Magnetic susceptibilities, specific heat, and crystal structure of four S = 3/2, three-dimensional antiferromagnets

The zero-field, ac magnetic susceptibilities of single crystals of four S=3/2 trigonal salts containing the tris(1,2-diaminoethane)chromium(III) cation, [Cr(en)3]3+, and heat-capacity measurements on one of them, [Na(OH2)6][Cr(en)3]2Cl7, are reported. The crystal structures of two of them, [Na(OH2)6][Cr(en3]2Cl7 and [Na(OH)2)6][Cr(en)3]2Br6Cl, have been determined. They both belong to the trigonal P3¯cl space group, with a=11.513(2), c=15.566(6) Å; Z=2; and a=11.740(5), c=16.008(9) Å; Z=2, respectively, and contain discrete octahedral hexaquasodium (i) cations. The salt [K(OH2)6][Cr(en)3]2Cl7 appears to be isomorphous with its sodium analog, and [Cr(en)3]Cl3·3H2O belongs to the same space group. The magnetic measurements on the four salts extend over the temperature interval 60 mK to 4.2 K, and antiferromagnetic ordering is found in all of them. The zero-field-splitting energy is of the same order of magnitude as the magnetic exchange energy. The susceptibility data have been fitted with the parameters 2D/kB=-0.091(8) K, g?=1.994, g¿=1.988, and zJ/kB=-0.061(2) K for [Cr(en)3]Cl3·3H2O; 2D/kB=-0.058(8) K, g?=2.01, g¿=2.00, and zJ/kB=-0.068(4) K for [Na(OH2)6][Cr(en)3]2Cl7; 2D/kB =-0.060(8) K, g?=1.993, g¿=1.951, and zJ/kB=-0.046(4) K for [K(OH2)6][Cr(en)3]2Cl7; and 2D/kB=+0.064(8) K, g?=2.001, g¿=1.991, and zJ/kB=-0.066(4) K for [Na(OH2)6][Cr(en)3]2Br6Cl, where longitudinal (¿) and transverse (¿) refer to the unique threefold crystallographic axis. The ordering temperatures are 0.124(5), 0.116(5), 0.093(5), and 0.112(5) K, respectively. The easy axis for the chloride compounds lies parallel to the longitudinal axis, whereas the easy axis for the bromide lies in the transverse plane. Heat-capacity measurements on [Na(OH2)6][Cr(en)3]2Cl7 confirm that magnetic ordering takes place at 0.112(5) K. The heat-capacity curve and magnetic entropy calculations agree with the three-dimensional character of the ordering of an S=3/2, effective bcc magnetic lattice

Search for Darkonium in e+e- Collisions

Collider searches for dark sectors, new particles interacting only feebly with ordinary matter, have largely focused on identifying signatures of new mediators, leaving much of dark sector structures unexplored. In particular, the existence of dark matter bound states (darkonia) remains to be investigated. This possibility could arise in a simple model in which a dark photon (A0 ) is light enough to generate an attractive force between dark fermions. We report herein a search for a JPC ¼ 1−− darkonium state, the ϒD, produced in the reaction eþe− → γϒD, ϒD → A0 A0 A0 , where the dark photons subsequently decay into pairs of leptons or pions, using 514 fb−1 of data collected with the BABAR detector. No significant signal is observed, and we set bounds on the γ − A0 kinetic mixing as a function of the dark sector coupling constant for 0.001 < mA0 < 3.16 GeV and 0.05 < mϒD < 9.5 GeV.publishedVersio

Enhanced laccase stability through mediator partitioning into hydrophobic ionic liquids

Partitioning mediators into water-immiscible ionic liquids protects laccase from inactivation.</p

