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.     

The effect of key process parameters on crystallographic texture and magnetic properties of PrFeB HD sintered magnets produced using high-energy milling

A combination of hydrogen decrepitation and planetary ball milling has been used to produce sintered Pr₁₆Fe₇₆B₈ magnets. The effects of key process parameters and texture have been studied. The alignment degree (cos Θ) has been investigated by X-ray pole figure analysis using the (0 0 4) reflection. Magnets prepared from the alloy decrepitated for 3.6 ks and milled for 1.8 ks exhibited a low degree of crystal alignment (0.71±0.02) due to polycrystalline particles. Increasing the milling time to 4.5ks has led to an improvement in cos Θ to 0.84±0.02. This has been ascribed to the smaller particle size with a narrower size distribution as well as a more favorable particle shape for orientation. Superior alignment degree (cos Θ=0.88±0.02) has been achieved for the sintered magnet from the alloy decrepitated for 120 s and milled for 5.4 ks. This particular processing condition has led to a magnet with (BH)_max=250±5 kJ m⁻³, value found in magnets produced using roller ball milling, with the advantage of a reduced milling time (about 90%).     

Discontinuous Solutions to Unbounded Differential Inclusions under State Constraints. Applications to Optimal Control Problems

We consider a nonconvex and unbounded differential inclusion derived from a control system whose control sets are time and space-dependent. We extend the inclusion in order to allow discontinuous trajectories. We prove that the set of solutions of the original inclusion is dense in the set of solutions of the extended inclusion and, moreover, these last solutions are stable with respect to the initial data. Both of these results are also proven in the presence of state and integral constraints (assuming suitable conditions at the boundary of the constraining set). As an application, the value function of a Mayer problem is shown to be continuous and the unique viscosity solution of a Hamilton–Jacobi equation with suitable boundary conditions.     

The parameter space for the direct spinning of fibres and films of carbon nanotubes

We have recently introduced a method for the continuous spinning of carbon nanotube fibres and films directly from the gas phase of a chemical vapour deposition furnace [Y. Li, et al., Science 304 (2004) 276]. In this work the effect of the process parameters on the ability to spin continuously is studied, with particular focus on the carrier gas and feedstock flow rates. Catalyst dilution by high carrier gas flow rates led to smaller diameter nanotubes but these conditions are found the hardest to spin.     

Semiempirical INDO/S study on the absorption spectrum of violacein

Violacein is the major pigment produced by Chromobacterium violaceum. We now report the results of semiempirical calculations on the electronic spectrum of violacein. We have used the AM1 and Intermediate Neglect of Differential Overlap (INDO) model Hamiltonians. Solvent effects have been included with the SCRF model for spectroscopy as proposed by Zerner and Karelson. Our results suggest that in the gas phase violacein is almost planar while in ethanolic solution the H-bond interactions force an internal rotation due to sterical factors. The calculated UV-visible spectrum with the inclusion of specific solvent interactions in the Hamiltonian is on good agreement with the experimental spectrum.     

Bioluminescence flow sensor for determination of creatine kinase activity in blood

A bioluminescent flow sensor was developed for the assay of creatine kinase (CK) using firefly luciferase immobilized on a nylon coil. The CK-catalysed reaction of creatine phosphate with ADP took place in a cuvette before the injection into the bioluminescent detector coil. The response was linear from 0.1 to 100 U l^? at 25°C. An advantage of the flow sensor is a detection limit of less than 0.1 U l^?1, which, together with a high precision, allows determination of the CK activity in blood sera in about 5 min. The intra- and inter-assay reproducibilities (RSD) were less than 10% and the recovery range was 86–110%. The results agreed well with those obtained with a spectrophotometric method and with the normal reference values.     

Structure of self-organized multilayer nanoparticles for drug delivery

The combined use of cryo-TEM, dynamic light scattering, and small-angle X-ray and neutron scattering techniques allows a detailed structural model of complex pharmaceutical preparations of soybean lecithin/chitosan nanoparticles used as drug vectors to be worked out. Charge-driven self-organization of the lipid(-)/polysaccharide(+) vesicles occurs during rapid injection, under mechanical stirring, of an ethanol solution of soybean lecithin into a chitosan aqueous solution. We conclude that beyond the charge inversion region of the phase diagram, i.e., entering the redissolution region, the initial stages of particle formation are likely to be affected by a re-entrant condensation effect at the nanoscale. This behavior resembles that at the mesoscale which is well-known for polyion/amphiphile systems. Close to the boundary of the charge inversion region, nanoparticle formation occurs under a maximum condensation condition at the nanoscale and the complexation-aggregation process is driven toward a maximum multilamellarity. Interestingly, the formulation that maximizes vesicle multilamellarity corresponds to that displaying the highest drug loading efficiency.