Spin dynamics and structure formation in a spin-1 condensate in a magnetic field

We study the dynamics of a trapped spin-1 condensate in a magnetic field. First, we analyze the homogeneous system, for which the dynamics can be understood in terms of orbits in phase space. We analytically solve for the dynamical evolution of the populations of the various Zeeman components of the homogeneous system. This result is then applied via a local-density approximation to trapped quasi-one-dimensional condensates. Our analysis of the trapped system in a magnetic field shows that both the mean-field and Zeeman regimes are simultaneously realized, and we argue that the border between these two regions is where spin domains and phase defects are generated. We propose a method to experimentally tune the position of this border

Spectral statistics of molecular resonances in erbium isotopes: How chaotic are they?

We perform a comprehensive analysis of the spectral statistics of the molecular resonances in $^{166}$Er and $^{168}$Er observed in recent ultracold collision experiments [Frisch et al., Nature {\bf 507}, 475 (2014)] with the aim of determining the chaoticity of this system. We calculate different independent statistical properties to check their degree of agreement with random matrix theory (RMT), and analyze if they are consistent with the possibility of having missing resonances. The analysis of the short-range fluctuations as a function of the magnetic field points to a steady increase of chaoticity until $B \sim 30$ G. The repulsion parameter decreases for higher magnetic fields, an effect that can be interpreted as due to missing resonances. The analysis of long-range fluctuations allows us to be more quantitative and estimate a $20-25\%$ fraction of missing levels. Finally, a study of the distribution of resonance widths provides additional evidence supporting missing resonances of small width compared with the experimental magnetic field resolution. We conclude that further measurements with increased resolution will be necessary to give a final answer to the problem of missing resonances and the agreement with RMT.Comment: 9 pages, 6 figure

Density functional study of two-dimensional He-4 clusters

Binding energies and density profiles of two-dimensional systems of liquid He-4 with different geometries are studied by means of a zero-range density functional adjusted to reproduce the line tension obtained in a previous diffusion Monte Carlo calculation (lambda_{DMC}=0.121 K/A). It is shown that this density functional provides accurate results for the binding energy of large clusters with a reasonable computational effort.Comment: RevTeX4, 11 pages + 2 tables + 6 figure

Spin mixing in colliding spinor condensates: formation of an effective barrier

The dynamics of F=1 spinor condensates initially prepared in a double-well potential is studied in the mean field approach. It is shown that a small seed of $m=0$ atoms on a system with initially well separated m=1 and m=-1 condensates has a dramatic effect on their mixing dynamics, acting as an effective barrier for a remarkably long time. We show that this effect is due to the spinor character of the system, and provides an observable example of the interplay between the internal spin dynamics and the macroscopic evolution of the magnetization in a spinor Bose-Einstein condensate.Comment: Accepted for publication at the Europhysics Letter

Some Issues on the Concept of Causality in Spatial Econometric Models

A specific feature of spatial econometric models is the simultaneity of the relations, which complicates the distinction between causes and effects. However, the notion of cause is of paramount importance in any specification. In fact, a model is a statement pointing that a variable, called endogenous, reacts to the variables that appear in the right hand side, the regressors. Our impression is that this problem has been scarcely treated in the Spatial Econometrics literature. The content of the paper focuses on questions related to the specification procedure for spatial models. We examine what may be called the ''current traditional practice'' and discuss the role that the concepts of identification and causality should play. Our purpose is to claim for the development of clear econometric guidelines to help the users to improve the theoretical foundations of their specifications. An application to the relation between per capita income and weight of the agricultural sector in the Spanish provinces illustrates our discussion

Mur-Dueñas, P. and Šinkūnienė, J. (eds) (2018) Intercultural Perspectives on Research Writing. Amsterdam & Philadelphia: John Benjamins. 301 pp.

