Search

Huntington’s disease (HD) is caused by an expansion of a poly glutamine (polyQ) stretch in the huntingtin protein (HTT) that is necessary to cause pathology and formation of HTT aggregates. Here we ask whether expanded polyQ is sufficient to cause pathology and aggregate formation. By addressing the sufficiency question, one can identify cellular processes and structural parameters that influence HD pathology and HTT subcellular behavior (i.e. aggregation state and subcellular location). Using Drosophila, we compare the effects of expressing mutant full-length human HTT (fl-mHTT) to the effects of mutant human HTTexon1 and to two commonly used synthetic fragments, HTT171 and shortstop (HTT118). Expanded polyQ alone is not sufficient to cause inclusion formation since full-length HTT and HTTex1 with expanded polyQ are both toxic although full-length HTT remains diffuse while HTTex1 forms inclusions. Further, inclusions are not sufficient to cause pathology since HTT171-120Q forms inclusions but is benign and co-expression of HTT171-120Q with non-aggregating pathogenic fl-mHTT recruits fl-mHTT to aggregates and rescues its pathogenicity. Additionally, the influence of sequences outside the expanded polyQ domain is revealed by finding that small modifications to the HTT118 or HTT171 fragments can dramatically alter their subcellular behavior and pathogenicity. Finally, mutant HTT subcellular behavior is strongly modified by different cell and tissue environments (e.g. fl-mHTT appears as diffuse nuclear in one tissue and diffuse cytoplasmic in another but toxic in both). These observations underscore the importance of cellular and structural context for the interpretation and comparison of experiments using different fragments and tissues to report the effects of expanded polyQ.

Integrating Hydro-Climate Science into Policy Decisions for Climate-Resilient Infrastructure and Livelihoods in East Africa (HyCRISTAL) is a Future Climate for Africa (FCFA) project funded to deliver new understanding of East African climate change and its impacts, and to demonstrate use of climate change information in long-term decision-making in the region. Here, we briefly summarise key findings from HyCRISTAL so far on climate change, as well as key findings from the pan-African FCFA project “IMPALA” relevant to East Africa, both in the context of previous literature on the topic.

Although Huntington's disease is caused by the expansion of a CAG triplet repeat within the context of the 3144-amino acid huntingtin protein (HTT), studies reveal that N-terminal fragments of HTT containing the expanded PolyQ region can be produced by proteolytic processing and/or aberrant splicing. N-terminal HTT fragments are also prevalent in postmortem tissue, and expression of some of these fragments in model organisms can cause pathology. This has led to the hypothesis that N-terminal peptides may be critical modulators of disease pathology, raising the possibility that targeting aberrant splicing or proteolytic processing may present attractive therapeutic targets. However, many factors can contribute to pathology, including genetic background and differential expression of transgenes, in addition to intrinsic differences between fragments and their cellular effects. We have used Drosophila as a model system to determine the relative toxicities of different naturally occurring huntingtin fragments in a system in which genetic background, transgene expression levels and post-translational proteolytic processing can be controlled. These studies reveal that among the naturally occurring N-terminal HTT peptides, the exon 1 peptide is exceptionally pathogenic and exhibits unique structural and biophysical behaviors that do not appear to be incremental changes compared with other fragments. If this proves correct, efforts to specifically reduce the levels of exon 1 peptides or to target toxicity-influencing post-translational modifications that occur with the exon 1 context are likely to have the greatest impact on pathology.

Insights about the manufacturing technique and preservation state of a precious Chinese lacquered cabinet were obtained non-invasively by terahertz time-domain imaging (THz-TDI). THz frequency analysis as well as false color rendering (FC) allowed a better discrimination of surface materials by means of areal mapping and contrast enhancement.

