Fractional volume integration in two-dimensional NMR spectra: CAKE, a Monte Carlo approach

Quantitative information from multi-dimensional NMR experiments can be obtained by peak volume integration. The standard procedure (selection of a region around the chosen peak and addition of all values) is often biased by poor peak definition because of peak overlap. Here we describe a simple method, called CAKE, for volume integration of (partially) overlapping peaks. Assuming the axial symmetry of two-dimensional NMR peaks, as it occurs in NOESY and TOCSY when Lorentz-Gauss transformation of the signals is carried out, CAKE estimates the peak volume by multiplying a volume fraction by a factor R. It represents a proportionality ratio between the total and the fractional volume, which is identified as a slice in an exposed region of the overlapping peaks. The volume fraction is obtained via Monte Carlo Hit-or-Miss technique, which proved to be the most efficient because of the small region and the limited number of points within the selected area. Tests on simulated and experimental peaks, with different degrees of overlap and signal-to-noise ratios, show that CAKE results in improved volume estimates. A main advantage of CAKE is that the volume fraction can be flexibly chosen so as to minimize the effect of overlap, frequently observed in two-dimensional spectra.     

Mapping fibre orientation in complex-shaped biological systems with micrometre resolution by scanning X-ray microdiffraction

A fully automated procedure to extract and to image local fibre orientation in biological tissues from scanning X-ray diffraction is presented. The preferred chitin fibre orientation in the flow sensing system of crickets is determined with high spatial resolution by applying synchrotron radiation based X-ray microbeam diffraction in conjunction with advanced sample sectioning using a UV micro-laser. The data analysis is based on an automated detection of azimuthal diffraction maxima after 2D convolution filtering (smoothing) of the 2D diffraction patterns. Under the assumption of crystallographic fibre symmetry around the morphological fibre axis, the evaluation method allows mapping the three-dimensional orientation of the fibre axes in space. The resulting two-dimensional maps of the local fibre orientations - together with the complex shape of the flow sensing system - may be useful for a better understanding of the mechanical optimization of such tissues.     

Investigation of prolate-oblate shape-coexistence in 74Kr

The atomic nucleus ⁷⁴Kr has been investigated using combined conversion-electron (CE) and γ-ray spectroscopy. In order to confirm the existence of the expected low-lying isomeric 0⁺ ₂ state, the possibility of an electric-monopole (E0) decay to the ground state was examined. The observation of an E0 transition at 508 keV allowed the determination of the mixing between coexisting prolate and oblate shapes. Received: 16 November 1998     

Alpha decay of221Rn and217Po; level structure of217Po and the213Pb ground state

Alpha recoil sources of²²¹Rn were used to study the level structure of²¹⁷Po and the ground state of²¹³Pb. The half-life of²¹⁷Po was measured to be (1.6±0.2) s. When combined with unpublished data, an alpha-decay hindrance factor (HF) of 1.3 was obtained for the alpha-decay, strongly suggesting a g_9/2 → g_9/2 transition between²¹⁷Po and²¹³Pb ground states. Alpha-gamma coincidence studies confirm the previously observed 11/2⁺ band head in²¹⁷Po. It is suggested that an unobserved 9/2⁺ ground state lies below the 11/2⁺ state in²¹⁷Po and an attempt is made to observe connecting links between these two parts of the²¹⁷Po level scheme.     

Measurements of the dispersion relation in an ion beam-plasma system

Measurements of the dispersion relation and of the damping rate in an ion beam-plasma system are performed. Near the exciter three normal modes, the ion acoustic, slow and fast ion-beam modes exist. Agreement between experiment and theory is found.     

Treatment of singularities in 2-D domains using BIEM

The singularities which arise when there is a sudden change of boundary conditions are modelled using spectral shape interpolation functions. The procedure can be used for elasticity as well as potential theory and to any degree of accuracy with respect to the smooth part of the curve.     

The effects of parallel viscosity on stationary convection in plasmas

Stationary convection in a simple cylindrical plasma model driven interchange-unstable by an applied heat source is considered in the presence of large parallel ion viscosity. The nature of the spectrum and the cellular convective pattern at marginal stability are quite different from that obtained using only perpendicular ion viscosity.     

Odd-proton alpha-decay systematics and nuclear structure just beyond208Pb

The level structures populated in alpha decay of all odd-Z-even-N nuclei withZ=(83–93) andN=(126–142) up to 500 keV are presented. More data on the 4n+3 nuclear sequences are given from²¹⁵Bi to²³⁵Np. Particular emphasis is placed on the hindrance factors to alpha decay in interpreting the level structures in term of the shell model, the octupole-quadrupole model and the Nilsson model. The level structures and the hindrance factors go through transition region in which mixtures of the properties of two different nuclear models are appropriate. These transition regions represent a challenge to nuclear theorists to develop more all-encompassing nuclear models.     

Nonlinear dynamics of a machining system with two interdependent delays

The dynamics of turning by a tool head with two rows, each containing several cutters, is considered. A mathematical model of a process with two interdependent delays with the possibility of cutting discontinuity is analyzed. The domains of dynamic instability are derived, and the influence of technological parameters on system response is presented. The numeric analysis show that there exists specific conditions for given regimes in which one row of cutters produces an intermittent chip form while the other row produces continuous chips. It is demonstrated that the contribution of parametric excitation by shape roughness of an imperfect (unmachined) cylindrical workpiece surface is not substantial due to the special filtering properties of cutters that are uniformly distributed circumferentially along the tool head.