Topological magnon band structure of emergent Landau levels in a skyrmion lattice.

The motion of a spin excitation across topologically nontrivial magnetic order exhibits a deflection that is analogous to the effect of the Lorentz force on an electrically charged particle in an orbital magnetic field. We used polarized inelastic neutron scattering to investigate the propagation of magnons (i.e., bosonic collective spin excitations) in a lattice of skyrmion tubes in manganese silicide. For wave vectors perpendicular to the skyrmion tubes, the magnon spectra are consistent with the formation of finely spaced emergent Landau levels that are characteristic of the fictitious magnetic field used to account for the nontrivial topological winding of the skyrmion lattice. This provides evidence of a topological magnon band structure in reciprocal space, which is borne out of the nontrivial real-space topology of a magnetic order.

Multiple Magnetic Bilayers and Unconventional Criticality without Frustration in BaCuSi_{2}O_{6}.

The dimerized quantum magnet BaCuSi_{2}O_{6} was proposed as an example of "dimensional reduction" arising near the magnetic-field-induced quantum critical point (QCP) due to perfect geometrical frustration of its interbilayer interactions. We demonstrate by high-resolution neutron spectroscopy experiments that the effective intrabilayer interactions are ferromagnetic, thereby excluding frustration. We explain the apparent dimensional reduction by establishing the presence of three magnetically inequivalent bilayers, with ratios 3∶2∶1, whose differing interaction parameters create an extra field-temperature scaling regime near the QCP with a nontrivial but nonuniversal exponent. We demonstrate by detailed quantum Monte Carlo simulations that the magnetic interaction parameters we deduce can account for all the measured properties of BaCuSi_{2}O_{6}, opening the way to a quantitative understanding of nonuniversal scaling in any modulated layered system.

Magnetodielectric detection of magnetic quadrupole order in Ba(TiO)Cu4(PO4)4 with Cu4O12 square cupolas.

In vortex-like spin arrangements, multiple spins can combine into emergent multipole moments. Such multipole moments have broken space-inversion and time-reversal symmetries, and can therefore exhibit linear magnetoelectric (ME) activity. Three types of such multipole moments are known: toroidal; monopole; and quadrupole moments. So far, however, the ME activity of these multipole moments has only been established experimentally for the toroidal moment. Here we propose a magnetic square cupola cluster, in which four corner-sharing square-coordinated metal-ligand fragments form a noncoplanar buckled structure, as a promising structural unit that carries an ME-active multipole moment. We substantiate this idea by observing clear magnetodielectric signals associated with an antiferroic ME-active magnetic quadrupole order in the real material Ba(TiO)Cu4(PO4)4. The present result serves as a useful guide for exploring and designing new ME-active materials based on vortex-like spin arrangements.

Inelastic neutron scattering study of a nonmagnetic collapsed tetragonal phase in nonsuperconducting CaFe2As2: evidence of the impact of spin fluctuations on superconductivity in the iron-arsenide compounds.

The relationship between antiferromagnetic spin fluctuations and superconductivity has become a central topic of research in studies of superconductivity in the iron pnictides. We present unambiguous evidence of the absence of magnetic fluctuations in the nonsuperconducting collapsed tetragonal phase of CaFe2As2 via inelastic neutron scattering time-of-flight data, which is consistent with the view that spin fluctuations are a necessary ingredient for unconventional superconductivity in the iron pnictides. We demonstrate that the collapsed tetragonal phase of CaFe2As2 is nonmagnetic, and discuss this result in light of recent reports of high-temperature superconductivity in the collapsed tetragonal phase of closely related compounds.

Stripe antiferromagnetic spin fluctuations in SrCo2As2.

Inelastic neutron scattering measurements of paramagnetic SrCo2As2 at T=5 K reveal antiferromagnetic (AFM) spin fluctuations that are peaked at a wave vector of Q(AFM)=(1/2,1/2,1) and possess a large energy scale. These stripe spin fluctuations are similar to those found in AFe2As2 compounds, where spin-density wave AFM is driven by Fermi surface nesting between electron and hole pockets separated by Q(AFM). SrCo2As2 has a more complex Fermi surface and band-structure calculations indicate a potential instability toward either a ferromagnetic or stripe AFM ground state. The results suggest that stripe AFM magnetism is a general feature of both iron and cobalt-based arsenides and the search for spin fluctuation-induced unconventional superconductivity should be expanded to include cobalt-based compounds.

