Classical Spin Nematic Transition in LiGa_{0.95}In_{0.05}Cr_{4}O_{8}.

We present the results of a combined ^{7}Li-NMR and diffraction study on LiGa_{0.95}In_{0.05}Cr_{4}O_{8}, a member of the LiGa_{1-x}In_{x}Cr_{4}O_{8} "breathing" pyrochlore family. Via specific heat and NMR measurements, we find that the complex sequence of first-order transitions observed for LiGaCr_{4}O_{8} is replaced by a single second-order transition at T_{f}=11 K. Neutron and x-ray diffraction rule out both structural symmetry lowering and magnetic long-range order as the origin of this transition. Instead, reverse Monte Carlo fitting of the magnetic diffuse scattering indicates that the low-temperature phase may be described as a collinear spin nematic state, characterized by a quadrupolar order parameter. This state also shows signs of short-range order between collinear spin arrangements on tetrahedra, revealed by mapping the reverse Monte Carlo spin configurations onto a three-state color model.

From spin glass to quantum spin liquid ground states in molybdate pyrochlores.

We present new magnetic heat capacity and neutron scattering results for two magnetically frustrated molybdate pyrochlores: S=1 oxide Lu_{2}Mo_{2}O_{7} and S=1/2 oxynitride Lu_{2}Mo_{2}O_{5}N_{2}. Lu_{2}Mo_{2}O_{7} undergoes a transition to an unconventional spin glass ground state at T_{f}∼16 K. However, the preparation of the corresponding oxynitride tunes the nature of the ground state from spin glass to quantum spin liquid. The comparison of the static and dynamic spin correlations within the oxide and oxynitride phases presented here reveals the crucial role played by quantum fluctuations in the selection of a ground state. Furthermore, we estimate an upper limit for a gap in the spin excitation spectrum of the quantum spin liquid state of the oxynitride of Δ∼0.05 meV or Δ/|θ|∼0.004, in units of its antiferromagnetic Weiss constant θ∼-121 K.

z+: Neutron cross section separation from wide-angle uniaxial polarization analysis.

We introduce a simple method to extract the nuclear coherent and isotope incoherent, spin incoherent, and magnetic neutron scattering cross section components from powder scattering data measured using a single neutron beam polarization direction and a position-sensitive detector with large out-of-plane coverage. The method draws inspiration from polarized small-angle neutron scattering and contrasts with conventional so-called "xyz" polarization analysis on wide-angle instruments, which requires measurements with three orthogonal polarization directions. The viability of the method is demonstrated on both simulated and experimental data for the classical "spin ice" system Ho2Ti2O7, the latter from the LET direct geometry spectrometer at the ISIS facility. The cross section components can be reproduced with good fidelity by either fitting the out-of-plane angle dependence around a Debye-Scherrer cone or grouping the data by angle and performing a matrix inversion. The limitations of the method and its practical uses are discussed.

Temperature dependence of the [Formula: see text] anomaly in the excitation spectrum of the 2D quantum Heisenberg antiferromagnet.

It is well established that in the low-temperature limit, the two-dimensional quantum Heisenberg antiferromagnet on a square lattice (2DQHAFSL) exhibits an anomaly in its spectrum at short-wavelengths on the zone-boundary. In the vicinity of the [Formula: see text] point the pole in the one-magnon response exhibits a downward dispersion, is heavily damped and attenuated, giving way to an isotropic continuum of excitations extending to high energies. The origin of the anomaly and the presence of the continuum are of current theoretical interest, with suggestions focused around the idea that the latter evidences the existence of spinons in a two-dimensional system. Here we present the results of neutron inelastic scattering experiments and Quantum Monte Carlo calculations on the metallo-organic compound Cu(DCOO)[Formula: see text]D2O (CFTD), an excellent physical realisation of the 2DQHAFSL, designed to investigate how the anomaly at [Formula: see text] evolves up to finite temperatures [Formula: see text]. Our data reveal that on warming the anomaly survives the loss of long-range, three-dimensional order, and that it is thus a robust feature of the two-dimensional system. With further increase of temperature the zone-boundary response gradually softens and broadens, washing out the [Formula: see text] anomaly. This is confirmed by a comparison of our data with the results of finite-temperature Quantum Monte Carlo simulations where the two are found to be in good accord. In the vicinity of the antiferromagnetic zone centre, there was no significant softening of the magnetic excitations over the range of temperatures investigated.

