High-pressure developments for resonant X-ray scattering experiments at I16.

An experimental setup to perform high-pressure resonant X-ray scattering (RXS) experiments at low temperature on I16 at Diamond Light Source is presented. The setup consists of a membrane-driven diamond anvil cell, a panoramic dome and an optical system that allows pressure to be measured in situ using the ruby fluorescence method. The membrane cell, inspired by the Merrill-Bassett design, presents an asymmetric layout in order to operate in a back-scattering geometry, with a panoramic aperture of 100° in the top and a bottom half dedicated to the regulation and measurement of pressure. It is specially designed to be mounted on the cold finger of a 4 K closed-cycle cryostat and actuated at low-temperature by pumping helium into the gas membrane. The main parts of the body are machined from a CuBe alloy (BERYLCO 25) and, when assembled, it presents an approximate height of 20-21 mm and fits into a 57 mm diameter. This system allows different materials to be probed using RXS in a range of temperatures between 30 and 300 K and has been tested up to 20 GPa using anvils with a culet diameter of 500 µm under quasi-cryogenic conditions. Detailed descriptions of different parts of the setup, operation and the developed methodology are provided here, along with some preliminary experimental results.

Vacancy defects and monopole dynamics in oxygen-deficient pyrochlores.

The idea of magnetic monopoles in spin ice has enjoyed much success at intermediate temperatures, but at low temperatures a description in terms of monopole dynamics alone is insufficient. Recently, numerical simulations were used to argue that magnetic impurities account for this discrepancy by introducing a magnetic equivalent of residual resistance in the system. Here we propose that oxygen deficiency is the leading cause of magnetic impurities in as-grown samples, and we determine the defect structure and magnetism in Y2Ti2O7-δ using diffuse neutron scattering and magnetization measurements. These defects are eliminated by oxygen annealing. The introduction of oxygen vacancies causes Ti(4+) to transform to magnetic Ti(3+) with quenched orbital magnetism, but the concentration is anomalously low. In the spin-ice material Dy2Ti2O7 we find that the same oxygen-vacancy defects suppress moments on neighbouring rare-earth sites, and that these magnetic distortions markedly slow down the long-time monopole dynamics at sub-Kelvin temperatures.

Suppression of thermal conductivity by rattling modes in thermoelectric sodium cobaltate.

The need for both high electrical conductivity and low thermal conductivity creates a design conflict for thermoelectric systems, leading to the consideration of materials with complicated crystal structures. Rattling of ions in cages results in low thermal conductivity, but understanding the mechanism through studies of the phonon dispersion using momentum-resolved spectroscopy is made difficult by the complexity of the unit cells. We have performed inelastic X-ray and neutron scattering experiments that are in remarkable agreement with our first-principles density-functional calculations of the phonon dispersion for thermoelectric Na(0.8)CoO2, which has a large-period superstructure. We have directly observed an Einstein-like rattling mode at low energy, involving large anharmonic displacements of the sodium ions inside multi-vacancy clusters. These rattling modes suppress the thermal conductivity by a factor of six compared with vacancy-free NaCoO2. Our results will guide the design of the next generation of materials for applications in solid-state refrigerators and power recovery.

Strain control of a bandwidth-driven spin reorientation in Ca3Ru2O7.

The layered-ruthenate family of materials possess an intricate interplay of structural, electronic and magnetic degrees of freedom that yields a plethora of delicately balanced ground states. This is exemplified by Ca3Ru2O7, which hosts a coupled transition in which the lattice parameters jump, the Fermi surface partially gaps and the spins undergo a 90∘ in-plane reorientation. Here, we show how the transition is driven by a lattice strain that tunes the electronic bandwidth. We apply uniaxial stress to single crystals of Ca3Ru2O7, using neutron and resonant x-ray scattering to simultaneously probe the structural and magnetic responses. These measurements demonstrate that the transition can be driven by externally induced strain, stimulating the development of a theoretical model in which an internal strain is generated self-consistently to lower the electronic energy. We understand the strain to act by modifying tilts and rotations of the RuO6 octahedra, which directly influences the nearest-neighbour hopping. Our results offer a blueprint for uncovering the driving force behind coupled phase transitions, as well as a route to controlling them.

Guiding antiferromagnetic transitions in Ca[Formula: see text]RuO[Formula: see text].

