89 research outputs found
Nonlinear optical properties of push–pull polyenes for electro-optics
Improved nonlinear organic chromophores of varying conjugation length with either thiobarbituric acid or 3-dicyanomethylene-2,3-dihydrobenzothiophene-1,1-dioxide (FORON® Blue) acceptors have been synthesized and investigated for their nonlinear optical properties. Very large quadratic hyperpolarizabilities β(−2ω; ω, ω) have been found, up to 25,700×10^(−48) esu at λ=1.91 μm. In a guest–host polymer very high electro-optic (EO) coefficients, of up to 55 pm/V, have been determined at λ=1.31 μm with 20-wt % chromophore loading. We find good agreement between molecular parameters evaluated by electric-field-induced second-harmonic generation (EFISH) and the measurements of guest–host solid–solid solutions. The latter method is well suited to the determination of the product of dipole moment μ and hyperpolarizability β quickly and reliably at the wavelength of interest for EO applications without the complications associated with EFISH measurements
Competition between phonon superconductivity and Kondo screening in mixed valence and heavy fermion compounds
We consider competition of Kondo effect and s-wave superconductivity in heavy
fermion and mixed valence superconductors, using the phenomenological approach
for the periodic Anderson model. Similar to the well known results for
single-impurity Kondo effect in superconductors, we have found principal
possibility of a re-entrant regime of the superconducting transition
temperature, , in heavy fermion superconductors in a narrow range of model
parameters and concentration of f-electrons. Suppression of in mixed
valence superconductors is much weaker. Our theory has most validity in the
low-temperature Fermi liquid regime, without re-entrant behavior of . To
check its applicability, we performed the fit for the -dependence of
in CeLaRuSi and obtained an excellent agreement with the
experimental data, although no re-entrance was found in this case. Other
experimental data are discussed in the light of our theoretical analysis. In
particular, we compare temperatures of the superconducting transition for some
known homologs, i.e., the analog periodic lattice compounds with and without
f-elements. For a few pairs of homologs superconductivity exists only in the
heavy fermion materials, thus confirming uniqueness of superconductivity
mechanisms for the latter. We suggest that for some other compounds the value
of may remain of the same order in the two homologs, if superconductivity
originates mainly on some light Fermi surface, but induces sizable
superconducting gap on another Fermi surface,for which hybridization or other
heavy fermion effects are more significant.Comment: 11 pages, 4 figures, pd
Effects of La substitution on superconducting state of CeCoIn5
We report effects of La substitution on superconducting state of heavy
fermion superconductor CeCoIn5, as seen in transport and magnetization
measurements. As opposed to the case of conventional superconductors, pair
breaking by nonmagnetic La results in depression of Tc and indicates strong gap
anisotropy. Upper critical field Hc2 values decrease with increased La
concentration, but the critical field anisotropy, gamma=Hc2(a)/Hc2(c), does not
change in the Ce_{1-x}La_xCoIn5 (x=0-0.15). The electronic system is in the
clean limit for all values of x.Comment: Submitted to Phys. Rev.
Surprised at All the Entropy: Hippocampal, Caudate and Midbrain Contributions to Learning from Prediction Errors
Influential concepts in neuroscientific research cast the brain a predictive machine that revises its predictions when they are violated by sensory input. This relates to the predictive coding account of perception, but also to learning. Learning from prediction errors has been suggested for take place in the hippocampal memory system as well as in the basal ganglia. The present fMRI study used an action-observation paradigm to investigate the contributions of the hippocampus, caudate nucleus and midbrain dopaminergic system to different types of learning: learning in the absence of prediction errors, learning from prediction errors, and responding to the accumulation of prediction errors in unpredictable stimulus configurations. We conducted analyses of the regions of interests' BOLD response towards these different types of learning, implementing a bootstrapping procedure to correct for false positives. We found both, caudate nucleus and the hippocampus to be activated by perceptual prediction errors. The hippocampal responses seemed to relate to the associative mismatch between a stored representation and current sensory input. Moreover, its response was significantly influenced by the average information, or Shannon entropy of the stimulus material. In accordance with earlier results, the habenula was activated by perceptual prediction errors. Lastly, we found that the substantia nigra was activated by the novelty of sensory input. In sum, we established that the midbrain dopaminergic system, the hippocampus, and the caudate nucleus were to different degrees significantly involved in the three different types of learning: acquisition of new information, learning from prediction errors and responding to unpredictable stimulus developments. We relate learning from perceptual prediction errors to the concept of predictive coding and related information theoretic accounts
Dissociating dynamic probability and predictability in observed actions-an fMRI study
© 2014 Ahlheim, Stadler and Schubotz
Prefrontal cortex activation reflects efficient exploitation of higher-order statistical structure
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Analysis of a diesel-electric hybrid urban bus system
A hybrid bus powered by a diesel engine and a battery pack has been analyzed over an idealized bus-driving cycle in Chicago. Three hybrid configurations, two parallel and one series, have been evaluated. The results indicate that the fuel economy of a hybrid bus, taking into account the regenerative braking, is comparable with that of a conventional diesel bus. Life-cycle costs are slightly higher because of the added weight and cost of the battery
Einfluss der Feuerung auf die Emission an Schwermetallen
The pertinent synopsis is published in Chem.-Ing.-Tech. (1985) v. 57(3)SIGLEAvailable as manuscript MS 1330/85 from VCH Verlagsgesellschaft m.b.H., Weinheim (Germany, F.R.) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
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