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1.
Christian Steglich 《Results in Mathematics》1995,27(1-2):188-193
While in Euclidean, equiaffine or centroaffine differential geometry there exists a unique, distinguished normalization of a regular hypersurface immersion x: M n → An+1, in the geometry of the general affine transformation group, there only exists a distinguished class of such normalizations, the class of relative normalizations. Thus, the appropriate invariants for speaking about affine hypersurfaces are invariants of the induced classes, e.g. the conformai class of induced metrics and the projective class of induced conormal connections. The aim of this paper is to study such invariants. As an application, we reformulate the fundamental theorem of affine differential geometry. 相似文献
2.
A. Loidl A. Krimmel K. Knorr G. Sparn M. Lang C. Geibel S. Horn A. Grauel F. Steglich B. Welslau N. Grewe H. Nakotte F. R. de Boer A. P. Murani 《Annalen der Physik》1992,504(2):78-91
Elastic and inelastic neutron-scattering studies on the system Ce(Cu1?xNix)2Ge2 are reported. These measurements are complemented by measurements of the magnetic susceptibility, high-field magnetization, heat capacity, thermal expansion, electrical resistivity and thermopower. The results reveal an interesting T-x phase diagram consisting of two different antiferromagnetic phases for x < 0.2 and 0.2 < x < 0.75, respectively, and a heavy-Fermi-liquid regime at higher Ni concentrations. The experimental results are interpreted in terms of an alloying-induced transition from local-moment to itinerant heavy-fermion magnetism. Fingerprints of this latter phase are a strongly reduced ordered moment and a short incommensurate ordering wave vector, in accord with theoretical predictions. A surprisingly good agreement between theory and experiment is found for x > 0.5. Further experimental evidence for different types of antiferromagnetic ordering derives from a line-shape analysis of the quasielastic neutron-scattering intensity, from magnetization and thermopower experiments. 相似文献
3.
Anthony Herlt Lewis Mander Rymond Rumampuk Wolfgang Steglich Franz von Nussbaum 《Tetrahedron》2004,60(29):6101-6104
Bisdemethylaaptamine (6), a proposed biosynthetic precursor of the aaptamines has been isolated from an Aaptos sp. marine sponge harvested off the Indonesian coast, and its identity confirmed by comparison of its spectral data with that of synthetic material. Bisdemethylaaptamine-9-O-sulfate (7) was also isolated from the same source. This is the first report of a sulfated aaptamine. 相似文献
4.
The structure of the strongly cytotoxic marine alkaloid halitulin (1) has been confirmed by total synthesis and its absolute configuration determined as (15S). The synthesis follows a strategy previously reported by one of us and uses an efficient preparation of the quinoline-7,8-diol unit by modified Baeyer-Villiger and Skraup reactions. The O-benzyl protecting groups were removed in the last step of the synthesis by transfer hydrogenolysis without concomitant reduction of the quinoline ring. The method can be applied for the synthesis of halitulin analogues. 相似文献
5.
M. Weiden J. Köhler G. Sparn M. Köppen M. Lang C. Geibel F. Steglich 《Zeitschrift für Physik B Condensed Matter》1995,98(2):167-169
We present an investigation of the spin-Peierls transition atT
SP=14.5 K in polycrystalline CuGeO3 through specific-heat and thermal-expansion measurements. Clear second-order phase-transition anomalies are found in both properties atT
SP, although only a small entropy of S0.1 Rn2 is released at the transition. Most of the entropy is released atT
SP<T<150 K, where the temperature dependence of the magnetic contribution to the specific heat as well as the thermal expansion exhibit extrema atT
*40 K. These are caused by one-dimensional antiferromagnetic fluctuations along the Cu chains, possibly accompanied by structural fluctuations. Using Ehrenfest's relation, a hydrostatic pressure coefficient (T
SP/p)p0 (0.45±0.06) K/kbar is derived. 相似文献
6.
7.
8.
We report on specific heat measurements of (La1–x
Ce
x
)Al2 samples, with 1.5 a/ox100 a/o, performed in magnetic fields of up to 5 T between 0.3 and 10 K. In the Ce rich alloys, and especially in CeAl2, a-type peak of an antiferromagnetic phase transition, and at lower temperatures spin waves and very large electronic contributions are clearly visible. In higher magnetic fields, that is when antiferromagnetic order can be suppressed, the specific heat of the alloys exhibits a broadened Schottky peak. All these phenomena add up tok ln 2, i.e. to the correct entropy change per single Ce3+ ion in its
7 crystal field ground state.We interpret experimental results as an interplay between cooperative magnetism and the single-ion Kondo effect which describes a gradual turning off of one magnetic moment. The broadening of the Schottky peak is directly related to the Kondo temperatureT
K
, which we determine with a simple resonance level model.T
K
increases by an order of magnitude whenx increases from 1.5 a/o to 100 a/o. This is interpreted as caused by a lattice contraction.A quadraticx dependence of the Néel temperature suggests that (forTT
K
) stable Ce moments can only exist through pair interactions. The very large (and almost field independent) specific heat term linear in temperature with a coefficient=135 mJ/K2 mole for CeAl2 is attributed to the Kondo effect—still present in the antiferromagnetically ordered state. Our evaluation of the experimental data is backed by a molecular field theory for a simplified antiferromagnetic structure combined with the simplest possible Kondo theory.Preliminary results have been presented at the Int. Conf. on Magnetic Alloys and Oxides, Haifa 1977 [Bredl, C.D., Steglich, F.: J. Magnetism and Magnetic Materials, in press] 相似文献
9.
W. Franz A. Grießel F. Steglich D. Wohlleben 《Zeitschrift für Physik B Condensed Matter》1978,31(1):7-17
We report measurements of the electrical resistivity, the thermal conductivityk and the thermoelectric powerS between 1.5K and 300K on the anomalous CeCu2Si2 compound and on LaCu2Si2 as reference compound. For LaCu2Si2 the temperature dependences of andS are in accord with those found in otherd band metals. For CeCu2Si2 the observed resistivity (220 µ cm at 200K) leads to a very short electronic mean free path which is of the order of the Ce-Ce spacing. Correspondingly,k is almost identical with the phonon contributionk
p
. Below 20K, resistivity and thermoelectric power strongly suggest Fermi liquid behavior with a degeneracy temperature between 20K and 40K. Above 200K, both andS decrease proportionally to –ln(T/1 K).Work performed within the research program of the Sonderforschungsbereich 125 Aachen/Jülich/KölnPart of this work will be presented at the Int. Conf. on Rare Earths in the Metallic State, St. Pierre de Chartreuse, Sept. 1978 相似文献
10.
J. Aarts W. Felsch H. v. Löhneysen F. Steglich 《Zeitschrift für Physik B Condensed Matter》1980,40(1-2):127-132
The frequency dependence of the freezing temperatureT
f() is determined for the dilute spin glass systems (La, Gd)B6 and (Y, Gd)Al2 in the frequency range 10–1,000 Hz. While for (La, Gd)B6,T
f() is found to be weak, for (Y, Gd)Al2
T
f() is even stronger than for the previously studied system (La, Gd)Al2. Both, measurements of the temperature dependence of the susceptibility nearT
f and calculations of the RKKY pair interaction, suggest that this difference is correlated with a different sign of the nearest-neighbor interaction, which appears to be antiferromagnetic for (La, Gd)B6 and ferromagnetic for (Y, Gd)Al2 as well as (La, Gd)Al2. 相似文献