24,261 research outputs found
Mn L edge resonant x-ray scattering in manganites: Influence of the magnetic state
We present an analysis of the dependence of the resonant orbital order and
magnetic scattering spectra on the spin configuration. We consider an arbitrary
spin direction with respect to the local crystal field axis, thus lowering
significantly the local symmetry. To evaluate the atomic scattering in this
case, we generalized the Hannon-Trammel formula and implemented it inside the
framework of atomic multiplet calculations in a crystal field. For an
illustration, we calculate the magnetic and orbital scattering in the CE phase
of \lsmo in the cases when the spins are aligned with the crystal lattice
vector (or equivalently ) and when they are rotated in the
-plane by 45 with respect to this axis. Magnetic spectra differ
for the two cases. For the orbital scattering, we show that for the former
configuration there is a non negligible ()
scattering component, which vanishes in the 45 case, while the () components are similar in the two cases. From the
consideration of two 90 spin canted structures, we conclude there is a
significant dependence of the orbital scattering spectra on the spin
arrangement. Recent experiments detected a sudden decrease of the orbital
scattering intensity upon increasing the temperature above the N\' eel
temperature in \lsmo. We discuss this behavior considering the effect of
different types of misorientations of the spins on the orbital scattering
spectrum.Comment: 8 figures. In the revised version, we added a note, a reference, and
a few minor changes in Figure 1 and the text. Accepted in Physical Review
Decuplet baryon magnetic moments in a QCD-based quark model beyond quenched approximation
We study the decuplet baryon magnetic moments in a QCD-based quark model
beyond quenched approximation. Our approach for unquenching the theory is based
on the heavy baryon perturbation theory in which the axial couplings for baryon
- meson and the meson-meson-photon couplings from the chiral perturbation
theory are used together with the QM moment couplings. It also involves the
introduction of a form factor characterizing the structure of baryons
considered as composite particles. Using the parameters obtained from fitting
the octet baryon magnetic moments, we predict the decuplet baryon magnetic
moments. The magnetic moment is found to be in good agreement with
experiment: is predicted to be compared to the
experimental result of (2.02 0.05) .Comment: 19 pages, 2 figure
Analytical description of ballistic spin currents and torques in magnetic tunnel junctions
In this work we demonstrate explicit analytical expressions for both charge
and spin currents which constitute the 2x2 spinor in magnetic tunnel junctions
with noncollinear magnetizations under applied voltage. The calculations have
been performed within the free electron model in the framework of the Keldysh
formalism and WKB approximation. We demonstrate that spin/charge currents and
spin transfer torques are all explicitly expressed through only three
irreducible quantities, without further approximations. The conditions and
mechanisms of deviation from the conventional sine angular dependence of both
spin currents and torques are shown and discussed. It is shown in the thick
barrier approximation that all tunneling transport quantities can be expressed
in an extremely simplified form via Slonczewski spin polarizations and our
effective spin averaged interfacial transmission probabilities and effective
out-of-plane polarizations at both interfaces. It is proven that the latter
plays a key role in the emergence of perpendicular spin torque as well as in
the angular dependence character of all spin and charge transport considered.
It is demonstrated directly also that for any applied voltage, the parallel
component of spin current at the FM/I interface is expressed via collinear
longitudinal spin current components. Finally, spin transfer torque behavior is
analyzed in a view of transverse characteristic length scales for spin
transport.Comment: 10 pages, 6 figure
The Mid-infrared Fine-structure Lines of Neon as an Indicator of Star For mation Rate in Galaxies
The fine-structure lines of singly ([Ne II] 12.8 micron) and doubly ([Ne III]
15.6 micron) ionized neon are among the most prominent features in the
mid-infrared spectra of star-forming regions, and have the potential to be a
powerful new indicator of the star formation rate in galaxies. Using a sample
of star-forming galaxies with measurements of the fine-structure lines
available from the literature, we show that the sum of the [Ne II] and [Ne III]
luminosities obeys a tight, linear correlation with the total infrared
luminosity, over 5 orders of magnitude in luminosity. We discuss the formation
of the lines and their relation with the Lyman continuum luminosity. A simple
calibration between star formation rate and the [Ne II]+[Ne III] luminosity is
presented.Comment: To appear in ApJ. 8 page
Robust ecological pattern formation induced by demographic noise
We demonstrate that demographic noise can induce persistent spatial pattern
formation and temporal oscillations in the Levin-Segel predator-prey model for
plankton-herbivore population dynamics. Although the model exhibits a Turing
instability in mean field theory, demographic noise greatly enlarges the region