Tumorigenesis and tumor progression are associated with dysfunction of the nuclear transport machinery at the level of import and export receptors (karyopherins). Recent studies have shown that the nuclear import factor karyopherin-α2 (KPNA2) is a novel prognostic marker for poor prognosis in human breast cancer. Based on the well-defined hallmarks of cancer progression, we performed a detailed in vitro characterization of the phenotypic effects caused by KPNA2 overexpression and KPNA2 silencing in benign and malignant human breast cells. KPNA2 overexpression clearly increased proliferation of MCF7 tumor cells and further led to a reduction of cell-matrix adhesion in benign MCF10A cells, whereas cell migration was significantly increased (P

The performance of numerical weather forecasts made with the Met Office Unified Model is evaluated using near-surface measurements made at a comprehensively instrumented site over the course of the annual cycle, with the aim of characterizing the forecasting system's generic behaviour in the surface layer. The study is focused on the seasonal diurnal cycles of the screen-level and surface temperatures and the surface flux budget. High-resolution versions of the model simulate seasonal composite diurnal cycles of the screen temperature to an accuracy of about 1 K, but appear to show a cold bias in the surface skin temperature by day and a warm bias at night, while underestimating the magnitude of the difference in temperature between the screen level and the surface, particularly in conditions of light winds and strong surface cooling. The consistency of the measured surface fluxes is assessed by deriving the full annual cycle of the monthly mean atmospheric surface fluxes. The measured surface flux budget at this site is closed to an accuracy better than 5 W m−2. Comparison of the modelled and measured fluxes shows that in spring and summer the modelled downward shortwave fluxes are too large, while the latent heat fluxes are overestimated. Copyright © 2011 British Crown Copyright. Published by John Wiley & Sons Ltd.

Tissue marking with soot-covered fine needles enables the optical coherence tomography (OCT) scanning plane to be localized within the histological specimen to an accuracy of approximately 50 microm. Tissue water content is an especially important parameter for in vitro measurements. Dehydration tends to produce an increase in surface reflections and a reduction in imaging depth.The aim of this in vitro study was to evaluate parameters relevant to the visualization and conservation process to allow optimal images to be generated for later differentiation between healthy and degenerated tissue in vivo.Various methods of marking samples were applied in vitro to achieve accurate overlaps of the OCT scanning plane and the corresponding section of the histological specimen. The influence of temperature and tissue water content was investigated using both porcine and human tissue. Samples were marked using fine needles, ablation craters generated by laser application, and colour markers introduced into the tissue.It was demonstrated that the water content of tissue exerts a direct influence on OCT imaging, whereas above 15 degrees C temperature had no effect on image quality. With regard to the marking of samples, the best results were obtained using sooted fine needles.

Bei einem 41-jahrigen Patienten mit einer supraventrikularen Tachycardie kam es unter antiarrhythmischer Therapie mit Adenosin (Adrekar®) zu einem Grand mal-Anfall. Der Patient hatte keine zentralen Krampfanfalle in der Vorgeschichte. Nach der Aufnahme auf die Intensivstation wurde der Patient primar wegen eines Druckgefuhles in der Brust mit Morphin versorgt und spurte darunter eine deutliche Besserung der Beschwerden. Die circa 5–10 min spater begonnene intravenose antiarrhythmische Therapie mit zuerst 6mg und circa 3–5min spater 9mg Adenosin blieb bis auf ein Warmegefuhl ohne Nebenwirkung. Nach Injektion weiterer 12mg Adenosin mit einem zeitlichen Abstand von circa 3–5min kam es zu einem kurzzeitigen (ungefahr 5–10s) Grand mal-Anfall und ausgepragtem Flush an der gesamten sichtbaren Korperoberflache. Der Patient war post-iktal sofort wieder gut kontaktfahig und orientiert. 28 Stunden spater entwickelte der Patient die Symptome eines Pradelir und wurde von der Intensivstation in eine psychiatrische Abteilung verlegt. Im weiteren Verlauf wurde die Diagnose eines chronischen Alkoholabusus gestellt. Aufgrund des zeitlichen Zusammenhanges mit der Adenosin-Injektion und dem Profil des Anfalles muss das Medikament als auslosender Faktor diskutiert werden, wobei der Alkoholabusus ein pradisponierender Faktor fur einen Krampfanfall sein kann.