Scale-free antiferromagnetic fluctuations in the s = 1/2 kagome antiferromagnet herbertsmithite.

Neutron spectroscopy and diffuse neutron scattering on herbertsmithite [ZnCu(3)(OH)(6)Cl(2)], a near-ideal realization of the s=1/2 kagome antiferromagnet, reveal the hallmark property of a quantum spin liquid: instantaneous short-ranged antiferromagnetic correlations in the absence of a time-averaged ordered moment. These dynamic antiferromagnetic correlations are weakly dependent of neutron-energy transfer and temperature, and persist up to 25 meV and 120 K. At low energy transfers a shift of the magnetic scattering to low Q is observed with increasing temperature, providing evidence of gapless spinons. It is argued that these observations provide important evidence in favor of resonating-valence-bond theories of (doped) Mott insulators.

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.

Fractional excitations in the square lattice quantum antiferromagnet.

Quantum magnets have occupied the fertile ground between many-body theory and low-temperature experiments on real materials since the early days of quantum mechanics. However, our understanding of even deceptively simple systems of interacting spins-1/2 is far from complete. The quantum square-lattice Heisenberg antiferromagnet (QSLHAF), for example, exhibits a striking anomaly of hitherto unknown origin in its magnetic excitation spectrum. This quantum effect manifests itself for excitations propagating with the specific wave vector (π, 0). We use polarized neutron spectroscopy to fully characterize the magnetic fluctuations in the metal-organic compound CFTD, a known realization of the QSLHAF model. Our experiments reveal an isotropic excitation continuum at the anomaly, which we analyse theoretically using Gutzwiller-projected trial wavefunctions. The excitation continuum is accounted for by the existence of spatially-extended pairs of fractional S=1/2 quasiparticles, 2D analogues of 1D spinons. Away from the anomalous wave vector, these fractional excitations are bound and form conventional magnons. Our results establish the existence of fractional quasiparticles in the high-energy spectrum of a quasi-two-dimensional antiferromagnet, even in the absence of frustration.

Nod factor-induced expression of leghemoglobin to study the mechanism of NH4NO3 inhibition on root hair deformation.

Nod factors secreted by Rhizobium leguminosarum by, viciae induce root hair deformation, the formation of nodule primordia, and the expression of early nodulin genes in Vicia sativa (vetch). Root hair deformation is induced within 3 h in a small, susceptible zone (+/-2 mm) of the root. NH4NO3, known to be a potent blocker of nodule formation, inhibits root hair deformation, initial cortical cell divisions, and infection thread formation. To test whether NH4NO3 affects the formation of a component of the Nod factor perception-transduction system, we studied Nod factor-induced gene expression. The differential display technique was used to search for marker genes, which are induced within 1 to 3 h after Nod factor application. Surprisingly, one of the isolated cDNA clones was identified as a leghemoglobin gene (VsLb1), which is induced in vetch roots within 1 h after Nod factor application. By using the drug brefeldin A, it was then shown that VsLb1 activation does not require root hair deformation. The pVsLb1 clone was used as a marker to show that in vetch plants grown in the presence of NH4NO3, Nod factor perception and transduction leading to gene expression are unaffected.

Nuclear magnetic resonance spectroscopy: biochemical evaluation of brain function in vivo and in vitro.

Nuclear magnetic resonance spectroscopy (MRS) offers a unique opportunity to monitor mmolar concentrations of high energy phosphates, glucose, lactate and amino acids. The possibility of obtaining information about chemical constituents noninvasively is of great importance. MRS and chemical shift imaging (CSI) are emerging as tools for tumor grading, monitoring of treatment, ischemia research, in pediatric research for follow-up of children with borderline mental retardation, for defining brain death and to define epileptic foci. It is important to know which cell type (neuronal or glial) shows changes as a result of external manipulations (e.g. excitotoxins) or internal changes (brain pathology). Metabolic studies have been carried out on brain cell cultures. By using 13C labeled glucose and acetate in combination with 13C MRS it was shown that astrocytes release lactate, glutamine, citrate and alanine and that cerebral cortical neurons use glutamine released from astrocytes as a precursor for GABA synthesis. An important feature in MRS is the localization of N-acetyl aspartate in neurons, since this enables monitoring of neuronal reactions, such as survival after neurotoxic insults. Recent advances have yielded high speed functional echo planar imaging (EPI) techniques that are sensitive to changes in cerebral blood volume, blood flow and blood oxygenation (Functional MRI). During cognitive task performance, local alterations in neuronal activity induce local changes in cerebral metabolism and cerebral perfusion, which can now be detected with MRI.