The growing importance of English in international academic communities has recently become one of the key issues in applied linguistics and discourse studies. The international role of English and the intercultural nature of most academic communities has emphasised the need for cross-cultural studies and in particular of cross-cultural rhetoric. Considered from this perspective, Pilar Mur-Dueñas and Jolanta Šinkūnienė’s edited volume on academic writing across cultures is a timely addition to the literature on Intercultural Rhetoric (IR). Thevolume not only continues the tradition of publications dedicated to various aspects of contrastive rhetoric, but also makes an original contribution to the field of intercultural studies by adopting IR approaches to the analysis of academic texts written in L2 English. The volume devotes particular attention to academic genres such as research articles, conference abstracts, PhD abstracts and research abstracts by writers of Czech, Lithuanian, Spanish, French, Italian, Chinese and Malaysian, with a focus on a wide variety of lexico-grammatical, discursive and rhetorical features, such as shell nouns, reformulation markers, the anticipatory it structure, personal pronouns, hedges, boosters, citations, evaluative acts and evaluative language.The volume consists of a preface by Ken Hyland and an introduction by the editors, followed by thirteen contributions which are organised into three thematic parts: Part I is devoted to a three-fold intercultural analysis, comparing L1, L1 English and L2 English academic texts; Part II focuses on a twofold intercultural analysis, comparing English L1 and L2 academic texts; Part III explores English L1 and L2 as examples of ELF academic texts. An afterword by Ulla Connor closes the book.A preface by Ken Hyland entitled Academic writing and non-Anglophone scholars sets the volume in the context of both intercultural studies and academic discourse studies. The preface highlights the close connection between the two approaches but also emphasises that the chapters “offer rich and nuanced findings of academic writing across cultures” (p. ix), as they contribute to a better understanding of the role of multilingual or EAL (English as an Additional Language) research in the context of increasing international English-medium publication.The introduction by the editors offers a nice overview of intercultural research in EAP and ELF and stresses the importance of adopting IR approaches to the analysis of academic texts written by non-Anglophone scholars in order to explore “the challenges they face while writing and publishing in English for an international readership” (p. 1).The three papers in Part I offer analyses of research articles (RAs) written in English by Czech and by Lithuanian scholars and are compared to RAs in their respective L1s and to RAs written by L1 English scholars in the Humanities. In the first, Olga Dontcheva-Navratilova looks at the rhetorical functions of integral and non-integral citations across the generic moves of research articles in a specialised corpus of Linguistics research articles including Czech-medium and English-medium texts written by Czech authors and English-medium texts by Anglophone scholars. Her careful analysis shows that Czech linguists writing in English tend to use fewer citations than their Anglophone colleagues, suggesting that these divergences are related to the linguacultural background in which Anglophone and Czech linguists strive to construct their identities as members of the global and/or local academic community. The next paper by Jūratė Ruzaitė and Rūta Petrauskaitė discusses the trends of internationalisation with a focus on academic conventions in Linguistics RAs articles published in a Lithuanian journal as compared to those published in a well established international English journal. Their paper points at an interesting finding that “in the field of Linguistics it is no so much the language that predetermines differences in the two journals, but the academic conventions that differ across cultures and publishing houses” (p. 39). Jolanta Šinkūnienė’s paper closes Part I with the analysis of personal pronoun use in Linguistics research articles written in Lithuanian and in English by Lithuanian scholars, and in English by British scholars. Interestingly, she finds that “Lithuanian linguists tend to employ personal pronouns more frequently when they write in English than when they write in Lithuanian” (p. 77), suggesting that this tendency is “the result of the influence of the Anglo-American academic writing tradition” and it reflects “an attempt of the scholars to adapt their writing style to the conventions of the language in which they compose the text” (p. 77).The focus of the four papers of Part II is on L2 and L1 English academic texts, covering genres such as research articles, PhD abstracts, conference abstracts, written by French, Malaysian, Chinese, and Czech writers in English and by Anglophone writers. By investigating the use of shell nouns in a comparable interdisciplinary corpus of 400 PhD abstracts written in English by English and French native speaking writers, Geneviève Bordet shows that “the discipline expresses its identity not only through the choice of specific encapsulating functions but also the adequacy of the selected labeling term considering this function” (p. 101). From a cross-cultural perspective, this result, as she suggests, may be related to a narrower available lexical range for writers of English in a Francophone context. In the second paper of Part II Maryam Mehrjooseresht and Ummul K. Ahmad investigate the use of evaluation markers in thesis abstracts (MA and PhD) written in English by Malaysian novice researchers in Science and Engineering fields. Interestingly, they find cross-disciplinary differences in the use of evaluation across the abstracts as well as some rhetorical difficulties by novice scholars to frame such evaluation, leading them to appear very assertive by using expressions of certainty. The third study by Xinren Chen is based on a corpus of 95 Linguistics research articles written by Chinese researchers with a research background in Applied Linguistics and published in the only English-language teaching journal entitled Chinese Journal of Applied Linguistics, representing three periods of time (1996, 2005-2006, 2015-2016). The author analyses the rhetorical structure of the introductory part of the RAs under investigation in an attempt to reveal whether and to what extent Chinese writers “move over time towards the conventional construction of the identity as creators of a research space in the introductory part of their RAs published in a national context” (p. 129). The study highlights a diachronic change, showing that Chinese writers, from the most recent period (2015 2016), tend to transfer Swales’ CARS model