Divergence-Conforming Velocity and Vorticity Approximations for Incompressible Fluids Obtained with Minimal Facet Coupling.

We introduce two new lowest order methods, a mixed method, and a hybrid discontinuous Galerkin method, for the approximation of incompressible flows. Both methods use divergence-conforming linear Brezzi-Douglas-Marini space for approximating the velocity and the lowest order Raviart-Thomas space for approximating the vorticity. Our methods are based on the physically correct viscous stress tensor of the fluid, involving the symmetric gradient of velocity (rather than the gradient), provide exactly divergence-free discrete velocity solutions, and optimal error estimates that are also pressure robust. We explain how the methods are constructed using the minimal number of coupling degrees of freedom per facet. The stability analysis of both methods are based on a Korn-like inequality for vector finite elements with continuous normal component. Numerical examples illustrate the theoretical findings and offer comparisons of condition numbers between the two new methods.

Simulations of single- and two-tone Tm-doped optical fiber laser amplifiers.

This work uses numerical simulations of a thulium-doped optical fiber amplifier to predict various performance characteristics such as peak temperatures, expected output powers and efficiencies, presence of amplified spontaneous emission (ASE), and transverse mode instability (TMI) onset power thresholds. Single- and two-tone configurations are studied. In the latter case, the two laser sources are separated in frequency by the amount that corresponds to the peak Raman gain, and a few seed ratios at various total seed powers are examined. The goal is to provide the field with pertinent information on what is feasible for this type of amplifier.

Developing Intense Blue and Magenta Colors in α-LiZnBO3 : The Role of 3d-Metal Substitution and Coordination.

We describe the synthesis, crystal structures, and optical absorption spectra/colors of 3d-transition-metal-substituted α-LiZnBO3 derivatives: α-LiZn1-x MIIx BO3 (MII =CoII (0

Structural manipulation and tailoring of dielectric properties in SrTi1-xFexTaxO3 perovskites: Design of new lead free relaxors.

We report composition dependent structure evolution from SrTiO3 to SrFe0.5Ta0.5O3 by powder X-ray and neutron diffraction studies of SrTi1-2xFexTaxO3 (0.00 ≤ × ≤ 0.50) compositions. Structural studies reveal cubic (Pm3m) perovskite-type structure of the parent SrTiO3 for x up to 0.075 and cation disordered orthorhombic (Pbnm) perovskite-type structure for x ≥ 0.33. A biphasic region consisting of a mixture of cubic and orthorhombic structures is found in the range for 0.10 ≤ × ≤ 0.25. Dielectric studies reveal transformation from a normal dielectric to relaxor like properties with increasing Fe(3+) and Ta(5+) concentration. Dielectric response is maximum at x = 0.33 in the series. The results establish a protocol for designing new lead-free relaxor materials based on the co-substitution of Fe(3+) and Ta(5+) for Ti(4+) in SrTiO3. A complex interplay of strain effects arising from distribution of cations at the octahedral sites of the perovskite structure controls the dielectric properties.

Oxygen-participated electrochemistry of new lithium-rich layered oxides Li3MRuO5 (M = Mn, Fe).

