10,197 research outputs found
Formation of X-Ray Cavities by the Magnetically Dominated Jet-Lobe System in a Galaxy Cluster
We present cosmological magnetohydrodynamic simulations of the formation of a
galaxy cluster with magnetic energy feedback from an active galactic nuclei
(AGN). We demonstrate that X-ray cavities can be produced by the magnetically
dominated jet-lobe system that is supported by a central axial current. The
cavities are magnetically dominated and their morphology is determined
jointedly by the magnetic fields and the background cluster pressure profile.
The expansion and motion of the cavities are driven initially by the Lorentz
force of the magnetic fields, and the cavities only become buoyant at late
stages ( Myr). We find that up to of the injected magnetic
energy goes into doing work against the hot cluster medium, heating it, and
lifting it in the cluster potential.Comment: 11 pages, 3 figures, minor correction
Controllable coherent population transfers in superconducting qubits for quantum computing
We propose an approach to coherently transfer populations between selected
quantum states in one- and two-qubit systems by using controllable
Stark-chirped rapid adiabatic passages (SCRAPs). These {\it evolution-time
insensitive} transfers, assisted by easily implementable single-qubit
phase-shift operations, could serve as elementary logic gates for quantum
computing. Specifically, this proposal could be conveniently demonstrated with
existing Josephson phase qubits. Our proposal can find an immediate application
in the readout of these qubits. Indeed, the broken parity symmetries of the
bound states in these artificial "atoms" provide an efficient approach to
design the required adiabatic pulses.Comment: 4 pages, 6 figures. to appear in Physical Review Letter
Ba3Ga3N5 - A Novel Host Lattice for Eu2+ - Doped Luminescent Materials with Unexpected Nitridogallate Substructure
The alkaline earth nitridogallate Ba3Ga3N5 was synthesized from the elements in a sodium flux at 760°C utilizing weld shut tantalum ampules. The crystal structure was solved and refined on the basis of single-crystal X-ray diffraction data. Ba3Ga3N5 (space group C2/c (No. 15), a = 16.801(3), b = 8.3301(2), c = 11.623(2) Å, β = 109.92 (3)°, Z = 8) contains a hitherto unknown structural motif in nitridogallates, namely, infinite strands made up of GaN4 tetrahedra, each sharing two edges and at least one corner with neighboring GaN4 units. There are three Ba2+ sites with coordination numbers six or eight, respectively, and one Ba2+ position exhibiting a low coordination number 4 corresponding to a distorted tetrahedron. Eu2+ - doped samples show red luminescence when excited by UV irradiation at room temperature. Luminescence investigations revealed a maximum emission intensity at 638 nm (FWHM =2123 cm−1). Ba3Ga3N5 is the first nitridogallate for which parity allowed broadband emission due to Eu2+ - doping has been found. The electronic structure of both Ba3Ga3N5 as well as isoelectronic but not isostructural Sr3Ga3N5 was investigated by DFT methods. The calculations revealed a band gap of 1.53 eV for Sr3Ga3N5 and 1.46 eV for Ba3Ga3N5
Non-generality of the Kadowaki-Woods ratio in correlated oxides
An explicit expression for the Kadowaki-Woods ratio in correlated metals is
derived by invoking saturation of the (high-frequency) Fermi-liquid scattering
rate at the Mott-Ioffe-Regel limit. Significant deviations observed in a number
of oxides are quantitatively explained due to variations in carrier density,
dimensionality, unit cell volume and the number of individual sheets in the
Brillouin zone. A generic re-scaling of the original Kadowaki-Woods plot is
also presented.Comment: 9 pages of text, 1 table, 2 figure
Cosmological extrapolation of MOND
Regime of MOND, which is used in astronomy to describe the gravitating
systems of island type without the need to postulate the existence of a
hypothetical dark matter, is generalized to the case of homogeneous
distribution of usual matter by introducing a linear dependence of the critical
acceleration on the size of region under consideration. We show that such the
extrapolation of MOND in cosmology is consistent with both the observed
dependence of brightness on the redshift for type Ia supernovae and the
