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The spectra of levels in the hypernuclei /sup 13//sub ..lambda../C, /sup 14//sub ..lambda../N, and /sup 18//sub ..lambda../O, excited by 800-MeV/c kaons in the (K/sup -/,..pi../sup -/) reaction, have been observed at the Brookhaven alternating gradient Synchrotron. Data were recorded for scattering angles from 0/sup 0/ to 25/sup 0/, corresponding to momentum transfers from 50 to 330 MeV/c. The levels are interpreted in terms of a ..lambda.. hyperon coupled to a strangeness-zero nuclear core. The results provide insights into the properties of the ..lambda..-nucleon and ..lambda..-nucleus interactions.

We show that the superconducting transition temperature ${T}_{c}$ of ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ba}}_{\mathrm{x}}$${\mathrm{CuO}}_{4}$ as a function of barium content (0\ensuremath{\le}x\ensuremath{\le}0.25, determined by mutual inductance measurements) has two maxima, both ${T}_{c}$\ensuremath{\approxeq}25 K, near compositions x=0.09 and x-0.15. Between these two maxima is a local minimum (${T}_{c}$ about 5 K) for x=0.12. dc magnetization data are also reported for six compositions. Anomalies in electrical resistance appear near T=50--60 K at compositions 0.10\ensuremath{\le}x\ensuremath{\le}0.125. Many samples clearly show a second resistive superconducting transition near 30 K in addition to the bulk transition most clearly observed magnetically. The variation of ${T}_{c}$ with composition is discussed in relation to the occurrence of resistance anomalies. The tetragonal lattice parameters at room temperature are consistent with previous work, and show no obvious anomalies. The sample preparation procedures are discussed in detail.

$\ensuremath{\gamma}$-ray transitions of energy 2.034 \ifmmode\pm\else\textpm\fi{} 0.023 MeV in the hypernucleus $_{\ensuremath{\Lambda}}^{7}\mathrm{Li}$ and 3.079 \ifmmode\pm\else\textpm\fi{} 0.040 MeV in the hypernucleus $_{\ensuremath{\Lambda}}^{9}\mathrm{Be}$ are observed. In both cases, the energy of the $\ensuremath{\gamma}$ ray in the hypernucleus $_{\ensuremath{\Lambda}}^{A}Z$ is very close to the energy of the first excited state of the nuclear core. The $\ensuremath{\gamma}$ rays are interpreted as arising from core transitions in the presence of the $\ensuremath{\Lambda}$ particle. The size of the shift places limits on the strength of the $\ensuremath{\Lambda}N$ spin-dependent interaction.

We report polarization-dependent extended x-ray-absorption fine-structure (EXAFS) measurements of the superconducting Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$. Measurements made at the Cu and Y $K$ edges with the x-ray polarization vector oriented perpendicular and parallel to the $c$ axis have enabled us to probe scattering atoms in the horizontal layer plane as well as in the vertical layer plane. Three different Cu-O vibrational modes which are associated with the Cu(1)-O pair and the Cu(2)-O pair along the $c$ axis and the planar Cu-O pair are distinguished. The lowest vibrational frequency of the Cu(2)-O pair along the $c$ axis indicates that its bond strength is much weaker than those of other Cu-O pairs. No anomalies are observed in the temperature dependence of the mean-square relative displacements ${\ensuremath{\sigma}}^{2}(T)$ for Cu-O and $\mathrm{Y}\ensuremath{-}X$ ($X=\mathrm{O}, \mathrm{Cu}, \mathrm{Ba}, \mathrm{and} \mathrm{Y}$) pairs. There appears to be no significant softening of any phonons which modulate Cu-O bond lengths due to coupling with electrons, thus casting some doubt on the importance of phonons for superconductivity in Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$. The relation between EXAFS results and other vibrational investigations is presented. The discrepancy between current data and other EXAFS reports is also discussed. Furthermore, a careful examination of orientation-dependent Y spectra has ruled out the possibility of extensive Cu and Y antisite disorder.

Orientation-dependent x-ray-absorption near-edge measurements have been made on the Cu and Y $K$ edges in oriented ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$Cu${\mathrm{O}}_{4}$ and $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ superconductors. The orientation dependence of the Cu edges is quite similar to that for other ${\mathrm{Cu}}^{2+}$ planar compounds, and allows a clear identification of a number of near-edge features. The results also demonstrate the strong similarity of the Cu-O planes in the two materials, and clearly establish that ${\mathrm{Cu}}^{1+}$ is being formed on the linear-chain sites for $x=0.77$.