Bulk Y 1 Ba 2 Cu 3 O y was melt-textured without the use of seed crystals as well as by applying top-seeding with different seeds resulting in different orientations of the c -axis. Samples were examined by elastic neutron scattering and levitation force. The levitation force of the samples strongly depends on the orientation of the c -axis. The local superconducting parameters were found to be reduced with increasing distance from the seed. In order to study this influence, two cubes were prepared by top-seeding, but with seeds of Nd123 that had a parallel and perpendicular orientation of the c -axis of the Nd123-seed with respect to the contact area of the high- T c superconductor. By this, different distances of the levitating surface, which is the surface that faces directly the magnet, from the seed were obtained. Results are presented and discussed.

Melt textured Sm 1 Ba 2 Cu 3 O y -composites with different amounts of Sm 2 Ba 1 Cu 1 O 5 and other dopants such as Ba 3 Cu 5 O x , UO 2 and Ba-enriched composites have been prepared in air and characterized. The decrease of the critical temperature T c due to the formation of solid solutions Sm 1+ x Ba 2− x Cu 3 O y ( x >0) depends on the composition. By successive annealing T c can be increased. Heat treatments at different atmospheres, temperatures and holding times have been applied to Sm123 compounds of different compositions. The positive influence of these annealing steps on the properties, such as X-ray diffraction data, critical current density and levitation force, is shown.

To investigate the correlation between the levitation force of YBaCuO cylinders when approached by a permanent magnet and the texture of these YBaCuO cylinders some of these specimens were selected which are free of microcracks, have the same oxygen load, show no isotropic fraction or other undesired parasitic c-axis orientations. To gain a maximum levitation force the c-axis orientation of the crystalline domains has to have a small divergence between the c-axis and the cylinder axis. By measurements of the (002) pole figures by neutron diffraction with a mesh width no more than 6° undesired c-axis orientations have been analyzed. The distribution of the c-axis near the cylinder axis has been measured at the (005) reflection of 7 times higher intensity than the (002) reflection. The angular limit within which lie 94% of all c-axis orientations is a practical value for comparison of the c-axis orientations and the levitation forces of the different YBaCuO cylinders.

Melt textured Nd 1 Ba 2 Cu 3 O y - and Sm 1 Ba 2 Cu 3 O y -composites with different additions of Nd 4 Ba 2 Cu 2 O 10 /Sm 2 Ba 1 Cu 1 O 5 have been prepared. The temperature schedule, the oxygen atmosphere during melt texturing and the amount of additions determines the resulting superconducting properties. From the evaluation of critical temperature and critical current density for fields up to 5 T, the necessity of different processing parameters for Nd 1 Ba 2 Cu 3 O y - and Sm 1 Ba 2 Cu 3 O y -composites was deduced. Fabrication of Nd 1 Ba 2 Cu 3 O y composites is more complicated and not yet optimized. In contrast, Sm 1 Ba 2 Cu 3 O y shows good results of microstructure, shown by flux maps, and of high j c leading to higher levitation forces.

YBaCuO cylinders are needed for the construction of magnetic bearings. In these YBaCuO cylinders superconducting currents are induced by approaching a permanent magnet. To obtain a high induced current in concentric circles around the cylinder axis of the YBaCuO cylinder, the c-axes of the crystalline domains have to be aligned as well as possible in normal direction to the induced superconducting currents. This condition is fulfilled, if the c-axes of the domains are in parallel to the cylinder axis of the YBaCuO cylinder. But it allows the c-axes to be tilted each in a same plane with the cylinder axis. Global texture cannot distinguish between different tilting directions of the c-axes of individual parts of the specimen. Therefore, the cylindrical specimen has been cut into 9 pieces, one central piece and 8 boundary pieces. An equal area texture measurement by neutron diffraction has been performed at the Geesthacht reactor with a grid width of 1.5° in the central region of the pole sphere up to Δ X = 19.5° from the cylinder axis of the YBaCuO cylinder. For each of the 9 parts of the specimen this neutron texture measurement has been performed. The best suited distribution of the c-axes has been determined in the central piece. The orientation distribution of the c-axes has been found to be broadened at the boundary pieces, especially in diagonal direction of the rectangular seed crystal which was implanted in the molten state into the center of the recrystallized specimen.

