Quantitative high-resolution on-line NMR spectroscopy in reaction and process monitoring

On-line nuclear magnetic resonance spectroscopy (on-line NMR) is a powerful technique for reaction and process monitoring. Different set-ups for direct coupling of reaction and separation equipment with on-line NMR spectroscopy are described. NMR spectroscopy can be used to obtain both qualitative and quantitative information from complex reacting multicomponent mixtures for equilibrium or reaction kinetic studies. Commercial NMR probes can be used at pressures up to 35 MPa and temperatures up to 400 K. Applications are presented for studies of equilibria and kinetics of complex formaldehyde-containing mixtures as well as homogeneously and heterogeneously catalyzed esterification kinetics. Direct coupling of a thin-film evaporator is described as an example for the benefits of on-line NMR spectroscopy in process monitoring.     

BOLD MRI response to hypercapnic hyperoxia in patients with meningiomas: correlation with Gadolinium-DTPA uptake rate

Because meningiomas tend to recur after (partial) surgical resection, radiotherapy is increasingly being applied for the treatment of these tumors. Radiation dose levels are limited, however, to avoid radiation damage to the surrounding normal tissue. The radiosensitivity of tumors can be improved by increasing tumor oxygen levels. The aim of this study was to investigate if breathing a hyperoxic hypercapnic gas mixture could improve the oxygenation of meningiomas. Blood oxygen level-dependent magnetic resonance imaging and dynamic Gadolinium (Gd)-DTPA contrast-enhanced MRI were used to assess changes in tumor blood oxygenation and vascularity, respectively. Ten meningioma patients were each studied twice; without and with breathing a gas mixture consisting of 2% CO(2) and 98% O(2). Values of T(2)* and the Gd-DTPA uptake rate k(ep) were calculated under both conditions. In six tumors a significant increase in the value of T(2)* in the tumor was found, suggesting an improved tumor blood oxygenation, which exceeded the effect in normal brain tissue. Contrarily, two tumors showed a significant T(2)* decrease. The change in T(2)* was found to correlate with both k(ep) and with the change in k(ep). The presence of both vascular effects and oxygenation effects and the heterogeneous response to hypercapnic hyperoxia necessitates individual assessment of the effects of breathing a hyperoxic hypercapnic gas mixture on meningiomas. Thus, the current MRI protocol may assist in radiation treatment selection for patients with meningiomas.     

Performance and early applications of a versatile double aberration-corrected JEOL-2200FS FEG TEM/STEM at Aalto University

Applications relevant to carbon based nano-materials have been explored using a newly installed JEOL-2200FS field emission gun (FEG) (scanning) transmission electron microscope (S)TEM which is integrated with two CEOS aberration correctors for both the TEM image-forming and the STEM probe-forming lenses. The performance and utility of this newly commission hardware has been reviewed with a particular focus on operation at an acceleration voltage of 80 kV, thus bringing the primary electron beam voltage below the knock-on threshold for carbon materials and opening up a range of possibilities for the study of carbon-based nanostructures in the aberration-corrected electron microscope. The ability of the microscope to obtain both atomic TEM images and high-quality electron diffraction patterns from carbon nanotubes was demonstrated. The chiral structure of a double-walled carbon nanotube was determined from its diffraction pattern. The aberration corrected TEM imaging technique facilitates a unique approach to accurate determination of single-walled carbon nanotube diameters. On the other hand, the probe-corrected high angle annular dark field (HAADF) STEM imaging performance allows for the detection of single gold atoms at 80 kV and was used to study the graphite interlayer spacing in a multi-walled carbon nanotube.     

3D molecular imaging SIMS

Thin monolayer and bilayer films of spin cast poly(methyl methacrylate) (PMMA), poly(2-hydroxyethyl methacrylate) (PHEMA), poly(lactic) acid (PLA) and PLA doped with several pharmaceuticals have been analyzed by dynamic SIMS using SF₅⁺ polyatomic primary ion bombardment. Each of these systems exhibited minimal primary beam-induced degradation under cluster ion bombardment allowing molecular depth profiles to be obtained through the film. By combing secondary ion imaging with depth profiling, three-dimensional molecular image depth profiles have been obtained from these systems. In another approach, bevel cross-sections are cut in the samples with the SF₅⁺ primary ion beam to produce a laterally magnified cross-section of the sample that does not contain the beam-induced damage that would be induced by conventional focussed ion beam (FIB) cross-sectioning. The bevel surface can then be examined using cluster SIMS imaging or other appropriate microanalysis technique.     