Understanding and controlling the transition between antiferromagnetic states having different symmetry content with respect to time-inversion and space-group operations are fundamental challenges for the design of magnetic phases with topologically nontrivial character. Here, we consider a paradigmatic antiferromagnetic oxide insulator, Ca[Formula: see text]RuO[Formula: see text], with symmetrically distinct magnetic ground states and unveil a novel path to guide the transition between them. The magnetic changeover results from structural and orbital reconstruction at the transition metal site that in turn arise as a consequence of substitutional doping. By means of resonant X-ray diffraction we track the evolution of the structural, magnetic, and orbital degrees of freedom for Mn doped Ca[Formula: see text]RuO[Formula: see text] to demonstrate the mechanisms which drive the antiferromagnetic transition. While our analysis focuses on a specific case of substitution, we show that any perturbation that can impact in a similar way on the crystal structure, by reconstructing the induced spin-orbital exchange, is able to drive the antiferromagnetic reorganization.

Local magnetism, magnetic order and spin freezing in the 'nonmetallic metal' FeCrAs.

We present the results of x-ray scattering and muon-spin relaxation ([Formula: see text]SR) measurements on the iron-pnictide compound FeCrAs. Polarized non-resonant magnetic x-ray scattering results reveal the 120° periodicity expected from the suggested three-fold symmetric, non-collinear antiferromagnetic structure. [Formula: see text]SR measurements indicate a magnetically ordered phase throughout the bulk of the material below [Formula: see text] K. There are signs of fluctuating magnetism in a narrow range of temperatures above [Formula: see text] involving low-energy excitations, while at temperatures well below [Formula: see text] behaviour characteristic of freezing of dynamics is observed, likely reflecting the effect of disorder in our polycrystalline sample. Using density functional theory we propose a distinct muon stopping site in this compound and assess the degree of distortion induced by the implanted muon.

Role of defects in determining the magnetic ground state of ytterbium titanate.

Pyrochlore systems are ideally suited to the exploration of geometrical frustration in three dimensions, and their rich phenomenology encompasses topological order and fractional excitations. Classical spin ices provide the first context in which it is possible to control emergent magnetic monopoles, and anisotropic exchange leads to even richer behaviour associated with large quantum fluctuations. Whether the magnetic ground state of Yb2Ti2O7 is a quantum spin liquid or a ferromagnetic phase induced by a Higgs transition appears to be sample dependent. Here we have determined the role of structural defects on the magnetic ground state via the diffuse scattering of neutrons. We find that oxygen vacancies stabilise the spin liquid phase and the stuffing of Ti sites by Yb suppresses it. Samples in which the oxygen vacancies have been eliminated by annealing in oxygen exhibit a transition to a ferromagnetic phase, and this is the true magnetic ground state.

Diffusion mechanism in the sodium-ion battery material sodium cobaltate.

High performance batteries based on the movement of Li ions in Li x CoO2 have made possible a revolution in mobile electronic technology, from laptops to mobile phones. However, the scarcity of Li and the demand for energy storage for renewables has led to intense interest in Na-ion batteries, including structurally-related Na x CoO2. Here we have determined the diffusion mechanism for Na0.8CoO2 using diffuse x-ray scattering, quasi-elastic neutron scattering and ab-initio molecular dynamics simulations, and we find that the sodium ordering provides diffusion pathways and governs the diffusion rate. Above T ~ 290 K the so-called partially disordered stripe superstructure provides channels for quasi-1D diffusion, and melting of the sodium ordering leads to 2D superionic diffusion above T ~ 370 K. We obtain quantitative agreement between our microscopic study of the hopping mechanism and bulk self-diffusion measurements. Our approach can be applied widely to other Na- or Li-ion battery materials.

Characterization of oxytocin, vasopressin, and neurophysin from the bovine corpus luteum.

Acid extracts of corpora lutea collected from nonpregnant cows were found to contain oxytocin, arginine vasopressin, and neurophysin. The inhibition curves of the oxytocin and vasopressin extracts showed parallelism with the appropriate standard preparations in specific RIAs and eluted at the same position as the standards using high performance liquid chromatography (HPLC). The neurophysin extract showed parallelism in a bovine neurophysin I RIA and had a similar elution position to the standard on both Sephadex G-50 and HPLC. However, its immunoreactive profile on HPLC differed slightly from that obtained with hypophyseal bovine neurophysin I. In nonpregnant cows the oxytocin content (about 1 microgram g-1 wet wt of tissue) was three orders of magnitude greater than the vasopressin content. Levels of luteal oxytocin were considerably lower in pregnant animals. These results show that the bovine ovary is a rich source of neurohypophysial peptides and suggest that oxytocin biosynthesis may occur within the corpus luteum.

Biosynthesis of oxytocin in the corpus luteum.

