On the Smith normal form of a skew‐symmetric d‐optimal design of order

We show that the Smith normal form of a skew‐symmetric D ‐optimal design of order is determined by its order. Furthermore, we show that the Smith normal form of such a design can be written explicitly in terms of the order , thereby proving a recent conjecture of Armario. We apply our result to show that certain D ‐optimal designs of order are not equivalent to any skew‐symmetric D ‐optimal design. We also provide a correction to a result in the literature on the Smith normal form of D ‐optimal designs.     

Viscous waves and wave-structure interaction in a tank using adapting quadtree grids

Viscous waves and waves over a submerged cylinder in a stationary tank are simulated using a volume-of-fluid numerical scheme on adaptive hierarchical grids. A high resolution interface-capturing method is used to advect the free surface interface and the Navier–Stokes equations are discretised using finite volumes with collocated primitive variables and solved using a Pressure Implicit with Splitting of Operators (PISO) algorithm. The cylinder is modelled by using the technique of Cartesian cut cells. Results of flow of a single fluid past a cylinder at Reynolds number Re=100 are presented and found to agree well with experimental and other numerical data. Viscous free surface waves in a tank are simulated using uniform and quadtree grids for Reynolds numbers in the range from 2 to 2000, and the results compared against analytical solutions where available. The quadtree-based results are of the same accuracy as those on the equivalent uniform grids, and retain a sharp interface at the free surface while leading to considerable savings in both storage and CPU requirements. The nonlinearity in the wave is investigated for a selection of initial wave amplitudes. A submerged cylinder is positioned in the tank and its influence on the waves as well as the hydrodynamic loading on the cylinder is investigated.     

Amorphous arsenic

An attempt is made to unify current knowledge of the optical, vibrational, transport and defect-related properties of amorphous As in terms of its structure and the nature of the bonding. The importance of remnant mesomeric bonding, particularly in determining preparation-dependent variations in the optical gap, is stressed. Topological disorder is taken as a central theme and it is shown how the ring statistics dictate the radial distribution function. The relationship between atomic structure and the electron and phonon densities of states is discussed. A review is given of the transport properties of amorphous As: these point to a pinned Fermi level. Variations in s–p hybridization are considered in relation to the types of point defect likely to occur and it is shown how both paired and unpaired spin states are possible. Finally some experimental results on crystallization kinetics, specific heat and thermal conductivity are discussed.     

Synthesis and characterization of La0.8Sr1.2Co0.5M0.5O4−δ (M=Fe, Mn)

The M⁴⁺-containing K₂NiF₄-type phases La_0.8Sr_1.2Co_0.5Fe_0.5O₄ and La_0.8Sr_1.2Co_0.5Mn_0.5O₄ have been synthesized by a sol–gel procedure and characterized by X-ray powder diffraction, thermal analysis, neutron powder diffraction and Mössbauer spectroscopy. Oxide ion vacancies are created in these materials via reduction of M⁴⁺ to M³⁺ and of Co³⁺ to Co²⁺. The vacancies are confined to the equatorial planes of the K₂NiF₄-type structure. A partial reduction of Mn³⁺ to Mn²⁺ also occurs to achieve the oxygen stoichiometry in La_0.8Sr_1.2Co_0.5Mn_0.5O_3.6. La_0.8Sr_1.2Co_0.5Fe_0.5O_3.65 contains Co²⁺ and Fe³⁺ ions which interact antiferromagnetically and result in noncollinear magnetic order consistent with the tetragonal symmetry. Competing ferromagnetic and antiferromagnetic interactions in La_0.8Sr_1.2Co_0.5Fe_0.5O₄, La_0.8Sr_1.2Co_0.5Mn_0.5O₄ and La_0.8Sr_1.2Co_0.5Mn_0.5O_3.6 induce spin glass properties in these phases.     

Aerodynamic levitation and laser heating:

Aerodynamic levitation is an effective way to suspend samples which can be heated with CO₂ lasers. The advantages of this containerless technique are the simplicity and compactness of the device, making it possible to integrate it easily in different kinds of experiments. In addition, all types of materials can be used, including metals and oxides. The integration of aerodynamic levitation at synchrotron and neutron sources provides powerful tools to study the structure and dynamics of molten materials. We present here an overview of the existing techniques and of the developments made at the CEMHTI in Orléans, as well as a few examples of experimental results already obtained.     

Evaluation of novel ZnO–Ag cathode for CO2 electroreduction in solid oxide electrolyser

CO₂ and steam/CO₂ electroreduction to CO and methane in solid oxide electrolytic cells (SOEC) has gained major attention in the past few years. This work evaluates, for the very first time, the performance of two different ZnO–Ag cathodes: one where ZnO nanopowder was mixed with Ag powder for preparing the cathode ink (ZnO_mix–Ag cathode) and the other one where Ag cathode was infiltrated with a zinc nitrate solution (ZnO_inf –Ag cathode). ZnO_mix–Ag cathode had a better distribution of ZnO particles throughout the cathode, resulting in almost double CO generation while electrolysing both dry CO₂ and H₂/CO₂ (4:1 v/v). A maximum overall CO₂ conversion of 48% (in H₂/CO₂) at 1.7 V and 700 °C clearly indicated that as low as 5 wt% zinc loading is capable of CO₂ electroreduction. It was further revealed that for ZnO_inf –Ag cathode, most of CO generation took place through RWGS reaction, but for ZnO_mix–Ag cathode, it was the synergistic effect of both RWGS reaction and CO₂ electrolysis. Although ZnO_inf –Ag cathode produced trace amount of methane at higher voltages, with ZnO_mix–Ag cathode, there was absolutely no methane. This seems to be due to strong electronic interaction between Zn and Ag that might have suppressed the catalytic activity of the cathode towards methanation.

