Liquid crystals with novel terminal chains as ferroelectric hosts

Changes to the molecular structure of liquid crystals can have a significant effect upon their mesomorphism and ferroelectric properties. Most of the research in liquid crystal for display applications concentrates on the design and synthesis of novel mesogenic cores to which straight terminal alkyl or alkoxy chains are attached. However, little is known about the effects upon the mesomorphism and ferroelectric properties ofvarying the terminal chains. The compounds prepared in this work have a common core - a 2,3-difluoroterphenyl unit with a nine-atom alkyl (nonyl) or alkoxy (octyloxy) chain at the 4-position, but with an unusual chain at the 4”-position. In some cases the terminal chain contains hetero atoms such as silicon, oxygen, chlorine and bromine or has a bulky end group. In total 46 final materials were synthesised in an attempt to understand the effect of an unusual terminal chains on mesomorphism and for some o f these compounds the effect upon the switching times when added to a standard ferroelectric mixture were investigated. It was found that most compounds containing a bulky end group only displayed a smectic C phase, compounds with a halogen substituent as an end unit displayed a smectic A phase and that increasing the chain flexibility by introducing an oxygen atom in the chain reduces the melting and clearing points. The electro-optical measurements carried outon ferroelectric mixtures containing a bulky end group compound showed that shorter switching times were produced than for the ferroelectric mixture containing a straight chain compound. It is suggested that a bulky end group diminishes the extent o f inter­ layer mixing in the chiral smectic C phase and therefore the molecules move more easily with ferroelectric switching

Insights into water coordination associated with the Cu(II)/Cu(I) electron transfer at a biomimetic Cu centre.

International audienceThe coordination properties of the biomimetic complex [Cu(TMPA)(H2O)](CF3SO3)2 (TMPA = tris(2-pyridylmethyl)amine) have been investigated by electrochemistry combined with UV-Vis and EPR spectroscopy in different non-coordinating media including imidazolium-based room-temperature ionic liquids, for different water contents. The solid-state X-ray diffraction analysis of the complex shows that the cupric centre lies in a N4O coordination environment with a nearly perfect trigonal bipyramidal geometry (TBP), the water ligand being axially coordinated to Cu(II). In solution, the coordination geometry of the complex remains TBP in all media. Neither the triflate ion nor the anions of the ionic liquids were found to coordinate the copper centre. Cyclic voltammetry in all media shows that the decoordination of the water molecule occurs upon monoelectronic reduction of the Cu(II) complex. Back-coordination of the water ligand at the cuprous state can be detected by increasing the water content and/or decreasing the timescale of the experiment. Numerical simulations of the voltammograms allow the determination of kinetics and thermodynamics for the water association-dissociation mechanism. The resulting data suggest that (i) the binding/unbinding of water at the Cu(I) redox state is relatively slow and equilibrated in all media, and (ii) the binding of water at Cu(I) is somewhat faster in the ionic liquids than in the non-coordinating solvents, while the decoordination process is weakly sensitive to the nature of the solvents. These results suggest that ionic liquids favour water exchange without interfering with the coordination sphere of the metal centre. This makes them promising media for studying host-guest reactions with biomimetic complexes

Ethnographier la blanchité dans les migrations françaises à Abu Dhabi : tensions épistémologiques et éthiques d’un « cynisme méthodologique »

