Repetition rate increase and diffraction-limited focal spots for a nonthermal-equilibrium 100-TW Nd:glass laser chain by use of adaptive optics

Dynamic wave-front correction is applied before each shot on a 100-TW, 30-J/300-fs high-power laser facility by use of an adaptive-optics system. This system allows us to increase the repetition rate of high-energy lasers while maintaining excellent and constant beam focusability with a Strehl ratio of >0.75 despite the amplifiers' not being in thermal equilibrium. The best results in terms of the highest Strehl ratio and intensities are obtained when locking the system on wave-front sensing after pulse recompression.     

New oxidative tools for the functionalization of the cephalostatin north 1 hemisphere

Dimethyldioxirane (DMDO) C-H oxidation of ketone 17 to hemiketal 18 (82%), bis-dehydration to vinyl ether 21 (77%), and DMDO again provides C-23 axial alcohol 23 (99%). Routine processing, including a double-stereoselective Sharpless AD reaction (de >98%), gives alcohols 7 and 32. C-23 deoxy substrate 7 undergoes Suarez hypoiodite oxidative cyclization to (natural) beta spiroketal 34, but compound 32, bearing a C-23 silyl ether, generates unnatural spiroketal 33. [reaction: see text]     

Virtual Compton scattering off the pseudoscalar meson octet

We present a calculation of the virtual Compton scattering amplitude for the pseudoscalar meson octet in the framework of chiral perturbation theory at O(p ⁴). We calculate the electromagnetic generalized polarizabilities and compare the results in the real Compton scattering limit to available experimental values. Finally, we give predctions for the differential cross section of electron-meson bremsstrahlung.     

Dynamic force spectroscopy of conservative and dissipative forces in an Al-Au(111) tip-sample system

The conservative and dissipative interaction between an aluminum tip and a gold (111) surface were investigated using dynamic force spectroscopy in UHV. Complete force vs distance curves and friction coefficient vs distance curves were obtained quantitatively. The force curves were compared to the model by Muller, Yushenko, and Derjaguin, and long and short range interactions were subsequently quantified without fit parameters. A short range conservative interaction was separated from longer range van der Waals forces. The long range behavior of the damping coefficient obeys an inverse power law of third order.     

Measurement of the radiative cooling rates for high-ionization species of krypton using an electron beam ion trap

We describe a measurement of the radiative cooling rate for krypton made at the Berlin electron beam ion trap (EBIT). The EBIT was tuned to a charge-state distribution approaching the ionization balance of a plasma at a temperature of about 5 keV. To determine the cooling rate, we made use of EBIT's capabilities to sample a wide range of electron-beam energies and distinguish between different radiation channels. We have measured the x-ray emission from bremsstrahlung, radiative recombination, dielectronic recombination, and line radiation following electron-impact excitation. The dominant contribution to the cooling rate is made by the n=3-2, n=4-2, ellipsis x rays of the L-shell spectra of krypton, which produce more than 75% of the total radiation loss. A difference with theoretical calculations is noted for the measured total cooling rate. The predicted values are lower by a factor of 1.5-2, depending on the theoretical model. For our measurement of the cooling rate, we estimate an uncertainty interval of 22-30 %.     

Search for color singlet technicolor particles in p&pmacr; collisions at radicals = 1.8 TeV

We search for color singlet technirho and technipion production in p&pmacr; collisions at sqrt[s] = 1.8 TeV recorded with the Collider Detector at Fermilab. These exotic technimesons are present in a model of walking technicolor. The signatures studied are lepton plus two jets plus E(T) and multijet final states. No excess of events is seen in either final state. We set an upper limit on the technirho production cross section and exclude a region in the technipion mass versus technirho mass plane.     

Diffractive dijets with a leading antiproton in &pmacr;p collisions at sqrt

We report results from a study of events with a leading antiproton of beam momentum fraction 0.9057 GeV. Using the dijet events, we evaluate the diffractive structure function of the antiproton and compare it with expectations based on results obtained in diffractive deep inelastic scattering experiments at the DESY ep collider HERA.     

Can shadowing mimic the QCD phase transition?

The directed flow of protons is studied in the quark-gluon string model as a function of the impact parameter for S+S and Pb+Pb reactions at 160 AGeV/c. A significant reduction of the directed flow in midrapidity range, which can lead to the development of the antiflow, is found due to the absorption of early emitted particles by massive spectators (shadowing effect). This effect can mimic the formation of the quark-gluon plasma (QGP). However, in the absorption scenario the antiflow is stronger for the system of light colliding nuclei than for the heavy ones, while in the case of the plasma creation the effect should be opposite.