Pion Compton scattering and bremsstrahlung

The pion-polarizability functions are structure functions of pion-Compton scattering. They can be assessed in high-energy pion-nucleus bremsstrahlung reactions, $\pi^- +A\to\pi^- +\gamma +A$. We present numerical expectations for pion-nucleus bremsstrahlung cross sections in the Coulomb region, i.e. the small-angle region where the nuclear scattering is dominated by the Coulomb interaction. We investigate the prospects of measuring the polarizability functions for pion-Compton c.m. energies from threshold up to 1 GeV. A meson-exchange model is used for the pion-Compton amplitude.Comment: 20 pages, 11 figure

Hard pion bremsstrahlung in the Coulomb region

Hard high-energy pion-nucleus bremsstrahlung, $\pi^- +A\to\pi^- +\gamma +A$, is studied in the Coulomb region, i.e. the small-angle region where the nuclear scattering is dominated by the Coulomb interaction. Special attention is focussed on the possibility of measuring the pion polarizability in such reactions. We study the sensitivity to the structure of the underlying the pion-Compton amplitude through a model with $\sigma$, $\rho$, and a_1 exchanges. It is found that the effective energy in the virtual pion-Compton scattering is often so large that the threshold approximation does not apply.Comment: 18 pages, 5 figure

Import of apocytochrome c into the mitochondrial intermembrane space along a cytochrome c1 sorting pathway

The question of whether cytochrome c could be functionally sorted to the mitochondrial intermembrane space along a "conservative sorting" pathway was investigated using a fusion protein termed pLc1-c. pLc1-c contains 3-fold targeting information, namely, the complete bipartite presequence of the cytochrome c1 precursor joined to the amino terminus of apocytochrome c. pLc1-c could be selectively imported into the intermembrane space either directly across the outer membrane along a cytochrome c import route or along a cytochrome c1 route via the matrix. Thus, apocytochrome c could be sorted along a conservative sorting pathway; however, following reexport from the matrix, apo-Lc1-c could not be converted to its holo counterpart. Despite the apparent similarity of structure and functional location of the heme lyases and similarity of the heme binding regions in their respective apoproteins, cytochrome c heme lyase and cytochrome c1 heme lyase apparently have different and nonoverlapping substrate specificities

Coulomb-nuclear interference in pion-nucleus bremsstrahlung

Pion-nucleus bremsstrahlung offers a possibility of measuring the structure functions of pion-Compton scattering from a study of the small-momentum-transfer region where the bremsstrahlung reaction is dominated by the single-photon-exchange mechanism. The corresponding cross-section distribution is characterized by a sharp peak at small momentum transfers. But there is also a hadronic contribution which is smooth and constitutes an undesired background. In this communication the modification of the single-photon exchange amplitude by multiple-Coulomb scattering is investigated as well as the Coulomb-nuclear interference term.Comment: 21 pages, 5 figures. Eqs.(51,52) corrected; some new figure

Analysis of the sign regressor least mean fourth adaptive algorithm

A novel algorithm, called the signed regressor least mean fourth (SRLMF) adaptive algorithm, that reduces the computational cost and complexity while maintaining good performance is presented. Expressions are derived for the steady-state excess-mean-square error (EMSE) of the SRLMF algorithm in a stationary environment. A sufficient condition for the convergence in the mean of the SRLMF algorithm is derived. Also, expressions are obtained for the tracking EMSE of the SRLMF algorithm in a nonstationary environment, and consequently an optimum value of the step-size is obtained. Moreover, the weighted variance relation has been extended in order to derive expressions for the mean-square error (MSE) and the mean-square deviation (MSD) of the proposed algorithm during the transient phase. Computer simulations are carried out to corroborate the theoretical findings. It is shown that there is a good match between the theoretical and simulated results. It is also shown that the SRLMF algorithm has no performance degradation when compared with the least mean fourth (LMF) algorithm. The results in this study emphasize the usefulness of this algorithm in applications requiring reduced implementation costs for which the LMF algorithm is too complex