of parameter space where pattern formation occurs. To distinguish between
patterns generated by fluctuations and those present at the mean field level in
real ecosystems, we calculate the power spectrum in the noise-driven case and
predict the presence of fat tails not present in the mean field case. These
results may account for the prevalence of large-scale ecological patterns,
beyond that expected from traditional non-stochastic approaches.Comment: Revised version. Supporting simulation at:
http://guava.physics.uiuc.edu/~tom/Netlogo
The "quasi-stable" lipid shelled microbubble in response to consecutive ultrasound pulses
Controlled microbubble stability upon exposure to consecutive ultrasound exposures is important for increased sensitivity in contrast enhanced ultrasound diagnostics and manipulation for localised drug release. An ultra high-speed camera operating at 13 × 10 6 frames per second is used to show that a physical instability in the encapsulating lipid shell can be promoted by ultrasound, causing loss of shell material that depends on the characteristics of the microbubble motion. This leads to well characterized disruption, and microbubbles follow an irreversible trajectory through the resonance peak, causing the evolution of specific microbubble spectral signatures. © 2012 American Institute of Physics
A site-specific standard for comparing dynamic solar ultraviolet protection characteristics of established tree canopies
A standardised procedure for making fair and comparable assessments of the ultraviolet protection of an established tree canopy that takes into account canopy movement and the changing position of the sun is presented for use by government, planning, and environmental health authorities. The technique utilises video image capture and replaces the need for measurement by ultraviolet radiometers for surveying shade quality characteristics of trees growing in public parks, playgrounds and urban settings. The technique improves upon tree shade assessments that may be based upon single measurements of the ultraviolet irradiance observed from a fixed point of view. The presented technique demonstrates how intelligent shade audits can be conducted without the need for specialist equipment, enabling the calculation of the Shade Protection Index (SPI) and Ultraviolet Protection Factor (UPF) for any discreet time interval and over a full calendar year
Electromagnetic Moments of the Baryon Decuplet
We compute the leading contributions to the magnetic dipole and electric
quadrupole moments of the baryon decuplet in chiral perturbation theory. The
measured value for the magnetic moment of the is used to determine
the local counterterm for the magnetic moments. We compare the chiral
perturbation theory predictions for the magnetic moments of the decuplet with
those of the baryon octet and find reasonable agreement with the predictions of
the large-- limit of QCD. The leading contribution to the quadrupole
moment of the and other members of the decuplet comes from one--loop
graphs. The pionic contribution is shown to be proportional to (and so
will not contribute to the quadrupole moment of nuclei), while the
contribution from kaons has both isovector and isoscalar components. The chiral
logarithmic enhancement of both pion and kaon loops has a coefficient that
vanishes in the limit. The third allowed moment, the magnetic octupole,
is shown to be dominated by a local counterterm with corrections arising at two
loops. We briefly mention the strange counterparts of these moments.Comment: Uses harvmac.tex, 15 pages with 3 PostScript figures packed using
uufiles. UCSD/PTH 93-22, QUSTH-93-05, Duke-TH-93-5
Jahn-Teller Spectral Fingerprint in Molecular Photoemission: C60
The h_u hole spectral intensity for C60 -> C60+ molecular photoemission is
calculated at finite temperature by a parameter-free Lanczos diagonalization of
the electron-vibration Hamiltonian, including the full 8 H_g, 6 G_g, and 2 A_g
mode couplings. The computed spectrum at 800 K is in striking agreement with
gas-phase data. The energy separation of the first main shoulder from the main
photoemission peak, 230 meV in C60, is shown to measure directly and rather
generally the strength of the final-state Jahn-Teller coupling.Comment: 5 pages, 3 figure
Splitting The Gluon?
In the strongly correlated environment of high-temperature cuprate
superconductors, the spin and charge degrees of freedom of an electron seem to
separate from each other. A similar phenomenon may be present in the strong
coupling phase of Yang-Mills theories, where a separation between the color
charge and the spin of a gluon could play a role in a mass gap formation. Here
we study the phase structure of a decomposed SU(2) Yang-Mills theory in a mean
field approximation, by inspecting quantum fluctuations in the condensate which
is formed by the color charge component of the gluon field. Our results suggest
that the decomposed theory has an involved phase structure. In particular,
there appears to be a phase which is quite reminiscent of the superconducting
phase in cuprates. We also find evidence that this phase is separated from the
asymptotically free theory by an intermediate pseudogap phase.Comment: Improved discussion of magnetic nature of phases; removed
unsubstantiated speculation about color confinemen
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