X-type Structure Research Articles

SLOW RISE AND PARTIAL ERUPTION OF A DOUBLE-DECKER FILAMENT. II. A DOUBLE FLUX ROPE MODEL

Force-free equilibria containing two vertically arranged magnetic flux ropes of like chirality and current direction are considered as a model for split filaments/prominences and filament-sigmoid systems. Such equilibria are constructed analytically through an extension of the methods developed in Titov & D\'emoulin (1999) and numerically through an evolutionary sequence including shear flows, flux emergence, and flux cancellation in the photospheric boundary. It is demonstrated that the analytical equilibria are stable if an external toroidal (shear) field component exceeding a threshold value is included. If this component decreases sufficiently, then both flux ropes turn unstable for conditions typical of solar active regions, with the lower rope typically being unstable first. Either both flux ropes erupt upward, or only the upper rope erupts while the lower rope reconnects with the ambient flux low in the corona and is destroyed. However, for shear field strengths staying somewhat above the threshold value, the configuration also admits evolutions which lead to partial eruptions with only the upper flux rope becoming unstable and the lower one remaining in place. This can be triggered by a transfer of flux and current from the lower to the upper rope, as suggested by the observations of a split filament in Paper~I (Liu et al. 2012). It can also result from tether-cutting reconnection with the ambient flux at the X-type structure between the flux ropes, which similarly influences their stability properties in opposite ways. This is demonstrated for the numerically constructed equilibrium.

About Buckling of X-Type Bracing

In X-type bracing structures generally it does not take into account the structural contribution of the compressed member, since it is assumed to have a negligible compressive strength; it considered that the stretched member takes the total stress. In the following we analyse as the stretched diagonal, joined in the middle to the compressed one, improves the structural behaviour of this both with respect to the buckling in-plane or out-of -plane of the structure. First we recall the link between the Euler buckling load of a rod free and braced depending on the stiffness k of the brace. Then we analyse the in-plane and out-of-plane buckling of the rod and, for the two situations, we value the increase of the buckling load due to the elastic brace. In the end for both cases we show in what condition the stretched rod causes that the compressed one buckles in the second mode.

Structural and magnetic properties of Fe2CoGa Heusler nanoparticles

Fe2CoGa Heusler nanoparticles are synthesized by a chemical method. The structure and magnetic properties of Fe2CoGa Heusler nanoparticles are investigated by x-ray diffraction, extended x-ray absorption fine structure and Mössbauer spectroscopy. The crystal structure of Fe2CoGa nanoparticles is described by the X-type structure (prototype: Li2AgSb). Magnetic measurements reveal the presence of small Fe2CoGa nanoparticles and lower magnetic moments compared with the theoretically predicted values.

Crystal structures and hardness of novel compounds: Hexagonal Mo(CuxAl1−x)6Al4, MoCu2Al8−x and orthorhombic {Mo,W,Re}Ni2−xAl8+x

The crystal structures of a series of compounds have been solved from X-ray single crystal diffractometry: Mo(CuxAl1−x)6Al4 (x = 0.416), MoNi2−xAl8+x (x = 0.165), WNi2−x−y□yAl8+x−z□z, (x = 0.162, y = 0.015, z = 0.010) and ReNi2Al8−x (x = 0.033). Mo(CuxAl1−x)6Al4 crystallizes with hexagonal symmetry and lattice parameters, a = 0.50030(1) and c = 0.76279(3) nm; space group P6/mmm, No. 191, as an unfilled structure variant of the MgFe6Ge6-type with a vacant 2c site. This structure is made up of alternate blocks of (unfilled) CaCu5 and Zr4Al3 in a ratio of 1:1. A superstructure of this compound (a = a0√3, c = 2c0) was solved with a Rietveld refinement of X-ray powder diffraction data as a fully ordered structure with formula MoCu2Al8−x. It adopts space group P6, No. 168 with lattice parameters a = 0.86769(1), c = 1.52149(2) nm. A Bärnighausen tree was derived reflecting the close relation among these two structure types. The compounds {Mo,W,Re}Ni2−xAl8+x crystallize in a novel structure type (ReNi2Al8−x–type; space group Pbam, No. 55). Whereas ReNi2Al8−x is a fully ordered structure with some defects in the two 4g sites occupied by Al, Ni + Al atoms randomly share one crystallographic site in isotypic {Mo,W}Ni2−xAl8+x, which causes splitting of three neighboring Al-sites. Lattice parameters and residual values of the refinements were: a = 1.00320(2), b = 1.51258(3), c = 0.83890(2) nm; RF2 = 0.017 for the Re-compound, a = 1.00664(2), b = 1.53108(2), c = 0.85205(2) nm, RF2 = 0.035 for the Mo-compound and a = 1.00683(2), b = 1.53236(3), c = 0.85232(2) nm; RF2 = 0.024 for the W-compound. As the ReNi2Al8−x-type structure is another superstructure of the hexagonal Mo(CuxAl1−x)6Al4 type, a Bärnighausen tree was derived, which documents the close relation among these two structure types. Phase equilibria in the Al-rich corner of W–Ni–Al at 930 °C is also reported showing the presence of a WNi2Al8 phase. Precise atom positions have been derived from X-ray single crystal data for binary Ni2Al3 confirming the space group P3¯m1 (No. 164). Atom positions and lattice parameters (a = 0.40533(2), c = 0.49038(3) nm) are very close to the parameters hitherto reported in the literature from X-ray powder diffraction data. Vicker’s hardness was measured for all isotypic compounds {Mo,W,Re}Ni2Al8−x revealing a hardness of HV = 965 ± 25 MPa for the Re-containing material, which is higher by about 100 MPa in comparison to the Mo and W containing phases.

