A gasdynamic jet carrying excited metal atoms as a spectral light source and a chemical reactor

A gasdynamic jet is described, which carries excited metal atoms in subsonic or supersonic flow. The excitation is performed by a hot hollow cathode discharge. The jet expands parallel into an atmosphere of a few mbar. Its use will be in atomic and molecular spectroscopy, in chemistry and spectroscopy of free radicals, and in electronic-transition chemical laser design.     

Heteronuclear decoupling interference during symmetry-based homonuclear recoupling in solid-state NMR

We examine the influence of continuous-wave heteronuclear decoupling on symmetry-based double-quantum homonuclear dipolar recoupling, using experimental measurements, numerical simulations, and average Hamiltonian theory. There are two distinct regimes in which the heteronuclear interference effects are minimized. The first regime utilizes a moderate homonuclear recoupling field and a strong heteronuclear decoupling field; the second regime utilizes a strong homonuclear recoupling field and a weak or absent heteronuclear decoupling field. The second regime is experimentally accessible at moderate or high magic-angle-spinning frequencies and is particularly relevant for many realistic applications of solid-state NMR recoupling experiments to organic or biological materials.     

A catalogue of isomerization transformations of fullerene polyhedra

Representation of isomerization and carbon insertion or extrusion mechanisms as patch replacements on a fullerene surface allows construction of a catalogue of topologically distinct local transformations of fullerenes, classified by patch boundary and pentagon content. All isomerization patches and isomerization pairs containing up to five pentagons and with an upper limit for the boundary length depending on the number of pentagons are listed. Several infinite series of transformations are identified.     

Separation of quadrupolar and magnetic contributions to spin-lattice relaxation in the case of a single isotope

We present a NMR pulse double-irradiation method which allows one to separate magnetic from quadrupolar contributions in the spin–lattice relaxation. The pulse sequence fully saturates one transition while another is observed. In the presence of a Δm = 2 quadrupolar contribution, the intensity of the observed line is altered compared to a standard spin-echo experiment. We calculated analytically this intensity change for spins I = 1, , , thus providing a quantitative analysis of the experimental results. Since the pulse sequence we used takes care of the absorbed radiofrequency power, no problems due to heating arise. The method is especially suited when only one NMR sensitive isotope is available. Different cross-checks were performed to prove the reliability of the results obtained. The applicability of this method is demonstrated by a study of the plane oxygen ¹⁷O (I = ) in the high-temperature superconductor YBa₂Cu₄O₈: the ¹⁷O spin–lattice relaxation rate consists of magnetic as well as quadrupolar contributions.     

The necessity for harmonisation of accreditation and recognition of testing laboratories, inspection bodies and certification bodies in the regulated and voluntary areas

 There have been two essential developments in current accreditation practices. One tends towards a flexible confirmation of competence of the testing laboratory for the adaptation of existing test methods and the development of new test methods. The other development attempts to assess and confirm the testing activity in terms of concrete processes for a specific application. These polarised tendencies, both in the preparatory work of the testing laboratory and in the assessment activity of the accreditation body, lead to increased costs. This paper examines the necessity for a harmonisation of these opposing sets of requirements by means of a categorised synopsis, citing actual examples. Efforts made to bring about such a harmonisation have, up to now, hardly progressed beyond first attempts and declarations of intention.     

Tuning ranges of an injection-locked excimer laser

The advantages and the practical limitations of injection locking are discussed. Experimental results for a system working in the regime between ideal injection locking and regenerative amplification are presented.