${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ba}}_{\mathrm{x}}$${\mathrm{CuO}}_{4}$ has been found to undergo the following sequence of transformations upon cooling: tetr.(I4/mmm) \ensuremath{\rightarrow}ortho.(Bmab)\ensuremath{\rightarrow}tetr.(P${4}_{2}$/ncm), over a range of composition 0.05lxl0.20. The newly discovered low-temperature tetragonal phase can be thought of as a coherent superposition of the twin-related Bmab structures. The system can be modeled as an XY-spin system with temperature-dependent quartic anisotopy, v(T). Slight differences between orthorhombic and tetragonal structures appear to have large effects upon the superconductivity.

The hypernuclei Σ 6 H and Σ 16 C were observed by the (K − , π + ) reaction on targets of 6 Li and liquid O, respectively, at 713 MeV/ c incident K − momentum. Structure is seen in Σ 6 H which may be interpreted in terms of particle-hole excitations similar to the previously observed states in Λ 6 Li. The inablitity to resolve individual Σ hypernuclear levels in Σ 16 C, due in part to the excitation of non-coherent states as a result of the large momentum transfer of about 130 MeV/ c , precludes the extraction of the Σ-nucleus spin-orbit potential strength. The Σ-nucleus well depth appears to be 7 to 10 MeV less than that for the Λ.

Combining the assumptions that in orthorhombic YBa/sub 2/Cu/sub 3/O/sub 6+//sub x/ oxygen is removed from the CuO chains one chain at a time and that the Cu atoms in the twofold coordinated sites of the empty chains have a valence of +1 leads to the prediction that the number of Cu/sup 1+/ ions per unit cell is equal to 1-x. X-ray absorption measurements at the Cu K edge in both oriented and unoriented quenched samples with 0

Rationale The preclinical characterization of a series of aryloxypyridine amides has identified JNJ-39220675 ((4-cyclobutyl-1,4-diazepan-1-yl)(6-(4-fluorophenoxy)pyridin-3-yl)methanone) as a high-affinity histamine H3 receptor antagonist and a candidate for further drug development particularly in the treatment of alcohol-related behaviors.

Using an electron diffraction technique, the thicknesses of the (nonorthorhombic) twin boundary layers were measured for pure and alloyed YBa2(Cu1−xMx)3O7−δ. Boundary thickness varied from ∼0.7 nm for M=Ni, x=0.02, and δ≂0 to ∼2.6 nm for M=Al, x=0.02, and δ≂0, while it was ∼1.0 nm for a pure YBa2Cu3O7. High‐resolution transmission electron imaging of similar specimens supports the existence of such twin boundary layers.

Orientation dependent x-ray absorption measurements have been on a number of high-T c superconductors using powders oriented in a magnetic field. Both the near edge and EXAFS show a strong orientation dependence which has proven very useful in understanding these anisotropic materials.

The effect of Ga substitution for Cu in YBa/sub 2/(Cu/sub 1-//sub x/Gai/sub x/)/sub 3/O/sub y/ has been investigated for nominal compositions xless than or equal to0.10. Samples are tetragonal for x>0.03. For xgreater than or equal to0.05, evidence for second phase appears in x-ray-diffraction diagrams. Superconducting transition temperature T/sub c/ falls systematically with increasing x. The systematic variations in T/sub c/ and lattice parameters with nominal x suggest that Ga solid solution may extend to x = 0.05. However, electron microprobe results indicate that Ga incorporation into the superconducting phase is extremely limited; the Ga content x of the superconducting phase appears to be xless than or equal to0.01. A Ga-rich second phase is also observed by microprobe for 0.01less than or equal toxless than or equal to0.10.

High resolution electron microscopy of the twin boundary layers in YBa2(Cu1-xMx)3O7–8 for x=0 and 0.02 and M=Zn, Fe and Al showed that the boundary widths are ∼1 nm for the pure and the Zn substituted YBa2Cu3O7, 2.5∼3 nm for the Fe and Al substituted oxide. It was found that the lattice plane is shifted across the twin boundary by (1/3 ∼ 1/2)·2d(110) along the boundary. The broadening of the layer for the cases of Fe and Al is also thought to be associated with a reduction of the twin boundary energy, which also leads to an increased twin density.

X-ray absorption measurements have been made on powder samples of YBa2Cu3O7 and La1.85sr0.15CuO4 oriented in a magnetic field. Measurements made at the Cu K edge with the x-ray polarization oriented perpendicular and parallel to the c-axis show distinct differences for both materials, indicating a strong anisotropy of the electronic states about the Cu atoms. The Y edge measurements show a much smaller anisotropy as expected due to its more symmetric environment. Preliminary analysis indicates these measurements should be useful in choosing between the conflicting interpretations of the near edge structure in these materials.