On the Origin, 3D Structure and Dynamic Evolution of CMEs Near Solar Minimum

We have conducted a statistical study 27 coronal mass ejections (CMEs) from January 2007 – June 2008, using the stereoscopic views of STEREO SECCHI A and B combined with SOHO LASCO observations. A flux-rope model, in conjunction with 3D triangulations, has been used to reconstruct the 3D structures and determine the actual speeds of CMEs. The origin and the dynamic evolution of the CMEs are investigated using COR1, COR2 and EUVI images. We have identified four types of solar surface activities associated with CMEs: i) total eruptive prominence (totEP), ii) partially eruptive prominence (PEP), iii) X-ray flare, and iv) X-type magnetic structure (X-line). Among the 27 CMEs, 18.5% (5 of 27) are associated with totEPs, 29.6% (8 of 27) are associated with PEPs, 26% (7 of 27) are flare related, and 26% (7 of 27) are associated with X-line structures, and 43% (3 of 7) are associated with both X-line structures and PEPs. Three (11%) could not be associated with any detectable activity. The mean actual speeds for totEP-CMEs, PEP-CMEs, flare-CMEs, and X-line-CMEs are 404 km s−1,247 km s−1,909 km s−1, and 276 km s−1, respectively; the average mean values of edge-on and broadside widths for the 27 CMEs are 52 and 85 degrees, respectively. We found that slow CMEs (V≤400 km s−1) tend to deflect towards and propagate along the streamer belts due to the deflections by the strong polar magnetic fields of corona holes, while some faster CMEs show opposite deflections away from the streamer belts.

Solution growth of the Gd–Cu–Al systems in the low-gadolinium concentration range

Abstract Solution growth of Gd–Cu–Al resulted in the formation of single crystals of GdCu4Al8 with tetragonal ThMn12-type structure (a = 8.751 Å, c = 5.148 Å), Gd2Cu9.4 – 6.7Al7.6 – 10.3 with hexagonal Th2Zn17-type structure (a = 8.83 Å, c = 1.28 Å), and Gd(Cu, Al)4 with orthorhombic CeNi2+x Sb2 – x -type structure. An antiferromagnetic ordering of GdCu4Al8 was found below 35 K, which is in agreement with the previously reported TN = 35 K and TN = 32 K measured on polycrystalline samples. In the temperature range 50 – 320 K the magnetic susceptibility χ follows the Curie–Weiss law with μeff = 7.8 μB/f. u. and θp = – 17 K for B c, μeff = 7.9 μB/f. u. and θp = – 18 K for B ⊥ c. The a-axis is the easy magnetization direction. The Gd(Cu, Al)4 and Gd(Cu, Al)4 compounds order antiferromagnetically below TN = 35 K and TN = 31 K, respectively.

Ultralight X-type lattice sandwich structure (I): Concept, fabrication and experimental characterization

A new type of ultra-lightweight metallic lattice structure (named as the X-type structure) is reported. This periodic structure was formed by two groups of staggered struts in the traditional pyramid structure, and fabricated by folding expanded metal sheet along rows of offset nodes and then brazing the folded structure (as the core) with top and bottom facesheets to form sandwich panels. The out-of-plane compressive and shear properties of the X-type lattice sandwich structure were investigated experimentally and compared to those of the sandwich having a pyramidal truss core. It is found that the formation of the 2-dimensional staggered nodes can effectively make the X-type structure more resistant to inelastic and plastic buckling under both compression and shear loading than the pyramidal lattice truss. Obtained results show that the compressive and shear peak strengths of the X-type lattice structure are about 30% higher than those of the pyramidal lattice truss having the same relative density.

