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Measurement of the Gd and Sm isotopic compositions in the Luna 16, G-2 soil, a sample which has the largest low energy neutron fluence yet observed in a lunar sample. The ratio of the number of neutrons captured per atom by Sm-149 to Gd-157 is 0.76, which is distinct from the value of 0.86 observed at the Apollo 11, 12, and 14 sites. This indicates a softer neutron energy spectrum at the Sea of Plenty.
An electron microscopy study has been carried out to characterize the microstructure of a sintered Gd-Ba-Cu-O superconductor alloy. The GdBa2Cu3O(7-x) phase in the oxygen annealed sample is orthorhombic, while in the vacuum annealed sample it is tetragonal. It is shown that the details of the fine structure in the 001-line zone axis convergent beam patterns can be used to distinguish between the orthorhombic form and the tetragonal form. In addition to this matrix phase, an amorphous phase is frequently observed at the triple grain junctions. Gd-rich inclusions have been observed inside the matrix phase.
We report observations of the extreme ultraviolet spectrum of the hot degenerate star GD 246 obtained with the EUVE. Our initial attempt at modeling the photospheric emission from the white dwarf reveals a relatively uncontaminated pure H spectrum in the range above 200 A, allowing a study of interstellar continuum absorption features in the line of sight of GD 246. Modeling of the He I autoionization transition discussed by Rumph et al. (1993), and the EUV continuum using the white dwarf as a source of background radiation provides measurements of both neutral and, for the first time, singly ionized He column densities in the local ISM (LISM). We estimate the He ionization fraction He II/(He I + He II) at roughly 25 percent with a total He column of 1.40-1.65 x 10 exp 18/sq cm. We have measured and compared H I column densities from the saturated Ly-alpha ISM absorption in IUE high-dispersion spectroscopy and from EUV continuum absorption: the two measurements are in good agreement with a total H column of 1.2-1.6 x 10 exp 19/sq cm. We discuss some implications for the nature of the LISM, particularly in the context of current models of the EUV radiation field.
It has been demonstrated that R2BaCuO(5-x) (R = Y, Sm, Gd, Dy, Ho, Er, Yb) does not undergo significant densification unless the sintering temperatures are near the incongruent melting point or the sintering times are long. Good quality powders of Y2BaCuO(5-x) have been synthesized by using oxide raw materials or precursors such as acetates and nitrates. The acetates- and the nitrates-derived yttrium green phase resulted in finer particle sizes, acceptable dielectric properties and lower melting temperatures than those processed via oxide raw materials. The hot pressing technique has been employed to produce a dense R2BaCuO(5-x) (R=Y,Gd) substrate with satisfactory dielectric properties. Reactivity to reducing conditions, i.e. graphite die, limited the optimization of the properties. A high sensitivity to the annealing atmosphere has been demonstrated in Y2BaCuO,.,,. Oxygen treatment at 950 OC has been shown to improve the dielectric properties while treatment in nitrogen, at the same temperature, degraded desirable properties. A high sensitivity to the annealing atmosphere has been demonstrated in Y2BaCuO(5-x). Oxygen treatment at 950 C has been shown to improve the dielectric properties while treatment in nitrogen, at the same temperature, degraded desirable properties. The dielectric constants of the rare earth green phases R2BaCuO(5-x) were found to be low. Relaxation peaks were detected at low temperatures (T less than 150 K) and at high temperatures (150 less than T greater than 420 K). The dielectric losses and conductivities at 77 K were measured to be in the range of 10(exp -4) and 10(exp -12) (Omega-cm)(exp -1), respectively. Many parameters were found to exhibit dependencies on the rare earth cation sizes.
