3,322 research outputs found
Switching Exciton Pulses Through Conical Intersections
Exciton pulses transport excitation and entanglement adiabatically through
Rydberg aggregates, assemblies of highly excited light atoms, which are set
into directed motion by resonant dipole-dipole interaction. Here, we
demonstrate the coherent splitting of such pulses as well as the spatial
segregation of electronic excitation and atomic motion. Both mechanisms exploit
local nonadiabatic effects at a conical intersection, turning them from a
decoherence source into an asset. The intersection provides a sensitive knob
controlling the propagation direction and coherence properties of exciton
pulses. The fundamental ideas discussed here have general implications for
excitons on a dynamic network.Comment: Letter with 4 pages and 4 figures. Supplemental material with 4 pages
and 4 figure
Approaches and tools to manipulate the carbonate chemistry
Although the chemistry of ocean acidifi cation is very well understood (see chapter 1), its impact on marine organisms and ecosystems remains poorly known. The biological response to ocean acidifi cation is a recent field
of research, the fi rst purposeful experiments have only been carried out as late as the 1980s (Agegian, 1985)
and most were not performed until the late 1990s. The potentially dire consequences of ocean acidifi cation
have attracted the interest of scientists and students with a limited knowledge of the carbonate chemistry and
its experimental manipulation. Perturbation experiments are one of the key approaches used to investigate
the biological response to elevated p(CO2). Such experiments are based on measurements of physiological or
metabolic processes in organisms and communities exposed to seawater with normal and altered carbonate chemistry. The basics of the carbonate chemistry must be understood to perform meaningful CO2 perturbation experiments (see chapter 1). Briefl y, the marine carbonate system considers
€ CO2 ∗(aq) [the sum of CO2 and H2CO3], € HCO3 −, € CO3 2−,
H+, € OH− , and several weak acid-base systems of which borate-boric acid (€ B(OH)4 − , B(OH)3) is the most
important. As discussed by Dickson (chapter 1), if two components of the carbonate chemistry are known, all
the other components can be calculated for seawater with typical nutrient concentrations at given temperature,
salinity, and pressure. One of the possible pairs is of particular interest because both components can be
measured with precision, accuracy, and are conservative in the sense that their concentrations do not change
with temperature or pressure. Dissolved inorganic carbon (DIC) is the sum of all dissolved inorganic carbon
species while total alkalinity (AT) equals € [HCO3 − ] + 2
€ [CO3 2− ] + € [B(OH)4 − ] + € [OH− ] - [H+] + minor components, and refl ects the excess of proton acceptors over proton donors with respect to a zero level of protons (see chapter 1 for a detailed defi nition). AT is determined by the titration of seawater with a strong acid and thus can also be regarded as a measure of the buffering capacity. Any changes in any single component of the carbonate system will lead to changes in several, if not all, other components. In other words, it is not possible to vary a single component of the carbonate system while keeping all other components constant. This interdependency
in the carbonate system is important to consider when performing CO2 perturbation experiments.
To adjust seawater to different p(CO2) levels, the carbonate system can be manipulated in various ways that
usually involve changes in AT or DIC. The goal of this chapter is (1) to examine the benefi ts and drawbacks of
various manipulation methods used to date and (2) to provide a simple software package to assist the design
of perturbation experiments
Dynamics of photo-activated Coulomb complexes
Intense light with frequencies above typical atomic or molecular ionization
potentials as provided by free-electron lasers couples many photons into
extended targets such as clusters and biomolecules. This implies, in contrast
to traditional multi-photon ionization, multiple single-photon absorption.