We describe the synthesis, crystal structure and lithium deinsertion-insertion electrochemistry of two new lithium-rich layered oxides, Li3MRuO5 (M = Mn, Fe), related to rock salt based Li2MnO3 and LiCoO2. The Li3MnRuO5 oxide adopts a structure related to Li2MnO3 (C2/m) where Li and (Li0.2Mn0.4Ru0.4) layers alternate along the c-axis, while the Li3FeRuO5 oxide adopts a near-perfect LiCoO2 (R3[combining macron]m) structure where Li and (Li0.2Fe0.4Ru0.4) layers are stacked alternately. Magnetic measurements indicate for Li3MnRuO5 the presence of Mn(3+) and low spin configuration for Ru(4+) where the itinerant electrons occupy a π*-band. The onset of a net maximum in the χ vs. T plot at 9.5 K and the negative value of the Weiss constant (θ) of -31.4 K indicate the presence of antiferromagnetic superexchange interactions according to different pathways. Lithium electrochemistry shows a similar behaviour for both oxides and related to the typical behaviour of Li-rich layered oxides where participation of oxide ions in the electrochemical processes is usually found. A long first charge process with capacities of 240 mA h g(-1) (2.3 Li per f.u.) and 144 mA h g(-1) (1.38 Li per f.u.) is observed for Li3MnRuO5 and Li3FeRuO5, respectively. An initial sloping region (OCV to ca. 4.1 V) is followed by a long plateau (ca. 4.3 V). Further discharge-charge cycling points to partial reversibility (ca. 160 mA h g(-1) and 45 mA h g(-1) for Mn and Fe, respectively). Nevertheless, just after a few cycles, cell failure is observed. X-ray photoelectron spectroscopy (XPS) characterisation of both pristine and electrochemically oxidized Li3MRuO5 reveals that in the Li3MnRuO5 oxide, Mn(3+) and Ru(4+) are partially oxidized to Mn(4+) and Ru(5+) in the sloping region at low voltage, while in the long plateau, O(2-) is also oxidized. Oxygen release likely occurs which may be the cause for failure of cells upon cycling. Interestingly, some other Li-rich layered oxides have been reported to cycle acceptably even with the participation of the O(2-) ligand in the reversible redox processes. In the Li3FeRuO5 oxide, the oxidation process appears to affect only Ru (4+ to 5+ in the sloping region) and O(2-) (plateau) while Fe seems to retain its 3+ state.

Centrosome-declustering drugs mediate a two-pronged attack on interphase and mitosis in supercentrosomal cancer cells.

Classical anti-mitotic drugs have failed to translate their preclinical efficacy into clinical response in human trials. Their clinical failure has challenged the notion that tumor cells divide frequently at rates comparable to those of cancer cells in vitro and in xenograft models. Given the preponderance of interphase cells in clinical tumors, we asked whether targeting amplified centrosomes, which cancer cells carefully preserve in a tightly clustered conformation throughout interphase, presents a superior chemotherapeutic strategy that sabotages interphase-specific cellular activities, such as migration. Herein we have utilized supercentrosomal N1E-115 murine neuroblastoma cells as a test-bed to study interphase centrosome declustering induced by putative declustering agents, such as Reduced-9-bromonoscapine (RedBr-Nos), Griseofulvin and PJ-34. We found tight 'supercentrosomal' clusters in the interphase and mitosis of ~80% of patients' tumor cells with excess centrosomes. RedBr-Nos was the strongest declustering agent with a declustering index of 0.36 and completely dispersed interphase centrosome clusters in N1E-115 cells. Interphase centrosome declustering caused inhibition of neurite formation, impairment of cell polarization and Golgi organization, disrupted cellular protrusions and focal adhesion contacts-factors that are crucial prerequisites for directional migration. Thus our data illustrate an interphase-specific potential anti-migratory role of centrosome-declustering agents in addition to their previously acknowledged ability to induce spindle multipolarity and mitotic catastrophe. Centrosome-declustering agents counter centrosome clustering to inhibit directional cell migration in interphase cells and set up multipolar mitotic catastrophe, suggesting that disbanding the nuclear-centrosome-Golgi axis is a potential anti-metastasis strategy.

A molecular dynamics study of ambient and high pressure phases of silica: structure and enthalpy variation with molar volume.

Extensive molecular dynamics studies of 13 different silica polymorphs are reported in the isothermal-isobaric ensemble with the Parrinello-Rahman variable shape simulation cell. The van Beest-Kramer-van Santen (BKS) potential is shown to predict lattice parameters for most phases within 2%-3% accuracy, as well as the relative stabilities of different polymorphs in agreement with experiment. Enthalpies of high-density polymorphs - CaCl2-type, α-PbO2-type, and pyrite-type - for which no experimental data are available as yet, are predicted here. Further, the calculated enthalpies exhibit two distinct regimes as a function of molar volume-for low and medium-density polymorphs, it is almost independent of volume, while for high-pressure phases a steep dependence is seen. A detailed analysis indicates that the increased short-range contributions to enthalpy in the high-density phases arise not only from an increased coordination number of silicon but also shorter Si-O bond lengths. Our results indicate that amorphous phases of silica exhibit better optimization of short-range interactions than crystalline phases at the same density while the magnitude of Coulombic contributions is lower in the amorphous phase.

