1,400 research outputs found
Anomalous Angular Dependence of the Dynamic Structure Factor near Bragg Reflections: Graphite
The electron energy-loss function of graphite is studied for momentum
transfers q beyond the first Brillouin zone. We find that near Bragg
reflections the spectra can change drastically for very small variations in q.
The effect is investigated by means of first principle calculations in the
random phase approximation and confirmed by inelastic x-ray scattering
measurements of the dynamic structure factor S(q,\omega). We demonstrate that
this effect is governed by crystal local field effects and the stacking of
graphite. It is traced back to a strong coupling between excitations at small
and large momentum transfers
Chromium at High Pressures: Weak Coupling and Strong Fluctuations in an Itinerant Antiferromagnet
The spin- and charge-density-wave order parameters of the itinerant
antiferromagnet chromium are measured directly with non-resonant x-ray
diffraction as the system is driven towards its quantum critical point with
high pressure using a diamond anvil cell. The exponential decrease of the spin
and charge diffraction intensities with pressure confirms the harmonic scaling
of spin and charge, while the evolution of the incommensurate ordering vector
provides important insight into the difference between pressure and chemical
doping as means of driving quantum phase transitions. Measurement of the charge
density wave over more than two orders of magnitude of diffraction intensity
provides the clearest demonstration to date of a weakly-coupled, BCS-like
ground state. Evidence for the coexistence of this weakly-coupled ground state
with high-energy excitations and pseudogap formation above the ordering
temperature in chromium, the charge-ordered perovskite manganites, and the blue
bronzes, among other such systems, raises fundamental questions about the
distinctions between weak and strong coupling.Comment: 11 pages, 9 figures (8 in color
Experimental demonstration of quantum teleportation of a squeezed state
Quantum teleportation of a squeezed state is demonstrated experimentally. Due
to some inevitable losses in experiments, a squeezed vacuum necessarily becomes
a mixed state which is no longer a minimum uncertainty state. We establish an
operational method of evaluation for quantum teleportation of such a state
using fidelity, and discuss the classical limit for the state. The measured
fidelity for the input state is 0.85 0.05 which is higher than the
classical case of 0.730.04. We also verify that the teleportation process
operates properly for the nonclassical state input and its squeezed variance is
certainly transferred through the process. We observe the smaller variance of
the teleported squeezed state than that for the vacuum state input.Comment: 7 pages, 1 new figure, comments adde
Detection of abundant solid methanol toward young low mass stars
We present detections of the absorption band at 3.53 micron due to solid
methanol toward three low-mass young stellar objects located in the Serpens and
Chameleon molecular cloud complexes. The sources were observed as part of a
large spectroscopic survey of ~40 protostars. This is the first detection of
solid methanol in the vicinity of low mass (M <1 Msol) young stars and shows
that the formation of methanol does not depend on the proximity of massive
young stars. The abundances of solid methanol compared to water ice for the
three sources are in the range 15-25% which is comparable to those for the most
methanol-rich massive sources known. The presence of abundant methanol in the
circumstellar environment of some low mass young stars has important
consequences for the formation scenarios of methanol and more complex organic
species near young solar-type stars.Comment: Accepted for publication in A&A letter
Criteria for the experimental observation of multi-dimensional optical solitons in saturable media
Criteria for experimental observation of multi-dimensional optical solitons
in media with saturable refractive nonlinearities are developed. The criteria
are applied to actual material parameters (characterizing the cubic
self-focusing and quintic self-defocusing nonlinearities, two-photon loss, and
optical-damage threshold) for various glasses. This way, we identify operation
windows for soliton formation in these glasses. It is found that two-photon
absorption sets stringent limits on the windows. We conclude that, while a
well-defined window of parameters exists for two-dimensional solitons (spatial
or spatiotemporal), for their three-dimensional spatiotemporal counterparts
such a window \emph{does not} exist, due to the nonlinear loss in glasses.Comment: 8 pages, to appear in Phys. Rev.
