294 research outputs found
Relativistic J-matrix method
The relativistic version of the J-matrix method for a scattering problem on
the potential vanishing faster than the Coulomb one is formulated. As in the
non-relativistic case it leads to a finite algebraic eigenvalue problem. The
derived expression for the tangent of phase shift is simply related to the
non-relativistic case formula and gives the latter as a limit case. It is due
to the fact that the used basis set satisfies the ``kinetic balance
condition''.Comment: 21 pages, RevTeX, accepted for publication in Phys. Rev.
Quantum Spin Excitations through the metal-to-insulator crossover in
We use inelastic neutron scattering to study the temperature dependence of
the spin excitations of a detwinned superconducting YBaCuO
( K). In contrast to earlier work on YBaCuO (
K), where the prominent features in the magnetic spectra consist of a sharp
collective magnetic excitation termed ``resonance'' and a large
( meV) superconducting spin gap, we find that the spin
excitations in YBaCuO are gapless and have a much broader
resonance. Our detailed mapping of magnetic scattering along the
/-axis directions at different energies reveals that spin
excitations are unisotropic and consistent with the ``hourglass''-like
dispersion along the -axis direction near the resonance, but they are
isotropic at lower energies. Since a fundamental change in the low-temperature
normal state of YBaCuO when superconductivity is suppressed
takes place at with a metal-to-insulator crossover (MIC), where the
ground state transforms from a metallic to an insulating-like phase, our
results suggest a clear connection between the large change in spin excitations
and the MIC. The resonance therefore is a fundamental feature of metallic
ground state superconductors and a consequence of high- superconductivity.Comment: 9 pages, 7 figures, accepted by Phys. Rev.
Incommensurate Spin Ordering and Fluctuations in underdoped La_{2-x}Ba_{x}CuO_{4}
Using neutron scattering techniques, we have studied incommensurate spin
ordering as well as low energy spin dynamics in single crystal underdoped \LBCO
with x0.095 and 0.08; high temperature superconductors with T 27
K and 29 K respectively. Static two dimensional incommensurate magnetic order
appears below T=39.5 0.3 K in \LBCO (x=0.095) and a similar
temperature for x=0.08 within the low temperature tetragonal phase. The spin
order is unaffected by either the onset of superconductivity or the application
of magnetic fields of up to 7 Tesla applied along the c-axis in the x=0.095
sample. Such magnetic field {\it independent} behaviour is in marked contrast
with the field induced enhancement of the staggered magnetisation observed in
the related \LSCO system, indicating this phenomenon is not a universal
property of cuprate superconductors. Surprisingly, we find that
incommensurability is only weakly dependent on doping relative to
\LSCO. Dispersive excitations in \LBCO (x=0.095) at the same incommensurate
wavevector persist up to at least 60 K. The dynamical spin susceptibility of
the low energy spin excitations saturates below \tc, in a similar manner to
that seen in the superconducting state of LaCuO.Comment: 9 pages, 7 figures, submitted to PRB, figures update
Efisiensi Pemasaran Jagung di Kelurahan Kalampangan Kecamatan Sabangau Kota Palangka Raya
The aim of this research is to analyze marketing channel, marketing institution, marketing function, marketing margin, marketing cost, marketing profit, corn farmer's share, marketing efficiency of maize in various channel in Kalampangan village. The results showed that: (1) marketing of corn in Kalampangan village there are two kinds of channels, where channel I involves four institutions namely: farmers, merchants village, retailers, and consumers. While channel II involves two institutions only, namely, farmers as traders and consumers. Maize's marketing functions are: sales function, purchasing function, storage function, transport function and facility function. (2) From calcution result at Marketing Channel I, total marketing margin of maize in Kalampangan Villge is Rp. 3.860,-/kg, total cost of corn marketing is Rp. 310,-/kg, total profit of corn marketing is Rp. 3.550,-/kg and the result obtained by corn farmer are 58,04%. From calculating result at Marketing Channel II, total margin of maize in Kalampangan Village is Rp. 2.160,-/kg, total cost of corn marketing is Rp. 310,-/kg, total profit of corn marketing is Rp. 1.850,-/kg and the result obtained by corn farmer are 71,20%. (3) marketing efficiency at Marketing Channel I equal to 41.96%, and on Marketing Channel II is 28,80%. Marketing efficiency value in Channel I is lower than marketing efficiency II, it is considered more efficient marketing Channel II
J-matrix method of scattering in any L2 basis
The restriction imposed on the J-matrix method of using specific L2 bases is
lifted without compromising any of the advantages that it offers. This opens
the door to a wider range of application of the method to physical problems
beyond the restrictive SO(2,1) dynamical symmetry. The numerical scheme