Magnonlike dispersion of spin resonance in Ni-doped BaFe2As2.

Inelastic neutron scattering measurements on Ba(Fe0.963Ni0.037)2As2 manifest a neutron spin resonance in the superconducting state with anisotropic dispersion within the Fe layer. Whereas the resonance is sharply peaked at the antiferromagnetic (AFM) wave vector Q(AFM) along the orthorhombic a axis, the resonance disperses upwards away from Q(AFM) along the b axis. In contrast to the downward dispersing resonance and hourglass shape of the spin excitations in superconducting cuprates, the resonance in electron-doped BaFe2As2 compounds possesses a magnonlike upwards dispersion.

Effects of transition metal substitutions on the incommensurability and spin fluctuations in BaFe2As2 by elastic and inelastic neutron scattering.

The spin fluctuation spectra from nonsuperconducting Cu-substituted, and superconducting Co-substituted, BaFe(2)As(2) are compared quantitatively by inelastic neutron scattering measurements and are found to be indistinguishable. Whereas diffraction studies show the appearance of incommensurate spin-density wave order in Co and Ni substituted samples, the magnetic phase diagram for Cu substitution does not display incommensurate order, demonstrating that simple electron counting based on rigid-band concepts is invalid. These results, supported by theoretical calculations, suggest that substitutional impurity effects in the Fe plane play a significant role in controlling magnetism and the appearance of superconductivity, with Cu distinguished by enhanced impurity scattering and split-band behavior.

Incommensurate spin-density wave order in electron-doped BaFe2 As2 superconductors.

Neutron diffraction studies of Ba(Fe(1-x)Co(x))(2)As)(2) reveal that commensurate antiferromagnetic order gives way to incommensurate magnetic order for Co compositions between 0.056 < x < 0.06. The incommensurability has the form of a small transverse splitting (0, ± ε, 0) from the commensurate antiferromagnetic propagation vector Q(AFM) = (1,0,1) (in orthorhombic notation) where ε ≈ 0.02-0.03 and is composition dependent. The results are consistent with the formation of a spin-density wave driven by Fermi surface nesting of electron and hole pockets and confirm the itinerant nature of magnetism in the iron arsenide superconductors.

Open anterior fracture dislocation of the hip: a case report and review of literature.

Open anterior fracture dislocation of the hip is an extremely rare injury and is the result of a violent trauma. Such a case is being reported in a 15-year-old female, who also had other adjacent bony injuries. In spite of early treatment, necrosis and infection could not be controlled, resulting in permanent disability in this young girl.

Primary amoebic meningoencephalitis in the Western Province.

Six cases of primary amoebic meningoencephalitis were diagnosed and treated at the Balimo Health Centre between December 1986 and September 1988. This disease has not previously been reported in Papua New Guinea although from information derived from other studies it should be occurring in the lowlands of Papua New Guinea from time to time. Although less than optimum treatment was given to the early cases the case fatality rate in the series was only 66%. This compares very favorably with a case fatality rate of nearly 100% from other studies. Early diagnosis and prompt treatment should help to reduce mortality.

Alterations of the cat's electroretinogram induced by the lesioning of the indoleamine-accumulating amacrine cells.

The neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) was used to destroy the indoleamine-accumulating amacrine cells located in the cat's retina. With 100 micrograms of 5,7-DHT, the alterations in the electroretinogram (ERG) were present in all of the treated eyes and the morphological changes were confined to some of the processes in the inner plexiform layer. The ERGs recorded from treated eyes consisted of negative waves at low intensities and depressed b wave amplitude at higher intensities. The duration of the b wave was not altered but the oscillatory potentials were strongly depressed. The changes were probably permanent. The differences in the ERG changes in cats and rabbits were suggested to arise from the differences in signal processing in the inner retina of rabbits and cats.

Giant cell tumour of ilium.

Most common tumours of ilium are chondrosarcoma and reticulum cell sarcoma. Giant cell tumour commonly presents at the ends of long bones. It is quite uncommon to find osteoclastoma in flat bones, especially ilium. This is the only case of osteoclastoma of ilium seen during the last 7 years in this institution and is reported for its rarity.

Incidence of osteomalacia in fractures of the proximal end of femur.

Twenty-six cases of fractures of the proximal end of the femur were studied to assess the role of osteomalacia. Biochemical, radiological and histological investigations were carried out in all the cases. Osteomalacia, commonly subclinical, was found to be the underlying cause in 65 per cent of cases. Histological analysis of iliac crest biopsy was the only reliable way of diagnosing subclinical osteomalacia.