High-temperature superconductor bulk parts are batch processed using a semi-automated processing technique based on the melt-texturation process. Levitation properties under static and dynamic load levels were analysed using a test bench with a three-dimensional force sensor unit. Measurements of levitation force give no detailed suggestions on texture, secondary domains or cracks. Therefore other measurements to control homogeneity of the bulk were performed. Texture on full-size pellets (FWHM ) was verified by elastic neutron scattering. To study the influence of local texture on properties a pellet was divided into nine segments. Preliminary results indicate that a correlation between neutron data and levitation force needs further investigations. Flux maps of samples magnetized by permanent magnets or by a pulsed magnetization unit were used to verify the homogeneity and domain structure of the material and to evaluate macroscopic critical currents.

We present a processing technique for fabrication of advanced semi-finished parts and products based on the high-temperature superconductor (HTSC) YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO). High-quality YBCO bulk components are produced powder metallurgically by sintering and partial melting of precursor powders. Depending on size, shape, tolerances and levitation requirements, parts are either die-pressed or precision machined from isostatically pressed blocks. The oxygenation process can be monitored in-situ by a macro-thermogravimetric analyzer. The texture of the bulk of full-size pellets was verified by elastic neutron scattering. Levitation properties under static and dynamic load levels were analyzed using a test bench with a three dimensional force sensor unit. Flux mapping was used to verify the homogeneity of the material, to evaluate macroscopic critical currents and to investigate the field trapping capability. Several HTSC frictionless bearing modules have been built. They are manufactured in various sizes, ranging from O 40 mm to O 140 mm. Lifting forces are up to 200 N per bearing module. Applications for the bearings are seen for mechanical components in high speed rotating machinery, in cryogenic systems, gyroscopes, transportation systems and vibration isolation.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder. The HD gene encodes the huntingtin protein (HTT) that contains polyglutamine tracts of variable length. Expansions of the CAG repeat near the amino terminus to encode 40 or more glutamines (polyQ) lead to disease. At least eight other expanded polyQ diseases have been described. HD can be faithfully modeled in Drosophila with the key features of the disease such as late onset, slowly progressing degeneration, formation of abnormal protein aggregates and the dependence on polyQ length being evident. Such invertebrate model organisms provide powerful platforms to explore neurodegenerative mechanisms and to productively speed the identification of targets and agents that are likely to be effective at treating diseases in humans. Here we describe an optical pseudopupil method that can be readily quantified to provide a fast and sensitive assay for assessing the degree of HD neurodegeneration in vivo. We discuss detailed crossing schemes as well as factors including different drivers, various constructs, the number of UAS sites, genetic background, and temperature that can influence the result of pseudopupil measurements.

We discuss the results of inelastic neutron time-of-flight spectroscopy on powder samples of C60, K3C60 and Rb3C60. A well structured density of states is obtained from the raw data where the details can be attributed to translational acoustic/optic and librational modes. The intermolecular excitation spectra for all three compounds can be well understood within the frame-work of lattice dynamics of a molecular crystal. We show that a particular sample preparation is necessary to avoid impurity contributions in particular within the gap region between inter- and intramolecular vibrations. There are indications for a weak anomalous temperature dependence of low energy phonons in K3C60 atT c .

Lithium-borate glasses containing 0.1-10 mol% Gd2O3 have been studied by 155Gd Mossbauer spectroscopy. Isomer shifts near 0.6 mm s-1, independent of the Gd concentration, are in the range typical of ionic Gd compounds. The spectra are very well described by a distribution of quadrupole splittings corresponding to a random distribution of ligand coordinations. Additional temperature-independent broadening of the resonance lines is ascribed to effects of spin-spin relaxation of Gd moments.

