623 research outputs found
Universal features in sequential and nonsequential two-photon double ionization of helium
We analyze two-photon double ionization of helium in both the nonsequential
and sequential regime. We show that the energy spacing between the two emitted
electrons provides the key parameter that controls both the energy and the
angular distribution and reveals the universal features present in both the
nonsequential and sequential regime. This universality, i.e., independence of
photon energy, is a manifestation of the continuity across the threshold for
sequential double ionization. For all photon energies, the energy distribution
can be described by a universal shape function that contains only the spectral
and temporal information entering second-order time-dependent perturbation
theory. Angular correlations and distributions are found to be more sensitive
to the photon energy. In particular, shake-up interferences have a large effect
on the angular distribution. Energy spectra, angular distributions
parameterized by the anisotropy parameters, and total cross sections presented
in this paper are obtained by fully correlated time-dependent ab initio
calculations.Comment: 12 pages, 8 figure
Documenting of Geologic Field Activities in Real-Time in Four Dimensions: Apollo 17 as a Case Study for Terrestrial Analogues and Future Exploration
During the Apollo exploration of the lunar surface, thousands of still images, 16 mm videos, TV footage, samples, and surface experiments were captured and collected. In addition, observations and descriptions of what was observed was radioed to Mission Control as part of standard communications and subsequently transcribed. The archive of this material represents perhaps the best recorded set of geologic field campaigns and will serve as the example of how to conduct field work on other planetary bodies for decades to come. However, that archive of material exists in disparate locations and formats with varying levels of completeness, making it not easily cross-referenceable. While video and audio exist for the missions, it is not time synchronized, and images taken during the missions are not time or location tagged. Sample data, while robust, is not easily available in a context of where the samples were collected, their descriptions by the astronauts are not connected to them, or the video footage of their collection (if available). A more than five year undertaking to reconstruct and reconcile the Apollo 17 mission archive, from launch through splashdown, has generated an integrated record of the entire mission, resulting in searchable, synchronized image, voice, and video data, with geologic context provided at the time each sample was collected. Through www.apollo17.org the documentation of the field investigation conducted by the Apollo 17 crew is presented in chronologic sequence, with additional context provided by high-resolution Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) images and a corresponding digital terrain model (DTM) of the Taurus-Littrow Valley
Proposed magnetostratigraphy susceptibility magnetostratotype for the Eifelian-Givetian GSSP (Anti-Atlas, Morocco)
The magnetosusceptibility event and cyclostratigraphy (MSEC) record for the Eifelian-Givetian Global Boundary Stratotype Section and Point (GSSP) located in the western Sahara of southeastern Morocco is used to establish a sequence of magnetostratigraphic susceptibility units organized into magnetostratigraphic susceptibility zones (MSZ) and magnetostratigraphic susceptibility subzones (MSSZ). Magnetic susceptibility data are summarized into two complete MSZs (Atrous and Mech Irdane) and two partial MSZs (Gheris and Rissani). The Atrous (Upper Eifelian) is comprised of 3 MSSZs and the Mech Irdane (uppermost Eifelian and lowermost Givetian) of 11 MSSZs. The Eifelian-Givetian boundary falls within Mech Irdane MSSZ 2 making the magnetosubzone an important boundary marker unit. Large-scale transgressive and regressive patterns in the MSEC data establish that the Eifelian-Givetian boundary in the GSSP sequence occurs immediately after the first regressive pulse following the transgressive conditions established during the Atrous MSZ. The Lower Kačák/otomari Event occurs in Atrous MSSZ 3 and Kačák/otomari Event occurs in Mech Irdane MSSZ 1. The magnetic properties of the MSZs and MSSZs are tested by comparison with a coeval magnetostratigraphic susceptibility sequence in the Montagne Noire region of southern France
Vascular Flora of Hooper Branch Savanna Nature Preserve, Iroquois County, Illinois
INHS Technical Report prepared for Illinois Department of Natural Resources, Division of
Natural Heritag
Nonsequential two-photon double ionization of helium
We present accurate time-dependent ab initio calculations on fully
differential and total integrated (generalized) cross sections for the
nonsequential two-photon double ionization of helium at photon energies from 40
to 54 eV. Our computational method is based on the solution of the
time-dependent Schroedinger equation and subsequent projection of the wave
function onto Coulomb waves. We compare our results with other recent
calculations and discuss the emerging similarities and differences. We
investigate the role of electronic correlation in the representation of the
two-electron continuum states, which are used to extract the ionization yields
from the fully correlated final wave function. In addition, we study the
influence of the pulse length and shape on the cross sections in time-dependent
calculations and address convergence issues.Comment: 14 pages, 10 figures; final version (acknowledgements and reference
added, typos fixed
Interactions of B = 4 Skyrmions
It is known that the interactions of single Skyrmions are asymptotically
described by a Yukawa dipole potential. Less is known about the interactions of
solutions of the Skyrme model with higher baryon number. In this paper, it is
shown that Yukawa multipole theory can be more generally applied to Skyrmion
interactions, and in particular to the long-range dominant interactions of the
B = 4 solution of the Skyrme model, which models the alpha-particle. A method
that gives the quadrupole nature of the interaction a more intuitive meaning in
the pion field colour picture is demonstrated. Numerical methods are employed
to find the precise strength of quadrupole and octupole interactions. The
results are applied to the B = 8 and B = 12 solutions and to the Skyrme
crystal.Comment: 21 pages, 11 figure
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L1 transfer in the acquisition of manner and path in Spanish by native speakers of English
In this article the authors argue that L1 transfer from English is not only important in the early stages of L2 acquisition of Spanish, but remains influential in later stages if there is not enough positive evidence for the learners to progress in their development (Lefebvre, White, & Jourdan, 2006). The findings are based on analyses of path and manner of movement in stories told by British students of Spanish (N = 68) of three different proficiency levels. Verbs that conflate motion and path, on the one hand, are mastered early, possibly because the existence of Latinate path verbs, such as enter and ascend in English, facilitate their early acquisition by British learners of Spanish. Contrary to the findings of Cadierno (2004) and Cadierno and Ruiz (2006), the encoding of manner, in particular in boundary crossing contexts, seems to pose enormous difficulties, even among students who had been abroad on a placement in a Spanish-speaking country prior to the data collection. An analysis of the frequency of manner verbs in Spanish corpora shows that one of the key reasons why students struggle with manner is that manner verbs are so infrequent in Spanish. The authors claim that scarce positive evidence in the language exposed to and little or no negative evidence are responsible for the long-lasting effect of transfer on the expression of manner
Language and memory for object location
In three experiments, we investigated the influence of two types of language on memory for object location: demonstratives (this, that) and possessives (my, your). Participants first read instructions containing demonstratives/possessives to place objects at different locations, and then had to recall those object locations (following object removal). Experiments 1 and 2 tested contrasting predictions of two possible accounts of language on object location memory: the Expectation Model (Coventry, Griffiths, & Hamilton, 2014) and the congruence account (Bonfiglioli, Finocchiaro, Gesierich, Rositani, & Vescovi, 2009). In Experiment 3, the role of attention allocation as a possible mechanism was investigated. Results across all three experiments show striking effects of language on object location memory, with the pattern of data supporting the Expectation Model. In this model, the expected location cued by language and the actual location are concatenated leading to (mis)memory for object location, consistent with models of predictive coding (Bar, 2009; Friston, 2003)
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