     

Requirements for soft magnetic underlayer (SUL)—Micromagnetic simulations of single-pole-type write heads and SUL systems

Landau-Lifshitz-Gilbert micromagnetic models were used to analyze the head field distributions and high-frequency responses for various soft magnetic underlayer thicknesses (t-SUL) and saturation magnetization flux densities (B_s) of single-pole-type (SPT) head-SUL systems. It was found that B_s of 10-12 kG and t-SUL of 30-45 nm would be sufficient for the examined head and perhaps for most next generation head-SUL systems. Antiferromagnetic coupling in the SUL affects the head and SUL magnetization and, eventually, the head field. With regard to the head magnetization response, it was found that the magnetization under the coil responded first, while the response at the main pole tip was quite slow, even compared with the head field. The main pole tip of the head was fully saturated and the main pole yoke was almost saturated, while the SUL was not saturated in the examined head-SUL system.     

Energy and line width in the induced emission of Mössbauer radiation

Summary Some promising schemes proposed for extending the range of lasers to the X-ray and gamma-ray regions are those involving a transition from a long-lived nuclear excited state. While metastable states allow the creation of conditions for population inversion, they also give rise to problems due to the narrowness of the expected line width. We discuss the line width of the radiation due to gamma transitions between excited states and derive a corrected relation for the cross-section in this case. Criteria for choosing an appropriate isotope are deduced from the corrected crosssection, showing that the problems derived from the narrowness of the line width can be avoided in a transition from an isomeric state to a lower short-lived excited state in which case the line width of the radiation is totally determined by the breadth of the lower excited state.

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Riassunto Alcuni schemi promettenti proposti per estendere il campo dei laser alle regioni dei raggi X e dei raggi gamma sono quelli che coinvolgono una transizione da uno stato eccitato nucleare a vita lunga. Mentre gli stati metastabili permettono la creazione delle condizioni per l’inversione della popolazione, essi danno luogo anche ai problemi dovuti alla ristrettezza dell’ampiezza della linea attesa. Si discute l’ampiezza di linea della radiazione dovuta alle transizioni gamma tra gli stati eccitati e si deduce una relazione corretta per la sezione d’urto in questo caso. Si deducono i criteri per scegliere un isotopo appropriato dalla sezione d’urto corretta, mostrando che i problemi che derivano dalla ristrettezza dell’ampiezza di linea si possono evitare in una transizione da uno stato isomerico a uno stato eccitato piú basso a vita breve, nel qual caso l’ampiezza di linea della radiazione si determina totalmente dalla larghezza dello stato eccitato piú basso.

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Резюме Были предложены обнадеживающие схемы для расширения области лазеров в рентгеновскую и гамма-области. Эти схемы вкяючают переход из долгоживущего ядерного возбужденного состояния. Так как метастабильные состояния допускают создание условий для инверсной заселенности, то они также приводят к проблемам, обусловленным узостью ожидаемой ширины линии. Мы обсуждаем ширину линии излучения, обусловленную гамма-переходами между возбужденными состояниями и выводим соотношение для поперечного сечения в этом случае. Выводятся критерии для выбора соответствующего изотопа из полученного поперечного сечения. Показывается, что проблемы, связанные с узостью ширины линии, можно обойти в случае перехода из изомерного состояния в низшее короткоживущее возбужденное состояние, причем в этом случае ширина линии излучения полностью определяется шириной низшего возбужденного состояния.

     

Numerical simulation of fluid flows using an unstructured finite volume method with adaptive tri‐tree grids

A tri‐tree grid generation procedure is developed together with a finite volume method on the unstructured grid for solving the Navier–Stokes equations. A hierarchic numbering system for the data structure is used. The grid is adapted by adding and removing cell elements dependent on the vorticity magnitude. A special treatment is developed to ensure good quality triangular elements around the cylinder boundary. The adopted finite volume method is based on the cell‐centred scheme. The pressure–velocity coupling is treated using the SIMPLE algorithm. A modified QUICK scheme for unstructured grids is derived. The developed method is used to simulate the flow past a single and multiple cylinders at low Reynolds number. The obtained results are in good agreement with the published data. Copyright © 2002 John Wiley & Sons, Ltd.     

The Structural Characterization of Tin- and Titanium-Dopedα-Fe2O3Prepared by Hydrothermal Synthesis

The structural characteristics of tin- and titanium-dopedα-Fe₂O₃prepared by hydrothermal methods have been investigated by Rietveld structure refinement of the X-ray powder diffraction data. The analysis reveals that the dopant ions adopt two distinct sites: in addition to partially substituting at the octahedral Fe sites, they also occupy the interstitial octahedral sites which are vacant in theα-Fe₂O₃structure. The structural model deduced involves clusters of three substituted cations and is rational in that it represents microstructural regions of the rutile structure within a matrix ofα-Fe₂O₃.