A new μs isomer in 136Sb produced in the projectile fission of 238U

Rapidity correlations in 800 GeV proton interactions with emulsion nuclei are investigated for different targets and multiplicity regions. To study the energy dependence, the results have been compared with proton interactions at 200 GeV and 400 GeV. A common feature of all the interactions is the existence of strong, short-range correlations. However, no dependence of cluster parameters on primary energy or target mass is found. A marginal increase of correlation strength with multiplicity is observed. Received: 30 March 2001 / Accepted: 18 September 2001     

A study of high spin states in the transitional nucleus90Mo

The reaction⁵⁸Ni(³⁶Ar, 4p)⁹⁰Mo has been studied at a beam energy of 149 MeV. A detector array consisting of the OSIRIS spectrometer (12 Compton-suppressed Ge detectors), four charged-particleδE detectors and seven NE-213 neutron detectors at the VICKSI accelerator in Berlin has been used to measure the gamma radiation inγγ- and particle-γγ-coincidence mode. An additional Ge detector was placed at 162? to the beam direction to provide information on DCO ratios. The level scheme of⁹⁰Mo has been extended up to an excitation energy of about 12 MeV and probable spin 23?. Some 70 transitions and 40 levels have been newly identified. Spin assignments have been proposed on the basis of measured DCO ratios. Shell model calculations in a model space consisting of the proton 1f _5/2, 2p _3/2, 2p _1/2, and 1g _9/2 orbits and the neutron 2p _1/2, 1g _9/2, 1g _7/2, 2d _5/2, 2d _3/2, and 3s _1/2 orbits with some truncation were made for states above 9? and the predicted structure of these states is discussed.     

The A = 51 mirror nuclei 51Fe and 51Mn

Eighteen previously unknown γ-ray transitions were identified in the T _z = - 1/2 nucleus ⁵¹Fe following the fusion-evaporation reaction ³²S(²⁸Si,2α1n)⁵¹Fe. The level scheme reaches the fully aligned I ^π = 27/2^- terminating state of the five holes in the f _7/2 shell. The 17/2^- state was found to be isomeric, and the lifetime was measured to be 2.87 ns. The mirror symmetry of ⁵¹Fe and ⁵¹Mn is discussed, and the level scheme of ⁵¹Fe is compared to shell-model calculations. Received: 20 July 2000 / Accepted: 1 August 2000     

Braided surfaces and seifert ribbons for closed braids

Apositive band in the braid groupB _n is a conjugate of one of the standard generators; a negative band is the inverse of a positive band. Using the geometry of the configuration space, a theory of bands andbraided surfaces is developed. Each representation of a braid as a product of bands yields a handle decomposition of aSeifert ribbon bounded by the corresponding closed braid; and up to isotopy all Seifert ribbons occur in this manner. Thus,band representations provide a convenient calculus for the study of ribbon surfaces. For instance, from a band representation, a Wirtinger presentation of the fundamental group of the complement of the associated Seifert ribbon inD ⁴ can be immediately read off, and we recover a result of T. Yajima (and D. Johnson) that every Wirtinger-presentable group appears as such a fundamental group. In fact, we show that every such group is the fundamental group of a Stein manifold, and so that there are finite homotopy types among the Stein manifolds which cannot (by work of Morgan) be realized as smooth affine algebraic varieties.     

The microwave spectra of ortho-fluorotoluene with the asymmetric internal rotors CH2D and CD2H

The rotational spectra of αd₁- and αd₂-ortho-fluorotoluene in the ground state of the methyl group torsion have been measured. The evaluation of the spectra has been based on the theory for the internal rotation of an asymmetric internal top formulated earlier by several authors. The barrier potential being threefold symmetric (V₃), each torsional level consists of three nondegenerate substates, designated as sy and ±asy. The sy-state is assigned to the conformation with the unique methyl hydrogen isotope within the molecular heavy-atom plane (sy-rotamer), while the ±asy-states belong to the respective out-of-plane conformation (asy-rotamer). In the torsional ground state the level spacing between the ±asy substates is very small and numerous accidental close degeneracies are present between the rotational level systems based on these torsional substates. The rotational levels involved are strongly perturbed by the coupling between molecular overall rotation and internal rotation. Large deviations from a rigid rotor spectrum and (+) ? (?) intersystem (“tunneling”) transitions are observed. The spectrum of the asy-rotamer can be well reproduced by a “two-dimensional” Hamiltonian containing 11 “rotational constants,” 9 of which are determined by a fit to the spectrum. Several are sufficiently barrier-dependent to derive V₃. We obtain (in cal/mole) 567 ± 48 for αd₁-ortho-fluorotoluene, 711 ± 40 for the αd₂-isotope. The deviations from 649 cal/mole for the normal isotope are appreciable, probably indicating shortcomings of the semirigid model. The sy-rotamer presents a rigid rotor spectrum.     

