Influence of constitution and charge on radical pairing interactions in tris-radical tricationic complexes

The results of a systematic investigation of trisradical tricationic complexes formed between cyclobis(paraquat-p-phenylene) bisradical dicationic (CBPQT2(•+)) rings and a series of 18 dumbbells, containing centrally located 4,4′-bipyridinium radical cationic (BIPY•+) units within oligomethylene chains terminated for the most part by charged 3,5-dimethylpyridinium (PY+) and/or neutral 3,5-dimethylphenyl (PH) groups, are reported. The complexes were obtained by treating equimolar amounts of the CBPQT4+ ring and the dumbbells containing BIPY2+ units with zinc dust in acetonitrile solutions. Whereas UV–Vis–NIR spectra revealed absorption bands centered on ca. 1100 nm with quite different intensities for the 1:1 complexes depending on the constitutions and charges on the dumbbells, titration experiments showed that the association constants (Ka) for complex formation vary over a wide range, from 800 M–1 for the weakest to 180 000 M–1 for the strongest. While Coulombic repulsions emanating from PY+ groups located at the ends of some of the dumbbells undoubtedly contribute to the destabilization of the trisradical tricationic complexes, solid-state superstructures support the contention that those dumbbells with neutral PH groups at the ends of flexible and appropriately constituted links to the BIPY•+ units stand to gain some additional stabilization from C–H···π interactions between the CBPQT2(•+) rings and the PH termini on the dumbbells. The findings reported in this Article demonstrate how structural changes implemented remotely from the BIPY•+ units influence their non-covalent bonding interactions with CBPQT2(•+) rings. Different secondary effects (Coulombic repulsions versus C–H···π interactions) are uncovered, and their contributions to both binding strengths associated with trisradical interactions and the kinetics of associations and dissociations are discussed at some length, supported by extensive DFT calculations at the M06-D3 level. A fundamental understanding of molecular recognition in radical complexes has relevance when it comes to the design and synthesis of non-equilibrium systems

Experiments in vortex avalanches

Avalanche dynamics is found in many phenomena spanning from earthquakes to the evolution of species. It can be also found in vortex matter when a type II superconductor is externally driven, for example, by increasing the magnetic field. Vortex avalanches associated with thermal instabilities can be an undesirable effect for applications, but "dynamically driven" avalanches emerging from the competition between intervortex interactions and quenched disorder constitute an interesting scenario to test theoretical ideas related with non-equilibrium dynamics. However, differently from the equilibrium phases of vortex matter in type II superconductors, the study of the corresponding dynamical phases - in which avalanches can play a role - is still in its infancy. In this paper we critically review relevant experiments performed in the last decade or so, emphasizing the ability of different experimental techniques to establish the nature and statistical properties of the observed avalanche behavior.Comment: To be published in Reviews of Modern Physics April 2004. 17 page

Mesoscopic Superconducting Disc with Short-Range Columnar Defects

Short-range columnar defects essentially influence the magnetic properties of a mesoscopic superconducting disc.They help the penetration of vortices into the sample, thereby decrease the sample magnetization and reduce the upper critical field. Even the presence of weak defects split a giant vortex state (usually appearing in a clean disc in the vicinity of the transition to a normal state) into a number of vortices with smaller topological charges. In a disc with a sufficient number of strong enough defects vortices are always placed onto defects. The presence of defects lead to the appearance of additional magnetization jumps related to the redistribution of vortices which are already present on the defects and not to the penetration of new vortices.Comment: 14 pgs. RevTex, typos and figures corrected. Submitted to Phys. Rev.

Geographically touring the eastern bloc: British geography, travel cultures and the Cold War

This paper considers the role of travel in the generation of geographical knowledge of the eastern bloc by British geographers. Based on oral history and surveys of published work, the paper examines the roles of three kinds of travel experience: individual private travels, tours via state tourist agencies, and tours by academic delegations. Examples are drawn from across the eastern bloc, including the USSR, Poland, Romania, East Germany and Albania. The relationship between travel and publication is addressed, notably within textbooks, and in the Geographical Magazine. The study argues for the extension of accounts of cultures of geographical travel, and seeks to supplement the existing historiography of Cold War geography

Shedding light on the elusive role of endothelial cells in cytomegalovirus dissemination.

Cytomegalovirus (CMV) is frequently transmitted by solid organ transplantation and is associated with graft failure. By forming the boundary between circulation and organ parenchyma, endothelial cells (EC) are suited for bidirectional virus spread from and to the transplant. We applied Cre/loxP-mediated green-fluorescence-tagging of EC-derived murine CMV (MCMV) to quantify the role of infected EC in transplantation-associated CMV dissemination in the mouse model. Both EC- and non-EC-derived virus originating from infected Tie2-cre(+) heart and kidney transplants were readily transmitted to MCMV-naïve recipients by primary viremia. In contrast, when a Tie2-cre(+) transplant was infected by primary viremia in an infected recipient, the recombined EC-derived virus poorly spread to recipient tissues. Similarly, in reverse direction, EC-derived virus from infected Tie2-cre(+) recipient tissues poorly spread to the transplant. These data contradict any privileged role of EC in CMV dissemination and challenge an indiscriminate applicability of the primary and secondary viremia concept of virus dissemination

