Double Ionisation in R-Matrix Theory Using a 2-electron Outer Region

We have developed a two-electron outer region for use within R-matrix theory to describe double ionisation processes. The capability of this method is demonstrated for single-photon double ionisation of He in the photon energy region between 80 eV to 180 eV. The cross sections are in agreement with established data. The extended RMT method also provides information on higher-order processes, as demonstrated by the identification of signatures for sequential double ionisation processes involving an intermediate He$^{+}$ state with $n=2$.Comment: 5 pages, 4 figure

A computational study of the double hydrogen migration in the molecular ions of endo tricyclo[5.2.1.02,6]decene

AbstractPrevious field ionization kinetic experiments have supported strongly that the double hydrogen migration prior to the elimination of C5H8 from the molecular ions of the endo isomers of 8,9-disubstituted tricyclo[5.2.1.02,6]decenes, which is not observed for the exo isomers, proceeds in a concerted, i.e., dyotropic way. This paper describes the results of ab initio calculations at the ROHF/4-31G and DFT level of theory, performed on the double hydrogen migration for the ionized endo isomer of unsubstituted tricyclo[5.2.1.02,6]decene. An intrinsic reaction coordinate calculation at the DFT level has shown indeed a direct connection between the structures of the molecular ions of the endo isomer before and after the double hydrogen migration, thus corroborating the earlier suggested concerted, i.e., dyotropic pathway of this double hydrogen rearrangement

Stock Selection Strategies in Emerging Markets

Recent empirical evidence suggests that value and momentum strategies generate significant excess returns in emerging markets. We confirm these results and extend them in several directions. First, we examine a broader range of stock selection strategies, including strategies based on analysts' earnings revisions. We also consider multivariate strategies, whereby stocks are selected on multiple characteristics, and find that this enhances the overall performance. Excess returns also increase if country selection is incorporated into the strategies, but the risk of the strategies increases proportionally. Second, we test whether the strategies can be implemented successfully in practice by a large institutional investor, facing a lack of liquidity, restrictions on foreign ownership and substantial transaction costs. We find that even under such more realistic circumstances the strategies earn significant excess returns. Third, we examine several popular explanations for the excess returns. We find no evidence of higher market risk or lower liquidity of the strategies. Instead, based on the developments of earnings and earnings revisions after portfolio formation, we find that the results are consistent with behavioral explanations

The Success Of Stock Selection Strategies In Emerging Markets: Is It Risk Or Behavioral Bias?

We examine competing explanations, based on risk and behavioral models, for the profitability of stock selection strategies in emerging markets. We document that both emerging market risk and global risk factors cannot account for the significant excess returns of selection strategies based on value, momentum and earnings revisions indicators. The findings for value and momentum strategies are consistent with the evidence from developed markets supporting behavioral explanations. In addition, for value stocks, the most important behavioral bias appears to be related to underestimation of long-term growth prospects, as indicated by overly pessimistic analysts' earnings forecasts and above average earnings revisions for longer postformation horizons and by quite rapidly improving earnings growth expectations. Furthermore, we find that overreaction effects play a limited role for the earnings revisions strategy, as there is no clear return reversal up until five years after portfolio formation, setting this strategy apart from momentum strategies

Quasiclassical double photoionization from the 2^{1,3}S excited states of helium including shakeoff

We account for the different symmetries of the 2^{1,3}S helium excited states in a quasiclassical description of the knockout mechanism augmented by a quantum shakeoff contribution. We are thus able to formulate the separate contribution of the knockout and shakeoff mechanisms for double photoionization for any excess energy from the 2^{1,3}S states. Photoionization ratios and singly differential cross sections calculated for the 2^{1,3}S excited states of helium are found to be in very good agreement with recent theoretical results.Comment: 9 pages, 5 figure

Electron correlation and short-range dynamics in attosecond angular streaking

We employ the R matrix with time-dependence method to study attosecond angular streaking of F−. Using this negative ion, free of long-range Coulomb interactions, we elucidate the role of short-range electron correlation effects in an attoclock scheme. Through solution of the multielectron time-dependent Schrödinger equation, we aim to bridge the gap between experiments using multielectron targets, and one-electron theoretical approaches. We observe significant negative offset angles in the photoelectron momentum distributions, despite the short-range nature of the binding potential. We show that the offset angle is sensitive to the atomic structure description of the residual F atom. We also investigate the response of co- and counter-rotating electrons, and observe an angular separation in their emissio

Photoionization of H₂ using the molecular R-matrix with time approach

We present results of the first calculations using the variational ab initio molecular R-matrix with time approach. We have calculated two and four-photon ionization cross sections for H2 and studied the effects of electron correlation and choice of the Gaussian atomic basis sets. Our results are compared with earlier calculations

Solving non-uniqueness in agglomerative hierarchical clustering using multidendrograms

In agglomerative hierarchical clustering, pair-group methods suffer from a problem of non-uniqueness when two or more distances between different clusters coincide during the amalgamation process. The traditional approach for solving this drawback has been to take any arbitrary criterion in order to break ties between distances, which results in different hierarchical classifications depending on the criterion followed. In this article we propose a variable-group algorithm that consists in grouping more than two clusters at the same time when ties occur. We give a tree representation for the results of the algorithm, which we call a multidendrogram, as well as a generalization of the Lance and Williams' formula which enables the implementation of the algorithm in a recursive way.Comment: Free Software for Agglomerative Hierarchical Clustering using Multidendrograms available at http://deim.urv.cat/~sgomez/multidendrograms.ph

Formalin fixation for optimal concordance of programmed death-ligand 1 immunostaining between cytologic and histologic specimens from patients with non-small cell lung cancer

Background Immunohistochemical staining of programmed death-ligand 1 (PD-L1) is used to determine which patients with non-small cell lung cancer (NSCLC) may benefit most from immunotherapy. Therapeutic management of many patients with NSCLC is based on cytology instead of histology. In this study, concordance of PD-L1 immunostaining between cytology cell blocks and their histologic counterparts was analyzed. Furthermore, the effect of various fixatives and fixation times on PD-L1 immunoreactivity was studied. Methods Paired histologic and cytologic samples from 67 patients with NSCLC were collected by performing fine-needle aspiration on pneumonectomy/lobectomy specimens. Formalin-fixed, agar-based or CytoLyt/PreservCyt-fixed Cellient cell blocks were prepared. Sections from cell blocks and tissue blocks were stained with SP263 (standardized assay) and 22C3 (laboratory-developed test) antibodies. PD-L1 scores were compared between histology and cytology. In addition, immunostaining was compared between PD-L1-expressing human cell lines fixed in various fixatives at increasing increments in fixation duration. Results Agar cell blocks and tissue blocks showed substantial agreement (kappa = 0.70 and kappa = 0.67, respectively), whereas fair-to-moderate agreement was found between Cellient cell blocks and histology (kappa = 0.28 and kappa = 0.49, respectively). Cell lines fixed in various alcohol-based fixatives showed less PD-L1 immunoreactivity compared with those fixed in formalin. In contrast to SP263, additional formalin fixation after alcohol fixation resulted in preserved staining intensity using the 22C3 laboratory-developed test and the 22C3 pharmDx assay. Conclusions Performing PD-L1 staining on cytologic specimens fixed in alcohol-based fixatives could result in false-negative immunostaining results, whereas fixation in formalin leads to higher and more histology-concordant PD-L1 immunostaining. The deleterious effect of alcohol fixation could be reversed to some degree by postfixation in formalin