Enhanced superconductivity in zirconium after H(D) implantation

Zirconium foils (superconducting transition atT _c =0.7 K) were implanted at liquid helium temperatures with hydrogen, deuterium and helium. In all cases a remarkable increase ofT _c was observed. Implantation of the inert He atoms leads only to the introduction of lattice defects, which is known to increaseT _c of Zr. However, the implanted H and D atoms exert an additional influence on the superconducting behavior based on a change of the electronic properties and an increase of the electron-phonon coupling. Introduction of lattice defects seems to account for theT _c increase to 1.49 K after He implantation, whereasT _c is even more enhanced by implantation of the hydrogen isotopes. The maximum values forT _c are 3.14 K for H and 4.65 K for D implantation. The concentration necessary to produce a saturation inT _c for both isotopes is H(D)/Zr0.13. The remarkably highT _c for the heavier isotope corresponds to an extreme inverse isotope effect. A smaller inverse isotope effect was found earlier in the Pd –H(D) system, where it could be explained by anharmonic effects.Dedicated to Prof. Dr. W. Buckel on the occasion of his 60th birthday     

Optimal broadcast on parallel locality models

In this paper matching upper and lower bounds for broadcast on general purpose parallel computation models that exploit network locality are proven. These models try to capture both the general purpose properties of models like the PRAM or BSP on the one hand, and to exploit network locality of special purpose models like meshes, hypercubes, etc., on the other hand. They do so by charging a cost l(|i−j|) for a communication between processors i and j, where l is a suitably chosen latency function.An upper bound T(p)=∑_i=0^loglogp2ⁱ·l(p^1/2i) on the runtime of a broadcast on a p processor H-PRAM is given, for an arbitrary latency function l(k).The main contribution of the paper is a matching lower bound, holding for all latency functions in the range from l(k)=Ω(logk/loglogk) to l(k)=O(log²k). This is not a severe restriction since for latency functions l(k)=O(logk/log¹⁺log(k)) with arbitrary >0, the runtime of the algorithm matches the trivial lower bound Ω(logp) and for l(k)=Θ(log¹⁺k) or l(k)=Θ(k), the runtime matches the other trivial lower bound Ω(l(p)). Both upper and lower bounds apply for other parallel locality models like Y-PRAM, D-BSP and E-BSP, too.     

On the strategic origin of Brownian motion in finance

This paper is concerned with the strategic use of a private information on the stock market. A repeated auction model is used to analyze the evolution of the price system on a market with asymmetric information.  The model turns out to be a zero-sum repeated game with one-sided information, as introduced by Aumann and Maschler.  The stochastic evolution of the price system can be explicitly computed in the n times repeated case. As n grows to ∞, this process tends to a continuous time martingale related to a Brownian Motion.  This paper provides in this way an endogenous justification for the appearance of Brownian Motion in Finance theory. Received: February 2002     

Structure of the Triplet of low-lying states in101Mo

The properties of the triplet of low-lying states in¹⁰¹Mo have been studied through spectroscopy of theγ radiation following thermal neutron capture in¹⁰⁰Mo and β^? decay of¹⁰¹Nb and through a measurement of the proton angular distributions in the¹⁰⁰Mo(d,p) reaction with 14 MeV deuteron energy. The half-lives of the 13.5 keV state and the 57.0 keV 5/2⁺ state have been measured as 226(7) and 133(7)ns, respectively. These values and the quadrupole/dipole mixing ratios of the 13.5 keV and 43.5 keV transitions yield spin and parity 3/2⁺ for the 13.5 keV level. The E2 components in the 13.5 (3/2⁺ →1/2⁺) and 43.5 keV (5/2⁺→3/2⁺) transitions are ≦ 8·10^?4 and 54(9)%, respectively. The possibility of an additional state near to the 57.0 keV level is discussed. IBFM/PTQM calculations, taking into consideration the transitional character of the¹⁰⁰Mo boson core, account for the electromagnetic-transition and transfer-reaction pattern of the triplet of states.     

Study of hadronic events inpp collisions at\sqrt s = 62GeV and comparison with hadronic events ine + e − collisions

We present an analysis of minimum bias events from proton-proton collisions at \(\sqrt s = 7GeV\) in the CERN ISR. We remove the effects of both the leading protons and compare theB=0 mesonic residue of the events to the hadronic events of similar energy produced ine ⁺ e ^? collisions. This comparison is presented in terms of the standard jet-type analyses involving quantities such as sphericity and aplanarity. We find significant differences between these data and the data frome ⁺ e ^? annihilations. The data of this experiment are consistent with the predictions of a longitudinal phase space model.     

Positive pion photoproduction from hydrogen at photon energies between 500 MeV and 1,400 MeV in forward direction

The differential cross section of the reactionγ+p→π ⁺ was measured at pion CM-angles of 20° and 30° for photon energies between 500 MeV and 1,400 MeV. The pions were detected in a magnetic spectrometer. By measuring each pion trajectory and by offline calculation of the initial pion parameters an energy resolution of about 2.5% FWHM was achieved. The results complete a set of data which were measured in recent years at the Bonn 2.5 GeV synchrotron. In comparison to photoproduction analyses two effects were revealed: The η cusp appears in the energy dependence of the cross section as a sharp drop atK _γ=710 MeV. In the region of the third resonance the data show a greater enhancement than predicted by most of the analyses.     

Measurement of the polarization of positive muons produced in high-energy antineutrino interactions

The question whether scalar-type interactions contribute to weak interactions at large momentum transfer has been investigated by a measurement of the longitudinal polarization of positive muons produced in charged-current interactions of high-energy antineutrinos with iron. At an average momentum transfer <Q ²>=4 GeV² the muon spin is found to be oriented forward with respect to the muon momentum vector, with an average polarization of 1.10±0.24, consistent with positive helicity. A limit on scalar contributions of σ_{s, p}/σ_tot <7% at the 95% confidence level can be deduced. A search for violation of time reversal invariance which could manifest itself by a polarization component perpendicular to the muon production plane gave a limit of σ_tv/σ_tot <16% (95% c.l.). It is concluded that the weak leptonic charged current retains its dominant vector and axial vector structure at large momentum transfers.     

Time-resolved experiments on the photoablation of polystyrene and PMMA by ArF-laser radiation

The photoablation of polystyrene (PS) and polymethylmethacrylate (PMMA) was studied in real-time during the uv laser pulse at 193 nm. The transmission and total reflection of thin polymer layers on quartz glass substrates was measured time-resolved. From the results for the strongly absorbing PS it can be concluded that the emission of material starts within the first few nanoseconds of the laser pulse. Photoablation of PMMA, which is a relatively weak absorber at 193 nm, is accompanied by strong modifications of the transmission by the first several ten laser pulses.