Evaluation of the performance of sensors based on optical imaging of a chemically sensitive layer

Interest in the use of the optical properties of chemical indicators is growing steadily. Among the optical methods that can be used to capture changes in sensing layers, those producing images of large-area devices are particularly interesting for chemical sensor array development. Until now, few studies addressed the characterization of image sensors from the point of view of their chemical sensor application. In this paper, a method to evaluate such performance is proposed. It is based on the simultaneous measurement of absorption events in a metalloporphyrin layer with an image sensor and a quartz microbalance (QMB). Exploiting the well-known behaviour of QMB, comparison of signals enables estimation of the minimum amount of absorbed molecules that the image sensor can detect. Results indicate that at the single pixel level a standard image sensor (for example a webcam) can easily detect femtomoles of absorbed molecules. It should therefore be possible to design sensor arrays in which the pixels of images of large-area sensing layers are regarded as individual chemical sensors providing a ready and simple method for large sensor array development.     

Influence of spatial laser energy distribution on evaluated soot particle sizes using two-colour laser-induced incandescence in a flat premixed ethylene/air flame

Time-resolved laser-induced incandescence (LII) has been developed rapidly during the last decade as a useful non-intrusive technique for particle size determination. Still several parameters should be investigated in order to improve the accuracy of LII for particle sizing and the spatial distribution of the laser energy is one of these. Generally a top-hat profile is recommended, as this ensures a uniform heating of all particles in the measurement volume. As it is generally not straightforward to create a uniform beam profile, it is of interest to establish the influence of various profiles on the evaluated particle sizes. In this work we present both an experimental and a theoretical investigation of the influence of the spatial profile on evaluated sizes. All experiments were carried out using a newly developed setup for two-colour LII (2C-LII) which provides online monitoring of both the spatial and temporal profile as well as the laser pulse energy. The LII measurements were performed in a one-dimensional premixed sooting ethylene/air flame, and evaluated particle sizes from LII were compared with thermophoretically sampled soot particles analysed using transmission electron microscopy (TEM). The results show that although there is some influence of the spatial laser energy distribution on the evaluated particle sizes both in modelling and experiments, this effect is substantially smaller than the influence of the uncertainties in gas temperature and the thermal accommodation coefficient.     

Soot volume fraction measurements in aero-engine exhausts using extinction-calibrated backward laser-induced incandescence

Control and reduction of soot particle emissions from aeronautic turbines requires a monitoring system suitable for quantification of these emissions. Currently, such emissions are estimated using the technique of smoke number. This is an extractive method, which is not sensitive enough for the low emission levels of modern gas turbines. Within a recent European project, AEROTEST, part of the project aimed at investigating an alternative soot monitoring technique, laser-induced incandescence (LII) as an in-situ optical diagnostic for quantification of soot emissions. For aero-engine applications, especially those involving large-scale turbines, it is necessary to perform the measurements at long distance from the turbine. The LII technique is favourable in this respect as it provides for non-intrusive measurements and, by detecting the isotropic LII signal along the same axis as the incoming laser beam (so called backward LII), both the laser and the detector can be built inside one system located several meters from the turbine. The concept was initiated in the previous European projects, AEROJET I and II. This paper describes the modified version of the system and the procedure developed to achieve reliable and quantitative soot volume fraction measurements in the exhausts of aero-engines. Application of the backward LII technique is demonstrated in the exhaust of a military turbojet engine for different engine speeds.     

A half year's experience with the facit-algol 1 compiler

The Facit-Algol 1 compiler is described briefly. Restrictions compared to Algol 60 and compatibility with other compilers is mentioned. The paper then discusses the experience with the compiler in the areas of teaching, programming, punching, debugging, and program exchanging. The conclusion is that Algol has done well and represents a great step forward.     

Geometry of Black Hole Thermodynamics

The Hessian of the entropy function can be thought of as a metric tensor on the state space. In the context of thermodynamical fluctuation theory Ruppeiner has argued that the Riemannian geometry of this metric gives insight into the underlying statistical mechanical system; the claim is supported by numerous examples. We study this geometry for some families of black holes. It is flat for the BTZ and Reissner–Nordström black holes, while curvature singularities occur for the Reissner–Nordström–anti–de Sitter and Kerr black holes.     

Wess–Zumino actions and Dirichlet boundary conditions for super p-branes with exotic fractions of supersymmetry

The general solutions in the models of closed and open superstring and super p-branes with exotic fractions of the N=1 supersymmetry are considered and the spontaneously broken character of the OSp(1,2M) symmetry of the models is established. It is shown that extending these models by Wess–Zumino terms generates the Dirichlet boundary conditions for superstring and super p-branes. Using the generalized Wess–Zumino terms new OSp(1,2M)-invariant super p-brane and Dp-brane-like actions preserving (M−1)/M fraction of supersymmetry are proposed. For M=32 these models suggest new superbrane vacua of M-theory preserving 31 from 32 global supersymmetries.     

High-resolution digital transmission microscopy—a Fourier holography approach

A spherical reference field is used to construct a digital holographic system with a demonstrated resolution up to 228 line pairs per mm. The reference field originates from a GRIN lens placed 1 mm from the illuminated object. This allows the use of a standard sensor to record the hologram with the required numerical aperture. The image is determined by evaluation of the Rayleigh–Sommerfeld diffraction integral that relates the object field in the image plane to the object field in the sensor plane. Experimental results are given for two charge coupled device sensors and one complementary metal-oxide-semiconductor active pixel sensor.     

Hydroxylated oxanes as xyloside analogs for determination of the minimal binding requirements of β4GalT7

β-1,4-Galactosyltransferase 7 (β4GalT7) is a key enzyme in the biosynthesis of glycosaminoglycan (GAG) chains. Natural and synthetic xylosides can be used to both inhibit and prime GAG synthesis by acting as inhibitors or substrates for β4GalT7. In this report, we exploit hydroxylated oxanes as deoxygenated xyloside analogs to clarify the minimum protein-ligand interactions required for galactosylation and/or inhibition. Enantiomerically pure substances were synthesized using a chiral pool approach whereas the corresponding racemates were obtained from simple starting materials. The results of a β4GalT7 assay show that a single hydroxyl group on an oxane ring is insufficient to induce galactosylation or inhibition, which implies that at least two substituents, one of which being 3-OH, needs to be present.