Subordinate Actors’ Institutional Maintenance in Response to Coercive Reforms

Institutional work research shows how actors purposively create, maintain, and disrupt institutions. Failed or unintended consequences of institutional maintenance remain relatively unexplored, for two reasons. First, the role of coercive disruption actors (e.g., a state) has not been fully explored. Second, existing literature takes scant account of power and disregards the resistance tactics of subordinate actors. Drawing on a longitudinal case study of a migrant workers’ union in China, we show how subordinate actors were first able to maintain institutional arrangements followed by a maintenance failure under the disruption work performed by the authoritarian state. This study extends the institutional maintenance literature in two ways. First, subordinate actors can sustain institutions insofar as they collectively deploy superficial deference and hidden forms of resistance. Second, maintenance work is vulnerable in the sense that it is contingent on the systems of domination and the level of pressure exerted by the disruption actors

The representation of voluntourism in search engines: The case of South Africa

© 2015, © 2015 Government Technical Advisory Centre (GTAC). This paper responds to the paucity of research on the linkages between voluntourism and digital technology and seeks to understand the online representation of the phenomenon in a developing context. In particular, the researchers investigate the so-called ‘online domain’ of voluntourism in South Africa. The researchers collected a series of web results from search engines and analysed the presence of traditional and social media websites, the most relevant presented topics, and the type of argumentation found. Results identify the context and representation of voluntourism as it transpires virtually. This will contribute to the understanding of the interplay between voluntourism and digital technology, with specific emphasis on web presence. Ultimately, results will shed light on how digitally accessible voluntourism is in South Africa and will set the basis for future investigations

ELL’s science meaning making in multimodal inquiry: a case-study in a Hong Kong bilingual school

This paper reports on a multimodal teaching approach delivered to grade 5 elementary students in a bilingual school in Hong Kong, as part of a larger research study aimed at supporting English Language Learners (ELLs) in science class. As language demands of reading, writing and talking science place additional challenges on ELLs, there is much research interest in exploring the use of multiple modes of communication beyond the dominant use of verbal and written language. Research has shown that students develop a better scientific understanding of natural phenomena by using and alternating between a variety of representations. Yet, questions remain as to what meanings ELLs make during a multimodal discourse and, in turn, how such discourse provides support to ELLs in learning science. Drawing on social semiotics, which theorizes language as a meaning making resource comprising a range of modes (e.g. gestures and diagrams), we used a case-study approach to examine how a multimodal instructional approach provided 10 students with multiple avenues to make sense of science learning. Video recordings (capturing gestures, speech and model manipulation) and student works (drawing and writing) were collected during nine inquiry science lessons, which encompassed biology, physics and chemistry science units. Multimodal transcription allowed discourse to be analysed at a fine-grain level which, together with analysis of student works, indicated that the multimodal instructional approach provided the necessary inquiry opportunities and variety of language experiences for ELLs to build science understandings. Analysis also revealed how the affordances of modes attributed to the meaning making potentials for the ELLs and how they provided alternate communication avenues in which new meanings could be made. The findings from this study have implications for ELLs learning science within the growing multilingual Asia-Pacific region

Collaboration and knowledge exchange between scholars in Britain and the empire, 1830–1914

In recent years there has been a growing interest among historians in the British Empire as a space of knowledge production and circulation. Much of this work assumes that scholarly cooperation and collaboration between individuals and institutions within the Empire had the effect (and often also the aim) of strengthening both imperial ties and the idea of empire. This chapter argues, however, that many examples of scholarly travel, exchange, and collaboration were undertaken with very different goals in mind. In particular, it highlights the continuing importance of an ideal of scientific internationalism, which stressed the benefits of scholarship for the whole of humanity and prioritized the needs and goals of individual academic and scientific disciplines. As the chapter shows, some scholars even went on to develop nuanced critiques of the imperial project while using the very structures of empire to further their own individual, disciplinary and institutional goals

Social meanings and understandings in patient-nurse interaction in the community practice setting: a grounded theory study

Provisional: Background: The patient-nurse relationship is a traditional concern of healthcare research. However, patient-nurse interaction is under examined from a social perspective. Current research focuses mostly on specific contexts of care delivery and experience related to medical condition or illness, or to nurses' speciality. Consequentially, this paper is about the social meanings and understandings at play within situated patient-nurse interaction in the community practice setting in a transforming healthcare service. Methods: Grounded theory methodology was used and the research process was characterised by principles of theoretical sensitivity and constant comparative analysis. The field of study was four health centres in the community. The participants were patients and nurses representative of those attending or working in the health centres and meeting there by scheduled appointment. Data collection methods were observations, informal interviews and semi-structured interviews. Results: Key properties of 'Being a good patient, being a good nurse', 'Institutional experiences' and 'Expectations about healthcare' were associated with the construction of a category entitled 'Experience'. Those key properties captured that in an evolving healthcare environment individuals continually re-constructed their reality of being a patient or nurse as they endeavoured to perform appropriately; articulation of past and present healthcare experiences was important in that process. Modus operandi in role as patient was influenced by past experiences in healthcare and by those in non-healthcare institutions in terms of engagement and involvement (or not) in interaction. Patients' expectations about interaction in healthcare included some uncertainly as they strived to make sense of the changing roles and expertise of nurses and, differentiating between the roles and expertise of nurses and doctors. Conclusions: The importance of social meanings and understandings in patient-nurse interaction is not fully apparent to nurses, but important in the patient experience. Seeking understanding from a social perspective makes a contribution to enhancing knowledge about patient-nurse interaction with subsequent impact on practice, in particular the development of the patient-nurse relationship. The implications are that the meanings and understandings patients and nurses generate from experiences beyond and within their situated interaction are pivotal to the development of their relationship in the transforming community healthcare environment