Recent results in electron-positron annihilation above 2 GeV

We review recent results in electron-positron annihilation above a center-of-mass energy of 2 GeV with particular emphasis on the production and properties of new particles. Topics include the total e⁺e^? cross section, the properties of jet-like structure in high energy multi-particle events, the properties of the Ψ family of charmonium states, the production and properties of the charmed D mesons, and evidence for and the properties of the τ, a new charged lepton.     

Arytenoid dislocation

Arytenoid dislocation is a common yet infrequently diagnosed complication of laryngeal trauma. It may result in various symptoms, including permanent dysphonia, although immediate voice change is not always present. Early reduction is the treatment of choice; however, late reduction is often successful in restoring voice. A high index of suspicion based on the history of the patient is necessary to recognize arytenoid dislocation. Thorough physical examination and objective tests are helpful in confirming this diagnosis.     

The atomic absorption spectroscopy of chromium

Conditions were studied for the determination of trace amounts of chromium by atomic absorption spectroscopy. Solution matrix, flame composition, and extraction procedures were the variables studied. A detection limit of 0.006 p.p.m. of chromium was observed with an air-hydrogen flame and methyl isobutyl ketone as the solvent.     

Molecular beam epitaxy and reconstructed surfaces

In the last years molecular beam epitaxy (MBE) has become a very important method to create new materials. Scattering and channeling of high-energy ions is a mass-dispersive, surface-sensitive crystallographic technique, particularly suited for the investigation of epitaxial systems. The combination of both techniques allows new insight into some of the fundamental processes at interfaces and surfaces. As an example we discuss the influence of substrate reconstruction on epitaxial growth. We show for the Si/Ge and Si/Si systems that the reordering of the reconstruction-induced displacements at the substrate surface, a necessary condition for epitaxial growth, is critically dependent on the type of reconstruction: Deposition of Ge or Si on Si(100)2×1 at room-temperature relieves the reconstruction, whereas Si(111)7×7 appears unaffected. This difference is discussed in terms of structural models for these surfaces. We shall also discuss the implications of these results with respect to MBE and, in particular, to Si homoepitaxial temperatures.     

Simplified Bethe-Salpeter equation for positronium

The Bethe-Salpeter equation for a fermion-antifermion system, coupled by photons, is considered in the Feynman gauge. The kernel is that resulting from exchange of a single photon. The usual reduction of the sixteen B-S spinor amplitudes in terms of tensors leads to 16 coupled integro-differential equations. By straightforward application of charge conjugation-, parity-, and Lorentz-invariance, the system of coupled equations is reduced to ones involving no more than eight and as few as three scalar structure functions for the various parity, charge conjugation, and total angular momentum states. The results hold for arbitrary coupling strength. As a check of the equations obtained, a perturbation theory is carried out for the Coulomb interaction. It leads to effective potentials in agreement with those obtained previously to order mα⁴ for positronium.     

Allenyl azide cycloaddition chemistry. synthesis of pyrrolidine-containing bicycles and tricycles via the possible intermediacy of azatrimethylenemethane species

Thermolysis of 5-azidoallenes bearing a C(1) methyl group and either an aryl ring or an alkene on C(1) furnishes tricyclic (from the aryl substrates) or bicyclic (from the alkenyl substrates) pyrrolidine products following formal H-CN addition across an intermediate imine. High levels of diastereoselectivity are observed in all cases studied. This reaction cascade presumably passes through unobserved triazoline and azatrimethylenemethane diyl intermediates en route to product.     

Legendre transforms and r-particle irreducibility in quantum field theory: The formal power series framework

We study the higher Legendre transforms Γ^(r) {A } of the generating functional G for connected Green's functions in Euclidean boson field theories. To analyze Γ^(r) {A } rigorously even when it does not make sense as an ordinary functional, we develop the framework of formal power series in A. For r = 1, 2 we isolate regularity conditions on G that ensure the existence of Γ^(r) as a formal power series and we verify these conditions for the weakly coupled P(φ)₂ model. We also establish the improved regularity of the functional Φ^(r) obtained by subtracting from Γ^(r) its trivial singular part.     

Divergenzen von Wahrscheinlichkeitsverteilungen — Integralgeometrisch Betrachtet

Ohne ZusammenfassungDie Arbeit entstand während eines Aufenthaltes an der Michigan State University, East Lansing.     

Allenyl azide cycloaddition chemistry. Synthesis of annelated indoles from 2-(allenyl)phenyl azide substrates

[reaction: see text] Thermolysis of 2-(allenyl)phenyl azides leads to a cascade cyclization sequence furnishing both C(2)-C(3) and N-C(2) cyclopentannelated indoles.     

Quantum phase transition between a Luttinger liquid and a gas of cold molecules

We consider cold polar molecules confined in a helical optical lattice similar to those used in holographic microfabrication. An external electric field polarizes molecules along the axis of the helix. The large-distance intermolecular dipolar interaction is attractive but the short-scale interaction is repulsive due to geometric constraints and thus prevents collapse. The interaction strength depends on the electric field. We show that a zero-temperature second-order liquid-gas transition occurs at a critical field. It can be observed under experimentally accessible conditions.