The appearance of superconductivity at relatively high temperatures in alkali metal-doped C(60) fullerene provides the challenge to both understand the nature and origin of the superconductivity and to determine the upper limit of the superconducting transition temperature (T(c)). Towards the latter goal, it is shown that doping with potassium-thallium and rubidium-thallium alloys in the 400 to 430 degrees C temperature range increases the T(c) of C(60)/C(70) mixtures to 25.6 K and above 45 K, respectively. Similar increases in T(c) were also observed upon analogous doping of pure C(60). Partial substitution of potassium with thallium in interstitial sites between C(60) molecules is suggested by larger observed unit cell parameters than for the K(3)C(60) and K(4)C(60) phases. Contrary to previous results for C(60) doped with different alkali metals, such expansion does not alone account for the changes in critical temperature.

We report the dependence of the oxygen isotope shift on transition temperature {ital T}{sub {ital c}} in the system YBa{sub 2{minus}{ital x}}La{sub {ital x}}Cu{sub 3}O{sub {ital z}} with 0{le}{ital x}{le}0.5. We find a significant oxygen isotope shift at low temperatures ({alpha}{sub 0}=0.38 at {ital T}{sub {ital c}}=38.3 K), which decreases gradually with increasing {ital T}{sub {ital c}} and finally falls rapidly above 73 K to {alpha}{sub 0}=0.025 for {ital T}{sub {ital c}}=92.3 K. Our data are well fitted by the expression {alpha}{sub 0}({ital T}{sub {ital c}})=0.5(1{minus}{ital T}{sub {ital c}}/{ital T}{sub {ital c}0}){sup 0.59}, with {ital T}{sub {ital c}0}=92.8 K. Our results suggest a dominant role for conventional electron-phonon coupling in the high-temperature cuprate superconductors, with strong suppression of the isotope effect as {ital T}{sub {ital c}} approaches its maximum value in this system.

Aggregation and deposition of proteins are found in several diseases, e.g. atherosclerosis and amyloidosis. Deposition of amyloid proteins, characterized by fibers with abnormal structural folding in various organs, is thought to be responsible for diseases like Alzheimer disease, Huntington disease, Parkinson disease and systemic amyloidosis, which frequently affects cardiac and renal tissues. Limitations in the diagnosis of early forms of amyloid deposits in formalin-fixed and paraffin embedded tissues with light microscopy and Congo red staining can be overcome by transmission electron microscopy using glutaraldehyd-fixed tissues. Here we describe a powerful method to perform transmission electron microscopy on primary paraffin-embedded cardiac tissue. Primary glutaraldehyd-fixed cardiac tissues from the same patient were used as control.

Heparan sulfate proteoglycans (HSPGs) are extracellular macromolecules found on virtually every cell type in eumetazoans. HSPGs are composed of a core protein covalently linked to glycosaminoglycan (GAG) sugar chains that bind and modulate the signaling efficiency of many ligands, including Hedgehog(Hh), Wingless (Wg) and Bone morphogenetic proteins (BMPs). Here, we show that, in Drosophila, loss of HSPGs differentially affects embryonic Hh, Wg and BMP signaling. We find that a stage-specific block to GAG synthesis prevents HSPG expression during establishment of the BMP activity gradient that is crucial for dorsal embryonic patterning. Subsequently, GAG synthesis is initiated coincident with the onset of Hh and Wg signaling which require HSPGs. This temporal regulation is achieved by the translational control of HSPG synthetic enzymes through internal ribosome entry sites (IRESs). IRES-like features are conserved in GAG enzyme transcripts from diverse organisms, suggesting that this represents a novel evolutionarily conserved mechanism for regulating GAG synthesis and modulating growth factor activity.

N/A

A modified spectral domain immittance approach is presented which takes into account all practical parameters for the calculation of slow-wave and loss characteristics in modem MMIC and high-Tc superconductor microsmp transmission line structures. The method is capable of considering multilayered anisotropic substrates, conductor, dielectric and gyromagnetic losses, alternative directions for the magnetic bias, the finite-thickness of conventional or super-conducting strips, and lossy ground metallizations. At the example of ferrite-dielectric layered high-Tc superconducting microstrip lines, it is demonstrated that the line characteristics largely depend on both losses and the tensor parameters of anisotropic materials.

