39,080 research outputs found
Real photons produced from photoproduction in collisions
We calculate the production of real photons originating from the
photoproduction in relativistic collisions. The
Weizscker-Williams approximation in the photoproduction is
considered. Numerical results agree with the experimental data from
Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC). We find
that the modification of the photoproduction is more prominent in large
transverse momentum region.Comment: 2 figure
Magnetic-Field Tuning of Light-Induced Superconductivity in Striped LaBaCuO
Optical excitation of stripe-ordered LaBaCuO has been shown
to transiently enhance superconducting tunneling between the CuO planes.
This effect was revealed by a blue-shift, or by the appearance of a Josephson
Plasma Resonance in the terahertz-frequency optical properties. Here, we show
that this photo-induced state can be strengthened by the application of high
external magnetic fields oriented along the c-axis. For a 7-Tesla field, we
observe up to a ten-fold enhancement in the transient interlayer phase
correlation length, accompanied by a two-fold increase in the relaxation time
of the photo-induced state. These observations are highly surprising, since
static magnetic fields suppress interlayer Josephson tunneling and stabilize
stripe order at equilibrium. We interpret our data as an indication that
optically-enhanced interlayer coupling in LaBaCuO does not
originate from a simple optical melting of stripes, as previously hypothesized.
Rather, we speculate that the photo-induced state may emerge from activated
tunneling between optically-excited stripes in adjacent planes.Comment: 35 pages, 13 figure
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Experimental and Numerical Investigation on Progressive Collapse Resistance of Post-tensioned Precast Concrete Beam-Column Sub-assemblages
In this paper, four 1/2 scaled precast concrete (PC) beam-column sub-assemblages with high performance connection were tested under push-down loading procedure to study the load resisting mechanism of PC frames subjected to different column removal scenarios. The parameters investigated include the location of column removal and effective prestress in tendons. The test results indicated that the failure modes of unbonded post-tensioned precast concrete (PTPC) frames were different from that of reinforced concrete (RC) frames: no cracks formed in the beams and wide opening formed near the beam to column interfaces. For specimens without overhanging beams, the failure of side column was eccentric compression failure. Moreover, the load resisting mechanisms in PC frames were significantly different from that of RC frames: the compressive arch action (CAA) developed in concrete during column removal was mainly due to actively applied pre-compressive stress in the concrete; CAA will not vanish when severe crush in concrete occurred. Thus, it may provide negative contribution for load resistance when the displacement exceeds one-beam depth; the tensile force developed in the tendons could provide catenary action from the beginning of the test. Moreover, to deeper understand the behavior of tested specimens, numerical analyses were carried out. The effects of concrete strength, axial compression ratio at side columns, and loading approaches on the behavior of the sub-assemblages were also investigated based on validated numerical analysis
Singularity in the boundary resistance between superfluid He and a solid surface
We report new measurements in four cells of the thermal boundary resistance
between copper and He below but near the superfluid-transition
temperature . For fits of to the data yielded ,
whereas a fit to theoretical values based on the renormalization-group theory
yielded . Alternatively, a good fit of the theory to the data could
be obtained if the {\it amplitude} of the prediction was reduced by a factor
close to two. The results raise the question whether the boundary conditions
used in the theory should be modified.Comment: 4 pages, 4 figures, revte
Phase properties of hypergeometric states and negative hypergeometric states
We show that the three quantum states (Plya states, the
generalized non-classical states related to Hahn polynomials and negative
hypergeometric states) introduced recently as intermediates states which
interpolate between the binomial states and negative binomial states are
essentially identical. By using the Hermitial-phase-operator formalism, the
phase properties of the hypergeometric states and negative hypergeometric
states are studied in detail. We find that the number of peaks of phase
probability distribution is one for the hypergeometric states and for the
negative hypergeometric states.Comment: 7 pages, 4 figure
X-ray Properties of Radio-Selected Dual Active Galactic Nuclei
Merger simulations predict that tidally induced gas inflows can trigger
kpc-scale dual active galactic nuclei (dAGN) in heavily obscured environments.
Previously with the Very Large Array, we have confirmed four dAGN with
redshifts between and projected separations between 4.3 and
9.2 kpc in the SDSS Stripe 82 field. Here, we present X-ray
observations that spatially resolve these dAGN and compare their
multi-wavelength properties to those of single AGN from the literature. We
detect X-ray emission from six of the individual merger components and obtain
upper limits for the remaining two. Combined with previous radio and optical
observations, we find that our dAGN have properties similar to nearby
low-luminosity AGN, and they agree well with the black hole fundamental plane
relation. There are three AGN-dominated X-ray sources, whose X-ray
hardness-ratio derived column densities show that two are unobscured and one is
obscured. The low obscured fraction suggests these dAGN are no more obscured
than single AGN, in contrast to the predictions from simulations. These three
sources show an apparent X-ray deficit compared to their mid-infrared continuum
and optical [OIII] line luminosities, suggesting higher levels of obscuration,
in tension with the hardness-ratio derived column densities. Enhanced
mid-infrared and [OIII] luminosities from star formation may explain this
deficit. There is ambiguity in the level of obscuration for the remaining five
components since their hardness ratios may be affected by non-nuclear X-ray
emissions, or are undetected altogether. They require further observations to
be fully characterized.Comment: 11 pages, 5 figures, Accepted for publication in the Astrophysical
Journa
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