Neutron powder diffraction data have been collected from samples of La1.9Ba0.1CuO4 and La1.85Ba0.15CuO4 in the temperature range 11–293 K. The first material undergoes a phase transition from the tetragonal K2NiF4-type structure (space group 14/mmm) to the orthorhombic La2CuO4-type structure (space group Bmab) at about 280 K, and then a second transition to another type of tetragonal (or near-tetragonal) structure with probable space group P42/ncm. The latter transition occurs predominantly between 50–40 K, but about 10% of the orthorhombic phase persists down to 15 K. Rietveld refinement was carried out at selected temperatures in the different structural regions. The differences among the low temperature structures can be cb acterized by tilting of the CuO6 octahedra about different rotation axes on the basis of the simple X-Y model previously proposed by Axe and coworkers. The tilt angle, which is a measure of the long-range order parameter, is about 3.5° at 15 K.Data sets were also collected from La1.85Ba0.15CuO4 at 293, 90 and 11K. At the two latter temperatures there was some peak broadening consistent with the distortions observed in previous high resolution neutron [Paul and co-workers] and x-ray [Axe and co-workers] powder studies. Rietveld analysis of the data indicated the presence of local octahedral displacements, but it was not possible to determine the nature of the correlations.

In this study, we describe X‐ray absorption measurements designed to determine the influence of subsitutents on the location of dopants, the valence of dopants, structural changes, and modifications of electronic densities of states. Several possible mechanisms are offered which may elucidate Tc suppression due to metal dopings.

A series of polycrystalline YBa2(Cu1‐xMx)3O7‐δ (1:2:3) samples with a typical grain size > 10μm was prepared using well controlled and reproducible precedures. This relatively large grain size allowed microprobe studies of individual grains to determine M content of the 1:2:3 phase. Solubility limits of substitutions for Cu in these samples are estimated. Superconducting transition temperatures and lattice parameters are presented. In the case of Ga, microprobe studies show no evidence for Ga content of 1:2:3 above x=0.01. Preliminary studies show no evidence for solid solution above x=0.01 when substituting Mn, Cr, Zr, and Ti for Cu in 1:2:3.

Superconductivity near 30 K in the La-Ba-Cu-O system, first observed by Bednorz and Müller [1], was soon found to be attributable to the K2NiF4-type (at room temperature) compound La(2-x)BxxCuO4 [2]. Substitution of Sr and Ca for Ba yielded superconducting systems, also with high superconducting transition temperature Tc. Replacement of La by Y led to the discovery of the 90 K superconductors.

Photoemission from high Tc superconductors crucially depends on surface stoichiometry as well as the interaction of impurities with the reactive surface. In this paper we discuss the photoemission spectra of clean YBa2Cu3O7 and YBa2Cu3O6.25 as well as the spectra after the interaction of CO, CO2 and H2O with both the high Tc 1‐2‐3 compound and Ba metal.

The upper critical magnetic field of a series samples of YBa2(Cu1-xNix)3O7 is measured. Other related parameters, such as the lower critical magnetic field Hc1, the Ginsberg-Landau parameter k, the jump in the specific heat ∆C/Tc, the superconducting coherence length ξ, and the penetration depth λ, are calculated from Tc, dHc2/dT and dM/dH. The results show that Hc2(0), and consequently ξ(0), are essentially constant, but Hc and ∆C/Tc decrease with increasing Ni content.

Both near edge features and EXAFS results unequivocally demonstrate that Fe perferentially substitutes for Cu(1) atoms at the linear chain site for YBa 2 (Cu 1−x Fe x ) 3 O 7+δ , where x=0.02 to 0.15. Electronic and atomic structural changes associated with Fe content are discussed.

The upper critical magnetic field H c2 up to 5T and dM(T)/dH¦ Hc2 for aligned powders of pure and Al and Ni substituted YBa 2 (Cu .98 M .02 ) 3 O 7+δ are measured magnetically. dH c2 /dT¦ tc is linear with slopes of -2.2T/K, -2.4T/K and -2.8T/K for the pure, Ni and Al samples respectively. The values of H cl , K , and ΔC/T c were deduced from dM(T)/dH¦ Hc2 .

The (110) twin structure of YBa2Cu3O7 superconductor oxide, which is formed to reduce the strain energy of the tetragonal to orthorhombic phase transformation by alternating the a-b crystallographic axis across the boundary, was extensively investigated. Up to now the structure of the twin boundary still remained unclear. In order to gain insight into the nature of the twin boundary in Y-Ba-Cu-O system, a study using electron diffraction techniques including optical and computed diffractograms, as well as high resolution structure imaging techniques with corresponding computer simulation and processing was initiated.Bulk samples of Y-Ba-Cu-O oxide were prepared as described elsewhere. TEM specimens were produced by crushing bulk samples into a fine powder, dispersing the powder in acetone, and suspending the fine particles on a holey carbon grid. The electron microscopy during this study was performed on both a JEOL 2000EX and 2000FX electron microscopes operated at 200 kV.