The General Dynamics (GD) S-Band software defined radio (SDR) in the Space Communications and Navigation (SCaN) Testbed on the International Space Station (ISS) provides experimenters an opportunity to develop and demonstrate experimental waveforms in space. The SCaN Testbed was installed on the ISS in August of 2012. After installation, the initial checkout and commissioning phases were completed and experimental operations commenced. One goal of the SCaN Testbed is to collect long term performance metrics for SDRs operating in space in order to demonstrate long term reliability. These metrics include the time the SDR powered on, the time the power amplifier (PA) is powered on, temperature trends, error detection and correction (EDAC) behavior, and waveform operational usage time. This paper describes the performance of the GD SDR over the first year of operations on the ISS.
GdB3O6 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Gd3+ is bonded in a 8-coordinate geometry to ten O2- atoms. There are a spread of Gd–O bond distances ranging from 2.34–2.90 Å. There are two inequivalent B3+ sites. In the first B3+ site, B3+ is bonded in a trigonal planar geometry to three O2- atoms. There are a spread of B–O bond distances ranging from 1.34–1.42 Å. In the second B3+ site, B3+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.46 Å) and two longer (1.49 Å) B–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two equivalent Gd3+ and two B3+ atoms. In the second O2- site, O2- is bonded in a 2-coordinate geometry to one Gd3+ and two B3+ atoms. In the third O2- site, O2- is bonded in a distorted single-bond geometry to two equivalent Gd3+ and one B3+ atom.
GdMn2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Gd3+ is bonded in a body-centered cubic geometry to eight equivalent Si4- atoms. All Gd–Si bond lengths are 3.05 Å. Mn+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing MnSi4 tetrahedra. All Mn–Si bond lengths are 2.32 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Gd3+, four equivalent Mn+2.50+, and one Si4- atom. The Si–Si bond length is 2.55 Å.
GdCu2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Gd3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Gd–Si bond lengths are 3.07 Å. Cu+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CuSi4 tetrahedra. All Cu–Si bond lengths are 2.40 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Gd3+, four equivalent Cu+2.50+, and one Si4- atom. The Si–Si bond length is 2.36 Å.
GdNi2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Gd3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Gd–Si bond lengths are 3.07 Å. Ni+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing NiSi4 tetrahedra. All Ni–Si bond lengths are 2.31 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Gd3+, four equivalent Ni+2.50+, and one Si4- atom. The Si–Si bond length is 2.44 Å.
GdNi2P2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Gd3+ is bonded in a distorted body-centered cubic geometry to eight equivalent P3- atoms. All Gd–P bond lengths are 2.99 Å. Ni+1.50+ is bonded to four equivalent P3- atoms to form a mixture of corner and edge-sharing NiP4 tetrahedra. All Ni–P bond lengths are 2.28 Å. P3- is bonded in a 9-coordinate geometry to four equivalent Gd3+, four equivalent Ni+1.50+, and one P3- atom. The P–P bond length is 2.33 Å.
GdFe2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Gd3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Gd–Si bond lengths are 3.10 Å. Fe+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of corner and edge-sharing FeSi4 tetrahedra. All Fe–Si bond lengths are 2.27 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Gd3+, four equivalent Fe+2.50+, and one Si4- atom. The Si–Si bond length is 2.60 Å.
GdNi2Sb2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Gd3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Sb3- atoms. All Gd–Sb bond lengths are 3.38 Å. Ni+1.50+ is bonded to four equivalent Sb3- atoms to form a mixture of edge and corner-sharing NiSb4 tetrahedra. All Ni–Sb bond lengths are 2.49 Å. Sb3- is bonded in a 9-coordinate geometry to four equivalent Gd3+, four equivalent Ni+1.50+, and one Sb3- atom. The Sb–Sb bond length is 2.87 Å.
GdRu2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Gd3+ is bonded in a 8-coordinate geometry to eight equivalent Si4- atoms. All Gd–Si bond lengths are 3.23 Å. Ru+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of corner and edge-sharing RuSi4 tetrahedra. All Ru–Si bond lengths are 2.39 Å. Si4- is bonded in a 4-coordinate geometry to four equivalent Gd3+ and four equivalent Ru+2.50+ atoms.
