The computation of stability boundaries in state space for a class of biochemical engineering systems

The stability of a class of biochemical processes defined by a set of m biochemical reactions involving n components is analysed. The processes operate in a continuous mode and possess at least two stable equilibrium states: the normal operating point and a biological wash out state. Using a canonical state representation of the process dynamics the geometric structure of the operating point's stability boundary is characterized. Numerical algorithms are developed to evaluate this boundary and to visualize its extent in state space. The proposed technique is illustrated with a representative engineering example.     

Mechanistic study on benzylic oxidations catalyzed by bismuth(III) salts: X-ray structures of two bismuth-picolinate complexes

We report studies that are consistent with benzylic oxidation reactions catalyzed using bismuth(III) salts proceeding via a radical mechanism. Additionally, X-ray structures of two potential bismuth-picolinate complex intermediates are reported.     

Recent developments in methodology for the direct oxyamination of olefins

1,2-Amino alcohols are high-value, versatile functional groups that are found in scores of biologically active molecules and other interesting synthetic targets such as ligands and auxiliaries. Given their prominent position within organic compounds of import, it is no surprise to note that many routes have been developed to access this motif and there are many different starting points from which a synthetic chemist might embark on a synthesis. However, one particular approach stands out from the others, and this is the direct conversion of an alkene to a vicinal amino alcohol derivative (oxyamination). Research in this field has been particularly active in recent years and many interesting new methodologies have been reported. The purpose of this review is to give the reader a tour of the methods that have emerged in the last few years so one can appreciate the myriad of different metals and reagents that can accomplish the oxyamination of alkenes. There are still many challenges to be overcome and, herein, we also outline the areas that are ripe for further development and which bode well for the future.     

Multi-frequency electron paramagnetic resonance study of irradiated human finger phalanxes

Electron paramagnetic resonance (EPR) is often used in dosimetry using biological samples such as teeth and bones. It is generally assumed that the radicals, formed after irradiation, are similar in both tissues as the mineral part of bone and tooth is carbonated hydroxyapatite. However, there is a lack of experimental evidence to support this assumption. The aim of the present study was to contribute to that field by studying powder and block samples of human finger phalanxes that were irradiated and analyzed by multi-frequency EPR. The results obtained from bones are different from the ones obtained in enamel by several respects: the ordering of the apatite crystallites is much smaller in bone, complicating the assignment of the observed CO2- radicals to a specific location, and one type of CO3(3-) radical was only found in enamel. Moreover, a major difference was found in the non-CO2- and non-CO3(3-) signals. The elucidation of the nature of these native signals (in bone and tooth enamel) still represents a big challenge.     

31P and1H powder ENDOR study of ozonide radicals in carbonated apatites,synthesized from aqueous solutions

An O ₃ ^? defect in Na⁺ CO ₃ ^2? containing apatite powder has been investigated with ENDOR after X-irradiation. The powder, synthesized by a hydrolysis of octo-calciumphosphate (OCP) and Na₂CO₃ was dried at 25°C until constant weight was reached. At low temperatures, both³¹P and¹H ENDOR spectra were recorded for different settings of the magnetic field (i.e., when the magnetic field is swept through the EPR O ₃ ^? spectrum). The ENDOR powder spectra were thoroughly analyzed using computer simulations based on the “orientation selection principle”. Interactions with two types of protons and two types of³¹P nuclei could be resolved. In this way, a detailed model could be established for the O ₃ ^? ion in the hydroxyapatite lattice. The defect is located between two successive vacant hydroxyl sites. The axis connecting the two outer oxygen atoms (g _y-axis) of the O ₃ ^? ion is found to be along the hexagonalc-axis of the lattice. The twofold axis of the defect ion (g _z-axis) is parallel to theb-axis of the lattice.     

