458 research outputs found
Complete Photoionization Experiments via Ultrafast Coherent Control with Polarization Multiplexing II: Numerics & Analysis Methodologies
The feasibility of complete photoionization experiments, in which the full
set of photoionization matrix elements are determined, using multiphoton
ionization schemes with polarization-shaped pulses has recently been
demonstrated [Hockett et. al., Phys. Rev. Lett. 112, 223001 (2014)]. Here we
extend on our previous work to discuss further details of the numerics and
analysis methodology utilised, and compare the results directly to new
tomographic photoelectron measurements, which provide a more sensitive test of
the validity of the results. In so doing we discuss in detail the physics of
the photoionziation process, and suggest various avenues and prospects for this
coherent multiplexing methodology
Maximum information photoelectron metrology
Photoelectron interferograms, manifested in photoelectron angular
distributions (PADs), are a high-information, coherent observable. In order to
obtain the maximum information from angle-resolved photoionization experiments
it is desirable to record the full, 3D, photoelectron momentum distribution.
Here we apply tomographic reconstruction techniques to obtain such 3D
distributions from multiphoton ionization of potassium atoms, and fully analyse
the energy and angular content of the 3D data. The PADs obtained as a function
of energy indicate good agreement with previous 2D data and detailed analysis
[Hockett et. al., Phys. Rev. Lett. 112, 223001 (2014)] over the main spectral
features, but also indicate unexpected symmetry-breaking in certain regions of
momentum space, thus revealing additional continuum interferences which cannot
otherwise be observed. These observations reflect the presence of additional
ionization pathways and, most generally, illustrate the power of maximum
information measurements of this coherent observable
Quantum beat photoelectron imaging spectroscopy of Xe in the VUV
Time resolved pump probe measurements of Xe, pumped at 133 nm and probed at 266 nm, are presented. The pump pulse prepared a long lived hyperfine wave packet in the Xe 5p5 2P amp; 8728;1 2 6s2[1 2] amp; 8728;1 manifold E 77185cm amp; 8722;1 9.57eV . The wave packet was monitored via single photon ionization and velocity map photoelectron images were measured. The images provide angle and time resolved data which, when obtained over a large time window 900 ps , constitute a precision quantum beat spectroscopy measurement of the hyperfine state splittings. Additionally, analysis of the full photoelectron image stack provides a quantum beat imaging modality, in which the Fourier components of the photoelectron images correlated with specific beat components can be obtained. This may also permit the extraction of isotope resolved photoelectron images in the frequency domain, in cases where nuclear spins hence beat components can be uniquely assigned to specific isotopes as herein , and also provides phase information relating to the ionization dynamics. The information content of both raw and inverted image stacks is investigated, suggesting the utility of the Fourier analysis methodology in cases where images cannot be inverte
The Value of Literacy Practices
The concepts of literacy events and practices have received considerable attention in educational research and policy. In comparison, the question of value, that is, âwhich literacy practices do people most value?â has been neglected. With the current trend of cross-cultural adult literacy assessment, it is increasingly important to recognise locally valued literacy practices. In this paper we argue that measuring preferences and weighting of literacy practices provides an empirical and democratic basis for decisions in literacy assessment and curriculum development and could inform rapid educational adaptation to changes in the literacy environment. The paper examines the methodological basis for investigating literacy values and its potential to inform cross-cultural literacy assessments. The argument is illustrated with primary data from Mozambique. The correlation between individual values and respondentsâ socio-economic and demographic characteristics is explored
Photoionization from the Xe 4d orbitals of XeF2
We present a comparison of the photoionization dynamics of the 4d shell of XeF2 from threshold to 250 eV to those of the prototypical 4d shell of atomic Xe. The new experimental data include spinâorbit and ligand-field-resolved partial cross sections, photoelectron angular distributions, branching fractions, and lifetime widths for the 4d-hole states. The spinâorbit branching fractions and angular distributions are remarkably similar to the corresponding distributions from atomic Xe across a broad energy interval that includes both the intense shape resonance in the f continuum and a Cooper minimum in the same channel. The angular distributions and branching fractions are also in reasonably good agreement with our first-principles theoretical calculations on XeF2. Data are also presented on the lifetime widths of the substate-resolved 4d-hole states of XeF2. While the trends in the widths are similar to those in the earlier experimental and theoretical work, the linewidths are considerably smaller than in the previous measurements, which may require some reinterpretation of the decay mechanism. Finally, we present new data and an analysis of the Auger electron spectra for ionization above the 4d thresholds and resonant Auger spectra for several pre-edge features
Taphonomic Criteria for Identifying Iberian Lynx Dens in Quaternary Deposits
For decades, taphonomists have dedicated their efforts to assessing the nature of the massive leporid accumulations recovered at archaeological sites in the northwestern Mediterranean region. Their interest lying in the fact that the European rabbit constituted a critical part of human subsistence during the late Pleistocene and early Holocene. However, rabbits are also a key prey in the food webs of Mediterranean ecosystems and the base of the diet for several specialist predators, including the Iberian lynx (Lynx pardinus). For this reason, the origin of rabbit accumulations in northwestern Mediterranean sites has proved a veritable conundrum. Here, we present the zooarchaeological and taphonomic study of more than 3000 faunal and 140 coprolite remains recovered in layer IIIa of Cova del Gegant (Catalonia, Spain). Our analysis indicates that this layer served primarily as a den for the Iberian lynx. The lynxes modified and accumulated rabbit remains and also died at the site creating an accumulation dominated by the two taxa. However, other agents and processes, including human, intervened in the final configuration of the assemblage. Our study contributes to characterizing the Iberian lynx fossil accumulation differentiating between the faunal assemblages accumulated by lynxes and hominins
Direct and indirect aboutness topics
We propose a definition of aboutness topicality that not only encompasses individual denoting DPs, but also indefinites. We concentrate on the interpretative effects of marking indefinites as topics: they either receive widest scope in their clause, or they are interpreted in the restrictor of an overt or covert Q-adverb. We show that in the first case they are direct aboutness topics insofar as they are the subject of a predication expressed by the comment, while in the second case they are indirect aboutness topics: they define the subject of a higher-order predication â namely the set of situations that the respective Q-adverb quantifies over
Revising the Language Map of Korea
As linguists develop a deeper understanding of the properties of individual varieties of speech, they often find it necessary to reclassify dialects as independent languages, based on the criterion of intelligibility. This criterion is applied here to Jejueo, the traditional variety of speech used on Jeju Island, a province of the Republic of Korea. Although Jejueo has long been classified as a nonstandard dialect of Korean, evidence from an intelligibility experiment shows that it is not comprehensible to monolingual speakers of Korean and therefore should be treated as a separate language, in accordance with the usual practice within linguistics. This finding calls for a revision to the standard language map of Kore
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