in their writing of the RA introductory part. The focus of the last paper in Part II by Renata Povolná is on the textual organisation of 80 conference abstracts written in English by both Anglophone scholars and scholars from countries where Slavonic languages are spoken (Czech, Slovak, Polish and Ukrainian). The author finds an interesting difference in the types of moves and patterns of move sequences applied by scholars from different groups: Anglophone writers show preference for a three-move pattern whereas non-Anglophone writers prefer a two-move pattern. As she suggests, this can be influenced “by a relatively lengthy style often associated with L1 academic texts, which authors of Slavonic origin sometimes transfer from their L1 texts into academic genres written in English” (p. 168).Part III of the book contains six papers, focusing on texts produced by non-native English scholars from various linguacultural backgrounds with the aim of exploring their impact on shaping English as a Lingua Franca (ELF) in research settings. In the first paper Rosa Lorés-Sanz explores three corpora (abstracts written in English as L1, in English as ELF, and English abstracts translated from Spanish) to identify the rhetorical patterns which characterise English research article abstracts in Sociology. She highlights interesting differences between the English abstracts translated from Spanish and the texts written in L1 English and  in ELF. More specifically, she finds that the English abstracts translated from Spanish have “a less complex rhetorical structure (fewer moves in the structure)” (p. 188), showing a general level of hybridity as a result of the translation into English. On the other hand, she shows that in the abstracts written in ELF there is a co-existence of different rhetorical patterns together with the conventional ones. This, as she suggests, arises “as a result of contact among users of ELF” (p. 188). The second study by Jingjing Wang and Feng (Kevin) Jiang investigates hedges, boosters and self-mentions as main expressions of epistemic positioning used in research writing by Chinese PhD students as compared to expert writers’ texts across four science disciplines: Physics, Life Science, Material Science, Computer Science. Differences in their use have been found both across the two groups of authors and across disciplines. The authors emphasise the need to raise novice scholars’ awareness on the expression of stance and of constructing an authorial identity in expected, conventional ways within the discipline. The next four papers of Part III are based on the SciELF corpus, consisting of academic articles written by users of ELF in different disciplines (SciELF 2015). The papers have not undergone any professional proofreading and most of them are final drafts of unpublished manuscripts. Marina Bondi and Carlotta Borelli focus on markers of authorial voice and metadiscourse in a subcorpus of the ScieELF, collected from articles in the field of economics (the SciELF-Ec corpus). The results are contrasted with those from a corpus of published articles in English for general reference. They find that the SciELF-Ec corpus is “characterised by prototypical metadiscursive elements: frequencies insist on a restricted range of evidentials, frame markers pointing to topic and focus, as well as prototypical general labelling nouns and forms of locative self-mention” (p. 232). The paper provides valuable insights into the role of the “cooperative imperative” of ELF users, requiring language accommodation to ensure communication (Seidlhofer 2009). Silvia Murillo investigates reformulation markers and the processes they introduce. She contrasts these markers in the SciELF corpus and in a comparable corpus of English as a Native Language (ENL) texts (SERAC). The comparison between ELF and native English reformulation markers points to similar tendencies regarding their general frequency. However, as the author shows, the findings also “reveal a tendency towards specialisation/simplification in the SciELF corpus, in the types of reformulation markers used and in the functions performed” (p. 249). Enrique Lafuente-Millán’s study looks at evaluation in RA introductions in the Social Sciences extracted from the SciELF corpus and contrasts it with a corpus of published RA introductions written by ENL researchers (SERAC). His results reveal that ELF writers use evaluation much less often to promote the importance, comprehensiveness and usefulness of their own research, which can be a challenge when trying to get their research results accepted for publication in a competitive, international context. Part III closes with Pilar Mur-Dueñas’ study which looks at a specific lexico-grammatical feature, the anticipatory it pattern, in the SciELF corpus, with the aim of investigating its interpersonal functions. The results are compared to those found in a comparable corpus of ENL published RAs from the SERAC corpus. She nicely demonstrates that differences emerge from the specific realisations of the pattern, which appear to be creative uses of the language to express interpersonal meanings. As she suggests, “this reveals some degree of dynamism in the English language as it is being used internationally for scholarly communication” (p. 294).The afterword by Ulla Connor closes the volume emphasising the importance of IR approaches to academic writing studies in an English as a Lingua Franca world.Overall, Intercultural Perspectives on Research Writing offers a significant representation of corpus and discourse work on intercultural studies of academic writing. The organisation of the volume provides readers with the opportunity to either read the chapters in sequence or choose most relevant sections. The volume will be essential reading for scholars undertaking research in the field of intercultural studies, but it will be also relevant to anyone with an interest inIntercultural Rhetoric and ELF.                                                                                                                                           Giuliana Dian

Predicting spinor condensate dynamics from simple principles

We study the spin dynamics of quasi-one-dimensional F=1 condensates both at zero and finite temperatures for arbitrary initial spin configurations. The rich dynamical evolution exhibited by these non-linear systems is explained by surprisingly simple principles: minimization of energy at zero temperature, and maximization of entropy at high temperature. Our analytical results for the homogeneous case are corroborated by numerical simulations for confined condensates in a wide variety of initial conditions. These predictions compare qualitatively well with recent experimental observations and can, therefore, serve as a guidance for on-going experiments.Comment: 4 pages, 2 figures. v3: matches version appeared in PR