Morphological findings in retinitis pigmentosa with early diffuse rod dysfunction.

The retina from the postmortem donor eye of a 64-year-old man with advanced autosomal dominant retinitis pigmentosa (RP) was studied with light and electron microscopy. Two children of the donor were tested with two-color, dark-adapted static perimetry and found to have Type 1 or D-type RP, the psychophysical subtype with early onset of severe rod dysfunction diffusely affecting the entire retina. In the macula of the donor retina, rods and cones were clustered in irregularly shaped patches, in association with pigmented retinal pigmented epithelial cells. Only cones in the middle of these patches possessed outer segments, and these were poorly organized. Of the few photoreceptors remaining outside of the macula, those in the superior retina had well-formed terminals and appeared to be rods. Rods were also observed superior to the disk and in the temporal mid-periphery. The few photoreceptors remaining in the inferior retina were also rod-like, but had less well-formed terminals. The retinal pigmented epithelium was relatively normal near surviving photoreceptors, but was depigmented, had thinned, or was absent in regions of photoreceptor dropout. These findings represent the first reported morphology of the retina from an eye donor with known psychophysical subtype of RP.

Intranuclear rodlets in the rabbit retina following treatment with MPTP.

Retinas from pigmented rabbits treated with N-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP, a chemical inducer of Parkinsonism in man and monkeys) were studied using light- and electron microscopy. The nuclei of many cells in the inner nuclear layer and the ganglion cell layer of the treated retinas contained crystalloids (intranuclear rodlets) of varying length (0.5-8 microns) which were composed of bundles of 12 nm filaments and which were seen only rarely in untreated retinas. The induced rodlets are oval to round cylinders, 15-20 filaments across (although they are smaller in untreated retinas). Similar intranuclear inclusions have been described under varying conditions in neurons and glia in the central nervous system of several animal species. In rabbits injected acutely with MPTP, most of the affected cells are in the inner nuclear layer in the position of bipolar cells, while in the chronically injected animals, clearly identifiable amacrine cells, and the nuclei of some cells in the ganglion cell layer also contained the inclusions. Evidence is presented that the rodlet-containing cells in the ganglion cell layer include both ganglion cells and displaced amacrine cells. These anatomic findings are relevant to understanding the physiological and biochemical effects of the drug on the retina which we reported previously (Wong, Ishibashi, Tucker and Hamasaki, 1985).

Refractile bodies in the inner segments of cones in the aging human retina.

Refractile inclusion bodies (approximately 0.80 micron in size) were found in the inner segments of cone photoreceptors in the aging human retina. They were easily resolved with the light microscope. They were never seen in rods, and occurred primarily in retinas from eye donors older than 40 years of age. The incidence of these inclusion bodies is related significantly to age (they occur more frequently with increasing age) and to sex (they are more likely to occur in the aging female than in the aging male). They were often smaller in size and fewer in number in the cones of males compared with females, and in males, fewer cones contained the RB than in females. Electron microscopy revealed that these inclusions are membrane-bound organelles having granular, fibrous, and tubular subcomponents. The occurrence of the RB appears to be unrelated to specific disease processes, medications in use at the time of enucleation, or specimen preparation times.

Snailtracks of the corneal endothelium.

An unusual pattern of corneal endothelial cell alterations has been observed at the slitlamp in eyes following intraocular surgery. Because of their appearance, we have called these changes "snailtracks". We have commonly seen these snailtracks following extracapsular cataract extraction. Similar changes have been noted in cadaver corneas stored in McCarey-Kaufman (M-K) medium. This study presents information which suggests that these changes represent corneal endothelial cell damage.

The photoreceptors of the West Indian manatee.

Using light and electron microscopy we found that the manatee retina has both rodlike and conelike photoreceptors in accord with its diurnal behavior pattern. Outer segment disks in both cell types appear to be enclosed along most of their length within the plasma membrane. The synaptic terminals are simple, with small, superficial postsynaptic contacts. The cones have long inner segments, short, conical outer segments and terminals with numerous synaptic ribons and deeply embedded postsynaptic elements. There are two cone subclasses that may subserve color vision. Morphometry shows that there are more ganglion cells of small size ventrally, and that the thickness of the nerve fiber layer there is reduced, suggesting the presence of a specialized visual area in the retina. However, there were no pronounced differences in cone cell density in any of the regions examined.