Exploring the color of transition metal ions in irregular coordination geometries: new colored inorganic oxides based on the spiroffite structure, Zn(2-x)M(x)Te3O8 (M = Co, Ni, Cu).

We describe the synthesis, crystal structures, and optical absorption spectra of transition metal-substituted spiroffite derivatives, Zn(2-x)M(x)Te3O8 (M(II) = Co, Ni, Cu; 0 < x ≤ 1.0). The oxides are readily synthesized by solid state reaction of stoichiometric mixtures of the constituent binaries at 620 °C. Reitveld refinement of the crystal structures from powder X-ray diffraction (XRD) data shows that the Zn/MO6 octahedra are strongly distorted, as in the parent Zn2Te3O8 structure, consisting of five relatively short Zn/M(II)-O bonds (1.898-2.236 Å) and one longer Zn/M(II)-O bond (2.356-2.519 Å). We have interpreted the unique colors and the optical absorption/diffuse reflectance spectra of Zn(2-x)M(x)Te3O8 in the visible, in terms of the observed/irregular coordination geometry of the Zn/M(II)-O chromophores. We could not however prepare the fully substituted M2Te3O8 (M(II) = Co, Ni, Cu) by the direct solid state reaction method. Density Functional Theory (DFT) modeling of the electronic structure of both the parent and the transition metal substituted derivatives provides new insights into the bonding and the role of transition metals toward the origin of color in these materials. We believe that transition metal substituted spiroffites Zn(2-x)M(x)Te3O8 reported here suggest new directions for the development of colored inorganic materials/pigments featuring irregular/distorted oxygen coordination polyhedra around transition metal ions.

Spin-electron-phonon excitation in Re-based half-metallic double perovskites.

A remarkable hardening (~30 cm(-1)) of the normal mode of vibration associated with the symmetric stretching of the oxygen octahedra for the Ba(2)FeReO(6) and Sr(2)CrReO(6) double perovskites is observed below the corresponding magnetic ordering temperatures. The very large magnitude of this effect and its absence for the antisymmetric stretching mode provide evidence against a conventional spin-phonon coupling mechanism. Our observations are consistent with a collective excitation formed by the combination of the vibrational mode with oscillations of Fe or Cr 3d and Re 5d occupations and spin magnitudes.

Study of Ba3M(II)M(IV)WO9 (M(II) = Ca, Zn; M(IV) = Ti, Zr) perovskite oxides: competition between 3C and 6H perovskite structures.

We describe an investigation of Ba3MIIMIVWO9 oxides for MII = Ca, Zn, and other divalent metals and MIV = Ti, Zr. In general, a 1:2-ordered 6H (hexagonal, P63/mmc) perovskite structure is stabilized at high temperatures (1300 degrees C) for all of the Ba3MIITiWO9 oxides investigated. An intermediate phase possessing a partially ordered 1:1 double perovskite (3C) structure with the cation distribution, Ba2(Zn2/3Ti1/3)(W2/3Ti1/3)O6, is obtained at 1200 degrees C for Ba3ZnTiWO9. Sr substitution for Ba in the latter stabilizes the cubic 3C structure instead of the 6H structure. A metastable Ba3CaZrWO9 that adopts the 3C (cubic, Fmm) structure has also been synthesized by a low-temperature metathesis route. Besides yielding several new perovskite oxides that may be useful as dielectric ceramics, the present investigation provides new insights into the complex interplay of crystal chemistry (tolerance factor) and chemical bonding (anion polarization and d0-induced distortion of metal-oxygen octahedra) in the stabilization of 6H versus 3C perovskite structures for the Ba3MIIMIVWO9 series.

