4,968 research outputs found
Statistics of Cosmological Black Hole Jet Sources: Blazar Predictions for GLAST
A study of the statistics of cosmological black-hole jet sources is applied
to EGRET blazar data, and predictions are made for GLAST. Black-hole jet
sources are modeled as collimated relativistic plasma outflows with radiation
beamed along the jet axis due to strong Doppler boosting. The comoving rate
density of blazar flares is assumed to follow a blazar formation rate (BFR),
modeled by analytic functions based on astronomical observations and fits to
EGRET data. The redshift and size distributions of gamma-ray blazars observed
with EGRET, separated into BL Lac object (BL) and flat spectrum radio quasar
(FSRQ) distributions, are fit with monoparametric functions for the
distributions of the jet Lorentz factor \Gamma, comoving directional power
l'_e, and spectral slope. A BFR factor ~10 x greater at z ~ 1 than at present
is found to fit the FSRQ data. A smaller comoving rate density and greater
luminosity of BL flares at early times compared to the present epoch fits the
BL data. Based on the EGRET observations, ~1000 blazars consisting of ~800
FSRQs and FR2 radio galaxies and ~200 BL Lacs and FR1 radio galaxies will be
detected with GLAST during the first year of the mission. Additional AGN
classes, such as hard-spectrum BL Lacs that were mostly missed with EGRET,
could add more GLAST sources. The FSRQ and BL contributions to the EGRET
gamma-ray background at 1 GeV are estimated at the level of ~10 - 15% and ~2 -
4%, respectively. EGRET and GLAST sensitivities to blazar flares are considered
in the optimal case, and a GLAST analysis method for blazar detection is
outlined.Comment: 17 pages, 9 figures, ApJ, in press, v.660, May 1, 2007 (minor changes
from previous version
Adiabatic Quantum State Manipulation of Single Trapped Atoms
We use microwave induced adiabatic passages for selective spin flips within a
string of optically trapped individual neutral Cs atoms. We
position-dependently shift the atomic transition frequency with a magnetic
field gradient. To flip the spin of a selected atom, we optically measure its
position and sweep the microwave frequency across its respective resonance
frequency. We analyze the addressing resolution and the experimental robustness
of this scheme. Furthermore, we show that adiabatic spin flips can also be
induced with a fixed microwave frequency by deterministically transporting the
atoms across the position of resonance.Comment: 4 pages, 4 figure
Electromagnetically Induced Transparency and Light Storage in an Atomic Mott Insulator
We experimentally demonstrate electromagnetically induced transparency and
light storage with ultracold 87Rb atoms in a Mott insulating state in a three
dimensional optical lattice. We have observed light storage times of about 240
ms, to our knowledge the longest ever achieved in ultracold atomic samples.
Using the differential light shift caused by a spatially inhomogeneous far
detuned light field we imprint a "phase gradient" across the atomic sample,
resulting in controlled angular redirection of the retrieved light pulse.Comment: 4 pages, 4 figure
Coherence properties and quantum state transportation in an optical conveyor belt
We have prepared and detected quantum coherences with long dephasing times at
the level of single trapped cesium atoms. Controlled transport by an "optical
conveyor belt" over macroscopic distances preserves the atomic coherence with
slight reduction of coherence time. The limiting dephasing effects are
experimentally identified and are of technical rather than fundamental nature.
We present an analytical model of the reversible and irreversible dephasing
mechanisms. Coherent quantum bit operations along with quantum state transport
open the route towards a "quantum shift register" of individual neutral atoms.Comment: 4 pages, 3 figure
The Tenerife Cosmic Microwave Background Maps: Observations and First Analysis
The results of the Tenerife Cosmic Microwave Background (CMB) experiments are
presented. These observations cover 5000 and 6500 square degrees on the sky at
10 and 15 GHz respectively centred around Dec.~ +35 degrees. The experiments
are sensitive to multipoles l=10-30 which corresponds to the Sachs-Wolfe
plateau of the CMB power spectra. The sensitivity of the results are ~31 and
\~12 microK at 10 and 15 GHz respectively in a beam-size region (5 degrees
FWHM). The data at 15 GHz show clear detection of structure at high Galactic
latitude; the results at 10 GHz are compatible with these, but at lower
significance. A likelihood analysis of the 10 and 15 GHz data at high Galactic
latitude, assuming a flat CMB band power spectra gives a signal Delta
T_l=30+10-8 microK (68 % C.L.). Including the possible contaminating effect due
to the diffuse Galactic component, the CMB signal is Delta T_l=30+15-11 microK.
