Symmetry of re-entrant tetragonal phase in Ba1-xNaxFe2As2: Magnetic versus orbital ordering mechanism

Magneto-structural phase transitions in Ba1-xAxFe2As2 (A = K, Na) materials are discussed for both magnetically and orbitally driven mechanisms, using a symmetry analysis formulated within the Landau theory of phase transitions. Both mechanisms predict identical orthorhombic space-group symmetries for the nematic and magnetic phases observed over much of the phase diagram, but they predict different tetragonal space-group symmetries for the newly discovered re-entrant tetragonal phase in Ba1-xNaxFe2As2 (x ~ 0.24-0.28). In a magnetic scenario, magnetic order with moments along the c-axis, as found experimentally, does not allow any type of orbital order, but in an orbital scenario, we have determined two possible orbital patterns, specified by P4/mnc1' and I4221' space groups, which do not require atomic displacements relative to the parent I4/mmm1' symmetry and, in consequence, are indistinguishable in conventional diffraction experiments. We demonstrate that the three possible space groups are however, distinct in resonant X-ray Bragg diffraction patterns created by Templeton & Templeton scattering. This provides an experimental method of distinguishing between magnetic and orbital models

Clinical pharmacology becomes a specialty in South Africa

South Africa recently became the first African country where clinical pharmacology has been approved as a specialty. This article outlines the need for clinical pharmacologists, their role in advancing public health, the potential benefits to the country, and recommendations for ensuring a healthy future for the discipline

Current and future treatments of pulmonary arterial hypertension

Therapeutic options for pulmonary arterial hypertension (PAH) have increased over the last decades. The advent of pharmacological therapies targeting the prostacyclin, endothelin, and NO pathways has significantly improved outcomes. However, for the vast majority of patients, PAH remains a life‐limiting illness with no prospect of cure. PAH is characterised by pulmonary vascular remodelling. Current research focusses on targeting the underlying pathways of aberrant proliferation, migration, and apoptosis. Despite success in preclinical models, using a plethora of novel approaches targeting cellular GPCRs, ion channels, metabolism, epigenetics, growth factor receptors, transcription factors, and inflammation, successful transfer to human disease with positive outcomes in clinical trials is limited. This review provides an overview of novel targets addressed by clinical trials and gives an outlook on novel preclinical perspectives in PAH

The effects of buserelin microparticles on ovarian function in healthy women

Objective. To investigate the tolerance, pharmacokinetics and pharmacodynamJcs of the microparticle fonnulation of buserelin, when it wasaaministered subcutaneously.Design. A single-blind, randomised, parallel-group design was used to investigate the duration of suppression of ovarian function associated with doses of 1,8, 3,6 and 7,2 mg buserelin administered subcutaneously as microparticles.Setting. The study was carried out at the Hoechst Research Centre for Clinical Pharmacology, Department of Pharmacology, University of the Orange Free State, Bloemfontein.Patients. Thirty-two healthy premenopausal female volunteers aged between 19 and 39 years and weighing between 52 and 85 kg completed the study.Outcome measures. Serum progesterone and oestradiol concentrations were measured twice weekly until normal ovarian function resumed, i.e. when serum progesterone concentrations increased to at least 8 nmoVI (a sign of ovulation) and oestradiol concentrations increased to values above 300 pmol/l. Serum and urinary concentrations of buserelin were measured at the same times as those of progesterone and oestradiol.Results. Doses of 1,8,3,6 and 7,2 mg elicited anovulation for mean periods of 52, 77 and 113 days and suppressed ovarian production of oestrogen for 19, 38 and 69 days. Resumption of normal ovarian function occurred when serum buserelin concentrations decreased to between 0,03 and 0,05 lJg/ml. The correlation coefficient between dose and duration of anovulation was 0,75; the correlation coefficient between dose and duration of suppression of oestrogen production was 0,76.Conclusion. Apart from minor side-effects such as hot flushes, vaginal spotting and acne, the compound was tolerated well. We conclude that a good relationship exists between dose and duration of suppression of ovarian function. Doses of 3,6 - 7,2 mg buserelin should suppress oestrogen production for approximately 6 - 9 weeks and ovulation for 11 - 16 weeks

Prioritizing testing of organic compounds detected as gas phase air pollutants: structure-activity study for human contact allergens.

Organic compounds that are used or generated anthropogenically in large quantities in cities can be identified through their presence in the urban atmosphere and in air pollutant source emissions. Compounds identified by this method were screened to evaluate their potential to act as contact allergens. The CASE and MULTICASE computer programs, which are based on the detection of structure-activity relationships (SAR), were used to evaluate this potential. These relationships first are determined by comparing chemical structures to biological activity within a learning set comprised of 458 compounds, each of which had been tested experimentally in human trials for its sensitization potential. Using the information contained in this learning set, CASE and MULTICASE predicted the activity of 238 compounds found in the atmosphere for their ability to act as contact allergens. The analysis finds that 21 of 238 compounds are predicted to be active contact allergens (probability >0.5), with potencies ranging from mild to very strong. The compounds come from chemical classes that include chlorinated aromatics and chlorinated hydrocarbons, N-containing compounds, phenols, alkenes, and an S-containing compound. Using the measured airborne concentrations or emission rates of these compounds as an indication of the extent of their use, together with their predicted potencies, provides an efficient method to prioritize the experimental assessment of contact sensitization of untested organic compounds that can be detected as air pollutants

Spectroscopic evidence for preformed Cooper pairs in the pseudogap phase of cuprates

Angle-resolved photoemission on underdoped La$_{1.895}$Sr$_{0.105}$CuO$_4$ reveals that in the pseudogap phase, the dispersion has two branches located above and below the Fermi level with a minimum at the Fermi momentum. This is characteristic of the Bogoliubov dispersion in the superconducting state. We also observe that the superconducting and pseudogaps have the same d-wave form with the same amplitude. Our observations provide direct evidence for preformed Cooper pairs, implying that the pseudogap phase is a precursor to superconductivity

Neutron and X-ray evidence of charge melting in ferromagnetic layered colossal magnetoresistance manganites

Recent x-ray and neutron scattering studies have revealed static diffuse scattering due to polarons in the paramagnetic phase of the colossal magnetoresistive manganites La2-2xSr1+2xMn2O7, with x = 0.40 and 0.44. We show that the polarons exhibit short-range incommensurate correlations that grow with decreasing temperature, but disappear abruptly at the combined ferromagnetic and metal-insulator transition in the x = 0.40 system because of the sudden charge delocalization, while persisting at low temperature in the antiferromagnetic x = 0.44 system. The "melting" of the polaron ordering as we cool through T-C occurs with the collapse of the polaron scattering itself in the x = 0.40 system. This short-range polaron order is characterized by an ordering wave vector q = (0.3,0,1) that is almost independent of x for x greater than or equal to 0.38, and is consistent with a model of disordered stripes. (C) 2001 American Institute of Physics