11,325 research outputs found
Do Quasars Lens Quasars?
If the unexpectedly high frequency of quasar pairs with very different
component redshifts is due to the lensing of a population of background quasars
by the foreground quasar, typical lens masses must be \sim10^{12}M_{\sun} and
the sum of all such quasar lenses would have to contain times the
closure density of the Universe. It then seems plausible that a very high
fraction of all \sim10^{12} M_{\sun} gravitational lenses with redshifts
contain quasars. Here I propose that these systems have evolved to
form the present population of massive galaxies with M and M
>5\times10^{11} M_{\sun}.Comment: 6 pages, aas style, ams symbols, ApJL (accepted
Acknowledgments and LMIC
We appreciate the help of the individuals, organizations, and firms that have contributed to the beef research program through financial support, product donations, or services. The Livestock and Meat Industry Council also helps support animal agriculture research, teaching, and education
Dissolved iron in the tropical and subtropical Atlantic Ocean
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95150/1/gbc1254.pd
Opening the Rome-Southampton window for operator mixing matrices
We show that the running of operators which mix under renormalization can be
computed fully non-perturbatively as a product of continuum step scaling
matrices. These step scaling matrices are obtained by taking the "ratio" of Z
matrices computed at different energies in an RI-MOM type scheme for which
twisted boundary conditions are an essential ingredient. Our method allows us
to relax the bounds of the Rome-Southampton window. We also explain why such a
method is important in view of the light quark physics program of the RBC-UKQCD
collaborations. To illustrate our method, using n_f=2+1 domain-wall fermions,
we compute the non-perturbative running matrix of four-quark operators needed
in K->pipi decay and neutral kaon mixing. Our results are then compared to
perturbation theory.Comment: 8 pages, 7 figures. v2: PRD version, minor changes and few references
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Exotic and excited-state radiative transitions in charmonium from lattice QCD
We compute, for the first time using lattice QCD methods, radiative
transition rates involving excited charmonium states, states of high spin and
exotics. Utilizing a large basis of interpolating fields we are able to project
out various excited state contributions to three-point correlators computed on
quenched anisotropic lattices. In the first lattice QCD calculation of the
exotic 1-+ eta_c1 radiative decay, we find a large partial width Gamma(eta_c1
-> J/psi gamma) ~ 100 keV. We find clear signals for electric dipole and
magnetic quadrupole transition form factors in chi_c2 -> J/psi gamma,
calculated for the first time in this framework, and study transitions
involving excited psi and chi_c1,2 states. We calculate hindered magnetic
dipole transition widths without the sensitivity to assumptions made in model
studies and find statistically significant signals, including a non-exotic
vector hybrid candidate Y_hyb? -> eta_c gamma. As well as comparison to
experimental data, we discuss in some detail the phenomenology suggested by our
results and the extent to which it mirrors that of quark potential models and
make suggestions for the interpretation of our results involving exotic quantum
numbered states
Investigating the role of verbal working memory in young children's sentence comprehension
This study considers the role of verbal working memory in sentence comprehension in typically developing English-speaking children. Fifty-six (N = 56) children aged 4;0–6;6 completed a test of language comprehension that contained sentences which varied in complexity, standardized tests of vocabulary and nonverbal intelligence, and three tests of memory that measured the three verbal components of Baddeley's model of Working Memory (WM): the phonological loop, the episodic buffer, and the central executive. The results showed that children experienced most difficulty comprehending sentences that contained noncanonical word order (passives and object relative clauses). A series of linear mixed effects models were run to analyze the contribution of each component of WM to sentence comprehension. In contrast to most previous studies, the measure of the central executive did not predict comprehension accuracy. A canonicity by episodic buffer interaction showed that the episodic buffer measure was positively associated with better performance on the noncanonical sentences. The results are discussed with reference to capacity-limit and experience-dependent approaches to language comprehension
Skill Requirements of ERP Graduates
This research develops a list of the key skills that organizations expect from recent graduates of university programs in Enterprise Resource Planning (ERP). Quantitative and qualitative analysis of 105 surveys from IT professionals involved in the implementation or support of ERP systems (e.g., IT project managers, systems analysts, IT consultants) indicate a wide variety of skills needed by ERP graduates. These skills are classified as ERP Technical Knowledge, Technology Management Knowledge, Business Functional Knowledge, Interpersonal Skills, and Team Knowledge and Skills. The specific skills that comprise each group are identified and discussed. The main benefit of this study is that it presents a list of key skills that business schools must consider teaching when implementing their own ERP program. For business schools with existing ERP programs, this research provides a list of skills that can be used to help determine how well their program is meeting the needs of industry
Comparing Post-Newtonian and Numerical-Relativity Precession Dynamics
Binary black-hole systems are expected to be important sources of
gravitational waves for upcoming gravitational-wave detectors. If the spins are
not colinear with each other or with the orbital angular momentum, these
systems exhibit complicated precession dynamics that are imprinted on the
gravitational waveform. We develop a new procedure to match the precession
dynamics computed by post-Newtonian (PN) theory to those of numerical binary
black-hole simulations in full general relativity. For numerical relativity NR)
simulations lasting approximately two precession cycles, we find that the PN
and NR predictions for the directions of the orbital angular momentum and the
spins agree to better than with NR during the inspiral,
increasing to near merger. Nutation of the orbital plane on the
orbital time-scale agrees well between NR and PN, whereas nutation of the spin
direction shows qualitatively different behavior in PN and NR. We also examine
how the PN equations for precession and orbital-phase evolution converge with
PN order, and we quantify the impact of various choices for handling partially
known PN terms
The Evolution of Radio Galaxies at Intermediate Redshift
We describe a new estimate of the radio galaxy 1.4 GHz luminosity function
and its evolution at intermediate redshifts (z~0.4). Photometric redshifts and
color selection have been used to select Bj<23.5 early-type galaxies from the
Panoramic Deep Fields, a multicolor survey of two 25 sq deg fields.
Approximately 230 radio galaxies have then been selected by matching early-type
galaxies with NVSS radio sources brighter than 5 mJy. Estimates of the 1.4 GHz
luminosity function of radio galaxies measure significant evolution over the
observed redshift range. For an Omega_M=1 cosmology the evolution of the radio
power is consistent with luminosity evolution where P(z)=P(0)(1+z)^{k_L} and
3<k_L<5. The observed evolution is similar to that observed for UVX and X-ray
selected AGN and is consistent with the same physical process being responsible
for the optical and radio luminosity evolution of AGN.Comment: 26 pages, 9 Figures, Accepted for Publication in A
Finding Gravitational Lenses With X-rays
There are , 0.1 and 0.01 gravitationally lensed X-ray sources per
square degree with soft X-ray fluxes exceeding and
respectively. These sources will be detected
serendipitously with the Chandra X-ray Observatory at a rate of 1--3 lenses per
year of high resolution imaging. The low detection rate is due to the small
area over which the HRC and ACIS cameras have the <1\farcs5 FWHM resolution
necessary to find gravitational lenses produced by galaxies. Deep images of
rich clusters at intermediate redshifts should yield one wide separation
(\Delta\theta \gtorder 5\farcs0) multiply-imaged background X-ray source for
every , 30 and 300 clusters imaged to the same flux limits.Comment: 13 pages, including 5 figures, submitted to ApJ Letter
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