Cet article rend compte des conditions éthiques et épistémologiques auxquelles s’est confrontée l’ethnographie des migrations françaises à Abu Dhabi (Émirats arabes unis), en particulier dans l’analyse de leur position dans les rapports sociaux de race, appréhendée par le concept de blanchité. L’article explore les avantages et les tensions méthodologiques associés à l’usage de l’entretien biographique et de l’observation non-déclarée, en prenant au sérieux leur spécificité et leur plus-value épistémologique respectives, mais également en nuançant leur opposition terme à terme. L’article soutient que les choix épistémologiques et éthiques sont indissociables, en ce qu’il n’est pas de parti pris éthique qui n’ait de conséquence épistémologique, et inversement.This article accounts for the ethical and epistemological conditions of an ethnography of French migrations to Abu Dhabi (United Arab Emirates). Drawing on the concept of whiteness, this ethnography has paid particular attention to the migrants’ position within racial relations. The article explores the advantages and methodological tensions tied to the use of biographical interviews and undisclosed observation. While acknowledging their respective specificity and epistemological added value, it also attempts to nuance their dichotomous opposition. The author defends that epistemological and ethical choices are closely entangled in the conduct of research, in that every ethical stance has epistemological consequences, and vice versa

Altering absence: From race to empire in readings of Foucault

This article will address sexuality as a medium of empire, approaching this question through the absence of empire in Foucault’s history of sexuality. This absence of empire is all the more enigmatic given that it coincides with the omnipresence of race. To that extent, I argue for an “alteration of absence” in the reading of Foucault. Acknowledging the paradoxical presence of race--perhaps even its centrality--in Foucault’s analysis of sexuality and liberalism is a necessary step to reveal the depth of another absence, that of empire and coloniality. The article discusses this blind spot in Foucault’s work, arguing that a form of racial distinction operates through sexuality.It attempts to assess how influential this “imperial absence” is to the genealogy of sexuality and race. Lastly, it also sketches some possible reconfigurations of Foucault’s theses when read in colonial or postcolonial contexts

The Ecoformative and Transformative Issues of Nature in the Schoolyard: An Exploration of the Relationship Between Everyday Experiences of Nature and Well-being at School

In urban areas, the implementation of schoolyard facilities (especially through the greening of these spaces) aims to promote children\u27s contact with nature to improve well-being and increase their awareness of environmental preservation. In this study, we use the prospect of schoolyard landscaping in two French schools to conduct research on pupils’ relationship with nature and well-being at school. We explore cognitive and social mechanisms that affect children\u27s perceptions and behaviour in their relationships with nature on a daily basis and in the school context, with a view toward implementing schoolyard designs. The research aims are (i) to gain a better understanding of the perceptions and uses that shape children\u27s day-to-day interactions, (ii) to document their perceived well-being in the school environment, and (iii) to elicit pupils\u27 views on changes to the school grounds, in order to better understand the characteristics and dynamics underlying the organisation of direct and sensitive relationships with nature. The results of this study are intended to contribute to an understanding of the issues, obstacles and levers involved in implementing schoolyard development projects, and to provide input for a reflective approach to these initiatives. The results show that children\u27s daily experiences of nature are constructed at the convergence of direct contact with the environment and the social framework that supports these interactions. These experiences foster the construction of perceptions and links with the natural environment, which reciprocally feed into further experience. The presence of nature in school grounds directly promotes pupils\u27 perceived well-being; a greater degree of experience and appreciation of nature positively influences it. We observe a lack of explicit recognition of nature\u27s contribution to well-being and examine the social and contextual reasons behind this, as well as the impact on pupils\u27 choices about schoolground planning. We then discuss the limits of urban policies based on schoolyard modifications and explore ways of including social-ecological relationships through children’s participation

Pre-organized structure of viral DNA at the binding-processing site of HIV-1 integrase

The integration of the human immunodeficiency virus type 1 DNA into the host cell genome is catalysed by the viral integrase (IN). The reaction consists of a 3′-processing [dinucleotide released from each 3′ end of the viral long terminal repeat (LTR)] followed by a strand transfer (insertion of the viral genome into the human chromosome). A 17 base pair oligonucleotide d(GGAAAATCTCTAGCAGT), d(ACTGCTAGAGATTTTCC) reproducing the U5-LTR extremity of viral DNA that contains the IN attachment site was analysed by NMR using the classical NOEs and scalar coupling constants in conjunction with a small set of residual dipolar coupling constants (RDCs) measured at the (13)C/(15)N natural abundance. The combination of these two types of parameters in calculations significantly improved the DNA structure determination. The well-known features of A-tracts were clearly identified by RDCs in the first part of the molecule. The binding/cleavage site at the viral DNA end is distinguishable by a loss of regular base stacking and a distorted minor groove that can aid its specific recognition by IN

Periodicity of Single-Molecule Magnet Behaviour of Heterotetranuclear Lanthanide Complexes across the Lanthanide Series: A Compendium.