Oxygen-release/storage properties of Ce0.5M0.5O2 (M = Zr, Hf) oxides: interplay of crystal chemistry and electronic structure.

Fluorite-type Ce0.5Zr0.5O2 and Ce0.5Hf0.5O2 have been synthesized by a solution combustion route, and their oxygen release and reduction have been investigated up to 850 degrees C. On reduction, the zirconium system forms two pyrochlore phases, Ce2Zr2O7 (pyrochlore-I) and Ce2Zr2O6.2 (pyrochlore-II), while the hafnium system forms only a disordered fluorite phase with the composition Ce0.5Hf0.5O1.77, under the same experimental conditions. The crystal structures of the reduction products have been characterized by powder X-ray diffraction and Rietveld refinement, and their electronic structures have been investigated by photoelectron spectroscopy and electrical conductivity measurements. Pyrochlore-I (a = 10.6727(4) A) is a semiconductor, while pyrochlore-II (a = 10.6463(8) A) is a good conductor (with a nearly temperature independent resistivity of approximately 2.5 ohm.cm in the 400-1000 K range). X-ray photoelectron spectroscopy (XPS) shows an admixture of Ce(5d,6s) with Zr(4d) and O(2p) and a significant density of states near EF in the highly reduced pyrochlore-II phase. The changes have been rationalized in terms of a qualitative energy band scheme that brings out the special role of zirconium vis-à-vis hafnium in the reduction/oxygen release properties of Ce0.5Zr0.5O2 and Ce0.5Hf0.5O2.

Incipient orbital order in half-metallic Ba2FeReO6.

Largely unquenched Re 5d orbital magnetic moments in half-metallic Ba2FeReO6 drive a symmetry lowering transition from a cubic paramagnet to a compressed tetragonal (c/a < 1) ferrimagnet below Tc ~ 305 K, with a giant linear magnetoelastic constant and the spins lying spontaneously along the unique tetragonal axis. The large orbital magnetization and degree of structural deformation indicate proximity to a metal-insulator transition. These results point to an incipient orbitally ordered state in the metallic ferrimagnetic phase.

Reversible cation/anion extraction from K2La2Ti3O10: formation of new layered titanates, KLa2Ti3O9.5 and La2Ti3O9.

A new soft-chemical transformation of layered perovskite oxides is described wherein K2O is sequentially extracted from the Ruddlesden-Popper (R-P) phase, K2La2Ti3O10 (I), yielding novel anion-deficient KLa2Ti3O(9.5) (II) and La2Ti3O9 (III). The transformation occurs in topochemical reactions of the R-P phase I with PPh4Br and PBu4Br (Ph = phenyl; Bu = n-butyl). The mechanism involves the elimination of KBr accompanied by decomposition of PR4+ (R = phenyl or n-butyl) that extracts oxygen from the titanate. Analysis of the organic products of decomposition reveals formation of Ph3PO, Ph3P, and Ph-Ph for R = phenyl, and Bu3PO, Bu3P along with butane, butene, and octane for R = butyl. The inorganic oxides II and III crystallize in tetragonal structures (II: P4/mmm, a = 3.8335(1) A, c = 14.334(1) A; III: I4/mmm, a = 3.8565(2) A, c = 24.645(2) A) that are related to the parent R-P phase. II is isotypic with the Dion-Jacobson phase, RbSr2Nb3O10, while III is a unique layered oxide consisting of charge-neutral La2Ti3O9 anion-deficient perovskite sheets stacked one over the other without interlayer cations. Interestingly, both II and III convert back to the parent R-P phase in a reaction with KNO3. While transformations of the R-P phases to other related layered/three-dimensional perovskite oxides in ion-exchange/metathesis/dehydration/reduction reactions are known, the simultaneous and reversible extraction of both cations and anions in the conversions K2La2Ti3O10 right harpoon over left harpoon KLa2Ti3O9.5 right harpoon over left harpoon La2Ti3O9 is reported here for the first time.