Fabrication and fluidic characterization of static micromixers made of low temperature cofired ceramic (LTCC)

Microreaction devices used for chemical synthesis must possess a high resistance against corrosive chemicals. Therefore, microreaction devices were made of glass, steel or ceramics. Photolithographic steps combined with etching processes as well as micropowder blasting or micromilling processes were applied for the formation of appropriate structures. The low temperature cofired ceramics (LTCC) technology combines easy structuring, assembling and packaging techniques with the high chemical resistance of a glass ceramic material. In contrast to the known ceramic technologies, the LTCC technology enables a fast and easy fabrication of microfluidic devices. Here, we present two micromixers made of LTCC and its fluidic characterization. Laser ablation was used for the structuring of green tapes which were layered and cofired to form the micromixers. X-type fluidic barriers were realized inside a 1mm2 squared meandered channel of about 160mm length. A meandered channel mixer without X-type mixing structures was used as a reference. The pressure drop was measured for aqueous media with various viscosities and the friction factors were calculated. An exponential equation for the friction factor prediction is given. The residence time distribution was determined for both devices by pulse trace experiments and the dispersion model was used to describe the residence time distribution for low Reynolds numbers.

Two categories of mammalian galactose-binding receptors distinguished by glycan array profiling

Profiling of the four known galactose-binding receptors in the C-type lectin family has been undertaken in parallel on a glycan array. The results are generally consistent with those of previous assays using various different formats, but they provide a direct comparison of the properties of the four receptors, revealing that they fall into two distinct groups. The major subunit of the rat asialoglycoprotein receptor and the rat Kupffer cell receptor show similar broad preferences for GalNAc-terminated glycans, while the rat macrophage galactose lectin and the human scavenger receptor C-type lectin (SRCL) bind more restricted sets of glycans. Both of these receptors bind to Lewis x-type structures, but the macrophage galactose lectin also interacts strongly with biantennary galactose- and GalNAc-terminated glycans. Although the similar glycan-binding profiles for the asialoglycoprotein receptor and the Kupffer cell receptor might suggest that these receptors are functionally redundant, analysis of fibroblasts transfected with full-length Kupffer cell receptor reveals that they fail to endocytose glycosylated ligand.

99/00325 Efficient thermochemical cycle for CO 2 gasification of coal using a redox system of reactive iron-based oxide

The crystal structures of a series of compounds have been solved from X-ray single crystal diffractometry: Mo(CuxAl1−x)6Al4 (x = 0.416), MoNi2−xAl8+x (x = 0.165), WNi2−x−y□yAl8+x−z□z, (x = 0.162, y = 0.015, z = 0.010) and ReNi2Al8−x (x = 0.033). Mo(CuxAl1−x)6Al4 crystallizes with hexagonal symmetry and lattice parameters, a = 0.50030(1) and c = 0.76279(3) nm; space group P6/mmm, No. 191, as an unfilled structure variant of the MgFe6Ge6-type with a vacant 2c site. This structure is made up of alternate blocks of (unfilled) CaCu5 and Zr4Al3 in a ratio of 1:1. A superstructure of this compound (a = a0√3, c = 2c0) was solved with a Rietveld refinement of X-ray powder diffraction data as a fully ordered structure with formula MoCu2Al8−x. It adopts space group P6, No. 168 with lattice parameters a = 0.86769(1), c = 1.52149(2) nm. A Bärnighausen tree was derived reflecting the close relation among these two structure types. The compounds {Mo,W,Re}Ni2−xAl8+x crystallize in a novel structure type (ReNi2Al8−x–type; space group Pbam, No. 55). Whereas ReNi2Al8−x is a fully ordered structure with some defects in the two 4g sites occupied by Al, Ni + Al atoms randomly share one crystallographic site in isotypic {Mo,W}Ni2−xAl8+x, which causes splitting of three neighboring Al-sites. Lattice parameters and residual values of the refinements were: a = 1.00320(2), b = 1.51258(3), c = 0.83890(2) nm; RF2 = 0.017 for the Re-compound, a = 1.00664(2), b = 1.53108(2), c = 0.85205(2) nm, RF2 = 0.035 for the Mo-compound and a = 1.00683(2), b = 1.53236(3), c = 0.85232(2) nm; RF2 = 0.024 for the W-compound. As the ReNi2Al8−x-type structure is another superstructure of the hexagonal Mo(CuxAl1−x)6Al4 type, a Bärnighausen tree was derived, which documents the close relation among these two structure types. Phase equilibria in the Al-rich corner of W–Ni–Al at 930 °C is also reported showing the presence of a WNi2Al8 phase. Precise atom positions have been derived from X-ray single crystal data for binary Ni2Al3 confirming the space group P3¯m1 (No. 164). Atom positions and lattice parameters (a = 0.40533(2), c = 0.49038(3) nm) are very close to the parameters hitherto reported in the literature from X-ray powder diffraction data. Vicker’s hardness was measured for all isotypic compounds {Mo,W,Re}Ni2Al8−x revealing a hardness of HV = 965 ± 25 MPa for the Re-containing material, which is higher by about 100 MPa in comparison to the Mo and W containing phases.