Inelastic X-Ray Scattering Study of Exciton Properties in an Organic Molecular crystal
Excitons in a complex organic molecular crystal were studied by inelastic
x-ray scattering (IXS) for the first time. The dynamic dielectric response
function is measured over a large momentum transfer region, from which an
exciton dispersion of 130 meV is observed. Semiempirical quantum chemical
calculations reproduce well the momentum dependence of the measured dynamic
dielectric responses, and thus unambiguously indicate that the lowest Frenkel
exciton is confined within a fraction of the complex molecule. Our results
demonstrate that IXS is a powerful tool for studying excitons in complex
organic molecular systems. Besides the energy position, the IXS spectra provide
a stringent test on the validity of the theoretically calculated exciton wave
functions.Comment: 4 pages, 4 figure
EVALUATION OF XYLEM MATURTATION PROCESS AND EFFECTS OF RADIAL GROWTH RATE ON CELL MORPHOLOGIES IN WOOD OF BALSA (OCHROMA PRYAMIDALE) TREES
The radial variations of cell morphologies (cell lengths, vessel diameter, vessel frequency and cell wall thickness of wood fibers) were investigated for 7-year-old Ochroma pyramidale trees planted in East Java, Indonesia by developing the linear or nonlinear mixed-effects models. In addition, xylem maturation process based on the cell morphologies and effects of radial growth rate on cell morphologies were discussed. The mean values of cell morphology were as follow: vessel element length 0.59 mm, fiber length 2.16 mm, vessel diameter 221 µm, and fiber wall thickness 1.03 µm. Radial variations of cell length and vessel diameter were well explained by Michaelis-Menten equation: values increased from pith to certain position and then it became almost stable. Vessel frequency, wood fiber diameter, and wood fiber wall thickness was expressed by the formula of logarithmic formula, quadratic formula, and linear formula, respectively. Variance component ration of category was 66.8%, 46.1%, 31.4%, 1.5%, and 33.7% for vessel element length, wood fiber length, vessel diameter, vessel frequency, and wood fiber wall thickness, respectively, suggesting that many cell morphologies influenced by the radial growth rate. Smaller values of mean absolute error obtained in the models in relation to distance from pith were found in all cell morphologies, except for vessel frequency and wood fiber diameter. Thus, xylem maturation of this species depended on diameter growth rather than cambial age. Boundary of core wood and outer wood was 5 to 10 cm from pith in which increasing ratio of cell length reached less than 0.3%. Core wood was characterized as lower wood density and mechanical properties with shorter cell lengths and thinner wood fiber walls, whereas outer wood was characterized as higher wood density and mechanical properties with longer cell length and thicker wood fiber walls
Noncommutative U(1) Instantons in Eight Dimensional Yang-Mills Theory
We study the noncommutative version of the extended ADHM construction in the
eight dimensional U(1) Yang-Mills theory. This construction gives rise to the
solutions of the BPS equations in the Yang-Mills theory, and these solutions
preserve at least 3/16 of supersymmetries. In a wide subspace of the extended
ADHM data, we show that the integer which appears in the extended ADHM
construction should be interpreted as the -brane charge rather than the
-brane charge by explicitly calculating the topological charges in the case
that the noncommutativity parameter is anti-self-dual. We also find the
relationship with the solution generating technique and show that the integer
can be interpreted as the charge of the -brane bound to the -brane
with the -field in the case that the noncommutativity parameter is
self-dual.Comment: 22 page
Water formation at low temperatures by surface O2 hydrogenation I: characterization of ice penetration
Water is the main component of interstellar ice mantles, is abundant in the
solar system and is a crucial ingredient for life. The formation of this
molecule in the interstellar medium cannot be explained by gas-phase chemistry
only and its surface hydrogenation formation routes at low temperatures (O, O2,
O3 channels) are still unclear and most likely incomplete. In a previous paper
we discussed an unexpected zeroth-order H2O production behavior in O2 ice
hydrogenation experiments compared to the first-order H2CO and CH3OH production
behavior found in former studies on hydrogenation of CO ice. In this paper we
experimentally investigate in detail how the structure of O2 ice leads to this
rare behavior in reaction order and production yield. In our experiments H
atoms are added to a thick O2 ice under fully controlled conditions, while the
changes are followed by means of reflection absorption infrared spectroscopy
(RAIRS). The H-atom penetration mechanism is systematically studied by varying
the temperature, thickness and structure of the O2 ice. We conclude that the
competition between reaction and diffusion of the H atoms into the O2 ice
explains the unexpected H2O and H2O2 formation behavior. In addition, we show
that the proposed O2 hydrogenation scheme is incomplete, suggesting that
additional surface reactions should be considered. Indeed, the detection of
newly formed O3 in the ice upon H-atom exposure proves that the O2 channel is
not an isolated route. Furthermore, the addition of H2 molecules is found not
to have a measurable effect on the O2 reaction channel.Comment: 1 page, 1 figur
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