2D-3D transformation of layered perovskites through metathesis: synthesis of new quadruple perovskites A2La2CuTi3O12 (A = Sr, Ca).

We describe the synthesis of two new quadruple perovskites, Sr(2)La(2)CuTi(3)O(12) (I) and Ca(2)La(2)CuTi(3)O(12) (II), by solid-state metathesis reaction between K(2)La(2)Ti(3)O(10) and A(2)CuO(2)Cl(2) (A = Sr, Ca). I is formed at 920 degrees C/12 h, and II, at 750 degrees C/24 h. Both the oxides crystallize in a tetragonal (P4/mmm) quadruple perovskite structure (a = 3.9098(2) and c = 15.794(1) A for I; a = 3.8729(5) and c = 15.689(2) A for II). We have determined the structures of I and II by Rietveld refinement of powder XRD data. The structure consists of perovskite-like octahedral CuO(4/2)O(2/2) sheets alternating with triple octahedral Ti(3)O(18/2) sheets along the c-direction. The refinement shows La/A disorder but no Cu/Ti disorder in the structure. The new cuprates show low magnetization (0.0065 micro(B) for I and 0.0033 micro(B) for II) suggesting that the Cu(II) spins are in an antiferromagnetically ordered state. Both I and II transform at high temperatures to 3D perovskites where La/Sr and Cu/Ti are disordered, suggesting that I and II are metastable phases having been formed in the low-temperature metathesis reaction. Interestingly, the reaction between K(2)La(2)Ti(3)O(10) and Ca(2)CuO(2)Cl(2) follows a different route at 650 degrees C, K(2)La(2)Ti(3)O(10) + Ca(2)CuO(2)Cl(2) --> CaLa(2)Ti(3)O(10) + CaCuO(2) + 2KCl, revealing multiple reaction pathways for metathesis reactions.

Topochemical anion metathesis routes to the Zr2N2S phases and the Na2S and ACl derivatives (A = Na, K, Rb).

Anion metathesis reactions between ZrNCl and A(2)S (A = Na, K, Rb) in the solid state follow three different pathways depending on reaction temperature and reactant stoichiometry: (1) the reaction of ZrNCl with A(2)S in the 2:1 stoichiometry at 800 degrees C/72 h/in vacuo yields alpha-Zr(2)N(2)S with the expected layered structure of La(2)O(2)S. Above 850 degrees C, alpha-Zr(2)N(2)S (P3 macro m1; a = 3.605(1) A, c = 6.421(3) A) neatly transforms to beta-Zr(2)N(2)S (P6(3)/mmc: a = 3.602(1) A, c = 12.817(1) A). The structures of the alpha- and beta-forms are related by an a/2 shift of successive Zr(2)N(2) layers. (2) The same reaction at low temperatures (300-400 degrees C) yields ACl intercalated phases of the formula A(x)Zr(2)N(2)SCl(x) (0 < x < approximately 0.15), where alkali ions are inserted between the S/Cl.S/Cl van der Waals gap of a ZrNCl-type structure. The S and Cl ions are disordered and the c lattice parameters are alkali dependent (R3 macro m, a approximately 3.6 A, c approximately 28.4 (Na), 28.9 (K), and 30.5 A (Rb). A(x)Zr(2)N(2)SCl(x) phases are hygroscopic and reversibly absorb water to give monohydrates. (3) Reaction of ZrNCl with excess A(2)S at 400-1000 degrees C gives A(2)S intercalated phases of the formula A(2)(x)Zr(2)N(2)S(1+)(x) (0 < x < 0.5), where the alkali ions reside between the S.S van der Waals gap of a ZrNCl type structure (R3 macro m, a approximately 3.64 A, c approximately 29.48 A). Structural characterization of the new phases and implications of the results are described.

Structurally modulated magnetic properties in the A(3)MnRu(2)O(9) phases (A = Ba, Ca): the role of metal-metal bonding in perovskite-related oxides.