parameters of large-scale structure of Universe in the evolution, that is
determined by the presence of a cosmological constant, the ordinary matter of
baryons and electrons as well as the photon and neutrino radiation without any
dark matter.Comment: 20 pages, 5 figures, comments adde
Influence of Mg, Ag and Al substitutions on the magnetic excitations in the triangular-lattice antiferromagnet CuCrO2
Magnetic excitations in CuCrO, CuCrMgO,
CuAgCrO, and CuCrAlO have been
studied by powder inelastic neutron scattering to elucidate the element
substitution effects on the spin dynamics in the Heisenberg triangular-lattice
antiferromagnet CuCrO. The magnetic excitations in
CuCrMgO consist of a dispersive component and a flat
component. Though this feature is apparently similar to CuCrO, the energy
structure of the excitation spectrum shows some difference from that in
CuCrO. On the other hand, in CuAgCrO and
CuCrAlO the flat components are much reduced, the
low-energy parts of the excitation spectra become intense, and additional
low-energy diffusive spin fluctuations are induced. We argued the origins of
these changes in the magnetic excitations are ascribed to effects of the doped
holes or change of the dimensionality in the magnetic correlations.Comment: 7 pages, 5 figure
Possible interpretation of the (10610) and (10650) in a chiral quark model
Motivated by the two charged bottomonium-like resonances (10610) and
(10650) newly observed by the Belle collaboration, the possible molecular
states composed of a pair of heavy mesons, , etc (in S-wave), are investigated in the framework of chiral quark
models by the Gaussian expansion method. The bound states and
with quantum numbers , which are good
candidates for the and respectively, are obtained.
Other three bound states with ,
with are predicted. These
states may be observed in open-bottom or hidden-bottom decay channel of highly
excited . When extending directly the quark model to the hidden color
channel of the multi-quark system, more deeply bound states are found. Future
experimental search of those states will cast doubt on the validity of applying
the chiral constituent quark model to the hidden color channel directly.Comment: 13 pages, 1 figure, title and some arguments in the abstract and
section 5 are revised, results unchange
Structural and Luminescence Properties of Silica-Based Hybrids Containing New Silylated-Diketonato Europium(III) Complex
A new betadiketonate ligand displaying a trimethoxysilyl group as grafting function and a diketone moiety as complexing site (TTA-Si = 4,4,4-trifluoro-2-(3-trimethoxysilyl)propyl)-1-3-butanedione (C4H3S)COCH[(CH2)3Si(OCH3)3]COCF3) and its highly luminescent europium(III) complex [Eu(TTA-Si)3] have been synthesized and fully characterized. Luminescent silica-based hybrids have been prepared as well with this new complex grafted on the surface of dense silica nanoparticles (28 (+/-3 nm) or on mesoporous
silica particles. The covalent bonding of Eu(TTA-Si)3 inside the core of uniform silica
nanoparticles (40 (+/- 5 nm) was also achieved. Luminescence properties are discussed in relation to the europium chemical environment involved in each of the three hybrids. The general methodology proposed allowed high grafting ratios and overcame chelate release and tendency to agglomeration, and it could be applied to any silica matrix (in the core or at the surface, nanosized or not, dense or mesoporous) and therefore numerous applications such as luminescent markers and luminophors could be foreseen
The N = 16 spherical shell closure in 24O
The unbound excited states of the neutron drip-line isotope 24O have been
investigated via the 24O(p,p')23O+n reaction in inverse kinematics at a beam
energy of 62 MeV/nucleon. The decay energy spectrum of 24O* was reconstructed
from the momenta of 23O and the neutron. The spin-parity of the first excited
state, observed at Ex = 4.65 +/- 0.14 MeV, was determined to be Jpi = 2+ from
the angular distribution of the cross section. Higher lying states were also
observed. The quadrupole transition parameter beta2 of the 2+ state was
deduced, for the first time, to be 0.15 +/- 0.04. The relatively high
excitation energy and small beta2 value are indicative of the N = 16 shell
closure in 24O.Comment: to be submitted to Physical Review Letter
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