In vitro proton NMR spectroscopy of extracts from human breast tumours and non-involved breast tissue.

Proton (1H) nuclear magnetic resonance (NMR) spectra were obtained from perchloric acid (PCA) extracts of 11 breast tumours and non-involved breast tissue from 7 of the same patients. The spectra were correlated with histopathologic diagnosis. The tumour group consisted of 8 ductal carcinomas, 1 ductal carcinoma with an extensive intraductal component, 1 intraductal carcinoma and 1 fibroadenoma. Higher content of lactate, succinate and phosphocholine and low levels of glucose and inositol were characteristic findings in the tumour group as compared to non-involved breast tissue. 1H NMR spectra of PCA extracted breast specimens provide a comprehensive window into the metabolic activities of the tissue.

Comparison between magnetic resonance imaging findings and knee stability: measurements after anterior cruciate ligament repair with and without augmentation. A five- to seven-year followup of 52 patients.

We compared magnetic resonance imaging findings with knee stability measurements in a group of 52 patients 5 to 7 years after repair of an acute anterior cruciate ligament rupture. The patients underwent one of three surgical procedures: nonaugmented repair using the Palmer technique, repair with synthetic augmentation, and repair with biologic augmentation. The appearances of the menisci, subchondral bone, and cartilage were also assessed. Of the patients with clinically stable knees in the nonaugmented repair group, the repaired ligament appeared to be present and intact in 54% (7 of 13) of the patients. In the group with the repair augmented with the ligament augmentation device, 33% (4 of 12) demonstrated repair integrity, whereas in the group with patellar tendon augmentation of the repair, 82% (14 of 17) of the patients with clinically stable knees had intact ligaments on magnetic resonance imaging. Twelve patients had new and complete ruptures of one of the menisci, nine of which occurred in unstable knees. Thirteen patients had subcortical bone changes in the femoral condyles. Eight of these knees had major degenerative cartilage changes overlying the bone changes. Magnetic resonance imaging signals in the repaired ligament augmented with the patellar tendon were highly predictive of clinical stability, but the integrity of the nonaugmented and ligament augmentation device-augmented anterior cruciate ligament repairs did not closely correlate with the clinical findings.

Cerebral magnetic resonance imaging and cerebral computerized tomography for patients with solvent-induced encephalopathy.

To compare the results of cerebral magnetic resonance imaging (MRI) and computerized tomography (CT) for patients with solvent-induced encephalopathy, a parallel study was performed with nine patients. The diagnosis had been given three to five years earlier on the basis of relevant exposure to solvents, findings on neuropsychological tests, a neurological examination, and cerebral CT. There was no progression of pathological lesions from the first to the second CT examination. Four patients with atrophy in the CT examination also had atrophy in the MRI examination. In addition three patients with normal CT findings showed atrophy in the MRI examination. It was concluded that MRI should be the modality of choice whenever diagnostic imaging is necessary in the clinical workout of patients with diagnosed or suspected solvent-induced encephalopathy.

The use of MRI in the diagnosis of chronic lymphedema of the lower extremity.

Magnetic resonance imaging (MRI) was used in 10 female patients with chronic lymphedema of the leg. Soft tissue changes in lymphedema is best visualized by T2-weighted sequences. Three patients had a characteristic honeycomb pattern of the subcutanous tissue, whereas the other patients had either diffuse edema or a reticular pattern. The muscular compartments were normal, while the dermis was significantly thickened in 9 out of 10 patients. In conclusion, characteristic changes were observed in MR images of patients with chronic lymphedema of the leg. Further investigations are necessary to evaluate the role of MRI as an aid in the choice of therapy.

Low-energy spin dynamics of the s = 1/2 kagome system herbertsmithite.

The low-energy (ε = hω < 1 meV), low-temperature (T = 0.05 K) spin dynamics of the s = 1/2 kagome candidate herbertsmithite are probed in the presence of magnetic fields up to 2.5 T. The zero-field spectra reveal a very weak continuum of scattering at T = 10 K and a broad inelastic peak centred at ε(max) = 0.2 meV at lower temperatures, T < 1 K. The broad peak is found to be strongly damped, with a liquid-like structure factor implying correlations at length scales up to r = 6 Å. The field dependence of the peak appears to follow the Zeeman splitting of s = 1/2 excitations, consistent with the weakly split 'doublets' observed in low-temperature specific heat. A possible explanation of these observations is a short-range correlated state involving defect spins between the kagome planes and moments in the kagome layers.

