Two-kaon correlations in central Pb+Pb collisions at 158 a GeV/c

Two-particle interferometry of positive kaons is studied in Pb+Pb collisions at mean transverse momenta approximately 0.25 and 0.91 GeV/c. A three-dimensional analysis was applied to the lower p(T) data, while a two-dimensional analysis was used for the higher p(T) data. We find that the source-size parameters are consistent with the m(T) scaling curve observed in pion-correlation measurements in the same collisions, and that the duration time of kaon emission is consistent with zero within the experimental sensitivity.     

Kaon interferometry in heavy-ion collisions at the CERN SPS

K⁺K⁺ and K^–K^– correlations from S+Pb collisions at 200 GeV/c per nucleon and K⁺K⁺ correlations from p+Pb collisions at 450 GeV/c per nucleon, are presented as measured by the focusing spectrometer of the NA44 experiment at CERN. Multidimensional fits are performed in order to characterize the kaon-emission volume, which is found to be smaller than the pion-emission volume.     

Palladium catalysed aryl enol ether synthesis from vinyl triflates

Vinyl triflates can be efficiently converted into the corresponding aryl enol ethers by treatment with a phenol, NaO(t)Bu and a catalyst generated from Pd2dba3 and 2-(di-(t)Bu-phosphino)biphenyl.     

A formal total synthesis of platencin

The readily available and enantiomerically pure trienes 12 undergo a thermally induced intramolecular Diels-Alder reaction to give the corresponding mixture of compounds 13 and 14. This mixture has been elaborated to an advanced intermediate associated with Nicolaou's recently reported total synthesis of the natural enantiomeric form of the antibiotic platencin (2).     

The total synthesis of the crinine alkaloid hamayne via a Pd[0]-catalyzed intramolecular alder-ene reaction

The racemic form of the title alkaloid, 1, has been prepared in 13 steps from the ring-fused gem-dibromocyclopropane 7. Key transformations include the thermally induced electrocyclic ring-opening of compound 7, the Pd[0]-catalyzed intramolecular Alder-ene (IMAE) reaction of the derived sulfonamide (±)-12, and the conversion of the ensuing C-3a-arylhexahydroindole (±)-16 into (±)-hamayne via a Pictet-Spengler reaction.     

A mathematical basis for strain-gradient plasticity theory—Part I: Scalar plastic multiplier

Strain-gradient plasticity theories are reviewed in which some measure of the plastic strain rate is treated as an independent kinematic variable. Dislocation arguments are invoked in order to provide a physical basis for the hardening at interfaces. A phenomenological, flow theory version of gradient plasticity is constructed in which stress measures, work-conjugate to plastic strain and its gradient, satisfy a yield condition. Plastic work is also done at internal interfaces and a yield surface is postulated for the work-conjugate stress quantities at the interface. Thereby, the theory has the potential to account for grain size effects in polycrystals. Both the bulk and interfacial stresses are taken to be dissipative in nature and due attention is paid to ensure that positive plastic work is done. It is shown that the mathematical structure of the elasto-plastic strain-gradient theory has similarities to conventional rigid-plasticity theory. Uniqueness and extremum principles are constructed for the solution of boundary value problems.     

A mathematical basis for strain-gradient plasticity theory. Part II: Tensorial plastic multiplier

A phenomenological, flow theory version of gradient plasticity for isotropic and anisotropic solids is constructed along the lines of Gudmundson [Gudmundson, P., 2004. A unified treatment of strain-gradient plasticity. J. Mech. Phys. Solids 52, 1379-1406]. Both energetic and dissipative stresses are considered in order to develop a kinematic hardening theory, which in the absence of gradient terms reduces to conventional J₂ flow theory with kinematic hardening. The dissipative stress measures, work-conjugate to plastic strain and its gradient, satisfy a yield condition with associated plastic flow. The theory includes interfacial terms: elastic energy is stored and plastic work is dissipated at internal interfaces, and a yield surface is postulated for the work-conjugate stress quantities at the interface. Uniqueness and extremum principles are constructed for the solution of boundary value problems, for both the rate-dependent and the rate-independent cases. In the absence of strain gradient and interface effects, the minimum principles reduce to the classical extremum principles for a kinematically hardening elasto-plastic solid. A rigid-hardening version of the theory is also stated and the resulting theory gives rise to an extension to the classical limit load theorems. This has particular appeal as previous trial fields for limit load analysis can be used to generate immediately size-dependent bounds on limit loads.     

Critical behavior in the relaminarization of localized turbulence in pipe flow

The statistics of the relaminarization of localized turbulence in a pipe are examined by direct numerical simulation. As in recent experimental data [J. Peixinho and T. Mullin, Phys. Rev. Lett. 96, 094501 (2006)10.1103/PhysRevLett.96.094501], the half-life for the decaying turbulence is consistent with the scaling (Rec-Re) -1, indicating a boundary crisis of the localized turbulent state familiar in low-dimensional dynamical systems. The crisis Reynolds number is estimated as Rec=1870, a value within 7% of the experimental value 1750. We argue that the frequently asked question, of which initial disturbances at a given Re trigger sustained turbulence in a pipe, is really two separate questions: the "local phase space" question (local to the laminar state) of what threshold disturbance at a given Re is needed to initially trigger turbulence, followed by the "global phase space" question of whether Re exceeds Rec at which point the turbulent state becomes an attractor.