GdCo2B2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Gd3+ is bonded in a body-centered cubic geometry to eight equivalent B3- atoms. All Gd–B bond lengths are 2.92 Å. Co+1.50+ is bonded to four equivalent B3- atoms to form a mixture of distorted edge and corner-sharing CoB4 tetrahedra. All Co–B bond lengths are 2.00 Å. B3- is bonded in a 4-coordinate geometry to four equivalent Gd3+ and four equivalent Co+1.50+ atoms.
GdCr2Si2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. Gd3+ is bonded in a body-centered cubic geometry to eight Si4- atoms. There are three shorter (3.00 Å) and five longer (3.01 Å) Gd–Si bond lengths. There are two inequivalent Cr+2.50+ sites. In the first Cr+2.50+ site, Cr+2.50+ is bonded to four Si4- atoms to form a mixture of edge and corner-sharing CrSi4 tetrahedra. All Cr–Si bond lengths are 2.41 Å. In the second Cr+2.50+ site, Cr+2.50+ is bonded to four Si4- atoms to form a mixture of edge and corner-sharing CrSi4 tetrahedra. There are one shorter (2.40 Å) and three longer (2.41 Å) Cr–Si bond lengths. There are two inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 9-coordinate geometry to four equivalent Gd3+, four Cr+2.50+, and one Si4- atom. The Si–Si bond length is 2.50 Å. In the second Si4- site, Si4- is bonded in a 9-coordinate geometry to four equivalent Gd3+, four Cr+2.50+, and one Si4- atom.
GdCo12B6 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Gd3+ is bonded in a hexagonal planar geometry to six equivalent B3- atoms. All Gd–B bond lengths are 3.04 Å. There are two inequivalent Co+1.25+ sites. In the first Co+1.25+ site, Co+1.25+ is bonded to four equivalent B3- atoms to form a mixture of distorted edge and corner-sharing CoB4 trigonal pyramids. There are two shorter (2.02 Å) and two longer (2.04 Å) Co–B bond lengths. In the second Co+1.25+ site, Co+1.25+ is bonded in a T-shaped geometry to three equivalent B3- atoms. There are one shorter (2.09 Å) and two longer (2.10 Å) Co–B bond lengths. B3- is bonded in a 7-coordinate geometry to one Gd3+ and seven Co+1.25+ atoms.
GdCo4B4 crystallizes in the tetragonal P4_2/nmc space group. The structure is three-dimensional. Gd3+ is bonded in a 12-coordinate geometry to twelve equivalent B3- atoms. There are eight shorter (2.88 Å) and four longer (2.90 Å) Gd–B bond lengths. Co+2.25+ is bonded in a 5-coordinate geometry to five equivalent B3- atoms. There are a spread of Co–B bond distances ranging from 2.05–2.11 Å. B3- is bonded in a 6-coordinate geometry to three equivalent Gd3+, five equivalent Co+2.25+, and one B3- atom. The B–B bond length is 1.75 Å.
GdFe4P12 crystallizes in the cubic Im-3 space group. The structure is three-dimensional. Gd3+ is bonded to twelve equivalent P1- atoms to form GdP12 cuboctahedra that share faces with eight equivalent FeP6 octahedra. All Gd–P bond lengths are 2.99 Å. Fe+2.25+ is bonded to six equivalent P1- atoms to form FeP6 octahedra that share corners with six equivalent FeP6 octahedra and faces with two equivalent GdP12 cuboctahedra. The corner-sharing octahedral tilt angles are 59°. All Fe–P bond lengths are 2.25 Å. P1- is bonded in a 2-coordinate geometry to one Gd3+, two equivalent Fe+2.25+, and two equivalent P1- atoms. There are one shorter (2.31 Å) and one longer (2.35 Å) P–P bond lengths.