Acetato-bridged palladium-lanthanide tetranuclear heterometallic complexes of the form [Pd2 Ln2 (H2 O)2 (CH3 COO)10 ]⋅2 CH3 COOH [Ln2 =Ce2 (1), Pr2 (2), Nd2 (3), Sm2 (4), Tb2 (5), Dy2 (6), Dy0.2 Y1.8 (6''), Ho2 (7), Er2 (8), Er0.24 Y1.7 (8''), Tm2 (9), Yb2 (10), Y2 (11)] were synthesised and characterised by experimental and theoretical techniques. All complexes containing Kramers lanthanide ions [Ln3+ =Ce (1), Nd (3), Sm (4), Dy (6), DyY (6''), Er (8), ErY (8''), Yb (10)] showed field-induced slow magnetic relaxation, characteristic of single-molecule magnetism and purely of molecular origin. In contrast, all non-Kramers lanthanide ions [Ln3+ =Pr (2), Tb (5), Ho (7), Tm (9), Y3+ (11) is diamagnetic and non-lanthanide] did not show any slow magnetic relaxation. The variation in the electronic structure and accompanying consequences across the complexes representing all Kramers and non-Kramers lanthanide ions were investigated. The origin of the magnetic properties and the extent to which the axial donor-acceptor interaction involving the lanthanide ions and an electron-deficient d z 2 orbital of palladium affects the observed magnetic and electronic properties across the lanthanide series are presented. Unique consistent electronic and magnetic properties of isostructural complexes spanning the lanthanide series with properties dependent on whether the ions are Kramers or non-Kramers are reported

Coupling between ferroelasticity and magnetization in two-dimensional organic–inorganic perovskites (C6H5C2H4NH3)2MCl4 (M = Mn, Cu, Fe)

Materials with coexistence of two or more ferroic orders are known as multiferroics. Magneto-elastic multiferroics, where ferromagnetism and ferroelasticity coexist, have been rarely reported previously. We studied the magneto-elastic multiferroic properties of two-dimensional organic–inorganic perovskites having the formulas (PEA)2MnCl4, (PEA)2CuCl4 and (PEA)2FeCl4 (PEA = C6H5C2H4NH3). All three exhibited ferroelasticity but the manganese and iron compounds showed canted antiferromagnetism and the copper one showed ferromagnetism. Also, only (PEA)2FeCl4 displayed a shift of magnetization when the sample was cooled in a magnetic field from above the magnetic ordering temperature. We propose that the magnetization shift originates from the coupling between ferroelasticity and magnetization via spin–orbit coupling (SOC). This work would shed light on understanding the coupling mechanism between ferroelasticity and magnetization towards the interesting role of SOC in ferroelastic materials

Deep sea tests of a prototype of the KM3NeT digital optical module

The first prototype of a photo-detection unit of the future KM3NeT neutrino telescope has been deployed in the deepwaters of the Mediterranean Sea. This digital optical module has a novel design with a very large photocathode area segmented by the use of 31 three inch photomultiplier tubes. It has been integrated in the ANTARES detector for in-situ testing and validation. This paper reports on the first months of data taking and rate measurements. The analysis results highlight the capabilities of the new module design in terms of background suppression and signal recognition. The directionality of the optical module enables the recognition of multiple Cherenkov photons from the same (40)Kdecay and the localisation of bioluminescent activity in the neighbourhood. The single unit can cleanly identify atmospheric muons and provide sensitivity to the muon arrival directions