A search for new hot subdwarf stars by means of Virtual Observatory tools

Hot subdwarf stars are faint, blue objects, and are the main contributors to the far-UV excess observed in elliptical galaxies. They offer an excellent laboratory to study close and wide binary systems, and to scrutinize their interiors through asteroseismology, as some of them undergo stellar oscillations. However, their origins are still uncertain, and increasing the number of detections is crucial to undertake statistical studies. In this work, we aim at defining a strategy to find new, uncatalogued hot subdwarfs. Making use of Virtual Observatory tools we thoroughly search stellar catalogues to retrieve multi-colour photometry and astrometric information of a known sample of blue objects, including hot subdwarfs, white dwarfs, cataclysmic variables and main sequence OB stars. We define a procedure to discriminate among these spectral classes, particularly designed to obtain a hot subdwarf sample with a low contamination factor. In order to check the validity of the method, this procedure is then applied to two test sky regions: the Kepler FoV and to a test region of around (RA:225, DEC:5) deg. As a result, we obtained 38 hot subdwarf candidates, 23 of which had already a spectral classification. We have acquired spectroscopy for three other targets, and four additional ones have an available SDSS spectrum, which we used to determine their spectral type. A temperature estimate is provided for the candidates based on their spectral energy distribution, considering two-atmospheres fit for objects with clear infrared excess. Eventually, out of 30 candidates with spectral classification, 26 objects were confirmed to be hot subdwarfs, yielding a contamination factor of only 13%. The high rate of success demonstrates the validity of the proposed strategy to find new uncatalogued hot subdwarfs. An application of this method to the entire sky will be presented in a forthcoming work.Comment: 13 pages, 7 figure

PG 1613+426: a new sdB pulsator

We report the detection of short period oscillations in the hot subdwarf B (sdB) star PG 1613+426 from time-series photometry carried out with the 91-cm Cassegrain telescope of the Catania Astrophysical Observatory. This star, which is brighter than the average of the presently known sdB pulsators, with B = 14.14 mag, has $T_{\rm eff}=34 400 {\rm K}$ and $\log g = 5.97$, its position is near the hot end of the sdB instability strip, and it is a pulsator with a well observed peak in the power spectrum at $144.18\pm 0.06 \rm s$. This star seems to be well suited for high precision measurements, which could detect a possible multi-mode pulsation behaviourComment: 3 pages, 4 figures. to appear on A&

Using Computerized Corpus Analysis To Investigate The Textlinguistic Discourse Moves Of a Genre

This post-peer-review, pre-copyedit version of the article submitted to IUPUI ScholarWorks as part of the OASIS Project. Article reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Permission granted through posted policies on copyright owner’s website or through direct contact with copyright owner.Recently there has been a growing interest in and recognition of the value of specialized corpora, such as learner corpora [Granger, S. (1998). The computer learner corpus: a versatile new source of data for SLA research. In S. Granger, Learner English on computer (pp. 3–18). New York: Longman], in facilitating discourse analysis. Despite this trend, most corpus-based analyses have centered on the lexico–grammatical patterning of texts with less regard for functional and rhetorical, textlinguistic aspects [Flowerdew, L. (1998). Corpus linguistic techniques applied to textlinguistics. System, 26, 541–552]. The goals of this study were: (1) to demonstrate the efficacy of a multi-level analysis of a genre-specific learner corpus that included both a hand-tagged moves-analysis coupled with a computerized analysis of lexico-grammatical features of texts; and (2) to show how a pragmatic concept such as politeness can be operationalized to allow for computer generated counts of linguistic features related to that concept. In this study of politeness strategies used by Americans, Finns, and Belgians in a learner corpus of letters of application, we found that Americans as a group tended to be much more patterned, even formulaic, in their politeness strategies. The Belgians, on the other hand, showed more individuality in their letters with the Finns exhibiting both traits to lesser degrees. In this paper we argue for a textlinguistic approach that considers the special features of genre-specific corpora