Almost block independence and bernoullicity of ℤ d -actions by automorphisms of compact abelian groups

Summary We prove that a ^d -action by automorphisms of a compact, abelian group is Bernoulli if and only if it has completely positive entropy. The key ingredients of the proof are the extension of certain notions of asymptotic block independence from -actions to ^d -action and their equivalence with Bernoullicity, and a surprisingly close link between one of these asymptotic block independence properties for ^d -actions by automorphisms of compact, abelian groups and the product formula for valuations on global fields.Oblatum 20-X-1994     

Wiener-Wintner return-times ergodic theorem

We state a new ergodic theorem, combining the Wiener-Wintner theorem and Bourgain’s theorem concerning the convergence of ergodic averages along return-times sequences. We consider ergodic averages of the form $$\frac{1}{N}\sum\limits_{n = 0}^{N - 1} {e^{in\theta } \cdot f'(S^n y) \cdot f(T^n x)} $$ and we show that the behaviour of these averages characterizes an algebraC of functions, which contains the Kronecker algebra and has interesting properties, linked with multiple recurrence ergodic theorems.     

A network approach to the modelling of active magnetic bearings

The modelling of active magnetic bearings based on a network approach is considered. Unlike in the standard modelling approach, where a linearization of the current-force relation for the centred shaft position is used, network models permit to include the position dependence of the bearing force in the force model. This becomes necessary when model based controllers are used to stabilize a magnetically supported shaft in tracking applications.

The approach is based on the well known application of network models to magnetic circuits. Further simplifying assumptions are discussed which allow one to obtain a network with a limited number of lumped parameters describing the magnetic behaviour of a magnetic bearing. The modelling of a combined radial and axial bearing serves as an example for the application of the proposed approach. Furthermore, the fitting of the network based model to measured characteristic force curves is discussed. In this context, a method for including saturation effects in the model is sketched.     

Synthesis of 1,3-diamino-7,8,9,10-tetrahydropyrido[3,2-f]-quinazolines. Inhibitors of Candida albicans dihydrofolate reductase as potential antifungal agents

A series of novel 1,3-diamino-7,8,9,10-tetrahydropyrido[3,2-f]quinazolines were synthesized starting from 6-amino-5-cyanoquinoline (4). These compounds inhibited Candida albicans dihydrofolate reductase with K_i values of ≤0.60 aM. One analogue exhibited moderate in vivo efficacy in a C. albicans-infected mouse model.     

Assessing weak intramolecular donor-acceptor interactions using 1H-117Sn J-HMQC spectroscopy

It is demonstrated that long-range nJ(1H,117Sn) coupling constants down to 0.3 Hz, can be accurately quantified from non-linear fitting of the sine modulation of the associated 1H-117Sn correlation cross-peak intensities sampled as a function of the heteronuclear antiphase coherence preparation time in the 1H-117Sn J-HMQC pulse sequence. The contribution of additional, undesired modulations is illustrated and assessed using the product operator formalism, and is traced back to contributions that arise from miss-setting of the wandering 180 degrees pulse angle in the constant time period. The power of the method and its use in the characterization of weak intramolecular donor-acceptor interactions are illustrated by the determination of long-range nJ(1H,117Sn) coupling constants of bis[3-(dimethylamino)propyl]tin derivatives, [Me2N(CH2)3]2SnR2 (', R = Me; 3, R = Ph; 4, R = t-Bu). By comparing these with the values found for the corresponding bis(4-methylpentyl)tin derivatives, [Me2CH(CH2)3]2SnR2 (2', R = Me; 3', R = Ph), which lack such interactions, the use of long-range coupling constants to detect intramolecular donor-acceptor interactions is evaluated. It is concluded that nJ(1H,117Sn) couplings up to six bonds through an organic carbon chain can be quantified, whether donor-acceptor interactions are present or not. Furthermore, evidence is presented that, when two scalar coupling pathways co-exist, the pathway involving an intramolecular donor-acceptor interaction can have opposite sign, thus decreasing the overall coupling constant to a value smaller than that actually measured in the absence of a donor-acceptor interaction, where only one coupling pathway is active. There is nevertheless clear numerical value discrimination in the series of compounds investigated between long-range couplings in derivatives without weak intramolecular donor-acceptor interactions and those where such interactions can exist.