Studies in Drosophila and vertebrate systems have demonstrated that heparan sulfate proteoglycans (HSPGs) play crucial roles in modulating growth factor signaling. We have isolated mutations in sister of tout velu (sotv), a gene that encodes a co-polymerase that synthesizes HSPG glycosaminoglycan (GAG) chains. Our phenotypic and biochemical analyses reveal that HS levels are dramatically reduced in the absence of Sotv or its partner co-polymerase Tout velu (Ttv), suggesting that both copolymerases are essential for GAG synthesis. Furthermore, we find that mutations in sotv and ttv impair Hh, Wg and Decapentaplegic(Dpp) signaling. This contrasts with previous studies that suggested loss of ttv compromises only Hh signaling. Our results may contribute to understanding the biological basis of hereditary multiple exostoses (HME), a disease associated with bone overgrowth that results from mutations in EXT1 and EXT2, the human orthologs of ttv and sotv.

A fast and efficient mode-matching technique is applied to the analysis and design of polarizer components in ridged circular waveguide technology. Two different structures (the septum polarizer and the longitudinal-ridge polarizer) are investigated with respect to the validity of approximating the rectangular-cross-section septa by conically shaped ridges in theory. Measurements of two different prototypes demonstrate, first, that the axial ratio response is not potentially critical to this approximation and, second, that some differences occur with respect to return loss and isolation performance, but that these difference have only been encountered beyond the 25 dB margin. A CPU time comparison with HFSS results in a ten-minutes-versus-three-hours advantage of the mode-matching technique.

We have designed, built and tested a prototype of a conduction cooled HTSC bearing module. A superconducting ring, measuring ∅ 102 mm × 13 mm high was assembled from HTSC bulk material. Total mass is 547 g. Lifting force and stability at 77 K and 2 mm gap are approximately 150 N and 80 N/mm, respectively. The superconductor is integrated on a metallic cold plate. Modelling has been used for evaluation of thermal losses and optimization of the cryogenic design. For the present module, total losses at 0.01 Pa insulation vacuum are as small as 1 W, mainly due to radiation. Based on the thermal model the scaling behavior with respect to thermal losses as a function of maximum lifting capability was evaluated. The cooling power was found to be equivalent to about 400 mW electrical power per kg of levitated mass which compares quite favorably to the typical 0.1 …1 W per kg for conventional active magnetic bearings. Details of both experimental work and modelling will be reported.

Mutations in the Drosophila variable nurse cells (vnc) gene result in female sterility and oogenesis defects, including egg chambers with too many or too few nurse cells. We show that vnc corresponds to Arrest Defective1 (Ard1) and encodes the catalytic subunit of NatA, the major N-terminal acetyl-transferase complex. While N-terminal acetylation is one of the most prevalent covalent protein modifications in eukaryotes, analysis of its role in development has been challenging since mutants that compromise NatA activity have not been described in any multicellular animal. Our data show that reduced ARD1 levels result in pleiotropic oogenesis defects including abnormal cyst encapsulation, desynchronized cystocyte division, disrupted nurse cell chromosome dispersion, and abnormal chorion patterning, consistent with the wide range of predicted NatA substrates. Furthermore, we find that loss of Ard1 affects cell survival/proliferation and is lethal for the animal, providing the first demonstration that this modification is essential in higher eukaryotes.

Iron doped compounds GdBa 2 (Cu 1−x Fe x ) 3 O 7−δ with 0.03 ≦ x ≦ 0.23 have been investigated by Mossbauer spectroscopy with 57 Fe and with 155 Gd. Mossbauer spectra of 57 Fe are decomposed into 4 doublets. One of them has been determined to arise from Fe on Cu-2 sites. Nonzero values of the asymmetry parameter η for 155 Gd show that for all Fe concentrations up to x=0.23, the local symmetry at Gd sites is orthorhombic.

