76 research outputs found
Heavy-Fermions in LiV2O4: Kondo-Compensation vs. Spin-Liquid Behavior?
7Li NMR measurements were performed in the metallic spinel LiV2O4. The
temperature dependencies of the line width, the Knight shift and the
spin-lattice relaxation rate were investigated in the temperature range 30 mK <
T < 280 K. For temperatures T < 1 K we observe a spin-lattice relaxation rate
which slows down exponentially. The NMR results can be explained by a
spin-liquid behavior and the opening of a spin gap of the order 0.6 K
Emergence of Antiferromagnetic Correlation in LiTi2-xVxO4 via 7Li NMR
We report 7Li NMR studies of V-substitution effects on spinel oxide
superconductor LiTi2O4 (Tc = 13.4 K). In LiTi2-xVxO4 (x = 0-0.4), the V
substitution for the Ti site suppressed the relative volume fraction of
superconductivity faster than Tc. From the observation of fairly homogeneous
enhancement in a 7Li nuclear spin-lattice relaxation rate, we conclude that the
V substitution changes electron correlation effects through electron carrier
doping from quarter electron filling 3d0.5 to 3d1.5 and then the
antiferromagnetic correlation emerges.Comment: 4 pages, 7 figure
Orbital state and magnetic properties of LiV_2 O_4
LiV_2 O_4 is one of the most puzzling compounds among transition metal oxides
because of its heavy fermion like behavior at low temperatures. In this paper
we present results for the orbital state and magnetic properties of LiV_2 O_4
obtained from a combination of density functional theory within the local
density approximation and dynamical mean-field theory (DMFT). The DMFT
equations are solved by quantum Monte Carlo simulations. The trigonal crystal
field splits the V 3d orbitals such that the a_{1g} and e_{g}^{pi} orbitals
cross the Fermi level, with the former being slightly lower in energy and
narrower in bandwidth. In this situation, the d-d Coulomb interaction leads to
an almost localization of one electron per V ion in the a_{1g} orbital, while
the e_{g}^{pi} orbitals form relatively broad bands with 1/8 filling. 2The
theoretical high-temperature paramagnetic susceptibility chi(T) follows a
Curie-Weiss law with an effective paramagnetic moment p_{eff}=1.65 in agreement
with the experimental results.Comment: 11 pages, 10 figures, 2 table
Detection and Alignment of 3D Domain Swapping Proteins Using Angle-Distance Image-Based Secondary Structural Matching Techniques
This work presents a novel detection method for three-dimensional domain swapping (DS), a mechanism for forming protein quaternary structures that can be visualized as if monomers had “opened” their “closed” structures and exchanged the opened portion to form intertwined oligomers. Since the first report of DS in the mid 1990s, an increasing number of identified cases has led to the postulation that DS might occur in a protein with an unconstrained terminus under appropriate conditions. DS may play important roles in the molecular evolution and functional regulation of proteins and the formation of depositions in Alzheimer's and prion diseases. Moreover, it is promising for designing auto-assembling biomaterials. Despite the increasing interest in DS, related bioinformatics methods are rarely available. Owing to a dramatic conformational difference between the monomeric/closed and oligomeric/open forms, conventional structural comparison methods are inadequate for detecting DS. Hence, there is also a lack of comprehensive datasets for studying DS. Based on angle-distance (A-D) image transformations of secondary structural elements (SSEs), specific patterns within A-D images can be recognized and classified for structural similarities. In this work, a matching algorithm to extract corresponding SSE pairs from A-D images and a novel DS score have been designed and demonstrated to be applicable to the detection of DS relationships. The Matthews correlation coefficient (MCC) and sensitivity of the proposed DS-detecting method were higher than 0.81 even when the sequence identities of the proteins examined were lower than 10%. On average, the alignment percentage and root-mean-square distance (RMSD) computed by the proposed method were 90% and 1.8Å for a set of 1,211 DS-related pairs of proteins. The performances of structural alignments remain high and stable for DS-related homologs with less than 10% sequence identities. In addition, the quality of its hinge loop determination is comparable to that of manual inspection. This method has been implemented as a web-based tool, which requires two protein structures as the input and then the type and/or existence of DS relationships between the input structures are determined according to the A-D image-based structural alignments and the DS score. The proposed method is expected to trigger large-scale studies of this interesting structural phenomenon and facilitate related applications