Ca(3)MnRu(2)O(9) and Ba(3)MnRu(2)O(9) were synthesized from transition metal dioxides and alkaline earth metal carbonates at 1100-1300 degrees C. Ca(3)MnRu(2)O(9) adopts the prototypical GdFeO(3)-type perovskite structure with Mn and Ru statistically disordered over the single metal atom site. The susceptibility shows Curie-Weiss behavior above 240 K with mu(eff) = 3.14 micro(B)/metal atom, which is in excellent agreement with the expected spin-only moment of 3.20 micro(B). Below 150 K, the compound shows spin-glass-like short-range ferrimagnetic correlations. The high-temperature region of the electrical resistivity reveals a small activation energy of 17(1) meV whereas the low-temperature region is nonlinear and does not fit a variable range hopping model. Ba(3)MnRu(2)O(9) crystallizes in the 9-layer BaRuO(3)-type structure containing M(3)O(12) face-shared trioctahedral clusters in which Mn and Ru are statistically disordered. Ba(3)MnRu(2)O(9) shows nonlinear reciprocal susceptibility at all temperatures and is described by a variable-spin cluster model with an S = (1)/(2) ground state with thermally populated excited states. The low spin value of this system (S = (1)/(2)) is attributed to direct metal-metal bonding. Below 30 K, the compound shows short-range magnetic correlations and spin-glass-like behavior. The high-temperature region of the electrical resistivity indicates a small activation energy of 8.8(1) meV whereas the low-temperature region is nonlinear. The importance of metal-metal bonding and the relationships to other related compounds are discussed.

A[Bi(3)Ti(4)O(13)] and A[Bi(3)PbTi(5)O(16)] (A = K, Cs): New n = 4 and n = 5 Members of the Layered Perovskite Series, A[A'(n)()(-)(1)B(n)()O(3)(n)()(+1)], and Their Hydrates.

We describe the synthesis and structural characterization of new layered bismuth titanates, A[Bi(3)Ti(4)O(13)] and A[Bi(3)PbTi(5)O(16)] for A = K, Cs, corresponding to n = 4 and 5 members of the Dion-Jacobson series of layered perovskites of the general formula, A[A'(n)()(-)(1)B(n)()O(3)(n)()(+1)]. These materials have been prepared by solid state reaction of the constituents containing excess alkali, which is required to suppress the formation of competitive Aurivillius phases. Unlike the isostructural niobates and niobium titanates of the same series, the new phases reported here are spontaneously hydrated-a feature which could make them potentially useful as photocatalysts for water splitting reaction. On hydration of the potassium compounds, the c axis expands by ca. 2 Å and loses its doubling [for example, the tetragonal lattice parameters of K[Bi(3)Ti(4)O(13)] and its dihydrate are respectively a = 3.900(1) Å, c = 37.57(2) Å; a = 3.885(1) Å, c = 20.82(4) Å]; surprisingly, the cesium analogues do not show a similar change on hydration.

Antioxidant activity of mechanically separated pork extracts.

Utilization of synthetic carnosine as a food additive is limited by both regulatory and economic hurdles. Therefore, the potential of producing carnosine-containing antioxidant extracts from an underutilized skeletal muscle source, mechanically separated pork (MSP), was investigated. Carnosine-containing MSP extracts were capable of inhibiting lipid oxidation both in vitro and in salted ground pork. Heating (60-80°C) the MSP extract removed iron and increased in vitro antioxidant activity. Isolation of a low molecular weight fraction of the MSP extract by ultrafiltration was effective at decreasing iron but did not substantially increase in vitro antioxidant activity. Freeze dried extracts (untreated, 80°C, ultrafiltration permeate) were capable of inhibiting both TBARS and lipid peroxide formation in ground, salted pork stored at -15°C. While MSP extracts were capable of inhibiting lipid oxidation both in vitro and in salted, ground pork, their antioxidant activity was low suggesting that their use as a food additive would be impractical.