Ionic liquid crystals: hexafluorophosphate salts

A series of novel hexafluorophosphate salts, based on N,N¾-dialkylimidazolium and substituted N-alkylpyridinium cations, display liquid crystalline behaviour at temperatures above their melting point. The temperature range over which liquid crystalline behaviour is observed increases markedly with increasing alkyl chain length. Alkyl substitution at the 3- and 4-positions on the pyridinium ring results in a decrease in the melting point compared with the equivalent unsubstituted salt, but also leads to a large decrease in the tendency towards liquid crystalline behaviour (or mesogenicity). The salts prepared are fully characterised using a wide variety of techniques, including NMR and IR spectroscopy, DSC, and single crystal X-ray diffraction in the case of 1-dodecyl-3-methylimidazolium hexafluorophosphate. The effect of preparing mixtures containing different proportions of two cations is also reported

Novel ionic media for liquid lasers

In a search for 3-5 µm lasing materials, crystals Of AlBr6Sb are isolated from a phosphorus tribromide-aluminium tribromide-antimony tribromide (PBr3-AlBr3-SbBr3) solution: this solid contains infinite chains of alternating [SbBr2]+ cations and [AlBr4]+ anions, linked by weak coordinate bonds, and represents the first structure containing the dibromostibinium(III) cation

Supercritical fluids in ionic liquids

Ionic liquids and supercritical fluids are both alternative environmentally benign solvents, but their properties are very different. Ionic liquids are non-volatile but often considered highly polar compounds, whereas supercritical fluids are non-polar but highly volatile compounds. The combination of these two types of solvents has some unique features. It has been discovered that the solubility of supercritical carbon dioxide in several ionic liquids is very high but that the solubility of ionic liquids in supercritical carbon dioxide is negligibly low. Therefore, organic solutes can be extracted from an ionic liquid using supercritical carbon dioxide without any contamination by the ionic liquid. The phase behaviour of many binary or ternary (ionic liquid+supercritical carbon dioxide) systems was subsequently studied. Combined with the fact that ionic liquids are excellent reaction media for catalysed reactions, this led to the development of chemical processes where the reaction was carried out in the ionic liquid and the product was extracted afterwards with supercritical carbon dioxide. Newest developments include the multi-functional use of supercritical carbon dioxide as extraction medium, transport medium, and miscibility controller in these processes, resulting in higher reaction and separation rates

Understanding the operation and regulation of specialized drug shops in Kenya

Background: A high proportion of people in Sub-Saharan Africa receive treatment from specialized drug shops (SDSs) such as pharmacies and drug stores because they provide convenient access to medicines. There is increasing interest in how policy makers can work with such retailers, but little knowledge on how their operation relates to legal and regulatory frameworks, and what factors influence regulatory behaviour of providers and front-line regulatory staff. This thesis aims to address these gaps in the context of Western Kenya. Methodology: Document reviews and key informant interviews were used to map the legal and regulatory framework governing retail provision of medicines in Kenya. Provider and mystery shopper surveys were used to investigate regulatory compliance among SDSs in two districts in Western Kenya. Finally, qualitative methods were used to describe factors underlying regulatory behaviour of SDS and regulatory staff, comprising focus group discussions with SDS operators and in-depth interviews with front-line and senior regulatory staff. Key findings: Low regulatory compliance was observed, especially among rural shops, to both structural and dispensing requirements. Compliance was not influenced significantly by the frequency of regulatory inspections. Qualitative data suggested that relationships between front- line staff and SDS operators strongly influenced regulatory behaviour of SDSs, often resulting in perverse outcomes such as corruption. In practice, separate regulatory streams operated in urban and rural locations, based on the differing relationships between inspectors and operators, and broader differences in the competitive environment. Moreover, the regulatory system lacked effective incentive structures to encourage regulatory enforcement. Key recommendations: The main recommendations include developing appropriate incentive contracts for front-line staff, and considering the introduction of lower retail practice requirements for rural SDSs in recognition of the vast differences in rural and urban SDS practice environments, allowing shops currently operating unlawfully to be brought within the regulatory framework without compromising the relatively higher quality among urban SDSs.EThOS - Electronic Theses Online ServiceGBUnited Kingdo