6,540 research outputs found
Magnon Heat Conductivity and Mean Free Paths in Two-Leg Spin Ladders: A Model-Independent Determination
The magnon thermal conductivity of the spin ladders
in has been investigated at low doping levels
, 0.125, 0.25, 0.5 and 0.75. The Zn-impurities generate nonmagnetic
defects which define an upper limit for and therefore allow
a clear-cut relation between and to
be established independently of any model. Over a large temperature range we
observe a progressive suppression of with increasing
Zn-content and find in particular that with respect to pure is strongly suppressed even in
the case of tiny impurity densities where ~{\AA}.
This shows unambiguously that large ~{\AA} which
have been reported for and on basis of a kinetic model are in the correct order
of magnitude
Observation of twin beam correlations and quadrature entanglement by frequency doubling in a two-port resonator
We demonstrate production of quantum correlated and entangled beams by second
harmonic generation in a nonlinear resonator with two output ports. The output
beams at wavelength 428.5 nm exhibit 0.9 dB of nonclassical intensity
correlations and 0.3 dB of entanglement.Comment: 5 pages, 7 figure
Influence of temperature fluctuations on plasma turbulence investigations with Langmuir probes
The reliability of Langmuir probe measurements for plasma-turbulence
investigations is studied on GEMR gyro-fluid simulations and compared with
results from conditionally sampled I-V characteristics as well as self-emitting
probe measurements in the near scrape-off layer of the tokamak ASDEX Upgrade.
In this region, simulation and experiment consistently show coherent in-phase
fluctuations in density, plasma potential and also in electron temperature.
Ion-saturation current measurements turn out to reproduce density fluctuations
quite well. Fluctuations in the floating potential, however, are strongly
influenced by temperature fluctuations and, hence, are strongly distorted
compared to the actual plasma potential. These results suggest that
interpreting floating as plasma-potential fluctuations while disregarding
temperature effects is not justified near the separatrix of hot fusion plasmas.
Here, floating potential measurements lead to corrupted results on the ExB
dynamics of turbulent structures in the context of, e.g., turbulent particle
and momentum transport or instability identification on the basis of
density-potential phase relations
Disorder-induced Spin Gap in the Zigzag Spin-1/2 Chain Cuprate Sr_{0.9}Ca_{0.1}CuO_2
We report a comparative study of 63Cu Nuclear Magnetic Resonance spin lattice
relaxation rates, T_1^{-1}, on undoped SrCuO_2 and Ca doped
Sr_{0.9}Ca_{0.1}CuO_2 spin chain compounds. A temperature independent T_1^{-1}
is observed for SrCuO_2 as expected for an S=1/2 Heisenberg chain.
Surprisingly, we observe an exponential decrease of T_1^{-1} for T < 90,K in
the Ca-doped sample evidencing the opening of a spin gap. The data analysis
within the J_1-J_2 Heisenberg model employing density-matrix renormalization
group calculations suggests an impurity driven small alternation of the
J_2-exchange coupling as a possible cause of the spin gap.Comment: 4 pages, 4 figure
Complexity-Entropy Causality Plane as a Complexity Measure for Two-dimensional Patterns
Complexity measures are essential to understand complex systems and there are
numerous definitions to analyze one-dimensional data. However, extensions of
these approaches to two or higher-dimensional data, such as images, are much
less common. Here, we reduce this gap by applying the ideas of the permutation
entropy combined with a relative entropic index. We build up a numerical
procedure that can be easily implemented to evaluate the complexity of two or
higher-dimensional patterns. We work out this method in different scenarios
where numerical experiments and empirical data were taken into account.
Specifically, we have applied the method to i) fractal landscapes generated
numerically where we compare our measures with the Hurst exponent; ii) liquid
crystal textures where nematic-isotropic-nematic phase transitions were
properly identified; iii) 12 characteristic textures of liquid crystals where
the different values show that the method can distinguish different phases; iv)
and Ising surfaces where our method identified the critical temperature and
also proved to be stable.Comment: Accepted for publication in PLoS On
Recommended from our members
Glasses and glass-ceramics of the system CaO-MgO-Al2O3-SiO2 obtained from natural sedimentary raw materials
Common and low-cost natural sedimentary raw materials such as ball clay, dolomite, quartz sand and diatomite were used as the main constituents for the production of glasses and glass-ceramics of the system CaO-MgO-Al2O3-SiO2. The crystallization of the glassy batch was promoted by the addition of a nucleation agent (TiO2). The crystallization sequence was examined by DTA, XRD, SEM, and thermal expansion analyses. Wollastonite and diopside are the main phases detected and the amount and grain size/shape of crystals were found to be strongly dependent on titania additions and on the annealing conditions. The characterization of relevant functional parameters of glass and glass-ceramic samples revealed interesting results
New heat treatment to prepare high quality polycrystalline and single crystal MgB2 in single process
We report here on a new heat treatment to prepare both dense polycrystalline
and single crystal MgB2 high quality samples in one single process. Resistivity
measurements for polycrystalline part of the sample gives a residual
resistivity ratio RRR=16.6 and a very low normal state resistivity rho(40K)=
0.28 microOhmcm. Both SEM and SQUID study on polycrystals reveal the high
quality, dense character and well coupling of grain boundaries. On the other
hand, the high quality single crystals have a unique shape that resembles the
hexagonal crystal structure. SQUID measurements reveals very weak flux pinning
character implying our single crystals to be very clean. In this study, we
conclude that heat treatment is playing a major rule on the characteristics of
both polycrystalline and single crystal MgB2. Samples are thoroughly
characterized by x-ray, resistivity, dc SQUID and SEM
- …