Determination of the neutron electric form factor in the D(e,e′n)p reaction and the influence of nuclear binding

The electric form factor of the neutron G _E,n has been determined at the Mainz Microtron MAMI at the low momentum transfer Q ²= 0.15 (GeV/c)² in a measurement of the recoil polarisation ratio P _x/P_z in the quasifree reaction D(e,e′n)p. At this Q ² the influence of the nuclear binding is strong. A purely kinematical model is used to get some insight into the effect of the initial Fermi momentum distribution of the neutron. The influence of the final state interaction is determined quantitatively by a model of Arenh?vel et al.. After the corresponding corrections a value of G _E,n(0.15 (GeV/c)²) = 0.0481±0.0065_stat±0.0053_syst is obtained. Received: 12 April 1999     

Zur Synthese von Sialylglykosiden (Darstellung von Methyl-6-O-benzyl-(4,7,8,9-tetra-O-acetyl-5-acetylamino-3,5-didesoxy-D-glycero-α bzw. β-D-galacto-2-nonulopyranosäure-methylester)-α bzw. β-D-glucopyranosid)

Silver triflate promoted condensations of 5-acetamido-4,7,8,9-tetra-O-acetyl-2-chloro-2,3,5-trideoxy-β-D-glycero-D-galacto-2-nonulopyranosidonic acid methylester with methyl-2,3,4-tri-O-benzyl-α or β-D-glucopyranoside to the title products are reported.     

Bestimmung von Calcium und Barium in Natrium-Metall im ppm-Bereich nach chemischer Anreicherung mit Hilfe der Röntgenfluorescenz-Spektrometrie

A method is described for the determination of Ca and Ba in the μg range. Ca and Ba are precipitated in NH₄OH-NH₄Cl-buffered solution by the sodium salt of N-hydroxy-naphthalimide after addition of 500 μg Sr as a coprecipitant. The precipitations which are filtered off through membranes are analysed for Ca and Ba with the X-ray fluorescence spectrometer. The limit of detection of this method is 0.6 μg for Ca and 0.3 μg for Ba which allows the safe control of the required purity of sodium < 1 ppm Ca for a weighed portion of 4 g of sodium metal. The method described was applied also to the determination of Ca and Ba in H₂WO₄.     

Experimental and Computational Studies on the CH Amination Mechanism of Tetrahydrocarbazoles via Hydroperoxides

The acid‐catalyzed reactions of photochemically generated tetrahydrocarbazole peroxides with anilines have been studied experimentally and computationally to identify the underlying reaction mechanism. The kinetic data indicate a reaction order of one in the hydroperoxide and zero in the aniline. Computational investigations using density functional theory support the experimental findings and predict an initial tautomerization between an imine and enamine substructure of the primarily generated tetrahydrocarbazole peroxide to be the rate controlling step. The enamine tautomer then loses hydrogen peroxide upon protonation, generating a stabilized allylic carbocation that is reversibly trapped by solvent or aniline to form the isolated products.     

Synthesis of 2‐Hydroxy‐1,4‐oxazin‐3‐ones through Ring Transformation of 3‐Hydroxy‐4‐(1,2‐dihydroxyethyl)‐β‐lactams and a Study of Their Reactivity

The reactivity of 3‐hydroxy‐4‐(1,2‐dihydroxyethyl)‐β‐lactams with regard to the oxidant sodium periodate was evaluated, unexpectedly resulting in the exclusive formation of new 2‐hydroxy‐1,4‐oxazin‐3‐ones through a C3? C4 bond cleavage of the intermediate 4‐formyl‐3‐hydroxy‐β‐lactams followed by a ring expansion. This peculiar transformation stands in sharp contrast with the known NaIO₄‐mediated oxidation of 3‐alkoxy‐ and 3‐phenoxy‐4‐(1,2‐dihydroxyethyl)‐β‐lactams, which exclusively leads to the corresponding 4‐formyl‐β‐lactams without a subsequent ring enlargement. In addition, this new class of functionalized oxazin‐3‐ones was further evaluated for its potential use as building blocks in the synthesis of a variety of differently substituted oxazin‐3‐ones, morpholin‐3‐ones and pyrazinones. Furthermore, additional insights into the mechanism and the factors governing this new ring‐expansion reaction were provided by means of density functional theory calculations.     

Multiple Solutions for Gradient Elliptic Systems with Nonsmooth Boundary Conditions

In this paper we prove the existence of at least three solutions of gradient elliptic systems with nonhomogeneous and nonsmooth Neumann boundary conditions. Our investigations complete the results of J. Fernandez Bonder, S. Martinez, J.D. Rossi (NoDEA Nonlinear Differential Equations Appl. 2007). We use a recent generalization of a three critical points theorem of B. Ricceri (Nonlinear Anal. 2008) for locally Lipschitz functionals given by A. Kristály, W. Marzantowicz, Cs. Varga (J. Global Optim. 2010).     

Multiplicity results for a class of quasilinear eigenvalue problems on unbounded domains

Using a recent result of Ricceri [10] we prove a multiplicity result for a class of quasilinear eigenvalue problems with nonlinear boundary conditions on an unbounded domain. Our paper completes previous results obtained by Carstea and Rădulescu [4], Chabrowski [1], [2], Kandilakis and Lyberopoulos [6] and Pflüger [7]. Received: 17 April 2007     

Photoemission of spinpolarized electrons from strained GaAsP

Strained layer GaAs_.95P_.05 photo cathodes are presented, which emit electron beams spinpolarized to a degree of P = 75% typically. Quantum yields around QE = 0.4% are observed routinely. The figure of merit P² × QE = 2.3 × 10^–3 is comparable to that of the best strained layer cathodes reported in literature. The optimum wavelength of irradiating light around 830 nm is in convenient reach of Ti:sapphire lasers or diode lasers respectively. The cathodes are produced using MOCVD-techniques. A GaAs_.55P_.45-GaAs_.85P_.15 superlattice structure prevents the migration of dislocations from the substrate and bottom layers to the strained overlayer. The surface is protected by an arsenic layer so that no chemical cleaning is necessary before installation into vacuum. The source of polarized electrons attached to the Mainz race track microtron MAMI works with such cathodes now. More than 1000 hours beamtime have been performed successfully.