35,939 research outputs found
An analysis of turbulent diffusion flame in axisymmetric jet
The kinetic theory of turbulent flow was employed to study the mixing limited combustion of hydrogen in axisymmetric jets. The integro-differential equations in two spatial and three velocity coordinates describing the combustion were reduced to a set of hyperbolic partial differential equations in the two spatial coordinates by a binodal approximation. The MacCormick's finite difference method was then employed for solution. The flame length was longer than that predicted by the flame-sheet analysis, and was found to be in general agreement with a recent experimental result. Increase of the turbulence energy and scale resulted in an enhancement of the combustion rate and, hence, in a shorter flame length. Details of the numerical method as well as of the physical findings are discussed
Theory of ferromagnetism in (A,Mn)B semiconductors
A brief review of theory of ferromagnetism of dilute magnetic semiconductors
of the form (A,Mn)B based on the double exchange model is first given. A
systematic investigation of the phenomena extending the current theory is
outlined. We begin with an investigation of the regions of instability of the
nonmagnetic towards the ferromagnetic state of a system of Mn-atoms doped in
AB-type semiconductor. A self-consistent many-body theory of the ferromagnetic
state is then developed, going beyond the mean field approaches by including
fluctuations of the Mn-spins and the itinerant hole-gas. A functional theory
suitable for computation of system properties such as Curie temperature as a
function of hole and the Mn-concentration, spin-current, etc. is formulated.Comment: 16 page
Dimerized and trimerized phases for spin-2 Bosons in a one-dimensional optical lattice
We study the phase diagram for spin-2 bosons loaded in a one-dimensional
optical lattice. By using non-Abelian density matrix renormalization group
(DMRG) method we identify three possible phases: ferromagnetic, dimerized, and
trimerized phases. We sketch the phase boundaries based on DMRG. We illustrate
two methods for identifying the phases. The first method is based on the
spin-spin correlation function while in the second method one observes the
excitation gap as a dimerization or a trimerization superlattice is imposed.
The advantage of the second method is that it can also be easily implemented in
experiments. By using the scattering lengths in the literature we estimate that
Rb, Na, and Rb be ferromagnetic, dimerized, and trimerized
respectively.Comment: 4 pages, 3 figures. Add acknowledgemen
Resiliently evolving supply-demand networks
Peer reviewedPublisher PD
Induced Lorentz- and CPT-violating Chern-Simons term in QED: Fock-Schwinger proper time method
Using the Fock-Schwinger proper time method, we calculate the induced
Chern-Simons term arising from the Lorentz- and CPT-violating sector of quantum
electrodynamics with a term. Our
result to all orders in coincides with a recent linear-in- calculation
by Chaichian et al. [hep-th/0010129 v2]. The coincidence was pointed out by
Chung [Phys. Lett. {\bf B461} (1999) 138] and P\'{e}rez-Victoria [Phys. Rev.
Lett. {\bf 83} (1999) 2518] in the standard Feynman diagram calculation with
the nonperturbative-in- propagator.Comment: 11 pages, no figur
Large-scale radio continuum properties of 19 Virgo cluster galaxies The influence of tidal interactions, ram pressure stripping, and accreting gas envelopes
Deep scaled array VLA 20 and 6cm observations including polarization of 19
Virgo spirals are presented. This sample contains 6 galaxies with a global
minimum of 20cm polarized emission at the receding side of the galactic disk
and quadrupolar type large-scale magnetic fields. In the new sample no
additional case of a ram-pressure stripped spiral galaxy with an asymmetric
ridge of polarized radio continuum emission was found. In the absence of a
close companion, a truncated HI disk, together with a ridge of polarized radio
continuum emission at the outer edge of the HI disk, is a signpost of ram
pressure stripping. 6 out of the 19 observed galaxies display asymmetric 6cm
polarized emission distributions. Three galaxies belong to tidally interacting
pairs, two galaxies host huge accreting HI envelopes, and one galaxy had a
recent minor merger. Tidal interactions and accreting gas envelopes can lead to
compression and shear motions which enhance the polarized radio continuum
emission. In addition, galaxies with low average star formation rate per unit
area have a low average degree of polarization. Shear or compression motions
can enhance the degree of polarization. The average degree of polarization of
tidally interacting galaxies is generally lower than expected for a given
rotation velocity and star formation activity. This low average degree of
polarization is at least partly due to the absence of polarized emission from
the thin disk. Ram pressure stripping can decrease whereas tidal interactions
most frequently decreases the average degree of polarization of Virgo spiral
galaxies. We found that moderate active ram pressure stripping has no influence
on the spectral index, but enhances the global radio continuum emission with
respect to the FIR emission, while an accreting gas envelope can but not
necessarily enhances the radio continuum emission with respect to the FIR
emission.Comment: 37 pages, 26 figures, accepted for publication in A&
Quantum Critical Spin-2 Chain with Emergent SU(3) Symmetry
We study the quantum critical phase of a SU(2) symmetric spin-2 chain
obtained from spin-2 bosons in a one-dimensional lattice. We obtain the scaling
of the entanglement entropy and finite-size energies by exact diagonalization
and density-matrix renormalization group methods. From the numerical results of
the energy spectrum, central charge, and scaling dimension we identify the
conformal field theory describing the whole critical phase to be the SU(3)
Wess-Zumino-Witten model. We find that while in the whole critical phase the
Hamiltonian is only SU(2) invariant, there is an emergent SU(3) symmetry in the
thermodynamic limit
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