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  • 1990-1994  (5)
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  • 1990-1994  (5)
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  • 1
    ISSN: 1432-1106
    Keywords: Caudate nucleus ; Accumbens ; Hippocampal epilepsy ; Inhibition ; Cat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Previous experimental evidences showed that the caudate nucleus has a modulatory effect on hippocampal epilepsy. The caudate's regulating action might reach the hippocampus either via the septal region or, retrogradely, via the accumbens nucleus. In order to obtain new data about the pathway involved in caudate hippocampal influence the spreading of abnormal activity towards the nucleus accumbens was studied. Furthermore the effects of caudate stimulation in animals with electrolytic lesions of the nucleus accumbens were analyzed. It was observed that abnormal penicillin-induced activity spreaded from the hippocampus to the nucleus accumbens in about 30 minutes. In animals with and without lesions of nucleus accumbens, caudate stimulation brought about a significant decrease in the frequency and amplitude of hippocampal activity. The results suggest that the nucleus accumbens is reached by the spreading of hippocampal epilepsy but does not participate in the control exerted by the caudate nucleus on the hippocampus. Thus the caudate-induced inhibition takes place through an anterograde caudate-hippocampal circuit, while at the same time excluding retrograde activation by way of a caudate-accumbens-hippocampal pathway.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the reactionse + e −→hadrons,e + e −, μ+ μ− and τ+ τ−, in the energy range 88.2 $$ \leqq \sqrt s \leqq 94.2$$ GeV. A total luminosity of 5.5 pb−1, corresponding to approximately 115000 hadronic and 10000 leptonicZ 0 decays, has been recorded with the L3 detector. From a simultaneous fit to all of our measured cross section data, we obtain assuming lepton universality: $$\begin{gathered} M_z = 91.181 \pm 0.010 \pm 0.02 (LEP) GeV, \hfill \\ \Gamma _z = 2501 \pm 17 MeV, \hfill \\ \Gamma _{had} = 1742 \pm 19 MeV, \Gamma _t = 83.6 \pm 0.8 MeV. \hfill \\ \end{gathered}$$ If we do not assume lepton universality, we obtain for the partial decay widths of theZ 0 intoe + e − μ+ μ− and τ+ τ−: $$\begin{gathered} \Gamma _e = 83.3 \pm 1.1 MeV, \Gamma _\mu = 84.5 \pm 2.0 MeV, \hfill \\ \Gamma _\tau = 84.0 \pm 2.7 MeV. \hfill \\ \end{gathered}$$ From the measured ratio of the invisible and the leptonic decay widths of theZ 0, we determine the number of light neutrino species to beN v =3.05±0.10. We include our measurements of the forward-backward asymmetry for the leptonic channels in a fit to determine the vector and axial-vector neutral current coupling constants of charged leptons to theZ 0. We obtain $$\bar g_V = - 0.046_{ - 0.012}^{ + 0.015}$$ and $$\bar g_A = - 0.500 \pm 0.003$$ . In the framework of the Standard Model, we estimate the top quark mass to bem t =193 −69 +52 ±16 (Higgs) GeV, and we derive a value for the weak mixing angle of sin2θ W =1−(M W /M Z )2=0.222 ± 0.008, corresponding to an effective weak mixing angle of $$\sin ^2 \bar \theta _W = 0.2315 \pm 0.0025$$ .
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The structure of hadronic events fromZ 0 decay is studied by measuring event shape variables, factorial moments, and the energy flow distribution. The distributions, after correction for detector effects and initial and final state radiation, are compared with the predictions of different QCD Monte Carlo programs with optimized parameter values. These Monte Carlo programs use either the second order matrix element or the parton shower evolution for the perturbative QCD calculations and use the string, the cluster, or the independent fragmentation model for hadronization. Both parton shower andO(α 2 s matrix element based models with string fragmentation describe the data well. The predictions of the model based on parton shower and cluster fragmentation are also in good agreement with the data. The model with independent fragmentation gives a poor description of the energy flow distribution. The predicted energy evolutions for the mean values of thrust, sphericity, aplanarity, and charge multiplicity are compared with the data measured at different center-of-mass energies. The parton shower based models with string or cluster fragmentation are found to describe the energy dependences well while the model based on theO(α 2 s calculation fails to reproduce the energy dependences of these mean values.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report on a search for the neutral and charged Higgs bosons predicted by models of spontaneous symmetry breaking with more than one Higgs doublet field. No signals are observed. We set model-independent limits on masses or branching ratios of singly and pair-produced neutral and charged Higgs bosons. In addition, we interpret our results in the framework of a general two-doublet Higgs model and the Minimal Supersymmetric extension of the Standard Model.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1434-6052
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report on the measurement of the leptonic and hadronic cross sections and leptonic forward-backward asymmetries at theZ peak with the L3 detector at LEP. The total luminosity of 40.8 pb−1 collected in the years 1990, 1991 and 1992 corresponds to 1.09·106 hadronic and 0.98·105 leptonicZ decays observed. These data allow us to determine the electroweak parameters. From the cross sections we derive the properties of theZ boson: $$\begin{gathered} M_Z = 91195 \pm 9MeV\Gamma _{\rm Z} = 2494 \pm 10MeV \hfill \\ \Gamma _{had} = 1748 \pm 10MeV\Gamma _\ell = 83.49 \pm 0.46MeV \hfill \\ \end{gathered} $$ assuming lepton universality. We obtain an invisible width of Γinv=496.5±7.9 MeV which, in the Standard Model, corresponds to a number of light neutrino species ofN v=2.981±0.050. Using also the three leptonic forward-backward asymmetries and the average tau polarization, we determine the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons to be: $$\bar g^\ell v = - 0.0378_{ - 0.0042}^{ + 0.0045} \bar g^\ell _A = - 0.4998 \pm 0.0014.$$ Within the framework of the Standard Model, and including our measurements of the $$Z \to b\bar b$$ forward-backward asymmetry and partial decay width, we derive an effective electroweak mixing angle of $$sin^2 \bar \theta _W = 0.2326 \pm 0.0012$$ . We obtain an estimate for the strong coupling constant, αS=0.142 ± 0.013 and for the top-quark mass,m t =158 −40 +32 ±19(Higgs) GeV, where the second error arises due to the uncertainty in the Higgs-boson mass.
    Type of Medium: Electronic Resource
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