7,208 research outputs found
Convexity of the effective action from functional flows
We show that convexity of the effective action follows from its functional
flow equation. Our analysis is based on a new, spectral representation. The
results are relevant for the study of physical instabilities. We also derive
constraints for convexity-preserving regulators within general truncation
schemes including proper-time flows, and bounds for infrared anomalous
dimensions of propagators.Comment: 4 pages, 3 figure
Effect of the nearby levels on the resonance fluorescence spectrum of the atom-field interaction
We study the resonance fluorescence in the Jaynes-Cummings model when nearby
levels are taking into account. We show that the Stark shift produced by such
levels generates a displacement of the peaks of the resonance fluorescence due
to an induced effective detuning and also induces an asymmetry. Specific
results are presented assuming a coherent and a thermal fields
Delayed Scattering of Solitary Waves from Interfaces in a Granular Container
In granular media, the characterization of the behavior of solitary waves
around interfaces is of importance in order to look for more applications of
these systems. We study the behavior of solitary waves at both interfaces of a
symmetric granular container, a class of systems that has received recent
attention because it posses the feature of energy trapping. Hertzian contact is
assumed. We have found that the scattering process is elastic at one interface,
while at the other interface it is observed that the transmitted solitary wave
has stopped its movement during a time that gets longer when the ratio between
masses at the interfaces increases. The origin of this effect can be traced
back to the phenomenon of gaps opening, recently observed experimentally.Comment: To appear in Physical Review E, vol 7
Scattering of solitary waves in granular media
A detailed numerical study of the scattering of solitary waves by a barrier,
in a granular media with Hertzian contact, shows the existence of secondary
multipulse structures generated at the interface of two "sonic vacua", which
have a similar structure as the one previously found by Nesterenko and
coworkers.Comment: 4 pages, 9 figures (fig 5, replaced). Submitted to PR
Extended analytical study of the free-wing/free-trimmer concept
The free wing/free trimmer concept was analytically studied in order to: (1) compare the fore and aft trimmer configurations on the basis of equal lift capability, rather than equal area; (2) assess the influence of tip mounted aft trimmers, both free and fixed, on the lateral directional modes and turbulence responses; (3) examine the feasibility of using differential tip mounted trimmer deflection for lateral control; (4) determine the effects of independent fuselage attitude on the lateral directional behavior; and (5) estimate the influence of wing sweep on dynamic behavior and structural weight. Results indicate that the forward trimmer concept is feasible with the reduced size examined, but it remains inferior to the aft trimmer in every respect except structural weight. Differential motion of the aft trimmer is found to provide powerful lateral control; while the effect of fuselage deck angle is a reduction of the dutch roll damping ratio for nose-down attitudes
Model for Dissipative Highly Nonlinear Waves in Dry Granular Systems
A model is presented for the characterization of dissipative effects on
highly nonlinear waves in one-dimensional dry granular media. The model
includes three terms: Hertzian, viscoelastic, and a term proportional to the
square of the relative velocity of particles. The model outcomes are confronted
with different experiments where the granular system is subject to several
constraints for different materials. Excellent qualitative and quantitative
agreement between theory and experiments is found.Comment: Link to the Journal: http://prl.aps.org/abstract/PRL/v104/i11/e11800
Strong Clustering of Lyman Break Galaxies around Luminous Quasars at z~4
In the standard picture of structure formation, the first massive galaxies
are expected to form at the highest peaks of the density field, which
constitute the cores of massive proto-clusters. Luminous quasars (QSOs) at z~4
are the most strongly clustered population known, and should thus reside in
massive dark matter halos surrounded by large overdensities of galaxies,
implying a strong QSO-galaxy cross-correlation function. We observed six z~4
QSO fields with VLT/FORS exploiting a novel set of narrow band filters custom
designed to select Lyman Break Galaxies (LBGs) in a thin redshift slice of
Delta_z~0.3, mitigating the projection effects that have limited the
sensitivity of previous searches for galaxies around z>~4 QSOs. We find that
LBGs are strongly clustered around QSOs, and present the first measurement of
the QSO-LBG cross-correlation function at z~4, on scales of 0.1<~R<~9 Mpc/h
(comoving). Assuming a power law form for the cross-correlation function
xi=(r/r0_QG)^gamma, we measure r0_QG=8.83^{+1.39}_{-1.51} Mpc/h for a fixed
slope of gamma=2.0. This result is in agreement with the expected
cross-correlation length deduced from measurements of the QSO and LBG
auto-correlation function, and assuming a linear bias model. We also measure a
strong auto-correlation of LBGs in our QSO fields finding
r0_GG=21.59^{+1.72}_{-1.69} Mpc/h for a fixed slope of gamma=1.5, which is ~4
times larger than the LBG auto-correlation length in random fields, providing
further evidence that QSOs reside in overdensities of LBGs. Our results
qualitatively support a picture where luminous QSOs inhabit exceptionally
massive (M_halo>10^12 M_sun) dark matter halos at z~4.Comment: 25 pages, 22 figures, submitted to the Ap
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