2,822 research outputs found

    Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars

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    The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064-μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ~1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64° in latitude × 1/32° in longitude (1 × 2 km^2 at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100-m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100-m-scale surface roughness and 1.064-μm reflectivity with an accuracy of 5% have also been obtained

    SU(2) reductions in N=4 multidimensional supersymmetric mechanics

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    We perform an su(2) Hamiltonian reduction in the bosonic sector of the su(2)-invariant action for two free (4, 4, 0) supermultiplets. As a result, we get the five dimensional N=4 supersymmetric mechanics describing the motion of an isospin carrying particle interacting with a Yang monopole. We provide the Lagrangian and Hamiltonian descriptions of this system. Some possible generalizations of the action to the cases of systems with a more general bosonic action, a four-dimensional system which still includes eight fermionic components, and a variant of five-dimensional N=4 mechanics constructed with the help of the ordinary and twisted N=4 hypermultiplets were also considered.Comment: 11 pages, LaTeX file, no figures; 3 references added, minor correction

    Heat increments and oxidation enthalpies of (Y,Pr,Gd)BaCo2O6-δ double perovskites

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    Complex oxides (Y,Gd,Pr)BaCo2O6-δ attracts researchers’ attention due to it are promising materials for cathodes for solid state fuel cells. However, fundamental thermodynamic properties of these double perovskites such as heat increments, heat capacity and enthalpy of oxidation are not investigated so far. Powder samples of (Y,Gd,Pr)BaCo2O6-δ were prepared using glycerol–nitrate technique. Phase composition of investigated double perovskites was controlled by X-ray powder diffraction. Then samples with composition GdBaCo2O5.51, PrBaCo2O5.77, YBaCo2O5.33 were prepared by slowly cooling with speed rate 100 K/h, whereas sample YBaCo2O5.0 was prepared by annealing at 1373 K and quenching. Enthalpy increments of all as-prepared samples were measured by high temperature drop-calorimetry method on the SETARAM MHTC 96 calorimeter. Since YBaCo2O6-δ is stable only above 1123 K in air, calorimetry measurements were carried out in region 1123≤T, K≤1323. Oxidation enthalpies of (Gd,Pr)BaCo2O6-δ were measured by means of DSC sensors of MHTC 96 calorimeter at 1173K. Oxidation enthalpy of YBaCo2O6-δ was calculated from heat increments measurements. Obtained data allow us to calculate a heat capacity dependency from temperature for these compounds. Acknowledgement: This study was supported by the Russian Foundation for Basic Research (Grant No. 18-33-20243)

    N=4 mechanics, WDVV equations and roots

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    N=4 superconformal multi-particle quantum mechanics on the real line is governed by two prepotentials, U and F, which obey a system of partial differential equations linear in U and generalizing the Witten-Dijkgraaf-Verlinde-Verlinde (WDVV) equation for F. Putting U=0 yields a class of models (with zero central charge) which are encoded by the finite Coxeter root systems. We extend these WDVV solutions F in two ways: the A_n system is deformed n-parametrically to the edge set of a general orthocentric n-simplex, and the BCF-type systems form one-parameter families. A classification strategy is proposed. A nonzero central charge requires turning on U in a given F background, which we show is outside of reach of the standard root-system ansatz for indecomposable systems of more than three particles. In the three-body case, however, this ansatz can be generalized to establish a series of nontrivial models based on the dihedral groups I_2(p), which are permutation symmetric if 3 divides p. We explicitly present their full prepotentials.Comment: 1+25 pages; v2: major revision (more general analysis, new solutions, additional references); v3: improvements in sects.5,8,9, refs. adde
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