A new species of Lomanoxia Martínez from Costa Rica (Coleoptera: Scarabaeidae: Aphodiinae)

A new species of Lomanoxia Martínez is described from Costa Rica: L. canthonopsis Skelley and Howden. This represents the first member of the genus reported from Central America. The status of the tribe Lomanoxini Stebnicka is evaluated and is here synonymized under Eupariini LePeletier and Serville

Magnetoelastic effects in multiferroic YMnO3_3

We have investigated magnetoelastic effects in multiferroic YMnO$_3$ below the antiferromagnetic phase transition, $T_N \approx 70$ K, using neutron powder diffraction. The $a$ lattice parameter of the hexagonal unit cell of YMnO$_3$ decreases normally above $T_N$, but decreases anomalously below T$_N$, whereas the $c$ lattice parameter increases with decreasing temperature and then increases anomalously below T$_N$. The unit cell volume also undergoes an anomalous contraction below $T_N$. By fitting the background thermal expansion for a non-magnetic lattice with the Einstein-Gr\"uneisen equation, we determined the lattice strains $\Delta a$, $\Delta c$ and $\Delta V$ due to the magnetoelastic effects as a function of temperature. We have also determined the temperature variation of the ordered magnetic moment of the Mn ion by fitting the measured Bragg intensities of the nuclear and magnetic reflections with the known crystal and magnetic structure models and have established that the lattice strain due to the magnetoelastic effect in YMnO$_3$ couples with the square of the ordered magnetic moment or the square of the order parameter of the antiferromagnetic phase transition

High-temperature synthesis, single-crystal X-ray and neutron powder diffraction, and materials properties of Sr3Ln10Si18Al12O18N36 (Ln = Ce, Pr, Nd)

The novel oxonitridoaluminosilicates (sialons) Sr3Ln10Si18Al12O18N36 (Ln = Ce, Pr, Nd) were obtained by the reaction of the respective lanthanide metals with Si(NH)2, SrCO3, and AlN using a radiofrequency furnace at temperatures between 1550–1650°C. The crystal structures of the isotypic sialons were determined by single-crystal X-ray investigations (Sr3Ce10Si18Al12O18N36: I3m, Z = 2, a = 1338.2(2) pm, R1 = 0.0333; Sr3Pr10Si18Al12O18N36: a = 1334.54(6) pm, R1 = 0.0296; Sr3Nd10Si18Al12O18N36: a = 1332.85(6) pm, R1 = 0.0271) and in the case of Sr3Pr10Si18Al12O18N36 with powder neutron diffraction as well. The three-dimensional sialon network is built up by SiON3, SiN4, and AlON3 tetrahedra. Besides the bridging O and N atoms of the sialon network there are isolated O2− which are tetrahedrally coordinated by Sr and Ln. The crystallographic differentiation of Si/Al and O/N seemed to be possible by a careful evaluation of the single-crystal X-ray diffraction data combined with lattice energy calculations using the MAPLE concept (Madelung Part of Lattice Energy). In the case of Sr3Pr10Si18Al12O18N36 the differentiation of O and N and the proposed ordering was completely confirmed by powder neutron diffraction

A new species of \u3ci\u3eLomanoxia Martínez\u3c/i\u3e from Costa Rica (Coleoptera: Scarabaeidae: Aphodiinae)

A new species of Lomanoxia Martínez is described from Costa Rica: L. canthonopsis Skelley and Howden. This represents the first member of the genus reported from Central America. The status of the tribe Lomanoxini Stebnicka is evaluated and is here synonymized under Eupariini LePeletier and Serville

Metamagnetism and soliton excitations in the modulated ferromagnetic Ising chain CoV2O6

