606 research outputs found
LES study on the shape effect of ground obstacles on wake vortex dissipation
The lingering wake vortex following a landing aircraft has long been a hazard to aviation safety. Previous studies at the German Aerospace Center (DLR) confirmed the effectiveness of applying ground-based obstacles to improve the dissipation of the wake vortex pair by triggering the onset of the vortex bursting by the artificial introduction of shortwave instability. Following the design of the plate line obstacles as proposed by DLR for vortex dissipation, we further investigate the influence of the shape of the ground obstacles on dissipating wake vortex in the present work. The secondary vortex structure, resulting from the interaction between the vortical flow and the obstacle plate, stems from the location of the obstacle and travels outward along the vortex axis, thus spreading instability to the vortex structure along the way. 3D numerical simulations were conducted using Large Eddy Simulation with OpenFOAM solver
Entanglement in SU(2)-invariant quantum spin systems
We analyze the entanglement of SU(2)-invariant density matrices of two spins
, using the Peres-Horodecki criterion. Such density
matrices arise from thermal equilibrium states of isotropic spin systems. The
partial transpose of such a state has the same multiplet structure and
degeneracies as the original matrix with eigenvalue of largest multiplicity
being non-negative. The case , can be solved completely
and is discussed in detail with respect to isotropic Heisenberg spin models.
Moreover, in this case the Peres-Horodecki ciriterion turns out to be a
sufficient condition for non-separability. We also characterize SU(2)-invariant
states of two spins of length 1.Comment: 5 page
Characterizing the entanglement of symmetric many-particle spin-1/2 systems
Analyzing the properties of entanglement in many-particle spin-1/2 systems is
generally difficult because the system's Hilbert space grows exponentially with
the number of constituent particles, . Fortunately, it is still possible to
investigate many-particle entanglement when the state of the system possesses
sufficient symmetry. In this paper, we present a practical method for
efficiently computing various bipartite entanglement measures for states in the
symmetric subspace and perform these calculations for . By
considering all possible bipartite splits, we construct a picture of the
multiscale entanglement in large symmetric systems. In particular, we
characterize dynamically generated spin-squeezed states by comparing them to
known reference states (e.g., GHZ and Dicke states) and new families of states
with near-maximal bipartite entropy. We quantify the trade-off between the
degree of entanglement and its robustness to particle loss, emphasizing that
substantial entanglement need not be fragile.Comment: Updated version reflects changes made in January 200
Localization of electromagnetic waves in a two dimensional random medium
Motivated by previous investigations on the radiative effects of the electric
dipoles embedded in structured cavities, localization of electromagnetic waves
in two dimensions is studied {\it ab initio} for a system consisting of many
randomly distributed two dimensional dipoles. A set of self-consistent
equations, incorporating all orders of multiple scattering of the
electromagnetic waves, is derived from first principles and then solved
numerically for the total electromagnetic field. The results show that
spatially localized electromagnetic waves are possible in such a simple but
realistic disordered system. When localization occurs, a coherent behavior
appears and is revealed as a unique property differentiating localization from
either the residual absorption or the attenuation effects
Observed photodetachment in parallel electric and magnetic fields
We investigate photodetachment from negative ions in a homogeneous 1.0-T
magnetic field and a parallel electric field of approximately 10 V/cm. A
theoretical model for detachment in combined fields is presented. Calculations
show that a field of 10 V/cm or more should considerably diminish the Landau
structure in the detachment cross section. The ions are produced and stored in
a Penning ion trap and illuminated by a single-mode dye laser. We present
preliminary results for detachment from S- showing qualitative agreement with
the model. Future directions of the work are also discussed.Comment: Nine pages, five figures, minor revisions showing final publicatio
Diffusive and localization behavior of electromagnetic waves in a two-dimensional random medium
In this paper, we discuss the transport phenomena of electromagnetic waves in
a two-dimensional random system which is composed of arrays of electrical
dipoles, following the model presented earlier by Erdogan, et al. (J. Opt. Soc.
Am. B {\bf 10}, 391 (1993)). A set of self-consistent equations is presented,
accounting for the multiple scattering in the system, and is then solved
numerically. A strong localization regime is discovered in the frequency
domain. The transport properties within, near the edge of and nearly outside
the localization regime are investigated for different parameters such as
filling factor and system size. The results show that within the localization
regime, waves are trapped near the transmitting source. Meanwhile, the
diffusive waves follow an intuitive but expected picture. That is, they
increase with travelling path as more and more random scattering incurs,
followed by a saturation, then start to decay exponentially when the travelling
path is large enough, signifying the localization effect. For the cases that
the frequencies are near the boundary of or outside the localization regime,
the results of diffusive waves are compared with the diffusion approximation,
showing less encouraging agreement as in other systems (Asatryan, et al., Phys.
Rev. E {\bf 67}, 036605 (2003).)Comment: 8 pages 9 figure
Lipopolysaccharide-pretreated plasmacytoid dendritic cells ameliorate experimental chronic kidney disease
Plasmacytoid dendritic cells play important roles in inducing immune tolerance, preventing allograft rejection, and regulating immune responses in both autoimmune disease and graft-versus-host disease. In order to evaluate a possible protective effect of plasmacytoid dendritic cells against renal inflammation and injury, we purified these cells from mouse spleens and adoptively transferred lipopolysaccharide (LPS)-treated cells, modified ex vivo, into mice with adriamycin nephropathy. These LPS-treated cells localized to the kidney cortex and the lymph nodes draining the kidney, and protected the kidney from injury during adriamycin nephropathy. Glomerulosclerosis, tubular atrophy, interstitial expansion, proteinuria, and creatinine clearance were significantly reduced in mice with adriamycin nephropathy subsequently treated with LPS-activated plasmacytoid dendritic cells as compared to the kidney injury in mice given naive plasmacytoid dendritic cells. In addition, LPS-pretreated cells, but not naive plasmacytoid dendritic cells, convert CD4+CD25â T cells into Foxp3+ regulatory T cells and suppress the proinflammatory cytokine production of endogenous renal macrophages. This may explain their ability to protect against renal injury in adriamycin nephropathy
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum
P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in
combination with WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when
dropping prior assumptions about curvature, neutrinos, tensor modes and the
equation of state. Our results are in substantial agreement with the joint
analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive
consistency check with independent redshift survey data and analysis
techniques. In this paper, we place particular emphasis on clarifying the
physical origin of the constraints, i.e., what we do and do not know when using
different data sets and prior assumptions. For instance, dropping the
assumption that space is perfectly flat, the WMAP-only constraint on the
measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running
tilt, neutrino mass and equation of state in the list of free parameters, many
constraints are still quite weak, but future cosmological measurements from
SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
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