annual time scales, yet represent only 0.3% of precipitating days and 9% of annual precipitation volume. Of the 25 downscaled model projections examined here, 21 agree that precipitation frequency will decrease by the 2060s, with a mean reduction of 6–14 days yr−1. This reduces California\u27s mean annual precipitation by about 5.7%. Partly offsetting this, 16 of the 25 projections agree that daily precipitation intensity will increase, which accounts for a model average 5.3% increase in annual precipitation. Between these conflicting tendencies, 12 projections show drier annual conditions by the 2060s and 13 show wetter. These results are obtained from 16 global general circulation models downscaled with different combinations of dynamical methods [Weather Research and Forecasting (WRF), Regional Spectral Model (RSM), and version 3 of the Regional Climate Model (RegCM3)] and statistical methods [bias correction with spatial disaggregation (BCSD) and bias correction with constructed analogs (BCCA)], although not all downscaling methods were applied to each global model. Model disagreements in the projected change in occurrence of the heaviest precipitation days (\u3e60 mm day−1) account for the majority of disagreement in the projected change in annual precipitation, and occur preferentially over the Sierra Nevada and Northern California. When such events are excluded, nearly twice as many projections show drier future conditions
Probabilistic estimates of future changes in California temperature and precipitation usingstatistical and dynamical downscaling
Sixteen global general circulation models were used to develop probabilistic projections of temperature (T) and precipitation (P) changes over California by the 2060s. The global models were downscaled with two statistical techniques and three nested dynamical regional climate models, although not all global models were downscaled with all techniques. Both monthly and daily timescale changes in T and P are addressed, the latter being important for a range of applications in energy use, water management, and agriculture. The T changes tend to agree more across downscaling techniques than the P changes. Year-to-year natural internal climate variability is roughly of similar magnitude to the projected T changes. In the monthly average, July temperatures shift enough that that the hottest July found in any simulation over the historical period becomes a modestly cool July in the future period. Januarys as cold as any found in the historical period are still found in the 2060s, but the median and maximum monthly average temperatures increase notably. Annual and seasonal P changes are small compared to interannual or intermodel variability. However, the annual change is composed of seasonally varying changes that are themselves much larger, but tend to cancel in the annual mean. Winters show modestly wetter conditions in the North of the state, while spring and autumn show less precipitation. The dynamical downscaling techniques project increasing precipitation in the Southeastern part of the state, which is influenced by the North American monsoon, a feature that is not captured by the statistical downscaling
Absence of Persistent Magnetic Oscillations in Type-II Superconductors
We report on a numerical study intended to examine the possibility that
magnetic oscillations persist in type II superconductors beyond the point where
the pairing self-energy exceeds the normal state Landau level separation. Our
work is based on the self-consistent numerical solution for model
superconductors of the Bogoliubov-deGennes equations for the vortex lattice
state. In the regime where the pairing self-energy is smaller than the
cyclotron energy, magnetic oscillations resulting from Landau level
quantization are suppressed by the broadening of quasiparticle Landau levels
due to the non-uniform order parameter of the vortex lattice state, and by
splittings of the quasiparticle bands. Plausible arguments that the latter
effect can lead to a sign change of the fundamental harmonic of the magnetic
oscillations when the pairing self-energy is comparable to the cyclotron energy
are shown to be flawed. Our calculations indicate that magnetic oscillations
are strongly suppressed once the pairing self-energy exceeds the Landau level
separation.Comment: 7 pages, revtex, 7 postscript figure
The Cluster and Field Galaxy AGN Fraction at z = 1 to 1.5: Evidence for a Reversal of the Local Anticorrelation Between Environment and AGN Fraction
The fraction of cluster galaxies that host luminous AGN is an important probe
of AGN fueling processes, the cold ISM at the centers of galaxies, and how
tightly black holes and galaxies co-evolve. We present a new measurement of the
AGN fraction in a sample of 13 clusters of galaxies (M >= 10^{14} Msun) at
1<z<1.5 selected from the Spitzer/IRAC Shallow Cluster Survey, as well as the
field fraction in the immediate vicinity of these clusters, and combine these
data with measurements from the literature to quantify the relative evolution
of cluster and field AGN from the present to z~3. We estimate that the cluster
AGN fraction at 1<z<1.5 is f_A = 3.0^{+2.4}_{-1.4}% for AGN with a rest-frame,
hard X-ray luminosity greater than L_{X,H} >= 10^{44} erg/s. This fraction is
measured relative to all cluster galaxies more luminous than M*_{3.6}(z)+1,
where M*_{3.6}(z) is the absolute magnitude of the break in the galaxy
luminosity function at the cluster redshift in the IRAC 3.6um bandpass. The
cluster AGN fraction is 30 times greater than the 3sigma upper limit on the
value for AGN of similar luminosity at z~0.25, as well as more than an order of
magnitude greater than the AGN fraction at z~0.75. AGN with L_{X,H} >= 10^{43}
erg/s exhibit similarly pronounced evolution with redshift. In contrast with
the local universe, where the luminous AGN fraction is higher in the field than
in clusters, the X-ray and MIR-selected AGN fractions in the field and clusters
are consistent at 1<z<1.5. This is evidence that the cluster AGN population has
evolved more rapidly than the field population from z~1.5 to the present. This
environment-dependent AGN evolution mimics the more rapid evolution of
star-forming galaxies in clusters relative to the field.Comment: ApJ Accepted. 16 pages, 8 figures in emulateapj forma
Density of states of a type-II superconductor in a high magnetic field: Impurity effects
We have calculated the density of states of a dirty but
homogeneous superconductor in a high magnetic field. We assume a dilute
concentration of scalar impurities and find how behaves as one
crosses from the weak scattering to the strong scattering limit. At low
energies, for small values of the impurity
concentration and scattering strength. When the disorder becomes stronger than
some critical value, a finite density of states is created at the Fermi
surface. These results are a consequence of the gapless nature of the
quasiparticle excitation spectrum in a high magnetic field.Comment: 20 pages in RevTeX, 4 figures, to appear in Phys. Rev. B (July 1,
1997
Characterization of an Oct1 orthologue in the channel catfish, Ictalurus punctatus: A negative regulator of immunoglobulin gene transcription?