developed to achieve this objective projects the J-matrix formalism in terms of
the eigenvalues of a finite Hamiltonian matrix and its submatrices in any
convenient L2 basis. Numerical stability and convergence of the original
analytic J-matrix method is still maintained in the proposed scheme, which can
be applied to multi-channel nonrelativistic as well as relativistic scattering
problems
Spatio-temporal Signatures of Elasto-inertial Turbulence in Viscoelastic Planar Jets
The interplay between viscoelasticity and inertia in dilute polymer solutions
at high deformation rates can result in inertio-elastic instabilities. The
nonlinear evolution of these instabilities generates a state of turbulence with
significantly different spatio-temporal features compared to Newtonian
turbulence, termed elasto-inertial turbulence (EIT). We explore EIT by studying
the dynamics of a submerged planar jet of a dilute aqueous polymer solution
injected into a quiescent tank of water using a combination of schlieren
imaging and laser Doppler velocimetry (LDV). We show how fluid elasticity has a
nonmonotonic effect on the jet stability depending on its magnitude, creating
two distinct regimes in which elastic effects can either destabilize or
stabilize the jet. In agreement with linear stability analyses of viscoelastic
jets, an inertio-elastic shear-layer instability emerges near the edge of the
jet for small levels of elasticity, independent of bulk undulations in the
fluid column. The growth of this disturbance mode destabilizes the flow,
resulting in a turbulence transition at lower Reynolds numbers and closer to
the nozzle compared to the conditions required for the transition to turbulence
in a Newtonian jet. Increasing the fluid elasticity merges the shear-layer
instability into a bulk instability of the jet column. In this regime, elastic
tensile stresses generated in the shear layer act as an "elastic membrane'"
that partially stabilizes the flow, retarding the transition to turbulence to
higher levels of inertia and greater distances from the nozzle. In the fully
turbulent state far from the nozzle, planar viscoelastic jets exhibit unique
spatio-temporal features associated with EIT. The time-averaged angle of jet
spreading, an Eulerian measure of the degree of entrainment, and the centerline
velocity of the jets both evolve self-similarly with distance from the nozzle.
LDV measurements of the velocity fluctuations at the jet centerline reveal a
frequency spectrum characterized by a power-law exponent, different from
the well-known power-law exponent characteristic of Newtonian
turbulence. We show that the higher spectral energy of long wavelength modes in
the EIT state results in coherent structures that are elongated in the
streamwise direction, consistent with the suppression of streamwise vortices by
elastic stresses
Spin Waves in the Ferromagnetic Ground State of the Kagome Staircase System Co3V2O8
Inelastic neutron scattering measurements were performed on single crystal
Co3V2O8 wherein magnetic cobalt ions reside on distinct spine and cross-tie
sites within kagome staircase planes. This system displays a rich magnetic
phase diagram which culminates in a ferromagnetic ground state below Tc~6 K. We
have studied the low-lying magnetic excitations in this phase within the kagome
plane. Despite the complexity of the system at higher temperatures, linear
spin-wave theory describes most of the quantitative detail of the inelastic
neutron measurements. Our results show two spin-wave branches, the higher
energy of which displays finite spin-wave lifetimes well below Tc, and
negligible magnetic exchange coupling between Co moments on the spine sites.Comment: 4 pages and 4 figure
Scattering phase shift for relativistic exponential-type separable potentials
The J-matrix method of scattering is used to obtain analytic expressions for
the phase shift of two classes of relativistic exponential-type separable
potentials whose radial component is either of the general form r^(n-1)exp(-r)
or r^(2n)exp(-r^2), where n = 0, 1, or 2. The rank of these separable
potentials is n + 1. The nonrelativistic limit is obtained and shown to be
identical to the nonrelativistic phase shift. An exact numerical evaluation for
higher order potentials (n > 2) can also be obtained in a simple way as
illustrated for the case n = 3.Comment: Accepted for publication in J. Phys. A, to appear in January 2002.
Replaced with a more portable PDF versio
Gapped Excitations in the High-Pressure Antiferromagnetic Phase of URuSi
We report a neutron scattering study of the magnetic excitation spectrum in
each of the three temperature and pressure driven phases of URuSi. We
find qualitatively similar excitations throughout the (H0L) scattering plane in
the hidden order and large moment phases, with no changes in the
-widths of the excitations at the = (1.407,0,0) and =
(1,0,0) points, within our experimental resolution. There is, however, an
increase in the gap at the point from 4.2(2) meV to 5.5(3) meV,
consistent with other indicators of enhanced antiferromagnetism under pressure.Comment: 5 pages, 3 figures, 1 tabl
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