These values are highly stable against the Galactic cut chosen. Assuming a
Harrison-Zeldovich spectrum for the primordial fluctuations, the above values
imply an expected quadrupole Q_RMS-PS=20+10-7 microK which confirms previous
results from these experiments, and which are compatible with the COBE DMR.Comment: 17 pages, 7 figures. Submitted to Ap
Large-Scale QSO-Galaxy Correlations and Weak Lensing
Several recent studies show that bright, intermediate and high redshift
optically and radio selected QSOs are positively correlated with nearby
galaxies on a range of angular scales up to a degree. Obscuration by unevenly
distributed Galactic dust can be ruled out as the cause, leaving weak
statistical lensing as the physical process responsible. However the amplitude
of correlations on < 1 degree scales is at least a factor of a few larger than
lensing model predictions. A possible way to reconcile the observations and
theory is to revise the weak lensing formalism. We extend the standard lensing
formulation to include the next higher order term (second order) in the
geodesic equation of motion for photons. We derive relevant equations
applicable in the weak lensing regime, and discuss qualitative properties of
the updated formulation. We then perform numerical integrations of the revised
equation and study the effect of the extra term using two different types of
cosmic mass density fluctuations. We find that nearby large-scale coherent
structures increase the amplitude of the predicted lensing-induced correlations
between QSOs and foreground galaxies by ~ 10% (not a factor of several required
by observations), while the redshift of the optimal, i.e. `most correlated'
structures is moved closer to the observer compared to what is predicted using
the standard lensing equation.Comment: extended Section 2; 20 pages, including 4 figures, accepted to Ap
New Cosmological Structures on Medium Angular Scales Detected with the Tenerife Experiments
We present observations at 10 and 15 GHz taken with the Tenerife experiments
in a band of the sky at Dec.=+35 degrees. These experiments are sensitive to
multipoles in the range l=10-30. The sensitivity per beam is 56 and 20 microK
for the 10 and the 15 GHz data, respectively. After subtraction of the
prediction of known radio-sources, the analysis of the data at 15 GHz at high
Galactic latitude shows the presence of a signal with amplitude Delta Trms ~ 32
microK. In the case of a Harrison-Zeldovich spectrum for the primordial
fluctuations, a likelihood analysis shows that this signal corresponds to a
quadrupole amplitude Q_rms-ps=20.1+7.1-5.4 microK, in agreement with our
previous results at Dec.+=40 degrees and with the results of the COBE DMR.
There is clear evidence for the presence of individual features in the RA range
190 degrees to 250 degrees with a peak to peak amplitude of ~110 microK. A
preliminary comparison between our results and COBE DMR predictions for the
Tenerife experiments clearly indicates the presence of individual features
common to both. The constancy in amplitude over such a large range in frequency
(10-90 GHz) is strongly indicative of an intrinsic cosmological origin for
these structures.Comment: ApJ Letters accepted, 13 pages Latex (uses AASTEX) and 4 encapsulated
postscript figures
Results of the Second High Protein-High Lysine Wheat Observation Nursery Grown in 1976
This is the second report of results from a high protein-high lysine (HP-HL) observation nursery organized in 1974 by the Nebraska Agricultural Experiment Station and the Science and Education Administration, U. S. Department of Agriculture, under a contract with the Agency for International Development, U. S. Department of State. Primary objectives of this nursery are to: (1) Systematically provide breeders and cooperators with superior genetic germplasm for elevated levels of protein and/or lysine. (2) Test the degree of expression of the high protein and high lysine traits in a diverse array of environments. Funding from USAID has permitted the Nebraska wheat program to establish breeding nurseries at Lincoln, Nebraska, for evaluation of winter genotypes and at Yuma, Arizona, for both spring and winter wheats. Advanced experimental lines distributed to breeders and cooperators in the 2nd HP-HL nursery were selected from numerous hybrid combinations of both spring and winter types. All exhibited elevated protein and/or elevated lysine in nursery trials at Nebraska and Arizona. The lines were screened for growth habit at Nebraska, and were assigned to the designated spring or winter sections of the 2nd HP-HL nursery
Results of the Second High Protein-High Lysine Wheat Observation Nursery Grown in 1976
This is the second report of results from a high protein-high lysine (HP-HL) observation nursery organized in 1974 by the Nebraska Agricultural Experiment Station and the Science and Education Administration, U. S. Department of Agriculture, under a contract with the Agency for International Development, U. S. Department of State. Primary objectives of this nursery are to: (1) Systematically provide breeders and cooperators with superior genetic germplasm for elevated levels of protein and/or lysine. (2) Test the degree of expression of the high protein and high lysine traits in a diverse array of environments. Funding from USAID has permitted the Nebraska wheat program to establish breeding nurseries at Lincoln, Nebraska, for evaluation of winter genotypes and at Yuma, Arizona, for both spring and winter wheats. Advanced experimental lines distributed to breeders and cooperators in the 2nd HP-HL nursery were selected from numerous hybrid combinations of both spring and winter types. All exhibited elevated protein and/or elevated lysine in nursery trials at Nebraska and Arizona. The lines were screened for growth habit at Nebraska, and were assigned to the designated spring or winter sections of the 2nd HP-HL nursery
Results of the Second High Protein-High Lysine Wheat Observation Nursery Grown in 1976
This is the second report of results from a high protein-high lysine (HP-HL) observation nursery organized in 1974 by the Nebraska Agricultural Experiment Station and the Science and Education Administration, U. S. Department of Agriculture, under a contract with the Agency for International Development, U. S. Department of State. Primary objectives of this nursery are to: (1) Systematically provide breeders and cooperators with superior genetic germplasm for elevated levels of protein and/or lysine. (2) Test the degree of expression of the high protein and high lysine traits in a diverse array of environments. Funding from USAID has permitted the Nebraska wheat program to establish breeding nurseries at Lincoln, Nebraska, for evaluation of winter genotypes and at Yuma, Arizona, for both spring and winter wheats. Advanced experimental lines distributed to breeders and cooperators in the 2nd HP-HL nursery were selected from numerous hybrid combinations of both spring and winter types. All exhibited elevated protein and/or elevated lysine in nursery trials at Nebraska and Arizona. The lines were screened for growth habit at Nebraska, and were assigned to the designated spring or winter sections of the 2nd HP-HL nursery
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