We report a combination of physical property and neutron scattering measurements for polycrystalline samples of the one-dimensional spin chain compound CoV2O6. Heat capacity measurements show that an effective S = 1/2 state is found at low temperatures and that magnetic fluctuations persist up to 6.Tn. Above Tn = 6.3 K, measurements of the magnetic susceptibility as a function of T and H show that the nearest neighbour exchange is ferromagnetic. In the ordered state, we have discovered a crossover from a metamagnet with strong fluctuations between 5 K and Tn to a state with a 1/3 magnetisation plateau at 2 < T < 5 K. We use neutron powder diffraction measurements to show that the AFM state has incommensurate long range order and inelastic time of flight neutron scattering to examine the magnetic fluctuations as a function of temperature. Above Tn, we find two broad bands between 3.5 and 5 meV and thermally activated low energy features which correspond to transitions within these bands. These features show that the excitations are deconfined solitons rather than the static spin reversals predicted for a uniform FM Ising spin chain. Below Tn, we find a ladder of states due to the confining effect of the internal field. A region of weak confinement below Tn, but above 5 K, is identified which may correspond to a crossover between 2D and 3D magnetic ordering.Comment: Expanded version, includes results from arXiv:0804.2966 and neutron powder diffraction. To appear in PR

Neutron diffraction studies of magnetostrictive Fe–Ga alloy ribbons

Melt-spun Fe–Ga ribbons were prepared and some ribbons were annealed at 1000 °C for 1 h then slowly cooled to room temperature. X-ray diffraction patterns revealed no evidence of texture and only bcc phase in the as-quenched ribbons. However, high-resolution neutron diffraction patterns gave more information on the structure of these ribbons. Only diffractions from the disordered bcc A2 phase were found in as-quenched ribbons with 15, 17.5, and 19.5 at. % Ga content, without any trace of satellite peaks or splitting peaks from the proposed Ga–Ga pairing superlattice structure. The broadening of the base of the �110� peaks for all samples except the as-quenched 15 at. % Ga ribbon might indicate the existence of some kind of short range ordering. Ribbons developed L12 phase after annealing especially in the Fe 19.5 at. % Ga ribbon where the formation of L12 phase reduced the Ga content in the remaining A2 phase and decreased its lattice parameter dramatically. D03 phase formed in the as-quenched 22.5 at. % Ga ribbon and the following annealing treatment transformed more A2 phase into D03 phase

How Historical and Current Management Practices have Affected Milk River Riparian Habitat in Northcentral Montana

Riparian and wetland communities support the greatest concentration of plants and animals, yet only constitute 4 percent of Montana’s land cover.  Because they are more productive than surrounding uplands, they are attractive to livestock and wildlife as they provide important forms of cover and forage.  For private and public land managers interested in maintaining long-term integrity and functionality of riparian and wetland communities on their lands, management strategies that accommodate on-site resource needs must be implemented.  Determining habitat types and their associated community types on these sites can help identify historical impacts that have affected community type succession, and how current management strategies could be affecting the trend towards one seral stage or another.  Both natural and artificial disturbances can affect community type succession, yet succession from one type to another can take several years and even decades.  Thus, changes from year to year can be very subtle, and as land managers implement current management practices, they may overlook the visual cues indicating these trends, simply because these processes can be very slow.  This presentation summarizes an evaluation of a riparian area located in the Milk River Valley in Northcentral Montana. An illustration of how historical impacts have affected community type succession, and how this site has been affected by a significant change in management practices that occurred over 20 years ago, is provided. Depending on what goals are desired for this site will determine if a change in current management practices is warranted

Charge order at the frontier between the molecular and solid states in Ba3NaRu2O9

We show that the valence electrons of Ba3NaRu2O9, which has a quasi-molecular structure, completely crystallize below 210 K. Using an extended Hubbard model, we show that the charge ordering instability results from long-range Coulomb interactions. However, orbital ordering, metal-metal bonding and formation of a partial spin gap enforce the magnitude of the charge separation. The striped charge order and frustrated hcp lattice of Ru2O9 dimers lead to competition with a quasi-degenerate charge-melted phase under photo-excitation at low temperature. Our results establish a broad class of simple metal oxides as models for emergent phenomena at the border between the molecular and solid states.Comment: Minor changes, with supporting information. To appear in Phys. Rev. Let