Onset of antiferromagnetism in UPt_{3} via Th-substitution studied by muon spin spectroscopy
Muon spin spectroscopy has been used to study in detail the onset of
large-moment antiferromagnetism (LMAF) in UPt_{3} as induced by Th
substitution. Zero-field experiments have been carried out on a series of
polycrystalline U_{1-x}Th_{x}Pt_{3} (0 <= x <= 0.05) samples in the temperature
range 0.04 - 10 K. At low Th content (x <= 0.002) magnetic ordering on the time
scale of the uSR experiment (10^{-8} s) is not detected. For x = 0.005 a weak
magnetic signal appears below T = 2 K, while for 0.006 <= x <= 0.05,
spontaneous oscillations in the uSR spectra signal the presence of the LMAF
phase. The data are well described by a two-component depolarization function,
combining the contribution of a polycrystalline antiferromagnet and a
Kubo-Lorentzian response. However, the transition into the antiferromagnetic
phase is quite broad. For x = 0.01 and 0.02, a weak magnetic signal appears
below about 7 K, which is well above the mean-field transition temperatures.
The broadening may be a result of the effects of disorder on the time
fluctuations associated with anomalous small-moment antiferromagnetism.Comment: 29 pages, 9 figure
Transition from magnetic ordering to Kondo behavior in Ce3-xLaxAl11
Transition from magnetic ordering to Kondo behavior in Ce3-xLaxAl11 / W. Trinkl ; S. Corsépius ; G. R. Stewart. - In: Journal of alloys and compounds. 239. 1996. S. 46-4
New clues for understanding the magnetic behavior of UPt3
New clues for understanding the magnetic behavior of UPt3 / W. Trinkl ; S. Corsépius ; G. R. Stewart. - In: Journal of alloys and compounds. 240. 1996. S. 96-10
Spin glass behaviour in doped and pure UPt
While studying doped , we employed the standard technique of
measuring in both zero-field–cooled and field-cooled states
to check for possible spin glass behaviour. The results of these studies lead
to the discovery that nominally pure itself has a tendency
towards spin glass behaviour. This instability makes for very sample-dependent
properties (as is typical in spin glasses), especially for superconductivity,
and is likely the long-sought "hidden parameter" linking a large number of
the unusual behaviours in . Thus, the measured spin glass
behaviour in reported here can explain the extreme sample
dependence of , the observed aging effect on , and the
destruction of superconductivity in by grinding. In addition,
the discovery of spin glass behaviour in UPt 3 may have implications
for understanding the small-moment magnetism below 5Â K and the double
superconducting transition in some samples, as well as helping to explain the
known important role of defects in
Monte Carlo simulation of semiconductor detector response to <sup>222</sup><em>Rn</em> and <sup>220</sup><em>Rn</em> environments.
A new electronic radon/thoron monitor employing semiconductor detectors based on a passive diffusion chamber design has been recently developed at the Helmholtz Zentrum München (HMGU). This device allows for acquisition of alpha particle energy spectra, in order to distinguish alpha particles originating from radon and radon progeny decays, as well as those originating from thoron and its progeny decays. A Monte-Carlo application is described which uses the Geant4 toolkit to simulate these alpha particle spectra. Reasonable agreement between measured and simulated spectra were obtained for both (220)Rn and (222)Rn, in the energy range between 1 and 10 MeV. Measured calibration factors could be reproduced by the simulation, given the uncertainties involved in the measurement and simulation. The simulated alpha particle spectra can now be used to interpret spectra measured in mixed radon/thoron atmospheres. The results agreed well with measurements performed in both radon and thoron gas environments. It is concluded that the developed simulation allows for an accurate prediction of calibration factors and alpha particle energy spectra
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