Thereby, many electrons are removed from their bound states and either released
or trapped if the target charge has become sufficiently large. We develop a
simple model for this photo activation to study electron migration and
interaction. It satisfies scaling relations which help to relate quite
different scenarios. To understand this type of multi-electron dynamics on very
short time scales is vital for assessing the radiation damage inflicted by that
type of radiation and to pave the way for coherent diffraction imaging of
single molecules.Comment: 14 pages, 6 figures, 1 tabl
Magnetotransport in Sr3PbO antiperovskite with three-dimensional massive Dirac electrons
Novel topological phenomena are anticipated for three-dimensional (3D) Dirac
electrons. The magnetotransport properties of cubic
antiperovskite, theoretically proposed to be a 3D massive Dirac electron
system, are studied. The measurements of Shubnikov-de Haas oscillations and
Hall resistivity indicate the presence of a low density ( ) of holes with an extremely small cyclotron mass of
0.01-0.06. The magnetoresistance is linear in
magnetic field with the magnitude independent of temperature. These results
are fully consistent with the presence of 3D massive Dirac electrons in . The chemical flexibility of the antiperovskites and our findings
in the family member, , point to their potential as a model
system in which to explore exotic topological phases
Multiple ionization of neon by soft X-rays at ultrahigh intensity
At the free-electron laser FLASH, multiple ionization of neon atoms was
quantitatively investigated at 93.0 eV and 90.5 eV photon energy. For ion
charge states up to 6+, we compare the respective absolute photoionization
yields with results from a minimal model and an elaborate description. Both
approaches are based on rate equations and take into acccout a Gaussian spatial
intensity distribution of the laser beam. From the comparison we conclude, that
photoionization up to a charge of 5+ can be described by the minimal model. For
higher charges, the experimental ionization yields systematically exceed the
elaborate rate based prediction.Comment: 10 pages, 3 figure
Comment on: `Pipe Network Model for Scaling of Dynamic Interfaces in Porous Media'
We argue that a proposed exponent identity [Phys. Rev. Lett 85, 1238 (2000)]
for interface roughening in spontaneous imbibition is wrong. It rests on the
assumption that the fluctuations are controlled by a single time scale, but
liquid conservation imposes two distinct time scales.Comment: 1 page, to appear in Phys. Rev. Let
Inelastic semiclassical Coulomb scattering
We present a semiclassical S-matrix study of inelastic collinear
electron-hydrogen scattering. A simple way to extract all necessary information
from the deflection function alone without having to compute the stability
matrix is described. This includes the determination of the relevant Maslov
indices. Results of singlet and triplet cross sections for excitation and
ionization are reported. The different levels of approximation -- classical,
semiclassical, and uniform semiclassical -- are compared among each other and
to the full quantum result.Comment: 9 figure
Molecular effects in the ionization of N, O and F by intense laser fields
In this paper we study the response in time of N, O and F to
laser pulses having a wavelength of 390nm. We find single ionization
suppression in O and its absence in F, in accordance with experimental
results at nm. Within our framework of time-dependent density
functional theory we are able to explain deviations from the predictions of
Intense-Field Many-Body -Matrix Theory (IMST). We confirm the connection of
ionization suppression with destructive interference of outgoing electron waves
from the ionized electron orbital. However, the prediction of ionization
suppression, justified within the IMST approach through the symmetry of the
highest occupied molecular orbital (HOMO), is not reliable since it turns out
that, e.g. in the case of F, the electronic response to the laser pulse is
rather complicated and does not lead to dominant depletion of the HOMO.
Therefore, the symmetry of the HOMO is not sufficient to predict ionization
suppression. However, at least for F, the symmetry of the dominantly
ionized orbital is consistent with the non-suppression of ionization.Comment: 19 pages, 5 figure
Semiclassical initial value calculations of collinear helium atom
Semiclassical calculations using the Herman-Kluk initial value treatment are
performed to determine energy eigenvalues of bound and resonance states of the
collinear helium atom. Both the configuration (where the classical motion
is fully chaotic) and the configuration (where the classical dynamics is
nearly integrable) are treated. The classical motion is regularized to remove
singularities that occur when the electrons collide with the nucleus. Very good
agreement is obtained with quantum energies for bound and resonance states
calculated by the complex rotation method.Comment: 24 pages, 3 figures. Submitted to J. Phys.
On the recombination in high-order harmonic generation in molecules
We show that the dependence of high-order harmonic generation (HHG) on the
molecular orientation can be understood within a theoretical treatment that
does not involve the strong field of the laser. The results for H_2 show
excellent agreement with time-dependent strong field calculations for model
molecules, and this motivates a prediction for the orientation dependence of
HHG from the N_2 3s_g valence orbital. For both molecules, we find that the
polarization of recombination photons is influenced by the molecular
orientation. The variations are particularly pronounced for the N_2 valence
orbital, which can be explained by the presence of atomic p-orbitals.Comment: 6 pages 7 figure
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