Double null points and magnetic reconnection

2D reconnection is possible only in connection with the existence of a singularity in the magnetic field line topology, associated with a magnetic null point or a current sheet. Both of these provide an X-type structure of the magnetic field where fields of opposite polarity meet and reconnect. In 3D a similar topology is found in a null point pair, when the null points are connected by a separator line. The separator is defined as the intersection line of the two null-point fan planes. This paper reports on the topological evolution of this configuration with respect to different perturbations emerging from imposed boundary velocities, using a nonlinear numerical approach.

The Al-Rich Part of the System CaO-Al 2O 3-MgO : PART II. Structure Refinement of Two New Magnetoplumbite-Related Phases

Crystals of two new phases, which were recently found in the system CaO-Al 2O 3-MgO lying on the join connecting calcium hexaaluminate (CaAl 12O 19) of the magnetoplumbite structure and spinel (MgAl 2O 4), were grown by the floating zone method. The stoı̀chı̀ometrı̀c formulas for these two phases can be given as Ca 2Mg 2Al 28O 46 (CAM-I) and CaMg 2Al 16O 27 (CAM-II). On the basis of the stacking sequence revealed by high-resolution electron microscopy, the structure models were made, and further, the structure refinement was conducted by using single crystal X-ray diffraction data. It was shown that both phases have magnetoplumbite-related structures composed of two types of structure units, M(CaAl 12O 19; magnetoplumbite unit) and S (Mg 2Al 4O 8; spinel unit), and that the stacking sequences are ( M 2 S) n for CAM-I ( c = 79.810 Å) and ( MS) n for CAM-II ( c = 31.288 Å). In the terminology of hexagonal ferrite structure system, CAM-I is of the "X-type structure" with space group R3̄ m and CAM-II is of the " W-type structure" with P6̄ m 2 symmetry.

Preparation, Structure Refinement, and Properties of Some Compounds with Dy 2Fe 2Si 2C- and LaMn 11C 2- x-Type Structure

The new compounds Tm 2Fe 2Si 2C and Lu 2Fe 2Si 2C were prepared by are-melting cold-pressed pellets of the elemental components. They crystallize with the monoclinic Dy 2Fe 2Si 2C-type structure. The crystal structure of Tm 2Fe 2Si 2C was refined from single-crystal X-ray data: C2/ m, a = 1049.7(3) pm, b = 388.2(1) pm, c = 664.6(2) pm, β = 128.96(2)°, R = 0.020 for 296 structure factors, and 21 variable parameters. The structure may be considered as consisting of two-dimensionally infinite polyanionic layers of [Fe 2Si 2C 6-] n separated by the rare-earth cations. The hydrolysis of Er 2Fe 2Si 2C with diluted hydrochloric acid yields mainly methane besides about 20 wt% of C 2 and C 3 hydrocarbons. Tm 2Fe 2Si 2C orders antiferromagnetically at T N = 2.7(2) K. The magnetization behavior for this compound suggests metamagnetism. Lu 2Fe 2Si 2C is Pauli paramagnetic. Electrical conductivity measurements of polycrystalline samples of Tm 2Fe 2Si 2C and Lu 2Fe 2Si 2C indicate metallic conductivity. ThFe 10SiC 2- x has a tetragonal LaMn 11C 2- x -type structure with the lattice constants a = 1005.3(2) pm and c = 651.6(2) pm.

ChemInform Abstract: Crystal Structure of MoB2.

AbstractSingle crystals of MoB2.0 are grown from a high‐temp.

Studies of Langmuir-Blodgett films of poly(1-benzyl-L-histidine) -stearic acid mixtures

The structures of monolayers and multilayers of poly-1-benzyl-L-histidine (PBLH)-stearic acid (StA) mixtures have been investigated. The force-area (FA) curves of the monolayer had a plateau region which can be attributed to a transition from the liquid to the solid phase rather than that from a monolayer to a bilayer, as reported for α-helical polypeptides such as poly-γ-benzyl-L-glutamate. The cyclic FA curve measurements, i.e. the cycles of compression and successive expansion of the monolayer, showed that the structural change in the monolayer from the liquid to the solid phase was practically reversible. The FA curves of the mixed monolayer showed a strong dependence on the cation species in the subphase. The mixed multilayers prepared by a horizontal lifting method gave X-ray diffraction patterns which suggested that they had a Y-type structure, despite the fact that this method would lead one to expect the formation of an X-type structure. Studies on the relationship between the UV absorption spectra of the Langmuir-Blodgett films and the surface pressure for deposition suggested that a change in the orientation of PBLH chromophores occured at the plateau region in the FA curves.