In this report we demonstrate that ovine and bovine luteal cells synthesise oxytocin by way of a precursor protein similar to that found in the hypothalamus. Isolated ovine or bovine luteal cells were incubated for up to 12 h with [35S]cysteine. Neurophysin-Sepharose column separation and HPLC of cell extracts demonstrated the presence of [35S]oxytocin. Incorporation of [35S]cysteine was confirmed by performic acid oxidation. Immunoprecipitation of cell extract with anti-rat oxytocin-neurophysin followed by SDS-PAGE yielded 2 radioactive bands of 14 kDa and 11-12 kDa. Immunoprecipitation with anti-oxytocin yielded 1 band at 14 kDa. On SDS-PAGE the 14 kDa band had a similar mobility to rat-hypothalamic oxytocin precursor.

Oestrogen-induced myometrial quiescence in the post-partum rat is not mediated by adrenaline or by alpha- or beta-adrenoceptor activation.

Ovariectomized post-partum rats exhibit in vivo continuous stable myometrial activity with a frequency of 45--50 pressure cycles per h, and a mean maximum amplitude of 45--50 mmHg for many days. Oestradiol benzoate (5 micrograms) reduced the frequency of intra-uterine pressure cycles to 5 cycles per h by 20 h after treatment. The decrease in frequency was due to increased periods of uterine quiescence. Pretreatment with reserpine caused significant reductions in the concentration of uterine adrenaline and noradrenaline as measured by a fluorometric assay but had no effect on the extent or time-course of oestrogen-induced myometrial quiescence. Neither intravenous infusion of the adrenergic beta-blocker, propranolol, altered the extent or the time-course of the reduction of intra-uterine pressure cycles after oestrogen treatment. These results suggest that the mechanism by which oestrogen induces myometrial quiescence does not involve adrenaline mediation or alpha- or beta-adrenoceptor activation.

Evidence that inhibition of myometrial activity by oestradiol in the rat is mediated by an RNA synthetic pathway.

Within some 14 h of treatment with oestradiol benzoate (5 microgram), the intra-uterine pressure cycles in ovariectomized puerperal rats were almost abolished. However, treatment with 600 microgram actinomycin D 30 min before the administration of oestradiol benzoate interfered significantly with the inhibition of uterine mechanical activity during the following 14h. Treatment of rats with actinomycin D alone produced no significant fall in the frequency of pressure cycles. These results suggest that oestrogen inhibits myometrial activity in the rat through a mechanism which involves the synthesis of protein.

Relaxin inhibits spontaneous and prostaglandin-driven myometrial activity in anaesthetized rats.

Porcine relaxin (250 guinea-pig units/mg) infused intravenously into anaesthetized rats at 20 micrograms/h reversibly abolished spontaneous intra-uterine pressure cycles yet left the myometrium responsive to oxytocin in doses of 4--8 mu. The inhibition was found to be primarily of the frequency, rather than of the amplitude, of pressure cycles. Relaxin (5 or 10 micrograms) was capable of completely suppressing uterine activity driven by prostaglandin F2 alpha infusion in oestrogen-treated ovariectomized rats. Whereas the beta-adrenergic blocker, propranolol, had no effect on relaxin-induced inhibition, phentolamine, an alpha-blocker, significantly delayed the relaxin effect. It is unlikely, however, that relaxin operates through an alpha-inhibitory receptor. The results show that relaxin acts primarily as a frequency modulator and is capable of antagonizing an exogenous myometrial stimulant.

Inhibition of oxytocin-or prostaglandin F2alpha-driven myometrial activity by relaxin in the rat is oestrogen-dependent.

Relaxin in doses of 5 microgram i.v. completed but reversibly abolishes "spontaneous' myometrial activity in anaesthetized ovariectomized rats. Similar levels of myometrial activity, evoked in oestrogen-treated rats (which normally have quiescent uteri) by infusions of oxytocin or prostaglandin F2alpha (PGF2alpha), were also reduced to complete quiescence by relaxin in small doses. However when spontaneous myometrial activity in untreated ovariectomized rats was slightly stimulated by oxytocin the uterus became completely refractory to the inhibitory effects of relaxin even at doses of 50 microgram. Relaxin was also ineffective in reducing myometrial activity in similar rats during intra-arterial infusion of PGF2alpha. It is suggested that the ability of relaxin to inhibit uterine smooth muscle during exogenous stimulation is oestrogendependent.

Rat myometrial activity in vivo: effects of oestradiol-17 beta and progesterone in relation to the concentrations of cytoplasmic progesterone receptors.

