84 research outputs found
139La NMR evidence for phase solitons in the ground state of overdoped manganites
Hole doped transition metal oxides are famous due to their extraordinary
charge transport properties, such as high temperature superconductivity
(cuprates) and colossal magnetoresistance (manganites). Astonishing, the mother
system of these compounds is a Mott insulator, whereas important role in the
establishment of the metallic or superconducting state is played by the way
that holes are self-organized with doping. Experiments have shown that by
adding holes the insulating phase breaks into antiferromagnetic (AFM) regions,
which are separated by hole rich clumps (stripes) with a rapid change of the
phase of the background spins and orbitals. However, recent experiments in
overdoped manganites of the La(1-x)Ca(x)MnO(3) (LCMO) family have shown that
instead of charge stripes, charge in these systems is organized in a uniform
charge density wave (CDW). Besides, recent theoretical works predicted that the
ground state is inhomogeneously modulated by orbital and charge solitons, i.e.
narrow regions carrying charge (+/-)e/2, where the orbital arrangement varies
very rapidly. So far, this has been only a theoretical prediction. Here, by
using 139La Nuclear Magnetic Resonance (NMR) we provide direct evidence that
the ground state of overdoped LCMO is indeed solitonic. By lowering temperature
the narrow NMR spectra observed in the AFM phase are shown to wipe out, while
for T<30K a very broad spectrum reappears, characteristic of an incommensurate
(IC) charge and spin modulation. Remarkably, by further decreasing temperature,
a relatively narrow feature emerges from the broad IC NMR signal, manifesting
the formation of a solitonic modulation as T->0.Comment: 5 pages, 4 figure
Spin-polarized oxygen hole states in cation deficient La(1-x)CaxMnO(3+delta)
When holes are doped into a Mott-Hubbard type insulator, like lightly doped
manganites of the La(1-x)CaxMnO3 family, the cooperative Jahn-Teller
distortions and the appearance of orbital ordering require an arrangement of
Mn(3+)/Mn(4+) for the establishment of the insulating canted antiferromagnetic
(for x<=0.1), or of the insulating ferromagnetic (for 0.1<x<= 0.2) ground
state. In the present work we provide NMR evidence about a novel and at the
same time puzzling effect in La(1-x)CaxMnO(3+delta) systems with cation
deficience. We show that in the low Ca-doping regime, these systems exhibit a
very strong hyperfine field at certain La nuclear sites, which is not present
in the stoichiometric compounds. Comparison of our NMR results with recent
x-ray absorption data at the Mn K edge, suggests the formation of a
spin-polarized hole arrangement on the 2p oxygen orbitals as the origin of this
effect.Comment: 10 pages, 4 Figures, submitted to PR
Decoration of Carbon Nanotubes with CoO and Co Nanoparticles
Multiwall carbon nanotubes (MWNTs) decorated with CoO nanocrystals were synthesized by in-situ thermal decomposition of Co(acac)2 in oleyl amine under reflux conditions open in the air. The CoO/MWNTs composite material can be easily converted to metallic Co/MWNTs through annealing under reducing atmosphere (4% H2) at 500°C without any significant sintering effect. The composite materials characterized by X-ray diffraction, transmission electron microscopy, and Nuclear Magnetic Resonance (NMR) spectroscopy. The structural and morphological characterization shows that the CoO has cubic face (fcc) and the particles deposited uniformly on the external surface of the carbon nanotubes. In the annealed materials, the NMR shows that the fcc and hcp metallic Co phases coexist with a significant percentage of stacking faults. The magnetic measurements indicated that the CoO/MWNTs composite is largely composed of CoO nanoparticles with uncompensated surface spins. The fluctuations of spins persist in partially reduced CoO grains as shown by nuclear spin-lattice relaxation measurements
B NMR study of pure and lightly carbon doped MgB superconductors
We report a B NMR line shape and spin-lattice relaxation rate
() study of pure and lightly carbon doped MgBC for
, 0.02, and 0.04, in the vortex state and in magnetic field of 23.5 kOe.
We show that while pure MgB exhibits the magnetic field distribution from
superposition of the normal and the Abrikosov state, slight replacement of
boron with carbon unveils the magnetic field distribution of the pure Abrikosov
state. This indicates a considerable increase of with carbon doping
with respect to pure MgB. The spin-lattice relaxation rate
demonstrates clearly the presence of a coherence peak right below in pure
MgB, followed by a typical BCS decrease on cooling. However, at
temperatures lower than K strong deviation from the BCS behavior is
observed, probably from residual contribution of the vortex dynamics. In the
carbon doped systems both the coherence peak and the BCS temperature dependence
of weaken, an effect attributed to the gradual shrinking of the
hole cylinders of the Fermi surface with electron doping.Comment: 8 pages, 6 figures, submitted to Phys. Rev.
On the modelling of infilled RC frames through strut models
Infill panels largely affect the seismic response of framed constructions. The wide variety in their mechanical and geometrical features has produced many different models and assumptions in their analytical representation. In this paper the simplest and most diffuse analytical approach, based on the introduction of equivalent struts, has been checked. An overview is presented, focusing on the strut dimensions, strength and number. Two case-studies, taken by two different experimental campaigns, have been considered and reproduced. The obtained results have been compared to the experimental ones, and some parameters have been checked for selecting the model to use for analysis
Research needs towards a resilient community: Vulnerability reduction, infrastructural systems model, loss assessment, resilience-based design and emergency management
Most of the literature on resilience is devoted to its assessment. It seems time to move from analysis to design, to develop the tools needed to enhance resilience. Resilience enhancement, a close relative of the less fashionable risk mitigation, adds to the latter, at least in the general perception, a systemic dimension. Resilience is often paired with community, and the latter is a system. This chapter therefore discusses strategies to enhance resilience, endorses one of prevention rather than cure, and focuses in the remainder on the role played by systemic analysis, i.e. the analysis of the built environment modelled beyond a simple collection of physical assets, with due care to the associated interdependencies. Research needs are identified and include challenges in network modelling, the replacement of generic fragility curves for components, how to deal with evolving state of information
Safety & efficacy of lifileucel (LN-144) tumor infiltrating lymphocyte therapy in metastatic melanoma patients after progression on multiple therapies – independent review committee data update
Treatment options are limited for patients with
advanced melanoma who have progressed on checkpoint
inhibitors and targeted therapies such as BRAF/MEK inhibitors
(if BRAF-V600E mutated). Adoptive cell therapy utilizing
tumor-infiltrating lymphocytes (TIL) has shown antitumor efficacy with durable responses in heavily pretreated melanoma
patients. Safety and efficacy of lifileucel, a centrally manufactured cryopreserved autologous TIL therapy assessed by both
investigator and an independent review committee (IRC), are
presented
Seismic Design of Open-Storey Infilled RC Buildings.
Abstract not availableJRC.(ISIS)-Institute For Systems, Informatics And Safet
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