2,280 research outputs found
Spin excitations in a single LaCuO layer
The dynamics of S=1/2 quantum spins on a 2D square lattice lie at the heart
of the mystery of the cuprates
\cite{Hayden2004,Vignolle2007,Li2010,LeTacon2011,Coldea2001,Headings2010,Braicovich2010}.
In bulk cuprates such as \LCO{}, the presence of a weak interlayer coupling
stabilizes 3D N\'{e}el order up to high temperatures. In a truly 2D system
however, thermal spin fluctuations melt long range order at any finite
temperature \cite{Mermin1966}. Further, quantum spin fluctuations transfer
magnetic spectral weight out of a well-defined magnon excitation into a
magnetic continuum, the nature of which remains controversial
\cite{Sandvik2001,Ho2001,Christensen2007,Headings2010}. Here, we measure the
spin response of \emph{isolated one-unit-cell thick layers} of \LCO{}. We show
that coherent magnons persist even in a single layer of \LCO{} despite the loss
of magnetic order, with no evidence for resonating valence bond (RVB)-like spin
correlations \cite{Anderson1987,Hsu1990,Christensen2007}. Thus these
excitations are well described by linear spin wave theory (LSWT). We also
observe a high-energy magnetic continuum in the isotropic magnetic response.
This high-energy continuum is not well described by 2 magnon LSWT, or indeed
any existing theories.Comment: Revised version to appear in Nature Materials; 6 pages,4 figure
A quantitative study on the growth variability of tumour cell clones in vitro
Objectives: In this study, we quantify the growth variability of tumour cell
clones from a human leukemia cell line. Materials and methods: We have used
microplate spectrophotometry to measure the growth kinetics of hundreds of
individual cell clones from the Molt3 cell line. The growth rate of each clonal
population has been estimated by fitting experimental data with the logistic
equation. Results: The growth rates were observed to vary among different
clones. Up to six clones with a growth rate above or below the mean growth rate
of the parent population were further cloned and the growth rates of their
offsprings were measured. The distribution of the growth rates of the subclones
did not significantly differ from that of the parent population thus suggesting
that growth variability has an epigenetic origin. To explain the observed
distributions of clonal growth rates we have developed a probabilistic model
assuming that the fluctuations in the number of mitochondria through successive
cell cycles are the leading cause of growth variability. For fitting purposes,
we have estimated experimentally by flow cytometry the maximum average number
of mitochondria in Molt3 cells. The model fits nicely the observed
distributions of growth rates, however, cells in which the mitochondria were
rendered non functional (rho-0 cells) showed only a 30% reduction in the clonal
growth variability with respect to normal cells. Conclusions: A tumor cell
population is a dynamic ensemble of clones with highly variable growth rate. At
least part of this variability is due to fluctuations in the number of
mitochondria.Comment: 31 pages, 5 figure
Efetividade de genes de resistĂȘncia de trigo a oĂdio, safra 2007.
bitstream/CNPT-2010/40711/1/p-do93.pd
Spin-Orbit-Induced Orbital Excitations in Sr2RuO4 and Ca2RuO4: A Resonant Inelastic X-ray Scattering Study
High-resolution resonant inelastic X-ray scattering (RIXS) at the oxygen
K-edge has been used to study the orbital excitations of Ca2RuO4 and Sr2RuO4.
In combination with linear dichroism X-ray absorption spectroscopy, the
ruthenium 4d-orbital occupation and excitations were probed through their
hybridization with the oxygen p-orbitals. These results are described within a
minimal model, taking into account crystal field splitting and a spin-orbit
coupling \lambda_{so}=200~meV. The effects of spin-orbit interaction on the
electronic structure and implications for the Mott and superconducting ground
states of (Ca,Sr)2RuO4 are discussed.Comment: accepted in PRB 201
Supermassive black holes in the EAGLE Universe. Revealing the observables of their growth
We investigate the evolution of supermassive black holes in the âEvolution and Assembly of GaLaxies and their Environmentsâ (EAGLE) cosmological hydrodynamic simulations. The largest of the EAGLE volumes covers a (100âcMpc)3 and includes state-of-the-art physical models for star formation and black hole growth that depend only on local gas properties. We focus on the black hole mass function, Eddington ratio distribution and the implied duty cycle of nuclear activity. The simulation is broadly consistent with observational constraints on these quantities. In order to make a more direct comparison with observational data, we calculate the soft and hard X-ray luminosity functions of the active galactic nuclei (AGN). Between redshifts 0 and 1, the simulation is in agreement with data. At higher redshifts, the simulation tends to underpredict the luminosities of the brightest observed AGN. This may be due to the limited volume of the simulation, or a fundamental deficiency of the underlying model. It seems unlikely that additional unresolved variability can account for this difference. The simulation shows a similar âdownsizingâ of the AGN population as seen in observational surveys
Efetividade de genes de resistĂȘncia de trigo a oĂdio, safra 2005.
bitstream/CNPT-2010/40691/1/p-do73.pd
Testbeam and Laboratory Characterization of CMS 3D Pixel Sensors
The pixel detector is the innermost tracking device in CMS, reconstructing
interaction vertices and charged particle trajectories. The sensors located in
the innermost layers of the pixel detector must be upgraded for the ten-fold
increase in luminosity expected with the High- Luminosity LHC (HL-LHC) phase.
As a possible replacement for planar sensors, 3D silicon technology is under
consideration due to its good performance after high radiation fluence. In this
paper, we report on pre- and post- irradiation measurements for CMS 3D pixel
sensors with different electrode configurations. The effects of irradiation on
electrical properties, charge collection efficiency, and position resolution of
3D sensors are discussed. Measurements of various test structures for
monitoring the fabrication process and studying the bulk and surface
properties, such as MOS capacitors, planar and gate-controlled diodes are also
presented.Comment: 14 page
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