Determination of titanium content in pyrope by Raman spectroscopy

The titanium content of pyrope garnet can be quantified using the intensity of a Raman band at about 830 cm⁻¹ that is normalized to the 363 cm⁻¹ band using a spectrometer‐specific calibration using 10 to 15 chromian pyropes from Bohemia, Czech Republic. An accuracy of 0.025 wt% could be achieved for TiO₂ contents between 0.17 and 0.67 wt% TiO₂ with a Raman spectrometer with a spectral resolution of better than 3.9 cm⁻¹. The technique can be used in petrological and gemmological studies. Copyright © 2015 John Wiley & Sons, Ltd.     

Highly sensitive bend sensor with hybrid long-period and tilted fiber Bragg grating

We demonstrate a new type of fiber optic bend sensor with a hybrid structure made up of a long period grating (LPG) and a tilted fiber Bragg grating (TFBG). The sensing mechanism is based on the spectrum of power transfers between the core and cladding modes from a TFBG located downstream from a LPG. We show that the curvature of a beam can be determined by the reflected power difference between the core mode and the recoupled cladding modes. We further provide design rules for the LPG and TFBG to optimize and linearize the sensor response. In addition, the temperature cross-sensitivities of this configuration are also investigated for two different types of fiber.     

Fluctuations of an Evaporating Black Hole from Back Reaction of Its Hawking Radiation: Questioning a Premise in Earlier Work

This paper delineates the first steps in a systematic quantitative study of the spacetime fluctuations induced by quantum fields in an evaporating black hole. We explain how the stochastic gravity formalism can be a useful tool for that purpose within a low-energy effective field theory approach to quantum gravity. As an explicit example we apply it to the study of the spherically-symmetric sector of metric perturbations around an evaporating black hole background geometry. For macroscopic black holes we find that those fluctuations grow and eventually become important when considering sufficiently long periods of time (of the order of the evaporation time), but well before the Planckian regime is reached. In addition, the assumption of a simple correlation between the fluctuations of the energy flux crossing the horizon and far from it, which was made in earlier work on spherically-symmetric induced fluctuations, is carefully analyzed and found to be invalid. Our analysis suggests the existence of an infinite amplitude for the fluctuations of the horizon as a three-dimensional hypersurface. We emphasize the need for understanding and designing operational ways of probing quantum metric fluctuations near the horizon and extracting physically meaningful information. Dedicated to Rafael Sorkin on the occasion of his 60th birthday.     

Long vectors for quasi-Newton updates

This work concerns the derivation of formulae for updating quasi-Newton matrices used in algorithms for computing approximate minima of smooth unconstrained functions. The paper concentrates strictly on the techniques used to derive update formulae. It demonstrates a technique in which problems of finding matrices in ℝ ^{n ×n} of minimum Frobenius norm are converted to equivalent problems, using vector representations in ℝ ⁿ² and ℝ ^n(n+1)/2 of these matrices, and then solvingl ₂-minimization problems. These problems are more directly dealt with, and indeed, the paper demonstrates how this technique may be used to handle weighted sparse updates.     

On the scattering of waves by a disk

Zusammenfassung Es wird gezeigt, dass das Problem, die Beugung einer ebenen Welle an einer kreisförmigen Öffnung oder Scheibe zu bestimmen, auf die Lösung von regulären Fredholmschen Integralgleichungen zweiter Art zurückgeführt werden kann. Die Lösungen dieser Integralgleichungen liefern uns für die Scheibe im Falle der Neumannschen Bedingung die radiale Variation der Unstetigkeiten der Wellenfunktion und im Dirichletschen Falle die Unstetigkeiten ihrer normalen Ableitung. Ist das Produkt von Öffnungsradius und Wellenzahl klein, so können die Integralgleichungen gelöst werden. Für die Ableitung der Integralgleichungen verwenden wir einerseits die Poissonsche Darstellung für die Wellenfunktion und andererseits die Fortsetzung der Helmholtzschen Darstellung in die komplexe Ebene.