Pattern-specific neural network design

We present evidence that the performance of the traditional fully connected Hopfield model can be dramatically improved by carefully selecting an information-specific connectivity structure, while the synaptic weights of the selected connections are the same as in the Hopfield model. Starting from a completely disconnected network we let genuine Hebbian synaptic connections grow, one by one, until a desired degree of stability is achieved. Neural pathways are thus fixed notbefore, butduring the learning phase.     

Ground-state energy of a quantum chain with competing interactions

We show rigorously that the ground state of a quantum chain with competing ferromagnetic nearest and antiferromagnetic next nearest interactions undergoes a transition from ferromagnetic to helical type, in the isotropic case, for a certain value of the relevant ratio of coupling constants. Boundaries of the phase diagram are also determined in the anisotropic case. The stability of a special quantum state (corresponding to a classical modulated phase of =/3) is analyzed by an extension of Holstein-Primakoff arguments, along a line of constant ratio of couplings, showing in particular a sequence of (instability) gaps. Finally, a natural adaptation of a variational wave function due to Huse and Elser is used to study several portions of the phase diagram, with very good agreement with previous theoretical results.     

Coincidence experiments with electrons

Coincidence experiments with electrons provide new information on the structure of nucleons and nuclei. Using new CW accelerators, kinematic regions can be explored with high precision which have not been accessible previously. The equipment and the necessary steps in the analysis of (e,ep) experiments will be discussed and illustrated with new data taken at the MAMI facility.Lectures given at the Indian-Summer School on Electron Scattering of Nucleons and Nuclei, Prague (Czech Republic), September 1994.     

C*-dynamical systems that are asymptotically highly anticommutative

It is shown that with probability 1 on , resp. ongx the irrational rotation algebra with respect to the CAT map and the generalized Price-Powers shiftA _X are asymptotically highly anticommutative.     

Determination of the atmospheric neutrino spectra with the Fréjus detector

The combined analysis of the final event set of data on neutrino interactions inside the detector, upward going stopping muons and horizontal muons recorded in the Fréjus experiment is presented. The absolute atmospheric neutrino spectra in the energy range for electron neutrinos and for muon neutrinos are determined. Based on the parameterization of Volkova for thev ^µ a spectral index of =2.66±0.05 is obtained from the ratio of horizontal muons over upward going stopping muons and from the measurement of the energy loss of horizontal muons inside the detector. The neutrino spectra are compared with various flux calculations. They do not show any evidence for neutrino oscillations in agreement with earlier analyses of the Fréjus data.Now atUniversity of Michigan, Ann Arbor, USA     

Measurement of the forward-backward asymmetry of charm and bottom quarks at theZ pole usingD*± mesons

The forward-backward asymmetries for the processes and at theZ resonance are measured using identifiedD ^*± mesons. In 905,000 selected hadronic events, taken in 1991 and 1992 with the DEL-PHI detector at LEP, 4757D ^*+D ⁰⁺ decays are reconstructed. Thec andb quark forward-backward asymmetries are determined to be:

Full-wave analysis of waveguide-to-microstrip transitions for millimeter wave applications

A full-wave solution is presented for the waveguide to microstrip transition. The exact Green's function of the transition is used in a moment method procedure. The behavior of the microstrip transition to a rectangular waveguide is studied with respect to the critical dimensions of the microstrip width, length and backshort location. The convergence characteristics of the full wave analysis method are investigated, along with the current distribution and the input impedance. Results given for the return loss is compared with measurements.     

B* production in Z decays

The decayB ^*B has been observed with the DELPHI detector at LEP, where theB ^* meson is produced inZ boson decays. The combination of inclusively reconstructedB mesons with well-measured converted photons yields a measurement of the flavour-averagedB ^*-B mass difference of 45.5±0.3 (stat.) ±0.8 (syst.) MeV/c². 95% confidence level upper limits at 6 MeV/c² are placed on both the isospin (i.e.B ⁺-B ⁰) and theB _s -B _ud splitting of the mass difference. The production ratio ofB ^* toB mesons inZ decays is measured to be 0.72±0.03 (stat.) ±0.06 (syst.). Limits on the production cross-section of other hypothetical excitedB hadron states decaying radiatively are established. The differentialB ^* cross section has been measured to be in good agreement with the averageb fragmentation, yielding an average fractionalB ^* energy of x _E =0.695±0.009 (stat.) ±0.013 (syst.). From the decay angular distribution the relative contribution of longitudinalB ^* polarisation states is measured to be _L/(_L + _T) = 0.32 ± 0.04 (stat.) ±0.03 (syst.).CICYT_AEN93-0832