BACKGROUND: The enhancer (Eμ3') of the immunoglobulin heavy chain locus (IGH) of the channel catfish (Ictalurus punctatus) has been well characterized. The functional core region consists of two variant Oct transcription factor binding octamer motifs and one E-protein binding μE5 site. An orthologue to the Oct2 transcription factor has previously been cloned in catfish and is a functionally active transcription factor. This study was undertaken to clone and characterize the Oct1 transcription factor, which has also been shown to be important in driving immunoglobulin gene transcription in mammals. RESULTS: An orthologue of Oct1, a POU family transcription factor, was cloned from a catfish macrophage cDNA library. The inferred amino acid sequence of the catfish Oct1, when aligned with other vertebrate Oct1 sequences, revealed clear conservation of structure, with the POU specific subdomain of catfish Oct1 showing 96% identity to that of mouse Oct1. Expression of Oct1 was observed in clonal T and B cell lines and in all tissues examined. Catfish Oct1, when transfected into both mammalian (mouse) and catfish B cell lines, unexpectedly failed to drive transcription from three different octamer-containing reporter constructs. These contained a trimer of octamer motifs, a fish V(H )promoter, and the core region of the catfish Eμ3' IGH enhancer, respectively. This failure of catfish Oct1 to drive transcription was not rescued by human BOB.1, a co-activator of Oct transcription factors that stimulates transcription driven by catfish Oct2. When co-transfected with catfish Oct2, Oct1 reduced Oct2 driven transcriptional activation. Electrophoretic mobility shift assays showed that catfish Oct1 (native or expressed in vitro) bound both consensus and variant octamer motifs. Putative N- and C-terminal activation domains of Oct1, when fused to a Gal4 DNA binding domain and co-transfected with Gal4-dependent reporter constructs were transcriptionally inactive, which may be due in part to a lack of residues associated with activation domain function. CONCLUSION: An orthologue to mammalian Oct1 has been found in the catfish. It is similar to mammalian Oct1 in structure and expression. However, these results indicate that the physiological functions of catfish Oct1 differ from those of mammalian Oct1 and include negative regulation of transcription
Theory of Scanning Tunneling Spectroscopy of Magnetic-Field-Induced Discrete Nodal States in a D-Wave Superconductor
In the presence of an external magnetic field, the low lying elementary
excitations of a d-wave superconductor have quantized energy and their momenta
are locked near the node direction. It is argued that these discrete states can
most likely be detected by a local probe, such as a scanning tunneling
microscope. The low temperature local tunneling conductance on the Wigner-Seitz
cell boundaries of the vortex lattice is predicted to show peaks spaced as . The peak is anomalous, and it is present only
if the superconducting order parameter changes sign at certain points on the
Fermi surface. Away from the cell boundary, where the superfluid velocity is
nonzero, each peak splits, in general, into four peaks, corresponding to the
number of nodes in the order parameter.Comment: RevTeX 3.0, 4 pages, 3 figures (included
Kinematics of diffuse ionized gas in the disk halo interface of NGC 891 from Fabry-P\'erot observations
The properties of the gas in halos of galaxies constrain global models of the
interstellar medium. Kinematical information is of particular interest since it
is a clue to the origin of the gas. Here we report observations of the
kinematics of the thick layer of the diffuse ionized gas in NGC 891 in order to
determine the rotation curve of the halo gas. We have obtained a Fabry-P\'erot
data cube in Halpha to measure the kinematics of the halo gas with angular
resolution much higher than obtained from HI 21 cm observations. The data cube
was obtained with the TAURUS II spectrograph at the WHT on La Palma. The
velocity information of the diffuse ionized gas extracted from the data cube is
compared to model distributions to constrain the distribution of the gas and in
particular the halo rotation curve. The best fit model has a central
attenuation tau_H-alpha=6, a dust scale length of 8.1 kpc, an ionized gas scale
length of 5.0 kpc. Above the plane the rotation curve lags with a vertical
gradient of -18.8 km/s/kpc. We find that the scale length of the H-alpha must
be between 2.5 and 6.5 kpc. Furthermore we find evidence that the rotation
curve above the plane rises less steeply than in the plane. This is all in
agreement with the velocities measured in the HI.Comment: A&A, in press. 13 pages, 19 figure
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