Electron paramagnetic resonance study of a Eu related defect in CsBr:Eu needle image plates for computed radiography

The electron paramagnetic resonance (EPR) spectrum of needle image plates of CsBr doped with Eu²⁺, which are proposed as new X-ray storage phosphors for computed radiography, is studied at room temperature and Q-band microwave frequencies (34 GHz). X-ray diffraction analysis demonstrates that the CsBr:Eu²⁺ needles have an 0 0 1 out of plane (perpendicular to the plate) orientation, and contrary to expectation that the in plane orientation is not random. The room temperature EPR spectrum is attributed to a single centre which is related to Eu²⁺ with axial 0 0 1 symmetry. Using the spin Hamiltonian parameters extracted from the spectrum recorded with the magnetic field parallel to the needles’ axes, we convincingly simulate both the spectrum of a powdered image plate and the single crystal like angular dependence of intact pieces of image plate. The knowledge of the symmetry of this centre, which appears to be related with the radiation sensitivity of the plate, presents a first step in finding its model and role in the X-ray storage process.     

EPR, ENDOR and HYSCORE study of X-ray induced centres in K2YF5 thermoluminescent phosphors

X-Ray irradiation at room temperature produces several paramagnetic centres in rare-earth activated K2YF5 crystals, whose thermal annealing behaviour can be linked with the occurrence of thermoluminescence (TL) glow peaks. In this paper, continuous wave (CW) and pulsed paramagnetic resonance techniques are used to study the structure of a very stable radiation-induced centre, which may be involved in the TL peak at approximately 390 degrees C reported for Ce- and Tb-activated crystals. From the spectra the centre's g tensor and hyperfine (nuclear quadrupole) tensors for several 19F and 39K neighbouring nuclei are extracted, but no self-hyperfine interaction could be detected. Based on the analysis of the interaction tensors, a model is constructed consisting of an oxygen-related radical (e.g. O(-) or O2(-)) on a substitutional F(-) position in the mirror plane of the YF7 polyhedra. Such a centre most probably corresponds to a trapped-hole state.     

Extended focused imaging of a microparticle field with digital holographic microscopy

We present a numerical technique for extended focused imaging and three-dimensional analysis of a microparticle field observed in a digital holographic microscope working in transmission. The three-dimensional localization of objects is performed using the local focus plane determination method based on the integrated amplitude modulus. We apply the refocusing criterion locally for each pixel, using small overlapping windows, to obtain the depth map and a synthetic image in which all objects are refocused independent from their refocusing distance. A successful application of this technique in the analysis of the microgravity particle flow experiment is presented.     

Automated On-Line GPC-GC-FPD Involving Co-Solvent Trapping and the On-Column Interface for the Determination of Organophosphorus Pesticides in Olive Oils

The robustness of an automated on-line GPC-GC-FPD method for the determination of Organophosphorus (OP) Pesticides in olive oil has been significantly improved, now allowing a routine operation. The original GPC-GC transfer technique employed a loop type interface with an early vapor exit and co-solvent trapping. Shooting, caused by boiling delay and malfunctioning of the solvent vapor exit during the transfer of the 3 mL solvent fraction to the retention gap, resulted in insufficient focusing of the OP-pesticides. In this interfacing concept, the GPC fraction is introduced directly into the carrier gas stream during a certain time interval using the Dualchrom pressure- and flow regulation, resulting in a very stable transfer. The interface now basically corresponds to an on-column interface with flow regulation. Via a Pyrex glass door behind the GC-oven door it can be seen that the liquid flow is broken up into alternating gas-liquid segments by the carrier gas flow during transfer. This avoids shooting in the retention gap and broadens the temperature range for successful transfer. By using a smaller sized GPC column the solvent fraction transferred was reduced to 1.3 mL. Methyl acetate/cyclopentane and the co-solvent n-nonane were selected for their lower boiling points. The modified method is very robust and has been applied to the analysis of 28 different OP-pesticides in olive oil with an overall detection limit of 0.002 mg/kg. Routinely 24 h of unattended operation is possible with a cycle time of 75 min.     

Crack identification method in beam-like structures using changes in experimentally measured frequencies and Particle Swarm Optimization

In this paper, a technique is presented for the detection and localization of an open crack in beam-like structures using experimentally measured natural frequencies and the Particle Swarm Optimization (PSO) method. The technique considers the variation in local flexibility near the crack. The natural frequencies of a cracked beam are determined experimentally and numerically using the Finite Element Method (FEM). The optimization algorithm is programmed in MATLAB. The algorithm is used to estimate the location and severity of a crack by minimizing the differences between measured and calculated frequencies. The method is verified using experimentally measured data on a cantilever steel beam. The Fourier transform is adopted to improve the frequency resolution. The results demonstrate the good accuracy of the proposed technique.