Iron‐doped compounds GdBa2(Cu1−xFex)3O7−δ with 0.03≤x≤0.25 and δ 0.7 have been investigated by Mossbauer spectroscopy with 155Gd and 57Fe. For each iron concentration x, samples with different transition temperatures Tc (at constant oxygen content, δ 0.7 either at 650 °C under vacuum or at 950 °C in a N2 atmosphere, followed by a quench to room temperature. A comparison of 57Fe Mossbauer spectra for samples treated by these different procedures has yielded an unambiguous determination of the fraction of iron atoms occupying Cu(2) sites. This fraction extrapolates to ∼4% for x→0. It increases monotonously with x to ∼17% for x=0.12. In samples reduced at 950 °C for 44 h, the fraction of iron on Cu(2) sites is doubled, and this large Cu(2) site occupancy is maintained when the material is reoxidized at 450 °C. From the systematic variation of the parameters associated with the remaining quadrupole double...

Most rare‐earth ‐(R) iron compounds R2Fe17 crystallize in the hexagonal Th2Ni17 structure with two inequivalent rare‐earth sites in the unit cell. For Tm2Fe17 magnetic anisotropy of opposite character has been determined for the two Tm sites.1 Nevertheless, the axial anisotropy of one Tm site dominates at low temperatures and forces the magnetic moments to the direction parallel to the c axis below the spin‐reorientation temperature TSR=74 K. Magnetization measurements on Yb2Fe17 gave no indication for a spin reorientation.2 In this compound, the Fe sublattice anisotropy seems to dominate at all temperatures, confining the moments to the plane perpendicular to the c axis. This has now been confirmed by 174Yb Mossbauer spectra of Yb2Fe17 in the temperature range 1.6–100 K. The different crystal fields acting on the Yb 4f shell at the two sites lead to a large difference in the static moments as revealed by the different hyperfine fields. From the temperature dependence of the magnetic and electric hyperfin...

The compound Yb 2 Fe 17 was investigated by 174 Yb Mossbauer spectroscopy and magnetic measurements. It is shown that the crystal field interaction leads to different preferred easy magnetization directions for the two Yb sites in the hexagonal Th 2 Ni 17 structure of Yb 2 Fe 17 . Thus, the anisotropy energies of Yb at the 2 sites nearly cancel, and the easy direction of magnetization perpendicular to the c -axis is determined by the iron sublattice. The large difference between the magnetic hyperfine fields at the 2 Yb sites is in accordance with this model.

The compound Yb 2 Fe 14 B has been investigated by Mossbauer spectroscopy with 174 Yb in the temperature range 4–125 K. Values of crystal field parameters and Yb-Fe exchange energies have been derived from a simultaneous fit to 5 spectra. The results are compared with those derived from single-crystal magnetization data for isostructural compounds with other rare earth ions.

Two samples of the compound GdBa2Cu3O7-x, one with x approximately 0 (Tc=93.5 K) and one with x>0.5 (Tc

The coexistence of magnetism and superconductivity in the high-Tc compound GdBa2Cu3O7-x (x approximately 0) and the influence of oxygen deficiency on the magnetic properties in a sample with x>0.5 have been studied by measurements of the specific heat and the bulk magnetisation and by 155Gd Mossbauer spectroscopy. The magnetic ordering is found to have a pronounced two-dimensional character. The orientation of the ordered Gd moments parallel to the c axis shows the ordering to be due to an anisotropic superexchange interaction. The effect of oxygen vacancies on the magnetic properties is marginal. No indications for magnetic moments at Cu ions was found.

We report on a study of transition temperatures T c and of the structure of iron doped compounds GdBa 2 (Cu 1− x Fe x ) 3 O z with 0⩽ x ⩽0.25. The oxygen content z was close to 7 in all samples. For given iron content x , a wide range of transition temperatures T c and a linear relationship between the values of T c and of the lattice parameter c was found. Our results point to a strong influence of the distribution of Fe impurities over Cu(1) sites on the structure and on T c . The relevant measure for the suppression of T c by randomly distributed Fe impurities is given by the lowest T c values reported in the literature for iron-doped compounds.

The temperature dependence of hyperfine interactions at 155Gd nuclei in Gd2Fe14B has been studied in the temperature range from 4.2 to 120 K. The results indicate that the Fe-Gd exchange interactions at the two Gd sites may be different. The frequency spectrum of Gd vibrations has been derived from the temperature dependence of the absorption intensity.