Nitrat

Ohne Zusammenfassung     

The thermodynamics of proton dissociation of adenine

The thermodynamic quantities associated with ionization of the N₁ and N₉ protons of adenine have been calorimetrically determined as a function of temperature. The H values for proton dissociation of these groups, with pK values of 4.19 and 9.92, were found to be 5.1 and 9.1 kcal/mole, respectively, at 25°C, =0.025. The C _p values for proton dissociation of these groups were estimated to be –11 and –17 cal/mole-deg. These results indicate that the large heat capacity changes observed during conformational transitions of polynucleotides are not the result of ionization of the bases.     

Hyperfine structure in 5s 4d 3 D —5snf transitions of87Sr

The hyperfine spectra of the 5s4d ³ D ₁-5s20f, 5s4d ³ D ₂-5s23f, and 5s 4d ³ D ₃-5s32f transitions of⁸⁷Sr (I=9/2) have been measured by collinear fast beam laser spectroscopy. The structure in the upper configurations is highly perturbed by fine structure splitting that is of comparable size to the hyperfine interaction energy. These perturbations can be adequately treated with conventional matrix diagonalization methods, using the 5s-electron magnetic dipole interaction terma _5s and the unperturbed fine structure splittings as input parameters. Additionally, hyperfine constants for the lower 5s4d ³ D configurations, including theA- andB-factors and a separation of the individuals- andd-electron contributions to these factors, are derived.     

Observation of the neutron radiative decay

The aim of this work is the experimental observation of and research into a rare neutron mode, the radiative beta decay, where a new particle, the radiative gamma quantum, is formed along with the expected decay products: a beta electron, a recoil proton, and an antineutrino. The discovery of this rare neutron decay mode was conducted through identification of triple-coincidence events: simultaneous registration of a beta electron, a proton, and a radiative gamma quantum. The ordinary neutron decay was registered by double coincidences of a beta electron and a recoil proton. The statistics collected allow one to deduce the branching ratio (BR) BR = (3.2 ± 1.6) × 10⁻³ (90% C.L.) in the gamma energy region greater than 35 keV. This value of BR is consistent with standard electroweak theory. The text was submitted by the authors in English. An erratum to this article is available at .     

Relaxation of spin polarized 3He by magnetized ferromagnetic contaminants

In the first in a series of three papers on wall relaxation of spin polarized ³He we have reported on a breakdown of relaxation times which is observed after exposing the ³He containing glass cells to a strong magnetizing field. In this third paper we give a quantitative analysis of this phenomenon, based on magnetic signal detection by means of SQUIDs, on the pressure dependence of relaxation times in magnetized cells, as well as on Monte Carlo simulations of ³He-relaxation in a macroscopic dipole field. Our analysis allows to identify the contaminants as being aggregates of dust-like Fe₃O₄ particles (magnetite) with a radius R ? 10 mR \approx 10~\mu m and a remanent magnetic moment of the order of m ≈O(10 ^-10 ^{-10}~ A m²). The particles are located at or close to the inner glass surface.     

Ablation of polymer foils for backside opening of thin film layered flexible polymer substrates

For increasing the packing density of electronic devices and enabling 3D wiring, new concepts of interconnection for flexible circuit boards are required. The backside wiring is one innovative concept which, however, requires interconnections from the back to the front side by means of vias.Results on backside opening of polymer foils for exposing a thin metal film deposited at the front side are presented. For the experiments, a thin polyimide foil covered with a thin molybdenum metal film was used. By using mask projection of a pulsed UV-laser beam (248 nm, 20 ns) polymer foil was ablated. The laser ablation process must be adjusted in the manner to avoid damage of the thin metal film, to prevent cones formation at laser ablation, but still enabling the clean ablation of the polymer. The influence of process parameters on the backside opening is discussed and compared with theoretical estimations of the laser-induced temperatures. Using a two-step ablation process applying first high fluences to ablate the main part of the foil and finishing with low laser fluence turns out to be advantageous. This backside opening (BSO) can be used to perform an electrical contact from the backside.     

Superfluid-helium converter for accumulation and extraction of ultracold neutrons

We report the first successful extraction of accumulated ultracold neutrons (UCN) from a converter of superfluid helium, in which they were produced by downscattering neutrons of a cold beam from the Munich research reactor. Windowless UCN extraction is performed in vertical direction through a mechanical cold valve. This prototype of a versatile UCN source is comprised of a novel cryostat designed to keep the source portable and to allow for rapid cooldown. We measured time constants for UCN storage and extraction into a detector at room temperature, with the converter held at various temperatures between 0.7 and 1.3 K. The UCN production rate inferred from the count rate of extracted UCN is close to the theoretical expectation.     

Spin glass and antiferromagnetism in Kondo-lattice disordered system

The competition between spin glass (SG), antiferromagnetism (AF) and Kondo effect is studied here in a model which consists of two Kondo sublattices with a Gaussian random interaction between spins in different sublattices with an antiferromagnetic mean J ₀ and standard deviation J. In the present approach there is no hopping of the conduction electrons between the sublattices and only spins in different sublattices can interact. The problem is formulated in the path integral formalism where the spin operators are expressed as bilinear combinations of Grassmann fields which can be solved at mean field level within the static approximation and the replica symmetry ansatz. The obtained phase diagram shows the sequence of phases SG, AF and Kondo state for increasing Kondo coupling. This sequence agrees qualitatively with experimental data of the Ce₂Au_1-x Co _x Si₃ compound.Received: 9 April 2003, Published online: 9 September 2003PACS: 05.50.+q Lattice theory and statistics; Ising problems - 64.60.Cn Order disorder transformations; statistical mechanics of model systems     

ps-laser scribing of CIGS films at different wavelengths

Continuous growth of the thin-film electronics market stimulates the development of versatile technologies for large-scale patterning of thin-film materials on rigid and flexible substrates, and laser technologies are a promising method to accomplish the scribing processes. Lasers with picosecond pulse duration were applied in scribing of complex multilayered CuIn _x Ga_(1−x)Se₂ (CIGS) solar cells deposited on a polyimide substrate. The ablative properties of the films were examined as a function of the wavelength of laser radiation, pulse energy, and the irradiation dose. The selective removal of ITO and CIGS layers was achieved with 355 nm irradiation without any significant damage to the underlying layers in the ITO/CIGS/Mo/PI solar cell system. The 355 nm wavelength was also found to be favorable for scribing of absorber layer in a ZnO/CIGS/Mo/PI solar cell system. 266 nm radiation significantly modified the film structure due to high absorption. Extensive melt formation in the CIGS layer was found when 532 nm radiation was applied, though the trenches were smooth and crack-free.