The amplitude, frequency and rate of rise of intra-uterine pressure cycles in rats (postpartum, ovariectomized) were unaffected by treatment with progesterone. Amplitude was also unaffected by a combination of treatments with progesterone and oestradiol-17 beta, which was adequate to ensure the survival of 84% of foetuses in ovariectomized pregnant rats. The failure of progesterone to influence myometerial activity could not be attributed to a lack of "true" progesterone receptors since these were present in the myometria of the test animals in concentrations exceeding those of oestrous animals. Evidence was obtained which suggested that a high-affinity binding protein, different from the "true" receptor may predominate in the myometrium of the pregnant rat. Oestradiol-17 beta in single or repeated doses of from 0.25 to 5 microgram, however, was found to reduce the frequency of pressure cycles but to increase significantly their rate of rise of pressure. There was a latency of 6--8 h in these effects of oestradiol. The possibility that inhibition of the myometrium by oestrogen may play a part in the preparation for parturition is discussed.

Rapid increase in relaxin gene expression in early pregnancy in the pig.

Relaxin mRNA concentrations in porcine corpora lutea were examined during the peri-implantation period and throughout pregnancy using Northern and slot blot analysis. Total RNA was extracted from corpora lutea obtained from pigs of known breeding dates and pregnancy was confirmed by embryo recovery. A 32P-labelled porcine relaxin cDNA probe identified the 1.0 kilobase relaxin transcript. Slot blots were subsequently used to quantify relaxin mRNA concentrations. Relaxin mRNA was detectable in the corpus luteum of the regular cycle and was also present at similar low levels in corpora lutea of days 10, 11 and 12 of pregnancy. In corpora lutea from day 16 of pregnancy onwards 100-fold greater quantities of relaxin mRNA were observed. The intensity remained similar in samples between days 16 and 102 of pregnancy. These studies indicate that elevated relaxin gene expression commences very early in pregnancy and is first detectable in the peri-implantation period.

Identification of oxytocin and vasopressin in the testis and in adrenal tissue.

Oxytocin, vasopressin and neurophysin-like immunoreactivity have been identified and measured by radioimmunoassay in extracts of human and rat testis and human fetal adrenal tissue. The authenticity of these polypeptides has been confirmed by their behaviour on high performance liquid chromatography. The concentrations of the hormone were too great to be explained by known circulating levels of the polypeptides, and their presence in steroid secreting organs suggests a possible role for them in steroidogenesis. The peptides may be taken up and concentrated by the tissues but the co-localisation of neurophysins with the hormones points towards local synthesis.

Effects of relaxin on matrix remodeling enzyme activity of cultured equine ovarian stromal cells.

Relaxin participates in extracellular matrix (ECM) remodeling in many reproductive organs, including the ovary, by regulating proteolytic enzyme activity. Accumulated evidence indicates this action of relaxin is involved in ovarian follicle development and ovulation. Equine follicles are embedded in cortex that is at the center of the ovary and they must expand/emigrate to the fossa, the only site in the ovary for ovulation. Due to the tremendous expansion of the follicle in this species, we hypothesized that ovarian stromal remodeling would be extensive. Therefore, cultured equine ovarian stromal cell (EOSC) lines were obtained from stroma at the apex of large follicles and the effects of relaxin on gelatinases A and B, tissue inhibitors of matrix metalloproteinases (TIMPs), plasminogen activators (PAs) and PA inhibitor-1 (PAI-1) activities were assessed. Our results showed that equine relaxin increased the activity of total gelatinase A (both pro forms and mature forms) and latent progelatinase B present in conditioned medium, latent progelatinase A present in cell extracts, and TIMP-1 and TIMP-2 present in conditioned medium. This study also revealed that equine relaxin increased the urokinase-type PA activity in conditioned medium and cell extracts, tissue-type PA activity in ECM and PAI-1 activity in conditioned medium. These results suggest that relaxin may contribute to equine follicle growth and migration, and facilitate ovulation by modulating the degradation of ECM in ovarian stromal tissue.

Relaxin is not associated with poor milk yield in the postpartum sow.

Porcine relaxin (pRXN) titers were measured in 109 plasma samples drawn between 24 and 120 h post-partum from good (n = 34), and poor (n = 25) milking sows and from sows (n = 12) exhibiting overt signs of hypogalactia located on six swine farms in Ontario. Mean plasma pRXN titers among the three groups at 24 h post-partum were not significantly different although there was considerable variation. By 48 h however, the pRXN titers had declined markedly in all groups and between 72 and 120 h, pRXN was cleared from the plasma of all sows examined except one hypogalactic animal that had a titer of 1.13 ng/mL at 96 h. These results suggest that, although pRXN may be identifiable in the corpora lutea during the puerperium, it does not contribute to either hypogalactia or poor lactational performance in sows. The data also encourage the view that pRXN could be used at farrowing without deleterious effects on suckling.