Spangolite: an s = 1/2 maple leaf lattice antiferromagnet?

Spangolite, Cu(6)Al(SO(4))(OH)(12)Cl·3H(2)O, is a hydrated layered copper sulfate mineral. The Cu(2+) ions of each layer form a systematically depleted triangular lattice which approximates a maple leaf lattice. We present details of the crystal structure, which suggest that in spangolite this lattice actually comprises two species of edge linked trimers with different exchange parameters. However, magnetic susceptibility measurements show that despite the structural trimers, the magnetic properties are dominated by dimerization. The high temperature magnetic moment is strongly reduced below that expected for the six s = 1/2 in the unit cell.

A sporulation-inhibiting substance from vegetative thalli of the green alga Ulva mutabilis, Føyn.

The formation of zoospores or gametes in the green alga Ulva mutabilis Føyn is shown to be blocked by some substance(s) which can be extracted into fresh growth medium from a suspension of living thallus fragments. The inhibiting power of thallus extract is greatly reduced by heat treatment, but heat-stable components may also be present since active extracts can be produced by boiling algal thalli in growth medium. Separation of the extract on a Sephadex G25 column gave two peaks of inhibitory activity which corresponded with the fraction's content of high molecular carbohydrate (probably ulvin). Various mono- and disaccharides were inactive. In order to block meiotic zoospore formation completely, thallus extracts must be applied at least 6-7 h prior to the cells' visible entry into the meiotic prophase.

Epilepsy and anomalies of neuronal migration: MRI and clinical aspects.

Neuronal migration disorders are the result of disturbed brain development. In such disorders, neurons are abnormally located. In diagnosing these conditions, magnetic resonance imaging is superior to any other imaging technique. This enables us to improve our knowledge of the clinical correlates of neuronal migration. With reference to migrational disorder, a retrospective study of all 303 patients with epileptic seizures referred for magnetic resonance imaging during a 3-year period was performed, 13 patients (aged 12-41, mean age 27) were identified. They represent 4.3% of the entire study group. Of the patients with known epilepsy, 6.7% and of the mentally retarded, 13.7% had migrational disorders. Four patients had schizencephaly as the dominant finding, one was classified as hemimegalencephaly, 2 had isolated heterotopias, and 6 had localized pachy- and/or poly-microgyria. The clinical pictures are complex. Ectopias of grey matter are recognised foci of epilepsy, but from an epileptological and a clinical viewpoint little attention has been given to these disorders. The present study shows that malmigration is not rare in epilepsy patients, especially not in the mentally retarded.

[Consequences of diagnostics with magnetic tomography]. / Konsekvenser av diagnostikk med magnettomografi.

Physicians referring patients to examinations by magnetic resonance tomography (MT) were asked to answer almost identical questionnaires before and after the examination. The questions referred to diagnosis and planned patient management. Impact of MT was measured by examining the changes in patient diagnoses and planned management after the MT scans. In 33% of the group (400 patients) the main diagnosis (four digit ICD-9 code) changed after MT. Diagnostic security was better for 43%, and further diagnostic follow-up changed for 56%, surgery for 20% and radiation therapy for 11%. MT was assumed to have had real consequences for 33% of the patients in terms of significant changes in the doctors planned management or in his concept of the disease. In a follow-up study 1.5-2 years after MT, 64% of the referring doctors were of the opinion that the MT scan had had consequences for the patient and they placed the emphasis on less active patient follow-up after MT.

[Magnetic tomography in the examination of edema and pain in the leg]. / Magnettomografi ved undersøkelse av hevelse og smerte i leggen.

Magnetic resonance imaging (MRI) was used to investigate 38 patients suffering from leg oedema or pain of various etiology. Spin echo series with 10 mm transverse slices of both legs were obtained. Soft tissue changes were visualized best by T2-weighted sequences. Characteristic changes could be observed by MR images of patients with closed compartment syndrome (n = 2), chronic lymph oedema (n = 10) and post-reconstructive leg oedema following vascular surgery (n = 14). MRI can also show typical soft tissue changes in patients with deep vein thrombosis (n = 5) or post-thrombotic syndrome (n = 3). For most of these conditions, the diagnosis can usually be established using simpler methods. However, MRI is an excellent supplementary method for showing soft tissue changes, and is a promising way of investigating conditions that may give rise to leg oedema and pain.